JPH11115240A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately align a starting position for writing by a plurality of laser light sources in a main scanning direction. SOLUTION: In this image forming apparatus, photodetector elements 109, 110 for detecting laser lights emitted from semiconductor laser devices 107, 108 before the scanning of the laser lights in the main scanning direction, are disposed to be juxtaposed in the main scanning direction corresponding to the respective semiconductor laser devices 107, 108. In the case where each spot of the respective semiconductor laser devices 107, 108 is scanned on the corresponding photodetector element 109, 110, the other spot is not emitted thereto while a horizontal synchronizing signal is detected from the output of the photodetector element. As a result, the horizontal synchronizing signal for the plurality of spots is generated independently to each of the outputs of the plurality of photodetector elements.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam writing type image forming apparatus for performing optical writing using a plurality of light beams.

[0002]

2. Description of the Related Art In recent years, a multi-beam writing type image forming apparatus for performing optical writing using a plurality of light beams has been studied. FIG. 9 shows an example of a laser printer using such a multi-beam writing method. In FIG. 9, the laser printer 1 is connected to an external device 31 such as a computer, and prints on a recording sheet under the control of the external device 31. The external device 31 supplies various control signals and image information to the video controller 27, and the video controller 27 develops the image information into a dot image and outputs it as a video signal. The print control unit 26 is a control circuit for controlling each unit in the apparatus.

FIG. 10 shows the operation timing of the image forming apparatus shown in FIG. First, the video controller 27
When the RDY signal from the external device 31 becomes TRUE as shown in FIG. 10 (a), the PRIN signal as shown in FIG.
The T signal is set to TRUE. The print control unit 26 has a PRI
When the NT signal becomes TRUE, the drive of the main motor 23 and the polygon motor 14 is started as shown in FIGS. The photosensitive drum 17, the fixing roller of the fixing unit 9, and the discharge roller 11 are driven by the driving of the main motor 23.
Starts to rotate. Thereafter, the print control unit 26 starts the light amount control of the semiconductor laser 13 and sequentially drives the primary charger 19, the developing unit 20, and the transfer charger 21 at a high voltage.

When a time T1 elapses from the start of driving of the polygon motor 14 as shown in FIG. 10G and the rotation of the polygon motor 14 is in a steady state, the print controller 26 feeds the paper as shown in FIG. The clutch 24 is turned on to drive the paper feed roller 5 to feed the recording paper S in the paper feed cassette 2 toward the registration roller 6. Then, the print controller 26 outputs a VSREQ signal to the video controller 27 as shown in FIG. 10C at the timing when the recording paper S reaches the registration roller 6, and the paper feed clutch 24 as shown in FIG. Is turned off, and the driving of the paper feed roller 5 is stopped. On the other hand, when the video controller 27 finishes developing the image information from the external device 31 into the dot image and completes the preparation for the output of the VDO signal, the VSRE of FIG.
After confirming that the Q signal is TRUE, FIG.
As shown in (d), the VSYNC signal is set to TRUE.
Then, in synchronization with this, the time Tv as shown in FIG.
Thereafter, the output of the VDO signal is started as image data for one page.

At this time, the print control unit 26
Time T from the rising of the VSYNC signal as shown in (i).
After three, the registration roller clutch 25 is turned on, and the registration roller 6 is driven. The driving of the registration roller 6 is performed as shown in FIG.
Is performed for a period T4 before passing through. During this time, the print control unit 26 drives the semiconductor laser 13 according to the VDO signal from the video controller 27.

As described later, two semiconductor lasers 13 are provided. The print controller 26 drives each of the semiconductor lasers in accordance with the VDO signal, and laser light emitted from the two semiconductor lasers is transmitted to the scanner unit 7. The scanning is converted into a linear scan in the main scanning direction by the rotation of the polygon mirror 15, and is irradiated on the photosensitive drum 17 by the mirror 16. By scanning the two laser beams modulated in accordance with the VDO signal on the photosensitive drum 17 in this manner, a two-line latent image is formed on the photosensitive drum 17,
Thereafter, the same operation is repeated to form a one-page latent image on the photosensitive drum 17.

The latent image formed on the photosensitive drum 17 is developed by a developing device 20, and thereafter, a toner image is transferred to a recording sheet S by a transfer charger 21. When the transfer is completed, the recording paper S is conveyed to the fixing device 9 and the toner image is fixed on the recording paper S. Then, the recording paper S is discharged out of the apparatus by the discharge roller 11. When the next page is to be printed, the print control unit 26 sets the time T as shown in FIG.
After five, the PRINT signal is set to TRUE, and the same control as that for printing the first page is performed.

FIG. 11 is a plan view of the scanner unit 7. In FIG. 11, the print control unit 26 controls the scanner motor driver 201 to rotate the polygon mirror 1 at a predetermined speed. The laser light emitted from the two semiconductor lasers is a polygon mirror 15 that is constantly rotating.
And is incident on the mirror 16 through the fθ lenses 203 and 204. At this time, the laser light reflected by the polygon mirror 15 is reflected by the BD mirror 205 and detected by the BD sensor 207. The BD sensor 207 outputs a horizontal synchronizing signal to the print control unit 26 when the light amount reaches a predetermined value. The horizontal synchronization signal is used as a signal for aligning the write start position of the image signal in the main scanning direction.

Thereafter, the laser beams of the two semiconductor lasers scan in the main scanning direction with the rotation of the polygon mirror 15, and are irradiated on the photosensitive member 17 by the mirror 16. On the other hand, the print control unit 26 supplies an image signal to the laser driver 213, and drives the two lasers according to the image signals. As a result, the photosensitive member 17 is irradiated with laser light modulated in accordance with an image signal, and a two-line latent image is formed on the photosensitive member 17. Thereafter, the same operation is repeated to form a one-page latent image on the photoconductor 17.

FIG. 12 shows spots formed by two semiconductor lasers on the BD sensor 207. The two spots A and B are arranged on a straight line inclined at a predetermined angle with respect to the main scanning direction (arrow direction). This is because the spot interval in the sub-scanning direction is determined according to the pixel density, but it is physically difficult to actually reduce the spot interval in the sub-scanning direction to the same level as the pixel density. By arranging the two spots A and B of the semiconductor laser obliquely with respect to the sub-scanning direction, the spot interval in the sub-scanning direction is reduced to the pixel interval. Therefore, two spots A,
B has a certain interval in the main scanning direction.

[0011]

FIG. 13 shows a case where two spots scan on the BD sensor as shown in FIG.
The change in the amount of light on the sensor is shown. 148 indicates a change in light amount due to the preceding spot A, and 149 indicates a subsequent spot B.
This is a change in light quantity due to Here, the slit (not shown) of the BD sensor is larger than the spot interval, and the spot diameter is wider than the light emitting point on the BD sensor.
The change in the amount of light on the sensor has a continuous waveform as shown by 150.

However, the BD of such a light amount waveform
A threshold is set for the sensor output as indicated by 151 and B
When trying to obtain the D signal, the light amount waveform on the BD sensor is a continuous waveform, and therefore, only one pulse signal can be obtained as indicated by 152 in FIG. Therefore,
Conventionally, for example, a method has been adopted in which the write positions of two spots are matched by delaying a predetermined time and setting the write position of the subsequent spot with reference to the BD signal of the preceding spot. However, in such a method, for example, since there is an error in the light emitting point interval for each semiconductor laser chip, the delay time differs for each body, and it is difficult to accurately align the writing positions of the two spots in the main scanning direction. Met.

The present invention has been made in consideration of the above-described conventional problems, and has been made in consideration of the above-described conventional problems. It is intended to provide a device.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a plurality of laser light sources arranged so that each laser spot scans in a state of being shifted in the main scanning direction, and a laser emitted from each laser light source. By scanning the light in the main scanning direction with a deflector, an image forming apparatus that simultaneously forms a plurality of lines of latent images on an image carrier, the plurality of laser light sources corresponding to the plurality of laser light sources, respectively. A plurality of light detecting elements for detecting emitted laser light prior to scanning in the main scanning direction are arranged in a line in the main scanning direction, and each spot of the plurality of laser light sources corresponds to a corresponding light detecting element. During scanning, other spots are not illuminated while detecting the horizontal synchronizing signal from the output of the corresponding photodetector, so that multiple outputs can be obtained independently of the outputs of the plurality of photodetectors. It is achieved by an image forming apparatus and generating a horizontal synchronizing signal of the spot.

It is another object of the present invention to provide a deflector which comprises a plurality of laser light sources arranged so that each laser spot scans in a state of being shifted in the main scanning direction, and the laser light emitted from each laser light source is deflected. In an image forming apparatus that forms a plurality of lines of latent images on the image carrier at the same time by scanning in the main scanning direction, the image forming apparatus is arranged in the main scanning direction corresponding to the plurality of laser light sources, A plurality of photodetectors for detecting laser beams emitted from a plurality of laser light sources prior to scanning in the main scanning direction; and a plurality of photodetectors provided corresponding to the plurality of photodetectors, the output of each photodetector and each light A plurality of comparators for outputting a horizontal synchronizing signal of each spot of the plurality of laser light sources by comparing a threshold value set in accordance with the amount of spot light emitted for each detection element. It is achieved by an image forming apparatus characterized by.

[0016]

Embodiments of the present invention will be described below. FIG. 1 is a block diagram showing a main configuration of an image forming apparatus according to a first embodiment of the present invention. In addition,
The overall configuration of the device is the same as that shown in FIG. 9, and two lines are simultaneously written using two semiconductor lasers. In FIG. 1, a CPU 100 is a control circuit that performs print control of the apparatus, and controls unblanking signal generation circuits 105 and 106. Unblanking signal generation circuits 105 and 106 are semiconductor lasers 107 and 108, respectively.
Is a circuit for generating a control signal for turning on and off the light. BD sensors 109 and 110 are semiconductor lasers 107 and 108, respectively.
, And are arranged in the main scanning direction. The BD sensors 109 and 110 detect the laser beam reflected from the polygon mirror 15 in FIG. 11 before scanning in the main scanning direction, and
From the output of 110, a BD signal (horizontal synchronization signal) of the spot of the two semiconductor lasers 107 and 108 is detected.

FIG. 2 shows how spots are scanned by the semiconductor lasers 107 and 108 on the two BD sensors 109 and 110. The BD sensors 109 and 110 are juxtaposed in the main scanning direction as described above. The preceding spot A is a spot by the semiconductor laser 107,
The subsequent spot B is a spot formed by the semiconductor laser 108. Each spot is indicated by ○ and ●,
○ indicates a spot in a lighting state, and ● indicates a spot in a non-lighting state. In the present embodiment, first, two semiconductor lasers 10
When the spots 9 and 110 start scanning in the main scanning direction, the CPU 100
And the two semiconductor lasers 107 and 10
Scanning is started in a state where 8 is simultaneously turned on.

FIG. 2A shows semiconductor lasers 107 and 108.
, Spots A and B start scanning, and the preceding spot A reaches the BD sensor 109.
When the spot A reaches the BD sensor 109 in this way, a BD signal of the spot A is obtained from the output of the BD sensor 109. When the BD signal is output from the BD sensor 109, the blanking signal generation circuit 105 turns off the preceding spot A and continues scanning with only the succeeding spot B turned on as shown in FIG. . Next, as shown in FIG.
When the value reaches 0, the BD signal of the spot B is obtained from the output of the BD sensor 110.

FIG. 3 shows a change in the amount of light on the BD sensor when the lighting of the spots A and B is controlled as described above.
FIG. 3A shows a change in the light amount of the BD sensor 109, and FIG.
Represents a change in light amount of the BD sensor 110. First, FIG.
13A, reference numeral 113 denotes a light amount change according to the present embodiment,
Reference numeral 114 denotes a change in light amount when scanning is performed while two spots are simultaneously lit. In this embodiment, when the preceding spot A reaches the BD sensor 109 and a BD signal is output as described with reference to FIG. 2, the preceding spot A is turned off. The amount of light decreases in response to the turning off of. Here, FIG.
When a threshold value 115 is set to the threshold value and the output of the BD sensor 109 is compared with the threshold value 115 using a comparator (not shown), a BD signal is obtained as shown in FIG. That, B which inverted to a low level at the timing of T ₁
D signal is obtained, to start writing by spot A that precedes the T ₁ as the reference timing after a predetermined time.

In FIG. 3B, reference numeral 117 denotes a light amount waveform when scanning is performed in a state where two spots A and B are simultaneously lit, and reference numeral 116 denotes a light amount waveform according to the present embodiment. In the present embodiment, as shown in FIG. 2C, only the spot B that follows on the subsequent BD sensor 110 is turned on and scanned, so that the light quantity waveform as indicated by 116 is obtained. Here, a threshold value indicated by 118 is set, and the BD sensor 1 is
FIG. 3 (b) shows a comparison between the output value of 10 and the threshold value 118.
BD signal for inverting is obtained to a low level at the timing of T _2, as shown in. This BD signal corresponds to T _{1 in} FIG.
Falling to the low level with a delay time corresponding to the spot interval than the timing to start writing by spot B to trailing after a predetermined time as the reference timing to the timing of T _2. In this way, the writing positions of the two spots in the main scanning direction are aligned, and the writing operation in the main scanning direction is synchronized. Thereafter, each time the laser light of the two semiconductor lasers 107 and 108 scans in the main scanning direction, the BD signal of each spot is detected by the same method, and the writing start positions of the two spots are synchronized with each other on the photosensitive member. Write.

In this embodiment, since the preceding spot A reaches the corresponding BD sensor 109 and is turned off when the BD signal is output, the following spot B scans the corresponding BD sensor 110. Sometimes, only the succeeding spot is turned on and scanned, and the BD of the succeeding spot B is scanned.
The signal can be obtained independently of the BD signal of the preceding spot A. Therefore, regardless of the error of the light emitting point interval of the semiconductor laser chip, the writing position by the two spots can be accurately adjusted, and the jitter is small.
A good recorded image can be obtained. Further, since the BD sensors are arranged corresponding to the respective semiconductor lasers, it is possible to detect a failure of each semiconductor laser.

Next, a second embodiment of the present invention will be described. FIG. 4 shows the configuration of the present embodiment. 4, the same parts as those in FIG. 1 are denoted by the same reference numerals. In the present embodiment, when two spots start scanning in the main scanning direction, only the preceding spot is turned on, and when the preceding spot reaches the preceding BD sensor 109 and a BD signal is output, an unblanking signal is output. The preceding spot is turned off by the generation circuit 105, and the unblanking signal generation circuit 1
At 06, the following spot is lit. Otherwise,
This is the same as the first embodiment.

FIG. 5 shows that two spots A and B have two BDs.
The state of scanning on the sensor is shown. The preceding spot A is a spot by the semiconductor laser 107, and the following spot B is a spot by the semiconductor laser. ○ indicates a spot in a lighting state, and ● indicates a spot in a non-lighting state. In the present embodiment, two spots A and B
Starts scanning in the main scanning direction, the preceding spot A is turned on under the control of the CPU 100, and the following spot B is turned off. Scanning is started in this state, and FIG.
As shown in (a), when the preceding spot A reaches the preceding BD sensor 109, a BD signal of the spot A is obtained from the BD sensor 109. When a BD signal is output from the BD sensor 109, the preceding spot A is turned off and the succeeding spot B is turned on as shown in FIG.
Then, as shown in FIG. 5 (c), when the trailing spot B reaches the subsequent BD sensor 110, the BD sensor 110
, The BD signal of the spot B is obtained.

FIG. 6 shows a change in the amount of light on the BD sensor when the lighting of two spots is controlled as shown in FIG. FIG. 6A shows a change in the light amount of the BD sensor 109 in the preceding stage,
FIG. 6B shows a change in the light amount of the BD sensor 110 at the subsequent stage. First, in FIG. 6A, reference numeral 133 denotes a light amount change according to the present embodiment, and reference numeral 134 denotes a light amount change when two spots A and B are simultaneously lit and scanned. In the present embodiment, when the preceding spot A reaches the BD sensor 109, the preceding spot A is turned off and the succeeding spot B is turned on, so that substantially one spot is irradiated. , 133.
Here, a threshold value indicated by 135 is set, and the output of the BD sensor 109 is compared with the threshold value using a comparator. As shown in FIG.
That BD signal for inverting is obtained to a low level at the timing of T _1.

In FIG. 6B, reference numeral 136 denotes a light amount change according to the present embodiment, and 137 denotes a light amount change when two spots are simultaneously lit and scanned. In the present embodiment, only the spot B that follows is turned on to scan over the BD sensor 110 in the subsequent stage.
The light amount waveform is exactly the same as that of (b)). Therefore, when the threshold value 138 is set and the output of the BD sensor 110 is compared with the threshold value by the comparator, a BD signal corresponding to the spot B can be obtained as shown in FIG. That is, a time corresponding to the spot intervals than the timing of T _1, and after the two time intervals of scanning the BD sensor 109, 110, BD signal becomes a low level at the timing of T ₂ are obtained. As described above, also in the present embodiment, BD signals corresponding to two spots can be obtained independently, and the same effect as in the first embodiment can be obtained.

In the first and second embodiments, two spots are scanned at the same time. However, the present invention can be used for scanning more spots at the same time. For example, when scanning three spots simultaneously, the third spot is scanned after the spot B in FIG.
A third BD sensor is juxtaposed next to the sensor 110. Thereafter, when the spot B reaches the BD sensor 110 in the same manner, the light is turned off, and only the third spot is turned on to scan the third BD sensor. Thereby, the BD signal corresponding to the third spot can be obtained independently.

Next, a third embodiment of the present invention will be described. In the present embodiment, first, as shown in FIG. 7, two BD sensors 109 and 110 are arranged side by side in the main scanning direction, and two spots A and B are simultaneously turned on for scanning. 7A shows a state in which the preceding spot A has reached the preceding BD sensor 109, and FIG. 7B shows a state in which the following spot B has reached the following BD sensor 110. FIG. 8 shows changes in the light amounts on the BD sensors 109 and 110 when two spots are scanned in this way.

In this embodiment, as shown in FIG. 8, a threshold value 145 according to the light amount of one spot is set, and the output of the BD sensor 109 is compared with the threshold value using a comparator. Further, a threshold value 144 corresponding to the light amounts of the two spots is set, and the output of the BD sensor 110 is compared with the threshold value 144 by a comparator. First, as shown in FIG. 7A, when the preceding spot reaches the BD sensor 109 in the preceding stage, the threshold value 145 is set according to the light amount of one spot. A BD signal of A is obtained. That, BD signal inverted to a low level at the timing of T ₁ as shown in FIG. 8 is obtained.

Since the threshold value 144 is set according to the light amounts of the two spots, as shown in FIG.
When the two spots A and B scan the BD sensor 110 at the same time, that is, when the following spot B reaches the subsequent BD sensor 110, the BD signal of the following spot B is obtained from the output of the comparator. . That is, time corresponding to the spot interval than the timing of T _1, as shown in FIG. 8, and the BD signal for inverting the BD sensor 109, 110 to a low level at the timing of T ₂ of the following time interval in which the laser beam scans Is obtained. Also in this embodiment, the BD of two spots is exactly the same as in the first and second embodiments.
Signals are obtained independently, and the same effects as in the first and second embodiments can be obtained.

In the third embodiment, two spots are scanned at the same time, but the present invention can also be used for scanning more spots at the same time. For example, when scanning three spots simultaneously, the third spot is scanned after the spot B in FIG.
Next to 10, a third BD sensor is juxtaposed. Then, a threshold value is set according to the light amounts of the three spots, and the comparator compares the threshold value with the output of the third BD sensor. Thereby, a BD signal corresponding to the third spot can be obtained.

[0031]

As described above, according to the present invention, the horizontal synchronizing signals of the corresponding spots can be independently obtained from the outputs of the respective photodetectors, whereby the interval between the light emitting points of the semiconductor laser chip can be obtained. Irrespective of the error of the image, the write start positions of the plurality of lines in the main scanning direction can be accurately adjusted, and a high-quality recorded image with small jitter can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a diagram for explaining the operation of the embodiment of FIG. 1;

FIG. 3 shows BDs arranged in the main scanning direction in the embodiment of FIG. 1;
FIG. 4 is a diagram showing the light amount on a sensor.

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

FIG. 5 is a diagram for explaining the operation of the embodiment of FIG. 4;

FIG. 6 shows BDs arranged in the main scanning direction in the embodiment of FIG. 4;
FIG. 4 is a diagram showing the light amount on a sensor.

FIG. 7 is a diagram for explaining a third embodiment of the present invention.

FIG. 8 is a diagram showing a light amount on a BD sensor according to the embodiment of FIG. 7;

FIG. 9 is a configuration diagram showing a conventional laser printer.

FIG. 10 is a time chart for explaining the operation of the laser printer of FIG. 9;

FIG. 11 is a diagram illustrating a scanner unit of the laser printer in FIG. 9 in detail.

FIG. 12 is a diagram showing a state where two laser spots scan on a BD sensor.

FIG. 13 is a diagram showing the light amount on the BD sensor when two spots scan on the BD sensor as shown in FIG. 12;

[Explanation of symbols]

 100 CPU 105, 106 Unblanking signal generation circuit 107, 108 Semiconductor laser 109, 110 BD sensor

Claims (2)

[Claims] A plurality of laser light sources arranged so that each laser spot scans in a state shifted in the main scanning direction, and a laser beam emitted from each laser light source is scanned in a main scanning direction by a deflector. Thereby, in an image forming apparatus that simultaneously forms a plurality of lines of latent images on an image carrier, a laser beam emitted from the plurality of laser light sources is scanned in a main scanning direction corresponding to each of the plurality of laser light sources. Prior to the arrangement, a plurality of light detection elements for detection are arranged side by side in the main scanning direction, and when each spot of the plurality of laser light sources scans the corresponding light detection element,
While detecting the horizontal synchronization signal from the output of the corresponding photodetector, by not irradiating another spot, a horizontal synchronization signal of a plurality of spots is generated independently from the output of each of the plurality of photodetectors. An image forming apparatus comprising: 2. A laser scanning apparatus comprising: a plurality of laser light sources arranged so that each laser spot scans in a state shifted in a main scanning direction; and a laser beam emitted from each laser light source is scanned in a main scanning direction by a deflector. By doing so, in an image forming apparatus that simultaneously forms a plurality of lines of latent images on an image carrier, the plurality of lines are arranged in the main scanning direction in correspondence with the plurality of laser light sources, and emitted from the plurality of laser light sources. A plurality of light detecting elements for detecting the laser light prior to scanning in the main scanning direction, provided in correspondence with the plurality of light detecting elements, and the output of each light detecting element and the light emitted for each light detecting element. A plurality of comparators for outputting a horizontal synchronization signal for each spot of the plurality of laser light sources by comparing the threshold value set in accordance with the amount of the spot light. Forming equipment.