JPS643092Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention is a non-contact type photo sensor for detecting the presence or absence of an object or the position of an origin, etc., which has an additional function to detect an abnormal state due to a short circuit or disconnection of the photo sensor itself. It is related to circuits.

Microswitches, photo sensors, and the like have been used as conventional position detection sensors, but in recent years, non-contact type photo sensors have come to be mainly used due to their advantages such as longevity and reliability. However, while conventional microswitches use two cables: a common terminal and a make or break terminal, non-contact type photo sensors use two cables: the anode terminal of the light emitting diode and the photo terminal, as shown in Figure 1. A photo sensor circuit was constructed by connecting three cables, each with the common terminals of the collector terminal of the transistor, the cathode of the light emitting diode, and the emitter of the phototransistor, connected to a current limiting resistor, a comparator, and ground.
For this reason, in devices that use a large number of photo sensor circuits, there are problems such as an increase in the number of cables, which increases the number of wiring man-hours, and the complexity of inspections in the event of a poor connection at a wiring location or a short circuit or disconnection of a cable.

In order to solve the above-mentioned drawbacks, the present invention reduces the number of cables connected to the photo sensor to two, similar to the micro switch, to reduce the frequency of short circuits or disconnections, and also has a function to detect abnormal conditions due to short circuits or disconnections. It was added.

That is, a current limiting resistor, a light emitting diode, and a phototransistor are each connected in series between a power supply voltage terminal and a ground terminal, and a current branching resistor and the current limiting resistor are connected in parallel to the phototransistor. A photo sensor circuit with a minimum number of two cables connected to the photo sensor is configured with a comparator that compares the voltage value output to the connection terminal with the light emitting diode and an operating state determination reference value, and the operating state is determined. While making it possible,
The abnormal state can also be detected by switching the operating state determination reference value to an abnormal state determination reference value due to a short circuit or disconnection, and comparing it with a voltage value output to a connection terminal between the current detection resistor and the light emitting diode. This made it possible.

FIG. 2 shows an embodiment of the present invention, in which R ₁ and R ₂ are resistors, D is a light emitting diode, Q is a phototransistor, 1 is a power supply voltage terminal, and 2 is a voltage output to terminal 5. An output terminal of a comparator 4 that compares the value with a reference value for determining each state of abnormality due to operation, short circuit or disconnection; 3 is a terminal for inputting the reference value for determining each state of abnormality due to operation, short circuit or disconnection;
5 and 7 are the resistor _R1 and the light emitting diode D
6 and 8 are terminals, and 9 is a shield, respectively. Here, the resistor R ₂ is used to flow a minimum amount of current necessary to cause the light emitting diode D to emit light when the phototransistor Q is in the OFF state. Next, to explain the operation, in FIG. 2, when the shield 9 enters between the light emitting diode D and the phototransistor Q and blocks the light, the phototransistor Q becomes the CFF state, and the voltage drop of the light emitting diode D is reduced to V _DOFF. , the voltage at terminal 5 is V _POFF ,
If the voltage at terminal 1 is V _C , then V _POFF = (V _C・R ₂ +
V _DOFF R ₁ )/(R ₁ + R ₂ ). Furthermore, when the shield 9 is not inserted between the light emitting diode D and the phototransistor Q, the phototransistor Q is in the ON state, and the voltage drop of the light emitting diode D is reduced to V _DON ,
If the voltage at terminal 5 is V _PON and the voltage between the collector and emitter of phototransistor Q is V _Q , then V _PON
=V _DON +V _Q. Assuming that the voltage drop of the light emitting diode D is V _D ≒ V _DOFF ≒ V _DON , the operating state determination reference voltage V _SA of the comparator 4 is V _SA = (V _PON + V _POFF )/
2≒V _C・R ₂ +V _D (2R ₁ +R ₂ ) +V _Q (R ₁ +R ₂ )/
2・(R ₁ + R ₂ ), which is the operating state judgment reference value.
By inputting V _SA to terminal 3 and comparing it with the voltage at terminal 5, the operating state of the photo sensor circuit can be determined.

Next, if there is a short circuit between terminals 5 and 6, the voltage at terminal 5 will be approximately 0 volts, so select the short circuit condition determination reference value V _SS to an appropriate value within the range of 0 < V _SS < V _SA and set the voltage between terminals 5 and 6. By switching the input to terminal 3 and comparing it with the voltage at terminal 5, it is possible to determine an abnormal state due to a short circuit. Furthermore, if there is a disconnection between terminals 5 and 6, the voltage at terminal 5 will be approximately the power supply voltage V _C , so select an appropriate value for the disconnection condition determination reference value V _SO in the range of V _SA < V _SO < V _C. By switching input to the terminal 3 and comparing it with the voltage at the terminal 5, it becomes possible to determine an abnormal state due to a disconnection. In addition, the reference values for determining each state of abnormality due to the above operation, short circuit, or disconnection can be determined by switching inputs using relays, analog switches, etc.
It goes without saying that a switching input based on program settings by the A converter may also be used.

As described above, according to the present invention, it is possible to obtain a photo sensor circuit which minimizes the number of cables, reduces the frequency of occurrence of short circuits or disconnections, and has the function of detecting abnormal conditions due to short circuits or disconnections.

[Brief explanation of the drawing]

Fig. 1 shows a wiring diagram of a conventionally used photo sensor circuit, and Fig. 2 shows a wiring diagram of a photo sensor circuit with abnormality detection according to the present invention, where R ₁ and R ₂ are resistors,
D is a light emitting diode, Q is a phototransistor,
4 is a comparator, 9 is a shield, 1, 2, 3, 5, 6,
7 and 8 indicate terminals.

Claims (1)

[Scope of utility model registration request] A current limiting resistor R ₁ , a light emitting diode D and a phototransistor Q are connected in series between the power supply voltage terminal 1 and the ground terminal 6, and a current branching resistor R ₂ is connected in parallel to the phototransistor Q. , the voltage value output to the connection terminal 5 between the current limiting resistor R ₁ and the light emitting diode D, and the reference value for determining each state of abnormality due to operation, short circuit or disconnection that has been applied to the terminal 3 from the outside in advance. 1. A photo sensor circuit with an abnormality detection function, comprising a comparator 4 for comparison, and detecting an abnormal state occurring in the photo sensor circuit.