JP2005070136A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which speed improvement is made without impairing the fixing performance. <P>SOLUTION: The image forming apparatus includes a toner layer thickness detection means which detects the thickness of a toner layer, from the value of the density of the predetermined area of a processed color multi-level image; and a means for detecting the maximum value in a page. The apparatus further includes a speed control means which performs fixing, at such a speed that the fixing of the image having the detected maximum thickness of the toner layer is ensured. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fixing device of an electrophotographic color printer, and more particularly to an image forming apparatus that detects a toner layer thickness on a recording medium and forms an image by conveying the recording medium at a speed corresponding to the toner layer thickness.
[0002]
[Prior art]
Conventionally, an image signal is input from a host device, the number of colored (with dots) dots for each color is obtained from the input image signal, the total number of colored dots is calculated for each main scanning line, and the total number of colored dots The fixing speed was determined corresponding to
[0003]
If the number of dots in one line is 2560 dots, 1 to 2560 dots are set at the first fixing speed, 2561 to 5120 dots are set at the second fixing speed, and 5121 to 7680 dots are set at the third fixing speed. Printing was performed at the fourth fixing speed.
[0004]
[Patent Document 1]
JP-A-1-239578
[0005]
[Problems to be solved by the invention]
However, even if the total number of colored dots for each color of the main scanning line is obtained, the toner layer thickness cannot be determined accurately. For example, if the total number of dots in one line is 2560 dots, of which 1920 dots are colorless (no dots) and the remaining 640 dots are printed in four colors, the total number of colored dots is 640 * 4 = This is 2560 dots, which is indistinguishable from the case of 1560-color printing of 2560 dots.
[0006]
In this case, the toner layer thickness is determined to be one layer, and the first fixing speed is set as the fixing speed, and fixing is performed at the fastest speed. However, in reality, the color printing area has four layers, and the color printing area has to be fixed at the fourth fixing speed that is the slowest, but printing is performed at the first fixing speed. Is insufficient to cause poor fixing.
If the fixing speed is set to be slow when the total number of dots is 2560 dots, the fixing temperature becomes excessive in the case of monochrome printing of 2560 dots, and the fixing temperature needs to be lowered.
[0007]
In addition, in the case of an image where colored and colorless dots appear alternately, such as when halftone processing is performed, the fixing speed can be set high because the heat capacity is considered to be equivalent to the thinned toner layer thickness. However, even if the number of colored dots in the main scanning line is the same, in the case of an image concentrated on a portion having colored dots, fixing failure occurs if the same fixing speed is set.
[0008]
[Means for Solving the Problems]
An image forming apparatus according to the present invention includes a transport mechanism that transports a recording medium, an image recording section that forms a toner image based on input print data, and transfers the toner image to the recording medium transported by the transport mechanism section. A fixing unit for fixing the toner image transferred onto the recording medium,
Analyzes the input print data for each process color, divides the print data in the page into predetermined areas and calculates the density in the predetermined area for each color, and each color obtained by the density detector Add the density for each predetermined area to obtain the added density value,
A maximum addition density determination unit that determines the maximum addition density value in the page, and a toner layer thickness determination unit that determines the toner layer thickness from the maximum addition density value.
[0009]
Further, a storage unit for storing a table in which the toner layer thickness is associated with the recording medium conveyance speed is provided, and the medium conveyance speed is obtained from the toner layer thickness obtained by the toner layer thickness determination unit and the table stored in the recording unit. The above object is achieved by including a conveyance speed determination unit and a conveyance drive control unit that operates the rear part of the conveyance machine based on the recording medium conveyance speed obtained by the conveyance speed determination unit.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described using specific examples.
<Specific example 1>
[0011]
FIG. 1 is a block diagram of a printing mechanism according to the present invention.
Reference numeral 190 denotes a medium cassette in which the print medium 100 is stored, a mounting plate 190a for stacking the print medium 100, a spring 190b for biasing the stack plate 190a, and a hopping roller for feeding and transporting the stacked print medium 100. 190c.
Reference numeral 191 denotes a registration roller for once again abutting the leading end of the printing medium 100 fed and conveyed by the hopping roller 190c to correct skewing and further conveying the printing medium.
Reference numeral 192 denotes a conveying belt 192 that is stretched between the driving roller 192a and the idle roller 192b and electrostatically attracts and conveys the conveyed recording medium 100.
[0012]
Reference numeral 193 denotes a motor for driving the hopping roller 190c, the registration roller 191 and the driving roller 192a of the conveying belt 192 via a transmission mechanism (not shown).
Reference numerals 131, 132, 133, and 134 form an electrostatic latent image on the surface by electrophotographic charging and exposure processes, and attach toner to the formed electrostatic latent image by a development process to form a toner image on the surface. This is a photosensitive drum as an image carrier, and is provided for each color (black K, yellow Y, magenta M, cyan C). The photosensitive drums 131 to 134 for the respective colors are provided side by side with the conveyance belt 192.
[0013]
Reference numerals 181, 182, 183, and 184 denote drum motors for rotationally driving the photosensitive drums 131 to 134 at the same speed as the medium conveyance speed. Reference numerals 141, 142, 143, and 144 denote chargers for charging the photosensitive drums 131 to 134.
151, 152, 153, and 154 irradiate light to the photosensitive drums 131 to 134 charged by the chargers 141 to 144 in accordance with the image data generated based on the print data input from the host device, and perform photosensitivity. The print head forms an electrostatic latent image on the surface of the body drums 131 to 134. Reference numerals 161, 162, 163, and 164 denote developing units for developing toner images by developing the electrostatic latent images formed on the photosensitive drums 131 to 134 with toner.
Reference numerals 171, 172, 173, and 174 denote transfer units to which a voltage having a polarity opposite to that of the toner is applied from the back surface of the recording medium 100 in order to transfer the toner images formed on the photosensitive drums 131 to 134 to the recording medium 100. . Reference numerals 175, 176, 177 and 178 denote cleaning means for scraping off the toner remaining on the photosensitive drums 131 to 134 after the transfer.
[0014]
Reference numeral 110 denotes a fixing device for fixing the toner image transferred to the print medium 100, and a heat roller 111 having a heater 112 therein and a backup roller 114 for pairing with the heat roller 111 and pressurizing the print medium 100. The thermistor 113 detects the temperature of the heat roller 111.
Reference numeral 115 denotes a fixing device motor that rotationally drives the backup roller 114 via a transmission mechanism (not shown). Reference numeral 195 denotes a stacker for discharging and stacking the print medium 100 fixed by the fixing device 110.
[0015]
FIG. 2 is a print control block in the present invention.
A print control unit 200 is configured by a microprocessor, a ROM, a RAM, an input / output port, a timer, etc., receives print data and control commands from a host device, performs sequence control of the entire printer unit, and performs a print operation. I do.
Furthermore, the print control unit 200 determines the conveyance speed of the recording medium 100 and performs conveyance control of the recording medium 100 based on the determined recording medium conveyance speed.
[0016]
Reference numeral 201 denotes an I / F control unit that transmits printer information to the host device, analyzes a command input from the host device, and processes print data received from the host device.
Reference numeral 202 denotes image processing for performing PDL rendering, color matching, RGB → CMYK conversion, resolution conversion, UCR processing, gamma conversion, halftoning, and the like for print data received from the host device via the I / F control unit 201. And a data processing unit comprising a memory for storing image-processed data.
[0017]
An operation unit 203 includes an LED for displaying the status of the printer, an LCD, and a switch for giving an instruction from the operator to the printer.
Reference numeral 204 denotes a plurality of sensors for detecting the transport position of the print medium 100, a sensor for detecting temperature and humidity in the apparatus, and a sensor for density measurement. The output of each sensor is input to the print control unit 200. Yes.
[0018]
Reference numeral 205 denotes a charging voltage control unit that performs control for charging the surfaces of the photosensitive drums 131 to 134 by applying a voltage to the charging units 141 to 144 according to an instruction from the printing control unit 200. The charging voltage control unit 205 controls each color and controls the voltage applied to the K charger 141, the Y charger 142, the M charger 143, and the C charger 144, respectively.
[0019]
Reference numeral 206 denotes an exposure control unit that performs control for exposing the surfaces of the photosensitive drums 131 to 134 to light by the print heads 151 to 154 in accordance with image data stored in a memory in the data processing unit. It is. The exposure control unit 206 has a control for each color, and performs control for transmitting image data to the K head 151, Y head 152, M head 153, and C head 154 at a predetermined timing.
[0020]
Reference numeral 207 denotes a development voltage control unit for attaching toner to the electrostatic latent images generated by the print heads 151 to 154 on the surfaces of the photosensitive drums 131 to 134. The development voltage control unit 207 applies a voltage to each of the developers 161 to 164. Control to apply. The development voltage control unit 207 controls the voltages applied to the K development unit 161, the Y development unit 162, the M development unit 163, and the C development unit 164, respectively. Then, toner images are formed on the portions exposed by the print heads 151 to 154.
[0021]
Reference numeral 208 denotes a transfer voltage control unit for transferring the toner images generated on the surfaces of the photosensitive drums 131 to 134 to the print medium 100 conveyed by the conveyance belt 192. Control for applying a voltage to the transfer units 171 to 174 is performed. The transfer voltage control unit 208 controls the voltage applied to the K transfer unit 171, the Y transfer unit 172, the M transfer unit 173, and the C transfer unit 174, and the toner images formed by the respective developers 161 to 164. Are sequentially transferred to the print medium 100.
[0022]
Reference numeral 209 denotes an ID drum motor control unit for driving the photosensitive drums 131 to 134, the chargers 141 to 144, and the developers 161 to 164. The K motor 181, the Y motor 182, the M motor 183, and the C motor 184 are respectively connected. To drive.
Reference numeral 210 denotes a fixing control unit for fixing the toner image transferred to the printing medium 100, and performs temperature control according to an instruction from the printing control unit 200. In the temperature control, the temperature of the heat roller 111 is detected by the thermistor 113 and the heater is turned on / off to heat the heat roller 111 to a constant temperature. When the temperature of the heat roller 111 reaches a predetermined temperature, the fixing motor 115 for rotating the heat roller 111 and the backup roller 114 is also controlled.
[0023]
Reference numeral 211 denotes a motor control unit of a motor 193 for driving a hopping roller 190, a registration roller 191, and a conveyance belt 192 for feeding and conveying the print medium 100 from the medium cassette 190.
[0024]
Next, the general operation of the printer configured as described above will be described.
The print control unit 200 receives a control command and print data transmitted from the host device via the I / F control unit 201. When receiving a printing instruction from the host device, first, the fixing control unit 210 is instructed to heat the heater 112. When the surface of the heat roller 111 rises to a predetermined temperature, the fixing control unit 210 drives the fixing device motor to rotate the heat roller 111 and the backup roller 114.
[0025]
Next, the print control unit 200 drives the photosensitive drums 131 to 134, the chargers 141 to 144, and the development units 161 to 164 via the ID drum motor control unit 209, and at the same time, the charging voltage control unit 205 and the development voltage control unit. 207, instructs the transfer voltage control unit 208 to apply voltages to the chargers 141 to 144, the developers 161 to 164, and the transfer units 171 to 174 of the respective colors. The print control unit 200 detects the print medium 100 set in the medium cassette 190 by using a print medium remaining amount sensor and a print medium size sensor, and conveys the print medium according to the type of the print medium 100. In order to start, an instruction is given to the transport motor control unit 211 to start transport of the print medium.
[0026]
Here, the print medium conveyance motor 193 can be driven in both directions. By first driving in the reverse direction, the print medium 100 is taken out from the medium cassette 190 until the print medium suction sensor detects it. Only the set amount is sent. Subsequently, by driving the printing medium conveyance motor 193 in the forward direction, the registration roller 191 is rotated to convey the printing medium 100, and the conveying belt 192 is driven to send the printing medium 100 into the printing mechanism of the printer.
[0027]
When the print medium 100 reaches a printable position, the print control unit 200 sends a timing signal, reads image data from the memory in the data processing unit 202 for each color, and sends it to the exposure control unit 206. When the exposure control unit 206 receives image data for one line and transfers the image data to the print (LED) heads 151 to 154, the exposure control unit 206 sends a latch signal to the print heads 151 to 154 to print the image data for each print. The heads 151 to 154 are held. Thereafter, the exposure control unit 206 sends a light emission drive signal to each of the print heads 151 to 154 before the next line timing signal.
As a result, each of the print heads 151 to 154 emits light for each line according to the held image data.
[0028]
Each of the photosensitive drums 131 to 134 charged to a negative potential is irradiated with light according to the image data, thereby forming a dot with an increased potential on the surface of each of the photosensitive drums 131 to 134. It is formed.
Then, the toner charged to a negative potential is attracted to each dot by an electrical attraction force, and a toner image is formed. Thereafter, the toner image is sent to each transfer portion formed between each photoconductive drum 131 to 134 and each transfer unit 171 to 174. On the other hand, the print control unit 200 instructs the transfer voltage control unit 208 to apply a positive transfer voltage to each of the transfer units 171 to 174.
[0029]
As a result, each of the transfer units 171 to 174 transfers the toner image to the print medium 100 that passes through each transfer unit. Then, the print medium 100 having the transferred toner image passes between the rollers of the fixing device 110, and the toner image is fixed to the printing medium 100 by the heat of the fixing device 110. The print medium 100 having the fixed toner is further fed and discharged from the rear of the printer to the outside of the printer through the print medium discharge port sensor. When printing is completed and the print medium 100 passes through the print medium discharge port sensor, voltage application to each of the chargers 141 to 144, each of the developers 161 to 164, and each of the transfer units 171 to 174 is terminated, and at the same time, each ID drum The motors 181 to 184, the conveying motor 193, and the fixing device motor 115 also stop operating. Thereafter, the above operation is repeated.
[0030]
Next, the fixing speed determination process of the present invention will be described.
FIG. 3 is a block diagram showing an internal configuration of the data processing unit 202 of FIG.
301 performs image processing such as PDL rendering, color matching, RGB> CMYK conversion, resolution conversion, UCR (under color removal), and gamma conversion on various print data input via the I / F control unit 201; The image processing unit generates CMYK multi-value bitmap data.
[0031]
Reference numeral 302 denotes a CMYK multilevel image memory for storing multi-level bitmap data for one page generated by the image processing unit 301. Multi-value bitmap data is stored for each color.
303 extracts the multi-value bitmap data generated by the image processing unit 301 from the CMYK multi-value image memory 302 and converts it into CMYK binary pseudo-gradation images suitable for the printing process to generate binary color image data. A digital halftoning processing unit.
[0032]
Reference numeral 304 denotes a binary color image memory that accumulates one page of binary color image data binarized by the digital halftoning processing unit 303 for each color. The binarized binary color image data is transmitted to each exposure control unit 206.
A maximum density detection unit 305 detects the maximum value of the color density of each pixel from the CMYK multilevel bitmap data generated by the image processing unit 301. The detected maximum value of color density is transmitted to the print control unit 200.
[0033]
<Operation>
Next, the operation of the specific example 1 will be described.
The print data sent through the I / F control unit 201 is input to the image processing unit 301. If the print data sent from the host device is RGB multilevel bitmap data, the bitmap image data is first subjected to RGB> CMYK conversion and converted to CMYK multilevel data by the image processing unit 301. The
After that, the resolution is converted to the original resolution of the printing apparatus and converted into CMYK multi-value bitmap data.
[0034]
The generated CMYK multi-value bitmap data is sent to the multi-value image memory 302 and stored therein.
The CMYK multi-value bitmap data is also sent to the maximum density detector 305 at the same time, and the maximum density value in the image is detected.
[0035]
FIG. 4 shows a processing flow of the maximum density detection unit 305.
At the beginning of the page, the memory in which the maximum density value is stored (density MAX) is initialized to zero. (Step S-1)
It is determined whether or not one page of CMYK multi-value bitmap data has been input. If no page has been input (No), the process proceeds to step S-3, and if one page has been input, the process ends. (Step S-2)
A density value for one pixel of CMYK multi-value bitmap data is input. (Step S-3)
The input CMYK multi-value bitmap data is obtained by adding the CMYK color density values for each pixel to obtain the pixel density value. (Step S-4)
Pixel density = Y density + M density + C density + K density
[0036]
If the maximum density of each color of CMYK (each one color) is expressed as 100%, the possible range of the density value to which CMYK colors are added is 0 to 400%. The density MAX value stored in the memory in the maximum density detection unit 305 is compared with the calculated pixel density value. If the current pixel density value is lower, the process proceeds to step S-2 and the density of the next pixel is reached. If the current pixel density is higher than the density MAX value, the process proceeds to step S-6.
(Step S-5)
The current pixel density value is updated as the density MAX value. (Step S-6)
The density MAX value is compared with the maximum density value (400%) that can be taken by the printing apparatus. When the density value reaches the maximum density value (400%), no further density value exists, and the process is terminated. If the maximum density value (400%) has not been reached, the process proceeds to step S-2 and the process is repeated. (Step S-7)
[0037]
The above processing is performed on the CMYK multivalued image for one page, and the maximum density value of the entire one page image is detected.
The detected maximum density value is transferred to the print control unit 200 in FIG.
[0038]
The CMYK multilevel image created in the multilevel image memory 302 is further sent to the digital halftoning processing unit 303, converted into a CMYK binary pseudo gradation image, and stored in the binary image memory 304.
Pseudo gradation processing is generally area gradation processing, and this is also a change in the amount of toner in a predetermined area. In particular, in the case of a color process, each color toner overlaps. You can also catch it.
[0039]
FIG. 5 shows the relationship between each color density value and the toner layer thickness when the 8 × 8 dither method is used.
The upper four rows (Cyan screen, Magenta screen, Yellow screen, Black screen) show examples of matrix patterns by the 8x8 dither method when the density values of each color are 25%, 50%, and 75%. . “1” indicates a colored dot (with a dot), and “0” indicates a colorless dot (without a dot).
In the case of creating pseudo gradation data by the dither method, the dither pattern for each color has a screen angle to prevent moire, and the dither pattern for each color is generally not the same. Therefore, the arrangement of colored dots for each color is different.
[0040]
The fifth row (all color addition values) shows the amount of toner expected to be transferred to each dot position in the matrix when the density value of each color is 25%, 50%, and 75%, respectively.
This is a value obtained by adding the values of the upper four-stage matrix for four colors for each dot position.
As can be seen from this example, the average toner amount in the matrix, that is, the average toner layer thickness, is considered to be 100%, 200%, and 300%, respectively. When the density is 25%, the total number of colored dots in the 8 * 8 matrix is 64 dots, which is 100%. Similarly, when the density is 50%, the total number of colored dots is 128 dots, and when the density is 75%, the total number of colored dots is Becomes 192 dots, which are 200% and 300%, respectively.
[0041]
Depending on the dot position, for example, in the case of 75% density for each color of CMYK, a toner amount, that is, a toner layer thickness of 1 or 4 can be seen at a specific dot position in the matrix. When considering the fixing property of the heat roll fixing device, it is almost negligible.
[0042]
As described above, when the density value having a spread is considered, by performing halftoning processing, each color density addition value of the process color multi-value image may be considered equivalent to the toner layer thickness.
[0043]
The print control unit 200 includes a medium conveyance speed determination table shown in FIG. In the medium conveyance speed determination table, the media is determined from the type or thickness of the medium, and the medium conveyance speed is set from the media and the maximum density value. 200 is stored in the memory.
For example, media 1 is thin paper, media 2 is plain paper, media 3 is OHP paper or cardboard, media 4 is postcard, and media 5 is an envelope.
When the maximum density value detected by the maximum density detection unit 305 is input to the print control unit 200, the recording media setting is determined in advance by setting the type or thickness of the recording medium set by the host device. The conveyance speed is determined from the maximum density value and the recording media setting.
[0044]
The print control unit 200 drives the ID drum motor control unit 209 and the transport motor control unit 211 in accordance with the determined speed based on the determined transport speed. At this time, an image is formed by changing the voltage application timing of each image process as the recording medium is conveyed. Since the description of each image process has already been described, it is omitted here.
Although the operation of the maximum density detection unit 305 has been described with reference to a flowchart, it may be configured by dedicated hardware or by a programmed CPU. Further, although the description has been given by inputting the type and thickness of the recording medium from the host device, the same can be done even if set by the operation unit 203.
[0045]
<Effect of Specific Example 1>
As described above, according to the specific example 1, the maximum value in the page of the density value for each pixel of the process color multi-value image is detected, and the maximum value of the toner layer thickness is determined from the maximum density value. Since the fixing is performed at the maximum medium conveyance speed that does not impair the fixing property in the toner layer thickness, both high fixing performance and high printing speed can be achieved.
[0046]
<Specific example 2>
FIG. 7 is a block diagram of the data processing unit 202 in the second specific example. Instead of the maximum density detection unit 305 in the first specific example, the CMYK color multilevel bitmap memory is divided into predetermined pixel areas. An area maximum density detector 306 is provided for calculating the average density in the area and detecting the maximum value of the calculated average density value.
[0047]
FIG. 8 is a block diagram showing the configuration of the region maximum density detection unit 306.
The matrix memory 401 is a memory that can store CMYK color multi-valued images for M × M pixels, and is prepared for four colors of CMYK.
The memory access unit 402 is a memory access unit that sequentially copies images of M × M pixels from the CMYK multi-valued image memory to the matrix memory 401.
[0048]
The density average processing unit 403 is a means for calculating the average density of the M × M image of each color from the image data in the matrix memory 401, and is prepared for each of four colors of CMYK.
An adder 404 is an adder that adds the results of the four colors of the density average processing unit 403.
The peak detector 405 is a peak detector that detects the maximum value in the page of the output of the adder 404.
[0049]
<Operation>
As in the first specific example, CMYK multi-valued images are stored in the image memory 302 for one page.
The area maximum density detection unit 306 uses the memory access unit 402 to sequentially extract M × M pixel image data from the multi-valued image memory 302 and copy the image data into the matrix memory 401 as shown in FIG.
[0050]
In the density average processing unit 403, every time an M × M image is cut out, an average value of area density is calculated for each color, and the density average value for each color is added for all colors by an adder 404. Is calculated. If the density of all the M × M pixels of each color is 100%, the average density value of each color is 100%, and the output of the adder 404 at this time is 400%. Therefore, the value that can be taken by the adder 404 is 0 to 400% as in the first specific example.
[0051]
The above-described image cutout and density calculation are performed for one page, and the maximum value of each area density is detected by the peak detection unit 405. Thereafter, according to the maximum value of the area density, the medium conveyance speed is determined and the printing process is performed in the same manner as in the first specific example.
[0052]
<Effect of specific example 2>
As described above, the color multi-value bitmap is cut into a predetermined area, the average density in each area is calculated, and a means for detecting the maximum value in one page of the average density is provided, thereby providing a certain spread. Since the maximum value of the toner layer thickness can be detected, more appropriate printing speed control can be performed as compared with the first specific example.
[0053]
In the second specific example, a memory capable of storing one page of multi-valued images is prepared, and an example in which the region maximum density is detected after storing one page of images in this memory is shown. An image memory for the number of lines larger than the number of vertical dots is prepared, and density calculation, maximum value detection, and binarization by the digital halftoning processing unit are performed in parallel, so that an image memory for one page is necessarily required. It ’s not good.
[0054]
<Specific example 3>
Specific example 3 is a raster image data obtained by binarizing an image target for image density detection.
FIG. 10 is a block diagram illustrating the configuration of the data processing unit of the third specific example.
The line area maximum density detection unit 307 receives a CMYK binary line image instead of the specific example 1, the maximum density detection unit 305, calculates the average density of a certain pixel area in the line direction, and calculates the maximum of the calculated average density. A means for detecting a value is configured to receive a CMYK binary image directly generated by the digital halftoning processing unit 303 or the image processing unit 301.
[0055]
FIG. 11 shows the configuration of the line area maximum density detector 307.
The shift registers 501a, b, c, and d are memories that store line direction images for M pixels of CMYK color binary images, and have an M-bit shift register structure.
[0056]
Reference numerals 502a, b, c, and d denote adders that count the number of colored bits in the shift registers 501a, b, c, and d for each color of CMYK.
An adder 503 further adds the values of the respective colors of the adder 502.
Reference numeral 504 denotes peak detection means for detecting the maximum value in one page of the output of the adder 503.
[0057]
<Operation>
The CMYK binary raster image data generated by the image processing unit 301 and the digital halftoning processing unit 303 is input to the CMYK binary image memory and simultaneously input to the line region maximum density detection unit 307 at the same time.
[0058]
The input CMYK color image data is sequentially input to FIG. 9, M-bit shift registers 501a, b, c, and d, respectively.
The input binary image is stored in the shift register 501 for M bits in the line direction, and the colored bits in the M bits are counted by the adders 502a, b, c, and d.
[0059]
The counted number of CMYK colored dots is further added by the adder 503 for four colors.
At this time, the output of the adder 503 is M when all the M pixels for one color of the shift register 501 match in color, and 4 × M when all the M pixels for four colors are colored. Become.
The output of the adder 403 is sent to the peak detector 504, where the maximum value in one page is detected and passed to the print control unit 200.
[0060]
The print control unit 200 sets the maximum density detection value / M × 100 (%) as the average density value, determines the medium conveyance speed using the same speed table as in the first embodiment, and prints the contents of the binary image memory 304. Will be.
[0061]
<Effect of specific example 3>
As described above, according to the third embodiment, the average of the image density in a certain area of the line direction data of the CMYK binarized image data is obtained, and the maximum value of the density average is detected, whereby the line It becomes possible to detect the maximum value of the toner layer thickness having a spread in the direction, and it can be expected that the image processing speed is increased and the cost is reduced as compared with the specific example 2.
[0062]
In this specific example 3, a line buffer for a predetermined number of lines, for example, an M line buffer, is provided, and an image for M pixels in each line buffer, that is, colored dots that can be placed in an M × M pixel region are counted. By calculating this density average from the maximum value in the page, it becomes possible to detect the maximum value of the toner layer thickness that spreads not only in the main scanning direction but also in the sub-scanning direction.
[0063]
In the specific examples described above, in order to calculate the toner layer thickness, each color addition density value of the process color multi-valued image or the average value of the predetermined number of pixels is regarded as the toner layer thickness as it is, and the processing is performed. In some cases, a predetermined conversion is performed between the density value and the toner layer thickness.
[0064]
In the specific example, an example in which the medium conveyance speed and the fixing speed coincide with each other is shown. However, in the case of a printing apparatus in which the fixing speed and other printing process speeds can be individually set, the fixing speed control alone can be applied.
[0065]
In the specific example, an example of full-color printing of four colors of CMYK is shown, but it can be applied to a color electrophotographic printer of two or more colors such as CMY.
[0066]
In the specific example, the medium conveyance speed is determined by the two parameters of the recording medium setting and the maximum density value. However, other parameters such as an environmental parameter such as temperature and humidity may be additionally determined.
[0067]
【The invention's effect】
As described above, according to the present invention, the maximum value in the page of the density value for each pixel of the process color multi-value image is detected, the maximum value of the toner layer thickness is determined from the maximum density value, and this toner Since the fixing is performed at the maximum medium conveying speed that does not impair the fixing property in the layer thickness, both high fixing performance and high printing speed can be achieved.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an entire printing apparatus according to specific examples 1 to 3. FIG.
FIG. 2 is a block diagram illustrating a configuration of a control unit in specific examples 1 to 3;
FIG. 3 is a block diagram showing a configuration of a data processing unit of a specific example 1;
FIG. 4 is an explanatory diagram illustrating an operation of a maximum density detection unit according to a specific example 1;
FIG. 5 is an explanatory diagram showing a relationship between a density value and a toner layer thickness by pseudo gradation processing of a specific example.
FIG. 6 is a table for determining a medium conveyance speed from a recording medium type and a maximum density value in a specific example.
7 is a block diagram showing a configuration of a specific example 2; FIG.
FIG. 8 is an explanatory diagram showing a memory access operation of an image in a CMYK multilevel memory in specific example 2;
FIG. 9 is a block diagram illustrating a configuration of a region maximum density detection unit according to a specific example 2;
10 is a block diagram showing a configuration of a specific example 3; FIG.
FIG. 11 is a block diagram illustrating a configuration of a line area maximum density detection unit according to a specific example 3;
[Explanation of symbols]
131-134 Photosensitive drums for CMYK colors
141-144 CMYK chargers for each color.
151-154 LDE heads for CMYK colors.
161-164 Development units for CMYK colors.
171 to 174 CMYK transfer units for each color.
190 Hopping roller
191 Registration Roller
192 Conveyor belt unit
110 Heat roll fixing device
200 Print controller
201 Interface control unit
202 Data processing unit
203 Operation unit
204 Various sensors
205 Charge voltage controller
206 Exposure control unit
207 Development voltage controller
208 Transfer voltage controller
209 ID drum motor controller
210 Fixing control unit
211 Transport motor controller
301 Image processing unit
302 CMYK multilevel image memory
303 Digital halftoning part
304 CMYK binary image memory

Claims (4)

A transport mechanism for transporting a recording medium;
An image recording unit that forms a toner image based on the input print data and transfers the toner image to a recording medium conveyed by the conveyance mechanism;
A fixing unit for fixing the toner image transferred on the recording medium;
A density detector that analyzes the input print data for each color and detects a density value for each color in the page for each color;
A maximum addition density determination unit that adds the density for each color obtained by the density detection unit to obtain an addition density value, and determines the maximum addition density value in the page;
A toner layer thickness determination unit for determining the toner layer thickness from the maximum added density value;
A conveyance speed setting unit for setting a recording medium conveyance speed from the obtained toner layer thickness;
An image forming apparatus comprising: a conveyance drive control unit configured to operate the conveyance mechanism unit based on a recording medium conveyance speed set by the conveyance speed setting unit. The image forming apparatus according to claim 1, wherein the predetermined area corresponds to one pixel of a process color multi-value bitmap, and the density in the predetermined area is a density value of the one image. The predetermined area is an image area having a predetermined bit height and bit width in a process color multilevel bitmap image,
The image forming apparatus according to claim 1, wherein the density in the predetermined area is an average value of color density values of all pixels in the image area. The predetermined area is a line segment image for a predetermined number of bits on the scanning line data of the process color binary image,
2. The image forming apparatus according to claim 1, wherein the density in the predetermined area is an average value of each color binary image data of the line segment image, and the maximum added density value directly corresponds to a toner layer thickness.

Images