Novel fractional hybrid impedance control of series elastic muscle-tendon actuator

Abstract

Purpose This paper aims to develope a novel fractional hybrid impedance control (FHIC) approach for high-sensitive contact stress force tracking control of the series elastic muscle-tendon actuator (SEM-TA) in uncertain environments. Design/methodology/approach In three different cases, the fractional parameters of the FHIC were optimized with the particle swarm optimization algorithm. Its adaptability to the pressure of the sole of the foot on real environments such as grass (soft), carpet (medium) and solid floors (hard) is far superior to traditional impedance control. The main aim of this paper is to derive the dynamic simulation models of the SEM-TA, to develop a control architecture allowing for high-sensitive contact stress force control in three cases and to verify the simulation models and the proposed controller with experimental results. The performance of the optimized controllers was evaluated according to these parameters, namely, maximum overshoot, steady-state error, settling time and root mean squared errors of the positions. Moreover, the frequency robustness analysis of the controllers was made in three cases. Findings Different simulations and experimental results were conducted to verify the control performance of the controllers. According to the comparative results of the performance, the responses of the proposed controller in simulation and experimental works are very similar. Originality/value Origin approach and origin experiment.

Asymmetric time‐varying BLF‐based model‐free hybrid force/position control for SEA‐based 2‐DOF manipulator

“…Theorem 1. If SEA-based 2-DOF manipulator system ( 5) and ( 6) satisfies Assumptions 1 and 2, applying the proposed ABLF-MFC ( 15) and ( 16), for the parameters satisfying p ≥ 𝜎 ≥ 𝛾 1 , 𝛾 2 = 𝛾 1 − 𝜀 > 0, 𝛾 3 = 𝛾 2 − 𝜀 ≥ 0, 𝜀 and 𝜂 are constant numbers, then it follows that z 1 converges in finite time and satisfies the inequality (13).…”

“…From ( 51) and (53), one can draw the conclusion that −𝜇 1,i < z 1,i < 𝜇 2,i , and consider the definition of z 1,i so inequality (13) holds. Finally, it can be conclude that the tracking error e 1,i can be kept within the preset boundary −𝜇 1,i and 𝜇 2,i .…”

“…For the lower‐limb exoskeleton, an impedance modulation control is proposed, 12 which obtains the reference trajectory through the impedance modulation strategy combined with the active force of the patient, and then tracks the reference trajectory through a position controller to finally realize the assistance to the patient. Then, for the SEA‐based ankle joint exoskeleton, a fractional‐order impedance controller is proposed, 13 which generates the reference trajectory through the impedance model, and tracks the reference trajectory through the position controller to realize the tracking of its output force and trajectory. The above method is to realize the hybrid force/position control through the idea of impedance control, which is achieved by adjusting the dynamic relationship between the reference trajectory and the interaction force.…”

Fractional Order KDHD Impedance Control of the Stewart Platform

“…Other alternative impedance control schemes are based on Fractional Calculus (FC), which deals with derivatives and integrals of non-integer order [13]. Using FC, the endeffector damping can be proportional not to the first-order derivative of the position error, but to a derivative with non-integer order µ [14,15], with possible benefits in terms of accuracy of the regulation of the contact forces [16]. This fractional-order impedance control, which is referred to as KD µ , represents an n-dimensional version (where n is the number of external coordinates) of the fractional-order PD µ control scheme for single-input single-output systems [17], while KD impedance control conceptually corresponds to the PD scheme.…”

Application of the Half-Order Derivative to Impedance Control of the 3-PUU Parallel Robot

“…This kind of impedance control generalizes to a three-dimensional system the fractional-order PD µ control scheme for SISO systems [28]. Fractional-order impedance can be used, for example, to perform contact force tracking control more accurately than traditional impedance control [29].…”