JPH027005B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a force generation mechanism used, for example, in a weighing machine, and particularly to a force generation mechanism that applies a force to a coil placed in a constant magnetic field by passing a current through the coil. This invention relates to a force generation mechanism that generates force.

[Conventional technology and problems]

FIG. 4 schematically shows a conventional force generation mechanism, which includes a main yoke 41, a center yoke 42,
It consists of a permanent magnet 43 and a coil 45 disposed in an air gap 44. It is assumed that the coil 45 is supported movably in the direction of arrow F. Permanent magnet 43
A constant magnetic flux flows through the center yoke 42, the air gap 44, and the main yoke 41 as shown by the solid arrow _B0 .

When a current I is passed through the coil 45, a force F = B ₀ Il is generated in the direction of the arrow F in a portion of the conductor length l (however, B ₀ is the magnetic flux density), and the force F and the current I are proportional. Therefore, force F is measured from the value of current I using this proportional relationship.

However, strictly speaking, force F and current I are not proportional. That is, when a current I is passed through the coil 45,
This itself generates a magnetic flux ΔB as shown by the dotted line. This magnetic flux △B is proportional to the current I, so △
If B=kI (k is a proportionality constant), then the magnetic flux density in the air gap 44 when the current I flows through the coil 45 becomes B=B ₀ +kI or B ₀ −kI. Therefore, strictly speaking, the force acting on the coil 45 is F=(B ₀ ±kI)Il.

In other words, F=B ₀ lI±klI ² , and 2 of the current I
A term proportional to the power appears, so it cannot be said that the force F is linearly proportional to the current I.

Therefore, a problem arises in that, for example, in a weighing machine, accurate weighing cannot be performed using the measuring method using this force generating mechanism.

[Object and structure of the invention]

The present invention was made in view of the above problems, and an object of the present invention is to provide a force generation mechanism that can measure force more precisely than before. According to the present invention, in the above configuration, a magnetic sensor is disposed close to the coil in the magnetic field, the current flowing through the coil is used as an analog input, and the output of the magnetic sensor is spanned. This is achieved by a force generating mechanism characterized in that the magnitude of the force is measured by the digital output of an analog/digital converter as an input.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS A ram type weighing machine according to an embodiment of the present invention will be described below with reference to the drawings.

In the figure, the ramrod type weighing machine is indicated as 1 as a whole, and the ramrod, so-called pole 2, is supported at a fulcrum 4 on one support 3a of a frame 3, and a loading plate 6 is suspended via a fulcrum 5 at one end thereof. It's hanging. Also,
At the other end, the actuating rod 8 of the load-measuring actuator 7 is pivotally mounted.

In addition to the above-mentioned actuating rod 8, the load measuring actuator 7 includes a bobbin 9 and a coil 1 wound around the bobbin 9.
0, permanent magnet 11, yoke 12a, 12b, 12
c and the yoke 1 close to the coil 10 in the gap g.
2b, the magnetic flux _B0 from the permanent magnet 11 crosses the coil 10 as shown by the solid arrow, and then passes through the yokes 12a, 12.
b, 12c. When a direct current is applied to the coil 10 in a predetermined direction, a magnetic flux △B as shown by the dotted line flows through the coil 10, but the interaction between this current and the magnetic flux in the air gap g generates a downward force F, causing the operation. Pull the rod 8 downward as shown by the arrow. By controlling the magnitude of the current applied to the coil 10, this force F is adjusted and balanced with the weight of the object to be measured placed on the placing plate 6.

As shown in FIG. 3, one end of the coil 10 is connected to a variable DC power supply 21, and the other end is connected to a resistor R and an analog input terminal 22 of an analog/digital converter 22.
connected to a. The magnetic sensor 20 is, for example, a Hall element, and its output terminal is connected to the span input terminal 22b of the analog/digital converter 22 via an amplifier 23. Span input terminal 22b
The analog input terminal 22
The digital conversion ratio of the analog input supplied to a is controlled. The output terminal 22c of the analog/digital converter 22 is connected to, for example, a weight display, although not shown. Note that it is assumed that a DC constant current source is connected to the magnetic sensor 20 even though it is not shown in the drawings.

A stopper mounting block 13 is fixed on the other support column 3b of the frame 3, and the tip of the rod 2 is inserted through a through hole 13a formed in the stopper mounting block 13.
The detected portion (metal) 14 formed at the tip faces the proximity switch 15 at a predetermined distance when the rod 2 is in a balanced state as shown.

Screw holes 13b and 13c are formed above and below the through hole 13a of the stopper mounting block 13, and these are provided with stopper screws 16 and 17, respectively.
is screwed on. The displacement width A of the rod 2 is determined by adjusting the screws 16 and 17. That is, the upper screw 16 determines the upper limit of rotation of the rod 2,
The lower limit of rotation of the rod 2 is determined by the screw 17 on the lower side. The displacement width A, or the upper and lower limits of rotation, are the characteristics of the proximity switch 15, and this switch 15 and rod 2.
It is determined by taking into account the distance between the fulcrum and the detected part 14, the distance between the fulcrums 4 and 5, the distance between the fulcrum 4 and the actuating rod 8, and the like.

Although the embodiment of the present invention is configured as described above,
Next, this action, effect, etc. will be explained.

Now, if the object to be measured is placed on the mounting plate 6, the rod 2 rotates clockwise in the figure around the fulcrum 4. Along with this, coil 1 of actuator 7
0 from the variable DC power supply 21, and a downward force F acts on the actuating rod 8. That is, the rod 2 is rotated counterclockwise around the fulcrum 4.

When the object to be measured is placed on the mounting plate 6, the rod 2 rotates clockwise, but the tip of the rod 2 collides with the lower end of the stopper screw 16, preventing further upward rotation. It will be done. Proximity switch 15 detects that rod 2 is above the balance position, which causes the current in coil 10 of actuator 7 to increase. The force F acting on the actuating rod 8 increases, and the rotational force of the rod 2 in the counterclockwise direction increases.
That is, the rod 2 increases the rotational force toward the balance position.

When the rod 2 rotates downward beyond the balance position, the proximity switch 15 detects this,
The current flowing through the coil 10 of the actuator 7 is reduced. In this way, when the rod 2 assumes a balanced state as shown in the figure, the current flowing through the coil 10 is kept at a constant value. Conventionally, the weight of the object placed on the mounting plate 6 was directly measured from this value, but according to the present invention, the current value is converted into digital data over a span corresponding to the output of the magnetic sensor 20. In other words, when the magnetic flux density ΔB due to the current flowing through the coil 10 is opposite in direction to the magnetic flux density B ₀ of the permanent magnet 11, the actual magnetic flux density B is smaller than the magnetic flux density B ₀ , so this is the magnetic sensor. 20, and the span is reduced by this amount. Therefore, even if the current is constant, a smaller digital output is obtained from the transducer 22 than if the magnetic flux density were B ₀ , and this is displayed as a weight on the display. In addition, if the magnetic flux density ΔB due to the current flowing through the coil 10 is in the same direction as the magnetic flux density B ₀ of the permanent magnet 11, the actual magnetic flux density B will be larger than the magnetic flux density B ₀ , so this is the magnetic sensor. 20, and the span is increased by this amount. Therefore, even when the current is constant, a larger digital output is obtained from the converter 22 than if the magnetic flux density were B ₀ , and this is displayed as a weight on the display.

That is, according to this embodiment, the force is measured by digitally converting the current value flowing through the coil 10, but rather than always converting at a constant rate, the actual magnetic flux density in the air gap g is measured. B is detected and converted with a span corresponding to this. Therefore,
The force acting on the coil 10 can be precisely measured.

The embodiments of the present invention have been described above, but of course the present invention is not limited thereto, and various modifications can be made based on the technical idea of the present invention.

For example, in the above embodiment, the proximity switch 15 was used to detect the position of the rod 2, but a differential transformer or a photoelectric switch may be used instead.

Further, in the above embodiment, the mounting plate 6 suspended from the fulcrum 5 was used to load the weight of the object to be measured on the pole 2, but the load may be applied via another mechanism.

Furthermore, in the above embodiment, the shapes of the yokes 12a, 12b, and 12c in the load actuator 7 are different from those shown in FIG. 1, which shows the conventional example, but of course,
The shape is not limited to this, and may be similar to the conventional example, for example.

Further, in the above embodiment, the permanent magnet 11 was used to provide a constant magnetic field, but a DC electromagnet may be used instead. Further, in the above embodiments, a Hall element was used as the magnetic sensor, but the present invention is not limited to this, and other centers such as a magnetoresistive element may be used.

Further, in the above embodiment, the actuator 7 was applied to the weighing machine 1, but it can also be applied to other devices.

〔Effect of the invention〕

As described above, according to the force generation mechanism of the present invention, the magnitude of the acting force acting on the coil can be accurately detected.

[Brief explanation of drawings]

Fig. 1 is a side view of a ram-type weighing machine according to an embodiment of the present invention, Fig. 2 is a front view in the - line direction in Fig. 1, and Fig. 3 is a partially enlarged view showing the electrical wiring of the main part in Fig. 1. It is. FIG. 4 is a schematic diagram of a conventional force generating mechanism. In the figure, 7...load measuring actuator, 10...coil, 11...permanent magnet, 12a, 1
2b, 12c... Yoke, 20... Magnetic sensor, 2
2...Analog/digital converter.

Claims (1)

[Claims] 1. In a force generating mechanism that generates force in a coil placed in a constant magnetic field by passing a current through the coil, a magnetic sensor is disposed close to the coil in the magnetic field, and the coil is placed in the magnetic field. The force generating mechanism is characterized in that the magnitude of the force is measured by the digital output of an analog/digital converter which uses the current flowing through the magnetic sensor as an analog input and the output of the magnetic sensor as a span input.