Robust position control of a novel series elastic actuator via disturbance observer

Abstract

This paper proposes a new robust position control method for a novel series elastic actuator (SEA). It is a wellknown fact that SEAs provide many benefits in force control, e.g., lower reflected inertia and impedance, greater shock tolerance, safety, and so on. However, current SEA designs have a common performance limitation due to the compromise on the selection of spring stiffness. The performance of an SEA can be significantly improved by changing the stiffness of the spring; however, designing a variable-stiffness SEA is a quite challenging task. In this paper, a novel variable-stiffness SEA, which can relax the fundamental performance limitation of conventional SEAs, is proposed. It consists of torsional and linear springs, which have different compliances, in series. The soft and hard springs improve the performance when low and high force control applications are performed, respectively. Although SEAs have several advantages in force control, their position control problem is more complicated than the force control one. Moreover, using extra springs increases the number of vibration mode, which may significantly deteriorate the performance, in the position control problem of the SEA. In this paper, a new position control system, which improves the performance by increasing the robustness and suppressing the vibration, is proposed for a novel SEA. Experimental results are given to validate the proposal.

Design and Control of a Novel Variable Stiffness Series Elastic Actuator

“…The main drawback of this actuation method is the limited stiffness range which depends on the number of springs employed in the actuator design. Moreover, the discrete stiffness modulation method leads to several challenges in controller analysis and synthesis such as the stability problem of switching systems [40,42]. Therefore, continuous stiffness modulation methods are mainly considered in this paper.…”

A Sliding Mode Force and Position Controller Synthesis for Series Elastic Actuators

“…Resonance ratio control (RRC) was originally proposed for the vibration control problem of industrial robots with flexible joints, and it was recently applied to SEAs in refs. [7,16]. An RRC-based position controller is sensitive to load and link uncertainties as the robustness is degraded to suppress the vibration of link.…”

Trajectory Tracking Control for Flexible-Joint Robot Based on Extended Kalman Filter and PD Control

“…The disturbance observer proposed by Ohnishi in 1987 can be used for the disturbance that is difficult to measure in the system (Nakao et al, 1987). The external disturbance is estimated by the input amount and the feedback value of the inner loop, as the observation compensation amount, and it is added to the control to cancel the actual interference (Sariyildiz and Ohnishi, 2013; Sariyildiz et al, 2015). However, as the order for the filter increases, the large phase lag causes the system to be underdamped and even makes the system unstable.…”