Control mode changing over method for servo control system

• US 5,986,422 A
• Filed: 04/29/1997
• Issued: 11/16/1999
• Est. Priority Date: 08/31/1995
• Status: Expired due to Fees

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Okita, Tadashi, Iwashita, Yasusuke
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): LOCKETT, KIMBERLY R
• Application Number:
  US08/836,427
• Time in Patent Office: 931 Days
• Field of Search: 318/432, 318/433, 318/434, 318/609, 318/610, 318/568.2, 318/590, 318/567
• US Class Current: 318/567
• CPC Class Codes: G05B 19/39 using a combination of the means covered by at least two of the preceding groups G05B19/21, G05B19/27 and G05B19/33
• CPC Class Codes: G05B 2219/42008 P regulator for position loop
• CPC Class Codes: G05B 2219/42011 PI regulator for speed loop
• CPC Class Codes: G05B 2219/42123 Position loop then force, current loop
• CPC Class Codes: G05B 2219/42126 Bumpless, smooth transfer between two control modes

Abstract

A control mode changing over method for a servo control system, which is capable of reducing a shock occurring in changing over a control mode from a torque control mode to a position/velocity control mode. In the torque control mode, a value of an integrator in a velocity loop for the position/velocity control mode is rewritten into a torque command value for torque control so that the value of the integrator is always set to the same value as the torque command. When a control mode is changed over from the torque control mode to the position/velocity control mode, a torque command value for a servo motor is obtained based on the value of the integrator rewritten in the torque control mode. Thus, a continuous torque command value is given to the servo motor in changing over the control mode.

Claims

1. A control mode changing over method for a servo control system operable in either a torque control mode controlling a torque of a servo motor or a position/velocity control mode controlling a position and a velocity of a servo motor using a position loop and a velocity loop, comprising the steps of:

(a) rewriting a value stored in an integrator provided in said velocity loop to a torque command for torque control when said servo control system is operating in the torque control mode, such that the value stored in the integrator coincides with the torque command in the torque control mode; and

(b) obtaining a torque command value for said servo motor using the value of said integrator rewritten in said step (a) when the control mode is changed from the torque control mode to the position/velocity control mode.

2. The control mode changing over method for a servo control system according to claim 1, wherein said step (a) further includes the step of rewriting the value of said integrator for each position and velocity loop processing.

3. A method for controlling a servo control system operating in a either a torque control mode or a position/velocity control mode, comprising the steps of:

rewriting a value stored in an integrator into a torque command when the servo control system is operating in the torque control mode, such that the value stored in the integrator coincides with the torque command in the torque control mode; and

outputting a torque command value using the value rewritten in the integrator when the control mode is changed from the torque control mode to the position/velocity control mode.

4. A servo control system for controlling a machine tool or robot, comprising:

a motor driving one of a movable part of the machine tool and an axis of the robot;

a device writing a command for predetermined distribution periods;

a circuit executing position and velocity control in a position/velocity control mode and torque control in a torque control mode;

a memory storing the command for exchange between the device and the circuit; and

an amplifier driving the motor based on the command from the circuit, wherein the command coincides with a torque command in the torque control mode.

5. A servo control system for controlling a servo motor in a torque control mode or a position/velocity control mode, comprising:

an integrator rewriting a value stored therein to a torque command for torque control when the system is operating in the torque control mode, and obtaining a torque command value using the value rewritten in the integrator such that the value stored in the integrator coincides with the torque command in the torque control mode; and

a switch determining the control mode and outputting the torque command for the servo motor, driving the servo motor.