Distance measuring device, distance measuring system, distance measuring method and procedure

Abstract

The problem of the present invention is to provide a distance measuring device, a distance measuring system, a distance measuring method and a program, all of which are configured or designed to improve the measurement accuracy of the distance to a target. The distance measuring device (10) includes a control unit (11) and a measuring unit (12). The control unit (11) controls a photodetector unit (3). The photodetector unit (3) includes a photoelectric converter element (D10) and an output unit (32). The photoelectric converter element (D10) generates an electric charge when receiving light reflected from a target as a part of the measurement light emitted from a light emitting unit (2). The output unit (32) outputs an electric signal representing the amount of electric charge generated by the photoelectric converter element (D10). The measuring unit (12) calculates the distance to the target within a measurable range based on the electric signal. The control unit (11) sets a ratio of the amount of electric charge generated by the photoelectric converter element (D10) to the amount of light received by the photoelectric converter element (D10) in each of a plurality of intervals (R1-R7) constituting a measurable range (FR).

Description

Technical Field

[0001] The present disclosure generally relates to a distance measurement device, a distance measurement system, a distance measurement method, and a program. More specifically, the present disclosure relates to a distance measurement device, a distance measurement system, a distance measurement method, and a program configured or designed to measure the distance to a target. Background Art

[0002] Patent document 1 discloses a distance measuring device. The distance measuring device of Patent document 1 includes a solid-state image sensor, a signal processor, a computer, and a light source. The solid-state image sensor includes a plurality of pixels arranged two-dimensionally. Each pixel includes: a light sensing circuit for detecting an incident light beam arriving at a photosensitive element within a predetermined exposure time; a counter circuit for counting the number of arrivals of the incident light beam based on a light sensing signal provided from the light sensing circuit; a comparator circuit for outputting a comparison signal based on a count value provided from the counter circuit; and a storage circuit for storing a time signal as a distance signal when the comparison signal provided from the comparator circuit is ON.

[0003] Patent Document 1 describes that the measurable distance range can be expanded by a solid-state image sensor having such a structure. However, Patent Document 1 does not teach how to improve the measurement accuracy over the entire measurable range of the distance to the target.

[0004] Citation List

[0005] Patent Literature

[0006] Patent Document 1: JP 2018-169162 A Summary of the invention

[0007] The problem is to provide a distance measuring device, a distance measuring system, a distance measuring method and a program, all of which are configured or designed to improve the measurement accuracy over the entire measurable range of the distance to a target.

[0008] A distance measuring device according to one aspect of the present disclosure includes a control unit and a measuring unit. The control unit controls a photodetector unit. The photodetector unit includes a photoelectric converter element and an output unit. When receiving light reflected from a target as a part of the measurement light emitted from a light emitting unit, the photoelectric converter element generates an electric charge. The output unit outputs an electric signal representing the amount of electric charge generated by the photoelectric converter element. The measuring unit calculates the distance to the target within a measurable range based on the electric signal. The control unit sets a conversion rate of the amount of electric charge generated by the photoelectric converter element relative to the amount of light received by the photoelectric converter element in each of a plurality of intervals constituting the measurable range.

[0009] A distance measurement system according to another aspect of the present disclosure includes the above-mentioned distance measurement device, a light emitting unit, and a photodetector unit.

[0010] A distance measurement method according to another aspect of the present disclosure includes a control step and a measurement step. The control step includes controlling a photodetector unit. The photodetector unit includes a photoelectric converter element and an output unit. When receiving light reflected from a target as a part of the measurement light emitted from a light emitting unit, the photoelectric converter element generates an electric charge. The output unit outputs an electric signal representing the amount of electric charge generated by the photoelectric converter element. The measuring unit calculates the distance to the target within a measurable range based on the electric signal. The control step includes setting a conversion rate of the amount of electric charge generated by the photoelectric converter element relative to the amount of light received by the photoelectric converter element in each of a plurality of intervals constituting the measurable range.

[0011] A program according to still another aspect of the present disclosure is designed to cause one or more processors to execute the above distance measurement method. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a block diagram of a distance measurement system according to an exemplary embodiment;

[0013] Figure 2 A distance measurement system is shown;

[0014] Figure 3 is a circuit diagram of a photoelectric converter element of a distance measuring system;

[0015] Figure 4 Schematically shows how the distance measurement system operates;

[0016] Figure 5 Schematically shows how the distance measurement system operates;

[0017] Figure 6 Schematically shows how the distance measurement system operates;

[0018] Figure 7 A first method for controlling a distance measurement system is shown;

[0019] Figure 8 A second method for controlling a distance measurement system is shown; and

[0020] Fig. 9 An exemplary structure of a plurality of intervals constituting a measurable range according to a modification is shown. DETAILED DESCRIPTION

[0021] 1. Example

[0022] 1.1. Overview

[0023] Figure 1 1 shows a distance measurement system 1 according to an exemplary embodiment. The distance measurement system 1 includes a distance measurement device 10. The distance measurement device 10 includes a control unit 11 and a measuring unit 12. The control unit 11 controls a photodetector unit 3. The photodetector unit 3 includes Figure 1 and Figure 2 The photoelectric converter element D10 and the output unit 32 shown. The photoelectric converter element D10 generates electric charge when receiving the light L2 reflected from the target 100 as a part of the measurement light L1 emitted from the light emitting unit 2. The output unit 32 outputs an electric signal indicating the amount of electric charge generated by the photoelectric converter element D10. The measuring unit 12 calculates the distance to the target within the measurable range FR based on the electric signal. The control unit 11 sets the ratio of the amount of electric charge generated by the photoelectric converter element D10 to the amount of light received by the photoelectric converter D10 in each of the plurality of intervals R1-R7 constituting the measurable range FR.

[0024] This distance measuring device 10 can appropriately set the conversion rate in each of the multiple intervals R1-R7 constituting the measurable range FR. That is, the distance measuring device 10 can set the conversion rate to an appropriate value according to the position of the target 100. Therefore, the distance measuring device 10 helps to improve the measurement accuracy throughout the measurable range of the distance to the target 100.

[0025] 1.2. Details

[0026] Will refer to Figures 1 to 8 The distance measurement system 1 is described in more detail. The distance measurement system 1 measures the distance to the target 100 by means of a time of flight (TOF) technique. The distance measurement system 1 includes a distance measurement device 10, a light emitting unit 2, a photodetector unit 3, a voltage source 4, and a current measurement unit 5. Figure 2 As shown, the distance measuring system 1 measures the distance to the target 100 by using light (reflected light) L2 reflected from the target 100 as a part of the measuring light L1 emitted from the light emitting unit 2. The distance measuring system 1 is suitable for use, for example, as an object recognition system used as an in-vehicle device of an automobile to detect an obstacle, a monitoring camera for detecting an object (human), and a security camera.

[0027] The light emitting unit 2 includes a light source 21 for irradiating the target 100 with the measuring light L1. The measuring light L1 is a pulse light beam. Figure 2, the measuring light L1 is conceptually represented by a dotted line. In this regard, when measuring the distance by the TOF technique, the measuring light L1 appropriately has a single wavelength, a relatively short pulse width, and a relatively high peak intensity. In addition, considering the use of the distance measurement system 1 (distance measurement device 10) in, for example, an urban area, the wavelength of the measuring light L1 appropriately falls within a near-infrared wavelength range where the photometric factor is low for the human eye and is not easily affected by ambient light from the sun. In the present embodiment, the light source 21 is implemented as, for example, a laser diode, and emits a pulsed laser beam. The intensity of the pulsed laser beam emitted from the light source 21 meets Class 1 or Class 2 of the "Laser Product Safety" standard (JIS C 6802) formulated by Japan. Note that the light source 21 does not have to be a laser diode, but may also be, for example, a light emitting diode (LED), a vertical cavity surface emitting laser (VCSEL), or a halogen lamp. Optionally, the measuring light L1 may also fall within a wavelength range different from the near-infrared wavelength range.

[0028] The photodetector unit 3 includes a photoelectric converter element D10 and an output unit 32. The photoelectric converter element D10 generates electric charge when receiving the light L2 reflected from the target 100 as a part of the measurement light L1 emitted from the light emitting unit 2. The output unit 32 outputs an electric signal (pixel signal) indicating the amount of electric charge generated by the photoelectric converter element D10. In the present embodiment, the photodetector unit 3 includes an image sensor 31 and an output unit 32. Figure 1 As shown, the image sensor 31 includes a plurality of pixels 311 arranged two-dimensionally. Each of the plurality of pixels 311 can receive light only during the exposure duration. The output unit 32 outputs the electrical signal provided from (the pixel 311 of) the image sensor 31 to the distance measurement device 10.

[0029] Figure 3 is a circuit diagram of each pixel 311. Figure 3 As shown, the pixel 311 includes a photoelectric converter element D10, a charge storage device C10, a floating diffusion element FD, an amplifier A10, transfer transistors ST1, ST2, ST3, and reset transistors SR1, SR2, SR3.

[0030] The photoelectric converter element D10 generates an electric charge when receiving the light L2 reflected from the target 100 as a part of the measurement light L1 emitted from the light emitting unit 2. The photoelectric converter element D10 is configured to change the conversion rate according to the voltage applied (to the photoelectric converter element D10 itself). As used herein, the conversion rate refers to the ratio of the amount of charge generated by the photoelectric converter element D10 to the amount of light (number of photons) received by the photoelectric converter element D10. For example, the conversion rate of the photoelectric converter element D10 can be changed within a range equal to or greater than 1. In the present embodiment, the photoelectric converter element D10 is implemented as an avalanche photodiode. The avalanche photodiode has a linear multiplication mode and a Geiger multiplication mode. When a first bias voltage (e.g., -25V) is applied, the avalanche photodiode operates in a linear multiplication mode. In the linear multiplication mode, when a photon is incident on the avalanche photodiode, an amount of charge generally proportional to the number of photons causing the photoelectric conversion is collected at the cathode of the avalanche photodiode. On the other hand, when a second bias voltage (e.g., –27 V) having an absolute value greater than that of the first bias voltage is applied to the avalanche photodiode, the avalanche photodiode operates in a Geiger multiplication mode. In the Geiger multiplication mode, when one of the photons incident on the avalanche photodiode causes photoelectric conversion, a saturation amount of charge (i.e., a saturation charge amount) is collected at the cathode of the avalanche photodiode. That is, the amount of charge generated in response to the incidence of one photon becomes constant. It can be seen that the multiplication factor of the avalanche photodiode varies depending on the magnitude of the bias voltage, that is, it varies depending on the magnitude of the voltage (reverse voltage) applied to the avalanche photodiode. In the present embodiment, the conversion rate of the photoelectric converter element D10 is the multiplication factor of the avalanche photodiode.

[0031] The charge storage device C10 stores at least a portion of the charge generated by the photoelectric converter element D10. The charge storage device C10 is a capacitor. The capacitance of the charge storage device C10 is set to a value that allows the charge generated by the photoelectric converter element D10 to be stored multiple times. That is, the charge storage device C10 allows the charge generated by the photoelectric converter element D10 to be accumulated, thereby contributing to increasing the signal-to-noise ratio SNR of the electrical signal as the output signal of the image sensor 31, and ultimately improving the measurement accuracy. In the present embodiment, the first terminal of the charge storage device C10 is grounded.

[0032] The floating diffusion element FD is arranged between the photoelectric converter element D10 and the charge storage device C10, and is used to store charge. The amplifier A10 outputs an electrical signal (pixel signal) to the output unit 32, the size of which corresponds to the amount of charge generated by the photoelectric converter element D10 (i.e., the size corresponding to the amount of charge stored in the charge storage device C10). The transistor ST1 connects the cathode of the photoelectric converter element D10 to the floating diffusion element FD. The transistor ST2 connects the floating diffusion element FD to the second terminal of the charge storage device C10. The transistor ST3 connects the floating diffusion element FD to the input terminal of the amplifier A10. The transistor SR1 connects the cathode of the photoelectric converter element D10 to the internal power supply VDD. The transistor SR2 connects the second terminal of the charge storage device C10 to the internal power supply VDD. The transistor SR3 connects the floating diffusion element FD to the internal power supply VDD.

[0033] In the pixel 311, the charge generated by the photoelectric converter element D10 is transferred and stored in the charge storage device C10 through the transistors ST1 and ST2. After the charge generated by the photoelectric converter element D10 has been stored in the charge storage device C10 for many times, the charge is transferred from the charge storage device C10 to the amplifier A10 by the transistor ST3. This causes the amplifier A10 to output an electrical signal (pixel signal) whose magnitude corresponds to the amount of charge generated by the photoelectric converter element D10 (i.e., the magnitude corresponds to the amount of charge stored in the charge storage device C10). Subsequently, the unnecessary charge remaining in the photoelectric converter element D10, the floating diffusion element FD and the charge storage device C10 is appropriately removed by the transistors SR1, SR2 and SR3. This control of the pixel 311 is performed by the control unit 11.

[0034] The voltage source 4 applies a DC control voltage to the photodetector unit 3. The magnitude of the control voltage applied by the voltage source 4 can be changed. In this embodiment, the voltage source 4 is electrically connected to the anode of the photoelectric converter element D10 in each of the multiple pixels 311 of the image sensor 31 of the photodetector unit 3. This allows the voltage source 4 to apply a control voltage to the photoelectric converter element D10 in each of the multiple pixels 311 of the image sensor 31 of the photodetector unit 3. Specifically, the voltage source 4 can be used to apply a reverse voltage (reverse bias) as a control voltage to the photoelectric converter element D10. That is, the operation mode of the photoelectric converter element D10 can be switched from a linear multiplication mode to a Geiger multiplication mode, or vice versa, by the voltage source 4. The voltage source 4 is controlled by the control unit 11. This allows the control unit 11 to cause the voltage source 4 to switch the operation mode of the photoelectric converter element D10. Note that the voltage source 4 can be implemented as a known power supply, such as a switching power supply, so its detailed description will be omitted here.

[0035] The current measuring unit 5 measures the magnitude of the current flowing from the voltage source 4 to the photodetector unit 3. The current measuring unit 5 provides the value thus measured to the control unit 11. The current measuring unit 5 can be implemented as a well-known current measuring instrument (ammeter) such as a current transformer, and a detailed description thereof is omitted here.

[0036] The distance measuring device 10 calculates the distance to the target 100 within the measurable range FR. In the distance measuring device 10, the measurable range FR is divided into a plurality of (e.g., seven) intervals R1-R7, such as Figure 2 As shown. In other words, the measurable range FR is composed of a plurality of intervals R1-R7. For example, the measurable range FR may have a length of tens of centimeters to tens of meters, but this is not necessary. Each of the plurality of intervals R1-R7 has the same length. For example, each of the plurality of intervals R1-R7 may have a length of several centimeters to several meters. Note that the plurality of intervals R1-R7 do not necessarily have the same length, and the number of intervals provided is not limited to any particular number.

[0037] The distance measuring device 10 includes a control unit 11, a measuring unit 12, and an output unit 13. Note that each of the control unit 11 and the measuring unit 12 can be implemented as a computer system including one or more processors (microprocessors) and one or more memories. That is, the computer system performs the functions of the control unit 11 and the measuring unit 12 by causing one or more processors to execute one or more programs (applications) stored in one or more memories. In the present embodiment, the program is pre-stored in one or more memories. However, this is only an example and should not be construed as a limitation. The program can also be downloaded via a telecommunication line such as the Internet, or distributed after being stored in a non-temporary storage medium such as a memory card.

[0038] The control unit 11 is configured to control the light emitting unit 2 and the photodetector unit 3. For the light emitting unit 2, the control unit 11 controls, for example, the timing at which the light source 21 emits the measuring light L1 (i.e., the light emission timing) and the pulse width of the measuring light L1 emitted from the light source 21. On the other hand, for the photodetector unit 3, the control unit 11 controls, for example, the timing at which each pixel 311 (photoelectric converter element D10) enters an exposure state (i.e., the exposure timing), the exposure duration (exposure time period), and the operation time of each transistor ST1-ST3.

[0039] In addition, the control unit 11 is further configured to control the conversion rate of each photoelectric converter element D10. Specifically, the control unit 11 controls the conversion rate of the photoelectric converter element D10 in each of the multiple intervals R1-R7 constituting the measurable range FR. Since the distance measuring device 10 uses the TOF technology, the multiple intervals R1-R7 of the distance correspond to the multiple time periods T1-T7, respectively. Figure 4 As shown. Therefore, the control unit 11 sets the conversion rate using the voltage applied to the photoelectric converter element D10 in each of the multiple time periods T1-T7 corresponding to the multiple intervals R1-R7, respectively. That is, the control unit 11 sets the conversion rate of the photoelectric converter element D10 by setting the control voltage applied to the photoelectric converter element D10 by the voltage source 4 in the multiple intervals R1-R7 (corresponding to the multiple time periods T1-T7). In the present embodiment, the conversion rate of the photoelectric converter element D10 is the multiplication factor of the avalanche photodiode. The control unit 11 sets the multiplication factor of the avalanche photodiode to the multiplication factor of the linear multiplication mode or the multiplication factor of the Geiger multiplication mode. Figure 4 , VSUB represents a control voltage applied to the photoelectric converter element D10 by the voltage source 4. V1 represents a first bias voltage (i.e., a voltage that switches the photoelectric converter element D10 to the linear multiplication mode). V2 represents a second bias voltage (i.e., a voltage that switches the photoelectric converter element D10 to the Geiger multiplication mode).

[0040] As described above, in the linear multiplication mode, the amount of charge generated by the photoelectric converter element D10 is generally proportional to the number of photons incident on the photoelectric converter element D10. On the other hand, in the Geiger multiplication mode, the amount of charge generated by the photoelectric converter element D10 is constant, regardless of the number of photons incident on the photoelectric converter element D10. Therefore, when the photoelectric converter element D10 is switched to the linear multiplication mode, the distance to the target 100 can have a higher resolution than when the photoelectric converter element D10 is switched to the Geiger multiplication mode. On the other hand, the Geiger multiplication mode generates a greater amount of charge in response to the incidence of photons than the linear multiplication mode. Therefore, if a relatively large number of photons are incident on the photoelectric converter element D10 (i.e., if the photoelectric converter element D10 receives a relatively large amount of light), the photoelectric converter element D10 is appropriately operated in the linear multiplication mode. On the other hand, if a relatively small amount of photons is incident on the photoelectric converter element D10 (i.e., if the photoelectric converter element D10 receives a relatively small amount of light), the photoelectric converter element D10 is appropriately operated in the Geiger multiplication mode. The light received by the photoelectric converter element D10 includes the light L2 reflected from the target 100 and the ambient light (mainly the light from the environment surrounding the photodetector unit 3). The amount of light received by the photoelectric converter element D10 varies according to the duration for which the photoelectric converter element D10 can receive light from the target 100 (i.e., the exposure duration). In addition, the amount of light L2 reflected from the target 100 is also affected by the distance to the target 100 and the surface condition of the target 100. Examples of the surface condition of the target 100 include the (surface) reflectivity of the target 100.

[0041] In the present embodiment, the control unit 11 sets the conversion rate based on various factors including the estimated distance to the target 100, the amount of ambient light, the exposure duration, and the amount of light received by the photoelectric converter element D10 from the target 100, etc. In this case, the control unit 11 reduces the conversion rate when it is necessary to increase the resolution of the distance to the target 100 (linear multiplication mode), and increases the conversion rate when it is necessary to reduce the resolution (Geiger multiplication mode).

[0042] The control unit 11 classifies the plurality of intervals R1-R7 into a first interval and a second interval, and the second interval corresponds to a longer distance from the photoelectric converter element D10 (i.e., the distance measurement system 1) than the first interval. The control unit 11 reduces the conversion rate in the first interval and increases the conversion rate in the second interval. In the present embodiment, the control unit 11 operates the photoelectric converter element D10 in a linear multiplication mode in the first interval and operates the photoelectric converter element D10 in a Geiger multiplication mode in the second interval. For example, in Figure 4In the example shown, the control unit 11 regards the interval R1-R5 as the first interval, and regards the intervals R6 and R7 as the second interval. In this case, the control unit 11 causes the photoelectric converter element D10 to operate in the linear multiplication mode by setting the control voltage VSUB of the voltage source 4 to V1 during the time periods T1-T5 corresponding to the intervals R1-R5, respectively. On the other hand, the control unit 11 causes the photoelectric converter element D10 to operate in the Geiger multiplication mode by setting the control voltage VSUB of the voltage source 4 to V2 during the time periods T6 and T7 corresponding to the intervals R6 and R7, respectively.

[0043] In addition, the control unit 11 also changes the conversion rate according to the amount of ambient light. More specifically, if the amount of ambient light is large, the control unit 11 reduces the conversion rate, and if the amount of ambient light is small, the control unit 11 increases the conversion rate. In the present embodiment, the control unit 11 compares the amount of ambient light with a threshold value in each of a plurality of intervals R1-R7. When it is found that the amount of ambient light is equal to or less than the threshold value, the control unit 11 causes the photoelectric converter element D10 to operate in a Geiger multiplication mode, and when it is found that the amount of ambient light is greater than the threshold value, the control unit D10 causes the photoelectric converter element D10 to operate in a linear multiplication mode. For example, assume that the amount of ambient light is greater than the threshold value in intervals R1-R5, and that the amount of ambient light is equal to or less than the threshold value in intervals R6, R7. In this case, as Figure 4 As shown, the control unit 11 causes the photoelectric converter element D10 to operate in the linear multiplication mode by setting the control voltage VSUB of the voltage source 4 to V1 during the time periods T1-T5 corresponding to the intervals R1-R5, respectively. On the other hand, the control unit 11 causes the photoelectric converter element D10 to operate in the Geiger multiplication mode by setting the control voltage VSUB of the voltage source 4 to V2 during the time periods T6 and T7 corresponding to the intervals R6 and R7, respectively. It is assumed that the amount of ambient light has decreased to be equal to or less than the threshold value in the interval R4. In this case, the control unit 11 causes the photoelectric converter element D10 to operate in the linear multiplication mode by setting the control voltage VSUB of the voltage source 4 to V1 during the time periods T1-T3 corresponding to the intervals R1-R3, respectively, as shown in FIG. Figure 5 On the other hand, the control unit 11 causes the photoelectric converter element D10 to operate in the Geiger multiplication mode by setting the control voltage VSUB of the voltage source 4 to V2 during the period T4-T7 corresponding to the interval R4-R7.

[0044] In addition, the control unit 11 also changes the conversion rate according to the length of the exposure duration. More specifically, if the exposure duration is long, the control unit 11 reduces the conversion rate, and if the exposure duration is short, the control unit 11 increases the conversion rate. In the present embodiment, the control unit 11 compares the length of the exposure duration with a threshold value in each of the plurality of intervals R1-R7. The control unit 11 causes the photoelectric converter element D10 to operate in the Geiger multiplication mode when it is found that the length of the exposure duration is equal to or less than the threshold value, and causes the photoelectric converter element D10 to operate in the linear multiplication mode when it is found that the length of the exposure duration is greater than the threshold value.

[0045] In addition, the control unit 11 also changes the conversion rate according to the amount of light received by the photoelectric converter element D10 from the target 100 (that is, the amount of light L2 reflected from the target 100). More specifically, if the amount of light L2 is large, the control unit 11 reduces the conversion rate, and if the amount of light L2 is small, the control unit 11 increases the conversion rate. In the present embodiment, the control unit 11 compares the amount of light L2 with a threshold value in each of a plurality of intervals R1-R7. When it is found that the amount of light L2 is equal to or less than the threshold value, the control unit 11 may set the conversion rate of the photoelectric converter element D10 to a first value, and when it is found that the amount of light L2 is greater than the threshold value, the conversion rate of the photoelectric converter element D10 may be set to a second value greater than the first value. In this case, the first value is a conversion rate corresponding to a linear multiplication mode of the photoelectric converter element D10, and the second value is a conversion rate corresponding to a Geiger multiplication mode of the photoelectric converter element D10. For example, assume that the amount of light L2 is greater than the threshold value within the interval R1-R5. In this case, as Figure 4 As shown, the control unit 11 causes the photoelectric converter element D10 to operate in the linear multiplication mode by setting the control voltage VSUB of the voltage source 4 to V1 during the time periods T1-T5 corresponding to the intervals R1-R5, respectively. In addition, it is assumed that the amount of light L2 has decreased to be equal to or less than the threshold value in the interval R3. In this case, the control unit 11 causes the photoelectric converter element D10 to operate in the Geiger multiplication mode by setting the control voltage VSUB of the voltage source 4 to V2 during the time period T3 corresponding to the interval R3, as shown in FIG. Figure 6 shown.

[0046] In addition, the control unit 11 changes the conversion rate according to the amount of current flowing through the photoelectric converter element D10. More specifically, the control unit 11 changes the conversion rate of the photoelectric converter element D10 according to the measurement value obtained by the current measuring unit 5. That is, the control unit 11 switches the operation mode of the photoelectric converter element D10 from the linear multiplication mode to the Geiger multiplication mode, or vice versa, according to the measurement value obtained by the current measuring unit 5. Specifically, when it is found that the measurement value obtained by the current measuring unit 5 is equal to or less than the first threshold value while the photoelectric converter element D10 is operating in the linear multiplication mode, the control unit 11 switches the photoelectric converter element D10 to the Geiger multiplication mode. On the other hand, when it is found that the measurement value obtained by the current measuring unit 5 is greater than the second threshold value while the photoelectric converter element D10 is operating in the Geiger multiplication mode, the control unit 11 switches the photoelectric converter element D10 to the linear multiplication mode. That is, when the amount of current flowing through the photoelectric converter element D10 is small, the amount of charge generated by the photoelectric converter element D10 is also small, and therefore the amount of light incident on the photoelectric converter element D10 should also be small. Therefore, the control unit 11 switches the photoelectric converter element D10 to the Geiger multiplication mode instead of the linear multiplication mode. On the contrary, when the amount of current flowing through the photoelectric converter element D10 is large, the amount of charge generated by the photoelectric converter element D10 is also large, so the amount of light incident on the photoelectric converter element D10 should also be large. Therefore, the control unit 11 switches the photoelectric converter element D10 to the linear multiplication mode instead of the Geiger multiplication mode. In this case, the first threshold value and the second threshold value may be the same value or different values ​​from each other.

[0047] In addition, the control unit 11 controls the light emitting unit 2 and the photodetector unit 3 in different ways depending on whether the photoelectric converter element D10 is operated in the linear multiplication mode or the Geiger multiplication mode. More specifically, if the photoelectric converter element D10 is operated in the linear multiplication mode, the control unit 11 performs a first control method. On the other hand, if the photoelectric converter element D10 is operated in the Geiger multiplication mode, the control unit 11 performs a second control method. That is, the first control method is applicable to a case where the resolution is high (i.e., a case where the amount of light received by the photoelectric converter element D10 is relatively large). On the other hand, the second control method is applicable to a case where the resolution is low (i.e., a case where the amount of light received by the photoelectric converter element D10 is relatively small).

[0048] Figure 7 How to perform the first method is explained, Figure 8 shows how to perform the second method. Figure 7 and Figure 8VE represents exposure timing. Q1 represents the amount of charge generated by the photoelectric converter element D10. VA represents the operation timing of transistors ST1, ST2. Q2 represents the amount of charge stored in the charge storage device C10. VT represents the operation timing of transistor ST3. VR represents the operation timing of transistors SR1-SR3.

[0049] First, refer to Figure 7 A first control method is described. In this example, transistors ST1-ST3 and SR1-SR3 should all be turned off before time t0.

[0050] At time t0, the control unit 11 turns on the transistors SR1-SR3 to remove the charge from the charge storage device C10. Next, in the time period from time t1 to time t3, the control unit 11 causes the light source 21 of the light emitting unit 2 to emit the measuring light L1. Therefore, in the time period from time t2 to time t4, the photoelectric converter element D10 of the photodetector unit 3 receives the light L2 reflected from the target 100. However, since the control unit 11 sets the exposure duration starting from time t3, the photoelectric converter element D10 receives the light L2 in the time period from time t3 to time t4, and generates a charge corresponding to the amount of light L2. Next, at time t5 after time t4, the control unit 11 turns on the transistors ST1, ST2 to transfer the charge generated by the photoelectric converter element D10 to the charge storage device C10 through the floating diffusion element FD.

[0051] Subsequently, during the time period from time t6 to time t8, the control unit 11 causes the light source 21 of the light emitting unit 2 to emit the measuring light L1. Therefore, during the time period from time t7 to time t9, the photoelectric converter element D10 of the photodetector unit 3 receives the light L2 reflected from the target 100. However, since the control unit 11 sets the exposure duration starting from time t8, the photoelectric converter element D10 receives the light L2 during the time period from time t8 to time t9, and generates a charge corresponding to the amount of the light L2. Next, at time t10 after time t9, the control unit 11 turns on the transistors ST1, ST2 to transfer the charge generated by the photoelectric converter element D10 to the charge storage device C10 through the floating diffusion element FD.

[0052] The control unit 11 repeats the process of transferring the charge generated by the photoelectric converter element D10 to the charge storage device C10 a predetermined number of times. When the process is performed for the last time, the control unit 11 causes the light source 21 of the light emitting unit 2 to emit the measuring light L1 in the time period from time t11 to time t13. Therefore, in the time period from time t12 to time t14, the photoelectric converter element D10 of the photodetector unit 3 receives the light L2 reflected from the target 100. However, since the control unit 11 sets the exposure duration starting from time t13, the photoelectric converter element D10 receives the light L2 in the time period from time t13 to time t14, and generates a charge corresponding to the amount of light L2. Next, at time t15 after time t14, the control unit 11 turns on the transistors ST1 and ST2 to transfer the charge generated by the photoelectric converter element D10 to the charge storage device C10 through the floating diffusion element FD. Subsequently, the control unit 11 extracts the charge stored in the charge storage device C10 by keeping the transistor ST3 turned on during the time period from time t16 to time t17. In this way, the control unit 11 causes an electric signal (pixel signal) to be output from the pixel 311 .

[0053] Next, we will refer to Figure 8 The second control method is described. In this example, transistors ST1-ST3 and SR1-SR3 should all be turned off before time t20.

[0054] At time t20, the control unit 11 turns on the transistors SR1-SR3 to remove the charge from the charge storage device C10. Next, in the time period from time t21 to time t22, the control unit 11 causes the light source 21 of the light emitting unit 2 to emit the measuring light L1. Therefore, the photoelectric converter element D10 of the photodetector unit 3 receives the light beams L21, L22 as the light L2 reflected from the target 100. The light beams L21, L22 come from the target 100 located relatively far from the distance measurement system 1. During the time period from time t22 to time t23, the light beams L21, L22 reach the photoelectric converter element D10. However, since the control unit 11 sets the exposure duration from time t23, the photoelectric converter element D10 has not yet generated a charge corresponding to the amount of the light beam L2. Next, in the time period from time t25 to t26 after time t24, the control unit 11 turns on the transistors ST1, ST2, and transmits the charge generated by the photoelectric converter element D10 to the charge storage device C10 via the floating diffusion element FD. In this case, the photoelectric converter element D10 does not generate charges, and thus the charges are not stored in the charge storage device C10.

[0055] Subsequently, during the time period from time t27 to time t28, the control unit 11 causes the light source 21 of the light emitting unit 2 to emit the measuring light L1. Therefore, the photoelectric converter element D10 of the photodetector unit 3 receives the light beams L23, L24 as the light L2 reflected from the target 100. The light beams L23, L24 are from the target 100 located relatively far from the distance measuring system 1, similarly to the light beams L21, L22. The light beam L23 reaches the photoelectric converter element D10 during the time period from time t28 to time t29. On the other hand, the light beam L24 reaches the photoelectric converter element D10 during the time period from time t29 to time t30. However, since the control unit 11 sets the exposure duration from time t29, the photoelectric converter element D10 does not generate a charge corresponding to the amount of the light beam L23, but generates a charge corresponding to the amount of the light beam L24. Next, at time t31 after time t30 , the control unit 11 turns on the transistors ST1 , ST2 to transfer the charge generated by the photoelectric converter element D10 to the charge storage device C10 via the floating diffusion element FD.

[0056] The control unit 11 repeats the process of transferring the charge generated by the photoelectric converter element D10 to the charge storage device C10 a predetermined number of times. When the process is performed for the last time, the control unit 11 causes the light source 21 of the light emitting unit 2 to emit the measuring light L1 in the time period from time t32 to time t33. Therefore, the photoelectric converter element D10 of the photodetector unit 3 receives the light beams L25, L26 as the light L2 reflected from the target 100. The light beams L25, L26 are from the target 100 located relatively far from the distance measurement system 1, similarly to the light beams L21, L22. The light beam L25 reaches the photoelectric converter element D10 during the time period from time t33 to time t34. On the other hand, the light beam L26 reaches the photoelectric converter element D10 during the time period from time t34 to time t35. However, since the control unit 11 sets the exposure duration from time t34, the photoelectric converter element D10 does not generate a charge corresponding to the amount of the light beam L25, but generates a charge corresponding to the amount of the light beam L26. Next, at time t36 after time t35, the control unit 11 turns on the transistors ST1, ST2 to transfer the charge generated by the photoelectric converter element D10 to the charge storage device C10 via the floating diffusion element FD. Thereafter, the control unit 11 extracts the charge stored in the charge storage device C10 by keeping the transistor ST3 turned on during the period from time t37 to time t38. In this way, the control unit 11 causes the electric signal (pixel signal) to be output from the pixel 311.

[0057] It can be seen that the control unit 11 appropriately sets the conversion rate (in the present embodiment, from the linear multiplication mode to the Geiger multiplication mode) in each of the plurality of intervals R1-R7 constituting the measurable range FR. Then, the control unit 11 controls the light emitting unit 2 and the photodetector unit 3 based on the conversion rate thus set, so that the electrical signal (pixel signal) is output from the photodetector unit 3 to the measuring unit 12.

[0058] The measuring unit 12 calculates the distance to the target 100 within the measurable range FR based on the electrical signal (pixel signal) provided from the photodetector unit 3. The measuring unit 12 calculates the distance to the target 100 for each of the plurality of pixels 311 (photoelectric converter element D10) of the image sensor 31 of the photodetector unit 3. In this embodiment, the measuring unit 12 calculates the distance to the target 100 by two methods. The two methods are two different types of TOF techniques. The first method is phase shift TOF, and the second method is range gated TOF. Phase shift TOF is capable of calculating distances in the order of centimeters. On the other hand, range gated TOF is capable of calculating distances in the order of meters, but allows calculation of longer distances than phase shift TOF. For the first group of the plurality of intervals R1-R7, the measuring unit 12 calculates the distance to the target 100 by the phase shift TOF method. On the other hand, for the second group of the plurality of intervals R1-R7, the measuring unit 12 calculates the distance to the target 100 by the range gated TOF method. In this case, the first group includes a series of intervals among the plurality of intervals R1-R7, and the second group includes one or more intervals among the plurality of intervals R1-R7 that are different from the first group. The conversion rate of each interval included in the first group is smaller than that of the second group. That is, in the present embodiment, each interval included in the first group (i.e., an interval to which the phase shift TOF is applied) is an interval in which the photoelectric converter element D10 is switched to the linear multiplication mode (i.e., an interval in which the high resolution is set), such as Figures 4 to 6 On the other hand, each section included in the second group (ie, a section where the range gate TOF is applied) is a section where the photoelectric converter element D10 is switched to the Geiger multiplication mode (ie, a section where a low resolution is set).

[0059] The measuring unit 12 obtains the distance based on the ratio of the electrical signals respectively corresponding to a plurality of adjacent intervals in a series of intervals included in the first group, when the phase shift TOF is applied (i.e., for the first group). More specifically, the measuring unit 12 extracts a combination of adjacent intervals from a series of intervals included in the first group, in which the sum of the magnitudes of the electrical signals is greater than the threshold and is the largest. The distance D to the target 100 is given by D=k×Sk+1 / (Sk+Sk+1), where Sk and Sk+1 are the magnitudes of the electrical signals in the extracted interval combination. Note that k is a proportional factor that can be appropriately set. On the other hand, when the range-gated TOF is applied (i.e., for the second group), the measuring unit 12 obtains the distance based on the interval with the largest electrical signal magnitude in one or more intervals included in the second group. More specifically, the distance to the interval with the largest electrical signal magnitude is used as the distance to the target 100. The measuring unit 12 adopts a longer distance selected from the group consisting of the distance determined for the first group and the distance determined for the second group as the distance to the target 100.

[0060] by Figure 4 For example, the first group includes intervals R1-R5, and the second group includes intervals R6 and R7. Assume that the magnitudes of the electrical signals corresponding to intervals R1-R7 are represented by S1-S7, respectively. According to the phase shift TOF, the measuring unit 12 obtains the sum of the magnitudes of the electrical signals in two adjacent intervals R1 and R2 (S1+S2), the sum of the magnitudes of the electrical signals in two adjacent intervals R2 and R3 (S2+S3), and the sum of the magnitudes of the electrical signals in two adjacent intervals R3 and R4 (S3+S4). In this case, it is assumed that the sum of the magnitudes of the electrical signals in two adjacent intervals R2 and R3 (S2+S3) is equal to or greater than the threshold value and greater than any of these sums. In this case, the distance D to the target 100 is given by D=k×S3 / (S2+S3). On the other hand, according to the range selection TOF, the distance is obtained based on the electrical signal with the largest magnitude in the electrical signals corresponding to intervals R5-R7, respectively. In this case, if S6 is greater than S5 or S7, the distance to interval R6 is used as the distance to the target 100. If the distance determined for the first group is greater than the distance determined for the second group, the control unit 11 adopts the distance determined for the first group as the distance to the target 100 .

[0061] The output unit 13 is configured to output the calculation result (measurement result) of the distance to the target 100 obtained by the measurement unit 12 to the external device 6. The external device 6 may be a display device, such as a liquid crystal display or an organic electroluminescent (EL) display. The output unit 13 outputs the measurement result obtained by the measurement unit 12 to the external device 6 so that the external device 6 displays the measurement result obtained by the measurement unit 12. In addition, the output unit 13 may also output image data generated based on the pixel signal to the external device 6 so that the external device 6 displays the image data. Note that the external device 6 does not have to be a display device, and may be any other type of device.

[0062] 1.3. Summary

[0063] As can be seen from the above description, the distance measuring device 10 includes a control unit 11 and a measuring unit 12. The control unit 11 controls the photodetector unit 3. Figure 1 and Figure 2 As shown, the photodetector unit 3 includes a photoelectric converter element D10 and an output unit 32. The photoelectric converter element D10 generates a charge when receiving the light L2 reflected from the target 100 as a part of the measurement light L1 emitted from the light emitting unit 2. The output unit 32 outputs an electrical signal indicating the amount of charge generated by the photoelectric converter element D10. The measuring unit 12 calculates the distance to the target within the measurable range FR based on the electrical signal. The control unit 11 sets the ratio of the amount of charge generated by the photoelectric converter element D10 to the amount of light received by the photoelectric converter element D10 in each of the plurality of intervals R1-R7 constituting the measurable range FR. Therefore, the distance measuring device 10 helps to improve the measurement accuracy of the distance to the target 100.

[0064] In other words, it can be said that the distance measuring device 10 performs the following method (distance measuring method). The distance measuring method includes a control step and a measuring step. The control step includes controlling the photodetector unit 3. The photodetector unit 3 includes a photoelectric converter element D10 and an output unit 32. The photoelectric converter element D10 generates an electric charge when receiving the light L2 reflected from the target 100 as a part of the measurement light L1 emitted from the light emitting unit 2. The output unit 32 outputs an electric signal representing the amount of the electric charge generated by the photoelectric converter element D10. The measuring step includes calculating the distance to the target 100 within the measurable range FR based on the electric signal. The control step includes setting a conversion rate of the amount of the electric charge generated by the photoelectric converter element D10 relative to the amount of light received by the photoelectric converter element D10 in each of the multiple intervals R1-R7 constituting the measurable range FR. This distance measuring method contributes to improving the measurement accuracy of the distance to the target 100 in the same manner as the distance measuring device 10.

[0065] The distance measuring device 10 is implemented as a computer system (including one or more processors). That is, the function of the distance measuring device 10 is realized by causing one or more processors to execute a program (computer program). The program is designed to cause one or more processors to execute the distance measurement method. This program and the distance measurement method also help to improve the measurement accuracy of the distance to the target 100.

[0066] 2. Variant

[0067] Note that the above embodiment is only one of the exemplary embodiments of the various embodiments of the present disclosure and should not be interpreted as limiting. Without departing from the scope of the present disclosure, the exemplary embodiments can be easily modified in various ways according to design selection or any other factors. Next, the variations of the exemplary embodiments will be listed one by one.

[0068] In the above embodiment, the measurable range FR is composed of a plurality of intervals R1-R7 that do not overlap with each other. Alternatively, the measurable range FR may also be composed of Fig. 9 The multiple intervals R1-R7 shown are composed of. Specifically, interval R1 corresponds to the time period T10-T12, interval R2 corresponds to the time period T11-T13, interval R3 corresponds to the time period T12-T14, interval R4 corresponds to the time period T13-T15, interval R5 corresponds to the time period T15-T16, interval R6 corresponds to the time period T16-T17, and interval R7 corresponds to the time period T17-T18. In this example, intervals R1 and R2 partially overlap with each other, intervals R2 and R3 partially overlap with each other, and intervals R3 and R4 partially overlap with each other. For such a measurable range FR, the distance can also be calculated by the phase shift TOF method of the embodiment described above.

[0069] In the above-described embodiment, the control unit 11 changes the conversion rate of the photoelectric converter element D10 from a value corresponding to the linear multiplication mode to a value corresponding to the Geiger multiplication mode, and vice versa. However, this is only an example and should not be construed as a limitation. Alternatively, the control unit 11 may also change the conversion rate of the photoelectric converter element D10 between a plurality of values ​​corresponding to the linear multiplication mode.

[0070] In the above-described embodiment, the control unit 11 sets the conversion rate based on various factors, including the distance to the target 100, the amount of ambient light, the exposure duration, the amount of light received by the photoelectric converter element D10 from the target 100, and the amount of current flowing through the photoelectric converter element D10. However, this is only an example and should not be construed as a limitation. According to a variation, the control unit 11 may set the conversion rate based on at least one of these various factors, including the distance to the target 100, the amount of ambient light, the exposure duration, the amount of light received by the photoelectric converter element D10 from the target 100, and the amount of current flowing through the photoelectric converter element D10.

[0071] In the embodiment described above, the conversion rate is changed for the photoelectric converter elements D10 in all the multiple pixels 311 of the image sensor 31. However, this is only an example and should not be construed as a limitation. According to another variation, the control unit 11 may change the conversion rate for the photoelectric converter element D10 in at least one pixel 311 among the multiple pixels 311. That is, the control unit 11 may change the conversion rate (or multiple conversion rates) only for a necessary one (or more) of the multiple photoelectric converter elements D10.

[0072] In addition, in the embodiment described above, the photoelectric converter element D10 is implemented as an avalanche photodiode. However, this is only an example and should not be construed as a limitation. The photoelectric converter element D10 can be any photoelectric converter as long as the photoelectric converter can change the conversion rate. The photoelectric converter element D10 can also be a photodiode of a different type from the avalanche photodiode, or a solid-state image sensor. Optionally, the photodetector unit 3 may include a plurality of photoelectric converter elements D10 having a plurality of different conversion rates. In this case, the control unit 11 can determine which of the plurality of photoelectric converter elements D10 should be used for each interval.

[0073] According to another variant, the distance measuring device 10 can also be implemented as multiple computers. For example, the functions of the distance measuring device 10 (in particular the functions of the control unit 11 and the measuring unit 12) can also be distributed in multiple devices.

[0074] The subject that performs the functions of the above-mentioned distance measuring device 10 includes a computer system. The computer system includes a processor and a memory as main hardware components. The function of the distance measuring device 10 according to the present disclosure can be performed by the subject by causing the processor to execute a program stored in the memory of the computer system. The program can be pre-stored in the memory of the computer system. Alternatively, the program can also be downloaded via a telecommunication line, or the program can be recorded in a computer-readable non-temporary storage medium such as a memory card, an optical disk or a hard disk drive and then distributed. The processor of the computer system can be implemented as a single or multiple electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). Optionally, a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC) programmed after manufacturing the LSI or a reconfigurable logic device that allows the connection or circuit part inside the LSI to be reconfigured can also be used for the same purpose. These electronic circuits can be appropriately integrated on a single chip or distributed on multiple chips. These multiple chips can be integrated in a single device without restriction, or distributed in multiple devices.

[0075] 3. Multiple aspects

[0076] From the above description of the embodiment and its variations, it can be seen that the present disclosure has the following aspects. In the following description, reference numerals are inserted in brackets only to clarify the corresponding relationship between the following aspects of the present disclosure and the constituent elements of the above exemplary embodiments.

[0077] The first aspect is implemented as a distance measuring device (10). The distance measuring device (10) according to the first aspect includes a control unit (11) and a measuring unit (12). The control unit (11) controls a photodetector unit (3). The photodetector unit (3) includes a photoelectric converter element (D10) and an output unit (32). The photoelectric converter element (D10) generates electric charge when receiving light (L2) reflected from a target (100) as a part of a measurement light (L1) emitted from a light emitting unit (2). The output unit (32) outputs an electric signal representing the amount of electric charge generated by the photoelectric converter element (D10). The measuring unit (12) calculates the distance to the target (100) within a measurable range (FR) based on the electric signal. The control unit (11) sets a conversion rate of the amount of electric charge generated by the photoelectric converter element (D10) relative to the amount of light received by the photoelectric converter element (D10) in each of a plurality of intervals (R1-R7) constituting the measurable range (FR). This, on the one hand, helps to improve the measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

[0078] The second aspect is a specific embodiment of the distance measuring device (10) according to the first aspect. In the second aspect, the photoelectric converter element (D10) changes the conversion rate according to the voltage applied thereto. The control unit (11) sets the conversion rate in each of the plurality of intervals (R1-R7) by the voltage applied to the photoelectric converter element (D10). This aspect facilitates setting the conversion rate.

[0079] The third aspect is a specific embodiment of the distance measuring device (10) according to the second aspect. In the third aspect, the photoelectric converter element (D10) includes an avalanche photodiode. The conversion rate is a multiplication factor of the avalanche photodiode. This aspect is conducive to setting the conversion rate.

[0080] The fourth aspect is a specific implementation of the distance measuring device (10) according to the second aspect or the third aspect. In the fourth aspect, the control unit (11) changes the conversion rate according to the amount of ambient light. This aspect can reduce the influence of ambient light on the measurement accuracy.

[0081] A fifth aspect is a specific embodiment of the distance measuring device (10) according to any one of the second to fourth aspects. In the fifth aspect, the control unit (11) reduces the conversion rate when the resolution of the distance to the target (100) is to be increased, and increases the conversion rate when the resolution is to be reduced. This aspect helps to improve the measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

[0082] The sixth aspect is a specific embodiment of the distance measuring device (10) according to the fifth aspect. In the sixth aspect, the plurality of intervals (R1-R7) include: a first interval (R1-R7); and a second interval (R1-R7), the second interval (R1-R7) corresponding to a longer distance to the photoelectric converter element (D10) than the first interval (R1-R7). The control unit (11) reduces the conversion rate in the first interval (R1-R7) and increases the conversion rate in the second interval (R1-R7). This aspect helps to improve the measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

[0083] A seventh aspect is a specific embodiment of the distance measuring device (10) according to any one of the second to sixth aspects. In the seventh aspect, the control unit (11) changes the conversion rate in at least one of the plurality of intervals (R1-R7) according to the amount of light received by the photoelectric converter element (D10) from the target (100). This aspect helps to improve the measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

[0084] The eighth aspect is a specific embodiment of the distance measuring device (10) according to any one of the second to seventh aspects. In the eighth aspect, the control unit (11) changes the conversion rate according to the amount of current flowing through the photoelectric converter element (D10). This aspect helps to improve the measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

[0085] A ninth aspect is a specific embodiment of the distance measuring device (10) according to any one of the second to eighth aspects. In the ninth aspect, the control unit (11) changes the conversion rate according to the length of the exposure duration that allows the photoelectric converter element (D10) to receive light from the target (100). This aspect helps to improve the measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

[0086] The tenth aspect is a specific implementation of the distance measuring device (10) according to any one of the first to ninth aspects. In the tenth aspect, the plurality of intervals (R1-R7) include: a first group, the first group including a series of intervals (R1-R7); and a second group, the second group including one or more intervals (R1-R7) different from the first group. The conversion rate of the first group is less than the conversion rate of the second group. For the first group, the measuring unit (12) determines the distance based on the ratio of electrical signals corresponding to a plurality of adjacent intervals (R1-R7) respectively selected from the series of intervals (R1-R7) included in the first group. This aspect helps to improve the measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

[0087] The eleventh aspect is a specific implementation of the distance measuring device (10) according to the tenth aspect. In the eleventh aspect, for the second group, the measuring unit (12) determines the distance by referring to a specific interval (R1-R7) corresponding to the electrical signal of the maximum size selected from one or more intervals included in the second group. The measuring unit (12) adopts a longer distance selected from the group consisting of the distance determined for the first group and the distance determined for the second group as the distance to the target (100). This aspect helps to improve the measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

[0088] The twelfth aspect is a specific embodiment of the distance measuring device (10) according to any one of the first to eleventh aspects. In the twelfth aspect, the photodetector unit (3) includes a charge storage device (C10) to store at least a portion of the charge generated by the photoelectric converter element (D10). The control unit (11) stores the charge generated by the photoelectric converter element (D10) in the charge storage device (C10) multiple times. The electrical signal has a size corresponding to the amount of charge stored in the charge storage device (C10). This aspect helps to improve the measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

[0089] The thirteenth aspect is implemented as a distance measurement system (1). The distance measurement system (1) according to the thirteenth aspect comprises a distance measurement device (10) according to any one of the first to twelfth aspects, a light emitting unit (2) and a photodetector unit (3). This aspect helps to improve the measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

[0090] The fourteenth aspect is implemented as a distance measurement method. The distance measurement method according to the fourteenth aspect includes a control step and a measurement step. The control step includes controlling a photodetector unit (3). The photodetector unit (3) includes a photoelectric converter element (D10) and an output unit (32). The photoelectric converter element (D10) generates an electric charge when receiving light (L2) reflected from a target (100) as a part of a measurement light (L1) emitted from a light emitting unit (2). The output unit (32) outputs an electric signal representing the amount of electric charge generated by the photoelectric converter element (D10). The measurement step includes calculating the distance to the target (100) within a measurable range (FR) based on the electric signal. The control step includes setting a conversion rate of the amount of electric charge generated by the photoelectric converter element (D10) relative to the amount of light received by the photoelectric converter element (D10) in each of a plurality of intervals (R1-R7) constituting the measurable range (FR). This aspect helps to improve the measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

[0091] The fifteenth aspect is implemented as a program designed to cause one or more processors to execute the distance measurement method according to the fourteenth aspect. This aspect helps to improve the measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

[0092] Reference numerals list

[0093] 1 Distance measurement system

[0094] 2 Lighting units

[0095] 3 Photodetector unit

[0096] D10 Photoelectric Converter Component

[0097] C10 Charge Storage Device

[0098] 10 Distance measuring equipment

[0099] 11 Control Unit

[0100] 12 Measuring units

[0101] FR Measurable range

[0102] R1–R7 interval (first interval, second interval)

[0103] L1 Measuring light

[0104] L2 Light

[0105] 100 goals.

Claims

1. A distance measuring device, comprising: a control unit configured to control a photodetector unit including a photoelectric converter element configured to generate electric charge upon receiving light reflected from a target as a part of the measurement light emitted from the light emitting unit, and an output unit configured to output an electric signal indicating an amount of electric charge generated by the photoelectric converter element; as well as a measuring unit configured to calculate the distance to the target within a measurable range according to the electrical signal, The control unit is configured to set a conversion rate of the amount of charge generated by the photoelectric converter element relative to the amount of light received by the photoelectric converter element in each of a plurality of intervals constituting the measurable range, wherein The photoelectric converter element is configured to change the conversion rate according to a voltage applied thereto, and the control unit is configured to set the conversion rate by a voltage applied to the photoelectric converter element in each of the plurality of intervals according to an amount of light received by the photoelectric converter element from the object, The plurality of intervals include: a first group, the first group including a series of intervals; and a second group including one or more intervals different from the first group, The conversion rate of the first group is less than the conversion rate of the second group, and The measuring unit is configured to: for the first group, determine the distance based on a ratio of electrical signals respectively corresponding to a plurality of adjacent intervals selected from a series of intervals included in the first group, The measuring unit is configured to: for the second group, determine the distance by referring to a specific interval corresponding to the electrical signal of the maximum size selected from one or more intervals included in the second group, and The measuring unit is configured to adopt, as the distance to the target, a longer distance selected from the group consisting of the distances determined for the first group and the distances determined for the second group.

2. The distance measuring device according to claim 1, wherein The photoelectric converter element includes an avalanche photodiode, and The conversion rate is a multiplication factor of the avalanche photodiode.

3. The distance measuring device according to claim 1 or 2, wherein The control unit is configured to vary the conversion rate according to an amount of ambient light.

4. The distance measuring device according to claim 1 or 2, wherein The control unit is configured to reduce the conversion rate when the resolution of the distance to the target is to be increased, and to increase the conversion rate when the resolution is to be decreased.

5. The distance measuring device according to claim 4, wherein The multiple intervals include: First interval; and a second interval corresponding to a longer distance to the photoelectric converter element than the first interval, and The control unit is configured to reduce the conversion rate in the first interval and increase the conversion rate in the second interval.

6. The distance measuring device according to claim 1 or 2, wherein The control unit is configured to change the conversion rate according to an amount of current flowing through the photoelectric converter element.

7. The distance measuring device according to claim 1 or 2, wherein The control unit is configured to change the conversion rate according to the length of an exposure duration during which the photoelectric converter element is allowed to receive light from the object.

8. The distance measuring device according to claim 1 or 2, wherein The photodetector unit comprises a charge storage device configured to store at least a portion of the charge generated by the photoelectric converter element, The control unit is configured to store the charge generated by the photoelectric converter element in the charge storage device a plurality of times, and The electrical signal has a magnitude corresponding to an amount of charge stored in the charge storage device.

9. A distance measurement system, comprising: The distance measuring device according to any one of claims 1 to 8; Light emitting unit; as well as Photodetector unit.

10. A distance measurement method, comprising: a control step including controlling a photodetector unit including a photoelectric converter element configured to generate electric charge upon receiving light reflected from a target as a part of the measurement light emitted from the light emitting unit, and an output unit configured to output an electric signal indicating an amount of the electric charge generated by the photoelectric converter element; as well as a measuring step, the measuring step comprising calculating the distance to the target within a measurable range based on the electrical signal, The control step includes setting a conversion rate of the amount of charge generated by the photoelectric converter element relative to the amount of light received by the photoelectric converter element in each of a plurality of intervals constituting the measurable range, wherein The photoelectric converter element is configured to change the conversion rate according to a voltage applied thereto, and The controlling step includes setting the conversion rate by a voltage applied to the photoelectric converter element in each of the plurality of intervals according to the amount of light received by the photoelectric converter element from the object, The plurality of intervals include: a first group including a series of intervals; and a second group including one or more intervals different from the first group, The conversion rate of the first group is less than the conversion rate of the second group, and The measuring step includes: for the first group, determining the distance based on a ratio of electrical signals respectively corresponding to a plurality of adjacent intervals selected from a series of intervals included in the first group, The measuring step includes: for the second group, determining the distance by referring to a specific interval corresponding to the maximum magnitude of the electric signal selected from one or more intervals included in the second group, and The measuring step includes adopting, as the distance to the target, a longer distance selected from the group consisting of a distance determined for the first group and a distance determined for the second group. 11 . A computer-readable non-transitory storage medium storing a program, wherein the program is designed to cause one or more processors to execute the distance measurement method according to claim 10 .

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