Modeling Gimbal Axis Misalignments and Mirror Center Offset in a Single-Beam Laser Tracking Measurement System

Abstract

The calibration of robots and machine tools normally requires external pose measuring devices to provide precision cal ibration measurement data. Among the various coordinate measuring techniques, laser tracking systems based on in terferometry offer the potential for continuously producing noninvasive and highly accurate measurements over a large work volume. This article addresses the error modeling is sue for laser tracking coordinate measuring systems, which is crucial in the accuracy enhancement of such systems. Relative distance measurements provided by laser interfer ometers have an extremely high resolution. However, accuracy errors of a coordinate measuring machine based on laser tracking are dominated by geometric errors in the tracking mir ror system. Major geometric error sources include gimbal axis misalignments and mirror center offset. In this article a kine matic model for the single-beam tracker is developed in which a necessary and sufficient number of kinematic parameters are used to represent these two types of error sources for ar bitrary target positions. This model, together with its error model, which is also presented in this article, can be used for design, calibration, and control of single-beam laser tracking measurement systems.