Development of parallel mechanism with six degrees of freedom for ankle rehabilitation

The use of less than six degrees of freedom (dof) mechanisms instead of six-dof ones is always recommended when the application makes it possible, since their architectures and control are simpler to manufacture and implement respectively. Three-dof mechanisms constitute an important subset of less-than-six-dof mechanisms, since either translational or spherical motion can be obtained through three-dof spatial mechanisms and many industrial applications require the only translational or spherical motion. This paper presents a new translational parallel mechanism (TPM), named translational 3-URC. The new mechanism belongs to the parallel architectures with 3-URC topology, which contain another architecture that is a spherical parallel wrist. The proposed TPM is not overconstrained and has three equal legs whose kinematic pairs are three revolute pairs and one passive cylindrical pair per leg. Its actuated pairs are three revolute pair located on the frame. The position and velocity analyses of the translational 3-URC will be addressed and solved. Its singularity conditions will be written in explicit form and geometrically interpreted.

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Motion/Force Transmission Analysis of Parallel Mechanisms With Planar Closed-Loop Subchains

Journal of Mechanical Design ◽

10.1115/1.4033338 ◽

2016 ◽

Vol 138 (6) ◽

Cited By ~ 12

Author(s):

Kristan Marlow ◽

Mats Isaksson ◽

Jian S. Dai ◽

Saeid Nahavandi

Keyword(s):

Performance Measures ◽

Parallel Mechanism ◽

Degrees Of Freedom ◽

Closed Loop ◽

Screw Theory ◽

Parallel Mechanisms ◽

Force Transmission ◽

Six Degrees Of Freedom ◽

Lower Mobility ◽

Transmission Ability

Singularities are one of the most important issues affecting the performance of parallel mechanisms. A parallel mechanism with less than six degrees of freedom (6DOF) is classed as having lower mobility. In addition to input–output singularities, such mechanisms potentially suffer from singularities among their constraints. Furthermore, the utilization of closed-loop subchains (CLSCs) may introduce additional singularities, which can strongly affect the motion/force transmission ability of the entire mechanism. In this paper, we propose a technique for the analysis of singularities occurring within planar CLSCs, along with a finite, dimensionless, frame invariant index, based on screw theory, for examining the closeness to these singularities. The integration of the proposed index with existing performance measures is discussed in detail and exemplified on a prototype industrial parallel mechanism.

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Design and analysis of a six degrees of freedom serial–parallel robotic mechanism with multi-degree of freedom legs

International Journal of Advanced Robotic Systems ◽

10.1177/1729881418812643 ◽

2018 ◽

Vol 15 (6) ◽

pp. 172988141881264

Author(s):

Ziwei Zhang ◽

Guoying Meng

Keyword(s):

Parallel Mechanism ◽

Degrees Of Freedom ◽

Simple Structure ◽

Parallel Mechanisms ◽

Universal Joint ◽

Six Degrees Of Freedom ◽

In Series ◽

Peristaltic Movement ◽

High Flexibility ◽

Analytic Models

A novel mobile serial–parallel mechanism with legs for in-pipe use is proposed. The mobile robotic mechanism is composed of two identical three-universal joint–prismatic joint–universal joint parallel mechanisms connected in series and two gripping modules. The proposed parallel mechanism has two rotational freedoms and one translational freedom. In addition, the parallel mechanism can achieve continuous and equivalent rotation. The singularities of the parallel mechanism are analyzed. The overall serial–parallel mechanism has six degrees of freedom, and each gripping module has four degrees of freedom. Each parallel mechanism in the waist module is driven by three servo-electric cylinders and each leg mechanism in the gripping modules is controlled by a linear actuator. The robotic mechanism can perform peristaltic movement and turning in space. The robotic mechanism possesses a simple structure and high flexibility, along with the merits of serial–parallel mechanism. In this article, analytic models for the kinematics and dynamics of the robotic mechanism are derived. Additionally, numerical examples are given, and their solutions are validated based on results obtained by SimMechanics and Adams.

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A Screw Theory-Based Semi-Analytical Approach for Elastodynamics of the Tricept Robot

Journal of Mechanisms and Robotics ◽

10.1115/1.4043047 ◽

2019 ◽

Vol 11 (3) ◽

Cited By ~ 1

Author(s):

Chenglin Dong ◽

Haitao Liu ◽

Tian Huang ◽

Derek G. Chetwynd

Keyword(s):

Lower Order ◽

Parallel Mechanism ◽

Degrees Of Freedom ◽

Analytical Approach ◽

Screw Theory ◽

Mode Shapes ◽

Fe Model ◽

Six Degrees Of Freedom ◽

Static Condensation ◽

Elastodynamic Modeling

Taking the well-known Tricept robot as an example, this paper presents a semi-analytical approach for elastodynamic modeling of five or six degrees of freedom (DOF) hybrid robots composed of a 3-DOF parallel mechanism plus a 2- or 3-DOF wrist. Drawing heavily on screw theory combined with structural dynamics, the kinetic and elastic potential energies of the parallel mechanism and of the wrist are formulated using the dual properties of twist/wrench systems and a static condensation technique. This results in a 9-DOF dynamic model that enables the lower-order dynamic behavior over the entire workspace to be estimated in a very efficient and accurate manner. The lower-order natural frequencies and mode shapes estimated by the proposed approach are shown to have very good agreement with those obtained by a full-order finite element (FE) model. It thus provides a very time-effective tool for optimal design within a virtual prototyping framework for hybrid robot-based machine tools.

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Singularity Analysis of Large Workspace 3RRRS Parallel Mechanism Using Line Geometry and Linear Complex Approximation

Journal of Mechanisms and Robotics ◽

10.1115/1.4002815 ◽

2010 ◽

Vol 3 (1) ◽

Cited By ~ 7

Author(s):

Alon Wolf ◽

Daniel Glozman

Keyword(s):

Parallel Mechanism ◽

Degrees Of Freedom ◽

Screw Theory ◽

Singularity Analysis ◽

Community Research ◽

Parallel Mechanisms ◽

Line Geometry ◽

Equilibrium Equations ◽

Six Degrees Of Freedom ◽

Singular Configurations

During the last 15 years, parallel mechanisms (robots) have become more and more popular among the robotics and mechanism community. Research done in this field revealed the significant advantage of these mechanisms for several specific tasks, such as those that require high rigidity, low inertia of the mechanism, and/or high accuracy. Consequently, parallel mechanisms have been widely investigated in the last few years. There are tens of proposed structures for parallel mechanisms, with some capable of six degrees of freedom and some less (normally three degrees of freedom). One of the major drawbacks of parallel mechanisms is their relatively limited workspace and their behavior near or at singular configurations. In this paper, we analyze the kinematics of a new architecture for a six degrees of freedom parallel mechanism composed of three identical kinematic limbs: revolute-revolute-revolute-spherical. We solve the inverse and show the forward kinematics of the mechanism and then use the screw theory to develop the Jacobian matrix of the manipulator. We demonstrate how to use screw and line geometry tools for the singularity analysis of the mechanism. Both Jacobian matrices developed by using screw theory and static equilibrium equations are similar. Forward and inverse kinematic solutions are given and solved, and the singularity map of the mechanism was generated. We then demonstrate and analyze three representative singular configurations of the mechanism. Finally, we generate the singularity-free workspace of the mechanism.

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Workspace Analysis of a Novel Six-Degrees-of-Freedom Parallel Manipulator With Coaxial Actuated Arms

Journal of Mechanical Design ◽

10.1115/1.4024723 ◽

2013 ◽

Vol 135 (10) ◽

Cited By ~ 11

Author(s):

Mats Isaksson ◽

Matthew Watson

Keyword(s):

Parallel Mechanism ◽

Degrees Of Freedom ◽

Kinematic Chain ◽

Parallel Manipulators ◽

Limited Range ◽

Parallel Mechanisms ◽

Six Degrees Of Freedom ◽

Serial Robots ◽

High Acceleration ◽

Redundantly Actuated

Parallel manipulators possess several advantages compared to serial robots, including the possibilities for high acceleration and high accuracy positioning of the manipulated platform. However, the majority of all proposed parallel mechanisms suffer from the combined drawbacks of a small positional workspace in relation to the manipulator footprint and a limited range of rotations of the manipulated platform. This paper analyses a recently proposed six-degrees-of-freedom parallel mechanism that aims to address both these issues while maintaining the traditional advantages of a parallel mechanism. The investigated manipulator consists of six actuated coaxial upper arms that are allowed to rotate indefinitely around a central cylindrical base column and a manipulated platform where five of the six joint positions are collinear. The axis-symmetric arm system leads to an extensive positional workspace while the proposed link arrangement increases the range of achievable platform rotations. The manipulator workspace is analyzed in detail and two methods to further increase the rotational workspace are presented. It is shown that the proposed manipulator has the possibility of a nonsingular transition of assembly modes, which extends the usable workspace. Furthermore, it is demonstrated how an additional kinematic chain can be utilized to achieve infinite platform rotation around one platform axis. By introducing additional mobility in the manipulated platform, a redundantly actuated mechanism is avoided.

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A New Six-DoF Parallel Mechanism for Captive Model Test

Polish Maritime Research ◽

10.2478/pomr-2020-0041 ◽

2020 ◽

Vol 27 (3) ◽

pp. 4-15

Author(s):

Yun Lu ◽

Jinbo Wu ◽

Weijia Li ◽

Yaozhong Wu

Keyword(s):

Parallel Mechanism ◽

Degrees Of Freedom ◽

Offshore Structures ◽

Hydrodynamic Performance ◽

Hydrodynamic Coefficients ◽

New Device ◽

Six Degrees Of Freedom ◽

Technical Requirements ◽

Test Platform ◽

Six Dof

AbstractIn order to obtain the hydrodynamic coefficients that can save cost and meet the accuracy requirements, a new hydrodynamic test platform based on a 6DoF (six degrees of freedom) parallel mechanism is proposed in this paper. The test platform can drive the ship to move in six degrees of freedom. By using this experimental platform, the corresponding hydrodynamic coefficients can be measured. Firstly, the structure of the new device is introduced. The working principle of the model is deduced based on the mathematical model. Then the hydrodynamic coefficients of a test ship model of a KELC tank ship with a scale of 1:150 are measured and 8 typical hydrodynamic coefficients are obtained. Finally, the measured data are compared with the value of a real ship. The deviation is less than 10% which meets the technical requirements of the practical project. The efficiency of measuring the hydrodynamic coefficients of physical models of ships and offshore structures is improved by the device. The method of measuring the hydrodynamic coefficients by using the proposed platform provides a certain reference for predicting the hydrodynamic performance of ships and offshore structures.

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