The National Science Foundation's (NSF) Tokyo Office periodically receives and disseminates reports on research developments in Japan that are related to the Foundation's mission. NSF-sponsored researchers currently working in Japan prepare many of these reports. These reports present information for use by NSF program managers and policy makers; they are not statements of NSF policy.
Special Scientific Report #00-03 (September 01, 2000)
Ms.
Wendy Huei-Wen Cheng, a graduate student in Mechanical Engineering,
Stanford University, prepared the following report. Ms.
Cheng was a participant in the 2000
Summer Institute sponsored in the United States by NSF/NIH/USDA and the
Science and Technology Agency and Japan Science and Technology Corporation
in Japan. Dr. Shigeo Hirose of
the Department of Mechanical and Aerospace Engineering at Tokyo
Institute of Technology in Tokyo, hosted Ms. Cheng. Ms.
Cheng can be reached via email at: chengw@stanford.edu
[NB: Ms. Cheng's original report
included a number of illustrations, most of which have been removed by the
NSF Tokyo Regional Office to save space on our server.
Her original report is available in electronic form on request from
wblanpied@nsf.gov or directly from Ms. Cheng.]
1.0
Summary
During the summer of 2000, I was fortunate enough to conduct a research
project at the Hirose & Yoneda Laboratory of the Tokyo Institute of
Technology (http://mozu.mes.titech.ac.jp/).
While at the Hirose & Yoneda Laboratory, I mainly focused on the
mechanical design of a new omnidirectional robot.
For this project, I worked closely with Mr. Riichiro Damoto, and under
the guidance of Prof. Shigeo Hirose. This
robot was based on the Vuton, an omnidirectional vehicle that was previously
developed in the Hirose & Yoneda Laboratory, and on the omniwheel, a new
high-load, veer-free caster. This
new robot is designed to be low in cost, short in stature, and reasonably high
in payload. During the summer
program, I also had the great opportunity to study some of the other robots
associated with the Hirose & Yoneda laboratory, as well as visit other
robotics laboratories at the Tokyo Institute of Technology, the University of
Tokyo, and Tsukuba Science City.
2.0
Background
Wheeled omnidirectional robots and vehicles are not new.
Many previous versions of omnidirectional robots incorporate
omnidirectional wheels such as the example given in http://mozu.mes.titech.ac.jp/research/mobile/vuton/v_fig1.html.
This wheel contains passive, rolling components placed orthogonally to
the driven direction, so that the wheel can roll freely in this orthogonal
direction.
The previous omnidirectional robot of the Hirose & Yoneda
laboratory, the Vuton, utilizes a novel mechanism that combines passive, rolling
mechanisms with a driven chain of cylindrical rollers (Illustrations of several
of the laboratory's robots referred to in this report can be found on: http://mozu.mes.titech.ac.jp/research/mobile/vuton/).
The Vuton combines four roller chains such that the mapping from desired
orthogonal and angular velocities to individual roller motions is relatively
simple. It was designed to satisfy
the need in factories, hospitals, and other facilities for low, maneuverable
transport vehicles that can turn freely within narrow confines.
The Vuton (which sounds like zabuton
in Japanese) is capable of traveling over fragile terrain, such as tatami
mats and carpet, while carrying high payload.
Experiments have demonstrated that three grown men can ride on the Vuton
while traversing and not damaging a tatami
mat. The Vuton can carry this high
payload because it distributes this load over four lines of contact where the
rollers contact the surface; if conventional omnidirectional wheels such as the
one shown in Fig. 1 are used in place of the chains of rollers, then only four
contact points support the load.
Specifications
for the Vuton are: 29.5 kg without batteries, 560 mm wide by 560 mm long by 135
mm high, and a maximum estimated payload capacity of 1090 kg (http://mozu.mes.titech.ac.jp/research/mobile/vuton/.)
The omniwheel is a special, high load caster developed for the SMC
project at the Tokyo Institute of Technology.
This caster takes inspiration from the paddle wheel boats of the 19th
century, where the paddle wheels utilize eccentric shafts to ensure that
individual paddles are always vertical (http://www.destinparadise.com//emeraldqueen/sale.htm).
The omniwheel caster assembly also introduces eccentricity between its
shafts. This ensures that
individual wheels of the assembly are always aligned in the same direction, and
that the omniwheel caster can always roll freely in the same direction.
3.0
Mechanical
Design
Vuton’s layout of actuators is combined with the omniwheel to form the
new omnidirectional robot. The
design of this new robot is focused on maintaining a short stature, keeping the
power requirements low, and ensuring a reasonable payload capacity.
Four new omniwheel casters will be used in the robot.
These new omnidirectional casters have been designed largely as
individual modules to facilitate the future use of ominwheel casters on other
bases. As compared with the SMC
casters, these new caster assemblies incorporate larger and more numerous wheels
to increase payload. The height of
this new caster module will approximately 82 mm, or 25 percent taller than the
original SMC caster assembly (the SMC assembly is 66 mm to the top of its
driving gear.) The actuators for
these omniwheel casters will also be replaced with cheaper motors that are
usually used to drive the turrets of model tanks.
The shape of the mechanism will be octagonal, and it can be contained
within a square with 760 mm long sides. With
the addition of the robot base, the total height of the mechanism will be a bit
less than 100 mm. It is expected
that the new robot will be able to carry a child, and operate autonomously for
approximately 20 minutes.
Table 1 consists of a bill of materials of custom or adapted parts for
the omniwheel (32 different customized part types are required.)
Table 1: Bill of materials of
the new omnidirectional robot
Drawing # Part Name
Material
Quantity
1 wheel_post_top
A5056 32
2 wheel_post_mid
A5052 32
3 wheel_post_btm
A5056 32
4 wheel_shaft
A5056 32
5 wheel_spcr A5052
64
6 bearing_mf128_spcr
A5052 64
7 leafspring SUS304
4
8 upperplate A5052
4
9 ecc_shaft_btm_plate
A5052 4
10 ecc_shft_spcr_btm
A5052 4
11 ecc_shft_btm
A5056 4
12 ecc_shaft_mid_plate
A5052 4
13 ecc_shft_spcr_top
A5056 4
14 ecc_shft_top
A5056 4
15 miter_gear_motor
S45C 4
16 miter_gear_shaft
S45C 4
17 spur gear S45C
4
18 shaft_miter
super shaft 4
19 mounting_plate_btm
A5052 4
20 battery_holder
A5052 1
21 main_plate_mid
FOAM 1
22 main_plate_top
A5052 1
23 main_plate_btm
A5052 1
24 battery_cover_plate
A5052 1
25 circuit_cover
ACRYLIC 1
26 actuator_body_plate
A5052 4
27 mounting_plate_side
A6063 4
28 mounting_plate_wedge
A5052 4
29 mounting_plate_top
A5052 4
30 mounting_plate_motor
A5052 4
31 circuit_bottom_spacers
A5056 4
32 battery_center_block
FOAM 1
4.0
Conclusions
During
the second to last week of the NSF/STA Summer Institute 2000 program, the
drawings of the customized parts were presented to the manufacturing company
typically used by the Hirose & Yoneda Laboratory.
The parts are now being manufactured.
Mr. Riichiro Damoto will continue with the project after the Summer
Institute 2000 program.
5.0
References
Shigeo Hirose, Shinichi Amano; 1993l; “The VUTON: High Payload High
Efficiency Holonomic Omni-Directional Vehicle;” Proc. Int.Symp.on Robotics Research, pp.253-260.
6.0
Acknowledgements
This
was a fantastic summer, and I have had a great time both inside and outside the
laboratory. For this, I must thank
NSF and STA for their sponsorship of the program, the NSF and the Japan
International Science and Technology Exchange Center (JISTEC) personnel for
their outstanding planning and execution of Summer Institute 2000, the Hirose
& Yoneda laboratory for hosting me, the Hirose & Yoneda personnel for
their assistance during the summer, and Prof. Shigeo Hirose and Mr. Riichiro
Damoto for the “Omniwheel” project. I
am indebted to these organizations and individuals.