Patent Publication Number: US-2021181308-A1

Title: Optical distance measuring device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is the U.S. bypass application of International Application No. PCT/JP2019/030434 filed on Aug. 2, 2019 which designated the U.S. and claims priority to Japanese Patent Application No. 2018-150303 filed on Aug. 9, 2018, the contents of both of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an optical distance measuring device. 
     BACKGROUND 
     With regard to an optical distance measuring device, for example, JP 2015-78953 A describes a radar device in which reflected light of a laser beam emitted from a light source is detected on a light receiving surface on which a plurality of pixels are arranged in a two-dimensional matrix. The laser beam irradiation surface irradiated with the laser beam is formed in a rectangular shape, and a range of the light receiving surface irradiated with the reflected light also has a rectangular shape. This device prohibits operation of the pixels outside the light receiving range of the light receiving surface, thereby reducing the influence of erroneous detection of light. 
     SUMMARY 
     A first aspect of the present disclosure provides an optical distance measuring device. The optical distance measuring device includes: a light source unit that irradiates a measurement region with irradiation light; a light receiving unit that has a light receiving surface including a plurality of light receiving elements capable of receiving reflected light from a range including the measurement region corresponding to irradiation with the irradiation light and outputs a signal corresponding to a light receiving state of the reflected light for each of the light receiving elements; and a measurement unit that measures a distance to an object in the measurement region by using the signal outputted from the light receiving unit. The light receiving unit has a function of selecting a light receiving element that outputs the signal so that a light receiving position at which the reflected light is received is variable, and the light receiving unit changes the light receiving position to a plurality of positions with respect to a position of the reflected light. 
     A second aspect of the present disclosure provides an optical distance measuring device. The optical distance measuring device includes: a light receiving unit that has a light receiving surface including a plurality of light receiving elements capable of receiving reflected light from a measurement region and outputs a signal corresponding to a light receiving state of the reflected light for each of the light receiving elements; a light source unit that irradiates the measurement region with irradiation light while changing an irradiation azimuth so that the reflected light is moved on the light receiving surface, the irradiation azimuth being an azimuth in which the measurement region is irradiated with the irradiation light; and a measurement unit that measures a distance to an object in the measurement region by using the signal outputted from the light receiving unit. The light receiving unit receives the reflected light while moving a light receiving position toward a predetermined direction and the light receiving position is a position of a light receiving element that receives the reflected light, and the light source unit changes the irradiation azimuth to a plurality of azimuths for each single light receiving position at which the reflected light is received. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above features of the present disclosure will be made clearer by the following detailed description, given referring to the appended drawings. In the accompanying drawings: 
         FIG. 1  is a diagram showing a schematic configuration of an optical distance measuring device; 
         FIG. 2  is a diagram showing a configuration of the optical distance measuring device; 
         FIG. 3  is a diagram showing a relationship between a position of reflected light and a light receiving position on a light receiving surface; 
         FIG. 4  is a diagram showing a relationship between the position of the reflected light and the light receiving position; 
         FIG. 5  is a diagram showing a comparative example of the relationship between the position of the reflected light and the light receiving position; 
         FIG. 6  is a diagram showing an example of a histogram; 
         FIG. 7  is a diagram showing a configuration of an optical distance measuring device according to a second embodiment; 
         FIG. 8  is a diagram showing a change in amount of movement of the light receiving position according to temperature; 
         FIG. 9  is a diagram showing a relationship between the position of the reflected light and the light receiving position on the light receiving surface; 
         FIG. 10  is a diagram showing a relationship between the position of the reflected light and the light receiving position according to a third embodiment; 
         FIG. 11  is a diagram showing a configuration of an optical distance measuring device according to a fourth embodiment; 
         FIG. 12  is a diagram showing another configuration of the optical distance measuring device according to the fourth embodiment; 
         FIG. 13  is a diagram showing a configuration of an optical distance measuring device according to a fifth embodiment; and 
         FIG. 14  is a diagram showing a configuration of an optical distance measuring device according to a sixth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the optical distance measuring device described in JP 2015-78953 A, due to temperature characteristics of a lens, a holder, an adhesive, and the like used in the optical distance measuring device, there is a possibility that a light receiving position for the reflected light on the light receiving surface may change according to the surrounding temperature. In such a case, the reflected light may not be able to be appropriately received in the light receiving range, resulting in deterioration in distance measurement performance. 
     The present disclosure can be implemented as the following aspects. 
     A first aspect of the present disclosure provides an optical distance measuring device. The optical distance measuring device includes: a light source unit that irradiates a measurement region with irradiation light; a light receiving unit that has a light receiving surface including a plurality of light receiving elements capable of receiving reflected light from a range including the measurement region corresponding to irradiation with the irradiation light and outputs a signal corresponding to a light receiving state of the reflected light for each of the light receiving elements; and a measurement unit that measures a distance to an object in the measurement region by using the signal outputted from the light receiving unit. The light receiving unit has a function of selecting a light receiving element that outputs the signal so that a light receiving position at which the reflected light is received is variable, and the light receiving unit changes the light receiving position to a plurality of positions with respect to a position of the reflected light. 
     According to the optical distance measuring device of the first aspect, the light receiving position for the reflected light in the light receiving unit is changed to the plurality of positions, and accordingly, the reflected light is more likely to be appropriately received. Thus, when the light receiving position for the reflected light on the light receiving surface is changed according to the surrounding temperature, the distance measurement performance is less likely to be deteriorated. 
     A second aspect of the present disclosure provides an optical distance measuring device. The optical distance measuring device includes: a light receiving unit that has a light receiving surface including a plurality of light receiving elements capable of receiving reflected light from a measurement region and outputs a signal corresponding to a light receiving state of the reflected light for each of the light receiving elements; a light source unit that irradiates the measurement region with irradiation light while changing an irradiation azimuth so that the reflected light is moved on the light receiving surface, the irradiation azimuth being an azimuth in which the measurement region is irradiated with the irradiation light; and a measurement unit that measures a distance to an object in the measurement region by using the signal outputted from the light receiving unit. The light receiving unit receives the reflected light while moving alight receiving position toward a predetermined direction and the light receiving position is a position of a light receiving element that receives the reflected light, and the light source unit changes the irradiation azimuth to a plurality of azimuths for each single light receiving position at which the reflected light is received. 
     According to the optical distance measuring device of the second aspect, the azimuth in which the measurement region is irradiated with the irradiation light for each single light receiving position at which the reflected light is received is changed to the plurality of azimuths, and accordingly, the reflected light is more likely to be appropriately received. Thus, when the light receiving position for the reflected light on the light receiving surface is changed according to the surrounding temperature, the distance measurement performance is less likely to be deteriorated. 
     The present disclosure can also be implemented in various forms other than the optical distance measuring device. For example, the present disclosure can be implemented in forms such as an optical distance measuring method, a vehicle equipped with the optical distance measuring device, and a control method of controlling the optical distance measuring device. 
     Embodiment according to an optical distance measuring device will be described with reference to  FIG. 1  to  FIG. 14 . 
     A. First Embodiment 
     As shown in  FIG. 1 , an optical distance measuring device  10  as a first embodiment of the present disclosure includes a housing  15 , a light source unit  20 , a light receiving unit  30 , and a measurement unit  40 . The light source unit  20  and the light receiving unit  30  are fixed to the housing  15 , for example, with an adhesive. The light source unit  20  emits irradiation light IL to a measurement region MR. In the present embodiment, the light source unit  20  scans the irradiation light IL in a scanning direction SD. The irradiation light IL forms a rectangular shape whose longitudinal direction is a direction orthogonal to the scanning direction SD. The light receiving unit  30  receives reflected light from a range including the measurement region MR corresponding to irradiation with the irradiation light IL, and outputs a signal corresponding to a light receiving state of the reflected light. By using the signal outputted from the light receiving unit  30 , the measurement unit  40  measures a distance to an object that is present in the measurement region MR. The optical distance measuring device  10  is, for example, mounted on a vehicle and used to detect an obstacle and measure a distance to the obstacle. 
       FIG. 2  shows a more specific configuration of the optical distance measuring device  10 . As shown in  FIG. 2 , in addition to the light source unit  20 , the light receiving unit  30 , and the measurement unit  40  shown in  FIG. 1 , the optical distance measuring device  10  includes a control unit  50 . The control unit  50  is configured as a computer including a CPU and a memory, and controls the light source unit  20  and the light receiving unit  30 . 
     The light source unit  20  includes a laser light source  21  and a first scanning unit  22 . The laser light source  21  is composed of a semiconductor laser diode, and emits a pulse laser beam as irradiation light. The irradiation light emitted from the laser light source  21  is formed into the vertical irradiation light IL as shown in  FIG. 1  by an optical system (not shown). The first scanning unit  22  rotates a mirror  222  around a rotation axis  221  to perform a one-dimensional scanning of the irradiation light IL over the measurement region MR. The mirror  222  is composed of, for example, a MEMS mirror. The rotation of the mirror  222  is controlled by the control unit  50 . The first scanning unit  22  performs a one-dimensional scanning of the irradiation light IL, and thus, the light source unit  20  irradiates the measurement region MR with the irradiation light IL while changing an azimuth in which the measurement region MR is irradiated with the irradiation light IL. In the present embodiment, a light source of the light source unit  20  is a laser diode element  18 , but another light source such as a solid-state laser may be used. 
     Irradiation light emitted from the light source unit  20  is reflected by an object OB in the measurement region MR. The reflected light reflected by the object OB is received by the light receiving unit  30 . In the present embodiment, the light receiving unit  30  receives the reflected light through a light receiving lens configured so that the size of the reflected light on the light receiving surface  32  is smaller than the size of the light receiving surface  32 . Apart (e.g., apart at an end in the longitudinal direction) of the reflected light may be received by the light receiving unit  30  so as to protrude from the light receiving surface  32 . 
     As shown in  FIGS. 2 and 3 , the light receiving unit  30  includes a plurality of pixels  31  that are two-dimensionally arranged on the light receiving surface  32  that is irradiated with the reflected light. The pixel  31  is also referred to as “light receiving element”. The pixel  31  includes a plurality of light receiving devices capable of outputting a signal according to incidence of the reflected light from the object OB. In the present embodiment, the pixel  31  includes a SPAD (single photon avalanche diode) as the light receiving device. The pixel  31  includes, for example, 4 SPADs wide by 4 SPADs high, i.e., 16 SPADs in total. The light receiving surface  32  of the light receiving unit  30  is configured, for example, such that 64 pixels  31  are arranged in the longitudinal direction and 256 pixels  31  are arranged in the lateral direction. When light (photon) is inputted into the SPAD, with a certain probability, the SPAD outputs a pulse output signal indicating incidence of light. Thus, the pixel  31  outputs 0 to 16 pulse signals according to the intensity of the received light. 
     The light receiving unit  30  has a function of selecting a light receiving element that outputs a signal so that a light receiving position at which the reflected light is received is variable. Specifically, the light receiving unit  30  turns pixels  31  ON (active) in a column specified by the control unit  50 , and uses the active pixels  31  to receive the reflected light. In other words, the light receiving unit  30  turns the pixels  31  OFF (inactive) in the columns other than the column specified by the control unit  50 , and no reflected light is received by the inactive pixels  31 . The column of pixels  31  specified for light reception by the control unit  50  is referred to as “light receiving position”. Instead of turning ON/OFF the pixels  31  so that the light receiving position is variable, for example, the measurement unit  40  (described later) may select, from the signals outputted from the light receiving unit  30 , a signal to be used for distance measurement so that the light receiving position in the light receiving unit  30  is substantially variable. 
     In the present embodiment, as shown in  FIG. 3 , due to a scanning of the irradiation light IL in the scanning direction SD by the first scanning unit  22 , the vertical reflected light is moved in a predetermined direction on the light receiving surface  32 . The direction in which the reflected light is moved is hereinafter referred to as “first direction”. The fact that the reflected light is moved in the first direction indicates that the light source unit  20  irradiates the measurement region MR with the irradiation light IL while changing an azimuth in which the measurement region MR is irradiated with the irradiation light IL among a plurality of azimuths so that the reflected light is moved toward the first direction on the light receiving surface  32 . The “plurality of azimuths” refers to azimuths of the irradiation light IL corresponding to the light receiving positions on the light receiving surface  32 . 
     In the present embodiment, the light receiving unit  30  changes, to a plurality of positions in the first direction, the light receiving position at which the reflected light is received depending on the azimuth in which the measurement region MR is irradiated with the irradiation light IL. Specifically, the control unit  50  controls ON/OFF of the pixels  31  of the light receiving unit  30  to change the light receiving position so that while the reflected light is moved by a single column of pixels in the first direction, the light receiving position is moved forward column by column by three columns of pixels toward the first direction and then moved backward by two columns of pixels. That is, in the present embodiment, the light receiving unit  30  changes the light receiving position to a plurality of positions by moving the light receiving position toward the first direction. Furthermore, in the present embodiment, the light receiving unit  30  moves the light receiving position at a speed higher than a speed at which the reflected light is moved on the light receiving surface  32 . Furthermore, in the present embodiment, every time a light receiving process is completed for irradiation with the irradiation light IL in a single azimuth, the light receiving unit  30  moves the light receiving position in a direction opposite to the first direction. The light receiving process is a process of changing the light receiving position to a plurality of positions in order to receive the irradiation light IL from a single azimuth. Furthermore, in the present embodiment, when the light receiving process is completed, the light receiving unit  30  moves the light receiving position in the direction opposite to the first direction to move the light receiving position back to a position (position adjacent on the right to the left end in  FIG. 3 ) closer to the first direction side than the light receiving position (position at the left end in  FIG. 3 ) was when irradiation with the irradiation light in the previous azimuth is started. The change in the light receiving position in this manner is hereinafter referred to as “reciprocating movement” of the light receiving position. According to instructions from the control unit  50 , the light receiving unit  30  repeatedly performs a reciprocating movement of the light receiving position for each of the plurality of azimuths in which the measurement region MR is irradiated with the irradiation light IL. When the light receiving position is moved back and forth in this manner, the light receiving position can be changed to a plurality of positions according to the movement of the reflected light; thus, the reflected light is more likely to be received. The amount of movement (three columns of pixels) by which the light receiving position is moved in the first direction and the amount of movement (two columns of pixels) by which the light receiving position is moved backward in the direction opposite to the first direction are not limited to the amounts described above and may be set as appropriate. 
       FIG. 4  shows a graph of a relationship between the position of the reflected light and the light receiving position on the light receiving surface  32 . In the graph shown in  FIG. 4 , the horizontal axis represents a time at which distance measurement is performed by the measurement unit  40 , and the vertical axis represents the position of the reflected light and the light receiving position on the light receiving surface  32 . In order to measure the distance for a single frame indicating the entire measurement region MR, the measurement unit  40 , which will be described later in detail, performs distance measurement during a “distance measurement period” while the light receiving position and the azimuth of the irradiation light IL are changed. Then, during a “non-distance-measurement period”, the light receiving position and the azimuth of the irradiation light IL are moved back to the initial positions. That is, after the distance measurement for the “plurality of azimuths” described above is completed by the measurement unit  40 , during the non-distance-measurement period which is a period in which no distance measurement is performed, the light receiving unit  30  moves the light receiving position back to the initial position. 
     As shown in  FIG. 4 , in the present embodiment, during the distance measurement period, while the position of the reflected light is linearly changed with time, the light receiving position is moved back and forth by being moved forward and backward in the first direction on the light receiving surface  32  to be gradually moved toward the first direction. In  FIG. 4 , a position at which a polygonal line representing the position of the reflected light intersects a polygonal line representing the light receiving position indicates the light receiving position at which the reflected light is received. In the present embodiment, the light receiving position is moved back and forth; thus, not only when the reflected light is received at a normal position as shown in the upper portion in  FIG. 4 , but also when a position on the light receiving surface  32  irradiated with the reflected light is deviated from the normal position as shown in the lower portion in  FIG. 4 , the reflected light can be appropriately received at any of the positions between which the light receiving position is moved back and forth. On the other hand, as shown in  FIG. 5 , if the light receiving position is not moved back and forth, when a position on the light receiving surface  32  irradiated with the reflected light is deviated from the normal position as shown in the lower portion in  FIG. 5 , there is a possibility that the position irradiated with the reflected light does not match the light receiving position and the reflected light cannot be appropriately received. 
     Next, the measurement unit  40  shown in  FIG. 2  will be described. The measurement unit  40  includes an addition unit  41 , a histogram generation unit  42 , a peak detection unit  43 , and a distance calculation unit  44 . These units are configured as, for example, one or more integrated circuits. The units may be functional units that are implemented by software through execution of a program by a CPU. 
     The addition unit  41  is a circuit that adds up, for each of the pixels  31  included in the light receiving position, the number of pulse signals outputted from the pixel  31  to obtain an addition value. More specifically, the addition unit  41  obtains an addition value for each of the pixels  31  by counting the number of pulse signals outputted substantially at the same time from the plurality of SPADs included in the pixel  31 . In the present embodiment, as shown in  FIG. 3 , every time the reflected light is moved by a single pixel in the first direction on the light receiving surface  32 , the light receiving position is moved by three pixels in the first direction. Thus, the addition unit  41  adds up addition values for the three pixels by which the light receiving position is moved, and outputs the obtained value. 
     The histogram generation unit  42  is a circuit that generates a histogram for each of the pixels  31  on the basis of the addition value outputted from the addition unit  41 .  FIG. 6  shows an example of the histogram. The class (horizontal axis) of the histogram represents time of flight of light from emission of the irradiation light IL to reception of the reflected light by the pixel  31 . Hereinafter, the time is referred to as TOF (Time Of Flight). On the other hand, the frequency (vertical axis) of the histogram represents the addition value calculated by the addition unit  41 , and indicates the intensity of light reflected by the object OB. The histogram generation unit  42  generates a histogram by recording the addition value outputted from the addition unit  41  for each TOF according to a predetermined recording timing signal. When the object OB is present in the measurement region MR, light is reflected by the object OB, and the addition value is recorded in the class of TOF corresponding to the distance to the object OB. 
     The peak detection unit  43  is a circuit that detects a peak in the histogram. The peak detection unit  43  determines, as the peak, a part of the histogram with the highest frequency. The peak in the histogram indicates that the object OB is present at a position (distance) corresponding to TOF at the peak. 
     The distance calculation unit  44  is a circuit that obtains a distance value D from TOF corresponding to the peak detected by the peak detection unit  43 . The distance calculation unit  44  calculates the distance value D by the following equation (1), where “At” represents TOF corresponding to the peak, “c” represents the speed of light, and “D” represents the distance value. The distance calculation unit  44  calculates the distance value D for all the histograms, i.e., for all the pixels  31 . 
         D =( c×Δt )/2  Equation (1)
 
     The distance value D measured by the measurement unit  40  is outputted from the optical distance measuring device  10  to an ECU of the vehicle or the like. The ECU of the vehicle can detect an obstacle in the measurement region MR and measure a distance to the obstacle by using the distance value for each of the pixels  31  that is acquired from the optical distance measuring device  10 . 
     According to the optical distance measuring device  10  of the present embodiment described above, even when the positions at which the light source unit  20  and the light receiving unit  30  are assembled to the housing  15  change according to the surrounding temperature due to the temperature characteristics of the adhesive with which these units are fixed to the housing  15  and thus the position of the reflected light on the light receiving surface  32  is deviated from the normal position, the light receiving position for the reflected light on the light receiving surface  32  depending on the azimuth in which the measurement region MR is irradiated with the irradiation light IL is changed to a plurality of positions, and accordingly, the reflected light is more likely to be appropriately received. Thus, when the light receiving position for the reflected light on the light receiving surface  32  is changed according to the surrounding temperature, the distance measurement performance is less likely to be deteriorated. 
     According to the present embodiment, the reflected light is more likely to be received without an increase in area of the light receiving position; thus, a smaller number of pixels  31  are required to be active at a time. This can reduce power consumption of the light receiving unit  30 , and disturbance light is less likely to be incident on the light receiving position. Furthermore, in the present embodiment, the light receiving position is only simply moved in the first direction, leading to an improvement in the distance measurement performance, for example, without performing complicated control such as searching for a light receiving position with the highest intensity on the basis of the intensity of the reflected light. 
     B. Second Embodiment 
     As shown in  FIG. 7 , an optical distance measuring device  10   b  of a second embodiment includes a sensor  60 . The sensor  60  includes a temperature sensor and a humidity sensor. In the present embodiment, according to the temperature or humidity around the optical distance measuring device  10   b  that is measured by the sensor  60 , the control unit  50  changes the number of positions to which the light receiving position is changed depending on the azimuth in which the irradiation light is moved. Specifically, as shown in  FIG. 8 , the control unit  50  sets the amount of movement of the light receiving position to be larger as the temperature is higher or the humidity is higher. Setting the amount of movement of the light receiving position to be larger indicates that the amount of movement of the light receiving position is increased by causing the light receiving position to be moved a larger distance in the first direction while the irradiation light is moved for a single azimuth on the light receiving surface  32 . Thus, when the amount of movement of the light receiving position is increased, even if variation in the position irradiated with the reflected light on the light receiving surface  32  is increased, the reflected light is more likely to be appropriately received. The sensor  60  may include only one of the temperature sensor and the humidity sensor. The present embodiment is also applicable to other embodiments described later. 
     C. Third Embodiment 
     In the first embodiment, the reflected light is more likely to be received by moving the light receiving position for the reflected light back and forth as shown in  FIG. 3  while the irradiation light IL is scanned in the scanning direction SD. On the other hand, in the third embodiment, the light receiving unit  30  receives the reflected light while moving the light receiving position at which the reflected light is received toward the first direction, and the light source unit  20  changes, to a plurality of azimuths, the azimuth in which the measurement region MR is irradiated with the irradiation light IL for each single light receiving position. 
     Specifically, in the present embodiment, as shown in  FIG. 9 , the control unit  50  controls the light receiving unit  30  to move the light receiving position by a single column of pixels in the first direction. The control unit  50  changes the azimuth in which the measurement region MR is irradiated with the irradiation light so that while the light receiving position is moved by a single column of pixels, the reflected light is moved column by column by three columns of pixels in the first direction on the light receiving surface  32  and then moved backward by two columns of pixels in the direction opposite to the first direction. Thus, as shown in  FIG. 10 , the reflected light is gradually moved toward the first direction while being moved back and forth on the light receiving surface  32 . 
     In the present embodiment, the azimuth of the irradiation light IL is changed so that the reflected light is moved on the light receiving surface  32  at a speed higher than the speed at which the light receiving position is moved. Furthermore, in the present embodiment, every time reception of light at a single light receiving position is completed, the light source unit  20  changes the azimuth in which the measurement region MR is irradiated with the irradiation light IL to a direction opposite to the scanning direction SD. Then, the light source unit  20  moves the azimuth back to a position closer to the scanning direction SD side than the azimuth was before the change. 
     In the present embodiment, every time the light receiving position is moved by a single pixel in the first direction, the reflected light is moved by three pixels in the first direction. Thus, during distance measurement, the addition unit  41  of the measurement unit  40  adds up addition values for the number of times (three times) in which the reflected light is moved while the light receiving position is moved by a single pixel in the first direction. 
     According to the third embodiment described above, the azimuth in which the measurement region MR is irradiated with the irradiation light IL for each single light receiving position at which the reflected light is received is changed to the plurality of azimuths, and accordingly, the reflected light is more likely to be appropriately received. Thus, as in the first embodiment, when the light receiving position for the reflected light on the light receiving surface  32  is changed according to the surrounding temperature, the distance measurement performance is less likely to be deteriorated. Furthermore, in the present embodiment, the reflected light is more likely to be received by changing the azimuth of the irradiation light IL without increasing the width of the range irradiated with the irradiation light IL. This can prevent a reduction in SN ratio of the reflected light received by the light receiving unit  30 . 
     Note that also in the present embodiment, as in the second embodiment, the control unit  50  may change the amount of reciprocating movement of the irradiation light according to the temperature or humidity measured by the sensor  60 . 
     D. Fourth Embodiment 
     In the optical distance measuring device  10  of the first embodiment, the irradiation light emitted from the laser light source  21  is scanned by the first scanning unit  22 , and the reflected light of the irradiation light is received by the light receiving unit  30 . On the other hand, in an optical distance measuring device  10   d  of a fourth embodiment shown in  FIG. 11 , the irradiation light emitted from the laser light source  21  is scanned by the first scanning unit  22 , and the reflected light of the irradiation light is further scanned by a second scanning unit  33  and is received by a light receiving unit  30   d . The second scanning unit  33  includes a rotation axis  331  and a mirror  332  that is rotated on the rotation axis  331 . The rotation of the mirror  332  is controlled by the control unit  50 . 
     In the present embodiment, as in the first embodiment, the first scanning unit  22  changes the direction in which the measurement region MR is irradiated with the irradiation light toward the scanning direction SD (see  FIG. 1 ). The reflected light of the irradiation light scanned in this manner is scanned by the second scanning unit  33 , and an image is formed on the light receiving surface  32  by the second scanning unit  33  so that the reflected light is received at a predetermined position on the light receiving surface  32  of the light receiving unit  30   d . Specifically, the second scanning unit  33  scans the reflected light reflected from the measurement region MR so that the same position on the light receiving surface  32  is irradiated with the reflected light. Thus, in the present embodiment, the reflected light is not moved on the light receiving surface  32 , and accordingly, fewer columns of pixels  31  are required for the light receiving unit  30   d . In the present embodiment, the light receiving surface  32  has a width of three columns of pixels. 
     In the present embodiment, while the direction in which the measurement region MR is irradiated with the irradiation light IL is moved for a single azimuth, the control unit  50  controls the light receiving unit  30   d  to move the light receiving position in a range of three columns of pixels in the first direction. Then, every time irradiation with the irradiation light IL in a single azimuth is ended, the light receiving position is moved back to the initial position. By controlling the second scanning unit  33  and the light receiving unit  30   d  as described above, also in the present embodiment, as in the first embodiment, the reflected light is more likely to be appropriately received. 
     In the present embodiment, the first scanning unit  22  and the second scanning unit  33  may be integrally formed. Specifically, the rotation axis  221  and the rotation axis  331  may have the same axis and the mirror  222  and the mirror  332  may be integrated with each other. In such an optical distance measuring device, for example, the irradiation light IL emitted from the laser light source  21  is scanned over the measurement region MR by being reflected by the rotating mirror, and the reflected light reflected from the measurement region MR is guided to the light receiving surface  32  through an optical path that is composed of the mirror and another optical component. 
     As shown in  FIG. 12 , as in the second embodiment, the optical distance measuring device  10   d  of the present embodiment may include the sensor  60 . Then, the number of positions to which the light receiving position is changed depending on the azimuth in which the irradiation light IL is moved may be changed according to the temperature or humidity around the optical distance measuring device  10   d  that is measured by the sensor  60 . 
     E. Fifth Embodiment 
     In the first embodiment, the light source unit  20  uses the first scanning unit  22  to scan the irradiation light IL in the scanning direction SD. On the other hand, in an optical distance measuring device  10   e  of a fifth embodiment shown in  FIG. 13 , a light source unit  20   e  is configured as a light emitting array in which vertically oriented light emitting units are coupled in the lateral direction. The control unit  50  sequentially turns on the light emitting units in the scanning direction SD to change the azimuth in which the measurement region MR is irradiated with the irradiation light. According to such a configuration, as in the first embodiment, the reflected light is more likely to be appropriately received. 
     F. Sixth Embodiment 
     In an optical distance measuring device  10   f  of a sixth embodiment shown in  FIG. 14 , as in the fifth embodiment, a light source unit  20   f  is configured as a light emitting array. Furthermore, as in the fourth embodiment, the reflected light is scanned by the second scanning unit  33  and is received by a light receiving unit  30   f . According to such a configuration, as in the first embodiment, the reflected light is more likely to be appropriately received. 
     As described above, in the fourth embodiment and the sixth embodiment, the reflected light is not moved on the light receiving surface  32 ; thus, the direction of movement of the light receiving position in the light receiving unit  30  is not limited to the first direction. For example, the light receiving position may be moved in the direction opposite to the first direction. Alternatively, the light receiving position may be sequentially changed leftward or rightward from a center of the light receiving surface  32 . Alternatively, the light receiving position may be randomly changed so that the light receiving positions are not overlapped with each other. 
     In the fourth embodiment and the sixth embodiment, since the reflected light is not moved on the light receiving surface  32 , the size of the reflected light with respect to the light receiving surface  32  may be smaller than the light receiving surface  32  or substantially equal to the light receiving surface  32 . When the light receiving surface  32  is irradiated with at least part of the reflected light, the reflected light can be appropriately received by moving the light receiving position. 
     G. Other Embodiments 
     (G-1) In the above embodiments, the light receiving position in the light receiving unit  30  at which the reflected light is received has a width of a single column of pixels. However, the light receiving position may have a width of two columns of pixels or more. In this case, the light receiving unit  30  may move the light receiving position so that the light receiving positions are not overlapped with each other or may move the light receiving position so that the light receiving positions are spaced apart from each other. The light receiving unit  30  may move the light receiving position so that the light receiving positions are partially overlapped with each other or may move the light receiving position while changing the width of the light receiving position. Furthermore, the range of the light receiving surface  32  that is irradiated with the reflected light may not necessarily have a width of a single column of pixels and may have a width of two columns of pixels or more. 
     (G-2) In the above embodiments, the light receiving unit  30  moves the light receiving position toward the direction (first direction) in which the reflected light is moved on the light receiving surface  32 . However, the light receiving unit  30  may move the light receiving position toward the direction opposite to the first direction depending on the azimuth in which the measurement region MR is irradiated with the irradiation light IL. In this case, the light receiving unit  30  may move the light receiving position at a speed lower than the speed at which the reflected light is moved on the light receiving surface  32 . Furthermore, in this case, the light receiving unit  30  may move the light receiving position in the first direction every time irradiation with the irradiation light IL in a single azimuth is completed. Furthermore, in this case, the light receiving unit  30  may move the light receiving position in the first direction so that the light receiving position is moved back to a position closer to the first direction side than the light receiving position was before the movement. 
     (G-3) In the above embodiments, as shown in  FIG. 1 , the light source unit  20  scans the irradiation light IL in a single direction (scanning direction SD). However, the light source unit  20  may perform a back-and-forth scanning of the irradiation light IL in the scanning direction SD and the direction opposite to the scanning direction SD. In this case, when the reflected light is moved forward, the light receiving position is moved as in the first embodiment, and when the reflected light is moved backward, the light receiving position is moved in a direction opposite to the direction in the first embodiment. In this case, the non-distance-measurement period shown in  FIG. 4  is not present, and the process of moving the light receiving position for the reflected light back to the initial position becomes unnecessary. 
     (G-4) In the above embodiments, the addition unit  41  of the measurement unit  40  adds up the addition values for the number of pixels by which the light receiving position is moved (in the fourth embodiment, the number of pixels by which the reflected light is moved). However, for example, the addition unit  41  may average the addition values instead of adding up the addition values. The addition unit  41  may select the largest addition value. Alternatively, the addition unit  41  may calculate an SN ratio of each addition value and add up, average, or select only the addition values with an SN ratio of a specified value or more. The addition unit  41  may add up, average, or select only the addition values with higher SN ratios. 
     (G-5) The above embodiments show an example in which the irradiation light IL and the light receiving position are scanned in a single direction. However, the scanning method is not limited to the one-dimensional scanning. For example, the irradiation light may be scanned in two directions which are the lateral direction and the longitudinal direction, and the irradiation light may be moved in two directions which are the lateral direction and the longitudinal direction on the light receiving surface  32 . In this case, the control unit  50  moves the light receiving position according to the direction of the movement of the reflected light. Even in this case, by moving the light receiving position or the azimuth of the irradiation light back and forth, as in the above embodiments, the reflected light is more likely to be received. 
     (G-6) In the above embodiments, the pixel  31  of the light receiving unit  30  is composed of a SPAD. However, the pixel  31  may be composed of alight receiving device other than the SPAD, such as a pin photodiode or an avalanche photodiode. In this case, when the light receiving device can output a signal at a level corresponding to the intensity of the received reflected light, the distance can be measured by using the level of the signal without forming a histogram. 
     (G-7) The optical distance measuring device as an embodiment of the present invention only needs to be able to change a light receiving position for reflected light from an object to a plurality of positions, and it is not essential for the optical distance measuring device to change an azimuth of the irradiation light. 
     The present disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from the scope of the present disclosure. For example, in order to solve some or all of the problems described above or to achieve some or all of the effects described above, replacement or combination may be performed as appropriate in the technical features in the embodiments. Unless the technical features are described as essential in the present specification, the technical features may be omitted as appropriate.