JP2008215878A - Light receiving device, laser radar device and vehicle - Google Patents

Abstract

Provided are a light receiving device, a laser radar device including the light receiving device, and a vehicle including the laser radar device, in which a decrease in measurement accuracy or an erroneous detection of an object is sufficiently prevented.
Bias voltage _{V ba} is applied to the A APD81. When light enters the APD 81, a current corresponding to the incident light amount P flows through the APD 81. Capacitor 83 removes the DC component of the output current of the APD81, and outputs the incident light current _{I d.} I-V conversion circuit 84 converts the incident light current _{I d} on the incident light voltage _{V d.} Amplifier circuit 85 amplifies the incident light voltage _{V d,} and outputs the received pulse _{V a.} Inverting amplifier circuit 86 inverts and amplifies the received pulse _{V a,} and outputs the inverted and amplified voltage _{V ia.} The half-wave rectifier circuit 87 half-wave rectifies the inverted amplified voltage V _ia and outputs a noise level V _nDC . Bias control circuit 88 is controlled by negative feedback bias voltage _{V ba} on the basis of the noise level _{V NDC.}
[Selection] Figure 4

Description

  The present invention relates to a light receiving device that receives laser light, a laser radar device including the light receiving device, and a vehicle including the laser radar device.

  Conventionally, various vehicle laser radars have been proposed to measure the distance from a vehicle to an object. In the laser radar, the object is irradiated with laser light from the light transmitting unit, and the reflected light from the object is received by the light receiving unit. The distance to the object is calculated by measuring the time required from the emission of the laser beam by the light transmitting unit to the reception of the reflected light by the light receiving unit.

In such a laser radar, when external light such as sunlight is incident on the light receiving unit, the measurement accuracy is lowered. Therefore, in the vehicle laser radar described in Patent Document 1, the distance to the object is measured based on the time difference from light transmission to light reception, and the DC fluctuation due to the external light in the light reception signal of the light receiving unit is detected and measured. Is corrected based on the DC fluctuation.
JP-A-5-119147

  However, in the above-described conventional laser radar, when the external light includes a high frequency component, a high frequency noise component is superimposed on the light reception signal of the light receiving unit. Thereby, the S / N (signal-to-noise ratio) of the received light signal is lowered. Further, there is a possibility that a noise component due to extraneous light is erroneously determined as a component due to reflected light from an object. As a result, the measurement accuracy of the distance may be reduced or the object may be erroneously detected. For example, when the vehicle travels toward the sunset, strong extraneous light is incident on the light receiving portion of the laser radar. In such a case, a decrease in distance measurement accuracy or an erroneous detection of an object becomes significant.

  An object of the present invention is to provide a light receiving device, a laser radar device including the light receiving device, and a vehicle including the laser radar device, in which a decrease in measurement accuracy or erroneous detection of an object is sufficiently prevented.

  (1) A light receiving device according to a first aspect of the present invention is a light receiving device that receives laser light emitted from a light transmitting device and reflected by a detection object, and that receives a laser beam reflected by the detection object. A diode, a bias application circuit that applies a bias voltage to the avalanche photodiode, and a conversion unit that converts the output current of the avalanche photodiode into a voltage from which a DC component has been removed. The bias application circuit is obtained by the conversion unit. A rectifier that generates a noise level by rectifying a component having a polarity opposite to that of a pulse component caused by laser light in a generated voltage, and a bias that controls a bias voltage by negative feedback based on the noise level generated by the rectifier A bias applying circuit for applying a bias voltage to the avalanche photodiode including the control circuit. The bias application circuit converts the output current of the avalanche photodiode into a voltage from which the DC component has been removed, and a high-frequency component having a polarity opposite to the pulse component caused by the laser light in the voltage obtained by the conversion unit. It includes a rectifier that generates a noise level by rectification, and a bias control circuit that controls the bias voltage with negative feedback based on the noise level generated by the rectifier.

  In the light receiving device, a bias voltage is applied to the avalanche photodiode by a bias application circuit. The laser light reflected by the detection object is received by the avalanche photodiode. The output current of the avalanche photodiode is converted into a voltage from which the DC component has been removed by the converter.

  Here, the voltage obtained by the conversion unit includes a pulse component caused by laser light and a noise component caused by extraneous light. Since the DC component is removed from this voltage, the high frequency noise component changes to positive and negative.

  A noise level is generated by rectifying a component having a polarity opposite to the pulse component caused by the laser light in the voltage obtained by the conversion unit by the rectification unit. Thereby, the high frequency noise component is accurately detected as the noise level without being affected by the pulse component caused by the laser beam.

  Further, the bias voltage is controlled by negative feedback by the bias control circuit based on the noise level generated by the rectifier. In this case, as the noise level increases, the bias voltage applied to the avalanche photodiode decreases. Thereby, the multiplication factor of the avalanche photodiode is reduced, and the voltage obtained by the conversion unit is reduced. As a result, noise components included in the voltage obtained by the conversion unit are reduced.

  Further, when the environmental temperature varies, the multiplication factor of the avalanche photodiode varies, and the voltage obtained by the conversion unit varies. Also in this case, a noise level is generated by rectifying the component having the opposite polarity to the pulse component caused by the laser light in the voltage obtained by the conversion unit by the rectification unit. Thereby, the noise component due to the fluctuation of the environmental temperature is accurately detected as the noise level without being influenced by the pulse component caused by the laser beam. Further, the bias voltage is controlled by negative feedback by the bias control circuit based on the noise level generated by the rectifier. As a result, fluctuations in the multiplication factor of the avalanche photodiode are suppressed.

  In this way, the noise component can be sufficiently reduced without being affected by the component caused by the laser beam reflected by the detection target. Therefore, the pulse component resulting from the laser light can be accurately detected. As a result, information on the detection target can be measured with high accuracy based on the voltage obtained by the conversion unit, and erroneous detection of the detection target can be prevented.

  (2) The conversion unit includes a removal circuit that removes a direct current component of the output current of the avalanche photodiode, a current-voltage conversion circuit that converts the output current of the removal circuit into a voltage, and an amplification that amplifies the output voltage of the current-voltage conversion circuit And a circuit.

  In this case, the direct current component of the output current of the avalanche photodiode is removed by the removal circuit. As a result, the high-frequency noise current caused by extraneous light changes between positive and negative. The output current from which the direct current component has been removed is converted into a voltage by a current-voltage conversion circuit and amplified by an amplifier circuit. Thereby, the output voltage of the amplifier circuit includes a pulse component caused by the laser beam and a high-frequency noise component that changes positively and negatively. By controlling the bias voltage with negative feedback by the rectifier and the bias control circuit, the noise component of the output voltage of the amplifier circuit is reduced.

  (3) The rectifier unit includes an inverting amplifier circuit that inverts and amplifies the voltage obtained by the conversion unit, and a half-wave rectifier circuit that generates a noise level by performing half-wave rectification on the positive component of the output voltage of the inverting amplifier circuit. May be included.

  In this case, the pulse component resulting from the laser light included in the output voltage of the inverting amplifier circuit has a negative polarity. As a result, the positive component of the output voltage of the inverting amplifier circuit is half-wave rectified, so that the noise level corresponding to the noise component can be accurately generated without being affected by the pulse component caused by the laser beam.

  (4) The bias control circuit may generate the bias voltage by adding the inverted component of the noise level generated by the rectifier to the reference bias voltage.

  In this case, when the noise component increases, the noise level inversion component decreases, and when the noise component decreases, the noise level inversion component increases. Thereby, the bias voltage can be controlled by negative feedback by adding the inverted component of the noise level to the reference bias voltage.

  (5) The avalanche photodiode may be arranged to receive a part of the laser light emitted by the light transmitting device.

  In this case, the voltage obtained by the conversion unit includes a pulse component resulting from part of the laser light emitted by the light transmitting device. Accordingly, it is possible to accurately detect the pulse component caused by the laser light emitted by the light transmitting device and the pulse component caused by the laser light reflected by the detection target. As a result, the distance to the detection target can be measured with high accuracy based on the pulse component included in the voltage obtained by the conversion unit, and the occurrence of erroneous detection of the detection target can be prevented.

  (6) A laser radar device according to a second aspect of the present invention includes a light transmitting device that emits laser light and a light receiving device that receives the light, and the light receiving device is emitted by the light transmitting device and reflected by a detection object. Including an avalanche photodiode that receives the laser light, a bias application circuit that applies a bias voltage to the avalanche photodiode, and a conversion unit that converts the output current of the avalanche photodiode into a voltage from which a DC component has been removed. The circuit includes a rectifier that generates a noise level by rectifying a component having a polarity opposite to a pulse component caused by laser light in a voltage obtained by the converter, and a bias voltage based on the noise level generated by the rectifier. And a bias control circuit for controlling the current with negative feedback.

  In the laser radar device, laser light is emitted by a light transmitting device, and light is received by a light receiving device. A bias voltage is applied to the avalanche photodiode by the bias application circuit of the light receiving device. The laser light reflected by the detection object is received by the avalanche photodiode. The output current of the avalanche photodiode is converted into a voltage from which the DC component has been removed by the converter.

  Here, the voltage obtained by the conversion unit includes a pulse component caused by laser light and a noise component caused by extraneous light. Since the DC component is removed from this voltage, the high frequency noise component changes to positive and negative.

  A noise level is generated by rectifying a component having a polarity opposite to the pulse component caused by the laser light in the voltage obtained by the conversion unit by the rectification unit. Thereby, the high frequency noise component is accurately detected as the noise level without being affected by the pulse component caused by the laser beam.

  Further, the bias voltage is controlled by negative feedback by the bias control circuit based on the noise level generated by the rectifier. In this case, as the noise level increases, the bias voltage applied to the avalanche photodiode decreases. Thereby, the multiplication factor of the avalanche photodiode is reduced, and the voltage obtained by the conversion unit is reduced. As a result, noise components included in the voltage obtained by the conversion unit are reduced.

  Further, when the environmental temperature varies, the multiplication factor of the avalanche photodiode varies, and the voltage obtained by the conversion unit varies. Also in this case, a noise level is generated by rectifying the component having the opposite polarity to the pulse component caused by the laser light in the voltage obtained by the conversion unit by the rectification unit. Thereby, the noise component due to the fluctuation of the environmental temperature is accurately detected as the noise level without being influenced by the pulse component caused by the laser beam. Further, the bias voltage is controlled by negative feedback by the bias control circuit based on the noise level generated by the rectifier. As a result, fluctuations in the multiplication factor of the avalanche photodiode are suppressed.

  In this way, the noise component can be sufficiently reduced without being affected by the component caused by the laser beam reflected by the detection target. Therefore, the pulse component resulting from the laser light can be accurately detected. As a result, information on the detection target can be measured with high accuracy based on the voltage obtained by the conversion unit, and erroneous detection of the detection target can be prevented.

  (7) The avalanche photodiode of the light receiving device is arranged so as to receive a part of the laser light emitted by the light transmitting device, and the laser light emitted by the light transmitting device at the voltage obtained by the conversion unit of the light receiving device. You may further provide the distance calculation part which calculates the distance from a light transmission apparatus to a detection target object based on the time interval of the pulse component resulting from the pulse component resulting from and the laser beam reflected by the detection target object.

  In this case, it is possible to accurately detect the pulse component caused by the laser light emitted by the light transmitting device and the pulse component caused by the laser light reflected by the detection target. Therefore, the distance from the light transmission device to the detection target is highly accurate based on the time interval between the pulse component due to the laser light emitted by the light transmission device and the pulse component due to the laser light reflected by the detection target. And the occurrence of erroneous detection of the detection object can be prevented.

  (8) The light transmission device may emit a pulsed laser beam at a constant cycle, and the laser beam emission cycle may be 1000 times or more the emission time of the laser beam.

  In this case, since the time of the pulse component caused by the laser light is remarkably shorter than the time of the noise component, the noise component can be accurately detected without being affected by the pulse component caused by the laser light.

  (9) The light transmitting device may include a laser diode that emits laser light and a laser light rotation system that rotates the traveling direction of the laser light emitted by the laser diode in a plane.

  In this case, since the laser beam is emitted in all directions by the light transmitting device, it is possible to measure information relating to the detection target existing in all directions of the laser radar device with high accuracy.

  (10) The laser radar device is caused by an angle detection unit that detects a rotation angle in a traveling direction of the laser beam by a laser beam rotation system, and a laser beam reflected by a detection target in a voltage obtained by a conversion unit of the light receiving device. A pulse detection unit that detects a pulse component to be detected, and an azimuth calculation unit that calculates the azimuth of the detection target based on the angle of the traveling direction of the laser beam detected by the angle detection unit when the pulse component is detected by the pulse detection unit Further, it may be provided.

  In this case, the direction of the detection target can be measured with high accuracy based on the angle of the traveling direction of the laser beam detected by the angle detection unit when the pulse component is detected by the pulse detection unit. The occurrence of detection can be prevented.

  (11) A vehicle according to a third invention is obtained by a main body, a drive unit for moving the main body, the laser radar device according to the second invention provided in the main body, and the conversion unit of the laser radar device. And an informing unit for informing the passenger of information based on the voltage.

  In the vehicle, a laser radar device is provided in a main body that is moved by a driving unit. Information based on the voltage obtained by the conversion unit of the laser radar device is notified to the occupant by the notification unit. As a result, the occupant can obtain information on the detection target around the vehicle. In particular, in the laser radar device, the noise component can be sufficiently reduced without being affected by the component caused by the laser beam reflected by the detection target. Therefore, the pulse component resulting from the laser light can be accurately detected. As a result, information on the detection target can be measured with high accuracy based on the voltage obtained by the conversion unit, and erroneous detection of the detection target can be prevented.

  According to the present invention, the noise component can be sufficiently reduced without being affected by the component caused by the laser beam reflected by the detection target. Therefore, the pulse component resulting from the laser light can be accurately detected. As a result, information on the detection target can be measured with high accuracy based on the voltage obtained by the conversion unit, and erroneous detection of the detection target can be prevented.

(1) Signal Processing System of Laser Radar Device FIG. 1 is a block diagram showing a configuration of a signal processing system of a laser radar device according to an embodiment of the present invention. This laser radar device is mounted on a vehicle, for example.

  The laser radar device 1 in FIG. 1 is used to detect the distance to the detection target 10 and the orientation of the detection target 10. Here, the azimuth of the detection target 10 is represented by an angle from the reference direction. The reference direction is determined in a direction perpendicular to the traveling direction, for example. The reference direction is not limited to this, and may be a direction parallel to the traveling direction, or can be determined in an arbitrary direction.

  The light transmission device 70 emits laser light. Hereinafter, the laser light emitted from the light transmission device 70 is referred to as emission light EL. The motor 30 rotates a reflecting mirror, which will be described later, in order to rotate the direction of the emitted light EL from the light transmitting device 70 by 360 degrees in the horizontal plane. The encoder 40 outputs an encoder pulse EP corresponding to the rotation angle of the motor 30 and outputs an origin pulse OP for each rotation of the motor 30. The motor rotation speed control unit 20 controls the rotation speed of the motor 30 to be constant based on the encoder pulse EP output from the encoder 40.

  The light emission interval pulse generator 50 generates the light emission interval pulse EI by multiplying the encoder pulse EP output from the encoder 40. The light emission trigger generation unit 60 generates the light emission trigger ET in synchronization with the light emission interval pulse EI generated by the light emission interval pulse generation unit 50. The light transmission device 70 emits the emission light EL in synchronization with the light emission trigger ET generated by the light emission interval pulse generation unit 50.

The light receiving device 80 receives the reflected light RL from the detection target 10, receives the emitted light EL and the extraneous light DI from the light transmitting device 70, and outputs _a received light pulse Va.

The signal processing unit 90 outputs a binary signal BS based on the received pulse V _a which is output from the light emission trigger ET and the light receiving device 80 is generated by the light emitting trigger generator 60.

  The distance generation unit 100 generates a distance signal DS indicating a distance based on the light emission trigger ET generated by the light emission trigger generation unit 60 and the binarized signal BS output from the signal processing unit 90, and generates a distance. The distance generation signal DG shown is output.

  On the other hand, the angle generation unit 110 indicates an angle based on the origin pulse OP output from the encoder 40, the light emission trigger ET generated by the light emission trigger generation unit 60, and the distance generation signal DG generated by the distance generation unit 100. A signal AS is generated.

  The radar image generation unit 120 displays a radar image to be described later on the display screen based on the distance signal DS generated by the distance generation unit 100 and the angle signal AS generated by the angle generation unit 110.

  The light emission interval pulse generator 50, the light emission trigger generator 60, the signal processor 90, the distance generator 100, the angle generator 110, and the radar image generator 120 are hardware and programs such as a CPU (Central Processing Unit) and a memory. It is realized by software such as.

  Note that some or all of the light emission interval pulse generation unit 50, the light emission trigger generation unit 60, the signal processing unit 90, the distance generation unit 100, the angle generation unit 110, and the radar image generation unit 120 are realized by hardware such as a logic circuit. May be.

(2) Optical System of Laser Radar Device FIG. 2 (a) is a schematic diagram showing the configuration of the optical system of the laser radar device 1 of FIG. 1, and FIG. 2 (b) shows the configuration of the reflecting mirror 250 of the laser radar device 1. It is a perspective view.

  In FIG. 2A, the light transmitting device 70 is attached to the center of the bottom of the cylindrical holder 200. The light transmitting device 70 includes a laser diode (hereinafter referred to as LD) 71 and a holding member 72. The LD 71 is held by a holding member 72 so as to emit laser light vertically upward. In the present embodiment, for example, a near infrared pulse laser having a wavelength of 870 nm is used as the LD 71.

  Inside the holding body 200, a reflecting mirror 210 having an opening at the center is attached so as to be inclined at an angle of 45 degrees with respect to a horizontal plane. A light receiving device 80 is provided on the side wall of the holding body 200. The light receiving device 80 includes an avalanche photodiode (hereinafter referred to as APD) 81, a holding member 81a, and a plurality of circuits to be described later. The APD 81 is held by the holding member 81a so that the optical axis is oriented in the horizontal direction.

  A light projecting / receiving lens 220 is attached above the reflecting mirror 210 inside the holder 200. The central axis of the light projecting / receiving lens 220 faces the vertical direction.

  A protective cover 240 is attached to the inner peripheral surface of the upper end portion of the holding body 200 via a plurality of bearings 230 so as to be rotatable around a vertical axis. As shown in FIG. 2B, the reflecting mirror 250 is fixed to the protective cover 240 so as to be inclined at an angle of 45 degrees with respect to the vertical direction. The protective cover 240 is provided to prevent light incident on the reflecting mirror 250 from being attenuated.

  In FIG. 2A, the motor holding portion 201 is integrally formed so as to protrude in the horizontal direction from the outer peripheral surface of the upper end portion of the holding body 200. The motor 30 is held by the motor holding unit 201 so that the rotation axis faces the vertical direction. A pulley 31 is attached to the rotating shaft of the motor 30. The pulley 31 and the protective cover 240 are connected by a belt 32. As the motor 30 rotates, the protective cover 240 rotates. Thereby, the reflecting mirror 250 rotates around the vertical axis while being inclined by 45 degrees with respect to the horizontal plane.

  Laser light (emitted light EL) emitted vertically upward from the LD 71 of the light transmitting device 70 passes through the opening of the reflecting mirror 210 and the light projecting / receiving lens 220, is reflected by the reflecting mirror 250, and travels in the horizontal direction. When the reflecting mirror 250 is rotated by the motor 30, the traveling direction of the emitted light EL is rotated 360 degrees about the vertical axis.

  The reflected light RL from the detection target 10 is reflected downward by the reflecting mirror 250 and condensed by the light projecting / receiving lens 220. The condensed reflected light RL is reflected by the reflecting mirror 210 and enters the APD 81 of the light receiving device 80. Similarly, the extraneous light DI is also reflected downward by the reflecting mirror 250 and collected by the light projecting / receiving lens 220. The collected extraneous light is reflected by the reflecting mirror 210 and enters the APD 81 of the light receiving device 80. In this case, part of the emitted light EL from the LD 71 is irregularly reflected on the surface of the light projecting / receiving lens 220 and enters the APD 81.

(3) Operation of Laser Radar Device FIG. 3 is a timing chart for explaining the operation of the laser radar device 1 of FIG. The operation of the laser radar device 1 of FIG. 1 will be described below with reference to FIG.

The horizontal axis in FIG. 3 is time. The origin pulse OP and encoder pulse EP are shown in the first and second stages. In the third to fifth stages, the light emission interval pulse EI, the light emission trigger ET, and the light emission pulse Em are shown. The light emission interval pulse EI, the light emission trigger ET, and the light emission pulse Em are enlarged on the time axis compared to the encoder pulse EP. Further, the sixth stage and seventh stage pulses received V _a and the binary signal BS are shown. Photodetection pulse V _a and the binary signal BS is further enlarged over time compared to the emission pulse Em axis.

  Each time the motor 30 in FIG. 1 rotates by a predetermined angle, the encoder 40 outputs an encoder pulse EP. In the present embodiment, the encoder pulse EP is generated every time the motor 30 rotates 6 °. Therefore, when the motor 30 makes one revolution, the encoder 40 generates 60 encoder pulses EP. Further, every time the motor 30 makes one rotation, the encoder 40 outputs an origin pulse OP. Therefore, the cycle T1 of the origin pulse OP corresponds to a cycle of one rotation of the motor 30. In the present embodiment, the encoder 40 generates the origin pulse OP every time 60 encoder pulses EP are generated.

  The motor rotation speed control unit 20 controls the rotation speed of the motor 30 to be constant in response to the encoder pulse EP. In this case, the motor rotation speed control unit 20 controls the motor 30 so that the cycle T1 of the origin pulse OP is constant.

  The light emission interval pulse generator 50 generates the light emission interval pulse EI by multiplying the encoder pulse EP. In the present embodiment, the cycle T2 of the light emission interval pulse EI is 20 times the cycle of the encoder pulse EP. Here, an angle at which the motor 30 rotates during the period T2 of the light emission interval pulse EI (hereinafter referred to as a unit angle) is denoted by Δθ. In the present embodiment, the unit angle Δθ is 0.3 °. In this case, the light emission interval pulse EI is generated every time the motor 30 rotates 0.3 °. Hereinafter, the cycle T2 of the light emission interval pulse EI is referred to as the light emission interval T2.

  The light emission trigger generation unit 60 generates a light emission trigger ET that falls in synchronization with the rise of the light emission interval pulse EI.

  The light transmitting device 70 generates a light emission pulse Em that rises in synchronization with the fall of the light emission trigger ET, and emits laser light as emission light EL in synchronization with the light emission pulse Em. Thereby, the emitted light EL is emitted every time the motor 30 rotates by the unit angle Δθ.

  The emitted light EL from the LD 71 of the light transmitting device 70 is irradiated to the detection target 10. A part of the emitted light EL is incident on the APD 81 of the light receiving device 80. Therefore, after the emitted light EL from the light transmitting device 70 is received by the light receiving device 80, the reflected light RL from the detection target 10 is received by the light receiving device 80. In this case, the time from when the light receiving device 80 receives the emitted light EL to when the reflected light RL is received is proportional to the distance from the laser radar device 1 to the detection target 10.

  The light emission interval T2 is preferably not less than 1000 times and not more than 100,000 times the light emission time (the width of the light emission pulse Em) of the LD 71 of the light transmitting device 70. For example, when the light emission time of the LD 71 is 10 ns, the light emission interval T2 is preferably 10 μs or more and 1 ms or less.

As described above, the emitted light EL from the light transmitting device 70, the reflected light RL from the detection target 10, and the extraneous light DI are incident on the APD 81 of the light receiving device 80. As described below, the noise component caused by the extraneous light DI is reduced in the light pulse V _a output from the light receiving device 80. Therefore, the photodetection pulse V _a output from the light receiving device 80 includes a pulse component of the pulse component and the reflected light RL of the firing light EL.

The signal processing unit 90 generates a binarized signal by comparing the level of the light reception pulse Va with _a predetermined threshold every unit time Δt. The binary signal is received pulse V _a level logic value "1" when higher than the threshold of the logical value "0" when the level of the light receiving pulse V _a is less than or equal to the threshold . For example, the signal processing unit 90 determines a logical value “1” and a logical value “0” every 1 ns. Further, the signal processing unit 90 maintains the logical value “1” at the center position in each block composed of a plurality of consecutive logical values “1” in the binarized signal, and sets the other logical value “1” as a logical value. By replacing with “0”, the binarized signal BS is generated. In FIG. 3, the logical value “1” of the binarized signal BS is represented by a thick line filled with black.

  In response to the light emission trigger ET, the distance generation unit 100 calculates the distance from the laser radar device 1 to the detection target 10 based on the time interval T3 of the adjacent logical values “1” of the binarized signal BS, A distance signal DS indicating the calculated distance is generated.

  Specifically, when the number of logical values from the logical value “1” at the generation of the light emission trigger ET to the next logical value “1” is m and the speed of light is c, the laser radar device 1 detects the detection target. The distance D to the object 10 is calculated by the following equation.

D = Δt · m · c / 2
The angle generation unit 110 calculates an angle θ [°] based on the origin pulse OP, the light emission trigger ET, and the distance generation signal DG, and generates an angle signal AS representing the angle θ.

  Specifically, the angle generation unit 110 resets the angle θ to 0 ° in response to the origin pulse OP, and adds the unit angle Δθ to the angle θ for each light emission trigger ET. When the distance generation signal DG is given by the distance generation unit 100, the angle generation unit 110 outputs an angle signal AS indicating the angle θ.

(4) Configuration of Light Receiving Device 80 FIG. 4 is a block diagram showing a configuration of the light receiving device 80 of FIG.

  As shown in FIG. 4, the light receiving device 80 includes an APD 81, a resistor 82, a capacitor 83, an IV (current-voltage) conversion circuit 84, an amplification circuit 85, an inverting amplification circuit 86, a half-wave rectification circuit 87, and a bias control circuit. 88. The inverting amplifier circuit 86, the half-wave rectifier circuit 87 and the bias control circuit 88 constitute a bias application circuit 810.

  The APD 81 is connected between the node N1 and the node N2. Resistor 82 is connected between node N2 and the ground terminal. Capacitor 83 is connected between node N 2 and IV conversion circuit 84.

A bias voltage _Vba is output from the bias control circuit 88 to the node N1. Thereby, the bias voltage _{V ba} is applied to the APD81. When the bias voltage V _ba applied to the APD 81 increases, the multiplication factor of the APD 81 increases, and when the bias voltage V _ba applied to the APD 81 decreases, the multiplication factor of the APD 81 decreases.

When light enters the APD 81, a current corresponding to the incident light amount P flows through the APD 81. Capacitor 83 passes the high frequency component of the output current of APD 81. Thereby, the direct current component of the output current of the APD 81 is removed. Hereinafter referred to as the output current of the capacitor 83 and the incident light current I _d.

I-V conversion circuit 84 converts the incident light current _{I d} on the incident light voltage _{V d.} Amplifier circuit 85 amplifies the incident light voltage _{V d,} and outputs the received pulse _{V a.} Inverting amplifier circuit 86, inverts and amplifies the received pulse _{V a,} and outputs the inverted and amplified voltage _{V ia.} The half-wave rectification circuit 87 half-wave rectifies the inverted amplification voltage V _ia and outputs a noise level V _nDC . Bias control circuit 88 outputs a bias voltage _{V ba} to the node N1 based on the noise level _{V NDC.} Details of the configuration and operation of each part of the light receiving device 80 will be described later.

Figure 5 is a waveform diagram showing a binary signal BS generated by the pulses received V _a and the signal processing section 90 is outputted from the light receiving device 80, (a) is a noise component due to the external light DI to receiving pulses V _a There shows a case superimposed, (b) shows a case where the noise component of the received light pulse V _a is reduced. The horizontal axis in FIG. 5 is time.

As shown in FIGS. 5A and 5B, a binarized signal BS is obtained by comparing the level of the light reception pulse Va with _a threshold value TH. Thereby, the pulse Pe by the emitted light EL and the pulse Pr by the reflected light RL are generated. The distance from the laser radar device 1 to the detection target 10 is calculated based on the pulse Pe generated by the emitted light EL and the pulse Pr generated by the reflected light RL.

As shown in FIG. 5 (a), when the noise component due to external light DI is superimposed on the light receiving pulse V _a is the pulse due to a noise component in addition to the pulse Pr by pulse Pe and the reflected light RL by emission light EL Pn1 ~ Pn4 is generated. In this case, the calculation accuracy of the distance deteriorates due to the pulses Pn1 and Pn4, and the detection target is erroneously detected due to the pulses Pn2 and Pn3.

In this embodiment, by the bias voltage V _ba of APD81 it is controlled in the light receiving device 80, as shown in FIG. 5 (b), noise components superimposed on the pulses received V _a is reduced. Thereby, only the pulse Pe by the emitted light EL and the pulse Pr by the reflected light RL are generated.

  As a result, the calculation accuracy of the distance is improved and the occurrence of erroneous detection of the detection target is prevented.

(5) Operation of Each Part of Light Receiving Device 80 Hereinafter, the operation of each part of the light receiving device 80 will be described with reference to FIGS.

  FIG. 6 is a diagram for explaining the operation of the APD 81. 6A is a block diagram illustrating the function of the APD 81, FIG. 6B is a waveform diagram illustrating the amount of light incident on the APD 81, and FIG. 6C is a waveform diagram illustrating the incident photocurrent output from the capacitor 83.

The APD81, bias voltage _{V ba} is applied. Here, the multiplication factor M of the APD 81 is expressed by the following equation.

M = f ₁ (V _ba )
In the above equation, f ₁ (V _ba ) is an increasing function. When the extraneous light DI enters the APD 81 together with the emitted light EL from the light transmitting device 70 and the reflected light RL from the detection target 10, an incident photocurrent determined by the incident light amount P and the multiplication factor M flows through the APD 81. The direct current component of the incident photocurrent of the APD 81 is removed by the capacitor 83. Thereby, the incident light current I _d, represented by the following equation is output from the capacitor 83.

I _d = f ₂ (M, P)
The function f ₂ (M, P) in the above equation is expressed by the following equation.

f ₂ (M, P) = k ₁ P ^(1/2) {f ₁ (V _ba )} ^{1 + X}
In the above equation, k ₁ is a proportionality constant and X is an excess noise figure.

The incident light current _{I d,} the pulse current Pei by emission light EL, include noise current ni by pulse current Pri and external light DI due to the reflected light RL. The noise current ni changes between positive and negative. The noise current ni increases as the incident light amount P and the multiplication factor M increase.

  FIG. 7 is a diagram for explaining the operation of the IV conversion circuit 84. 6A is a block diagram showing the function of the IV conversion circuit 84, FIG. 6B is a waveform diagram showing an incident photocurrent applied to the IV conversion circuit 84, and FIG. 6C is an IV conversion circuit. 8 is a waveform diagram showing an incident light voltage output from 84. FIG.

The I-V conversion circuit 84, the incident light current _{I d} outputted from the capacitor 83 is applied. The IV conversion circuit 84 converts the incident photocurrent _Id into a voltage. Thereby, the incident photovoltage V _d proportional to the magnitude of the incident photocurrent I _d is output from the IV conversion circuit 84. The incident light voltage _{V d} is a positive pulse voltage Pev by emission light EL, include noise voltage nv by the positive pulse voltage Prv and external light DI due to the reflected light RL. The noise voltage nv changes between positive and negative.

The input impedance of the I-V conversion circuit 84 and _{Z in,} when the voltage gain of the I-V conversion circuit 84 and _{A v1,} incident light voltage _{V d} is expressed by the following equation.

V _d = Z _in A _v1 I _d (1)
The larger noise current ni contained in the incident light current I _d is the noise voltage nv included in incident light voltage V _d is increased.

  FIG. 8 is a diagram for explaining the operation of the amplifier circuit 85. 8A is a block diagram showing the function of the amplifier circuit 85, FIG. 8B is a waveform diagram showing an incident photovoltage applied to the amplifier circuit 85, and FIG. 8C shows a received light pulse output from the amplifier circuit 85. It is a waveform diagram.

The amplifier circuit 85 is supplied with incident light voltage _{V d} output from the I-V conversion circuit 84. Amplifier circuit 85 amplifies the incident light voltage _{V d,} and outputs the received pulse _{V a.} The light reception pulse Va includes _a positive pulse component PEV due to the emitted light EL, a positive pulse component PRV due to the reflected light RL, and a noise component NV due to the external light DI. The noise component NV changes between positive and negative.

The greater the incident light voltage V _d is, pulses received V _a increases. When the voltage gain of the amplifier circuit 85 and A _v2, photodetection pulse V _a is expressed by the following equation.

V _a = A _v2 V _d (2)
FIG. 9 is a diagram for explaining the operation of the inverting amplifier circuit 86. 9A is a block diagram showing the function of the inverting amplifier circuit 86, FIG. 9B is a waveform diagram showing the received light pulse applied to the inverting amplifier circuit 86, and FIG. 9C is an inverting amplifier output from the inverting amplifier circuit 86. It is a wave form diagram which shows a voltage.

The inverting amplifier circuit 86, receiving the pulse V _a output from the amplification circuit 85 is provided. Inverting amplifier circuit 86, inverts and amplifies the received pulse _{V a,} and outputs the inverted and amplified voltage _{V ia.} The inverted amplification voltage V _ia includes a negative pulse component PEV caused by the emitted light EL, a negative pulse component PRV caused by the reflected light RL, and a noise component NV caused by the extraneous light DI. The noise component NV changes between positive and negative.

The greater the light receiving pulse _{V a} is also increased inverted amplified voltage _{V ia.} When the voltage gain of the inverting amplifier circuit 86 and the A _v3, inverted and amplified voltage V _ia is expressed by the following equation.

V _ia = −A _v3 V _a (3)
FIG. 10 is a diagram for explaining the operation of the half-wave rectifier circuit 87. FIG. 10A is a block diagram illustrating the function of the half-wave rectifier circuit 87, and FIG. 10B is a waveform diagram illustrating the noise level output from the half-wave rectifier circuit 87.

The half-wave rectifier circuit 87 is _supplied with the inverted amplification voltage V _ia output from the inverting amplifier circuit 86. The half-wave rectification circuit 87 outputs a noise level V _nDC that is a DC voltage having an effective value of the inverted amplification voltage V _ia by half-wave rectifying the inverted amplification voltage V _ia . The noise level V _nDC is expressed by the following equation.

V _nDC = f ₃ (V _ia )
When the effective value of the inverted amplification voltage V _ia is V _iaRMS , the above function f ₃ (V _ia ) is expressed by the following equation.

f ₃ (V _ia ) = V _iaRMS
Therefore, the noise level V _nDC is as follows.

V _nDC = V _iaRMS (4)
Since the pulse component PEV by the emitted light EL and the pulse component PRV by the reflected light RL are negative, the noise level V _nDC can be accurately generated from the noise component NV without being affected by the pulse components PEV and PRV.

  FIG. 11 is a diagram for explaining the operation of the bias control circuit 88. 11A is a block diagram showing the function of the bias control circuit 88, and FIG. 11B is a waveform diagram showing the noise level given to the bias control circuit 88.

The bias control circuit 88 is _supplied with the noise level V _nDC and the bias reference voltage V _ref output from the half-wave rectifier circuit 87. The bias control circuit 88 outputs a value obtained by adding a value proportional to the noise level V _nDC and the bias reference voltage V _ref as the bias voltage V _ba . The bias voltage _Vba is expressed by the following equation.

_{V ba = f 4 (V ref} , V nDC)
When the voltage amplification factor is A _v4 , the function f ₄ (V _ref , V _nDC ) in the above equation is expressed by the following equation.

f ₄ (V _ref , V _inDC ) = − A _v4 V _nDC + V _ref (5)
From the above equations (1) to (5), the bias voltage _Vba is expressed by the following equation.

V _ba = −A _v4 A _v3 A _v2 A _v1 Z _in i _dRMS + V _ref (6)
Here, i _dRMS is the effective value of the incident photocurrent I _d .

From the above equation, the bias voltage _Vba becomes smaller as the noise current increases due to the stronger external light DI. Thereby, the multiplication factor M becomes small. Therefore, the light receiving device 80 functions as a negative feedback control circuit in which the multiplication factor M changes according to the intensity of the external light DI.

(6) Display of Radar Image Generation Unit 120 FIG. 12 is a schematic diagram showing a display example of a radar image by the radar image generation unit 120 of FIG.

  1 displays a distance D and an angle θ to the detection target 10 based on the distance signal DS generated by the distance generation unit 100 and the angle signal AS generated by the angle generation unit 110. A radar image is displayed on the 350 screen.

  In the display example of FIG. 12, it is displayed as an image that the detection target exists at a distance D in the direction of the right front angle θ. Actually, the angle θ and the distance D are displayed numerically.

(7) In the laser radar apparatus 1 according to the effect the present embodiment of the laser radar apparatus 1, the pulse component PEV due to emission light EL and the reflected light RL included in the inverting amplifier voltage V _ia, PRV is negative polarity, noise The component NV changes to positive and negative. As a result, the positive component of the inverted amplification voltage V _ia is half-wave rectified, and the noise level V _nDC corresponding to the noise component NV is not affected by the pulse components PEV and PRV caused by the emitted light EL and the reflected light RL. Can be generated accurately. Further, since the light emission interval of the LD 71 is sufficiently larger than the light emission time, the noise level V _nDC is further less affected by the pulse components PEV and PRV caused by the emitted light EL and the reflected light RL.

The noise level _{V NDC} bias voltage _{V ba} based on is controlled by the negative feedback. In this case, when the noise level V _nDC due to the external light DI increases, the bias voltage V _ba applied to the APD 81 decreases. Thereby, the multiplication factor M of the APD 81 is lowered, and the noise level V _nDC is lowered. As a result, the noise component NV contained in the received pulse V _a is reduced.

Further, when the environmental temperature fluctuates, fluctuates multiplication factor M of the APD81, photodetection pulse _{V a} is varied. Again, pulses received V _a pulse component due to the emission light EL and the reflected light RL in PEV, the PRV component of opposite polarity noise level V _NDC by being half-wave rectified is produced. Thereby, the noise component due to the fluctuation of the environmental temperature is accurately detected as the noise level V _nDC without being affected by the pulse components PEV and PRV caused by the emitted light EL and the reflected light RL. The noise level _{V NDC} bias voltage _{V ba} based on is controlled by the negative feedback. As a result, fluctuations in the multiplication factor M of the APD 81 are suppressed.

In this way, the noise component NV can be sufficiently reduced without being affected by the pulse components PEV and PRV caused by the emitted light EL and the reflected light RL. Accordingly, it is possible to accurately detect the pulse components PEV and PRV caused by the emitted light EL and the reflected light RL. As a result, the distance and angle of the detection target 10 can be measured with high accuracy on the basis of the received pulse V _a, it is possible to prevent erroneous detection of the detection object 10.

(8) Vehicle Provided with Laser Radar Device Next, a motorcycle will be described as an example of a vehicle provided with the laser radar device 1 according to the above embodiment.

  FIG. 13 is a schematic diagram showing a motorcycle equipped with the laser radar device 1.

  In the motorcycle 300 of FIG. 13, a front wheel 320 is provided below the front part of the vehicle body 310, and a rear wheel 330 is provided below the rear part. An ECU (electronic control unit) 340 is provided at the center of the vehicle body 310. The laser radar device 1 according to the above embodiment is attached to the front end portion and the rear end portion of the vehicle body 310, respectively.

  In addition, a display 350 is provided at a lower rear portion of the handle 360 in the vehicle body 310.

  The laser radar device 1 at the front end mainly measures the distance and angle of an object in front and side of the motorcycle 300. The laser radar device 1 at the rear end mainly measures the distance and the angle of the object behind and on the side of the motorcycle 300. The distance and angle measured by the laser radar device 1 at the front end and the rear end are given to the ECU 340.

  ECU 340 causes display 350 to display the distance and angle measured by laser radar device 1 at the front end and the rear end as a radar image. Accordingly, the occupant can visually recognize the distance to the surrounding object and the orientation of the object.

(9) Correspondence between each constituent element of claim and each element of the embodiment Hereinafter, an example of correspondence between each constituent element of the claim and each element of the embodiment will be described. It is not limited to.

  In the above embodiment, the APD 81 is an example of an avalanche photodiode, the bias application circuit 810 is an example of a bias application circuit, the capacitor 83 and the IV conversion circuit 84 are examples of a conversion unit, and the inverting amplifier circuit 86. The half-wave rectification circuit 87 is an example of a rectification unit, and the bias control circuit 88 is an example of a bias control circuit.

  The capacitor 83 is an example of a removal circuit, the IV conversion circuit 84 is an example of a current-voltage conversion circuit, and the amplifier circuit 85 is an example of an amplifier circuit.

  Further, the distance generation unit 100 is an example of a distance calculation unit, the motor 30 and the reflecting mirror 250 are examples of a laser light rotation system, the encoder 40 is an example of an angle detection unit, the signal processing unit 90 and the distance generation unit. 100 is an example of a pulse detection unit, and the angle generation unit 110 is an example of an azimuth calculation unit.

  The vehicle body 301 is an example of a main body, the rear wheel 330 is an example of a drive unit, and the display 350 is an example of a notification unit.

  As each constituent element in the claims, various other elements having configurations or functions described in the claims can be used.

(10) Other Embodiments In the above embodiment, the capacitor 83 is used as the removal circuit, but a low-pass filter may be used instead of the capacitor 83 as the removal circuit. Further, the removal circuit and the current-voltage conversion circuit may be provided in reverse.

Furthermore, if the level of incident light voltage V _d output from the I-V conversion circuit 84 is high, it may not be provided an amplifier circuit 85.

  Further, laser elements having various wavelengths can be used as the LD 71 of the light transmitting device 70.

  Moreover, you may use the audio | voice output apparatus which alert | reports the distance and angle of the detection target object 10 with an audio | voice instead of the display 350 as an alerting | reporting part.

  The laser radar device 1 is not limited to a motorcycle, but can be used for various vehicles such as a four-wheeled vehicle, a three-wheeled vehicle, an electric bicycle, a planing boat, a watercraft, and an electric wheelchair.

  The present invention can be used to measure information such as a distance to a detection target using a laser beam.

It is a block diagram which shows the structure of the signal processing system of the laser radar apparatus which concerns on one embodiment of this invention. (A) is a schematic diagram which shows the structure of the optical system of the laser radar apparatus of FIG. 1, (b) is a perspective view which shows the structure of the reflective mirror of a laser radar apparatus. FIG. 2 is a timing diagram for explaining the operation of the laser radar device of FIG. 1. It is a block diagram which shows the structure of the light-receiving device of FIG. It is a wave form diagram which shows the binarization signal produced | generated by the light reception pulse output from a light-receiving device, and a signal processing part. It is a figure for demonstrating the operation | movement of APD. It is a figure for demonstrating operation | movement of an IV conversion circuit. It is a figure for demonstrating operation | movement of an amplifier circuit. It is a figure for demonstrating operation | movement of an inverting amplifier circuit. It is a figure for demonstrating operation | movement of a half-wave rectifier circuit. It is a figure for demonstrating operation | movement of a bias control circuit. It is a schematic diagram which shows the example of a display of the radar image by the radar image generation part of FIG. It is a mimetic diagram showing a motorcycle provided with a laser radar device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser radar apparatus 10 Target object 20 Motor rotation speed control part 30 Motor 31 Pulley 32 Belt 40 Encoder 50 Light emission interval pulse production | generation part 60 Light emission trigger production | generation part 70 Light transmitter 71 Laser diode (LD)
72 holding member 80 light receiving device 81 avalanche photodiode (APD)
81a holding member 82 resistor 83 capacitor 84 IV conversion circuit 85 amplifier circuit 86 inverting amplifier circuit 87 half-wave rectifier circuit 88 bias control circuit 90 signal processor 100 distance generator 110 angle generator 120 radar image generator 200 holder 201 Motor holding portion 210 Reflector 220 Light emitting / receiving lens 230 Bearing 240 Protective cover 250 Reflector 300 Motorcycle 310 Vehicle body 320 Front wheel 330 Rear wheel 340 ECU
350 Display EL Emitted light RL Reflected light DI External light AS Angle signal BS Binary signal DG Distance generation signal DS Distance signal EI Light emission interval pulse EP Encoder pulse ET Light emission trigger OP Origin pulse I _d Incident photocurrent V _a Light reception pulse V _d Incident light voltage V _ba bias voltage V _ia inverted amplification voltage V _iaRMS inverted amplification voltage effective value V _nDC noise level V _ref bias reference voltage NV noise component PEV, PRV pulse component

Claims (11)

A light receiving device that receives a pulsed laser beam emitted by a light transmitting device and reflected by a detection object,
An avalanche photodiode that receives the laser light reflected by the detection object;
A bias application circuit for applying a bias voltage to the avalanche photodiode;
A conversion unit that converts the output current of the avalanche photodiode into a voltage from which a DC component has been removed, and
The bias application circuit includes:
A rectifying unit that generates a noise level by rectifying a component having a polarity opposite to a pulse component caused by laser light in the voltage obtained by the conversion unit;
And a bias control circuit that controls the bias voltage by negative feedback based on a noise level generated by the rectifier. The converter is
A removal circuit for removing a direct current component of the output current of the avalanche photodiode;
A current-voltage conversion circuit that converts the output current of the removal circuit into a voltage;
The light receiving device according to claim 1, further comprising an amplifier circuit that amplifies the output voltage of the current-voltage conversion circuit. The rectifying unit is
An inverting amplifier circuit for inverting and amplifying the voltage obtained by the converter;
3. The light receiving device according to claim 1, further comprising a half-wave rectifier circuit that generates the noise level by half-wave rectifying a positive component of an output voltage of the inverting amplifier circuit. The bias control circuit includes:
The light receiving device according to claim 1, wherein the bias voltage is generated by adding an inversion component of a noise level generated by the rectifying unit to a reference bias voltage. The light receiving device according to claim 1, wherein the avalanche photodiode is arranged to receive a part of the laser light emitted by the light transmitting device. A light transmission device that emits laser light to a detection object;
A light receiving device for receiving light,
The light receiving device is:
An avalanche photodiode that receives the laser light emitted by the light transmitting device and reflected by the detection target;
A bias application circuit for applying a bias voltage to the avalanche photodiode;
A conversion unit that converts the output current of the avalanche photodiode into a voltage from which a DC component is removed, and
The bias application circuit includes:
A rectifying unit that generates a noise level by rectifying a component having a polarity opposite to a pulse component caused by laser light in the voltage obtained by the conversion unit;
And a bias control circuit that controls the bias voltage by negative feedback based on a noise level generated by the rectifier. The avalanche photodiode of the light receiving device is arranged to receive a part of the laser light emitted by the light transmitting device;
Based on the time interval between the pulse component caused by the laser beam emitted by the light transmitting device and the pulse component caused by the laser beam reflected by the detection target in the voltage obtained by the conversion unit of the light receiving device. The laser radar device according to claim 6, further comprising a distance calculating unit that calculates a distance from the light transmitting device to the detection target. The laser according to claim 6 or 7, wherein the light transmitting device emits a pulsed laser beam at a constant cycle, and the laser beam emission cycle is 1000 times or more of the emission time of the laser beam. Radar device. The light transmitting device is:
A laser diode that emits laser light;
The laser radar apparatus according to claim 6, further comprising a laser light rotation system that rotates a traveling direction of the laser light emitted by the laser diode in a plane. An angle detection unit for detecting a rotation angle in a traveling direction of the laser beam by the laser beam rotation system;
A pulse detection unit for detecting a pulse component caused by the laser beam reflected by the detection target in the voltage obtained by the conversion unit of the light receiving device;
An azimuth calculating unit that calculates an azimuth of a detection target based on an angle in a traveling direction of a laser beam detected by the angle detecting unit when the pulse component is detected by the pulse detecting unit. Item 10. The laser radar device according to any one of Items 6 to 9. The main body,
A drive unit for moving the main body unit;
The laser radar device according to any one of claims 6 to 10, provided on the main body,
A vehicle comprising: an informing unit for informing an occupant of information based on a voltage obtained by the conversion unit of the laser radar device.

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