Method of feedforward control for servomotor

• US 5,654,619 A
• Filed: 09/25/1995
• Issued: 08/05/1997
• Est. Priority Date: 09/26/1994
• Status: Expired due to Term

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Iwashita, Yasusuke
• Primary Examiner(s): Masih, Karen
• Application Number:
  US08/533,649
• Time in Patent Office: 680 Days
• Field of Search: 318/636, 318/610, 318/609, 318/560, 318/568.22, 318/569, 318/571, 318/635, 318/632, 388/800, 388/842, 388/906, 388/902, 388/907.5, 364/148, 364/164, 364/174, 364/178, 364/424.05
• US Class Current: 318/636
• CPC Class Codes: G05B 19/19 characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path
• CPC Class Codes: G05B 21/02 electric
• CPC Class Codes: G05B 2219/49088 As a function of, regulate feed as function of material, tool
• CPC Class Codes: G05B 2219/50025 Go to reference, switches and dog detect origin, combine with pulse from encoder

Abstract

A control method of a servomotor, such that a moving command for position-velocity processing, which is executed in every sampling period obtained by dividing a distribution period of moving commands into N units of equal parts, is determined from the above described moving commands of the distribution period. A velocity compensatory component is obtained on the basis of a moving command in a distribution period preceding by one period the present distribution period and is added to a velocity command, and an acceleration compensatory component obtained on the basis of a moving command preceding the time of the present position-velocity loop processing is added to a torque command, so that the phase of acceleration compensatory data is advanced from that of velocity compensatory data in feedforward operations.

Claims

1. A method of feedforward control for a servomotor, to control the servomotor through position-velocity loop control to be executed by a moving command in each sampling period obtained by dividing a present distribution period of the moving command into N equal parts, said method comprising the steps of:

reading a moving command in a distribution period preceding by one period the present distribution period to determine a moving command for each position-velocity loop processing, multiplying the determined moving command by a positional feedforward coefficient to produce a positional feedforward amount, performing positional loop processing to obtain a velocity command, and adding the position feedforward amount to the velocity command obtained by positional loop processing to determine the velocity command with respect to velocity loop processing; and

determining a moving command preceding the time of the present position-velocity loop processing, multiplying a differentiated value of the obtained moving command by a velocity feedforward coefficient so produce a velocity feedforward amount, performing velocity loop processing to produce a torque command, and adding the velocity feedforward amount to the torque command obtained by velocity loop processing to determine a torque command to the servomotor.

2. A method of feedforward control for a servomotor according to claim 1, further comprising the step of setting the time precedence substantially equal to one sampling period.

3. A method of feedforward control for a servomotor, to claim 1, further comprising the step of setting the time precedence within one sampling period.

4. A method of feedforward control for a servomotor, to control the servomotor through position-velocity loop control to be executed by a moving command obtained in each sampling period obtained by dividing a moving command obtained in each sampling period obtained by dividing a present distribution period of the moving command into N equal parts, said method comprising the steps of:

reading a moving command in a distribution period preceding by one period the present distribution period to determine a moving mean value of moving commands corresponding to N units of position-velocity loop processing periods centering around the period of each position-velocity loop processing, multiplying the determined moving mean value by a positional feedforward coefficient to produce a positional feedforward amount, performing positional loop processing to determine a velocity command, and adding the positional feedforward amount to the velocity command obtained by positional loop processing to determine the velocity command with respect to velocity loop processing; and

determining a moving mean value of moving commands corresponding to N units of position-velocity loop processing periods centering around the time preceding the period of the present position-velocity loop processing, multiplying a differentiated value of the obtained moving mean value by a velocity feedforward coefficient to produce a velocity feedforward amount, performing velocity loop processing to produce a torque command, and adding the velocity feedforward amount to the torque command obtained by velocity loop processing to determine a torque command to the servomotor.

5. A method of feedforward control for a servomotor according to claim 4, further comprising the step of setting the time precedence substantially equal to one sampling period.

6. A method of feedforward control for a servomotor according to claim 4, further comprising the step of setting the time precedence within one sampling period.

7. A method of feedforward control for a servomotor, to control the servomotor through position-velocity loop control to be executed by a moving command in each sampling period obtained by dividing a present distribution period of the moving command into N equal parts, said method comprising the steps of:

reading a moving command in a distribution period preceding by one period the present distribution period to determine a moving command for each position-velocity loop processing, to produce a velocity compensatory component;

determining a moving average value of moving commands corresponding to N units of position of moving commands, corresponding to N units of position-velocity loop processing periods centering around the period preceding the period of the position-velocity loop processing used to obtain the velocity compensatory component, differentiating the moving average value and multiplying the differentiated value by a velocity feedforward coefficient, to produce an acceleration compensatory component;

performing velocity loop processing using the velocity compensatory component to produce a torque command;

advancing a phase of the acceleration compensatory component from that of the velocity compensatory component; and

adding the phase advanced acceleration compensatory component to the torque command, to produce a new torque command to the servomotor.

8. A method of feedforward control for a servomotor according to claim 7, wherein the step of advancing the phase comprises adjusting the phase by the unit of one of the sampling periods.

9. A method of feedforward control for a servomotor according to claim 7, wherein the step of advancing the phase comprises adjusting the phase by a fraction of one of the sampling periods.

10. A method of feedforward control for a servomotor according to claim 7, wherein the step of advancing the phase comprises adjusting the phase by a combination of the unit of one of the sampling periods and a fraction of the one of the sampling periods.

11. A method of feedforward control for a servomotor according to claim 7, wherein the step of advancing the phase comprises adjusting the phase by adding a fraction of the acceleration compensatory component having a phase advancement of one sampling period to a remainder of the acceleration compensatory component other than the fraction which is not phase advanced.