Specifity of Including of Structural Nonlinearity in Model of Dynamics of Cable-Driven Robot

The paper deals with a problem of modeling of the dynamics of a parallel cable-driven robot with the inclusion of structural nonlinearity of cables in a mathematical model. Mathematical model is implemented in a computer model with the possibility of using of symbolic calculations. Parallel cable robots as a type of robotics have been developing in the last two or three decades. The research in the theoretical field was being carried out and the mathematical model of the cable system was being refined with the spread of the practical use of cable robots. This is a non-trivial task to draw up a dynamic model of a cable-driven robot. Cable-driven robots are highly nonlinear systems, because of the main reason for the nonlinearity is the properties of the cable system. As an element of a mechanical system, the cable or the wire rope is a unilateral constraint, since the cable works only for stretching, but not for compression. Thus, the cables are structurally nonlinear elements of the system. On the other hand, cables have the property of sagging under their own weight. Thus, the cables are geometrically nonlinear elements of the system. Under the condition of a payload mass that is utterly greater than the mass of each cable, the cables can be considered strained without sagging and geometric nonlinearity can be neglected. Since symbolic computations can be used in a computer model which implements a mathematical model of the dynamics of a robot, in such a way it must provide the possibility of symbolic computations with the condition of structural nonlinearity. The main aim of this work is to develop a method that ensures the inclusion of the structural nonlinearity of the cable system in the mathematical model. It is supposed to consider the possibility of implementation of the computer model with symbolic computations. The problem of including a mathematical model of cables as unilateral constraints in the model of highly loaded cable robots is considered. The justification for including the activation functions in a system of differential equations of dynamics of cable-driven robot is formulated. A model of wire ropes as unilateral constraints is represented via including the activation functions in a system of differential equations. With using of the proposed method, numerical solution of a problem of forward dynamics has been obtained for high-loaded parallel cable-driven robot.

Artificial Neural Network Prediction of Deflection Maps for Cable-Driven Robots

In this paper, the learning models of cable-driven robots are developed applying the artificial neural network (ANN). For known input and output data and known relationships (regression problem), the deflection maps of cable-driven parallel robots are predicted utilizing a multi-layer ANN. Two cable robots, a planar robot and a translational spatial robot, are examined to evaluate their models. The deflection maps of these cable robots are generated using the ANN and a non-linear optimization method. The predicted deflections of the ANN models, using much less number of poses for training, are highly satisfactory and comparable to the results obtained by a nonlinear optimization method throughout the pertinent discretized workspaces. In addition, ANN models could predict the deflections for poses that the nonlinear optimization methods may not. Moreover, with variations in robot/task parameters, such as payload, ANN models may predict accurate deflections.

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

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.

STRUCTURAL ANALYSIS AND CLASSIFICATION OF ROBOTIC SYSTEMS WITH DRIVING MECHANISMS ON THE BASIS OF CABLE ELEMENTS

The mechanisms of the parallel structure are very diverse. Cable-driven robots that use cables instead of retractable rods to control the position of the output link are of particular interest. They have several advantages, such as large workspace, easy assembly, and disassembly, high mobility, but also there are disadvantages associated with controlling the movement of robot cables. The paper gives examples of some of the first cable robots, their purpose, and application. The article also considers Russian and foreign scientists who deal with these issues and analyzes their work. As a result of the structural analysis, the classification of cable robots is compiled and considered in detail: by the method of placing the reels, by the DOF number of the working body and the number of flexible links, by the application method, by the type of base, by the method of cable fastening. The cable robot structure for the movement of goods is given. However, there are still many areas open to theoretical research. In conclusion, the topics that need more research are considered. The most obvious area of research is control, also optimizing the workspace for different applications of these devices, finding and take advantage of all the benefits offered by cable devices.