Tool path generation method and machine tool using rate of change of curvature based smoothing

• US 10,248,101 B2
• Filed: 10/29/2014
• Issued: 04/02/2019
• Est. Priority Date: 10/29/2014
• Status: Active Grant

• Current Assignee: Makino Milling Machine Company Limited
• Original Assignee: Makino Milling Machine Company Limited
• Inventors: Oda, Mitsunari, Furuta, Megumi, Shinone, Akihiro, Kawai, Toshimune
• Primary Examiner(s): Lindsay, Bernard G
• Application Number:
  US15/517,455
• Publication Number:
  US 20170300029A1
• Time in Patent Office: 1,616 Days
• Field of Search: None
• CPC Class Codes: G05B 19/19 characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path
• CPC Class Codes: G05B 19/4093 characterised by part programming, e.g. entry of geometrical information as taken from a technical drawing, combining this with machining and material information to obtain control information, named part programme, for the NC machine
• CPC Class Codes: G05B 19/4103 Digital interpolation
• CPC Class Codes: G05B 2219/35097 Generation of cutter path, offset curve
• CPC Class Codes: G05B 2219/36221 Entry of chamfer, beveling, rounding of corner shape
• CPC Class Codes: G05B 2219/45202 Edge finishing

Abstract

A tool path generation method for generating a second tool path by performing a smoothing process on a first tool path for processing a work with a machine tool includes a change rate calculation step of calculating a curvature change rate of the first tool path at a plurality of moving points (P_n) of the first tool path. The tool path generation method includes: a weight calculation step of calculating a moving average weight on the basis of the curvature change rate of the first tool path at each of the moving points (P_n); and a step of calculating coordinate values of the moving average of the moving points (P_n) using the weight at each of the moving points (P_n), and setting the coordinate values of the moving average of the moving points (P_n) as moving points of the second tool path.

Claims

1. A method of machining a workpiece with a machine tool using a second tool path generated by performing smoothing treatment with respect to a first tool path for machining the workpiece with the machine tool, the method comprising:

generating the first tool path in which movement points, each associated with a coordinate value, are connected by straight lines;

a step of identifying the movement points in the first tool path;

a rate-of-change calculation step for calculating a rate of change in curvature of the first tool path at each of the movement points;

a weight calculation step for calculating a weight of a moving average at each of the movement points based on the rate of change in the curvature of the first tool path at each of the movement points;

the moving average being based on the respective movement point and a number of adjacent movement points on the first tool path and the weight, and the weight comprising a weight distribution that is adjusted so that smoothing increases as the corresponding rate of change of curvature increases;

a step of calculating a coordinate value of the moving average of each of the movement points by using the weight at each of the movement points and coordinate values of the movement point and the number of adjacent movement points;

setting the coordinate value of the moving average of each movement point as a coordinate value of a corresponding movement point of the second tool path; and

machining the workpiece along the second tool path.

2. The method according to claim 1, wherein the rate-of-change calculation step includes a step of calculating a moving average value in the curvature at each of the movement points of the first tool path, and

a step of calculating the rate of change in the curvature based on the calculated moving average value in the curvature.

3. The method according to claim 1, wherein the weight calculation step includes

a step of calculating a standard deviation of a normal distribution based on the rate of change in the curvature, and

a step of calculating the weight of the moving average based on the normal distribution including the calculated standard deviation.

4. The method according to claim 1, wherein

an allowable value of a dimensional error of a machined workpiece is determined in advance, and

the weight calculation step includes a step of setting the number of movement points to be used for calculation of the moving average based on the allowable value.

5. A machine tool comprising a control device that generates a second tool path by performing smoothing treatment on a first tool path set by a first machining program, in the first tool path movement points, each associated with a coordinate value, being connected by straight lines,

wherein the control device includes:

a movement point setting part that identifies the movement points based on the first tool path;

a rate-of-change calculation part that calculates a rate of change in curvature of the first tool path at each of the movement points;

a weight setting part that calculates a weight of a moving average at each of the movement points based on the rate of change in the curvature of the first tool path at each of the movement points;

the moving average being based on the respective movement point and a number of adjacent movement points on the first tool path and the weight, and the weight comprising a weight distribution that is adjusted so that smoothing increases as the corresponding rate of change of curvature increases;

a movement point correction part that calculates a coordinate value of the moving average of each of the movement points by using the weight at each of the movement points and coordinate values of the movement point and the number of adjacent movement points, and sets the coordinate value of the moving average of each of the movement points as a coordinate value of a corresponding movement point of the second tool path; and

a program generation part that generates a second machining program based on the coordinate values of the movement points of the second tool path; and

wherein the machine tool is configured to machine the workpiece based on the second machining program.