JPH0879469A - Laser scanning beam detection signal generating circuit - Google Patents

Abstract

PURPOSE: To reduce an influence caused by the fluctuation of the output of a photosensor by comparing the output of the photosensor with a signal obtained by delaying that output and further shifting its level while using a comparator. CONSTITUTION: A photosensor 1 is arranged on a laser scanning line, a signal to be outputted in the case of passing a laser scanning beam 6 through the photosensor 1 is delayed on a time base and further, its voltage level is shifted. The shifted signal is compared with the signal not to be worked from the photosensor 1 by a comparator 4 and the result is outputted. Even when the output from the photosensor 1 is deformed by any factor, the shifted signal to be compared is similarly deformed as well. Thus, its influence is suppressed a little and the fluctuation of a detection signal 7 to be provided as a result is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser scanning light detection signal generation circuit, and more particularly to a horizontal period signal generation circuit by a photosensor of a laser beam type electrophotographic printing apparatus.

[0002]

2. Description of the Related Art In a conventional laser beam type electrophotographic printer, a photosensor is prepared for generating a horizontal period signal.

Referring to FIG. 6 showing a signal generating circuit by this photosensor, this circuit includes a photosensor 1 for receiving a laser scanning light 6, a reference voltage generating circuit 5, an output of the photosensor 1 and a circuit 5. A comparator 4 for comparing the output of the constant voltage is provided, and the output of the comparator 4 is used as the laser scanning light detection signal 7.

FIG. 7A showing the circuit operation of FIG.
Referring to (b) and (c), the waveform is the output waveform of the photosensor 1 of FIG. 6, and the waveform is the reference voltage generation circuit 5
Which is the output waveform of the comparator 4, that is, the waveform of the laser scanning light detection signal 7.

In FIG. 7A, when the laser scanning light 6 passes through the photo sensor 1, the photo sensor 1 outputs a waveform signal, and the comparator 4 outputs the output of the reference voltage generating circuit 5 shown in the waveform. , The output of the photosensor 1 shown in the waveform is compared, and as shown in the waveform, when the potential level of the output of the photosensor 1 becomes higher than the reference voltage, the logical value 0 is output, and the other values are logical. The value 1 is output.

Further, a synchronizing circuit of an optical scanning device using a semiconductor laser array as a light source is disclosed in Japanese Patent Laid-Open No. 56-13777.
Referring to Japanese Patent Publication No. 0, as shown in FIG.
A comparator 20 and the like for comparing the signal obtained by amplifying the signal from 8 with the amplifier 19 with the reference voltage VS are shown.

On the other hand, referring to Japanese Unexamined Patent Publication No. 4-261562, as shown in FIG. 9, a comparator for comparing the output of the optical sensor 102 and the voltage of the reference voltage source 69 with the circuit of the multicolor image forming apparatus. A (comparator) 70 is provided.

[0008]

Since the conventional laser scanning light detection signal generating circuit of FIG. 6 described above compares the output of the photosensor 1 with the output of the reference voltage generating circuit 5,
When the output of the photo sensor 1 is reduced, the output of the comparator 4 is likely to be affected. For example, in comparison with the case of the output of the normal photosensor 1 shown in the waveform of FIG.
When the output of the photosensor 1 is small as shown in the waveform of FIG. 3, the output of the comparator 5 is as shown in the waveforms of (a) and (b), respectively, and the change of the pulse width and the timing of pulse generation are shown. And so on. This is because the output of the reference voltage generation circuit 5 to be compared is (a),
This is due to the constant voltage as shown in the waveform of (b). Further, the output of the photo sensor 1 is shown in FIG.
When it becomes extremely small as shown in the waveform of (c),
This output does not intersect with the waveform output from the reference voltage generating circuit 5, and there is a drawback in that no pulse is generated from the comparator 4 as shown in the waveform (c).

As a cause of the decrease in the output of the photo sensor 1 described above, it is considered that the characteristics of the photo sensor 1 are deteriorated, the output of the laser light is decreased, the irradiation position of the laser light is displaced, and the like.

Further, since the circuits disclosed in Japanese Patent Laid-Open No. 56-137770 and Japanese Patent Laid-Open No. 4-261562 also use a constant reference voltage, the above-mentioned pulse width change and pulse generation timing shift, Or an accident such as no pulse is inevitable.

In view of the above problems, the present invention has the following problems. (1) The pulse width of the laser scanning light detection signal and the generation timing of the pulse timing are made constant. (2) Eliminate the accident that the pulse of the laser scanning light detection signal cannot be obtained. (3) The above (1) and (2) should be achieved even if the output of the photo sensor varies due to various causes. (4) The circuit of the laser scanning light detection signal generation circuit is not complicated and has a simple configuration. (5) The design margin of this circuit is ensured so that the above problems (1) and (2) can be achieved even if the power supply voltage of the laser scanning light detection signal generation circuit varies. (6) Even if the components of the photo sensor to be configured are replaced, it is not necessary to readjust. (7) Maintenance-free, ensuring a long service life.

[0012]

According to the present invention, there is provided a photosensor for receiving a laser scanning light, a light-receiving reversal means for receiving an output of the photosensor to obtain first and second outputs, and A comparator for comparing the first output and the second output as inputs, and the light-reversing means for receiving light always has a predetermined potential difference when the photosensor does not receive light.
It is characterized by having a function of holding the second output and reversing the potential difference between the first and second outputs when receiving light.

Particularly, in the configuration of the first embodiment of the present invention, a photosensor for receiving laser scanning light, a delay circuit for delaying and outputting the output of the photosensor, and a predetermined output level of the delay circuit. It is characterized by comprising a level shift circuit that shifts by a potential and a comparator that compares the output of the photosensor and the output of the level shift circuit as inputs.

Further, in the configuration of the second embodiment of the present invention, the photosensor for receiving the laser scanning light, the low-pass filter receiving the output of the photosensor as an input, and the output level of the low-pass filter are set to a predetermined potential. And a comparator for comparing the output of the photo sensor with the output of the low pass filter as an input.

Further, in the second embodiment, the low-pass filter is a filter composed of a capacitor and a resistor, and the level shift circuit comprises a diode connected between two inputs of the comparator and a means for biasing the diode in the forward direction. It is characterized by

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the first and second embodiments of the present invention, the structure of the present invention will be described with reference to FIG. Referring to FIG. 1, the configuration of the present invention includes a photosensor 1 that receives a laser scanning light 6, a light-receiving reversal unit 30 that receives the output of the photosensor 6 to obtain first and second outputs, and And a comparator 31 for comparing the first and second outputs as inputs, and the light-reversing means 30 always holds the first and second outputs by a predetermined potential difference when the photosensor 1 does not receive light. When the light is received, it has a function of reversing the potential difference between the first and second outputs.

Therefore, for example, even if the characteristics of the photosensor 1 are deteriorated, the predetermined potential difference is always secured when light is not received, so that the comparator 31 is not inverted or malfunctions. When the photosensor 1 is replaced, the photosensor 1 has variations in characteristics, but this is also absorbed, so that readjustment is not necessary. This is because the reversing means at the time of receiving light can maintain one output at a high potential by a predetermined potential difference with reference to the voltage level of the output at the time of non-reception of the photosensor 1.

Further, even if the power supply voltage fluctuates, there is no fear of malfunction due to the above configuration.

On the other hand, only when the laser beam is received,
Since the potential difference is inverted, the pulse width and the timing of the pulse timing can be made constant.

The light receiving reversal means 30 does not receive a fixed potential as in the conventional case, but uses only the signal obtained from the photosensor 1 as a reference.

Next, a concrete circuit of the light-reception inverting means 30 will be described below as first and second embodiments.

FIG. 2 is a block diagram showing a laser scanning light detection signal generating circuit according to the first embodiment of the present invention. In FIG. 2, in this embodiment, a photosensor 1 arranged on the light beam of the laser scanning light 6, a delay circuit 2 having an output of the photosensor 1 as an input, an output of the photosensor 1 and a level shift circuit 3 are provided. And a comparator 4 that receives the output of Here, the light receiving reversal means 30 is composed of the delay circuit 2 and the level shift circuit.

The delay circuit 2 is a circuit that delays the output signal obtained by the photosensor 1 as it is. Figure 2
Referring to FIG. 3A showing the circuit operation of the above, the level shift circuit 3 is a circuit for pulling up the output of the delay circuit 2 from the input by a constant potential VL. Photo sensor 1
When there is no laser detection signal from, the output of the level shift circuit 3 is set higher than the output waveform 1 of the photosensor 1 by the constant potential VL. Therefore, the output waveform 3 of the comparator 4 has the logical value 1 Is maintained.

In FIG. 3A, the output waveform of the comparator shows a low potential, that is, a logical value 0 only during the period when the waveform has a higher potential than the waveform.

First, when the laser scanning light 6 passes through the photosensor 1, a pulse signal having a waveform is output. The delay circuit 2 delays the output of the photosensor 1 shown in the waveform and further outputs it to the level shift circuit 3.
The level shift circuit 3 level-shifts the output of the photosensor 1 delayed by the delay circuit 2 and outputs the waveform shown in the waveform. The comparator 4 compares the output waveform of the photo sensor 1 with the output waveform of the level shift circuit 3, and outputs a signal as shown in the waveform.

FIGS. 3B and 3C show the relationship among the output waveforms of the photosensor 1, the level shift circuit 3, and the comparator 4 when the output of the photosensor 1 of FIG. 1 varies. It is a waveform diagram. here,
(A) shows the case where the output of the photo sensor 1 is in a normal signal state, and (b) and (c) of the figure show the case where the output changes.

The output of the photosensor 1 changes from a normal signal state as shown in the waveform of (a) to (b) a waveform having a low peak value due to a change in the amount of laser scanning light, (c).
It is assumed that the signal waveform is changed to a signal waveform with a lower peak value as shown in the waveform of. The output of the comparator 4 at that time is
Not only does the pulse width and the pulse generation timing hardly change as shown in the waveforms (b) and (c), respectively, but also no pulse is generated. still,
Only the constant potential VL is always kept constant.

The reason why such a stable output waveform is obtained is that the two inputs of the comparator 4 are both obtained from the output of the photosensor 1. Therefore, for example, the output of the photosensor 1 varies. However, even if the photo sensor is replaced with another photo sensor, both of the two inputs change, so that the comparators 4 cancel each other out, and the output change of the detection signal 7 does not substantially occur. Further, even if the power supply voltage of this circuit fluctuates, the voltages of the two inputs also change, so that the comparators 4 cancel each other and the detection signal 7 does not change.

The configuration of this embodiment does not have the conventional reference voltage generating circuit, but only the delay circuit 2 and the level shift circuit 3 are used in place of the conventional reference voltage generating circuit, and there is an advantage that the configuration is not particularly complicated. is there.

Here, the delay circuit 2 is preferably an analog signal delay circuit, but may be a digital signal delay circuit. The level shift circuit 3 has a function of outputting a signal level that is higher than the waveform of the photosensor 1 by a constant potential VL based on the level of the output waveform of the photosensor 1 when there is no signal. A level difference that can be discriminated is required. As the comparator 4, a comparison amplifier, a differential amplifier, an operational amplifier or the like is used. A comparator having a wide dynamic range is selected as the comparator 4 so that the comparator 4 can accurately respond to a temporal change in the level of the photosensor 1 when there is no signal. The pulse width of the obtained detection signal 7 needs to be wide enough to be detected in the subsequent stage, and it is used as it is or by inverting it.

In the above embodiment, the photo sensor 1 is adapted to obtain a high level output waveform when receiving light. However, depending on the circuit configuration, a low level output waveform may be obtained. In case of level shift circuit 3
Is a constant potential VL from the level of the photo sensor 1 when there is no signal.
The circuit configuration will be lower.

FIG. 4 is a circuit diagram showing a laser scanning light detection signal generating circuit according to the second embodiment of the present invention. In FIG. 4, this embodiment shows a low-pass filter 10 and a resistor 1.
Except for the series circuit of the diodes 5 and 17 and the diode 16, it is common to the first embodiment, and the description of the common parts is omitted. The low-pass filter 10 is a CR filter,
A series circuit of a resistor and a capacitor is connected to the input end, and its common connection point serves as the output end. This output end serves as one input of the comparator 4. The common connection point of the series circuit of the resistor 15 and the diode 16 becomes the other input of the comparator 4. Further, the common connection point of the series circuit of the diode 16 and the resistor 17 serves as one input. One end 14 of the series circuit of the resistor 15, the diode, and the resistor 17 is connected to a predetermined low potential, and the other end 13 is connected to a predetermined high potential.
6 is forward biased, and this bias voltage is necessary to secure a constant potential VL. Resistors 15 and 17
Is preferably a resistance value higher than the output impedance of the photosensor 1 by one digit or more. The resistance value of the resistor 11 and the capacitance value of the capacitor 12 are appropriately selected in order to obtain a pulse output signal having a predetermined width.

Referring to FIG. 5A showing the operation of this circuit, when the waveform of the output signal of the photosensor 1 when it receives light appears at a high level, the level of the filter 10 rises exponentially, and this level rises. When the waveform of is higher than the waveform of, the output waveform of the comparator 4 becomes the high level when there is no light reception.

Referring to FIG. 5B, which shows a case where the waveform of the photosensor 1 when receiving light is reduced due to a change with time or the like, an output waveform of the filter 10 corresponding to this is obtained. The pulse width PW2 is substantially equal to the pulse width PW1 of the waveform in the case of (a).

When the waveform of the photosensor 1 when receiving light is a reverse signal, the capacitance in the filter 10 is not grounded and is biased to a high potential, the diode 16 is connected in the reverse direction, and the one end 14 and the other end 13 are connected. The bias level is also reversed.

[0036]

As described above, according to the present invention, the above problems are all solved, and the output from the sensor is processed into a signal whose time axis and voltage axis are shifted, and this is compared with the output before processing. Thus, even if the output from the sensor fluctuates, it is possible to generate a signal that is not affected by the change.

Further, the present invention is a circuit for setting the output of the photosensor when no light is received as a reference to a higher level by a predetermined potential and comparing the reference level with the set level. Even if the output of the photo sensor fluctuates due to changes in the output over time or replacement of the photo sensor, these fluctuations will cancel out, so a stable output at no light reception can be obtained at all times. A stable detection signal can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a laser scanning light detection signal generation circuit of the present invention.

FIG. 2 is a block diagram showing a first embodiment of the present invention.

3 (a), (b) and (c) are waveform charts showing the operation of the first embodiment of the present invention.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

5 (a) and 5 (b) are waveform charts showing the operation of the second embodiment of the present invention.

FIG. 6 is a block diagram showing a conventional laser scanning light detection signal generation circuit.

7 (a), (b) and (c) are waveform charts showing the operation of the circuit of FIG.

FIG. 8 is a circuit diagram showing a known example of a conventional laser scanning light detection signal generation circuit.

FIG. 9 is a block diagram showing another known example of a conventional laser scanning light detection signal generation circuit.

[Explanation of symbols]

 1 Photosensor 2 Delay circuit 3 Level shift circuit 4, 20 Comparator 5 Reference voltage generation circuit 6 Laser scanning light 7 Detection signal 10 Low pass filter 11, 15, 17 Resistor 12 Capacitance 10a, 18 Optical sensor 19 Amplifier 30 Reversing means at light reception 32 , 33 outputs 69 reference voltage source 70 comparator

Claims (5)

[Claims] 1. A photosensor for receiving laser scanning light, a light-receiving reversal unit for obtaining first and second outputs by using an output of the photosensor as an input, and a first and second outputs as inputs for comparison. The photo-inversion means always holds the first and second outputs by a predetermined potential difference when the photo sensor does not receive light, and outputs the first and second outputs when light is received. A laser scanning light detection signal generation circuit having a function of reversing a potential difference. 2. A photosensor that receives laser scanning light, a delay circuit that delays and outputs the output of the photosensor, a level shift circuit that shifts the output level of the delay circuit by a predetermined potential, and the photosensor. A laser scanning light detection signal generation circuit comprising: a comparator that compares the output of the sensor and the output of the level shift circuit as an input. 3. A photosensor for receiving laser scanning light, a low-pass filter having an output of the photosensor as an input, a level shift circuit for shifting an output level of the lowpass filter by a predetermined potential, and a photosensor of the photosensor. A laser scanning light detection signal generation circuit comprising: a comparator for comparing an output and an output of the low pass filter as inputs. 4. The laser scanning light detection signal generation circuit according to claim 3, wherein the low-pass filter is a filter including a capacitor and a resistor. 5. The laser scanning light detection signal generation circuit according to claim 3, wherein the level shift circuit comprises a diode connected between two inputs of the comparator and a means for biasing the diode in the forward direction.