Cable-driven Parallel Manipulator Research Articles

Expanding the wrench feasible workspace of quadrotor-based mobile cable-driven parallel manipulators using multi-objective optimization and machine learning

Quadrotor-based Reconfigurable Cable-Driven Parallel Manipulators (QRCDPMs) have previously been introduced as having significant potential in extending the feasible workspace of Cable-Driven Parallel Manipulators (CDPMs). However, such configurations have limitations in executing positive Z-direction trajectories resulting in non-optimal workspace and performance. This study proposes a novel Quadrotor-based Enhanced Reconfiguration Cable-Driven Parallel Manipulator (QERCDPM) that significantly enhances the Wrench Feasible Workspace (WFW). This allows for extended safe platform operation along all XYZ directions by adjusting the bottom cable exit point. Simulation results indicate that the proposed setup achieves a 96.39 % ratio of safe workspace to available workspace in various cable exit points configurations. Tension Distribution analysis for different trajectories demonstrates the proposed setup's superior cable tension management, increased flexibility and reachability. A Random Forest based Particle Swarm Optimization - Modified Frequency Bat Algorithm (RFPSOMFB) optimization algorithm is proposed, which outperforms existing methods in terms of run time and solution quality. The findings hold significance for applications requiring safe and efficient trajectory execution in dynamic and constrained environments, contributing to the evolution of multi-robot based intelligent and distributed systems.

Adaptive Position Feedback Control of Parallel Robots in the Presence of Kinematics and Dynamics Uncertainties

Uncertainties in the kinematic and dynamic parameters of a parallel robot are unavoidable. The problem is more crucial in the cases where the manipulator interacts with the environment and when it is large–scale or deployable. Furthermore, precise measurement of the velocity of the end-effector is almost inaccessible in practice. This paper addresses the above shortcomings by designing of an adaptive trajectory tracking controller with merely position feedback of joint and task space variables. Simplicity of implementation, separation of adaptation laws of dynamic and kinematic parameters, and reduction of the number of adaptation laws such that in some cases, e.g., cable-driven robots, it is identically equivalent to the number of unknown parameters are some advantages of the proposed controller. The method’s efficiency is shown via implementation on a cable-driven parallel manipulator and an intraocular surgery robot. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —In order to achieve a suitable response in parallel robots with traditional controllers, a precise knowledge of kinematic and dynamic parameters, together with accurate measurement of velocity, is required. In practice, these values are usually derived by robot calibration and identification. Since the system’s parameters may alter or depend on external factors such as temperature, these time-consuming methods should be implemented repeatedly while the robot is out of duty. Additionally, precise velocity measurement is a prohibitive task and requires expensive instruments. This article presents a controller to address the above shortcomings. By this means, a simple adaptive controller based on position feedback is designed such that via suitable estimation of kinematic and dynamic parameters, trajectory tracking is obtained without the need for accurate initial estimates of the parameters. The proposed method has a number of advantages, including separation of the adaptation laws of kinematic parameters and dynamic parameters, simple representation of the Jacobian matrix in regressor form, and there is no requirement for velocity feedback. Furthermore, a force distribution method is introduced for redundant robots. Hence, the proposed controller is an appropriate alternative to traditional controllers widely used in industries.

Model-Free Force Control of Cable-Driven Parallel Manipulators for Weight-Shift Aircraft Actuation

Model-Free Force Control of Cable-Driven Parallel Manipulators for Weight-Shift Aircraft Actuation

Design of an Airship On-Board Crane

This paper presents the design and mathematical model of an innovative smart crane, CHAYA-SC, based on the principle of a cable-driven parallel manipulator, as well as its stabilization. This crane is mounted on the airship hold and intended for handling at altitude. Our objective is to design a precise light crane that can be used for container loading or unloading, particularly in deep-sea ports. Thus, the model developed includes the oscillations as well as the transverse and longitudinal vibrations of the heavy cable supporting the load to be handled. The highly nonlinear partial differential equations (PDE) and ordinary derivative equations (ODE) that govern the motion of the system are obtained via the Lagrange equations coupled with a modal synthesis. So that the mathematical model of the system is compatible with control and real time, we developed a simplified dynamic model which proved to be equivalent to the complete model. As a first validation of the modelling, a simple control vector is applied to stabilize the airship and its load under the effect of a squall. Numerical simulations are presented at the end of the paper to show the relevance of the design.

Dynamics of cable-driven parallel manipulators with variable length vibrating cables

A parametric nonlinear model of cable-driven parallel manipulators endowed with a three-dimensional end-effector is formulated and discussed in this paper. The proposed model considers the distributed stiffness, inertia, and damping of time-varying length cables and allows to study and characterize the dynamic response of manipulators equipped with a generic number n of cables. The equations of motion of each of the n cables are first derived via a total lagrangian formulation together with the compatibility equations prescribing the connectivity between the cables and the end-effector mass, while the dynamics of the end-effector are described by enforcing the balance of its linear and angular momentum. A discretization procedure, based on admissible trial functions, is used to reduce the nonlinear partial differential equations of motion of the cables to a set of ordinary differential equations. The resulting equations are coupled with those describing the motion of the end-effector and the approximate solution is calculated via numerical time integration. Direct and inverse dynamic problems are then formulated and solved for selected case-study manipulators; finally, the role on the dynamic response of the system of the main mechanical parameters and of the degree of over-actuation is discussed.

Planar Cable-Driven Manipulators for Inspection of Large Surfaces

Cable-Driven Parallel Manipulators (CDPM) are a type of parallel robots in which the rigid links connecting the base with the terminal link, also called end-effector, are replaced by cables. This kind of system has been introduced during the last two decades, since then many issues have been addressed, but there are still open problems. Thanks to the nature of the cables, lightweight if compared to the overall structure, and the very large workplace, their possible applications are increasing. Recently, Robotics and Automation have been applied to the inspection of structures and infrastructure; therefore, they are starting to be used to substitute personnel in dangerous or unsafe operations. Related to the inspection, autonomous or tele-operated systems can be used for securing the access to the buildings or infrastructure. In this paper, we propose the application of CDPMs for the inspection of large surfaces, constituted by buildings facades, top roofs, and parts of infrastructures. The development of suitable model of the system, also called Digital Twin, allows the managing of the operation in safe conditions. As new application, we propose the use of a planar CDPM for being applied to the inspection and monitoring. The 3D model acts as a Digital Twin of the real prototype that has been developed and used for experimental testing. Since the purpose is to drive the end-effector to point of interest carrying suitable sensors, tests for trajectory planning and experimental tests are proposed. The inspection of structures and infrastructures has become a very important issue for the security of critical infrastructures, not only at European level but worldwide.

Dynamic Modeling, Workspace Analysis and Multi-Objective Structural Optimization of the Large-Span High-Speed Cable-Driven Parallel Camera Robot

Since most of the cable-driven parallel manipulators (CDPMs) are small in dimension or low in speed, the self-weight or inertia of the cable is neglected when dealing with the problems of kinematics, dynamics and workspace. The cable is treated as a massless straight line, and the inertia of the cable is not discussed. However, the camera robot is a large-span high-speed CDPM. Thus, the self-weight and inertia of the cable cannot be negligible. The curved cable due to the self-weight is modeled as a catenary to accurately account for its sagging effect. Moreover, the dynamic model of the camera robot is derived by decomposing the motion of the cable into an in-plane motion and an out-plane motion, based on which an iterative-based tension distribution algorithm and a workspace generation algorithm are presented. An optimization model is presented to simultaneously improve the workspace volume, anti-wind disturbance ability and impulse of tensions on the camera and pan–tilt device system (CPTDS) by selecting the proper optimal variables under the linear and nonlinear constraints. An improved genetic algorithm (GA) is proposed, and the simulation results demonstrate that the improved GA offers a stronger ability in global optimization compared to the standard genetic algorithm (SGA). The ideal-point method is employed to avoid the subjective influence of the designer when performing the multi-objective optimization, and a remarkable improvement of the performance is obtained through the optimization. Furthermore, the distribution characteristics of the optimization objects are studied, and some valuable conclusions are summarized, which will provide some valuable references in designing large-span high-speed CDPMs.

Control Design for CABLEankle, a Cable Driven Manipulator for Ankle Motion Assistance

A control design is presented for a cable driven parallel manipulator for performing a controlled motion assistance of a human ankle. Requirements are discussed for a portable, comfortable, and light-weight solution of a wearable device with an overall design with low-cost features and user-oriented operation. The control system utilizes various operational and monitoring sensors to drive the system and also obtain continuous feedback during motion to ensure an effective recovery. This control system for CABLEankle device is designed for both active and passive rehabilitation to facilitate the improvement in both joint mobility and surrounding muscle strength.

Overconstrained Cable-Driven Parallel Manipulators Statics Analysis Based on Simplified Static Cable Model

Overconstrained Cable-Driven Parallel Manipulators Statics Analysis Based on Simplified Static Cable Model

Rapid and safe wire tension distribution scheme for redundant cable-driven parallel manipulators

AbstractA non-iterative analytical approach is investigated to plan the safe wire tension distribution along with the cables in the redundant cable-driven parallel robots. The proposed algorithm considers not only tracking the desired trajectory but also protecting the system against possible failures. This method is used to optimize the non-negative wire tensions through the cables which are constrained based on the workspace conditions. It also maintains both actuators’ torque and cables’ tensile strength boundary limits. The pseudo-inverse problem solution leads to an n-dimensional convex problem, which is related to the robot degrees of redundancy. In this paper, a comprehensive solution is presented for a 1–3 degree(s) of redundancy in wire-actuated robots. To evaluate the effectiveness of this method, it is verified through an experimental study on the RoboCab cable robot in the infinity trajectory tracking task. As a matter of comparison, some standard methods like Active-set and sequential quadratic programming are also presented and the average elapsed time for each method is compared to the proposed algorithm.

Practical robust nonlinear PD controller for cable-driven parallel manipulators

Practical robust nonlinear PD controller for cable-driven parallel manipulators

Wrench-Closure Condition of Cable-Driven Parallel Manipulators

Cable-driven parallel manipulators (CDPM) have parallel structures that consist of moving platforms connected to the fixed platform through many flexible cables. The moving platform is driven by many winches, and because of the unidirectional property of cables (cables can only pull and not push in the moving platform), some specific workspaces of CDPM are limited and often do not exist (Gouttefarde and Gosselin 2006). Therefore, determining workspaces for CDPM become an important task, in order to easily plan the trajectory or control the robot. In this paper, we are interested in a set of poses of moving platforms, in which CDPM is always able to generate wrenches that balance any given external wrench exerted on the moving platform. This set of poses is also called wrench-closure workspace (WCW). In this work, we propose a novel procedure used to determine whether a pose of moving platform belongs to WCW. The condition used to check the feasibility of a certain pose in WCW is also called wrench closure condition (WCC). The proposed WCC is able to apply to completely or redundantly restrained CDPM. By analyzing the geometric properties of CDPM and applying the method used to check the feasibility of a system of inequalities, the algorithm used to check the presence of a given pose in WCW is established. To verify the performance of the proposed WCC, the test has been done in two different CDPMs that are clearly described in the introduction section.

Enhanced Dynamic Capability of Cable-Driven Parallel Manipulators by Reconfiguration

SUMMARYCable-driven parallel manipulators (CDPMs) offer advantages over traditional parallel manipulators. Though their ability to accelerate is higher than the traditional motion platforms, the capabilities are often not used optimally. The issues of cable slackening (especially at higher accelerations) and the emergence of singularity poses have traditional limitations. This paper analyzes and generates manipulator configurations that reduce the effect of these two essential hindrances of deploying CDPMs. A methodology, inspired by rigid body dynamics of multiple contact problems, used to optimize the positions of attachment points, is shown to be effective.

Robust Adaptive Control of Fully Constrained Cable-Driven Serial Manipulator with Multi-Segment Cables Using Cable Tension Sensor Measurements.

The structure of the cable-driven serial manipulator (CDSM) is more complex than that of the cable-driven parallel manipulator (CDPM), resulting in higher model complexity and stronger structural and parametric uncertainties. These drawbacks challenge the stable trajectory-tracking control of a CDSM. To circumvent these drawbacks, this paper proposes a robust adaptive controller for an n-degree-of-freedom (DOF) CDSM actuated by m cables. First, two high-level controllers are designed to track the joint trajectory under two scenarios, namely known and unknown upper bounds of uncertainties. The controllers include an adaptive feedforward term based on inverse dynamics and a robust control term compensating for the uncertainties. Second, the independence of control gains from the upper bound of uncertainties and the inclusion of the joint viscous friction coefficient into the dynamic parameter vector are realised. Then, a low-level controller is designed for the task of tracking the cable tension trajectory. The system stability is analysed using the Lyapunov method. Finally, the validity and effectiveness of the proposed controllers are verified by experimenting with a three-DOF six-cable CDSM. In addition, a comparative experiment with the classical proportional–integral–derivative (PID) controller is carried out.

Applying Deep Reinforcement Learning to Cable Driven Parallel Robots for Balancing Unstable Loads: A Ball Case Study.

The current pandemic has highlighted the need for rapid construction of structures to treat patients and ensure manufacturing of health care products such as vaccines. In order to achieve this, rapid transportation of construction materials from staging area to deposition is needed. In the future, this could be achieved through automated construction sites that make use of robots. Toward this, in this paper a cable driven parallel manipulator (CDPM) is designed and built to balance a highly unstable load, a ball plate system. The system consists of eight cables attached to the end effector plate that can be extended or retracted to actuate movement of the plate. The hardware for the system was designed and built utilizing modern manufacturing processes. A camera system was designed using image recognition to identify the ball pose on the plate. The hardware was used to inform the development of a control system consisting of a reinforcement-learning trained neural network controller that outputs the desired platform response. A nested PID controller for each motor attached to each cable was used to realize the desired response. For the neural network controller, three different model structures were compared to assess the impact of varying model complexity. It was seen that less complex structures resulted in a slower response that was less flexible and more complex structures output a high frequency oscillation of the actuation signal resulting in an unresponsive system. It was concluded that the system showed promise for future development with the potential to improve on the state of the art.

Geometrically exact three-dimensional modeling of cable-driven parallel manipulators for end-effector positioning

Geometrically exact three-dimensional modeling of cable-driven parallel manipulators for end-effector positioning

Geometrically exact three-dimensional modeling of cable-driven parallel manipulators for end-effector positioning

A geometrically exact analytical model of cable-driven parallel manipulators operating in a three-dimensional space is formulated and discussed in this work. The model aims at investigating the exact positioning of a rigid body in a Cartesian space by a m-cables-driven parallel manipulator taking into account the cables mass, their elasticity and, consequently, the sag effect. The direct kinematic problem is formulated by means of 3(m+1) nonlinear equations expressing compatibility and equilibrium in the same number of unknowns, namely, 3m components of the constraint reactions and 3 finite rotations. A novel approach to the solution of the inverse kinematic problem is formulated by adding a set of m target equations to obtain 4m+3 nonlinear algebraic equations solved in terms of an equal number of unknowns. The latter are defined by the 3(m+1) increments of the variables of the direct problem and m additional unknowns, i.e., the increments of the cable unstretched lengths. The elastostatic problem of point mass end-effector is then derived. Consequently, the direct and the inverse kinematic problems are formulated by means of 3m and 4m nonlinear equations, respectively, in the equal number of unknowns. Examples with an increasing number of cables are considered, showing that, although solving the inverse kinematic problem may imply very slack cables configurations, the proposed approach allows to find a solution.

Empirical Quasi-Static and Inverse Kinematics of Cable-Driven Parallel Manipulators Including Presence of Sagging

Cable-driven parallel manipulators (CDPMs) have been of great interest to researchers in recent years because they have many advantages compared to the traditional parallel robot. However, in many studies they lack the cable’s elasticity that leads to flexible cables just being considered as extendable rigid links. Furthermore, an external force acts on the extremities of cable and the self-weight is relevant to the length of it. Experimentally, a small change in length produces a huge change in tension act on the entire cable. By this property, the adjusting length of cable is often added to the traditional inverse kinematic solution in order to reduce the tension force exerted on the cable. This means that the load on the actuator is also reduced. Because of the relationship between tension that acts on the cable and its length, the kinematic problem itself does not make sense without concerning the static or dynamic problems. There is often interest in planning forces for actuators and the length of cables based on a given quasi-static trajectory of the moving platform. The mentioned problem is combined with the quasi-static problem with the inverse kinematic problem of CDPM. In this study, we introduce a novel procedure to produce the quasi-static model and inverse kinematic model for CDPM with the presence of sagging by using both an analytic approach and empirical approach. The produced model is time-efficient and is generalized for spatial CDPM. To illustrate the performance of the proposed model, the numerical and experimental approaches are employed to determine particular solutions in the feasible solutions set produced by our model in order to control the two redundant actuators’ CDPM tracking on a certain desired trajectory. Its results are clearly described in the experimental section.

Haptic Intracorporeal Palpation Using a Cable-Driven Parallel Robot: A User Study.

Intraoperative palpation is a surgical gesture jeopardized by the lack of haptic feedback which affects robotic minimally invasive surgery. Restoring the force reflection in teleoperated systems may improve both surgeons' performance and procedures' outcome. A force-based sensing approach was developed, based on a cable-driven parallel manipulator with anticipated seamless and low-cost integration capabilities in teleoperated robotic surgery. No force sensor on the end-effector is used, but tissue probing forces are estimated from measured cable tensions. A user study involving surgical trainees (n = 22) was conducted to experimentally evaluate the platform in two palpation-based test-cases on silicone phantoms. Two modalities were compared: visual feedback alone and both visual + haptic feedbacks available at the master site. Surgical trainees' preference for the modality providing both visual and haptic feedback is corroborated by both quantitative and qualitative metrics. Hard nodules detection sensitivity improves (94.35 ± 9.1% vs 76.09 ± 19.15% for visual feedback alone), while also exerting smaller forces (4.13 ± 1.02 N vs 4.82 ± 0.81N for visual feedback alone) on the phantom tissues. At the same time, the subjective perceived workload decreases. Tissue-probe contact forces are estimated in a low cost and unique way, without the need of force sensors on the end-effector. Haptics demonstrated an improvement in the tumor detection rate, a reduction of the probing forces, and a decrease in the perceived workload for the trainees. Relevant benefits are demonstrated from the usage of combined cable-driven parallel manipulators and haptics during robotic minimally invasive procedures. The translation of robotic intraoperative palpation to clinical practice could improve the detection and dissection of cancer nodules.

A Vision-Based Referencing Procedure for Cable-Driven Parallel Manipulators

Abstract In the last three decades, cable-driven parallel robots (CDPRs) have captured a growing attention in the robotics field. Indeed, they promise to bring automation in fields where it is not affirmed yet, granting ease of scaling and reconfigurability. For large-workspace cable robots, accuracy is an important issue. In this paper, a look-and-move procedure is proposed, based on a wireless camera, to refer the coordinate frame of the CDPR platform to another known coordinate frame. Two sample cases are studied and presented. In the first, the proposed vision-based system is employed to let the platform precisely attain its home position. In the second, the platform is referenced to an external coordinate frame, in order to accurately accomplish an assigned task. For both cases, experiments are successfully carried out.