US2387478A

US2387478A - Safety means for power-operated tools

Info

Publication number: US2387478A
Application number: US528487A
Authority: US
Inventors: Frank E Tiffany
Original assignee: Lockheed Aircraft Corp
Current assignee: Lockheed Corp
Priority date: 1944-03-28
Filing date: 1944-03-28
Publication date: 1945-10-23
Anticipated expiration: 1962-10-23

Description

1945. F. E. TIFFANY SAFETY MEANS FOR POWER OPERATED TOOLS Filed March 28, 1944 INVENTOR. FRANK E YY FFANY AGENT Patented Oct. 23, 1945 r SAFETY MEANS FOR POWEIt- OPERATED TOOLS Frank E. Tiffany, llai'emont, Calif.l assi'gnor to Lockheed Aircraft Corporation; Burbank, Calif.

Application March 23, 1944, Serial Natas a 16 Claims. (Cl. 192 1s0 This invention relates to power operatedtools and equipment, and relates moreparticularly to manually controlled power operated tools and machines such as rivetingmachines, and the like. It is a general object of this invention toprovide a practical, inexpensive and dependable character. Many power actuated tools machines so that the operators hands are free to handle the work and place it between the active-parts of the machine. .In the event the" pedal is depressed" at a time when the operator's hands 1 are between the active machine parts,

serious" physical injury may result. Safety guards and devices installed at the'active machine parts have been introduced to reduce the hazard, but such guards and devices are not satisfactory because they interfere with the handling and locating of the workpieces.

An object of the present invention is to provide a safety means fora squeezing, pressing, punching or riveting machine that positively preciudesthe possibility of injury to the operator in. the event'the machine is put into operation when his hand or any other part of his body is between the active parts of the machine. The safety means is such that the active force or full power of the machine cannot come into playin the event any part of: the operator's bodyor clothing is accidentally or unintentionally en: gazed between the squeezing, punching, pressing orriveting'elements of the machine when the machine is .put-into operation. The safety control is entirely dependable and will respond to the presence of even a single: thickness ofpaper engaged betweenthe work. piece and an active machine-part.

Another objectof the invention is to provide a safetymeans of the character referred to that does: not in any way alter the normal operation of the machine. or interfere with the customary It isanother object of the invention to provide a safety means oftheclass referred to that does s fetyj means for tools and machines of such and machines such as riveters, squeezers, punches, presses, etc., are} dangerous to operate. It is customary toprovide foot pedals for: initiating the operation of such] it elements at the active working parts of the ma- I manual acts requiredin the: handling of the work the 1 control of the machine: The safety mt require the use of guards, shields or other chine; and there is nothing to interfere with the free, normal handling of the work piece.

- Another object of the invention isto provide a safety means of the character mentioned that may be constructed in the form of. an appliance of attachment for ready connection with a tool or machine, or that may be embodied in the tool or machine as an original partthereof. In eitherinstance, the employment of the safety device does not necessitate material alteration of the.

machine or change in its normal mode. of operation.

' Still another obiect of the invention is to pro.-. vide a safety. means of the class mentioned which. embodies a signal conditioned to automatically go into: operation. in the event the circuit of the safety means is shorted.

A. further object of the invention is to provide a safety means of the class. referred to that serves to positively prevent operation of the. power machine in the event the control circuit becomes shorted. If for any reason the control circuit of the. safety means becomes shorted, the: signal is immediately put into operation and the main circuit of the safety'device is held open. preventing operation of the machine until such time as theshort is cured.

'A still further object of the invention is to providea safety control of the kind above referred to in which a low potential control circuit must be completed through the work parts tocondition the tool or machine for operation Any object such as a workmans hand or: finger interposed. between the work and anactive part of the machine prevents completion. of the low potential control circuit and the tool or machine cannot operate or complete its operation. The low potential control circuit can-notinjure either the work pieces or the operator.

Other objects and features of the invention will be readily understood from the following detailed description of a typical preferred form of the invention wherein reference will he made to the accompanying drawing in which:

Figure 1 is a side elevation of a squeezer machine provided with or embodying the safety means of the invention;

Figure 2 is an enlarged fragmentary side. elevation of the. outer portions of the machine arms with portions appearing in vertical cross seclar applications, In the following detailed description'I will refertoth'e form ofthe invention illustrated in the drawing, it being understood that this description is not to be construed as limiting either the scope or application of the invention.

The tool or machine illustrated is a pneumat-" ically operated riveter or squeezer suited for squeezing or driving aluminum alloy rivets, etc. The machine includes a post or pedestal l9 suitably supported on the floor. A clamp or yoke H on the upper end of the pedestal l carries the main cylinder and piston mechanism 12. A lower arm [3 projects forwardly from the mechanism I132 andis fixed or stationary. An upper arm I4 is hingedor pivoted onthe lower arm I3 at l5 and is operated by the mechanism l2. The present invention' is not primarily. concerned with the details of the operative connection between the mechanism l2 and the upper arm, and it will suffice to say that this connection includes the linkage indicated at I6. Anair pressure supply pipe I], extending from a suitable source of air under pressure, leads to. a valve l8 at the rear of the mechanism l2. The valve I8'is adapted for control by a foot pedal arrangement. In the case illustrated, a foot'pedal I9 is pivoted on the base portion of the pedestal l9 below a guard 20. A link or rod 2! is pivotally connected with the pedal I9 and extends upwardly in parallel relation to the pedestal, being guided by oneor more guides 22.' An arm 23 on the rod 2| acts on the stem of thelValVe I8 to operate the valve when the ped l I9 is depressed. Thisoperation of the valve I8 results in actuation of the mechanism l2 to force the arm l4 downwardly, assuming that actuating air under pressure is supplied to the valve. When thepressure is removed from the pedal H], the valve l8 returns to its normal position and the mechanism I2 operates to restore the arm M to its raised or open position. Opposed and vertically aligned bosses 24 are provided On the outer partsof the arms-l3 and I4. Aligned openings 25"extend through the arms [3 and I4 and their bosses 24; see Figure 2. The openings 25 are providedito receive the work-engaging parts to be later described. The-machine thus far described may be considered as conventional or standard.

The safety means of the invention may be said to comprise generallya main circuit A operable to control the delivery oi'actuating pressure to the mechanism IZ, alow pressure cylinder and piston mechanism'B for'initiating operation of the arm M, a low potential'circuit C adapted to be completed through the work piece to control the main circuit A, and a secondary safety and signal circuit D operable to hold the main circuit A open and provide a signalin the event a shortoccurs in the control circuit C;

The main circuit A includes a suitable solenoid operated valve 26 interposed in the main air sup-- ply line ll. Any selected type of solenoid operated valve may be utilized, and I have shown a conventional valve and a

solenoid combination

26 and 21 in a diagrammatic manner. Themain circuit A further includes a relay 28 and leads 29 extending between theterminals' of the solenoid 21 and the contacts of the relay 2B. The circuit valve. A pressure reducing device or valve 34,. 50 is connected in the line 33. The pressure supply ing from a power source 31. The relay 28 is preferably housed in a box 9 arranged at the upper end of the low pressure mechanism B, and the leads 29 are preferably carried in a protective or shielded conduit. The valve 26 is such that it is normally closed to prevent the passage of fluid pressure to the valve [8 of the mechanism l2 and the relay 28.15, such that it is normally open to maintain the valve 26 in its closed position. A0

cordinglythe valve 26 is open only during such time as the relay 29 is energized. The low pressure cylinder and piston mechanism B is operable to move the upper machine arm 7 l4 toward the arm l3 under a relatively low pressure. This action of the arm l4 normally serves to complete the control circuit C through the medium of the work piece W to bring about completion of the main circuit A. However, if the control circuit C cannot be completed through the medium of the work W loy reasorrofthe presence of the workmans hand or fingerat the work piece, or between the

parts

35 and 36, the main circuit A cannot be completedas a result of downward movement of the arm l4 and the machine will remain idle. I j The low pressure cylinder and piston mecha-f nism B may be secured to the top of the clamp or yoke II of the machine. I have shown the mechanism B arranged in spaced parallel ,rela-. 30 tion to the main fluid pressure mechanism l2.

Suitable linkage serves to operatively connect the low pressure mechanism B with the upper arm.

In practice links 30 may be pivotally connected with the piston rod of the mechanism B and the arm l4:to serveas the operative connection. A

valve 3| is provided tocontrol the mechanism 3.

The valve 3| is shown arranged at the rear'of.

the mechanism B and is equipped with an operating lever 32. The valve lever 32is pivotally 40 connected with the upper end of the pedal rod 2|. This linkage is such that depression of the pedal [9 operates the valve 3| to a positionto cause operation of the mechanismB and downward movement of the machine arm M. A pipe 33extends from the fluid pressure supply line I! to the valve 3|. The pipe 33 is connected in the supply line H at the upstream side of the solenoid operated valve 26 to be independent of that line I! may normally carry air under substantial pressure, say, at 100 pounds pressure, and it is desirable to deliver actuating air pressure to they I auxiliary mechanism Bat a relatively low pressure, say, at 5 or 6 pounds.

time the pedal I9 is depressed. The mechanism B exerts a small force and moves the arm M downwardlyunder; say, 4 or 5 pounds pressure,

This low pressure is'insuiiicient to cause injury 'to a hand or finger that may be at the work piece. When the foot pressure is removed from the pedal IS the valve 3| returns to its normal position'permitting restoration of the low pressure cylinder and piston mechanism B. The control circuit C is 'a feature of the invention. It includes active work-engaging

parts

35 and 36 carried by the machine arms l3 and -I4 and adapted to act on the work; see Figure 2. The control circuit C is completed through these

parts

35 and 36 and the work to cause en-' Ais suitably tapped into

lines

38 and 39 extendergization of the relay 28 and resultant opening source. Forexample, it may be connected into a 110 volt source 31. A lead or conductor 36 may extend directly from oneside of the power source31 to a terminal of the relay 26. A lead 36 extends from the other side of the power source r31 to a contact Q40 of :a relay 4|. The relay 4| is housed in the boxil. A conductor :42

extends from the contactor "4-3 .of the relay 4| to the second terminal of the relay 28. It will be seen that upon energization of the relay 4|, the

contacts

46 and 43 close to bring about energizati'onof the relay 28 to complete the circuit A'and open the valve 26.

" The control circuit C further includes a low voltage transformer 44 and a low potential circuit extending from the transformer to the work pants35 and 36. The transformer 4| is preferably housed in the box 9. Leads 8 extend from the

conductors

38 and 39 to the terminals of the primary. winding of the transformer 44. The connections may be such that the transformer 44 is atuall times connected in the powercircuit. A lead 45 extends from one end of the transformer's secondary to the active work-engaging part .35 and a similar lead 46 extends from the other terminal of the secondary to the workengaging part 36. The turns ratio of the transformer 44 is such that the

leads

45 and 46 are suppliedwith a low potential current of, say, 6 volts. The leads 45 and :46 are suitably shielded and extend through or alon the arms I4 and I3 respectively to connect with their work-enaging parts 35 and 36., The coil 1 of the relay 4| is connected in the potential circuit. I have shown the relaywinding 1 interposed in the lead 45.

Thework-engaging

parts

35 and 36 may be varied depending upon the nature of the operation to be performed. The part 35 may be in the form of a hammer and the part 36 may be in the natureof an anvil. As illustrated, the work comprises two work pieces having lapped edge portions and a rivet R is arranged through openings in the lapped portions. The part 35 has a socket 46in its end to receive the rivet head while the part 36 presents a flat end face for cooperating with the end of the rivet shank. In

theeyent the rivets to be driven have an anodic coating or other dielectric covering, the socket 41 may have a sharp point 48 for piercing the coating to insure an electrical connection between the work part 35 and the rivet R when the two come .into pressure contact. The active surfaceof the part 36 may be knurled or engraved as shown at 46 to likewise insure electrical con{ cover the walls of the openings .25 and their.

endsareflanged to .be held against displacement. Inner sleeves of steel, copper or other conductlow. mat ial a e a 03 m re; is,

electnicsleevcs '56. The conductors 45 and 460i the low potential circuit are electrically .connected. with the :outer ends of the sleeves 45 as by soldering. 'Ihe sleeves 5| are providedwith resilient inwardly projecting latch knobs :52. The active work engaging parts 35 and 136 have shanks adapted to be entered into the sleeves 5|. Annular grooves 53 are provided in the shanks to receive the knobs 52. The engagement of the knobs 52 in the grooves 53 removably latches the

parts

35 and 36 in their working positions on the arms |3 and I4 and insures good electrical contact between the parts and sleeves 51. His to be understood that the parts 35 :and 36 may be readily replaced -by similar parts suited for acting .on rivets and the like, :of different h sizes and types,

A switch Sis interposed in the lead '36 and is arranged to be closed upon depression of the pedal 19. The control part of the switch S may be operatively associated with the above described lever 32 .so that the switch is closed "simultaanism B. With the structure thus far described,

depression of the pedal 1.9 results in actuation of the mechanism B and downward movement of the arm 64, and upon engagement of the part 35 with the rivet R the low potential circuit 4546 is completed to energize 'the'relay 4|. The relay 4| in turn completes the circuit through the relay '28 so that the "valve 26 is opened to deliver air under substantial pressure to the mechanism l2 to complete the rivet squeezing operation. If, however, the operators hand or any dielectric object is between the

parts

35 and 36, or interferes with the engagement of either work

part

35 or 36 with the rivet R, the low potential circuit is not completed, with the result that the relays 4| and 28 remain de-energized and the squeezing operation cannot take place.

The secondary safety or protective circuit D serves to positively prevent completionof the main circuit A in the event a short develops in the low potential circuit 45-46 and further operates to provide a signal in the event of such ashort. It is preferred to cover the inner portions of the

arms

35 and 36 with a dielectric :shield 55 to prevent the work from shorting between the

parts

35 and 36 and the machine structure. When the shield 55 is used there is little possibility of the work W contacting the machine frame to produce a short in the low potential circuit 45-46.

6 56 may fail or wear and cause shorting of the terminal of a relay 51.

circuit 45-46. The safety circuit D includes a center tap or lead 56 extending from the sec-. ondary winding of the transformer 44 to one The other side of the relay 51 is grounded to the frame. The relay 5! may be housed in the box 9. The center tap 56 supplying the relay 51 carries a low potential current of, say, 3 volts. Therelay 51 has a pair of spaced contacts 58 and 59 and a contactor -66 movable between the contacts. The contact 58 and the contactor 66 are connected in the lead 39 which supplies current to the relay 2.8 of the main circuit A. The contactor 66 is biased to normally engage the contact 58. When the relay 51 is energized, the contactor 66 is disengaged from the contact 58 and the circuit to the relay 28 cannot thereafter be completed even though the relay 4| may be energized. The action ofv the relay 51 positively prevents energization of However, the dielectric sleeves;

visible or audible signals, or both. In the simple case illustrated, a lamp 62 is connected in the lead 6| to constitute the signal means. The lamp 62 may be exposed at the front ofthe box'9 where it may be provided with a suitable lens. Upon energization of the relay 51, as a result v of. a short'in the circuit 4546, a circuit is com.

pleted from the power line 38 through the lead 6|, contact 59 and contactor 6!] to the power lead 39, thus energizing the signal light 32.

"Ihe relay of the safety circuitD further includes a second movable contactor 6,3 and a stationary contact 64'. A lead 65 extends from the contact 64 to'one terminal of the relay 4| and a similar lead 66 extends from the contactor 63 to the other terminal of the relay. The

conductors

65 and 66 constitute'a shunt and when the relay 5'! is energized to bring the contactor 63 into engagement with the contactor 64 the relay'4l is shunted out. Thus the relay 4| is prevented from operating in the event a short develops in the low

potential circuit

45 and 46. With the relay 4| shunted out the circuit to the relay 28 of the main circuit A cannot be completed to open the valve 26. a i

It' is believed that the operation of the safety means of the invention will be readily understood from the foregoing description. The work W carrying the rivet R is placed or held in the machine so that the rivet R rests on the part 36. The operator then depresses the pedal l9. This operates the valves I8 and 3|. and closes switch S. Operation of the valve 3| causes the low pressure'mechanism B to move the arm 14 downwardly so that the part 35 engages the rivet head R and exerts a pressure of, say, 5' or G'p'oundson" the rivet R. If there is no intervening dielectric object between the

parts

35 and 36 and the rivet R, the low potential circuit 4546 is completed to energize the relay 4|. Energization of the relay 4| completes the circuit to the relay 28. En-' ergization of relay 28 completes the main circuit A to 'open the valve 26. This, admits the high pressure air to the mechanism 12 and the arm I4 is actuated with sufiicient force to squeeze or upset the rivet R, completing the riveting operation.

In the event a dielectric object or the operators hand prevents direct engagement of the

parts

35 and 36 or prevents direct contact of either the work part 35 or the work part 36' with the rivet R, downward movement of the arm it produced by the low pressure mechanism 3 will fail to complete the low potential circuit 45-"46. So long as the low potential circuit remains open, the relay fll remains de-ene-rgized andthe circuit A cannot be completed to open the valve 25;

Accordingly, the high pressure mechanism |2 does not go into operation. The minor force exerted by the low pressure mechanism B does not injure the operators hand, and because the high pr esa signal if a short develops in the low potential circuit.

llt is to be noted that the safety means does not change in any way the normal mode of operation of the machine and does not require the installation of equipment that may interfere with the work at the active parts of the machine. The safety means is entirely automatic and requires no control or adjustment.

Having described only a typical form of the invention, I do not wish'to be limited to the specific details herein set forth, but wish to reserve to myself any variation or modifications that may appear to those skilled in the art or fall within the scope ofthe following claims.

I claim:

1. In a machine having a part movable into engagement with a work piece, a mechanism for operating said part to act on the work piece, and a power source for said mechanism, the combination of means for controlling the delivery of power from said source to said mechanism, means for moving said part against the work piece, and a low potential circuit capable of being completed through the work piece and said part following actuation of the last named means and operable when thus completed to cause the first named means to deliver power to said mechanism.

2. In a machine having a part for acting on a work piece and a mechanism for operating said.

part, the combination of a control no-rmallylpreventing operation of said mechanism and operable when actuated to cause operation of said mechanism, means for moving said pant into engagement with the work piece, and a circuitcompleted through said part and the work piece fol lowing operation of the last named means to cause actuation of said control.

3. In a, machine having a part for acting on a workpiece and a mechanism for operating said part, the combination of a control normally preventing operation of said mechanism and operable when actuated to cause operation of said mechanism, a circuit for actuating said control,

means for moving said part into light pressure engagement with the work piece, and a circuit adapted to be completed through the work piece and said part following said engagement to influence the first namedoircuit and thus cause actuation of said control.

4. In a machine having a movable part for acting on a work piece and a high pressure mechanism for operating said part, the combination of a primary control normally preventing operation of said mechanism and operable when actuated to cause operation of said mechanism, a. low pressure means for moving said part into contact with the work piece, and safety means operable fol-' lowing said contact of said part with the work piece to actuate the primary control, the safety means including a low potential circuit completed through said part and the work piece upon said contact, the completion of said circuit being essential to the operation of the safety means.

5. In a machine having a movable part for acting on a work piece and a high pressure mecha-' nism for operating said part, the combination of a first control normally preventing operation of said mechanism and operable when actuated to cause operation of said mechanism, a low pressure means for moving said part into contact with the" work piece, and a second control operable following said contact of said partwith the work piece to actuate the first control, the second control including a circuit operable when conditioned .firstinamd circuit for the.

6.. Inamaohine acancre to: actuate: the first: controhand a normally open claw potential. circuit: that. is; completed; through part and workpiece: when there. is. nothing i to interfere with electrical: contact therebetween niszulbtorwoperating said part, the combination of a: comrolsinormally preventing operation of saidmechimism and operable when: actuatedl to cause operation; or said: mechanism, a low: pres:-

bination of a main control normally preventing operation of said mechanism and operable when actuated to cause operation of the mechanism, a second mechanism for moving said movable part against the work so that the work piece is engaged between said parts under a light pressure, and asecond control including a normally open lowpotential circuit completed through said parts and the work piece upon said engagement of the work piece and operable when completed to cause actuation of the main control.

8. In a machine having a pair of spaced parts for acting on the work piece, at least one of said parts being movable, and a high pressure mechanism for operating the movable part, the combination of a main control normally preventing operation of said mechanism and operable when actuated to cause operation of the mechanism, the main control including a main circuit and a relay controlling the circuit, a second mechanism for moving said movable part so that the work piece is held between said parts under a light pressure, and a second control for energizing said .relayto actuate the main control, the second control comprising a low potential circuit completed only upon the direct engagement of said parts with the work piece and operable when completed to cause energization of said relay.

9. In a machine having a pair of spaced parts for acting on the work piece, one of which is movable, and a high pressure mechanism for operating the movable part, the combination of a maincontrol normally preventing operation of ,said mechanism and operable when actuated to cause operation of the mechanism, the main control including a circuit and a relay controlling the circuit, a second mechanism for moving said movable part so that the work piece is held between said parts under a light pressure, and a second control for energizing said relay to actuate the main control, the second control comprising a low potential circuit completed only upon the direct engagement of said parts with the work piece and operable when completed to cause energization of said relay, and means for producing a signal in the event said low potential circuit becomes shorted.

10. In a machine having a movable part for acting on a work piece and a high pressure mechanism for operating said part, the combination or ac'firstv control normally preventing operation of said; mechanism and operable: when actuated to cause.- operation. oi saidi mechanism, a lowpressuremeansfor'moving said part: into contactlwith the work piece, and. a second control operable following saidv contact of said part. with the work piece. toactuate. the. first control, the: second con.- trol' including acircuittoperable when conditioned to actuate; the:firsi;. control, a normally opern low potential circuit that is completed through said part and'xwork' piece when there; is nothing to intcrferawith electrical contact therebetween, and operable: when. completed to condition. the first named circuit for theactuation; of the. first. control, and mean zresponsiver to ashort circuit condition in said low potential circuit; for'preventing said conditioning of said first. named circuit and for providing a,signal..

acting'on a work piece and a high pressure mechanism for operating said part, the combination of a first control normally preventing operation of said mechanism and operable when actuated to causeoperation of said mechanism, a low pressure means for moving said part into contact with the work piece, and a second control operable following said contact of said part with the work piece to actuate the first control, the second control including a circuit operable when. conditioned to actuate the first control, a normally open low potential circuit that is completed through said part and work piece when there is nothing to interfere with electrical contact therebetween and operable when completed to condition the first named circuit for the actuation of the first control, and means responsive to a short circuit condition in said low potential circuit for preventing said conditioning of said first named circuit and for providing a signal.

12. In a machine having a pair of spaced parts for acting on the work piece, one of which is movable, and a high pressure mechanism for operating the movable part, the combination of a main control normally preventing operation of said mechanism and operable when actuated to cause operation of the mechanism, a low pressure mechanism for moving said movable part against the. work so that the work piece is engaged between said parts under a light pressure, and a safety control including a low potential circuit adapted to be completed through said parts and the work to cause operation of the main control.

13. In a machine having a pair of spaced parts for acting on the work piece, at least one of which is movable, and a high pressure mechanism for operating the movable part, the combination of a main control normally preventing operation of said mechanism and operable when actuated to cause operation of the mechanism, a second mechanism for moving said movable part against the work so that the work piece is engaged between said parts under a light pressure, means for insulating said parts from the machine, and a second control for actuating the main control upon said engagement of the work piece between said parts, the second control including a normally open lowpotential circuit completed through said parts and the work piece upon said engagement of the work piece and operable when completed to cause actuation of the main control.

14. A machine of the character described comprising a stationary part, a movable part, said parts being adapted to act on a work piece, a high pressure cylinder and piston mechanism for operating the movable part, a. valve for controlling the delivery of actuating fluid pressure to said mechanism, a main circuit controlling said valve, a low pressure mechanism for moving said movable part against the Work, a manually operable valve controlling the low pressure mechanism, a relay controlling said main circuit and having an energizing circuit, a relay in the ener- 'gizing circuit, and a low potential circuit completed through said parts and the work piece upon actuation of the low pressure mechanism and operable to energize the last named relay and thus complete the energizing circuit.

15. A safety control for a machine having a mechanism for moving one work part toward another to act on a work piece arranged between said parts, the control including'means -for moving the first named work part against the work piece under a low pressure, and means for initiating operation of said mechanism following operation of the first named means comprising an electrical circuit adapted to be completed through said work parts and the work piece. y

16. A safety control for a machine having a mechanism for moving one work part toward another under high pressure to act on a Work piece arranged between said parts, the control comprising manually controlled means for moving the first named part into low pressure contact with the work piece, and means for initiating operation of said mechanism to continue actuation of said first named work part under high pressure including an electrical circuitccompleted through said work parts and work piece upon said first named part being moved into low pres- FRANK E. 7 i