JP5100205B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine, and more particularly to a color image forming apparatus capable of forming a full color image.

In a color image forming apparatus, calibration (density adjustment) plays an important role in matching colors. For this reason, it is necessary to improve the correction accuracy of density adjustment, and it is required to perform density adjustment without reducing productivity.
The density adjustment in the color image forming apparatus is performed based on the measured density of each color toner patch formed on the transfer belt during continuous printing. In such density adjustment, in order to prevent variations in surface properties of the intermediate transfer belt from affecting measurement accuracy, the density of the same position of the intermediate transfer belt is measured before and after the toner patch formation. The density of the toner patch is calculated by subtracting the density before and after the toner patch formation (for example, Patent Document 1).
JP 2000-221738

However, in order to measure the density at the same position on the intermediate transfer belt a plurality of times by the sensor, the intermediate transfer belt must be rotated more than necessary, and much time is required for density adjustment. For this reason, the speed of continuous printing is reduced, and the productivity of the image forming apparatus is reduced.
SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide an image forming apparatus capable of accurately performing density adjustment while suppressing a decrease in productivity.

In order to achieve the above object, the invention according to claim 1 is to convey an image forming unit (2) and a plurality of sheets (P) intermittently at predetermined intervals to the image forming unit. And an image forming apparatus (1) capable of continuous printing processing for continuously transferring an image (40) formed by the image forming unit on a plurality of sheets to be conveyed. The image forming unit includes a rotating body (3) that supports a continuous image to be transferred onto a sheet at a predetermined pitch on a surface thereof, and a predetermined measurement position (on the surface of the rotating body at the time of density adjustment). 31, 32, 33, 34), density detection image forming means (9, 11, 13, 15) for forming a density detection image between the images, and the density of the density detection image And the density detection image is Measuring means (8) for measuring the density at the measurement position before being formed, and the density of the image for density detection measured by the measuring means based on the density at the measurement position measured by the measuring means. And correcting the density of the density detection image with a reference density set in advance so that the density of the image formed by the image forming unit is used as the reference density. Means for adjusting (30, 10, 12, 14, 16) and the rotating body so that the measurement position before formation of the image for density detection is positioned between the images at the time of density adjustment. The pitch of the image carried on the m is a length of m / n times the circumference of the rotating body ( where m is an integer of 2 to 7, n is an integer greater than m and not a multiple of m ). Hand to set the first pitch (30) and means (30) for setting the pitch of the image carried on the rotating body to a second pitch narrower than the first pitch except during the density adjustment. The image forming apparatus.

The numbers in parentheses indicate corresponding components in the embodiments described later. The same applies hereinafter.
According to a second aspect of the present invention, the image forming unit further includes a photosensitive drum (4, 5, 6, 7) for forming the image, and the rotating body is continuously formed by the photosensitive drum. 2. An image forming apparatus according to claim 1, wherein the image forming apparatus is an endless transfer belt (3) for temporarily carrying the formed image.

According to a third aspect of the present invention, the image forming unit is a color image forming unit (2), and the density detection image forming unit forms density detection images of a plurality of different colors. A plurality of measurement positions (31, 32, 33, 34) corresponding to the color of the density detection image to be formed are formed on the surface of the rotating body, and the first color measurement positions (31 32) and the measurement position (33, 34) for the second color are shifted by s times the first pitch ( where s is an integer of 2 or more ) in the rotation direction of the rotating body. The image forming apparatus according to claim 1 , wherein the image forming apparatus is an image forming apparatus.

The image pitch refers to the distance from the end of one image of the continuous image carried on the surface of the rotating body to the end of the next image.
According to the first aspect of the present invention, the image is continuously carried on the surface of the rotator at the first pitch during the density adjustment, and the surface of the rotator is more than the first pitch when the density is not adjusted. The images are continuously carried at a narrow second pitch.

  A density detection image is formed at a predetermined measurement position on the surface of the rotator, and the density of the density detection image and the background density of the measurement position are measured. The concentration is required. Since the pitch of the image is set to the first pitch, after measuring the background density at the measurement position, if the rotator is rotated by m turns, the measurement position is positioned between the images again. . Therefore, the density of the density detection image and the background density at the measurement position can be appropriately obtained. Further, since the measurement position and the density of the density detection image can be measured without rotating the rotating body many times, the density adjustment can be performed in a relatively short time.

  Since the pitch of the image is set to be narrow when the density is not adjusted, the time required for continuous printing is shortened. It is not necessary to set the pitch of the image to m / n times the circumference of the rotating body except at the time of density adjustment. Therefore, even if the pitch of the image is narrower than the first pitch, there is a particular problem. Absent. Thereby, the density adjustment can be performed with high accuracy while suppressing a decrease in productivity.

According to the second aspect of the present invention, the density detection image is formed at a predetermined measurement position of the endless transfer belt, and the density of the density detection image and the density of the background of the transfer belt are measured. Then, the corrected density of the density detection image is obtained.
According to the invention described in claim 3, the measurement position for the first color and the measurement position for the second color are shifted by s times the first pitch ( where s is an integer of 2 or more ). Thus, if the measurement position for the first color is positioned between the images, the measurement position for the second color is also positioned between the images. Therefore, it is possible to measure the background density and the detection image density for a plurality of different colors without rotating the rotator many times. Thereby, the density adjustment of a plurality of colors can be performed with high accuracy while suppressing a decrease in productivity.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view schematically showing the main configuration of a color printer 1 which is an example of an image forming apparatus according to the present invention. The color printer 1 includes a tandem type image forming unit 2 for forming a color image.
The image forming unit 2 includes a transfer belt 3, a cleaning device 28 for cleaning the surface of the transfer belt 3, and a magenta array arranged so as to be in contact with the transfer belt 3 along the moving direction 24 of the transfer belt 3. A photosensitive drum 4 for cyan, a photosensitive drum 5 for cyan, a photosensitive drum 6 for yellow, and a photosensitive drum 7 for black. Further, the density for measuring the density of toner patches 41 to 44 (see FIG. 3), which are density detection images, on the downstream side of the black photosensitive drum 7 when viewed from the moving direction 24 of the transfer belt 3. A sensor 8 is arranged.

  The magenta photosensitive drum 4 includes a magenta developing unit 9 for developing an electrostatic latent image formed on the peripheral surface of the photosensitive drum 4 with magenta toner, and a peripheral surface of the photosensitive drum 4. Adjacent is a magenta charger 10 for charging. Similarly, the cyan photosensitive drum 5 includes a cyan developing unit 11 for developing the electrostatic latent image with cyan toner, and a cyan charging unit for charging the peripheral surface of the photosensitive drum 5. 12 is adjacent. The yellow photosensitive drum 6 is provided with a yellow developing device 13 for developing the electrostatic latent image with yellow toner and a yellow charging device 14 for charging the peripheral surface of the photosensitive drum 6 adjacent thereto. Has been. Adjacent to the black photosensitive drum 7 are a black developing device 15 for developing the electrostatic latent image with black toner, and a black charging device 16 for charging the peripheral surface of the photosensitive drum 7. Has been. Further, in order to transfer the toner images carried on the peripheral surfaces of the photosensitive drums 4 to 7 to the transfer belt 3, transfer rollers are provided on the peripheral surfaces of the photosensitive drums 4 to 7 with the transfer belt 3 interposed therebetween. 17, 18, 19, and 20 are arranged.

The transfer belt 3 is stretched between the driving roller 21 and the driven roller 22 and is given a predetermined tension by the tension roller 23. The transfer belt 3 moves in the moving direction 24. Therefore, the four photosensitive drums 4 to 7 rotate counterclockwise in FIG.
Each of the photosensitive drums 4 to 7 is charged at a predetermined potential by the chargers 10, 12, 14, and 16, respectively, and an image corresponding to the original image is written therein by an LSU (laser scanning unit) or the like. Thereby, an electrostatic latent image is formed. The electrostatic latent images are developed into toner images of different colors by the developing devices 9, 11, 13, and 15, respectively. The toner images of the respective colors are once carried on the transfer belt 3 by the transfer rollers 17 to 20, and the toner images are superimposed on the transfer belt 3.

  On the other hand, the paper P is drawn out by a drawing roller (not shown) from a cassette (not shown) that can store a plurality of sheets P. A plurality of sheets P are conveyed toward the image forming unit 2 at a predetermined interval by the conveyance roller 26. The toner image once carried on the transfer belt 3 is transferred by the transfer roller 27 to the paper P conveyed to the image forming unit 2.

  The control unit 30 controls image forming operations by the photosensitive drums 4 to 7, the developing devices 9, 11, 13 and 15, the charging devices 10, 12, 14 and 16, and the transfer rollers 17 to 20. Further, the control unit 30 controls the transport mechanism including the transport roller 26. Further, the detection output of the density sensor 8 is supplied to the control unit 30, whereby the control unit 30 can measure the density of the toner patches 41 to 44 that are density detection images. .

  In the color printer 1 according to this embodiment, density adjustment processing (calibration processing) for adjusting the color of an image is prepared. The calibration process is performed during the continuous printing operation so as not to reduce the productivity of the color printer 1. The continuous printing operation is started on condition that there is a print job in a memory (not shown) of the control unit 30.

FIG. 2 is a flowchart illustrating an example of a continuous printing operation in the color printer 1. FIG. 3 is a diagram schematically showing an image carried on the transfer belt 3. FIG. 3A shows the transfer belt 3 in a normal state, and FIG. 3B shows the transfer belt 3 in a calibration mode to be described later.
When the continuous printing operation is started, the control unit 30 recognizes the size and orientation of the image 40 that is the object of image formation (step S1), and based on the size and orientation of the image, the pitch of the image 40 (image The distance from the end of 40 to the end of the next image 40) is set as the normal pitch (second pitch A) and the calibration mode pitch (first pitch B) (step S2). The second pitch A is set narrower than the first pitch B. When the size of the image 40 is “A4” and the direction is “horizontal”, the second pitch A can be exemplified by 270 mm (the width of the paper 40 is 210 mm, and the interval between the papers 40 is 60 mm). Further, as the first pitch B in this case, for example, 300 mm (the width of the sheet 40 is 210 mm, the interval between the sheets 40 is 90 mm) can be exemplified.

  Thereafter, a printing operation is performed (step S3). This printing operation is continuously executed until printing of one print job is completed (steps S4 and S5). In the printing operation of step S3, the image 40 (see FIG. 4) is continuously carried on the surface of the transfer belt 3. Normally, the control unit 30 controls the photosensitive drums 4 to 7, the developing devices 9, 11, 13, and 15 and the charging units so that the pitch between the image 40 and the previous image 40 becomes the second pitch A. The image forming operation by the devices 10, 12, 14, and 16 is controlled (see step S3, FIG. 3A). Accordingly, the pitch of the images 40 continuously carried on the surface of the transfer belt 3 is the second pitch A in the normal state.

R shown in FIG. 3A is the peripheral length of the endless transfer belt 3. As this circumference R, for example, 900 mm can be exemplified. In other words, the first pitch B is set to 1/3 of the circumference R.
When the number of printed sheets reaches a predetermined number by the end of printing of the print job (for example, when the number of printed sheets from the end of the previous calibration process has reached the predetermined number) (YES in step S5), continuous printing is performed. A calibration mode in which calibration processing is executed in parallel with the operation is entered.

FIG. 4 is a flowchart illustrating an example of a printing operation and calibration processing executed in the calibration mode.
In the printing operation in the calibration mode, the control unit 30 controls the photosensitive drums 4 to 7, the developing devices 9, 11, 13, and 15, and the respective units so that the pitch with the previous image 40 becomes the first pitch B. The chargers 10, 12, 14, and 16 are controlled to form the image 40 (see step S13, FIG. 3B). For this reason, the pitch of the images 40 continuously carried on the transfer belt 3 is the first pitch B. Toner patches 41 to 44 that are density detection images are formed between the images 40 that are continuous at the first pitch B. These toner patches 41 to 44 are formed at predetermined measurement positions 31 to 34 on the surface of the transfer belt 3. The printing operation is continued until the calibration process is completed (step S20).

When it is time to form the toner patches 41 to 44 (YES in step S11), the control unit 30 sets the photosensitive drums 4 to 7, the developing units 9, 11, 13, 15 and the charging units 10, The toner patches 41 to 44 are formed at the measurement positions 31 to 34 by controlling 12, 14, and 16 (step S12).
Referring to FIG. 3B, toner patches 41, 42, 43, and 44 are magenta, cyan, yellow, and black toner patches, respectively. The magenta toner patch 41 is for measuring the magenta density of the image. The cyan toner patch 42 is for measuring the cyan density of the image. The yellow toner patch 43 is for measuring the yellow density of the image. The black toner patch 44 is for measuring the black density of the image.

  On the transfer belt 3, a measurement position 31 and a measurement position 32 are juxtaposed along the rotation direction 24 of the transfer belt 3. In addition, a measurement position 33 is provided behind the measurement position 31 with a distance C. At this measurement position 33, a measurement position 34 is arranged along the rotation direction 24 of the transfer belt 3. The measurement position 32 and the measurement position 34 are also provided with an interval C therebetween. This interval C is set to the same length as the first pitch B. In other words, the measurement positions 31 and 32 for magenta and cyan are shifted from the measurement positions 33 and 34 for yellow and black by the first pitch B.

A magenta toner patch 41 is formed at the measurement position 31. A cyan toner patch 42 is formed at the measurement position 32. The yellow toner patch 43 is formed at the measurement position 33. A black toner patch 44 is formed at the measurement position 34.
In this embodiment, not only the density of each toner patch 41 to 44 is measured, but also the background density of the measurement positions 31 to 34 on the surface of the transfer belt 3 on which each toner patch 41 to 44 is formed is measured. The density measurement values 41 to 44 are corrected by using the ground density measurement value. Therefore, it is possible to obtain the density of each of the toner patches 41 to 44 with almost no influence from the dirt (noise) on the surface of the transfer belt 3. The measurement of the background density at each measurement position 31 to 31 is performed before the toner patches 41 to 44 are formed.

  Since the pitch (first pitch) of the image 40 carried on the surface of the transfer belt 3 in the calibration mode is 1/3 of the circumferential length R of the transfer belt 3, each measurement position 31 to 34 is the image 40. When the transfer belt 3 is rotated once, the measurement positions 31 to 34 are positioned between the image 40 and the image 40 again. For this reason, the density of the density detection image and the background density of the measurement position can be appropriately obtained. Further, the measurement positions 31 to 34 and the toner patches 41 to 44 can be obtained without rotating the transfer belt 3 many times. Since the concentration can be measured, the concentration adjustment can be performed in a relatively short time.

  When the measurement positions 31 to 34 of the transfer belt 3 face the density sensor 8 (step S14), it is checked whether or not the background density has been measured. If the background density has not been measured yet (NO in step S15). ), The density of the ground at the measurement positions 31 to 34 is measured by the density sensor 8 (step S16). If the background density has already been measured (YES in step S15), the density of the toner patches 41 to 44 is measured by the density sensor 8 (step S17).

  Then, the control unit 30 calculates the density of the toner patches 41 to 44 by subtracting the measured values of the toner patches 41 to 44 from the measured values of the background (step S18). Then, the control unit 30 changes the output condition of the image forming unit 2 based on the density of the toner patches 41 to 44 of each color (magenta, cyan, yellow, black) (step S19). As the change of the output condition of the image forming unit 2, for example, adjustment of the charging voltage of the corresponding color chargers 10, 12, 14, 16 can be exemplified. After the output conditions of the image forming unit 2 are changed, the calibration process ends (YES in step S20), is saved from the calibration mode, returns to the normal time, and the printing operation is continued until the print job is completed. In this normal printing operation, the image formed image 40 is continuously carried on the surface of the transfer belt 3 at a second pitch A that is narrower than the first pitch B.

As described above, according to this embodiment, the image 40 is continuously carried on the surface of the transfer belt 3 at the first pitch B during density adjustment, and the surface of the transfer belt 3 is normally held on the surface of the transfer belt 3 more than the first pitch B. Images 40 are continuously carried at a narrow second pitch A.
Since the pitch of the images 40 (second pitch A) is set to be relatively narrow except during normal times, the time required for the continuous printing process can be shortened. Thereby, the density adjustment can be performed with high accuracy while suppressing a decrease in productivity.

  Further, the measurement positions 31 and 32 for magenta and cyan on the surface of the transfer belt 3 and the measurement positions 33 and 34 for yellow and black are shifted by the first pitch B. Therefore, the measurement positions 31 to 34 for all colors. Is located between the image 40 and the image 40. Therefore, it is possible to measure the toner patches 41 to 44 and the background density of the measurement positions 31 to 34 for a plurality of different colors without rotating the transfer belt 3 many times. Thereby, the density adjustment of a plurality of colors can be performed with high accuracy while suppressing a decrease in productivity.

As mentioned above, although embodiment of this invention was described, this invention can also be implemented with another form.
For example, in the above description, the case where the first pitch B is set to 1/3 of the circumferential length R of the transfer belt 3 has been described. However, for example, the first pitch B is set to 5 / of the circumferential length R. It is also possible to set the length to 16 (for example, 281.3 mm). In such a case, the transfer belt 3 is moved until the measurement positions 31 to 34 are positioned between the images 40 after the measurement positions 31 to 34 are positioned between the images 40 and 40. It is necessary to rotate five times.

  In addition, as the size of the image and its direction, the sizes of “A3 vertical”, “A4 vertical”, and “A5 horizontal” can be used. In the case of “A3 vertical”, the combination of the first pitch B and the second pitch A is, for example, 484.6 mm (the length of 7/13 of the circumferential length R, the vertical length of the paper is 420 mm, the interval between the papers is 64.mm). 6 mm) and 480 mm (420 mm length of paper, 60 mm interval between papers). In the case of “A4 vertical”, the combination of the first pitch and the second pitch is, for example, 360 mm (2/5 of the circumferential length R, paper length 298 mm, paper interval 62 mm), 358 mm (paper 298 mm in length and 60 mm between the sheets). In the case of “A5 side”, the combination of the first pitch and the second pitch is, for example, 210 mm (length of 7/30 of the circumference R, length of paper 149 mm, interval between papers 61 mm), 209 mm (paper 149 mm in length and 60 mm between the sheets).

Further, although it has been described that the distance C between the magenta and cyan measurement positions 31 and 32 and the yellow and black measurement positions 33 and 34 on the surface of the transfer belt 3 is the first pitch B, the distance C is the first pitch B. S times (s is an integer).
Further, the measurement positions 31 to 34 may be provided at intervals C, respectively.
Furthermore, in the above-described embodiment, the toner amount of each toner image is controlled by adjusting the charging voltage of the chargers 10, 12, 14, and 16, but the toner amount is controlled in addition to this. This can be done by adjusting the developing bias applied to the developing rollers of the developing units 9, 11, 13, and 15, the exposure intensity of the exposure unit, the transfer voltage, and the like. The toner amount control can be realized not only by image formation control but also by control of parameters relating to image processing such as image control gradation.

Further, the density sensor 8 measures the density of the surface of the surface of the transfer belt 3 and the toner patches formed on the surface of the peripheral surface of the photosensitive drums 4 to 7, not the toner patches 41 to 44. It is also possible to detect the density of the ground on the paper P and the toner patch formed on the paper P.
In the above description, a color printer has been described as an example of the image forming apparatus. However, the present invention can also be applied to a monochrome printer, and can also be applied to other image forming apparatuses such as a copying machine and a multifunction machine. .

  In addition, various design changes can be made within the scope of matters described in the claims.

1 is a cross-sectional view schematically showing an internal configuration of a color printer which is an example of an image forming apparatus according to the present invention. 4 is a flowchart illustrating an example of continuous printing control in a color printer. It is a figure which shows typically the image carry | supported on a transfer belt. (A) shows a transfer belt in a normal state, and (b) shows a transfer belt in a calibration mode to be described later. It is a flowchart which shows an example of the printing operation performed in a calibration mode, and a calibration process.

Explanation of symbols

1 Color printer (image forming device)
2 Image forming unit 3 Transfer belt 4, 5, 6, 7 Photosensitive drum 8 Density sensor 9, 11, 13, 15 Developer 10, 12, 14, 16 Charger (density adjusting means)
17, 18, 19, 20 Transfer roller 30 Control unit 31, 32, 33, 34 Measurement position 40 Image 41, 42, 43, 44 Toner patch (density detection image)
P paper

Claims (3)

An image forming unit; and a conveying unit that intermittently conveys a plurality of sheets with a predetermined interval to the image forming unit. In an image forming apparatus capable of continuous printing processing for continuously transferring formed images,
The image forming unit includes:
A rotating body that carries a continuous image to be transferred onto a sheet at a predetermined pitch on its surface;
A density detection image forming means for forming a density detection image between the images at a predetermined measurement position on the surface of the rotating body at the time of density adjustment;
Measuring means for measuring the density of the density detection image and the density at the measurement position before the density detection image is formed;
Means for correcting the density of the density detection image measured by the measuring means based on the density at the measurement position measured by the measuring means;
Means for comparing the density of the corrected image for density detection with a reference density set in advance and adjusting the density of the image formed by the image forming unit to be the reference density;
At the time of the density adjustment, the pitch of the image carried on the rotating body is set to the circumference of the rotating body so that the measurement position before the formation of the density detection image is located between the images. means for setting the first pitch to a length of m / n times ( where m is an integer of 2 to 7, n is an integer greater than m and not a multiple of m );
An image forming apparatus comprising: means for setting a pitch of an image carried on the rotating body to a second pitch that is narrower than the first pitch except during the density adjustment. The image forming unit further includes a photosensitive drum for forming the image,
The image forming apparatus according to claim 1, wherein the rotating body is an endless transfer belt that temporarily holds an image continuously formed by the photosensitive drum. The image forming unit is a color image forming unit,
The density detection image forming unit forms density detection images of a plurality of different colors,
A plurality of measurement positions corresponding to the color of the density detection image to be formed are formed on the surface of the rotating body,
The measurement position for the first color and the measurement position for the second color are shifted by s times the first pitch ( where s is an integer of 2 or more ) in the rotation direction of the rotating body. The image forming apparatus according to claim 1 , wherein the image forming apparatus includes:

Images