Method of and apparatus for controlling a plurality of servomotors

• US 6,046,566 A
• Filed: 04/21/1999
• Issued: 04/04/2000
• Est. Priority Date: 04/21/1998
• Status: Expired due to Fees

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Sonoda, Naoto, Maeda, Kazuomi, Toyosawa, Yukio
• Primary Examiner(s): Nappi, Robert E.
• Assistant Examiner(s): Duda, Rina I.
• Application Number:
  US09/295,105
• Time in Patent Office: 349 Days
• Field of Search: 318/52, 318/66-69, 318/77, 318/81, 318/85, 318/568.22, 318/625, 318/5, 318/8, 318/98, 318/99
• US Class Current: 318/625
• CPC Class Codes: G05B 19/182 characterised by the machine tool function, e.g. thread cutting, cam making, tool direction control G05B19/21 - G05B19/40 take precedence

Abstract

A method of and an apparatus for controlling a plurality of servomotors, in which one driven body is driven by one main servomotor and at least one subordinate servomotor. Synchronous control is performed with good response and high accuracy and repetitive control is performed with simple arrangement preventing interference between axes, and further operation mode of the plurality of servomotors is easily switched between coupled driving and independent driving. A plurality of servomotors comprises one main servomotor and at least one other servomotor subordinate to the main servomotor, and position control is performed on the main servomotor side while velocity control and current control are performed individually for each servomotor. A velocity command for the main servomotor is subjected to a position adjustment based on a position deviation between the main servomotor and subordinate servomotor and the adjusted velocity command is used for the subordinate servomotor. Thus, the response is improved and synchronous control is performed with high accuracy.

Claims

1. A method of controlling a main servomotor and at least one sub-servomotor to cooperatively drive one driven body by synchronizing said main servomotor and said sub-servomotor with each other, comprising the steps of:

(a) performing position control processing for said main servomotor to output a common velocity command for said main servomotor and for said sub-servomotor;

(b) performing velocity control processing for said main servomotor based on said common velocity command;

(c) obtaining a position adjusting value for said sub-servomotor by multiplying a difference between a position feedback value of said main servomotor and a position feedback value of said sub-servomotor by a gain having the same value as that of a position gain used in the position control processing for said main servomotor, and adjusting said common velocity command using said position adjusting value;

(d) performing velocity control processing for said sub-servomotor based on the adjusted velocity command.

2. A method of controlling a main servomotor and at least one sub-servomotor according to claim 1, said step (a) including the steps of correcting a periodic element in a deviation between a position command and the position feedback value of said main servomotor, and performing the position control processing using the corrected position deviation.

3. A method of controlling a main servomotor and at least one sub-servomotor to cooperatively drive one driven body, comprising the steps of:

(a) switching into one of a synchronized operation mode in which said main servomotor and said sub-servomotor operate in synchronism with each other and an independent operation mode in which said main servomotor and said sub-servomotor operate independently of each other;

(b) performing position control processing for said main servomotor to output a velocity command;

(c) performing velocity control processing for said main servomotor based on said velocity command;

(d) in the synchronized operation mode, obtaining a position adjusting value for said sub-servomotor by multiplying a difference between a position feedback value of said main servomotor and a position feedback value of said sub-servomotor by a gain having the same value as that of a position gain used in the position control processing for said main servomotor, and adjusting said velocity command using said position adjusting value, and in the independent operation mode, obtaining a velocity command for said sub-servomotor by multiplying a difference between a position command and the position feedback value of said sub-servomotor by the gain having the same value as that of the position gain used in the position control processing for said main servomotor;

(e) in the synchronizing operation mode, performing velocity control processing for said sub-servomotor based on the adjusted velocity command, and in the independent operation mode, performing velocity control processing for said sub-servomotor based on the velocity command for said sub-servomotor.

4. A method of controlling a main servomotor and at least one sub-servomotor according to claim 3, said step (b) including the steps of:

correcting a periodic element in a deviation between a position command and the position feedback value, and performing the position control processing using the corrected position deviation.

5. An apparatus for controlling a main servomotor and at least one sub-servomotor to cooperatively drive one driven body by synchronizing said main servomotor and said sub-servomotor with each other, comprising:

position control means for performing position control processing for said main servomotor to output a common velocity command for said main servomotor and for said sub-servomotor;

main velocity control means for performing velocity control processing for said main servomotor based on said common velocity command;

position adjusting means for obtaining a position adjusting value for said sub-servomotor by multiplying a difference between a position feedback value of said main servomotor and a position feedback value of said sub-servomotor by a gain having the same value as that of a position gain used in the position control processing for said main servomotor, and adjusting said common velocity command using said position adjusting value;

sub-velocity control means for performing velocity control processing for said sub-servomotor based on the adjusted velocity command.

6. An apparatus for controlling a main servomotor and at least one sub-servomotor according to claim 5, said position control means including periodic element correcting means for correcting a periodic element in a deviation between a position command and the position feedback value of said main servomotor, and performs the position control processing using the corrected position deviation.

7. An apparatus for controlling a main servomotor and at least one sub-servomotor to cooperatively drive one driven body, comprising:

switching means for switching into one of a synchronized operation mode in which said main servomotor and said sub-servomotor operates in synchronism with each other and an independent operation mode in which said main servomotor and said sub-servomotor operates independently of each other;

position control means for performing position control processing for said main servomotor to output a velocity command;

main velocity control means for performing velocity control processing for said main servomotor based on said velocity command;

position adjusting/control means for, in the synchronized operation mode, obtaining a position adjusting value for said sub-servomotor by multiplying a difference between a position feedback value of said main servomotor and a position feedback value of said sub-servomotor by a gain having the same value as that of a position gain used in the position control processing for said main servomotor, and adjusting said velocity command using said position adjusting value, and in the independent operation mode, obtaining a velocity command for said sub-servomotor by multiplying a difference between a position command and the position feedback value of said sub-servomotor by a gain having the same value as that of the position gain used in the position control processing for said main servomotor;

sub-velocity control means for, in the synchronized operation mode, performing velocity control processing for said sub-servomotor based on the adjusted velocity command, and in the independent operation mode, performing velocity control processing for said sub-servomotor based on the velocity command for said sub-servomotor.

8. An apparatus for controlling a main servomotor and at least one sub-servomotor according to claim 7, said position control means including periodic element correcting means for correcting a periodic element in a deviation between a position command and the position feedback value of said main servomotor, and performs the position control processing using the corrected position deviation.