JP2018044852A - Laser emission device, control method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control emission power without requiring installation of a photodiode for dedicated monitors, or the like.SOLUTION: In a laser emission device, an emission unit emits a laser beam while changing the direction of emission. The emitted laser beam is reflected by a reference reflector provided in a prescribed direction of emission, and a receiving unit receives the reflected return beam. Meanwhile, a control unit controls the emission power of the laser beam on the basis of the return beam from the reference reflector.SELECTED DRAWING: Figure 15

Description

  The present invention relates to control of laser beam emission power by a lidar.

  Devices that detect surrounding objects using laser light are known. For example, Patent Document 1 describes an object detection device that emits laser light to a target area and detects an object based on reflected light from the object. In this document, laser light emitted from the rear surface side of a laser element of a laser light source is received by a photodiode for back monitoring, and APC control of the emitted laser light is performed based on the amount of received light.

JP 2014-48128 A

  In the technique of Patent Document 1, since it is necessary to provide a monitoring photodiode in order to control the emission power of laser light, the apparatus configuration becomes complicated, large, and expensive.

  Examples of the problem to be solved by the present invention include the above. An object of the present invention is to provide a laser emitting apparatus capable of controlling the emission power without providing a dedicated monitor photodiode or the like.

  The invention according to claim 1 is a laser emitting device, wherein an emitting unit that emits laser light while changing an emitting direction, a reference reflector that is arranged in a predetermined emitting direction and reflects the laser light, and A light receiving unit that receives the return light of the laser light, and a control unit that controls the emission power of the laser light emitted from the emission unit based on the return light from the reference reflector.

  According to a sixth aspect of the present invention, an emission unit that emits laser light while changing the emission direction, a reference reflector that is arranged in a predetermined emission direction and reflects the laser light, and a return light of the laser light are received. A control method that is executed by a laser emitting device including a light receiving unit that controls an emission power of the laser beam emitted from the emission unit based on return light from the reference reflector Have

  According to a seventh aspect of the present invention, an emission unit that emits laser light while changing an emission direction, a reference reflector that is arranged in a predetermined emission direction and reflects the laser light, and a return light of the laser light are received. A program that is executed by a laser emitting device that includes a light receiving unit and a computer that controls emission power of the laser light emitted from the emitting unit based on return light from the reference reflector The computer is caused to function as a control unit.

1 shows an overall configuration of a rider according to an embodiment. The structure of a transmitter and a receiver is shown. The structure of a scanning optical part is shown. The register setting example of the control signal which a synchronous control part produces | generates is shown. The time relationship of the control signal which a synchronous control part produces | generates is shown. It is a graph which shows the relationship between an ADC output signal and a gate. It is another graph which shows the relationship between an ADC output signal and a gate. The time relationship of the pulse train of a rotary encoder is shown. The time relationship between the encoder pulse and the segment slot in the steady state is shown. It is a block diagram of the signal processing by DSP. An example of a filtered segment is shown. A configuration for performing APC of LD and AGC of APD is shown. It is the figure which showed roughly arrangement | positioning of a reference | standard reflector. An example of a table of injection power and avalanche gain is shown. It is a flowchart of APC processing. It is a flowchart of AGC processing.

  In one preferred embodiment of the present invention, a laser emission device includes an emission unit that emits laser light while changing an emission direction, a reference reflector that is arranged in a predetermined emission direction and reflects the laser light, and A light receiving unit that receives the return light of the laser light, and a control unit that controls the emission power of the laser light emitted from the emission unit based on the return light from the reference reflector.

  In the laser emission apparatus, the emission unit emits laser light while changing the emission direction. The emitted laser light is reflected by a reference reflector disposed in a predetermined emission direction, and the light receiving unit receives the reflected return light. And a control part controls the emission power of a laser beam based on the return light from a reference | standard reflector. As a result, it is possible to control the laser beam emission power without providing a photodetector for monitoring the laser beam.

  In one aspect of the laser emission apparatus, the emission unit includes a laser light source that emits the laser light, and the control unit applies a voltage applied to the laser light source based on return light from the reference reflector. To control. In this aspect, the emission power is controlled by controlling the voltage applied to the laser light source.

  Another aspect of the laser emission apparatus includes a storage unit that stores a table indicating a relationship between a peak amplitude value of return light from the reference reflector and the emission power, and the control unit includes the table. The applied voltage is controlled so that the level of the return light becomes a peak amplitude value corresponding to the target emission power. Preferably, the table shows a relationship between a peak amplitude value of return light from the reference reflector and the emission power under a condition where the gain of the light receiving unit is a predetermined value.

  Another aspect of the laser emitting apparatus includes a detection unit that performs at least one of detection of the object and measurement of a distance to the object based on return light from an object other than the reference reflector. In this aspect, the surrounding object can be detected or the distance to the object can be measured in a state where the emission power of the laser beam is appropriately maintained based on the return light from the reference reflector.

  In another preferred embodiment of the present invention, an emission unit that emits laser light while changing the emission direction, a reference reflector that is arranged in a predetermined emission direction and reflects the laser light, and return light of the laser light And a control step executed by a laser emitting apparatus including a light receiving unit that controls the emission power of the laser beam emitted from the emission unit based on return light from the reference reflector. Have Also by this method, it is possible to control the laser beam emission power without providing a photodetector for monitoring the laser beam.

  In another preferred embodiment of the present invention, an emission unit that emits laser light while changing the emission direction, a reference reflector that is arranged in a predetermined emission direction and reflects the laser light, and return light of the laser light A program executed by a laser emitting device including a light receiving unit that receives light and a computer controls emission power of the laser light emitted from the emitting unit based on return light from the reference reflector The computer is caused to function as a control unit. By executing this program on a computer, the above laser emission apparatus can be realized. This program can be stored and handled in a storage medium.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[Device configuration]
(overall structure)
FIG. 1 shows an overall configuration of a rider according to the embodiment. The lidar 1 scans the surrounding space by appropriately controlling the emission direction of the light pulse that is repeatedly emitted (hereinafter referred to as “scanning direction”), and observes the return light to thereby detect an object existing in the vicinity. Information about the distance (for example, distance, existence probability or reflectance). Specifically, the lidar 1 emits a light pulse (hereinafter referred to as “emitted light”) Lo and is reflected by an external object (target) (hereinafter referred to as “returned light”) Lr. Is received to generate information about the object.

  As shown in FIG. 1, the lidar 1 roughly includes a system CPU 5, an ASIC 10, a transmitter 30, a receiver 40, and a scanning optical unit 50. The transmitter 30 repeatedly outputs a laser light pulse having a width of about 5 nsec in accordance with the pulse trigger signal PT supplied from the ASIC 10. The light pulse output from the transmitter 30 is guided to the scanning optical unit 50.

  The scanning optical unit 50 emits the light pulse output from the transmitter 30 in an appropriate direction, and collects the return light Lr that is returned when the emitted pulse encounters an object in space and is reflected or scattered. To the receiver 40. The receiver 40 outputs a signal proportional to the intensity of the return light Lr to the ASIC 10.

  The ASIC 10 analyzes the output signal of the receiver 40 to estimate and output a parameter related to the object in the scanning space, for example, the distance. Further, the ASIC 10 controls the scanning optical unit 50 so that appropriate scanning is performed. Further, the ASIC 10 supplies the transmitter 30 and the receiver 40 with the high voltages required by each.

  The system CPU 5 performs initial setting, monitoring, and control of the ASIC 10 through at least a communication interface. Other functions differ depending on the application. In the case of the simplest lidar, the system CPU 5 only converts the target information TI output from the ASIC 10 into an appropriate format and outputs it. For example, the system CPU 5 converts the target information TI into a highly versatile point cloud format, and then outputs it through the USB interface.

(Transmitter)
The transmitter 30 outputs an optical pulse having a width of about 5 nsec in response to the pulse trigger signal PT supplied from the ASIC 10. The structure of the transmitter 30 is shown in FIG. The transmitter 30 includes a charging resistor 31, a driver circuit 32, a capacitor 33, a charging diode 34, a laser diode (LD) 35, and a switch 36.

The pulse trigger signal PT input from the ASIC 10 drives a switch 36 such as a CMOS via the driver circuit 32. The driver circuit 32 is inserted to drive the switch 36 at high speed. During the non-assertion period of the pulse trigger signal PT, the switch 36 is open, and the capacitor 33 in the transmitter 30 is charged with the high voltage V _TX supplied from the ASIC 10. On the other hand, in the assertion period of the pulse trigger signal PT, the switch 36 is closed, and the charge charged in the capacitor 33 is discharged through the LD 35. As a result, an optical pulse is output from the LD 35.

(Receiver)
The receiver 40 outputs a voltage signal proportional to the intensity of the return light Lr from the object. In general, a photodetection element such as a PD or APD has a current output, so the receiver 40 converts this current into a voltage (I / V conversion) and outputs it. The structure of the receiver 40 is shown in FIG. The receiver 40 includes an APD (Avalanche Photodiode) 41, an I / V conversion unit 42, a resistor 45, a capacitor 46, and a low-pass filter (LPF) 47. The I / V conversion unit 42 includes a feedback resistor 43 and an operational amplifier 44.

In the present embodiment, APD 41 is used as the light detection element. A high voltage V _RX supplied from the ASIC 10 is applied to the APD 41 as a reverse bias, and a detection current proportional to the return light Lr from the object flows. By applying a reverse bias close to the breakdown voltage of the APD 41, a high avalanche gain can be obtained and a weak return light can be detected. The LPF 47 at the final stage is installed for the purpose of limiting the signal bandwidth prior to sampling by the ADC 20 in the ASIC 10. In this embodiment, the sampling frequency of the ADC 20 is 512 MHz, and the cutoff frequency of the LPF 47 is about 250 MHz.

(Scanning optics)
The scanning optical unit 50 emits the light pulse input from the transmitter 30 as an emitted light Lo in an appropriate direction, and returns when the emitted light Lo encounters an object in space and is reflected or scattered. The light Lr is guided to the receiver 40. A configuration example of the scanning optical unit 50 is shown in FIG. The scanning optical unit 50 includes a rotary mirror 61, a collimator lens 62, a condenser lens 64, an optical filter 65, a coaxial mirror 66, and a rotary encoder 67.

The light pulse output from the LD 35 of the transmitter 30 enters the collimator lens 62. The collimator lens 62 collimates the laser light at an appropriate divergence angle (generally, about 0 to 1 °). The light emitted from the collimator lens 62 is reflected vertically downward by a small coaxial mirror 66 and enters the rotation axis (center) of the rotary mirror 61. The rotating mirror 61 reflects the laser beam incident from vertically above in the horizontal direction and emits it to the scanning space. The rotating mirror 61 is attached to the rotating portion of the motor 54, and the laser beam reflected by the rotating mirror 61 scans the horizontal plane as the emitted light Lo as the motor 54 rotates.

  The return light Lr returned to the lidar 1 by being reflected or scattered by an object existing in the scanning space is reflected vertically upward by the rotating mirror 61 and enters the optical filter 65. In addition to the return light Lr, background light generated when the object is illuminated by the sun or the like also enters the optical filter 65. The optical filter 65 is installed to selectively exclude such background light. Specifically, the optical filter 65 selectively allows only a component of about ± 10 nm before and after the wavelength of the emitted light Lo (905 nm in this embodiment). When the pass band of the optical filter 65 is wide, a lot of background light enters the receiver 40 at the subsequent stage. As a result, a large DC current component appears in the output of the APD 41 in the receiver 40, and the SN deteriorates due to the influence of shot noise (background light shot noise) caused by this DC component, which is not preferable. However, when the pass band is excessively narrow, the emitted light itself is suppressed, which is not preferable. The condensing lens 64 condenses the light that has passed through the optical filter 65 and guides it to the APD 41 of the receiver 40.

  A rotary encoder 67 is attached to the motor 54 in order to detect the scanning direction. The rotary encoder 67 includes a turntable 68 attached to the motor rotating unit and a code detector 69 attached to the motor base. A slit indicating the rotation angle of the motor 54 is formed on the outer periphery of the rotating disk 68, and the code detector 69 reads and outputs this. Note that specific specifications of the rotary encoder 67 and motor control based on the output will be described later.

  In the above configuration, the collimator lens 62 constitutes the transmission optical system 51 shown in FIG. 1, the rotating mirror 61 and the motor 54 constitute the scanning unit 55 shown in FIG. 1, and the optical filter 65 and the condenser lens 64 are shown in FIG. 1 and the rotary encoder 67 constitutes the scanning direction detector 53 in FIG.

(ASIC)
The ASIC 10 performs timing control of the emitted light pulse, AD conversion of the APD output signal, and the like. Further, the ASIC 10 estimates parameters (distance, return light intensity, etc.) related to the object by performing appropriate signal processing on the AD conversion output, and outputs the estimation result to the outside. As shown in FIG. 1, the ASIC 10 includes a register unit 11, a clock generation unit 12, a synchronization control unit 13, a gate extraction unit 14, a reception segment memory 15, a DSP 16, and a transmitter high voltage generation unit (TXHV). ) 17, a receiver high voltage generation unit (RXHV) 18, a preamplifier 19, an AD converter (ADC) 20, and a scanning control unit 21.

  The register unit 11 includes a register for communication with the system CPU 5 which is an external processor. The registers provided in the register unit 11 are roughly classified into R registers that can only be referenced from the outside and W registers that can be set from the outside. The R register mainly holds status values inside the ASIC, and the system CPU 5 can monitor the internal status of the ASIC 10 by reading these values through the communication interface. On the other hand, the W register holds various parameter values referred to inside the ASIC 10. These various parameter values can be set from the system CPU 5 through the communication interface. Note that the communication register may be realized by a flip-flop or a RAM.

  The clock generation unit 12 generates a system clock SCK and supplies it to each block in the ASIC 10. Many blocks of the ASIC 10 operate in synchronization with the system clock SCK. In this embodiment, the frequency of the system clock SCK is 512 MHz. The system clock SCK is generated by a PLL so as to be synchronized with a reference clock RCK input from the outside. Usually, a crystal oscillator is used as a generation source of the reference clock RCK.

  The TXHV 17 generates a DC high voltage (about 100 V) required by the transmitter 30. The high voltage is generated by boosting a low voltage (about 5V to 15V) by a DCDC converter circuit.

  The RXHV 18 generates a DC high voltage (about 100 V) required by the receiver 40. The high voltage is generated by boosting a low voltage (about 5V to 15V) by a DCDC converter circuit.

  The synchronization control unit 13 generates and outputs various control signals. The synchronization control unit 13 in this embodiment outputs two control signals, that is, a pulse trigger signal PT and an AD gate signal GT. An example of setting these control signals is shown in FIG. 4, and their temporal relationship is shown in FIG. As shown in FIG. 5, these control signals are generated in synchronization with time intervals (segment slots) divided at a predetermined interval. The time interval width (segment period) of the segment slot can be set by “nSeg”. In the present embodiment, it is assumed that “nSeg = 8192” is set in a range not specifically mentioned.

  The pulse trigger signal PT is supplied to a transmitter 30 provided outside the ASIC 10. The transmitter 30 outputs an optical pulse according to the pulse trigger signal PT. For the pulse trigger signal PT, the delay “dTrg” and the pulse width “wTrg” with respect to the segment slot start point can be set. Note that the pulse width wTrg is determined in view of the trigger response specification of the transmitter 30 because the transmitter 30 does not respond if it is too narrow.

  The AD gate signal GT is supplied to the gate extraction unit 14. As will be described later, the gate extraction unit 14 extracts only the asserted period of the AD gate signal GT from the ADC output signal input from the ADC 20 and stores it in the reception segment memory 15. For the AD gate signal GT, the delay time “dGate” and the gate width “wGate” with respect to the segment slot start point can be set.

  The preamplifier 19 amplifies the analog voltage signal input from the receiver 40 installed outside the ASIC 10 and supplies the amplified voltage to the subsequent ADC 20. The voltage gain of the preamplifier 19 can be set by the W register.

  The ADC 20 performs AD conversion on the output signal of the preamplifier 19 to convert it into a digital series. In this embodiment, the system clock SCK is used as the sampling clock of the ADC 20, and the input signal of the ADC 20 is sampled at 512 MHz.

  The gate extraction unit 14 extracts only the asserted period of the AD gate signal GT from the ADC output signal input from the ADC 20 and stores it in the reception segment memory 15. The section signal extracted by the gate extraction unit 14 is hereinafter referred to as “reception segment signal RS”. That is, the reception segment signal RS is a real vector whose vector length is equal to the gate width wGate.

Here, the relationship between the ADC output signal and the reception segment and the setting of the gate position will be described. FIG. 6A shows a segment slot. As shown in FIG. 6B, the pulse trigger signal PT is asserted with a delay of dTrg with respect to the segment slot start point. In the example of FIG. 6, since dTrg = 0, the pulse trigger signal PT is asserted at the segment slot start point. FIG. 6C shows an ADC output signal (received segment signal RS) when an object is placed at the scanning origin of the lidar. That is, FIG. 6C illustrates the received segment signal RS when the target distance (radial radius R) is 0 m. As shown in the figure, even when R = 0 m, the rising edge of the received pulse is observed with a delay of the system delay D _SYS from the rising edge of the pulse trigger signal. The system delay D _SYS is caused by the electrical delay of the LD driver circuit in the transmitter 30, the optical delay in the transmission optical system 51, the optical delay in the reception optical system 52, and the electrical delay in the receiver 40. A delay, a conversion delay in the ADC 20, and the like can be considered.

FIG. 6D illustrates the received segment signal RS when the object is placed on the moving radius R. In this case, as compared with FIG. 6C, the delay increases by the round-trip time of light from the scanning origin to the object. This increased delay is a so-called “TOF (Time Of Flight) delay”. If this TOF delay is D samples, the radius R can be calculated by the following equation.

FIG. 6F illustrates the AD gate signal GT when dGate = 0. As described above, the gate extraction unit 14 extracts only the assert period of the AD gate signal GT from the ADC output signal. The DSP 16, which will be described later, performs parameter estimation on the object based only on this extraction section. Therefore, when the TOF delay time is long, the return pulse component from the object protrudes from the gate, and a valid parameter cannot be estimated. In order to perform proper parameter estimation, it is necessary that the TOF delay time D satisfies the following equation:

Here, L _IR is the length of the overall impulse response of the system, and D _MAX is defined as the maximum TOF delay time that allows valid parameter estimation. FIG. 6E illustrates the received segment signal RS when the TOF delay time is equal to the maximum TOF delay time.

  FIG. 7 is a diagram similar to FIG. 6 but illustrates each signal when the gate delay dGate is set equal to the system delay time. By setting in this way, it is possible to estimate a valid parameter up to an object at a longer distance.

  The scanning control unit 21 monitors the output of the rotary encoder 67 installed outside the ASIC 10, and controls the rotation of the motor 54 based on this. Specifically, the scanning control unit 21 supplies the torque control signal TC to the motor 54 based on the scanning direction information SDI output from the rotary encoder 67 (scanning direction detection unit 53) of the scanning optical unit 50. The rotary encoder 67 in the present embodiment outputs two pulse trains of A phase and Z phase (hereinafter referred to as “encoder pulses”). The time relationship between both pulse trains is shown in FIG. As shown in the figure, for the A phase, one pulse is generated and output every 1 ° of rotation of the motor 54. Therefore, 360 A-phase encoder pulses are generated and output every rotation of the motor 54. On the other hand, for the Z phase, one pulse per rotation of the motor 54 is generated and output corresponding to a predetermined rotation angle.

  The scanning control unit 21 measures the rise time of the encoder pulse as a counter value of the system clock SCK, and controls the torque of the motor 54 so that this becomes a desired value. That is, the scanning control unit 21 performs PLL control of the motor 54 so that the encoder pulse and the segment slot have a desired time relationship.

  The time relationship between the encoder pulse and the segment slot can be set by the W register shown in FIG. In “nPpr”, the number of A-phase encoder pulses for each motor rotation is set. This is a value determined by the specification of the rotary encoder 67. In the present embodiment, the above-described 360 is set. “NRpf” gives the number of rotations for each frame, and “nSpf” gives the number of segments for each frame. “DSmpA” and “dSmpZ” are prepared for adjusting the time relationship between the rising edge of the encoder pulse and the segment slot in units of sample clocks, and can define the delay of the encoder pulse with respect to the segment slot start point. . On the other hand, “dSegZ” is prepared for adjusting the time relationship between the rise of the Z-phase pulse and the frame in units of segments.

  FIG. 9 shows the time relationship between the encoder pulse and the segment slot in the steady state. As shown in the figure, in the default setting, one frame is composed of 1800 segments, and the motor 54 makes one rotation in one frame.

(DSP)
A block diagram of signal processing performed by the DSP 16 is shown in FIG. As illustrated, the DSP 16 includes a reception filter 71, a peak detector 72, a determination unit 73, and a formatter 74. The DSP 16 sequentially reads the received segments y _{frm and seg} from the received segment memory 15 and processes them. Here, “frm” is a frame index, and “seg” is a segment index. Hereinafter, the description of these indexes is omitted within a range where there is no risk of misunderstanding. The reception segment y is a real vector having a vector length wGate and is represented by the following expression.

  The reception filter 71 convolves a predetermined impulse response with the reception segment y to calculate a filtered segment z. The peak detector 72 detects the point where the amplitude is maximum in the filtered segment z, that is, the peak point, and outputs the delay D and the amplitude A of the peak point. The determination unit 73 selectively sends only the points where the amplitude A is larger than the predetermined threshold value tDet to the formatter 74. The formatter 74 converts the delay D and amplitude A, the frame index frm and the segment index seg of the segment into appropriate formats, and outputs them to the outside. Hereinafter, each block will be described in detail.

  The reception filter unit 71 calculates a filtered segment z by convolving a predetermined impulse response h with the reception segment y (cyclic convolution). The impulse response of the reception filter unit 71 can be set by the W register, and is set in advance by the system CPU 5 so as to increase the SNR at the filter output.

For example, the filter impulse response h is set so as to satisfy the following expression. With this setting, when the noise is white and the system total impulse response is significantly shorter than wGate, optimal performance (high SNR) can be realized.
In the above equation, the reference pulse g is a received segment waveform observed when an object is placed at the scanning origin (R = 0 m), and represents the overall impulse response of the entire system including the transmitter 30 and the receiver 40. If it is difficult to actually place an object at the scanning origin, for example, the received segment waveform at R = 1 m is observed, and the reference pulse can be measured equivalently by mathematically shifting this time. .

The peak detector 72 detects the point where the amplitude is maximum within the filtered segment, that is, the peak point with sub-sample accuracy, and outputs the delay D and the amplitude A of the peak point. FIG. 11 illustrates a filtered segment when R = 10 m. The curve in the figure represents a continuous time waveform before sampling, and a round dot indicates a sampling point. The peak detector 72 calculates the peak position in the continuous time system based on the sampling series. In the example of FIG. 11, the peak position in units of samples on the filtered segment {zk: k = 0, 1,..., 1023} is k = 34. On the other hand, the peak position in the continuous time waveform, that is, the sub-sample accuracy is
D = R · Fsmp / (c / 2) = 34.157
It is. The peak detector 72 estimates and calculates the delay D 1 and the amplitude A of the peak point with the sub-sample accuracy.

Various algorithms can be applied to the peak point detection process with sub-sample accuracy. An example is shown below.
(Procedure 1) A sample point (point P in FIG. 11) having the maximum amplitude is obtained.
(Procedure 2) A quadratic curve passing through these three points is obtained for the point (P point) obtained in Procedure 1 and the points before and after it (Point A and Point B).
(Procedure 3) The delay D and the amplitude A are obtained as the maximum points of the quadratic curve obtained in the procedure 2.

  Based on the peak point information D and A (delay D, amplitude A) output from the peak detection unit 72, the determination unit 73 determines whether or not an object exists at the detection point. This determination is performed by comparing the amplitude A of the peak point with the determination threshold value tDec. Specifically, the determination unit 73 determines that “the object exists” when A> tDec, and outputs the peak point information. On the other hand, if A ≦ tDec, the determination unit 73 determines that “the object does not exist” and does not output the peak point information.

The formatter 74 converts the peak point information D, A output from the determination unit 73 and the scanning information (frame index frm, segment index seg) corresponding to the peak point into a format that is easy for the user (higher system) to use. The formatter 74 in this embodiment performs the following format conversion.
(1) The frame index frm is output as it is.
(2) The segment index seg is converted into a horizontal scanning angle θ and output.
(3) The delay D is converted into a radius vector (distance) R and output (R = D (c / 2) / Fsmp).
(4) The amplitude A is output as it is.
(5) The reflectance U is calculated from the amplitude A and the radius vector R and output (U = A / Ψ (R)).
Here, the function Ψ (R) is a reflectance conversion table and can be set from an external CPU. By setting this table to the expected value of the peak amplitude obtained from a Lambertian diffuser with 100% reflectivity installed at the radius R, reflectivity estimation with less error can be performed.

  In the above configuration, the transmitter 30 is an example of the emission unit of the present invention, the receiver 40 is an example of the light receiving unit of the present invention, the DSP 16 is an example of the control unit of the present invention, and the LD 35 is the laser light source of the present invention. It is an example.

[APC of emitted light pulse]
Next, APC (Automatic Gain Control) of an optical pulse emitted from the transmitter 30 will be described. Usually, even if the voltage applied to the LD 35 is kept constant, the emission power from the LD 35 is not constant due to individual variations of LD, temperature changes, aging changes, and the like. For this reason, APC of LD35 is required. In this embodiment, a reference reflector is arranged in a specific scanning direction of the lidar 1 and APC is performed based on the return light reflected by the reference reflector. First, the reference reflector will be described.

(Reference reflector)
FIG. 13A is a diagram schematically showing the arrangement of the reference reflector 7. In FIG. 13A, the reference reflector 7 is disposed in the vicinity of the housing 25 of the substantially cylindrical lidar 1 that accommodates the scanning unit 55 and the like. Here, the reference reflector 7 is a direction outside the detection target that is a direction other than the direction in which the lidar 1 detects the object among the irradiation directions of the emitted light Lo of 360 degrees scanned by the scanning unit 55 (see arrow A1). Is provided. In the example of FIG. 13A, the reference reflector 7 exists on the wall surface of the casing 25 behind the lidar 1 irradiated with the emitted light Lo for an angle “θa” (for example, 60 degrees). In this case, the reference reflector 7 is provided, for example, inside the transparent cover of the casing 25 that transmits the emission light Lo and the return light Lr. Hereinafter, a period in which the APD 41 receives the emitted light Lo irradiated to the reference reflector 7 within a period in which the scanning unit 55 performs one scan (that is, one frame period) is also referred to as a “reference reflector period”. Call. The reference reflector period includes a plurality of segment periods corresponding to each scanning angle at which the reference reflector 7 is irradiated with the emitted light Lo.

  FIG. 13B shows a state where the emitted light Lo is emitted in the direction in which the reference reflector 7 is arranged in the example of FIG. The reference reflector 7 reflects the emitted light Lo with a predetermined reflectance when the emitted light Lo is incident. Here, it is desirable that the reflectivity of the reference reflector 7 is such that the level of the return light Lr is not too small compared to the noise and does not saturate with respect to the dynamic range of the ADC 20. More specifically, the reflectance of the reference reflector 7 is not too small and not too large under the conditions of the target injection power of the LD 35 and the target avalanche gain of the APD 41 that are obtained in the normal operation state of the lidar 1. To be determined.

  As described above, in this embodiment, the reference reflector 7 is provided, and the APC of the emitted light pulse is performed based on the return light Lr. Therefore, it is necessary to provide a monitor photodetector for the LD 35 that is the light source of the emitted light pulse. Absent.

(APC)
Next, APC of the emitted light pulse will be described. APC is a control for adjusting the voltage applied to the LD 35 so that a predetermined target injection power (for example, 10 W) is obtained, and is mainly executed by the DSP 16 shown in FIG. Specifically, as shown in FIG. 12, the DSP 16 supplies the control signal Ct to the TXHV 17, thereby changing the high voltage V _TX generated by the TXHV 17 and adjusting the voltage applied to the LD 35 in the transmitter 30.

Here, in the present embodiment, as preprocessing, the avalanche gain (hereinafter also referred to as “M value”) of the APD 41 in the receiver 40 is set to a predetermined M value for adjustment. Specifically, the applied voltage V _RX to the APD 41 is adjusted so that the M value of the APD 41 becomes the adjustment M value. Here, the M value for adjustment is set in a region where the temperature sensitivity of the M value of the APD 41 is low, that is, a value that is not easily affected by the temperature change, for example, about M = 2. By setting the adjustment M value in a region where the temperature sensitivity is low, the accuracy of detecting the injection power of the LD 35 is ensured.

  In performing APC, a table (hereinafter also referred to as “eject power table”) showing the relationship between the emission power of the LD 35 and the peak amplitude value PK of the reception segment is prepared in advance. The peak amplitude value PK of the reception segment is a peak amplitude value of a pulse included in the reception segment signal RS output from the ADC 20, as shown in FIG. The injection power table prepared here indicates the relationship between the emission power of the LD 35 and the peak amplitude value PK of the reception segment when the M value of the APD 41 on the receiver 40 side is the above-described adjustment M value. . Note that the injection power table is created based on measurements performed in the manufacturing stage or the development stage of the lidar 1. Further, it is assumed that this measurement is performed using the reference reflector 7 mounted on the actual rider 1.

FIG. 14A shows an example of an injection power table. The horizontal axis represents the peak amplitude value PK of the received segment signal RS, and the vertical axis represents the emission power P of the emitted light pulse from the LD 35. As shown in the figure, the peak amplitude value PK and the injection power P basically have a linear relationship. If the predetermined target injection power P is “Pt”, the target peak amplitude value PK corresponding to the target injection power Pt is “PKpt”. The target injection power Pt is a power required in a normal operation state (a state in which an object is detected and measured) by the lidar 1 and is actually a distance to an object to be detected and measured. To be determined. In order to set the injection power P from the LD 35 to the target injection power Pt using the injection power table, the applied voltage V _{TX of the} LD 35 is adjusted so that the peak amplitude value PK of the received segment signal RS becomes the target peak amplitude value PKpt. It will be good. The injection power table is stored in a memory or the like inside the DSP 16.

FIG. 15 shows a flowchart of the APC process. This process is mainly executed by the DSP 16 shown in FIG. First, as preprocessing, the DSP 16 adjusts the voltage applied to the APD 41 so that the M value of the APD 41 in the receiver 40 becomes the adjustment M value (step S11). Specifically, the DSP 16 adjusts the voltage applied to the APD 41 in the receiver 40 by supplying the control signal Cr to the RXHV 18 and changing the high voltage V _RX generated by the RXHV 18.

Next, the DSP 16 detects the peak amplitude value PK of the received segment signal RS based on the received segment y in the reference reflector period among the received segments y input from the received segment memory 15 (step S12). Further, the DSP 16 refers to the injection power table and obtains a target peak amplitude value PKpt corresponding to the target injection power Pt (step S13). Then, the DSP 16 adjusts the voltage applied to the LD 35 so that the peak amplitude value PK detected in step S12 becomes the target peak amplitude value PKpt (step S14). Specifically, the DPS 16 adjusts the voltage applied to the LD 35 by supplying the control signal Ct to the TXHV 17 and changing the high voltage V _TX generated by the TXHV 17. Thus, by making the peak amplitude value PK coincide with the target peak amplitude value PKpt, the injection power from the LD 35 is maintained at the target injection power Pt.

  In the above embodiment, the DSP 16 controls the emission power based on the peak amplitude value PK of the reception segment signal RS, but the reception segment signal RS has a clear pulse waveform as shown in FIG. If not, the pulse integral value of the received segment signal RS may be used. That is, instead of the peak amplitude value, an integral value of a section where the return light is significantly present in the received segment signal RS may be calculated and used. In that case, an injection power table showing the relationship between the injection power and the integral value of the received segment signal RS is prepared. Then, the DPS 16 refers to the injection power table to obtain the target integrated value corresponding to the target injection power Pt, and sets the applied voltage of the LD 35 so that the integrated value detected from the received segment signal RS matches the target integrated value. Adjust it.

[APC AGC]
Next, AGC (Automatic Gain Control) of the APD 41 in the receiver 40 will be described. Normally, even if the voltage applied to the APD 41 is kept constant, the avalanche gain (M value) of the APD 41 does not become constant due to variations in individual APD, temperature changes, secular changes, and the like. For this reason, AGC of APD41 is required. In this embodiment, a reference reflector is arranged in a specific scanning direction of the lidar 1 and AGC is performed based on the return light reflected by the reference reflector. Note that the reference reflector 7 used for AGC is the same as that used for the APC of the LD 35, and thus the description thereof is omitted.

AGC is control for adjusting the voltage applied to the APD 41 so as to obtain a predetermined target avalanche gain (for example, M = 30), and is mainly executed by the DSP 16 shown in FIG. Specifically, as shown in FIG. 12, the DSP 16 supplies the control signal Cr to the RXHV 18, thereby changing the high voltage V _RX generated by the RXHV 18 and adjusting the voltage applied to the APD 41 in the receiver 40.

  When performing AGC, a table (hereinafter also referred to as “gain table”) showing the relationship between the avalanche gain of the APD 41 and the peak amplitude value PK of the received segment is prepared in advance. This gain table is a table in the case where the injection power of the LD 35 is the aforementioned target injection power. The gain table is created based on the measurement performed in the manufacturing stage or the development stage of the lidar 1. This measurement is based on the premise that the measurement is performed using the reference reflector 7 mounted on the actual rider 1.

FIG. 14B shows an example of the gain table. The horizontal axis indicates the peak amplitude value PK of the received segment signal RS, and the vertical axis indicates the avalanche gain M of the APD 41. As illustrated, the peak amplitude value PK and the avalanche gain M basically have a linear relationship. Assuming that the predetermined target avalanche gain M is “Mt”, the target peak amplitude value PK corresponding to the target avalanche gain Mt is “PKgt”. In order to set the avalanche gain M of the APD 41 as the target avalanche gain Mt using the gain table, the applied voltage V _RX to the APD 41 is adjusted so that the peak amplitude value PK of the received segment signal RS becomes the target peak amplitude value PKgt. It will be good. The gain table is stored in a memory or the like inside the DSP 16.

  FIG. 16 shows a flowchart of the AGC process. This process is mainly executed by the DSP 16 shown in FIG. As a precondition for performing the AGC process, it is required that the injection power of the LD 35 is adjusted to the target injection power by the APC process of the LD 35 described above.

First, the DSP 16 detects the peak amplitude value PK of the received segment signal RS based on the received segment y in the reference reflector period among the received segments y input from the received segment memory 15 (step S21). Next, the DSP 16 refers to the gain table and acquires the target peak amplitude value PKgt corresponding to the target avalanche gain Mt (step S22). Then, the DSP 16 adjusts the voltage applied to the APD 41 so that the peak amplitude value PK detected in step S21 becomes the target peak amplitude value PKgt (step S23). Specifically, the DPS 16 adjusts the voltage applied to the APD 41 by supplying the control signal Cr to the RXHV 18 and changing the high voltage V _RX generated by the RXHV 17. Thus, by matching the peak amplitude value PK with the target peak amplitude value PKgt, the avalanche gain of the APD 41 is maintained at the target avalanche gain Mt.

  In the above embodiment, the DSP 16 controls the avalanche gain of the APD 41 based on the peak amplitude value PK of the received segment signal RS. However, the received segment signal RS is clear as shown in FIG. If it is not a pulse waveform, the pulse integral value of the received segment signal RS may be used. That is, instead of the peak amplitude value, an integral value of a section where the return light is significantly present in the received segment signal RS may be calculated and used. In that case, a gain table showing the relationship between the avalanche gain and the integral value of the received segment signal RS is prepared. Then, the DPS 16 refers to the gain table, acquires the target integral value corresponding to the target avalanche gain Mt, and adjusts the applied voltage of the APD 41 so that the integral value detected from the received segment signal RS matches the target integral value. do it.

  The following are mentioned as an example of the effect by said Example. In the lidar 1, if the injection power of the LD 35 is lower than the target or the avalanche gain of the APD 41 is lower than the target, the object detection performance and the distance measurement performance of the lidar 1 are deteriorated. Further, if the injection power is higher than the target or the avalanche gain is higher than the target, the eye-safe requirement for the user cannot be satisfied, or the ADC is saturated and the object detection performance and the distance measurement performance are deteriorated. In this regard, in the present embodiment, the injection power is kept constant by the APC processing of the LD 35, and the avalanche gain of the APD 41 is kept constant by the AGC processing of the APD 41, so that the desired performance of the lidar 1 is maintained. Is possible.

1 Rider 7 Reference reflector 10 ASIC
16 DSP
17 Transmitter high voltage generator (TXHV)
18 High voltage generator for receiver (RXHV)
30 Transmitter 35 LD
40 receiver 50 scanning optical section

Claims (8)

An emission part that emits laser light while changing the emission direction;
A reference reflector disposed in a predetermined emission direction and reflecting the laser beam;
A light receiving unit for receiving the return light of the laser beam;
Based on the return light from the reference reflector, a control unit for controlling the emission power of the laser beam emitted from the emission unit;
A laser emitting apparatus comprising: The emission unit includes a laser light source that emits the laser light,
The laser emitting apparatus according to claim 1, wherein the control unit controls a voltage applied to the laser light source based on return light from the reference reflector. A storage unit for storing a table indicating a relationship between a peak amplitude value of return light from the reference reflector and the emission power;
The laser emission apparatus according to claim 2, wherein the control unit refers to the table and controls the applied voltage so that a level of the return light becomes a peak amplitude value corresponding to a target emission power.   The laser emission apparatus according to claim 3, wherein the table shows a relationship between a peak amplitude value of return light from the reference reflector and the emission power under a condition where a gain of the light receiving unit is a predetermined value.   5. The detector according to claim 1, further comprising a detection unit configured to perform at least one of detection of the object and measurement of a distance to the object based on return light from an object other than the reference reflector. The laser emission apparatus according to item. Laser emission comprising: an emission part that emits laser light while changing the emission direction; a reference reflector that is arranged in a predetermined emission direction and reflects the laser light; and a light receiving part that receives return light of the laser light A control method executed by an apparatus,
A control step of controlling the emission power of the laser beam emitted from the emission unit based on the return light from the reference reflector;
A control method. An emission unit that emits laser light while changing the emission direction, a reference reflector that is arranged in a predetermined emission direction and reflects the laser light, a light receiving unit that receives return light of the laser light, and a computer, A program executed by a laser emitting apparatus comprising:
A program that causes the computer to function as a control unit that controls emission power of the laser light emitted from the emission unit based on return light from the reference reflector.   A storage medium storing the program according to claim 7.