Gravimeter

Abstract

To achieve a gravimeter with a simple configuration by reducing the number of strain measuring sensors to be used.SOLUTION: A gravimeter is used having: a top plate on which an object to be measured is mounted; a strain body that is arranged below the top plate with a space therebetween; three or more projections that connect the top plate and the strain body to each other; a bottom plate that is arranged below the strain body; a fixing part that is part of the strain body and fixes the strain body and the bottom part to each other; and two or more strain measuring sensors that are provided between the fixing part and the three or more projections in plan view, and are fixed to a top face of the strain body. The number of strain measuring sensors is smaller than the number of projections.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a weighing scale, and particularly to a technique effective for application to a weighing scale that measures weight using a semiconductor strain sensor.

Background Art

[0002] For weight measurement, various weighing scales such as a balance or a weighing scale are used. In a weighing scale, a physical quantity of a force applied to a strain body inside the weighing scale is detected by a strain measurement sensor provided on the strain body and converted into an electrical signal. Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2020-193810) describes a load cell including at least three strain sensors. Patent Documents 2 (Japanese Unexamined Patent Application Publication No. 2001-343295) and 4 (Japanese Unexamined Patent Application Publication No. 2002-286538) describe a load cell for measuring weight that includes eight strain gauges. Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2022-133175) describes a weighing scale having four load cells each including two strain gauges.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] The structure of a general weighing scale is, for example, as described in Patent Document 3, where load cells are installed at the four corners of the weighing scale. Since a load cell has at least one strain measurement sensor, the number of strain measurement sensors used is four or more. Although the structures of Patent Documents 1 and 2 are different from that of Patent Document 3, they are the same in that four or more strain measurement sensors are used. Using four or more strain measurement sensors, which are relatively expensive among the components of the weighing scale, is a factor contributing to an increase in the manufacturing cost of the weighing scale. Therefore, simplifying the configuration of the weighing scale by reducing the number of strain measurement sensors used is desired.

[0005] Other problems and novel features will become apparent from the description of this specification and the accompanying drawings.

Means for Solving the Problems

[0006] Among the embodiments disclosed in the present application, the outline of a representative one will be briefly described as follows.

[0007] A weighing scale according to an embodiment has a top plate on which an object to be measured is placed, a strain generating body disposed below the top plate with a space therebetween, three or more protrusions connecting the top plate and the strain generating body, a bottom plate disposed below the strain generating body, a fixing portion that is part of the strain generating body and fixes the strain generating body and the bottom plate, and two or more strain measurement sensors provided between the fixing portion and the three or more protrusions in a plan view and fixed to the upper surface of the strain generating body. Here, the number of the strain measurement sensors is less than the number of the protrusions.

Advantages of the Invention

[0008] According to an embodiment, a weighing scale with a simple configuration can be realized.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments, members having the same function are denoted by the same reference numerals, and repeated explanations thereof are omitted. Further, in the embodiments, unless particularly necessary, explanations of the same or similar parts are not repeated as a rule.

[0011] <Embodiment 1> Referring to FIGS. 1 to 9, the weighing scale according to Embodiment 1 will be described.

[0012] First, each direction used in the drawings of this embodiment will be described. Here, as shown in FIG. 1, an x-direction, a y-direction, and a z-direction that are perpendicular to each other are set. The x-direction and the y-direction are directions perpendicular to each other within the plane on which the heavy object is placed, and are directions along the upper surface of the strain generating body 3 described later. The direction in which the first structure 19 and the second structure 20 constituting the strain generating body 3 described later are arranged is defined as the x-direction. Also, the direction perpendicular to the x-direction in plan view is defined as the y-direction. The x-direction and the y-direction are directions along the upper surface of the strain generating body 3. The z-direction is a direction perpendicular to each of the upper and lower surfaces of the strain generating body 3. Also, the force acting in the z-direction (that is, the weight) is represented by Fz. In the weighing scale 1 of this embodiment, it is necessary to measure this Fz.

[0013] FIG. 1 is a perspective view of the weighing scale 1 of this embodiment, FIG. 2 is a side view of the weighing scale 1, and FIG. 3 is a plan view of the strain generating body 3 used in the weighing scale 1. FIG. 4 is an enlarged detailed view of the contact portion between the strain generating body 3 and the top plate 4 used in the weighing scale 1 of this embodiment, and FIG. 5 is a cross-sectional view of the depression (elongated hole) 25 provided on the upper surface of the strain generating body. FIG. 6 is a plan view of the semiconductor strain sensor module 2 installed on the strain generating body 3 of the weighing scale 1, and FIG. 7 is a cross-sectional view of the semiconductor strain sensor module 2 installed on the strain generating body 3 of the weighing scale 1. FIGS. 6 and 7 show the sensor module 2 of the type in which the semiconductor strain sensor 13 is mounted on the metal plate 14. FIG. 8 is a plan view of the semiconductor strain sensor module 2 installed on the strain generating body 3 of the weighing scale 1, and FIG. 9 is a cross-sectional view of the semiconductor strain sensor module 2 installed on the strain generating body 3 of the weighing scale 1. FIGS. 8 and 9 show the sensor module 2 of the type in which the semiconductor strain sensor 13 is mounted on the ceramic plate 9. FIGS. 10 and 11 are plan views of the semiconductor strain sensor 13 used in the semiconductor strain sensor module 2. FIGS. 12 and 13 are diagrams for explaining the principle by which the weight can be measured in the weighing scale 1 of this embodiment.

[0014] As shown in Fig. 1, the weighing scale is composed of components including a cover 7, a top plate 4 (including a protrusion 5), a strain generating body 3 (including a semiconductor strain sensor module 2 and a substrate 21), and a bottom plate 6, which are stacked in the z direction from top to bottom. The cover 7 is shaped to cover the top plate 4, the strain generating body 3, and the bottom plate 6 in a plan view, and has a function of preventing these components from being damaged from the outside. Each of the cover 7, the top plate 4, the strain generating body 3, and the bottom plate 6 has an upper surface (the first main surface) and a lower surface (the second main surface) on the opposite side of the upper surface. In the present application, the plan view means looking at the weighing scale 1 or each of its components in the z direction. The planar shape of each of the cover 7, the top plate 4, the strain generating body 3, and the bottom plate 6 is, for example, substantially rectangular.

[0015] A weight is placed on the upper surface of the cover 7. The cover 7 is installed in contact with the upper surface of the top plate 4 and not in contact with the side surface of the strain generating body 3. This is because if the cover 7 is in contact with the side surface of the strain generating body 3, there is a concern that the deformation state of the strain generating body 3 may fluctuate when a weight is placed, deteriorating the measurement accuracy of the weighing scale 1. The material of the cover 7 is, for example, a metal material such as steel, stainless steel, or aluminum alloy, or a resin material. The manufacturing method of the cover 7 may include bending. Note that if there is no concern about the top plate 4, the strain generating body 3, and the bottom plate 6 being damaged from the outside, it is also possible not to use the cover 7.

[0016] Next, the top plate 4 will be described. When the cover 7 is not used, a heavy object is placed on the upper surface of the top plate 4. The upper surface of the top plate 4 is where the object to be inspected is placed. Protrusions 5 are provided at the four corners on the lower surface side of the top plate 4. The protrusions 5 are fixed to the top plate 4 by the top plate side bolts 8. However, the fixing method is not limited to bolt fastening, and other methods such as adhesion may be used for fixing. Regarding each of the protrusions 5 at the four corners, the shortest distances between the x-axis (described later) and each protrusion 5 are all the same. Also, the shortest distances between the y-axis (described later) and each protrusion 5 are all the same. The protrusions 5 connect the lower surface of the top plate 4 and the upper surface of the strain generating body 3. A plurality of protrusions 5 are provided between the top plate 4 and the strain generating body 3 to support the top plate 4, so that the top plate 4 and the strain generating body 3 are separated from each other. The tip (lower end) of the protrusion 5 in contact with the upper surface of the strain generating body 3 has a rounded shape. The materials of the top plate 4 and the protrusions 5 are, for example, metal materials such as steel, stainless steel, or aluminum alloy, etc.

[0017] Here, the top plate 4 is placed on the upper surface of the strain generating body 3, and by this, the tip of the protrusion 5 comes into contact with the upper surface of the strain generating body 3, thereby connecting the top plate 4 and the strain generating body 3. The connection method is not limited to this, and the tip of the protrusion 5 may be adhered to the upper surface of the strain generating body 3, or the tip of the protrusion 5 may be joined to the upper surface of the strain generating body 3 by welding. Also, the tip of the protrusion 5 may be fastened to the upper surface of the strain generating body 3 using bolts and fixed thereby.

[0018] Next, the strain generating body 3 will be described. The strain generating body 3 is disposed below the top plate 4 with a space therebetween. As shown in FIGS. 1 and 2, the strain generating body 3 is composed of a first structure 19 located on both outer sides in the x direction and a second structure 20 located on the inner side. In other words, the strain generating body 3 is composed of the first structure 19, the second structure 20, and the first structure 19 arranged in order in the x direction. More specifically, each of the two first structures 19 and the second structure 20 are connected to each other by a third structure 31 located between each of the two first structures 19 and the second structure 20. That is, the strain generating body 3 is composed of the first structure 19, the third structure 31, the second structure 20, the third structure 31, and the first structure 19 arranged continuously in order in the x direction.

[0019] The first structure 19, the second structure 20, and the third structure 31 are integrally formed with each other and are made of one material. The material of the strain generating body 3 is, for example, a metal material such as steel, stainless steel, or an aluminum alloy. A bottom plate 6 is disposed below the strain generating body 3. The lower surface of the second structure 20 is in contact with the bottom plate 6, the lower surface of the first structure 19 is not in contact with the bottom plate 6, and there is a space (gap) between the first structure 19 and the bottom plate 6. That is, between the first structure 19 and the bottom plate 6, nothing connecting the first structure 19 and the bottom plate 6 is provided, and the first structure 19 and the bottom plate 6 are separated from each other.

[0020] On the upper surfaces of the respective third structures 31 that sandwich the second structure 20 in the x direction, the semiconductor strain sensor module 2 is attached with an adhesive. That is, the semiconductor strain sensor module 2 is fixed by adhering to the upper surface of the strain generating body 3. Further, as shown in FIGS. 4 and 5, depressions 24, 25, and 26 are provided at the four corners (the upper surface of the first structure 19) of the upper surface of the strain generating body 3. The positions of the depressions 24 to 26 in plan view correspond to the positions of the protrusions 5 provided on the top plate 4. The depressions 24 and 25 are located on the same diagonal line of the upper surface of the strain generating body 3 in plan view. Two depressions 26 are provided, and they are located on the other diagonal line of the upper surface of the strain generating body 3 in plan view. The shape of any one of the depressions 24 is a spherical seat, the depression 25 is a long hole with a rounded bottom (see FIG. 5), and the remaining two depressions 26 are flat seats. In the spherical seat depression 24, the position of the top plate 4 is determined at one point, in the long hole depression 25 with a rounded bottom, the rotation of the top plate 4 around the z direction is fixed, and in the remaining two flat seat depressions 26, the position of the top plate 4 in the z direction is determined. It should be noted that it is also possible to make the shapes of all four depressions spherical seats.

[0021] The second structure 20 is provided with bolt holes, and the second structure 20 and the bottom plate 6 are fixed by bolts 22 on the bottom plate side. That is, the second structure 20 includes a fixing portion that is fixed to the bottom plate 6. That is, the fixing portion is a part that constitutes a part of the strain generating body 3 and is a part that fixes the strain generating body 3 to the bottom plate 6. The upper surface of the bottom plate 6 has a convex portion that faces upward (toward the strain generating body 3) only directly below the second structure 20 including the fixing portion, and the upper surface of the bottom plate 6 directly below each of the first structure 19 and the third structure 31 is lower in height than the upper surface of the bottom plate 6 directly below the second structure 20.

[0022] The positions of the plurality of bolt holes are line-symmetric in plan view with respect to the following x-axis and y-axis. The fixing method is not limited to bolt fixing, and other methods such as an adhesive method are also possible as long as the lower surface of the second structure 20 and the bottom plate 6 are fixed. The third structure 31 is not a fixing portion and is separated from the bottom plate 6 in the same manner as the first structure 19. The third structure 31 may be considered as a part of the first structure 19.

[0023] At two positions on the x-axis Xs (see FIG. 3) along the x-direction, which is an axis passing through the center of the upper surface of the distortion generating body 3, two semiconductor strain sensor modules 2 are installed. These two semiconductor strain sensor modules 2 are installed at positions that are line-symmetric about the y-axis Ys (see FIG. 3) along the y-direction, which is an axis passing through the center of the upper surface of the distortion generating body 3, and are attached to the upper surface of the third structure 31 (the upper surface of the distortion generating body 3) via an adhesive. In other words, in the x-direction, the two semiconductor strain sensor modules 2 are arranged at symmetric positions with the center of the upper surface of the distortion generating body 3 in between. The semiconductor strain sensor module 2 measures the strain in the x-direction of the sensor attachment portion to which the semiconductor strain sensor module 2 is attached. A control unit, which will be described later, calculates the weight of the heavy object placed on the upper surface of the top plate 4 from the total value of the strain values generated in the third structure 31 of the distortion generating body 3 measured by these two semiconductor strain sensor modules 2. The measurement principle and effects will be described later. The center of the upper surface (or lower surface) of the distortion generating body 3 as referred to in the present application refers to the intersection point of the diagonals of the upper surface (or lower surface) of the distortion generating body 3 whose planar shape is substantially rectangular.

[0024] In a plan view, two semiconductor strain sensor modules 2 are provided between the fixing portion (second structure 20) and the protrusion 5. If the number of semiconductor strain sensor modules 2 is less than the number of protrusions 5, three or more may be arranged. One of the main features of the present embodiment is that the number of semiconductor strain sensor modules 2 (that is, the number of strain measurement sensors) is less than the number of protrusions 5 in this way.

[0025] In the y-direction, notches 27 are provided at both ends of each of the two third structures 31 of the strain generating body 3. Four notches 27 are provided and are located at positions symmetric with respect to the x-axis Xs and the y-axis Ys. By providing the notches 27, the amount of strain generated in the third structure 31 can be increased, and the strain sensitivity with respect to weight can be increased. Also, without providing the notches 27, by thinning the positions corresponding to the notches 27, it is also possible to adjust the strain sensitivity. Further, it is also possible to adopt a structure without providing the notches 27 or the thin portions. FIGS. 1 to 3 show a structure in which both the notches 27 and the thin portions are provided. Thus, by providing the notches 27 or the thin portions, the mechanical strength of the third structure 31 is lower than that of either the first structure 19 or the second structure 20.

[0026] Next, the bottom plate 6 will be described. A screw hole 28 is provided near the center of the bottom plate 6 in plan view and is connected to the fixing portion of the strain generating body 3 by a bolt 22. The width L1 of the bottom plate 6 in the x-direction is larger than the width L2 of the second structure 20 of the strain generating body 3 in the x-direction. In the present embodiment, a structure in which the screw hole 28 is formed in the bottom plate 6 and the strain generating body 3 and the bottom plate 6 are fixed is shown, but it is also possible to form a screw in the strain generating body 3 and fix the strain generating body 3 and the bottom plate 6. Further, the fixing method is not limited to bolt fixing, and other methods such as an adhesion method are also possible. If the lower surface side of the second structure 20 of the strain generating body 3 is fixed, it is also possible not to use the bottom plate 6.

[0027] Next, the substrate (control substrate) 21 will be described. The substrate 21 is equipped with a connector for connecting a flexible wiring drawn from the semiconductor strain sensor module 2 and a wireless unit for wirelessly transmitting the measured strain sensor data. The substrate 21 constitutes a control unit. Note that it is also possible to transmit the measurement data by wire without using wireless communication and display the weight value on a separately prepared display unit.

[0028] Next, the semiconductor strain sensor module 2 will be described. As shown in FIGS. 1 to 3, the semiconductor strain sensor module 2 is attached to the third structure 31 of the strain generating body 3 by an adhesive. The adhesive is, for example, an epoxy resin. FIG. 6 is a plan view of the semiconductor strain sensor module 2, and FIG. 7 is a cross-sectional view taken along line C-C of FIG. 6. As shown in FIGS. 6 and 7, the semiconductor strain sensor module 2 mainly includes a semiconductor strain sensor 13, a flexible wiring board 10 electrically connected to the semiconductor strain sensor 13, a metal plate 14 on which the semiconductor strain sensor 13 is mounted via a bonding material 11, and a sealing resin 12 that seals the upper surface and side surfaces of the semiconductor strain sensor 13. The bonding material 11 is made of, for example, a metal solder material such as an AuSn-based material.

[0029] The upper surface of the semiconductor strain sensor 13 and the electrode portion provided on the upper surface of the flexible wiring board 10 are connected by an Au wire (not shown in FIGS. 6 and 7). FIGS. 6 and 7 show the semiconductor strain sensor module 2 using the metal plate 14, while FIGS. 8 and 9 show the semiconductor strain sensor module 2 using a ceramic plate 9 instead of the metal plate 14. FIG. 8 is a plan view of the semiconductor strain sensor module 2. However, the flexible wiring and the sealing resin provided on the upper surface of the ceramic plate are not shown. FIG. 9 is a cross-sectional view taken along line D-D of FIG. 8. As shown in FIGS. 8 and 9, the semiconductor strain sensor module 2 is configured by joining a semiconductor strain sensor 13 to the ceramic plate 9 via a bonding material 11. The upper surface of the semiconductor strain sensor and the electrode portion provided on the upper surface of the ceramic plate are connected by an Au wire (not shown in FIGS. 8 and 9). Further, the upper part of the semiconductor strain sensor 13 is sealed with the sealing resin 12, and the electrode portion 29 provided at the peripheral portion of the ceramic plate and the flexible wiring (not shown) are soldered.

[0030] The chip mounted on the semiconductor strain sensor module 2 is a semiconductor strain sensor (strain measurement sensor) 13. The semiconductor strain sensor 13 is a device that utilizes semiconductor piezoresistors formed by doping impurities into a semiconductor such as silicon (Si). The semiconductor strain sensor has a resistance change rate with respect to strain that is several tens of times larger than that of a strain gauge using a metal thin film, and is capable of measuring minute strains. Also, since the semiconductor strain sensor has a large resistance change, the obtained electrical signal can be used without using an external amplifier.

[0031] The semiconductor strain sensor 13 will be described with reference to FIGS. 10 and 11. The semiconductor strain sensor 13 is a device that utilizes semiconductor piezoresistors formed by doping impurities into a semiconductor such as silicon (Si) instead of a metal thin film for the strain detection part. The semiconductor strain sensor 13 has a resistance change rate with respect to strain that is several tens of times larger than that of a strain gauge using a metal thin film, and is capable of measuring minute strains. Also, in the case of a strain gauge with a metal thin film, since the resistance change is small, an external amplifier for amplifying the obtained electrical signal is required. Since the semiconductor strain sensor has a large resistance change, the obtained electrical signal can be used without using an external amplifier. Even when an amplifier is required, since it is possible to fabricate an amplifier circuit in the semiconductor chip of the semiconductor strain sensor, miniaturization and high precision can be achieved.

[0032] FIGS. 10 and 11 are plan views schematically showing the configuration on the surface side of the semiconductor strain sensor. In the example shown in FIGS. 10 and 11, for example, it forms a square with a side length of about 2 mm to 5 mm. The semiconductor strain sensor 13 includes a plurality of resistance elements 15 (piezoresistance elements) formed in a sensor region 16 located at the central portion on the surface 13a side. The plurality of electrode pads 17 are electrically connected to the plurality of resistance elements 15 (piezoresistance elements). The electrode pads 17 are formed in an input / output circuit region located on the peripheral side rather than the sensor region 16 on the surface 13a side. The plurality of resistance elements 15 are constituted by impurity diffusion regions formed by doping and diffusing impurities on the element formation surface of a silicon substrate having, for example, a (100) plane.

[0033] The semiconductor strain sensor 13 includes, for example, a Wheatstone bridge circuit (detection circuit) 18 in which four resistor elements 15 are electrically connected. This Wheatstone bridge circuit 18 constitutes a detection circuit (strain detection circuit) that measures the resistance change of the resistor element 15 due to the piezoresistive effect to detect strain. Further, the Wheatstone bridge circuit 18 is connected to a plurality of electrode pads 17 via a plurality of wirings. The plurality of electrode pads 17 serve as input / output terminals of the semiconductor strain sensor 13. These input / output terminals include, for example, a terminal Vcc for supplying a power supply potential (first power supply potential) to the sensor chip, a terminal GND for supplying a reference potential (second power supply potential), and a terminal SIG for outputting a detection signal.

[0034] The layout of the plurality of resistor elements 15 constituting the Wheatstone bridge circuit 18 is not limited to the mode shown in FIG. 10, but in the present embodiment, it has the following configuration. That is, when the semiconductor substrate (for example, a silicon (Si) substrate) included in the semiconductor strain sensor 13 is a single crystal (silicon single crystal), the extending directions (longitudinal directions) of the plurality of resistor elements 15 constituting the Wheatstone bridge circuit 18 coincide with the <110> direction or the <100> direction of the semiconductor substrate having the (100) plane. In the example shown in FIG. 10, in the semiconductor substrate (silicon substrate) included in the semiconductor strain sensor 13, four p-type diffusion regions (regions doped with impurities having a p-type conductivity type) are formed so that current flows along the crystal orientation in the <110> direction (the X direction and the Y direction orthogonal to the X direction in FIG. 10) of the silicon single crystal. In other words, in the semiconductor strain sensor, four resistor elements 15 are formed by doping p-type impurities at four locations so as to extend along the crystal orientation in the <110> direction of the silicon single crystal of the silicon substrate.

[0035] Also, as in the example shown in FIG. 11, four n-type impurities may be doped at four locations so as to extend along the crystal orientation in the <100> direction of the single crystal silicon of the silicon substrate, and four resistance elements 15 may be formed. In this case, in the semiconductor substrate (silicon substrate), four n-type diffusion regions (regions doped with impurities having an n-type conductivity type) are formed so that current flows along the crystal orientation in the <100> direction of the single crystal silicon (the X direction and the Y direction orthogonal to the X direction in FIG. 11). As shown in FIGS. 10 and 11, the semiconductor strain sensor 13 in which the extending directions of the plurality of resistance elements 15 constituting the detection circuit coincide with the <110> direction or the <100> direction of the semiconductor substrate having the (100) plane can output, for example, the difference between the strain in the X direction and the strain in the Y direction shown in FIGS. 10 and 11. Specifically, the difference between the strain in the X direction and the strain in the Y direction can be output as a potential difference from the terminal SIG shown in FIGS. 10 and 11.

[0036] Thus, the measurement method of outputting the difference between the strain in the X direction and the strain in the Y direction is advantageous from the viewpoint of reducing the influence of the thermal strain applied to the semiconductor strain sensor 13. The semiconductor strain sensor module 2 equipped with the semiconductor strain 13 is attached to the strained body 3 as shown in FIGS. 1 to 3. Therefore, when the measurement environment temperature changes, thermal strain occurs due to the difference in the linear expansion coefficient of the strained body 3, the metal plate 14 or the ceramic plate 9 constituting the semiconductor strain sensor module 2, etc. Since this thermal strain is a noise component different from the strain to be measured, it is preferable to reduce the influence of the thermal strain. By using the semiconductor strain sensor 13 as shown in FIGS. 10 and 11, the influence of the thermal strain can be reduced, and thus the variation in the strain value due to the change in the environmental temperature can be reduced. In addition, since each member such as the resistance element 15 and the electrode pad 17 constituting the semiconductor strain sensor 13 can be formed by applying the manufacturing technology of known semiconductor devices, miniaturization of the elements and wirings is easy. Also, the manufacturing efficiency can be improved and the manufacturing cost can be reduced.

[0037] Next, the weight measurement principle in this embodiment will be described with reference to FIGS. 12 and 13. FIG. 12 is a perspective view showing the strain generating body 3 and the bottom plate 6, and FIG. 13 is a side view showing the strain generating body 3 and the bottom plate 6. In FIGS. 12 and 13, illustrations of the top plate and the cover on the strain generating body 3 are omitted. As shown in FIG. 12, the names of the respective protrusions and the respective semiconductor strain sensor modules are the protrusions 5a, 5b, 5c, and 5d, and the modules 2a and 2b. The module 2a is a module existing on the side of the first structure 19 where the protrusions 5a and 5b are located, and the module 2b is a module existing on the side of the first structure 19 where the protrusions 5c and 5d are located.

[0038] That is, the protrusions 5a and 5b are symmetrically positioned with respect to the protrusions 5c and 5d across the y-axis along the y-direction passing through the center of the upper surface of the strain generating body 3, and the protrusions 5a and 5c are symmetrically positioned with respect to the protrusions 5b and 5d across the x-axis along the x-direction passing through the center of the upper surface of the strain generating body 3. Here, of the two first structures 19, the protrusions 5a and 5b are in contact with one of the first structures 19, and the protrusions 5c and 5d are in contact with the other first structure 19.

[0039] The load Fz due to the weight placed on the top plate is transmitted from the four locations of the protrusions 5a, 5b, 5c, and 5d to the strain generating body 3. Here, due to the force transmitted from the protrusions 5a and 5b, as shown by the black curved arrow in FIG. 13, a bending deformation 32 in the x-direction occurs in the first structure 19. The bending strain generated by this bending deformation 32 is measured by the module 2a. Here, due to the force transmitted from the protrusions 5a and 5b, a bending moment in the y-direction also occurs. However, since the bottom surface of the second structure 20 is fixed, the second structure 20 hardly deforms. Since the region where the module is attached is in the vicinity of the second structure 20, hardly any strain occurs in the y-direction. Also, since the bottom surface of the second structure 20 is fixed and does not deform, no strain occurs at the position of the module 2b due to the force transmitted from the protrusions 5a and 5b. The same can be said for the protrusions 5c and 5d side.

[0040] From the above, module 2a can measure only the forces transmitted from protrusions 5a and 5b, and module 2b can measure only the forces transmitted from protrusions 5c and 5d. By summing the load values calculated from both modules, the weight of the heavy object can be estimated. In order to verify this measurement principle, the inventors conducted stress analysis with the position where the heavy object is placed as a parameter. As an example, the inventors performed analysis when the top plate size was 150 mm square and a heavy object with a diameter of 75 mm was placed at the center of the top plate and at the corner of the top plate. As a result, the inventors confirmed that the difference in the total strain value generated in the two semiconductor strain sensor modules was 0.4%, and the influence of the position where the heavy object was placed was almost negligible.

[0041] <This is the effect of the embodiment> In a weighing scale, it is required to suppress an increase in manufacturing cost. As a method for achieving this, it is effective to reduce the number of strain measurement sensors used. Also, in the case of a large-sized weighing scale, when using four or more strain measurement sensors, the wiring between these sensors becomes complicated, and there is also a problem that the manufacturing and assembly property deteriorates. That is, it is desirable to simplify the structure of the weighing scale.

[0042] Therefore, in the present embodiment, a weighing scale is used that includes three or more protrusions that support the top plate on the strain generating body, and two or more strain measurement sensors (semiconductor strain sensor modules) arranged between the fixed portion of the strain generating body and the protrusions in a plan view. Here, since the number of strain measurement sensors is smaller than that of the protrusions, an increase in the manufacturing cost of the weighing scale can be suppressed. Also, by reducing the number of strain measurement sensors used, complication of the wiring connected to the strain measurement sensors can be prevented. That is, the structure of the weighing scale can be simplified.

[0043] <Embodiment 2> Referring to FIG. 14, the weighing scale of Embodiment 2 will be described. FIG. 14 is a cross-sectional view of the strain generating body 3 and the bottom plate 6 used in this embodiment. The basic configuration of this embodiment is the same as that of Embodiment 1. In FIG. 14, illustrations of the top plate, protrusions, cover, etc. on the strain generating body 3 are omitted. FIG. 14 is a view showing a cross-section at a position corresponding to the A-A line of FIG. 3 which is Embodiment 1. As shown in FIG. 14, in this embodiment, a storage portion 30 is provided in the second structure 20 of the strain generating body 3. The storage portion 30 is formed by a recess formed on the upper surface of the second structure 20. In Embodiment 1, as shown in FIG. 2, the substrate 21 is installed in the space existing between the top plate 4 and the uppermost surface of the strain generating body 3, but in Embodiment 2, the substrate 21 is stored in the storage portion 30. By storing the substrate 21, it becomes possible to reduce the thickness of the entire weighing scale.

[0044] <Embodiment 3> Referring to FIG. 15, the weighing scale of Embodiment 3 will be described. FIG. 15 is a plan view of the strain generating body 3 used in the weighing scale of this embodiment. In FIG. 15, illustrations of the top plate, protrusions, cover, etc. on the strain generating body 3 are omitted. The basic configuration of this embodiment is the same as that of Embodiment 1, and the description will focus on the differences from Embodiment 1.

[0045] The strain generating body 3 of this embodiment is different from Embodiment 1 in that the number of protrusions 5 is three, and the number of depressions 24, 25, and 26 corresponding to those protrusions 5 is three. Among the two first structures 19, the fact that one depression 24 and one depression 26 are formed on the upper surface of one of the first structures 19 is the same as in Embodiment 1, but only one depression 25 is formed on the upper surface of the other first structure 19, and depression 26 is not formed. Depression 25 is provided at the center of the first structure 19 in the y direction. Depression 25 is aligned with the two semiconductor strain sensor modules in the x direction. In other words, depression 25 and the two semiconductor strain sensor modules 2 arranged with the second structure 20 in between in plan view overlap the x-axis Xs in plan view.

[0046] In plan view, the shape of the depression 25 is rectangular and extends in the x direction. The bottom surface of the depression 25 has a radius centered on an axis (an axis at a position different from the Y axis Ys) along the y direction. In the depression 25 of the long hole with a radius, the rotation of the top plate 4 around the z axis is fixed, and in the depression 26 of the remaining one-point plane seat, the position of the top plate 4 in the z direction is determined. It should be noted that it is also possible to make the shapes of the three depressions 24, 25, and 26 all spherical seats. Also, although not shown, the top plate is provided with protrusions at three positions corresponding to the depressions 24, 25, and 26 provided in the strain generating body in plan view. That is, the protrusions are installed at three positions on the lower surface of the top plate, and each of the protrusions installed at two of the three positions is symmetrically located with respect to each other in plan view across the x axis. Also, the protrusion installed at the remaining one of the three positions is located on the x axis Xs. Among the three positions, each of the protrusions installed at two positions and the protrusion located on the x axis Xs are in contact with different first structures 19.

[0047] There are semiconductor strain sensor modules 2 at two positions on the x axis Xs which is the central axis of the strain generating body. Both modules are attached to the upper surface of the first structure with an adhesive and measure the strain in the x direction of the sensor attachment part. The strain value of the first structure of the strain generating body measured by these two modules is multiplied by the strain sensitivity coefficient of each module, and the weight placed on the top plate is calculated from the sum.

[0048] As described above, the invention made by the present inventors has been specifically described based on the embodiments. However, it goes without saying that the present invention is not limited to the above embodiments and can be variously modified without departing from the gist thereof.

Explanation of Reference Numerals

[0049] 1 Weighing scale 2 Sensor module 2a, 2b Modules 3 Strain generating body 4 Top plate 5, 5a, 5b, 5c, 5d Protrusions 6 Bottom plate 7 Cover 8 Top plate side bolt 9 Ceramic plate 10 Flexible printed circuit board 11 Bonding material 12 Encapsulating resin 13 Sensor 13a Surface 14 Metal plate 15 Resistance element 16 Sensor area 17 Electrode pad 18 Wheatstone bridge circuit 19 First structure 20 Second structure 21 Substrate 22 Bolt 28 Hole 29 Electrode part 30 Storage part 31 Third structure

Claims

1. A top plate on which an object to be measured is placed, A strain generating body disposed via a space below the top plate, Three or more protrusions connecting the top plate and the strain generating body, A bottom plate disposed below the strain generating body, A fixing portion that is part of the strain generating body and fixes the strain generating body and the bottom plate, Two or more strain measurement sensors provided between the fixing portion and the three or more protrusions in a plan view and fixed to the upper surface of the strain generating body, having, The number of the strain measurement sensors is less than the number of the protrusions, a weighing scale.

2. In the weighing scale according to Claim 1, The top plate and the strain generating body are connected by any one of contact, adhesion, welding joint by placing the protrusion fixed to the lower surface of the top plate and the upper surface of the strain generating body, or fixing by fastening using bolts, a weighing scale.

3. In the weighing scale according to Claim 1, The strain generating body is composed of two first structures and a second structure located between the two first structures in a plan view, The lower surface of the second structure is fixed to the bottom plate by the fixing portion, and the lower surfaces of the two first structures are not fixed to the bottom plate and are spaced apart from the bottom plate, a weighing scale.

4. In the weighing scale according to Claim 1, The number of the strain measurement sensors is two, a weighing scale.

5. In the weighing scale according to Claim 4, The strain generating body is composed of two first structures and a second structure located between the two first structures in a plan view, In a first direction in which the first structure, the second structure, and the first structure are arranged in order, the two strain measurement sensors are arranged at symmetric positions sandwiching the center of the upper surface of the strain generating body, a weighing scale.

6. In the weighing scale according to Claim 3, The protrusions are installed at respective four corners of the top plate in a plan view, When the direction in which the first structure, the second structure, and the first structure are arranged in this order is defined as the first direction, and the direction orthogonal to the first direction in plan view is defined as the second direction, among the four protrusions, namely the first protrusion, the second protrusion, the third protrusion, and the fourth protrusion, the first protrusion and the second protrusion are symmetrically positioned with respect to the third protrusion and the fourth protrusion across an axis passing through the center of the upper surface of the strain generating body and extending along the second direction, and the first protrusion and the third protrusion are symmetrically positioned with respect to the second protrusion and the fourth protrusion across an axis passing through the center of the upper surface of the strain generating body and extending along the first direction. A weighing scale in which, among the two first structures, the first protrusion and the second protrusion are in contact with one of the first structures, and the third protrusion and the fourth protrusion are in contact with the other first structure.

7. In the weighing scale according to claim 1, the strain generating body is composed of two first structures, a second structure positioned between the two first structures in plan view, and a third structure between each of the two first structures and the second structure. A weighing scale in which the third structure has a lower mechanical strength than the first structure and the second structure.

8. In the weighing scale according to claim 7, the thickness of the third structure is thinner than the thicknesses of the first structure and the second structure respectively, or notches are provided at both ends of the third structure in a second direction orthogonal to the first direction in which the first structure, the second structure, and the first structure are arranged in this order in plan view.

9. In the weighing scale according to claim 7, A weighing scale in which the strain gauge sensor is provided directly above the third structure.

10. In the weighing scale according to claim 3, when the direction in which the first structure, the second structure, and the first structure are arranged in this order is defined as the first direction, and the direction orthogonal to the first direction in plan view is defined as the second direction, the protrusion is installed at three locations on the lower surface of the top plate. Of the three locations, the fifth protrusion and the sixth protrusion installed at two of the locations are symmetrically positioned with respect to each other in plan view across an axis passing through the center of the upper surface of the strain generating body and extending along the first direction. The seventh protrusion installed at the remaining one of the three locations is positioned on the axis. A weighing scale in which the fifth protrusion and the sixth protrusion are in contact with different first structures from the seventh protrusion.

11. In the weighing scale according to claim 1, the weighing scale further comprising a cover disposed on the top plate and covering the top plate and the strain generating body in plan view.

12. In the weighing scale according to claim 3, the weighing scale wherein, in a first direction in which the first structure, the second structure and the first structure are arranged in order, the width of the bottom plate is larger than the width of the fixing portion on the lower surface of the strain generating body.

13. In the weighing scale according to claim 1, the weighing scale wherein the strain measurement sensor is a semiconductor strain sensor in which a piezoresistive element is formed on the surface of a semiconductor substrate.

14. In the weighing scale according to claim 13, the weighing scale wherein the member on which the semiconductor strain sensor is mounted is a ceramic plate or a metal plate.

Images