Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1998-09-28
2001-10-30
Wiley, David (Department: 2155)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S180000, C700S187000, C711S159000
Reexamination Certificate
active
06311098
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of generating tool movement path data for machining three-dimensional surfaces, a device for generating the data, and machining method and system using the generated data, and more particularly to techniques for suitably determining a tool movement path depending upon the geometry of the three-dimensional surface to be generated by machining.
2. Discussion of the Related Art
It is widely practiced to machine three-dimensional surfaces such as those of a die, by using a machining tool for cutting or grinding, such as a ball end mill and other rotary tools. An example of a method for such machining is disclosed in JP-A-5-346814. This method consists of the steps of: (a) determining a tool constraining surface for constraining a machining tool to machine a three-dimensional surface, the tool constraining surface corresponding to the three-dimensional surface; (b) determining a tool path constraining plane for constraining a movement path of the above-indicated machining tool, such that the tool path constraining plane intersects the above-indicated tool constraining surface; (c) determining as the movement path of the machining tool a line of intersection between the above-indicated tool constraining surface and tool path constraining plane; and (d) moving the machining tool along the determined movement path, relative to the workpiece.
FIG. 38
is a view for explaining such a machining method, wherein an NC data generating device
10
such as a CAM device obtains a line of intersection
16
between a tool constraining surface
12
and a tool path constraining plane
14
, in the form of a three-dimensional curved line equation, which is supplied to an NC machine tool
18
as NC data (tool movement path data), so that a rotary machining tool
20
is moved along the three-dimensional curved line, for generating a desired three-dimensional surface
22
. The tool constraining surface
12
is an offset surface which is offset from the desired three-dimensional surface
22
in a direction normal to the surface
22
, by an amount equal to a radial dimension of the rotary machining tool (radius of curvature of the tip of the tool), and the movement path of the machining tool is a movement path taken by the center of the tool (the center of the sphere of the tool tip).
However, the conventional method described above does not necessarily permit adequate determination of the movement path of the machining tool for the three-dimensional surface to be generated by machining, leading to a possibility of drawbacks such as incapability to obtain high machining efficiency, abrupt change in the machining direction of the machining tool, and deterioration of the machining accuracy. Where a three-dimensional surface as shown in
FIG. 9
, for example, it is desired to smoothly move the tool along waves (follow the geometry) of the three-dimensional surface, as indicated at (a) by broken lines. In the conventional method, however, the tool movement path is constrained within the tool path plane, as indicated at (b) by broken lines, and the determined tool movement path may have abrupt changes in its direction. Where a conical shape as indicated in
FIG. 10
is machined, it is desired to effect continuous machining from the small-diameter end to the large-diameter end, by moving the tool along a helical path, as indicated at (a) by broken line. In the conventional method, the machining is effected in steps along paths having respective different diameters, whereby the machining efficiency and accuracy (smoothness of the machine surface) are deteriorated.
Where a three-dimensional surf ace is machined while the attitude of the machining tool is controlled, the conventional method is adapted to determine the tool path defining points (cutter locations) at a predetermined spacing interval on the intersection line between the tool constraining surface and the tool path constraining plane, and obtain normal vectors of the tool constraining surface at the individual tool path defining points, so that the attitude of the tool is determined based on the obtained normal vectors. This method requires a lot of time to calculate the normal vectors, and suffers from limited freedom in determining the tool path defining points.
The present invention was made in view of the background art described above. It is an object of the present invention to suitably determine a movement path of the tool depending upon the geometry of a three-dimensional surface to be generated by machining. It is another object of the invention to generate tool movement path data including data of the tool attitude, in a short time and with increased freedom in determining the tool path defining points, even where the normal vectors are used to determine the tool attitude.
SUMMARY OF THE INVENTION
The above objects may be achieved according to the present invention, which provides a method of generating tool movement path data for moving a machining tool relative to a workpiece for generating a desired three-dimensional surface, characterized by comprising: (a) a first constraining surface determining step of determining a first constraining surface for constraining the above-indicated machining tool to generate the above-indicated three-dimensional surface, the first constraining surface corresponding to the three-dimensional surface; (b) a second constraining surface determining step of determining a second constraining surface for constraining a movement path of the above-indicated machining tool, the second constraining surface consisting of a surface other than a straight surface and intersecting the above-indicated first constraining surface; (c) an intersection line calculating step of obtaining a three-dimensional curved line equation representing a line of intersection between the above-indicated first and second constraining surfaces; and (d) a movement path data obtaining step of obtaining the movement path data including the above-indicated three-dimensional curved line equation obtained in the intersection line calculating step.
In the present method, the second constraining surface for constraining the movement path of the machining tool can be determined to be a desired curved surface, so that the machining tool is moved along the intersection line between the second constraining surface and the first constraining surface. Thus, the freedom in determining the tool movement path is increased, and the tool movement path can be suitably determined according to the geometry of the three-dimensional surface to be generated. Further, the intersection line between the first and second constraining surfaces is obtained as the three-dimensional curved line equation, and the tool movement path data generated include the three-dimensional curved line equation. Therefore, the tool movement path data have a reduced volume but assure high machining accuracy, as compared with tool movement path data consisting of a multiplicity of cutter location points to which the tool is moved.
The tool movement path data including the three-dimensional curved line equation as described above are used to move the machining tool relative to the workpiece, in a machining device such as an NC machine tool, which is adapted to sequentially determine target positions on the three-dimensional curved line represented by the equation, by circular interpolation, so that the machining tool is moved to the determined target positions.
The machining tool preferably has a machining end portion which has a semi-spherical shape. The shape of the machining end portion includes a shape of a locus taken by the cutting edges during rotation thereof. The machining tool having a semi-spherical shape at the machining end portion may be a ball end mill or an electrical discharge machining electrode. Various other types of machining tools can be used for machining the desired three-dimensional surface by movement of the tool relative to the workpiece along the surface to be generate
Higasayama Haruhisa
Kajisa Eisuke
Kato Hagemu
Muta Yoshiki
Tamaoka Kouji
Backer Firmin
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Toyota Jidosha & Kabushiki Kaisha
Wiley David
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