JPH0645904A - Contactless switch - Google Patents

Abstract

PURPOSE:To detect an object in a wide detecting area. CONSTITUTION:A loop-like transmission coil L1 is prepared and driven by an oscillation circuit 1. A receiving coil L2 is prepared so that a part of the coil L2 is overlapped to the coil L1. When the coil L1 is driven in a state that no object approaches, magnetic flux obtained in the coil L2 is balanced and receiving voltage is made almost zero. When the receiving voltage of the coil L2 is amplified and the balanced state is lost when an object approaches, the object can be detected based upon the rise of an output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a proximity switch having a feature in an object detection area.

[0002]

2. Description of the Related Art A high-frequency oscillation type proximity switch has been widely used as a device for detecting the presence or absence of a metal body. This proximity switch radiates a high frequency magnetic field, and a coil is arranged on the front surface of the proximity switch to catch the change so that the object to be detected can be effectively recognized. This detection surface generally has a columnar shape or a prismatic shape, and a circle or a square is used. This is because the detection coil and the core arranged around it have a circular cross-sectional shape, and the efficiency in radiating a high frequency magnetic field is good.

[0003]

In many cases, the entering or passing position of the object to be detected is limited, but when it largely fluctuates, it may deviate from the detection area of the detection switch. In such a case, a plurality of detection switches 101 are arranged in parallel as shown in FIG.
Need to be wide. However, when a plurality of proximity switches are arranged in parallel, if the detection distance is set to d1, there is a drawback that a dead zone is likely to occur at the boundary portion of the detection area of each detection switch 101 depending on the type of object. Therefore, it is necessary to set the detection distance to d2 or less close to the detection switch. Further, if a plurality of proximity switches are arranged close to each other, mutual interference occurs, so that it is necessary to make the oscillation frequency different for each proximity switch, and there is a drawback that the configuration becomes complicated.

There are also proximity switches with a long detection distance,
In this case, since the working distance becomes long, there is a drawback that it is easily influenced by surrounding metals other than the object to be detected.

The present invention has been made in view of the above problems of the conventional proximity switch, and it is a technical object to provide a proximity switch in which the detection area is made larger than the detection distance and the detection area is widened. It is an issue.

[0006]

According to a first aspect of the present invention, there is provided an oscillation circuit which oscillates at a constant frequency and amplitude, and a transmission coil which is driven by the oscillation circuit and whose magnetic flux reaches a detection area of an object. The receiver coil is arranged so as to partially overlap the transmitter coil, and the receiver coil is arranged at a position where the magnetic flux interlinking drivingly of the transmitter coil is balanced, an amplifier circuit for amplifying the signal obtained in the receiver coil, and an amplifier circuit. A signal processing circuit unit that detects an object based on the increase in the obtained output,
It is characterized by including.

Further, the invention of claim 2 of the present application has a shield metal case including a transmission coil and a reception coil, and a compensation loop coil arranged at a position for canceling an anti-magnetic flux due to an eddy current of the shield metal case. It is characterized by.

[0008]

According to the present invention having such characteristics, the oscillation coil drives the transmission coil at a constant frequency and a constant amplitude. By driving the transmitting coil, magnetic fluxes in different directions are generated in the receiving coil. Therefore, the receiving coil is arranged so that the magnetic flux interlinking with the receiving coil is balanced. Then, the output of the receiving coil is amplified. If there is no object, the magnetic flux is balanced and the received voltage is almost zero.
When an object approaches, the balance is lost and the reception voltage is obtained. Therefore, an object detection signal can be obtained by detecting the amplified output.

According to the second aspect of the present invention, the shield case is provided around the transmitting coil and the receiving coil. In order to cancel the influence of the eddy current of the shield case, a loop coil for compensation is arranged to balance the magnetic fluxes that the receiving coil links. By doing so, the influence of the shield metal case is eliminated, and the object can be detected without being affected by the outside.

[0010]

1 is a principle diagram of a proximity switch according to an embodiment of the present invention. In the figure, the coil L1 is a loop-shaped transmission coil and has a rectangular shape. Then, the transmission coil L1 is driven by the high frequency current of the oscillation circuit 1. The transmitter coil L1 is shown in FIGS.
As shown in, the receiving coil L2 is arranged so as to partially overlap with each other when viewed from the upper surface. The receiving coil L2 is also a rectangular loop coil.

[0011] Referring now to apply a high-frequency current to the transmitting coil L1, resulting magnetic flux [Phi _A and [Phi _B as shown, the magnetic flux [Phi _A, the voltage due to [Phi _B occurs whereby the receiving coil L2. This magnetic flux is shown in a vector diagram as shown in FIG.
It becomes what is shown in (c). Since the directions of these magnetic fluxes are opposite, the phases at the time of reception are also opposite. If the areas of the overlapping portions are adjusted so that the reception voltages due to the respective components of the magnetic fluxes Φ _A and Φ _B interlinking with the reception coil L2 become equal, the reception voltage Er becomes almost zero. The differential coupling state at this time is called a balanced state. Then, when an object approaches the vicinity of the transmission coil L1 or the reception coil L2, FIG.
The equilibrium state indicated by is broken, and a reception voltage is generated by the magnetic flux interlinking with the reception coil L2.

In the present invention, the proximity of the object is detected by detecting the increase in the reception level. FIG. 2 is a block diagram showing the electrical configuration of the proximity switch of this embodiment.
As described above, the transmission coil L1 is driven by the oscillation circuit 1 at a constant amplitude and a constant frequency. Here, if the oscillation frequency of the oscillation circuit 1 is set to several tens KHz, the degree of balance can be easily obtained. The receiving circuit 2 is connected to the receiving coil L2. The receiving circuit 2 has a bandpass filter that passes a frequency equal to the oscillation frequency of the oscillation circuit 1,
The output is amplified through the amplifier circuit 3. A variable resistor for gain adjustment is connected to the amplifier circuit 3. The output of the amplification circuit 3 is given to the detection circuit 4. The detection circuit 4 obtains a DC level signal corresponding to the amplitude by detecting the amplified output,
The output is given to the discrimination circuit 5. A threshold value of a predetermined level is set in the discrimination circuit 5, and when the input signal exceeds the threshold level or less, the discrimination signal is output to the output circuit 6. Then, the output circuit 6 outputs the object detection signal to the outside. Here, the detection circuit 4, the discrimination circuit 5, and the output circuit 6 are
A signal processing circuit unit that detects an object according to an increase in the amplified output is configured. In this case, the range where the equilibrium state of the receiving coil L2 is destroyed due to the proximity of the object is the object detection area.

In this embodiment, as shown in FIG. 1, the transmitting coil L1 and the receiving coil L2 are formed in a rectangular shape, and one of them is moved in parallel so as to be overlapped, but it is not always necessary to arrange them in this way. There is no. For example, the transmission coil L1 and the reception coil L2 may be crossed with each other as long as a balanced state can be obtained. The shape of the coil is not limited to the rectangular shape, and various other shapes can be used.

Next, a second embodiment of the present invention will be described. Proximity switches may require a proximity switch with a shield in order to reduce the influence of metal around the mounting portion. In the conventional proximity switch, since the core is provided around the coil, the influence of the shield case is small, but in the present embodiment, the influence is large because the shield case is not used. FIG. 3 is a diagram showing a coil portion of a proximity switch having such a shield case. As shown in the figure, the above-mentioned transmitting coil L1 and receiving coil L
Attach the shield case 11 to the outer peripheral portion of 2. The shield case 11 may cover only the sides of the transmission coil L1 and the reception coil L2, or may cover the entire coil portions as illustrated.

In this case, assuming that the high frequency magnetic fields generated by the transmission coil L1 are Φ _A and Φ _B , an eddy current also flows in the shield case 11 by this, and an anti-magnetic flux is generated. This is Φ _S as shown in FIG. This Φ
_{When S} occurs, the balance of the magnetic flux passing through the receiving coil L2 deteriorates. Therefore, a compensating loop coil L3 is arranged to cancel this Φ _S. Compensation loop coil L3
Is a rectangular coil having a width narrower than that of the transmission coil above the transmission coil L1. Since the compensating loop coil L3 has a closed circuit configuration, the secondary current I ₃ is generated by driving the transmitting coil L1. A secondary magnetic flux Φ _S ′ is generated by this current I ₃ . The compensating loop coil L3 is arranged in parallel on the same plane as the receiving coil L2, and adjusts the number of interlinkages between Φ _S and Φ _S ′. By doing so, in the vector diagram, Φ _S and Φ _S ′ are balanced as shown in FIG. In the receiving coil L2, since the magnetic fluxes that are linked to each other are balanced, the receiving voltage becomes almost zero as in the first embodiment.

When an object approaches the inside of the shield case 11, the equilibrium state is changed and the reception voltage rises. Therefore, the object can be detected by the same detection circuit as in the first embodiment. Figure 4
(B) is a diagram showing the relationship of the loop coil, and as shown in FIG. 2, the receiving coil L2 is connected with each block of the receiving circuit 2 and the amplifying circuit 3 and below. By doing so, it is possible to detect the metal object coming into the inside of the shield case 11 as in the first embodiment.

[0017]

As described above in detail, according to the present invention, the transmitting coil and the receiving coil are provided, and the detection area of the object is formed by the area of the loop coil. Therefore, it is possible to obtain an effect that an object in a wide range can be surely detected. Further, since the core is not required around the coil, the degree of freedom in manufacturing the head portion can be increased. Further, almost the same detection sensitivity can be obtained regardless of whether the object to be detected is magnetic or non-magnetic metal.

[Brief description of drawings]

FIG. 1 is a principle diagram showing a principle of a proximity switch according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an electrical configuration of the first embodiment of the present invention.

FIG. 3 is a principle diagram showing a principle of a proximity switch according to a second embodiment of the present invention.

FIG. 4A is a vector diagram of magnetic flux of the second embodiment,
FIG. 7B is a diagram showing a part of a transmitting / receiving coil, a compensating coil and a receiving circuit of the second embodiment.

FIG. 5 is a schematic diagram showing a relationship between a detection area and a detection area using a plurality of conventional proximity switches.

[Explanation of symbols]

 L1 transmitter coil L2 receiver coil L3 compensation loop coil 1 oscillator circuit 2 receiver circuit 3 amplifier circuit 4 detector circuit 5 discrimination circuit 6 output circuit 11 shield case

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H01H 36/00 A 9176-5G // F42C 13/04 9111-2C

Claims (2)

[Claims] 1. An oscillating circuit that oscillates at a constant frequency and amplitude, a transmitting coil that is driven by the oscillating circuit and has a magnetic flux range as an object detection region, and is arranged so as to partially overlap the transmitting coil. A receiver coil arranged at a position where the driving flux of the transmitter coil is balanced, an amplifier circuit for amplifying a signal obtained in the receiver coil, and an object based on an increase in output obtained in the amplifier circuit. And a signal processing circuit section for detecting the. 2. A shield metal case including the transmitter coil and the receiver coil, and a compensating loop coil arranged at a position for canceling an anti-magnetic flux due to an eddy current in the shield metal case. Proximity switch described in 1.