This paper introduces a screw theory based approach termed the freedom and actuation method (FAM) to the synthesis of decoupled spatial translational compliant parallel mechanisms (XYZ CPMs) with consideration of actuator isolation (input decoupling). This approach is unique in that (a) actuator arrangement is taken into account; and (b) it is based on a set of rules and mathematical expressions, rather than rigid-body mechanism design experience mainly used at present. According to the rules, XYZ CPMs are firstly decomposed into simple function modules, and the degrees of freedom (DOF) of each function module are identified based on the mathematical expressions. Each function module is then synthesized based only on the DOF without consideration of the actuator arrangement, so existing flexure mechanism design approaches such as the constraint-based design, the screw-theory-based method, and the freedom and constraint topology can be employed for the synthesis of the function module. The synthesis process is finally summarized and demonstrated step by step via a monolithic XYZ CPM design example. It can be envisaged that a variety of configurations of each function module can be derived under a specific DOF. Therefore, one can obtain a great number of XYZ CPM designs with consideration of actuator isolation through changing the structure of each function module, even though there is no any rigid-body mechanism design experience. The proposed FAM will enable designers to (a) decompose XYZ CPMs into the function modules; (b) yield multiple solutions to meet the DOF requirement of each compliant function module; and (c) obtain a variety of XYZ CPMs with consideration of actuator isolation.

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