Cable-based Parallel Manipulator Research Articles

Failure Analysis of Cable Based Parallel Manipulators

In this study, the effect of a cable failure on the performance of the manipulator is investigated. The post failure trajectory and cable tensions after failure are analysed and ship position optimization is conducted in order to minimize the cable tensions after failure. The optimization is demonstrated with six, eight and ten ships in a cable based parallel manipulator (CPM). The performance of the system after failure is improved with higher number of cables in a CPM.

Combined Criterion for Ship Position Optimization in Cable Based Parallel Manipulators

In this study, ship position optimization is conducted on a cable-driven parallel manipulator (CPM) operating inside deep sea. The workspace and stiffness of the manipulator is analysed as well as cable tensions after failure are reported and a combined criterion of ship position optimization has been established. Based on the criterion, the CPM will have maximum workspace and stiffness as well as minimum cable tensions in case of a failure. The optimization is demonstrated with six, eight and ten ships CPMs. The performance of the system is improved with higher number of cables in a CPM.

A kinematic characterization of human walking by using CaTraSys

This paper presents an experimental characterization of the biomechanics of human gait by means of Cassino Tracking System (CaTraSys). CaTraSys is a passive cable-based parallel manipulator that is used to determine pose and exerted force of mechanical systems along large trajectories. It is a low-cost easy-operable system that has been used in this work for a clinical application as an assessing device for diagnosis and rehabilitation procedures. A procedure is outlined for experimental tests and analysis of acquired trajectory data. Basic characteristics are discussed by referring to two-dimensional and three-dimensional resulting gait patterns. Using spatiotemporal parameters, different test conditions and anthropometric characteristics are evaluated in order to assess their influence on human walking from the kinematic point of view.

Design issues for human-machine platform interface in cable-based parallel manipulators for physiotherapy applications

We outline problems and potential solutions for feasible human-machine interfaces using cable-based parallel manipulators for physiotherapy applications. From an engineering perspective, we discuss the design constraints related to acceptance by patients and physiotherapist users. To date, most designs have focused on mobile platforms that are designed to be operated as an end-effector connected to human limbs for direct patient interaction. Some specific examples are illustrated from the authors’ experience with prototypes available at Laboratory of Robotics and Mechatronics (LARM), Italy.

Characterization of a Cable-Based Parallel Mechanism for Measurement Purposes#

This article describes the main characteristics of a cable-based parallel manipulator called Milli-Cassino Tracking System (Milli-CaTraSys), which was developed at LARM in Cassino. Operation models and formulations are proposed both for kinematics and statics. In particular, a procedure is proposed for error estimation to know error effects on the end-effector pose. Numerical simulations have been carried out to characterize both the procedure results and system behavior. Results of experimental tests and simulations are also compared to show the feasibility and practical efficiency of a Milli-CaTraSys prototype.

Modelling, Simulation and Testing of a Reconfigurable Cable-Based Parallel Manipulator as Motion Aiding System

This paper presents results on the modelling, simulation and experimental tests of a cable-based parallel manipulator to be used as an aiding or guiding system for people with motion disabilities. There is a high level of motivation for people with a motion disability or the elderly to perform basic daily-living activities independently. Therefore, it is of great interest to design and implement safe and reliable motion assisting and guiding devices that are able to help end-users. In general, a robot for a medical application should be able to interact with a patient in safety conditions, i.e. it must not damage people or surroundings; it must be designed to guarantee high accuracy and low acceleration during the operation. Furthermore, it should not be too bulky and it should exert limited wrenches after close interaction with people. It can be advisable to have a portable system which can be easily brought into and assembled in a hospital or a domestic environment. Cable-based robotic structures can fulfil those requirements because of their main characteristics that make them light and intrinsically safe. In this paper, a reconfigurable four-cable-based parallel manipulator has been proposed as a motion assisting and guiding device to help people to accomplish a number of tasks, such as an aiding or guiding system to move the upper and lower limbs or the whole body. Modelling and simulation are presented in the ADAMS environment. Moreover, experimental tests are reported as based on an available laboratory prototype.

An application of CaTraSys, a cable-based parallel measuring system for an experimental characterization of human walking

SUMMARYIn this paper, an application is presented of a cable-based parallel manipulator as measuring system for an experimental identification of human walking characteristics. Experimental results have been obtained by means of a new version of CaTraSys (Cassino Tracking System), which is a measuring system that has been designed and built at Laboratory of Robotics and Mechatronics (LARM) in Cassino, Italy. The new version of the CaTraSys system has been used to determine the trajectory of the human limb extremity during walking operation and furthermore the system is able to measure forces that are exerted by a limb. Experimental determination of articulation mobility is also presented with numerical and experimental results.

Optimization of Actuator Forces in Cable-Based Parallel Manipulators Using Convex Analysis

In cable-driven parallel manipulators (CPMs), cables can perform only under tension, and therefore, redundant actuation, which can be provided by redundant limbs, is needed to maintain the cable tensions. By optimizing the distribution of the forces in the cables and the redundant limbs, the average size of actuators can be reduced resulting in lower cost. Optimizing the force distribution in CPMs requires consideration for the inequality constraints imposed on the cable forces as a result of the unilateral driving property of the cables. In this study, a projection method is presented to calculate optimum solutions for the actuators force distribution in CPMs. Two solutions are presented: 1) a minimum-norm solution that minimizes the 2-norm of all forces in the cables and redundant limbs and 2) a solution that minimizes the 2-norm of the forces in the cables only. The optimization problem is formulated as a projection on an intersection of convex sets and the Dykstra's projection method is used to obtain the solutions. This method is successfully applied to a 3-DOF CPM.

Design Issues and Application of Cable-Based Parallel Manipulators for Rehabilitation Therapy

In this study, cable-based manipulators are proposed for application in rehabilitation therapies. Cable-based manipulators show good features that are very useful when the system has to interact with humans. In particular, they can be used to aid motion or as monitoring/training systems in rehabilitation therapies. Modelling and simulation of both active and passive cable-based parallel manipulators are presented for an application to help older people, patients or disabled people in the sit-to-stand transfer and as a monitoring/training system. Experimental results are presented by using built prototypes.

Erratum: “Stiffness of Cable-based Parallel Manipulators With Application to Stability Analysis” [Journal of Mechanical Design, 2006, 128(1), pp. 303–310

Erratum: “Stiffness of Cable-based Parallel Manipulators With Application to Stability Analysis” [Journal of Mechanical Design, 2006, 128(1), pp. 303–310

Time-optimal trajectory planning in cable-based manipulators

In this paper, the trajectory planning of high-speed cable-based parallel manipulators is studied for a given geometrical path. The time-optimal trajectory-planning technique is adapted for these manipulators in which cable forces must be maintained tensile. This condition is represented as a constraint on the acceleration of the end-effector along the path. The results of this technique are evaluated experimentally on DeltaBot, a cable-based manipulator developed at the University of Waterloo. The performance of the time-optimal technique is examined both for the moving time of the manipulator and the computational time of the trajectory generation.

DESIGN AND TESTING OF AN ULTRA-HIGH-SPEED CABLE ROBOT

The goal of this paper is to introduce the design and testing of a new ultra-high-speed robot. This robot is able to reach speeds of over 120 cycles per minute for pick-and-place applications. A parallel manipulator design was chosen because of its low inertia and high stiffness. The inertia of the robot was further reduced by replacing some of the rigid links with cables. The use of cables requires a method for keeping the cables in tension, which was provided by a central compression member between the moving and fixed plate. The compression member keeps all the cables in tension but does not interfere with the robot's workspace. The new cable-based parallel manipulator design, called DeltaBot, is kinematically constrained to have three pure translational degrees of freedom. A prototype of DeltaBot was built and tested. The DeltaBot prototype is capable of reaching 150 cycles per minute with a position repeatability of less than 0.1 mm.

Stiffness of Cable-based Parallel Manipulators With Application to Stability Analysis

The stiffness of cable-based robots is studied in this paper. Since antagonistic forces are essential for the operation of cable-based manipulators, their effects on the stiffness should be considered in the design, control, and trajectory planning of these manipulators. This paper studies this issue and derives the conditions under which a cable-based manipulator may become unstable because of the antagonistic forces. For this purpose, a new approach is introduced to calculate the total stiffness matrix. This approach shows that, for a cable-based manipulator with all cables in tension, the root of instability is a rotational stiffness caused by the internal cable forces. A set of sufficient conditions are derived to ensure the manipulator is stabilizable meaning that it never becomes unstable upon increasing the antagonistic forces. Stabilizability of a planar cable-based manipulator is studied as an example to illustrate this approach.

Design of reduced DOF parallel cable-based robots

In this paper, a new approach for the study and design of cable-based robots are presented. In the cable-based robots, a telescopic element is used to apply a force to the end-effector in order to maintain tension in all cables. As a result, cables tensions or internal forces in the manipulator appear in the design procedure which in turn makes the design procedure more complex than rigid-link robots. The main focus of this work is to introduce a geometrical approach for the study of this problem. In this approach, the capability of the end-effector for applying force and torque to external object is called force/torque capacity and is considered as the main target of the design process. The force and torque capacity of the manipulator is illustrated in a 3D space whose axes are force or torque components. It is shown that the force and torque capacity have a convex cone and parallelepiped shape, respectively. The design problem is then reduced to the sizing of these shapes according to the design requirements and manufacturing limitations. The approach is applied to the design of DeltaBot, a 3DOF cable-based parallel manipulator and the results are presented.