ROBOT DESIGN FOR DEXTEROUS MANIPULATIONDivya SHAH (PhD Student) ; Giorgio METTA (Vice Scientific Director) ; Alberto PARMIGGIANI (Technologist)

iCub Facility; Istituto Italiano di Tecnologia, Genova, ITALY

DESIRED WRIST CHARACTERISTICS

3. ORIENTATION WORKSPACE ANALYSIS

MECHANISMS

2. CAD-BASED APPROACH

1. MOTIVATION

September, 2018

In today’s times, it is essential for the humanoids to match up to the dexterity of thehumans. These skills contribute significantly in their capacities for feeling, exploring,learning, planning and subsequently acting. iCub Humanoid, developed at our facility, wasdesigned explicitly to promote research for the same. In this work, we focus on theenhancement of the wrist dexterity.

4. ISOTROPY ANALYSIS

1. 2DOF Gimbal MechanismSerial mechanism with the

desired behaviour. This is our point of reference.

2. 4-UU Mechanism4 identical limbs with mirror-symmetric architecture of

RRRR chains.

3. Spherical Six-Bar MechanismSix spherical linkages connected by R joints with a central gimbal.

divya.shah@iit.itiit.it/people/divya-shah

5. CONCLUSIONS

The mechanism isotropy is defined as follows; where ‘J’ are the Jacobianmatrices computed numerically from the simulation data and ‘m’ is the order ofthe task space:

GIMBAL 4-UU S6B

RO

LL

YA

WP

ITC

H

Compact Design

Higher Payload-to-Weight Ratio

Simpler Kinematics

Large Range of Motion

Regular/Symmetric Workspace

Full Pitch-Yaw Decoupling

01

02

03

04

05

06

ISO

TR

OP

Y

NEW WRIST

Work in Progress …

=

Spherical Parallel Mechanism

Multibody Mechanism Simulation

Extract Workspace Measures

Contour Plots

CAD Model of the architecture

a) Warping in the Workspace: Mechanism behaviours are notsymmetric, i.e., the plots are not centered with absolute zero. Workspacediverges towards the extremes, as in case of 4-UU.

c) Asymmetric Parasitic Roll Motion: Platform posses undesiredRoll motion in case of 4-UU, which becomes difficult to becompensated. Central gimbal prevents the same for S6B.

b) Yaw-Pitch Coupling: Unlike gimbal, pitch and yaw contours are notstraight lines, i.e., the motions are coupled with each other and one inputproduces both outputs.

d) Anisotropy: Mechanisms are not fully isotropic throughout theworkspace. S6B best with Δ ≥ 0.9 for significantly large section of theworkspace.