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The MEMS Flow Sensor -- Created by a system that surpassed departments to allow full cooperation
A centrifugal separation structure overcomes a weakness for dust
  • -- How is a MEMS Flow Sensor different from other types?
  • Flow Path Development・Ueda
    D6F-W MEMS Flow Sensor
  • Ueda:
    The D6F-W MEMS Flow Sensor was developed in response to a customer's request for a type that could be built into a projector. Whereas other Flow Sensors use only clean air, this one had to use ordinary air containing dust particles. This was the biggest difference.

    The MEMS Flow Sensor actually has a weakness when it comes to dust, which made it necessary to remove the dust and send only clean air to the chip when using ordinary air.
  • When we tried to use the usual kind of dust trap (See Figure 8), which works on gravity, we discovered that the accumulation of dust narrowed the flow path and impaired the measurement accuracy. We then tried mounting the chip in the opposite direction, but this caused the dust to adhere to the chip. It was clear that this type of dust trap wasn't suited to use in a projector, which has to be installable in various directions.

    We were then faced with the need to develop a new dust-removal method that would not be affected by gravity.
  • A dust trap that uses the force of gravity
    Fig.8 A dust trap that uses the force of gravity
  • -- How did you eventually remove the dust?
  • Original, 3D flow path structure
    Fig.9
    Original, 3D flow path structure
  • Ueda:
    We came up with the idea of using an original, 3D flow path structure that would separate and discharge the dust by using centrifugal and inertial forces. (See Figure 9.)

    The advantages of this method are that the dust gets discharged instead of accumulating inside the Sensor, and even if some of the dust does accumulate, it is not allowed to flow into the detection path regardless of the installation direction.
  • Airflow inside the centrifugal separation chamber
  • As you can see in Figure 10, the air flows in a cyclone manner inside the centrifugal separation chamber. The centrifugal force of the cyclone separates the dust and sends it in the direction of the outer wall regardless of whether the chamber is installed facing up, down, left, or right. Even if dust accumulates, this structure uses gravitational force to ensure that the dust does not flow into the detection path.

    Nozoe:
    I'm actually the one who suggested the possibility of using centrifugal separation for the dust, but I never imagined we'd end up using two centrifugal separation chambers (laugh).

    Sasaki:
    To tell the truth, I thought the original request would be out of the question (laugh), but I've got to say that the level of perfection in the end result is incredible considering the small packaging size and the simple, easy-to-build-in structure.
  • -- I heard that you used simulations for the flow design.
  • Flow analysis simulation
  • We took full advantage of simulations for designing the flow path and analyzing the flow of dust, but it was difficult to simulate actual dust conditions in a way that our customers would find realistic and convincing.

    So we ran a number of simulations of the dust particles that JIS standards stipulate for actual tests, and found that dust particles with a diameter of about 2 to 4 microns represent the harshest condition for the flow velocity range of this Sensor. Backed by this information, we ran actual verification tests using dust particles of this size.

    It helped us greatly to narrow down the necessary conditions by using simulations. This kept the actual tests, which are extremely time-consuming, to a minimum and helped us to show optimal data to our customers, which in turn speeded up the development process.
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