  This paper aims to develop an approach for the reconfiguration of a parallel
kinematic manipulator (PKM) with four degrees of freedom (DoF) designed to
tackle tasks of diagnosis and rehabilitation in an injured knee. The original
layout of the 4-DoF manipulator presents Type-II singular configurations within
its workspace. Thus, we proposed to reconfigure the manipulator to avoid such
singularities (owing to the Forward Jacobian of the PKM) during typical
rehabilitation trajectories. We achieve the reconfiguration of the PKM through
a minimization problem where the design variables correspond to the anchoring
points of the robot limbs on fixed and mobile platforms. The objective function
relies on the minimization of the forces exerted by the actuators for a
specific trajectory. The minimization problem considers constraint equations to
avoid Type-II singularities, which guarantee the feasibility of the active
generalized coordinates for a particular path. To evaluate the proposed
conceptual strategy, we build a prototype where reconfiguration occurs by
moving the position of the anchoring points to holes bored in the fixed and
mobile platforms. Simulations and experiments of several study cases enable
testing the strategy performance. The results show that the reconfiguration
strategy allows obtaining trajectories having minimum actuation forces without
Type-II singularities.
