JP2008309874A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for suppressing transfer unevenness and color tone shift of images by correcting a toner mounted amount corresponding to thickness distribution of a direction intersected with a conveying direction of a recording material. <P>SOLUTION: The thickness distribution of the recording material P taken out from a paper feed cassette 17 in a direction orthogonal to the conveying direction is measured by a medium thickness detection sensor 34. An engine controller 40 regulates a PWM modulation amount along a main scanning line of a laser beam of an exposure device 1 in response to the thickness distribution of the measured recording material. Even when transfer efficiency deteriorates by being caused by the thickness distribution along the main scanning line, the toner images transferred secondarily from an intermediate transfer belt 4 to the recording material P form the same high quality images as the recording material of the uniform thickness distribution since the toner mounted amount of the toner images formed at a corresponding position of a photoreceptor drum 3 is proportionally increased by that much. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus for electrically transferring a toner image carried on an image carrier or an intermediate transfer member to a recording material, and more specifically, transfer irregularities and image defects caused by uneven thickness distribution of the recording material. It relates to control to reduce.

  2. Description of the Related Art Image forming apparatuses in which a toner image carried on an image carrier or an intermediate transfer member is electrically transferred to a recording material and thermally fixed are widely used. In recent years, the image forming apparatus can deal not only with recording materials with uniform thickness distribution such as plain paper and coated paper, but also with recording materials with non-uniform thickness distribution such as sealed letters, folded paper, and booklets. It has been demanded.

  However, when electrical transfer is performed with a recording material having a non-uniform thickness distribution, transfer defects and uneven transfer are more likely to occur than in the case of a uniform thickness distribution. This is because, in a region where the thickness of the recording material is large, transfer efficiency is lower than that in a region where the thickness is small, for example, because the resistance value in the thickness direction is relatively high.

  In addition, when forming a color image by superimposing a plurality of color toner images in a mesh pattern, if an image is formed on a recording material having a non-uniform thickness distribution, the brightness of the image between a region with a large thickness and a region with a small thickness Differences and hue differences may occur.

  Patent Document 1 discloses a full-color image forming apparatus in which yellow, magenta, cyan, and black image forming units are arranged along a recording material conveyance body. Here, a recording material thickness measuring device including a pair of pressure contact rollers is disposed upstream of the image forming unit in the recording material conveyance path. Then, the heating temperature of the fixing device is adjusted according to the measured maximum thickness of the recording material.

  Patent Document 2 discloses an image forming apparatus that transfers a toner image from an image carrier to a recording material by passing the recording material through a transfer portion where an image carrier and a transfer rotator are pressed against each other. Here, a recording material thickness measurement sensor constituted by a non-contact distance meter is arranged on the upstream side of the transfer portion in the recording material conveyance path. Then, the transfer voltage applied to the transfer unit in the process in which the recording material passes through the transfer unit is adjusted in accordance with the measured thickness distribution in the conveyance direction of the recording material. As a result, a high transfer voltage is applied to a portion having a large thickness in the conveyance direction of the recording material, and a low transfer voltage is applied to a portion having a small thickness.

JP 2003-149887 A Japanese Patent Application Laid-Open No. 08-292626

  Since the image forming apparatus of Patent Document 2 changes the transfer voltage according to the thickness distribution measured in the direction along the recording material conveyance direction, at least a belt-like region located immediately below the measured position has a transfer failure or transfer. Unevenness can be prevented. However, since a uniform and uniform transfer voltage corresponding to the thickness immediately below the measured position of the thickness distribution is applied to the entire width of the recording material passing through the transfer portion, the direction (width direction) orthogonal to the conveyance direction of the recording material The thickness distribution of is ignored. For this reason, when the thickness is large in a part in the width direction of the recording material, the transfer efficiency is locally reduced in that part, and there is a high possibility of causing density unevenness and transfer failure.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of correcting the amount of applied toner according to the thickness distribution in the direction intersecting the recording material conveyance direction and suppressing image transfer unevenness and color tone deviation.

  The image forming apparatus of the present invention includes an image carrier, a charging unit that charges the surface of the image carrier, a writing unit that writes an electrostatic image of an image on the charged surface, And a developing unit that supplies the toner to the image and develops the toner image, and sequentially transfers the toner image to the recording material along the conveyance direction of the recording material. And an identification unit that identifies a thickness distribution of the recording material in a direction that intersects the transport direction, and a toner that controls the writing unit based on the identified thickness distribution and that intersects the toner according to the thickness distribution. Control means for forming on the image carrier a toner image of which the applied amount distribution is adjusted.

  In the image forming apparatus of the present invention, the writing means adjusts the writing amount distribution in the direction corresponding to the intersecting direction in accordance with the thickness distribution of the recording material in the direction intersecting the conveying direction of the recording material at the time of transfer. A toner image in which the amount of applied toner at each position is adjusted in a direction that cancels out the transfer efficiency difference at each position due to the thickness distribution in the intersecting direction of the recording material is formed on the image carrier. On the premise of the transfer efficiency difference at each position, a toner image in which the distribution of the applied toner amount is corrected so that a necessary amount of toner is transferred to the recording material at each position is formed on the image carrier. A toner application amount sufficient to compensate for variations in transfer efficiency due to a difference in thickness at each position is ensured at each position.

  Therefore, it is possible to secure a toner image having a toner application amount on the recording material after transfer, in which the influence of the thickness distribution of the recording material in the direction (width direction) intersecting the recording material conveyance direction is reduced. Even with a recording material whose thickness varies in the direction crossing the transport direction, it is possible to form an image with reduced transfer unevenness and color tone deviation.

  Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings. The present invention replaces a part or all of the configuration of each embodiment with an alternative configuration as long as the toner image whose toner application amount is adjusted according to the thickness distribution of the recording material is transferred to the recording material. Other embodiments can also be implemented.

  The present invention is implemented not only in an image forming apparatus that transfers a plurality of color toner images formed on a single photosensitive member on an intermediate transfer member, but also in an image forming apparatus that directly transfers a single color image from an image carrier to a recording material. it can. A so-called tandem type image forming apparatus in which a plurality of photoconductors are arranged along an intermediate transfer member or a recording material conveyance member can also be implemented.

  In each embodiment, only main parts related to toner image formation will be described. However, in the present invention, necessary equipment, equipment, and a housing structure are added, and a printer, various printing machines, a copier, a FAX, It can be implemented in various applications such as a multifunction machine.

  Further, the general matters relating to the configuration or control of the image forming apparatus disclosed in Patent Documents 1 and 2 are not illustrated and redundant description is omitted.

<First Embodiment>
FIG. 1 is a schematic explanatory diagram of the configuration of the image forming apparatus of the first embodiment, and FIG. 2 is a flowchart of control of the exposure apparatus.

  As shown in FIG. 1, the image forming apparatus 100 according to the first embodiment is an electrophotographic full-color laser beam printer using an intermediate transfer belt 4. The image forming apparatus 100 primarily transfers the toner image formed on the photosensitive drum 3 to the intermediate transfer belt 4 at the primary transfer portion T1, and then performs secondary transfer from the intermediate transfer belt 4 to the recording material P at the secondary transfer portion T2. To do.

The intermediate transfer belt 4 is formed in an endless shape, and is supported around a driving roller 36, a secondary transfer inner roller 37, a tension roller 39, and a primary transfer roller 38. The intermediate transfer belt 4 is driven by a driving roller 36 connected to the driving mechanism 25 and circulates in a counterclockwise direction in the drawing at a process speed of 137 mm / sec.

  The photosensitive drum 3 rotates in the clockwise direction in the drawing with a surface speed equal to the circulation speed of the intermediate transfer belt 4. The photosensitive drum 3 is configured by applying an organic photoconductor layer (OPC) to the outer peripheral surface of an aluminum cylinder having a diameter of 30 mm.

  The photosensitive drum 3 is rotatably supported at both ends in the axial direction by flanges, and is rotated by transmitting a driving force from the drive mechanism 25 to one end. Around the photosensitive drum 3, a primary charger 22, an exposure device 1, a rotary developing device 10, a primary transfer roller 38, and a drum cleaning device 2 are arranged.

  The primary charger 22 applies a charging voltage in which an AC voltage is superimposed on a negative DC voltage from a power source D3 to a conductive roller that is in contact with the photosensitive drum 3, so that the surface of the photosensitive drum 3 is uniformly negatively charged. Charge to potential.

  The exposure apparatus 1 is controlled by the engine controller 40 and reflects the laser beam LB output from the laser unit 6 by the polyhedral mirror 7 to scan the surface of the photosensitive drum 3 in the axial direction. As a result, an electrostatic image is formed on the surface of the rotating photosensitive drum 3 by reducing the potential of the portion where the toner should adhere in the separated images of yellow, magenta, cyan, and black. The scanner motor 8 rotates the polyhedral mirror 7. The beam detection signal generation circuit 48 detects the laser beam LB scanned by the polyhedral mirror 7 at the end of the scanning amplitude, and outputs a writing timing signal in the main scanning direction.

  As shown in FIG. 1, the rotary developing device 10 can be rotated to move the yellow developing device 10 a, the magenta developing device 10 b, the cyan developing device 10 c, and the black developing device 10 d to positions facing the photosensitive drum 3. It is. Since the yellow developing unit 10a, the magenta developing unit 10b, the cyan developing unit 10c, and the black developing unit 10d are formed in the same manner, the cyan developing unit 10c will be described below as a representative.

  The cyan developing device 10c rotates the developing sleeve S4 carrying the charged cyan toner in a thin layer state with a slight gap from the photosensitive drum 3.

  The power source D4 applies a developing voltage obtained by superimposing an AC voltage to a DC voltage having the same polarity as the charging polarity of the toner to the developing sleeve S4, and moves the toner on the developing sleeve S4 side to the exposed portion of the photosensitive drum 3. As a result, toner sufficient to cancel out the amount of charge in the exposed portion as viewed from the DC voltage adheres to the electrostatic image, and a reversely developed cyan toner image is formed.

  As shown in FIG. 1, the yellow developing device 10a, the magenta developing device 10b, and the black developing device 10d form the respective color toner images using yellow toner, magenta toner, and black toner, respectively.

  The primary transfer roller 38 is pressed against the photosensitive drum 3 via the intermediate transfer belt 4 to form a primary transfer portion T <b> 1 between the photosensitive drum 3 and the intermediate transfer belt 4. The primary transfer roller 38 is applied with a positive direct current voltage from the power source D 1, thereby attracting and moving the negative toner image on the photosensitive drum 3 side to the intermediate transfer belt 4. Transfer residual toner remaining on the photosensitive drum 3 after passing through the primary transfer portion T1 is removed by the drum cleaning device 2.

  A secondary transfer outer roller 27 and a belt cleaning device 15 are disposed on the outer peripheral surface of the intermediate transfer belt 4. The secondary transfer outer roller 27 can be brought into contact with / separated from the intermediate transfer belt 4 by the drive mechanism 29 and the belt cleaning device 15 by the drive mechanism 26, respectively.

  In the state where the secondary transfer outer roller 27 and the belt cleaning device 15 are separated from each other, toner images of four colors of yellow, magenta, cyan, and black are primarily transferred onto the intermediate transfer belt 4 in order. When the four color toner images are transferred to the intermediate transfer belt 4, the secondary transfer outer roller 27 comes into contact with the intermediate transfer belt 4 whose inner surface is supported by the secondary transfer inner roller 37, and the secondary transfer portion T2. Form.

  The secondary transfer inner roller 37 is connected to the ground potential, and the secondary transfer outer roller 27 is connected to the power source D2. The secondary transfer portion T2 sandwiches and conveys the recording material P on the intermediate transfer belt 4 on which the toner image is primarily transferred.

  The power source D2 applies a positive DC voltage to the secondary transfer outer roller 27 to secondary-transfer the toner image on the intermediate transfer belt 4 to the recording material P passing through the secondary transfer portion T2.

  The recording material P electrostatically converts the negative four-color toner images carried on the intermediate transfer belt 4 in the process of being fed from the paper feed cassette 17 or the manual feed tray 19 and passing through the secondary transfer portion T2. Batch secondary transfer. Untransferred toner remaining on the intermediate transfer belt 4 after passing through the secondary transfer portion T2 is removed by a belt cleaning device 15 in contact with the intermediate transfer belt 4.

  The pickup roller 30 pulls out the uppermost recording material P from the paper feed cassette 17 that stores the recording material P in an overlapping manner, and supplies the recording material P to the separation roller 31. The separation roller 31 separates the multi-feed recording material P one by one and delivers it to the registration roller 32. The registration roller 32 sends the recording material P to the secondary transfer portion T2 in synchronization with the toner image on the intermediate transfer belt 4. The conveyance guides 33 are provided in pairs on the conveyance path of the recording material P reaching the registration rollers 32 so as to sandwich the recording material P in the thickness direction.

  The manual feed tray 19 is used when the recording material P is manually fed. The manual tray paper size detection sensor 21 detects the size of the manual sheet. When a manual paper guide (not shown) is slid and moved to a position corresponding to the recording material P, a voltage signal corresponding to the size of the recording material P is output from the manual tray paper size detection sensor 21.

  The fixing device 16 fuses the toner image transferred to the recording material P to the surface of the recording material P by heating and pressing. The recording material P that has passed through the secondary transfer portion T2 is conveyed to the fixing device 16 and is heated and pressurized by the fixing portion T3 to fix the full-color image on the surface, and is discharged from the discharge port 20 to the stacking tray 23. Is done.

  The home position detection sensor 5 detects the HP mark 12 affixed to the inner surface of the intermediate transfer belt 4 and generates a timing signal for starting to write an electrostatic image of each color image on the photosensitive drum 3. The environment sensor 28 detects the temperature and humidity of the environment of the photosensitive drum 3.

  The patch detection sensor 13 is a density detection sensor that optically detects the density (color material amount) of the color patch toner image formed on the photosensitive drum 3. The engine controller 40 experimentally forms a density detection toner image (hereinafter referred to as a batch) for each color on the photosensitive drum 3 in order to determine the density reproduction status at the time of image formation. The engine controller 40 automatically detects the patch density based on the output of the patch detection sensor 13 and feeds it back to the image forming conditions such as the exposure amount and the developing bias.

  The engine controller 40 receives the outputs of various sensors, outputs them to various actuators, and executes setting capture and necessary display through the operation panel 108. The engine controller 40 controls the exposure apparatus 1 and executes necessary image forming jobs by linking the units of the apparatus main body 100A.

  As shown in FIG. 2 with reference to FIG. 1, the engine controller 40 starts image forming control when an image forming job accompanied by image data is input (YES in S31).

  When the attached document reading device reads a document image or receives image data from the outside, the image controller 41 separates the received image data into four primary color screen patterns and performs predetermined image processing. The image processed image data is converted into scanning line image data of each color having an information amount of a plurality of bits and sent to the engine controller 40.

  Next, the engine controller 40 starts the start-up operation of the apparatus main body 100A while the image controller 41 performs image processing control (S32). The engine controller 40 starts energizing the heater of the fixing device 16 to shift to the preheating state, and supplies the recording material P based on the print size information set on the operation panel 108, the document size detected by the document reader, and the like. The paper cassette 17 is selected.

  Next, the engine controller 40 operates the pickup roller 30 and the separation roller 31 to pull out the recording materials P one by one from the paper feed cassette 17 (S33), conveys them to the registration roller 32, and waits (S34).

  Next, the engine controller 40 detects the output voltage of the temperature sensor attached to the fixing device 16 and determines whether or not the fixing unit T3 has reached the target temperature (S35). When the target temperature is reached (YES in S35), the engine controller 40 separates the secondary transfer outer roller 27 and the belt cleaning device 15 and activates the intermediate transfer belt 4, the photosensitive drum 3, etc. The operation is started (S36). Then, at the timing when the home position detection sensor 5 detects the HP mark 12 of the intermediate transfer belt 4, the exposure apparatus 1 is operated to start image formation (S37).

  In the case of a full color image, the rotary developing device 10 sequentially develops the electrostatic image formed on the photosensitive drum 3 with a yellow developing device 10a, a magenta developing device 10b, a cyan developing device 10c, and a black developing device 10d. The developed toner image is primarily transferred onto the intermediate transfer belt 4 every time it is formed. The engine controller 40 detects the output of the environmental sensor 28 and sets a transfer voltage reflecting the environmental conditions.

  When four color toner images are prepared on the intermediate transfer belt 4, the engine controller 40 brings the secondary transfer outer roller 27 and the belt cleaning device 15 into contact with the intermediate transfer belt 4. Then, the engine controller 40 activates the registration roller 32 to resume conveyance of the recording material P, feeds the recording material P to the secondary transfer portion T2, and nips and conveys it over the toner image (S37). The engine controller 40 detects the output of the environmental sensor 28 and sets a transfer current according to the environmental conditions. The power source D2 performs constant current control on the transfer voltage applied to the secondary transfer outer roller 27 using the set transfer current.

  Next, the recording material P on which the toner image has been secondarily transferred from the intermediate transfer belt 4 in the secondary transfer portion T2 is conveyed to the fixing device 16 in which the fixing portion T3 is controlled to a predetermined temperature. The fixing device 16 heats and pressurizes the recording material P and nipping and conveying the recording material P, thereby thermally fixing the toner image on the surface of the recording material P (S38).

  Finally, when the trailing end of the recording material P passes through the paper discharge unit 20 located downstream of the fixing device 16, the image forming operation is finished (YES in S39).

  In the case of a monochrome image, the rotary developing device 10 develops the electrostatic image formed on the photosensitive drum 3 by the black developing device 10d, and only the formed black toner image is primarily transferred to the intermediate transfer belt 4. . Thereafter, the process of secondary transfer of the toner image from the intermediate transfer belt 4 to the recording material P and discharging after fixing is performed in the same manner as in the case of a full-color image.

<Control of exposure apparatus>
FIG. 3 is a diagram for explaining the relationship between the recording material thickness and the transfer efficiency, and FIG. 4 is an explanatory diagram for an additional rate of applied toner according to the thickness distribution of the recording material. FIG. 5 is an explanatory diagram of the control for adjusting the amount of applied toner according to the thickness distribution of the recording material, and FIG. 6 is a lookup table of correction values in the PWM control of the exposure apparatus. FIG. 7 is a block diagram for explaining the connection between the image controller and the exposure apparatus, and FIG. 8 is a flowchart for controlling the exposure apparatus. In FIG. 5, (a) is the recording material thickness, (b) is the exposure amount, (c) is the electrostatic image, and (d) is the toner image.

  When the thickness of the recording material P increases, the transfer efficiency in the secondary transfer portion T2 decreases as shown in FIG. 3, and among the toner images on the intermediate transfer belt 4, the transfer residual toner passes through the secondary transfer portion T2. The rate of becoming increases. In FIG. 3, d corresponds to a standard plain paper having a thickness of 80 μm.

  For this reason, when the toner image on the intermediate transfer belt 4 is transported to the secondary transfer portion T2 and is secondarily transferred to the recording material P, if the in-plane thickness distribution of the recording material P varies, the density unevenness may appear in the image. And uneven color tone will be formed. This is because when the thickness of each part of the recording material P is different, the transfer efficiency is lowered in the thick part compared to the thin part, and the amount of toner transferred to the recording material P is reduced. This is because, as a result of the variation in the amount of toner transferred to the recording material, density unevenness and color tone unevenness corresponding to the thickness distribution of the recording material are formed in the fixed image.

  Therefore, in the first embodiment, the thickness distribution in the direction orthogonal to the transport direction is measured for each recording material P fed to the secondary transfer portion T2, and is reflected in the toner amount of the toner image on the intermediate transfer belt 4. I am letting. The toner image transferred to the thick portion of the recording material P is exposed to the photosensitive drum 3 by the exposure device 1 so that the reduction in the transfer efficiency can be offset as shown in FIG. The amount of applied toner is increased.

  In other words, since the amount of toner applied on the intermediate transfer body 4 is corrected according to the thickness distribution of the recording material P, even if the transfer efficiency is reduced at a portion where the thickness of the recording material P is large, the reduction in transfer efficiency is offset. The applied toner amount is secondarily transferred to the recording material P.

  In the first embodiment, by exposing the laser beam to pulse width (PWM) modulation in accordance with the partial density of an image to be formed, the exposure apparatus 1 converts an electrostatic image of screen pattern dots of area gradation into a photosensitive drum. 3 to form. Then, the dot exposure time is extended for a portion where the recording material P has a large thickness, and a required apparent density is ensured in the toner area of the dot even if the toner transfer thickness is reduced.

  As shown in FIG. 5A, when the thickness of the recording material changes in the main scanning direction, as shown in FIG. 5B, the density gradation for each dot along the scanning line is obtained. Accordingly, the laser beam whose pulse width is modulated is scanned. The dots in the thick portion of the recording material have a longer pulse width than the thin portions.

  As shown in FIG. 5C, in each dot region, the charging potential VD of the photosensitive drum 3 is lowered to the exposure portion potential VL by an area corresponding to the density gradation of the pixel. In the thick dot portion of the recording material, since the pulse length is long, the area where the exposure portion potential VL in the dot is lowered becomes larger than in the thin portion.

  As shown in FIG. 5C, the electrostatic image is developed using a DC voltage VB set between the charging potential VD of the photosensitive drum 3 and the exposure portion potential VL. As a result, toner sufficient to cancel out the charge amount of the exposed portion potential VL viewed from the DC voltage VB adheres to the electrostatic image (exposed portion), and is reversely developed as shown in FIG. A toner image primarily transferred to the intermediate transfer belt 4 is formed.

  In the first embodiment, when the secondary transfer from the intermediate transfer belt 4 to the recording material is performed, in the thick portion of the recording material, the transfer efficiency is reduced, the toner transferred to the recording material is reduced, and the toner in the dots adheres. The density of the part decreases. However, since the area to which the toner in the dots adheres is increased, the amount of toner applied per dot is secured to the same level as the thin portion of the recording material. In other words, the toner adhesion area in each dot is increased by the amount corresponding to the untransferred toner remaining on the intermediate transfer belt 4.

  As shown in FIG. 1, the engine controller 40 identifies the thickness distribution of the recording material P based on the output of the medium thickness detection sensor 34, and adjusts the scanning line image data developed by the image controller 41 according to the thickness distribution. . The engine controller 40 controls the exposure apparatus 1 using scanning line image data in which the exposure time for each dot is adjusted as shown in FIG. 6 according to the thickness of each position of the recording material.

  The medium thickness detection sensor 34 is disposed downstream of the conveyance guide 33 where the recording material P is in a stable behavior state, and detects a thickness distribution corresponding to one line in the main scanning direction of the recording material P as needed. The medium thickness detection sensor 34 is composed of a large number of light emitting elements and light receiving elements arranged on the main scanning line 1 on the recording material P as a reflection focal point, and according to the thickness at each position on the main scanning line. The output of the light receiving element at each position changes. The analog output of the medium thickness detection sensor 34 is transmitted to the engine controller 40. The engine controller 40 compares the detection levels of the light receiving elements at each position on one main scanning line to identify the thickness distribution of the recording material P in the main scanning direction.

  A similar medium thickness detection sensor 34 is also arranged in the conveyance path for guiding the recording material P fed from the manual feed tray 19 to the registration roller 32, and the thickness distribution of the recording material P is identified by the engine controller 40.

  As shown in FIG. 7, the image controller 41 exchanges data with a document reading device, a network-connected personal computer, etc., and receives and holds transmitted image data.

  The image controller 41 forms density image data of yellow, magenta, cyan, and black separation colors from the input image data, performs γ correction, etc., and develops them into scanning line image data.

  The engine controller 40 operates the exposure apparatus 1 using the scanning line image data formed by the image controller 41. The CPU 44 controls the AD processing unit 46, the PWM processing unit 45, and the exposure apparatus 1 according to a program stored in the ROM 43.

  The ROM 43 is a storage element that stores a program and control data for controlling the exposure apparatus 1.

  The AD processing unit 46 performs an AD conversion process on the analog output transmitted from the medium thickness detection sensor 34 to convert the analog output into a digital signal, and inputs the digital signal to the CPU 44.

  The CPU 44 identifies the in-plane thickness distribution for each recording material P based on the output of the medium thickness detection sensor 34. The CPU 44 corrects the scanning line image data sent from the image controller 41 with reference to the lookup table (recording material thickness-scanning line image data correction value) shown in FIG.

  The recording material thickness-scanning line image data correction value table shows the recording material thickness shown in FIG. 4 for each transfer voltage / transfer current set based on the relationship between the environmental conditions shown in FIG. 3 and the transfer voltage and transfer current. And the transfer efficiency is defined. The specified amount is set such that one pixel of 600 dpi image data is set in units of 8 bits from the image controller 41, whereas one pixel of 600 dpi image data corrected by the engine controller 40 is set in 9 bits. It has become. Therefore, for example, when the image data from the image controller 41 is 0xFF and the recording material thickness is 4, the value corresponding to 116% in FIG. 6 is set to 0x128.

  The CPU 44 sets the transfer voltage / transfer current as described above based on the output of the environment sensor (28: FIG. 1). The CPU 44 corrects the scanning line image data for each scanning line at the timing of the scanning synchronization signal generated by the beam detection signal generation circuit 48, and sends the corrected scanning line image data to the PWM processing unit 45.

  The PWM processing unit 45 temporarily accumulates the corrected scanning line image data of a plurality of scanning lines, and converts the corrected scanning line image data into a laser drive signal by performing pulse width modulation. The PWM processing unit 45 determines the exposure amount for each dot along the scanning line based on the scanning line image data corrected according to the thickness distribution of the recording material P identified by the CPU 44, and sets the exposure amount to the pulse width gradation. To generate a PWM signal.

  The laser drive signal is sent to the laser driver 42 at the timing of the scanning synchronization signal generated by the beam detection signal generation circuit 48 to drive the laser unit 6. The laser driver 42 drives the laser unit 6 to emit light using a PWM signal that reflects the thickness distribution of the recording material P.

  As shown in FIG. 8 with reference to FIG. 7, the engine controller 40 performs the thickness distribution in the main scanning direction of the medium thickness detection sensor 34 in the process in which the recording material passes through the medium thickness detection sensor 34 (S <b> 33: FIG. 2). Is repeatedly taken in every 10 scanning lines (S11). The main scanning direction is a direction intersecting (orthogonal) with the conveyance direction of the recording material.

  Next, when the recording material finishes passing through the medium thickness detection sensor 34, the engine controller 40 calculates the in-plane thickness distribution of the recording material based on the acquired many thickness distributions as described above (S12). ).

  Next, when the maximum thickness exceeds the specified value (YES in S13) and the maximum thickness / minimum thickness ratio exceeds the specified value (YES in S14), the engine controller 40, as described above, The scanning line image data for each scanning line is corrected (S15).

  However, when the maximum thickness is not more than the specified value (NO in S13) and when the maximum thickness / minimum thickness ratio is not more than the specified value (NO in S14), the transfer efficiency difference in the surface of the recording material P is determined. Since it cannot be accurately captured, the scanning line image data for each scanning line is not corrected. The specified value of the maximum thickness is 3d = 240 μm in which no substantial decrease in transfer efficiency is observed (see FIG. 6). The specified value of the maximum thickness / minimum thickness ratio is 10% in consideration of the measurement error and statistical error of the medium thickness detection sensor 34.

  The engine controller 40 supplies a PWM signal to the exposure apparatus 1 and writes an electrostatic image reflecting the thickness distribution of the recording material on the photosensitive drum (3: FIG. 1) (S36: FIG. 2). In the PWM signal, the exposure duty of each pixel along the scanning line is optimized based on the scanning line image data after correction processing corresponding to the thickness distribution of the recording material P. The laser driver 42 controls the light emission of the laser unit 6 based on the received PWM signal signal, and scans and exposes the photosensitive drum (3: FIG. 1) (S16).

<Correspondence with Invention>
The first embodiment is an example of an image forming method having the following first to fourth steps.

  In the first step, the distribution of the exposure amount in the exposure image in which the image is written on the image carrier is adjusted as a result corresponding to the thickness distribution of the recording material on which the image is to be formed.

  In the second step, an exposure image is written on the image carrier to form an electrostatic image of the image.

  In the third step, a charged toner is attached to the electrostatic image, so that a toner image in which the toner load distribution is adjusted according to the thickness distribution of the recording material is formed on the image carrier.

  In the fourth step, the toner image having the adjusted toner amount distribution is brought into contact with the recording material and electrically transferred.

  The photosensitive drum 3, which is an example of an image carrier, carries an electrostatic image and carries a toner image.

  A primary charger 22 as an example of a charging unit charges the surface of the image carrier.

  The exposure apparatus 1 as an example of a writing unit writes an electrostatic image of an image on the surface of a charged image carrier.

  A cyan developing device 10c, which is an example of a developing unit, supplies charged toner to an electrostatic image and develops the toner image.

  In the image forming apparatus 100 as an example of the image forming apparatus, the toner images are sequentially and electrically transferred to the recording material along the recording material conveyance direction.

  The engine controller 40, which is an example of an identification unit, identifies the recording material thickness distribution in the direction intersecting the recording material conveyance direction based on the output of the medium thickness detection sensor 34.

  The engine controller 40, which is an example of the control means, controls the writing means based on the identified thickness distribution of the recording material, and the toner image whose toner application amount distribution in the intersecting direction is adjusted according to the thickness distribution is image-bearing. Let the body form.

  The exposure apparatus 1 which is an example of a writing unit scans the surface of the image carrier with a laser beam modulated according to the image density along the scanning line corresponding to the intersecting direction.

  The engine controller 40, which is an example of a control unit, adjusts the modulation amount of the laser beam in a direction to increase the density of the toner image when the thickness of the recording material increases along the scanning line.

  If the thickness distribution is within a predetermined range, the engine controller 40, which is an example of a control unit, sets a modulation amount according to the dot density of the screen pattern regardless of the thickness distribution.

  The image forming apparatus 100 includes a voltage applied to the developing unit to form a toner image on the surface of the image carrier, and a voltage applied from the power source D2 as a power source to the secondary transfer portion T2 as a transfer portion. Is set irrespective of the thickness distribution of the recording material. In other words, even if these are set regardless of the thickness distribution, it is possible to ensure a toner applied amount distribution that is not significantly affected by the thickness distribution.

  The intermediate transfer belt 4, which is an example of an intermediate transfer body, carries a toner image primarily transferred from the surface of the image carrier at the primary transfer portion. The carried toner images are sequentially and electrically transferred to the recording material at the secondary transfer portion where the intermediate transfer member is in contact with the conveyed recording material.

  In the first embodiment, the thickness distribution of the recording material is detected in the main scanning direction, and the detection result is fed back to the electrostatic image formed on the image carrier. By correcting the output of the laser unit 6 (exposure apparatus 1) according to the thickness distribution of the recording material P along the main scanning line, the toner on the photosensitive drum 3 partially according to the thickness variation of the recording material P. The loading amount is adjusted. The photosensitive drum 3 primarily transfers the toner image of the photosensitive drum 3 developed by the rotary developing device 10 to the intermediate transfer belt 4.

  This control cancels out the fluctuations in the transfer result due to the thickness fluctuation of the recording material, so that a uniform transfer result can be obtained regardless of the thickness fluctuation of the recording material, and a high-quality image is output to the recording material. it can.

  In the first embodiment, the exposure image is corrected according to the thickness distribution of the recording material at the stage of the scanning line image data in which the four primary color screen patterns are developed. However, the color separation data of the four primary color screen patterns before the formation of the scanning line image data is corrected to increase the density of the primary color dots forming each color screen to offset the decrease in transfer efficiency due to the thickness distribution of the recording material. May be.

  In the first embodiment, the application to PWM modulation has been described. However, so-called PAM control in which the exposure output is changed according to the scanning line image data can be similarly implemented by increasing the beam intensity according to the thickness distribution of the recording material as shown in FIG.

  In the first embodiment, a full-color image is formed with a screen pattern that avoids overlapping of each color dot. However, even if the exposure amount of each color is set for each pixel and the toner images of a plurality of colors overlap each other, the amount of applied toner is adjusted according to the thickness distribution of the recording material, and the final transfer result on the recording material Can be arranged. However, in this case, it is desirable to increase the amount corresponding to the decrease in transfer efficiency for the lowermost toner image in contact with the intermediate transfer belt. This is because the lower layer toner image remains on the intermediate transfer belt.

  In the first embodiment, the medium thickness detection sensor 34 is provided, and the thickness distribution is actually measured for each recording material on which an image is to be formed. However, the thickness distribution may be measured only for a predetermined number of sheets or only for the recording material at the beginning of the job.

  In addition, the thickness distribution of the recording material for adjusting the exposure conditions is not limited to the embodiment in which actual measurement is performed. The recording material data accompanying the job data may be transmitted including the thickness distribution data, and the exposure conditions may be adjusted based on the received thickness distribution data. The thickness distribution may be manually set by operating the operation panel 108, and the exposure conditions may be adjusted based on the set content.

Second Embodiment
FIG. 9 is an explanatory diagram for controlling the amount of applied toner according to the thickness distribution of the recording material, and FIG. 10 is a look-up table of the correction amount of the laser light amount according to the thickness of the recording material. FIG. 11 is a block diagram for explaining the connection between the image controller and the exposure apparatus, and FIG. 12 is a flowchart for controlling the exposure apparatus. In FIG. 9, (a) is the recording material thickness, (b) is the exposure amount, (c) is the electrostatic image, and (d) is the toner image.

  The second embodiment is the same as the first embodiment except that the dot exposure amount is adjusted by the pulse height of the PWM signal, and will be described with reference to FIGS. Also, in FIG. 11, the same reference numerals are given to the same components as those in FIG.

  As shown in FIG. 1, also in the second embodiment, the exposure device 1 of the image forming apparatus 100 is controlled to adjust the amount of toner applied on the photosensitive drum 3 according to the thickness distribution of the recording material. However, as shown in FIG. 9 (b), by changing the pulse height without changing the pulse width of the PWM signal, the scanning line is changed according to the thickness distribution along the scanning line of the recording material P. The exposure amount for each dot along the line is adjusted.

  As shown in FIG. 9A, when the thickness of the recording material changes in the main scanning direction, as shown in FIG. 9B, the density gradation for each pixel along the scanning line is obtained. Accordingly, the laser beam whose pulse width is modulated is scanned. In the pixel where the recording material is thick, the pulse height of the PWM signal is increased, and the pixel density pulse-width-modulated by a laser having higher intensity than the thin part is written.

  As shown in FIG. 9C, in each pixel region, the charging potential VD of the photosensitive drum 3 is lowered to the exposure portion potential VL by an area corresponding to the density gradation of the pixel. Then, since the pulse height is high in the pixel of the thick portion of the recording material, the potential is lowered to VL2 that is one step lower than the exposure portion potential VL1 in the thin portion of the pixel, and a so-called deep electrostatic image is formed. The

  As shown in FIG. 9C, the electrostatic image is developed using a DC voltage VB set between the charging potential VD of the photosensitive drum 3 and the exposure portion potential VL1. As a result, toner sufficient to cancel out the charge amounts of the exposed portion potentials VL1 and VL2 viewed from the DC voltage VB adheres to the electrostatic image (exposed portion), and as shown in FIG. Thus, a toner image primarily transferred to the intermediate transfer belt 4 is formed.

  In the second embodiment, when the secondary transfer from the intermediate transfer belt 4 to the recording material is performed, the transfer efficiency is reduced in the thick portion of the recording material, the toner transferred to the recording material is reduced, and the toner in the pixels is attached. The density of the part decreases. However, since the height at which the toner in the pixel adheres is increased, the amount of toner applied to the pixel is secured to the same level as the thin portion of the recording material. In other words, the toner adhesion height in each pixel is increased by an amount corresponding to the residual transfer toner remaining on the intermediate transfer belt 4.

  As shown in FIG. 10, the exposure intensity at each position of the exposure image is set according to the thickness distribution of the recording material. Assuming that the exposure intensity for a recording material having a thickness of 80 μm is 50 in 100 steps, the output light amount of the laser beam is increased according to the thickness of each part of the recording material onto which the toner image is transferred.

  As shown in FIG. 11, the image controller 41 forms density image data of yellow, magenta, cyan, and black separation colors from the input image data, performs γ correction, etc., and develops them into scanning line image data. .

  The engine controller 40 operates the exposure apparatus 1 using the scanning line image data formed by the image controller 41. The CPU 44 sends scanning line image data for each scanning line to the PWM processing unit 45 at the timing of the scanning synchronization signal generated by the beam detection signal generation circuit 48.

  The AD processing unit 46 performs an AD conversion process on the analog output transmitted from the medium thickness detection sensor 34 to convert the analog output into a digital signal, and inputs the digital signal to the CPU 44. The CPU 44 identifies the in-plane thickness distribution for each recording material P based on the output of the medium thickness detection sensor 34.

  The CPU 44 refers to the recording material thickness-laser light amount correction value table of FIG. 10 stored in advance in the ROM 43, and forms laser light amount correction data corresponding to the scanning line image data sent from the image controller 41. . The CPU 44 sends the scanning line image data for each scanning line to the PWM processing unit 45 at the timing of the scanning synchronization signal generated by the beam detection signal generation circuit 48, while the DA processing unit 71 supplies the laser light amount correction data for each scanning line. To send.

  The PWM processing unit 45 temporarily accumulates scanning line image data of a plurality of scanning lines, and performs pulse width modulation on the scanning line image data to convert it into a laser drive signal.

  The DA processing unit 71 converts the laser light amount correction data into an analog voltage and inputs the analog voltage to the laser driver 42.

  The laser driver 42 outputs to the laser unit 6 a voltage signal obtained by superimposing an analog voltage on the laser drive signal voltage signal, and changes the intensity of the PWM-modulated laser light at each position of the scanning line according to the thickness distribution. As shown in FIG. 12 with reference to FIGS. 1 and 11, the engine controller 40 captures the thickness distribution of the medium thickness detection sensor 34 in the main scanning direction in the process of passing the recording material through the medium thickness detection sensor 34 ( S21).

  Next, as described above, the engine controller 40 calculates the thickness distribution of the recording material based on the acquired thickness distribution (S22).

  Next, when the maximum thickness exceeds the specified value (YES in S23) and the maximum thickness / minimum thickness ratio exceeds the specified value (YES in S24), the engine controller 40, as described above, The laser output is corrected (S25).

  However, when the maximum thickness is less than the specified value (NO in S23) and when the maximum thickness / minimum thickness ratio is less than the specified value (NO in S24), there is a difference in transfer efficiency in the surface of the recording material P. Since it is small, the scanning line image data is not corrected for each scanning line.

  The engine controller 40 supplies the exposure apparatus 1 with a PWM signal and a laser output correction signal and writes an electrostatic image reflecting the thickness distribution of the recording material on the photosensitive drum 3.

  The laser driver 42 controls the light emission of the laser unit 6 based on the received PWM signal and laser output correction signal, and scans and exposes the photosensitive drum (3: FIG. 1) (S26).

  In the second embodiment, the thickness distribution of the recording material is identified based on the detection information of the thickness distribution in the main scanning direction of the recording material. In accordance with the thickness distribution of the identified recording material, the exposure condition of the black and white image or color image is adjusted at each position along the main scanning line. The emission intensity of the laser beam that is PWM-modulated according to the image density is changed according to the thickness of the recording material. Thus, a toner applied amount that can realize the density of the image to be formed is realized on the recording material by offsetting the variation in transfer efficiency due to the thickness distribution of the recording material.

  As a result, it is possible to prevent the occurrence of image defects in the transfer portion due to the thickness variation of the recording material. For example, in a black and white image, a transfer defect in an all black image can be suppressed in a portion thicker than the average thickness of the recording material, and in a multicolor image, an image failure such as gloss unevenness in a fixing portion can be suppressed in a portion thicker than the average thickness of the recording medium. . The image on the recording material that is finally discharged from the image forming apparatus can be provided to the user with high quality.

  By the way, since the recording medium such as an envelope or a medicine bag has a bag shape, the end portion is folded and adhered, and the thickness is partially increased, and accordingly the impedance at the same location is partially increased. Therefore, in envelopes and medicine bags, when a black and white image is printed at the end of the recording material, it is easy to cause a transfer failure of the all black image portion, and when a multicolor image is printed, it is different from the portion other than the end portion. May occur and image quality may deteriorate.

  In addition, it is difficult to think of a recording material having a variation in the thickness of a booklet shape, not limited to an envelope and a medicine bag, so that the recording material is not necessarily conveyed so as to have a medium thickness variation perpendicular to the sub-scanning direction.

  However, even in such a case, it is possible to output a target image with high reproducibility and high quality by performing control to increase the amount of toner applied to a thick portion on the assumption of a difference in transfer efficiency due to thickness distribution. Not only for booklet-shaped recording materials with stepwise thickness variation in the sub-scanning direction, but also for envelope-shaped recording materials with thickness variation in the main scanning direction (width direction) Images with little unevenness and variation can be output stably and with high reproducibility.

1 is a schematic explanatory diagram of a configuration of an image forming apparatus according to a first embodiment. It is a flowchart of control of an exposure apparatus. It is a diagram explaining the relationship between recording material thickness and transfer efficiency. FIG. 6 is an explanatory diagram of an extra rate of applied toner according to the thickness distribution of a recording material. FIG. 6 is an explanatory diagram of control for adjusting a toner applied amount according to a thickness distribution of a recording material. It is a lookup table of correction values in PWM control of the exposure apparatus. It is a block diagram explaining the connection of an image controller and exposure apparatus. It is a flowchart of control of an exposure apparatus. FIG. 7 is an explanatory diagram of toner application amount control according to the thickness distribution of a recording material. 6 is a look-up table of a correction amount of a laser light amount corresponding to the thickness of a recording material. It is a block diagram explaining the connection of an image controller and exposure apparatus. It is a flowchart of control of an exposure apparatus.

Explanation of symbols

1 Writing means (exposure device)
3 Image carrier (photosensitive drum)
4 Intermediate transfer member (intermediate transfer belt)
6 Laser unit 10c Developing means (cyan developing device 10c)
17 Paper feed cassette 19 Manual feed tray 22 Charging means (primary charger)
34 Identification means (medium thickness detection sensor)
40, 44 Identification means, control means (engine controller, CPU)
41 Image Controller 42 Laser Driver 45 PWM Processing Unit 71 DA Processing Unit 100 Image Forming Device D2 Power Supply T1 Primary Transfer Unit T2 Secondary Transfer Unit

Claims (6)

An image carrier;
Charging means for charging the surface of the image carrier;
Writing means for writing an electrostatic image of an image on the charged surface;
Developing means for supplying charged toner to the electrostatic image and developing the toner image,
In the image forming apparatus in which the toner images are sequentially and electrically transferred to the recording material along the conveyance direction of the recording material,
Identification means for identifying the thickness distribution of the recording material in the direction intersecting the transport direction;
Control means for controlling the writing means on the basis of the identified thickness distribution and forming a toner image in which the applied toner amount distribution in the intersecting direction is adjusted in accordance with the thickness distribution on the image carrier. An image forming apparatus comprising the image forming apparatus. The writing means is an exposure apparatus that scans the surface with a laser beam modulated according to the density of an image along a scanning line corresponding to the intersecting direction,
The image forming apparatus according to claim 1, wherein the control unit adjusts the modulation amount of the laser beam in a direction of increasing the density when the thickness of the recording material increases along the scanning line.   3. The image forming apparatus according to claim 2, wherein the control unit sets the modulation amount according to the density regardless of the thickness distribution if the thickness distribution is within a predetermined range. .   At least one of a voltage applied by the developing unit to move the toner to the surface and a voltage applied by the power source to the transfer unit is set regardless of the thickness distribution. The image forming apparatus according to claim 1. An intermediate transfer member carrying the toner image primarily transferred from the surface at a primary transfer portion;
5. The image according to claim 1, wherein the toner images are sequentially and electrically transferred to the recording material at a secondary transfer portion where the intermediate transfer member is in contact with the conveyed recording material. Forming equipment. A first step of adjusting an exposure amount distribution in an exposure image in which the image is written on the image carrier in correspondence with a thickness distribution of a recording material on which an image is to be formed;
A second step in which the exposure image is written on the image carrier to form an electrostatic image of the image;
A third step of forming, on the image carrier, a toner image in which a toner application amount distribution is adjusted according to the thickness distribution by attaching a charged toner to the electrostatic image;
And a fourth step of electrically transferring the toner image, the toner amount distribution of which has been adjusted, in contact with a recording material.

Images