This paper proposed an iterative learning control (ILC) scheme for deformable open-frame cable-driven parallel robots (D-CDPRs). In contrast to the straightforward inverse kinematics of the rigid frame cable-driven parallel robots (CDPRs), accurate modeling of the deformable frame poses challenges due to errors and uncertainties. To address these issues, the authors propose the use of ILC, a control strategy that modifies the control input over iterations based on previous results. ILC has been successfully applied to traditional cable robots, particularly in handling model uncertainty. The paper presents a novel ILC control scheme specifically designed for D-CDPRs, with a focus on reducing tracking errors over repetitive operations. Additionally, hardware experiments are conducted to validate the effectiveness and reliability of the proposed ILC approach. The results demonstrate the efficacy of ILC in mitigating tracking errors, even in scenarios where the dynamic model of the D-CDPRs is unknown.

This article proposes a generalized type of cable-driven parallel robot with deformable frames (D-CDPRs). The class of D-CDPRs allows: first, inevitable deformation of traditional rigid frame CDPRs to be considered; and second, new possibilities to develop CDPRs with lightweight frames that would deform. Comparatively, such lightweight CDPRs are easier to set up and largely reduce the cost of material and construction. However, the analysis and control of D-CDPRs are challenging as existing works usually assume the CDPR frame is rigid, such that the cable exit points on the frame are known and fixed. If the modeling errors induced by the deformable frame are not addressed appropriately, the control performance of D-CDPRs will be inaccurate and even unstable. To tackle this problem, novel modeling, analysis, and control approaches are proposed accordingly for D-CDPRs. Using the Euler–Bernoulli beam equations to develop a D-CDPR model, the workspace analysis is proposed and explored. Furthermore, the model-based feedforward length (MBFL) controller is proposed, where it is shown that cable length can be used to execute the tension control for D-CDPRs. Finally, the proposed work is validated in both simulation and hardware experiments.

The wrench feasibility and twist feasibility are the workspace conditions that indicate whether the mobile-platform (MP) of the cable-driven parallel robots (CDPRs) can provide a sufficient amount of wrench and twist. Traditionally, these two quantities are evaluated independently from the actuator's torque and speed limits, which are assumed to be fixed in the literature, but they are, indeed, coupled. This results in a conservative usage of the actuator capability and, hence, hinders the robot's actual feasibility. In this study, new approaches to analyzing and commanding CDPRs by considering the coupling effect are proposed. First, the required wrench of the MP is mapped into the twist space by the motors' torque–speed relationship and becomes the wrench-dependent available twist set. Then, a new workspace condition and a new metric are introduced based on the available twist set. The metric shows the maximum allowable MP speed map of the workspace. Finally, a varying speed trajectory is designed based on the metric to optimize the total MP traveling time. This study shows the potential of robot wrench–twist capability and enhances the robot hardware effectiveness without any hardware changes.