Precise assembly of ring part with optimized hollowed finger
Fukukawa et al. Robomech J
Precise assembly of ring part with optimized hollowed finger
Tomoya Fukukawa 0
Junji Takahashi 2
Toshio Fukuda 1
0 Department of Mechanical Science and Engineering, Nagoya University , Furo-cho, Chikusa-ku, Nagoya 464-8603 , Japan
1 Faculty of Science and Engineering, Meijo University , 1-501, Shiogamaguchi, Tenpaku-ku, Nagoya 468-8502 , Japan
2 Department of Integrated Information Technology, Aoyama Gakuin University , 1-10-5, Fuchinobe, Chuo-ku, Sagamihara 252-5258 , Japan
We deal with a technical issue of assembling a ring part into a shaft part with the clearance of several micrometers by using a robotic manipulator. This issue is difficult because of deformation of a ring part compared with peg-in-hole assembly. We propose a precise assembly method of a ring part with finger shape to solve this issue. We also propose a method to decide design parameters of the finger by maximizing a closed area in Jamming diagram, which represents a successful condition of assembling rigid parts by quasi-static force analysis. Finally, availability of the proposed method is verified by an experiment of ring assembly with a robotic hand attached to the designed fingers.
Peg-in-hole; Ring assembly; Robotic manipulator
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Background
In recent years, many manufacturing companies have
adopted Factory Automation (FA). Introduction of FA
brings automation of various production processes,
which are conducted by human workers, by machines,
and can improve productivity, manufacturing cost, and
quality of products. Although a paint process, a weld
process and an inspection process have been automated
increasingly, most of the assembly processes have been
conducted manually by human workers even now. This is
because assembly processes by a robot has many issues
with regard to the precision and flexibility.
Assembly methods by a robot are divided into two
categories by focusing on a process of mating: a passive
assembly method and an active assembly method. The
passive assembly method is a method that adjusts
position and orientation of a part automatically by using
mechanical elastic elements or guiding jig. The passive
assembly has advantage of high speed assembly because
of sensor-less. However, the method is applied for only
simple parts.
In contrast, the active assembly method is a method
that controls impedance of an end effector properly with
sensor feedback. The method has advantage of versatility
and can be applied for difficult assembly such as
assembly of complex shape parts or flexible parts. However, the
assembly time of the method tends to be larger than the
passive assembly method.
Passive assembly methods have been studied since the
1980s. As a representative research of a passive
assembly method, Whitney proposed Jamming diagram, which
represents a successful condition in peg-in-hole task
[1]. As a concrete example of passive assembly method,
Remote Center Compliance (RCC) device has been also
developed. Moreover, many researches have been
studied, and have extended application range of RCC devices
[2–4]. Mouri et al. dealt with narrow clearance assembly
and solved problems of high friction and jamming by
adding high-frequency vibration to a peg during
insertion process [5]. These conventional approaches have
disadvantages: A mechanical element, such as a spring and a
rubber, need frequent maintenance due to their
degradation; the system tends to become large; the cost of design
and production tends to become large.
Active assembly methods have been proposed much in
recent years. Many researches of force sensor feedback
[6, 7] or vision sensor feedback have been studied. Today,
there are strong demand for assembly for flexible parts
such as a cable and rubber. For example, Nakagaki et al.
© 2016 Fukukawa et al. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License
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tackled automatic insertions of linear and tubular
flexible parts based on shape detection by vision sensor [8].
Even though many active assembly methods have been
proposed, the methods that are used actually are few.
One reason of this is difficulty of developing the system.
Another reason is adaptability. Although human workers
can detect and recover an error state of assembly quickly
and succeed in the assembly smoothly, many assembly
automation system cannot perform as well as human
work.
In this paper, we focus on a precise ring assembly task
as an example of difficult assembly. In the case of precise
assembly that a clearance between a ring part and a shaft
part is several micro meters, the assembly by a robotic
manipulator is difficult. This is because a ring part
deforms if t (...truncated)