JPH0329324B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention includes a plurality of pairs of light emitters and light receivers,
Repeats a scan that individually detects whether the light from each pair of emitters to the receiver is blocked with a small time difference, and converts the multiple detection signals obtained from the scan into serial signals. A multi-optical axis photoelectric switch that sequentially compares the detection signal with a threshold value and converts the detection signal into a binary signal that changes between high level and low level depending on whether it exceeds the threshold value and outputs the signal. In particular, the present invention relates to a multi-optical axis photoelectric switch with individual hysteresis that can individually apply hysteresis to each of the detection signals corresponding to the plurality of light receivers when converting the detection signal into a binary signal. .

Conventional technology A multi-optical axis photoelectric switch equipped with multiple pairs of emitters and receivers has conventionally been used as a safety device for processing machines or press machines, or as a device for detecting the presence or absence of an object on a conveyor line. It was generally used to detect the presence or absence of an object in a three-dimensional space. Therefore, in conventional multi-optical axis photoelectric switches, it is sufficient to judge whether or not all of the multiple optical receivers are in the light-receiving state at the same time, and output an output signal according to the judgment result. This is because the distance between the optical axes is sufficiently small compared to the size of the object whose presence or absence is being determined, and if an object exists, at least one of the optical axes will be completely blocked. , to determine whether each receiver is in the light receiving state,
It was sufficient to compare the light detection signals output from each light receiver with a uniformly set threshold.

Problems to be Solved by the Invention However, when this multi-optical axis photoelectric switch is used to detect the size and shape of an object, for example, to detect the height of an object being conveyed on a conveyor line, Unlike the case of a conventional multi-optical axis photoelectric switch for detecting the presence or absence of the object, it is necessary to individually recognize whether each light receiver is in a light receiving state. Therefore, as in the past, the detection signal output from each photoreceiver is compared with a uniformly set threshold value, and based on the comparison result, it is decided whether each photoreceiver is in the light receiving state or not. Then, when the optical axis is partially blocked and the detection signal output from the photoreceiver reaches a magnitude close to the threshold, the output signal representing the light receiving state of the photoreceiver will reverse in a short period of time. There is a problem that a stable output signal cannot be obtained repeatedly.

Therefore, it is conceivable to prepare two threshold values to be compared with the detection signal output from each light receiver, and to add hysteresis when converting each detection signal into a binary signal corresponding to the presence or absence of light reception. If hysteresis is added when converting each detection signal into a binary signal corresponding to the presence or absence of light reception,
Even if the optical axis is partially blocked and the detection signal becomes approximately the same size as one of the thresholds, the binary signal remains constant, and the signal remains stable depending on whether or not light is received from each receiver. An output signal can be obtained.

However, in the conventional multi-optical axis photoelectric switch for detecting the presence or absence of an object, one output line is provided for one optical axis, and the detection signal output from each photoreceptor ultimately determines the presence or absence of an object. Processing was performed in parallel until a judgment was made, so the configuration of the conventional multi-optical axis photoelectric switch was applied to a multi-optical axis photoelectric switch for detecting the size and shape of an object, and it was If you try to stabilize the output signal of each photoreceiver, you will need the same number of circuits to add hysteresis as there are optical axes, which increases the number of parts, increases the size of the device, and increases cost. I can't escape it.

Means for Solving the Problems As a result of various studies, the inventors have determined that:
Similar to the invention previously proposed in Japanese Patent Application No. 59-199190, the detection signals output in parallel from each photoreceiver are converted into time-division serial signals, and then the detection signals converted into serial signals are converted into We came up with the idea that if we were to apply hysteresis to each optical axis individually, it would be possible to use a circuit that provides hysteresis in common for each optical axis, which would solve the above-mentioned problems.

The multi-optical axis photoelectric switch with individual hysteresis according to the present invention was made based on such knowledge, and its gist is that it is provided with a plurality of pairs of emitters and receivers, and that each pair of emitters In addition to repeating a scan that individually detects with a minute time difference whether or not the light directed toward the receiver is blocked, the multiple detection signals obtained from the scan are converted into serial signals and sequentially detected. In the multi-optical axis photoelectric switch that compares the detection signal with a threshold value and converts the detected signal into a binary signal that changes between high level and low level depending on whether the detected signal exceeds the threshold value and outputs the binary signal, the scanning Accordingly, each time a photoreceiver that supplies a detection signal to be compared with the threshold value is switched, the binary signal corresponding to the detection signal from the photoreceiver is stored, and at the next scan, the received light is A storage means is provided for outputting the binary signal stored corresponding to the light receiver at the time of the previous scan when the detection signal from the receiver is compared with the threshold value. If the binary signal corresponds to a detection signal exceeding the threshold value during the previous scan,
Set the threshold to the lower of two thresholds of different heights; otherwise, set the threshold to the higher of those two thresholds. The present invention is characterized in that a threshold value changing means for setting a value is provided, thereby making it possible to individually apply hysteresis to each of the detection signals corresponding to the plurality of light receivers. In addition, here, 2
The lower threshold of the two thresholds refers to the threshold that has a level close to the level of the detection signal when the amount of light received by the light receiver is low, and the higher threshold is a threshold value having a level close to the level of the detection signal when the amount of light received by the light receiver is large.

Furthermore, when converting the plurality of detection signals into serial signals, the light receivers may be selectively activated, or the detection signals from the plurality of light receivers operating simultaneously may be selectively output in sequence. It's okay. In addition, if the light emitted from each emitter is received only by the receiver that is paired with the emitter, it is also possible to obtain a serial signal by operating the emitters in sequence. It is possible.

Functions and Effects According to such a multi-optical axis photoelectric switch with individual hysteresis, when the detection signals from each optical receiver are converted into binary signals, the circuit common to each optical receiver converts the detection signals into individual signals. hysteresis is added to. Therefore, it is possible to individually and stably output a binary signal indicating whether each light receiver is in a light receiving state while avoiding an increase in size and cost.

Moreover, in the present invention, the plurality of binary signals representing whether or not each light receiver is in the light receiving state are output as time-divided serial signals. If the power is supplied from the mounting part to the specified controller, it becomes unnecessary to provide a signal line for each optical axis, and compared to conventional multi-optical axis photoelectric switches, wiring, connections, and even connectors are required. It has the advantage of being simple. Note that the detection signal from each light receiver output as a serial binary signal is processed as is or converted into a parallel signal as necessary.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing the overall configuration of a multi-optical axis photoelectric switch for detecting the height of an object being conveyed on a conveyor line. As is clear from the figure, this photoelectric switch is composed of a light projecting section 10, a light receiving section 12, and a control section 14. It is being The light projector 10 includes a plurality of light emitting diodes as light projectors, as will be described in detail later, and the light receiver 12 includes the same number of phototransistors (or photodiodes) as light receivers. Light projector 1
The light emitting diodes 0 are arranged in a line vertically at regular intervals, and the phototransistors of the light receiving section 12 are provided at positions corresponding to the respective light emitting diodes. Therefore, if there is no light blocking object, the light emitted from each light emitting diode will be directed along optical axes 18 parallel to each other, as shown by the broken lines in FIG.
a, 18b, 18c, 18d along the light receiving section 12
The light from the light emitting diode is received by all the phototransistors. However, as shown by the two-dot chain line in the figure, those optical axes 18a to 18d
When an object 20 is conveyed by the conveyor 16 into a detection plane that includes
(here, the optical axis 18
c, 18d) is blocked, and the transistor corresponding to the optical axis from which the light is blocked does not receive the light, thereby making it possible to detect the height of the object 20.

The control unit 14 includes a power supply circuit that supplies power to the light emitter 10 and the light receiver 12 via a power line 22, and a serial signal sent from the light receiver 12 via a signal line 24, which is returned to a parallel signal and output. It is provided with an output section for outputting to lines 26a, 26b, 26c, and 26d. Further, the light projecting unit 10 is connected to the signal line 2
A synchronizing signal, which will be described in detail later, is supplied to the light receiving section 12 and the control section 14 via the control section 8. The light projecting section 10, the light receiving section 12, and the control section 14 are housed in separate cases, and the control section 14 and the light receiving section 12 are connected by a cord including a power line 22 and signal lines 24, 28. The light projector 10 and the light receiver 12 are connected by a cord including a power line 22 and a signal line 28.

Hereinafter, the configurations of the light projecting section 10, the light receiving section 12, and the control section 14 will be explained in order.

First, FIG. 2 shows the light projecting section 10. As shown in FIG. As is clear from this figure, the light projecting section 10 includes a synchronizing signal generating circuit 30, light emitting diodes 32a, 32b, 32c,
32d and the drive circuit 3 of those light emitting diodes
4a, 34b, 34c, and 34d. The synchronization signal generation circuit 30 includes an oscillation circuit, a ring counter, etc., and generates a synchronization signal and outputs it from a terminal 36, and sequentially outputs a drive signal synchronized with the synchronization signal to drive the light emitting diode drive circuits 34a to 3.
4d to cause the light emitting diodes 32a to 32d to sequentially emit light with a small time difference. FIG. 5 shows a timing chart of the signals output from these synchronization signal generation circuits 30. In addition, in FIG. 2, 38a, 38b, 38c and 38d are light emitting diodes 32a to 3, respectively.
This is a lens provided corresponding to 2d.

Next, the light receiving section 12 will be explained based on FIG. The light receiving section 12 includes phototransistors 40a, 40b, 40c facing each of the light emitting diodes 32a, 32b, 32c, and 32d of the light projecting section 10.
and 40d. Phototransistors 40a to 40d are light emitting diodes 32a to 32d.
When receiving the light from the , a positive detection signal having a magnitude corresponding to the amount of received light is outputted and supplied to the first stage amplifiers 42a, 42b, 42c and 42d, and the first stage amplifiers 42a to 42d output these detection signals. The signal is amplified and supplied to the analog multiplexer 44. And the analog multiplexer 44 is
The detection signals from the initial amplifiers 42a to 42d are selected according to the light emission times of the corresponding light emitting diodes 32a to 32d, and the detection signals from the initial amplifiers 42a to 42d are
Each detection signal from 44d is converted into a time-division serial signal and supplied to the waveform shaping circuit 46.

For this purpose, the multiplexer 44 has a counter 4.
8 is connected to the clock terminal of this counter 48.
CK and the clear terminal CL are connected from the terminal 36 of the light emitter 10 to the terminal 50 of the light receiver 12 via the signal line 28.
The synchronization signal supplied to the synchronization separation circuit 52 and the output signal of the synchronization separation circuit 52 are respectively inputted. The synchronization separation circuit 52 emits a high level signal when the time interval of input pulse signals exceeds a set value, and as shown in FIG. The time interval T ₁ between each pulse in one set of synchronization pulses is short, and the light emitting diode 32d
After the light emitting diode 32a is made to emit light, the light emitting diode 32a
The light emitting diodes _32a to 32d are 1
A clear signal is supplied to the clear terminal CL of the counter 48 each time the light is emitted. Further, the synchronizing signal is supplied to the clock terminal CK of the counter 48 via the inverting circuit 53. As a result, the contents of the counter 48 are incremented by 1 each time one of the series of light emitting diodes 32a to 32d is emitted, and when the last light emitting diode (in this embodiment, the light emitting diode 32d)
is cleared after the counter 48 emits light, and the analog multiplexer 44 controls each light emitting diode 32a to 3 based on the output signal of the counter 48.
Phototransistors 40a to 40 corresponding to 2d
The detection signal from d is selected and supplied to the waveform shaping circuit 46. For ease of understanding, the diodes from which the lines corresponding to each phototransistor 40a-40d are selected by analog multiplexer 44 are shown in FIG. Although in FIG. 3 the analog multiplexer 44 is shown as having contacts for ease of understanding, it is actually electronic and does not have contacts. Further, in FIG. 3, 54a, 54b, 54c, and 54d are lenses provided corresponding to the phototransistors 40a to 40d, respectively.

The waveform shaping circuit 46 mainly includes an operational amplifier 56, and an analog multiplexer 44.
The serial signal from the operational amplifier 56 is divided by a first resistor 58 and a second resistor 60.
It is designed to be supplied to the non-inverting input terminal of . Further, a signal from a shift register 62, which will be described later, is voltage-divided by a third resistor 64 and a second resistor 60 and supplied to a non-inverting input terminal of the operational amplifier 56. In other words, the resistors 58 and 6 are connected to the non-inverting input terminal of the operational amplifier 56.
The sum voltage of the serial signal voltage-divided by 0 and the signal from the shift register 62 voltage-divided by resistors 64 and 60 is applied.

On the other hand, the inverting input terminal of the operational amplifier 56 is supplied with a reference voltage obtained by dividing the power supply voltage by the fourth resistor 56 and the fifth resistor 68. The operational amplifier 56 sets the output signal to a high level when the added voltage applied to the non-inverting input terminal is higher than this reference voltage, and conversely sets the output signal to a low level when it is lower. . Note that in this embodiment, the resistors 66 and 6
The reference voltage set by 8 is 1/2 of the optical axis.
When the detection signal from the phototransistor is cut off, the voltage 1/2V ₀ divided by the resistors 58 and 60 and the high level from the shift register 62 (more precisely, from the inverting circuit 78 described later) The voltage is equal to the sum of the voltage ΔV divided by the resistors 64 and 60.

The signal output from the operational amplifier 56 is supplied to a reset terminal R of a reset flip-flop (hereinafter abbreviated as R-SFF) 70. Further, the synchronizing signal is input to the set terminal S of the R-S FF 70 via a differentiating circuit 72, and the signal from the output terminal Q of the R-S FF 70 is input to the data input of the shift register 62. The signal is supplied to the terminal D, and is also output from the terminal 76 via the output circuit 74.

The shift register 62 is of a serial input/parallel output type having the same number of memory sections as the photoreceiver (here, four stages), and converts the contents of the signal supplied to the data input terminal D into the pulse input to the clock terminal CK. At the same time, the content of each stage is shifted to the next stage, and if the content of the highest stage corresponds to the high level of the signal from R-S FF70, the contents of each stage are shifted to the next stage. A high-level signal is output from the output terminal Q ₄ corresponding to the highest stage, and the high-level signal is inverted by the inverting circuit 78 and sent to the non-inverting input terminal of the operational amplifier 56 via the third resistor 64 as described above. supply. Then, such a shift register 62
The synchronizing signal inverted by the inverting circuit 53 is input to the clock terminal CK of the clock.

On the other hand, the control section 14 includes an output section as shown in FIG. In this figure, 80 is a terminal connected to the terminal 76 of the light receiving section 12 by the signal line 24, and is a terminal connected to the terminal 76 of the light receiving section 12, and
The serial signal output from the shift register 82 is supplied to the data input terminal D of the shift register 82 via this terminal 80. Also, 84 is the signal line 2
The synchronizing signal supplied to this terminal 84 is inverted by an inverting circuit 86 and supplied to a clock terminal CK of a shift register 82.

The shift register 82 has the same structure as the shift register 62 of the light receiving section 12, and therefore the storage section of each bead of this shift register 82 stores the same contents as the contents stored in each stage of the shift register 62. The contents are memorized. For example, if the highest stage of the shift register 62 stores contents corresponding to the detection signal from the phototransistor 40a, the highest stage of the shift register 82 also stores contents corresponding to the detection signal from the phototransistor 40a. It will be done. Then, the contents stored in each stage of this shift register 82 are transmitted to output terminals Q ₁ , Q ₂ , Q 3 and Q ₃ provided corresponding to each stage.
From _Q4 to each input terminal A, B of data latch 88,
C and D are supplied in parallel.

Further, the synchronization signal supplied to the terminal 84 is also supplied to a synchronization separation circuit 90. This synchronization separation circuit 90 is similar to the above-mentioned synchronization separation circuit 52, and emits a high-level signal of a certain width after a certain period of time after being supplied with a set of synchronization pulses, and sends this high-level signal to the data latch 88. Supplied to the strobe terminal STB.

The data latch 88 latches the signals input to each input terminal A, B, C, and D in response to the rise of the signal supplied to the strobe terminal STB, and holds the signals until the next latching operation is performed. be. Output terminal for each of these latched signals
It is designed to output from Q _A , Q _B , Q _C and Q _D. The signals output from each output terminal Q _A to Q _D of data latch 88 are supplied to output terminals 94 a, 94 b, 94 c, and 94 d via output circuits 92 a, 82 b, 92 c, and 92 d, respectively. It is designed to be outputted from output lines 26a to 26d connected to terminals 94d to 94d. The serial signal supplied to the terminal 80 is converted into a parallel signal and output. In this embodiment, as described above, since the data latch 88 latches in response to the rise of the high level signal output from the synchronization separation circuit 90, the respective output lines 26a to 26d output a photo signal. Output signals corresponding to transistors 40d, 40c, 40b and 40a are output.

In such a multi-optical axis photoelectric switch, as shown in FIG. Of the light emitted from the light emitting diodes 32a and 32b, only the light emitted from the light emitting diodes 32a and 32b is received by the light receiving unit 12, and the light emitted from the light emitting diodes 32c and 32d is completely blocked by the object 20. think. In this case, as shown in FIG.
Each time the light is emitted, a high level (voltage V ₀ ) detection signal is output with a slight delay after the light is emitted.
These signals are converted into time-division serial signals from the analog multiplexer 44 and output.
Note that low level detection signals are output from the photodiodes 40c and 40d.

By the way, when the optical axis is completely blocked or not blocked at all, the reference voltage applied to the inverting input terminal of the operational amplifier 56 and the signal voltage ΔV from the shift register 62 applied to the non-inverting input terminal are respectively Since it is set as described above, the height relationship of the detection signal from the phototransistor corresponding to the optical axis with respect to the reference voltage is constant regardless of whether or not the signal voltage ΔV from the shift register 62 is applied. Become. Therefore, in the above case, the output of the operational amplifier 56 becomes high level every time the detection signals from the phototransistors 40a and 40b are input, and becomes low level otherwise. Then, such a signal is input to the reset terminal R of the R-S FF70. On the other hand, since the synchronization signal differentiated by the differentiating circuit 72 as described above is input to the set terminal S of the R-S FF70, the R-S FF7
The signal output from the output terminal Q of 0 is as shown in FIG. The level state of such an output signal is stored in the shift register 62 in response to the fall of the synchronization signal. That is, in this case, the light emitting diode 3 based on one set of synchronization signals
At the stage when the series of light emission from 2a to 32d is completed, the highest stage and the previous stage of the shift register 76 store the low level contents corresponding to the high level detection signals from the phototransistors 40a and 40b, respectively, and the first stage The high level contents corresponding to the low level detection signals from the phototransistors 40d and 40c are stored in the next stage. In addition, the control section 1
4 shift register 82 also has shift register 62
The same contents are stored, and the contents are latched by the data latch 88, so that output signals corresponding to the phototransistors 40a-40d are outputted from the output lines 26a-26d, respectively, as described above. Furthermore, as is clear from the above description, in this embodiment, the shift registers 62 and 8
The high level content stored in 2 corresponds to the state in which the optical axis is blocked, and the content corresponding to low level corresponds to the state in which the optical axis is not blocked.

Next, in a state where the above-mentioned contents are stored in the storage section of each stage of the shift register 62,
Consider a case where the height of the object 20 increases and a portion occupying a little more than half of the optical axis corresponding to the phototransistor 40b is blocked. In this case, when the light emitting diode 32a emits light, the light is received by the phototransistor 40a without being blocked, so the operational amplifier 5
A detection signal similar to that shown in FIG. 8 is supplied to the non-inverting input terminal 6. On the other hand, at this time, the highest stage of the shift register 62 has R-S F based on the previous light reception by the phototransistor 40a.
Since the contents corresponding to the low level of the output signal of F.70 are stored, a voltage ΔV based on the output of the inverting circuit 78 is also applied to the non-inverting input terminal. Therefore, in this case, the voltage obtained by adding ΔV to the voltage V ₀ of the detection signal from the phototransistor 40a is compared with the reference voltage, as shown in FIG. The high level output of is supplied to the reset terminal R of the R-S FF70. As a result, as in the case described above, contents corresponding to the low level are stored in the shift register 62 in response to the detection signal from the phototransistor 40a.

Further, even when the light emitting diode 32b is caused to emit light, the voltage obtained by adding ΔV to the voltage of the detection signal from the phototransistor 40b is compared with the reference voltage, as in the case where the light emitting diode 32a is caused to emit light. However, in this case, as shown in FIG. 9, even if ΔV is added to the voltage of the detection signal, it becomes smaller than the reference voltage, so the output signal of the operational amplifier 56 becomes low level, and the R-S
Since no reset signal is input to the reset terminal R of the FF 70, the output signal of the R-S FF 70 is maintained at a high level. Therefore, this high level content is stored in the shift register 62 in response to the fall of the synchronization level.

Further, when the light emitting diodes 32c and 32d emit light, the contents of the highest stage of the shift register 62 are at a high level, so a high level signal is not output from the inverting circuit 78, and each phototransistor 40c and 40d The detection signals from the two are directly compared with the reference voltage. As a result, the operational amplifier 56 outputs a low level signal similar to the previous scan, and this causes the R-S F.
The high level contents corresponding to the output signal of F.70 will be stored in the shift register 62. In other words, through the series of detection scans described above, the contents of the shift register 62 are updated in accordance with the new detection state, and at the same time, the contents of the shift register 82 are updated.
The contents of each phototransistor 40 are also updated.
Output signals corresponding to the new contents are output from the output lines 26a to 22d corresponding to a to 40d.

On the other hand, consider a state in which the contents of the shift register 62 have been updated as described above, the height of the object 20 has become slightly lower, and approximately half of the optical axis corresponding to the light emitting diode 32b is blocked. In this state, when the light emitting diode 32b emits light, the voltage of the detection signal output from the phototransistor 40b becomes 1/2V ₀ , which is lower than the reference voltage by approximately ΔV, as shown in FIG. Therefore, when ΔV is added to the voltage of this detection signal, the output of the operational amplifier 56 becomes unstable due to fluctuations in the detection signal, but in this case, the highest stage of the shift register 62 has an R -S Since the contents corresponding to the high level of the output signal of the FF 70 are stored, the output of the inverting circuit 78 becomes a low level, and the voltage of the detection signal is directly compared with the reference voltage. Therefore, the output of the operational amplifier 56 is maintained at a low level, and the output becomes stable.
In other words, hysteresis is added to the detection signal output from the phototransistor 40b.

In addition, each light emitting diode 32a, 32c, 32
The operation based on the light emission of d is the same as in the previous scan, and therefore output signals having the same content as the previous time are output from each output line 26a to 26d.

Note that in the above description, the phototransistor 4
Although we have described the case where the amount of light received by the phototransistor 0b fluctuates, this also applies to the case where the amount of light received by other phototransistors fluctuates, and as is clear from this, this example In this case, hysteresis is individually applied to the detection signals output from each of the phototransistors 40a to 40b. Further, as is clear from the above description, in this embodiment, the shift register 62 is used as a storage means, and the operational amplifier 5
The waveform shaping circuit 46, which is mainly configured by the waveform shaping circuit 6, is used as the threshold value changing means, and the reference voltage applied to the inverting input terminal of the operational amplifier 56 has two modes that are relatively different from each other with respect to the detection signal. It is considered a threshold value.

Although one embodiment of the present invention has been described above, this is literally an illustration, and the present invention should not be interpreted as being limited to this embodiment.

For example, in the embodiment described above, the multi-optical axis photoelectric switch has been described as including the control section 14 that converts a serial signal into a parallel signal, but such a control section 14 is provided as necessary. Strictly speaking, the multi-optical axis photoelectric switch according to the present invention has a light projecting section 10 and a light receiving section 12.
It can be said that it consists of. Note that a circuit for converting a serial signal into a parallel signal can also be integrated into the case of the light receiving section 12. In this case, by connecting data latch 88 directly to shift register 62, a parallel signal can be obtained.

Further, in the above embodiment, a light emitting diode and a photodiode were used as the emitter and the light receiver, respectively, but it is also possible to use elements other than these, and the pair of the emitter and light receiver may also be used as in the above embodiment. The number of pairs is not limited to four, and may be changed as appropriate depending on the purpose.

Further, in the above embodiment, a serial input parallel output type shift register is used as the storage means, but it is also possible to use other types of shift registers such as a parallel input parallel output type. It is also possible to use other memory.

Furthermore, in the embodiment described above, while the reference voltage, which is the threshold value, is kept at a constant voltage value, the detection signal from each phototransistor is level-shifted based on the light reception state stored in the previous scan. Therefore, the threshold value was changed relative to the detection signal, and hysteresis was applied to each detection signal individually. It is also possible to provide hysteresis by directly changing the reference voltage. To do this, instead of inverting the signal output from the highest stage of the shift register 62 and supplying it to the non-inverting input terminal of the operational amplifier 56 in the embodiment described above, the signal is inverted without being inverted. The signal may be supplied to the inverting input terminal of the operational amplifier 56 via a resistor having a resistance value. Note that, contrary to the above case, even if the detection signal from each phototransistor is supplied to the inverting input terminal of the operational amplifier 56, and the threshold voltage is supplied to the non-inverting input terminal, the present invention still applies. It is possible to construct a photoelectric switch.

Further, in the above embodiment, the R-S FF 70 is interposed between the waveform shaping circuit 46 as a threshold value changing means and the shift register 62 as a storage means, so that the optical axis can be switched between the blocked state and the blocked state. High-level and low-level contents are stored in the shift register 62 depending on the state in which the signal is not stored, and a high-level signal is output from the highest stage of the shift register 62 when the contents are at a high level. However, by linearly storing the output of the waveform shaping circuit 46 in the shift register 62, the relationship between the stored contents of the shift register 62 and the optical axis cut-off state is reversed, and the memory corresponding to the optical axis unblocked state is created. The multi-optical axis photoelectric switch according to the present invention can also be constructed by causing the shift register 62 to output a high-level output signal when the content is present.

Further, in the above embodiment, the detection signal from each of the phototransistors 40a to 40d is output as a positive signal having a magnitude corresponding to the amount of received light, but the detection signal increases as the amount of received light increases. It may be a positive signal whose absolute value becomes smaller, or it may be a negative signal whose absolute value becomes larger as the amount of received light increases. However, in either case, the threshold value is set to a level close to the level of the detection signal as the amount of light received by each receiver increases, and the threshold value with which the detection signal is compared as the amount of light received decreases. It is necessary to set the level close to the level of the detection signal when the amount of received light is small. Note that in any of the above cases, the relative magnitudes of both thresholds to the detection signal can be changed as appropriate depending on the purpose.

Furthermore, in the embodiment described above, the serial signal supplied to the control unit 14 was output from the operational amplifier 56, but the shift register 6
It is also possible to output from 2.

Furthermore, in the embodiment described above, in order to detect the height of the object 20 being conveyed on the belt conveyor, a plurality of pairs of light emitters and light receivers are arranged in correspondence with each other in one plane with the belt conveyor 16 in between. The present invention was applied to a transmission-type multi-optical axis photoelectric switch, but the present invention also applies to a multi-optical axis photoelectric switch for detecting the shape of an object in a three-dimensional space,
The present invention can also be applied to a reflective multi-optical axis photoelectric switch in which a light projector and a light receiver are provided on the same side.

In addition, the specific circuit configuration of the waveform shaping circuit, etc.
Although not listed in detail, it goes without saying that the present invention can be implemented with various modifications, improvements, etc. without departing from the spirit thereof.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of a multi-optical axis photoelectric switch according to an embodiment of the present invention. 2, 3, and 4 are circuit diagrams showing details of the light projecting section, light receiving section, and control section in FIG. 1, respectively. FIG. 5 is a timing chart related to the light projecting section, and FIGS. 6 to 9 are timing charts related to the light receiving section. 10: Light projecting section, 12: Light receiving section, 14: Control section, 16: Belt conveyor, 18a, 18
b, 18c, 18d: optical axis, 20: object, 24:
Signal line, 32a, 32b, 32c, 32d: Light emitting diode (light projector), 40a, 40b, 40c,
40d: Phototransistor (light receiver), 44:
Analog multiplexer, 46: Waveform shaping circuit (threshold changing means), 52: Synchronization separation circuit, 5
6: Operational amplifier, 58, 60, 64, 66, 6
8: Resistor, 62: Shift register (memory means),
70: Reset flip-flop, 82:
Shift register, 88: data latch.

Claims (1)

[Claims] 1. A device comprising a plurality of pairs of light emitters and light receivers, and repeating scanning to individually detect with a minute time difference whether or not the light directed from each pair of light emitters to the light receiver is blocked; The multiple detection signals obtained through the scanning are converted into serial signals and sequentially compared with a threshold value, and the detection signals are set to high level or low level depending on whether or not they exceed the threshold value. A multi-optical axis photoelectric switch that converts and outputs a binary signal that changes in accordance with The above 2 corresponds to the detection signal from the photoreceiver.
In addition to storing the value signal, when the detection signal from the light receiver in question is compared with the threshold value in the next scan, the binary signal stored corresponding to the light receiver in the previous scan is outputted. On the other hand, if the binary signal outputted from the storage means corresponds to a detection signal exceeding the threshold value in the previous scan, the threshold values are threshold value changing means for setting the threshold value to the lower of two different threshold values, and otherwise setting the threshold value to the higher of the two threshold values. 1. A multi-optical axis photoelectric switch with individual hysteresis, wherein hysteresis can be individually applied to each of the detection signals corresponding to the plurality of light receivers. 2. The storage means is a shift register having the same number of stages as the number of light receivers, and the output signal of the highest stage is a binary signal supplied to the threshold value changing means. A multi-optical axis photoelectric switch according to scope 1.