Motor control method and control device

• US 20050057200A1
• Filed: 09/10/2004
• Published: 03/17/2005
• Est. Priority Date: 09/12/2003
• Status: Active Grant

• Current Assignee: Brother Kogyo Kabushiki Kaisha (Brother Industries Limited)
• Original Assignee: Brother Kogyo Kabushiki Kaisha (Brother Industries Limited)
• Inventors: Akiyama, Shigeki
• Granted Patent: US 7,821,216 B2
• Time in Patent Office: Days
• US Class Current: 318/66
• CPC Class Codes: H02P 23/20 Controlling the acceleration or deceleration
• CPC Class Codes: H02P 27/08 with pulse width modulation

Abstract

When motor drive is initiated, firstly a PWM value at time of driving initiation is set to an initial setting value start_pwm1, and gradually increased by a specified amount in specified period. When an encoder edge is detected, the PWM value is reset to the initial setting value, and increased again in the same manner. From second edge detection, next PWM initial value is set corresponding to a PWM value at the time of edge detection. If the PWM value at the time of edge detection is larger than det_pwm_max owing to load on the motor becoming large and thereby driving velocity becoming slower, a PWM value which is larger than previous PWM initial value is set as a new PWM initial value. The driving target can be driven stably irrelevant to fluctuation of the load on the motor.

Claims

1. A motor control method, comprising the steps of:

(a) driving a motor such that the driving force of the motor gradually increases from an initial driving force;

(b) repeatedly performing the step (a), each time an object to be driven by the motor is driven by a specified amount; and

(c) changing the driving force of the motor for the next time depending on the state of driving at the end of the driving of the object to be driven by the specified amount, such that the object to be driven is driven at a target driving velocity.

2. A motor control method, comprising the steps of:

(a) setting an initial driving force of a motor;

(b) driving the motor such that the driving force of the motor increases by a fixed amount at a specific cycle from the initial driving force set in the step (a);

(c) performing the step (a) and the step (b), each time an object to be driven by the motor is driven by a specified amount; and

(d) changing the initial driving force in the step (a) depending on the driving force at the end of the driving of the object to be driven by the specified amount, such that the object to be driven is driven at a target driving velocity.

3. The motor control method as Bet forth in claim 2, wherein each time the object to be driven is driven by the specified amount, at least one of the processings of:

(e) increasing the initial driving force when the driving force at the end of the driving by the specified amount is larger than a predetermined maximum driving force threshold, and

(f) decreasing the initial driving force when the driving force at the end of the driving by the specified amount is smaller than a predetermined minimum driving force threshold is performed.

4. The motor control method as set forth in claim 3,

wherein the amount of increase in the case of increasing the initial driving force in the processing of (e) is a predetermined standard fixed amount of increase,

and wherein the amount of decrease in the case of decreasing the initial driving force in the processing of (f) is a predetermined standard fixed amount of decrease.

5. The motor control method as set forth in claim 3,

wherein the amount of increase in the case of increasing the initial driving force in the processing of (e) is determined so as to continuously or gradually become greater as the difference between the driving force at the end of the driving of the object to be driven by the specified amount and the maximum driving force threshold becomes greater,

and wherein the amount of decrease in the case of decreasing the initial driving force in the processing of (f) is determined so as to continuously or gradually become greater as the difference between the minimum driving force threshold and the driving force at the end of the driving of the object to be driven by the specified amount becomes greater.

6. A motor control method, comprising the steps of:

(a) setting an initial driving force of a motor;

(b) driving the motor such that the driving force of the motor increases by a fixed amount at a specific cycle from the initial driving force set in the step (a);

(c) performing the step (a) and the step (b), each time an object to be driven by the motor is driven by a specified amount; and

(d) changing the initial driving force in the step (a) depending on the time taken for the driving of the object to be driven by the specified amount, such that the object to be driven is driven at a target driving velocity.

7. The motor control method as set forth in claim 6, wherein each time the object to be driven by the motor is driven by the specified amount, at least one of the processings of:

(e) increasing the initial driving force when the time taken for the driving by the specified amount is longer than a predetermined maximum elapsed time threshold, and

(f) decreasing the initial driving force when the time taken for the driving by the specified amount is shorter than a predetermined minimum elapsed time threshold is performed.

8. The motor control method as set forth in claim 7,

wherein the amount of increase in the case of increasing the initial driving force in the processing of (e) is a predetermined standard fixed amount of increase,

and wherein the amount of decrease in the case of decreasing the initial driving force in the processing of (f) is a predetermined standard fixed amount of decrease.

9. The motor control method as set forth in claim 7,

wherein the amount of increase in the case of increasing the initial driving force in the processing of (e) is determined so as to continuously or gradually become greater as the difference between the time taken for the driving of the object to be driven by the specified amount and the maximum elapsed time threshold becomes greater,

and wherein the amount of decrease in the case of decreasing the initial driving force in the processing of (f) is determined so as to continuously or gradually become greater as the difference between the minimum elapsed time threshold and the time taken for the driving of the object to be driven by the specified amount becomes greater.

10. A motor control method, comprising the steps of

(a) setting an initial driving force of a motor;

(b) driving the motor such that the driving force of the motor increases by a fixed amount at a specific cycle from the initial driving force set in the step (a);

(c) performing the step (a) and the step (b), each time an object to be driven by the motor is driven by a specified amount; and

(d) changing the initial driving force in the step (a) depending on the driving velocity of the object to be driven at the end of the driving of the object to be driven by the specified amount, such that the object to be driven is driven at a target driving velocity.

11. The motor control method as set forth in claim 10, wherein each time the object to be driven by the motor is driven by the specified amount, at least one of the processings of:

(e) increasing the initial driving force when the driving velocity at the end of the driving by the specified amount is lower than a predetermined minimum velocity threshold, and

(f) decreasing the initial driving force when the driving velocity at the end of the driving by the specified amount is higher than a predetermined maximum velocity threshold is performed.

12. The motor control method as set forth in claim 11,

wherein the amount of increase in the case of increasing the initial driving force in the processing of (e) is a predetermined standard fixed amount of increase,

and wherein the amount of decrease in the case of decreasing the initial driving force in the processing of (f) is a predetermined standard fixed amount of decrease.

13. The motor control method as set forth in claim 11,

wherein the amount of increase in the case of increasing the initial driving force in the processing of (e) is determined so as to continuously or gradually become greater as the difference between the minimum velocity threshold and the driving velocity at the end of the driving of the object to be driven by the specified amount becomes greater,

and wherein the amount of decrease in the case of decreasing the initial driving force in the processing of (b) is determined so as to continuously or gradually become greater as the difference between the driving velocity at the end of the driving of the object to be driven by the specified amount and the maximum velocity threshold becomes greater.

14. A motor control apparatus, comprising:

a driving detection device that outputs a driving detection signal, each time an object to be driven by a motor is driven by a specified amount, indicating completion of the driving by the specified amount;

a control device that outputs a driving force control signal to gradually increase the driving force of the motor from an initial driving force, each time the driving detection signal is output from the driving detection device;

a motor driving device that rotationally drives the motor in accordance with the driving force control signal from the control device; and

a driving force changing device that changes the driving force for the next time, each time the driving detection signal is output from the driving detection device, depending on the state of driving at the end of the driving of the object to be driven by the specified amount, such that the object to be driven is driven at a target driving velocity.

15. A motor control apparatus, comprising:

a driving detection device that outputs a driving detection signal, each time an object to be driven by a motor is driven by a specified amount, indicating completion of the driving by the specified amount;

a control device that outputs a driving force control signal to increase the driving force of the motor from a set initial driving force by a fixed amount at a specific cycle, each time the driving detection signal is output from the driving detection device; and

a motor driving device that rotationally drives the motor in accordance with the driving force control signal from the control device,

wherein the motor control apparatus further includes an initial driving force changing device that changes the set initial driving force, each time the driving detection signal is output from the driving detection device, depending on the driving force at the time of the output, such that the object to be driven is driven at a target driving velocity.

16. The motor control apparatus as set forth in claim 15, further comprising a driving force determination device that determines, each time the driving detection signal is output, whether or not the driving force at the time of the output is larger than a predetermined maximum driving force threshold,

wherein the initial driving force changing device increases the initial driving force, when it is determined by the driving force determination device that the driving force at the time of the output is larger than the predetermined maximum driving force threshold.

17. The motor control apparatus as set forth in claim 16, wherein the amount of increase in the case of increasing the initial driving force by the initial driving force changing device is a predetermined standard fixed amount.

18. The motor control apparatus as set forth in claim 16, further comprising:

a first difference value calculating device that calculates a first difference value as a difference between the driving force at the time of output of the driving detection signal and the maximum driving force threshold when it is determined by the driving force determination device that the driving force is larger than the maximum driving force threshold; and

an increase amount setting device that sets an amount of increase of the initial driving force in accordance with the first difference value,

wherein the initial driving force changing device increases the initial driving force by the amount of increase set by the increase amount setting device in the case of increasing the initial driving force.

19. The motor control apparatus as set forth in claim 18, further comprising:

a first difference determination device that determines whether or not a first difference value calculated by the first difference value calculating device is larger than a predetermined first difference threshold,

wherein the increase amount setting device sets the amount of increase such that the amount of increase is larger when it is determined by the first difference determination device that the first difference value is larger than the predetermined first difference threshold compared with when it is not determined that the first difference value is larger.

20. The motor control apparatus as set forth in claim 18, wherein the increase amount setting device sets the amount of increase in accordance with the first difference value such that the amount of increase becomes larger as the first difference value calculated by the first difference value calculating device becomes larger.

21. The motor control apparatus as set forth in claim 15, further comprising a driving force determination device that determines, each time the driving detection signal is output, whether or not the driving force at the time of the output is smaller than a predetermined minimum driving force threshold,

wherein the initial driving force changing device decreases the initial driving force, when it is determined by the driving force determination device that the driving force at the time of the output is smaller than the predetermined minimum driving force threshold.

22. The motor control apparatus as set forth in claim 21, wherein the driving force determination device determines whether or not the driving force at the time of the output of the driving detection signal is larger than a predetermined maximum driving force threshold which is at least equal to the predetermined minimum driving force threshold or more,

wherein the initial driving force changing device increases the initial driving force, when it is determined by the driving force determination device that the driving force at the time of the output of the driving detection signal is larger than the predetermined maximum driving force threshold.

23. The motor control apparatus as set forth in claim 22,

wherein the predetermined minimum driving force threshold and the predetermined maximum driving force threshold are values different from each other,

and wherein the initial driving force changing device sets the initial driving force to a set value at the time of the previous output of the driving detection signal, when it is determined by the driving force determination device that the driving force at the time of the output of the driving detection signal more than the minimum driving force threshold and also less than the maximum driving force threshold.

24. The motor control apparatus as set forth in claim 22, wherein the amount of increase in the case of increasing the initial driving force by the initial driving force changing device is a predetermined standard fixed amount.

25. The motor control apparatus as set forth in claim 22, further comprising:

a first difference value calculating device that calculates a first difference value as a difference between the driving force at the time of output of the driving detection signal and the maximum driving force threshold when it is determined by the driving force determination device that the driving force is larger than the maximum driving force threshold; and

an increase amount setting device that sets an amount of increase of the initial driving force in accordance with the first difference value,

wherein the initial driving force changing device increases the initial driving force by the amount of increase set by the increase amount setting device in the case of increasing the initial driving force.

26. The motor control apparatus as set forth in claim 21, wherein the amount of decrease in the case of decreasing the initial driving force by the initial driving force changing device is a predetermined standard fixed amount.

27. The motor control apparatus as set forth in claim 21, further comprising:

a second difference value calculating device that calculates a second difference value as a difference between the minimum driving force threshold and the driving force at the time of output of the driving detection signal, when it is determined by the driving force determination device that the driving force is smaller than the minimum driving force threshold; and

a decrease amount setting device that sets an amount of decrease of the initial driving force in accordance with the second difference value,

wherein the initial driving force changing device decreases the initial driving force by the amount of decrease set by the decrease amount setting device in the case of decreasing the initial driving force.

28. The motor control apparatus as set forth in claim 27, further comprising:

a second difference determination device that determines whether or not a second difference value calculated by the second difference value calculating device is larger than a predetermined second difference threshold,

wherein the decrease amount setting device sets the amount of decrease such that the amount of decrease is larger when it is determined by the second difference determination device that the second difference value is larger than the predetermined second difference threshold compared with when it is not determined that the second difference value is larger.

29. The motor control apparatus as set forth in claim 27, wherein the decrease amount setting device sets the amount of decrease in accordance with the second difference value such that the amount of decrease becomes larger as the second difference value calculated by the second difference value calculating device becomes larger.

30. The motor control apparatus as set forth in claim 15, wherein the initial driving force changing device does not change the initial driving force, when the driving detection signal is output from the driving detection device for the first time since the start of the driving of the object to be driven.

31. The motor control apparatus as set forth in claim 15,

wherein the motor driving device rotationally drives the motor by the driving force corresponding to an input PWM signal,

and wherein the control device outputs the PWM signal indicating a PWM duty value as the driving force control signal, and increases the PWM duty value by a fixed amount at a specific cycle from an initial PWM duty value corresponding to the initial driving force, each time the driving detection signal is output.

32. A motor control apparatus, comprising:

a driving detection device that outputs a driving detection signal, each time an object to be driven by a motor is driven by a specified amount, indicating completion of the driving by the specified amount;

a control device that outputs a driving force control signal to increase the driving force of the motor from a set initial driving force by a fixed amount at a specific cycle, each time the driving detection signal is output from the driving detection device; and

a motor driving device that rotationally drives the motor in accordance with the driving force control signal from the control device,

wherein the motor control apparatus further includes an initial driving force changing device that changes the set initial driving force, each time the driving detection signal is output from the driving detection device, depending on the elapsed time from the previous output to the current output of the driving detection signal, such that the object to be driven is driven at a target driving velocity.

33. The motor control apparatus as set forth in claim 32, further comprising an elapsed time determination device that determines, each time the driving detection signal is output, whether or not the elapsed time is longer than a predetermined maximum elapsed time threshold,

wherein the initial driving force changing device increases the initial driving force, when it is determined by the elapsed time determination device that the elapsed time is longer than the predetermined maximum elapsed time threshold.

34. The motor control apparatus as set forth in claim 33, wherein the amount of increase in the case of increasing the initial driving force by the initial driving force changing device is a predetermined standard fixed amount.

35. The motor control apparatus as set forth in claim 33, further comprising:

a first difference value calculating device that calculates a first difference value as a difference between the elapsed time and the maximum elapsed time threshold when it is determined by the elapsed time determination device that the elapsed time is longer than the maximum elapsed time threshold; and

an increase amount setting device that sets an amount of increase of the initial driving force in accordance with the first difference value,

wherein the initial driving force changing device increases the initial driving force by the amount of increase set by the increase amount setting device in the case of increasing the initial driving force.

36. The motor control apparatus as set forth in claim 35, further comprising:

a first difference determination device that determines whether or not the first difference value calculated by the first difference value calculating device is larger than a predetermined first difference threshold,

wherein the increase amount setting device sets the amount of increase such that the amount of increase is larger when it is determined by the first difference determination device that the first difference value is larger than the predetermined first difference threshold compared with when it is not determined that the first difference value is larger.

37. The motor control apparatus as set forth in claim 35, wherein the increase amount setting device sets the amount of increase in accordance with the first difference value such that the amount of increase becomes larger as the first difference value calculated by the first difference value calculating device becomes larger.

38. The motor control apparatus as set forth in claim 32, further comprising an elapsed time determination device that determines, each time the driving detection signal is output, whether or not the elapsed time is shorter than a predetermined minimum elapsed time threshold,

wherein the initial driving force changing device decreases the initial driving force, when it is determined by the elapsed time determination device that the elapsed time is shorter than the predetermined minimum elapsed time threshold.

39. The motor control apparatus as set forth in claim 38,

wherein the elapsed time determination device also determines whether or not the elapsed time is longer than a predetermined maximum elapsed time threshold which is at least equal to or longer than the predetermined minimum elapsed time threshold,

and wherein the initial driving force changing device increases the initial driving force, when it is determined by the elapsed time determination device that the elapsed time is longer than the predetermined maximum elapsed time threshold.

40. The motor control apparatus as set forth in claim 39,

wherein the predetermined minimum elapsed time threshold and the predetermined maximum elapsed time threshold are values different from each other,

and wherein the initial driving force changing device sets the initial driving force to a set value at the time of the previous output of the driving detection signal, when it is determined by the elapsed time determination device that the elapsed time is longer than the predetermined minimum elapsed time threshold and also less than the predetermined maximum elapsed time threshold.

41. The motor control apparatus as set forth in claim 39, wherein the amount of increase in the case of increasing the initial driving force by the initial driving force changing device is a predetermined standard fixed amount.

42. The motor control apparatus as set forth in claim 39, further comprising:

a first difference value calculating device that calculates a first difference value as a difference between the maximum elapsed time threshold and the elapsed time at the time of the output of the driving detection signal when it is determined by the elapsed time determination device that the elapsed time is longer than the maximum elapsed time threshold; and

an increase amount setting device that sets an amount of increase of the initial driving force in accordance with the first difference value,

wherein the initial driving force changing device increases the initial driving force by the amount of increase set by the increase amount setting device in the case of increasing the initial driving force.

43. The motor control apparatus as set forth in claim 38, wherein the amount of decrease in the case of decreasing the initial driving force by the initial driving force changing device is a predetermined standard fixed amount.

44. The motor control apparatus as set forth in claim 38, further comprising:

a second difference value calculating device that calculates a second difference value as a difference between the minimum elapsed time threshold and the elapsed time, when it is determined by the elapsed time determination device that the elapsed time is shorter than the minimum elapsed time threshold; and

a decrease amount setting device that sets an amount of decrease of the initial driving force in accordance with the second difference value,

wherein the initial driving force changing device decreases the initial driving force by the amount of decrease set by the decrease amount setting device in the case of decreasing the initial driving force.

45. The motor control apparatus as set forth in claim 44, further comprising:

a second difference determination device that determines whether or not a second difference value calculated by the second difference value calculating device is larger than a predetermined second difference threshold,

wherein the decrease amount setting device sets the amount of decrease such that the amount of decrease is larger when it is determined by the second difference determination device that the second difference value is larger than the predetermined second difference threshold compared with when it is not determined that the second difference value is larger.

46. The motor control apparatus as set forth in claim 44, wherein the decrease amount setting device sets the amount of decrease in accordance with the second difference value such that the amount of decrease becomes larger as the second difference value calculated by the second difference value calculating device becomes larger.

47. The motor control apparatus as set forth in claim 32, wherein the initial driving force changing device does not change the initial driving force, when the driving detection signal is output from the driving detection device for the first time since the start of the driving of the object to be driven.

48. The motor control apparatus as set forth in claim 32,

wherein the motor driving device rotationally drives the motor by the driving force corresponding to an input PWM signal,

and wherein the control device outputs the PWM signal indicating a PWM duty value as the driving force control signal, and increases the PWM duty value by a fixed amount at a specific cycle from an initial PWM duty value corresponding to the initial driving force, each time the driving detection signal is output.

49. A motor control apparatus, comprising:

a driving detection device that outputs a driving detection signal, each time an object to be driven by a motor is driven by a specified amount, indicating completion of the driving by the specified amount;

a control device that outputs a driving force control signal to increase the driving force of the motor from a set initial driving force by a fixed amount at a specific cycle, each time the driving detection signal is output from the driving detection device; and

a motor driving device that rotationally drives the motor in accordance with the driving force control signal from the control device,

wherein the motor control apparatus further includes an initial driving force changing device that changes the set initial driving force, each time the driving detection signal is output from the driving detection device, depending on the driving velocity of the object to be driven at the time of the output, such that the object to be driven is driven at a target driving velocity.

50. The motor control apparatus as set forth in claim 49, further comprising a velocity determination device that determines, each time the driving detection signal is output, whether or not the driving velocity at the time of the output is lower than a predetermined minimum velocity threshold,

wherein the initial driving force changing device increases the initial driving force, when it is determined by the velocity determination device that the driving velocity at the time of the output is lower than the predetermined minimum elapsed time threshold.

51. The motor control apparatus as set forth in claim 50, wherein the amount of increase in the case of increasing the initial driving force by the initial driving force changing device is a predetermined standard fixed amount.

52. The motor control apparatus as set forth in claim 50, further comprising:

a first difference value calculating device that calculates a first difference value as a difference between the minimum velocity threshold and the driving velocity at the time of the output of the driving detection signal when it is determined by the velocity determination device that the driving velocity is lower than the minimum velocity threshold; and

an increase amount setting device that sets an amount of increase of the initial driving force in accordance with the first difference value,

wherein the initial driving force changing device increases the initial driving force by the amount of increase set by the increase amount setting device in the case of increasing the initial driving force.

53. The motor control apparatus as set forth in claim 52, further comprising:

a first difference determination device that determines whether or not a first difference value calculated by the first difference value calculating device is larger than a predetermined first difference threshold,

wherein the increase amount setting device sets the amount of increase such that the amount of increase is larger when it is determined by the first difference determination device that the first difference value is larger than the predetermined first difference threshold compared with when it is not determined that the first difference value is larger.

54. The motor control apparatus as set forth in claim 52, wherein the decrease amount setting device sets the amount of decrease in accordance with the second difference value such that the amount of decrease becomes larger as the second difference value calculated by the second difference value.

55. The motor control apparatus as set forth in claim 49, further comprising a velocity determination device that determines, each time the driving detection signal is output, whether or not the driving velocity at the time of the output is higher than a predetermined maximum velocity threshold,

wherein the initial driving force changing device decreases the initial driving force, when it is determined by the velocity determination device that the driving velocity at the time of the output is higher than the predetermined maximum velocity threshold.

56. The motor control apparatus as set forth in claim 55,

wherein the velocity determination device also determines whether or not the driving velocity at the time of the output of the driving detection signal is lower than a predetermined minimum velocity threshold which is at least equal to or lower than the predetermined maximum velocity threshold,

and wherein the initial driving force changing device increases the initial driving force, when it is determined by the velocity determination device that the driving velocity at the time of the output of the driving detection signal is lower than the predetermined minimum velocity threshold.

57. The motor control apparatus as set forth in claim 56,

wherein the predetermined minimum velocity threshold and the predetermined maximum velocity threshold are values different from each other,

and wherein the initial driving force changing device sets the initial driving force to a set value at the time of the previous output of the driving detection signal, when it is determined by the driving velocity determination device that the driving velocity at the time of the output of the driving detection signal is higher than the minimum driving velocity threshold and also lower than the maximum driving velocity threshold.

58. The motor control apparatus as set forth in claim 56, wherein the amount of increase in the case of increasing the initial driving force by the initial driving force changing device is a predetermined standard fixed amount.

59. The motor control apparatus as set forth in claim 56, further comprising:

a first difference value calculating device that calculates a first difference value as a difference between the minimum velocity threshold and the driving velocity at the time of the output of the driving detection signal, when it is determined by the velocity determination device that the driving velocity is lower than the minimum velocity threshold; and

an increase amount setting device that sets an amount of increase of the initial driving force in accordance with the first difference value,

wherein the initial driving force changing device increases the initial driving force by the amount of increase set by the increase amount setting device in the case of increasing the initial driving force.

60. The motor control apparatus as set forth in claim 65, wherein the amount of decrease in the case of decreasing the initial driving force by the initial driving force changing device is a predetermined standard fixed amount.

61. The motor control apparatus as set forth in claim 55, further comprising:

a second difference value calculating device that calculates a second difference value as a difference between the driving velocity at the time of the output of the driving detection signal and the maximum velocity threshold, when it is determined by the velocity determination device that the driving velocity is higher than the maximum velocity threshold; and

a decrease amount setting device that sets an amount of decrease of the initial driving force in accordance with the second difference value,

wherein the initial driving force changing device decreases the initial driving force by the amount of decrease set by the decrease amount setting device in the case of decreasing the initial driving force.

62. The motor control apparatus as set forth in claim 61, further comprising:

a second difference determination device that determines whether or not a second difference value calculated by the second difference value calculating device is larger than a predetermined second difference threshold,

wherein the decrease amount setting device sets the amount of decrease such that the amount of decrease is larger when it is determined by the second difference determination device that the second difference value is larger than the predetermined second difference threshold compared with when it is not determined that the second difference value is larger calculating device becomes larger.

63. The motor control apparatus as set forth in claim 61, wherein the decrease amount setting device sets the amount of decrease in accordance with the second difference value such that the amount of decrease becomes larger as the second difference value calculated by the second difference value calculating device becomes larger.

64. The motor control apparatus as set forth in claim 49, wherein the initial driving force changing device does not change the initial driving force, when the driving detection signal is output from the driving detection device for the first time since the start of the driving of the object to be driven.

65. The motor control apparatus as set forth in claim 49,

wherein the motor driving device rotationally drives the motor by the driving force corresponding to an input PWM signal,

and wherein the control device outputs the PWM signal indicating a PWM duty value as the driving force control signal, and increases the PWM duty value by a fixed amount at a specific cycle from an initial PWM duty value corresponding to the initial driving force, each time the driving detection signal is output.