A Panorama of Methods for Dealing with Sagging Cables in Cable-Driven Parallel Robots

Abstract

We are considering cable-driven parallel robot (CDPR), where the legs of the robot are constituted of cables that can be independently coiled/uncoiled. We show that whatever the size of the CDPR is we may have slack cables so that using a sagging cable model that takes into account both the mass and elasticity of the cables will improve the positioning accuracy.Being able to solve the inverse and direct kinematics (IK/DK) with sagging cables is crucial for kinematic analysis while being quite complex as both IK/DK may have multiple solutions. We present a panorama of solving methods for the IK/DK with their advantages and drawbacks.

Constant Distance and Orientation Following of an Unknown Surface with a Cable-Driven Parallel Robot

“…This adds to the complexity of profile-following tasks. Most of the research works focus on improving the CDPR model, especially regarding cable elasticity and sagging [1], [2], [3], [4], [5], [6], [7] but other approaches such as vision-based control have also been proposed to improve the precision of CDPRs [8], [9]. The robustness of trajectory planning and tracking for CDPRs was evaluated in [10].…”

Direct dynamics of 2D cable-driven parallel robots including cables mass effect and its influence in the control performance

“…However, in some situations, these models do not represent the dynamic behavior of the robot with the required level of accuracy. These scenarios include large robots where, due to the cross-section and length of the cables, the cables mass cannot be neglected [4]. Static analyses were already performed by means of a geometrically exact model proposed in [5].…”

Cable-Driven Parallel Robot Actuators: State of the Art and Novel Servo-Winch Concept

“…The latter approach is widely used thanks to well-established techniques in the solution to the forward kinematic problem and thanks to the fact that no sensors other than the ones embedded in the actuators for their low-level feedback control need to be added to the robot (additional sensors can be added to speed-up computation, improve accuracy [43,44], or if embedded sensors are not sufficient [45]). However, accurate pose information is achievable through forward kinematics if and only if (i) a cable model suitable to the application requirement is used [46][47][48], and (ii) there is a clear correlation between actuator displacement ∆θ and cable displacement ∆l, namely the actuation unit transmission ratio K = ∆l/∆θ. If the latter condition is not satisfied, it is unlikely that the use of a suitable cable model would work without additional sensors.…”