Type synthesis of single-loop 3T1R-parallel mechanisms with a multi-DOF drive system

Type synthesis of 2R2T parallel mechanisms based on motion equivalent chain method

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406214527271 ◽

2014 ◽

Vol 228 (17) ◽

pp. 3209-3217 ◽

Cited By ~ 8

Author(s):

Wei Ye ◽

Yuefa Fang ◽

Sheng Guo ◽

Haibo Qu

Keyword(s):

Parallel Mechanism ◽

Screw Theory ◽

Parallel Mechanisms ◽

Motion Pattern ◽

Type Synthesis ◽

Constraint Force ◽

Single Loop ◽

Loop Chain ◽

Serial Chains

In this paper, the motion equivalent chain method is proposed and then applied to the type synthesis of a class of 2R2T parallel mechanism. The equivalent serial chains are synthesized for a specific 2R2T motion pattern based on screw theory. Feasible limb structures that provide a constraint couple and a constraint force are enumerated according to the reciprocity of the twist and wrench systems. Several motion equivalent single loop chains are constructed with the equivalent serial chains. Using motion equivalent single loop chains to replace the equivalent serial chains, a class of 2R2T parallel mechanisms is obtained based on the foundation of motion equivalent single loop chain structures.

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Type Synthesis of Single-Loop Overconstrained 6R Spatial Mechanisms for Circular Translation

Journal of Mechanisms and Robotics ◽

10.1115/1.4028130 ◽

2014 ◽

Vol 6 (4) ◽

Cited By ~ 12

Author(s):

Xianwen Kong

Keyword(s):

Parallel Mechanisms ◽

Type Synthesis ◽

Single Loop ◽

Plane Symmetric ◽

Research Areas ◽

Revolute Joints ◽

Spatial Mechanisms ◽

Special Cases ◽

Overconstrained Mechanisms ◽

Self Motion

To discover single-degree-of-freedom (DOF) single-loop overconstrained mechanisms is still an open problem. This paper deals with the type synthesis of single DOF single-loop overconstrained 6RMCTs (6R spatial mechanisms for circular translation). These mechanisms provide alternatives to planar parallelograms and are also associated with self-motion of several translational parallel mechanisms. 6RMCTs are to be obtained using a construction approach in combination with the approaches to the type synthesis of parallel mechanisms. By imposing certain conditions on the hybrid overconstrained 6R (plano-spherical, plano-Bennett, double-spherical, and spherico-Bennett) mechanisms, Bricard plane symmetric mechanism, and Bricard line symmetric mechanism, six special cases of 6RMCTs are obtained. By combining planar parallelograms with these special mechanisms, the general cases of 6RMCTs are then constructed. Finally, 4R2H, 2R4H, and 6H mechanisms for circular translation are obtained from the above 6RMCTs by replacing one or more pairs of R (revolute) joints with parallel axes each with a pair of H (helical) joints with parallel axes and the same pitch. This work contributes to the research on overconstrained six-bar mechanisms and further reveals that the research areas of parallel mechanisms and single-loop overconstrained mechanisms are closely related.

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Type Synthesis of 1T2R Parallel Mechanisms Using Structure Coupling-Reducing Method

Chinese Journal of Mechanical Engineering ◽

10.1186/s10033-019-0403-1 ◽

2019 ◽

Vol 32 (1) ◽

Author(s):

Haitao Liu ◽

Ke Xu ◽

Huiping Shen ◽

Xianlei Shan ◽

Tingli Yang

Keyword(s):

Explicit Form ◽

Parallel Mechanism ◽

Analytic Solutions ◽

Forward Kinematics ◽

Parallel Mechanisms ◽

Type Synthesis ◽

Real Time Control ◽

Time Control ◽

Topological Characteristics ◽

Zero Coupling

Abstract Direct kinematics with analytic solutions is critical to the real-time control of parallel mechanisms. Therefore, the type synthesis of a mechanism having explicit form of forward kinematics has become a topic of interest. Based on this purpose, this paper deals with the type synthesis of 1T2R parallel mechanisms by investigating the topological structure coupling-reducing of the 3UPS&UP parallel mechanism. With the aid of the theory of mechanism topology, the analysis of the topological characteristics of the 3UPS&UP parallel mechanism is presented, which shows that there are highly coupled motions and constraints amongst the limbs of the mechanism. Three methods for structure coupling-reducing of the 3UPS&UP parallel mechanism are proposed, resulting in eight new types of 1T2R parallel mechanisms with one or zero coupling degree. One obtained parallel mechanism is taken as an example to demonstrate that a mechanism with zero coupling degree has an explicit form for forward kinematics. The process of type synthesis is in the order of permutation and combination; therefore, there are no omissions. This method is also applicable to other configurations, and novel topological structures having simple forward kinematics can be obtained from an original mechanism via this method.

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

Chinese Journal of Mechanical Engineering ◽

10.1186/s10033-020-00487-7 ◽

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.

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