Safety device

Abstract

A safety device (50) is provided with: a light projector (60) that emits a light beam (LB) at predetermined time intervals; a light receiver (70) that outputs a determination signal (Sd2) indicating whether or not a light receiving element (80) is detecting light; and a control unit (102). The control unit (102): determines whether or not the light receiving element (80) is detecting light on the basis of the determination signal (Sd2) output from the light receiver (70), for each periodically occurring period during which the light beam (LB) is not being emitted from the light projector (60); stops the operation of a processing machine (1) and stops the emission of the light beam (LB) from the light projector (60) when it is determined that the light receiving element (80) is detecting light; and then resumes the emission of the light beam (LB) from the light projector (60) and restores the processing machine (1) to an operable state when it is determined that the light receiving element (80) is not detecting light.

Description

Safety device 【0001】 This disclosure relates to a safety device. 【0002】 A bending machine (press brake) is equipped with a safety device that detects obstacles based on the presence or absence of interruption of a light beam. This safety device has a projector that projects a light beam (detection light) for detecting obstacles and a receiver that receives the detection light projected from the projector. When the detection light projected from the projector is not received by the receiver, the press brake determines that there is an obstacle in the monitoring area, that is, an abnormal state, and stops the processing operation. 【0003】 In the above-described safety device, a method of using a pulsed light beam that flickers at a predetermined period as the detection light is known. By adopting this method, (a) even when ambient light interferes, it is possible to distinguish between the ambient light and the detection light by utilizing the difference in the frequencies of the light beams, and (b) it is possible to monitor whether the light reception state of the detection light at the receiver remains stuck on the on side (light reception side) or the off side (light shielding side). 【0004】 Patent Document 1 describes a technique for accurately determining an abnormal state by each safety device even when the detection lights output from the projectors of two safety devices that project pulsed light beams of the same design interfere with each other at the receivers. 【0005】 Japanese Patent Application Laid-Open No. 2021-137868 【0006】 In the above-described safety device, when a single-color laser beam is used, "fluctuations" of the laser beam may occur depending on the usage environment. This "fluctuation" is a phenomenon in which a portion with a strong light intensity occurs due to refraction of the laser beam. 【0007】If the high intensity of the light generated by this "fluctuation" enters the safety device's light receiver as a disturbance, it can interfere with the monitoring process described in (b) above. For example, even if the light receiver is not actually stuck in the detection light state, it may be mistakenly recognized as stuck in the ON position. In this case, the system may determine that an abnormal condition has occurred in the press brake, causing it to stop and requiring a restart to resume operation, which can be inconvenient for the user. 【0008】 A safety device for managing the safety of a processing machine that performs a prescribed operation according to one or more embodiments comprises a light emitter that emits a light ray at predetermined time intervals, a light receiver that includes a light-receiving element and outputs a determination signal indicating whether or not the light-receiving element is detecting light, and a control unit. The control unit determines whether or not the light-receiving element is detecting light based on the determination signal output from the light receiver, for each period that occurs periodically during which no light ray is emitted from the light emitter. If the control unit determines that the light-receiving element is detecting light, it stops the operation of the processing machine and stops the emission of a light ray from the light emitter. If, after stopping the emission of the light ray, the control unit determines that the light-receiving element is not detecting light based on the determination signal output from the light receiver, it restarts the emission of a light ray from the light emitter and restores the processing machine to an operational state. 【0009】 According to one or more embodiments of the safety device, false detection of light other than the light beam output from the floodlight can be avoided, and the safety of the processing machine can be managed with high accuracy. 【0010】Figure 1 is a block diagram showing the configuration of a press brake to which a safety device according to the embodiment is applied. Figure 2 is a block diagram showing the configuration of a safety device according to the embodiment. Figure 3 is a flowchart showing the operation of the safety device when the press brake is in operation. Figure 4 is a timing chart showing the changes over time of various operating states of the equipment inside the press brake, which are recognized when a temporary fluctuation of the detection light occurs while the press brake is in operation. Figure 5 is a timing chart showing the changes over time of various operating states of the equipment inside the press brake, which are recognized when an abnormality occurs in the safety device while the press brake is in operation. 【0011】 The following describes the case where one or more embodiments of the safety device 50 are applied to the press brake 1 with reference to the drawings. The schematic configuration of the press brake 1 will be explained using Figure 1. The press brake 1 is a processing machine that performs a bending operation, which is a specified operation, on a plate-shaped workpiece (sheet metal) W using a pair of molds (punch and die). The press brake 1 comprises an upper table 10, a lower table 20, and a press brake control device 30. 【0012】 The upper table 10 holds the upper die, which is the punch 14. Specifically, an upper die holder (not shown) is attached to the upper table 10, and the punch 14 is mounted on the upper die holder. 【0013】 The upper table 10 is capable of moving up and down by the raising and lowering of actuators 11L and 11R, which are hydraulic cylinders located on the left and right sides. Each actuator 11L and 11R is equipped with a pump and a motor. The vertical position of the upper table 10 is detected by a position detection unit, such as a linear encoder (not shown). The position information detected by the position detection unit is supplied to the press brake control device 30. The actuators 11L and 11R are not limited to hydraulic cylinders; electric motors may also be used. 【0014】The lower table 20 is located below the upper table 10. The lower table 20 holds the die 24, which is the lower mold. Specifically, a lower mold holder (not shown) is attached to the lower table 20, and the die 24 is mounted on the lower mold holder. For example, the workpiece W is placed on the die 24. When the upper table 10 is lowered, the workpiece W is sandwiched and bent between the punch 14 and the die 24. 【0015】 The press brake control device 30 can be configured as an NC device. The press brake control device 30 raises or lowers the actuators 11L and 11R. The press brake control device 30 controls the vertical position of the upper table 10 based on position information detected by the position detection unit. When a safety signal off is supplied from the safety control device 100, as will be described later, the press brake control device 30 stops the lowering of the upper table 10 and interrupts the bending of the material by the press brake 1. 【0016】 The press brake 1 is further equipped with a safety device 50 that manages the safety of the press brake 1 by monitoring for the intrusion of foreign objects (intruders) other than the workpiece W into the protected area between the punch 14 and the die 24. The safety device 50 comprises a light emitter 60, a light receiver 70, and a safety control device 100. 【0017】 The floodlight 60 is mounted, for example, on the right side of the upper table 10 via an arm 15R. The floodlight 60 emits detection light (light beam) LB at predetermined time intervals so that it passes between the punch 14 and the die 24. 【0018】 The light receiver 70 is mounted, for example, on the left side of the upper table 10 via an arm 15L. The light receiver 70 is positioned opposite the light emitter 60. The light receiver 70 receives the detection light that has passed between the punch 14 and the die 24. 【0019】The safety control device 100 is a control device that controls the safety device 50. The safety control device 100 controls the light emitter 60 and the light receiver 70. Based on the information acquired from the light receiver 70, if the safety control device 100 determines that no foreign matter has entered the protected area, it supplies a safety signal ON (operation permission signal) to the press brake control device 30. On the other hand, if the safety control device 100 determines that a foreign matter has entered the protected area, it supplies a safety signal OFF (operation stop signal) to the press brake control device 30. 【0020】 The specific configuration of the safety device 50 will be explained using Figure 2. The light emitter 60 outputs a detection light LB. The detection light LB is, for example, a laser beam. The light emitter 60 includes a laser light source and a collimating lens that adjusts the beam emitted by the laser light source to a parallel state. 【0021】 The light receiver 70 comprises a light receiving element 80 and a determination unit 90. 【0022】 The light-receiving element 80 detects light with an intensity of a predetermined value or higher, including the detection light LB. When the light-receiving element 80 detects light with an intensity of a predetermined value or higher, it outputs a detection signal (electrical signal) Sd1. The detection signal Sd1 output from the light-receiving element 80 is output to the determination unit 90. The light-receiving element 80 can be composed of a photodiode or a two-dimensional image sensor. The two-dimensional image sensor is, for example, a CCD (Charge Coupled Device). 【0023】 The determination unit 90 determines, based on the detection result of the light-receiving element 80, whether the light-receiving element 80 is in a light-receiving state where it detects (receives) the detection light LB, or whether the light-receiving element 80 is in a light-shielding state where it does not detect the detection light LB. The determination unit 90 outputs a determination signal Sd2 indicating the determination result to the safety control device 100. 【0024】 In this embodiment, the light receiver 70 integrates the light receiving element 80 and the determination unit 90. However, the determination unit 90 may be provided outside the light receiver 70. For example, the determination unit 90 may be configured as part of the safety control device 100. 【0025】The safety control device 100 includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and an input / output (I / O) interface. The safety control device 100 controls the operation of the safety device 50 by having the CPU read various programs according to the processing content from the ROM, etc., load them into RAM, and execute the loaded programs. 【0026】 Functionally speaking, the safety control device 100 includes a light projection control unit 101 and a safety control unit 102. 【0027】 The light projection control unit 101 controls the light emitter 60 to control the detection light LB emitted from the light emitter 60. The light projection control unit 101 outputs a control signal Sc to the light emitter 60. The light emitter 60 turns on in response to the control signal Sc being turned on and turns off in response to the control signal Sc being turned off. 【0028】 The safety control unit 102 determines the safety status of the press brake 1 based on the determination signal Sd2 output from the determination unit 90 and the operating status of the press brake 1. Based on the determined safety status, the safety control unit 102 controls the state of the safety signal supplied to the press brake control device 30. The safety control unit 102 manages the safety of the press brake 1 by automatically stopping the press brake 1 according to the state of the safety signal. 【0029】 In this embodiment, the safety control device 100 is configured with a CPU or the like, and the safety device 50 is controlled by software processing. However, the safety control device 100 may also be configured with hardware circuits, and the safety device 50 may be controlled by hardware circuits. 【0030】 The basic operation of the safety device 50 according to this embodiment, which is light shielding monitoring, will now be explained. Light shielding monitoring refers to the operation of outputting detection light LB from the light emitter 60 and monitoring whether this detection light LB is shielded from light. 【0031】Prior to light shielding monitoring, the light emission control unit 101 starts the light emission process. When the light emission process starts, the light emission control unit 101 outputs a pulsed control signal Sc that turns on and off at a predetermined frequency. The light emitter 60 flashes by emitting a detection light LB of a predetermined frequency at predetermined time intervals in response to the on / off status of the control signal Sc from the light emission control unit 101. By flashing the detection light LB of the light emitter 60 in this way, the safety device 50 can recognize that there is no abnormality caused by the light receiving state of the light receiver 70 being stuck on the on side (receiving side) or off side (shielding side), and that the device is operating normally. 【0032】 The detection light LB output from the light emitter 60 passes between the punch 14 and the die 24 and is incident on the light receiving element 80 of the light receiver 70. When the light receiving element 80 receives the detection light LB of a predetermined frequency, it outputs a detection signal Sd1 corresponding to the intensity of the incident detection light LB. 【0033】 The determination unit 90 receives a detection signal Sd1 from the light-receiving element 80 in accordance with the duration of the light emission of the detection light LB. Based on the presence or absence of the detection signal Sd1 from the light-receiving element 80, the determination unit 90 determines whether the light-receiving element 80 is in a light-receiving state where it receives the detection light LB, or in a light-shielding state where it does not receive the detection light LB. 【0034】 Specifically, the determination unit 90 determines that a light-receiving state is in effect if the light-receiving element 80 receives the detection light LB and outputs a detection signal Sd1 of a predetermined voltage value or higher from the light-receiving element 80. The determination unit 90 then outputs a determination signal Sd2 indicating the determination result, which is "1" indicating that the detection light LB is not blocked. On the other hand, if the light-receiving element 80 does not receive the detection light LB and no detection signal Sd1 of a predetermined voltage value or higher is output from the light-receiving element 80, the determination unit 90 determines that a light-blocking state is in effect. The determination unit 90 then outputs a determination signal indicating the determination result, which is "0" indicating that the detection light LB is blocked. 【0035】The safety control unit 102 determines the safety status of the press brake 1 based on the determination signal Sd2 output from the determination unit 90 and the operating status of the press brake 1. Based on the determined safety status, the safety control unit 102 generates and outputs a safety signal (OSSD: Output Signal Switching Device) that determines whether or not to stop the lowering of the upper table 10. If the value of the safety signal is "1" (on), it indicates permission to continue the lowering of the upper table 10 without stopping the movement, and if the value is "0" (off), it indicates permission not to stop the lowering of the upper table 10. 【0036】 If the detection light LB is not blocked by an intruder such as a hand, the determination signal from the determination unit 90 will be "1" (on). In this case, the safety control device 100 outputs the value "1" as a safety signal. On the other hand, if the detection light LB is blocked by an intruder such as a hand, the determination signal from the determination unit 90 will be "0" (off). In this case, the safety control device 100 outputs the value "0" as a safety signal. When the safety control unit 102 outputs "0" as a safety signal, the press brake control device 30 stops the lowering of the upper table 10 and interrupts the bending of the material by the press brake 1. 【0037】 The safety control unit 102 monitors the light reception status of the detection signal Sd1 and determines whether the light reception status remains stuck on the ON or OFF side. Through this determination, the safety control unit 102 can detect a malfunction in the safety device 50. 【0038】 The operation of the safety device 50, along with a series of operations of the press brake 1, will be explained with reference to Figures 3 to 5. Figure 3 is a flowchart showing the operation of the safety device 50 when the press brake 1 is in operation. Figure 4 is a timing chart showing the changes over time of various operating states of the equipment inside the press brake 1, which are recognized when a temporary fluctuation in the detection light LB occurs while the press brake 1 is in operation. Figure 5 is a timing chart showing the changes over time of various operating states of the equipment inside the press brake 1, which are recognized when an abnormality occurs in the safety device 50 while the press brake 1 is in operation. 【0039】In the initial state, the light projection processing function of the light projection control unit 101 is in the ON state, that is, it is in a state where light projection processing is performed. While light projection processing is being performed, the light emitter 60 blinks by repeatedly turning on (emitting detection light LB) and turning off at predetermined intervals Pr, in accordance with the ON / OFF status of the control signal Sc output by the light projection control unit 101. 【0040】 Furthermore, in the initial state, the safety signal (OSSD) is ON based on the safety status of the press brake determined by the safety control unit 102, and the closing pedal (not shown) operation function for instructing the press brake 1 to perform a processing operation, specifically the operation to lower the upper table 10 when processing the workpiece W, is enabled and the closing pedal is held in the depressed position (ON state). 【0041】 On the other hand, when the light-receiving element 80 of the light receiver 70 detects the detection light LB emitted from the light emitter 60, it outputs a detection signal Sd1. In addition to detecting the detection light LB emitted from the light emitter 60, the light-receiving element 80 also outputs a detection signal Sd1 when it detects ambient light of an intensity exceeding a predetermined value due to fluctuations in the detection light LB, etc. 【0042】 Fluctuations in the detection light LB occur, for example, when the temperature of the mold (punch 14 or die 24) rises during the use of the press brake 1. This creates a difference in temperature between the mold and the air, causing the detection light LB to refract. As a result, some of the light is concentrated in a portion of the space, increasing its intensity. These fluctuations in the detection light LB are temporary and occur only when the emission of the detection light LB stops. 【0043】 The determination unit 90 determines whether the light-receiving element 80 is in a light-receiving state or a light-blocking state based on the presence or absence of a detection signal Sd1 output from the light-receiving element 80. When there is an output of the detection signal Sd1, the determination unit 90 determines that the light-receiving element 80 is in a light-receiving state and outputs "1" as the determination signal Sd2. When there is no output of the detection signal Sd1, the determination unit 90 determines that the light-receiving element 80 is in a light-blocking state and outputs "0" as the determination signal Sd2. 【0044】Regarding the process executed by the safety control unit 102 when fluctuations in the detection light LB temporarily occur during the execution of the above-described light projection process, it will be described with reference to FIGS. 3 and 4. The safety control unit 102 periodically determines whether light is detected by the light receiving element 80 based on the determination signal Sd2 sequentially output from the light receiver 70 for each light-off period during which the detection light LB is not emitted from the projector 60 (times t1, t2,... in FIG. 4). That is, the safety control unit 102 periodically monitors the determination signal Sd2 output from the light receiver 70 during the period when the detection light LB is not emitted from the projector 60 (times t1, t2,...). 【0045】 At times t1 and t2, since no light is detected by the light receiving element 80, a determination signal Sd2 of "0" is output from the determination unit 90, and the on state of the OSSD output is maintained. 【0046】 After that, when the light receiving element 80 detects light and the determination signal Sd2 continuously becomes "1" a predetermined number of times (step S1: YES), the safety control unit 102 switches the OSSD to the off state and outputs message information indicating to stop the operation of the press brake 1 from the connected display device (not shown) (steps S2, time t13). Here, since the operation of the closed pedal is invalid when the OSSD is in the off state, the press brake 1 does not operate. 【0047】 When the safety control unit 102 switches the OSSD to the off state, it stops the emission of the detection light LB from the projector 60 by turning off the light projection processing function of the light projection control unit 101 (step S3, time t13). Note that the safety control unit 102 may switch the OSSD to the off state after turning off the light projection processing function of the light projection control unit 101. 【0048】 Even after stopping the emission of the detection light LB, the safety control unit 102 periodically monitors the determination signal Sd2 sequentially output from the light receiver 70 and determines whether light is detected by the light receiving element 80 (times t14, t15,...). 【0049】If the reason the judgment signal Sd2 became "1" for a predetermined number of consecutive times was due to a temporary fluctuation caused by the detection light LB, this fluctuation disappears when the light emitter 60 is turned off. Once the fluctuation disappears, the light receiving element 80 no longer detects light, and thereafter the judgment unit 90 outputs a judgment signal Sd2 of "0". 【0050】 When the safety control unit 102 recognizes that the "0" judgment signal Sd2 has been output a predetermined number of times consecutively (time t16), it determines that the safety device 50 has returned to a normal state (step S4: YES), and restarts the light emission processing from the light emitter 60 by the light emission control unit 101 (step S5). 【0051】 Furthermore, when it is determined that the safety device 50 has returned to a normal state, the safety control unit 102 switches the OSSD output from the off state to the on state after a predetermined time has elapsed (time t21) since the OSSD output switched to the off state. When the safety device 50 returns to a normal state and the OSSD output switches to the on state, the pedal closing operation function becomes active. 【0052】 In response, when the safety control unit 102 detects that the operator has operated the closing pedal (step S6: YES, time t23), it outputs an instruction to erase the message information output in step S2. Also, since the OSSD output is ON, the operation of the closing pedal is valid, and when the closing pedal is operated, the press brake control device 30 starts the table operation, and the press brake 1 returns to its normal state (step S7). 【0053】Furthermore, the process executed by the safety control unit 102 when an abnormality occurs in the safety device 50 during the light projection process will be explained with reference to Figures 3 and 5. Similar to the case in Figure 4, when the processes in steps S1 to S3 are executed (time t43), if an abnormality occurs in which the light receiving state of the light receiver 70 is stuck on the ON side, in step S4 the safety control unit 102 determines that an abnormality has occurred in the safety device 50 because the judgment signal Sd2 of "0" has not been output for a predetermined number of consecutive times (step S4: NO, time t52), and outputs an alarm as an abnormality occurrence signal (step S8). In this case, the closed pedal remains in an invalid state, so even if the closed pedal is operated, this operation is not accepted, and the bending process is not executed. 【0054】 In the embodiment described above, the safety control unit 102 may be composed of two systems, a first control unit and a second control unit, and the determination signal Sd2 output sequentially from the light receiver 70 may be alternately acquired by the first control unit and the second control unit. 【0055】 In this configuration, the timing at which the OSSD to be judged in step S2 switches to the off state can be set as follows, for example: (1) When the first control unit or the second control unit acquires a judgment signal Sd2 of "1" a predetermined number of times consecutively. (2) When the cumulative value of the number of times the judgment signal Sd2 of "1" has been acquired by the first control unit and the second control unit exceeds a predetermined value. 【0056】 Furthermore, in this configuration, the timing at which the safety device 50, which is judged in step S4, returns to a normal state can be set, for example, as follows: (3) When the first control unit and the second control unit acquire a judgment signal Sd2 of "0" a predetermined number of times consecutively. 【0057】 By performing the processing as described above, the redundancy of the safety device 50 can be increased. 【0058】A safety device 50 for managing the safety of a processing machine 1 that performs a prescribed operation according to one or more embodiments comprises a light emitter 60 that emits a light beam LB at predetermined time intervals, a light receiver 70 that includes a light receiving element 80 that detects light and outputs a determination signal Sd2 indicating whether or not the light receiving element 80 is detecting light, and a safety control unit 102. The safety control unit 102 periodically determines whether the light receiving element 80 is detecting light based on the determination signal Sd2 output from the light receiver 70 during periods when the light LB is not being emitted from the light emitter 60. If it determines that the light receiving element 80 is detecting light, it stops the operation of the processing machine 1 and stops the emission of the light LB from the light emitter 60. If, after stopping the emission of the light LB, it determines based on the determination signal Sd2 output from the light receiver 70 that the light receiving element 80 is not detecting light, it restarts the emission of the light LB from the light emitter 60 and returns the processing machine 1 to an operational state. 【0059】 This makes it possible to avoid false detections caused by light other than the light beam LB output from the light emitter 60, or by disturbances, and to accurately manage the safety of the processing machine 1. 【0060】 If the safety control unit 102 determines that the light receiving element 80 has detected light based on the determination signal Sd2 output from the light receiver 70 after stopping the emission of the light beam LB, it may output an abnormality signal. This allows for proper notification when an abnormality occurs in the safety device 50. 【0061】 The safety control unit 102 may periodically monitor the determination signal Sd2 output from the light receiver 70 during periods when the light ray LB is not being emitted from the light emitter 60, and if it recognizes that the light receiving element 80 has detected light for a predetermined number of consecutive times, it may determine that the light receiving element 80 has detected light. This allows the light detection process by the light receiving element 80 to be executed with high accuracy. 【0062】The specified operation is bending, meaning that the processing machine 1 may be a bending machine. The safety control unit 102 may stop the operation of the bending machine 1 by disabling the processing operation instruction to the bending machine when stopping the emission of the light beam LB from the light source 60, and restore the bending machine 1 to an operational state by re-enabling the processing operation instruction to the bending machine 1 when restarting the emission of the light beam LB from the light source 60. This allows for management to ensure that the bending machine 1 can be operated safely. 【0063】 The safety control unit 102 is composed of two systems, a first control unit and a second control unit, and the determination signal Sd2 output sequentially from the light receiver 70 may be acquired alternately by the first control unit and the second control unit. The safety control unit 102 may stop the emission of the light beam LB from the light emitter 60 and stop the operation of the processing machine 1 when the first control unit or the second control unit acquires the determination signal Sd2 indicating that the light receiving element 80 is detecting light a predetermined number of times consecutively, or when the cumulative value of the number of times the first control unit and the second control unit have acquired the determination signal Sd2 indicating that the light receiving element 80 is detecting light exceeds a predetermined value. 【0064】 The safety control unit 102 may restart the emission of the light beam LB from the light emitter 60 and restore the processing machine 1 to an operational state when the first control unit and the second control unit acquire a determination signal Sd2 indicating that the light receiving element 80 is not detecting light for a predetermined number of consecutive times. This allows the redundantly configured safety device 50 to properly perform the light detection process by the light receiving element 80. 【0065】 In the above-described embodiment, an example was given in which the safety device 50 avoids false detection of an abnormality when the light reception state of the detection light LB in the light receiver 70 is stuck on the ON side (receiving side), but the invention is not limited to this. For example, it can also be applied to false detection of an abnormality when a crosstalk failure occurs between multiple light receiving elements 80. 【0066】 The present invention is not limited to the one or more embodiments described above, and can be modified in various ways without departing from the spirit of the invention. 【0067】 The entire contents of Japanese Patent Application No. 2024-217427 (filing date: December 12, 2024), filed with the Japan Patent Office, are incorporated herein by reference.

Claims

1. A safety device for managing the safety of a processing machine that performs prescribed work, comprising: a light emitter that emits a light ray at predetermined time intervals; a light receiver that includes a light-receiving element for detecting light and outputs a determination signal indicating whether or not the light-receiving element is detecting light; and a control unit that periodically determines whether or not the light-receiving element is detecting light based on the determination signal output from the light receiver during periods when no light ray is emitted from the light emitter, and if it determines that the light-receiving element is detecting light, it stops the operation of the processing machine and stops the emission of the light ray from the light emitter, and if it determines that the light-receiving element is not detecting light based on the determination signal output from the light receiver after the emission of the light ray has been stopped, it restarts the emission of the light ray from the light emitter and restores the processing machine to an operational state.

2. The safety device according to claim 1, wherein the control unit, after stopping the emission of the light ray, determines that the light-receiving element has detected light based on the determination signal output from the light receiver, and outputs an abnormality signal.

3. The safety device according to claim 1, wherein the control unit periodically monitors the determination signal output from the light receiver during periods when no light rays are emitted from the light emitter, and determines that the light receiving element has detected light for a predetermined number of consecutive times.

4. The safety device according to claim 1, wherein the prescribed operation is bending, and the control unit stops the operation of the processing machine by invalidating the processing operation instruction to the processing machine when stopping the emission of light rays from the light emitter, and restores the processing machine to an operational state by re-enabling the processing operation instruction to the processing machine when restarting the emission of light rays from the light emitter.

5. The safety device according to claim 1, wherein the control unit is composed of two systems, a first control unit and a second control unit, and the determination signals output sequentially from the light receiver are alternately acquired by the first control unit and the second control unit, and the control unit stops the emission of light rays from the light emitter and stops the operation of the processing machine when the first control unit or the second control unit acquires the determination signals indicating that the light receiving element is detecting light for a predetermined number of consecutive times, or when the cumulative value of the number of times the determination signals indicating that the light receiving element is detecting light has been acquired by the first control unit and the second control unit exceeds a predetermined value.

6. The safety device according to claim 5, wherein the control unit, when the first control unit and the second control unit acquire the determination signal indicating that the light receiving element is not detecting light for a predetermined number of consecutive times, restarts the emission of light rays from the light emitter and restores the processing machine to an operational state.

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