A General Degree of Freedom Formula for Parallel Mechanisms and Multiloop Spatial Mechanisms

2012 ◽  
Vol 4 (1) ◽  
Author(s):  
Ting-Li Yang ◽  
Dong-Jin Sun
Keyword(s):  
Screw Theory ◽  
Degree Of Freedom ◽  
Parallel Mechanisms ◽  
Spatial Mechanisms ◽  
Vector Algebra ◽  
Algebra Theory ◽  
Position And Orientation ◽  
Displacement Group ◽  
Selection Of

Based on the position and orientation characteristic (POC) set and the POC equations for serial mechanisms and parallel mechanisms proposed by authors, this paper presents a novel general degree of freedom (DOF) formula which is totally different from approaches based on the screw theory and the displacement group. It can be used to determine the full-cycle DOF of parallel mechanisms (PMs) and multiloop spatial mechanisms using symbolic “union” and “intersection” operations for POC sets. These operations involve only several rules and only simple mathematical tools (vector algebra, theory of sets, etc.) are used. Furthermore, criteria for determination of the inactive joints and selection of the actuating joints are proposed. The presented approach is illustrated with several examples.

A General Formula of Degree of Freedom for Parallel Mechanisms

2008 ◽  
Author(s):  
Ting-Li Yang ◽  
Dun-Jin Sun
Keyword(s):  
General Formula ◽  
Screw Theory ◽  
Degree Of Freedom ◽  
Parallel Mechanisms ◽  
Characteristic Equations ◽  
Position And Orientation ◽  
Symbolic Operation ◽  
Selection Of

In this paper, a general formula of degree of freedom (DOF) for parallel mechanisms has been presented which could provide the full-cycle DOF. The key parameters in the formula can be determined via the position and orientation characteristic equations and their symbolic operations of serial and parallel mechanisms proposed by author and the symbolic operation is simple. It is totally different from the methods based on screw theory and based on displacement subgroup. The formula has been used for selection of driving pairs and determination of idle pairs. The formula may also be used for determining the DOF of other multi-loop mechanisms besides parallel mechanisms.

A Systematical Approach for Structure Synthesis of Parallel Mechanisms Based on Single-Open-Chain Modules and Its Application

2009 ◽  
Author(s):  
Ting-Li Yang ◽  
An-Xin Liu ◽  
Qiong Jin ◽  
Yu-Feng Luo ◽  
Lu-Bin Hang ◽  
...  
Keyword(s):  
Parallel Mechanism ◽  
Systematic Approach ◽  
Screw Theory ◽  
Parallel Mechanisms ◽  
Type Synthesis ◽  
Open Chain ◽  
Structure Synthesis ◽  
Vector Algebra ◽  
Algebra Theory ◽  
Position And Orientation

Based on previous research results presented by authors, this paper proposes a novel systematic approach for structure synthesis of all parallel mechanisms (excluding Bennett mechanism etc), which is totally different from the approaches based on screw theory and based on displacement subgroup. Main characteristics of this approach are: (a) the synthesized mechanisms are non-instantaneous ones, and (b) only simple mathematical tools (vector algebra, theory of sets, etc.) are used. Main steps of this approach include: (1) Determining functional and structural requirements of the parallel mechanism to be synthesized, such as position and orientation characteristic (POC) matrix, degree of freedom (DOF), etc. (2) Type synthesis of branches. (3) Assembling of branches (determining the geometry constraint conditions among the branches attached between the moving platform and the frame, and checking the DOF). (4) Identifying the inactive joints. (5) Selecting the actuating joints. In order to illustrate the whole procedure, the type synthesis of spherical parallel mechanisms is studied using this approach.

Structure Synthesis of Rank-Degenerated Serial Mechanisms and Over-Constrained Single-Loop Kinematic Chains

2009 ◽  
Author(s):  
Ting-Li Yang ◽  
An-Xin Liu ◽  
Qiong Jin ◽  
Yu-Feng Luo ◽  
Hui-Ping Shen ◽  
...  
Keyword(s):  
Systematic Approach ◽  
Screw Theory ◽  
Degree Of Freedom ◽  
Parallel Mechanisms ◽  
Single Loop ◽  
Kinematic Chains ◽  
Structure Synthesis ◽  
Vector Algebra ◽  
Position And Orientation

Based on the Position and orientation characteristic (POC) equation of serial mechanisms proposed by the author, this paper presents a novel systematic approach for structure synthesis of rank-degenerated serial mechanisms and over-constrained single-loop kinematic chains (KCs) (excluding the Bennett mechanism etc). This approach is totally different from the approaches based on the screw theory and based on the displacement subgroup, and only simple mathematical tools (vector algebra, etc.) are used. Using this approach, the structure types of serial mechanisms with the specified ranks and the specified degree of freedom (DOF) are synthesized firstly. After that, using the structure types of the obtained serial mechanisms, structure types of over-constrained single-loop KCs with the specified ranks and the specified DOF can be generated in a straightforward way. The structure types of the obtained serial mechanisms can be used as branches of parallel mechanisms. The structure types and the ranks of the obtained over-constrained single-loop KCs can be used to calculate the DOF of multi-loop mechanisms. In fact, the systematic approach proposed in this paper is a key component of the systematic approach for structure synthesis of parallel mechanisms.

scholarly journals A New Method for Type Synthesis of 2R1T and 2T1R 3-DOF Redundant Actuated Parallel Mechanisms with Closed Loop Units

2020 ◽  
Vol 33 (1) ◽  
Author(s):  
Yongquan Li ◽  
Yang Zhang ◽  
Lijie Zhang
Keyword(s):  
Closed Loop ◽  
Screw Theory ◽  
Line Graph ◽  
Degree Of Freedom ◽  
Parallel Mechanisms ◽  
Type Synthesis ◽  
Allocation Criteria ◽  
Grassmann Line Geometry ◽  
Moving Platform ◽  
Atlas Method

Abstract The current type synthesis of the redundant actuated parallel mechanisms is adding active-actuated kinematic branches on the basis of the traditional parallel mechanisms, or using screw theory to perform multiple getting intersection and union to complete type synthesis. The number of redundant parallel mechanisms obtained by these two methods is limited. In this paper, based on Grassmann line geometry and Atlas method, a novel and effective method for type synthesis of redundant actuated parallel mechanisms (PMs) with closed-loop units is proposed. Firstly, the degree of freedom (DOF) and constraint line graph of the moving platform are determined successively, and redundant lines are added in constraint line graph to obtain the redundant constraint line graph and their equivalent line graph, and a branch constraint allocation scheme is formulated based on the allocation criteria. Secondly, a scheme is selected and redundant lines are added in the branch chains DOF graph to construct the redundant actuated branch chains with closed-loop units. Finally, the branch chains that meet the requirements of branch chains configuration criteria and F&C (degree of freedom & constraint) line graph are assembled. In this paper, two types of 2 rotational and 1 translational (2R1T) redundant actuated parallel mechanisms and one type of 2 translational and 1 rotational (2T1R) redundant actuated parallel mechanisms with few branches and closed-loop units were taken as examples, and 238, 92 and 15 new configurations were synthesized. All the mechanisms contain closed-loop units, and the mechanisms and the actuators both have good symmetry. Therefore, all the mechanisms have excellent comprehensive performance, in which the two rotational DOFs of the moving platform of 2R1T redundant actuated parallel mechanism can be independently controlled. The instantaneous analysis shows that all mechanisms are not instantaneous, which proves the feasibility and practicability of the method.

Position and Orientation Characteristic Equation for Topological Design of Parallel Mechanisms

2008 ◽  
Author(s):  
Ting-Li Yang ◽  
An-Xin Liu ◽  
Qiong Jin ◽  
Yu-Feng Luo ◽  
Hui-Ping Shen ◽  
...  
Keyword(s):  
Topological Structure ◽  
Parallel Mechanism ◽  
Screw Theory ◽  
Parallel Mechanisms ◽  
Output Link ◽  
Geometrical Meaning ◽  
Operation Rules ◽  
The Matrix ◽  
Position And Orientation ◽  
Symbolic Operation

This paper presents the explicit mapping relations between topological structure of parallel mechanism and position and orientation characteristic (in short, POC) of its motion output link. It deals with: (1) The symbolic representation and the invariant of topological structure of mechanism; (2) The matrix representation of POC of motion output link; (3) The POC equations of parallel mechanism and its symbolic operation rules. The symbolic operation involves simple mathematic tools and fewer operation rules, and has clear geometrical meaning. So, it is easy to use. The forward operation of the POC equations can be used for structural analysis; its inverse operation can be used for structural synthesis. The method proposed in this paper is totally different from the methods based on screw theory and based on displacement subgroup.

scholarly journals Automatic Mobility Analysis of Parallel Mechanisms: An Algorithm Approach Based on Position and Orientation Characteristic Equations

2019 ◽  
Author(s):  
Xiaorong Zhu ◽  
Huiping Shen ◽  
Chengqi Wu ◽  
Damien Chablat ◽  
Tingli Yang
Keyword(s):  
Systematic Approach ◽  
Fundamental Problem ◽  
Parallel Mechanisms ◽  
Mobility Analysis ◽  
Topological Structures ◽  
Design And Optimization ◽  
Logical Operations ◽  
Intelligent Analysis ◽  
Position And Orientation

Abstract The determination of the mobility of parallel mechanisms (PM) is a fundamental problem. An automatic and intelligent analysis software will be a significant tool for the design and optimization of mechanical systems. Based on the theory of position and orientation characteristics (POC) equations, a systematic approach to computer-aided mobility analysis of PMs is presented in this paper. First, a digital model for topological structures which has a mapping relationship with position and orientation characteristics of mechanism is proposed. It describes not only the dimension of the motion output, but also gives the mapping relationship between the output characteristic and the axis of the kinematic joints. Secondly, algorithmic rules are established that convert the union and intersection operations of POC into the binary logical operations and the automatic analysis of POC are realized. Then, the algorithm of the automatic mobility analysis of PMs and its implementation with VC++ are written. The mobility and its properties (POC) will also be analyzed and displayed automatically after introducing by users of the data of topological structures representation. Finally, typical examples are provided to show the effectiveness of the software platform.

Variable Degree-of-Freedom Spatial Mechanisms Composed of Four Circular Translation Joints

2020 ◽  
Author(s):  
Xianwen Kong
Keyword(s):  
Configuration Space ◽  
Screw Theory ◽  
Degree Of Freedom ◽  
Variable Degree ◽  
Circular Trajectory ◽  
Spatial Mechanism ◽  
Spatial Mechanisms ◽  
Motion Modes ◽  
Multi Mode ◽  
Motion Mode

Abstract This paper deals with the construction and reconfiguration analysis of a spatial mechanism composed of four circular translation (G) joints. Two links connected by a G joint, which can be in different forms such as a planar parallelogram, translate along a circular trajectory with respect to each other. A spatial 4G mechanism, which is composed of four G joints, usually has 1-DOF (degree-of-freedom). Firstly, a 2-DOF 4G mechanism is constructed. Then a novel variable-DOF spatial 4G mechanism is constructed starting from the 2-DOF 4G mechanism using the approach based on screw theory. Finally, the reconfiguration analysis is carried out in the configuration space using dual quaternions. The analysis shows that the variable-DOF spatial 4G mechanism has one 2-DOF motion mode and one to two 1-DOF motion modes and reveals how the 4G mechanism can switch among these motion modes. By removing one link from two adjacent G joints each and two links from each of the remaining two G joints, we can obtain a queer-rectangle and a queer-parallelogram, which are the generalization of the queer-square or derivative queer-square in the literature. The approach in this paper can be extended to the analysis of other types of coupled mechanisms using cables and gears and multi-mode spatial mechanisms involving G joints.

scholarly journals Type Synthesis of 2T1R Decoupled Parallel Mechanisms Based on Lie Groups and Screw Theory

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Shuwei Qu ◽  
Ruiqin Li ◽  
Shaoping Bai
Keyword(s):  
Lie Groups ◽  
Lie Group ◽  
Screw Theory ◽  
New Method ◽  
Parallel Mechanisms ◽  
Type Synthesis ◽  
Compact Structure ◽  
Selection Of

Decoupled parallel mechanisms (DPMs) have the characteristics of compact structure and simple control with wide applications. This paper presents a new method of type synthesis for DPMs by virtue of Lie groups and screw theory. The method consists of synthesis at limb level and configuration level. At limb level, Lie group is used to synthesize the limbs with required DOFs. At configuration level, screw theory is adopted to determine configuration with synthesized limbs that satisfy the type synthesis criteria of DPMs. The type synthesis criteria including limb decoupling and selection of the driving pairs are presented. Upon the formulation, the procedure of type synthesis of DPMs is developed. Type synthesis is conducted with the proposed method, which leads to new spatial and planar fully decoupled 2T1R mechanisms.

On the Correctness and Strictness of the Position and Orientation Characteristic Equation for Topological Structure Design of Robot Mechanisms

2013 ◽  
Vol 5 (2) ◽  
Author(s):  
Ting-Li Yang ◽  
An-Xin Liu ◽  
Hui-Ping Shen ◽  
Yu-Feng Luo ◽  
Lu-Bin Hang ◽  
...  
Keyword(s):  
Topological Structure ◽  
Screw Theory ◽  
Structure Design ◽  
Parallel Mechanisms ◽  
Operation Rules ◽  
Structure Synthesis ◽  
Union Operation ◽  
Intersection Operation ◽  
Velocity Characteristic ◽  
Position And Orientation

Position and orientation characteristic (POC) equations for topological structure synthesis of serial and parallel mechanisms were proposed in a published paper by the authors. This paper will further prove the correctness and strictness of the theoretical foundation for POC equations and also be a reply to the reviewers of our follow-up papers. The main contents of this paper include: symbolic representation of mechanism topological structure and its invariance, velocity characteristic (VC) set and POC set of link and its invariance, one-to-one correspondence between elements of the VC set and POC set, POC equations for the serial mechanism and 10 corresponding “union” operation rules, and POC equations for the parallel mechanism and 14 corresponding “intersection” operation rules. In addition, the interrelations and differences among three methods (POC set based method, screw theory based method, and displacement subgroup based method) for mechanism topological structure design are concluded.

Comparison Study on Three Approaches for Type Synthesis of Robot Mechanisms

2009 ◽  
Author(s):  
Ting-Li Yang ◽  
An-xin Liu ◽  
Yu-Feng Luo ◽  
Li-Ping Zhang ◽  
Hui-Ping Shen ◽  
...  
Keyword(s):  
Screw Theory ◽  
Mathematical Representation ◽  
Parallel Mechanisms ◽  
Comparison Study ◽  
Type Synthesis ◽  
Basic Principles ◽  
Operation Rules ◽  
Structure Synthesis ◽  
Vector Algebra ◽  
Basic Equations

Basic principles and main characteristics of three approaches for structure synthesis of robot mechanisms (the screw theory-based approach, the displacement subgroup-based approach and the approach based on position and orientation characteristic (in short, POC) ) are studied and compared in this paper. The comparison deals with the mathematical tools, the symbolic representation of mechanism topological structure, the mathematical representation of POC of the output motion link with respect to the frame link, the basic equations for structure synthesis of serial and parallel mechanisms and relevant operation rules, and the characteristics of their synthesized mechanisms, etc. This comparative study shows that the POC-based approach is totally different from the other two approaches: (1) the POC-based approach requires only simple mathematical tools (such as vector algebra, set theory, etc), (2) the POC-based approach is conceptually simpler and therefore easier to understand and to use, and (3) the POC-based approach is more general.

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