JPH0435694B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an object detection device that detects the amount of powder, liquid, etc. using a piezoelectric vibrator.

In general, this type of object detection device has a piezoelectric vibrator disposed at the bottom of a container containing an object to be detected such as powder or liquid, and when the object to be detected comes into contact with the piezoelectric vibrator, the piezoelectric vibrator is activated. Object detection is performed by utilizing the change in the oscillation state of the piezoelectric vibrator due to the application of pressing force due to bulk and density.

By the way, conventional object detection devices have a self-excited oscillation circuit configured to oscillate at the fundamental resonance frequency unique to the piezoelectric vibrator, and when there is an object to be detected, the resonance impedance of the piezoelectric vibrator changes and the oscillation cannot be sustained. Object detection is known from the fact that the piezoelectric vibrator stops, but oscillation can easily stop due to external factors such as the mounting position of the piezoelectric vibrator, the tightening pressure, and distortion of the support that supports the piezoelectric vibrator. The operation was extremely unstable. Another disadvantage was that it was difficult to set the detection sensitivity and variations were likely to occur.

The present invention eliminates the above-mentioned drawbacks and enables the piezoelectric vibrator to operate at at least one of the resonance frequencies of the piezoelectric vibrator and the support supporting the piezoelectric vibrator, which exist in a frequency range exceeding the fundamental resonance frequency of the piezoelectric vibrator itself. By driving the object detection device, the object detection device has stable detection operation, easy setting of detection sensitivity, and good responsiveness.

Embodiments of the object detection device according to the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a mounting structure for a piezoelectric vibrator in an embodiment of the object detection device of the present invention. In this figure, a cylindrical protruding support body 2 is integrally formed at the bottom of a container 1 for storing powder P, etc., and the peripheral part of a piezoelectric vibrator 3 is directly connected to the upper end surface of this support body 2. The support is fixed.

As shown in FIGS. 2 and 3, the piezoelectric vibrator 3 is
A disk-shaped piezoelectric ceramic 11 is attached onto a disk-shaped diaphragm 10 made of a thin non-magnetic metal plate such as copper or aluminum, and electrodes 12A and 12B are formed on this piezoelectric ceramic 11. Here, diaphragm 10
functions as a common electrode facing each electrode 12A, 12B, and the diaphragm 10 and each electrode 12
A and 12B have lead wires 13A for electrical connection.
13C to 13C are connected. In use, such a piezoelectric vibrator 3 contacts the contents in the container 1 at the diaphragm 10, and the piezoelectric device 1
1 and electrodes 12A, 12B are designed so that they do not come into direct contact with the contents, and the diaphragm 10 normally
The thickness is set to about 30 to 500μ.

The material of the cylindrical support body 2 is the same as that of the container 1, such as a heat-resistant noryl resin that does not emit chlorine gas. Furthermore, when the diameter of the piezoelectric vibrator 3 is 20 mm, the outer diameter of the cylindrical support body 2 is also 20 mm, and the height of the support body 2 is 2.2 mm so as not to adversely affect the bending vibration of the piezoelectric vibrator. The thickness was 0.5 mm to 2.2 mm.

On the other hand, FIG. 4 is a reference example of the electrical configuration of the object detection device according to the present invention, and is for explaining the principle circuit operation. In this figure, the transistor oscillation circuit 20 has the piezoelectric vibrator 3 inserted into a feedback circuit, and an oscillation coil T is provided on the collector side of the transistor Q ₁ , and a resistor R ₁ is provided on the base of the transistor Q ₁ . , _R2 provides base bias, and a variable resistor for gain adjustment is connected between the emitter of transistor _Q1 and ground.
VR is inserted. A capacitor _C1 is connected in parallel to the primary winding _N1 of the oscillation coil T to form a parallel resonant circuit, and the DC voltage supplied to the power supply terminal 21 via this parallel resonant circuit is applied to the collector of the transistor _Q1 . is applied to Oscillation coil T
One end of the secondary winding N ₂ is grounded, and the other end is connected to one electrode of the piezoelectric vibrator 3 (electrode 12 in FIG.
A). The other electrode of the piezoelectric vibrator 3 (electrode 12B in FIG. 3) is a transistor Q ₁
connected to the base of

What is important about the transistor oscillation circuit 20 is that the piezoelectric vibrator 3 is not driven at its own fundamental resonance frequency, but the piezoelectric vibrator 3 and the support 2 are driven at a frequency that far exceeds this fundamental resonance frequency. This means that the piezoelectric vibrator 3 is driven at at least one of the resonance frequencies of the combined structure. Therefore, the primary side resonance frequency of the oscillation coil T is also set to the frequency that actually drives the piezoelectric vibrator 3.

Figure 5 shows the fundamental resonance frequency ₀ when a piezoelectric vibrator 3 with a diameter of 20 mm is used, and the piezoelectric vibrator 3 is connected to the support 2 (outer diameter 20 mm, wall thickness 0.5 mm,
Resonant frequencies ₁ and ₂ due to the combination structure of both when mounted at a height of 2.2 mm) and piezoelectric vibrator 3
The relationship between the thickness and vibration frequency ₃ was obtained through experiments. As you can see from this figure, the fundamental resonant frequency
Assuming that ₀ is around 2500Hz, the resonance frequency of the combined structure of piezoelectric vibrator and support _{is 1} , ₂
is around 60kHz or 120kHz, which is much higher than ₀ . Furthermore, the thickness vibration frequency ₃ is much higher than those, around 4MHz.

In this example, the resonance frequency ₁ or
₂ drives the piezoelectric vibrator 3, and the piezoelectric vibrator 3 at this time functions as an electroacoustic transducer for supplying vibration energy to the vibrating body consisting of the piezoelectric vibrator 3 and the support body 2. is working.

Now, the output of the transistor oscillation circuit 20 in Fig. 4 is connected to the capacitor from the collector of the transistor _Q1 .
It is taken out via _C2 , rectified by diodes _D1 and _D2 , smoothed by capacitor _C3 , and then added to the base of transistor _Q2 . A resistor _R3 is connected between the base and emitter of this transistor _Q2 , and a resistor _R4 is connected between the collector of the transistor _Q2 and the base of the transistor _Q2 .
Furthermore, the collector of transistor Q ₃ and the power terminal 2
A lamp 23 as a display element is inserted between the power supply line 22 connected to Further, the power supply line 22 is grounded through a capacitor _C4 . In the reference example shown in FIG. 4 above, if the amount of powder P in the first container 1 is sufficient, a pressing force due to the bulk and density of this powder P will be applied to the piezoelectric vibrator 3. The impedance of the transistor oscillation circuit 20 changes, and the oscillation conditions at the preset frequency ₁ or ₂ are not satisfied, and the transistor oscillation circuit 20 does not oscillate. Therefore, transistor Q ₂ is off, transistor Q ₃ is also off, and lamp 23 does not light up. On the other hand, container 1
When the amount of powder P in the piezoelectric vibrator 3 and the support body _becomes less than a certain value or _completely disappears, the transistor oscillation circuit 20
oscillates. This oscillation output is connected to diodes D ₁ and D ₂
Since the current is rectified by and applied to the base of the transistor Q ₂ , the transistor Q ₂ is turned on, and therefore the transistor Q ₃ is also turned on, and the lamp 23 is lit. The lighting of this lamp 23 indicates the necessity of replenishing the powder P.

As described above, by using the piezoelectric vibrator mounting structure shown in FIG. 1 and the circuit configuration of the reference example shown in FIG. 4, the following effects can be achieved.

(1) When using the fundamental resonance frequency of the piezoelectric vibrator 3 itself as in the past, it is necessary to reduce the acoustic coupling between the piezoelectric vibrator 3 and the support 2 as much as possible. Although the piezoelectric vibrator is bonded to the support 2 with elastic resin, etc., it is impossible to eliminate the bond between the piezoelectric vibrator and the support or container. However, in the case of the reference examples shown in Figures 1 and 4, it causes instability in operation due to external factors such as tightening pressure when installing it on equipment and strain on the support side.
Since the piezoelectric vibrator 3 and the cylindrical support 2 to which it is attached are driven at the resonance frequency when viewed as one vibrating body, the piezoelectric vibrator 3 can be directly fixed to the support 2, and the piezoelectric It is possible to prevent variations in the mounting conditions of the vibrator 3, reduce variations in detection sensitivity, and improve reliability.

(2) The detection sensitivity, that is, the setting of how much feedback is required to cause oscillation, is determined by the transistor
Any state can be determined depending on the bias depth or gain of _Q1 . For example, the detection sensitivity can be variably set by changing the variable resistor VR inserted into the emitter of the transistor _Q1 .

FIG. 6 shows another reference example for explaining the principle of circuit operation. In this case, a two-terminal piezoelectric vibrator 3A
The transistor oscillation circuit 20A is constructed using the following. In other words, a resistor is connected in series with the piezoelectric vibrator 3A.
_R5 is inserted, and the feedback voltage generated at _R5 is applied to the base of transistor _Q1 via capacitor _C5 . The oscillation output of the transistor oscillation circuit 20A is taken out from the emitter side of the transistor _Q1 via the capacitor _C2 . Note that the other circuit configurations are the same as in the case of FIG. 4.

According to the reference example shown in FIG. 6 above, a two-terminal piezoelectric vibrator 3A can be used, and since the oscillation output is taken out from the emitter side of the low impedance transistor _Q1 , the transistor connected to the transistor oscillation circuit 20A It has the advantage of being less susceptible to fluctuations due to circuits using Q ₂ , Q ₃ , etc.

By the way, in the reference example circuits shown in FIGS. 4 and 6 above, the transistor oscillation circuit continuously oscillates during the detection operation, so it consumes a lot of power and is uneconomical. In some cases, there is a problem that the oscillated high frequency waves may interfere with other circuit parts. Therefore, in the present invention, the oscillation circuit is configured to oscillate only during the arrival period of the external trigger pulse, thereby reducing power consumption and preventing interference with other circuits.

FIG. 7 shows a circuit configuration of an embodiment of the present invention. In this figure, a transistor oscillation circuit 20
B is a transistor Q ₁ , an oscillation coil T, a piezoelectric vibrator 3, a capacitor C ₁ , a variable resistor VR, and a resistor
_R6 , it does not have a self-bias circuit and can only oscillate when an external trigger pulse as a base bias is applied to the trigger terminal TG. The oscillation output of the transistor oscillation circuit 20B is applied to the flip-flop FF as a state holding circuit via the capacitor C ₂ and the diodes D ₃ and D ₄ to set the flip-flop FF.
It is assumed that the flip-flop FF maintains the output terminal 30 at a high level voltage when a positive input pulse arrives.

In the configuration of the above embodiment, the trigger terminal TG
If a high-speed pulse with a pulse width of several tens of microseconds is supplied like a sampling pulse at a rapid repetition period, the object to be detected can be detected digitally at high speed. For example, even if the object to be detected is in a non-contact state with the piezoelectric vibrator 3 for only a very short period of time, the short-term oscillation operation of the transistor oscillation circuit 20B is maintained by the flip-flop FF, so that the non-contact state is maintained. can be detected.

Further, in FIG. 7, other digital circuits may be connected in place of the flip-flop.
For example, a shift register or a counter may be provided in place of the flip-flop so that a predetermined signal appears at the output terminal when the frequency of oscillation of the transistor oscillation circuit exceeds a predetermined number of times.

Furthermore, as shown in FIG. 8, a piezoelectric vibrator having a configuration in which a piezoelectric ceramic 11A having a diameter considerably smaller than that of the diaphragm 10A is attached to the diaphragm 10A may be used.

As described above, according to the present invention, the piezoelectric vibrator can be connected to the piezoelectric vibrator at the resonant frequency of the combination structure of the piezoelectric vibrator and the support that supports it, which exists in a frequency range exceeding the fundamental frequency of the piezoelectric vibrator itself. The piezoelectric vibrator can be fixed directly to the support, which eliminates variations in the mounting conditions of the piezoelectric vibrator, stabilizes the detection operation, and improves the detection sensitivity. It is possible to obtain an object detection device that is easy to set up and has good adaptability. Furthermore, since the detection operation is executed only when the trigger pulse arrives, the power consumption of the transistor oscillation circuit can be reduced.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a piezoelectric vibrator mounting structure in an embodiment of an object detection device according to the present invention, FIG. 2 is a front view of the piezoelectric vibrator in the embodiment, and FIG. 3 is a bottom view of the same, and FIG. Fig. 4 is a circuit diagram showing the electrical configuration of the reference example, Fig. 5 is a graph for explaining the operation of the reference example, Fig. 6 is a circuit diagram showing another reference example, and Fig. 7 is an implementation of the present invention. Schematic in example,
FIG. 8 is a plan view showing another specific example of the piezoelectric vibrator. DESCRIPTION OF SYMBOLS 1... Container, 2... Support, 3... Piezoelectric vibrator, 10
...Diaphragm, 11...Piezoelectric ceramic, 20, 20
A, 20B...Transistor oscillation circuit, 23...Lamp, _C1 to _C5 ...Capacitor, _R1 to _R6 ...Resistor,
_D1 to _D4 ...diode, _Q1 to _Q3 ...transistor, T...oscillator coil, FF...flip-flop.

Claims (1)

[Claims] 1. An object in which a piezoelectric vibrator is attached to a container containing an object to be detected, and the piezoelectric vibrator is driven by a transistor oscillation circuit in which the piezoelectric vibrator is inserted into a feedback circuit, and changes in the oscillation state of the piezoelectric vibrator are utilized. In the detection device, the transistor oscillation circuit is configured to oscillate only during the arrival period of an external trigger pulse, a support body projecting in a cylindrical shape with respect to the container is integrally formed, and the piezoelectric vibrator is configured to include a piezoelectric element and a disc-shaped diaphragm. The periphery of the piezoelectric vibrator is directly supported and fixed by the support so that the diaphragm contacts the object to be detected, and the vibration frequency far exceeds the fundamental resonance frequency of the piezoelectric vibrator itself. At least one of the resonant frequencies of the combined structure of the piezoelectric vibrator and the support body existing in the frequency range
An object detection device characterized in that, in one step, the piezoelectric vibrator is driven.