Influence-Coefficient Method for Identifying Maximum-Load Configurations and Variable-Load Issues in Manipulators

Raffaele Di Gregorio,Erkan Yilmaz

doi:10.3390/machines9020027

Abstract

The dimensioning of general-purpose machines such as manipulators involves the solution of a number of preliminary issues. The determination of reference external loads and the identification of machine configurations that give the maximum internal load for each component are two of these issues. These two problems are commonly addressed through trial-and-error procedures based on dynamic modelling, which are implemented with the support of simulation software, since static analyses are commonly considered inadequate to solve them. Despite this, here, a technique based on influence coefficients and static analyses is presented which solves them. Such technique is also able to foresee and justify dynamic issues (i.e., possible vibrations, etc.) that could heavily affect the machine behavior. The effectiveness of the proposed technique is proved by implementing it on a 3T1R parallel manipulator. The presented design method is general and applicable to any type of non-overconstrained manipulator or mechanism.

Highlights

The mechanical design of manipulators has mandatory steps summarizable as follows: type synthesis [1,2,3,4], dimensional synthesis [1,2,4], and machine-element design [5,6,7]
The actuated C pair of the CRS limb is obtained by means of a PR chain with the sliding direction of the P pair parallel to the axis of the R pair. Such a parallel manipulators (PMs) architecture has four degrees of freedom [31] and constrains the platform to perform spatial translations (3T) plus rotations around axes with one fixed direction (1R), that is, the platform can perform only motions of 3T1R type, named Scara or Schoenflies motions [30]. This Scara PM has been ideated [20,31] at the Laboratory of Mechatronics and Virtual Prototyping (LaMaViP) of the University of Ferrara and, hereafter, for the sake of brevity, it will be named “LaMaViP’s CRS-RRC”
In the context of the Scara PMs, LaMaViP’s CRS-RRC is interesting because it can be actuated by keeping all the motors on the base and using commercial components, and it has the platform translation decoupled from the platform rotation [20,31]

Summary

Introduction

The mechanical design of manipulators has mandatory steps summarizable as follows: type synthesis [1,2,3,4], dimensional synthesis [1,2,4], and machine-element design [5,6,7]. Various performance indices were conceived for identifying PMs’ reachable-workspace regions that are free and far from singularities, where safely locating the useful workspace [11,12,13,14,15,16,17,18] These indices well identify kinetostatic issues and can be useful to perform the dimensional synthesis and to locate the useful workspace (see, for instance, [19,20]) far from singularities. They fail in relating the “distance” from singularities to the actual internal loads of the links

Methods

Results

Discussion

Conclusion