This paper presents the design of a locomotion interface for gait simulation and interaction with a virtual environment. The proposed mechanical interface is based on two planar two-degree-of-freedom belt-driven mechanisms which fully decouple the vertical and horizontal motion of two supporting footplates. Force sensors are mounted under the footplates in order to move the end effectors according to the user's intentions. The user's feet are rigidly attached to the footplates but a system of hinges allows an additional unactuated two-degree-of-freedom motion. A lag controller allows the user to move the end-effectors freely and a virtual floor based on a virtual spring and damper restrains the end-effectors' movements so that the user experiences an intuitive contact with the ground. Finally, preliminary experiments are reported in order to demonstrate the capability of the locomotion interface for gait simulation.

This paper presents two trajectory-planning approaches for the point-to-point motion of planar two-degree-of-freedom (dof) cable-suspended parallel mechanisms. The proposed techniques can be used to plan trajectories that extend beyond the static workspace of the mechanism. Trajectories are specified as a list of target points that must be reached in sequence, with a zero velocity at each of the target points. In the first technnique, polynomial trajectories are designed to connect the target points, while the second approach uses trigonometric functions. Both techniques ensure continuity of the accelerations. Based on the dynamic model of the robot, algebraic inequalities are obtained that represent the constraints on cable tensions. These inequalities are used to determine the feasibility of the planned trajectories. Polynomial trajectories must be discretized in order to verify feasibility, while trajectories that are based on trigonometric functions can be verified globally, based on a set of simple algebraic equations. Example trajectories are given in order to illustrate the approach. An experimental validation is also presented using a two-dof prototype, and two video extensions are provided to demonstrate the results.

This paper presents a trajectory planning approach for cable-suspended parallel mechanisms. A planar two-degree-of-freedom parallel mechanism is used for the analysis. Based on the dynamic model of the suspended robot, a set of algebraic inequalities is obtained that represents the constraints on the cable tensions. Parametric Cartesian trajectories are then defined and substituted into the constraints in order to obtain global conditions on the trajectory parameters which ensure that the trajectories are feasible. Special frequencies arise from the equations that are akin to natural frequencies of pendulum-type systems. An experimental validation is also presented using a two-dof prototype. The proposed trajectory planning approach can be used to plan dynamic trajectories that go beyond the static workspace of the mechanism, thereby opening novel applications and possibilities for cable-suspended robots.

This paper is a contribution to an invited session on the benchmarking of parallel mechanisms. The aim of the session is to compare different existing designs and prototypes of parallel mechanisms using a common set of benchmarking criteria. First, the kinematic architectures of parallel mechanisms of the multipteron family are presented. In addition to the tripteron and the quadrupteron, the pentapteron, a five-degree-of-freedom (dof) parallel mechanism is introduced. Then, the benchmarking criteria are applied to the prototypes of the tripteron (3-dof) and the quadrupteron (4-dof) prototypes. Although the tripteron and quadrupteron parallel mechanisms have been presented elsewhere, their properties, highlighted by the benchmarking analysis presented here are revealed for the first time.