Design and analysis of an ultraprecision rotary motor

Abstract

An ultraprecision rotary inchworm motor that is capable of a micro radian positioning is presented. The driving principle of this rotary motor is an inchworm procedure of two wrapped belts. The presented inchworm motor has especial advantages compared with conventional inchworm motors. A compact structure is realized by integrating a clamping part and a drag part, and this motor has an unlimited operating range. To assemble simply and reduce the number of components, two symmetric lever mechanisms with flexure hinges are used for the rotary inchworm motor. For exact mathematical analysis of the lever mechanism, a new elastic modeling method is presented. This method regards the total lever mechanism as a connection of hinges and prismatic simple rectangular beams. The proposed modeling method had a fairly closed result with commercial FEM software (I-DEAS). From analyses, it is known that the presented modeling method is appropriate for the lever mechanism with flexure hinges. The design of the lever mechanism for the inchworm rotary motor was performed by the optimization using the elastic modeling method. Dimensions of the lever mechanism were determined to obtain a maximum displacement on the output point and a high resonance frequency with predetermined size constraints. The modeling of the inchworm rotary motor was performed to estimate driving characteristics. The inchworm driving procedure of the rotary motor is mathematically expressed to calculate a rotating angle and a torque. In addition, the moving displacements of the belt driven by two opposite lever mechanisms are calculated. This analysis shows that the difference of moving displacements of the belt by two opposite lever mechanism is about 1/100 of the total value. To remove these unbalanced movements of the belt, input displacements of two opposite lever mechanisms should be given properly. So, desired input displacements are calculated by the numerical models of belt movement curves. The proto...