Optoelectronic sensor and optical distance measuring device

Abstract

Provided is an inexpensive photoelectric sensor capable of properly detecting light in a wide dynamic range without using multiple transimpedance amplifiers. Provided is a photoelectric sensor including: a light projecting section that outputs measurement light; a light receiving section that converts reflected light, which is diffusely reflected by an object on which the measurement light impinges, into a current signal; a preamplifier that converts the current signal converted by the light receiving section into a voltage signal; a first signal processing system that includes a first amplifier that amplifies the output signal of the preamplifier at a first amplification rate A1 and a first binary circuit that binarizes the output signal of the first amplifier at a first threshold value Vth1; and a second signal processing system that includes a second amplifier that amplifies the output signal of the preamplifier at a second amplification rate A2 and a second binary circuit that binarizes the output signal of the second amplifier at a second threshold value Vth2, the first and second threshold values and the first and second amplification rates being set to satisfy the following relationship: 1 < (Vth2 / Vth1) < α = (A2 / A1).

Description

TECHNICAL FIELD

[0001] The present application relates to a photoelectric sensor and a light range finder. BACKGROUND

[0002] A photoelectric sensor for detecting an object in a monitoring area is disclosed in Patent Literature 1, which aims to amplify a signal as faithfully as possible to a received signal in a wide dynamic range.

[0003] The photoelectric sensor is provided with a light emitter for emitting light, a light receiver for converting light that is diffusely reflected by hitting an object into a photoelectric current, and an evaluation section for determining a characteristic of the object from a received signal derived from the photoelectric current, between the light receiver and the evaluation section, in order to detect the diffusely reflected light in a wider dynamic range, a high-sensitivity reception path having an amplifier with higher sensitivity and a low-sensitivity reception path having an amplifier with lower sensitivity are provided, and the received signal is generated from the photoelectric current divided to the reception path in the high-sensitivity reception path or the low-sensitivity reception path according to the intensity of the diffusely reflected light.

[0004] Further, at least the low-sensitivity reception path is configured to have a diode array, the threshold value of the intensity of the diffusely reflected light is defined using the forward voltage of the diode array, and the photoelectric current is caused to flow in the low-sensitivity reception path only in the case where the threshold value is exceeded.

[0005] According to the photoelectric sensor described above, the received signal is amplified almost without losing information in a dynamic range wider than that of each reception path. The current flows into the amplifier of the low-sensitivity reception path only in the case where the forward voltage is exceeded, and in the case where the reception output is small, the photoelectric current as a whole is introduced into the high-sensitivity reception path, so that no sensitivity loss occurs.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT LITERATURE

[0008] Patent Literature 1: JP Patent Publication No. 2014-142340 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] However, the photoelectric sensor described in Patent Literature 1 requires a high-priced transimpedance amplifier in each of the single or multiple low-sensitivity reception paths and the high-sensitivity reception path provided with a diode array, and there is a problem of an increase in component cost.

[0011] The present application has an object to provide an inexpensive photoelectric sensor and a light distance measuring device capable of appropriately detecting light in a wide dynamic range without using a plurality of transimpedance amplifiers.

[0012]

[0013] To achieve the object, a first feature of the photoelectric sensor of the present application is a photoelectric sensor that detects an object in a monitoring area, including: a light projecting section that outputs a measurement light toward the monitoring area; a light receiving section that converts reflected light, which is diffusely reflected by the object, into a current signal; a preamplifier that converts the current signal converted by the light receiving section into a voltage signal; a first signal processing system that includes a first amplifier that amplifies an output signal of the preamplifier at a first amplification rate Al and a first binary circuit that binary-converts an output signal of the first amplifier at a first threshold value Vthl; and a second signal processing system that includes a second amplifier that amplifies the output signal of the preamplifier at a second amplification rate A2 and a second binary circuit that binary-converts an output signal of the second amplifier at a second threshold value Vth2, the first threshold value Vthl and the second threshold value Vth2, and the first amplification rate Al and the second amplification rate A2 being set to satisfy the following relational expression: 1 < (Vth2 / Vthl) < α = (A2 / Al).

[0014] The reflected light, which is diffusely reflected by the object, is detected in the light receiving section and converted into a current signal, and the current signal is converted into a voltage signal in the preamplifier and input to the first signal processing system and the second signal processing system. In the first signal processing system, a pulse signal obtained by binary- converting the voltage signal after amplification at the first amplification rate Al by the first amplifier at the first threshold value Vthl of the first binary circuit is output. Similarly, in the second signal processing system, a pulse signal obtained by binary- converting the voltage signal after amplification at the second amplification rate A2 (Al < A2) by the second amplifier at the second threshold value Vth2 (Vthl < Vth2) of the second binary circuit is output. Further, since the first threshold value Vthl and the second threshold value Vth2, and the first amplification rate Al and the second amplification rate A2 are set to satisfy the relational expression: 1 < (Vth2 / Vthl) < α = (A2 / Al), even if an input signal of a low level, which cannot be binary-converted in the first signal processing system, is input, binary-converted output can be obtained in the second signal processing system.

[0015] ​The second feature structure, based on the first feature structure described above, has a distance calculation circuit that calculates a distance from the photosensor to an object based on an output timing of the measurement light output from the light projecting section and a rising timing of the binary signal output from the first signal processing system or the second signal processing system.

[0016] The distance calculation circuit calculates a propagation time of light between the photosensor and the object from the output timing of the measurement light and the rising timing of the binary signal, i.e., the detection timing of the diffuse reflection light, and calculates the distance from the photosensor to the object based on the propagation time of light and the speed of light.

[0017] The third feature structure, based on the first or second feature structure described above, has a distance correction circuit that corrects the distance calculated by the distance calculation circuit based on a pulse width of the binary signal.

[0018] The rising edge of the binary signal varies depending on the characteristics of the voltage signal input to the binary circuit, and if the peak value of the voltage signal is high, the rising is steep, and if the peak value of the voltage signal is low, the rising is gentle. For this reason, the peak value of the voltage signal input to the binary circuit can be estimated based on the time from the rising timing to the falling timing of the binary signal, i.e., the pulse width. For this reason, the distance correction circuit calculates a correction amount for each rising timing of the binary signal so that it becomes the rising timing of the binary signal for a voltage signal set in advance as a reference, and corrects the distance calculated by the distance calculation circuit as a correction distance corresponding to the correction amount.

[0019] The fourth feature structure, based on the second or third feature structure described above, has a time determination circuit that permits the distance calculation circuit to calculate the distance if the pulse width of the binary signal is equal to or greater than a given threshold value, and prohibits the distance calculation circuit from calculating the distance if the pulse width is less than the given threshold value.

[0020] In the case where the pulse width of the binary signal corresponding to the light detected at the light receiving section is very short compared to the pulse width of the measurement light, it can be determined that it is an interference. For this reason, the time determination circuit determines that it is a true diffuse reflection light if the pulse width of the binary signal is equal to or greater than a given threshold value, and thus permits the distance calculation circuit to calculate the distance, and determines that it is an interference if the pulse width is less than the given threshold value, and thus prohibits the distance calculation circuit from calculating the distance.

[0021] The fifth feature structure, based on any one of the second to fourth feature structures described above, has a signal selection circuit that selects a binarized signal output from the first signal processing system when binarized signals are simultaneously output from both the first signal processing system and the second signal processing system, selects a binarized signal output from the second signal processing system when binarized signals are output only from the second signal processing system, and outputs to the distance calculation circuit.

[0022] In a case where binarized signals are output from the first signal processing system having the first amplifier with a small gain and the second signal processing system having the second amplifier with a large gain, respectively, it is possible that gain compression occurs in the second amplifier provided in the second signal processing system, thereby causing waveform blunting. For this reason, by selecting a binarized signal output from the first signal processing system through the signal selection circuit, a more correct distance can be obtained. Further, in a case where binarized signals are output only from the second signal processing system, by selecting a binarized signal obtained by appropriately amplifying a weak voltage signal that cannot be binarized in the first signal processing system with the second amplifier with a high gain, even a weak voltage signal can be appropriately calculated for distance.

[0023] The sixth feature structure, based on any one of the second to fourth feature structures described above, has an output selection circuit that outputs a first distance calculated by the distance calculation circuit based on a binarized signal output from the first signal processing system when a difference between the first distance and a second distance calculated by the distance calculation circuit based on a binarized signal output from the second signal processing system is less than a given distance threshold value, and outputs the second distance when the second distance is equal to or greater than a given long distance threshold value.

[0024] In a case where a difference between the first distance and the second distance is less than a given distance threshold value, since it is highly likely that the diffuse reflection light comes from the same object, the output selection circuit outputs the first distance based on a binarized signal output from the first signal processing system that is appropriately amplified, and in a case where the second distance is equal to or greater than a given long distance threshold value, it is determined that it is difficult to calculate a correct distance in the first signal processing system having the first amplifier with a small gain, and by outputting the second distance regardless of whether the first distance is calculated or not, a high-precision distance can be output in a wide range from a short range to a long range from the photosensor.

[0025] The seventh feature structure, based on the first feature structure described above, has an output interface circuit that outputs both an output signal of the first signal processing system and an output signal of the second signal processing system to the outside.

[0026] By outputting both the output signal of the first signal processing system and the output signal of the second signal processing system to the outside through the output interface circuit, the user of the photosensor can flexibly perform distance calculation taking into account the respective characteristics of the first signal processing system and the second signal processing system according to the use situation of the photosensor.

[0027] The light distance measuring apparatus according to the present application is characterized by comprising: the photosensor according to any one of the second to sixth aspects described above; a light deflection section that deflects the measurement light output from the light projecting section in a given direction; and / or a light scanning section that scans the measurement light output from the light projecting section in a given direction.

[0028] By comprising the light deflection section and / or the light scanning section that deflect or scan the measurement light output from the light projecting section of the photosensor according to any one of the aspects described above, the light distance measuring apparatus that calculates the distance to an object present in a specific direction can be realized.

[0029] -Effects of Invention-

[0030] As described above, according to the present application, a photosensor and a light distance measuring apparatus that can detect light in a wide dynamic range without using multiple transimpedance amplifiers and that are inexpensive can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a configuration explanatory view of a light distance measuring apparatus that comprises a photosensor.

[0032] Figure 2 is an explanatory view of a signal processing circuit that the photosensor comprises.

[0033] Figure 3 is an explanatory view of the relationship between the size of the output signal of an amplifier and a binary signal.

[0034] Figure 4 is an explanatory view of the output signals of a first amplifier and a second amplifier with respect to the same input signal. DETAILED DESCRIPTION

[0035] Hereinafter, embodiments of the photosensor and the light distance measuring apparatus according to the present application will be described.

[0036] In Figure 1A light distance measuring device 200 equipped with a photoelectric sensor 1 and a signal processing circuit 100 incorporated in the photoelectric sensor 1 are shown in FIG. 1. The light distance measuring device 200 is housed in a housing (illustrated as a cylindrical body shown by a broken line in the figure) C equipped with a light-transmitting window, and is equipped with: the photoelectric sensor 1 that detects an object within a monitoring region; and a light scanning section 10 that scans measurement light output from the photoelectric sensor 1 toward the monitoring region, and guides reflected light that is diffusely reflected from a surface of an object present in the monitoring region to the photoelectric sensor 1.

[0037] The photoelectric sensor 1 is equipped with: an illuminating section 2 that outputs measurement light toward the monitoring region via the light-transmitting window equipped in the housing C; an illuminating lens 15; a condensing lens 12 that condenses reflected light that is diffusely reflected by an object present in the monitoring region after the measurement light is waveform-shaped by the illuminating lens 15; a light receiving section 3 that receives the reflected light condensed by the condensing lens 12 and converts it into a current signal; and the signal processing circuit 100 that processes the current signal converted in the light receiving section 3. The signal processing circuit 100 is constituted by a plurality of circuit elements mounted on a substrate, and is actually housed in the bottom portion or the like of the housing C.

[0038] The light scanning section 10 is equipped with: a deflection mirror 11 that deflects the measurement light output from the illuminating section 2 toward the monitoring region, and guides the reflected light from the object to the light receiving section 3; a motor 13 that rotationally drives the deflection mirror 11 around a rotation axis P; and an encoder 14 that detects the rotational speed of the motor 13. The encoder 14 is constituted by: a disc 14A that is formed with slits at given intervals on the outer periphery and rotates around the rotation axis P; and a light interrupter 14B of a transmission type that detects light that is transmitted through the slits formed in the disc 14A.

[0039] The deflection mirror 11 is fixed in a posture inclined at 45 degrees with respect to the rotation axis P, and the light receiving section 3, the condensing lens 12, the illuminating section 2, and the illuminating lens 15 are respectively disposed on the axis of the rotation axis P. The measurement light output from the illuminating section 2 passes through the illuminating lens 15, propagates along a light guide 16 after being waveform-shaped into parallel light, is deflected at a right angle by the deflection mirror 11, is deflection scanned together with the rotation of the deflection mirror 11, and is output to the monitoring region.

[0040] The reflected light from the object propagates in the space around the light guide 16 and is incident on the deflection mirror 11, passes through the condensing lens 12 after being deflected toward the axis direction of the rotation axis P, and is incident on the light receiving section 3. A laser diode that outputs near-infrared region laser light is used as the illuminating section 2, and an avalanche photodiode (hereinafter, also referred to as "avalanche photodiode 3") is used as the light receiving section 3.

[0041] The signal processing circuit 100 includes a motor drive circuit 20, a light-emitting section drive circuit 30, a light-receiving section drive circuit 40, a light-receiving signal processing circuit 50, a system control circuit 60, an input / output control circuit 70, and a memory 80.

[0042] The system control circuit 60 is a circuit block composed of an FPGA, etc., which controls the motor drive circuit 20, the light-emitting part drive circuit 30, the light-receiving part drive circuit 40, and the light-receiving signal processing circuit 50, and performs distance measurement calculations and stores the calculation results in the memory 80.

[0043] The input / output control circuit 70 is a circuit block that reads the calculation results stored in the memory 80, performs necessary processing, and exchanges processing results and other signals with an external device via Ethernet (registered trademark). Furthermore, the communication interface with the external device is not limited to Ethernet (registered trademark).

[0044] The motor drive circuit 20 is a circuit that transmits pulse signals from the encoder 14 to the system control circuit 60, and drives the motor 13 based on the control signals from the system control circuit 60.

[0045] The projection section drive circuit 30 is a circuit that pulses to drive the laser diode constituting the projection section 2 based on the control signal from the system control circuit 60. The system control circuit 60 controls the rotation position of the deflector 11 based on the pulse signal from the encoder 14 and controls the driving timing of the laser diode, and outputs a control signal to the projection section drive circuit 30.

[0046] like Figure 2 As shown, the light-receiving section drive circuit 40 is a circuit that controls the drive voltage of the avalanche photodiode 3 constituting the light-receiving section 3. It includes a temperature sensor Sth that detects the ambient temperature of the light-receiving section 3 and a high-voltage generation circuit. The output voltage of the high-voltage generation circuit is adjusted based on a control signal from the system control circuit 60. In order to compensate for the temperature characteristics of the light-receiving section 3 based on the output of the temperature sensor, the system control circuit 60 variably controls the output voltage of the high-voltage generation circuit to be around a given voltage (approximately 150V in this embodiment).

[0047] like Figure 1 , 2As shown, the light-receiving signal processing circuit 50 is a circuit that processes a current signal obtained by photoelectrically converting reflected light by the avalanche photodiode 3, and includes: a preamplifier 51 using a transimpedance amplifier TIA that converts a current signal into a voltage signal; a first signal processing system 50A including: a first amplifier 52 that amplifies an output signal of the preamplifier 51 at a first amplification ratio Al; and a first binarization circuit 53 that binarizes an output signal of the first amplifier 52 at a first threshold value Vth1; and a second signal processing system 50B including: a second amplifier 54 that amplifies an output signal of the preamplifier 51 at a second amplification ratio A2; and a second binarization circuit 55 that binarizes an output signal of the second amplifier 54 at a second threshold value Vth2.

[0048] The current signal obtained by photoelectrically converting the reflected light by the avalanche photodiode 3 is divided by a resistance dividing circuit, and after being converted into an alternating current signal from which a direct current component is removed by a coupling capacitor, is input to the preamplifier 51.

[0049] The first amplifier 52 is constituted by an inverting amplifier AMP1 using an OP amplifier, and the second amplifier 54 is constituted by an inverting amplifier AMP2 (54A) and a differential amplifier AMP3 (54B) using OP amplifiers. The second amplifier 54 can also be a single inverting amplifier.

[0050] The first threshold value Vth1 and the second threshold value Vth2 are set to satisfy the following relational expression.

[0051] 1 < (Vth2 / Vth1) < a = (A2 / A1)

[0052] That is, Vth1 < Vth2 < a x Vth1, 1 < a = A2 / A1

[0053] Thus, even if an input signal of a low level that cannot be binarized in the first signal processing system 50A, a binarized output can be obtained in the second signal processing system 50B.

[0054] In the present embodiment, the amplification ratio of the preamplifier 51 is set to 80 dB, the first amplification ratio Al of the first amplifier 52 is set to 16 dB, and the second amplification ratio A2 of the second amplifier 54 is set to 41 dB. The value a = A2 / A1 of the ratio of the second amplification ratio A2 to the first amplification ratio Al in a linear display is equal to the value of the difference (25 dB (= 41 dB - 16 dB)) of the amplification ratios in a logarithmic display. Therefore, the value a of the ratio of the amplification ratios is about 17.8, which is larger than 1.

[0055] Further, the first threshold value Vthl is set to 0.16 V, and the second threshold value Vth2 is set to 0.40 V. The value of the ratio in the true value display of the second threshold value Vth2 with respect to the first threshold value Vthl is 2.5, which is larger than 1, and smaller than the ratio α. Further, the value of the difference in the logarithmic display of the second threshold value Vth2 with respect to the first threshold value Vthl is 7.96 dB, which is larger than 0 dB, and smaller than the value of the difference in the amplification ratio in the logarithmic display of the second amplification ratio A2 with respect to the first amplification ratio Al (25 dB).

[0056] That is, the first signal processing system 50A becomes a low-sensitivity signal processing system, and the second signal processing system 50B becomes a high-sensitivity signal processing system. Since the output signal of the preamplifier 51 is supplied to the first signal processing system 50A and the second signal processing system 50B, respectively, even if an input signal of a low level such as a binary output cannot be obtained in the low-sensitivity first signal processing system 50A, a binary output can be obtained in the high-sensitivity second signal processing system 50B.

[0057] In the system control circuit 60, in addition to the control of the above-described motor drive circuit 20, light projecting section drive circuit 30, and light receiving section drive circuit 40, a distance calculation circuit, a distance correction circuit, a time determination circuit, and the like are provided, and an output selection circuit and the like are provided in the input / output control circuit 70. The distance calculation circuit, the distance correction circuit, and the time determination circuit operate each time the unit scan of the light scanning section 10 is performed, calculate the distance to an object in the monitoring area and the scan angle, and store the results in the memory 80.

[0058] The signals binary-converted in the first binary conversion circuit 53 provided in the first signal processing system 50A and the second binary conversion circuit 55 provided in the second signal processing system 50B are input to the distance calculation circuit of the system control circuit 60, and the time difference between the output timing of the drive signal to the light projecting section 2 and the rising timing of the binary-converted signal of the reflected light photoelectrically converted is calculated by the Time-to-Digital Converter circuit provided in the distance calculation circuit, and the distance to the object is calculated based on the time difference and the speed of light. Further, since the scan angle of the measuring light is found based on the rotation position (scan angle) of the deflection mirror 11 at the output timing of each measuring light, which is grasped based on the pulse signal from the encoder 14, the distance to the object and the direction are determined.

[0059] That is, the distance calculation circuit is configured to calculate the distance from the photosensor to the object based on the output timing of the measuring light output from the light projecting section 2 and the rising timing of the binary-converted signal output from the first signal processing system 50A or the second signal processing system 50B.

[0060] AsFigure 3 As shown, even when the voltage signals corresponding to the reflected light amplified by the amplifiers 52, 54 are the same in time ΔT from the rising period rising from the ground level to the falling period falling to the ground level thereafter but different in peak value, the slopes of the rising are different, and even when binarization is performed with the same threshold value Vth, the binarized signal for the voltage signal with the low peak value is slower in the rising period and shorter in the pulse width than the binarized signal for the voltage signal with the high peak value (in Figure 3 In the above, the pulse width of the binarized signal for the voltage signal with the low peak value is denoted by ΔTL, and the pulse width of the binarized signal for the voltage signal with the high peak value is denoted by ΔTH).

[0061] Therefore, the rising period of the binarized signal varies depending on the characteristics of the voltage signal input to the binarization circuits 53, 55, and if the peak value of the voltage signal is high, the rising is steep, and if the peak value of the voltage signal is low, the rising is gentle. Also, between the pulse width which is the time from the rising period to the falling period of the binarized signal and the time difference from the point t0 at which the original reflected light arrives to the rising point of the binarized signal, there is a given correlation. For this reason, the time difference (for example, dt1, dt2) from the point t0 at which the original reflected light arrives to the rising point of the binarized signal can be estimated based on the pulse width (for example, ΔTL, ΔTH) of an arbitrary binarized signal.

[0062] For this reason, by preparing a correction table based on the above correlation and calculating the time difference dt up to the point t0 at which the original reflected light arrives from the pulse width of the binarized signal for an arbitrary voltage signal in advance, a correction amount (time difference dt) is calculated. In addition, a correction table can be used instead of a correction table.

[0063] In fact, in order to exclude the influence of the component deviations of the light projecting section 2, the light receiving section 3, and the circuit elements, the detection of the voltage signal for the reflected light from the reference reflection plate housed in the housing C and having a known reference distance as a reference voltage signal, the calculation of a correction coefficient for correcting the time difference dt with respect to the rising point t0 of the reference voltage signal so that the distance calculated from the time difference between the output period of the drive signal to the light projecting section 2 and the rising period of the binarized reference voltage signal becomes the reference distance, and the correction of each correction amount (time difference dt) of the above correction table with the correction coefficient are performed.

[0064] The distance correction circuit calculates a correction amount (time difference dt) from the correction table for any of the binary signals, calculates a correction distance based on the correction amount corrected with the correction coefficient described above, and corrects the distance calculated in the distance calculation circuit. In addition, the distance correction circuit can separately include a correction table for the first signal processing system 50A and a correction table for the second signal processing system 50B.

[0065] The time determination circuit is configured to allow the distance calculation circuit to calculate the distance when the pulse width of the binary signal is equal to or greater than a given threshold value, and to prohibit the distance calculation circuit from calculating the distance when the pulse width of the binary signal is less than the given threshold value.

[0066] In the case where the pulse width of the binary signal corresponding to the light detected in the light receiving section 3 is much shorter than the pulse width of the measuring light, it can be determined that it is an interference. For this reason, the time determination circuit determines that it is a true diffuse reflection light when the pulse width of the binary signal is equal to or greater than a given threshold value, and thus allows the distance calculation circuit to calculate the distance, and determines that it is an interference when the pulse width is less than the given threshold value, and thus prohibits the distance calculation circuit from calculating the distance. As the given threshold value, it is preferable to set a value in the range of 0.2 to 0.4 times the pulse width of the measuring light, but it is not limited to this value. It is sufficient to set a value shorter than the pulse width of the measuring light.

[0067] Thus, the distance to the object and the direction are calculated for each of the binary signals input through the first signal processing system 50A and the second signal processing system 50B, respectively. Furthermore, the calculated values are subjected to a filter process, and the distance and the direction determined to be appropriate as the object to be detected are stored in the memory 80.

[0068] As the filter process, a size determination filter or the like can be used, and the object is detected for a given number or more continuously along the adjacent scanning direction, and if the difference between the distances is within a given value, it is determined to be a valid object, and if not, it is removed as noise. By such a process, it is possible to exclude interference such as raindrops, fog, and the like.

[0069] The output selection circuit included in the input / output control circuit 70 reads out the distance and the direction written in the memory 80 every unit scanning period, calculates the difference between the first distance corresponding to the first signal processing system 50A and the second distance corresponding to the second signal processing system 50B, and outputs the first distance to the external device in the case where the difference is less than a given distance threshold value, that is, in the case where it can be determined that it is the same object.

[0070] Since the possibility is high that the diffuse reflection light is from the same object in the case where the difference between the 1st distance and the 2nd distance is not enough of the given distance threshold, the output selection circuit outputs the 1st distance based on the binarized signal output from the 1st signal processing system after being properly amplified in the case where the 2nd distance is above the given long distance threshold, judges that it is difficult to calculate the correct distance in the 1st signal processing system having the 1st amplifier with small gain, and outputs the 2nd distance regardless of whether the 1st distance is calculated or not, and can output the distance with high accuracy in a wide range from a short range to a long range from the light sensor.

[0071] Further, the output selection circuit is configured to output the 2nd distance in the case where the 2nd distance is above the given long distance threshold. This is because the object in the far distance that cannot be detected in the 1st signal processing system 50A with low sensitivity can be detected by the 2nd signal processing system 50B with high sensitivity.

[0072] Further, the output selection circuit has a near distance removal function that does not perform output in the case where the distance to the detected object is not enough of a given near distance threshold. Thus, the reflected light due to the stain of the housing C is prevented from being output as an effective object. The near distance threshold can be set to individual values in the 1st signal processing system 50A with low sensitivity and the 2nd signal processing system 50B with high sensitivity.

[0073] In Figure 4 , the output signal of the 1st amplifier 52 included in the 1st signal processing system 50A and the output signal of the 2nd amplifier 54 included in the 2nd signal processing system 50B are shown in correspondence with the measurement light output at a certain scanning angle. The near distance signal of the reflected light due to the stain of the housing C, the 1st echo signal, the 2nd echo signal, and the 3rd echo signal are shown.

[0074] In this case, the signal corresponding to the stain not enough of the near distance threshold is excluded by the output selection circuit described above, the 1st echo and the 2nd echo at substantially the same distance are calculated based on the signal after binarizing the output signal of the 1st amplifier 52 included in the 1st signal processing system 50A, and the 3rd echo above the long distance threshold is calculated based on the signal after binarizing the output signal of the 2nd amplifier 54 included in the 2nd signal processing system 50B. In addition, as shown in Figure 4 , since the signal waveforms of the 1st echo and the 2nd echo amplified by the 2nd amplifier 54 are oversaturated, it is difficult to calculate the correct distance.

[0075] Further, it is configured to judge that the first echo is an invalid signal and to avoid output in the case where it is judged that the first echo is a signal corresponding to an invalid object such as rain or fog through the above-described filtering processing. Further, a system that gives priority to processing the distance of the first echo in the near distance in order to prevent collision, a system that uses the second echo in order to detect an object located behind a thin object, and the like, and a system that selects / uses an echo in combination with various filtering processing according to the purpose can be made.

[0076] Hereinafter, other embodiments will be shown.

[0077] The system control circuit 60 can also have the function of the output selection circuit described in the above-described embodiments. Specifically, it can be configured as follows: in the case where the binarized signals are output simultaneously from both the first signal processing system 50A and the second signal processing system 50B, the binarized signal output from the first signal processing system 50A is selected, in the case where the binarized signal is output only from the second signal processing system 50B, the binarized signal output from the second signal processing system 50B is selected, and the selected binarized signal is output to the distance calculation circuit. The case where the binarized signals are output simultaneously from both refers to the case where the time difference of the rising edges of the binarized signals enters a given allowable range.

[0078] In the above-described embodiments, the optical distance measuring device 200 provided with the light scanning section 10 that deflects and scans the measurement light output from the light projecting section 2 provided in the photosensor 1 in a given direction is described, but an optical distance measuring device provided with a light deflecting section that deflects the measurement light output from the light projecting section in a given direction can also be configured.

[0079] In the above-described embodiments, the photosensor 1 incorporated in the optical distance measuring device 200 is described, but a separate photosensor 1 can also be used.

[0080] An output interface circuit that outputs both the output signal of the first signal processing system 50A and the output signal of the second signal processing system 50B provided in the photosensor 1 to the outside together with a signal indicating the output timing of the measurement light can also be provided. The user of the photosensor 1 can flexibly perform distance calculation taking into account the respective characteristics of the first signal processing system and the second signal processing system according to the use situation of the photosensor.

[0081] The light-receiving signal processing circuit 50 of the above-described embodiment can also include a preamplifier 51 that uses a transimpedance amplifier TIA to convert a current signal obtained by photoelectric conversion of reflected light by the avalanche photodiode 3 into a voltage signal, and can also include an nth signal processing system 50n that includes an nth amplifier that amplifies the output signal of the preamplifier 51 at an nth amplification rate An, and an nth binarization circuit that binarizes the output signal of the nth amplifier at an nth threshold value Vthn (n: an integer of 3 or more).

[0082] The (n-1)th signal processing system and the nth signal processing system can be configured so that the (n-1)th threshold value Vth(n-1) and the nth threshold value Vthn, and the (n-1)th amplification rate A(n-1) and the nth amplification rate An satisfy the following relationship.

[0083] 1 < (Vthn / Vth(n-1)) < α = (An / A(n-1))

[0084] Thus, even if an input signal of a low level that cannot be binarized in the (n-1)th signal processing system, a binarized output can be obtained in the nth signal processing system.

[0085] Further, the nth signal processing system 50n can be configured as a processing system of an intermediate sensitivity between the first signal processing system 50A of a low sensitivity and the second signal processing system 50B of a high sensitivity. As long as at least the first signal processing system 50A and the second signal processing system 50B satisfy the relationship 1 < (Vth2 / Vth1) < α = (A2 / A1), and as long as the nth amplifier that amplifies the output signal of the preamplifier 51 at the nth amplification rate An and the nth binarization circuit that binarizes the output signal of the nth amplifier at the nth threshold value Vthn are provided, a binarized output can be obtained.

[0086] The above-described embodiments are merely one example of the present application, and do not limit the scope of the present application by the description, and the specific structure of each part can be appropriately changed within the range in which the effects of the present application are exerted.

[0087] Industrial Applicability

[0088] The present application can achieve a low-cost photoelectric sensor and a light distance measuring device that can detect light in a wide dynamic range without using multiple transimpedance amplifiers.

[0089] -Explanation of Symbols-

[0090] 1: Photoelectric sensor

[0091] 2: Light projecting section

[0092] 3: light receiving section

[0093] 10: optical scanning section

[0094] 11: deflection mirror

[0095] 12: condenser lens

[0096] 20: motor drive circuit

[0097] 30: light projecting section drive circuit

[0098] 40: light receiving section drive circuit

[0099] 50: light receiving signal processing circuit

[0100] 50A: first signal processing system

[0101] 50B: second signal processing system

[0102] 51: preamplifier

[0103] 52: first amplifier

[0104] 53: first binary circuit

[0105] 54: second amplifier

[0106] 55: second binary circuit

[0107] 60: system control circuit

[0108] 70: input / output control circuit

[0109] 80: memory

[0110] 100: signal processing circuit

Claims

1. An optical sensor that detects an object in a monitoring area, the optical sensor characterized by comprising: a light projecting section that outputs a measurement light toward the monitoring area; a light receiving section that converts reflected light that is diffusely reflected by the measurement light hitting the object into a current signal; a preamplifier that converts the current signal converted by the light receiving section into a voltage signal; a first signal processing system that includes a first amplifier that amplifies the output signal of the preamplifier at a first amplification rate Al and a first binary circuit that binarizes the output signal of the first amplifier at a first threshold value Vthl; a second signal processing system that includes a second amplifier that amplifies the output signal of the preamplifier at a second amplification rate A2 and a second binary circuit that binarizes the output signal of the second amplifier at a second threshold value Vth2; a distance calculation circuit that calculates a distance from the optical sensor to the object based on the output timing of the measurement light output from the light projecting section and the rising timing of the binarized signal output from the first signal processing system or the second signal processing system; and an output selection circuit that outputs a first distance calculated by the distance calculation circuit based on the binarized signal output from the first signal processing system when the difference between the first distance and a second distance calculated by the distance calculation circuit based on the binarized signal output from the second signal processing system is less than a given distance threshold value, wherein the first threshold value Vthl and the second threshold value Vth2, and the first amplification rate Al and the second amplification rate A2 satisfy the following relationship 1 < (Vth2 / Vthl) < α = (A2 / A1).

2. The optical sensor according to claim 1, wherein the output selection circuit outputs the second distance when the second distance is greater than or equal to a given long distance threshold value.

3. The optical sensor according to claim 1 or 2, characterized by further comprising: a distance correction circuit that corrects the distance calculated by the distance calculation circuit based on the pulse width of the binarized signal.

4. The optical sensor according to claim 1 or 2, characterized by further comprising: a time determination circuit that permits the distance calculation circuit to calculate the distance when the pulse width of the binarized signal is greater than or equal to a given threshold value, and prohibits the distance calculation circuit from calculating the distance when the pulse width is less than the given threshold value.

5. The optical sensor according to claim 1 or 2, characterized by further comprising: a signal selection circuit that selects the binarized signal output from the first signal processing system when the binarized signal is output simultaneously from both the first signal processing system and the second signal processing system, selects the binarized signal output from the second signal processing system when the binarized signal is output only from the second signal processing system, and outputs the selected binarized signal to the distance calculation circuit.

6. The optical sensor according to claim 1, characterized in that ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The photoelectric sensor is provided with: an output interface circuit that outputs both an output signal of the first signal processing system and an output signal of the second signal processing system to the outside.

7. An optical ranging device, characterized in that provided with: the photoelectric sensor according to any one of claims 1 to 6; a light deflection section that deflects the measurement light output from the light projecting section in a given direction; and / or a light scanning section that scans the measurement light output from the light projecting section in a given direction.

Images