Column

New Expectations for MEMS Devices
Isao Shimoyama, Professor
Department of Mechano-Informatics
Graduate School of Information Science and Technology
The University of Tokyo

Tactile Sensing
In settings where humans and machines coexist, humans
sometimes touch or ride on the machines. By sensing the stateof forces exerted when industrial robots and humans work
together to assemble parts, or by detecting whether a passenger
riding in a personal mobility vehicle is sitting in the seat and isin contact with the backrest, such machines can be preciselycontrolled, properly accelerated and decelerated, and usedwithout incident on stairways and elevators. We may be able topredict when a vehicle could slip on a road surface by detecting
the frictional forces and coefficient of friction between the tires
and road surface. It can be said that MEMS provides us withnew functions by enabling us for the first time to detect
forces that humans and machines exert on each other and thedistribution of force vectors produced through contact between
humans and machines.
Increasing Sensitivity and Reducing Drift in PhysicalSensors
Industrial robots, service robots, and personal mobility
vehicles are constructed by assembling together rigid bodies.
Encoders attached to the joints of the rigid bodies detect theangle of rotation between bodies in order to calculate the positionand orientation of the links. Links are usually heavy in order topreserve rigidity, making the overall robot stiff and heavy.
However, through the combined use of accelerometers andgyrosensors, the states of the links and robot fingers can be
accurately learned, even when the links are flexible, making it
possible to produce much lighter robots. Therefore, a newchallenge facing R&D in robotics is to maintain the sensitivity ofexisting MEMS accelerometers and to reduce drift in gyrosensors.
Environmental AwarenessMeasurements using light are effective in robots, automobiles,
and personal mobility vehicles for detecting the state of objects
in the vicinity. Currently laser rangefinders are being used todetermine the distance to an object by emitting a laser pulse
and measuring the time that the pulse takes to reflect off thetarget and return. However, in order for laser rangefinders togain popularity, they must come down in both size and price.

Vietnamese Exchange Students and Japan’sAging Society
There are three Vietnamese students working in ourlaboratory, and all of them are excellent at their work. In fact,
all three had papers selected for presentation at theinternational conference MEMS 2011, which will be held inCancun, Mexico in January this year.
According to The University of Tokyo Guidebook, thenumber of foreign students accepted at the University of Tokyoin 2010 accounted for 250 of the total 14,172 undergraduate
students and 2,084 of the total 13,820 graduate students, andthe numbers increase each year. After graduating from highschool in Vietnam, the three students in my lab passed theentrance examination for the University of Tokyo and enteredthe undergraduate program as international students sponsoredby the Japanese government. All three continued on tograduate school and are now enthusiastically conducting
research in our lab.
Students in countries of East Asia and Southeast Asia receivea rich education in fundamental subjects, such as mathematics
and physics. This has proven to be an advantage for theVietnamese students, even after entering the University of Tokyo.
Further, there are no barriers to the wealth of information onthe Internet for students who have no problems with the English
language. Using information available over the Internet gives
these students a capacity to perform advanced simulations thatappears to surpass that of the average Japanese student at theUniversity of Tokyo.
The ability to attract capable young people with such
enthusiasm from overseas may benefit Japan, for which thedeclining birthrate and proportion of elderly in the population is
expected to increase, as they may play an important role inhelping to reform our social system and to improve its efficiency
through science and technology. Because Japan’s declining
birthrate and aging population is advancing faster than the restof the world, I believe that it is the country best-suited toproposing and popularizing new lifestyles.

As illustrated in the above examples, MEMS excels at adding
new functionality, improving the performance of existing devices,and making things smaller, lighter, and less expensive, andMEMS devices are indispensible for operating machines in thesame settings as humans. When listening to the Year-end GrandSong Festival on New Year’s Eve, I heard the group AKB48 singa song that included the lyrics “Are we dreaming?” and “Don’t
open someone else’s map” and thought that I would like topursue the dream in the former and the originality in the latter
while researching MEMS devices in 2011.

The Role of MEMS Devices in Our Coexistencewith Machines and Robots
In order to maintain our international competitive edge
despite our aging society, we will have to make efficient use of
our environment, resources, and labor force, and optimize traffic
logistics, for example. Collaborative work among people andindustrial robots is increasing at factories, and the popularizationof service robots and household robots, not necessarily humanoid
in form, has begun to appear a reality. As was reported in anarticle in the Mainichi Shimbun on January 2, 2011 entitled“2010 Traffic Death Toll at 4,863, with Half Aged 65 andAbove,” safety is a vital issue in taking measures to produce anefficient transportation system for our aging society. Yet thisproblem applies to the younger generation as well as the elderly.
MEMS devices serve as a core technology for improving thereliability and safety of machines that coexist with humans.
These devices can accurately detect the circumstances at pointsof contact between machines and humans and the surrounding
environment. With a low volume of information, it is difficult toremove all uncertainty, even with intelligent processing of theinformation. However, if the quantity and quality of information
is improved using MEMS devices to acquire more data, safety
and reliability of machines can be improved.
Here, I will describe some concrete uses for MEMS devices.

Contact with seat andbackrest good=>OK to accelerate or rotate

Grip on armrest: 3N=>Relaxed=>Speed appropriate
Sample measurement of pressuredistribution on footrest

Slippery surface conditions(e.g., puddle or manhole)

Message for user!!! Caution !!!

Bump/slope
Cross sectionof tireTires may slip if speed isincreased.

MEMS triaxial tactile sensors(with vertically embedded
piezoresistive cantilevers formeasuring shear stress)
Cantilever for
shear yMeasured data
X-axis(front-back):30N
Y-axis(left-right):7N
Z-axis(up-down):240N=> Coefficient of friction: 0.125

Beam fornormalstress

Road surfaceFigure2Cantilever for
shear xNumerical targets
Size: 2x2x0.8 mmSensor resolution: 0.5% of output at rated load
Load capacity: 200 kPa (normal stress) and50 kPa (shear stress)