JPH0815057A - Thin type load cell - Google Patents

Abstract

PURPOSE:To realize a compact and highly accurate thin type load cell corresponding to a small capacity wherein lateral deflection due to deflection of a pressure receiving base for receiving load can be absorbed, thickness of the load cell is thinned to the utmost extent, and whose structure is easy to machine in the strain gage type load cell. CONSTITUTION:An outside circumference is made of external frame 1 of a square plate-like raw material. The center part thereof is made as a pressure- receiving base 2 for receiving load, and a plurality of long grooves 4 are provided so that they may penetrate a groove 5 between the external frame 1 and terminal grooves 6, 6' in both the ends thereof. A plurality of short grooves 7, 7' are provided on both sides so as to span the two terminal grooves 6, 6', and a plurality of detection parts 3 are set so that a thin strain production part may form an H-shape. Strain gages wherein torsion strains corresponding to loads are detected and output are stuck on the side of the strain production part respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a weighing machine that uses one or a plurality of other scales such as wheel weight and total weight of a vehicle and other thin scales by utilizing its thinness. The present invention relates to a strain gauge type thin load cell which is configured.

[0002]

2. Description of the Related Art Conventionally, strain gauge type thin load cells of this type have been shown in FIGS. FIG. 7A is an external perspective view of this load cell, in which 41 is a rigid outer frame, 42 is a rigid pressure receiving base that receives a load W indicated by an arrow, and 43A to 43D are four sides between the outer frame 41 and the pressure receiving base 42. It is a load detecting portion which is arranged and connected in a flexible shape, and these 41 to 43 have an integral structure. A strain gauge 44 is attached to each of the detectors 43A to 43D. FIG. 7B is a diagram of a shear strain detection structure in the above-mentioned detection unit adopted for a large capacity. Generally, a rectangular cross section of a long side a and a short side b is formed, and one surface 45 is formed on the outer frame 41 and the other surface 45 is formed. The surface 46 is connected to the pressure receiving table 42,
Strain gauges 44 are attached to both sides of the surfaces 45 and 46, and a shear strain is generated on the surface of the strain gauge 44 attached by the load W indicated by an arrow, and the strain gauge detects the strain and converts it into an electric signal. And then take it out. FIG. 7C shows the load detection units 43A to 43D of FIG. 7A.
In the figure of the bending strain detecting structure adopted for small capacity instead of the above, generally, a rectangular cross section of the short side C and the long side d is formed, one surface 55 is the outer frame 41, and the other surface 56 is the pressure receiving table 42. To form load detectors 53A to 53D. As shown in FIG. 7C, the upper and lower surfaces of the load detecting portion have two thin portions in the direction of the short sides C, 57 and 57, respectively.
7 ', 58, 58' are formed, and the strain gauges 54 are adhered at four places on the surfaces 7 ', 58, 58', and bending strain is generated on the adhered surfaces of the strain gauge 54 by the load W indicated by an arrow in FIG. The strain gauge detects it, converts it into an electric signal, and takes it out.

FIG. 8 shows a cross section taken along the line XX 'of FIG. 7A, a solid line shows a state before a load W shown by an arrow is applied, and a dotted line shows a state where each member is distorted by the load. As shown in this figure, when a load is applied, the pressure receiving base 42 and the load detecting unit 4
3A and 43C are bent as shown by the dotted lines, the length L of the pressure receiving table 42 is slightly contracted in the lateral direction of the arrow, the outer frame 41 is pulled in the direction of the arrow, and the space between the bottom surface 47 of the outer frame 41 and the floor surface 48 is pulled. Slip and distortion occur depending on the contact force.

Further, as a conventional technique, JP-A-63-30
734. According to the present invention, a bending beam is arranged tangentially to a circular arc extending concentrically with respect to the center of a plate-shaped extension member connected to one holder, and a bending strain is detected. However, it is designed not to cause erroneous conversion in the deflected beam. Further, JP-A-6-43045 and JP-A-6-43046
There are also those disclosed in. This invention uses a plate-shaped material in the same manner as described above, and provides a pair of front and rear long grooves to make the center part a load receiving part, and devises the structure of the pressure receiving part and the fixing part to fix the receiving part by the bending of the frame. It is designed to alleviate slippage and detect shear strain.

[0005]

However, in the case shown in FIGS. 7 and 8, the outer frame 41 is distorted and the contact point with the floor surface changes and slippage occurs, resulting in poor nonlinearity and hysteresis characteristics of the load cell output. Become. Further, in order to realize a small capacity with the shear strain detection structure shown in FIG. 7B, the thickness b of the detection portion for detecting the weight must be extremely thin, which results in poor workability and therefore in processing accuracy. There is a problem that it becomes difficult and the mechanical strength in the direction perpendicular to the detection direction also becomes weak. Further, if it is attempted to reduce the thickness t of the outer frame shown in FIG. 7A to realize a compact small-capacity type, the strain gauge is attached to the pressure receiving surface side and the opposite side in the bending strain detection structure shown in FIG. 7C. There is a problem in that the thickness of the insulating protective film on the surface is limited so that it does not come into contact with the surface, and the rigidity of the detection portion cannot be increased like the shear strain detection structure described above, which makes machining extremely difficult. Further, in JP-A-63-30734, the load point is centered, but when the load point deviates from the center, one-sided deflection is large,
In addition, the load plate due to the load rotates slightly in addition to bending in the vertical direction. Further, since the strain gauge is stuck on the upper surface, it is necessary to protect the gauge from being damaged by the load when loading and unloading the load. Therefore, there is a problem that the thickness becomes thicker, etc., and therefore, JP-A-6-43045 and JP-A-6-4304.
Even in No. 6, when a load is applied to the load receiving portion, the load is transmitted from the detecting portion to the fixed portion via the free end portion. Therefore, in addition to the same downward force as in the load direction, the fixed portion is not slightly bent or twisted. Since a force is applied, some adverse effects are unavoidable, and there is a problem that it is difficult to practically manufacture a load cell having a small capacity with these structures. Therefore, the present invention is capable of absorbing lateral bending due to bending of the pressure receiving table, and is compact and highly accurate as a structure that is easy to machine while the load cell is made as thin as possible in order to accommodate a small capacity. Is to provide.

[0006]

SUMMARY OF THE INVENTION The present invention is a plate-shaped material having a rectangular or circular shape, the outer periphery of which is an outer frame, and the central portion thereof is a pressure receiving base for receiving a load. A plurality of long grooves are provided so as to surround the pressure receiving table in between, and both ends are formed as wide end grooves, and short grooves are provided on both sides so as to straddle the two end grooves, and a thin strain element is formed. A plurality of load detecting units are provided, and a thin load cell is configured such that a strain gauge that detects a twisting strain corresponding to a load and transmits an electric output is attached to a side surface of the strain generating unit. . In configuring the above-mentioned one detection unit, the width of the short groove may be narrowed at a position off the end groove of the long groove, or the short groove may be provided only on one side of the end groove. Further, when the strain generating portion of one detection portion has an H shape, the strain gauge may be attached only to one pair on one side of the H shape.

[0007]

The operation will be described with reference to FIGS. Load W in these figures
Is applied to the pressure receiving base 2, a clockwise torque in a direction in which the pressure receiving base 2 is lowered is generated in the connecting beam 10 of the strain generating portion, and a twisting stress is generated in the strain generating portions 8, 8 ′, 9, 9 ′. Torsional strain is generated in balance with the reaction force of the torque, and an output voltage proportional to the load W is generated due to the connection of the strain gauge shown in FIG. In this case, even when the pressure receiving base 2 is bent by a load as shown in FIG. 3C, the left strain-flexing portions 8 and 8 ′ and the right strain-flexing portions 9 and 9 ′ that form the H-shaped strain-flexing portion. Since they are twisted in opposite directions, they do not appear in the strain gauge bridge as shown in Fig. 4A and do not appear as an error due to bending of the pressure receiving base. Even with a thin type, a small to large capacity high-precision load cell is realized. it can.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First and second embodiments of the present invention are shown in FIGS.
Shown in 1A and 1B are perspective views showing the appearance of a thin load cell, FIG. 1A shows a first embodiment, 1 is a rectangular outer frame, and the inside thereof is a pressure receiving table 2 for receiving a load W in the central portion. The load detectors 3 are provided at the four corners of the diagonal, and the whole is integrally structured to form a thin load cell. The load detecting section 3 is provided around the pressure receiving base 2 through a long groove 4 composed of four grooves 5 and end grooves 6 and 6'at both ends of the pressure receiving table 2, and is short with the end grooves 6 and 6'in between. Similarly, the grooves 7 and 7 ′ are provided so as to penetrate therethrough to form a thin-walled portion, which serves as a strain-generating portion. Therefore, when a load W indicated by an arrow is applied to the pressure receiving base 2, the detecting portions 3 at the four corners are distorted and an output proportional to the load W is generated by the strain gauge attached to the thin portion. FIG. 1B shows a second embodiment, 1 is a rectangular outer frame, 2 is a pressure receiving base similar to the above, and the difference from the first embodiment is that 3 load detectors sandwich the pressure receiving base. It has been installed at four locations on the opposite side.

The details of FIGS. 2 to 4 will be described in comparison with FIG. 1A. FIG. 2A is an enlarged plan view of one detection unit 3, FIG. 2B is a sectional view taken along line XX ′ of FIG. 2A. 2C is Figure 2
It is a YY 'sectional view of A. 8, in these figures
Reference numeral 8'denotes a strain generating portion located between the short groove 7 and the end grooves 6 and 6'of the long groove 4, which is a rectangular cross section with the short side b'and the long side a ', and the horizontal direction of the short side b'. Is easy to bend, and the long side a ′ has a shape with an appropriate rigidity that is hard to bend in the direction of the load W shown by the arrow in FIG. 1A. Similarly, 9 and 9 ′ are strain-flexing parts located between the short groove 7 ′ and the same end grooves 6 and 6 ′ as described above, and are located in parallel with the above 8 and 8 ′ with a distance d ′ therebetween. The cross-sectional shape is the same as the above 8 and 8 '. Between the end grooves 6 and 6 ', there is a connecting beam 10, 8, 8'and 9,
9'and 10 are H-shaped. The strain-flexing part 8,
Strain gauges 11, 12, 13, 14, 15, 16, 17, 18 for detecting torsional stress are provided on the side surfaces of 8 ', 9, 9'.
Are respectively attached as shown in the figure, and the upper surface thereof is coated with a material 19 for protection against moisture and insulation and treated for long-term stability.

FIG. 3A is a view showing an unloaded state in the ZZ ′ cross section of FIG. 2A, and FIG. 3B is a state in which a load W shown by an arrow is applied to the pressure receiving base 2 and the pressure receiving base 2 is bent due to the deflection of the detecting portion 3. Is a diagram showing a state in which vertical deflection of dimension e is occurring, and FIG. 3C also shows that the pressure receiving table 2 itself bends and bends under a load condition,
It is a figure which shows the state where the bending of the said detection part 3 was added. In these figures, when a load W is applied to the pressure receiving base 2, a torque T (= W × d ′) in the direction indicated by the arrow in FIG. 3B is generated on the connecting beam 10 shown in FIG. 2A, and this torque T
And the reaction force TR of the torque generating the twisting stress τ of the strain-flexing portions 8, 8′9, 9 ′ are balanced and the twisting stress τ (= T / 4 ×
K) is required. However, K is a constant depending on the shape. Further, as shown in FIG. 3C, even when the pressure receiving base 2 is bent by the load W, the strain-flexing portions 8, 8'and 9, 9'are twisted in the opposite directions, so that the strain gauge bridge Are canceled out and do not appear as an output, and an error due to the bending of the pressure receiving table 2 does not occur. Further, when the pressure receiving base 2 in FIG. 3B is bent like the load base 42 in FIG. 8, the pressure receiving base 2 contracts slightly in the direction of the arrow indicated by the dotted line, but the amount thereof is the strain-flexing portions 8, 8 ′ shown in FIG. 2A.
Since 9 and 9'are bent in the horizontal direction and almost absorbed, a large lateral load is not applied to the outer frame 1, and slippage between the outer frame 1 and the floor surface is reduced. If the short side b'of the strain-flexing portion is too thin, the force of the tool bends during machining, which makes it difficult to perform processing and it is difficult to obtain accuracy. Therefore, the distance d'is selected according to the capacity of the load cell and the short side b'is selected. The size can be easily processed.

As shown in FIG. 2A, FIG. 4A shows strain gauges 11 to 1 for detecting a torsional stress in one detector 3.
8 is a diagram in which all eight sheets of No. 8 are attached and connected in a bridge shape, where k is a gauge factor, G is a lateral elastic modulus of a strain-flexing portion, and e
When i is the bridge input voltage, the electric output e0 corresponding to the distortion proportional to the load W is e0 = k * [tau] * ei / 2G, and the load W can be obtained from the above e0. FIG. 4B is a diagram in which the number of strain gauges of the bridge circuit is reduced and the cost is reduced, so that the number of strain gauges is 11, 13, 16, 18 or four of 12, 14, 15, 17 shown in parentheses, respectively. The same effect as the eight-sheet configuration is obtained. Also, as shown in FIG. 3B, when the pressure receiving base 2 has a small bending strain, or
Even if there is a bending strain of the pressure receiving table 2 as shown in, if the error is tolerable, set the strain gauges to 11, 1 respectively.
It is also possible to have a four-sheet configuration of 2, 13, 14 or 15, 16, 17, 18. FIG. 4C is a connection diagram of a bridge circuit when the number of detection units 3 is four as shown in FIGS. 1A and 1B.
However, the description of the strain gauge is omitted.

FIG. 5 shows a third embodiment of the present invention, in which elongated detectors 23 are formed at two locations on opposite sides of the outer frame 21 and the pressure receiving base 22, and the number of strain gauges is also halved according to the number of detectors halved. The function is similar to that of the first and second embodiments. Furthermore, a fourth embodiment of the present invention is shown in FIG.
Shown in In this embodiment, the rectangular outer frame in the previous embodiment is a circular outer frame 31, and the pressure receiving table 32 and the detecting portion 33 are provided in two places as in the third embodiment, but the number of strain gauges is further halved. The function is the same as that of each of the above-described embodiments.

[0013]

EFFECT OF THE INVENTION By making the shape of the detecting portion H-shaped, the dimensional change such as bending expansion and contraction of the pressure receiving table is absorbed and alleviated by the strain-generating portion of the H-shaped portion, and harmful bending and pulling on the fixed portion of the outer frame is prevented. It is configured to relieve force and detect torsional strain, so the thickness of small and medium capacity load cells can be made extremely thin, and the workability is good and the strain gauge can be easily insulated, so it is compact and highly accurate. There is an effect that can realize a thin load cell.

[Brief description of drawings]

FIG. 1 is an external perspective view A according to a first embodiment of the present invention and an external perspective view B according to a second embodiment of the present invention.

FIG. 2 is an enlarged plan view A, XX ′ cross-sectional view B and YY ′ cross-sectional view C of the detecting portion in the first and second embodiments of the present invention.
Is.

3A shows an unloaded state in the ZZ ′ cross section of FIG. 2A, FIG. 3B shows a state in which the pressure receiving base vertically bends due to a load, and FIG. 3B shows a state in which the pressure receiving base itself bends and bends due to a load. FIG.

FIG. 4 is a connection diagram A in which strain gauges are all attached to the side faces of the strain-flexing part in one detection part shown in FIG. 2A,
FIG. 8 is a connection diagram B when a strain gauge is attached only to one side strain portion of the H-shaped strain portion to reduce the number of gauges by half, and a connection diagram C when there are four detection portions.

FIG. 5 is an external perspective view of a third embodiment of the present invention.

FIG. 6 is an external perspective view showing a fourth embodiment of the present invention.

7A is a perspective view of a conventional load cell, FIG. 7B is a shear strain detection structure for large capacity, and FIG. C is a bending strain detection structure for small capacity.

FIG. 8 is a diagram showing a strained state when a load W is applied in a cross-sectional view taken along the line XX ′ of the conventional load cell in FIG. 7A.

[Explanation of symbols]

1, 21, 31, 41 Outer frame 2, 22, 32, 42 Pressure receiving table 3, 23, 33, 43A to 43D, 53A to 53D Load detecting section 4 Long groove 5 Groove 6, 6'End groove 7, 7'Short groove 8, 8 ', 9, 9'Strain element 10 Connecting beam 11, 12, 13, 14, 15, 16, 17, 18, 4
4,54 Strain gauge 19 Insulation protection material

Claims (5)

[Claims] 1. A rectangular or circular plate-shaped outer frame,
A pressure receiving base located in the central portion and receiving a load, and a plurality of long grooves formed between the outer frame and the pressure receiving base so as to surround the pressure receiving base and a terminal groove wider at both ends than the groove. And a plurality of load detectors each including a thin strain element formed by a plurality of short grooves provided on both sides so as to extend over two of the end grooves, and an end groove and a short groove of the strain element. A thin load cell, which is composed of strain gauges that are attached to the side surfaces of each and that emits an electrical output according to the load. 2. The thin load cell according to claim 1, wherein the strain generating portions of the plurality of load detecting portions form an H shape by the end groove of the long groove and the short groove. 3. The plurality of short grooves according to claim 1 have wide ends at both ends, and the strain generating portions are formed so that the wide portions at both ends are on both sides of the end groove of the long groove to form a plurality of load detecting portions. A thin load cell featuring. 4. A thin load cell, wherein a plurality of short grooves according to claim 1 are provided only on one side of an end groove of a long groove to form a strain generating portion, and a plurality of load detecting portions are provided. 5. A thin load cell, characterized in that the strain gauge according to any one of claims 1 to 4 is adapted to detect torsional strain.