Nonlinear disturbance observer design for robotic manipulators

Abstract

Robotic manipulators are highly nonlinear and coupled systems that are subject to different types of disturbances such as joint frictions, unknown payloads, varying contact points, and unmodeled dynamics. These disturbances, when unaccounted for, adversely affect the performance of the manipulator. Employing a disturbance observer is a common method to reject such disturbances. In addition to disturbance rejection, disturbance observers can be used in force control applications. Recently, research has been done regarding the design of nonlinear disturbance observers (NLDOs) for robotic manipulators. In spite of good results in terms of disturbance tracking, the previously designed nonlinear disturbance observers can merely be used for planar serial manipulators with revolute joints (Chen, W.H., Ballance, D.J., Gawthorp, P.J., O'Reilly, J., 2000. A nonlinear disturbance observer for robotic manipulators. IEEE Trans. Ind. Electron. 47, 932-938), (Nikoobin, A., Haghighi, R., 2009. Lyapunov-based nonlinear disturbance observer for serial n-link manipulators. J. Intell. Robot. Syst. 55,[135][136][137][138][139][140][141][142][143][144][145][146][147][148][149][150][151][152][153]. In this paper, a general systematic approach is proposed to solve the disturbance observer design problem for robotic manipulators without restrictions on the number of degrees-of-freedom (DOFs), the types of joints, or the manipulator configuration. Moreover, this design method does not need the exact dynamic model of the serial robotic manipulator. This method also * Corresponding author, Tel.: +1 (647) unifies the previously proposed linear and nonlinear disturbance observers in a general framework. Simulations are presented for a 4-DOF SCARA manipulator to show the effectiveness of the proposed disturbance observer design method. Experimental results using a PHANToM Omni haptic device further illustrate the effectiveness of the design method.

Force Sensorless Compliance Control of a Lower-limb Exoskeleton Robot

“…(17). However, the disturbance observer proposed by Mohammadi et al [14] has the same error dynamic even without acceleration feedback. We propose an acceleration-free disturbance observer.…”

“…In addition, M, C, and g ∆ ∆ ∆ are additive uncertainties present in robot model as respectively shown in Eqs. (12), (13), and (14).…”

“…Finally, using the LMI method proposed in [14], the invertible gain matrix X -1 can be found in Eq. (25).…”

“…It is very hard to design a disturbance observer since acceleration sensor is noisy. Therefore, in this subsection, the non-linear disturbance observer [14] is used with free acceleration. Some parameter settings must be determined to achieve the desired disturbance observer response or obtain any external force around the robotic environment.…”

Robust Course Keeping Control of a Fully Submerged Hydrofoil Vessel with Actuator Dynamics: A Singular Perturbation Approach

“…Disturbance observer based control (DOBC) approaches can estimate the generalized disturbances and improve the robustness of the systems in an active way. Control applications in many different fields have validated the effectiveness of the DOBC, such as manipulator tracking control [20], power system control [17,18], and missile guidance and 2 Mathematical Problems in Engineering control [19,21]. Due to the simple structure of the DOB, it is often used in real-time control applications for high precision.…”