JP2604040B2 - Automatic balance measuring instrument - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a so-called auto-balance type measuring instrument based on a zero method.

<Conventional Technology> In an automatic balancing type measuring instrument based on a zero method (zero order method), generally, a feedback control system which acts to cancel an input to be measured is configured, and the feedback amount itself is taken out as a measured value. Like that.

FIG. 9 shows a basic configuration of a conventional automatic balancing type measuring instrument.

A detection signal of a physical quantity such as force or pressure is converted into an electric signal by a deviation detector 92 through an addition point 91, then subjected to PID processing in a PID control circuit 93, and added through a feedback element 94. At point 91, it is fed back to the detection signal. Then, the PID output to be fed back is taken out as the measurement output. Note that PI processing or PD may be used instead of PID processing.

Here, the PID control circuit 93, those having a differentiating capacitor C ₁ and the integration capacitor C ₂ is used, for example, tenth feedback amplifier shown the circuit diagram in FIG mainly.

An electronic balance is a typical measuring instrument based on the zero method, and all of them basically use the control system as described above (for example, Japanese Utility Model Publication No. 55-39293 and Japanese Patent Application Laid-Open No. 54-482).
No. 77, JP-A-64-169522).

In the configuration shown in FIG. 9, when the system is a second-order delay system, its initial response is as shown in FIG. That is, if a step-like input is entered at point A,
The PID output, which is the total output of the P (proportional), I (integral), and D (differential) calculation results, reaches the stable point B as shown by the dashed line, and becomes stable.

<Problems to be Solved by the Invention> Meanwhile, in the conventional control system as described above, when a measurement input includes a disturbance, the operation is performed to suppress the disturbance.

That is, as shown by the chain line in FIG. 12, when a disturbance acts after the point C, the PID output fluctuates in response to the disturbance in order to stabilize the system against the disturbance. Therefore, while the system as a whole is stable, the measured value (measurement output) also includes a disturbance suppression signal. As a result, it is necessary to take measures such as passing through a filter to obtain a stable measured value. There is a disadvantage that the responsiveness of the value deteriorates. Also, the higher the response, the more sensitive to disturbance. Furthermore, in the case of a high-precision measuring instrument, if a filter is used, the capacitor used for the filter has a phenomenon called dielectric absorption that is much larger or smaller, so it is necessary to wait for a considerably longer time than the theoretically determined response time. The disadvantage is that the values are not constant, which also causes a slow response.

An object of the present invention is to reduce the stability of the entire system without impairing it.
Also, even if a filter that passes the measurement output is not used or simplified, the stability of the measurement output with respect to disturbance is maintained and the responsiveness is improved, and the measurement accuracy is not deteriorated and the cost is not increased. An object of the present invention is to provide an automatic balance type measuring instrument.

<Means for Solving the Problems> A configuration for achieving the above object will be described with reference to the basic conceptual diagram of FIG. 1 (a). A calculation means b for individually performing an integration operation among respective calculations such as proportional and integration, and a synthesis means c for synthesizing the integration operation result and another operation result among the above-described operations. The subsequent signal is fed back via the feedback element d, and only the signal subjected to the integration operation is extracted as the measurement output.

Here, in the present invention, it is not always necessary to individually perform the proportional and differential operations, and the basic conceptual diagram is also shown as a main part in FIG. 1 (b).

<Operation> A composite signal of the calculation results of P and I or R, I and D is fed back, and the same control as in the related art is performed as a whole system.

Then, only I before synthesis, that is, only the result of the integration operation is extracted as the measurement output.

As is apparent from FIG. 12, the reason why the PID output fluctuates greatly in order to stabilize the system in response to a disturbance is mainly that the P and D outputs fluctuate in response to a large reaction. However, when attention is paid only to the I output, the disturbance is integrated and the smoothing is performed, and the fluctuation is smaller than the actual disturbance fluctuation. The present invention makes use of this point and maintains the control of the entire system as before, makes only the measurement output stable against disturbance, and does not require a filter or the like, or a very weak filter can be used. Therefore, a stable measured value is obtained without impairing the response.

Here, the result of the integration operation is synthesized at the signal level by the synthesizing means c with another operation result, and then fed back via the feedback element d, so that the signal subjected to the integration operation and the signal subjected to the other operation may interfere with each other. It is not necessary to perform any other operation or to change other mechanisms other than the electrical configuration, and the intended purpose can be achieved without deteriorating the measurement accuracy or increasing the cost.

<Embodiment> FIG. 2 is a block diagram showing a configuration of an embodiment of the present invention, showing an example in which the present invention is applied to an electromagnetic force balance using analog PID calculation.

The load-balancing mechanism 1 is a well-known structure including a plate 11, a load receiving portion 12, a force coil 13, and the like.
Is detected by the displacement sensor 2, and the force coil 13 is placed in a static magnetic field created by a magnetic circuit (not shown). By controlling the current flowing through the force coil 13 by the following servo system, an electromagnetic force that balances the load acting on the plate 11 is created, and the displacement of the load receiving portion 12 is reduced to zero, and described later. The measured value is displayed on the display 9 as shown in FIG.

After the output of the displacement sensor 2 is amplified by the amplifier 3 (the displacement sensor 2 and the amplifier 3 constitute a deviation detector), it is input to the proportional operation circuit 4, the differentiation operation circuit 5, and the integration operation circuit 6. . Then, the results of the proportional, differential, and integral operations, which are the outputs of the arithmetic circuits, are input to the voltage addition / voltage-current conversion circuit 7.

The voltage addition / voltage-current conversion circuit 7 includes an operational amplifier 7a that combines the P, I, and D outputs by inputting the results of the respective operations through the resistors R _p , R _d, and R _i , respectively, It is constituted by a resistor 7b for converting the output voltage of the operational amplifier 7a into a current. After the P, I and D outputs are combined, a current-converted signal is passed through the force coil 13.

Among the outputs of the respective arithmetic circuits described above, the I (integral) output is A-
The data is also input to the D converter 8 and the digital conversion data is displayed on the display 9 as a measured value.

According to the above-described embodiment of the present invention, the load on the plate 11 is the displacement of the load receiving portion 12, and the displacement is detected by the displacement sensor 2. The displacement detection signal passes through an amplifier 3, is subjected to individual arithmetic processing by proportional, differentiating and integrating circuits 4, 5 and 6, and is then combined into a PID signal, which is further converted into a current and fed back to a force coil 13. ,
An electromagnetic force that keeps the displacement of the load receiving unit 12 at zero is generated in cooperation with the magnetic field.

In a completely balanced state, the displacement becomes zero. In this state, the current flowing through the force coil 13 is held by the output of the integration operation circuit 6, and this value is
It will be proportional to the above load. Accordingly, by digitizing the output of the integration operation circuit 6 by the A / D converter 8 based on a predetermined conversion coefficient, the digital value becomes a value representing the load on the plate 11, and the display 9 shows The measured value representing the load on the pan 11 will be displayed.

When a disturbance acts in this state, a signal subjected to PID processing is fed back to the force coil 13 in the same manner as in the related art, and this feedback signal (PID output) is indicated by a chain line after point C in FIG. In addition, it fluctuates greatly in response to disturbance to stabilize the system. However, the output I of the integration operation circuit 6 hardly fluctuates due to smoothing of the disturbance as shown in the figure, so that the weighing display value on the display 9 remains almost stable.

Incidentally, in a conventional balance of this type, the current flowing through the force coil 13 is converted into a voltage value by a precision resistor or the like and subjected to A / D conversion. In other words, the PID output itself is displayed as a measured value.

Then, it has already been described that the use of a filter at the input of the A / D converter further deteriorates the response due to the dielectric absorption of the capacitor. In the case of the present invention, the output of the integrator is directly input to the A / D converter (a weak filter may be used in combination). Another major feature is that no error occurs due to the following reason.

In other words, the integrator displaces its output until the input of the deviation detector (in the case of a balance, a displacement sensor and an amplifier) becomes 0, but if the output starts to change due to dielectric absorption, the integrator starts to balance. Therefore, the integrator input changes as much as that, and eventually the integrator output does not change, and the effect of dielectric absorption does not appear on the display or is greatly suppressed.

Here, in the configuration shown in FIG. 2, each of the proportional, differential and integral arithmetic circuits and a circuit for synthesizing these outputs are:
Actually, it can be realized by using a PID operation circuit as exemplified in FIG.

In this example, divided output from the amplifier into two systems, with guides to the PD operation circuit 31 for performing differential and proportional operation one provided with a operational amplifier differentiating capacitor C _1, the integrating capacitor C ₂ other integration I operation circuit 32 that performs only operation
Leading to. Then, these outputs are added to the next-stage addition circuit.
Combined at 33 to produce PID output and force coil 1
Pour into 3. The output of the I operation circuit 32 is separately extracted as a measurement output.

FIG. 4 is a block diagram showing the configuration of another embodiment of the present invention. This example also shows an example in which the present invention is applied to an electromagnetic force balance type using digital PID calculation.

In FIG. 4, members that are the same as in FIG. 2 are given the same reference numerals, and descriptions thereof are omitted.

In this example, after the output of the displacement sensor 2 is amplified by the amplifier 3, it is digitized by the A / D converter 41 and the digitally converted data is taken into the digital PID operation unit 42 at a predetermined cycle. The digital PID operation unit 42 performs a proportional, integral, and differential process on the digital data by an operation described later, and supplies the combined result P + I + D to the pulse current generation unit 43.

The pulse current generation unit 43 includes a pulse duty conversion circuit 43a that outputs a pulse in which the ratio of H and L changes within a certain period in proportion to the data from the digital PID calculation unit 42, and a pulse duty conversion circuit 43a. ON with pulse signal
The electronic switch 43b that is turned off and the constant current generation circuit 43
and a pulse-shaped current obtained by chopping a constant current from the constant current generating circuit 43c by the electronic switch 43b flows through the force coil 13. With this configuration, the duty of the pulse current flowing through the force coil 13 is proportional to the magnitude of the PID output supplied from the digital PID calculation unit 42, and the electromagnetic force generated by the average current value balances the load receiving unit 12. Let it.

Then, the digital PID calculation unit 42 outputs the I output alone together with the PID composite signal as described above, and supplies the data to the mass conversion unit 44, where the I output is converted into a mass value and displayed on the display unit 9. It is configured to display.

In the above configuration, the digital PID calculation unit 42 and the mass conversion unit 44 are actually configured by a microcomputer, and each calculation or conversion is executed by software. FIG. 5 is a flow chart showing the main part of the program of the microcomputer, in which the A / D converter 41 is used.
Are taken in at a fixed cycle (ST1), and after the deviation from the neutral point is obtained (ST2), the proportional, integral and differential calculations are performed by the following formula (ST3).

_{P x = K p x n ......} (1) I x = I x (n-1) + K i x n ...... (2) D x = K d (x n -x n-1) ...... (3) Where K _p , _Ki and K _d are the proportional, integral and derivative coefficients, respectively, x _n is the deviation from the neutral point of the latest sampled data, and x _n-1 is the neutral point of the previous sampled data Deviation, I
_{x (n-1)} is the previous integration result.

Of the above respective calculation results, the mass W using only integration result I _x are determined (ST), At the same time P _x, I _x, the calculation result of the D _x are synthesized pulse current generating circuit 43 (ST5, ST6).

In this embodiment, in the balanced state, the A / D converter
The output of 41 is zero, therefore is a value also 0 of P _x and D _x, PID output is only the value of I _x. That duty of the pulse current flowing in the force coil 13 in this state is proportional to the value of I _x, the load and I _x on pan 11 in other words is proportional, by converting the I _x mass Display 9 to display
Displays a value representing the mass on the dish 11.
Note that the method of PID calculation is not limited to this example, and various modifications are possible.

Particularly noteworthy points in each of the above embodiments are the proportionality,
In spite of performing differentiation and integration individually, the result of each of these operations is combined, and then is passed to one force coil 13 as one feedback signal. Thereby, as a magnetic circuit that forms the force coil 13 and a static magnetic field in which the force coil 13 is placed,
The same structure as the conventional ordinary one can be used, and the electromagnetic force generated by the current flowing through the force coil 13 also has the same high precision current-generated electromagnetic force as the conventional ordinary one. It has characteristics.

That is, when the integration operation is performed separately from other operations to extract the signal subjected to the integration operation, the signal after the integration operation is not combined with the signal subjected to the other operation, and the current It is also conceivable to convert the current into two force coils, for example. In this case, however, an interference phenomenon such as a change in the current-generated electromagnetic force characteristic of another force coil caused by a current flowing through a certain force coil. And high-precision measurement becomes impossible. In addition, in order to arrange a plurality of force coils in a static magnetic field, it is necessary to increase the static magnetic field space as compared with the case where one force coil is arranged as usual. The need for strong permanent magnets increases costs. On the other hand, by adopting a configuration in which the signal after the integration operation and the signal after the other operation are performed at the signal level and flown to one force coil 13 as described above, such a problem is caused. Does not occur, and the cost is high and the cost does not increase.

By the way, in the present invention, the stability can be further improved by increasing the integration time or shortening the differentiation time according to the condition of the input (for example, the load value on the plate 11), Similarly, the response can be improved by increasing the proportional gain according to the input situation. Furthermore, when the input deviation is large, control is performed so that the integration is weak (shortening the integration time), the differentiation is strong (the differentiation time is long), the proportional gain is large, and if the deviation is small, it is reversed. By doing so, it is possible to improve the responsiveness and to increase the stability after the automatic equilibrium. Alternatively,
When the input is small, the gain of the amplifier 3 is reduced,
It is also effective to use a non-linear characteristic in which the gain is increased when the value is large.

Fig. 6 shows an analog PI constructed from this point of view.
Which shows an example of a D calculation circuit, this example is an added improvement to the integration circuit of the PID arithmetic circuit shown in Fig. 3, insert a feedback resistor R ₉₂ to the integrating capacitor C ₂ in series At the same time, the amplifier output can be directly led to the feedback circuit of the integration circuit via the resistor _R91 and the switch 61. Then, the switch 61 is switched by a level comparator 62 that inputs an amplifier output (PID input).

Here, the level comparator 62 operates the switch as shown in FIG. 7 according to the magnitude of the input voltage.

With this configuration, immediately after the sample is placed on the pan 11, the PI
Since the D input is large, the switch 61 is connected to the contact a side.

The switch 61 is contact a state, when the input resistance of the integrating circuit and the R _i, the integrating circuit, , That is, while acting as a P (proportional) element, the integration time t _i Serves as the I (integral) element of

Therefore, quickly becomes a voltage is charged in the capacitor C _2, the system becomes closer to promptly equilibrium.

When the PID input approaches 0 when the equilibrium state is approached, the switch 61 switches to the contact b side, and becomes a simple integration circuit of amplification degree 0, and the integration time t _{ib in} this state is t _ib = R _i as large as C _2. As a result, a change in the I output with respect to the disturbance is suppressed to be small, and a balance that is resistant to the disturbance and has improved responsiveness can be obtained.

FIG. 8A shows a simplified configuration from the same viewpoint as FIG. In this example, by inserting a resistance element Z of the voltage dependent on the input resistor R _i in series with the integrating circuit, when the input is large and Z is low, the integration time is shortened, response is up Like that. In this case, R _i is the effect is obtained by setting smaller than that shown in Figure 6.

Here, as the voltage-dependent resistance element, for example, an element in which diodes are connected in reverse to each other as shown in FIG. 8B can be used.

Note that the present invention is not limited to the above embodiments, and can be applied to any measuring device using a zero method other than the balance, and many modifications other than the configurations of the above embodiments are possible. For example, in the case of performing digital PID calculation, the displacement sensor can be replaced with a digital output type sensor, in which case an AD converter becomes unnecessary. In the case of a balance that adopts digital PID calculation and sends a pulse current to the force coil, in addition to chopping a constant current, a balance that switches a positive / negative pulse current to the force coil, or The present invention can also be applied to a system in which two types of pulse currents are produced, one of which is adapted to a large load and the other is adapted to a small load, the pulse duty of which is changed, and these are superimposed and applied to one force coil.

<Effects of the Invention> As described above, according to the present invention, in an auto-balancing type measuring instrument, PI or PID calculation is individually performed, and a feedback signal is obtained by synthesizing these, and the measurement output is Since only the I operation result is extracted and used, the system as a whole responds to the detection signal or the disturbance contained therein under the same operation as the conventional one, but the measurement output (measurement value) does not correspond to the disturbance. Therefore, it becomes much more stable than before. As a result, a filter that passes the measurement output as in the related art can be eliminated or greatly simplified. Therefore, there is also an advantage that the influence of dielectric absorption of the filter capacitor at the time of high precision can be eliminated. In particular, when a second-order lag system is provided, PID control is required, and the derivative (D) has a large output with respect to disturbance.
By applying the present invention, the above-mentioned effects are extremely useful. Moreover, the I operation result is combined with another P or D operation result and fed back as one signal.
There is no particular need for modification, and there is no inconvenience due to the application of the present invention, such as interference caused by the addition of a new mechanism or element, which impairs measurement accuracy or increases costs.

Further, according to the configuration of the present invention, it is possible to bring out the advantage that the stability of the measured value is not deteriorated even when the response is increased by increasing the proportional gain or making the differentiation effective, in addition to the above-described effects.

Further, from the above, it is possible to realize a measuring instrument capable of obtaining a stable measurement value even in a place or environment where measurement has conventionally been difficult.

[Brief description of the 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 in which the present invention is applied to an analog PID operation type balance, and FIG. FIG. 4 is a block diagram showing a specific example of a circuit configuration, FIG. 4 is a block diagram showing a configuration in which the present invention is applied to a digital PID operation type balance according to another embodiment of the present invention, and FIG. FIG. 6 is a flow chart showing a main part of the contents, and FIG. 6 is a diagram showing a PI when the present invention is applied to an analog operation type balance
FIG. 7 is a circuit configuration diagram showing another embodiment of the D operation circuit, FIG. 7 is an operation explanatory diagram of the level comparator 62, FIG. 8 is a circuit configuration diagram showing a simplified example of the PID operation circuit of FIG. 9
The figure shows the basic circuit configuration of a conventional auto-balancing measuring instrument.
The figure is a circuit configuration diagram showing an example of a conventional PID operation circuit, FIG. 11 is an explanatory diagram of the PID output of the automatic balancing type measuring instrument, and FIG. 12 is the PID output disturbance of the automatic balancing type measuring apparatus. FIG. DESCRIPTION OF SYMBOLS 1 ... Load balance mechanism 11 ... Dish 12 ... Load receiving part 13 ... Force coil 2 ... Displacement sensor 3 ... Amplifier 4 ... Proportional operation circuit 5 ... Differential operation circuit 6 ... Integration operation circuit 7 ... ... Voltage addition / voltage-current conversion circuit 8 ... A / D converter 9 ... Display 41 ... A / D converter 42 ... Digital PID calculator 43 ... Pulse current generator 44 ... Mass converter

Claims (1)

(57) [Claims] 1. A deviation signal obtained by adding a feedback signal to a detection signal is inputted to a deviation detector, amplified, and then subjected to at least a proportional and integral operation, and further provided as a feedback signal via a feedback element. In the measuring instrument having an automatic control system for setting the input deviation to the deviation detector to 0, the operation means for individually performing the integration operation among the respective operations, the integration operation result and the It has a synthesizing means for synthesizing the result of each operation with other operation results. The synthesized signal is used as a feedback signal, and only the signal subjected to the integration operation is extracted as a measurement output. Automatic balance type measuring instrument.