PID control with gravity compensation for hydraulic 6-DOF parallel manipulator

Abstract A novel model-based controller for 6 degree-of-freedom (DOF) hydraulic driven parallel manipulator considering the nonlinear characteristic of hydraulic systems-proportional plus derivative with dynamic gravity compensation controller is presented, in order to improve control performance and eliminate steady state errors. In this paper, 6-DOF parallel manipulator is described as multi-rigid-body systems, the dynamic models including mechanical system and hydraulic driven system are built using Kane method and hydromechanics methodology, the numerical forward kinematics and inverse kinematics is solved with Newton-Raphson method and close-form solutions. The model-based controller is developed with feedback of actuator length, desired trajectories and system states acquired by forward kinematics solution as the input and servovalve current as its output. The hydraulic system is decoupled by local velocity compensation in inner control loop prerequisite for the controller. The performance revolving stability, accuracy and robustness of the proposed control scheme for 6-DOF parallel manipulator is analyzed in theory and simulation. The theoretical analysis and simulation results indicate the controller can improve the control performance and eliminate the steady state errors of 6-DOF hydraulic driven parallel manipulator

Two-mode overconstrained three-DOFs rotational-translational linear-motor-based parallel-kinematics mechanism for machine tool applications

The paper introduces a family of three-DOFs translational-rotational Parallel-Kinematics Mechanisms (PKMs) as well as the mobility analysis of such family using Lie-group theory. Each member of this family has two-rotational one-translational DOFs. A novel mechanism is presented and analyzed as a representative of that family. The use and the practical value of that modular mechanism are emphasized.<br /

A reconfigurable asymmetric 3-UPU parallel robot

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Parallel robots with three UPU legs have received a lot of attention due to the possibility of assembling these legs so that the robot performs either a pure translational or a pure rotational motion. Nevertheless, some arrangements, despite their theoretical interest, are of doubtful practical utility due to their sensitivity to errors and the presence in their workspaces of mixed-modes that involve both translations and rotations. The introduction of some sort of asymmetry has been revealed of relevance to come up with more robust designs. In this context, we present an asymmetric 3-P robot, that can be reconfigured to work either as a translational or as a rotational robot by simply flipping upside down its moving platform.Peer ReviewedPostprint (author's final draft

Kinematic design of a non-parasitic 2R1T parallel mechanism with remote center of motion to be used in minimally invasive surgery applications

In minimally invasive surgery applications, the use of robotic manipulators is becoming more and more common to enhance the precision of the operations and post-operative processes. Such operations are often performed through an incision port (a pivot point) on the patient's body. Since the end-effector (the handled surgical tool) move about the pivot point, the manipulator has to move about a remote center of motion. In this study, a 3-degrees-of-freedom parallel mechanism with 2R1T (R: rotation, T: translation) remote center of motion capability is presented for minimally invasive surgery applications. First, its kinematic structure is introduced. Then, its kinematic analysis is carried out by using a simplified kinematic model which consists of three intersecting planes. Then the dimensional design is done for the desired workspace and a simulation test is carried out to verify the kinematic formulations. Finally, the prototype of the final design is presented.Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK

Parallel Manipulators

In recent years, parallel kinematics mechanisms have attracted a lot of attention from the academic and industrial communities due to potential applications not only as robot manipulators but also as machine tools. Generally, the criteria used to compare the performance of traditional serial robots and parallel robots are the workspace, the ratio between the payload and the robot mass, accuracy, and dynamic behaviour. In addition to the reduced coupling effect between joints, parallel robots bring the benefits of much higher payload-robot mass ratios, superior accuracy and greater stiffness; qualities which lead to better dynamic performance. The main drawback with parallel robots is the relatively small workspace. A great deal of research on parallel robots has been carried out worldwide, and a large number of parallel mechanism systems have been built for various applications, such as remote handling, machine tools, medical robots, simulators, micro-robots, and humanoid robots. This book opens a window to exceptional research and development work on parallel mechanisms contributed by authors from around the world. Through this window the reader can get a good view of current parallel robot research and applications

Accuracy Analysis of 3T1R Fully-Parallel Robots

International audienceParallel robots with Shoenflies motions (also called 3T1R parallel robots) are increasingly being used in applications where precision is of great importance. Clearly, methods for evaluating the accuracy of these robots are therefore needed. The accuracy of well designed, manufactured, and calibrated parallel robots depends mostly on the input errors (sensor and control errors). Dexterity and other similar performance indices have often been used to evaluate indirectly the influence of input errors. However, industry needs a precise knowledge of the maximum orientation and position output errors at a given nominal configuration. An interval analysis method that can be adapted for this purpose has been proposed in the literature, but gives no kinematic insight into the problem of optimal design. In this paper, a simpler method is proposed based on a detailed error analysis of 3T1R fully-parallel robots that brings valuable understanding of the problem of error amplification