Patent Publication Number: US-2022236046-A1

Title: Rotation angle detection apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of International Application No. PCT/JP2020/034735 filed on Sep. 14, 2020, which is based on and claims priority from Japanese Patent Application No. 2019-188329 filed on Oct. 15, 2019. The entire contents of these applications are incorporated by reference into the present application. 
    
    
     BACKGROUND 
     1 Technical Field 
     The present disclosure relates to rotation angle detection apparatuses. 
     2 Description of Related Art 
     In incremental rotation angle detection apparatuses, code wheels (see, for example, Japanese Patent Application Publication No. JP H07-43134 A) are widely used which include both a scale dedicated for detection of a rotation angle and a scale dedicated for detection of a reference angle. The scale dedicated for detection of the rotation angle is provided over the entire circumference of the code wheel in the circumferential direction. On the other hand, the scale dedicated for detection of the reference angle is provided at a single reference position in the circumferential direction. 
     SUMMARY 
     A scale dedicated for detection of a reference angle is generally required to be accurately formed. Therefore, compared to a code wheel with only one scale dedicated for detection of a rotation angle, a code wheel with two types of scales (i.e., a scale dedicated for detection of a rotation angle and a scale dedicated for detection of a reference angle) is more difficult to form, larger in size and higher in cost. Moreover, a rotation angle detection apparatus employing a code wheel with two types of scales is generally required to have both a circuit dedicated for detection of the rotation angle and a circuit dedicated for detection of the reference angle; therefore, such a rotation angle detection apparatus is larger in size and higher in cost than a rotation angle detection apparatus employing a code wheel with only one scale dedicated for detection of the rotation angle. Hence, it is desired to detect both a rotation angle and a reference angle with a compact and low-cost configuration. 
     The present disclosure has been accomplished in view of the above circumstances. 
     According to the present disclosure, there is provided a rotation angle detection apparatus for detecting a rotation angle of an object. The rotation angle detection apparatus includes an incremental rotary scale and a detector. The rotary scale is configured to rotate together with the object and includes both a detection region and a non-detection region. The detection region is provided along a circumferential direction of the rotary scale and has a scale formed therein for detecting the rotation angle of the object. The non-detection region adjoins the detection region in the circumferential direction and has no scale formed therein. The detector is configured to generate an electrical signal based on an input signal and detect the rotation angle of the object based on the electrical signal. The input signal indicates change in the position of the scale of the detection region. The position of the scale of the detection region changes according to change in the rotation angle of the object. The electrical signal periodically changes according to the change in the position of the scale of the detection region. Moreover, the rotary scale has no scale dedicated for detection of a reference angle for the rotation angle of the object. The detector is further configured to detect the reference angle by counting the number of positional changes from an end of the scale of the detection region of the rotary scale; the positional changes are indicated by the input signal. 
     In the above rotation angle detection apparatus according to the present disclosure, the rotary scale has the scale formed in the detection region thereof for detecting the rotation angle of the object, but no scale dedicated for detection of the reference angle for the rotation angle of the object. The detection region is provided along the circumferential direction of the rotary scale so as to match the angle range of the rotation angle of the object which is less than one revolution (i.e., less than 360°). The detector generates, based on the input signal indicating change in the position of the scale of the detection region, the electrical signal that periodically changes according to the change in the position of the scale of the detection region; the position of the scale of the detection region changes according to change in the rotation angle of the object. Further, the detector detects the rotation angle of the object based on the electrical signal. Furthermore, the detector detects the reference angle by counting the number of positional changes from an end of the scale of the detection region of the rotary scale; the positional changes are indicated by the input signal. That is, the detector detects the reference angle based on the number of periodical changes of the electrical signal, which changes according to the change in the position of the scale of the detection region, with respect to a boundary position between the detection region and the non-detection region. Consequently, it becomes possible to detect both the rotation angle of the object and the reference angle with a compact and low-cost configuration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating the overall configuration of an object detection apparatus which includes a rotation angle detection apparatus according to a first embodiment. 
         FIG. 2  is a schematic diagram illustrating the configuration of the rotation angle detection apparatus according to the first embodiment. 
         FIG. 3  is a schematic diagram illustrating both A-phase and B-phase detection signals outputted from a rotation angle sensor of the rotation angle detection apparatus according to the first embodiment. 
         FIG. 4  is a flow chart illustrating an exemplary self-diagnosis process of the rotation angle detection apparatus according to the first embodiment. 
         FIG. 5  is a flow chart illustrating another exemplary self-diagnosis process of the rotation angle detection apparatus according to the first embodiment. 
         FIG. 6  is a schematic diagram illustrating the configuration of a rotary scale according to a second embodiment. 
         FIG. 7  is a schematic diagram illustrating the configuration of another rotary scale according to the second embodiment. 
         FIG. 8  is a schematic diagram illustrating the configuration of a rotary scale according to a third embodiment. 
         FIG. 9  is a schematic diagram illustrating the configuration of a rotary scale according to a fourth embodiment. 
         FIG. 10  is a schematic diagram illustrating the configuration of a rotation angle detection apparatus according to a fifth embodiment. 
         FIG. 11  is a schematic diagram illustrating the configuration of a rotation angle detection apparatus according to a sixth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Exemplary embodiments will be described hereinafter with reference to the drawings. It should be noted that for the sake of clarity and understanding, identical components having identical functions throughout the whole description have been marked, where possible, with the same reference numerals in the drawings and that for the sake of avoiding redundancy, explanation of identical components will not be repeated. 
     First Embodiment 
       FIG. 1  illustrates the overall configuration of an object detection apparatus  100  which includes a rotation angle detection apparatus according to the first embodiment. 
     In the present embodiment, the object detection apparatus  100  is configured as a Lidar (Light Detection and Ranging) apparatus. As shown in  FIG. 1 , the object detection apparatus  100  includes a controller (or control unit)  10 , a light emitter (or light emitting unit)  22 , a rotating body (or rotating member)  24 , a light receiver (or light receiving unit)  26 , an actuator  30 , an actuator driver (or actuator driving unit)  32  and a rotation angle detector (or rotation angle detection unit)  50 . 
     The controller  10  may be implemented by, for example, a microprocessor, an FPGA (Field-Programmable Gate Array), an ASIC (Application-Specific Integrated Circuit) or an SoC (System-on-Chip). Although not shown in the drawings, the controller  10  includes an operation unit, a storage unit and an input/output unit. The controller  10  controls, through execution by the operation unit of various programs stored in the storage unit, operation of the actuator  30  according to the rotation angle of the rotating body  24  detected by the rotation angle detector  50 . 
     In addition, the actuator  30  is provided to drive the rotating body  24  that rotates together with a rotating shaft  40 . Since the azimuth of an object is detected through rotation of the rotating body  24 , the rotation angle of the rotating body  24  may also be referred to as the azimuth angle. 
     The controller  10  further controls emission timing at which light is irradiated by the light emitter  22 . The irradiated light may be transmitted, via the rotating body  24 , to an object and then reflected by the object to form reflected light. In this case, the controller  10  calculates the distance from the object detection apparatus  100  to the object based on the time from when the irradiated light is emitted from the light emitter  22  until the reflected light is received by the light receiver  26 . 
     The controller  10  is connected to the light emitter  22 , the light receiver  26 , the actuator driver  32  and the rotation angle detector  50  via signal lines. The controller  10  receives signals outputted from the light receiver  26  and the rotation angle detector  50 . Moreover, the controller  10  sends control signals to the light emitter  22  and the actuator driver  32 . 
     The actuator  30  is configured to rotationally drive the rotating body  24  that is provided at an end of the rotating shaft  40 . Specifically, the actuator  30  controls rotation of the rotating body  24  through current control that is performed by the actuator driver  32  upon receipt of a drive control signal from the controller  10 . The actuator  30  may be implemented by a magnetic actuator capable of instantaneously switching the rotation direction of the rotating body  24 , such as a rotary solenoid. In addition, the actuator  30  may alternatively implemented by various electric motors such as a brushless motor. 
     The light emitter  22 , the light receiver  26  and the rotating body  24  together constitute an object detector (or object detection unit). The light emitter  22  may include, for example, a laser diode as a light source and emit an infrared laser beam as the irradiated light. Moreover, the light emitter  22  may further include a light source driver (not shown) to drive the laser diode, with a light emission pattern corresponding to a light emission control signal received from the controller  10 , to irradiate the laser beam. In addition, the light emitter  22  may include only one light source or a plurality of light sources. 
     The light receiver  26  may include, for example, only one photodiode as a light receiving element or a plurality of photodiodes as a light receiving element array. The light receiver  26  converts electric current, which corresponds to the amount of light incident on the light receiving element(s), into a voltage and outputs the resultant voltage as a light receiving signal or as digital data to the controller  10 . 
     The rotating body  24  may include, for example, a one-sided mirror. The light emitter  22  and the light receiver  26  are arranged along the rotating shaft  40  so that the laser beam irradiated by the light emitter  22  can be transmitted through the mirror to scan an object within a predetermined range of horizontal azimuth angles. Moreover, the laser beam reflected by the object can be transmitted through the same optical path as the irradiated laser beam and incident on the light receiver  26  through the mirror. As a result, scanning can be performed, within the predetermined azimuth angle range θar, to detect the object. 
     Alternatively, the rotating body  24  may include no mirror; and the object detection apparatus  100  may include a plurality of light emitters  22  and a plurality of light receivers  26  arranged in an array. In this case, the laser beam is irradiated by the light emitters  22  directly to outside of the object detection apparatus  100  and the reflected laser beam is received directly by the light receivers  26 . 
     In addition, the scanning range or the range of scanning rotation angle of the object detection apparatus  100 , i.e., the range within which scanning is performed by the object detector with the irradiated laser beam, may be preferably set to the angle range θar that is less than one revolution, i.e., less than 360°. 
     The rotation angle detector  50 , which is an incremental rotation angle detection apparatus, detects the rotation angle of the rotating body  24  connected to the rotating shaft  40 . Hereinafter, the rotation angle detector  50  will also be referred to as the “rotation angle detection apparatus  50 ”. 
     As shown in  FIG. 2 , the rotation angle detection apparatus  50  includes a rotary scale  510  and a detector (or detection unit)  520 . Moreover, the detector  520  includes a rotation angle sensor  530  and a detection processor (or detection processing unit)  540 . The detection processor  540  detects the rotation angle of the rotating body  24  based on detection signals of two phases (i.e., A and B phases) outputted from the rotation angle sensor  530 . 
     The rotary scale  510  has both a detection region  514  and a non-detection region  516  on an annular area at an outer peripheral edge of a disk surface  512  that is perpendicular to a central axis Ar of the rotary scale  510 . The detection region  514  corresponds to the angle range θar from a left end angle θel to a right end angle θer, whereas the non-detection region  516  corresponds to an angle range other than the angle range θar. In the detection region  514 , there is formed, along the circumferential direction, a scale for detecting the rotation angle θr of the rotating body  24 . The scale of the detection region  514  is a scale in which reflective portions (i.e., white portions in  FIG. 2 ) capable of reflecting the irradiated light are formed alternately in the circumferential direction with non-reflective portions (i.e., black portions in  FIG. 2 ) not capable of reflecting the irradiated light. On the other hand, in the non-detection region  516 , there is formed only a non-reflective portion or only a reflective portion over the entire circumferential range of the non-detection region  516 . More particularly, in the present embodiment, there is formed only a non-reflective portion in the non-detection region  516 . 
     In the present embodiment, a scale (shown with dashed lines in  FIG. 2 ) dedicated for detection of a reference angle θc is omitted from the rotary scale  510 . That is, the rotary scale  510  has no scale dedicated for detection of the reference angle θc. In addition, the rotary scale  510  is an incremental rotary scale. 
     The rotary scale  510  is connected to the rotating shaft  40  so as to rotate together with the rotating shaft  40  with a central axis of the rotating shaft  40  coinciding with the central axis Ar of the rotary scale  510 . Moreover, the rotary scale  510  is connected to the rotating shaft  40  so that the detection region  514  of the rotary scale  510  coincides with the range of the rotation angle of the rotating body  24 . 
     The rotation angle sensor  530  includes a light emitter (or light emitting unit)  532 , a light receiver (or light receiving unit)  534 , a light emission driver (or light emission driving unit)  536  that drives the light emitter  532 , and a conversion processor (or conversion processing unit)  538  that converts a light receiving signal, which is an electrical signal outputted from the light receiver  534 , into a detection signal. 
     The light emitter  532  may include, for example, a Light Emitting Diode (LED) as a light source. Upon application of a predetermined voltage thereto by the light emission driver  536 , the light emitter  532  irradiates light, the amount of which depends on the applied voltage, to the rotary scale  510 . In addition, the light emitter  532  may be constituted of only one LED or a plurality of LEDs. 
     The light receiver  534  may include, for example, a pair of photodiodes constituting A-phase and B-phase light receiving elements, or a plurality of pairs of photodiodes constituting A-phase and B-phase light receiving element arrays. The light irradiated by the light emitter  532  on the rotary scale  510  is reflected by the detection region  514  of the rotary scale  510 ; and the reflected light is incident on the light receiving elements of the light receiver  534 . The light receiver  534  converts electric currents, which are generated according to the amount of the optical signal (i.e., the reflected light) incident on the light receiving elements of the light receiver  534 , into voltages and outputs the resultant voltages as light receiving signals to the conversion processor  538 . The amount of the optical signal incident on the light receiver  534  as an input signal periodically changes according to change in the position of the scale of the detection region  514 . Therefore, the light receiver  534  outputs both the A-phase and B-phase light receiving signals according to the periodic change of the optical signal. 
     As shown in  FIG. 3 , the conversion processor  538  converts the A-phase and B-phase light receiving signals outputted from the light receiver  534  into pulsed A-phase and B-phase detection signals and outputs the resultant detection signals. In the present embodiment, the A-phase and B-phase light-receiving elements or light-receiving element arrays are arranged so that the B-phase detection signal is offset in phase from the A-phase detection signal by T/4, where T is the period of the A-phase detection signal. Specifically, as shown in  FIG. 3 , when the rotation direction is the forward direction (e.g., the clockwise direction in  FIG. 2 : also referred to as the “right rotation direction” hereinafter), the B-phase detection signal lags the A-phase detection signal by T/4. On the other hand, when the rotation direction is the reverse direction (e.g., the counterclockwise direction in  FIG. 2 ; also referred to as the “left rotation direction” hereinafter), the B-phase detection signal leads the A-phase detection signal by T/4. 
     In addition, the detection signals are not limited to the pulsed periodic signals. For example, the detection signals may alternatively be sinusoidal or triangular periodic signals. 
     The detection processor  540  detects the rotation direction of the rotating body  24  based on the aforementioned phase relationship between the A-phase detection signal and the B-phase detection signal. Moreover, the number of the graduations (i.e., the number of the reflective and non-reflective portions) of the scale of the detection region  514  within the angle range θar is a known number set in advance; and the number of the graduations of the scale of the detection region  514  between the left end angle θel or the right end angle θer and the reference angle θc between the two angles θel and θer is also a known number set in advance. Therefore, in the present embodiment, the detection processor  540  detects the current rotation angle θr of the rotating body  24  by counting the number of pulses in the A-phase or B-phase detection signal; the pulses are generated due to change in the rotation angle θr between the position of the left end angle θel and the position of the right end angle θer of the detection region  514  shown in  FIG. 2 . Further, the detection processor  540  detects the position of the reference angle θc by counting the number of pulses in the A-phase or B-phase detection signal, which are generated due to change in the rotation angle θr from the left end angle θel or the right end angle θer, and detecting the rotation angle θr at which the counted number of the pulses becomes equal to a number corresponding to the reference angle θc. 
     As described above, in the present embodiment, with the rotary scale  510  having no scale dedicated for detection of the reference angle θc, the rotation angle detection apparatus  50  can detect the rotation angle θr of the rotating body  24  within the angle range θar, the position of the reference angle θc, and the position of the rotation angle θr with respect to the reference angle θc. Consequently, it becomes possible to detect both the rotation angle θr and the reference angle θc with a compact and low-cost configuration. 
     Furthermore, in the present embodiment, the detection processor  540  performs a self-diagnosis process as shown in  FIG. 4 . In this self-diagnosis process, the detection processor  540  diagnoses whether the rotation angle detection operation of the rotation angle detection apparatus  50  performed during a scanning process is normal or abnormal; in the scanning process, the rotation direction of the rotating body  24  (see  FIG. 1 ) is switched alternately between the right rotation direction and the left rotation direction. 
     Specifically, in the self-diagnosis process, first, the right rotation direction scanning (step S 110 ) is repeated with the actuator  30  being driven by the actuator driver  32  under control of the controller  10  (see  FIG. 1 ), until no pulses are generated for a predetermined time ts (step S 130 : NO). 
     During the right rotation direction scanning, the detection processor  540  detects the rotation angle θr in the right rotation direction by counting the number of pulses in a detection signal (i.e., either the A-phase detection signal or the B-phase detection signal) outputted from the rotation angle sensor  530 . 
     In addition, the predetermined time ts is set to a time during which the rotational position of the rotating body  24  can be determined to have reached an end of the detection region  514  (see  FIG. 2 ), i.e., the right end corresponding to the right end angle θer or the left end corresponding to the left end angle θel. 
     Moreover, during the repetition of the right rotation direction scanning (step S 110 ), the detection processor  540  determines whether the pulse count TC is less than or equal to a predetermined number N (step S 120 ). If TC&gt;N (step S 120 : NO), the detection processor  540  notifies the controller  10  of a false detection where the pulse count TC is excessively large (step S 124 ). In addition, the predetermined number N is set to a pulse number corresponding to the number of the graduations of the scale of the detection region  514  which has been known. 
     If no pulses are generated for the predetermined time ts (step S 130 : YES), the detection processor  540  determines that the rotation angle θr becomes the right end angle θer and thus the rotational position of the rotating body  24  has reached the right end of the detection region  514  (step S 140 ). Then, based on the determination by the detection processor  540 , the controller  10  switches the scanning direction from the right rotation direction to the left rotation direction. 
     The left rotation direction scanning (step S 150 ) is repeated with the actuator  30  being driven by the actuator driver  32  under control of the controller  10 , until no pulses are generated for the predetermined time ts (step S 170 : NO). 
     During the left rotation direction scanning, the detection processor  540  detects the rotation angle θr in the left rotation direction by counting the number of pulses in the detection signal outputted from the rotation angle sensor  530 . 
     Moreover, during the repetition of the left rotation direction scanning (step S 150 ), the detection processor  540  determines whether the pulse count TC is less than or equal to the predetermined number N (step S 160 ). If TC&gt;N (step S 160 : NO), the detection processor  540  notifies the controller  10  of a false detection where the pulse count TC is excessively large (step S 164 ). 
     If no pulses are generated for the predetermined time ts (step S 170 : YES), the detection processor  540  determines that the rotation angle θr becomes the left end angle θel and thus the rotational position of the rotating body  24  has reached the left end of the detection region  514  (step S 180 ). 
     Then, the detection processor  540  determines whether the pulse count TC is equal to the predetermined number N (step S 190 ). If TC&lt;N (step S 190 : NO), the detection processor  540  notifies the controller  10  of a false detection where the pulse count TC is excessively small (step S 194 ). On the other hand, if TC=N (step S 190 : YES), the detection processor  540  notifies the controller  10  that the rotation angle detection operation is normal (step S 200 ). 
     Thereafter, based on the determination by the detection processor  540  in step S 180 , the controller  10  switches the scanning direction from the left rotation direction to the right rotation direction and the right rotation direction scanning (step S 110 ) is repeated again. 
     With the above-described self-diagnosis process shown in  FIG. 4  which is performed during the rotation angle detection operation, when the number of pulses detected during the scanning of the rotating body  24  within the angle range from one end to the other end thereof is not equal to the known number, the detection processor  540  can notify the controller  10  of a false detection of the rotation angle. Then, the control unit  10  can determine whether the operation of the rotation angle detection apparatus  50  is normal or abnormal based on the notification of the false detection received from the rotation angle detection apparatus  50  (i.e., the rotation angle detector  50 ). 
     For example, in cases where the false detection is highly probably caused by noise and it is highly probable that the detection operation can be returned to the normal operation, such as in the case of the false detection being notified only once, it is possible to keep the object detection apparatus  100  operating without being stopped. On the other hand, in cases where the false detection is caused by a physical defect (e.g., dust or water droplets adhering to the rotary scale  510 ) and it is highly probable that the detection operation cannot be returned to the normal operation, such as in the case of false detections of the same type (e.g., small pulse-count false detections or large pulse-count false detections) being notified a plurality of times, it is possible to diagnose the rotation angle detection apparatus  50  as being in a fault state and stop the operation of the object detection apparatus  100 . 
     In the above-described self-diagnosis process shown in  FIG. 4 , the rotation angle detection apparatus  50  only notifies the controller  10  of the false detection; and the diagnosis as to whether the rotation angle detection apparatus  50  is in a fault state is performed by the superordinate controller  10  based on the notification of the false detection received from the rotation angle detection apparatus  50 . Alternatively, the rotation angle detection apparatus  50  may perform, instead of the self-diagnosis process shown in  FIG. 4 , a self-diagnosis process shown in  FIG. 5  which includes steps for diagnosing whether the rotation angle detection apparatus  50  is in a fault state. 
     Compared to the self-diagnosis process shown in  FIG. 4 , the self-diagnosis process shown in  FIG. 5  further includes: step S 122  before step S 124  and steps S 126  and S 128  after step S 124 ; step S 162  before step S 164  and steps S 166  and S 168  after step S 164 ; step S 192  before step S 194  and steps S 196  and S 198  after step S 194 ; and steps S 210  and S 220 . These added steps will be described in detail hereinafter. 
     In step S 122 , the detection processor  540  determines whether the number EX of false detections where TC&gt;N is less than or equal to a predetermined number M. If EX≤M (step S 122 : YES), the detection processor  540  notifies the controller  10  of a false detection where the pulse count TC is excessively large (step S 124 ). Moreover, if there is a stop command sent from the controller  10  in response to the notification of the false detection (step S 126 : YES), the detection processor  540  stops the rotation angle detection operation (step S 128 ). On the other hand, if EX&gt;M (step S 122 : NO), the detection processor  540  diagnoses the rotation angle detection apparatus  50  as being in a fault state and notifies the controller  10  of the fault state (step S 210 ). Then, the detection processor  540  stops the operation of the rotation angle detection apparatus  50  (step S 220 ). Further, upon receipt of the notification of the fault state, the controller  10  stops the rotational operation of the rotating body  24 . 
     Steps S 162 , S 166  and S 168  are the same as steps S 122 , S 126  and S 128  described above. Therefore, explanation of steps S 162 , S 166  and S 168  is omitted hereinafter. 
     In step S 192 , the detection processor  540  determines whether the number ES of false detections where TC&lt;N is less than or equal to a predetermined number P. In addition, the predetermined number P may be set such that P≤M or such that P≥M. If ES≤P (step S 192 : YES), the detection processor  540  notifies the controller  10  of a false detection where the pulse count TC is excessively small (step S 194 ). Moreover, if there is a stop command sent from the controller  10  in response to the notification of the false detection (step S 196 : YES), the detection processor  540  stops the rotation angle detection operation (step S 198 ). On the other hand, if ES&gt;P (step S 192 : NO), the detection processor  540  diagnoses the rotation angle detection apparatus  50  as being in a fault state and notifies the controller  10  of the fault state (step S 210 ). Then, the detection processor  540  stops the operation of the rotation angle detection apparatus  50  (step S 220 ). Further, upon receipt of the notification of the fault state, the controller  10  stops the rotational operation of the rotating body  24 . 
     With the above-described self-diagnosis process shown in  FIG. 5 , when false detections of the same type (e.g., small pulse-count false detections or large pulse-count false detections) have occurred a plurality of times, the detection processor  540  can diagnose the fault state of the rotation angle detection apparatus  50  and notify the controller  10  of the fault state. 
     In addition, in the present embodiment, the detection processor  540  is included in the detector  520  of the rotation angle detection apparatus  50  (see  FIG. 2 ). However, the detection processor  540  may alternatively be included in the controller  10 . 
     Second Embodiment 
     In the above-described first embodiment, the light emitter  532  of the rotation angle detection apparatus  50  (see  FIG. 2 ) is configured to irradiate light on the detection region  514  of the rotary scale  510  upon application of a predetermined voltage by the light emission driver  536  to the light emitter  532 ; the amount of the irradiated light depends on the applied voltage. 
     In contrast, the light emission driver  536  may automatically control the light emission of the light emitter  532  by controlling the voltage applied to the light emitter  532  so as to have the amount of light actually received by the light receiver  534  within a predetermined range. This automatic control of the amount of light emitted by the light emitter is also referred to as APC (Automatic Power Control). In addition, the APC may be implemented not only by methods of automatically controlling the amount of light emitted by the light emitter, but also by methods of automatically controlling the photosensitivity (or gain) of the light receiver. 
     In the case of controlling the amount of light emitted by the light emitter  532  by APC, with the rotary scale  510  described in the first embodiment where there is formed only a non-reflective portion (or alternatively only a reflective portion) over the entire non-detection region  516  (see  FIG. 2 ), the rotation angle detection operation may become unstable. 
     For example, in the case of the non-detection region  516  having only one non-reflective portion formed over the entire circumferential range thereof, when the rotation angle of the rotating body  24  is at either end of the angle range θar, the detected amount of the emitted light is kept small equally for both the A and B phases; therefore, the amount of the emitted light is controlled by APC so as to be increased. In this case, if the rotation angle detection is performed by the rotation angle detection apparatus  50  with rotation of the rotating body  24  after the amount of the emitted light is increased by APC, the amount of light received by the light receiver  534  may become saturated, causing failure in the operation of detecting change in the amount of light due to the reflection and non-reflection. On the other hand, in the case of the non-detection region  516  having only one reflective portion formed over the entire circumferential range thereof, when the rotation angle of the rotating body  24  is at either end of the angle range θar, the detected amount of the emitted light is kept large; therefore, the amount of the emitted light is controlled by APC so as to be decreased. In this case, if the rotation angle detection is performed by the rotation angle detection apparatus  50  with rotation of the rotating body  24  after the amount of the emitted light is suppressed by APC, the amount of light received by the light receiver  534  may become insufficient, causing failure in the operation of detecting change in the amount of light due to the reflection and non-reflection. 
     In view of the above, according to the second embodiment, there is provided a rotary scale  510   a  as shown in  FIG. 6 , which is suitable for use in the case of performing APC. 
     Compared to the rotary scale  510  according to the first embodiment (see  FIG. 2 ), the rotary scale  510   a  according to the present embodiment differs in that the non-detection region  516  is replaced with a non-detection region  516   a.    
     The non-detection region  516   a  has both a non-reflective portion  516   nr  formed on the radially inner side (or inner peripheral side) and a reflective portion  516   r  formed on the radially outer side (or outer peripheral side). The radial widths of the non-reflective portion  516   nr  and the reflective portion  516   r  are set so that: without APC, the amount of the reflected light of the light irradiated to either end of the non-detection region  516   a , which is received by the light receiver  534 , is substantially equal to ½ of the difference in the amount of light between the reflective portions and the non-reflective portions of the detection region  514  and substantially equal for both the A phase and the B phase; and the areas of the non-reflective portion  516   nr  and the reflective portion  516   r  per unit angle are substantially equal to each other. In addition, the non-detection region  516   a  may alternatively have a reflective portion  516   r  formed on the radially inner side and a non-reflective portion  516   nr  formed on the radially outer side. 
     With the above configuration of the non-detection region  516   a , when APC is performed, it is possible to prevent the amount of light received by the light receiver  534  from becoming saturated or insufficient due to the APC, thereby preventing failure from occurring in the operation of detecting change in the amount of light caused by the reflection and non-reflection. 
       FIG. 7  shows another rotary scale  510   b  according to the second embodiment, which is also suitable for use in the case of performing APC. 
     The rotary scale  510   b  includes a non-detection region  516   b  which has only one intermediately-reflective (or semi-reflective) portion formed thereon; the amount of light reflected by the intermediately-reflective portion is substantially equal to ½ of the difference in the amount of light between the reflective portions and the non-reflective portions of the detection region  514 . That is, the non-detection region  516   b  is configured so that the amount of the reflected light of the light irradiated to either end of the non-detection region  516   b  is substantially equal to ½ of the difference between the maximum amount of light and the minimum amount of light in the detection region  514  and substantially equal for both the A phase and the B phase. 
     In addition, it should be noted that the expression “substantially equal” is not limited to “exactly equal”, but includes a difference to the extent that there is no operational problem if it is treated as “exactly equal”. 
     Third Embodiment 
     In the rotary scale  510  according to the first embodiment (see  FIG. 2 ), both the detection region  514  and the non-detection region  516  are formed on the disk surface  512  that is perpendicular to the central axis Ar of the rotary scale  510 . 
     In contrast, as shown in  FIG. 8 , in a rotary scale  510   c  according to the third embodiment, both a detection region  514   c  and a non-detection region  516   c  are formed on a side surface  518  of the rotary scale  510   c ; the side surface  518  is a curved surface extending around the central axis Ar of the rotary scale  516   c  and along the circumferential direction of the rotary scale  516   c.    
     With the above rotary scale  510   c  according to the present embodiment, it is also possible to achieve the same advantageous effects as achievable with the rotary scale  510  according to the first embodiment. 
     In addition, although not shown in the drawings, the non-detection region  516   c  of the rotary scale  510   c  according to the present embodiment may alternatively have the same configuration as the non-detection region  516   a  of the rotary scale  510   a  or the non-detection region  516   b  of the rotary scale  510   b  according to the second embodiment. 
     Fourth Embodiment 
     In the rotary scale  510  according to the first embodiment, there is formed only one detection region  514  (see  FIG. 2 ). 
     In contrast, as shown in  FIG. 9 , a rotary scale  510   d  according to the fourth embodiment has a plurality of detection regions  514 , more particularly two detection regions  514 _ 1  and  514 _ 2 . The two detection regions  514 _ 1  and  514 _ 2  are offset from each other by, for example, 180°. Moreover, the angle ranges of the two detection regions  514 _ 1  and  514 _ 2  are set to be equal to each other. In addition, it should be noted that the angle ranges of the two detection regions  514 _ 1  and  514 _ 2  may alternatively be set to be different from each other. 
     With the above rotary scale  510   d  according to the present embodiment, it is also possible to achieve the same advantageous effects as achievable with the rotary scale  510  according to the first embodiment. 
     Moreover, with the above rotary scale  510   d  according to the present embodiment, it is possible to detect not only the rotation angle (or the angle of rotational movement) of an object that rotationally reciprocates within a predetermined angle range, but also the rotation angle of a rotating object. In addition, in this case, in the non-detection regions, the operation of the actuator may be controlled based on estimation from the angle information acquired in the detection regions. 
     In addition, although not shown in the drawings, each of the rotary scales  510   a  and  510   b  according to the second embodiment and the rotary scale  510   c  according to the third embodiment may also be modified to have a plurality of detection regions  514  formed therein. 
     Fifth Embodiment 
     The rotation angle detection apparatus  50  according to the first embodiment includes the rotary scale  510  which is a light reflection type rotary scale (see  FIG. 2 ). 
     In contrast, as shown in  FIG. 10 , a rotation angle detection apparatus  50   e  according to the fifth embodiment includes a light transmission type rotary scale  510   e.    
     Moreover, in the present embodiment, the rotation angle detection apparatus  50   e  further includes a detector  520   e  in addition to the rotary scale  510   e.    
     As shown in  FIG. 10 , the light transmission type rotary scale  510   e  includes both a detection region  514   e  having a scale formed therein and a non-detection region  516   e  sandwiching the detection region  514   e  and having no scale formed therein. The scale of the detection region  514   e  is a scale in which transmitting portions (i.e., white portions in  FIG. 10 ) are formed alternately in the circumferential direction with non-transmitting portions (i.e., black portions in  FIG. 10 ). The transmitting portions allow the irradiated light to be transmitted therethrough, whereas the non-transmitting portions block the irradiated light from transmitting therethrough. On the other hand, in the non-detection region  516   e , there is formed only a non-transmitting portion or only a transmitting portion over the entire circumferential range of the non-detection region  516   e . More particularly, in the present embodiment, there is formed only a non-transmitting portion in the non-detection region  516   e.    
     In the present embodiment, the detector  520   e  includes a rotation angle sensor  530   e  instead of the rotation angle sensor  530  described in the first embodiment (see  FIG. 2 ). The rotation angle sensor  530   e  includes a light emitter  532  and a light receiver  534  that are arranged to have the rotary scale  510   e  sandwiched therebetween. Consequently, of the light irradiated from the light emitter  532  on the rotary scale  510   e , only the light which has transmitted through the transmitting portions of the rotary scale  510   e  is received by the light receiver  534 . 
     With the rotation angle detection apparatus  50   e  according to the present embodiment, it is also possible to achieve the same advantageous effects as achievable with the rotation angle detection apparatus  50  according to the first embodiment. 
     In addition, as described above, in the present embodiment, the non-detection region  516   e  of the rotary scale  510   e  is configured to have only a non-transmitting portion or only a transmitting portion formed therein over the entire circumferential range thereof. However, the non-detection region  516   e  may alternatively be configured to have both a non-transmitting portion and a transmitting portion formed therein; one of the non-transmitting portion and the transmitting portion is formed on the radially inner side while the other of the non-transmitting portion and the transmitting portion is formed on the radially outer side. With this alternative configuration of the non-detection region  516   e , it is possible to prevent detection failure from occurring due to APC as described in the second embodiment. 
     Sixth Embodiment 
     The rotation angle detection apparatus  50  according to the first embodiment includes the rotary scale  510  which is a light reflection type rotary scale (see  FIG. 2 ). 
     In contrast, as shown in  FIG. 11 , a rotation angle detection apparatus  50   f  according to the sixth embodiment includes a magnetic rotary scale  510   f.    
     Moreover, in the present embodiment, the rotation angle detection apparatus  50   f  further includes a detector  520   f  in addition to the rotary scale  510   f.    
     As shown in  FIG. 11 , the magnetic rotary scale  510   f  includes both a detection region  514   f  having a scale formed therein and a non-detection region  516   f  sandwiching the detection region  514   f  and having no scale formed therein. The scale of the detection region  514   f  is a scale in which N-pole portions (i.e., white portions in  FIG. 11 ) are formed alternately in the circumferential direction with S-pole portions (i.e., black portions in  FIG. 11 ). Each of the N-pole portions is magnetized into an N pole, whereas each of the S-pole portions is magnetized into an S pole. On the other hand, in the non-detection region  516   f , there is formed only an N-pole portion or only an S-pole portion over the entire circumferential range of the non-detection region  516   f . More particularly, in the present embodiment, there is formed only an S-pole portion in the non-detection region  516   f.    
     In the present embodiment, the detector  520   f  includes a rotation angle sensor  530   f  instead of the rotation angle sensor  530  described in the first embodiment (see  FIG. 2 ). The rotation angle sensor  530   f  includes a magnetic sensor  534   f  that is configured to detect change in a magnetic field whose strength periodically changes according to change in the position of the scale of the detection region  514   f.    
     With the rotation angle detection apparatus  50   f  according to the present embodiment, it is also possible to achieve the same advantageous effects as achievable with the rotation angle detection apparatus  50  according to the first embodiment. 
     In addition, as described above, in the present embodiment, the non-detection region  516   f  of the rotary scale  510   f  is configured to have only an N-pole portion or only an S-pole portion formed therein over the entire circumferential range thereof. However, the non-detection region  516   e  may alternatively be configured to have only a nonmagnetic portion formed therein over the entire circumferential range thereof; the nonmagnetic portion is not magnetized into any magnetic pole. With this alternative configuration of the non-detection region  516   f , it is possible to prevent detection failure from occurring due to APC as described in the second embodiment. 
     Moreover, the detection region  514   c  and the non-detection region  516   c  of the rotary scale  510   c  according to the third embodiment may be modified to have the same configuration as the detection region  514   f  and the non-detection region  516   f  of the rotary scale  510   f  according to the present embodiment. 
     While the above particular embodiments have been shown and described, it will be understood by those skilled in the art that various modifications, changes and improvements may be made without departing from the spirit of the present disclosure. 
     (1) For example, in the rotary scales according to the above-described embodiments, the non-detection regions are formed over the entire angle range except for the angle range corresponding to the detection regions in one round (i.e. 360°). However, the non-detection regions may alternatively be formed, within only part of the entire angle range except for the angle range corresponding to the detection regions, so as to adjoin the detection regions in the circumferential direction. 
     (2) The rotary scales according to the above-described embodiments are disk-shaped. However, the rotary scales may alternatively have other shapes such that the detection and non-detection regions can be formed along the circumferential direction (or rotational direction) of the rotary scales. For example, the rotary scales may alternatively be fan-shaped. 
     (3) In steps S 130  and S 160  of the self-diagnosis processes shown in  FIGS. 4 and 5 , a determination is made as to whether no pulses are generated for the predetermined time ts; if the determination results in a “YES” answer, the detection processor  540  determines that the rotational position of the rotating body  24  has reached the left end of the detection region corresponding to the left end angle θel or the right end of the detection region corresponding to the right end angle θer. 
     As an alternative, a determination may be made as to whether no pulses are generated for a time whose length is X times the period of the pulses generated with rotation of the rotary scale, where 0&lt;X&lt;2; and the detection processor  540  may determine, upon the determination resulting in a “YES” answer, that the rotational position of the rotating body  24  has reached the left end or the right end of the detection region. 
     As another alternative, a determination may be made as to whether both the output of the A-phase detection signal and the output of the B-phase detection signal are at a low level corresponding to the non-reflective portions of the rotary scale; and the detection processor  540  may determine, upon the determination resulting in a “YES” answer, that the rotational position of the rotating body  24  has reached the left end or the right end of the detection region. 
     (4) In the above-described embodiments, the rotation angle detection apparatus is applied to the object detection apparatus  100  (see  FIG. 1 ). However, the rotation angle detection apparatus can also be applied to other apparatuses that rotate an object within a desired rotation angle range, such as a light irradiation apparatus for irradiating light, a spray apparatus for spraying a drug or the like, and imaging apparatus for capturing images of objects or an ambient environment. 
     In addition, the controllers and the control methods thereof described in the present disclosure may be realized by a dedicated computer that includes a processor and a memory for performing one or more functions embodied by a computer program. As an alternative, the controllers and the control methods thereof described in the present disclosure may be realized by one or more dedicated hardware logic circuits. As another alternative, the controllers and the control methods thereof described in the present disclosure may be realized by a combination of a dedicated computer, which includes a processor and a memory for performing one or more functions embodied by a computer program, and one or more dedicated hardware logic circuits. Moreover, the computer program may be stored, as instructions to be executed by the computer, in a computer-readable non-transitory tangible recording medium.