Failure Analysis of a Collaborative 4-1 Cable-Driven Parallel Robot

Caro, S. and Merlet, J.P., “Failure Analysis of a Collaborative 4-1 Cable-Driven Parallel Robot”, Proceedings of the 8th European Conference on Mechanism Science (EuCoMeS2020), Cluj-Napoca, Romania, September 7–10, 2020Cable-Driven Parallel Robots (CDPRs) have been little used so far for collaborative tasks with humans. One reason is the lack of solutions to guarantee the safety of the operators in case of failure. Therefore, this paper aims to determine the possible failures of CDPRs when they are used for collaborative work with humans and to provide technical solutions to ensure the safety of the operators. A translational three degrees-of-freedom CDPR composed of four cables connected to a point-mass end-effector is considered as an illustrative example. The cables are supposed to be ideal, namely, they are not elastic and do not exhibit sagging

FIXTURELESS CALIBRATION OF PARALLEL MANIPULATORS

Identification objective functions considering end effector pose errors and branch end distance errors for the calibration of parallel manipulators are discussed. Based on the elimination of the need for fixturing devices, branch end distance error based objectives are demonstrated preferred. Kinematic calibration models that include device geometric parameters, for the RSI 6 degree of freedom hand controller, are introduced. Calibrations considering more complete models are demonstrated to yield improved calibrations in comparison to models considering only original non-zero length and angle parameters and potentiometer parameters. The complete calibration model is found to return error values within a range of the same order of magnitude as branch end distance fluctuation due to joint displacement sensors’ noise. To achieve higher precision, it is concluded that noise-free joint displacement sensing and accurate passive spherical branch end joints are required. </jats:p

Dynamic Recovery of Cable-Suspended Parallel Robots After a Cable Failure

International audienceThis paper studies how emergencies and failures can be managed in cable-driven parallel robots, in particular in the case of a redundant cable-suspended robot subjected to a cable breakdown. The objective is to present and test via numerical simulation the feasibility of an emergency strategy that allows the robot platform to be dynamically recovered to a safe position. Preliminary results, based on a simplified robot with a point-mass platform suspended by 4 cables, show that the proposed strategy may be an effective way to guide the platform from an unstable pose determined by the cable failure to a new static equilibrium pose