Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1996-03-15
1997-08-05
Ip, Paul
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318571, 318572, 36447421, 36447429, 36447432, G05B 1933, G05B 1918
Patent
active
056546181
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns method for the determination of two-dimensional work-area contours to monitor safe zones for numerically controlled lathes, whereby a safe zone is specified through determination of an axis-parallel segment contour of the workpiece and/or of the environment of the workpiece and a tool segment contour is defined for the portions of the tool including the tool support which are located on the side facing the safe zone and the work-area contour is calculated for a particular reference point of the tool segment contour.
Since collisions normally lead to substantial losses which can be caused both by repair costs as well as by down-time, it is advantageous to avoid these types of collisions through monitoring of the work process.
The use of sensors comprising, for example, one or more cameras for the purpose of collision monitoring is known in the art, the cameras being connected to an image analysis unit for prior recognition of collision events and the prevention thereof. Other sensors are used to determine the forces occurring in a lathe, in particular, at the tool and the tool support.
Image analysis has the disadvantage of being very difficult and therefore expensive and when forces are determined, collisions are first recognized after they have already occurred and have already possibly induced even minor damage.
Methods for the monitoring of collisions are known in the art which function without sensors by providing means for geometrical calculation of possible collision points which are then excluded during the work process. In this fashion, a working region is defined within which one must remain. The disadvantage of this procedure is the high amount of data which must be processed. This leads to large computing times which are prohibitive for online-monitoring unless sufficiently large computing power is available.
With lathes, this large amount of data can be substantially reduced since the lathe process can be largely described by two-dimensional calculations with the working area only being determined two-dimensionally. Despite this simplification, a large amount of data must nevertheless be processed so that online-monitoring is only possible with substantial computer power.
A digitizing method is known in the art from European laid-open publication EP 0 450 113 A1 with which the workpiece is sampled with a probe for recording geometrical data of three dimensional workpieces which are clamped to a machine, the workpiece surroundings also being sampled, with the probe sampled signals being utilized both for generating the workpiece geometrical data as well as to check for collisions with tools which, for their part, can likewise be sampled.
This method has the disadvantage that when utilized, for example, with a plurality of tools for processing a workpiece each change in a work tool requires a new sampling and new construction of a safe zone thereby causing substantial losses in time. Furthermore, the sampled values represent a particular situation which changes, for example, with a subsequent workpiece in the event that the position is even only slightly changed.
It would therefore be desirable to provide a method for the two-dimensional determination of work-area contours with which the work-area contour can be determined for collision monitoring using an acceptable amount of computer power, the method being safe and flexibly applicable.
This purpose is achieved in that at least the outer contour vertices of the safe zone and of the tool segment contour are determined and stored as coordinate values; in a monotonically increasing safe zone, each contour vertex of the safe zone is overlaid with each vertex of the tool segment contour and the coordinate value of the reference point is calculated for each overlay; and a work-area segment contour is determined in that those coordinate values which, when connected together, form a monotonically increasing segment contour, are sequentially chosen in the travel direction as vertex coordinates for the
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Werkstattechnik, vol. 78, No. 9, Sep. 1988, Berlin/Germany pp. 509-514, "Echtzeit-Kollisionschutzsysteme fur NC-Dreh-maschinen" by U. Pilland.
Konstruktion, vol. 37, No. 10, Oct. 1985, Berlin/Germany pp. 387-394, "CAM-Aufgaben losen mit CAD-Algorithmen" by H. Diedenhoven.
Dr. Johannes Heidenhain GmbH
Ip Paul
Vincent Paul J.
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