Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1991-03-25
1993-01-19
Ip, Paul
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318570, 318571, 36447403, 36447402, B23Q 3512, G05B 1924
Patent
active
051809575
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
Background of the Invention
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.
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, and as a result, the overshot machining into the workpiece by the same amount of over-run, and thus the machining precision at corners is lost.
SUMMARY 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 command values 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 command values and by moving the above tracer head along the surface of the model, comprising calculating means for calculating predetermined values in proportion to the amounts of change in the above speed command values of the respective axes, and a movement control means for moving only the model in parallel with the above respective axes by amounts corresponding to the above respective predetermined values.
A sub-table on which only the model is placed is provided on a main table of a tracing machine tool. This sub-table is moved in the same direction as the direction of movement of the main table, by an amount proportional to the amount of change in the speed command value, for example, the amount of delay in the reaction of a servo system. 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 sub-table is returned by the amount corresponding to the reduction in the axis speed. This return amount corresponds to the amount of over-run of the tracer head in the axial direction, and thus the amount by which the cutter is moved is reduced by the amount of this over-run of the tracer head, whereby 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 present invention;
FIG. 2 is a diagram showing the arrangement of a tracing machine tool connected to a tracing control system according to an embodiment of the present invention;
FIG. 3 is an illustration showing a corner of a model; and
FIG. 4 is a graph showing movement of a tracer head and a cutter at a corner, in accordance with the embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the present invention will hereinafter be described with reference to the drawings.
FIG. 1 is a block diagram showing the hardware of a tracing control system according to an embodiment of the present invention. In FIG. 1, a processor 11 reads a system program stored in a ROM 12, through a bus 10, and controls
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Aramaki Hitoshi
Matsuura Hitoshi
Fanuc Ltd.
Ip Paul
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