Patent Application
20250013164
The present invention relates to an image forming apparatus that forms a toner image for bonding together a plurality of sheets.
An electro-photographic image forming apparatus uniformly charges a photosensitive drum, exposes the photosensitive drum to light, forms an electrostatic latent image, and applies toner to the electrostatic latent image to form a toner image. A photosensitive layer provided on a core metal of a photosensitive drum gradually decreases in thickness each time a toner image is formed. As a result, the density of the toner image is gradually reduced. Japanese Patent Laid-Open No. H09-120245 proposes obtaining the thickness of photosensitive layer according to the number of sheets to be supplied to an image forming apparatus and changing an exposure condition according to the thickness.
With this known technique, it is expected that the thickness of photosensitive layer is uniformly reduced at all positions of the surface of the photosensitive body according to the number of sheets where an image is to be printed. However, the amount of reduction in the thickness of photosensitive layer depends on the type of the image being formed. Thus, across the entire surface of the photosensitive body, there may be a disparity in the thickness of photosensitive layer. For example, at a specific position in a main scan direction (a direction parallel with a rotary shaft of the photosensitive body) of the photosensitive body, an adhesive toner image that bonds together a plurality of sheets is often formed. In this case, the thickness of photosensitive layer at the specific position in the main scan direction is reduced more than at other positions.
The present disclosure provides an image forming apparatus comprising: a rotationally driven photosensitive body; a charging device that charges a surface of the photosensitive body; an exposure light source that forms an electrostatic latent image by exposing the surface of the photosensitive body to light; a developing device that forms a toner image by developing the electrostatic latent image using toner; a transfer member that transfers the toner image to a sheet; a first memory that stores a cumulative image formation amount for each one of N exposure regions of the surface of the photosensitive body; and a control circuit that controls the exposure light source so that an exposure condition is determined on a basis of the cumulative image formation amount for each one of the N exposure regions and each one of the N exposure regions is exposed with light according to the exposure condition.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the claimed invention. Multiple features are described in the embodiments, but limitation is not made to an invention that requires all such features, and multiple such features may be combined as appropriate. Furthermore, in the attached drawings, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted.
As illustrated in
The image forming apparatus 100 includes a sheet cassette 8, an image forming portion 10, a fixing device 6, and a casing 19 that houses these. The image forming portion 10 forms a toner image on the sheet S fed from the sheet cassette 8. The fixing device 6 performs a fixing process to fix the toner image on the sheet S.
The sheet cassette 8 is provided on the lower portion of the image forming apparatus 100. The sheet cassette 8 is inserted into the casing 19 in a removable manner and can house a plurality of the sheets S. In the present example, the maximum size of the sheet S where an image can be formed is assumed to be the A4 size (length 297 mm×width 210 mm). The long side of the A4 sized sheet S is parallel with the conveyance direction of the sheet S. A conveyance roller 81 feeds the sheets S from the sheet cassette 8 and passes the sheets S to a conveyance roller pair 82. The sheets S can also be fed one at a time from a multi-tray 20.
The image forming portion 10 is a tandem electrophotographic unit includes four process cartridges 7n, 7y, 7m, 7c, an exposure apparatus 2, and a transfer unit 3. “y”, “m”, and “c” correspond to yellow, magenta, and cyan, respectively. n refers to the adhesive toner. The characters ymnc indicating the toner colors may be omitted from the reference signs. The color of the adhesive toner may be transparent or black. In a case where the color of the adhesive toner is transparent, black achieved by appropriately mixing yellow, magenta, and cyan (process black). The type (material) of the toner used as the yellow, magenta, and cyan toner and the adhesive toner is thermoplastic resin. Examples of thermoplastic resin include, for example, a polyester resin, a vinyl resin, an acrylic resin, a styrene acrylic resin, and the like. The process cartridges 7n, 7y, 7m, 7c include integrally replaceable components involved in the image forming process. In other words, a plurality of components are integrally formed to form the process cartridges 7n, 7y, 7m, 7c.
The process cartridges 7n, 7y, 7m, 7c each include, respectively, a corresponding developing apparatus Kn, Ky, Km, Kc, photosensitive drum Dn, Dy, Dm, Dc, and charging roller Cn, Cy, Cm, and Cc. Except for the toner type, the process cartridges 7n, 7y, 7m, 7c share essentially the same structure.
The developing apparatuses Ky, Km, Kc respectively house yellow, magenta, and cyan toner for forming a visual image on the sheet S. The developing apparatus Kn houses an adhesive toner Tn. The adhesive toner Tn is used in forming a user image (document image) and the thermocompression bonding of a plurality of the sheets S in the post-processing apparatus 130. Note that an image formed by the adhesive toner Tn is formed on a photosensitive drum Dn by developing the adhesive toner Tn.
The image forming portion 10 may include a fifth process cartridge that uses toner for bonding or black toner. Note that depending on the application of the image forming apparatus 100, the type and number of the printing toners can be changed.
The charging rollers Cn, Cy, Cm, and Cc are charging devices that uniformly charge the surface of their corresponding photosensitive drum Dn, Dy, Dm, Dc. The exposure apparatus 2 is disposed below the process cartridges 7n, 7y, 7m, 7c and above the sheet cassette 8. The exposure apparatus 2 emits laser beams Jn, Jy, Jm, and Jc at the corresponding photosensitive drums Dn, Dy, Dm, and Dc to form electrostatic latent images. The exposure apparatus 2 may be referred to as an optical scanning apparatus.
The developing apparatuses Kn, Ky, Km, Kc adhere toner to the electrostatic latent images on the photosensitive drums Dn, Dy, Dm, and Dc to form toner images. The developing apparatuses Kn, Ky, Km, Kc may be referred to as developing devices.
The transfer unit 3 includes a transfer belt 30 that functions as an intermediate transfer body (secondary image carrier). The transfer belt 30 is an endless belt installed on an inner roller 31 and a tensioning roller 32. The outer circumferential surface (image forming surface) of the transfer belt 30 faces the photosensitive drums Dn, Dy, Dm, and Dc. Primary transfer rollers Fn, Fy, Fm, and Fc are disposes so that the inner circumferential side of the transfer belt 30 faces the photosensitive drums Dn, Dy, Dm, and Dc.
The primary transfer rollers Fn, Fy, Fm, and Fc transfer the toner images from the corresponding photosensitive drum Dn, Dy, Dm, and Dc to the transfer belt 30. The primary transfer rollers Fn, Fy, Fm, and Fc may be referred to as primary transfer devices. When the transfer belt 30 rotates anticlockwise, the toner images are conveyed to the secondary transfer unit.
A secondary transfer roller 5 is disposed facing the inner roller 31, forming a transfer nip 52 between the secondary transfer roller 5 and the transfer belt 30. The transfer nip 52 transfers the toner images from the transfer belt 30 to the sheet S. The transfer nip 52 may be referred to as a secondary transfer unit.
The fixing device 6 is disposed above (on the downstream side in the conveyance direction of the sheet S) the secondary transfer roller 5. The fixing device 6 applies heat and pressure to the sheet S passing through a fixing nip 61. This fixes the toner image on the sheet S. Note that the fixing device 6 includes a fixing heater 62 for heating the toner image and the sheet S. The fixing heater 62 is a halogen heater or a ceramic heater, for example.
As illustrated in
The print region 211 of the adhesive toner Tn may be formed on both sides of the sheet S or on only one side of the sheet S. Whether to form the print region 211 of the adhesive toner Tn on only one side or on both sides may be selected taking into account, for example, the adhesive capability of the post-processing apparatus 130, the adhesive capability of the adhesive toner Tn, the type of the sheet S, the function required for the booklet, and the like. A booklet treated as a special edition is required to have reliable adhesiveness. In a case where a thick paper or special sheet S is used as the cover of the booklet, reliable adhesiveness is also required. Thus, in such cases, the print region 211 of the adhesive toner Tn is provided on both sides of the sheet S. In a case where a simple primary-use booklet is formed, the print region 211 of the adhesive toner Tn is formed only on one side of the sheet S.
Now we will return to the description of
The discharge rollers 34 convey the sheet S to the intermediate conveyance unit 120. The intermediate conveyance unit 120 includes a conveyance roller pair 121, 122. The conveyance roller pair 121, 122 convey the sheet S to the post-processing apparatus 130.
The post-processing apparatus 130 is a floor-standing sheet handling apparatus. The post-processing apparatus 130 has a function for buffering a plurality of sheets, a function for aligning a plurality of sheets, and a function for bonding together a sheet bundle.
Hereinafter, the end portion of the sheet S on the front side in the conveyance direction will be referred to as the front end. The end portion of the sheet S on the back side in the conveyance direction will be referred to as the back end. Of the two end portions of the sheet S, the end which enters the post-processing apparatus 130 before the other is referred to as the first end. Of the two end portions of the sheet S, the end which enters the post-processing apparatus 130 after the other is referred to as the second end. Note that when the post-processing apparatus 130 performs switch back conveying, the front end may change from the first end to the second end, and the back end may change from the second end to the first end.
The sheet S conveyed from the intermediate conveyance unit 120 is passed to an inlet roller 21 of the post-processing apparatus 130. A sheet sensor 27 referred to as an inlet sensor is disposed downstream from the inlet roller 21. When the sheet sensor 27 detects the back end of the sheet S, a conveyance roller pair 22 accelerate the sheet S. When the back end of the sheet S with an upper tray 25 set as the discharge destination arrives between the conveyance roller pair 22 and a conveyance roller pair 24, the conveyance roller pair 22 decelerates. Accordingly, the conveyance speed of the sheet S is made to match a predetermined discharge speed. The conveyance roller pair 22 discharges the sheet S to the upper tray 25.
When the back end of the sheet S with a lower tray 37 set as the discharge destination passes a backflow prevention valve 23, the conveyance roller pair 22 stops conveying the sheet S. Thereafter, the conveyance roller pair 22 starts rotating in reverse. Accordingly, the sheet S is switched back and conveyed to a conveyance roller pair 26. When the front end of the sheet S is detected by a sheet sensor 60 provided downstream from the conveyance roller pair 26, the two rollers forming the conveyance roller pair 24 separate from one another. This allows the subsequent sheet S to be received by the conveyance roller pair 24. Also, with the preceding sheet S held between the conveyance roller pair 26, the conveyance roller pair 26 stop. Coinciding with the arrival of the subsequent sheet S, the conveyance roller pair 26 starts rotating in reverse. Accordingly, the subsequent sheet S is layered on top of the preceding sheet S. By the conveyance roller pair 26 repeatedly performing switch back on the sheets S, the plurality of sheets S are layered, forming a sheet bundle. Such an operation for forming a sheet bundle may be referred to as a buffering operation. The unit that implements the buffering operation may be referred to as a buffering portion 80.
When the sheet bundle is completed at the buffering portion 80, the conveyance roller pair 26 convey the sheet bundle to an intermediate stacker 42. The sheet bundle passes a conveyance roller pair 28 and a sheet sensor 50. Also, the sheet bundle is conveyed to the intermediate stacker 42 by a kick-out roller 29. A movable vertical alignment plate 39 is disposed at the most downstream portion of the intermediate stacker 42 in a standby position. By abutting the sheet bundle against the vertical alignment plate 39, the sheet bundle is aligned.
A plurality of sheet bundles are stacked in order at the intermediate stacker 42. Accordingly, a predetermined number of the sheets S for forming a booklet are stacked at the intermediate stacker 42. When the alignment of the predetermined number of sheets S ends, a thermocompression bonding unit 51 performs a binding operation (thermocompression bonding process) to form a booklet. When the vertical alignment plate 39 moves from the standby position to the discharge position, the booklet is pushed toward discharge rollers 38. When the front end of the booklet is held between the discharge rollers 38, the vertical alignment plate 39 stops and then returns to the standby position. The discharge rollers 38 discharge the booklet received from the vertical alignment plate 39 from a discharge opening 46 to the lower tray 37.
As described above, using the buffering portion 80, the post-processing apparatus 130 forms a sheet bundle made from the plurality of sheets S and conveys the sheet bundle to the intermediate stacker 42. However, one sheet S may be conveyed to the intermediate stacker 42.
A Y direction is the direction parallel with the stacking surface (stacking plate) for the sheets S at the intermediate stacker 42 and the direction parallel with the conveyance direction in which the sheets S are conveyed from the kick-out roller 29 to the intermediate stacker 42. The Y direction may be referred to as the vertical direction. An X direction is the direction parallel with the stacking surface of the sheets S at the intermediate stacker 42 and orthogonal to the Y direction. The X direction may be referred to as the horizontal direction. A Z direction is the direction orthogonal to the X direction and the Y direction (normal direction of the stacking surface, thickness direction of the stacked sheets S). The Z direction may be referred to as the height direction. The opposite directions of the X direction, the Y direction, and the Z direction may be referred to as the −X direction, the −Y direction, and the −Z direction, respectively.
The vertical alignment plate 39 and a vertical alignment roller 40 function as a first alignment unit that aligns the sheets S in the first direction (Y direction). The vertical alignment plate 39 is disposed at the most downstream portion of the intermediate stacker 42 in the Y direction. The vertical alignment plate 39 is a reference member (first reference member) corresponding to the reference for the sheet position in the Y direction. The vertical alignment roller 40 is a conveying member that conveys the sheets S in the Y direction to abut the sheets S with the vertical alignment plate 39 and align them. The vertical alignment plate 39 includes a plurality of abutting portions 39a to 39c disposed at intervals in the X direction. The plurality of abutting portions 39a to 39c come into contact with the end portions of the sheets S. Note that the vertical alignment plate 39 and the vertical alignment roller 40 are integrally formed as a movable unit 59 that can move in the Y direction. The movable unit 59 can move in the Y direction via a drive source such as a motor. In other words, the position of the vertical alignment plate 39 and the vertical alignment roller 40 can be adjusted in the Y direction. Horizontal alignment joggers 41a to 41c function as a second alignment unit that aligns sheets in the second direction (X direction) orthogonal to the first direction.
The horizontal alignment joggers 41a to 41c move in the X direction via a drive source such as a motor and press against the side ends of the sheets S stacked in the intermediate stacker 42. Horizontal alignment plates 72a and 72b are reference members corresponding to the reference for the position of the sheets S in the X direction. The horizontal alignment plates 72a and 72b are disposed facing the horizontal alignment joggers 41a and 41b in the X direction.
As illustrated in
The thermocompression bonding unit 51 performs the thermocompression bonding operation on the sheets S1 to S5 after alignment is complete. During this time, the horizontal alignment joggers 41a to 41c retract in the −X direction. Accordingly, the intermediate stacker 42 is put in a state in which the next plurality of sheets S can be received. Thereafter, the sheet bundle W including the sheets S6 to S10 generated at the buffering portion 80 are stacked on the sheets S1 to S5.
Thereafter, the four stages described above are repeated for the sheets S1 to S10. Accordingly, the sheets S1 to S10 are bonded in a highly-accurately aligned state.
As an example, the sheet bundle W includes five sheets S. However, the number of the sheets S forming the sheet bundle W may be two, three, or the like. In other words, the number of the sheets S included in the sheet bundle W is equal to or less than the maximum number of the sheets S that can be layered at the buffering portion 80.
A developing apparatus K includes a toner container 411 containing toner T. A stirring member 412 rotates to charge the toner T while stirring it. A supplying roller 413 supplies the toner T held in the toner container 411 to a developing roller 414. A developing bias is applied to the developing roller 414 from a developing power supply 403. The developing roller 414 forms a toner image by adhering the toner on the photosensitive drum D.
When the laser beam J is emitted, the negative charge existing at the surface of the photosensitive drum D is canceled out. Accordingly, light area potential VL is formed on the surface of the photosensitive drum D. For example, in a case where the laser beam amount (hereinafter, referred to as exposure amount) is 0.2 J/cm2, the light area potential VL is 100 V.
A developing bias Vdc is approximately −250 V. The surface potential of the region of the surface of the photosensitive drum D where the toner image is formed is the light area potential VL. A potential difference Vcont between the developing bias Vdc and the light area potential VL corresponds to the electrical force when developing an electrostatic latent image on the photosensitive drum D using toner. Note that Vback illustrated in
When transfer of the toner image is complete, the charging roller C returns the surface potential of the photosensitive drum D from the light area potential VL to the dark area potential VD. At this time, a discharge current flows from the charging roller C to the photosensitive drum D. All of the electrical energy of the discharge current is not used in charging the photosensitive drum D. A portion of the electrical energy of the discharge current electrically stimulates the polymeric material of the surface of the photosensitive drum D. As a result, the molecule bonds in the polymeric material become easier to break. As a result, the surface of the photosensitive drum D tends to wear more due to the sliding of the cleaning blade 400 and the like.
When the thickness of the photosensitive drum D decreases, the dark area potential VD of the photosensitive drum D increases in the negative direction. Coinciding with this, the light area potential VL of the photosensitive drum D also increases in the negative direction. However, the developing bias Vdc is constant. As a result, since the potential difference Vcont decreases, the density of the toner image formed on the sheet S decreases.
To make the image density constant, the light area potential VL needs to be kept constant. This is achieved by changing the exposure amount to correspond with the variation amount of the dark area potential VD of the photosensitive drum D.
In this manner, as images with a high print ratio are printed on more sheets S, the thickness of the surface layer of the photosensitive drum D tends to decrease. For example, in the image forming system 1 including a booklet manufacturing apparatus (post-processing apparatus 130), as illustrated in
The image forming apparatus 100 may include a counter (
For example, the number of printed pixels per one sheet S is obtained as follows. As a calculation condition, the resolution of the image forming portion 10 is assumed to be 600 dots per inch (dpi). The sheet S is an A4 sized sheet (length 297 mm×width 210 mm). The region of the sheet S where an image can be formed is 287 mm×200 mm. Thus, the number of printed pixels per one sheet S is 4724×6780 (=32,292,264). For example, the number of printed pixels when the print ratio is 50% is 16,014,632. The number of printed pixels when the print ratio is 10% is 3,202,926.
As seen in
The image forming apparatus 100 predicts the thickness reduction amount from the cumulative number of pixels per main scanning position (region) and corrects the exposure amount on the basis of the prediction value to make the density of the printed images constant.
Here, Pa is a first correction coefficient. Pb is a second correction coefficient. These correction coefficients may be different due to the type of the toner, the type of the photosensitive drum D, the memory address distribution method, and the like. Thus, these correction coefficients may be changed according to related information (for example, toner type) input by the user. The image forming apparatus 100 can decrease the disparity in density in the main scan direction of the photosensitive drum D by correcting the exposure amount corresponding to the cumulative number of pixels per main scanning position.
To evaluate the change in density due to printing, first, a reference value was obtained. The image density for the solid black region, the HT(100) image region, and the region corresponding to the memory addresses E−95 to E−81 were each measured out of five points. The Macbeth RD-918 was used as the reflective densitometer. The average value was obtained from the five point measurement values. The image density of the solid black was 1.44. The image density of the HT(100) image was 0.80. Using these values as reference values, it was evaluated as to whether each image density was within ±0.02.
As illustrated in
In the Comparative Example II, the image density of the solid black was 1.45, a value almost the same as the reference value. However, the image density of the HT(100) image was 0.91, a value higher than the reference value. In the Comparative Example II, the exposure amount is uniformly corrected at all of the main scanning positions corresponding to the number of passed sheets S. Thus, at the region of the surface of the photosensitive drum D where toner is not printed, the exposure amount increases excessively, and the image density increases.
In the first embodiment, the exposure amount is corrected corresponding to the cumulative number of pixels of each main scanning region. As a result, the image density of the solid black was 1.44. The image density of the HT(100) image was 0.81. Both are similar to their respective reference values.
In this manner, according to the first embodiment, the exposure amount is corrected corresponding to the cumulative number of pixels per main scanning region. Thus, the density of each main scanning region is made substantially constant, and the disparity in density of the image in the main scan direction is reduced.
An image processing unit 1312 converts input image data to bitmap data, converts color space, and generates image signals (exposure signals) to be supplied to the exposure apparatus 2. A dither unit 1313 executes dither processing on the image data.
An operation unit 1304 includes an input apparatus and a display apparatus. A coefficient setting unit 1314 sets a first correction coefficient Pa and a second correction coefficient Pb in a determination unit 1317 on the basis of information input from the operation unit 1304. As described above, the coefficient setting unit 1314 may be input with the first correction coefficient Pa and the second correction coefficient Pb from the operation unit 1304. The coefficient setting unit 1314 may determine the first correction coefficient Pa and the second correction coefficient Pb according to the toner type or the like input from the operation unit 1304. As described below, the coefficient setting unit 1314 may determine the first correction coefficient Pa and the second correction coefficient Pb according to an environmental condition (for example, environment temperature or environment humidity) detected by an environment sensor 1305.
An equation selection unit 1315 selects the equation for calculating the exposure amount on the basis of the environment condition or the like used in other embodiments. An HP sensor 1306 detects an absolute position (home position) in the sub-scan direction of the photosensitive drum D used in other embodiments. A position monitoring unit 1316 identifies the coordinates of the surface region of the photosensitive drum D on the basis of a signal (vertical synchronizing signal) output from the HP sensor 1306 and a BD signal (horizontal synchronizing signal) output from the exposure apparatus 2 used in other embodiments. In the first embodiment, the position monitoring unit 1316 informs the determination unit 1317 and an exposure control unit 1320 of the current exposure region (the main scanning region in the first embodiment).
The determination unit 1317 determines the exposure amount Pi for each main scanning region on the basis of the cumulative number of pixels Mi. For example, a calculation unit 1318 calculates the exposure amount Pi in the i-th main scanning region on the basis of the first correction coefficient Pa, the second correction coefficient Pb, and the cumulative number of pixels Mi. A selection unit 1319 determines the contents of the dither processing to be applied to the i-th main scanning region according to the cumulative number of pixels Mi and sets this in the dither unit 1313.
The exposure control unit 1320 controls the exposure apparatus 2 so that the i-th main scanning region of the photosensitive drum D is exposed to light by the exposure amount Pi designated by the determination unit 1317. The CPU 1301 also controls the charging power supply 402 and the developing power supply 403.
In step S1401, the CPU 1301 (image analysis unit 1311) obtains the number of printed pixels per exposure region (main scanning region in the first embodiment) from the image data.
In step S1402, the CPU 1301 (image analysis unit 1311) adds the number of printed pixels per exposure region to the cumulative number of pixels stored in the counter 1307.
In step S1501, the CPU 1301 (coefficient setting unit 1314) obtains the first correction coefficient Pa and the second correction coefficient Pb.
In step S1502, the CPU 1301 (position monitoring unit 1316) identifies the exposure region (main scanning region) in the main scan direction.
In step S1503, the CPU 1301 (determination unit 1317) obtains the cumulative number of pixels of the identified exposure region from the counter 1307.
In step S1504, the CPU 1301 (determination unit 1317) determines the exposure condition on the basis of the first correction coefficient Pa, the second correction coefficient Pb, and the cumulative number of pixels. The exposure condition is the exposure amount Pi determined using Formula EQ. 1, for example.
In step S1505, the CPU 1301 (exposure control unit 1320) performs exposure of the identified exposure region according to the exposure condition. Note that the steps from S1501 to S1505 are repeated while the toner image is being formed on the basis of the image data.
The items that the second embodiment has in common with the first embodiment are given the same reference sign as in the first embodiment and description thereof is omitted. The items not described in the second embodiment are as described in the first embodiment.
In the first embodiment, the exposure amount is determined per main scanning region using the cumulative number of pixels Mi. As illustrated in
The image analysis unit 1311 obtains the number of printed pixels at the coordinates (x, y) by analyzing the image data and adding this to the cumulative number of pixels Mx,y stored in the counter 1307.
The position monitoring unit 1316 identifies the coordinates (x, y) of the exposure region on the basis of the signal from the HP sensor 1306 and the BD signal from the exposure apparatus 2. The calculation unit 1318 of the determination unit 1317 calculates the exposure amount Px,y at the coordinates (x, y) from the cumulative number of pixels Mx,y using Formula EQ.1. Note that the exposure amount Pi of Formula EQ.1 is substituted for the exposure amount Px,y. The cumulative number of pixels Mi is substituted for the cumulative number of pixels Mx,y. The exposure control unit 1320 exposes the exposure region of the coordinates (x, y) to light on the basis of the exposure amount Px,y determined by the determination unit 1317.
For the second embodiment, experiments were carried out using experiment conditions similar to those of the first embodiment.
The memory addresses E−100,−38 to E−80,−18 of the counter 1307 store the cumulative number of pixels of the exposure region A. The memory addresses E−100,−0 to E−80,−20 store the cumulative number of pixels of the exposure region B. The memory addresses E80,−38 to E100,−18 store the cumulative number of pixels of the exposure region C. The memory addresses E80,0 to E100,20 store the cumulative number of pixels of the exposure region D.
In the exposure region A, two solid blacks are printed on one sheet S. In the exposure region B, one solid black is printed on one sheet S. Since the number of solid blacks printed differ according to position in the sub-scan direction, the cumulative number of pixels is different per exposure region in the sub-scan direction. In the exposure region C, two HT(100) images are printed on one sheet S. In the exposure region D, one HT(100) image are printed on one sheet S.
The test image was formed on 400000 sheets S, and the image density of each exposure region was measured. The densometer, statistical method, evaluation method are as in the first embodiment. According to the second embodiment, the image density of each exposure region ABCD was confirmed to be roughly equal to the reference value.
In step S1801, the CPU 1301 (coefficient setting unit 1314) obtains the first correction coefficient Pa and the second correction coefficient Pb.
In step S1802, the CPU 1301 (position monitoring unit 1316) identifies the exposure region on the basis of the main scanning position x and the sub-scan position y. In other words, the coordinates (x, y) of the exposure region for processing are identified.
In step S1803, the CPU 1301 (determination unit 1317) obtains the cumulative number of pixels of the identified exposure region from the counter 1307.
In step S1804, the CPU 1301 (determination unit 1317) determines the exposure condition on the basis of the first correction coefficient Pa, the second correction coefficient Pb, and the cumulative number of pixels. The exposure condition is the exposure amount Px,y, for example.
In step S1805, the CPU 1301 (exposure control unit 1320) performs exposure of the identified exposure region according to the exposure condition. Note that the steps from S1801 to S1805 are repeated while the toner image is being formed on the basis of the image data.
According to the second embodiment, memory addresses are distributed to combinations of the main scanning position x and the sub-scan position y of the photosensitive drum D. The circumferential surface of the photosensitive drum D is divided into a plurality of exposure regions arranged in a matrix pattern, and the cumulative number of pixels are stored per exposure region. Then, the exposure condition is determined per exposure region. In this manner, in not only the main scan direction but also the sub-scan direction, disparity in the density is reduced.
In the first embodiment, the main scan direction is divided into a plurality of exposure regions, and in the second embodiment, the entire surface of the photosensitive drum D is divided into a plurality of exposure regions. However, this is merely an example. Even in a case where the sub-scan direction is divided into a plurality of exposure regions (sub-scan regions), the concepts of the first embodiment and the second embodiment are applicable. In other words, the cumulative number of pixels may be stored per sub-scan regions, and the exposure amount of each sub-scan region may be determined according to the cumulative number of pixels.
The items that the third embodiment has in common with the first and second embodiment are given the same reference sign as in the first and second embodiment and description thereof is omitted. The items not described in the third embodiment are as described in the first and second embodiment.
The environment conditions of the first and second embodiment is expected to be constant (temperature=23° C., humidity=50% RH). However, the actual environment conditions may change. For example, the environment conditions may be low temperature and low humidity (for example, temperature=15° C., humidity=10% RH) or may be high temperature and high humidity (temperature=30° C., humidity=80% RH). The discharge voltage of the photosensitive drum D is dependent on the environment condition. However, the thickness reduction amount with respect to the cumulative number of pixels may change depending on the environment condition.
The thickness reduction amount with respect to the cumulative number of pixels dependent on three different environment conditions were measured. A normal condition (hereinafter, referred to as NN) is an environment temperature of 23° C. and an environment humidity of 50% RH. A low temperature low humidity condition (hereinafter, referred to as LL) is an environment temperature of 15° C. and an environment humidity of 10% RH. A high temperature high humidity condition (hereinafter, referred to as HH) is an environment temperature of 30° C. and an environment humidity of 80% RH. The test image illustrated in
Printing in the same experiment conditions as in the first embodiment was performed in the NN environment, the LL environment, and the HH environment, and the effects of the third embodiment were confirmed. As a result, in the third embodiment also, the image density of the solid black and the image density of the HT(100) image were confirmed to be within 0.02 of their reference values.
In step S2001, the CPU 1301 obtains the environment condition using the environment sensor 1305.
In step S2002, the CPU 1301 (equation selection unit 1315) obtains the first correction coefficient Pa and the second correction coefficient Pb corresponding to the environment condition. Note that in a case where the equation already includes the correction coefficient, step S2002 is not required.
In step S2003, the CPU 1301 (position monitoring unit 1316) identifies the exposure region. The exposure region identification method may be as in the first and second embodiment.
In step S2004, the CPU 1301 (determination unit 1317) obtains the cumulative number of pixels of the identified exposure region from the counter 1307.
In step S2005, the CPU 1301 (determination unit 1317) determines the exposure condition on the basis of the equation selected by the equation selection unit 1315 and the cumulative number of pixels. The exposure condition is the exposure amount Pi or the exposure amount Px,y, for example.
In step S2006, the CPU 1301 (exposure control unit 1320) performs exposure of the identified exposure region according to the exposure condition. Note that the steps from S2001 to S2006 are repeated while the toner image is being formed on the basis of the image data.
According to the third embodiment, the exposure condition is determined from the cumulative number of pixels using the equation corresponding to the environment condition. In this manner, disparity in image density is reduced even if the environment conditions change.
In the first to third embodiments, the exposure condition is determined per exposure region according to the cumulative number of pixels. Instead of this, the image processing condition (for example, dither processing) may be changed per exposure region according to the cumulative number of pixels. The image processing condition should be a condition that affects the image density.
In step S2101, the CPU 1301 (position monitoring unit 1316) identifies the exposure region. The exposure region identification method may be as in the first and second embodiment.
In step S2102, the CPU 1301 (determination unit 1317) obtains the cumulative number of pixels of the identified exposure region from the counter 1307.
In step S2103, the CPU 1301 (selection unit 1319) determines the image processing condition to be applied to the image data of the identified exposure region on the basis of the cumulative number of pixels. The image processing condition may be the contents of the dither processing (for example, the error diffusion method or other dithering method), for example.
In step S2104, the CPU 1301 (dither unit 1313) applies image processing (for example, dither processing) according to the determined image processing condition to the image data.
In step S2105, the CPU 1301 (exposure control unit 1320) performs exposure of the identified exposure region on the basis of the image data. Note that the steps from S2101 to S2105 are repeated while the toner image is being formed on the basis of the image data.
The CPU 1301 may determine whether or not to apply the first to fourth embodiments in response to a user instruction input from the operation unit 1304. In other words, the CPU 1301 may switch from a normal mode in which correction is not performed and a correction mode in which correction is performed.
The memory 1302 stores the cumulative image formation amount (for example, cumulative number of pixels Mi, Mx, y) for each one of the N exposure regions of the surface of the photosensitive body. The CPU 1301 and the determination unit 1317 are an example of a control circuit that determines the exposure condition on the basis of the cumulative image formation amount for each one of the N exposure regions. The CPU 1301 and the exposure control unit 1320 may control the exposure light source to expose each one of the N exposure regions to light according to the exposure condition. According to the present embodiment, since the exposure condition is determined on the basis of the cumulative image formation amount per exposure region, disparity in the density of the toner image is reduced more than in the related art.
The CPU 1301 may determine the exposure condition for each one of the N exposure regions so that the exposure amount increases as the cumulative image formation amount increases. In this manner, the density of the toner image decreases as the cumulative image formation amount increases. Thus, by increasing the exposure amount, the density of the toner image is maintained and disparity in the density is reduced.
The N exposure regions may be arranged in a first direction parallel with a rotary shaft of the photosensitive body. In this manner, disparity in the density in the first direction is decreased.
The N exposure regions may be arranged in a second direction orthogonal to a first direction parallel with a rotary shaft of the photosensitive body. In this manner, disparity in the density in the second direction is decreased.
The N exposure regions may be arranged in a matrix pattern on the surface of the photosensitive body. In this manner, disparity in the density across substantially the entire surface of the sheet S is decreased.
The CPU 1301 may determine the exposure condition for each one of the N exposure regions on a basis of the cumulative image formation amount and the environment condition detected by the environment sensor 1305. In this manner, disparity in the density is reduced even if the environment conditions vary.
The memory 1302 may function as a storage unit that stores a plurality of correction formulas (for example, equations) associated in a one-to-one relationship with a plurality of different environment conditions. The CPU 1301 may determine the exposure condition for each one of the N exposure regions by selecting, from among the plurality of correction formulas, a correction formula corresponding to the environment condition detected by the environment sensor 1305 and using the selected correction formula. In this manner, disparity in the density is more reliably reduced.
The environment condition includes at least one of temperature and humidity. Here, temperature and humidity affect the discharge current that is produced at the surface of the photosensitive drum D. In other words, temperature and humidity affect the thickness reduction amount of the photosensitive drum D. Thus, by selecting the correction formula taking into account at least one of the temperature and the humidity, disparity in the density is more reliably reduced.
The CPU 1301 may multiply the cumulative image formation amount for each one of the N exposure regions and a first correction coefficient (for example, Pa) to obtain a product, add a second correction coefficient (for example, Pb) to the product, and determine an exposure amount for the exposure condition. In this manner, disparity in the density is more reliably reduced.
The first correction coefficient and the second correction coefficient may be determined according to the type of the toner. The types of the toner mainly relate to the material. Examples of the material include a polyester resin, a vinyl resin, an acrylic resin, a styrene acrylic resin, and the like. In this manner, by determining the exposure condition according to the toner type, disparity in the density is more reliably reduced.
The first correction coefficient and the second correction coefficient may be determined according to the type of the photosensitive body. Examples of the photosensitive body type include, for example, the material of the photosensitive layer, thickness, and the like. In this manner, by determining the exposure condition taking these into account, disparity in the density is more reliably reduced.
The first correction coefficient and the second correction coefficient may be determined according to the N corresponding to the number of the exposure regions. In this manner, by determining the exposure condition according to the number (N) of divisions of the exposure region, disparity in the density is more reliably reduced.
The operation unit 1304 is an example of an input device that accepts input of the first correction coefficient and the second correction coefficient. In this manner, the user may input and adjust the correction coefficient. The user input may be a numerical value or may be a command instructing to increase or decrease the numerical value.
The memory 1302 may store a thickness of a photosensitive layer of N exposure regions of the surface of the photosensitive body or thickness information relating to a reduction amount of the thickness. The CPU 1301 is an example of a control circuit that determines the exposure condition on the basis of the thickness information for each one of the N exposure regions. Also, the CPU 1301 may control the exposure light source to expose each one of the N exposure regions to light according to the exposure condition.
According to the first to fourth embodiment, the cumulative number of images per exposure region is stored in the memory 1302. The cumulative number of images may be thickness information relating to the thickness or the thickness reduction amount. For example, the thickness or the thickness reduction amount may be calculated from the cumulative number of images, and the thickness or the thickness reduction amount per exposure region may be stored in the memory 1302. In this case, in the formula EQ.1, the thickness or the thickness reduction amount is substituted into the equation (correction formula) as the input. In this manner, by determining the exposure condition individually for each one of the N exposure regions, disparity in the density may be reduced.
The CPU 1301 and the selection unit 1319 are an example of a control circuit that determines the content of image correction on the basis of the cumulative image formation amount for each one of the N exposure regions. The CPU 1301 and the image processing unit 1312 may function as an image correction unit that corrects image data corresponding to the N exposure regions according to the content of the image correction determined for each one of the N exposure regions. In this manner, by selecting the image processing condition individually per exposure region on the basis of the cumulative number of pixels, disparity in the density may be reduced.
The content of the image correction include dither processing. Here, dither processing is image processing relating to image density. Thus, by selecting the dither processing individually per exposure region on the basis of the cumulative number of pixels, disparity in the density may be reduced.
The post-processing apparatus 130 is an example of a booklet manufacturing apparatus that forms a sheet bundle including layers of sheets discharged from the image forming apparatus, heats the adhesive toner image of the sheet bundle to re-melt the adhesive toner image, and presses the sheet bundle to bond together the sheet bundle and manufacture a booklet. As illustrated in
Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2023-110258, filed Jul. 4, 2023 which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-110258 | Jul 2023 | JP | national |
