On the Design of Precise Linear Motion Bearing Mechanism in Vacuum

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The purpose of this research is 1) to investigate the dry frictional behavior of a slider in vacuum and its effect on the motion accuracy, and 2) to propose a design procedure of a sliding mechanism. Here, t he goal of its performance is higher load capacity, longer stroke (meter order) and higher accuracy (micron meter order) than the conventional ones.The slider for experiment is made of stainless steel which dimensions are 90x120x20 (sliding face is 2. width, 120 mm length, 2 rows, contact pressure 39kPa) and was driven by a wire. The rail is also made of stainless steel and its length is 600 mm. Three gap sensors and 2-axes laser interferometry system were used to measure the slider's angular and linear motion during sliding. Frictional coefficient was measured by a strain gage attached on the driving shaft.As the experimental conditions, pressure were set as atmosphere, 1.3x10^<-4> and 1.3x10^<-5>. Pa and sliding speed was adjusted up to 40 mm/s. Under these conditions, the following was clarified.1) Coefficient of friction does not depend on sliding speed so much, however, the tendency is different. That is, in atmosphere the coefficient decrease with the speed increase, on the other hand in vacuum th e coefficient is increase.2) In vacuum, the mean value of coefficient of friction increase, however, the its scatter becomes small.3) After some cycles of slide, the coefficient of friction suddenly increase and sliders are locked.(adhesion).The motion accuracy did not necessarily depend on the coefficient of friction. Some good motion accuracy was observed. However, when the coefficient of friction scatter, the accuracy became low. After the adhesion has occurred, the accuracy became extremely low.According to the experimental results, some design guideline was studied.