JP3104380B2 - Electronic balance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic force balance.

[0002]

2. Description of the Related Art An electromagnetic force generated by flowing a current through a force coil provided in a magnetic field is balanced with a load to be measured, and a load to be measured is obtained from a current value required to obtain the equilibrium state. In the balance of the formula, an analog servo mechanism is usually used to detect the displacement of the load receiving portion and control the current flowing through the force coil so that the displacement becomes zero.

When an analog servo mechanism is used, the integration of the circuit has a certain limit, and there are many adjustment points of the circuit, so that it is difficult to make the performance of the product as a balance uniform. In addition, there is a limit in stability of a display value with respect to disturbance.

In view of such a point, the present inventor has already
A pulse current is caused to flow through the force coil, the displacement of the load receiving portion is taken in as a digital signal, and after performing a digital PID calculation, the duty of the pulse current to be passed through the force coil is determined from the calculation result. (Japanese Unexamined Patent Publication No. 3-63)
No. 526).

[0005]

By the way, in the above proposal, a plurality of types of force coil currents having different current values are produced, and pulse duty data is supplied to each of them, so that a difference between the current value (peak value) and the duty is obtained. A plurality of types of pulse currents are supplied to the force coil, and weighted addition is performed to improve the resolution.

In this method, even if the resolution (number of bits) of each pulse current generating means is limited, the total resolution is the sum of these, and the number of pulse current generating means and the division number of pulse duty data There is an advantage that there is no limit to the improvement of the resolution by increasing the number.

However, this method is disadvantageous in terms of cost in applications that do not require much accuracy. An object of the present invention is to supply a pulse current to a force coil and control an electromagnetic force balancing mechanism by digital computation.
An object of the present invention is to provide a balance capable of improving resolution without increasing cost.

[0008]

According to the present invention, a pulse current having a duty determined by a smaller number of bits (resolution) than the display resolution of the balance is supplied to a force coil. The duty of the pulse current is forcibly changed at a predetermined ratio within a predetermined time.

[0009]

With the pulse current based on the number of bits smaller than the display resolution, which is the ratio between the weighing capacity of the balance and the minimum display, the resolution required for the electronic balance will not be reached. , The current flowing through the force coil differs during that time compared to the case where this change is not applied, and the resolution improves in a pseudo manner.

For example, if the cycle of the pulse current is 2 ms, 100 pulses flow through the force coil for 0.2 seconds. If the duty is increased, for example, by one pulse during this time, the pulse duty is reduced to 1/1 on average.
This is equivalent to the case of increasing by 00, and the resolution can be substantially improved by two digits.

When a plurality of pulses give a duty change within a certain period of time, the pulses giving the change are dispersed evenly among the pulses generated between them, so that the variation of the generated electromagnetic force is small. It is desirable, and filtering becomes easy.

[0012]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. The balance mechanism 1 is a known load detecting mechanism of an electromagnetic force balance type. The force coil 13 is placed in a magnetic field formed by a magnetic circuit (not shown), and is generated by passing a current through the force coil 13. This is a mechanism for applying an electromagnetic force to the load receiving portion 12 engaging with the plate 11 to balance the load W on the plate 11. Here, it is desirable that the movable part including the plate 11 restricts the movement direction only in the vertical direction by a roberval mechanism (not shown, also called a parallel guide).

This balance is achieved by processing the digitally converted data of the output of the displacement sensor 14 for detecting the displacement of the load receiving portion 12 in the balance mechanism 1 by a microcomputer 5 described later, and applying a pulse of a current flowing to the force coil 13. It is obtained by changing the duty.

The displacement detection signal of the load receiver 12 by the displacement sensor 14 is amplified by the preamplifier 3, digitized by the A / D converter 4, and taken into the microcomputer 5. In this figure, for convenience of explanation, the microcomputer 5 is shown in a block diagram separately for each function.

A practical circuit as the AD converter 4 is shown in FIG.
As shown in FIG. 5, a sawtooth wave generator 41 for outputting a sawtooth wave having a constant period, a comparator 42 for inputting the sawtooth wave generator 41 and the output of the displacement sensor 14, and an AND for inputting the output of the comparator 42 and a clock pulse
A gate 43 and a counter 44 for counting clock pulses passing through the AND gate 43 can be constituted. The output of the comparator 42 forms a pulse width signal correlated with the magnitude of the input signal. By counting clock pulses as gate signals, digitally converted data of the displacement detection signal can be obtained for each cycle of the sawtooth wave.

Now, the digitized displacement data is P
It is incorporated into the ID calculation unit 51, and undergoes PID processing by digital calculation, that is, proportional, integration, and differentiation processing. Then, the PID output is guided to the pulse duty conversion unit 53 via the data processing unit 52, where a pulse duty signal is formed and sent to the pulse current generation unit 2. The output data from the data processing unit 52 is configured to be displayed on the display unit 6 as a measured value.

The pulse current generator 2 includes a constant current generator 2
1 and an electronic switch 22 that opens and closes based on the duty signal from the pulse duty conversion unit 53, and has a constant peak value based on the output current from the constant current generation circuit 21, and an output from the pulse duty conversion unit 53. A pulse current having a duty corresponding to the data is generated and supplied to the force coil 13.

That is, basically, the pulse duty conversion unit 53 outputs a duty signal in which the ratio of H and L changes at a constant cycle according to the digital data from the data processing unit 52. The duty signal from the pulse duty converter 53 turns the electronic switch 22 ON / OFF.
The electronic switch 22 chops the DC current from the constant current generating circuit 21. As a result, a pulse current whose duty changes according to the output data of the data processing unit 52 flows through the force coil 13.

The most characteristic feature of the embodiment of the present invention is that, for example, when the required resolution is set to 1 / 1,000,000,
The duty signal generated by the pulse duty conversion unit 53 is 2
Although 0 bits are required, the present embodiment is 16 bits. That is, if the clock pulse of the pulse duty conversion unit is 30 MHz and the pulse duty cycle is 2 ms, the internal count value is about 65,000.
Count $ 16 bits is the limit.

The shortage of the number of bits is achieved by periodically increasing or decreasing the duty signal, as will be described later, so that a high-resolution pulse current is caused to flow through the force coil 13. I have.

The current generated by the constant current generating circuit 21 is determined by the temperature of a permanent magnet (not shown) of the magnetic circuit by the temperature sensor 15 inserted into the balance mechanism 1.
The temperature is compensated to change at a rate equal to the change in the magnetic field.

Next, the operation of the embodiment of the present invention will be described in detail with reference to the ON / OFF timing chart of the electronic switch 22 (or the waveform of the pulse duty signal from the pulse duty converter 53) illustrated in FIG. I do.

As described above, the pulse duty converter 53 produces only a duty signal having a resolution of 16 bits. For example, next to 5000H is 5001H, but the resolution of this balance is, for example, 20 bits.

Now, in such a configuration, FIG.
As shown in (A) and (B), the duty of the pulse duty signal for producing 5001H is larger by the width t corresponding to the resolution of 16 bits than in the case of 5000H. In FIG. 3, the pulse in the case of 5000H is denoted by A, and the pulse in the case of 5001H is denoted by B.

When a signal of such resolution is used to generate, for example, a hexadecimal number 50001H, as shown in FIG. 3C, a pulse A of 5000H is generated 15 times and a pulse B of 5001H is generated during 16 pulse generations. Occurs once. Also, if it is 50002H, the pulse A is also repeated 14 times,
Pulse B is set to twice.

Then, as shown in FIG.
If H, pulse A and pulse B during 16 pulse generations
Is generated eight times, but when the pulse B having the increased pulse width is generated many times in one cycle as described above, the pulse B can be averagely dispersed in one cycle as in this example. This is advantageous for filtering. That is, when the movable portion such as the load receiving portion 12 vibrates by the pulse current, it is advantageous that the pulse current is averaged. In addition, there is a method in which the pulse current is converted into a direct current through a filter circuit. However, there is little ripple in filtering, which is advantageous.

As described above, when the balance mechanism 1 is balanced by the pulse duty signal equivalent to the load, the output of the A / D converter 4 is 0 or a predetermined reference value (the minus side cannot be measured). In the A / D converter of the type, for example, in the example of FIG. 2, a count value of の of the full scale is determined as a reference value in the balance state, and the pulse duty value is controlled so as to be the reference value. A-D
The number of bits, linearity, span change, etc. of the converter 4 do not matter. That is, since the A / D converter 4 functions only as a means for the balance mechanism 1 to follow up to the balance state, the stability is 0, or 1 / full scale.
Only the reference value of 2 is important.

In the above embodiment, the case where the output of the analog type displacement sensor 14 is subjected to AD conversion has been described. However, as shown in FIG. 4, the displacement sensor is, for example, a CCD line sensor 140 or the like. If the digital type is used, the A / D converter 4 can be dispensed with. (A technology using a digital displacement sensor in an electronic balance in which a pulse current is supplied to control an electromagnetic force balance mechanism by digital PID calculation is disclosed in Japanese Patent Laid-Open No. The present invention has already been proposed in US Pat. No. -162631, but the present invention can also be applied to this type for the purpose of improving the resolution.)

In the above embodiment, the displacement sensor 14
From the displacement detection data from the PI
Although the case of performing the D arithmetic processing has been described, the present invention
Instead of ID calculation processing, optimal control and

[0030]

(Equation 1)

It goes without saying that arithmetic processing based on so-called modern control theory can be employed. That is, the present invention does not perform any automatic control calculation processing to restore the displacement of the load receiving portion due to the load to the original state, and converts the result as it is to pulse current duty as pulse duty data. Based on this, the pulse current resolution is artificially improved by forcibly changing the pulse current within the specified time, which has a coarser resolution than the resolution required by the balance. Therefore, the calculation method of the automatic control is not limited at all.

[0032]

As described above, according to the present invention,
A pulse current is caused to flow through the force coil, and a predetermined automatic control calculation process such as a PID calculation process is performed to restore the displacement using the digital value of the displacement detection value of the load receiving portion. In the above-described method of determining the duty of the pulse current, the number of bits (resolution) of the duty of the pulse current to be passed through the force coil is set to be smaller than the display resolution of the balance, and the duty of the pulse current is determined. By forcibly changing the pulse duty at a predetermined ratio in a predetermined cycle, the resolution of the pulse duty is improved in a pseudo manner, so that when a pulse current of a kind of peak value is simply applied to one coil, for example, a clock pulse is generated. In the case of 30 MHz, the resolution is limited to about several tens of thousands, whereas in the present invention, the resolution is several hundreds of millions. It is possible to improve.
In addition, there is no need to generate a plurality of force coil currents as compared with JP-A-3-63526, which is advantageous in terms of cost.

When a PID output is set to a pulse duty signal when there is a disturbance, data processing is performed such as averaging and then setting, or if the disturbance is temporary, the pulse duty is not changed. Since the countermeasure such as setting after the software can be performed by software, it is possible to obtain an electronic balance in which the stability of the displayed value with respect to disturbance is greatly improved as compared with the conventional method.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a block diagram showing a specific circuit configuration example of the AD converter 4;

FIG. 3 is a diagram illustrating the operation of the embodiment of the present invention.

FIG. 4 is an explanatory view of a displacement sensor according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Balance mechanism part 11 Plate 12 Load receiving part 13 Force coil 14 Displacement sensor 15 Temperature sensor 2 Pulse current generation part 21 Constant current generation circuit 22 Electronic switch 3 Preamplifier 4 A / D converter 41 Saw wave generator 42 Comparator 43 AND gate 44 counter 5 microcomputer 51 PID operation unit 52 data processing unit 53 pulse duty conversion unit 6 display unit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01G 7/04 G01G 23/37

Claims (1)

(57) [Claims] 1. A balance that balances a force generated in a force coil provided in a magnetic field with a load, and obtains the magnitude of the load from a current value flowing through the force coil in that state.
Pulse current generating means for generating a duty pulse current based on input data and supplying the pulse coil to the force coil;
The displacement detection signal of the load receiving portion due to the load is taken in, and after performing a predetermined automatic control calculation process on the displacement detection signal to restore the displacement, the pulse detection data is converted into pulse duty data having a predetermined number of bits. A data processing unit for supplying the pulse current to the force coil, the pulse duty of the pulse current supplied to the force coil is configured to be converted into a mass value and displayed, and the force coil has a higher resolution than the display resolution of the balance. A pulse current having a duty determined by the number of bits of a small capacity is supplied, and the duty of the pulse current is forcibly changed at a predetermined ratio within a predetermined time. And electronic balance.