Design of a precision rotary-linear dual-axis positioning system with a surface encoder

This paper presents a prototype rotary/linear dual-axis positioning system consisting of a θ-Z actuator and a rotary-linear angle sensor. In the system, an aluminum rotor (moving element) can be moved along and rotated about the axis (Z) of a ceramic cylinder (driving rod). The θ-Z actuator is composed of a Z-piezoelectric actuator (maximum stroke: 12 μm) for linear motion, two θ-piezoelectric actuators (maximum strokes: 9.1 μm) with an added weight for rotation, a driving rod and a rotor. The two θ-piezoelectric actuators with the added weight are attached to the driving rod via a clamping device made with steel. The inner face of the rotor is made contact to the driving rod with a certain friction force. The linear-axis positioning employs the smooth impact drive mechanism to achieve a large stroke by applying a periodic saw-toothed motion from the Z-piezoelectric actuator to the rotor via the driving rod. Sinusoidal motions are applied to the θ-piezoelectric actuators for rotary positioning, which is with a different mechanism form the smooth impact drive mechanism. The stroke of the prototype system along the Z-axis, which is limited by the length of the cylinder, is designed to be 10mm and there is no limitation in the rotary motion. The positioning resolution and maximum speed along the Z-direction are approximately a few nanometers and 2.4mm/sec, respectively. The maximum revolution speed is approximately 50 rpm. An optical surface encoder is also designed for precision positioning of the rotor.