阅读说明：本技术 距离测量设备、距离测量系统、距离测量方法和程序 (Distance measuring device, distance measuring system, distance measuring method, and program ) 是由 香山信三 广濑裕 冲野彻 斋藤繁 石井基范 小田川明弘 于 2020-02-26 设计创作，主要内容包括：本发明的问题是提供距离测量设备、距离测量系统、距离测量方法和程序,它们均配置或设计为提高到目标的距离的测量精度。距离测量设备(10)包括控制单元(11)和测量单元(12)。控制单元(11)控制光电探测器单元(3)。光电探测器单元(3)包括光电转换器元件(D10)和输出单元(32)。光电转换器元件(D10)在接收到作为从发光单元(2)发射的测量光的一部分从目标反射的光时产生电荷。输出单元(32)输出表示由光电转换器元件(D10)产生的电荷的量的电信号。测量单元(12)根据电信号在可测量范围内计算到目标的距离。控制单元(11)在构成可测量范围(FR)的多个区间(R1-R7)中的每一个区间中,设置光电转换器元件(D10)产生的电荷的量相对于光电转换器元件(D10)接收到的光的量的比率。(The problem of the present invention is to provide a distance measuring device, a distance measuring system, a distance measuring method, and a program, each of which is configured or designed to improve the measurement accuracy of a distance to a target. The distance measuring device (10) comprises a control unit (11) and a measuring unit (12). A control unit (11) controls 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 upon receiving light reflected from a target as part of measurement light emitted from the light emitting unit (2). The output unit (32) outputs an electrical signal representing the amount of charge generated by the photoelectric converter element (D10). The measuring unit (12) calculates the distance to the target within a measurable range from the electrical signal. The control unit (11) sets a ratio of an amount of electric charge generated by the photoelectric converter element (D10) to an amount of light received by the photoelectric converter element (D10) in each of a plurality of sections (R1-R7) constituting the measurable range (FR).)

1. A distance measuring device comprising:

a control unit configured to control a photodetector unit including a photoelectric converter element configured to generate an electric charge upon receiving light reflected from a target as part of measurement light emitted from a light emitting unit, and an output unit configured to output an electric signal representing an amount of the electric charge generated by the photoelectric converter element; and

a measuring unit configured to calculate a distance to the target within a measurable range from the electric signal,

the control unit is configured to set a conversion ratio of an amount of electric charge generated by the photoelectric converter element with respect to an amount of light received by the photoelectric converter element in each of a plurality of sections constituting the measurable range.

2. The distance measuring apparatus according to claim 1, wherein

The photoelectric converter element is configured to change the conversion rate in accordance with a voltage applied thereto, an

The control unit is configured to set the conversion ratio by a voltage applied to the photoelectric converter element in each of the plurality of sections.

3. Distance measuring device according to claim 2, wherein

The photoelectric converter element includes an avalanche photodiode, and

the conversion ratio is the multiplication factor of the avalanche photodiode.

4. Distance measuring device according to claim 2 or 3, wherein

The control unit is configured to vary the conversion rate in dependence on an amount of ambient light.

5. The distance measurement device according to any one of claims 2 to 4, wherein

The control unit is configured to decrease the conversion rate when a resolution of a distance to the target is to be increased, and increase the conversion rate when the resolution is to be decreased.

6. Distance measuring device according to claim 5, wherein

The plurality of intervals include: a first interval; and a second section corresponding to a longer distance to the photoelectric converter element than the first section, an

The control unit is configured to decrease the conversion rate in the first interval and increase the conversion rate in the second interval.

7. The distance measurement device according to any one of claims 2 to 6, wherein

The control unit is configured to change the conversion rate in accordance with an amount of light received by the photoelectric converter element from the target in at least one of the plurality of sections.

8. The distance measurement device according to any one of claims 2 to 7, wherein

The control unit is configured to change the conversion rate in accordance with an amount of current flowing through the photoelectric converter element.

9. Distance measuring device according to any of claims 2 to 8, wherein

The control unit is configured to change the conversion rate in accordance with a length of an exposure duration that allows the photoelectric converter element to receive light from the target.

10. The distance measuring apparatus according to any one of claims 1 to 9, wherein

The plurality of intervals include: a first group comprising a series of intervals; and a second group comprising 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, an

The measurement unit is configured to: for the first group, the distance is determined based on ratios of electrical signals respectively corresponding to a plurality of adjacent intervals selected from a series of intervals included in the first group.

11. The distance measuring apparatus according to claim 10, wherein

The measurement unit is configured to: for the second group, the distance is determined by referring to a specific interval corresponding to the electrical signal of the maximum magnitude selected from one or more intervals included in the second group, and

the measurement unit is configured to: employing, as the distance to the target, a longer distance selected from the group consisting of the distance determined for the first group and the distance determined for the second group.

12. The distance measuring apparatus according to any one of claims 1 to 11, wherein

The photodetector cell includes 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 electric charges generated by the photoelectric converter element in the charge storage device a plurality of times, an

The electrical signal has a magnitude corresponding to an amount of charge stored in the charge storage device.

13. A distance measurement system comprising:

the distance measuring device according to any one of claims 1 to 12;

a light emitting unit; and

a photodetector unit.

14. A distance measurement method comprising:

a control step of controlling a photodetector unit including a photoelectric converter element configured to generate electric charges upon receiving light reflected from a target as part of measurement light emitted from a light emitting unit, and an output unit configured to output an electric signal representing an amount of the electric charges generated by the photoelectric converter element; and

a measuring step including calculating a distance to the target within a measurable range from the electric signal,

the control step includes: in each of a plurality of sections constituting the measurable range, a conversion ratio of an amount of electric charge generated by the photoelectric converter element with respect to an amount of light received by the photoelectric converter element is set.

15. A program designed to cause one or more processors to perform the distance measuring method according to claim 14.

Technical Field

The present disclosure generally relates to a distance measuring device, a distance measuring system, a distance measuring method, and a program. More particularly, the present disclosure relates to a distance measuring device, a distance measuring system, a distance measuring method, and a program configured or designed to measure a distance to a target.

Background

Patent document 1 discloses a distance measuring apparatus. 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 reaching the photosensor within a predetermined exposure time; a counter circuit for counting the number of arrivals of an 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 the count value supplied from the counter circuit; and a storage circuit that stores the time signal as the distance signal when the comparison signal supplied from the comparator circuit is ON.

Patent document 1 describes that the measurable distance range can be expanded by the 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.

CITATION LIST

Patent document

Patent document 1: JP 2018-169162A

Disclosure of Invention

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 the target.

A distance measuring apparatus according to an aspect of the present disclosure includes a control unit and a measuring unit. The control unit controls the photodetector unit. The photodetector unit includes a photoelectric converter element and an output unit. The photoelectric converter element generates an electric charge upon receiving light reflected from a target as a part of measurement light emitted from a light emitting unit. The output unit outputs an electric signal representing an amount of electric charge generated by the photoelectric converter element. The measuring unit calculates a distance to a target within a measurable range from the electrical signal. The control unit sets a conversion ratio of an amount of electric charge generated by the photoelectric converter element with respect to an amount of light received by the photoelectric converter element in each of a plurality of sections constituting a measurable range.

A distance measuring system according to another aspect of the present disclosure includes the above distance measuring device, a light emitting unit, and a photodetector unit.

A distance measuring method according to still another aspect of the present disclosure includes a control step and a measuring step. The controlling step comprises controlling the photodetector unit. The photodetector unit includes a photoelectric converter element and an output unit. The photoelectric converter element generates an electric charge upon receiving light reflected from a target as a part of measurement light emitted from a light emitting unit. The output unit outputs an electric signal representing an amount of electric charge generated by the photoelectric converter element. The measuring unit calculates a distance to a target within a measurable range from the electrical signal. The control step includes: a conversion ratio of an amount of electric charge generated by the photoelectric converter element with respect to an amount of light received by the photoelectric converter element is set in each of a plurality of sections constituting a measurable range.

A program according to yet another aspect of the present disclosure is designed to cause one or more processors to execute the above distance measurement method.

Drawings

FIG. 1 is a block diagram of a distance measurement system according to an exemplary embodiment;

FIG. 2 shows a distance measurement system;

FIG. 3 is a circuit diagram of a photoelectric converter element of the distance measuring system;

FIG. 4 schematically illustrates how the distance measurement system operates;

FIG. 5 schematically illustrates how the distance measurement system operates;

FIG. 6 schematically illustrates how the distance measurement system operates;

FIG. 7 illustrates a first method for controlling a distance measurement system;

FIG. 8 illustrates a second method for controlling a distance measurement system; and

fig. 9 shows an exemplary structure of a plurality of sections constituting a measurable range according to a modification.

Detailed Description

1. Examples of the embodiments

1.1. Overview

Fig. 1 shows a distance measuring system 1 according to an exemplary embodiment. The distance measuring system 1 includes a distance measuring device 10. The distance measuring device 10 includes a control unit 11 and a measuring unit 12. The control unit 11 controls the photodetector unit 3. The photodetector unit 3 includes a photoelectric converter element D10 and an output unit 32 as shown in fig. 1 and 2. The photoelectric converter element D10 generates electric charges upon receiving light L2 reflected from the target 100 as 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 electric charge generated by the photoelectric converter element D10. The measuring unit 12 calculates the distance to the target within the measurable range FR from the electrical 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 D10 in each of a plurality of sections R1-R7 constituting the measurable range FR.

Such a distance measuring apparatus 10 can appropriately set the conversion ratio in each of the plurality of sections R1-R7 constituting the measurable range FR. That is, the distance measuring apparatus 10 can set the conversion rate to an appropriate value according to the position of the target 100. Therefore, the distance measuring apparatus 10 contributes to improvement in measurement accuracy over the entire measurable range of the distance to the target 100.

1.2. Details of

The distance measuring system 1 will be described in more detail with reference to fig. 1 to 8. The distance measuring system 1 measures the distance to the target 100 by a time-of-flight (TOF) technique. The distance measuring system 1 comprises a distance measuring device 10, a light emitting unit 2, a photodetector unit 3, a voltage source 4 and a current measuring unit 5. As shown in fig. 2, 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 measurement light L1 emitted from the light emitting unit 2. The distance measuring system 1 is suitable for use in, for example, 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 being), and a security camera.

The light emitting unit 2 includes a light source 21 for irradiating the target 100 with the measurement light L1. The measuring light L1 is a pulsed light beam. In fig. 2, the measurement light L1 is conceptually represented by a broken line. In this regard, when the distance is measured by the TOF technique, the measurement light L1 suitably has a single wavelength, a relatively short pulse width, and a relatively high peak intensity. In addition, in view of the use of the distance measuring system 1 (distance measuring apparatus 10) in, for example, an urban area, the wavelength of the measuring light L1 suitably falls within a near-infrared wavelength range in which the photometric factor is low for human eyes 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 pulse laser beam emitted from the light source 21 satisfies level 1 or level 2 of the "laser product safety" standard (JIS C6802) set in japan. Note that the light source 21 need not be a laser diode, but may be, for example, a Light Emitting Diode (LED), a Vertical Cavity Surface Emitting Laser (VCSEL), or a halogen lamp. Alternatively, the measurement light L1 may also fall within a wavelength range different from the near-infrared wavelength range.

The photodetector unit 3 includes a photoelectric converter element D10 and an output unit 32. The photoelectric converter element D10 generates electric charges upon receiving light L2 reflected from the target 100 as part of the measurement light L1 emitted from the light emitting unit 2. The output unit 32 outputs an electric signal (pixel signal) representing 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. As shown in fig. 1, the image sensor 31 includes a plurality of pixels 311 arranged two-dimensionally. Each of the plurality of pixels 311 may receive light only during the exposure duration. The output unit 32 outputs the electric signal supplied from (the pixel 311 of) the image sensor 31 to the distance measuring device 10.

Fig. 3 is a circuit diagram of each pixel 311. As shown in fig. 3, 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, SR 3.

The photoelectric converter element D10 generates electric charges upon receiving light L2 reflected from the target 100 as 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 in accordance with a voltage applied (to the photoelectric converter element D10 itself). As used herein, the conversion ratio refers to a ratio of the amount of electric charge generated by the photoelectric converter element D10 to the amount of light (photon number) received by the photoelectric converter element D10. For example, the conversion ratio of the photoelectric converter element D10 can be changed in a range equal to or greater than 1. In the present embodiment, the photoelectric converter element D10 is implemented as an avalanche photodiode. Avalanche photodiodes have 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 photons are incident on the avalanche photodiode, an amount of charge generally proportional to the number of photons causing photoelectric conversion is collected at the cathode of the avalanche photodiode. On the other hand, when a second bias voltage (e.g., -27V) having an absolute value greater than the first bias voltage is applied to the avalanche photodiode, the avalanche photodiode operates in the geiger multiplication mode. In the geiger multiplication mode, when one of the photons incident on the avalanche photodiode causes photoelectric conversion, a saturated amount of charge (i.e., a saturated 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 according to the magnitude of the bias voltage, i.e., according to the magnitude of the voltage (reverse voltage) applied to the avalanche photodiode. In the present embodiment, the conversion ratio of the photoelectric converter element D10 is the multiplication factor of the avalanche photodiode.

The charge storage device C10 stores at least a part of the electric charges generated by the photoelectric converter element D10. 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 electric charges generated by the photoelectric converter element D10 to be accumulated, thereby contributing to an increase in the signal-to-noise ratio SNR of the electric signal as the output signal of the image sensor 31 and eventually improving the measurement accuracy. In this embodiment, the first terminal of charge storage device C10 is connected to ground.

The floating diffusion FD is disposed between the photoelectric converter element D10 and the charge storage device C10, and is used to store electric charges. The amplifier a10 outputs an electric signal (pixel signal) having a magnitude corresponding to the amount of electric charge generated by the photoelectric converter element D10 (i.e., a magnitude corresponding to the amount of electric charge stored in the charge storage device C10) to the output unit 32. 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 FD to the second terminal of the charge storage device C10. The transistor ST3 connects the floating diffusion FD to the input terminal of the amplifier a 10. The transistor SR1 connects the cathode of the photoelectric converter element D10 to the internal power supply VDD. Transistor SR2 connects the second terminal of charge storage device C10 to the internal power supply VDD. The transistor SR3 connects the floating diffusion FD to the internal power supply VDD.

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, ST 2. After the charge generated by the photoelectric converter element D10 has been stored in the charge storage device C10 a plurality of times, the charge is transferred from the charge storage device C10 to the amplifier a10 by the transistor ST 3. This causes the amplifier a10 to output an electric signal (pixel signal) whose magnitude corresponds to the amount of electric charge generated by the photoelectric converter element D10 (i.e., which magnitude corresponds to the amount of electric charge stored in the charge storage device C10). Subsequently, the undesired electric charges remaining in the photoelectric converter element D10, the floating diffusion element FD, and the charge storage device C10 are appropriately removed by the transistors SR1, SR2, SR 3. Such control of the pixels 311 is performed by the control unit 11.

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 may vary. In this embodiment, the voltage source 4 is electrically connected to the anode of the photoelectric converter element D10 in each of the plurality of 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 plurality of pixels 311 of the image sensor 31 of the photodetector unit 3. Specifically, the voltage source 4 may be used to apply a reverse voltage (reverse bias) to the photoelectric converter element D10 as a control voltage. That is, the operation mode of the photoelectric converter element D10 can be switched from the linear multiplication mode to the geiger multiplication mode or vice versa by the voltage source 4. The voltage source 4 is controlled by a 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 may be implemented as a known power supply, such as a switching power supply, and thus a detailed description thereof will be omitted here.

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 supplies the thus measured value to the control unit 11. The current measuring unit 5 may be implemented as a well-known current measuring instrument (ammeter) such as a current transformer, and a detailed description thereof is omitted herein.

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, as shown in fig. 2. 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 several tens of centimeters to several tens of meters, but this is not essential. 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.

The distance measuring apparatus 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 measurement unit 12 may 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 measurement 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 stored in advance in one or more memories. However, this is only an example and should not be construed as limiting. The program may also be downloaded through a telecommunication line such as the internet, or distributed after being stored in a non-transitory storage medium such as a memory card.

The control unit 11 is configured to control the light emitting unit 2 and the photodetector unit 3. With the light emitting unit 2, the control unit 11 controls, for example, the timing at which the light source 21 emits the measurement light L1 (i.e., the light emission timing) and the pulse width of the measurement 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., exposure timing), the exposure duration (exposure period), and the operation time of the respective transistors ST1-ST 3.

Further, the control unit 11 is also configured to control the conversion ratio of each photoelectric converter element D10. Specifically, the control unit 11 controls the conversion ratio of the photoelectric converter element D10 in each of a plurality of sections R1-R7 constituting the measurable range FR. Since this distance measuring apparatus 10 uses the TOF technique, a plurality of intervals R1-R7 of the distance correspond to a plurality of time periods T1-T7, respectively, as shown in fig. 4. Therefore, the control unit 11 sets the conversion ratio with the voltage applied to the photoelectric converter element D10 in each of the plurality of periods T1 to T7 corresponding to the plurality of sections R1 to R7, respectively. That is, the control unit 11 sets the conversion ratio of the photoelectric converter element D10 by setting the control voltage applied to the photoelectric converter element D10 by the voltage source 4 in a plurality of intervals R1 to R7 (corresponding to a plurality of periods T1 to T7). In the present embodiment, the conversion ratio 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. In fig. 4, VSUB denotes a control voltage applied to the photoelectric converter element D10 by the voltage source 4. V1 denotes a first bias voltage (i.e., a voltage that switches the photoelectric converter element D10 to the linear multiplication mode). V2 denotes a second bias voltage (i.e., a voltage that switches the photoelectric converter element D10 to the geiger multiplication mode).

As described above, in the linear multiplication mode, the amount of electric 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 electric charges 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, in the geiger multiplication mode, the photoelectric converter element D10 generates a larger amount of electric charge in response to incidence of photons than in the linear multiplication mode. Therefore, if a relatively large amount 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 are 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 light L2 reflected from the target 100 and ambient light (mainly light from the environment around the photodetector unit 3). The amount of light received by the photoelectric converter element D10 varies depending on the duration of time that the photoelectric converter element D10 can receive light from the object 100 (i.e., the exposure duration). In addition, the amount of light L2 reflected from target 100 is also affected by the distance to target 100 and the topography of target 100. Examples of surface conditions of the target 100 include (surface) reflectivity of the target 100.

In the present embodiment, the control unit 11 sets the conversion ratio 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, and the like. In this case, the control unit 11 decreases the conversion rate (linear multiplication mode) when resolution increasing to the distance of the target 100 is required, and increases the conversion rate (geiger multiplication mode) when resolution is required to be decreased.

The control unit 11 classifies the plurality of sections R1-R7 into a first section and a second section corresponding to a longer distance from the photoelectric converter element D10 (i.e., the distance measurement system 1) than the first section. The control unit 11 decreases 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 the linear multiplication mode in the first section, and operates the photoelectric converter element D10 in the geiger multiplication mode in the second section. For example, in the example shown in fig. 4, the control unit 11 regards the intervals R1-R5 as the first interval, and regards the intervals R6, 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 periods T1 to T5 corresponding to the intervals R1 to R5, respectively. On the other hand, the control unit 11 causes the photoelectric converter element D10 to operate in the geiger-multiplied mode by setting the control voltage VSUB of the voltage source 4 to V2 during the periods T6, T7 corresponding to the sections R6, R7, respectively.

Further, 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 decreases 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 the plurality of zones R1-R7. When the amount of the ambient light is found to be equal to or less than the threshold value, the control unit 11 causes the photoelectric converter element D10 to operate in the geiger-multiplication mode, and when the amount of the ambient light is found to be greater than the threshold value, the control unit D10 causes the photoelectric converter element D10 to operate in the linear-multiplication mode. For example, it is assumed that the amount of ambient light is greater than the threshold value in the intervals R1-R5, and the amount of ambient light is equal to or less than the threshold value in the intervals R6, R7. In this case, as shown in fig. 4, 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 periods T1 to T5 corresponding to the intervals R1 to R5, respectively. On the other hand, the control unit 11 causes the photoelectric converter element D10 to operate in the geiger-multiplied mode by setting the control voltage VSUB of the voltage source 4 to V2 during the periods T6, T7 corresponding to the sections R6, 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 R5. 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 periods T1 to T4 corresponding to the intervals R1 to R4, respectively, as shown in fig. 5. On the other hand, the control unit 11 causes the photoelectric converter element D10 to operate in the geiger-multiplied mode by setting the control voltage VSUB of the voltage source 4 to V2 during the periods T5 to T7 corresponding to the intervals R5 to R7.

Further, 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 decreases 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 the threshold in each of the plurality of sections R1-R7. The control unit 11 causes the photoelectric converter element D10 to operate in the geiger-multiplication mode when finding 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 finding that the length of the exposure duration is greater than the threshold value.

Further, the control unit 11 also changes the conversion ratio in accordance with the amount of light received by the photoelectric converter element D10 from the target 100 (i.e., the amount of light L2 reflected from the target 100). More specifically, if the amount of light L2 is large, the control unit 11 decreases 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 the threshold value in each of the plurality of sections R1-R7. The control unit 11 may set the conversion rate of the photoelectric converter element D10 to a first value when the amount of the light L2 is found to be equal to or less than the threshold value, and may set the conversion rate of the photoelectric converter element D10 to a second value larger than the first value when the amount of the light L2 is found to be greater than the threshold value. In this case, the first value is a conversion rate corresponding to the linear multiplication mode of the photoelectric converter element D10, and the second value is a conversion rate corresponding to the geiger multiplication mode of the photoelectric converter element D10. For example, assume that the amount of light L2 is greater than a threshold value within the interval R1-R5. In this case, as shown in fig. 4, 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 periods T1 to T5 corresponding to the intervals R1 to R5, respectively. Further, it is assumed that the amount of light L2 has been reduced to be equal to or less than the threshold value in the section R3. In this case, the control unit 11 causes the photoelectric converter element D10 to operate in the geiger-multiplied mode by setting the control voltage VSUB of the voltage source 4 to V2 during the period T3 corresponding to the section R3, as shown in fig. 6.

Further, the control unit 11 changes the conversion rate in accordance with the amount of current flowing through the photoelectric converter element D10. More specifically, the control unit 11 changes the conversion ratio of the photoelectric converter element D10 in accordance with the measurement value obtained by the current measurement unit 5. That is, the control unit 11 converts the operation mode of the photoelectric converter element D10 from the linear multiplication mode to the geiger multiplication mode or vice versa, based on the measurement value obtained by the current measurement unit 5. Specifically, when the measurement value obtained by the current measurement unit 5 is found to be equal to or smaller 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 the measurement value obtained by the current measuring unit 5 is found to be larger 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 electric charges 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, not the linear multiplication mode. In contrast, when the amount of current flowing through the photoelectric converter element D10 is large, the amount of electric charges generated by the photoelectric converter element D10 is also large, and therefore 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, not the geiger multiplication mode. In this case, the first threshold value and the second threshold value may be the same value or may be different values from each other.

Further, the control unit 11 controls the light emitting unit 2 and the photodetector unit 3 in different manners depending on whether the photoelectric converter element D10 operates in the linear multiplication mode or the geiger multiplication mode. More specifically, if the photoelectric converter element D10 operates in the linear multiplication mode, the control unit 11 executes the first control method. On the other hand, if the photoelectric converter element D10 operates in the geiger-multiplied mode, the control unit 11 executes the second control method. That is, the first control method is suitable for the case where the resolution is high (i.e., the 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 suitable for the case where the resolution is low (i.e., the case where the amount of light received by the photoelectric converter element D10 is relatively small).

Fig. 7 illustrates how the first method is performed, and fig. 8 illustrates how the second method is performed. In fig. 7 and 8, VE denotes exposure timing. Q1 represents the amount of electric charge generated by the photoelectric converter element D10. VA denotes the operation timing of the transistors ST1, ST 2. Q2 represents the amount of charge stored in charge storage device C10. VT denotes the operation timing of the transistor ST 3. VR represents the timing of the operation of transistors SR1-SR 3.

First, the first control method will be described with reference to fig. 7. In this example, the transistors ST1-ST3 and SR1-SR3 should all turn off before time t 0.

At time t0, the control unit 11 turns on transistors SR1-SR3 to remove charge from the charge storage device C10. Next, in a 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 measurement light L1. Therefore, in the 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 from time t3, the photoelectric converter element D10 receives the light L2 in the period from time t3 to time t4, and generates electric charges corresponding to the amount of the light L2. Next, at time t5 after time t4, the control unit 11 turns on the transistors ST1, ST2 to transfer the electric charges generated by the photoelectric converter element D10 to the charge storage device C10 through the floating diffusion element FD.

Subsequently, in a 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 measurement light L1. Therefore, in the 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 from time t8, the photoelectric converter element D10 receives the light L2 in the period from time t8 to time t9, and generates electric charges 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 electric charges generated by the photoelectric converter element D10 to the charge storage device C10 through the floating diffusion element FD.

The control unit 11 repeats the process of transferring the electric charges 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 measurement light L1 for a period from time t11 to time t 13. Therefore, in the 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 from time t13, the photoelectric converter element D10 receives the light L2 in the period from time t13 to time t14, and generates electric charges corresponding to the amount of the light L2. Next, at a time t15 after the time t14, the control unit 11 turns on the transistors ST1, ST2 to transfer the electric charges 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 turning on the holding transistor ST3 during the period from time t16 to time t 17. Thus, the control unit 11 causes an electric signal (pixel signal) to be output from the pixel 311.

Next, a second control method will be described with reference to fig. 8. In this example, the transistors ST1-ST3 and SR1-SR3 should all turn off before time t 20.

At time t20, the control unit 11 turns on transistors SR1-SR3 to remove charge from the charge storage device C10. Next, in a 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 measurement light L1. Therefore, the photoelectric converter element D10 of the photodetector unit 3 receives the light beams L21, L22 as light L2 reflected from the target 100. The light beams L21, L22 come from a target 100 located relatively far from the distance measuring system 1. During a 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 the time t23, the photoelectric converter element D10 has not yet generated electric charges corresponding to the amount of the light beam L2. Next, in a period of time t25 to t26 after time t24, the control unit 11 turns on the transistors ST1, ST2, transferring the electric charges 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 generates no electric charge, and therefore the electric charge is not stored in the charge storage device C10.

Subsequently, in a 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 measurement light L1. Therefore, the photoelectric converter element D10 of the photodetector unit 3 receives the light beams L23, L24 as light L2 reflected from the target 100. The light beams L23, L24 come from the target 100 located relatively far from the distance measuring system 1, as do the light beams L21, L22. The light beam L23 reaches the photoelectric converter element D10 during a period from time t28 to time t 29. On the other hand, the light beam L24 reaches the photoelectric converter element D10 during a period from time t29 to time t 30. However, since the control unit 11 sets the exposure duration from the time t29, the photoelectric converter element D10 does not generate electric charges corresponding to the amount of the light beam L23, but generates electric charges 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 electric charges generated by the photoelectric converter element D10 to the charge storage device C10 via the floating diffusion element FD.

The control unit 11 repeats the process of transferring the electric charges 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 measurement light L1 for a period from time t32 to time t 33. Therefore, the photoelectric converter element D10 of the photodetector unit 3 receives the light beams L25, L26 as light L2 reflected from the target 100. The light beams L25, L26 come from the target 100 located relatively far from the distance measuring system 1, as do the light beams L21, L22. The light beam L25 reaches the photoelectric converter element D10 during a period from time t33 to time t 34. On the other hand, the light beam L26 reaches the photoelectric converter element D10 during a period from time t34 to time t 35. However, since the control unit 11 sets the exposure duration from the time t34, the photoelectric converter element D10 does not generate electric charges corresponding to the amount of the light beam L25, but generates electric charges 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 electric charges 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 turning on the holding transistor ST3 during the period from time t37 to time t 38. Thus, the control unit 11 causes an electric signal (pixel signal) to be output from the pixel 311.

It can be seen that the control unit 11 appropriately sets the conversion ratio (in the present embodiment, from the linear multiplication mode to the geiger multiplication mode) in each of the plurality of sections 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 ratio thus set, so that an electric signal (pixel signal) is output from the photodetector unit 3 to the measurement unit 12.

The measurement unit 12 calculates a distance to the target 100 within the measurable range FR based on the electric signal (pixel signal) supplied from the photodetector unit 3. The measurement unit 12 calculates a distance to the target 100 for each of the plurality of pixels 311 (photoelectric converter elements D10) of the image sensor 31 of the photodetector unit 3. In this embodiment, the measurement unit 12 calculates the distance to the target 100 by two methods. These two methods are two different types of TOF techniques. The first method is phase-shift TOF, and the second method is range-gated TOF. The phase shift TOF can calculate the distance in the order of centimeters. On the other hand, the range gated TOF can calculate distances on the order of meters, but allows calculation of longer distances than the phase shifted TOF. For a first group of the intervals R1-R7, the measurement unit 12 calculates the distance to the object 100 by a phase shift TOF method. On the other hand, for the second group of the plurality of intervals R1-R7, the measurement 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 of the plurality of intervals R1-R7, and the second group includes one or more intervals of 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 section included in the first group (i.e., the section to which the phase shift TOF is applied) is a section in which the photoelectric converter element D10 switches to the linear multiplication mode (i.e., a section in which high resolution is set), as shown in fig. 4 to 6. On the other hand, each interval included in the second group (i.e., the interval to which the range gate TOF is applied) is an interval in which the photoelectric converter element D10 switches to the geiger multiplication mode (i.e., an interval in which low resolution is set).

The measurement unit 12 obtains the distance based on the ratios of the electric signals respectively corresponding to a plurality of adjacent intervals in a series of intervals included in the first group, with the phase shift TOF applied (i.e., for the first group). More specifically, the measurement unit 12 extracts a combination of adjacent sections, in which the sum of the magnitudes of the electric signals is larger than a threshold value and is maximum, from a series of sections included in the first group. The distance D to the target 100 is given by D ═ k × Sk +1/(Sk + Sk), where Sk and Sk +1 are the magnitudes of the electrical signals in the extracted bin combination. Note that k is a scale factor that can be set appropriately. On the other hand, in the case of applying the range gated TOF (i.e., for the second group), the measurement unit 12 obtains the distance based on the section in which the magnitude of the electric signal is largest among the one or more sections included in the second group. More specifically, the distance to the section in which the magnitude of the electric signal is the largest is used as the distance to the target 100. The measurement unit 12 employs, as the distance to the target 100, a longer distance selected from the group consisting of the distance determined for the first group and the distance determined for the second group.

Taking the example shown in fig. 4 as an example, the first group comprises the intervals R1-R5, while the second group comprises the intervals R6, R7. It is assumed that the magnitudes of the electric signals corresponding to the intervals R1-R7 are denoted by S1-S7, respectively. According to the phase shift TOF, the measurement unit 12 obtains the sum of the magnitudes of the electric signals in the two adjacent intervals R1, R2 (S1+ S2), the sum of the magnitudes of the electric signals in the two adjacent intervals R2, R3 (S2+ S3), and the sum of the magnitudes of the electric signals in the two adjacent intervals R3, R4 (S3+ S4). In this case, it is assumed that the sum (S2+ S3) of the magnitudes of the electric signals in the two adjacent intervals R2, R3 is equal to or larger than the threshold value and larger than any one 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 gate TOF, the distance is obtained based on the electrical signal having the largest magnitude among the electrical signals respectively corresponding to the intervals R5 to R7. In this case, if S6 is greater than S5 or S7, the distance to the section R6 is used as the distance to the target 100. If the distance determined for the first group is larger 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.

The output unit 13 is configured to output a calculation result (measurement result) of the distance to the target 100 obtained by the measurement unit 12 to the external apparatus 6. The external device 6 may be a display device such as a liquid crystal display or an organic Electroluminescence (EL) display. The output unit 13 outputs the measurement result obtained by the measurement unit 12 to the external device 6 to cause the external device 6 to display 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 signals to the external device 6 to cause the external device 6 to display the image data. Note that the external device 6 is not necessarily a display device, and may be any other type of device.

1.3. Summary of the invention

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. As shown in fig. 1 and 2, the photodetector unit 3 includes a photoelectric converter element D10 and an output unit 32. The photoelectric converter element D10 generates electric charges upon receiving light L2 reflected from the target 100 as 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 electric charge generated by the photoelectric converter element D10. The measuring unit 12 calculates the distance to the target within the measurable range FR from the electrical 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 sections R1-R7 constituting the measurable range FR. Therefore, the distance measuring apparatus 10 contributes to improvement in the measurement accuracy of the distance to the target 100.

In other words, it can be said that the distance measuring apparatus 10 performs the following method (distance measuring method). The distance measuring method includes a control step and a measuring step. The controlling step comprises 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 electric charges upon receiving light L2 reflected from the target 100 as 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 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 from the electrical signal. The controlling step includes setting a conversion ratio of the amount of electric charge generated by the photoelectric converter element D10 with respect to the amount of light received by the photoelectric converter element D10 in each of a plurality of sections R1-R7 constituting the measurable range FR. This distance measurement method contributes to improving the measurement accuracy of the distance to the target 100 as well as the distance measurement apparatus 10.

The distance measuring device 10 is implemented as a computer system (including one or more processors). That is, the functions of the distance measuring apparatus 10 are realized by causing one or more processors to execute a program (computer program). The program is designed to cause one or more processors to perform a distance measurement method. This procedure contributes to improving the accuracy of measuring the distance to the target 100 as well as the distance measuring method.

2. Variants

Note that the above-described embodiment is only one of exemplary embodiments among various embodiments of the present disclosure, and should not be construed as a limitation. The exemplary embodiments may be easily modified in various ways according to design choice or any other factors without departing from the scope of the present disclosure. Next, modifications of the exemplary embodiments will be enumerated one by one.

In the above embodiment, the measurable range FR is composed of a plurality of intervals R1 to R7 that do not overlap with each other. Alternatively, the measurable range FR may also consist of a plurality of intervals R1-R7 shown in fig. 9. Specifically, the interval R1 corresponds to the period T10-T12, the interval R2 corresponds to the period T11-T13, the interval R3 corresponds to the period T12-T14, the interval R4 corresponds to the period T13-T15, the interval R5 corresponds to the period T15-T16, the interval R6 corresponds to the period T16-T17, and the interval R7 corresponds to the period T17-T18. In this example, the intervals R1, R2 partially overlap each other, the intervals R2, R3 partially overlap each other, and the intervals R3, R4 partially overlap 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.

In the above-described embodiment, the control unit 11 changes the conversion ratio of the photoelectric converter element D10 from the value corresponding to the linear multiplication mode to the value corresponding to the geiger multiplication mode, and vice versa. However, this is merely an example and should not be construed as limiting. Alternatively, the control unit 11 may also change the conversion ratio of the photoelectric converter element D10 between a plurality of values corresponding to the linear multiplication mode.

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 merely an example and should not be construed as limiting. According to a modification, the control unit 11 may set the conversion ratio 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.

In the embodiment described above, the conversion ratio is changed for the photoelectric converter elements D10 in all of the plurality of pixels 311 of the image sensor 31. However, this is merely an example and should not be construed as a limitation. According to another modification, the control unit 11 may change the conversion ratio for the photoelectric converter element D10 in at least one pixel 311 of the plurality of pixels 311. That is, the control unit 11 may change the conversion ratio (or conversion ratios) only for a necessary one (or ones) of the plurality of photoelectric converter elements D10.

In addition, in the embodiment described above, the photoelectric converter element D10 is implemented as an avalanche photodiode. However, this is merely an example and should not be construed as limiting. The photoelectric converter element D10 may be any photoelectric converter as long as the photoelectric converter can change the conversion rate. The photoelectric converter element D10 may also be a photodiode of a different type from an avalanche photodiode, or a solid-state image sensor. Alternatively, 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 may determine which one of the plurality of photoelectric converter elements D10 should be used for each section.

According to another variant, the distance-measuring device 10 can also be implemented as a plurality of 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) may also be distributed among a plurality of devices.

The main body that performs the functions of the distance measuring apparatus 10 described above includes a computer system. The computer system includes a processor and memory as the main hardware components. The functions of the distance measuring device 10 according to the present disclosure may be performed by the main body by causing a processor to execute a program stored in a memory of a computer system. The program may be stored in advance in the memory of the computer system. Alternatively, the program may be downloaded via a telecommunication line, or may be recorded in a non-transitory computer-readable storage medium such as a memory card, an optical disk, or a hard disk drive and distributed. The processor of the computer system may be implemented as a single or multiple electronic circuits including a semiconductor Integrated Circuit (IC) or a large scale integrated circuit (LSI). Alternatively, a Field Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC) programmed after manufacturing an LSI, or a reconfigurable logic device allowing reconfiguration of connections or circuit portions inside the LSI may also be used for the same purpose. These electronic circuits may suitably be integrated on a single chip or may be distributed over a plurality of chips. These multiple chips may be integrated in a single device, or distributed among multiple devices, without limitation.

3. Aspects of the invention

As can be seen from the above description of the embodiments and their modifications, the present disclosure has the following aspects. In the following description, reference numerals are inserted in parentheses only for clarifying the correspondence of the constituent elements between the following aspects of the present disclosure and the above-described exemplary embodiments.

The first aspect is realized as a distance measuring device (10). The distance measuring device (10) according to the first aspect comprises a control unit (11) and a measuring unit (12). A control unit (11) controls 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 upon receiving light (L2) reflected from a target (100) as part of measurement light (L1) emitted from the light emitting unit (2). The output unit (32) outputs an electrical signal representing the amount of charge generated by the photoelectric converter element (D10). The measuring unit (12) calculates the distance to the target (100) within a measurable range (FR) from the electrical signals. The control unit (11) sets, in each of a plurality of sections (R1-R7) constituting the measurable range (FR), a conversion ratio of the amount of electric charge generated by the photoelectric converter element (D10) with respect to the amount of light received by the photoelectric converter element (D10). This aspect contributes to an increased measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

A 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 in accordance with a voltage applied thereto. The control unit (11) sets a conversion ratio by a voltage applied to the photoelectric converter element (D10) in each of a plurality of sections (R1-R7). This aspect is advantageous for setting the conversion rate.

The third aspect is a specific embodiment of the distance measuring device (10) according to the second aspect. In a third aspect, the photoelectric converter element (D10) comprises an avalanche photodiode. The conversion ratio is the multiplication factor of the avalanche photodiode. This aspect is advantageous for setting the conversion rate.

A fourth aspect is a specific embodiment of the distance measuring device (10) according to the second or third aspect. In a fourth aspect, a control unit (11) changes the conversion rate in accordance with the amount of ambient light. This aspect may reduce the effect of ambient light on measurement accuracy.

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

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

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 accordance with the amount of light received by the photoelectric converter element (D10) from the target (100) in at least one of the plurality of sections (R1-R7). This aspect contributes to an increased measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

An 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 in accordance with the amount of current flowing through the photoelectric converter element (D10). This aspect contributes to an increased measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

A ninth aspect is a specific embodiment of the distance measuring apparatus (10) according to any one of the second to eighth aspects. In a ninth aspect, a control unit (11) changes a conversion rate in accordance with the length of an exposure duration for allowing a photoelectric converter element (D10) to receive light from a subject (100). This aspect contributes to an increased measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

A tenth aspect is a specific embodiment of the distance measuring device (10) according to any one of the first to ninth aspects. In a tenth aspect, the plurality of intervals (R1-R7) includes: a first group comprising a series of intervals (R1-R7); a second group comprising one or more intervals (RI-R7) different from the first group. The conversion ratio of the first group is smaller than the conversion ratio of the second group. For the first group, the measurement unit (12) determines the distance on the basis of the ratios of the electrical signals respectively corresponding to a plurality of adjacent intervals (R1-R7) selected from a series of intervals (R1-R7) included in the first group. This aspect contributes to an increased measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

An eleventh aspect is a specific embodiment of the distance measuring device (10) according to the tenth aspect. In an eleventh aspect, for the second group, the measurement unit (12) determines the distance by referring to a specific section (R1-R7) corresponding to the electrical signal of the largest magnitude selected from one or more sections included in the second group. The measuring unit (12) uses 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 contributes to an increased measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

A twelfth aspect is a specific embodiment of the distance measuring apparatus (10) according to any one of the first to eleventh aspects. In a twelfth aspect, the photodetector cell (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 electric charge generated by the photoelectric converter element (D10) in the charge storage device (C10) a plurality of times. The electrical signal has a magnitude corresponding to an amount of charge stored in the charge storage device (C10). This aspect contributes to an increased measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

A thirteenth aspect is realized as a distance measuring system (1). A distance measuring system (1) according to a thirteenth aspect comprises a distance measuring device (10) according to any of the first to twelfth aspects, a light emitting unit (2) and a photodetector unit (3). This aspect contributes to an increased measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

A fourteenth aspect is embodied as a distance measurement method. The distance measuring method according to the fourteenth aspect includes a control step and a measurement step. The controlling step comprises 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 upon receiving light (L2) reflected from a target (100) as part of measurement light (L1) emitted from the light emitting unit (2). The output unit (32) outputs an electrical signal representing the amount of charge generated by the photoelectric converter element (D10). The measuring step comprises calculating the distance to the target (100) within a measurable range (FR) from the electrical signal. The controlling step includes setting a conversion ratio of an amount of electric charge generated by the photoelectric converter element (D10) with respect to an amount of light received by the photoelectric converter element (D10) in each of a plurality of sections (R1-R7) constituting the measurable range (FR). This aspect contributes to an increased measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

A 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 contributes to an increased measurement accuracy over the entire measurable range (FR) of the distance to the target (100).

List of reference numerals

1 distance measuring system

2 light emitting unit

3 photo-detector unit

D10 photoelectric converter element

C10 charge storage device

10 distance measuring device

11 control unit

12 measuring cell

Measurable range of FR

Interval R1-R7 (first interval, second interval)

L1 measuring light

L2 light

100 target.