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Ch03-I044963.fm Page 9 Tuesday, August 1, 2006 12:24 PM
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Tuesday, August 1,2006
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EVALUATION OF OPERABILITY OF
AN ELECTRIC CART HANDLE
WITHOUT THE BENDING MOTION OF WRISTS

Yuki TNOUE, Junichi KURATA and Hironobu UCHTYAMA
Department of Mechanical Systems Engineering Kansai University,
3-3-35, Yamatechou, Suita, Osaka 564-8680, JAPAN

ABSTRACT
Most electric carts employ on oval steering handle mechanism, which is seemed to make operation
difficult. When the operator turns the handle, great flexion of wrist joint is observed at both grips,
causing distortion of the upper part of the body. As operator moves his upper part to avoid this
inconvenience in turning the handle, the center of gravity of the cart and operator is moved to the
extreme centrifugal direction. To resolve this problem, we propose a new type of handle, which can
be operated with a straight-line motion, without any bending of the wrist joint, a bending torque forced
upon wrist joints, a curved shape of upper body and large movement of the center of gravity of cart
system. We confirmed that this type of handle was quite comfortable for electric carts by various
experimental results.

KEYWORDS
Human behavior, Electric cart, Elderly people, Handicapped people, Four parallel links, Wrist

INTRODUCTION

As motion-support machines for the elderly and physically handicapped, electric carts and wheelchairs
are useful. Since electric carts can be easily operated with only a handle and an accelerator lever,
they should be very useful. However, most of these carts employ oval steering handle, which
requires large flexion of the wrist joint at both grips of the handle. This results large distortion of the
upper part of operator's body. And this distortion causes large shift of the center of gravity, and the
cart system makes the center of gravity to the outside of the body center axis. In order to resolve this
problem, we propose a new type of handle instead of ordinary oval shape, which has a structure of four
parallel linkages. In the case of new handle, it can be operated by only forward or backward motion
of the operator's arm without any bending or twisting motion of his wrist joint.

Research on the characteristic of upper part of operator's body caused by bending or twisting of the
wrist joint has not been reported very much before. The remarkable inquires into arms in progress
reported by Mussa-Ivaldi (1985) was the first report about multi-joint stiffness measurements. They