JP5704803B2 - Pressure sensor - Google Patents

Description

The present invention relates to a pressure sensor, and provides a pressure sensor that can be used in a wide range of fields such as robots, printing apparatuses, and dispensers, and can perform highly sensitive pressure measurement while being particularly small and thin. .

  Conventionally, a pressure sensor that measures a pressing force is used to perform various controls. For example, there is one that converts a pressing force into an electric signal using a piezoelectric element. However, with a pressure sensor using a piezoelectric element, it has been difficult to measure a small pressing force with high accuracy.

  Therefore, in the following Patent Document 1, a coil is embedded in an elastically deformable soft resin in which soft magnetic powder such as ferrite is dispersed, and the magnetic permeability is increased by the action of the pressing force so that the inductance increases. An inductance element is described that makes it possible to measure the pressing force using changing.

Japanese Patent Laid-Open No. 5-267066

  However, the inductance element described in Patent Document 1 inevitably causes the elastic deformation resin embedded in the coil to be larger than the coil, and is required to be arranged in a gap of several mm and measure the pressing force in this gap. If so, it was difficult to adopt. That is, in order to insert this inductance element into a gap of several mm, only a small number of turns can be formed, and there is a problem that sufficient sensitivity cannot be obtained.

  In addition, in order to form a conventional inductance element, it is necessary to go through a special manufacturing process of embedding a specially shaped coil in a special resin, which raises the problem of increasing the manufacturing cost. In addition, the smaller the coil, the greater the effect that molding error has on the measurement value, and there is a problem that high-precision measurement becomes more difficult.

Therefore, an object of the present invention is to provide a highly accurate pressure sensor that can be formed into a thin sheet that can be disposed in a narrow gap and that can measure the pressing force with sufficient sensitivity.

In order to solve the above problems, the present invention provides the following pressure sensor .
Between the first and second substrates, a first substrate having a first coil formed by a winding-shaped wiring pattern, a second substrate having a second coil formed by a winding-shaped wiring pattern, and An elastic body layer that can be compressed and deformed by a pressing force to interpose the two substrates and change the distance between the two substrates, and a single pressure-sensitive coil by connecting the first and second coils in series. A pressure sensitive element having a jumper portion that has a total thickness in the range of 0.5 mm to 2 mm, and
A detection circuit for detecting the pressing force from a change in inductance of the pressure sensitive coil due to a variation in a distance between the first and second coils formed on the first and second substrates of the pressure sensitive element;
The detection circuit is a pressure sensor that is an LC oscillation circuit that detects a change in inductance based on a change in oscillation frequency .

In the pressure-sensitive element, the first and second coils are formed by winding-shaped wiring patterns. Therefore, a pressure-sensitive coil having a large number of turns can be easily obtained by accurately forming the wiring pattern on each substrate. be able to. That is, the inductance of the coil can be increased accordingly, and high measurement sensitivity can be obtained. In addition, the formation of the wiring pattern on the substrate can be easily formed by a method already known per se in the formation of a wiring pattern on a printed wiring board, etc., so that not only the manufacturing cost can be reduced, but also with extremely high accuracy. Since it can be formed, there is little variation in characteristics.

Since the first and second coils are connected in series via a jumper portion to form one pressure-sensitive coil, the inductance of the pressure-sensitive coil is an elastic body interposed between the first and second substrates. Increase or decrease depending on the thickness of the layer. The elastic layer interposed between the substrates on which the coils of the winding-shaped wiring pattern are formed is compressed and deformed by receiving a pressing force, whereby the distance between the substrates is reduced according to the pressing force. The inductance of the coil increases with the pressing force. That is, the pressure sensing element can detect the pressing force as the magnitude of the inductance.

At least one of the first and second substrates may be a laminated substrate in which the wiring pattern is formed in each layer.
In this case, at least one of the first and second coils may be formed by connecting a plurality of wiring patterns respectively formed on each layer of the laminated substrate.
With such a configuration, the number of turns of the coil can be increased to increase the inductance of the pressure sensitive coil. That is, the measurement sensitivity can be improved accordingly. Multi-layering of the wiring pattern by the multilayer substrate can be realized by existing manufacturing technology, and an extremely accurate pressure-sensitive coil can be easily formed.

The pressure-sensitive element includes a first substrate in which a first coil is formed by a winding-shaped wiring pattern, a second substrate in which a second coil is formed by a winding-shaped wiring pattern, And an elastic body layer that is interposed between the second substrates and can be compressed and deformed by a pressing force to bring both substrates close to each other, and the distance between the substrates can be changed. the substrate and the elastic layer it is possible to form thin, Ru can der be formed into a sheet shape as a whole pressure-sensitive element.

At least one of the first and second substrates may be a hard substrate. Both may be hard substrates.
Examples of such a hard substrate include those known as glass epoxy substrates that are excellent in mechanical strength and heat resistance. By adopting such a hard substrate, sufficient mechanical strength can be obtained while suppressing the manufacturing cost, and the reliability can be improved.
Other examples of the hard substrate include a ceramic substrate and a composite substrate.

Further, at least one of the first and second substrates may be a flexible substrate. Both may be flexible substrates.
When the substrate is a flexible substrate, the flexibility of the substrate is improved, so that it is possible to detect the pressing force while suppressing damage due to external force. Furthermore, it can be exemplified those film-like as the base material of the flexible substrate, such full I Lum since thinner than the solid substrate is suitable for measuring the pressing force in the more narrow the gap. Examples of a base material for a flexible substrate, a polyester film, a polyimide full I Lum like. These are rich in corrosion resistance, and the polyimide film is particularly excellent in heat resistance.

  Examples of the elastic layer include a butyl rubber layer and an elastic silicon resin layer (silicon rubber layer). Such an elastic layer is excellent in robustness and can be sufficiently compressed and deformed when subjected to a pressing force. That is, the detection sensitivity can be increased accordingly. In addition, since silicon rubber is excellent in heat resistance, when the elastic layer is a silicon rubber layer, the pressure sensitive element can be placed in a high temperature environment by using the substrate having excellent heat resistance. It can be arranged and used.

  The jumper portion may be disposed outside an elastic body layer that can be compressed and deformed. By doing so, disconnection of the jumper portion due to deformation of the elastic layer can be prevented. If the pressure sensitive element can be used with a desired lifetime, the jumper portion may be passed through the elastic layer.

A plurality of the pressure sensitive elements may be arranged on a plane in a grid shape, a honeycomb shape or the like to constitute a composite pressure sensitive element. By arranging in this way, for example, the measurement of the pressing force can be performed for each pressure-sensitive coil, and the distribution of the pressing force can be measured.

  (This paragraph is omitted)

According to the pressure sensor of the present invention, it is possible to detect the pressing force from the inductance of the pressure-sensitive coil using the pressure-sensitive element and output this as an electric signal.
The detection circuit may be formed collectively on the first or second substrate, may be formed dispersed on the first and second substrates, or may be formed outside the substrate. .
If the detection circuit is formed on the substrate together with the pressure sensitive element, the pressure sensor can be downsized. However, the detection circuit may be formed on another substrate or the like electrically connected to the pressure sensitive element by wiring.

When a plurality of pressure-sensitive coils are formed on one plane as described above, if the detection circuit is connected to each pressure-sensitive coil, the pressing force of each part can be measured simultaneously, and the pressure distribution can also be measured.
However, for example, a plurality of pressure-sensitive coils can be connected to one detection circuit via a switch switching unit. In this case, it is convenient in terms of reducing the pressure sensor manufacturing cost and downsizing the pressure sensor.

The said detection circuit employs a LC oscillation circuit for detecting a change in the inductance by a change in the oscillation frequency. When such a detection circuit is used, the detection value of the pressing force can be FM-modulated and output. Therefore, the detection value can be transmitted by electromagnetic waves or the like by appropriately selecting the transmission frequency. The subsequent signal processing can be easily performed. Further, since the change in inductance of the pressure sensitive coil can be directly converted into an electric signal, the response speed can be increased as much as possible.

By employing a detection circuit such as this, it is possible to more accurately detect the inductance of the pressure sensitive coils can be increased that much measurement sensitivity.

As described above, according to the present invention, it is possible to provide a high-accuracy pressure sensor that can be formed into a thin sheet that can be disposed in a narrow gap and that can measure the pressing force with sufficient sensitivity. .

  The pressure sensor according to the present invention can detect the pressing force from the inductance of the pressure-sensitive coil using the pressure-sensitive element according to the present invention, and output this as an electric signal. Therefore, it can be used when highly precise pressure control is performed in a control device such as a robot, a narrow space in a printing device, or a dispenser.

It is a disassembled perspective view which shows the pressure sensitive element and pressure sensor which concern on 1st Embodiment. It is a longitudinal cross-sectional view which shows the structure of the pressure sensitive element of 1st Embodiment, and a pressure sensor. It is a longitudinal cross-sectional view which shows the state which the pressing force acted in FIG. It is a figure which shows the structure of the detection circuit of the said pressure sensor. It is a disassembled perspective view which shows the pressure sensitive element and pressure sensor which concern on 2nd Embodiment. It is a figure explaining the structure of the reference example detection circuit of the said 2nd Embodiment. It is an expanded view explaining the principal part structure of the pressure sensitive element of 3rd Embodiment. It is a perspective view of the pressure sensitive element of a 3rd embodiment. It is a figure which shows the modification of the said pressure sensitive element. It is a figure which shows another modification of the said pressure sensitive element.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an exploded perspective view showing configurations of a pressure sensitive element and a pressure sensor according to the first embodiment, FIG. 2 is a longitudinal sectional view of the pressure sensitive element and the pressure sensor, and FIG. It is a figure which shows the state which applied the pressure.

  The pressure sensor 1 of the present embodiment includes a pressure-sensitive element 2 that can detect a pressing force electrically, and a detection circuit 3 that is connected to the pressure-sensitive element 2 and detects the pressing force. The pressure sensitive element 2 includes a first substrate 4 on which a first coil L1 is formed by a winding-shaped wiring pattern, and a second substrate 5 on which a second coil L2 is formed by a winding-shaped wiring pattern. An elastic body layer 6 interposed between the first and second substrates 4 and 5 and a jumper portion 7 in which the first and second coils L1 and L2 are connected in series to form one pressure-sensitive coil L; Is provided.

  Both the substrates 4 and 5 are rigid substrates made of glass epoxy (epoxy resin reinforced with glass fiber), thereby sufficiently obtaining electrical insulation and mechanical strength while suppressing manufacturing costs. Can do. Further, the thicknesses d1 and d2 of the substrates 4 and 5 made of glass epoxy are about 0.8 mm in this example. Thus, the substrates 4 and 5 can obtain appropriate robustness and can increase the inductance of the pressure-sensitive coil L. In general, the thicknesses d1 and d2 can be exemplified by selecting from a range of approximately 0.6 mm to 2 mm.

In this example, the first and second coils L1 and L2 are formed by forming a copper film on the substrates 4 and 5 and forming a mask pattern on the copper film to obtain a wiring pattern having a predetermined winding shape. This is obtained by etching a portion that has not been formed. Note that the coil forming method is not limited to this.
In any case, by forming such a pattern, it is possible to form coils L1 and L2 having a large number of turns in a narrow region. In the case of this embodiment, the coils L1 and L2 each form a winding of 10 turns. Is.

  The first coil L1 is formed in a winding shape that turns counterclockwise from the outside to the inside, and the second coil L2 is formed in a counterclockwise winding shape from the inside to the outside. Has been. The outer end of the coil L1 is connected to the detection circuit 3. A land R1 is formed at the inner end of the coil L1, and a land R2 is formed at the inner end of the coil L2 corresponding to the land R1. Is formed. A jumper wire made of a conductor that can be flexibly bent between these lands R1 and R2 penetrates the elastic body layer 6 and is electrically connected to the jumper portion 7 (hereinafter referred to as a jumper wire 7 in this embodiment). The two coils L1 and L2 are connected in series as one pressure-sensitive coil L.

  A land R3 is formed at the outer end of the second coil L2, and a land R4 connected to the detection circuit 3 by a wiring pattern is formed at the position of the first substrate 4 corresponding thereto. . The jumper wire 8 is electrically connected between the lands R3 and R4, so that the pressure-sensitive coil L is electrically connected to the detection circuit 3.

  Here, the elastic body layer 6 is a silicon rubber layer having excellent heat resistance, and particularly in this embodiment, it is an elastic silicon resin layer that is excellent in robustness and can be sufficiently compressed and deformed when subjected to a pressing force. Generally speaking, the thickness t can be selected from a range of about 1.65 mm to 9.60 mm in consideration of the thickness of the substrates 4 and 5, but excludes cases where the thickness is thinner or thicker than this. Instead, as described above, when each of the substrates 4 and 5 is 0.8 mm and the total thickness of the pressure-sensitive elements is approximately 2 mm or less, t may be about 0.4 mm.

  Thus, by setting the thickness of the elastic body layer 6 to be small, the inductance of the pressure-sensitive coil L can be increased, and a change in inductance due to the pressing force can be detected largely.

As shown in FIG. 2, the first and second coils L1 and L2 are arranged with the elastic layer 6 having a thickness t sandwiched between them without receiving a pressing force, and therefore the average area of the coils L1 and L2 If S is S, the inductance of the pressure-sensitive coil L increases in proportion to the square of the number of turns, the square of the radius a of the coils L1 and L2, and the inverse of the distance (t + d1) between the coils L1 and L2. Therefore, the inductance of the coil L can be expressed by the following equation 1 using the constant K. In addition, in order to simplify description in the following formula | equation (1), the inductance of the coil L is demonstrated using the same code | symbol L. FIG.
L = K × 20 × 20 × a × a / (t + d1) (1)

  As shown in FIG. 3, when the pressing force F acts on the substrate 4, the elastic layer 6 is compressed and deformed, and the thickness t ′ becomes thinner than the thickness t in the open state. At this time, the jumper wires 7 and 8 are bent in accordance with the compression deformation of the elastic body layer 6. At this time, the inductance of the pressure-sensitive coil L is increased by the amount that the thickness of the elastic layer 6 is reduced to t ′. That is, the pressure sensitive element 2 of the present embodiment can detect the magnitude of the pressing force F as the magnitude of the inductance L. In this embodiment, the number of turns of the coils L1 and L2 is set to 10 turns so that the drawing can be simplified. However, by forming a large number of turns using the current printed wiring board forming technique, It is also possible to increase the detection sensitivity of the pressing force.

  In the above-described embodiment, the first and second coils L1 and L2 are formed on the upper surfaces of the first substrates 4 and 5, but the first and second coils L1 and L2 are in contact with the elastic body layer 6. The first coil L <b> 1 may be formed on the lower surface of the substrate 4. It is also conceivable to form the coils L1 and L2 on the upper and lower surfaces of the elastic body layer 6. In addition, in the present invention, the detection circuit 3 is not limited to being provided on the first substrate 4 side, and may be formed separately on the second substrate 5 or both substrates 4 and 5. Further, the pressure sensitive element 2 and the detection circuit 3 may be formed on another substrate electrically connected by lead wires.

FIG. 4 is a diagram illustrating the configuration of the detection circuit 3. The detection circuit 3 shown in FIG. 4 is a Colpitts-type LC oscillation circuit that converts a change in the inductance L into a change in the transmission frequency.
Reference numerals 9a to 9c denote inverters (NOT circuits) connected in series, which are connected to the output unit O via a resistor R11 and a coaxial cable Ga. Among the series of inverters 9a to 9c, the first inverter 9a has a pressure sensing coil L connected in a loop through a resistor R12, and capacitors C1, C2 having one end grounded at both ends of the pressure sensing coil L. Are connected to each other. The Colpitts oscillation circuit configured as described above oscillates an AC signal having a frequency fO as shown in the following equation (2). In equation (2), the values C1 and C2 represent the values of the capacitors C1 and C2.
fO = 1 / √ ((C1 × C2) × L / (C1 + C2)) (2)

  Therefore, the detection circuit 3 including an LC oscillation circuit using the pressure-sensitive coil L as an oscillation element converts the magnitude of the pressing force F (see FIG. 3) into the oscillation frequency fO (FM modulation) and outputs it to the output unit O. Can do. This FM modulated measurement is suitable for transmission over a communication line. In addition, since the change in the magnitude of the inductance L is directly converted into the oscillation frequency fO, there is an advantage that the response becomes faster.

FIG. 5 is a diagram showing the configuration of the pressure sensor 10 and its pressure sensitive element 20 according to the second embodiment of the present invention. In FIG. 5, the difference from the pressure sensor 1 of the first embodiment is that the first and second substrates 40 and 50 form winding-shaped wiring patterns La1, Lb1, Lc1, La2, and Lb2 in the respective layers. And the detection circuit 30 shown as a reference example includes a bridge circuit 3a and an adjustment circuit 3b. Further, the elastic layer 60 of the present embodiment is made of butyl rubber that has sufficient robustness and easily compresses and deforms when subjected to a pressing force.

  The wiring patterns La1, Lb1, Lc1 and the wiring patterns La2, Lb2 of each layer are connected in series by through holes to constitute first and second coils L1 ′ and L2 ′, and these coils L1 ′, L2 ′. Are connected in series by a jumper wire 7, and thus constitute one pressure-sensitive coil as a whole. That is, this pressure-sensitive coil L ′ has 2.5 times the number of turns compared to the pressure-sensitive coil L of the first embodiment, and its inductance is about 6 times, so that the sensitivity of the pressure-sensitive element 20 is increased accordingly. Can be increased.

Needless to say, the present embodiment can be modified similarly to the first embodiment. It is also conceivable to double the number of turns by using a double-sided board instead of the laminated board .

FIG. 6 is a diagram showing the configuration of the detection circuit 30. As shown as a reference example in FIG. 6, detection circuit 30 is a variable resistor Ra, and the first line 31 to the pressure sensitive coil L 'are connected in series, the variable resistor Rb, the combined parallel resistance and a variable resistor Rc of the variable capacitor C A second line 32 connected in series, an AC power source V for applying an AC voltage between the branch connection portions 33 and 34 at both ends of the first and second lines 31 and 32, and a first and a second intermediate portion. A bridge circuit 3a including a current detector D connected so as to cross between the provided branch connection portions 35 and 36 is provided. Further, a resistor denoted by a reference symbol R ′ indicates a resistance component included in the pressure sensitive coil L ′.

The adjustment circuit 3b adjusts the values of the variable resistors Ra to Rc and the variable capacitor C so that the current detected by the detector D becomes 0 (that is, a state where the equilibrium condition is satisfied). . Since the bridge circuit 3a is a Maxwell bridge circuit for measuring an unknown inductance using a Whiston bridge circuit, the value of each of the variable resistors Ra to Rc and the variable capacitor C in the equilibrium state can be expressed by 3) can be used to determine the inductance L ′ of the pressure sensitive coil.
L ′ = Ra X Rc X C (3)

  In particular, since the inductance L 'using the bridge circuit 3a can be measured with extremely high accuracy, the adjustment circuit 3b can output the pressing force determined with high accuracy.

  In each of the above-described embodiments, the first and second substrates constituting the pressure-sensitive coils L and L ′ are solid substrates. However, the present invention is not limited to this point. That is, the substrates L1 and L2 may be formed of a flexible substrate.

  7 and 8 are views for explaining a third embodiment of the present invention. FIG. 7 is a development view for explaining the main configuration of the pressure-sensitive element 21 and FIG. 8 is a perspective view of the pressure-sensitive element 21. FIG. . The pressure-sensitive element 21 of the present embodiment is different from the first and second embodiments in that each of the first and second substrates 4 ′ and 5 ′ is formed by a single flexible substrate, and the first and second substrates The jumper part 7 ′ for electrically connecting the two coils L1, L2 is also different in that it is formed on the same flexible substrate. In addition, lands R5 and R6 for connecting a conductor such as a lead wire to the pressure sensitive element 21 are formed at the ends of the coils L1 and L2.

As shown in FIG. 8, since the flexible substrate can be easily bent, the first and second coils are arranged so as to face each other with the elastic layer 6 sandwiched between them. can do. Further, the jumper portion 7 'is disposed outside the elastic layer that can be compressed and deformed.
Such a flexible substrate can be obtained from a film such as a polyester film or a polyimide film. Generally speaking, the thickness of the flexible substrate may be about 12 μm to 1.6 mm.
In this example, each flexible substrate is made of a polyester film having a thickness of 50 μm.

  The pressure-sensitive element 21 of the third embodiment can be easily bent and deformed by receiving a pressing force, and the elastic body layer 6 can be compressed and deformed by the pressing force. Further, even when the elastic layer 6 is compressed and deformed, a large force is not applied to the jumper portion 7 ′, so that the jumper portion 7 ′ can be prevented from being disconnected. Further, since the pressure sensitive element 21 of the present embodiment has a very simple configuration, its manufacturing cost can be reduced as much as possible.

  In each of the above-described embodiments, an example in which one set of the first or second coils L1 and L2 is formed on one substrate 4 and 5 is shown. However, the present invention is limited to such a configuration. is not.

  That is, as shown in FIG. 9, a plurality of coils L1,..., L2. It is useful because the distribution of the pressing force can be detected by detecting the position. That is, for example, a thin keyboard or touch panel can be formed.

  Also, as shown in FIG. 10, a plurality of coils L1,..., L2. More coils L1, L2 per unit area can be formed by arranging the coils L1,..., L2,... In a honeycomb shape as in the example shown in FIG.

  As shown in FIGS. 9 and 10, when a plurality of coils L1... (L2...) Are formed on a substrate plane, the substrate can be bent by being a flexible substrate, not a solid substrate. preferable.

1, 10 Pressure sensor 2, 20, 21 Pressure sensitive element
3 detection circuit 3a bridge circuit 3b adjustment circuit 4, 4 ', 40 first substrate 5, 5', 50 second substrate 6, 60 elastic body layer 7, 7 'jumper F pressing force L, L' pressure sensing coil L1 , L1 ′ first coil L2, L2 ′ second coil

Claims (8)

Between the first and second substrates, a first substrate having a first coil formed by a winding-shaped wiring pattern, a second substrate having a second coil formed by a winding-shaped wiring pattern, and An elastic body layer that can be compressed and deformed by a pressing force to interpose the two substrates and change the distance between the two substrates, and a single pressure-sensitive coil by connecting the first and second coils in series. comprising a jumper section that, the pressure-sensitive element and is in the range of a total thickness of 0.5mm~2mm
A detection circuit for detecting the pressing force from a change in inductance of the pressure sensitive coil due to a variation in a distance between the first and second coils formed on the first and second substrates of the pressure sensitive element;
The pressure sensor according to claim 1, wherein the detection circuit is an LC oscillation circuit that detects a change in the inductance by a change in an oscillation frequency . At least one of the first and second substrates is a laminated substrate having the wiring pattern formed on each layer, and at least one of the first and second coils is formed on each layer of the laminated substrate. 2. The pressure sensor according to claim 1, wherein the plurality of wiring patterns are connected to each other. The pressure sensor according to claim 1, wherein the jumper portion is disposed outside the elastic layer which can be compressed and deformed. The pressure sensor according to any one of claims 1 to 3, wherein the elastic layer is an elastic layer selected from a butyl rubber layer and an elastic silicon resin layer. The pressure sensor according to claim 1, wherein at least one of the first and second substrates is a flexible substrate. The pressure sensor according to claim 1, wherein at least one of the first and second substrates is a hard substrate. A pressure sensor in which a composite pressure sensitive element in which a plurality of the pressure sensitive elements according to any one of claims 1 to 6 are arranged in a grid pattern or a honeycomb pattern on a plane is adopted as the pressure sensitive element. A composite pressure sensor including a plurality of pressure sensors according to any one of claims 1 to 6, wherein pressure-sensitive element portions of the plurality of pressure sensors are arranged in a grid pattern or a honeycomb pattern on a plane. .