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

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.

Actuation Spaces Synthesis of Lower-Mobility Parallel Mechanisms Based on Screw Theory

“…The configuration synthesis [7][8][9][10][11] of lower-mobility parallel mechanisms is regarded as an effective tool to find multiple solutions in the conceptual design phase of PMs, a series of systematic approaches for achieving a comprehensive type synthesis have been proposed, and a large variety of PMs generating a specified motion pattern have been developed. On this basis, Yu et al [12] presented a unified approach for synthesizing both rigid and flexure parallel mechanisms in the framework of screw theory.…”

Force Analysis of the Overconstrained Mechanisms Based on Equivalent Stiffness Considering Limb Axial Deformation

“…Its applications involve areas such as deployable antennas, machine tools, robots, medical equipment and entertainment facilities. According to the different generation methods of overconstraints and actuated modes, overconstrained mechanism is divided into passive overconstrained mechanism [1][2][3], active overconstrained mechanism [4][5][6][7] and passive-input overconstrained mechanism [8].…”

“…Active overconstrained mechanism is defined as the mechanism that causes overconstraints due to actuation redundancy, i.e., the number of active inputs being greater than the number of DOFs. The introduction of actuation redundancy has played an important role in avoiding singularities, expanding the working space [4], eliminating the gap of the kinematic joint [27], improving the rigidity of the machine and actuated stability [28], and especially improving the bearing load capacity [29][30]. Introduction of redundant actuation results in a statically indeterminate force analysis of active overconstrained mechanism.…”

Type Synthesis of 3-Translational Redundant Actuated Parallel Mechanisms With Closed-Loop Branch Chains Based On Graphical Approach

“…The authors then compared the static stiffness of two mechanisms, finding that the latter had significantly increased stiffness. Li et al [23][24][25] synthesized a class of 2T1R and 2R1T parallel mechanisms using the graphical approach, including the redundancy to mechanisms aiming to improve their stiffness and stability. Similarly, Wen Yong [26] synthesized a class of 3-translational parallel mechanisms and carried out stiffness analysis of one of the mechanisms, the pose error analysis was also carried out at the end of the mechanism, considering only joint clearance.…”