JP3302452B2 - Weighing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for rotating a non-magnetic metal body so as to pass a position through which a constant magnetic field generated by a field portion passes, so that the field portion generates a force.
The present invention relates to a weighing device that weighs an article using this force.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional force generating mechanism used in a weighing device.
It comprises a center yoke 2, a permanent magnet 3, and a coil 5 arranged in the gap 4. Coil 5 is wound on the bobbin 6, the bobbin 6 is movably supported in the vertical direction of the arrows F _1. Constant magnetic flux from the permanent magnet 3, center yoke 2 as indicated by a solid line arrow B _0, through the space 4 and the main yoke 1 medium.

Now, when a current I is applied to the coil 5, a force of F ₂ = B ₀ IL is generated in the direction of the arrow F _{2 in} a portion of the conductor length L (B ₀ is a magnetic flux density). Since this force F ₂ is proportional to the current I, the current I
The force F ₂ can be measured from the value of In other words, in a state where the force F ₂ and the electromagnetic force F ₂ based on the weight of the objects to be weighed articles are balanced, it is possible to obtain the load of the article based on the current I.

However, (1) copper current is generated when the current I flows through the coil 5, and the heat corresponding to the copper loss raises the temperature of the coil 5, the bobbin 6, the center yoke 2, the permanent magnet 3, and the like. And (2) Since the magnetic flux ΔB generated by the current I flowing through the coil 5 passes through the coil 5, the bobbin 6, the center yoke 2, the permanent magnet 3, and the like, when the current I fluctuates, the magnetic flux ΔB also fluctuates. Causes heat loss, and the heat corresponding to the iron loss causes the temperature of each of the above portions to rise, thereby causing the magnetic flux density B acting on the coil 5 to fluctuate.

In order to compensate for the variation in the magnetic flux density B acting on the coil 5, the magnetic flux density B acting on the coil 5
A magnetic sensor (not shown) for directly measuring the force F _2, and measuring the force F ₂ from the formula F ₂ = BIL based on the magnetic flux density B obtained by the magnetic sensor and the current I. A mechanism has been invented (see Japanese Patent Publication No. 2-7005).

[0006]

[Problems to be solved by the invention]
The force generating mechanism disclosed in Japanese Patent Application Laid-Open Publication No. H10-107 can compensate for fluctuations in the magnetic flux density B by directly measuring the magnetic flux density B acting on the coil 5 using a magnetic sensor. There is a problem that the measurement error of the measurement lowers the measurement accuracy. Due to this problem, there are certain limitations in improving the weighing accuracy of articles. Further, since it is necessary to provide a magnetic sensor and a device associated therewith, there is also a problem that the cost is high.

[0007] It is an object of the present invention to provide a weighing device capable of obtaining high weighing accuracy due to small fluctuations in magnetic flux density.

[0008]

According to the first aspect of the present invention, the field unit generates a force by rotating a non-magnetic metal body so as to pass a fixed magnetic field generated by the field unit. Thus, the weight of the article to be weighed is measured by measuring the number of rotations of the non-magnetic metal body capable of balancing the force generated in the field portion and the weight of the article to be weighed. It was done.

According to a second aspect of the present invention, there is provided a weighing device which rotates a non-magnetic metal body driven by a driving unit, irradiates the non-magnetic metal body with a constant magnetic flux, and rotates the non-magnetic metal body in a substantially tangential direction. A field portion movably provided, and a loading device for placing the article to be weighed, wherein the weight of the article to be weighed is applied to the field portion in a direction substantially opposite to the direction of the force generated by the field portion; A detection unit for detecting a distance that the field unit has moved from a predetermined equilibrium position; a control unit for controlling a rotation speed of the nonmagnetic metal body based on the distance detected by the detection unit; A rotation speed measuring device for measuring a rotation speed of the non-magnetic metal body in a state where the magnetic part is located at the equilibrium position.

[0010]

According to the first aspect of the invention, when the non-magnetic metal body is rotated so as to pass the magnetic field generated by the field portion, an eddy current is generated in the non-magnetic metal body according to Fleming's right-hand rule. When an eddy current flows through the non-magnetic metal body, an electromagnetic force in the same direction as the rotation direction of the non-magnetic metal body is generated in the field portion according to Fleming's left-hand rule. Then, the rotation speed of the non-magnetic metal body is selected so that the electromagnetic force generated in the field portion and the weight of the article to be weighed can be balanced, and the weight of the article to be weighed is measured by measuring the rotation speed. Can be weighed.

According to the second aspect, when the non-magnetic metal body is rotated by the drive unit so as to pass the magnetic field generated by the field part, an eddy current is generated in the non-magnetic metal body by Fleming's right-hand rule. I do. When an eddy current flows through the non-magnetic metal body, an electromagnetic force in the same direction as the rotation direction of the non-magnetic metal body is generated in the field portion according to Fleming's left-hand rule. This electromagnetic force acts in a direction to move the field part in the rotation direction of the non-magnetic metal body. On the other hand, the weight of the article to be weighed loaded on the loading device acts in a direction opposite to the direction of the electromagnetic force generated by the field portion. Then, when the balance between the two forces is lost and the field portion is shifted from a predetermined equilibrium position,
The position detecting section detects the shifted distance, and the control section controls the rotation speed of the non-magnetic metal body to return the field section to the equilibrium position based on the shifted distance detected by the position detecting section. Then, the rotation speed measuring device measures the rotation speed of the non-magnetic metal body. Since the measured rotation speed corresponds to the weight of the article to be weighed, the weight of the article can be weighed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a weighing device according to the present invention will be described with reference to FIGS. In each figure, 7 is a non-magnetic metal body, 8 is a driving unit, 9 is a field unit, 10 is a loading device,
Reference numeral 11 denotes a detection unit, 12 denotes a control unit, and 13 denotes a rotation speed measurement device. FIG. 1 is a perspective view of the weighing device, and FIG. 2 is a cross-sectional view of the weighing device.

As shown in FIGS. 1 and 2, the non-magnetic metal member 7 is a disk 7 made of a non-ferrous metal material such as copper or aluminum (hereinafter, the non-magnetic metal member 7 is referred to as a disk 7).
It is. The disk 7 has a thickness of 3 to 5 mm, and a shaft 14 is fixed at a center position. This shaft 14 is provided with ball bearings 16, 1 built in bearing bases 15, 15.
6 so as to be rotatable.

The drive unit 8 is, for example, a DC motor, and is provided on one of the bearing bases 15 as shown in FIGS. 1 and 2, and the rotating shaft 17 is connected to the shaft 14. The drive unit 8 drives the disk 7 to rotate.

As shown in FIGS. 1 and 2, the field portion 9
A substantially horseshoe-shaped permanent magnet (hereinafter, field part 9 is simply referred to as magnet 9)
That. ). The magnet 9 is fixedly attached to two places of the seesaw lever 18 at a distance from each other with the periphery of the disk 7 sandwiched therebetween. In addition,
As shown in FIG. 2, one magnet 9
The two magnets 9 are attached so that the N pole side of the other magnet 9 is positioned on the S pole side of FIG. And seesaw lever 1
2, ball bearings 19, 19 are attached to the center position of the two magnets 9 as shown in FIG. 2, and are rotatably supported on the shaft 14 via the ball bearings 19, 19.

The loading device 10 has a loading plate 20 shown in FIG. 1, and this loading plate 20 is suspended from the tip of a seesaw lever 18 via a blade 21 and a blade receiver 22. Note that the seesaw lever 18 is provided with a stopper 23 for preventing the inclination thereof from exceeding a predetermined angle. The stopper 23 is provided on a base 24.

The detecting unit 11 includes a photoelectric device 25 and a slit plate.
26. The photoelectric device 25 is, as shown in FIG.
A loading device 10 for the seesaw lever 18 is provided.
Is provided in a state of sandwiching the leading end in a non-contact state,
As shown in FIG. 4, the light projecting element 27 and the light receiving element PH₁as well as
PH_TwoIt consists of The light emitting element 27 emits two lights.
These two lights are generated by the light receiving element PH₁And PH
_Two, Respectively. The slit plate 26 is
As shown in 4, each is provided upside down
It is provided with two wedge-shaped slits 26a and 26b.
Cover the window hole (not shown) provided in the seesaw lever 18.
Installed at That is, the light emitting element 27
The two lights radiated from the respective slits correspond to the respective slits.
G (26a, 26b) is transmitted (or passed) and corresponds to each
Light receiving element PH₁And PH_TwoIt is receiving light. This inspection
The protruding portion 11 is configured such that the seesaw lever 18 is
When ascending, the light receiving element PH₁The amount of light entering the
Optical element PH₁The current flowing through the light-
PH_TwoThe amount of light entering the light receiving element PH_TwoThe flow
Current increases. Conversely, the seesaw lever 18 descends
Then, the light receiving element PH ₁The amount of light entering the
Child PH₁Current flowing through the light-receiving element PH
_TwoThe amount of light entering the light receiving element PH_TwoElectricity flowing through
Flow is reduced.

The control section 12 has an electric circuit shown in FIG. Bridge circuit 2 provided in this electric circuit
8, light receiving elements PH ₁ and PH ₂ are connected, and when the light receiving amount of the light receiving element PH ₁ becomes larger than the light receiving amount of the light receiving element PH ₂ , that is, the seesaw lever 18 shown in FIGS. When rotational movement in the counterclockwise direction (downward direction), becomes larger than the current the current flowing through the light-receiving element PH ₁ shown in FIG. 3 through the light receiving element PH _2, photoelectric conversion voltage generated terminal a, the b are equilibrium compared to rise as in the (PH ₁ and PH state ₂ to flow current are equal). The photoelectric conversion voltages generated at the terminals a and b are input to the preamplifier 29. When the seesaw lever 18 moves downward (or upward) and the photoelectric conversion voltage of the terminals a and b rises (or falls), the preamplifier 29 moves the seesaw lever 1
The output voltage of the preamplifier 29 is increased (or decreased) so that the output voltage 8 returns to the predetermined equilibrium position shown in FIG. Then, the voltage output from the preamplifier 29 is supplied to the main amplifier 30. The main amplifier 30 raises the signal voltage supplied from the preamplifier 29 to a level necessary for driving the driving unit 8, and drives the driving unit 8 with the amplified signal voltage. In this case, the signal voltage supplied to the drive unit 8 rises (or falls) as compared with the voltage in the above-described equilibrium state, and the rotation speed of the rotating shaft 17 of the drive unit 8 increases in proportion thereto. (Or decelerate).

[0019] Conversely, when the seesaw lever 18 shown in FIGS. 1 and 4 is rotated and moved in a clockwise direction (upward), less than the current the current flowing through the light-receiving element PH ₁ shown in FIG. 3 through the light receiving element PH ₂ That is, the photoelectric conversion voltages generated at the terminals a and b are lower than those in the state of equilibrium. That is, the operation is performed as described in the parentheses. That is, since the signal voltage supplied to the driving unit 8 is lower than the voltage in the above-mentioned equilibrium state, the rotation speed of the rotating shaft 17 of the driving unit 8 is reduced in proportion thereto.

The rotational speed measuring device 13 is provided with a rotary generator 31 such as a DC generator. This rotary generator 31
(Not shown) is directly connected to the rotation shaft 17 of the drive unit 8. The rotary generator 31 generates an electric signal corresponding to the rotation speed of the drive unit 8, and this electric signal is
Are input to a display 34 via an amplifier (buffer amplifier) 32 and an A / D converter 33 shown in FIG. The display 34 displays the weight based on the input signal.

A balance weight 35 is provided at the right end of the seesaw lever 18 shown in FIG. The balance weight 35 is used to position the seesaw lever 18 at a predetermined equilibrium position in a state where the disk 7 rotates at a predetermined rotation speed and no articles to be weighed are placed on the platen 20. It is fixed at an appropriate position with an adjusting screw 36.

Next, the operation of the weighing device having the above configuration will be described. Now, when the power of this apparatus is turned on in a state where the articles to be weighed are not placed on the platen 20, the drive unit 8 drives the disk 7 to rotate, and the disk 7 shown in FIG. It rotates at a predetermined rotation speed ω ₀ . Then, the electromagnetic force F ₃ to the two pairs of magnets 9,9 When the disc 7 rotates is generated, the electromagnetic force F ₃ generated in this two sets of magnets 9, seesaw lever 18
Is to be rotated in the direction of arrow 37 in FIG. 1 with a moment of 2F ₃ · r ₁ . r ₁ is the distance from the magnet 9 to the center of the disk 7. On the other hand, the seesaw lever 18 has a bias of the center of gravity of the seesaw lever 18 and a balance weight 3.
5. Set the seesaw lever 18 to F
_An attempt is made to rotate in the direction of arrow 38 in FIG. 1 with a moment of ₄ · r ₂ . r ₂ is the distance from the hanging position of the plate 20 to the center of the disk 7. Here, 2F ₃ · r ₁ =
Since the balance weight 35 is attached so as to be F ₄ · r ₂ , the seesaw lever 18 is stopped at a predetermined equilibrium position shown in FIG. When the drive unit 8 rotates in this equilibrium state, the weight displayed on the display 34 is zero.

Next, as shown in FIG. 1, when an object 39 having a certain weight WG is placed on the plate 20, the moment of WG · r _{2 in} the counterclockwise direction (downward) is applied to the seesaw lever 18.
The seesaw lever 18
Moves counterclockwise. When the seesaw lever 18 is moved in a counterclockwise direction, as described with reference to FIG. 4, to increase the amount of light incident on the light receiving element PH _1, the terminal shown in FIG. 3 a, the voltage between b is increased, The rotation speed of the drive unit 8 increases. When the rotational speed of the drive unit 8 is increased electromagnetic force F ₃ is increased, the moment for moving the seesaw lever 18 in the clockwise direction increases. Thereby, the seesaw lever 18
Is pushed back clockwise (upward), but when the seesaw lever 18 returns to the predetermined equilibrium position shown in FIG. 4, the rotation speed of the drive unit 8 stops increasing and becomes constant, and the electromagnetic force F ₃ Is also a constant force. In this state, the total moment of WG · r ₂ and F ₄ · r ₂ generated by the article 39 to be weighed becomes equal to 2F ₃ · r ₁ , and the seesaw lever 18 is in an equilibrium state. Then, at this time, a voltage based on the rotation speed of the drive unit 8 is output by the rotary generator 31, and the weight corresponding to the output voltage is displayed on the display 34.

The bearings 16 and 19 supporting the disk 7 and the seesaw lever 18 generate kinetic frictional resistance when the disk 7 and the like rotate or move. However, since the disk 7 is constantly rotating, the kinetic frictional resistance is reduced. Hardly fluctuates and therefore
There is almost no effect on weighing accuracy.

Next, the rotation of the disk 7 causes the magnet 9 to rotate.
In addition to the description of the principle of generating a rotational moment, it will be proved that the rotational moment acting on the magnet 9 increases as the rotational speed of the disk 7 increases. Since the disk 7 is irradiated with the magnetic flux generated by the two sets of magnets 9, when the disk 7 rotates, an induced voltage is generated by Fleming's right-hand rule, and the induced voltage causes an eddy current (induced current) in the disk 7. ) Occurs. The induced voltage e is represented by e = dφ / dt (1). Here, dφ is the amount of change in the magnetic flux, and dt is the time required for the change in the magnetic flux. When this equation (1) is expressed by the magnetic flux density B of the magnetic field generated by the magnet 9, the length L of the flow path through which the eddy current I flows, and the moving speed v of this flow path, e = dφ / dt = B · L · v (2) Therefore, the eddy current I can be obtained by I = e / R (Ohm's law) (3). R is the resistance value of the flow path of the disk 7 through which the eddy current flows. Then, when the equation (2) is substituted into the equation (3), I = BＩL v / R (4)

On the other hand, when the disk 7 which generated eddy currents are rotated, the electromagnetic force F ₃ for urging the magnet 9 in the rotational direction of the disk 7 is caused by the Fleming's left-hand rule. This electromagnetic force F
₃ is represented by F ₃ = B · I · L (5) Here, B is the magnetic flux density of the magnet 9, I is the eddy current, and L is the length of the eddy current flow path in the magnetic field. Here, when the equation (4) is substituted into the equation (5), F ₃ = B ² · L ² · v / R (6), and B ² · L ² / R is constant. When this value is set to K, the equation (6) is as follows: F ₃ = K · v = K · r ₁ · ω ₀ = K · r ₁ · 2πN (7) Here, r ₁ is the radius of rotation of the magnet 9 as shown in FIG. 1, and ω ₀ is the angular velocity of the disk 7. That is,
There is a relationship v = r ₁ · ω ₀ . N is the rotation speed of the disk 7 and has a relationship of ω ₀ = 2πN.

Therefore, the electromagnetic force F ₃ acting on the magnet 9 is
According to the equation (7), it increases or decreases in proportion to the rotational speed N of the disk 7. That is, as described in the above embodiment, the electromagnetic force F
₃ increases or decreases the rotational moment acting on the seesaw lever 18 to balance the seesaw lever 18 to a predetermined equilibrium position, and measures the rotation speed of the disk 7 in this equilibrium state to weigh the article to be weighed. be able to.

However, in the above embodiment, a DC motor was used as the drive unit 8 and the rotation speed of the DC motor was detected by the rotary generator 31. However, a pulse motor was provided instead of the DC motor, and the rotary generator was used. A digital control system can be provided by providing a pulse generator instead of 31.
In this case, the A / D converter 33 and the preamplifier 32 shown in FIG. 3 are not required, but a pulse control device needs to be provided instead of the main amplifier 30. This pulse control device controls the number of pulses (frequency) based on the output signal of the preamplifier 29 to control the number of revolutions of the pulse motor.

In the above embodiment, the rotary generator 3
A pulse generator is provided instead of 1, and the pulse generator generates pulses at a period proportional to the rotation speed of the drive unit 8, and the number of pulses per time generated by the pulse generator is counted by a pulse counter. The display unit may be configured to convert the number of pulses per time into a weight and display the weight.

Although the magnet 9 is a permanent magnet, it may be an electromagnet.

[0031]

According to the measuring device of the present invention, when an eddy current flows through a non-magnetic metal body, copper loss occurs, and heat corresponding to the copper loss raises the temperature of the non-magnetic metal body and the field portion. However, since the iron loss does not occur in the non-magnetic metal body, it is possible to prevent the temperature of the field portion from increasing due to the amount of heat corresponding to the iron loss. As a result, as compared with the conventional force generating mechanism shown in FIG. 5 (the conventional one generates the copper loss and the iron loss), it is possible to suppress the temperature rise of the field part to be low. In addition, the amount of change in the magnetic flux density of the magnetic field generated by the field part can be made smaller than in the related art. As a result, FIG.
There is an effect that the measuring accuracy can be improved as compared with the conventional measuring device using the force generating mechanism shown in FIG.

If a magnetic sensor for compensating for variations in magnetic flux density and a device associated therewith are not provided in order to obtain a desired measurement accuracy, the cost required for the magnetic sensor and the device accompanying it is reduced. There is an effect that it can be reduced.

There is also an effect that the degree of compensation of the compensating device required to obtain a predetermined weighing accuracy can be reduced as compared with the conventional force generating mechanism shown in FIG.

[Brief description of the drawings]

FIG. 1 is a perspective view of a weighing device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the weighing device of the embodiment.

FIG. 3 is a diagram showing an electric circuit of the weighing device of the embodiment.

FIG. 4 is a perspective view showing a detection unit of the embodiment.

FIG. 5 is a diagram showing a force generating mechanism used in a conventional weighing device.

[Explanation of symbols]

 7 disk 8 drive unit 9 magnet 10 loading device 11 detection unit 12 control unit 13 rotation speed measurement device

Claims (2)

(57) [Claims] 1. A non-magnetic metal body is rotated so as to pass a constant magnetic field generated by a field part, so that the field part generates a force. A weighing device configured to measure the weight of the article to be weighed by measuring the rotation speed of the nonmagnetic metal body capable of balancing the weight of the article to be weighed. 2. A non-magnetic metal body driven and rotated by a drive unit, and a field irradiating the non-magnetic metal body with a constant magnetic flux and movably provided in a substantially tangential direction of rotation of the non-magnetic metal body. A loading device for placing the article to be weighed, wherein the weight of the article to be weighed is applied to the field section in a direction substantially opposite to the direction of the force generated by the field section; and A detection unit that detects a distance moved from a predetermined equilibrium position, a control unit that controls a rotation speed of the nonmagnetic metal body based on the distance detected by the detection unit, and a field unit that moves to the equilibrium position. A rotating speed measuring device for measuring a rotating speed of the non-magnetic metal body in a positioned state.