Patent Publication Number: US-2021173056-A1

Title: Sensor controller, sensor control method, sensor control program

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims the benefit of priority of Japanese Patent Application No. 2019-222340, filed on Dec. 9, 2019, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure generally relates to sensor control technology for controlling an optical sensor of a vehicle. 
     BACKGROUND INFORMATION 
     Conventionally, a plurality of optical sensors are mounted on a vehicle so that the scanning beam irradiation ranges are different (e.g., shifted) from each other. As a result, the total scanning capability of the vehicle as a whole is improved. 
     SUMMARY 
     It is an object of the present disclosure is to provide a sensor controller that suppresses a decrease/deterioration in total scanning capability even when abnormality occurs in an optical sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Objects, features, and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram for explaining a sensor system mounted on a vehicle together with a sensor controller according to an embodiment; 
         FIG. 2  is a block diagram of an overall configuration of the sensor controller according to an embodiment; 
         FIG. 3  is a block diagram of a detailed configuration of the sensor controller according to an embodiment; 
         FIG. 4  is a schematic diagram illustrating a beam control block according to an embodiment; 
         FIG. 5  is a schematic diagram illustrating the beam control block according to an embodiment; 
         FIG. 6  is a schematic diagram illustrating the beam control block according to an embodiment; 
         FIG. 7  is a schematic diagram illustrating the beam control block according to an embodiment; 
         FIGS. 8A, 8B, 8C  are respectively a characteristic diagram illustrating the beam control block according to an embodiment; 
         FIGS. 9A, 9B, 9C  are respectively a characteristic diagram illustrating the beam control block according to an embodiment; 
         FIGS. 10A, 10B, 10C  are respectively a characteristic diagram illustrating the beam control block according to an embodiment; 
         FIGS. 11A, 11B, 11C  are respectively a characteristic diagram illustrating the beam control block according to an embodiment; 
         FIGS. 12A, 12B, 12C  are respectively a characteristic diagram illustrating the beam control block according to an embodiment; 
         FIGS. 13A, 13B, 13C  are respectively a characteristic diagram illustrating the beam control block according to an embodiment; 
         FIGS. 14A, 14B, 14C  are respectively a characteristic diagram illustrating the beam control block according to an embodiment; 
         FIGS. 15A, 15B, 15C  are respectively a characteristic diagram illustrating the beam control block according to an embodiment; 
         FIG. 16  is a flowchart illustrating a sensor control method according to an embodiment; 
         FIG. 17  is a schematic diagram for explaining a sensor system mounted on a vehicle together with a sensor controller according to a modification of the embodiment; 
         FIG. 18  is a schematic diagram for explaining a sensor system mounted on a vehicle together with a sensor controller according to another modification of the embodiment; and 
         FIGS. 19A, 19B  are respectively a characteristic diagram illustrating the beam control block according to yet another modification of the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described based on the drawings. 
     In  FIG. 1 , a sensor controller  1  according to an embodiment of the present invention is mounted on a vehicle  2 . The vehicle  2  is, for example, an advanced driving assistance vehicle or an autonomous driving vehicle that travels based on an estimation result of self-movement. Of horizontal directions of the vehicle  2  on the horizontal plane, e.g., on a road, a direction of straight travel of the vehicle  2  is defined as a front-rear direction. 
     In  FIGS. 1 to 3 , a vehicle  2  is equipped with a sensor controller  1  and a sensor system  3 . 
     The sensor system  3  is configured to at least include optical sensors  30  and  31 . The optical sensors  30  and  31  are so-called LIDARs (Light Detection and Ranging, or Laser Imaging Detection and Ranging) that can be used for motion estimation of the vehicle  2 , for example. The optical sensors  30  and  31  output an optical image lo according to a beam reflection from a target  6  observed by a beam irradiation toward an outside of the vehicle  2 . In the present embodiment, a single, first optical sensor  30  (also known as a front sensor) is mounted at the center of a front part of the vehicle  2 , while a pair of second optical sensors  31  ( 31 L and  31 R) is mounted on the left and right side in the front part of the vehicle  2 , respectively. The pair of optical sensors  31  is also known as a left sensor  31 L and a right sensor  31 R. 
     As shown in  FIG. 3 , the optical sensors  30  and  31 L have beam elements  300  and  310 , imaging elements  301  and  311 , and imaging circuits  302  and  312 , respectively. The imaging circuits  302  and  312  control the corresponding beam elements  300  and  310  and the imaging elements  301  and  311 , respectively. The right sensor  31 R is similar to the left sensor  31 L. 
     For simplicity, initially consider only the front sensor  30  and the left sensor  31 L. Specifically, the imaging circuits  302  and  312  each intermittently emit a respective laser beam, which is directed toward the outside of the vehicle  2  from the beam elements  300  and  310  in a form of a pulsed light having a substantially constant intensity, as indicated by broken line arrows in  FIGS. 1 and 4 to 7 . In the course of irradiation, beam irradiation ranges R 1  and R 2 L, which are the scanning ranges of the optical sensors  30  and  31 L respectively, are set to an angular range which centers respectively on beam reference directions C 1  and C 2 L, and the beam irradiation ranges R 1  and R 2 L spread to both sides around beam steering axes AF and AL by set angles. Here, the front beam irradiation range R 1  is set in the front sensor  30  with the front beam reference direction C 1  being set as a front direction along a line in the front-rear direction of the vehicle  2 . 
     In the left sensor  31 L on the left side, the beam irradiation range R 2 L with the beam reference direction C 2 L is set along a line extending toward a left front side of the vehicle  2 . In the right optical sensor  31 R on the right side, the beam irradiation range R 2 R with the beam reference direction C 2 R is set along a line extending toward a right front side of the vehicle  2 . In each of the optical sensors  30 ,  31 L, and  31 R, the respective beam steering axis A, A 1 , and A 2  is a starting point of the respective beam irradiation ranges R 1 , R 2 L, and R 2 R, and are set to a vertical direction of the vehicle  2  with respect to the horizontal plane. Alternatively, one or more of the steering axes may be inclined with respect to the vertical direction. 
     The imaging circuits  302  and  312  switch the respective beam steering angles θF and θL around the respective beam steering axis AF and AL, which determines the beam irradiation direction within the beam irradiation ranges R 1  and R 2 L, for each intermittent beam irradiation timing at a constant time interval. In the course of such switching, the imaging circuits  302  and  312  define the beam steering angles θF and θL for each beam irradiation timing shown in  FIGS. 4 to 7  at equal intervals or uneven intervals to determine the beam irradiation density in the beam irradiation ranges R 1  and R 2 L, for even or uneven distribution of beam irradiation density. Therefore, the imaging circuits  302  and  312  adjust the distribution patterns of the beam irradiation density in the beam irradiation ranges R 1  and R 2 L as beam patterns P 1  and P 2 L of the optical sensors  30  and  31 , respectively. For the right sensor  31 R, the right beam irradiation range R 2 R, the right steering angle θR, and the right beam pattern P 2 R may be mirror images with respect to the left sensor  31 L. 
     As shown in  FIGS. 8A /B/C to  11 A/B/C, in the front beam irradiation range R 1  of the front sensor  30  that scans forward (i.e., a front field of the vehicle), the left beam steering angle θF takes a negative value in a left side region of the front beam reference direction C 1  that is an angle zero (0), and takes a positive value in a right side region of the same direction C 1 , in definition. The left beam irradiation range R 2 L of the left sensor  31 L that scans substantially laterally leftward. The right beam irradiation range R 2 R of the right sensor  31 R scans substantially laterally rightward. The beam steering angles θL and θR each take a negative value in a frontward region of the respective beam reference directions C 2 L and C 2 R, which are defined as angle zero (0), and each take a positive value in a rearward region of the same directions C 2 L and C 2 R respectively, by definition. 
     As shown in  FIG. 2 , a combination of the front sensor  30  and the left sensor  31 L is defined as a left sensor set SL. In the left sensor set SL, the beam irradiation range R 1  of the front sensor  30  and the beam irradiation range R 2  of the left sensor  31  have their respective beam steering axes AF and AL as shown in  FIGS. 1, 5, 6 , to form a left overlapping region RL that is a partial overlap of the two ranges R 1  and R 2 L. The left overlapping region RL of the present embodiment is set as a part (i) including a left end of the front beam irradiation range R 1 , and (ii) including a front end of the right beam irradiation range R 2 . 
     On the other hand, a combination of the first optical sensor  30  and the right-side second optical sensor  31  is defined as a right sensor set SR. In the right sensor set SR, the beam irradiation range R 1  of the first optical sensor  30  and the beam irradiation range R 2  of the right-side second optical sensor  31  have their beam steering axes A shifted substantially in parallel to each other as shown in  FIGS. 1, 5, 7 , to form a right overlapping region RR that is a partial overlap of the two ranges R 1  and R 2 . 
     The right overlapping region RR of the present embodiment is set as a part (i) including a right end of the region right of (a line in) the beam reference direction C 1  in the beam irradiation range R 1 , and (ii) including a front end of the region on a front side of the beam reference direction C 2  in the beam irradiation range R 2 . 
     The imaging circuits  302  and  312  shown in  FIG. 3  respectively expose, column by column, their plurality of pixels arranged in a column and row two-dimensions in the imaging elements  301  and  311 , sequentially and at timings corresponding to each of the beam irradiation timings in the beam irradiation ranges R 1  and R 2 L. 
     In such manner, the imaging circuits  302  and  312  which adopt a rolling shutter of sequential exposure make each pixel of the column exposed by the imaging elements  301  and  311  a scanning target. The imaging circuits  302  and  312  convert (i) a half value of a beam arrival time from the beam irradiation timing to a detection of the beam reflection in each pixel in the scanning target column into (ii) a distance value from the imaging elements  301  and  311  to the target  6 . The imaging circuits  302  and  312  generate, as data, optical images (a front optical image loF and a left optical image loL) as (i) so-called distance images or (ii) point cloud images by associating the converted distance value with each pixel of the respective columns for data generation. 
     Note that, in the imaging elements  301  and  311 , a brightness value corresponding to a beam reflection intensity sensed by each pixel in a column may also be associated with each pixel together with the converted distance value to generate, as data, the front optical image loF or the left optical image loL. Further, the imaging elements  301  and  311  may be provided with a function of picking up an image of an outside world of the vehicle  2  in accordance with an external light detected during an interruption period of the intermittent beam irradiation. In this case, the brightness value according to an intensity of the external light sensed by each pixel in the column in the imaging elements  301  and  311  may be associated with each pixel together with the converted distance value to generate, as data, the optical images loF and loL. Similarly, a right optical image IoR is generated. 
     As shown in  FIG. 2 , the sensor controller  1  is connected to the sensor system  3  via at least one of a LAN (Local Area Network), a wire harness, an internal bus, and the like. 
     The sensor controller  1  may be an ECU (Electronic Control Unit) dedicated to driving control, which performs advanced driving assistance or automatic driving control of the vehicle  2 . 
     The sensor controller  1  may be an ECU (Electronic Control Unit) of a locator used for advanced driving assistance or automatic driving control of the vehicle  2 . 
     The sensor controller  1  may be an ECU of a navigation device that navigates the driving of the vehicle  2 . 
     The sensor controller  1  may be shared by at least one of the imaging circuits  302  and  312  of the optical sensors  30  and  31 L. 
     The sensor controller  1  may be configured by a combination of plural types of these ECUs, circuits  302 ,  312 , and the like that bear functions described below. 
     The sensor controller  1  is a dedicated computer including at least one memory  10  and one processor  12 . The memory  10  stores or “memorizes” a computer-readable program and data in at least one kind of non-transitory, tangible storage medium (e.g., semiconductor memory, magnetic medium, optical medium, etc.). The processor  12  includes, as a core, at least one of a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), a RISC (Reduced Instruction Set Computer)-CPU, and the like. 
     The processor  12  performs a plurality of instructions included in the sensor control program stored in the memory  10 . Thereby, the sensor controller  1  constructs a plurality of functional blocks that collectively control the optical sensors  30 ,  31 L, and  31  R as shown in  FIG. 3 . As described above, in the sensor controller  1 , the sensor control program stored in the memory  10  for controlling the optical sensors  30 ,  31 L, and  31 R causes the processor  12  to execute a plurality of instructions, thereby constructing a plurality of functional blocks. A sensor determination block  100  and a beam control block  120  are included in the plurality of functional blocks. The functional blocks may be partially or totally electric circuits. 
     The sensor determination block  100  monitors the states of the optical sensors  30 ,  31 L, and  31 R. 
     More specifically, when the sensor determination block  100  monitors the left sensor set SL and finds abnormality occurring in any of the optical sensors  30  and  31 L forming the left sensor set SL, the sensor determination block  100  distinctively determines, as shown in  FIGS. 5, 6 , the abnormal sensor Sa in which abnormality has occurred and the normal sensor Sn, which maintains the normality. As a result of monitoring the right sensor set SR, if any of the optical sensors  30  and  31  R forming the right sensor set SL has abnormality, the sensor determination block  100  distinctively determines the abnormal sensor Sa in which abnormality has occurred and the normal sensor Sn maintaining normality, or operating normally, as shown in  FIGS. 5, 7 . 
     In addition to the discrimination process, for the sensor sets SL and SR in which both the optical sensors  30 ,  31 L, and  31 R are maintaining normality, the sensor determination block  100  recognizes both of them as normal sensors Sn as shown in  FIG. 4 . It should be noted that the sensor determination block  100  is premised that an event in which a plurality of the optical sensors  30  and  31  become abnormal at the same time does not occur. 
     The abnormality monitored by the sensor determination block  100  includes at least one of a steady failure of the optical sensors and a temporary malfunction of the optical sensors. Regardless of whether it is caused by the malfunction or failure of any of the components  300 ,  301 ,  302 ,  310 ,  311  and  312  of the optical sensors, when no normal optical image lo is output, the sensor determination block  100  may determine such a situation as abnormality of the sensors  30  and  31 . Further, in either case of failure or malfunction, the sensor determination block  100  may determine a situation that at least one of the optical images (IoF, loL, or IoR) is not properly transmitted to the processor  12  from the optical sensors (the imaging circuits) as abnormal. 
     As shown in  FIG. 3 , the beam control block  120  controls the beam patterns P 1  and P 2 L and P 2 R of the optical sensors  30  and  31 L and  31 R in response to the monitoring result of the sensor determination block  100 . More specifically, the beam control block  120  performs a normal process in case of  FIG. 4 , in which both the common first optical sensor  30  and the individual second optical sensors ( 31 L and  31 R) in the sensor sets SL ( 30  and  31 L), and SR ( 30  and  31 R) are respectively determined as normal sensors Sn. 
       FIGS. 4, 8A /B/C, and  12 A/B/C illustrate a normal process. In the normal process shown in  FIGS. 4, 8A /B/C and  12 A/B/C, the beam control block  120  controls the beam patterns P 1  and P 2 L and P 2 R adjusted by the imaging circuits  302  and  312  of the normal sensors Sn to a normal pattern Pn. As shown in  FIGS. 4 and 12 , the normal pattern Pn defines the beam steering angles θ for each beam irradiation timing t at equal intervals, so that the beam irradiation densities are even in the beam irradiation ranges R 1  and R 2 L and R 2 R of the normal sensors Sn (i.e., realizing even distribution of beam irradiation density). In  FIG. 4 , the normal pattern Pn for the left sensor  31 L may be a mirror image of the normal pattern Pn for the right sensor  31 R. 
       FIGS. 5, 9A /B/C, and  13 A/B/C illustrate a side degeneration process. In case of  FIG. 5 , in which the beam control block  120  determines that the first optical sensor  30  (common to the sensor sets SL and SR) is determined as an abnormal sensor Sa, and the left sensor  31 L and right sensor  31 R are determined as normal sensors Sn the sensor sets SL and Sr, then the beam control block  120  performs a side degeneration process. 
     In the side degeneration process shown in  FIGS. 5, 9A /B/C and  13 A/B/C, the beam control block  120  prohibits the adjustment of the beam pattern P 1  to the imaging circuit  302  of the abnormal sensor Sa by stopping the function of the abnormal sensor Sa. At the same time, the beam control block  120  controls the beam patterns P 2 L and P 2 R adjusted by the imaging circuit  312  of each normal sensor Sn to a side degeneration pattern Pds. 
     As shown in  FIGS. 5 and 13A /B/C, the side degeneration pattern Pds defines the beam steering angles θ for each beam irradiation timing t at uneven intervals, so that the beam irradiation density is not uniform in the beam irradiation range R 2  of each normal sensor Sn (i.e., realizing uneven distribution of beam irradiation density). In the course of realizing such uneven distribution, the side degeneration pattern Pds makes the beam distribution in the beam irradiation range R 2  of each normal sensor Sn denser for the beam directed toward the overlapping regions RL and RR that partially overlap the beam irradiation ranges R 1 L and R 1 R of the abnormal sensors Sa than the beam directed toward the outside of those regions RL and RR. 
     Further, in particular, the side degeneration pattern Pds of the present embodiment makes the beam directed toward the outside of the overlapping regions RL, RR less dense (i.e., more sparse) than the beam in the normal pattern Pn of the normal process. 
     By performing the control of the side degeneration pattern Pds, the beam pattern P 2  of each normal sensor Sn ( 31 L and  31 R) is concentrated toward (i.e., made denser in a region close to) the beam irradiation range R 1  of the abnormal sensor Sa. For example, the normal process in  FIG. 4  shows that  9  of  13  evenly spaced beams for the sensor  31 L are located outside of the left overlap region RL. In contrast, the side degeneration process in  FIG. 5  shows only  6  of  13  beams for the sensor  31 L located outside of the left overlap region RL, resulting in a relatively sparse pattern outside of the left overlap region RL. 
       FIGS. 6, 10A /B/C, and  14 A/B/C illustrate a left-side front degeneration process. In case of  FIG. 6 , in which the left sensor (the left-side second optical sensor)  31 L is determined as an abnormal sensor Sa and the first optical sensor  30  is determined as a normal sensor Sn in the left sensor set SL, the beam control block  120  performs a left-side front degeneration process. 
     In the left-side front degeneration process shown in  FIGS. 6, 10A /B/C, and  14 A/B/C, the beam control block  120  prohibits the adjustment of the beam pattern P 2  with respect to the imaging circuit  312  of the abnormal sensor Sa by stopping the function of the abnormal sensor Sa. At the same time, the beam control block  120  controls the front beam pattern P 1  adjusted by the imaging circuit  302  of the normal sensor Sn to a left-side front degeneration pattern Pdf. 
     As shown in  FIGS. 6 and 14A /B/C, the front degeneration pattern Pdf defines the beam steering angles θ for each beam irradiation timing t at uneven intervals, so that the beam irradiation density is not uniform in the beam irradiation range R 1  of a normal sensor Sn (i.e., realizing uneven distribution of beam irradiation density). 
     In the course of such uneven distribution, the front degeneration pattern Pdf of the left-side front degeneration process makes the beam distribution in the beam irradiation range R 1  of the normal sensor Sn denser for the beam directed toward the left overlapping region RL that partially overlaps the beam irradiation range R 1  of the abnormal sensor Sa ( 31 L in this case) than the beam directed toward the outside of the region RL. Further, in particular, the front degeneration pattern Pdf (for a left-side front degeneration process in  FIGS. 6, 10, and 14 ) makes the beam directed toward the outside of the left overlapping region RL less dense than the beam in the normal pattern Pn of the normal process. By performing the control of the front degeneration pattern Pdf, the beam pattern P 1  of the normal sensor Sn is concentrated toward (i.e., made denser in a region overlapping) the beam irradiation range R 2 L of the abnormal sensor Sa. Note that the normal process of the normal pattern Pn is performed for the right sensor  31 R which is maintained as a normal sensor Sn in the right sensor set SR. 
       FIGS. 7, 11, and 15  illustrate a right-side front degeneration process. In case of  FIG. 7 , in which the right sensor  31 R is determined as an abnormal sensor Sa, and the first optical sensor  30  is determined as a normal sensor Sn in the right sensor set SR, the beam control block  120  performs a right-side front degeneration process. The right-side front degeneration process shown in  FIGS. 7, 11A /B/C, and  15 A/B/C is a process in which the “left side” is replaced with the “right side” with respect to the above left-side front degeneration process. 
     In particular, as shown in  FIGS. 7 and 15A /B/C, the right-side front degeneration pattern Pdf of the right-side front degeneration process makes the beam distribution in the beam irradiation range R 1  of the normal sensor Sn (front sensor  30  in this case) denser for the beam directed toward the right overlapping region RR that partially overlaps the beam irradiation range R 1  of the abnormal sensor Sa (right sensor  31 R in this case) than the beam directed toward the outside of the region RR. 
     In the above, the beam control block  120  determines the beam irradiation density according to the process type in the beam irradiation ranges R 1  and R 2 L and R 2 R of the optical sensors  30  and  31 L and  31 R serving either as a normal sensor Sn or an abnormal sensor Sa as a function of the beam steering angles about their respecive beam steering axes. 
     That is, the beam control block  120  defines a density function Fd to be realized in the beam irradiation ranges R 1  and R 2  of the optical sensors  30  and  31  for each process type, as shown in  FIGS. 8A /B/C to  11 A/B/C. 
     The beam control block  120  further converts the defined density function Fd into a cumulative distribution function Fc in which the beam irradiation density is accumulated with respect to the beam steering angleθ as shown in  FIGS. 12A /B/C to  15 A/B/C. 
     The beam control block  120  defines a beam steering angle (θL, θF, or θR) corresponding to each beam irradiation timing t at equal intervals in the converted cumulative distribution function Fc for each process type. Here, in the degeneration process of the present embodiment as shown in  FIGS. 9A /B/C to  11 A/B/C, the density function Fd (i.e., the beam irradiation density) has a step shape stepping up in the overlapping regions RL and RR where the beam is made dense with respect to other regions outside the regions RL, RR. 
     As a result, in the degeneration process of the present embodiment as shown in  FIGS. 13A /B/C to  15 A/B/C, the cumulative distribution function Fc in the overlapping regions RL and RR where the beam is made dense is a linear function having a slope different from (greater than) that outside the regions RL and RR. 
     In such manner, the distribution of the beam steering angle θ defined for each beam irradiation timing t is given as a distribution of the beam irradiation density that satisfies the density function Fd, i.e., as the beam patterns P 1  and P 2  according to the process type, to the optical sensors  30  and  31 . That is, the beam patterns P 1  and P 2  of the optical sensors  30  and  31  are controlled by the beam control block  120  as one of the normal pattern Pn and the degeneration patterns Pds and Pdf that satisfies the density function Fd for each process type. 
     According to the above, in the present embodiment, the sensor determination block  100  corresponds to a “sensor determination unit” and the beam control block  120  corresponds to a “beam control unit”. 
     A flow of a sensor control method in which the sensor controller  1  controls the optical sensors  30  and  31  in cooperation with the sensor determination block  100  and the beam control block  120  described so far is described with reference to  FIG. 16 . It should be noted that this flow of control is performed for each shutter frame that is commonly repeated by the optical sensors  30  and  31  after the start of traveling of the vehicle  2 . Further, “S” in this flow means a plurality of steps performed by a plurality of instructions included in the sensor control program. 
     In S 101 , the sensor determination block  100  monitors the states of the optical sensors  30  and  31  forming the sensor sets SL and SR. 
     In subsequent S 102 , the sensor determination block  100  determines whether or not an abnormality has occurred in any of the optical sensors  30  and  31  in each sensor set SL and SR. 
     In S 102 , when all of the optical sensors  30  and  31 L and  31 F of the sensor sets SL and SR maintain normality (S 102 =NO, there is no abnormality), the sensor determination block  100  proceeds downward to S 103 . The sensor determination block  100  in S 103  determines that all the optical sensors  30  and  31 L and  31 R are all normal sensors Sn. In subsequent S 104 , the beam control block  120  performs the normal process as discussed above regarding  FIGS. 4 ,  8 A/B/C, and  12 A/B/C. 
     In S 102 , when an abnormality occurs in the front sensor  30  of each sensor set SL, SR, the sensor determination block  100  proceeds to S 105 . The sensor determination block  100  in S 105  determines the front sensor  30  in which the abnormality has occurred is an abnormal sensor Sa. At the same time, the sensor determination block  100  in S 105  determines the as the left sensor  31 L and the right sensor  31 R are normal. 
     In S 106  subsequent to S 105 , the beam control block  120  performs the side degeneration process as discussed above regarding  FIGS. 5, 9A /B/C, and  13 A/B/C. 
     When an abnormality occurs in the left sensor  31 L of the left sensor set SL in S 102 , the sensor determination block  100  proceeds to S 107 . The sensor determination block  100  in S 107  determines the left sensor  31 L in which the abnormality has occurred is an abnormal sensor Sa. At the same time, the sensor determination block  100  in S 107  determines the front sensor  30  and the right sensor  31 R are normal. 
     In S 108  subsequent to S 107 , the beam control block  120  performs the left-side front degeneration process as discussed above regarding  FIGS. 6, 10A /B/C, and  14 A/B/C. 
     Note that, in S 108 , the beam control block  120  performs the normal process for the right sensor  31 R. 
     In S 102 , when an abnormality occurs in the right sensor  31 R of the right sensor set SR, the sensor determination block  100  performs S 109 , and then the beam control block  120  performs S 110 . Step S 110  performs a right-side front degeneration process as described above with respect to  FIGS. 7, 11A /B/C, and  15 . 
     The beam control block  120  in S 104 , S 106 , S 108 , and S 110  sets the beam irradiation densities in the beam irradiation ranges R 1  and R 2 L and R 2 R of the optical sensors  30  and  31  L and  31 R of the normal sensor Sn or the abnormal sensor Sa as a function of the beam steering angle for each process type. Therefore, the beam control block  120  in S 104 , S 106 , S 108 , and S 110  controls the beam patterns P 1 , P 2 L, and P 2 R of the optical sensors  30 ,  31 L, and  31 R respectively to make a density function satisfying pattern, which satisfies the density function Fd made from the beam patterns Pn, Pds, Pdf for each process type. Note that, when any one of S 104 , S 106 , S 108 , and S 110  corresponding to the determination result in S 102  ends, a current execution cycle of the flow is complete. 
     As described above, in the present embodiment, S 101 , S 102 , S 103 , S 105 , S 107 , and S 109  correspond to a “sensor determination process,” and S 104 , S 106 , S 108 , and S 110  correspond to a “beam control process”. 
     (Operational Effects) 
     The effects of the present embodiment described above are described below. 
     According to the present embodiment, the sensors  30  and  31 L and  31 R are mounted on the vehicle  2 , which respectively cover the beam irradiation ranges R 1  and R 2 L and R 2 R for scanning the front direction and the side directions of the vehicle in an overlapping manner, with the shift of those irradiation ranges from each other. When abnormality occurs in one of the optical sensors under such mounting configuration, the abnormal sensor Sa in which abnormality has occurred and the normal sensors Sn that maintain normality are distinctively determined. As a result, the beam patterns P 1  and P 2 L and P 2 R in the beam irradiation range of the normal sensors Sn are controlled to have the degeneration patterns Pdf and Pds, thereby the beam irradiation range of the abnormal sensor Sa is scanned (i.e., covered) as much as possible, by the beam irradiation range of the normal sensor Sn concentrated toward the beam irradiation range of the abnormal sensor. Therefore, it is possible to suppress the deterioration of the total scanning capability. 
     According to the present embodiment, the beam irradiation density in the beam irradiation range of the normal sensor Sn is set as a function of the beam steering angle  8 , for controlling the beam patterns P 1  and P 2 L and P 2 R of the normal sensor Sn to have degeneration patterns (such as Pdf and Pds satisfying the density function Fd). According to such configuration, certain regions (i.e., the overlapping regions RL and RR in the present embodiment) in the beam irradiation range of the normal sensor Sn to be concentrated toward the beam irradiation range of the abnormal sensor Sa are increased so as to increase a coverage ratio for scanning for the abnormal sensor Sa, thereby enabling an accurate control of such regions RL, RR with respect to the beam steering angles. Therefore, it is possible to contribute to the suppression of the reduction in the total scanning capability. 
     The beam pattern control to the degeneration patterns Pdf and Pds according to the present embodiment is performed in such a manner that the beams directed to the overlapping regions RL and RR that partially overlap the beam irradiation range of the abnormal sensor Sa in the beam irradiation range of the normal sensor Sn are made denser than the beams directed outside of the regions RL and RR. According to such configuration, the coverage ratio for scanning for the abnormal sensor Sa can be increased by the beam that is concentrated in the overlapping regions RL and RR with the abnormal sensor Sa in the beam irradiation range of the normal sensor Sn. Therefore, it is possible to secure the effects of suppressing the decrease in the total scanning capability. 
     Other Embodiments 
     Although one embodiment has been described above, the present disclosure is not construed as being limited to the embodiment, and can be applied to various embodiments without departing from the scope of the present disclosure. 
     The sensor controller  1  of a modification of the above may be a dedicated computer including at least one of a digital circuit and an analog circuit as a processor. Here, in particular, the digital circuit includes, for example, at least one of ASIC (Application Specific Integrated Circuit), FPGA (Field Programmable Gate Array), SOC (System on a Chip), PGA (Programmable Gate Array), and CPLD (Complex Programmable Logic Device) and the like. Such a digital circuit may include a memory in which a program is stored. 
     In the sensor system  3  of another modification, as shown in  FIG. 17 , even if the beam steering axes AF, AL, and AR that are the start points of the beam irradiation ranges R 1  and R 2 L and R 2 R in the respective optical sensors  30  and  31 L and  31 R may match (that is, may be coaxial) with each other. 
     In the sensor system  3  of yet another modification, as shown in  FIG. 18 , a rear sensor  30 B having a beam reference direction C 1 B of the beam irradiation range R 1 B oriented in a rear direction of the vehicle  2  may be mounted on a rear part of the vehicle  2 . In such case, the beam irradiation range R 1  of the rear sensor  30 B that scans a rear field of the vehicle  2  may be mounted in place of or in addition to the first optical sensor  30  that mainly scans the front field. Here, particularly in the latter case, when one of the front and rear sensors  30  and  30 B is determined as an abnormal sensor Sa, the other of the two sensors may be determined as a normal sensor Sn and the normal process may be performed for such sensor. 
     Continuing with  FIG. 18 , some of the beam irradiation ranges may be completely non-overlapping (e.g., the range R 1 R of the rear sensor  30  does NOT overlap with either of the ranges R 2 L and R 2 R of the side sensors  31 L and  31 R). Note that the beam irradiation range R 1 B of the rear  3 B 0  (that scans mainly in the rear field illustrated in  FIG. 18 ) may partially overlap (not shown) the beam irradiation range R 2 L and R 2 R to form overlap regions (not shown) similar to the overlap regions RL and RR described above. 
     In S 104 , S 106 , S 108 , and S 110  by the beam control block  120  of the modification, the beam intensity for each beam steering angle θ at equal intervals or uneven intervals may be adjusted to control the beam patterns P 1  and P 2  of the beam irradiation density. 
     In S 106 , S 108 , and S 110  by the beam control block  120  of the modification, the degeneration patterns Pds and Pdf may have the “outside” beam having substantially the same density as the beam in the normal pattern Pn of the normal process (i.e., “outside” beams directed to the outside of the overlapping regions RL and RR). 
     In S 106 , S 108 , and S 110  by the beam control block  120  of the modification, the density function Fd in the overlapping regions RL and RR in which the beams are made denser may be set to have a non-linearly increased function relative to the region outside of the regions RL and RR as shown in  FIGS. 19A /B (i.e., an example of S 106  is shown in  FIGS. 19A /B). In such case, a cumulative distribution function Fc in the overlapping regions RL and RR where the beams are made dense becomes a non-linear function different from a linear function outside the regions RL and RR as shown in  FIGS. 19A /B.