Photoelectric sensor and light-receiving unit

Abstract

To provide a photoelectronic sensor capable of blocking more disturbance light.SOLUTION: A photoelectronic sensor includes a light emitting unit for emitting a pulse light group including predetermine number of pulse light with a predetermined cycle, and a light receiving unit for receiving the pulse light group emitted from the light emitting unit, the light receiving unit includes a light receiving element for receiving light including the pulse light group and outputting a first signal base on the received light, a conversion circuit for converting a first signal outputted from the light receiving element to a second signal, a filter circuit for performing predetermined filtering to the second signal outputted from the conversion circuit and outputting a filtered signal, and a cycle detection circuit for identifying a predicted cycle for the filtered signal, identifying a light receiving cycle and a light receiving period for the pulse light group on the basis of the predicted cycle thus identified, and setting the identified light receiving cycle and the light receiving period to the conversion circuit, and the conversion circuit accepts the first signal in the set light receiving cycle and the light receiving period.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a photoelectric sensor and a light receiving unit.

Background Art

[0002] Patent Document 1 forms a light projecting unit with a synchronization generation circuit that generates a high-frequency burst signal composed of a plurality of pulses at a predetermined period and a light emitting element that is blink-controlled by the burst signal, and receives light from the light projecting unit and converts it into an electrical signal. A light receiving element, a filter circuit that extracts the frequency component of the burst signal from the received light signal output from the light receiving element, and a detection discrimination circuit that detects whether or not the output of the filter circuit is equal to or higher than a predetermined level in synchronization with the generation timing of the burst signal to discriminate the presence or absence of an object to be detected. A photoelectric switch is disclosed which forms a light receiving unit with an output circuit controlled by a detection discrimination circuit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The photoelectric sensor disclosed in Patent Document 1 performs light projection control with a burst signal and includes a filter that extracts the frequency component of the same burst signal from the received light signal. Therefore, electrical signals related to disturbing light having different frequencies are blocked by the filter. However, the photoelectric sensor disclosed in Patent Document 1 cannot block disturbing light having the same frequency as the burst signal, and the blocking of disturbing light is insufficient.

[0005] An object of the present disclosure is to provide a photoelectric sensor and a light receiving unit that can block more disturbing light.

Means for Solving the Problems

[0006] The photoelectric sensor of the present disclosure includes a light projecting unit that projects a pulse light group including a predetermined number of pulse lights at a predetermined period, and a light receiving unit that receives the pulse light group projected from the light projecting unit. The light receiving unit includes a light receiving element that receives light including the pulse light group and outputs a first signal based on the received light, a conversion circuit that converts the first signal output from the light receiving element into a second signal, a filter circuit that applies a predetermined filter to the second signal output from the conversion circuit and outputs a filtered signal, and a period detection circuit that specifies a predicted period of the filtered signal, specifies a light reception period and a light reception duration of the pulse light group based on the specified predicted period, and sets the specified light reception period and the light reception duration in the conversion circuit. The conversion circuit receives the first signal at the set light reception period and the light reception duration.

[0007] The light receiving unit of the present disclosure includes a light receiving element that receives light including a pulse light group including a predetermined number of pulse lights projected at a predetermined period and outputs a first signal based on the received light, a conversion circuit that converts the first signal output from the light receiving element into a second signal, a filter circuit that applies a predetermined filter to the second signal output from the conversion circuit and outputs a filtered signal, and a period detection circuit that specifies a light reception period and a light reception duration of the pulse light group based on a predicted period of the filtered signal and sets the specified light reception period and the light reception duration in the conversion circuit. The conversion circuit receives the first signal at the set light reception period and the light reception duration.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide a photoelectric sensor and a light receiving unit that can block more ambient light.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2A

Figure 2B

Figure 3

Figure 4A

Figure 4B

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with appropriate reference to the drawings. However, a more detailed description than necessary may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of substantially the same configurations may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate the understanding of those skilled in the art. Note that the attached drawings and the following description are provided for those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims thereby.

[0011] (Embodiment 1) FIG. 1 is a block diagram showing a configuration example of a photoelectric sensor 1 according to Embodiment 1. FIG. 2A is a diagram for explaining an example of light reception processing when a pulse light group including a predetermined number (for example, three) of pulse lights is projected. FIG. 2B is a diagram for explaining an example of light reception processing when pulse light is projected.

[0012] The photoelectric sensor 1 includes a light projecting unit 10 and a light receiving unit 20 disposed opposite to the light projecting unit 10. That is, the photoelectric sensor 1 is a transmissive photoelectric sensor 1. The light projecting unit 10 and the light receiving unit 20 are not connected by a synchronization wiring. The photoelectric sensor 1 projects pulsed light from the light projecting unit 10 and receives the pulsed light by the light receiving unit 20, thereby detecting whether an object exists in a space region (hereinafter referred to as an object detection region) between the light projecting unit 10 and the light receiving unit 20.

[0013] The light projecting unit 10 includes an oscillation circuit 11, a modulation circuit 12, a drive circuit 13, and a light projecting element 14.

[0014] The oscillation circuit 11 generates a clock signal having a predetermined frequency.

[0015] The modulation circuit 12 modulates the clock signal output from the oscillation circuit 11 to output a pulse signal so that the pulsed light projected from the light projecting element 14 has a light projection pattern shown in (a) of FIG. 2A. That is, the modulation circuit 12 modulates the clock signal to output a pulse signal so that a pulse light group including a predetermined number (for example, three) of pulsed lights is projected from the light projecting element 14 at a predetermined period T0. Hereinafter, the number of pulsed lights originally included in the pulse light group is referred to as the original number of pulsed lights.

[0016] Alternatively, the modulation circuit 12 modulates the clock signal output from the oscillation circuit 11 to output a pulse signal so that the pulsed light projected from the light projecting element 14 has a light projection pattern shown in (a) of FIG. 2B. That is, the modulation circuit 12 modulates the clock signal to output a pulse signal so that one pulsed light is projected from the light projecting element 14 at a predetermined period T0.

[0017] The drive circuit 13 supplies a pulse current corresponding to the pulse signal output from the modulation circuit 12 to the light projecting element 14.

[0018] The light projecting element 14 is constituted by, for example, an LED (Light Emitting Diode), and emits light according to the pulsed current output from the drive circuit 13. Thereby, pulsed light groups as shown in Fig. 2A(a) or pulsed light as shown in Fig. 2B(a) are projected from the light projecting element 14 at a period T0.

[0019] The light receiving unit 20 receives the pulsed light group (or pulsed light) projected from the light projecting unit 10. As described above, the light receiving unit 20 is not connected to the light projecting unit 10 by a synchronization wiring. Therefore, the light receiving unit 20 cannot obtain the timing at which the pulsed light group (or pulsed light) is projected (hereinafter referred to as the light projection timing) and the period T0 (hereinafter referred to as the light projection period T0) from the light projecting unit 10 through the synchronization wiring. Therefore, the light receiving unit 20 is required to discriminate between the original pulsed light group (or pulsed light) projected from the light projecting unit 10 and disturbing light different from the original pulsed light group (or pulsed light), and block the disturbing light. Therefore, hereinafter, the light receiving unit 20 that can block disturbing light as much as possible without obtaining information from the light projecting unit 10 will be described.

[0020] The light receiving unit 20 includes a light receiving element 21, an IV conversion circuit 22, an amplification circuit 23, an AD conversion circuit 24, a filter circuit 25, a comparison circuit 26, a determination circuit 27, and a period detection circuit 28.

[0021] The light receiving element 21 is constituted by, for example, a photodiode, and outputs an electrical signal (current) of a level corresponding to the amount of received light of the received light. The light receiving element 21 can receive disturbing light in addition to the pulsed light group (or pulsed light) projected from the light projecting element 14.

[0022] The IV conversion circuit 22 converts the current input from the light receiving element 21 into a voltage. The IV conversion circuit 22 outputs a pulsed signal (voltage signal) converted into a voltage as shown in Fig. 2A(b) or Fig. 2B(b).

[0023] As shown in Fig. 2A (c) or Fig. 2B (c), the amplifier circuit 23 amplifies the pulse signal input from the IV conversion circuit 22. The amplifier circuit 23 outputs the amplified pulse signal.

[0024] The AD conversion circuit 24 converts the analog signal (e.g., the first signal) input from the amplifier circuit 23 into a digital signal (e.g., the second signal) and outputs it.

[0025] The filter circuit 25 sequentially applies a (e) high-pass filter, (f) full-wave rectification, and (g) low-pass filter to the pulse signal input from the AD conversion circuit 24 as shown in "Filter" in Fig. 2A. Alternatively, the filter circuit 25 applies a (g) low-pass filter to the pulse signal input from the AD conversion circuit 24 as shown in Fig. 2B. Hereinafter, the signal that has passed through the filter circuit 25 is referred to as the post-filter signal.

[0026] The cut-off frequency of the high-pass filter is set according to the frequency of the pulsed light to be projected in order to remove low-frequency noise lower than the frequency of the pulsed light to be projected.

[0027] The cut-off frequency of the low-pass filter may be set so that a signal after full-wave rectification of high-frequency components higher than the frequency of the original pulse signal is blocked. The waveform of the envelope signal of the signal after full-wave rectification changes depending on the number of pulses (e.g., the width or period of the burst). For example, the width of the waveform of the envelope signal is determined based on the frequency and the number of pulses. The frequency and the number of pulses may be set independently. The low-pass filter may be set to block the input envelope signal when the width of the waveform of the input envelope signal is narrower than the width of the waveform of the envelope signal corresponding to the frequency of the original pulse signal. Thereby, it is possible to block disturbing light having a frequency higher than the frequency of the original pulsed light.

[0028] That is, the filter circuit 25 passes a signal having the frequency of the original pulsed light and blocks a signal having a frequency lower or higher than the frequency of the original pulsed light. Thereby, the light receiving unit 20 can block disturbing light having a frequency different from the frequency of the original pulsed light.

[0029] Also, as shown in FIG. 2B, when pulsed light is projected, the cut-off frequency of the low-pass filter may be set such that a pulsed signal having a frequency higher than the frequency of the pulsed light is blocked.

[0030] As shown in (h) of FIG. 2A or (h) of FIG. 2B, the comparison circuit 26 outputs an on signal (for example, outputs a signal having a predetermined magnitude) when the magnitude of the post-filter signal is equal to or greater than a predetermined threshold Th, and outputs an off signal (for example, does not output a signal) when the magnitude of the post-filter signal is less than the predetermined threshold Th.

[0031] The determination circuit 27 determines whether an on signal or an off signal is input from the comparison circuit 26 for each period in which a pulsed light group (or pulsed light) is projected. In addition, as shown in (i) of FIG. 2A or (i) of FIG. 2B, when the on signal is continuously input a predetermined number or more of times (for example, 8 times or more), the determination circuit 27 determines that no object exists in the object detection area, and when the off signal is continuously input a predetermined number or more of times (for example, 8 times or more), the determination circuit 27 may determine that an object exists in the object detection area. When the determination circuit 27 determines that no object exists in the object detection area, the determination circuit 27 may output an on signal (for example, output a signal having a predetermined magnitude), and when the determination circuit 27 determines that an object exists in the object detection area, the determination circuit 27 may output an off signal (for example, does not output a signal). In this way, by determining whether an object exists when the same type of signal is continuously input a predetermined number or more of times, it is possible to prevent the determination circuit 27 from erroneously determining the detection of an object when the signal input from the comparison circuit 26 is temporarily switched on or off due to temporary disturbing light.

[0032] As shown in (d) of Fig. 2A or (d) of Fig. 2B, the period detection circuit 28 sets the light reception period and the light reception duration in the AD conversion circuit 24 in accordance with the period in which the original pulse light group (or pulse light) is projected. The AD conversion circuit 24 may operate during the light reception period and does not need to operate outside the light reception period. Thereby, it is possible to block the disturbance light received by the light receiving element 21 outside the light reception period. For example, even if the light receiving element 21 receives disturbance light having the same frequency as the original pulse light, which is difficult to block by the filter circuit 25 described above, outside the light reception period, the AD conversion circuit 24 is not operating, so that the disturbance light can be blocked. In addition, since the AD conversion circuit 24 operates during the light reception period and does not operate outside the light reception period, the current consumption of the AD conversion circuit 24 can be suppressed.

[0033] As described above, since the light receiving unit 20 and the light projecting unit 10 are not connected by a synchronization wiring, the period detection circuit 28 predicts by itself the period (i.e., the light projection period) in which the original pulse light group (or pulse light) is projected. The predicted light projection period may be the light reception period that is the period of the light reception period.

[0034] Next, an example of a method for the period detection circuit 28 to predict the light projection period and a method for determining the light reception period will be described. The period detection circuit 28 executes a reference detection process 41 and a period prediction and margin control process 42. Hereinafter, the light projection period predicted by the period detection circuit 28 is referred to as a predicted period.

[0035] Fig. 3 is a diagram for explaining a method for calculating the predicted period. Fig. 4A is a diagram for explaining a method for determining the light reception period when an initial value of the predicted period is set. Fig. 4B is a diagram for explaining a method for determining the light reception period when an initial value of the predicted period is not set.

[0036] For example, the light receiving unit 20 performs the processes of the following steps S11 to S16.

[0037] (Step S11) As shown in FIG. 2A or FIG. 2B, the reference detection process 41 of the period detection circuit 28 detects the amplitude peak P1 from the post-filter signal. Then, the reference detection process 41 of the period detection circuit 28 sets the initial predicted period T1 and the initial light reception period R to the AD conversion circuit 24 with the timing at which the peak P1 is detected as the start timing of the predicted period.

[0038] (Step S12) The period prediction and margin control process 42 of the period detection circuit 28 counts the period from the previous timing to the timing until the reference detection process 41 detects the next peak P1 (hereinafter referred to as the next timing). Note that, in the first time, the previous timing may be the start timing.

[0039] (Step S13) The period prediction and margin control process 42 of the period detection circuit 28 calculates the difference D between the value counted in Step S12 (hereinafter referred to as the count period) and the current predicted period T1. Note that, in the first time, the current predicted period T1 may be the initial predicted period T1.

[0040] (Step S14) The period prediction and margin control process 42 of the period detection circuit 28 calculates the next predicted period T1 by averaging the current predicted period T1 and the count period. Here, when the count period deviates significantly from the predicted period T1, the period prediction and margin control process 42 of the period detection circuit 28 may not use the count period for calculating the average. This is because the count period that deviates significantly from the predicted period T1 is likely not a normal signal period.

[0041] (Step S15) The period prediction and margin control process 42 of the period detection circuit 28 determines the light reception period R based on the next predicted period T1 and a predetermined margin period (±ΔT). Note that the margin period ΔT may be determined by the following (Equation 1). ΔT = absolute value of difference D + predetermined value …(Equation 1) That is, the smaller the absolute value (difference) of the difference D is, the shorter the margin period ΔT may be, and the larger the absolute value (difference) of the difference D is, the longer the margin period ΔT may be.

[0042] (Step S16) The period prediction and margin control process 42 of the period detection circuit 28 sets the determined next predicted period T1 (light reception period) and the light reception period R in the AD conversion circuit 24.

[0043] The light reception unit 20 repeatedly executes the processes from step S12 to step S16 described above. As a result, the predicted period T1 approaches the light emission period T0, and the light reception period R approaches the time width of the original pulse train signal or pulse signal.

[0044] If the initial value of the predicted period is not set, as shown in FIG. 4B, in step S11, the period detection circuit 28 may set the light reception period from the start timing when the first peak P1 is detected to the timing when the next peak P1 is detected. Then, the period detection circuit 28 may count the period from the start timing to the next timing, and use this counted value as the first predicted period T1. Then, the period detection circuit 28 may set this first predicted period T1 and the initial value of the light reception period R in the AD conversion circuit 24. After that, similar to the above, the processes from step S12 to step S14 may be repeatedly executed.

[0045] Also, in the processes from step S11 to step S16 described above, as shown in FIG. 2A or FIG. 2B, the period detection circuit 28 may detect an edge P2 in the post-filter signal whose amplitude exceeds a predetermined threshold Th, and use the edge P2 instead of the peak P1 described above.

[0046] (Embodiment 2) In Embodiment 2, for the components that are the same as those described in Embodiment 1, the same reference numerals may be used, and the description may be omitted in some cases.

[0047] FIG. 5 is a block diagram showing a configuration example of the light receiving unit 20 according to the second embodiment. In FIG. 5, the description of the light projecting unit 10 is omitted.

[0048] As shown in FIG. 5, the light receiving unit 20 according to the second embodiment includes a burst detection circuit 30 and a band - pass filter circuit 31 in addition to the components shown in FIG. 1.

[0049] The band - pass filter circuit 31 blocks signals having frequencies outside a predetermined frequency band from the signal input from the amplifier circuit 23. That is, the band - pass filter circuit 31 allows signals in a predetermined frequency band to pass through. This facilitates burst detection in the burst detection circuit 30 described later.

[0050] The burst detection circuit 30 is a circuit for detecting an original pulse train signal from the signal input from the AD conversion circuit 24. For example, when the burst detection circuit 30 detects a pulse train signal including the original number of pulse signals from the input signal, it outputs a valid pulse signal to the period prediction and margin control process 42 of the determination circuit 27 and the period detection circuit 28. In other words, when the burst detection circuit 30 detects a pulse train signal (that is, a signal corresponding to extraneous light) including a number of pulse signals different from the original number of pulses from the input signal, it does not output a valid pulse signal.

[0051] When a valid pulse signal is input, the determination circuit 27 operates the AD conversion circuit 24. And when a valid pulse signal is input, the period prediction and margin control process 42 of the period detection circuit 28 may perform the processes from steps S12 to S16 above. In other words, when a valid pulse signal is not input, the period prediction and margin control process 42 of the period detection circuit 28 does not have to perform the processes from steps S12 to S16. This is because when a valid pulse signal is not input, it is highly likely to be a signal related to extraneous light and is not suitable for use in calculating the predicted period T1 and the margin period ΔT. Thereby, similar to the photosensor 1 shown in FIG. 1, more extraneous light can be blocked.

[0052] Note that the light projection unit 10 may be configured to arbitrarily set at least one of the number of pulse lights included in the pulse light group (i.e., the number of bursts) and the light projection period of the pulse light group. In this case, the period prediction and margin control process 42 of the period detection circuit 28 may be configured to be able to preset the light projection period set in the light projection unit 10. Further, the filter circuit 25 may be configured to be able to preset a frequency filter according to the frequency of the pulse light group set in the light projection unit 10. Further, the burst detection circuit 30 may be configured to be able to preset the number of bursts set in the light projection unit 10.

[0053]

[0054] (Embodiment 3) In Embodiment 3, the same components as those described in Embodiment 1 may be denoted by the same reference numerals, and the description thereof may be omitted.

[0055] ​FIG. 6 is a block diagram showing a configuration example of the light receiving unit 20 according to Embodiment 3. Note that in FIG. 6, the description of the light projecting unit 10 is omitted.

[0056] As shown in FIG. 6, the light receiving unit 20 according to Embodiment 3 includes a simple AD conversion circuit 29 and a changeover switch 32 in addition to the components shown in FIG. 1.

[0057] Similar to the AD conversion circuit 24, the simple AD conversion circuit 29 converts the analog signal input from the amplifier circuit 23 into a digital signal and outputs it. The resolution of the simple AD conversion circuit 29 is lower than that of the AD conversion circuit 24. For example, the resolution of the simple AD conversion circuit 29 is 4 bits, and the resolution of the AD conversion circuit 24 is 12 bits. As a result, the current consumption of the simple AD conversion circuit 29 is lower than that of the AD conversion circuit 24. The AD conversion circuit 24 may be read as the first AD conversion circuit, and the simple AD conversion circuit 29 may be read as the second AD conversion circuit.

[0058] The changeover switch 32 switches the output destination of the signal provided from the amplifier circuit 23 to either the AD conversion circuit 24 or the simple AD conversion circuit 29.

[0059] Instead of step S11 described in Embodiment 1, the light receiving unit 20 executes the following process of step S11a. Note that when the process of step S11a is executed, the changeover switch 32 is switched so that the signal provided from the amplifier circuit 23 is output to the simple AD conversion circuit 29.

[0060] (Step S11a) The reference detection process 41 of the period detection circuit 28 detects the amplitude peak P1 (or edge P2) from the filtered signal provided through the simple AD conversion circuit 29 and the filter circuit 25. Then, the reference detection process 41 switches the changeover switch 32 so that the signal provided from the amplifier circuit 23 is output to the AD conversion circuit 24. Then, the reference detection process 41 sets the initial predicted period T1 and the initial light reception period R to the AD conversion circuit 24, with the timing at which the peak P1 (or edge P2) is detected as the start timing of the predicted period.

[0061] Thereafter, the light reception unit 20 may repeatedly execute the processes of step S12 to step S16 described in Embodiment 1.

[0062] In this way, by adopting a configuration that uses the simple AD conversion circuit 29 until the initial peak P1 (or edge P2) is detected, the current consumption in the light reception unit 20 can be reduced.

[0063] Note that when the light shielding continues for a predetermined period or longer, that is, when the reference detection process 41 of the period detection circuit 28 cannot detect the peak P1 (or edge P2) for a predetermined period or longer, either of the following (A1) or (A2) may be performed.

[0064] (A1) The reference detection process 41 of the period detection circuit 28 switches the changeover switch 32 so that the signal provided from the amplifier circuit 23 is output to the simple AD conversion circuit 29. That is, the light reception unit 20 performs the process again from step S11a above. Thereby, the deviation between the predicted period and the light projection period that may occur during the light shielding can be reset.

[0065] (A2) The light-receiving unit 20 repeatedly executes the processes from step S12 to step S16 described in the first embodiment, and increases the margin period ΔT in step S15. For example, in the period prediction and margin control process 42 of the period detection circuit 28, the "predetermined value" in the above-mentioned (Equation 1) is made larger than the predetermined value before the light shielding continues for a predetermined period or more. Thereby, the deviation between the predicted period and the light projection period that may occur during light shielding can be absorbed by extending the light-receiving period R.

[0066] (Embodiment 4) In Embodiment 4, for the components that are the same as the components described in the first embodiment, the same reference numerals may be given, and the description may be omitted.

[0067] FIG. 7 is a block diagram showing a configuration example of the photoelectric sensor 1 according to Embodiment 4.

[0068] The photoelectric sensor 1 shown in FIG. 7 includes a variable-resolution AD conversion circuit 33 instead of the AD conversion circuit 24 shown in FIG. 1.

[0069] The variable-resolution AD conversion circuit 33 can switch the resolution when converting the input analog signal into a digital signal and outputting it. For example, based on an external signal, similar to the third embodiment, AD conversion is performed by switching the resolution between 4 bits and 12 bits.

[0070] Instead of step S11 described in the first embodiment, the light-receiving unit 20 executes the following step S11b. Note that when the process of step S11b is executed, the resolution of the variable-resolution AD conversion circuit 33 is set to 4 bits.

[0071] (Step S11b) In the reference detection process 41 of the period detection circuit 28, the peak P1 (or edge P2) of the amplitude is detected from the post-filter signal provided through the variable-resolution AD conversion circuit 33 and the filter circuit 25. Then, in the reference detection process 41, a signal is sent to the variable-resolution AD conversion circuit 33 to switch its resolution to 12 bits. Then, in the reference detection process 41, using the timing at which the peak P1 (or edge P2) is detected as the start timing of the predicted period, the initial predicted period T1 and the initial light reception period R are set in the variable-resolution AD conversion circuit 33.

[0072] As described above, the embodiments have been explained with reference to the accompanying drawings, but the present disclosure is not limited to such examples. It is obvious that those skilled in the art can conceive of various modification examples, correction examples, substitution examples, addition examples, deletion examples, and equivalent examples within the scope described in the claims, and it is understood that those also belong to the technical scope of the present disclosure. Also, within the scope not departing from the gist of the invention, the components in the above-described embodiments may be arbitrarily combined.

Industrial Applicability

[0073] The technology of the present disclosure is applicable to a photoelectric sensor or a light reception unit, and can be used, for example, in an object detection device using optical pulses.

Explanation of Reference Numerals

[0074] 1 Photoelectric sensor 10 Light projection unit 11 Oscillation circuit 12 Modulation circuit 13 Drive circuit 14 Light projection element 20 Light reception unit 21 Light reception element 22 IV conversion circuit 23 Amplification circuit 24 AD conversion circuit 25 Filter circuit 26 Comparison circuit 27 Judgment circuit 28 Period detection circuit 29 Simple AD conversion circuit 30 Burst detection circuit 31 Bandpass filter circuit 32 Switching switch 33 Variable resolution AD conversion circuit

Claims

1. A photoelectric sensor comprising: a light projecting unit that projects a pulse light group including a predetermined number of pulse lights at a predetermined period; and a light receiving unit that receives the pulse light group projected from the light projecting unit, wherein the light receiving unit, a light receiving element that receives light including the pulse light group and outputs a first signal based on the received light; a conversion circuit that converts the first signal output from the light receiving element into a second signal; a filter circuit that applies a predetermined filter to the second signal output from the conversion circuit and outputs a post-filter signal; a period detection circuit that specifies a predicted period of the post-filter signal, specifies a light reception period and a light reception duration of the pulse light group based on the specified predicted period, and sets the specified light reception period and the light reception duration in the conversion circuit; a burst detection circuit that detects the second signal corresponding to the pulse light group; and the conversion circuit receives the first signal at the set light reception period and the light reception duration, the period detection circuit uses the post-filter signal corresponding to the second signal detected by the burst detection circuit as corresponding to the pulse light group for specifying the predicted period, a photoelectric sensor.

2. A photoelectric sensor comprising: a light projecting unit that projects a pulse light group including a predetermined number of pulse lights at a predetermined period; and a light receiving unit that receives the pulse light group projected from the light projecting unit, wherein the light receiving unit, a light receiving element that receives light including the pulse light group and outputs, as a first signal, an analog signal based on the received light; an AD conversion circuit that converts the first signal output from the light receiving element into a second signal that is a digital signal; a filter circuit that applies a predetermined filter to the second signal output from the AD conversion circuit and outputs a post-filter signal; a period detection circuit that specifies a predicted period of the post-filter signal, specifies a light reception period and a light reception duration of the pulse light group based on the specified predicted period, and sets the specified light reception period and the light reception duration in the AD conversion circuit; wherein the AD conversion circuit, has a lower resolution before the first light reception period and the light reception duration are specified than after the first light reception period and the light reception duration are specified, and receives the first signal at the set light reception period and the light reception duration, a photoelectric sensor.

3. The light receiving unit, A simple AD conversion circuit that converts an analog signal into a digital signal with a resolution lower than that of the AD conversion circuit, A switching switch that switches the output destination of the analog signal output from the light receiving element to either the AD conversion circuit or the simple AD conversion circuit, The switching switch uses the simple AD conversion circuit as the output destination before the first light reception period and the light reception period are specified, and uses the AD conversion circuit as the output destination after the first light reception period and the light reception period are specified, The photoelectric sensor according to claim 2.

4. The period detection circuit specifies the prediction period based on the interval between the peaks of the amplitude of the signal after filtering, The photoelectric sensor according to any one of claims 1 to 3.

5. The period detection circuit specifies the prediction period based on the interval between the timings when the amplitude of the signal after filtering exceeds a predetermined threshold value, The photoelectric sensor according to any one of claims 1 to 3.

6. The period detection circuit specifies the light reception period by averaging a plurality of the prediction periods, The photoelectric sensor according to any one of claims 1 to 5.

7. The period detection circuit does not include a prediction period that is equal to or greater than a predetermined threshold value as an element of the average, The photoelectric sensor according to claim 6.

8. The period detection circuit determines the light reception period based on the difference between the prediction period and the light reception period, The photoelectric sensor according to any one of claims 1 to 7.

9. The predetermined filter includes a low-pass filter, The photoelectric sensor according to any one of claims 1 to 8.

10. A light receiving element that receives light including a pulse light group including a predetermined number of pulse lights projected at a predetermined period and outputs a first signal based on the received light, A conversion circuit that converts the first signal output from the light receiving element into a second signal, A filter circuit that applies a predetermined filter to the second signal output from the conversion circuit and outputs a signal after filtering, A period detection circuit that specifies the light reception period and the light reception period of the pulse light group based on the prediction period of the signal after filtering, and sets the specified light reception period and the light reception period in the conversion circuit, A burst detection circuit that detects the second signal corresponding to the pulse light group, The conversion circuit receives the first signal at the set light reception period and the light reception period, The period detection circuit uses the post-filter signal corresponding to the second signal detected by the burst detection circuit as corresponding to the pulse light group for specifying the prediction period. Light receiving unit. **Claim 11**: A light receiving element that receives light including a pulse light group including a predetermined number of pulse lights emitted at a predetermined period, and outputs a first signal that is an analog signal based on the received light; An AD conversion circuit that converts the first signal output from the light receiving element into a second signal that is a digital signal; A filter circuit that applies a predetermined filter to the second signal output from the AD conversion circuit and outputs a post-filter signal; A period detection circuit that specifies a light reception period and a light reception period of the pulse light group based on a prediction period of the post-filter signal, and sets the specified light reception period and the light reception period in the AD conversion circuit; The AD conversion circuit: The resolution before the first light reception period and the light reception period are specified is set lower than the resolution after the first light reception period and the light reception period are specified; Receives the first signal at the set light reception period and the light reception period; Light receiving unit.

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