Abstract
A series elastic actuator (SEA) includes an elastic spring in series with an actuator. SEAs provide more accurate force and impedance control than conventional rigid actuators. They are ideal for robots and machines that need to interact safely with the environment. The majority of existing SEAs uses brushless or brushed DC motors as the actuators. The advantages of using step motors as the actuators of SEAs have not received enough attention. Step motors have much higher torque-to-weight ratio and torque-to-inertia ratio than other DC motors. Hence they can provide better stability and high-speed accuracy of force control while maintaining lightweight. When the rotor position feedback is used, step motors can achieve accurate dynamic position response smoothly. This paper develops the dynamic model of a linear series elastic step motor and presents its prototype. Force and impedance control responses will be provided to show the advantages due to the high torque-to-inertia ratio of step motors. It is expected that the results presented here can offer a better actuator selection of SEAs when high-performance dynamic force control is required.
Highlights
Robotic actuators with inherent compliance [1]–[6] are suitable for applications whose main objective is fast and accurate force interaction with a human or environment
As the advantage of high torque-to-weight ratio is quite obvious, this paper primarily investigates the advantage of high torque-to-inertia ratio
While benchmark comparisons were not ready in [23], this paper shows the performance comparisons of our series elastic step motor (SESM) with series elastic actuator (SEA) that are based on brushed or brushless DC motors
Summary
Robotic actuators with inherent compliance [1]–[6] are suitable for applications whose main objective is fast and accurate force interaction with a human or environment. The type of motion and structure of the elastic spring are not the same, the majority of SEAs in the literature uses brushed or brushless direct-current (DC) motors as the actuators. Lin et al.: Improving the Dynamic Force Control of Series Elastic Actuation Using Motors of High Torque-to-Inertia Ratios. For the same torque requirement and gearbox ratio, step motors have much smaller rotor inertia. Methods (e.g., [9]) to improve the force control response of SEAs have been developed, but VOLUME 8, 2020 the merits of using motors of high torque-to-inertia ratios to improve the force response are underexplored. Lin et al.: Improving the Dynamic Force Control of Series Elastic Actuation Using Motors of High Torque-to-Inertia Ratios TABLE 1. The va and vb values are substituted into Eq (1) to generate the required phase currents ia and ib, and the actual motor torque τm
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