JP2001221859A - Reflection light modulating type detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the erroneous operation due to the noise of continuous high frequency in a reflection light modulating type detector. SOLUTION: A light-emitting element projects the light modulated according to the pulse signal generated from an oscillation circuit 21. If an object 29 exist there, reflected light is incident on a light receiving element 24 and light receiving output is selected by a BPF 34 and amplified by an AC amplifier 25, to be compared with a reference level by a comparator before inputted to a signal detection circuit 31 and a noise detection circuit 32. The light- receiving output is sampled with a timing shifted from the light-emitting timing of the light-emitting element 23 in the noise detection circuit 32. The matter 29 is detected, on the basis of the detection signal from the signal detection circuit 31, and the absence of the matter 29 is decided on the basis of the noise signal from the noise detection circuit 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection-type light-modulation type detector for projecting pulse-modulated light from a light emitting element and detecting the presence or absence of an object reflecting the projected light according to whether or not to receive reflected light. Related to the device.

[0002]

2. Description of the Related Art Conventionally, photodetectors such as photointerrupters have been widely used for detecting the presence or absence of an object. The light detection device has a light emitting element and a light receiving element, and is arranged so that light from the light emitting element is projected on the light receiving element. When an object is present between the light emitting element and the light receiving element, A transmission type that detects objects by blocking light,
Usually, the light-receiving element is arranged so as not to receive the light from the light-receiving element, and the light-emitting element is roughly classified into a reflection type in which the object is detected by receiving the reflected light when the object is present by the light-receiving element.

[0003] JP-A-62-222130 and JP-A-62-241383 disclose a modulated light receiving type photosensor for receiving pulse-width modulated light, and a pulse light emission for projecting pulse-width modulated light. Prior arts for devices are disclosed respectively. Also, JP-A-63-03
Japanese Patent No. 7713 discloses a prior art regarding a pulse-modulated light detection circuit for receiving light subjected to pulse-width modulation. In these prior arts, performing pulse width modulation to emit light as a periodic pulse is less susceptible to disturbance light noise and power consumption than making the light emitting element of the photodetector emit light with DC power. It is shown that miniaturization is possible.

FIGS. 4 and 5 show an optical modulation type detection device disclosed in Japanese Patent Publication No. 4-7958 as FIGS. 1 and 3, respectively, and a partial configuration thereof. As shown in FIG. 4, the light modulation type detection device includes an oscillation circuit 1, a light emitting element driving circuit 2, a light emitting element 3, a light receiving element 4, an AC amplifier 5, a determination circuit 6, a synchronization detection circuit 7, and an output circuit 8. Have been. FIG. 5 shows a circuit configuration of the synchronization detection circuit 7 of FIG. The synchronization detection circuit 7 includes two D-type flip-flops (hereinafter, abbreviated as “D-FF”) 9, 10 and 2
One AND gate 11 and 12 and one OR gate 1
3 and a D-FF 15.

[0005] As shown in FIG. 4, the light emitting element 3 is driven by a light emitting element driving circuit 2 based on a pulse signal generated periodically by the oscillation circuit 1. The light projected from the light emitting element 3 is reflected directly or on an object, etc.
, The light-receiving output of the light-receiving element 4 is amplified by an AC amplifier, converted into a digital signal by a determination circuit 6, and input to a synchronization detection circuit 7. The synchronization detection circuit 7 synchronizes with the light emission pulse of the light emitting element 3 and has two different timings.
It has two detection points A and B, detects the presence or absence of disturbance light at the detection point A when the light emitting element 3 is not emitting light, and if there is disturbance light, keeps the output state immediately before and disturbs no disturbance light. Only in this case, the output from the AC amplifier 5 is taken in at the detection point B at the time of light emission.

[0006] As shown in FIG.
It has two D-FFs 9, 10, and 15. First D-FF
The timing pulse signal of the detection point A is input to the clock terminal CL of No. 9. The timing pulse signal at the detection point B is input to the clock terminal CL of the D-FF 10. The detection point A is a timing shifted from the light emission timing of the light emitting element 3, and the detection point B
Is the timing that matches the timing at which the light emitting element 3 emits light.

FIG. 6 shows the timing of the signals of the respective sections assuming that the light modulation type detection device shown in FIGS. 4 and 5 is operated as a reflection type. The light emitting element 3 projects light on a pulse at a constant cycle according to the light emission signal of (a). Since there is no reflective object, the light projected from the light emitting element 3 does not enter the light receiving element 4 because there is no reflective object. However, as shown in FIG. 6B, there is a case where disturbance light is present. The disturbance light may be a synchronous high frequency that matches the timing of the light emission signal, or an asynchronous high frequency that does not match the light emission signal. As shown in (C), an output from the AC amplifier 5 is obtained corresponding to the synchronous high frequency and the asynchronous high frequency, and is binarized by the determination circuit 6 and supplied to the synchronous detection circuit 7. In the synchronization detection circuit 7, a noise detection circuit using the D-FF 9 and a signal detection circuit using the D-FF 10 are formed. When a signal detection gate signal synchronized with the light emission signal as shown in FIG. 6D is given to the clock terminal CL of the D-FF 10 which is a signal detection circuit, a signal detection output is output for a synchronous high frequency of disturbance light. can get. The clock terminal CL of the noise detection circuit by the D-FF 9 is
As shown in the figure, a noise detection gate signal whose timing is shifted from the emission signal is supplied. From D-FF9, FIG.
The noise detection output shown in (g) is obtained corresponding to the asynchronous high frequency of the disturbance light. Although a signal detection output is obtained as shown in FIG. 6E by the one-shot synchronous high-frequency disturbance light, such a single disturbance light can be ignored by providing an integrating circuit or the like. When there is no reflective object, the output of the output circuit 8 is L as shown in FIG.
Keep ow level. When there is a reflective object, FIG.
The light emission signal shown in FIG.
The output of the AC amplifier 5 shown in (c) is also obtained corresponding to the light emission signal. Since the output of the AC amplifier is synchronized with the signal detection gate signal shown in FIG. 6D, a signal detection output is obtained as shown in FIG. 6E, and the output of the output circuit 8 shown in FIG. The output becomes High level.

[0008] The prior art relating to the light modulation type detection device includes:
Japanese Patent Publication Nos. 3-39640, 4-53395, 4-33397, and 4-7
No. 0807 is also disclosed. Tokuhei 4-533
Japanese Patent Publication No. 95, Japanese Patent Publication No. 4-33397, Japanese Patent Publication No. 4-33397
Japanese Patent Publication No. 70807/1992 discloses a technique disclosed in Japanese Patent Publication No. 4-7958.
The signal detection and the noise detection as disclosed in Japanese Patent Application Laid-Open No. H11-157572 are performed at different timings, and the effects of noise are hardly affected when the respective changes are determined.
In the prior art disclosed in Japanese Patent Publication No. 3-39640, a switching circuit is provided between a light receiving element and an AC amplifier so that the light receiving output maintains a constant level at a timing other than the light emission timing of the light emitting element. It is composed.

In the synchronous light modulation type detection device as shown in FIGS. 4 and 5, the light is incident at a timing other than the timing of the gate signal of the D-FF 10 which is a signal detection gate circuit for detecting the light receiving output from the light receiving element 4. Although high-frequency disturbance light is detected by the D-FF 9 as a noise signal detection gate circuit, when light enters the light receiving element 4 at the detection timing of the noise signal detection gate, the signal detection gate is set by the D-FF 15. It holds the output value that is the result of the circuit determination. In recent years, many fluorescent lamps and the like that emit light by an inverter method are used in many cases, and a method of continuously emitting high-frequency light is used in the inverter-type fluorescent lamp. For this reason, when continuous high-frequency light from an inverter-type fluorescent lamp or the like is incident on the reflection type light modulation type detection device, the amount of light exceeds the determination reference level of the determination circuit 6,
The noise detection output is continuously obtained from the D-FF 9 which is the noise signal detection gate circuit, and the output as the synchronization detection circuit 7 maintains the output before the inverter light enters.

[0010]

As shown in FIG. 6, while the output is high with a reflective object present,
When a continuous high-frequency wave is incident as disturbance light, a High-level output corresponding to the presence of a reflective object is continuously derived even if the reflective object disappears. For example,
When there is no continuous high frequency light such as inverter light,
When a detection object such as paper is passed in front of the reflection type light modulation type detection device, the light from the light emitting element 3 is reflected by the detection object during the passage, and the reflected light enters the light receiving element 4 to be in a detection state. . After the detection object has passed, the light from the light emitting element 3 is not reflected, is not incident on the light receiving element 4, and is in a non-detection state. However, in a state where continuous high-frequency light such as inverter light is incident on the light receiving element 4 as disturbance light, a detection object such as paper is passed between the disturbance light and the reflection type light modulation type detection device. At this time, during the passage, the light from the light emitting element 3 is reflected by the detection object, and the light enters the light receiving element 4 to be in a detection state. After the detection object has passed, the light from the light emitting element 3 is not reflected, and the light is not incident on the light receiving element 4, but the disturbance light is incident on the light receiving element 4. This disturbance light is detected by the D-FF 9 which is a noise detection gate circuit, and the output as the synchronization detection circuit 7 maintains the detection state.

The problem of keeping the detection state even without such a detected object is described in Japanese Patent Publication Nos. 4-7958, 4-53395, 4-33397 and 4-70807. In the prior art disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, the same can occur. In addition, 3-396
In the prior art of Japanese Patent Publication No. 40, when continuous high-frequency disturbance light is incident on the light receiving element even when the light emission timing of the light emitting element is adjusted, it may be erroneously determined that there is a reflective object without a reflective object. There is.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reflection-type light modulation type detection device which does not cause erroneous determination even when continuous high-frequency disturbance light such as an inverter-type fluorescent lamp is incident.

[0013]

SUMMARY OF THE INVENTION The present invention is directed to an object for projecting light which is projected from a light emitting element by projecting light modulated so that the emission intensity changes periodically and the light receiving element receives reflected light. In a reflection-type light modulation type detection device that detects the presence or absence of a signal, a signal detection circuit that synchronously samples the light receiving output of the light receiving element so as to match the timing when the light emission intensity of the light emitting element is high, and derives a sampling result as a detection signal. A noise detection circuit that synchronously samples the light receiving output of the light receiving element so that the light emission intensity of the light emitting element does not overlap with a high timing, and derives a sampling result as a noise signal, based on a detection signal from the signal detection circuit. And a determination circuit that determines the non-detection of an object based on a noise detection signal from the noise detection circuit. A reflective optical modulation type detection apparatus according to.

According to the present invention, the reflection type light modulation type detection device projects the light modulated from the light emitting element so that the light emission intensity changes periodically, and the light receiving element receives the reflected light to project the light. The presence or absence of an object that reflects light is detected. The reflection type light modulation type detection device includes a signal detection circuit, a noise detection circuit, and a determination circuit. The signal detection circuit synchronously samples the light receiving output of the light emitting element so as to match the timing when the light emitting intensity of the light emitting element is high, and derives a sampling result as a detection signal. The noise detection circuit synchronously samples the light receiving output of the light receiving element so as not to overlap with the timing when the light emission intensity of the light emitting element is high, and derives a sampling result as a noise signal. The determination circuit determines the detection of the object based on the detection signal from the signal detection circuit, and determines the non-detection of the object based on the noise detection signal from the noise detection circuit. Since the object is detected by the reflection type, if the object is present, light does not enter the light receiving element, and even if continuous high-frequency disturbance light is present, it does not appear in the light receiving output from the light receiving element. If the object disappears, high-frequency noise is detected at a timing when the light emission intensity of the light emitting element is increased or at a timing different from the timing. That is, when noise is detected by the noise detection circuit, it can be determined that there is no object, and even if high-frequency noise from an inverter fluorescent lamp or the like is continuously incident, no erroneous determination is made that there is no object. You can do so.

Further, in the present invention, when the noise detection signal from the noise detection circuit indicates reception of reflected light to the light receiving element, the detection signal from the signal detection circuit reflects the reflected light to the light receiving element. Is characterized in that the determination of non-detection of the object is performed even when the light reception is performed.

According to the present invention, the non-detection of an object is determined by giving priority to the detection signal from the signal detection circuit in determining that the object does not exist based on the noise detection signal from the noise detection circuit. Can be quickly determined to change the determination result.

In the present invention, the determination circuit may reflect the change in the determination result only when the detection signal from the signal detection circuit continuously represents the same sampling result for a preset number of times or more. Features.

According to the present invention, when the detection signal is continuously represented by the signal detection circuit for the preset number of times or more, the same sampling result is reflected in the change of the determination result. The influence can be removed and a reliable determination can be made.

Further, in the present invention, the determination circuit reflects the change of the determination result only when the noise signal from the noise detection circuit continuously represents the same sampling result for a preset number of times or more. Features.

According to the present invention, the change in the determination result is reflected only when the noise detection signal from the noise detection circuit continuously represents the same sampling result for a preset number of times or more, so that the noise detection is reliably performed. be able to.

Further, the present invention provides a driving signal generating circuit for generating a driving signal for driving the light emitting element by modulating the light emitting element with a preset pulse width so as to increase the light emitting intensity; Synchronizing with the drive signal, the signal detection circuit is configured to sample the light-receiving output of the light-receiving element at the same timing as the timing at which the light emission intensity increases in the light-emitting element or at a timing delayed by the signal delay time. And a gate signal generation circuit provided to

According to the present invention, the light emitting device is driven by modulating the light emitting intensity with a preset pulse width so as to increase the light emitting intensity, and the same timing or the signal delay time as the timing when the light emitting intensity becomes higher in the light emitting device. The light receiving output of the light receiving element can be sampled and detected by the signal detection circuit at the timing delayed by the above.

Further, in the present invention, the gate signal generating circuit comprises:
The noise detection circuit generates a gate signal for sampling a light reception output of the light receiving element at a timing different from a gate signal to be supplied to the signal detection circuit, and supplies the gate signal to the noise detection circuit.

According to the present invention, the noise detection circuit can reliably detect noise at a timing different from the timing at which the light emission intensity of the light emitting element increases.

Further, in the present invention, the drive signal generation circuit is characterized in that a ratio between a pulse width for increasing the light emission intensity of the light emitting element and a pulse period can be adjusted.

According to the present invention, since the ratio between the pulse width and the pulse period for increasing the light emitting element in the light emitting element can be adjusted, the ratio that makes the light emitting element less susceptible to noise in accordance with the state of disturbance light or the like. Can be adjusted.

According to the present invention, the light receiving output of the light receiving element is compared with a preset reference level, and when the light receiving output is lower than the reference level, the light receiving output is not input to the signal detection circuit and the noise detection circuit. A comparison circuit is further included.

According to the present invention, the light receiving output of the light receiving element is compared with a reference level set in advance by a comparing circuit, and
When the level is lower than the reference level, the signal is not input to the signal detection circuit and the noise detection circuit. Therefore, even if weak disturbance light enters the light receiving element, the light can be prevented from being affected.

Further, in the present invention, the comparison circuit is characterized in that a reference level at which the light receiving output is not input to the signal detection circuit and the noise detection circuit can be separately adjusted.

According to the present invention, since the reference level at which the comparison circuit compares the received light output can be separately adjusted by the signal detection circuit and the noise detection circuit, a reference level suitable for signal detection and noise detection is set. Thus, the object can be reliably detected.

Further, the present invention further comprises a band-pass filter for filtering the light-receiving output of the light-receiving element with a pass frequency band characteristic matching the frequency at which the light-emitting intensity of the light-emitting element changes. .

According to the present invention, the light receiving output of the light receiving element is
Since the light is filtered by a band-pass filter having a pass frequency band characteristic that matches the frequency at which the light emission intensity of the light emitting element changes, it is possible to reduce the influence of low-frequency disturbance light or the like.

[0033]

FIG. 1 shows a schematic configuration of a reflection type light modulation type detection apparatus 20 as one embodiment of the present invention. In the reflection type light modulation type detection device 20 of the present embodiment, the light emitting element driving circuit 22 is configured to change the light emitting element driving circuit 22 based on a pulse signal oscillated by the oscillation circuit 21 which is a driving signal generating circuit, such as a light emitting diode, which is abbreviated as LED. Is electrically driven to project pulse-modulated light. A light receiving element 24 such as a photodiode or a phototransistor is arranged at a position shifted from a direction in which light from the light emitting element 23 is projected. When light enters the light receiving element 24, a light receiving output corresponding to the light intensity is electrically derived, amplified by the AC amplifier 25, and input to the comparator 26. In the comparator 26, which is a comparison circuit, a reference level set in advance and the AC amplifier 2
The input level of the light receiving signal amplified in step 5 is compared, the light receiving output below the reference level is ignored, and only the light receiving output exceeding the reference level is given to the signal processing circuit 27 for binarization.
The signal processing circuit 27 processes the comparison result from the comparator 26 based on the oscillation output of the oscillation circuit 21. The output of the signal processing circuit 27 is output to the outside via an output circuit 28, and indicates whether or not an object 29 that reflects light exists between the light emitting element 23 and the light receiving element 24.

In the signal processing circuit 27, a judgment circuit 30,
A signal detection circuit 31, a noise detection circuit 32, and a gate signal generation circuit 33 are included. The determination circuit 30 determines whether the object 29
Is determined for the presence or absence of The signal detection circuit 31 samples the light receiving output from the light receiving element 24 at the timing when the light emitting element 23 is driven by pulse modulation and the light emission intensity increases, and derives a sampling result as a detection signal. The noise detection circuit 32 samples the received light output from the light receiving element 24 at a timing different from the timing when the light emission intensity from the light emitting element 23 increases, and derives the sampling result as a noise detection signal. The gate signal generation circuit 33 generates a gate signal for performing sampling in the signal detection circuit 31 and the noise detection circuit 32 based on the pulse signal from the oscillation circuit 21, and outputs the gate signal to the signal detection circuit 31 and the noise detection circuit 32, respectively. give. The determination circuit 30 determines the presence or absence of the object 29 based on the detection signal and the noise signal from the signal detection circuit 31 and the noise detection circuit 32. The signal representing the determination result from the determination circuit 30 is provided to the output circuit 28 and to the comparator 26.

The comparator 26 has a hysteresis characteristic at the reference level, and after changing from a state where there is no detection signal to a certain state, lowers the reference level for judging that there is no detection signal, and the light emitting element 23 and the light receiving element 24 The output chattering caused by the minute vibration of the object 29 passing through the optical path between them is prevented. Further, a bypass filter (hereinafter, abbreviated as “BPF”) 34 is inserted between the light receiving element 24 and the AC amplifier 25. The pass frequency band of the BPF 34 is
In accordance with the frequency of the pulse signal generated from the oscillation circuit 21, signal components outside the pass frequency band are removed, thereby making it less susceptible to disturbance noise. In the oscillation circuit 21, the pulse width and cycle of the pulse signal can be adjusted by the adjuster 35. By adjusting the ratio between the pulse width and the pulse period by the adjuster 35, the object 29 can be detected in a state where it is hardly affected by disturbance light or the like. In addition,
The pulse width is, for example, about 8 μS (125 kHz frequency), and the pulse cycle is, for example, 130 μS (frequency 7.7).
kHz). This is comparable to current light modulation type detection devices. Most of the current inverter fluorescent lamps have a frequency of 30 kHz to 60 kHz. Therefore, if this frequency region is avoided, the influence of the inverter fluorescent lamp can be reduced. In particular, since the pulse width is the pulse period of signal detection, the BPF3
4 can be set to a frequency avoiding the frequency band of the inverter fluorescent lamp, and the influence of disturbance light can be reduced.

FIG. 2 shows a configuration of the signal detection circuit 31 and the noise detection circuit 32 shown in FIG. The signal detection circuit 31 and the noise detection circuit 32 include an AND gate 40, a shift register 41, a count setting register 42, and a comparison circuit 4.
3 is included. The shift register 41 includes the comparator 2
The light receiving outputs from 6 are taken in according to the gate signal supplied from the gate signal generating circuit 33 and sequentially shifted. In the number-of-times setting register 42, the number of times of changing the state when the light reception output continuously gives the same sampling result is set. The comparison circuit 43 compares the state of the input to the shift register 41 with the value set in the number-of-times setting register 42. If the comparison results match, the shift register 4
1 is cleared by the clear signal. Hereinafter, a description will be given on the assumption that 3 is set in the number-of-times setting register 42 in the signal detection circuit 31 and 2 is set in the noise detection circuit 32.

FIG. 3 shows the relationship between signals of various parts in the reflection type light modulation type detection device 20 of the embodiment shown in FIGS. 1 and 2 in the operation corresponding to the passage of the object 29 in the presence of disturbance light. Is shown. FIG. 3A shows a light emission signal from the light emitting element 23. The light emitting element 23 is driven by the light emitting element drive circuit 22 based on a pulse signal generated periodically by the oscillation circuit 21, and projects light corresponding to the pulse signal of the oscillation circuit 21 onto a pulse. Even if disturbance light as shown in FIG. 3B is incident without a reflecting object, low-frequency disturbance light is A
It is removed by the C amplifier 25 and does not appear in the AC amplifier output shown in FIG. Even if the signal appears at a low level, the signal can be removed by the comparator 26 if it is lower than the reference level of the comparator 26. The low-frequency disturbance light is not detected by the signal detection gate signal and the noise detection gate signal shown in FIGS. 3D and 3F, and is not detected by the signal detection output shown in FIG. ) Is not output as the noise detection output shown in FIG.
The output of FIG. 3H, which is the output of L, indicates the non-detection state.
Keep ow level.

The disturbance light as shown in FIG.
When the light enters the light receiving element 24 as a synchronous high frequency at the High level timing of the light emission signal shown in FIG.
The signal cannot be removed by the PF 34, the AC amplifier 25, and the comparator 26, and is input to the signal detection circuit 31 and the noise detection circuit 32 as an AC amplifier output shown in FIG. Since the output of this AC amplifier matches the timing of the signal detection gate signal shown in FIG.
From the signal detection circuit 31, a signal detection output shown in FIG. Since the timing does not match the noise detection gate signal shown in FIG.
2 does not derive the noise detection output shown in FIG. However, the signal detection output shown in FIG.
3 (h), the output shown in FIG.
The w level is maintained.

When the asynchronous high frequency wave shown in FIG. 3B is incident on the light receiving element 24 as disturbance light, A shown in FIG.
The signal is input to the signal detection circuit 31 and the noise detection circuit 32 as a C amplifier output. Since the timing of the AC amplifier output is different from the timing of the signal detection gate signal shown in FIG. 3D, the signal detection output shown in FIG. 3E does not appear. Since the AC amplifier output has the same timing as the noise detection gate signal shown in FIG. 3 (f), the noise detection output is derived as shown in FIG. 3 (g).
Even if the noise detection output is derived, the output shown in FIG. 3H does not change because the output at the Low level indicates that the object 29 is not detected. Moreover, in this case, unless the noise detection output is input twice in succession, the determination result does not change, and in any case, the output shown in FIG. 3H maintains the Low level.

Next, when there is a reflective object, the disturbance light is blocked by the reflective object and does not enter the light receiving element 24, and the pulse light of the emission signal shown in FIG. The light enters the element 24. This pulse light is sampled by the signal detection gate signal shown in FIG. 3D into the output of the AC amplifier shown in FIG.
The signal detection output shown in FIG. Since the disturbance light is blocked by the object 29, the noise detection output of FIG. 3G sampled at the timing of the noise detection gate signal shown in FIG. 3F keeps the Low level.
In this case, when the signal detection output is input three times in succession, the output shown in FIG. 3H changes from the Low level to the High level, and the object 29 is detected. If there is no disturbance light shown in FIG. 3B, the state where the object 29 is deviated from the optical path between the light emitting element 23 and the light receiving element 24 and the light reflected by the object 29 is not received by the light receiving element 24 more than three times. If continuous, the output shown in FIG. 3 (h) is changed from High to Low.
And the object 29 is in a non-detection state.

In the state where the reflective object is present and the continuous high-frequency disturbance light is incident, the continuous high-frequency disturbance light is generated between the light emitting element 23 and the light receiving element 24 as shown in FIG. When present in the optical path, the light receiving element 24
, But enters the light receiving element 24 when there is no reflective object. The received light output corresponding to the continuous high frequency cannot be removed by the BPF 34, the AC amplifier 25, and the comparator 26, and since the BPF 34 has a pass frequency band, the output is hardly affected. Therefore, it is input to the signal detection circuit 31 and the noise detection circuit 32. This A
Since the output of the C-amplifier matches the signal detection gate signal shown in FIG. 3D and the noise detection gate signal shown in FIG. 3F, the signal detection output shown in FIG.
The noise detection output shown in (g) is continuously obtained. Since the noise detection output shown in FIG. 3G is obtained twice consecutively, the output shown in FIG. 3H changes from the High level to the Low level indicating the non-detection state. Thereby, as shown in FIG. 6, it is possible to avoid a malfunction such that the output continues at the High level. The reflection type light modulation type detection device 20 of the present embodiment can be suitably used for the purpose of detecting the presence / absence of paper by a copying machine or a printer, for example. If a conventional photo-interrupter is used and a copier or the like is directly installed in a place where disturbance light such as an inverter-type fluorescent lamp is easily incident, the presence of paper may be erroneously detected. On the other hand, if the reflection type light modulation type detection device 20 of the present embodiment is used, it is possible to reliably detect the presence or absence of paper and the like.

The reflection type light modulation type detection device 20 of this embodiment
Although the BPF 34 is inserted between the output side of the light receiving element 24 and the input side of the AC amplifier 25, it can be inserted at another position such as the output side of the AC amplifier 25.
Further, the influence of disturbance light having a low frequency can be removed to some extent only by cutting the DC component on the input side of the AC amplifier 25 without using the BPF 34. Further, the comparator 26
Is commonly used by the signal detection circuit 31 and the noise detection circuit 32. However, if the signal detection circuit 31 and the noise detection circuit 32 are provided separately and the reference levels can be adjusted, the input state of disturbance light In accordance with the conditions, the object 29 can be adjusted to a condition that can be detected more reliably.

Although both the signal detection circuit 31 and the noise detection circuit 32 are configured as shown in FIG. By reflecting the result in
The circuit configuration can be simplified by using only the ND gate 40. Also, the signal processing circuit 27 can be realized by a program operation of a microcomputer.

[0044]

As described above, according to the present invention, even if continuous high-frequency disturbance light enters while detecting an object by reflected light, it is detected as noise after the object disappears. In addition, since it is determined that there is no object based on the noise detection result, it is possible to realize a reflection type light modulation type detection device with less erroneous determination. As a result, it can be used as a reflective photo-interrupter for detecting the presence or absence of paper in copiers and printers. When detecting the presence / absence or the like, erroneous determination or the like can be suppressed.

Further, according to the present invention, the object detection is determined by giving priority to the noise detection result. Therefore, after detecting an object that reflects light as a reflection type light detection device, the object is detected after the object disappears. Erroneous determination due to the influence of noise can be prevented.

Further, according to the present invention, only when the detection signal continuously represents the same sampling result for a preset number of times or more, the change is reflected in the change of the determination result. Even so, the effects can be prevented.

According to the present invention, since the determination result is reflected only when the noise detection signal continuously represents the same sampling result for a preset number of times or more, the noise detection signal is generated only once due to disturbance or the like. Is input, the result of the determination is not changed, and the noise can be reliably detected.

Further, according to the present invention, since the gate signal can be supplied to the signal detection circuit at the timing when the light emission intensity is increased by optically modulating the light emitting element, the signal detection can be reliably performed.

Further, according to the present invention, since the gate signal is supplied to the noise detection circuit at a timing different from the timing when the light emission intensity of the light emitting element is increased, the noise can be reliably detected.

Further, according to the present invention, since the ratio between the pulse width and the pulse period for increasing the light emission intensity of the light emitting element can be adjusted, it is possible to prevent the light emitting element from being affected by disturbance light.

Further, according to the present invention, the light receiving output of the light receiving element is compared with a predetermined reference level. When the light receiving output is lower than the reference level, the light receiving output is not supplied to the signal detection circuit and the noise detection circuit. Even small levels of input can be ignored.

Further, according to the present invention, since the reference level at which the light receiving element does not provide the light receiving element with the signal detecting circuit and the noise detecting circuit can be separately adjusted, the object can be detected efficiently and the influence of the noise can be improved. Can be adjusted to make it less susceptible.

Further, according to the present invention, since the light receiving output of the light receiving element is filtered using the band-pass filter, it is possible to easily remove noise of a component deviating from a frequency at which the light emitting intensity of the light emitting element increases.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic electrical configuration of a reflection type light modulation type detection device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a signal detection circuit 31 and a noise detection circuit 32 of FIG.

FIG. 3 is a time chart showing operation timings of respective parts of the reflection type light modulation type detection device 20 of FIG.

FIG. 4 is a block diagram showing a schematic electrical configuration of a conventional light modulation type detection device.

FIG. 5 is a block diagram illustrating a configuration of a signal processing circuit 27 of FIG. 4;

FIG. 6 is a time chart showing operation timing of each unit of the light modulation type detection device of FIG. 5;

[Explanation of symbols]

 REFERENCE SIGNS LIST 20 reflection type light modulation type detection device 21 oscillation circuit 23 light emitting element 24 light receiving element 25 AC amplifier 26 comparator 27 signal processing circuit 29 object 30 determination circuit 31 signal detection circuit 32 noise detection circuit 33 gate signal generation circuit 34 BPF 35 adjuster 42 Count setting register

Claims (10)

[Claims] 1. A reflection type light for projecting light modulated so that a light emission intensity changes periodically from a light emitting element, and receiving a reflected light by a light receiving element to detect the presence or absence of an object reflecting the projected light. In a modulation type detection device, a light detection output of a light receiving element is synchronously sampled so as to coincide with a timing at which a light emission intensity of a light emitting element is high, and a signal detection circuit for deriving a sampling result as a detection signal; A noise detection circuit that synchronizes sampling so that the light emission intensity of the light emitting element does not overlap with a high timing, and derives a sampling result as a noise signal, and determines detection of an object based on a detection signal from the signal detection circuit. A determination circuit for determining whether or not an object is detected based on a noise detection signal from the noise detection circuit. Output device. 2. The method according to claim 1, wherein the detecting circuit receives the reflected light to the light receiving element when the noise detection signal from the noise detecting circuit indicates the reception of the reflected light to the light receiving element. The reflection-type light-modulation-type detection device according to claim 1, wherein the determination of non-detection of the object is performed even when the expression is expressed. 3. The method according to claim 1, wherein the determination circuit reflects the change in the determination result only when the detection signal from the signal detection circuit continuously represents the same sampling result for a preset number of times or more. 3. The reflection type light modulation type detection device according to claim 1, wherein 4. The method according to claim 1, wherein the determination circuit reflects the change in the determination result only when the noise signal from the noise detection circuit continuously represents the same sampling result for a preset number of times or more. The reflection type light modulation type detection device according to claim 1. 5. A driving signal generating circuit for generating a driving signal for driving the light emitting element by modulating the light emitting element with a predetermined pulse width so as to increase the light emitting intensity, and a driving signal from the driving signal generating circuit. A gate for synchronizing and providing a gate signal to the signal detection circuit so as to sample the light receiving output of the light receiving element at the same timing as the timing at which the light emission intensity increases in the light emitting element or at a timing delayed by the signal delay time. 5. The reflection type light modulation type detection device according to claim 1, further comprising a signal generation circuit. 6. The gate signal generating circuit generates a gate signal for sampling the light receiving output of the light receiving element by the noise detecting circuit at a timing different from a gate signal supplied to the signal detecting circuit. 6. The reflection type light modulation type detection device according to claim 5, wherein the reflection type light modulation type detection device is provided to a detection circuit. 7. The reflection type light according to claim 5, wherein the drive signal generation circuit is capable of adjusting a ratio between a pulse width for increasing a light emission intensity of the light emitting element and a pulse period. Modulation type detector. 8. A comparison circuit for comparing a light receiving output of the light receiving element with a preset reference level, and, when the light receiving output is lower than the reference level, a comparator circuit which does not input the light receiving output to the signal detection circuit and the noise detection circuit. The reflection type light modulation type detection device according to claim 1, further comprising: 9. The reflection type light according to claim 8, wherein the comparison circuit can separately adjust a reference level at which the light reception output is not input to the signal detection circuit and the noise detection circuit. Modulation type detector. 10. The apparatus according to claim 1, further comprising a band-pass filter for filtering a light receiving output of the light receiving element with a pass frequency band characteristic matching a frequency at which a light emission intensity of the light emitting element changes. 10. The reflection-type light modulation type detection device according to any one of claims 9 to 9.