A Review of the Literature on the Lower-Mobility Parallel Manipulators of 3-UPU or 3-URU Type

Abstract

Various 3-UPU architectures feature two rigid bodies connected to one another through three kinematic chains (limbs) of universal–prismatic–universal (UPU) type. They were first proposed in the last decade of the 20th century and have animated discussions among researchers for more-or-less two decades. Such discussions brought to light many features of lower-mobility parallel manipulators (PMs) that were unknown until then. The discussions also showed that such architectures may be sized into translational PMs, parallel wrists, or even reconfigurable (metamorphic) PMs. Even though commercial robots with these architectures have not yet been built, the interest in them remains. Consequently, a review of the literature on these architectures, highlighting their contribution to the progress of lower-mobility PM design, is still of interest for the scientific community. This paper aims at presenting a critical review of the results that have been obtained up until now.

A Novel 3-URU Architecture with Actuators on the Base: Kinematics and Singularity Analysis

“…Out of constraint singularities [8,11], a 3-URU architecture is a TPM if it is manufactured and assembled so that in each URU limb the axes of the two ending R-pairs are parallel to one another and the axes of the three intermediate R-pairs are all parallel [8]. Figure 1 shows the reference geometry for a LaMaViP 3-URU.…”

“…Type-II(a) singularities are named "constraint singularities" [11] since the additional platform DOFs acquired at such singularities may make the platform change its type of motion (operating mode). In particular, in a TPM, such additional DOFs can only be instantaneous rotations which may make the platform exit from the pure-translation operating mode; that is why TPMs' constraint singularities are also named "rotation singularities" and TPMs' type-II(b) singularities are also named "translation singularities" [8].…”

“…TPMs are a particular family of lower-mobility PMs. DELTA-like architectures [1,2] are the most known and affirmed [3] TPM architectures, even though many (see [4][5][6][7][8] for instances and for further Refs.) other TPM architectures have been proposed and studied in the literature.…”

“…TPMs with 3-URU 1 architectures [8] have been studied by many researchers. Such architectures feature three limbs of Universal-Revolute-Universal (URU) type that simultaneously connect the Putting the actuators on the base allows a significant reduction of the mobile masses, thus promising good dynamic performances, and makes the remaining part of the limb a simple chain constituted by only passive R-pairs.…”

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

“…The third step needs, as input data, the reference external loads applied to the machine and the identification of the machine configurations that give the maximum internal loads for each component. In general-purpose machines, such as manipulators, these input data are not straightforwardly obtainable from the design requirements and their deduction becomes even more difficult when dealing with parallel manipulators (PMs) since PMs' reachable workspace usually includes particular configurations, named "parallel" singularities [8][9][10], where the end effector cannot carry any (even infinitesimal) load without breaking down the PM.…”