Although several papers addressed the wrench capabilities of cable-driven parallel robots (CDPRs), few have tackled the dual question of their twist capabilities. In this paper, these twist capabilities are evaluated by means of the more specific concept of twist feasibility, which was defined by Gagliardini et al. in a previous work. A CDPR posture is called twist-feasible if all the twists (point-velocity and angular-velocity combinations), within a given set, can be produced at the CDPR mobile platform, within given actuator speed limits. Two problems are solved in this paper: (1) determining the set of required cable winding speeds at the CDPR winches being given a prescribed set of required mobile platform twists; and (2) determining the set of available twists at the CDPR mobile platform from the available cable winding speeds at its winches. The solutions to both problems can be used to determine the twist feasibility of n-degree-of-freedom (DOF) CDPRs driven by m ≥ n cables. An example is presented, where the twist-feasible workspace of a simple CDPR with n = 2 DOF and driven by m = 3 cables is computed to illustrate the proposed method.
This paper addresses the optimum design, configuration, and workspace analysis of a cable-driven parallel robot (CDPR) with an embedded tilt-roll wrist. The manipulator consists in a tilt-roll wrist mounted on the moving platform of a suspended CDPR. The embedded wrist provides large amplitudes of tilt and roll rotations and a large translational workspace obtained by the CDPR. This manipulator is suitable for tasks requiring large rotation and translation workspaces such as tomography scanning, camera-orienting devices, and visual surveillance. The moving-platform is an eight-degree-of-freedom articulated mechanism with large translational and rotational workspaces, and it is suspended from a fixed frame by six cables. The manipulator employs two bi-actuated cables, i.e., cable-loops to transmit the power from motors fixed on the ground to the tilt-roll wrist. Therefore, the manipulator achieves better dynamic performances due to a lower inertia of its moving-platform.
This paper introduces the concept of a new planar Cable-Driven Parallel Crane (CDPC) for lifting and carrying payloads with a moving hoist mechanism connected in parallel to the ceiling. In contrast to bridge-crane, CDPC is inexpensive and practicable for diverse tasks with simple assembly setup. The hoist mechanism is an under-constrained moving-platform articulated through a bi-actuated cable circuit, namely, a cable loop. The hoist is connected to a suspended moving-platform with four degrees of freedom. The power is transmitted directly from the motors fixed on frames to the hoist through the cable loop. Therefore, the dynamic performance of the robot is increased due to lower inertia of the moving-platform. However, the moving-platform undergoes some parasitic inclinations because of the cable loop. This paper investigates the parasitic inclination and its effect on the positioning of the payload. The workspace of the CDPC is studied in terms of static equilibrium. Moreover, the geometrico-static and elasto-static models of the CDPC are presented.
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