JPH08201155A - Electronic balance - Google Patents

Abstract

(57) [Summary] [Purpose] The parallelism adjusting mechanism of the Roverval mechanism of an electronic balance should be a mechanism that does not cause zero-point fluctuation and has little temperature drift. [Structure] A Roberval mechanism in which a fixed column 1, a movable column 2, and upper and lower parallel guides 3 and 4 are connected by a leaf spring.
By pulling the central portion of the fixed column 1 against the support wall 9 with the push screw 11, the fixed column is deformed, and thereby the leaf spring 5 and the leaf spring 6 are flexed in the same manner, thereby changing the distance between them. And adjust the parallelism of the upper and lower parallel guides.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic balance having a Roberval mechanism, and more particularly to a mechanism for adjusting the parallelism of the Roberval mechanism.

[0002]

2. Description of the Related Art An electronic balance has a fixed column 7 as shown in FIG.
1, the movable column 72 is connected by a link 81 called a Roberval mechanism, and the load on the movable column 72 by the sample placed on the upper plate 85 is supported by the fulcrum 84. Measure the load by balancing In this Roberval mechanism, since the upper and lower parallel guides 73 and 74 must be exactly parallel, a mechanism for adjusting them in parallel is provided.
FIG. 6 shows a conventional example of an adjusting mechanism for making the upper and lower parallel guides parallel. The fixed pillar 71 is divided into a fixed portion 71a and a movable portion 71b by a split 71c, and the movable portion 71b.
The upper end surface 71d of the is displaced up and down with respect to the fixed portion 71a by the pull screw 76 and the push screw 77. According to the displacement of the upper end surface 71d, the upper parallel guide 73 fixed to the upper end surface 71d via the leaf spring 75 is moved up and down and adjusted in parallel with the lower parallel guide 74. .

[0003]

In the prior art example, as shown in FIG. 6, the parallelism of the upper and lower parallel guides is adjusted by deforming only the upper part of the fixed column, so that the flat spring connecting the fixed column and the parallel guide is adjusted. Strain is generated only on the deformed portion side and acts on the electromagnetic balance portion as torque (rotational force) through the movable column. Therefore, each time the parallelism is adjusted, the weight measurement value changes at the zero point. In addition, since the structures at the upper and lower end faces of the fixed column are not symmetrical, considering the effect of changes in ambient temperature, changes in the elastic modulus of the spring and changes in the point of action due to thermal expansion do not become the same at the top and bottom, and the weight measurement Value temperature drift occurs. An object of the present invention is to provide an electronic balance that does not cause a zero point change when adjusting the parallelism of a parallel guide and has a small temperature drift of a weight measurement value.

[0004]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a movable column that receives a load in the axial direction, a fixed column that is arranged substantially parallel to the movable column, and a Roberval consisting of parallel guides and leaf springs. In an electronic balance that is supported via a mechanism, a screw mechanism that simultaneously deforms both end surfaces of the fixed column in the opposite direction by an equal amount is provided at approximately the center of the fixed column.

[0005]

[Operation] With the Roberval mechanism in which the fixed column, the movable column, and the upper and lower parallel guides are connected by the leaf springs, when the upper and lower end surfaces of the fixed column are simultaneously deformed in the opposite directions by equal amounts, the upper and lower ends of the fixed column are correspondingly deformed. The leaf springs connecting the upper and lower parallel guides bend in the opposite directions by equal amounts, and the distance between the upper leaf spring and the lower leaf spring changes. On the other hand, since the distance between the upper and lower leaf springs that connect the movable pillar attached to the movable pillar and the parallel guide does not change, the parallelism between the upper and lower parallel guides can be adjusted by adjusting the distance between the upper and lower leaf springs on the fixed pillar side. Can be adjusted.

When the parallelism of the upper and lower parallel guides is adjusted, the deflections of the upper and lower leaf springs become almost equal, so that the weight measurement value does not change at the zero point, and the upper and lower ends of the fixed column are symmetrical in structure. Even if the ambient temperature changes, the influences on the upper and lower leaf springs become almost equal and cancel each other out, and the drift due to the temperature change is small.

[0007]

1 is a view showing a Roberval mechanism 21 of an electronic balance according to an embodiment of the present invention. Two parallel guides (upper) and parallel guides (lower) between the fixed column 1 and the movable column 2.
The upper and lower parallel guides and the fixed column are connected by leaf springs 5 and 6, and the upper and lower parallel guides and the movable column are also connected by leaf springs 7 and 8. . Although not shown in the figure, the sample to be measured is placed on an upper plate provided on the movable column 2 and its load is applied in the axial direction of the movable column. The weight of the sample is measured by balancing the load with an electromagnetic balance portion not shown in the figure. In order to measure the weight accurately and to avoid the so-called eccentricity error (also called the four-corner error) that occurs due to the position of the sample placed on the upper plate, the upper and lower parallel guides must be precisely parallel. There must be.

In this embodiment, in order to adjust the upper and lower parallel guides to be parallel to each other, a pulling screw 10 for pulling the fixed column 1 with respect to the support wall 9 is fixed, and the pulling screw 10 is fixed around the pulling screw 10. A push screw 11 for pushing the pillar 1 is provided. The male screw part cut on the outer circumference of the push screw 11 is screwed into the female screw cut on the support wall 9, and the male screw part cut on the outer circumference of the pull screw 10 is changed to the female screw cut on the fixed column 1. It is screwed. FIG. 2 is a diagram for explaining the adjustment mechanism. The fixed column 1 is deformed by pulling the central portion of the fixed column 1 with respect to the support wall 9 by the pulling screw 10, and the upper and lower end surfaces are inclined as shown in FIG. Along with that, the left end of the parallel guide (upper) 3 is pushed down, and the parallel guide (lower)
The left edge of 4 is pushed up. Since the ends of the upper and lower parallel guides on the side of the movable column are fixed to the movable column 2, the distance is constant, and the distance 1 between the two of the upper and lower parallel guides on the side of the fixed column is changed by the deformation of the fixed column 1. Therefore, the parallelism between the upper and lower parallel guides can be adjusted. Since this adjustment can be performed only in the direction in which the distance 1 becomes smaller, the length of the fixed column 1 must be designed in advance to be slightly longer than the length of the movable column 2.

If the support wall 9 is provided with a groove into which the fixed column fits, it is convenient that the fixed column is not laterally displaced. In addition, a groove or a hole into which the tip of the push screw fits may be provided in a portion of the fixed column where the push screw abuts.

As shown in FIG. 2, the inclination angle of the upper end of the fixed column is θ1, the inclination angle of the lower end of the fixed column is θ2, the distance from the center of the fixed column to the upper or lower end is a, and the center line of the fixed column is a leaf spring. 5, the distance to the center of 5 is b, the lateral displacement of the central portion of the fixed column is d, the vertical displacement of the leaf spring 5 is e1, the leaf spring 6
Let e2 be the vertical displacement of. Since the central portion of the fixed column 1 is pulled by the pulling screw 10, the deformation is vertically symmetrical. Therefore, since θ1 = θ2, e1 =
e2, and when the torques applied to the upper and lower parallel guides are T1 and T2, T1 = T2. Also, e1 is approximately equal to (b / a) · d. Therefore, when adjusting the parallelism of the upper and lower parallel guides, the zero point change of the weight measurement value does not occur. Further, the structures of the upper and lower ends of the fixed column 1 are equal to each other, and the flexures of the leaf spring 5 and the leaf spring 6 are also substantially equal to each other. Therefore, when the ambient temperature is changed, the elongation of the leaf spring and the change of elastic modulus are also equal. The effects offset each other.

FIG. 3 shows a Roberval mechanism portion of another embodiment, showing another example of a screw mechanism for simultaneously deforming both end surfaces of a fixed column by an equal amount in opposite directions. The fixed column 31 has an approximately U-shape, and nut holding holes 32 and 33 are formed on the upper and lower sides. A screw 34 having a right-hand thread on the upper side and a left-hand thread on the lower side is combined with a right-hand screw nut 37 and a left-hand screw nut 38 screwed into the respective screws,
The nut retainer holes 32 and 33 are laterally fitted. When the screw 34 is rotated in a state where the fixed column 31 and the screw 34 and the nuts 37 and 38 are combined, the fixed column 31
The upper end surface 39 and the lower end surface 40 of the are pushed or separated. By doing so, the parallelism of the upper and lower parallel guides 3 and 4 connected to the upper end surface 39 and the lower end surface 40 of the fixed column 31 via the leaf springs 5 and 6 can be adjusted.

FIG. 4 shows still another embodiment, which is another example of a screw mechanism for simultaneously deforming both end faces of a fixed column by equal amounts in opposite directions. In this figure, only the screw mechanism is taken out and drawn. The fixed column 51 is divided into a central bar 52, an upper bar 53 including an upper end surface 57, and a lower bar 54 including a lower end surface 58, and the upper bar and the lower bar can be bent up and down by splits 55 and 56. Accordingly, the upper end surface 57 and the lower end surface 58, to which the parallel guides of the Roberval mechanism are attached via the leaf springs 5 and 6, also move up and down. The screw 59 on the right side of the drawing is screwed into the right end of the central bar 52, and by screwing the screw 59, the taper block 60 is moved to the upper bar 53 and the lower bar 54.
Push the slanted surface that is made in to spread them apart from each other. On the other hand, the pressing screw 61 penetrates the upper bar 53 and the central bar 52 and is screwed into the lower bar 54. By screwing the pressing screw 61, the upper bar 53 and the lower bar 54 are brought closer to each other. Also press screw 6
A spring 62 is inserted between the head of No. 1 and the upper bar 53, and plays a role of a cushioning material for the force of expanding by the screw 59 and the force of compressing by the pressing screw 61. With the above mechanism, the parallelism of the upper and lower parallel guides 3 and 4 connected to the upper end surface 57 and the lower end surface 58 of the fixed column 51 via the leaf springs 5 and 6 can be adjusted.

Although not explicitly shown in the drawings of some of the above-mentioned embodiments, there are usually two fixed columns, and an electromagnetic balance section or the like is arranged in the space between the two fixed columns arranged side by side. . The two fixed columns and the one movable column are connected by a parallel guide whose plan view is approximately V-shaped. The parallelism adjusting mechanism described above is provided for each of the two fixed columns.

[0014]

The parallelism of the upper and lower parallel guides is not adjusted by deforming one of the upper and lower leaf springs.
Since the upper and lower leaf springs are adjusted or deformed symmetrically at the same time by a single operation, the amounts of deformation of the upper and lower leaf springs are the same. Therefore, the torque applied to the movable column is canceled by the deformation of the leaf spring, and the zero change of the weight measurement value does not occur. In addition, since the structure of the upper and lower end faces of the fixed column is symmetrical, considering the effect of changes in ambient temperature, changes in the elastic modulus of the spring and changes in the point of action due to thermal expansion are the same at the top and bottom, and the temperature of the weight measurement value No drift occurs.

[Brief description of drawings]

FIG. 1 is a Roberval mechanism that is a main part of an embodiment of the present invention.

FIG. 2 is a diagram showing the operation of the embodiment of the present invention.

FIG. 3 is a diagram showing another embodiment of the present invention.

FIG. 4 is a diagram showing still another embodiment of the present invention.

FIG. 5 is a schematic view of a conventional electronic balance.

FIG. 6 is an example of a conventional parallelism adjusting mechanism.

[Explanation of symbols]

1 ... Fixed column 2 ... Movable column 3 ...
Parallel guide (upper) 4 ... Parallel guide (lower) 5 ... Leaf spring 6 ...
Leaf spring 7 ... Leaf spring 8 ... Leaf spring 9 ...
Support wall 10 ... Drawing screw 11 ... Pushing screw 21
... Roberval mechanism 31 ... Fixed column 32 ... Nut hold hole 33
… Nut retainer hole 34… Screw 35… Right screw bolt 36
Left screw bolt 37 Right screw nut 38 Left screw nut 39
... Upper end surface 40 ... Lower end surface 51 ... Fixed column 52 ... Center bar 53
… Upper bar 54… Lower bar 55… Split 56
... Split 57 ... Upper end surface 58 ... Lower end surface 59
… Screw 60… Taper block 61… Pressing screw 62
… Spring 71… Fixed column 72… Movable column 73
… Parallel guide (top) 74… Parallel guide (bottom) 75… Leaf spring 76
… Pulling screw 77… Pushing screw 81… Roberval mechanism 82… Electromagnetic balance part 83
… Balance beam 84… Support point 85… Plate

Claims (1)

[Claims] 1. An electronic balance in which a movable column receiving a load in an axial direction is supported by a fixed column arranged substantially parallel to the movable column via a Roberval mechanism composed of a parallel guide and a leaf spring. An electronic balance characterized in that a screw mechanism for simultaneously deforming both end faces of the fixed column in the opposite directions by an equal amount is provided in the substantially central portion of the column.