Control Of Cable-driven Parallel Robot Research Articles

Dynamic modeling and adaptive finite-time control of cable-driven parallel robots for ship cleaning

ABSTRACT Ship cleaning, often manually performed by numerous workers, is crucial in the shipping industry. This study introduces a marine cable-driven parallel cleaning robot (MCDPCR) to enhance cleaning security and efficiency. To investigate trajectory tracking under the moving base, the dynamic model of MCDPCR is established, and the optimisation of cable forces is considered. Then, an adaptive terminal sliding mode controller is designed, integrating the discontinuous sign function term to obtain a continuous actual control law and thus a chattering-free response. Meanwhile, the uncertainty is compensated by an adaptive method. The stability of the control strategy is analyzed using the Lyapunov stability theory. Finally, the effectiveness of the proposed control strategy is verified by several simulation scenarios. The results show that the controller has a fast global convergence speed, high tracking accuracy, and strong robustness. The method can provide a valuable reference for developing automated marine cleaning equipment.

Noniterative Positive Constrained Control of Cable-Driven Parallel Robots

Noniterative Positive Constrained Control of Cable-Driven Parallel Robots

High-Precision Adaptive Control of Cable-Driven Parallel Robots With Convergence Guarantee

High-Precision Adaptive Control of Cable-Driven Parallel Robots With Convergence Guarantee

Jerk-Limited Time-Optimal Model Predictive Path Following Control of Cable-Driven Parallel Robots

Jerk-Limited Time-Optimal Model Predictive Path Following Control of Cable-Driven Parallel Robots

Research on workspace visual-based continuous switching sliding mode control for cable-driven parallel robots

AbstractAchieving the high-precision control of cable-driven parallel robots (CDPRs) is complex because of their structural properties. In this paper, a quintessential redundant CDPR is designed as the research subject, and a continuous switching sliding mode controller based on workspace vision is implemented to enhance the accuracy and stability of trajectory tracking. In addition, a virtual prototype of the CDPR with uncertainties is created in the simulation analysis software ADAMS, and co-simulation is performed with the control system designed in Simulink to validate the effectiveness of the proposed control strategy. Furthermore, a CDPR platform is established for trajectory tracking experiments using the visual-based position feedback method. The trajectory tracking performance with the three control schemes is then evaluated. The experimental results show that the continuous switching sliding mode control algorithm can significantly decrease trajectory tracking errors and exhibit superior trajectory tracking performance compared to the other control strategies.

Active fault-tolerant control of cable-driven parallel robots

Active fault-tolerant control of cable-driven parallel robots

Dual-Loop Dynamic Control of Cable-Driven Parallel Robots Without Online Tension Distribution

Achieving high-precision position control while maintaining positive cable tensions is the most challenging issue for the motion control of cable-driven parallel robots, which should be considered significantly. Different from the existing control schemes with online tension distribution that needs real-time computing in each control cycle, a novel dual-loop dynamic control scheme is proposed in this article, where a paralleled dual-loop tracking strategy is introduced to provide a more compatible scheme, which consists of two tracking loops: 1) the tension control loop and 2) the position control loop. In the former loop, the offline tension distribution is adopted to avoid cable hanging loosely and the real-time feasibility of the distribution method is no longer a necessary demand. In the latter loop, due to the complex dynamics characterized by the cable-driven form, the cooperative motion relation among multiple cables and inevitable external disturbances are investigated comprehensively, and the robust synchronization method is included to guarantee the high-precision position control. Afterward, the Lyapunov method is adopted to analyze the strict stability of the whole closed-loop system with both the position and tension control feedback. The experiments indicate that by synthesizing the two control loops, the proposed scheme can dramatically reduce the tracking errors in the trajectory tracking while avoiding the cable relaxation, and particularly, has a satisfactory control effect when the velocity and acceleration of the trajectory have significant oscillations. Additionally, the strong disturbance rejection ability is also validated via robustness experiments.

A Reaction-Based Stabilizer for Nonmodel-Based Vibration Control of Cable-Driven Parallel Robots

Considering a simplified model of cables is an essential assumption in the design of state-estimator and vibration control of cable-driven parallel robots (CDPRs). Such an assumption however, impacts the effectiveness of controllers and state-estimators in such systems. This article presents a reaction-based stabilizer for nonmodel-based vibration control of CDPRs to address such model dependence. It is proved analytically that by using only three actuators and not involving the cable-connected winches, the proposed stabilizer regulates all undesired vibrations of the platform. It is also shown that the proposed stabilizer needs only the directly measurable position and velocity of its actuators to form its closed-loop control feedback signals. Effectiveness of the proposed system is more significant in CDPRs with considerable nonlinear effects of cables, where such effects are computationally costly to model, such that the performance of real-time controllers and state-estimators are spoiled. To provide a case study, a multibody nonlinear dynamic model of a suspended CDPR equipped-with the proposed stabilizer with zero cable damping effects is developed in SimMechanics/MATLAB, where a fine-tuned proportional-derivative controller is applied on each actuator to suppress all vibrations of the system. In addition, a suspended CDPR with extremely stretchable nonlinear-stiffness elastomer cables is fabricated and tested, where performance of the proposed stabilizer to suppress the high-amplitude nonlinear oscillations of the whole system is demonstrated.

Input Shaping for Feed-Forward Control of Cable-Driven Parallel Robots

Abstract This paper deals with the use of input-shaping filters in conjunction with a feed-forward control of cable-driven parallel robots (CDPRs), while integrating cable tension calculation to satisfy positive cable tensions along the prescribed trajectory of the moving platform. This method aims to attenuate the oscillatory motions of the moving platform. Thus, the input signal is modified to make it self-cancel residual vibrations. The effectiveness, in terms of moving-platform oscillation attenuation, of the proposed closed-loop control method combined with shaping inputs is experimentally studied on a suspended and nonredundant CDPR prototype. This confirms residual vibration reduction improvement with respect to the unshaped control in terms of peak-to-peak amplitude of velocity error, which can achieve 72% while using input-shaping filters.

Adaptive Synchronization Control of Cable-Driven Parallel Robots With Uncertain Kinematics and Dynamics

Cable-driven parallel robots (CDPRs) are a new type of parallel robots with a mobile platform driven by several cables. The flexibility of the structure not only helps them perform better than traditional parallel robots, but also brings about the issues of model uncertainty and multicable coordination. To handle these problems, a novel adaptive synchronization control (ASC) scheme is proposed to suppress the uncertainties of kinematics and dynamics simultaneously, regulate the coordination motion of multiple cables, and finish high-precision tracking tasks. In the proposed scheme, apart from tracking error, a new synchronization error is introduced to describe the coordination motion relationship between adjacent cables. According to these defined errors, the kinematic and dynamic adaptation laws are designed through the linear expressions of kinematic and dynamic models, respectively. Finally, the ASC scheme is presented as well as a tension distribution algorithm. The tracking experiments are implemented on a redundantly actuated 3-degree-of-freedom CDPR with four cables. The proposed ASC scheme can effectively complete the correction of the model parameters by using the feedback of errors and enhance the tracking accuracy of each cable and the synchronization accuracy between all the cables significantly, thereby ultimately improving the control performance of the mobile platform.

Adaptive Cross-Coupled Control of Cable-Driven Parallel Robots With Model Uncertainties

Cable-driven parallel robots (CDPRs) are robots with novel structures, wherein flexible cables, instead of rigid links, are employed to pull mobile platforms. This structural change enables CDPRs to not only offer potential advantages, but also introduces control challenges with regard to frictional uncertainties, dynamic modeling errors, and multi-cable motion coordination. To address these concerns, a novel adaptive cross-coupled control (ACCC) scheme, capable of achieving high-accuracy trajectory tracking control, has been proposed in this study. In the proposed ACCC scheme, a new synchronization error variable has been defined to adjust the coordination motion of adjacent cables; additionally, an adaptive dynamic control strategy has been designed to compensate for the inertia and friction of winches linked to cables. Lastly, an adaptive robust control has been used to restrain un-modeled dynamics and external disturbances. The proposed ACCC scheme was compared against the synchronization control (SC) scheme and the well-known adaptive control (AC) scheme of Slotine-Li by applying them to an actual non-redundant CDPR during trajectory tracking experiments. Corresponding results demonstrated that compared to the SC and the AC scheme, the proposed ACCC scheme serves to improve both tracking and synchronization accuracies of cables, thereby ultimately enhancing the control performance of mobile platforms. Robustness of the ACCC scheme against external disturbance has also been verified.

RISE Feedback Control of Cable-Driven Parallel Robots: Design and Real-Time Experiments

Control of Cable-Driven Parallel Robots (CDPRs) is considered as a challenging task due to their highly nonlinear dynamic behavior, abundant uncertainties, low-stiff cables, parameters variation, cable tensions, and actuation redundancy. Hence, a robust controller is needed to obtain higher performance despite the above mentioned issues. In this paper, we propose a Robust Integral of the Sign of the Error (RISE) control scheme to solve the problem of reference trajectory tracking. RISE feedback control is a robust nonlinear continuous controller which can guarantee a semi-global asymptotic tracking under limited assumptions on the system’s structure. RISE ensures the closed-loop system robustness towards parametric uncertainties and external disturbances. The proposed control solution is designed and implemented in real-time experiments on a fully constrained 4-DOF Cable-Driven Parallel Robot (CDPR) named PICKABLE. The obtained experimental results show that the proposed controller outperforms the classical PID controller and the first-order Sliding Mode Control (SMC) in terms of tracking performances and robustness towards payload variations.

Analysis of the effect of system parameters for combined nonlinear cable elongation characteristics in CDPR

The polymer cable is a widely used material in the cable-driven parallel robot (CDPR) system because of its many advantages such as high sensitivity, large workspace and so on. However, the accurate control of CDPR is not easy because of complicated response of the cable. In our previous study, the integrated cable model was derived. Based on the model, parametric studies were progressed in this paper. While operating CDPR, various parameters such as length, applied tension, and tensile rate can be changed and dominantly affect the dynamics of CDPR. For this reason, parametric study was based on these parameters. In this investigation, dynamic creep, hardening factor and short-term recovery were saturated as processing cyclic load. Each saturation rate was dominantly influenced by cable length and applied tension. As the tensile rate was increased, the dynamic creep was decreased. The hysteresis was the characteristic combining all of dynamics. So, the hysteresis also had saturation trends. When the exerted tension was decreased, the length of cable could be reduced or elongated because the creep and recovery occur at the same time.

Vibration reduction of Cable-Driven Parallel Robots through elasto-dynamic model-based control

This paper deals with the elasto-dynamic model-based control of Cable-Driven Parallel Robots (CDPRs), which manifests in the coupling of a PID feedback controller with a model-based feed-forward control scheme. The feed-forward controller is derived from an inverse elasto-dynamic model of CDPR, which compensates the end-effector dynamics and specifically its vibrations due to cable elasticity. The integration of cable tension calculation into this control strategy guarantees positive cable tensions along the trajectory. Simulations and experimentations while using a suspended and non-redundant CDPR show that tracking errors and vibrations can be reduced by the proposed strategy compared to conventional rigid-body model-based control.

Trajectory Tracking Control of Cable-driven Parallel Robots by Using High-speed Vision

Trajectory Tracking Control of Cable-driven Parallel Robots by Using High-speed Vision

Adaptive neural network control of cable-driven parallel robots with input saturation

In this paper, an adaptive neural trajectory tracking controller with a bounded-input property is developed for cable-driven parallel robots (CDPRs). Due to the fact that the cables in these robotic systems should always remain in tension in a trajectory tracking task, a more precise tracking controller is needed for CDPRs comparing to the conventional rigid-link robotic systems. To achieve this objective, this paper proposes a new nonlinear controller with a learning ability for the robot dynamics. The controller includes an adaptive multi-layer neural network to compensate for the modeling uncertainties of the system, and utilizes an auxiliary dynamics to provide a priori bounded tension command for the cables. In addition to this novelty, a bounded-input controller is designed for the dynamics of the actuators, coupled with gearboxes, in order to follow the tensions, defined through the controller of robot dynamics. The boundedness feature of the controller facilitates considering the upper limit of the actuators in choosing the control gains. Stability of the whole system is well studied, and the uniformly ultimately bounded stability is guaranteed. The effectiveness of the proposed control scheme is validated through simulations on a 4-cable planar robot in both nominal and perturbed conditions.

Tracking Control of Cable-driven Parallel Robots Considering Cable Sag Effects

Parabolic equation is utilized to represent the curve of a long span cable. The relationship among cable force, cable end displacement and cable length variation is derived by using parabolic equation. Dynamics model of cable-driven robots is established on the basis of cable mechanical equation, which shows that the resultant cable force acting on the end-effector is directly related to cable length and end-effector pose. A linear expansion of the mechanical equation is carried out to facilitate introducing the mechanical model into the control design, then the relationship between the cable force increment acting on end-effector and the cable length variation and the end-effector displacement is obtained. The cable force on end-effector can be expressed as the addition of its desired value and a corresponding increment resulting from the error of cable length and the error of end-effector pose. In the control design, a feedback controller is first designed for the cable force by using Lyapunov method. Then, by utilizing the above-mentioned incremental relationship, a nonlinear controller based on the end-effector pose feedback is constructed, in which the cable length adjustment quantity serves as the controller for output control. It is essentially a nonlinear PD controller with compensation terms. Controller parameters can be adjusted automatically along with the variation of system state. Numerical examples validate the control algorithm.