Efficient Calibration of Cable-Driven Parallel Robots with Variable Structure

This paper presents an efficient practical approach for the combined explicit and implicit approximated calibration of cable-driven parallel robots (wire robots, CDPR) mainly developed to tackle the problems with variable system structures, i.e. often reconfigurable common robot platform. Indeed, the developed calibration procedure can also be applied to the systems with stationary (end-effector- i.e. gripper-like) platforms, however the benefits of the new methods are mainly expressed in the variable structure systems. The variable structure CDPR systems cover classes of robots in which the common robot platform represents a working object to be manipulated, itself. Such systems are typical in novel CDPRs referred as extended-cranes wire robots or rehabilitation wire robots (e.g. STRINGMAN [1]). An additional specific system case belonging to the considered class is large mobile CDPR developed for applications in agriculture, which with changes of the application fields should be often periodically reconfigured and commissioned (calibrated). The paper provides detailed mathematical modelling of the novel calibration approach based on the parameter sensitivity analysis of the robot kinematic models including wire pulley systems. The implementation of the calibration procedures including required sensory systems and control supports has also been considered. Finally, practical examples illustrate the performance of the developed calibration method.