JPH0136157Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an object detection device using a piezoelectric vibrator, and more particularly to an object detection device that detects the presence or absence of an object by utilizing changes in the resonance characteristics of a piezoelectric ceramic vibrator.

Devices that detect the presence of an object have been in practical use for a long time, using objects that block optical beams, and are suitable for detecting the presence or absence of toner (powder) used in plain paper copiers, for example. It is used in However, when such an optical method is used, if the object to be detected is a fluid, powder, granules, etc., the object cannot be detected satisfactorily.

In order to eliminate these drawbacks, the applicant has previously filed a patent application for an object detection device that uses a piezoelectric vibrator, for example, as an object detection device that operates stably regardless of the type of object to be detected. 54−021974
Disclosed in the issue. As shown in FIG. 1, this type of object detection device includes a piezoelectric ceramic assembly 1 in which a piezoelectric ceramic vibrator is adhered to a non-magnetic thin plate, and the piezoelectric ceramic assembly 1 is provided as shown in the figure. Lid body 2;
It has a base body 3 whose internal space is closed by the lid body 2. An oscillation circuit that utilizes the resonance characteristics of the piezoelectric vibrator is accommodated in the internal space of the base body 3, and the lid body 2 and the base body 3 are fixed at at least two places with, for example, bolts 4a and 4b.

The object detection device configured as described above detects various objects close to the lid 2 depending on the oscillation state of the oscillation circuit, but as shown in FIG. Due to the tightening force F,
The drawback was that the oscillation range of the oscillation circuit was extremely limited. In other words, Figure 2 shows the impedance of the piezoelectric ceramic in the object detection device configured as shown in Figure 1.
This is an actual measurement of the relationship between Zr (kΩ) and tightening force F (Kg). As is clear from the figure, the oscillation region of the oscillation circuit is affected by the tightening force and is limited to an extremely narrow range (1 kg or less) of the tightening force.

The present invention was developed based on this viewpoint, and its purpose is to provide an object detection device that stably detects objects without being affected by the tightening force between the base housing the piezoelectric ceramic and its lid. It's about doing.

To achieve this purpose, the object detection device of the present invention has a convex lid body having a cylindrical protrusion that protrudes outward from approximately the center of the object so as to be in contact with the object whose presence or absence is to be detected. and a flat piezoelectric device including a non-magnetic piezoelectric ceramic vibrator that converts electrical vibration into mechanical vibration and applies it to the object, and the piezoelectric ceramic vibrator is fixed to the tip of the protrusion. a porcelain assembly; a concave base that forms a closed space when fixed to the lid by fixing means formed around the porcelain assembly; and an oscillation circuit that generates the electrical vibration at a substantially predetermined frequency, and detects the presence of the object based on the resonance characteristics of the piezoelectric ceramic vibrator that changes depending on the presence or absence of the object to be detected. The device detects the presence and includes a vibration absorbing member made of a material having a mass greater than the mass of the material forming the lid body and bonded to the inner surface of the protrusion.

The lid body and the base body each have an engaging means that elastically engages with each other at a position between the fixing means formed on the peripheral portion and the center portion of the piezoelectric ceramic vibrator. good.

Further, the engaging means may be located between the piezoelectric ceramic assembly and the fixing means approximately symmetrically from the center of the piezoelectric timing vibrator.

Further, the engaging means on the lid side is a through hole, and the engaging means on the base side is a split pin having one end fixed to the base and the other end pressed against an inner wall of the through hole. Good too.

Embodiments of this invention will be described below with reference to the drawings.

FIG. 3 is a cross-sectional perspective view showing an embodiment of the object detection device according to the present invention, FIG. 4a is a configuration example of a piezoelectric ceramic assembly, and FIG. 4B is a configuration example of an oscillation circuit.

In the figure, reference number 10 is a lid made of plastic, for example, and the lid 10 has a cylindrical protrusion 11.
protrudes in a cylindrical shape from approximately the center of the lid 10 to the outside of the lid 10, and fixes a flat piezoelectric ceramic assembly 20 to the tip thereof approximately parallel to the surface of the lid 10. A bolt hole 12 for fixing to a base body 30, which will be described later, is formed in the portion. The bolt holes 12 are formed in at least two places in the lid body 10. In order to securely fix the lid 10 and the base 30, the lid 10 having the above structure is fixed to the base 30 with bolts or the like passing through the holes 12 and 31. A piezoelectric ceramic assembly 20 is fixed to the protrusion 11 by adhesive or other means so as to close the end face thereof.

The lid having the above structure is fixed to the base body 30 with bolts passing through the holes 12 and 31.

The piezoelectric ceramic assembly 20, as shown in FIG. 4a, has a piezoelectric ceramic 22 made of ceramic attached approximately at the center of a non-magnetic metal thin plate substrate (for example, copper or aluminum) 21. Electrode layers 23 and 24 are formed on the piezoelectric ceramic 22 by adhesion. Here, the non-magnetic metal thin plate substrate 21 functions as a common electrode of the piezoelectric ceramic 22 facing each electrode layer, and the non-magnetic metal thin plate substrate 21 and each electrode layer 23, 24 are provided with lead wires (25a
~25c) are connected to each other. Electrode layer 2
3 and 24 are circular and annular in shape, as shown in FIG. 4, in order to fit well with the inner surface shape of the protrusion 11, and are arranged so that the electrode 24 is surrounded by the electrode 23.

A ring-shaped vibration absorbing member 40 is provided on the protrusion 11.
is glued onto the inner surface of the protrusion 11. The vibrator absorbing member 40 has a mass larger than that of the plastic lid 10, and is made of a material having a large impedance against mechanical vibrations, such as metal. That is, the vibration absorbing member 40 is for absorbing the vibration of the piezoelectric ceramic 22 at the protruding part 11 without propagating the vibration from the protruding part 11 to the lid 10. is glued to.

In the internal space formed by the base body 30, a fourth
As shown in FIG. b, an oscillation circuit that utilizes the resonance characteristics of the piezoelectric ceramic 22 is accommodated. The oscillation circuit includes an amplifier A and a transistor that amplifies the output of the amplifier A.
Tr, an amplifier A, resistors R ₁ to _{R 5} connected to the transistor Tr, and a display device IND for displaying the output of the transistor Tr. An oscillation circuit is formed by connecting between them. Therefore, this oscillation circuit oscillates at a frequency approximately equal to the resonant frequency of the piezoelectric ceramic vibrator.

FIG. 5 shows the impedance characteristics of the piezoelectric ceramic vibrator. The horizontal axis of the figure shows the frequency, and the vertical axis shows the impedance of the piezoelectric ceramic. The resonance characteristics of the piezoelectric ceramic 22 show a sharp peak as shown by the solid line a in FIG. 5, the Q value of the piezoelectric ceramic 22 is lower than that of the piezoelectric ceramic 22 alone, and its characteristics become as shown by the dotted line b in FIG. Therefore, when the piezoelectric ceramic 22 is in a no-load state and has the characteristic a in FIG. 5, the oscillation circuit is enabled to oscillate. Further, in order to configure the object detection device, the constants of the resistors R ₁ to R ₅ are selected so that the oscillation circuit stops oscillating in the state shown in FIG. 5b where the contents contact the piezoelectric ceramic 22 as a load. . Thereby, the presence or absence of contents is detected through the oscillation state of the oscillation circuit. That is, the oscillation circuit stops oscillating when the contents are present, and oscillates when the contents are not present. The oscillation of the oscillation circuit is amplified by the transistor Tr and displayed by the display device IND. The display of the display device IND depends, for example, on the presence or absence of an audible, visual or electrical control signal, corresponding to the presence or absence of contents. Note that when the device is in use, the contents to be detected come into contact only with the piezoelectric ceramic assembly 20 made of a non-magnetic metal thin plate substrate, but non-sensing objects directly contact the electrode layers 23 and 24 inside the piezoelectric ceramic assembly 20. There will be no contact.

FIG. 6 shows experimental results showing the relationship between the impedance Zr (kΩ) of the piezoelectric ceramic configured in the above embodiment and the clamping force F (Kg). The characteristics of this example are shown by the solid line in the figure. As is clear from the figure, this configuration is not affected by the tightening force F between the lid 10 and the substrate 30, and satisfies the range in which oscillation is possible over a wide range. Note that the broken line in the figure is the measurement result of the conventional example shown in FIG.

7 and 8 are cross-sectional perspective views showing another embodiment of the object detection device according to the present invention. The feature is that, in addition to the configuration of the above-described embodiment, an engagement means is provided between the base body 30 and the lid body 10 using elastic uneven portions for vibration absorption. That is, the recess of the engaging means is the through hole 50b formed in the lid 10.
On the other hand, the convex portion is a split pin 50a formed on the base body 30. The engagement means may also be other elastically engaging concavities and convexities. This uneven portion is often formed between the piezoelectric ceramic assembly 20 and the fixed portion 12, and the uneven portion is located at symmetrical positions about the center point of the piezoelectric ceramic assembly 20, as shown in FIG. It is preferable to form at least one set. Note that the same reference numerals as in FIG. 3 indicate the same parts.

According to the above configuration, the vibration absorbing member 40
The vibrations that could not be absorbed by the base body 30 are further transmitted to the base body 30 via the above-mentioned elastic uneven portions, and are thereby absorbed.

Figure 9 shows the piezoelectric ceramic 2 with the above configuration.
2 impedance Zr (kΩ), base body 30 and lid body 1
This is the actual measurement of the relationship between the tightening force F (Kg) and the
B shows the measurement results according to this example. As is clear from the figure, according to this example, there is almost no change in Zr with respect to F, and it can be seen that the oscillation conditions are always satisfied.

As explained above, according to the present invention, it is possible to obtain an object detection device that stably detects the presence or absence of an object without being affected by the tightening force between the base and the lid. can be detected reliably.

[Brief explanation of the drawing]

Fig. 1 is an example of an object detection device, Fig. 2 is a diagram showing the relationship between impedance and tightening force in the configuration of Fig. 1, Fig. 3 is an example of an object detection device according to the present invention, and Fig. 4 a is an example of a piezoelectric ceramic assembly.
Fig. 4b is an example of an oscillation circuit, Fig. 5 is a diagram showing the impedance characteristics of piezoelectric ceramics, Fig. 6 is a diagram showing the relationship between impedance and tightening force in the configuration of Fig. 3, Figs. 7 and 8 9 is another embodiment of the object detection device according to the present invention, and FIG. 9 is a diagram showing the relationship between impedance and clamping force in the configurations of FIGS. 7 and 8. 10... Lid body, 11... Protrusion part, 12, 31... Hole,
20... Piezoelectric ceramic assembly, 30... Base, 50a... Cotter pin, 50b... Through hole.

Claims (1)

[Claims for Utility Model Registration] 1. A convex lid body having a cylindrical protrusion that protrudes outward from approximately the center thereof so as to be in contact with an object whose presence or absence is to be detected; a flat piezoelectric ceramic assembly including a non-magnetic piezoelectric ceramic vibrator that converts into mechanical vibration and applies it to the object, the piezoelectric ceramic vibrator being fixed to the tip of the protrusion; and fixing means. a concave base that forms a closed space when fixed to the lid, and an oscillator that is housed in the space and generates the electrical vibration at a frequency approximately determined by the resonance characteristics of the piezoelectric ceramic vibrator. An object detection device that detects the presence or absence of the object based on the resonance characteristic of the piezoelectric ceramic vibrator that changes depending on the presence or absence of the object to be detected, comprising: a circuit; What is claimed is: 1. An object detection device comprising: a vibration absorbing member made of a material having a mass greater than the mass of the material that is attached to the protrusion, and bonded to an inner surface of the protrusion. 2. The lid body and the base body each have engaging means that elastically engage with each other at a position between the fixing means formed on the peripheral portion and the center of the piezoelectric ceramic vibrator. An object detection device according to claim 1 of the utility model registration claim. 3. Utility model registration claim 2, characterized in that the engaging means is located between the piezoelectric ceramic assembly and the fixing means substantially symmetrically from the center of the piezoelectric timing oscillator. The object detection device described. 4. The engaging means on the lid side is a through hole,
Utility model registration claim 1 or 2, wherein the engaging means on the base body side is a split pin having one end fixed to the base body and the other end pressed against the inner wall of the through hole. Or the object detection device according to item 3.