Drive control circuit for electric motor

1. A semiconductor device, comprising:

a drive control circuit that generates a drive signal for driving an electric motor having a permanent magnet and a coil, wherein

the drive control circuit generates the drive signal based on a positional signal which indicates relative position of a first drive member and a second drive member of the electric motor,

a signal level of the drive signal becomes a first voltage level in a first interval,

a signal level of the drive signal becomes a second voltage level which is different from the first voltage level in a second interval, and

the coil of the electric motor is not provided with a current in the first interval,

wherein a length of the second interval is shorter than a length of interval between a point at which a signal level of a timing signal based on the positional signal becomes a fourth level from a third level and a point at which the signal level of the timing signal becomes the third level.

2. A semiconductor device, comprising:

a drive control circuit that generates a drive signal for driving an electric motor having a permanent magnet and a coil, wherein

the drive control circuit generates the drive signal based on a positional signal which indicates relative position of a first drive member and a second drive member of the electric motor,

a signal level of the drive signal becomes a first voltage level in a first interval,

a signal level of the drive signal becomes alternately the first voltage level and a second voltage level which is different from the first voltage level in a second interval, and

the coil of the electric motor is not provided with a current in the first interval,

wherein a length of the second interval is shorter than a length of interval between a point at which a signal level of a timing signal based on the positional signal becomes a fourth level from a third level and a point at which the signal level of the timing signal becomes the third level.

3. A semiconductor device for driving an electric motor, comprising:

an original drive signal generator that generates an original drive signal;

an excitation interval setter that is able, for each half cycle of respective length π in each 2π excitation cycle of the original drive signal, to set an excitation interval to excite coils of the electric motor to either one of a symmetrical interval centered on a center of each half-cycle and an unsymmetrical interval;

a drive signal shaping circuit that generates a drive signal for driving the electric motor, by validating the original drive signal during the excitation intervals and invalidating the original drive signal during non-excitation intervals other than the excitation interval; and

a clock signal generator that generates a clock signal;

wherein the excitation interval setter sets the excitation interval utilizing the clock signal.

4. The semiconductor device according to claim 3 , further comprising:

an analog-digital converter that converts the positional signal to digital values;

wherein the original drive signal generator generates the original drive signal based on the digital positional signal values.

5. The semiconductor device according to claim 4 , further comprising:

an amplifier that amplifies the positional signal;

wherein the analog-digital converter converts the amplified positional signal to digital values.

6. A drive control circuit for an electric motor, comprising:

an original drive signal generator that generates an original drive signal;

an excitation interval setter that is able, for each half cycle of respective length π in each 2π excitation cycle of the original drive signal, to set an excitation interval to excite coils of the electric motor to either one of a symmetrical interval centered on a center of each half-cycle and an unsymmetrical interval; and

a drive signal shaping circuit that generates a drive signal for driving the electric motor, by validating the original drive signal during the excitation intervals and invalidating the original drive signal during non-excitation intervals other than the excitation interval;

wherein

the original drive signal generator generates the original drive signal based on a positional signal which indicates relative position of a first drive member and a second drive member of the electric motor; and

the excitation interval setter includes:

an interval measurer that measures a first level interval representing a length of time for which a periodic timing signal synchronized with the positional signal shows a first level;

a start time setter that multiplies the first level interval by a first coefficient value which is a positive value less than 1, to derive a first interval;

an end time setter that multiplies the first level interval by a second coefficient value which is a value greater than the first coefficient value and less than 1, to derive a second interval; and

an excitation interval controller that controls the excitation interval by comparing the first interval with a first level-elapsed interval which represents elapsed time after the timing signal shows a transition from a second level to the first level, and starting the excitation interval at a timing at which the first level-elapsed interval becomes equal to the first interval; and comparing the second interval with the first level-elapsed interval, and starting the non-excitation interval at a timing at which the first level-elapsed interval becomes equal to the second interval.

7. The drive control circuit according to claim 6 , wherein

the excitation interval setter sets the excitation interval to the unsymmetrical interval.

8. The drive control circuit according to claim 6 , wherein

the excitation interval controller further

controls the excitation interval by comparing the first interval with a second level-elapsed interval which represents elapsed time after the timing signal shows a transition from the first level to the second level, and starting the excitation interval at a timing at which the second level-elapsed interval becomes equal to the first interval; and comparing the second interval with the second level-elapsed interval, and starting the non-excitation interval at a timing at which the second level-elapsed interval becomes equal to the second interval.

9. The drive control circuit according to claim 6 , wherein

the excitation interval controller performs the comparison using the first interval and the second interval that have been derived based on the first level interval of the timing signal immediately prior to performing the comparison.

10. The drive control circuit according to claim 6 , wherein

a sum of the first coefficient value and the second coefficient value is 1.

11. The drive control circuit according to claim 6 wherein

the original drive signal generator includes a PWM signal generator that generates a PWM signal based on the positional signal, as the original drive signal.

12. An electric motor, comprising the drive control circuit according to claim 6 .

13. A device, comprising:

the electric motor according to claim 12 ; and

a driven member which is driven by the electric motor.

14. A device according to claim 13 , wherein

the device is a projector.

15. A device according to claim 13 , wherein

the device is a mobile device.

16. A device according to claim 13 , wherein

the device is a robot.

17. A device according to claim 13 , wherein

the device is a movable body.

18. A drive control circuit for an electric motor, comprising:

an original drive signal generator that generates an original drive signal;

an excitation interval setter that is able, for each half cycle of respective length π in each 2π excitation cycle of the original drive signal, to set an excitation interval to excite coils of the electric motor to either one of a symmetrical interval centered on a center of each half-cycle and an unsymmetrical interval; and

a drive signal shaping circuit that generates a drive signal for driving the electric motor, by validating the original drive signal during the excitation intervals and invalidating the original drive signal during non-excitation intervals other than the excitation interval;

wherein

the original drive signal generator generates the original drive signal based on a positional signal which indicates relative position of a first drive member and a second drive member of the electric motor; and

the excitation interval setter includes:

an interval measurer that measures a first level interval representing a length of time for which a periodic timing signal synchronized with the positional signal shows a first level, and a second level interval representing a length of time for which the timing signal shows a second level;

a start time setter that derives a first interval equal to the first level interval multiplied by a first coefficient value which is a positive value less than 1, and a third interval equal to the second level interval multiplied by the first coefficient value;

an end time setter that derives a second interval equal to the first level interval multiplied by a second coefficient value which is a value greater than the first coefficient value and less than 1, and a fourth interval equal to the second level interval multiplied by the second coefficient value; and

an excitation interval controller that controls the excitation interval by

comparing the first interval with a first level-elapsed interval which represents elapsed time after the timing signal shows a transition from the second level to the first level, and starting the excitation interval at a timing at which the first level-elapsed interval becomes equal to the first interval;

comparing the second interval with the first level-elapsed interval, and starting the non-excitation interval at a timing at which the first level-elapsed interval becomes equal to the second interval;

comparing the third interval with a second level-elapsed interval which represents elapsed time after the timing signal shows a transition from the first level to the second level, and starting the excitation interval at a timing at which the second level-elapsed interval becomes equal to the third interval; and

comparing the fourth interval with the second level-elapsed interval, and starting the non-excitation interval at a timing at which the second level-elapsed interval becomes equal to the fourth interval.

19. The drive control circuit according to claim 18 , wherein

the excitation interval controller performs the comparison using the first through fourth intervals that have been derived based on the at least one of the first level interval and the second level interval of the timing signal immediately prior to performing the comparison.