US 3912924 A
Description (OCR text may contain errors)
United States Patent [191 [111 Barrett Jr. Oct. 14, 1975 1 MACHINE SAFETY CONTROL 3.478.220 ll/l969 Milroy 2,5 0 )1 3.624.454 u l97l Adk  lnvenm" 3.104.396 :11912 Ana-63mm 250/221 x 3.746.863 1/1913 Pro novost 30/25: 2
- 3.789.384 |/|914 Akers o 2  Ass'gnee' g' 't ifi' r i ggg5:33a 3.805.061 4/l914 De Miuimy el al. 250/221 x I I  Fllcd: Nov. 7, I973 ] App] No a 398 Primary Examiner-Walter Stolwoln  US. Cl 250/221; 250/209; 340/258 B [SI] Int. Cl. 606M 7/00 (57] ABSTRACT  Field of Search 250/22l. 208. 209, 572.
250/222 R; 340/258 B. 258 R; 307/3l5 Multiple photocells employing an OR-gate arrangement avoid injury to machine operators.  References Cited UNITED STATES PATENTS 3 Claims, 2 Drawing Figures 2.758.7l2 8/1956 Linderman 250/572 X U.S. Patent 0.14, 1975 Sheet2of2 3,912,924
BACKGROUND OF THE INVENTION l. Field of the invention This invention relates to a safety device for preventing injury to machine operators. More particularly, it relates to an automatic photosensory arrangement of a plurality of photocells which stops operation of a press or similar piece of industrial or like equipment when any part of the rays employed in a danger zone is interrupted.
2. Deseri tlon of Prior Art interrupt on of one or more photoelectric beams which more or less blanket the area of operation of a tool or machine so as to initiate a response mechanism which prevents injury to any part or parts of the body of 'the tool or machine operator, for example, the operator of a press, is known. For example, U.S. Pat. No. 2,058,668 describes a photoelectric safety control which has light sources supplied to illuminate photoelectric cells to render them conductors of electricity. According to the patentee, a beam of light passes from an incandescent light to the photoelectric cell by way of an opening or slit. The beams are so spaced from pressing elements that an operator standing near the press to place work thereon will intercept the beam of light which extends across the front of the press machine. According to said U.S. Pat. No. 2,058,668, if no shadow is cast on the photoelectric cells, a solenoid will hold an intake valve open and an exhaust valve closed. Any passing shadow on the photoelectric cells or interruption of the above-mentioned beams will cause an interruption in the power supplied to a relay, and an armature will move away from a contact to break the circuit to the solenoid. With the solenoid no longer energized, a spring will close the intake valve and open the exhaust valve, thereby stopping the action of the press and preventing it from closing on any part of the operator's body which has interrupted the beams of light.
On the other hand, U.S. Pat. No. 2,798,583 has to do with an electric eye barrier guard which employs a number of phototubes and a plurality of exciter lamps connected in series with terminals of a suitable source of voltage. By this arrangement, if one light fails, or if one light beam is interrupted, all will fail and thereby stop a press. The mechanism of operation is similiar to that of aforementioned U.S. Pat. No. 2,058,668 in that the phototube and exciter lamps form a light barrier across the entrance to a press bed, and, if a beam is interrupted by an operator's hands and any other part or parts of his body by reaching or protruding into the work area, a response mechanism stops the press. The response mechanism of said U.S. Pat. No. 2,798,583 involves an amplification bridge circuit comprising two parallel electrical paths connected across supply lines. The bridge circuit is completed by a single winding of a relay meter connected across the two parallel paths at the junction of two vacuum tubes and two resistors.
it can readily be seen that the response mechanisms of said U.S. Pat. Nos. 2,058,668 and 2,798,583 are highly complex and therefore subject to malfunction if any single part of the elaborate circuitry fails. it is accordingly clear that since neither of the abovedescribed safety devices is fool-proof, any commercial user cannot use same without risking injury to his press operators.
SUMMARY OF THE INVENTION After extended investigation I have found a substantially fool-proof way of protecting a press or other-type machine operator from injury by the equipment which he is manipulating. According to my invention, l employ an OR-gate arrangement which responds susbtantially immediately, that is, within a few milliseconds, when one or more of a plurality of beams between photocells and sources of light is interrupted. An OR- gate is a logic device which has a single output and multiple inputs that will give an out ut signal lfnny one or more inputs receive a signal. I? there is no single input, there is no output. However, when voltage indicates the presence of one or more signals or inputs, the output will so indicate. i prefer to use one or more Silicon-Darlington amplifiers. When i do so, i employ a simplified arrangement which enables use of bipolar transistors with very high impedance. This prevents the necessity of using two separate transistors connected externally to a considerably more complex and more elaborate circuitry. Accordingly, I can now operate a response mechanism with a larger ohmage source and by means of a single integrated circuit configuration which enables use of one or more Silicon-Darlington amplifiers incorporated in a single transistor case. The beauty of this arrangement is that it permits all interconnections to be inside a single case. The Silicon-Darlington amplifiers which i prefer to use employ two transistors. The first has an emitter joined to the base of the second and a collector joined to a collector of the second. The aforementioned output stops the press or other moving machine part by deactivating a relay, for example, by thorough removal of power from a press brake-clutch or other similar system.
DESCRIPTION 0F THE DRAWING For a better understanding of my invention, reference will now be made to the drawing which forms a part hereof.
in the drawing:
FIG. 1 is a diagrammatic view of the photocell safety device of the invention depicting how the light barrier operates to prevent injury to a press or like-machine operator by immediately stopping the machine when penetrated by an arm, leg, or other part of the operators body.-
FIG. 2 is a schematic drawing of a representative electrical circuit useful as the response mechanism according to the invention and showing how a signal received when the light barrier is broken' results in interruption of operation of the press.
Referring now to FIG. 1, a plurality of photocells 10 is excited by a single light source 12, from which a plurality of rays or beams of light 14 is collimated to the individual photocells 10 by a plurality of slots l6, 18, 20 and others (not shown) arranged between light source 12 and photocells 10. When rays or beams 14 are interrupted by the machine operator extending an arm or leg, for example, into the zone of operation of the device 24, a signal is transmitted via an OR-gate electrical circuit such as that depicted in P16. 2 and consisting of Silicon-Darlington amplifiers and resistors to immediately stop operation thereof.
in FIG. 2, which represents an electronic configuration of the receiver and central unit of the safety device of the invention, transformer 26, diode 28, capacitor 30, resistor 32, Silicon-Darlington amplifier 34, and zener diode 36 comprise a direct current power supply. The power supply provides a voltage across photocells 38 which are attached to bases 40 of multiple Silicon-Darlington amplifiers 42 in an OR-gate configuration.
Potentiometer 44, in conjunction with resistors 46 and 48, provides an adjustable voltage at emitters 50 of the Silicon-Dariington amplifiers 42, whereby the Silicon-Darlington amplifiers are biased off when there is no obstruction between photocells 38 and a light source such as shown in FlG. l. obstructing one or more beams from the light source to any photocell 38 produces an increase in photocell resistance, which in turn, produces a voltage rise at the bases 40 of the Siiicon-Darlington amplifiers 42, which are attached to any particular photocell 38 which may be obstructed. The voltage rise at any Silicon-Dariington amplifier base 40 turns on Silicon-Darlington amplifiers 42, causing a current flow through resistors 54 and 56. The current flow through resistor 56 lowers the voltage at the base 58 of Silicon-Darlington amplifier 60 below the voltage produced at Silicon-Dariington amplifier emitter 62 by a voltage division network consisting of resistor 64 and resistor 66, thereby turning on Silicon- Dariington amplifier 60 and producing a rise in voltage across resistor 68 and at the base 70 of Silicon-Darlington amplifier 72. Silicon-Darlington amplifier 72 switches on, de-energizing a coil 74 of a double-pole, double-throw relay 76. The de-energization of coil 74 causes contact group 78, 80, 82, which is interlocked with appropriate controls (not shown) of the machine to be guarded, to stop hazardous machine motion. Contact group 84, 86, 88 of the relay switches in such a way as to turn on an indicator light 90, warning that an obstruction exists in the hazard area, or to completely stop the machine, e. g., by means of a valve (not shown).
While the invention has been described in tenns of preferred embodiments, the claims appended hereto are intended to encompass all embodiments which fall within the spirit of the invention.
1. A photoelectric safety mechanism for machine operators comprising a plurality of photocells disposed at one side of a machine work area, a single source of light disposed on the opposite side of said work area for energizing said plurality of photocells, an OR-gate circuit electrically connected to said plurality of photocells and comprising a plurality of Darlington amplifiers, said photocells being responsive to said single source of light and controlling the current flow in said OR-gute circuit, said OR-gate circuit being responsive to and actuated by interruptions in one or more beams projected from said light source, said one or more beams being coilimated to said photocells by a plurality of slots in a member, each slot. being associated with a single one of said photocells, and means connecting said OR-gate circuit controlling the stopping and starting of said machine, and means being operable to pre vent injury to an operator of said machine by said machine in response to said interruption of said one or more-beams.
2. The safety mechanism of claim 1 wherein the OR- gate circuit comprises a plurality of Silicon-Darlington amplifiers whereby an input signal results from a change of resistance which causes a change of voltage upon said interruption of one or more beams, said interruption of said one or more beams causing a decrease in the light energy which impinges on said one or more photocells, said decrease increasing the resistance of said one or more photocells and causing an increase in the voltage across said one or more photocells, thereby causing an increase in the input voltage of said plurality of Silicon-Darlington amplifiers and causing said Silicon-Dariington amplifiers to stop operation of said machine.
3. The safety device of claim 2 wherein a switch automatically stops the operation of the machine upon receipt of a signal of said increase in the input voltage of said plurality of Siiicon-Darlington amplifiers.
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