US2877814A - Power operated screw driver - Google Patents

Description

M h 17, 1 c. o. MERCHANT EIAL 2,877,814

POWER OPERATED SCREW DRIVER Filed July 18, 1957 2 Sheets-Sheet 1 INVENTCR CHESTER O. MERCHANT ALLEN R. DAVIDSON March 1 1959 c. o. MERCHANT ETAL 2,877,814

POWER OPERATED SCREW DRIVER 2 Sheets-Sheet 2 Filed July 18, 1957 INVENTOR.

CHESTER O. MERCHANT B xyl. LEN R. mwaosou FIG-5 United States Patent POWER OPERATED SCREW DRIVER Chester 0. Merchant, Harborcreek Township, Erie County, and Allen R. Davidson, Erie, Pa., assignors to Swanson-Erie Corporation, Erie, Pa., a corporation of Pennsylvania Application July 18, 1957, Serial No. 672,788

6 Claims. (Cl. 144-32) This invention relates to power tools and, morepartieularly, to a tool for setting screws and nuts.

Various devices have been provided by way of power operated means for screw drivers and wrenches wherein friction clutches would provide a slippage between the driving element and the tool when a predetermined torque had been exerted on the screw or nut. Devices which used friction clutches relied upon slippage at the point where the torque reached its predetermined amount and would allow the driving mechanism to keep on spinning after the nut was tightened. Where a time delay was put in the driving mechanism as has been done in previous devices, a heating of the machine would result. Therefore, a change in the torque exerted by the tool at the time 'when the tool was cold to the time at which the tool became heated would result.

The present invention utilizes a clutch which will be released by an electrical impulse from a circuit which acts rapidly so that the tool will actually be released during the time it is driven as little as one quarter of a turn after the predetermined torque has been reached.

It is, accordingly, an object of this invention to provide a machine for tightening screws, nuts, and the like which is simple in construction, economical to manufacture, and simple and efficient in operation.

Another object of the invention is to provide a power driven screw driver wherein the moment of inertia of rotation of the driven member is very low.

Another object of the invention is to provide a power driven screw driver or nut tightening device in combination with an improved circuit for releasing the torque exerted on the tool of the device in a very short period of time after the device has tightened the nut to a predetermined torque.

Still another object of this invention is to provide a power operated tool wherein the power to the tool is cut off when a predetermined torque has been reached.

With the above and other objects in view, the present invention consists of the combination and arrangement of parts hereinafter more fully described, illustrated in the accompanying drawings and more particularly pointed out in the appended claims, it being understood that changes may be made in the form, size, proportions, and minor details of construction without departing from the spirit or sacrificing any of the advantages of the invention.

In the drawings:

Fig. 1 is a longitudinal cross sectional view of a power operated tool according to the invention;

Fig. 2 is a schematic diagram of an electronic circuit for operating the tool shown in Fig. 1; and

Fig. 3 is a schematic diagram of the controls of the machine.

Now with more specific reference to the drawings, a power operated machine for rotating a tool such as a screw driverblade 11 is disclosed. The machine has a frame which may be supported on a base 12. The

base 12 supports an electric motor 13 which is attached and fixed to the base 12 by means of a bracket 14 which is attached to a mounting member 15 on the top of the motor 13. A mounting member 16 on the bottom of the motor 13 is attached to the lower leg of the bracket 14.

A motor shaft 50 is attached to a shaft segment 53 by means of a friction clutch. A shaft 51 is hollow and keyed to rotate with the motor shaft 50 at 52. A stud 54 is threadably attached to the segment 53 and its headed end extends up into the hollow of the shaft 51. The stud 54 has a head 60 and a washer 61 supported thereon abutting the head 60. The lower end of the hollow in the shaft 51 terminates in inwardly directed shoulders 62. A helical compression spring 55 is disposed on the stud 54. The spring 55 rests at its lower end on the shoulders 62 and at its upper end against the Washer 61. A fibre washer 56 is supported between the adjacent ends of the hollow shaft 51 and the segment 53. Therefore, the compression spring 55 urges the shaft segment 53 toward the hollow shaft 51 and the force exerted on the fibre washer 56 is determined by the adjustment of the stud 54. That is, by tightening the stud 54, the torque which can be transmitted through the fibre washer 56 from the motor M or 13 to the shaft segment 53 can be increased.

A blade bracket 30 comprises a tool supporting means which is slidable vertically on a guide 32. The guide 32 is attached to a bracket 33. A stud 36 threadably engages the bracket 33 and is locked thereto by a nut 37 which constitutes an adjustable mechanical limit stop for limiting the downward travel of the bracket 30 and the parts attached thereto. A headed stud 37a is attached to the lower surface of the bracket 30 to engage a stud 35, should the downward movement not be stopped by a limit switch 26. A stud 36 threadably engages the guide 32 at the stud 35. An upper end 38 of the guide 32 is disposed in a bore in a bracket 39. The brackets 33 and 39 are fixed to the frame 10. The bracket 30 has a bore 31 which slidably receives the guide 32.

The bracket 30 has a flange 24 integral therewith and the flange 24 is threadably attached to a piston rod 22 at 23. A lock nut 25 prevents the piston rod 22 from loosening from the flange 24. A cylinder 17 is attached and fixed to the frame 10 by brackets 18 and 19 at 20 and 21, respectively. The cylinder 17 has a double acting piston therein which moves the bracket 30 up wardly and downwardly. The limit switches 26 and 27 are fixed to the frame 10 at fixed positions as shown and the flange 24 moves up and down therebetween. An adjusting screw 46 is threadably attached to the flange 24 at 41 as shown. When the bracket 30 is in the upper position shown, the screw 40 engages an actuating member 28 of the limit switch 27. .When the bracket 30 is in its lower position, the screw 40 engages an actuating member 29 of the limit switch 26. The cylinder 17 is supplied air through a filter and a pipe 161.

The screw driver blade 11 is rotatably supported on the bracket 30 by means of an anti-friction hearing 44 which is held in a counterbore 45 by a washer 46 which is attached to the bracket Why a screw 47. A quill 43 is threadably attached to the screw driver blade 11 and has a flat surface 58 which slidably engages a comple mentary surface on the shaft segment 53. A tube 59 is disposed around the ends of the shaft 53 and the quill 43 to hold their relatively sliding surfaces against-separation. As the bracket 30 is moved up and-down by the cylinder 17, the complementary surfaces of the quill 43 and the shaft segment 53 slide relative to each-other and. are constrained to rotate togetherhy their com 'M when it is running free.

3 plementary surfaces engaging at. 58. A splined joint could be substituted for the complementary surfaces 58.

The electronic circuit for operating the machine is shown in Fig. 2. The motor M shown as 13 in Fig. 1 is connected to a variable contact 63 on an auto transformer T4 which is in turn connected across lines A and B. A terminal 4 of the motor M is connected through a .primary winding 90 of a transformer T2. Resistors 91 and 92 are connected in parallel with the winding 90. The resistors 91 and 92 may each be of the value of one ohm ten watt resistors in a typical example. A secondary 72 of the transformer T2 is connected in parallel with a resistor R1 and a condenser C1 which may be of the value of fifteen ohms, ten watts and twenty microfarads, one hundred fifty volts, respectively. A resistor R4 will have a value of five hundred thousand ohms and be connected in series with a control grid 75 of a tube 76. A wire 71 is connected to one terminal of the secondary 72 of the transformer T2 and will be connected to a variable resistor terminal 70 of a potentiometer 69 which will have a value of twenty-five thousand ohms, preferably. A voltage regulator tube 68 is connected in parallel with the potentiometer 69 between a wire 66 and a terminal 81. The potentiometer 69 will be used for presetting the torque at which the screw driver will be released.

A primary winding 65 of a. transformer T1 is connected across lines A and B and the secondary terminals 79 and 81 are connected to a terminal 94 of a relay L1 and to a cathode 89 of the tube 76, respectively. A terminal 95 of the relay L1 is connected to an anode 78 of the tube 76. The cathode 80 is heated by a heater powered by a secondary winding 97 of the transformer T1.

A network made up of a potentiometer 69, condensers C4 and C5, and resistors 83 and 88 is connected as shown. The potentiometer 69 preferably has a value of twentyfive ohms, condensers C4 and C5 preferably have values of forty and sixty microfarads, respectively, each at three hundred fifty watts, and resistors 83 and 88 preferably have values of sixty-eight ohms, ten watts, and six thousand five hundred ohms, ten watts, respectively.

The relay L1 has a contact 99 which closes when the relay L1 is excited. A transformer T3 has its primary connected across the lines A and B and its secondary 102 connected between an air valve solenoid U and an air valve solenoid D at 100. The solenoids U and D are solenoids for supplying air to the pistons of the cylinder 17.

Since the torque exerted by the motor M is proportional to its armature current and the armature current determines the current which flows through the primary winding 90 of the transformer T2 from the line A to the line B and since this current on the primary winding 90 is reflected on the secondary 72, the current changes the grid bias on the control grid 75 of the tube 76. The torque and, therefore, the armature current, increases as a screw is tightened andv it will increase the current passing through the tube 76 to cause the relay L1 to close when the torque and, therefore, the motor current, has reached a predetermined value, thereby connecting power from the secondary 102 through the contact 99 and through the solenoid U to move the piston up, thereby raising the bracket 30.

When the machine is to be used, the operator will connect the lines A and B to a source of alternating current electrical power, preferably one hundred ten volts. He will then adjust the contact 63 on the transformer T4 until the current through the motor M is reduced to a minimum value for satisfactory operation of the motor If the motor used were connected directly across the lines A and B, there would not be a satisfactory change in motor current from full load (when a screw is being driven) to a non-load condition. At this time,. the bracket 30- will be in its upper position as shown with the screw 40 engaging the actuating member 28 and holding the switch 27 closed. This will energize the solenoid D and open a valve 117, thus connecting air from a port 115 to a port 113. This will drive a piston 116 down. The screw driver blade 11 will engage a screw to be driven and the motor M will rotate the screw until it has tightened to a predetermined amount, depending upon the setting of the voltage divider potentiometer 69.

As the screw is tightened, the load on the motor M will increase. Therefore, the armature current and, consequently, the current through the primary winding of the transformer T2 will also increase. As the primary current of the transformer T2 increases, the grid bias on the grid 75 of the electronic tube 76 will increase. Therefore, the current conducted by the tube 76 through the relay L1 will increase. When the current through the electronic tube 76 and, therefore, through the relay L1 has increased to a predetermined value, the relay L1 will close the contact 99 and this will complete a circuit from the secondary winding 102 of the transformer T3 and the valve solenoid U will be energized. This will open a valve 112 and admit air from the port 115 to a port 114 and below the piston 116 which will raise the bracket 30 and the screw driver blade 11. The shaft segment 53 can be adjusted to allow the quill 43 to slip on the washer 56 if the piston is not raised quickly enough to release the torque on the screw being driven. If no screw were in place to be driven, the bracket 30 would move down until it struck the limit switch 26. This would complete a circuit through the solenoid U which would cause the piston to raise the quill 43.

The foregoing specification sets forth the invention in its preferred practical forms but the structure shown is capable of modification within a range of equivalents without departing from the invention, which is to be understood is as broadly novel as is commensurate with the appended claims and the prior art teachings.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A power operated tool comprising a frame, an electric motor supported on said frame, said motor having a source of electrical current connected thereto, tool supporting means, means to move said tool supporting means toward and away from said motor, a tool on said tool supporting means, and means operatively connecting said tool to said motor, said means for moving said tool supporting means being actuated by means responsive to the current flowing through said motor.

2. The tool recited in claim 1 wherein said tool supporting means comprises a bracket, and means on said frame for guiding said bracket toward and away from said motor, said tool being rotatably supported on said bracket, said means connecting said tool to said motor comprising shaft means.

3. The tool recited in claim 1 wherein said means for moving said tool supporting means comprises guide means on said frame, means on said tool supporting means engaging said guide means and guiding said tool supporting means thereon, a fluid motor having a piston therein, valve means connecting said fluid motor to a fluid source, said piston being connected to said tool supporting means, and actuating means for said valve means, said actuating means connecting said fluid motor to said fluid source to raise said tool supporting means when said tool in said tool supporting means exerts a torque of a predetermined value on an article to be tightened, said actuating means being actuated by electric current flowing through said motor.

4. The tool recited in claim 3 wherein said actuating means comprises an electronic tube having a control grid, said control grid being connected to an electronic circuit actuated by current flowing through said motor, whereby the current through said tube is controlled by the current flowing through said motor.

5. The tool recited in claim 4 wherein said means connecting said tool supporting means to said motor comprises a clutch, said clutch having means thereon to set it to slip when a torque of a predetermined value is exerted by said motor on said tool.

6. A tool for tightening articles of manufacture comprising a frame, an electric motor supported on said frame, said motor having a shaft, tool supporting means, guide means on said frame for guiding said tool supporting means to slide toward and away from said motor, a fluid motor with a piston therein attached to said frame, said piston being connected to said tool supporting means, means actuating said fluid motor to move said tool supporting means up when the torque exerted by said motor on a tool reaches a predetermined value, said means to actuate said fluid motor comprising a transformer and an electronic tube, said transformer having one winding connected in series with said motor and the other winding connected to the control grid of said tube, whereby as the torque exerted by said motor on said tool increases, said tube conducts a greater amount of current, and a relay in series with said tube, said relay being connected to means on said fluid motor to drive said fluid motor to move said tool supporting means toward said motor when said relay is actuated.

References Cited in the file of this patent

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