JP2000292720A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively and easily reduce in the relative deviation of plural beams in a main scanning direction by measuring and re-correcting the relative deviation after electrically correcting the write start timing of either beam and the other. SOLUTION: A main scanning direction relative positional deviation detection means 1 detects the relative main scanning positional deviation between plotting by a 1st laser beam and plotting by a 2nd laser beam at respective positions in the main scanning direction, that is, plural positions from starting write to finishing write. A beam detector(BD) signal correction means 2 decides how much a BD signal is delayed or advanced in order to make the absolute value of the relative deviation minimum based on the relative main scanning positional deviation at the respective positions. A corrected BD signal generation means 4 generates the BD signal corrected to be actually used based on the result obtained by the correction means 2. Thus, the relative deviation in the main scanning direction is restrained without using an expensive optical correction means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic image forming apparatus, and more particularly, to an image forming apparatus which forms an image by scanning with a plurality of beams.

[0002]

2. Description of the Related Art Conventionally, this type of apparatus forms an electrostatic latent image by exposing and scanning a photoreceptor using a laser beam modulated in accordance with input information, and developing the electrostatic latent image with a developer. There is known a so-called laser beam printer which transfers an image to recording paper. By the way, in response to recent demands for high-speed image forming apparatuses, multi-laser printers using a plurality of semiconductor laser arrays have been developed and commercialized, instead of those using a single semiconductor laser.

FIG. 10 shows an example of a dual laser beam printer using two laser beams. FIG.
At 0, 101 is a laser substrate on which a laser and a laser drive unit are mounted, and 102 is a laser unit that emits laser light L1 and L2, and the emitted laser light L1 and L2
Is incident on the beam expander 103 and becomes a laser beam having a predetermined beam diameter. This laser light is incident on a polyhedral mirror 104 having a plurality of mirror surfaces. Since the polyhedral mirror 104 is rotated at a predetermined speed by the constant speed motor 105, the laser light emitted from the beam expander 103 is reflected by the predetermined rotating polyhedral mirror 104 and scanned substantially horizontally. Then, the light passes through the imaging lens 106 having the f-θ characteristic, passes through the return mirror 109, and is formed as a spot light on the photosensitive drum 110 charged to a predetermined polarity by a charger (not shown).

Reference numeral 108 denotes a beam detector (Be) for detecting the laser beam reflected by the beam detecting reflection mirror 107.
am Detector, hereinafter referred to as "BD". ). BD
Is used as a horizontal synchronizing signal for creating a BD signal and synchronizing in the main scanning direction. Therefore, the photosensitive drum 11
The timing of the modulation operation of the semiconductor laser 102 to obtain desired optical information on
Determined by the D signal. On the other hand, on the photosensitive drum 110, a laser beam image-formed and scanned according to input information is used.
An electrostatic latent image is formed. This latent image is visualized by a developer of each color in a developing device 111 and then transferred to a recording paper 112. When the image passes through a fixing device (not shown), the image is fixed on the recording paper 115 and is discharged to a discharging device (not shown).

The main scanning synchronization of the dual laser printer as described above will be described in detail. FIG. 11A shows an image diagram of a light emitting point of the multi-beam semiconductor laser 102. Laser light L1, L2 modulated by image data
Becomes substantially parallel light and reaches the photosensitive drum.
The light emitting points of the L1 and L2 semiconductor lasers 102 are physically separated by a distance d. By the way, in order to obtain the resolution of 600 dpi required by the printer, the dot pitch of the main scanning and the sub-scanning is 42.3 μm.
In the case of a multi-laser printer, a plurality of lines are simultaneously drawn in the sub-scanning direction. Therefore, if the distance d between the light emitting points of the L1 and L2 semiconductor lasers 102 can be set to, for example, 42.3 μm, the multi-beam semiconductor laser 102 is moved in the sub-scanning direction. , And it is possible to draw a plurality of lines simultaneously in the sub-scanning direction. However, since the distance d between the light emitting points of the semiconductor laser 102 is required to be several times to ten times the dot pitch of 600 dpi, the distance d is adjusted obliquely as shown in FIG. Is set to 42.3 μm. L emitted from the semiconductor laser 102
FIG. 11B shows an image diagram of the photosensitive drums 1 and L2 on the photosensitive drum.
Shown in As shown in the figure, L1 and L2 whose light emitting points are separated by a distance d are substantially separated on the photosensitive drum by a distance d so that the pitch in the sub-scanning direction is secured and the semiconductor laser 102 is tilted.
Is installed, so that one laser beam is
The image is drawn with a delay of the distance b. That is, FIG.
In 1 (b), in order to draw at the same main scanning position, L2 needs to be drawn with a time tb corresponding to the distance b delayed from L1. BD in FIG. 11 (b)
108 is a BD1 signal which is a BD signal for L1.
And a BD2 whose time is delayed by tb is created.
1 uses BD1, laser beam L2 uses BD2 to synchronize main scanning, and two laser beams can be drawn at the same position in the main scanning direction and 600 dpi pitch in the sub-scanning direction. Becomes

[0006]

However, the laser beams L1 and L2 are substantially parallel light beams when they reach the photosensitive drum. However, due to the demand for downsizing of the laser printer, the optical path length is designed to be short. Therefore, it is not exactly parallel light. For this reason, aberration occurs due to the difference between the optical systems L1 and L2 passing through the same main scanning position on the photosensitive drum.
The spot No. 2 had a relative displacement on the photosensitive drum in the main scanning direction. Since the relative displacement in the main scanning direction on the photosensitive drum is directly reflected on the recording paper 112, there is a problem that the relative displacement in the main scanning direction becomes large. The relative displacement in the main scanning direction due to L1 and L2 is a problem peculiar to a multi-beam. To reduce the relative displacement, an expensive optical system must be designed, and an inexpensive multi-beam printer is required. Was a problem for designing.

The present invention provides an image forming apparatus capable of suppressing relative displacement of a plurality of beams in the main scanning direction by simple and inexpensive means.

[0008]

According to the present invention, there is provided an image forming apparatus for forming an image on a recording medium by scanning a rotary photosensitive member with a plurality of beams via a polyhedral mirror. First correction means for electrically correcting the write timing with the other beam;
Measuring means for measuring the relative displacement of the one beam and the other beam in the main scanning direction after the correction, and, according to the measured relative displacement, the one beam and the other beam A second correction means for electrically re-correcting the writing timing with the beam.

Further, in the image forming apparatus according to the present invention, in the above-described image forming apparatus, the measuring unit uses the one beam and the other beam at a plurality of different locations in the main scanning direction of the rotating photosensitive member. The relative displacement is measured by drawing a vertical line apart and measuring the vertical line interval between the one beam and the other beam at each of a plurality of different locations in the main scanning direction of the rotating photoconductor. It is characterized by the following.

Further, in the image forming apparatus according to the present invention, in the above-described image forming apparatus, the second correction means may include the one beam and the other beam at a plurality of different locations in the main scanning direction of the rotating photoconductor. The writing timing of the one beam and the other beam is electrically re-corrected so that the sum of the absolute values of the relative deviation amounts of the beams in the main scanning direction is minimized.

Further, according to the image forming apparatus of the present invention, an image forming apparatus for forming an image on a recording medium by scanning a rotating photosensitive member with a plurality of beams via a polyhedral mirror is provided. First correcting means for electrically correcting the writing start timing of the first beam, measuring means for measuring a relative displacement amount of the one beam and the other beam in the main scanning direction after the correction, and Setting means for setting a re-correction amount of the writing timing of the one beam and the other beam according to the target deviation amount, and at the time of printing, according to the set re-correction amount,
And a second correction unit for electrically re-correcting the writing timing of the one beam and the other beam.

Further, in the image forming apparatus according to the present invention, in the above-mentioned image forming apparatus, the setting means may include an EEPROM.
M or a flash memory.

According to the present invention, by detecting a relative shift amount in the main scanning direction, L at each position in the main scanning direction is detected.
By grasping the relative shift amount between 1 and L2 and adjusting the write start position of L2 so that the absolute value of the shift becomes small, the relative shift in the main scanning direction can be suppressed by simple and inexpensive means. It becomes possible.

[0014]

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, reference numeral 3 denotes a conventional BD signal generating means for generating a BD2 which is delayed by td from BD1 as described above. It can be created easily due to differences in time. Reference numeral 1 denotes a main scanning direction relative positional deviation amount detecting unit, which is a relative main unit for drawing by L1 and drawing by L2 at each position in the main scanning direction, that is, at a plurality of positions from the start of writing to the end of writing. This is for detecting a scanning position shift amount. Reference numeral 2 denotes a BD signal correction unit, which is used to minimize the absolute value of the relative shift amount based on the relative main scan position shift amount at each position.
This determines how much to delay or advance the D signal. Reference numeral 4 denotes a correction BD signal generation unit.
Based on the result obtained by the D signal correcting means 3, a corrected NBD 2 to be actually used is created.

This will be described in detail with reference to FIGS. FIG. 2 is a diagram on the recording paper 112 in which a plurality of vertical lines are drawn. At the writing start position, the intermediate position, and the writing end position in the main scanning direction, L1 and L2 are determined by the aberration of the optical system.
Despite the delay due to the time to reach the BD 108, there is a relative displacement in the main scanning direction between the drawing by L1 and the drawing by L2. In FIG. 3, the horizontal axis shows the main scanning position, and the vertical axis shows the relative amount of displacement in the main scanning direction between L1 and L2. The + direction on the vertical axis indicates that L2 is relatively delayed from L1, and the-direction on the vertical axis indicates that L2 is L1.
It indicates that it is relatively advanced compared to. In FIG. 3A, there is a delay of L2 as a whole, and a time Δ corresponding to Δh corresponding to an intermediate value between the maximum value of the delay and the minimum value of the delay.
If the writing time of L2 is further delayed by th,
It can be seen that the absolute value of the relative main scanning position shift amount becomes smaller. That is, as shown in FIG. 3B, h1 = h2
The writing position is shifted by Δh so that FIG. 4 shows the actual waveforms of the conventional BD1 and BD2 and the waveforms of the BD1 and the corrected NBD2 of the present embodiment.
(A) and (b) show. According to this figure, conventionally, L1
And the time to reach the BD 108 of L2, by td,
Although the BD2 is delayed, in the present embodiment, it is determined that the image is actually drawn on the recording paper, and further delayed by Δth in consideration of a relative shift due to optical aberration. The means for delaying by Δth is not shown here, but can be easily configured by using a delay line, a counter, or the like. As a result, the absolute value of the relative main scanning position shift amount was successfully reduced by Δh as a whole as compared with the conventional example.

[Embodiment 2] FIGS. 5, 6 and 7 show an example of relative displacement measuring means in the main scanning direction using a reflection type sensor. In FIG. 5A, the left side is a vertical line drawn by the first laser beam L1, and the right side is a vertical line drawn by the second laser beam L2. As shown in FIG. 5, for example, a vertical line in which L1 and L2 are simultaneously drawn at a certain interval is drawn in the main scanning direction using an LED as shown in FIG. 6 and a reflective sensor 11 including a phototransistor. Upon scanning, an output waveform as shown in FIG. 5B is obtained. From this output waveform and the time of scanning in the main scanning direction, the amount of displacement between the vertical line by the laser beam L1 and the vertical line by the laser beam L2 can be measured. L1 and L2
Since the ideal positional deviation amount in the main scanning direction can be estimated from the time difference between the BD signals, the relative positional deviation amount in the vicinity can be estimated from the difference between the two. It is desirable to measure at the same main scanning position, but if L1 and L2 are drawn at the same position, they will overlap, and it will not be possible to determine which is the L1 line and which is the L2 line, making measurement impossible. Since the relative position characteristics of the main scanning do not greatly deviate, for example, if the position is a few dots away, for example, the position of the vertical lines L1 and L2 is slightly shifted to facilitate the measurement. For example, as shown in FIG. 7, two such vertical lines are drawn from the start of writing in the main scanning direction to the end of writing in 5 directions.
The image is drawn at a location, and the reflection type sensor 11 is scanned in the main scanning direction to measure a relative main scanning position shift characteristic as shown in FIG. This makes it possible to estimate the relative deviation of the main scanning position by curve interpolation or the like and calculate the write start position correction amount Δh. If the scanning speed of the reflective sensor 11 is reduced, the amount of displacement can be measured with high accuracy, and an error due to noise can be canceled by drawing and measuring a vertical line at the same main scanning position a plurality of times. . Also,
By using a CCD line sensor instead of the reflection sensor 11, a mechanism for scanning the reflection sensor 11 can be eliminated. In addition, the measurement was performed by printing on a recording paper, but the developed vertical line on the photosensitive drum may be used. Alternatively, if the apparatus has a transfer belt or a transfer drum, the vertical line drawn on the transfer belt or the transfer drum may be used. Of course, it does not matter if it is a line.

[Embodiment 3] FIG. 8 shows another embodiment 3 of the present invention. In the present embodiment, a corrected BD signal generation unit that can suppress a relative main scanning position shift without using an expensive relative main scanning position measurement unit will be described. In FIG. 8, the main scanning direction relative positional deviation amount detecting means 1 is the same as described above, but is not included in the main body configuration, and is replaced with, for example, a factory adjustment jig. Instead, a main scanning direction relative position shift amount setting unit 5 is provided on the main body side. That is,
Once the relative displacement in the main scanning direction is measured once using a factory adjustment jig, etc., the optical system does not fluctuate greatly unless the environment such as temperature changes. It has means for setting a correction amount, and performs correction at the time of actual drawing according to the set amount.

[Embodiment 4] FIG. 9 shows another embodiment 4 of the present invention. In the present embodiment, an example of a specific unit of the relative position shift amount setting unit 5 in the main scanning direction in the third embodiment will be described. In FIG. 9, the laser substrate 101
EEPROM (Electrically Programmable and Erasable PRO)
M) 12 was installed. The correction value obtained by the above-mentioned factory jig or the like is written in the EEPROM, and the BD2 signal is corrected at the time of actual printing based on the correction value at the time of actual drawing. This makes it possible to provide an inexpensive multi-beam laser printer that does not have an expensive relative main scanning position shift measuring unit. In addition, when the aberration of the optical system fluctuates due to environmental fluctuations such as temperature and the correction value needs to be fluctuated, by writing the correction value together with the temperature data, the main scanning direction which is not easily influenced by the environmental fluctuation can be easily obtained. It is possible to realize a relative displacement amount setting means.
It should be noted that the main scanning direction relative position shift amount setting means 3 is set to an EEPROM.
Although described as M12, a flash memory may be used.

In the embodiment of the present invention, the laser light is 2
Although only two dual beam lasers have been described, it is needless to say that the present invention can be applied to three, four, and more laser beams, or an array laser.

[0020]

As described above in detail, according to the present invention, by detecting the relative shift amount in the main scanning direction, L1 at each position such as writing, intermediate, and end of writing in the main scanning direction is detected. By grasping the relative shift amount of the L2 and L2 and adjusting the write start position of the L2 so that the absolute value of the relative shift becomes small, an inexpensive and simple method can be used without using expensive optical correction means. With this method, it is possible to suppress the relative displacement in the main scanning direction, and it is possible to configure an inexpensive and small multi-laser beam printer.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a first diagram illustrating a relative shift in the main scanning direction according to the first embodiment of the present invention.

FIG. 3 is a second diagram illustrating a relative shift in the main scanning direction according to the first embodiment of the present invention.

FIG. 4 is a timing chart of a BD signal according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating a method for measuring a relative shift in the main scanning direction according to the second embodiment of the present invention.

FIG. 6 is a diagram of a reflective sensor for measuring a relative shift in the main scanning direction according to the second embodiment of the present invention.

FIG. 7 is a diagram illustrating a configuration for measuring a relative shift in the main scanning direction according to the second embodiment of the present invention.

FIG. 8 is a block diagram of a third embodiment of the present invention.

FIG. 9 is a configuration diagram of a fourth embodiment of the present invention.

FIG. 10 is a conceptual diagram of a multi-beam printer to which the present invention is applied.

FIG. 11 is a diagram illustrating a dual beam laser.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 main scanning direction relative positional deviation amount detecting means 2 BD signal correcting means 3 BD signal generating means 4 corrected BD signal generating means 5 main scanning direction relative positional deviation setting means 11 reflective sensor 12 memory 101 laser substrate 102 semiconductor laser 103 beam Expander 104 Polyhedral mirror 105 Scanner motor 106 Imaging lens 107 Reflection mirror for beam detection 108 Beam detector 109 Folding mirror 110 Photosensitive drum 111 Developing cartridge 112 Recording paper

Claims (5)

[Claims] 1. An image forming apparatus for forming an image on a recording medium by scanning a rotating photoreceptor with a plurality of beams via a polyhedral mirror, and electrically corrects a writing timing of one beam and the other beam. First correcting means for measuring, and measuring means for measuring a relative shift amount in the main scanning direction between the one beam and the other beam after the correction,
An image forming apparatus comprising: a second correction unit that electrically re-corrects a writing timing of the one beam and the other beam in accordance with the measured relative shift amount. . 2. The image forming apparatus according to claim 1, wherein the measuring unit separates a vertical line formed by the one beam and the other beam at a plurality of different locations in the main scanning direction of the rotating photoconductor. The relative displacement is measured by measuring the interval between vertical lines of the one beam and the other beam at a plurality of different locations in the main scanning direction of the rotating photoconductor. Image forming apparatus. 3. The image forming apparatus according to claim 2, wherein the second correction unit performs the main scanning of the one beam and the other beam at a plurality of different locations in the main scanning direction of the rotating photoconductor. An image forming apparatus, wherein the writing timing of the one beam and the other beam is electrically re-corrected so that the sum of the absolute values of the relative deviation amounts in the directions is minimized. 4. An image forming apparatus that forms an image on a recording medium by scanning a rotating photosensitive member with a plurality of beams via a polyhedral mirror, and electrically corrects a writing timing of one beam and another beam. First correcting means for measuring, and measuring means for measuring a relative shift amount in the main scanning direction between the one beam and the other beam after the correction,
Setting means for setting the re-correction amount of the writing timing of the one beam and the other beam according to the measured relative deviation amount, and, at the time of printing, according to the set re-correction amount. And a second correcting unit for electrically re-correcting the writing timing of the one beam and the other beam. 5. The image forming apparatus according to claim 4, wherein said setting means is an EEPROM or a flash memory.