JPH07210167

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DESCRIPTION JPH07210167
[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,
for example, in an electronic blood pressure monitor.
[0002]
2. Description of the Related Art Electronic blood pressure monitors often use an air pump to
pressurize a cuff. In addition to static pressure and pulse waves, when pressure is applied by this
air pump, inconvenient pressure noise is generated in measurements due to motor characteristics
and the like. In order to remove the pressure noise, conventionally, in order to attenuate the
frequency band where the pressure noise exists, an active filter composed of circuit elements
such as a resistor and a capacitor and an operational amplifier has been used.
[0003]
SUMMARY OF THE INVENTION In the method of removing pressure noise using the abovedescribed conventional active filter, the electronic circuit becomes complicated. Since the number
of electronic components is large, the circuit board size is large. Therefore, the case for housing
the circuit board is large. The number of mounting steps on the circuit board increases. The
number of inspection steps after circuit board mounting increases. The current consumption of
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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.
[0004]
The present invention has been made focusing on the above problems, and when incorporated in
an electronic device such as an electronic blood pressure monitor, the circuit configuration for
noise removal is simplified and miniaturized, the number of manufacturing steps is small, and
inexpensive. It is an object of the present invention to provide an acoustic filter that can reduce
the current consumption of the circuit.
[0005]
The acoustic filter according to the present invention is provided with an air pressure inlet,
narrow grooves for forming a thin tube, and a recess for forming an air tank, and the air inlet has
narrow grooves and a recess. A filter main body in series communication, and a packing which is
stacked on the filter main body and which forms a thin tube and a tank by the narrow groove and
the concave portion, and is stacked on the upper surface of the packing and pressing the packing
against the filter main body A plate and an outlet projecting outward from the tank are
characteristically provided to output air pressure from the tank to the outside.
[0006]
If the inlet of this acoustic filter is connected to the pressure system of the cuff by a pump, for
example, and a pressure sensor is attached to the outlet, pressure noise will be included in the air
pressure input from the pump to the inlet. In the filter part, pressure noise is removed and only
the measured pressure is input to the outlet, ie the pressure sensor.
Therefore, an active filter circuit for removing pressure noise is not required downstream of the
pressure sensor.
Therefore, the electronic component which comprises an active filter is also unnecessary, and
also a circuit board becomes small, the case which encloses it also becomes small, and the
mounting man-hour of components and an inspection man-hour decrease. Of course, the current
consumption of the electronic circuit also decreases.
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[0007]
The present invention will be described in more detail by way of 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 cut along line A-A of
FIG. It is a cross-sectional view cut ¦ disconnected by line B-B of FIG.
[0008]
The acoustic filter of this embodiment comprises a filter body 1, a packing 2, a plate 3 and a
screw 4. The filter main body 1 has a rectangular shape in a plan view, a bottom surface of which
is inclined, and is formed of resin. Of course, the component material may be metal instead of
resin. The shape may not particularly be as shown in FIG. A tubular input 1a is provided on one
side of the filter main body 1, and a thin tube 1b, a tank 1c, a thin tube 1d, and a tank 1e are
formed in the inside in series communication with the inlet 1a. Both of the thin tubes 1b and 1d
are formed in a repeated bending manner so that the length can be increased in a narrow region.
[0009]
The thin tubes 1b and 1d are formed in the grooves opened at the upper part when forming the
resin of the filter body 1, and the tanks 1c and 1e are formed in the empty chamber the upper
part opened at the same time when forming the resin. . The packing 2 is made of an elastic
material such as silicon, and is stacked on the upper surface of the filter body 1 to cover the
grooves and spaces of the filter body 1 to form the thin tubes 1b and 1d and the tanks 1c and 1e.
In addition, the packing 2 integrally has a cylindrical outlet 2a that opens outward from the tank
1e. Since the outlet 2a is also an elastic material such as silicone rubber, which is the same as the
packing material, the pressure sensor can be easily directly joined to the outlet 2a.
[0010]
A plate 3 made of resin or metal is further stacked on the upper surface of the packing 2, and the
plate 3 is tightened and fixed to the filter body 1 with a screw 4. In the configuration of the
acoustic filter, when the length of the thin tube 1b is l1 and the length of the thin tube 1d is l2 in
the configuration of the thin film and the tank, the direct current impedances of both thin tubes
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are different by setting l1 <l2. Assuming that the capacity of the tank 1c is V1 and the capacity of
the tank 1e is V2, the relationship of V1> V2 is established. This acoustic filter is shown in FIG. 4
as an electrical equivalent circuit, where the resistance R1 is that of the capillary 1b, the
resistance R2 is that of the capillary 1d, and these are proportional to the length of the capillary.
On the other hand, the capacitor C1 is the electrostatic capacity of the tank 1c, and the capacitor
C2 is the electrostatic capacity of the tank 1e, which are in proportion to the capacity of the tank.
[0011]
In this embodiment, the time constants R1 and C1 of the thin tube 1b and the tank 1c, and the
time constants R2 and C2 of the thin tube 1d and the tank 1e are set equal to make the filter
characteristics steep. The transfer function of the above equivalent circuit is given by
[0013]
An inlet 1a (inlet of air containing pressure noise) corresponds to IN in the equivalent circuit, and
an outlet 2a (outlet of air whose 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 in the acoustic filter of the embodiment, and the removed air is applied to the
pressure sensor from the outlet 2a.
[0014]
In the above embodiment, the inlet 1a is provided on the side surface of the filter body 1 and the
outlet 2a is integrally formed on the packing 2. However, as shown in FIG. 5, the inlet 2b is
similar to the outlet 2a. Further, the packing 2 may be formed integrally with the packing 2 in
the vicinity of the inlet 2 b, a connection port 2 c for connecting an exhaust valve, and a
connection port 2 d for connecting a pump. In this case, the filter body forms in the filter body 1
a tank communicating with the inlet 2 b for cuff connection and the connection port 2 c for
pump connection, and the air passage from the pump to the cuff is formed large. Thus, by
providing the connection ports 2b, 2c and 2d in the packing 2, the connection of the pump, the
cuff and the exhaust valve is facilitated. Moreover, although the outlet 2a is projected on the
upper surface in the said Example, you may provide the outlet 2a in the side part of the filter
main body 1 similarly to the inlet 1a. In this way, a flat filter can be configured, which is
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convenient for storage in the device.
[0015]
FIG. 6 is a cross-sectional view showing an example of connecting a pressure sensor to the
embodiment acoustic filter. Here, the pressure sensor 12 is mounted on the circuit board 11, and
the pressure detection circuit unit 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, the outlet 2a of the acoustic
filter is inserted through the hole 14, and the pressure receiving portion of the pressure sensor
12 is at the outlet 2a of the acoustic filter It is fixed. By doing this, a rubber pipe or the like
connecting the outlet 2a and the pressure sensor 12 becomes unnecessary.
[0016]
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, FIG. 8 is a longitudinal sectional view cut along
the line A-A of FIG. It is a cross-sectional view cut ¦ disconnected by line B-B of FIG. The acoustic
filter of this embodiment is in addition to the configuration of the acoustic filter shown in FIGS. 1
to 3 and further provided with adjusting screws 5 and 6. The head of each of the adjusting
screws 5 and 6 is out of the filter body 1, and the end of the adjusting screw 5 protrudes into the
tank 1 c and the adjusting screw 6 protrudes into the tank 1 e. When the heads of the adjusting
screws 5 and 6 are rotated by a screwdriver or the like, the length of the portion projecting into
the tanks 1 c and 1 e changes. 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 this makes it possible to make the impedance of the filter section variable. , Can change the
frequency characteristics of the filter. Since this adjustment is mainly performed at the
manufacturing stage, the screw is hardened with an adhesive or the adjustment screws 5, 6 are
maintained so that the space between the adjustment screws 5, 6 and the filter main body 1 is
kept airtight after the adjustment. Pre-wrap an airtight tape.
[0017]
10 to 12 show still another embodiment of the present invention, and FIG. 10 is an external
perspective view of the same acoustic filter, FIG. 11 is a longitudinal sectional view cut along line
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A-A, and FIG. B is a cross-sectional view taken along the line B-B. The acoustic filter of this
embodiment is in addition to the configuration of the acoustic filter shown in FIGS. 1 to 3 and is
provided with a height adjustment boss 7. Then, the height adjustment 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 the hole 3 a for inserting the screw 4. When the screw portion of the plate 3 and the screw
portion of the height adjusting screw are aligned and the height adjusting boss 7 is rotated, the
adjusting boss advances or retreats with respect to the plate 3. If the screw 4 is tightened with
the height adjustment boss 7 retracted to the plate 3, the plate 3 will be pressed strongly against
the packing 2 before the lower end of the height adjustment boss 7 hits the filter body 1. 2
narrows the thin tubes 1b and 1d by pressure. The narrowing is to reduce the cross-sectional
area of the thin tubes 1b and 1d, and the resistance of the filter portion is increased accordingly.
Conversely, if height adjustment boss 7 is advanced to plate 3, the head of screw 4 is the height
adjustment boss while the large pressing force is not applied to plate 3 by tightening screw 4.
The upper end is hit and the screw 4 does not advance any further. Therefore, since the packing
2 is not compressed so much, it can not sandwich the thin tubes 1b and 1d, so the cross-sectional
area of the thin tube is relatively large, and the resistance of the filter portion is small
accordingly. Thus, by adjusting the advancing / retracting state of the height adjusting boss 7
with respect to the plate 3, the impedance of the filter can be varied, and accordingly, by
adjusting the height adjusting boss 7, the frequency characteristic of the filter can be made
appropriate. can do.
[0018]
According to the present invention, since the acoustic filter can be constituted by the capillary
tube and the tank and pressure noise can be eliminated, the electronic circuit constituting the
filter becomes unnecessary, and accordingly, when it is incorporated in the electronic device ,
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 becomes smaller. The
number of mounting steps on the circuit board is reduced. The number of inspection steps after
circuit board mounting is reduced. The current consumption of the circuit is reduced, and the
battery life can be extended when the battery is used as a power supply.
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