A novel non-contact torque measurement method for ultrasonic micromotors based on Tunnel Magnetoresistance angle sensor

Abstract

Ultrasonic micromotors are extensively utilized in microsystems; however, measuring torque in these motors presents a significant challenge due to the small size of the motors, which are on the millimeter scale. This paper introduces a torque measurement method for micromotors utilizing the Tunnel Magnetoresistance (TMR) sensor. The output torque is accurately computed through the measurement of angular acceleration and rotational inertia. Angular acceleration is derived from the angular velocity and angle measured by the TMR sensor, while rotational inertia is determined by the rotor’s mass and dimensions. This method offers several advantages, such as non-contact measurement, low uncertainty, rapid response, and high accuracy. In particular, by performing high-precision encoder calibration, temperature coefficient calibration, and Kalman filtering on the TMR sensor, the error compensation rate for angle measurement was 87 %, significantly improving the accuracy and precision of the TMR sensor. The experimental results indicate that within the normal operating temperature range, there is a good linear relationship between the motor’s torque and the applied voltage. Furthermore, experiments on drive frequency and starting torque reveal that the motor’s starting torque reaches its maximum near the resonant frequency, providing an efficient method for rapid estimation of the resonant frequency. Uncertainty evaluation confirms that the relative combined standard uncertainty of the system is 3.43%. These results demonstrate the effectiveness and reliability of the proposed torque measurement method for ultrasonic micromotors, providing a promising solution for precise motor control and performance optimization in microsystems.