A Two-DOF Linear Ultrasonic Motor With High Thrust Force Density and High Power Density Utilizing Torsional/Centrosymmetric-Bending/ Symmetric-Bending Modes

In this article, a new two-DOF linear ultrasonic motor operating in three vibration modes is developed and its capability to exhibit high thrust force density and high power density is tested. Here, the driving force is produced by synchronously exciting the torsional (T) and centrosymmetric-bending (B c ) modes, whereas the normal force is generated with the symmetric-bending (B s ) mode. Initially, the T-B c /B s hybrid transducer in cross shape is designed through modal degeneration and the working principle is verified by simulation. Subsequently, a 50-mm-high 130-mm-long transducer prototype is fabricated to make the slider movable along two horizontal axes ( x and y ). Finally, the performance is assessed via experiments. When the voltage is 250 V and the working frequency is ∼21.6 kHz, the motor yielded the maximal thrust force, no-load sliding speed, and maximal output power of, respectively, 84.3 N, 1562 mm/s, and 33.2 W in the x -axis; and 86.2 N, 1531 mm/s, and 34.1 W in the y -axis. Moreover, the thrust force density and power density reached, respectively, 78.4 N/kg and 31.0 W/kg, exceeding the values of most conventional two-DOF linear ones. This article validates the T-B c /B s motor's high actuating capability and also provides a new approach to design powerful two-DOF linear motors.