JP4178681B2 - Precision scale - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an upper pan scale, and more particularly, to an upper pan scale equipped with a Roverval mechanism and a load transmission lever mechanism.
[0002]
[Prior art]
As shown in FIGS. 4 and 5, in an upper pan balance or an upper balance, generally, the sample pan 20 is supported by supporting the sample pan 20 via a Roverval mechanism (also referred to as a parallel guide) 10. The horizontal displacement is restricted so that the sample is displaced up and down, so that an error associated with the displacement of the sample with respect to the sample dish 20, that is, a so-called displacement error (also referred to as a four-corner error) does not occur.
[0003]
The Roverval mechanism 10 has a structure in which a movable column 13 is connected to a fixed column 14 via two parallel upper and lower beams 11 and 12 having flexible portions 11a, 11b and 12a, 12b that serve as hinges at both ends. The sample tray 20 is supported on the movable column 13. A load acting on the sample pan 20 is transmitted to a load sensing unit 40 such as a load cell or an electromagnetic force generation mechanism via a lever 30 connected to the movable column 13.
[0004]
The lever 30 is normally supported by an elastic fulcrum 31, and a force point 32 at one end thereof is connected to the movable column 13 via a connecting piece 50, while the other end is connected to the load sensitive portion 40, The load to be measured applied to 20 is reduced based on a lever ratio of a fraction to one hundredth and transmitted to the load sensing unit 40. Here, the force point 32 of the lever 30 has flexibility in the front-rear rotation direction (movement of the lever 30 in the longitudinal direction, indicated by an arrow R in FIG. 5, the same applies hereinafter), and the connecting piece 50 and the movable column. The flexible connecting elastic fulcrum 51 is also interposed in the forward and backward rotation direction at the connecting portion with the connecting portion 13, and the load is applied to the sample pan 20 by the connecting elastic fulcrum 51 and the flexible force point 32. It is intended to absorb a slight displacement in the front-rear direction of the movable column 13 and a slight displacement in the front-rear direction of the force point 32 due to the inclination of the lever 30.
[0005]
By the way, in such a robust mechanism 10, generally, the parallelism of the upper and lower beams 11 and 12 is important, and for the first time under the condition that the upper and lower beams 11 and 12 are accurately parallel to each other. The deviation error of the load on the sample pan 20 is eliminated. That is, a deviation deviation error occurs unless the dimensions H and H ′ shown in FIG. This adjustment is not a measure that can be performed by measuring the dimensions of H and H ', for example, in the case of precision electromagnetic force balance type electronic balances, and so on. In the adjustment operation, the parallelism is finely adjusted so that the measurement value does not change at each position while moving the load placed on the sample pan 20.
[0006]
However, due to the recent demands for smaller and thinner scales, it is necessary to measure a large load with a small mechanism by making the lever ratio larger than before, but simply increasing the lever ratio of the conventional product When miniaturization of the device is attempted, a deviation error tends to occur and the specification cannot be satisfied.
[0007]
That is, when the lever ratio is increased and the distance between the elastic fulcrum 31 and the force point 32 of the lever 30 and L1 is shortened to about 1 mm or less, the displacement in particular in the front-rear direction (horizontal direction) depends on the magnitude of the load. The error is easily variable, and even if the deviation error with respect to a certain load is strictly adjusted using the adjustment mechanism as described above, the deviation error is caused with another load, and it becomes impossible to use as a scale.
[0008]
Therefore, even if the lever ratio is increased and the size and thickness are reduced, the change in the deviation error due to the magnitude of the load is reduced as in the prior art. For example, as previously filed in Japanese Patent Application No. 7-257801. In addition, the lower beam 12 on the side close to the coupling elastic fulcrum 51 of the upper and lower beams 11 and 12 is larger than the rigidity of the beam 11 on the other side, for example, the lower beam The thickness of 12 is increased. Thereby, even if the movable column is tilted due to the displacement, the rotation center K of the movable column is in the vicinity of the coupling elastic fulcrum 51, so that the position of the coupling elastic fulcrum 51 moves in the lever longitudinal direction (horizontal direction). Therefore, highly accurate measurement can be performed.
[0009]
[Problems to be solved by the invention]
However, if the beam is thickened to suppress the expansion and contraction of the beam itself, on the other hand, the bending rigidity of the beam increases. Therefore, for an upper pan scale equipped with a robust mechanism that can measure the load by bending the beam. This was a factor that lowered the measurement sensitivity.
[0010]
An object of the present invention is to solve such a problem and provide an upper pan scale capable of suppressing an offset error without lowering measurement sensitivity.
[0011]
[Means for Solving the Problems]
To solve the problems as described above, the present invention, the movable pole is connected to the fixing post via a mutually parallel upper and lower two substantially identical thickness of the beam member having a flexible portion at both ends The sample plate is supported on the movable column of the Roverval mechanism, and the movable column is connected to the force point of the lever mechanism having the elastic fulcrum via the connecting elastic fulcrum. In an upper pan scale that is connected and the load on the sample pan is transmitted to the load-sensitive portion by the lever mechanism, when the ratio of the distance from the upper and lower beams to the upper and lower beams centered on the elastic fulcrum for connection is A: B, A beam member having the same thickness as that of the beam member is further provided so that the ratio of the number of the upper and lower beams is B: A , so that the rigidity is enhanced, and even if an eccentric load is applied to the sample pan, it is movable. rotation center pillars substantially coincides with the said connection elastic fulcrum, before The movement of the connecting elastic fulcrum in the front-rear direction (horizontal direction) is suppressed, and the increase in bending rigidity of the beam member is minimal. It is suppressed.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a mechanism diagram of an embodiment in which the first configuration of the present invention is applied to an electromagnetic force balanced balance. The basic structure of the Roverval mechanism 10 is the same as that of the conventional one shown in FIG. 4 or FIG. 5, and the upper beam portion 11 and the lower side each having flexible portions 11a, 11b and 12a, 12b at both ends, respectively. The beam portion 12 has a structure in which the movable column 13 and the fixed column 14 are connected, and the sample tray 20 is supported on the movable column 13. The upper beam portion is composed of one beam 11 and the lower beam portion 12 is composed of two beams 12A and 12B, and the thicknesses of these beams are substantially the same.
[0013]
Further, as in the prior art, the load acting on the movable column 13 is transmitted to the electromagnetic force generator 40 which is a load sensitive part via the lever 30 supported by the elastic fulcrum 31. In other words, the force point 32 provided at one end of the lever 30 is connected to the movable column 13 by the connecting piece 50 via the connecting elastic fulcrum 51, and the lever 30 has the electromagnetic force generator 40 on the opposite side across the fulcrum 31. The force coil 42 is fixed. In the electromagnetic force generator 40, a force coil 42 fixed to the lever 30 is movably disposed in a static magnetic field generated by a magnetic circuit 41 mainly composed of a permanent magnet 41a. The current flowing in the force coil 42 is controlled so that the displacement detection result detected by the displacement sensor 34 that detects the position of the slit 33 formed in the section is always zero. Then, the load on the sample pan 20 is detected from the magnitude of the current.
[0014]
The height direction position of the connecting elastic fulcrum 51 is closer to the lower beam portion 12 of the upper and lower beams of the Roverval mechanism 10, and the vertical dimension between the upper beam portion 11 and the connecting elastic fulcrum 51 is A, the lower side. When the vertical dimension of the beam portion 12 and the connecting elastic fulcrum 51 is B, A> B.
[0015]
As described above, the upper beam portion 11 is composed of one beam 11, whereas the lower beam portion 12 is provided with two beams 12A and 12B. In this embodiment, in particular, Since these beams have substantially the same thickness, the rigidity of the lower beam portion 12 having a large number of beams is higher than that of the upper beam portion 11.
[0016]
Specifically, an attempt to up compression stiffness in the horizontal direction twice, doubling the thickness of a single beam, flexural rigidity, the second moment ^{I = bt 3/12 (t} : thickness, b: width), 2 ³ = 8 times. On the other hand, if the same stiffness is used and the compression stiffness is doubled, the flexural stiffness is simply doubled, and the increase in flexural stiffness doubles the thickness of one beam. Compared to the case, the sensitivity of the upper balance that can be measured by bending the upper and lower beam portions 11 and 12 of the Roverval mechanism is suppressed.
[0017]
In FIG. 2, when the ratio of the distance from the upper and lower beams centering on the connecting elastic support point 51 is A: B, the expansion / contraction ratio δ ₁ : δ ₂ of the beam is equal to the ratio A: B. The rotation center K of the movable column due to the displacement coincides with the coupling elastic support point 51, and the movement of the coupling elastic support point 51 is almost eliminated.
[0018]
In this embodiment, A: B = 2: 1 centering on the coupling elastic support point 51, and in order to make the rotational center K of the movable column due to the displacement coincide with the coupling elastic support point 51, δ ₁ : Since δ ₂ = 2: 1 needs to be set and the rigidity of the lower beam portion 12 needs to be twice that of the upper beam portion 11, in this embodiment, two are provided in the lower beam portion 12. The beam is provided. In addition, when A: B = 3: 1, the rigidity of the lower beam portion 12 needs to be three times that of the upper beam portion 11, so that the lower beam portion 12 is provided with three beams. become.
[0019]
Note that the upper beam portion 11 can also be composed of a plurality of beams. In this case, the lower beam portion 12 needs to be composed of a larger number of beams than the upper beam portion 11.
[0020]
Further, in this embodiment, the thicknesses of the individual beams constituting the upper beam portion 11 and the lower beam portion 12 are substantially the same (the rigidity is substantially the same), but the thicknesses are different from each other as necessary. These beams may be used in combination. For example, when it is desired to obtain a rigidity effect that is three times that of the upper beam portion 11 in the lower beam portion 12, use two 1.5 times thick beams or one double thickness beam. Can be used in combination with one beam of the original thickness, and the bending stiffness is (1.5 ³ ) × 2 = 6.75 times, 2 ³ + 1 = 9 times, respectively. The bending stiffness when the thickness of the beam is tripled is 3 ³ = 27 times, whereas the increase in bending stiffness can be suppressed. However, when three original-thickness beams are used, the bending rigidity can be minimized by a factor of three. However, if the number of beams cannot be increased due to the restriction in the height direction of the Roverval mechanism, etc. Depending on various conditions, as described above, the beam portion is composed of a combination of beams having different thicknesses.
[0021]
FIG. 3 shows an example in which the present invention is applied to a one-piece type Roverval mechanism as a modification of the present embodiment. The load side (movable side) 101 is supported by the upper beam portion 103 and the lower beam portion 104 with respect to the fixed side 102, but the lower beam portion 104 has the same size as the Roverval 105 of the upper beam portion 103. It is formed of a single piece of Roverval 105, and an effect equivalent to that of the Roverval mechanism in the electronic balance of FIG. 1 described above can be obtained.
[0022]
【The invention's effect】
As described above, according to the configuration of the present invention, of the upper and lower beam portions of the Roverval mechanism, the number of beams on the side close to the connecting elastic fulcrum that connects the power point of the movable column and the lever is set to By providing more than the number, the rigidity of the lower beam can be increased to move the connecting elastic fulcrum in the front-rear direction without causing a synergistic increase in bending stiffness that affects the decrease in measurement sensitivity. Can be reduced, and measurement errors due to the eccentric load can be reduced.
[Brief description of the drawings]
FIG. 1 is a mechanism diagram showing an embodiment applied to an electromagnetic balance electronic balance.
2 is an operation explanatory diagram when an eccentric load is applied to the mechanism of FIG. 1; FIG.
FIG. 3 is a diagram showing application to a one-piece type roval mechanism;
FIG. 4 is a view showing a general configuration of a conventional balance or balance having a Robertval mechanism and a lever.
FIG. 5 is a mechanism diagram of the pan scale or the balance shown in FIG. 4 and an explanatory diagram of operation when an eccentric load is applied.
[Explanation of symbols]
11 Upper beam portion 12 Lower beam portions 12A and 12B Beam 20 Sample pan 51 Elastic fulcrum for connection

Claims (1)

The movable pillar Roberval mechanism formed is connected to the fixed post through the mutually parallel upper and lower two substantially identical thickness of the beam member having a flexible portion at both ends, the sample pan is supported on the movable pole The movable column is connected to the force point of the lever mechanism having an elastic fulcrum through a connecting elastic fulcrum located between the upper and lower beam members, and the load on the sample pan is caused by the lever mechanism. in upper tray instrument which is transmitted to the load sensing portion, the ratio of the distance to the upper and lower beam about said connecting elastic support point a: when is B, the ratio of the number of upper and lower beams B: the so that a An upper pan scale characterized by further providing a beam member having substantially the same thickness as the beam member , thereby increasing the rigidity of the beam portion.

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