JP3538529B2 - Detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detecting device, and more particularly, to a detecting device which outputs a changing AC signal upon detecting that an object to be detected approaches, and has a switching means which operates based on the AC signal. .

[0002]

2. Description of the Related Art FIG. 5 shows a circuit diagram of a general proximity switch as an example of a conventional detection device.

[0005] In FIG. 5, an output voltage of an oscillation circuit 2 having a detection coil L for detecting approach of an object to be detected is rectified.
The level of the DC output that has been rectified and smoothed by the smoothing circuit 3 is discriminated by the comparator 4. 1 is a timer circuit,
This output is input to the AND circuit 6 together with the binary output of the comparator 4, and is subjected to AND operation. The operation output controls the switching of the output transistor Qout.

In general, the proximity switch requires several milliseconds to several tens of milliseconds when the power (Vin) is turned on via the power supply circuit 10 until the oscillation amplitude of the oscillation circuit 2 is sufficiently increased. That is, during this time, although the object to be detected is not near the detection surface, the discrimination output of the comparator 4 has the same value as in the state where detection is being performed, and the other input of the AND circuit 6 becomes high level. If so, the output transistor Qout is turned on.

The above-mentioned timer circuit 1 is for prohibiting the ON operation of the output transistor Qout for a predetermined time when the power is turned on, and includes a resistor R 1, an integration capacitor C for time limit, and a charge detection circuit 5.

When the power is turned on, charging of the capacitor C via the resistor R1 is started, and until the input voltage of the charge detection circuit 5 reaches a predetermined voltage value, the AND circuit 6 receives a high-level signal from the charge detection circuit 5. No input is made, and the output transistor Qout does not operate while being forced off regardless of the output value of the comparator 4.

When the charge detection circuit 5 detects that the charge voltage of the capacitor C has reached a predetermined level, the AND circuit 6
To output a high-level signal to enable the output value from the comparator 4 to be transmitted to the output transistor Qout.

On the other hand, a short-circuit detection circuit 8 turns on the transistor Q5 when it detects that an overcurrent has flown through the output transistor Qout and the potential at the upper end of the resistor R3 has risen.
By discharging the capacitor C of the timer circuit 5, the output of the charge detection circuit 5 is set to low level,
Output transistor Qout regardless of the output signal from
Is forcibly turned off. The resistor R2 is a resistor for giving a time constant to the discharge of the capacitor C when the transistor Q5 is turned on.
When an instantaneous overcurrent flows out, the short circuit detection circuit 8 is not operated.

[0009]

However, since the proximity switch which is the conventional detection device as described above uses a capacitor in the timer circuit, it is difficult to form an integrated circuit, which is disadvantageous for miniaturization. There were challenges.

In view of the above, the present invention has been made in view of the above points, and has an integrated and miniaturized structure capable of preventing malfunction at power-on and performing appropriate switching against overload during steady-state operation. It is an object of the present invention to provide a detection device that is easy to use.

[0011]

According to a first aspect of the present invention, there is provided an apparatus for outputting an AC signal for detecting an object to be detected, and an AC output means for outputting an AC signal for detecting an object to be detected. DC output means for outputting a DC signal having a level corresponding to the DC signal level, binary signal output means for outputting a binary signal corresponding to the DC signal level, gating means for gating the binary signal with a control signal, A detection device comprising switching means for switching in accordance with the output of the gate means, wherein the shaping means for shaping the AC signal generated almost simultaneously with power-on and outputting a rectangular wave synchronized with the AC signal; and Counting means for counting the rectangular waves and outputting the control signal, and the gate means switches the binary signal according to the control signal until the counting means counts the rectangular waves by a predetermined number. It is not output to the ring means, until the amplitude of the AC signal reaches a predetermined amplitude, characterized in that prohibited the operation of the switching means.

Here, in the apparatus according to the present invention, the overcurrent detecting means for detecting that an overcurrent has flowed in the switching means, and the counting means is reset by detecting the overcurrent. Reset means may be further provided.

In this case, in the apparatus according to the third aspect of the present invention, when the overcurrent detection unit outputs a detection signal, the reset unit includes another counting unit that counts the rectangular wave from the shaping unit. When the other counting means counts the rectangular wave by another predetermined number, the counting means is reset, so that the counting means is not reset for the instantaneous overcurrent.

Here, in the apparatus according to the present invention, the power supply voltage is detected, and when the power supply voltage is equal to or less than a predetermined value, the other reset means resets the counting means or the other counting means. May be further provided.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIG. 1 is a block diagram showing a first embodiment of a detection apparatus according to the present invention, and shows an embodiment using a proximity switch as an example. 1, the same components as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

Reference numeral 2 denotes an oscillation circuit which oscillates and outputs an AC signal for detecting the object to be detected almost at the same time as the power is turned on. When the object to be detected approaches the associated coil L from outside, this is detected. The oscillation circuit 2 does not completely stop oscillation when the oscillation amplitude is attenuated due to the approach of the object to be detected. The oscillating output voltage of the oscillating circuit 2
Therefore, the output of the rectification / smoothing circuit 3 is a DC signal having a level corresponding to the oscillation power of the oscillation circuit 2. The DC signal is discriminated by the comparator 4 at a predetermined threshold, and a binary logic ON / OFF signal corresponding to the signal level is output.

On the other hand, reference numeral 11 denotes a waveform shaping circuit, which shapes the waveform of the AC oscillation voltage of the oscillation circuit 2 and converts and outputs it as a rectangular wave signal synchronized with the oscillation frequency. The output from the waveform shaping circuit 11 which has been made into a rectangular wave is input to the counter circuit 12, and a predetermined counting operation is performed.

The count output of the counter circuit 12 and the above-described binary signal output of the comparator 4 are input to an AND circuit 6 to perform a logical product operation. That is, the AND circuit 6 gates the output of the comparator 4 using the count output of the counter circuit 12 as a control signal. Then, the output transistor Qout performs a switching operation in accordance with the output of the AND circuit 6, and outputs a detection signal to its collector terminal (OUT) depending on whether or not an object to be detected has been detected.

A voltage detection circuit 13 detects a power supply voltage, and resets the counter circuit 12 when the power supply voltage is lower than a predetermined value.

FIG. 2 is a circuit diagram showing a specific example of the voltage detection circuit 13.

The voltage detection circuit 13 comprises a series circuit of a Zener diode ZD and a resistor R4, and a transistor Q2 having a base and an emitter connected to both ends of the resistor R4.

When the output voltage of the power supply circuit 10 exceeds the Zener voltage of the Zener diode ZD, the transistor Q2 is turned on to enable the counter circuit 12, and when the output voltage of the power supply circuit 10 is lower than the Zener voltage, the transistor Q2 Is turned off, and the counter circuit 12 is reset. This is because, for example, when the power is turned on or when the power supply voltage is lower than the rated value, the circuit of the detection unit may not operate normally, so that the counter circuit 12 is reset and the operation of the output transistor Qout is forcibly performed. It is prohibited.

Returning to FIG. 1, the power supply circuit 1 will now be described.
Oscillation circuit 2 starts oscillating almost at the same time when power supply voltage Vin is applied through 0, but the voltage amplitude of the oscillation output is naturally 0 V immediately after power-on Vin is applied. And
It takes about several milliseconds to several tens of milliseconds to gradually increase from 0 V and reach the steady state saturation level. During this time, the comparator 4 outputs to the AND circuit 6 a binary signal having the same value as the state in which the detection target is being detected.

On the other hand, the waveform shaping circuit 11 performs waveform shaping even in a transient state in which the oscillation voltage of the oscillation circuit 2 is gradually increasing, and outputs a rectangular wave signal synchronized with the oscillation frequency to the counter circuit 12. The counter circuit 12 counts this signal until it reaches a predetermined number, and outputs a high-level signal to the AND circuit 6 when the signal reaches the predetermined number. This counter circuit 1
No. 2 outputs a low level from when the power is turned on until a predetermined number is counted.

That is, the AND circuit 6 is connected to the comparator 4
Is gated using the count output of the counter circuit 12 as a control signal. Therefore, until the counter circuit 12 completes a predetermined number of counts, 2
The value signal output is not transmitted to the output transistor Qout,
Until the amplitude of the oscillation voltage reaches the predetermined amplitude, the switching operation is prohibited while the output transistor Qout is forcibly turned off. Therefore, malfunction of the output transistor Qout when the power supply Vin is turned on can be prevented.

FIG. 3 is a timing chart showing the operation of the apparatus according to the first embodiment when the power is turned on.

At time t0, the power supply Vin (FIG. 3)
(A)) After being turned on, the oscillation voltage of the oscillation circuit 2 (FIG. 3 (B))
Gradually increases and reaches a substantially constant saturation level at time t3 after a predetermined time has elapsed. A DC voltage similar to the envelope of the oscillation voltage is output from the rectifying / smoothing circuit 3. Therefore, the comparator 4 outputs a high-level signal in the detected state until the time t2 when this DC voltage (here, the envelope of (B)) reaches the predetermined threshold value V2 of the comparator 4 (FIG. 3 ( C)).

On the other hand, when the oscillating voltage of the oscillating circuit 2 is a minute level and the DC output of the rectifying / smoothing circuit 3 is V1, the waveform shaping circuit 11 sends a rectangular wave output (FIG. 3D) to the counter circuit 12. However, the counter circuit 12 does not output a high-level signal until the predetermined count is completed at time t4 (FIG. 3E).

In FIG. 3, the oscillation voltage of the oscillation circuit 2 corresponding to the DC output V1 of the rectifying / smoothing circuit 3 when the waveform shaping circuit 11 starts sending a rectangular wave output to the counter circuit 12 is not shown here. However, it is needless to say that the oscillation voltage is lower than the oscillation voltage when the object to be detected approaches and comes close to the detection surface of the detection device of the present invention. The time t until the oscillation voltage increases and the DC output reaches V1 is t
No. 1 has no problem in the operation of this circuit.

Next, returning to FIG. 1, the operation when the output transistor Qout is overloaded in the steady operation state will be described.

When an overcurrent flows through the output transistor Qout due to a short circuit of a load connected to the outside, the resistance R3
The short-circuit detection circuit 8 detects that the upper end potential has risen to a predetermined level. At this time, the configuration is such that the reset signal is output from the short circuit detection circuit 8 to the counter circuit 12. Therefore, when an overcurrent flows through the output transistor Qout, the counter circuit 12 is reset, and the input of the output transistor Qout is stopped and remains off as in immediately after the power is turned on, thereby protecting the output transistor Qout from overcurrent.

At this time, when the counter circuit 12 is reset and the output transistor Qout is turned off, no current flows through the resistor R3, and the short circuit detecting circuit 8 returns to the normal state. That is, it is instantaneous that the short-circuit detection circuit 8 outputs the reset signal to the counter circuit 12,
Counts the rectangular wave signal from the waveform shaping circuit 11 immediately after reset and immediately after power-on, turns off the output transistor Qout until a predetermined number is counted, and thereafter outputs the output transistor Qout by the binary signal from the comparator 4. Switches.

According to this embodiment, the oscillating voltage of the oscillating circuit 2 for detecting the object to be detected is shaped into a rectangular wave signal, and this signal is equivalently counted by the counter circuit 12 by a predetermined number. Since the timed circuit is configured, the integrating capacitor used in the conventional timer circuit can be eliminated.
Further, since the oscillation voltage of the oscillation circuit 2 for detection is used as the count signal of the counter circuit 12, another pulse generation circuit is not required. Therefore, there is an effect that integration and miniaturization are facilitated.

(Second Embodiment) In a second embodiment shown in FIG. 4, the counter circuit 12 is reset after a predetermined time delay from the time when the short-circuit detection circuit 8 detects an overload and operates. It is like that. The operation at the time of turning on the power is the same as that of FIG. 1 (see FIG. 3), and the description is omitted.

In FIG. 4, reference numeral 14 denotes a counter circuit which is reset when the short circuit detection circuit 8 does not output an overload detection signal, and is enabled when the short circuit detection circuit 8 outputs an overload detection signal. When an overload is detected, the counter circuit 14 starts counting the rectangular waves from the waveform shaping circuit 11, and when a predetermined number is counted, outputs a reset signal to reset the counter circuit 12.

In the configuration of FIG. 4, the output transistor Qou
Even if an overcurrent flows at t and the short circuit detection circuit 8 detects an overload, the counter circuit 12 is not reset for a predetermined time until the counter circuit 14 counts a predetermined number of rectangular waves from the waveform shaping circuit 11, During this time, the output transistor Qout keeps on. Thereby, the output transistor Qo
Even if an instantaneous overcurrent flows in ut, it is regarded as a normal state and the output is not turned off.

When the power supply voltage falls below a predetermined value, the counter circuit 14 operates as described above.
Is reset together with the counter circuit 12.

According to the present embodiment, the same effect as that of the first embodiment can be obtained when the power is turned on, and a detection device that does not malfunction due to instantaneous overload even in a steady state can be easily provided. It can be integrated and miniaturized.

[0040]

As described above, according to the present invention, the gate means does not output the binary signal to the switching means by the control signal output from the counting means until the counting means counts a predetermined number of rectangular waves. Since the operation of the switching means is prohibited until the amplitude of the AC signal output from the AC output means reaches a predetermined amplitude, another oscillator such as a pulse generating circuit other than the AC output means is not required. In addition, a configuration that does not require a timer circuit using a capacitor can prevent a malfunction of the switching means when the power is turned on, and has an effect that integration and miniaturization are easy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a detection device of the present invention.

FIG. 2 is a circuit diagram showing a specific example of a voltage detection circuit 13;

FIG. 3 is a timing chart showing an operation when power is turned on in the first embodiment.

FIG. 4 is a block diagram showing a detection device according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram of a general proximity switch as an example of a conventional detection device.

[Explanation of symbols]

2 Oscillation circuit 3 Rectifier / smoothing circuit 4 Comparator 6 AND circuit 8 Short circuit detection circuit 11 Waveform shaping circuit 12,14 counter circuit 13 Voltage detection circuit Qout output transistor ZD Zener diode

Continued on the front page (51) Int.Cl. ⁷ Identification code FI H03K 17/78 H03K 17/78 G

Claims (4)

(57) [Claims] An AC output means for outputting an AC signal for detecting an object to be detected, a DC output means for outputting a DC signal having a level corresponding to the AC signal, and a binary signal corresponding to the DC signal level Binary signal output means for outputting a signal, gating means for gating the binary signal by a control signal,
A switching means for switching in accordance with an output of the gate means, wherein the shaping means shapes the AC signal generated almost at the time of power-on and outputs a rectangular wave synchronized with the AC signal. And counting means for counting the rectangular wave and outputting the control signal, wherein the control signal causes the gate means to switch the binary signal to the switching means until the counting means counts the rectangular wave by a predetermined number. By not outputting to
The detecting device, wherein the operation of the switching means is prohibited until the amplitude of the AC signal reaches a predetermined amplitude. 2. The apparatus according to claim 1, further comprising: an overcurrent detection unit configured to detect an overcurrent flowing in the switching unit; and a reset unit configured to detect the overcurrent and reset the counting unit. Item 2. The detection device according to Item 1. 3. The reset means includes another counting means for counting the rectangular wave from the shaping means when the overcurrent detection means outputs a detection signal, and the other counting means converts the rectangular wave into another. The detection device according to claim 1, wherein the counting unit is reset after a predetermined number of times, so that the counting unit is not reset for the instantaneous overcurrent. 4. The apparatus according to claim 1, further comprising another reset means for detecting a power supply voltage and resetting said counting means or said other counting means when said power supply voltage is equal to or lower than a predetermined value. 3. The detection device according to any one of 3.