Measurement results of the output stepping rotary angle of a piezoelectric-driven rotary actuator by means of inchworm motion have been compared with results obtained from three-dimensional Finite Element Analysis (FEA). Comparison results showed a good quantitative agreement, and confirmed the validity and accuracy of the finite element method in the design and analysis of the inchworm-type rotary actuators. In addition, the effect of the gap between the stator and rotor on the working

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... nce of the actuator was investigated by using FEA. With the increase of the gap, both the stepping rotary angle and the output torque of the rotor decrease significantly. Therefore, this factor must be taken into consideration in the design and machining of this kind of actuators.