JP4729988B2 - Electronic balance - Google Patents

Description

  The present invention relates to an electronic balance, and more particularly to a high-accuracy electronic balance that balances a load of an object to be weighed and an electromagnetic force, measures a current required to generate the electromagnetic force, and measures a load on the pan.

  2. Description of the Related Art Conventionally, electronic balances that balance the load and electromagnetic force of an object to be weighed and calculate a measured value from an electric current required to generate the electromagnetic force are generally used. FIG. 6 shows a configuration example of a conventional electromagnetic force balance type electronic balance. A tray 51 on which an object to be weighed is mounted is provided on a load detection mechanism 5 including two beams 52 a and 52 b having thin portions and a movable column 53. The load of the object to be weighed, that is, the dish load W is transmitted to the movable column 53, and the dish load W is a magnetic flux proportional to the magnetic field strength of the permanent magnet 56 via the balanced beam 55 supported at the fulcrum 54. It is compared with the electromagnetic force generated in proportion to the product of the density and the coil current flowing in the coil 57, the deviation is detected by the displacement sensor 58, and the coil current I is controlled by the PID controller 59 so as to be in a balanced state. The coil current I is converted into a voltage signal by the reference resistor 60, and then subjected to arithmetic processing by the A / D converter 61 and the arithmetic processing unit 62, and the measured value of the pan load W is displayed on the display unit 63. .

  In such electronic balances, zero / span drift occurs with the course of use or with environmental changes such as temperature changes. It has been. Of the environmental changes, the influence of the ambient temperature is particularly large. In particular, the influence of the magnetic field intensity change due to the temperature change of the permanent magnet 56 is large. Therefore, a temperature sensor 64 is disposed near the permanent magnet 56 and the temperature correction circuit 65 is arranged. The temperature of the reference voltage source 66 of the A / D converter 61 is corrected by providing a temperature coefficient, or the output signal of the temperature sensor 64 is taken into the CPU of the arithmetic processing unit 62 and the temperature is calculated by arithmetic processing. The measures such as correcting the influence of the are taken.

However, in the case of a high-precision electronic balance, not only the above-mentioned aging and temperature effects but also the humidity effects cannot be ignored. Since the influence of this humidity also affects the calibration of the internal copper, a means for incorporating a humidity sensor, measuring the humidity during calibration, and correcting the mass of the internal copper based on the humidity value is disclosed.
JP 2003-214932 A Japanese Patent Laid-Open No. 2000-121422 JP 2001-13001 A

  A conventional electronic balance is configured as described above, and when the humidity in the electronic balance becomes high, components used for the movable part of the electromagnetic force balance mechanism part (for example, a coil suspended in a magnetic field of a permanent magnet, The coil lead wire resin material, adhesive, etc.) absorbs moisture, or moisture adheres to the surface, and the mass of the portion increases. Conversely, when the humidity decreases, the mass decreases. A so-called zero point drift occurs in which the zero point shifts due to a change in humidity, which is one of the environmental parameters.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a highly accurate electronic balance in which a zero point drift due to a change in humidity is small.

In order to achieve the above object, an electronic balance of the present invention includes an electromagnetic force balance mechanism unit including a force coil that generates electromagnetic force, a measurement pan for applying a load to be measured, a humidity correction member, The load of the measurement object, the electromagnetic force, and the load of the humidity correction member are transmitted, the balance frame having a fulcrum, and the position of the humidity correction member are variable, and the humidity correction member in the balance frame An adjustment mechanism that adjusts the distance between the point of application of the load and the fulcrum, and the humidity correction member is a material having the same adsorption and hygroscopic properties as the resin for the insulating film used in the force coil. .

  The electronic balance of the present invention can correct both the zero-point drift caused by temperature changes and the zero-point drift caused by changes in humidity, and can realize a balance with a small zero-point drift against changes in temperature and humidity. it can.

The electronic balance provided by the present invention has the following characteristics. The first feature is an electronic balance that balances a dish load and an electromagnetic force and measures the dish load. In order to correct a zero point drift due to a humidity change, a humidity change disposed in the dish load operating unit is provided. A humidity correction member with known mass change due to temperature, a temperature sensor that measures the temperature of the electromagnetic force balance mechanism that balances the load on the dish and the electromagnetic force, and a load measurement value and a reference temperature measured in advance at a plurality of temperature points. Storage means for storing the load measurement value, and correction calculation means for calculating the load measurement value based on the stored value corresponding to the measured temperature.
The second feature is that the humidity correction member is attached to the electromagnetic force balance mechanism at a plurality of positions or continuously movable, and the humidity correction member is attached at a position where the zero point drift can be optimally corrected. .

A third feature is that an electromagnetic force balance mechanism is attached to a humidity correction member having a mass, a surface area and a material capable of optimally correcting the zero point drift.
Therefore, the basic configuration of the best mode is an electronic balance having the configuration having the features of claims 1, 2, and 3.

Hereinafter, the electronic balance of the present invention will be described in detail by way of examples. FIG. 1 is a side view (A) and a top view (B) of an electromagnetic force balance mechanism 1 used in an electronic balance of the present invention, and FIG. 3 is an operation principle diagram illustrating the operation of the electronic balance.
The electronic balance includes an electromagnetic force balance mechanism unit 1 that converts a load into a current amount using a load detection cell 2 formed of a single block as shown in FIGS. 1 and 2, and a coil that flows through a force coil 12 shown in FIG. The servo amplifier 3 controls the current I, and the weighing display unit 4 that displays the load weighing value of the object to be weighed.

  The load detection cell 2 is formed by drilling or wire electric discharge machining on a single block such as a strong aluminum alloy to provide a plurality of holes and slits indicated by thick lines as shown in FIG. 22 and a lever block 23 are formed. The Roverval mechanism 22 includes a movable column 24 that is movable in the vertical direction and a fixed column 25 that is fixed and used on the other end side, and two upper and lower beams 26a provided with flexible portions e at regular intervals. It constitutes a quadrilateral connected by 26b.

  The lever block 23 is connected to force point springs 27a and 27b formed on the upper and lower sides of the connecting portion 27 and a fulcrum spring 28. When a plate load W is applied from the upper part of the movable column 24, the force point springs 27a and 27b are Moving downward, the lever block 23 rotates clockwise about the fulcrum spring 28.

  The electromagnetic force balance mechanism 1 is fixed with screws and nuts via four collars 10 on both sides of the load detection cell 2 and the lever block 23 of the load detection cell 2 as shown in FIG. A balance frame 11, a frame 13 around which a force coil 12 screwed to the left end of the balance frame 11 is wound, and a weight plate that balances in the longitudinal direction fixed to the screw shaft at the front right end by a nut so as to be able to advance and retreat. 14, a weight plate 15a, 15b which rotates with the screw shaft at the rear right end eccentrically and balances in a direction perpendicular to the longitudinal direction, and a tip section screwed to the upper right end of the load detection cell 2 has a parabolic shape. A measuring plate 17 fitted on the column 16, a humidity correction member 6 fixed to the back side of the measuring plate 17 with a stopper 17 a, and a magnetic field for generating a magnetic field having a predetermined magnetic flux density in the force coil 12. Occurrence And a location 19. The load detection cell 2 and the magnetic field generator 19 are fixed to the base plate 20 by screws or the like.

  The humidity correction member 6 is used for correcting a load change due to a humidity change in a part that is most susceptible to humidity among the movable parts of the electromagnetic force balance mechanism 1, and is used for the force coil 12 in this configuration. A material having the same adsorption and hygroscopic properties as the insulating coating resin that is used, for example, a polyimide resin processed into a washer shape is used. It is preferable that the surface area and mass of the humidity correction member 6 be adapted to the temporal change of the zero point drift.

  In the electronic balance having the above-described configuration, when a pan load W is applied as shown in FIG. 3, the measuring pan 17 is lowered, and the balance frame 11 rotates clockwise around the fulcrum spring 28. The displacement of the right end side of the balance frame 11 is detected by a displacement sensor 18, and the coil current I flowing from the servo amplifier 3 to the force coil 12 is controlled by the output voltage signal, and the balance frame 11 is returned to the reference position. The on-dish load W and the electromagnetic force F are balanced. The coil current I is converted into a voltage signal by the current / voltage converter 48, A / D converted by the interface 41 of the measurement display unit 4 together with the output voltage of the temperature sensor 49, and stored in the memory 42 with temperature correction. Based on the weighing value calculation processing program, the CPU 43 performs calculation processing, and the load weighing value whose temperature has been corrected is displayed on the display 44.

In the present electronic balance, the rotational moment acting on the fulcrum spring 28 is equal to the load on the pan W and the electromagnetic force F at a constant reference temperature and reference humidity. When the distances are a and b, the relationship of the following formula (1) is maintained between the dish load W and the electromagnetic force F.
F = (b / a) W (1)
When the humidity changes by a certain value from this reference state, assuming that the load on the force coil 12 side is changed by ΔW1 and the load on the humidity correction member 6 is changed by ΔW2, the relationship of the following equation (2) is maintained.
F + ΔW1 = (b / a) W + (b / a) ΔW2 (2)
Accordingly, the zero point drift is eliminated if the relationship of the following equation (3) is established between the load change ΔW2 of the humidity correction member 6 and the load change ΔW1 of the force coil 12.
ΔW2 = (a / b) ΔW1 (3)

  Since the load ΔW1 varies depending on individual electronic balances, the load ΔW1 is measured on a plurality of electronic balances of the same type in advance with the humidity correction member 6 removed, and the averaged average load is expressed as Δ Used as W1. On the other hand, the humidity correction member 6 uses a humidity correction member 6 that satisfies the above equation (3) by measuring the load ΔW2 in advance for different masses, surface areas, and materials.

  The shape of the humidity correction member 6 and the mounting position thereof are not limited to the above-described embodiment. For example, as shown in FIG. You may adhere to the column part 24a. By using these humidity correction members 6 and 6A in common for each electronic balance, the humidity correction is simplified and the manufacturing effort is simplified.

  4 and 5 show an embodiment in which accurate humidity correction is performed in accordance with the zero point drift of each electronic balance using a humidity correction member having a predetermined shape. FIG. 4 shows that the screw shaft 14a with the screw shaft 14a on which the weight plate 14 of the electromagnetic force balance mechanism 1 is screwed is screwed with the humidity correction member 6B with a screw hole to change the distance to the fulcrum spring 28. It is something that can be done. FIG. 5 shows a configuration in which a plurality of tap holes 11a are formed on the side surface of the balance frame 11 and the humidity correction member 6C is screwed to vary the distance to the fulcrum spring 28. The humidity correction members 6B and 6C have the opposite directions of correction, and can be corrected in either direction. In either case, after the electronic balance is individually installed in a thermostatic chamber and the zero point is calibrated, the zero drift caused by giving a constant humidity change is measured, and the humidity correction member 6B is placed at a position where the zero point drift is minimized. Fix 6C. Further, by providing the humidity correction members 6, 6A, 6B, and 6C with different masses, surface areas, and materials, the humidity can be more accurately adjusted to the time delay of the drift of each electronic balance with respect to zero point drift and humidity change. Correction can be performed.

  In the above embodiment, the load detecting cell 2 made of a single block is used for the electromagnetic force balance mechanism 1, but the present invention is not limited to this, and this may be configured with individual parts. It is also possible to use different materials. As a result, the portion where the load change due to the humidity change also changes, so the mounting position of the humidity correction member is not limited to the dish load side. Further, it is also possible to make the adjustment position of the humidity correction member continuously variable by making it a long hole (not shown).

    The present invention is used for a high-precision electronic balance in which the influence of humidity cannot be ignored.

It is the side view (A) and top view (B) of the electromagnetic force balance mechanism part 1 used for the electronic balance of this invention. It is a side view of the load detection cell 2 concerning an Example. It is an operation | movement principle figure explaining operation | movement of an electronic balance. It is a figure which shows the attachment method of the humidity correction member 6B concerning an Example. It is a figure which shows the attachment method of 6 C of humidity correction members concerning an Example. It is a figure which shows the structural example of the conventional electronic balance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electromagnetic force balance mechanism part 2 Load detection cell 3 Servo amplifier 4 Weighing display part 5 Load detection mechanism 6, 6A, 6B, 6C Humidity correction member 10 Color 11 Balance frame 11a Tap hole 12 Force coil 13 Frame 14 Weight plate 14a Screw Axis 15a, 15b Weight plate 16 Support column 17 Measuring plate 17a Stopper 18 Displacement sensor 19 Magnetic field generator 20 Base plate 22 Rover valve mechanism 23 Lever block 24 Movable column 24a Column portion 25 Fixed column 26a, 26b Beam 27 Connecting portion 27a, 27b Power point Spring 28 Support point spring 41 Interface 42 Memory 43 CPU
44 Display 48 Current / Voltage Converter 49 Temperature Sensor 51 Trays 52a, 52b Beam 53 Movable Column 54 Supporting Point 55 Balance Beam 56 Permanent Magnet 57 Coil 58 Displacement Sensor 59 PID Control Unit 60 Reference Resistor 61 A / D Converter 62 Arithmetic Processing unit 63 Display unit 64 Temperature sensor 65 Temperature correction circuit 66 Reference voltage source

Claims (1)

Electromagnetic force balance mechanism having a force coil that generates electromagnetic force, a measuring pan for applying a load to be measured, a humidity correction member, the load of the measurement target, the electromagnetic force, and the humidity correction The load of the member is transmitted, and the balance frame having a fulcrum and the position of the humidity correction member are variable, and the adjustment of adjusting the distance between the load application point of the humidity correction member and the fulcrum in the balance frame The electronic balance is characterized in that the humidity correction member is made of a material having the same adsorption and hygroscopic properties as the insulating film resin used for the force coil .

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