JPH05268044A - Photoelectric switch - Google Patents

Abstract

PURPOSE:To obtain the photoelectric switch with excellent reliability without mutual interference by eliminating the effect of magnetic noise invaded suddenly from the outside of the system. CONSTITUTION:A switch circuit 1 is provided across a reception coil 5, and the switch circuit is closed to short-circuit across the reception coil 50 for a period when a magnetic signal (t) sent from a pre-stage photoelectric switch S2 is not received by a post-stage photoelectric switch S1. The switch circuit consists of a circuit receiving an output signal (a) and outputting a reception signal (q) through a filter 2, a detection smoothing circuit 3, and a comparator 4, a counter 6 outputting a one-pulse counter signal (r) for each prescribed time, a NOR gate 7 NORing the signals q, r, and an electronic switch 8 turned on/off by a short-circuit signal (s) outputted from the NOR gate 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric switch for determining the presence or absence of an object by projecting light and detecting the presence or absence of the reflected light, and a photoelectric switch in which a plurality of such photoelectric switches are sequentially arranged. Regarding the system.

[0002]

2. Description of the Related Art A photoelectric switch is known as a means for detecting the presence or absence of an object moving on a conveyor line or the like. This is to determine the presence / absence of an object by projecting light onto the path of the object and detecting the presence / absence of reflected light from the moving object. In such a photoelectric switch, in order to reduce power consumption and prevent mutual interference, the projection light is pulsed and projected intermittently (hereinafter, this projection light is referred to as sensing light). Usually, a plurality of photoelectric switches are used to detect the presence or absence of an object.
For example, in a conveyor line, multiple photoelectric switches are installed in one place such as a photoelectric switch that projects light from the lateral direction, a photoelectric switch that projects light from below, and a photoelectric switch that projects light from above to enable more accurate object detection. I have to. However, when a plurality of photoelectric switches are installed at one location and each photoelectric switch continuously projects light, each photoelectric switch may receive the sensing light projected by the other photoelectric switches. This is called mutual interference as described above.In a photoelectric switch, light is emitted intermittently so that the light emission timing does not overlap with other photoelectric switches, and the reflected light from its own light emission and the light emission of other photoelectric switches cause A means for distinguishing the received light (interference light) is provided.

However, even in this case, if each photoelectric switch operates independently, the timing of the sensing light may overlap in two or more photoelectric switches, and mutual interference will occur. Conventionally, various techniques for preventing such mutual interference have been proposed, but all of them require complicated and expensive means, and the influence of mutual interference cannot be completely eliminated.

Therefore, the present applicant first sent the synchronous timing signal to a series of photoelectric switches in sequence, and the SST system in which the timing of the sensing light in these photoelectric switches was made different from each other in accordance with this synchronous timing signal. We proposed a calling photoelectric switch (Japanese Patent Application No. 3-7371)
No. 5). The photoelectric switch will be briefly described below with reference to FIG.

In the figure, this photoelectric switch basically has a light projecting section 33 and a light receiving section 3 for generating sensing light.
7, a gate circuit 41, an integration circuit 43, a determination circuit 45, and a pulse generation circuit 30, the pulse generation circuit 30
To enable external synchronization,
Exciting section 54 is added.

First, the basic components will be described. The pulse generating circuit 30 generates a clock having a constant period and a clock generating circuit 31 which divides the clock (for example, divides by 16) to generate a pulse d having a constant period. And a frequency dividing circuit 32, which can be reset by an output pulse c of a one-shot circuit 53 of the receiving section 49 described later, so that the pulse d can be synchronized with this pulse c. This pulse d is applied to the exciting unit 54 and the light projecting unit 3.
3 and the integrating circuit 43.

The light projecting section 33 comprises a one-shot circuit 34, a switching transistor 35, and an LED 36. The one-shot circuit 34 is triggered by the falling edge of the output pulse d of the frequency dividing circuit 32, and generates an "H" (high level) pulse e having a narrow constant pulse width at each trigger. This pulse e turns on the transistor 35 for that pulse period. Therefore, when the transistor 35 is turned on, a drive current flows through the LED 36 and the sensing light is emitted from the LED 36 with the same cycle and the same duty ratio as the pulse e.

The light receiving section 37 comprises a photodiode 38, an amplifier 39 and a comparator 40. Upon receiving the light, the photodiode 38 generates a pulse having a pulse width equal to the light receiving period. This pulse is amplified by the amplifier 39 and supplied to the comparator 40 as the pulse f. The comparator 40 compares the level of the pulse f with a reference level and outputs a binarized pulse g of "L" (low level). When there is an object (not shown) in the vicinity, the sensing light from the LED 36 is reflected by this object and is received by the photodiode 38, so that a pulse f whose timing coincides with the output pulse e of the one-shot circuit 34 is obtained. However, when other photoelectric switches are installed close to each other, the sensing light is also received by the photodiode 38 as interference light, and as a result, the pulse f due to the interference light is also obtained. All of these pulses f are binarized by the comparator 40, and an "L" pulse g is obtained. This pulse g is supplied to the gate circuit 41 together with the output pulse e of the one-shot circuit 34.

The gate circuit 41 comprises a D-FF circuit 42, and its data input D is an output pulse g of the comparator 40 and its clock input CK is an output pulse e of the one-shot circuit 34. The D-FF circuit 42 samples and holds the level of the pulse g at the rising edge (front edge) of the "H" pulse e. As a result, the comparator 40
Only the pulse of the output pulse g that matches the timing of the pulse e is extracted and held by the D-FF circuit 42. Therefore, the pulse g whose timing does not match the pulse e is removed by the D-FF circuit 42. When the pulse g whose timing coincides with the pulse e is sequentially supplied at the cycle T of N pulse e, the D-FF 42 rises at the timing of the first pulse of the N pulses, and the pulse width is N · T. The "h" pulse h is output.

The integrating circuit 43 comprises a 4-bit shift register 44, for example. This shift register 4
4 uses the falling edge of the output pulse d of the frequency dividing circuit 32 as a clock CK, and the D-FF circuit 4 for each clock CK.
The output of 2 is taken in and sequentially shifted. So now,
If the D-FF circuit 42 outputs a pulse h of "H", this pulse h is taken in by the clock CK, the Q _A output of the D-FF circuit 44 becomes "H", and then the clock CK is supplied. Q _B , Q _C ,
It becomes "H" in the order of Q _D output. Therefore, four or more pulses g whose timing matches the pulse e are consecutively D-
4N from the D-FF circuit 42 taken into the FF circuit 42
When · T or more pulses h pulse width is output, Q _A to Q _D output of the shift register 44 becomes "H" at the same time.

The determination circuit 45 is the Q of the shift register 44.
And _A to Q _D AND gate 46 for receiving the output, also set pulse output of the NOR circuit 47, and AND gate 46 and inputs these Q _A to Q _D output, the output of the NOR circuit 47 as a reset pulse R / S-FF circuit 4
It consists of eight. AND gate 46 rises to all Q _A to Q _D output of the shift register 44 becomes "H", and generates a set pulse i of falling "H" and the those of even one "L", the set Pulse i
The R · S-FF circuit 48 is set at the rising edge of. NOR circuit 47, the shift register 44 Q _A to Q _D
A reset pulse j of “L” is generated which falls when even one of the outputs becomes “H” and rises when all of these outputs become “L”, and R is generated at the rising edge of this reset pulse j.
-The S-FF circuit 48 is reset. This gives R
The output of the S-FF circuit 48, that is, the output k of the determination circuit 45
Q _A to Q _D output of the shift register 44 is all time from when the "H" until all become "L""H"
Becomes

By the operation of each of the above parts, the pulse g whose timing matches the output pulse e of the one-shot circuit 34
Are sequentially obtained from the comparator 40 in the cycle of the pulse e, the output k of the determination circuit 45 becomes “H”, which means that the sensing light from the LED 36 is reflected by the object and is received by the photodiode 38. , That is,
It means that an object exists. Judgment circuit 45
When the output k of H becomes "H", this indicates the existence of an object.

The presence or absence of the object is determined as described above. Next, the exciting section 54 and the receiving section 49 for making this photoelectric switch function as the SST system.
Will be described.

The exciting unit 54 comprises a frequency dividing circuit 55, a one-shot circuit 56, a differentiating circuit 57, a diode 58, and a transmitting coil 59. The output pulse d of the frequency dividing circuit 32 is frequency-divided by the frequency dividing circuit 55. Here, the frequency dividing circuit 55 divides the pulse d into four, and the timing of the falling edge of the output pulse 1 of the frequency dividing circuit 55 coincides with the falling edge of the pulse d.
The one-shot circuit 56 outputs the output pulse l of the frequency dividing circuit 55.
Triggered on the falling edge of, a pulse m of "L" having a constant pulse width ΔT is generated. This pulse m is differentiated by the differentiating circuit 57, and the differential pulse n generated at the rising edge (rear edge) of the pulse m is extracted by the diode 58 and the coil 59 is excited. Therefore, a pulse-shaped magnetic signal is generated from the transmission coil 59 and transmitted to the photoelectric switch at the next stage (slave side).

The receiving section 49 is for receiving the magnetic signal output from the exciting section 54 of the photoelectric switch (not shown) at the preceding stage (master side) having the same structure, and the receiving coil 50, It is composed of an amplifier 51, a comparator 52, and a one-shot circuit 53. A pulse voltage is induced in the receiving coil 50 by the pulse-shaped magnetic signal sent from the exciting unit 54 in the photoelectric switch in the preceding stage, is amplified by the amplifier 51 to become the synchronization timing signal a, and is binarized by the comparator 52. It One-shot circuit 53
Is triggered by this binarized sync timing signal to generate a sync timing signal c of "H" having a narrow constant pulse width. As described above, the frequency dividing circuit 32 of the pulse generating circuit 30 is reset at the leading edge of the synchronization timing signal c. Here, the magnetic signal output from the coil 59 of the exciting unit 54 has a timing later than that of the sensing light output from the LED 36, and the synchronization timing signal received by the coil 50 is the exciting unit 54 of the photoelectric switch in the preceding stage.
Therefore, the synchronization timing signal c output from the one-shot circuit 53 is delayed by the time ΔT from the emission timing of the sensing light of the photoelectric switch in the previous stage. That is, the front edge of the synchronization timing signal c coincides with the falling edge of the output pulse d of the frequency dividing circuit 32, and the output pulse e of the one-shot circuit 34, and thus the emission timing of the sensing light from the LED 36, is frequency divided. Since it coincides with the falling edge of the output pulse d of the circuit 32, the light emission timing of the sensing light from the LED 36 is delayed by the time ΔT from the light emission timing of the sensing light from the preceding photoelectric switch.
Similarly, the one-shot circuit 56, the differentiating circuit 57, and the diode 58 of the exciting unit 54 cause the photoelectric switch in the next stage to emit the sensing light with a delay of time ΔT from the emission timing of the sensing light from the LED 36.

A plurality of such photoelectric switches are sequentially arranged,
When the magnetic signal of the synchronization timing signal is sent to the next stage to operate, the timings of the sensing lights of the respective photoelectric switches are sequentially shifted by the time ΔT in the order of arrangement. It is possible to prevent the timings from overlapping.
By doing so, in each photoelectric switch, the one-shot circuit 3 of the output pulse g of the comparator 40 is output.
The pulse whose timing coincides with the output pulse e of No. 4 is always due to the fact that the photodiode 38 receives the reflected light of the sensing light from its own LED 36, and the judgment result of the judgment circuit 45 is very high except mutual interference. The accuracy is high.

[0017]

However, the photoelectric switch system of the above example includes a transmitting coil and a receiving coil in the photoelectric switch, and transmits a magnetic signal from the photoelectric switch on the front stage side to the photoelectric switch on the rear stage side. Since the synchronization timing signal c is obtained by this, even when magnetic noise suddenly jumps into the photoelectric switch from outside the system, a pulsed voltage is induced in the receiving coil. Therefore, the erroneous synchronization timing signal c is likely to be output from the one-shot circuit 53 provided in the receiving section 49, and as a result, the above mutual interference is likely to occur. An object of the present invention is to solve such problems and provide a photoelectric switch having high reliability against magnetic noise.

[0018]

In order to achieve the above object, the present invention is provided in the receiving unit when the receiving unit does not receive a magnetic signal from another photoelectric switch installed in the preceding stage. A switch circuit for short-circuiting both ends of the receiving coil was provided. As the switch circuit, it detects that no other photoelectric switch of the same kind is installed in the preceding stage, and both ends of the receiving coil provided in the receiving unit while the other photoelectric switch is not installed in the preceding stage. , And that the other photoelectric switch of the same kind is installed in the previous stage, and the output cycle of the magnetic signal output from the other photoelectric switch installed in the previous stage is detected, and the magnetic signal is There is a type in which both ends of the receiving coil provided in the receiving unit are short-circuited during a period from the time of being detected until the time of detecting the next magnetic signal.

[0019]

When the both ends of the receiving coil are short-circuited, even if magnetic noise jumps into the photoelectric switch from outside the system, a pulsed voltage is not induced in the receiving coil. Therefore, the one-shot circuit 53 provided in the receiver 49 does not output the erroneous synchronization timing signal c, and the above mutual interference is prevented. Detecting that no other photoelectric switch of the same type is installed in the previous stage, short-circuit both ends of the receiving coil for the period when the other photoelectric switch of the same type is not installed in the previous stage, or other similar photoelectric switch in the previous stage. From the detection of the magnetic signal output from the other photoelectric switch installed in the previous stage and the detection of the next magnetic signal. By short-circuiting both ends of the receiving coil only during the period, the magnetic signal from the photoelectric switch at the preceding stage can be detected, so that normal operation of the photoelectric switch system is not impaired.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS.
It will be explained based on. FIG. 1 is a block diagram showing a circuit configuration of a photoelectric switch according to this example, and FIG. 2 is a waveform diagram showing waveforms of signals generated from respective parts of the device of FIG.

In FIG. 1, a switch circuit is generally denoted by reference numeral 1 and receives an output signal a of an amplifier 51 provided in a receiving section 49 to remove high frequency noise and select signal o. , A detection / smoothing circuit 3 for detecting / smoothing the selection signal o to output a smoothing signal p, and slicing the smoothing signal p with a preset threshold value to obtain a rectangular reception signal q. A comparator 4 for outputting, an oscillator 5, a counter 6 for counting the output pulses of the oscillator 5, and outputting a counter signal r of one pulse at preset constant time intervals, the reception signal q and the counter signal r.
(NOR) gate 7 for taking the negative logical sum of the above and an electronic switch 8 which is connected to both ends of the receiving coil 50 provided in the receiving section 49 and is turned on and off by the short circuit signal s output from the NOR gate 7. It consists of and.
Other parts corresponding to those in FIG. 5 described above are indicated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 2, one photoelectric switch S ₁
When another photoelectric switch S ₂ of the same type is installed on the front side of the above, and the differential pulse n is applied from the exciting unit 54 of the front side photoelectric switch S ₂ to the transmission coil 59 on the front side, The magnetic signal t is transmitted from the transmission coil 59 on the preceding stage side.
Occurs, and a reception signal corresponding to the magnetic signal t is induced in the reception coil 50 on the subsequent stage side.

When this signal is amplified by the amplifier 51 and passed through the filter 2, the detection / smoothing circuit 3 and the comparator 4, a square received signal q is obtained. On the other hand, the counter 6 outputs from the counter 6 a counter signal r of one pulse at a preset fixed time
Is output. Therefore, the reception signal q and the counter signal r are input to the two input terminals of the NOR gate 7,
Taking a negative logical sum, the received signal q falls at the rising edge,
A rectangular short circuit signal s that rises at the falling edge of the counter signal r is obtained.

Therefore, when the short-circuit signal s is output from the NOR gate 7, the electronic switch 8 is turned on to short-circuit both ends of the receiving coil 50 on the rear stage side. Even if a large magnetic noise suddenly jumps into the coil 50, no voltage is induced in the receiving coil 50, so that a signal corresponding to the noise rises in the output pulse c of the one-shot circuit 53 of the receiver 49. Absent. Therefore, the one-shot circuit 53 of the receiver 49 does not output the erroneous synchronization timing signal c, and mutual interference is prevented. Outside the output period of the short-circuit signal s, both ends of the receiving coil 50 are not short-circuited, so that the magnetic signal t is received from the photoelectric switch S _{2 in} the preceding stage, and the operation of the pulse generation circuit 30 and the subsequent steps is performed. This is the same as that shown in the section of the prior art, and therefore its explanation is omitted.

In this embodiment, the switch circuit 1 is provided with the counter 6 and the electronic switch 8 is provided at regular intervals.
Since the short circuit of the receiving coil 50 is turned off by turning off the switch, the photoelectric switch of the same kind is arranged in the front stage of the one photoelectric switch after the system operation, and the photoelectric switch of the front stage is switched to the photoelectric switch of the rear stage. When the transmission of the magnetic signal t is started, the start of the transmission of the magnetic signal t from the photoelectric switch in the preceding stage can be detected by the photoelectric switch in the subsequent stage. Therefore, there is also an advantage that the light emission timings of the newly added front-stage photoelectric switch and the rear-stage photoelectric switch are automatically adjusted even if the system power is not turned off and then turned on again.

The output interval ΔT ₁ of the counter signal r can be set arbitrarily, but 0.1 second to 10 seconds is preferable. The pulse width ΔT ₂ of the counter signal r has another photoelectric switch S ₂ of the same type installed in the preceding stage to prevent hazards, and the receiving coil 50 is short-circuited. When the magnetic signal t from the photoelectric switch S ₂ is received, a time longer than the time T _x from the reception coil 50 receiving the magnetic signal t until the reception signal q rises at the output end of the comparator 4. Is set to.

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a block diagram showing the circuit configuration of the photoelectric switch according to the present example, and FIG. 4 is a waveform diagram showing the waveform of the signal generated from each part of the device of FIG.

As shown in FIG. 3, the switch circuit 1 of the present embodiment receives the output signal a of the amplifier 51 provided in the receiving section 49, removes high frequency noise, and outputs a selection signal o. And a detection / smoothing circuit 3 for detecting / smoothing the selection signal o to output a smoothing signal p, and slicing the smoothing signal p with a preset threshold value to obtain a square reception signal q.
A comparator 4 that outputs a binary signal u by slicing the output signal a of the amplifier 51 with a preset threshold, and a pulse of ΔT ₃ triggered by the binary signal u. A one-shot circuit 12 that outputs a reception start timing signal v having a width, and a one-shot circuit 13 that outputs a reception timing signal w having a pulse width of ΔT ₄ in response to the fall of the reception start timing signal v,
The gate circuit 14 calculates a (reception signal q-reception timing signal w) and outputs a short circuit signal x, and an electronic switch 8 that is turned on / off by the short circuit signal x.

As shown in FIG. 4, one photoelectric switch S ₁
When another photoelectric switch S ₂ of the same type is installed on the front side of the above, and the differential pulse n is applied from the exciting unit 54 of the front side photoelectric switch S ₂ to the transmission coil 59 on the front side, The magnetic signal t is transmitted from the transmission coil 59 on the preceding stage side.
Occurs, and a reception signal corresponding to the magnetic signal t is induced in the reception coil 50 on the subsequent stage side.

When this signal is amplified by the amplifier 51 and passed through the filter 2, the detection / smoothing circuit 3 and the comparator 4, a square received signal q is obtained. On the other hand, when the output signal a of the amplifier 51 is passed through the comparator 11 and the one-shot circuits 12 and 13, a reception timing signal w having a pulse width larger than that of the binarized signal u is obtained in synchronization with the binarized signal u. .. When the gate circuit 14 calculates (reception signal q−reception timing signal w), the reception signal q corresponding to the magnetic signal t transmitted from the photoelectric switch S ₂ on the preceding stage is induced in the reception coil 50. The gate circuit 14 outputs the short circuit signal x at each interval.

Therefore, when the short circuit signal x is output from the gate circuit 14 and the electronic switch 8 is turned on to short-circuit both ends of the receiving coil 50 on the rear stage side, the reception on the rear stage side is performed during the output period of the short circuit signal x. Even when a large magnetic noise suddenly jumps into the reception coil 50, the reception coil 50
Since a voltage is not induced in the signal, the output pulse c of the one-shot circuit 53 of the receiver 49 does not have a signal corresponding to noise. Therefore, the one-shot circuit 53 of the receiving unit 49
Since only the synchronization timing signal c corresponding to the magnetic signal t transmitted from the photoelectric switch S ₂ on the preceding stage side is output, the mutual interference is prevented.

In the above embodiment, only one switch circuit for removing noise is provided in the preceding stage of one photoelectric switch when no other photoelectric switch of the same type is installed (FIG. 1, FIG. 2), and another photoelectric switch of the same kind is installed on the front side of the photoelectric switch 1 and removes noise in a period in which the receiving coil does not receive a magnetic signal from the photoelectric switch on the front side. When only the switch circuit to perform is provided (Fig. 3,
Although the embodiment of FIG. 4) has been described, the circuit of FIGS. 1 and 2 can be combined to form a switch circuit capable of removing noise in both periods.

[0033]

As described above, according to the present invention,
A switch circuit was provided between both ends of the receiving coil, and the electronic switch was turned on to short-circuit between both ends of the receiving coil while the magnetic signal transmitted from the preceding photoelectric switch was not received by the latter photoelectric switch. Therefore, even if magnetic noise jumps from outside the system within a period in which both ends of the receiving coil are short-circuited, a pulsed voltage is not induced in the receiving coil. Therefore, the one-shot circuit provided in the receiving unit outputs only the synchronization timing signal corresponding to the received signal induced in the receiving coil, so that mutual interference between the photoelectric switches is prevented. Therefore, a highly reliable photoelectric switch system that is not easily affected by magnetic noise can be constructed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of a photoelectric switch according to a first embodiment.

FIG. 2 is a waveform diagram showing a waveform of a signal output from each unit of the apparatus shown in FIG.

FIG. 3 is a block diagram showing a circuit configuration of a photoelectric switch according to a second embodiment.

FIG. 4 is a waveform diagram showing waveforms of signals output from each unit of the apparatus of FIG.

FIG. 5 is a block diagram showing a circuit configuration of a photoelectric switch according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 switch circuit 2 filter 3 detection / smoothing circuit 4,11 comparator 5 oscillator 6 counter 7 NOR gate 8 electronic switch 12,14 one-shot circuit 13 AND gate 30 pulse generation circuit 33 light emitting section 37 light receiving section 49 receiving section 50 receiving coil 54 Excitation Unit 59 Transmission Coil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ikuro Ouchi 1-13-10 Nishi-Odori, Hanamaki-shi, Iwate Shanpol 203

Claims (3)

[Claims] 1. A photoelectric switch, a plurality of which can be arrayed and fixed in a row by a mounting member, each of which includes a light projecting portion for outputting a pulsed detection light for irradiating an object to be detected, and the object to be detected. When the light receiving section that receives the detection light that is reflected by the detection object or is not blocked by the detection object, the excitation section that generates a pulsed magnetic signal and outputs it to the outside, and when arranged in the above 1 row And a receiving unit that receives the magnetic signal output from the exciting unit in the previous stage, an output timing of the detection light in the light projecting unit and a magnetic signal received by the receiving unit, and When the receiving unit does not receive the magnetic signal from another photoelectric switch installed in the preceding stage, the control unit that sets the output timing of the magnetic signal and shorts both ends of the receiving coil provided in the receiving unit. Switch circuit Photoelectric switch characterized by. 2. The receiving unit according to claim 1, wherein the switch circuit detects that another photoelectric switch of the same type is not installed in a preceding stage, and the other photoelectric switch is not installed in a preceding stage. A photoelectric switch characterized by short-circuiting both ends of a receiving coil provided in the. 3. The switch circuit according to claim 1, wherein another photoelectric switch of the same type is installed in the preceding stage, and the output of the magnetic signal output from the other photoelectric switch installed in the preceding stage. A photoelectric switch characterized by short-circuiting both ends of a receiving coil provided in the receiving section during a period from the detection of the cycle and the detection of the magnetic signal to the detection of the next magnetic signal.