US2082210A

US2082210A - Safety device

Info

Publication number: US2082210A
Application number: US646629A
Authority: US
Inventors: Archie J Mcmaster
Original assignee: G M LAB Inc
Current assignee: G M LAB Inc; G-M LABORATORIES Inc
Priority date: 1932-12-10
Filing date: 1932-12-10
Publication date: 1937-06-01
Anticipated expiration: 1954-06-01

Description

June 1, 1937. A. J. McMAs-rER 2,082,210

SAFETY DEVICE Filed Dec. l0, 1932 4 Sheets-Sheet 1 H. 'I f5 June 1, 1937. A. .1. MoMAsTER 2,082,210

SAFETY DEVICE Filed Dec. l0, 1932 4 Sheets-Sheet 2 June 1, 1937. A. J. McMAsTER 2,082,210

SAFETY DEVICE Filed Dec. l0, 1932 4 Sheets-Sheet 3 June 1, 1937. A. J. McMAsTr-:R 2,082,210

SAFETY DEVICE Filed Dec. l0, 1932 4 Sheets-Sheet 4 @if/g@ fao i Patented June 1937 SAFETY DEVICE Archie J. McMaster, Highland Park, Ill., assignor to G--M Laboratories, Inc., Chicago, lll.

Application December 10, 1932, Serial No. 646,629

9 Claims. (Cl. 'I4-615) My invention relates to safety devices for the protection of machine operators.

It is well recognized that the operation of certain machines exposes the operators thereof to such considerable hazards that ordinary care jury Specifically, aCCOrdiug t0 011e manuel' 0f 5 and vigilance on their part can not provide an carrying out my invention: I direct, a beam of adequate precaution against serious accidents. light aCrOSS the table 0f a punch Dress 01 Other As a result vanous devices have been devised, machine in such e position that the operator from time to time, for protecting the operators must interrupt the beam whenever he ls in a of such machines against personal injury, but position to be injured, and I provide photoelecl0 such prior devices have been more or less untrie means Operative uPOrl au interruptin 0f satisfactory in that they have hampered producthe beam during the descent 0f the ram t0 StOD tion and have constituted a source of constant the Dressannoyance to the operators. My present invention further contemplates the The punch press, one of the important tools DIOVisOn 0f a normally rlOPeratiVe safety at- 15 of modern low cost and high speed production, ieehment for a punch press or the like capable is an outstanding example of dangerous maof being brought into action at any time durirlsr chinery of this class. Such safety devices as the descent of the rem of the press should the have been heretofore employed with punch Operator inadvertently place hls hand into the presses and the like generally consist of some danger Zelle after initiating the OperatiOn 0f 20 form of mechanical guard operated in timed the machine. Such a safety attachment may relation with the ram of the press, the guard consist of a normally inoperative mechanical being arranged to strike the hands or arms of guard and this, under Certain Conditions is the the operator or even brush them aside should preferred manner 0f carrying out the present he fail to remove them from the machine in. invention. 25 time.4 However, these devices, because they op- In Order t0 acquaint those Skilled in the art erate continuously, often deliver severe raps to with the teachings and ,praetice of my invention, the hands and wrists of the operator when he I shall now describe certain embodiments thereis in fact in no immediate danger whatsoever. 0f, reference being had t0 the aCCOmPanyirlg In addition the guard often seriously interferes drawings forming a part of this speciication and 30 with the feeding of work into the dies so that in which: the speed of production is considerably decreased. Figure 1 illustrates more 01 less sehematieally Consequently, an operator will often surreptian embodiment of my invention in which I protiously remove the guard from his press, prefervide photoelectrcally controlled means lfor autoing to entrust his safety to his own skill and matlcally stopping a punch press should an op- 35 vigilance rather than endure the annoyance of erator place his hand into the danger zone dur- She guard. ing the descent of the ram;

It is therefore a primary object of my present Figure 2 illustrates similarly an embodiment invention to provide an improved safety device of my .invention in which a mechanical guard for punch presses. is photoelectrically controlled so as to operate 40 It is a further object to provide a'safety deonly when an operator is in immediate danger vice for a machine which functions so as to of injury; cause a minimum of annoyance and inconven- Figures 3, 4, 5, and 6 are detail views of the ience to the operator of the machine. mechanical guard of Figure 2;

A further object is the provision of means for Figure 7 is a geometrical diagram for. facilltat- 45 affording a machine operator proper protection against serious injury Without hampering him in his attendance upon the machine.

A lfurther object is the provision of a protective device operative only when accident or injury is imminent.

A further object is the provision of a photoelectrically controlled machine guard.

Other objects and advantages will appear hereinafter.

My present invention contemplates the use of a light responsive system for controlling one ormore safety devices to actuate the same whenever the operator is in immediate danger of ining the description;

Figure 8 shows in perspective another type of mechanical guard adapted to photoelectric control; and

Figure 9 is a detail view of the guard shown in Figure 8.

In Figure l, I have illustrated a punch press Il, having a driving motor I2 geared to its idywheel I 3 and a foot treadle I5 controlling a dog for bringing the ilywheel into driving engagement with the crank I5 of the press, all of which is well known in the art and usual in the construction of punch presses. The press II is further provided with a brake I8 which is normally set by a spring to arrest the motion of the crank I6 and which is released by means of a magnet I9. A solenoid magnet 2i (shown in its normal condition), positioned near the treadle I5 is arranged to eject a pin when energized which blocks the treadle I5 so as to prevent flywheel I8 from being brought, into driving engagement with the crank I6. Mounted on opposite sides of the bed of the press are a light source 24 and a photoelectric cell or light responsive device 25. The light source 24 includes a lens which directs a beam of light across the bed oi.' the press, to normally illuminate the cell 25. The beam is preferably positioned directly in front of the dies at such a level that the light will be interrupted by the operator's hands whenever he reaches into the path of the ram of the press.

A commutator 21 is diagrammatically indicated as being associated with the crank shaft I6 to be driven in synchronous relation thereto. Preferably the commutator is mounted directly on the shaft I6. It includes a brush 26 which rides successively over an insulated section 28 and over a contact or conducting portion 29. l

The photoelectric cell 25 is associated with a suitable amplier circuit 38 comprising an electron valve 3l and powered by a transformer 32 from a pair of

power conductors

34 and 35. A relay 4I (shown in its normal condition) has its operating coil in the plate circuit oi' the electron valve 8i and is provided with a normally closed contact controlling the energization of a. control lead 43 from the power conductor 35. A manual switch 45 serves to connect one terminal of the solenoid 2i to the control lead 43, the other terminal oi.' the solenoid being con- 'nected to the power conductor 34. 'I'he control lead 43 also extends through the commutator 21 to the operating coil of a normally closed relay 41 (shown in its normal position).

A pilot circuit comprising a normally open push button 48, normally closed push button 49 and the normally closed contacts of the relay 41 controls the operating coil of a. magnetic contactor 5I (shown in its normal position). The contactor 5I is provided with two normally

open contacts

52 and 53. The contact 52 shunts the push button switch 48 and the contact 53 controls the operation of the driving motor I2 and brake magnet I9 of the punch press II.

The motor I2 is started by pressing the push button switch 48. This closes the circuit to the coil of the contactor 5I which upon operating closes its contact 52 to maintain its coil circuit when the button 48 is released. The contactor also closes its contact 53 to energize the motor I2 to start the same, and to energize also the magnet I9 to dlsengage the brake I8. 'I'he press may then be operated in the usual manner by depressing the foot treadle I5, providing that the beam of light from the lamp 24 to the photocell 25 is uninterrupted at the time. The light beam and the photo cell operate to usurp the control of the machine whenever that is necessary for the protection of` the operator. The operation is as follows: y

'I'he light cell is normally illuminated by the light beam but is necessarily darkened whenever the operator reaches into the dies or inany other manner places his hands into such position that they may be caught and injured by the descending ram, that is, whenever they are inserted into the danger zone of the machine. The amplifier responds to the degree of illumination of the cell 25 to operate the relay 4I, the relay drawing up its armature to open its contacts whenever the cell is illuminated and closing its contacts when the cell is darkened by the interruption of the light beam. Therefore, if the switch 45 is closed, the solenoid 2| will be actuated whenever the cell 25 is darkened and the treadle I5 will be thereby blocked to prevent the press from being tripped until the operator withdraws his hands far enough from the dies and the ram ot the press to leave the light beam substantially unobstructed. Any

i obstruction of the light beam when the ram is in a raised position will prevent its operation. 'I'he ram itself will not interrupt the beam to interfere with its own operation since the light beam is purposely positioned just outside of the danger zone, that is, just outside the path oi' the ram.

The press having been tripped, it will drive the ram down to close the dies and then return the ram to the raised position provided the light beam remains unobstructed. The commutator 21 is shown in its normal condition, that is the condition it assumes when the ram of the press is in its uppermost position. In this condition the brush 26 engages the insulated portion 28 so that the circuit to relay 41 is open. When the press is tripped the commutator 21 revolves with the crank shaft I6 of the press and brings the contact portion 29 into engagement with the brush 26 to condition the circuit of relay 41 to be controlled by the operation of relay 4I. If the light beam to the cell 25 remains unobstructed the relay 4I will hold up its armature and the press will complete its cycle of operation. However, should the operator replace his hands in the danger zone after the press has been tripped, he will interrupt the light beam to cause the relay 4I to close its contact. This will complete the circuit through the commutator contacts to energize the coil of the relay 41. The relay 41 will then draw up its armature to open the pilot circuit lto the contactor 5I, causing the same to open its

contacts

52 and 53. 'I'he opening of the contact 52 prevents the pilot circuit from being reestablished and the opening of the contact 53 de-energizes the motor I2 and the magnet I9 thereby removing the driving force from the press and applying the brake I8.

Thus the press is automatically brought to an abrupt stop merely due to the operators hand or body approaching the danger zone.

'I'he press may be subsequently restarted by pressing the push button 48, provided however that the light beam is unobstructed. The normally closed push button switch 49 serves as a stop button for stopping the motor I2 when desired.

Under certain conditions of operation, it may be desirable to open the switch 45 so as to render the solenoid 2I inoperative, thereby permitting the operator tol trip the press before his hands are completely withdrawn from the danger zone. This procedure will often speed up production, and with the motor and brake photoelectrically controlled in accordance with my invention, it will expose the operator to no unnecessary danger; The ram of the press must descend a certain distance, usually about a halt aoeacio of its travel before the Idies close sucient to f catch or injure the operator. I, therefore, prefer to so arrange the commutator 21 that the brush 26 comes into engagement with the contact segment 29 only after the ram has descended a predetermined distance. During the time that the ram is descending that distance the relay 41 cannot be actuated even though the light beam be obstructed. After that time, however,

the commutator contacts are closed and the-relay 41 is again under control of the relay 4| and the photo cell 25. If, then, the operator does not remove his hands before the commutator contacts close, the relay 41 will be energized and the press will be stopped before the dies close.l

The commutator 21 must be arranged to close its contacts early enough so that the press may be stopped before the ram descends far enough to cause any injury should the operators hand remain in the danger zone. As shown in the drawings the crank revolves approimately 60 degrees before closing the commutator contacts, which will bring the ram down approximately one quarter of its complete descent. The commutator contacts again open after 180 rotation of the crank, that is when the ram is in its lowermost position. There is small chance of injury during the ascent of the ram and it will be therefore usually preferred to let the ram complete its up stroke regardless of the position of the operators hands.

Figure 2 of the drawings illustrates a punch press 6| equipped with a light source 62 and a photoelectric cell 63 in'a manner similar to the punch press of Figure 1. The photo cell 63 is associated with an amplifier 64 and a normally closed relay 65 (shown in its normal condition), the contacts of which are interposed between a power conductor 68 and the winding of a series relay 69. A connection from the coil of relay 69 extends to a terminal block 10 on the punch press 6|. The contacts of the relay 69 shunt those of relay 65. Another power conductor 61 is connected to a brush 19 of a commutator 14 driven by the crank of the punch press. A contact portion 15 of the commutator is connected to the terminal block 10.

The punch press 6| is also provided with a guard 80 which may be better understood by referring also to Figures 3 to 6 inclusive. The guard member 80 is pivotally supported on a shaft 8| so as to swing across the front of the press and pass between the operator and the danger zone of the machine. A connecting rod 82 has its lower end pivotally secured to the ram of the press and its upper end engaging a curved arm 83 which extends out from the guard member 80. As is shown more clearly in Figure 4 the arm 83 is offset back towards the press so that the guard portion 80 may swing freely without interfering with the connecting rod 82. A coil spring 85 encircles the shaft 8| and engages the guard 80 to normally urge it toward the left as viewed in Figures 2 and 3.

- The engagement of the connecting rod 82 with the curved arm 83 is had by means of a special carriage 9| secured to the upper end of the rod 82 and arranged to normally travel along the arm 83. A pin 92 in the end of the arm 83 serves as a stop to prevent the carriage 9| from slipping off the end thereof. As is shown more in detail in Figures 5 and 6, the carriage 9| comprises a pair of

shell members

93 and 94 which fit together to form a substantially tubular casing and are secured in assembled relation by means of rivets 95. These rivets carry rollers 96 which engage the arm 83 to guide the carriage 9| thereon. Riveted into the sides of the shells 93 and E4 are a pair of

trunnions

98 and 99 which turn in a yoke I! carried by the upper end of the connecting rod 82. The inner end of the trunnion 98 is recessed to receive Ia pad of friction material |03. The other trunnion'99 is provided with a central bore into which is fitted a slidable plunger |04, the inner end of which is faced with a friction pad |05. l

Mounted on one arm of the yoke |01 Yis an electro-magnet H0, the armature of which is hinged at and provided with a short heel portion ||2. The heel ||2 operably engages one arm of a link or bellcrank ||4 which is also supported on the yoke |0I. The'other arm of the bell crank ||4 slldably engages one end of a short connecting rod ||5. The rod I| is'provided with a pair of retaining pins ||6 to limit its motion relative to the link II4, and it is also provided with a compression spring l1 bearing against one of the pins ||6 and against the link ||4 to urge the rod ||5 to the left as viewed in Figure 5. 'I'he other end of the rod ||5 makes.

a ball-and-'socket connection with the plunger |04. The magnet 0, when energized, operates to move the plunger |04 in against the arm 83 so as to grip the same between the two friction pads |03 and |05, the resilience of the spring ||1 permitting the magnet to close completely while allowing an accurate control of the gripping force exerted by the friction pads on the arm 83. A tension spring I8 normally holds the plunger |04 withdrawn a sufficient distance to release the grip on the arm 83. The operating coil of the magnet ||0 is connected by means of wires |20 with the terminal block shown in Figure 2 and is thereby connected into circuit with the commutator 14 and relays 65 and 69.

In the operation of the embodiment shown in Fig. 2, the photo-electric cell 63 is normally illuminated by the lamp 62 so that the relay 65 draws up its armature to open its contacts. Whenever the operator of the press inserts his hand into the danger zone he interrupts the light beam and causes the relay 65 to close its contacts. The commutator 14 is shown in its normal position, that is, the position it occupies when the ram of the press is in its uppermost position, with the brush 19 engaging the insulated portion so that the circuit therethrough is open. Consequently, as long as the ram is in its uppermost position, the operation of the relay 65 does not complete any circuit. During the down stroke of the ram, the commutator brings its contact portion into engagement with the brush 19, so that if the beam of light is interrupted while the ram is moving down, the contacts of the relay 65 will close to complete a circuit through the coil of the relay 69, the magnet ||0 and the commutator 14. Current flowing in this circuit will energize relay 69 which will close its contacts to shunt the contacts of relay 65. Thereafter the circuit will be maintained through the contacts of relay 69 regardless of whether or not the light beam continues to be interrupted. 'I'he circuit will be opened by the commutator 14 when the ram reaches the end of its clown stroke.

Referring now to Figure 3, the guard member 80 together with its arm 83, normally does not operate but remains in the positionv indicated in the full lines. The ram of the press in moving up and down moves the connecting rod 82 between the position shown in full lines and the position 82b` shown in dotted lines, the carriage 8| traveling along the arm 83. If during the down stroke of the ram, the light beam be interrupted and the magnet ||8 energized, the carriage 8| will grip the arm 83 and maintaining the grip will cause the connecting rod 82 to swing the arm 83 down to occupy the position 83-c when the ram reaches the end of its down stroke. At that time the connecting rod 82 will occupy some position 82-c, the exact position of the carriage 8| on the arm 83 being determined by the time at which the light beam was interrupted. The guard 88 has thereby been moved to the position 88-c and in so doing has swept across the front of the press to brush the operators hands out of the danger zone before the ram descends far enough to inflict an injury. As previously pointed out, the commutator 14 opens its contact at the end of the down stroke of the ram so that the carriage 8| releases its grip and is again free to move along the arm 83. As the ram starts its up stroke, the connecting rod 82 and the arm 83 being in positions 82-c and 83-c, respectively, the rod 82 bears against the arm 83 in a direction substantially perpendicular to the tangent thereof. 'I'he carriage 8| therefore exhibits little or no tendency to move along the arm 83 at the beginning of the up strokeand the rod 82 forces the arm 83 to swing up and the guard 88 to swing to the left. This return motion is aided by the spring 85. As the arm 83 swings upward the angle between the same and the connecting rod 82 quickly decreases to such a value that neither can exert any considerable driving force against the other. Thereafter the arm swings up under the action of the spring 85 alone and the rod 82 continues to move up with the ram of the press. It may happen under certain conditions, that as the two

members

82 and 83 thus move more or less independently, the carriage 8| will tend to run off the end of the arm 83. In such a case the carriage will engage the pin 92 and movement of the carriage along the arm 83 being thereby prevented, the rod 82 will urge the arm 83 upwards. It is thus seen that the guard must return to its normal position at or before the time that the ram reaches its uppermost position.

It is to be noted that at the time the carriage 8| grips the arm 83, the carriage together with the connecting rod 82 will usually be in motion whereas the guard member will be at rest. It is therefore apparent that some precaution must be taken to avoid a locking-grip, for such would tend to set the guard abruptly into motion and produce excessive mechanical strains in the apparatus. As was pointed out above, the resiliency of the spring ||1 (Figure 5) controls the gripping force so that locking is prevented. A certain amount of slippage may therefore occur between the gripping surfaces during the brief time that it takes the guard to accelerate into step with the motion of the connecting rod 82. Thus the rod is started easily and undue strains are avoided at all times. Inl addition the inherent resiliency of the parts themselves also serve to limit the accelerating forces.

Figure '7 illustrates the geometrical lay out of the linkage system employed in the guard of Figure 3 and is to be taken in comparison therewith. The curve ABC is an arc about the center M, having radius r equai to the length of the connecting rod 82, the point M being at the axis of the lower pivot of the rod 82 when the ram of the press is in its lowermost position. The curve BD is an arc having a radius of about one third of the length of the connecting rod 82 and is taken about a point on the line MB so that the two arcs AB and BD will run smoothly into each other. The curve ABD is then taken as the center line of the arm 83 when in its lowermost position and a point O is chosen slightly above the arc ABD and at a distance to the right of a vertical line through M equal to about the full stroke of the ram. The point O represents the axis of the shaft 8| so that as the guard operates, the arc ABD swings about the point O. The point B may be taken at a distance to the right of a vertical line through M equal to about one half of the stroke of the ram or it may be chosen in a somewhat diierent manner as follows:

My guard as shown in Figure 3, swings through an angle of about degrees. I therefore swing the arc ABC through an angle of 45 degrees about the point O to a position A B C and select the position B' such that it is at a distance r, equal to the length of the connecting rod 82 from a point P, the point P being taken on the vertical line through M and at a distance above M equal to about one third of the stroke of the ram. That is, P represents the location of the lower end of the connecting rod 82 when the ram has completed about two thirds of its down stroke and the point B' represents the position of the upper end of the rod 82 at the same time.

If the carriage 9| grips the arm 83 at any place between A' and B it will swing the arm to the position ABD but if it grips the arm on the portion B' D' the arm will swing down until the upper end of the connecting rod 82 reaches the arc BC and the arm 83 will fall short of reaching the position ABD by an amount depending on the exact position at which the carriage 8| grips the arm.

The sharpened curvature of the portion BD together with the location of the point O off the are ABC thus serves to limit the extent and speed of operation of the guard and also to limit the force required for the operation thereof when that operation is initiated near the end of the down stroke of the ram. Obviously, the linkage system of my invention might employ other geometrical relationships between its members, the above being merely illustrative of what is believed to be the preferred arrangement.

Figure 8 illustrates another guard embodying the principle of my present invention. A punch press |38 is provided with a guard comprising a spring operated pantograph gate |32 adapted to extend across the front of the press between the danger zone and the operator. A tubular post |35 is xed to the bed of the press and a pair A of collars |36 and |31 carried thereby support the gate |32. The lower collar |36 is secured fast while the collar |31 slides on the post to operate the gate. A spring |38 is compressed between the collar |31 and a third collar |38 to continuously tend to expand the gate. A bumper |48 of U-section covering the right or outer end of the expanding guard |32 is pivoted thereto at its lower end and is slidably secured at its upper end.

The gate is arranged to be normally retained in its contracted or closed position by means of a catch mechanism which is shown more in detail in Figure 9. The post |35 is provided with a pair of slits |41 through which extends a pm' |48 which is secured to the sliding collar |31. A rod |43 disposed within the tubular post |35 has an eye |58 at its lower end encircling the pin |48 and has an enlarged head portion |5| at its upper end. The collar |89 carries a catch |45 in which a pair of hooks are pivoted on a pin |55. These hooks are adapted to catch the head |5| of the rod |48 to hold the collar 5 |31 in its raised position against the force of the spring |38 and thereby to retain the gate |32 in its retracted or set position. Preferably the collar |39 has a contracted throat |51 for guiding the head |5| into engagement with the l hooks |54. Mounted in the top of the housing is a solenoid magnet having a core |6| which Cil 2. The combination with a machine which s/I automatically operable througlnacyclef nor- 1c maily inoperatiye'rguard/nans and means for is connected by means of links |62 to the hoolrsmaactuatlngsaid guard means at Yany time during |54, and operable wllgrlfnergzedtorelease the r'od rem-engag 'ementwithfthe-hooks."44V I lti;J'I'hep'uci press |30 is also provided with a light source |1| arranged to cast a beam of light across the bed of the press to normally illuminate a photoelectrlc cell or light sensitive device |12. The beam of light is preferably directed so that it must be interrupted by the operator whenever he brings his hands or other portion of his body into a position to be injured by the machine. Associated with the light sensitive cell |12 is an amplier including a thermionic valve |16 and a relay |11 having a normally closed contact |18. The contact |18 together with a commutator |80 are connected in series relation With the magnet |36 to control the same. The commutator |80 is driven synchronously with the ram of the press.

In operation the relay |11 is controlled by the light sensitive cell |12 to maintain the contact |18 open whenever the light beam from the lamp |18 falls on the cell and to close its contact whenever the beam is interrupted. The operator in feeding the press will necessarily interrupt the light and cause the relay 11 to close its contact |18. Ii at the same time the circuit is 'completed through the commutator 40 |80, the magnet of the catch |45 will be energized so as to release the guard member |32. In the operation of a punch press, the operator usually can not be in any danger of receiving an injury unless the ram is descending and accordingly the commutator |80 is ,arranged to prevent operation of the guard at all other times. It may be preferable, under certain conditions to arrange the commutator as shown in Figure 8 so as to permit the guard to be released during only a. certain part of the down stroke of the ram.

Thus the guard member |32 is normally held in its rest or closed position by the catch and does not operate if the operator keeps his hands out of danger. If, however, upon tripping the press, he fails to remove them from the danger zone of the machine before the commutator |80 closes its contacts, the guard |32 will be released and it will shoot out due to the force of the spring |38. In so doing it will brush his hands out of the danger zone before the dies close on them and so save him from a serious injury. Furthermore the guard, having expanded remains between the operator and the danger zone and prevents him from inadvertently reinserting his hands into the danger zone as a result of being startled by the operation of the guard. The guard may be subsequently reset by hand.

While I have shown and described certain useful and convenient embodiments of my present invention, it will be apparent to those skilled in the art that the ysame are merely illustrative. I therefore do not Wish to be limited except by the 75 scope of the appended claims.

a predetermined portion of the cycle of Yoperation of the machine, operating means for said guard means including a crank and including also link means adapted to make driving engagement with said crank at a distance from the axis of rotation thereof, and means for varying according to the cyclic operation of the machine while said guard means is in its inoperative condition, the distance from said axis at which said link means is adapted to make driving engagement with said crank.

3. In a device of the character described, la member rotatable about an axis, said member including a guard portion, a connecting rod, rst means for cyclically moving one end of said rod, second means for connecting the other end of said rod to said rotatable member, said second means being movable with respect to said member along a path the direction of each point of which has a component radial of said axis, third means for normally retaining said member in such position that said second means moves along said path in accordance with the cyclic movement of said rod by said first means, and fourth means for preventing movement of said second means along said path so as to rotate said member in accordance with the movement of said rod by said iirst means.

4. In a guard for a machine, in combination, a guard member rotatable about an axis, a curved arm extending therefrom, a carriage movable along said arm to vary its distance from said axis, a connecting rod connecting said carriage to a cyclically movable part of the machine, 45 means for normally retaining said member in a rest position, such that said carriage moves back and forth along said arm in response to the cyclic motion of said cyclically movable part of the machine, means for preventing movement of said carriage along said arm in the direction toward said axis whereby to rotate said guard member, and means for limiting the movement of said carriage along said arm in the direction away from said axis.

5. In combination in a safety device for a punch press, a guard member comprising an arm adapted to swing between the dies of the press and an operator thereof, means for urging said guard toward a rest position and for normally retaining it in that position, link means for connecting said guard to a cyclically movable part of the press, an arm extending from said guard member, said link being slideably connected thereto, said arm extending in such direction that when said guard member is in its rest position, said link means slides along said arm in accordance with the motion of said cyclically movable part and when said link means is prevented from sliding along said arm said guard member is operated thereby in accordance with the motion of said cyclically movable part, electromagnetic means for preventing motion of said link means along said arm, light responsive means controlling said electromagnetic means, means for pro- Ll y jecting a beam of light across the press i'or controlling said light responsive means, and commutator means operating according to the cyclic operation of the press ior preventing actuation oi said electromagnetic means by said photoelectric means during a predetermined portion oi' the cycle of said cyclic operation.

6. In combination in a safety device for a punch press or the like, a guard member operable to move away from a rest position to pass between a-danger zone ofthe machine and an operator thereofh said guard member including means tending to move said guard member away "msaid-reslmsltlgv pass between said danger zone and said operatormeans-fornormalll retaining said guard memberin said rest position, and light controlled means for releasing said member from said rest position in response to the presence of an object in said danger zone.

7. In combination in a safety device for a punch press or the like, a guard, operating means urging said guard away from a rest position to pass between a danger zoneand an operator, a catch for normally retaining said guard in said rest position, electromagnetic means for releasing saidy catch, light responsive means for controlling said electromagnetic means, means for projecting a beam of light across said danger zone for controlling said light responsive means and means for preventing the release of said catch during a predetermined part of the cycle of operation oi' the press.

8. In a device of the character described, a movable member, a driving member, a link connected to said driving member, means engaging said link with said movable member at variable m' distances from the center of movement of said movable member without causing movement of said movable member, and means cooperating with said first-mentioned means for preventing the variation of-said distanceA to compel a movement csim'ovabie member. t. L

9. In combination in a safety devicemfg;zam'hf` punch press or the like, a movable guard member operable to move away from a rest position to pass between a. danger zone of the machine and an operator thereof, means to operate said guard, means normally retaining said guard member in said rest position, and control means including a light sensitive cell for controlling the actuation of said guard member.

ARCHIE J. MCMAS'I'ER.