US3183377A - Electrical control circuits - Google Patents

Description

May 11, 1965 F. H. HOLLAND 3,183,377

ELECTRICAL CONTROL CIRCUITS Filed May 3, 1961 4 Sheets-Shevt 1 l'FRANK H. HOLLAND May 1l, 1965 F. H. HOLLAND 3,183,377

ELECTRICAL CONTROL CIRCUITS Filed May 3, 1961 4 Sheets-Sheet 2 AIR SOURCE as a? 2e 29 I d J5- Fs F /g. 2 ,4 o Lm `R2 R5 CQNTACTS CONTACT 5o c. OPERATION 54556 97074 CONTACT 3| l:- RU" X x CONTACT s2 l:- coNTmuous x x x x ,NCH x x CONTACT 35 Il l- DENOTES CLOSED Fig. 4

X DENOTES CLOSED Fig. 3

MMM

May 11, 1965 F. H. HOLLAND 3,183,377

ELECTRICAL CONTROL CIRCUITS Filed Nay s, 1961 4 Sheets-Sheet 3 CONTACT so ACONTACT n3 El: CONTACT 3| a CONTACT "4l- CoNTACT 32 lcoNTAcT N5:- CoNTACT sa I CONTACT N2 E l DENOTES CLOSED Y [L /g 7 INVENTOR FRANK H. HOLLAND May 11, 1965 F. H. HOLLAND 3,13,377

ELECTRICAL CONTROL `CIRCUITS Filed May s, 196i 4 sheets-sneer 4 INVENTOR.

FRANK H. HOLLAND United States Patent O 3,183,377 ELECTRICAL CONTROL CIRCUITS Frank H. Holland, Cleveland, Ohio, assigner to The Clark Controller Company, Cleveland, Ohio, a corporation of Ohio Filed May 3, 1961, Ser. No. 123,603 34 Claims. (Cl. 367-113) My invention relates to electrical control circuits and more particularly to electrical control circuits for safely controlling the operation of a punch press.

Punch presses may be of many varied sizes and types. One type utilizes a continuously running motor driving a flywheel. The iiywheel is engaged with and disengaged from the press shaft by means of an air operated clutch. An air operated brake is utilized to rapidly stop and hold the press when desired. An air valve is utilized to control the flow of air from an air source to the clutch and brake, and the air valve is controlled by a winding on an electromagnet.

A second type of punch press utilizes an eddy current clutch and brake which perform the same functions as the air operated clutch and brake. The eddy current brake and clutch are controlled by an electromagnetic winding. The eddy current brake is used in stopping the press and a friction brake is used to assist in stopping and to hold the press.

Another type of punch press is a direct connected press. Here the motor is connected directly to the press ram and the operation of the press ram is controlled by the starting and stopping of the motor. The motor is controlled by a starter having an electromagnetic winding. A friction brake is also used to stop and hold the press when desired.

In the normal operation of most presses, the operating personnel are required to place their arms between the dies of the press to feed material to the press, remove the punched parts from the press, and to clean the press. It is therefore seen that presses are potentially dangerous should the control equipment malfunction causing the press to operate when not desired.

Therefore, it is the primary requirement that control for operating a punch press provide the optimum in ultimate safety to personnel, protection for the expensive equipment while still maintaining Ithe maximum production rates.

Heretofore, press control systems have been devised whereby the operator is required to keep his hands on separate push buttons during the time that the press ram is moving downward to engage the dies. One such control system is illustrated by United States Letters Patent Number 2,299,007.

However, these systems were not capable of protecting against changes made by the operators themselves in order to increase their piece rate, nor were they capable of protecting against the mulfunction of the control components.

It is therefore the primary object of my invention to provide a press control circuit which will overcome the above mentioned difficulties .and which will provide maximum safety in its operation.

It is another object of my invention to provide a press control circuit which prevents operation should any of the normally open contacts of the operators push buttons be short circuited.

It is still another object of my invention to provide a press control circuit which will stop the operation of the press should the limit switches or their contacts not be operating properly.

A further object of my invention is to stop the press should a control device connected in the circuit fail to operate properly when required to do so.

A still further object of my invention is to provide a press control circuit which requires that all operators push buttons be released before the press can be restarted at any point in its operating cycle.

The present embodiment of my invention utilizes a pair of push buttons for each operator, each push button has a normally open and a normally closed contact. A first contactor is connected to be energized through the normally colsed contacts of the push buttons. Once energized, the irst contactor holds itself in through its own contacts.

A second contactor is connected to be energized through the normally open contacts of the push button and normally open contacts of the first contactor. When the push buttons are depressed by the operator, the second contactor is energized through the described circuit to operate and close its contacts. The second contactor then is maintained energized through the normally open contacts of the push buttons and its own contacts. A contact of the second contactor is connected so when operated, it opens the energizing circuit of the first contactor, causing it to become ie-energized.

A third contactor is connected to be energized through normally open contacts of the second contactor and normally closed contacts of the first contactor and the normally open contacts of the push buttons.

After operation of the third contactor, the device controlling the operation of the punch press, the air valve or main motor starter, as the case may be, is energized through the normally open contacts of the push button, the normally closed contacts of the rst contactor and normally open contacts of the second and third contactors.

The press is then connected to operate and its ram moves downward. Should the operator remove either hand or both from the push buttons, the normally open contacts of the push button will open the circuit energizing the press controlling device and the press will stop immediately. The second and third contactors are also de-energized, and the operator must release both push buttons to re-energize the first contactor. Then, depress both push buttons to re-energize the second and third contactors before he. can restart the operation of the press.

Contacts of cyclically timed switches are connected in the circuit so that after the press ram has gone beyond the point where the operator cannot injure himself, the energization of the press operating device is transferred from the normally open contacts of the push buttons to the contacts of the cyclically timed switches. These contacts open at the end of each stroke to stop the press, unless the operator has properly released and then depressed the push buttons.

Throughout the operation cycle of the press, the components of the circuit are checked by the operation of the circuit to ensure that they have operated properly. If one of the components should fail for any reason whatsoever, the press will stop when it reaches the point in the operating cycle where the failed device is checked or should have operated.

A second embodiment of my invention protects against false operation of the press should the normally open contacts of the push button become short circuited. For presses having only one operator, a single pair of push buttons is used and the first contactor is replaced by two contactors. Each contactor is connected in series with a different one of the normally closed push button contacts. Therefore, if one of the push button normally open contacts is shorted, the second contactor cannot become energized to operate the press if only one push button is depressed.

For presses having more than one operator, a setup contactor is connected to be energized through the normally closed contacts of all the operator push buttons. When this contactor is energized, its various contacts set up a circuit for each norm-ally open push button contact to connect one side of the source to a latch relay. If any of the normally open contacts are shorted, the latch relay operates and mechanically holds its contacts operated to prevent operationrof the press. The other side of the latch relay is connected to the other side of the source through the push button normally closed contacts. Because it is desirable to have one each of the push button pairs on either side of the line, it is necessary to have two latch relays, one to check the normally open contacts on each side of the source.

A third embodiment of my invention checks the limit switch contacts from failure to operate or from the limit switch from becoming disconnected from the press. This is accomplished by having a second limit switch separately connected to the press and connected into the circuit so that it is mandatory that the limit switch contacts operate properly each cycle of press operation. If they do not, the power is removed from the circuit causing the press to stop.

Many other objects and advantages of my invention wiil become readily apparent to those skilled in the art when'the following description is read with reference to the drawings in which:

FIGURE 1 is a schematic representation of the circuit for operating the press controlling device;

FIGURE 2 is a diagrammatic representation of a press and its operating equipment;

FIGURE 3 is a diagrammatic representation of a selector switch to illustrate the condition of its contacts in its various operated positions;

FIGURE 4 is adiagrammatic representation of the condition and operating points for the contacts of the limit switches in FIGURES 2 and 5 with respect to the press operating cycle;

, FIGURE 5 is a schematic representation of a press control circuit to illustrate `another embodiment of my invention;

FIGURE 6 is a schematic representation of a press control circuit illustrating a variation from FIGURE 5;

FIGURE 7 is a diagrammatic representation of the Y condition andthe operating points for the contacts of the two limit switches of FIGURE 6 with respect to the operating cycle of the press.

Reference is first made to FIGURE 2 which illustrates part of an air clutch typer press mechanism, it being understood that my'invention can be used with other types of presses and that reference to this particular type Y of press mechanism is made only, toY describe a mode of operation, as is required by law.

A main shaft It? of the press is provided with cranks II--Il to reciprocate the press ram,in a well known manner, and is rotatably supported in bearings on a main frame 12. Shaft ttt is driven by a motor 13 through a motor pinion 14 land a gear 15. Gear 15 has a hub I6 and'is normally rotated idly on main shaft It like a flywheel.

Motor I3 is connected to a source of A.C. supply I7 by lines 18, 19 and 2t?.

A pneumatic cylinder 21, supported on main frame 12 I; of the press, has a piston 22 therein with a piston rod 23 projecting therefrom. by a spring 24.

Hub 16 and piston rod 23 project into a clutch and Piston 22 is normally retracted brake mechanism indicated diagrammatically at 25. 'flicV mechanism comprises elements,.by'which, when piston Z2 Vis retracted by spring 24, the brake grips shaft ttl and When piston'rod 23 isfprojectedV forbehind piston 2 2, the brake, is

stops the press.

4 released and hub 16 Vis connected to shaft 10 by the clutch to cause gear I5 to'drive shaft 10 and the press. The clutch is released when piston rod 23 is retracted to its rearward position by spring 24.

On the free end of shaft It are mouted cams 26 to 29 that rotate with shaft It) and operate contacts 30 to 33, respectively, to open `and close them. The cams are adjustable around shaft I0 to cause the contacts to operate at preselected times or points in the press cycle. In most practical applications, the cams and cam operated contacts are not an integral part of the press, but takeV the form-of a limit switch which is mechanically connected to shaft Itl.

An air valve housing 34 communicates with a source of air 35 under pressure. Within housing 34tis a main valve, not shown, controlled by a reciprocal pilot valve indicated at 36. Pilot valve 36 is reciprocated to its operated position upon energization of a winding 37 of an electromagnet 3S. When winding 37 is energized, the main valve is operated by air pressure to effect communication of air pressure through a conduit 39 tovcylinder 21 and moves piston 22 and rod 23 forwardly to operate clutch and brake mechanism 25, starting operation of the press.

When winding37 is cle-energized, a spring 4t) restores pilot valve 36, causing the main valve to restore and cut off communication of tiuid pressure to conduit 39 and open exhaust conduit d1. Cylinder spring 24 returns piston rod 23 and operates clutch and brake mechanism Z5 to release the clutch `and set the brake to stop the press. Y

YPart of the energizing circuit at 4t2-43.

The air valve described above, operating responsive to energization and de-energization of a winding, and shown diagrammatically in FIGURE 2, may be that constituting the subject matter of United States Letters Patent 2,902,- 052, issued on September 1, 1959 to which reference may be had for structural details.

In FIGURE 1, which illustrates the invention as applied to press controls, the aforesaid contacts 30 to 33, the

for winding 37 is shown velectromagnet 38 and its winding 37 and the energizing circuit 42-43 are reproduced from FIGURE 2 with the same reference numerals. Y

Wires 44 and 45 are connected toa suitable source of alternating current. Wire 45 directly, and wire 44 through a normally closed stop push button 45 and a wire 47.

Connected across wires 44 and 45 is a contactor F having a winding 43 and normally open contacts FI through F5 and a normally Vclosed contact F6. The circuit consists of a start push button 49, contact ZCRS, contact SCRS, contact 50 of a key operated selector switch, contact R5, winding 48.

Contact F4 is connected in parallel with start push button 49, contact ZCRS and contact CR5.Y Contact R4 is connected in parallel with contact F4. i

Asecond contactor R, having a winding 51 and normally open contacts R1 through vRd and normally closed contact R5, is connected in parallel with key operatedV selector switch contact 50, contact R5 Vand winding 48 ofY contactor F. This circuit consists of a second contact 52' Vof the key operated selector switch, contact F6 and winding 51 of contactor R. Y Contacts F1 to F3 of contactor F, when closed, connect motor 13 to source 17 through wires 18, 19 and 2t! to Voperate motor 15in the forward direction (see FIG- UREy 2).

Contacts R1 to R3 of contactor R, when closed, con- Y neet motor I3 to source 17 through wires 18, 19 and 20 toY operate motor I3 in the reverse direction.

A contactor ICR, having a winding 53 and normallyj open contacts ICRI to ICR4 and normally closed contacts 1CR5 and ICRS, is connectedracrossilines 44 and contacter ICR, contact 1CR2, contact 2CR7 and selector switch contact 55. Normally closed contact 56 of a push button 57 is connected in parallel with contact 2CR6 and contact lCRl. Similarly, normally closed contact 58 of a push button 59 is connected in parallel with contacts 1CR2 and 2CR7.

A wire Gil is connected to this circuit between Contact F and contact 2CR6. A second wire 61 is connected to this circuit between contact 2CR7 and -selector switch contact 55.

A contactor ZCR, having a winding 62 and normally open contacts 2CR1 to 2CR4 and normally closed contacts 2CR5 to 2CR9, is connected across lines 60 and 61 by a circuit consisting of normally open contact 63 of push button 57, contact 1CR3, winding 62 of contactor 2CR, contact 1CR4, and normally open contact 64 of push button 59. Contact 3CR6 and contact 2CR1 are connected in parallel with contact 1CR3. Contact ZCRZ is connected in parallel with contact 1CR4. Contact 3Q of the cyclically timed switch is connected in parallel with contact SCRS.

Another contactor SCR, having a Winding 65 and normally open contacts 3CR1 to 3CR4 and normally closed contacts 3CR5 to 3CR7, is connected across wires 60 and 61 by a circuit consisting of contact 63 of push button 57, Contact lCRS, contact 2CR3, Winding 65 of contactor SCR, contact ZCRS, contact ZCR4, contact 1CR6 and contact 64 of push button 59. Contact 33 of the cyclically timed switch is connected in parallel with contact ZCRS.

A second circuit connects winding 65 of contactor 3CR to wires 60 and 61 and consists of contact 31 of the cyclically timed switch, contact 3CR1, winding 65, contact ZCRS, contact 3CR2 and contact 32 of the cyclically timed switch.

Connected between contact 31 and contact 3CR1 is a circuit consisting of wire 66, contact SCRS, wire 42, winding 37 of the air valve, wire 43, contact 3CR4 and wire 67 which connects between Contact SCRZ and contact 32.

Selector switch contact 68 is connected in parallel with switch 31.

Selector switch contact 69 is connected in parallel with switch 32..

Winding 37 of the air valve may be connected directly to lines 44 and 45 by an inching circuit. This consists of selector switch contact 70, normally open contact 71 of an inching push button 72, contact 2CR9, wire 42, winding 37, wire 43, contact 3CR7, contact 73 of inching push button 72 and selector switch contact 74.

FIGURE 3 represents the position ofthe selector switch contacts 54, 55, 68, 69, 70 and 74 for the various types of press operation. Selector switches of this type are readily available. When desired to run the press, the selector switch is rotated to close contacts 54 and 55 leaving the remaining contacts open. When desired to operate the press continuously, the selector switch is rotated to close contacts 54, 55, 68 and 69 leaving the remaining contacts open. When desired to inch the press, the selector switch is rotated to close contacts 79 and '74 and open contacts 54, 55, 68 and 69.

Operation To begin operation, the operator must turn the key operated selector switch so contact 50 is closed and contact 52 is open. Start push button 49 is then depressed to energize winding 48 of contactor F through the aforedescribed circuit. Contactor F operates to close contacts F1 to F5 and open contact F6` Contacts F1 to F3 operate to connect motor 13 to source 17 through lines 18, 19 and 2i? in a manner to be operated in the forward direction.

Contact F4 closes and connects winding 48 of contactor F to line 44 so that the operator can now release start button 49.

Normally, a press is operated in one of three methods.

One is to inch the press. This is to connect the press so that it will operate only as long as a push button is held depressed. By this means, the movement of the press ram can be controlled for extremely short distances and is used primarily to ensure the mating of dies when setting up a press.

Another type of operation is to run the press. This method of operation is used most of the time in the press productive operation. Here, the control is connected so that each operator must depress a push button with each hand to start the press operation. The press continues in its operation only if the push buttons are held depressed and will stop automatically at the end of each cycle of operation. The push buttons may be released as soon as the press ram has passed the point at which it Would be dangerous to the operators hands. During this interval, the operators may release the push buttons and use their hands to remove the finished work from the press throat and put a new piece of raw material in the dies.

The third method is the continuous method of operating =a press. In these instances, the material is automatically fed into and retracted from the press sothat it can run continuously once its initial operation is started.

Once the type or" operation has been determined, the selector switch is moved to the proper position. Normally, this selector switch is of the lock type so that it cannot be operated by unauthorized individuals. FIG- URE 3 is a diagrammatic representation of the selector switch and indicates which contacts are closed for the Various types of operation.

When the selector switch is moved to its run position, contacts 54 and 55 become closed. Thus, with contact F5 closed, contactor 1CR is energized through normally closed contacts 56 and 58 of push buttons 57 and 59, respectively. Winding 53 of contactor ICR is energized and contactor CR -operates to close contacts 1CR1 and 1CR4 and open contacts 1CR5 and 1CR6.

After contacter 1CR becomes energized, the circuit is in the state ready for operation.

Depending upon the type and the size of the press, it may have one or more operators. While the circuit of FIGURE 1 Ishows only two push buttons, 57 and 59, it is noted that when more .than one operator is required, an additional pair of push buttons must be added for each operator. When this is done, one of the pair is connected in series with push button 57 and the other of the pairs is connected -in series with push button 59. This requires that the operators must depress all of the push buttons and maintain them depressed while the press is going through its unsafe portion of its operating cycle.

To operate, the operator must depress push buttons 57 and 59 to open contacts 56 and 58 and close contacts 63 and 64. The closing of contacts 63 and 64 connects winding 62 of contactor ZCR so it is energized through contact 63 of push button 57, contact 1CR3, contact CRft, and contact 64 of ypush button 59. Contactor 2CR operates to close contacts 2CR1 and 2CR4 and open contacts ZCRS to 2CR9.

Even though the depression `of push buttons 59 and 57 opened contacts 56 and S8, contactor ICR remains energized through contacts lCRl and 1CR2. As soon as contactor ZCR becomes operated, contacts 2CR6 and 2CR7 open, -to de-energize contactor 1CR and contacts lCRl to 1CR6 return to their unoperated position.

Contactor ZCR is now maintained energized through contacts 3CR6 and 2CR1 in parallel with contact 1CR3, and contact ZCRZ which is in parallel with contact 1CR4. It is also maintained energized by limit switch contact 3i? which is in parallel with contact 3CR6.

It is seen that should the operator release either or both of the push buttons 57 and 59, the opening of either contact 63 or 64 would de-energize contactor ZCR. If only one push button was released, he would have to release the other one to re-energize contactor ICR and ,laser then depress both push buttons again to re-energize contactor ZCR.

The reclosing ot contacts ECRS and iCRo now connect winding 65 of contactor SCR so it is energized through contact 63 of push button 57, contact lCRS, contact ZCRS, winding 65 of contactor SCR, limit switch contact 33, contact ZCRi, contact lCRo and contact oli of push button S. Contactor SCR operates to close contacts SCRi to SCRL.A and open contacts 3CR5 to 3CR'7.

The closing of these contacts connects winding 37 so it is energized through contact o3 of push button 57, contact lCRS, contact 2CR3, contact CRl, wire do, contact SCRS, wire 42, winding 37, wire d3, contact -SCRL wire 67, contact ECRZ, cont-act ZCRLi, contact liCR, and contact 64 of push Ibutton 59.

Winding 37 is now energized so electromagnet 38 operates to operate the air valve and air under pressure is supplied by conduit 39 to cylinder 2.1 behind piston 22. Piston 22 is moved forwardagainst the bias of spring Zd and causes piston rod 23 to disengage the brake and engage the clutch. Gear i5 is connected to shaft tti to cause the press to begin its cycle of operation.

When contactor SCR operates to open contact 3CR6, contactor ZCR is maintained energized by parallel connected limit switch contact 39.

FIGURE 4 is a diagrammatic representation of the portion of the press cycle of operation that each of the individual limit switch contacts are opened and closed. It is noted at the beginning of the cycle that limit switch contact 3i) is maintained closed until approximately 180 of the press cycle. This is the point at which the press ram has reached its maximum down stroke. lit is also noted that limit switch contacts 3l and 32 become closed shortly before limit switch contact 59 opens. Further, limit switch 33 remains closed throughout the major portion of the press cycle and opens only momentarily `at about the press 270 portion.

Therefore, when limit switch contacts 3i and 32 close, contactor SCR and winding 37 are energized directly from wires 6i? and 6i and, thus, push buttons 57 and@ need no longer be held depressed by the operator. It is to be -noted Vhere that since the press ram has reached the bottom of its stroke, the operator cannot injure vhimself by putting his hand in the press throat.

Contactor SCR is maintained energized by the circuitY consisting oi limit switch contact 3i, contact 3CR1, winding o5 of contactor SCR, limit switch contact 33, contact CRZ and limit switch contact 32. Likewise, winding 37 is energized through the circuit consisting of limit switch contact 3l, wire 66, contact SCRS, wire 42a',` winding 37, wire 43, contact SCRK, wire 67 and limit switch contact 32.

As soon as limit switch contact 3i) opens, winding 62 of contactor ZCR becomes de-energized and its contacts ZCRl to ZCR@ return to their normal condition,

The press continues to operate as described until it reaches the 360 point of its cycleof operation at which point limit switch contacts 31 and .'52 open to dc-energize contactor SCR and winding 37.

The de-energization of winding 37 allows electromagnet 38 to reiease pilot valve 36 and it moves up under the bias oi its spring liti. The air valve becomes unopK erated and shuts od the supply of air from cylinder 21 and allo-ws the air in conduit 3S and cylinder 2i to eX- haust back and out through conduit 4,1.

Piston 22 and piston rod 23 are moved rearward by the bias of spring A24 to disengage the clutch and set the brake to .stop further movement of the press.

It is to be noted that limit switch contact 33 Vopened at approximately 270 of the press cycle, but that winding @d ofcontactor SCR was maintained Yenergized through contact ZCRS, which is connected in parallel with limit switch contact This operation of limit switch contact 33 checked the operation of contactor ZCR to make sure that it became deenergizedproperlyl it had not, the opening of limit switch contact 33 would cause contactor BCR to become `cte-energized immediately to stop the press.

Had the operator maintained push buttons 57 and 59 depressed, contactor ZCR would still become deenergized and unoperated when limit switch contact Sti opened. Also, when limit switch contacts 31 and 32 opened at the end of the machine cycle, contactor SCR and winding '37 would still become de-energized because ot contacts ZCR3 and ZCRI connected in its energizing circuit.

After the operator has released push buttons 57 and I S9 and limit switch contact Si? has opened to de-energize contactor ECR, contactor ICR Ywill'becorne energized, as described, and ready for the next cycle of operation.

'it is seen that should the operator release his hands from either or both push buttons 57 and 59 during the iirst of the press cycle, either contact 63 or contact 6dor both ot them open the energizing circuit to winding to stop the press. This also opens the energizing circuit for contactors'ZCR and SCR and they become 'de-energized. However, since the energizing circuit for winding e2 of ZCR is through contacts llCRS and lCRd, it is necessary that the operator release both push buttons 57 and 5%, at the same time, to re-energize contactor iCR, and then re-depress both push buttons to re-energize contactor ZCR.

ln applicationsY ot this type, it isV desirous to not stop the press at the end o each cycle provided the operators have had an opportunity to remove the finished material from the dies and insert the new material therein before the end of the cycle. This is referred to as jumping the press and is accornpiished as follows.

As soon as the operators have accomplishedthis work, and provided it is after the `press has reached the point in its cycle where limit switch contact 3i) has opened and again reclosed7 all the operators may put their hands back on the push buttons and depress them. This will bring in contactor ZCR in the same manner as before described and cause contactor iCR tobecome de-energized. Contactor ZCR is maintained energized through its own contacts and limit switch contact 39, which again closed shortly after the point in the press cycle' that limit switch contact 33 reclosed.V Therefore, contactor SCR and winding 37 are maintained energized by current through the contact 63 of push button 57 and contact 6d of push button S9 in the circuit as before described and will not become cie-energized at the end of the cycle, when limit switch contacts 31 and 32 opened. Jumping the press is provided to facilitate production, yet allows it to be done only if all of the operators work has been accomplished Yand their hands in the safe position on the push buttons.

Should it be desirous to operate the press in its continuous condition, the selector swit'clr'is turned to its continuous position where selector switch'contacts 68 and 69 are closed aiong with contactsfd and 55. in this type` of operation, the initial starting of the press is accomplished in the same manner as aforedescribed. However, iminediateiy after starting movement of the press, the operator can remove his lhands from both push buttons and the press will continue to operate'until a stop button, such as do, is depressed. lf desired, a stop button may .be connected in series with selector switch Contact so only the press control circuit may be' deenergizcd and not that of mot-or i3.

Continuous operation is accomplished as follows, With Vpush Ybuttons 57 and 59 in theirk up position, contactor llCR is energized to operate its contacts. The operator may then push the push buttons to close contacts 63 and 64, and open contacts 56 and58. Contact orY CR is'energized through contacts llCR3 and lCRi and' rnaintainedV energizedithrough itslown contacts, ZCRl and ZCRZ, and limit switch contact 3o. Contacter YLCR Yis 9 de-energized by contacts 2CR6 and 2CR7 and becomes unoperated.

Contactor SCR is operated by current through push button contact 63, contact ICRS, contact 2CR3, winding 64 yof contactor SCR, limit switch contact 33, Contact 2CR4, contact ICR6 and contact 64 of push button 58.

As soon as contactor SCR becomes operated to close its contact, winding 37 becomes energized as before described. Since selector switch contacts 66 and 69 are closed for continuous operation, contactor SCR is now maintained energized from wire 60 directly through selector switch contact 68, contact BCRI, winding 65 of contactor SCR, limit switch contact 33, contact 3CR2, and selector switch contact 69 to wire 6I. Winding 37 is also maintained energized directly by the circuit consisting of selector switch contact 68, wire 66, contact 3CR3, wire 42, winding 37, wire 43, contact 3CR4, wire 67 and selector switch Contact 69 to wire 6I.

The operator may now release his hands from the push buttons, completely independent of the position of the press ram. Contactor ZCR then becomes de-energized to close contact ZCRS and maintains contactor SCR and its winding 65 energized through closed Contact ZCRS, which is parallel with limit switch contact 33. The press will now continue to operate continuously until such time that the operator pushes a stop button to remove the power from the press control circuit.

For the other type or inching operation, the selector switch is turned to the inching position, at which point, selector switch contacts 70 and 74 are closed and selector switch contacts 54, 55, 68 and 69 are opened. By pushing inching push button 72, the operator can connect winding 37 directly to the source by lines te and 45 through the circuit consisting of selector switch contact 7G, contact 7I of push button 72, normally closed Contact 2CR9, wire 42, winding '37, wire 43, contact 2CR7, contact 73 of push button 72 and selector switch contact 74. In this type of operation, the press will operate when push button 72 is depressed and will continue to operate only as long as it is held depressed. This is true completely independent of the position of the ram in the press operating cycle. As before described, the use of this type of operation is primarily in the settingy up and the matching of the press die.

FIGURE 5 is similar to FIGURE I except it has the added feature of protecting against the possible short circuiting of the push buttons normally open contacts when only two push buttons are used. Therefore, like parts have been given the same reference characters, and only the portion of FIGURE l necessary to described the feature has been shown.

Contactor ICRA has a winding 75 and normally open contacts `ICRAI and ICRAZ and normally closed contacts ICRA3 and ICR/3x4. It is connected across wires 6i) and l6I by normally closed contact 56 of push button 57. Contacts ICRAI and 2CR6 are connected in parallel wit-h contact 56.

Contacter ICRB has a winding 76 yand normally open contacts ICRBI and ICRBZ, and normally closed contacts ICRBS and .ICRBe It is connected across wires 6d) and 61 by normally closed contact 58 of push button 59. Contactors ICRBI and 2CR7 are connected in parallel with contact 53.

The remainder of the circuit for FIGURE 5 is identical with that of FIGURE l except that contact ICRAZ replaces contact ICRll, contact ICRBZ replaces Contact IiCRZ, contacts ICRAS and ICRB3I replace contact ICRS, and .contacts ICRA4 and ICRB4 replace contact ICR6.

Therefore, the operation of the two circuits to energize winding 37 are identical except that whenever contactor ICR operated in FIGURE 1 Iboth contactors ICRA and ICRB yoperate in FIGURE 5. Itis believed that the operation of FIGURE 5 for the normal modes of operation described for FIGURE l are understood, and for the sake 10 of brevity, a complete re-description of these modes of operation will not be made.

As stated, FIGURE 5 protects against the possible short circuiting of either normally open push button contacts 63 or 64. This is as follows.

Assuming that contact 63 has become shorted due to an accident, contactor ZCR still cannot become energized because of contact 64 being open. However if only push button 64 is depressed, an unsafe condition is created since the operators other hand is free and therefore, the press should not be allowed to operate. When this occurs, contactor ZCR operates its contacts. The opening of contact 2CR7 causes contactor ICRB to become deenergized. Contactor `ICRA does not become de-energized since it is maintained energized through contact 56 of push button 57 which has not -been depressed.

Therefore, contacts -ICRA3 and ICRA4 in the energizing circuit for contactor SCR remain open to prevent it from becoming energized. Thus, winding 37 cannot become energized and the press will not operate.

If both push buttons 57 and 59 are depressed when contact 63 is shorted, the press will operate in the normal manner. However, since :both push buttons are depressed, an unsafe condition does not exist and operation of the press will not be harmful or dangerous.

It is to be noted that the circuit of FIGURE 5 can only be used with two push Ibuttons or one operator. If more than one operator is required, which necessitates the use of -rnore than two push buttons, the circuit of FIGURE 6 must be used.

Here again, FIGURE 6 is very similar to FIGURES I and 5, and like parts of the two figures have been given the same reference characters. Also, only that portion of FIGURE I necessary to describe the feature has been shown.

FIGURE 6 has four push buttons 77, 73, 79 and 86. Each push button has a normally open Contact SI, 82, 83 and S4, and a normally closed Contact 85, 86, 87 and 88, respectively.

The normally closed contacts are connected from wire 60 by a wire S9, contact 8S, contact 86, a wire 9i), winding 91 of a contactor CR, a wire 92, contact 87, contact 88 and a wire 93 to wire 6-1.

Contacter 96 has normally open contacts CRI to CR6 and normally closed contacts CR7 to CRIQ.

A first latch relay ISR having a latching winding 94 is connected by three possible separate circuits between wires 92 and 60. Latch relay also has a trip winding 95 and a normally open Contact ISRI and normally closed contacts ISRZ and ISR3.

The first of the possible circuits is through a normally open contact 96 of a first selector switch 97 and a normally open contact 98 of a second selector switch 99 to wire 60. 'Ihe purpose of selector switches 97 and 99 will be described in more detail hereinafter.

The second circuit is through contact CRI, a normally closed contact 16) of selector switch 99, contact 84 of push button Si) to wire 66.

The third circuit is through contact CRI, a normally closed contact Itll of selector switch 97, contact 83 of push button 79, and contact (SR2 to wire 66.

A second latch relay ZCR having a latching winding I6?. is connectable by two possible separate circuits between wire and wire 6I. Latch relay ZSR also has a trip .winding 163 `and a normally open contact ZSRI and normally closed contacts ZSRZ and ZSRS.

The `lrst possible circuit is through Contact CRS, a normally closed contact IM of selector switch 97, contact 82 of push button 78 and contact CIMl to wire 6l..

The second circuit is through contact CRB, a normally closed contact IGS of selector swltch 99, and contact SI of push button 77 to wire 6I.

Trip windings and 163 are connected in parallel with each other and in series with a normally open contact 14.76 across wires 66 and 6I.

Contacts lSRl and ZSRl are connected in parallel with each other and in series with an indicating 'lamp 107 across Wires et? and 6l.

The normally open contact ofthe push butt-ons are connected from Wire 60, contact 34, contact CR?, contact 83, contact CRS, contact lSRZ, contact ZSRZ, contact ECR-3, Winding 52 of contactor ECR, contact TCR-1t, contact 2SR3, contact llSRS, contact CRS, contact 32?., contact CRM, and contact 3l to wire 6l.

Contactor TCR is connected across wires o@ and el by contact CRS, Winding 53 of contactor E CR and con tact CR6. Contacts 2CR6 and lCRl are connected in series with each other and in parallel with contact CRE. Contacts lCRZ and ZCR? are connected in series wit-l1 each other and in parallel with contact CR6.

A second indicating lamp Hi8 is connected across Wires 6i) and 6l by a circuit from wire 60 consisting of wire 89, indicating lamp 108, normally open contact 109 of selector switch 9'! to wire 6l.

A third indicating lamp llt) is connected across wires 60 and 61 by a circuit from wire 60 consisting of Wire 89, indicating lamp 110, normally open contact lll of selector switch 99 to Wire 6l.

This circuit operates as follows.

When all ofthe push buttons are released, contactor CR Y is energized by the circuit from wire 60 through wire 89, contacts S and Se, wire ht), Winding 91 of contactor CR, wire 92, contacts 87 and 88, and Wire 93 to wire 6l. Contactor CR operates to close contacts CRl to CR@ and open contacts CR7 to CRN. v

Should any of the normally open contacts of the push buttons be shorted, this fault is automatically indicated at this time and operation of the press is prevented since an unsafe condition may possibly exist.

If the short exists across contacts S3, latch relay ILSR is energized by the circuit from Wire 60 through contact CRZ, shorted contact 83, contact itil, contact CRL latch Winding 94 of latch relay lSR, wirel 92, contacts S7 and 88, and wire 93 to wire 6l.

If the short exists across contacts 84, latchl relay lSR is energized by the circuit from wire 60 through shorted contact 84, contact 100, contact CRll, latch winding 94 of latch relay TSR, Wire 92, contacts S7 and 38, and wire 93 to wire 61.

When latch winding 94 of latch relay lSR is energized, it operates to close contact lSRll and open contacts lSRZ and lSR. The closing of contact lSRl connects indicating lamp llti across wires o@ and 61 to illuminate it, giving a visual indication that a short exists. The opening of contacts lSRZ and lSRS opens the energizing circuitrfor contactor ZCR so it cannot be operated, thereby preventing the energization of contactor SCR and Winding 37, and operation of the press.

lf a short exists acrosscontacts 8l, latch relay ZSR is energized by the circuit from wire 69 through wire S9,

contacts 85 and 86, wire 9d, latch Winding 162 of latch v relay ZSR, contact CRS, contact ltlS, and shorted contact 8l to wire 6l. Y Y

ita short exists across contact 82, latch relay ZSR is energized by the circuit from wire et) through wire 89,

contacts S5 and 86, wire 99, latch winding to2 ot latchV relay 23R', contact CRS, contact N4, shorted Contact 32,

and contact CRA to wire 6l.

When latch winding 192 of latch relay ZSR is energized, it operates to close contact 2SRl and open contacts ZSRZ and ZSRS. The closing of contact ZSRlY connects indicating lamp lltlv across wires o@ and el to illuminate it, giving a visual indication that a short exists. The opening of contacts ZSRZ and ZSRS opens the energizing circuit Y for contactor ZCR so it cannot be energized, thereby preventing the energization of contactor SCR and winding 37, and operation of the press. Y g

Latch relays lSR and ZSR are of the well known type where the contacts are operated by'energirzation ofthe Y latch winding, and once operated, the contacts are mainl2 tained operated by a mechanical latch independent of the energization of the latch winding. Subsequent energization of the trip winding after deenergization of the latch winding releases the contacts so they can return to their unoperated condition.

Therefore, indicating lamp 107 remains illuminated and the energizing circuit for contactor ZCR remains open even though the push buttons may later be depressed.

After the shorted contact of the push button has been repaired, the circuit energizing the latch winding becomes open. To reset the circuit so the press can be operated, contact 105, which may be a contact of a push button or other suitable device, is closed. This energizes trip windings 95 and 103 of latch relays ISR and ZSR, respectively, to, as described, release the latch mechanism and allow their contacts to become unoperated.

The press may now be operated as follows.

Contactor CR is operated as described when all the push buttons are released.

Winding 53 of contactor lCR is now energized by the circuit from Wire through contact CRS, winding 53, and contact CRS; to wire 6l. Contactor lCR operates to close contacts lCRl to 1CR4 and open contacts lCRS and lCR6. v

Push buttons 77, 78, 79 and 84B can now be depressed to open their contacts 85, Y8o, 87 and 88. This de-energizes winding 91 of contactor CR, causing its contacts to become unoperated.

Contacter llCR remains operated by the circuit through contacts ZCRo and ICR] connected in series with each other and in parallel with contact CRS, and contacts lCRZ and 2CR7 which are connected in series With each other and in parallel with contact CR6.

The depression ot the push buttons also close contacts Y 8l, 82, S3 and 84 to operate contactor 2CR. lts winding SCR is energized through the circuits consisting of con`V tacts S4, CR7, 83, CRl, lSRZ, ZSRZ, 2CR3 andrlCRS to winding 65, and thence through contacts 33, lCRo, 2CR4, ZSRS, ESR, CR9, 82, CRM and 8l. Winding 37 is energized through contacts SCRL SCRS, 3CR4 and SCR?. Yin addition to the above described circuit except for Winding and contact 33. The'details o'operation for this circuit are the same as described for FIGURE l, which for the `sake of brevity will not be repeated.

While I have described this feature connected in a circuit that utilizes four `push buttons, it is understood that the feature is operable in a circuit having any number of push buttons. This is accomplished by making a separate circuit available for each normally open contact of each of the push buttons through which one of the latch windings of latch relays lSR or ZSR can be energized.

Selector switches @7 and 99 have been included in the circuit to permit the use of dummy plugs. Their use is well known in the art of presslcontrol and they are used to close both the normally open and closed contacts of the push buttons. The purpose is to reduce the number of push buttons required, when a fewer number of operators are needed to operate the press. V v V Y To replace an operator in FlGURE 6, a durnrnyplugY may be inserted for push buttons 78 and 79. VThis closes contacts 82, 83, 86 and S7, vand if no changes are made in the circuit, latch relays lSR and ZSR would operate to indicate that contacts 82 and 33 were shorted.Y Also, the operation of latch relays lSR and ZSR would, as described, prevent energization of vwinding 37 and operation ofthe press.

Y YThe operationY of latch relays llSR and ZYSR is prevented Y areas?? by turning selector switch 97 to close contacts 96 and 109, and open contacts 101 and 104. The opening et contact 101 prevents latch relay lSR from being energized through the new closed contact 83. The opening of contact 104 prevents latch relay 23R from being energized through the new closed contact 82. The closing of contact 109 connects indicating lamp 108 to wire 61 and by wire 89 to wire 60 se it is illuminated te indicate that one set of dummy plugs have been inserted for push buttons 78 and 79.

It is seen that if all the push buttons are replaced by the dummy plugs the press will not operate because of the operation of contacter CR, but it still would create an undesirable and potentially unsafe condition. Therefore, it is further protected against, since if both selector switches 97 and 99 are not turned to the dummy plug position, latch relays 1SR and/or 2SR will operate. lf both selector switches are turned to the dummy plug position, contacts 96 and 98 will be closed to energize latch winding 94 of latch relay 1SR from wire 60 through contacts 96 and 98, winding 94, wire 92, contacts 07 and 88, and wire 93 to wire 61. Latch relay 1SR thus operates te prevent operation of the circuit and indicate by lamp 107 that something is Wrong, as has been previously described.

It is to be noted that one selector switch is required for each pair of push buttons or for each operator.

FIGURE 6 also illustrates another safety feature which may be incorporated with the circuits of FIGURES l and if desired. This safety feature is to provide protection against the faulty operation of the limit switch contacts or the disconnection of the limit switch from the press. To achieve this safety feature, a fifth cam and a contact 112 operated thereby must be added to the limit switch in FIGURE 2 and a second limit switch having three cams and cam operated contacts 113, 114, and 115 must be connected directly te shaft of the press (not shown).

These contacts are connected to operate in the circuit of FIGURE 6 as follows.

Contact 115 of the second limit switch is connected in FIGURE 6 in the same manner that contact 32 is connected in FIGURES l and 5. That is, between Contact 3CR2 and wire 61. Contact 32 is connected in series with contact 114 between wire 61 and selector switch contact 55. Contact 113 is connected in parallel With contact 32 and Contact 112 is connected in parallel with contact 114. The contacts of the cam operated limit switches of FIGURE 6 operate in the sequence shown by the diagrammatic representation of FIGURE 7.

Contacts 30, 31 and 33 of FGURE 6 operate in the same manner described for them in FIGURE l and contact 115 operates the same as described for contact 32 in FIGURE 1. That is, contact opens at approximately the 180 point to de-energize winding 62 of contacter ZCR and reclese at approximately the 270 point to permit jumping the press as described. Contacts 31 and 115 close at approximately the 170 point to allow the operators to release the push buttons without stopping ythe press and reopen at the end of the press cycle. Contact 33 opens at approximately the 200 point and then recloses at the 250 point te insure that contact 2CR has operated properly, and if not to stop the press. The details of operation for these contacts in the circuit is set forth in the description for FlGURE l and for the sake of brevity will not be repeated here.

At the beginning of the press cycle, contacts 32 and 114 are closed and contacts 112 and 113 are open. Therefore, the circuit from wire 61 to wire 45 is completed through contacts 32 and 114 and Contact S5.

At approximately the 60 point in the press cycle, centacts 112 and 113 close and at about the 70 point contacts 32 and 114 open. New the circuit from wire 61 to wire is completed through contacts 112 and 113.

Contacts 32 and 114 reclese at about the 90 point and Cil 14 contacts 112 and 113 re-epen at about the 100 point to transfer the circuit back through contacts 32 and 114.

If either of the limit switches had become broken or disconnected from shaft 10 at a point in the press operating cycle when either contact 112 er 113 was open, then when the above described transfer of the circuit took place to contacts 112 and 113, the press would stop immediately because the open contact disconnects the source of power from the circuit.

Had the limit switch breken or become disconnected with either of the contacts 112 or 113 were closed, an unsafe condition would not occur. It is seen that when centacts 112 and 113 are closed, contacts 31 and 115 are open.

Therefore, when the press reached the point for closing contacts 31 and 115 only one would do so and the other would remain open to prevent the energizatien ef contacter `CR and winding 37 from being transferred from the normally closed contacts of the push buttons. Thus, as soon as the operator released his hands from the push buttons, the press would stop regardless of its position. rThis gives the indication that Something is wrong which should be corrected and makes the condition safe by compelling the operators hands to be on the push buttons.

Although I have described my invention with a certain degree ef particularity, it is understood that the above disclosure has been made only by way of example as required by law and that many changes in the details of circuitry may be resorted te by those skilled in the art without departing from the spirit and the scope of my invention as hereinafter claimed.

I claim:

1. A circuit for controlling energization of a work device comprising a first, second, and third contacter; each contacter having a plurality of normally open closed contacts; a source of electrical power; an operator push button having a normally open and a normally closed contact; said tirst contacter energized through the normally closed contact of the push button and sustained energized through a normally closed contact of the second contacter and a normally open Contact of the rst contacter; upon depression of the operator push button, the second contacter is energized through the normally open contacts of the push hutten and a normally open Contact of the first contacter means, and sustained energized by a normally open contact of the second contacter; and the third contacter is energized through the normally open contacts of the push button and a normally closed contact of the first contacter and a normally open Contact of the second contacter; and the device is energized through the push button normally open contact, a normally closed contact 'of the first contacter, a normally open contact of the second and third centactors.

2. A circuit for controlling"energization of a Work device comprising a first, second, and third contacter; each contacter having a plurality of normally open and normally closed contacts; a source of electrical power; an operator push button having a normally open and a normally closed contacter; said first contacter energized from the source through the normally closed contact of the push button and sustained energized through a normally closed contact of the second contacter and a nerrnally open contact of the first contacter; upon depression of the push hutten, the second contacter is energized from the source through the normally open contact of the push button and a normally open contact of the rst contacter' and sustained energized by a lirst and device operated switch and a normally open contact of the second contacter; and the third contacter is energized through the normally open contact of the push button, a normally closed contact of the iirst contacter and a normally open contact of the second contacter; and the device is energized through the push button normally open contact, a normally closed contact of the first conmally open contact of the first contactor; upon depression of the push button, the second contactor is energized from the source through the normally open contacts of the push button and a normally open contact of the first contactor and sustained energized by a first device operated switch connected in parallel with a normally closed contact of the third contactor, and hoth connected ink series with a normally open Ycontact of the second contactor; and the third contactor is energized through the normally open contact of the push button, a" normally closed contact of the first contactor and a normally open contact of the second contactor; and the device is energized through the push button normally open contacts,

- vnormally closed contacts of the first contactor, and a normally open contact of the second and third contactors. 4. A circuit for controlling energization of a work ydevice comprising a first, second, and a third contactor each contactor having a plurality of normally open and normally closed contacts; a source of electrical power; an operator push button having a normally open and a normally closed contact; said first contactor energized from the'source through the normally closed contact of the push button' and sustained energized through a normally closed contact of lthe second contactor and a normally open contact of said first contactor; upon depression of the push button, the second contactor is energizednfrorn the source through the push button normally open contact anda normally open contact of the Yfirst contactor and sustained energized through a norrnally open contact of the second contactor; and operation of the second contactor causes its normally closed contact in the sustaining circuit of the first contactor to (le-energize the first contactor; and the third contactor is energized through the normally open Contact of the push button, a normally closed contact of the first contactor, and a normally open contact of the second conmally open Contact of the push hutten, a normally closed contact of the first contactor, and a normally open convtact of the second and third contactor.

5. A latchiru7 circ-uit comprising a iirst and second contactor; each contactor having a plurality of normally open and normally closed contacts; a source of electrical power; an operator push button having a normally open and a normally closed contact connected inthe circuit; said first contactor energized through the normally closed contact ofthe push button and sustained energized through a normally closed contact of the second contactor and a normally open contact of the rst contactor; and upon depression or" the push button, saidl second contactor is energized through the normally open contact of the push button and a normally open contact of the first contactor and sustained energized by a normally open contact Vof the second contactor, and said first contactor remains energized until'rsaid second contactor is operated to open Vits'noriiially closed contact in the sustaining circuit of the first contactor.

6. A circuit for energizing a Worlr deviceto control a cyclically operating machine comprising a first, second, and third contactor; each contactor having a plurality of normally open and normally closed contacts; aV source Y of electrical power; an operator push Vbuttonhaving a normally open and a normally closed Contact; said first contactor energized from the sourcethrough `the normali Ytactor; and the work device is energized through the norclosed'contact of the push button and sustained energized through a normally closed contact of the second contactor and a normally open contact of said first contactor; upon depression or the push button, the second contactor is energized through the normally open contact of the push button and a normally open contact of the first contactor and sustained energized through a normally open contact or the second contactor; and the third contactor is energized through the normally open Contact of the push button, normally closed contacts of the first contactor and a normally open'contact of the second contactor; and the device is energized through the normally open contact of the push button, a normally closed contact ol the first contactor and a normally open Contact of the second and third contactors, and a first normally open machine operated switchV is set to close at a safe point in the machines cycle of operation to connect the source to energize the third contactor and the work device directly through a normally open contact of the third contactor.

7. A circuit for energizing a work device to operate a cyclically operating machine as described in claim 6 wherein a normally closed second machine operated switch is connected in the sustaining circuit of the second contactor and Vset Vto open at a point in the machine cycle after the closing of the firs-t machine operated switch to thereby cle-energize said second contactor.

8. A circuit for energizing a work device for operating a cyclically operating machineas set forth in claim 7 wherein a normally closed third machine operated switch is connected in the energizing circuit of the third con- Vtactor and has a normally closed contact'of the second contactor connected in parallel with said third machine operated switch, and whereby said third machine operated switch is arranged to be opened momentarily after opening or said second machine operated switch to insure that said second contactor means has become unoperated.

9. A circuit for energizing a work device to control a cyclically operating machine comprising, a first, second,` and third contactor; each contactor having a plurality of normally open and normally closed contacts, a source of electrical power; an operator push button having a normally open and a normally closed contact; said first contactor energized from the source through the normally closed Contact of the push button and sustained energized through a normally closed contact of the second contactor and a normally open Contact of said first contactor; upon depressionY of the push button,`the second contactor is energized through the normally open Contact of the push ybutton and a normally open contact of the first contactor and sustained energized through a normally closed first machine operated switch connected in parallel with a normally closed contact of the third contactor and both in series with a normally Vopen contact of the second contactor; and after the second contactor is energized, the first contactor is cle-energized by the opening of the Y normally closed contact in its sustaining circuit; and the VVthird contactor is energized through the normally open contact of the push button, normally closed contacts of the first contactor and a normally open contact of the second contactor; and the device is energized through the normally openy contact of the push button, a normally closed Contact ofY the rst contactor, a normally open Contact of the second and third contactor. l

l0. Al circuit for energizing a work device .for controlling a cyclically operating machine comprising a first, second and third contactor; each contactor having a plurality of normally open and normally closed contacts; a

source of electrical power; an operator push button having Va normally open and a normally closed Contact; said first contactor energized from the source through the normally Y Y closed Contact of the push buttonY and sustained energized through a normally closed contact ofthe second contactor andenormally open contact of said tlrst contactor; upon depression of the push button, the second contactor'is energized through the normally open contact of the push button and normally open contact of the first contactor and sustained energized by a normally closed first machine operated switch and a normally open contact of the second contactor; whereby operating of the second contactor opens the sustaining circuit to the first contactor causing it to become unoperated; and the third contactor is energized through the normally open contact of the push button, normally closed contacts of the first contactor, normally closed contacts of the second contactor, and a normally closed second machine operated switch; a normally closed Contact of the second contactor is connected in parallel with said normally closed second machine operated switch; whereby the device is energized through the normally open contact of the push button, normally closed contacts of the rst contactor, normally open contacts of the second contactor and normally open contacts of the third contactor to start operation of the cyclically operating machine and after its unsafe portion of operation, a normally open third machine operated switch closes to connect the third contactor to the source through its own normally open contact and said parallel connected second machine operated switch and normally closed contact of the second contactor, and also connects the work device to the source through normally open contacts of the third contactor thereby allowing release of said push buttons, and said first machine operated switch is set to open to de-energize the second contactor, and thereafter said second machine operated switch opens momentarily to insure said second contactor has become unoperated and at the end of said machines operating cycle, said third machine operated switch opens to de-energize the third contactor and the work device to stop the machine.

11. A circuit for controlling a cyclically operating machine as set forth in claim wherein a normally closed contact of the third contactor is connected in parallel with the normally closed first machine operated switch to prevent it opening from de-energizing the second contactor until after the third contactor has been energized.

12. A latching circuit comprising a first, second, and third contactor; each contactor having a plurality of normally open and normally closed contacts; a source of electrical power; a pair of operating push buttons, each having a normally open and a normally closed contact; said first contactor energized from the source through the normally closed contact of one of said push buttons and having a sustaining circuit of one of its normally open contacts and a normally closed contact of said third contactor; said second contactor energized from the source through the normally closed contacts of the other push button and having a sustaining circuit containing one of its normally open contacts and a normally closed contact of said third contactor; and upon depression of said push buttons said third contactor is energized through the push buttons normally opened contacts and a normally open Contact of said first and second contactor, said third contactor having a sustaining circuit through the normally open contacts of the push buttons and its normally open contacts, whereby said first and second contactors become unoperated due to the opening of said normally closed third con-tactor contacts in their sustaining circuit.

13. A circuit for controlling energization of a work device comprising a first, second, third, and fourth contactor; each contactor having a plurality of normally open and normally closed contacts; a source of electrical power; a pair of operator push buttons, each having a normally open and a normally closed contact; said first contactor energized through a normally closed contact of one of said push buttons and sustained energized through one of its normally open contacts and a normally closed contact of said third contactor; said second contactor energized through the normally closed contact of the other push button and sustained energized through one of its normally open contacts and a normally closed contact of said third contactor; said third contactor energized through the normally open contact of said push bu-ttons and a normally open contact of said first and second contactors and sustained energized through the normally open contacts of said push buttons and one of its normally open contacts; said fourth contactor energized from the source through the normally open contact of said push buttons and a normally closed contact of said first and second contactors and a normally open contact of said third contactor; and said work device energized through said normally open contact of both push buttons, said normally closed contacts of said first and second contactors, normally open contacts of said third contactor, and normally open contacts of said fourth contactor.

14. A circuit for energizing a work device to control a cyclically operating machine comprising a first, second, third, and fourth contactor; each contactor having a plurality of normally open land normally closed contacts; a source of electrical power; a pair of operator push buttons, each having a normally open and a normally closed contact; said first contactor energized through a normally closed contact of one of said push buttons and sustained energized through one of its normally open contacts and a normally closed contact of said third contactor; said second contactor energized through the normally closed contact of the other push button and sustained energized through one of its normally open contacts and a normally closed contact of said third contactor; said third contactor energized through the normally open contact of said push buttons and a normally open contact of said first and second contactors and sustained energized through the normally open contacts of said push buttons and one of its normally open contacts; and after the third contactor is energized, the first and second contactors are de-energized by the opening of said normally closed third contactor contacts in their sustaining circuit; said fourth contactor is energized from the source through the normally open contact of said push buttons and a normally closed contact of said first and second contactors and a normally open contact of said third contactor; and said work device energized through said normally open contact of both push buttons, said normally closed contacts of said first and second contactors, normally open contacts of said third contactor, and normally open contacts of said fourth contactor to operate the machine, and a first normally open machine operated switch set to close ata safe point in the machine cycle of operation to connect the source through normally open contacts of the fourth contactor and maintain the fourth contactor and the work device energized and the machine operating.

15. A circuit for energizing a work device to operate a cyclically operating machine as described in claim 14 wherein a normally closed second machine operated switch is connected in the sustaining circuit of the third contactor and set to open at a point in the machine cycle after the closing of the first machine operated switch to thereby de-energize said third contactor.

16. A circuit for energizing a work device to operate a cyclically operating machine as described in claim 15 whereln a normally closed contact of the fourth contactor is connected in parallel with the second machine operated switch to thereby insure that the fourth contactor is energized before the third contactor can be de-energized by opening of the second machine operated switch.

17. A circuit for energizing a work device to operate a cyclically operating machine as described in claim 16 wherein a normally closed third machine operated switch is connected in the energizing circuit of the fourth contactor and has a normally closed contact of the third contactor connected in parallel with said third machine operated switch, and whereby said third machine operated switch is arranged to be opened momentarily after opening of said second machine operated switch to insure that said third contactor has become unoperated.

18. A circuit for detecting a shorted condition of normsgstr? mally open contacts of an operable push button which are connected to energize an operating circuit from a source of electrical power comprising; normally closed contacts on said push button; a first contactor having a normally open contact and an operating means connected to be energized from the source through the normally closed push button contacts to close said normally open control of said first contactor; indicating means connected in series with the source, the normally closed push button contacts, the normally open contact of the first contactor, and the normally open push button contacts whereby if the said normally open push button contacts are in a shorted condition when the push button is in its normal position said indicating means is energized.

19. A detecting circuit as set forth in claim 18 wherein the indicating means is a second contactor having normally closed contacts connected in the operating circuit whereby if said normally open push button contact is shorted said second contactor is energized to open itsv contacts and de-energize the operating circuit.

20. A detecting circuit as set forth in claim 18 wherein the indicating means is a latch relay having normally closed contacts connected in the operating circuit whereby if said normally open push button contact is shorted said latch relay is energized to open its contacts to make and maintain the operating circuit until the latch relay is reset.

2l. A circuit for detecting a shorted condition of normally open contacts connected in series to energize an operating circuit from a source of electrical power comprising; a plurality of push buttons, each having a said normally open contact and a normally closed contact; a first contactor having normally open and normally closed contacts, and connected to be energized from the source through the normally closed push button contacts; a second contactor connected to be energized from the source through the normally closed push button contacts and a plurality of isolated circuits, each circuit having a normally open push button contact and at least one normally open contact of said first contactor and said circuits made isolated by the normally closed contacts of the rst contactor, whereby if one of the normally open push button contacts is shorted, the second contactor is energized.

22. A circuit for detecting a short circuit condition as described in claim 2l wherein the second contactor has normally closed contacts connected in the operating circuit whereby when said second contactor is energized, it opens its contacts to cle-energize the operating circuit.

23. A circuit for controlling energization of a work device comprising a first, second, third, and fourth contactor; each contactor having a plurality of normally open and normally closed contacts; a fifth contactor having a normally closed Contact; a source of electrical power for energizing the contactors and work device; an oper* ators push button having a normally open and a normally closed contact; the first contactor connected to be energized through the normally closed push button contact; the fifth contactor connected to be energized through the normally closed push button contact and through a separate circuit containing the normally open push button contact and at least one normally open contacts of said first contactor, said separate circuit established by a normally closed contacts of said first contactor; said second contactor energized through a normally open contact of the first contactor and maintained energized through one of its normally open contacts and a normally closed contact of said third contactor; said third contactor energized through the normally closed contact of the push button, a normally closed contact of the first and fifth contactor and a normally open contact of the second contactor, and sustained energized through one of its normally open contacts; said fourth contactor energized through a normally closed contact of first and second and fifth contactor, and a normally open contact of said third contactor; said work device energized through a riormally closed contact of the first and second and fifth contactor, and a normally open contact of the third and fourth contactor.

24. A circuit for controlling energization of a workk device comprising a first, second, third, and fourth contactor; each contactor having a plurality of normally open and normally closed contacts; a fifth contactor having a normally closed contact; a source of electrical powerV for energizing the contactors and work device; a plurality of operators push buttons, each having a normally open and a normally closed contact; the first contactor connected to be energized through the normally closed push buttonV contacts; the fifth contactor connected to be energized through the normally closed push button contacts and a plurality of separate circuits; each separate circuit containing one of the normally open push button contacts and at least one normally open contacts of said first contactor and established by normally closed contacts of said first contactor; said second contactor through normally open contacts of the first contactor and maintained energized through one of its normally open contacts and a normally closed contact of said third contactor; said third contactor energized through the normally closed contacts of the push buttons, Va normally closed contact of the first and fifth contactor and a normally open contact of the second contactor, and sustained energized through one of its normally open contacts; said fourth contactor energized through a normally closed contact of first and second and fifth contactor, and normally open conta-cts of said third contactor; said work device energized through a normally closed contact of the first and second and fifth contactor, and a normally open contact of the third and fourth contactor.

25. A circuit for energizing a work device to control a cyclically operating machine comprising a first, second, third, and fourth contactor; each contactor having a plurality of normally open and normally closed contacts; a fifth contactor having a normally closed contact; a source of electrical power for energizing said contactor and work device; and operators push button having a normally open and normally closed contact; said first contactor connected toY be energized through the normally closed push button contact; said fifth contactor connected to be energized through the normally closed push button contact, a normally open push button contact and normally open contact of the first contactor; Said second contactor energized through a normally open contact of the first contactor and sustained energized through one of its normally open contacts and a normally closed contact of the third contactor; and upon depression of said push button said first contactor is deenergized and said third contactor is energized through the normally open contact of the push button, a normally closed contact of said rst and fifth contactor and a normally open contact of said second contactor, and sustained energized through one of its normally open contacts; said second contactor becoming de-energized by the opening of the normally closed Contact of the third contactor in its energizing circuit; said fourth contactor energized through the normally open contact of the push button, a normally closed contact of said first and second and fifth contactors, and a normally open contact of said third contactor; said work device energized through the normally open contact of the push button, a normally closed Contact of said first and second and fifth contactors, and a normally open contact of said third and fourth contactors to operate the machine, and a rst normally open machine operated switch set to close at a safe point in the machines operating cycle whereby the fourth contactor and the work device are maintained energized through said switch and a normally `open contact of the fourth contactor to keep the machine operating.

26. A circuit for energizing a work device to control a cyclically operating machine comprising a first, second,

third, and fourth contactor; each contactor having a plurality of normally open and normally closed contacts; a fifth contactor having a normally closed contact; a source of electrical power for energizing said contactor and work device; a plurality of operators push buttons, each having a normally open and normally closed contact; said fir-st contactor connected to be energized from the source through the normally closed push buttons contacts; said fifth contactor connected to be energized through the normally closed push buttons contacts and a plurality of separate circuits, each separate circuit containing one of the normally open push button contacts and at least one normally open contact of said first contactor and established by normally closed contacts of said first contactor; Said second contactor energized through normally open contacts of the first contactor and sustained energized through one of its normally open contacts and a normally closed contact of the third contactor; and upon depression of said push button said first contactor is de-energized and said third contactor is energized through the normally closed contacts of the push button, a normally closed contact of said first and fifth contactor and a normally open contact of Said second contactor, and sustained energized through one of its normally open contacts; said second contactor becoming de-energized by the opening of the normally closed contact of the third contactor in its energizing circuit; said fourth contactor energized through the normally open contacts of the push buttons, a normally closed contacts of said first and second and fifth contactors and a normally open contact of said third contactor; said work device energized through the normally open contacts of the push buttons, a normally closed contact of said first and second and fifth contactors, and a normally open contact of said third and fourth contactors to operate the machine, and a first normally open machine operated switch set to close at a safe point in the machines operating cycle whereby the fourth contactor and the work device are maintained energized through said switch and a normally open contact of the fourth contactor to keep the machine operating.

27. A circuit for energizing a work device to control a cyclically operating machine comprising a iirst, second, and third contactor; each contactor having a plurality of normally open and normally closed contacts; a first and second limit switch operated by the machine, each switch having a plurality of contacts set to operate at various preselected points in the machines operating cycle; a source of electrical power for energizing the contactor and work device and connected to the circuit through a normally closed first contact of each limit switch; a normally open second contact of each limit switch connected in parallel with its respective normally closed contact; an operator push button having a normally open and a normally closed contact; said rst contactor energized through the normally closed contact of the push button and sustained energized through one of its normally open contacts and a normally closed contact of the second contactor; upon depression of the push button, the second contactor is energized through the normally open contact of the push button and a normally open contact of the first contactor and sustained energized through one of its normally open contacts, and after the second contactor is energized, the first contactor is de-energized by the opening of the normally closed Contact in its sustaining circuit; the third contactor is energized through the normally open contact of the push button, a normally closed contact of the first contactor and a normally open contact of the second contactor; and the device is energized through the normally open contact of the push button, a normally closed contact of the first contactor, a normally open contact of the second contactor and a normally open contact of the third contactor to operate the machine and said second contacts of both limit switches are set to close and immediately thereafter said first contacts of both limit switches open momentarily and then reclose, after which said second contacts of both limit switches reopen to thereby check the operation of both limit switches and if one should not be operating to disconnect the source of power from the circuit.

28. A circuit for energizing a work device to control a cyclically operating machine comprising a iirst, second, and third contactor; each contactor having a plurality of normally open and normally closed contacts; a first and second limit switch operated by the machine, each switch having a plurality of contacts set to operate at Various preselected points in the machines operating cycle; a source of electric power for energizing the contactors and work device and connected to the circuit through a normally closed first contact of each limit switch; a normally open second contact of each limit switch connected in parallel with its respective normally closed contact; an operator push button having a normally open and a normally closed contact; said first contactor energized through the normally closed contact of the push button and sustained energized through one of its normally open contacts and a normally closed contact of the second contactor; upon depression of the push button, the second contactor is energized through the normally open contact of the push button and a normally open contact of the first contactor and sustained energized through one of its normally open contacts and a normally closed Contact of the third contactor, and after the second contactor is energized, the first contactor is (1e-energized by the opening of the normally closed contact in its sustaining circuit; a normally closed third contact of the first limit switch connected in parallel with the normally closed contact of the third contactor; and the third contactor is energized through the normally open contact of the push button, a normally closed contact of the first contactor and a normally open contact of the second contactor and the second contactor remains energized through its normally open contact and the third contact of the rst limit switch; and the device is energized through the normally open contact of the push button, a normally closed contact of the first contactor, a normally open contacts of the second contactor and a normally open contact of the third contactor to operate the machine, said second contacts of both limit switches arranged to close and said first contacts of both limit switches arranged to momentarily open and then reclose their contacts after which said second contacts reopen in the unsafe portion of the machines cycle, and after said unsafe portion a normally open fourth contact of the first limit switch and a normally open third contact of the second limit switch are arranged to close to maintain the third contactor and Work device energized through said third and fourth contacts and normally open contacts of the third contactor to keep the machine operating.

29. A circuit for energizing a work device to operate a cyclically operating machine as described in claim 28 wherein a normally closed fifth contact of the first limit switch is connected in the energizing circuit of the third contactor and having a normally closed contact of the second contactor connected in parallel therewith, and whereby said fifth limit switch contact is arranged to be opened momentarily after said third contact of the first limit switch opens to insure that said second contactor has become unoperated, and if not, to de-energize the third contactor and the work device to stop the machine.

30. A circuit for energizing a work device to control a cyclically operating machine comprising a first, second, third, and fourth contactor; each contactor having a plurality of normally open and normally closed contacts; a first and second machine operated limit switch,

areas?? each limit switch having contacts operated at various preselected positions in the machines cycle of operation; a source of electrical power for energizing the contactors and the werk device and connected te the circuit through a normally closed first contact of each limit switch, a normally open second contact of the respective limit switches connected in paral` l with the normally closed first contact; a pair of operator push buttons, each having a normally open and a normally closed contact; said first contacter energized through a normally closed contact of one of said push buttons and sustained energized through one of its normally open contacts and a normally closed contact of said third contacter; said second contacter energized through the normally closed contacts of the other push button and sustained energized through one of its normally open contacts and a normally closed contact of said third contacter; said third contacter energized through the normally open contact of said push buttons and a normally open contact of said first and second contactors, and sustained energized through the normally open contacts of said push buttons and one of its nermally open contacts; and after the third contacter is energized, the first and second contactors are de-energized by the opening of said normally closed third contacter contacts in their sustaining circuits; said fourth contacter energized through the normally open contacts of the push buttons, a normally closed contact of said first and second contactors and a normally open contact of said third contacter; and said werk device energized through said normally open contact of the push buttons, a normally closed contact of said first and second contactors and a normally open contact of said third contacter and said fourth contacter to operate' the machine, and said second contacts of both limit switches are set to close and immediately thereafter said first contacts of beth limit switches open and then reclese, and ysaid second contacts of both limit switches repoen te thereby disconnect the source from the c ircuit should either ef said limit switches not he operating properly.

3l. A circuit for energizing a work `device to control a cyclically operating machine comprising la first, second, third, and fourth contacter; each contacter having a plurality of normally open and normally closed contacts; a first and second machine operated limit switch, each limit switch having contacts operated at various preselected positions in the machines cycle of operation; a source of electrical power for energizing the contactors and the werk device, and connected to the circuit through a normally closed first contact of each limit switch, la normally open second contact of the respective limit switches connected in parallel with the normally closed first contact; a pair of operator push buttons, each having a normally open and a normally closed Contact; said first centactor energized through a normally closed contact of one of said push buttons and sustained energized through one of its normally open contacts and a normally closed centact e-f said third contacter; said second contacter energized through the normally closed contacts of the other push button and sustained energized through one of its normally open contacts and a norrnaly closed contact of said third contacter; said third f actor energized and a normally open contact of said rst andV second contactors, and sustained energize-d through the normally open contacts of said push buttons and one of its normally open contacts and a parallel connected normally closed contact of the fourth contacter and a third contact of the first limit switch respectively; and after the third contacter is energized, the first `and' second contactors are de-energized by the opening of said normally closed third contacter contacts in their sustaining circuits; said fourth contacter energized through the non mally open contacts of the push buttons and a normally through the normally open contact or said push buttons Y closed contact of said first and second contactors; and a normally open contact of said third contacter; and said third contacter remains energized through its normally open Contact and the third contact of the first limit switch; and said werk device is energized through said normally open contact of the push buttons, a normally closed contact of said first and second contactors and a normally open contact of said third contacter and said fourth centacter to operate the machine, said second contacts of both limit switches arranged to close and said first contacts of both limit switches arranged to `open and then reclose after which said second contacts reopen in the unsafe portion ef the machines cycle, and after said unsafe portion of the cycle a normally operi fourth contact of the first limit switch and a normally open third contact of the second limit switch are arranged te close to maintain the fourth contacter and the work device energized through said third yand fourth contact and normally open contacts of the fourth contacter to keep the machine operating.

32. A circuit for energizing `a work device te operate a cyclically operating machine as described in claim 3l wherein a normally closed fifth contact of the first limit switch is connected in the energizing circuit ef the fourth contacter and having a normally closed contact of the third contacter connected in parallel therewith, and whereby said fifth contact is arranged to he opened momentarily after said third Contact of the first limit switch opens to insure that said third contacter has become unoperated, and if not, to de-energize the third contacter and the work device to stop the machine.

33, A circuit for energizing a work device te control a cyclically operating machine comprising a first, second, third, and fourth contacter; each contacter having a plurality of normally open and normally closed contacts; a fifth contacter having normally closed contacts; a first and second machine operated limit switch, each limit switch having contacts set to operate at various preselected points in the machines operating cycle; a source of electrical power for energizing the contacter and the work device, `and connected te the circuit through normally closed first contacts of hoth limit switches, each normally closed contact having a normally open contact of its respective limit switch connected in parallel therewith; an operator push button having a normally open and a normally closed contact; said first contacter to be connected to energize through the normally closed contact of the push button; said fifth contacter connected te be energized through the normally closed contact of the push button, a normally open contact of the first contacter and riorinally open contact of the push button; said second contacter energized through a normally open contact of said first contacter and sustained energized through one ef its own normally open contacts and a normally closed contacts of said third contacter; and upon depression of said push button said first contacter is de-energized and said third contacter is energized through the norm-ally open contact of the push button, a normally closed centact of said first and fifth contactors, and a normally open contact of said second contacter, and sustained en- Y ergized through one of its normally open contacts; and after the third contacter is energized, the second contacter is de-energized by the opening of said normally closed third contacter Contact in its sustaining circuit; said fourth contacter isvene'rgized tlirougli'theV normally open contact of the push button, a normally. closed`con tact of the first and second and fifth contactors, and a normally open contact of the third contacter; and said werk device is energized through the normally open centact of said push button, a normally closed contact of said first and second and fifth contactors, and a normallf,l open contact of said third and fourth contactors te oper ate the machine whereby said second contacts of the limit switches are operated` te close and immediately thereafter said first contacts of the limit switches are operated to open and reclose, and said second contacts are operated to reopen to thereby de-energize the circuit and stop the machine should either of the limit switches not be operating properly.

34. A circuit for energizing a work device to control a cyclically operating machine comprising a first, second, third, and fourth contactor; each contactor having 4a plurality of normally open and normally closed contacts; a fifth contactor having normally closed contacts; a rst and second machine operated limit switch, each limit switch having contacts set to operate at various preselected points in the machines operating cycle; a source of electrical power for energizing the contactors and the work device, and connected to the circuit through normally closed first contacts of both limit switches, each normally closed contact having la normally open contact of its respective limit switch connected in parallel therewith; a plurality of operators push buttons, each having a normally open and a normally closed contact; said first contactor connected to be energized through the normally closed contact o' the push buttons; said fifth contactor connected to be energized through the normally closed contact of the push buttons and a plurality of separate circuits, each separate circuit containing one of the normally open push button contacts and at least one normally open contact of said rst contactor and established by normally closed contacts of said first contactor; said second contactor energized through a normally open contact of said first contactor and sustained energized through one of its own normally open contacts and a normally closed contact of said third contactor; and upon depression of said push buttons said first contactor is deenergized and said third contactor is energized through the normally open contact of said push buttons, a norm-ally closed contact of said first and fifth contactors, and a normally open contact of said second contactor, and sustained energized through one of its normally open contacts; and after the third contactor is energized, the second contactor is de-energized by the opening of said normally closed third contactor contact in its sustaining circuit; said fourth contactor is energized through the normally open contact of the push buttons, normally closed contact of the first and second and fth contactors, and a normally open contact of the third contactor; and said work device is energized through the normally open contact of said push buttons, a normally closed Contact of said first and second and fifth contactors, and a normally open contact of said third and fourth contactors to operate the machine whereby said second contacts of the limit switches are operated to close and immediately thereafter said first contacts of the limit switches are operated to open and reclose, and said second contacts are operated to reopen to thereby deenergize the circuit and stop the machine should either of the limit switches not be operating properly.

References Cited by the Examiner UNITED STATES PATENTS 2,250,141 7/41 Thurston 307--113 X 2,676,293 4/54 Mudd 307-113 X 2,944,120 7/60 Ruben 307-113 X LLOYD MCCOLLUM, Primary Examiner. MlLTON O. HIRSHFIELD, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,183,377 May ll, 1965 Frank H. Holland It is hereby certified that error appears in the above numbered patent reqiring correction and that the said Letters Patent should read as eorreotedbelow.

Column Z, line ll, for "colsed" read Closed Column 14, line 35, after "open" insert and normally Column 19, line 8, for "Control" read Contact Signed and sealed this 23rd day of November 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER AIM-,sting Officer Commissioner of Patents

Claims (1)

1. 33. A CIRCUIT FOR ENERGIZING A WORK DEVICE TO CONTROL A CYCLICALLY OPEATING MACHINE COMPRISING A FIRST, SECOND, THRID, AND FOURTH CONTACTOR; EACH CONTACTOR HAVING A PLURALITY OF NORMALLY OPEN AND NORMALLY CLOSED CONTACTS; A FIFTH CONTACTOR HAVING NORMALLY CLOSED CONTACTS; A FIRST AND SECOND MACHINE OPERATED LIMIT SWITCH, EACH LIMIT SWITCH HAVING CONTACTS SET TO OPERATE AT VARIOUS PRESELECTED POINTS IN THE MACHINES OPERATING CYCLE; A SOURCE OF ELECTRICAL POWER FOR ENERGIZING THE CONTACTOR AND THE WORK DEVICE, AND CONNECTED TO THE CIRCUIT THROUGH NORMALLY CLOSED FIRST CONNECTED OF BOTH LIMIT SWITCHES, EACH NORMALLY COLSED CONTACT HAVING A NORMALLY OPEN CONTCT OF ITS RESPECTIVE LIMIT SWITCH CONNECTED IN PARALLEL THEREWITH; AN OPERATOR PUSH BUTTON HAVING A NORMALLY OPEN AND A NORMALLY CLOSED CONTACT; SAID FIRST CONTACTOR TO BE CONNECTED TO ENERGIZE THROUGH THE NORMALLY CLOSED CONTACT OF THE PUSH BUTTON; SAID FIFTY CONTACTOR CONNECTED TO BE ENERGIZED THROUGH THE NORMALLY CLOSED CONTACT OF THE PUSH BUTTON, A NORMALLY OPEN CONTACT OF THE FIRST CONTACTOR AND NORMALLY OPEN CONTACT OF THE PUSH BUTTON; SAID SECOND CONTACTOR ENERGIZED THROUGH A NORMALLY OPEN CONTACT OF SAID FIRST CONTACTOR AND SUSTAINED ENERGIZED THROUGH ONE OF ITS OWN NORMALLY OPEN CONTACTS AND A NORMALLY CLOSED CONTACTS OF SAID THRID CONTACTOR; AND UPON DEPRESSION OF SAID PUSH BUTTON SAID FIRST CONTACTOR IS DE-ENERGIZED AND SAID THIRD CONTACTOR IS ENERGIZED THROUGHT THE NORMALLY OPEN CONTACT OF THE PUSH BUTTON, A NORMALLY CLOSED CONTACT OF SAID FIRST AND FIFTH CONTACTORS, AND A NORMALLY OPEN CONTACT OF SAID SECOND CONTACTOR, AND SUSTAINED ENERGIZED THROUGH ONE OF ITS NORMALLY OPEN CONTACTS; AND AFTER THE THIRD CONTACTOR IS ENERGIZED, THE SECOND CONTACTOR IS DE-ENERGIZED BY THE OPENING OF SAID NORMALLY CLOSED THRID CONTACTOR CONTACT IN ITS SUSTAINING CIRCUIT; SAID FOURTH CONTACTOR IS ENERGIZED THROUGH THE NORMALLY OPEN CONTACT OF THE PUSH BUTTON, A NORMALLY CLOSED CONTACT OF THE FIRST AND SECOND AND FIFTH CONTACTORS, AND A NORMALLY OPEN CONTACT OF THE THRID CONTACTOR; AND SAID WORK DEVICE IS ENERGIZED THROUGH THE NORMALLY OPEN CONTACT OF SAID PUSH BUTTON, A NORMALLY CLOSED CONTACT OF SAID FIRST AND SECOND AND FIFTH CONTACTORS, AND A NORMALLY OPEN CONTACT OF SAID THRID AND FOUTH CONTACTORS TO OPERATE THE MACHINE WHEREBY SAID SECOND CONTACTS OF THE LIMIT SWITCHES ARE OPERATED TO CLOSE AND IMMEDIATELY THEREAFTER SAID FIRST CONTACTS OF THE LIMIT SWITCHES ARE OPERATED TO OPEN AND RECLOSE, AND SAID SECOND CONTACTS ARE OPERATED TO REOPEN TO THEREBY DE-ENERGIZE THE CIRCUIT AND STOP THE MACHINE SHOULD EITHER OF THE LIMIT SWITCHES NOT BE OPERATING PROPERLY.

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