Passive compensation for straightness errors due to non-parallelism between two air bearing guideway surfaces

Linear motion carriage with opposing air bearings arrangement for achieving preload force is the target of the study. Such arrangement for preloading the air bearings requires high degree of parallelism between the two opposing bearing surfaces. By introducing a compliant mechanism behind each of the air bearing pads at one bearing surfaces, the parallelism requirements as well as the flatness of the bearing surface are effectively alleviated, which in term will reduce the cost of manufacturing the high-precision linear motion guideway. The compliance is obtained by a number of properly stacked disc springs to create a relative constant force over the range of the transverse displacement resulted from the parallelism error between the two bearing surfaces. Experiments show that the higher the compression force generated by the compliance mechanisms; the better the straightness of the motion guideway conforms to the reference surface. By means of the passive compensation, the transverse displacement error is reduced from 2.04 µm to 0.88 µm with respect to the reference surface. The compliant force achieved by the mechanism is also tested for high-speed motion. At 20 m/s², the steady state error of 1 µm is obtained with a settling time of 0.85s. It demonstrated that sufficient compliant force is achieved for good dynamic stiffness of the air bearing guideway.