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Highly accurate articulated coordinate measuring machine

  • US 6,668,466 B1
  • Filed: 10/19/2000
  • Issued: 12/30/2003
  • Est. Priority Date: 10/19/2000
  • Status: Active Grant
First Claim
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1. A highly-accurate, articulated coordinate measuring machine, comprising:

  • a probe arm, having a proximal end and a distal end;

    a probe tip attached to the distal end of the probe arm;

    a first revolute joint, having a first axis of rotation, rigidly attached to the proximal end of the probe arm, and comprising a first angle encoder for measuring the rotation angle of the first joint;

    a second revolute joint, comprising a second angle encoder for measuring the rotation angle of the second joint, the second angle encoder comprising;

    a first circular encoder wheel, having an outside cylindrical surface, and having a second axis of rotation oriented perpendicular to the first circular encoder wheel;

    first bearing means for rotatably supporting the first encoder wheel, thereby permitting free rotation of the first encoder wheel about the second axis of rotation;

    a plurality of uniformly spaced marks disposed around at least a portion of the outside cylindrical surface of the first encoder wheel; and

    a first sensor, rigidly attached to the first bearing means, for detecting the motion of at least some of the marks as the first encoder wheel rotates;

    a first support arm, having a proximal end rigidly attached to the first encoder wheel, and having a distal end rigidly attached to the first joint;

    a second support arm, having a proximal end, and having a distal end rigidly attached to the second revolute joint;

    a third revolute joint, having a third axis of rotation, rigidly attached to the proximal end of the second support arm; and

    further comprising a third angle encoder for measuring the rotation angle of the third joint;

    second bearing means for rotatably supporting the third revolute joint;

    means for kinematically constraining the second bearing means to a working surface;

    coordinate processing means, operatively connected to the first, second and third angle encoders, for converting the output of the first, second and third angle encoders into a set of coordinates representing the position of the probe tip relative to a reference coordinate system; and

    a riser block rigidly attached to the first circular encoder wheel and rigidly attached to the proximal end of the first support arm;

    wherein the riser block is rigidly attached to the first circular encoder wheel by using the following manufacturing steps, in the order presented;

    a) rough machining the first circular encoder wheel and the riser block;

    b) clamping together the rough-machined first circular encoder wheel and the rough-machined riser block to form a first subassembly;

    c) precision match drilling a first central bore hole into the first subassembly, the hole being aligned with the second axis of rotation of the first circular encoder wheel; and

    d) precision finishing the outside cylindrical surface of the first circular encoder wheel.

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