R-Min: a Fast Collaborative Underactuated Parallel Robot for Pick-and-Place Operations

Abstract

This paper introduces an intrinsically safe parallel manipulator dedicated to fast pick-and-place operations, called R-Min. It has been designed to reduce the risk of injury during a collision with a human operator, while maintaining high speed and acceleration. The proposed architecture is based on a modification of the well-known planar five-bar mechanism, where additional passive joints are introduced to the distal links in order to create a planar seven-bar mechanism with two degrees of underactuation, so that it can passively reconfigure in case of collision. A supplementary passive leg, in which a tension spring is mounted, is added between the base and the end-effector in order to constrain the additional degrees of freedom.A prototype of this new collaborative parallel robot is designed and its equilibrium configurations under several types of loadings are analyzed. Its dynamics is also studied. We analyze the impact force occurring during a collision between our prototype and the head of an operator and compare these results with those that would have been obtained with a rigid five-bar mechanism. Simulation results of impact during a standard pick-and-place trajectory of duration 0.3 s show that a regular five-bar mechanism would injure a human, while our robot would avoid the trauma.

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

“…So intuitively, an impact on the links may lead to less energy transmission during collision than an impact on the end-effector. This behavior was shown in the simulations performed in [17].…”

“…In this section, we present the results obtained numerically to the direct (DGSP) and inverse (IGSP) problems. These methods are applied to the R-Min prototype [17] presented in Fig. 4.…”

“…In a previous paper [17], we introduced the R-Min robot whose architecture is based on the well-known planar five-bar mechanism, where additional passive joints are introduced to the distal links. The obtained mechanism is a planar seven-bar mechanism with two degrees of underactuation, authorizing the robot to passively self-reconfigure in case of collision.…”

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

“…4. It corresponds to the set of stable solutions to the geometrico-static problem, satisfying inequalities ( 11)- (16). The parameters of the prototype provided in Tab.…”

“…The use of a parallel architecture to design safe robots has been little investigated in the literature [15], although it allows to reduce the mass of the moving links. In previous works [16], we introduced the R-Min robot, an underactuated parallel robot, whose design is based on the architecture of the five-bar mechanism in which two supplementary passive joints are added. The obtained robot can self-configure in case of a collision with the environment allowing to mitigate the severity of an impact with a human being.…”