Design of integrated eccentric mechanisms and exact constraint fixtures for micron-level repeatability and accuracy

This paper introduces an eccentric ball-shaft kinematic fixture which is capable of six-axis alignment corrections and thereby improved fixture accuracy. A kinematic model for an eccentric ball-shaft fixture was developed and used to simulate the effect of: (1) tolerances, (2) actuation errors and (3) bearing run out on fixture accuracy. The kinematic model and these errors were used to determine when it is practical to use the technology to improve fixture accuracy. The kinematic model was used to design a prototype whose performance matched the kinematic model to within 10%. Diagnosis of experimental data indicates that differences between theory and data may be explained through statistical analysis of error sources. The stabilized 1σ repeatability of the prototype was measured at better than 1.9 μm/3.6 μrad.