JPS59207740A - Proximity switch - Google Patents

Abstract

PURPOSE:To enable clear distinction between the proximity of an object to be detected and the abnormality of a circuit by providing a circuit that outputs a signal responding to the repetition of oscillation and stoppage of oscillation and a circuit that outputs a signal responding to continuous oscillation and stoppage. CONSTITUTION:When an object to be detected is proximate to a coil L, an oscillation circuit 4 oscillates at a fixed amplitude, amplifies 5, rectifies 6 and inputs to a discriminator circuit 7. As the level is higher than the reference level, the output of the circuit 7 is 0. When the object is proximate to the coil L, the circuit 4 stops oscillation, and the circuit 7 leads out an output 1. By this signal 1 an on-delay circuit 8 outputs 1, and a non-shot multi circuit 9 outputs 1 for a specified time, and turns a transistor (TR) on to oscillate the circuit 4. Thus, the circuit 7 becomes output 0, the TR becomes off, and the circuit 4 stops oscillation, and oscillation and stoppage are repeated. This is detected by an off- delay circuit 11 and a proximate detection signal S4 is outputted. In the case of abnormality such as the breakage of the coil L, cable 2, continuous oscillation stoppage is caused and this is detected by an on-delay circuit 12.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to a proximity switch, in particular, a coil in which when a sensing object approaches a coil, the oscillation state changes. This invention relates to a so-called high frequency oscillation type proximity switch.

Main) Prior art and its problems In general, proximity switches are often used in adverse environmental conditions where there are vibrations, shocks, rapid temperature changes, etc. that make contact switches unusable. On the other hand, as the machines in which they are used and installed become smaller, proximity switches
There was a strong demand for miniaturization of the sensor head itself.
In recent years, sensor heads have built-in components such as detection coils or resonance capacitors, and the main circuits such as the oscillation circuit and discrimination circuit are installed in separate amplifier units.
That is, there are an increasing number of proximity switches having a so-called amplifier-separated type configuration in which a sensor head part and a circuit part are connected by a coaxial cable.

In this type of proximity switch, due to the demand for miniaturization, as the sensor head becomes smaller, the diameter of the coaxial cable also becomes smaller, and the overall mechanical strength decreases.
As described above, under adverse environments, failures such as disconnections and short circuits of the detection coil/L/or coaxial cable are increasingly occurring. If such a failure occurs, like a conventional proximity switch, the oscillation circuit has an oscillation circuit whose amplitude changes rapidly depending on the presence or absence of a sensing object, and when the sensing object approaches, the output is 11'', and when the sensing object approaches Sometimes, in a device that derives only the rOJ output signal, if a short circuit or disconnection occurs, the distribution force becomes either "0" or "1", and the detection output of the sensing object is The problem was that it was not possible to tell whether the problem was caused by a fault or a malfunction.

Object of the Invention Therefore, the object of the present invention is to solve the problem of the conventional proximity switch mentioned above and to solve the problem of disconnection of the detection coil.

To provide a proximity switch that distinguishes between a case where an abnormality occurs in an oscillation circuit such as a short circuit, and a change in the oscillation state due to the presence or absence of a sensing object, and allows the user to immediately know the failure status when an abnormality occurs in the oscillation circuit, etc. be.

In order to achieve the object of ``Construction and Effects of the Invention'', the proximity switch of the present invention has a first oscillation circuit that stops oscillation when a sensing object approaches.
It is possible to switch between the state of When the oscillation of the oscillation circuit stops in the vicinity, means for setting the sensitivity switching means in a second state for a predetermined second time after a predetermined first time in response to the stop of oscillation;
The output circuit includes a circuit that outputs a detection object proximity signal in response to repetitions of oscillation stop and oscillation during the first and second times of the oscillation circuit, and a circuit abnormality due to continuous oscillation stop output from the oscillation circuit. and a circuit for outputting a signal.

According to the proximity switch of the present invention, when a sensing object approaches while the 5 oscillation circuit is operating normally, the 9 oscillation circuit is made to intermittently repeat oscillation stop and oscillation, and in response to this repetition, It outputs a proximity signal of the detected object, and also outputs a circuit abnormality signal with a series of 5 oscillation stop outputs in response to a complete oscillation stop due to an abnormality in the oscillation circuit such as a disconnection or short circuit of a coil or cable, etc. Therefore, these outputs can be used to determine whether the 9 circuits are operating normally or not depending on the status of the signal.
It is possible to clearly distinguish whether an abnormality has occurred in the circuit.

0→Description of Examples The present invention will be described in further detail with reference to the following nine drawings.

FIG. 1 is a circuit diagram of a proximity switch showing one embodiment of the present invention. The proximity switch shown in the same figure is a sensor head 1 and 2 which have built-in vL (carp), a circuit section 6 and a sensor head 1.
and a cape (v2) that connects the circuit section. The trench circuit section 3 has 9 oscillation circuits 4. An amplifier circuit 5 for AC amplifying the oscillation signal from the oscillation circuit 4. This amplifier circuit 5
A rectifier circuit that rectifies and smoothes the AC signal amplified by 6. A discrimination circuit 7 which derives an output signal "1" when the signal level of the rectifier circuit 6 is below the reference level. Discrimination circuit 7
An on-delay circuit 8 which outputs a pulse signal after time T1 when the output becomes "1". A one-shot multi-circuit 9 which receives this pulse signal and outputs a signal "1" for a time T2. A sensitivity switching circuit 10 receives the output of the one-shot multi-circuit 9 and switches the sensitivity of the oscillation circuit 4. Discrimination circuit 7
The output of the discrimination circuit 7 is received and output as is, and the output of the discrimination circuit 7 is "
Off-delay circuit 11° discriminator circuit 7 whose output becomes rOJ after time T3 (T2<T3) after falling from “1” to “0”
The time T 4 (T
The on-delay circuit 12 outputs "1" after I(T4).

The sensitivity switching circuit 10 includes resistors R1, R2, R3 and NPN
The resistor R2, which is connected in series with the resistor R1, is short-circuited or connected in series by turning on and off the transistor TR.

The sensitivity of the oscillation circuit 4 is changed over.

When a sensing object approaches the carp/l/L with the transistor TR off and the resistors R1 and R2 connected in series, the oscillation circuit 4 stops oscillation. However, when the transistor TR is on and the resistor R2 is shorted, the coil/
When a sensing object approaches l/L, the five oscillation circuit 4 continues to oscillate at a constant amplitude even in the closest state.

The on-delay circuit 8 and the one-shot multi-circuit 9 turn on the transistor TR of the sensitivity switching circuit 10 for a time T2 (second time) after a time Ti (first time) after the oscillation circuit 4 stops. It is set in.

The off-delay circuit 11 outputs the proximity signal of the detected object from the output terminal 13 when the detected object approaches while the 5-oscillation circuit 4 is operating normally, that is, when the oscillation circuit 4 repeats oscillation stop and oscillation. It is a circuit of the end,
The on-delay circuit 12 is a circuit that outputs a 9-circuit abnormality signal from the output terminal 14 when the 9-oscillation circuit 4 is abnormal and the oscillation completely stops, that is, when the 9-oscillation circuit 4 stops oscillating continuously.

Next, Tie A, which shows the operation of the embodiment circuit described in FIG.
Coil) V L , Cable 2, etc. have no disconnections or short circuits, and the circuit is operating normally, and B indicates the timing when the sensing object is close to Coil L, Cape/I/
2 shows the timing when the circuit is not operating normally due to disconnections, short circuits, etc., and C is the output waveform of the oscillation circuit 4, and S1...S5 are signal waveforms of other parts of the circuit.

First, an explanation will be given of the operation when the circuit is normal with no disconnection or short circuit in the coil L, cape/I/2, etc.

When the detected object is not close to carp (carp) VL.

The oscillation circuit 4 oscillates with a constant amplitude (see FIG. 2C), and this oscillation signal is amplified by the amplifier circuit 5.

The rectifier circuit 6 rectifies and smoothes the signal and inputs it to the discriminator circuit 7, but since its level is higher than the reference level of the discriminator circuit 7, the signal "1" is not derived from the output of the discriminator circuit 7 (Fig. 2, 81). reference). therefore.

Of course, both output terminals 13 and 14 have an output signal "1".
” is not derived.

When the sensing object approaches the coil lvL by a predetermined distance, the oscillation circuit 4 stops oscillating and its amplitude becomes O (see t1 in FIG. 2C). Therefore, the signal input to the discrimination circuit 7 is 0.
, and a signal "1" is derived at its output (see FIG. 2 81). After receiving this signal "1", the output of the on-delay circuit 8 becomes "11" after a time T1 (see FIG. (See Figure 2 86)
. The output Qr1j of the one-shot multi-circuit 9 turns on the transistor TR of the sensitivity switching circuit 10 and short-circuits the resistor R2. As a result, the oscillation circuit 4 starts oscillating again even though the sensing object is close, and continues oscillating for 5 hours T2. Therefore, the output of the discrimination circuit 7 becomes "O" during this period. When the time T2 elapses, the output of the one-shot multi-circuit 9 falls to "O", thereby turning off the transistor TR, and if the sensing object is still in the nearby area, the oscillation of the 5-oscillation circuit 4 stops again, and from then on The oscillation is stopped for 5 hours T1, and then the one-shot multi-circuit 9 is set again, so the transistor TR is turned on again.
The oscillation circuit 4 starts oscillating again. In this way, while the sensing object is in the proximity area.

The oscillation circuit 4 intermittently repeats stopping oscillation at time T1 and oscillating at time T2. On the other hand, while this state continues, the output signal "1" of the discrimination circuit 7 is applied to the off-delay circuit 11, and since the delay time T3 of the off-delay circuit 11 is set larger than the time T2, the off-delay circuit A signal "1" is continuously derived at the output of 11 (see FIG. 2 84).

The output signal "1" of this off-delay circuit 11 becomes the proximity signal of the detected object. The output signal "1" of the discrimination circuit 7 is also input to the on-delay circuit 12, but since the on-delay time T4 is set larger than the time T1, the signal "1" is output from the on-delay circuit 12. It is never derived. This indicates that there is no abnormality in the circuit.

If a wire breakage, short circuit, etc. occurs in the carp/L/L or the cape zlz2, the oscillation of the oscillation circuit 4 stops regardless of whether or not there is a sensing object in the vicinity. Therefore, the signal "1" is derived from the output of the discrimination circuit 7 from the time when the abnormality occurs (see t2 in FIG. 2B), and the output of this signal "1" continues until the abnormality disappears.

Therefore, the signal "1" is output from the off-delay circuit 11.
is derived, but since the time for the output of the discrimination circuit 7 to be "1" is longer than the delay time T4 of the on-delay circuit 12, the output of the on-delay circuit 12 also has a signal "1".
is derived. The signal "1" derived from the output of this on-delay circuit 12 is a signal indicating a circuit abnormality.

As described above, according to the circuit of the above embodiment, when a detection object approaches, an output signal is obtained only to the off-delay circuit 11, and proximity detection can be performed. If there is a circuit abnormality such as a disconnection or short circuit in the second class,
Since the abnormal signal is also output to the on-delay circuit 12,
It is possible to clearly distinguish whether the detection output signal is due to the true proximity of the detected object or due to an abnormality in one circuit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a proximity switch showing an embodiment of the present invention, and FIG. 2 is a time chart for explaining the operation of the proximity switch. L: Coil, 4: Oscillator circuit, 8: On-delay circuit + 9: One-shot multi-circuit. 10: Sensitivity switching circuit, 11: Off-delay circuit,
12: On-delay circuit. Patent applicant Tateishi Electric Co., Ltd. Agent Patent attorney Shigeru Nakamura

Claims (1)

[Claims] (1) In a proximity switch including an oscillation circuit that includes a coil and whose oscillation state changes when a sensing object approaches the coil, and an output circuit that receives the oscillation output of the oscillation circuit and outputs a sensing object proximity signal. The oscillation circuit is switchable between a first state in which oscillation stops when a sensing object approaches, and a second state in which oscillation continues at a predetermined amplitude when the sensing object approaches the sensing object, and
The sensitivity switching means is initially in a first state, and when a detection object approaches and the oscillation of the oscillation circuit stops, the sensitivity switching means changes from a predetermined first time to a predetermined second time in response to the oscillation stop. means for setting the sensitivity switching means to a second state,
The output circuit is a circuit that outputs a detection object proximity signal in response to repetitions of oscillation stop and oscillation at the first and second times of the oscillation circuit. A proximity switch comprising a circuit that outputs a circuit abnormality signal by quickly reading an oscillation stop output from the oscillation circuit.