JPH0415407B2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to an electronic dish balance.

Generally, when a load is placed unevenly in the front-back or left-right direction on the pan of a precision balance, a weighing error E occurs due to the rotational moment M acting on the pan. Therefore, it was necessary to adjust the geometric accuracy of the Roberval mechanism. In other words, if the Roberval mechanism has sufficient rigidity, the rotational moment M due to eccentricity
and weighing error E are expressed by straight line A or straight line B in Figure 1.
This relationship is adjusted so that it becomes, for example, a straight line S within the allowable limit range, but such adjustment requires a high level of skill. For example, 1/1 million to 1/2 million
If you try to adjust a precision balance with an accuracy of
Adjustment accuracy of 0.1 to 0.05μ was required. Furthermore, providing sufficient rigidity to the Roberval mechanism will result in an increase in price.

If the Roberval mechanism does not have sufficient rigidity, the weighing error E with respect to the bending moment M due to the eccentric load will not change linearly, resulting in a relationship such as curves C and D in Figure 1. Even if geometric adjustments were made to the above, the relationship would only be like a curve T between them, and it would not be possible to bring it within the allowable limit range.

This invention was made to eliminate the above-mentioned conventional drawbacks, and it is possible to easily perform adjustments for correcting eccentricity errors with high precision without requiring adjustment of the geometric accuracy of the mechanism. The purpose is to provide electronic precision balances.

In order to achieve the above object, the present invention includes a vertical load measuring means for measuring a vertical load on a plate;
A moment detection unit that detects the deflection of the plate support rod interposed between the plate and the Roberval mechanism due to the bending moment caused by the eccentric load on the plate, divided into two orthogonal components; It is characterized by comprising an eccentricity error correction means for calculating an error caused by the eccentricity of the load on the plate included in the measured value of the vertical load measuring means using the detected value.

Embodiments of the present invention will be described below based on the drawings. FIG. 2 is a diagram showing a load measuring mechanism according to an embodiment of the present invention. The pan 1 of the precision balance is supported by a Roberval mechanism 3 via a tray support rod 12, and a vertical load measuring section 4 is connected to the lower part of the Roberval mechanism 3. A moment detection unit 2 for measuring deflection due to a bending moment caused by an eccentric load is provided on a plate support rod 12 between the plate 1 and the roberval mechanism 3.

The vertical load measuring unit 4 is a means for measuring the load on the plate 1 through the Roberval mechanism 3, and is composed of an electromagnetic force generator that generates an electromagnetic force balanced with the load, and outputs a signal W corresponding to the applied vertical load. can do.

The moment detection unit 2 detects the deflection caused by the bending moment when the load 11 is eccentrically placed on the plate 1 by dividing it into two orthogonal components.
As shown in the figure, strain gauges _a1 , _a2 , _b1 ,
The bridge consisting of b ₂ , c ₁ , c ₂ , d ₁ , d ₂ (c ₁ , c ₂ , d ₁ , d ₂ are not shown) allows the horizontal movement due to the slight inclination of the dish support rod 12 to be controlled. Outputs a moment-induced deflection signal fx and a longitudinal moment-induced deflection signal fy. Further, as shown in FIG. 5, capacitance or inductance may be used as means for detecting the bending moment. That is, elements 51 for changing capacitance or inductance are attached to the four sides of the plate support rod 12, and a detector 50 is provided to detect changes in capacitance or inductance without contacting these elements. In this case, a flexible portion 52 is provided below the dish support rod 12 in order to obtain a larger change in inclination. In the case of FIG. 3, many lead wires are required for the strain gauge, but in the case of FIG. 5, these are not required, and the strain gauge is resistant to external disturbances and has high measurement accuracy.

FIG. 4 is a block diagram showing the circuit configuration of the embodiment of the present invention shown in FIG. 2.

The output signal W of the vertical load measuring section 4 mentioned above is input to the eccentricity error correction calculator 7, and the output signals fx and fy of the moment detecting section 2 are input to the amplifier 5, respectively.
a, 5b and the signal via adjustment parts 6a, 6b.
Fx and Fy are similarly taken into the eccentricity error correction calculator 7. The eccentricity error correction calculation unit 7 uses these signals to calculate a load measurement value f(W) with the eccentricity error corrected as shown below.

That is, f(W)=W+f ₁ (Fx)+f ₂ (Fy)...(1) Here, f ₁ (Fx)=K ₁ xFx+K ₂ F ² x+K ₃ xF ³ x+..., and f ₂ ( Fy)=K ₁ yFy+K ₂ yF ² y+K ₃ yF ³ y+...

The coefficients K ₁ x and K ₁ y are values determined by the geometrical accuracy of the Roberval mechanism 3, and are determined by the correction amount adjustment units 6a and 6.
Set in b. The coefficients K ₂ x, K ₂ y, K ₃ x, K ₃ y, etc. are set in advance by the setting device 8 and set in the eccentricity error correction calculator 7.
This is especially necessary when the rigidity of the Roberval mechanism 3 is insufficient, for example when it is necessary to correct an error as shown in Figure 1, but it can be set to zero for practical purposes except for balances with particularly high sensitivity. In some cases. The eccentricity error correction calculator 7 can be constructed from an operational amplifier or the like, but can be implemented at low cost if it is constructed from a microcomputer built into the balance.

The signal f(W) obtained by the eccentricity error correction calculator 7 is sent to the calculator 9, where it is converted into a weight value using a known method and displayed on the display 10, or transmitted to the outside as a digital output. It is configured so that

Next, the operation of this embodiment will be explained.

When a load 11 is placed on the plate 1, the load 1
The bending moment due to 1 is detected as a resistance change in the bridge strain gauge. In other words, the bridge consisting of resistors a ₁ , a ₂ , c ₁ , and c ₂ generates a deflection signal fx due to the moment in the left and right direction, resistors b ₁ ,
Deflection signals fx due to longitudinal moments are input to amplifiers 5b and 5a _, respectively, by the bridges b ₂ , d 1 and d ₂ . The operator adjusts the correction adjustment section 6.
After adjusting a and 6b and determining the coefficients K ₁ x and K ₁ y, we get
The respective output signals Fx and Fy of the correction adjustment units 6a and 6b corresponding to the signals fx and fy are introduced into the eccentricity error correction calculator 7. Coefficients K ₂ x, K ₂ y, K ₃ x,
The arithmetic unit 7 in which K ₃ y etc. are set receives the signal Fx,
Input Fy and W and calculate f ₁ (Fx) and f ₂ (Fy),
f(W) in equation (1) is output to the calculation section 9. the result,
The curves C and D in Figure 1 are corrected and straightened, and the first
It can be placed within the allowable width as shown by the straight line S in the figure.

As described above, according to the present invention, eccentricity errors can be corrected by simply adjusting the correction calculation unit such as a trimmer without making any mechanical geometric adjustments, and the accuracy required by the user can be corrected. It can be adjusted freely at the time of manufacture or by the user depending on the
It is possible to obtain an electronic precision balance with an accuracy of 1/1 million to 1/2 million.

[Brief explanation of drawings]

Figures 1 and 3 are error-bending moment relationship diagrams when the rigidity is sufficient and when the rigidity is insufficient, respectively. Figure 2 is a diagram showing the load measuring mechanism of the embodiment of the present invention. Figure 3 is the moment detection section. FIG. 4 is a block diagram showing the circuit configuration thereof, and FIG. 5 is an explanatory diagram of a moment detecting section according to another embodiment of the present invention. 1...Plate, 2...Moment detection section, 3...Roberval mechanism, 4...Vertical load measurement section, 6a, 6
b...Correction amount adjustment section, 7...Eccentricity error correction calculator, 12...Dish support rod.

Claims (1)

[Claims] 1. In a device that is equipped with a Roberval mechanism that supports a plate and measures the load on the plate, a vertical load measuring means that measures the load in the vertical direction on the plate is interposed between the plate and the Roberval mechanism. A moment detection unit detects the deflection of the plate support rod due to the bending moment caused by the eccentric load on the plate, dividing it into two orthogonal components, and using the detected value by the moment detection unit, the vertical load is detected. An electronic precision balance, characterized in that it is equipped with an eccentricity error correction means for correcting an error caused by the eccentricity of the load on the pan, which is included in the measurement value of the measuring means.