JPH025375Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is a load cell for a load cell scale that detects weight by changes in the electrical characteristics of a detection element such as a strain gauge attached to the load cell frame. The present invention relates to a load cell for a load cell scale that can reliably detect weight without stress affecting a detection element.

Conventionally, a load cell frame is made of an elastic material and is formed into a rectangular shape with a predetermined thickness, and a rectangular hollow part is formed near the center of the load cell frame. A load cell is constructed by pasting a detection element such as a strain gauge on a quadrilateral load cell frame, one end of the load cell frame is supported by a support member, and
A weighing pan is attached to the movable end of the load cell frame, and when a load is placed on the weighing pan, the load cell frame and the detection element attached to it are distorted in response to the weight of the load, and this distortion occurs. A load cell scale has been put into practical use that detects the weight of the load by converting the change in the electrical characteristics of the detection element corresponding to the quantity into weight, and this type of scale has a relatively simple configuration. As mentioned above, the parallelogram type load cell has the advantage of being highly accurate even when an unbalanced load (four corner loads) is applied to the weighing pan, and since it outputs an electrical signal, it can be used as is in electronic digital display scales, etc. It has the advantage of being easy to use.

Furthermore, as mentioned above, one end of the load cell is attached to the support member, but in conventional parallelogram type load cell scales, as shown in Fig. One end of the load cell a, to which a detection element g such as a strain gauge is attached at a nearby predetermined position, is fixed to a support member c fixed to a stand b by tightening a plurality of screws e, etc. A plate mounting member d was fixed to the end portion with a plurality of screws f, and a weighing plate h was attached to this. In order to prevent the plate mounting member d and the load cell from shifting due to unbalanced loads or impact loads, the mounting pitches with the screws are spaced as far as possible. In this way, the load cell a is attached to the support member c or the plate mounting member d using a plurality of screws e and f.
When it is tightened and fixed, the tightening force of screws e and f causes internal stress and partial distortion in the mounting part of the load cell a, and when the screw hole of the mounting part of the parallelogram type load cell and the detection element g become close, Since the internal stress is directly propagated to the detection element g, the detection element g of the load cell a detects the internal stress generated by this tightening force. There were cases in which the performance changed and reliable weight detection was not possible. In addition, the load cell frame is made of a special material, while the support member, plate mounting member, and mounting screws are made of general steel materials. The amount of thermal expansion and contraction when exposed to heat is different, but since these are connected by multiple screws e and f, internal stress may occur near the mounting portions of both screws e and f of load cell a, and temperature changes may occur. However, since the internal stress also changes, the zero point and span change.

This idea was devised to improve the above-mentioned situation, and its purpose is to prevent the local strain and internal stress generated in the load cell mounting part from affecting the detection element, and to prevent the It is an object of the present invention to provide a load cell for a load cell scale that can accurately and reliably detect weight.

This invention will be explained below with reference to embodiments shown in FIGS. 2 to 4. In the figure, reference numeral 1 denotes a load cell, and this load cell 1 is composed of a load cell frame 2, which will be described later, and a detection element 3 made of a strain gauge attached to the load cell frame 2. The load cell frame 2 is formed into a rectangular shape with a predetermined thickness, and a rectangular hollow part 2a is formed in the center thereof. 4 of the upper and lower surfaces 6 of the load cell frame 2 corresponding to the thin wall portion 5 are cut.
A sensing element 3 made of a strain gauge is pasted at this location, and the thickness of the pasting part of the sensing element 3 (the distance between the upper and lower surfaces 6 and the arcuate concave surface of the thin part 5) is adjusted to a predetermined dimension with high precision. The area near where the detection element 3 and the detection element 3 of the load cell 1 are attached is called a strain detection part.

Note that the detection element 3 consisting of the four strain gauges described above is electrically connected in a bridge circuit format,
Electrical signals from the detection element 3 made up of four strain gauges are combined and output. Furthermore, the upper and lower directions are located on both sides of the detection element 3 and slightly closer to the center than the side edges of the support end 7 on one end side of the load cell frame 2 and the movable end 8 on the other end side. A gap 10 is formed between both sides of the load cell frame 2, leaving a central portion 9 serving as a connecting portion, thereby forming attachment portions of a predetermined thickness on both sides of the load cell frame 2. In this case, the mounting portion on the right side in FIG. 2 will be referred to as the supporting side mounting portion 11, and the mounting portion on the left side will be referred to as the movable side mounting portion 12. Therefore, the detection element 3 of the load cell 1 and both mounting portions 11 and 12 are partially separated from each other via the gap 10, and are partially connected via the central portion 9. Furthermore, the support side attachment part 11 and the movable side attachment part 1
A supporting side mounting part screw hole 13 and a movable side mounting part screw hole 13 are respectively formed along the horizontal direction at two upper and lower places near the upper and lower surfaces of 2. The neighboring parts are separated from each other by the gap 10. In addition, four support legs 14 are fixed to the inside of each corner of a support member bent into a rectangular frame shape (hereinafter referred to as support plate 15), and another support plate 15a is fixed to the inside of the support plate 15. is fixed, and two screw insertion holes 16 are formed in the upper and lower central portions of this support plate 15a. Furthermore, after abutting the support end 7 of the load cell 1 on the center of the support plate 15a and aligning the screw insertion hole 16 of the support plate 15a with the screw hole 13 of the support side attachment part 11 of the load cell 1,
Tighten the screws 17 to support the load cell 1 on the support plate 15a. In addition, the two screw insertion holes 19 formed in the vertical part of the plate mounting member 18 formed in an L shape are inserted into the movable side mounting part 1 of the load cell 1.
2, and tighten the screw 20 to attach the plate mounting member 18 to the load cell 1. Further, a flat weighing plate 31 is fixed to the upper part of the plate mounting member 18 via a mounting base 30. Note that 21 and 22 are upper and lower cases attached to the upper and lower parts of the support leg 14, respectively.

When a load is placed on the weighing pan 31, the weight of the load acts on the movable end 8 side of the load cell 1, causing the thin wall portion 5 of the load cell 1 (near the arcuate cut portion) to become distorted, causing the adhesive to stick to this portion. The detection element 3 made up of four strain gauges attached to the sensor is also distorted, and outputs an electric signal corresponding to the amount of distortion.
Since the detection element 3 consisting of two strain gauges is connected in a bridge circuit format, these electric signals are integrated, enlarged and output, and the output amount of this electric signal is converted into weight and displayed. , to measure the weight of the load.

Therefore, even if a load is applied to the four corners of the weighing pan 31 or an impact load is applied so that a torsional moment acts on the load cell 1, the mounting member 18 to which the weighing pan 31 is attached and the load cell 1 are still attached. The support plate 15a is attached to this plate mounting member 18.
Since the screw holes 13 for attaching the support plate 15a are formed sufficiently spaced apart vertically, the support plate 15a can be reliably attached to each attachment portion of the load cell 1 without shifting.

In this invention, the load cell frame 2
When attaching the support side attachment part 11 to the support plate 15a, if the screw 17 is screwed into the support side attachment part screw hole 13 and tightened, the tightening force of the screw acts on the vicinity of the tightening part of the screw 17 of the load cell frame 2. Internal stress and local distortion occur in the lever part, but since the vicinity of the tightening part of the screw 17 is separated from the vicinity of the attachment part of the detection element 3 through a gap 10, this is caused by tightening the screw 17. Since the internal stress does not propagate directly to the detection element 33 but instead circulates around it, the generated internal stress becomes small and does not affect the detection element 3. Furthermore, when the support side attachment part 11 of the load cell frame 2 and the support plate 15a undergo different thermal expansion and contraction due to temperature changes, internal stress generated between both screws 17 due to thermal expansion and contraction and changes in internal stress due to temperature changes occur. Even if this internal stress occurs within the support-side mounting portion 11 at one end of the load cell 1, this internal stress is not directly propagated to the detection element 3 through the gap 10. Therefore, the internal stress generated at the tightening part of the screw 17 is not directly propagated to the detection element 3 through the gap 10, so the internal stress is small and the detection element 3 is not affected, so that the performance of the load cell 1 is improved. does not change,
The weight of a loaded object can always be detected reliably. In addition, since the weighing plate mounting portion of the load cell 1 has a structure similar to that of the above-mentioned support portion, the internal stress generated by the tightening force of the screw 20 on the weighing plate mounting portion side is absorbed by the gap 10 in the same manner as above. Since the internal stress is not directly propagated to the detection element 3, the internal stress is small and does not affect the detection element 3, so that the weight can be detected reliably.

As described above, each mounting portion 11 of the load cell 1,
The internal stress generated in 12 does not propagate directly through the gap 10 and becomes smaller, so the detection element 3 is not affected. Therefore, even if the load cell is replaced or the tightening force of the screw is changed, the internal stress will be reduced. Since this does not directly propagate to the detection element, the load cell can exhibit the same performance as the previous time, and there is no need for wasted time and effort such as readjusting the load cell.

Note that the deeper the gap 10 is, the more securely it will be possible to prevent the propagation of internal stress due to tightening, etc. However, since the center portion 9 must reliably withstand stress such as bending moment applied to the load cell, the load The depth, width, and shape are arbitrary depending on the size and width of the dish. Further, even if the depth is insufficient for the screw hole 13, the internal stress will propagate to the surface depending on the location, so it will of course have a certain effect. Further, in this embodiment, two screw holes are provided for the supporting side mounting portion and two screw holes for the movable side mounting portion are provided, one above the other, but the present invention is not limited to this.

As detailed above, in this invention, a gap of a predetermined depth is provided between the supporting side mounting part screw hole and the movable side mounting part screw hole formed on both sides of the load cell and the detection element bonding part. Internal stresses and local strains caused by the tightening force generated at the load cell mounting part and thermal expansion and contraction due to the difference in linear expansion coefficient between the load cell material and a different material are directly propagated to the detection element and have a negative effect on weight detection. It has no effect on me. In addition, the load cell and plate mounting member can be supported reliably at all times, and the performance of the load cell will not change due to the internal stress caused by the tightening force of the mounting screw or thermal expansion and contraction, so there will be no change in zero point or span. It is possible to always detect the weight of a loaded object with high precision and reliability. In addition, even if the load cell is replaced, the internal stress caused by the tightening force of the screws does not affect the detection element, so the load cell can exhibit the same performance as before, eliminating wasted time such as readjusting the load cell. Doesn't require any effort.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a conventional load cell scale, Figure 2 is a vertical sectional view of an embodiment of this invention, Figure 3 is an exploded perspective view of the main parts of the same example, and Figure 4 is an exploded perspective view of the same example. It is a perspective view of a support member. 1...Load cell, 2...Load cell frame, 3
... Detection element consisting of a strain gauge, 7 ... Support end, 8 ... Movable end, 9 ... Center part (connection part), 10 ... Gap, 11 ... Support side mounting part, 1
2... Movable side mounting part, 13... Support side and movable side mounting part screw hole, 14... Support leg, 15... Support plate, 17... Screw, 18... Pan mounting member, 20...
…screw.

Claims (1)

[Scope of Claim for Utility Model Registration] A load cell frame is formed into a rectangular shape with a predetermined thickness and has a rectangular hollow part near the center thereof, with thinner parts formed near both sides of the upper and lower horizontal beams. , and is supported by one support-side mounting part formed integrally with both sides of the parallelogram-shaped load cell frame body, in which a detection element such as a strain gauge is bonded to multiple detection element bonding areas corresponding to the thin-walled part. A side mounting part screw hole is formed, a movable side mounting part screw hole is formed in the other movable side mounting part, a support plate is fixed to the supporting side mounting part screw hole with a screw, and the movable side mounting part screw In a load cell for a load cell scale in which a plate mounting member is fixed to the hole with a screw, the supporting side mounting part screw hole and the movable side mounting part screw hole are provided near the upper and lower surfaces of the supporting side mounting part and the movable side mounting part. , a gap is formed between the sensing element bonding part and the supporting side mounting screw to prevent internal stress generated by tightening the screws fixing the support plate and the plate mounting member from directly propagating to the sensing element. A load cell for a load cell scale, characterized in that a hole is formed between the hole and a screw hole of a movable side mounting part.