Electricity: motive power systems – Positional servo systems – Antibacklash systems
Patent
1998-11-20
2000-08-22
Ro, Bentsu
Electricity: motive power systems
Positional servo systems
Antibacklash systems
318600, 318632, G05B 19404, G05D 312
Patent
active
061077712
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to correction of move command for reducing the difference between a commanded position and an actual position occurring when reversing the move command in a servo control system to control a machine tool. More particularly, the present invention relates to a move command correction suitable for repetitive machining in the same condition.
DESCRIPTION OF THE RELATED ART
In case of repetitive machining in the same condition, learning control (repetitive control) effective in realizing highly-accurate machining by making use of repetition of a machining command has been heretofore known, as disclosed in Japanese Patent Publications such as Japanese Patent Laid-open Nos. Hei 4-323705 and Hei 6-309021, for instance.
FIG. 2 shows a servo control system in a semiclosed loop mode which performs the learning control. This servo control system finds a positional deviation by subtracting an amount of positional feedback Pf, outputted from a position/speed detector 6 mounted on a servo motor 5, from a move command Pc, issued from a numerical control device 1, adds an amount of correction found by a learning controller 2 to the positional deviation and delivers the sum into a position/speed/current controller 3.
The position/speed/current controller 3 finds a speed command by multiplying the sum of the positional deviation and the amount of correction by a positional gain, finds a speed deviation by subtracting a speed feedback value, detected and fed back by the position/speed detector 6, from the speed command, finds a torque command (a current command) through proportional integral control or the like, further performs current feedback control on the basis of current fed back from a current detector provided in a servo amplifier 4, and applies current to the servo motor 5 through the servo amplifier 4 composed of a transistor inverter or the like to drive the servo motor 5.
The servo motor 5 converts a revolving motion into a linear motion with a ball screw
ut mechanism 7 to drive a table mounted with a work or a tool. FIG. 2 shows an instance of driving a tool 8 with the ball screw
ut mechanism 7.
The learning controller 2 is composed of a delay element memory stored with data for one cycle portion (i.e., for n-sampling cycle portion) of the move command Pc, issued repeatedly in a predetermined cycle according to the same pattern, and a dynamic characteristic compensation element. Then, the data resulting from adding the data stored in the delay element memory, i.e., data precedent to a current cycle by one cycle to the positional deviation, is stored in the delay element memory after undergoing filter processing. Further, the data precedent to the current cycle by one cycle is outputted as an amount of correction from the learning controller 2 through the delay element memory after having been compensated for a phase delay of a control object and a reduction in gain by the dynamic characteristic compensation element. This amount of correction is added to the positional deviation to correct the positional deviation, and the corrected positional deviation is transferred to a speed control loop.
In case of applying the learning control to the servo control system in the semi-closed loop mode as described above, a rotation position of the servo motor 5 is corrected through the learning control so as to track more accurately the move command Pc issued from the numerical control device 1, so that servo motor 5 can be driven accurately according to the move position.
However, backlash occurs in the ball screw
ut mechanism 7, and so when a sign of the move command is reversed, that is, the revolving direction of the servo motor 5 is reversed, the table or the tool 8 which moves linearly by the ball screw
ut mechanism 7 stops an amount corresponding to a backlash so that it does not follow up the move command Pc. A follow-up delay caused by backlash cannot be compensated by the learning control.
Such backlash has been heretofore corrected according to a method, wherein t
REFERENCES:
patent: 4128794 (1978-12-01), Burleson
patent: 4251761 (1981-02-01), Inoue
patent: 4504917 (1985-03-01), Grimm et al.
patent: 4916375 (1990-04-01), Kurakake et al.
patent: 5204602 (1993-04-01), Iwashita
patent: 5329215 (1994-07-01), Fraser et al.
patent: 5691616 (1997-11-01), Iwashita
Fanuc Ltd.
Ro Bentsu
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