JP2005096114A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve an adjustment of a highly precise joint by changing the width of a toner image line and uniquely relating a signal of a detecting means to a light beam when a position or a gap is detected by dividing the light beam and using it for scanning to form an image. <P>SOLUTION: If the period with a preset level Vs or higher is a time Ts or longer, the wave-form part is judged to correspond to the first writing system I. In a wave shape (Fig. 9) of an output signal, the wave-form part on the left side on a time axis corresponds to the first writing system I. In this case, a distance between two lines can be detected by detecting a distance between rising and falling positions. In Fig. 10, the light beams of the first and second writing systems are reversed left and right. If a left/right relation of the wave forms on the time axis in Fig. 9 is correct, in order to bring the condition from the condition of Fig. 9 (with a big error) to the condition of Fig. 10, the amount of delay of a synchronized signal in the first or the second writing system is decreased. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to light beam position adjustment of an image forming apparatus that uses a plurality of light beams connected together.

In digital copying machines and facsimile machines, scanning devices using light beams are widely used. In this light beam scanning apparatus, the surface to be scanned is scanned with a beam, so there is an optical limit to widen the scanning region of the beam to a certain extent. Various techniques have been proposed to overcome the limitations while taking advantage of the light beam.
Japanese Patent No. 3287289 Japanese Patent Laid-Open No. 10-20221 JP 2000-235155 A JP 2000-267027 A

The technique described in Patent Document 1 relates to control of an image forming apparatus and a split light scanning device, and has a plurality of partial exposure ranges in the main scanning direction of the light beam, and each partial exposure range is exposed by another light beam ( Split scan). In addition, it has an overlapping exposure range where adjacent partial exposure ranges overlap, and by detecting the density after development of the overlapping portion, the positional relationship of the light beam is judged and controlled so as to obtain a desired positional relationship. Yes.
The inventions described in Patent Document 2 to Patent Document 4 all have a synchronization sensor and a light beam position sensor, and when connecting a plurality of light beams in the main scanning line direction, the light beam is detected according to the signal of the light beam position sensor. A technique for changing the lighting position is disclosed.

By the way, in the invention of Patent Document 4, there is provided a light beam passage position detecting means (one-dimensional CCD) in the sub-scanning direction, and the shift of the scanning line in the sub-scanning direction caused by temperature fluctuations (of the housing or the lens system). It has been proposed to detect the occurrence of a slight change in the optical path due to thermal expansion and to correct the misalignment of the two seams.
As described above, when adjusting the misalignment between the joints of the light beams, the positions of the two light beams (writing start positions) can be accurately detected and adjusted easily so that the light beams can be used for image formation using a scanning device. Is important.

Accordingly, a first object of the present invention is to form two toner image lines in each of the main and sub directions in the adjustment process of an apparatus for forming an image by dividing and scanning a light beam, and detecting the position or interval thereof. By changing the width (thickness) of the toner image line so that the signal of the detection means (position on the time axis) and the beam can be uniquely matched, even if the position of each beam fluctuates greatly, the adjustment process An object of the present invention is to provide an image forming apparatus provided with a light beam scanning device that can prevent malfunction and achieve high-precision joint adjustment.
The second object of the present invention is to provide two toner image lines in the main and sub-directions in the adjustment process of an apparatus for forming an image by dividing and scanning a light beam, and to detect the position and interval in a simple manner. It is an object of the present invention to provide an image forming apparatus including a light beam scanning device that can achieve high-precision joint adjustment by simple signal processing.
A third object of the present invention is to prepare two toner image lines in each of the main and sub directions in an adjustment process of an apparatus for forming an image by dividing and scanning a light beam, and to detect the interval between the two toner image lines. Provided with a light beam scanning device capable of achieving highly accurate joint adjustment even when the toner image line intermittently reaches the detection range of the detection means or toner other than the two toner image lines adheres. An image forming apparatus is provided.
The fourth object of the present invention is to adjust the distance between the two lines in the main and sub directions in the adjustment process of the apparatus for forming an image by dividing and scanning the light beam. And providing an image forming apparatus provided with a light beam scanning device that prevents misoperation of the adjustment process and achieves high-precision joint adjustment.

  According to the first aspect of the present invention, in an image forming apparatus that forms an image using a light beam scanning device that scans by dividing a scanning line of at least two light beams on a photosensitive member and scanning in a main scanning direction, Synchronization detection means for detecting the scanning line reference position of the light beam corresponding to the optical beam, and main scanning for changing the distance in the main scanning direction from the synchronization detection position detected by the synchronization detection means to the image start position Changing means, sub-scanning changing means for changing the distance in the sub-scanning direction from the synchronization detection position detected by the synchronization detecting means to the image start position, and a plurality of latent images on the photosensitive member in each of the main and sub-scanning directions A latent image line forming means for forming a line, a visualizing means for visualizing a latent image formed on the photosensitive member, a visible image line detecting means for detecting a visible image line by the visualizing means, This visual line inspection Line image detecting means for detecting the position or interval of the line signals in the main and sub-scanning directions by calculating the position and interval of the specific signal of the output signal of the means; And a control unit that changes a plurality of line image positions or intervals to a predetermined value by changing the sub-scanning changing unit, and the visualization unit includes a scanning line interval in each scanning direction. In forming the visible image line, the width (thickness) of the visible image line formed by each beam is different to achieve the first object.

According to a second aspect of the present invention, in the first aspect of the present invention, a plurality of values are obtained from a relationship between an output signal value of the visible line detection means and a preset value when a plurality of visible lines are detected. Each visible line is associated with a position (on the time axis) in the output signal.
According to a third aspect of the present invention, in the first aspect of the present invention, after associating each visual line with a position (on the time axis) in the output signal, the thickness of the visual line is changed and the visible line is changed. The second object is achieved by detection by the image line detection means.
In the invention of claim 3, in the invention of claim 2, after associating each visible line with a position (on the time axis) in the output signal, the thickness of the visible line is changed and the visible line is changed. The second object is achieved by detection by the image line detection means.
According to a fourth aspect of the present invention, in the first aspect of the present invention, the moving visible image line for detection is expressed by the relationship between the output signal of the visible line detection means and a preset value. The third object is achieved by determining whether or not it is within the detection range of the image line detection means.
According to a fifth aspect of the present invention, in the first aspect of the present invention, the light beam scanning lines by the control means are connected to adjust the image writing start position of each light beam, and at the time of image creation. The fourth object is achieved by the difference in scanning direction intervals of the visible image lines corresponding to the beams by the visualizing means.

According to the first and second aspects of the present invention, in forming the two toner image lines in the main and sub directions in the adjusting process of the apparatus for forming an image by dividing and scanning a plurality of light beams, each of the toners Since the thickness of the image line is different, the correspondence with each beam is facilitated, and malfunction can be prevented.
According to the third aspect of the present invention, when forming two toner image lines in the main and sub-directions in the adjustment process of the apparatus for forming an image by dividing and scanning a plurality of light beams, each toner image line and each The thickness of the toner image line is set to a thickness suitable for each detection at the time of detection for associating the beam and the detection of the position or interval of the toner image line. Line position or interval can be detected.

  According to the fourth aspect of the present invention, in forming and detecting two toner image lines in the main and sub directions in the adjustment process of the apparatus for forming an image by dividing and scanning a plurality of light beams, the toner image lines are detected. Therefore, even if the toner image line reaches the detection range of the detection means intermittently or toner other than the toner image line adheres, it is reliable and highly accurate. In addition, the position or interval of the toner image line can be detected.

  According to the fifth aspect of the present invention, when forming and detecting two toner image lines in the main and sub directions in the adjustment process of the apparatus for forming an image by dividing and scanning a plurality of light beams, the toner image lines are detected. Since the interval is arbitrarily set according to the detection means, the position or interval of the toner image line can be detected with high accuracy without malfunction.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 1 is a perspective view showing a schematic configuration of a light beam scanning apparatus according to the present embodiment, and shows an example used in an optical writing apparatus of an image forming apparatus such as a digital copying machine. The light beam scanning device (optical writing device) shown in FIG. 1 includes two semiconductor laser (LD) light sources 1-1 and 1-2 as light sources that emit light beams, and each of the semiconductor laser light sources 1-1 and 1-1. Collimating lenses 2-1 and 2-2 and cylindrical lenses 3-1 and 3-2 are provided for the two outgoing beams, respectively.
A single polygon as a deflecting means having a plurality of deflecting surfaces for deflecting two light beams respectively guided through the collimating lenses 2-1 and 2-2 and the cylindrical lenses 3-1 and 3-2. A mirror 4 is provided. As image forming means for forming images of the two light beams deflected by the polygon mirror 4 on the photosensitive drum 10 which is the surface to be scanned, the first Fθ lenses 5-1 and 5-2 and the second Fθ lenses 5-1 and 5-2 are used. Fθ lenses 6-1 and 6-2 are provided, respectively.
Further, as the scanning direction changing means, two mirrors, that is, first mirrors 7-1 and 7-2 and second mirrors 8-1 and 8-2 are arranged in each of the two optical paths. .

Furthermore, on the optical path of the imaging optical system, a third mirror 9-1 for guiding the scanning light whose scanning direction is changed by the first and second mirrors to the photosensitive drum 10 which is the surface to be scanned. 9-2.
As described above, the light beam scanning apparatus (optical writing apparatus) shown in FIG. 1 includes two systems of optical writing systems, and the polygon mirror 4 is shared by the two systems of optical writing systems.
Here, the optical writing system on the left half of the polygon mirror 4 serving as the deflecting means is called the first writing system I, and the optical writing system on the right half is called the second writing system II.

In the first writing system I, the semiconductor laser (LD) light source 1-1 emits laser light modulated in accordance with an image signal under the control of a driving device (not shown), and this laser light is emitted from the collimating lens 2-1. The laser beam that has been made parallel light and made parallel light by the collimator lens 2-1 enters the polygon mirror 4 through the cylindrical lens 3-1.
The polygon mirror 4 is rotated by a motor (not shown), and the laser beam incident on the polygon mirror 4 is reflected by the deflection surface and deflected and scanned.
The light beams deflected and scanned by the polygon mirror 4 are changed from the constant angular velocity deflection to the constant velocity deflection by the first and second Fθ lenses 5-1 and 6-1, respectively. 1, the scanning direction is changed by 1 and 8-1, and then reflected by the third mirror 9-1 and guided to the direction of the photosensitive drum 10 which is the surface to be scanned, and the predetermined scanning on the photosensitive drum 10 is performed. Scan from the center of the position toward one end.

The second writing system II has the same configuration as the first writing system I, and is arranged at a position obtained by rotating the first writing system I by 180 ° about the polygon mirror 4. The laser light emitted from the semiconductor laser (LD) light source 1-2 is collimated by the collimating lens 2-2, then enters the polygon mirror 4 through the cylindrical lens 3-2, and is deflected and scanned by the polygon mirror 4. Then, the first and second Fθ lenses 5-2 and 6-2 and the first, second, and third mirrors 7-2, 8-2, and 9-2 are passed to the photosensitive drum 10.
Then, scanning is performed from the center of a predetermined scanning position on the photosensitive drum 10 toward the end portion in the direction opposite to the first writing system I.

Reference numerals 11-1 and 11-2 in FIG. 1 are synchronization detection units of the first and second writing systems I and II, respectively. Each synchronization detection unit 11-1 and 11-2 is a laser beam scanning unit. Provided outside the region, the scanning timing of the laser beam is detected for each scanning of the laser beam.
A writing control circuit (not shown) synchronizes the scanning timing of the laser beams of the first and second writing systems I and II and the writing start position according to the timing detected by the synchronization detecting units 11-1 and 11-2. Is configured to take.

FIG. 2 is a schematic plan view of the light beam scanning apparatus shown in FIG. 1 as viewed from above. The two-dot chain line of M in the drawing indicates that the scanning light is the first and second mirrors 7-1, 8-1, (7-2, 8-2) is reflected at the positions (reflecting surfaces of the first and second mirrors), the two-dot chain line of M ′ is the scanning light, and the third mirror 9-1 (9-2 ) Are reflected (the reflecting surface of the third mirror), the dot-dash line of Q is the center line of the photosensitive drum 10, and the dot-dash line of R is the imaging optics on the scanning plane. The optical axis of the system (the optical axis of the scanning beam) is shown.
In the figure, an arrow 13 indicates the direction of rotation of the polygon mirror 4, and an arrow 14 indicates the direction in which the scanning line is scanned on the photosensitive drum 10 (beam scanning direction).
3 and 4 are diagrams showing an outline of an optical path when the light beam scanning apparatus of FIG. 2 is viewed from the direction A, FIG. 3 is an outline of an optical path of only the first writing system I, and FIG. The schematic shows the optical paths of both the first writing system I and the second writing system II.

  Note that the light beam scanning apparatus having the above-described configuration is normally sealed inside an optical box (not shown), and is fixed and arranged with high accuracy because it does not like adhesion of dust or the like. However, since the laser emission port needs to be opened, a laser emission port is provided in the optical box, and dust-proof glass 12-1, 12-2, etc. are arranged in the emission port as shown in FIG. Etc. are prevented.

The configuration example of the light beam scanning apparatus according to the present embodiment has been described above. In this light beam scanning apparatus, two scanning lines that are divided and scanned on the same photosensitive drum (scanned surface) 10 are provided. Since deflection scanning is performed by one polygon mirror 4, it is not necessary to synchronize the deflectors themselves as compared to the case where a plurality of deflectors such as polygon mirrors 4 are used. For this reason, it is possible to easily align the timing of writing the two scanning lines in the sub-scanning direction, and to prevent the positional deviation of the scanning lines in the sub-scanning direction.
Next, light beam (laser beam) position adjustment using the line interval sensor 15 will be described.
As shown in FIG. 1, a plurality of interval detection lines 16-n (n = 1, 2, 3,... N) are formed on the photosensitive drum 10 in the circumferential direction of the drum.

2 shows the second mirrors 8-1 and 8-2, the third mirrors 9-1 and 9-2, the synchronization detection units 11-1 and 11-2, and the synchronization detection sensors: rear 13-1 and 13. -2 (used to detect fluctuations in writing magnification due to environmental fluctuations, but description of the operation is omitted here), line interval sensor 15, photoconductor drum 10, and interval detection line 16-n on photoconductor drum 10. (Toner visible image, plural n = 1, 2, 3, n), the relative positions of the respective parts of the first and second image forming beams are shown (the relationship between the shapes is not considered).
FIG. 2 shows optical paths a and c of the light beam reaching the synchronization detection units 11-1 and 11-2 and optical paths b and d for image formation reaching the photosensitive drum 10. Optical paths b ′ and d ′ of the light beam indicate that an image can be superimposed and drawn at the joint. Black circles (corresponding to optical paths a, b, c, d) and gray circles (corresponding to optical paths b ′, d ′) are reflections of light beams on the mirrors 8-1, 8-2, 9-1, 9-2. Indicates the position.
The light beam forms dots on the photosensitive drum 10 and has a diameter (width in the main and sub directions) of 40 to 1000 μm.

FIG. 3 shows the synchronization detection unit 11-1 of the first writing system, the synchronization detection sensor: rear 13-1, and the first dot (writing start position) of the first and second writing systems. Synchronization detection unit 11-2 of second writing system II, synchronization detection sensor: Signals of rear 13-2 are omitted. Since the first and second image forming beams intersect with each other, the synchronization detection units 11-1 and 11-2 are opposite to the corresponding first and second beam dots (on the basis of the center). .
FIG. 4 is a timing chart showing the relationship between the LD lighting signal LD of the first writing system I, the synchronization signal: front DET, the delayed synchronization signal DDET, the synchronization signal: rear DET-2, and the pixel clock CLK. Each of the two writing systems is independent (represented as a single symbol).
DDET is a signal obtained by delaying DET by TD1 time by delay means (delay 1 in FIG. 13). The interval TL1 (converted to the number of clocks) of the synchronization detection signal: before and the synchronization detection signal: after detects the magnification (variation).

The light beam produced by the first writing system is deflected by the rotation of the polygon mirror-4. First, the virtual photoconductor surface (assuming that the mirrors 9-1 and 9-2 are sufficiently long in the longitudinal direction, the mirror 9-1, 9-2 is reflected on the surface of the photosensitive drum 10 and the surface of the photosensitive drum 10 is disposed on a surface provided on the extension line of the light beam reflected by the actual mirrors 8-1 and 8-2. The light enters the synchronous detection unit 11. At this time, the LD is the LD signal LDS in FIG. 4A (the first write system is LDS1 and the second write system II is LDS2, but two are representative LDS. In the same case as the first and second cases, the same notation is used), and the light beam is incident on the synchronization detection unit 11-1 in a continuous lighting state.
When the optical beam is incident on the synchronization detection unit 11-1, a synchronization signal for horizontal synchronization of the optical beam: the previous DET is asserted and used to determine the reference position (timing) in the main scanning direction. Is done. After DDET is asserted, the LD is temporarily turned off. The writing start position is changed by changing the time TD1.

The rotatable third mirrors 9-1 and 9-2 and the stepping motors 14-1 and 14-2 move the scanning start position in the sub-scanning direction so that the scanning line (and hence the writing start position) moves in the sub-scanning direction. Means. There are HP sensors 1 and 2 that detect the reference positions of the third mirrors 9-1 and 9-2, which are not shown in FIG. 1 (shown in FIG. 13). When the mirrors 9-1 and 9-2 are rotated (scan line position change), a reference signal for rotating the third mirrors 9-1 and 9-2 is generated. Each mirror position (rotation angle) can be adjusted by the reference signal (and therefore the reference position) and the number of stepping motor driving pulses (generated inside the control unit 30). The adjustment amount is determined by a control value obtained from the signal of the line interval sensor 15.
A reduction mechanism (not shown) is provided between the stepping motors 14-1 and 14-2 and the third mirrors 9-1 and 9-2, and the rotation angle of the folding mirror is set at a minute pitch. It is configured to be able to.

In this example, the line interval sensor 15 has a configuration using a two-dimensional PSD (Position Sensing Device). The PSD has a configuration of 256 rows × 256 columns (total 65536 pixels). Each pixel interval (pitch) is about 8 μm.
Light from the LED light source (FIG. 10) for the line interval sensor 15 is reflected on the photosensitive drum 10 and is incident on the light receiving portion of the line interval sensor 15 which is an area sensor. The PSD (position sensor) inputs a clock CLK and a start signal (determining accumulation start, position sensor scanning time interval) ST, analog output signals Vx1 (signal corresponding to the main scanning direction), and Vy1 (corresponding to the sub scanning direction). Signal) and trigger signal Trig1.

FIG. 7 is a diagram showing the relationship among the clock signal CLK, the start signal ST, the output signal Vo (represented in the main and sub-direction output signals), which is an input signal of the line interval sensor 15, and the Trig.
After the start signal ST (ON at L) is turned ON, the analog output signal Vo and the trigger signal Trig are output in synchronization with CKL. The trigger signal Trig is also synchronized with the analog output signal Vo, and is input to the control unit 30 via the subsequent amplifier and AD converter shown in FIG. The clock CLK and the start signal ST can be input independently in the X direction (main scanning direction) and the Y direction (sub scanning direction), but are shown as one signal for simplification of the description. .
The output signals are also output independently in the X direction (main scanning direction) and the Y direction (sub scanning direction), but are shown as one signal for simplification.

Each pixel of the line interval sensor 15 generates charges by receiving light of TSS for one period of the start signal ST (almost equal to the accumulation time. Actually, charge transfer and reset time are required, so the accumulation time is shorter than TSS). . The electric charge is stored for each row and column, converted into a voltage and output. Therefore, the analog output signal of TSS for one cycle is 512 analog values in total, that is, serial signal VX composed of 256 values in the row direction and serial signal Vy composed of 256 values in the column direction for each position sensor. It becomes by.
The output signal is a signal corresponding to the projection in the row and column directions of the two-dimensional image. Note that the value of the output signal Vo corresponds to one period TS (accumulation time) immediately before the output.

FIG. 13 is a block diagram showing a signal-related configuration.
The line interval sensor 15 is supplied with a clock CLK and a start signal ST from the control unit 30, and an output signal Vx1 corresponding to the main scanning direction (row), an output signal vy1 corresponding to the sub-scanning direction (column), and a trigger signal Trig1. Is output. The output signal Vx1 is input to an amplifier including an operational amplifier OP1, resistors R1, R2, R3, and a variable resistor VR1. The output of the amplifier is converted into a digital signal Dx1 by the AD converter ADC1, and then input to the control unit 30. The acquisition of the input signal of the AD converter ADC1 is started at the falling timing of Trig1, and AD conversion is performed before the rising. The digital signal after AD conversion is held until the next falling timing, and is taken into the control unit 30 while being held.

Similarly, the output signal Vy1 is input to an amplifier including an operational amplifier OP2, resistors R4, R5, and R6, and a variable resistor VR2. The output of the amplifier is converted into a digital signal Dy1 by the AD converter ADC2, and then input to the control unit 30. The AD conversion and the loading to the control unit 30 are performed in the same manner as the processing performed in Vx1.
The signal DET 1-1 of the synchronization detection unit 11-1 is delayed by a delay 1 and becomes a delayed synchronization signal DDET 1 and is input to the control unit 30. The delay 1 changes the delay time in the range of 0 to 256 nS at 1 nS intervals (corresponding to 1 μm in the main scanning direction on the photosensitive drum 10 as an example) by the control signal S1 from the control unit 30. Synchronous sensor: The later signal DET2-1 is input to the control unit 30.
Similarly, the signal DET 2-1 of the synchronization detection unit 11-2 is delayed by a delay 2 to become a delayed synchronization signal DDET 2 and input to the control unit 30. The delay 2 changes the delay time in the range of 0 to 256 nS at 1 nS intervals by the control signal S2 from the control unit 30. Synchronous sensor: The later signal DET2-2 is input to the control unit 30.

FIG. 4 also shows the relationship among the LD signal LDS, the synchronization signal: front DET, the delayed synchronization detection signal DDET, the synchronization signal: rear DET-2, and the pixel clock CLK.
DDET is an output signal with a delay of 1, and is delayed by TD1 with respect to DET. When the delay time TD1 is increased or decreased, the image area (therefore, the writing start position, DOT1 described later) moves in the main scanning direction. When the delay time TD1 is increased, DOT1 moves away from the center (joint). Therefore, the interval between two lines increases. The delay time is changed by a TD1 (described later) control signal S1. The control signal S1 is output from the control unit 30 based on a value calculated by the control unit 30 using the signal Vx1 of the line interval sensor 15. The interval between the two lines can be controlled by the total delay time TD (= TD1 + TD2) of the first and second write systems. Although not shown, TD2 is determined in the same manner as TD1.
Each delay time TD1, TD2 is set when the distance between the joint pixels of the two beams is an appropriate value (42.3 ± 10 μm at 600 DPI), near the center of the adjustment range of the delay means (example 0 to 256 nS) It is desirable to come to.

The pixel clock CLK is generated based on the delayed delay synchronization detection signal DDET, and the LD lighting signal becomes a write start timing after a predetermined number of clocks (Ng1 clock in this example) from the delay synchronization detection signal DDET. Start modulation based on the data. The image data of the first writing system I for drawing the two lines for beam adjustment for the main scanning direction beam has a value for lighting the dot (corresponding to DOT1) after Ns1.
The image data of the second writing system II has a value for dot lighting (corresponding to DOT2) after Ns2 (not shown). By generating DOT1 and DOT2 for each beam, two lines in the sub-scanning direction (latent image) for adjusting the main scanning direction are formed on the photosensitive drum 10.
Although the line length is determined by the number of dots of DOT1 and DOT2, the number of dots corresponding to the line length and several mm is used.
In order to create two lines in the main scanning direction for adjusting the sub-scanning direction, scanning is performed by continuously turning on and off several mm LD from the writing start position (included in the image area) on one main scanning line, and then the image area. The scanning with the LD turned off is repeated (for 0.5 mm on the drum), and scanning is performed again to continuously turn on and turn off several mm LD from the writing start position in the main scanning direction.
Each latent image line becomes a visible image line with toner by an electrophotographic process (not shown).
In the main / sub line creation, the timing is set so that there are a total of four interval detection lines 16 as shown in FIG.

  8 to 11 are diagrams showing the output Vo (representative of Vx1 and Vy1) of the line interval sensor 15. FIG. Where the toner line is, it is in the + direction. An output signal Vx (same for Vy) of the line interval sensor 15 when the detection line image of FIG. 5 is detected is shown. In addition, 15a (inside a wavy line) in FIG. 5 indicates a detection region of the line interval sensor 15, and indicates that main and sub lines can be detected simultaneously.

  FIG. 8 shows a case where the toner image lines have the same thickness, and FIGS. 9 and 10 show output signals when the thicknesses are intentionally different. Although the line interval can be detected in FIG. 8, even if the line interval is a preset value, a large error may occur. This is because it is unclear which (first or second) writing system each peak portion of the output signal having two peaks corresponds to.

Further, when the line interval is increased or decreased, it cannot be determined whether or not the delay amount of the synchronization signal should be increased. Therefore, a case will be described in which one line, here, the line of the first writing system I is thickened (satisfying preset values Vs and Ts described later). This can also be realized in the same way when the second writing system II line is thickened. This is to make each peak portion of the output signal correspond to each light beam (first and second writing systems).
The interval detection line image 16-n enters the detection range of the line interval sensor 15 at an interval. Therefore, when the output of the line interval sensor 15 has two (mountain-shaped) portions greater than or equal to Vs (shared with Vs, which can be another value), the interval detection is performed in the detection region of the line interval sensor 15. It is determined that the service line 16-n has entered (can be detected).

If a period of time equal to or higher than a preset level Vs is equal to or greater than time Ts (Ns as a value converted to the number of pixel intervals of the line interval sensor 15), the waveform portion (a part of the output signal of the line interval sensor 15) is the first. It is determined that it corresponds to the writing system I. In the waveform of the output signal (consisting of a waveform portion having a flat plateau level and a waveform portion having a peak) (FIG. 9), the left waveform portion on the time axis corresponds to the first writing system I. . Here, in order to detect the interval between the two lines, it is also possible to detect between the falling positions (falling to a certain value).
FIG. 10 shows a case where the light beams of the first and second writing systems are reversed left and right (or front and back). The description will be continued assuming that the left-right relationship of each waveform on the time axis in FIG. 9 is correct. 9 can be realized by reducing the delay amount of the synchronization signal of the first or second writing system (first and second writing systems). Both delays may be reduced).
In the above description, the line interval is detected while the line thickness remains different. Hereinafter, a method of detecting the line interval after returning the line thickness to the same (thinner) will be described. Since the relationship between the left and right partial waveforms on the time axis of the output signal and each beam is found, the relationship between the partial waveform and each beam is known even if the thickness is the same.
The interval detection line 16-n enters the detection range of the line interval sensor 15 at an interval. Therefore, it is determined whether or not the interval detection line 16-n is within the detection range of the line interval sensor 15 by collating the output signal under a preset condition. Here, there are two cases where the output signal exceeds the predetermined value Vs (FIG. 8) and then becomes equal to or lower than Vs in one cycle period Ts (accumulation time) of the line interval sensor 15 according to the preset condition. To do.

The signal VX is AD-converted and processed. Here, a signal before AD conversion will be described.
LX is calculated | required by calculating | requiring the maximum value of FIG. 8, and calculating | requiring the maximum value space | interval (NX as a value converted into the number of line interval sensor pixel intervals).
Lx = 8 NX (μm) − (1) 8 (μm): pixel interval in the main scanning direction of the line interval sensor, and the magnification of the line interval sensor and the drum is 1/1.
Ly is obtained in the same manner.
LY = 8 NY (μm)

In FIG. 11, the toner lines are close to each other, and not only the peak positions P2 and P3 of the output signal of the line interval sensor 15 are difficult to detect, but also the peak positions P2 and P3 are the positions P1 and P2 of the toner lines (broken lines). The line interval and line position cannot be detected. Naturally, even when the toner lines are overlapped (ideal state as the adjustment position in the sub-scanning direction), it cannot be detected.
Therefore, when the detection is performed by the line interval sensor 15, the toner line interval is set so as to be easily detected based on a preset beam control value (offset is provided), and detection is performed. After controlling the toner line interval to a target value (a value including an offset value), a beam control value excluding the offset is set. This enables detection and control even when the toner lines are close to each other (including completely overlapping toner lines).

FIG. 6 is a diagram illustrating that the photosensitive drum 10 moves up and down due to the eccentricity of the drum and the writing start position in the main scanning direction varies. Note that the fluctuation in the writing start position in the sub-scanning direction due to vertical movement is a level that can be ignored (when the extension line of the light beam is close to the rotation center of the photosensitive drum 10).
In the figure, b represents the light beam of the first writing system I, and c represents the light beam of the second writing system II. When the photosensitive drum 10 is in the vertical direction H2, the joint is appropriate, that is, the dot interval between the writing start dots (positions) of the first and second writing systems is 42.3 ± 10 μm (in the case of 600 DPI). It shows where it is. When the photosensitive drum 10 moves up and down from the position H2 between the upward direction H1 and the downward direction H2, the dot interval at each writing start position at the joint varies between Lx10 and Lx30 with Lx20 (proper value) interposed therebetween. It is shown that.

In creating the interval detection line 16-n, even if the LD is controlled and created at the same (TD1 constant) timing (managed by the synchronization signal DET reference time), writing is performed in the up-and-down motion as described in FIG. The start position varies, and therefore, the line interval in the main scanning direction varies by the same amount. The relationship between this situation and correction is shown in FIG.
By detecting the interval detection line 16-n by the line interval sensor 15, the line interval variation is detected (line interval in FIG. 12: before correction). Each line interval: Before correction, the drum is detected for one rotation around the photosensitive drum 10 signal.
The correction value is a value indicating how much the line interval should be changed in order to set the line interval to an appropriate value (therefore, the dot interval at the writing start position is set to the appropriate value Lx2).

In FIG. 12, the vertical axis represents the line interval Lx in the main scanning direction, the horizontal axis represents the position of the photosensitive drum 10 (value replaced by the number of scanning lines starting from the signal of the photosensitive drum 10), and the sine wave solid line is Line interval: Indicates before correction. The line interval Lx obtained using the interval detection sensor 15 indicates the minimum value Lx1 and the maximum value Lx3 with the appropriate value Lx2 interposed therebetween.
When the value is the appropriate value Lx2, the dot interval Lx20 at each writing start position at the joint in FIG. 6 is 42.3 ± 10 μm (in the case of 600 DPI). The relationship between the interval values in FIGS. 6 and 12 is shown below (strictly, it is not a symbol, but there is no problem even if it is practical).
Lx1 = Lx10 + constant value (setting value)
Lx2 = Lx20 + constant value (setting value)
Lx3 = Lx30 + constant value (setting value)
The constant value is an arbitrary set value of 0.2 to 1.0 mm. This is set in consideration of the detection range of the line interval sensor 15 and the line thickness.
Since the line interval Lx changes depending on the position of the photosensitive drum 10, the dot interval at each writing start position at the joint also changes. The deviation ΔLxm of the line interval Lx from the appropriate value Lx2 varies depending on the position of the photosensitive drum 10.

In FIG. 12, the deviation at the position Pm of the drum circumferential distance lm (the number of main scanning lines, that is, the number m of the synchronization signals) after the signal of the photosensitive drum 10 is asserted (L → H) is indicated by ΔLxm. (A correction value example ΔLxm ′ of Pm ′ at different positions is also shown).
The deviation ΔLxm is composed of a component ΔLxm1 that periodically changes due to drum rotation and a component ΔLx2 that does not change due to drum rotation (varies due to other causes).
ΔLxm = ΔLxm1 + ΔLx2
Each value ΔLxm, ΔLxm1, and ΔLx2 in this equation has polarity.
The polarity of the deviation ΔLxm indicates that the interval is too wider than the appropriate value in +, and that − is too narrow. ΔLxm1 is + when the sine wave solid line (line interval: before correction) is above (+) the drum vertical movement center (one-dot broken line), and − when it is below. ΔLx2 is set to + when the appropriate interval is above (+) (two-dot broken line), and is set to-when it is below. The polarity explanation on the right side is for interpreting the equation, and it is not necessary to decompose ΔLxm into two components on the right side.
Actually, the polarity of ΔLxm may be + when the line interval LX is above (+) than LX2, and it may be − when it is below.

It can be seen that at the position Pm on the photosensitive drum 10 (the position of the mth main scanning line from the rising edge of the drum signal L → H), it is only necessary to make the line small by an interval ΔLxm. The detection of the line interval by the line interval sensor 15 is not performed for each main scanning line. Detection is performed at intervals of several tens of mm in the drum circumferential (sub-scanning) direction.
Therefore, the deviation ΔLxm of the section where the line interval is not detected is obtained by interpolation from the value actually detected by the sensor. A deviation set ΔLxn (1, 2, 3,... N) of deviations obtained by the line interval sensor 15 and deviations obtained by interpolation can be made to correspond to each main scanning line for one revolution of the drum.

The deviation set ΔLxn (1, 2, 3,... N) is used to create a correction value ΔLxnc for correcting the write start position with delays 1 and 2 (FIG. 13). If delay 1 and 2 are 1 nS delay and the 1 μm write start position moves (the relationship between the delay time and the amount of movement varies depending on the system. It can be handled only by the conversion formula), the part corresponding to 1 μm or less of ΔLxn is rounded off to the polarity (In the case of +, the interval is too wide than the appropriate value, and-indicates that the interval is too narrow).
The correction value ΔLxnc is held in the non-volatile memory in such a manner that the relationship with the position of the photosensitive drum 10 (therefore, the number of main scanning lines from the drum signal L → H. Indicated here by n) is known. . The correction value ΔLxmc for each line interval is updated at a timing when image formation is not performed as necessary. The update is performed by creating an interval detection line 16n-n, detecting ΔLxn for one revolution of the drum, and overwriting the correction value ΔLxnc based on the value in the nonvolatile memory.

Pf indicates the image start position on the drum. Pf moves (when viewed from the drum signal) according to the image forming timing of the apparatus. Ps indicates a position where the line interval is appropriate.
For image formation when copying and printing, the main scanning writing start position is made appropriate on the drum by using the correction value ΔLxn in synchronization with the drum signal (the line interval is set to the appropriate value Lx2). . Since the main scanning writing start position is changed using the delays 1 and 2, the correction value ΔLxnc is output from the control unit 30 as the delay signals S1 and S2. In creating the delay signals S1 and S2 from the correction value ΔLxn, the total of the write position movements of the first and second write systems is considered to make the deviation ΔLxm zero.
Since the correction value ΔLxmc corresponding to the position from the drum signal (synchronization signal: the number m of the previous asserted) is prepared, correction can be performed at any position on the photosensitive drum 10, and there is little deviation from the set value. The writing start position can be adjusted. After the correction, the sinusoidal line interval having the deviation of FIG. 12: the curve before the correction is a two-dot chain line (showing the value of Lx2).

If the adjustment of the interval detection line 16-n is always performed (except during the image writing process), the deviation ΔLxm of the interval is reduced. However, the method of always controlling the toner consumption, power consumption, This is not a good idea because it involves mechanical wear.
ΔLxm ≦ ± 10 μm − (6)
Is sufficient.
The detection area of the line interval sensor 15 is about 2 × 2 mm, and the line length of the interval detection line 16-n in FIG. 5 may be as long as the length and width of the detection area.

The relationship between the interval detection line 16-n and the light beam adjustment in the sub-scanning direction will be described.
In the present invention, one line in the conventional main scanning direction is divided into two. Even if each line divided into two is extended at the joint part, and the joint part is detected by the line interval sensor 15, the output signal becomes as shown in FIG. It will be very difficult to do. Therefore, in creating the interval detection line 16-n, the line interval in the sub-scanning direction is set to an interval convenient for detecting by the line interval sensor 15 (eg, about 0.5 mm).
Note that this line interval changes depending on the environment and time (the change is detected by the line interval sensor 15 and the seam is corrected by holding it at a predetermined value).
The convenient interval is set by delaying writing of one light beam by a predetermined number of scans (12 examples). In the original image creation process (not the adjustment process) after performing the joint correction, the predetermined number of scans (example 12) delay is deleted and light beam scanning is performed.

  The detection timing of the interval detection line (toner image) by the line interval sensor 15 may be any of temperature change of the writing system, number of image formations, time, ON / OFF timing of the main switch, assembly of the photosensitive drum 10, etc., replacement, etc. Or a combination thereof, which is not necessary at the time of image formation, so that the number of times can be reduced as much as possible, toner consumption can be reduced, energy saving and device life can be increased.

It is a perspective view which shows schematic structure of the light beam scanning apparatus concerning this Embodiment. It is the schematic plan view which looked at the light beam scanning device from the upper part. FIG. 3 is a diagram showing an outline of an optical path when the light beam scanning apparatus of FIG. 2 is viewed from the direction A, and is a diagram showing an outline of an optical path of only a first writing system I. FIG. 3 is a diagram illustrating an outline of an optical path when the light beam scanning apparatus of FIG. 2 is viewed from a direction A, and is a diagram illustrating an outline of both the first writing system I and the second writing system II. It is a figure explaining the joint of the 1st writing system picture field and the 2nd writing system picture field. FIG. 5 is a diagram showing that the drum moves up and down due to the eccentricity of the drum and the writing start position in the main scanning direction varies. It is the figure which showed the relationship between the clock signal CLK which is an input signal of a line space | interval sensor, the start signal ST, the output signal Vo (representing the output signal of the main and sub direction), and Trig. It is the figure which showed the output Vo of the line space | interval sensor. It is the figure which showed the output Vo of the line space | interval sensor. It is the figure which showed the output Vo of the line space | interval sensor. It is the figure which showed the output Vo of the line space | interval sensor. When the writing start position varies due to the vertical movement of the drum, it is a diagram showing the relationship between correction and the manner in which the line interval in the main scanning direction varies corresponding to the variation amount. It is the block diagram which showed the structure relevant to a signal.

Explanation of symbols

1-1, 1-2 Light sources 2-1, 2-2 Collimate lens 3-1, 3-2 Cylindrical lens 4 Polygon mirror 5-1, 5-2 First Fθ lens 6-1, 6-2 Second Fθ lenses 7-1 and 7-2 First mirrors 8-1 and 8-2 Second mirrors 9-1 and 9-2 Third mirror 10 Photosensitive drum 15 Line interval sensor 16 Interval detection line 30 Control unit

Claims (5)

In an image forming apparatus that forms an image using a light beam scanning device that divides and scans in the main scanning direction by connecting scanning lines of at least two light beams on a photoconductor,
Synchronization detecting means for detecting the scanning line reference position of the light beam corresponding to each light beam;
Main scanning change means for changing the distance in the main scanning direction from the synchronization detection position detected by the synchronization detection means to the image start position;
Sub-scanning change means for changing the distance in the sub-scanning direction from the synchronization detection position detected by the synchronization detection means to the image start position;
Latent image line forming means for forming a plurality of latent image lines in each of the main and sub-scanning directions on the photosensitive member;
A visualizing means for visualizing the latent image formed on the photoreceptor;
A visible line detecting means for detecting a visible line by the visualizing means;
Line image detection means for detecting the line image position or interval in the main and sub-scanning directions by calculating the position and interval of the specific signal of the output signal of the visible line detection means,
A control unit that changes a plurality of line image positions or intervals to a predetermined value by changing the image writing start position of the light beam by the main scanning changing unit and the sub-scanning changing unit;
2. An image forming apparatus according to claim 1, wherein when the visualizing means forms the visible image line for the scanning line interval in each scanning direction, the width (thickness) of the visible image line formed by each beam is different.   The position (on the time axis) within each of the plurality of visible lines and the output signal based on the relationship between the output signal value of the visible line detection means and a preset value when detecting the plurality of visible lines The image forming apparatus according to claim 1, wherein:   3. The visual line detection unit detects the visual line by changing the thickness of the visual line after associating each visible line with a position (on the time axis) in the output signal. Image forming apparatus.   Based on the relationship between the output signal of the visible line detecting means and a preset value, it is determined whether or not the moving visible visible line is within the detection range of the visible line detecting means. The image forming apparatus according to claim 1.   The scanning line of the light beam by the control unit is connected, the image line scanning corresponding to each beam by the visualization unit at the time of the adjustment process for determining the image writing start position of each light beam and at the time of image creation The image forming apparatus according to claim 1, wherein the direction intervals are different.

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