Electricity: motive power systems – Positional servo systems – With stabilizing features
Patent
1984-11-15
1986-07-29
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
With stabilizing features
318572, G05B 501
Patent
active
046032860
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This application is related to copending U.S. patent application having U.S. Ser. No. 471,474 now U.S. Pat. No. 4,555,758.
BACKGROUND OF THE INVENTION
The present invention relates to an acceleration/deceleration control system of a servo motor used in a numerical control (NC) machine tool and a robot.
FIG. 1 is a block diagram of a servo motor acceleration/deceleration control system. A typical example of the conventional acceleration/deceleration system of this type is an exponential acceleration/deceleration control system.
In this system, an exponential function type acceleration/deceleration control unit is used as an acceleration/deceleration control section 1 shown in FIG. 1. When a position instruction is supplied as a displacement V.sub.0 per unit time to the acceleration/deceleration section 1, i.e., when a pulsed input shown in FIG. 2(a) is entered as a value V.sub.0 which is substantially the same as the velocity, an exponential output shown in FIG. 2(b) is obtained.
As shown in this response waveform, an acceleration speed is high at a leading edge (indicated by .alpha. in FIG. 2) due to the influence of a high-frequency component, so that a servo control section 2 and a load system are subjected to shock, resulting in vibrations. As shown in FIG. 2(b), a long period of time is required to decelerate and stop the servo motor, resulting in inconvenience. For these reasons, for example, when X- and Y-axis servo motors are used to shift a table of a machine tool in an arcuated manner, the table has a locus smaller than that designated by an instruction.
A linear acceleration/deceleration control system can be used in place of the exponential acceleration/deceleration control system. An output waveform shown in FIG. 5(b) is obtained in response to a step input shown in FIG. 5(a). As indicated by this output waveform, an acceleration speed abruptly changes, and a servo control system and a load system are subjected to shock, resulting in vibrations. For example, an arm of a robot or the like continues to vibrate when it is stopped quickly, resulting in inconvenience.
Furthermore, since the servo control system and the load system have natural frequencies, when the servo control system and the load system are driven by frequency components similar to their natural frequencies, respectively, the servo control system and the load system vibrate by themselves. For this reason, vibration of the natural frequency components included in position instruction for the servo control system and the load system must be cut off.
SUMMARY OF THE INVENTION
A transfer function in an exponential acceleration/deceleration control section for generating the output shown in FIG. 2(b) in response to the step input shown in FIG. 2(a) is a transfer function H(S) having a time-lag of first order as follows:
This transfer function is obtained by a first-order low-pass filter. The conventional acceleration/deceleration control section 1 given by this transfer function indicates that a low-frequency component included in the position instruction (input) passes through but a high-frequency component is cut off, and that the resultant frequency component as the position instruction is supplied to the servo control section 2. However, as indicated by the output waveform shown in FIG. 2(b), the influence of a high-frequency component occurs at the leading edge or the like to cause an abrupt change in velocity. For this reason, in order to cut off the high-frequency component, a time constant of the transfer function given by equation (1) must be increased. However, when the time constant is increased, a response time becomes slow, and a time for stopping the servo motor becomes prolonged.
This can be overcome by using a higher-order low-pass filter in place of the first-order low-pass filter. In this case, the position instruction to the servo motor is filtered through this higher-order low-pass filter, and the servo motor is driven by the filtered component. As the order of the low p
REFERENCES:
patent: 4422150 (1983-12-01), Keller et al.
patent: 4437067 (1984-03-01), McKenzie et al.
Bergmann Saul M.
Fanuc Ltd
Shoop Jr. William M.
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