Air vehicle simulator: an application for a cable array robot

The development of autonomous air vehicles can be an expensive research pursuit. To alleviate some of the financial burden of this process, we have constructed a system consisting of four winches each attached to a central pod (the simulated air vehicle) via cables - a cable-array robot. The system is capable of precisely controlling the three dimensional position of the pod allowing effective testing of sensing and control strategies before experimentation on a free-flying vehicle. In this paper, we present a brief overview of the system and provide a practical control strategy for such a system. ©2005 IEEE

Design and control of a robotic cable-suspended camera system for operation in 3-D industrial environment

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (leaves 52-54).Cable-suspended robots offer many advantages over conventional serial manipulators. The main benefit of cable robots is their large workspace size, which makes them well suited for broadcasting, transporting/loading, and construction applications. Since cables can only pull and not push the end-effector however, designing and controlling cable robots becomes more challenging. This thesis describes the design of a three-cable underconstrained robot which was built and then tested using a velocity feedback loop with a built-in PI controller. The endeffector of the robot consists of a camcorder mounted on a platform. The objective of the robot is to manipulate the camcorder in 3-D space with minimal tracking error. The dynamic equations of the system are derived along with the kinematic relationships and a closed-loop controller is designed. The controller is tested by prescribing a trajectory to the end-effector. Simulink derives the motor velocities given the desired Cartesian positions of the end-effector and simultaneously controls all three motors. The results of the experiment show that the error in the trajectory, which is on the order of about seven centimeters in the x -y plane, is small compared to the size of the robot's workspace. However, depending on the required precision, improvements may have to be made to the robot to reduce error. Future research ideas are presented to expand the scope of the robot.by Vladimir Gordievsky.S.B

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 METHODOLOGY FOR CHOOSING ACTUATORS OF CABLE-SUSPENDED PARALLEL ROBOTS

A novel methodology for choosing actuators of a CPR system was defined. This methodology was based on a novel procedure for analysis and synthesis of the workspace of Cable-suspended parallel robot, CPR system. Besides the kinematic and dynamic models of the CPR system, this procedure includes the complete mathematical model of the actuator as well. On this basis, this procedure presents a novel solution for the analysis and synthesis of CPR system’s workspace. When using the proposed methodology for choosing actuators of a CPR system, user and designer together define the corresponding technical requirements, one of them being the relative size of the feasible work space of the CPR system. Based on these requirements, the developed methodology tests available actuators from its data base and extracts the useful ones for the predefined specific purpose. The purpose of this research is to interconnect theoretical contributions from CPR system’s modelling and needs of the user and designer during their practical implementation. For this purpose, a user friendly program package called PPACM was generated. The program package PPACM and obtained results were validated through the presentation of several case studies

Low Mobility Cable Robot with Application to Robotic Warehousing

Cable-based robots consist of a rigid mobile platform connected via flexible links (cables, wires, tendons) to a surrounding static platform. The use of cables simplifies the mechanical structure and reduces the inertia, allowing the mobile platform to reach high motion acceleration in large workspaces. These attributes give, in principle, an advantage over conventional robots used for industrial applications, such as the pick and place of objects inside factories or similar exterior large workspaces. However, unique cable properties involve new theoretical and technical challenges: all cables must be in tension to avoid collapse of the mobile platform. In addition, positive tensions applied to cables may affect the overall stiffness, that is, cable stretch might result in unacceptable oscillations of the mobile platform. Fully constrained cable-based robots can be distinguished from other types of cable-based robots because the motion and force generation of the mobile platform is accomplished by controlling both the cable lengths and the positive cable tensions. Fully constrained cable-based robots depend on actuator redundancy, that is, the addition of one or more actuated cables than end-effector degrees of freedom. Redundancy has proved to be beneficial to expand the workspace, remove some types of singularities, increase the overall stiffness, and support high payloads in several proposed cable-based robot designs. Nevertheless, this strategy demands the development of efficient controller designs for real-time applications. This research deals with the design and control of a fully constrained cable-based parallel manipulator for large-scale high-speed warehousing applications. To accomplish the design of the robot, a well-ordered procedure to analyze the cable tensions, stiffness and workspace will be presented to obtain an optimum structure. Then, the control problem will be investigated to deal with the redundancy solution and all-positive cable tension condition. The proposed control method will be evaluated through simulation and experimentation in a prototype manufactured for testing

Analysis and Optimization of a New Differentially Driven Cable Parallel Robot

In this paper, a new three degrees of freedom (DOF) differentially actuated cable parallel robot is proposed. This mechanism is driven by a prismatic actuator and three cable differentials. Through this design, the idea of using differentials in the structure of a spatial cable robot is investigated. Considering their particular properties, the kinematic analysis of the robot is presented. Then, two indices are defined to evaluate the workspaces of the robot. Using these indices, the robot is subsequently optimized. Finally, the performance of the optimized differentially driven robot is compared with fully actuated mechanisms. The results show that through a proper design methodology, the robot can have a larger workspace and better performance using differentials than the fully driven cable robots using the same number of actuators

Manipuladores paralelos actuados por cables

En este trabajo se realiza un informa sobre los manipuladores paralelos actuados por cables. Un manipulador paralelo es una cadena cinemática cerrada con una plataforma móvil conectada a una base fija mediante varias cadenas cinemáticas independientes. Si los actuadores que unen la base fija con la plataforma móvil son cables, entonces se denominan manipuladores paralelos actuados por cables. Para su realización se ha recopilado toda la información posible ya sea de internet, de revistas de ingeniería o de libros de la Escuela Técnica Superior de Ingeniería (ETSI) y se ha expuesto con la finalidad de que cualquier persona pueda acudir a este trabajo en busca de información. En él se puede encontrar información acerca de qué es un manipulador paralelo actuado por cables, qué características tiene, qué tipos hay, para qué se usan y cuáles son las ecuaciones que rigen su movimiento.Lan honetan kableen bidez eragindako manipulatzaile paraleloei buruzko txosten bat egiten da. Manipulatzaile paralelo bat: kate- zinematikoa itxita plataforma mugikor batekin base finko bati lotuta aparteko kate-zinematikoa batzuen bidez. Base finkoa plataforma higikorrari lotzen dituzten eragingailuak kableak badira, kableen bidez eragindako manipulatzaile paraleloak deitzen dira. Lana burutzeko interneteko, ingenieritza-aldizkarietako edo ETSIko liburuetako informazioa bilduko da, eta edozeinek informazioa bilduko da, eta edozeinek informazioa bila lan honetara etor dezake manipulatzaile paralelo zer den, zein mota dauden, zertarako erabiltzen diren eta zein ekuazio eraentzen dituen bere mugimendua bilatzeko.This work deals a report about cable driven parallel manipulators. A parallel manipulator is a closed kinematic chain with an end-effector connected to a fixed base by several independent kinematic chains. If the actuators connecting the fixed base to the end- effector are cables, then it is called cable driven parallel manipulators. For its realization, all posible information will be collected, wether from the Internet, engineering journals or books of the High Technical School of Engineering (ETSI), and it will be exposed so that anyone can go to this work searching for information. It contains information about what a cable driven parallel manipulator is, what characteristics it has, what types there are, what they are used for and what are the equations that govern their movement

Two dimensional agonistic control

The conventional method of precise multiple-axis motion control entails use of a multiple axis positioning system with each axis carrying not only the workpiece but also the positioning system of the remaining axes. The resultant structure is heavy, sluggish, and expensive. An alternative positioning technique is being investigated in which the motion of the workpiece is controlled by pulling it with tendons, each of which has its own actuator. Since the actuators can be mounted on the base of the structure instead of being carried by motion system of the other axes, they can be relatively large and powerful without the need for a massive structure such as is found in a conventional motion control system. This method of control is given the appellation agonistic, based on the usages of the word suggesting tension or a contest. Agonistic control system can be used for low cost accurate positioning of workpiece. The control task can be moving the workpiece from one point to another point and kept there or tracking a given trajectory. While the workpiece moves, the tendons should be always kept in tension. In this thesis, the model of two dimensional agonistic control (in the case of tendons of infinite elastic modulus) is established. It leads to a nonlinear multi-variable control problem. Based on this nonlinear model, a full-state feedback control law is synthesized. It is composed of two parts. The first part is a feedforward control to cancel the nonlinear dynamics. The second part is a PD control term which requires velocity information. In the practice, velocity measurement may be contaminated by noise. In order of only using position measurement in the control law, a nonlinear observer is designed to provide the velocity information. Numerical simulation is performed to verify the ability of the proposed control law. In reality, the tendon has some elasticity. This finite elasticity, if not accounted for, can render the closed-loop system unstable. The investigation shows that the effect of elastic tendons can be compensated for by appropriately modifying the control law designed for inelastic tendons. In particular, the control law is synthesized using the singular perturbation method. It consists of a fast control and a slow control. The fast control is used to stablize the oscillations incurred by the finite elasticity of the tendon. The slow control drives the system to track the desired trajectory. Robustness of the controller is enhanced by using sliding mode control. In the chapter 4, the design of observer in the elastic case is addressed. Linear uncertain system theory is used. The observer is globally stable. The use of decentralized control scheme makes very simple the controller design and reduces the computational complexity. It is very useful for real time agonistic control. A design approach is presented for the decentralized control scheme. A simple linear second order model is used instead of complex nonlinear model used in centralized version. In this approach, the tension in each tendon is treated as disturbance, estimated by an observer, to be compensated