In this paper, vibrational response of a variable-length cable in longitudinal, lateral and torsional directions is analysed in a cable robot using FE method. The flexibility of cables has remarkable effect on positioning of the end-effector in cable robots. Also considering the fact that the length of the cables are time dependent in a dynamic cable structure like robocrane, the numerical approaches are preferable compared to analytic solutions. To do so, the cable is divided into finite elements in which the virtual work equation and Galerkin method can be implemented for the equations. Considering the stiffness matrix, the characteristic equations and Eigen values of each element can be defined. A simulation study is done in the ANSIS on a planar robocrane with 2-DOF and also for a spatial case with 6-DOF that is controlled by the aid of six variable-length flexible cables in the space for two different types of solid and flexible end-effectors. Whole the cable robot flexibility is analyzed simultaneously instead of separation calculation of each cable. Not only all of the 3-D vibrating behaviour of the whole structure is studied in this paper but also the lengths of the cables are considered as variable. The vibrating response of mode shapes, amplitude and frequencies are extracted and analysed, and the results are compared for two case of solid and flexible end-effector which shows the effect of the flexibility in the position of the end-effector and the tension of the cables in different situations. تفاصيل المقالة

A new mechanism is presented in this paper for simulating the athlete performance and training the sportsman’s exercises, using a closed loop six degrees of freedom (DOFs) cable suspended robot. This robot cancels the necessity of presence of a sport coach for training the sportsman. Using the proposed robot, it is possible to program the robot for training the athlete limb (arm, leg and etc.) within a predefined trajectory corresponding to his special sport performance. The limb of the sportsman which is involved in the game and should be trained could be attached to the end-effector of the cable robot. Since in many sports a large environmental space needs to be covered by the athlete movement, ordinary robots are not capable to be employed for this application while cable robots are applicable since a large dynamic workspace can be covered by them. Moreover, training the sportsman limb requires a precise movement of the mentioned end-effector on a predefined trajectory. This importance could not be satisfied without using a proper closed loop controlling system since a variable external disturbing force applies on the end-effector as a result of the weight of the sportsman limb and its dynamic movement. Studio cams and automatic brancard for carrying the damaged sportsman out of the field are also of other applications of the presented closed loop cable robot. So required dynamic and control formulation of the end-effector of the cable robot is derived for handling the athlete limb on a predefined trajectory in a closed loop way. Simulation on using the MATLAB confirms the possibility of the mentioned claim for simulating the sportsman training. Finally the efficiency of the proposed mechanism in training the athletes’ limb is also proved by conducting experimental test on Iran University of Science and Technology (IUST) cable robot (ICaSbot). تفاصيل المقالة