Planar Cable-driven Parallel Robot Research Articles

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.

Available wrench set robustness under hybrid joint-space control to uncertain wrench for a cable-driven parallel robot

For a overconstrained cable-driven parallel robot (CDPR), the number of cables is more than the number of the moving platform degrees of freedom. Therefore, a hybrid joint-space control method is used, where as many cables as the moving platform degrees of freedom are kinematically controlled, and the redundant ones are tension controlled. However, the selection of which cables to tension control is not straightforward. This work aims at evaluating the maximum value of the resistance to the wrench deviation, while tension-controlling a chosen cable set, by computing a performance index called available wrench set robustness (AWSR). In this case, the wrench deviation refers to the difference between the actual wrench and the nominal model wrench, which is related to the wrench uncertainties influenced by elements such as varying mass, shifted centre of mass and environmental disturbances. Firstly, owing to the inhomogeneous wrench deviation, a normalization method was proposed. Based on this, geometrically, the AWSR is defined as the minimum distance from the nominal wrench to the hyperplane boundary of available wrench set. As an application example of a planar CDPR with four cables and a spatial CDPR with eight cables, a comparison with previous methods illustrated that the proposed method significantly increased the range of wrench deviation, and this avoids situations where the configuration is not feasible using the traditional method. Therefore, the proposed method is more suitable for uncertain wrenches.

An approach for predicting the calibration accuracy in planar cable-driven parallel robots and experiment validation

An approach for predicting the calibration accuracy in planar cable-driven parallel robots and experiment validation

Mechatronic design of a class of planar cable-driven parallel robots

Mechatronic design of a class of planar cable-driven parallel robots

On Research of Cable Tension Distribution Algorithm for Four Cables - Three DOF Planar Cable-Driven Parallel Robot

One of the main concerns in controlling the cable-driven parallel robot (CDPR) mechanism is dealing with the distribution of tension on each cable, which is critical to the operation of the entire cable system. It can be said that adjusting the cable tension will determine the power consumption of the motors and the stiffness of the structure. Therefore, the problem that needs to be solved is how to handle the cable tension when the end-effector moves throughout the entire workspace. The tension of each cable needs to be adjusted properly to ensure it remains the same. Moment and force act in a static state, keeping the kinematic position of the end moving platform from being deflected and the main purpose is to ensure that the robot achieves a rigid state and eliminates vibration when moving. Because of that essential demand, this article will refer to the Quadratic programming algorithm to solve the problem of tension distribution for the Planar Cable-Driven Parallel Robot consisting of 4 cables with 3 degrees of freedom. This article will be the foundation for applying this algorithm to an 8-cable robot with 6 degrees of freedom (Spatial Cable-Driven Parallel Robot for example). At the same time, in this article, the simulation results for the algorithm will also be presented in this paper.

Data-Driven Dynamics Modeling and Control Strategy for a Planar n-DOF Cable-Driven Parallel Robot Driven by n + 1 Cables Allowing Collisions

Abstract Scholars have proposed to allow collisions of cables with the base, the end-effector, or obstacles to expand the workspace of cable-driven parallel robots (CDPRs) in recent years. However, allowing collisions also leads to new challenges in kinematics and dynamics modeling for CDPRs. To this end, this article focuses on a planar fully constrained n-degree-of-freedom (DOF) CDPR driven by n + 1 cables allowing collisions and develops a data-driven dynamics modeling strategy. The data-driven dynamics modeling strategy can address the collisions and optimal tension distribution issues simultaneously. Based on the data-driven dynamics modeling strategy, this article proposes a data-driven dynamics-based control strategy for the planar CDPR allowing collisions. A planar two-DOF CDPR prototype driven by three cables is established to evaluate the data-driven dynamics modeling strategy and data-driven dynamics-based control strategy.

Position Control of a Fully Constrained Planar Cable-Driven Parallel Robot With Unknown or Partially Known Dynamics

In this article, we propose an intelligent proportional-integral-derivative (iPID) controller to control the position of a planar cable-driven parallel robot (CDPR). The proposed control method is based on ultralocal model estimation in short time intervals using only the system input–output behavior. We first employed the reference model-free iPID control, which requires the complete system dynamics estimation for the robot. Then, we modified the controller to utilize the partially known system dynamics represented in the feedback linearized form of the nonlinear model. Only the remaining unmodeled dynamics are estimated with the modified controller. We experimentally investigated the classical model-free intelligent proportional and derivative (iPD) controller and the modified iPD controller performances on the planar CPDR. The results show that significant performance improvement is achieved with the modified iPD controller.

Dynamic Model of a Novel Planar Cable Driven Parallel Robot with a Single Cable Loop

Cable-Driven Parallel Robots (CDPRs) are a special kind of parallel manipulator that uses cables to control the position and orientation of the mobile platform or end effector. The use of cables instead of rigid links offers some advantages over their conventional rigid counterparts. As cables can only pull but not push, the number of cables (n) required to command the end-effector is always n+1. This configuration is known as fully-constrained, and it is the most extended configuration for CDPRs. Although CDPRs have many advantages, such as their ability to cover large working areas, one of their main problems is that their working area (workspace) is limited in comparison to its frame area (planar case) or frame volume (spatial case), due to the minimum and maximum allowed tensions. Depending on these tension values, the workspace can notoriously decrease. In order to tackle this problem, lots of works focus on solving kinematics or dynamics problems for cable sagging, i.e., they take into account sagging when modelling the robot kinematic and include these poses inside the usable robot workspace. Taking into account phenomena such as this increases the mathematical complexity of the problem, and much more complex techniques are required. On the other hand, the lack of workspace problem can be tackled by adding active or passive elements to the robot design. In this sense, this paper proposes two mechanical modifications: to add passive carriages to the robot frame and to use a single cable loop to command the end-effector position and orientation. This work presents the kinematic, static, and dynamic models of the novel design and shows the gain of workspace for a planar case while taking into account different parameters of the robot.

Impact of Tuned Mass Dampers and Electromagnetic Tuned Mass Dampers on Geometrically Nonlinear Vibrations Reduction of Planar Cable Robots

Vibration is one of the problems that limits the applications of cable driven parallel robots (CDPR). The problem is bigger in CDPR with planar configuration due to the presence of out-of-plane vibrations, which have a larger amplitude and settling time. Some authors have proposed solutions such as the increase in tension of the wires, increase in the end effector mass, or the use of active dampers. In this research, we investigated the performance of tuned mass dampers (TMD) and electromagnetic tuned mass dampers (ETMD) which are integrated in the end effector of a CDPR in a planar configuration with eight wires. The essential idea is to reduce the settling time of the end effector through free vibrations without the use of external energy. This research followed an analytical and experimental methodology with the following steps. Three mathematical models were formulated and analysed using numerical simulations. Then, a test bench to validate the analytical results was designed and built. The effectiveness of the dampers was evaluated by comparing the settling times of the following three cases: without damper, with TMD, and with ETMD. During the investigation, it was observed that the use of AMS can reduce the settling time using the appropriate parameters. The effectiveness of AEMS is highly dependent on frictions and can be effective in some scenarios. Reductions in settling time from marginal values to 95% can be obtained. This research implies a viable solution for the out-of-plane vibrations of planar CDPR.

Dynamic Control of a Novel Planar Cable-Driven Parallel Robot with a Large Wrench Feasible Workspace

Cable-Driven Parallel Robots (CDPRs) are special manipulators where rigid links are replaced with cables. The use of cables offers several advantages over the conventional rigid manipulators, one of the most interesting being their ability to cover large workspaces since cables are easily winded. However, this workspace coverage has its limitations due to the maximum permissible cable tensions, i.e., tension limitations cause a decrease in the Wrench Feasible Workspace (WFW) of these robots. To solve this issue, a novel design based in the addition of passive carriages to the robot frame of three degrees-of-freedom (3DOF) fully-constrained CDPRs is used. The novelty of the design allows reducing the variation in the cable directions and forces increasing the robot WFW; nevertheless, it presents a low stiffness along the x direction. This paper presents the dynamic model of the novel proposal together with a new dynamic control technique, which rejects the vibrations caused by the stiffness loss while ensuring an accurate trajectory tracking. The simulation results show that the controlled system presents a larger WFW than the conventional scheme of the CDPR, maintaining a good performance in the trajectory tracking of the end-effector. The novel proposal presented here can be applied in multiple planar applications.

A novel design for fully constrained planar Cable-Driven Parallel Robots to increase their wrench-feasible workspace

Cable-Driven Parallel Robots (CDPRs) are a special kind of parallel manipulators that offer several advantages compared to the conventional rigid parallel robots. One of the most interesting advantages is their ability to cover large working areas since long cables can be easily coiled. The practical limitation on the permissible cable tensions, however, causes a considerable decrease in the size of the wrench-feasible workspace (WFW) of these robots. To solve this problem in the case of fully-constrained planar CDPR with 3 degrees-of-freedom, this work proposes a novel design, based on the addition of passive carriages to the robot frame. It allows to significantly reduce the variation in the cables direction and therefore in the cable forces, resulting in a notable increase in the size of the WFW. This work presents the kinematic and static models of the new robot and proposes a preliminary approach for the resolution of the static equilibrium. The WFW of the new robot is investigated in different situations and compared to that of a conventional planar CDPR, showing a significant improvement in every case studied.

Offset-free nonlinear model predictive control for improving dynamics of cable-driven parallel robots with on-board thrusters

In this article, thrusters embedded on a cable-driven parallel robot (CDPR) platform are proposed to improve the CDPR dynamics and trajectory tracking performance. On-board thrusters with their short response time can compensate for the reduced bandwidth of the winch actuation due to winding speed limit and low cable stiffness. To compute and allocate control signals to winches and thrusters, a nonlinear model predictive controller (NMPC) is designed. A model of a CDPR with its hybrid actuation dynamics and saturation is introduced, including an alternative model of the thrust actuation that removes the need of thrust sensors and reduces the size of the NMPC optimization problem. To achieve a zero steady-state error with the NMPC, which becomes offset-free, an augmented model including additional disturbance states is proposed. The theoretical conditions to achieve offset-free control are checked. The proposed NMPC scheme is validated experimentally on a planar CDPR with three cables and four propeller-based thrusters. Results show that onboard thrusters contribute to a tracking error reduction along complex trajectories and an efficient damping of the platform vibration.

Inverse and Forward Kineto-Static Solution of a Large-Scale Cable-Driven Parallel Robot using Neural Networks

This kineto-static problem of cable-driven parallel robot (CDPR) considering cable mass and elasticity is a highly non-linear and computationally complex problem. Numerical methods are conventionally employed to solve this problem. However, numerical methods are highly dependent on initial values, iterative in nature, computationally unbounded, and have slow convergence speed, making them unreliable for real-time scenarios. Therefore, this paper proposes a neural network-based approach to obtain the inverse kineto-static (IKS) as well as the forward kineto-static (FKS) solution of CDPR with significant cable mass and elasticity. The simulation results are presented for two cases, i.e., for a redundantly constrained planar CDPR (RP-CDPR) and a minimally constrained spatial CDPR (MS-CDPR). The training time, dataset requirement and testing error is observed to be significantly lower for MS-CDPR in comparison to RP-CDPR. For both the cases, the proposed approach shows a significant improvement in the computational speed when compared to numerical methods for both IKS and FKS problem. Owing to the advantage of bounded and low computational time, the proposed neural network-based approach is recommended for use in real-time applications.

Out-of-Plane Vibration Suppression and Position Control of a Planar Cable-Driven Robot

Cable-driven parallel robots (CDPRs) are more convenient to use in large-scale applications than rigid-link robots due to the advantages such as simple structure, high load capacity, and low inertia of cables. However, using cables to drive an end-effector comes with the low equivalent stiffness issue in out-of-plane direction for the CDPRs’ planar configuration, which causes long-lasting and high amplitude out-of-plane vibrations under an external disturbance. This article presents a novel method to suppress the out-of-plane vibrations without distorting in-plane positioning control simultaneously for planar CDPRs. The proposed method provides the ease of using only the cable tensioning forces instead of an additional actuator to control the out-of-plane vibrations by decoupling the in-plane and out-of-plane dynamics. The switching stiffness control method is used for out-of-plane vibration control, while a classical control method is used for in-plane dynamics control. These two control inputs are then coupled by a bias torque variation in a torque distribution algorithm. The effectiveness of the proposed method is presented both in simulations and experimental results. The experiments are performed for the specified in-plane positions and an in-plane trajectory tracking study when the planar CDPR is excited to out-of-plane vibration in the normal direction. The out-of-plane vibration suppression time is considerably reduced compared to the free-vibration case, and any distortion on the in-plane positioning control is not observed.

Position control of a planar cable-driven parallel robot using reinforcement learning

AbstractThis study proposes a method based on reinforcement learning (RL) for point-to-point and dynamic reference position tracking control of a planar cable-driven parallel robots, which is a multi-input multi-output system (MIMO). The method eliminates the use of a tension distribution algorithm in controlling the system’s dynamics and inherently optimizes the cable tensions based on the reward function during the learning process. The deep deterministic policy gradient algorithm is utilized for training the RL agents in point-to-point and dynamic reference tracking tasks. The performances of the two agents are tested on their specifically trained tasks. Moreover, we also implement the agent trained for point-to-point tasks on the dynamic reference tracking and vice versa. The performances of the RL agents are compared with a classical PD controller. The results show that RL can perform quite well without the requirement of designing different controllers for each task if the system’s dynamics is learned well.

Design and analysis of a class of planar cable-driven parallel robots with arbitrary rotation

This paper presents and analyzes a novel class of planar cable-driven parallel robots. The design allows an arbitrary rotation of the end-effector by wrapping the cables on a cylindrical fixture on the end-effector platform. In contrast to the state of the art, this results in a simple and robust design without additional moving parts attached to the end effector. Based on Burnside's lemma known from group theory, the set of all possible design configurations for a fixed number of cables is derived. Moreover, the workspace is analyzed by means of the classical manipulability measure known from the literature. In order to also capture the minimum tension in the cables and the directional dependence of the achievable forces, which are determining factors for the workspace, a new force manipulability measure is introduced. This yields results which are related to the well-known wrench-feasible workspace. The proposed concepts are demonstrated by two different designs for planar cable-driven parallel robots with 4 and 6 cables.

Design of a Planar Cable-Driven Parallel Robot for Non-Contact Tasks

Cable-driven parallel robots offer significant advantages in terms of workspace dimensions and payload capability. Their mechanical structure and transmission system consist of light and extendable cables that can withstand high tensile loads. Cables are wound and unwound by a set of motorized winches, so that the robot workspace dimensions mainly depend on the amount of cable that each drum can store. For this reason, these manipulators are attractive for many industrial tasks to be performed on a large scale, such as handling, pick-and-place, and manufacturing, without a substantial increase in costs and mechanical complexity with respect to a small-scale application. This paper presents the design of a planar overconstrained cable-driven parallel robot for quasi-static non-contact operations on planar vertical surfaces, such as laser engraving, inspection and thermal treatment. The overall mechanical structure of the robot is shown, by focusing on the actuation and guidance systems. A novel concept of the cable guidance system is outlined, which allows for a simple kinematic model to control the manipulator. As an application example, a laser diode is mounted onto the end-effector of a prototype to perform laser engraving on a paper sheet. Observations on the experiments are reported and discussed.

A Simulation Study of a Planar Cable-Driven Parallel Robot to Transport Supplies for Patients with Contagious Diseases in Health Care Centers

Currently, a large number of investigations are being carried out in the area of robotics focused on proposing solutions in the field of health, and many of them have directed their efforts on issues related to the health emergency due to COVID-19. Considering that one of the ways to reduce the risk of contagion is by avoiding contact and closeness between people when exchanging supplies such as food, medicine, clothing, etc., this work proposes the use of a planar cable-driven parallel robot for the transport of supplies in hospitals whose room distribution has planar architecture. The robot acts in accordance with a procedure proposed for each task to be carried out, which includes the process of disinfection (based on Ultraviolet-C light) of the supplies transported inside the robot’s end effector. The study presents a design proposal for the geometry of the planar cable-driven parallel robots and its end effector, as well as the software simulations that allow evaluating the robot’s movement trajectories and the responses of the position control system based on Fuzzy-PID controllers.

Development of a planar cable parallel robot for practical application in the educational process

Cable-driven parallel robot (CDPR) has the great potential for various applications in industry and in everyday life. They consist of an end effector and a base, which connected by several cables. CDPRs have a large workspace compared to the workspace of classic parallel robots. CDPR have a simpler structure have good dynamic properties, high carrying capacity, mobility and low cost. The only drawback is that the CDPR cables can only work for retraction and cannot push. This article presents the design of a prototype of a planar CDPR with four cables for practical use in the educational process. This prototype of a planar CDPR is necessary for a better understanding of the design features, structure, kinematics, statics and dynamics of the CDPR by students. The planar CDPR performs two translational motions, due to the controlled 4 cables, and one rotational motion of the end effector. The research of the kinematics and statics of the planar cable-driven parallel robot is carried out. Simulation of the motion of a planar cable-driven parallel robot in the Python programming language has been carried out. A design was developed and a prototype of the planar cable-driven parallel robot was manufactured. Experimental researches of a prototype of the planar cable-driven parallel robot have been carried out. The results of experimental researches have shown that the CDPR works well enough. During the tests of the prototype of the planar cable-driven parallel robot, it was found that the distortions of the trajectory of the end effector depend on the tension of the cables. It is necessary to monitor the tension level using strain gauges. Based on the analysis of the results obtained, the effectiveness of the use of the prototype of a planar CDPR in the educational process of the robotics course has been confirmed

Research on a 3-DOF Planar Cable-Driven Parallel Robot Based on Fuzzy Adaptive PD Computed Torque Control

Cable-driven parallel robots (CDPR) with spatial configuration are widely used while ones with plannar configuration are rarely applied. Therefore, this paper studies the modeling and control characteristics of a three degree-of-freedom cable-driven planar parallel robot with great application prospects. Aiming at the shortcomings of the existing control methods towards CDPR, a new method based on fuzzy adaptive PD computing torque control is proposed which contains a reasonable optimal distribution of cable forces. To validate the method, the tracking control simulation research and analysis are carried out for the trajectory of high-order interpolation planning, the results of which show that the control method has favorable dynamic tracking accuracy and mechanical properties. Moreover, compared with the fixed-gain computed torque control, the proposed control method can overcome the influence of model inaccuracy more effectively.