JP5061387B2 - Electrode probe and capacitance load cell using the same - Google Patents

Description

  The present invention relates to a probe having a capacitance measuring electrode on its surface and a capacitance load meter using the probe.

  There are several types of load cells with different load measurement principles, and various load cells are used in various fields depending on their characteristics. For example, in the ground anchor method for stabilizing the slope and supporting the structure, etc., with tension applied to a tension material such as a PC strand that is fixed at one end to the anchor body in the ground, A plate or structure for stabilizing the slope is fixed, and a load meter is installed at the other end fixing part for measuring tension fluctuation during construction of the tension material and monitoring long-term tension after construction. Yes. Similarly, load cables for measuring tension are often installed on cables of suspension structures. As the load cell, one that uses the change in electrical resistance of the strain gauge when a load is applied (strain gauge type) is generally used, and one that uses the pressure change of the enclosed oil (hydraulic enclosure type) In some cases, a magnetostrictive type that uses a magnetic change due to magnetostriction is used.

  However, among the various load cells, the strain gauge type and the magnetostrictive type have a problem that the overall size of the load cell tends to be large, and the hydraulically sealed type can be downsized but has a low measurement accuracy. In either method, since the main body and the sensor part are integrally formed, it is difficult to replace only the sensor part in a loaded state. When a failure occurs or when periodic inspections are performed, the load load is completely removed. After that, it is necessary to replace the entire load cell, and this replacement work is very troublesome. For this reason, the practical application of a load cell that can replace these types is desired, and a capacitive load cell is one of the candidates.

As shown in FIG. 9, the capacitance type load cell is formed with a circular hole 51b between two parallel pressure receiving surfaces 51a of a plate 51 that receives a load, and two circular pressure holes 51b are formed on the inner peripheral surface of the circular hole 51b. The plate-like electrode 52 is fixed in a state of being opposed to each other in parallel with a predetermined gap along a direction orthogonal to the plate pressure receiving surface 51a, and the distance between the electrodes 52 due to elastic deformation of the plate 51 under load. It is designed to measure the load based on the change in capacitance due to the change (see, for example, Patent Documents 1 and 2). In principle, it can be made smaller than the strain gauge type or magnetostrictive type. And equivalent measurement accuracy can be obtained.
Japanese Patent Laid-Open No. 56-130629 (FIG. 1) JP 54-103082 A (FIG. 1)

  However, in the above-described conventional capacitive load cell, each electrode is fixed to the inner peripheral surface of the circular hole of the plate that is elastically deformed by receiving a load, and it is difficult to replace only this sensor portion in the loaded state. For this reason, there is the same problem as other various load cells in that it is necessary to replace the entire load cell except for the load when it breaks down.

  An object of the present invention is to enable replacement of only a sensor portion of a capacitive load cell in a loaded state.

  In order to solve the above problems, in the present invention, as a part of a capacitive load cell, it is inserted into a circular hole formed between two parallel pressure receiving surfaces of a plate that receives a load. An electrode is provided on the outer peripheral surface of the insulating cylindrical body formed to have a diameter smaller than the inner diameter of the circular hole of the plate along a partial region in the circumferential direction, and is pressed against the inner peripheral surface of the circular hole of the plate An attachment member is provided, and the attachment member is made of an elastic member, and with the electrode, a predetermined gap is formed between the electrode and the plate side electrode provided on the inner peripheral surface of the circular hole of the plate. A probe was adopted.

  That is, an attachment member is provided that presses a probe with an electrode, which is a sensor portion inserted into a circular hole of a plate of a capacitive load meter, onto a cylindrical body having an electrode on the outer peripheral surface thereof to the inner peripheral surface of the circular hole of the plate. Since the electrode is supported by the plate in a state of facing the plate side electrode with a predetermined gap, it can be easily attached to and detached from the plate even when the capacitive load meter is in a loaded state. I did it.

  Here, the mounting member is a ball plunger in which a spring and a ball used as the elastic member are accommodated in a case, and the ball urged by the spring is partially protruded from the opening of the case. When the ball is fixed to the cylindrical body in a state of being urged outward in the radial direction of the cylindrical body and the ball is pressed against the inner peripheral surface of the circular hole of the plate, the probe is more stable. It will be supported by the plate.

  And the capacitance type load cell of the present invention inserts the electrode-provided probe of the above configuration into the circular hole of the plate, and presses the mounting member of the probe against the inner peripheral surface of the circular hole of the plate, A load acting on the pressure receiving surface of the plate is supported by supporting the probe in a state where the electrode of the probe is opposed to the plate side electrode provided on the inner peripheral surface of the circular hole of the plate with a predetermined gap. Measurement is based on the change in capacitance between the electrode of the probe and the plate-side electrode caused by the deformation of the circular hole caused by the elastic deformation of the plate. Can be replaced.

  Here, the plate may be made of metal and used as the plate-side electrode, or may be made of an insulator, and the plate-side electrode formed in a cylindrical shape is fitted on the inner peripheral surface of the circular hole. And may be integrally deformed with the plate side electrode.

  In the capacitance type load cell having the above configuration, a plurality of electrodes of the probe are provided at 90 ° intervals in the circumferential direction of the cylindrical body, and at least one of these electrodes is orthogonal to the pressure receiving surface of the plate. A capacitance between electrodes facing the plate side electrode along the direction and facing along the direction orthogonal to the plate pressure receiving surface, and electrodes facing along the direction parallel to the plate pressure receiving surface It is desirable to obtain the load acting on the pressure receiving surface of the plate using the difference between the capacitance between the plate and the plate. At this time, by using the average value of the two measured values as the capacitance in the direction orthogonal to the plate pressure receiving surface and the capacitance in the direction parallel to the plate pressure receiving surface, the eccentricity generated when the probe is replaced is determined. The influence can be reduced.

  In other words, in the capacitance type load cell, the capacitance between the electrodes changes even when the plate is deformed due to the temperature change of the environment. By measuring the capacitance in the compression direction and expansion direction of the circular hole of the plate that receives the load from the plate, and obtaining the load using the difference, the temperature effect of the measured change in capacitance is offset. Measurement accuracy can be ensured without correction.

  Here, if the plate has an annular shape with both end faces as the pressure receiving surfaces, the load meter is suitable for measuring the tension acting on the wire rod-like member.

  Further, if the circular plate is provided with a plurality of radial holes in the annular plate and the probe is inserted into any of the circular holes, the measurement position of the pressure receiving surface can be easily changed, The load distribution on the pressure receiving surface can also be obtained using a probe.

  As described above, according to the present invention, only the electrode-equipped probe as the sensor portion can be easily replaced even when the capacitance load meter is in a loaded state. The work efficiency can be greatly improved by omitting the unloading process and the reloading process when the machine breaks down or when performing periodic inspection.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 8. As shown in FIG. 1, the capacitive load cell 1 according to this embodiment is formed between an annular plate 2 having both pressure-receiving surfaces 2 a parallel to each other, and both pressure-receiving surfaces 2 a of the plate 2. It is basically composed of a probe 3 with an electrode inserted into a plurality of circular holes 2b.

  The plate 2 is made of stainless steel, and the inner peripheral surface of each circular hole 2 b is also used as a plate-side electrode facing the probe 3. Each circular hole 2b is formed radially at equal intervals in the circumferential direction of the plate, and probes 3 are inserted into every other one of them. Further, in the vicinity of the outer periphery, a hole 2c used for positioning of the probe 3 is formed so as to penetrate from each pressure receiving surface 2a to each circular hole 2b as described later.

  Here, the material of the plate is not limited as long as it is elastically deformed to some extent under load, and may be formed of a metal other than stainless steel, or the plate is formed of an insulator such as hard rubber, and the circular hole A thin plate-side electrode formed in a cylindrical shape may be fitted on the inner peripheral surface so that the plate and the plate-side electrode are integrally deformed.

  As shown in FIGS. 2 and 5, disc-shaped lids 4 and 5 are attached to both ends of each circular hole 2 b of the plate 2 to block the opening of the circular hole 2 b and protect the probe 3. The lid 4 on the inner peripheral side of the plate is inserted into the circular hole 2b from the outer peripheral side of the plate, and is adhered to the inner surface of the annular protrusion 2d formed at the inner peripheral side end of the circular hole 2b. On the other hand, the lid 5 on the outer peripheral side of the plate has a threaded portion on the outer periphery thereof, and is bonded to the counterbore 2e at the outer peripheral side of the plate of the circular hole 2b. The materials of the lids 4 and 5 and the female screw member 6 are preferably made of a synthetic resin that has durability and has little influence on the elastic deformation of the plate 2.

  As shown in FIGS. 2 to 5, the probe 3 is formed on an outer peripheral surface of a cylindrical body 7 formed by an insulator so as to have a diameter smaller than the inner diameter of the circular hole 2 b of the plate 2 at 90 ° intervals along the circumferential direction. Four electrodes 8 are provided so as not to contact each other, and four ball plungers (attachment members) 9 are provided at both ends of the cylindrical body 7 so as not to interfere with each electrode 8. Of the ball plungers 9, four on one end side of the cylindrical body 7 are arranged at the same cylindrical circumferential position as the electrode 8, and four on the other end side of the cylindrical body 7 are arranged around the electrode 8 and the cylindrical body periphery. Arranged alternately in the direction. The insulator forming the cylindrical body 7 is preferably engineering plastic or ceramic having durability and small thermal deformation. In this embodiment, polyether ether ketone (PEEK) is used.

  As shown in FIG. 2, the electrode 8 includes a rectangular plate-shaped measurement electrode 8a and a rectangular frame plate-shaped protective electrode 8b surrounding the measurement electrode 8a with a slight space therebetween. It is welded to the outer peripheral surface with a welding film (not shown). This protective electrode 8b prevents the disturbance of the electric field generated at the outer periphery of the measurement electrode 8a and stabilizes the measured value of the capacitance. Gold, silver, copper, nickel, copper nickel, or the like can be used as the material for the measurement electrode 8a and the protective electrode 8b. As shown in FIG. 5, the measuring electrode 8a and the protective electrode 8b are connected to a lead wire 11 through metal conducting pins 10 that penetrate the cylindrical body 7 in the radial direction, and the lead wire 11 is It passes through a protective tube 12 that penetrates the center of the lid 5 on the outer peripheral side of the plate and is drawn out.

  As shown in FIGS. 3 and 5, the ball plunger 9 accommodates a coil spring 14 and a ball 15 as elastic members in a cylindrical case 13, and the ball 15 biased by the spring 14 is accommodated in the case 13. The case 13 is partially protruded from the opening at one end, and the case 13 penetrates the cylindrical body 7 in the radial direction, and the ball 15 is fixed to the cylindrical body 7 in a state of being urged toward the radial outer side of the cylindrical body 7. ing. In addition, among the ball plungers 9 on one end side of the cylindrical body 7, a pair facing each other has a radial size larger than the others in order to perform positioning when the probe 3 is inserted into the plate 2 as described later. The one with large is used.

  Then, the probe 3 is inserted into the circular hole 2b so that one end side of the cylindrical body 7 is located on the outer peripheral side of the plate 2, and the balls 15 of the pair of ball plungers 9 having a large radial size are inserted into the positioning holes of the plate 2. When aligned with the position of 2c, two of the electrodes 8 of the probe 3 are along the direction orthogonal to the plate pressure receiving surface 2a, and the other two are along the direction parallel to the plate pressure receiving surface 2a. The ball 15 of each ball plunger 9 is pressed against the inner peripheral surface of the circular hole 2b so as to face the inner peripheral surface, that is, the plate-side electrode. Thereby, the probe 3 is stably supported by the plate 2 in a state where a predetermined gap is formed between each electrode 8 and the plate-side electrode. Although not shown in the drawings, a static electricity is provided between a lead wire connected to the ground electrode plate or the direct plate 2 provided in advance for the probe 3 and a lead wire 11 connected to each electrode 8 of the probe 3 for grounding. By connecting a capacitance meter, the capacitance can be measured in the direction in which the circular hole 2b is compressed and the direction in which it is expanded when a load is applied to the plate pressure receiving surface 2a. Moreover, since the probe 3 simply presses the ball 15 biased by the spring 14 against the inner peripheral surface of the circular hole 2b of the plate 2, it can be easily attached and detached even when a load is applied to the plate 2. it can.

Next, a test for confirming the change behavior of the capacitance measurement value when a load was applied to the load cell 1 was performed. In this test, as shown in FIG. 6, both loadings are performed with a Teflon sheet 18 as an insulator sandwiched between the upper and lower loading boards 16, 17 of the compression testing machine and the plate pressure receiving surface 2 a of the load cell 1. A load was applied stepwise from the panels 16 and 17 to the load cell 1 and the change in capacitance between each electrode 8 of the probe 3 and the inner peripheral surface of the circular hole 2b of the plate 2 was measured. The test conditions are as follows. The reason why the Teflon sheet 18 is sandwiched between the loading boards 16 and 17 and the load cell 1 is to make the measurement ungrounded. If the probe 3 is connected to the ground via the plate 2 or is grounded directly from the probe 3 to the ground, the Teflon sheet 18 is not required. However, in order to stabilize the measured value, a non-grounded type is required. Is preferable.
<Test conditions>
・ Plate dimensions: 120mm outer diameter, 68mm inner diameter, 30mm height
・ Load load: 0-200kN
・ Input voltage: 5V

FIG. 7 shows the measurement results of the change in capacitance in the above test. Of these, FIG.
A measured value of the capacitance between the upper and lower electrodes 8 of the probe 3 and the inner peripheral surface of the circular hole 2b of the plate 2, that is, between the electrodes facing each other along the direction orthogonal to the plate pressure receiving surface 2a (upper and lower average value) FIG. 7 (b) is a diagram between the left and right electrodes 8 of the probe 3 and the inner peripheral surface of the circular hole 2b of the plate 2, that is, between the electrodes facing each other along the direction parallel to the plate pressure receiving surface 2a. The measured value of capacitance (left and right average value) is shown. FIG. 7C shows the difference between the measured upper and lower average value of the capacitance and the left and right average value.

  As is clear from FIG. 7, when the load applied to the load meter 1 increases, the vertical average value of the electrostatic capacitance is substantially increased as the circular hole 2b of the plate 2 is compressed in the vertical direction and expanded in the horizontal direction. It increases linearly, and the left and right average value decreases almost linearly. For this reason, the difference between the vertical average value and the horizontal average value is also substantially proportional to the load, and it was confirmed that the load can be measured from the measured capacitance value using this relationship.

  As described above, the capacitance type load cell 1 can easily replace the probe 3 with an electrode inserted into the circular hole 2b of the annular plate 2 even in a loaded state. When a failure occurs during the inspection or when a periodic inspection is performed, the unloading process and the reloading process are not required, and the work can be performed efficiently.

  In addition, since the capacitance is measured in the compression direction and the expansion direction of the circular hole 2b of the plate 2 that receives a load from one direction, and the difference can be used to measure the load, the diameter of the circular hole 2b depends on the environmental temperature. Even if it changes as a whole, it is not affected by the change in capacitance. Similarly, the influence of the electrical in-phase fluctuation and the secular change of the inner peripheral surface property of the circular hole 2b can be suppressed, and the measurement accuracy can be ensured without correcting the temperature influence as in the conventional case.

  Of course, like the conventional capacitance type load cell, it can be made smaller than the strain gauge type or magnetostriction type, and the load can be measured from a minute deformation of the plate 2, so that the plate 2 can be made robust. By doing so, the load resistance can be increased and the measurement range can be widened.

  FIG. 8 shows an example of a usage state of the capacitive load cell 1 of the embodiment described above. In this usage example, the tension of the PC strand 20 used as a tension material for fixing the anchor plate 19 on the slope G is measured in the ground anchor method for slope stability. One end of the PC strand 20 is passed through the anticorrosion pipe 21 and fixed with a grout 22 with one end fixed to the ground and pulled. A load meter 1 sandwiched between two pressure receiving plates 24 is installed between a fixing tool 23 attached to the other end of the PC strand 20 and the anchor plate 19.

  Here, the load meter 1 is a ring-shaped plate 2 with both end surfaces being pressure-receiving surfaces 2a, so that it is suitable for measuring the tension acting on the wire rod-like member as in the above-described use example. Yes. The plate 2 is provided with a plurality of circular holes 2b in a radial pattern so that the probe 3 can be inserted into any circular hole 2b, so that the measurement position of the pressure receiving surface 2a can be easily changed. In addition, the load distribution on the pressure receiving surface 2a can be obtained using a plurality of probes 3.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  For example, the shape of the plate is not limited to the annular shape as in the embodiment, but may be a rectangular plate shape or a disk shape depending on the application, and at least one circular hole or probe electrode is provided. It only has to be. Further, the probe can be used not only as a set with a plate but also by being inserted into a circular hole formed in the load measurement target member itself. Further, the probe mounting member does not necessarily adopt the ball plunger as in the embodiment, and an elastic member such as rubber attached to the cylindrical body may be directly pressed against the inner peripheral surface of the circular hole of the plate.

a is an external perspective view of the capacitive load cell of the embodiment, b is a front view of a, and c is a partially cutaway plan view of a. Fig. 1 (c) main part enlarged plan sectional view Sectional view along line III-III in FIG. Sectional view along line IV-IV in FIG. Sectional view along line VV in FIG. Explanatory drawing of the test method for the load cell in FIG. a, b, and c are graphs showing test results of the load cell of FIG. Explanatory drawing of usage example of load cell of FIG. Front view of the main parts of a conventional capacitive load cell

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Capacitance type load cell 2 Plate 2a Pressure receiving surface 2b Circular hole 3 Probe 4, 5 Lid 7 Cylindrical body 8 Electrode 9 Ball plunger 13 Case 14 Spring 15 Ball

Claims (4)

As a part of the capacitance type load cell, it is inserted into a circular hole formed between two parallel pressure-receiving surfaces of a plate that receives a load, and is formed with a diameter smaller than the inner diameter of the circular hole of the plate. An electrode is provided on the outer peripheral surface of the insulating cylindrical body along a partial region in the circumferential direction, and an attachment member that is pressed against the inner peripheral surface of the circular hole of the plate is provided. The attachment member is made of an elastic member. As a thing, the probe with an electrode which can replace even if the load meter which made the predetermined clearance gap formed between the said electrode and the plate side electrode provided in the circular hole inner peripheral surface of the said plate is a load state . The mounting member is a ball plunger in which a spring and a ball used as the elastic member are housed in a case, and the ball urged by the spring is partially projected from the opening of the case, and the ball plunger is the cylindrical body. The ball according to claim 1, wherein the ball is fixed in a state of being urged outward in the radial direction of the cylindrical body, and the ball is pressed against the inner peripheral surface of the circular hole of the plate. Probe with electrodes that can be replaced even when the load cell is under load . 3. The probe with an electrode according to claim 1 or 2 is inserted into a circular hole of the plate, and an attachment member of the probe is pressed against an inner peripheral surface of the circular hole of the plate, whereby the electrode of the probe is made circular. A circular hole generated by elastic deformation of the plate that supports the probe in a state facing a plate-side electrode provided on the inner peripheral surface of the hole with a predetermined gap and acts on the pressure-receiving surface of the plate In a capacitive load meter that measures based on a change in capacitance between the electrode of the probe and the plate-side electrode due to deformation of the probe,
The plate is formed of an insulator, and the plate-side electrode formed in a cylindrical shape is fitted on the inner peripheral surface of the circular hole so that the plate and the plate-side electrode are deformed integrally. Capacitive load cell.   A plurality of electrodes of the probe are provided at intervals of 90 ° in the circumferential direction of the cylindrical body, and at least one of these electrodes is opposed to the plate side electrode along a direction orthogonal to the pressure receiving surface of the plate, Using the difference between the capacitance between the electrodes facing along the direction orthogonal to the plate pressure-receiving surface and the capacitance between the electrodes facing along the direction parallel to the plate pressure-receiving surface, 4. The capacitive load cell according to claim 3, wherein a load acting on the pressure receiving surface of the plate is obtained.

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