Design and Characterization of the Torsion Spring-Motor Integrated Series Elastic Actuator

A Series Elastic Actuator (SEA) is a mechanical system that consists of a motor, an elastic material, and an end-effector placed in a series. By actuating the motor and loading the elastic material, the SEA can generate forces at the end-effector. Once the elastic material is loaded, the SEA can continuously produce forces without requiring additional motor actuation. This paper proposes a torsion spring-motor integrated SEA, specifically designed for applying consistent forces on a robot arm that can potentially contribute to achieving stability in robot poses. The SEA configuration comprises a motor securely attached to the body frame and a torsion spring connected between the robot arm and the motor shaft. When the robot arm contacts the ground, the actuating motor causes a deflection in the torsion spring. A force sensor positioned beneath the robot arm measures the pushing forces resulting from the deflection of the torsion spring. The torques can then be calculated by multiplying the distance between the SEA shaft and the robot arm by the measured force. Other design variations are also discussed with different assembly orders. The hardware tests show that the difference between the measured and estimated torques computed using Hooke's law of two suggested designs was an average of 0.0847 N-m and the normalized root mean square error of 13.48%.