Patent Publication Number: US-2020301017-A1

Title: Range finding device, range finding method and storage medium

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2019-050471, filed on Mar. 18, 2019 in the Japan Patent Office, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     Technical Field 
     This disclosure relates to a range finding device, a range finding method, and storage medium. 
     Background Art 
     Conventionally, the time of flight (TOF) method can be used as one method of finding a range from an imaging device to an object, in which an irradiation or projection light is emitted to the object and a reflection light coming from the object is received, and then a range or distance to the object is calculated using a time difference between a time of emitting the irradiation or projection light and a time of receiving the reflection light. As to the TOF method, the irradiation or projection light having a given irradiation pattern is emitted to the object and then the reflection light coming from the object is received at an image sensor, and a time difference between the time of emitting the irradiation light and the time of receiving the reflection light detected by each pixel of the image sensor to calculate the range or distance to the object. The calculated range or distance value is set for each as bitmap data, and then stored as a distance image. 
     However, conventional range finders (TOF cameras) using the TOF system have no function to capture images of wider angle of view. As to the TOF camera, it is required that the irradiation light reaches the entire image capture range. If the irradiation range is set wider corresponding to the wider angle of view, the irradiation light diffuses and the amount of light per unit solid angle decreases, and thereby the measurable or detectable range of distance becomes shorter. As a countermeasure to this issue, the brightness of the light source can be increased, but this causes power consumption of the light source to increase, which is not preferable. Further, if a plurality of sets of the light emitting unit that emits the irradiation light and the sensor unit that receives the reflection light is used to capture an image of object at the same time, one set may receive the reflection light of the irradiation light emitted from another set, and thereby the range or distance cannot be accurately measured. 
     As to the range finding device, one conventional technology uses two light sources and two TOF systems for acquiring distance data used for projection mapping. Further, another conventional technology uses a plurality of light sources for acquiring distance data at a far-side positions. 
     However, some issues may occur in these conventional technologies, such as the accuracy of range finding or distance measurement deteriorates due to overlapping of the light emission timings of the two light sources, and further, when the light emission timings of the two light sources overlap, the peak power consumption increases, in which sufficient power may not be supplied by a battery drive or the like. 
     SUMMARY 
     In one aspect of the present invention, a range finding device is devised. The range finding device includes a plurality of light sources, each configured to emit irradiation light to an object; a plurality of light reception units configured to receive reflection light coming from the object when the irradiation light hits and reflects from the object, the number of plurality of light reception units being the same number of the plurality of light sources; and circuitry configured to shift light emission timing of at least one or more light sources among the plurality of light sources; and calculate a distance to the object based on information output from each of the plurality of light reception units. 
     In another aspect of the present invention, a method of finding a range to an object is devised. The method includes shifting light emission timing of at least one or more light sources among a plurality of light sources, each light source being configured to emit irradiation light to the object; receiving, using a plurality of light reception units, reflection light coming from the object when the irradiation light hits and reflects from the object, the number of plurality of light reception units being the same number of the plurality of light sources; and calculating a distance to the object based on information output from each of the plurality of light reception units. 
     In another aspect of the present invention, non-transitory computer readable storage medium storing one or more instructions that, when performed by one or more processors, cause the one or more processors to execute a method of finding a range to an object. The method includes shifting light emission timing of at least one or more light sources among a plurality of light sources, each light source being configured to emit irradiation light to the object; receiving, using a plurality of light reception units, reflection light coming from the object when the irradiation light hits and reflects from the object, the number of plurality of light reception units being the same number of the plurality of light sources; and calculating a distance to the object based on information output from each of the plurality of light reception units. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the description and many of the attendant advantages and features thereof can be readily acquired and understood from the following detailed description with reference to the accompanying drawings, wherein: 
         FIG. 1  illustrates an example of a configuration of a range finding device according to an embodiment of this disclosure; 
         FIG. 2  illustrates an angle of view of a range finding device according to an embodiment of this disclosure; 
         FIG. 3  illustrates an example of a hardware block diagram of a range finding device according to an embodiment of this disclosure; 
         FIG. 4  illustrates an example of a functional block diagram of a range finding device according to an embodiment of this disclosure; 
         FIG. 5  illustrates an example of a timing chart of light emission timing and light reception timing when light emission timings from two light sources of a range finding device are set to the same timing; 
         FIG. 6  illustrates an example of a timing chart of light emission timing and light reception timing when light emission timings from the two light sources of a range finding device are shifted; 
         FIG. 7  is a flowchart illustrating an example of a flow of operation of a range finding device according to the embodiment; 
         FIG. 8  illustrates an example of a hardware block diagram of a range finding device according to modification example 1 of an embodiment of this disclosure; 
         FIG. 9  illustrates an exterior view of a range finding device according to modification example 2 of an embodiment of this disclosure; 
         FIG. 10  illustrates an angle of view of a range finding device according to modification example 2 of an embodiment of this disclosure; 
         FIG. 11  illustrates an exterior view of a range finding device according to modification example 3 of an embodiment of this disclosure; 
         FIG. 12  illustrates an angle of view of the range finding device according to modification example 3 of an embodiment of this disclosure; 
         FIG. 13  illustrates an example of a functional block diagram of a range finding device according to modification example 3 of an embodiment of this disclosure; 
         FIG. 14  illustrates an example of a timing chart of light emission timing when light emission timings of all of light sources included a range finding device according to modification example 3 of an embodiment are shifted; and 
         FIG. 15  illustrates an example of a timing chart when light emission timings of some of a plurality of light sources of a range finding device according to modification example 3 of an embodiment set to the same timing. 
     
    
    
     The accompanying drawings are intended to depict embodiments of this disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION 
     A description is now given of exemplary embodiments of this disclosures. It should be noted that although such terms as first, second, etc. may be used herein to describe various elements, components, regions, layers and/or units, it should be understood that such elements, components, regions, layers and/or units are not limited thereby because such terms are relative, that is, used only to distinguish one element, component, region, layer or unit from another region, layer or unit. Thus, for example, a first element, component, region, layer or unit discussed below could be termed a second element, component, region, layer or unit without departing from the teachings of the present inventions. 
     In addition, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present inventions. Thus, for example, as used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Moreover, the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Hereinafter, a description is given of a range finding device and a range finding method according to an embodiment of the present invention with reference to the drawings. Also, the following embodiments are not limited to the present invention. Further, various omissions, substitutions, modifications, and combinations of components may be made within the scope of the following embodiments without departing from the scope of the present invention. 
     (Configuration of Range Finding Device) 
       FIG. 1  illustrates an example of a configuration of a range finding device  1  according to an embodiment. Hereinafter, a description is given of the configuration of the range finding device  1  with reference to  FIG. 1 . 
     As illustrated in  FIG. 1 , the range finding device  1  includes, for example, light sources  11   a  and  11   b , light source optical systems  12   a  and  12   b , time of flight (TOF) sensors  13   a  and  13   b  (light reception units), sensor optical systems  14   a  and  14   b , a control unit  21 , and a battery  22 . 
     Each of the light sources  11   a  and  11   b  is a light-emitting device, such as a laser diode, vertical cavity surface emitting laser (VCSEL), and light emitting diode (LED). 
     The light source optical system  12   a  is an optical system used for projecting the light (hereinafter, irradiation light or projection light) emitted from the light source  11   a  with a given angle of view using a lens or the like. 
     The light source optical system  12   b  is an optical system used for projecting the light (hereinafter, irradiation light or projection light) emitted from the light source  11   b  with a given angle of view using a lens or the like. 
     The TOF sensor  13   a  is a light receiving sensor that measures the time difference between a time of emitting the irradiation light from the light source  11   a  via the light source optical system  12   a  and a time of receiving the reflection light coming from an object when the irradiation light hits and reflects from the object. 
     The TOF sensor  13   b  is a light receiving sensor that measures the time difference between a time of emitting the irradiation light from the light source  11   b  via the light source optical system  12   b  and a time of receiving the reflection light coming from an object when the irradiation light hits and reflects from the object. 
     Thus, the distance to the object can be calculated based on the time difference between the time of emitting the irradiation light and the time of receiving the reflection light, and the light speed. 
     The TOF sensors  13   a  and  13   b  have a given structure, in which sensor elements are arranged in a two-dimensional array. The TOF sensors  13   a  and  13   b  are not limited to the light receiving sensors that measure the time difference between the time of emitting the irradiation light and the time of receiving the reflection light. For example, each of the TOF sensors  13   a  and  13   b  can be an image sensor using a solid-state image sensor, such as charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS). 
     The sensor optical system  14   a  is an optical system that uses lens or the like to guide, to the TOF sensor  13   a , the reflection light reflecting from the object when the irradiation light is emitted from the light source  11   a  and the light source optical system  12   a  toward the object and then reflected from the object. 
     The sensor optical system  14   b  is an optical system that uses lens or the like to guide, to the TOF sensor  13   b , the reflection light reflecting from the object when the irradiation light is emitted from the light source  11   b  and the light source optical system  12   b  toward the object and then reflected from the object. 
     The control unit  21  includes a control board circuit that controls the light reception time by the TOF sensors  13   a  and  13   b  and the image capturing timing (light reception timing) by the TOF sensors  13   a  and  13   b.    
     The battery  22  supplies power to the light sources  11   a  and  11   b  to emit the light. The battery  22  also supplies power used for the processing performed by the TOF sensors  13   a  and  13   b , and the control unit  21 . In the configuration illustrated in  FIG. 1 , the battery  22  is provided as a mobile battery, but is not limited thereto. For example, the battery  22  can be an external power supply battery, or can be a combination of the mobile battery and the external power supply battery. 
       FIG. 1  illustrates one example configuration having two sets of the light source and the TOF sensor, such as the two light sources  11   a  and  11   b  and the two TOF sensors  13   a  and  13   b , but is not limited thereto. For example, three or more sets of the light source and the TOF sensor can be used. 
     (Angle of View of Range Finding Device) 
       FIG. 2  illustrates an angle of view of the range finding device  1 . Hereinafter, a description is given of the angle of view of the range finding device  1  with reference  FIG. 2 . 
     As illustrated in  FIGS. 1 and 2 , the range finding device  1  employs a configuration disposing the light source  11   a , the light source optical system  12   a , the TOF sensor  13   a  and the sensor optical system  14   a  at one side, and disposing the light source  11   b , the light source optical system  12   b , and the sensor optical system  14   b  at the opposite side to enable to acquire range or distance information of full-view spherical range. 
     For example, the irradiation light emitted from the light source  11   a  and the light source optical system  12   a  has an angle of view  201   a  of 180 degrees or more as illustrated in  FIG. 2 . Similarly, the irradiation light emitted from the light source  11   b  and the light source optical system  12   b  has an angle of view  201   b  having an angle of view  201   b  of 180 degrees or more as illustrated in  FIG. 2 . With this configuration, the range finding device  1  can acquire the range or distance information of full-view spherical range. 
     Since the angle of view of the irradiation light emitted from each of the light source optical systems  12   a  and  12   b  is set to 180 degrees or more, the angle of view of the irradiation light emitted from the light source optical system  12   a  and the angle of view of the irradiation light emitted from the light source optical system  12   b  partially overlap with each other as illustrated in  FIG. 2 . 
     The sensor optical system  14   a  guides the reflection light, reflected from the object when the irradiation light emitted with the angle of view  201   a  hits the object, to the TOF sensor  13   a  so that the reflection light is focused on the TOF sensor  13   a  with the same angle of view. 
     Similarly, the sensor optical system  14   b  guides the reflection light, reflected from the object when the irradiation light emitted with the angle of view  201   b  hits the object, to the TOF sensor  13   b  so that the reflection light is focused on the TOF sensor  13   b  with the same angle of view of the irradiation light. 
     (Hardware Configuration of Range Finding Device) 
       FIG. 3  illustrates an example of a hardware block diagram of the range finding device  1  according to the embodiment. Hereinafter, a description is given of the hardware configuration of the range finding device  1  with reference  FIG. 3 . 
     As illustrated in  FIG. 3 , the range finding device  1  includes, for example, a light emission unit  15   a  including a light source  11   a  and a light source optical system  12   a , a light emission unit  15   b  including a light source  11   b  and a light source optical system  12   b , a light reception unit  16   a  including a TOF sensor  13   a  and a sensor optical system  14   a , a light reception unit  16   b  including a TOF sensor  13   b  and a sensor optical system  14   b , and a control unit  21 . 
     The control unit  21  transmits image capture signals (operation signals), each is shifted in timing, to the TOF sensors  13   a  and  13   b , to be described later. When the TOF sensors  13   a  and  13   b  respectively receives the image capture signals from the control unit  21 , the TOF sensors  13   a  and  13   b  respectively transmit the light emission signals (light emission patterns) to the light sources  11   a  and  11   b , respectively, to control the light emitting operations of the light sources  11   a  and  11   b , respectively. 
     Then, the light sources  11   a  and  11   b  respectively emit the light in accordance with the light emission signals received from the TOF sensors  13   a  and  13   b , and project the light as the irradiation light through the light source optical systems  12   a  and  12   b , respectively. 
     In an example case of  FIG. 3 , the irradiation light emitted from the light source optical system  12   a  hits and reflects from an object  50   a  disposed at a far side (“A side”), and the TOF sensor  13   a  receives the reflection light via the sensor optical system  14   a.    
     Further, the irradiation light emitted from the light source optical system  12   b  hits and reflects from an object  50   b  disposed at a near side (“B side”), and the TOF sensor  13   b  receives the reflection light via the sensor optical system  14   b.    
     The TOF sensors  13   a  and  13   b  receive the reflection light, and output the detection information including information about the time difference between the time of emitting the irradiation light and the time of receiving the reflection light detected by each sensor element, to the control unit  21 . Then, based on the detection information received from the TOF sensors  13   a  and  13   b , the control unit  21  calculates a distance image by converting the time information into a distance value for each pixel. The measurement operation of distance can use typical phase detection method of the TOF camera, and can use the operation described in JP-2018-077143-A. 
     (Functional Configuration of Range Finding Device) 
       FIG. 4  illustrates an example of a functional block diagram of the range finding device  1 . Hereinafter, a description is given of the functional configuration of the range finding device  1  with reference  FIG. 4 . 
     As illustrated in  FIG. 4 , the range finding device  1  includes, for example, a first light reception unit  101  (light reception unit), a second light reception unit  102  (light reception unit), a first light emission unit  103 , a second light emission unit  104 , an imaging control unit  111  (operation control unit), and a range finding unit  112  (measurement unit). 
     The first light reception unit  101  is a functional unit that receives the reflection light reflected from the object when the irradiation light emitted from the first light emission unit  103  hits and reflects from the object, in accordance with the image capture signal received from the imaging control unit  111 . 
     Further, when the first light reception unit  101  receives the image capture signal from the imaging control unit  111 , the first light reception unit  101  outputs the light emission signal to the first light emission unit  103  to control the light emitting operation. 
     Further, when the first light reception unit  101  receives the reflection light, the first light reception unit  101  outputs the detection information including the information about the time difference between the time of emitting the irradiation light and the time of receiving the reflection light. The first light reception unit  101  can be implemented by the light reception unit  16   a , the TOF sensor  13   a  and the sensor optical system  14   a  illustrated in  FIG. 3 . 
     The second light reception unit  102  is a functional unit that receives the reflection light reflected from the object when the irradiation light emitted from the second light emission unit  104  hits and reflects from the object, in accordance with the image capture signal received from the imaging control unit  111 . 
     Further, when the second light reception unit  102  receives the image capture signal from the imaging control unit  111 , the second light reception unit  102  outputs the light emission signal to the second light emission unit  104  to control the light emitting operation. 
     Further, when the second light reception unit  102  receives the reflection light, the second light reception unit  102  outputs the detection information including the information about the time difference between the time of emitting the irradiation light and the time of receiving the reflection light. The second light reception unit  102  can be implemented by the light reception unit  16   b , the TOF sensor  13   b  and the sensor optical system  14   b  illustrated in  FIG. 3 . 
     The first light emission unit  103  is a functional unit that emits the light emitted from the light source  11   a  to the outside in accordance with the light emission signal received from the first light reception unit  101 . The first light emission unit  103  can be implemented by the light emission unit  15   a , that is the light source  11   a  and the light source optical system  12   a  illustrated in  FIG. 3 . 
     The second light emission unit  104  is a functional unit that emits the light emitted from the light source  11   b  to the outside in accordance with the light emission signal received from the second light reception unit  102 . The second light emission unit  104  can be implemented by the light emission unit  15   b , that is the light source  11   b  and the light source optical system  12   b  illustrated in  FIG. 3 . 
     The imaging control unit  111  is a functional unit that controls the operation of the first light reception unit  101  and the second light reception unit  102 . Specifically, the imaging control unit  111  transmits one image capture signal (operation signal) to the first light reception unit  101  and another image capture signal (operation signal) to the second light reception unit  102  by shifting the timing of one image capture signal and the timing of another image capture signal so that the imaging operation using the first light reception unit  101  and the imaging operation using the second light reception unit  102  are shifted (i.e., light receiving operation, light emitting operation by the first light emission unit  103  and the second light emission unit  104 ). That is, the light emitting operation of the first light emission unit  103  and the light emitting operation of the second light emission unit  104  is controlled using the image capture signals output by the imaging control unit  111 . 
     Further, the imaging control unit  111  receives the detection information from the first light reception unit  101  and the second light reception unit  102 , respectively. The imaging control unit  111  can be implemented by the control unit  21  illustrated in  FIG. 3 . 
     The range finding unit  112  is a functional unit that generates a distance image by converting the time information into a distance value for each pixel based on the detection information that the imaging control unit  111  has received from the first light reception unit  101  and the second light reception unit  102 . The range finding unit  112  can be implemented by the control unit  21  illustrated in  FIG. 3 . 
     Since  FIG. 4  conceptually illustrates the first light reception unit  101 , the second light reception unit  102 , the first light emission unit  103 , the second light emission unit  104 , the imaging control unit  111 , and the range finding unit  112 , the configuration is not limited thereto. That is, a plurality of functional units illustrated as separate functional units in the range finding device  1  of  FIG. 4  can be implemented as one functional unit. For example, the imaging control unit  111  and the range finding unit  112  are separate units in  FIG. 4 , but can be implemented as one unit. On the other hand, the function of one functional unit in the range finding device  1  of  FIG. 4  can be divided into a plurality of functions, and a plurality of functional units can be configured. 
     Further, the first light reception unit  101  and the second light reception unit  102  are configured to output the detection information including the information about the time difference between the time of emitting the irradiation light and the time of receiving the reflection light, but is not limited thereto. That is, the first light reception unit  101  and the second light reception unit  102  can be configured to calculate the distance based on the information about the time difference between the time of emitting the irradiation light and the time of receiving the reflection light, and directly output the distance information as the detection information. 
     (Light Emission Timing of Light Emission Unit and Light Reception Timing of Light Reception Unit) 
       FIG. 5  illustrates an example of a timing chart of light emission timing and light reception timing when the light emission timing from two light sources of the range finding device  1  are set to the same timing. Hereinafter, a description is given of an operation when the light emission timings of the two light sources  11   a  and  11   b  are set to the same timing with reference to  FIG. 5 . 
     As above described with reference to  FIG. 3 , there is a case that the object  50   a  is disposed at the far side (A side) and the irradiation light is emitted from the first light emission unit  103  while the object  50   b  is disposed at the near side (B side) and the irradiation light is emitted from the second light emission unit  104 . 
     The irradiation light emitted to the A side, that is, the irradiation light emitted from the first light emission unit  103  hits and reflects from the object  50   a , and then the reflection light is received by the first light reception unit  101 . 
     At this time, the time difference of “A_Diff,” which is the difference between the timing when the irradiation light is emitted to the A side (A-side light emission timing) and the timing when the reflection light is received at the A side (A-side light reception timing) can be used to calculate a time required for traveling between the range finding device  1  and the object  50   a , and then the distance between the range finding device  1  and the object  50   a  can be calculated based on the calculated time. 
     Further, the irradiation light irradiation light emitted to the B side, that is, the irradiation light emitted from the second light emission unit  104  hits and then reflects from the object  50   b , and then the reflection light is received by the second light reception unit  102 . 
     At this time, the time difference of “B_Diff,” which is the difference between the timing when the irradiation light is emitted to the B side (B-side light emission timing) and the timing when the reflection light is received at the B side (B-side light reception timing) can be used to calculate a time required for traveling between the range finding device  1  and the object  50   b , and then the distance between the range finding device  1  and the object  50   b  can be calculated based on the calculated time. 
     In this case, since the distance from the range finding device  1  to the object  50   a  is longer than the distance from the range finding device  1  to the object  50   b , as illustrated in  FIG. 5 , the time difference of “A_Diff” becomes longer than the time difference of “B_Diff.” 
     In an example of  FIG. 5 , since the A-side light emission timing and the B-side light emission timing are set to the same timing, as indicated by the waveform of power consumption in the lower part of  FIG. 5 , the first light emission unit  103  and the second light emission unit  104  simultaneously emit the light, so that the peak power consumption increases with the effect of simultaneous emission of the light. 
     When the peak power consumption becomes greater, the battery  22  cannot supply sufficient power if the battery  22  is a mobile battery that stores relatively smaller electricity charges, and the light quantity of the irradiation light emitted from the first light emission unit  103  and the second light emission unit  104  becomes smaller, and the measurable distance becomes shorter. 
     Further, as to the range finding device  1  for capturing the full-view spherical range illustrated in  FIG. 1 , the projection or irradiation range of the first light emission unit  103  (the range of the angle of view  201   a  illustrated in  FIG. 2 ) and the projection or irradiation range of the second light emission unit  104  (the range of the angle of view  201   b  illustrated in  FIG. 2 ) are mostly different ranges, but the projection or irradiation ranges are partially overlapped as illustrated in  FIG. 2 . 
     Therefore, when the A-side light emission timing and the B-side light emission timing are the same timing, each of the first light reception unit  101  and the second light reception unit  102  cannot determine whether the reflection light corresponds to the irradiation light emitted from the first light emission unit  103  or the irradiation light emitted from the second light emission unit  104 , so that the range finding cannot be performed accurately, and thereby the range finding precision may decrease. 
       FIG. 6  illustrates an example of a timing chart of light emission timing and light reception timing when the light emission timings from two light sources of the range finding device  1  are shifted. Hereinafter, a description is given of an operation when the light emission timings of the two light sources  11   a  and  11   b  are shifted with reference  FIG. 6 . 
     As to the range finding device  1 , as illustrated in  FIG. 6 , the irradiation light is emitted to the A side at one timing (A-side light emission timing) by the first light emission unit  103  and the irradiation light is emitted to the B side at another timing (B-side light emission timing) by the second light emission unit  104  without overlapping the A-side light emission timing and the B-side light emission timing. 
     As a result, as illustrated in the waveform of power consumption in the lower part of  FIG. 6 , the peak of power consumption waveform occurs at different timings for the first light emission unit  103  and the second light emission unit  104  because the first light emission unit  103  and the second light emission unit  104  independently emit the light at the different timing, so that the peak of the power consumption waveform illustrated in  FIG. 6  can become smaller than the peak of power consumption waveform illustrated in  FIG. 5 . 
     That is, the total power consumption of the operation performed by setting the light emission timing of the first light emission unit  103  and the light emission timing of the second light emission unit  104  at the same timing (see  FIG. 5 ) and the total power consumption of the operation performed by setting the light emission timing of the first light emission unit  103  and the light emission timing of the second light emission unit  104  at the different timings ( FIG. 6 ) may become the same value. However, in a case of  FIG. 6 , the battery  22  can supply sufficient power even if the battery  22  is a mobile battery, and the light quantity of the irradiation light emitted from the first light emission unit  103  and the light quantity of the irradiation light emitted from the second light emission unit  104  become given sufficient levels, and the measurable or detectable distance can be set longer. 
     Further, when the A light emission timing and the B side light emission timing are shifted, each of the first light reception unit  101  and the second light reception unit  102  can correctly determine whether the reflection light corresponds to the irradiation light emitted from the first light emission unit  103  or the irradiation light emitted from the second light emission unit  104 , so that the range finding can be performed accurately, and thereby the range finding precision can be enhanced. 
     (Flow of Overall Operation of Range Finding Device) 
       FIG. 7  is a flowchart illustrating an example of a flow of operation of the range finding device  1  according to the embodiment. Hereinafter, a description is given of a flow of operation of the range finding device  1  with reference  FIG. 7 . 
     Steps S 11  and S 12 : The imaging control unit  111  transmits the image capture signal to the first light reception unit  101  to instruct a start of the imaging operation by the first light reception unit  101 . When the first light reception unit  101  receives the image capture signal, the first light reception unit  101  outputs the light emission signal to the first light emission unit  103  to start to emit the irradiation light. Then, the sequence proceeds to step S 13 . 
     Step S 13 : When the first light reception unit  101  receives the reflection light with respect to the irradiation light emitted from the first light emission unit  103 , the first light reception unit  101  outputs detection information including information about the time difference between the time of emitting the irradiation light and the time of receiving the reflection light. Then, the imaging control unit  111  receives the detection information from the first light reception unit  101  (acquiring data), and then transmits the detected information to the range finding unit  112 . Then, based on the detection information that the imaging control unit  111  has received from the first light reception unit  101 , the range finding unit  112  calculates a distance image by converting the time information into a distance value for each pixel. 
     When the range finding unit  112  completes the calculation of distance image for the first light reception unit  101  (step S 13 : Yes), the sequence proceeds to step S 14 . If the range finding unit  112  does not yet complete the calculation of distance image for the first light reception unit  101  (step S 13 : No), step S 13  is repeated. The timing of calculation of distance image by the range finding unit  112  is not limited thereto. For example, the calculation of distance image by the range finding unit  112  can be performed after completing a series of processing illustrated in  FIG. 7 . 
     Step S 14  and S 15 : The imaging control unit  111  transmits the image capture signal to the second light reception unit  102  to instruct a start of the imaging operation by the second light reception unit  102 . When the second light reception unit  102  receives the image capture signal, the second light reception unit  102  outputs the light emission signal to the second light emission unit  104  to start to emit the irradiation light. Then, the sequence proceeds to step S 16 . 
     Step S 16 : When the second light reception unit  102  receives the reflection light with respect to the irradiation light emitted from the second light emission unit  104 , the second light reception unit  102  outputs detection information including information about the time difference between the time of emitting the irradiation light and the time of receiving the reflection light. Then, the imaging control unit  111  receives the detection information from the second light reception unit  102  (acquiring data), and then transmits the detection information to the range finding unit  112 . Then, based on the detection information that the imaging control unit  111  has received from the second light reception unit  102 , the range finding unit  112  calculates a distance image by converting the time information into a distance value for each pixel. 
     When the range finding unit  112  completes the calculation of distance image for the second light reception unit  102  (step S 16 : Yes), the sequence is terminated. If the range finding unit  112  does not yet complete the calculation of distance image for the second light reception unit  102  (step S 16 : No), step S 16  is repeated. 
     The range finding device  1  performs the sequence of steps S 11  to S 16  to execute the entire operation. 
     In an example case in  FIG. 7 , the imaging operation by the first light reception unit  101  and the imaging operation by the second light reception unit  102  are terminated by performing one imaging operation, but is not limited thereto. For example, the sequence of imaging operation of  FIG. 7  can be repeated for a given number of times. If the imaging operation is repeated for a given number of times, for example, the average of distance values of each pixel indicated by the distance images derived by the range finding unit  112  can be obtained. 
     As described above, the range finding device  1  shifts the timing of the irradiation (light emission) by the first light emission unit  103  and the timing of the irradiation (light emission) by the second light emission unit  104  so that the timing of the irradiation (light emission) by the first light emission unit  103  and the timing of the irradiation (light emission) by the second light emission unit  104  do not overlap with each other. 
     Thus, as illustrated in the waveform of power consumption in the lower part of  FIG. 6 , the peak of power consumption waveform becomes different in each of the first light emission unit  103  and the second light emission unit  104  because the first light emission unit  103  and the second light emission unit  104  independently emit the light at the different timings, so that the peak of the power consumption waveform illustrated in  FIG. 6  can become smaller than the peak of power consumption waveform illustrated in  FIG. 5 . 
     In this case, the battery  22  can supply sufficient power, and the light quantity of the irradiation light emitted from the first light emission unit  103  and the light quantity of the irradiation light emitted from the second light emission unit  104  become given sufficient levels, and the measurable distance can be set longer, so that the angle of view can be widened by a combination of the plurality of light emission units (first light emission unit  103  and second light emission unit  104 ) and the light reception unit (first light reception unit  101  and the second light reception unit  102 ). 
     Further, when the timing of the irradiation (light emission) by the first light emission unit  103  is different from the timing of the irradiation (light emission) by the second light emission unit  104 , each of the first light reception unit  101  and the second light reception unit  102  can correctly determine whether the reflection light corresponds to the irradiation light emitted from the first light emission unit  103  or the irradiation light emitted from the second light emission unit  104 , so that the range finding can be performed accurately, and thereby the range finding precision can be enhanced. 
     Modification Example 1 
       FIG. 8  illustrates an example of a hardware block diagram of a range finding device  1   a  according to modification example 1 of the embodiment. Hereinafter, a description is given of a hardware configuration of the range finding device  1   a  with reference  FIG. 8 . 
     As illustrated in  FIG. 8 , the range finding device  1   a  includes, for example, a light emission unit  15   a  including a light source  11   a  and a light source optical system  12   a , a light emission unit  15   b  including a light source  11   b  and a light source optical system  12   b , a light reception unit  18   a  including a TOF sensor  17   a  and a sensor optical system  14   a , a light reception unit  18   b  including a TOF sensor  17   b  and a sensor optical system  14   b , and a control unit  21   a.    
     In the same manner as the above described control unit  21 , the control unit  21   a  transmits the image capture signals (operating signals) respectively to the TOF sensors  17   a  and  17   b  by shifting the timings. Further, the control unit  21   a  transmits the light emission signals (light emission patterns) to the light sources  11   a  and  11   b  in synchronization with the image capture signals for the TOF sensors  17   a  and  17   b . Then, the light sources  11   a  and  11   b  emit the light in accordance with the light emission signals received from the control unit  21   a , and then emit the light as the irradiation light through the light source optical systems  12   a  and  12   b , respectively. 
     In an example case of  FIG. 8 , the irradiation light emitted from the light source optical system  12   a  is reflected by the object  50   a  disposed at the A side (far side), and then received by the TOF sensor  17   a  via the sensor optical system  14   a . Further, the irradiation light emitted from the light source optical system  12   b  is reflected by the object  50   b  disposed at the B side (near side), and then received by the TOF sensor  17   b  via the sensor optical system  14   b.    
     When each of the TOF sensor  17   a  and  17   b  receives the reflection light, each of the TOF sensor  17   a  and  17   b  outputs the detection information including information about the time difference between the time of emitting the irradiation light and the time of receiving the reflection light detected by each sensor element, to the control unit  21   a.    
     Then, based on the detection information received from the TOF sensors  17   a  and  17   b , the control unit  21   a  calculates a distance image by converting the time information into a distance value for each pixel. 
     As described above, as to the range finding device  1   a  according to the modification example 1, the TOF sensor does not transmit the light emission signal to the light source, but the control unit  21   a  transmits the light emission signal to the light sources  11   a  and  11   b . This configuration can also provide the same effect as the range finding device  1  according to the above described embodiment. 
     Modification Example 2 
       FIG. 9  is an external view of a range finding device  1   b  according to modification example 2 of the embodiment. Hereinafter, a description is given of an external configuration of the range finding device  1   b  with reference  FIG. 9 . 
     Instead of the light source optical systems  12   a  and  12   b  and the sensor optical systems  14   a  and  14   b  of the range finding device  1   a  described above, as illustrated in  FIG. 9 , the range finding device  1   b  includes, for example, light source optical systems  32   a  and  32   b , and sensor optical systems  34   a  and  34   b.    
     As illustrated in  FIG. 9 , the light source optical systems  32   a  and  32   b  and the sensor optical systems  34   a  and  34   b  are disposed on the same face of a housing of the range finding device  1   b . That is, the optical axis of the light source optical system  32   a  and the optical axis of the light source optical system  32   b  are set parallel each other, and the irradiation light emitted from the light source optical system  32   a  and the irradiation light emitted from the light source optical system  32   b  are projected in the same direction. Further, the optical axis of the sensor optical system  34   a  and the optical axis of the sensor optical system  34   b  are set parallel to each other. The operation of the range finding device  1   b  is the same as that of the range finding device  1  according to the above-described embodiment. 
       FIG. 10  illustrates an angle of view of the range finding device  1   b  according to the modification example 2. Hereinafter, a description is given of the angle of view of the range finding device  1   b  with reference  FIG. 10 . 
     As illustrated in  FIG. 10 , the irradiation light emitted from the light source optical system  32   a  has an angle of view  211   a , and the irradiation light emitted by the light source optical system  32   b  has an angle of view  211   b . Therefore, as illustrated in  FIG. 10 , the angle of view of the irradiation light emitted from the light source optical system  32   a  and the angle of view of the irradiation light emitted from the light source optical system  32   b  overlap in a wider range. 
     However, similar to the above described range finding device  1 , as to the range finding device  1   b , the timing of the irradiation from the light source optical system  32   a  and the timing of the irradiation from the light source optical system  32   b  are shifted so as not overlap with each other. 
     Thus, the peak of power consumption waveform becomes different in each of the light source optical system  32   a  and the light source optical system  32   b  because the light source optical system  32   a  and the light source optical system  32   b  independently emit the light at the different timings, so that the peak of the power consumption can become smaller compared to a case where the timing of the irradiation is set to the same timing. 
     In this case, the battery  22  can supply sufficient power, and the light quantity of the irradiation light emitted from the light source of the light source optical system  32   a  and the light quantity of the irradiation light emitted from the light source of the light source optical system  32   b  become given sufficient levels, and the measurable distance can be set longer, so that the angle of view can be widened in a direction parallel to the face of the housing arranging the light source optical systems  32   a  and  32   b  as illustrated in  FIG. 10 . 
     Further, when the timing of the irradiation (light emission) from the light source optical system  32   a  and the timing of the irradiation (light emission) from the light source optical system  32   b  are shifted, each of the TOF sensor  17   a  (corresponding to the TOF sensor  13   a ) corresponding to the sensor optical system  34   a  and the TOF sensor  17   b  (corresponding to the TOF sensor  13   b ) corresponding to the sensor optical system  34   b  can correctly determine whether the reflection light corresponds to the irradiation light emitted from the light source optical system  32   a  or the light source optical system  32   b , so that the range finding can be performed accurately, and thereby the range finding precision can be enhanced. 
       FIG. 9  illustrates one example configuration having two sets of the light source and the TOF sensor. For example, three or more sets of the light source and the TOF sensor can be used. 
       FIG. 9  illustrates one example configuration disposing the light source optical systems  32   a  and  32   b  and the sensor optical systems  34   a  and  34   b  are on the same face of the housing of the range finding device  1   b , but is not limited thereto. For example, a face of the housing disposing the light source optical system  32   a  and the sensor optical system  34   a  and a face of the housing disposing the light source optical system  32   b  and the sensor optical system  34   b  can be different faces. 
     Modification Example 3 
     Hereinafter, a description is given of a range finding device  1   c  according to modification example 3 with reference to differences compared to the range finding device  1  according to the above-described embodiment. The above-described range finding device  1  employs one configuration including two sets of the light source and the TOF sensor. As to the modification example 3, the range finding device  1   c  employs a configuration including four sets of the light source and the TOF sensor. 
     (Configuration and Angle of View of Range Finding Device) 
       FIG. 11  is an external view of the range finding device  1   c  according to a modification example 3.  FIG. 12  illustrates an angle of view of the range finding device  1   c  according to the modification example 3. Hereinafter, a description is given of the configuration and the angle of view of the range finding device  1   c  with reference to  FIGS. 11 and 12 . 
     As illustrated in  FIG. 11 , the range finding device  1   c  includes, for example, light source optical systems  42   a  to  42   d , and sensor optical systems  44   a  to  44   d . Further, the range finding device  1   c  includes the light source corresponding each of the light source optical systems  42   a  to  42   d , and includes the TOF sensor corresponding to each of the sensor optical systems  44   a  to  44   d . Further, the range finding device  1   c  includes the control unit  21  and the battery  22 , which are included in the range finding device  1  according to the above-described embodiment. 
     As illustrated in  FIG. 11 , the range finding device  1   c  includes the light source optical system  42   a  and the sensor optical system  44   a  on a first side face, the light source optical system  42   b  and the sensor optical system  44   b  on a second side face, the light source optical system  42   c  and the sensor optical system  44   c  on a third side face, and the light source optical system  42   d  and the sensor optical system  44   d  on a fourth side face, in which each of the side faces configure the rectangular parallelepiped housing of the range finding device  1   c.    
     Further, as illustrated in  FIG. 12 , the irradiation light emitted from the light source optical system  42   a  to the A side has an angle of view  221   a  of 90 degrees or more, the irradiation light emitted from the light source optical system  42   b  toward the B side has an angle of view  221   b  of 90 degrees or more, the irradiation light emitted from the light source optical system  42   c  toward the C side has an angle of view  221   c  of 90 degrees or more, and the irradiation light emitted from the light source optical system  42   c  has an angle of view  221   d  of 90 degrees or more. Since the angle of views  221   a  to  221   d  of the irradiation light emitted respectively from the light source optical systems  42   a  to  42   d  is 90 degrees or more, the angle of views overlap partially with each other as illustrated in  FIG. 12 . 
     Since each of the sensor optical systems  44   a  to  44   d  uses the respective TOF sensor to receive the respective reflection light with respect to the respective irradiation light emitted with the angle of views  221   a  to  221   d , the respective reflection light is focused on the respective TOF sensor with the same angle of view of the irradiation light emitted from the respective light source optical systems  42   a  to  42   d.    
     (Functional Configuration of Range Finding Device) 
       FIG. 13  illustrates an example of a functional block diagram of the range finding device  1   c  according to the modification example 3. Hereinafter, a description is given of a functional block diagram of the range finding device  1   c  with reference to  FIG. 13 . 
     As illustrated in  FIG. 13 , the range finding device  1   c  includes, for example, a first light reception unit  121  (light reception unit), a second light reception unit  122  (light reception unit), a third light reception unit  123  (light reception unit), a fourth light reception unit  124  (light reception unit), a first light emission unit  125 , a second light emission unit  126 , a third light emission unit  127 , a fourth light emission unit  128 , an imaging control unit  131  (operation control unit), and a range finding unit  132  (measurement unit). 
     The first light reception unit  121  is a functional unit that receives the reflection light, which is the light reflected from an object when the irradiation light emitted from the first light emission unit  125  hits and reflects from the object, in accordance with the image capture signal received from the imaging control unit  131 . 
     Further, when the first light reception unit  121  receives the image capture signal from the imaging control unit  131 , the first light reception unit  121  outputs the light emission signal to the first light emission unit  125  to control the light emitting operation. 
     Further, when the first light reception unit  121  receives the reflection light, the first light reception unit  121  outputs detection information including information about the time difference between the time of emitting the irradiation light and the time of receiving the reflection light. 
     The first light reception unit  121  can be implemented by the sensor optical system  44   a  illustrated in  FIG. 11  and the corresponding TOF sensor. 
     The second light reception unit  122  is a functional unit that receives the reflection light, which is the light reflected from an object when the irradiation light emitted from the second light emission unit  126  hits and reflects from the object, in accordance with the image capture signal received from the imaging control unit  131 . 
     Further, when the second light reception unit  122  receives the image capture signal from the imaging control unit  131 , the second light reception unit  122  outputs the light emission signal to the second light emission unit  126  to control the light emitting operation. 
     Further, when the second light reception unit  122  receives the reflection light, the second light reception unit  122  outputs detection information including information about the time difference between the time of emitting the irradiation light and the time of receiving the reflection light. 
     The second light reception unit  122  can be implemented by the sensor optical system  44   b  illustrated in  FIG. 11  and the corresponding TOF sensor. 
     The third light reception unit  123  is a functional unit that receives the reflection light, which is the light reflected from an object when the irradiation light emitted from the third light emission unit  127  hits and reflects from the object, in accordance with the image capture signal received from the imaging control unit  131 . 
     Further, when the third light reception unit  123  receives the image capture signal from the imaging control unit  131 , the third light reception unit  123  outputs the light emission signal to the third light emission unit  127  to control the light emitting operation. 
     Further, when the third light reception unit  123  receives the reflection light, the third light reception unit  123  outputs detection information including information about the time difference between the time of emitting the irradiation light and the time of receiving the reflection light. 
     The third light reception unit  123  can be implemented by the sensor optical system  44   c  illustrated in  FIG. 11  and the corresponding TOF sensor. 
     The fourth light reception unit  124  is a functional unit that receives the reflection light, which is the light reflected from an object when the irradiation light emitted from the fourth light emission unit  128  hits and reflects from the object, in accordance with the image capture signal received from the imaging control unit  131 . 
     Further, when the fourth light reception unit  124  receives the image capture signal from the imaging control unit  131 , the fourth light reception unit  124  outputs the light emission signal to the fourth light emission unit  128  to control the light emitting operation. 
     Further, when the fourth light reception unit  124  receives the reflection light, the fourth light reception unit  124  outputs detection information including information about the time difference between the time of emitting the irradiation light and the time of receiving the reflection light. 
     The fourth light reception unit  124  can be implemented by the sensor optical system  44   d  illustrated in  FIG. 11  and the corresponding TOF sensor. 
     The first light emission unit  125  is a functional unit that projects the irradiation light emitted from the corresponding light source to the outside in accordance with the light emission signal received from the first light reception unit  121 . The first light emission unit  125  can be implemented by the light source optical system  42   a  illustrated in  FIG. 11  and the corresponding light source. 
     The second light emission unit  126  is a functional unit that projects the irradiation light emitted from the corresponding light source to the outside in accordance with the light emission signal received from the second light reception unit  122 . The second light emission unit  126  can be implemented by the light source optical system  42   b  illustrated in  FIG. 11  and the corresponding light source. 
     The third light emission unit  127  is a functional unit that projects the irradiation light emitted from the corresponding light source to the outside in accordance with the light emission signal received from the third light reception unit  123 . The third light emission unit  127  can be implemented by the light source optical system  42   c  illustrated in  FIG. 11  and the corresponding light source. 
     The fourth light emission unit  128  is a functional unit that projects the irradiation light emitted from the corresponding light source to the outside in accordance with the light emission signal received from the fourth light reception unit  124 . The fourth light emission unit  128  can be implemented by the light source optical system  42   d  illustrated in  FIG. 11  and the corresponding light source. 
     The imaging control unit  131  is a functional unit that controls the operations of the first light reception unit  121 , the second light reception unit  122 , the third light reception unit  123  and the fourth light reception unit  124 . 
     Specifically, the imaging control unit  131  transmits the image capture signals (operation signals) respectively to the first light reception unit  121 , the second light reception unit  122 , the third light reception unit  123  and the fourth light reception unit  124  while shifting the transmission timing of the image capture signals to control the imaging operations performed by the first light reception unit  121 , the second light reception unit  122 , the third light reception unit  123  and the fourth light reception unit  124  (i.e., light receiving operation, light emitting operations of the first light emission unit  125 , second light emission unit  126 , third light emission unit  127 , and fourth light emission unit  128 ) by shifting each of the imaging operations. 
     Further, the imaging control unit  131  receives the detection information from the first light reception unit  121 , the second light reception unit  122 , the third light reception unit  123 , and the fourth light reception unit  124 . 
     The imaging control unit  131  can be implemented by a control circuit corresponding to the control unit  21  illustrated in  FIG. 3 . 
     The range finding unit  132  is a functional unit that generates a distance image by converting the time information into a distance value for each pixel based on the detection information that the imaging control unit  131  has received from the first light reception unit  121 , the second light reception unit  122 , the third light reception unit  123 , and the fourth light reception unit  124 . The range finding unit  132  can be implemented by control circuit corresponding to the control unit  21  illustrated in  FIG. 3 . 
     Further, the first light reception unit  121 , the second light reception unit  122 , the third light reception unit  123 , the fourth light reception unit  124 , the first light emission unit  125 , the second light emission unit  126 , the third light emission unit  127 , the fourth light emission unit  128 , the imaging control unit  131  and the range finding unit  132  of the range finding device  1   c  are conceptually illustrated in  FIG. 13 , and the functional units are not limited thereto. That is, a plurality of functional units illustrated as separate functional units in the range finding device  1   c  of  FIG. 13  can be implemented as one functional unit. On the other hand, the function of one functional unit in the range finding device  1   c  of  FIG. 13  can be divided into a plurality of functions, and a plurality of functional units can be configured. 
     Further, the first light reception unit  121 , the second light reception unit  122 , the third light reception unit  123 , and the fourth light reception unit  124  output the detection information including the information about the time difference between the time of emitting the irradiation light and the time of receiving the reflection light, but is not limited thereto. That is, the first light reception unit  121 , the second light reception unit  122 , the third light reception unit  123 , and the fourth light reception unit  124  can be configured to calculate the distance based on information of the time difference between the time of emitting the irradiation light and the time of receiving the reflection light, and directly output the distance information as the detection information. 
     (Light Emission Timing of Light Emission Unit and Light Reception Timing of Light Reception Unit) 
       FIG. 14  illustrates an example of a timing chart of light emission timing when the light emission timings of all of the light sources included in the range finding device  1   c  are shifted. 
       FIG. 15  illustrates an example of a timing chart of light emission timings when the light emission timing of some of a plurality of light sources included in the range finding device  1   c  are set to the same timing. 
     Hereinafter, a description is given of an operation in a case when the light emission timings of the four light emission units (first light emission unit  125 , second light emission unit  126 , third light emission unit  127 , fourth light emission unit  128 ) are shifted with reference to  FIG. 14 . 
     As illustrated in  FIG. 14 , as to the range finding device  1   c , for example, the light-emission timing of the light emitted by the first light emission unit  125  (A side light-emission timing), the light-emission timing of the light emitted by the second light emission unit  126  (B side emitting timing), the light-emission timing of the light emitted by the third light emission unit  127  (C side light emission timing), and the light-emission timing of the light emitted by the fourth light emission unit  128  (D side light emission timing) are shifted so as not to overlap with each other. 
     Thus, the peak of power consumption waveform becomes different in each of the first light emission unit  125 , the second light emission unit  126 , the third light emission unit  127  and the fourth light emission unit  128  because the first light emission unit  125 , the second light emission unit  126 , the third light emission unit  127  and the fourth light emission unit  128  independently emit the light at the different timings, so that the peak of the power consumption waveform can become smaller. 
     In this case, the battery  22  can supply sufficient power even if the battery  22  is a mobile battery, and the light quantity of the irradiation light emitted from the first light emission unit  125 , the second light emission unit  126 , the third light emission unit  127  and the fourth light emission unit  128  become given sufficient levels, and the measurable distance can be set longer. 
     Further, if the A side light emission timing, the B side light emission timing, the C side emitting timing and the D side light emission timing are shifted, the first light reception unit  121 , the second light reception unit  122 , the third light reception unit  123  and the fourth light reception unit  124  can correctly determine whether the reflection light corresponds to which irradiation light emitted from the first light emission unit  125 , the second light emission unit  126 , the third light emission unit  127 , or the fourth light emission unit  128 , so that the range finding can be performed accurately, and thereby the range finding precision can be enhanced. 
     Further, the shifting of each light emission timing is not limited to one example case illustrated in  FIG. 14 . For example, if at least any two light emission timing does not overlap with each other, the shifting of each light emission timing can be satisfied. 
     In an example case illustrated in  FIG. 14 , all of the light emission timings are shifted, but is not limited thereto. For example, as illustrated in  FIG. 15 , the light emission timing on the A side and the light emission timing on the C side, which do not have an overlapping of the angle of views as illustrated in  FIG. 11  can be set to the same timing, and the light emission timing on the B side and the light emission timing on the D side, which do not have an overlapping of the angle of views as illustrated in  FIG. 11  can be set to the same timing. 
     In this configuration, since the angle of views of the irradiation light emitted from the different light sources at the same timing do not overlap with each other, the first light reception unit  121 , the second light reception unit  122 , the third light reception unit  123  and the fourth light reception unit  124  correctly determine whether the reflection light corresponds to which irradiation light emitted from the first light emission unit  125 , the second light emission unit  126 , the third light emission unit  127 , or the fourth light emission unit  128 , so that the range finding can be performed accurately, and thereby the range finding precision can be enhanced. 
     In the configuration of shifting some of the light emission timings (see  FIG. 15 ), although the peak of power consumption may become greater compared to the configuration of shifting all of the light emission timings (see  FIG. 14 ), the time period required for the imaging operation can be shortened. 
     Further, in the configuration of shifting some of the light emission timings (see  FIG. 15 ), the peak of power consumption can be reduced compared to the configuration setting all of the light emission timings at the same timing. 
     In the modification example 3, the configuration using four sets of the light source and the TOF sensor is described, but is not limited thereto. For example, if a configuration using five or more sets of the light source and the TOF sensor is provided, and the light sources having angle of views not overlapping with each other emit the light at the same timing, the above described effects can be obtained. 
     As to the above described embodiment and modification examples, the range finding device and the range finding method can reduce an increase in the peak power consumption even if a plurality of light sources used, and can improve the accuracy of range finding. 
     The respective functions (e.g., imaging control unit  111 , range finding unit  112 ) of the above-described embodiment and the modification examples can be implemented by one or more processing circuits. The processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), digital signal processor (DSP), field programmable gate array (FPGA), system on a chip (SOC), graphics processing unit (GPU), and conventional circuit components arranged to perform the recited functions. 
     Further, in the above-described embodiment and the modification examples, if at least one of the functional units of the range finding devices  1 , la,  1   b , and  1   c  is implemented executing one or more programs, the programs can provided by installing the programs on the ROM or the like in advance. 
     Further, in the above-described embodiment and the modification examples, the programs executed by the range finding devices  1 , la,  1   b , and  1   c  may be recorded and provided on a computer-readable recording medium, such as compact disk read only memory (CD-ROM), flexible disk (FD), compact disk-recordable (CD-R), and digital versatile disc (DVD). 
     Further, in the above-described embodiment and the modification examples, the programs executed by the range finding devices  1 , la,  1   b , and  1   c  can be provided by storing the programs in a computer connected to a network such as the Internet, and downloading the programs via the network. 
     Further, in the above-described embodiment and the modification examples, the programs executed by the range finding devices  1 , la,  1   b , and  1   c  can be provided or distributed via a network such as the Internet. 
     Further, in the above-described embodiment and the modification examples, the programs executed by the range finding devices  1 , la,  1   b , and  1   c  can be created using modules including at least any of the above-described functional units, and in the actual hardware, the CPU reads the programs from the storage device and executes the programs to load the above-described functional units on a main storage device. 
     Each of the functions of the above-described embodiments can be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), digital signal processor (DSP), field programmable gate array (FPGA), system on a chip (SOC), graphics processing unit (GPU), and conventional circuit components arranged to perform the recited functions. 
     Each of the embodiments described above is presented as an example, and it is not intended to limit the scope of the present disclosure. Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the disclosure of this specification can be practiced otherwise than as specifically described herein. Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above.