JPH0776713B2 - Electronic balance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to an electronic balance, and more particularly to a mechanism of an electronic balance.

<Prior Art> In an electronic balance, generally, in order to prevent the dish from tilting or falling, the dish is supported by a Roberval mechanism (also referred to as a parallel guide), and the displacement direction is restricted only up and down. Is done. The Roberval mechanism is a mechanism in which a fixed column and a movable column are arranged at both ends of two beams that are parallel to each other via flexible portions, and the dish is supported by the movable column. The load acting on the dish is transmitted to a load sensor such as a balanced electromagnetic force generator by a lever mechanism connected to the movable column of the Roberval mechanism.

Here, it is necessary that the movable column of the Roberval mechanism only moves up and down, that is, performs balanced movement, and that the lever is tilted about a fulcrum. Therefore, an elastic member is usually used for the connecting portion between the movable column and the lever and the above-mentioned fulcrum for the purpose of preventing the movements of these members from interfering with each other. On the other hand, as the movable column portion and the lever, a rigid body is preferable to a material having elasticity because of its function. Therefore, conventionally, the material is made of a material different from the Roberval mechanism or the lever and the connecting portion, for example, aluminum alloy die-cast and high elastic steel, and they are assembled by screwing, caulking, or adhering each other.

According to the conventional electronic balance as described above, due to the difference in the coefficient of thermal expansion between the connecting portion including the above-mentioned fulcrum and the Roberval mechanism or the lever, the drift based on the relative dimensional change due to the change in the ambient temperature, There is a drawback in that drift due to deformation (combination of two materials having different expansion coefficients causes bending due to temperature like bimetal, and in particular, deformation of the elastic fulcrum attachment portion greatly affects performance).

There is also a problem that the number of different parts is increased, the number of assembling steps is increased, and the cost is increased.

In order to solve these problems, the inventor of the present invention, for example, as shown in FIG. 3, constructs a Roberval mechanism by using two elastic portions 11, 12 and 21, 22 respectively having flexible portions 11, 12 and 21, 22 respectively. The beam portions 1 and 2, the fixed column portion 3, the movable column portion 4, the lever 5, its elastic fulcrum 6, and the elastic connecting portion 7 are integrally formed by hollowing out from one base material. An electronic balance with a structure has already been proposed (Japanese Patent Application No. 62-113133).
issue). In the figure, 8 is a load sensor, 41 is a pan support rod,
9 is a spacer for fixing to the balance base.

With such a structure, the thermal expansion coefficient of each part becomes the same, the occurrence of drift or the like due to changes in ambient temperature, etc. can be eliminated, and the number of assembly steps can be reduced.

<Problems to be Solved by the Invention> In the mechanism of an electronic balance, when a large lever ratio is desired, the distance between the elastic fulcrum corresponding to the fulcrum of the lever and the force point and the elastic connecting portion must be narrowed.

In the conventional assembly type electronic balance, in order to achieve this purpose, it is possible to take a measure to dispose the fulcrum and the force point in a plane. That is, the elastic fulcrum of the lever and the elastic connecting portion are not aligned, but an elastic connecting portion 71 is provided at the tip end portion thereof on the axis of the lever 51 as shown in the perspective view of FIG. Upon receiving F, two elastic fulcrums 61 and 62 are provided at positions symmetrical to the axis of the lever 51.
With such a three-dimensional structure, the distance L between the elastic fulcrums 61, 62 and the elastic connecting portion 71 can be considerably shortened.

However, in the integrated structure as shown in FIG.
From the point of view of its processing, it is impossible to adopt the above-mentioned three-dimensional structure. Therefore, as shown in FIG. 5, the distance l between the elastic fulcrum 6 of the lever 5 and the elastic connecting portion 7 is shortened. However, there is a problem that the lever ratio is restricted by this limit. Further, when it is desired to take a particularly large lever ratio, a method of assembling the lever ratio in two stages can be considered, but there is a drawback that the structure becomes complicated.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an electronic balance having a structure integrally cut from a base material and capable of easily increasing the lever ratio.

<Means for Solving the Problems> In order to achieve the above-mentioned object, in the present invention, as shown in FIG. 1 which is an embodiment drawing, one end portion of the lever 5 has four connecting portions each having a flexible portion. The parallel link mechanism 10 formed of 105, 106, 107 and 108 is integrally formed integrally with one link 101, and one of the common link 101 and the link 102 facing the common link 101 is flexible. Department
It is connected to the movable column portion 4 via 109, and the other is connected to the flexible portion 1.
It is connected to the fixing member (arm 30) via 10. The Roberval mechanism (1, 2, 3, 4), the lever 5, the parallel link mechanism 10, and the flexible portions 109, 110 for connection are integrally formed by a flat plate-like base material.

<Operation> As shown in FIG. 2, when the load F acts on one point Q (center of the flexible portion 109) on the link 101 of the parallel link mechanism 10,
Each of the links 101, 102, 103 and 104 is displaced about the point P (center of the flexible portion 110) on the link 102 from the state of the two-dot chain line in the figure as shown by the solid line, and the lever 5 integrated with the link 101 is also moved. Incline. At this time, links 101 and 10
Since points 2,103 and 104 are always parallel to each other, point P
A point P ′ on the link 101 on the vertical line (axis) passing through
Does not move at all regardless of the size of the inclination angle θ of the lever 5. That is, the lever 5 including the link 101 at the tip is
The point P ′ is a virtual fulcrum, and the point Q is a force point. The distance between P'Q on the link 101 is not limited in terms of processing and mechanism, and the intended purpose can be achieved.

<Examples> Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view showing the structure of the embodiment of the present invention, in which a Roberval mechanism, a lever 5 and a parallel link mechanism 10 are described below.
Also, these mutual connecting portions and the like are integrally formed by cutting out from a base material such as a flat plate-like high-strength aluminum alloy. Further, in this structure, the flexible parts 11, 12, 21, 22, 105,
106, 107, 108, 109 and 110 are obtained by forming constrictions in the base material.

Now, the fixed pillar portion 3 and the movable pillar portion 4 are connected by two elastic beam portions 1 and 2 which are provided with flexible portions 11, 12 and 21, 22 at both ends and are parallel to each other. It forms a Roberval mechanism. The fixed column portion 3 is fixed to the balance base via a spacer 9, and the movable column portion 4 is fixed to a dish receiving rod 41 for supporting a dish (not shown).

The load F acting on the movable column portion 4 is transmitted to the parallel link mechanism 10 via the flexible portion 109. The parallel link mechanism 10 includes links 101 and 102 and 103 and 104 which are parallel to each other, and these are connected by flexible portions 105, 106, 107 and 108 located at respective corners of the parallelogram. . The above-mentioned flexible portion 109 is provided at a substantially central portion of one of the links 101. The link 102 facing the link 101 has a flexible portion 110 at a substantially central portion thereof.
Is connected to a highly rigid arm 30 protruding from the fixed column portion 3 via.

Here, a line passing through the center of the flexible portion 109 and parallel to 103 and 104 (hereinafter referred to as an axis of the flexible portion 109) is a flexible portion 110.
The movable column portion 4 with respect to a line that passes through the center of the link 103 and is parallel to the links 103 and 104 (hereinafter referred to as the axis of the flexible portion 110).
It is offset by 1 to the side.

The link 101 is integrally formed with one end of the lever 5 so as to be shared. The lever 5 is for transmitting the load F acting on the movable column portion to the load sensor 8 via the parallel link mechanism 10, and the other end thereof is engaged with the load sensor 8.

The load sensor 8 is, for example, a balanced electromagnetic force generator,
A displaceable force coil 82 is arranged in a magnetic circuit 81 composed of a permanent magnet, a ball piece, a yoke, etc., and the force coil 82 is provided at the other end of the lever 5 described above.
Are fixed, and the magnetic circuit 81 side is fixed to the lower surface of the arm 30 described above. Then, the position of the force coil 82 is detected by a displacement sensor (not shown), an electric current is passed through the force coil 82 so as to balance at a predetermined position, and the magnitude of the electric current and a lever ratio l / l _b described later are used. , Load on plate F
Is configured to detect.

Next, the operation will be described.

FIG. 2 is an operation explanatory view showing the parallel link mechanism 10 in a skeleton form. In the figure, the axis of the flexible portion 109 and the link 1
The intersection of the axis of 01 with the axis of the flexible part 110 and the axis of the link 102 is P, and the intersection of the axis of the flexible part 110 with the axis of the link 101 is P ′.

The load F acting on the plate is transmitted to the point Q on the link 101 via the movable column portion 4 and the flexible portion 109. By this F, the parallel link mechanism 10 is changed from the state of the chain double-dashed line in the figure to a solid line. Lever 5 displaced as shown and integrated with link 101
Also tilts. At this time, links 101 and 102, and 103 and 1
The points 04 on the link 101 are always parallel to each other in accordance with the mechanical restrictions, so that the point P ′ on the link 101 is the inclination angle θ of the lever 5.
Regardless of size, it will always be in a fixed position without moving at all. That is, the lever 5 including the link 101 is
Due to the action of the load F, it always inclines about the point P '. In other words, the lever 5 moves with the point Q as the force point and the point P'as a virtual fulcrum.
Therefore, the lever ratio is represented by l / l _b , where ▲ ▼ is l and the distance between the axis of the flexible portion 110 and the center of the load sensor 8 is l _b (FIG. 1) as described above. It will be.

Here, since no structure actually exists at the point P'on the link 101, there is no mechanical or working restriction in shortening l.

The position of the point P on the link 102 is not particularly limited, but it is desirable to set it at the center of the link 102 because the loads acting on the links 103 and 104 are equal.

In addition to the balanced electromagnetic force generator, a well-known sensor such as one using string vibration or one using tuning fork vibration can be used as the load sensor 8. Further, the load sensor 8 may be disposed inside the Roberval mechanism as shown in FIG. 1 and may be fixed to the outside of the Roberval mechanism, for example, the outer side surface of the fixed column portion 3.

Furthermore, the axis of the flexible portion 109 may be displaced toward the fixed column portion 3 side with respect to the axis of the flexible portion 110, in which case the movement of the lever 5 is reversed.

Further, in the above embodiment, an example in which the link 101 in which the flexible portion 109 for connection with the movable column portion 4 is arranged is integrated with the lever 5 is shown. The link 102 provided with the flexible portion 110 for this can be integrated with the lever 5. In this case, the lever 5 makes a motion with the point P as a fulcrum and the intersection of the axis of the flexible portion 109 and the axis of the link 102 as a virtual force point, but the restriction for shortening l is the same. There is none.

Further, it goes without saying that the upper link 102 of the parallel link mechanism 10 and the movable column portion 4 may be connected, and the lower link 101 may be connected to a fixed member such as the arm 30.

In an electronic balance, the inclination of the lever 5 is generally small, and particularly when the balanced electromagnetic force generator is used as a load sensor, the load is detected at the equilibrium position where the inclination of the lever 5 is zero. Therefore, the parallel link mechanism 10 does not need to be such that the opposing links are strictly parallel to each other. As described above, the lever 5 may be any mechanism that can move by using a fulcrum or a force point as a virtual one. Extremely speaking, a non-parallel four-bar linkage may be used, and the present invention also includes this.

In addition to the electronic balance, the mechanism of the present invention can be applied to a mechanism for externally applying a minute displacement, a mechanism for enlarging a minute displacement, and the like.

<Effects of the Invention> As described above, according to the present invention, the lever for transmitting the load acting on the movable column portion engaged with the dish to the load sensor is either a fulcrum or a force point by the parallel link mechanism. One of them will move as a virtual one,
There is no mechanical or machining restriction on shortening the distance l between the fulcrum and the force point. For example, this distance l can be easily set to 1 mm.
It is also possible to set the ratio below, and the lever ratio can be arbitrarily set as required. This not only makes it possible to miniaturize the electronic balance having an integrated structure, but also achieves the compactness without adopting the conventional complicated structure shown in FIG. 4 and the two-step lever system.
It is possible to obtain an electronic balance that is compact and that is significantly lower in cost than the electronic balance that is assembled.

[Brief description of drawings]

FIG. 1 is a front view showing the structure of an embodiment of the present invention, FIG. 2 is an operation explanatory view showing the vicinity of the parallel link mechanism 10 as a skeleton, and FIG. 3 is an explanatory view of an electronic balance having an integrated structure, and FIG. FIG. 5 is an explanatory diagram of a two-stage lever system in an assembled electronic balance, and FIG. 5 is an explanatory diagram of a lever ratio constraint of a conventional integrated electronic balance. 1,2 …… Elastic beam part 3 …… Fixed column part 4 …… Movable column part 5 …… Lever 8 …… Load sensor 10 …… Parallel link mechanism 101,102,103,104 …… Link 105,106,107,108,109,110 …… Flexible part

Claims (1)

[Claims] 1. A load applied to a dish supported by a movable bar portion of a Roberval mechanism in which a fixed pillar portion and a movable pillar portion are arranged at both ends of two elastic beam portions which are parallel to each other. In a balance configured to transmit to a load sensor by a lever whose one end engages with a movable column part, a parallel link mechanism in which the one end of the lever has four connecting parts each formed of a flexible part. Is integrally formed with one of the links, and one of the common link and the link facing the common link is connected to the movable column portion via the flexible portion, and the other is The flexible member is connected to the fixing member via a flexible portion, and the Roberval mechanism, the lever, the parallel link mechanism, and the flexible portions for the connection are integrally formed by a flat plate-like base material. Characterized by , Electronic balance.