Electricity: motive power systems – Positional servo systems – Digital or numerical systems
Patent
1987-12-22
1989-08-08
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
Digital or numerical systems
318603, 36447428, G05B 1929
Patent
active
048556572
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a positioning system for use in a numerical control apparatus, a robot control apparatus, or the like. More particularly, the present invention is directed to a positioning system which uses a feedback signal as a positional information signal to effect a highly accurate and high-speed positioning operation.
Conventional positioning systems have employed a pulse train having a certain weight, e.g., a pulse corresponding to, for example, 1 .mu.m, or any other predetermined time period, as a feedback signal. One example of such an arrangement is shown in FIG. 3 of the accompanying drawings. Denoted in FIG. 3 at 1 is a pulse distributor for generating distribution pulses in response to a tape input or the like, 2 a command processor for comparing pulses from the pulse distributor 1 and feedback pulses and issuing a servo command signal, 3 a servoamplifier responsive to the servo command signal from the command processor 2 for driving a servomotor 4 to actuate a movable unit (not shown. The servomotor 4 includes an encoder 5 as a position detector coupled to the shaft of the servomotor 4 for generating feedback pulses 8 as a feedback signal, and an up/down counter 7 for counting the feedback pulses 8. The count is read by the command processor 2.
For a numerical control apparatus and the like, there are demands for higher positioning accuracy and higher pulse distribution rate. The conventional systems have difficulty in meeting such demands.
More specifically, the pulse distribution rate of conventional systems is on the order of 1 MHz because of the characteristics of the transmission path for feedback pulses. The rate of the resolution "0.1 micron/pulse" at the pulse distribution rate is given by: ##EQU1## 0.1.times.10.sup.-6 indicates a numerical value representing "0.1 micron/pulse" in terms of meters (m), 10.sup.6 indicates the transmission rate for feedback pulses (1 MHz expressed by pps), and 60 indicates a numerical value for conversion to a value per minute. From the above equation, the speed of movement of the movable unit is 6 m/minute, indicating that a sufficiently high speed cannot be obtained.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a positioning system which will solve the aforesaid problems and is capable of a high-speed positioning operation even at highly accurate resolution.
To solve the above problems, there is provided, in accordance with the present invention, a positioning system comprising a servomotor rotatable in response to a command value for moving a movable unit, command means for comparing a feedback signal from a position detector mounted on the servomotor or the movable unit with the command value and issuing a servo command value, and positional information generating means for generating a positional information signal indicative of positional information of the servomotor or the movable unit. The arrangement is such that the positional information signal from the positional information generating means is fed back to the command means for providing a positioning operation.
Since the feedback signal is a positional information signal for the servomotor or the movable unit, this signal is read at given periods by a command processor which calculates the distance by which the movable unit is moved from a preceding positional information signal.
For example, assuming that the resolution is 0.1 micron/pulse and the maximum range of movement of the movable unit is 100 m, the range may be expressed in binary notation as follows: command processor is 1 ms, then the pulse transmission rate may be 30 bits per 1 ms: transmission rate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a positioning system according to an embodiment of the present invention;
FIG. 2 is a block diagram of the encoder in FIG. 1; and
FIG. 3 is a block diagram of a conventional positioning system.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the present invention will hereinaf
REFERENCES:
patent: 4725959 (1988-02-01), Nagata
patent: 4751442 (1988-06-01), Kurakake
Isobe Shin-ichi
Kagawa Yoshimasa
Bergmann Saul M.
Fanuc Ltd.
Shoop Jr. William M.
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