JP5211771B2 - Printing device - Google Patents

Description

The present invention relates to a printing apparatus for self-diagnosis of problems such as printing misalignment.

In an image forming apparatus such as a printer, a print head using an LED element or the like is used. This print head emits light to the photosensitive drum according to the print data, and a number of LED elements are arranged in a line to emit light to the photosensitive drum. This light emission is performed through an imaging lens array in which a lens is formed for each LED element, and an electrostatic latent image is formed on the photosensitive surface of the photosensitive drum.
In this case, it is necessary that the focal points of light emitted from the LED elements coincide on the photosensitive surface. For this reason, conventional focus adjustment is performed, and the relative position of the print head and the photosensitive drum is adjusted. For example, the print density formed on the recording paper is visually determined to adjust the position of the print head.
In addition, an image is formed on the recording paper to make a visual determination for printing misalignment, generation of white or black belt-like or streak-like streaks, and scumming.

Patent Document 1 relates to a focus adjustment device that adjusts the focus of a print head. In particular, an image forming state is compared, and an advanced adjustment technique is required by setting the middle of a distance where the state coincides as a true focal position. Provided is a focus adjustment device for a print head that does not.
JP 2003-112441 A

However, in the conventional case, the center position of the focus is estimated and the determination is made by visually observing the image. For this reason, there are variations in the determination of the focus position, printing misalignment, and the like, and it has not been possible to accurately determine the quality of the printing quality.
Therefore, the present invention automatically determines focus, streak, blur, etc., and accurately determines whether the print quality is good or not, and makes necessary adjustments and replacement of consumables and defective products accurately. The present invention provides a printing apparatus that can be used.

The above object is achieved according to the present invention, there is provided a printing apparatus including a print head having a plurality of chips including a plurality of pixels, reading reads the focus determination test pattern image printed by the print head is a focus determination target means and analyzes the focus determination test pattern read by said read means, a first calculating means for calculating a standard deviation of the printing density of each of the chip on the basis of the printing density of each of the pixels, all the chips when the calculation result of exceeding a predetermined threshold value, possess a determination unit and focus is good, and the reading unit is provided in the device, read out from the sheet, wherein the focus determination test pattern is printed performed based on the image data, the focus judgment test pattern on each predetermined number of dots, the image data is a printing apparatus to repeat off It can be achieved by providing.

  According to a second aspect of the invention, the reading unit is provided in a printing apparatus, and can be achieved by providing a printing apparatus that performs the reading based on image data read from a sheet on which the focus determination test pattern is printed.

According to the third aspect of the invention, the focus determination test pattern can be achieved by providing a printing apparatus that is image data that repeatedly turns on and off every predetermined number of dots .

According to the present invention, it is possible to perform automatic focus determination.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 is a schematic cross-sectional view illustrating the internal configuration of the printing apparatus illustrating the embodiment of the present invention. The printing apparatus 1 used in this example is provided with an image reading apparatus 2.

  In FIG. 1, a printing apparatus 1 includes an image forming unit 3, an intermediate transfer medium 4, a paper feeding unit 5, and a fixing unit 6, and the image reading device 2 is disposed at the top. The image forming unit 3 has a configuration in which four image forming units are arranged side by side. The image forming units 3M (magenta image forming units), 3C (cyan image forming units), 3Y (yellow image forming unit) and 3K (black image forming unit) are arranged in this order. The magenta (M), cyan (C), and yellow (Y) image forming units 3M to 3Y are used for color printing by subtractive color mixing, and the black (K) image forming unit 3K is used for monochrome printing.

  Here, each of the image forming units 3M to 3K has the same configuration except for the toner (color) stored in the developing container, and is disposed in the vicinity of the photosensitive drum 8 and the peripheral surface of the photosensitive drum 8. The charger 9, the print head 10, and the developing roll 11 are sequentially arranged, the photosensitive drum 8 is rotated in the direction of the arrow, the charge is applied from the charger 9, and optical writing based on the print information from the print head 10 As a result, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 8, and a toner image is formed by development processing by the developing roll 11.

  The intermediate transfer medium 4 includes a transfer belt 12, a drive roll 13 that rotates the transfer belt 12, a driven roll 14, and the like. The toner image formed on the photosensitive drum 8 is transferred to the transfer belt 12, and the drive roll 13. Is sent to the transfer section 15. The transfer unit 15 is supplied with a sheet transported from a sheet feeding unit (sheet feeding cassette) 5 by a conveying roller 16, and the toner image on the transfer belt 12 is transferred to the sheet and is fixed to the sheet by the fixing unit 6. .

  On the other hand, the image reading apparatus 2 is provided with a document reading unit 20 and an ADF (Auto Document Feeder). The document reading unit 20 includes a light source 22, a mirror 23, a document table motor 24, and a CCD unit 25, and the document image placed on the document table glass 27 is read by driving the document table motor 24.

  FIG. 1 is a diagram illustrating a system configuration of the printing apparatus 1 having the above configuration. As described above, the image reading apparatus 2 is provided in the printing apparatus 1, and the printing apparatus 1 includes an interface controller (hereinafter referred to as an I / F controller) 30 and an engine controller 31. A host device 33 such as a personal computer (PC) is connected to the printing apparatus 1 of this example. The output of the engine controller 31 is connected to the print head 10 described above.

  Print data output from the host device 33 is supplied to the image processing unit 36 via the LAN interface 34 or the USB interface 35, and is temporarily stored in the memory unit 38 having a function as a reception buffer. The CPU 37 in the I / F controller 30 analyzes the command of the print data stored in the memory unit 38, converts it into bitmap data, and develops it in the drawing area of the memory unit 38. For example, when the image data for one page is developed, the video I / F 39 instructs the engine controller 31 to start printing, and the image data is then output for each line according to the horizontal synchronization signal output from the engine controller 31. It is transferred to the controller 31.

  The engine controller 31 includes a head control unit 40, a CPU 41, and a memory unit 42. The engine controller 31 transfers image data transferred from the I / F controller 30 to the print head 10 according to the control of the CPU 41, and performs the above-described printing process on paper. Do. The supply of high voltage power to the above-described photosensitive drum 8 and the like is performed according to the control of the high voltage controller 43.

  On the other hand, the image reading apparatus 2 includes a CCD unit 25 (CCD sensor 25a), an analog / digital conversion circuit (hereinafter referred to as an A / D conversion circuit) 45, an MCU 48, a document table motor 24, and an ADF motor 26. Then, the data read by the CCD sensor 25 a is transmitted to the I / F controller 30 via the A / D conversion circuit 45 and the MCU 48 and supplied to the image processing unit 36.

  FIG. 3 shows an example of a test chart for inspection output from the host device 33. Note that the example in the figure is a diagram showing where each test chart is printed on the paper. The test chart for inspection is a focus determination test pattern and a streak determination test pattern. Information on the focus determination test pattern is printed in the area A, and information on the streak determination test pattern is printed in the area B. Then, a fogging image to be described later is printed in the area C.

  The focus determination test pattern is, for example, 2-dot on / off image data, and the streak determination test pattern is, for example, 100-200 LPD halftone image data. In addition, in the streak determination area of region C, a fogging image that is intentionally formed with no exposure and in a weakly charged state is printed.

Next, the processing operation of this example will be described.
First, when the “test pattern printing” button 52 shown in FIG. 4 is pressed, processing according to the flowchart shown in FIG. 5 is started. First, focus determination test pattern data is transferred from the host device 33 to the printing apparatus 1 (step (hereinafter referred to as S) 1). As described above, this data is input to the image processing unit 36 of the I / F controller 30 and stored in the memory unit 38 (reception buffer).

  Next, the test pattern data for streak determination is transferred from the host device 33 (S2). This data is also input to the image processing unit 36 of the I / F controller 30 and stored in the memory unit 38 (reception buffer). When the input of the test pattern is completed, the CPU 37 performs command analysis, outputs image data of the test pattern to the engine controller 31 via the video I / F 39, and performs printing processing on the paper according to the control of the head control unit 40.

  In the printing process on the paper, after the focus determination test pattern and the streak determination test pattern are printed, a charging voltage switching process is performed (S3). That is, the voltage output control of the high voltage controller 43 is performed according to the control of the CPU 41, and the supply voltage to the charger 9 is switched. For example, in printing in the above-described region C, switching is performed to reduce the high voltage applied voltage.

  FIG. 6 shows an example of setting the charging voltage to the photosensitive drum 8. For example, when printing a test pattern for focus determination in the area A and printing a test pattern for streak determination in the area B, a high voltage of −500 V is applied, and in the area C, the charging voltages are −255 V and −275 V, respectively. , -300V, -325V. Here, in this example, the reason why the charging voltage in the region C is switched in four steps is to set the charging voltage in four steps in consideration of the characteristics of the photosensitive drum 8 when an unexposed image corresponding to the region C is formed.

Through the above processing, the printing result of the test chart for inspection corresponding to FIG.
Next, the paper on which the test pattern printed out by the above processing is printed is placed on the above-described original glass table 27, and the image reading device 2 is driven. In other words, the document table motor 24 is driven, the light emitted from the light source 22 is irradiated onto the sheet through the mirror 23, and the reflected light is detected by the CCD sensor 25a.

  FIG. 7 is a flowchart for explaining the processing of the document image detected by the CCD sensor 25a. Data of the document image detected by the CCD sensor 25a is controlled by the MCU 48 described above, and the image processing unit 36 of the I / F controller 30. (Step (hereinafter referred to as ST) 1). Then, it is temporarily stored in the memory unit 38.

  Next, when the “image determination” button 53 shown in FIG. 4 is pressed, an inspection process for the image stored in the memory unit 38 is started (ST2). That is, the image data stored in the memory unit 38 is read under the control of the CPU 37 and the following inspection is performed.

First, focus determination is performed (ST3). In this process, the quality of the focus is determined based on the image data of the focus determination test pattern printed in the area A shown in FIG.
FIG. 8 is a diagram illustrating a focus determination method. FIG. 4A shows the case where the focus is good, and FIG. 4B shows the case where the focus is bad. FIG. 5C shows a calculation formula that is a reference for focus determination. In FIGS. 2A and 2B, the vertical direction indicates the amplitude, and the horizontal direction indicates the arrangement direction of the pixels (dots).

  In this example, a print head in which 40 chips having 192 light emitting elements are arranged in the main scanning direction is used, and the focus determination test pattern is turned on and off every two dots as described above. Repeated image data. Accordingly, in FIGS. 4A and 4B, a hatched circle indicates a print dot, and an open circle indicates a non-print dot.

  In the case where the focus shown in FIG. 5A is good, the amplitude is large, and the average density is low (thin) as shown by the alternate long and short dash line a1. On the other hand, in the case where the focus shown in FIG. 5B is poor, the amplitude is small, and the average density is high (dark) as shown by the alternate long and short dash line a2.

  Therefore, in this example, the above characteristics are used to analyze the focus and determine whether the focus is good or bad before and after a predetermined threshold. Specifically, whether or not the focus is good is determined using the calculation formula of FIG.

  This calculation formula is for determining whether the print head is good or bad in units of 40 chips, and n is the number of data included in one chip, for example, 192. Xi represents the amplitude which is the print density level of the target pixel (target chip), and Xave represents the average value of the pixel data in the chip. Therefore, this calculation formula shows the standard deviation of the target pixel.

  Therefore, whether the focus is good or bad is determined based on a certain threshold with respect to the result of the standard deviation calculated for each target pixel (for each target chip). FIG. 9 is a diagram showing a specific example. For example, when the threshold is set to “20”, when the result shown in b is obtained according to the above calculation formula, all the calculation results are equal to or greater than the threshold. The print head is determined to be in focus. On the other hand, when the result of c shown in the figure is obtained, it is determined that all the calculation results are equal to or less than the threshold value and the print head is in poor focus.

  By performing processing in this way, it is possible to automatically perform focus determination. Further, this determination result is simply displayed as shown in FIG. 4. For example, when a focus shift is found as a result of focus determination, “NG” is displayed. In this case, for example, focus adjustment is performed by a focus adjustment mechanism (not shown). Also, the print head is replaced.

Next, streak determination processing is performed (ST4).
This streak is a phenomenon in which streak or band-like blur due to lens unevenness occurs on a printed image, and streaks are detected based on the image data of the streak determination test pattern printed in the area B shown in FIG. Make a decision.

  FIG. 10 is a diagram for explaining the streak determination method, and shows an example of a halftone dot with a screen angle of 0 degrees of 150 DPI. In the process of this example, the streak is determined by extracting a density step between neighboring pixels adjacent to the target pixel.

  For example, the example shown in FIG. 5A is a configuration in which streak determination is performed on a 600 DPI pixel with a halftone dot of 25%. The streak determination is performed with the target pixel being four pixels and the surrounding pixels being, for example, 32 pixels. It is an example to do. In this case, the pixel of interest is shifted by one dot in the main scanning direction (arrow direction), and the moving average difference of the peripheral pixels with respect to the pixel of interest is calculated according to the calculation formula shown in FIG.

  In the above formula, Xi represents pixel data of the target pixel, n represents the number of data of the target pixel, Yi represents pixel data of the peripheral pixel, and m represents the number of data of the peripheral pixel. In the above example, an example of halftone dots of 25% has been described, but halftone dots of 12%, 33%, 48%, etc. can be calculated in the same manner.

  FIG. 6C is a diagram showing an example of white or black band determination. In order to determine white or black streaks, a relatively large 8 pixels are used as the number of pixels of interest, and 192 pixels are used as peripheral pixels. In this case, if there is a large density step, the amplitude of the scan data increases as shown in FIG. 5C, and streak is determined depending on whether or not the threshold is exceeded.

  FIG. 4D is a diagram showing an example of white or black streak determination. In order to determine white or black streak streaks, for example, a relatively small four pixels are used as the number of pixels of interest. 32 pixels are used as peripheral pixels. Also in this case, if there is a large density step, the amplitude of the scan data increases as shown in FIG. 4D, and streaks are similarly determined by whether or not a predetermined threshold is exceeded.

  FIG. 11 is a diagram illustrating an analysis example in which a white or black band is extracted from image data for an image having streak. FIG. 6B shows the calculation result. For example, the threshold value of streak is set to ± 5, and the position of the density difference larger than that is set to NG. FIG. 4A shows the result of white or black band determination according to the threshold value. The white band shown in FIG. 5A is a case where the threshold value of − (minus) 5 or less is exceeded, and the black band is a case where the threshold value of + (plus) 5 or more is exceeded.

  On the other hand, FIG. 12 is a diagram showing an analysis example in which white or black streaks are extracted from image data for an image having streak, and FIG. 12B is a diagram showing the above calculation result. Is set to ± 5, and the density difference position larger than that is set to NG. Also in this case, FIG. 9A shows the determination result of white or black stripes according to the threshold value. The white streaks shown in FIG. 5A are cases where the threshold value of − (minus) 5 or less is exceeded, and the black streaks are cases where the threshold value of + (plus) 5 or more is exceeded.

As described above, by analyzing the image data of the halftone dot image, white or black stripes, white or black streaks are digitized, and whether or not the streak is within an allowable range is automatically determined. The quality of the service can be determined.
Further, the streak determination result is simply displayed as shown in FIG. 4. For example, when a streak defect is found, the streak is displayed on the streak. In this case, for example, the light amount correction value is adjusted. Also, the print head is replaced.

  Next, as the case where streaks occur, the cause of streaks is caused by a process failure such as the above-described photosensitive drum 8 or developing roll 11, or is based on printing unevenness of the print head. Processing for determining whether will be described.

  As described above, in printing the streak determination test pattern in the region B, a high voltage of −500 V is applied to determine white or black belt or white or black stripe. Further, when printing in the region C, the charging voltage is switched to −255V, −275V, −300V, and −325V, and the printing process is performed without performing exposure from the print head 10. Accordingly, the image formed in the region C is a so-called fog image based on the characteristics of the process because the image forming conditions are set so that the defect of the image forming component is intentionally emphasized and appears in the image formation.

  FIG. 13B is a streak image formed in the region C, and FIG. 13A is the streak image shown in FIG. Therefore, by comparing the analysis results of FIGS. 4A and 4B, it can be determined whether the cause of the streak is caused by the process or the variation of the print head 10.

  For example, the white streak A1 shown in FIG. 13A is also present in FIG. 13B and is a so-called process streak. A white streak A2 shown in FIG. 13A is also present in FIG. 13B and is a process streak. On the other hand, the white streak A3 shown in FIG. 13A does not exist in FIG. 13B and is streak caused by the print head 10.

  Similarly, white streaks A4, A5, and A6 shown in FIG. 13A also exist in FIG. 13B and are process streaks. A black streak A7 shown in FIG. It does not exist in (b) and is streaks by the print head 10.

  As described above, the white or black streaks existing only in the image (b) of the region C are streaks based on the process, and the white or black streaks included in the image data of the region B are printed. It can be seen that the streak is based on the variation of the head 10.

  Therefore, the process of this example can identify the defective portion. For example, when the process is defective, the drum set including the photosensitive drum 8 or the toner set including the developing unit is replaced, and the print head 10 is replaced. If there is variation, the print head 10 is replaced. Further, the determination can be easily known from the display shown in FIG.

Next, the quality determination of lens unevenness will be described.
FIG. 14 is a diagram for explaining the processing of this example, and is a configuration for detecting the positional deviation between the imaging points of the Selfoc lens (SLA) and the LED array.

  FIG. 4A shows an example when the lens unevenness is large, and FIG. 4B shows an example when the lens unevenness is small. From both figures, when the lens unevenness is large (when the density unevenness is large), it becomes remarkable particularly at a period of 13.5 dots (about 0.6 mm).

  In this example, the image data is calculated by the calculation formula shown in FIG. Here, T is the amount of data, and determination is performed based on the calculation result. FIG. 4D shows the power spectrum when the lens unevenness is large, and FIG. 4E shows the power spectrum when the lens unevenness is small. Figures (f) and (g) are graphs obtained by converting the power spectrum into decibels (dB).

  Here, if the lens unevenness threshold is set to 65 dB, the vicinity of the 13.5 dots (about 0.6 mm) exceeds the threshold when the lens unevenness shown in FIG. On the other hand, when the lens unevenness shown in FIG. 5G is small, the vicinity of the 13.5 dots (about 0.6 mm) is below the threshold value.

  By processing in this way, it is possible to automatically detect lens unevenness. For example, when lens unevenness is detected, adjustment of a light amount correction value, replacement of a print head, or the like is performed.

  Further, it is possible to determine the blurring of the image based on the density level of the image data. The determination process in this case is shown in FIG. In this case as well, a predetermined threshold is set, and the quality of the blur is determined. In the example of FIG. 8, the density level “165” is used as a threshold value to determine whether the blur is good or bad.

FIG. 16 is a configuration diagram of a printing apparatus showing a modification of the present invention.
The printing apparatus shown in the figure has a configuration in which the toner image formed on the transfer belt 12 is read by the sensor 50 without using the document reading unit 20, and the above-described focus determination and streak determination are performed. Note that the specific methods of focus determination and streak determination are the same as those described in the above embodiment.

  In FIG. 16, the sensor is not limited to the position below the transfer belt 12 and may be provided near the paper conveyance path after passing through the fixing device 6. For example, the sensor 51 shown in the figure is provided in the vicinity of the paper conveyance path after passing through the fixing device 6.

1 is a diagram illustrating a system configuration of a printing apparatus. It is a schematic sectional drawing explaining the internal structure of the printing apparatus explaining this embodiment. It is a figure which shows the example of the test chart for a test | inspection output from a host apparatus. It is a figure explaining the structure of a display operation part. It is a flowchart explaining the processing operation of test pattern printing. It is a figure explaining the charging voltage supplied to a photoconductive drum. It is a flowchart explaining an image determination process. It is a figure explaining the determination method of a focus, (a) is a figure which shows an example with good focus, (b) is a figure which shows an example with poor focus, (c) becomes a reference | standard of the determination of focus It shows a calculation formula. It is a figure which shows the example of determination of a focus quality. (A) is a figure which shows the structure which performs streak determination with respect to the pixel of 600 DPI with a halftone dot of 25%, (b) is a figure which shows a calculation formula, (c) is a white or black belt | band | zone. (D) is a figure which shows the example of a determination of a white or black stripe. It is a figure which shows the analysis example which extracted the white or black belt | band | zone with respect to the image in which a streak exists from image data, (a) shows the determination result of a white or black belt | band | zone according to a threshold value, (b) It is a figure which shows the said analysis result. It is a figure showing an analysis example in which white or black streaks for an image in which streaks are extracted from image data, (a) is a figure showing a determination result of white or black streaks according to a threshold, (b) It is a figure which shows an analysis result. (A) is an analysis result including process streaks and streak of the print head, and (b) is an analysis result including streaks of only process streaks. It is a figure explaining the determination method of lens nonuniformity. It is a figure which shows the example of determination of an image blur. It is a schematic sectional drawing explaining the internal structure of the printing apparatus of the modification of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Printing apparatus 2 ... Image reading apparatus 3 ... Image formation part 4 ... Intermediate transfer medium 5 ... Paper feed part 6 ... Fixing part 8 ... Photosensitive drum 9 ... · Charger 10 ·· Print head 11 · Development roll 12 · Transfer belt 13 · Drive roll 14 · Driver roll 15 · Transfer unit 20 · Document reading unit 21 · ADF
22 .. Light source 23 .. Mirror 24 .. Original table motor 25 .. CCD unit 27 .. Original table glass 30 .. I / F controller 31 .. Engine controller 33 .. Host device 34 .. LAN interface 35. USB interface 36 .. image processing unit 38 .. memory unit 39 .. video I / F
40..Head controller 41..CPU
42. Memory unit 43. High voltage control unit 45. Analog-digital conversion circuit 46. Document table motor 47. ADF motor 48. MCU
50, 51 ... Sensor 52, 53 ... Button

Claims (2)

A printing apparatus including a print head having a plurality of chips each including a plurality of pixels,
Reading means for reading the focus determination test pattern image printed by the print head is a focus determination of a subject,
Analyzing the focus determination test pattern read by said read means, a first calculating means for calculating a standard deviation of the printing density of each of the chip on the basis of the printing density of each pixel,
A determination means for determining that the focus is good when the calculation results of all the chips exceed a predetermined threshold;
I have a,
The reading unit is provided in the apparatus, and is performed based on image data read from a sheet on which the focus determination test pattern is printed,
The printing apparatus according to claim 1, wherein the focus determination test pattern is image data that is repeatedly turned on and off every predetermined number of dots . The printing apparatus according to claim 1, wherein the standard deviation has a large value when the print density of each pixel is low and a small value when the print density of each pixel is high.