JP2013079837A - Surface pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface pressure sensor which has small variation with time and small temperature dependence, capable of measuring accurate values through repetitive use.SOLUTION: A surface pressure sensor comprises a substrate 11, and a plurality of metal resistance strain gauges 12 which are directly disposed on the substrate 11. The lower face side of the substrate 11 is provided with recesses 14 at the positions corresponding to the one or more metal resistance strain gauges 12 such that the substrate 11 is deformable.

Description

  The present invention relates to a surface pressure sensor for measuring a pressure distribution.

For example, a sheet-like surface pressure sensor is generally used to measure press pressure, roll pressure, and the like. Hereinafter, examples of conventionally known surface pressure sensors and pressure measuring methods will be described.
In the surface pressure sensor shown in Patent Document 1, a row electrode and a column electrode arranged in an orthogonal direction are arranged between two flexible films, and a pressure sensitive property is provided between the row electrode and the column electrode. Conductive ink is interposed.
When a pressure is applied to the surface pressure sensor, the resistance value between the row electrode and the column electrode differs depending on the location. Therefore, the pressure distribution can be measured by detecting the resistance value at each intersection.

  Moreover, the pressure measurement method shown in Patent Document 2 uses a pressure measurement film (so-called pressure paper) whose color development state changes when pressed. In this measurement method, a pressure measurement film is sandwiched between members to be measured with an elastic sheet or the like interposed therebetween, and a pressure distribution is read from a change in color development state.

Japanese Patent No. 3089455 Japanese Patent No. 3911363

The surface pressure sensor described in the above-mentioned Patent Document 1 has a problem that a change with time and temperature dependence are large, and the reliability of the measured pressure value is low.
Moreover, in the pressure measuring method described in Patent Document 2, since the pressure measuring film can be used only once, there is a problem that it is desired to use it repeatedly. In addition, since the pressure must be determined based on the shade of the color, there is a problem that measurement with an accurate value cannot be performed.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a surface pressure sensor that is small in change with time and temperature dependency, can be repeatedly used, and can measure an accurate value.

According to the surface pressure sensor of the present invention, the substrate includes a substrate and a plurality of metal resistance strain gauges directly formed on the substrate, and one or more metal resistance strains are provided on the lower surface side of the substrate. A recess is formed at a position corresponding to the gauge so that the substrate can be deformed.
As a result, when the pressure-sensitive conductive ink as in Patent Document 1 is used, the output fluctuation of the surface pressure sensor due to the temperature change of several% / ° C. is the resistance as the sensor element of the surface pressure sensor. By adopting a metal resistance strain gauge with a small temperature coefficient, it was possible to achieve output fluctuation of the surface pressure sensor due to a temperature change of 1% / ° C. or less. Therefore, the surface pressure sensor of the present invention can reduce the temperature dependence, and the change with time is small, so that it can be used repeatedly. And an exact pressure value can be measured.
Since the metal resistance type strain gauge is directly formed on the substrate, the metal resistance type strain gauge can be arranged at an extremely small interval, and a finer pressure distribution can be measured. Furthermore, by forming the metal resistance strain gauge directly on the substrate, it is possible to obtain a thin surface pressure sensor, and at the manufacturing stage of the surface pressure sensor, it is possible to significantly reduce the number of man-hours. Reduces variation when attaching gauges and contributes to improved measurement accuracy.

In addition, in order to allow a constant current to flow through all the metal resistance type strain gauges, the metal resistance type strain gauges are wired in series so that the resistance values of the metal resistance type strain gauges can be measured by a four-terminal method. A constant current wiring to be formed is formed, and resistance value measuring wirings for measuring a resistance value are formed at both ends of each of the metal resistance strain gauges.
Wiring of a conventional surface pressure sensor is generally a matrix circuit, but the measured value in the matrix circuit includes the wiring resistance, and thus correction is necessary. Although there are various correction methods, it was not possible to detect a change only in the sensitive element, and an accurate resistance value in the sensitive element could not be detected. For load cells, etc., a wiring method using a bridge circuit is generally adopted. However, in a bridge circuit, four wires are required for one sensing element, and a bridge resistance is required. Was necessary.
However, according to the said structure of this invention, the measurement of the exact resistance value in each metal resistance type | mold strain gauge is possible by measuring by a four terminal method. By wiring current paths in series with all the metal resistance strain gauges, the number of wirings can be reduced, and the sensor can be saved in space and reduced in size.

In addition, a wiring portion for electrical connection between a measuring device outside the substrate and each metal resistance strain gauge in the substrate is formed on the flexible printed circuit board, and the constant current wiring and the resistance value of the substrate The measurement wiring may be electrically connected to the wiring portion of the flexible board, and the board and the flexible printed board may be integrally formed with a film.
According to this configuration, since the flexibility including the wiring portion can be enhanced as a whole, for example, in the case of measuring the roll pressure, it is easy to route.

The top surface of the substrate covers the metal resistance strain gauge, the constant current wiring, and the resistance measurement wiring, and can be elastically deformed to facilitate deformation of the substrate when subjected to pressure. A protective film may be formed.
For example, when a hard plate-like member is the object to be measured, there is a possibility that measurement cannot be performed because the substrate is not deformed. However, according to this configuration, the protective film is elastically deformed. Measurement is possible.

  According to the surface pressure sensor of the present invention, changes with time and temperature dependence are small, and it can be used repeatedly and an accurate value can be measured.

It is a top view of a 1st embodiment of a surface pressure sensor concerning the present invention. It is A-A 'sectional drawing of FIG. It is explanatory drawing which shows that the pressure was applied to the whole surface in sectional drawing of FIG. It is explanatory drawing which shows that the pressure was applied to a part in sectional drawing of FIG. It is a top view of a 2nd embodiment of a surface pressure sensor. It is a top view of a 3rd embodiment of a surface pressure sensor. It is an enlarged view of the A part of FIG. It is an enlarged view of the B part of FIG. It is a top view which shows the place which connected the wiring to an external apparatus to the surface pressure sensor of FIG.

A preferred embodiment of a surface pressure sensor according to the present invention will be described below.
FIG. 1 is a plan view showing the overall configuration of the surface pressure sensor, and FIG. 2 is a cross-sectional view taken along the line AA ′ in FIG.
The surface pressure sensor 10 is configured by arranging a plurality of metal resistance strain gauges 12 on a substrate 11.
In this embodiment, in order to make the structure easy to understand, a metal resistance type strain gauge 12 having a small number of metal resistance type strain gauges of 9 in 3 rows and 3 columns is taken as an example for explanation.

As the substrate 11 in this embodiment, a ceramic such as zirconia is employed. Depending on the application, for example, when used for measuring the roll pressure, the thickness of the substrate 11 is assumed to be about 0.1 mm.
A plurality of recesses 14 are formed on the lower surface of the substrate 11. In the present embodiment, one circular recess 14 in plan view is formed below one metal resistance strain gauge 12. By forming such a concave portion 14 below the metal resistance strain gauge 12, the upper surface of the formed concave portion 14 becomes thinner than other portions where no concave portion is formed, and deforms when pressure is applied, The metal resistance strain gauge 12 can be deformed.

In the present embodiment, the depth of the recess 14 is assumed to be about 50 μm, which is a half of the thickness when the substrate thickness is 0.1 mm.
Further, the measurement range of the surface pressure sensor 10 can be changed by adjusting the depth of the recess 14. For example, if the concave portion 14 is deepened, it becomes a low pressure range, and if it is shallow, it becomes a high pressure range.

  A metal resistance strain gauge 12 is directly formed on the substrate 11. As a method of directly forming a film, vapor deposition or sputtering can be considered. Specifically, in the present embodiment, a Cr—N thin film is formed by reactive sputtering as the metal resistance type strain gauge 12. The Cr-N thin film is formed by reactive sputtering of an alloy containing Cr and other metals in a nitrogen atmosphere, and the nitrogen flow rate is controlled in a very small region and annealed after the thin film is formed. It is formed with a very low resistance temperature coefficient. Such a method for producing a Cr—N thin film having a very low temperature coefficient of resistance has already been proposed in the past patent application (Japanese Patent No. 3642449) of the present applicant.

For example, according to the method described in the above-mentioned patent document, the resistance temperature coefficient is 48 ppm / ° C., and when converted to sensor output, a metal resistance strain gauge of 0.16% / ° C. can be created.
By employing the metal resistance type strain gauge 12 having such performance, an accurate resistance value can be detected even under various temperature environments.

In addition, by directly forming the metal resistance type strain gauge 12 on the substrate 11, it is possible to save the trouble of attaching the strain gauge that has been made in advance to the substrate, and to shorten the manufacturing process. In addition, by forming the metal resistance strain gauge 12 directly on the substrate 11, the metal resistance strain gauges 12 can be arranged at minute intervals, and the pressure distribution can be measured in a very fine range.
In the present invention, the metal resistance strain gauge 12 is not limited to a Cr—N thin film, and Ni—Cr or the like may be adopted.

The metal resistance strain gauge 12 is formed so that its resistance value can be measured by a four-terminal method. The four-terminal method is a measurement method that can eliminate the influence of the impedance of the wiring portion when measuring the resistance value.
In addition, the constant current flowing to each metal resistance type strain gauge 12 is performed by one constant current wiring 16. That is, the metal resistance strain gauges 12 are connected in series by the constant current wiring 16.

For example, taking FIG. 1 as an example, the wiring structure of each metal resistance strain gauge 12 will be described in detail.
In FIG. 1, on the lower side of the drawing, terminal portions of wirings connected to the respective metal resistance type strain gauges 12 are formed. The rightmost side a of this terminal portion is one end of the constant current wiring 16. When the constant current wiring 16 is traced upward, the metal resistance strain gauge 12 at the upper right is reached. The constant current wiring 16 connects the upper three metal resistance strain gauges 12 in series, and extends downward from the upper left metal resistance strain gauge 12. Then, the three metal resistance strain gauges 12 in the middle row are connected in series (it is difficult to understand because they coincide with the line AA ′ in the figure), and head to the metal resistance strain gauge 12 in the lower right. The three metal resistance strain gauges 12 in the lower row are connected in series, and the metal resistance strain gauge 12 on the lower left is directed to the terminal portion. The fourth b from the left of the terminal portion is the other end of the constant current wiring 16.

Further, a plurality of wirings are further formed in the terminal portion, which are the ends of the resistance value (voltage) measurement wirings 19 connected to both ends of each metal resistance type strain gauge 12. . However, since nine metal resistance strain gauges 12 are connected in series by one constant current wiring 16, the resistance value measurement wiring 19 disposed between the adjacent metal resistance strain gauges 12 is Shared with the adjacent metal resistance type strain gauge 12.
Thus, by connecting each metal resistance type strain gauge 12 in series with the constant current wiring 16, the number of wirings can be reduced, and the entire sensor can be miniaturized.

  As shown in FIG. 2, a metal resistance strain gauge 12 is formed on the upper surface of the substrate 11, and a protective film 20 for protecting the metal resistance strain gauge is formed thereon. The protective film 20 may be any material as long as it is an insulating and flexible material. As the protective film 20, for example, a material such as polyimide can be employed.

Further, by providing the protective film 20 that is elastically deformed to some extent, the substrate 11 can be smoothly deformed.
For example, if the object to be measured is a soft flat plate or the like, it is considered that the substrate 11 can be easily deformed. However, if the object to be measured is a hard flat plate or the like, the pressure at the metal resistance strain gauge 12 is not deformed. Measurement may be difficult.
Therefore, by providing the protective film 20, even if the measurement object is a hard flat plate or the like, the substrate 11 is also deformed by the elastic deformation of the protective film 20, and the pressure can be reliably measured.

  In addition, if the thickness of the protective film 20 is large, the elastic deformation of the protective film 20 also increases and the substrate 11 can be reliably deformed. . Therefore, by forming minute protrusions on the protective film 20 at a plurality of locations, the deformation of the substrate 11 can be ensured even if the thickness is reduced, and the roll pressure and the like can be easily measured because the thickness is thin. Is called.

3 to 4 show a state where pressure is applied to the surface pressure sensor.
FIG. 3 shows a state in which pressure is applied to the entire surface of the surface pressure sensor 10 by a pressing member 30 such as a flat plate or a roll while the surface pressure sensor 10 is placed on the base 31.
When pressure is applied to the entire surface of the surface pressure sensor 10, the substrate 11. The portion where the recess 14 is formed is deformed, and the metal resistance strain gauge 12 present at the position corresponding to the recess 14 is also deformed. The resistance value changes due to the deformation of the metal resistance strain gauge 12, and the pressure distribution can be measured as a surface pressure sensor by converting the resistance value into a pressure value.

FIG. 4 shows a state in which pressure is applied to a part of the surface pressure sensor 10 by a pressing member 30 such as a flat plate or a roll while the surface pressure sensor 10 is placed on the base 31. In the present embodiment, the pressure is applied only to the center of the drawing.
When pressure is applied only to a predetermined portion of the surface pressure sensor 10, a portion where the concave portion 14 is formed in the portion where the pressure is applied is deformed, and the metal resistance strain gauge 12 existing at a position corresponding to the concave portion 14 is also deformed. . Here, since only the metal resistance type strain gauge 12 located in the center of the drawing is deformed and the resistance value changes, it is possible to detect that only the center portion of the drawing is under pressure and measure the pressure value.

FIG. 5 shows a plan view of another embodiment.
The surface pressure sensor 10 shown in FIG. 5 has a total of 25 metal resistance strain gauges 12 arranged in 5 rows and 5 columns.
The embodiment described above is different from the embodiment described above only in the number of metal resistance type strain gauges 12, and the other configuration is the same as that of the embodiment described above. Accordingly, the same components as those in the above embodiment are denoted by the same reference numerals and description thereof is omitted here.

  In the surface pressure sensor 10 shown in FIG. 5, the pattern widths of the terminal portions a and b of the constant current wiring 16 are formed wider than the pattern width of the resistance value measurement wiring 19. For this reason, the impedance of the constant current wiring 16 itself can be reduced.

FIG. 6 shows a plan view of another embodiment.
The surface pressure sensor shown in FIG. 6 has a total of 40 metal resistance strain gauges 12 arranged in 40 rows and 1 column. Accordingly, the sensor has a shape that is long in the vertical direction in the drawing.
7 shows an enlarged view of a portion A of the surface pressure sensor of FIG. 6, and FIG. 8 shows an enlarged view of a portion B of the surface pressure sensor of FIG.
As shown in FIG. 7, each metal resistance type strain gauge 12 has a zigzag folded shape in which the thin film is folded at two left and right positions. Each metal resistance type strain gauge 12 having such a shape is formed continuously in the vertical direction. A constant current wiring 16 for sending a constant current is connected to the uppermost and lowermost metal resistance strain gauges 12, and a constant current is passed through each metal resistance strain gauge 12.

Further, the plurality of metal resistance strain gauges 12 are formed continuously, and in this embodiment, five metal wires extending in the lateral direction (left and right direction) are used as one metal resistance strain gauge 12.
In order to measure the resistance value of one metal resistance type strain gauge 12, one resistance value measurement wiring 19 is connected from both the left and right sides of one metal resistance type strain gauge 12. In the present embodiment, since the plurality of metal resistance strain gauges 12 are continuously formed, the resistance measurement wiring 19 of the metal resistance strain gauge 12 adjacent in the vertical direction is the adjacent metal resistance strain gauge. 12 and shared.

In addition, the concave portion 14 in the present embodiment is different from that described in the first embodiment, and a plurality of metal resistance-type strains are formed by continuously forming one concave portion 14 that is elongated in the vertical direction. It is provided below the gauge 12.
As described above, the shape and number of the concave portions 14 can be appropriately changed according to the shape of the metal resistance strain gauge 12.

As shown in FIG. 8, the terminal portions of the constant current wiring 16 and the resistance value measuring wiring 19 are aligned in the horizontal direction at a predetermined interval.
In the present embodiment, the wiring width is 0.1 mm, and the distance from each wiring is also 0.1 mm.

The surface pressure sensor 10 of each embodiment described above is connected to a computer which is an external device, and the pressure distribution is analyzed. The electrical connection between the terminal portion of the surface pressure sensor 10 and the computer may be performed by a flexible printed circuit (FPC).
FIG. 9 shows a sensor structure in which the surface pressure sensor 10 of the embodiment shown in FIG. 5 is connected to a flexible substrate 22.
The terminal portion of the substrate 11 and the wiring 24 formed on the flexible substrate 22 can be connected using, for example, an anisotropic conductive film (ACF). In addition, the substrate 11 and the flexible substrate 22 may be covered with some film so that the substrate 11 and the flexible substrate 22 are integrally formed. For example, it is possible to strengthen the bonding between the substrate 11 and the flexible substrate by covering the flexible substrate with polyimide as the protective film 20 of the substrate 11.

  Thus, by wiring the electrical connection between the surface pressure sensor 10 and the computer with the flexible board 22, the surface pressure sensor 10 can be used with flexibility. For example, also in the measurement of a roll pressure etc., routing becomes easy.

  In addition, although the ceramic was demonstrated as a material of the board | substrate 11 mentioned above, metals, such as stainless steel, are also employable as a material. However, if the substrate 11 is made of metal, it is necessary to provide an insulating layer between the metal resistance strain gauge 12. However, if an insulating layer is provided, the substrate 11 may be warped due to a difference in thermal expansion coefficient, which is not a preferable mode.

DESCRIPTION OF SYMBOLS 10 Surface pressure sensor 11 Board | substrate 12 Metal resistance type strain gauge 14 Recessed part 16 Constant current wiring 19 Resistance value measurement wiring 20 Protective film 22 Flexible substrate 24 Wiring 30 Pressing member 31 Base

Claims (4)

A substrate,
A plurality of metal resistance type strain gauges formed directly on the substrate,
A surface pressure sensor characterized in that a recess is formed on the lower surface side of the substrate at a position corresponding to one or more metal resistance strain gauges so that the substrate can be deformed. In order to be able to measure the resistance value of each metal resistance type strain gauge by the four probe method,
In order to flow a constant current to all of the metal resistance type strain gauges, a constant current wiring for wiring the metal resistance type strain gauges in series is formed,
2. The surface pressure sensor according to claim 1, wherein resistance value measurement wiring for measuring a resistance value is formed at both ends of each of the metal resistance strain gauges. A wiring part for electrical connection between the measuring device outside the board and each metal resistance strain gauge inside the board is formed on the flexible printed board,
The constant current wiring and the resistance value measurement wiring of the substrate are electrically connected to the wiring portion of the flexible substrate,
The surface pressure sensor according to claim 1, wherein the substrate and the flexible printed circuit board are integrally formed of a film.   A protective film that covers the metal resistance strain gauge, the constant current wiring, and the resistance measurement wiring on the upper surface of the substrate, and is elastically deformable to facilitate deformation of the substrate when subjected to pressure The surface pressure sensor according to claim 1, wherein the surface pressure sensor is formed.

Images