JP2010223595A - Position detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a position detection device mountable on an existing rack-and-pinion type drive mechanism. <P>SOLUTION: The position detection device is mountable on the rack-and-pinion type drive mechanism whose rack (12) is made of magnetic material, and the detection device includes: a sensor unit (10) for detecting a change in magnetic flux accompanying movement of the rack; an oscillation circuit for generating a predetermined input waveform to input it to the sensor unit; and a converter composed of a phase difference detection circuit for measuring an output waveform output from the sensor unit and detecting a phase difference corresponding to a movement of the rack. An object of detection for this sensor unit is the rack itself. This sensor unit has three sets of magnetic sensor blocks composed of magnetic sensors and permanent magnets. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a magnetic position detector that can be directly attached to a rack and pinion type drive device or the like.

  Conventionally, position detectors that measure displacement by detecting a change in magnetic flux using a magnetic sensor are known. In general, there are optical and magnetic type position measuring instruments, but the magnetic type has an advantage that it can be used even in a bad environment that is easily contaminated by vibration, oil, moisture, or the like.

  In a magnetic position detector, in general, in order for a magnetic sensor to measure a change in magnetic flux, it is necessary to attach a magnetic body plate or the like provided with grooves or irregularities of equal pitch on a detection target. However, when gears are usually formed of a magnetic material and are provided with irregular pitches of equal pitch, the amount of displacement can be accurately measured by measuring the change in magnetic flux of the “gear itself” to be detected. There is an advantage that can be measured.

  For example, Patent Document 1 discloses a “position displacement sensor” that can accurately measure the displacement of a magnetic material having gear-like irregularities using a semiconductor magnetoresistive element (paragraphs 17 to 23, etc.). reference). According to this document, “a sinusoidal AC voltage is applied as a voltage V applied to a series-parallel circuit of a semiconductor magnetoresistive element that generates a shared voltage including a sine displacement or a cosine displacement”, and “2 consisting of an α-phase output and a β-phase output is used. After taking out the phase output and applying the trigonometric addition theorem to these two-phase outputs, and then obtaining the solution, "by counting the time difference between any zero cross point and the zero cross point of the applied voltage, the gear itself or The displacement of a magnetic material having gear-like irregularities is accurately measured. More specifically, the four magnetoresistive elements are used so that “the arrangement interval of each pair of semiconductor magnetoresistive elements electrically connected in series corresponds to a half of the gear pitch” In addition, a configuration is adopted in which the pair of arrays and the pair of adjacent arrays in the semiconductor magnetoresistive element are in a complementary relationship (see paragraphs 16 to 17 and FIGS. 2 and 4).

JP 2004-271423 A

  However, in Patent Document 1 described above, since it is a two-phase phase difference method of an α phase and a β phase, ripples are likely to increase, and it is considered that there is a problem in terms of reliability of detection results. Further, since a series-parallel circuit (that is, one “bridge circuit”) composed of four semiconductor magnetoresistive elements is used as the magnetic sensor, it is considered that the reliability is low in terms of mounting accuracy.

  The present invention has been made in view of the above, and an object thereof is to provide a highly reliable magnetic position detector that can measure at high speed and with high resolution.

  A position detector according to the present invention includes a pinion that is a gear, and a rack that is provided with teeth that fit with the teeth of the pinion and moves linearly according to the rotation of the pinion, and the rack is made of a magnetic material. -It can be attached to a drive mechanism of an & pinion type. This position detector measures a sensor unit that detects a change in magnetic flux accompanying the movement of the rack, an oscillation circuit that generates a predetermined input waveform for input to the sensor unit, and an output waveform output from the sensor unit. A converter comprising a phase difference detection circuit for detecting a phase difference corresponding to the amount of movement of the rack, and this sensor unit is characterized in that the rack itself is to be detected.

  Desirably, the sensor unit has three sets of magnetic sensor blocks including a magnetic sensor and at least one permanent magnet arranged so that the magnetic flux penetrates substantially perpendicularly to the magnetic sensor.

  This sensor unit is preferably provided so as to be rotatable in a horizontal plane with respect to a portion to which a portion for detecting magnetic flux in the sensor unit is fixed. This is because when the rack pitch is slightly smaller than the original optimum value, the distance between the magnetic sensor blocks S1, S2, and S3 is apparently smaller than the rack by rotating the sensing unit with respect to the mounting unit. This is because there is an effect that the original accuracy of the sensor is ensured in conformity with the pitch.

  Furthermore, by configuring the shape of the rack teeth to be similar to the output waveform (for example, a trigonometric function such as a sine curve), the change in magnetic flux detected by the magnetic sensor becomes sin, and the trigonometric addition theorem is more accurate. The accuracy of the sensor is improved. Since the magnetic field strength is inversely proportional to the square of the distance, by configuring the shape of the rack tooth to be similar to √ (sin x), the change in magnetic flux corresponds to the change in the rack tooth, so reading accuracy is further improved. It is done.

  Furthermore, it is preferable to arrange the sensor unit so that when the voltage amplitude of the trigonometric function waveform is given as the input waveform, the change of the magnetic circuit characteristics becomes the current amplitude of the trigonometric function within one pitch. Specifically, in this method, as described in the embodiments described later, the magnetic sensor block is adjusted by adjusting the gap G between the sensor unit and the rack or by rotating the sensor unit in the horizontal plane as described above. It is conceivable to make the interval of these apparently small.

  According to the present invention, since the rack itself is a detection target, it is not necessary to separately provide a magnetic scale, the cost is reduced, the structure is simple, and the reading accuracy can be improved.

FIG. 1 is a diagram showing an example of an embodiment of a position sensor according to the present invention. FIG. 2 is an enlarged view showing the positional relationship between the magnetic sensor group 11 and the rack 12. FIG. 3 is an overall configuration diagram of the position detection apparatus according to the embodiment of the present invention. 4A is a side view of the sensor unit 10, and FIG. 4B is a front view. FIG. 5 is a diagram illustrating a part of trigonometric function (Y = sin A) and functions Y = √ (sin A) and Y = −√ (sin A). FIG. 6 is a diagram illustrating a relative positional relationship between the sensor unit 10 and the rack 12. FIG. 7 is a diagram illustrating how the magnetic flux changes.

(First embodiment)
First, the overall configuration of the position detection apparatus according to the embodiment of the present invention will be described with reference to FIG. This apparatus is roughly divided into a head amplifier 50 and a converter 20. The head amplifier 50 is a combination of three magnetic sensors that detect changes in magnetic flux and convert them into electrical signals, and a differential amplifier. The converter 20 detects an oscillation circuit 30 for generating a three-phase AC signal (U phase, V phase, W phase) as an input signal waveform to the head amplifier 50, and a phase difference signal fed back from the head amplifier 50. And a phase difference detection circuit 40 to be measured.

The oscillation circuit 30 includes a crystal oscillator, a CPU (central processing unit), a D / A converter, and the like, and generates a three-phase alternating current (U phase, V phase, W phase) voltage waveform. Each waveform is composed of a voltage waveform of a sine wave whose phase is different by 2π / 3 (= 120 °) as represented by the following Expression 1.
(Formula 1)
V ₁ = V ₀ sin θ
V ₂ = V ₀ sin (θ + (2n + 2/3) · π)
V ₃ = V ₀ sin (θ + (2n + 4/3) · π)
(However, V0 is a constant and n is an integer.)
Further, the interval between the magnetic sensor blocks S1, S2, S3 is between S1 and S2: (N + 1/3) · P
Between S1 and S3: (M + 2/3) · P
(However, N and M are integers, and P is the length of one pitch.)
It is arranged to satisfy the relationship. Θ can also be expressed as θ = ω · t using the angular velocity ω and time t.

  It is possible to configure four (two pairs) magnetic sensors and generate a two-phase AC signal as an input signal in the oscillation circuit 30, but the reading accuracy is lower than that of the above-described three-phase type. In addition, since four sensor units are required, the configuration is complicated. In the case of the two-phase system, the phase difference between the two input signals is π (= 180 °).

  FIG. 1 shows an embodiment of a position detection device according to the present invention. As shown in this figure, the position detection device according to the present invention is attached to a “rack and pinion” type drive mechanism. The sensor unit 10, the rack 12, and the pinion 14 are attached by support members 1, 2, and 4. The pinion 14 is a rotating gear and is connected to a rotational driving source such as a motor. The rack 12 is provided with teeth that fit into the teeth of the pinion 14. For this reason, the rack 12 can move linearly with the driven body 3 in accordance with the rotation of the pinion 14.

  The sensor unit 10 includes a magnetic sensor and at least one permanent magnet arranged so that magnetic flux penetrates substantially perpendicularly to the magnetic sensor. The magnetic sensor may be an element having a function of detecting a change in magnetic flux, such as a Hall element, a bridge circuit composed of four series-parallel circuits of magnetoresistive elements, or a GMR (Giant Magneto Resistive Head).

  As shown in FIG. 1, the sensor unit 10 is provided so as to be opposed to the tooth row of the rack 12 and is slightly contacted with no contact. The separation distance varies depending on the strength of the magnetic flux. On the other hand, the rack is usually made of a metal (particularly paramagnetic or ferromagnetic). For this reason, when the rack 12 moves, the magnetic flux from the permanent magnet of the sensor unit 10 changes according to the unevenness of the dentition. This change is detected by the sensor unit 10 and converted into an electrical signal. However, unless the rack 12 itself has spontaneous polarization, it is necessary to have a permanent magnet on the sensor unit 10 side. When the rack 12 itself is magnetized, the permanent magnet of the sensor unit 10 can be omitted.

  4A shows a side view of the sensor unit 10, and FIG. 4B shows a front view. As shown in this figure, the sensor unit 10 may be configured to be provided so as to be rotatable in a horizontal plane with a point O shown in the figure as a center of rotation with respect to a portion where a magnetic flux detecting portion in the sensor unit is fixed. . This is because when the rack pitch is slightly smaller than the original optimum value, the distance between the magnetic sensor blocks S1, S2, and S3 is apparently smaller than the rack by rotating the sensing unit with respect to the mounting unit. This is because there is an effect that the original accuracy of the sensor is ensured in conformity with the pitch.

  By applying a trigonometric function waveform (sine waveform) as an input voltage to the sensor unit 10 and detecting an output current waveform from the sensor unit 10, the unevenness of the dentition is converted into a phase change (time change). Therefore, it is possible to operate as a position detector capable of digitally representing the amount of rack displacement by detecting the zero crossing with the phase detection circuit 40 of the converter 20 and counting with the counting circuit.

  FIG. 2 is an enlarged view showing the positional relationship between the magnetic sensor group 11 and the rack 12. As shown in this figure, when the rack pitch is P, the three adjacent magnetic sensors are spaced apart by (P + P / 3) and (2P + 2P / 3).

  Arranged in this way, the three-phase AC signal of the above trigonometric function is applied as an input signal waveform, and zero cross is detected by the phase difference detection circuit, while maintaining high speed, 1 pitch of 2 13 to 2 A resolution as high as about 1/16 power can be obtained.

The position detector according to the embodiment of the present invention can correspond to a rack having a pitch of 1/2 ⁿ pitch with one type of sensor unit.

  In the above embodiment, the input signal has been described as a voltage waveform and the output signal as a current waveform. However, since excitation is possible for both current and voltage, the input signal can be a current waveform and the output signal can be a voltage waveform. Good.

(Second Embodiment)
FIG. 5 shows one period of the trigonometric function (Y = sin A) and the functions Y = √ (sin A) and Y = −√ (sin A). By configuring the tooth shape of the rack to be similar to the output waveform (for example, a trigonometric function such as a sine curve), the change in magnetic flux detected by the magnetic sensor becomes sin, and the addition theorem of the trigonometric function is more accurately satisfied. As a result, the accuracy of the sensor is improved. Since the change in the magnetic flux is inversely proportional to the square of the distance, it is considered that the accuracy can be further improved if the shape of the rack teeth is similar to √ (sin x).

  FIG. 6 shows the relative positional relationship between the sensor unit 10 and the rack 12. Further, FIG. 7 shows a state of magnetic flux change when the distance G between the sensor unit 10 and the rack 12 is small and large, and a part of a graph of a trigonometric function (cos function). This figure shows that the distance G between the sensor unit 10 and the rack 12 affects the change in magnetic flux. It can be seen that the smaller the distance G is, the closer the curve is to the cos function (or sin function) curve than when the distance G is large. That is, if the distance G is finely adjusted appropriately, it means that the reading accuracy is improved. The fine adjustment of the relative positional relationship includes both the adjustment of the distance G, that is, the vertical distance, and the adjustment by rotating the sensor unit 10 in the horizontal plane described with reference to FIG. The reading accuracy is improved by providing a mechanism for finely adjusting the relative positional relationship between the rack 12 and the rack 12.

  Since the present invention can accurately identify the position from the displacement amount of the rack by attaching the sensor unit in a non-contact manner to the “rack” of the existing rack-and-pinion type drive device that is widely used at present, The availability is enormous.

1, 2, 4 Support member 3 Driven body 10 Sensor unit 11 Magnetic sensor group 12 Rack (gear with infinite gear diameter)
14 Pinion (Rotating gear)
20 Converter 30 Oscillation circuit 40 Phase difference detection circuit 50 Head amplifier

Claims (10)

A pinion that is a gear, and a rack that is provided with teeth that fit with the teeth of the pinion and moves linearly according to the rotation of the pinion,
The rack is a position detector that can be attached to a rack and pinion type driving mechanism made of a magnetic material,
The position detector includes a sensor unit that detects a change in magnetic flux accompanying the movement of the rack, an oscillation circuit that generates a predetermined input waveform to be input to the sensor unit, and an output waveform output from the sensor unit. A converter comprising a phase difference detection circuit for measuring and detecting a phase difference corresponding to the amount of movement of the rack;
The position detector, wherein the sensor unit targets the rack itself as a detection target. The sensor unit includes three sets of magnetic sensor blocks each including a magnetic sensor and at least one permanent magnet arranged so that magnetic flux penetrates substantially perpendicularly to the magnetic sensor. Item 1. The position detector according to Item 1. When the sensor unit is arranged so that the detection surface is substantially horizontally opposed to the tooth row of the rack, and one cycle of the crest and trough of the rack teeth is one pitch,
The position detector according to claim 2, wherein a change in magnetic circuit characteristics due to a change in an interval between the rack and the magnetic sensor block within the one pitch is detected. When a voltage or current amplitude of a trigonometric function waveform is given as the input waveform,
4. The position detector according to claim 3, wherein the sensor unit is arranged so that the change in the magnetic circuit characteristics is a trigonometric current or voltage amplitude within one pitch. The sensor unit includes V ₁ = V ₀ sin θ between the input terminals of the bridge circuit of the three magnetic sensor blocks S1, S2, and S3.
V ₂ = V ₀ sin (θ + (2n + 2/3) · π)
V ₃ = V ₀ sin (θ + (2n + 4/3) · π)
(However, V0 is a constant and n is an integer.)
AC voltage waveform or an alternating current waveform similar to this is applied,
The interval between the magnetic sensor blocks S1, S2 and S3 is between S1 and S2: (N + 1/3) · P
Between S1 and S3: (M + 2/3) · P
(However, N and M are integers, and P is the length of one pitch.)
The position detector according to claim 4, wherein the position detector is disposed so as to satisfy the relationship. 6. The position detector according to claim 5, wherein both N and M are 0. 3. The position detector according to claim 2, wherein the magnetic sensor comprises a set of magnetoresistive elements or Hall elements that constitute a bridge circuit. The position according to any one of claims 2 to 7, wherein the sensor unit is provided so as to be rotatable in a horizontal plane with respect to a portion to which a portion for detecting a magnetic flux in the sensor unit is fixed. Detector. The position detector according to claim 1, wherein the rack has a shape that forms the output waveform. A pinion that is a gear, and a rack that is provided with teeth that fit with the teeth of the pinion and moves linearly according to the rotation of the pinion,
The rack is a position detector that can be attached to a rack and pinion type drive mechanism made of a ferromagnetic material,
The position detector includes a sensor unit that detects a change in magnetic flux accompanying the movement of the rack, an oscillation circuit that generates a predetermined input waveform to be input to the sensor unit, and an output waveform output from the sensor unit. A converter comprising a phase difference detection circuit for measuring and detecting a phase difference corresponding to the amount of movement of the rack;
The position detector, wherein the sensor unit has the rack itself as a detection target and does not have a permanent magnet in the sensor unit.

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