Increase of singularity-free zones in the workspace of parallel manipulators using mechanisms of variable structure

Abstract

This paper is focused on the study of singularity of planar parallel manipulators taking into account the force transmission, i.e. study of singularity of planar manipulator by introducing the force transmission factor. Thus the singularity zones in the workspace of the manipulator are defined not only by kinematic criterions from the theoretical perfect model of the manipulator but also by the quality of force transmission. For this purpose, the pressure angle is used as an indicator of force transmission. The optimal control of the pressure angle for a given trajectory of the manipulator is realized by means of legs with variable structure. The suggested procedure to determination of the optimal structure of the planar parallel manipulator 3-RPR is illustrated by two numerical simulations.

Kinematic and Dynamic Modeling of a Parallel Manipulator with Eight Actuation Modes

“…The concept of variable actuated mechanism (VAM) was introduced in [2,11]. Indeed, they derived a VAM from the architecture of the 3-RPR planar parallel manipulator (PPM) by actuating either the f rst revolute joint or the prismatic joint of its limbs.…”

“…The common approach to solve this problem is to introduce actuation redundancy, that involves force control algorithms [1]. Another approach is to use the concept of joint-coupling as proposed by [11] or to select the actuated joint in each limb with regard to the pose of the moving-platform, [2].…”

Comparison of 3-RPR planar parallel manipulators with regard to their kinetostatic performance and sensitivity to geometric uncertainties

“…From [22,23], the transmission angle of a 3-DOF PPM can be also used to evaluate its kinetostatic performance. Here, we prefer to use the transmission angle as a kinetostatic performance index as it does not require the normalization of the kinematic Jacobian matrix.…”

NAVARO II, a Novel Scissor-Based Planar Parallel Robot1

“…Another approach is to use the concept of joint coupling as proposed by [5]. Moreover, in each leg where actuation reduncancy is implemented, it is possible to select the articulation which will be actuated in relation to the end-effector pose, [6].…”