JPH04152242A - Hardness sensor - Google Patents

Abstract

PURPOSE:To prevent a vibratory plate from separating off from a piezo element, even when a strong shock is applied, by fitting piezo element between projections installed at the base end of the vibratory plate, and fixing the vibratory plate. CONSTITUTION:An approx. triangular vibratory plate 22 is made of metal, wherein the tip is formed with an acute angle, and plate-shaped projections 23, 24 are formed protruding backward from the oversurface and undersurface of the tail part of this vibratory plate 22. An oversurface electrode 5 and an undersurface electrode 6 are formed on the major faces of the base board 4 of a piezo element 7, whose end is fitted between the upper and lower projections 23, 24 and adhered to the tail face of the vibratory plate 22 and the inner surfaces of the projections 23, 24. Thus an oscillator 25 is constituted. Even though a shear stress or flextural stress is generated between the piezo element 7 and vibratory plate 22, which might cause slipping-off of the vibratory plate 22, such a shear or flectural stress is borne by the projections 23, 24. Thereby the vibratory plate is precluded from slipping off from the piezo element even in case a strong shock is applied or the vibratory plate is pressed to object with an excessive force.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a hardness sensor that utilizes self-excited oscillation of a piezoelectric element, and is for detecting the hardness of an object surface.

[Background Art] FIG. 7 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 7 in a thickness/length vibration mode (the direction of displacement due to vibration is indicated by a double arrow), which has an upper surface electrode 5 and a lower surface electrode 6 formed on both main surfaces of a piezoelectric substrate 4 made of piezoelectric ceramics or the like. A diaphragm 8 made of Bakelite, resin, metal, etc., which has a substantially triangular plate shape on the tip surface.
The rear end surface of the is bonded with 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 made of piezoelectric ceramic or the like having a thickness/length vibration mode (the direction of displacement due to vibration is indicated by a double arrow). It is something. 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 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 upper surface electrode 5 of the oscillator 2 (and the lower surface electrode 11 of the vibration detector 3) is grounded, the upper surface 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 It is connected to the lower surface electrode 6 of the oscillator 2, and the oscillator 2, vibration detector 3, and 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 through the upper and lower electrodes 5 and 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 in the same phase again, so that the oscillator 2 begins to vibrate continuously, and self-sustained oscillation is established.

When the tip of the diaphragm 8 of the oscillator 2 which is self-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. Change. In order to detect this change in oscillation frequency, a frequency count circuit 1θ 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 self-excited oscillation whose oscillation frequency changes due to contact with the detected object 15 as described above,
After being detected by the vibration detector 3 and amplified by the amplifier 12,
The frequency count circuit 16 counts the oscillation frequency. Next, the frequency difference-voltage conversion circuit 17
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 is converted into voltage output and quantified, and this is displayed as a hardness value. It outputs to the device 18 and displays it on the display 18.

[Problem to be solved by the invention] A hardness sensor using a piezoelectric element transmits the vibrations generated by the piezoelectric element to a diaphragm as described above, and brings the tip of the diaphragm into contact with an object to be detected. Therefore, large stress is generated between the piezoelectric element of the oscillator and the diaphragm. In particular, when the diaphragm is brought into contact with an object with a force greater than a predetermined value, a large stress is generated at the bonding surface between the diaphragm and the piezoelectric element. Thus, when a large stress (particularly shear stress or bending stress) is generated on the 11 surface where the diaphragm and the piezoelectric element come into contact, there is a problem in that the diaphragm falls off from the piezoelectric element. Further, even when a strong impact is applied to the oscillator due to a drop or the like, the diaphragm easily comes off from the piezoelectric element.

The present invention has been made in view of the drawbacks of the conventional example of inclined top, and its purpose is to apply a strong impact,
To provide a hardness sensor in which a diaphragm does not fall off a piezoelectric element even if the diaphragm is pressed too strongly against an object.

[Means for Solving the Problems] A first hardness sensor according to 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 sensor detects the hardness of the object. In a sensor that detects the hardness of an object by detecting an oscillation frequency that changes accordingly, a protrusion is provided at the base end of a diaphragm for direct contact with the object to be detected.

The oscillator is characterized in that the piezoelectric element is fitted between the protrusions and the diaphragm is fixed to the piezoelectric element to form the oscillator.

Further, the second hardness sensor according to the present invention causes an oscillator having a piezoelectric element to self-oscillate, and when the oscillator is brought into contact with an object to be detected, the oscillation frequency changes depending on the hardness of the object. In a sensor that detects the hardness of an object by detecting the hardness of the object, a recess is provided at the base end of the diaphragm for direct contact with the object to be detected, and the piezoelectric element is fitted into the recess to cause the piezoelectric element to vibrate. A feature is that the oscillator is constructed by fixing plates.

Further, a third hardness sensor according to the present invention causes an oscillator having a piezoelectric element to self-oscillate, and when the oscillator is brought into contact with an object to be detected, the oscillation frequency changes depending on the hardness of the object. In a sensor that detects the hardness of an object by detecting the hardness of the object, the oscillator is It is characterized by its composition.

Further, the fourth hardness sensor according to the present invention causes an oscillator having a piezoelectric element to self-oscillate, and when the oscillator is brought into contact with an object to be detected, an oscillation frequency that changes depending on the hardness of the object. In the sensor that detects the hardness of the object by detecting the hardness of the object, the end of the piezoelectric element is formed so that the width becomes gradually narrower on the tip side, and the tip of the piezoelectric element is brought into contact with the object to be detected. It is characterized by detecting the hardness of the object being contacted.

Furthermore, in the fourth hardness sensor, a coating may be applied to the surface of the tip portion of the piezoelectric element.

[Function] In the first and second hardness sensors of the present invention, vibrations can be suppressed by eliminating projections or recesses at the base of the diaphragm and fitting piezoelectric elements between the projections or within the recesses of the diaphragm. This increases the strength of the bond between the plate and the piezoelectric element.

Therefore, even if the diaphragm is brought into strong contact with the surface of the object to be detected or a shock is applied to the diaphragm due to a fall or the like, the diaphragm is unlikely to fall off from the piezoelectric element.

In addition, in the third hardness sensor, the diaphragm is attached to the main surface of the piezoelectric element so that it overlaps with the main surface of the piezoelectric element, so the area of attachment between the diaphragm and the piezoelectric element can be increased, and the diaphragm does not fall off from the piezoelectric element. It becomes difficult.

In addition, in the fourth hardness sensor, the piezoelectric substrate itself has a part for contacting the detected object, so there is no need to glue the diaphragm to the piezoelectric element, and therefore the diaphragm does not fall off. .

Therefore, according to each hardness sensor of the present invention, there is no fear that the diaphragm of the oscillator will fall off from the piezoelectric element, and the durability and impact resistance of the hardness sensor are improved.

Furthermore, in the fourth hardness sensor of the present invention, since the piezoelectric element itself is brought into contact with the object to be detected, there is a risk that the piezoelectric element will be worn out. However, if the part of the piezoelectric element that comes into contact with the object to be detected is coated, Wear of the piezoelectric element can be reduced, and the life of the hardness sensor is improved.

[Example] Hereinafter, an example of the present invention will be described in detail based on the accompanying drawings. Note that the same parts as in the conventional example are given the same reference numerals, and detailed explanation will be omitted.

The hardness sensor 21 of the first embodiment of the present invention shown in FIGS. 1 and 2(a) and (b) is a substantially triangular plate-shaped hardness sensor 21 with an acute angle at the tip, made of Bakelite, synthetic resin or Plate-shaped projections 23 and 24 project rearward from the upper and lower surfaces of the rear end of the metal diaphragm 22, respectively. Then, the ends of the piezoelectric element 7, which has upper and lower electrodes 5 and 6 formed on the main surface of the piezoelectric substrate 4, are connected to the upper and lower protrusions 2.
3.24, and connect the end of the piezoelectric element 7 to the vibration plate 22.
The oscillator 25 is constructed by adhering it to the rear end surface of the protrusion 23 and the inner surface of the projections 23 and 24 with an adhesive. Further, the vibration detector 3 is bonded to the upper surface of the piezoelectric element 7, and the upper surface type gA5 of the piezoelectric element 7 and the lower surface electrode 11 of the vibration detector 3 are electrically connected.

This hardness sensor 21 is also used by connecting a driving and measuring circuit as shown in FIG. 8, like the conventional hardness sensor.

Here, in this second hardness sensor, the end of the piezoelectric element 7 is held between the protrusions 23 and 24 of the diaphragm 22, so
Even if shear path force or bending stress that causes the diaphragm 22 to fall off occurs between the piezoelectric element 7 and the diaphragm 22, the shear path force or bending stress is held by the projections 23,24. Further, by providing the protrusions 23 and 24, the bonding area between the piezoelectric element 7 and the diaphragm 22 is also increased. As a result,
The strength of the attachment of the diaphragm 22 to the piezoelectric element 7 is increased, so that even if the tip of the diaphragm 22 is strongly pressed against the object to be detected 15 or an impact is applied to the diaphragm 22, the diaphragm 22 will not attach to the piezoelectric element 7. It becomes difficult to fall off.

3(a) and 3(b) are a partially cutaway plan view of a hardness sensor 26 according to a second embodiment of the present invention and a rear view of its diaphragm 27. In this embodiment, a recess 28 having a size approximately equal to the cross section of the piezoelectric element 7 is formed in the rear end surface of the diaphragm 27 having a substantially triangular plate shape. The end of the piezoelectric element 7 is fitted into the recess 28, and the end of the piezoelectric element 7 and the inner surface of the recess 28 are bonded together with an adhesive to form an oscillator 29.

In this embodiment as well, the piezoelectric element 7 and the diaphragm 27 are not only bonded together, but also the ends of the piezoelectric element 7 are held in the recesses 28.
Even if shear road force or bending stress occurs between 7 and 7, the recess 28
The piezoelectric element 7 is held by this, and the bonding surface between the diaphragm 27 and the piezoelectric element 7 becomes difficult to separate. Furthermore, the adhesion area is increased by the recess 28. Therefore, the bonding strength between the diaphragm 27 and the piezoelectric element 7 is increased, and the diaphragm 27 is less likely to fall off due to impact or the like.

What is shown in FIGS. 4(a) and 4(b) is a hardness sensor 30 according to a third embodiment of the present invention, in which a diaphragm 31 has a portion 31a having approximately the same area as the main surface of the piezoelectric element 7. , further has a portion 31b projecting from one end of the piezoelectric element 7 in an acute angle shape. The oscillator 32 is constructed by bonding a portion 31a of the diaphragm 31 with approximately the same area as the piezoelectric element 7 to the lower main surface of the piezoelectric element 7, and an acute-angled portion 31b is one end of the piezoelectric element 7. It protrudes from the bottom. When the tip of the acute-angled portion 31b of the diaphragm 31 is brought into contact with an object to be detected, the self-excited vibration generated in the piezoelectric element 7 is transmitted from the bottom surface of the piezoelectric element 7 to the diaphragm 31, and further The signal is transmitted from the tip to the object to be detected 15 .

In this embodiment, since the bonding area between the piezoelectric element 7 and the diaphragm 31 can be made very large, the bonding strength of the diaphragm 31 is extremely large, so that no impact is applied to the diaphragm 31, and the diaphragm 31 is not connected to the object 1 to be detected. Even if the pressing force is too strong, the diaphragm 31 is unlikely to fall off the piezoelectric element 7.

What is shown in FIG. 5 is a hardness sensor 33 according to a fourth embodiment of the present invention, in which a corner of one end of a piezoelectric substrate 34 is cut to form an acute angle. An upper surface electrode 35 and a lower surface electrode 36 are provided on the upper and lower surfaces, respectively, and an oscillator 38 is constituted by only the piezoelectric element 37. That is,
A part of the piezoelectric element 37 also functions as a diaphragm for concentrating vibration energy at one point. The tip 3B of the piezoelectric element 37 is brought into direct contact with the object to be detected 15 to measure the hardness of the object.

In this embodiment, since the diaphragm which is a separate member from the piezoelectric element 37 is not used, the diaphragm does not fall off from the piezoelectric element 37. Furthermore, in this embodiment, the piezoelectric element 37
Since the vibration plate is not bonded to the piezoelectric element 37 and the vibration is directly transmitted to the pressure object 15 to be tested, the attenuation of the vibration is small and the S/N ratio in the vibration detector 3 is improved. Also,
The structure of the oscillator 38 is also simplified.

What is shown in FIGS. 6(a) and 6(b) is a hardness sensor 4o according to a fifth embodiment of the present invention. This is because in the hardness sensor 33 of the fourth embodiment, the tip 39 of the piezoelectric element 37 is
A coating 41 of resin (particularly wear-resistant resin) or the like is applied to the surface. Hardness sensor 33 of fourth embodiment
In this case, since the piezoelectric element 37 is brought into direct contact with the object to be detected 15, there is a possibility that the tip portion 39 of the piezoelectric element 37 will be easily worn out. Therefore, as in this embodiment, if the tip 39 of the piezoelectric element 37 is coated with a coating 41 of wear-resistant resin or the like, the wear of the piezoelectric element 37 can be prevented.
The durability of the hardness sensor is improved.

[Effects of the Invention] In the first to third hardness sensors of the present invention, the bonding strength of the diaphragm to the piezoelectric element can be increased. Therefore, even if the force that brings the diaphragm into contact with the surface of the object to be detected is too strong or a shock is applied to the diaphragm, the diaphragm will not easily fall off from the piezoelectric element, improving the impact resistance and durability of the hardness sensor. Improves sex.

Further, in the fourth hardness sensor, since the piezoelectric element itself is brought into contact with the object to be detected, the diaphragm is not required, and the diaphragm does not fall off. Therefore, even with this hardness sensor, the durability and impact resistance of the hardness sensor are improved.

In addition, in addition to the effects of the fourth hardness sensor, the fifth hardness sensor can prevent wear of the piezoelectric element that is in direct contact with the detected object, further improving the life of the hardness sensor. It has the advantage of being able to

[Brief explanation of drawings]

Fig. 1 is a side view showing one embodiment of the present invention, Fig. 2(a)
(b) is a plan view and a side view showing the diaphragm of the same embodiment as above, and FIGS. 3(a) and 3(b) are a partially broken plan view and the back side of the diaphragm showing another embodiment of the present invention. Figure, Figure 4 (
5(a) and 6(b) are plan views and side views showing still another embodiment of the present invention, FIGS. Figures (a) and (b) are a plan view and a side view showing still another embodiment of the present invention, Figure 7 is a perspective view showing a conventional hardness sensor, and Figure 8 is a circuit block diagram of the hardness sensor. It is. 3... Vibration detector 7.37... Piezoelectric element 15... Object to be detected 22.27.31... Vibration plate 25.29, 32.38... Oscillator 23.24... Protrusion 28...Recess 40...Coating

Claims (5)

[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. In the sensor for detection, protrusions are provided at the base end of the diaphragm for direct contact with the object to be detected, and the piezoelectric element is fitted between the protrusions to fix the diaphragm to the piezoelectric element. A hardness sensor characterized by the following configuration. (2) The hardness of the object is determined by causing an oscillator with a piezoelectric element to self-oscillate, and by detecting the oscillation frequency that changes depending on the hardness of the object when the oscillator is brought into contact with the object. In the sensor to be detected, the oscillator is configured by providing a recess at the base end of the diaphragm for direct contact with the detected object, fitting the piezoelectric element into the recess, and fixing the diaphragm to the piezoelectric element. A hardness sensor characterized by: (3) By causing an oscillator with a piezoelectric element to self-oscillate, and when the oscillator contacts an object to be detected, the oscillation frequency that changes depending on the object's hardness is detected, thereby determining the hardness of the object. A hardness sensor for detecting a hardness sensor, characterized in that the oscillator is constructed by overlapping and fixing a diaphragm on the main surface of the piezoelectric element for direct contact with the object to be detected. (4) The hardness of the object is determined by causing an oscillator with a piezoelectric element to self-oscillate, and when the oscillator contacts the object to be detected, the oscillation frequency changes depending on the hardness of the object. In the sensor for detection, the end portion of the piezoelectric element is formed so that the width becomes gradually narrower on the tip side, and the tip portion of the piezoelectric element is brought into contact with the object to be detected to detect the hardness of the object to be contacted. A hardness sensor characterized by: (5) The hardness sensor according to claim 4, wherein a coating is applied to the surface of the tip end of the piezoelectric element.