JP2001080122A - Printing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct highly accurately with a small memory capacity by correcting image date in units of lines in a sub scanning direction on the basis of an amount of a relative inclination of print heads, and correcting the corrected image data by a unit smaller than one line in the sub scanning direction. SOLUTION: A first skew-correcting part 42a roughly skew corrects image data in an image memory DRAM 34 in units of one lines for a mechanical unevenness of print heads 46. A second skew-correcting part 42b skew corrects data corrected by the first skew-correcting part 42a by a unit smaller than one line. Printing is controlled in units of 1/3 dots in a sub scanning direction according to the embodiment. In executing 1/3 line skew correction, it is enough for the second skew-correcting part 42b to use 3n correction information (n is a natural multiple) as an integral multiple of the divide number. The correction in unit of one line is set (n) to process simply.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a tandem type color printing device.

[0002]

2. Description of the Related Art In a tandem type printing apparatus such as a tandem type color printer, recording units for four colors of yellow (Y), magenta (M), cyan (C) and black (K) are arranged in one line. You. In printing, a plurality of C, M, Y, and K toner images generated by the recording unit are superimposed and transferred to one sheet to form a color image. In this type of printing apparatus, in order to improve the quality of color printing, it is necessary to reduce the displacement of the transferred multicolor toner images. The positional deviation includes a positional deviation in the main scanning direction, a positional deviation in the sub-scanning direction, and a skew amount representing a line inclination in the main scanning direction. The misalignment between the print heads is divided into three parts: the main scanning direction, the sub-scanning direction, and the inclination.
Classified into types. The positional deviation between the main scanning direction and the sub-scanning direction can be corrected relatively easily by controlling the timing of outputting the print data from the printer controller.
However, for the inclination, it is necessary to correct the image data according to the amount of inclination. Furthermore, in order to print the corrected image smoothly, it is necessary to perform correction in units smaller than one pixel.

[0003]

In correcting a skew occurring between print heads of a tandem type printer, a line buffer corresponding to the maximum amount of inclination that needs to be corrected is arranged immediately before the print head, and the line buffer is arranged. When the image data is corrected in the buffer according to the amount of tilt, the tilt can be reduced. However, in this method, a large amount of memory capable of high-speed operation is required for correction, and correction cannot be performed if the estimated maximum inclination is exceeded.

An object of the present invention is to correct skew occurring between print heads of a tandem type printing apparatus.
An object of the present invention is to provide a printing apparatus that enables high-accuracy correction processing with a small memory capacity.

[0005]

A printing apparatus according to the present invention employs a plurality of print heads arranged in a line to perform printing.
A first correction unit that corrects image data in a sub-scanning direction on a line basis based on a relative tilt amount between print heads; The image data corrected by the means is
A second correction unit for correcting in the sub-scanning direction in units smaller than the line. By performing the correction twice, for example, the correction in units of one line can be performed in the image memory, and the correction in units smaller than one line can be performed in the FIFO memory or the print head unit. As a result, the amount of a special memory such as a FIFO memory required for correction can be reduced, and cost reduction can be realized. Further, in this printing apparatus, the inclination amount is detected as an integral multiple of a correction unit in the correction by a unit smaller than one line by the second correction unit. This simplifies the configuration of the second correction means and enables highly accurate correction processing.

[0006]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same reference symbols indicate the same or equivalent ones. FIG. 1 shows a schematic configuration of a tandem type color printer. Imaging units 10y, 10m of four colors of yellow (Y), magenta (M), cyan (C), and black (K);
The transfer belts 10c and 10k are sequentially arranged in a line along the moving direction (sub-scanning direction) of the paper on the transfer belt 12. Each imaging unit 10y, 10m, 10c,
Inside the 10k, elements necessary for performing an electrophotographic process are arranged around a photoreceptor whose rotation axis is arranged along the main scanning direction. The image forming photoconductors Y, M, C, and K rotate counterclockwise in FIG.
The image forming processes at 0c and 10k are continuously performed. The image data sent from the host is converted into yellow, magenta, cyan, and black print data by the control unit 14, and each of the imaging units 1 is printed.
It is sent to the exposure heads within 0y, 10m, 10c and 10k. Each exposure head emits a laser in accordance with an electric signal of the image data sent thereto, performs one-dimensional scanning of the light with a polygon mirror, and exposes the photoconductor along a main scanning direction. The latent image formed on the photoconductor is developed with each color toner. The toner image on the photoconductor is transferred onto the transfer belt 12 by a transfer charger (not shown) provided in the transfer belt 12 so as to face each of the photoconductors. On the other hand, the paper is sent from the paper feed cassette 16 to the transfer unit by the pickup roller 18. Transfer belt 1
The transfer roller 20 transfers the toner image on the sheet 2 to a sheet. After the toner image is heated and melted by the fixing unit 22 and is fixed on the sheet, the toner image is discharged to the tray 24 via the sheet conveying path. Further, the toner remaining on the transfer belt 12 after the transfer is removed by the cleaner 26.

Further, the imaging units 10y, 10y
At the most downstream of m, 10c, and 10k, three registration correction sensors 28 are arranged in a line in a direction perpendicular to the conveying direction of the belt 12 (in the main scanning direction). When a resist pattern is formed on the transfer belt 12 using each of the imaging units 10y, 10m, 10c, and 10k, this sensor detects the amount of color misregistration of the Y, M, C, and K toner images in the main and sub scanning directions. The image data control unit performs drawing position correction and image distortion correction. This prevents color misregistration of the Y, M, C, and K toner images on the paper.

In the control unit 14 shown in FIG.
U30 controls the operation of the entire control unit. A ROM 32 and a DRAM 34 are connected to the CPU 30. The memory / I / O control unit 36 controls signal input / output between the memory and the outside. The CPU 30 is also connected to a host interface unit 38, a video interface unit 40, and a skew correction control unit 42. The image data is stored in the DRAM 34 via the host interface unit 38. The skew correction control unit 42 controls skew correction using the line buffer 44.

Next, the skew correction will be described. FIG. 3 shows the imaging units 10y, 10m, 10c,
5 shows an example of skew between printheads within 10k. Here, the skew distortions of yellow, magenta, and cyan are each relatively shown with reference to the black (K) line. The skew distortion is caused by the inclination of the print head or the like, and is detected by the registration correction sensor 28.

FIG. 4 shows an outline of a correction procedure performed by the skew correction control unit 42. The first skew correction unit 42a performs rough skew correction on a line-by-line basis for image data in the image memory (DRAM 34) with respect to mechanical variations of the print head. Next, the second skew correction unit 42b performs skew correction on the data corrected by the first skew correction unit in units smaller than one line. In the present embodiment, the printing is performed by 1/3 in the sub-scanning direction.
It is assumed that control can be performed in dot units. Therefore, when performing the skew correction in units of 1/3 line, the second skew correction unit 42b may use 3n (n is a natural number) correction information that is an integral multiple of the division number. In this case, the correction amount for each line can be set to n, and the processing can be performed by a simple circuit. That is, if the correction information in units of 1/3 line is 3n + 1 or 3n + 2, a fraction is generated. Therefore, a circuit for processing the fraction is further required. 1 /
Although the number is reduced to 3, the above-described processing of the fraction becomes unnecessary, and the circuit can be simplified. The obtained image data is sent to the print head. As described above, by performing the correction in two steps, for example, the correction in units of one line is performed on the image memory, and the correction in units smaller than one line is performed by the FIFO.
Can be done with memory or printhead. As a result, the amount of a special memory such as a FIFO memory required for correction can be reduced, and cost reduction can be realized.

For example, as shown in the upper part of FIG. 5, a line formed by a yellow, magenta or cyan print head is inclined with respect to a reference black line, thereby causing skew distortion. I do. Here, a black circle represents one dot. As shown in the center of FIG. 5, the first skew correction unit 42a performs correction in units of one line. Next, as shown in the lower part of FIG. 5, the second skew correction unit 42b performs correction in units of 1/3 line. By printing using the corrected data, the skew distortion can be reduced to less than one line.

In this embodiment, the skew correction for each line is performed by processing the image data stored in the bit map memory area in the DRAM 34 in the memory. The skew distortion can be canceled by sending image data corrected in advance for the skew distortion to the print head.

FIG. 6 shows image data in skew correction in a two-dimensional space. The correction in the memory will be described with reference to FIG. Upper left (a) of FIG.
As shown in FIG. 7, in the bitmap memory, white data areas are provided at the leading end (upper part in the figure) 52 and the trailing end (lower part in the figure) 52 of the image data (before correction) 50 received from the host. The area of the white data has a size equal to or larger than the maximum inclination amount to be corrected.

In the skew correction, first, the first line of the image data 50 before correction is transferred to the upper white area 52 using the line buffer 44 as shown in the upper right side (b) of FIG. . At this time, the transfer position becomes oblique in accordance with the skew distortion detected by the registration correction sensor 28. Here, the top image data is a white area 52.
Is transferred to the position in contact with the top of The data of the second and subsequent lines are sequentially transferred to the position following the data of the first line in the same manner as shown in the lower left part (c) of FIG. The lower right side (d) of FIG. 6 shows the image data after the transfer is completed.
Since the data in the white area 54 is also transferred in the same manner, the white data is automatically stored in a portion below the image data where the image data has disappeared. In this way, the white area on the lower side of the image is enlarged upward, and it becomes unnecessary to remove the data in the bitmap memory where there is no image data at the time of data transfer or after the data transfer.

FIG. 7 shows an address generation circuit for performing skew correction in the memory 34 as shown in FIG.
The address generation circuit is provided in the skew correction control unit 42. In the address generation circuit, an address counter 60
Counts with the image clock using the start address stored in the start address register 62 as an initial value. At the time of reading, when an image clock signal is input, the address counter 60 increases the count value by one and outputs it as a read address. At the time of writing, the count value of the address counter 60 and the offset register 64
Is added by the first adder 66 and output to the second adder 68. On the other hand, when the pixel clock signal is input, the skew counter 70
Is a skew correction value register 72 based on a line synchronization signal.
Is input, and counting is performed using the skew correction value as an initial value. The multiplier 74 calculates the product of the count value of the skew counter 70 and the value of the main scanning register 76 and outputs the result to the second adder 68 as a skew correction value. The second adder 68 adds the two input values and outputs the result as a write address.

In another embodiment, in the skew correction for each line, the correction is performed while outputting the image data in the bit map memory at a high speed. Referring to FIG. 8, as shown in the upper left part (a), in the image data received from the host, white data areas are provided in the upper and lower parts of the image data in a two-dimensional space. The area of the white data has a size equal to or larger than the maximum inclination amount to be corrected. (This is the same as in the case of the first embodiment shown in FIG. 6.) In the skew correction, the address generation circuit (see FIG. 13) moves the position of the skew correction obliquely in accordance with the skew distortion correction information. Generate a read address indicated by a line. That is, image data stored as shown in (a) in the two-dimensional space is read obliquely so as to cancel the skew distortion. First, as shown on the upper right side (b) of FIG. 8, the first line of the image data is read as video data at a read position indicated by an oblique line. On the first line, only the last quarter data is image data. The data of the second and subsequent lines are similarly transferred to the position following the first line as shown in the lower left side (c) of FIG. The lower right side (d) of FIG. 8 shows the last reading of the last line of the image data. In this last line, only the first quarter of the data is image data.

Next, the burst access mode will be described. Conventionally, for example, as shown in an access timing chart of FIG.
Read from the set address. Here, a 4-word access is shown. On the other hand, in the present embodiment, image data is read out by burst access. In the burst access, when a head address is designated, a plurality of words (here, four words) are accessed collectively. FIG. 10 shows the timing of burst access. In the line-by-line correction, image data is read by a plurality of words at a time by burst access. Therefore, 1
An address to be read from the bitmap memory is generated for each burst access, and four data are read continuously. That is, when an address is output, data of four addresses including that address is continuously accessed. Since the reading of the image data is performed by the burst access, the access time can be shortened and the correction processing can be speeded up as can be seen from comparison with FIG.

Next, the correction circuit 42a for each line will be described with reference to FIG. An address for one line is sequentially output to the image memory 34 from an address generation circuit (see FIG. 13) 80 by burst access. The output data of the image memory 34 is sent directly to the selector 84 and the selector 8
4 The selector 84 combines one line of image data from two lines of data in pixel units in accordance with a select signal from a select signal generation circuit (see FIG. 14) 86 and outputs the combined data.

Referring to FIG. 12, a correction circuit 4 for each line is provided.
Skew correction using burst access in 2a will be described. For skew correction, data before correction is read out in words in a two-dimensional space. Here, the unit of skew correction based on the inclination of the print head (hereinafter referred to as a correction unit) is not necessarily an integral multiple of the unit read out in one burst access (hereinafter referred to as an access unit). The upper part of FIG. 12 shows that, for the data before correction, the read data by the nth, (n + 1) th, and (n + 2) th burst accesses overlap. Therefore, when data is read in access units, unnecessary data indicated by hatching is also read. As a result, it is impossible to read necessary data overlapping with the data. Therefore,
As shown in the middle part of FIG. 11, correction is performed using a line buffer (FIFO memory) 44 for one line. In the example shown in the figure, portions of the data of three correction units, which are already indicated in white, are stored in the line buffer 44 as indicated by arrows. Here, the hatched part is
The data read out by the burst access is not included in the correction unit, and thus represents a portion not stored in the line buffer 44. Next, when image data is newly read out, as shown by the arrow, data that could not be read out previously (portion shown in white) is synthesized at the corresponding position of the line, and is also stored in the line buffer 44 at the same time. I do. In this way, as shown in the lower part of FIG. 12, one line of data is synthesized from two lines of data in pixel units.

FIG. 13 is a block diagram of an address generation circuit 80 by burst access. The image clock is
It is input to the dot counter 800 and the frequency divider 802. The frequency divider 802 divides the frequency of the image clock into burst access units (access units), and the address counter 80
Send to 4. The address counter 804 is incremented in access units using the start address input from the start address register 806 as an initial value, and outputs the address to the adder 808. On the other hand, the dot counter 800 outputs a count pulse to the line counter 812 every time the number of pixels to be corrected stored in the skew correction value counter 810 is reached. Line counter 8
The output value of 12 and the line size from the line size register 814 are multiplied by a multiplier 816 and output to an adder 818. Thereby, the multiplier 816 calculates how many lines are to be corrected. The dot counter 800 and the line counter 812 are reset by the line synchronization signal. Adder 818 adds the two input values and outputs a read address.

FIG. 14 is a block diagram of the select signal generating circuit 86, and FIG. 15 is a timing chart thereof. Word counter 860 and skew counter 862
Is a repetition counter for counting pixel clocks.
The word counter 860 is reset every time the unit of burst access (access unit) stored in the word register 864 is reached.
The reference numeral 62 is reset each time the pixel unit to be corrected stored in the skew register 866 is reached. The skew register 866 outputs the stored value according to the output signal of the skew counter 862 or the line synchronization signal, resets the skew counter 862, and outputs the word register 8
Numeral 64 outputs the stored value according to the output signal of the word counter 860 or the line synchronization signal, and resets the word counter 860. The flip-flop 868 is reset by the output signal of the skew counter 862,
It is set by an output signal from the word counter 864 and outputs a select signal. When the select signal is set, data from the line buffer 44 is selected, and when reset, data from the image memory 34 is selected.

As described above, white data areas are provided at the leading end and the trailing end of the image data in the bit map memory (see the upper left part (a) of FIG. 8). Outputs data while performing line-by-line correction. In this manner, the correction can be performed in units of one line using the line buffer 44 for at least one line. As a result, the amount of a special memory such as a FIFO memory required for skew correction can be reduced, and cost reduction can be realized.

In order to print an image smoothly, it is required to perform correction in units smaller than one pixel. Next, the correction by the second skew correction unit 42b in units smaller than one line (1/3 line unit in this embodiment) will be described. As shown in FIG. 4, the correction in units smaller than one line is performed on the image data corrected in units of one line by the first skew correction unit 42a. In the correction in a unit smaller than one line, as shown in FIG.
Controlled in line units.

FIG. 16 shows a correction circuit 4 for each 1/3 line.
2b and the print head 46 are shown. Video data that has already been corrected in units of one line is delayed via the line buffer 90. The video data or video data delayed by one line is combined with the print head 46 (FIG. 1) as a video 0 signal, a video 1 signal, and a video 2 signal.
9). The video 0 signal, the video 1 signal, and the video 2 signal are print data sequentially printed in units of 1/3 line. The video 0 signal is video data delayed via the line buffer 90. On the other hand, the video data and the output data of the line buffer are output to the first selector 92 and the second selector 94, respectively. The first selector 92 and the second selector 94 respectively convert the video data selected in consideration of the skew according to the select 1 signal and the select 2 signal from the select signal generation circuit 96 (see FIG. 17) into the video 1 signal. It is output to the print head 46 as a video 2 signal.

FIG. 17 shows a configuration of the select signal generation circuit 96, and FIG. 18 shows a timing chart of the select signal generation circuit 96. In the select signal generation circuit 96, the sub dot counter 960 and the skew counter 9
Reference numeral 62 counts the pixel clock. The sub-dot counter 960 is reset each time the value stored in the sub-dot register 964 is reached, and the skew counter 962 is reset each time the value stored in the skew register 966 is reached. The skew register 966 outputs the stored value according to the output signal of the skew counter 962 or the line synchronization signal, and the subdot register 964 outputs the stored value according to the output signal of the subdot counter 960 or the line synchronization signal.
The shift register 968 is reset by the output signal of the skew counter 962, and the sub-dot counter 960
Shifts the input signal at the H level according to the output signal from the controller and outputs the select 1 signal and the select 2 signal.

As shown in FIG. 18, the sub dot counter 960 and the skew counter 962 are reset by the line synchronization signal and start counting, and output a shift clock signal and a clear signal, respectively. In response, shift register 968 outputs a select 1 signal and a select 2 signal. Thereby, the first selector 92
Receives the select 1 signal, outputs the video 1 signal to the print head 46, and receives the select 2 signal, and outputs the video 2 signal to the print head 46.

FIG. 19 shows the configuration of the print head 46. In the timing chart of the print head 46 of FIG. 20, the lower chart (b) is an enlarged view of the broken line portion of the upper chart (a). Print head 9
8 is an LED array 10 arranged in one row in the main scanning direction.
0 is provided. The video 0 signal, video 1 signal, and video 2 signal from the second skew correction unit 42b (FIG. 16) are input to three shift registers 102, respectively, and are shifted in the line direction using a pixel clock as a shift clock. The image data (the video 0 signal, the video 1 signal, and the video 2 signal) of each cell of the three-line shift register 102 is latched in the three-stage shift register 104 by a line synchronization signal. The video 0 signal, the video 1 signal, and the video 2 signal of the three-stage shift register 104 are converted by the 1/3 line synchronization signal into the shift register 10.
The light is shifted at three stages in a direction orthogonal to the second shift direction, and is output to each LED of the LED array 100.

[0028]

In the skew correction occurring between the print heads of the tandem type printer, the correction is performed in two stages, so that the correction processing can be performed with a small memory capacity and with high accuracy.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of the overall configuration of a color printer.

FIG. 2 is a block diagram of an image data control unit.

FIG. 3 is a diagram for explaining the concept of skew correction;

FIG. 4 is a diagram showing a procedure of skew correction.

FIG. 5 is a diagram illustrating an example of skew correction;

FIG. 6 is a diagram for explaining skew correction in a memory;

FIG. 7 is a block diagram of an address generation circuit.

FIG. 8 is a diagram for explaining skew correction when reading from a memory;

FIG. 9 is a timing chart of conventional access.

FIG. 10 is a timing chart of burst access.

FIG. 11 is a correction circuit diagram for each line.

FIG. 12 is a timing chart of correction by burst access.

FIG. 13 is a block diagram of an address generation circuit.

FIG. 14 is a block diagram of a select signal generation circuit.

FIG. 15 is a timing chart of a select signal generation circuit.

FIG. 16 is a correction circuit diagram for each 1/3 line.

FIG. 17 is a block diagram of a select signal generation circuit.

FIG. 18 is a timing chart of a select signal generation circuit.

FIG. 19 illustrates a configuration of a print head unit.

FIG. 20 is a timing chart of a print head unit.

[Explanation of symbols]

34 image memory, 42 skew correction unit, 4
4 line buffers, 46 printheads, 80
Address generation circuit, 82 line buffer,
84 selector, 86 select signal generation circuit
96 Select signal generation circuit.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H04N 5/95 H04N 5/95 DF term (reference) 2C055 KK04 KK05 2C087 AA15 AC01 2C262 AA24 AA26 AA27 AB15 BB03 FA06 GA14 GA40 5C052 AA11 AA17 AB04 DD02 GA05 GA07 GA08 GB01 GC00 GD01 GE02 GE04 GE05 GF05 5C053 FA04 FA27 KA02 KA03 KA08 KA19 KA20 KA24 LA03 LA14

Claims (2)

[Claims] 1. A printing apparatus for performing printing on one sheet by using a plurality of print heads arranged in one line, wherein image data is lined based on a relative inclination amount between the print heads. A printing apparatus comprising: a first correction unit that corrects in the sub-scanning direction in units; and a second correction unit that corrects image data corrected by the first correction unit in the sub-scanning direction in units smaller than one line. 2. The printing method according to claim 1, wherein the amount of inclination is detected by an integral multiple of a unit of correction in a unit smaller than one line by the second correction unit. apparatus.