JPS5932851B2 - Proximity switch - Google Patents

Description

[Detailed description of the invention] The present invention relates to a high frequency oscillation type proximity switch.

Most conventional high-frequency oscillation type proximity switches are assembled from discrete circuit components.

Then, the oscillation circuit is put into a hard oscillation state (a state where the amplitude grows and stops in a jumping manner using the nonlinearity of the amplifier that makes up the oscillator), and the stepability is increased as the oscillation output, and the subsequent circuit consists of a simple detection and amplification circuit.

However, when attempting to integrate a proximity switch circuit with a bipolar monolithic IC or the like, it is meaningless and even difficult to adopt the circuit configuration as described above.

In view of the above, an object of the present invention is to provide a proximity switch which has a circuit configuration suitable for IC implementation and which prevents chattering during switching.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic circuit configuration when constructed from a bipolar monolithic IC circuit.

The oscillator 4 includes a parallel circuit of a detection coil 2 and a capacitor 3 which are externally attached to an IC circuit.

The oscillator 4 shown as a block mainly consists of an amplifier.

The detection coil 2 and capacitor 3 constitute a parallel resonant circuit, and the impedance at the resonance point is r.

Then, its loss conductance G.

is o--- r□ It becomes.

If the amplifier has good frequency characteristics and linearity due to gain amplitude, and has an amplification rate sufficient to compensate for the loss Go (if the amplification rate is A1 and the feedback rate is β, then A×β ≧1), it is oscillating, and the oscillation width is large.

An object (usually a magnetic metal object such as iron) that is close to this detection coil 2
As 1 approaches, the loss increases, making it impossible to oscillate at a predetermined amplification rate, and the oscillation width becomes smaller.

This change in the oscillation width of the oscillator 4 is detected by the subsequent circuits.

That is, first, the voltage comparator 5 compares the output of the oscillator 4 with a first reference voltage, and the voltage averaging circuit 6 averages the output obtained as a result of this comparison.

Furthermore, the output of this voltage averaging circuit is compared with the second reference voltage in the second voltage comparator 7, and the output obtained as a result is outputted from the output circuit 8 as a detection output.

This detection output is fed back positively to the oscillator 4 and the voltage comparator 7, and if the oscillation width is reduced and a detection signal is generated, the oscillator 4 is controlled in a direction to further reduce the oscillation width. .

Moreover, if the output of the voltage averaging circuit 6 becomes large and an output is generated from the voltage comparator 7, this voltage comparator 7
The reference voltage is lowered to operate with positive feedback.

The positive feedback operation for the oscillator 4 is to stabilize the operation by adding hysteresis to the oscillation width of the oscillator 4, and the positive feedback operation for the voltage comparator 7 is to prevent chattering (described in detail later). be.

Note that the power supply circuit 9 supplies a constant voltage sT to each circuit.

A concrete circuit of the voltage averaging circuit 6 and the voltage comparator 7 is shown in FIG.

That is, the voltage averaging circuit 6 includes a constant current circuit including a resistor 61 and a transistor 62, and a parallel circuit including a capacitor 63 and a resistor 64.

When the oscillation width exceeds the first reference voltage, this transistor 62 turns on and supplies a constant current to the capacitor 63.
supply and charge.

Therefore, even when the charging/discharging time constant is increased in consideration of noise resistance and surge resistance, the output of the voltage averaging circuit 6 (the input voltage Vir+ of the voltage comparator 7) is generated by the oscillator 4. (When the oscillation width exceeds the first reference voltage, the transistor 62 turns on and off at a repetition frequency corresponding to the oscillation frequency, and the capacitor 63 is repeatedly charging and discharging).

The voltage comparator 7 includes a differential operation type comparison circuit including transistors 71 and 72 and a constant current circuit 73, a voltage dividing circuit including resistors 81 to 83 that provide a reference voltage, and transistors 74 to 7.
6 and a transistor 17 for shorting the resistor 83.

When the input voltage Vin exceeds the reference voltage s given by the voltage dividing circuit of resistors 81 to 83, the transistor 71 is turned on.

The transistors 74, 75, and 76 for this purpose are turned on and a predetermined current flows to the collector of the transistor 76, and the transistor 77 is turned on and the resistor 83 is short-circuited.

As a result, the reference voltage VS, which was determined by the voltage division ratio of resistor 81 and resistor 82.83, is now determined by the voltage division ratio of resistor 81 and resistor 82, and the reference voltage VS decreases as shown in Figure 3. I am made to do so.

Therefore, even if the input voltage Vin has a ripple as shown in FIG. 3 described above, once the input voltage Vin.

Since the reference voltage is lowered when it exceeds the reference voltage ■s, it is possible to prevent chuckling from occurring due to this ripple.

This ripple has a fundamental frequency component corresponding to the oscillation frequency, and therefore is always faster than the response speed of the positive feedback operation to the oscillator 4.

Therefore, from the perspective of this ripple, the rise in the oscillation width of the oscillator 4 due to the positive feedback operation is slow as shown in FIG. In some cases, chattering may occur.

This inconvenience is prevented by changing the reference voltage of the second comparator 7.

In other words, since the response speed of the positive feedback loop in the voltage comparator 7 is extremely fast, chattering due to ripples and the like can be prevented.

In other words, this means that it works effectively against noise and surges.

Changing the reference voltage of the voltage comparator 7 in this way does not cause any change in the operating distance as a proximity switch, but the changed value of the reference voltage is a constant voltage from the power supply circuit 9
It is preferable to appropriately determine it based on sT, noise, and ripple voltage.

Note that the present invention is not limited to the circuit shown in FIG. 2, and various circuits can be adopted as a circuit for changing the reference voltage. It may be configured as follows.

As described in the embodiments above, the present invention includes an oscillator formed together with a detection coil, a first voltage comparator that compares the output of the oscillator with a first reference voltage, and a first voltage comparator that compares the output of the oscillator with a first reference voltage. a voltage averaging circuit that averages the output of the voltage averaging circuit; and a second voltage comparator that compares the output of the voltage averaging circuit with a second reference voltage; In a proximity switch that uses an output as a detection signal, the detection signal is fed back to the oscillator to give hysteresis to the output of the oscillator, and the second voltage comparator is connected to the emitters of the first and second transistors. The second reference voltage obtained from the voltage dividing circuit includes a differential operation type comparator circuit in which this connection point is grounded via a constant current circuit, and a voltage dividing circuit in which a plurality of resistors are connected in series. a second reference voltage generation circuit applied to the base of the second transistor;
The first transistor is connected in parallel to at least one of the plurality of resistors of the voltage divider circuit, and is turned on when the voltage input to the base of the first transistor reaches the second reference voltage. and a third transistor that lowers the second reference voltage by short-circuiting a resistor, and the detection signal is fed back to the oscillator to provide hysteresis. In addition to the loop, a partial loop is provided in the second voltage comparator, and the overall loop provides positive feedback with a slow response speed to detect when the sensing object approaches the operating point. It prevents low-speed chattering in which the detection signal repeats on and off, and provides positive feedback with an extremely fast response speed in a partial loop, thereby reliably preventing high-speed chattering due to ripples and the like.

In other words, first, the overall feedback loop to the oscillator provides positive feedback with a slow response speed, and when the sensing object approaches the operating point, the oscillation amplitude decreases, and as a result, a sensing signal is generated. A positive feedback operation is performed in which the oscillator is controlled to further decrease the oscillation amplitude, and conversely, when the oscillation amplitude increases and a detection signal is generated, the oscillator is controlled to further increase the oscillation amplitude. This prevents chattering during detection, and then compares the voltages of the oscillator outputs and further averages the output. Even if the ripple of the oscillator output remains, the second voltage is set so as not to be affected by this ripple. By configuring the comparator, which is a two-stage chuckling or ripple removal configuration, it is possible to realize a proximity switch that eliminates the possibility of erroneous output as much as possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram schematically showing one embodiment of the present invention;
FIG. 2 is a circuit diagram specifically showing the voltage averaging circuit 6 and the voltage comparator 7, and FIG. 3 is a waveform diagram for explaining the operation. 2...detection coil, 4...oscillator, 5,
7... Voltage comparator, 6... Voltage averaging circuit, 8... Output circuit, 9... Power supply circuit.

Claims (1)

[Claims] 1. An oscillator formed together with a detection coil, a first voltage comparator that compares the output of this oscillator with a first reference voltage, and voltage averaging that averages the output of this first voltage comparator. and a second voltage comparator that compares the output of the voltage averaging circuit with a second reference voltage, the proximity switch having the output of the second voltage comparator as a detection signal. A detection signal is fed back to the oscillator to provide hysteresis to the output of the oscillator, and the second voltage comparator is connected to the first . A differential operation type comparator circuit is formed by connecting the emitter of the second transistor and grounding this connection point via a constant current circuit, and a voltage dividing circuit having a plurality of resistors connected in series. a second reference voltage generating circuit that applies the obtained second reference voltage to the base of the second transistor; and at least one of the plurality of resistors of the voltage dividing circuit.
is connected in parallel to the first transistor, and turns on when the voltage input to the base of the first transistor reaches the second reference voltage, shorting the resistor and increasing the second reference voltage. A proximity switch comprising: a third transistor that lowers the current.