Distance measuring device emitter and distance measuring device

Abstract

This suppresses power waste caused by discharging residual charge. [Solution] The emitter 10 of the distance measuring device 1 for measuring the distance to an object comprises a transmitting unit that outputs a transmission wave to irradiate the object, a capacitor 120 that is charged by a power supply and supplies current to the transmitting unit, a switching element 150 that controls the current flowing to the transmitting unit, a drive circuit that controls the switching element, and a control unit 180 that, after irradiating with a transmission wave, sends a control signal to the drive circuit to continuously irradiate with a transmission wave of an irradiable distance according to the residual charge of the capacitor 120.

Description

Technical Field

[0001] The present invention relates to an emitter of a distance measuring device and a distance measuring device.

Background Art

[0002] In order to detect the position, distance, direction of existence, etc. of a preceding vehicle, an oncoming vehicle, a pedestrian, etc., for example, a distance measuring device such as a LiDAR (Light Detection and Ranging) device that irradiates laser light and measures the reflected light thereof to detect the distance, shape, etc. of an object is used.

[0003] For example, Patent Document 1 discloses an emitter array of a LiDAR device. The emitter array includes an emitter bank coupled between a high-side switch and a low-side switch for each of a plurality of channels. The high-side switch is coupled between a capacitor and a power supply that supplies a voltage for charging the capacitor, and controls the charging of the capacitor. When the charging is completed, after turning off the high-side switch, the low-side switch is turned on to discharge, and the emitter bank can be driven.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in order to irradiate light only on the target channel, it is necessary to discharge the residual charge stored in the capacitor after irradiation. Since the residual charge to be discharged does not contribute to the irradiation, power waste occurs. In addition, a switch for discharging the residual charge is required.

[0006] The present invention has been made in view of the above, and aims to suppress electrical waste caused by the discharge of residual charge. [Means for solving the problem]

[0007] The emitter of the distance measuring device according to the present invention is an emitter of a distance measuring device that measures the distance to an object, and comprises: a transmitting unit that outputs a transmitting wave to irradiate the object; a capacitor that is charged by a power supply and supplies current to the transmitting unit; a switching element that controls the current flowing to the transmitting unit; a drive circuit that controls the switching element; and a control unit that, after irradiation with the transmitting wave, sends a control signal to the drive circuit to continuously irradiate the transmitting wave at an irradiation distance that can be irradiated according to the residual charge of the capacitor. [Effects of the Invention]

[0008] According to the present invention, by continuously irradiating the capacitor with the transmitted wave at an irradiation distance that can be irradiated according to the residual charge of the capacitor, it is possible to suppress power waste caused by discharging the residual charge. [Brief explanation of the drawing]

[0009] [Figure 1] This is a block diagram showing the configuration of a distance measuring device according to an embodiment of the present invention. [Figure 2] This is a block diagram showing the configuration of the emitter of a distance measuring device according to an embodiment of the present invention. [Figure 3] This figure shows the voltage fluctuation of a capacitor during laser irradiation. [Figure 4] This figure shows the voltage fluctuation of the capacitor during laser irradiation when the capacitor's capacitance is changed. [Figure 5] This figure shows an example of measuring distance using a distance measuring device according to an embodiment of the present invention, where (a) is a front view as seen from the front of the vehicle, and (b) is a top view as seen from above the vehicle. [Figure 6]This diagram shows examples of irradiation distance combinations, with (a) showing the irradiation distance combinations for two consecutive irradiations and (b) showing the irradiation distance combinations for three consecutive irradiations. [Modes for carrying out the invention]

[0010] Hereinafter, a distance measuring device according to an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same or equivalent parts are denoted by the same reference numerals.

[0011] Figure 1 is a block diagram showing the configuration of the distance measuring device 1. In this embodiment, the distance measuring device 1 is a LiDAR device, which is an optical distance measuring device. The distance measuring device 1 is mounted, for example, on the front of a vehicle and detects preceding vehicles, oncoming vehicles, pedestrians, obstacles, etc. The distance measuring device 1 includes an emitter 10, which is a laser irradiation device that irradiates a target object with laser light; a scanning device 11 that scans the irradiated laser light within the measurement range; a receiver 12, which is a light receiving device that receives light reflected from the target object; and a control device 13 that controls the operation of the emitter 10, the scanning device 11, and the receiver 12 and calculates the distance to the target object.

[0012] The emitter 10 includes, for example, a light source which is a transmitting unit with a number of channels corresponding to the vertical resolution, and the light source for each channel is arranged vertically. The light source is a laser diode and emits, for example, pulsed near-infrared laser light with a wavelength of approximately 900 nm as the transmitted wave. The timing of illumination and extinction of the light source for each channel is controlled individually. Details of the emitter will be described later.

[0013] The scanning device 11 scans the laser light emitted from the emitter 10 within the measurement range using an optical deflector. The optical deflector is composed of, for example, a MEMS (Micro Electro Mechanical System) mirror. The optical deflector reflects incident light entering from a certain direction using mirrors that rotate around mutually orthogonal axes, and emits it as scanning light.

[0014] The receiver 12 receives the reflected light from the object after the laser light emitted from the emitter 10 is reflected by the object. The receiver 12 has multiple light-receiving elements arranged in two dimensions. The light-receiving elements are composed of, for example, SPAD (Single Photon Avalanche Diode), CMOS (Complementary Metal Oxide Semiconductor), CCD (Charge Coupled Device), etc. The receiver 12 outputs a detection signal to the control device 13 according to the intensity of the received light.

[0015] The control device 13 controls the operation of the emitter 10, the scanning device 11, and the receiver 12. The control device 13 selects the channel of the light source that emits light within the emitter 10 and controls the driving of the mirror of the optical deflector in the scanning device 11. It also calculates the distance to the object using the detection signal input from the receiver 12. The control device 13 calculates the time of flight (TOF) from when the laser beam is emitted until the reflected light is received, and calculates the distance to the object from the calculated time of flight and the speed of the laser beam, and outputs the distance measurement result. The control device 13 is composed of, for example, a microcomputer.

[0016] Next, Figure 2 shows a block diagram illustrating the configuration of the emitter 10 of the distance measuring device 1 in Figure 1. Here, Figure 2 shows the configuration for one channel, but in reality, the same configuration is provided for each channel. The emitter 10 comprises a laser diode 110, a capacitor 120, a resistor 130, a channel selection switch 140 for receiving a channel selection signal to select a channel and connecting the power supply Vcc to the capacitor 120, a switching element 150 for turning the light emission of the laser diode 110 on and off, a gate driver 160 which is a drive circuit that controls the on / off switching of the switching element 150, a voltage detection unit 170 for detecting the voltage of the capacitor 120, and a control unit 180 which supplies a signal for the light emission timing of the laser diode 110 to the gate driver 160.

[0017] The capacitor 120 is connected at one end to the power supply Vcc and the laser diode 110 via the channel selection switch 140. Also, the other end of the capacitor 120 is connected to the ground. The power supply Vcc supplies a DC voltage and charges the capacitor 120 when the channel selection switch 140 is in the on state. The resistor 130 is connected to set the current value flowing through the laser diode 110. The charged capacitor 120 supplies current to the laser diode 110 and causes the laser diode 110 to emit light. It is possible to change the amount of light by changing the capacitance of the capacitor 120 and the resistance value of the resistor 130.

[0018] The channel selection switch 140 is a switch for connecting the capacitor 120 to the power supply Vcc to charge it and is also a switch for selecting the laser diode 110 of the channel to emit light. As described above, the capacitor 120 and the channel selection switch 140 are provided for each channel, and by sequentially selecting each channel, the laser diode 110 of the selected channel is caused to emit light sequentially. The selection signal for the channel causing the laser diode 110 to emit light is supplied from the control device 13. When the switch receives a selection signal for selecting its own channel, it is switched from the off state to the on state. When the channel selection switch 140 is turned on, the power supply Vcc is connected to the capacitor 120 and the capacitor 120 is charged. The channel selection switch 140 is turned off after being turned on for a certain period when the charging of the capacitor 120 is completed. Regarding the transition from the on state to the off state, it may be kept in the on state only while receiving the selection signal and then transition to the off state.

[0019] The switching element 150 is a field effect transistor (FET). The drain D of the switching element 150 is connected to the laser diode 110 via the resistor 130, and the source S is connected to the ground. The switching element 150 is turned on and off according to the gate voltage. By turning on the switching element 150, the charge stored in the capacitor 120 flows to the laser diode 110, causing the laser diode 110 to emit light.

[0020] The gate driver 160 is a drive circuit that is connected to the gate G of the switching element 150 and applies a voltage for controlling the on and off of the switching element 150. The gate driver 160 drives the switching of the switching element 150 based on an input signal from the control unit 180.

[0021] The control unit 180 is connected to the control device 13, the voltage detection unit 170, and the gate driver 160, and outputs a control signal to the gate driver 160 based on input signals from the control device 13 and the voltage detection unit 170. A laser emission timing signal, which is a timing signal for causing the laser diode 110 to emit light, is supplied to the control unit 180 from the control device 13. Also, a detection signal of the charging voltage of the capacitor 120 detected by the voltage detection unit 170 is supplied to the control unit 180. The control unit 180 supplies a pulsed trigger signal for causing the laser diode 110 to emit light in a pulsed manner to the gate driver 160 based on the detection signal, using the laser emission timing signal as the timing of the start of emission.

[0022] The voltage detection unit 170 is connected in parallel with the capacitor 120 and detects the charging voltage of the capacitor 120. The voltage is detected, for example, by connecting a detection resistor to one end of the capacitor 120. The detection signal is supplied to the control unit 180. This enables the control unit 180 to detect how much charge remains in the capacitor 120.

[0023] The emitter 10 receives a channel selection signal from the control device 13, switches on, and charges the capacitor 120. Then, the control unit 180 receives a light emission timing signal from the control device 13, supplies a trigger signal to the gate driver 160, and the gate driver 160 turns on the switching element 150 for a predetermined pulse time, causing the laser diode 110 to emit light. Here, the capacitor 120 must have a capacity that can supply energy to satisfy the desired amount of light according to the irradiation distance of the laser beam. The relationship between the discharge characteristics of the capacitor 120 and the irradiation time of the emitter 10 must also be considered. The irradiation distance is the distance at which the transmitted laser beam reaches the target object with an amount of light sufficient to detect it, and is also called the detection distance.

[0024] Figure 3 shows the voltage fluctuation of capacitor 120 during laser irradiation, with the vertical axis representing voltage and the horizontal axis representing time. The discharge curve 30, shown by the dotted line, shows the discharge characteristics of capacitor 120. First, with the capacitor fully charged, the first irradiation is performed for a predetermined pulse period. This discharges the charge stored in capacitor 120. However, when utilizing the region where capacitor 120 has a high response speed, it is not possible to completely discharge the charge of capacitor 120 in a single irradiation. As shown in discharge curve 31, which is part of discharge curve 30, although the voltage drops after the first irradiation, it only drops from 30V to 19.5V, and not all the charge is discharged. Once the first irradiation is complete, the control unit 180 detects the voltage of capacitor 120 from the voltage detection unit 170. This allows the control unit 180 to detect how much charge remains in capacitor 120. Based on the detected voltage value and discharge characteristics, the control unit 180 determines whether further irradiation is possible, and if so, it determines the irradiable distance. Once the irradiation distance is determined, a second irradiation is performed for a predetermined pulse duration. When the second irradiation begins, the residual charge is discharged according to the discharge curve 30, and the voltage decreases as shown in the discharge curve 32, which is part of the discharge curve 30.

[0025] Once the second irradiation is complete, the control unit 180 again detects the voltage of the capacitor 120 from the voltage detection unit 170. Based on the detected voltage value and discharge characteristics, the control unit 180 determines whether further irradiation is possible, and if so, it determines the irradiable distance. Once the irradiation distance is determined, the third irradiation is performed for a predetermined pulse period. When the third irradiation begins, the residual charge is discharged according to the discharge curve 30, and the voltage decreases as shown in the discharge curve 33, which is part of the discharge curve 30.

[0026] Similarly, after each irradiation is completed, the control unit 180 detects the voltage of the capacitor 120 from the voltage detection unit 170, determines whether irradiation can continue based on the detected voltage value and discharge characteristics, and if irradiation is possible, it determines the irradiable distance and repeats the irradiation for a predetermined pulse period. If it is determined that irradiation is not possible, the above process is terminated.

[0027] Figure 4 shows examples of voltage fluctuations across capacitor 120 when its capacitance is changed. Here, examples are shown using capacitors 120 with three different capacitances (large, medium, and small), assuming a continuous irradiation count of five times. Discharge curve 41 shows the voltage fluctuation when capacitor 120 has a large capacitance, discharge curve 42 shows the voltage fluctuation when capacitor 120 has a medium capacitance, and discharge curve 43 shows the voltage fluctuation when capacitor 120 has a small capacitance. From this, even if the initial voltage is the same, the voltage drop due to discharge required for one irradiation is greater in discharge curve 43 than in discharge curve 42. That is, the larger the capacitance of capacitor 120, the greater the charge accumulated, so the voltage drop due to discharge required for one irradiation is smaller. Therefore, the larger the capacitance of capacitor 120, the longer the irradiation distance can be for the second and subsequent irradiations, and the capacitance of capacitor 120 is set according to the irradiation distance for the second and subsequent irradiations.

[0028] Next, Figure 5 shows an example of distance measurement using the distance measuring device 1 according to this embodiment. Figure 5 shows distance measurement when the distance measuring device 1 is mounted on a vehicle 51, and the distance measuring device 1 irradiates laser light from the front end of the vehicle 51 in order to measure the distance in front of the vehicle 51. Figure 5(a) shows a front view as seen from the front of the vehicle 51, and Figure 5(b) shows a top view of the vehicle 51 as seen from above. In front of the vehicle 51, there is a vehicle 52 crossing in front of it, and a wall 53 behind the vehicle 52. The distance measuring device 1 continuously irradiates two types of laser light with different irradiation distances: irradiation light 54, which is pulsed light with a long irradiation distance, and irradiation light 55, which is pulsed light with a shorter irradiation distance. Here, irradiation light 54 has an irradiation distance (detection distance) that can detect the distance to the wall 53 located behind the vehicle 52. In contrast, irradiation light 55 has an irradiation distance (detection distance) that can detect the distance to the vehicle 52, but cannot detect the distance to the wall 53. In this way, by continuously irradiating with laser pulses of light with different irradiation distances, the detection accuracy when detecting objects overlapping in the depth direction is improved. With the irradiation light 54, which has a longer irradiation distance, the vehicle 52, which is the object in the foreground, and the wall 53, which is the object in the background, overlap, and the outline of the vehicle 52, which is the boundary between the vehicle 52 and the wall 53, is detected in an ambiguous state. By irradiating with the irradiation light 55, which has a shorter irradiation distance, it becomes possible to detect only the vehicle 52, which is the object in the foreground, and thus the detection accuracy for objects at close range can be improved.

[0029] In the above embodiment, a voltage detection unit 170 was provided to detect the voltage of the capacitor 120, determine the irradiation distance, and control the irradiation timing of the continuously irradiated laser pulse light. In contrast, without providing a voltage detection unit 170 and without using the detection results from the voltage detection unit, multiple irradiation distances are determined using numerical values ​​that have been pre-modeled as parameters, such as the capacitance of the capacitor 120, the resistance value of the resistor 130, and multiple irradiation timings, and continuous irradiation is controlled based on these multiple irradiation distances. The numerical values ​​are set by measurement during the manufacturing or adjustment of the distance measuring device 1 or emitter 10. Alternatively, past settings for the capacitance of the capacitor 120, the resistance value of the resistor 130, and multiple irradiation timings for multiple irradiation distances and number of irradiations may be stored, and the numerical values ​​may be set based on these. In addition, the number of irradiations may be further increased to 3, 4, etc., in conjunction with tuning the capacitance of the capacitor 120.

[0030] When irradiating with laser pulses of multiple irradiation distances in succession, detection accuracy can be improved by setting combinations of irradiation distances according to the detection purpose. Here, as an example, Figure 6(a) shows combinations of irradiation distances for two consecutive irradiations, and Figure 6(b) shows combinations of irradiation distances for three consecutive irradiations.

[0031] In the example of two consecutive irradiations, if the irradiation distance for the first irradiation is long, the irradiation distance for the second irradiation can be either long, medium, or short. Therefore, as shown in Figure 6(a), there are three possible combinations of the first and second irradiations: long distance + long distance, long distance + medium distance, and long distance + short distance.

[0032] Furthermore, in the example of three consecutive irradiations, for each of the three combinations described above for the two consecutive irradiations, the irradiation distance for the third irradiation will be either long, medium, or short. However, if the irradiation distance for the second irradiation was medium, the irradiation distance for the third irradiation cannot exceed the amount of residual charge on capacitor 120, and will therefore be either medium or short. Also, if the irradiation distance for the second irradiation was short, the irradiation distance for the third irradiation cannot exceed the amount of residual charge on capacitor 120, and will therefore be short only. Thus, as shown in Figure 6(b), there are six possible combinations for three consecutive irradiations: long + long + long, long + long + medium, long + long + short, long + medium + medium, long + medium + short, and long + short + short. Depending on the distance at which you want to improve detection accuracy, you can select from these combinations and set up the control of continuous irradiation with multiple irradiation distances.

[0033] As described above, the irradiation distance of the subsequent laser beam can be calculated from the voltage and discharge characteristics of the capacitor 120, allowing for the continuous irradiation of laser pulses with different irradiation distances in a single charging operation. By setting laser pulses with different irradiation distances, the accuracy of detecting the boundaries between objects and the contours of objects that overlap due to objects at different distances is improved, thereby enhancing safety. Furthermore, since the residual charge of the capacitor 120 is used for the second and subsequent irradiations, there is no waste from simply discharging and discarding the residual charge. In addition, a switch for discharging and discarding the residual charge is not required, resulting in cost reduction, simplification, and miniaturization.

[0034] In the above embodiment, an FET was given as an example of the switching element 150, but it is not limited to this, and a bipolar transistor or an insulated gate transistor may also be used.

[0035] Furthermore, in the above embodiment, the voltage detection signal is input to the control unit 180, and the control unit 180 generates a control signal to cause the laser diode 110 to emit pulsed light. However, the embodiment is not limited to this, for example, the voltage detection signal may be input to the control device 13, and the control device 13 may generate a control signal to cause the laser diode 110 to emit pulsed light.

[0036] Furthermore, in the above embodiment, the laser diode 110 was provided with a number of channels, and the laser diode 110 of the selected channel was sequentially made to emit light by sequentially selecting each channel. In contrast, a flash-type device that irradiates light over a wide area without scanning the light may also be used.

[0037] Furthermore, although the above embodiment uses LiDAR as an example of a distance measuring device, it is not limited to this; for example, an ultrasonic sensor that measures distance using ultrasound may also be used.

[0038] Although embodiments of the present invention have been described above, the scope of the present invention is not limited to the embodiments described above, but includes the scope of the invention as described in the claims and its equivalents. [Explanation of Symbols]

[0039] 1...Distance measuring device, 10...Emitter, 11...Scanning device, 12...Receiver, 13...Control device, 110...Laser diode, 120...Capacitor, 130...Resistor, 140...Channel selection switch, 150...Switching element, 160...Gate driver, 170...Voltage detection unit, 180...Control unit, 30,31,32,33,41,42,43...Discharge curve, 51,52...Vehicle, 53...Wall, 54,55...Irradiation light, Vcc...Power supply

Claims

1. An emitter for a distance measuring device that measures the distance to an object, A transmitting unit that outputs a transmission wave to irradiate the aforementioned object, A capacitor that is charged by a power source and supplies current to the transmitting unit, A switching element that controls the current flowing through the transmitting unit, A drive circuit for controlling the switching element, The system includes a control unit that, after irradiation with the transmitted wave, sends a control signal to the drive circuit to continuously irradiate the transmitted wave at an irradiation distance that can be irradiated according to the residual charge of the capacitor, Distance measuring device emitter.

2. The system includes a voltage detection unit that detects the voltage of the capacitor, The control unit determines the irradiation distance corresponding to the residual charge of the capacitor based on the voltage detected by the voltage detection unit, and sends the control signal to the drive circuit to irradiate the transmitted wave at the irradiation distance. The emitter of the distance measuring device according to claim 1.

3. The control unit determines the irradiation distance using the capacitance of the capacitor, the resistance value that sets the current value flowing through the transmitting unit, and numerical values ​​that model the timing of multiple irradiations as parameters, and sends the control signal to the drive circuit to irradiate the transmitted wave at the irradiation distance. The emitter of the distance measuring device according to claim 1.

4. The distance measuring device is a LiDAR device. The emitter of the distance measuring device according to claim 1.

5. The distance measuring device is an ultrasonic sensor. The emitter of the distance measuring device according to claim 1.

6. An emitter according to any one of claims 1 to 5, A scanning device that scans the transmitted wave to be irradiated within a measurement range, A receiver that receives the transmitted wave reflected from the object, The system includes a control device that controls the operation of the emitter, the scanning device, and the receiver, and calculates the distance to the object. Ranging device.

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