Suspended Cable-driven Parallel Robots Research Articles

Experimental study on controlling suspended cable-driven parallel robots for autonomous video-capturing of football games and obtaining the statistics of the games

Experimental study on controlling suspended cable-driven parallel robots for autonomous video-capturing of football games and obtaining the statistics of the games

Design of a 3-Degrees-of-Freedom Cable-Driven Parallel Robot for Automated Construction Based on Workspace and Kinematic Sensitivity

AbstractIn recent years, there has been an increased interest in automating construction tasks to produce more affordable houses at an increased production rate. With this in mind, this article explores the design of a suspended cable-driven parallel robot (CDPR) used as an automated platform for in situ construction. The selected robot topology arranges pairs of cables in parallel to connect the frame and mobile platform. This forms a series of parallelograms that restrict the mobile platform to a pure translational motion so long as the cables are maintained in tension. Contrary to previous works, the CDPR is parameterized to allow more freedom in the definition of the orientation of the parallelograms. The CDPR is designed based on workspace and kinematic sensitivity requirements, while avoiding singularities and mechanical interferences throughout the robot’s desired workspace. The result is an optimal CDPR based on the targeted 3D printing and pick-and-place tasks. It is shown that the parallelogram’s orientation can be selected to improve the robot’s kinematic sensitivity.

Simulation of suspended cable-driven parallel robot on SimulationX

Currently, research is being carried out on a new type of parallel robots, such as cable-driven parallel robot. The cable-driven parallel robot are parallel robots with flexible (cables), with a large workspace, with high speeds and accelerations of the end effector. In the cable-driven parallel robot, cables can only work in tension, and cable-driven parallel robot lose their performance when they are compressed. This feature severely limits the development and application of cable-driven parallel robots and requires further development of cable-driven parallel robot modeling on various software systems. Currently, Adams multibody dynamics software is widely used to create and test virtual prototypes of mechanical systems. But for cable-driven parallel robot modeling, the Adams program is quite complex and expensive to use. In this article, the simulation of the cable-driven parallel robot is carried out on the SimulationX software. Unlike other software packages, SimulationX is more accessible and cheaper and is well suited for cable-driven parallel robot simulation. Cable-driven parallel robot modeling on SimulationX allows you to identify the main design flaws even before its prototype is made. A model on the SimulationX software of a suspended cable-driven parallel robot with a point mass end effector, taking into account the elastic-dissipative properties of cables, was developed. The prototype of suspended cable-driven parallel robot with a point mass end effector was manufactured. Experimental researches of the prototype of the suspended cable-driven parallel robot with a point mass end effector confirmed the correctness of the application of the model on SimulationX for practical calculations.

A Suspended Cable-Driven Parallel Robot With Articulated Reconfigurable Moving Platform for Schönflies Motions

Cable-driven parallel robots (CDPRs) can provide large translational workspace with high payload, but their rotational capability is generally limited due to the inherent design. Additionally, among the existing topology structures of CDPRs, few lower mobility CDPRs with subspatial motions are reported till now. Aiming to narrow the abovementioned research gaps, this article presents a novel suspended CDPR with an articulated reconfigurable moving platform to generate Schönflies motions and enhance the rotational capability. The proposed robot uses four pairs of parallel cables to constrain the redundant motions. The moving platform consists of one end-effector gripper and two subplatforms, which are articulated through revolute joints. A gearbox is embedded in the moving platform to amplify the rotational motion about the vertical axis. For the proposed robot, the kinematic and static modeling is given in detail. The multiobjective optimal design is conducted to determine the dimensional parameters. The reconfiguration of the moving platform is formulated as an optimization problem and demonstrated through a case study. The interference-free static workspace is determined through a numerical approach. A prototype of the proposed robot is fabricated, and experimental tests are performed to evaluate the feasibility of the proposed robot.

Human-cable collision detection with a cable-driven parallel robot

This paper deals with human-cable collision detection with a Cable-Driven Parallel Robot (CDPR) and a control strategy to safely release the tension in the cable in contact with a human operator. The main purpose of this work is to contribute to the development of safety solutions allowing collaborative work between human and robot with CDPRs in production tasks. Using a geometric model of cable deformations under an external collision, a direct relationship is established between the initial cable tension, the collision force and the increase in cable tension. This relationship is validated experimentally with an ad-hoc test bench. Collision force levels are set to admissible values in order to prevent harm for human operators. A collision detection is then implemented on the 8-cable suspended CDPR CRAFT prototype using this method, continuously comparing the cable tensions measured by sensors with admissible cable tension increases. Using these results, an approach aiming at releasing a collided cable so as to minimize risks for operators and the environment of the robot is proposed with an adaptive control scheme, based on a progressive cable tension management once a collision is detected. This cable tension management is simulated and represented in the null space of CDPR wrench matrix. Feasibility domain of this tension management and alternative solutions outside of it are also discussed. This work contributes to the safety of collaborative CDPRs by determining a direct relationship between collision force and cable tensions in the event of a collision and by introducing a collision detection method.

Kinematic and Dynamic Modeling and Workspace Analysis of a Suspended Cable-Driven Parallel Robot for Schönflies Motions

In recent years, cable-driven parallel robots (CDPRs) have drawn more and more attention due to the properties of large workspace, large payload capacity, and ease of reconfiguration. In this paper, we present a kinematic and dynamic modeling and workspace analysis for a novel suspended CDPR which generates Schönflies motions. Firstly, the architecture of the robot is introduced, and the inverse and forward kinematic problems of the robot are solved through a geometrical approach. Then, the dynamic equation of the robot is derived by separately considering the moving platform and the drive trains. Based on the dynamic equation, the dynamic feasible workspace of the robot is determined under different values of accelerations. Finally, experiments are performed on a prototype of the robot to demonstrate the correctness of the derived models and workspace.

Forward Kinematics for Suspended Under-Actuated Cable-Driven Parallel Robots With Elastic Cables: A Neural Network Approach

Abstract Kinematic analysis of under-constrained cable-driven parallel robots (CDPR) has been a topic of interest because of the inherent coupling between the loop-closure and static equilibrium equations. The non-linearity of the problem is magnified with the addition of the coupling between the cable lengths and their tensions based on the elastic cable model. The paper proposes an unsupervised neural network algorithm to perform real-time forward geometrico-static analysis of such robots in a suspended configuration under the action of gravity. The formulation determines a non-linear function approximation to model the problem and proves to be efficient in solving consecutive and close waypoints in a path. The methodology is applied on a six-degree-of-freedom spatial under-constrained suspended CDPR. Specific comparison results in simulation and hardware to show the effectiveness of the proposed method in tracking a given path are illustrated. Finally, the degree of constraint satisfaction is presented against the results obtained from non-linear least-square optimization.

Experimental study on the control of a suspended cable-driven parallel robot for object tracking purpose

AbstractIn this paper, control of a suspended cable-driven parallel robot has been experimentally investigated based on the dynamic model of the robot for object tracking purpose. In order to improve the tracking ability of the robot, three control approaches, namely kinematic PID, dynamic PD, and a kinematic sliding mode control (SMC), have been implemented, both on the Simscape and on the robot constructed at the Human and Robot Interaction Laboratory. Neural network controller and dynamic SMC have been implemented on the Simscape model. Afterward, the effectiveness of each approach has been investigated by employing the root mean square error (RMSE) index. Simulation and experimental results reveal the ability of each controller for precise and smooth control. For precise and real-time object tracking, YOLOv5-s and YOLOv4-tiny model are trained. By comparing the obtained index values, the kinematic PID demonstrates the best performance with the maximum RMSE value of 0.018 compared to other methods.

Control Strategies for a Cable-Driven Parallel Robot with Varying Payload Information

A suspended Cable-Driven Parallel Robot (CDPR) composed of eight cables and a moving platform (MP) is used in a pick-and-place application of metal plates with different shapes, sizes and masses. In order to ensure robust control despite mass variation, several combinations of control schemes and control laws have been experimented on a prototype at IRT Jules Verne, France. The main objective of this paper is to provide recommendations on the selection of a control strategy depending on the available information on the carried mass, and the presence or absence of force sensors. Three scenarios are considered representing a degradation of the information on the carried mass to observe the impact on the performance of applicable control strategies. In a first case, force sensors are assumed available to measure cable tension, allowing the real-time estimation of the carried mass. In a second case, the mass of the MP is known, but not the mass of the carried metal plate whereas the third case considers no information at all on both the MP and the carried metal plate. The tested control laws include a standard proportional–derivative controller (PD), and a recently developed nonlinear controller balancing between sliding mode and linear algorithms (SML). The performances of each control strategy are analyzed along a test trajectory for several payloads, and a decision tree is proposed.

Analysis of Reachable Workspace for Spatial Three-Cable Under-Constrained Suspended Cable-Driven Parallel Robots

Abstract The workspace is an important reference for designs of cable-driven parallel robots (CDPRs). Most current researches focus on calculating the workspace of redundant CDPRs. However, few literature study the workspaces of under-constrained CDPRs. In this paper, the static equilibrium reachable workspaces (SERWs) of spatial 3-cable under-constrained CDPRs are solved numerically since expressions describing workspace boundaries cannot be obtained in closed forms. The steps to solve the SERWs are as follows. First, expressions that describe the SERWs and their boundaries are proposed. Next, these expressions are instantiated through a novel anchor points model composed of linear equations, quadratic equations, and tension limits in cables. Then, based on the reformulated linearization technique (RLT), the constraints system is transformed into a system containing only linear equality constraints and linear inequality constraints. Finally, the framework of the branch-and-prune (BP) algorithm is adopted to solve this system. The effect of the algorithm is verified by two examples. One is searching the SERWs boundaries of a special three-cable-driven parallel robot (CDPR) whose anchor points layouts both on the moving platform (MP) and on the base are equilateral triangles, followed by a method to extract the SERW boundary where cables do not interfere with each other. The other is searching the SERWs boundaries of a general three-cable CDPR with randomly selected geometry arrangement. The presented method in this paper is universal for calculating the SERWs of spatial three-cable CDPRs with arbitrary geometry parameters.

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.

A Cable-Driven Parallel Robot With An Embedded Tilt-Roll Wrist

Abstract This paper addresses the optimum design, configuration, and workspace analysis of a cable-driven parallel robot (CDPR) with an embedded tilt-roll wrist. The manipulator consists in a tilt-roll wrist mounted on the moving platform of a suspended CDPR. The embedded wrist provides large amplitudes of tilt and roll rotations and a large translational workspace obtained by the CDPR. This manipulator is suitable for tasks requiring large rotation and translation workspaces such as tomography scanning, camera-orienting devices, and visual surveillance. The moving-platform is an eight-degree-of-freedom articulated mechanism with large translational and rotational workspaces, and it is suspended from a fixed frame by six cables. The manipulator employs two bi-actuated cables, i.e., cable-loops to transmit the power from motors fixed on the ground to the tilt-roll wrist. Therefore, the manipulator achieves better dynamic performances due to a lower inertia of its moving-platform.

A new control scheme of cable-driven parallel robot balancing between sliding mode and linear feedback

Abstract This paper deals with the design of a robust control scheme for a suspended Cable-Driven Parallel Robot (CDPR), composed of eight cables and a moving-platform (MP), for a pick-and-place application of metal plates of various shapes, sizes and masses. The set composed of the MP and a metal plate can have a mass of up to 700 kg. In order to achieve good accuracy and repeatability of the MP pose despite the variability of the transported mass, a robust control scheme must be implemented on the robot. A recently developed controller balancing between sliding mode and linear algorithms (SML) is considered for the application. The performances of the SML controller are analyzed on a CDPR prototype located at IRT Jules Verne, Nantes, France, along a test trajectory for several payloads. The results obtained without any information on the platform or metal plate mass are compared to those of standard proportional-derivative (PD) based control schemes.

Dynamic and Oscillatory Motions of Cable-Driven Parallel Robots Based on a Nonlinear Cable Tension Model

In this paper, dynamic modeling of cable-driven parallel robots (CDPRs) is addressed where each cable length is subjected to variations during operation. It is focusing on an original formulation of cable tension, which reveals a softening behavior when strains become large. The dynamic modulus of cable elasticity is experimentally identified through dynamic mechanical analysis (DMA). Numerical investigations carried out on suspended CDPRs with different sizes show the effect of the proposed tension formulation on the dynamic response of the end-effector.

Trajectory planning of a suspended cable driven parallel robot with reconfigurable end effector

Abstract In this paper, a new suspended cable driven parallel robot (CDPR) with reconfigurable end effector is presented. This robot has been conceived for pick and place operations in industrial environments. For such applications, the possibility to change the configuration of the cables at the end-effector level is a promising way to avoid collisions with obstacles in the approaching phases, while reducing at the same time the duration of motion in the remaining part of the trajectory. An optimized trajectory planning algorithm is proposed, which implements a pick and place operation in the operational space with dynamic on-line reconfiguration of the end effector. The results on a simplified scenario demonstrate the ability of the system to obtain reduced movement times together with obstacle avoidance.

Workspace optimization for a planar cable-suspended direct-driven robot

Abstract The present work is inspired by an industrial task, i.e. spray painting a large area by means of a robotic system consisting in a Cable-Driven Parallel Robot (CDPR). In many cases, the area of the robot workspace is smaller than the area to be painted. For this reason, the base of the robot has to be shifted several times during the painting process. These robots are referred to as Repetitive Workspace Robots (RWR). In other words, in order to accomplish the whole task, they need to be moved after they have completed a sub-task locally. A cable suspended CDPR is an ideal candidate for such tasks; it can be thin, light, flexible and cost-efficient. The question is: which is the best shape of the local workspace in these conditions? In fact, not always a larger area of the local workspace guarantees an efficient painting process. This is because the efficiency relies mainly on the shape rather than on the local workspace area itself. In this work we employ an index [Seriani S, Gallina P, Gasparetto A, 2014] to evaluate the efficiency of the workspace of a 2-link CDPR. Finally, we show how the index value changes in relation to some geometrical parameters of the robot, thus laying the foundations for a general design methodology.