The SCARA-Tau parallel manipulator was derived with the objective to overcome the limited workspace-to-footprint ratio of the DELTA parallel manipulator while maintaining its many benefits. The SCARA-Tau family has later been extended and a large number of variants have been proposed. In this paper, we analyse four of these variants, which together encompass the main differences between all the proposed SCARA-Tau manipulators. The analysed manipulator variants utilise an identical arrangement of five of the six linkages connecting the actuated arms and the manipulated platform and exhibit the same input-output Jacobian. The normalised reciprocal product between the wrench of the sixth linkage and the twist of the platform occurring without this linkage provides a measure on how effectively the sixth linkage constrains the manipulated platform. A comparison of the manipulator variants with respect to this measure demonstrates each variants suitability for specific applications.

Although parallel manipulators possess the benefits of high acceleration and accuracy, they typically suffer from a limited workspace to footprint ratio. This paper presents a workspace analysis of two recently proposed axis-symmetric parallel manipulators designed to overcome this problem. The studied manipulators are parametrized, their inverse kinematic models are derived and an in-depth singularity analysis is performed. Next, the architectural parameters are generated for one of the manipulators, using a meta-heuristic algorithm to produce the maximum singularity-free workspace. Thereafter, a second parameter calculation is performed to examine the relationship between maximizing the global conditioning index (GCI) and the resultant achievable workspace for the manipulators.