JPH08210900A - Electronic balance - Google Patents

Abstract

PURPOSE: To obtain a high-resolution electronic balance by making a pulse current from a pulse current generating section to flow to a coil together with a pulse current which is obtained by changing peak value of a pulse current from another pulse current generating section and compensating the limit of the duty resolution of the balance. CONSTITUTION: The output of a displacement sensor 5 is inputted to a PID calculating section 13 through a displacement detecting circuit 11 and A/D converter 12 and the calculating section 13 decides the feeding back value of, for example, 24 bits to a coil 3 at every displacement data. Input data of 17 high-order bits and 7 low-order bits are respectively inputted to pulse current generating sections 14 and 15 in addition to clocks for feedback and for duty. The generating section 14 makes a pulse current having a fixed peak value and duty proportional to the input data to flow to the coil 3 in a fixed period and, when the supply of the pulse current to the coil 3 is completed, makes another pulse current having a duty which is made constant against a clock period for duty and a peak value proportional to the input data to flow to the coil 3. Therefore, the resultant current of the coil 3 is changed in accordance with the fed-back value and comes to have 24-bit resolution.

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 type electronic balance.

[0002]

2. Description of the Related Art In an electronic balance of electromagnetic force balance type, an electromagnetic force generated by passing an electric current through a coil placed in a magnetic field is applied to a rod to balance it with a load to be measured. The magnitude of the load to be measured is calculated from the magnitude of the flowing current. In order to stabilize the system, the current actually applied to the coil is determined by PID (proportional / integral / derivative) calculation on the detection result of the rotational displacement of the rod, and is determined based on the PID calculation result. As a current flowing through this coil, there is a method of D-A converting the PID calculation result to flow a direct current through the coil. In addition, in a high-end machine, generally, it is not a direct current but a pulse current with a constant period, A so-called pulse width modulation method is adopted in which the pulse duty is changed according to the PID calculation result.

By the way, in the pulse width modulation type electromagnetic force balance type balance, if the pulse current having the duty based on the PID calculation result is simply passed through the coil, the resolution of the pulse duty determines the resolution as the electronic balance. I will end up. Regarding the pulse duty, normally, after raising the pulse current, the clock of about 10 to 20 MHz is counted, and the pulse current is lowered when the counted value matches the PID calculation result. 1
The resolution is limited because it is determined by the clock frequency that can be generated during one cycle of the pulse current of about ms. Therefore, conventionally, various proposals have been made to make the resolution of the electronic balance higher than the resolution of the pulse duty.

For example, a method of performing arithmetic processing such as a moving average on the data of the number of times proportional to the required resolution squared, a quantization error due to pulse width modulation is integrated, and the feedback value (coil current value) is quantized. A method of performing arithmetic processing such as moving average of required number of data after adding,
The method of performing two pulse width modulations, fine and coarse, and superimposing them on each other and flowing them to the coil. In addition to pulse width modulation, the peak value of the pulse is also used as a variable, and the product of the resolution of the pulse width and the resolution of the pulse height. A method of obtaining a resolution equivalent to the above has been proposed.

[0005]

Among the above proposals for increasing the resolution, the method is effective only when Gaussian noise of a required multiple of the resolution is superimposed on the signal or data, and There is a problem that the response is delayed by the average number of data. The method (1) also has a drawback that the response is delayed by the amount of data for moving average.

On the other hand, although the methods (1) and (2) do not cause a delay in response, in (1) and (2), the data distribution to the fine and coarse and the weighting calculation are complicated, and in (1), the data distribution to the pulse width and the pulse height becomes complicated. .

An object of the present invention is to employ a pulse width modulation method and to perform a measurement with a resolution higher than the pulse duty resolution without causing a delay in response under a relatively simple control. It is to provide an electronic balance that can.

[0008]

A structure for achieving the above object will be described with reference to FIG. 1 which is an embodiment drawing, and an electronic balance of the present invention has a coil 3 provided in a magnetic field.
In an electronic balance in which an electromagnetic force generated by applying a current to a load is balanced with a load, and the magnitude of the load is obtained from the current value flowing in the coil 3 in that state, the rotational displacement of the rod 2 on which the load and the electromagnetic force act. The digital PID calculation unit 13 which takes in the detected value of the signal in a predetermined cycle, performs PID calculation processing on the value and outputs digital data of a predetermined bit, and the cycle and the crest value are constant, and depending on the size of the input data. Of the first pulse current generator 14 for generating a pulse current of a different duty, and a pulse current of a constant duty having a peak value according to the size of the input data in synchronization with the first pulse current generator 14. A second pulse current generating unit 15 for generating is provided, and the digital data from the digital PID calculating unit 13 is divided into upper predetermined bits and other lower bits. The Chi upper bit first pulse current generator 14, lower bit second pulse current generator 15
And is supplied as input data, and both of the pulse currents from the first and second pulse current generators 14 and 15 are supplied to the coil 3.

[0009]

The present invention compensates the limit of the resolution of the duty of the pulse current generated by the first pulse current generator 14 by changing the peak value of the pulse current from the second pulse current generator 15, and Both are intended to obtain an electronic balance with high resolution as a whole by flowing them through the coil 3.

That is, the data from the PID calculator 13 is, for example, 24 bits, and the first pulse current generator 1
4 has a resolution of, for example, about 17 bits, only the upper 17 bits of the output of the PID calculator 13 are used to determine the pulse duty of the first pulse current generator 14, and the remaining The lower 7 bits are used for determining the pulse crest value of the second pulse generator 15, so that a current whose magnitude is determined based on the resolution of 24 bits flows through the coil 3. Therefore, the equilibrium operation is performed based on the resolution, and the 24-bit data as the PID calculation result can be used as it is for determining the measured value of the load to be measured. Moreover, the coil 3 has 1
Since the feedback current having a substantially high resolution as described above is supplied for each data processing, that is, for each feedback cycle, the response is not delayed.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram schematically showing the overall construction of an embodiment of the present invention. Measuring pan 1 on which measured load W is placed
Is supported on one end of a rod 2 which is rotatable around a fulcrum 2a. A coil 3 is wound around the other end of the rod 2 via a winding frame 3a. This coil 3 is arranged in a magnetic field created by a magnetic circuit 4 mainly composed of a permanent magnet 4a, and has first and second pulse current generators 14 and 1 to be described later.
The pulse current from 5 is passed together.

A displacement sensor 5 is arranged at the tip of the other end of the rod 2, and the output of the displacement sensor 5 is input to a displacement detection circuit 11 which detects the rotational displacement of the rod 2. A corresponding analog voltage signal E (θ) is output.
The output of the displacement detection circuit 11 is digitized by the AD converter 12, and then the displacement data E is sent to the PID calculator 13.
(Θ _N ) is taken in every fixed period T.

In the PID calculator 13, the AD converter 12 is used.
Each time the displacement data E (θ _N ) from is fetched, the feedback value F (N) for the coil 3 is calculated by the following calculation.
To decide.

[0014]

[Equation 1]

Note that E (θ _N ) is the latest displacement data, and E (θ _N-1 ) is the displacement data collected immediately before that. In addition, the A / D converter 12 and the PID calculator 1
The operation timing of the cycle T of 3 is based on the clock from the feedback clock generator 16. The frequency of this feedback clock is, for example, 1 kHz.
Therefore, the period T is 1 ms. Also, P
The ID calculation unit 13 can actually be configured by a computer in which an appropriate program is written.

Now, as described above, the displacement data E (θ _N )
The feedback value obtained by performing the PID process on is the 24-bit digital data, of which upper predetermined bits, for example, 17 bits, are supplied to the first pulse current generator 14 and the remaining lower 7 bits are supplied. Are supplied to the second pulse current generator 15.

The first pulse current generator 14 includes a high order 17
Using the input data of bits, the feedback clock (cycle T), and the duty clock (cycle Δt) of, for example, about 20 MHz from the duty clock generator 22, a wave is generated under a constant cycle T. A pulse current P1 having a constant high value and a duty proportional to the input data is generated and passed through the coil 3.

On the other hand, the second pulse current generator 15 uses the lower 7-bit input data, the feedback clock and the duty clock to terminate the pulse current from the first pulse current generator 14. at the same time,
The duty clock cycle for one duty ((Δ
The pulse current P2, which is constant with t) and whose peak value is proportional to the input data, is generated and is also passed through the coil 3. In addition,
The generation timing of the second pulse current is not limited to the above, and may be any time within one cycle of the feedback clock.

As a result, in the coil 3, a combination of the pulse currents from the first and second pulse current generators 14 and 15 flows as shown in FIG. 2, and the pulse current is fed back. It changes every moment by the feedback value F (N) which changes every cycle T,
Balance. That is, the first pulse current generator 1
Even if the resolution of 4 is 17 bits, a current having a resolution of 24 bits flows through the coil 3 every period T, and high resolution measurement can be performed with high response. The measured value of the load to be measured is determined based on the 24-bit data from the PID calculator 13.

FIG. 3 is a more specific circuit configuration diagram of the above-mentioned first and second pulse current generators 14 and 15. In this example, the first and second pulse current generators 14 and 15 are Adopted a configuration in which some of them are shared.

In this example, the pulse duty conversion section 31 uses, for example, a latch circuit for the upper 17 bits of data from the PID calculation section 13, the data latched by the latch circuit as a preset value, and a 20 MHz duty clock pulse. A down counter that counts down, a flip-flop that is set by a signal output when the count value of the down counter reaches 0, and is reset by the input of a feedback clock of 1 kHz, and the like. The upper 17 bits Then, a pulse voltage signal having a cycle T having a duty corresponding to the data value is generated and supplied to the adder 33. Further, the pulse duty conversion unit 31 supplies the DA converter 32 with a pulse having the same peak value and a duty of one duty clock, following the generation of the pulse voltage signal as described above.

The DA converter 32 multiplies the pulse voltage signal from the pulse duty converter 31 and the lower 7-bit digital signal from the PID calculator 13 and outputs the product. The output of this DA converter 32 is the lower 7
If all the digits of the bit digital data are 1, that is, the maximum possible value, the output thereof matches the peak value of the pulse voltage signal from the pulse duty conversion unit 31, that is, the input digital data is maximum. When the value is a value, the input voltage signal is multiplied by 1 and output to the adder 33. Therefore,
The output of the D-A converter 32 has a peak value proportional to the lower 7-bit input data, and the maximum peak value is the peak value of the output pulse from the pulse duty conversion unit 31. The pulse voltage has a duty equal to the cycle Δt of
This coincides with the falling time of the pulse voltage signal from the pulse duty conversion unit for the adder 33.

The adder 33 adds these pulse voltage signals and then supplies them to a current amplifier (voltage / current converter) 34. The output of the current amplifier 34 is passed through the coil 3 described above. With such a configuration, a pulse current having a waveform as shown in FIG. 2 flows through the coil 3.

[0024]

As described above, according to the present invention,
The measured load and the displacement of the rod on which the electromagnetic force that opposes it actuates the digital PID to obtain a digital feedback value of a predetermined bit, and the upper predetermined bit of the load is first
To generate a first pulse current having a constant peak value having a duty corresponding to the magnitude of the first pulse current at a constant cycle, and the remaining lower predetermined bits of the digital feedback value to the second predetermined value. The pulse current generator supplies the pulse current generator with a crest value corresponding to the magnitude of the pulse current generator to generate a second pulse current of a constant duty in synchronization with the first pulse current. Since both of the pulse currents of # 1 and # 2 are supplied to the coil for electromagnetic force generation, the current flowing in the coil is the pulse duty resolution of the first pulse current generation unit and the peak value of the second pulse current generation unit. In addition, a high-resolution electronic balance can be obtained, and since such a high-resolution electric current flows in each feedback cycle, the response of the balance is degraded. No.

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing the overall configuration of an embodiment of the present invention.

FIG. 2 is a time chart showing waveforms of an output value of the PID calculator 13 and a pulse current flowing through the coil 3.

3 is a circuit configuration diagram showing a specific example of first and second pulse current generators 14 and 15 in the embodiment of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measuring dish 2 Rod 3 Coil 4 Magnetic circuit 5 Displacement sensor 11 Displacement detection circuit 12 A / D converter 13 PID calculation unit 14 First pulse current generation unit 15 Second pulse current generation unit 16 Feedback clock generation unit 17 Duty clock generator 31 Pulse duty converter 32 DA converter 33 Adder 34 Current amplifier

Claims (1)

[Claims] 1. An electronic balance that balances an electromagnetic force generated by passing an electric current through a coil provided in a magnetic field with a load and determines the magnitude of the load from the value of the current flowing through the coil in that state. The detected value of the rotational displacement of the rod on which the electromagnetic force acts is taken in at a predetermined cycle, and the value is subjected to PID calculation processing to output digital data of predetermined bits, and the cycle and the peak value are constant. And a first pulse current generator that generates a pulse current having a duty corresponding to the size of the input data, and a second pulse current generator that generates a pulse current having a peak value corresponding to the size of the input data. The digital data from the digital PID calculator is divided into upper predetermined bits and other lower bits, and the upper bit is the first bit. The lower bit is supplied as input data to the second pulse current generator, and both of the pulse currents from the first and second pulse current generators are supplied to the first pulse current generator. An electronic balance, characterized in that it is configured to flow through the coil.