JP2011190733A - Ultrasonic standing wave-driven micropump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic wave pump having an extremely simple structure, a free choice of driving liquid, and a novel constitution easily achieving microminiaturization. <P>SOLUTION: In this ultrasonic wave pump, an ultrasonic standing wave having intensity exceeding a microcavitation generation threshold is formed in liquid by using a means for radiating ultrasonic wave within a KHz band, the introducing port of a discharge pipe having an inside diameter sufficiently smaller than the wavelength of the ultrasonic wave in the liquid is set at the position of the maximum pressure variation point of the standing wave, and the liquid is continuously pumped up from the introducing port of the discharge pipe to a discharge port. The pump includes: a vessel 2; the means 3 for radiating the ultrasonic wave within the KHz band, formed on the bottom surface of the vessel; the outflow port 4b of a suction pipe, passed through the wall of the vessel and formed in a position close to the bottom of the liquid in the vessel; and the discharge pipe 5 inserted from the upper surface of the vessel to the position of the maximum pressure variation point so as to be opposed to the means for radiating the ultrasonic wave, and having the inside diameter sufficiently smaller than the wavelength of the ultrasonic wave. The pump is operated with the height of a space in the vessel being equal to the half wavelength of the ultrasonic wave in the liquid and the vessel filled with the liquid. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultrasonic standing wave drive valveless micro pump.

  Common requirements for micropumps used in fields such as machinery, chemistry, and biotechnology include ultra-miniaturization, high precision, quietness, and long life, regardless of the driving liquid.

  Conventional electromagnetic and centrifugal pumps are not suitable for miniaturization. Diaphragm-type piezoelectric pumps require a check valve, so that wear and vibration of the movable part becomes a problem. Diaphragm type valveless micropumps (Patent Document 1) using asymmetry of the flow in the suction flow path and discharge flow path and traveling wave valveless micropumps using a piezoelectric actuator (Non-Patent Document 1) have been proposed. The structure and control are complicated. EHD type micro pumps are limited in the types of fluids that can be used, and the flow rate or maximum discharge pressure is extremely small, making them less practical.

  In Patent Documents 2 and 3, an ultrasonic wave that causes a liquid to flow out of a discharge port by providing a suction port and a discharge port in a container filled with a liquid, facing the discharge port, and radiating ultrasonic waves from an ultrasonic radiation means. A pump has been proposed. In any case, a device has been devised that uses ultrasonic waves in the MHz band and focuses the ultrasonic waves toward the discharge port. However, there is no description about the range of various parameters such as the diameter of the discharge port, the distance from the ultrasonic radiation means to the discharge port, the maximum discharge pressure and flow rate obtained by the pump, and the performance as a pump cannot be judged. . Actually, if the above parameters are different, the pumping mechanism of the ultrasonic pump is completely different, but there is no explanation about it.

  On the other hand, the phenomenon that liquid is sucked up by ultrasonically vibrating a tube immersed in the liquid has been known for a long time, and an ultrasonic pump (Non-patent Document 2) using this phenomenon has been developed. However, the examined pipes are limited to those with an inner diameter of about 3 mm, and the discharge pressure in that case is about 1 KPa. If a flat plate is placed at the end of the tube and a gap of about 10 μm is provided, the discharge pressure can be increased several times.However, high accuracy is required for assembly, and if clogging due to impurities occurs, the treatment is difficult. is there.

Japanese Patent Laid-Open No. 10-110681 JP-A-55-005464 JP 2007-187095 A

Takaaki Suzuki, 4 other authors, Development of traveling wave type valveless micro pump using piezoelectric actuator, Journal of AEM Society of Japan, Vol. 13, No. 4, 2005, pp. 310-315. Takeshi Hasegawa, research on miniaturization and performance improvement of ultrasonic pumps, master's thesis in 2004, Graduate School of Science and Engineering, Tokyo Institute of Technology.

  Provided is an ultrasonic micropump having a novel structure that has an extremely simple structure, can be used in any driving liquid, can be easily miniaturized, and can have a long service life.

  The present invention uses an ultrasonic radiation means in the KHz band to form an ultrasonic standing wave having an intensity exceeding the microcavitation generation threshold in a liquid, and at the maximum pressure fluctuation point of the standing wave, an ultrasonic wave is generated. The main feature is that an inlet of a discharge pipe having an inner diameter sufficiently smaller than the wavelength of the nozzle is installed, and liquid is continuously pumped from the inlet of the discharge pipe to the outlet of the discharge pipe.

  It is possible to provide an ultrasonic pump that has an extremely simple structure, does not have a movable part other than minute vibrations by ultrasonic waves, and can be easily miniaturized.

It is sectional drawing of the ultrasonic pump of 1st Embodiment of this invention. It is a related figure of the discharge pipe internal diameter and maximum discharge pressure of the ultrasonic pump of a 1st embodiment of the present invention. It is sectional drawing of the ultrasonic pump of 2nd Embodiment of this invention. It is sectional drawing of the discharge pipe of this invention. It is sectional drawing of the discharge pipe as another modification. It is sectional drawing of the discharge pipe as another modification. It is sectional drawing of the discharge pipe as another modification. It is sectional drawing of an integrated discharge pipe.

  FIG. 1 shows a cross-sectional view of the ultrasonic pump according to the first embodiment of the present invention. The ultrasonic pump 1a includes a container 2, an ultrasonic radiation means 3 in the KHz band formed on the bottom surface of the container, a suction pipe 4 penetrating the lateral wall of the container and attached to a position close to the bottom surface, and an upper surface of the container. The discharge pipe 5 is configured so that the inner diameter (d) inserted to the ultrasonic pressure radiation means to the maximum pressure fluctuation point does not exceed 1/20 of the wavelength (λ) of the ultrasonic wave in the liquid. This pump is made so that the height from the bottom surface to the top surface of the inner wall of the container is equal to or slightly larger than the half wavelength (λ / 2) of ultrasonic waves in liquid, and the liquid is removed from the bottom surface of the container. It is operated in a state filled up to the height of the wavelength (λ / 2).

  The displacement node of the ultrasonic standing wave in the liquid is theoretically located at a distance of 1/4 wavelength (λ / 4) in the ultrasonic radiation direction from the oscillation wall surface. In the displacement section of the ultrasonic standing wave in liquid, the pressure fluctuation becomes the maximum. When the output of the ultrasonic radiation means is increased above a certain level, microcavitation occurs intermittently around the maximum pressure fluctuation point. When the discharge pipe is inserted at that position, microcavitation is periodically generated at the tip of the discharge pipe, and the resulting cluster-like microbubbles approach or leave the inlet of the discharge pipe. The tip of the discharge pipe is also excited by pressure fluctuations due to ultrasonic waves and microcavitation. In the negative half cycle, the maximum negative pressure is limited by the effect of microcavitation. On the other hand, there is no such limitation in the positive half cycle. As a result, a certain amount of fluid is pushed into the inlet 5a at the tip of the discharge pipe in one cycle of pressure fluctuation. When the inner diameter of the discharge pipe is sufficiently smaller than the wavelength of the ultrasonic wave, the pressure fluctuation is efficiently converted into a flow in a direction along the flow path in the discharge pipe. In fact, when the discharge pipe is installed, the pipe and the ultrasonic wave in the liquid interfere with each other, and the maximum pressure fluctuation point changes. In the present invention, the point at which the tip of the discharge pipe is excited most intensely is regarded as the maximum pressure fluctuation point. From the above, the liquid is continuously sent from the introduction port 5a of the discharge pipe to the discharge port 5b. The maximum discharge pressure can be obtained when the ultrasonic standing wave in the liquid to be formed is 1/4 wavelength or an integral multiple of 1/4 wavelength.

  FIG. 2 shows the relationship between the inner diameter of the discharge pipe and the maximum discharge pressure when an ultrasonic radiation means of 42 KHz is used as an example of the configuration of FIG. It was confirmed that when the inner diameter of the discharge pipe was 1 mm or less, the maximum discharge pressure increased in inverse proportion to the inner diameter of the discharge pipe and reached several KPa. The estimated flow rate was about 6 ml / min. As for the waveform of the applied voltage, a higher discharge pressure and flow rate were obtained for the square wave than for the sine wave.

  FIG. 3 shows a cross-sectional view of the ultrasonic pump 1b of the second embodiment. The height from the bottom surface to the top surface of the inner wall of the container 2 is equal to a quarter wavelength of the ultrasonic wave in liquid, and the inlet 5a of the discharge pipe is installed on the upper surface of the container inner wall so as to face the ultrasonic radiation means 3. It is characterized by.

  The inlet 5a of the discharge pipe is processed into any shape shown in FIGS. 4 and 5, each has a shape in which the tip of the tube is cut from a cone or a hemisphere from the inside. 6 and 7, the tip of the tube is processed into a plane that is oblique or perpendicular to the central axis of the tube. When a discharge pipe having a relatively large inner diameter is used, the shape shown in FIGS. 4 and 5 can maintain a more positive pressure, and a higher discharge pressure can be obtained compared to other shapes. The shape of FIG. 7 has a drawback that the maximum discharge pressure becomes unstable. As the inner diameter of the discharge pipe becomes smaller, the above difference is almost eliminated. FIG. 8 shows an example of the structure of the collecting tube for increasing the flow rate.

DESCRIPTION OF SYMBOLS 1 Ultrasonic standing wave drive micro pump 2 Container 3 Ultrasonic radiation means of KHz band 4 Suction pipe 4a Suction pipe inlet 4b Suction pipe outlet 5 Discharge pipe 5a Discharge pipe inlet 5b Discharge pipe outlet

Claims (5)

  Using ultrasonic radiation means in the KHz band, an ultrasonic standing wave having a strength exceeding the microcavitation generation threshold is formed in the liquid, and the inner diameter is liquid at the position of the maximum pressure fluctuation point of this standing wave. A pump characterized by installing a discharge pipe inlet that does not exceed 1/20 of the wavelength of medium ultrasonic waves, and continuously pumping liquid from the discharge pipe inlet to the outlet. The maximum pressure fluctuation point is theoretically located at 1/4 wavelength and an odd multiple of 1/4 wavelength in the ultrasonic radiation direction from the oscillation wall surface. In the present invention, the tip of the discharge pipe is excited most intensely. Take it as a position.   The container, the ultrasonic radiation means in the KHz band formed on the bottom surface of the container, the suction port installed near the bottom of the liquid inside the container through the wall of the container, and the ultrasonic radiation means from the top surface of the container However, it has a discharge pipe inlet that has an inner diameter set at the position of the maximum pressure fluctuation point and does not exceed 1/20 of the wavelength of ultrasonic waves in liquid, and the height of the inner space of the container is 1/4 wavelength of ultrasonic waves in liquid or A pump that is equal to an integral multiple of a quarter wavelength and is operated in a state where the inside of the container is filled with a liquid.   3. The pump according to claim 1, wherein the ultrasonic radiation means includes amplitude changing means for changing the amplitude of the standing wave, or the waveform of the applied voltage is any one of a sine wave, a square wave, and a triangular wave. A pump characterized by being.   4. The pump according to claim 1, wherein the discharge pipe corresponds to any of the following shapes. The inlet of the discharge pipe is formed by cutting a cone or a hemisphere from the inside. This is a shape in which the inlet of the discharge pipe is machined into a plane that is oblique or perpendicular to the central axis of the pipe. The discharge pipe is constituted by collecting a plurality of pipes whose inner diameter does not exceed 1/20 of the wavelength of ultrasonic waves in liquid. The flow passage section of the discharge pipe is simply changed from a circular shape to an ellipse or a rectangle.   5. The pump according to claim 2, wherein the direction from the bottom surface to the top surface is changed to a horizontal or arbitrary angle.