1. Field of the Invention
The present invention relates to a numerical controller, and particularly relates to a numerical controller that performs wire electrode compensation in consideration of a machined surface length.
2. Description of the Related Art
Wire electric discharge machining (wire-EDM) generates discharge by applying a voltage between a workpiece and a wire electrode, and machines the workpiece into an arbitrary shape using this discharge phenomenon. As illustrated in FIG. 7, in the wire-EDM, a wire electrode 2 is fed in a direction from an upper surface to a lower surface of a workpiece 4 at a constant speed while being supported by an upper guide 3a and a lower guide 3b, and discharge is generated at a position at which the workpiece 4 and the wire electrode 2 face each other to remove a part of the workpiece 4, thereby performing machining.
In the wire-EDM, the wire electrode is consumed by discharge with the workpiece as machining of the workpiece advances. For example, in a case illustrated in FIG. 7, each time discharge is generated between the workpiece 4 and the wire electrode 2 during feeding from the upper surface to the lower surface of the workplace 4, the wire electrode 2 is consumed and becomes thinner, and a diameter thereof becomes smaller.
Meanwhile, since a center of the wire electrode 2 and an offset quantity (a value obtained by adding a gap amount between the wire electrode 2 and the workplace 4 to a radius of the wire electrode) of a shape to be machined from a program path are fixed, the gap amount increases toward a lower side of the workpiece 4 as the wire electrode 2 becomes thinner, so that the machining becomes insufficient. Further, a machining groove width and a machining amount become small.
For example, as illustrated in FIG. 7, when it is assumed that the wire electrode 2 is consumed by a wire electrode consumption amount d while being fed by a distance corresponding to a workpiece thickness h, a wire electrode diameter b around the lower surface of the workpiece 4 corresponds to a value obtained by subtracting the wire electrode consumption amount d from an original wire electrode diameter a (d=a−b), and an uncut portion of a width d/2 is generated on a product side on the lower surface of the workpiece 4.
In a conventional technology, to prevent an uncut portion from being generated on a workpiece product side caused by consumption of the wire electrode 2, as illustrated in FIG. 8, paths of the upper guide 3a and the lower guide 3b are corrected by adjusting the offset quantity (for example, see Japanese Patent Application Laid-open No. 2004-142027). Here, since an offset quantity to be used here is uniquely determined by a combination of a workpiece thickness, a workpiece material, a type of the wire electrode, a diameter of the wire electrode, a machining condition, etc., values measured by performing machining in advance with respect to a plurality of combinations thereof may be stored in advance in a nonvolatile memory of a control apparatus, and an offset quantity can be determined in subsequent machining by reading a combination having a matching workpiece thickness h, workpiece material, type of the wire electrode, diameter of the wire electrode, machining condition, etc. from the nonvolatile memory.
However, the above-described technology disclosed in Japanese Patent Application Laid-Open No. 2004-142027 does not adapts to a situation in which the wire electrode consumption amount d changes during the wire-EDM. For example, as illustrated in FIG. 9, when a distance between the upper surface and the lower surface of the workpiece 4 to be machined varies depending on the machining position, the wire electrode consumption amount d changes depending on the position (machining position) of the wire electrode 2 in the middle of a movement path according to one movement command. Thus, in a method of correcting a path by offset such as a method described in Japanese Patent .Application Laid-Open No. 2004-142027 in which a set offset value is used without, change, compensation cannot be performed according to the wire electrode consumption amount d that changes from moment to moment, and thus there is a problem that an uncut portion is generated.
In addition, considering performing taper machining illustrated in FIG. 10A, a machined surface length (hi to h5) of the workpiece 4 illustrated in FIG. 10B changes from moment to moment, and the wire electrode consumption amount d changes depending on the position (machining position) of the wire electrode 2 in the middle of a movement path according to one movement command. For this reason, in a method of correcting a path by offset such as the above-described technology of Japanese Patent Application Laid-Open No. 2004-142027, as illustrated in FIG. 11, compensation cannot be performed according to the wire electrode consumption amount that changes from moment to moment, and thus there is a problem that an uncut portion is generated.