JPS5926498Y2 - Proximity switch - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a high frequency oscillation type proximity switch that detects the presence and position of a metal object without contact.

A conventional proximity switch is generally constructed as shown in FIG.

In FIG. 1, the proximity switch 10 is mainly composed of an IC circuit 11 forming a proximity sensor circuit, and a transistor 33 connected to the IC circuit 11 since the output current capacity is insufficient by itself.

This IC circuit 11 has an oscillation circuit 12. Comparator 13, integration circuit 14, comparator 15, output circuit 1
6. It has a constant voltage circuit 17 and a power supply reset circuit 18, and has a detection coil 21.6. A variable resistor 22 for adjusting sensitivity, a bypass capacitor 23, an integrating capacitor 24, a capacitor 25 for power supply offset, etc. are externally attached.

The oscillation circuit 12 includes a detection coil 21 and oscillates, and when an object approaches the detection coil 21, the oscillation width attenuates or the oscillation stops.

As a result, the NL (normal low) output is "L?+" during normal times (when not detected), and becomes "H" when detected.

Therefore, current flows out from the output terminal of the proximity switch 10 during normal times, but does not flow out during detection.

By the way, if the power supply voltage Vcc rises as shown in FIG. 2, the oscillation output will rise with a delay.

Time T until this oscillation output reaches the detection level.

During this period, the oscillation output is small as when an object is present, so even though there is no object, there is a possibility that a detection output similar to that produced when an object is present may be erroneously generated.

Therefore, conventionally, as shown in FIG. 1, a power supply reset circuit 18 is provided to adjust the time T.

During the longer time T3, no output signal is generated from the output circuit 16.

However, the power supply voltage Vcc does not necessarily rise sharply as shown in FIG. 2, but may rise gradually as shown in FIG. 3.

In particular, when the IC circuit 11 is configured with a bipolar IC, the maximum voltage is approximately 30V, so if you want to be able to use a maximum of 40V as a power source for the proximity switch 10, it is necessary to insert a voltage drop resistor 31. There is also a capacitor 32 in order to stabilize the power supply voltage Vcc.
Therefore, the voltage Vcc is connected to the resistor 3.
1 and the time constant determined by the constants of the capacitor 32, the voltage rises gradually as shown in FIG.

As shown in FIG. 3, when the power supply voltage Vcc rises only during the holding time T or once, the oscillation circuit 12 does not start oscillating during the time T1 until it reaches a certain voltage 1.
Furthermore, after the start of oscillation, an oscillation output power that reaches the detection level is obtained only at a time T2.

This time T2 is the time T2 in FIG. 2 because the source voltage Vcc gradually rises.

Although it is shorter, the oscillation circuit 12 may not be in a steady oscillation state for a long period of time T1+T2 after the power supply voltage starts to be applied, and there is a possibility that an erroneous output may be generated.

Therefore, in preparation for such a case, it becomes necessary to set the power supply reset time T3 longer than the time T1+T2.

Since it must be assumed that the time T may be extremely long, the power supply reset time T3 must be made quite long, but in this case, if the power supply voltage rises suddenly as shown in Figure 2. In this case, it would be wasteful to take a long power supply reset time T3.

In view of the above, the present invention varies the power supply reset time according to the rise speed of the power supply voltage, so that the necessary and sufficient power supply reset time is always obtained, and erroneous output is reliably prevented without wasting time. It is an object of the present invention to provide a proximity switch having a power supply reset circuit that prevents malfunctions even in response to noise.

An embodiment of the present invention will be described below with reference to FIG. 4.

In FIG. 4, the voltage detection circuit 40 includes Zener diodes 41 .
This is achieved from transistors 42, 43, and 44, and the output voltage V5 of the constant voltage circuit is a predetermined value V.

Below, transistor 43 is on; above, transistor 4 is on.
3 is turned off.

The timer circuit 50 includes transistors 51-58, resistors 59.
60 and an external power supply reset capacitor 61.
It consists of a diode 62.

When the transistor 43 is on, the capacitor 61 is not charged, and is only charged when the transistor 43 is turned off.

Transistors 55 and 56 constitute a comparator as a voltage discrimination circuit, and when the charging voltage of capacitor 61 becomes higher than the reference voltage determined by resistor 59 and 60,
Transistor 55 turns on and a current flows through transistor 54, which is determined by the current flowing through transistor 57.

When the charging voltage of the capacitor 61 is lower than the reference voltage, the transistor 56 is on and the transistor 56 is turned on.
5 is off, and no current flows through the transistor 54.

The output circuit 70 is composed of transistors 71, 72, and 73, and this transistor 71 is connected to the transistor 51.
Together with this, they form a current mirror circuit.

Therefore, a current approximately equal to the current flowing through the emitter-collector path of transistor 54 flows through the emitter-collector path of transistor 71.

Therefore, when no current flows through transistor 54, no current is supplied to transistors 72 and 73, and both transistors 72 and 73 are in an off state.

Therefore, no matter what the signal from the comparator (indicated by 15 in FIG. 1) is, the output signal will be no current and no voltage.

When current flows through transistor 54, transistor 7
Since current is supplied to the transistors 72 and 73 via the comparator 15, an output signal is generated in response to the signal from the comparator 15.

In the circuit shown in FIG. 4, the transistors 44, 51, 52 and 53, 57, 58 constitute a current mirror circuit, respectively, and function as a constant current sink circuit and a current circuit when the constant voltage Vs is a constant value.

Furthermore, when the voltage Vs in the voltage detection circuit 40 is extremely low, the current supplied from the transistor 44 of the current source circuit is also small, so the transistor 43 does not turn on.
At this time, the current flowing from the transistor 51 to the capacitor 61 is also small, and the charging voltage of the capacitor 61 does not rise.

Therefore, no current is supplied through transistor 71.

Note that this voltage detection circuit 40 can be configured in various other ways.

As described above, according to the circuit shown in FIG. 4, the voltage Vs in the voltage detection circuit 40 is V.

The timer circuit 50 is operated from the time of this detection to reset the power supply for a certain period of time.

Assuming that the fixed time limit set by this timer circuit 50 is T5, when the power supply voltage Vcc rises gradually as shown in FIG. When =0, the power supply reset time is only T5.

In this way, the time T4 changes depending on the rising speed of the power supply voltage.

The voltage ■ that this voltage detection circuit 40 should detect.

is the voltage level at the time when the oscillation circuit starts oscillating, and the timer time T5 may be set as the time from the time when the oscillation starts until the oscillation output reaches a predetermined value.

Furthermore, no problem occurs even when noise enters from the constant voltage Vs.

That is, assuming that there is no diode 62, as shown in FIG. 6, when noise is added to the constant voltage Vs, the transistor 42 is momentarily turned off, so the transistor 43 is momentarily turned on. Become.

Therefore, the charge stored in the capacitor 61 will be discharged via this transistor 43.
Even after the oil has disappeared, the supply of current (2) is stopped for a long time until the capacitor 61 is recharged.

In other words, if the diode 62 is not provided, there is an inconvenience that the power supply reset will be activated for a relatively long time when noise arrives.

In the present invention, as shown in FIG. 4, the diode 62 is connected between the collector of the transistor 43 and one end of the capacitor 61, so even if the transistor 43 is turned on due to noise, The capacitor 61 is not discharged or discharged, and its charging voltage Vc decreases, thereby eliminating the problem described above.

Note that when the power is turned off, the seventh voltage is connected to the terminal that outputs the constant voltage Vs by the action of the bypass capacitor 23 connected to the terminal that outputs the constant voltage Vs in order to prevent the oscillation output from being superimposed on the constant voltage Vs.
As shown in the figure, even if the power supply voltage Vcc becomes zero, the constant voltage V
s becomes zero with a delay.

Therefore, until the constant voltage Vs becomes zero, the charge in the capacitor 61 is discharged through the transistors 55, 57 and the resistor connected to the emitter of the transistor 57.

Therefore, when the power is turned on again, charging of the capacitor 61 is started from zero, so that the timer operation of the time limit T5 is performed without any problem.

According to the present invention, the voltage detection circuit detects the power supply voltage, turns on the switching element when the power supply voltage is below a predetermined value, turns off the switching element when it exceeds the predetermined value, and uses the switching element to control the timer through the rectifier. Since the charging current of the capacitor in the circuit is controlled and the output circuit is turned off until the charging voltage of the capacitor of this timer circuit becomes high, the time point at which current supply to the timer circuit starts according to the rise of the power supply voltage is controlled. changes, and if the rise is steep, the current will be supplied earlier, and if the rise is slow, the current will be supplied with a corresponding delay, and the output circuit will be in operation after a certain period of time from the point when this current supply starts. .

Therefore, in response to the rise of the power supply voltage, the power supply can be reset efficiently and reliably in terms of time.

Furthermore, the rectifying element connected between the switching element and the capacitor of the timer circuit prevents the inconvenience of discharging the capacitor even if the switching element is turned on due to noise, and is not affected by noise.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional example, Figures 2 and 3 are circuit diagrams showing a conventional example.
FIG. 4 is a circuit diagram showing a part of the circuit of a proximity switch according to an embodiment of the present invention, and FIGS. FIG. 3 is a waveform chart for explaining each figure. 10... Proximity switch, 11... IC circuit forming a proximity sensor, 12... Oscillation circuit, 1
3.15...Comparator, 14...
Integration circuit, 16.70.80... Output circuit, 1
7... Constant voltage circuit, 18... Power supply reset circuit, 40... Voltage detection circuit, 50...
...Timer circuit.

Claims (1)

[Scope of utility model registration request] A switching element that turns on when the power supply voltage is below a predetermined value and turns off when it exceeds a predetermined value in a proximity switch that forms an oscillation circuit that includes a detection coil and generates an output signal according to changes in the oscillation amplitude of this oscillation circuit. a timer circuit having a voltage detection circuit including a capacitor whose charging current is controlled by the switching element and a voltage discrimination circuit that operates when the charging voltage of the capacitor reaches a predetermined level; and an output of the timer circuit. 1. A proximity switch comprising: an output circuit to which a current is supplied according to the current; and a rectifying element connected in a forward direction from a power supply side terminal of the switching element toward the capacitor.