JPS594808B2 - Proximity switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency oscillation type proximity sensor 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 with only the IC circuit 11. This IC circuit 11 internally includes an oscillation circuit 12, a comparator 13, and an integration circuit 1.
4. Comparator 15, output circuit 16, constant voltage circuit IT
and a power supply reset circuit 18, the detection coil 1
02L Sensitivity adjustment variable resistor 22, bypass capacitor 23,
An integrating capacitor 24, a power supply reset capacitor 25, 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 15 attenuates or the oscillation stops. As a result, under normal conditions (non-detection), NL (normal
The low) output is "L" and becomes "H" at the time of detection. Therefore, the current flows from the output terminal of the proximity switch 10 under normal conditions, but does not flow at the time of detection. Of course.
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 time, the oscillation output is small, just like when an object is present, so
Despite the absence of an 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 is provided to prevent the output signal from being generated from the output circuit 16 during a time period T3 that is longer than the time period To (90). 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 composed of a bipolar IC, the maximum 95 voltage is about 30V, so the proximity switch 10
If it is desired to use a power supply of up to 40V, it is necessary to insert a resistor 31 for voltage drop, and also connect a capacitor 32 to stabilize the power supply voltage Vcc.

Then, the voltage Cc rises gradually as shown in FIG. 3 in accordance with the time constant determined by the constants of the resistor 31 and capacitor 32. As shown in FIG. 3, when the power supply voltage Cc rises slowly for only a time T, the oscillation circuit 12 does not start oscillating until it reaches a certain voltage V2, and only for a time T2 after starting oscillation. Obtain an oscillation output that once reaches the detection level.

This time T2 is the time T in FIG. 2 because the power supply voltage Vcc has gradually risen. 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 set time T3 must be quite long.
Then, when the power supply voltage rises sharply as shown in FIG. 2, it becomes wasteful to take a long power supply reset time T3. Therefore, it is conceivable to provide a logic circuit inside the IC circuit 11 to inhibit the output circuit 16 unless the power supply voltage Vcc exceeds a certain value, but this is not possible for the following reason.

That is, the output voltage Vs of the constant voltage circuit 17 rises with the power supply voltage Cc as shown in FIG. 4, but when this voltage Vs is lower than the constant value V1, the state of the logic circuit inside the 1C circuit 11 is It's completely left to random situations. Therefore, after the voltage Vs reaches V1, the logic circuit works normally and it is possible to inhibit the output circuit 16, but in the time T4 until the voltage s reaches the voltage 1, as shown in FIG. This is because erroneous output may occur as shown in the figure below. In view of the above, the present invention
A power supply that changes the power supply set time as necessary and sufficient in response to times when the power supply voltage rises quickly or slowly, and that ensures that erroneous output is prohibited while making improvements to prevent wasted time. An object of the present invention is to provide a proximity switch having a reset circuit.

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

In FIG. 5, the voltage detection circuit 40 includes a Soena diode 41,
It is composed of transistors 42, 43, and 44, and the output voltage Vs of the constant voltage circuit is a predetermined value. Below, the transistor 43 is turned on, and above, the transistor 43 is turned off. The timer circuit 50 includes transistors 51 to 5.
8, a resistor 59, 60, and an external power supply reset capacitor 61. Said transistor 4
3 is on, the capacitor 61 is not charged, and is only charged when it is off. Transistors 55 and 56 constitute a comparator, and when the charging voltage of capacitor 61 becomes higher than the reference voltage determined by resistors 59 and 60, transistor 55 turns on and a current determined by the current flowing through transistor 57 is generated. flows through transistor 54. When the charging voltage of the capacitor 61 is lower than the reference voltage, the transistor 56 is on, the transistor 55 is turned on, and no current flows through the transistor 54. The output circuit 70 is composed of transistors 71, 72, and 73, and the transistor 71 and the transistor 51 constitute 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 bus of transistor 71. Therefore, when no current flows through the transistor 54, the transistor 72,
No current is supplied to transistor 73, and both transistors 72, 7
3 is in the off state. Therefore, the comparator (
No matter what kind of signal there is from 15 (indicated by 15 in FIG. 1), the output signal will be no current and no voltage. When current flows through the transistor 54, the current is supplied to the transistors 72 and 73 via the transistor 71, so that an output signal is generated in response to the signal from the comparator 15. Note that in the circuit of FIG. 5, the transistors 44, 51,
52, 53, 57, and 58 each constitute a current mirror circuit, which functions as a constant current sink circuit and a current source circuit when the constant voltage Vs is a constant value. Note that if an output circuit 80 similar to the output circuit 70 is connected and an output signal of the opposite polarity is introduced from the comparator 15, the output circuit 70
, 80 can respectively obtain NL output and NH output (normal high output).

Further, when the voltage s in the voltage detection circuit 40 is extremely low, the current applied from the transistor 44 of the current source circuit is also small, so the transistor 43 is not turned on, but at this time, the current flowing from the transistor 51 to the capacitor 61 is also small. The charging voltage of the capacitor 61 does not increase.

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. 5, the voltage detection circuit 40 detects that the voltage Vs has reached VO, and from the time of this detection, the timer circuit 50 is operated to reset the current for a certain period of time. I have to.

Assuming that the fixed time limit set by this timer circuit 50 is T6, when the power supply voltage Cc rises slowly as shown in FIG. Therefore, when T5=O, the power supply reset time is only T6. In this way time T5
varies depending on the rise speed of the power supply voltage. The voltage o to be detected by the voltage detector 40 may be set to the voltage level at the time when the oscillation circuit starts oscillating, and the timer time T6 may be set as the time from the time the oscillation starts until the detection output reaches a predetermined value. . As described in the embodiments above, according to the present invention, in a proximity switch that includes a detection coil to form an oscillation circuit and generates an output in accordance with a change in the oscillation amplitude of the oscillation circuit, the power supply voltage is set to a predetermined voltage value. a voltage detection circuit that derives a detection output when the voltage detection circuit reaches the voltage detection circuit; a timer circuit that starts operating according to the detection output of this voltage detection circuit; Since the output circuit forcibly maintains the power source in a predetermined state, the power supply reset time can be controlled in accordance with the rising state of the power supply voltage. In other words, if the power supply voltage rises quickly, the timer operation is started early to release the power supply reset quickly, and if the power supply voltage rises slowly, the timer operation is started later and the power supply reset is released after the power supply voltage is stabilized. You can postpone it until Therefore, depending on the individual case, the power reset time can be set so that it is not too short or too long, so that the power reset time is time-efficient and the power supply is reliably set to prevent erroneous output. You can apply a set.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a conventional example, Figures 2, 3, and 4.
The figures are waveform diagrams for explaining FIG. 1, FIG. 5 is a circuit diagram showing a part of the circuit of a proximity switch according to an embodiment of the present invention, and FIG. 6 is a waveform diagram for explaining FIG. 5. FIG. 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)

[Claims] 1 In a proximity switch that includes a detection coil to form an oscillation circuit and generates an output according to changes in the oscillation amplitude of this oscillation circuit, a voltage detection circuit that derives a detection output when the power supply voltage reaches a predetermined voltage value. , a timer circuit that starts operating in response to the detection output of this voltage detection circuit, and an output circuit that is controlled by this timer circuit and forcibly holds the output signal in a predetermined state before this timer circuit times out. A proximity switch comprising: