Manufacturing products for space applications
together with mass produced goods
on the same line

Minebea Co., Ltd., began operations as a manufacturer specializing in bearings in 1951 under the name Nippon Miniature Bearing Co., Ltd. A proactive push to engage in mergers and acquisitions subsequently allowed the company to grow into a general precision manufacturer for which rotating equipment, electronic equipment, and other electric- and electronic-related products account for over half of overall sales.

Shinko Communication Industry Co., Ltd., a strain-measuring instruments manufacturer with which this company merged by absorption in 1981, constitutes the parent body of the Measuring Components Business Unit of this company. Presently, strain gauges, load cells, pressure sensors, torque sensors, and other types of measuring instruments to which this technology has been applied are produced at four different sites: the Fujisawa plant (in Fujisawa City, Kanagawa Prefecture) and Karuizawa plant (Miyotamachi in Nagano Prefecture) in Japan, the Lopburi plant in Thailand, and the Xicen plant in Shanghai, China.

Pressure sensors used in the field of space are made with strain gauges manufactured using SOS (silicon-on-sapphire) technology for high-precision measurements. In order to manufacture gauges at low cost, they are produced on the same line as that used to manufacture mass-produced articles without having to set up a dedicated line. The company’s sensors are currently employed to measure the pressure of liquid oxygen and liquid hydrogen tanks for the large H-IIA/B rocket, measure rocket combustion pressure, and to monitor the pressurizing components on HTV space station transfer vehicles.

Minebea’s Karuizawa plant, a site where pressure sensors for space are developed and manufactured, is also the parent plant for manufacturing sites scattered around the globe.

Manufactured with SOS (silicon-on-sapphire) technology, a strain gauge is built by integrating a semiconductor strain gauge onto a sapphire substrate.

A heat-treatment furnace for diffusing impurities on silicon has been set up in the clean room.

Metal pieces are welded together using an electron beam welder. A wired gauge is shown on the right.

The thickness of a strain gauge is measured. A margin of error of only 3 μm over or under the thickness of 400 μm is permitted.

Metal pieces are welded together using an electron beam welder. A wired gauge is shown on the right.

The resistance value of signal wires is measured.

The process is for fine-tuning resistance by combining chip resistance(left).
The final assembly step is completed by connecting a hybrid IC or connector and setting the cover in place(right).

Pressure sensors used with the LE-7A first-stage engine for the H-IIA/B rocket.(left)
For the final inspection step, the quality of the completed pressure sensors is carefully checked using inspection equipment for space use.(right)

MINEBEA

HQ Location Miyotamachi, Kitasaku-gun, Nagano
Established 1951
Employees 51,406 (consolidated; as of the end of March 2012)
Sales 251,358,000,000 yen (consolidated; fiscal year ended March 2012)
Main Facilities Fujisawa Plant (Fujisawa City, Kanagawa Prefecture)
Karuizawa Plant (Miyotamachi, Nagano Prefecture)
Lopburi Plant (Thailand)
Xicen Plant (Shanghai, China)
Main Products Load cells, pressure gauges, torque transducers, equipment for instrumentation, strain-measuring instruments, tension and compression testing equipment, and more
Main Astronautics Equipment Produced Pressure sensors for liquid oxygen and liquid hydrogen tanks for the H-IIA/B rocketPressure sensors for measuring combustion pressure for the LE-7A and LE-5B enginesPressure sensors embedded inside pressurizing carriers for HTV space station transfer vehicles
Corporate site http://www.minebea.co.jp/english/index.html

INTERVIEW

インタビュー

Taking on the challenges of an unfamilior field is essential for succeeding
in the world of manufacturing.

MINEBEA
Head pf the Measuring Components Business Unit, Electronic Equipment Manufacturing Division
Hideo Asagawa

--While precision bearings are famously known as products produced by Minebea, what sorts of products are developed and manufactured by the Measuring Components Business Unit of the Electronics Equipment Manufacturing Division?

The parent body of this business unit is a company known as Shinko Communication Industry Co., Ltd. In 1974, Shinko Communication Industry merged with Nippon Miniature Bearing Corporation (present-day Minebea) to become what is nowadays referred to as the Measuring Components Business Unit.
By adopting technologies from American companies, Shinko Communication Industry was engaged in manufacturing and selling strain gauges and compatible products. Even today, strain gauges, load cells, pressure sensors, torque sensors, and other types of measuring instruments to which this technology has been applied constitute the primary products of this business unit. The products are used in everything from automobiles to game equipment and more.

--What prompted you to make the foray into the field of space?

We had previously dealt with Mitsubishi Heavy Industries in the aerospace field. Our load cells and other products were used for test equipment designed to measure thrust in experiments on jet engines.
It was in this connection that we received a request from Mitsubishi Heavy Industries to help them develop a pressure sensor to be embedded in the large H-IIA rocket. This took place in 1996. One of our domestic rivals delivered pressure sensors for the H-II, the predecessor of the H-IIA. Perhaps the biggest reason for this request was the need to reduce costs. We were asked to develop highly reliable sensors at low cost. Of course, we welcomed this opportunity to expand the scope of applications for our products with open arms. We happily accepted this job and commenced full-scale development in January 1997.
In 2005, we also fielded an inquiry regarding pressure sensors for placement inside pressurizing carriers for HTV space station transfer vehicles and fundamentally worked on pressure sensors designed for use with the H-IIA.

--Was the first product you developed for space application as difficult as you had expected it would be?

This goes without saying given the high level of reliability that is demanded compared to mass-produced products. That said, we wouldn’t be meeting what is expected of us if costs were to increase no matter how effectively we might be able to create highly reliable pressure sensors.

Thus, rather than setting up a manufacturing line for making a single article at a time by hand with a focus on the field of space, we decided to produce pressure sensors for space using our conventional mass-production line. While using this line, we were able to achieve the requested level of reliability by properly overseeing personnel, equipment, and production processes. For us, this approach represents a highly significant piece of expertise.

Pressure sensors for space are built using semiconductors for which a silicon membrane has been deposited on top of a sapphire substrate according to what is known as the silicon-on-sapphire (SOS) technology. Compared to sensors made with metal, sapphire demonstrates a high linearity of response to pressure. For this reason, SOS is dramatically better in terms of accurate pressure detection. SOS is used often in different types of testing equipment where precision of 0.1% or less is required. It was thus decided that we would use SOS.

Most of the manufacturing processes share commonalities with processes for manufacturing private sector articles. However, the inspection process does involve a strict checking of durability against the variables of vibration and temperature in the inspection room for space applications. The fundamentals of quality control are more or less the same whether we are talking about products for automobiles or products for space. In the case of space, however, configuration management is something that is emphasized. For each part, such questions as what sub-components have been put together to constitute the given part, what materials have been used, and under what conditions the given part was produced are all tied together to allow people to track what needs to be tracked at a later date. For this reason alone, it is essential that everything be recorded.

--To what extent are pressure sensors being currently used with the H-IIA and HTV?

For rockets, they are being used not just with the H-IIA but also with the H-IIB. We are in charge of sensors for measuring the combustion pressure of H-IIA/B rockets and the pressure of liquid oxygen and liquid hydrogen tanks, as well as sensors for measuring the combustion pressure of the LE-7A stage 1 engine and LE-5B stage 2 engine. Since the pressure that is being measured will differ according to differences in the targets, the form may be the same but the pressure sensors in use will differ from one another. For the H-IIB rocket, 71 pressure sensors are used. For the HTV, three pressurizing monitors can be found in the pressurizing carrier.

--Are the development and production of products for space applications having any spillover effects on civilian (consumer) products?

The most important point concerning pressure sensors for space is the high level of reliability in the ability to present accurate values over an extended period of time. While you might be under the impression that it would suffice for pressure sensors used with rockets to operate accurately for just a dozen minutes or so around the time of the launch, testing must in fact be conducted over a prolonged period of time after pressure sensors are mounted onto a rocket engine. Only pressure sensors that have passed repeated reliability testing over an extended period of time finally make it to the rocket launch pad.

Our business unit is attempting to apply our approach to quality control obtained through the development of sensors for space applications to other products. Consequently, we are also contributing to quality improvements for other products. In addition, the motivation of our workers rises significantly. We celebrate together when we see rocket launches live. Indeed, since we even receive messages of congratulations from retired members, it is clear that the effect on the cohesiveness of our single-minded pursuit of our targets is something quite awesome to behold.

If a model of a rocket is lying around, we might sometimes pick it up and explain to others that our components can be found in this part of the real rocket. At such times, we might allow ourselves to be a bit proud of what we do. If Japanese rockets are launched more frequently, our contributions will no doubt help improve the level of manufacturing technology in this country.

--What does all this ultimately mean for your company from a business standpoint?

Unfortunately at this time, pressure sensors for space applications are not a product that is making huge contributions to the profits of our business unit. As can be seen in what transpired when we made our foray into the automotive sector, however, we expect to see the challenges we face in making pressure sensors for space lead to the sort of technological breakthroughs that we managed to achieve to date with a single-minded focus on strain gauges.

Unless one steps forth into a new field, the world will not change. If we were to only make the same things and do the same things all the time, there would be no opportunities open to us to expand into new businesses. Taking on the challenges of an unfamiliar field is essential for succeeding in the world of manufacturing and in the world of technology.

The kind of load cells we were making ten years ago is now being made by Chinese manufacturers. We will ultimately lose out to our competition unless we are also taking on new challenges and making new things. When we take on the challenges of a new field, there are no guarantees that results can be attained simply by committing a certain number of personnel and a certain amount of money to the endeavor.

Nevertheless, it is utterly essential that we continue to take up challenges if we are to have any hope of steering a course for future success.

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