JP3384058B2 - Proximity switch - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency oscillation type proximity switch utilizing an alternating magnetic field.

[0002]

2. Description of the Related Art In a conventional proximity switch, a metal body is detected based on a change in the oscillation state of an oscillation circuit due to the approach of the metal body. FIG. 6 is a circuit diagram showing an example of a conventional proximity switch. In this figure, this proximity switch has a parallel resonance circuit 1 including a capacitor C1 and a detection coil L1. One end of the parallel resonance circuit 1 is grounded, and the other end is connected to the emitter of a diode-connected transistor Q1. The base of the transistor Q1 is connected to the base of the oscillation transistor Q2, and the emitter thereof is connected to the midpoint of the detection coil L1 via the feedback resistor R1. Further, a resistor R2 is connected to the base of the transistor Q2, and an integrating capacitor C2 for stabilizing oscillation is connected to the collector between the transistor Q2 and the ground terminal 3, which form an oscillation circuit.

Further, the collector of the transistor Q2 is a resistor R
An output transistor connected to the power supply terminal 2 via the power supply terminal 2, a series connection circuit of resistors R4 and R5 between the power supply terminal 2 and the collector terminal, and a base connected to the midpoint thereof, and an emitter connected to the power supply terminal 2. Q3 is connected. A resistor R6 having a large resistance value is connected in parallel between the emitter and collector of the transistor Q3, and one end of the collector is connected to the resistor R2 and is grounded via the Zener diode D1. The power supply V _S and the load resistance R are provided between the power supply end 2 and the ground end 3.
_L is connected in series. These form an output circuit that controls the output current depending on whether or not the oscillation circuit oscillates.

In this oscillation circuit, the output of the resonance circuit of the detection coil L1 and the capacitor C1 is lifted by a diode-connected transistor Q1 to generate an oscillation transistor Q1.
It is positively fed back via 2 and oscillates at the resonance frequency of this parallel resonance circuit 1. At the time of oscillation, the transistor Q2 is turned on for each half-wave and a collector current flows, and is integrated by a resistor R3 and an integrator circuit including a resistor C3 connected in parallel with the resistor R3 and a capacitor C2. , The terminal voltage of the capacitor C2 is lower than that of the power supply, and is a substantially constant voltage. Therefore, current always flows through the resistor R4 and the transistor Q3 is turned on. Therefore, a series circuit of the Zener diode D1 and the load resistance R _L is connected as a load to the power supply V _S. Therefore, assuming that the voltage of the Zener diode D1 is V _D1 , the following current I ₁ flows through the load resistor R _{L. I 1 = (V S -V D1} ) / R L

On the other hand, when an object approaches the detection coil L1, the magnetic flux of the coil passes through the metal body and an eddy current is generated on the metal surface. Therefore, the conductance g of the detection coil L1 increases and the oscillation stops. When the oscillation is stopped, no current flows through the resistor R3, the resistor R6 connected in parallel with the transistor Q3, the Zener diode D1 and the load R _L become the load of the power source V _S , and the following minute current I ₂ becomes the load R _L.
It will flow to. _{I 2 = (V S -V D1} ) / can detect the presence or absence of the object based on the (R _L + R6) Thus the current value I ₁ flowing through the load resistor R _L, I _2.

[0006]

However, in such a conventional proximity switch, the amount of change in the conductance of the detection coil differs depending on the material of the metal body. If the oscillation frequency is set to several MHz or more, a high frequency causes a skin effect in which the magnetic flux does not easily pass inside the detector, and the amount of change in conductance varies depending on the surface state. Therefore, even when the metal body approaches the same position, the amount of change in the conductance of the detection coil differs depending on the material and surface condition.
There is a problem that the detection distance of the proximity switch is also different.

The present invention has been made in view of such conventional problems, and it is a technical subject to reduce the influence of the material and surface condition of a metal body so that an object can be detected. .

[0008]

The present invention is a detection target.
Provided outside the pass region of that metal body, a first parallel resonant circuit including an oscillator coil, one end of the first parallel resonance circuit is connected to the control terminal, that the amplified output first parallel co < The oscillation amplification element that returns to the vibration circuit and the gold to be detected.
A second parallel resonance circuit including a detection coil and a capacitor, which is provided in a passage region of the metal body and is magnetically coupled to the oscillation coil; and a resonance frequency of the second parallel resonance circuit. , lower than the oscillation frequency of the first parallel resonance circuit, is characterized in that it has an oscillator circuit which is set to a frequency loss may increase the oscillation coil on the basis of the approaching of the metal body.

[0009]

According to the present invention having such a feature, the detection coil magnetically coupled to the oscillation coil of the oscillation circuit including the oscillation coil and the capacitor is provided. The detection coil is mounted outward of the proximity switch to detect the proximity of the object. When an object approaches, the inductance of the detection coil decreases, so that the impedance also increases and the loss of the oscillation coil increases.
Further, the loss resistance generated in the detection coil of the second parallel resonance circuit due to the detection of the object also increases. Due to the increase of the loss resistance and the loss of the oscillation coil due to the increase of the impedance of the second parallel resonant circuit, the oscillation is rapidly stopped.

[0010]

1 is a circuit diagram showing the configuration of a proximity switch according to an embodiment of the present invention. In this figure, the same parts as those of the conventional example described above are designated by the same reference numerals, and detailed description thereof will be omitted. In this embodiment, the oscillation coil L2 and the capacitor C
1 and the first parallel resonance circuit 4 is formed, and the emitter of the diode-connected transistor Q1 is connected to the hot end thereof. The bases of the transistors Q1 and Q2 are commonly connected. The transistor Q2 is an oscillating amplification element for amplifying the output of the parallel resonance circuit 4, and the amplified output is fed back to the center tap of the parallel resonance circuit 4 via the resistor R1. Connection between transistor Q3 for detecting oscillation current and resistors R3 to R6 and Zener diode D1
The connection is also the same as in the conventional example.

In the present embodiment, a detection coil L3 magnetically coupled by a mutual inductance (M) is provided near the oscillation coil L2, a capacitor C3 and a resistor R7 are inserted in series with the detection coil L3, and the parallel resonance circuit 5 is connected. Make up. The detection coil is formed outward of the proximity switch so that a metal body approaching the proximity switch can be detected. The resonance frequency determined by the detection coil L3 and the capacitor C3 of the parallel resonance circuit 5 is a frequency f _T slightly lower than the resonance frequency f _{OSC of} the first parallel resonance circuit 4. This resonance frequency f _T approaches the oscillation frequency f _OSC when an object approaches the detection coil L3, and the oscillation coil L2
It is assumed that the frequency is set such that the loss due to the parallel resonant circuit 5 seen from the above increases. The detection coil L3 that constitutes the parallel resonance circuit 5 is preferably made of the same material and structure as the oscillation coil L2 that constitutes the parallel resonance circuit 4, and the capacitor C
The capacitors C1 and C3 are of the same type.

Next, the operation of this embodiment will be described. FIG. 2 is a graph showing changes in loss due to the parallel resonant circuit 5 as seen from the oscillation coil L2 with respect to frequency. The oscillation circuit when an object in the detection coil L3 is not close, it is assumed that oscillates at the resonance frequency f _{OS C} of the parallel resonance circuit 4. In this case, the level G1 of the loss due to the parallel resonance circuit 5 seen from the oscillation coil L2 determined by the frequency f _OSC of the curve A is small, and the total loss of the oscillation coil L2 is also low. When an object approaches the detection coil L3, the inductance of the detection coil L3 decreases, and the curve A in FIG. 2 changes to the higher frequency side as shown by the curve A1. Therefore, the loss due to the parallel resonance circuit 5 seen from the oscillation coil L2 in terms of the frequency f _OSC increases as shown from G1 to G2.

FIG. 3A shows the loss (conductance) of the oscillation coil L2 with respect to the distance L to the object when a magnetic metal such as iron approaches, and FIG. 3B shows a nonmagnetic metal. Shows the loss of the oscillating coil L2 with respect to the distance when is approached. The loss due to the increase in the resonance frequency shown in FIG. 2 is shown as an increase in R7 ′ in FIGS. 3 (a) and 3 (b). Further, in FIG. 3, R0 indicates a loss resistance component generated in the oscillation coil L2 via the detection coil L3 due to the proximity of an object.

As shown in FIG. 3, when the metal body is a non-magnetic body such as aluminum, the amount of increase in the loss resistance component R0 generated in the detection coil due to the vicinity of the body is smaller than that of the magnetic body metal, and the oscillation. The same applies to the coil. However, since the amount of decrease in inductance is large, the increase in frequency shown in FIG. 2 is large, and the loss R7 'of the oscillation coil L2 corresponding to this is large.
Grows. Therefore, by these actions, the characteristics B and C of the magnetic substance and the non-magnetic substance can be made substantially the same, and the oscillation can be rapidly stopped. In this way, the oscillation resistance is rapidly stopped due to the loss resistance component generated in the detection coil L3 and the loss component of the oscillation coil due to the change in the inductance. Here, in FIGS. 3A and 3B, the conductance value g _C indicates a conductance that is a threshold value for stopping the oscillation, and when the conductance is equal to or more than this value, the oscillation is stopped. Therefore, by appropriately selecting the resistance value of the resistor R7 or the capacitance value of the capacitor C3, the curves B and C in FIGS. 3A and 3B can be made to substantially coincide with each other, and the metal body can be detected at substantially the same distance. Therefore, it is less affected by the material and surface condition of the approaching metal body, and the effect that the change in the detection distance can be reduced can be obtained.
Further, if the two parallel resonance circuits 4 and 5 are made of the same material and have the same structure and type of coil and capacitor, the drift due to the temperature change has the same characteristics, so that it is not necessary to perform temperature compensation.

Next, the structure of the proximity switch of this embodiment will be described. 4 is an assembly configuration diagram showing a configuration of a proximity switch for detecting a metal sphere, and FIG. 5 (a) is a front view showing a print pattern of the printed circuit board, FIG.
(B) is a rear view. As shown in FIG. 4, this proximity switch has a case 11 whose flat upper surface is open, and an octagonal prism 11a having the same height as the surrounding frame-like portion at a position deviated to either one from the center thereof. Is provided and the inside is opened. Further, a pair of openings 11b and 11c are formed on the side wall of the case 11 at symmetrical positions. A printed circuit board 12 is provided in the case 11. As shown in the pattern of FIG. 5, the printed circuit board 12 is formed by integrally forming an octagonal opening and a flat plate-shaped portion at one end thereof, and surrounds the octagonal portion to detect the detection coil L3 described above. Is configured. An oscillation coil L2 is formed as a pattern on the printed circuit board 12 at the center of the printed circuit board 12, similar to the detection coil L3. A pattern of the detection coil L3 is formed on the back surface of the printed circuit board 12, and other circuit components are mounted in the central portion. Then, with the printed circuit board housed in the case 11, a cover 13 is put on as shown in FIG. As shown in the figure, the cover 13 has an elastic portion 13a having a claw on the outer side and an elastic portion 13b (not shown) formed on the lower side as shown in the figure, and an octagonal opening 13c is formed at the same position as the case 11.
have. In this way, the printed circuit board 12 is placed in the case 11
The elastic portions 13a and 13b of the cover 13 in a state of being housed inside
The proximity switch is formed by fitting and fitting the openings to the openings 11b and 11c of the side wall of the case 11.

4 and 5, a proximity switch for detecting a metal ball is described, but it goes without saying that the present invention can be applied to proximity switches of various other shapes and uses. .

[0017]

As described in detail above, according to the present invention, it is possible to obtain an effect that an object can be detected with almost no influence of the material and surface condition of the approaching metal body.

[Brief description of drawings]

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

FIG. 2 is a graph showing changes in the impedance of the resonance circuit with respect to the frequency of this embodiment.

FIG. 3 is a graph showing the loss (conductance) of the oscillation coil with respect to the distance to the object of this example.

FIG. 4 is an assembly configuration diagram showing a proximity switch of the present embodiment.

FIG. 5 is a diagram showing a print pattern on a printed circuit board according to the present embodiment.

FIG. 6 is a circuit diagram showing a configuration of a conventional proximity switch.

[Explanation of symbols]

1,4,5 Parallel resonance circuit 2 power end 3 ground end 11 cases 12 printed circuit boards 13 cover L2 oscillation coil L3 detection coil

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-57-31231 (JP, A) JP-A-47-35864 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03K 17/95 H01H 36/00

Claims (2)

(57) [Claims] 1. A device provided outside a passage area of a metal body to be detected.
And a first parallel resonant circuit including an oscillation coil, and one end of the first parallel resonant circuit connected to a control terminal,
An oscillation amplification element for feeding back the amplified output to the first parallel resonance circuit, a detection coil provided in a passage area of a metal body to be detected and arranged so as to be magnetically coupled to the oscillation coil, and a capacitor. A second parallel resonant circuit including the second parallel resonant circuit, wherein a resonance frequency of the second parallel resonant circuit is equal to the first parallel resonant circuit.
Lower than the oscillation frequency of the column resonant circuit, proximity switch, characterized in that it comprises an oscillator circuit loss is set to a frequency increase of the oscillation coil on the basis of the approaching of the metal body. 2. The oscillating coil and the detecting coil are formed on a common substrate, and the substrate is the gold to be detected.
The proximity switch according to claim 1, wherein the member has an opening for penetrating the detection coil .