US 4,031,369 AGranted

Interpolation and control apparatus and method for a numerical control system

AssigneeThe Bendix Corporation

InventorsJames Patrick Heaman, James Anthony Michaud

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Abstract

A numerical control system having both linear and circular interpolating capabilities is described. Data from a permanent storage medium such as tape are input to a preprocessor. The preprocesor processes the data into a form acceptable to the system logic and makes all parameters for both linear and circular interpolation available to the system logic. Because linear interpolation is used, straight lines as well as arbitrary curves which are simulated by a series of short straight line segments can be drawn or cut. Additionally, because circular interpolation is used, arbitrary curves can be simulated by a series of arcs, each of the arcs being a portion of a different circle and the various circles having varying radii in accordance with the dictates of the arbitrary curve being cut or drawn. The ability to use both circular and linear interpolation substantially reduces the data processing because the interpolation technique requiring the least definition can be conveniently employed. Also, because of the particular interpolation techniques employed, a minimum of multiplication and division is required so that the system logic is substantially reduced. Additionally, because of the particular linear and circular interpolation techniques and because of the data processing technique employed, the execution time of real time tasks is reduced. This results in a substantial reduction in demands on the computing capabilities of the system, thereby significantly increasing the overall capabilities of the system.

A numerical control system for controllably moving an element along a motion path of arbitrary configuration;

said system including means for receiving data numerically defining said motion path from a storage medium, system logic for preprocessing and interpolating said data, and means for receiving said data from said system logic and moving said element along said path, said system logic including:
preprocessor means for receiving said data and providing linear interpolating data and circular interpolating data;
said linear interpolating data defining the movement of said element as a straight line segment lying between a start point and an end point at an arbitrary angle with respect to at least two mutually perpendicular axes;
said preprocessor means including means for generating a plurality of sample intervals for each of said segments, the number and length of said sample intervals varying for different segments so that each segment includes an integral number of said sample intervals and said end point for each segment is accurately forced;
said circular interpolating data defining the movement of said element as the rotation of the end of a radius through a total angular excursion from a first position to a final position;
said preprocessor means including means for generating a plurality of subangular excursions for each of said angular excursions, the number and extent of said subangular excursions varying for different angular excursions so that each angular excursion includes an integral number of said subangular excursions and said final position for each angular excursion is accurately forced;
linear interpolating means receiving said linear interpolating data for generating linear interpolated data indicative of the end points for each linear sample interval and apply said linear interpolated data to said means for receiving and moving;
circular interpolating means receiving said circular interpolating data for generating circular interpolated data indicative of the end points for each subangular excursion and applying said circular interpolated data to said means for receiving and moving.

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Abstract

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