Realization of a Precision Hysteresis Brake Driver and Torque Regulator for Medical-Grade Dynamometers

In medical applications, geared DC motors may be used for active implants and other instruments. It is strictly important that the motors and their embedded gearboxes meet the specifications, as they are used in sensitive applications. Thus, a test bench, called a dynamometer, is required to verify the geared motors' specifications and ensure they are within acceptable tolerances. The dynamometer checks the electrical and mechanical properties of the system by testing the motor at different applied voltages and torque settings, while measuring the motor's speed and current. In this application, a hysteresis brake is used to generate torque, and a sensor module is integrated to measure the torque and the speed. The aim of this work is to realize a controller that regulates the brake torque to a desired value, which is set by the test commands, and provides a bridge between the mechanical instruments of this dynamometer, which are the sensor and the brake, and the dynamometer’s control logic. Through this project, the low-speed properties of a hysteresis brake are studied, and a current controller is designed for that brake. Furthermore, a sensor interface is realized to measure the sensor's analog signal corresponding to the measured torque with sufficient precision and to measure the speed from the encoder pulses. A torque control logic is implemented to regulate the output torque by measuring the sensor and generating a setpoint for the mentioned current controller. Also, a power supply system is designed to power all of the digital and analog circuitry, with supply line filters. Finally, a protocolled serial interface is designed to connect this standalone circuit to the rest of the dynamometer’s logic.