ROTATIONAL POSITION DETECTING METHOD FOR AC SERVOMOTOR AND SIMPLE ENCODER

• US 20100181956A1
• Filed: 05/30/2007
• Published: 07/22/2010
• Est. Priority Date: 05/30/2007
• Status: Active Grant

• Current Assignee: Harmonic Drive Systems Inc.
• Original Assignee: Harmonic Drive Systems Inc.
• Inventors: Sasaki, Kozo
• Granted Patent: US 8,232,757 B2
• Time in Patent Office: Days
• US Class Current: 318/653
• CPC Class Codes: G01P 3/481 of pulse signals
• CPC Class Codes: G01P 3/487 delivered by rotating magnets
• CPC Class Codes: G01P 3/489 Digital circuits therefor
• CPC Class Codes: G05B 19/401 characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes G05B19/19 takes precedence
• CPC Class Codes: G05B 2219/37155 Encoder and delta position counter
• CPC Class Codes: G05B 2219/37163 Marker derived from phase of motor

Abstract

A motor rotational position detecting method detects the magnetic pole position of each phase of a three-phase AC servomotor, generates a three-phase square wave signal having a phase difference of 120 degrees, allocates data on the rotational position of a motor shaft to the edge of each square wave signal, calculates the rotational speed of the motor on the basis of the elapsed time from the previous edge detection point to this time edge detection point, and estimates the rotational position of the motor shaft at a certain period and outputs it on the basis of the rotational speed of the motor and the rotational position allocated to this time edge in the rotational section from this time edge detection point to the next edge detection point. As a result, a detection mechanism can be constructed with a small installation space and at low cost and the output of a high-resolution encoder can be obtained in a pseudo manner.

Claims

1. A method for detecting a rotational position of an AC servomotor, comprising:

detecting the magnetic pole position of each phase of a three-phase AC servomotor;

generating a three-phase square wave signal having a phase difference of 120 degrees as a rotational shaft of the AC servomotor rotates;

outputting, as a rotational position of the motor shaft, rotational position data of the motor shaft allocated in advance to a detected edge of a square wave signal each time the edge is detected;

computing the rotational speed of the motor each time the edge of a square wave signal is detected, on the basis of the time elapsed from the previous edge detection time to a current edge detection time; and

estimating the rotational position of the motor shaft at a certain period and outputting the estimated rotational position as the rotational position of the motor shaft in a rotational section from the current edge detection time to the next edge detection time, on the basis of the computed rotational speed of the motor and the rotational position allocated to the current edge.

2. The method for detecting a rotational position of an AC servomotor according to claim 1, further comprising:

dividing a rotational angle range that corresponds to one electrical angle rotation of the motor shaft into six rotational sections and allocating a single rotational position angle data to each rotational section on the basis of a combination of signal levels of the square wave signals;

detecting the signal level of each square wave signal when a power supply is activated;

detecting in which of the six rotational sections the motor rotational shaft is positioned on the basis of the detected signal level; and

outputting the rotational position data allocated to the detected rotational section as the initial rotational position of the motor shaft at the time of power supply activation.

3. The method for detecting a rotational position of an AC servomotor according to claim 2, wherein rotational position data corresponding to a center position of each rotational section are allocated for each rotational section.

4. The method for detecting a rotational position of an AC servomotor according to claim 3, wherein the rotational speed of the motor is computed as the speed at which the motor shaft rotates through half a rotational section in the elapsed time from activation of the power supply to detection of the edge when the first edge is detected after activation of the power supply.

9. A simple encoder for an AC servomotor, comprising:

a magnetic pole detector for detecting each magnetic pole position of a three-phase AC servomotor and generating a three-phase square wave signal having a phase difference of 120 degrees; and

a signal processing circuit for detecting the rotational position of a motor shaft of the AC servomotor on the basis of each square wave signal;

wherein

the signal processing circuit detects the rotational position of the motor shaft by the method according to claim 1.

11. The simple encoder for an AC servomotor according to claim 9, wherein the signal processing circuit outputs the rotational position of the motor shaft in the form of serial binary data.

12. The simple encoder for an AC servomotor according to claim 9, wherein the signal processing circuit outputs the rotational position of the motor shaft in the form of a two-phase pulse signal having a phase difference of 90 degrees.

13. A simple encoder for an AC servomotor, comprising:

a magnetic pole detector for detecting each magnetic pole position of a three-phase AC servomotor and generating a three-phase square wave signal having a phase difference of 120 degrees; and

a signal processing circuit for detecting the rotational position of a motor shaft of the AC servomotor on the basis of each square wave signal;

wherein

the signal processing circuit detects the rotational position of the motor shaft by the method according to claim 2.

14. A simple encoder for an AC servomotor, comprising:

a magnetic pole detector for detecting each magnetic pole position of a three-phase AC servomotor and generating a three-phase square wave signal having a phase difference of 120 degrees; and

a signal processing circuit for detecting the rotational position of a motor shaft of the AC servomotor on the basis of each square wave signal;

wherein

the signal processing circuit detects the rotational position of the motor shaft by the method according to claim 3.

15. A simple encoder for an AC servomotor, comprising:

a magnetic pole detector for detecting each magnetic pole position of a three-phase AC servomotor and generating a three-phase square wave signal having a phase difference of 120 degrees; and

a signal processing circuit for detecting the rotational position of a motor shaft of the AC servomotor on the basis of each square wave signal;

wherein

the signal processing circuit detects the rotational position of the motor shaft by the method according to claim 4.

5. A method for detecting a rotational position of an AC servomotor, comprising:

detecting the magnetic pole position of each phase of a two-phase AC servomotor;

generating a two-phase square wave signal having a phase difference of 90 degrees as a rotational shaft of the AC servomotor rotates;

outputting, as a rotational position of the motor shaft, rotational position data of the motor shaft allocated in advance to a detected edge of a square wave signal each time the edge is detected;

computing the rotational speed of the motor each time the edge of a square wave signal is detected, on the basis of the time elapsed from the previous edge detection time to a current edge detection time; and

estimating the rotational position of the motor shaft at a certain period and outputting the estimated rotational position as the rotational position of the motor shaft in a rotational section from the current edge detection time to the next edge detection time, on the basis of the computed rotational speed of the motor and the rotational position allocated to the current edge.

6. The method for detecting a rotational position of an AC servomotor according to claim 5, further comprising:

dividing a rotational angle range that corresponds to one electrical angle rotation of the motor shaft into four rotational sections and allocating a single rotational angle position data to each rotational section on the basis of a combination of signal levels of the square wave signals;

detecting the signal level of each square wave signal when a power supply is activated;

detecting in which of the four rotational sections the motor rotational shaft is positioned on the basis of the detected signal level; and

outputting the rotational position data allocated to the detected rotational section as the initial rotational position of the motor shaft at the time of power supply activation.

7. The method for detecting a rotational position of an AC servomotor according to claim 6, wherein rotational position data corresponding to a center position of each rotational section are allocated for each rotational section.

8. The method for detecting a rotational position of an AC servomotor according to claim 7, wherein the rotational speed of the motor is computed as the speed at which the motor shaft rotates through half a rotational section in the elapsed time from activation of the power supply to detection of the edge when the first edge is detected after activation of the power supply.

10. A simple encoder for an AC servomotor, comprising:

a magnetic pole detector for detecting each magnetic pole position of a two-phase AC servomotor and generating a two-phase square wave signal having a phase difference of 90 degrees; and

a signal processing circuit for detecting the rotational position of a motor shaft of the AC servomotor on the basis of each square wave signal;

wherein

the signal processing circuit detects the rotational position of the motor shaft by the method according to claim 5.

16. A simple encoder for an AC servomotor, comprising:

a magnetic pole detector for detecting each magnetic pole position of a two-phase AC servomotor and generating a two-phase square wave signal having a phase difference of 90 degrees; and

a signal processing circuit for detecting the rotational position of a motor shaft of the AC servomotor on the basis of each square wave signal;

wherein

the signal processing circuit detects the rotational position of the motor shaft by the method according to claim 6.

17. A simple encoder for an AC servomotor, comprising:

a magnetic pole detector for detecting each magnetic pole position of a two-phase AC servomotor and generating a two-phase square wave signal having a phase difference of 90 degrees; and

a signal processing circuit for detecting the rotational position of a motor shaft of the AC servomotor on the basis of each square wave signal;

wherein

the signal processing circuit detects the rotational position of the motor shaft by the method according to claim 7.

18. A simple encoder for an AC servomotor, comprising:

a magnetic pole detector for detecting each magnetic pole position of a two-phase AC servomotor and generating a two-phase square wave signal having a phase difference of 90 degrees; and

a signal processing circuit for detecting the rotational position of a motor shaft of the AC servomotor on the basis of each square wave signal;

wherein

the signal processing circuit detects the rotational position of the motor shaft by the method according to claim 8.

19. The simple encoder for an AC servomotor according to claim 10, wherein the signal processing circuit outputs the rotational position of the motor shaft in the form of serial binary data.

20. The simple encoder for an AC servomotor according to claim 10, wherein the signal processing circuit outputs the rotational position of the motor shaft in the form of a two-phase pulse signal having a phase difference of 90 degrees.