JPH0321048B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a displacement measuring device using a differential transformer.

<Prior art> Conventionally, in devices using a differential transformer such as length measuring machines and weight measuring machines, the core of the differential transformer is displaced in a linear direction in proportion to the length or weight to be measured. Length, weight, etc. are measured based on the voltage difference between the output voltages of the two secondary coils, which changes according to this displacement.

That is, as shown in FIG. 1, when the core 1a of the differential transformer 1 is displaced in the X direction, the primary coil 1b
The output voltages e ₁ and e 2 of the two secondary coils 1c and _1d facing each other change in proportion to the displacement of the core 1a, as shown in FIG. Therefore, since the differential voltage e ₁ -e ₂ between the two changes in proportion to the change in the core 1a, the differential voltage signal is extracted from the output signals of the secondary coils 1c and 1d and is amplified, detected, and A/D. It is converted and output as the amount of displacement of the core 1a.

Therefore, as shown in FIG. 2, the output voltages e ₁ and e ₂ change almost linearly with respect to the displacement of the core 1a within a certain range |X'|, but within a certain range |X'|
In the above, due to the change in mutual inductance,
Changes non-linearly.

For this reason, beyond a certain range |X'|, the measurement accuracy deteriorates rapidly, and countermeasures against this result have been problematic.

In addition to such non-linearity of the output of the differential transformer, measurement errors also increase due to temperature changes, changes over time, etc. in the characteristics of the differential transformer and other circuits.

As one measure against this, conventionally, an object of a standard length or a standard weight is measured every measurement or intermittently, and correction calculations are performed based on the actual measurement values.

In addition, as another countermeasure, conventionally, a method has been used in which non-linear changes are stored as data through actual measurements, and correction calculations are performed from the actual measured values based on this data.

<Problems to be Solved by the Present Invention> However, in the former method, time is taken to measure the reference quantity, which reduces measurement efficiency and requires a special structure for supplying the reference object. There were problems such as:

In addition, the latter method has problems such as not being able to compensate for sensitivity drift due to temperature changes or changes over time, and when the differential transformer is replaced, it is necessary to obtain correction data again, making calculations extremely complicated. Ta.

Furthermore, although any of these methods can correct the nonlinearity of the differential transformer, there is also a problem in that they cannot cope with the temperature changes and changes over time.

The present invention solves the above problems and is a displacement measuring device that can automatically correct measurement errors due to nonlinearity of a differential transformer, temperature changes, and changes over time using simple calculations. is intended to provide.

<Means for solving the above problems> In order to solve the above problems, the displacement measuring device of the present invention includes: a differential voltage output circuit that outputs a differential voltage signal between the output voltages of the two secondary coils; a changeover switch for switching the input to the amplification/detection circuit to either the difference voltage output circuit or the sum voltage output circuit; and a changeover switch for switching the input to the sum voltage signal side when the displacement of the core of the differential transformer is approximately zero. a non-displacement time-sum voltage storage circuit that stores the non-displacement time-sum voltage output value of the A/D converter when connected to the A/D converter; and the switching when the displacement of the core of the differential transformer reaches approximately the maximum. a displacement time-sum voltage storage circuit that stores a displacement time-sum voltage output value of the A/D converter when a switch is connected to the sum voltage signal side; a timing circuit that outputs a timing signal for switching the changeover switch from the sum voltage signal side to the difference voltage signal side; and a real side output of the A/D converter when the changeover switch is switched to the difference voltage signal side. an arithmetic circuit that multiplies the value by a ratio of the displacement time-sum voltage output value of the displacement time-sum voltage storage circuit to the non-displacement time-sum voltage output value of the non-displacement time-sum voltage storage circuit, and for each displacement measurement. It is characterized in that the changeover switch is switched from the sum voltage signal side to the difference voltage signal side by the timing signal of the timing circuit, and the calculation output of the calculation circuit is outputted as the displacement of the core.

<Function> Because of this configuration, the changeover switch is switched by the timing signal of the timing circuit every time displacement is measured, and the non-displacement time sum voltage before measurement and the displacement time sum voltage during measurement are stored, and these two The actual measured value is corrected by the arithmetic circuit according to the ratio of the two values,
Output as displacement amount.

<Embodiment of the present invention> An embodiment of the present invention will be described below based on the drawings.

FIG. 3 is a block diagram showing an embodiment of the displacement measuring device of the present invention.

In the figure, 11 is an oscillation circuit that outputs an oscillation signal of a predetermined frequency.

Reference numeral 12 denotes a differential transformer whose core 12a is displaced in proportion to the displacement in the linear direction to be measured.
is excited, and output voltages e ₁ and e ₂ corresponding to the displacement of the core 12a are output from the two secondary coils 12c and 12d connected with opposite polarities, respectively.

13 is the secondary coil 12 of the differential transformer 12
The difference voltage e ₁ −e _{2 between the output voltages e 1 and e 2 of c} and 12d is,
It is an input transformer that is taken out to the secondary coil 13b, and from the intermediate tap of the primary coil 13a of the input transformer 13, the average voltage of e ₁ and e ₂ (e ₁ + e ₂ )/2
is taken out.

14 is a changeover switch, and input transformer 1
The output terminal A from the secondary coil 13b of No. 3 and the output terminal B from the intermediate tap of the primary coil 13a are switched by a timing signal from the timing circuit 22.

15 is an AC amplifier that amplifies the output signal from terminal A or B via the changeover switch 14.

16 is a detector that detects the output signal of the AC amplifier 15 and converts it into a DC signal. 17 is the detector 1
This is a DC amplifier that amplifies the output signal of 6.

18 is an A/D converter that converts the output signal of the DC amplifier 17 into a digital signal.

19 is the A/D converter 1 when the changeover switch 14 is connected to the A side before measurement, that is, when the displacement of the core 12a of the differential transformer 12 is approximately zero.
This is a non-displacement time-sum voltage storage circuit (first storage circuit) that stores the no-displacement time-sum voltage output value E _M1 of 8.

20 is the displacement time sum voltage output value of the A/D converter 18 when the changeover switch 14 is connected to the low side at the time of measurement, that is, when the displacement of the core 12a of the differential transformer 12 has reached almost the maximum. This is a displacement time-sum voltage storage circuit (second storage circuit) that stores E _M2 .

21 is the actual measured output of the A/D converter 18 when the changeover switch 14 is switched from the B side to the A side at the time of measurement, that is, when the displacement of the core 12a of the differential transformer 12 has reached almost the maximum. This is an actual measured output value storage circuit (third storage circuit) that stores the value E _M3 .

22 is the changeover switch 1 at each timing mentioned above.
4 switching signals and write signals to the first, second, and third memory circuits 19, 20, and 21, and the first, second, and third memory circuits 19, 20, and 20 after writing is completed.
This is a timing circuit that outputs a read signal to 21.

For example, in the case of weight measurement, as shown in FIG. 4, when an object to be weighed is transferred to a scale, the displacement X of the core 12a gradually increases from almost zero, stabilizes at the maximum value, and then the object leaves the scale. It returns to almost zero. As shown in FIG. 4, at timing _t1 before placing the object to be weighed on the scale, the non-displacement time sum voltage output value E _M1 is stored in the first storage circuit 19, and the object to be weighed is placed on the scale. The timing when the displacement X almost reached its maximum
At _t2 , the displacement time sum voltage output value E _M2 is stored in the second storage circuit 20, and at timing _t3 immediately thereafter, the measured output value E _M3 is stored in the third storage circuit 21.

23 is the first, second, and third memory circuits 11, 2;
Receiving each of the stored values of 0 and 21, an operation (E _M1 /E _M2 ) x multiplying the actual measured value E _M3 by the ratio of the displacement time sum voltage output value E _M2 to the non-displacement time sum voltage output value E _M1 E _M3
This is a calculation circuit that calculates at timing _t3 and outputs the calculation result as a displacement signal.

24 is a display circuit that displays this displacement signal.

Next, the operation of the above embodiment will be explained.

The primary coil 12b of the differential transformer 12 is excited by the oscillation signal from the oscillation circuit 11, and the output voltages e ₁ and e ₂ of the secondary coils 12c and 12d are the same as those of the core 1.
It changes in response to the displacement of 2a. input transformer 1
A differential voltage e ₁ -e ₂ is generated in the secondary coil 13b of No. 3, and a sum voltage (e ₁ +e ₂ )/2 is generated in the intermediate tap of the primary coil 13a.

As shown in FIG. 2, within a certain range |X'| according to the displacement of the core 12a, the secondary coils 12c, 1
Since the output voltages e ₁ and e ₂ of 2d change almost linearly, the differential voltage e ₁ −e ₂ also changes almost linearly. On the other hand, the sum voltage (e ₁ + e ₂ )/2 is in the same range |
It becomes approximately constant within X′| regardless of changes in the core 12a. Therefore, the differential voltage e ₁ −e ₂ and the sum voltage (e ₁ +
e ₂ )/2 is output with the characteristics shown in FIG. 2 as the core 12a moves during measurement.

By switching the changeover switch 14, the output signal from terminal A representing the above-mentioned differential voltage e ₁ −e ₂ and the output signal from terminal B representing the sum voltage (e ₁ +e ₂ )/2 are both the same. via circuits 15 to 18. That is, the signal is amplified by an amplifier 15, detected by a wave detector 16 and converted into a DC signal, amplified by a DC amplifier 17, and converted into a digital signal by an A/D converter 18.

Then, at timing t ₁ when the displacement of the core 12a is almost zero immediately before measurement, the first storage circuit 19 stores the sum voltage (e ₁ +e ₂ )/2, that is, A when the changeover switch 14 is connected to the lower side. The non-displacement time sum voltage output value E _M1 of the /D converter 18 is stored.

Then, at timing t ₂ when the displacement of the core 12a reaches almost the maximum value during measurement, the second
The storage circuit 20 has a sum voltage (e ₁ +e ₂ )/2, that is, A/2 when the changeover switch 14 is connected to the low side.
The displacement time sum voltage output value E _M2 of the D converter 18 is stored.

Immediately thereafter, at timing _t3 , the changeover switch 14 is switched to the A side, and the differential voltage _e1
The actual measured output value E _M3 of the A/D converter 18 when connected to the -e ₂ side, that is, the A side, is stored.

The arithmetic circuit 23 calculates (E _M1 /E _M2 )×E _M3 based on the output values of each memory circuit 19, 20, 21,
It is output as a displacement signal, and the displacement is displayed on the display circuit 24.

When the maximum value of the displacement amount X is within the range of |X'|, since E _M1 /E _M2 is approximately 1, the measured output value E _M3 is directly output as the displacement amount.

If the displacement X of the core 12a exceeds |X'|, the third storage circuit 21
The actual measurement value E _M3 stored in deviates from the straight line,
It is lower than the true value E _MD on the extension of the straight line.

However, the displacement time sum voltage output value E _M2 stored in the second memory circuit 20 also falls off the straight line, and the no-displacement time sum stored in the first memory circuit 19 in the case of zero displacement also decreases. The voltage output value E is lower than _M1 .

Therefore, if the displacement output E _M2 is raised to the non-displacement output E _M1 , the actual measured value E _M2 will also approach the true value E _MD .

Therefore, the value obtained by multiplying the actual measurement value E _M3 by the ratio E _M1 /E _M2 approximates the true value E _MD located on the straight line, so the calculation circuit 23 calculates the measurement error of the non-linear part. The correct corrected value, that is, the E _MD value on the straight line will be output.

As shown in Figure ₅ , if the linearity of e _{1 and e 2 is} extremely poor even within the range of | linearity deteriorates. Therefore, the measured value E _M3 deviates from the true value E _MD , but E _M2 also deviates from E _M1 , so multiplying E _M3 by (E _M1 / E _M2 ) yields the true value. This will bring us closer to E _MD .

Therefore, even in the case of the characteristics shown in FIG. 5, a displacement signal with measurement errors corrected can be obtained as a calculation result.

Note that instead of storing E M1 at each measurement, the first storage circuit 19 may store E _M1 intermittently.

It is also possible to correct sensitivity drift due to temperature changes and changes over time.

That is, when calibrating a scale, E _M1 is stored in the first memory circuit 19 when nothing is placed on the scale, and (e ₁ + e ₂ )/2 when a calibration weight is placed on the scale. value
E _M2 is stored in the second storage circuit 20, and at the same time,
Store the value E _M3 of e ₁ - e ₂ in the third storage circuit, calculate (E _M1 / E _M2 ) x E _MD at this time, adjust so that this result becomes the calibration value, and from now on at this time The value E _M1 of the first memory circuit 19 is held and memorized, and each time the memorized value is calculated based on the value of E _M1 for each measurement.
By performing the calculation (E _M1 /E _M2 ) x E _M3 with _{E M2} and E M3, sensitivity change can be corrected at the same time as linearity correction.

<Effects of the Invention> As explained above, in the displacement measuring device of the present invention, the changeover switch is switched by the timing signal of the timing circuit every time displacement is measured, and the non-displacement time sum voltage before measurement and the displacement during measurement are changed. The actual measurement value is corrected by the arithmetic circuit according to the ratio of these two values and output as a displacement amount. There is no need to actually measure the weight, and the displacement measurement can be automatically corrected to the correct value just by simple calculations at the time of measurement. Further, even if an error occurs in the actually measured output value due to temperature change or change over time, it is automatically corrected to the correct value by calculation for the same reason and output, so that accurate displacement measurement can be performed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a differential transformer, FIG. 2 is a diagram showing output characteristics with respect to core displacement of the differential transformer, FIG. 3 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. FIG. 5 is a diagram showing the displacement of the core during measurement, and FIG. 5 is a diagram showing the output characteristics with respect to the displacement of the core of the differential transformer when the nonlinearity is significant. 11...Oscillation circuit, 12...Differential transformer, 1
4... Selector switch, 17... DC amplifier, 19
...First memory circuit (non-displacement time sum voltage output value memory circuit), 20...Second memory circuit (displacement time sum voltage output value memory circuit), 21...Third memory circuit (actually measured output value memory circuit), 23... arithmetic circuit.

Claims (1)

[Claims] 1. An oscillation circuit that generates an oscillation signal of a predetermined frequency, a primary coil is excited by the oscillation signal of the oscillation circuit, and the output voltages of the two secondary coils correspond to the displacement of the core. a differential voltage output circuit that outputs a difference voltage signal between the output voltages of the two secondary coils; an amplification and detection circuit that amplifies and detects the difference voltage signal; and an output signal of the amplification and detection circuit. an A/D converter that converts the output voltage into a digital signal; and a displacement measuring device that outputs the output from the A/D converter as a displacement signal of the core, the sum voltage signal of the output voltages of the two secondary coils being a sum voltage output circuit for outputting, a changeover switch for switching the input to the amplification and detection circuit to either the difference voltage output circuit or the sum voltage output circuit; , a non-displacement time-sum voltage storage circuit that stores a non-displacement time-sum voltage output value of the A/D converter when the changeover switch is connected to the sum voltage signal side; a displacement time sum voltage storage circuit that stores a displacement time sum voltage output value of the A/D converter when the changeover switch is connected to the sum voltage signal side when the value is almost at the maximum; and a core of the differential transformer. a timing circuit that outputs a timing signal for switching the changeover switch from the sum voltage signal side to the difference voltage signal side when the displacement of the changeover switch reaches approximately the maximum; an arithmetic circuit that multiplies the real side output value of the A/D converter by the ratio of the displacement time-sum voltage output value of the displacement time-sum voltage storage circuit to the non-displacement time-sum voltage output value of the non-displacement time-sum voltage storage circuit; and the changeover switch is switched from the sum voltage signal side to the difference voltage signal side using the timing signal of the timing circuit every time displacement is measured, and the calculation output of the calculation circuit is outputted as the displacement of the core. A displacement measuring device featuring: