JPH07907Y2 - Force detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a detector for converting a force into an electric signal, and particularly measures a force by detecting a change in frequency due to a change in tension of a string. Regarding the device.

<Prior Art> An example of a device for detecting a force by a change in frequency due to a change in tension of a string is disclosed in Japanese Utility Model Laid-Open No. 59-97438. As shown in FIG. 1 of the publication, the basic configuration is such that a vibrating string is stretched between a main elastic body and a sub elastic body, and a force to be measured is applied to the main elastic body to change the strain. Then, the change in the tension of the vibrating string due to this is detected by the change in the frequency of the string. The change in the frequency of the string is detected by, for example, an electric circuit shown in FIG. 2 of the publication.

When such a force detector is used for weight measurement in a balance, there has been a main elastic body using a Roberval type elastic body as shown in FIGS. The Roberval type elastic body is one in which a vertical fixed end portion and a force applying end portion are connected in a parallelogram shape by an upper beam and a lower beam having thin-walled flexible portions at both ends,
It is configured to deform while maintaining a parallelogram when force is applied. The sub elastic body is arranged substantially parallel to the upper beam and the lower beam in the window of the main elastic body as shown in FIG. 3 or FIG. 4 of the publication, or as shown in FIG. The elastic member is arranged above or below the elastic body substantially parallel to the upper and lower beams.

The string shape of this type of force detector is, for example, Jikken Sho 61.
-26898 is disclosed. The materials and dimensions are as follows.

Material Copper alloy, niobium-zircon alloy, etc.Dimensions Effective length: 20 to 25 mm Thickness: 0.1 to 0.2 mm Width: 0.15 to 0.4 mm <Problems to be solved by the invention> As described in Japanese Utility Model Publication No. 59-97438. In the Roberval type elastic body as described above, it is very difficult to process the strain-generating portion (thin-walled portion), and if it is not formed into a perfect parallelogram, a slight dimensional error greatly affects the weighing accuracy. In particular, if a load is applied to each corner of the weighing pan, the load display will deviate. Therefore, in order to eliminate such a deviation of the weight display due to the unbalanced load, it is necessary to perform correction processing on the strain-flexing portion and adjust so that the weight display is the same regardless of which corner the load is applied. This correction processing is usually called four-corner adjustment.

A four-corner adjustment method for a load cell in which a strain gauge is attached to the strain-flexing portion of a Roberval elastic body is described in, for example,
No. 58-51604. The main elastic body of the force detecting device disclosed in Japanese Utility Model Laid-Open No. 59-97438 must also be adjusted at the four corners by a method similar to this. That is, a weighing dish is attached to the main elastic body in which a string is stretched between the sub elastic body, and loads are sequentially applied to the four corners of the dish to display the weight due to the unbalanced load, and correction is made so that the displayed values are uniform. It is processed. Therefore, it is desired that such an elastic body has a structure in which the four corners can be easily adjusted.

Next, considering the appearance of the error due to the unbalanced loads applied to the four corners of the dish, the height of the Roberval elastic body has a great influence. As shown in FIG. 4, fixed end FF ', force applying end AA', upper beam AF, lower beam A'F '
In the Roberval type elastic body consisting of
To the fixed end FF 'is a, and the length of the fixed end FF' is b
And the force application end AA 'is shorter than the fixed end FF' by δ,
As a result, it is assumed that the lower beam A′F ′ is inclined by θ. If the load W is placed on the plate D at a position deviated from the center by C, the rotation efficiency of W _c acts on the plate in the clockwise direction. The reaction force f acting on the point A is horizontal, but the reaction force f ′ acting on the point A ′ is in the same direction as the lower beam A′F ′. The horizontal component of the reaction force f ′ has the same magnitude as the reaction force f, but the direction is opposite,
Although it does not affect the balance, the reaction force f ′ vertical component force E affects the balance because it acts in the direction of making the dish lighter. The magnitude of the vertical component E in this case is Given in. That is, the weighing error is as follows: (I) The larger the difference δ in length between the fixed end and the force applying end is, (II) The shorter the length a of the beams AF and A′F ′ is. (III) Fixed end FF The shorter the length b of ′, the greater the length.

On the other hand, the force application end AA ′ of the Roberval elastic body is easily twisted in the plane perpendicular to the paper surface in FIG. 4, and when such twist occurs, the tension of the vibrating string does not correspond to the load W.
This twist increases as (I) the length a of the beams AF and A'F 'is longer, and (II) the length b of the fixed end FF' is shorter, and the weighing error increases.

When these weighing error factors are combined, the length a of the beam is preferably long from the viewpoint of the weighing error due to the dimensional error δ, but short from the viewpoint of the weighing error due to the twisting, so either long or short is desirable. It is hard to draw a conclusion. However, it is desirable that the length b of the fixed end portion FF ′ is long in terms of both the weighing error due to the dimensional error δ and the weighing error due to the twist. Young
If the length b is short, a weighing error due to the dimensional error δ and a weighing error due to twisting may be added, and a large weighing error may occur.

In addition, it is necessary for measurement accuracy that the string hardly causes a creep phenomenon, a hysteresis phenomenon, and the like when loaded.
For this reason, it is not appropriate to use a string that is bent or twisted from the beginning, or one that has internal stress.Be sure to install the string accurately so that it does not bend or twist when attached to an elastic body. I have to. Then, after mounting, it is necessary to apply an appropriate load and confirm that it does not twist or bend at that time.

For this reason, it is desired that the elastic body has a structure that allows easy attachment of the strings and also facilitates confirmation of the attachment state of the strings.

The structure shown in FIG. 3 and FIG. 4 of Japanese Utility Model Laid-Open No. 59-97438 is such that a sub-elastic body and a base end portion of the sub-elastic body are formed into a main elastic body in a window of a Roberval-shaped main elastic body. Since there are a mounting member for mounting on the body, a string, and a magnet for applying a magnetic field to the string, it is difficult to adjust the four corners, and the string mounting work is also difficult. Although such a problem can be remedied considerably by increasing the size of the main elastic body, it becomes difficult to implement it when the material cost is high and the size of the force detecting portion is restricted.

In the structure shown in FIGS. 5, 6, and 7 of the publication, since the strings are located outside the Roberval-type main elastic body, their attachment is relatively easy. However, when the height of the force detection part is restricted, the height of the main elastic body becomes low, which not only makes it difficult to adjust the four corners, but also exerts a large influence of the unbalanced load. This problem is particularly remarkable in the case of FIGS. 6 and 7 in which the string is below the main elastic body.

Therefore, in the present invention, in the string vibration type force detector using the Roberval type main elastic body, the height of the main elastic body can be made large, and the four corners can be adjusted and the strings can be easily attached. It is something to do.

<Means for Solving the Problem> The force detector of the present invention has a main elastic body, a sub elastic body, and a force detecting vibration string stretched between the ends of these elastic bodies. The main elastic body has a vertical fixed end portion and a force application end portion, and an upper beam and a lower beam, which are integrally coupled to each other by thin-walled flexible portions to form a Roberval shape. It has a window defined by each thin flexible portion. A part of this window is enlarged so as to bite into the force application end. The sub elastic body is integrally connected to the fixed end portion in the window, and the tip of the sub elastic body reaches into the window enlarged portion. The end surface of the force applying end portion is provided with a slit groove in the force applying direction, and the groove bottom surface is located in the same plane as the tip end surface of the sub elastic body. The force detecting vibration string is stretched between the groove bottom surface and the tip end surface of the sub elastic body in the slit groove.

<Operation> In the force detector described above, when a force to be measured is applied to the force application end of the main elastic body, the main elastic body is deformed while maintaining the parallelogram, and between this and the sub elastic body. The tension of the stretched vibrating string changes, and the natural frequency also changes accordingly. Therefore, for example, an electric circuit as shown in FIG. 2 of the above publication can detect the change in the natural frequency of the string, and from this, the magnitude of the applied force can be obtained.

In this force detector, since the sub-elastic body is inside the window of the main elastic body, if the total height of the force detector is limited, the height of the main elastic body can be set to the above-mentioned limit, so that an unbalanced load is applied. It is possible to reduce the weighing error due to and to easily adjust the four corners. Also, the vibrating string can be mounted by operating it from the front inside the slit groove, so the mounting work is easy and it can be mounted without twisting or bending, and the inspection after mounting is also easy. be able to.

<Embodiment> In FIGS. 1 to 3, reference numeral 1 denotes a main elastic body, which is a fixed end portion 2 and a force application end portion 3 which are perpendicular to each other, and a thin wall between the upper ends of these portions 2 and 3. It consists of a horizontal upper beam 6 whose both ends are connected by flexible portions 4 and 5, and a horizontal lower beam 9 whose both ends are connected by thin flexible portions 7 and 8 between the lower ends of these portions 2 and 3, respectively. , A window 10 surrounded by parts 2, 3 and an upper beam 6 and a lower beam 9. Part 2, 3 and upper beam 6
The lower beam 9 and the lower beam 9 can be deformed while maintaining the parallelogram by the bending of the thin flexible portions 4, 5, 7, 8.
Configure the Roberval mechanism.

A vertical slit 11 is formed on the end face of the force application end 3. The upper portion of the window 10 has an enlarged portion 12 that is enlarged over the portion where the slit groove 11 is formed. In the window 10, an auxiliary elastic body 14 joined to the fixed end portion 2 by a thin flexible portion 13 extends parallel to the upper beam 6, and the tip thereof is in the window expansion portion 12 a groove bottom surface 15 of the slit groove 11. It is located in the same plane as.

A vibrating string 18 is stretched between the groove bottom surface 15 and the tip end surface of the sub elastic body 14 by fittings 16 and 17, respectively. The vibrating string 18 can be attached by operating from the front while viewing the fixtures 16, 17 and the vibrating string 18 from the front.
Therefore, the mounting work can be performed accurately and easily.

The fixed end 2 of the main elastic body 1 is fixed to the base 19 by any suitable means.
Fixed to. 20 is a plate, and legs 21, 21 hanging in a fork shape from the lower surface thereof are attached to the end face of the force applying end portion 3 of the main elastic body 1 on both sides of the slit groove 11 with bolts 22, 22 ,. There is.

In the scale described above, for example, as shown in FIG. 2 of the above-mentioned publication, a magnetic pole is provided by sandwiching a vibrating string 18 on the edge of the window enlarging portion 12 or the bottom surface 15 of the groove, and vibrating between the fixtures 16, 17. Oscillation is caused by passing a current, and the load on the plate 20 can be measured by measuring the oscillation frequency.

<Effects of Device> As is apparent from the above description, according to the present invention, (a) the main elastic body and the sub elastic body are integrally formed, so that the number of parts is reduced and the processing time is significantly shortened. To be done.

(B) Even if the height of the force detector is limited, the height of the Roberval elastic body can be made sufficiently large, so that the measurement error due to an eccentric load is small.

(C) Since the strings can be mounted from the front, the mounting can be performed accurately, the measurement error due to the twisting or bending of the strings can be reduced, and the time required for the mounting work can be shortened. In addition, it is easy to inspect under a load applied state after mounting the strings.

(D) Adjusting the four corners against an unbalanced load after mounting the plate is easy because there are few obstacles because the Roberval elastic body has a sufficient height and only the sub elastic body exists in the window. It can be carried out.

It is possible to obtain a force detector having a small overall size and a high measurement accuracy in which a short machining time and adjustment time can be achieved.

[Brief description of drawings]

FIG. 1 is a side view of a scale embodying the present invention, FIG. 2 is a front view thereof, FIG. 3 is a bottom view thereof, and FIG. 4 is an explanatory view of a dimensional error of a main elastic body. 1 ... Main elastic body, 2 ... Fixed end, 3 ... Force applying end,
6 ... upper beam, 9 ... lower beam, 11 ... split groove, 14 ... secondary elastic body, 15 ... groove bottom, 16 and 17 ... fixture, 18 ... vibrating string.

Claims (1)

[Scope of utility model registration request] Claims: 1. A fixed end portion and a force application end portion, which are both vertical, and an upper beam and a lower beam are integrally connected to each other by thin flexible portions to form a Roberval type main elastic body, and four corners are formed. Expands the window defined by each thin flexible portion so as to bite into the force application end, and a sub elastic body whose one end is integrally connected to the fixed end is formed in the window. Extending into the enlarged portion, providing a slit groove in the force applying direction on the end face of the force applying end portion so that the groove bottom surface coincides with the tip end surface of the sub elastic body, and within the slit groove, the groove bottom surface and the sub groove A force detector consisting of a vibrating string for force detection stretched between the tip of an elastic body.