Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1992-07-01
1994-05-10
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
31856822, 318611, G05B 19407
Patent
active
053111109
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a feedforward control method permitting smooth and stable operation of a servomotor.
DESCRIPTION OF THE RELATED ART
In servo systems in which servomotors are installed in various machines, such as machine tools and robots, as drive sources, they are controlled in such a manner that the deviation of an actual motor position from a commanded motor position becomes zero, and the position deviation increases if there is a follow-up delay with respect to the position command. This system, however, has a disadvantage that, for example, the shaping error tends to occur in the operation using machine tool, and such an error is very likely to occur particularly during a high-speed machining operation in which the position command changes rapidly.
Therefore, in servo systems wherein a position/speed loop process is executed at intervals shorter than predetermined pulse distribution intervals in accordance with a move command which is supplied from an upper-level control device at the pulse distribution intervals, a differential value of the position command is added to the speed command corresponding to the position deviation to provide a phase-lead compensation or a position feedforward control on the position command, thereby eliminating the response delay of the servo system with respect to the position command. In these types of servo systems, when the move command from the upper-level control device changes stepwise, an averaging of move commands will be made among the periods of the position loop processes belonging to one pulse distribution period, but the move command can change stepwise between the last position loop processing period in one pulse distribution period and the first position loop processing period in the subsequent pulse distribution period. More particularly, the speed command that has been subjected to the phase-lead compensation contains more high-frequency components than that on which no such compensation is performed. On the other hand, in conventional servo systems, the speed control loop for providing a current command corresponding to the deviation of an actual speed from the speed command does not have an adequate response to high-frequency components in the speed command.
Accordingly, in conventional servo systems, the position deviation undergoes wavy changes. Even if an acceleration/deceleration control is applied to the position command to make the position command change smoothly, a wavy change of the position deviation may still occur. As a result, a shock will be given to the servomotor and thus to a mechanical system using the motor as the drive source.
To eliminate such a drawback, a feedforward control device has been proposed (Japanese Patent Application No. 1-150481) in which a feedforward controlled variable, obtained by differentiating the position command, is subjected to an acceleration/deceleration process and then is added to a controlled variable obtained by the position control loop to obtain a speed command. This device not only can eliminate high-frequency noise components contained in the feedforward controlled variable but also can considerably reduce wavy changes of the position deviation. Nevertheless, the smoothing process used in this type of feedforward control devices for reducing wavy changes of the position deviation involves averaging past data, and therefore, the feedforward controlled variable is subject to a time lag with respect to the command. As a result, still wavy changes of the position deviation cannot always be sufficiently reduced.
DISCLOSURE OF THE INVENTION
An object of this invention is to provide a feedforward control method having an improved follow-up characteristic with respect to a command of a servo system and thus to enable a servomotor to operate smoothly and stably.
To achieve the above object, this invention provides a feedforward control method for a servo system in which a position/speed loop process is periodically carried out a plural number of times within one distr
REFERENCES:
patent: 4533991 (1985-08-01), Georgis
patent: 5055761 (1991-10-01), Mills
patent: 5073747 (1991-12-01), Dupraz et al.
patent: 5107193 (1992-04-01), Iwashita
Fanuc Ltd.
Shoop Jr. William M.
Sircus Brian
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