JP5611793B2 - Load cell - Google Patents

Description

  The present invention relates to a load cell having an assembly-type robust mechanism.

  The ROBERVAL mechanism used in the load cell is a single piece of material that is cut and cut to form a fixed part that is connected and fixed to the measurement location, a movable part that can be displaced, and an elastic beam part that can bend and deform. There are known a body type and an assembly type (for example, see Patent Document 1) in which an elastic beam made of a thin plate material is erected and connected between a fixed block and a movable block.

JP 2004-151047 A

  The integrated load cell with a Roverval mechanism has a simple and easy-to-use structure using a single material, but on the other hand, the material is largely cut and cut, resulting in high material costs and high material costs. . In addition, the characteristics will be standardized according to the processed shape, and if the required characteristics change, it will be necessary to remanufacture the corresponding ones, and it seems that some parts such as the elastic beam have been damaged In some cases, it was necessary to replace the whole.

  On the other hand, in the assembly type load cell having the Roverval mechanism, the number of parts increases, but each part can be processed with a high yield, and the whole can be manufactured at low cost. In addition, various characteristics can be obtained by combining the elastic beam and the movable block having different specifications, and those according to the required characteristics can be easily and inexpensively manufactured. Even if some parts are damaged, they can be easily replaced.

  As described above, the assembly type load cell has the advantages as described above. For example, in Patent Document 1, the elastic beam is simply elasticated with a bolt to connect the elastic beam across the fixed block and the movable block. Since the beam was tightened and connected to each block, when the elastic beam was bent and deformed by a load, a part of the elastic beam was removed from the beam mounting surface of the fixed block or movable block when it was removed from the bolt tightening point. It may be lifted and deformed locally. In this Roverval mechanism, the edge of the beam mounting surface of the fixed block or the movable block is designed as a fulcrum for the bending deformation of the elastic beam. As described above, the elastic beam is the beam of the fixed block or the movable block. By lifting and deforming from the mounting surface, the fulcrum shifts and the measurement accuracy decreases.

  The present invention has been made paying attention to such a situation, and in a load cell having an assembling type robotic mechanism, the occurrence of a fulcrum shift at the time of bending deformation of an elastic beam is prevented, and the measurement accuracy is lowered. The main purpose is to prevent this.

  In order to achieve the above object, the present invention is configured as follows.

(1) A load cell according to the present invention includes a fixed block, a displaceable movable block, an upper beam that connects the fixed block and the upper portion of the movable block, and a lower link that connects the lower portion of the fixed block and the movable block. A load cell including a beam, wherein both end portions of the upper beam are pressed and clamped by pressing surfaces of the pressing members with respect to upper surfaces of the fixed block and the movable block, respectively, of the fixed block and the movable block. While connecting the upper part, the both ends of the lower beam are pressed and clamped by the pressing surfaces of the pressing members against the lower surfaces of the fixed block and the movable block to connect the fixed block and the lower part of the movable block. The upper beam and the lower beam are made of a thin plate material having elasticity that can be flexibly deformed. In addition, a strain detecting portion is provided, and a strain detecting element is attached to the strain generating portion of at least one of the upper beam and the lower beam, and each pressing member includes the fixed block. Alternatively, it is made of a plate material that is fastened and fixed to the upper surface or the lower surface of the movable block. Between the pair of strain generating portions of the upper beam, a rib is bent upward so as to project, and the pair of strain generating of the lower beam. A rib is bent and projected between the parts, and a part is provided in a space surrounded by the fixed block, the movable block, and the upper and lower beams .

  According to the load cell of the present invention, both ends of the upper beam and the lower beam are firmly sandwiched between the pressing surface of the pressing member and the upper surface or the lower surface of the fixed block or the movable block. When each beam bends and deforms, lifting deformation from the upper or lower surface of the fixed block and the movable block is prevented by the pressing surface, and the position of the fulcrum with respect to each beam of the fixed block and the movable block is not shifted, and the measurement accuracy Can be prevented from decreasing.

According to the load cell of the present invention, the upper and lower surfaces of the fixed block and the movable block and the pressing surfaces of the pressing members sandwich the both ends of the upper and lower beams made of a thin plate material, respectively, By tightening and fixing each to the upper or lower surface of the block, both ends of each beam can be firmly pressed and clamped by the block body and each pressing member, and each beam bends and deforms under a load. Then, the amount of deformation can be detected by a strain detection element attached to the strain generating portion.

According to the load cell of the present invention , the rib portion protrudes to increase the rigidity of the beam portion between the two strain-generating portions, thereby suppressing the bending deformation, and more efficiently concentrating the bending deformation on the strain-generating portion. can do. In addition, the rib of the upper beam protrudes upward and the rib of the lower beam protrudes downward, so that the rib does not protrude into the space surrounded by the fixed block, the movable block, and the upper and lower beams. The parts can be provided by effectively utilizing the space.

(2) In a preferred embodiment of the load cell of the present invention, the part may be a weight part, and the weight part may be connected to the movable block.

  According to this embodiment, the weight of the movable part displaced by the load can be arbitrarily adjusted by the weight component, and the natural frequency of the load cell can be adjusted.

( 3 ) In the embodiment of ( 2 ) above, the fixed block may be fixed to a measurement location, and vibration at the measurement location may be detected.

  According to this embodiment, for example, the load cell is installed in the vicinity of a place where a weighing device for weighing an object to be weighed is installed, and the vibration of the place where the weighing device is installed, so-called floor vibration is applied. It can be detected by the load cell, and thereby the floor vibration component detected by the load cell can be removed from the weighing signal of the weighing device to correct the weighing value of the object to be weighed.

  Moreover, the natural vibration of the load cell can be matched with the natural vibration of the load cell for weight measurement of the weighing device by the weight component.

  As described above, according to the load cell of the present invention, in the load cell provided with the assembly-type Roverval mechanism, it is possible to prevent the fulcrum from being displaced when the elastic beam is bent and deformed, thereby preventing the measurement accuracy from being lowered.

FIG. 1 is a perspective view of a load cell according to an embodiment of the present invention. FIG. 2 is a vertical side view of the load cell of FIG. FIG. 3 is a plan view of the load cell of FIG. FIG. 4 is a side view of the load cell of FIG. FIG. 5 is an exploded perspective view of the load cell of FIG. FIG. 6 is a perspective view of a load cell according to another embodiment of the present invention. FIG. 7 is a plan view of the load cell of FIG. FIG. 8 is a side view of the load cell of FIG. FIG. 9 is a perspective view of a load cell according to a reference example of the present invention. FIG. 10 is a plan view of the load cell of FIG. FIG. 11 is a side view of the load cell of FIG. FIG. 12 is a side view of a load cell of another reference example of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
1 is a perspective view of a load cell according to an embodiment of the present invention, FIG. 2 is a longitudinal side view thereof, FIG. 3 is a plan view thereof, FIG. 4 is a side view thereof, and FIG. FIG.

 The load cell 1 of this embodiment is installed close to a place where a load cell for weight measurement is installed in a weighing device that measures the weight of an object to be weighed, and detects vibration at that place, so-called floor vibration, It is used to correct the measurement value by removing the floor vibration component from the detection output of the original load cell for weight measurement.

  The load cell 1 includes a fixed block 2 fixed at a vibration measurement location, a movable block 5 that can be displaced, and a pair of upper and lower elastic beams as upper and lower beams that connect the upper and lower portions of both blocks 2 and 5 respectively. 3, a strain gauge 4 as a strain detection element affixed to two locations in the front-rear direction (the left-right direction in FIGS. 2 and 3) of each elastic beam 3, and a pair of upper and lower as a beam fixing pressing member The pressing plates 6 and 7 and a weight part 8 connected to the movable block 5 are configured as an assembly-type Roverval mechanism.

  The fixed block 2 is formed of a metal block body cut into a rectangular parallelepiped shape, and two mounting holes 10 for connecting each one end of each elastic beam 3 as a beam mounting surface on the upper and lower surfaces thereof in the front-rear direction. Each is formed at intervals along the same. On the front surface of the fixed block 2, two mounting holes 9 for fastening and fixing the fixed block 2 to the measurement location are formed at intervals along the vertical direction.

  The movable block 5 is also made of a metal block body cut into a rectangular parallelepiped shape, and the upper and lower surfaces thereof have two mounting holes 12 for connecting the other end portions of the elastic beams 3 as beam mounting surfaces. Are formed at intervals along each other. In addition, two weight attachment holes 14 penetrating in the front-rear direction for connecting the weight component 8 are formed on the front surface of the movable block 5 at intervals along the vertical direction.

  The pair of parallel upper and lower elastic beams 3 are formed by punching and pressing a metal such as a leaf spring material, for example, a thin plate material made of aluminum, 5 is attached.

  Each elastic beam 3 is made of a thin plate material having elasticity that can be bent and deformed, and a pair of front and rear strain generating portions 3a are constricted between the fixed block 2 and the movable block 5 with a predetermined front and rear span, The ribs 3b are bent and protruded from both sides of the beam between the two strain-generating portions 3a. The rigidity of the beam portion between the two strain-generating portions 3a is increased to suppress deformation and bend to the strain-generating portion 3a. Deformation is concentrated. The ribs 3b of the upper elastic beam 3 are connected to the blocks 2 and 5 so as to protrude upward, and the ribs 3b of the lower elastic beam 3 protrude downward. This prevents each rib 3b from interfering with the attachment of the weight component 8 to the space between the upper and lower elastic beams 3.

  The strain gauge 4 is attached and fixed to the surface of the strain generating portion 3a, and the strain generated in the strain generating portion 3a is converted into a change in electric resistance value. In this way, the strain gauge 4 only needs to be attached to the thin plate material constituting the elastic beam 3, and it is not necessary to attach the strain gauges to the upper surface and the lower surface as in the case of an integrated load cell. Become.

  One end of each elastic beam 3 is formed long in the front-rear direction corresponding to the upper and lower surfaces of the fixed block 2 to which the one end is connected, and bolts 11 attached to the two mounting holes 10 of the fixed block 2 are provided. Each of the two insertion holes 20 is inserted. The other end of each elastic beam 3 is formed to be elongated in the left-right direction corresponding to the upper and lower surfaces of the movable block 5 to which the other end is connected, and is attached to the two attachment holes 12 of the movable block 5. There are two insertion holes 21 through which the bolts 13 are inserted.

  A pair of upper and lower pressing plates 6 that press and hold one end of each of the upper and lower elastic beams 3 against the upper and lower surfaces of the fixed block 2 are weighted from the rectangular plate-shaped side portions corresponding to the upper and lower surfaces of the fixed block 2. The arm portion 6a is extended toward the component 8 side, and the stopper 16 screwed and attached to the extended end portion via the nut 22 is disposed so as to face the upper surface and the lower surface of the weight component 8 with a predetermined gap, respectively. Is done. The pressing plate 6 has two insertion holes 23 through which the bolts 11 attached to the two attachment holes 10 on the upper and lower surfaces of the fixed block 2 are inserted.

  The pair of upper and lower pressing members 7 that press and hold the other end portions of the upper and lower elastic beams 3 against the upper and lower surfaces of the movable block 5 are rectangular plate shapes corresponding to the upper and lower surfaces of the movable block 5, respectively. There are two insertion holes 24 through which bolts 13 attached to the two attachment holes 12 on the upper and lower surfaces of the movable block 5 are inserted.

  The weight component 8 adjusts the weight of the movable part in the load cell 1 for vibration detection in accordance with the natural frequency of the load cell for weight measurement of the weighing device described above, and has a rectangular parallelepiped shape so as to obtain a desired weight. It consists of a cut metal block. The weight component 8 is inserted into a space formed between the fixed block 2 and the movable block 5, and is fastened and fixed to the back surface of the movable block 5 by a bolt 15 inserted through the weight mounting hole 14.

  In the load cell 1 of this embodiment, one end portion of each of the upper and lower elastic beams 3 is sandwiched between the upper and lower surfaces of the fixed block 2 and the pressing surface of each pressing plate 6 with their edges aligned, and the bolt 11 On the other hand, the other end of each elastic beam 3 is clamped and fixed with bolts 13 while the other edges of each elastic beam 3 are sandwiched between the upper and lower surfaces of the movable block 5 and the pressing surface of each pressing plate 7 with their edges aligned. When the elastic beams 3 are bent and deformed under load, the pressing plates 6 and 7 prevent the elastic blocks 3 from being lifted and deformed from the upper or lower surfaces of the fixed block 2 and the movable block 5. The position of the fulcrum with respect to each elastic beam 3 remains unchanged, and the distance D between the strain-generating portions is constant as shown in FIG.

  In addition, in this embodiment, the fixing block 2 is bolted and fixed to a measurement location via a rigid bracket or the like, and the elastic beam 3 is bent up and down by vibrations acting on the load cell 1, so that four pieces are deformed. The output from the arithmetic circuit to which the strain gauge 4 is bridge-connected varies, and the vibration applied to the measurement location can be detected from the output.

  Further, in this embodiment, since the arm portion 6a of the pressing plate 6 fastened and fixed to the fixing block 2 by the bolt 11 is provided with a stopper 16, the stopper 16 moves the weight component 8 upward and downward. The contact limit of the displacement can be restricted, whereby the deformation amount of the elastic beam 3 can be limited to prevent the elastic beam 3 and the strain gauge 4 from being damaged by overload. In addition, the stopper 16 is provided on the pressing plate 6 for pressing the elastic beam 3 and restricts displacement by contact with the weight component 8 that adjusts the weight, so that the deformation amount of the elastic beam 3 due to overload is reduced. As the parts constituting the overload protection device that restricts and protects, the pressing plate 6 and the weight part 8 are used together, and it is not necessary to provide a dedicated part, and the number of parts can be reduced.

(Embodiment 2)
FIG. 6 is a perspective view of another embodiment of the present invention, FIG. 7 is a plan view thereof, FIG. 8 is a side view thereof, and portions corresponding to the above-described embodiment are denoted by the same reference numerals. Attached.

  In the load cell 1 of this embodiment, by forming the fixed block 2 and the movable block 5 to have the same specifications that can be shared, the elastic beam 3 can be shaped symmetrically in the front-rear and left-right directions. There is no directionality of parts, and assembly workability is improved. Further, by forming the fixed block 2 and the movable block 5 to the same specification, the front and rear pressing plates 6 and 7 can be made to have the same specification, and the number of parts can be reduced to reduce the processing cost. Effective to reduce.

  Although not shown, in this case as well, durability against overload can be enhanced by providing a stopper 16 on the pressing plate 6 on the fixed side and facing the weight component 8.

( Reference example )
9 is a perspective view of a reference example of the present invention, FIG. 10 is a plan view thereof, FIG. 11 is a side view thereof, and portions corresponding to the above-described embodiment are denoted by the same reference numerals.

In the load cell 1 of this reference example , the weight of the movable part is a weight corresponding to the natural frequency of the load cell for load measurement of the weighing device described above without providing the weight component 8. Is omitted.

In this reference example , since the parts such as the weight parts 8 are not provided in the space surrounded by the fixed block 2, the movable block 5, and the upper and lower elastic beams 3, the rib 3b of the upper elastic beam 3 The rib 3b of the lower elastic beam 3 protrudes upward.

  As another embodiment, circuit parts such as an A / D conversion circuit are provided in a space surrounded by the fixed block 2, the movable block 5, and the upper and lower elastic beams 3, and the entire sensor using a load cell is provided. It can also be made compact. In this case, by mounting circuit components or the like on the movable block 5 side so that the center of gravity of the movable system in the free state approaches the center between the strain generating portions, the moment error can be reduced and the measurement error can be reduced. .

(Other embodiments)
In each of the above-described embodiments, the strain gauges 4 are attached to the upper and lower elastic beams 3, respectively. However, as another embodiment of the present invention, the strain gauges 4 may be attached to only one of the elastic beams 3.

In each of the above-described embodiments, the deformation deformation of the elastic beam 3 made of a thin plate material is directly detected by the strain gauge 4. However, as another reference example, the deformation deformation of the elastic beam 3 is used as the displacement of the movable block 5. It can also be set as the form to detect. For example, as shown in the reference example of FIG. 12 , the fixed electrode plate 25 is attached to the fixed block 2 via the attachment portion 27, while the movable block 5 is movable via the attachment portion 28 so as to face the fixed electrode 25. It is also possible to attach the electrode plate 26 and detect the displacement of the movable block 5 as a change in capacitance between the electrode plates 25 and 26.

2 Fixed Block 3 Elastic Beam 3a Straining Section 3b Rib 4 Strain Gauge 5 Movable Block 6, 7 Pressing Plate 8 Weight Part 16 Stopper

Claims (3)

A load cell comprising: a fixed block; a movable block that can be displaced; an upper beam that connects the fixed block and an upper part of the movable block; and a lower beam that connects the lower part of the fixed block and the movable block;
While the both ends of the upper beam are pressed and clamped by the pressing surfaces of the pressing members against the upper surfaces of the fixed block and the movable block, respectively, the upper portion of the fixed block and the movable block is connected,
Both ends of the lower beam are pressed and clamped by the pressing surfaces of the pressing members to the lower surfaces of the fixed block and the movable block, respectively, and the lower portions of the fixed block and the movable block are connected ,
The upper beam and the lower beam are each made of a thin plate material having elasticity that can be bent and deformed, and each has a pair of strain-generating portions,
A strain detecting element is attached to the strain generating portion of at least one of the upper beam and the lower beam,
Each pressing member is made of a plate material fastened and fixed to the upper surface or the lower surface of the fixed block or the movable block,
Between the pair of strain-generating portions of the upper beam, ribs are bent and projected upward, and between the pair of strain-induced portions of the lower beam, ribs are bent and projected downward,
A component is provided in a space surrounded by the fixed block, the movable block, and the upper and lower beams.
A load cell characterized by that. The part is a weight part, and the weight part is coupled to the movable block;
The load cell according to claim 1. The fixed block is fixed to a measurement location and detects vibration of the measurement location;
The load cell according to claim 2 .

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