JPS61292084A - Processing circuit for detection signal of magnetic sensor - Google Patents

Abstract

PURPOSE:To discriminate and detect a conductive magnetic material and other magnetic materials regardless of external conditions such as temp. by subjecting the detection signal of a magnetic sensor and the signal obtd. by inversion amplification or non-inversion amplification of the differential signal thereof to analog-to-digital conversion. CONSTITUTION:The detection signal Vi of the magnetic sensor is received at an input terminal 30. One thereof is conducted to a differentiation circuit 31 and the other via a comparator 37 and an inverter 41 to an AND circuit 39. The output from the circuit 31 is conducted via inversion and non-inversion amplifiers 33, 32, comparators 35, 34 and an invert 36 to the circuit 30. The signal change by the approach of the magnetic material is faster than the signal change by a temp. change, etc. and therefore only the approach of the magnetic material can be detected from the magnitude of the differential output. If the conductive magnetic material approaches, the signal change is large and therefore the approach is detected by discriminating the conductive magnetic material and the other magnetic material by the AND of the varying magnitude of the detection signal and the magnitude of the differential output.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a processing circuit for a detection signal of a magnetic sensor used in an unmanned vehicle guidance system using a ferrite magnetic material as a marker.

(Prior art and its problems) The output of the magnetic sensor used to detect the presence of a magnetic object, that is, the detection signal, is an analog quantity, so in order to determine whether or not a magnetic object exists, the detection signal must be used. A processing circuit is required. Conventionally, as a circuit for this purpose, that is, a magnetic sensor detection signal processing circuit, a circuit using a comparator has been generally used and put into practical use. In this method, when the detection signal changes due to the approach of an object or the like to the magnetic sensor and becomes larger than a set standard, a comparison circuit operates to issue an on signal. However, with this circuit, when trying to detect a magnetic substance that is relatively far away, the change in the detection signal becomes small, which poses a problem in the reliability of detection. The problem is that malfunctions occur when the detection signal changes due to changes in temperature or other external or internal conditions even though the object to be detected is not approaching. This is always a problem when attempting to reliably detect slight changes in the detection signal in order to make the sensor highly sensitive. (For example, the method described in ``Measurement Control Differential Transformer and Its Applications'' by Joe Nishiguchi for ohm detection) In order to avoid this problem, the magnetic sensor is equipped with two detection coils, and their output (detection signal) is A differential method has also been considered, but this method requires two sensing coils, making it expensive and disadvantageous.

The prior art will be described below with reference to the drawings, taking a ferrite magnetic sensor as an example of a sensor.

FIG. 4(a) is a basic circuit diagram of a known magnetic sensor that detects the presence or absence of a ferrite magnetic material. This sensor is currently being used in unmanned vehicle guidance systems and visually impaired person guidance systems that use ferrite magnetic materials as markers. In this sensor, an alternating current is passed from an oscillator 1 to an excitation coil 2. An induced voltage then develops in the sensing filter 3 placed near the excitation coil 2. It is rectified by a rectifier circuit 4 and output as a detection signal vl to an output terminal 5. When the ferrite magnetic body 11 approaches this coil portion, the self-induction coefficient of the fill 2.3 and the mutual induction coefficient H of the detection coil 2 and excitation coil 3 change.
The detection signal vl changes and the approach of the ferrite can be detected.

FIG. 4(b) is a conceptual waveform diagram of the detection signal vl, in which time is plotted on the horizontal axis and level is plotted on the vertical axis.

1-1. When the ferrite approaches the sensor, the detection signal v1 becomes smaller. When a conductive magnetic material such as iron that generates an eddy current approaches, the level of the detection signal V+ increases, as shown in FIG. 3C, contrary to when the ferrite approaches.

Not limited to this example, the sensor detection signal v1 is generally an analog quantity. In order to convert this into a 1-bit digital signal indicating on/off, A/D conversion has conventionally been performed using a comparator circuit as shown in FIG. 5(a). In this circuit, the detection signal V and the reference voltage fEv are compared by a comparator 7, and the result is output as a judgment signal V.

FIG. 5(b) is a diagram showing conceptual waveforms of various signals in FIG. 1(a). When the detection signal V is larger than the reference voltage V, the judgment signal V is generated. changes from low level (0) to high level (
1). Conversely, the detection signal V is the reference voltage V
, the determination signal V changes from high level to low level. Detection signal V when ferrite approaches
Since l becomes smaller and the judgment signal V changes from high level to low level, an inverter is attached to the output and Ferrai!
・The level should be set to high when approaching, and set to low when not, but this is not an essential problem.

The conventional detection signal processing circuit described above with reference to the drawings has the following problems.

If the voltage of the detection signal vl (hereinafter referred to as the base voltage) when the ferrite does not approach changes due to changes in external and internal conditions such as temperature, and becomes larger or smaller than the reference voltage V, the ferrite will Judgment signal V even if you don't approach. This causes malfunctions such as going low level or not going low level even when the ferrite approaches. In order to prevent this, the conventional method T sets a reference voltage V that is sufficiently larger than the fluctuation of the base pressure as one measure. In this way, it was impossible to perform long-distance detection with small changes due to ferrite, or to detect ferrite with poor magnetic properties.

Another solution is to use two detection coils with similar properties in a magnetic sensor and detect the difference in their outputs. In this way, changes in external conditions such as temperature, which are common to the two coils, can be removed by the differential. For changes due to ferrite, place one coil in the sensitive position and the other coil,
By placing it in an insensitive position, it becomes possible to detect even a differential. However, since this method requires two sensing coils, it is expensive, and there are problems in that it is difficult to make two similar sensing coils and is not suitable for mass production.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a magnetic sensor detection signal processing circuit that can correctly determine the presence of a non-conductive magnetic material such as ferrite even if the level of the detection signal changes due to changes in environmental conditions or circuit characteristics.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the magnetic sensor detection signal processing circuit provided by the first invention of the present application includes a circuit for differentiating the detection signal of the magnetic sensor, and this differentiation circuit. an inverting amplifier and a non-inverting amplifier that receive the outputs of the inverting amplifier, and first and second analog-to-digital converters that convert the output signals of the inverting amplifier and the non-inverting amplifier into 1-bit first and second digital signals, respectively. and a third analog signal that converts the detection signal into a 1-bit third digital signal.
a digital converter, first and second logic circuits that respectively pass the first and second digital signals only during a period when the third digital signal is not at a logic value corresponding to the conductive magnetic material; The RS flip-flop is reset and set by the outputs of the first and second logic circuits.

Further, the magnetic sensor detection signal processing circuit provided by the second invention of the present application includes a first
and a second differentiating circuit, an inverting amplifier and a non-inverting amplifier receiving the outputs of the first and second differentiating circuits, respectively, and output signals of the inverting amplifier and the non-inverting amplifier.
first and second analog-to-digital converters for converting the sensing signal into first and second digital signals of bits, respectively; and a third analog-to-digital converter for converting the sense signal into a third digital signal of one bit. and first and second logic circuits that respectively pass the first and second digital signals only during a period when the third digital signal is not at a logical value corresponding to the conductive magnetic material. RS reset and set by the output of logic circuit 2
Consists of flip flop.

(Function) The present invention distinguishes between changes in the detection signal of a magnetic sensor due to changes in internal and external conditions such as temperature and changes in the detection signal due to the approach of a magnetic body, based on the difference in the time rate of change of these two signals. It only detects the approach of a body. Since the former mentioned above changes at a much slower rate than the latter, the two can be separated. In order to separate both signals, in the present invention, the detection signal is input into a differentiating circuit and differentiated, and the larger one of the differentiated outputs is determined to be a change in the latter. In order to express the judgment in binary terms, one of the differentiating circuit outputs is inverted and amplified, the other is non-inverted and amplified, and each is converted into a 1-bit digital signal. By performing signal processing in this manner, digital signal pulses are output only when the magnetic body approaches or moves away from the magnetic body. Furthermore, in the present invention, in order to continue outputting an ON signal while a magnetic body is in close proximity, as in the conventional detection signal processing circuit, both digital signals are input to an RS flip-flop and the output thereof is used as a determination signal.

Although the approach of a magnetic body can be detected with the above configuration alone, in order to further distinguish between conductive magnetic bodies such as iron and electrically poor conductive magnetic bodies such as ferrite, the following procedure is performed. The magnetic sensor can be adjusted such that the sense signal changes in opposite directions for a conductive magnetic material such as iron that generates eddy currents and for a magnetic material that is an electrically poor conductor. This makes it possible to detect only the defective magnetic conductor, but when a differential circuit is used as described above, the output of the differential circuit when the defective magnetic conductor approaches and when the conductive magnetic substance moves away are the same and cannot be distinguished. - Therefore, taking advantage of the fact that the level change of the detection signal due to conductive magnetic materials such as metals is large, the detection signal of the conductive magnetic material is processed by a third D/A converter without passing through the differentiation circuit. Detection signal 2
The presence of a conductive magnetic material is determined by converting it into a value, and the third output is
A detection signal that determines only the presence of a defective conductive magnetic material without sensing the conductive magnetic material by taking the logical product of the digital signal and the input to the RS flip-flop (first and second digital signals) described above. A processing circuit is created.

(Example) Next, the present invention will be explained in detail with reference to Examples.

FIG. 1 is a circuit diagram showing an embodiment of the first invention of this morning. The input terminal 30 receives the detection signal v1. A differentiating circuit 31 having a CR configuration differentiates this detection signal v1. The output of the differentiating circuit 31 is divided into two, and -X is sent to the non-inverting amplifier 32;
The other is led to an inverting amplifier 33. The outputs of the amplifiers 32, 33 are each compared with a reference voltage in a comparator 34, 35. The logic of the outputs of the comparators 34 and 35 is inverted by the inverter 36, and then passed through the AND circuit 39 to the RS flip-flop 3B.
guided by. Even if the AND circuit 39 is omitted and the output of the inversion circuit 36 is input directly to the RS flip-flop 38,
RS flip-flop 38 when the ferrite approaches
The output Q of is turned on, otherwise it is turned off.

However, malfunction may occur due to the proximity of conductive magnetic materials such as iron that generate eddy currents. Therefore, the detection signal v1 is divided into two parts, one is led to the comparator 37 without passing through the differentiating circuit 31, the output of the comparator 37 is inverted by the inverter 41, and the logical product of the inverter 36 and the inverter 41 is performed. is taken by the AND circuit 39, and the output of the AND circuit 39 is sent to the RS flip-flop 3.
Let it be the input of B. In this way, a determination signal VSS that does not respond to iron or the like but only represents ferrite can be obtained. Here, the reference voltage V of the comparator 37 can be set to be sufficiently larger than the change due to temperature or the like, since the change in the detection signal V due to iron or the like is sufficiently larger than that due to ferrite.

The waveforms of the signals at each point in the embodiment of FIG. 1 are indicated by the numbers in FIG. As shown in the figure, the detection signal V is the base voltage V when there is no ferrite, and when the ferrite approaches between 1-1° and t"t, the detection signal Vl becomes smaller. This detection signal v1 When inputted into the differentiating circuit 31, a signal V81 containing a falling pulse at t and a rising pulse at t is obtained as the output of the differentiating circuit 31, as shown in the figure. A voltage proportional to the time rate of change of the input is generated.Therefore, the differentiating circuit 31 detects changes in the base voltage due to changes in temperature, etc., because the rate of change is small.
It does not appear in the output Vat of the differentiating circuit. Non-inverting amplifier 32
amplifies V□ as it is, and an inverting amplifier 33 inverts the positive/negative polarity of Vat and amplifies it. The comparator 34 outputs a rectangular wave when the output V of the 41 anti-inverting amplifier 32 exceeds the reference voltage V, and the comparator 35 outputs the output V of the inverting amplifier 33. When exceeds the reference voltage V, a rectangular wave is output. The comparator 37 does not turn on unless a conductive magnetic material such as iron approaches, and the AND circuit 39 converts the output of the inverter 36 into the RS flip-flop 3.
Lead to B. Therefore, the determination signal V of the output of the RS flip-flop 3B. is 1. It becomes "1" between t and t.

On the other hand, when iron or the like approaches, the comparator 37 is turned on, the logic circuit 39 is turned off, and the RS flip-flop 3B does not operate.

FIG. 3 is a circuit diagram showing an embodiment of the second invention of the present application. This embodiment is equipped with two differentiating circuits. The operation after the differentiating circuit 31 is the same as that of the embodiment shown in FIG. 1, and the same effects can be obtained.

(Effects of the Invention) As explained in detail in Section 2, according to the present invention, the presence of a non-conductive magnetic material such as ferrite can be correctly determined even if the level of the detection signal changes due to changes in environmental conditions or circuit characteristics. A magnetic sensor detection signal processing circuit that can be used can be provided. Therefore, by using the processing circuit of the present invention, even when conventional processing circuits make incorrect decisions due to changes in external conditions such as temperature, accurate decisions can be made with high sensitivity. In recent years, with the trend toward automation and robotization, the importance of sensors has been emphasized.

The present invention provides a magnetic sensor detection signal processing circuit that is very effective in cases where highly reliable and highly sensitive sensors are required.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the first invention of the present application, Fig. 2 is a waveform diagram of various signals of the embodiment, and Fig. 3 is a circuit diagram showing an embodiment of the second invention of the present application. Figure 4 (a) is a basic circuit diagram of a general magnetic sensor, Figure 4 (b), (
Fig. 5(c) is a diagram conceptually showing the waveform of the detection signal of this magnetic sensor, Fig. 5(a) is a circuit diagram showing a conventional magnetic sensor detection signal processing circuit, and Fig. 5(b) is a diagram showing the waveform of the detection signal of this magnetic sensor. A waveform diagram conceptually showing the input signal and output signal of a conventional circuit.
- Oscillator, 2...excitation coil, 3...detection coil,
4... Rectifier, 31... Differential circuit, 32... Non-inverting amplifier, 33... Inverting amplifier, 37, 34.35.
...Comparator, 36.41...Inverter, 39...AND circuit, 3B...RS flip-flop 7p. Representative Patent Attorney Shinsuke Honjo Figure 4 mouth = meditation 11 ferrite 1° 8 appearance 1 interval Figure 5 (a) (b)

Claims (2)

[Claims] (1) A circuit that differentiates the detection signal of the magnetic sensor, an inverting amplifier and a non-inverting amplifier that receive the output of the differentiating circuit, and an output signal of the inverting amplifier and the non-inverting amplifier.
first and second analog-to-digital converters for converting the sensing signal into first and second digital signals of bits, respectively; and a third analog-to-digital converter for converting the sense signal into a third digital signal of one bit. and first and second logic circuits that respectively pass the first and second digital signals only during a period when the third digital signal is not at a logical value corresponding to the conductive magnetic material. RS reset and set by the output of logic circuit 2
A magnetic sensor detection signal processing circuit consisting of a flip-flop. (2) First and second for differentiating the detection signal of the magnetic sensor
a differentiating circuit, an inverting amplifier and a non-inverting amplifier receiving the outputs of the first and second differentiating circuits, respectively, and converting the output signals of the inverting amplifier and the non-inverting amplifier into 1-bit first and second digital signals. The first to convert each to
and a second analog-to-digital converter, a third analog-to-digital converter for converting the detection signal into a 1-bit third digital signal, and the third digital signal corresponds to a conductive magnetic material. first and second logic circuits that respectively pass the first and second digital signals only during periods when they are not at logical values; and an RS flip-flop that is reset and set by the outputs of these first and second logic circuits. A magnetic sensor detection signal processing circuit.