JPS5827460Y2 - Kinsetsu Switch - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a proximity switch that detects an object (particularly metal) by using a change in inductance of a loop coil.

A conventional proximity switch is constructed, for example, as shown in FIG.

That is, FIG. 1 shows a case where the proximity switch is applied to a metal detector, and in FIG. 1, the loop coil 11 is connected to the oscillator 12.
The oscillation frequency of the oscillator 12 is changed by changing the inductance of the loop coil due to the proximity of the metal.

This change in oscillation frequency is converted into a voltage change by the frequency-voltage conversion device 13.

The frequency-voltage converter 13 includes an amplitude limiting circuit 14, a frequency discrimination circuit 15, and a DC amplification circuit 16.

The output of this converter 13 is sent to a voltage discriminator 17,
When the amount of change reaches a certain level, a detection signal that drives the relay 18 is generated.

Further, the output of the converter 13 is sent to a variable capacitance circuit 19 via a feedback control circuit 20 to change the discrimination frequency of the frequency discrimination circuit 15.

In this way, the negative feedback circuit of the device 13 is constructed.

The operation of the metal detector shown in FIG. 1 is as follows.

Before the metal approaches the loop coil 11, the converter 1
The output of No. 3 is at level L shown in FIG.

It is stable.

In other words, it depends on the function of the negative feedback circuit. It is stabilized by

As the metal approaches, the output increases and exceeds levels L1 and L2.

Level L2 is an operating level, and when this level L2 is exceeded, voltage discriminator 17 operates to generate a detection signal.

The output is maintained at this level L2 by the action of the feedback circuit.

As the metal separates, the output drops from level L2 through Ll and Lo, but due to the action of the negative feedback circuit, it remains at level L, similar to the initial state.

It's stable.

The level L1 is a return level, and when the level falls below the level L1, the voltage discriminator 17 returns and the detection signal stops.

The above is a normal operation, but when the metal vibrates or jumps up, the distance from the loop coil 11 changes, so the output decreases to the return level L as shown by the dotted line in Figure 2.
It may occur that the value exceeds 1.

In conventional proximity switches, so-called chattering, in which the detection signal once turns ON and then turns OFF, may occur, which has been a drawback.

The object of this invention is to provide an improved proximity switch that eliminates the above-mentioned drawbacks and does not cause chattering.

An embodiment of the present invention will be described below with reference to FIG. 3 and subsequent drawings.

FIG. 3 shows an embodiment in which the present invention is applied to a metal detector, and the same parts as in FIG. 1 are omitted from illustration or are given the same numbers.

In FIG. 3, a voltage discrimination device 21 generates a detection signal for detecting the approach of a metal object, and the discrimination level of the voltage discrimination circuit 22 is an operating level L2.

The feedback level switching circuit 31 consists of a transistor 32, a resistor 33 connected between its collector and emitter, and a resistor 34 connected to its emitter.

The negative feedback device 41 includes a differential amplifier circuit 42 and a transistor 43.
, capacitor 44, FET 45, and variable capacitance diode 4
It consists of 6.

The reference voltage of the differential amplification circuit 42 is at level L.

It is. The feedback amount compensation circuit 51 is composed of a differential amplification circuit 52 and a transistor 53.

The reference voltage of this differential amplification circuit 52 is at level Lo.

The voltage discrimination devices 61, 71, 81, and 91 discriminate the level of the output of the converter 13, and are connected to the voltage discrimination circuits 62, 72, 82, and 92, respectively, and the output terminals of these circuits via diodes. Connected resistance 63°73.8
3.93.

Each voltage discrimination circuit 62.72, 82.92 has its respective discrimination level L3. L4. L5. When the output of the conversion device 13 is smaller than each discrimination level, its output terminal becomes H, and when it is larger, it becomes L, and one end of each resistor is grounded via a diode.

First, when metal is not close, the output of the converter 13 is at a stable level L.

trying to go below. Therefore, the output of the differential amplifier circuit 52 of the feedback amount compensation circuit 51 is turned OFF, and the transistor 53
turns off.

Therefore, the capacitor 44 of the negative feedback device 41 is rapidly charged by the feedback amount compensation circuit 51.

Therefore, the capacitance of the variable capacitance diode 46 increases, thus increasing the output of the converter 13.

Therefore, even if the metal objects are not close to each other, the converter 13
The output is at stable level L.

(See Figure 4). The output of the converter 13 is at level L.

If the voltage exceeds the operating level L2 but does not reach the operating level L2, the output of the voltage discrimination circuit 22 is at the H level.

Therefore, the transistor 32 of the feedback level switching circuit 31
is in the ON state.

Therefore, the output of the converter 13 is sent to the negative feedback device 41 via the collector-emitter path of the transistor 32.

In other words, the output of the conversion device 13 is sent directly to the negative feedback device 41.
, and due to the effect of negative feedback, the converter 1
The output of 3 is level L.

Calm down and maintain a stable state.

As the metal approaches, the output of the converting device 13 becomes level Lt, L2. as shown in FIG. L3. Assume that L4 is successively exceeded.

Then, when the operating level L2 is exceeded, the voltage discrimination circuit 22
The output changes from H to L, and a detection signal is generated.

Therefore, the transistor 32 of the feedback level switching circuit 31
is OFF L, and as a result, the output of the converter 13 is at the resistor 33.
The pressure will be divided by and 34.

Furthermore, level L3. Since the voltage exceeds L4, the output terminals of the voltage discrimination circuits 62 and 72 change from H to L.

Therefore, the resistors 63 and 73 are connected in parallel to the resistor 34, and the output of the converter 13 is this resistor 33,
The voltage is divided by a voltage dividing circuit composed of 34, 63, and 73 and sent to the negative feedback device 41.

According to this voltage dividing circuit, the outputs of the converter 13 are R1, R2, Ra, R4: Resistors 33, 34, 63.7
It is double the value expression of 3.

By the way, the values of the resistors 33, 34, 63.73, . . . are set so as to satisfy the following formula.

That is, as shown in FIG. 4, the output of the converter 13 that exceeds the level L4 is at the level L.

In other words, it has been converted to a level that exceeds that level.

Reference voltage level of the differential amplification circuit 42.

Therefore, the input of the differential amplifier circuit 42 is at level L due to the effect of negative feedback.

It is controlled so that

Therefore, the output of the converter 13 settles at level L4.

Therefore, even if the output of the converter 13 decreases as shown in FIG. 4 due to metal bounce or vibration, the output does not decrease to the recovery level L1 and there is no risk of chattering.

Note that level L2. L3. L4. The same goes for the other levels as well, as when each exceeds Ls..., it tries to stabilize at the highest level.

As described above with respect to an embodiment of the present invention, according to the present invention, the output of the converting device 13 is discriminated at multiple levels, and the highest level among the levels exceeded by the output of the converting device 13 is determined. Negative feedback control is used to stabilize the output.

Therefore, since the output of the converter 13 is stabilized at a higher output level, chattering due to metal bounce, vibration, etc. does not occur.

As described above, according to the present invention, the output level of the converter is stabilized at each stage due to the approach of a nearby object.

Therefore, it is possible to use this fact to determine the size of the nearby object.

In other words, when the loop coil 11 is arranged as shown in FIG. 5, when a plate-shaped proximate object passes above it as shown by the arrow, the area occupied by the coil 11 that the proximate object crosses is determined by The output of the converter 13 changes as shown in FIG.

By knowing the level of the output of the converting device 13, the occupancy rate can be determined, and it is therefore possible to know the size of the nearby object.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional example, FIG. 2 is a time chart for explaining the operation of FIG. 1, FIG. 3 is a circuit diagram showing an embodiment of the present invention, and FIG. FIG. 5 is a schematic diagram showing the relationship between the occupancy rate of the loop coil and a nearby body, and FIG. 6 is a graph showing the relationship between the occupancy rate and the output. 11... Loop coil, 12... Oscillator, 13... Frequency voltage converter, 14...
... amplitude limiting circuit, 15 ... frequency discrimination circuit, 16 ... direct current amplification circuit, 17 ... voltage discrimination device, 18 ... ... relay , 19...
・Variable capacitance circuit, 20... Feedback control circuit, 21
．． 61.71.81.91...Voltage discrimination device,
31... Feedback level switching circuit, 41...
... Negative feedback device, 51 ... Feedback amount compensation circuit.

Claims (1)

[Scope of utility model registration request] An oscillator whose oscillation state changes when a nearby object approaches, a converter that converts the oscillation output of this oscillator, the output of this converter is input, the difference between this input and a reference level is calculated, and a signal corresponding to this difference is generated. a negative feedback device that operates to eliminate the difference by providing negative feedback to the input side of the conversion device; and a first discrimination device that generates a detection signal by discriminating when the output of the conversion device has reached an operating level. a feedback amount compensation circuit that controls the negative feedback device to maintain the output of the conversion device at a stable level when the output of the conversion device does not reach the operating level; inserted between the input terminal of the feedback device,
a second discrimination device that discriminates the output of the conversion device into a plurality of levels at or above the operation level;
operates in response to the output of the discriminator, and when the converter output is smaller than the operating level, the converter output is directly transmitted to the negative feedback device input terminal, and the converter output is higher than the operating level. and a feedback level switching circuit that transmits the output of the conversion device divided by a voltage division ratio changed according to the level discriminated by the second discrimination device to the input terminal of the negative feedback device. Proximity switch.