JP2004235959A - Multiple optical axis photoelectric switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiple optical axis photoelectric switch capable of more favorably eliminating a state in which an excessive quantity of light is incident at an optical receiver side. <P>SOLUTION: After optical projection timing of each of LEDs 2a to 2e, an optical reception control circuit 17 that is arranged in an optical receiver 5 of the multiple optical axis photoelectric switch detects that undershooting has occurred in a corresponding optical reception signal that is output from a preamplifier circuit 9 and corresponds to each of the LEDs. Specifically, an optical reception signal level that is output from the preamplifier circuit 9 is compared with reference data and is detected after a predetermined time has elapsed from the light projection timing of the corresponding LED 2. Then, based on the detected state, a regulating means 21 varies gain of the preamplifier circuit 9 so as to reduce an undershooting level occurring in the optical reception signal. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
SUMMARY OF THE INVENTION The present invention provides a multi-optical axis photoelectric converter which causes a plurality of light emitting means and light receiving means to sequentially perform light emitting and receiving operations, and detects an object by scanning an optical axis formed by each light emitting means and light receiving means. About the switch.
[0002]
[Prior art]
In general, a multi-optical axis photoelectric switch is often provided with an amplifier (amplifier) for amplifying a light receiving signal in order to improve light receiving sensitivity on the light receiving side. In that case, if the installation interval between the light emitter and the light receiver becomes shorter than the distance assumed in the specification, for example, the light receiving signal level may become too high, resulting in an excessively incident light state.
[0003]
When the light receiving side becomes over-illuminated, the coupling capacitor disposed inside the light receiving amplifier becomes overcharged, and when the light receiving signal amplified by the amplifier is output with a positive polarity, the light receiving signal An undershoot in which the signal level appears on the negative positive side with the output occurs. When an undershoot occurs, holes are created in the parallel movement characteristics and angle characteristics between the projector and the receiver, the interference prevention performance between each optical axis is reduced, and the maximum number of optical axes is reduced due to the limitation of the scan cycle. Or need to be done.
[0004]
In order to solve such a problem, Patent Literature 1 employs a configuration in which, when it is detected that the light receiving side is in an excessive light incident state, the gain is adjusted so as to reduce the amplification factor of the light receiving amplifier.
[0005]
[Patent Document 1]
Japanese Patent No. 3353016
[0006]
[Problems to be solved by the invention]
However, in Patent Document 1, since the excessively incident light state is detected based on the peak value of the output signal of the light receiving amplifier, the detection sensitivity tends to be too sensitive, and the following problem may occur. there were. For example, even if the light emitter or light receiver is slightly displaced due to vibration or the like, an over-light state may be detected, and the amplification factor of the light-receiving amplifier is excessively reduced despite the originally normal light-receiving state, The light emission signal cannot be received and the light blocking state is detected.
[0007]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a multi-optical axis photoelectric switch capable of better eliminating the excessive light incident state on the light receiving device side.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a multi-optical axis photoelectric switch according to claim 1 includes: a light projector including a plurality of light projecting means;
A plurality of light receiving means arranged to face the light projector and respectively receiving the light emitted by the plurality of light emitting means; provided in correspondence with the plurality of light receiving means; output from each light receiving means; A light receiver comprising amplification means for amplifying a light reception signal,
A plurality of light projecting means and light receiving means for sequentially performing light emitting and receiving operations, and a light emitting and receiving control means for controlling to scan an optical axis formed by each light emitting means and light receiving means. At
The light receiver,
Excessive light detecting means for detecting that the level of the corresponding light receiving signal output from the amplifying means has changed to the opposite polarity side after the light emitting timing of each light emitting element,
Based on the detection state of the excessively incident light detecting means, at least one of the amplification factor of the amplifying means and the light emitting output level of the light projecting device side is adjusted so that the signal level of the light receiving signal on the opposite polarity side is reduced. An adjusting means for performing an adjusting operation by changing the adjusting means.
[0009]
That is, when the polarity of the amplified signal output from the amplifying unit appears in the opposite direction to the normal output state due to the excessively high light receiving signal level, the excessively incident light detecting unit directly detects the waveform state. Therefore, unlike the conventional method in which the over-light state is detected based on the level of the period during which the received light signal has the normal polarity, it is possible to reliably and stably detect the occurrence of the reverse polarity level in the received light signal. It becomes possible. Then, since the adjusting means performs the adjusting operation so that the reverse polarity level of the light receiving signal is reduced, the light receiving level can be adjusted favorably.
[0010]
In this case, it is preferable that the adjusting unit measures the time during which the level of the received light signal changes to the opposite polarity side and performs the adjusting operation based on the measured time. . That is, since the length of the measurement time has a correlation with the magnitude of the reverse polarity level of the received light signal, if the adjustment amount in the adjustment operation is set in accordance with the length of the measurement time, the light reception level adjustment can be improved. Can be performed.
[0011]
Further, in the above case, as described in claim 3, the excessive light detecting means is configured to change the level of the light receiving signal output from the amplifying means for a predetermined time from the light emitting timing of the corresponding light emitting element. Configured to detect an excessive light incident state by comparing with a reference level after elapse,
The adjustment means includes a storage means for storing at least one of an amplification factor of the amplification means and a light emission output level on the side of the projector, and the amplification factor or the projection rate is determined based on data stored in the storage means. Preferably, the adjustment operation is performed by changing at least one of the light output levels, and after the adjustment operation is completed, the data stored in the storage unit is updated.
[0012]
According to this structure, the excessively incident light detecting means can reliably detect the excessively incident light state based on the level of the light receiving signal output from the amplifying means. Since the adjusting means performs the adjusting operation based on the data stored in the storing means at each adjusting cycle, the amplification factor of the amplifying means is set so that the overshoot or undershoot generated in the light receiving signal is minimized. Alternatively, the light output level can be adjusted.
[0013]
Further, as set forth in claim 4, the adjusting means adjusts at least one of the amplification factor of the amplifying means and the light emission output level on the light emitter side in a lump for all light receiving elements or all light emitting elements. It is preferable to make it variable. With such a configuration, the configuration can be simplified and the time required for the adjustment can be reduced as compared with a configuration in which adjustment is performed for each optical axis.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. In FIG. 1 schematically showing an electrical configuration of a multi-optical axis photoelectric switch, a light projector 1 includes five LEDs 2a to 2e as a plurality of light emitting elements, and a light emitting control circuit (a light emitting / receiving control) including a microcomputer or the like. (Means) The light emitting circuit 4 causes the LEDs 2a to 2e to emit light sequentially based on the light emitting signal Sp from 3). On the other hand, the light receiver 5 is provided with five light receivers 6 a to 6 e corresponding to the LEDs 2 a to 2 e of the light projector 1.
[0015]
Each of the light receiving units 6a to 6e includes a series circuit of a photodiode 7 and a bias resistor 8 serving as a light receiving element connected between a DC power supply terminal VC and the ground, and a front end having an input terminal connected to a common connection terminal thereof. An amplifier circuit (amplifying means) 9 is provided. The photodiode 7 photoelectrically converts incident light, amplifies the converted weak electric signal by the preamplifier circuit 9, and outputs the amplified light signal as a light receiving signal. I have.
[0016]
The FETs 10a to 10e are provided corresponding to the respective light receiving units 6a to 6e, and the drain and source terminals thereof are connected in parallel with the resistor 8, and the gates are connected to the output terminals of the integration circuits 11a to 11e. . The input terminals of the integration circuits 11a to 11e are connected to the output terminals of the AND circuits 12a to 12e, respectively.
[0017]
The integration circuits 11a to 11e integrate the control pulse signal Sx supplied via the AND circuits 12a to 12e, and apply an integration voltage as an integrated value to the gates of the FETs 10a to 10e connected to the integration circuits. . Then, the FETs 10a to 10e change the conduction state between the drain and the source according to the value of the integrated voltage given to the gate, thereby changing the combined resistance value with the bias resistor 8 connected in parallel. Has become.
[0018]
The selection circuit 13 includes five analog switches 14a to 14e provided corresponding to the light receiving units 6a to 6e and five D-type flip-flops (hereinafter, referred to as DFFs) 15a to 15e. The light receiving circuit (light emitting / receiving control means) 16 includes a light receiving control circuit 17, a main amplifier circuit 18, a comparator 19, and an output circuit 21. The light receiving control circuit (excessive light detecting means) 17 is constituted by a microcomputer having a CPU, a ROM, a RAM, and the like, and stores a detection program described later in advance.
[0019]
Output terminals of the preamplifier circuit 9 in the light receiving units 6a to 6e are connected to input terminals of a main amplifier circuit 18 via analog switches 14a to 14e, respectively, and an output terminal of the main amplifier circuit 18 is connected to a comparator 19a. And the input terminal B of the light receiving control circuit 17. The input terminal B is connected to the input terminal of the A / D converter 20 arranged inside the light receiving control circuit 17.
[0020]
In this case, a voltage V1 corresponding to the detection level is set in the comparator 19 as a comparison reference voltage. Then, the comparator 19 supplies the “H” level detection signal Sa to the input terminal A of the light receiving control circuit 17 when the applied amplified output Vo exceeds the voltage V1. Also, the A / D converter 20 receives an input analog signal in both polarities and outputs a digital signal in, for example, an inverted offset binary format.
[0021]
One input terminal of each of the AND circuits 12a to 12e is connected to the gates of the analog switches 14a to 14e and connected to the output terminals Q1 to Q5 of the DFFs 15a to 15e, respectively. It is connected to the output terminal C of the circuit 17. The data input terminal D of the DFF 15a is connected to the output terminal D of the light receiving control circuit 17, and the data input terminals D of the DFFs 15b to 15e are connected to the output terminals Q1 to Q4 of the DFFs 15a to 15d, respectively. The clock input terminals CK of the DFFs 15a to 15e are connected to the output terminal E of the light receiving control circuit 17, and are supplied with the clock signal Sck.
[0022]
An input terminal F of the light receiving control circuit 17 is connected to an external input terminal P1, and a light emitting signal Sp as a synchronizing signal is given to the terminal P1 from an output terminal of the light emitting control circuit 3 via a synchronizing signal line. . The output terminal G of the light receiving control circuit 17 is connected to a terminal R via an output circuit 21 and supplies a detection signal Sz to a load circuit (not shown) via the terminal R.
Note that the FET 10, the integrating circuit 11, the AND circuit 12, the selecting circuit 13, and the light receiving control circuit 17 constitute an adjusting unit 21.
[0023]
Next, the operation of the present embodiment will be described with reference to FIGS. First, (1) the detection operation will be described. For the basic operation similar to that of Patent Document 1, the description will be simplified by clearly indicating the paragraph numbers in the specification, and only different parts will be described in detail. . FIG. 2 is a flowchart showing the contents of the detection operation and the sensitivity adjustment operation (detection program) performed by the light receiving control circuit 17, and FIG. 3 is a flowchart showing the contents of the detection routine which is step S3 in FIG. is there.
[0024]
FIG. 4 shows a case in which a light projection signal Sp (consisting of a start pulse Sp0 and five subsequent synchronization pulses Sp1 to Sp5) is supplied to the input terminal F of the light reception control circuit 17 from the light projection control circuit 3. 3 is a timing chart showing the timing of the signal output from the light receiving control circuit 17 and the accompanying signal output timing of the DFF 15. The light receiving control circuit 17 starts execution of the detection program when the light emitting signal Sp is given, and outputs a data pulse Sd and a clock pulse Sck from the output terminals D and E.
[0025]
First, the paragraph of Patent Document 1
[0033] ~
Since the operations up to this point are the same, an outline thereof will be described. The light projector 1 causes the light emission control circuit 3 to sequentially emit the LEDs 2a to 2e based on the light emission signal Sp. The light receiver 5 sequentially receives light by the light receiving units 6a to 6e corresponding to the five LEDs 2a to 2e, and inputs a signal photoelectrically converted by the photodiode 7 to the preamplifier circuit 9. The preamplifier circuit 9 amplifies the electric signal and outputs it as a light receiving signal.
[0026]
When receiving the start pulse Sp0 and starting the detection program, the light receiving control circuit 17 outputs one data pulse Sd from the output terminal D. Subsequently, the first clock pulse Sck1 is output from the output terminal E and supplied to the clock input terminals CK of the DFFs 15a to 15e. Then, only the DFF 15a outputs an “H” level signal from the output terminal Q1, and the analog switch 14a validates the light receiving signal from the light receiving section 6a and outputs it to the main amplifier circuit 18.
[0027]
The light receiving control circuit 17 selects the optical axis of the first channel of the light receiving section 6a as described above (step S1), and inputs the received light signal to the main amplifier circuit 18 (step S2). The light receiving control circuit 17 sequentially outputs the clock pulses Sck2 to Sck6 from the output terminal E in response to the synchronization pulses Sp1 to Sp5 given to the input terminal F, and receives the light receiving sections 6b to 6c corresponding to the optical axes of the second and subsequent channels. The selection operation of 6e is performed.
[0028]
Then, the main amplifier circuit 18 amplifies the light receiving signal input from the light receiving unit 6a and supplies the amplified output Vo to the comparator 19 and the input terminal B of the light receiving control circuit 17. As described above, the reference voltage V1 corresponding to the detection level is set in the comparator 19. When the level of the amplified output Vo exceeds the reference voltage V1, the comparator 19 outputs an "H" level light reception detection signal Sa.
[0029]
Further, the light receiving control circuit 17 refers to the output data of the A / D converter 20 and compares it with the reference data in an undershoot detection period following the detection timing of the light receiving signal. Then, it is determined whether an undershoot (that is, an excessive light incident state) has occurred in the light receiving signal waveform based on whether the output data exceeds the reference data on the negative side (see FIG. 5B). . Note that FIG. 5 shows a case where an excessive light incident state occurs when a light emission signal having a waveform as shown in FIG. 5A is output, and an undershoot occurs in a light reception signal waveform.
[0030]
In other words, while the amplitude level of the light receiving signal appears to have a positive polarity in the normal output state, the amplitude level swings to the positive side of the negative electrode, thereby causing an undershoot.
Here, in order to match the description of Patent Document 1, when an undershoot has occurred, it corresponds to "excessive light detection signal Sb is output".
[0031]
Subsequent operations are also basically the same as in the paragraph of Patent Document 1.
[0039]
The operation is the same as described above. That is, the light receiving control circuit 17 proceeds to the detection routine S3, and executes the detection routine program shown in FIG. The light receiving control circuit 17 determines whether or not the light receiving detection signal Sa is input from the comparator 19 in step R1, and if it is input, the process proceeds to step R2. If the light reception detection signal Sa has been input over one scan corresponding to five optical axes ("YES"), the light reception control circuit 17 proceeds to step R3 and outputs a light reception determination signal. On the other hand, when the light receiving control circuit 17 determines “NO” in step R1 or R2, the process proceeds to step R4 and stops outputting the light receiving determination signal.
[0032]
When the detection routine S3 ends, the light reception control circuit 17 proceeds to step S4 of the detection program shown in FIG. 2 again, and determines whether the excessive light detection signal Sb is input. If the light is properly input ("NO"), the process proceeds to step S5. If the optical axis for which the detection operation was performed in step S5 is not the last channel ("NO"), the process proceeds to step S6, and the light receiving unit 6b of the optical axis corresponding to the next channel is selected.
[0033]
In this case, the light receiving control circuit 17 outputs the clock pulse Sck2. Then, the DFF 15a outputs an “L” level signal to the output terminal Q1, and the DFF 15b outputs an “H” level signal to the output terminal Q2. As a result, an “H” level signal is given to the gate of the analog switch 14b, the light receiving signal output from the light receiving section 6b is validated and input to the main amplifier circuit 18. The light receiving control circuit 17 performs a detection operation in accordance with a detection program as described above. After the light receiving signal from the light receiving unit 6e is input to the main amplifier circuit 18 and its level is determined, if "YES" is determined in step S5, the detection operation for one scan is completed.
[0034]
(2) Automatic sensitivity adjustment operation during detection operation
Next, the sensitivity adjustment in the case where the level of the light receiving signal output from each of the light receiving sections 6a to 6e activated by the selection circuit 13 is high and the amount of light incident on each of the light receiving sections 6a to 6e is excessive (excessive light state). The operation will be described. In this case, since the data output from the A / D converter 20 exceeds the threshold value on the negative side, the light receiving control circuit 17 determines “YES” in step S4 after performing the above-described detection operation, Move to step S7.
[0035]
Then, the light receiving control circuit 17 immediately outputs the control pulse signal Sx from the output terminal C. At this time, the "H" level signal is still output from the output terminal Q1 of the DFF 15a, and the "H" level control pulse signal Sx is input to the input terminal of the integration circuit 11a via the AND circuit 12a. . The integration circuit 11a supplies an integration voltage according to the control pulse signal Sx to the gate of the FET 10a. The FET 10a in the off state changes the conduction state between the drain and source terminals by applying a bias to the gate.
[0036]
Then, since the conduction state of the FET 10a changes and the equivalent resistance value decreases, the combined resistance value in the parallel circuit with the bias resistor 8 also decreases. As a result, the bias voltage for the photodiode 7 decreases, and the light receiving sensitivity decreases.
[0037]
In the same manner, the light receiving control circuit 17 repeats the above-described operation at a substantially constant output frequency so that the level of the light receiving signal from the light receiving unit 6a does not exceed the excessively incident light level that causes overshoot. It becomes a steady state in which the control pulse signal Sx is output. Thereby, the light receiving control circuit 17 outputs the control pulse signal Sx at an output frequency corresponding to each of the light receiving units 6a to 6e, for example, and reduces the light receiving sensitivity to a substantially constant level less than the excessively incident light level. Control automatically.
[0038]
That is, the present embodiment differs from the first embodiment only in the method of detecting the occurrence of undershoot due to the received light signal. This is performed in the same manner as in Reference 1.
[0039]
As described above, according to the present embodiment, the light receiving control circuit 17 disposed in the light receiver 5 of the multi-optical axis photoelectric switch is configured to control the light output from the preamplifier circuit 9 after the light emission timing of each LED 2a to 2e. An undershoot is detected in the received light signal. Specifically, the level of the light receiving signal output from the preamplifier circuit 9 is detected by comparing it with reference data after a lapse of a predetermined time from the light emission timing of the corresponding LED 2. Then, the adjusting means 21 performs the adjusting operation by changing the amplification factor of the preamplifier circuit 9 based on the detection state so as to reduce the level of the undershoot generated in the light receiving signal.
[0040]
Therefore, unlike the conventional method in which the over-light state is detected based on the level of the period during which the received light signal has the normal polarity, it is possible to reliably and stably detect the occurrence of the reverse polarity level in the received light signal. It becomes possible. Since the adjusting means 21 performs the adjusting operation so that the reverse polarity level of the light receiving signal is reduced, the light receiving level can be satisfactorily adjusted to eliminate the excessive light incident state.
[0041]
Further, according to the method of directly detecting the occurrence of undershoot at a predetermined timing as described above, compared with the conventional method of detecting an excessively incident light state based on the level of a period in which a received light signal has a normal polarity. Thus, even if an inexpensive operational amplifier having a narrow amplification range and a small amplification factor is used as the preamplifier circuit 9, detection can be easily performed.
[0042]
(Second embodiment)
FIGS. 6 and 7 show a second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted. Only the different parts will be described below. FIG. 6 shows only a main part of the first embodiment corresponding to FIG. In the second embodiment, a comparator 31 for detecting a received light signal and a comparator (excess light detection means) 32 for detecting an undershoot are arranged between the preamplifier circuit 9 and the analog switch 14. At this stage, the signal is split into two systems.
[0043]
Then, the output signal DS1 of the comparator 31 is supplied to the input terminal A of the light receiving control circuit 17 via the analog switch 14 (and the main amplifier circuit 18). Therefore, the comparator 19 of the first embodiment is omitted. The output signal DS2 of the comparator 32 is supplied to the input terminal B of the light receiving control circuit 17 via the analog switch 33 (and an amplifier circuit (not shown) equivalent to the main amplifier circuit 18). The opening and closing of the analog switch 14 and the analog switch 33 (excess light detection means) are controlled by the output signal of the DFF 15 as in the first embodiment.
[0044]
Since the comparator 32 is for undershoot detection, the input / output voltage range is adjusted so that a high-level signal is output when the input signal level exceeds a negative threshold value.
Although not specifically shown, the A / D converter 20 arranged on the input terminal B side of the light receiving control circuit 17 in the first embodiment is also omitted.
[0045]
Next, the operation of the second embodiment will be described with reference to FIG. FIGS. 7A and 7B are the same as FIGS. 5A and 5B in the first embodiment. The light reception control circuit 17 detects light reception based on the output state of the output signal DS1 from the comparator 31 and outputs the output signal DS2 from the comparator 32 when the analog switches 14 and 33 corresponding to each optical axis open. Undershoot detection is performed depending on the state. That is, the light receiving control circuit 17 detects an undershoot based on whether the signal level of the input terminal B is “H”.
According to the second embodiment configured as described above, the same effects as in the first embodiment can be obtained.
[0046]
(Third embodiment)
FIGS. 8 and 9 show a third embodiment of the present invention. The same parts as those in the second embodiment are denoted by the same reference numerals, and description thereof will be omitted. Hereinafter, only different parts will be described. In FIG. 8 showing a main part of the electrical configuration, in the third embodiment, the analog switch 33 is deleted from the configuration of the second embodiment. The output terminals of the two comparators 31 and 32 are respectively connected to the input terminals of the OR circuit 34, and the output terminal of the OR circuit 34 is connected to the input side of the analog switch 14. Other configurations are the same as those of the first embodiment.
[0047]
Next, the operation of the third embodiment will be described with reference to FIG. When one of the light receiving signal output from the comparators 31 and 32 and the undershoot detection signal goes to the “H” level, the output terminal of the OR circuit goes to the “H” level. Therefore, as shown in FIG. 9C, when an undershoot occurs in the received light signal, the “H” level is indicated only for a period obtained by combining the output period of the normal received light signal and the undershoot occurrence period. A signal is output.
[0048]
That is, the light receiving signal output from the comparators 31 and 32 and the undershoot detection signal are shared by the OR circuit 34 and output to the input terminal A of the light receiving control circuit 17 as the signal DS1. Then, the light reception control circuit 17 refers to the input terminal A, and performs each detection of the signal DS1 in each of the light reception detection period and the undershoot detection period.
Also in the case of the third embodiment configured as described above, the same effects as in the first or second embodiment can be obtained.
[0049]
(Fourth embodiment)
FIGS. 10 and 11 show a fourth embodiment of the present invention. The same parts as those of the second embodiment are denoted by the same reference numerals, and description thereof will be omitted. Only different parts will be described below. In FIG. 10 showing the main part of the electrical configuration, in the fourth embodiment, the comparator 32 in the second embodiment is replaced by a comparator (excessive light detection means) 35.
[0050]
In the fourth embodiment, in the adjustment operation mode different from that during the normal operation, as shown in FIG. 11A, the main light output from the projector 1 for each optical axis for object detection and the like is provided. Following the light emission signal, a sub light emission signal is output for undershoot detection. The level of the sub light emission signal is set to a level lower than that of the main light emission signal.
[0051]
The reference value for comparison of the comparator 35 is set to a lower level than that of the comparator 31 to detect the sub-light emission signal (see FIG. 11B). In this case, if undershoot does not occur in the received light signal, or if the undershoot occurs but its amplitude is small, as shown in FIG. A component of the optical signal is detected.
[0052]
On the other hand, as shown in FIG. 11C, when the level of occurrence of undershoot increases, the sub-light emission signal component having a low level is absorbed by the undershoot and is not detected by the comparator 35.
Therefore, in the adjustment operation mode, the light reception control circuit 17 performs sensitivity adjustment so that a sub-light emission signal component is observed in the light reception signal.
[0053]
According to the fourth embodiment configured as described above, the light projector 1 outputs a sub-light emission signal following a main light emission signal for each optical axis, and the light reception control circuit 17 outputs a sub-light emission signal in the light reception signal. Since the sensitivity is adjusted so that the optical signal component can be observed, the adjustment can be performed so as to reduce the influence of the undershoot.
[0054]
(Fifth embodiment)
FIG. 12 shows a fifth embodiment of the present invention, and only parts different from the fourth embodiment will be described. In the fifth embodiment, unlike the fourth embodiment, a sub-light emission signal having a pulse width narrower than that of the main light emission signal is used. Even in such a case, the appearance of the sub-light emission signal component in the light-receiving signal waveform when the light-receiving device is affected by the undershoot is the same as in the fourth embodiment. Adjustments can be made by detecting the components.
[0055]
(Sixth embodiment)
13 to 15 show a sixth embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Only different parts will be described below. In FIG. 13 showing a main part of the electrical configuration, in the sixth embodiment, the FET 10, the integration circuit 11, and the AND circuit 12 are deleted from the configuration of the first embodiment. The light receiving control circuit 41 outputs control data Dx instead of the control pulse signal Sx from the output terminal C, and the control data Dx is given to the light projecting circuit 43 of the light projector 42. The light receiving control circuit 41 has a memory (storage means) 44 therein, and the light projecting circuit 43 has a D / A converter 45 built therein.
[0056]
FIG. 14 shows the internal configuration of the light emitting circuit 43. The anode of the LED 2 is connected to the drive power supply VCC, and the cathode is connected to the collector of the NPN transistor 46 for driving the LED. The base of each transistor 46 is connected to each output terminal of a shift register 47 that drives the transistor 46, and the emitter is commonly connected to the drain of an N-channel MOSFET 48. The source of the FET 48 is connected to the drain of the N-channel MOSFET 49, and the source of the FET 49 is connected to the ground.
[0057]
A light emission pulse signal is given to the gate of the upper FET 48, and the FET 48 is turned on in accordance with the timing at which each LED 2 emits light. An analog signal converted and output by the D / A converter 45 is provided to the gate of the lower FET 49.
That is, in the first embodiment, when the occurrence of undershoot is detected, the light-receiving sensitivity (amplification factor of the preamplifier 9) on the light-receiving side is adjusted. In the sixth embodiment, the light-receiving sensitivity is changed by changing the on-resistance of the FET 49. The light output level of the optical circuit 43 is adjusted. The light receiving control circuit 41, the D / A converter 45, and the FET 49 constitute an adjusting unit 50.
[0058]
Next, the operation of the sixth embodiment will be described with reference to FIG. FIG. 15 is a diagram corresponding to FIG. 2 in the first embodiment. Unlike the first embodiment, the light receiving control circuit 41 outputs control data Dx of a value corresponding to the output data to the light projecting circuit 43 when detecting an undershoot based on the output data of the A / D converter 20. It has become.
[0059]
That is, after execution of step S1, the control data Dx read from the memory 44 is output to the light emitting circuit 43 (step S10). Initial data is stored in the memory 44 in advance. At this time, the control data Dx is D / A converted by the D / A converter 45, and the analog signal voltage is given to the gate of the FET 49. Then, since the FET 49 exhibits an on-resistance corresponding to the gate voltage, the upper FET 48 is turned on at the light projection timing, and when one of the transistors 46 is turned on and the corresponding LED 2 emits light, the LED 2 is turned on. Is set according to the on-resistance of the FET 49.
[0060]
Then, in step S11 instead of step S4, the light receiving control circuit 41 determines whether or not the output data of the A / D converter 20 is the excessive light level (undershoot occurrence level). If it is ("YES"), the control data Dx read from the memory 44 in step S10 is reduced according to the degree of the excessive light level (difference from the determination threshold value) and output to the light emitting circuit 43 ( Step S12).
[0061]
Then, in the light emitting circuit 43, the gate voltage of the FET 49 decreases, so that the on-resistance increases, the current value flowing when the LED 2 is driven decreases, and the light emitting output level decreases. Therefore, the occurrence of undershoot is adjusted in a direction to be suppressed.
[0062]
Then, the light receiving control circuit 41 writes the updated control data Dx in the memory 44 and updates it (step S13), and then proceeds to step S5. Also, in step S11, if the light level is not excessive (“NO”), the process proceeds to step S5.
[0063]
As described above, according to the sixth embodiment, the adjusting unit 50 performs the adjusting operation by changing the light emitting output level of the light emitting circuit 42 collectively based on the control data Dx stored in the memory 44. The control data Dx stored in the memory 44 is updated after the adjustment operation is completed.
[0064]
Therefore, the adjustment operation is performed based on the data stored in the memory 44 in each adjustment cycle, so that the light emission output level is adjusted in a shorter time so that the undershoot generated in the light receiving signal is minimized. be able to. In addition, the configuration can be made simpler than that in which adjustment is performed for each optical axis, and the time required for adjustment can be shortened.
[0065]
(Seventh embodiment)
FIG. 16 shows a seventh embodiment of the present invention. Only parts different from the sixth embodiment will be described. In the seventh embodiment, the NPN transistor 46 in the sixth embodiment is replaced with a PNP transistor 51. The cathode of the LED 2 is connected to the emitter of the transistor 51, and the collector of the transistor 51 is connected to the ground.
[0066]
Further, the FET 49 is omitted, and a P-channel MOSFET 52 is provided instead of the FET 48. The anode of each LED 2 is commonly connected to the drain of the FET 52, and the analog signal converted and output by the D / A converter 45 is given to the source. The light emission pulse signal is supplied to the gate of the FET 52 via the NOT circuit 53. The light receiving control circuit 41, the D / A converter 45, and the FET 52 constitute an adjusting unit 54.
[0067]
According to the seventh embodiment configured as described above, when the FET 52 is turned on at each light projection timing, the voltage applied to the anode of the LED via the FET 52 is transmitted via the D / A converter 45. And output analog voltage. Therefore, in the seventh embodiment, the driving voltage of the LED 2 is changed instead of the driving current of the LED 2 in the sixth embodiment, and the same effect as in the sixth embodiment can be obtained.
[0068]
The present invention is not limited to the embodiment described above and shown in the drawings, and the following modifications or extensions are possible.
When the normal light receiving signal polarity is negative, it may be configured to detect overshoot.
In the configuration of the first embodiment, the amplification factor of the preamplifier circuit 9 may be digitally controlled as in the sixth embodiment.
The adjusting means may be configured to measure a time during which the level of the light receiving signal changes to the opposite polarity side, that is, an undershoot occurrence time, and to perform the adjusting operation based on the measured time. That is, since the length of the measurement time has a correlation with the magnitude of the reverse polarity level of the received light signal, if the adjustment amount in the adjustment operation is set according to the length of the measurement time, the light reception level can be adjusted well. be able to.
To detect that the level of the light receiving signal has changed to the opposite polarity side, for example, the detection may be performed by detecting the passage of the output signal level of the preamplifier circuit 9 through the zero cross point.
Although the sub-projection signal is used in the fourth or fifth embodiment, the sub-projection signal may be a signal having the same amplitude level and pulse width as the main projection signal. In this case, on the light receiving side, only the comparator 31 is provided, and it is determined that the signal is normal when the two signals are continuously received on one optical axis. Is reduced, and when only the first main light emission signal is received, the occurrence of the excessive light incident state may be determined.
[0069]
【The invention's effect】
According to the multi-optical axis photoelectric switch of the first aspect, the excess light detection means changes the level of the corresponding light reception signal output from the amplification means to the opposite polarity side after the light emission timing of each light emission element. The adjusting means detects the amplification factor of the amplifying means and the light emitting output level on the light emitting side based on the detection state of the excessive light detecting means so that the signal level of the received light signal on the opposite polarity side becomes small. The adjustment operation is performed by changing at least one of the above.
[0070]
Therefore, unlike the conventional method in which the over-light state is detected based on the level of the period during which the received light signal has the normal polarity, it is possible to reliably and stably detect the occurrence of the reverse polarity level in the received light signal. It becomes possible. Then, since the adjusting means performs the adjusting operation so that the reverse polarity level of the light receiving signal becomes small, the light receiving level can be satisfactorily adjusted to eliminate the excessive light incident state.
[0071]
According to the multi-optical axis photoelectric switch of the second aspect, the adjusting means measures the time during which the level of the light receiving signal changes to the opposite polarity side, and performs the adjusting operation based on the measured time. Can be performed more favorably.
[0072]
According to the multi-optical axis photoelectric switch of the third aspect, the excessive light detecting means compares the level of the light receiving signal with the reference level after a predetermined time has elapsed from the light emitting timing of the corresponding light emitting element. The light state is detected. Then, the adjusting means performs the adjusting operation by changing at least one of the amplification factor or the light emission output level based on the data stored in the storing means, and after the adjusting operation is completed, the data stored in the storing means is changed. Update. Therefore, it is possible to reliably detect the excessive light incident state based on the level of the light receiving signal output from the amplifying unit. Further, the amplification factor or the light output level of the amplifying means can be adjusted so that the overshoot or undershoot generated in the light receiving signal is minimized in each adjustment cycle.
[0073]
According to the multi-optical axis photoelectric switch of the fourth aspect, the adjusting means collectively sets at least one of the amplification factor of the amplifying means and the light emitting output level of the light emitting device side for all light receiving elements or all light emitting elements. Since it is variable, the configuration can be made simpler and the time required for the adjustment can be shortened as compared with the case where the adjustment is performed for each optical axis.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of an electric configuration of a multi-optical axis photoelectric switch according to a first embodiment of the present invention.
FIG. 2 is a flowchart showing the contents of a detection operation and a sensitivity adjustment operation (detection program) performed by a light receiving control circuit.
FIG. 3 is a flowchart showing the contents of a detection routine which is step S3 in FIG. 2;
FIG. 4 is a timing chart of each signal when a light projection signal Sp is given to an input terminal F of a light receiving control circuit.
FIG. 5B is a diagram showing a waveform when an incident light state occurs when a light emission signal having a waveform as shown in FIG.
FIG. 6 is a second embodiment of the present invention, showing only essential parts of FIG.
FIG. 7 is a timing chart of each signal.
FIG. 8 is a view corresponding to FIG. 6, showing a third embodiment of the present invention.
FIG. 9 is a diagram corresponding to FIG. 7;
FIG. 10 is a view corresponding to FIG. 6, showing a fourth embodiment of the present invention;
FIG. 11 is a diagram corresponding to FIG. 7;
FIG. 12 is a view corresponding to FIG. 11, showing a fifth embodiment of the present invention.
FIG. 13 is a view corresponding to FIG. 1, showing a sixth embodiment of the present invention.
FIG. 14 is a diagram showing an electrical configuration inside a light emitting circuit;
FIG. 15 is a diagram corresponding to FIG. 2;
FIG. 16 is a view corresponding to FIG. 14, showing a seventh embodiment of the present invention;
[Explanation of symbols]
1 is a light emitter, 2 is an LED (light emitting element), 3 is a light emitting control circuit (light emitting and receiving control means), 5 is a light receiver, 7 is a photodiode (light receiving element), 9 is a preamplifier circuit (amplifying means). , 16 is a light receiving circuit (light emitting / receiving control means), 17 is a light receiving control circuit (excessive light detecting means), 21 is an adjusting means, 32 is a comparator (excessive light detecting means), 33 is an analog switch (excessive light detecting means). Detecting means), 35 is a comparator (excessive light detecting means), 44 is a memory (storage means), and 50 and 54 are adjusting means.

Claims (4)

A floodlight comprising a plurality of floodlighting means,
A plurality of light receiving means arranged to face the light projector and respectively receiving the light emitted by the plurality of light emitting means; provided in correspondence with the plurality of light receiving means; output from each light receiving means; A light receiver comprising amplification means for amplifying a light reception signal,
A plurality of light emitting / receiving control means for controlling the plurality of light emitting means and the light receiving means to sequentially perform light emitting / receiving operations and scanning an optical axis formed by each light emitting means and the light receiving means. In the optical axis photoelectric switch,
The light receiver,
Excessive light detecting means for detecting that the level of the corresponding light receiving signal output from the amplifying means has changed to the opposite polarity side after the light emitting timing of each light emitting element,
Based on the detection state of the excessively incident light detecting means, at least one of the amplification factor of the amplifying means and the light emitting output level of the light projecting device side is adjusted so that the signal level of the light receiving signal on the opposite polarity side is reduced. A multi-optical axis photoelectric switch, comprising: adjusting means for performing an adjusting operation by changing the optical axis. 2. The multi-optical axis photoelectric switch according to claim 1, wherein said adjusting means measures a time when the level of the light receiving signal changes to the opposite polarity side, and performs an adjusting operation based on the measured time. The excess light detection means detects the excessive light state by comparing the level of the light reception signal output from the amplifying means with a reference level after a lapse of a predetermined time from the light emission timing of the corresponding light emitting element. Configured to do,
The adjusting means,
A storage unit for storing at least one of an amplification factor of the amplification unit and a light emission output level on the light emitter side,
Performing an adjustment operation by changing at least one of the amplification factor or the light emission output level based on the data stored in the storage means;
3. The multi-optical axis photoelectric switch according to claim 1, wherein data stored in said storage means is updated after the adjustment operation is completed. The adjustment unit is characterized in that at least one of an amplification factor of the amplification unit and a light emission output level on the light emitter side is configured to be collectively variable for all light receiving elements or all light emission elements. The multi-optical axis photoelectric switch according to claim 1.

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