Hybrid Position‐Compliance Control of Redundantly Actuated Parallel Kinematic Manipulators Equipped with Serial Elastic Actuators

Redundantly actuated parallel kinematic manipulators (RA‐PKM) are ideal candidates in robotic applications combining dynamic performance with high accuracy. Actuation redundancy further allows for modulation of the end‐effector (EE) stiffness. A recent trend in robotics is the use of inherently compliant and elastic components, eventually leading to soft continuum robots, which shall provide tailored solutions for human‐robot collaboration and assistance applications. One way to introduce compliance is to use serial elastic actuators (SEA). This yields two kinematically decoupled dynamic systems, the RA‐PKM mechanism and the actuation system, that are force‐coupled by (passive) elastic elements. The DOF of the actuation system exceeds the DOF of the RA‐PKM according to the degree of actuation redundancy. Due to the kinematic decoupling the RA‐PKM is underactuated. To address this issue, a flatness‐based feedback‐linearizing position control approach along with a stiffness modulation approach is proposed.