JPS59119629A - 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 [Technical Field to Which the Invention Pertains] The present invention relates to a proximity switch that detects the presence of a metal piece, metal sheet, or other metal body in a non-contact manner. More specifically, the present invention has a detection coil in the detection section, and when a metal object to be detected approaches or exists, the inductance of the coil changes, and a change in the oscillation width of the oscillation circuit or a stop of oscillation is detected. An oscillation type proximity switch that generates an output signal! It is related to ζ.

[Description of prior art]

FIG. 1 is a block diagram showing an example of a conventional oscillation type proximity switch. This device consists of coil L+ and coil L2.
and a capacitor C is connected in parallel with the coil L1 to form a tuned circuit, so that the oscillation circuit 1 oscillates via the mutual inductance M between the coils L+ and L2. This is what I did. 2 is a circuit that detects a change in the oscillation width of the oscillation circuit 1 and outputs a signal.

In this device, when a detected object N is inserted between coils L+ and Lg, mutual induction inductance M decreases,
Along with this, the oscillation width of the oscillation circuit 1 decreases, and finally the oscillation stops, and the approach of the object to be detected N can be detected.

By the way, this device can change or cut off the mutual induction inductance M between the coils L+ and L2.
.

For example, the coil L+ has the feature of being able to detect the approach of the detected object N regardless of whether it is a ferromagnetic material or a non-magnetic material.

If the distance between L2 and L2 is increased more than necessary, the mutual induction inductance M will become small and stable operation will not be possible. Therefore, the distance between the coils Ll and L2 must be kept small. It had the disadvantage of being restricted.

- Fig. 2 shows the coil L+t L in the conventional device shown in Fig. 1.
2 is a diagram showing the relationship between the distance d (expressed as a ratio to the opening diameter of the Bot core) and the mutual induction inductance M between the coils Ls and Lx.

When d becomes larger than the power, M becomes close to zero and the coil L
This indicates that it is not possible to install the distance d between + and L2 by more than V2.

Still another example of the conventional proximity switch is the one described in Japanese Patent Publication No. 48-467, for example. In this device, a resonator having a resonant frequency that is the same as or close to the oscillation frequency of the oscillation circuit is placed near the oscillation coil of an oscillation circuit whose output changes due to the approach of a nearby object, and the oscillation coil and resonator are connected to each other. This system is designed to detect the approach of an object to be detected that approaches between the two. This device has features such as high detection sensitivity and a wide operating range, but it cannot detect the object to be detected if the distance between the oscillation coil and the resonator approaches a certain side. Setting where to insert between the oscillation coil and the resonator is troublesome,
For example, in the case of a band-like object that vibrates up and down, it is difficult to detect.

[Object of the present invention]

The present invention was made in view of the drawbacks of the conventional devices described above, and is not affected by the size or shape of the object to be detected.
The aim is to realize a proximity switch with stable operation and high detection sensitivity.

In the proximity switch according to the present invention, two sets of resonant circuits each consisting of a coil and a capacitor are installed at a predetermined distance apart, and the resonant frequencies of the two sets of resonant circuits are set to be the same.
The characteristic lies in the fact that the value is selected to be close to the value.

[Explanation of Examples]

FIG. 3 is a block diagram showing two sides of the proximity switch according to the present invention. In this figure, 1 is an oscillation circuit implemented as an IC, and 2 is an output circuit that amplifies the oscillation width from the oscillation circuit 1 and outputs an output signal according to a predetermined level after detection. This output circuit includes an initial reset circuit that blocks the output signal when the power is turned on, and an oscillation circuit 1.
It includes a power supply circuit that supplies stabilized power to the power supply.

O8+ is a first resonant circuit composed of a coil Lt and a capacitor C1 connected in parallel, and is connected to the terminal 5 of the oscillation circuit 1.
It is connected between the ground line E and the earth line E.

O8s is coil L! and capacitor C! The second resonant circuit is connected between the terminal 4 of the oscillation circuit 1 and the earth line E. The first of these.
The second resonant circuit O8l, O8t is connected to the coil L1. L
x are placed a predetermined distance apart, and the resonant frequencies of these resonant circuits are carefully selected to be the same or close to each other.

In the oscillation circuit 1, 6 is a level shift circuit that controls the base voltage of the transistor 7 in order to stably operate the oscillation of the oscillation circuit 1, and 5 and 8 are a first resonant circuit connected to the terminal 3.4. os! , second resonant circuit O8! A constant current circuit for supplying constant currents Io and I2, respectively, and a transistor 7 to which the voltage el at one end of the level shift circuit 6 is applied to the base constitute an amplifier. R represents a resistor for adjusting the emitter current, and 9 conceptually represents a current feedback circuit, which is operated so that the constant current circuit 8 flows a current I2 corresponding to the collector current 1 of the transistor 7.

The operation of the device configured as described above is as follows. Now, power is being supplied from the outside, the object to be detected N is moving away from the coils Ll and L2, and the first resonant circuit O
Assume that a voltage eo is generated at 8l. This voltage eo is applied to the oscillation circuit 1 via the terminal 6. The base voltage is boosted by the n level shift circuit 6 to become el, which is applied to the base of the transistor 7. . In this case, a collector current 11 as shown in equation (1) flows through the collector of the transistor 7.

et -VBa 11'qI. −□・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・+11 However, VBm:
The base-emitter voltage Is of the transistor 7: ) The emitter current of the transistor 7 The collector current I, of the transistor 7 is fed back to the constant current circuit 8 via the current feedback circuit 9, and the constant current circuit 8 A constant current generator 2 at a predetermined ratio (for example, 1:1) is supplied to the second resonant circuit O82 via the terminal 4. In the second resonant circuit O82, this nK current ■2
When n is supplied, a voltage e2 multiplied by Q is generated here. At this time, coil L1. When a mutual induction inductance M is present between L2, the voltage e2 generated in the coil L2 induces an electromotive force in the opposing coil L1, and changes the voltage eo of the coil LL. Voltage e of coil L1.

changes, the same path as above, i.e., e1→1
1→■2→e2, and the oscillation by the oscillation circuit 1 continues.

Here, the first resonant circuit O8+ and the second resonant circuit O8z
Since the resonant frequencies of are selected to be the same or very close to each other, a voltage approximately Q times as high as that of Q is generated in the second resonant circuit.
As a result, a corresponding electromotive force is generated in the first resonant circuit O8l. Therefore, stable oscillation is maintained even if the mutual induction inductance M between the coils L1 and L2 is small. Therefore, the coil L+,
They can be arranged at a distance of L2, and it is also possible to detect the approach of a large or band-shaped object to be detected.

When the oscillation of the oscillation circuit 1 continues, in this state, the output circuit 2 outputs a signal indicating that the object to be detected N is not detected.

Next, when the object to be detected N is inserted between the coils L+ and L2, the mutual induction between both coils Ll and L2 is interrupted, and the voltage e2 generated in the coil 2 generates an electromotive force in the coil Ll. Therefore, the oscillation circuit 1 stops oscillating, and the detection circuit 1 outputs a signal indicating the approach of the detected object N.

[Effects of the present invention]

The proximity switch according to the present invention has two coils L1 and Lt.
According to the present invention, it is not affected by the size, shape, or material of the object to be detected, and the two sets of resonant circuits can generate one oscillation. Since it is included in the circuit, if the object to be detected is inserted between the coils, a detection signal can be output regardless of its position. Therefore, a proximity switch with a significantly expanded detection range and high detection sensitivity compared to conventional devices can be realized.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram showing an example of a conventional device, FIG. 2 is a diagram showing the relationship between coil spacing and mutual induction in the device shown in FIG. 1, and FIG. 6 is a configuration block diagram of a proximity switch according to the present invention. It is a diagram. O8+, O8! ...resonant circuit, Ls, L2・
... Coil, CI. C2... Capacitor, 1... Oscillation circuit) 2... Output circuit 〇 Agent Patent attorney Saburo Kimura

Claims (1)

[Claims] The coils of two sets of resonant circuits each consisting of a coil and a capacitor are arranged at a predetermined interval, an oscillation circuit is configured including the two sets of resonant circuits, and the resonant frequencies of the two sets of resonant circuits are adjusted. A proximity switch characterized in that n is selected to be the same or close to each other.