Method and apparatus for position control of an electric motor

• US 4,558,265 A
• Filed: 03/02/1983
• Issued: 12/10/1985
• Est. Priority Date: 03/03/1982
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Takahashi, Tadashi, Miyashita, Kunio, Hayashida, Hiroshi
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): Bergmann, Saul M.
• Application Number:
  US06/471,434
• Time in Patent Office: 1,014 Days
• Field of Search: 318/561, 318/618, 318/617, 318/602, 318/611, 318/367
• US Class Current: 318/561
• CPC Class Codes: G05B 19/416 characterised by control of velocity, acceleration or deceleration G05B19/19 takes precedence
• CPC Class Codes: G05B 2219/34215 Microprocessor
• CPC Class Codes: G05B 2219/37388 Acceleration or deceleration, inertial measurement
• CPC Class Codes: G05B 2219/41021 Variable gain
• CPC Class Codes: G05B 2219/41245 Discrimination of direction
• CPC Class Codes: G05B 2219/42237 Pwm pulse width modulation, pulse to position modulation ppm

Abstract

A control process and apparatus for positioning an electric motor provided with a rotation angle detector at a designated position positively at a high speed without being accompanied with hunting notwithstanding variation in the motor current and inertia of a load. The control process activated upon starting of the motor and ending at the stoppage of the motor at the designated position includes a first control region in which acceleration of the motor having been started is detected and subsequently a constant speed operation of the motor is effected at a maximum speed. A deceleration initiating time point is determined in dependence on the acceleration. A second control region is provided in which the motor is decelerated in accordance with a deceleration pattern determined in dependence on a rotation angle extending between a position corresponding to the deceleration initiating time point and the commanded stop position, and motor torque and inertia of load is detected at the deceleration initiating time point. During a third control region the motor is progressively decelerated by reducing correspondingly the gain of voltage (current) applied to the motor when the motor position approaches to the commanded stop position. The control process also includes a fourth control region in which, when the motor stops short of or beyond the commanded position, the duty ratio of voltage applied to the motor is progressively increased to thereby re-start the motor toward the commanded position, and a fifth control region in which the motor is held at the commanded stop position.

Claims

1. A method of controlling a position of an electric motor with the aid of a rotation angle detector for detecting a rotation angle of a rotating shaft of said motor or a rotating shaft constituting a part of a power transmission path for operatively coupling said rotating shaft of said motor to an apparatus constituting a load, said rotation angle detector providing signals representative of the rotation angle and a rotating speed of said rotating shaft, and a control circuit for controlling said motor so that said motor is positioned at a given position in accordance with a position command signal issued to said motor in consideration of said rotation angle and said rotating speed,

wherein a control process activated upon starting of said motor in response to said position command signal and ending upon stoppage of said motor at a position designated by said position command signal includes a first control region in which at least acceleration of said motor in an accelerating phase thereof is detected and subsequently a constant speed operation of said motor is effected at a maximum speed, a deceleration initiating time point determined on the basis of said acceleration, a second control region in which said motor is decelerated from said deceleration initiating time point in accordance with a deceleration pattern which is determined in dependence on a rotation angle between the deceleration initiating position and the commanded stop position, torque of said motor and magnitude of inertia of said load detected at the time point at which said deceleration is initiated, and a fifth control region in which said motor is held at the stop position designated by said position command signal.

2. A method of controlling a position of an electric motor according to claim 1, wherein there is interposed between said second control region and said fifth control region a second control region in which operation of said motor is controlled by progressively reducing a gain of an apparatus for energizing said motor.

6. An apparatus for controlling a position of an electric motor according to claim 2, wherein there is interposed between said third and fifth control region of a fourth control region in which when said motor is stopped short of or beyond the stop position designated by said position command signal, and wherein a duty ratio determined by said control circuit is progressively increased to thereby re-start said motor toward said stop position designated by said position command signal.

3. An apparatus for controlling a position of an electric motor, comprising a rotation angle detector for detecting a rotation angle of a rotating shaft of said motor or a rotating shaft constituting a part of a power transmission path for operatively coupling said rotating shaft of said motor to an apparatus constituting a load, said rotation angle detector providing signals representative of the rotation angle and a rotating speed of said rotating shaft, and a control system for controlling said motor so that said motor is positioned at a given position in accordance with a position command signal issued to said motor in consideration of said rotating speed,

wherein a control process activated upon starting of said motor in response to said position command signal and ending upon stoppage of said motor at a position designated by said position command signal includes a control region in which said motor is held at the stop position designated by said position command signal,

said control system being further so arranged as to output a duty for generating in said motor a torque of such magnitude and direction as to cancel a cogging torque of said motor for holding said motor at the commanded position in said control region.

4. An apparatus for controlling a position of an electric motor, comprising a rotation angle detector for detecting a rotation angle of a rotating shaft of said motor or a rotating shaft constituting a part of a power transmission path for operatively coupling said rotating shaft of said motor to an apparatus constituting a load, said rotation angle detector providing signals representative of the rotation angle and a rotating speed of said rotating shaft, and a control circuit for controlling said motor so that said motor is positioned at a given position in accordance with a position command signal issued to said motor in consideration of said rotating speed,

wherein a control process activated upon starting of said motor in response to said position command signal and ending upon stoppage of said motor at a position designated by said position command signal includes a control region in which when said motor is stopped short of or beyond the stop position designated by said position command signal, and wherein a duty ratio determined by said control circuit is progressively increased to thereby re-start said motor toward said stop position designated by said position command signal.

5. An apparatus for controlling a position of an electric motor, comprising a rotation angle detector for detecting a rotation angle of a rotating shaft of said motor or a rotating shaft constituting a part of a power transmission path for operatively coupling said rotating shaft of said motor to an apparatus constituting a load, said rotation angle detector providing signals representative of the rotation angle and a rotating speed of said rotating shaft, and a control system for controlling said motor so that said motor is positioned at a given position in accordance with a position command signal issued to said motor in consideration of said rotating speed,

said control system including a control circuit capable of applying a variable voltage of positive or negative polarity to said motor, said control circuit including a circuit for fetching a given positioning command, a circuit for deriving the motor speed signal and the motor position signal from the output signal of said rotation angle detector, a micro-computer for arithmetically processing said speed signal and said position signal, a program stored in said micro-computer for deciding whether said motor is to be stopped, and a H-control circuit, wherein when said motor is stopped at a position which is short of or beyond said commanded stop position, the motor is restarted by increasing progressively the voltage applied to the motor.