Cable-driven Parallel Robots Research Articles

A Novel, Soft, Cable-Driven Parallel Robot for Minimally Invasive Surgeries Based on Folded Pouch Actuators

This paper introduces a soft, cable-driven parallel robot for minimally invasive surgeries. The robot comprises a pneumatic inflatable scaffold, six hydraulic, folded pouch actuators, and a hollow, cylindrical end-effector offering five degrees of freedom. A key development is the design of the pouch actuators, which are small, low-profile, simple structures, capable of a high stroke of 180° angular displacement. The scaffold, actuators, and plastic cables are economically and rapidly fabricated using laser cutting and welding techniques. Constructed primarily from soft plastic materials, the robot can be compactly folded into a cylinder measuring 110 mm in length and 14 mm in diameter. Upon inflation, the scaffold transforms into a hexagonal prism structure with side lengths of 34 mm and edge lengths of 100 mm. The kinematic model of the robot has been developed for workspace calculation and control purposes. A series of tests have been conducted to evaluate the performance of the actuator and the robot. Repeatability tests demonstrate the robot’s high repeatability, with mean and root mean square errors of 0.3645 mm and 0.4186 mm, respectively. The direct connection between the end-effector and the actuators theoretically eliminates cable friction, resulting in a hysteresis angle of less than 2°, as confirmed by the tracking results. In addition, simulated surgical tasks have been performed to further demonstrate the robot’s performance.

Integrated simulation and control environment for the development and safe start-up of cable driven parallel robots

ABSTRACT This article presents a new environment designed to facilitate the conceptualization and automation of CDPRs (Cable Driven Parallel Robots). Utilizing a platform for robotic simulation, an industrial controller, and a data gateway to communicate both systems, it is possible to emulate CDPR motion in early design, development, and start-up phases. Thus, this simulation environment allows to test how the robot will behave in advance in order to obtain a safer and more reliable first operation with the real robot. An spatially under-constrained CDPR with four cables was used to validate the capabilities of the proposed integrated environment, comparing its performance against an industry-standard hardware prototype. Both the simulation model and the real prototype performed the same trajectory in order to assess a time delay and position errors between them. Evaluation results revealed that the simulation accurately replicated the performance of its industrial counterpart, with a peak divergence of 0.27% in the position of the robot under various speed scenarios. This occurs even when accounting for latency arising from data exchange connecting the industrial control unit to the simulation. The results have shown that the environment is suitable for trajectory control of new CDPR architectures under different dynamic conditions.

Analytic Center-Based Tension Distribution for Cable-Driven Platforms

Abstract A redundant cable-driven platform (CDP) is composed of m cables that exceed the degree-of-freedom (DoF) of the end-effector. The choice of tension along the cables admits infinite solutions. This paper proposes the use of the analytic center to solve the tension distribution problem. Adopting this technique allows finding tensions far from the tension limits, namely, robust as well as tension profiles continuous and differentiable in time. The continuity, differentiability, and uniqueness of the solution are also proven. Moreover, the possibility of including non-linear constraints acting on the tensions (e.g., friction) is a further contribution. The computational time with the proposed approach is compared to the existing techniques to assess its real-time applicability. Finally, several simulations using several cable-driven parallel robots’ (CDPRs) architectures are reported to demonstrate the method’s capabilities.

Hybrid cable tension–length compensation algorithm for dynamic performance improvement of mobile cable-driven parallel robot

Hybrid cable tension–length compensation algorithm for dynamic performance improvement of mobile cable-driven parallel robot

Type Synthesis of a 3DOF Wrist Applying the Coupled-Input Cable-Driven Parallel Robot

Abstract The spatial cable-driven parallel robots (CDPRs) with low DOF (degree-of-freedom; n < 6) are like the physiological structure of bone and muscles, which are suitable for designing humanoid joints. Therefore, the type synthesis of the CDPR is of great interest for the design of new humanoid wrist joints. In this paper, we present a type synthesis of the coupled-input CDPRs to design a 3DOF wrist. Coupled input means that one actuator controls more than one cable. First, the Yamanouchi symbols of the coupled-input CDPRs are listed using the permutation group. In addition, two winding methods for the cable and the actuator are defined in the coupled-input CDPRs. Finally, a topology configuration of the coupled-input CDPR suitable for the 3DOF wrist model is determined based on a comparative analysis of the workspaces of a class of coupled-input CDPRs. It is shown that type synthesis of the coupled-input CDPRs is an effective way to innovate low DOF CDPRs.

An Underactuated Cable-Driven Parallel Robot for Marine Automated Launch and Recovery Operations

Abstract This paper presents the feasibility study and preliminary testing of an underactuated cable-driven parallel robot for automated launch and recovery operations on the sea surface. The robot frame is mounted onto a primary vessel (PV) subject to sea-induced motions. During launch, the end-effector (EE) is required to deploy a secondary vessel (SV) by lowering it from the PV onto the sea surface. During recovery, the ee has to track and grasp a SV and the EE-SV assembly needs to be stabilized during lifting from the sea surface to the PV. Sea conditions and the underactuated nature of the ee influence the operational feasibility and the overall robot performance. The paper presents the conceptual design and the robot model, as well as the methodologies for winch dimensioning and robot control. An extensive simulation campaign is conducted to optimize performances and assess the system behavior. Finally, the operations are tested on a scaled prototype in a laboratory environment.

A modular computational framework for the dynamic analyses of cable-driven parallel robots with different types of actuation including the effects of inertia, elasticity and damping of cables

AbstractDynamic simulations of the cable-driven parallel robots (CDPRs) with cable models closer to reality can predict the motions of moving platforms more accurately than those with idealisations. Hence, the present work proposes an efficient and modular computational framework for this purpose. The primary focus is on the developments required in the context of CDPRs actuated by moving the exit points of cables while the lengths are held constant. Subsequently, the framework is extended to those cases where simultaneous changes in the lengths of cables are employed. Also, the effects due to the inertia, stiffness and damping properties of the cables undergoing 3D motions are included in their dynamic models. The efficient recursive forward dynamics algorithms from the prior works are utilised to minimise the computational effort. Finally, the efficacy of the proposed framework and the need for such an inclusive dynamic model are illustrated by applying it to different application scenarios using the spatial $4$ - $4$ CDPR as an example.

Online Self-Calibration of Cable-Driven Parallel Robots Using Covariance-Based Data Quality Assessment Metrics

Abstract This paper presents an algorithm to perform self-calibration of cable-driven parallel robots (CDPRs), where the CDPR's end-effector pose is estimated in conjunction with the calibration of biases in the CDPR's measurements. Two new metrics, known as the position dilution of precision (PDOP) and orientation dilution of precision (ODOP) are introduced as a means to quantify the quality of data collected with regards to self-calibration. These metrics are based on a covariance matrix that is computed online as part of the proposed self-calibration algorithm, which results in the PDOP and ODOP directly corresponding to the standard deviation of the position and orientation errors, respectively. These metrics are used to intuitively select which data points contribute to improved calibration, resulting in a computationally-efficient algorithm requiring few data points to maintain accurate calibration. Additionally, the PDOP and ODOP provide a means to assess when sufficient calibration data has been collected. Numerical results involving an inverse kinematic simulation with rigid cables and a dynamic simulation with flexible cables indicate that the proposed algorithm is capable of performing self-calibration in a computationally-efficient manner. Moreover, the simulation results indicate that the proposed PDOP and ODOP metrics result in smaller position and orientation errors when used to prune the data set compared to the observability indices found in the literature. Accuracy of the proposed algorithm is also confirmed through experiments when compared to ground-truth pose data.

A Self-Adaptive Inertia Hybrid Control of a Fully Constrained Cable-Driven Parallel Robot

A Cable-Driven Parallel Robot (CDPR) is a special type of parallel robot actuated by elastic cables instead of rigid links, which brings uncertainties of model nonlinearities and structural friction depending on the payload variation. A precise motion with minimum control effort against an unknown payload has been a challenging task. To conquer it, we propose an adaptive hybrid control approach for the fully-constrained CDPR with an unknown payload in this paper. A Cartesian space position control and a joint space cable force control are designed through inertia estimation to encounter the effect of the uncertain payload. And then, an artificial neural network (ANN) is employed to estimate the end-effector force in Cartesian space for precise force control and consecutive uncertainties compensation. The stability of the proposed controller is proven based on the Lyapunov method and the efficacy is verified by the experiments. As for feasibility results, the proposed adaptive hybrid control-based cable force estimation was evaluated on the Mini CDPR. Compared to the traditional control scheme, the tracking error was decreased approximately 56% and the utilized tension was significantly reduced for the given trajectory tracking test. Furthermore, the investigation of free movements of the helix trajectory and pick-and-place tasks showed that the proposed hybrid adaptive control can control the position and cable force altogether while being able to estimate the inertia of the end-effector. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —The study was motivated by the control problem of adjusting cable tensions of a cable-driven parallel robot (CDPR) against varying payloads at the end-effector. Several advanced control approaches were proposed for but limited to CDPR model parameter estimation and did not consider varying payload. This paper suggests a practical methodology capable of both self-adaptation to unknown payload inertia and consequently improving tracking control performance for a CDPR. In this paper, we derived an adaptive control model and proved stability to ensure safety. In order to encounter unmodeled uncertainties such as pulley friction and cable characteristics, we utilized an artificial neural network (ANN) trained by experiments. The experimental results could confirm that the proposed scheme can estimate the payload inertia and generate minimized cable tension while maintaining good trajectory tracking performance. In future research, we will show more practical validation for a scale-up CDPR with heavy objects toward logistics or pick-and-place application in practice.

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.

Cable Path Analysis and Kinematic Control of a Cable-Driven Parallel Robot Allowing Cables to Wrap on Cylinders or Spheres

Cable Path Analysis and Kinematic Control of a Cable-Driven Parallel Robot Allowing Cables to Wrap on Cylinders or Spheres

Fractional-order PID controller tuned by particle swarm optimization algorithm for a planar CDPR control

The use of cable-driven parallel robots (CDPRs) has been steadily increasing across various sectors due to their expansive workspaces, impressive payload-to-mass ratios, and cost-effective designs. Controlling these robots, particularly those with substantial actuation redundancy, can present challenges. This research paper proposes the implementation of a fractionalorder proportional-integral-derivative (FOPID) controller to effectively regulate the end-effector of a planar CDPR with four actuation cables. The parameters of the controller are fine-tuned using the particle swarm optimization (PSO) algorithm to ensure optimal performance. The proposed controller's performance is evaluated through two numerical experiments: target tracking and trajectory tracking using a point-to-point approach. Furthermore, a comparative study is conducted to highlight the controller's performance, comparing the proposed FOPID controller with both the classical PID controller and an optimized PID controller. The achieved results demonstrate that the proposed controller exhibits superior performance in terms of tracking accuracy and smoothness of control signals when compared to the other controllers under investigation. As a result, the proposed controller design represents a substantial advancement in control performance and can be regarded as a promising control strategy for CDPRs.

Optimal Reconfiguration Planning of a 3-DOF Point-Mass Cable-Driven Parallel Robot

Cable-driven parallel robots (CDPRs) have attracted much attention due to their advantages, such as large workspace and excellent load capacity. However, their adaptability to different tasks has been limited because of fixed configurations. To improve this, a novel 3-DOF point-mass reconfigurable CDPR (RCDPR) has been designed, and its configuration can be changed by adjusting the positions of multiple cable anchors. Since wrench feasible workspace (WFW) is an essential criterion that describes the configuration characteristics, an optimal reconfiguration planning method is proposed to schedule the sequence and number of all movable cable anchors for adjusting the WFW range. Based on a two-level optimization process, the method can realize static reconfiguration (SR) or dynamic reconfiguration (DR) of the RCDPR. If SR cannot provide the required WFW by finding a static optimal configuration, the WFW range will be dynamically adjusted by DR. Besides, the number of movable cable anchors is minimized in DR by applying <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> -norm optimization to the anchor velocity sequences. Simulations and experiments are implemented, and the results show that the proposed method can automatically determine when, which, and how the cable anchors move under physical constraints, and reducing the number of movable cable anchors can indeed save actuator energy effectively.

Dynamics of winch-integrated cable-driven parallel robots and acceleration space analysis

Dynamics of winch-integrated cable-driven parallel robots and acceleration space analysis

Disturbance observer‐based control for cable‐driven parallel robots with external disturbance using deep reinforcement learning

AbstractIn cable‐driven parallel robots (CDPRs) practical applications, external disturbances inevitably influence the actuator performance, leading to low positioning accuracy of end‐effector (EE), and even system crashes. This paper addresses a disturbance observer‐based control scheme using deep reinforcement learning (RL) to suppress the effect of external disturbances. A controller via the non‐singular terminal sliding mode (NTSM) is proposed to enhance the system robustness. The estimation of the disturbance is investigated, and the deep RL is employed to enhance the model‐based disturbance observer, namely, the RLDO, and a corresponding controller via NTSM (RLDO‐NTSMC) is proposed. Simulations and experimental results validate that the RLDO effectively improves the estimation accuracy, and the RLDO‐NTSMC significantly increases the control accuracy of CDPRs. The root mean square errors of the EE's positioning errors controlled by the RLDO‐NTSMC decreased by over 93% compared with the classical augmented proportional–derivative (APD) controller.

Design and Optimization of UAV Aerial Recovery System Based on Cable-Driven Parallel Robot.

Aerial recovery and redeployment can effectively increase the operating radius and the endurance of unmanned aerial vehicles (UAVs). However, the challenge lies in the effect of the aerodynamic force on the recovery system, and the existing road-based and sea-based UAV recovery methods are no longer applicable. Inspired by the predatory behavior of net-casting spiders, this study introduces a cable-driven parallel robot (CDPR) for UAV aerial recovery, which utilizes an end-effector camera to detect the UAV's flight trajectory, and the CDPR dynamically adjusts its spatial position to intercept and recover the UAV. This paper establishes a comprehensive cable model, simultaneously considering the elasticity, mass, and aerodynamic force, and the static equilibrium equation for the CDPR is derived. The effects of the aerodynamic force and cable tension on the spatial configuration of the cable are analyzed. Numerical computations yield the CDPR's end-effector position error and cable-driven power consumption at discrete spatial points, and the results show that the position error decreases but the power consumption increases with the increase in the cable tension lower limit (CTLL). To improve the comprehensive performance of the recovery system, a multi-objective optimization method is proposed, considering the error distribution, power consumption distribution, and safety distance. The optimized CTLL and interception space position coordinates are determined through simulation, and comparative analysis with the initial condition indicates an 83% reduction in error, a 62.3% decrease in power consumption, and a 1.2 m increase in safety distance. This paper proposes a new design for a UAV aerial recovery system, and the analysis lays the groundwork for future research.

Calibration of Static Errors and Compensation of Dynamic Errors for Cable-driven Parallel 3D Printer

As rigid robots suffer from the higher inertia of their rigid links, cable-driven parallel robots (CDPRs) are more suitable for large-scale three-dimensional (3D) printing tasks due to their outstanding reconfigurability, high load-to-weight ratio, and extensive workspace. In this paper, a parallel 3D printing robot is proposed, comprising three pairs of driving cables to control the platform motion and three pairs of redundant cables to adjust the cable tension. To improve the motion accuracy of the moving platform, the static kinematic error model is established, and the error sensitivity coefficient is determined to reduce the dimensionality of the optimization function. Subsequently, the self-calibration positions are determined based on the maximum cable length error in the reachable workspace. A self-calibration method is proposed based on the genetic algorithm to solve the kinematic parameter deviations. Additionally, the dynamic errors are effectively reduced by compensating for the elastic deformation errors of the cable lengths. Furthermore, an experimental prototype is developed. The results of dynamic error compensation after the self-calibration indicate a 67.4% reduction in terms of the maximum error along the Z-axis direction. Finally, the developed prototype and proposed calibration and compensation methods are validated through the printing experiment.

Noniterative Positive Constrained Control of Cable-Driven Parallel Robots

Noniterative Positive Constrained Control of Cable-Driven Parallel Robots

Overall stiffness derivation and enhancement algorithm of a flying cable-driven parallel robot

Overall stiffness derivation and enhancement algorithm of a flying cable-driven parallel robot

Force-Sensor-Free Implementation of a Hybrid Position–Force Control for Overconstrained Cable-Driven Parallel Robots

This paper proposes a hybrid position–force control strategy for overconstrained cable-driven parallel robots (CDPRs). Overconstrained CDPRs have more cables (m) than degrees of freedom (n), and the idea of the proposed controller is to control n cables in length and the other m−n ones in force. Two controller implementations are developed, one using the motor torque and one using the motor following-error in the feedback loop for cable force control. A friction model of the robot kinematic chain is introduced to improve the accuracy of the cable force estimation. Compared to similar approaches available in the literature, the novelty of the proposed control strategy is that it does not rely on force sensors, which reduces the hardware complexity and cost. The developed control scheme is compared to classical methods that exploit force sensors and to a pure inverse kinematic controller. The experimental results show that the new controller provides good tracking of the desired cable forces, maintaining them within the given bounds. The positioning accuracy and repeatability are similar those obtained with the other controllers. The new approach also allows an online switch between position and force control of cables.