Precision Engineering
from Keio's Faculty of Science and Technology Era of innovative
manufacturing ushered
in by intelligent technology

Aiming to create innovative machine tools with abilities comparable to humans

Associate Professor Yasuhiro Kakinuma specializes in precision engineering and the scope of his research is truly diverse and extensive. Using an interdisciplinary approach – sometimes taking advantage of knowledge from materials engineering and control engineering and from nanophotonics at other times – he has created a variety of innovative manufacturing technologies, which puts him in the spotlight. We asked him about his energetic research activities and achievements.

Dr. Kakinuma specializes in production engineering, centering on micro/nanomachining technology and development of machine elements. He currently tackles three pillars of research: ① development of machine elements based on electro-adhesive gels; ② development of intelligent machine tools that can “feel the applied force”; and ③ ultra-precision machining of hard-and-brittle materials and elastic polymers.
What characterizes his research activity is that in any project he challenges the development of unprecedented production engineering while introducing elements of other disciplines.
Take electro-adhesive gels, for example. These gels are based on “ElectroRheological (ER) fluids”, the viscosity of which changes by applying a voltage. A kind of functional fluid, ER fluids were discovered in the 1940s and their application development was energetically promoted in the 1990s mainly in the automotive industry.
“ER fluids are a functional fluid that changes viscosity when electricity is applied – like milk transforming into Bavarian cream and into cheese. In other words, it hardens by applying a voltage. As such, expectations are high for application of ER fluids in various industrial fields. But this fluid was not without problems: its effects decline as its particles precipitate and condense with a lapse of time; and as a fluid, it is hard to handle. In the early stage of my research, I aimed to develop an ER fluid-applied device. So I took one step further into the field of materials development, which was not my line though, in an attempt to make the ER fluid into a gel that is easier to handle. This attempt brought an unexpected result,” Dr. Kakinuma remarks.
One day, he mistakenly injected more than double the amount of a gelation material, which happened to produce an almost rubbery gel. He investigated the properties of this material and found to his surprise that its surface could take on adhesion when electricity was applied.
“Its image was like Scotch tape, the front surface of which has transformed into the reverse side due to electricity, so to speak. In this phenomenon, the adhesion was generated because micro particles, which had been dispersed in the silicone gel, condensed due to application of electricity. This in turn squeezed the gel inside out to the surface. Since this field was out of my line, I was conducting research with the cooperation of a chemical maker. As a non-specialist, I was not enmeshed by ready-made ideas, which eventually proved to be lucky for me,” he continues.
Taking advantage of electro-adhesive gels’ characteristic feature – the ability to fix things with adhesion simply by applying electricity – Dr. Kakinuma is now intent to develop its application: to the fixing of semiconductor silicon wafers during processing and transfer; to dampers for suppressing vibration; and to clutches and brakes of precision machinery.
He says, “I’m moving forward with application development of electroadhesive gels, making the most of my specialty, production engineering, by enhancing their adhesion by laminating and downsizing.”

With respect to the second pillar of research – development of intelligent machine tool that can “feel the applied force with no additional sensors” Dr. Kakinuma introduced knowledge from control engineering.
“This kind of machine is a system capable of observing servo information and controlling the machining force and torque freely without using sensors. The key to this system is the application of a “disturbance observer” (tasked with monitoring external loads) to the drive control system of a linear-motor-driven table. When there is a gap between the actual output and the theoretically available output for a given input, this technology allows us to estimate what external impact has been exerted.”
Intrinsically, a force sensor is required to directly measure an external force exerted on a machine. However, the disturbance observer can estimate the force applied. This is done based on an equation of motion and by using a positioning system incorporated in the machine tool, which reads the electric current flowing in the motor (input information) and output of motor speed or response position (output information). The disturbance observer thus allows dynamic processing loads to be estimated in real time – its main feature.
“As a general trend today, we see almost all machines and systems are equipped with sensors. However, sensors themselves are costly and maintenance costs inevitably increase due to shortened maintenance periods, which is another cost-raising factor. Therefore, “a sensorless mechanism” is a coveted requirement when it comes to machine tools and the like that are usually used for at least ten to twenty years. As such, sensorless process monitoring technologies are coming into focus of attention of the industry, which I’m striving to put into practical use within a few years.”
Based on the results of process monitoring, Dr. Kakinuma is also tackling the development of a technology that can control the processing force. He expects that the success of this development will make it possible to avoid “chatter vibration” – the so-called “hard-to-attain longtime challenge” in machining.
“Vibrations lead to defective products and machine malfunctions. Particularly problematic is self-excited vibration (a type of in-system vibration) that unexpectedly takes place when certain conditions are satisfied as a result of a machine tool’s dynamic characteristics and causes relating to its machining process. Occurrence of self-excited vibration is extremely difficult to predict; as of today, there is no effective way to prevent it. So I’m addressing this problem by using a disturbance observer to determine characteristics of such vibration in real time, the data from which I hope will provide the basis for a solution – control of a force. Some day in the future, I wish to create a machine that has human-like abilities in a true sense.”

Furthermore, in the field of ultraprecision machining of hard-and-brittle materials and elastic polymers, Dr. Kakinuma extended his scope of research to include analysis of phenomena peculiar to nanomachining. Based on this analysis, he is currently developing processing machines vitally needed in ultra-precision machining.
“When it comes to machining glass like a lens, it can break if you cut into the material in an ordinary way. However, a flawless, transparent lens can be produced if you use ultrasonic vibration or process it in the nano-range. I’m now in the process of analyzing this phenomenon. In this connection, I’m also working with young professor from the Department of Electronics and Electrical Engineering to develop an optical microresonator. The optical microresonator is designed to confine light, which travels at the light speed, in a certain place for a certain period of time. As such, it can become a device that will enable light-based signal processing” he points out.
With the current method of signal processing by means of electricity, energy loss due to Joule heat is unavoidable. Instead, if light-based signal processing becomes a reality, it will dramatically reduce such energy loss, leading to significant improvement of battery durability – our long-time headache. As you can see, Dr. Kakinuma’s research activity extends as far as nanophotonics, the frontier field of light control.
“I admit that interdisciplinary fusion involves hard challenges of learning unknown fields. On the other hand, by becoming versed in both machine and control technologies, it’s becoming possible to obtain heretofore unavailable research results. I’d like to continue to pursue innovative research that will benefit society,” he concludes enthusiastically

From kindergarten through senior high school, I was studying at Seijo Gakuen, a private educational institute adopting a consistent education system similar to Keio Gijuku. The education at Seijo Gakuen was unique; particularly its elementary school emphasized learning from nature and encouraged studying science and mathematics experientially, leading children to touch and feel actual objects. Not only did the school educate children through books, but also more importantly led them to have questions about things and think about “Why so?” For example, its curriculum included a unique two-hour-straight program known as “Stroll Time” – an opportunity for children to take plants and insects in their hands and learn from nature while strolling outside the school.
There were also art-oriented subjects such as painting, craft making, plastic art, audiovisual art and dramatic art. It seems that these curriculums together provided the foundation that helped nurture my interest in production engineering. In those days, at home I was absorbed in messing around with mechanical things, such as assembling/remodeling a radio-controlled model car.

No. My father was a university hospital doctor, whose back I had always being looking at. So it had been my dream, vague though, up to the junior high school days, to become a medical doctor like my father. Since Seijo University didn’t have a faculty of medicine, I had to take an entrance exam for a university with a faculty of medicine. In those days, the university I had in mind was a national university.
But I failed the national university entrance exams even after spending a gap year. So I decided to switch to the second choice – Keio University Faculty of Science and Technology. There were a couple of reasons for this choice: I liked to mess around with things mechanical since childhood, and physics was my favorite subject as a senior high school student. To tell the truth, I was not very much interested in biology, the imperative subject for medicine. Because of this, as a gap-year student I was really at a loss whether or not advancing to a faculty of medicine is the right way for me. The fact was I was beginning to find myself more attracted to science and technology. If I put it in terms of positive thinking, the failure in the national university entrance exams might have been the due course of my life after all. I can say this because I was eventually able to choose and follow the course of life most suitable for me.
Given my interest in interdisciplinary fusion studies, it was particularly the right decision that I chose the Department of System Design Engineering.

Well, I decided to enter into that career not only on my own initiative but also thanks to Prof. Aoyama’s advice. When I consulted with my parents on this matter for, they gave me their wholehearted support. More importantly, I myself was determined to follow the path of my own choosing. In this connection, Keio University made a decision to adopt me as a research assistant for the Department of System Design Engineering in 2005, the second year of my doctoral study. Adoption of a research assistant while he/she is still in the doctor’s course was a rarity, which renewed my motivation to emerge as the top-notch researcher in this field.
Also eager to meet the expectations of the people around me, I desperately devoted myself to studies and earned a doctor’s degree in two years. I was promoted in rapid succession to assistant professor in 2008 and to the current position as associate professor in 2011.
Incidentally, Prof. Aoyama was very generous. When I asked for his permission to join the seminar of Professor Kouhei Ohnishi (the authority of control technology) as the next step to materials study, he readily agreed. Back in those days (when I was a doctoral course student), I was lucky enough to meet Associate Professor Seiichiro Katsura (then a doctoral course student like myself), who was a member of the Ohnishi lab. Working with Dr. Katsura in a joint research project concerning accurate positioning for linear motor stage was a rewarding experience, which is still a great asset for me. It’s an interesting coincidence that both of us are now serving as associate professors at the Department of System Design Engineering (Laughter). I became well versed in both production engineering and control engineering thanks to the encounter with Dr. Katsura and having worked with him in a joint research, which is now my great strength as a researcher.

I have three children. I relax by viewing animations and playing with them. Having said that, my headache is that due to my busy research life I cannot afford sufficient time to be with my children, which both my wife and children always complain about. It may sound like an excuse, but I actually have a pile of things to do as a researcher, which interferes with my happy time with the family, you know (Laughter).

Student : Maybe because his age is close to ours, Dr. Kakinuma always takes good care of us, ready to give warm advice. What’s more, his advice looks ahead into the future and accurately indicates the course our research should follow, which is truly reassuring. All our lab members are very friendly with each other, so it’s no exaggeration that we come to the lab just because it’s a pleasant place to be in. No wonder we can devote ourselves to anything – in study or play.