JPH02129667A - Image forming device - Google Patents

Abstract

PURPOSE:To form an image of high precision by controlling the cycle of a main scanning synchronizing signal, which is outputted against an exposing device at the time of second image formation onward against a same paper responding to the elongation and contraction ratio of the paper. CONSTITUTION:A programmable controller 45 is controlled by a controlling signal from CPU 40, at the time of the second image formation, the cycle of the main scanning synchronizing signal is shortened to shorten the image length in a sub-scanning direction, responding to the contraction of the paper from fixing at the time of the first image formation. Furthermore, the setting value at the CPU 40 of the cycle of the main scanning synchronizing signal at the second image formation onward against the same paper is constituted to be arbitrarily settable/adjustable using an adjusting switch, etc., arranged on the side surface, etc., of a printer main body. Thus the image length can be compensated in the sub-scanning direction with high precision, responding to the elongation and contraction of the paper.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus, and particularly to an image forming apparatus that is equipped with a solid-state scanning type exposure means and is capable of forming images in a composite mode or a double-sided mode. .

(Prior Art) In image forming apparatuses such as printers and copying machines, electrophotographic image forming apparatuses that expose a photoreceptor to form an electrostatic latent image and develop this latent image with toner to form an image are conventionally known. It is well known from In addition to the optical exposure means that uses an optical system consisting of lenses and reflectors to irradiate the reflected light of the original image when there is an original, the exposure means can also be used to scan the original image, or to use a computer, word processor, etc. Exposure means for controlling a laser or LED for exposure based on originally created image data is also known. Laser exposure uses a modulated laser beam and is realized as a rotary scanning type exposure means that scans this laser beam with a rotating polygon mirror, while LED exposure uses an LED array in which a large number of LEDs are arranged at a fine pitch. It has been realized as a solid-state scanning type exposure means that controls the lighting of each LED using the following.

On the other hand, as image forming modes, in addition to the normal mode in which a single image is formed on one side of paper, there is a composite mode in which images are formed overlappingly on one side of paper, and a duplex mode in which images are formed on both sides of paper. Furthermore, in these combination and duplex modes, there are known methods in which image transfer and fixing are repeated two or more times on the same sheet of paper.

(Problem to be Solved by the Invention) However, in the composition and duplex mode in which transfer and fixing are performed multiple times on the same paper as described above, the paper is heated or pressurized during the first fixing, and as a result, the paper shrinks. If the image is transferred and fixed at the same magnification a second time, discrepancies will occur between the images, especially in the case of a composite image, and a proper image will not be obtained.

For example, Japanese Unexamined Patent Application Publication No. 62-17
Publication No. 7567 discloses that the paper shrinkage that occurs during composite and duplex modes is corrected by slowing down the paper transport speed during the second image formation, but the shrinkage can be corrected with high precision through mechanical control. The problem is that it is difficult to do so.

Furthermore, Japanese Patent Application Laid-Open No. 62-194269 discloses that in a copying apparatus equipped with an optical exposure means, the copying magnification is changed during compositing and double-sided copying to accommodate the expansion and contraction of paper. is applicable only to optical exposure means and cannot be applied to solid-state scanning exposure means.

Furthermore, in the case of laser exposure, by correcting the rotation speed of the polygon mirror and changing the scan period in the main scanning direction, it is possible to accommodate expansion and contraction in the sub-scanning direction (paper conveyance direction), and the modulation frequency of the laser beam. It is thought that expansion and contraction in the main scanning direction can be accommodated by changing the Since it is a control, there is a problem in that it is difficult to correct the shrinkage with high precision.

In view of the above-mentioned conventional problems, the present invention provides an image forming apparatus equipped with a solid-state scanning type exposure means. An object of the present invention is to provide an image forming apparatus that can expand and contract an image with high precision in response to expansion and contraction in the scanning direction.

(Means for Solving the Problems) In order to achieve the above object, the present invention has a solid-state scanning type exposure means that forms a latent image on a photoreceptor, and transfers and fixes multiple times onto the same sheet of paper. In an image forming device that enables
The present invention is characterized in that it includes means for controlling the period of the main scanning synchronization signal output to the exposure means in accordance with the expansion/contraction rate of the paper during the second and subsequent image formations on the same paper.

(Function) Since the present invention has the above configuration, when forming an image for the second and subsequent times, the period of the main scanning synchronization signal to the solid-state scanning type exposure means can be adjusted according to the expansion/contraction rate of the paper due to the fixing during the previous image formation. By changing this, the image length in the sub-scanning direction can be expanded or contracted to eliminate image discrepancies. In addition, the period of this main scanning synchronization signal can be controlled 100% electrically without being affected by mechanical factors, so the image length in the sub-scanning direction can be corrected with high precision in response to the expansion and contraction of the paper. can do.

Note that the expansion and contraction rate of paper due to fusing depends on the paper type, basis weight,
It changes depending on the fiber grain direction, moisture content, etc., but these do not change significantly in actual usage conditions, so
For example, if it is possible to adjust it during maintenance, there is almost no practical problem even if it is set to a constant value in advance. It is only necessary to correct the period of the signal.

(Example) Hereinafter, an example in which the present invention is applied to an LED printer will be described with reference to FIGS. 1 to 7.

First, the overall configuration and operation of an electrophotographic printer using an LED exposure method will be explained based on FIG.

Reference numeral 1 denotes a printer main body, in which a well-known electrophotographic image forming section 2 including a photosensitive drum 21, a charger 22, an LED array 23, a developing device 24, a transfer charger 25, a drum cleaner 26, etc. is disposed approximately in the center. It is set up. 3a
, 3b, and 3c are paper feed cassettes attached to one side of the main body l, from which a selected paper feed cassette is fed to the image forming section via the register roller 5 by corresponding paper feed rollers 4a, 4b, and 4c, respectively. A sheet of paper is supplied toward the transfer section 6 between the photosensitive drum 21 and the transfer charger 25 in FIG. The paper onto which the image has been transferred in the transfer section 6 is fixed in the fixing section 7, and then sent out to the duplex unit 10 by the discharge roller 8. At the bottom of the main body 1, the paper sent out from the duplex unit 10 is placed on the register roller 5.
In order to refeed the paper towards the
A paper refeed path 9 is provided.

The duplex unit 10 is provided with a first switching claw 14 between a carry-in roller 11 that receives paper ejected from the main body 1 and a paper ejection roller 13 that ejects the paper to a paper ejection tray 12. The paper is configured to select whether to send the paper toward the paper output tray 12 using the first switching claw 14 or to send the paper toward the second switching claw 16 via the transport roller 15 that can rotate in forward and reverse directions. . Second switching claw 1
6 determines whether the paper is sent to the switchback section 17, sent out to the refeeding path 9 via the delivery roller 19, or conversely, whether the paper from the switchback section 17 is sent out toward the refeeding path 9. , conveyance roller 15, first switching claw 1
4 to the paper discharge tray 12. Reference numeral 18 denotes a conveyance roller of the switchback portion that can rotate forward and backward.

20 is an optional paper feed section, 20a is its paper feed roller,
20b and 20c are conveyance rollers.

Next, basic printing operations in duplex and composite mode will be explained.

First, to explain the case of forming an image in double-sided mode, for example, paper is fed from the upper paper cassette 3a of the main body 1 by the paper feed roller 4a, the registration is adjusted by the register roller 5, and the paper is sent to the transfer section 6. The image formed by the image forming section 2 is transferred, fixed by the fixing section 7, and sent out to the duplex unit 10 by the discharge roller 8. The paper passes through the carry-in roller 11 and is sent to the switchback section 17 via the transport roller 15 by the first switching claw 14, after which the transport roller 18 rotates in the reverse direction, and the paper is sent out by the second switching claw 16. The paper is sent to the roller 19 side and sent out to the paper refeeding path 9 of the main body 1. The paper passes through the paper refeeding path 9 and reaches the register roller 5 again, where the registration is adjusted and the second image created by the image forming section 2 is transferred to the back side of the paper at the transfer section 6, and then transferred to the fixing section 7. and is fixed by the ejection roller 8.
, carry-in roller 11, first switching claw 14, paper ejection roller 13
The paper passes through and is discharged onto the paper discharge tray 12.

In addition, when discharging face down, the first switching claw 14 and the second switching claw 16 are used to temporarily move the switchback section 1.
7 side, the first switching claw 14 is switched and the paper passes through the conveyance roller 15 and the paper ejection roller 13 to the paper ejection tray 1.
2 is discharged on top.

When forming an image in the composite mode, the image created by the image forming unit 2 as described above is transferred to the surface of the paper by the transfer unit 6 and fixed by the fixing unit 7, and then transferred from the discharge roller 8 to the duplex unit 10. is sent out to the carry-in roller 11
, first switching claw 14, conveyance roller 15, second switching claw 1
6 and delivery roller 19 to the paper refeeding path 9, and is sent to the transfer unit 6 again via the register roller 5, where the second image created by the image forming unit 2 is superimposed and transferred onto the surface of the paper. , is fixed by the fixing unit 7, and is discharged onto the paper discharge tray 12 through the duplex unit IO.

FIG. 3 shows the configuration of an LED exposure unit 30 consisting of the LED array 23 and its drive control circuit. In FIG. 3, 31 is a shift register into which image data is sequentially input based on a shift clock, 32 is a latch register that latches the image data of the shift register based on a latch signal, and 33 is a latch register and register that is input based on a strobe signal. LE output according to the data latched in 32.
This is an LED driver that outputs and drives each LED of the D array 23.

As shown in the timing chart of FIG. 4, in this LED exposure unit 30, image data for 1 life is input to a shift register 31 in synchronization with a shift clock outputted using a main scanning synchronization signal as a start signal. After the input of image data for a line is completed, a latch signal is output and the image data is latched into the latch register 32. Thereafter, a strobe signal is output using the next main scanning synchronization signal as a start signal, and each LED of the LED array 23 is lit by the LED driver 33 based on the image data latched in the latch register 32, and the photoconductor 21
is exposed.

Next, with reference to FIG. 5, the operation of the LED exposure unit 30 when forming a first image and a second image on the same sheet of paper and during image formation in double-sided mode will be described. First, at the exposure start timing of the first image, the sub-scanning synchronizing signal changes from L level to H level, and the main scanning synchronizing signal is output at a predetermined period t1. A shift clock is issued and image data is input to the shift register 31, and when this is completed, a latch signal is issued and the image data is latched into the latch register 32. When the next main scanning synchronization signal is issued after an appropriate margin time has elapsed from this latch signal, the above operation is repeated and the LED lighting is controlled according to the image data latched by the strobe signal as explained earlier. Ru. The above operation is repeated for a predetermined number of lines for one image, and T
One hour later, the sub-scanning synchronization signal returns to L level.

Next, at the exposure start timing of the second image, the sub-scanning synchronization signal becomes H level again, and this time the main-scanning synchronization signal becomes tz=
The image data is output at a period of (t+-Δt), and similarly to the above, the image data is input to the shift register, latched, and the LED
The lighting is controlled. The above operation is repeated for a predetermined number of lines for one image, and the sub-scanning synchronization signal returns to the L level after a time period of Tt = (T+ - ΔT). In this way, when the second image is formed, the period of the main scanning synchronization signal is shortened by ΔL, so the time when the public scanning synchronization signal is at the H level is shortened by ΔT, and the peripheral speed of the photoreceptor 21 is constant. Therefore, the image length in the sub-scanning direction of the second image is shorter than that of the first image.

By making this reduction amount correspond to the shrinkage of the paper due to fixing during the first image formation, it is possible to prevent discrepancies between the two images even in the composite and double-sided mode.

Next, a circuit configuration for controlling the above operation will be explained based on FIG. 1. 40 is a CPU that controls the entire printer body 1 and the LED exposure unit 30; 41 is an oscillator that outputs a basic clock; 42 is an oscillator that receives the basic clock and outputs a predetermined number of shift clocks; A counter that outputs a timing signal for signals,
43. 44 is a monostable multivibrator (one shot) that outputs a latch signal and strobe signal with a predetermined pulse width; 45 is a programmable counter that receives a basic clock and a control signal from the CPU 40 and outputs a main scanning synchronization signal; 46 is a main This is an image creation section that outputs image data to the LED exposure unit 30 based on a scanning synchronization signal and a sub-scanning synchronization signal.

Then, when printing in the above compositing and duplex mode,
The programmable controller 45 is controlled by a control signal from the CPU 40, and as described above, when forming the second image, the image length in the sub-scanning direction is shortened in response to the shrinkage of the paper due to the fixing during the first image formation. The period of the main scanning synchronization signal is shortened. In addition, 2 for the same paper
CPU of the period of the main scanning synchronization signal during image formation after the first time
The setting values 40 are configured so that they can be adjusted as desired during maintenance or the like using an adjustment switch (not shown) placed on the side surface of the printer body 1 or the like.

Next, a control procedure by the CPU 40 will be explained.

FIG. 6 shows the main routine of the CPU 40.

When the power is turned on, the CPU 40 is reset, and the program is started, in step #1, the random access memory is cleared, various registers are initialized, and initial settings are made to put each device into the initial mode. Next, in step #2, an internal timer is started.

The internal timer determines the time required for one routine of this main routine and serves as a reference for the timers used in each subroutine, and its value is set in advance in step #1.

Next, in step #3, a key manual subroutine is executed, in step #4 a subroutine for print processing, and in step #5 a subroutine for processing other processes such as paper jams, etc.

After sequentially calling each of the above subroutines, step #
At step 6, the process waits for the internal timer to end and returns to step #2.

FIG. 7 shows a print processing subroutine executed in step #4.

Here, first, in step #11, it is determined whether the print mode is the composite mode, and if it is the composite mode, the process moves to step #13. If it is not the combination mode, it is determined in step #12 whether or not it is the duplex mode, and if it is the duplex mode, the process moves to step #13, and if it is neither the combination mode nor the duplex mode, the process moves to step #14. Step #1
In step 3, it is determined whether this is the second or subsequent print on the same paper, and if it is the first print, step #1 is performed.
4, and if it is the second or subsequent print, go to step #
15. In step #14, the period of the main scanning synchronization signal is set to tl, and in step #15, the period of the main scanning synchronization signal is set to tz = (-Δt), and the corresponding control signals are output to the programmable counter 45. Then, the process moves to step #16. In step #16,
It outputs a main scanning synchronization signal and a sub-scanning synchronization signal in synchronization with the operations of various devices in the image forming section 2 and paper feeding system, and also executes a print operation subroutine for controlling the image forming section 46 and printing. , return to the main routine.

The present invention is not limited to the above-mentioned embodiment. For example, although the above-mentioned embodiment shows an example in which an image is formed twice on the same sheet of paper, when an image is formed on the same sheet three or more times as in double-sided compositing, In order to accommodate this, the period of the main scanning synchronization signal corresponding to the paper shrinkage rate during each image formation is set in advance, and the main scanning synchronization signal with the corresponding period is output during each image formation. You can also make it so that

Furthermore, even if the paper does not shrink but expands due to fixing, this can be dealt with in the same way by increasing the period of the main scanning synchronization signal.

(Effects of the Invention) As is clear from the above description, according to the image forming apparatus of the present invention, during the second and subsequent image formations, solid state scanning is performed according to the expansion and contraction rate of the paper due to fixing during the previous image formation. By changing the cycle of the main scanning synchronization signal to the mold exposure means, the image length in the sub-scanning direction can be expanded or contracted to eliminate image discrepancies. In addition, the period of this main scanning synchronization signal can be controlled 100% electrically without being affected by mechanical factors, so the image length in the sub-scanning direction can be corrected with high precision in response to the expansion and contraction of the paper. It has the effect of being able to.

[Brief explanation of the drawing]

Figures 1 to 7 show an embodiment in which the present invention is applied to a printer, in which Figure 1 is a control circuit diagram of an LED exposure unit, Figure 2 is a general schematic diagram of the printer, and Figure 3 is an LED exposure unit. 4 is a timing chart of the same operation, FIG. 5 is an explanatory diagram of the effect of period correction of the main scanning synchronizing signal, FIG. 6 is a main flowchart of control, and FIG. 7 is a flowchart of print processing.・−・−・Image forming unit Photoreceptor LED array LED exposure unit・CPU −・−Programmable counter・・・Image creation unit 21−−−−・−・・−・23−1−−−−−−−・−・−・−・・−30−−−
−−−１・−１１１・・・・・・40−・・−・−
...

Claims (1)

[Claims] (1) In an image forming apparatus that has a solid-state scanning type exposure means that forms a latent image on a photoconductor and is capable of transferring and fixing onto the same sheet of paper multiple times, the second and subsequent images on the same sheet of paper are An image forming apparatus characterized by comprising means for controlling the period of a main scanning synchronization signal outputted to an exposure means in accordance with the expansion/contraction rate of paper during formation.