Title:
Safety device
United States Patent 2082210


Abstract:
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 and vigilance on their part can not provide an adequate precaution against...



Inventors:
Mcmaster, Archie J.
Application Number:
US64662932A
Publication Date:
06/01/1937
Filing Date:
12/10/1932
Assignee:
G M LAB INC
Primary Class:
Other Classes:
38/1C, 74/102, 192/129A, 192/134, 250/215, 250/221
International Classes:
F16P3/00
View Patent Images:



Description:

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 and vigilance on their part can not provide an adequate precaution against serious accidents.

As a result various devices have been devised, from time to time, for protecting the operators of such machines against personal injury, but such prior devices have been more or less unsatisfactory in that they have hampered production and have constituted a source of constant annoyance to the operators.

The punch press, one of the important tools of moder low cost and high speed production, is an outstanding example of dangerous machinery of this class. Such safety devices as have been heretofore employed with punch presses and the like generally consist of some form of mechanical guard operated in timed relation with the ram of the press, the guard being arranged to strike the hands or Arms of the operator or even brush them aside should he fail to remove them from the machine in time. However, these devices, because they operate continuously, often deliver severe raps to the hands and wrists of the operator when he is in fact in no immediate danger whatsoever. In addition the guard often seriously interferes with the feeding of work into the dies so that the speed of production is considerably decreased.

Consequently, an operator will often surreptitiously remove the guard from his press, prefering to entrust his safety to his own skill and vigilance rather than endure the annoyance of the guard.

It is therefore a primary object of my present invention to provide an improved safety device for punch presses.

It is a further object to provide a safety device for a machine which functions so as to cause a minimum of annoyance and inconvenience to the operator of the machine.

A further object is the provision of means for affording a machine operator proper protection against serious injury without hampering him in his attendance upon the machine.

A further 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 or more safety devices to actuate the same whenever the operator is in immediate danger of injury. Specifically, according to one manner of carrying out my invention; I direct, a beam of light across the table of a punch press or other machine in such a position that the operator must interrupt the beam whenever he is in a position to be injured, and I provide photoelectric means operative upon an interruption of the beam during the descent of the ram to stop the press.

My present invention further contemplates the provision of a normally inoperative safety attachment for a punch press or the like capable of being brought into action at any time during the descent of the ram of the press should the operator inadvertently place his hand into the danger zone after initiating the operation of the machine. Such a safety attachment may consist of a normally inoperative mechanical guard and this, under certain conditions is the preferred manner of carrying out the present invention. In order to acquaint those skilled in the art with the teachings and.practice of my invention, I shall now describe certain embodiments thereof, reference being had to the accompanying drawings forming a part of this specification and in which: Figure 1 illustrates more or less schematically an embodiment of my invention in which I provide photoelectrically controlled means for automatically stopping a punch press should an op- 3g erator place his hand into the danger zone during the descent of the ram; Figure 2 illustrates similarly an embodiment of my invention in which a mechanical guard is photoelectrically controlled so as to operate only when an operator is in immediate danger of injury; Figures 3, 4, 5, and 6 are detail views of the mechanical guard of Figure 2; Figure 7 is a geometrical diagram for.facilitating 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 1, I have illustrated a punch press II, having a driving motor 12 geared to its flywheel 13 and a foot treadle 15 controlling a dog for bringing the flywheel into driving engage- 66 ment with the crank I 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 18 which is normally set by a spring to arrest the motion of the crank 16 and which is released by means of a magnet 19. A solenoid magnet 21 (shown in its normal condition), positioned near the treadle 15 is arranged to eject a pin when energized which blocks the treadle 16 so as to prevent flywheel IS from being brought into driving engagement with the crank 16. 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 of 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 27 is diagrammatically indicated as being associated with the crank shaft 16 to be driven in synchronous relation thereto. Preferably the commutator is mounted directly on the shaft 16. It includes a brush 26 which rides successively over an insulated section 28 and over a contact or conducting portion 29.

The photoelectric cell 25 is associated with a suitable amplifier circuit 30 comprising an electron valve 31 and powered by a transformer 32 from a pair of power conductors 34 and 35. A relay 41 (shown in its normal condition) has its operating coil in the plate circuit of the electron valve 31 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 21 to the control lead 43, the other terminal of the solenoid being con'nected to the power conductor 34. The control lead 43 also extends through the commutator 27 to the operating coil of a normally closed relay 47 (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 47 controls the operating coil of a magnetic so contactor 51 (shown in its normal position).

The contactor 51 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 12 and brake magnet 19 of the punch press 11.

The motor 12 is started by pressing the push button switch 48. This closes the circuit to the coil of the contactor 51 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 12 to start the same, and to energize also the magnet 19 to disengage the brake 18. The press may then be operated in the usual manner by depressing the foot treadle 15, 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: The light cell is normally illuminated by the light beam but is necessarily darkened whenever the operator reaches into the dies or in any 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 41, 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 21 will be actuated whenever the cell 25 is darkened and the treadle 15 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 of the press to leave the light beam substantially unobstructed. Any obstruction of the light beam when the ram is in a raised position will prevent its operation.

The 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 of 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 27 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 47 is open. When the press is tripped the commutator 27 revolves with the crank shaft 16 of the press and brings the contact portion 29 into engagement with the brush 26 to condition the circuit of relay 47 to be controlled by the operation of relay 41.

If the light beam to the cell 25 remains unobstructed the relay 41 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 41 to close its contact. This will complete the circuit through the commutator contacts to energize the coil of the relay 47. The relay 47 will then draw up its armature to open the pilot circuit to the contactor 51, causing the same to open its contacts 52 and 53. The opening of the contact 52 prevents 5o the pilot circuit from being reestablished and the opening of the contact 53 de-energizes the motor 12 and the magnet 19 thereby removing the driving force from the press and applying the brake 18. 5; Thus the press is automatically brought to an abrupt stop merely due to the operator's hand or body approaching the danger zone.

The press may be subsequently restarted by pressing the push button 48, provided however o6 that the light beam is unobstructed. The normally closed push button switch 49 serves as a stop button for stopping the motor 12 when desired.

Under certain conditions of operation, it may be desirable to open the switch 45 so as to render the solenoid 21 inoperative, thereby permitting the operator to 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 half of its travel before the dies close sufficient to catch or injure the operator. I, therefore, prefer to so arrange the commutator 27 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 47 cannot be actuated even though the light beam be obstructed. After that time, however, the commutator contacts are closed and therelay 47 is again under control of the relay 41 and the photo cell 25. If, then, the operator does not remove his hands before the commutator contacts close, the relay 47 will be energized and the press will be stopped before the dies close.

The commutator 27 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 operator's hand remain in the danger zone. As shown in the drawings the crank revolves approximately 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 1800 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 operator's hands.

Figure 2 of the drawings illustrates a punch press 61 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 70 on the punch press 61. The contacts of the relay 69 shunt those of relay 65. Another power conductor 67 is connected to a brush 79 of a commutator 74 driven by the crank of the punch press. A contact portion 75 of the commutator is connected to the terminal block 70.

The punch press 61 is also provided with a guard 80 which may be better understood by referring 5O also to Figures 3 to 6 inclusive. The guard member 80 is pivotally supported on a shaft 81 so as to swing acrosp 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 r 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. Asisshown 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 81 and engages the guard 80 to normally urge it toward the left as viewed in Figures 2 and 3.

-j The engagement of the connecting rod 82 with the curved arm 83 is had by means of a special carriage 91 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 91 from slipping off the end thereof. As is shown more in detail in Figures 5 and 6, the carriage 91 comprises a pair of shell members 93 and 94 which fit together to form a substantially tubular casing and are 7r secured in assembled relation by means of rivets 95. These rivets carry rollers 96 which engage the arm 83 to guide the carriage 91 thereon. Riveted into the sides of the shells 93 and F4 are a pair of trunnions 98 and 99 which turn in a yoke 10 carried by the upper end of the connecting rod 82. The inner end of the trunnion 98 is recessed to receive .a pad of friction material 103.

The other trunnion 99 is provided with a central bore into which is fitted a slidable plunger 104, the inner end of which is faced with a friction pad 105.

Mounted on one arm of the yoke 101 is an electro-magnet 110, the armature of which is hinged at Ill and provided with a short heel portion 112. The heel 112 operably engages one arm of a link or bell crank 114 which is also supported on the yoke 101. The other arm of the bell crank 114 slidably engages one end of a short connecting rod 115. The rod 115 is provided with a pair of retaining pins 116 to limit its motion relative to the link 114, and it is also provided with a compression spring 117 bearing against one of the pins 116 and against the link 114 to urge the rod 115 to the left as viewed in Figure 5. The other end of the rod 115 makes a ball-and-socket connection with the plunger 104. The magnet 110, when energized, operates to move the plunger 104 in against the arm 83 so as to grip the same between the two friction pads 103 and 105, the resilience of the spring 1l7 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 118 normally holds the plunger 104 withdrawn a sufficient distance to release the grip on the arm 83. The operating coil of the magnet 110 is connected by means of wires 120 with the terminal block 70 shown in Figure 2 and is thereby connected into circuit with the commutator 74 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 o5 brush 79 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 75 into engagement with the brush 79, 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 110 and the commutator 74. 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. The circuit will be opened by the commutator 74 when the ram reaches the end of its down stroke.

Referring now to Figure 3, the guard member 80 together with its arm 83, normally does not operate but remains in the position 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 82-b shown in dotted lines, the carriage 91 traveling along the arm 83. If during the down stroke of the ram, the light beam be interrupted and the magnet 110 energized, the carriage 91 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 91 on the arm 83 being determined by the time at which the light beam was interrupted. The guard 80 has thereby been moved to the position 80-c and in so doing has swept across the front of the press to brush the operator's 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 91 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. The carriage 91 therefore exhibits little or no tendency to move along the arm 83 at the beginning of the up stroke and the rod 82 forces the arm 83 to swing up and the guard 80 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 91 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 91 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 117 (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. In addition the inherent g5 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 equal 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 81 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 different manner as follows: My guard as shown in Figure 3, swings through an angle of about 45 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 91 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 91 grips the arm.

The sharpened curvature of the portion BD together with the location of the point O off the arc 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 130 is provided with a guard comprising a spring operated pantograph gate 132 adapted to extend across the front of the press between the danger zone and the operator. A tubular post 135 is fixed to the bed of the press and a pair of collars 136 and 137 carried thereby support the gate 132. The lower collar 136 is secured fast while the collar 137 slides on the post to operate the gate. A spring 138 is compressed between the collar 137 and a third collar 139 to continuously tend to expand the gate. A bumper 140 of U-section covering the right or outer end of the expanding guard 132 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 135 is provided with a pair of slits 147 through which extends a pin 148 which is secured to the sliding collar 137.

A rod 149 disposed within the tubular post 135 has an eye 150 at its lower end encircling the pin 141 and has an enlarged head portion 151 7r at its upper end. The collar 139 carries a catch 145 in which a pair of hooks are pivoted on a pin 155. These hooks are adapted to catch the head 151 of the rod 149 to hold the collar 137 in its raised position against the force of the spring 138 and thereby to retain the gate 132 in its retracted or set position. Preferably the collar 139 has a contracted throat 157 for guiding the head 151 into engagement with the hooks 154. Mounted in the top of the housing is a solenoid magnet having a core 161 which is connected by means of links 162 to the hooks 154, and operable when energized to release the rodJA9 rorengagemen itih-the-hooks.-I5-Thi pun~ h press 130 is also provided with a light source 171 arranged to cast a beam of light across the bed of the press to normally Illuminate a photoelectric cell or light sensitive device 172. 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 172 is an amplifier including a thermionic valve 176 and a relay 177 having a normally closed contact 178. The contact 178 together with a commutator 180 are connected in series relation with the magnet 136 to control the same. The commutator 180 is driven synchronously with the ram of the press.

In operation the relay 17 is controlled by the light sensitive cell 172 to maintain the contact 178 open whenever the light beam from the lamp 178 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 177 to close its contact 178. If at the same time the circuit is completed through the commutator 180, the magnet of the catch 145 will be energized so as to release the guard member 132. 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 180 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 132 is normally held in its rest or closed position by the catch 145 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 180 closes its contacts, the guard 132 will be released and it will shoot out due to the force of the spring 138. 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 same are merely illustrative. I therefore do not wish to be limited except by the scope of the appended claims.

I claim.

1. In a safety appliance for a machine, normally inoperative guard means adapted to remove a portion of an operator's body from a danger zone of the machine, and light responsive means for actuating said guard means in response to the presence of said portion of the operator's body in said danger zone.

2. The combination with a machine which s--automatically operable through-a-cycldef nor- iC mally inoperative guar-i-neans and means for -actuating said guard means at any time during a predetermined portion of the cycle of operation 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, a member rotatable about an axis, said member including a guard portion, a connecting rod, first 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 first 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, 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 ,o 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 op- -0 erated 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 proJecting a beam of light across the press for controlling said light responsive means, and commutator means operating according to the cyclic operation of the press for preventing actuation of said electromagnetic means by said photoelectric means during a predetermined portion of 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 of the machine and an operator thereof, said guard member including means tending to move said guard member away -from-said-restjositon to pass between said danger zone and said operator,-eans-for normally_ retaining said guard member in 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 zone and an operator, a catch for normally retaining said guard in said rest position, electromagnetic means for releasing said 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 of 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 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 distance to compel a move- I) ment oi sa-ER movable member.

9. In combination in a safety device for a 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. McMASTER.