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.

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

Kinematic sensitivity analysis of the 3-UPU parallel mechanism

This paper presents the design and modeling of a new 6-DOF 8-PSS/SPS compliant dual redundant parallel robot with wide-range flexure hinges. This robot can achieve either high accurate positioning or rough positioning as well as a 6-DOF active vibration isolation and excitation to the payload placed on the moving platform. Adopting a kind of wide-range flexure hinge, we establish the kinematics model of the macro parallel mechanism system via the stiffness model and Newton–Raphson method, then we build up the dynamics model using Kane’s method for the micro-motion system. The investigations of this paper will provide suggestions to improve the structure and control algorithm optimization for a novel compliant dual redundant parallel mechanism in order to achieve the feature of larger workspace, higher motion precision and better dynamic characteristics. The results will be helpful in modifying the structure of the prototype platform to enhance its high kinematics and dynamics properties.

Design and analysis of a novel 6-DOF redundant actuated parallel robot with compliant hinges for high precision positioning

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.

Sun Joong Ryu

Papers

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