Force control in a parallel manipulator through virtual foundations

Abstract

An overwhelming controller provides robustness against uncertain parameters, disturbances and un-modelled dynamics. A simplified inverse dynamics model is used in the present paper to develop an overwhelming controller for a parallel manipulator (a Stewart platform), where the controller accommodates modelling uncertainties such as the simplifications made for development of the inverse model in order to improve the computational efficiency. Such a control strategy leads to good trajectory tracking accuracy in the presence of unknown disturbances. However, in addition to trajectory tracking performance, the controller for a Stewart platform should also be able to control or limit the interaction forces in applications such as robot assisted surgery and low-impact docking. The environmental forces can be accommodated during the interaction period by modulating the impedance at the interface of manipulator and environment through virtual flexible foundations. The positional error induced during the force control phase can be recovered during the free flight or idle phase. While this approach has been used successfully in the past to control serial manipulators, the closed loop kinematic architecture in a parallel manipulator introduces many difficulties. This paper proposes a modified overwhelming control scheme for parallel manipulators with compensations for interaction force control and positional error recovery. Bond graph modelling is used as an integrated model and controller development tool. Force controlled machining on a spherical surface, which is akin to a surgical operation, is considered as an example application of the developed control strategy. The simulation results from the bond graph model of the controlled Stewart platform are presented to demonstrate the performance of the developed hybrid position force controller.

Modal Decoupled Dynamics Feed‐Forward Active Force Control of Spatial Multi‐DOF Parallel Robotic Manipulator

“…Noshadi et al presented an active force control strategy combined with the classical PID controller for a 3-RRR (revolute-revoluterevolute) 3-DOF planar parallel robotic manipulator [29]. Bera et al proposed a virtual foundations force control in parallel robotic manipulator using bond graph modeling [30]. Lopes et al reported a method to obtain high performance of active force control by combing a robotic controlled impedance device (RCID) with a commercial industrial robot [31].…”

Control oriented model-based simulation and experimental studies on a compliant legged quadruped robot

“…It is to be noted that the required angle for CTF block are derived from the inverse transformation from body-fixed angular velocities to Euler angle rates [30]. The normal fixed velocities at the contact point 4 and 5 on the cylinder and piston along x and z directions by assuming a thin but long piston can be given as [35] x 4c =ẋ c + …”

“…Thus, utmost care should be taken at the time of generating bond graph model of the three dimensional prismatic link. Bond graph modeling of prismatic link is developed from the concept presented in [30,[32][33][34][35]. The schematic drawing of prismatic link is shown in Fig.…”

Fault-tolerant control of a compliant legged quadruped robot for free swinging failure

“…Detailed modeling of the prismatic link is discussed in Merzouki et al 25 and Bera et al 45,46 Furthermore, the design and detail modeling of prismatic link as part of a quadruped robot is discussed in Gor et al 14 The bond graph model of the quadruped body containing a leg dynamics with compliant link is developed using bond graph software SYMBOLS. 47 The multi-bond graph (or vector bond graph) representation of the model is shown in Figure 6, where the model of one of the legs is given in expanded form and other legs follow similar models.…”