Geometrico-Static Analysis of a New Collaborative Parallel Robot for Safe Physical Interaction

Abstract

This paper introduces a geometrico-static analysis of an intrinsically safe parallel manipulator called R-Min. This robot was designed to reduce the risk of injury during a collision with a human operator, thanks to an underactuated architecture which enables large internal displacements in case of a collision. Indeed, the R-Min architecture is based on a modification of the well-known planar five-bar mechanism, where additional passive joints are introduced on the distal links in order to create a planar seven-bar mechanism with two degrees of underactuation. These two additional degrees of freedom are passively driven through the use of a supplementary passive leg, in which a tension spring is mounted between the base and the end-effector. In this paper, the conditions satisfying the equilibrium and the stability of the mechanism are introduced, based on a geometrico-static analysis. The direct and inverse problems are then solved using a numerical approach. Solutions to both problems are presented and classified. One subset of solutions to the inverse problem is isolated and projected in the Cartesian space in order to obtain the payload-invariant workspace of the R-Min robot.

Experimental Safety Analysis of R-Min, an Underactuated Parallel Robot

“…In this section, the computation of the geometricostatic model of the R-Min robot is presented (in a more unified way than in [27]). The kinemato-static model 1 is derived from the geometrico-static model and allows to express the singularity conditions.…”

“…In what follows, the algorithm provided in [27] is used to draw the Cartesian workspace of the R-Min robot. Since, there exist multiple solutions to the geometricostatic problem of the R-Min robot (as detailed in [27]), the following inequalities are added in order to keep only the set of solutions corresponding to the configuration of the robot depicted in Fig. 2a:…”

“…The working mode depicted in Fig. 2a is suitable for multiple reasons: − both distal arms can fold in case of a collision with a human, − the preload bar does not present any risk of injury since it lies between both distal arms, − it offers a large Cartesian space for the controlled point, − the weight of the payload has no (or little) effect on the position of the end-effector, as shown in [27].…”

Parallel Image-Based Visual Servoing/Force Control of a Collaborative Delta Robot

“…Compared with serial robots, parallel robots show better performance in terms of high speeds and accelerations, payload, stability, stiffness, and accuracy. Due to these advantages, parallel robots is widely applied as collaborative robots (Zabihifar and Yuschenko, 2018 ; Jeanneau et al, 2020 ; Fu et al, 2021 ). However, the force/position control of parallel robots has been rarely addressed since the structure of parallel robots is complex and the relationship between the input and output of the controller is highly non-linear (Merlet, 2006 ; Dai et al, 2021 ).…”