JP3012579B2 - Horizontal synchronization signal generation method, laser optical unit, and image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a horizontal synchronizing signal generation system, a laser optical unit, and an image forming apparatus.
In particular, the present invention relates to a horizontal synchronizing signal generation method used for image formation by an electrophotographic method using a laser beam, a laser optical unit, and an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a horizontal synchronizing signal generation method of a laser beam used for forming an electrophotographic image is used for detecting a laser beam by using a photosensor and aligning a writing position of the laser beam on a photosensitive member. When the power of the laser scanning light changes, the width of the pulse signal obtained from the output of the photosensor changes, and an intermittent change in the image position called jitter occurs.

FIG. 4 is a block diagram showing a conventional technique. The polygon mirror 21 rotates and the laser oscillator 2 rotates.
The laser beam output from 3 is reflected, and the laser beam 24 is scanned on the photoconductor 1. The photosensor 30 installed next to the photoconductor 1 on the path of the laser scanning light outputs a signal when the laser beam passes. Comparator 31
Thus, an output obtained by comparing the output level of the photosensor 30 with the output potential of the reference voltage circuit 32 is used as the horizontal synchronizing signal 46 as it is.

Since the host controller determines the print data transmission timing in synchronization with the pulse edge of the horizontal synchronization signal 46, the output of the photo sensor 30 is output as shown in FIG.
5C, the horizontal synchronizing signal 46 output from the comparator 31 becomes a wide pulse as shown in FIG. 5C1. Conversely, when the output of the photo sensor 30 is small as shown in FIG.
Is as shown in FIG. 5 (c2). FIG.
As shown in (1) and FIG. 5 (c2), the horizontal synchronization signals 46 obtained from the two cases have the same center position, but the upper controller synchronizes at the edge of the pulse. Using either of the falling edges causes a shift in the synchronization position.

In order to prevent the occurrence of the synchronization shift, it is necessary that the signal output from the photosensor 30 always has the same waveform. However, it is difficult due to fluctuations in the output of the irradiated laser beam and variations in the characteristics of the photosensor. Met.

Japanese Patent Application Laid-Open No. 4-366978 proposes a method for preventing a synchronization shift due to a variation in laser beam output and a variation in characteristics of a photosensor. A horizontal synchronizing signal generating circuit that compares a detection output of the photosensor with a reference voltage and generates a horizontal synchronizing signal that determines an image recording position, and a pulse that converts the horizontal synchronizing signal output from the horizontal synchronizing signal generating circuit into a voltage A width-voltage conversion circuit;
A voltage holding circuit for holding the output voltage of the pulse width-voltage conversion circuit, and a reference voltage generating circuit for changing a reference voltage applied to the horizontal synchronizing signal generating circuit according to the output voltage of the voltage holding circuit. Configuration.

[0007]

The above-described conventional horizontal synchronizing signal generation method has a problem that jitter occurs due to a synchronization deviation due to fluctuations in the output of an irradiated laser beam and variations in the characteristics of a photosensor. there were.

On the other hand, in the method proposed in Japanese Patent Application Laid-Open No. 4-36697, jitter is improved, but there is a problem that the circuit becomes complicated.

An object of the present invention is to provide a horizontal synchronizing signal generating method for improving jitter by using a simple circuit and a laser optical unit having the horizontal synchronizing signal generating method.

[0010]

According to the horizontal synchronizing signal generation method of the present invention, in a horizontal synchronizing signal generation method of a laser beam used for forming an electrophotographic image, a sensor output for detecting a scanning position of the laser beam is set to a reference voltage and A pulse output is generated by comparison, and a horizontal synchronization signal is generated based on a middle point of the pulse width of the pulse output.

A horizontal synchronizing signal generating method according to the present invention is a horizontal synchronizing signal generating method for a laser beam used for forming an electrophotographic image. A voltage circuit, a comparator that compares the output of the sensor with the output of the reference voltage circuit and outputs a pulse signal, and generates a horizontal synchronization signal based on an intermediate point of the pulse width of the pulse signal output by the comparator. And a pulse generator that performs the operation.

A horizontal synchronizing signal generating method according to the present invention is a horizontal synchronizing signal generating method for a laser beam used for forming an electrophotographic image. A voltage circuit, a comparator that compares the output of the sensor and the output of the reference voltage circuit and outputs a pulse signal, and a measurement that outputs a value that is half the pulse width of the pulse signal output by the comparator A counter that sets a value output from the measuring device in synchronization with the trailing edge of the pulse signal to an initial count value and outputs a signal when a predetermined count value is reached, and a counter that synchronizes with the output of the counter. And a pulse generator for outputting a pulse signal.

In the horizontal synchronizing signal generation method according to the present invention, the comparator outputs a theoretical value 0 when the output potential level of the sensor is higher than the output of the reference voltage circuit, and outputs a theoretical value 1 when the output potential level is lower than the reference voltage circuit. The measuring device measures the time when the theoretical value of the output signal of the comparator is 0 from the falling edge of the pulse signal output by the comparator, and outputs a half value of the measured value. At the moment when the theoretical value of the pulse signal output from the comparator is inverted from 0 to 1, the count of the timer may be started using the output value of the measuring device as an initial count value.

A laser optical unit according to the present invention is a laser optical unit used for forming an electrophotographic image, wherein a laser beam output from a laser oscillator is scanned on a photosensitive member and a sensor output for detecting a scanning position of the laser beam is provided. A pulse output is generated in comparison with a reference voltage, and a horizontal synchronization signal is generated based on a middle point of a pulse width of the pulse output.

An image forming apparatus according to the present invention is an image forming apparatus for forming an image by an electrophotographic method, wherein a laser beam output from a laser oscillator is scanned on a photosensitive member,
A pulse output is generated by comparing a sensor output for detecting the scanning position of the laser beam with a reference voltage, and a horizontal synchronizing signal is generated based on an intermediate point of a pulse width of the pulse output.

[0016]

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an electrophotographic image forming apparatus using a laser beam.

The surface of the photosensitive member 1 is charged by the charger 2. The laser optical unit 3 receives the image signal 4 and irradiates the photoconductor 1 with a laser beam to form a latent image on the photoconductor 1. The developing device 5 develops the latent image on the photoconductor 1 to form a toner image. The paper 6 is fed from a paper feeding unit 7 and a toner image is transferred by a transfer unit 8. The toner remaining on the photoreceptor 1 without being transferred is cleaned by a cleaner 9. The toner image transferred to the paper 6 is fixed by the fixing device 10. A heat roller is generally used for fixing. The paper 6 on which the toner image has been fixed and the image formation has been completed is discharged out of the apparatus by the discharge unit 11.

Such an electrophotographic image forming apparatus is used for a printer, a plotter, a copying machine, a facsimile machine and the like. In the case of a printer or a plotter, the image signal 4 is print data from a computer as a host device. In the case of a copying machine, the image signal 4 is read data of a document reading unit. In the case of a facsimile machine, the image signal 4
Is facsimile reception data.

FIG. 2 shows the photosensitive member 1 and the laser optical unit 3
FIG. The laser optical unit 3 includes a polygon mirror 21, a polygon motor 22, a laser oscillator 23, and a horizontal synchronization signal generator 25. Horizontal synchronization signal generator 25
Are a photosensor 30, a comparator 31, a reference voltage circuit 32, a measuring instrument 33, a counter 34, and a pulse generator 35.
including.

A laser oscillator 23 outputs a laser beam toward a polygon mirror 21 rotated by a polygon motor 22, and the laser beam 24 reflected by the polygon mirror 21 scans the photosensitive member 1. The photo sensor 30 on the path of the laser scanning light is installed at a position just before the laser beam 24 starts scanning on the photoreceptor 1, and outputs a signal when the laser scanning light passes. The comparator 31 compares the output of the photo sensor 30 with the output of a reference voltage circuit 32 that outputs a signal of a constant potential level, and outputs a negative pulse signal. The measuring device 33 measures the pulse width from the comparator 31 from the falling edge, and outputs a half value thereof. The counter 34 sets the value from the measuring instrument 33 as the initial value of the count in synchronization with the rising edge of the output pulse of the comparator 31, and outputs a signal when the count value reaches the determined value. The pulse generator 35 is a counter 3
4 and outputs a pulse signal in synchronization with the output.

Next, the operation of the laser optical unit 3 will be described. FIG. 3 is a signal time chart showing an output signal of each block in FIG.

The polygon mirror 21 reflects the laser beam output from the laser oscillator 23 while rotating, and scans the photoconductor 1 with the laser beam 24. Photosensor 30 installed next to photoconductor 1 on the path of laser scanning light
Outputs a signal as shown in FIG. 3B at the moment when the laser scanning light passes. The reference voltage circuit 32 outputs a signal as shown in FIG. The comparator 31 compares the output of the photosensor 30 with the output level of the reference voltage circuit 32. When the potential level of the output of the photosensor 30 becomes higher than the reference voltage as shown in FIG. 0 is output, and otherwise, the theoretical value 1 is output.

The measuring device 33 measures the time when the theoretical value of the signal output from the comparator 31 is 0 from the falling edge of the output signal of the comparator 31, and halves the measured value.
The value of is output. The counter 34 inputs the value from the measuring device 33 and sets it as the initial value of the count. However, the counter 34 does not start counting while the theoretical value of the signal output from the comparator 31 is 0. At the moment when the theoretical value of the signal output from the comparator 31 is inverted from 0 to 1, the counter 34 starts counting by using the input value from the measuring device 33 at that moment as an initial count value. Here, the value output from the measuring device 33 to the counter 34 is the measured output pulse width T of the comparator 31.
When the theoretical value of the signal output from the comparator 31 is inverted from 0 to 1, the counter 34 counts up to the middle point of the output pulse of the comparator 31 shown in FIG. Counting is started, and it is equal to the state where counting has been continued until this moment. Thereafter, the counter 34 has a preset count value T.
When the number reaches 2, the signal shown in FIG. The pulse generator 35 outputs a pulse signal having a constant width as shown in FIG.

In this embodiment, an example in which one laser optical unit is used has been described. However, when the present invention is applied to an apparatus for forming a multicolor image by providing a plurality of laser optical units, color misregistration is prevented. High quality images can be obtained.

[0025]

As described above, according to the present invention, an intermediate point of a pulse can be detected by a measuring device for measuring a pulse width and a counter formed by a photo sensor, and the pulse is independent of the edge position of the pulse which varies every scanning. Since signal processing is performed with reference to the midpoint of the pulse, there is an effect that a high-quality image can be obtained with a stable and correct synchronization signal that is not affected by the width of a signal from a photosensor that detects laser scanning light.

Even when the characteristics of the photosensor deteriorate due to aging or the like and the width of the signal output from the photosensor changes, the midpoint of the width of the pulse signal generated from the photosensor is used as a reference. Since the synchronization signal is generated, there is an effect that the printing position is not affected.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an electrophotographic image forming apparatus using a laser beam.

FIG. 2 is a configuration diagram of a photoconductor and a laser optical unit.

FIG. 3 is a signal time chart showing output signals of respective blocks in FIG. 2;

FIG. 4 is a block diagram showing a conventional technique.

FIG. 5 is a signal time chart showing output signals of each block in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoreceptor 2 Charger 3 Laser optical unit 4 Image signal 5 Developing unit 6 Paper 7 Feeding unit 8 Transfer unit 9 Cleaner 10 Fixing unit 11 Discharge unit 21 Polygon mirror 22 Polygon motor 23 Laser oscillator 24 Laser beam 25 Horizontal synchronization signal generation Unit 30 photo sensor 31 comparator 32 reference voltage circuit 33 measuring instrument 34 counter 35 pulse generator 36 horizontal synchronization signal

Claims (15)

(57) [Claims] In a method for generating a horizontal synchronization signal of a laser beam used for forming an electrophotographic image, a pulse output is generated by comparing a sensor output for detecting a scanning position of the laser beam with a reference voltage, and a pulse of the pulse output is generated. A horizontal synchronizing signal generating method for generating a horizontal synchronizing signal based on a middle point of the width. 2. A sensor for detecting a scanning position of a laser beam, a reference voltage circuit for outputting a signal of a constant potential level, and an output of the sensor. And a comparator that compares the output of the reference voltage circuit and outputs a pulse signal, and a pulse generator that generates a horizontal synchronization signal with reference to an intermediate point of the pulse width of the pulse signal output by the comparator. A horizontal synchronizing signal generation method, characterized in that: 3. A sensor for detecting a scanning position of the laser beam, a reference voltage circuit for outputting a signal of a constant potential level, and an output of the sensor. A comparator that outputs a pulse signal by comparing the pulse signal with an output of the reference voltage circuit; a measuring instrument that outputs a value that is half the pulse width of the pulse signal output by the comparator; A counter that sets a value output from the measuring device to an initial count value in synchronization with the edge and outputs a signal when a predetermined count value is reached, and a pulse generator that outputs a pulse signal in synchronization with the output of the counter A horizontal synchronizing signal generation method comprising: 4. The comparator outputs a theoretical value of 0 when the output potential level of the sensor is higher than the output of the reference voltage circuit, and outputs a theoretical value of 1 when the output potential level is lower than the output of the reference voltage circuit. Is measured from the falling edge of the pulse signal output by the comparator, and outputs a half value of the measured value, and the counter outputs the value of the pulse signal output by the comparator. 4. The horizontal synchronizing signal generating method according to claim 3, wherein the counting of the timer is started at the moment when the theoretical value is inverted from 0 to 1, using the output value of the measuring device as an initial value of the counting. 5. A laser optical unit used for forming an electrophotographic image, wherein a laser beam output from a laser oscillator is scanned on a photosensitive member, and a sensor output for detecting a scanning position of the laser beam is compared with a reference voltage. A laser optical unit for generating a pulse output and generating a horizontal synchronization signal based on an intermediate point of a pulse width of the pulse output. 6. A laser optical unit used for forming an electrophotographic image, comprising: a laser oscillator for outputting a laser beam; a polygon mirror for scanning a laser beam from the laser oscillator on a photosensitive member; and a scanning position of the laser beam. A sensor to be detected, a reference voltage circuit that outputs a signal of a constant potential level, a comparator that compares an output of the sensor with an output of the reference voltage circuit and outputs a pulse signal, and the pulse signal that is output by the comparator And a pulse generator for generating a horizontal synchronizing signal based on an intermediate point of the pulse width of the laser optical unit. 7. A laser optical unit used for forming an electrophotographic image, comprising: a laser oscillator for outputting a laser beam; a polygon mirror for scanning a laser beam from the laser oscillator on a photosensitive member; and a scanning position of the laser beam. A sensor to be detected, a reference voltage circuit that outputs a signal of a constant potential level, a comparator that compares an output of the sensor with an output of the reference voltage circuit and outputs a pulse signal, and the pulse signal that is output by the comparator A measuring instrument that outputs a value of one-half of the pulse width of the pulse signal, and sets a value output from the measuring instrument in synchronization with the trailing edge of the pulse signal to an initial count value, and reaches a predetermined count value. A laser beam, comprising: a counter that outputs a signal; and a pulse generator that outputs a pulse signal in synchronization with the output of the counter. Study unit. 8. The comparator outputs a theoretical value of 0 when the output potential level of the sensor is higher than the output of the reference voltage circuit, and outputs a theoretical value of 1 when the output potential level is lower than the output of the reference voltage circuit. Is measured from the falling edge of the pulse signal output by the comparator, and outputs a half value of the measured value, and the counter outputs the value of the pulse signal output by the comparator. 8. The laser optical unit according to claim 7, wherein at the moment when the theoretical value is inverted from 0 to 1, the count of the timer is started with the output value of the measuring device as an initial count value. 9. An image forming apparatus for forming an image by an electrophotographic method, wherein a laser beam output from a laser oscillator is scanned on a photosensitive member, and a sensor output for detecting a scanning position of the laser beam is compared with a reference voltage. An image forming apparatus which generates a pulse output and generates a horizontal synchronizing signal based on an intermediate point of a pulse width of the pulse output. 10. An image forming apparatus for forming an image by electrophotography, a laser oscillator for outputting a laser beam, a polygon mirror for scanning a laser beam from the laser oscillator on a photoreceptor, and scanning of the laser beam. A sensor that detects a position, a reference voltage circuit that outputs a signal of a constant potential level, a comparator that compares an output of the sensor with an output of the reference voltage circuit and outputs a pulse signal, and a comparator that outputs a pulse signal. A pulse generator for generating a horizontal synchronizing signal based on an intermediate point of a pulse width of the pulse signal. 11. An image forming apparatus for forming an image by an electrophotographic method, a laser oscillator for outputting a laser beam, a polygon mirror for scanning a laser beam from the laser oscillator on a photoconductor, and scanning of the laser beam. A sensor that detects a position, a reference voltage circuit that outputs a signal of a constant potential level, a comparator that compares an output of the sensor with an output of the reference voltage circuit and outputs a pulse signal, and a comparator that outputs a pulse signal. A measuring device that outputs a value that is half the pulse width of the pulse signal, and a value output from the measuring device in synchronization with the trailing edge of the pulse signal is set to an initial count value and set to a predetermined count value. An image, comprising: a counter for outputting a signal when the counter reaches the signal; and a pulse generator for outputting a pulse signal in synchronization with the output of the counter. Forming equipment. 12. The comparator outputs a theoretical value of 0 when the output potential level of the sensor is higher than the output of the reference voltage circuit, and outputs a theoretical value of 1 when the output potential level is lower than the output of the reference voltage circuit. Is measured from the falling edge of the pulse signal output by the comparator, and outputs a half value of the measured value, and the counter outputs the value of the pulse signal output by the comparator. 12. The image forming apparatus according to claim 11, wherein at the moment when the theoretical value is inverted from 0 to 1, the count value of the timer is started with the output value of the measuring device as an initial count value. 13. The image forming apparatus according to claim 9, wherein the image forming apparatus is a printer. 14. The image forming apparatus according to claim 9, wherein the image forming apparatus is a copying machine. 15. The image forming apparatus according to claim 9, wherein the image forming apparatus is a facsimile machine.
3. The image forming apparatus according to 2.