JP2001027676A - Electromagnetic induction type detecting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic induction type detecting apparatus which can suppress effects of an a.c. magnetic field in an initial state to a minimum limit irrespective of a positional relationship of a magnetic field generation coil and a detection coil. SOLUTION: The apparatus has sensor part 1 consisting of a magnetic field generation coil 13 for generating an a.c. magnetic field in a detection area, a detection coil 11 for detecting a change of the a.c. magnetic field between when a conductor object is not present within the detection area in an initial state and when the object enters the detection area, and a cancelling coil 12 wound immediately above the detection coil 1 for generating an a.c. magnetic in the direction to cannel an induced electromotive voltage generated to the detection coil 11 by the a.c. magnetic field in the initial state, a receiving part 2 for amplifying a detect signal from the detection coil 11 and calculating an amplitude of the signal, a transmitting part 4 for supplying an a.c. of a specific frequency to the magnetic field generation coil 13, and a cancelling part 3 for supplying to the cancelling coil 12 an a.c. which generates an a.c. magnetic field totally opposite to the induced electromotive voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic induction system for detecting an induced electromotive voltage generated by an alternating magnetic field that changes when an object made of a conductor approaches in an alternating magnetic field in a detection area generated by a magnetic field generating coil. The present invention relates to a detection device.

[0002]

2. Description of the Related Art Conventionally, in this type of electromagnetic induction type detection device, the magnetic field generating coil and the detection coil are strictly aligned in a direction orthogonal to each other with mechanical precision, so that an initial state (a conductive object in the detection area) can be obtained. (When there is no), the effect of the AC magnetic field was suppressed as much as possible.

That is, conventionally, the induced electromotive voltage due to the AC magnetic field in the initial state is suppressed only by the positional relationship between the magnetic field generating coil and the detecting coil. However, this output does not become 0, and the detection is performed with higher sensitivity. In this case, when the current supplied to the magnetic field generating coil was increased, the output in the initial state increased in proportion to this. Therefore, there is a disadvantage that the amplification factor of the amplifier in the receiving unit cannot be increased.

[0004]

Further, in this method,
It was very difficult to adjust the positions of the magnetic field generating coil and the detection coil.

[0005] The present invention solves the above-mentioned problems and provides an electromagnetic induction type detection device capable of minimizing the influence of an AC magnetic field in an initial state regardless of the positional relationship between a magnetic field generating coil and a detection coil. It is in.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an AC magnetic field completely opposite to an AC magnetic field received in an initial state is applied to a cancel coil wound right above a detection coil. It is possible to minimize the influence of the AC magnetic field in the initial state, regardless of the positional relationship between the magnetic field generating coil and the detection coil,
Detection can be performed with higher sensitivity.

That is, according to the present invention, there is provided a magnetic field generating coil for generating an alternating magnetic field in a detection area, and a conductive object is disposed in a direction substantially orthogonal to the alternating magnetic field, and a conductive object is present in the detection area in an initial state. A detection coil that detects a change in an alternating magnetic field that occurs when the object does not exist and when the object enters; a detection coil that is wound right above the detection coil and cancels an induced electromotive force generated in the detection coil by the alternating magnetic field in an initial state. A sensor unit including a cancel coil that generates an AC magnetic field, a receiving unit that amplifies a detection signal from the detection coil and calculates the amplitude of the detection signal, and supplies an AC current having a specific frequency to the magnetic field generation coil. An electromagnetic induction having an initial state and a canceling unit for supplying an alternating current for generating an alternating magnetic field in a direction completely opposite to the induced electromotive force to the canceling coil. A detection device.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the whole of an electromagnetic induction type detecting apparatus according to an embodiment of the present invention. The electromagnetic induction type detection device of the present invention includes a sensor unit 1, a receiving unit 2 serving as a signal processing unit, a canceling unit 3, and a transmitting unit 4.

Next, the function of each block will be described. FIG. 2 is a diagram showing a functional system of the electromagnetic induction type detection device according to the embodiment of the present invention. As shown in FIG.
The magnetic field generating coil 13 in the sensor unit 1 generates an AC magnetic field in the detection area by the AC current supplied from the transmitting unit 4. The detection coil 11 detects a disturbance of the magnetic field generated when the conductive object approaches the detection area, and outputs a signal to the receiving unit 2. The canceling coil 12 is supplied with an AC magnetic field from the canceling unit 3 in a direction in which an induced electromotive voltage detected by the detecting coil 11 in the AC magnetic field generated by the magnetic field generating coil 13 is canceled in an initial state, thereby generating an AC magnetic field.

The receiving unit 2 includes a detecting coil 1 in the sensor unit 1.
1, an amplifier 21 for amplifying the signal of the magnetic field detected by 1, a synchronous detection circuit 22 a using this amplified signal and the oscillator 41 of the transmission unit 4 as a reference clock, and 9
A 90-degree phase shifter 23 for shifting the phase by 0 degree, a synchronous detection circuit 22b using this as a reference clock, and an arithmetic circuit 2 for calculating the amplitude of the input signal from the output of each synchronous detection circuit
4

The canceling unit 3 includes an oscillator 4 in the transmitting unit 4.
It comprises a 360-degree phase shifter 31 for adjusting the waveform of one signal and an amplitude adjuster 32.

The transmitting section 4 comprises an oscillator 41 for generating a fundamental frequency and an amplifier 42 for amplifying the signal and supplying the amplified signal to the magnetic field generating coil 13.

Next, a method for detecting a conductor approaching a detection area using the electromagnetic induction type detection device having the above-described configuration will be described.

The detection coil 11, the cancel coil 12,
Fixing the sensor unit 1 composed of the magnetic field generating coil 13;
An alternating current is applied to the magnetic field generating coil 13 at a frequency set by the transmitting unit 4. Thereby, an AC magnetic field is generated in the detection area. The detection coil 11 is arranged in a direction perpendicular to the AC magnetic field, and detects an induced electromotive voltage in an initial state generated only by the AC magnetic field unless a conductive object exists in the detection area. become. The AC magnetic field is disturbed by the approach of the conductive object, and a change in the AC magnetic field is detected to determine whether the conductive object has approached the detection area.

The cancel coil 1 is provided immediately above the detection coil 11.
In order to cancel the induced electromotive voltage generated by the AC magnetic field in the initial state by the cancel unit 3, an AC current for generating an AC magnetic field in a direction completely opposite to the AC magnetic field is supplied to the cancel coil 12, so that the initial state is apparently changed. Becomes zero, and can be canceled.

The cancellation method will be described.
In the initial state, an induced electromotive voltage generated by an AC magnetic field generated by the magnetic field generating coil 13 is detected by the detection coil 11. Since this signal has exactly the same frequency component as the alternating current supplied to the magnetic field generating coil 13, the signal of the transmitter 41 in the transmitting unit 4 is
An alternating current having a phase angle at which the induced electromotive voltage detected by the detection coil 11 is minimized is supplied to the cancel coil 12 and is fixed.

Further, the signal is input to the amplitude adjuster 32. Here, the alternating current having the amplitude value at which the induced electromotive voltage detected by the detection coil 11 becomes 0 is canceled.
2 and is fixed. for that reason,
It is an advantage of the present invention that the output of the detection coil in the initial state can be set to 0 under any conditions.

In the initial state, when the signal output from the detection coil 11 becomes 0, the cancel unit 3 fixes and holds the phase angle and the amplitude value of the alternating current supplied to the cancel coil 12. Then, the induced electromotive voltage due to the AC magnetic field detected by the detection coil 11 is determined as a signal when the conductive object approaches the detection area.

Therefore, in the present invention, the induced electromotive force of the AC magnetic field generated by the magnetic field generating coil 13 output in the initial state depending on the positional relationship between the magnetic field generating coil 13 and the detecting coil 11 or the surrounding environment in which the magnetic field generating coil 13 and the detecting coil 11 are arranged. The detection signal is supplied to the cancel coil 12 wound just above the detection coil 11 from the cancel unit 3 by supplying an AC current for generating an AC magnetic field completely opposite to the direction in which the induced electromotive voltage is generated, thereby detecting the initial state. The output from the coil 11 can be set to 0. Therefore, the amplification factor of the amplifier 21 in the receiving unit 2 can be set to the maximum, and a conductive object can be detected with higher sensitivity.

Since the output of the detecting coil 11 in the initial state is set to 0 without depending on the positional relationship between the magnetic field generating coil 13 and the detecting coil 11 and the surrounding environment in which the magnetic field generating coil 13 and the detecting coil 11 are arranged, a plurality of magnetic field generating coils can be detected. If there are the same number of cancel coils and cancel units as the number of detection coils in the combination of coils, the output of each detection coil can be set to zero.

[0022]

As described above, according to the present invention, there is provided an electromagnetic induction type detecting device which can minimize the influence of an AC magnetic field in an initial state regardless of the positional relationship between a magnetic field generating coil and a detecting coil. Could be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an entire electromagnetic induction detection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a functional system of the electromagnetic induction detection device according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sensor part 2 Receiving part 3 Canceling part 4 Transmitting part 11 Detecting coil 12 Canceling coil 13 Magnetic field generating coil 21 Amplifier 22a Synchronous detection circuit 22b Synchronous detection circuit 23 90 degree phase shifter 24 Arithmetic circuit 31 360 degree phase shifter 32 Amplitude adjustment Vessel 41 oscillator 42 amplifier

Claims (1)

[Claims] A magnetic field generating coil for generating an alternating magnetic field in a detection area; a magnetic field generating coil disposed in a direction substantially orthogonal to the alternating magnetic field; A detection coil for detecting a change in an AC magnetic field generated when an object enters, and a detection coil wound right above the detection coil and generating an AC magnetic field in a direction to cancel an induced electromotive voltage generated in the detection coil by the AC magnetic field in an initial state. A sensor unit including a cancel coil, a receiving unit that amplifies a detection signal from the detection coil and calculates an amplitude of the detection signal, and a transmission unit that supplies an AC current having a specific frequency to the magnetic field generation coil. An electromagnetic induction, comprising, in an initial state, an AC current for generating an AC magnetic field in a direction completely opposite to the induced electromotive voltage to the cancel coil. Type detection device.