JPH03130804A - Magnetic sensor - Google Patents

Abstract

PURPOSE:To secure the highly stable control even in such an adverse environment where the temperature conditions vary or the impact, etc., are easily received by providing a temporary storage and a differential amplifier in order to correct the difference of characteristics between two sensor coils. CONSTITUTION:A temporary storage 21 stores the unbalance value of bias levels between two symmetrical sensor coils L1 and L2 in absence of a magnetic mark. In an active state, the unbalance value is subtracted from outputs of both coils L1 and L2 and therefore never emerges as an output signal. Thus it is possible to correct in terms of circuit some characteristic variance produced at production of an energizing coil or the coils L1 and L2 and also to correct some attachment error of a magnetic sensor into a sensor unit. As a result, the production yield is improved and the production cost is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application J] The present invention relates to a magnetic sensor used for steering control of an automatic guided vehicle or the like.

[Conventional technology]

In recent years, magnetic induction systems that use ferrite or amorphous tape as magnetic markers have attracted attention, and have been put into practical use as automatic guidance systems for golf carts and wheelchairs. In these systems, a magnetic sensor for detecting a magnetic marker is mounted on a vehicle, and an example of its configuration is shown in FIG. Also,
FIG. 4 shows the signal processing circuit, and FIG. 5 shows the waveforms of each part.

In this magnetic sensor system, an alternating current is passed through the excitation core L provided inside the magnetic sensor unit 12 to form a magnetic field directly below it, and the magnetic marker 11 is magnetized, and the lines of magnetic force emitted by the magnetic marker 11 The reshaped magnetic field distribution is detected by the symmetrically arranged detection coils Ll.
, L2 picks up the induced voltage vL+ l VL
＊' occurs. These symmetrical sensing coils I, 1, 1
．． 2 Ni raw, l”, knee induced voltage vL+ ′, VLt′
is impedance-converted by each buffer Bl, B2, amplified by amplifier AI, A2, and then rectifier R1,
It is rectified at R2. This rectified output signal is differentially amplified by the differential amplifier G1, and becomes a signal (2) for steering control. 111.

[Problems to be Solved by the Invention] Normally, when the center of the magnetic sensor is positioned at the center of the magnetic marker 11, the detection coil Ll.

The positions of the detection coils Ll, I, and 2 are adjusted so that the output VL+'+VL*' of L2 becomes equal at room temperature.

In this case, the output VL+H when there is no magnetic marker 11
vLm also becomes equal. However, due to differences in the temperature characteristics of the coils Ll and L2, the outputs of the coils Ll and L2 may change significantly at low temperatures below 0°C and high temperatures above 30°C, and when a large shock is applied to the sensor unit, the coils Ll and L2 may By changing the position of the coils L1 and L2, the outputs of the coils L1 and L2 change greatly. The output signals of the left-right symmetrical detection coils Ll and L2 are VL, =V, , -V, with the induced voltage change due to the presence of the ferrite marker being VS+HVS, respectively.

v,,,’ = VL, Vs.

V,,, =K[V,, '-VL, '] =K[V
When such a variation occurs, the bias level VL
+ ) Since the difference in VLm is no longer 0, the output signal V0
1. This will include differences in bias levels.

Without such a difference, when the center position of the magnetic sensor is placed at the center of the magnetic marker 11, the original signal component V,
,, V□ are also equal, so the sensor output ■. . , should be 0, but VL+≠vL.

In the case of , the voltage K(V, , -VL
, ) occur, a state in which the center position of the magnetic sensor is placed closer to either the left or right than the center of the magnetic marker is mistakenly recognized as the center of the magnetic marker. As a result, the vehicle may not be controlled correctly, and the vehicle may sometimes deviate from the course indicated by the magnetic marker.

It is an object of the present invention to provide a magnetic sensor that eliminates such conventional drawbacks.

[Means for determining the problem] In order to achieve the above object, the magnetic sensor according to the present invention includes two symmetrically arranged detection coils that detect changes caused by magnetic markers in an alternating current magnetic field generated by an excitation coil. a pair of buffers for impedance converting the outputs of the two detection coils, a pair of amplifiers for amplifying the outputs of each buffer by a predetermined amount, and a first difference for obtaining a difference signal between the outputs of the respective amplifiers. a dynamic amplifier, a DC converter that converts the difference signal of the differential amplifier into DC, a temporary storage device that stores the difference signal in the absence of a magnetic marker as a digital signal and reads this as an analog signal, and A second differential amplifier obtains a difference signal between the output of the converter and the output of the temporary storage device.

Further, in the magnetic sensor according to the present invention, two detection coils are arranged symmetrically to detect a change in the alternating current magnetic field generated by the excitation coil due to the magnetic marker, and the outputs of the two detection coils are each impedance-converted. a pair of buffers, a pair of amplifiers that amplify the outputs of each of the buffers by a predetermined amount, a pair of DC converters that convert the outputs of the amplifiers to DC, and a difference signal from the output of each of the DC converters. a temporary storage device that stores a difference signal in the absence of a magnetic marker as a digital signal and reads this as an analog signal;
The second differential amplifier obtains a difference signal between the output of the differential amplifier and the output of the temporary storage device.

[Effect 1] When the ambient temperature changes or when the position of the sensing coil or excitation coil is shifted due to an external impact, the characteristics of the two symmetrical sensing coils change. According to the magnetic sensor of the present invention, the unbalance amount of the bias level of two symmetrical sensing coils in a state where there is no magnetic marker is stored in a temporary storage device, and the unbalance amount is recorded from the output of the sensing coil during operation. Since the amount of unbalance is subtracted, the amount of unbalance is no longer generated as an output signal. Normally, it is desirable to store the bias level imbalance amount at the time of system startup, but if the temperature conditions change, it is better to set and store the data as necessary.

With this configuration, even if there are slight variations in characteristics of the excitation coil and detection coil during manufacture,
Furthermore, even if there is some positional error in the mounting inside the sensor unit, it can be corrected using a circuit, so the manufacturing yield of the magnetic sensor unit is improved and the cost is reduced.

[Example] Hereinafter, an example of the present invention will be described in detail using the drawings.

(Example 1) FIG. 1 is a diagram showing the configuration of a magnetic sensor according to Example 1 of the present invention.

In the figure, the magnetic sensor according to the present invention includes buffers Bl and B2 that convert the impedance of the outputs of two sensing coils Ll and L2 that are arranged symmetrically, and a buffer Bl.
, Amplifiers AI and A2 that amplify the outputs of B2, a differential amplifier Gl that obtains a difference signal between the outputs of these amplifiers, and a sample hold circuit as a DC converter that converts the difference signal from the differential amplifier Gl into DC. S/H and temporary storage device 21
and a differential amplifier 22.

The temporary storage device 21 is for storing the output of the sample and hold circuit S/H, but during actual operation it takes in the DC-converted value of the difference signal generated when there is no magnetic sensor on the ferrite marker. For example, when starting up the system, the DC converted value of the difference signal is inputted by the initialized pulse φ and stored. DC conversion of the difference signal is performed by the sample hold circuit S/H using the pulse φgH as the difference signal v8.
This is done by sampling and holding the peak level of a sine wave. At this time, if there is an imbalance in the characteristics of the symmetrical sensing coil, the sensing coil L
When the outputs of L and L2 are VL+tVLm, V, =K(VL, -VL, ) is generated as the output v8 of the sample and hold circuit S/H, and the DC converted value of this signal is digitalized by the A/D converter 21a. It is converted into a quantity and stored in the memory 21b.

Here, K is the buffer Bl, B2 and the amplifier AI, A2
represents the product of the gains of When a system equipped with a magnetic sensor is guided on a ferrite marker, the output of the symmetrical detection coils Ll and L2 is reduced from +VL* by the induced voltage change VS+ + Vgm due to the magnetic field formed by the ferrite marker. and the following voltage VL
+′, vL+′.

V,, =V,, -Vs VLm =:VL, v5 As a result, the output vx of the sample hold circuit S/H via the differential amplifier Gl is v, =Kcvt,, '-VL, '] =K (VL
, -VL, , -(VS, -VS, )). However, the differential amplifier (gain G2) 22 provided after the sample and hold circuit S/H reads out the signal (K(VL, -VL, )) stored in the temporary storage device 21 and sends it to the D. The differential amplifier 22 subtracts the D/A converted signal by the /A converter 21c and amplifies it by a predetermined amount.
The output Vou+ no longer includes any bias components of the detection coils Ll and L2. That is, V, u, =
A signal G2K[Vs, -V, . . . ] is obtained, and only the originally required difference in induced voltage change due to the ferrite marker is used as a control signal.

With this configuration, the unbalance in the outputs of the two sensing coils Ll and L2 caused by temperature changes, shocks, etc., which has been a problem in the past, is completely absorbed, and the center position of the magnetic sensor is placed in the center of the magnetic marker. The output signal Ve
ut becomes 0, and the position of the magnetic sensor can be correctly recognized. Furthermore, the design tolerance of the excitation coil and the detection coil is increased, which simplifies the design and improves manufacturing yield.

In this embodiment, even if the DC converter S/H is a rectifier other than a sample-and-hold circuit, the spirit of the present invention will not be impaired.

(Example 2) FIG. 2 is a diagram showing the configuration of a magnetic sensor according to Example 2 of the present invention.

In this embodiment, a DC converter S/H is provided after each of the amplifiers AI and A2, and after converting to DC, the difference signal 8 is obtained from the differential amplifier GI.

This point differs from the first embodiment in which the difference between the two high-frequency signals (40 to 150 KHz) is taken, and then converted to direct current using one direct current converter. With such a configuration, it is not necessary to increase the band of the differential amplifier Gl, so that the differential amplifier can be easily manufactured using an inexpensive operational amplifier. Furthermore, the low-band amplifier configuration has the advantage that oscillations are less likely to occur. Since the other parts of the above structure are the same as those in the first embodiment, it goes without saying that the same effects as those obtained in the first embodiment can be obtained.

〔Effect of the invention〕

As explained in detail above, according to the present invention, by providing a temporary storage device and a differential amplifier, it is possible to correct the difference in characteristics between two sensing coils, and to compensate for differences in characteristics between two sensing coils, such as environments with different temperature conditions or the effects of impact, etc. This enables highly stable control even in harsh environments. In addition, since it becomes possible to have some tolerance for variations in the characteristics of the detection coil and excitation coil, it becomes easier to design and manufacture magnetic sensors, and it is now possible to manufacture coils on the line, which was previously considered a matter of know-how. Become.

This also results in reduced product costs.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a magnetic sensor according to Embodiment 1 of the present invention, FIG. 2 is a diagram showing the configuration of a magnetic sensor according to Embodiment 2 of the present invention, and FIG. 3 is a diagram showing the basic configuration of a magnetic sensor unit. FIG. 4 is a diagram showing the configuration of a conventional magnetic sensor, and FIG. 5 is a diagram showing a voltage waveform between detection coil terminals. Ll, L2...Detection coil Bl, B2...Buffer AI, A2...Amplifier Gl, 22.
... Differential amplifier S/H ... Sample hold circuit (DC converter) 21 ... Temporary storage device

Claims (2)

[Claims] (1) Two symmetrically arranged detection coils that detect changes in the alternating current magnetic field generated by the excitation coil due to the magnetic marker, a pair of buffers that convert the impedance of the outputs of the two detection coils, and each of the buffers. a first differential amplifier that obtains a difference signal between the outputs of the respective amplifiers, a DC converter that converts the difference signal of the differential amplifiers into direct current, and a magnetic a temporary storage device that stores a difference signal in the absence of a marker as a digital signal and reads this as an analog signal; and a second differential storage device that obtains a difference signal between the output of the DC converter and the output of the temporary storage device. A magnetic sensor comprising an amplifier. (2) A pair of two symmetrically arranged detection coils that detect changes in the alternating current magnetic field generated by the excitation coil caused by the magnetic marker, a pair of buffers that convert the outputs of the two detection coils into impedance, and each of the buffers. a pair of amplifiers each amplifying the output of the amplifier by a predetermined amount, and a pair of DC converters each converting the output of the amplifier into direct current;
a first differential amplifier that obtains a difference signal from the output of each of the DC converters; a temporary storage device that stores the difference signal in the absence of a magnetic marker as a digital signal and reads this as an analog signal; A magnetic sensor comprising: a second differential amplifier that obtains a difference signal between the output of the amplifier and the output of the temporary storage device.