JPS6323489B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an elastic member that is displaced according to a load.
Magnetic fluid (a liquid made by suspending fine iron oxide powder with a diameter of 1/100,000 mm in an organic solvent, which has the property of attracting magnets; when an external magnetic field is applied, each iron oxide particle becomes magnetized). The weight of the elastic member itself or the load on it is reduced by the buoyancy of the float installed in the device (which has the characteristic that the specific gravity of the liquid changes by changing the strength of the magnetic field). This invention relates to an electronic scale that cancels out added weight.

Conventionally, electronic scales are used to determine the weight of an object to be measured by electrically detecting the amount of displacement of an elastic member to which a load is applied by using a strain gauge or a displacement meter, as shown in Figures 1a and b. There is something like that.

That is, a weighing platform 5 is attached via a support 4 to the upper surface of a free end 3 of a metal elastic member 2 whose one end is fixed to a vertical wall surface of a base 1 . and,
A plurality of strain gauges 6 are attached to the elastic member 2. These strain gauges 6 are constructed of Wheatstone bridges as shown in FIG. 1B, and a strain gauge 7 is connected to this Wheatstone bridge. When the object to be measured is placed on the weighing table 5, the elastic member 2 is bent, and the strain meter 7 displays the amount of strain converted into the weight of the object to be measured.

However, electronic scales having such a configuration have the following problems. That is, a portion of the weight of the weighing platform 5, the support column 4, and the elastic member 2 itself is already applied to the free end 3 of the elastic member 2 even when no object is placed thereon. Therefore,
When actually measuring the weight of an object to be measured, only a region of the load-output voltage characteristic shown in FIG. 2 that exceeds a certain load can be used, and the measurable range becomes narrow.
Therefore, during measurement, it is necessary to increase the zero point correction of the signal or expand the signal.
There was a problem that measurement accuracy decreased.

In order to avoid such problems, an electromagnetic self-balancing electronic balance shown in FIG. 3 has been proposed. That is, in this electronic scale, two parallel springs 8a, 8b as elastic members are fixed at right angles to the vertical wall of the base 1, and an L-shaped frame is attached to the tips (free ends) of the parallel springs 8a, 8b. 9 is attached, and a weighing platform 10 is further attached to the upper end of the frame 9. Furthermore, a magnetic support mechanism 11 is interposed between the frame 9 and the horizontal surface of the base 1. As shown in the figure, this magnetic force support mechanism 11 includes an excitation coil 1 for linearity correction within a bottomed cylindrical yoke 12.
3 is wound around a permanent magnet 14, and a force coil 17 wound around a coil frame 16 at the lower end of a support rod 15 connected to the frame 9 is fitted onto the upper end of the permanent magnet 14. It is. Further, the frame 9 is provided with a displacement detector 18 that detects vertical displacement of the tip of the frame 9.

In the electronic scale configured in this way, when the object to be measured is placed on the weighing table 10, the parallel springs 8a, 8
b is bent and frame 9 is lowered, but this frame 9
The amount of displacement is detected by the displacement detector 18, and a current corresponding to this amount of displacement is passed through the force coil 17, and the frame 9 is returned to its original horizontal position by magnetic force. And force coil 1 at that time
The weight of the object to be measured can be determined from the value of the current flowing through 7.

However, although an electronic scale configured in this way can use the entire range of the load-output voltage characteristics shown in FIG. Extra current needs to flow. This has led to problems such as changes in characteristics due to excess heat generation and increased operating costs for the electronic scale.

Further, in order to hold the weight of the weighing platform 10, frame 9, etc., an electronic scale has been considered in which a preload spring is inserted between the frame 9 and the horizontal surface of the base 1, but the temperature of the preload spring etc. The change in spring constant due to Therefore, there was a problem that the measurement accuracy decreased.

The present invention was made based on these circumstances, and its purpose is to utilize the fact that when a magnetic field is applied to a magnetic fluid, the specific gravity of the magnetic fluid increases and the buoyancy becomes large. By canceling out the weight of the weighing platform and elastic member or the weight of the object to be measured, it is possible to expand the measurement range, reduce operating costs, and prevent characteristic changes due to excess heat generation. An object of the present invention is to provide an electronic scale that can suppress the problem and improve measurement accuracy.

FIG. 4a is a sectional view showing a schematic configuration of an electronic scale according to an embodiment of the present invention. That is, base 2
Two parallel springs 22a and 22b as elastic members are fixed in parallel to each other at right angles to a vertical wall of 1, and a frame 23 is attached so as to straddle both free ends of these parallel springs 22a and 22b. , frame 2
A weighing table 24 is attached to the upper surface of the weighing machine 3 via a support that is a part of the frame 23. frame 2
A support mechanism is interposed between the horizontal surface of the base 21 and the horizontal surface of the base 21. This support mechanism, as shown in the figure,
A bottomed cylindrical container 26 is fitted and fixed into a through hole formed in the upper wall of the cylindrical container-shaped yoke 25. A cylindrical permanent magnet 27 is provided so as to penetrate through the bottom wall of the cylindrical container 26 and expose its upper end. Further, the lower end portion of this permanent magnet 27 is fixed to the bottom wall of the yoke 25. This permanent magnet 27
The frame 23 is located at a position surrounding the outer peripheral surface of the upper end of the frame 23.
An annular float 2 connected to the lower surface of the
9 is placed. The cylindrical container 26 is filled with a magnetic fluid 30. Further, an excitation coil 31 is wound around the lower end of the permanent magnet 27, and this excitation coil 31 is connected to a DC power source 33 via a variable resistor 32 for current adjustment, as shown in FIG. 4c. has been done. Furthermore, frame 2
A support rod 3 fixed to the base 21 near the upper end of 3
A differential transformer 35 as a displacement detector supported by 4 is disposed. The output of the differential transformer 35 is input to a display device 37 via an amplifier 36, as shown in FIG. 4b.

If the electronic scale has such a configuration, the cylindrical container 2
The magnetic fluid 30 in the permanent magnet 6 is interposed in the magnetic gap formed between the S pole of the permanent magnet 27 and the inner peripheral surface of the through hole formed in the upper wall of the yoke 25. 27 acts on the magnetic field.
Then, buoyancy acts on the float 29. On the other hand, when the object to be measured is not placed on the weighing table 24, the weighing table 24, the support, the frame 23, the parallel spring 22
A downward force is applied to the frame 23 due to the weight of components a, 22b, etc. Therefore, by adjusting the volume of the float 29 and the magnetic force of the permanent magnet 27 itself, it is possible to cancel the downward force by the buoyant force. Note that by passing current through the excitation coil 31, the magnetic field by the permanent magnet 27 can be finely adjusted, so that the parallel springs 22a, 2
2b completely returns to the horizontal position, and differential transformer 3
The output signal of 5 can be adjusted to zero.

After setting the output signal of the differential transformer 35, that is, the instruction on the display 37 to zero, when the object to be measured is placed on the weighing platform 24, the two parallel springs 22a, 2
2b is bent, and the frame 23 is displaced downward by an amount corresponding to the weight of the object to be measured. Since this amount of displacement is detected by the differential transformer 35, the value obtained by converting the amount of displacement into weight is displayed on the display 37.

With such an electronic scale, the weight of the weighing platform 24, support column, frame 23, parallel springs 22a, 22b, etc. can be canceled out by the magnetic force of the permanent magnet 27, so The entire range of load-output voltage characteristics can be used, expanding the measurement range and improving measurement accuracy. Furthermore, since the amount of current that is constantly passed through the excitation coil 31 during operation of the electronic scale is extremely small, operating costs can be reduced.

Further, by appropriately selecting the type of magnetic fluid 30 and the shape of the float 29, it is possible to give the magnetic fluid 30 a function as a damper.
In this case, there is no need to separately install an oil damper for vibration absorption.

FIG. 5 is a control circuit diagram of an electronic scale according to another embodiment of the present invention, in which the same parts as in FIGS. 4b and 4c are given the same reference numerals. The mechanical configuration of this embodiment is the same as that of the embodiment shown in FIG. 4a described above, so a description thereof will be omitted.

In this embodiment, the output of the differential transformer 35 is input to a display 37 via an amplifier 36. On the other hand, the DC current output from the DC power supply device 38 is supplied to the excitation coil 31 wound around the permanent magnet 27 via the current control device 39. A displacement signal is input from the display 37 to the current control device 39, and an A/D converter 40 converts the current value flowing through the exciting coil 31 from analog to digital.
is connected, and the output of this A/D converter 40 is input to a digital load display 41.

In the electronic scale having such a configuration, the weighing platform 24
Before placing the object to be measured, the current controller 39 causes the current to flow through the excitation coil 31 so that the displacement signal indicating the displacement of the frame 23 output from the display 37 of the differential transformer 35 becomes zero. Set the current value for zero point adjustment. The current value for this zero point adjustment is A/D
After being A/D converted by the converter 40, the load display 4
1, but set the value at this time to 0 kg. Next, when the object to be measured is placed on the weighing platform 24,
The frame 23 tries to bend by the amount of displacement corresponding to the weight of the object to be measured, but when the displacement signal from the display 37 of the differential transformer 35 is input to the current control device 39, this current control device 29 The current flowing through the excitation coil 31 is increased until becomes zero. That is, as the current increases and the magnetic field applied to the magnetic fluid 30 increases, the buoyancy of the float 29 increases, pushing the frame 23 upward. Then, when the amount of displacement becomes zero, the increase in current is stopped. Therefore, the total value of the aforementioned zero point adjustment current and the current corresponding to the weight of the object to be measured flows through the excitation coil 31. As a result, the current flowing into the digital load display 41 is the above-mentioned total current, but since the zero point is set before placing the object to be measured, the load indicator 41 displays the above current value. The value converted to body weight is displayed.

With such an electronic scale, the weight of the weighing platform 24, support column, frame 23, parallel springs 22a, 22b, etc. can be canceled out by the magnetic force of the permanent magnet 27, so that Effects similar to those of the embodiments shown in -c can be obtained.

Furthermore, in this embodiment, since the weight of the object to be measured is also canceled out, the vertical position of the weighing table 24 does not change even if the object to be measured is placed on it. Therefore, a good self-balancing electronic balance can be obtained here.

FIG. 6 is a control circuit diagram of an electronic scale according to yet another embodiment of the present invention. This electronic scale is configured so that it can automatically and continuously measure many products having the same standard weight using a conveyor or the like.

That is, the secondary side output of the differential transformer 35, whose primary side is connected to the AC power source 51, is passed through the differential circuit 52, amplified by the AC amplifier 53, and then synchronously detected by the detector 54. After being amplified at 55, the load is displayed on a display 56. Also,
The output of the DC amplifier 55 is compared by a voltage comparator 57 with a reference voltage of, for example, zero V, which indicates the reference position of the weighing platform. The output of this voltage comparator 57 is applied to the excitation coil 31 via a relay contact 58, a sample and hold circuit 59, and an output amplifier 60. Further, the contact point 58 of the relay is connected to a timing circuit 61.
is connected to a position detector 62 that detects that the product is placed on a weighing platform formed in the shape of a roller platform, and when the product is placed on the weighing platform, the contact point 58 of the relay is opened. .

However, when no product is loaded onto the weighing platform, the output of the differential transformer 35 should be equal to the reference voltage, but water or dust may adhere to the weighing platform, causing the zero point to fluctuate. In this case, the output of the differential transformer 35 and the reference voltage are compared by the voltage comparator 57, and the current of the excitation coil 31 is increased or decreased via the output amplifier 60 based on the output of the voltage comparator 57, and the weighing platform is referenced. Automatically return to position.

Next, when the product is carried onto the weighing table, the relay contact 58 is opened, but the voltage at the time of no load immediately before the release is held in the sample hold circuit 57, and the voltage corresponding to this voltage is A constant current flows through the excitation coil 31. Therefore, the weighing platform is displaced by an amount corresponding to the weight of the product, and this displacement is detected by the differential transformer 35 and displayed as the weight of the product on the display 56 via the DC amplifier 55.

Further, when the product is removed from the weighing platform, the relay contact 58 is closed again, and the weighing platform automatically returns to the reference position.

An electronic scale with such a configuration can not only achieve the same effects as the embodiments shown in Figures 4 a to c above, but also measure zero point fluctuations caused by water, dust, etc. adhering to the weighing platform. Since the measurement is corrected each time, it is possible to further maintain a high level of measurement accuracy.

FIG. 7 is a circuit diagram showing a main part of a control circuit of an electronic scale according to still another embodiment of the present invention.

In this example, the buoyancy to be applied to the weighing platform for each standard weight of multiple types of products (5 types in this example) is set in advance, and when the product is carried into the weighing platform, the specified weight of the product is A buoyant force corresponding to the above is applied to the weighing platform, and the product is automatically balanced when placed on the weighing platform.

That is, 71 in the figure is a DC power supply, and this DC power supply 71 has four resistors 72a to 72a to divide the voltage.
72d is connected to each of these resistors 72a to 72d.
The voltage divided at 72d is input to the DC amplifier 74 via relay contacts 73a to 73e, respectively. The output of the DC amplifier 74 is applied to the exciting coil 31 via a voltage/current converter 75.

When the product is carried into the weighing platform, the relay contacts 73a to 73e of the product are closed by the determination signal from the product discriminator, and the voltage that generates the buoyancy corresponding to the weight of the product is applied to the DC amplifier 7.
4 to the voltage/current converter 75.
As a result, a current flows through the excitation coil 31, and the weighing platform automatically returns to its reference position.

With an electronic scale having such a configuration, in addition to being able to obtain the same effects as the embodiment shown in FIG. 5 described above, it is also possible to continuously measure a wide variety of products in an automatic balancing manner . Of course, the standard weight of each product is programmed into the computer, and the computer commands the contact 73 of each relay.
It is also possible to open and close a to 73e.

Note that the present invention is not limited to the embodiments described above. That is, in the embodiment, the permanent magnet 27 and the excitation coil 31 are used as the excitation mechanism, but a magnetic material may be used instead of the permanent magnet 27. Further, in the embodiments shown in FIGS. 4a and 4b, the direction of the current flowing through the excitation coil 31 was only one direction, but if the circuit configuration shown in FIG. 8 is adopted, the variable resistor 8
1, it is possible to cause current to flow in the excitation coil 31 in the forward direction and in the reverse direction. Therefore, the zero point adjustment of the weighing platform 24 can be made more accurately.

As explained above, according to the present invention, by utilizing the fact that the specific gravity of the magnetic fluid changes greatly when a magnetic field is applied to the magnetic fluid, the weight of the weighing platform and the parallel spring itself as an elastic member or its weight can be reduced. Since the weight of the object to be measured can be canceled out, the measurement range of the electronic scale can be expanded, operating costs can be reduced, and measurement accuracy can be improved.

[Brief explanation of drawings]

Figures 1a, b and 3 are schematic configuration diagrams showing conventional electronic scales, Figure 2 is a load-output voltage characteristic diagram of the electronic scale, and Figure 4a is an electronic scale according to an embodiment of the present invention. 4b and 4c are control circuit diagrams of the same electronic scale, FIG. 5 is a control circuit diagram of an electronic scale according to another embodiment of the present invention, and FIG. 6 is a control circuit diagram of the electronic scale according to another embodiment of the present invention. FIGS. 7 and 8 are circuit diagrams showing main parts of control circuits for electronic scales according to still other embodiments, respectively. 21... Base, 22a, 22b... Parallel spring (elastic member), 23... Frame, 24... Weighing stand, 27... Permanent magnet, 29... Float, 30...
Magnetic fluid, 31...Excitation coil, 35...Differential transformer, 37...Display device, 39...Current control device, 41...Load display device.

Claims (1)

[Scope of Claims] 1. A weighing platform on which an object to be measured is placed; an elastic member connected to the weighing platform and displacing in response to the weight of the object to be measured and the weighing platform; freedom of the elastic member; a support member attached to an end; a displacement detector for detecting the amount of displacement of the elastic member; a float attached to one end of the support member; a magnetic fluid for imparting buoyancy to the float; an excitation mechanism for changing the specific gravity of the magnetic fluid and generating a buoyancy force on the float corresponding to the amount of displacement of the displacement detector when the object to be measured is not placed on the weighing platform; An electronic scale comprising: weight detection means for determining the weight of the object to be measured from the amount of displacement of the displacement detector when the object to be measured is placed on a weighing platform. 2. The excitation mechanism is composed of a permanent magnet with one end immersed in magnetic fluid, an excitation coil wound around the other end of the permanent magnet, and a control device that supplies excitation current to the excitation coil. An electronic scale according to claim 1. 3. A weighing platform on which an object to be measured is placed; An elastic member connected to the weighing platform and displaced in response to the weight of the object to be measured and the weighing platform; A support attached to the free end of the elastic member. a member; a displacement detector for detecting the amount of displacement of the elastic member; a float attached to one end of the support member; a magnetic fluid for imparting buoyancy to the float; changing the specific gravity of the magnetic fluid. an excitation mechanism for applying a buoyancy force to the float corresponding to the amount of displacement generated in the displacement detector when the object to be measured is placed on the weighing platform; and a weight detecting means for determining the weight of the object to be measured from the amount of change in the magnetic field applied to the magnetic fluid. 4. The excitation mechanism is composed of a permanent magnet with one end immersed in magnetic fluid, an excitation coil wound around the other end of the permanent magnet, and a control device that supplies excitation current to the excitation coil. An electronic scale according to claim 3.