Stability and Robustness of Disturbance-Observer-Based Motion Control Systems

Abstract

This paper analyzes the robustness and stability of a disturbance observer (DOB) and a reaction torque observer (RTOB)-based robust motion control systems. Conventionally, a DOB is analyzed by using an ideal velocity measurement that is obtained without using a lowpass filter (LPF); however, it is impractical due to noise constraints. An LPF of velocity measurement changes the robustness of a DOB significantly and puts a new design constraint on the bandwidth of a DOB. An RTOB, which is used to estimate environmental impedance, is an application of a DOB. The stability of an RTOB-based robust force control system has not been reported yet since its oversimplified model is derived by assuming that an RTOB has a feedforward control structure. However, in reality, it has a feedback control structure; therefore, not only the performance but also the stability is affected by the design parameters of an RTOB. A new practical stability analysis method is proposed for an RTOB-based robust force control system. In addition to that, novel and practical design methods, which improve the robustness of a DOB and the stability and performance of an RTOB-based robust force control system, are proposed by using the new analysis methods. The validity of the proposals is verified by simulation and experimental results.Index Terms-Disturbance observer (DOB), motion control systems, reaction torque observer (RTOB), robustness and stability.

Whole body motion control of humanoid robots using bilateral control

“…To improve the robustness and estimate environmental impedance without using a force sensor, a DOb and reaction force observer (RFOb), which are shown in Figures 1a and 1b, respectively, are used in the design of the motion control systems [23]. In Figure 1, J m and J mn denote uncertain/exact and nominal inertias, A DOb estimates external disturbances and plant uncertainties such as external load, friction, and inertia variation.…”

Optimal Design and Hybrid Control for the Electro-Hydraulic Dual-Shaking Table System

“…In order to round the diameters, according to the hydraulic design handbook [36], the diameters of piston rod and piston are chosen as 100 mm/140 mm, which has a close effective area to the computed value in Equation (2). Consequently, the maximum static thrust/drawing forces of horizontal hydraulic cylinder designed are 384 kN/188.5 kN.…”

“…Equation (36) demonstrates that the system control error still exists even if the identified system model and designed system inverse model are completely accurate.…”

“…The disturbance observer as the most effective compensation control method has been widely used in various applications, which have disturbance, parameter uncertainty, noise signals and system nonlinearity, etc., and has a satisfactory control effect [36,48]. Thus, in this paper, the disturbance observer cooperating with the feed-forward inverse controller is adopted to the dualshaking table control system to restrain the system disturbance to obtain good tracking performance, as is shown in Figure 11.…”

Design of an Infinite-Order Disturbance Observer Enhancing Disturbance Suppression Performance

“…Especially, the acceleration controller realized by the DOB is an effective control concept for motion control systems (8) . The acceleration controller realizes an ideal acceleration response suppressing disturbances.…”