Type Synthesis of Self-Alignment Parallel Ankle Rehabilitation Robot with Suitable Passive Degrees of Freedom

Chinese Journal of Mechanical Engineering

Table 1 Passive kinematic pairs of PSAARR

Category	Type	Quantity
2R2P	\(\text{PP}{\hat{\text{R}}}{\hat{\text{R}}}\), \(\left( {\left( {\overline{\text{P}}{\tilde{\text{P}}}{\text{R}}_{1} } \right){\text{R}}} \right)\)	7
3R1P	\(\left( {\left( {{\overline{\text{P}}\text{R}}_{{1}} {\text{R}}_{{1}} } \right){\text{R}}} \right)\)	6
4R	\(\left( {\left( {{\text{R}}_{{1}} {\text{R}}_{{1}} {\text{R}}_{{1}} } \right){\text{R}}} \right)\)	2

Note: (i) \({\hat{\text{R}}}\) indicates that the axis of the revolute pair passed through the rotation center of the moving platform. (ii) R₁R₁ indicates that the axes of the revolute pairs were parallel. (iii) \({\overline{\text{P}}}\) or \({\tilde{\text{P}}}\) indicates that the axis of the prismatic pair was perpendicular to the axis of the revolute pair R₁, whereas \({\overline{\text{P}}}\) and \({\tilde{\text{P}}}\) were considered as the same element and were not distinguished when sorting. (iv) The elements in ( ) can be arranged and combined arbitrarily. For example, ((R₁R₁R₁)R), including RR₁R₁R₁ and R₁R₁R₁R. (v) Points (i) to (iv) are equally valid in the following