JPH0110585Y2 - - Google Patents

Description

[Detailed explanation of the idea]

INDUSTRIAL APPLICATION FIELD The present invention relates to a powder detector. One field of application of the powder detector according to the present invention is, for example, detection of the concentration or level of carrier or toner in a developer material in an electronic copying machine. Prior Art In copying machines, when the mixing ratio of toner to carrier in the developer material decreases, the density of the developed image becomes thinner, and when the mixing ratio increases, the density of the image becomes too high and fog increases. occurs. Therefore, in order to continuously obtain images of appropriate color tone, it is necessary to detect the toner concentration in the developing material and maintain the concentration at an appropriate constant level. Conventional powder detectors for detecting toner concentration utilize the fact that the volume of the developer material, which is a mixture of carrier and toner, changes depending on the toner concentration, and detects the level change due to the volume change into a light emitting element and a light receiving element. Therefore, a configuration in which optical detection is performed is known. Another conventional example is one that uses the fact that the mixed color changes due to the difference in the mixing ratio of toners and detects this optically, and one that detects this optically. There is also a known method that takes advantage of this change and detects a change in magnetic permeability of a developing material as a change in coil inductance or a change in induced voltage. However, in the case of a photoelectric toner concentration sensor, toner and other dust adheres to the surface of the photoelectric element or light receiving element, and the detection level changes depending on the adhesion state. It is difficult to maintain constant measurement conditions and measurement accuracy due to fluctuations in the surface level. Similar drawbacks exist in methods that optically detect changes in the mixed color due to differences in the mixing ratio of toners. Additionally, methods that detect changes in magnetic permeability of the developer material as changes in coil inductance or changes in induced voltage have the disadvantage of low detection sensitivity and poor measurement accuracy because the rate of change in coil inductance relative to changes in toner concentration is small. There is. In order to eliminate the above drawbacks of the prior art, a powder detector has recently been proposed in which a piezoelectric vibrator is bonded to one side of a diaphragm, and the other side of the diaphragm is used as a contact surface with powder. There is. This powder detector changes the vibration characteristics of a diaphragm that vibrates together with a piezoelectric vibrator in accordance with the specific gravity of powder such as developer material that comes into contact with the vibrating surface, and detects the developer material from the change in vibration characteristics. This device detects the concentration of the detected powder contained in powder such as toner, for example, the concentration of toner. Detection can be performed with high precision under constant measurement conditions without being affected by level fluctuations caused by magnet rollers, etc. FIG. 1 is a front cross-sectional view of a conventional piezoelectric vibrator-type powder sensor, in which a piezoelectric vibrator 1 is bonded to one surface 201 of a disk-shaped diaphragm 2, and this metal diaphragm 2 is The structure is such that the other surface 202 side is brought into contact with the powder. The periphery of the diaphragm 2 is supported by a case 3 made of a suitable material such as synthetic resin. The interior of the case 3 on the back side of the diaphragm 2 is an open space, the open end of which is closed by a printed circuit board 5 on which an oscillation circuit 4 is mounted. The powder detector described above supports the diaphragm 2 equipped with the piezoelectric vibrator 1 by the case 3, and
Since the oscillation circuit 4 that drives the piezoelectric vibrator 1 is built into the case 3, the manufacturer can inspect and evaluate the characteristics of the finished product, and provide the user with high quality and reliable powder detection. The number of parts and mounting area required for use by the user are small, and it is easy to integrate into high-density packaging equipment such as electrophotographic copying machines. The wiring up to the oscillation circuit 4 can be shortened, and there are advantages such as being able to reduce the influence of the wiring load on the vibration characteristics and the intrusion of noise into the wiring. Disadvantages of the Prior Art As mentioned above, the conventional piezoelectric powder detector has an open space inside the case 3 on the back side of the diaphragm 2, and the open end is connected to the printed circuit board 5 on which the oscillation circuit 4 is mounted. Since the structure is closed by the diaphragm 2, the resonant frequency of the cavity formed on the back side of the diaphragm 2 changes depending on how the circuit board 5 is fitted to the open end of the case 3, causing vibrations. There was a problem that the resonant frequency and impedance of the plate 2 changed. In addition, in the inspection process,
After evaluating the electrical characteristics as a sensor in the open state with the circuit board 5 removed, when the circuit board 5 is fitted and attached to the case 3 and assembled, the circuit board 5
Because the cavity resonance frequency differs before and after fitting and mounting, it has become difficult to accurately evaluate the vibration characteristics of the sensor. Purpose of the Present Invention Therefore, an object of the present invention is to provide a highly reliable piezoelectric powder detector that can keep the resonance frequency and impedance substantially constant even before and after the inspection process or assembly process. Structure of the Present Invention In order to achieve the above object, the present invention includes a diaphragm equipped with a piezoelectric vibrator, a case that supports the periphery of the diaphragm, and an oscillation device built in the case that drives the piezoelectric vibrator. In the powder detector comprising a circuit, the inside of the case is divided into upper and lower parts by a partition plate, an independent sealed space is provided on the back side of the diaphragm above the partition plate, and an independent sealed space is provided below the partition plate. The oscillation circuit is housed in a space. Embodiment FIG. 2 is a partial sectional view of a powder detector according to the present invention. In the figure, the same reference numerals as in FIG. 1 indicate the same components. In this embodiment, the inside of the case 3 is divided into two parts by a partition plate 31, and an independent sealed space 32 is provided on the back side of the diaphragm 2 above the partition plate 31.
It has a structure in which a space 33 for housing an oscillation circuit 4 mounted on a circuit board 5 is provided below the circuit board 1 . As described above, when the independent sealed space 32 is provided on the back side of the diaphragm 2, the cavity resonance on the back side of the diaphragm 2 is fixed to the cavity resonance frequency of the sealed space 32. Therefore, changes in the resonant frequency and impedance due to changes in the cavity resonant frequency are prevented. Moreover, since the cavity resonance frequency of the sealed space 32 is kept substantially constant regardless of the presence or absence of the circuit board 5,
The rate of change in resonance frequency and impedance before and after the inspection process and assembly process is significantly reduced. Table 1
2 shows experimental data on the rate of change in the resonant resistance or oscillation stop resistance before and after the circuit board 5 is mounted. When measuring resonance resistance, the third
As shown in the figure, the diaphragm 2 does not include the oscillation circuit 4.
The piezoelectric vibrator 1 attached to the was connected to an impedance analyzer 6, and its impedance frequency characteristics were measured. FIG. 4 is a diagram showing the impedance frequency characteristics in this case, where Ro is the resonant resistance.
Furthermore, as shown in Fig. 5, the oscillation stop resistance is the value of the resistance Rf when the oscillation circuit 4 is connected to the piezoelectric vibrator 1 to cause oscillation, and the resistance Rf is changed to stop the oscillation. . The resonance resistance and oscillation stop resistance were measured before and after the circuit board 5 was attached to the conventional powder detector shown in FIG. 1 and the powder detector of the present invention shown in FIG.

[Table] As is clear from Table 1, in the powder detector according to the present invention, the rate of change in the resonant resistance R before and after the circuit board 5 is attached is significantly smaller than that of the conventional product, and the resonant frequency It can be seen that this method has an excellent effect in keeping the impedance constant. Effects of the present invention As described above, according to the present invention, the following effects can be obtained. (a) Since the inside of the case is divided into upper and lower parts by a partition plate, and an independent sealed space is provided on the back side of the diaphragm above the partition plate, the resonant frequency and impedance can be maintained even before and after the inspection process or assembly process. It is possible to provide a piezoelectric powder detector that maintains a substantially constant temperature and is easy to inspect and assemble. (b) Since an independent sealed space is provided on the back side of the diaphragm above the partition plate, and the oscillation circuit that drives the piezoelectric vibrator is housed in the space below the partition plate, the manufacturer is able to control the characteristics of the finished product. It can be inspected and evaluated, and it is possible to supply high quality and highly reliable powder detectors to users. Moreover, when used on the user side, the number of parts and the mounting area required are small, and it can be used like an electrophotographic copier.
Easy to integrate into high-density mounting equipment. (c) An independent sealed space is provided on the back side of the diaphragm above the partition plate, and the oscillation circuit that drives the piezoelectric vibrator is housed in the space below the partition plate, so the distance between the piezoelectric vibrator and the oscillation circuit is The wiring can be short, and the influence of wiring load on vibration characteristics and noise intrusion into the wiring can be reduced.

[Brief explanation of the drawing]

Figure 1 is a partial sectional view of a conventional powder detector;
The figure is a partial cross-sectional view of the powder detector according to the present invention.
4 is a circuit diagram for measuring the resonance resistance, FIG. 4 is a circuit diagram for measuring the resonance characteristics, and FIG. 5 is a circuit diagram for measuring the oscillation stop resistance. 1... Piezoelectric vibrator, 2... Vibration plate, 3... Case, 5... Circuit board, 32... Closed space.

Claims (1)

[Scope of utility model registration request] In a powder detector comprising a diaphragm equipped with a piezoelectric vibrator, a case supporting the periphery of the diaphragm, and an oscillation circuit built in the case and driving the piezoelectric vibrator, the inside of the case is The powder is divided into upper and lower parts by a partition plate, an independent sealed space is provided on the back side of the diaphragm above the partition plate, and the oscillation circuit is housed in the space below the partition plate. Body detector.