A new flextensional piezoelectric ultrasonic motor-Design, fabrication and characterisation

This paper presents the techniques used for the characterisation of a new type of standing-wave piezoelectric ultrasonic motor. The motor uses a metallic flextensional amplifier, or "cymbal", to convert the radial mode vibrations of a piezoelectric ceramic disc into flexural oscillations, which are further converted to produce rotary actuation by means of an elastic fin friction drive. The motor operates on a single-phase electrical supply. A beryllium copper rotor design with three-fin configuration was adopted. The best stall torque, no load speed, transient time and efficiency for a 25 mm motor were 2 N mm, 680 rpm, 2 ms and 4.8%, respectively. The operational characteristics of the motor were evaluated by using two methods: one based on the pulley-brake principle and one on high-speed imaging. The results obtained from using these two techniques are contrasted and compared.