Distance measuring device

Abstract

To reduce an area in which a distance cannot be calculated occurring ahead of an object because of time required for calculating distance to the object.SOLUTION: An emission part 12 emits light. A light reception part 13 detects reflection light. A light quantity measurement part 14 measures the light quantity of the reflection light. A main calculation part 15 calculates a distance to an object by acquiring a light reception result of the reflection light. A control part 11 has a frame counter 111 and a start signal generation part 112. The frame counter 111 counts the number of frames on the basis of the number of times of generation of a pixel reference signal. The start signal generation part 112 generates a calculation start signal and transmits it to a sub-calculation part 16 at a lapse of calculation standby time corresponding to the number of frames from a point of time when the latest pixel reference signal is generated by referencing the number of frames. The sub-calculation part 16 maintains a state in which calculation of a distance from an own device to the object is not executed until the calculation start signal is received, and is shifted to a state in which calculation of the distance from the own device to the object can be executed when receiving the calculation start signal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to distance measuring device technology. [Background technology]

[0002] In obstacle detection using a laser radar, it is required to be able to distinguish between fog, dust, and obstacles.

[0003] Patent Document 1 discloses a laser radar device that detects objects at two detection performance levels: a high detection performance level that can detect a low-reflectivity object at a reference distance and at a reference angle relative to the device, and a low detection performance level that does not detect the object; and the detection performance level indicates how easy it is to detect an object, and is determined by the intensity of the laser light that is projected and the sensitivity of the reflected light that is received.The measurement unit detects objects at each of these two detection performance levels, and irradiates laser light outside the device while changing the irradiation direction, and determines whether an object is present in the irradiated direction based on the reflected light received at the low detection performance level.The measurement unit irradiates laser light in directions that include at least the directions in which it was not determined that an object was present, and determines whether an object is present based on the waveform width of the reflected light received at the high detection performance level being shorter than a fog determination width threshold.

[0004] Patent Document 2 discloses an obstacle detection device for construction machinery that irradiates a monitoring area around the construction machinery with measurement light, receives reflected light from the measurement light, generates distance measurement data that associates distance measurement values ​​measured using the TOF method with the position of each pixel in a distance image of the monitoring area viewed in the direction of irradiation of the measurement light, and detects the amount of reflected light received at the position of each of these pixels.When an object present in a specified area of ​​the monitoring area whose distance from a specified part of the construction machinery is less than a specified value, or an object predicted to enter the specified area, is detected based on the distance measurement data, the device detects the object as an obstacle, provided that the amount of received light in the area where the object present in the specified area or the object predicted to enter the specified area that is closest to the specified part of the construction machinery is greater than a predetermined threshold.

[0005] Patent Document 3 discloses a laser scan sensor that, when it is determined that distance information acquired for each measurement direction corresponds to another object closer to the original detection target and it is determined that interpolation based on distance information from an adjacent measurement direction or an earlier measurement cycle is possible, replaces the distance information for that measurement direction with an interpolated value based on distance information acquired in that measurement cycle in the adjacent measurement direction, or an interpolated value based on distance information acquired in that measurement direction in an earlier measurement cycle, and determines from this distance information which parts may correspond to an object or a human body based on the movement status over time, and outputs a warning signal if it is determined that an object or a human body is present. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-49230 [Patent Document 2] Japanese Patent Publication No. 2020-101442 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-59834 Summary of the Invention [Problem to be solved by the invention]

[0007] The technology described in Patent Document 1 is capable of distinguishing between fog and dust by using multiple detection performance levels, but it has difficulty detecting obstacles that exist beyond the fog or dust. The technology described in Patent Document 2 distinguishes between dust particles and obstacles using the amount of light received in addition to distance, but if there is an obstacle with a low amount of light received, it is difficult to distinguish it from dust particles and the like. The technology described in Patent Document 3 specifies a minimum pulse interval between the first reflected light and the second reflected light, which creates a dead zone (an area where distance cannot be calculated) of approximately 2 meters, so there is a risk that obstacles may be hidden in the dead zone.

[0008] One of the objects of the present invention is to reduce the area beyond an object where distance cannot be calculated due to the time required to calculate the distance to the object. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention provides: Pulse The light is emitted and detected by the light receiving section. Pulse Reflected light When detected of Depending on the timing and the amount of reflected light The present invention includes a main calculation unit and a sub-calculation unit that acquire a light reception result and calculate a distance to an object based on the light reception result, and the main calculation unit acquires the light reception result when the sub-calculation unit does not acquire the light reception result and calculates the distance to the object based on the light reception result. The sub-calculation unit starts acquiring a light reception result after a predetermined time period determined based on the distance calculated by the main calculation unit when the distance and the amount of light calculated by the main calculation unit satisfy a predetermined condition. A distance measuring device is provided as a first aspect.

[0010] According to the distance measuring device of the first aspect, the area beyond the object, from which the distance cannot be calculated, is reduced due to the time required to calculate the distance to the object.

[0011] In the distance measuring device of the first aspect, the sub-calculation unit an emission section that emits the pulsed light Start At the time from The aforementioned A second aspect may be adopted in which the acquisition of the light reception result is started after a predetermined time delay.

[0012] According to the distance measuring device of the second aspect, even if the main calculation unit is unable to calculate the distance to the object after a predetermined time has passed since startup, the sub-calculation unit can still calculate the distance.

[0013] In the distance measuring device of the first aspect, the sub-calculation unit Pulse Emits light At the time A third aspect may be adopted in which the acquisition of the light reception result is started a predetermined time after the start of the light reception.

[0014] According to the distance measuring device of the third aspect, PulseEven if the main calculation unit is unable to calculate the distance to the object after a predetermined time has passed since the light was emitted, the sub-calculation unit can still calculate the distance.

[0015] In the distance measuring device of the first aspect, a configuration may be adopted as a fourth aspect in which the sub-calculation section starts acquiring the light reception result after the main calculation section acquires the light reception result.

[0016] According to the distance measuring device of the fourth aspect, when the main calculation unit cannot calculate the distance to the object, the sub-calculation unit can calculate the distance.

[0017] In a fifth aspect, the distance measuring device according to any one of the first to fourth aspects may be configured to include a plurality of the sub-calculation units that start obtaining light reception results at different times.

[0018] According to the distance measuring device of the fifth aspect, when the main calculation unit and any one or more sub-calculation units cannot calculate the distance to the object, the other sub-calculation units can calculate the distance.

[0019] In the distance measuring device according to any one of the first to fifth aspects, a sixth aspect may be adopted in which the light receiving unit transmits a light receiving result to each of the main calculation unit and the sub calculation unit.

[0020] According to the distance measuring device of the sixth aspect, it is not necessary to provide a plurality of light receiving sections. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a diagram showing an example of the configuration of a distance measuring device 1 according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram for explaining an example of a dead zone caused by a dead time Δt. [Figure 3] FIG. 10 is a diagram for explaining a calculated waiting time. [Figure 4] FIG. 3 is a flowchart showing an example of the operation flow of the distance measuring device 1. [Figure 5]4A to 4C are diagrams for explaining an example of the effect of the distance measuring device 1. [Figure 6] FIG. 10 is a diagram for explaining a calculated standby time in which measurement is started from the time when light is emitted. [Figure 7] FIG. 10 is a flowchart showing an example of the flow of operations of the distance measuring device 1 according to a modified example. [Figure 8] FIG. 10 is a diagram showing an example of the configuration of a distance measuring device 1a according to a modified example. [Figure 9] FIG. 10 is a flowchart showing an example of the operation flow of the distance measuring device 1a in a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0022] <Embodiment> <Configuration of distance measuring device> 1 is a diagram showing an example of the configuration of a distance measuring device 1 according to an embodiment of the present invention. The distance measuring device 1 includes a control unit 11, an emission unit 12, a light receiving unit 13, a light quantity measurement unit 14, a main calculation unit 15, and a sub-calculation unit 16.

[0023] The control unit 11 has memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory), not shown, and controls each unit of the distance measuring device 1 by reading and executing a computer program (hereinafter simply referred to as a program) stored in the memory. The control unit 11 includes, for example, an FPGA (Field Programmable Gate Array). The control unit 11 may also have an ASIC (Application Specific Integrated Circuit) or other programmable logic device and perform control using these. The control unit 11 may also be, for example, a general-purpose processor such as a CPU (Central Processing Unit).

[0024] The control unit 11 has a quartz oscillator and generates a pixel reference signal at a predetermined cycle using a clock reference signal of a predetermined frequency generated by the quartz oscillator. The pixel reference signal is a signal for generating pixels that constitute an image, and is generated for each pixel. In the image, the pixels correspond to the direction in which the emission unit 12 emits light (e.g., a pulsed laser) while scanning it into space.

[0025] The process of generating pixel reference signals for the number of pixels that make up one image is called a frame. In the following example, the control unit 11 generates pixel reference signals 16 times per second, each of which corresponds to one image (number of pixels). In other words, the frame rate, which is indicated by the number of times the control unit 11 performs the above process per second, is 16 fps (frames per second). In this case, the frame period is 0.0625 seconds.

[0026] The pixel reference signal is a signal that periodically activates the emission unit 12. Hereinafter, the time when the pixel reference signal is generated will be referred to as the activation time of the emission unit 12.

[0027] The control unit 11 has a frame counter 111 and a start signal generation unit 112. The frame counter 111 and the start signal generation unit 112 are realized by, for example, a logic circuit on an FPGA.

[0028] The frame counter 111 counts the number of frames (referred to as the frame number) based on, for example, the number of times the pixel reference signal is generated. This frame number is reset at a predetermined interval. For example, if the control unit 11 generates the image reference signal at the above-mentioned 16 fps and the frame counter 111 resets the counted frame number every second, the frame number is an integer greater than or equal to 1 and less than or equal to 16.

[0029] The start signal generation unit 112 generates a calculation start signal when a predetermined time has elapsed since a predetermined time point and transmits it to the sub-calculation unit 16. The start signal generation unit 112 shown in FIG. 1 refers to the number of frames counted by the frame counter 111. Then, when a time corresponding to the number of frames (referred to as a calculation wait time) has elapsed since the most recent pixel reference signal was generated, the start signal generation unit 112 generates a calculation start signal and transmits it to the sub-calculation unit 16. The correspondence relationship between the number of frames and the calculation wait time is stored in the memory described above.

[0030] The sub-calculation unit 16 maintains a state in which it does not calculate the distance from its own device to the object until it receives a calculation start signal. Then, when it receives the calculation start signal, the sub-calculation unit 16 transitions to a state in which it can calculate the distance from its own device to the object.

[0031] 1 measures the calculation wait time by counting clocks. For example, if the frequency of the clock reference signal is 1 GHz, the time corresponding to one count is 1 ns (nanosecond). In this case, if the calculation wait time is 14 ns, the start signal generation unit 112 will not send a calculation start signal to the sub-calculation unit 16 until the number of clocks counted since the most recent pixel reference signal was generated reaches 14.

[0032] The emission unit 12 emits light under the control of the control unit 11. The emission unit 12 is activated every time it receives a pixel reference signal generated by the control unit 11, and adjusts the emission direction of light to a direction corresponding to the pixel indicated by the pixel reference signal. The control unit 11 shown in FIG. 1 causes the emission unit 12 to emit light when a predetermined time (referred to as an emission standby time) has elapsed since the most recent pixel reference signal was generated.

[0033] The control unit 11 measures the above-mentioned emission standby time by counting clocks. For example, if the frequency of the clock reference signal is 1 GHz and the emission standby time is 10 ns, the control unit 11 will not issue an instruction to the emission unit 12 to emit light until the number of clocks counted from the time the most recent pixel reference signal was generated reaches 10. This emission standby time is constant regardless of the number of frames.

[0034] 1 includes a driver 121, a light-emitting element 122, and a detector 123. The driver 121 receives instructions from the control unit 11 and drives the light-emitting element 122. The light-emitting element 122 is a device that emits light toward a space where an object may exist, and is, for example, a laser diode (LD). The detector 123 includes, for example, a photodiode and a signal processing circuit, and detects the timing when the light-emitting element 122 emits light and notifies the control unit 11.

[0035] When the light emitted by the emission unit 12 is reflected by an object, the light receiving unit 13 receives and detects the reflected light. The light receiving unit 13 shown in FIG.

[0036] The light receiving element 131 is an element that detects the reflected light from the object and generates a signal by a current, such as an APD (avalanche photodiode). The current-voltage converter 132 is a converter that converts the current generated when the light receiving element 131 detects the reflected light into a voltage, such as a TIA (transimpedance amplifier).

[0037] The light quantity measuring unit 14 measures the quantity of reflected light detected by the light receiving element 131. The light quantity measuring unit 14 shown in FIG.

[0038] Integrator 141 integrates a voltage value corresponding to the amount of reflected light detected by light receiving element 131, which is output from current-voltage converter 132 of light receiving unit 13. Peak hold circuit 142 holds the peak value of the value integrated by integrator 141. A / D converter 143 converts an analog signal of the amount of light indicated by the peak value held by peak hold circuit 142 into a digital signal and transmits it to control unit 11.

[0039] The main calculation unit 15 and the sub calculation unit 16 are devices that acquire the light reception result of the reflected light by the light receiving unit 13 and calculate the distance to the target object based on this light reception result. The main calculation unit 15 shown in FIG. 1 has a comparator 151 and a time information generator 152.

[0040] The comparator 151 is an element that compares the voltage value output from the current-voltage converter 132 of the light receiving unit 13 with a threshold value, and notifies the time information generator 152 of the timing when this voltage value exceeds the threshold value.

[0041] The time information generator 152 is a device that generates time information indicating the time from when the light emitting unit 12 emits light to when the reflected light is received by the light receiving unit 13. The time information generator 152 unconditionally receives the notification from the above-mentioned comparator 151, and regards the timing indicated by this notification as the timing when the light receiving unit 13 receives the reflected light.

[0042] The time information generator 152 shown in FIG. 1 includes, for example, a TDC (Time to Digital Converter) in order to achieve a time resolution according to the required spatial resolution.

[0043] This TDC is, for example, a so-called basic flash TDC, and includes a delay line configured by multiple stages of inverters and a D flip-flop. Note that the time information generator 152 may use a TDC with a different configuration, for example, a Vernier TDC.

[0044] This TDC calculates, with a time resolution higher than that of a crystal oscillator, the difference in reception time between the clock reference signal of a crystal oscillator included in control unit 11 and the signal (also called a pulse signal) received from comparator 151. By adding this calculated time difference to the time at which the above-mentioned clock reference signal was generated, this TDC specifies the timing at which the signal was received from comparator 151.

[0045] The time information generator 152 obtains information on the timing of light emission detected by the detector 123 of the emission unit 12 from the control unit 11, obtains information on the timing of receiving a signal from the comparator 151 using the above-mentioned TDC, and calculates the difference as time information.

[0046] However, due to its configuration, the TDC cannot receive the next signal transmitted by the comparator 151 and start processing the reception time of that signal until a certain amount of time has passed since it started calculating the difference in reception time. This time during which processing cannot be started is called dead time.

[0047] FIG. 2 is a diagram illustrating an example of a dead zone caused by a dead time Δt. The horizontal axis in FIG. 2 represents time, and the vertical axis represents distance from the distance measuring device 1. Time t1 in FIG. 2 is the time when light is emitted. As shown in FIG. 2, if there is fog at a distance ya from the distance measuring device 1, light is reflected by the fog, and the reflected light reaches the distance measuring device 1 at time ta. Since light travels a distance ya back and forth between time t1 and time ta, if the speed of light is c, the following equation (1) holds:

[0048] [Number 1] ya=c×(ta-t1) / 2 ……(1) When the light receiving unit 13 of the distance measuring device 1 receives the reflected light at time ta, the light receiving result is unconditionally transmitted to the main calculation unit 15, and the time information generator 152 enters a state in which it cannot receive the next signal. That is, the main calculation unit 15 is unable to perform calculations from time ta when the light receiving unit 13 receives the reflected light, throughout the dead time Δt shown in FIG. 2.

[0049] The timing when the dead time Δt has elapsed from time ta is time tc. When light emitted at time t1 is reflected by an object and the reflected light returns at time tc, the object is located at a distance yc as shown in Figure 2. Since light travels a distance yc back and forth between time t1 and time tc, if the speed of light is c, then the following equation (2) holds true.

[0050] [Number 2] yc=c×(tc-t1) / 2 ……(2) Once the main calculation unit 15 starts calculating the distance based on the light reflected from the fog at a distance ya, it is unable to calculate the next distance based on the reflected light until time tc. Therefore, the range from the distance ya to the distance yc, covering the depth Δy, is a dead zone for the main calculation unit 15. Since the depth Δy is the length obtained by subtracting the distance ya from the distance yc, it can be expressed by the following equation (3) using the above-mentioned equations (1) and (2).

[0051] [Number 3] Δy=c×(tc-ta) / 2=c×Δt / 2 ……(3) For example, if the dead time Δt is 15 ns, the speed of light c ≒ 3 × 10 8 Since the velocity is m / s, the depth Δy is approximately 2.2 meters. Therefore, in this case, if an obstacle exists within a range of approximately 2.2 meters beyond the fog as seen from the distance measuring device 1, the main calculation unit 15 cannot calculate the distance based on the light reflected by the obstacle.

[0052] The sub-calculation unit 16 supplements the main calculation unit 15 in the calculation-disabled state described above, and calculates the distance to an object present in the dead zone. The sub-calculation unit 16 shown in FIG. 1 includes a comparator 161 and a time information generator 162.

[0053] The comparator 161 has a function common to the above-mentioned comparator 151, and receives the voltage value output from the current-voltage converter 132 of the light receiving unit 13, and notifies the time information generator 162 of the timing when this voltage value exceeds a threshold value.

[0054] The light receiving unit 13 transmits the result of receiving the reflected light to the main calculation unit 15 and the sub calculation unit 16 by branching the signal of the voltage value described above. In other words, the light receiving unit 13 is an example of a light receiving unit that transmits the result of receiving light to each of the main calculation unit and the sub calculation unit.

[0055] Time information generator 162 has the same functions as the above-described time information generator 152, except that it receives a calculation start signal from start signal generator 112 of control unit 11. Time information generator 162 maintains a state in which it does not calculate the distance from its own device to the target object until it receives a calculation start signal from start signal generator 112.

[0056] When this "state in which distance calculation is not performed" is maintained, even if the comparator 161 notifies the time information generator 162 of the above-mentioned timing, the time information generator 162 does not receive this notification. In other words, when the time information generator 162 maintains the "state in which distance calculation is not performed", the sub-calculation unit 16 does not acquire the light reception result from the light receiving unit 13 as a whole.

[0057] In other words, this distance measuring device 1 is an example of a distance measuring device that has a main calculation unit and a sub-calculation unit that emits light, acquires the light reception result of the reflected light of the light by the light receiving unit, and calculates the distance to the target object based on the light reception result, and the main calculation unit acquires the light reception result when the sub-calculation unit has not acquired the light reception result, and calculates the distance to the target object based on the light reception result.

[0058] Then, when the time information generator 162 receives the calculation start signal, it transitions to a state in which it is possible to calculate the distance from the distance measuring device 1 (that is, the light emitting element 122 or the light receiving element 131 in this case) to the object.

[0059] When the time information generator 162 is in the "state where distance calculation can be executed", it receives the above-mentioned timing notification from the comparator 161 and calculates the distance to the target object based on that timing. In other words, when the time information generator 162 is in the "state where distance calculation can be executed", the sub-calculation unit 16 obtains the light reception result from the light receiving unit 13.

[0060] That is, the sub-calculation unit 16 included in the distance measurement device 1 is an example of a sub-calculation unit that starts acquiring the light reception result with a delay of a predetermined time after startup.

[0061] For example, as shown in FIG. 2, when an obstacle exists at a position of a distance yb that is farther than the distance ya and closer than the distance yc as seen from the distance measurement device 1, that is, within the dead zone, the reflected light from this obstacle reaches the distance measurement device 1 at time tb (ta < tb < tc). In this case, the main calculation unit 15 cannot calculate the distance to this obstacle. And in this case, in order to cause the sub-calculation unit 16 to calculate the distance to this obstacle, the time information generator 162 must already be in a state where it can be calculated at time tb.

[0062] Also, the sub-calculation unit 16 must not acquire and calculate the light reception result of the reflected light from the fog existing at the distance ya. If the sub-calculation unit 16 starts this calculation in parallel with the main calculation unit 15, an unmeasurable dead time Δt also occurs in the sub-calculation unit 16, and a corresponding dead zone occurs. Therefore, in this case, in order to cause the sub-calculation unit 16 to calculate the distance to the above-described obstacle, the time information generator 162 must maintain a state where it does not calculate at time ta.

[0063] That is, in order for the sub-calculation unit 16 to compensate for the dead zone of the main calculation unit 15, the start signal generator 112 of the control unit 11 must have a time t2 at which the generated calculation start signal is transmitted to the time information generator 162 of the sub-calculation unit 16 during the period from time ta to time tb.

[0064] However, since the distances ya and yb cannot be specified in advance, the period from time ta to time tb cannot be specified in advance either. Therefore, the control unit 11 of the distance measurement device 1 shown in FIG. 1 gives a different calculation waiting time to the sub-calculation unit 16 for each frame.

[0065] Fig. 3 is a diagram for explaining the calculation standby time. The horizontal direction in Fig. 3 indicates time advancing to the right, and shows the generation timing of the pixel reference signal, the standby control timing of the emission unit 12 and the sub-calculation unit 16 by the control unit 11, and the calculation control timing by the sub-calculation unit 16.

[0066] FIG. 3(a) shows the operation timing when the frame count is 1. When a pixel reference signal is generated at time t0, the control unit 11 counts clocks to measure the emission standby time. For example, the control unit 11 does not issue an instruction to the emission unit 12 to emit light until the number of clocks counted from the time the pixel reference signal was generated reaches 10, regardless of the frame count. For example, if the frequency of the clock reference signal is 1 GHz, it takes 10 ns for the number of clocks to reach 10. That is, in this case, the emission unit 12 emits light the moment 10 ns has elapsed since the pixel reference signal was generated. The timing for emitting this light is time t1.

[0067] Meanwhile, the control unit 11 counts clocks to calculate a calculated waiting time corresponding to the number of frames. For example, if the calculated waiting time associated with the number of frames is 14 ns and the frequency of the clock reference signal is 1 GHz, the control unit 11 will not send a calculation start signal to the sub-calculation unit 16 until the number of clocks counted from the timing at which the pixel reference signal was generated reaches 14. Therefore, as shown in FIG. 3(a), when the number of frames is 1, time t2 is the point in time when 14 ns has elapsed since time t0.

[0068] In this case, the time from time t1 to time t2 is 4 ns, which corresponds to the time it takes to travel a distance of approximately 0.6 m from the distance measuring device 1 and back. In other words, when the number of frames is 1, the distance measuring device 1 keeps the sub-calculation unit 16 on standby for a calculation standby time equivalent to a distance of approximately 0.6 m from the device itself, and after this calculation standby time has elapsed, makes the sub-calculation unit 16 start calculating the distance.

[0069] Figure 3(b) shows the operation timing when the number of frames is 2. The control unit 11 also measures a fixed 10 ns as the emission waiting time in this case. However, since the calculated waiting time is determined for each number of frames, when the number of frames is 2, the control unit 11 measures a calculated waiting time that is different from when the number of frames is 1 as shown in Figure 3(a).

[0070] For example, if the calculation wait time associated with the number of frames is 2 and the frequency of the clock reference signal is 1 GHz, the control unit 11 will not send a calculation start signal to the sub-calculation unit 16 until the number of clocks counted from the timing at which the pixel reference signal was generated reaches 18. Therefore, as shown in FIG. 3(b), when the number of frames is 2, time t2 is the point in time when 18 ns have elapsed since time t0.

[0071] In this case, the time from time t1 to time t2 is 8 ns, which corresponds to the time it takes to travel a distance of approximately 1.2 m from the distance measuring device 1 and back. In other words, when the number of frames is 2, the distance measuring device 1 keeps the sub-calculation unit 16 on standby for a calculation standby time equivalent to a distance of approximately 1.2 m from the device itself, and after this calculation standby time has elapsed, makes the sub-calculation unit 16 start calculating the distance.

[0072] 1 changes the calculation waiting time depending on the number of frames, and therefore the range that the sub-calculation unit 16 covers in its calculations changes as the number of frames changes.

[0073] As a result, if any of the times t2 at which the control unit 11 sends a calculation start signal to the sub-calculation unit 16 is after the time ta shown in Figure 2 and before the time tb, the sub-calculation unit 16 can obtain the results of receiving reflected light from an obstacle located at a distance yb that is farther than the distance ya and closer than the distance yc, instead of the main calculation unit 15, and calculate the distance yb based on this.

[0074] 4 is a flow diagram showing an example of the operation flow of the distance measuring device 1. The control unit 11 of the distance measuring device 1 determines whether or not generation of a pixel reference signal has been detected (step S101), and continues the determination of step S101 while determining that generation of a pixel reference signal has not been detected (step S101; NO). When the control unit 11 determines that generation of a pixel reference signal has been detected (step S101; YES), it refers to the number of frames (step S102).

[0075] The control unit 11 waits until a certain time (i.e., an emission waiting time) has elapsed (step S103). After the waiting time, the control unit 11 transmits an instruction to the emission unit 12 to emit light (step S104).

[0076] Furthermore, in parallel with steps S103 and S104, control unit 11 waits until a time corresponding to the current frame number (i.e., calculation wait time) has elapsed (step S105). After the wait, control unit 11 transmits a signal (i.e., calculation start signal) to sub-calculator 16 to enable distance calculation (step S106).

[0077] After completing both steps S104 and S106, the control unit 11 determines whether the calculation period of the sub-calculation unit 16 has ended (step S107). For example, if the calculation period for causing the sub-calculation unit 16 to calculate the distance is pre-stored in the memory or the like, the control unit 11 determines whether the stored calculation period has elapsed. Then, while determining that the calculation period of the sub-calculation unit 16 has not ended (step S107; NO), the control unit 11 continues this determination. If the control unit 11 determines that the calculation period of the sub-calculation unit 16 has ended (step S107; YES), the control unit 11 transmits a calculation end signal to the sub-calculation unit 16 to end the state in which distance calculation is possible (step S108).

[0078] 5 is a diagram illustrating an example of the effect of the distance measuring device 1 in the above-described embodiment. Light emitted from FIG. 1 is reflected, for example, at position P11 by fog 2. The reflected light reflected by fog 2 is detected by the light receiving unit 13, and the light reception result is unconditionally acquired by the main calculation unit 15. Therefore, if, as viewed from the distance measuring device 1, an obstacle 3a exists in the range beyond position P11 of the fog 2 to a depth Δy, the light reception result of the reflected light reflected at position P12 on the surface of the obstacle 3a cannot be acquired by the main calculation unit 15.

[0079] On the other hand, because the sub-calculation unit 16 is given a calculation standby time, it may not acquire the light reception result of the reflected light reflected at position P21 in the fog 2. In this case, even if an obstacle 3b exists in the range beyond position P21 of the fog 2 to a depth Δy as seen from the distance measuring device 1, the sub-calculation unit 16 will acquire the light reception result of the reflected light reflected at position P22 on the surface of the obstacle 3b.

[0080] In other words, by performing the operation shown in Figure 4, the distance measuring device 1 causes the sub-calculation unit 16 to maintain a ``state in which distance calculation is not performed'' until the calculation waiting time has elapsed from a predetermined reference timing, so that the area beyond the object where distance cannot be calculated is reduced due to the time required for the main calculation unit 15 to calculate the distance to the object.

[0081] The configurations, shapes, sizes, and layout relationships described in the above embodiments are merely schematic illustrations to enable understanding and implementation of the present invention. Therefore, the present invention is not limited to the described embodiments, and can be modified in various forms without departing from the scope of the technical ideas set forth in the claims.

[0082] <Modification> The above is a description of the embodiment, but the contents of this embodiment can be modified as follows. In addition, the following modifications can be combined.

[0083] <1> In the above-described embodiment, the control unit 11 of the distance measuring device 1 provides the sub-calculation unit 16 with a different calculation standby time for each frame, but if the sub-calculation unit has the main calculation unit acquire a light reception result when the sub-calculation unit has not acquired the light reception result and calculates the distance to the target based on the light reception result, the calculation standby time does not need to change. In this case, the control unit 11 does not need to have the frame counter 111.

[0084] <2> In the above-described embodiment, the start signal generation unit 112 generates a calculation start signal and transmits it to the sub-calculation unit 16 when the calculation wait time has elapsed since the most recent pixel reference signal was generated, but the reference time for the calculation wait time is not limited to the timing when the pixel reference signal was generated (i.e., at startup). For example, the reference time for the calculation wait time may be the time when the emission unit 12 emits light.

[0085] 6 is a diagram for explaining the calculated standby time, measurement of which starts from the time when light is emitted. As shown in FIG. 6, the control unit 11 measures the calculated standby time from time t1, not from time t0. In other words, the control unit 11 does not send a calculation start signal to the sub-calculation unit 16 until the number of clocks counted from the time when the emitting unit 12 emitted light reaches a predetermined value, not from the time when the pixel reference signal was generated.

[0086] 6, the control unit 11 does not send a calculation start signal to the sub-calculation unit 16 until the number of clocks counted from the timing when the emission unit 12 emits light reaches 4. Therefore, time t2 shown in FIG. 6 is the point in time when 4 ns has elapsed since time t1.

[0087] That is, the sub-calculation unit 16 in this modified example is an example of a sub-calculation unit that starts acquiring a light-reception result a predetermined time after emitting light. Even in this case, the main calculation unit 15 can acquire a light-reception result when the sub-calculation unit 16 has not acquired a light-reception result and calculate the distance to the object based on the light-reception result. Therefore, even if the main calculation unit 15 calculates the distance based on the light-reception result acquired when the sub-calculation unit 16 has not acquired a light-reception result, and therefore cannot acquire the light-reception result of reflected light from an object located in a dead zone, the dead zone can be reduced as long as the sub-calculation unit 16 is in a state where it can acquire the light-reception result.

[0088] <3> In the above-described embodiment, the calculation wait time is determined for each frame, but the calculation wait time for a pixel in a frame may be determined based on the distance calculated for that pixel by the main calculation unit 15 in one or more frames prior to that frame. In this case, the calculation wait time for the above-described frame may be determined based on the distance calculated by the main calculation unit 15 in one or more frames prior to that frame, as well as the amount of light measured by the light amount measurement unit 14. Furthermore, the calculation wait time for the above-described frame may be determined based on the distance calculated by the main calculation unit 15 in one or more frames prior to that frame when the amount of light satisfies a predetermined condition.

[0089] 7 is a flow diagram showing an example of the operation flow of the modified distance measuring device 1. The control unit 11 of the distance measuring device 1 acquires the distance to the object calculated by the main calculation unit 15 (step S201), and acquires the measured value of the light intensity of the reflected light used to calculate the distance by the light intensity measurement unit 14 (step S202).

[0090] Then, the control unit 11 determines whether the acquired distance and light intensity measurement values ​​(referred to as light intensity measurement values) satisfy predetermined conditions (step S203). The distance and light intensity measurement values ​​to be used for this determination may be those acquired in only this one frame, or may be those acquired over multiple frames. When the distance and light intensity measurement values ​​acquired over multiple frames are used for the determination, the control unit 11 stores these multiple sets of distance and light intensity measurement values ​​in memory.

[0091] The above-mentioned condition may be, for example, that the distance acquired n times (n is an integer equal to or greater than 2) falls within a predetermined range. Furthermore, the above-mentioned condition may be further that the light intensity measurement value exceeds a predetermined threshold.

[0092] If it is determined that the condition is not satisfied (step S203; NO), the control unit 11 returns the process to step S201. On the other hand, if it is determined that the condition is satisfied (step S203; YES), the control unit 11 sets the calculated waiting time corresponding to the acquired distance for the next frame (step S204), and then returns the process to step S201.

[0093] With this configuration, the calculation waiting time in a certain frame is determined according to the calculated distance to the object and the measured amount of reflected light in the previous frame, thereby improving accuracy when calculating the distance to, for example, a stationary object or an object moving at a speed that does not require detection on a frame-by-frame basis.

[0094] <4> In the above-described embodiment, the start signal generation unit 112 generates a calculation start signal and transmits it to the sub-calculation unit 16 when the calculation waiting time has elapsed since the most recent pixel reference signal was generated. However, the calculation start signal may also be transmitted when the calculation waiting time has elapsed since the main calculation unit 15 acquired the light reception result from the light receiving unit 13.

[0095] 8 is a diagram showing an example of the configuration of a distance measuring device 1a in a modified example. The distance measuring device 1a has a control unit 11a instead of the control unit 11 shown in FIG. 1, and a main calculation unit 15a instead of the main calculation unit 15.

[0096] The control unit 11a has a reset signal generating unit 113 and a flip-flop circuit 114 instead of the frame counter 111. Furthermore, the control unit 11a has a start signal generating unit 112a instead of the start signal generating unit 112.

[0097] The main calculation unit 15a is similar to the main calculation unit 15 in that it has a comparator 151 and a time information generator 152, but differs from the main calculation unit 15 in that the comparator 151 also transmits the pulse signal that it sends to the time information generator 152 to the flip-flop circuit 114 of the control unit 11a.

[0098] The reset signal generating unit 113 generates a reset signal and transmits it to the flip-flop circuit 114 when a time corresponding to the upper limit distance (hereinafter also referred to as the upper limit time) has elapsed since the light was emitted by the emitting unit 12.

[0099] The upper limit distance refers to the upper limit of the distance that the distance measuring device 1a measures. The upper limit time is the time it takes for the emitted light to travel the upper limit distance and back. For example, if the upper limit time is 300 ns, the distance that the light travels over the upper limit time is approximately 90 m. The upper limit distance is half of this, or approximately 45 m.

[0100] For example, if the frequency of the clock reference signal is 1 GHz, when the number of clocks counted from the time when light is emitted by the emission unit 12 reaches 300, the reset signal generation unit 113 generates a reset signal, assuming that the upper limit time of 300 ns has elapsed.

[0101] The flip-flop circuit 114 is a logic circuit that holds one bit of information. This one bit of information is represented by only two states: High and Low. When the flip-flop circuit 114 receives a reset signal from the reset signal generation unit 113, it sets its own state to Low (also referred to as resetting). At this time, the flip-flop circuit 114 sets its own state to Low, regardless of whether its own state before receiving the reset signal was High or Low.

[0102] Furthermore, when the flip-flop circuit 114 receives a pulse signal from the comparator 151, it sets its own state to High.

[0103] The start signal generation unit 112a refers to the state of the flip-flop circuit 114, and when this state becomes High, it generates a calculation start signal and transmits it to the time information generator 162 of the sub-calculation unit 16. When the time information generator 162 receives the calculation start signal from the start signal generation unit 112a, it transitions to a state in which it can calculate the distance from its own device to an object.

[0104] Furthermore, when the state of the flip-flop circuit 114 becomes Low, the start signal generation unit 112a transmits a calculation end signal to the time information generator 162 of the sub-calculation unit 16, which ends the state in which distance calculation is possible. Upon receiving the calculation end signal from the start signal generation unit 112a, the time information generator 162 transitions to a state in which calculation of the distance from its own device to the target object is not executed.

[0105] The timing at which the flip-flop circuit 114 goes high is the timing at which the pulse signal is received from the comparator 151, that is, the timing at which the main calculation unit 15a acquires the light-reception result from the light-receiving unit 13. Therefore, the sub-calculation unit 16 is an example of a sub-calculation unit that starts acquiring the light-reception result after the main calculation unit acquires the light-reception result.

[0106] 9 is a flow diagram showing an example of the operation flow of the distance measuring device 1a in the modified example. The control unit 11a of the distance measuring device 1a determines whether or not generation of a pixel reference signal has been detected (step S301), and continues the determination of step S301 while determining that generation of a pixel reference signal has not been detected (step S301; NO). When the control unit 11a determines that generation of a pixel reference signal has been detected (step S301; YES), it waits until a certain time (the above-mentioned emission waiting time, for example, 10 ns) has elapsed (step S302), and then transmits an emission instruction to the emission unit 12 (step S303).

[0107] The control unit 11a determines whether the main calculation unit 15a has acquired a light-reception result based on whether the flip-flop circuit 114 has received a pulse signal from the comparator 151 of the main calculation unit 15a (step S304). If the control unit 11a determines that the main calculation unit 15a has acquired a light-reception result (step S304; YES), the control unit 11a sends a calculation start signal to the sub-calculation unit 16 (step S305) and proceeds to step S306. On the other hand, if the control unit 11a determines that the main calculation unit 15a has not acquired a light-reception result (step S304; NO), the control unit 11a skips step S305 and proceeds to step S306.

[0108] The control unit 11a determines whether an upper limit time (e.g., 300 ns) has elapsed since the emission of light by the emission unit 12 (step S306). If it determines that the upper limit time has not elapsed since the emission of light (step S306; NO), the control unit 11a returns the process to step S304. On the other hand, if it determines that the upper limit time has elapsed since the emission of light (step S306; YES), the control unit 11a generates a reset signal and transmits it to the flip-flop circuit 114 (step S307), and returns the process to step S301.

[0109] According to this configuration, the sub-calculation unit 16 starts acquiring the light reception result after the main calculation unit 15a acquires the light reception result, and therefore, by acquiring the same light reception result as the main calculation unit 15a, simultaneous calculation failures are unlikely to occur.

[0110] <5> In the above-described modified example, the comparator 151 of the main calculation unit 15a branches the pulse signal and transmits it to the time information generator 152 and the flip-flop circuit 114, respectively. However, the transmission destination may be dynamically switched. For example, when the comparator 151 transmits a pulse signal to the time information generator 152, the time information generator 152 may control an analog switch to switch the connection of the signal line from the comparator 151 to the time information generator 152 to the connection of the signal line from the comparator 151 to the time information generator 162 of the sub calculation unit 16. In this case, the main calculation unit 15 and the sub calculation unit 16 may share one comparator 151, and the sub calculation unit 16 may not have its own comparator 161.

[0111] <6> In the above-described embodiment, the distance measuring device 1 has one sub-calculation unit 16, but it may have multiple sub-calculation units 16. In this case, it is preferable that the calculation standby times given to the multiple sub-calculation units 16 are different. This distance measuring device 1 is an example of a distance measuring device that has multiple sub-calculation units that start acquiring light reception results at different times. According to this configuration, at least two of the multiple sub-calculation units 16 included in the distance measuring device 1 have different calculation standby times, so that it is unlikely that these units will acquire the same light reception result and become unable to perform calculations at the same time. [Explanation of symbols]

[0112] 1...distance measuring device, 1a...distance measuring device, 11...control unit, 11a...control unit, 111...frame counter, 112...start signal generating unit, 112a...start signal generating unit, 113...reset signal generating unit, 114...flip-flop circuit, 12...emitting unit, 121...driver, 122...light-emitting element, 123...detector, 13...light-receiving unit, 131...light-receiving element, 132...current-to-voltage converter, 14...light amount measuring unit, 141...integrator, 142...peak hold circuit, 143...A / D converter, 15...main calculation unit, 15a...main calculation unit, 151...comparator, 152...time information generator, 16...sub-calculation unit, 161...comparator, 162...time information generator, 2...fog, 3a...obstacle, 3b...obstacle

Claims

1. a main calculation unit and a sub-calculation unit that emit pulsed light, acquire a light-receiving result according to the timing when a light-receiving unit detects reflected light of the pulsed light and the amount of the reflected light, and calculate a distance to an object based on the light-receiving result, wherein the main calculation unit acquires the light-receiving result when the sub-calculation unit has not acquired the light-receiving result, and calculates a distance to the object based on the light-receiving result; The sub-calculation unit is a distance measuring device that begins acquiring light reception results a predetermined time later than a reference point, determined based on the distance calculated by the main calculation unit when both the distance and light amount calculated by the main calculation unit n times (n is an integer greater than or equal to 2) satisfy respective specified conditions.

2. The sub-calculation unit starts acquiring the light reception result after a delay of the predetermined time from the time when the emission unit that emits the pulsed light is activated.

2. The distance measuring device according to claim 1.

3. The sub-calculation unit starts acquiring the light reception result a predetermined time after the time point when the pulsed light is emitted.

2. The distance measuring device according to claim 1.

4. The sub-calculation unit starts acquiring the light reception result after the main calculation unit acquires the light reception result.

2. The distance measuring device according to claim 1.

5. The sub-calculation unit has a plurality of sub-calculation units that start acquiring light receiving results at different times.

5. A distance measuring device according to claim 1.

6. The light receiving unit transmits the light receiving result to the main calculation unit and the sub calculation unit, respectively.

6. A distance measuring device according to claim 1.

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