Single-loop wrists which generate triangular structures

• Single-loop wrists with triangular architecture have actuators on/near to the base.
• All these wrists are identified and two, RU–RRPS and RU–RUPU, studied in depth.
• The position analysis problems of the two studied wrists are analytically solved.
• Also, their singularities are identified through analytic and geometric conditions.
• The kinematic features common to all triangular architectures are found.

Closed kinematic chains (parallel architectures) allow the actuators to be located on or near to the frame, which makes them much lighter and faster than their serial counterparts. Due to their multi-loop topology, these advantages are usually accompanied by reduced workspaces and complex kinematics. The reduction of the closed-loop number could be a design rule to attenuate these drawbacks, provided the resulting architectures still keep the above-mentioned advantages. Here, some single-loop architectures for parallel wrists are presented which still allow the actuators to be located on or near to the frame. Moreover, the kinematic analysis of these architectures is studied in depth.