US3011610A - Safety device for power presses - Google Patents

Description

Dec. 5, 1961 A. l. STIEBEL ET AL 3,011,610

SAFETY DEVICE FOR POWER PRESSES Filed Oct. 9, 1959 4 Sheets-Sheet 1 I N V EN TORJ 42/51 Z @vzzn f1 7 4 BY m w yZ/%wr%a2 Dec. 5, 1961 A. 1. STIEBEL ET AL 3,011,610

SAFETY DEVICE FOR POWER PRESSES Filed on. 9, 1959 4 Sheets-Sheet 2 IN V EN TOR-5 F/AZ [Jr/[ea Dec. 5, 1961 A. 1. STIEBEL ETAL 3,

SAFETY DEVICE FOR POWER PRESSES Filed Oct. 9, 1959 4 Sheets-Sheet 3 #7 me. 3 H

Dec. 5, 1961 A. 1. STIEBEL ET AL 3,011,610

SAFETY DEVICE FOR POWER PRESSES Filed Oct. 9. 1959 4 Sheets-Sheet 4 INV EN TOR5 49/51 [Jvzea ATTORNEYS United States Patent O1 3,011,610 SAFETY DEVICE FOR POWER PRESSES Ariel I. Stiehel, Detroit, and Miles G. Rigby, Birmingham, Mich, assignors to Rockwell-Standard Corporation, Coraopolis, Pa., a corporation of Pennsylvania Filed Oct. 9, 1959, Ser. No. 845,524 3 Claims. (Cl. 192-131) This invention relates to improvements in automatic safety devices for power machines and is more particularly concerned with electrically operated safety devices for operator-actuated power presses.

This application is a continuation-in-part of the copending application Serial No. 757,581 filed August 27, 1958.

In the power machine art, and more particularly with relation to punch and forming presses, it is customary to provide a cross-head or other work forming element reciprocating with respect to -a bed plate and having power machinery for effecting such reciprocation, so as to produce punching and forming operations in the machine. As usually constructed, the machine has a vertical reciprocating cross-head actuated by a crank shaft or other similar device on which there is mounted a large and heavy fly wheel, the fly wheel being in turn actuated by an electric motor or other power source. Such machines are constructed so as to include a clutch mechanism between the fly wheel and the crank shaft driven by the fly wheel so that during such intervals when the clutch mechanism is disengaged and the machine is not operating, the motor or other power source which supplies the motivating force is permitted to build up the speed of the fly wheel. When the operator desires to cause the cross-head and the tools that it carries to descend upon the bed plate in cooperating relation with the forming dies of the bed plate, he actuates a control which is usually in the form of a treadle positioned near the base of the press so that it can be operated by the operators foot leaving the operators hands free to hold or manipulate materials in and out of the power press. Actuation of the treadle engages the clutch and the stored energy of the fly wheel causes the crank shaft to turn and the cross-head to go through a working stroke.

This foot treadle control has been the cause of end less and serious accidents because the operators, after some period of work at the machine, tend to become careless and permit their fingers or hands to move into the path of actuation of the die forming element of the machine. A particular practice of some operators is to ride the treadle and attempt to time the insertion and removal of materials in and out of the machine in accordance with the cyclic speed of the machine, or attempt to manipulate parts into and out of the machine after it has started to move. As a result of these unsafe practices, serious injury has been experienced in many instances with respect to the arms and hands of the operators.

In the past, it has been proposed, in an effort to achieve safer working conditions, to provide hand controls which must be actuated by both hands of the operator andv held actuated in order to cause the machine to move. Such controls, while contributing to the safety of the operator, cause serious loss in production since the operator must operate the machine with his hands in addition to transferring materials in and out of the machine.

Other safety expedience presently on the market are inherently disadvantageous in that the machine may be run by the operator without utilizing the protective mechanisms provided. Thus, the safety factor involved in employing such devices depends entirely upon the will of the operator in deciding whether or not he will make use of the device provided for his safety.

3,9?!1 ,iilll Patented Dec. 5, 1961 An example of these prior devices is disclosed in the United States Letters Patent to Possons No. 1,417,346 dated May 23, 1922 wherein it is proposed that a safety pull-out guard device comprising a pair of cuffs to be worn by the operator and having cable connections between the cuffs and the movable forming element of the press be employed to forceably withdraw the operators hands from a dangerous position adjacent to or over the work area during the actuating period and work forming cycle of the machine. This device and a great majority of similar expedients present the inherent disadvantage in that the press may be run by the operator without utilizing the protective mechanism provided for his safety.

Accordingly, it is the primary object of the present invention to provide an improved form of the ?ossons safety device for use in power operated machines having a movable work forming element controlled by a treadleactuated clutch mechanism wherein a clutch controlling treadle is ren ered inoperative to actuate the clutch mechanism whenever the safety guard pull-away cable connections are not secured to the cuffs retained about the operators wrists Thus, where the operator has omitted to attach the pull-away cables to his safety wrist cuffs through inadvertence or for other purposes, the clutch-controlling treadle is rendered inoperative to effectuate movement of the work forming element and the machine, therefore, cannot be operated by actuation of the clutch controlling treadle.

In accordance with the present invention this is accomplished by providing electrical switches in an electrical control circuit for the power operated machine which are actuated by attaching the safety cables to cufis worn about the wrists of an operator. Actuation of the electrical switches energizes the control circuit which, in turn, functions to energize an electromagnetic coupling device operably coupling the control treadle to the clutch mechanism so that depression of the control treadle actuates the clutch mechanism to transmit power from a supply source to the work forming element to move the latter through its cycle of operation.

The safety cables when attached to the wrist cuffs are secured thereto in such a manner as to prevent the removal of the cuffs by the operator, and function to pull the operators hands away from the work area during a selected cycle of the operation. Consequently, to move away from the machine or to remove the wrist cuffs, the operator must first detach the safety cables to thereby render the machine inoperative by actuation of the operating foot treadle.

With the foregoing purposes and considerations in mind, therefore, it is a further major object of this invention to provide for a novel safety device for operatively disconnecting a control treadle of a power operated machine so as to render the treadle inoperative to set the work forming element of the machine in motion.

A further object of the present invention is to provide in a power operated machine equipped with a foot treadle actuated clutch, a novel safety device which includes the safety device according to our co-pending application Serial No. 757,581 and functions to operatively connect the foot treadle to the clutch whenever the safety device of said co-pending application is properly afiixed to the body of the operator.

It is a further object of this invention to provide in a power operated machine equipped with a foot treadle adapted to be actuated by an operator for controlling the operation of the machine, a novel electromagnetic coupling device which is operative when energized to permit operation of the machine with the treadle and which is energizable by an electrical control circuit when the safety 3 device in accordance with our said co-pending application is mounted to respond to the movement of the work forming element of the machine and attached to a selected part of the operators body.

A further object of the present invention resides in the provision of the electromagnetic coupling device of the preceding object wherein a novel guide screw construction assures self alignment between the core and the armature of the coupling by allowing limited side or lateral movement of the armature relative to the core and, at the same time, prevents the coupling from turning.

A further object of the present invention is to provide in a power driven machine having a work holding bed, a

work forming element movable into and out of working relation with the bed, a power source for driving the work forming element, a clutch mechanism operably connecting the power source to the Work forming element and a manually operated clutch operator for selectively actuating the clutch mechanism to control the movement of the work forming element by operatively engaging and disengaging the clutch mechanism, a novel safety device having safety cable connections adapted to be detachably latched to wrist cuffs retained about the Wrists of an operator and responsive to the movement of the work forming element for forceably withdrawing the hands of .the operator to a place of safety during the work forming stroke of the work forming element, an electromagnetic coupling device operable when energized to cou ple the clutch operator tothe clutch mechanism, and a special electrical control circuit for de-energizing the coupling device whenever the safety cable connections are unlatched from the wrist cuffs.

Further objects of the invention will presently appear as the description proceeds in connection with the appended claims and the annexed drawings wherein:

FIGURE 1 is an elevational View Of a power press provided with a safety device for operating an electromagnetic coupling according to one embodiment of the present invention;

FIGURE 2 is an enlarged front elevation partly in cross section of the electromagnetic coupling of FIG- URE-l;

FIGURE 3 is an enlarged side elevation partly in cross section taken substantially along line 3-3of FIGURE 2;

FIGURE 4 is a cross section showing the support for the magnetic coupling of FIGURE 1 and taken substantially along the line 44 of FIGURE 2;

FIGURE 5 is a cross section of the magnetic coupling taken substantially along'line 5-5 of FIGURE 2;

FIGURE 6 is a schematic wiring diagram of the electrical control circuit for the embodiment illustrated in FIGURE 1;

FIGURE 7 is a perspective view of the safety cable hook assembly attached to a cuff fastened about the wrist of the operator; and

FIGURE 8 is an elevation of the safety hook connection of FIGURE 7 having the side wall of the hook housing removed.

Although the construction embodying the principles of the present invention is shown and described in its application to a power press, the present invention further contemplates the utilization of the novel safety device hereinafter described generally for operator actuated power machines where there is a danger of injury occurring to the operator by coming in contact with the moving parts of the machine. For example, the present invention may be applied with respect to facilitating the safe operation of dye presses, stamping machines, and is particularly adapted wherein work pieces are moved by the operator into and out of the machine which has movable parts to perform some operation on the piece.

Thus, with reference now to the drawings and more particularly to FIGURE 1, wherein the construction emat 20 is illustrated to comprise a suitable cast base 22 upon which is mounted by bolts 23 a cast frame 24 for supporting the working parts of the press. Afiixed to the lower portion of the frame '24 by any suitable means is a conventional bed plate 26 towhich a stationary lower die 28 is removably secured for receiving a work piece (not shown). A cross head 30 provided with an upper die 32 is mounted for vertical reciprocal movement in alignment with the lower die 28 and bed plate 26 and is connected by a suitably journalled crank shaft 34 through a conventional clutch 36 such asa standard pressure-plate type to a flywheel 38. The flywheel 38 is mounted for rotation on the frame 24 and is drivingly connected by a belt 40 to a pulley (not shown) arTixed on an output shaft (not shown) of an electric motor 42 or other suitable prime mover.

In order to enable the operator to selectively actuate the clutch 36 to reciprocate cross head 36 so that the dies 28 and 32 engage and form the work piece positioned on the lower die 28, an operating foot treadle 58 is provided having one end pivotally secured to the lower portion of the base 22 as by pin 52. The treadle St) is biased to an upper disengaging position by a coil spring 54 which is secured at its upper end to the base 22 by a machine screw 56 and which is provided with a hook end 58 extending through ring 59 secured to the treadle 56 intermediate the ends thereof. Between the pivoted end at 52 and the spring connection at 59, an upstanding rod 6% is pivotally connected at one end to the foot tree le 5% so that it is movable with the treadle 50 as the treadle is depressed by the operator against the bias of the spring 54.

Referring now to FIGURES 1-5, the upper end of the rod 60 terminates in a threaded section which is threadedly received in a turnbuckle 62 (FIGURES 2 and 3). The opposite end of turnbuckle 62 threadedly receives, a short screw rod 64 which slidably extends through a guide bushing 66 and threadedly engages the cross piece of a soft iron horseshoe core768 of an electromagnetic coupling 79 which will hereinafter be described in detail.

T he guide bushing is provided with an externally threaded section 72 which is threadedly received through a centrally located aperture formed in the laterally extending ear 74 of a U-shaped bracket 76. The guide bushing 66 extends beyond the car 74 and is secured in place by tightening and lock nuts 78 and 80. This U-shaped bracket 76 supports the magnetic coupling 70 and is affixed to the frame 24 by bolts 82 which extend through the cross piece 84 of the bracket.

In accordance with the present invention, the magnetic coupling 70 functions to operatively disconnect the foot treadle 50 from the clutch 36 to thereby prevent operation of the cross head 30 by actuation of the foot treadle 59 as will become apparent. The core 68 of magnetic coupling 7tlis a conventional horseshoe type core having parallel upstanding legs 86 and 88 which are joined together by an integral cross piece 96. The cross piece 90 is formed with a centrally located internally threaded through bore which receives the threaded end section of rod 64 so that the cross piece 90 is supported on an annular shoulder 92 formed by rod 64. To establish a magnetic flux in the core 68, conventional coils 9 4 and 96 of a suitable number of turns respectively are wound around each core leg 86 and 88. The rectangular barshaped armature 98 of coupling 70 which is attracted by the core 68 when the coils 94 and 96 are energized, is formed with a centrally located internally threaded through bore which threadedly receives the reduced diameter end threaded section of a rod 100. This armature 98 spans the legs 86 and 88 of the core 68, and has the same width and spanned length as core 68 so that, in assembled relationship, the vertical faces of the armature are in the same mutually perpendicular vertical planes passing through the vertical surfaces of the core 68.

' In order to facilitate alignment of armature 98 with the core 60, the upper lateral car 102 of U-shaped bracket 76 overlying the armature 98 is formed with two opposed centrally located slots 104 and 106 as best illustrated in FIGURE 4. Two elongated guide screws 108 and 110 respectively freely extend downwardly through slots 164 and 186 and through enlarged bores 112 and 114 provided in the armature 98 and threadedly engage in internally threaded bores extending inwardly from the exposed planar end faces of the core legs 86 and 88. The through bores 112 and 114 provided in the armature 93 respectively with slots 104 and 196 and the slots 104 and 106 and bores 112 and 114 are of larger diameter than the screws 108 and 119 to provide for a free and relatively loose guiding fit therewith. As a resu'lt of this novel coupling guide screw construction, selfalignment of the coupling 70 is assured by limited side or lateral movement of the armature 98 relative to the core 68 and, at the same time, the coupling is prevented from turning.

The rod 169 is aligned with and slidably extends through an upper guide bushing 116 formed with a threaded section 118 which is threadedly received through a centrally located aperture formed in the upper lateral ear 192 of bracket 76 and extends beyond the top thereof to receive tightening and lock nuts 120 and 122 respectively. The guide bushing 116 is in axial alignment with guide bushing 66 and both guide bushings 66 and 116 provide a loose sleeve bearing fit for rods 64 and 100 respectively to maintain the armature 98 in substantial linear alignment with the core 68.

With continued reference to FIGURES 1-5, the linkage connecting the rod 100 to the cross head clutch 36 comprises a cylindrical adaptor 124 threadedly afiixed to the upper end of screw rod 100 and formed with a yoked end 126. The lower end of a link 128 is positioned between the legs of the adaptor yoked end 126 and is pivoted on a pin 129 carried by the yoked end 126.

The upper end of link 128 is pivotally mounted about an axis formed by bolt 130 of a bolt and nut assembly 132 carried by the yoked end 134 of a force multiplying lever 136. The force multiplying lever 136 is centrally fulcrummed about a machine screw 138 which is threadedly secured to the cast frame 24. The opposite righthand end of lever 136 as viewed from FIGURE 1 is suitably afiixed to the lower end of an upstanding rod 140 which has its upper end pivotally secured to the outer end of a horizontally extending clutch disc shifting rod 142 which functions to actuate the clutch 36 between engaged and disengaged positions.

By this construction, it will be appreciated that depression of the foot treadle 50 by the operator'shifts rod 60 downwardly. When the coils 94 and 96 of magnetic coupling 70 are energized, the armature 98 is attracted to the core 68 so that when the core 63 is shifted downwardly with rod 60 the armature is also shifted with it. This motion shifts link 128 to rotate the force multiplying lever 136 about its pivotal axis 138 from the dotted line position indicated at 144 (FIGURE 2) to the solid line position shown in FIGURES l3. This movement shifts rod 149 upwardly to move the clutch disc selector rod 142 so that the discs (not shown) of clutch 36 move into engaging position whereby the flywheel 38 is operatively coupled to cross head 30 through shaft 34.

The shift rod 142 may be spring suspended by means not shown so as to be biased to a clutch releasing position.

In order to electrically control the operation of the magnetic coupling 79, an electric control circuit 150 is provided as shown in FIGURE 6 and comprises a transformer 152 having a primary winding 154 connected directly to a source of alternating current voltage and a secondary winding 156 connected to taps 158 and 160. The transformer 152 functions to reduce the line voltage generally 117 volts) to an acceptable control circuit voltage (generally 6 volts) and also thereby eliminates the potential hazard of electrical shock to the operator of press 20 as will become aparent. The secondary winding 156 is connected to an electrical circuit which includes a relay 162 having a solenoid coil 164 connected across the secondary winding terminals 158 and by conductor 166 and conductor 168.

With continued reference to FIGURE 6, the relay 162 is provided with an armature 170 which is adapted to move a pair of mechanically interlocked switch blades 172 and 174. When the relay 162 is deenergized, the switch blade 174 is biased (by means not shown) to engage a stationary switch contact 176 and the switch blade 172 is biased (by means not shown) to be out of engagement with an associated stationary contact 178. When relay 162 is energized the switch blade 172 moves into engagement with its associated contact 178 and the switch blade 174 is disengaged from its associated contact 176. When switch blade 172 engages switch contact 178, an energizing circuit is serially completed through switch blade 172 and contact 178 to the primary winding 18% of a stepdown transformer 182 which is connected across a source of alternating current voltage, not shown.

With reference now to FIGURES 2, 3 and 6, the fixed terminals of the secondary winding 184 of the stepdown transformer '182 are connected by'conductors 186 and 188 respectively to terminals 190 and 192 mounted in a terminal plate 194 which is fixedly secured to the U- shaped bracket '76 as by screws 196 (FIGS. 2 and 3). The terminals 190 and 192 are suitably electrically insulated from the terminal plate 194 and are each respectively connected to one end of magnetic coupling coils 94 and 96 by conductors 197 and 198. The other ends of the coils 94 and 96 are connected together to establish a circuit that may be traced from the secondary 184, through the conductor 186 to terminal 191?, through conductor 197, through coil 94, through coil 96, through conductor 198 to terminal 192, and through conductor 188 to the secondary 184.

With continued reference to FIGURE 6 a resistance 199 of suitable capacity is interposed in conductor 166 in series circuit relationship with the solenoid coil 164. Switch blade 174 and stationary contact 176 are connected in parallel to the resistance 199 by means of conductors 288 and 291 which respectively connect switch blade 174 and contact 176 to conductor 166. Thus, when the relay 162 is deenergized and switch blade 174 moves into engagement with contact 176, the parallel circuit established through conductor 208, switch blade 174, contact 176 and conductor 28 1 functions to bypass the current flowing to energize the relay 162 around the resistance 199.

The capacity of resistance 199 is such to reduce the magnitude of current in control circuit 150 to a minimum value for retaining solenoid 164 with its armature 170 in energized position as long as continuity is maintained in the energizing circuit. Thus, the resistor 199 with the parallel switch 174 functions to prevent excessive heating and potential burn-out of the coil 164 whenever a power failure or break in the transformer second ary occurs since the circuit is shunted through the resistor 199 whenever the solenoid coil 164 is energized.

Since the capacity of resistor 199 is such to reduce the value of the current in the control circuit to a minimum holding current for retaining the armature 170 in energized position, it will be appreciated that any interruption in the control circuit 151 results in an immediate and positive action to deenergize the solenoid relay thereby interrupting current flowing through primary winding which serves to energize the magnetic coupling 71 and thereby renders the press inoperative. Thus, whenever the control circuit 158 is interrupted by the selected operation or by a power failure, the armature 170 is moved to its deenergized position immediately upon the '3 initial drop in current to disengage switch blade 172 from its associated contact 178 so as to deenergize the secondary load circuit of transformer 182.

Energization of relay 162 is controlled by a pair of microswitches 204 and 266 which are interposed and connected in series in conductor 168 between the transformer secondary terminal 158 and one end of the solenoid' coil 164. These microswitches 284 and 286215 shown in 'FTGURE 8 are identical to the spring-loaded pin actuated microswitch structure disclosed in our copending application S.N. 757,581.

By this circuitry it will be apparent that if either of the switches 204 or 206 are open, no current will flow through the solenoid coil 164. Thus, the stepdown transformer 182 and consequently the coils 94 and 96 of magnetic coupling 70 remain deenergized to render 'the foot treadle t} inoperative to engage the clutch 36 for operating the cross head 30 of punchpress 29.

In accordance with the present invention, the microswitches 204 and 206 are actuatable by a safety device generally indicated at 208, which functions to forceably withdraw the operators hands from a dangerous area adjacent to and over the work area and from around the die 28 and bed plate 26. This safety device 208 is identical to the structure shown and disclosed in our said copending application Serial No. 757,581 the disclosure of 'Which is hereby adopted and incorporated herein by referencet Safety device 268 according to the principles of said copending application comprises an upright standard 210 fixedly secured to the floor at a convenient space distance apart from the punch press 29 and to the left thereof as shown in FIGURE 1. With continued reference to FIGURE 1, standard 210 terminates in a sleeve 212 which supportingly receives one end of a horizontally extending cross rail 214. The cross rail 214 is fixedly secured in sleeve 212 as by set screws 216 and is supported at the other end thereof in a recessed adaptor 218 affixed to the cast frame 24. A rocker arm 220 rotatable about a fixed pivot 222 on cross rail 214 intermediate the ends thereof is provided with an integral gear segmentv224 which meshes with rack teeth 226- formed at the upper end of a connecting rod 228. The connecting rod 228 is rigidly secured at its lower end to the cross head 30 as by machine screws 238 for reciprocal movement therewith.

Afiixed to rocker arm 22% is a flexible cable 232 which passes over a sheave 234 rotatably mounted about a pin 236 rigidly supported by the standard 210'. Cable232 extends down through a tubular guide 238 secured to the standard 210 and branches into two separate flexible cables 249 and 242 below the tubular guide 238. Each of the branch cables 249 and 242 is pivotally connected at 245 to a safety hook assembly 244 as shown in FIGS. 7 and 8. These safety hook assemblies 244 are of identical structure as the structure shown in our said copending application Serial No. 757,581 and house micro switches 294 and 206 schematically shown in FIGURE 6. With continued reference to FIGURE 8, each of the micro switches 284 and 286 are actuatable to closed po sition by a flexible spring arm 246 which extends across the gap of the hook 248 and-is fixedly secured at one end to a casing 250 mounting the micro switch.

Referring now to FIGURES 1, 7 and 8, safety hook 248 is adapted to be removably attached to rigid ring staples 252' of wrist cuffs 254 which are retained about the Wrists of the operator. These wrist cuffs 254 are of identical structure. as that shown and disclosed in our said copending application Serial No. 757,581 so that they are not removable when the safety hooks 248 are hooked into the staples 252 thereon.

In assembled relation on the operators wrist, as dis- .closed in said copending application, the wrist cuff 254 ,is arcuately wrapped around the wrist so as to overlap .the end to which the staple 252 is afiixed; The staple 252 extends through a selected elongated slot 256 formed in the cuff 254 and the free, overlapping end of the cuff 254 is secured to an intermediate portion of the cuff by means of a buckle (not shown).

In order to actuate the micro switches 204 and 206 to closed position and thereby energize the control circuit to facilitate energization of the magnetic coupling '70, the safety hooks 248 of each hook assembly 244 are detachably latched on to their respective wrist cuif staples 252. In latching the hook 248 onto staple 252, the staple 2 52, as disclosed in said copending application, inwardly deflects the micro switch actuating flexible arm 246 and a shorter safety latching arm 258 extending across the gap of hook 248 and affixed at one end to case 258 adjacent and below arm 246. The staple 252 passes around the free end of the shorter lower arm 258 and thus permits this arm to deflect back to its original position closing the gap of hook 248 thereby lockingly latching the staple 252 to the hook 248. The upper switch actuating arm 246 is deflected by staple 252 from its undeflected position to a dotted-line position indicated at B, FIGURE 8, where it is held by staple 252 and depresses the'pin of micro switch 294 or 286 to actuate the switch to a circuit closing position.

In accordance with said copending application, by attaching'the safety hooks 248 to the wrist cuffs staples 252, the operator is unable to unwrap and remove the wrist cuffs 254 without first detaching the safety hooks. By this structure, it will be appreciated that the micro switches are actuated to a circuit energizing position only when the safety hooks 248 are removably latched to their respective staples 252 and are actuated to a circuit de-energizing position when the hooks 248are unlatched from the staples 252.

In operation, the operator standing between the standard 210 and the punch press 20 as viewed from FIGURE 1, is first required to affix the wrist cuffs 254 to his wrists and to latch the safety hook assemblies 244 to the wrist cuff staples 252. This actuates micro switches 204 and 206 to a circuit closed position and completes the control circuit 150 to energize the relay solenoid coil 164 through a circuit that may be traced from the transformer secondary winding 156, through the closed micro switches 204 and 206 and conductor 168, through solenoid coil 164, through conductor 166, through conductor 201, and contact 176, through switch blade 174, through conductor 200 and back to secondary 156. Energization of the solenoid coil 164 operates to move switch blade 174 out of engagement with contact 176 so as to shunt a relay holding current through resistance 199 as hereinbefore described.

Energization of solenoid coil 164 also moves switch blade 172 into engagement with contact 178 to energize the primary winding 180 of step down transformer 182. This causes energization of the secondary Winding 184 of transformer 182 to energize the magnetic coupling coils 94 and 96.

V The energization of coils 94 and 96 attract the armature 98 of magnetic coupling 70 to the core 68. Rigid engagement of the armature 98 with the core 68 establishes a connecting linkage between the foot treadle' 50 and the clutch 36, so as to facilitate operation of the latter by selective depression of the treadle 50 as hereinbefore described. The actuation of the clutch '36 couples flywheel 38 to cross head 30 to transmit power from the motor 42 to reciprocate the cross head 30.

As the cross head 30 descends, the connecting rod 228 is shifted downwardly to rotate the rocking arm 220 about its pivotal axis 222. This motion draws safety cable 232 upwardly through the tubular guide 238 so as to shorten the effective length of cable 232 and its branch cables 240 and 242.

Since branch cables 240 and 242 are aflixed to the safety hook assemblies 244, the movement of the cables 240 and 242 functions to force-ably withdraw the operators hands from a dangerous position.

On the upward stroke of the cross head 30, the connecting rod 228 rotates the rocking arm in a counterclockwise direction as viewed from FIGURE 1 to slacken and provide for a greater effective length of cables 240 and 242. Sufiicient slack is provided to allow free movement of the operators hands for the removal and insertion of work pieces in the punch press.

If for any reason the operator desires to leave the area adjacent the punch press 20, he must initially unlatch the safety hooks 248 from the wrist cuffs 254. This serves to open the micro switches 204 and 206 to de-energize the control circuit 150 and thereby de-energize the magnetic coupling energizing coils 94 and 96 so as to render the punch press inoperable by actuation of the foot pedal 50. Similarly, when the operator omits to attach the safety hooks 248 to the cuffs 254, it will be appreciated from the foregoing that the press cannot be rendered operable by actuation of the foot pedal 50 and consequently requiring the operator to attach the safety device 208 to his body before he can set the press in operation.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. In a power driven machine having a frame, a work holding bed mounted on said frame, a work forming element movable into and out of working relation with said bed, power means for driving said work forming element, means operably connecting said power means with said work forming element including a clutch mechanism, and a manually operated clutch operator for selectively actuating said clutch to control the movement of said work forming element by operatively connecting and disconnecting said power means and said work forming element; the improvement of: a safety device responsive to the movement of said work forming element for forceably withdrawing the hands of an operator to a place of safety during movement of said work forming element in a predetermined direction and including motion transmitting means movable in response to the movement of said work forming element, a pair of wrist cufis adapted to be removably fastened about the wrists of the operator, hook means adapted to be detachably latched to said cuifs for detachably securing said motion transmitting means thereto, means for preventing said cuffs from being unwrapped when said motion transmitting means is secured to said cuffs by said hook means, an electromagnetic coupling operable to connect and disconnect said clutch and said clutch operator, and means for energizing and deenergizing said coupling to respectively establish and disestablish operative connection of said clutch operator with said clutch comprising electrical circuit means including at least one circuit energizing electrical switch actuatable to circuit energizing position by latching said hook means to said cuffs.

2. In a safety device for use in a power-driven machine having a power supply source, a work forming element movable by power delivered from said power source, a clutch mechanism operably connecting said work forming element to said power source and a manually operated clutch operator for controlling the actuation of said clutch mechanism, comprising a pair of cuifs adapted to be retained about the wrists of an operator, flexible connection means detachably latched to said cuffs and responsive to movement of said work forming element for withdrawing the hands of the operator to a place of safety, an electromagnetic coupling device operable when energized to couple said clutch operator to said clutch mechanism, and means for deenergizing said coupling device whenever said fiexible connection means are unlatched from said wrist cuffs to thereby operably disconnect said clutch operator from said clutch mechanism.

3. In a safety device for use in a power-driven machine having a power supply source, a work forming element movable by power delivered from said power source, a clutch mechanism operably connecting said work forming element to said power source and a manually operated clutch operator for controlling the actuation of said clutch mechanism, comprising a pair of cuffs adapted to be retained about the wrists of an operator, flexible cable connection means detachably latched to said cuffs and responsive to movement of said work forming element for withdrawing the hands of the operator to a place of safety, an electromagnetic coupling device operable when energized to couple said clutch operator to said clutch mechanism, electrical circuit means for energizing said electromagnetic coupling device, at least one circuit energizing switch in said circuit means, and means for opening and closing said switch by respectively unlatching and latching said cable connection means to said wrist cuffs.

References (Jited in the file of this patent UNITED STATES PATENTS 786,473 Wenigmann Apr. 4, 1905 2,013,441 Gofi et al Sept. 3, 1935 2,199,501 MacBlane May 7, 1940 2,830,686 Blume et al Apr. 15, 1958 FOREIGN PATENTS 652,103 Germany Oct. 25, 1937

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