Abstract
The lower-mobility parallel mechanism has been widely used in the engineering field due to its numerous excellent characteristics. However, little work has been devoted to the actuator selection and placement that best satisfy the system’s functional requirements during concept design. In this study, a unified approach for synthesizing the actuation spaces of both rigid and flexure parallel mechanisms has been presented, and all possible combinations of inputs could be obtained, laying a theoretical foundation for the subsequent optimization of inputs. According to the linear independence of actuation space and constraint space of the lower-mobility parallel mechanism, a general expression of actuation spaces in the format of screw systems is deduced, a unified synthesis process for the lower-mobility parallel mechanism is derived, and the efficiency of the method is validated with two selective examples based on screw theory. This study presents a theoretical framework for the input selection problems of parallel mechanisms, aiming to help designers select and place actuators in a correct and even optimal way after the configuration design.
Highlights
The lower-mobility parallel mechanism (PM) [1] generally refers to parallel mechanisms with two to five degrees of freedom (DOFs)
It has been successfully applied in many engineering fields, such as flexible micro-positioning platforms [2], precision attitude adjusting devices [3], the Z3 spindle head based on the 3-PRS PM [4], the Tricept hybrid parallel manipulator [5], the space docking mechanism [6], and so on
In Refs. [23, 24], the relation between actuation and output motion was established based on screw theory, the selection and placement of linear actuators were considered on the basis of freedom space and constraint space, and a total of 26 actuation spaces were enumerated
Summary
The lower-mobility parallel mechanism (PM) [1] generally refers to parallel mechanisms with two to five degrees of freedom (DOFs). An important synthesis criterion stating that “any actuation space of lower-mobility PMs without redundant actuation is always linearly independent of its constraint space” is improved, a general expression of actuation spaces in the format of screw systems is deduced, and the synthesis process is obtained. It can be concluded that the actuation space is always linearly independent of its constraint space for the lower-mobility PMs without redundant actuation, when the mechanisms have definite motion. An important criterion for synthesizing the actuation space of both rigid and flexure parallel mechanisms is proposed, which is stated as: the actuation space is always linearly independent of its constraint space for the lower-mobility PMs without redundant actuation, when the mechanisms have definite motion. According to the criterion of comprehensive actuation space proposed, the actuation space is always linearly independent of its constraint space for the lower-mobility PMs without redundant actuation when the mechanisms have definite motion. By synthesizing the actuation spaces of the lowermobility parallel mechanism, several groups of reasonable combinations of input can be obtained, and the input optimization of the mechanisms can be achieved by further selecting the appropriate performance index and analyzing the performance of the mechanism with different combinations of inputs
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