Boots – shoes – and leggings
Patent
1996-12-23
1998-09-29
Ruggiero, Joseph
Boots, shoes, and leggings
36447424, G05B 194099
Patent
active
058154019
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a free-form curve interpolation method for a numerical control unit, and in particular, to a free-form curve interpolation method of a curve represented by a NURBS (Non-Uniform Rational B-Spline).
DESCRIPTION OF THE RELATED ART
In order to machine a workpiece with machine tools, NC programs executed by to a computer numerical control (CNC) unit are in many instances created by automatic programming function based on a form drawn by a CAD (Computer Aided Design), system etc. In this case, one who designs a profile of workpiece can freely draw various curves using a various functions of a CAD system.
However, it is difficult to smoothly connect free-form curves expressing complicated profiles with one another. To deal with this, a free-form curve is divided into relatively simple intervals called segments, in order to represent the curve. There is a Base Spline curve as one of the functions for defining the free-form curve, and it is commonly called a B-Spline curve. The B-Spline curve can be defined by a plurality of control vectors. Moreover, a parameter corresponding to a junction between segments of B-Spline curve is called a knot. The value of the knot gradually increases from the start point toward the end point of the B-Spline curve.
Then, the B-Spline curve which is nonuniform in the increase rate of knot is rationalized, and a curve thus obtained is called a NURBS (Non-Uniform Rational B-Spline) curve.
In the CAD system for a design of industrial products, etc., it is becoming popular to represent profiles of a curve and a curved surface with NURBS. This NURBS curve is adopted, as a form representing a free-form curve, in a standard of CAD data exchange, i.e., an IGES (Initial Graphics Data Exchange Specification).
On the other hand, in interpolating the free-form curve using a conventional CNC, it is necessary to do so by combining small blocks such as small straight lines, small circular arcs, etc. Therefore, in general, CAD data represented by the NURBS curve is approximated to small straight lines, small circular arcs of the free-form curve designed by the CAD system in the stage before the CNC unit prepares command formats.
However, as movement command blocks for the purpose of improving machining accuracy of industrial products are made smaller, various problems have arisen. For example, there are problems such as delay of command program transmission speed between a host computer and a CNC unit due to influence caused by the large number and size of command blocks, and a delay of command program analysis processing speed of the CNC unit, etc. As described above, the NURBS curve drawn by the CAD system has to be decomposed into smaller blocks in order to be processed by the numerical control unit for interpolation of NURBS curve by the numerical control unit. For this reason, complicate processing is required , thereby causing the problem of long execution time.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a free-form curve interpolation method and an apparatus thereof for a numerical control unit, which is capable of performing an interpolation of a NURBS curve by commanding data for specifying the NURBS curve directly to the numerical control unit.
A free-form curve interpolation method according to the present invention repeats a series of following processings: programs; period, on the basis of a feed rate command in the recognized interpolation command; calculated distance from a current position specified by a current value of the parameter; calculated change of the parameter and the current parameter, based on the defining formula of the aforesaid NURBS curve; position; and
A free-form curve interpolation apparatus according to the present invention comprises: interpolation command of a NURBS curve expressed by a function using a specific parameter as a variable, and calculating movement amount per unit time on the basis of a feed rate command in the interpolation command of the NURBS curve, thus output
REFERENCES:
patent: 5227978 (1993-07-01), Kato
patent: 5282143 (1994-01-01), Shirai et al.
patent: 5453934 (1995-09-01), Taghavi et al.
patent: 5510995 (1996-04-01), Oliver
patent: 5581672 (1996-12-01), Letcher, Jr.
IEEE Computer Graphics and Applications, vol. 11, No. 1, Jan. 1991, pp. 55-71.
Kozai Haruhiko
Otsuki Toshiaki
Wakinotani Yoshiyuki
Fanuc Ltd.
Ruggiero Joseph
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