JPH095147A - Electronic balance - Google Patents

Abstract

PURPOSE: To enable detecting of a correct weighed value with a smaller magnetic circuit by making a current for deciding the weighed value flow to a coil arranged at the central part of a uniform magnetic field of a magnetic circuit and the remaining current to the other coil. CONSTITUTION: An integral current signal ip of displacements of a lever 2 is supplied to a coil 5 and a proportional and differential 12 current signal iPD of displacements of the lever 2 is supplied to a coil 6. During the period, a current i1 is taken into a microcomputer 15 and a load weighed value is determined. Since located at the center of a uniform magnetic field in a magnetic field space M produced by a magnetic circuit 7, the coil 5 through which the current i1 flows will not be diverted from the uniform magnetic field even when the lever 2 is somewhat displaced. In addition, the current iPD is down to zero when a system is balanced and an electromagnetic force determined by a product of the size of the current iPD and a magnetic field is also down to zero. Hence, there is no error in a weighed value determined by the current i1 even when the coil 6 is outside the range of the uniform magnetic field. This enables the obtaining of a highly accurate weighed value with a smaller circuit 7 despite the use of the two coils 5 and 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic balance, and more particularly to an electromagnetic force balance type electronic balance.

[0002]

2. Description of the Related Art In an electronic balance of the electromagnetic force balance type,
Generally, it is generated by fixing a coil to a movable part such as a lever that is displaced by the load of the load to be measured, arranging the coil in a magnetic field created by a magnetic circuit mainly composed of a permanent magnet, and passing an electric current through it. The electromagnetic force is opposed to the load to be measured, the current flowing through the coil is controlled so that they are balanced, and the magnitude of the load to be measured is obtained from the coil current in the balanced state.

The current flowing through the coil is feedback-controlled so that the displacement of the movable part is detected by a displacement detector and a current according to the detection result flows through the coil. That is, the coil current is controlled by the servo mechanism that maintains the displacement of the movable portion at zero. Here, the displacement detection result is usually fed back to the coil as a current signal after PID (proportional / integral / derivative) calculation or PD (proportional / derivative) calculation, and constants for each calculation are calculated. It is considered that the responsiveness and stability of the system can be secured by appropriately setting. Further, the current flowing in the coil is converted into a voltage signal by passing through a precision resistor, for example, and is digitized by an AD converter every moment,
The metric value to be displayed is determined by performing an averaging operation or an operation such as multiplying by a span coefficient by a microcomputer.

By the way, in such an electronic balance, the magnitude of the load to be measured, that is, the measured value needs to be accurately calculated only when the system is stable to some extent, and therefore the measured value is determined. As for the signal required for the above, for the one having the PID calculation function, only the integral calculation result, or the proportional and integral calculation results are sufficient, and the remaining proportional and derivative or the differential calculation results are not required. In particular, the differential calculation result is mainly intended to improve the responsiveness of the system at the time of transient response, and it is also necessary to digitize the result and use it for calculation of the measured value by measuring the S / N of the measured value.
It is rather not preferable for improving Similarly, in the case of a device having a PD calculation function, it is sufficient to use only the proportional calculation result to determine the weighing value.

For this reason, conventionally, two coils are arranged in a magnetic field so as to be double-wound, and one of the coils is a current signal based on a calculation result used for determining a weighing value, that is, an integration calculation result. Or the result of proportional / integral calculation, or a current based on the result of proportional calculation is applied, and only that current is converted into a voltage signal and digitized, and introduced into the microcomputer to be used for determination of the measured value, while remaining calculation is performed in the other coil. By taking a measure to flow a current signal based on the result, that is, a proportional / differential calculation result or a differential calculation result, a highly accurate electronic balance with a high S / N is obtained.

[0006]

By the way, in an electromagnetic force balance type balance, the coil is placed in a uniform magnetic field,
It is needless to say that a signal corresponding to the load to be measured cannot be obtained and an accurate measured value cannot be obtained unless it is moved out of the uniform magnetic field area even if it moves for some reason. When one coil is double-wound and placed in the magnetic field, it is necessary to widen the region of the uniform magnetic field in the radial direction of the coil, as compared with a normal electronic balance in which one coil is placed in the magnetic field. Here, the magnetic circuit that creates this kind of magnetic field is composed of a permanent magnet and a pole piece, but a large permanent magnet and a pole piece are required to widen the area of the uniform magnetic field, which not only causes a cost increase. However, there is a problem that the balance becomes larger.

An object of the present invention is to dispose two coils in a magnetic field created by a magnetic circuit, and to calculate a current based on a calculation result of proportional / integral / derivative or proportional / differential calculation result, which is used for determining a measured value. In an electronic balance configured to separately flow a signal and a current signal based on the remaining calculation result in these two coils, an electronic balance that can obtain an accurate weighing value without using a large magnetic circuit To provide.

[0008]

In order to achieve the above object, an electronic balance of the present invention has a coil fixed to a movable part which is displaced by a load to be measured, and the coil is placed in a magnetic field created by a magnetic circuit. Along with the placement, the displacement detector detects the displacement of the movable part, and the detected signal is proportional / integral /
By performing differential operation (or proportional / differential operation) and then passing it as a current signal through the coil, the load to be measured and the electromagnetic force are balanced, and in the balance state, the measured value is determined from the current flowing through the coil. -Of the integral / derivative operation (or proportional / derivative operation), only the integrated or the signal after the proportional / integral operation (or the signal after the proportional operation) is used for determining the weighing value, and the two coils 5 are placed in the magnetic field. , 6 are provided so that the signal used for determining the weighing value and the remaining signal are separately passed through the respective coils, and the magnetic circuit 7 is provided with the coil 5 through which the signal used for determining the weighing value is passed. It is characterized in that it is arranged at the central portion of the uniform magnetic field in the magnetic field to be formed, and the other coil 6 is arranged either above or below the coil 5 in the axial direction. See Figure 1).

In the present invention, the displacement detection signal is proportional to
Electronic balances that perform integral / derivative calculations include those that use the integral calculation result or the proportional and integral calculation results to determine the weighing value, as well as the electronic balance that proportionally and differentially calculates the displacement detection signal. Include those that use the proportional calculation result for determination of the measured value.

[0010]

In order to obtain an accurate measured value, it is only the coil 5 to which a current signal based on the calculation result used for determination of the measured value is applied that needs to be placed in the uniform magnetic field. The coil 6 through which the signal is passed does not affect the measured value even if it is arranged in a magnetic field that is somewhat inhomogeneous.
The present invention has been made paying attention to this point, and the coil 5 to which a current signal based on the calculation result used for determination of the measured value is made to flow is placed at the center of the uniform magnetic field in the magnetic field created by the magnetic circuit 7, By placing the other coil 6 either above or below it or both, it is possible to obtain an accurate measured value by using the small magnetic circuit 7 even though it is an electronic balance having a high S / N.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an overall configuration diagram showing a mechanism diagram of an embodiment of the present invention and a block diagram showing an electrical circuit configuration together.

A plate 3 for applying a load W to be measured is provided at one end of a lever 2 rotatable about a fulcrum 1. The lever 2 has a first coil 5 and a second coil 5 which are wound in a cylindrical shape around a common vertical axis at a position opposite to the tray 3 with the fulcrum 1 interposed therebetween, with a supporting member 4 interposed therebetween. The coil 6 of is fixed. Here, the second coil 6
Is the two coils 6 divided above and below the first coil 5.
a and 6b, and the two coils 6a and 6b are connected to each other by a conductor 6c to substantially form one coil. The first and second coils 5 and 6 are placed in the magnetic field formed by the magnetic circuit 7.

The magnetic circuit 7 includes two permanent magnets 71, 72 arranged so that the same poles face each other along the vertical axis as shown in the figure, and a columnar or disk-shaped pole piece 73 arranged between them. , And a cylindrical yoke 74 that surrounds them, and forms a static magnetic field in a cylindrical gap between the outer peripheral surface of the pole piece 73 and the inner peripheral surface of the yoke 74. First and second coils 5 described above
And 6 are arranged in the cylindrical magnetic field space M in a wound state so as to be orthogonal to the direction of the magnetic field,
The intensity distribution of the magnetic field in the magnetic field space M and the coils 5, 6 (6
The positional relationship of a, 6b) is as shown in FIG. That is, the magnetic field generated by the magnetic circuit 7 is centered on a line ab passing through the center between the two permanent magnets 71 and 72, in other words, passing through the vertical center of the pole piece 73, as shown in the graph of FIG. The predetermined area in the vertical direction has a uniform strength, but the magnetic field strength decreases as the distance from the uniform magnetic field increases and decreases. The vertical position of the first coil 5 is centered on the line a-b and is entirely within the uniform magnetic field region. Further, the vertical dimension of the first coil 5 is shorter than the vertical distance of the uniform magnetic field region, and thus the uniform magnetic field region extends above and below the first coil 5 by a predetermined distance. on the other hand,
Two upper and lower coils 6a and 6b which form the second coil 6.
Are arranged such that some of them are out of the uniform magnetic field region.

A displacement detector 8 is provided at the tip of the lever 2 opposite to the mounting end of the tray 3, and the displacement detector 8 detects the displacement of the lever 2. The output of the displacement detector 8 is amplified by a preamplifier 10 and then introduced into an I (integration) operation processing amplifier 11 and a PD (proportional / derivative) operation processing amplifier 12. The I arithmetic processing amplifier 11 performs integral calculation on the displacement detection value of the lever 2 by the displacement detector 10, and then outputs a current signal i _I having a magnitude corresponding to the calculation result, and the PD arithmetic processing amplifier 12
Similarly, after performing a proportional calculation and a differential calculation on the displacement detection result from the displacement detector 10, outputs a current signal i _PD having a magnitude corresponding to the calculation result. The output current i _I from the I arithmetic processing amplifier 11 is passed through the first coil 5, and the output current i _PD from the PD arithmetic processing amplifier 12 is passed through the second coil 6.

The current i _I flowing through the first coil 5 is converted into a voltage signal by the resistor 13 and then converted into a voltage signal by the AD converter 1.
It is digitized by 4, and is loaded into the microcomputer 15 every moment as load data for determining the measured value.
In the microcomputer 15, this AD converter 14
The load data from 1 is averaged, and the magnitude of the load W to be measured is obtained by a known calculation such as multiplication by a span coefficient, and displayed on the display 16 as a measured value.

In the above-described embodiment of the present invention, when the load W to be measured acts on the dish 3, the lever 2 is rotationally displaced, the displacement amount is detected by the displacement detector 8, and the displacement detection result is for I. First integrated by the arithmetic processing amplifier 11
Is supplied as a current signal i _I to the coil 5 of
Secondly proportional and differentiated by the PD processing amplifier 12
Is supplied to the coil 6 as a current signal i _PD , and the electromagnetic force generated by each of these currents flowing in each coil acts on the lever 2 to balance the lever 2 against the load W to be measured. Then, during this period, the magnitude of the current i _I flowing through the first coil 5 is loaded into the microcomputer 15 as load data, and the measured value is determined. At this time,
Since the first coil 5 through which the current i _I used for determining the measured value flows is arranged at the center of the uniform magnetic field region in the magnetic field space M created by the magnetic circuit 7, even if the lever 2 is slightly displaced. The first coil 5 does not deviate from the uniform magnetic field region, and the current i _PD flowing through the second coil 6 becomes 0 when the system is in a balanced state, and the current i _PD flowing through the second coil 6 is i. Current i generated by _PD flowing
_{Since the} electromagnetic force determined by the product of the _PD size and the magnetic field is also 0, even if the second coil 6 is outside the uniform magnetic field region,
There is no error in the measured value determined based on the current i _I described above.

According to this embodiment of the present invention, the magnetic circuit 7 only needs to form a magnetic field such that only the first coil 5 is within the uniform magnetic field region.
Despite the provision of 6, all the feedback current may be of the same size as the magnetic circuit of a conventional electronic balance in which one coil is made to flow.

In the above embodiment, the second coil 6 in which the current i _PD which is not used for determination of the measured value is flowed is vertically arranged.
However, the present invention is not limited to this, and the second coil is not divided and the first coil is placed in the center of the uniform magnetic field region.
It may be arranged above or below the coil 5.

Further, in the above embodiment, the displacement detection result by the displacement detector 8 is calculated by P (proportional), I (integral) and D (differential) operations, and only the I (integral) result is the measured value. Although it is provided for the determination, it can be configured to provide the calculation result of P and I among the PID calculation results for the determination of the measured value. In this case, the first coil 5 placed at the center of the uniform magnetic field region It suffices to pass a current signal based on the calculation result of P and I.

Further, the present invention can be applied to an electronic balance of the type in which the P (proportional) and D (differential) operations are performed on the displacement detection result by the displacement detector 8 to form a feedback current. In this case, a current corresponding to the P calculation result may be supplied to the first coil 5 and used for determining the measured value at the same time.

[0021]

As described above, according to the present invention,
Displacement detection that determines the feedback current in an electronic balance equipped with a servo mechanism that causes a feedback current to flow through a coil in a magnetic field created by a magnetic circuit to balance the system and determine the measured value from the magnitude of the current required for the balancing. I of the PID calculation result of the value or the PD calculation result
Alternatively, P and I, or only the current based on the calculation result of P is used for determining the measured value, and two types of coils are provided in the magnetic field, one of which is the center of the uniform magnetic field in the magnetic field created by the magnetic circuit. The coil is placed in the central part of the uniform magnetic field, and the remaining current is applied to the other coil by arranging the other part above and below the other part or both. Since it is configured, by providing two types of coils in the magnetic field and passing a current for determining the measured value in one side, while obtaining a highly accurate electronic balance with high S / N,
A magnetic circuit equivalent to that of a normal electronic balance using one coil can be used, and cost reduction and miniaturization can be achieved as compared with the case where the coil is double wound.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing a mechanism diagram of an embodiment of the present invention and a block diagram showing an electrical circuit configuration together.

FIG. 2 is an explanatory view of the positions of the first coil 5 and the second coil in the magnetic field space M.

[Explanation of symbols]

 1 fulcrum 2 lever 3 plate 5 first coil 6 second coil 7 magnetic circuit 71, 72 permanent magnet 73 pole piece 74 yoke 8 displacement detector 11 for I (integration) processing amplifier 12 for PD (proportional / derivative) Operation processing amplifier 13 Resistance 14 A-D converter 15 Microcomputer

Claims (1)

[Claims] 1. A coil is fixed to a movable part that is displaced by a load to be measured, the coil is placed in a magnetic field created by a magnetic circuit, and the displacement of the movable part is detected by a displacement detector, and the detection is performed. Proportional / integral / derivative operation or proportional / integral operation of the signal is performed, and then the current is applied as a current signal to the coil to balance the measured load and the electromagnetic force. In the balance for determining, the above proportional / integral / derivative operation, or among the proportional / derivative operations, the integral or the signal after the proportional / integral operation, or only the signal after the proportional operation is provided for determining the weighing value. In addition, two coils are provided in the magnetic field, and the signals used for determining the measured value and the remaining signals are separately supplied to the respective coils. The coil through which the signal used for determining the value flows is arranged in the central portion of the uniform magnetic field in the magnetic field formed by the magnetic circuit, and the other coil is arranged either above or below the axial direction of the coil, or both. An electronic balance characterized in that