Precision Automatic Measuring of X-Y Coordinates

This paper reports the development of a computer-controlled machine for non-contact inspection of manufactured parts. The machine, called PAMM (Precision Automatic Measuring Machine), is capable of providing “on-the-fly” measurements accurate to within 100 microinches. The intersection of a rotating spiral slot with a stationary linear slot produces a moving aperture for scanning in small increments over a projected, enlarged image of a part. The scanner assembly moves along an overhead cantilever beam in the x direction, and the part being inspected moves in the y direction along the machine base; position in each direction is monitored by a separate laser interferometer. In the paper conventional methods of coordinate measuring are briefly reviewed, the details of the new design are presented, some experimentally obtained measurements are given, measurement errors induced by photodetector shot noise and aperture roughness are analyzed, and the computer-control and data-analysis techniques are discussed.