JP2699564B2 - Electronic balance - Google Patents

Description

The present invention relates to an electronic balance, and more particularly, to an electromagnetic force balance type balance.

<Conventional technology> In an electromagnetic force balance type balance, the electromagnetic force generated by passing a current through a force coil provided in a magnetic field is balanced with the load to be measured, and the current to be measured is obtained from the current value required to obtain the equilibrium state. Find the magnitude of the load.

With respect to this type of balance, the inventor of the present invention aims to obtain a quick and accurate measurement value by changing the force close to the load value to be measured while changing the preset digital value in steps of 1 count. And a second load evaluator for generating a force that balances the difference between the force of the first load evaluator and the load value to be measured. The sum of the forces generated by the load evaluator 2, that is, the sum of the loads shared and measured by the first and second load evaluators, determines the magnitude of the load value to be measured. We have proposed
−653).

<Problems to be solved by the invention> In the method based on the above proposal, accurate measurement values can be obtained in a short time under a simple configuration unless the load to be measured fluctuates, such as measurement of an unknown mass. Although obtained, but the measured load changes, such as measurement of the weight change of the sample,
There is a disadvantage that the measured display value temporarily fluctuates greatly. In addition, after this change, a time is required until the second load evaluation unit is stabilized again, and there is also a problem in responsiveness.

That is, in this type of measurement method, the force generated by the first load evaluator is changed by one step (one count) when the measurement range (generated force range) that is covered by the second load evaluator is exceeded. However, at that moment, it is necessary to greatly change the force that the second load evaluator performs.

Here, the magnitude of the current supplied to the force coil by the second load evaluator is controlled by the servo mechanism so that the displacement of a lever or the like in the mechanism of the balance is detected and becomes zero. The speed of change of the force generated by the second load evaluator is governed by the response of the servo system and cannot be changed more than a certain speed. As a result, the above-mentioned problem occurs.

More specifically, the first load evaluator generates, for example, a force of 1 to 200 g in 1 g steps,
Assuming that a force of up to 1 g is generated with a resolution of 0.1 mg, and that the sum of both represents the measured value, if there is a change in the load, 1 g
Each time, the force generated by the first load evaluator suddenly changes. At this time, the output of the PID controller in the servo mechanism of the second load evaluator cannot rapidly release voltage due to the integration operation. As a result, the combined force of the first and second load evaluation units temporarily becomes excessively large or small, and the display fluctuates.

That is, FIG. 5 when a change in load, such as (a), the example the force F ₁ to the first load evaluator at time t ₁ as shown in FIG. 3 (b) is generated, one step Increase and time
Similarly F ₁ is a decreased one step at t _2. Force F ₂ in which the second load evaluation unit is generated is reduced by the increase in the F ₁ instantly t _1, it is necessary to increase instantaneously at t _2, actually in FIG. 5 (c) As shown, a response delay occurs, and the sum F ₁ + F ₂ of the generated forces of the first and second load evaluators corresponding to the display value is:
Temporarily greatly varied t ₁ and t ₂ as shown in FIG. 2 (d), and requires a predetermined time until displaying the true weight value.

<Means for Solving the Problems> The present invention has been made to solve the above-mentioned problem by further improving the technique of Japanese Patent Publication No. 64-653, and its structure is shown in FIG. Describing with reference to the drawings, in the present invention, the second load evaluator B is provided with a PID controller 6 and its PID controller.
Means for obtaining a count value corresponding to the magnitude of the output of the controller 6 (for example, pulse width modulator 7, oscillator 91, counter 92)
And a data processing unit 93 that determines the duty of the second pulse current to be supplied to the force coil 3 in accordance with the count value. When the evaluation value exceeds the evaluation range of the evaluation unit B, the duty of the first pulse current supplied from the first load evaluation unit A to the force coil 2 is changed by one step, and at the same time, the duty of the second pulse current is changed. First
Is forcibly changed by a predetermined amount in the direction opposite to the direction of change in the duty of the pulse current.

<Operation> The servo mechanism of the second load evaluator B directly converts the output of the PID controller 6 into the duty of the second pulse current and does not feed it back to the force coil 3, but temporarily incorporates it into the data processor 93. When the first pulse current changes stepwise, a counteracting change is applied.

That is, when the value exceeds the evaluation range of the second load evaluator B, a predetermined amount of change is forcibly applied to the second pulse current in the opposite direction simultaneously with the change of the first pulse current for one step. As a result, the sudden change in the electromagnetic force generated by the first pulse current is canceled out, and the change in the electromagnetic force as a whole becomes very small.

<Embodiment> FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

The balance mechanism 1 is a well-known electromagnetic force-balanced load detection mechanism, in which first and second force coils 2 and 3 are placed in a magnetic field, and the electromagnetic force generated by these is balanced with the load on the plate 1a. It is a mechanism for. This balance is based on a servo system based on a signal from a position sensor 4 that detects a displacement of a lever or the like in the balance mechanism 1 (a second load evaluator B described later).
).

The first force coil 2 is a so-called main coil, and usually generates a constant electromagnetic force unless the measured value fluctuates greatly.

The second force coil 3 is a so-called sub-coil, and generates an electromagnetic force enough to balance a load that cannot be balanced by the electromagnetic force generated by the first force coil 2.

The current flowing through the first and second force coils 2 and 3 is a pulse current, and the generated electromagnetic force is changed by changing the pulse duty.
A current is supplied to the first focus coil 2 from the first load evaluator A, and a current is supplied to the second force coil 3 from the second load evaluator B.

The first load evaluator A includes a constant current generator 13 and a switch.
S ₁ , a first pulse duty conversion unit 11 and a first load evaluation value creation unit 94, and a first pulse duty conversion unit based on data from the first load evaluation value creation unit 94. the operation of the 11, and supplies the first pulse current a direct current i ₁ from the constant current generator 13 and chopping switch S ₁ to the first force coil 2.

The effective value of the first pulse current changes for each step of the magnitude set in advance in the first pulse duty conversion unit 94, and the timing of the change is determined by the second load evaluation unit B and the This is the moment when the value measured by the second force coil 3 exceeds the measurement range.

The second load evaluator B includes a position sensor 4, a position signal amplifier 5, a PID controller 6, a pulse width modulator 7, an oscillator 91, a counter 92, a data processor 93, a second pulse duty converter 12, and a switch. The balance mechanism 1 is constituted by S ₂ and a constant current generator 13, and generates an electromagnetic force corresponding to a difference between a generated force of the first force coil 2 and a load in the second force coil 3 to balance the balance mechanism 1.

That is, the detection value of the displacement of the lever and the like in the balance mechanism 1 by the position sensor 4 and the position signal amplifier 5 is introduced to the pulse width modulator 7 via the PID controller 6. The pulse width modulator 7 includes a sawtooth wave generator 71 and a comparator 72.
And outputs a square wave signal G having a time width according to the magnitude of the output of the PID controller 6. Then, this square wave signal G is input to the AND gate 8. That is, the comparator 72 compares the output of the PID controller 6 with the sawtooth wave, and outputs a square wave signal G in which the time from when the sawtooth wave rises to when the sawtooth wave exceeds the PID output becomes H. The AND gate 8 allows the clock pulse from the oscillator 91 to pass through the square wave signal G as a gate signal and guides the clock pulse to the counter 92. The counter 92 counts the input pulses while resetting the count value for each cycle of the sawtooth wave, and sequentially outputs the result. Therefore, the output of the counter 92 is proportional to the magnitude of the output of the PID controller 6.

The result of counting by the counter 92 is taken into the data processing unit 93. Then, the data processing unit 9 obtains data to be supplied to the second pulse duty conversion unit 12 by performing a process described later on the count value. Second pulse duty converting unit 12 drives the switch S ₂ on the basis of the data supplied from the data processing unit 93, the second pulse current by chopping the DC current i ₂ from the constant current generator 13 And supplies it to the second force coil 3.

The data processing unit 93 also sets the effective value of the first pulse current to 1 when the measurement range of the second load evaluation unit B is exceeded.
In order to change the step, a command to the first load evaluation value creating unit 94 is generated.

The data from the first load evaluation value creation unit 94 and the data processing unit 93 are summed with a predetermined weight by the weight addition unit 95, and the total value is displayed on the display 10 as a measured load value.

The currents i ₁ and i ₂ from the constant current generator 13 are temperature compensated by the output of the temperature sensor 14 provided in the balance mechanism 1.

Further, the above-described oscillator 91, counter 92, data processing unit 9
3. First load evaluation value creation unit 94 and weighting addition unit 95
Is actually constituted by the microcomputer 9.

FIG. 2 is a flowchart showing how data is processed by the data processing section 93. The operation will be described below with reference to FIG.

Flag f _1, f ₂ in this flowchart, in a steady state in which the second load evaluation unit B does not exceed the measurement range has become OFF, the flag f ₁ when exceeding the measurement range in the + direction, also , - flag f ₂ is turned oN respectively when it exceeds the side. In the second load evaluator B, the count value C from the counter 92 is defined as a measurement range in the range of C _{L to} C _H , and the whole range, that is, C _H -C _L is defined as Q, and It is assumed that an electromagnetic force equal to one load evaluation value of one step is generated.

Now, after taking in the count value C (ST1), the flag f
In ₁ and f ₂ are both OFF state, to determine whether exceeds a second measurement range of the load evaluation unit B on the basis of the count value C (ST2, ST3, ST4, ST5), does not exceed In this case, the value of C is used as it is as the data P for determining the duty of the second pulse current and the second load evaluation value D for calculating the weighing value (ST6). Each is supplied to the addition section 95 (ST7).

When exceeding the measurement range of the second load evaluation unit B in the + direction is a flag f ₁ (ST4, ST8), the first load evaluation value 1
Step up (ST9a) at the same time, the data P to determine a second pulse duty, regardless of the value of the count value _{C, P = C L + 0.1Q} ... (1) as the second pulse duty converting unit 12 and supplies to the supply as the second load evaluation value D, D = C _L ... (2) to the weighted addition unit 95 (ST9b, ST7).

Also, - erected side if flag f ₂ (ST5, ST10), the first load evaluation value at the same time as one step down (ST11a), the data P, and _{P = C H -0.1Q ... (3} ), Also, D is supplied to the second pulse duty conversion unit 12 and the weighting addition unit 95 as D = C _H (4) (ST11b, ST7).

That is, in this embodiment, the first load evaluation value increases or decreases by one step, and
Is forcibly changed in the opposite direction by an amount that generates an electromagnetic force of 90% of the electromagnetic force corresponding to one step.

Then, after such a step-like change in the first load evaluation value, when the first load evaluation value is on the + side, the change from ST2 to ST12 is performed.
To the latest count value C and the count value immediately before
The difference between the C ₀ | C-C ₀ | compared to a preset specified value alpha, the difference | C-C ₀ | data P until falls within the specified value alpha
P = C _L + (C−C _L ) × 0.1 (5) Data D is given by D = C _L (6), and is supplied to the second pulse duty conversion unit 12 and the weighting addition unit 95. (ST13, ST7).

On the negative side, go from ST3 to ST15,
Similarly, the latest count value C and the count value immediately before it
The difference between the C ₀ | C-C ₀ | is compared with a specified value alpha, the difference | C-C ₀ | until falls within the specified value alpha _{is, P = C H - (C} H -C) × 0.1 ... (7) D = C _H (8) is supplied to the second pulse duty conversion unit 12 and the weight addition unit 95 (ST16, ST7).

Then, ST12 or ST15 the difference | C-C ₀ | if fall is the alpha, beat flag f ₁ or f ₂ (ST14 or
ST17), proceed to ST6 to return to a steady state.

FIG. 3 shows a case where the first load evaluation value F ₁ increases by one step at time t ₁ and decreases by one step at t ₂ as shown in FIGS. 5 (a) and 5 (b). FIG. 7 is an explanatory view of the operation of the embodiment of the present invention, which is taken as an example.

Electromagnetic force F ₂ in which the second load evaluation unit B is generated, as shown in FIG. 3 (a), up to t ₁ is based on the count value C itself corresponding to the PID controller 6 second pulse current Is determined by determining the duty of the PID controller 6 which is substantially in a servo control state and is indicated by a solid line in FIG.
Is equal to the difference between the load to be measured and the force generated by the first load evaluator A, but at t ₁ irrespective of the output of the PID controller 6, Then, the first load evaluation value is increased by one step, and at the same time, a change is made so that a reverse electromagnetic force corresponding to 90% of the first load evaluation value is generated. Until the change in the output of the PID controller 6 falls within a certain range α, the output changes so as to approach the output of the PID controller 6.

After t ₁ ′, at which the change of the output of the PID controller 6 stops, the original servo control state is resumed. At time t ₂ , the first servo control is similarly performed.
At the same time as the reduction of the load evaluation value by one step, a forcible change is applied so that the reverse electromagnetic force corresponding to 90% of the load evaluation value is generated, and until t ₂ ′ at which the change in the output of the PID controller 6 stops. It changes asymptotically. During this time, the data D for calculating the measurement display value is in a transient state.
equal becomes F ₂ except t ₁ ~t ₁ and t ₂ ~t _2, is as shown by black dots in FIG At t ₁ ~t ₁ and t ₂ ~t _2.

Thus, as the total value of the electromagnetic force F ₁ and F ₂ the first and second load evaluating unit A and B generated are shown in FIG. 3 (b),
There is no large fluctuation as in the conventional case.

Note that it is not refused that the data P and D may be multiplied by a common coefficient to each of the above expressions.

For data D for calculating a display value,
It is not always necessary to hold a constant value in a transient state as in the above embodiment, but it can be determined by another appropriate method. For example, it may be configured to take the same value as the data P.

Further, when the first load evaluation value changes by one step, the magnitude of the electromagnetic force forcibly changed by the second load evaluation unit B is determined by the change in the first load evaluation value as in the above-described embodiment. It is needless to say that it is not limited to 90% of the amount, but can be any ratio. However, if it is set to 100%, it becomes difficult for the output of the PID controller 6 to return to a steady state, which is not preferable.

Incidentally, in the above-described embodiment, the most recent difference in the count value C and the count value C ₀ of the immediately preceding | C-C ₀ | time transient state until falls within α continues t ₁ ~t ₁ and t ₂ ~t ₂ is,
Although it depends on the responsiveness of the PID controller 6, the interval between the transient states can be shortened by using the technique of Japanese Patent Application No. 1-82295 already proposed by the inventor and the present invention in combination. be able to.

That is, as shown in FIG. 4, a discharge type constant current circuit 22 via a first switch 21 and an input terminal of an integrating circuit 6a in the PID controller 6 and via a second switch 23. Connect the suction type constant current circuit 24. The first and second switches 21 and 23 are configured to be turned ON / OFF by a command signal from the data processing unit 93, respectively, and the first switch 21 increases the first load evaluation value by one step. The second switch 23 closes for a certain time at the moment when the first load evaluation value decreases by one step at the same time.

By closing the first or second switch 21 or 23, a prescribed amount of electricity is injected or discharged into the integration circuit 6a. The amount of electricity is determined by the current flowing through the first force coil 2. 1 increase or decrease by a force F ₁ in step worth of change, current as the force F ₂ to the second force coil 3 is generated is reduced or increased by this second
Is set to flow through the force coil 3.

As a result, the output of the PID controller 6 quickly returns to the expected stable state when the first load evaluation value changes stepwise, until the difference | C−C ₀ | falls within α. time t ₁ ~t ₁ and t ₂ ~t ₂ transient state continues is very short.

Note that two force coils are not necessarily required,
The first and second pulse currents may be superimposed and flow in one force coil.

Also, regardless of the number of force coils, a current that alternates between positive and negative may be supplied instead of the ON / OFF current. In this case, an effect that the amount of heat generated by the force coil can be made constant can be expected.

<Effects of the Invention> As described above, according to the present invention, when the evaluation value exceeds the evaluation range of the second load evaluator B, the first pulse current is changed by one step at the same time and in the opposite direction. The second pulse current is forcibly changed by a predetermined amount, so that the weight change measurement and the weighing operation of the specified amount are performed in the same manner as in the related art.
At the same time, the "fluctuation" of the electromagnetic force caused by the response of the PID controller is eliminated, and the response is improved, enabling smooth measurement.

Further, even when the PID output fluctuates due to disturbance, the pulse duty of the second current is determined after averaging in the data processing unit, which is also effective in stabilizing the balance state.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a flowchart showing how data is processed by the data processing section 93, FIG. 3 is an explanatory diagram of the operation of the embodiment of the present invention, and FIG. FIG. 5 is a view for explaining the operation of an electronic balance having first and second conventional load evaluation sections according to another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... balance mechanism part 2 ... 1st force coil 3 ... 2nd force coil 4 ... position sensor 6 ... PID controller 7 ... pulse width modulator 8 ... AND gate 9 ... microcomputer 91 ... Oscillator 92 ... Counter 93 ... Data processing unit 94 ... First load evaluation value creation unit 95 ... Weighting addition unit 10 ... Display unit 11 ... First pulse duty conversion unit 12 ... 2 pulse duty converter 13: constant current generator A: first load evaluator B: second load evaluator S ₁ ... switch S ₂ ... switch

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 a magnitude of the load from a current value flowing through the force coil in that state. First of quantity of electricity
A first load evaluator for supplying a pulse current to the force coil to generate a predetermined force, and the force coil for balancing an unbalanced load remaining by the force of the first load evaluator by a servo mechanism. And a second load estimator for supplying a second pulse current to the first and second pulse currents so as to determine the load from the sum of the quantities of both the first and second pulse currents. The unit includes a PID controller, means for obtaining a count value corresponding to the magnitude of the output of the PID controller, and a data processing unit for determining the duty of the second pulse current in accordance with the count value. If the data processing unit exceeds the evaluation range of the second load evaluation unit due to a load change, the data processing unit
And the duty of the second pulse current is forcibly changed by a predetermined amount in a direction opposite to the direction of the change in the duty of the first pulse current. And an electronic balance.