Evaluation of Two Tension Sensors for Cable-Driven Parallel Manipulators

Cable-driven parallel manipulators (CDPMs) constitute a class of parallel robots in which the frame is connected to the end-effector through a set of cables. The weight reduction achieved by replacing rigid links with cables, along with their exceptionally large workspace, makes CDPMs suitable for applications such as positioning devices, large surface inspection, motion support systems, and automated storage systems. For effective use in these applications, accurate positioning capabilities are essential, which in turn require accurate measurements of the tension on each cable, and at a sampling rate that is less than or equal to the time constant of the actuator response. This paper first analyses the dynamics of the actuator for an over-constrained robot and provides concrete values of this constant considering the cable elasticity. Then, it proposes two tension sensors, presents the calibration procedures, and the methodologies to evaluate them in CDPMs so that they can be replicated and subsequently included in another CDPM configuration. They also serve as critical safety devices, continuously monitoring cable tension to detect any operations or situations that are out of range. Ensuring the safe and reliable condition of cables is crucial not only for CDPMs but also for lifting systems, transmission systems, and other mechanical or mechatronic systems that rely on cables.