Page 17 - Mechatronics for Safety, Security and Dependability in a New Era

Ch01-I044963.fm Page 1 Monday, August 7, 2006 11:24 AM
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Skill-Assist and Its Related Safety-Oriented
Technology
Yoji YAMADA
Intelligent Systems Institute,
National Institute of Advanced Industrial and Science Technology (AIST),
AIST Tsukuba Central 2, Tsukuba City, Ibaraki, 305-8568, Japan.

Abstract
Skill-Assist is a kind of power assist devices which has been introduced to labor-intensive final assembly lines
in automotive industry for helping workers mount such heavy modular parts as instrumental panels on vehicles with
high positioning accuracy. The paper briefly describes a current technology which has been already implemented
on the controller of the Skill-Assist for putting it to practical use, and a future safeguarding method that has been
developed on a laboratory basis. An important issue on putting Skill-Assist devices into practice was resoloved
by attaining a certain level of safeguarding technology which follows the initial productivity enhancement effort
of controlling the devices so as to reflect workers' desired skills in the statistical sense. We can report that no
accident or system failure has occurred since commencement of operation. The main part of this paper is focused
on description of our laboratory-based study concerning safeguarding scheme against human operational slip. Finally,
a comment is made on how to put human-coexistence type service robots into practice from the viewpoint of sceince
and technology study.
Index Terms
power assist device, FTA, operation slip, Hidden Markov Model, control policy, service robot

I. INTRODUCTION TO SKILL-ASSIST
In 1990's, increasing numbers of automobile manufacturers have adopted modular component assembly systems
which offer various merits. However, modular components are larger and heavier than individual parts. In view of
the fact that an assembly process involving human operators can easily change tasks and flexibly adapt to varying
demands, a technology that can reduce the physical workload on human operators during modular component
installation is an important element to be incorporated into the assembly process.
Power augmentation in heavy-duty conveyance operation, especially in the horizontal direction, is important
because large inertial force is exerted in the phase of positioning a heavy load. It results not only in decreased
production efficiency caused by deterioration in an operator's skill; it also engenders a condition among operators
that is known as coxalgia. Therefore, we proposed construction of a power assist device called "Skill-Assist" for
mounting operations in automobile assembly processes. Fig. 1 is a picture of Skill-Assist being maneuvered by
an operator (a worker) in an actual production line.

Skill-Assist

instrument
penel

vehicle body
operator
Fig. 1. Overview of a Skill-Assist introduced to a production line

The Skill-Assist varies mechanical impedance depending on phases in a task so that it reflects workers' desired
skills in the statistical sense. Concretely, phase-dependent variable impedance control is applied to controlling each