Study on the Torque Control Methods of Stepper Motors

Abstract

Actuators that can produce controllable compliant output motion are suitable for robots that need to interact safely with humans or the environment To obtain the accurate output torque required to control the compliant motion the conventional rigid actuators use torque sensor to measure the interaction force of the end effector However the rigid actuators are low backdrivable and require extra space to accommodate the torque sensor and its related bridge circuit In contrast to the rigid actuators the series elastic actuators (SEA) are highly backdrivable and provide more accurate torque control By adding an elastic spring between electromagnetic motor and the output and then measuring the deformation of the spring using encoders the actuator torque can be indirectly obtained and controlled Aside from SEAs sensorless torque control method is another option to generate compliant motion For DC motors the magnitude of motor current is proportional to the motor output torque and thus to estimate output torque This paper compares the performance of the rotary SEA and the sensorless torque control method of stepper motors to achieve the forward and inverse torque/impedance tracking control Stepper motors are used because of their high availability and reliability They also have a much higher torque-to-weight ratio and torque-to-rotor-inertia ratio than other DC motors It is expected that the result here can present the merits of the respective torque control method in compliant motion control

Date of Award	2020
Original language	English
Supervisor	Chao-Chieh Lan (Supervisor)