Search

Reactionless mechanisms have many important applications because of their zero reaction forces and moments at the base. However, in most cases, these mechanisms consume more energy than their unbalanced counterparts. This paper focuses on analyzing the relationship between the needed input torque and the dynamic parameters of reactionless four-bar linkages. The objective is to minimize the needed input torque by optimizing the relevant dynamic parameters. The dynamic analysis shows that the needed input torque mainly depends on the mass of the link, which needs to be balanced. The results obtained can be applied to the design optimization and dynamic control of the devices such as parallel manipulators composed of reactionless four-bar linkages. [DOI: 10.1115/1.4001337] Keywords: dynamic optimization, reactionless four-bar linkage, input torque

The intrinsic interaction of a robotic system that includes two 6-degree-of-freedom cable-driven platforms sharing a common workspace might result in cable interferences for random trajectories. This paper presents and analyzes computational methods for geometrically determining and managing these interferences for any trajectory constrained with variable loads. The algorithms considered determine which cable can be released from an active actuation state while allowing control in a minimal tension state, thereby ensuring that both platforms stay in a controllable workspace. The process of managing cable interferences constitutes a challenge as one must take into account the inherent limitations of the workspace, which not only include the possibility of interference itself, but also the geometry of the cable-driven locomotion interface (CDLI), its dynamics, the nonideal behavior of real cables, and the requirement that both platforms must be completely constrained at any time. As releasing a cable from an active actuation state might generate tension discontinuities in the other cables, this paper also proposes collision prediction schemes that are only applied to redundant actuators in order to reduce or completely eliminate such discontinuities. Finally, a simulation of a CDLI embedded as a peripheral in a virtual environment, in which the load applied on each platform comes from the wrench measured under the foot for a natural gait walking, is thoroughly analyzed. Index Terms--Cable, environment, interface, interference, locomotion, parallel, robot, virtual, wire.

This article provides a general framework for the use of low-impedance displacement sensors mounted on the links of a serial robot to provide an intuitive physical human–robot interaction. A general formulation is developed to handle the motion guidance problem, i.e., the mapping of the measured motion of the sensors into the required robot joint motions to provide intuitive responsiveness. The formulation is general and can be applied to any architecture of serial robot with any number of displacement sensors each having an arbitrary number of degrees of freedom. Then, the design of a novel three-degree-of-freedom low-impedance displacement sensor is presented as a particularly effective instantiation of the general concept. Partial force balancing is used to reduce the required elastic return action, thereby ensuring the low impedance of the interaction. A prototype of a three-degree-of-freedom displacement sensor is then introduced. Two such sensors are mounted on the links of a custom-built five-degree-of-freedom robot in order to demonstrate the proposed approach. Experimental results are provided and comparisons with other collaborative robots are given. It is shown that the proposed sensors and motion guidance approach yield very intuitive low-impedance interaction involving very low interaction forces. [ABSTRACT FROM AUTHOR]

Over the past decade, cable-driven parallel mechanisms have been used for several purposes. In this paper, a novel application is proposed, namely, using two 6DOF cable-driven parallel mechanisms sharing a common workspace to obtain the mechanical base for the design of a locomotion interface. The methodology used to develop the architecture of the mechanisms is presented, and the two main criteria used to optimize the geometry are described. These criteria are based on the wrench-closure workspace and a detection of the mechanical interferences between all the entities of the locomotion interface (cables and moving bodies). Then, the final design is described and its performances are given. Finally, in order to validate the relevance of the mechanism for the locomotion interface's design, tensile forces in the cables are computed to observe the maximal values reached during a typical human gait trajectory. [DOI: 10.1115/1.2965607] Keywords: cable-driven parallel mechanism, design optimization, locomotion interface