JPH11230836A - Load sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a load sensor in which the insulation resistance between electrodes does not drop much, even after the sensor is exposed to a high- temperature high-humidity atmosphere for a long time. SOLUTION: In the case 11 of a load sensor 30, a piezoelectric element 15, a pair of electrodes 16 and 16 holding the element 15 between them from the upper and lower sides, a pair of alumina ceramic insulating plates 17 and 17 holding the electrodes 16 and 16 between them from the upper and lower sides, and a pair of stainless steel made pressure receiving plates 18 and 18 holding the insulating plates 17 and 18 between them from the upper and lower sides are arranged. The whole surfaces of the insulating plates 17 are covered with fluoroplastic coating layers 31 and 31. When this sensor 30 is used, the insulation resistance between the electrodes 16 and 16 does not drop much, but meets a specified tolerance in the detecting frequency range of the sensor 30, even after the sensor 30 is exposed to a high-temperature high-humidity atmosphere for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a load sensor using a piezoelectric element.

[0002]

2. Description of the Related Art Heretofore, as a load sensor, there has been known a load sensor utilizing a property that an electrode is attached to a crystal or a piezoelectric element, and a charge is generated on a crystal surface when a mechanical pressure is applied to cause a strain. I have.

[0003]

Such a load sensor includes, for example, a piezoelectric element, a pair of electrodes sandwiching the piezoelectric element, a pair of ceramic insulating plates sandwiching the pair of electrodes, and a pair of insulating plates. It is conceivable to include a pair of pressure receiving plates that sandwich the plate, and a metal rivet that penetrates from one to the other of the pair of pressure receiving plates through an insulating sleeve to integrate them. When a variable load in the vertical direction is applied to this load sensor, an output voltage is generated between the pair of electrodes. By detecting this output voltage, it is possible to control the vibration load of industrial equipment and to prevent vibration.

By the way, the insulation resistance between a pair of electrodes of a load sensor is usually 10M because a piezoelectric element is interposed.
This is a large value of Ω or more. As for the relationship between the detection frequency of the load sensor and the output voltage, although the output voltage tends to decrease in a low frequency region, there is no noticeable decrease in the output voltage within the detection frequency range. In addition, the standard tolerance of the output voltage is set in the detection frequency range,
The load sensor must satisfy this standard tolerance as its performance.

However, the present inventors have made intensive studies and found that when this load sensor was exposed for a long time in a high-temperature, high-humidity atmosphere, the insulation resistance between a pair of electrodes was greatly reduced.
As a result, it has been found that the output voltage is greatly reduced in the low frequency range, and the standard tolerance cannot be satisfied in the detection frequency range.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide a load sensor that does not greatly reduce insulation resistance even when exposed to a high-temperature, high-humidity atmosphere for a long time.

[0007]

Means for Solving the Problems and Effects of the Invention In order to solve the above problems, a first invention comprises a piezoelectric element disposed in a case, a pair of electrodes sandwiching the piezoelectric element in the case, A pair of ceramic insulating plates that sandwich the pair of electrodes in the case, a pair of metal pressure plates that are provided so as to be partially exposed from the case, and sandwich the pair of ceramic insulating plates, and the pair of metals; A load including a pair of metal pressure plates, a pair of ceramic insulating plates, a pair of electrodes, and a metal fastening material that integrates the piezoelectric element by penetrating from one side to the other side of the pressure receiving plate via an insulating sleeve. A sensor, wherein at least a portion of the pair of ceramic insulating plates facing the case is coated with an insulating resin coating material.

When the portion of the ceramic insulating plate of the load sensor facing the case is not coated with an insulating resin coating material, the insulation resistance between the two electrodes is significantly reduced after exposure to high temperature and high humidity. On the other hand, when the portions were coated with an insulating resin coating material as in the present invention, the insulation resistance between the two electrodes did not decrease significantly even after exposure to high temperature and high humidity.

Although the reason for this is not clear, when a ceramic insulating plate whose surface facing the case is not coated is used, the electrons on one electrode are exposed to the side of the ceramic insulating plate on the same side as the case (the case). Through the water that has accumulated in the irregularities of the part that faces) to the metal pressure plate on the same side,
From there, the metal is transferred to the metal pressure plate on the opposite side via a metal fastening material, and a path is formed to reach the other electrode via the moisture accumulated on the side surface irregularities of the ceramic insulating plate on that side. It is considered that the insulation resistance of the sample was lowered. Note that the electric resistance of the path is referred to as surface insulation resistance. On the other hand, when a ceramic insulating plate coated with a portion facing the case as in the present invention is used, the unevenness of the side surface of the ceramic insulating plate is smoothed, so that moisture is not retained, and the above-described path is not provided. Is difficult to form,
As a result, it is considered that the surface insulation resistance between both electrodes did not decrease.

As described above, according to the load sensor of the first invention, the insulation resistance does not decrease so much even after exposure to high temperature and high humidity. Therefore, the output voltage does not decrease within the detection frequency range, and the standard tolerance is reduced. The effect of being satisfied can be obtained.
In the first invention, the pair of ceramic insulating plates may be entirely coated with the insulating resin coating material. In this case, there is an advantage that manufacturing is easier than coating only the portion of the ceramic insulating plate facing the case.

Next, a second invention provides a piezoelectric element disposed in a case, a pair of electrodes sandwiching the piezoelectric element in the case, and a pair of ceramics sandwiching the pair of electrodes in the case. An insulating plate, a pair of metal pressure plates provided so as to be partially exposed from the case, sandwiching the pair of ceramic insulating plates, and penetrating from one to the other of the pair of metal pressure plates via an insulating sleeve. A load sensor comprising the pair of metal pressure receiving plates, the pair of ceramic insulating plates, the pair of electrodes and a metal fastening member integrating the piezoelectric element, wherein the piezoelectric element, the pair of electrodes, Side surfaces of a structure including the pair of ceramic insulating plates and the pair of metal pressure receiving plates are coated with an insulating resin coating material. Here, the coated structure may be accommodated in a case, or the coating layer may be used as a case. The second invention has the same operation and effect as the first invention. Further, the entire surface of the structure may be coated with the insulating resin. In this case, there is an advantage that the structure is easier to manufacture than coating only the side surface of the structure.

Although the insulating resin coating material is not particularly limited, for example, a coating containing a fluorine resin, a silicone resin, a vinyl resin, a phenol resin, an aromatic hydrocarbon resin, an amino resin, an epoxy resin, etc. A material may be used. Among them, a fluororesin coating material containing tetrafluoroethylene resin and the like having excellent water repellency is preferable.

In addition, any resin having properties equivalent to those of the insulating resin (for example, a smoothing agent for smoothing the uneven surface of the ceramic insulating plate) can be included in the insulating resin of the present invention in a broad sense.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Reference Embodiment] Before describing an embodiment of the present invention, a load sensor as a premise thereof will be described as a reference embodiment. FIG. 1 is a plan view illustrating a schematic configuration of a reference embodiment, and FIG. 2 is a cross-sectional view taken along line AA of FIG. The load sensor 10 according to the reference embodiment is used for controlling a vibration load of industrial equipment, preventing vibrations, and the like, and is a type of a force sensor (dynamic sensor) that generates an output voltage when receiving a fluctuating load.

The load sensor 10 includes a case 11 made of PBT resin and a lead wire 1 extending from the case 11.
2 and a connector 1 provided at an end of the lead wire 12.
3 is provided. The sub-assembly 20 as the structure of the present invention is housed inside the case 11.

The sub-assembly 20 includes the piezoelectric element 15
And a pair of electrodes 1 sandwiching the piezoelectric element 15 from above and below.
6, 16; a pair of alumina ceramic insulating plates 17, 17 sandwiching the pair of electrodes 16, 16 from above and below; and a pair of SUS pressure receiving plates 18, sandwiching the pair of alumina ceramic insulating plates 17, 17 from above and below; 18.

The piezoelectric element 15, the pair of electrodes 16, 16, and the pair of alumina ceramic insulating plates 17, 17 are each formed in a donut shape, and an insulating sleeve 19 is fitted in the center thereof. The pressure receiving plate 18 has a hole 18a in the middle and an annular projection 18b on its outer surface. The sub-assembly 20 is integrated with a rivet 21 as a metal fastening member that extends from the hole 18 a of the pressure receiving plate 18 to the hole 18 a of the other pressure receiving plate 18 through the insulating sleeve 19. The periphery of the rivet 21 is filled with a sealing material 22 made of silicone resin, and the gap between the case 11 and the pressure receiving plate 18 is also filled with a similar sealing material 23. Note that a pair of electrodes 16, 16
Are connected to square spot terminals 24, 24, respectively.
Each terminal 24 is connected to the connector 13 via the lead wire 12.
It is connected to the.

An example of the operation of the load sensor 10 will be briefly described below. Connector 13 of load sensor 10
Is connected to a computer controller (not shown). When the load sensor 10 receives a variable load on the pressure receiving plates 18 from above and below, the piezoelectric element 15 is distorted and an output voltage is generated between the electrodes 16. This output voltage is detected by a computer control device, and the computer control device controls the vibration load of the industrial equipment and performs vibration prevention based on the detection signal.

[First Embodiment] FIG. 3 is an explanatory view of a main part of the first embodiment. The load sensor 30 of the first embodiment is the same as the load sensor 10 of the reference embodiment, except that the entire surface of each alumina ceramic insulating plate 17 is covered with a coating layer 31 of tetrafluoroethylene resin which is a fluororesin. Therefore, the same reference numerals are given to the same components, and the description thereof will be omitted. The coating layer 31 is formed by baking and coating a fluororesin.

[Second Embodiment] FIG. 4 is an explanatory view of a main part of a second embodiment. The load sensor 40 according to the second embodiment includes the side surface of the subassembly 20 and the annular protrusion 1 of the pressure receiving plate 18.
8b is the same as the load sensor 10 of the reference embodiment except that the outer peripheral portion of 8b is covered with a coating layer 41 of silicon resin, and the coating layer 41 is used instead of the case 11 made of PBT resin. Therefore, the same components are denoted by the same reference numerals, and the description thereof will be omitted. The coating layer 41 is formed by applying a silicone resin and curing by heating or room temperature.

[Third Embodiment] FIG. 5 is an explanatory view of a main part of a third embodiment. The load sensor 50 according to the third embodiment is the same as the load sensor 10 according to the reference embodiment except that the entire surface of the subassembly 20 is covered with the fluororesin coating layer 51.
Therefore, the same reference numerals are given to the same components, and the description thereof will be omitted. The coating layer 5
No. 1 is formed by baking and coating a fluororesin.

[Fourth Embodiment] FIG. 6 is an explanatory view of a main part of a fourth embodiment. The load sensor 60 of the fourth embodiment is the same as the load sensor 10 of the reference embodiment except that only the portion (that is, the side surface) of each alumina ceramic insulating plate 17 facing the case 11 is covered with the fluororesin coating layer 61.
Therefore, the same reference numerals are given to the same components, and the description thereof will be omitted. The coating layer 6
No. 1 is formed by baking and coating a fluororesin.

[Fifth Embodiment] FIG. 7 is an explanatory view of a main part of a fifth embodiment. The load sensor 70 according to the fifth embodiment is the same as the load sensor 10 according to the reference embodiment except that the side surface of the subassembly 20 is covered with a fluororesin coating layer 71.
Therefore, the same reference numerals are given to the same components, and the description thereof will be omitted. The coating layer 71
Is formed by baking and coating a fluororesin.

[Test Example of Reference Embodiment] In the load sensor 10 of the reference embodiment, the insulation resistance between the pair of electrodes 16 and 16 in the initial state in the room temperature atmosphere is 10,000 MΩ or more. The output characteristic indicated by the solid line in FIG.
The output characteristics were a preload of 17 kN, a fluctuating load of ± 5
It was measured under the condition of 0N. From this result, it was found that the load sensor 10 generates an output voltage satisfying the standard tolerance in a predetermined detection frequency range (here, 20 to 200 Hz) in the initial state.

On the other hand, when the load sensor 10 is set to 85 ° C. and 85% R
When the relationship between the time left in the H atmosphere and the insulation resistance between the pair of electrodes 16 and 16 was examined, the insulation resistance was approximately 24 hours or more as shown by the plot of “□” in FIG. It decreased to 10 MΩ or less. When the output characteristics when the insulation resistance became 10 MΩ or less were examined, a graph shown by a dotted line in FIG. 8 was obtained. From these results, it was found that the insulation resistance of the load sensor 10 was greatly reduced when exposed to a high-temperature and high-humidity atmosphere, and that the load sensor 10 did not satisfy the standard tolerance in a predetermined detection frequency range (especially on the low frequency side) when the load resistance was 10 MΩ or less. .

[Test Example of Embodiment] The load sensors 30 and 40 of the first and second embodiments have an insulation resistance of 100 between the pair of electrodes 16 in the initial state in a room temperature atmosphere.
The output characteristic was almost the same as that of the load sensor 10 of the above-described reference embodiment.

On the other hand, when the load sensors 30 and 40 are
The time left in a 5% RH atmosphere and the pair of electrodes 16
When the relationship between the insulation resistance and the insulation resistance between the load sensors 16 was examined, the insulation resistance was 10 MΩ or more even after 24 hours or more as shown by “○” and “△” in FIG.
0 is 3000 MΩ or more, the load sensor 40 of the second embodiment.
Is 1000 MΩ or more), and the insulation resistance did not decrease as much as the reference example. The output characteristics were not inferior to the initial state. From these results, the load sensors 30, 40
It was found that the insulation resistance did not decrease significantly even when exposed to a high-temperature and high-humidity atmosphere, and that the standard tolerance was satisfied in a predetermined detection frequency range.

Although the load sensors 30 and 40 of the first and second embodiments have been described here as representative examples, substantially the same results were obtained in other embodiments. [Surface Structure of Alumina Ceramic Insulating Plate] Alumina ceramic insulating plate 17 of load sensor 10 of the reference embodiment
And the coating layer 3 of the load sensor 30 of the first embodiment
The surface structure of the alumina ceramic insulating plate 17 provided with No. 1 was inspected by SEM (Scanning Electron Microscope: scanning electron microscope). Was. From this result, in the former, when exposed in a high-temperature and high-humidity atmosphere for a long time, moisture is retained on the fine uneven surface on the side of the alumina ceramic insulating plate 17 facing the case 11, and one electrode → the alumina ceramic on the same side Moisture held on the side surface irregularities of insulating plate 17 → pressure receiving plate 18 on the same side
→ A rivet 21 → a pressure receiving plate 18 on the opposite side → moisture held on the unevenness of the side surface of the alumina ceramic insulating plate 17 on the same side → the other electrode 16 is formed, and the surface insulation resistance is greatly reduced. It is considered that the insulation resistance between the two electrodes 16, 16 was greatly reduced. on the other hand,
In the latter, even if exposed for a long time in a high temperature and high humidity atmosphere,
Due to the presence of the coating layer 31, the unevenness of the side surfaces of the alumina ceramic insulating plate 17 is smoothed and moisture is not retained there. As a result, the above-mentioned path was difficult to be formed, so that the surface insulation resistance did not decrease so much. It is considered that the insulation resistance between them did not decrease so much.

The embodiments of the present invention are not limited to the above-described embodiments, and it goes without saying that various forms can be adopted as long as they fall within the technical scope of the present invention.

[Brief description of the drawings]

FIG. 1 is a plan view illustrating a schematic configuration of a load sensor according to a reference embodiment.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a cross-sectional view of a main part of the load sensor according to the first embodiment.

FIG. 4 is a sectional view of a main part of a load sensor according to a second embodiment.

FIG. 5 is a sectional view of a main part of a load sensor according to a third embodiment.

FIG. 6 is a sectional view of a main part of a load sensor according to a fourth embodiment.

FIG. 7 is a sectional view of a main part of a load sensor according to a fifth embodiment.

FIG. 8 is a graph (output characteristic) showing a relationship between a detection frequency and an output voltage.

FIG. 9 is a graph showing the relationship between the time during which a load sensor is left in a high-temperature and high-humidity atmosphere and the insulation resistance between electrodes.

[Explanation of symbols]

10 ... load sensor, 11 ... case, 12 ...
Lead wire, 13 ... connector, 15 ... piezoelectric element,
16 ... electrode, 17 ... alumina ceramic insulating plate, 18 ... pressure receiving plate, 18a ... hole, 18b ...
Annular protrusion, 19: insulating sleeve, 20: sub-assembly, 21: rivet, 22, 23: sealing material, 30, 40, 50, 60, 70: load sensor, 31, 41 , 51, 61, 71 ... coating layer.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Katsu Kondo 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Special Ceramics Co., Ltd.

Claims (4)

[Claims] A piezoelectric element disposed in a case; a pair of electrodes sandwiching the piezoelectric element in the case; a pair of ceramic insulating plates sandwiching the pair of electrodes in the case; And a pair of metal pressure receiving plates provided so as to partially expose the pair of ceramic insulating plates, and a pair of metal pressure receiving plates penetrating from one to the other of the pair of metal pressure receiving plates through an insulating sleeve. A load sensor comprising a pressure receiving plate, the pair of ceramic insulating plates, a metal fastening member integrating the pair of electrodes and the piezoelectric element, and at least a portion of the pair of ceramic insulating plates facing a case is A load sensor characterized by being coated with an insulating resin coating material. 2. The load sensor according to claim 1, wherein the entire surface of each of the pair of ceramic insulating plates is coated with the insulating resin coating material. A piezoelectric element disposed in the case; a pair of electrodes sandwiching the piezoelectric element in the case; a pair of ceramic insulating plates sandwiching the pair of electrodes in the case; And a pair of metal pressure receiving plates provided so as to partially expose the pair of ceramic insulating plates, and a pair of metal pressure receiving plates penetrating from one to the other of the pair of metal pressure receiving plates through an insulating sleeve. A load sensor comprising a pressure receiving plate, the pair of ceramic insulating plates, a metal fastening member for integrating the pair of electrodes and the piezoelectric element, wherein the piezoelectric element, the pair of electrodes, and the pair of ceramic insulating plates And a side surface of a structure comprising the pair of metal pressure receiving plates is coated with an insulating resin coating material. 4. The load sensor according to claim 3, wherein the entire surface of the structure is coated with the insulating resin coating material.