JP4180714B2 - Photoelectric switch - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photoelectric switch having a function of removing DC noise and white noise.
[0002]
[Problems to be solved by the invention]
FIG. 10 shows an example of the configuration of a conventional reflective photoelectric switch. In FIG. 10, in the light projecting unit 1 constituting the photoelectric switch, a light projecting current is output from the light projecting circuit 3 to the light projecting element 4 according to the oscillation signal of the oscillation circuit 2. Pulse light is projected.
[0003]
On the other hand, in the light receiving unit 5, the light received by the light receiving element 6 is photoelectrically converted by the photoelectric conversion circuit 7, and then the light reception signal is amplified by the AC amplification circuit 8. In this case, since the received light signal includes natural light (DC noise such as ambient light), the AC amplifier circuit 8 cuts the DC noise to separate and amplify the received light signal corresponding to the pulsed light from the received light signal. To do. In the integrating circuit 9, white noise generated from the photoelectric conversion circuit 7 or the AC amplifying circuit 8 is removed by integrating the amplified signal from the AC amplifying circuit 8. In other words, since white noise can be regarded as a set of sine wave noises, white noise contained in the amplified signal can be removed by integrating the amplified signal in a time sufficiently longer than the frequency component of the white noise. is there. The comparison circuit 10 compares the output of the integration circuit 9 with a reference value to determine the magnitude of the incoming pulsed light and output a detection output.
[0004]
Here, in order to increase the sensitivity of the photoelectric switch, it is necessary to increase the amplification degree of the AC amplifier circuit 8 that performs main amplification. The upper limit of the amplification degree of the AC amplifier circuit 8 is the upper limit of the level at which the output of the AC amplifier circuit 8 is saturated due to white noise generated from the photoelectric conversion circuit 7 including the light receiving element 6. This is because even if the amplification degree of the AC amplifier circuit 8 is further increased, the output of the AC amplifier circuit 8 is saturated with white noise and the signal component is not amplified. This is because in a state where the output is saturated, it is not possible to extract a signal component corresponding to the pulsed light no matter what signal processing is performed.
[0005]
In short, the conventional photoelectric switch does not operate correctly as a photoelectric switch when the received light signal photoelectrically converted corresponding to the pulsed light is smaller than the white noise, and this state is the light receiving sensitivity of the conventional photoelectric switch. It was the limit.
[0006]
By the way, in order to increase the sensitivity of the photoelectric switch without increasing the amplification degree of the AC amplifier circuit 8, it is necessary to increase the amount of light emitted or to increase the amount of received light by using the optical system of the photoelectric switch with higher sensitivity. Although it is conceivable, in order to increase the amount of light emitted and to use a high-sensitivity optical system, it is desirable to reduce the power consumption or size of the photoelectric switch and to reduce the cost. The increase in sensitivity has reached its limit, and it is becoming difficult to extract a minute signal buried in white noise.
[0007]
Further, it is conceivable to use an AC amplifier circuit 8 having a wide dynamic range so as to increase the degree of amplification so that the output is not saturated. However, the use of such an amplifier circuit having a high degree of amplification is significant. Incurs an increase in cost. Further, since the amplification degree of the AC amplifier circuit 8 is limited, it is difficult to extract a minute signal buried in white noise.
[0008]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a photoelectric switch capable of sufficiently increasing sensitivity without being affected by noise.
[0009]
[Means for Solving the Problems]
  The photoelectric switch of the present invention is provided with a light projecting circuit that projects pulsed light at a predetermined timing, and can receive the pulsed light from the light projecting circuit and outputs a light receiving signal at a level corresponding to the amount of light received A circuit is provided, and DC noise removing means for removing DC noise included in the light receiving signal is provided, and the light receiving signal is integrated with a time constant that is a multiple of the light projecting period in synchronization with the light projecting period of the light projecting circuit. And an amplifying means for amplifying and outputting the received light signal from which the DC noise and the white noise are separated by the DC noise removing means and the integrating means. Provided with detection means for outputting detection output based on signalThe DC noise removing means integrates the received light signal from the photoelectric conversion circuit for the same period as the integrating means during the non-light-projecting period of the light projecting circuit, the integration level of the integrating means and the auxiliary level Subtracting means that outputs the difference from the integration level of the integrating means(Claim 1).
[0010]
According to such means, when the photoelectric conversion circuit receives the pulsed light from the light projecting circuit, the photoelectric conversion circuit outputs a light reception signal corresponding to the amount of received light of the pulsed light.
By the way, since the photoelectric conversion circuit receives DC light such as disturbance light in addition to the pulsed light from the light projecting circuit, although the received light signal includes DC noise, the DC noise removing means includes the received light signal. Since the included DC noise is removed, it is possible to prevent the influence of the DC noise included in the received light signal.
[0011]
Also, since white noise is generated from the photoelectric conversion circuit, although the received light signal includes white noise, the integrating means integrates the received light signal in synchronization with the light projecting period of the light projecting circuit. It is possible to remove the white noise contained in the signal and prevent its influence. In this case, since the time constant of the integrating means is set to a multiple of the light projection period, white noise with unstable levels can be integrated sufficiently stably.
[0012]
The amplifying means amplifies the received light signal from which the direct current noise and the white noise have been removed by the direct current noise removing means and the integrating means, so that only the true received light signal corresponding to the light emitted from the light projecting circuit is amplified. Can do. Therefore, since the amplification degree of the amplification means can be set sufficiently high, the sensitivity of the photoelectric switch can be increased.
[0013]
  And since a detection means outputs a detection output based on the amplified signal from an amplification signal, it can judge a detection state reliably based on the detection output from a detection means.
  In this case, although the integration level of the integration means includes the integration level of the DC noise included in the received light signal, the subtraction means subtracts the integration level of the auxiliary integration means from the integration level of the integration means. Thus, DC noise can be removed. That is, the auxiliary integration means integrates the received light signal from the photoelectric conversion circuit for the same period as the integration means in the non-projection period, and the integration level of the auxiliary integration means is solely due to DC noise. The DC noise can be removed by subtracting the integration level of the auxiliary integration means from the integration level. In this case, the level difference between the integration level of the integration means and the integration level of the auxiliary integration means is whether or not the integration level of the true received light signal corresponding to the pulsed light from the light projecting circuit is included. By subtracting the integration level of the auxiliary integration means from the integration level of the integration means in the subtraction means, the integration level of the true received light signal can be obtained. Therefore, the detection means can reliably determine the detection state based on the integration level obtained by the subtraction means.
[0014]
In the above means, the integrating means may comprise a hold function for holding the integration level during the non-integration period.
[0015]
According to such means, since the integration means holds the integration level during the non-integration period, the integration level does not decrease during the non-integration period. You can reach the level enough. Therefore, the detection response speed can be increased as compared with the case where the integrating means does not have a hold function.
[0018]
  Further, it is desirable that the auxiliary integration means integrates the light reception signal from the photoelectric conversion circuit immediately before the light projection period of the light projection circuit.3).
[0019]
According to such means, the auxiliary integrating means integrates the received light signal from the photoelectric conversion circuit for the same period as the integrating means in the non-light emitting period immediately before the light emitting period of the light projecting circuit, thereby integrating the auxiliary means and the auxiliary means. Since the integration level of the DC noise of the integrating means is the same level, the DC noise included in the received light signal can be effectively nullified by the subtracting means.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a block diagram schematically showing the overall configuration of the photoelectric switch. In FIG. 1, the photoelectric switch 11 includes a light projecting unit 12 and a light receiving unit 13.
[0021]
In the light projecting unit 12, the pulse generator 14 includes a light projection pulse P0 corresponding to the light projection period, a light projection synchronization pulse P1 corresponding to the integration period in the same period as the light projection pulse P0, and immediately before the light projection pulse P0. In this non-projection period, the pulse P2 immediately before the projection corresponding to the same period as the projection pulse P0 and the reading pulse P3 corresponding to the non-output period of the projection synchronization pulse P1 and the pulse P2 just before the projection are output. (See FIG. 2).
The light projecting circuit 15 outputs a light projecting current to the light projecting element 16 at the timing of the light projecting pulse P 0 from the pulse generator 14.
[0022]
On the other hand, in the light receiving unit 13, the photoelectric conversion circuit 17 outputs a light reception signal at a level corresponding to the amount of light received by the light receiving element 18. In this case, the photoelectric conversion circuit 17 has a function as a mere voltage follower, or a function as a buffer amplifier having an amplification degree that does not saturate the output due to white noise generated in the light receiving element 18 or DC noise due to disturbance light. It is configured as follows.
[0023]
The first integration hold circuit 19 (corresponding to the integration means) integrates the light reception signal from the photoelectric conversion circuit 17 during the input period of the light projection synchronization pulse P1 from the pulse generator 14 and non-input period of the light emission synchronization pulse P1. Holds the integration level. The first integration hold circuit is provided to remove white noise contained in the light reception signal output from the photoelectric conversion circuit 17 by integrating the light reception signal. That is, the light receiving element 18 and the photoelectric conversion circuit 17 generate white noise that is thermal noise, and it becomes difficult to detect the received light signal due to the influence of the white noise. For this purpose, a first integration hold circuit 19 is provided.
[0024]
On the other hand, the second integration hold circuit 20 (corresponding to DC noise removal means and auxiliary integration means) integrates the light reception signal from the photoelectric conversion circuit 17 and projects it during the input period of the pulse P2 immediately before light projection from the pulse generator 14. The integration level is held during the non-input period of the pulse P2 immediately before light. The second integration hold circuit 20 is provided for detecting the integration level of DC noise included in the light reception signal. That is, the integration level of the first integration hold circuit 19 does not include the integration level of white noise, but still includes the integration level of DC noise due to ambient light, etc. The integration level will be described later. For this purpose, a second integration hold circuit 20 is provided. In this case, the second integration hold circuit 20 detects the integration level of the DC noise included in the light reception signal by integrating the light reception signal only during the light projection period in the non-light projection period immediately before the light projection period. Yes.
[0025]
Here, the first and second integration hold circuits 19 and 20 are configured such that the integration circuit has a hold function. This is because the signal level of the light reception signal from the photoelectric conversion circuit 17 is extremely small, and therefore, when a general integration circuit is used, the signal level decreases during the non-light projection period and the integration level does not increase. It is. In this case, the time constants of the first and second integration hold circuits 19 and 20 are set to be a multiple of the light projection period. This is because the signal level of white noise containing various frequency components is unstable, so when such white noise is integrated with an integration hold circuit with a short time constant, the integration level fluctuates greatly and is stable. This is because the voltage level at the hold timing of the integration hold circuit fluctuates every time and an accurate integration level cannot be output. Therefore, in the first and second integration hold circuits 19 and 20 of the present embodiment, the time constant is set to be a multiple of a multiple of the light projection period. White noise containing frequency components can be integrated while being sufficiently averaged.
[0026]
A subtraction circuit 21 (corresponding to DC noise removing means and subtraction means) subtracts the integration level of the second integration circuit hold circuit 20 from the integration level of the first integration circuit hold circuit 19. That is, since the integration level of the first integration hold circuit 19 still includes DC noise due to ambient light or the like, the subtraction circuit 21 causes the second integration from the integration level of the first integration circuit hold circuit 19. It is provided to subtract the integration level of the circuit hold circuit 20 to remove the integration level of DC noise and obtain only the integration level of the true light reception signal.
[0027]
An amplifier circuit 22 (corresponding to an amplifying means) amplifies the output of the subtraction circuit 21. In this case, since the output from the subtracting circuit 21 is based on a true light reception signal that is not affected by white noise and DC noise, the amplification degree of the amplification circuit 22 is set high or variable to an arbitrary amplification degree. It can be configured to be adjustable.
[0028]
The reading circuit 23 latches the output amplified by the amplifier circuit 22. The reading circuit 23 can be provided as necessary.
The comparison circuit 24 (corresponding to detection means) compares the output from the amplification circuit 22 with a specific reference value, and outputs a detection output according to the magnitude relationship.
[0029]
FIG. 3 shows a specific example of the electric circuit having the configuration shown in FIG. In FIG. 3, the photoelectric conversion circuit 17 is configured by connecting an inverting amplification circuit 29 including an operational amplifier 26 and resistors 27 and 28 to a common connection point between a resistor 25 and a light receiving element 18 as illustrated.
[0030]
The first integration hold circuit 19 is configured by connecting an analog switch 30 and an integration circuit 33 including a resistor 31 and a capacitor 32 as illustrated. In this case, the analog switch 30 passes the light reception signal from the photoelectric conversion circuit 17 at the input timing of the light projection synchronization pulse P1 from the pulse generator 14. The integration circuit 33 integrates the light reception signal from the photoelectric conversion circuit 17 according to the time constants of the resistor 31 and the capacitor 32.
[0031]
The second integration hold circuit 20 is configured by connecting an analog switch 34 and an integration circuit 37 including a resistor 35 and a capacitor 36 as illustrated. In this case, the analog switch 34 allows the light reception signal from the photoelectric conversion circuit 17 to pass at the input timing of the pulse P2 immediately before light projection from the pulse generator 14. The integration circuit 37 integrates the light reception signal from the photoelectric conversion circuit 17 according to the time constants of the resistor 35 and the capacitor 36.
[0032]
The subtraction circuit 21 includes a first non-inverting amplifier circuit 41 including an operational amplifier 38 and resistors 39 and 40, and a second non-inverting amplifier circuit 45 including an operational amplifier 42 and resistors 43 and 44 as illustrated. Connected and configured. The first non-inverting amplifier circuit 41 amplifies the integration level of the first integration hold circuit 19 with a predetermined magnification corresponding to the ratio of the resistance values of the resistors 39 and 40. The second non-inverting amplifier circuit 45 has a predetermined magnification based on the difference between the output level of the first non-inverting amplifier circuit 41 and the output level of the second integration hold circuit 20 and the ratio of the resistors 43 and 44. The integration level of the second integration hold circuit 20 is amplified.
[0033]
Here, the subtraction circuit 21 is a well-known circuit using two non-inverting amplifier circuits. That is, the first non-inverting amplifier circuit 41 amplifies the integration level V1 of the first integration hold circuit 19 to 2V1 if the values of the resistors 39 and 40 are the same. The second non-inverting amplifier circuit 45 has the same resistances 43 and 44 based on the level difference between the output voltage 2V1 from the first non-inverting amplifier circuit 41 and the integration level V2 of the second integration hold circuit 20. If so, the integration level V2 of the second integration hold circuit 20 is amplified to 2 (V2 -V1). Therefore, the subtraction circuit 21 can be configured by the first and second non-inverting amplifier circuits 41 and 45.
[0034]
The amplifier circuit 22 is composed of an inverting amplifier circuit 49 including an operational amplifier 46 and resistors 47 and 48, and amplifies the input voltage in a state where the polarity is inverted at a predetermined magnification according to the ratio of the resistance values of the resistors 47 and 48. And output.
[0035]
The reading circuit 23 is configured by connecting an analog switch 50, a capacitor 51, and an operational amplifier 52 as illustrated. The analog switch 50 passes the signal in synchronization with the read pulse P3 from the pulse generator 14. The capacitor 51 integrates and holds the signal level that has passed through the analog switch 50.
[0036]
The comparison circuit 24 is configured by connecting an operational amplifier 53 and a variable resistor 54 as shown in the figure, and outputs a detection output when the input voltage signal exceeds the reference level of the variable resistor 54.
[0037]
Next, the operation of the above configuration will be described.
The pulse generator 14 outputs a projection pulse P0, a projection synchronization pulse P1, a just before projection P2, and a reading pulse P3 at the timing shown in FIG.
Accordingly, pulse light is projected from the light projecting element 16 of the light projecting circuit 15 at a timing corresponding to the light projecting pulse P0 (see FIG. 4A).
[0038]
Now, when the pulsed light projected from the light projecting element 16 is reflected by the object to be detected, the light receiving element 18 of the photoelectric conversion circuit 17 receives the pulsed light, so that the photoelectric conversion circuit 17 responds to the pulsed light. A light reception signal is output (see FIG. 4E).
[0039]
At the timing when the light projection pulse P0 is output from the pulse generator 14, the analog switch 30 of the first integration hold circuit 19 is turned on by the light projection synchronization pulse P1, so that the light reception signal from the photoelectric conversion circuit 17 is the first. The integration circuit 33 of the integration hold circuit 19 integrates for the light projection period. At this time, since the analog switch 30 is turned off in the state where the output of the light projection synchronization pulse P1 is stopped, the integration level of the integration circuit 33 is held.
[0040]
By the way, since the received light signal from the photoelectric conversion circuit 17 includes white noise which is thermal noise, the first integration hold circuit 19 is configured to remove the white noise as follows.
[0041]
That is, white noise is irregular because noises of various frequencies overlap from high frequency noise of sine wave (see FIG. 4B) to low frequency noise of sine wave (see FIG. 4C). (See FIG. 4D). For this reason, the true light reception signal (see FIG. 5E) output from the photoelectric conversion circuit 17 in response to the reception of the pulsed light is buried in white noise, and the light reception signal from the photoelectric conversion circuit 17 is irregular. Thus, it is difficult to discriminate the true received light signal (see (f) in the figure).
[0042]
However, since the light reception signal from the photoelectric conversion circuit 17 is obtained by superimposing white noise on the true light reception signal, the white noise is averaged over a period sufficiently longer than the frequency component, and the white noise is averaged and invalidated. Can be Therefore, when the first integration hold circuit 19 integrates the received light signal from the photoelectric conversion circuit 17 in synchronization with the multiple light emission synchronization pulses P1, white noise is generated from the output of the first integration hold circuit 19. Will be removed.
[0043]
However, although the white noise included in the light reception signal from the photoelectric conversion circuit 17 can be removed as described above, the light reception signal includes DC noise due to ambient light in addition to the white noise. (Refer to FIG. 4 (g)) The influence of DC noise is prevented as follows.
[0044]
That is, in the second integration hold circuit 20, the analog switch 34 is turned on by the pulse P2 immediately before light projection output from the pulse generator 14 prior to the light projection pulse P0, so that the light reception signal from the photoelectric conversion circuit 17 is integrated. The circuit 37 integrates and holds. At this time, at the output timing of the pulse P2 immediately before the light projection, the light reception signal from the photoelectric conversion circuit 17 does not include a true light reception signal, but only white noise and DC noise. Here, since the white level is removed from the integration level of the second integration hold circuit 20 in the same manner as the first integration hold circuit 19, the output of the second integration hold circuit 20 is eventually the integration level of the DC noise. (See FIG. 4 (h)).
[0045]
Therefore, in the subtraction circuit 21, the DC noise can be removed by subtracting the integration level of the second integration hold circuit 20 from the integration level of the first integration hold circuit 19 (see FIG. 4 (i)). ).
[0046]
As described above, the output of the subtracting circuit 21 is based on a true light receiving signal corresponding to the pulsed light received by the light receiving element 18, so that the output is amplified by the amplifying circuit 22, thereby causing white noise and direct current. The received light signal can be amplified with a sufficiently large amplification without being affected by noise.
[0047]
In the reading circuit 23, since the reading pulse P3 is given at the timing when the first and second integration hold circuits 19 and 20 are not operating, impedance conversion is performed with the integration level held by the subtraction circuit 21 held at that timing. And output. In this case, the output of the reading circuit 23 is held until the next reading pulse P3 is given.
[0048]
The comparison circuit 24 outputs a detection output at a predetermined level when the output from the reading circuit 23 exceeds the reference level.
Therefore, the presence / absence of the detected object can be determined based on the detection output from the comparison circuit 24.
[0049]
Since the signal level of the light reception signal from the photoelectric conversion circuit 17 is extremely small, the light reception signal becomes a large level when the amplification degree of the amplifier circuit 22 is set large in accordance with such a small light reception signal. In some cases, the output of the amplifier circuit 22 is saturated, so that when a wide range of received light signal levels is to be processed, the amplification degree of the amplifier circuit 22 can be arbitrarily adjusted to match the received light signal size. Thus, it is desirable to perform amplification at a desired amplification degree.
[0050]
According to such an embodiment, the received light signal from the photoelectric conversion circuit 17 is integrated in the first integration hold circuit 19 in synchronization with the light projection pulse P0, thereby removing white noise contained in the received light signal. The subtraction circuit 21 subtracts the integration level of the second integration hold circuit 20 from the integration level of the first integration hold circuit 19 to remove DC noise contained in the integration level of the first integration hold circuit 19. Thus, the amplification circuit 22 can amplify only the integration level of the true light reception signal received by the light receiving element 18 in accordance with the pulsed light. Accordingly, the dynamic range of the amplifier circuit 22 can be increased to amplify the received light signal with a sufficient size, so that the dynamic range of the amplifier circuit cannot be sufficiently increased by amplifying in a state including white noise. Unlike the example, a highly sensitive photoelectric switch with high amplification can be manufactured.
[0051]
In this case, since the time constants of the first and second integration hold circuits 19 and 20 are set to a plurality of times of the light projection period, white noise is sufficiently canceled as compared with the case where the time constant is small. And the effect of white noise can be effectively nullified.
[0052]
In the second integration hold circuit 20, the received light signal from the photoelectric conversion circuit 17 is integrated and held at the timing immediately before the light projection pulse P0. Therefore, the integration of DC noise by the first integration hold circuit 19 is performed. The level and the integration level due to the DC noise of the second integration hold circuit 20 can be matched well, and the influence due to the DC noise can be effectively nullified.
[0053]
  (referenceForm)
  Next, the present inventionreference5 to FIG. 7, the same parts as those in the first embodiment are denoted by the same reference numerals, description thereof is omitted, and only different parts are described. thisreferenceThe feature of this embodiment is that an AC amplifier circuit is provided as a DC noise removing means. Note that the reading circuit 23 used in the first embodiment is omitted.
[0054]
FIG. 5 is a block diagram schematically showing the overall configuration of the photoelectric switch. In FIG. 5, the pulse generator 14 outputs a projection pulse P0 having a predetermined period and outputs a projection synchronization pulse P1 synchronized with the projection pulse P0 (see FIG. 6). The light projecting circuit 15 projects pulsed light according to the light projecting pulse P0.
[0055]
The light reception signal from the photoelectric conversion circuit 17 is amplified by the AC amplification circuit 55. Since the AC amplifier circuit 55 is configured to amplify only the AC signal, DC noise can be removed in the AC amplifier circuit. In this case, the amplification degree of the AC amplifier circuit 55 is set to be low. This is because the white noise generated from the light receiving element 18 is an AC signal composed of various frequency components and is therefore amplified by the AC amplifier circuit 55. Therefore, when the amplification degree of the AC amplifier circuit 55 is increased. , White noise will be amplified. For this reason, depending on the amplification degree of the AC amplifier circuit 55, the output is saturated due to the amplified white noise and collapses from the AC waveform. Therefore, the white noise that has collapsed from the AC waveform in this way is removed by the integration hold circuit. This is because even if integration is performed, white noise cannot be removed.
[0056]
The integration hold circuit 56 integrates the received light signal during the input period of the projection synchronization pulse P1 from the pulse generator 14 and holds the integration level during the non-input period of the projection synchronization pulse P1.
The operations of the amplifier circuit 22 and the comparison circuit 24 are the same as those in the first embodiment. The amplifier circuit 22 is configured as a two-stage amplifier.
[0057]
FIG. 7 shows the light receiving portion 13 of the photoelectric switch 11 shown in FIG. In FIG. 7, an AC amplifier circuit 55 is connected to the photoelectric conversion circuit 17 including a resistor 25 and a light receiving element 18. That is, the AC amplifier circuit 55 is configured by connecting an inverting amplifier circuit 61 in which an operational amplifier 57 and resistors 58 to 60 are connected as shown in the figure to the photoelectric conversion circuit 17 via a coupling capacitor 62. The coupling capacitor 62 cuts DC noise due to disturbance light received by the light receiving element 18.
[0058]
The integration hold circuit 56 includes an analog switch 63, an integration circuit 66 composed of a resistor 64 and a capacitor 65, and a voltage follower 69 composed of an operational amplifier 67 and a resistor 68 as shown in the figure. White noise is removed from the integration level of the integration hold circuit 56 by integrating and holding the received light signal from the photoelectric conversion circuit 17 at a timing according to the pulse P0.
[0059]
The amplification circuit 22 amplifies the integration level of the integration hold circuit 56, and the comparison circuit 24 compares the integration level with the reference level to output a detection output.
[0060]
  thisreferenceAccording to the embodiment, since the DC noise included in the light receiving signal output from the photoelectric conversion circuit 17 is removed by the AC amplifier circuit 55, the influence of the DC noise is prevented with a simple configuration of the AC amplifier circuit 55. be able to. Further, since the received light signal supplied to the integration hold circuit 56 does not include DC noise, it is not necessary to configure a subtraction circuit, and the entire configuration can be simplified.
[0061]
  (No.2Embodiment)
  Next, the first of the present invention2The embodiment will be described with reference to FIG. 8. The same reference numerals are given to the same parts as those of the first embodiment, and the description will be omitted. This first2The feature of this embodiment is that the first and second integration hold circuits of the first embodiment are configured as an integration circuit.
[0062]
That is, FIG. 8 shows the photoelectric conversion circuit 17, the first and second integration hold circuits 19, 20 and the subtraction circuit 21 shown in the first embodiment. In FIG. 8, discharge resistors 70 and 71 are connected in parallel to the integration circuits 33 and 37 constituting the first and second integration hold circuits 19 and 20, respectively. The resistance values of the discharge resistors 70 and 71 are set to be extremely large, and the hold function can be sufficiently exhibited while the first and second integration hold circuits 19 and 20 are configured as integration circuits.
[0063]
According to such an embodiment, the first and second integration hold circuits 19 and 20 can be operated in the same manner as the integration hold circuit by configuring the integration circuit like the integration circuit. While being used, white noise contained in the received signal can be effectively removed, and an amplifier circuit with a high amplification degree that can arbitrarily adjust the amplification degree can be used.
[0064]
  (No.3Embodiment)
  Next, the first of the present invention3The embodiment will be described with reference to FIG. This first3The feature of this embodiment is that light projection pulses are output at random.
[0065]
By the way, in each said embodiment, since the light projection period of the pulsed light from the light projection element 16 is constant, the high frequency periodic alternating current noise light, for example, the light from the illumination using an inverter power supply, is light projection timing. In such a detection environment, even if white noise and DC noise are removed, the photoelectric switch may malfunction due to the influence of AC noise light.
[0066]
Here, FIG. 9 shows the output timing of each pulse from the pulse generator 14, the output of the light projection pulse P0 is set at random, and the light projection synchronization pulse P1 and the light projection according to the timing. The output timing of the immediately preceding pulse P2 is set.
[0067]
According to the present embodiment, since the pulse light is projected randomly from the light projecting element 16, the probability that the incident timing of the AC noise light coincides with the projection timing becomes extremely low, and the AC noise An object to be detected can be reliably detected without being affected by light.
[0068]
The present invention is not limited to the above embodiments, and can be modified or expanded as follows.
You may make it apply to the transmission type photoelectric switch of the type which synchronized the light projection part and the light-receiving part.
If the sensitivity of the light receiving element 18 is high, a simple voltage follower for impedance conversion may be provided without providing the photoelectric conversion circuit with a signal amplification function. In short, it is important to configure the circuit so that the output is not saturated by white noise or DC noise.
[0069]
【The invention's effect】
As is clear from the above description, according to the photoelectric switch of the present invention, the DC noise included in the received light signal is removed by the DC noise removing means, and the white noise included in the received light signal is integrated by integrating the received light signal. Since it was removed, there is an excellent effect that the sensitivity can be sufficiently increased without being affected by noise.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an overall configuration according to a first embodiment of the present invention.
FIG. 2 is a diagram showing the output timing of each pulse from the pulse generator.
FIG. 3 is an electric circuit diagram showing the overall configuration.
FIG. 4 is a waveform diagram showing output signals from each circuit.
FIG. 5 shows the present invention.reference1 equivalent diagram showing the form of
6 is a view corresponding to FIG.
FIG. 7 is an electric circuit diagram showing a configuration of a light receiving unit.
FIG. 8 shows the first of the present invention.2Electrical circuit diagram showing photoelectric conversion circuit and integration circuit in the embodiment
FIG. 9 shows the first of the present invention.3FIG. 2 equivalent diagram showing the embodiment of
10 is a view corresponding to FIG. 1 showing a conventional example.
[Explanation of symbols]
11 is a photoelectric switch, 15 is a light projection circuit, 17 is a photoelectric conversion circuit, 19 is a first integration hold circuit (integration means), 20 is a second integration hold circuit (DC noise removal means, auxiliary integration means), 21 Is a subtracting circuit (DC noise removing means, subtracting means), 22 is an amplifying circuit (amplifying means), and 24 is a comparing circuit (detecting means).

Claims (3)

A light projecting circuit that projects pulsed light at a predetermined timing;
A photoelectric conversion circuit which is provided so as to be able to receive pulsed light from the light projecting circuit and outputs a light reception signal at a level corresponding to the amount of light received;
DC noise removing means for removing DC noise contained in the received light signal;
Integration means for removing white noise by integrating the light reception signal with a time constant of a multiple of the light projection period in synchronization with the light projection period of the light projection circuit;
Amplifying means for amplifying and outputting the received light signal from which direct current noise and white noise have been separated by the direct current noise removing means and the integrating means;
Detection means for outputting a detection output based on the amplified signal from the amplification means ,
The DC noise removing means is
Auxiliary integration means for integrating the received light signal from the photoelectric conversion circuit only during the same period as the integration means during a non-projection period of the light projection circuit;
A photoelectric switch comprising: a subtracting means for outputting a difference between an integration level of the integrating means and an integration level of the auxiliary integrating means .   2. The photoelectric switch according to claim 1, wherein the integrating means is configured to have a hold function for holding an integration level during a non-integration period. 3. The photoelectric switch according to claim 1 , wherein the auxiliary integration unit integrates a light reception signal from the photoelectric conversion circuit immediately before a light projection period of the light projection circuit .

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