JPH07210167A - Acoustic filter - Google Patents

Abstract

(57) [Summary] [Object] To provide an acoustic filter which, when incorporated into an electronic device, simplifies and downsizes a circuit configuration, has a small number of manufacturing steps, and is inexpensive and capable of reducing current consumption. [Structure] Air pressure inlet 1a and narrow groove 1b for forming a thin tube
And a recess for forming the air tank 1c, and the air inlet 1
Filter body 1 in which a narrow groove and a recess communicate with a in series
And is laminated on this filter body 1, and with the narrow groove and the concave portion,
The packing 2 forming the thin tube 1b and the tank 1c, the plate 3 laminated on the upper surface of the packing 2 for pressing the packing 2 against the filter body 1, and the air pressure output from the tank 1c to the outside of the tank 1c. The outlet 2a is provided so as to project toward the outside.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic filter for removing pressure noise generated during pressurization of an air pump used in, for example, an electronic blood pressure monitor.

[0002]

2. Description of the Related Art In an electronic blood pressure monitor, an air pump is often used to pressurize a cuff. When pressurizing with this air pump, inconvenient pressure noise is generated in measurement based on characteristics of the motor other than static pressure and pulse wave. In order to remove this pressure noise, conventionally, in order to attenuate the frequency band where pressure noise exists, an active filter composed of circuit elements such as resistors and capacitors and an operational amplifier has been used.

[0003]

In the conventional method of removing the pressure noise using the active filter described above, the electronic circuit becomes complicated. Since the number of electronic components is large, the circuit board size is large. Therefore, the case where the circuit board is housed becomes large. The number of mounting steps on the circuit board increases. The number of inspection steps after mounting the circuit board increases. The current consumption of the circuit is large. As a result, the product becomes expensive and
There is a problem that the life of the battery is shortened when the circuit is driven by the battery.

The present invention was made in view of the above problems, and when incorporated in an electronic device such as an electronic sphygmomanometer, the circuit structure for removing noise is simplified and downsized, and the number of manufacturing steps is reduced. It is an object of the present invention to provide an acoustic filter that is small in number, inexpensive, and can reduce current consumption of a circuit.

[0005]

The acoustic filter of the present invention is provided with an air pressure inlet, a narrow groove for forming a narrow tube, and a recess for forming an air tank, and the air inlet has a narrow groove and a recess. A filter body that communicates in series, and a packing that is laminated on the filter body and that forms the narrow tube and the tank with the narrow groove and the recess, and is stacked on the upper surface of the packing, and presses the packing onto the filter body. In order to output air pressure from the plate and the tank to the outside,
And an outlet projecting outward from the tank.

If the inlet of this acoustic filter is connected to a pressure system of a cuff by a pump, for example, and a pressure sensor is joined to the outlet, it is assumed that the air pressure input to the inlet from the pump contains pressure noise. Pressure noise is removed in the constructed filter portion, and only the measured pressure is input to the outlet, that is, the pressure sensor. Therefore, an active filter circuit for removing the pressure noise is not required in the subsequent stage of the pressure sensor. Therefore, the electronic components that form the active filter are not necessary, the circuit board is also small, the case for housing the same is downsized, and the man-hours for mounting and inspecting the parts are reduced. Of course, the current consumption of the electronic circuit is also small.

[0007]

The present invention will be described in more detail with reference to the following examples. 1 to 3 show an acoustic filter according to an embodiment of the present invention, FIG. 1 is an external perspective view of the acoustic filter, FIG. 2 is a longitudinal sectional view taken along line AA in FIG.
FIG. 3 is a cross-sectional view taken along the line BB of FIG.

The acoustic filter of this embodiment comprises a filter body 1, a packing 2, a plate 3 and a screw 4. The filter body 1 has a rectangular shape in a plan view, has an inclined bottom surface, and is made of resin. However, a metal may be used as the constituent material instead of the resin. The shape is not limited to that shown in FIG. A tubular input 1a is provided on one side of the filter main body 1, and a thin tube 1 is provided inside the filter main body 1 and communicates with the inlet 1a in series.
b, a tank 1c, a thin tube 1d, and a tank 1e are formed. Both of the thin tubes 1b and 1d are formed by repeatedly bending and are made to have a large length in a narrow area.

The thin tubes 1b and 1d are formed in a groove having an open upper portion when the filter body 1 is resin-formed, and the tank 1
Similarly, c and 1e are formed in a vacant chamber with an open top when resin is formed. The packing 2 is made of an elastic material such as silicon, and is laminated on the upper surface of the filter body 1 to cover the groove and the empty chamber of the filter body 1, and the thin tubes 1b and 1b.
d and the tanks 1c and 1e are formed. Also, packing 2
Is integrally provided with a cylindrical outlet 2a that opens outward from the tank 1e. Since the outlet 2a is also made of the same elastic material as the packing material, such as silicon rubber, the pressure sensor can be directly and easily joined to the outlet 2a.

A plate 3 made of resin or metal is further laminated on the upper surface of the packing 2, and the plate 3 is fastened and fixed to the filter body 1 with screws 4. In the configuration of the above acoustic filter, in the thin tube and the tank, if the length of the thin tube 1b is l ₁ and the length of the thin tube 1d is l ₂ ,
When the relationship of l ₁ <l ₂ is set, the two tubes have different DC impedances, and the capacity of the tank 1 c is V ₁ and the capacity of the tank 1 e is V ₂ , V ₁ >
The relationship is set to V ₂ . An electrical equivalent circuit of this acoustic filter is shown in FIG. 4, where the resistance R ₁ is the resistance of the thin tube 1b and the resistance R ₂ is the resistance of the thin tube 1d, which are proportional to the length of the thin tube. . On the other hand, the capacitor C ₁ is the electrostatic capacity of the tank 1c, and the capacitor C ₂
Is the electrostatic capacity of the tank 1e, and these are proportional to the capacity of the tank.

In the apparatus of this embodiment, the thin tube 1b and the tank 1 are
The time constant R ₁ · C _{1 of} c and the time constants R ₂ · C ₂ of the thin tube 1d and the tank 1e are set to be equal so that the filter characteristic becomes steep. The transfer function of the above equivalent circuit is shown by the following equation,

[0012]

[Equation 1]

The inlet 1a (inlet of air containing pressure noise) corresponds to IN of this equivalent circuit, and the outlet 2a (outlet of air in which pressure noise is attenuated) corresponds to Out. That is, air containing pressure noise from the cuff is input to the inlet 1a, the pressure noise is removed by the filter action by the acoustic filter of the embodiment, and the removed air is added to the pressure sensor from the outlet 2a.

In the above embodiment, the inlet 1a is
The outlet 2a is provided on the side surface of the filter body 1, and the outlet 2a is formed integrally with the packing 2. However, as shown in FIG. 5, the inlet 2b is formed in the packing 2 in the same manner as the outlet 2a, and further the inlet 2b is formed. In the vicinity, a connection port 2c for connecting an exhaust valve,
The connection port 2d for connecting the pump may be formed integrally with the packing 2. In this case, in the filter body, a tank communicating with the inlet 2b for cuff connection and the connection port 2c for pump connection is formed in the filter body 1, and the air passage from the pump to the cuff is formed large. in this way,
By providing the packing 2 with the connection ports 2b, 2c, 2d, it becomes easy to connect the pump, the cuff, and the exhaust valve. Also,
In the above-described embodiment, the outlet 2a is projected on the upper surface, but the outlet 2a may be provided on the side portion of the filter body 1 as with the inlet 1a. In this way, a flat filter can be constructed, and it is convenient to store in a device.

FIG. 6 is a sectional view showing an example of connecting a pressure sensor to the acoustic filter of the embodiment. Here, the pressure sensor 12 is mounted on the circuit board 11, and the pressure detection circuit portion including the pressure sensor 12 is surrounded by the shield case 13. Further, a through hole 14 is formed at a position corresponding to the pressure receiving portion of the pressure sensor 12 of the circuit board 11, and the outlet 2a of the acoustic filter is inserted into the hole 14.
The pressure receiving portion of the pressure sensor 12 is directly attached to the outlet 2a of the acoustic filter. By doing so, the exit 2a
A rubber tube or the like for connecting the pressure sensor 12 and the pressure sensor 12 is not necessary.

7 to 9 show another embodiment of the acoustic filter of the present invention, FIG. 7 is an external perspective view of the acoustic filter, and FIG. 8 is a vertical sectional view taken along line A--A of FIG. FIG. 9 is a cross-sectional view taken along the line BB of FIG. This embodiment acoustic filter is obtained by adding adjusting screws 5 and 6 to the configuration of the acoustic filter shown in FIGS. 1 to 3. The heads of the adjusting screws 5 and 6 are exposed to the outside of the filter body 1, and the tips of the adjusting screws 5 and 6 project into the tank 1c and the tank 1e, respectively. When the heads of the adjusting screws 5 and 6 are rotated by a screwdriver or the like, the lengths of the portions protruding into the tanks 1c and 1e change. When the length from the tip of the adjusting screws 5 and 6 to one end of the tanks 1c and 1e changes, the capacity of the tanks 1c and 1e changes as a result, and thus the impedance of the filter unit can be made variable. , The frequency characteristics of the filter can be changed. Since this adjustment is mainly performed in the manufacturing stage, after the adjustment, the screw parts are hardened with an adhesive so that the space between the adjusting screws 5 and 6 and the filter body 1 is kept airtight, or the adjusting screws 5 and 6 are fixed. Wrap an airtight tape beforehand.

FIGS. 10 to 12 show an acoustic filter according to still another embodiment of the present invention, FIG. 10 is an external perspective view of the acoustic filter, FIG. 11 is a vertical sectional view taken along line A--A, and FIG. FIG. 12 is a cross-sectional view taken along the line BB of FIG. 11. The acoustic filter of this embodiment is provided with a height adjusting boss 7 in addition to the configuration of the acoustic filter shown in FIGS. Then, the height adjusting boss 7 and the plate 3 are made of metal. The height adjustment boss 7 is a cylindrical body into which the screw 4 can be inserted, and has a screw portion on the outside. Further, the plate 3 has a screw portion formed in a hole 3a for inserting the screw 4. When the threaded portion of the plate 3 and the threaded portion of the height adjusting screw are combined and the height adjusting boss 7 is rotated, the adjusting boss advances toward the plate 3 or exits in the opposite direction. If the screw 4 is tightened with respect to the plate 3 with the height adjusting boss 7 retracted, the plate 3 is strongly pressed against the packing 2 before the lower end of the height adjusting boss 7 hits the filter body 1, and the packing 3 Reference numeral 2 narrows the thin tubes 1b and 1d due to the pressing force. Narrowing means reducing the cross-sectional area of the thin tubes 1b and 1d.
This will increase the resistance of the filter section. On the contrary, when the height adjusting boss 7 is advanced to the plate 3, by tightening the screw 4, the head of the screw 4 moves to the position of the height adjusting boss while a large pressing force is not applied to the plate 3. When it hits the upper end, the screw 4 does not move any further. Therefore, since the packing 2 is not pressed so much, the thin tubes 1b and 1d are not sandwiched, and therefore the cross-sectional area of the thin tubes is relatively large and the resistance of the filter portion is small accordingly. in this way,
By adjusting the advancing / retreating state of the height adjusting boss 7 with respect to the plate 3, the impedance of the filter can be made variable. Therefore, by adjusting the height adjusting boss 7, the frequency characteristic of the filter can be made appropriate. .

[0018]

According to the present invention, since an acoustic filter is composed of a thin tube and a tank and pressure noise can be removed, an electronic circuit forming the filter becomes unnecessary, and therefore, when incorporated in an electronic device. , The electronic circuit becomes simple. The number of electronic components is reduced and the circuit board size is reduced. The case for housing the circuit board is small.
The number of mounting steps on the circuit board is reduced. The number of inspection steps after mounting the circuit board is reduced. The current consumption of the circuit is reduced, and the battery life can be extended when a battery is used as the power source.

[Brief description of drawings]

FIG. 1 is an external perspective view of an acoustic filter showing an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view of the acoustic filter of the example taken along the line AA in FIG.

FIG. 3 is a cross-sectional view of the acoustic filter of the example taken along the line BB in FIG.

FIG. 4 is a circuit diagram showing an equivalent circuit of the acoustic filter of the example.

FIG. 5 is an external perspective view showing a packing used in an acoustic filter according to another embodiment of the present invention.

FIG. 6 is a cross-sectional view showing an example of connecting a pressure sensor to the acoustic filter of the embodiment.

FIG. 7 is an external perspective view of an acoustic filter showing another embodiment of the present invention.

8 is a longitudinal sectional view of the acoustic filter of the example taken along the line AA in FIG.

9 is a cross-sectional view of the acoustic filter of the example taken along the line BB in FIG.

FIG. 10 is an external perspective view of an acoustic filter showing still another embodiment of the present invention.

11 is a longitudinal sectional view of the acoustic filter of the example taken along the line AA in FIG.

FIG. 12 is a cross-sectional view of the acoustic filter of the example taken along the line BB of FIG. 11.

[Explanation of symbols]

 1 Filter Main Body 1a Inlet 1b, 1d Capillary 1e, 1d Tank 2 Packing 2a Outlet 3 Plate

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shinsaku Yanagi 24 Yamanouchi Yamanoshitamachi, Ukyo-ku, Kyoto City Omron Life Science Research Institute Co., Ltd.

Claims (12)

[Claims] 1. A filter body having an air pressure inlet, a narrow groove for forming a thin tube, and a recess for forming an air tank, wherein the air inlet is connected to the narrow groove and the recess in series, and a filter body is laminated on the filter body. A packing for forming a thin tube and a tank by the narrow groove and the recess, a plate laminated on the upper surface of the packing for pressing the packing to the filter body, and for outputting air pressure from the tank to the outside. And an outlet projecting from the tank toward the outside, the acoustic filter. 2. The acoustic filter according to claim 1, wherein the outlet is integrally formed with the packing. 3. The acoustic filter according to claim 1 or 2, wherein a plurality of air pressure inlets and outlets that are commonly communicated with the thin tube are integrally formed with the packing. 4. The acoustic filter according to claim 2 or 3, wherein a pressure sensor is directly coupled to an outlet projecting from the tank to the outside and integrally formed with the packing. 5. The acoustic filter according to claim 1, wherein the air pressure inlet and the air pressure outlet are provided on a side portion of a filter body. 6. The claim 1, claim 2, claim 3, claim 4, wherein the thin tube is formed in a repeating bent and folded shape.
Alternatively, the acoustic filter according to claim 5. 7. A primary filter composed of a pair of a thin tube and a tank, two or more primary filters being connected in series, and the DC resistance component of the primary filters in stages is made larger than the above. The acoustic filter according to claim 2, claim 3, claim 4, claim 5, or claim 6. 8. The acoustic filter according to claim 7, wherein the time constants of the two or more first-order filters are set to be substantially the same. 9. The cutoff frequency is made variable by adjusting the cross-sectional area of the thin tube or the capacity of the tank. The acoustic filter according to claim 6, claim 7, or claim 8. 10. The acoustic filter according to claim 9, wherein the tank is provided with a member that can be taken in and out from the outside to adjust the capacity in the tank. 11. The acoustic filter according to claim 9, wherein the capacity of the tank and the cross-sectional area of the thin tube are adjusted by making the amount of biting of the packing into the thin tube and the tank variable. 12. The acoustic filter according to claim 11, wherein the plate is provided with a height adjusting boss.