JP4919177B2 - Linear scale - Google Patents

Description

  The present invention relates to a linear scale, and more particularly to detecting the presence / absence and polarity of a magnetic mark at a high frequency.

  The inventor is considering performing motion control of a moving body by providing a linear scale on the moving body and detecting a magnetic mark on the ground side. The linear scale is provided with a coil array, a plurality of coils are set as one pitch, a plurality of pitches are provided in the coil array, and the pitch at which the magnetic mark is detected is detected by a Hall element (Patent Document 1: JP2009-). 2660A).

  FIG. 5 shows the problem of the prior art. It is assumed that the Hall element 14 is provided near the boundary of the pitch and the N pole of the magnetic mark 22 is detected, for example. If the direction of the permanent magnet in the magnetic mark is wrong, the magnetic mark is at the position indicated by 23 in FIG. In order to solve this problem, it is necessary to detect the S pole and the N pole while identifying the polarity. For example, when the Hall element 14 is moving from the left to the right in FIG. , S and the magnetic mark 23 are detected in the order of S, N, so that the magnetic marks 22, 23 can be distinguished. Furthermore, in motion control of a moving body, it is necessary to detect the position at a high frequency of, for example, 10 KHz or more, and it is necessary to detect the S pole and the N pole while identifying the polarity at a high frequency. In order to solve the problem of FIG. 5, it may be possible to arrange the Hall element 14-1 for detecting the N pole and the Hall element 14-2 for detecting the S pole in parallel as in the reference example of FIG. 6. Two Hall elements are required, and the signal processing circuit is complicated.

JP2009-2660A

  An object of the present invention is to detect the presence / absence and polarity of a magnetic mark at a high frequency.

In the present invention, in order to detect the position of the moving body, a magnet provided on the ground side along the moving path of the moving body is detected by a coil array in which a plurality of coils are arranged along the moving direction of the moving body. A linear scale,
A linear Hall element is provided in the coil array, that is, a linear Hall element is provided along the coil array,
A sine wave is applied to the Hall element, and a drive circuit is provided for determining the presence / absence and polarity of the magnet based on the output and phase of the linear Hall element with respect to the sine wave.

  In the present invention, the presence or absence of a magnet is detected based on the output of the linear Hall element, that is, based on the magnitude of the output, and the polarity of the magnet is determined from the phase of the output with respect to the exciting sine wave. For this reason, the presence / absence and polarity of a magnet can be determined by one Hall element, and further, as described with reference to FIG. Therefore, it is possible to cope with the case where the magnets are arranged in the opposite direction, and a position signal suitable for motion control of the moving body can be obtained from the linear scale.

  Preferably, the driving circuit compares the output of the Hall element with a threshold value in a region where the phase angle of the sine wave is 0 ° to 180 ° and a region where the phase angle is 180 ° to 360 °, respectively. And polarity. In this way, one of the N and S poles can be detected in the phase angle range of 0 ° to 180 °, and the other of the N and S poles can be detected in the phase angle range of 180 ° to 360 °. The discriminating circuit can be simplified. More preferably, the drive circuit compares the output of the Hall element with a threshold only at one point in the region where the phase angle is 0 ° to 180 ° and a point obtained by adding 180 ° to the one point in phase angle. To do. In this way, the discrimination circuit only needs to operate at one point in the phase angle range of 0 ° to 180 ° and one other point obtained by adding 180 ° to the one point in phase angle. It can be simplified.

Further preferably, the coil array is excited by the sine wave, and the linear scale according to claim 1 or 2. In this way, the excitation power source for the Hall element and the excitation power source for the coil array can be made common, and the drive circuit can be simplified.

Block diagram of the linear scale of the embodiment Block diagram showing signal processing from coil array and hall element in embodiment The figure shows the signal waveform of the Hall element, etc. in the example. 1) The voltage waveform of the excitation signal, 2) The output of the operational amplifier and the digital transistor when detecting the S pole, and 3) The N pole detection The output of the operational amplifier and the output of the digital transistor at time 4) shows the output of the operational amplifier when the S / N midpoint and magnet are not detected. Block diagram showing signal processing of Hall element in modification Diagram showing the problems of the conventional example A diagram showing a reference example for solving the problem of FIG.

  In the following, an optimum embodiment for carrying out the present invention will be shown.

  1 to 4 show a linear scale 2 of the embodiment and its modification. The linear scale 2 includes a coil array 4 whose longitudinal direction is a moving direction of a moving body (not shown), 6 is a magnetic core, and dummy coils 8 and 9 are preferably provided at both ends of the coil array 4. In the coil array 4, a plurality of coils 10 are wound around the magnetic core 6, for example, four coils 10 are combined into one pitch 12, and the coil array 4 has a plurality of pitches 12, for example, 10 pitches. Along with the longitudinal direction of the coil array, at least one, preferably a plurality of Hall elements 14 that provide a linear output type, that is, a linear output with respect to the magnetic flux, are provided. , 12 are arranged on the boundary between the Hall elements 14. The coil array 4, the dummy coils 8 and 9, and the hall element 14 constitute a detection head 15 of the linear scale 2.

  Reference numeral 16 denotes a processing circuit, which determines the pitch at which the magnetic mark 22 is detected based on the signal from the Hall element 14 and determines the position of the magnetic mark 22 relative to the pitch based on the signal from the coil array 4. The dummy coils 8 and 9 do not have to be provided for detecting the presence or absence of magnetic marks on both sides of the coil array 4. The sine wave power supply 18 applies a sine wave having an angular frequency ω to the coil array 4, the dummy coils 8 and 9, and the hall element 14, and the sine wave output has a positive phase voltage V1 and a reverse phase voltage V2, and these are excitation signals. There are times. The counter 20 generates a phase signal ωt having an angular frequency ω and supplies it to the sine wave power supply 18 and the processing circuit 16.

  The moving body is, for example, an overhead traveling vehicle, a tracked carriage that travels on a track on the ground, a stacker crane, a head of a machine tool, a head of a transfer device, and the like, and a plurality of magnetic marks 22 are arranged along the moving direction, The magnetic mark 22 is obtained by attaching a permanent magnet 25 to a yoke 24.

  FIG. 2 shows processing of signals from the coil array 4 and the Hall element 14. The counter 20 generates a phase signal ωt, and a table 26 in the sine wave power source 18 converts this signal into sinωt, converts it into an analog signal by a DA converter 28, and outputs the coil array 4 and Hall elements with output voltages V1 and V2. 14 is driven. For example, eleven Hall elements 14 are driven in parallel with output voltages V1 and V2.

  Each pitch 12 includes, for example, four coils 10-1 to 10-4, which are arranged in a bridge shape, for example, and a bridge output is amplified by operational amplifiers A1 and A2. In the embodiment, signals from ten pitches 12 are processed by common operational amplifiers A1 and A2, but a pair of operational amplifiers may be provided for each pitch 12. The phase of the magnetic mark 22 with respect to one pitch is represented by θ, and θ varies between 0 and 2π. For example, a signal of sin θ · sin ωt is obtained from the operational amplifier A1, and a signal of cos θ · cos ωt is obtained from the operational amplifier A2. This is input to the phase detector 30 to extract the phase θ.

  The equivalent circuit of the Hall element 14 can be represented by a bridge of four magnetic resistances M1 to M4. For each Hall element 14, an operational amplifier A3, a digital transistor Tr1 and resistors R1 to R5 are provided, and the output of the bridge is an operational amplifier. Amplified by A3 and compared with the threshold shown in FIG. 3 by the digital transistor Tr1, when the output of the operational amplifier A3 is larger than the threshold, the digital transistor Tr1 is turned on and the output becomes L level. Signals from 11 Hall elements 14 are input to the determination unit 32 in parallel, and the output of the digital transistor Tr1 is output only when the phase signal ωt has a predetermined timing such as 90 ° and 270 °, or 130 ° and 310 °, for example. And the pitch at which the magnetic mark 22 is detected is determined. The digital transistor may be replaced with another comparator, and active L or active H is arbitrary.

  The offset correction unit 34 corrects the offset according to the pitch at which the magnetic mark 22 is detected, and the correction table 36 corrects the data variation for each linear scale 2 and outputs the position signal x. In this way, the position of the moving body is obtained, and the motion control of the moving body is performed by feeding back to a travel control unit or a lift control unit (not shown).

  The detection speed of the position signal x will be described. In order to perform motion control of the moving body, it is necessary to obtain the position at, for example, 10 KHz or more, preferably about 20 to 100 KHz. Therefore, the angular frequency ω is, for example, 10 KHz or more, preferably 20 KHz to 100 KHz, the Hall element 14 is driven at this frequency, and the operational amplifier A3 and the digital transistor Tr1 process signals of this frequency. Furthermore, the Hall element 14 distinguishes and detects the N pole and the S pole of the magnetic mark 22. On the other hand, with the existing Hall element, it is difficult to detect the N and S magnetic poles in the magnet at a frequency of 10 KHz or higher while discriminating between the N pole and the S pole.

  FIG. 3 shows signal waveforms in the embodiment. 1) shows the excitation signal V1, and the excitation signal V2 has a phase opposite to that of the excitation signal V1. 2) shows the output of the operational amplifier and the output of the digital transistor when the S pole is detected. The output of the Hall element 14 changes at the same frequency as the excitation signal but has a delay and is linear with respect to the magnetic flux from the magnetic mark. It is. Therefore, when this output is amplified by the operational amplifier A3 and compared with the threshold value by the digital transistor Tr1, the lower output of 2) is obtained.

  When the N pole is detected, as shown in 3), the output of the operational amplifier is out of phase with the excitation signal V1, and when the output of the operational amplifier is compared with the threshold value by a digital transistor, the lower output of 3) is obtained. On the other hand, when the Hall element 14 faces the midpoint between the S pole and N pole of the magnetic mark 22 or when there is no magnetic mark around it, the output of the Hall element 14 is almost zero and the output of the operational amplifier is also a digital transistor. This threshold is never exceeded. Therefore, the digital transistor output is kept at H.

  By reading the output of the digital transistor at a predetermined phase with the excitation signal V1 as a reference, the presence / absence and type of the magnetic pole in the magnet can be detected, and the detection can be performed in synchronization with the frequency signal ωt. Therefore, the magnetic mark 22 can be detected together with its polarity at a high frequency necessary for motion control.

  In the circuit of FIG. 2, the bridge output from the Hall element 14 is processed by one operational amplifier A3, and the determination unit 32 samples only at a predetermined timing with ωt as a reference, thereby obtaining the S pole and the N pole. It can be detected. Therefore, each Hall element 14 can be driven by one operational amplifier A3 and one digital transistor. On the other hand, the detection of the S pole and the detection of the N pole can be performed separately, and such an example is shown in FIG. In FIG. 4, the signal for detecting the S pole is processed by the operational amplifier A4 and the digital transistor Tr2, and the detection result is stored in the capacitor C1. Further, the signal for detecting the N pole is processed by the operational amplifier A5 and the digital transistor Tr3, and the detection result is stored by the capacitor C2. R6 to R15 are resistors, and the capacitor C1 is kept low while the Hall element 14 is in contact with the S pole, and the capacitor C2 is kept low while in contact with the N pole. However, in the circuit of FIG. 4, two sets of detection circuits are required for each Hall element 14, which complicates the processing circuit.

In the embodiment, the following effects can be obtained.
(1) A linear output Hall element that can detect the presence of a magnet and its polarity at a high frequency. For this reason, a signal for motion control of the moving body is obtained, and it can be recognized that the direction of the magnetic mark is reversed.
(2) The processing circuit of FIG. 2 can extract the S pole detection signal and the N pole detection signal with one operational amplifier A3 and one digital transistor Tr1 for the Hall element 14, and the processing circuit is simplified. Can be
(3) The Hall element 14 can be driven by the same signal as the drive signal of the coil array, and can detect the presence / absence of the magnet and its polarity at the same frequency as the position is detected on the coil array side.

2 Linear scale 4 Coil array 6 Magnetic cores 8 and 9 Dummy coil 10 Coil 12 Pitch 14 Hall element 15 Detection head 16 Processing circuit 18 Sine wave power supply 20 Counter 22, 23 Magnetic mark 24 Yoke 25 Permanent magnet 26 Sin table 28 DA converter 30 Phase detection unit 32 Determination unit 34 Offset correction unit 36 Correction table

V1, V2 excitation output
M1-M4 magnetoresistive
A1 to A5 operational amplifier
Vcc circuit power supply
Tr1-Tr3 Digital transistor
R1 ~ R15 resistance
C1, C2 capacitors

Claims (4)

In order to detect the position of the moving body, a linear scale that detects a magnet provided on the ground side along the moving path of the moving body by a coil array in which a plurality of coils are arranged along the moving direction of the moving body. And
A linear Hall element attached to the coil array;
A linear scale characterized in that a sine wave is applied to the Hall element, and a drive circuit for determining the presence / absence and polarity of a magnet is provided based on the output and phase of the linear Hall element with respect to the sine wave.   The drive circuit compares the output of the Hall element with a threshold value in a region where the phase angle of the sine wave is 0 ° to 180 ° and a region where the phase angle is 180 ° to 360 °. The linear scale according to claim 1, wherein the linear scale is determined.   The drive circuit compares the output of the Hall element with a threshold only at one point in the region where the phase angle is 0 ° to 180 ° and a point obtained by adding 180 ° to the one point in phase angle. The linear scale according to claim 2.   The linear scale according to claim 1, wherein the coil array is excited by the sine wave.

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