Liangyun Y Xie

US Patent:

20100176270, Jul 15, 2010

Filed:

Jan 8, 2010

Appl. No.:

12/654911

Inventors:

Kam C. Lau - Potomac MD, US
Yuanqun Liu - North Potomac MD, US
Guixiu Qiao - Boyds MD, US
Liangyun Xie - Gaithersburg MD, US

International Classification:

G01J 1/20
G01C 3/08

US Classification:

2502032

Abstract:

A volumetric error compensation measurement system and method are disclosed wherein a laser tracker tracks an active target as the reference point. The active target has an optical retroreflector mounted at the center of two motorized gimbals to provide full 360 degree azimuth rotation of the retroreflector. A position sensitive detector is placed behind an aperture provided at the apex of the retroreflector to detect the relative orientation between the tracker laser beam and the retroreflector by measuring a small portion of the laser beam transmitted through the aperture. The detector's output is used as the feedback for the servo motors to drive the gimbals to maintain the retroreflector facing the tracker laser beam at all times. The gimbals are designed and the position of the retroreflector controlled such that the laser tracker always tracks to a pre-defined single point in the active target, which does not move in space when the gimbals and/or the retroreflector makes pure rotations. Special mechanism and alignment algorithm are used in the gimbal design and retroreflector centering alignment to achieve accurate rotational axis alignment and repeatability.