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Method for automatic compensation of probe offset in a coordinate measuring machine

  • US 4,866,643 A
  • Filed: 10/09/1987
  • Issued: 09/12/1989
  • Est. Priority Date: 10/09/1987
  • Status: Expired due to Term
First Claim
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1. In a machine for measuring coordinates of a generally planar surface on a workplace by contacting points with a probe having a prescribed diameter and continuously sampling and recording the coordinates of the probe, a method for automatically compensating the planar surface being measured for probe offset comprising the steps of:

  • (a) moving the probe toward the planar surface and measuring the coordinates of a direction point D just before contact between the probe and the planar surface;

    (b) moving the probe along the planar surface and measuring the coordinates of at least three contact points C1 -CN with the probe and the planar surface in contact;

    (c) fitting by electronic data processing means a plane S to the contact points C1 -CN, the plane S being defined by a normal vector Vn passing through the first contact point C1 and a coordinate of the intersection between plane S and vector Vn ;

    (d) calculating by electronic data processing means a directional vector Vd between the first contact point C1 and direction point D;

    (e) calculating by electronic data processing means an angle A between the normal vector Vn and the directional vector Vd, and when the angle A is greater than 90°

    , reversing the direction of the normal vector Vn ;

    (f) when the angle A is in the range between the predetermined range of acceptance and 90°

    , rejecting the direction point D as invalid and repeating the compensation procedure; and

    (g) when the angle A is within a predetermined range of acceptance, moving the plane S by electronic data processing means by the dimension of the probe offset in a direction opposite the direction of the normal vector Vn so that the plane S coincides with the planar surface, thereby compensating for probe offset.

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