TetraFLEX: Design and kinematic analysis of a novel self-aligning family of 3T1R parallel manipulators

A new family of 3T1R parallel manipulators (PMs) with self-aligning property, named TetraFLEX, is presented. 3T1R manipulators have many applications in different fields. Moreover, self-aligning property refers to the presence of passive joints in the PM limbs that are conceived to compensate for possible misalignments between the sliding directions of the actuated prismatic(P)-pairs. This property allows the fixation of the limbs in different frame geometries. Thus, this advantage broadens the PM applications to field robotics in several scenarios. Here, the position and singularity analyses of the new family of self-aligning PMs is addressed with a unified approach. The results are that both the direct and the inverse position analyses have simple closed-form solutions and that wide free-from-singularity regions of TetraFLEX PMs' workspace exist. The effectiveness of the technical proposal is also illustrated by discussing their design criteria and kinetostatics performances in a case study.