Electricity: motive power systems – Positional servo systems – Antibacklash systems
Patent
1986-09-11
1988-12-20
Ro, Bentsu
Electricity: motive power systems
Positional servo systems
Antibacklash systems
G05B 702
Patent
active
047927380
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a machine position sensing device for sensing the position of a movable machine part in tracer control equipment or the like.
Tracer control equipment is theoretically capable of machining even without the recognition of the position of a movable machine part. In recent years, however, tracer control units have been equipped with a simple position control function and machine position sensing function so as to enable tracing return control and stop control without involving the use of a mechanical switch such as a limit switch or to permit positioning of the movable machine part when tracing is switched from one tracing area to another. These functions are performed through utilization of feedback pulses available from a position sensor associated with a motor directly or indirectly. Incidentally, the detected position of the movable machine part is utilized not only for tracer control but also it is displayed for monitoring the tracing operation by an operator.
In the prior art, the position of the movable machine part is sensed by counting feedback pulses from the position sensor through use of a counter, reading out the count value from the counter at predetermined time intervals, applying a sign-inverted version of the thus read-out count value to the counter to cancel its contents, and adding the above read-out count value to machine position data obtained so far.
When backlash is present in the drive system, however, the feedback pulses from the position sensor will be generated even if the movable machine part is not actually driven. Therefore, the machine position data obtained only by adding up the counter contents being read out does not accurately indicate the position of the movable machine part under the influence of the backlash. In addition, the machine position data frequently changes in response to driving within the backlash, posing the problem that the display of the data flickers and hence is very hard to see.
SUMMARY OF THE INVENTION
The present invention is intended to solve such a problem of the prior art and has for its object to ensure preventing the machine position data from being varied by driving within the backlash.
According to the present invention intended for solving the above defect of the prior art, as shown in FIG. 1, a device which detects the position of a movable machine part 2, which is driven by a motor 1, through use of pulses available from a position sensor 3 mounted directly or indirectly on the motor 1, is provided with counting means 4 for counting the pulses from the position sensor 3, read means 5 for reading the count value of the counting means 4 at predetermined time intervals, cancel means 6 for cancelling the contents of the counting means 4 by a value equal to the count value read out therefrom, backlash amount storage means 7 for storing the amount of backlash in the drive system, amount-of-movement computing means 8 for computing the actual amount of movement of the movable machine part at the predetermined time intervals on the basis of the count value read out by the read means 5 and the amount of backlash, and integrating means 9 for adding up the amount of movement computed by the amount-of-movement computing means 8.
The count value which is read out by the read means 5 contains a value corresponding to the actual movement of the movable machine part 2 and a value corresponding to backlash, but since the amount-of-movement computing means 8 computes the actual amount of movement of the movable machine part 2 on the basis of the preset amount of backlash, the count value corresponding to the backlash is neglected and the integrating means indicates the accurate position of the movable machine part, besides the machine position data will not change in response to driving within the backlash.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram explanatory of the constitution of the present invention;
FIG. 2 is a block diagram illustrating the principal part of tracer control equ
REFERENCES:
patent: 3766461 (1973-10-01), Leenhouti
patent: 3828238 (1974-08-01), Kobayashi et al.
patent: 4042869 (1977-08-01), Eickelberg et al.
patent: 4251761 (1981-02-01), Inoue
patent: 4502108 (1985-02-01), Nozawa et al.
patent: 4507595 (1985-03-01), Rozsa
Matsuura Hitoshi
Yamazaki Etsuo
Fanuc Ltd
Ro Bentsu
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