JP4797381B2 - Electronic balance - Google Patents

Description

  The present invention relates to an electromagnetic balance electronic balance that measures the load on the pan by balancing the load to be measured on the pan with the force generated by passing a current through a coil provided in the magnetic field of the permanent magnet. In particular, the present invention relates to an electronic balance having a function of correcting a hysteresis error.

  Generally, in an electromagnetic force balance type electronic balance, a coil is attached to a movable part of a beam that is displaced according to a load to be measured on a pan, and this coil is placed in a magnetic field created by a permanent magnet, and a current is passed through the coil. The generated electromagnetic force is balanced with the load to be measured on the pan, and the magnitude of the load to be measured is measured from the coil current or the control signal for determining the coil current at the time of the balance. In this case, not only changes in the mechanical system of the balance, but also changes in the magnetic field strength due to the permanent magnet and coil current, the hysteresis of the electrical system inevitably occurs, affecting the measurement accuracy.

  In such an electromagnetic force balance type electronic balance, as shown in FIG. 1, a pole piece 1b sandwiched by upper and lower N, S pole permanent magnets 1a, 1a and a yoke 1c (hereinafter, these members are collectively referred to as a magnet body). 1) and a center line L1 of the coil 2 so as to coincide with the axis L2. This is because the magnetic flux density of the magnetic field of the coil current and the magnetic field of the upper and lower permanent magnets, that is, the number of magnetic flux lines per unit area perpendicular to the magnetic field is maximized, which is considered to be the most preferable. However, as described above, there is a problem that hysteresis of a mechanical system or an electric system inevitably occurs at the time of measurement, and a highly accurate measurement value cannot be obtained.

For example, Patent Document 1 and Patent Document 2 disclose means for compensating for such an error due to hysteresis and obtaining a highly accurate measurement value. Both of them include multi-steps involving complicated arithmetic processing. Necessary, and the system becomes complicated and expensive.
Japanese Patent Laid-Open No. 06-160164 JP-A-10-148666

  The inventor measured the hysteresis with the position where the center line L1 of the magnet body 1 and the axis L2 of the coil 2 coincided as the zero point position, and then the relative position of the magnet body 1 and the coil 2 was set to 0. 0. When the hysteresis was measured at a position moved by 5 mm, the hysteresis value was the smallest at a position moved from 1.5 mm to 2 mm from the 0 point position as shown in FIG. 5 and about one-fourth of the 0 point position. Turned out to decrease. At the same time, as shown in FIG. 6, when the magnetic flux density was measured at each moved position, the amount of change from the 0 point position was very small, for example, only 0.6% was deteriorated at the 1.5 mm position. Not found out. In this way, even if the positional relationship between the coil and the magnet body is moved to a position of 1.5 mm where the hysteresis is very small, the magnetic balance has almost no effect on the magnetic flux density and is a highly accurate electronic balance with little hysteresis. Will be obtained. Since the amount of change in magnetic flux density increases rapidly from the 1.5 mm position, the position near 1.5 mm is most preferable.

  Therefore, the present invention measures the hysteresis that occurs at different values for each product due to subtle assembly errors and minute variations in part dimensions after the product assembly is completed, and determines the magnet body and coil according to the value. The main object of the present invention is to provide an electronic balance that can move and adjust the relative position to the most preferable position.

  In order to achieve the above object, the present invention takes the following technical means. That is, in the electronic balance according to the present invention, the load on the plate is balanced by balancing the load to be measured on the plate and the force generated by passing a current through the coil 2 provided in the magnetic field of the magnet body 1. An electromagnetic balance type electronic balance to be measured, in which the magnet body 1 or the coil 2 is relatively movable so that the positions of the center line L2 of the magnet body 1 and the axis L2 of the coil 2 can be adjusted. It was set as the structure formed in.

  As means for enabling movement adjustment of the relative position between the center line L1 of the magnet body 1 and the axis L2 of the coil 2, for example, a fixing screw 4 for fixing the yoke 1c of the magnet body 1 to the frame 3 as shown in FIG. The plurality of spacers 5 are detachably attached between the yoke 1c and the frame 3, or the coil support 6 is fixed to the fixing screw 8 for fixing the coil support 6 supporting the coil 2 to the arm 7 as shown in FIG. A plurality of spacers 9 are detachably mounted between the arm 6 and the arm 7, and the relative positions of the magnet body and the coil can be adjusted by attaching / detaching the required number of spacers 5 or 9. In this case, if the thickness of the spacers 5 and 9 is set to 0.5 mm, for example, the relative movement amount of the magnet body and the coil can be accurately identified.

  As another movement adjusting means, for example, as shown in FIG. 3, an adjusting screw 10 for moving the yoke 1 c of the magnet body 1 up and down is provided separately from the fixing screw 4, and the fixing screw 4 is loosened during adjustment to loosen the frame 3. The fixing screw 4 may be fastened after the adjustment screw 10 is rotated and adjusted with a tool such as a screwdriver from below. Further, the relative position of the magnet body and the coil can be adjusted by using the adjusting screw 11 as shown in FIG. 4 instead of the fixing screw 8 for connecting the arm 7 and the coil support 6 shown in FIG. it can. When the relative position adjustment of the magnet body 1 and the coil 2 is performed by the rotation of the adjustment screws 10 and 11, the display unit for detecting and displaying the relative movement amount by the rotation or the adjustment screw 10 and 11 It is necessary to accurately identify the amount of movement due to the rotation by providing a scale representing the amount of movement proportional to the rotation angle of 11 on the periphery of the rotation operation portion of the adjustment screws 10 and 11.

Further, as means for measuring the hysteresis and determining the relative movement amount of the magnet body 1 and the coil 2 from the value, the relative position of the magnet body and the coil shown in FIG. A parameter indicating the correlation may be prepared in advance, and the moving amount of the magnet body or the coil may be determined based on the measured hysteresis value. For example, if the measured hysteresis is a value of −30 in FIG. 5, it corresponds to the hysteresis at the 1 mm position. Therefore, in order to obtain the most preferable hysteresis value at the 1.5 mm position from the relationship with the magnetic flux density, 0. It is only necessary to shift the distance away from the 0 point position by 5 mm. The hysteresis may be measured by a generally used method.
For example, it is possible to easily measure by preparing a plurality of weights, sequentially placing the weights on a plate up to a weighed value (maximum load), and then successively lowering the loaded weights.
Specifically, taking the case of measuring the hysteresis when a load of 100 g is placed on a plate, for example, two 100 g weights A and B are prepared. Wait for A to stabilize and place the first measurement. Subsequently, after the weight B is placed and stabilized, the weight B is lowered and the second measurement is performed after the weight B is stabilized again. The first measurement and the second measurement both measure the load when the weight A is placed on the plate. Nevertheless, during the second measurement, that is, when the load from the overload (ie, the load at the weight A + weight B) is gradually reduced to 0, the output of the load cell is the same as that at the time of the first measurement (when the load is gradually increased). Are slightly larger even if they are the same, and this fluctuation is measured as a hysteresis value.

  According to the electronic balance of the present invention, the magnet body or the coil is formed so as to be relatively movable so that the position of the center line of the magnet body and the axis of the coil can be adjusted. Hysteresis that occurs at different values for each product due to variations, etc., can be reduced to a predetermined value by relatively moving the magnet body or coil, thereby obtaining a highly accurate electronic balance. There is an effect such as.

(Means and effects for solving other problems)
In the above invention, the electronic balance may be provided with an identification means for recognizing the amount of movement when the relative position of the magnet body and the coil is moved. As a result, the desired amount of movement can be accurately captured.

Hereinafter, an electronic balance according to the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment of the present invention and is an enlarged sectional view of a magnet body portion of an electronic balance. The magnet body 1 is composed of a pole piece 1b sandwiched between upper and lower N and S permanent magnets 1a and 1a and a yoke 1c for supporting them, and is attached to the frame 3 via fixing screws 4. A coil 2 is arranged around a pole piece 1 b of the magnet body 1, and a coil support 6 that supports the coil 2 is fixed to an arm 7 via a fixing screw 8.
A plurality of spacers 5 are detachably interposed between the yoke 1 c and the frame 3 on the fixing screw 4 of the magnet body 1, and the magnet body 1 is moved up and down by attaching and detaching the spacers 5. It is formed so that the relative position to 2 can be adjusted. In this case, if the thickness of the spacer 5 is set to a predetermined thickness, for example, 0.5 mm, the relative movement amount of the magnet body 1 and the coil 2 can be accurately identified. Further, the adjustment is easy if the center line L1 of the magnet body 1 and the axis L2 of the coil 2 are assembled in advance so that the spacer 5 is removed according to the measured hysteresis value. As described above, as a means for measuring the hysteresis and determining the movement amount of the magnet body 1 from the value, the relative position of the magnet body and the coil based on FIG. It is sufficient to prepare a parameter indicating the correlation between the magnet body and determine the amount of movement of the magnet body based on the measured hysteresis value. For example, if the measured hysteresis is a value of −30 in FIG. 5, it corresponds to the hysteresis at the 1 mm position. Therefore, in order to obtain the most preferable hysteresis value at the 1.5 mm position from the relationship with the magnetic flux density, 0. It is only necessary to shift the distance 5 away from the 0 point position by 5 mm, so it is sufficient to remove one spacer 5.

  FIG. 2 shows an embodiment in which a spacer is attached to the coil side. The spacer 5 is fixed between the coil support 6 and the arm 7 on the fixing screw 8 for fixing the coil support 6 to the arm 7. A plurality of similar spacers 9 are detachably mounted. As a result, a required number of spacers 9 are attached and detached so that the coil 2 can be moved up and down to adjust the relative position with the magnet body 1.

  FIG. 3 is an embodiment showing another movement adjusting means. In addition to the fixing screw 4, the adjusting screw 10 for moving the yoke 1c of the magnet body 1 up and down is provided through the frame 3 from below. During adjustment, the fixing screw 4 is loosened and the adjusting screw 10 is rotated and adjusted with a tool such as a screwdriver from below the frame 3, and the magnet body 1 is moved steplessly by fastening the fixing screw 4. It is configured to be adjustable. In this case, it is possible to omit the fixing screw 4, but after adjusting with the adjusting screw 10, it is necessary to perform some kind of detent means for preventing the natural turning of the adjusting screw 10, such as soldering. .

  Further, as the movement adjusting means using the adjusting screw, the coil support 6 can be connected and held to the arm 7 by the adjusting screw 11 as shown in FIG. Thereby, by rotating the adjustment screw 11, the coil 2 can be moved and the relative position with the magnet body 1 can be easily adjusted. Also in this case, after adjusting with the adjusting screw 11, it is necessary to provide some kind of detent means for preventing natural rotation of the adjusting screw 11.

  The adjusting means using the adjusting screws 10 and 11 described above needs to be a means for accurately identifying the moving amount of the magnet body 1 or the coil 2 by the rotation of the adjusting screws 10 and 11. As the identification means, for example, a scale indicating a movement amount proportional to the rotation angle of the adjustment screws 10 and 11 is provided on the periphery of the rotation operation portion of the adjustment screws 10 and 11, or the movement amount by the rotation of the adjustment screws is determined. A display unit for detecting and displaying this may be provided on the electronic balance.

  The present invention can be applied to manufacture a high-precision electronic balance by reducing the hysteresis generated at different values for each product to a predetermined most preferable value.

BRIEF DESCRIPTION OF THE DRAWINGS The 1st Example of the electronic balance concerning this invention is shown, Comprising: Sectional drawing of a magnet body part. Sectional drawing similar to FIG. 1 which shows the 2nd Example of this invention. Sectional drawing similar to FIG. 1 which shows the 3rd Example of this invention. Sectional drawing similar to FIG. 1 which shows the 4th Example of this invention. The graph which shows the correlation of the fluctuation | variation of the relative position of a magnet body and a coil, and hysteresis. The graph which shows the correlation of the fluctuation | variation of the relative position of a magnet body and a coil, and magnetic flux density.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnet body 1a Permanent magnet 1b Pole piece 1c Yoke 2 Coil 3 Frame 4 Fixing screw 5 Spacer 6 Coil support 7 Arm 8 Fixing screw 9 Spacer 10 Adjustment screw 11 Adjustment screw

Claims (2)

And the measured load on the pan, in the electronic balance of the electromagnetic force balance type for measuring the load on the pan by balancing the force generated by supplying a current to a coil provided in the magnetic field of the magnet body provided with a port Rupisu there are, the position of the center line of the port Rupisu of the magnet and the axis of the coil the magnet or the coil for movement adjustment is relatively movable form, the port Rupisu of the magnet body the relative position in the vertical direction of the axis of the center line and the coil is a position where the position of the axis does not match the center line and the coil of the port Rupisu of the magnet body, port of the magnet body Rupisu The absolute value of the hysteresis is greater than the absolute value of the hysteresis generated from the magnet body and the coil at a position where the center line of the coil and the axis of the coil coincide with each other. Electronic balance, characterized in that within smaller position, is positioned. 2. The electronic balance according to claim 1, further comprising identification means for recognizing a moving amount when the relative position of the magnet body and the coil is moved.

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