JPH04166743A - Hardness detector - Google Patents

Abstract

PURPOSE:To make contact pressure constant and to improve detecting accuracy by providing a detecting element having the contact part in a hollow case so that the element can be freely slid, and energizing the contact part in the protruding direction with an elastic body. CONSTITUTION:A hardness sensor is brought into contact with a body to be detected, and the change in self-oscillating frequency is read. At this time, the frequency is changed by the hardness of the body and contact pressure. Then, a detecting element 33 is held in an approximately cylindrical hollow case 32 so that the element can be freely slid. The detecting element is energized in the protruding direction with an elastic body 34 such as a coil spring. When a contact part 36 of this detector 31 is brought into contact with the body to be detected and the front end of the case 32 is brought into contact with the surface of the body, the elastic body 34 is always contracted by a specified length, and the constant pushing force is obtained. As a result, the constant contact pressure is obtained without measuring the contact pressure, and the use of the detector becomes simple.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hardness detector equipped with a hardness detection element that utilizes self-oscillation of a piezoelectric element.

[Background Art] FIG. 13 shows a conventional example of a hardness sensor that utilizes self-excited oscillation of a piezoelectric element. This hardness sensor 1 consists of an oscillator 2 and a vibration detector 3. The oscillator 2 is a piezoelectric element having a thickness, length, vibration mode (the direction of displacement due to vibration is indicated by a double arrow), and has an upper surface electrode 5 and a lower surface electrode θ formed on both main surfaces of a piezoelectric substrate 4 made of a piezoelectric ceramic or the like. The rear end face of a substantially triangular plate-shaped diaphragm 8 made of Bakelite, resin, metal, etc. is adhered to the front end face of the vibration plate 7 with an adhesive.

On the other hand, the vibration detector 3 has an upper surface electrode 10 and a lower surface electrode 11 formed on both main surfaces of a piezoelectric substrate 9 such as a piezoelectric ceramic material having a thickness-length vibration mode (the direction of displacement due to vibration is indicated by a double-headed arrow a). This is what I did. This vibration detector 3 is placed on the upper surface of the oscillator 2 so that the displacement direction (or the polarization direction of each piezoelectric substrate 4.9) matches that of the oscillator 2, and the lower surface electrode 11 is placed on the upper surface of the oscillator 2. It is fixed to the upper surface of the oscillator 2 with an adhesive or the like so as to be electrically connected to the electrode 5.

Next, a circuit block diagram for operating this hardness sensor 1 is shown in FIG. The top electrode 5 of the oscillator 2 (and the bottom electrode 11 of the vibration detector) is grounded, the top electrode 10 of the vibration detector 3 is connected to the input terminal 13 of the amplifier 12, and the output terminal 14 of the amplifier 12 is connected to the oscillation detector. The oscillator 2, the vibration detector 3, and the amplifier 12 constitute a self-excited oscillation circuit. Therefore, when a start signal such as a trigger voltage is applied to the piezoelectric element 7 via the upper and lower electrodes 5.6 of the oscillator 2,
The piezoelectric element 7 is slightly displaced due to the inverse piezoelectric effect. This minute displacement causes the vibration detector 3 fixed to the top surface of the piezoelectric element 7 to also be displaced, and the piezoelectric effect of the vibration detector 3 induces a voltage between its top and bottom electrodes 10 and 11. After this induced voltage is amplified by the amplifier 12, it is fed back to the oscillator 2 again.
begins to vibrate continuously, establishing automatic oscillation.

When the tip of the diaphragm 8 of the oscillator 2 that is automatically oscillating in this way is brought into contact with the object to be detected 15 whose hardness is to be detected, the oscillation frequency changes depending on the hardness of the object to be detected 15. do. In order to detect this change in oscillation frequency, a frequency count circuit 16 is connected to the output terminal 14 of the amplifier 12.
, a frequency difference-voltage conversion circuit 17, and a display 18 are connected. Therefore, the automatic oscillation whose oscillation frequency is changed by contacting the object to be detected 15 as described above is detected by the vibration detector 3, amplified by the amplifier 12, and then the oscillation by the frequency count circuit 16. Frequency is counted. Next, frequency difference-voltage conversion circuit 1
7 converts the difference between the oscillation frequency count value when not in contact with the detected object 15 and the oscillation frequency count value when in contact with the detected object 15 into a voltage output and quantifies it;
This is output as a hardness value to the display 18 and displayed on the display 18.

[Problems to be Solved by the Invention] As described above, the hardness of the object to be detected can be measured by reading the change in the self-excited oscillation frequency when the hardness sensor is brought into contact with the object to be detected.

The oscillation frequency of the hardness sensor not only changes depending on the hardness of the object to be detected, but also changes depending on the contact pressure between the hardness sensor and the object to be detected.

Therefore, in order to accurately measure hardness, it is necessary to measure hardness using a hardness sensor while measuring the contact pressure so that the contact pressure of the hardness sensor against the object to be detected remains constant. .

The present invention has been made in view of the drawbacks of the conventional examples described above, and its purpose is to contact an object to be detected with a constant contact pressure without measuring the contact pressure to the object to be detected. The object of the present invention is to provide a hardness detector that can accurately measure the hardness of an object to be detected.

Means for Solving the Problem] The hardness detector of the present invention automatically oscillates an oscillator having a piezoelectric element, and when the oscillator is brought into contact with an object to be detected, the hardness changes depending on the hardness of the object. The hardness detector is equipped with a hardness detection element that detects the hardness of the object by detecting the oscillation frequency of the object, the hardness detection element is freely held in a hollow case, and the hardness detection element is freely held in a hollow case to detect the hardness of the object. The contact portion of the detection element with the object to be detected is made to protrude from the opening of the case, and the hardness detection element is elastically biased in the protruding direction by the elastic body, and the contact portion is made to resist the elastic force of the elastic body. It is characterized by being able to be pushed into the case.

This hardness detector may be provided with means for preventing rotation of the hardness detection element within the case.

Further, the case may be provided with a flexible or elastic cover so as to cover the opening of the case.

[Function] 1 In the hardness detector of the present invention, the contact portion of the hardness detection element is brought into contact with the surface of the object to be detected, and the contact portion is pushed into the case so that the front end of the case is brought into contact with the object to be detected. When brought into contact with the surface of the elastic body, the elastic body is always compressed by a certain length,
Alternatively, it is stretched and a constant pressing force is applied to the hardness detection element. Therefore, the contact portion of the hardness detection element can always be brought into contact with the object to be detected with the same contact pressure.

As a result, a constant contact pressure can be obtained without measuring the contact pressure, which simplifies the use of the hardness detector and improves hardness detection accuracy.

Further, by preventing the hardness detection element from rotating within the case, the hardness detection element can be smoothly pushed into the case, and contact pressure can be smoothly applied to the hardness detection element. Moreover, since the hardness detection element does not rotate, the cord is less likely to be twisted or cut.

Furthermore, by covering the opening of the case with a cover, a waterproof or dustproof structure can be achieved.

[Example] Hereinafter, an example of the present invention will be described in detail based on the accompanying drawings. Fig. 1 shows a hardness detector 31 of a first example in a sectional view. This has a hardness detection element 3 inside a substantially cylindrical hollow case 32.
3 is slidably held, and the hardness detection element 33 is elastically biased in the projecting direction by an elastic body 34 such as a coil spring.

As shown in FIGS. 11 and 12, the hardness detection element 33 has the hardness sensor 1 fixed in the housing 20 in a housed state. The housing 20 has a cylindrical shape, such as a cylindrical shape or a rectangular tube shape, with both ends open, and only the diaphragm 8 of the hardness sensor 1 protrudes from the housing 20 from one end. Further, a signal extraction cord 38 connected to the hardness sensor 1 is pulled out from the other end. A horizontal support stand 21 is provided at the center of the inner surface of the housing 20, and a screw 22 is passed through the housing 20 facing the support stand 21.
The hardness sensor 1 is firmly held between the hardness sensor 1 and the tip of the screw 22. The hardness sensor 1 has a structure similar to, for example, the conventional hardness sensor shown in FIG. It is fixed between the two.

The hardness detection element 33 is housed in the case 32, and the contact portion 36 of the hardness detection element 33 (the diaphragm 8 of the hardness sensor 1) can be seen through an opening 35 provided at one end of the case 32.
is made to protrude, and a cord 38 of the hardness sensor 1 is drawn out from a through hole 37 provided at the other end of the case 232. Further, an elastic body 3 such as a compression coil spring is provided between the rear end of the hardness detection element 33 and the end plate 32b of the case 32.
4 is inserted, and the contact portion 36 is elastically projected from the opening 35 by the spring force of the elastic body 34, and at the same time, the case end plate 32a at the edge of the opening 35 acts as a stopper, and the hardness detection element 33 has been stopped. In this way, when the hardness detection element 33 in the case 32 is pressed, the elastic body 34 is compressed and the hardness detection element 33 in the case 32 is moved back, so that the contact part 36 is pushed deeper than the opening 35. There is.

When the hardness detector 31 is used to detect the hardness of the object 15 to be detected, such as a rubber material or a resin material, the case 32 is held and the hardness detection element is moved as shown in FIG. The contact portion 36 of 33 is brought into contact with the surface of the object to be detected 15, the case end plate 32a is pressed against the surface of the object to be detected 15, and the hardness of the object to be detected 15 is measured in this state.

In this way, the hardness detection element 33 in the case 32 is moved back by the protruding length S from the opening 35 of the contact portion 36, and the
Shrink 4 by S. As a result, the spring constant of the elastic body 34 is kJ, and the elastic force when the contact portion 3θ is not in contact as shown in FIG. 1 is f. Then, the contact force f of the contact portion 36 to the detected object 15 is as follows: f=fo+ks (constant value). Therefore, the contact portion 3θ can be brought into contact with the object to be detected 15 with a constant contact pressure without measuring the contact pressure of the contact portion 36 to the object to be detected 15, and the hardness detector 31 can be used. The method can be simplified and the measurement accuracy can also be improved.

The hardness detector 41 of the second embodiment is shown in FIG. The elastic body 34 is arranged so as to be coiled, and both ends of the elastic body are engaged with a flange 42 provided at the front end of the hardness detection element 33 and a protrusion 43 provided at the rear of the inner surface of the case 32.

The hardness detector 41 of this embodiment is also used in the same manner as the first embodiment, but in this embodiment, the hardness detection element 33 and the elastic body 34 are arranged so as to overlap. Therefore, the length of the case 32 can be shortened, and the hardness detector 41 can be downsized.

In this embodiment, the entire length of the elastic body 34 overlaps with the hardness detection element 33, but only a portion of the elastic body 34 may overlap with the hardness detection element 33.

4 and 5 show a hardness detector 51 according to a third embodiment, in which a projection 52 is provided on the outer peripheral surface of the hardness detection element 33, and a projection 52 is provided on the inner peripheral surface of the case 32. A guide #1153 facing each other and extending in the axial direction is provided, and the protrusion 52 of the hardness detection element 33 is slidably fitted into the guide #1153.

In this embodiment, the protrusion 52 is guided straight by the guide groove 53, so when the hardness detection element 33 is moved back inside the case 32, the hardness detection element 33 is moved back straight without rotating. , the movement of the hardness detection element 33 can be made smooth. Furthermore, since the hardness detection element 33 does not rotate within the case 32, there is no risk that the cord 38 will be twisted or broken.

Moreover, what is shown in FIG. 6 is a hardness detector 5 of the fourth embodiment.
It is 6. Although the guide groove 53 in the third embodiment was a groove that did not penetrate from the inner peripheral surface to the outer peripheral surface of the case 32,
As in this embodiment, a long guide hole 57 is provided in the case 32.
may be perforated.

In addition, in the third and fourth embodiments, the protrusion 52, the guide 1l1153, or the guide hole 57 may be provided at multiple locations.

FIG. 7 shows a fifth embodiment. This hardness detector 61 is
The hardness detecting element 33 is freely housed in the case 32, and the hardness detecting element 3 is fixed with an elastic body 34 such as a coil spring.
3 in the protruding direction, and further the contact portion 3e and the opening 3
A cover 62 made of an elastic or flexible rubber sheet, vinyl sheet, or the like is placed on the front surface of the case so as to cover the case 5, and the entire circumference of the cover 62 is fixed to the outer circumference of the front surface of the case 32.

In this hardness detector 61, since the opening 35 of the case 32 is covered by the cover 62, water and dust cannot enter the inside of the hardness detector 61. Therefore, the hardness detector 61 has a waterproof and dustproof structure. Note that the material of the cover 62 may be selected from materials that have little effect on the sensor output.

What is shown in FIGS. 8(a) and 8(b) is a sixth embodiment of the present invention. In this hardness detector 71, the entire outer circumference of an annular cover 72 made of an elastic or flexible rubber sheet, vinyl sheet, etc. is fixed to the opening end of the case 32, and the inner circumference of the cover 72 is The entire inner circumference of the cover 72 is fixed to the front surface of the hardness detection element 33 so that the contact portion 36 is exposed.

Therefore, this embodiment also has a waterproof and dustproof structure, and the cover 72 connects the case 32 and the hardness detection element 33.
The gap 73 between the two can be sealed watertight, and water and dust can be prevented from entering the inside. Moreover, the contact part 3
6 is not covered by the cover 72 and is exposed, so the cover 72 is not interposed between the object to be detected 15 and the contact portion 36 during hardness detection, and the hardness of the cover 72 affects the sensor output. There is no risk of causing damage or reducing the accuracy of hardness measurements. There are also fewer restrictions on the selection of cover materials.

Note that the hardness detection element used in this example does not have a hardness sensor fixed in the housing with screws as shown in Fig. 11, but a flexible material such as silicone rubber between the housing and the hardness sensor. A waterproof hardness detection element filled with
[not shown] is desirable.

FIG. 9 shows a modification (seventh embodiment) of the embodiment shown in FIGS. The contact portion 3 of the hardness detection element 33 inside the case 32 due to the elasticity of
This is a hardness detector 81 configured to bias the hardness 6 to protrude.

That is, as shown in FIG. 10, when the contact portion 36 is pressed against the surface of the object to be detected 15, the cover 82 is stretched and the contact portion 36 of the hardness detection element 33 is pressed against the object to be detected with a constant contact pressure. It is pressed against the surface of 15.

Therefore, in this embodiment, the cover 82 has both the waterproof and dustproof functions and the function of an elastic body that urges the contact portion 36 to protrude, thereby streamlining the use of members. Furthermore, since the cover 82 is an elastic body, the eighth cover 82 uses an elastic body such as a coil spring as the elastic body.
Compared to the embodiments shown in Figures (a) and (b), it is much smaller.

Various embodiments of the present invention are possible in addition to the embodiments described above, and although not shown, a hardness sensor as shown in FIG. 13 may be housed as it is in a case as a hardness detection element and protruded with an elastic body. It may be energized.

In addition, as the elastic body used as the biasing means, although a coil spring or an elastic sheet made of rubber is shown, the examples are not limited to these, such as a plate spring, a metal or resin processed to give an elastic function, It is also possible to use flexible resin or rubber lumps (fillers).

[Effects of the Invention] According to the present invention, the contact portion of the hardness detection element can always be brought into contact with the object to be detected with the same contact pressure without measuring the contact pressure, making it easy to use the hardness detector. It is possible to improve the accuracy of hardness detection.

Further, by preventing the hardness detecting element from rotating within the case, the hardness detecting element can be smoothly pushed into the case, and the usability during measurement can be improved. Moreover,
Since the hardness detection element does not rotate, the cord is less likely to be twisted or cut.

Furthermore, by covering the opening of the case with a cover, a waterproof or dustproof structure can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing a first embodiment of the present invention, Fig. 2 is a sectional view showing the state of the same embodiment during hardness measurement, and Fig. 3 is a sectional view showing a second embodiment of the invention. 4 is a cross-sectional view showing the third embodiment of the present invention, FIG. 5 is a front view of the case taken along line X-X in FIG. 4, and FIG. 6 is a cross-sectional view showing the third embodiment of the present invention. FIG. 7 is a sectional view showing the fifth embodiment of the present invention, and FIG. 8 (aHb) is a front view showing the sixth embodiment of the present invention. 9 is a sectional view showing the seventh embodiment of the present invention, FIG. 10 is a sectional view showing the same state during hardness measurement, and FIGS. 11 and 12 are views of the hardness detection element. Sectional view and external perspective view showing the structure, No. 13
The figure is a perspective view showing a conventional hardness sensor, and FIG. 14 is a circuit block diagram of the hardness sensor. 2... Oscillator 3... Vibration detector 32... Case 33... Hardness detection element 34... Elastic body 36 like a coil spring...
Contact portion 82...Cover (elastic body) Patent applicant: OMRON Co., Ltd. Agent, Patent attorney: Masafusa Nakano

Claims (3)

[Claims] (1) A resonator having a piezoelectric element is caused to self-oscillate, and when the resonator is brought into contact with an object to be detected, the hardness of the object is detected by detecting the oscillation frequency that changes depending on the hardness of the object. A hardness detector equipped with a hardness detection element for detecting hardness, wherein the hardness detection element is slidably held in a hollow case, and the contact portion of the hardness detection element with the object to be detected is located inside the case. The hardness detection element is made to protrude from the opening and elastically biased in the protruding direction by an elastic body, so that the contact portion can be pushed into the case against the elastic force of the elastic body. hardness detector. (2) The hardness detector according to claim 1, further comprising means for preventing rotation of the hardness detecting element within the case. (3) The hardness detector according to claim 1 or 2, wherein the case is provided with a flexible or elastic cover so as to cover the opening of the case.