JP2932292B2 - Magnetic position detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a phase detection type magnetic position detection used in technical fields such as magnescale, phase detection, sample hold, timer, low-pass filter, comparator, and zero cross. It concerns the device.

[Conventional technology]

In a phase detection type magnetic position detection device, the output of the phase detector is very small, and therefore, amplification is several hundred to several thousand times in many cases. For this reason, the value of the center position of the output (the zero point of the sine wave) is significantly different due to the difference in the characteristics of the magnetic detector. Therefore, it is necessary to adjust the comparison position (voltage) of the comparator to an intermediate value between the maximum value and the minimum value of the output wave of the phase detector when converting the detection wave type into the pulse wave.

Conventionally, when performing zero-crossing control on a waveform in which an alternating current overlaps a direct current, two methods can be easily considered.

The first method is AC coupling using a capacitor. Since this method utilizes charging and discharging by a capacitor, the alternating waveform can be corrected to a zero potential point.

The second method is to adjust the voltage level by using an operational amplifier or a combination of a transistor and a resistor.

[Problems to be solved by the invention]

Of the above two conventional methods, the first method, the capacitor coupling method, has a zero-crossing function at low frequencies, for example, several Hz or less, because a phase delay due to a capacitor occurs and the tracking ability is poor depending on the frequency. Does not work.

In the second method, the voltage level is adjusted by an external mechanism such as a trimmer resistor. In this method, when the frequency and the center of amplitude change, the adjustment becomes complicated.

The present invention has been made in view of the above, and provides a magnetic position detecting device that can automatically find an intermediate point even when there is a variation in the magnetic detection unit and can accurately reproduce the shape of the magnetic detection portion. The purpose is to do so.

[Means for solving the problem]

In order to achieve the above object, a magnetic position detecting device according to the present invention includes a magnetic detector, a frequency generator that inputs a single alternating voltage to the magnetic detector, and a frequency generator. A phase detector for detecting the phase difference between the alternating voltages output from the magnetic detector, a low-pass filter for smoothing the output from the phase detector, and a phase detector and a low-pass filter. A comparator on the output side that compares both outputs to generate a pulse signal, a voltage holding circuit that receives the output of the low-pass filter and holds a voltage equal to or higher than a certain value, and a low-pass filter. The output frequency of the wave filter is measured, and when the frequency is equal to or lower than a certain frequency, a plurality of magnetic detection circuits each including a switch device for connecting a voltage holding circuit to a comparator on the output side are provided.

(Operation)

In the above configuration, the output from the magnetic detector of each magnetic detection circuit is input to the low-pass filter via the phase detector of the respective magnetic detection circuit, and is smoothed, so that the output is correct regardless of the frequency amplitude of the alternating waveform. The center voltage of the alternating waveform is output. When the DC-biased alternating waveform from the phase detector is below a certain frequency, a voltage holding circuit is connected to the comparator on the output side, and the voltage holding circuit holds the output from the comparator. When the alternating waveform from the phase detector reaches a certain frequency or higher, the output of the low-pass filter is again input to the output-side comparator.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention. Hereinafter, an embodiment of the present invention will be described with reference to this drawing.

In the figure, reference numeral 1 denotes a Maxwell bridge circuit constituting one magnetic detector, 2 denotes a frequency generator for inputting alternating power to the Maxwell bridge circuit 1 via a power amplifier 3, and 4 denotes a Maxwell bridge circuit 1. The differential amplifier 5 for detecting the unbalance of the phase and the phase of the input waveform and the output waveform to the Maxwell bridge circuit 1 are detected.
Phase detectors 6a and 6b for applying a DC bias thereto are first and second amplifiers for further amplifying the output from the differential amplifier 4, the first amplifier 6a is 30 times, and the second amplifier 6b Is
10 times. Reference numerals 7a, 7b, and 7c denote first, second, and third filters. The first and second filters 7a, 7b are interposed on the upstream side of the phase detector 5, and include a third filter. The wave detector 7c is provided downstream of the phase detector 5. 8a and 8b are amplifiers interposed on the output side of the phase detector 5.

9 is a low-pass filter for filtering the alternating waveform output from the phase detector 5 smoothly, 10 is comparing the output from the phase detector 5 with the output of the low-pass filter 9, The comparator generates a pulse signal according to the comparison value. Reference numeral 11 denotes a first analog switch interposed between the comparators 10 of the low-pass filter 9;
Reference numeral 11 has an ON position 11a for connecting the low-pass filter 9 and the comparator 10, and an OFF position 11b for connecting the comparator 10 to a voltage holding circuit 12, which will be described later. The analog switch 11 is switched by an output signal from an F / V converter circuit 13 described later.

The voltage holding circuit 12 includes a sample hold 14, a timer 15 for compensating the output hold of the sample hold 14, and an amplifier.
16 and a second analog switch 17. The input side of the voltage holding circuit 12 is connected to the low-pass filter 9.
Is connected to the output side.

On the other hand, the F / V converter circuit 13 includes an F / V converter 18 connected to the output side of the comparator 10, and a comparator 20 for comparing the output of the F / V converter 18 with a reference voltage circuit 19,
The output from the comparator 20 switches the first analog switch 11.

In the above configuration, for example, the frequency generator 2 is 60 KHz
Is input to the Maxwell bridge 1. Maxwell bridge circuit 1 is, for example, self-inductance L, L = 100 .mu.H, consists DC resistance 50 [Omega before and after the reactor 1a, a 1b, the resistance R ₁ of the fixed resistor 50 [Omega, R ₂ Prefecture. In the Maxwell bridge circuit 1, one of the reactors 1a is fixed to a rod having a reference magnetic permeability, and the other reactor 1b moves on a detection load in which a magnetic scale is represented by a change in magnetic permeability. When the detection rod moves relatively in the axial direction with respect to the other reactor 1b, the magnetic permeability change portion is detected and the self inductance L of the reactor 1b changes. The voltage generated based on the change in the inductance is amplified by the differential amplifier 4.

Then, the output from the differential amplifier 4 and the frequency from the frequency generator 2 are detected by the phase detector 5, and a DC bias is applied to this. Then, the output of the alternating waveform with DC bias from the phase detector 5 is smoothed by the low-pass filter 9, and the center value (average value of the voltage) of the alternating waveform is output from this. At this time, no phase shift occurs due to smoothing.

When the moving speed of the reactor 1b opposed to the detection rod of the Maxwell bridge circuit 1 is equal to or higher than a certain value, the first analog switch 11 is turned on when the output from the low-pass filter 9 is equal to or higher than a certain frequency. The output is input to the comparator 10 on the output side.

The comparator 10 on the output side compares the voltage output from the low-pass filter 9 with the DC-biased alternating waveform from the phase detector 5 to output a pulse waveform. The amount of movement with respect to the detection rod is detected by the pulse signal output from the comparator 10. The output from the low-pass filter 9 at this time is input to the voltage holding circuit 12 and held.

On the other hand, at this time, the output frequency of the comparator 10 on the output side is F / V
The frequency is input to the F / V converter 18 of the converter circuit 13, and the F / V converter 18 converts the frequency to a voltage. The output voltage is compared with the reference voltage from the reference voltage circuit 19 by a comparator.
The comparison is made at 20, and an ON / OFF signal is output from the comparator 20 according to the magnitude of the output voltage from the F / V converter 18, whereby the first analog switch 11 is turned ON / OFF.

That is, when the movement of the reactor 1b becomes slow, the output frequency from the phase detector 5 becomes low,
When the output frequency from the output side comparator 10 becomes low, the first analog switch 11 is turned off by the F / V converter circuit 13, and no new sampling is performed.
The comparator 10 on the output side is connected to a voltage holding circuit 12, which keeps the voltage constant. Then, the new sampling is restarted by switching the first analog switch 11 from the point where the alternating waveform with the DC bias exceeds a certain frequency.

Thus, even when the output frequency from the phase detector 5 is low, the threshold value of the output value of the comparator 10 on the output side is kept at a constant height. Therefore, when the output frequency from the phase detector 5 becomes the next higher (at the time of restart), the detected value is immediately compared by the comparator 10 and can be output as the comparison value at this time. In addition, it is possible to eliminate detection omission of the detection value.

For this reason, it is necessary that the holding voltage of the voltage holding circuit 12 always keep a certain value or more.

Although the voltage holding circuit 12 in this embodiment basically includes a capacitor, such a voltage holding circuit 12
Due to the nature of the capacitor, a slight leakage current occurs over time, causing a voltage drop. Since the voltage drop is a function of time at the same temperature and the same humidity, the voltage holding circuit 12 is connected to the amplifier 16 by the timer 15 at regular time intervals to compensate for the voltage drop. The timer 15 activates the amplifier 16 when the holding voltage reaches 90%, for example. The amplification factor of the amplifier 16 is set to 1.112. That is, the voltage drop of the holding circuit 12 is prevented from being reduced to 90% or less at an increasing rate.

If the voltage holding circuit 12 does not cause a voltage drop with time, or if a voltage holding circuit is used which is always supplied with a constant voltage so as to maintain a constant voltage, the above timer is used. 15 and amplifier 16 are not required.

Further, in this embodiment, a circuit including one Maxwell bridge circuit 1 and one output-side comparator 10 connected to the Maxwell bridge circuit 1 has been described. 1 and each circuit connected to each Maxwell bridge circuit 1.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to the present invention, even if a variation occurs when the magnetic permeability change is formed on the rod of the magnescale serving as the position detection unit, the output fluctuation due to the variation can be compensated without adjustment, and the shape of the magnetic detection portion is accurately reproduced. it can. Further, adjustment at the time of level shift is not required. Further, there is no phase shift at the time of the zero-cross point comparison. Further, even when the output of the phase detector 5 becomes zero in frequency, the position signal can be output by the operation of the voltage holding circuit 12.

[Brief description of the drawings]

The drawing is a circuit diagram showing an embodiment of the present invention. 1 is a Maxwell bridge circuit, 2 is a frequency generator, 5
Is a phase detector, 9 is a low-pass filter, 10 is a comparator, 11 is an analog switch, 12 is a voltage holding circuit, and 13 is an F / V converter circuit.

Claims (1)

(57) [Claims] 1. A magnetic detector and a phase detector for detecting a phase difference between alternating voltages output from the magnetic detector with reference to a frequency of a frequency generator for inputting a single alternating voltage to the magnetic detector. A low-pass filter that smoothes the output from the phase detector, a comparator on the output side that generates a pulse signal by comparing the outputs of both the phase detector and the low-pass filter, The output of the low-pass filter is input, and the voltage holding circuit that holds the voltage above a certain value and the output frequency of the low-pass filter are measured. A magnetic position detection device comprising: a plurality of magnetic detection circuits each including a switch device for connecting a voltage holding circuit to a switch.