JP3779710B2 - Beat-synchronized multi-optical axis transmission photoelectric switch - Google Patents

Description

  The present invention relates to a multi-optical axis photoelectric switch effective for detecting an object passing through a wide area, and more specifically, a novel synchronizing means for sequentially driving a plurality of light projecting elements and light receiving elements facing each other is used. The present invention relates to a multi-optical axis photoelectric switch.

  In the multi-optical axis photoelectric switch, it is an indispensable condition for detection that a plurality of light projecting elements and light receiving elements are opposed to each other and sequentially driven by a synchronous method. As the synchronization method, a synchronous cable type that is most reliable and excellent in reliability has been generally used. As shown in FIG. 10A, this cable type has a detection line 100 between the light projecting side and the light receiving side. There is a wiring problem that the synchronous cable 101 must be connected across the cable.

  Therefore, in recent years, an optical synchronization method in which the light projecting side and the light receiving side are synchronized by an optical signal has been used as a technology that replaces the cable synchronization method (see, for example, Patent Document 1). In this general optical synchronization method, as shown in FIG. 10B, the light emitting side and the light receiving side are synchronized via the synchronization optical signal 102, so that external light that is not regular synchronization light is used for synchronization. There is a risk of malfunction when entering the light receiving element.

In order to overcome such disadvantages of the general optical synchronization method, a method has been developed in which synchronization light from the light projecting element is received and integrated by the light receiving element to be distinguished from disturbance light and synchronized ( For example, see Patent Document 2), but this method eliminates the above-mentioned synchronization failure caused by disturbing light, but becomes extremely complicated in terms of circuitry, and if it malfunctions for some reason, all synchronization will be lost thereafter. Flawed.
Japanese Patent Publication No. 5-29168 JP-A-6-132803

  The object of the present invention is to positively shift the light reception timing on the light receiving side with respect to the cycle on the light projecting side in order to solve the problems of the synchronous cable method and the optical synchronization method as described above. It is intended to provide a multi-optical axis photoelectric switch utilizing a phenomenon (generally called “beat synchronization”) in which the light receiving side and the light receiving side coincide.

In general, the method called the beat method in telecommunications technology refers to applying a voltage of two different frequencies to a detector in a heterodyne receiver and taking out the output of the difference frequency (beat frequency). viewed from the period (TM1 and TM2) signal, to set the beat period 1 / _{f b} = αTM1 = βTM2 is the inverse of the beat frequency _{f b} consisting of the frequency difference f1 to f2, the TM1 periodic signal is repeated α times, At the same time, it means that a beat cycle in which the TM2 cycle signal is repeated β times is formed _fb times within a unit time, and the inherent time relationship between TM1 and TM2 is repeated for each beat cycle.

Therefore, “beat synchronization” of the multi-optical axis photoelectric switch in the present invention means that the light receiving side that detects and receives the light projection by the pulse train from the light projecting side is within the above beat cycle 1 / f _b = αTM1 = βTM2. It means that the synchronous operation is performed at least once (one period) using the phenomenon of coincident light reception.

In order to solve the above problems, the present invention relates to a multi-optical axis transmission type photoelectric switch, which includes a light projection period composed of a light projection pulse train having a number of pulses corresponding to the number of optical axes, and a light projection suspension period. A period TM1 is generated at a repetition frequency f1, and a light receiving period TM2 including a light receiving period constituted by light receiving pulse trains generated at the same interval (cycle) T corresponding to the light projecting pulse train and a unique light receiving pause period is set. By generating the repetition frequency f2 independently of the frequency f1 at a repetition frequency f2 (≠ nf1, or ≠ f1 / n, where n = 1 or more), a beat frequency f _b consisting of a difference between these frequencies f1 to f2 Is set to beat cycle 1 / f _b = αTM1 = βTM2, and within this beat cycle, at least one light projection period TM1 and a light reception period within at least one light reception cycle TM2 are allowed. The active period is configured to be substantially synchronized.

  The present invention further generates a pulse signal in which the light receiving unit lasts for the beat period or more based on the object non-detection output in the synchronized time period of the light projection and light reception periods, and detects the presence or absence of the object based on the presence or absence of the pulse signal. It is characterized by.

  Considering the effect of the above configuration in accordance with FIG. 1, in the multi-optical axis transmission type photoelectric switch of the present invention, the light projecting pulse train has the number of pulses corresponding to the number of optical axes (in this case, two) on the light projecting side A. A light projection period TM1 including a light projection period La and a light projection suspension period Lb is generated at a repetition frequency f1, and the light receiving side B is generated at the same interval (period) T corresponding to the light projection pulse train. A light receiving period TM2 consisting of a light receiving period Ra constituted by a light receiving pulse train and a unique light receiving pause period Rb, and a frequency f2 (≠ nf1, or ≠ f1 / n: where n = 1 or an integer greater than or equal to The reason for this will be described later), and is generated independently of the frequency f1.

  The time difference Rc between the light projection period TM1 and the light reception period TM2 is an accumulation time for beat synchronization. Here, TM1−TM2 = Rc = T / 2, but Rc = arbitrary time may be used. Large and small relationships are also free. In the case of FIG. 1, since the light receiving period TM2 is shorter than the light projecting period TM1 by Rc, it advances faster by Rc with respect to TM1 time, and beat synchronization is performed following the repetition of TM1. In the example shown in the figure, TM1 = 4T and TM2 = 3.5T, so when the n7 period has passed for TM1 from the first n1 period that happened to be synchronized, αTM1 = 7 × 4T = 28T, and n8 period for TM2 When the time elapses, they coincide with the least common multiple of βTM2 = 8 × 3.5T = 28T, and are synchronized in the next n8 period and n9 period, respectively. (However, since the light projection period La is shorter than the light receiving period Ra by one light projection margin time (t0) indicated by a broken line following the light projection pulse P as shown in the figure, the synchronization between both periods La and Ra is It is clear that there is a margin of 0 to t0 in the difference between the start times, and when the time difference Rc between the light projection period and the light receiving period is shorter than the margin time t0, the ni period and the next (Synchronization may be established over two or more consecutive periods such as nj periods.)

When this relationship is verified by applying well-known frequency difference (beat frequency) detection, since the beat frequency f _b = f 2 −f 1 = 1 / TM 2 1 / TM 1, f _b = (1/3. 5T) -1 / 4T = 1 / 28T becomes, _{f b} it is clear that the reciprocal of the beat period 28T. On the other hand, in the case of TM2> TM1 (f1> f2), the light receiving period TM2 is longer than the light projecting period TM1 by Rc. The beat frequency f _b = f1 to f2 is followed.

Incidentally, the fact that the beat frequency f _b are zero a f1 = f2, therefore TM1 = TM2, unless the light projecting side according to these periods and the light-receiving side are driven independently, when coincidental Except for, the effect of filling the time difference between the two periods does not occur, so it is impossible to achieve continuous synchronization (this mode will be described later with reference to the drawings). Further, including this case, that the beat frequency _{f b} is not an integer multiple of f1 or f2, the conditions of a repetition frequency f2 described above (f2 ≠ nf1, or ≠ f1 / n: where, n = 1 or more It is clear that if a regular relationship of nf1 = f2 or f1 = nf2 is established, the integer) must be protected because the same incompatibility occurs as in the case of f1 = f2.

  Therefore, as long as the light projecting element arrays in the relationship of nf1 = f2 or f1 = nf2 (where n = 1 or greater) are driven independently of each other, they are spatially close to each other or are in an opposing relationship. Even if it exists, a periodic and continuous synchronization relationship (beat synchronization) cannot be established.

  As described above, in the present invention, the synchronous operation state between the corresponding light projecting element and the light receiving element can be achieved without providing a synchronization line between the light projecting side and the light receiving side or a synchronization dedicated optical axis. It is established periodically in the beat cycle.

  Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS.

  FIG. 2 is a diagram showing a circuit block on the light projecting side in the embodiment. In this figure, a reference oscillation circuit 1 is a circuit that generates a reference frequency signal including a ceramic oscillator or a crystal oscillator, and a frequency division and timing circuit 2 receives the reference frequency signal and receives a projection pulse width t and It has a frequency division and timing function for generating a light projection pulse interval T (see FIG. 3). Reference numeral 3 denotes an inverter for inverting the projection pulse. Reference numeral 4 denotes a shift register which receives the inverted output as a clock timing and generates an output for sequentially emitting the projection element. Reference numeral 5 denotes each projection pulse and sequential emission from the shift register 4. This is an AND gate for receiving each output and causing each element of the light projecting element array 6 to emit light.

  Here, a case where four light emitting diodes composed of LED0, LED1, LED2, and LED3 are used as the light projecting element array 6 is shown. Of course, this number is freely determined according to the design. Accordingly, in this embodiment, each of the corresponding four AND gates 5 sequentially receives the first to fourth step outputs Q0, Q1, Q2, Q3 of the shift register 4, and the frequency dividing and timing circuit 2 These LEDs emit light sequentially when they coincide with the light projection pulse time t. The shift register 4 uses a decimal counter because of the degree of freedom in changing specifications, etc., but here it is reset by the Q6 output and functions as a hexadecimal counter.

  FIG. 3 is a timing chart showing each part of the light projecting side circuit of FIG. 2 and LED light emission timing. In FIG. 3, P is a light projection pulse having a time width t emitted from the frequency division and timing circuit 2 at an interval T, Q0, Q1, Q2, and Q3 start immediately after (falling) the light projection pulse P. The above-described step output lasts for the time until the projection pulse P falls (equal to the interval T), and Q6 is a reset pulse, and the shift register 4 is reset at the moment when it is issued. Shows that it ends in an instant.

  Thus, LED0, LED1, LED2, and LED3 emit light within the time t that coincides with the projection pulse P at the end of the shift register increment outputs Q0, Q1, Q2, and Q3, and the light emission sequence is performed every 6T. It is clear to repeat. In this embodiment, the time width (light projection period) of the light emission sequence is 3T + t when the light emission pulse period T and the pulse time width t are used as units, and the next light emission is performed after 3T has elapsed after the light emission of the LED 3. The sequence starts, that is, LED0 emits light, but this pause interval can be set as an integer multiple of T for convenience (in theory, arbitrarily).

  Next, an implementation circuit on the light receiving side will be described with reference to FIG. In FIG. 4, the reference oscillation circuit 11 is a circuit that generates a reference frequency signal including a ceramic oscillator or a crystal oscillator similarly to the light-emitting side circuit 1, and the frequency division and timing circuit 12 is a reference from the circuit 11. Upon reception of the frequency signal, the minimum time unit τ here (corresponding to the time difference Rc between the light projection period TM1 and the light reception period TM2), the reference pulse interval T having the same time width as the light emission side pulse interval T = 2τ. And its frequency dividing interval. The light receiving element array 13 includes four photodiodes PH0, PH1, PH2, and PH3 arranged corresponding to the LED elements of the light projecting element array 6, and the outputs of the photodiodes are AMP0 and AMP1 of the amplifier array 14, respectively. , AMP2, and AMP3 to each input of the analog multiplexer 15.

  When the analog multiplexer 15 receives a light receiving signal from each of the light receiving element rows 13 from the frequency dividing and timing circuit 12 within a light receiving period determined by the timing signals a, b, and c supplied to the multiplexer 15. A light receiving output d is generated and supplied to the comparator 16. The comparator 16 generates a true light reception output e if the input d is equal to or greater than a certain reference value and supplies it as a count input of the up counter 17. The up counter 17 is a quaternary counter and receives the same reset input f as the timing signal c from the frequency division and timing circuit 12. The quaternary output g from the up-counter 17 is used as a retrigger input of the monostable multivibrator 18, and the output h (low) indicating the stable state Q indicates the light-shielded state of any one of the optical axes. (High) represents a light-transmitting state (object non-detection). Such a state output h is supplied to the output circuit 19, and an amplified reliable output z is generated.

  Before describing the actual circuit operation (independent of the light projecting side) on the light receiving side in the above embodiment, forcible synchronization with the light projecting side is not performed, but inconvenience when performing the same periodic operation independently of each other explain. The same periodic operation means that the period of receiving light signals between the channels from the first optical axis to the fourth optical axis by the photodiodes PH0, PH1, PH2, and PH3 is the light emission between the channels of the light projecting element. The period is the same as the period T, and the period from the fourth optical axis light receiving period to the first optical axis light receiving period is 2T. Therefore, as shown in FIG. 5, when the trigger setting period of the monostable multivibrator 18 is set to 7T which is 1T longer than the total period 6T on the light projecting side, the light emission timing on the light projecting side and the light reception signal capturing timing on the light receiving side are coincidental. Is also synchronized.

  In this example, the light receiving side element PH0 is shielded from light at the first (A) cycle, incident light at the next (B) and (C) cycles, and then from the light at the (D) cycle. . Photodiodes PH0, PH1, PH2, and PH3 are incident as long as the light emission signals of LEDs 0 to LED3 are at a level capable of receiving and receiving light under the synchronous / total light incident conditions, but are most sensitive to the light of the opposing LEDs. However, it becomes smaller as it goes away diagonally. This appears in the strength of the peak waveforms of 0, 1, 2, and 3 in (A) to (D) of the PH0, PH1, PH2, and PH3 columns in FIG.

  First, in the period (A) portion of the time chart, since PH0 is blocked from the optical axis, the counter 17 only counts 3 by PH1, PH2, and PH3, and does not output. In the period (B), all the photodiodes are incident on the optical axis, and the Q3 output g of the counter 17 is emitted. Using this Q3 output g as a trigger signal, the monostable multivibrator 18 operates to generate an output z.

  Even in the period (C), all the photodiodes are incident on the optical axis, the Q3 output g of the counter 17 is emitted, and the monostable multivibrator 18 is retriggered as it is. Since PH0 is shielded again in the next period (D), the Q3 output g of the counter 17 is not generated, and when the 7T retrigger output of the monostable multivibrator 18 that ends soon is turned off, the output from the output circuit 19 The output z also disappears.

  Eventually, the state where the light projecting side and the light receiving side are synchronized means that the light projection pulse train for one round of the optical axis is within a light reception allowable period defined by the timing signal c (low) to the timing input C of the analog multiplexer 15. Is a match. This light reception possible period is slightly wider than the series interval of the projection pulse train (in this case, four), but when performing the same periodic operation without forced synchronization with the projection side, as described above, The probability of accidental synchronization is very low, and the condition that the probability of synchronization is very low will not change even if a search is made immediately at another timing if the synchronization is not performed when both the ON states are complete. In view of this point, in the present embodiment, the light reception pause period of the light reception period signal is changed by ½ (= τ) of the projection pulse train interval T, so that even if the start point is not synchronized, it is within a certain time. The synchronization state is always obtained.

  In the embodiment of the light receiving side circuit of FIG. 4 described above, the timing input A of the multiplexer 15 is supplied from the dividing and timing circuit 12 in this case by 5.5T time, that is, 5T by low / high every T time, The basic timing a of the light-receiving period signal consisting of ½T = τ time high is supplied, and the timing input B is divided by two to respond only to the low / high duration signal within T ≦ b <2T time in the basic timing a. A low / high signal (b in the inequality) is supplied, and the timing input C combines the basic timing a and the irregular divide-by-two low / high signal b as described above, and a light receiving tolerance period (low) consisting of 4T. ) And a light receiving pause period (high) of 1.5T are supplied alternately.

  Such a light reception period signal has a phase independent of the light projection period signal and a time length clearly different. As described above, the light reception pause period may not be 1.5T but may be 2.5T longer by 0.5T than the light projection pause period 2T, or another arbitrary time width difference may be given.

  FIG. 6 is a time chart generated by the light receiving side circuit of FIG. 4, and it is assumed that the photodiodes PH0, PH1, PH2, and PH3 are all in the light incident state. In the first period (E) of this time chart, the light reception signal and the light reception allowable period c low transmitted to the multiplexer 15 do not coincide with each other, so that only the three optical axes can be extracted as the light reception signal d from the multiplexer 15. However, since the light reception suspension period is 1.5T, which is shorter by 0.5T than the light projection suspension period 2T, the light reception signal of the four optical axes matches the timing of the multiplexer 15 in the periods (F) and (G), and each light reception allowable period. In the c row, the received light signals d and e for the four optical axes can be taken out.

  However, in the next period (H), the timing is shifted and the last PH3 light reception signal of the four optical axes overlaps with the light reception pause period c high, so that the peak of the light reception output d from the multiplexer 15 does not appear. Therefore, the Q3 output g of the counter 17 is not generated, and the monostable multivibrator 18 is not retriggered. In this case, since the monostable multivibrator 18 is retriggered by the Q3 output g of the counter 17 in the immediately preceding cycle (G), the high state indicating the absence of object is maintained for the trigger setting period from that point. Become.

  According to the present invention, the trigger setting period of the monostable multivibrator 18 is set to the least common multiple N = the integer N1 = 12 determined from the light projection period 6T = 12τ and the integer N2 = 11 determined from the light reception period 5.5T = 11τ. The number of times 144 [τ] obtained by adding N1 = 12 to 132, and therefore 72 times the period T between the optical axes. That is, the predetermined light projecting cycle 6T and the predetermined light receiving cycle 5.5T that overlap in a certain phase relationship always reproduce the phase relationship after (N / 2) T = 66T. Thus, a cycle in the same state as the substantially synchronized cycles (F) and (G) appears.

  Here, the substantially synchronized state in the period (G) in FIG. 6 is that the fourth optical axis barely remains in the light reception allowable period c low, and only the period (F) is substantially synchronized with a slight difference. If not, it can happen well. In such a case (not retriggered in period G), the trigger setting period of the monostable multivibrator 18 is set to (N / 2) T = 66T, and the stable state is reached in the next specific phase period (F′≈F). When the signal is returned to (low), the Q3 output g of the counter 17 overlaps with this return and chattering is likely to occur. Therefore, as described above, the trigger setting period of the monostable multivibrator 18 is 72T by adding (N1) T / 2 = 6T to (N / 2) T = 66T.

  While the state triggered by object non-detection continues for 72T, if the light-emitting side and the light-receiving side synchronize properly in the cycle immediately before the end (66T elapses), if the object is not detected at this time, it is monostable. The multivibrator 18 is retriggered and tries to continue this state for 72T. Conversely, if the object is not triggered by detecting the object at this time, the monostable multivibrator 18 is in a standby state, and if the object is not detected (all-optical bearing light) in the light emitting / receiving synchronous cycle that regularly arrives every 66T. As described above, the monostable multivibrator 18 is triggered.

  In the example described above, the period between the optical axes is set to a constant value T as shown in FIG. 3, and the interval from the last optical axis to the first optical axis is set to 3T. FIG. 7 shows the LED light emission timing in the embodiment from the timing pulse signal t of FIG. 3 and the step outputs Q0 to Q3 of the shift register 4, and the light emission pulse time t = 2 μ [seconds] with 4 optical axes. ], T = 10 μ [seconds].

When the above time value is adopted, the response speed is: 10μ × 66 (= 6T × 11) = 660μ [sec]
It becomes. However, practically, for noise countermeasures, the output is turned on only when the light is continuously received three times, and the output is turned off only when the light is continuously blocked three times. Accordingly, the actual response speed is 660 μ × 3 = 1.986 [milliseconds], and it is possible to cope with a sufficiently high-speed inspection line or the like.

  As a modification of the above embodiment, the periods between the optical axes may be different. In the example shown in FIG. 8, the second period T1 is 1.5 times that of the first period T, the third period T2 is 2.0 times, and the return time to the first period is T. It is a thing. As in the basic example of FIG. 7, in this modification, the light projection pulse is a rectangular wave or a substantially rectangular wave having a time width t, but the light projection waveform W is turned on / off at a high frequency as shown in FIG. It may be a repeated burst wave.

As described above, “beat synchronization” of the multi-optical axis photoelectric switch in the present invention means that the light receiving side that independently detects and receives the light projection by the pulse train from the light projecting side is the light projecting period TM1 = 1 / f1, The phenomenon of coincident light reception at least once (one period) within the beat cycle 1 / f _b = αTM1 = βTM2 obtained from the relationship of beat frequencies f _b = f1 to f2 occurring in the light receiving cycle TM2 = 1 / f2. It is used to operate synchronously.

  Therefore, in the present invention, the synchronous operation state between the corresponding light projecting element and the light receiving element is set to the beat cycle without providing a synchronization line between the light projecting side and the light receiving side or an optical axis dedicated for synchronization. Therefore, the circuit configuration is simple and can be manufactured at low cost.

  On the contrary, as long as the light projecting element arrays in the relationship of nf1 = f2 or f1 = nf2 (where n = 1 or greater) are driven independently from each other, the two are spatially close to each other or are opposed to each other Even if it is, the periodic and continuous synchronization relationship (beat synchronization) is a congested multiple that must maintain a beat synchronization relationship that is independent of each other while being close by using the condition that it never holds The industrial utility value is extremely high, such as the installation of a pair of photoelectric switch systems.

2 is a timing chart illustrating the principle of the present invention. It is a circuit block diagram by the side of the light projection in the Example of this invention. FIG. 3 is a time chart diagram of a basic part in the circuit block of FIG. 2. It is a circuit block diagram on the light receiving side in the embodiment of the present invention. In the light receiving side circuit block shown in FIG. 4, the time chart of each part on the light receiving side is shown in order to show inconvenience when it is assumed that the same periodic operation is performed although it is not forcibly synchronized with the light emitting side. is there. In the light receiving side circuit block shown in FIG. 4, in order to show the inconvenience when the timing is set so as to synchronize with the light emitting side naturally and periodically in accordance with the technical idea of the present invention, a time chart of each part on the light receiving side is shown. FIG. It is the time chart which obtained the light projection timing in the Example of this invention from the basic time chart of FIG. FIG. 8 is a time chart when the period between the optical axes in the time chart of FIG. 7 is varied as a modification of the embodiment. FIG. 8 is a time chart when the projection waveform W is a burst wave that repeats on / off at a high frequency according to the projection timing of FIG. 7. It is a perspective view which shows the outline of a structure of the wiring synchronous type (A) and optical synchronous type (B) in the conventional multi-optical axis wide type photoelectric switch.

Explanation of symbols

P Light emission pulse La Light emission period Lb Light emission pause period Ra Light reception period Rb Light reception pause period Rc Storage time TM1 Light emission period TM2 Light reception period 1 Reference oscillation circuit 2 Frequency division and timing circuit 3 Inverter 4 Shift register 5 AND gate 6 Light emission Optical element array LED0, LED1, LED2, LED3 Light emitting diode 11 Reference oscillation circuit 12 Frequency division and timing circuit 13 Light receiving element array PH0, PH1, PH2, PH3 Photodiode 14 Amplifier array 15 Analog multiplexer 16 Comparator 17 Up counter 18 Monostable multi Vibrator 19 output circuit

Claims (1)

A multi-optical axis transmission type photoelectric switch for detecting passage of an object,
A plurality of light emitting elements;
A plurality of light receiving elements arranged to face the plurality of light projecting elements;
Based on a light projection period TM1 (= 1 / f1, f1: light projection frequency) composed of a light projection period composed of a light projection pulse train having a number of pulses corresponding to the number of optical axes, and the light projection pause period, the light projecting element A light-emitting circuit that sequentially and repeatedly emits light,
A light receiving period TM2 composed of a light receiving pulse train generated at the same interval corresponding to the light emitting pulse train and a light receiving cycle TM2 (≠ nTM1 or ≠ TM1 / n, where n is an integer greater than or equal to n: 1, TM2 = 1 / f2, f2: light receiving frequency), a light receiving side circuit that repeatedly receives a light receiving signal from the light receiving element,
Difference f between light projection frequency f1 and light reception frequency f2 _b Beat cycle determined by 1 / f _b In (= αTM1 = βTM2), when the light projection pulse train and the light reception pulse train are synchronized at least once and a light reception signal is received corresponding to each of the light reception pulse trains, a pulse signal that lasts longer than the beat cycle is output. And a light receiving side circuit that
A multi-optical axis transmission type photoelectric switch that detects the passage of an object based on the presence or absence of the pulse signal.

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