JPS6018702A - Displacement measuring device - Google Patents

Abstract

PURPOSE:To make it possible to correct the measurement error due to non- linearity by simple operation without decreasing the measuring efficiency, by performing the specified operation by using the output value of a differential transformer under the specified conditions thereof. CONSTITUTION:When the displacement of a core 12a of a differential transformer 12 before measurement is approximately at timing t1 of zoro, a switch 14 is connected to the side (a). The output value EM1 of an A/D converter 18 at this time is memorized. When the displacement of the core 12a becomes the maximum value at the time of measurement, the switch 14 is connected to the side (b) and the output value EM2 of the converter 18 is memorized. At timing t3 immediately after that measurement, the switch is connected to the side (a), and the output EM3 of the converter 18 is memorized. An operating circuit 23 operates (EM1/EM2)XEM3 based on first to third memory circuits 19-21 and makes a display circuit 24 to display the results. Therefore, the value becomes approximately equal to the true value EMD, and the measurement error due to non-linearity can be corrected by the simple operation.

Description

[Detailed description of the invention] The present invention relates to a displacement measuring device using a differential transformer.

In devices that use 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, and this amount of displacement is converted into an electrical signal. It is converted to measure length, weight, etc. That is, when the core 1a of the differential transformer 1 is displaced in the X direction as shown in FIG.
The output voltages e1 and e2 of the secondary coil 1C11d change in proportion to the displacement of the core 1a, as shown in FIG. Therefore, the differential voltage θ1-e2 between the two changes in proportion to the displacement of the core 1a, so the displacement amount of the core 1a is measured by extracting the differential voltage signal from the output signal of the secondary coil 1(!, 1(1). .

As shown in Fig. 2, the output voltages θ1 and e2 change almost linearly with respect to the displacement of the core 1a within a certain range, but beyond a certain range, the output voltages θ1 and e2 change curves due to changes in mutual inductance. Draw and change. For this reason, measurement accuracy deteriorates rapidly beyond a certain range, and countermeasures against this result have been problematic.

As one measure against this problem, in the past, an object of a reference length or a reference weight was measured every measurement or intermittently, and correction calculations were performed based on the actual measurement values. However, this method has disadvantages in that it takes time to measure the reference quantity, reducing measurement efficiency, and requires a special structure for supplying the reference object.

Another countermeasure is to store non-linear changes from actual measurements as data, and then perform correction calculations from the measured values based on this data. There were disadvantages such as the inability to correct drift and the need to obtain correction data again when the differential transformer was replaced, making calculations extremely complicated.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks and provide a displacement measuring device that can correct measurement errors due to nonlinearity by simple calculations without reducing measurement efficiency.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

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

In the figure, 11 is an oscillation circuit that outputs an oscillation signal of a predetermined frequency, and 12 is a differential transformer whose core 12a is displaced in proportion to the linear displacement to be measured. The next coil 12b is excited,
Two secondary coils connected with opposite polarity/L'12C, 12
Output voltages θ1, e2 corresponding to the displacement of the core 12a from d
Output each. 13 is the secondary coil 1 of the differential transformer 12? , 12(l output voltage e1, difference voltage e of θ2
1-02 to the secondary coil 13b, and an average voltage of el and 82 (e1+82) is taken out from the intermediate tap of the primary coil 13a of the input quadrangle 13. 14 is a changeover switch, input quadrature transformer 1
The output terminal (A) from the secondary coil 131) of No. 3 and the output terminal (B) from the intermediate tap of the primary coil 13a are switched. 15 is an AC amplifier that amplifies the output signal from the 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 a detector 16 18 is an A/D converter that converts the output signal of the DC amplifier 17 into a digital signal.

19 stores the output value EM1 of the A/D converter 18 when the changeover switch 14 is connected to the (b) side before measurement, that is, when the displacement of the core 12a of the differential transformer 12 is approximately zero. Memory circuit 1, 20 is A when the changeover switch 14 is connected to the (b) side at the time of measurement, that is, when the displacement of the core 12a of the differential transformer 12 is almost at its maximum.
/ A second storage circuit 21 stores the output value EM2 of the D converter 18, that is, the core 1 of the differential transformer 12 at the time of measurement.
When the displacement of 2a reaches almost the maximum, selector switch 1
This is a third storage circuit that stores the output value EM3 of the A/D converter 18 when A/D converter 4 is connected to the (A) side. 22 is a switching signal of the changeover switch 14 at each timing, a write signal to the first, second, and third memory circuits 19, 20, and 21, and a signal for the first, second, and third memory after the writing is completed. This is a timing circuit that outputs a read signal to circuits 19, 20, and 21. For example, in the case of electric resistance welding measurement, as shown in Figure 4, when the object to be weighed is transferred to the scale, the displacement Then, he returned to Zero. As shown in FIG. 4, the first memory circuit 19 stores EM1 at timing t1 before placing the object on the scale, and when the displacement X reaches almost the maximum after placing the object on the scale. At timings t2 and t3 with a slight interval, the second and third
The storage circuit 20.21 stores 8M2.8M3.

23 receives each memory value of the first, second, and third memory circuits 19, 20, and 21, and executes (''/8M2) x BM3
24 is a display circuit that displays this displacement signal.

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

The primary coil 121) of the differential transformer 12 is the oscillation circuit 11
The secondary coil 12C1 is excited by the oscillation signal from the
The output voltages e1 and θ2 of the core 12d change in accordance with the displacement of the core 12a. An output voltage θ1-02 is generated at the secondary coil 13b of the input quadrature transformer 13, and (e, +1132)/2 is generated at the intermediate tap of the primary coil 13a.

As shown in FIG. 2, the output voltage θ1 of the secondary coils 12'l' and 12a changes within a certain range according to the displacement of the core 12a.
Since θ2 changes approximately linearly, the differential voltage e1-02 also changes approximately linearly. On the other hand, the average voltage (θ1+
02v2 becomes approximately constant within the same range regardless of the displacement of the core 12a. As shown in FIG. 4, the displacement X of the core 12a is zero before the measurement, gradually increases from zero during the measurement, stabilizes at the maximum value, and rapidly returns to zero at the end of the measurement. Therefore,
The differential voltage θ1-82 and the average voltage (e1+02)/2 are output with the characteristics shown in FIG. 2 as the core 12a moves during measurement.

By switching the changeover switch 14-, the above-mentioned differential voltage 8
The output signal from the terminal (a) representing 1-82 and the output signal from the terminal (b) representing the average voltage (e, 102)/2 both pass through the same circuits 15-18. 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 t1 when the displacement of the core 12a before measurement is almost zero, the first memory circuit 10 has an average voltage (e1+82)/
2, that is, the output value EM1 of the A/D converter 18 when the changeover switch 14 is connected to the (A) side is stored.

Then, at timing t2 when the displacement of the core 12a reaches almost the maximum value during measurement, the second storage circuit 20
The average voltage (e1+02)/2, ie, the output value EM2 of the A/D converter 18 when the changeover switch 14 is connected to the (b) side is stored. Then, at t3 immediately after that, the changeover switch 14 is switched to the (a) side, and the output value EM3 of the A/D converter 18 when connected to the differential voltage e 1e 2 side, that is, the (a) side, is be remembered. The arithmetic circuit 23 calculates (EMl/EM2)x8M3 based on the output values of the respective memory circuits 19, 20, 21 and outputs it as a displacement signal, and the display circuit 24 outputs the displacement.

If the displacement X of the core 12a exceeds 1t/1,
As shown in FIG. 2, the measured value EM3 stored in the third storage circuit 21 deviates from the linear change and is lower than the true value EMD, which is on the extension of the straight line. On the other hand, the second
The value EM2 stored in the storage circuit 20 also deviates from the linear portion and decreases, and is lower than the value EM1 for the displacement amount stored in the first storage circuit 19. Therefore %
If 8M2 is raised to EMl, % 8M3 is also the true value EM
This will bring us closer to D. Therefore, EMI has a ratio EM1/
Since the value multiplied by bM2 approximates the true value EMD, the arithmetic circuit 23 outputs a value in which the measurement error in the non-linear portion has been corrected. When the maximum value of the displacement amount X is within the range of 1-/1, EMi, 7ya, is approximately
Therefore, 8M3 is output as the result of the 1 calculation.

As shown in FIG. 5, when the linearity of θ1 and θ2 is extremely poor, the linearity of e, -e2 and (e1+02)/2 is similarly poor. Therefore, the measured value EM3 deviates from the true value EMD, but since 8M2 also deviates from EMl, multiplying 8M3 by (8M1/F), 2) approaches the true value EMD. Become. 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 the first memory circuit 10 stores EM1 for each measurement.
'Instead of being stored in ', it may be stored intermittently.

It is also possible to correct sensitivity drift.

That is, when calibrating a scale, EMl is stored in the first storage circuit 19 when nothing is placed on the scale, and the value EM2 of (e□+ex)/2 when a calibration weight is placed on the scale. is stored in the second storage circuit 20, and at the same time, the value EM3 of e□-82 is stored in the third storage circuit, and at this time (EMI /EM2
)×EM3, and adjust this result to become the calibration value, and thereafter use the value EM of the first storage circuit 19 at this time.
1 is retained and memorized, and the calculation (EM1/EM
2) By performing ×EM3, sensitivity change can be corrected at the same time as linearity correction.

As explained above, with the displacement measuring device of the present invention, there is no need to specifically measure the reference length or reference weight in order to correct measurement errors, and only simple calculations are required.
It becomes possible to perform automatically corrected displacement measurements without reducing measurement efficiency.

[Brief explanation of drawings]

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 of the differential transformer with respect to the displacement of the core when the nonlinearity is significant. 11... Oscillation circuit, 12... Differential transformer, 14...
...Selector switch, 17...DC amplifier, 19...
First memory circuit, 20...Second memory circuit, 21...
- Third memory circuit, 23... arithmetic circuit. Patent Applicant Anritsu Electric Co., Ltd. Agent Patent Attorney Makoto Hayakawa

Claims (1)

[Claims] 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 two secondary coils are excited.
A differential transformer in which the output voltage of the secondary coil changes in accordance with the displacement of the core; a differential voltage output circuit that outputs a differential voltage signal between the output voltages of the two secondary coils; and a sum voltage output circuit that outputs a sum voltage signal. a circuit; a changeover switch that switches between and outputs the difference voltage signal and the sum voltage signal; an amplification and detection circuit that amplifies and detects the output signal of the changeover switch; and A that converts the output signal of the amplification and detection circuit into a digital signal. /D converter; and the A/D converter when the changeover switch is connected to the sum voltage signal side when the displacement of the core of the differential transformer is approximately zero.
a first storage circuit that stores an output value EM1 of the D converter; an output value of the A/D converter when the changeover switch is connected to the sum voltage signal side when the core of the differential transformer is displaced; a second storage circuit that stores EM2; and a third storage circuit that stores the output value EM3 of the A/D converter when connected to the differential voltage signal side; EM2)
A displacement measuring device comprising: a calculation circuit that calculates EM3 and outputs the calculation result as a displacement signal of the core.