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.

翻译：本文旨在开发一种四自由度（DoF）并联运动机械臂（PKM）的重构方法，该机械臂专为膝关节损伤的诊断与康复任务而设计。原始构型的四自由度机械臂在其工作空间内存在II型奇异位形。为此，我们提出通过重构机械臂来规避典型康复轨迹中出现的此类奇异位形（源于PKM的正向雅可比矩阵）。我们通过最小化问题实现PKM重构，其中设计变量对应机器人支链在固定平台和移动平台上的锚固点位置。目标函数基于特定轨迹下驱动器输出力的最小化。该最小化问题引入约束方程以规避II型奇异位形，从而保证特定路径上主动广义坐标的可行性。为评估所提出的概念性策略，我们搭建了原型样机，通过将锚固点移动至固定平台和移动平台预钻孔位实现重构。通过多个案例的仿真与实验验证策略性能，结果表明该重构策略可在无II型奇异位形条件下获得驱动合力最小的运动轨迹。