Patent Publication Number: US-2023152468-A1

Title: Ranging device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is the U.S. bypass application of International Application No. PCT/JP2021/026134 filed on Jul. 12, 2021 which designated the U.S. and claims priority to Japanese Patent Application No. 2020-125659 filed on Jul. 22, 2020, the contents of both of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a ranging device. 
     BACKGROUND 
     LIDAR devices are known that measure distances to objects based on reflected light of laser light. A LIDAR device performs ranging processing that scans a predetermined ranging area with emitted laser light by rotating or oscillating a deflection member to change the emission azimuth of the laser light, and measures a distance to an object located in the emission azimuth based on reflected light received from the same azimuth as the emission azimuth. 
     SUMMARY 
     An aspect of the present disclosure is a ranging device including a plurality of ranging units and a control unit. The control unit is configured to control the ranging units. Each of the ranging units includes a deflection member that deflects laser light and is configured to perform ranging processing that scans a predetermined ranging area with emitted laser light by rotating or oscillating the deflection member to change the emission azimuth of the laser light, and measures a distance to an object located in the emission azimuth based on reflected light received from the same azimuth as the emission azimuth. The plurality of ranging units include a first ranging unit and a second ranging unit with the ranging areas overlapping with each other. The control unit causes the first ranging unit to perform the ranging processing and the second ranging unit to perform ranging processing in parallel with each other in a manner to prevent a first passage area traveled by laser light emitted by the first ranging unit and a second passage area traveled by laser light emitted by the second ranging unit from interfering with each other in the ranging areas. 
    
    
     
       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 the arrangement of ranging units on a vehicle; 
         FIG.  2    is a block diagram showing the configuration of a ranging device; 
         FIG.  3    is a schematic perspective view showing the configuration of a ranging unit; 
         FIG.  4    is a diagram showing periodic changes in the rotation angle of a deflection member; 
         FIG.  5    is a diagram showing rotational movement directions of the deflection member; 
         FIG.  6    is a diagram showing a state in which the passage areas of laser light emitted from a plurality of ranging units interfere with each other within ranging areas; 
         FIG.  7    is a diagram showing a state with the boundary surface of an object being within the area in which the passage areas of laser light emitted from the ranging units interfere with each other; 
         FIG.  8    is a diagram showing a state in which one ranging unit has received reflected light of laser light emitted from another ranging unit; 
         FIG.  9    is a diagram showing the ranging areas of two ranging units; 
         FIG.  10    is a diagram showing conditions concerning the timing of start according to the positional relationship of two ranging units; 
         FIG.  11    is a diagram showing the positional relationship of ranging units in a first arrangement example; 
         FIG.  12    is a diagram showing changes in the rotation angles of the deflection members of the ranging units in the first arrangement example; 
         FIG.  13    is a diagram showing changes in the rotation angles of the deflection members of the ranging units in another example of the first arrangement example; 
         FIG.  14    is a diagram showing the positional relationship of ranging units in a second arrangement example; 
         FIG.  15    is a diagram showing changes in the rotation angles of the deflection members of the ranging units in the second arrangement example; 
         FIG.  16    is a diagram showing the positional relationship of ranging units in a third arrangement example; 
         FIG.  17    is a diagram showing changes in the rotation angles of the deflection members of the ranging units in the third arrangement example; 
         FIG.  18    is a diagram showing the positional relationship of ranging units in another example of the third arrangement example; 
         FIG.  19    is a diagram showing changes in the rotation angles of the deflection members of the ranging units in the other example of the third arrangement example; 
         FIG.  20    is a diagram showing the positional relationship of ranging units in a fourth arrangement example; 
         FIG.  21    is a diagram showing changes in the rotation angles of the deflection members of the ranging units in the fourth arrangement example; 
         FIG.  22    is a diagram showing the positional relationship of ranging units in another example of the fourth arrangement example; 
         FIG.  23    is a diagram showing changes in the rotation angles of the deflection members of the ranging units in the other example of the fourth arrangement example; 
         FIG.  24    is a diagram showing the positional relationship of ranging units in a fifth arrangement example; 
         FIG.  25    is a diagram showing changes in the rotation angles of the deflection members of the ranging units in the fifth arrangement example; 
         FIG.  26    is a diagram showing the positional relationship of ranging units in a sixth arrangement example; 
         FIG.  27    is a diagram showing changes in the rotation angles of the deflection members of the ranging units in the sixth arrangement example; 
         FIG.  28    is a diagram showing the positional relationship of ranging units in another example of the sixth arrangement example; 
         FIG.  29    is a diagram showing changes in the rotation angles of the deflection members of the ranging units in the other example of the sixth arrangement example; 
         FIG.  30    is a diagram showing changes in current in the case where a plurality of ranging units scan synchronously; 
         FIG.  31    is a diagram showing changes in current in the case where a plurality of ranging units scan asynchronously; 
         FIG.  32    is a diagram showing changes in the rotation angles of the deflection members of ranging units according to a second embodiment; 
         FIG.  33    is a diagram showing ranging units aligned with the rotation axis of the deflection members; 
         FIG.  34    is a diagram showing changes in the rotation angles of the deflection members of ranging units with sinusoidal waveforms; 
         FIG.  35    is a diagram showing changes in the rotation angles of the deflection members of ranging units with waveforms different from each other; and 
         FIG.  36    is a diagram showing changes in the rotation angles of the deflection members of ranging units with aperiodic rotational movements. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     US2019/0011544 A describes a technique that uses a LIDAR device mounted on a vehicle to measure a distance to an object in the environment surrounding the vehicle. 
     When multiple ranging units that perform ranging processing are arranged in such a way that their ranging areas overlap each other, every object in a wide area may be detected. 
     However, detailed research carried out by the present inventors has revealed that when laser light emitted from one of the multiple ranging units is reflected by an object in an overlapping ranging area and received by another ranging unit, the distance to the object may be measured erroneously. 
     One aspect of the present disclosure provides a technique that prevents a plurality of ranging units having overlapping ranging areas from erroneously measuring a distance to an object. 
     An aspect of the present disclosure is a ranging device including a plurality of ranging units and a control unit. The control unit is configured to control the ranging units. Each of the ranging units includes a deflection member that deflects laser light and is configured to perform ranging processing that scans a predetermined ranging area with emitted laser light by rotating or oscillating the deflection member to change the emission azimuth of the laser light, and measures a distance to an object located in the emission azimuth based on reflected light received from the same azimuth as the emission azimuth. The plurality of ranging units include a first ranging unit and a second ranging unit with the ranging areas overlapping with each other. The control unit causes the first ranging unit to perform the ranging processing and the second ranging unit to perform ranging processing in parallel with each other in a manner to prevent a first passage area traveled by laser light emitted by the first ranging unit and a second passage area traveled by laser light emitted by the second ranging unit from interfering with each other in the ranging areas. 
     The technique according to the aspect can prevent a plurality of ranging units having overlapping ranging areas from erroneously measuring a distance to an object. 
     Exemplary embodiments of the present disclosure will now be described with reference to the drawings. 
     1. First Embodiment 
     [1-1. Whole Configuration] 
     As shown in  FIGS.  1  and  2   , a ranging device  1  according to the present embodiment is mounted on a vehicle  100 . The ranging device  1  is a device that measures a distance to a forward object in the environment surrounding the vehicle  100 . The ranging device  1  includes a control unit  20  and three ranging units, or specifically, a right ranging unit  10 R, a front ranging unit  10 F, and a left ranging unit  10 L. 
     Each of the right ranging unit  10 R, the front ranging unit  10 F, and the left ranging unit  10 L is configured to perform ranging processing. The ranging processing is processing that scans a predetermined ranging area with emitted laser light by rotating or oscillating a deflection member  13  described later to change the emission azimuth of the laser light, and measures a distance to an object located in the emission azimuth based on reflected light received from the same azimuth as the emission azimuth. 
     The ranging area is an object detection range defined in design. The ranging area is determined by, for example, an angular range scanned with laser light during a ranging period and the longest distance that allows object detection. 
     The right ranging unit  10 R is designed to scan a forward ranging area on the right of the vehicle  100  with laser light. The front ranging unit  10 F is designed to scan a forward ranging area in front of the vehicle  100  with laser light. The left ranging unit  10 L is designed to scan a forward ranging area on the left of the vehicle  100  with laser light. Each ranging unit is arranged in such a way that the ranging area overlaps with the ranging area of the adjacent ranging unit. In the present embodiment, the right ranging unit  10 R and the left ranging unit  10 L are arranged with their ranging areas overlapping with the ranging area of the front ranging unit  10 F. [1-2. Configuration of Ranging Unit] 
     The right ranging unit  10 R, the front ranging unit  10 F, and the left ranging unit  10 L have the same basic configuration. The configuration of each ranging unit will now be described with reference to  FIG.  3   . 
     Each ranging unit includes a projector  11 , a drive  12 , the deflection member  13 , and a light receiver  14 . 
     The projector  11  is a light source that emits laser light. The laser light in the present embodiment is pulsed laser light. The projector  11  is designed to emit laser light to the deflection member  13  in accordance with an instruction from the control unit  20 . 
     The drive  12  is an actuator that rotates or swings the deflection member  13 . The drive  12  includes a rod-shaped shaft  12   a  and rotates or swings the shaft  12   a . In the present embodiment, the drive  12  is a motor that swings the shaft  12   a . The rotation timing, the rotational movement direction, and the angular velocity of the shaft  12   a  are controlled by the control unit  20 . 
     The deflection member  13  is a deflector that deflects laser light. In the present embodiment, the deflection member  13  is a mirror. The deflection member  13  is fixed to the shaft  12   a  of the drive  12  and swings together with the shaft  12   a . When the deflection member  13  swings, laser light emitted from the projector  11  is deflected by the deflection member  13  depending on its rotation angle, and the ranging area is scanned. The scanning laser light is reflected by an object in the ranging area, and the reflected light is deflected by the deflection member  13  depending on its rotation angle and received by the light receiver  14 . 
     The light receiver  14  is a sensor that receives laser light. The light receiver  14  is installed at a position on which the reflected light is incident. The reflected light comes from the same azimuth as the emission azimuth of the scanning laser light directed by the deflection member  13 , and is deflected by the deflection member  13  and received. The light receiver  14  converts the received laser light into an electrical signal and outputs the signal to the control unit  20 . 
     [1-3. Configuration of Control Unit] 
     The control unit  20  shown in  FIG.  2    is an electronic controller that is mainly a well-known microcomputer including a CPU, a ROM, and a RAM (not shown). The CPU executes programs stored in the ROM, which is a non-transitory tangible recording medium. The execution of the programs implements the methods corresponding to the programs. The control unit  20  may include a single microcomputer or multiple microcomputers. The functions of the control unit  20  may not be implemented by software. Some or all of the functions may be implemented by one or more pieces of hardware. For example, for the functions implemented by an electronic circuit, which is a piece of hardware, the electronic circuit may be a digital circuit, an analog circuit, or a combination of these circuits. 
     The control unit  20  controls the right ranging unit  10 R, the front ranging unit  10 F, and the left ranging unit  10 L and measures a distance to an object in the environment surrounding the vehicle  100 . In  FIG.  4   , the horizontal axis represents time, and the vertical axis represents the rotation angle of the deflection member  13 , with the middle of the swing angular range of the deflection member  13  defined as 0. The cycle in which the deflection member  13  swings is the cycle in which each ranging unit performs distance measurement. Hereinafter, the cycle in which distance measurement is performed is also referred to as the ranging cycle. In the ranging cycle, the period during which distance measurement is performed is also referred to as the ranging period, and the period during which no distance measurement is performed is also referred to as the non-ranging period. In the present embodiment, to increase the proportion of the ranging period in the ranging cycle, the ranging unit is controlled in such a way that the angular velocity of the deflection member  13  during the non-ranging period is higher than the angular velocity of the deflection member  13  during the ranging period. The angular velocity of the deflection member  13  during the ranging period is also referred to as the ranging angular velocity. In  FIG.  5   , the deflection member  13  during the ranging period has a rotational movement direction R1, and the deflection member  13  during the non-ranging period has a rotational movement direction R2, with these directions indicated by arrows. In the example in  FIG.  5   , the ranging unit scans with laser light in a direction from left to right in  FIG.  5   . In the present embodiment, for the sake of simplicity, the whole period during which the deflection member  13  rotates in the rotational movement direction R1 is considered as the ranging period. Hereinafter, the direction in which the ranging unit scans with laser light is also referred to as the scanning direction. 
     In the present embodiment, the control unit  20  causes each ranging unit to perform ranging processing in the same scanning direction, in the same ranging cycle, and with the same ranging angular velocity. That is, each ranging unit performs ranging processing by cyclically scanning with laser light in a specific direction at a predetermined angular velocity. Specifically, the deflection member  13  swings in certain cycles, and during the period when the deflection member  13  moves in the specific direction in a rotational manner, the projector  11  emits laser light to the deflection member  13 . In other words, during the period when the deflection member  13  moves in a direction opposite the specific direction in a rotational manner, the projector  11  emits no laser light to the deflection member  13 . 
     [1-4. Mechanism for Preventing Erroneous Measurement Caused by Overlapping Ranging Areas] 
     As described above, the ranging units are arranged with their ranging areas overlapping with one another. This arrangement is intended to eliminate blind spots and enable every object to be detected. However, when laser light emitted by one of the ranging units is reflected by an object in the part of the ranging area overlapping with the ranging area of another ranging unit, the arrangement may cause erroneous measurement of the distance to the object. 
     The present inventors have found that the satisfaction of the following three conditions causes erroneous measurement. 
     First condition: as illustrated in  FIG.  1   , the ranging areas of a plurality of ranging units at least partly overlap with each other. 
     Second condition: the passage areas of laser light emitted from a plurality of ranging units interfere with each other within the ranging areas. In the example shown in  FIG.  6   , the passage area of laser light emitted from the right ranging unit  10 R interferes with the passage area of laser light emitted from the front ranging unit  10 F within the ranging areas (not shown). 
     Third condition: an object boundary surface is within the area of interference between the passage areas of emitted laser light. In the example shown in  FIG.  7   , an object boundary surface C is within the area of interference between the passage area of laser light emitted from the right ranging unit  10 R and the passage area of laser light emitted from the front ranging unit  10 F. In  FIG.  7   , the laser light passage areas are indicated by lines for the sake of simplicity. 
     The passage area of laser light emitted by a ranging unit is an area extending along the emission azimuth of the laser light, and emitted laser light passes through the area. That is, the passage area of laser light emitted by a ranging unit is an area having the same width of the laser light. For example, when emitted light is pulsed laser light, the area is determined during not only the ON period of pulse wave but also the OFF period. 
     With the above three conditions combined, when laser light emitted by one of the ranging units is reflected by an object in the part of the ranging area overlapping with the ranging area of another ranging unit, the other ranging unit may receive the reflected laser light. For example,  FIG.  8    shows the waveform of laser light received by the front ranging unit  10 F. In  FIG.  8   , the horizontal axis represents time, with the point in time of laser light emission by the front ranging unit  10 F defined as 0, and the vertical axis represents the intensity of received light. In this example, the reflected light of laser light emitted by the right ranging unit  10 R is received by the front ranging unit  10 F earlier. Thus, a waveform W F  of the reflected light of laser light emitted by the front ranging unit  10 F is detected after a waveform W R  of the reflected light of laser light emitted by the right ranging unit  10 R. The distance to an object is measured by the difference between the time of laser light emission and the time of reflected light reception, and thus the front ranging unit  10 F in this case will erroneously measure the distance to the object. 
     Among the above three conditions, the first condition is nearly inevitable because of the design. In addition, the third condition is due to an external cause and cannot be controlled. Thus, in the ranging device  1  according to the present embodiment, the control unit  20  controls each ranging unit in a manner to prevent the second condition from being satisfied. Specifically, the control unit  20  controls the start timing of laser light scanning by each ranging unit in a manner to prevent the passage areas of laser light emitted by the multiple ranging units from interfering with each other within the ranging areas. Conditions for the start timing vary depending on the positional relationship of the ranging units. 
     The conditions for the start timing depending on the positional relationship of two ranging units will now be described.  FIG.  9    shows any two of the three ranging units mounted on the vehicle  100  as a ranging unit  10 A and a ranging unit  10 B arranged with their ranging areas overlapping with each other. The signs used in  FIG.  9    have the meanings listed below, and the positions and the angles are determined as viewed from above in a direction along the rotation axis of the deflection member  13  included in the ranging unit  10 A or the ranging unit  10 B. In the present embodiment, the rotation axes of the deflection members  13  included in the ranging unit  10 A and the ranging unit  10 B are parallel with each other. However, the rotation axes may not be parallel but may be, for example, nearly parallel. 
     D A  . . . Reference azimuth of ranging unit  10 A 
     D B  . . . Reference azimuth of ranging unit  10 B 
     S A  . . . Starting azimuth of laser light scan by ranging unit  10 A 
     S B  . . . Starting azimuth of laser light scan by ranging unit  10 B 
     P A  . . . Origin position and point of laser light deflection on deflection member  13  of ranging unit  10 A 
     P B  . . . Origin position and point of laser light deflection on deflection member  13  of ranging unit  10 B 
     L A  . . . Line passing through origin position P A  and parallel with reference azimuth D A    
     γ A  . . . Starting angle, or angle of starting azimuth S A  relative to reference azimuth D A  defined as 0 
     γ B  . . . Starting angle, or angle of starting azimuth S B  relative to reference azimuth D B  defined as 0 
     γ d  . . . . Shifted position angle, or angle of reference azimuth D B  relative to reference azimuth D A  defined as 0 
     γ B_A  . . . Opening angle, or angle of starting azimuth S B  relative to reference azimuth D A  defined as 0 
     The reference azimuth of a ranging unit is an azimuth defined as a reference in design. For example, with a laser light transmissive window installed, the reference azimuth is typically the forward direction of the transmissive window, or specifically, the direction normal to the center or an area surrounding the center of the surface of the transmissive window. In the present embodiment, the reference azimuth coincides with the azimuth of the center of the angular range for laser light scanning during the ranging period. 
     The values of the starting angles γ A  and γ B , the shifted position angle γ d , and the opening angle γ B_A  increase as the respective azimuths turn in the scanning direction of the ranging unit  10 A. The starting angles γ A  and γ B , the shifted position angle γ d , and the opening angle γ B_A  each take positive values in the scanning direction with respect to the corresponding reference azimuth and negative values in the direction opposite the scanning direction. 
     As shown in  FIG.  10   , the conditions for the start timing are classified into six conditions in accordance with the positional relationship of the ranging unit  10 A and the ranging unit  10 B. The six conditions will now be described based on six examples of arrangement. 
     (First Arrangement Example) 
     As shown in  FIG.  11   , a first arrangement example is an example in which the ranging unit  10 A and the ranging unit  10 B are arranged in such a way that the origin position P B  is placed in the direction opposite the scanning direction of the ranging unit  10 A with respect to the reference line L A , and the starting angle γ A  and the opening angle γ B_A  satisfy the relation of γ B_A &lt;γ A . In the first arrangement example shown in  FIG.  11   , the ranging unit  10 A and the ranging unit  10 B are arranged with the reference azimuth D A  and the reference azimuth D B  parallel to each other. However, this is not a condition for the first arrangement example. 
       FIG.  12    shows changes in the rotation angle θ A  of the deflection member  13  of the ranging unit  10 A and the rotation angle θ B_A  of the deflection member  13  of the ranging unit  10 B in the first arrangement example. Both the rotation angle θ A  and the rotation angle θ B_A  are expressed as angles determined when the rotation angle for laser light emission in the reference azimuth D A  is defined as 0. The values of the rotation angle θ A  and the rotation angle θ B_A  increase during ranging periods and decrease during non-ranging periods. The non-ranging periods of the ranging unit  10 A and the ranging unit  10 B are expressed respectively as a non-ranging period α and a non-ranging period β. 
     The control unit  20  causes the ranging unit  10 A to perform its ranging processing and the ranging unit  10 B to perform its ranging processing in a manner to prevent the reversal of the magnitude relationship between the emission azimuth angle of laser light emitted by the ranging unit  10 A and the emission azimuth angle of laser light emitted by the ranging unit  10 B relative to the common reference azimuth D A , as viewed from above in a direction along the rotation axis of the deflection member  13  included in the ranging unit  10 A or the ranging unit  10 B. This is intended to prevent the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other within the ranging areas. The reversal of the magnitude relationship of the angles refers to a shift of the two angles denoted by  01  and  02  from the state of θ1&gt;θ2 to the state of θ1&lt;θ2 or a shift from the state of θ1&lt;θ2 to the state of θ1&gt;θ2. The reversal of the magnitude relationship of the angles does not include a shift from the state of θ1=θ2 to the state of θ1&gt;θ2 or θ1&lt;θ2, or a shift from the state of θ1&gt;θ2 or θ1&lt;θ2 to the state of θ1=θ2. 
     The emission azimuth angles of laser light emitted by the ranging unit  10 A and the ranging unit  10 B relative to the reference azimuth D A  are expressed as the rotation angle θ A  and the rotation angle θ B_A  during the ranging period. Thus, the control unit  20  causes the ranging unit  10 A to perform its ranging processing and the ranging unit  10 B to perform its ranging processing in a manner to prevent the reversal of the magnitude relationship between the values of the rotation angle θ A  and the rotation angle θ B_A  in the co-ranging state in which both the ranging unit  10 A and the ranging unit  10 B are in the ranging period. When the origin position P B  is placed in the direction opposite the scanning direction of the ranging unit  10 A with respect to the reference line L A , as shown in  FIG.  12   , the rotation angle θ B_A  is not to be greater than the value of the rotation angle θ A  in the co-ranging state. The rotation angle θ A  relative to the rotation angle θ B_A  increases as the time at which the ranging unit  10 B starts laser light scanning becomes earlier relative to the time at which the ranging unit  10 A starts laser light scanning. However, in the first arrangement example, the opening angle γ B_A  is smaller than the starting angle γ A . Thus, the time at which the ranging unit  10 B starts laser light scanning may be advanced as long as the rotation angle θ B_A  does not exceed the rotation angle θ A . In contrast, if the time at which the ranging unit  10 B starts laser light scanning is too late, the ranging period of the ranging unit  10 A may start before the end of the ranging period of the ranging unit  10 B. In this case, the rotation angle θ B_A  exceeds the rotation angle θ A . For this reason, it is necessary to prevent a time delay in the start of laser light scanning by the ranging unit  10 B from exceeding the non-ranging period β of the ranging unit  10 B. 
     Thus, in the first arrangement example, the control unit  20  controls the time t at which the ranging unit  10 B starts laser light scanning relative to the time at which the ranging unit  10 A starts laser light scanning, to be in the range of −Θ≤t≤β In this formula, Θ denotes a period of time taken to move by the angle between the starting azimuth S A  and the starting azimuth S B  in a rotational manner at the above ranging angular velocity. This control can prevent the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other. 
     The arrangement example shown in  FIG.  9    is another first arrangement example. In the first arrangement example shown in  FIG.  11   , the reference azimuth D A  and the reference azimuth D B  are parallel with each other. In the first arrangement example shown in  FIG.  9   , the reference azimuth D A  is facing in the scanning direction of the ranging unit  10 A relative to the reference azimuth D B . 
       FIG.  13    shows changes in the rotation angle θ A  and the rotation angle θ B_A  in the first arrangement example shown in  FIG.  9   . As in the first arrangement example shown in  FIG.  11   , in order to prevent the reversal of the magnitude relationship between the values of the rotation angle θ A  and the rotation angle θ B_A  in the co-ranging state, the rotation angle θ B_A  is not to be greater than the rotation angle θ A . Thus, similarly to the first arrangement example shown in  FIG.  11   , the control unit  20  can control the time t to be in the range of −Θ≤t≤β, preventing the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other. 
     (Second Arrangement Example) 
     As shown in  FIG.  14   , a second arrangement example is an example in which the ranging unit  10 A and the ranging unit  10 B are arranged in such a way that the origin position P B  is placed in the direction opposite the scanning direction of the ranging unit  10 A with respect to the reference line L A , and the starting angle γ A  and the opening angle γ B_A  satisfy the relation of γ B_A =γ A . 
       FIG.  15    shows changes in the rotation angle θ A  and the rotation angle θ B_A  in the second arrangement example. In the second arrangement example, the opening angle γ B_A  is equal to the starting angle γ A . Thus, the time at which the ranging unit  10 B starts laser light scanning needs to be the same as or after the time at which the ranging unit  10 A starts laser light scanning. However, if the time at which the ranging unit  10 B starts laser light scanning is too late, the ranging period of the ranging unit  10 A may start before the end of the ranging period of the ranging unit  10 B. In this case, the rotation angle θ B_A  exceeds the rotation angle θ A . For this reason, it is necessary to prevent a time delay in the start of laser light scanning by the ranging unit  10 B from exceeding the non-ranging period β of the ranging unit  10 B. 
     Thus, in the second arrangement example, the control unit  20  controls the time t at which the ranging unit  10 B starts laser light scanning relative to the time at which the ranging unit  10 A starts laser light scanning, to be in the range of 0≤t≤β. This control can prevent the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other. 
     (Third Arrangement Example) 
     As shown in  FIG.  16   , a third arrangement example is an example in which the ranging unit  10 A and the ranging unit  10 B are arranged in such a way that the origin position P B  is placed in the direction opposite the scanning direction of the ranging unit  10 A with respect to the reference line L A , and the starting angle γ A  and the opening angle γ B_A  satisfy the relation of γ B_A &gt;γ A . In the third arrangement example shown in  FIG.  16   , the ranging unit  10 A and the ranging unit  10 B are arranged with the reference azimuth D A  facing in the scanning direction of the ranging unit  10 A relative to the reference azimuth D B . However, this is not a condition for the third arrangement example. 
       FIG.  17    shows changes in the rotation angle θ A  and the rotation angle θ B_A  in the third arrangement example. In the third arrangement example, the opening angle γ B_A  is greater than the starting angle γ A . Thus, the time at which the ranging unit  10 B starts laser light scanning needs to be delayed so that the rotation angle θ B_A  does not exceed the rotation angle θ A . However, if the time at which the ranging unit  10 B starts laser light scanning is too late, the ranging period of the ranging unit  10 A may start before the end of the ranging period of the ranging unit  10 B. In this case, the rotation angle θ B_A  exceeds the rotation angle θ A . For this reason, it is necessary to prevent a time delay in the start of laser light scanning by the ranging unit  10 B from exceeding the non-ranging period β of the ranging unit  10 B. 
     Thus, in the third arrangement example, the control unit  20  controls the time t at which the ranging unit  10 B starts laser light scanning relative to the time at which the ranging unit  10 A starts laser light scanning, to be in the range of Θ≤t≤β This control can prevent the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other. 
     The arrangement example shown in  FIG.  18    is another example of the third arrangement example. In the third arrangement example shown in  FIG.  16   , the reference azimuth D A  is facing in the scanning direction of the ranging unit  10 A relative to the reference azimuth D B . In the third arrangement example shown in  FIG.  18   , the reference azimuth D B  is facing in the scanning direction of the ranging unit  10 A relative to the reference azimuth D A . 
       FIG.  19    shows changes in the rotation angle θ A  and the rotation angle θ B_A  in the third arrangement example shown in  FIG.  18   . Similarly to the third arrangement example shown in  FIG.  16   , the control unit  20  can control the time t to be in the range of Θ≤t≤β, preventing the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other. 
     (Fourth Arrangement Example) 
     As shown in  FIG.  20   , a fourth arrangement example is an example in which the ranging unit  10 A and the ranging unit  10 B are arranged in such a way that the origin position P B  is placed in the scanning direction of the ranging unit  10 A with respect to the reference line L A , and the starting angle γ A  and the opening angle γ B_A  satisfy the relation of γ B_A &lt;γ A . In the fourth arrangement example shown in  FIG.  20   , the ranging unit  10 A and the ranging unit  10 B are arranged with the reference azimuth D A  and the reference azimuth D B  parallel to each other. However, this is not a condition for the fourth arrangement example. 
     The control unit  20  causes the ranging unit  10 A to perform its ranging processing and the ranging unit  10 B to perform its ranging processing in a manner to prevent the reversal of the magnitude relationship between the emission azimuth angle of laser light emitted by the ranging unit  10 A and the emission azimuth angle of laser light emitted by the ranging unit  10 B relative to the common reference azimuth D A , as viewed from above in a direction along the rotation axis of the deflection member  13  included in the ranging unit  10 A or the ranging unit  10 B. This is intended to prevent the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other within the ranging areas. Specifically, the control unit  20  causes the ranging unit  10 A to perform its ranging processing and the ranging unit  10 B to perform its ranging processing in a manner to prevent the reversal of the magnitude relationship between the values of the rotation angle θ A  and the rotation angle θ B_A  in the co-ranging state. 
       FIG.  21    shows changes in the rotation angle θ A  and the rotation angle θ B_A  in the fourth arrangement example. When the origin position P B  is placed in the scanning direction of the ranging unit  10 A with respect to the reference line L A , as shown in  FIG.  21   , the rotation angle θ B_A  is not to be smaller than the rotation angle θ A . In the fourth arrangement example, the opening angle γ B_A  is greater than the starting angle γ A . Thus, the time at which the ranging unit  10 B starts laser light scanning needs to be advanced so that the rotation angle θ B_A  does not fall below the rotation angle θ A . However, if the time at which the ranging unit  10 B starts laser light scanning is too early, the ranging period of the ranging unit  10 B may start before the end of the ranging period of the ranging unit  10 A. In this case, the rotation angle θ B_A  falls below the rotation angle θ A . For this reason, it is necessary to prevent the start of laser light scanning by the ranging unit  10 B from leading by a time longer than the non-ranging period a of the ranging unit  10 A. 
     Thus, in the fourth arrangement example, the control unit  20  controls the time t at which the ranging unit  10 B starts laser light scanning relative to the time at which the ranging unit  10 A starts laser light scanning, to be in the range of −α≤t≤−Θ. This control can prevent the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other. 
     The arrangement example shown in  FIG.  22    is another example of the fourth arrangement example. In the fourth arrangement example shown in  FIG.  20   , the reference azimuth D A  and the reference azimuth D B  are parallel with each other. In the fourth arrangement example shown in  FIG.  22   , the reference azimuth D A  is facing in the scanning direction of the ranging unit  10 A relative to the reference azimuth D B . 
       FIG.  23    shows changes in the rotation angle θ A  and the rotation angle θ B_A  in the fourth arrangement example shown in  FIG.  22   . Similarly to the fourth arrangement example shown in  FIG.  20   , the control unit  20  can control the time t to be in the range of −α≤t≤−Θ, preventing the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other. 
     The fourth arrangement example may be regarded as an arrangement example in which the ranging unit  10 A and the ranging unit  10 B in the third arrangement example are interchanged. That is, the fourth arrangement example is substantially the same as the third arrangement example. 
     (Fifth Arrangement Example) 
     As shown in  FIG.  24   , a fifth arrangement example is an example in which the ranging unit  10 A and the ranging unit  10 B are arranged in such a way that the origin position P B  is placed in the scanning direction of the ranging unit  10 A with respect to the reference line L A , and the starting angle γ A  and the opening angle γ B_A  satisfy the relation of γ B_A =γ A . 
       FIG.  25    shows changes in the rotation angle θ A  and the rotation angle θ B_A  in the fifth arrangement example. In the fifth arrangement example, the opening angle γ B_A  is equal to the starting angle γ A . Thus, the time at which the ranging unit  10 B starts laser light scanning needs to be the same as or after the time at which the ranging unit  10 A starts laser light scanning. However, if the time at which the ranging unit  10 B starts laser light scanning is too early, the ranging period of the ranging unit  10 B may start before the end of the ranging period of the ranging unit  10 A. In this case, the rotation angle θ B_A  falls below the rotation angle θ A . For this reason, it is necessary to prevent the start of laser light scanning by the ranging unit  10 B from leading by a time longer than the non-ranging period α of the ranging unit  10 A. 
     Thus, in the fifth arrangement example, the control unit  20  controls the time t at which the ranging unit  10 B starts laser light scanning relative to the time at which the ranging unit  10 A starts laser light scanning, to be in the range of −α≤t≤0. This control can prevent the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other. 
     The fifth arrangement example may be regarded an arrangement example in which the ranging unit  10 A and the ranging unit  10 B in the second arrangement example are interchanged. That is, the fifth arrangement example is substantially the same as the second arrangement example. 
     (Sixth Arrangement Example) 
     As shown in  FIG.  26   , a sixth arrangement example is an example in which the ranging unit  10 A and the ranging unit  10 B are arranged in such a way that the origin position P B  is placed in the scanning direction of the ranging unit  10 A with respect to the reference line L A , and the starting angle γ A  and the opening angle γ B_A  satisfy the relation of γ B_A &gt;γ A . In the sixth arrangement example shown in  FIG.  26   , the ranging unit  10 A and the ranging unit  10 B are arranged with starting angle γ B , the shifted position angle γ d , and the opening angle γ B_A  satisfying the relation of γ B_A =γ B —γ d . However, this is not a condition for the sixth arrangement example. 
       FIG.  27    shows changes in the rotation angle θ A  and the rotation angle θ B_A  in the sixth arrangement example. In the sixth arrangement example, the opening angle γ B_A  is smaller than the starting angle γ A . Thus, the time at which the ranging unit  10 B starts laser light scanning may be delayed as long as the rotation angle θ B_A  does not fall below the rotation angle θ A . In contrast, if the time at which the ranging unit  10 B starts laser light scanning is too early, the ranging period of the ranging unit  10 B may start before the end of the ranging period of the ranging unit  10 A. In this case, the rotation angle θ B_A  falls below the rotation angle θ A . For this reason, it is necessary to prevent the start of laser light scanning by the ranging unit  10 B from leading by a time longer than the non-ranging period a of the ranging unit  10 A. 
     Thus, in the sixth arrangement example, the control unit  20  controls the time t at which the ranging unit  10 B starts laser light scanning, relative to the time at which the ranging unit  10 A starts laser light scanning, to be in the range of −α≤t≤Θ. This control can prevent the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other. 
     The arrangement example shown in  FIG.  28    is another sixth arrangement example. In the sixth arrangement example shown in  FIG.  26   , the starting angle γ B , the shifted position angle γ d , and the opening angle γ B_A  satisfy the relation of γ B_A =γ B −γ d . In the arrangement example shown in  FIG.  28   , the starting angle γ B , the shifted position angle γ d , and the opening angle γ B_A  satisfy the relation of γ B_A =γ d −γ B . 
       FIG.  29    shows changes in the rotation angle θ A  and the rotation angle θ B_A  in the sixth arrangement example shown in  FIG.  28   . Similarly to the sixth arrangement example shown in  FIG.  26   , the control unit  20  can control the time t to be in the range of −α≤t≤Θ, preventing the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other. 
     The sixth arrangement example may be regarded as an arrangement example in which the ranging unit  10 A and the ranging unit  10 B in the first arrangement example are interchanged. That is, the sixth arrangement example is substantially the same as the first arrangement example. 
     [1-5. Mechanism for Diversifying Scan Timing of Multiple Ranging Units] 
     The control unit  20  according to the present embodiment prevents erroneous measurement as described above as well as controls each ranging unit to diversify the scan timing of the multiple ranging units. Specifically, the control unit  20  controls each ranging unit to cause the ranging units to change the angular velocities of their deflection members  13  at different times. The control unit  20  also controls each ranging unit to cause the periods of the deflection members  13  having the highest angular velocities to have at least a non-overlapping time between the ranging units. Although a configuration with two ranging units is described below, the same applies to a configuration with three or more ranging units. 
     [1-5-1. Mechanism for Causing Multiple Ranging Units to Switch at Different Times] 
     In the ranging processing in the present embodiment, ranging periods alternate with non-ranging periods. Accordingly, as shown in  FIG.  30   , the rotation angle θ A  of the deflection member  13  in the ranging unit  10 A and the rotation angle θ B  of the deflection member  13  in the ranging unit  10 B increase for ranging periods and decrease for non-ranging periods. The rotation angle θ B  is expressed as an angle determined when the rotation angle for laser light emission in the reference azimuth D B  is defined as 0. The current flowing in the drive  12  of the ranging unit  10 A has a value I A  and the current flowing in the drive  12  of the ranging unit  10 B has a value IB, and each value surges when the control unit  20  changes the angular velocity of the deflection member  13 , or in other words, at switching between a ranging period and a non-ranging period. Thus, as shown in  FIG.  30   , when multiple ranging units switch at the same time, and instantaneous currents peak at the same time, the instantaneous current in the whole vehicle  100  increases, causing noise in electrical signals output from the light receiver  14 . Furthermore, the power supply for the whole vehicle  100  is designed to have redundancy based on the cumulative instantaneous current. 
     Thus, as shown in  FIG.  31   , the control unit  20  controls the multiple ranging units so that the ranging units switch at different times, or in other words, the switching is staggered. This control reduces the likelihood that instantaneous currents peak at the same time, preventing an increase in the instantaneous current in the whole vehicle  100 . 
     [1-5-2. Mechanism for Reducing Likelihood of Coinciding Periods of Deflection Members Having Highest Angular Velocities] 
     During the period of the deflection member  13  having the highest angular velocity, the value I A  of the current flowing in the drive  12  of the ranging unit  10 A and the value IB of the current flowing in the drive  12  of the ranging unit  10 B are greater than in the other period. As shown in  FIG.  30   , in the present embodiment, the ranging unit is controlled so that the angular velocity of the deflection member  13  in the non-ranging period is higher than the ranging angular velocity. That is, in the present embodiment, the non-ranging period is the period during which the deflection member  13  has the highest angular velocity. In this case, the value I A  of the current flowing in the drive  12  of the ranging unit  10 A and the value IB of the current flowing in the drive  12  of the ranging unit  10 B are greater during non-ranging periods than during ranging periods. Accordingly, for example, as shown in  FIG.  30   , when multiple ranging units have coinciding non-ranging periods, the current in the whole vehicle  100  increases, causing noise in electrical signals output from the light receiver  14 . Furthermore, the power supply for the whole vehicle  100  is designed to have redundancy based on the cumulative instantaneous current. 
     Thus, as shown in  FIG.  31   , the control unit  20  in the present embodiment controls the multiple ranging units to cause the non-ranging periods to have at least a non-overlapping time between the ranging units. For example, when the non-ranging periods of two ranging units have different lengths, it is inevitable that the longer non-ranging period does not precisely coincide with the shorter non-ranging period. Thus, such an example also means that the shorter non-ranging period does not precisely coincide with the longer non-ranging period. This control prevents an increase in the current in the whole vehicle  100 . 
     [1-6. Effects] 
     The embodiment described in detail above provides the following effects. 
     (1a) The ranging device  1  causes each ranging unit to perform its ranging processing in a manner to prevent the passage areas of laser light emitted by the multiple ranging units from interfering with each other within the ranging areas. This mechanism can prevent ranging units having overlapping ranging areas from erroneously measuring a distance to an object. In particular, the ranging device  1  causes the ranging units to perform ranging processing in parallel with each other and thus completes ranging processing on every ranging area more quickly than a mechanism in which ranging units do not perform ranging processing in parallel. 
     (1b) The ranging device  1  causes the ranging unit  10 A to perform its ranging processing and the ranging unit  10 B to perform its ranging processing in a manner to prevent the reversal of the magnitude relationship between the emission azimuth angle of laser light emitted by the ranging unit  10 A and the emission azimuth angle of laser light emitted by the ranging unit  10 B relative to the common reference azimuth D A , as viewed from above in a direction along the rotation axis of the deflection member  13  included in the ranging unit  10 A or the ranging unit  10 B. This mechanism can prevent the passage areas of laser light emitted by the ranging units from interfering with each other within the ranging areas. 
     (1c) The ranging device  1  causes each ranging unit to perform ranging processing in the same ranging cycle. This mechanism enables, by, for example, controlling the time to start laser light scanning, the phase difference between the ranging cycles of the ranging units to be set without the reversal of the magnitude relationship between the emission azimuth angle of laser light emitted by the ranging unit  10 A and the emission azimuth angle of laser light emitted by the ranging unit  10 B with respect to the common reference azimuth D A . 
     (1d) A ranging cycle includes a non-ranging period. This mechanism can prevent the passage areas of laser light emitted by the ranging units from interfering with each other within the ranging areas and also increase the flexibility to design parameters such as the time to start laser light scanning. 
     (1e) The ranging device  1  controls the times at which the two ranging units arranged with their ranging areas overlapping with each other start laser light scanning. The control is performed so that the rotation angle of the deflection member  13  in the ranging unit placed in the scanning direction does not exceed the rotation angle of the deflection member  13  in the ranging unit placed in the direction opposite the scanning direction. This mechanism can prevent the passage areas of laser light emitted by the ranging units from interfering with each other within the ranging areas. 
     (1f) The ranging device  1  controls the multiple ranging units so that the ranging units switch at different times. This mechanism can prevent instantaneous currents from peaking at the same time and also prevent an increase in the instantaneous current in the whole vehicle  100 . 
     (1g) The ranging device  1  controls the multiple ranging units to cause the periods of the deflection members  13  having the highest angular velocities to have at least a non-overlapping time between the ranging units. This mechanism can prevent instantaneous currents from peaking at the same time and also prevent an increase in the current in the whole vehicle  100 . 
     2. Second Embodiment 
     The second embodiment is basically similar to the first embodiment, and thus common components will not be described, whereas differences will be mainly described. The same reference numerals as in the first embodiment represent the same components and refer to the foregoing description and the drawings. 
     In the second embodiment, similarly to the first embodiment, the control unit  20  causes each ranging unit to perform ranging processing in the same scanning direction and ranging cycle. However, in the second embodiment, the control unit  20  causes the ranging units to perform ranging processing at different ranging angular velocities. 
     In the second embodiment, the ranging unit  10 A and the ranging unit  10 B are arranged as shown in  FIG.  9   . However, the ranging angular velocity of the ranging unit  10 A denoted by ω A  is greater than the ranging angular velocity of the ranging unit  10 B denoted by ω B . In order to prevent the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other within the ranging areas, as shown in  FIG.  32   , the rotation angle θ B_A  is set to be not greater than the rotation angle θ A  during a period TA of the co-ranging state. In  FIG.  32   , the ranging angular velocity ω A  and the ranging angular velocity ω B  are expressed respectively by the slopes of the lines representing the values of θ A  and θ B_A  during the respective ranging periods of the ranging unit  10 A and the ranging unit  10 B. The gap between the rotation angle θ A  and the rotation angle θ B_A  narrows rapidly as the ranging angular velocity ω B  of the ranging unit  10 B increases relative to the ranging angular velocity ω A  of the ranging unit  10 A. In addition, as the period TA of the co-ranging state becomes longer, the gap between the rotation angle θ A  and the rotation angle θ B_A  narrows. 
     Thus, the control unit  20  controls the ranging angular velocity ω A  of the ranging unit  10 A and the ranging angular velocity ω B  of the ranging unit  10 B to cause the period TA of the co-ranging state to be equal to or smaller than the value obtained by dividing the angle between the emission azimuths of the ranging unit  10 A and the ranging unit  10 B at the start of the co-ranging state by the difference between the ranging angular velocities of a second ranging unit and a first ranging unit in the co-ranging state. 
     If the time at which the ranging unit  10 B starts laser light scanning is too late, the ranging period of the ranging unit  10 A may start before the end of the ranging period of the ranging unit  10 B. In this case, the rotation angle θ B_A  exceeds the rotation angle θ A . Furthermore, if the time at which the ranging unit  10 B starts laser light scanning is too early, the ranging period of the ranging unit  10 B may start before the end of the ranging period of the ranging unit  10 A. Also in this case, the rotation angle θ B_A  exceeds the rotation angle θ A . 
     Thus, the control unit  20  controls the time at which the ranging unit  10 B starts laser light scanning relative to the time at which the ranging unit  10 A starts laser light scanning so that the scanning period controlled falls within the range defined by the lower limit that is the value representing the non-ranging period of the ranging unit  10 A and the upper limit that is the value representing the non-ranging period of the ranging unit  10 B. In other words, the control unit  20  controls the time t at which the ranging unit  10 B starts laser light scanning relative to the time at which the ranging unit  10 A starts laser light scanning, to be in the range of α≤t≤β. 
     In an example in which the ranging unit  10 A and the ranging unit  10 B start laser light scanning at the same time, the control unit  20  controls the ranging angular velocity ω A  of the ranging unit  10 A and the ranging angular velocity ω B  of the ranging unit  10 B so that the ranging angular velocity ω A  and the ranging angular velocity ω B  satisfy the relation of TA≤|γ B_A −γ A |/(ω B −ω A ). 
     This control can prevent the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other within the ranging areas. 
     3. Other Embodiments 
     Although the embodiments of the present disclosure have been described above, it is needless to say that the disclosure may take a variety of forms without being limited to the embodiments. 
     (3a) In each embodiment described above, each ranging unit performs ranging processing at least in the same scanning direction and the same ranging cycle. However, unlike those example mechanisms, at least one of them may not be the same. For example, the ranging processing may be performed in different ranging cycles. 
     (3b) In each embodiment described above, the control unit  20  has both the function of controlling the operation of each ranging unit and the function of centrally controlling the ranging processing by each ranging unit. However, the control unit  20  is not limited to those example mechanisms. For example, the function of controlling the operation of each ranging unit may be distributed among the ranging units. For example, in this case, the function of centrally controlling the ranging processing by each ranging unit may be implemented through communication between the control units included in the respective ranging units or may be implemented through control by a control unit other than these control units. 
     (3c) In each embodiment described above, the ranging units are aligned in the scanning direction. However, as shown in  FIG.  33   , the ranging unit  10 A and the ranging unit  10 B may be aligned in the direction of the rotation axes of the deflection members  13 . In this case, each ranging unit is arranged in such a way that the ranging area overlaps with the ranging area of the adjacent ranging unit in the direction of the rotation axis of the deflection member  13 . In the example shown in  FIG.  33   , each ranging unit scans with long laser light having a cross-sectional shape F extending in a direction orthogonal to the scanning direction. The control unit  20  causes each ranging unit to perform ranging processing in a manner to prevent the passage areas of laser light emitted by the multiple ranging units from interfering with each other within an overlap between the ranging areas. For example, with the same scanning direction, the same ranging cycle, and the same ranging angular velocity, the rotation angle θ A  and the rotation angle θ B_A  are to be different from each other. Specifically, when laser light scanning has the same angular range during the ranging periods, the scan timing is staggered. When laser light scanning has different angular ranges during the ranging periods, the scan timing is adjusted as long as the scans are not synchronized. 
     (3d) In the second embodiment described above, the ranging unit  10 B of the ranging unit  10 A and the ranging unit  10 B is placed in the direction opposite the scanning direction of the ranging unit  10 A, and the ranging angular velocity ω B  is greater than the ranging angular velocity ω A . However, the arrangement of each ranging unit and the magnitude relationship of the ranging angular velocities are not limited to this example configuration. For example, the ranging unit  10 B of the ranging unit  10 A and the ranging unit  10 B may be placed in the scanning direction of the ranging unit  10 A, and the ranging angular velocity ω A  may be greater than the ranging angular velocity WB. 
     (3e) In each embodiment described above, for example, as shown in  FIG.  12   , the drives  12  move the deflection members  13  of the ranging unit  10 A and the ranging unit  10 B in a rotational manner in such a way that changes in both the rotation angles represent periodic waveforms. Specifically, the rotational movement causes ranging periods to alternate with non-ranging periods in the form of triangular waves. However, the rotational movement of the deflection members  13  is not limited to the example mechanism. For example, as shown in  FIG.  34   , the drives  12  may move the deflection members  13  in a rotational manner in such a way that changes in the rotation angles represent sinusoidal waveforms. In this example, the entire ranging cycle is the ranging period. For example, with the same ranging cycle, the sinusoidal waves representing changes in the rotation angles of the deflection members  13  of the ranging unit  10 A and the ranging unit  10 B are expressed respectively by formulas (1) and (2) below. 
     [Math. 1] 
       θ A =γ A  sin(ω t )  (1)
 
       θ B_A =γ B  sin(ω t +θ)−γ d   (2)
 
     In the formulas, ω denotes the angular velocity of the deflection members  13  of the ranging unit  10 A and the ranging unit  10 B, t denotes time, and θ denotes the phase difference θ between θ A  and θ B_A . 
     With the ranging unit  10 A and the ranging unit  10 B arranged as shown in  FIG.  9   , the rotation angle θ B_A  is not to be greater than the value of the rotation angle θ A  in the co-ranging state so as to prevent the passage areas of laser light emitted by the ranging unit  10 A and the ranging unit  10 B from interfering with each other. Accordingly, the relation of formula (3) below is to be satisfied, and therefore, θ is to be set in a manner to satisfy the relation of formula (4). 
     
       
         
           
             
               
                 
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     In some examples, as shown in  FIG.  35   , the drives  12  may move the deflection members  13  of the ranging unit  10 A and the ranging unit  10 B in a rotational manner in such a way that changes in the rotation angles represent waveforms different from each other. In other examples, as shown in  FIG.  36   , the drives  12  may move the deflection members  13  of the ranging unit  10 A and the ranging unit  10 B in a rotational manner without periodicity. 
     (3f) In each embodiment described above, the drive  12  swings the deflection member  13 . However, the drive  12  may rotate the deflection member  13 . 
     (3g) In each embodiment described above, control is performed to prevent the passage areas of laser light emitted by the multiple ranging units from interfering with each other within the ranging areas as well as outside the ranging areas. However, the passage areas of laser light may be permitted to interfere with each other outside the ranging areas. 
     (3h) In each embodiment described above, the three ranging units are arranged to have ranging areas in front of the vehicle  100 . However, the number and arrangement of ranging units are not limited to the example. For example, two or four or more ranging units may be arranged to have ranging areas behind the vehicle  100 . 
     (3i) In each embodiment described above, the ranging device  1  is illustrated as being installed in the vehicle  100 . However, the ranging device is not limited to the example. For example, the ranging device may be mounted on a moving object other than a vehicle, or more specifically, on a flying object such as a drone. 
     (3j) In each embodiment described above, the drive  12  is a motor. However, the drive  12  is not limited to the example. For example, the drive  12  may also be a MEMS. MEMS stands for microelectromechanical systems. 
     (3k) In each embodiment described above, the deflection member  13  is a mirror. However, another deflection member capable of deflecting laser light, such as a prism, may also be used as the deflection member  13 . 
     (3l) The configuration of the ranging unit shown in  FIG.  3    is a mere example, and another configuration may also be used. For example, the ranging unit may have a configuration in which laser light from the projector  11  may pass through a semi-transparent mirror to the deflection member  13 , and reflected light from the deflection member  13  may be reflected by the semi-transparent mirror and received by the light receiver  14 . 
     (3m) The functions of a single component in the above embodiments may be distributed as multiple components, or the functions of multiple components may be integrated into a single component. Some of the components in the above embodiments may be omitted. At least some components in one of the above embodiments may be added to or substituted for components in another of the above embodiments.