JP4011177B2 - Load sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a load sensor using a piezoelectric element.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a load sensor is known that utilizes the property that charges are generated on the surface of a crystal when an electrode is attached to a crystal or piezoelectric element and mechanical strain is applied to cause strain.
[0003]
[Problems to be solved by the invention]
As such a load sensor, for example, a piezoelectric element, a pair of electrodes sandwiching the piezoelectric element, a pair of ceramic insulating plates sandwiching the pair of electrodes, a pair of pressure receiving plates sandwiching the pair of insulating plates, One having a metal rivet that penetrates from one to the other of the pair of pressure receiving plates through an insulating sleeve and integrates them can be considered. When an up and down fluctuating load is applied to the 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 the industrial equipment and to prevent vibration.
[0004]
By the way, the insulation resistance between the pair of electrodes of the load sensor is usually a large value of 10 MΩ or more because a piezoelectric element is interposed. As for the relationship between the detection frequency of the load sensor and the output voltage, the output voltage tends to decrease in the low frequency region, but there is no noticeable decrease in the output voltage within the detection frequency range. Further, the standard tolerance of the output voltage is determined in the detection frequency range, and the load sensor needs to satisfy this standard tolerance as its performance.
[0005]
However, as a result of intensive studies by the present inventors, when this load sensor is exposed to a high temperature and high humidity atmosphere for a long time, the insulation resistance between the pair of electrodes is greatly reduced, and thus the output voltage is reduced in the low frequency region. It has been found that the tolerance is greatly reduced and the standard tolerance cannot be satisfied in the detection frequency range.
[0006]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a load sensor in which the insulation resistance does not greatly decrease even when exposed for a long time in a high temperature and high humidity atmosphere.
[0007]
[Means for Solving the Problems and Effects of the Invention]
In order to solve the above problems, a first invention includes a piezoelectric element disposed in a case, a pair of electrodes that sandwich the piezoelectric element in the case, and a pair of electrodes that sandwich the pair of electrodes in the case A ceramic insulating plate, a pair of metal pressure plates provided so as to be partly exposed from the case, and sandwiching the pair of ceramic insulating plates, and from one to the other of the pair of metal pressure plates through an insulating sleeve A load sensor comprising a metal fastening material that penetrates the pair of metal pressure-receiving plates, the pair of ceramic insulating plates, the pair of electrodes, and the piezoelectric elements, and is attached to a case of the pair of ceramic insulating plates Only the facing portion is coated with an insulating resin coating material.
[0008]
When the part of the ceramic insulation plate of the load sensor that faces the case is not coated with an insulating resin coating material, the insulation resistance between the two electrodes decreased significantly after exposure to high temperature and high humidity. When the portion was coated with an insulating resin coating material as in the present invention, the insulation resistance between the electrodes was not significantly reduced even after being exposed to high temperature and high humidity.
[0009]
The reason for this is not clear, but when using a ceramic insulating plate that is not coated on the part facing the case, the electrons on one electrode are on the same side of the ceramic insulating plate (the part facing the case). ) Leads to the metal pressure plate on the same side through the moisture accumulated in the unevenness, then moves to the metal pressure plate on the opposite side through the metal fastening material, and collects the moisture accumulated in the side surface unevenness of the ceramic insulating plate on that side Therefore, it is considered that the insulation resistance between the two electrodes is reduced because the path to the other electrode is formed. The electrical resistance of the above 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, moisture is not retained because the side surface unevenness of the ceramic insulating plate is smoothed, and the above path As a result, it is considered that the surface insulation resistance between the two electrodes did not decrease.
[0010]
As described above, according to the load sensor of the first invention, the insulation resistance does not decrease so much even after being exposed to high temperature and high humidity, so that the output voltage does not decrease within the detection frequency range, and the standard tolerance can be satisfied. An effect is obtained.
[0011]
Next, a second invention for solving the above-described problems is a piezoelectric element disposed in a case, a pair of electrodes that sandwich the piezoelectric element in the case, and a pair of ceramics that sandwich the pair of electrodes in the case. A pair of insulating plates, a pair of metal pressure plates provided so as to be partially exposed from the case and sandwiching the pair of ceramic insulating plates, and a pair of metal pressure plates that penetrate from one to the other through an insulating sleeve A load sensor including a metal pressure plate, a pair of ceramic insulating plates, a pair of electrodes and a metal fastening material that integrates the piezoelectric elements, and each of the pair of ceramic insulating plates is entirely made of an insulating resin coating material. It is a load sensor characterized by being coated.
Also in the load sensor of the second invention, since the unevenness of the side surface of the ceramic insulating plate is smoothed as in the first invention, the insulation resistance does not decrease much even after exposure to high temperature and high humidity. There is no reduction in the output voltage within the range, and the effect that the standard tolerance can be satisfied is obtained.
In the second invention, the entire surface of the pair of ceramic insulating plates is coated with an insulating resin coating material. In this case, there is an advantage that the ceramic insulating plate is easier to manufacture than coating only the portion facing the case.
[0012]
The insulating resin coating material is not particularly limited. For example, a coating material containing a fluorine resin, a silicon resin, a vinyl resin, a phenol resin, an aromatic hydrocarbon resin, an amino resin, an epoxy resin, or the like is used. May be. Of these, a fluororesin coating material containing a tetrafluoroethylene resin having excellent water generation is preferred.
[0013]
Moreover, if it has the property equivalent to insulating resin (for example, the smoothing agent which smoothes the uneven surface of a ceramic insulating board), it can be included in the insulating resin of this invention in a broad sense.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
[Reference form]
Before describing an embodiment of the present invention, a load sensor as a premise thereof will be described as a reference mode. FIG. 1 is a plan view showing 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 of the reference form is used for control of vibration load of industrial equipment, vibration isolation, and the like, and is a kind of force sensor (dynamic sensor) that generates an output voltage when subjected to a variable load.
[0015]
The load sensor 10 includes a case 11 made of PBT resin, a lead wire 12 extending from the case 11, and a connector 13 provided at an end portion of the lead wire 12. A subassembly 20 as a structure of the present invention is accommodated in the case 11.
[0016]
The subassembly 20 includes a piezoelectric element 15, a pair of electrodes 16 and 16 that sandwich the piezoelectric element 15 from above and below, a pair of alumina ceramic insulating plates 17 and 17 that sandwich the pair of electrodes 16 and 16 from above and below, and the pair. A pair of SUS pressure receiving plates 18 and 18 sandwiching the alumina ceramic insulating plates 17 and 17 from above and below.
[0017]
The piezoelectric element 15, the pair of electrodes 16 and 16, and the pair of alumina ceramic insulating plates 17 and 17 are each formed in a donut shape, and an insulating sleeve 19 is fitted in the center thereof. The pressure receiving plate 18 includes a hole 18a in the middle and an annular protrusion 18b integrally on the outer surface thereof. A rivet 21 serving as a metal fastening material that extends from the hole 18a of one pressure receiving plate 18 to the hole 18a of the other pressure receiving plate 18 that passes through the insulating sleeve 19 is integrated with the subassembly 20. In addition, the periphery of the rivet 21 is filled with a sealing material 22 made of silicon resin, and a similar sealing material 23 is also filled in the gap between the case 11 and the pressure receiving plate 18. Note that square spot terminals 24 and 24 are connected to the pair of electrodes 16 and 16, respectively, and each terminal 24 and 24 is connected to the connector 13 via the lead wire 12.
[0018]
An example of the operation of the load sensor 10 will be briefly described below. A computer control device (not shown) is connected to the connector 13 of the load sensor 10. When the load sensor 10 receives a variable load on the pressure receiving plates 18 and 18 from above and below, the piezoelectric element 15 is distorted and an output voltage is generated between the electrodes 16 and 16. This output voltage is detected by a computer control device, and the computer control device performs control of vibration load of the industrial equipment and vibration isolation based on the detection signal.
[0019]
[First Embodiment]
FIG. 3 is an explanatory diagram 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 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 is omitted. The coating layer 31 is formed by baking and painting a fluororesin.
[0020]
[ Second Reference Embodiment ] FIG. 4 is an explanatory view of the main part of the second reference embodiment . In the load sensor 40 of the second reference embodiment , the side surface of the subassembly 20 and the outer peripheral portion of the annular protrusion 18b of the pressure receiving plate 18 are covered with a coating layer 41 made of silicon resin, and the coating layer 41 is made of the case 11 made of PBT resin. The load sensor 10 is the same as that of the reference embodiment except that it is used instead. For this reason, the same code | symbol is attached | subjected about the same component and the description is abbreviate | omitted. The coating layer 41 is formed by applying a silicon resin and curing by heating or room temperature.
[0021]
[ Third Reference Embodiment ] FIG. 5 is an explanatory view of the main part of the third reference embodiment . The load sensor 50 of the third reference embodiment is the same as the load sensor 10 of the reference embodiment except that the entire surface of the subassembly 20 is covered with the fluororesin coating layer 51. A description thereof will be omitted. The coating layer 51 is formed by baking and painting a fluororesin.
[0022]
[ Second Embodiment ] FIG. 6 is an explanatory view of the main part of the second embodiment . The load sensor 60 according to the second embodiment is the same as the load sensor 10 according to the reference embodiment except that each alumina ceramic insulating plate 17 is covered with the fluororesin coating layer 61 only at a portion facing the case 11 (that is, a side surface). Since it is the same, the same code | symbol is attached | subjected about the same component and the description is abbreviate | omitted. The coating layer 61 is formed by baking and painting a fluororesin.
[0023]
[ Fourth Reference Embodiment ] FIG. 7 is an explanatory view of the main part of the fourth reference embodiment . The load sensor 70 of the fourth reference embodiment is the same as the load sensor 10 of the reference embodiment except that the side surface of the subassembly 20 is covered with the fluororesin coating layer 71. The description is omitted. The coating layer 71 is formed by baking and painting a fluororesin.
[0024]
[Reference Example Test]
The load sensor 10 of the reference form has an insulation resistance of 10000 MΩ or more between the pair of electrodes 16 and 16 in an initial state in the room temperature atmosphere, and shows the fluctuation load applied to the pair of pressure receiving plates 18 and 18 from above and below. 8 had an output characteristic indicated by a solid line. This output characteristic was measured under the conditions of a preload of 17 kN and a variable load of ± 50 N. From this result, it was found that the load sensor 10 generates an output voltage that satisfies the standard tolerance in a predetermined detection frequency range (here, 20 to 200 Hz) in the initial state.
[0025]
On the other hand, when the relationship between the time during which the load sensor 10 was left in an atmosphere of 85 ° C. and 85% RH and the insulation resistance between the pair of electrodes 16 and 16 was examined, a plot of “□” is shown in FIG. Thus, when 24 hours or more passed, the insulation resistance generally decreased to 10 MΩ or less. Thus, when the output characteristic when the insulation resistance became 10 MΩ or less was examined, a graph indicated by a dotted line in FIG. 8 was obtained. From this result, it was found that when the load sensor 10 is exposed to a high-temperature and high-humidity atmosphere, the insulation resistance is greatly reduced, and when it is 10 MΩ or less, it does not satisfy the standard tolerance in a predetermined detection frequency range (particularly on the low frequency side). .
[0026]
[Test Example of Embodiment] The load sensors 30 and 40 of the first embodiment and the second reference embodiment have an insulation resistance between the pair of electrodes 16 and 16 of 10,000 MΩ or more in the initial state in the room temperature atmosphere, and their outputs. The characteristics were almost the same as those of the load sensor 10 of the reference embodiment.
[0027]
On the other hand, when the relationship between the time during which the load sensors 30 and 40 were left in an atmosphere of 85 ° C. and 85% RH and the insulation resistance between the pair of electrodes 16 and 16 was examined, “◯” and “Δ” in FIG. As shown in the figure, the insulation resistance is 10 MΩ or more even after 24 hours or more (the load sensor 30 of the first embodiment is 3000 MΩ or more, the load sensor 40 of the second reference form is 1000 MΩ or more), and the insulation resistance is the reference form. It did not drop as much. Also, the output characteristics were not inferior to the initial state. From this result, it was found that the load sensors 30 and 40 did not greatly decrease the insulation resistance even when exposed to a high temperature and high humidity atmosphere, and satisfied the standard tolerance in a predetermined detection frequency range.
[0028]
Although the load sensors 30 and 40 of the first embodiment and the second reference embodiment are mentioned here as representative examples, substantially the same results are obtained for the other embodiments.
[Surface Structure of Alumina Ceramic Insulating Plate] The surface structure of the alumina ceramic insulating plate 17 including the alumina ceramic insulating plate 17 of the load sensor 10 of the reference embodiment and the coating layer 31 of the load sensor 30 of the first embodiment is SEM. When inspected with a scanning electron microscope (Scanning Electron Microscope), the former was conspicuous, but the latter was smoothed by the coating layer 31. From this result, in the former, when exposed to a long time in a high temperature and high humidity atmosphere, moisture is retained on the fine irregular surface of the side surface facing the case 11 of the alumina ceramic insulating plate 17, and one electrode → the same side alumina ceramic Moisture held on the uneven surface of the insulating plate 17 → pressure receiving plate 18 on the same side → rivet 21 → pressure receiving plate 18 on the opposite side → water held on the uneven surface on the same side of the alumina ceramic insulating plate → the other electrode 16 is formed, and the surface insulation resistance is greatly reduced, and it is considered that the insulation resistance between the electrodes 16 and 16 is greatly reduced. On the other hand, in the latter case, even if the coating layer 31 is exposed for a long time in a high-temperature and high-humidity atmosphere, the side surface unevenness of the alumina ceramic insulating plate 17 is smoothed and moisture is not held there. It is considered that the surface insulation resistance did not decrease so much because it was difficult to form, and the insulation resistance between the electrodes 16 and 16 did not decrease so much.
[0029]
The embodiment of the present invention is not limited to the above-described embodiment, and it goes without saying that various forms can be adopted as long as it belongs to 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 cross-sectional view taken along the 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 cross-sectional view of a main part of a load sensor according to a second reference embodiment .
FIG. 5 is a cross-sectional view of a main part of a load sensor according to a third reference embodiment .
FIG. 6 is a cross-sectional view of a main part of a load sensor according to a second embodiment .
FIG. 7 is a cross-sectional view of a main part of a load sensor according to a fourth reference embodiment .
FIG. 8 is a graph (output characteristics) showing a relationship between a detection frequency and an output voltage.
FIG. 9 is a graph showing the relationship between the time when the load sensor is left in a high-temperature and high-humidity atmosphere and the insulation resistance between the electrodes.
[Explanation of symbols]
DESCRIPTION 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 ... subassembly, 21 ... rivet, 22, 23 ... sealing material, 30,40 , 50, 60, 70 ... load sensors, 31, 41, 51, 61, 71 ... coating layers.

Claims (2)

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;
A pair of metal pressure plates provided so as to be partially exposed from the case, and sandwiching the pair of ceramic insulating plates;
A metal fastening material that penetrates one to the other of the pair of metal pressure plates through an insulating sleeve and integrates the pair of metal pressure plates, the pair of ceramic insulation plates, the pair of electrodes, and the piezoelectric element; A load sensor comprising:
A load sensor characterized in that only portions of the pair of ceramic insulating plates facing the case are coated with an 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;
  A pair of metal pressure plates provided so as to be partially exposed from the case, and sandwiching the pair of ceramic insulating plates;
  A metal fastening material that penetrates one to the other of the pair of metal pressure plates through an insulating sleeve and integrates the pair of metal pressure plates, the pair of ceramic insulation plates, the pair of electrodes, and the piezoelectric element; A load sensor comprising:
  Each of the pair of ceramic insulating plates is coated with the insulating resin coating material on the entire surface thereof.

Images