Method for machining three dimensional contours utilizing a nume

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82 2B, 82 1C, 318572, 364167, G05B 1918, G06F 1546

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active

045649146

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to a method for the machining of a workpiece and, more particularly, to a method for operating a numerically controlled lathe to accomplish three dimensional workpiece contouring.
Typically, numerically controlled mills have been used in the machining of workpieces which require contouring in three dimensions. The milling tool, under computer control, produces cuts in the workpiece which define the desired three dimensional contouring.
A problem with the numerically controlled milling process is that it is relatively labor intensive. The milling of a part often requires manual intervention to reposition the part on the bed of the mill. Such repositioning is often critical to successful part fabrication and, as such, requires a significant amount of time by a skilled operator.
In addition, a mill produced part often requires substantial handwork, such as filing, to produce a finished part.
A numerically controlled lathe provides a much faster way of machining workpieces. Here, a workpiece is mounted to a rotating spindle. A cutting tool may be positioned with respect to the radial and axial axes of the workpiece under computer control. Thus, as the workpiece rotates, the cutting tool moves both axially and radially to cut the desired shape. Inasmuch as the workpiece need be positioned only once by an operator, the lathe process is substantially less labor intensive than is the milling process.
A drawback to the lathe process is, however, that heretofore it has only been useful for two dimensional contouring of a part. Prior attempts at adapting a numerically controlled lathe for three dimensional contouring have failed due to the complexities involved in reducing design information into suitable lathe control signals and to the volume of control signals which would be required to realize three dimensional lathe contouring.


SUMMARY OF THE INVENTION

It is desirable, therefore, to provide a method for machining three dimensional contours into a workpiece utilizing a numerically controlled lathe.
It is particularly desirable to provide the above method in a form which permits efficient reduction of design data into lathe control signals.
A yet further desirable feature is to provide the above method in a form which allows reduction of the data necessary to define the three dimensional contour.
Briefly, according to the invention, a method for machining a workpiece comprises the first step of providing a rotatable lathe spindle including means for mounting the workpiece thereto such that the workpiece may be rotated about a rotational axis. A cutting tool is provided as is positioning means which positions the cutting tool in response to applied control signals. The positioning means is operable to position the cutting tool with respect to both a first axis perpendicular to the axis of rotation of the spindle mounted workpiece and a second axis parallel to the axis of rotation of the spindle mounted workpiece, thereby positioning the cutting tool both radially and axially with respect to the workpiece. A set of control signals x, z, i and k are produced for each predetermined segment of rotation of the workpiece. The x control signal defines the position of the cutting tool in the first axis whereas the z control signal defines the position of the cutting tool in the second axis. Each i control signal defines the distance traveled by the cutting tool in the first axis for each revolution of the workpiece with each k control signal defining the distance traveled by the cutting tool in the second axis for each revolution of the workpiece.
More specifically, the desired machined shape of the workpiece is defined in a Cartesian coordinate system using mutually orthogonal axes having corresponding coordinates X, Y and Z. The X, Y and Z coordinates are compensated for offsets produced by the cutting tool to produce corresponding coordinates x', y' and z. The x', y' coordinates are converted to corresponding polar coordinates of radius R and angle .theta.. A set of

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"Segmented Thread-Lead Machining", Giddings and Lewis, Feb. 17, 1983.

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