JPS627733B2 - - 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.

When a large number of photoelectric switches are used in parallel, light from adjacent photoelectric switches may enter the switch, causing malfunctions. Therefore, in conventional devices, due to such mutual interference, it was not possible to arrange them closer to each other to some extent.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved photoelectric switch that solves the problem of mutual interference and can also be placed close to each other.

An embodiment of the present invention will be described below with reference to the drawings. The circuit configuration is as shown in FIG. 1, and the output of the oscillation circuit is sequentially input to T-type flip-flops (hereinafter abbreviated as FF) 11, 12, and 13 for frequency division. That is, the oscillation output a as shown in the time chart a in FIG. get. In response to this light projection pulse e, an LED driver drives an LED (light emitting diode) 61, which is a light projection element, and pulsed light is projected. The light reflected by the object enters a light receiving element 62 such as a photodiode, and passes through a light receiving circuit to obtain a light receiving signal h (see FIG. 2). This received light 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 (see Figure 2) is sent.
occurs. This light reception signal i is gated by a gate signal u in an AND circuit 36. The gate signal u is obtained from the OR circuit 41, but in this case the t point is always high (HIGH).
Since the output of the inverter 53 is always low, the output g of the AND circuit 34 is directly generated from the OR circuit 41, and this output g serves as the gate signal u. Since the signal obtained by inverting the oscillation output a via the inverter 51 and the light emitting pulse e are input to the AND circuit 34, this output g is the second half of the light emitting pulse e, as shown in FIG.
This will occur during period 2.

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, since a pulse current of 100 to 500 mA at the peak value is passed through the LED 61, it is inevitable that spike noise with the waveform as shown in Fig. 3h will occur.
Gating as described above is extremely effective.

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. Since both the outputs of the FFs 12 and 13 are input to the AND circuit 32, the output f thereof becomes high in the period immediately before the emission pulse e is generated, as shown in FIG. 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). Since this output k is input to the OR circuit 42, an extra pulse is added to the output l of the OR circuit 42 in addition to the Q output of the FF 12 (see FIG. 2). Therefore, since the FF 13 is triggered extra, the output f of the AND circuit 32 immediately becomes low, and the timing of the light emission 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, the emission pulse e is stopped until the electrical noise disappears.
Malfunctions caused by this noise can be prevented.

Signal j is applied to the set terminal of RS type FF14. 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 six 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. As a result, when receiving 5 consecutive reflected beams of the projected light pulse, the RS 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.You can select any operating mode by leaving or cutting off the shorting bar 63. You can choose.

According to the present invention, when deriving a signal from a pulse generator that generates a pulse that rises after the falling edge of a light emitting pulse and falls as the next light emitting pulse rises, noise is detected in response to light incident from the light receiving element. The device derives the signal. When deriving the signal from this noise detector, the light emitting pulse is delayed for a certain period of time, so when light other than the light emitting pulse is received, the generation of the light emitting pulse and gate signal is delayed, and the influence of the noise light can be avoided. Even if a large number of photoelectric switches are arranged in parallel, malfunctions due to mutual interference can be avoided.

[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...Short-circuiting piece.

Claims (1)

[Scope of Claims] 1. An oscillation circuit, a frequency dividing circuit that divides the output of the oscillation circuit to obtain a light emission pulse and a gate signal, and a light emission element that is driven in response to the light emission pulse and lights up in pulses. a photoelectric switch comprising: a light-receiving element that receives light emitted from the light-emitting element; and a gate circuit that gates a light-receiving signal from the light-receiving element with the gate signal; a pulse generator that generates a pulse that is triggered by a pulse obtained with the same period as the light emitting pulse, rises after the fall of the light emitting pulse, and falls at the same time as the next light emitting pulse rises; and a signal derivation from the pulse generator. The noise detector may include a noise detector that derives a signal in response to light incident from the light receiving element, and a delay circuit that delays the light emitting pulse and the gate signal for a certain period of time in response to the signal derivation. A photoelectric switch characterized by: