US 3704396 A
Photo-electric guard for machines, having a plurality of light sources and a corresponding plurality of photo-responsive devices. Each light source is powered by a modulated electric supply and is aimed at the corresponding one of the photo-responsive devices. The output of each photo-responsive device is reshaped and compared with the input to the light source, and any mismatch is effective to stop further machine operation.
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United States Patent Macdonald [s41 SAFETY DEVICE For: MACHINES  Inventor: John'L. Macdonald, Aurora, Ind.
 Assignees Cincinnati Incorporated, Cincinnati,
' Ohio 22 Filed: May 12,1971
21 Appl.No.: 142,620
 US. Cl. ..317/124, 250/220, 250/221,
, 317/127  Int. Cl. ..G02f l/28  Field of Search ..317/124, 127; 250/220, 221; 340/258 R, 258 B  References Cited UNITED STATES PATENTS 2,631,273 3/1953 Bagno ..340/258 B 3,181,035 4/1965 Adams etal ..317/127 1451 Nov. 28, 1972 3,370,284 2/ 1968 Bagnoa ..250/221 X 3,612,884 10/1971 Linardos ..317/124 3,543,260 11/1970 Engh ..340/258 B 2,912,683 11/1959 Bagno ..340/258 B Primary Examiner-Mlliam M. Shoop, Jr. Assistant ExaminerHarry E. Moose, Jr. Attomey--Me1vil1e, Strasser, Foster and Hoffman 57 ABSTRACT Photo-electric guard for machines, having a plurality of light sources and a corresponding plurality of photo-responsive devices. Each light source is powered by a modulated electric supply and is aimed at the corresponding one of the photo-responsive devices. The output of each photo-responsive device is reshaped and compared with the input to the light source, and any mismatch is effective to stop further machine operation.
13 Claims, 3 Drawing Figures PATENTEO Km 28 1912 SHEET 1 BF 2 ATTORNEYS PATENTEUK 3. 704,396
' sum 2 or 2 III'" Fin: 3
lNVENTOR/S JOHN L. MACDOA/ALQ ATTORN EYS SAFETY DEVICE FOR MACHINES BACKGROUND OF THE INVENTION This invention relates generally to a safety device for a variety of machine tools, and particularly to a photoelectric safety device adapted for use with presses and the like having a reciprocating ram.
Ram type machines of the type here under consideration have always presented a potential safety problem by virtue of the severity of the injury to personnel during the downward stroke of the machine cycle. This long extant safety problem is compounded by therapid advance of machine tool technology and particularly advanced control technology.
Mechanical guarding mechanisms are very difficult to apply, in large part because of the material handling problems and the ability of such machines to utilize different dies and the like and/or sizes of material. It is generally recognized by the skilled worker in the art that a guarding system which has to be removed or changed with every new setup will often be omitted or improperly installed and adjusted.
Other safety assists such as palm buttons or pull out devices for the operator are widely used, but these devices may not always be used during die changes or parts tryouts. In addition, they do not protect a third person such as a material handler or a supervisor who may also be in a hazardous area. I
The art has also attempted to utilize photo-electronic safety devices. Generally speaking, all such photo-electronic safety systems utilize a light source which is focused on a photo-electronic cell or receiver. Often, a plurality of light sources and photo-electronic receivers are arranged in parallel rows to define a curtain adjacent the hazardous area. If the transmitted light is blocked or is not received by the photo-electronic receiver, a signal is, produced which will instantly stop the machine.
Photo-electronic guard systems of the type now known suffer from several serious disadvantages. In the first place, all known systems are particularly susceptible to changes in ambient lighting. The ambient lighting problem is particularly acute in the case of machine tools which are-operated 24 hours a day. Specifically, if
the ambient light increases in a particular situation (such as daybreak), a condition can arise in which the operator could break the transmitted light curtain without affecting the output of the photo-electronic receiver. The potential dangerof such a condition should be obvious.
The problem of changes in ambient lighting may in part be alleviated by the provision of manual sensitivity adjustments. Experience with such systems has shown that the machine tool operator must spend valuable device rather than through which the operator could put his hand or arm without interrupting thelight on the correspondin photo-electronic receiver. 1
Bearing the foregoing comments in mind, it is an ob-. ject of this invention to provide a photo-electronic safety 'devicewhich will fully protect the operator and other personnel without decreasing working efficiency.
A more specific object of the invention is to provide a photo-electronic guarding system which does not require sensitivity adjustments for changes in ambient lighting conditions. a
It is another object of the invention to provide a photo-electronic guarding system which includes a logic control circuit for monitoring machine control functions as well as the output of the photo-electronic receivers. I
Still a further object of the invention is to provide a photo-electronic guarding system of fail no-fault design; that is, a system in which any malfunction in the system or associated circuitry will immediately shut down the machine.
SUMMARY OF THE INVENTION In its broadest terms, this invention contemplates a plurality of light sources and a corresponding number of photo-electronic responsive devices arranged to guard the danger zone of a machine tool. Each light source is powered by a modulated electric supply, effective to modulate the intensity of the light emitted by the light sources. The resulting output of the photoelectronic receivers is reshaped to compensate for variations introduced by the incandescent light sources, and the output is compared with the modulated supply. In the event there is any mismatch or lack of identity between the two signals, the machine tool will be stopped immediately. a
The logic control circuitry associated with the guard ing system, in addition to monitoring the comparisons briefly noted above, will also monitorv a variety of specific machine functions.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic, block diagram of the photoelectronic guarding system of this invention.
FIG. 2 is an electrical schematic diagram showing the automatic ambient light adjust, amplifier and wave reshaper associated with each photo-electronic receiving device.
FIG. 3 is an electrical schematic view showing the matrixing and comparing circuitry.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, the general arrangement of components and method of operation will be described. A square wave generator is indicated generally at 10. For present purposes, the square wave generator 10 puts out two square wave outputs out of phase. These outputs are indicated in the drawing as Phase A and Phase B.
The transmitter stand indicated generally at 12 includes a plurality of incandescent light sources 14a through 14g. It will of course be understood that any desired number of light sources may be utilized, and that the light sources may be arranged in any desired pattern. For example, the light sources may be arranged'to define a curtain which may be either horizontally or vertically arranged, depending on a variety of conditions.
The Phase A and Phase B outputs of the square wave generator are connected to alternate lamps in parallel. Specifically, Phase A output is connected to the lamps 14b, 14d, and 14f, while the Phase B output is connected to the lamps 14a, 14c, 14 e, and 14 g.
The transmitter stand 12 also includes a lens 16 for each of the light sources 14a through 143, by means of which the illumination of the respective lamps may be focused on a corresponding photovsensitive receiver.
The receiver stand indicated generally at 18 includes a photo-electronic receiver 20a through 20g corresponding in position and arrangement to the light sources 14a through 14g. Each of the photo-electronic receivers 200 through 20g is provided with a lens 22 for focusing the respective light beam.
The receiver stand also includes an amplifier and wave shaper 24 for each of the. photo-responsive devices 20a through 20g. The circuitry for the amplifier and wave shaper is shown in FIG. 2 and will be described in more detail hereinafter. For present purposes, it will be understood that since the light sources 14a through 14g are incandescent, the intensity of the emitted light will not be a perfect square wave; it will however, vary at the same rate as the input square wave. The amplifier and wave shaper 24 is designed to reshape the modulated output of the photo-electronic receivers 20a through 20g into a square wave.
The matrixing and comparing circuit indicated generally in FIG 1 at 26 is shown in more detail in FIG. 3. It will be seen that the matrixing and comparing circuit 26 receives the outputs from all of the amplifier and wave shapers 24; the circuitry combines all like phase outputs and compares them with the output of the same phase from the generator 10. When they compare correctly, there will be an output pulse for each cycle of each phase from the circuit 26.
The digital outputs for each phase from the matrixing and comparing circuit 26 is fed to the three timing circuits indicated in FIG. -1 at 28, 30 and 32. The circuits 28 and 30 are identical, and are arranged to measure the spacing of the digital pulses from the matrixing and comparing circuit 26. The timing circuit 32 measures the duration of each pulse from both digital phase outputs. A change in the output of any one of the timing circuits 28, 30 and 32 could be used with a nand gate to actuate the machine cycle relay 34, thereby stopping the machine instantly.
It will be recognized by the skilled worker in the art that the photo-electronic guarding system, as thus far described, will be effective during the entire machine cycle. In many applications, this is not desirable. In the first place, it is only the down stroke of the ram which presents a substantial safety problem; there is relatively little danger to the operator or other personnel during the up stroke. In this connection, it is common practice for an operator to enter the danger zone during the ram return stroke, as, for example, to remove a finished piece, to adjust the workpiece for a subsequent stroke, and the like. It is desirable that the machine operation not be stopped by these actions of the operator. Secondly, in the specific case of a press brake, the bending or forming portion of the cycle at the bottom of the downward stroke will generally lift the edge of the workpiece upwardly into a position where it may block the transmitted light signal. It will be obvious that this action of the workpiece should not stop further machine operation.
Thus, it is possible to add to the circuitry described above provision for muting or rendering inoperative the photo-electronic guarding system during specified portions of the machine cycle.
To this end, a matrixing and muting circuit 36 is interposed between the outputs of the timing circuits 28, 30 and 32, and the machine cycle relay 34.
Muting of the photo-electronic guarding system is controlled, in the embodiment shown, by either the manual key select switch 38 or the mute cam switch 40. These switches, along with the others to be described hereinafter, are connected to an AC input to digital converter 42. The AC input to digital converter will change the input signal to digital pulses. It may consist of a transformer, full wave rectification, a resistor divider network, filter network, and a group of nand gates used in a Schmidt trigger circuit.
Digital signals representing the position of the key select switch 38 and the mute cam switch 40 will be transmitted from the AC input to digital converter 42 to the mute control circuit 44; the output of the mute control circuit 44 may go to both the matrixing and muting circuit 36, as well as to a visual guard off sign 46.
The input to the matrixing and muting circuit 36 will mute or prevent actuation of the machine cycle relay, even though the other input to the matrixing and muting circuit 36 would indicate an interruption in the transmitted light.
The guard off sign 46 is a visual indication to the operator that the photo-electronic guard system is not in operation. The sign may include a translucent face plate having appropriate lettering on the back side, so that the lettering is not visible unless the internal lights are on. Thus, an operator will instantly know whether or not the photo-electronic system is in operation. Operation of the guard-off sign 46 is monitored. Failure of guard-off sign 46 to indicate an unguarded condition will result in actuation of machine power relay 58, shutting down the machine until repairs are made.
It will be recalled that early in this specification, reference was made to the utilization of the logic control circuits of this invention for monitoring a variety of machine control functions. The embodiment illustrated in FIG. 1 shows schematically the top dead center cam switch 48 and the overrun cam switch 50. In ordinary operation, the top dead center cam switch is utilized to stop the machine tool after each complete cycle. In other words, this switch should be effective to stop the ram at its top dead center position following each up stroke. The overrun cam switch 50 is, in effect, a check on the adjustment of the press. In other words, upon actuation of the top dead center cam switch 48, the ram should stop at its top dead center position. Through wear and/or lack of proper adjustment, the ram may overrun its top dead center position. The overrun cam switch 50 is arranged to detect a condition wherein the overrun is outside of normal tolerance limits.
As seen in FIG. 1, both the top dead center cam switch 48 and the overrun cam switch 50 are connected to the AC input to digital converter circuit 42. Actuation of the top dead center cam switch 48 is effective to trigger a one shot 52. The pulse from the one shot 52 triggers a secondone shot identified in FIG. 1 as the overrun check 54. The pulse from the one shot 52 also actuates the alternate phase non-repeat circuit 56. It will be seen that the Phase A and Phase B output of the square wave generator are connected to the lamps 14f and 14g across the alternate phase non-repeat circuit 56. The alternate phase non-repeat circuit 56includes flip-flops and gating circuitry effective so that the pulse from the one shot 52 will alternately interrupt the Phase A or Phase B input to the lamps 14f and 14g respectively for. the period of that pulse.
It will be apparent to the skilled worker in the art that an interruption in the supply to one of the lamps 14f or 14g will mean that the corresponding photo-responsive device f or 20g receives no modulated light signal. This in turn will mean that the output of one of the amplifier and wave shapers 24 will not match the input in the matrixing and comparing circuit 26, so that its out put will cause a change in output of one of the timing circuits 28, 30, and 32, acting through the matrixing and muting circuit 36 to actuate the machine cycle relay, stopping the machine.
It will also be noted that the output pulse from the one shot 52 is delivered to the mute control circuit 44 which will trigger a flip-flop to reset the circuit to the non-muting position.
The overrun check 54, as already indicated, is a second one shot which produces a pulse of a specified time duration. This pulse is used to measure the stopping time of the ram at top dead center. If the overrun cam 50 is depressed before the period of the overrun check 54 elapses, a signal will be transmitted to the machine po-wer relay 58 preventing further operation of the machine until the necessary period has elapsed.
It will also be observed in FIG. 1 that the top dead center cam switch 48 and the overrun cam switch 50 are used to check each other. That is, an output from the AC input to digital converter indicating the position of each of the switches is transmitted to the switch occurrence check 60. If either cam switch fails, the output of the switch occurrence check 60 to the machine power relay 58 will stop the machine. 1
Preferably, each of the two switches 48 and 50 are checked twice during an individual machine cycle.
Referring now to FIG. 2, an electrical schematic diagram is given which shows in more detail the amplifier and wave shaper 24 generally described above. It is this circuitry which, in addition to amplifying and reshaping the received light signal, automatically adjusts for changing ambient light conditions.
A photocell is indicated at 70, and is connected on one side to a suitable source of direct current. It will be recognized that the signal lead 72 of the photocell will have a varying DC voltage, depending upon the light intensity received by the photocell 70. As indicated earlier, there will be the rapid variations in intensity caused by the modulated light source, as well as more gradual changes in ambient lighting conditions. Ambient light causing gradual changes of voltage at signal lead 72 of the photocell 70 is monitored by the ambient light correction circuit, including resistors 74, 76 and 78, capacitors 80 and 82, and transistor 84, which is a time delayed negative feedback path which maintains an average voltage at photocell signal lead'72. This time delay circuit responds only to gradual changes in ambient light and not to the rapidly changing modulated light. Both the corrected ambient light signal voltage and the rapidly modulating light signal voltages appearing at signal lead 72, are applied to resistors 86 and 94,
which are input paths to the operational amplifier 92. Input path of resistors 86 and 88 and capacitor 90 comprises a time delay circuit which blocks rapidly changing modulated light voltages and responds only to the gradual change of ambient light. Input path through resistor 94 responds to both ambient light and modulated light. The operational amplifier inputs have a signal difference of only the rapidly modulating light.
The output of the operational amplifier 92 is connected across the resistor 96 to the base of the power transistor 98. The combined effect of the operational amplifier 92 and power transistor 98 is to reshape the output of the photocell 70 into a square wave. In other words, an incandescent light source is incapable of generating a true square wave output; hence, the signal received by the photocell 70 might be described as a rounded square wave. The combined high gain of the operational amplifier and the transistor 98 serves to reshape the wave and give a square wave output at the terminal 100.
FIG. 3 is an electrical schematic diagram showing the matrixing and comparing circuit indicated in FIG. 1 at 26. As already indicated, this circuit is designed to combine and compare all light phase outputs from the amplifier and wave shaper circuits 24 with the corresponding phase output from the square wave generator 10. When they compare correctly, there will be an output pulse for each cycle of each phase from this circuit.
FIG. 3 shows a matrixing and comparing circuit which will accommodate outputs from 16 amplifiers nand wave shapers as described above. The circuit includes two seventeen input NAND-gates, 102 and 104. The NAND-gate 102 is hard wired by the line 106 to the Phase A output of the square wave generator 10, The contacts 108 will be connected to the amplifier and wave shapers 24 associated with a light source energized by the Phase A supply. Similarly, the NAND- gate 104 is hard wired as at 110 to the Phase B output of the square wave generator 10, while the contacts 112 receive the output from the amplifier and wave shapers associated with the light sources energized by the Phase B supply. All inputs from the wave shapers of both phases are inverted by the inverters 1 14 and fed to the opposite NAND gate.
It will be recognized by the skilled worker in the art that the foregoing systems compares only lows. Each time there is a full and complete comparison, there will be an output pulse from the NAND gate. If any wave shaper 24 output stops in either the high or low state, one of the two NAND gates will not give an output.
No specific circuitry has been shown for the remaining components identified in FIG. 1. It is believed that in the light of the objectives to be accomplished as set forth earlier, development of the digital circuitry for obtaining the result is well within the purview of the skilled worker in the art.
While the described embodiment of the invention re-- lates to a guard system for a machine tool having a reciprocating ram, itwill of course be understood that it is equally applicable to any machine tool for other operation wherein an operating cycle, for safety reasons, should be interrupted upon the presence of personnel in a predetermined danger zone.
No limitations are to be inferred or implied from the foregoing exemplary embodiment, except insofar as specifically set forth in the claims which follow The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
l. A photo-electronic guard system for a machine comprising: i
a. at least one light source;
. b. means for supplying a modulated current to said light source to produce a modulated light signal;
c. a photo-responsive device arranged to receive said modulated light signal;
d. circuit means associated with said photo-responsive device for producing an output in response to said modulated light signal, said circuit means including a time delay feedback circuit whereby to maintain substantially constant potential across said photo-responsive device and prevent an output of photo-responsive device to ambient light changes;
e. comparator circuit means for comparing said output in response to said modulated light signal with said modulated current supply; and
f. means for stopping said machine at any time said output in response to said modulated light signal fails to match said modulated current supply.
-2. The guard system claimed in claim 1 wherein said means for supplying a modulated current to said light source comprises a square wave generator.
3. The system claimed in claim 2 wherein the frequency of modulation of said current is on the order of 500 cycles per second.
4. The guard system claimed in claim 1 including means for amplifying said output in response to said modulated light signal.
5. The guard system claimed in claim 1 including means for reshaping said response output in to said modulated light signal to eliminate variations introduced by said light source and to conform said response to said modulated current.
6. The guard system claimed in claim 1 wherein said comparator circuit means comprises means for receiving said response output in to said modulated light signal; means for receiving said modulated current; and means for producing an output pulse for each cycle in which said response and-said modulated current match.
7. The guard system claimed in claim 6 wherein said means for stopping said machine comprises means for receiving said output pulses from said comparator circuit means; and means responsive to a change in frequency or duration of said pulses to stop said machine.
8. The guard system claimed in claim 7 wherein said means responsive to a change in frequency or duration of said pulses includes a timing circuit adapted to receive and measure the spacing between said pulses; a
second timing circuit adapted to receive and measure the duratlon of each said pulse; each said timing circuit being adapted to produce a changed output in response to a predetermined change in input, said changed output being effective to stop said machine.
9. The guard system claimed in claim 1 including means for muting said guard system during a portion of the cycle of said machine.
10. The guard system claimed in claim 9 including means for indicating to an operator the period in which said system is muted.
11. The guard system claimed in claim 1 including means for automatically stopping said machine at a specified point in each cycle.
12. The guard system claimed in claim 1 wherein said means for stopping said machine at a specified point in each cycle comprises a circuit for interrupting the supply of current to at least one light source.
13. The apparatus claimed in claim 1 including logic circuit means for verifying the condition of machine controls prior to continuation of machine operation, and preventing continuation of operation in the event any such control does not function properly.
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