A fail-safe operation strategy for LAWEX (LARM wire driven EXercising device)

Abstract

Cable Driven Parallel Robots (CDPR) are widely used for application ranging from the operation of cable-suspended cameras to rehabilitation or home assistance devices. However, even though the above applications involve direct human interaction, safety for CDPR is still an open issue. This paper proposes an attempt to manage cable failures in CDPR by applying a general formulation to a specific case of study. Namely, the proposed case of study refers to a prototype of LAWEX (LARM Wire driven EXercising device) intended for upper limb rehabilitation. The proposed strategy to manage cable failures consists of generating a braking force, which prevents undesired motions of the end-effector, as soon as a cable failure is detected. A specific real-time computation is proposed for identifying a feasible set of cable tensions, which is able to generate the required breaking force. The proposed computation algorithm includes a state-of-the-art geometry based algorithm. Simulations are carried out and presented to prove the effectiveness of the proposed strategy in case of a cable failure.