Patent ID: 6668466
Filing Date: 2003-12-30
Classification: G01B

Abstract:
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.