Electricity: motive power systems – Positional servo systems – With compensating features
Patent
1992-12-04
1994-08-23
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
With compensating features
31856819, 31856822, 318570, G05D 23275
Patent
active
053410793
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tracing control system for machining a workpiece while tracing a model surface with a tracer head and, more particularly, to a tracing control system which reduces the extent to which the tracer head bites into the model surface.
2. State of the Relevant Art
Generally, to perform on-line tracing operation at high speed with high accuracy requires that a workpiece be simultaneously machined by a tracing control system.
FIG. 6 of the accompanying drawings schematically shows a conventional tracing control system. In FIG. 6, a stylus 142 of tracer head 141 moves in contact with an outer surface of a model 143, and displacements, .epsilon.x, .epsilon.y, .epsilon.z of the stylus 142 along these respective axes are detected by the tracer head 141. More specifically, the tracer head 141 detects displacements of the stylus 142 and generates corresponding displacement signals whose magnitudes correspond to the forces to which the stylus 142 is subjected, resulting from its contact with the model 143. A combining circuit 131 calculates the combined displacement .epsilon. of the stylus 142 according to an equation: .epsilon.=[(.epsilon.x.sup.2 +.epsilon.y.sup.2 +.epsilon.z.sup.2).sup.1/2 ]. An adder 132 calculates the difference .DELTA..epsilon. between the combined displacement .epsilon. and a reference displacement .epsilon..sub.0. A normal speed signal generator 133 multiplies the difference .DELTA..epsilon. by a predetermined gain to generate a normal speed signal Vn, i.e., a signal indicative of the speed in a normal direction. A tangential speed signal generator 134 generators a tangential speed signal Vt, i.e., a signal indicative of the speed in a tangential direction, from the difference .DELTA..epsilon. and a command tracing speed.
A switching circuit 135 selects the displacements along the respective axes in a tracing plane that is commanded. A tracing direction calculating circuit 136 calculates the cosine (cos.theta.) and sine (sin.theta.) of a tracing direction, or angle .theta., at which the model 143 is traced, from the selected displacements. An axis speed signal generator 137 processes the signals Vn, Vt, cos.theta., sin.theta., generated from the displacement signals, into axis speed signals Vx, Vy, Vz for the corresponding tracing axis of the tracer head 141. The axis speed signals Vx, Vy, Vz are supplied to the tracer head 141 to move the stylus 142 on the surface of the model 143 and also to a cutter head 162 to move the cutter head 162 at the speeds represented by the axis speed signals Vx, Vy, Vz for thereby machining a workpiece 163.
In the conventional tracing control system which effects such a simultaneous machining process on the workpiece 163, the cutter head 162 and the tracer 141 are mechanically coupled to each other such that the relative positional relationship between the workpiece 163 and the cutter head 162 is controlled so as to be equal to the relative positional relationship between the model 143 and the tracer head 141. However, there is a certain limitation on the tracing speed of the tracer head 141, and if the tracing speed is excessively high, the cutter head 162 tends to bite into the workpiece 163 in a region where the profile of the model 143 abruptly changes.
The cutter head 162 is caused to bite into the workpiece 163 because the cutter head 162 and the tracer head 141 are in the same relative position, and when the stylus 142 overshoots beyond a reference distance with respect to the tracer head 141, the overshooting of the stylus 142 is reflected directly in the biting engagement of the cutter head 162 with the workpiece 163.
There has been developed a digitizer for solving the above problem. The digitizer reads, from time to time, the positions of a tracer head along the respective axes as digital positional data, and the model surface is linearly approximately based on the digital positional data. The positional data is processed to prevent a cutter head from biting into a w
REFERENCES:
patent: 4504772 (1985-03-01), Matsuura et al.
JP, 59-42254 (Fanuc Ltd.) Mar. 8, 1984.
Matsuura Hitoshi
Nakajima Osamu
Okamoto Tetsuji
Fanuc Ltd.
Martin David
Shoop Jr. William M.
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