JP2005156348A - Device for detecting position - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the detection signal level in a position detection device which adopts a reluctance type detection method, especially a type with detection coil patterns laid on a printed board. <P>SOLUTION: The position detection device comprises a gear 110, having projections and depressions on the surface thereof and made of a magnetic material and the printed board 101 (a second member) which faces the gear 110 via a gap and relatively moves with respect thereto, detecting a relative displacement, on the basis of the change in the projections and depressions of a first member. The second member comprises the printed board 101, forming the detection coil patterns 102a, 102b and an iron core 120 around which an exciting coil 121 generating varying magnetic flux is wound. The varying magnetic flux, generated by the iron core 120 which fluctuates due to the change in the magnetoresistance between the projections and depressions of the gear 110 and the detection coil patterns 102a, 102b, is detected with an induced voltage of the detection coil patterns. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a position detection device used for industrial machines, machine tools, and the like, and more particularly to an improvement of a position detection device whose detection principle is a reluctance change detection type.

  In recent years, position detection devices used for industrial machines, machine tools, and the like have been desired to be robust against dirt, high temperatures, impacts, and the like from a poor usage environment. Position detection devices used in this field are roughly classified into two types, optical and magnetic. Optical detectors using a glass scale with a grid are not accurate due to condensation (cloudiness) of the glass scale due to condensation, splashing oil, etc., and mechanical strength due to the glass scale being made of glass. Have disadvantages such as vulnerability. In particular, it is often necessary to store the glass scale in a shield case in order to prevent contamination of the glass scale due to scattered oil or the like. Furthermore, in order to prevent condensation, it is often necessary to add a device for feeding air. Since the air supply device naturally includes an air filter circuit, it is necessary to neglect maintenance and inspection. As described above, the optical detector generally requires an auxiliary device in addition to the detection device itself in order to compensate for the weakness against dirt.

  For this reason, magnetic position detection devices that are resistant to dirt and have high robustness have attracted attention. Magnetic position detection devices are also classified into several types according to detection methods. There is a type that incorporates a magnetoresistive element in the sensor, a type that detects eddy current loss of the detection target (nonmagnetic material) with a coil, and a type that changes the reluctance change with the detection target (magnetic material) with a coil is there. In particular, a type that detects a change in reluctance is known as a sensor suitable for an inferior use environment because a detection target can be a steel material (magnetic material) and the temperature characteristics are good. A position detection device of a type that detects a change in reluctance often takes a form in which a detection target is a gear or rack tooth made of steel, and a winding is wound around pole teeth of a stator core made of a silicon steel plate. However, the diameter of the stator core is increased by enclosing the entire gear, and errors due to deviations in the winding positions of the pole teeth of the stator core are disadvantages of this configuration. In view of this, there is a type in which a coil is laid on a printed circuit board on the sensor side, and the sensor core is replaced with a winding wound around pole teeth of a stator core (Patent Document 1).

  FIG. 4 is a perspective view illustrating an example of a sensor unit and a detection target of a conventional position detection device in which a detection coil pattern is laid on a printed circuit board. A detection target gear 203 made of a steel material (magnetic material) is bonded and fixed to a rotation center of a rotation shaft (not shown) so that there is no runout. The rotation shaft is supported by a bearing (not shown) and is freely rotatable. It has become. The printed circuit board 401 is fixed at a position via the concave and convex portions on the outer peripheral surface of the gear 203 to be detected and a gap, and is not rotated. The printed circuit board 401 is provided with detection coil patterns 402a and 402b and an excitation coil pattern 403 surrounding them, and the excitation coil pattern 403 is connected to an excitation circuit (not shown) to generate a changing magnetic flux. The detection coil patterns 402a and 402b have a sinusoidal shape, and the wavelength thereof is the same as one pitch length (= π · mm: gear module) of the gear 203 to be detected. The detection coil patterns 402a and 402b are laid out while being shifted in the measurement axis direction by a quarter wavelength. The detection coil patterns 402a and 402b output, as an induced voltage, a magnetic flux in which the change magnetic flux generated by the excitation coil pattern 403 varies due to a change in magnetoresistance due to the unevenness of the gear 203 to be detected. Since the detection coil patterns 402a and 402b are shifted by ¼ wavelength, two-phase signals orthogonal to each other are output.

  In the example shown in FIG. 4, since the stator core is not used, it is easy to reduce the thickness, and the position accuracy in which the detection coil patterns 402a and 402b are laid is also good. However, since the magnetic path is not formed in the iron core (pole tooth) and the number of turns of the exciting coil pattern 403 is limited, the change magnetic flux itself is weak and the detected induced voltage value is also weak. was there. The case for fixing the printed circuit board 401 may be a copper material (magnetic material) or an aluminum material (non-magnetic material), but the magnetic flux of the changing magnetic flux generated from the exciting coil pattern 403 may be used. The road could be affected by the surrounding case material. When this occurs, variations occur in the magnetic flux interlinking the detection coil patterns 402a and 402b, which is an error factor.

JP-A-8-313295

  In the conventional position detection device, when an optical detection method is selected, it is necessary to consider a measure for preventing contamination, and there is a problem in strength itself. Among the magnetic detection methods, in the method of detecting eddy current loss, a nonmagnetic material with excellent conductivity must be selected as the detection target, and the surrounding mechanical parts that are often made of steel are used. The difference in the linear expansion coefficient was problematic. Among the magnetic detection methods in which the detection target is steel, when a magnetoresistive element is used for the sensor, the low contrast of the detection signal and the poor characteristics with respect to temperature changes have become problems. Among the magnetic detection methods that use steel as the detection target, in the type that detects the amount of change in magnetoresistance, such as a reluctance resolver, winding is performed after covering the pole teeth of the stator core with an insulating material such as a bobbin. There is a limit to miniaturization and miniaturization. Further, errors in the manufacturing stage such as aligned winding and winding position at the time of winding are errors as a position detecting device. Among the reluctance type detection methods, in the type in which the coil pattern for excitation and detection is laid on a plate material such as a printed circuit board, a magnetic path cannot be formed on the iron core (pole tooth) or the coil pattern for excitation There is a problem that the level of the induced voltage detected is weak because the number of turns is limited. Further, the magnetic path from the exciting coil pattern is not formed at a desired position due to the influence of the surrounding casing, which may cause an error.

  The present invention has been made in view of the circumstances as described above, and an object of the present invention is, among other magnetic detection methods, a type of detecting a magnetoresistive change amount in which a coil pattern for detection is laid on a printed circuit board. In spite of this, it is an object to provide a highly accurate position detection device with an increased detection signal level.

  The position detection device according to the present invention includes a first member made of a magnetic material on which repeated patterns having different magnetic resistances are formed, a first member that faces the first member through a gap and is relatively movable with respect to the first member. The second member includes a plate formed by forming a detection coil pattern and an exciting coil that generates a change magnetic flux, and the repetitive pattern of the first member and the second member A change magnetic flux generated by the exciting coil that fluctuates due to a change in magnetoresistance with the detection coil pattern is detected as an induced voltage of the detection coil pattern, and a relative movement amount between the first member and the second member is determined. In the position detecting device for detection, the exciting coil is wound around an iron core fixed to the back surface of the plate member.

  By winding an exciting coil around an iron core, a large detection signal can be obtained even at a relatively low frequency compared to a case where an exciting coil is laid on a plate material such as a printed circuit board. Moreover, a uniform magnetic flux can be emitted to the detection coil pattern by passing an iron core having a larger permeability than air in the magnetic path for excitation.

  FIG. 1 is a front view showing an example of a printed circuit board on which a detection coil pattern of a second member serving as a sensor unit of the position detection device of the present invention is formed. The detection coil pattern 102a having a sine wave pattern laid on the surface layer of the printed circuit board 101 is electrically connected to the detection coil pattern 102c having a sine wave pattern laid on the second layer by a through hole 103e. . The detection coil pattern 102a and the detection coil pattern 102c have a sinusoidal waveform phase that is opposite in phase, but the electrical phase is also opposite, so that the same phase is detected as a result. From this detection coil pattern 102a, the detection coil pattern 102b is pattern-formed at a position where the sine waveform phase is shifted by 90 ° (1/4 of one pitch) in the measurement axis direction. The detection coil pattern 102d is pattern-shaped at a position where the sinusoidal waveform phase is shifted by 90 ° in the measurement axis direction from the detection coil pattern 102c patterned on the layer. The detection coil pattern 102b and the detection coil pattern 102d are electrically connected through a through hole 103f.

  FIG. 2 is a perspective view showing an example of the relationship between the second member (sensor unit) of the position detection device of the present invention and the first member to be detected. The gear 110 to be detected, which forms the first member, is made by processing a steel material made of a magnetic material, and is geared so that the side facing the printed circuit board 101 has a repetitive pattern different from the uneven magnetic resistance. Has been. In the present invention, the second member including the printed circuit board is opposed to the gear 110 to be detected, that is, the first member via a gap, and the relative movement amount of both the members 101 and 110 is detected.

  In order to magnetically detect the rotation of the gear 110 to be detected as a reluctance change, an excitation coil that generates a change magnetic flux is required. In the present invention, this excitation coil is fixed to the back surface of the printed circuit board 101. A sufficiently large change magnetic flux is obtained by winding it on an iron core. In FIG. 2, an excitation coil 121 is wound around an iron core 120 made of soft ferrite as a base material, and is connected to an excitation circuit (not shown) and is in an excited state. Furthermore, the width of the iron core 120 in the relative movement direction of the first member and the second member, that is, the gear 110 to be detected, with respect to the printed circuit board 101 is a width corresponding to five pitches of the gear 110 to be detected. The back surface of the printed circuit board 101 and the iron core 201 are fixed with an adhesive. The gear 110 to be detected is located at a position through the surface of the printed circuit board 101 and an appropriate gap. Further, one pitch (= π · m) of the gear 120 to be detected and one wavelength of the detection coil patterns 102a to 102d in FIG.

  FIG. 3 is a schematic configuration diagram illustrating an example of a circuit that processes a detection signal from the sensor unit illustrated in FIGS. 1 and 2. The exciting coil 121 is supplied with an alternating current of 100 kHz by the exciting circuit 122, and a magnetic flux that changes at 100 kHz is emitted from the iron core 120 to the gear 110 to be detected. The AC magnetic flux generated from the iron core 120 is modulated according to the amount of change in magnetoresistance due to the concavo-convex pattern on the surface of the gear 110 to be detected. The detection coils 102a and 102c and 102b and 102d output voltages VSO and VCO proportional to the modulated magnetic flux. At this time, assuming that the number of teeth of the gear 110 to be detected is n, the rotation angle is θ, and the excitation current is sinωt, each coil 102a, 102c and The induced voltages generated in 102b and 102d can be expressed by equations (1) and (2).

  The voltage signals VSO and VCO expressed in this way are amplified by the differential amplifiers 130a and 130b to become signals VS and VC. The signals VS and VC are analog / digital converted by the analog / digital converters 131a and 131b at the timing when the excitation current generated by the timing generator 132 becomes zero (that is, cosωt = 1), and the digital signals DS, DC. At this time, the digital signals DS and DC can be expressed by equations (3) and (4).

The digital signals DS and DC are subjected to arc tangent calculation by the interpolation calculator 133, and n · θ indicating the rotational position of the gear 110 to be detected is calculated.

  In addition, when detecting the magnetic resistance change of the uneven part of the gear made of steel by AC magnetic flux, a very high frequency cannot be used due to the iron loss of the steel. Therefore, since the number of turns (the number of turns) is small in the excitation coil and the detection coil laid on the printed circuit board as in the type detecting eddy current loss, the detection voltage becomes very weak. For this reason, it is necessary to amplify the detection voltage with an amplifier circuit having a high amplification factor, which is disadvantageous in terms of cost and noise. In the present invention, the iron core around which the excitation coil is wound can generate a strong and uniform magnetic flux concentrated on the detection target side such as a gear, so that a large induced voltage can be generated from the detection winding even at a relatively low excitation frequency. Can be output. In addition, in the present invention, by adjusting the width of the iron core to an integral multiple of the uneven pitch on the surface of the gear or the like, the total amount of magnetic flux emitted from the iron core to the detection target side such as the gear becomes constant, and highly accurate position detection is possible. It is. Normally, when the width of the iron core is changed by ± 1/8 pitch or more with respect to an integral multiple of the uneven pitch, the total amount of magnetic flux emitted from the iron core to the uneven portion side changes when the uneven portion rotates (or moves). However, in the example as shown in FIG. 3, the variation is added to both the voltage signals VSO and VCO, which causes a problem that the detection error increases.

  Although the present invention has been described with respect to specific embodiments in the above examples, the present invention is not limited to this. For example, a magnetic body made of a steel material having irregularities on the surface to be detected can be made into a rack shape, and the position detection device of the present invention can be used as long as it detects the relative displacement amount of both members. it can. In addition, the plate on which the detection coil pattern is formed is not limited to the printed circuit board shown in the present embodiment. For example, the present invention may be applied even if the coil pattern is replaced with a film formed by applying semiconductor manufacturing technology. It can be set as a position detecting device.

It is a front view which shows an example of the 2nd member (sensor part) of the position detection apparatus of this invention. It is a perspective view which shows an example of the relationship between the 2nd member (sensor part) of the position detection apparatus of this invention, and the 1st member consisting of the gearwheel used as a detection target. It is a schematic block diagram which shows an example of the circuit which processes the detection signal from the sensor part shown by FIG.1 and FIG.2. It is a perspective view which shows the relationship between the sensor part of the conventional position detection apparatus, and a detection target.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 Printed circuit board, 102a, 102b, 102c, 102d Detection coil pattern, 103a, 103b, 103c, 103d, 103e, 103f Through hole, 110 Gear to be detected (first member), 120 Iron core, 121 Excitation coil, 122 Excitation circuit.

Claims (2)

A first member made of a magnetic material in which a repetitive pattern having different magnetic resistance is formed, and a second member that is opposed to the first member via a gap and is relatively movable with the first member;
The second member includes a plate material formed with a detection coil pattern, and an excitation coil that generates a change magnetic flux,
Detecting a change magnetic flux generated by the exciting coil, which is fluctuated by a magnetic resistance change between the repetitive pattern of the first member and the detection coil pattern of the second member, as an induced voltage of the detection coil pattern; In the position detection device that detects the relative movement amount between the first member and the second member,
The position detecting device, wherein the exciting coil is wound around an iron core fixed to the back surface of the plate member.   The position detection device according to claim 1, wherein the width of the iron core in the relative movement direction of the first member and the second member is substantially an integral multiple of the pitch of the repetitive pattern of the first member. .

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