Dynamics and control of a planar 3-DOF parallel manipulator with actuation redundancy

A simple robust autodisturbance rejection controller (ADRC) in linkspace is proposed to realize high precision tracking control of a general 6 degrees of freedom (DOF) Stewart platform in this paper. In practice, the performance of the controlled system is limited by how to select the high-quality differential signal in the presence of disturbances and measurement noise. Moreover, unmodeled nonlinear friction provides degradation on the motion precision. So, a nonlinear tracking differentiator in the feedforward path and an extended states observer in the feedback path are designed to obtain high quality differential signal and the real action component of unknown disturbance signals including nonlinear friction without a precise mathematical model. The nonlinear PD (proportional derivative) controller is used to synthesize the control action to give a superior performance. Extensive simulations and experimental results are presented to verify the effectiveness and ease of engineering implementation of the proposed method. The developed ADRC controller is simple and directly intuitive to the practitioners.

Disturbance-rejection high-precision motion control of a Stewart platform

Mechanism synthesis is mostly dependent on the designer's experience and intuition and is difficult to automate. This paper aims to develop a rigorous and precise geometric theory for analysis and synthesis of sub-6 DoF (or lower mobility) parallel manipulators. Using Lie subgroups and submanifolds of the special Euclidean group SE(3), we first develop a unified framework for modelling commonly used primitive joints and task spaces. We provide a mathematically rigorous definition of the notion of motion type using conjugacy classes. Then, we introduce a new structure for subchains of parallel manipulators using the product of two subgroups of SE(3) and discuss its realization in terms of the primitive joints. We propose the notion of quotient manipulators that substantially enriches the topologies of serial manipulators. Finally, we present a general procedure for specifying the subchain structures given the desired motion type of a parallel manipulator. The parallel mechanism synthesis problem is thus solved using the realization techniques developed for serial manipulators. Generality of the theory is demonstrated by systematically generating a large class of feasible topologies for (parallel or serial) mechanisms with a desired motion type of either a Lie subgroup or a submanifold.

/pdf/a-geometric-theory-for-analysis-and-synthesis-of-sub-6-dof-3tj379zsxn.pdf

A Geometric Theory for Analysis and Synthesis of Sub-6 DoF Parallel Manipulators

Kinematic sensitivity analysis of the 3-UPU parallel mechanism

http://homes.m-tech.aau.dk/shb/papers/MMT10-WSoptimization.pdf

Optimum design of spherical parallel manipulators for a prescribed workspace

This paper describes the design, construction, and performance analysis of the Eclipse, a redundantly actuated six-degree-of-freedom parallel mechanism intended for rapid machining. The Eclipse is a compact mechanism capable of performing five-face machining in a single setup while retaining the advantages of high stiffness and high accuracy characteristic of parallel mechanisms. We compare numerical and algebraic algorithms for the forward and inverse kinematics of a class of the Eclipse and formalize the notion of machine tool workspace. We also develop a simple method for the first-order elasto-kinematic analysis of parallel mechanisms that is amenable to design iterations. A complete characterization of the singularities of the Eclipse is given, and redundant actuation is proposed as a solution. The Eclipse case study demonstrates how diverse analytical tools originally developed in a robotics context can be synthesized into a practical design methodology for parallel mechanisms.

Design and analysis of a redundantly actuated parallel mechanism for rapid machining

This paper presents the Eclipse II, a new six-degrees-of-freedom parallel mechanism, which can be used as a basis for general motion simulators. The Eclipse II is capable of x, y, and z axes translations, and a, b, and c axes rotations. In particular, it has the advantage of enabling continuous 360/spl deg/ spinning of the platform. We first describe the computational procedures for the forward and inverse kinematics of the Eclipse II. Next, the complete singularity analysis is presented for the two cases of end-effector singularity and actuator singularity. Finally, two additional actuators are added to the original mechanism to eliminate both types of singularity within the workspace.

Eclipse II: a new parallel mechanism enabling continuous 360-degree spinning plus three-axis translational motions

This paper presents a robust, discrete, near time-optimal control algorithm for hard disk drives. Building on the continuous-time control law of Newman [Trans. Automatic Control 35 (7) (1990) 841] and Newman and Souccar [J. Dynamic Syst. Measure. Control 113 (1991) 363], the chattering phenomenon for continuous-time systems is first examined, and it is shown how additional chattering can occur in the discrete-time case. A criterion for the selection of control parameters to prevent chattering in the discrete-time case while assuring controller stability is then suggested. The controller developed is applied to a commercial hard disk drive. Compared to the more commonly used PTOS, the proposed controller significantly reduces chattering while maintaining comparable seek time to reach the destination track.

A robust, discrete, near time-optimal controller for hard disk drives

This article presents a simulation-based strategy for sizing the actuators of a redundantly actuated robotic mechanism. The class of robotic mechanisms we consider may contain one or more closed loops and possess an arbitrary number of active and passive joints, and the number of actuators may exceed the mechanism's kinematic degrees of freedom. Our approach relies on a series of dynamic simulations of the mechanism, by applying Taguchi's method to systematically perform the simulations. To efficiently perform each of the dynamic simulations, we develop, using tools from modern screw theory, new recursive algorithms for the forward and inverse dynamics of the class of redundantly actuated mechanisms described. © 2002 Wiley Periodicals, Inc.

Simulation‐based actuator selection for redundantly actuated robot mechanisms

This paper presents a newly developed rapid prototyping (RP) machine. The design of this machine is based on the Eclipse parallel mechanism invented by the authors. One of the advantages of the Eclipse mechanism as compared to Gough-Stewart-based parallel mechanisms and applied to machining processes is that the spindle can tilt to 90 degrees and enables five-face machining without any set-up change of the workpieces. This advantage has been fully utilized in designing the new RP machine. The RP process consists of four stages: (1) post-machining feature extraction, (2) the slicing of the deposition feature, (3) repeated deposition and machining of each sliced layer, and (4) post-machining. Whole stages are executed in one machine structure without any set-up change. Using the Eclipse-RP and standard test parts, remarkable gains in productivity are obtained, namely 2.5 times reduction in time and 8 times reduction in cost.

C.C. Iurascu

Papers

Design and analysis of a redundantly actuated parallel mechanism for rapid machining

Eclipse II: a new parallel mechanism enabling continuous 360-degree spinning plus three-axis translational motions

A robust, discrete, near time-optimal controller for hard disk drives

Simulation‐based actuator selection for redundantly actuated robot mechanisms

Eclipse-RP: A new RP machine based on repeated deposition and machining