JPS61273822A - Proximity switch - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] (Field of invention) The present invention relates to proximity switches.

(Summary of the Invention) In a proximity switch, the present invention utilizes the fact that when an object to be detected is made of metal, mutual inductance changes as the object approaches a magnetic field. Even if it is an object, it can be detected with high accuracy.

(Prior art and its problems) The following types of conventional proximity switches are known.

(i) First conventional example Detecting a change in the tuning frequency as the object to be detected approaches,
Objects were detected based on changes that exceeded the settings.

(ii) Second Conventional Example A change in capacitance due to the approach of an object to be detected is detected, and the object is detected based on a change greater than the set value.

(iii) Third conventional example A transducer consisting of a transmitter that projects ultrasonic waves and a receiver that receives reflected ultrasonic waves is provided, and ultrasonic waves are transmitted when reflected from a detected object and in other cases. The approach of the object to be detected was detected based on the time difference between the time of reception and the time of reception.

However, the conventional example having such a configuration has the following drawbacks.

■Disadvantages of the first conventional example Although the sensitivity is high and the object detection accuracy is excellent, the maximum detectable distance is 5CI11
For example, when detecting a product being conveyed on a belt conveyor on a production line, the position of the product varies in the width direction of the belt conveyor, so a proximity switch should be installed close to the object to be detected. The reality is that it cannot be used and cannot be used.

(2) Disadvantages of the second conventional example Similar to (2) above, although the sensitivity is high, the detectable distance is short.

■Although the defect detection distance of the third conventional example is sufficient, if we consider, for example, a case where the transducer is installed on a belt conveyor, when the height of the product is low, the reflection on the conveying surface of the belt conveyor. The time difference between when the object is reflected and when it is reflected by the product is short, which has the disadvantage of reducing object detection accuracy. Another drawback is that the ultrasonic waves are diffusely reflected by uneven objects, making object detection difficult.

(Object of the Invention) The present invention has been made in view of the above circumstances, and has an object to enable accurate detection of an object even if the object is located at a distance. purpose.

(Structure and Effects of the Invention) In order to achieve such an object, the present invention provides a transmitting coil having a magnetic core as a magnetic material disposed on either side of the detection area of a detected object, and a transmitting coil for transmitting the magnetic material. A high-frequency oscillation circuit that outputs an excitation current to the reliable coil, a receiving coil whose magnetic core is a magnetic material placed on the other side of the navigation detection area, and object detection in response to changes in the level of the receiving current of this receiving coil. and an output circuit that outputs a signal.

According to this configuration, when an excitation current is output from the high-frequency oscillation circuit to the transmitting coil, a magnetic field is formed from the transmitting coil to the receiving coil, and a current is induced in the receiving coil by this magnetic field. When an object to be detected approaches the magnetic field, magnetic flux passes through the object to be detected, reducing the magnetic resistance on the receiving coil side, increasing the density of the magnetic flux linking the receiving coil, and increasing the received current, or Alternatively, a level change occurs due to a decrease in the receiving current of the receiving coil due to eddy current loss, and in any case, the level of the receiving current changes compared to when the object to be detected is not close. The approach of the detected object can be detected based on the change.

Therefore, as long as the object to be detected is magnetic, such as a metal object, as long as the transmitting coil can form a good magnetic field, the received current will decrease as the object approaches. It is possible to clearly generate a level change, and furthermore, it is possible to prevent detection failures due to the height of the object, concavities on the surface, and white changes that occur when using ultrasonic waves. Since it is an active type that generates a magnetic field, it is less susceptible to surrounding influences such as external radio waves, and as a whole, it can detect objects with high accuracy even if the distance between the object and the object to be detected is large. became.

(Description of Examples) Hereinafter, the present invention will be described in detail based on examples shown in the drawings. FIG. 1 is a schematic configuration diagram of a proximity switch according to an embodiment of the present invention, and FIG. 2 is a circuit diagram. In these figures, l is a magnetic material 1a such as ferrite as a magnetic core,
A transmitting coil 2 wound thereon is a receiving coil wound around a magnetic material 2a such as ferrite as a magnetic core, and is placed on a belt conveyor 4 that conveys a metal product 3 as an object to be detected. , they are arranged on one side and the other side on both sides of the detection area for the product 3. Although not shown, both coils 1.2 and both magnetic bodies 1
a and 2a are attached and supported by support stays.

5 is a main body housing an electric circuit section.

Connected to the transmitting coil 1 is an excitation means 8 consisting of a high frequency oscillation circuit 6 that outputs an excitation current and an amplifier circuit 7 that amplifies the excitation current.

An output circuit 9 is connected to the receiving coil 2 and outputs an object detection signal in response to a change in the level of the receiving current. This output circuit 9 has an amplifier 1, 0, a bandpass filter 1, a detection circuit 12, and a leg 13, and after amplifying the received current from the receiving coil 2, outputs the bandpass filter 1. The noise component is removed by the detection circuit 12, and the detected signal is input to the determination section 13. In the determination section 13,
a switch circuit 14; a first capacitor 5 connected to the first contact of the switch circuit 14; a ninth capacitor 5 connected to the second contact of the switch circuit 14;
2 capacitor 16 and the first and second capacitors 15
．． 16 differential connected to each positive terminal
At the output terminals of the amplifier circuit 17 and the differential amplifier circuit 17,
A connected comparator 18 and the comparator 18
A constant voltage power supply 19 for determining the threshold voltage V ref of the switch circuit 14 and a timing circuit 20 for outputting a pulse signal C for switching the switch to the switch circuit 14 are provided.

The timing circuit 20 outputs the pulse signal C to the switch circuit 14 when the output of the comparator 18 is at the "L" level, and stops outputting the pulse signal C when the output of the comparator 18 is at the "H" level. It has become. Further, the switch circuit 14 is connected to the timing circuit 2.
When the pulse signal C from 0 is at the "H" level, the detection circuit 12 is connected to the first capacitor 15, and conversely, when the pulse signal C is at the "L" level, the detection circuit 12 is connected to the second capacitor 16. is configured to do so.

Next, the operation of this embodiment will be explained based on the time chart of FIG.

The excitation current from the high frequency oscillation circuit 6 is amplified by the amplifier circuit 7, and the excitation current excites the transmitting coil 1. As shown in FIG. 4(a), the transmitting coil 1 and the receiving coil 2 are
A magnetic field is created between the two.

The reception current received by the reception coil 2 is amplified by the amplifier circuit 7, noise components are removed by the bandpass filter 11, and the signal a is detected by the detection circuit 12 to become a signal.

When the product 3 is transported by the belt conveyor 4 and reaches the magnetic field, a pulse signal C is output from the timing circuit 20 to the switch circuit 14 and the switch circuit 1
4 switching is repeated. 1st capacitor 5
is charged by the input signal d when the pulse signal C is at the "H" level, and the second capacitor 16 is charged by the input signal e when the pulse signal is at the "L" level.

These input signals d and e are at the same level as the output signal of the detection circuit 12. first and second condenser arc, 1
1 and N 6 repeat charging and discharging alternately in response to switching operations, so that the charging voltage V of the first capacitor 5 and the charging voltage V of the second capacitor 16 are the same.

usually remain substantially equal.

By the way, as the product 3 reaches the magnetic field, as shown in Fig. 4 (b
), magnetic flux concentrates on the metal part of the product 3, and the mutual inductance between the transmitting coil 1 and the receiving coil 2 changes. Namely, Pandopa.

The amplitude of the output signal a of the filter 11 begins to increase, and the level of the output signal S of the detection circuit 12 also begins to increase accordingly. At this time, if the pulse signal C rises at time tl and the detection circuit 12 is connected to the first capacitor 5, the level of the input signal d to the first capacitor 15 is equal to that of the output signal from the detection circuit 12. In response to this, the level of the output signal r of the differential amplifier circuit 17 increases by a very small amount. However, the output signal f
Since the amount of increase in is small, the output signal f is lower than the threshold voltage V ref of the comparator 18, the output signal g of the comparator 18 maintains the "L" level, and the object detection signal S is not output.

When the pulse signal C falls at time t, and the detection circuit 12 is connected to the second capacitor 16, at this time the product 3 has entered the magnetic field significantly, and the level of the output signal of the detection circuit 12 is low. The level of the input signal e to the second capacitor 16 is sufficiently higher than the increase in the input signal d to the first capacitor 15 because rise significantly. Therefore, in the first capacitor 15, the charging voltage vI is maintained constant, but in the second capacitor 16, the charging voltage V is changed depending on the level of the input signal e thereto.
That is, it changes upward in response to a change in the level of the output signal of the detection circuit 12. As a result, the output signal f of the differential amplifier circuit 17 also rises, and its level becomes equal to the threshold voltage V.
ref, the output signal g of the comparator 18 becomes “H”
level. As a result, the object detection signal S is output to an external device (not shown), and the "H" level output signal g is input to the timing circuit 20, so that the pulse signal C from the timing circuit 20 is output. will be stopped.

As the product 3 passes through the magnetic field, 1.
As a result, the level of the output signal of the detection circuit 12 decreases. As a result, the output signal of the differential amplifier circuit 17 -f
The level of is the threshold voltage ' at time t,
Vref') t= i< tL 6 1. ．．
2. The output signal g of i-2187.6 becomes "L" level, and the object detection signal S is no longer output. Further, as a result of the above output signal g becoming "L@ level", the timing circuit 2
The pulse signal C is output from 0 to the switch circuit 14 and switching is restarted. As a result, the input signal d to the first and second capacitors 15, 16 respectively.

The level of e becomes low corresponding to the level of the output signal S of the detection circuit 12, and the output signal f from the differential amplifier circuit 17 also stabilizes at the "L" level.

The output signal from the detection circuit 12 is input to the amplifier circuit 7 of the excitation means 8, and the gain of the amplifier circuit 7 is automatically adjusted in response to the level of the output signal.

FIG. 5 is a schematic perspective view showing another embodiment, in which a transmitting coil l and a receiving coil 2 are connected to respective magnetic bodies 1.
The magnetic core of a, 2 a is located parallel to the conveying surface of the belt conveyor 4 and perpendicular to the conveying direction, and the magnetic core of 2 a is arranged so as to be perpendicular to the conveying direction. , is configured so that the product 3 can be detected satisfactorily without interfering with the transportation of the product 3.

The spacing and arrangement between the transmitting coil 1 and the receiving coil 2 can be set as appropriate depending on the size of the object to be detected, the moving route, etc. That is, according to the present invention, the detection area for the detected object can be obtained with an extremely high degree of freedom.

According to the configuration of the present invention, since the transmitting coil 1 and the receiving coil 2 are provided independently, for example, a memory card containing a ROM or RAM for transmitting and receiving data signals can be attached to the product 3. In this case, communication with the memory card can be performed well, and operating power can also be supplied to the transponder, which is extremely convenient in practice.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a proximity switch according to an embodiment of the present invention, FIG. 2 is a circuit diagram, FIG. 3 is a time chart, and FIG. 4 is a schematic side view showing the state of magnetic field formation. ) shows a state without a product, and (b) shows a state with a product. FIG. 5 is a schematic configuration diagram showing another embodiment. l... Transmission coil, la... Magnetic material of the transmission coil, 2... Receiving coil, 2a... Magnetic material of the receiving coil, 3... Product as detected object, 6 ...High frequency oscillation circuit, 9...Output circuit, S...Object detection signal.

Claims (1)

[Claims] (1) A transmitting coil having a magnetic core as a magnetic material disposed on one side of the detection area of the object to be detected, a high-frequency oscillation circuit that outputs an excitation current to the transmitting coil, and the other side of the detection area. A proximity switch comprising: a receiving coil having a magnetic core made of a magnetic material disposed in the receiving coil; and an output circuit that outputs an object detection signal in response to a change in the level of a reception current of the receiving coil.