JPH08201148A - Electronic balance - Google Patents

Abstract

PURPOSE: To provide an electronic balance which can measure higher resolution than that of a PWM with a simple structure without adding a special hardware. CONSTITUTION: An electronic balance has a pulse modulation type servo system for supplying a pulse current to a force coil 3, and comprises pulse initiating ratio calculating means (b) for counting the current pulses of different duties supplied within a period in synchronization with the increasing or decreasing period of the duty owing to the insufficient resolution of the duty of the pulse current to calculate its ratio, and measured data deciding means (c) for calculating the measured data of a load from the either the ratio and the duty of the current pulses fed within the period, wherein the load can be measured by the higher resolution than that of the duty of the pulse current actually fed to the coil 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called electromagnetic force balance type electronic balance provided with an electromagnetic force generating device for generating an electromagnetic force for balancing a balance mechanism against a load.
More specifically, the present invention relates to an electronic balance in which a pulse current is passed through a force coil of an electromagnetic force generator.

[0002]

2. Description of the Related Art In an electronic balance of electromagnetic force balance type, a displacement sensor detects a deviation from a balance point of a balance mechanism caused by a load to be measured, and a current according to the detection result is applied to a force in a magnetic field. It is equipped with a servo mechanism that balances the balance mechanism by generating an electromagnetic force corresponding to the load to be measured by flowing it through the coil.The load to be measured can be determined from the magnitude of the current flowing through the force coil when the balance mechanism is in balance. Looking for.

In such an electromagnetic force balance type electronic balance, conventionally, the current flowing in the force coil is set to DC.
If the C servo system is used, there is a limit to the stability and high resolution of the system. Therefore, a pulse current of a constant cycle is applied to the force coil, and the duty of the pulse current is changed according to the displacement detection result of the balance mechanism. A so-called pulse-modulation type of changing is widely used.

Conventionally, in the pulse modulation type electronic balance,
Basically, the current pulse is started at a constant cycle, and the current pulse is detected when the analog voltage signal obtained by subjecting the displacement detection value to the PID calculation process and the voltage value of the constant sawtooth voltage signal match. While ending
By counting the clocks generated during that time,
It is often used to measure the pulse width of the flowing current.

From this, the resolution of the duty of the pulse current passed through the force coil is determined by the number of clocks generated in one cycle of the pulse current. Normally, the pulse current cycle is about 1 to 2 ms, and the clock frequency is 30 MH
The z is only about 1 / 30,000 to 1/60000, which is insufficient as compared with the resolution required for the electronic balance.

Therefore, conventionally, various proposals have been made to make the resolution of the electronic balance higher than the resolution of the pulse duty. In JP-A-47-41772, the current pulse is not ended at the time when the analog voltage obtained by PID calculation of the displacement detection value and the sawtooth wave voltage signal match.
After the point of coincidence, the clock for measuring the current pulse width is first generated, and a fixed number, for example, 200 measurement results of the current pulse lengths are added to obtain a load measurement value. This eliminates the quantization error of each current pulse by averaging.

In Japanese Patent Publication No. 58-29856, the current pulse is terminated at the time when the analog voltage signal obtained by PID calculation of the displacement detection value and the sawtooth voltage coincide with each other, and the counting result of the clock generated during that time is calculated. By storing the included quantization error in a capacitor, etc., the next PID
The error is eliminated by adding it to the calculation result.

Further, in Japanese Examined Patent Publication No. 5-32684, a plurality of pulse currents having different peak values (current values) are prepared, and the displacement of the balance mechanism is captured as a digital signal to perform a digital PID calculation to determine a predetermined value. While obtaining the bit data, by allocating, for example, the upper bit to determine the duty of the pulse current having a high peak value and the lower bit to determine the duty of the pulse current having a low peak value, among the data, A plurality of pulse currents different in current value and duty are passed through the force coil, and even if the duty resolution of each pulse current is limited, an electronic balance with high resolution is obtained as a whole.

[0009]

By the way, among the above proposals, in Japanese Patent Application Laid-Open No. 47-41772, the quantization error included in the measurement result of the width of each current pulse is reduced to a preset number. Although it is intended to reduce the total or average of the pulse measurement results, the number of current pulses to be averaged is appropriately set in advance regardless of the physical condition of the system, The error disappears only when the directions (plus or minus) of the quantization error during that time are the same, and it cannot be said that an accurate metric value can be obtained.

[0010] Japanese Patent Publication No. 58-29856 has a PI
The analog voltage signal obtained by the D operation has a drawback that the circuit configuration for reflecting the quantization error amount at each time is complicated and the cost is significantly increased.

Further, also in Japanese Patent Publication No. 5-32684, the hardware cost is increased due to the necessity of generating pulse currents having a plurality of peak values. An object of the present invention is to provide an electronic balance that has a simple hardware and can achieve high resolution without increasing the cost.

[0012]

The structure for achieving the above object will be described with reference to the basic conceptual diagram shown in FIG. 1. In the electronic balance of the present invention, the balance mechanism 1 by load is described.
The displacement sensor 2 detects a displacement from the balanced state, and a current is supplied to the force coil 3 in accordance with the output of the displacement sensor 2 to control the current. Includes a pulse current generating means a that generates a pulse current whose duty changes at a constant cycle and with a predetermined resolution according to the output of the displacement sensor 2, and causes the pulse current to flow through the force coil 3. In the balance configured to balance the balance mechanism 1 according to the above, the cycle of the pulse current is synchronized with the cycle of increase or decrease of the duty of the pulse current generated by the insufficient resolution of the duty of the pulse current generated by the pulse current generating means a. The number of current pulses with different duties that flow in each pulse is calculated and the ratio is calculated. Measurement data determination means for calculating load measurement data from the generation rate calculation means b, the ratio calculated by the pulse generation rate calculation means b, and the pulse duty of any of the current pulses that flowed within the period. c
It is characterized by having.

[0013]

When the servo system is operated by passing a current from the pulse current generating means a having a resolution lower than that required for the balance of the balance mechanism 1 by the servo system, the pulse is generated. Due to the lack of duty resolution, the duty of the pulse current flowing through the force coil 3 is increased or decreased to balance the balance mechanism 1. That is, for example, when the resolution of the duty of the current pulse is 1/10000, the data relating to the duty of the current pulse necessary to balance the balance mechanism 1 under a certain load load is, for example, “10000.73”. At this time, the duty of the current pulse is increased / decreased (reciprocated) between “10000” and “10001” at a predetermined cycle, and the cycle of the increase / decrease is determined by the characteristics of the system mainly including the balance mechanism 1. For example, if the cycle is 0.1 s, the cycle of the pulse current is 1 m.
In the case of s, “10000” is 27 times and “1000” in 100 current pulses generated in 0.1 s.
1 ”appears only 73 times.“ 100 ”that appears in this cycle
The number of each pulse having a duty of "00" and "10001" is respectively counted, and the appearance ratio of these is calculated, and from the ratio and the duty of any current pulse flowing in this cycle, for example, "10000". , "10
It is possible to obtain measurement data with a load of 000.73 ″, and it is possible to perform measurement with a higher resolution than the resolution of the duty of the pulse current.

[0014]

FIG. 2 is a block diagram showing the structure of an embodiment of the present invention. The displacement from the balance point of the balance mechanism 1 supporting the dish 1a for applying the load to be measured is measured by the displacement sensor 2
Is detected by The balance mechanism 1 includes a permanent magnet 31
The force coil 3 placed in a movable state in a magnetic field created by a magnetic circuit 31 mainly composed of a is attached. A pulse current, which will be described later, is applied to the force coil 3, and the electromagnetic force generated thereby acts on the balance mechanism 1 in a direction to compensate the displacement from the balance point due to the measured load.

The displacement detection signal from the displacement sensor 2 is input to the PID arithmetic circuit 12 via the preamplifier 11 and subjected to PID (proportional / integral / differential) arithmetic processing. The PID calculation result is supplied to the pulse width conversion circuit 13 and is also taken into the computer 20.

As will be described later, the pulse width conversion circuit 13 generates a rectangular-wave voltage signal of a constant cycle having a pulse width corresponding to the magnitude of the input PID calculation result, and drives the electronic switch 14. The electronic switch 14 operates so that a constant DC current from the constant current source 15 is supplied to the force coil 3 when the rectangular wave voltage signal from the pulse width conversion circuit 13 is at H level, and to the ground when it is at L level. To do. As a result, a pulse current having a constant crest value flows through the force coil 3 at a constant cycle and with a duty corresponding to the size of the PID calculation result.

The filter 15 provided between the electronic switch 14 and the force coil 3 is for converting the pulse current into a direct current so as to reduce the vibration of the balance mechanism 1 due to the pulse current. Further, in FIG. 2, elements not related to the features of the present invention such as temperature compensation are omitted.

FIG. 3 shows a concrete circuit configuration example of the pulse width conversion circuit 13. In this example, the PID arithmetic circuit 12
The analog voltage signal from the sample hold circuit 13a
Is held by, and the value is digitized by the AD converter 13b. The PID calculation result digitized by the A / D converter 13b is latched by the latch circuit 13c as PWM data for determining the duty of the pulse current, and is sampled by the computer 20. At the same time, it is stored as a preset value in the down counter 13d. Supplied. The down counter 13d down-counts the separately supplied high-frequency clock signal CL of about 10 MHz, and supplies a reset signal to the flip-flop 13e when the content becomes 0. The clock signal CL is also supplied to the counter 13f at the same time. The counter 13f counts the clock signal CL and outputs a set signal to the flip-flop 13e and a down counter at every constant period T when the count value reaches a constant value. A load signal having a preset value is supplied to each of 13d.

With such a configuration, the flip-flop 13e can obtain a rectangular wave signal whose cycle matches the cycle T of the output signal from the counter 13f and whose duty is proportional to the size of the PWM data. The characteristic of the pulse width conversion circuit 13 is that the duty of the rectangular wave signal to be output is a digital amount determined by counting the clock signal CL based on the PWM data fetched by the computer 20, and therefore, depending on the rectangular wave signal. The pulse current that flows into the force coil 3 after being pulsed by the operating electronic switch 14 is also stored in the computer 20.
It becomes a digital amount corresponding to the PWM data taken in.

The duty resolution of the rectangular wave signal, that is, the duty resolution of the pulse current flowing through the force coil 3 is determined by the number of clock signals CL generated within the period T. For example, when the frequency of the clock signal CL is 10 MHz and the period T is 1 ms, the duty resolution of the pulse current is 1/10000.

The computer 20 obtains the measurement data of the load acting on the pan 1a of the balance mechanism 1 using the PWM data with a resolution higher than 1/10000 by the following program, and displays it on the display 21. Determine the weight value to be displayed.

FIG. 4 is a flow chart showing the contents of the program written in the computer 20, and the operation of the embodiment of the present invention will be described below with reference to this figure. The computer 20 uses the latch circuit 13c to set the P
Import WM data (ST1). First captured P
When the WM data is PWML, it is determined whether or not the next captured data is equal to this (ST2). If the data is equal to the original data PWML, the B ₀ counter is incremented by 1 (ST3). If they are not equal to each other, the count is larger than PWML by one count, that is, the PWM regulated by the resolution of the duty of the pulse current.
It is determined whether or not the data PWMH is the second largest after L (ST11). When the data is PWMH, the A ₀ counter is incremented by 1 (ST1
2). These counters A ₀ and B ₀ are cleared to 0 at the same time that the contents A to B are read when the other counter B ₀ or A ₀ becomes 1 (ST4, ST5, and ST13). , ST14).

The captured PWM data is the original PWML
If it is neither PWMH that is one count larger than that or PWMH is larger than PWMH, it is determined whether or not the data is larger than PWMH (ST21), and if it is larger, a value that is one count smaller than the PWM data becomes a new reference. PWM
If it is smaller, the PWM data is stored as a new PWML as it is (ST22, ST
24). Further, at the time of updating such a reference PWML, both the counters A ₀ and B ₀ are cleared (ST23, ST25).

Each time the counter A ₀ becomes 1, the load is determined by using the reference PWML value and the contents A of the counter A ₀ and the contents B of the counter B ₀ read immediately before that. The measured data D of D is calculated by D = PWML + A / (A + B) .. (1), and the display 21 is calculated based on this data D.
The measurement display value of is determined.

Now, assume that the PWM data corresponding to the current value to be passed through the force coil 3 in order to generate the electromagnetic force necessary for balancing the balance mechanism 1 under a certain load condition is 10000.73. Then, the servo system tries to operate so as to pass such a current through the force coil 3, but as described above, the duty of the pulse current flowing through the force coil 3, that is, the PWM data has only a resolution of 1/10000. , PWM data takes a value of 10000 or 10001. Now, assuming that the first PWM data is 10000, if the data is PWML, as shown in FIG. 5, after the PWML value continues for several times, the PWMH is one count larger than PWMH. Changes to the value of. Also, after the value of PWMH continues several times,
It changes to the value of PWML again. The cycle τ of such increase / decrease of PWM data is determined by the characteristics of the system mainly including the balance mechanism 1. If the cycle τ of increase / decrease of the data value is, for example, 100 times (0.1 s) the cycle T of the pulse current, within this period τ, 10000 in the above example.
(PWML) 27 times, 10001 (PWMH) 73
Appears only once. In this case, the value of the actual PWM data required to balance the balance mechanism 1 can be known from 10000 + 73 / (27 + 73) = 10000.73 (2).

In the flowchart of FIG. 4, the timing when the content of the B ₀ counter becomes 1 in ST4 is the time point of τb in FIG. 5, and the timing when the A ₀ counter becomes 1 in ST13 is also the timing of τa in FIG. It's time. Therefore, for example, the period between two τa, that is, the period from the time when the A ₀ counter becomes 1 to the time when the A ₀ counter becomes 1 next coincides with the period τ of increase and decrease of the data value. Then, each counter of A ₀ and B ₀ is cleared after its content is read every time the other counter becomes 1, so that the read contents A and B of the A ₀ counter and B ₀ counter respectively It represents the number of times PWMH and PWML appeared in the data value increase / decrease cycle τ.

Therefore, in ST31 and ST32, the above formula (1), which is calculated every time the A ₀ counter becomes 1, is the above formula (2). Also, the load measurement data D can be obtained with a resolution that is two orders of magnitude higher.

The operation of the equation (1) is performed by A
_In addition to the timing at which the ₀ counter becomes 1, the timing at which the B ₀ counter becomes 1 is also possible. In this case, the period shown in FIG. 6 is one cycle of measurement, and similar measurement data can be obtained even in this case.

Further, in the equation (1), PWML is used as a reference and the appearance ratio of each data is added to the value to obtain a measured value D. Instead of this, an operation based on PWMH D = PWMH- Of course, even with B / (A + B) ... (3), exactly the same measurement data can be obtained.

Further, in the above embodiment, the example in which the analog displacement detection signal from the displacement sensor 2 is processed by the analog PID arithmetic circuit 12 and then digitized is shown. However, after the output of the displacement sensor 2 is digitized. Needless to say, the PID calculation may be performed by digital calculation.

In each of the above examples, if the cycle τ of increase / decrease of PWM data becomes long due to the characteristics of the balance mechanism 1, an appropriate dither is injected into the output of the PID calculation circuit 12. do it. That is, PID
By injecting the dither into the output, switching between PWML and PWMH is performed substantially in synchronization with the dither cycle. By appropriately selecting this dither cycle and setting the cycle τ to the desired cycle, the output cycle of the load measurement data can be shortened and its responsiveness can be improved. Is advantageous in terms of.

[0032]

As described above, according to the present invention,
In an electronic balance that employs a pulse modulation type servo mechanism that applies a pulse current to the force coil, it is synchronized with the cycle of increasing or decreasing the duty of the pulse current that occurs due to insufficient resolution of the pulse current duty when the servo mechanism operates. Then, the number of the current pulses with different duties that flowed in the cycle is counted to calculate the ratio, and the ratio and any pulse duty of each pulse current that flows in the same cycle are calculated. Since it is configured to calculate the load measurement data, the measurement value with a higher resolution than the pulse duty resolution can be obtained with a simple configuration without adding special hardware. Therefore, an inexpensive and high-resolution electronic balance can be obtained. Moreover, the calculation of the measurement data is performed in synchronization with the cycle of the increase / decrease of the duty of the pulse current caused by the lack of resolution of the duty, so it is more difficult than simply calculating the average value of the duty of the pulse current flowing at an appropriate time. Therefore, significantly effective (accurate) measurement data can be obtained.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram showing the configuration of the present invention.

FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 3 is a block diagram showing a specific configuration example of the pulse width conversion circuit 13.

FIG. 4 is a flowchart showing the contents of a program written in the computer 20 according to the embodiment of the present invention.

FIG. 5 is an operation explanatory view of the embodiment of the present invention.

FIG. 6 is an explanatory diagram of an example of another operation method according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Balance mechanism 2 Displacement sensor 3 Force coil 31 Magnetic circuit 12 A-D converter 13 Pulse width conversion circuit 13a Sample hold circuit 13b A-D conversion circuit 13c Latch circuit 13d Down counter 13e Flip-flop 13f Counter 14 Electronic switch 15 Constant current Source 20 Computer 21 Display

Claims (1)

[Claims] 1. A servo system for balancing the balance mechanism by detecting a displacement of the balance mechanism from a balanced state due to a load by a displacement sensor and controlling a current flowing through a force coil according to the output of the displacement sensor. In addition, the servo system includes pulse current generating means for generating a pulse current whose duty changes at a constant cycle and with a predetermined resolution according to the output of the displacement sensor. In a balance configured to balance the balance mechanism by flowing it through a force coil, in synchronization with the cycle of increase / decrease of the duty of the pulse current caused by insufficient resolution of the duty of the pulse current generated by the pulse current generating means. The number of current pulses with different duties that flow in that period. The load is measured from the pulse rate calculating means for counting and calculating the rate, the rate calculated by the pulse rate calculating means, and the pulse duty of any of the current pulses flowing in the period. An electronic balance comprising a measurement data determining means for calculating data.