JP2007108027A - Electromagnetic induction type displacement sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent degradation of measurement accuracy of sensors when electromagnetic induction type displacement sensors are operated in atmospheres where the alternating field is present in. <P>SOLUTION: The displacement sensor includes a first winding coil section 1 outputting the first alternating current signals with external alternating field H, a second winding coil section 2 including winding coil elements L1 to L4 deployed at even intervals along the direction of shifting direction of a measured object, and a magnetic response member following to displacement of the measured object and arranged to the second winding coil section 2 with possible relative displacement so as to be deployed at a predetermined pitch along that shifting direction, the second winding coil section 2 is, according to the relative displacement, equipped with a moving section 3 inducing a plurality of the second alternating current signals with different amplitude function properties, amplitude of which is modulated to the first alternating current signals, and a displacement magnitude detector 4 generating synthetic signals from the aforementioned plural second alternating current signals input from the second winding coil section and detecting electric phase difference between the first alternating current signals input from the first winding coil section and the synthetic signals. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a displacement sensor that detects a displacement amount of a measurement object by an electromagnetic induction method.

  A conventional electromagnetic induction displacement sensor is provided so as to be relatively displaceable with respect to the winding portion and the winding portion, and is formed between the winding portion and the relative displacement with respect to the winding portion. And a member for changing the magnetic resistance of the magnetic circuit. The member that changes the magnetic resistance is composed of a rod having a repetitive pattern (magnetic scale portion) of a magnetic part and a non-magnetic part provided in the axial direction, and the winding part has a predetermined interval in the axial direction of the rod. Are arranged in such a manner that the cylindrical space formed inside the winding portion is concentric with the rod (patented). Reference 1).

In this configuration, a pair of primary coils are excited in phase with each other by a sine signal sin ωt, output AC signals from the corresponding pair of secondary coils are synthesized in opposite phases, and the other pair of primary coils are cosine signal cos ωt. And the AC output signals from the corresponding pair of secondary coils are synthesized in opposite phases. Further, a combined output signal of the output AC signals from these secondary coils is obtained. The composite output signal is obtained by phase-shifting the reference AC signal sin ωt by the phase angle φ corresponding to the relative linear displacement between the magnetic body portion of the rod and the winding portion. The linear position is detected by measuring the phase shift φ from the AC signal sin ωt.

Thus, the conventional electromagnetic induction type displacement sensor forms a magnetic circuit between the winding part and the primary coil excited by the alternating current signal and the secondary coil, and the winding part. Since it is composed of a member that changes the magnetic resistance of the magnetic circuit in accordance with the relative displacement with respect to, for example, when mounted on a machine that operates by non-contact power supply, it exists around the sensor A strong alternating magnetic field may become a noise source and reduce the measurement accuracy of the sensor. However, there has been a problem that the noise countermeasure is very difficult.
JP-A-9-89516 (paragraphs [0029] to [0039])

  Therefore, the subject of this invention is preventing the fall of the measurement precision of a sensor, when an electromagnetic induction type displacement sensor is used in the environment where an alternating magnetic field exists.

  In order to solve the above problems, the present invention is used in an environment in which an alternating magnetic field constantly exists, and is a first winding coil unit that outputs a first alternating signal induced by the alternating magnetic field. A second winding coil portion having a plurality of winding coil elements arranged at equal intervals along the displacement direction of the measurement object, and following the displacement of the measurement object and the second winding coil And a plurality of magnetic response members arranged at a predetermined pitch along the displacement direction, and the second winding coil portion includes the second winding coil portion according to the relative displacement. A movable portion that is amplitude-modulated with respect to one AC signal and induces a plurality of second AC signals having different amplitude function characteristics, and is connected to the first winding coil portion and the second winding coil portion, The plurality of input from the second winding coil unit A displacement amount detection unit that generates a composite signal from two AC signals and detects an electrical phase difference between the composite signal and the first AC signal input from the first winding coil unit; The electromagnetic induction type displacement sensor characterized by the above is configured.

In the above-described configuration, preferably, the second winding coil unit includes a cylindrical space including the four winding coil elements and extends in the axial direction, and the movable unit includes the second winding coil unit. The rod-shaped body is arranged so as to be slidable in the axial direction through the cylindrical space, and the cylindrical shape has a pitch of 4 times the interval between the winding coil elements along the axial direction of the rod-shaped body. Magnetic response members are arranged.
More preferably, the first AC signal is a sine wave signal Asin ωt, and the first to fourth lines arranged in order from one end side of the second winding coil portion according to the relative displacement x of the movable portion. Among the winding coil elements, an alternating current signal asin θ · sin ωt having an amplitude function characteristic of a sine function is generated from the pair of the first and third winding coil elements from the pair of the second and fourth winding coil elements. AC signals acos θ · sin ωt having an amplitude function characteristic of a cosine function are respectively output, and a composite signal asin (ωt ± θ) having an amplitude function characteristic of a sine function is generated from the AC signals having two different amplitude function characteristics. The

  According to the present invention, when the external magnetic field is a steady AC magnetic field, a magnetic field that becomes a base for detecting displacement by applying an excitation AC signal to the primary coil of the electromagnetic induction type sensor as in the prior art. Since the external AC magnetic field is directly used instead of generating the second winding coil portion (conventional secondary coil) according to the positional relationship with the movable portion, the change in inductance is detected. It is possible to prevent a decrease in measurement accuracy of the electromagnetic induction displacement sensor due to the presence of an external magnetic field.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing the configuration of an electromagnetic induction displacement sensor according to one embodiment of the present invention. As shown in FIG. 1, according to the present invention, a first winding coil unit 1 that outputs a first AC signal induced by an external AC magnetic field H that exists steadily, and an object to be measured (illustrated) The second winding coil part 2 having a plurality (four in this embodiment) of winding coil elements L1 to L4 arranged at equal intervals along the displacement direction Z, and the displacement of the measurement object And a plurality of magnetic response members arranged at a predetermined pitch along the displacement direction Z, in accordance with the relative displacement, The second winding coil unit 2 is provided with a movable unit 3 that induces a plurality of (two in this embodiment) second AC signals that are amplitude-modulated with respect to the first AC signal and have different amplitude function characteristics. .

  FIG. 2 is a perspective view showing the configuration of the second winding coil portion and the movable portion of the electromagnetic induction type sensor shown in FIG. 1. Referring to FIG. 2, the second winding coil portion 2 includes a cylindrical space 6 that includes four winding coil elements L1 to L4 and extends in the axial direction. Further, the movable part 3 is attached to the rod 4 made of metal or plastic that does not exhibit remarkable magnetism, and the distance 4 between the coil elements L1 to L4 along the axial direction thereof. It is formed as a rod-shaped body composed of cylindrical magnetic response members (ferromagnetic bodies) 5 arranged with a pitch of one pitch, and is slidable in the axial direction through the cylindrical space 6 of the second winding coil portion 2. Is arranged.

  A displacement amount detection unit 4 is connected to the first winding coil unit 1 and the second winding coil unit 2. The displacement amount detection unit 4 includes a first AC signal detection unit 7 to which the first AC signal output from the first winding coil unit 1 is input and a plurality of second AC signals input from the second winding coil unit 2. A second AC signal combining unit 8 that generates a combined signal of the two AC signals, a combined signal input from the second AC signal combining unit 8, and a first AC signal input from the first AC signal detecting unit 7 Is provided with a phase difference detecting unit 9 for detecting the electrical phase difference.

In this way, the first AC signal Asinωt is induced in the first winding coil 1 by the external AC magnetic field H, and this AC signal is detected by the first AC signal detector 7.
On the other hand, the winding coil elements L1, L2, L3, and L4 of the second winding coil unit 2 are induced by the external AC magnetic field H as in the first winding coil unit 1, but the sine wave signal Asinωt is movable. When the portion 3 is relatively displaced by the displacement amount x, a change in the inductance according to the relative position with the magnetic response member 5 provided in the movable portion 2 at a predetermined pitch causes a sinusoidal function in the pair of the winding coil elements L1 and L3. An AC signal asinθ · sinωt having an amplitude function characteristic is induced, and an AC signal acosθ · sinωt having an amplitude function characteristic of a cosine function is induced in the pair of winding coil elements L2 and L4.

The second AC signal asinθ · sinωt from the pair of winding coil elements L1 and L3 and the second AC signal acosθ · sinωt from the pair of winding coil elements L2 and L4 are input to the second AC signal synthesizing unit 8. Is done. The second AC signal synthesizer 8 receives the input second AC signal X = asin θ · sin ωt (1)
Y = acos θ · sin ωt (2)
Then, sin ωt in equation (1) is converted to cos ωt to obtain asin θ · cos ωt, and the addition theorem of trigonometric function is applied to obtain the combined signal asin θ · cos ωt ± acos θ · sin ωt = asin (ωt ± θ)
Is generated.

Then, the phase difference detection unit 9 detects the electrical phase difference θ between the combined signal asin (ωt ± θ) and the first AC signal Asinωt. As shown in FIG. 3, the phase difference θ is detected by counting the time from the zero cross point of the Asin ωt graph to the zero cross point of the asin (ωt + θ) graph.
Since the phase difference θ is in a proportional relationship with the position of the movable part 3, the amount of displacement from the position of the movable part 3 and hence the reference position is obtained by detecting the phase difference θ.

It is a block diagram which shows the structure of the electromagnetic induction type displacement sensor by one Example of this invention. It is a perspective view which shows the structure of the 2nd coil | winding coil part and movable part of the electromagnetic induction type displacement sensor of FIG. It is a figure which shows the time relationship between the graph of Asin (omega) t, and the graph of asin ((omega) t + (theta)).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st winding coil part 2 2nd winding coil part 3 Movable part 4 Displacement amount detection part 5 Rod 6 Magnetic response member 7 Cylindrical space 8 1st alternating current signal detection part 9 2nd alternating current signal synthetic | combination part 10 Phase difference detection part

Claims (3)

It is used in an environment where there is a constant AC magnetic field,
A first winding coil section for outputting a first AC signal induced by the AC magnetic field;
A second winding coil portion having a plurality of winding coil elements arranged at equal intervals along the displacement direction of the measurement object;
A plurality of magnetic response members arranged to follow the displacement of the measurement object and to be relatively displaceable with respect to the second winding coil portion and arranged at a predetermined pitch along the displacement direction; In response to the displacement, a movable part that induces a plurality of second AC signals that are amplitude-modulated with respect to the first AC signal and have different amplitude function characteristics in the second winding coil unit;
Connected to the first winding coil unit and the second winding coil unit, and generates a synthesized signal from the plurality of second AC signals input from the second winding coil unit, and the synthesized signal and the An electromagnetic induction displacement sensor comprising: a displacement amount detection unit that detects an electrical phase difference from the first AC signal input from the first winding coil unit. The second winding coil portion includes a cylindrical space that includes four winding coil elements and extends in the axial direction, and the movable portion passes through the cylindrical space of the second winding coil portion, and The rod-shaped body is arranged so as to be slidable in the axial direction, and the cylindrical magnetic response members are arranged along the axial direction of the rod-shaped body with a pitch of four times the spacing of the coiled coil elements as one pitch. The electromagnetic induction displacement sensor according to claim 1, wherein: The first AC signal is a sine wave signal Asinωt, and the first to fourth winding coil elements arranged in order from one end side of the second winding coil portion according to the relative displacement of the movable portion. Among them, an AC signal asin θ · sin ωt having a sinusoidal amplitude function characteristic from the pair of the first and third winding coil elements is an amplitude function of a cosine function from the pair of the second and fourth winding coil elements. AC signals acos θ and sin ωt having characteristics are respectively output, and a composite signal asin (ωt ± θ) having an amplitude function characteristic of a sine function is generated from the AC signals having two different amplitude function characteristics. The electromagnetic induction type displacement sensor according to claim 2.

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