JPS6113638B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a signal detection device using a differential transformer type magnetic head, for example, for detecting a sheet-like object colored or printed with a pigment or ink containing a metal component, and detecting a pattern drawn on the object. The present invention relates to a signal detection device using a differential transformer type magnetic head suitable for detecting patterns such as the following.

As shown in FIG. 1, the iron core 2 of this type of differential transformer type magnetic head 1 has two magnetic shunts 2a,
2b, and a part of these magnetic shunts 2a and 2b are common. A protruding detection section 3 that detects a printed matter (object to be detected) 10 and a pattern drawn thereon is located in the iron core portion forming one magnetic shunt 2a, and a gap 4 is formed in this detection section 3. . If necessary, a gap 5 is also formed in the core portion forming the other magnetic shunt 2b. An excitation coil 6 is wound around the common portion of the magnetic shunts 2a and 2b, and this excitation coil 6 is connected to a suitable alternating current power source. Further, secondary coils 7 and 8 are wound around both magnetic shunts 2a and 2b, respectively. Then, the difference between the induced voltages between the two secondary coils 7 and 8 is extracted as a differential output.

Now, such a differential transformer type magnetic head 1
When the printed matter 10 approaches the detection unit 3 and a magnetic path is formed through the magnetic material included in the printed matter 10, the magnetic flux of one magnetic shunt 2a increases, and the secondary coil 7
The induced voltage increases. As a result, a change appears in the differential output. The characteristics of the differential output with respect to the displacement of the magnetic material are shown in Figures 2a and 2b for amplitude and phase, respectively (the origin of displacement (position of zero displacement) varies depending on how the operating range is set). change).

As is clear from the graph in Figure 2a, the amplitude of the differential output voltage changes almost linearly with displacement in the area centered around the origin of displacement (range S) excluding the vicinity thereof. . However, since the differential transformer is not perfectly balanced, the amplitude of the differential output voltage does not become zero near the origin of displacement, and a residual voltage remains. Further, near the origin of displacement, the voltage amplitude changes slowly with respect to displacement.

Conventional signal detection equipment (for example,
40605), signals regarding the position, pattern, etc. of the magnetic body are extracted based only on the amplitude change of the differential output voltage, and therefore the range S in which the amplitude characteristics are linear is the operating range. was.

The principle of signal detection based on changes in differential output voltage amplitude is as follows. By adjusting the air gaps 4, 5, etc., the magnetic resistance of the magnetic shunt 2b is set to be slightly larger than that of the magnetic shunt 2a. In this way,
When the magnetic body is not close to the detection unit 3 (equilibrium point), the voltage V1 of the secondary coil 7 is slightly larger than the voltage V2 of the secondary coil 8, as shown in FIG. 3a. Let the difference between both voltages be V. When the magnetic body approaches the detection unit 3, the magnetic flux of the magnetic shunt 2a increases, and as a result, the voltage V1 increases as shown in FIG. 3b, so the differential voltage V also increases.

Conventional signal detection methods based on such voltage amplitudes have the following problems. That is, when the detection part 3 is worn out due to contact with a detected object such as printed matter 10 or other causes, the cross-sectional area of that part decreases, so the magnetic resistance of the magnetic shunt 2a increases, and the induced voltage V1 of the primary coil 7 decreases. decreases, and as a result, the differential voltage V also decreases, and the equilibrium point moves toward the differential voltage minimum point. In the vicinity of this minimum differential voltage, the amplitude change with respect to the displacement amount is very small as mentioned above, so even if the magnetic body approaches, the voltages V1 and V do not increase that much, and the magnetic body approach, and therefore it becomes difficult to accurately detect patterns on the printed matter 10.

By the way, as shown in FIG. 2b, near the minimum differential voltage, the phase of the differential output voltage changes greatly with respect to displacement. Therefore, if a change in the phase of the differential output voltage can be detected, it should be possible to detect a signal near the minimum differential voltage where the amplitude change is small.

Since the phase hardly changes in the above range S where the amplitude of the differential output voltage changes almost linearly with the displacement, it is necessary to provide a means that can detect the amplitude change as well as the phase change. .

This invention makes it possible to detect both the amplitude change and the phase change of the differential output voltage with a simple configuration, and enables signal detection to detect the displacement of a magnetic body over the entire range including the vicinity of the minimum point of the differential voltage. It provides equipment.

A signal detection device using a differential transformer type magnetic head according to the present invention includes an excitation coil and two
A differential transformer type magnetic head with a secondary coil, an oscillation circuit that generates an excitation signal to be applied to the excitation coil of the differential transformer type magnetic head, and a difference between two signals induced in the secondary coil of the differential transformer type magnetic head. It is characterized by comprising a differential circuit for detecting a signal, a multiplication circuit for multiplying the differential output signal of the differential circuit and a signal representing the excitation signal, and a filter circuit for smoothing the output signal of the multiplication circuit. do.

The signal detection device according to the present invention includes a multiplication circuit that multiplies a differential output signal and a signal representing an excitation signal, and the multiplication circuit identifies whether the amplitude change component included in the differential output signal is positive or negative. As well as taking it out,
The phase change component included in the differential output signal is also converted into a signal having an amplitude representing the amount and direction of the phase change. In this way, both the phase change and the amplitude change of the differential output of the differential transformer type magnetic head can be accurately extracted, making it possible to detect the entire range of the differential output characteristic curve. Therefore, even if the detection part of the differential transformer type magnetic head wears out and its cross-sectional area changes, it can be used as is, making it possible to use the magnetic head for a long time. Become. Furthermore, the configuration is extremely simple.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 4 and 5.

In FIG. 4, an oscillator 11 generates a sine wave excitation signal for driving the differential transformer type magnetic head 1, and the sine wave signal A is amplified by a magnetic head drive amplifier 12 to have the same waveform. current flows through the excitation coil 6. The frequency of the signal A is appropriately determined within a range to which the magnetic head 1 can respond, depending on the fineness of the pattern of the printed material 10 to be detected and the conveyance speed of the printed material 10. The magnetic head 1 is the same as that shown in FIG. It is preferable that the number of turns of the secondary coils 7 and 8 is equal. The induced voltages B and C of the secondary coils 7 and 8 are amplified by a differential amplifier 13 to become a signal D. In this example, it is assumed that the voltage signals B and C lead the sine wave signal A by 90 degrees in phase. Output signal D of differential amplifier 13
is input to the multiplier 15. On the other hand, the sine wave signal A of the oscillator 11 is also sent to the square wave generation circuit 14, and based on this signal A, a square wave signal E having the same frequency as the signal A and having a phase lead of 90 degrees is generated. E is sent to multiplier 15. Generation circuit 14
consists of a waveform shaping amplifier and a circuit that advances the phase by 90°. In the multiplier 15, both signals D and E
The product of is calculated. Then, the output signal F of the multiplier 15 is subjected to a low-pass filter 16 in which high frequency components including the excitation signal A component are removed, and then amplified by a signal amplifier 17 to become a detection signal G.

First, let us consider the case where there is no phase change in the differential output of the magnetic head 1 and only the amplitude changes. Referring to FIG. 5, the amplitude of the output voltage of the secondary coil 7 of the magnetic head 1 changes depending on the pattern of the magnetic material on the printed matter 10, as indicated by B1. The change in amplitude is represented by an envelope a shown by a chain line. It may be considered that the output voltage C1 of the secondary coil 8 hardly changes. The differential amplifier 13 calculates the difference between both signals B1 and C1, resulting in a signal D1. In the signal D1, a portion a where the amplitude of the signal B1 is large
1 and the small portion a2, the sign is exactly reversed (corresponding to b1 and b2 of the signal D1). Signal D
The envelope b of signal B1 coincides with the envelope a of signal B1. Next, the product of this signal D1 and the square wave signal E is calculated (signal F1), so for the part b1 where the sign of the signal D1 and the signal E are the same, the product is positive (part c1). , the product is negative for the part b2 with different positive and negative signs (part c2). It will be understood that the positive portion c1 of the signal F1 corresponds to the large amplitude portion a1 of the signal B1, and the negative portion c2 corresponds to the small amplitude portion a2. The pulse wave signal F1 is smoothed by the filter 16 to become a detection signal G1 shown by a broken line. This detection signal G1 corresponds to the envelope a of the signal B.

Next, consider the case where the differential output of the magnetic head 1 does not change in amplitude but only in phase. The output signal D2 of the differential amplifier 13 corresponds to the signal D1, and there is no change in amplitude.
The phase changes depending on the magnetic material pattern. The phase change of signal D2 appears as an increase or decrease in wavelength. Since the multiplier 15 calculates the product of the signal D2 and the signal E, as in the case of amplitude change, the part of the product signal F2 corresponding to the part where the signs of the signals D2 and E match is is positive (part d
1), it is negative in the non-matching part (part d2). Since the magnitude of the positive and negative parts of the signal F2 appears according to the phase change of the signal D2, the signal F2
The detection signal G2 obtained by smoothing the signal G2 with the filter 16 also corresponds to the phase change of the signal D2.
It matches 1. In this way, the signal detection device shown in FIG. 4 can detect both the amplitude change and the phase change of the differential output of the magnetic head 1 as the same result. Even if both an amplitude change and a phase change occur in the differential output due to the pattern of the printed matter 10, it can be detected in the same way.

In the above example, the output voltages B and C of the secondary coils 7 and 8 lead the excitation current A by 90 degrees in phase, but depending on the way the coils 6 to 8 are wound, the signals A and B,
It is also possible to shift the phase of C by 180°. In this case, the square wave signal E can be easily generated by two operations: shaping the signal A and inverting it using an inverter. Also,
When the phase difference between signal A and signal D is small, the phase of signal E does not necessarily have to match the phase of signal D. Furthermore, if necessary, the DC component of the output signal F of the multiplier 15 may also be removed. Furthermore, if a high-pass filter is connected to the output side of the differential amplifier 13 to remove low frequency components, the S/N ratio will be improved.

[Brief explanation of the drawing]

Figure 1 is a plan view showing a differential transformer type magnetic head, Figure 2 is a graph showing the differential output characteristic curve of the differential transformer type magnetic head, and Figure 3 is a vector diagram showing the operation of a conventional detection device. 4 is a block diagram showing an embodiment of the present invention, and FIG. 5 is a waveform diagram showing output signals of each block in the above block diagram. DESCRIPTION OF SYMBOLS 1... Differential transformer type magnetic head, 6... Excitation coil, 7, 8... Secondary coil, 11... Oscillator, 15...
Multiplier, 16...Low pass filter.

Claims (1)

[Scope of Claims] 1. A differential transformer type magnetic head having an excitation coil and two secondary coils, an oscillation circuit that generates an excitation signal to be applied to the excitation coil of the differential transformer type magnetic head, and a differential transformer type magnetic head. a differential circuit that detects a difference signal between two signals induced in the secondary coil of the differential circuit, a multiplier circuit that multiplies the differential output signal of the differential circuit and a signal representing the excitation signal, and an output signal of the multiplier circuit. A signal detection device using a differential transformer type magnetic head, which is equipped with a filter circuit for smoothing the signal.