JPH0241210B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photoelectric switch that detects an object using light and obtains a switching output.

A photoelectric switch normally uses an LED (light emitting diode) as the light emitting element, which is lit in pulses to emit pulsed light towards the detected object. By the way, in order to increase the peak value of the pulsed light, a pulsed current with a peak value of 100 to 500 mA is passed through the LED, so even if no reflected light from an object is incident on the light receiving element, the output of the light receiving element will have the above-mentioned effect. It was unavoidable that sharp spike noises were mixed in at the rise and fall of the pulse current, causing malfunctions.

In view of the above, an object of the present invention is to provide an improved photoelectric switch that eliminates the influence of spike noise and prevents malfunctions.

An embodiment of the present invention will be described below with reference to the drawings. The circuit configuration is as shown in FIG. Here, the light emitting pulse generation circuit is an oscillation circuit,
T-type flip-flop (hereinafter abbreviated as FF) 11,
12, 13, and an AND circuit 31, and a light emitting pulse is obtained as follows. First, the output of the oscillation circuit is sequentially input to the FFs 11, 12, and 13 and frequency-divided. That is, the oscillation output a as shown in the time chart a in FIG.
is input to obtain a light emitting pulse. In response to this light emitting pulse e, the LED driver is an LED that is a light emitting element.
61 is driven, and pulsed light is projected. The light reflected by the object is sent to a light receiving element 62 such as a photodiode.
The received light signal h passes through the light receiving circuit (see Figure 2).
get. This light reception signal h is sent to a comparator via a coupling capacitor, and when a signal higher than the operating level of this comparator is received, a signal i is sent to the comparator.
(See Figure 2) occurs. This received light signal i is
It is gated in an AND circuit (gate circuit) 36 by a gate signal u. The gate signal u is obtained from the OR circuit 41, but in this case, point t is always high (HIGH) and the inverter 53
Since the output of is always low,
The output g of AND circuit (inhibition circuit) 34 remains as is.
The output g is generated from the OR circuit 41 and serves as the gate signal u. AND circuit (prohibited circuit) 34
Since the signal obtained by inverting the oscillation output a via the inverter 51 and the light emitting pulse e are input to the oscillation output a, this output g is generated during the second half of the period of the light emitting pulse e, as shown in FIG. It will be something that occurs.

Therefore, as shown in an enlarged view in FIG. 3, it is possible to avoid the noise pulse generated in the signal i due to the spike noise contained in the signal h, and to gate it.
A signal j corresponding only to the optical signal can be obtained. In addition, the peak value of LED61 is 100 to 500mA.
Since it is inevitable that a spike noise having a waveform as shown in FIG. Furthermore, by gating in this way, the received light signal i is passed only while the gate signal u (signal g) is occurring, so of course it is possible to remove noise other than spike noise. .

Furthermore, the signal i is the output of the inverter 52,
The output of the AND circuit 32 is input to the AND circuit 33 to which the output is sent. The output of the inverter 52 receives the output of the inverter 53 which remains low as long as the LED 61 is connected as described above, so it is always high. In the AND circuit 32
Since both outputs of FF13 and FF13 are input,
As shown in FIG. 2, the output f is the light emission pulse e
get high during the period just before it occurs. Therefore, during this period, light enters from other photoelectric switches, etc., and optical noise is generated as shown in Fig. When this occurs, an output k is produced from the AND circuit 33 (see FIG. 2). This output k is OR circuit 42
Therefore, the output l of the OR gate circuit 42
, an extra pulse is added in addition to the Q output of FF12 (see Figure 2). Therefore FF13
is triggered extra, so the AND circuit 32
The output f immediately becomes low, and the timing of the light emitting pulse e from the AND circuit 31 is delayed. In other words, if optical noise enters just before the light emitting pulse e is about to be generated, the light emitting pulse e is emitted with a delay of the time that this optical noise would disappear, and the light emitting pulse e is emitted as it is and the object to be detected is detected. It is possible to avoid malfunctions caused by treating light that enters from another adjacent photoelectric switch as normal reflected light even though there is no reflected light. Similarly, in the case of electrical noise as shown in C, generation of the light emitting pulse e is stopped until the electrical noise disappears, so malfunctions caused by this noise can be prevented.

Signal j is applied to the set terminal of FF 14 of the R-S type. The reset terminal of this FF14 has
The output m of the AND circuit 35 to which the oscillation output, the output of FF11, and each Q output of FF12 and 13 are sent.
(See Figure 2) is input. Therefore FF1
Even if 4 is set, it is immediately reset after a short period of time. As a result, the output n of the FF 14 becomes intermittent in the form of pulses as shown in FIG.

This output n is sequentially sent to five D-type FFs 15 to 19, and five or more pulses of output n are generated, and the FF
When all Q outputs from 15 to 19 become high
The output o of the AND circuit 37 becomes high as shown in FIG. Furthermore, since these FFs 15 to 19 are driven using the light emitting pulse e as a clock pulse, when five or more pulses of output n are not generated,
All outputs of FF15-19 become high,
The output p of the AND circuit 38 becomes high. the result,
When receiving 5 consecutive reflected beams of the projected light pulse, the R-S type FF20 reverses and produces an output q.
Since the output q becomes low when the signal is not received continuously (see FIG. 4), even if the output n contains a one-off noise, it can be removed in this part and malfunctions can be prevented.

This output q is sent to the output circuit via the exclusive OR circuit 43, and an output signal is output to the outside, but the other input of the exclusive OR circuit 43 receives a high signal from the constant voltage circuit and is disconnected from the outside. Possible shorting piece 63
are constantly being added through. Therefore, the output output to the outside will be the inverted version of the output q, but if the shorting bar 63 is cut off, the output output to the outside will be the non-inverted version, and any operation can be performed depending on whether the shorting bar 68 is left or cut off. You can choose the mode.

The photoelectric switch according to the present invention includes an inhibiting circuit that inhibits gating for a predetermined period of time at the timing when a pulse generated by the light emitting pulse generating circuit changes, and a gate circuit that gates the light receiving signal obtained from the light receiving element and the light emitting pulse generating circuit. A gate is provided between the gates so that the gate is not activated for a predetermined period of time after the light projecting element is driven. Therefore, even if sharp spike noise occurs in the output of the light receiving element at the rising and falling points of the light emitting pulse when the light emitting element is pulse-driven, it will not be erroneously captured as a light receiving signal, and malfunction will not occur. A photoelectric switch can be realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the circuit configuration of a photoelectric switch according to an embodiment of the present invention, and FIGS. 2, 3, and 4 are time charts for explaining the operation of FIG. 1. 61... LED, 62... Light receiving element, 63...
Shorting strip.

Claims (1)

[Scope of Claims] 1. A light emitting pulse generation circuit, a light emitting element that is lit in pulses according to the pulses generated by the light emitting pulse generation circuit, a light receiving element, and a light emitting element that is lit in pulses according to the pulses generated by the light emitting pulse generation circuit. In the photoelectric switch, the light emitting pulse generating circuit and the gate circuit include a gate circuit that gates a light reception signal obtained from the light receiving element in response to a change in the light receiving element. A photoelectric switch characterized by being installed between.