Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1991-03-25
1992-06-09
Ip, Paul
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318570, 318571, 36447403, 36447435, 36416701, 409 80, 409 99, G05B 1918
Patent
active
051210410
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a tracing control system, and more particularly, to a tracing control system by which overshot machining at corners and the like of a workpiece is prevented.
BACKGROUND ART
A tracing control system uses a tracer head to detect amounts of displacement of respective axes applied to a stylus, and speed command values of the respective axes are calculated in a tracing calculating circuit by using these amounts of displacement. A cutter is moved relative to a workpiece by drive motors of the respective axes, in accordance with these speed command values, and at the same time, the tracer head is moved along the surface of a model at the same speed. This motion is repeated, and accordingly, the workpiece is machined to the same shape as the model.
Tracing control systems of this kind, however, have a problem in that regions of the model at which the shape is abruptly changed cannot be precisely traced. Namely, when the stylus comes to corners and the like of the model, an over-run of the tracer head occurs due to a delay in the reaction of the servo systems, or to the inertia of the machine or the like, and as a result, the overshot machining into the workpiece by the amount of over-run, and thus the machining precision at corners is lost.
DISCLOSURE OF THE INVENTION
The present invention has been created in view of the aforesaid drawbacks, and an object thereof is to provide a tracing control system by which overshot machining at corners, etc., of a workpiece is prevented, and thus the tracing control system has a high precision.
To achieve the above object, in accordance with the present invention there is provided a tracing control system for machining a workpiece through tracing by calculating speed commands of respective axes, using change amounts detected by a tracer head, by moving a cutter relative to the workpiece through a control of the speed of the respective axes in accordance with the speed commands, and by moving the above tracer head along the surface of the model, comprising a first delay means for obtaining first delay speed commands by delaying the above speed commands by predetermined time constants, a second delay means for obtaining second delay speed commands by delaying the above speed commands by time constants different from the above predetermined time constants, a difference calculating means for calculating differences between the above first delay speed commands and the above second delay speed commands, a first axis moving means for moving a predetermined axis based on the above first delay speed commands, and a second axis moving means for moving a specific axis in a manner such that it is superimposed on movement of the above predetermined axis and is parallel with the above predetermined axis, based on the above differences.
In addition to a conventional entire machine axis, an axis for moving only a tracer head in a manner such that it is superimposed on a movement of this entire machine axis is provided, and two delay speed commands are obtained by delaying speed commands by different time constants. One of the delay speed commands is used for the entire machine axis, and the difference between the speed commands for the axis is used for moving only the tracer head. As a result, the tracer head always precedes the cutter, and when the tracer head comes to a corner and the axis speed is reduced, the amount by which the tracer head precedes the cutter is canceled out (relatively returned) by the amount corresponding to the reduction in the axis speed. This return amount can be made equal to the over-run amount of the tracer head by setting each of the time constants of the delay speed commands at appropriate values, and thus the amount of movement of the cutter is reduced by the amount of this over-run of the tracer head, and accordingly, the overshot machining is prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the hardware of a tracing control system according to an embodiment of the presen
REFERENCES:
patent: 4639172 (1987-01-01), Kishi et al.
patent: 4646225 (1987-02-01), Matsuura
patent: 4746251 (1988-05-01), Yoshikawa et al.
patent: 4814998 (1989-03-01), Aramaki
patent: 4912385 (1990-03-01), Kawamura et al.
patent: 5015130 (1991-05-01), Matsuura et al.
Aramaki Hitoshi
Matsuura Hitoshi
Fanuc Ltd.
Ip Paul
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