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Method for calibration of coordinate measuring machine

  • US 4,939,678 A
  • Filed: 05/12/1988
  • Issued: 07/03/1990
  • Est. Priority Date: 11/19/1987
  • Status: Expired due to Fees
First Claim
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1. In a coordinate measuring machine including a first element and a second element, said first element being movable relative to said second element, said coordinate measuring machine further including scales for monitoring the position of the first element relative to the second element and providing scale readings, and computer means for storing said scale readings, said coordinate measuring machine being subject to errors in said scale readings, said errors being characterized by a set of error parameters including rigid error parameters which are a function only of relative position along an associated measurement direction and nonrigid error parameters which are a function of relative position along an associated measurement direction and of relative position along a second direction, a method for providing corrected scale readings of a workpiece, comprising the steps of:

  • measuring each of said rigid error parameters at point along a line that is parallel to the measurement direction, the step of measuring each of said rigid error parameters being performed by a calibration apparatus;

    measuring each of said nonrigid error parameters at corresponding sets of n points along n spaced-apart lines that are parallel to the measurement direction, each set of n points lying on a line parallel to said second direction to provide sets of nonrigid errors parameter measurements, the step of measuring each of said nonrigid error parameters being performed by said calibration apparatus;

    substituting each of said sets of nonrigid error parameter measurements and corresponding first element positions into n simultaneous equations having n coefficients, said equations describing the relationship between said nonrigid error parameters and the position of the first element along said second direction, the step of substituting each of the sets of nonrigid error parameter measurements and corresponding first element positions being performed by said computer means;

    for each of said sets of nonrigid error parameter measurements, solving the associated n simultaneous equations for said n coefficients, the step of solving the associated n simultaneous equations being performed by said computer means;

    measuring a workpiece by bringing said first element into contact with the workpiece and storing scale readings in said computer means; and

    using said rigid error parameters and said sets of n coefficients to correct said scale readings and provide corrected scale readings of the workpiece, the step of correcting said scale readings being performed by said computer means.

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