JP2004272288A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the time required for alignment of images in each color and adjusting the density of images in each color to improve the work efficiency of image forming work in a color image forming apparatus. <P>SOLUTION: A color image forming device is provided with: a plurality of alignment sensors 14 to 16 for detecting alignment marks 17 for respective colors transferred to an endless belt; and a density adjusting sensor 20 for detecting a density adjusting mark 18 which is arranged in such a position that its detection area in a direction orthogonal to the moving direction of the endless belt does not overlap the detection areas of the alignment sensors 14 to 16 and which is transferred to the endless belt. Detection of the alignment mark 17 by the alignment sensors 14 to 16 and detection of the density adjusting mark 18 by the density adjusting sensor 20 can be performed in parallel. Thus the time required for completion of alignment of images in each color based on the detection result of the alignment mark 17 and for completion of density adjustment of images based on the detection result of the density adjusting mark 18 is shortened. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention includes an endless belt such as a conveyance belt or an intermediate transfer belt for conveying a sheet, and a plurality of image processing units arranged along the moving direction of the endless belt to form images of different colors. The present invention relates to a tandem type color image forming apparatus.

  Conventionally, a tandem type color image forming apparatus having a plurality of image processing units has been widely used. An example of such a tandem type color image forming apparatus will be described with reference to FIGS. FIG. 7 is a schematic view showing the entire structure of the color image forming apparatus, FIG. 8 is a perspective view showing a part thereof, and FIG. 9 shows a registration mark transferred onto the conveyor belt and a sensor for detecting the mark. FIG. 10 is an explanatory view showing a density adjustment mark transferred on the transport belt and a sensor for detecting the mark.

  In this color image forming apparatus, four image processing units 1Y, 1M, 1C, and 1K for forming images of different colors (yellow Y, magenta M, cyan C, and black K), and the formed images are transferred. And a transport belt 3 that transports the sheet 2 to be transported. The transport belt 3 is an endless belt that is supported and rotated by a driving roller 4 and a driven roller 5, and includes four image processing units 1 Y, 1 M, 1 C, and 1 K along the moving direction of the transport belt 3. Are arranged in a line.

  The four image processing units 1Y, 1M, 1C, and 1K form images of yellow Y, magenta M, cyan C, and black K, respectively, and each of the image processing units 1Y, 1M, 1C, and 1K has the same structure. It is. Therefore, in the following description, the image processing unit 1Y will be specifically described, and the other image processing units 1M, 1C, and 1K will be replaced with M, C, and K in place of the component Y in the image processing unit 1Y. Only those with reference numerals are displayed in the figure.

Below the transport belt 3, a paper feed tray 6 for storing the paper 2 is arranged.
At the time of image formation, the sheets 2 stored in the sheet feed tray 6 are sent out in order from the top one, and are attracted to the transport belt 3 by electrostatic attraction. The sheet 2 adsorbed on the transport belt 3 is transported to the first image processing unit 1Y, where a yellow toner image is transferred.

  The image processing unit 1Y includes a photosensitive drum 7Y as an image carrier, a charger 8Y, an exposing unit 9, a developing unit 10Y, a photosensitive cleaner 11Y, a transfer unit 12Y, and the like arranged around the photosensitive drum 7Y. Have been. The exposing device 9 is commonly used not only in the image processing unit 1Y but also in the other image processing units 1M, 1C, and 1K. The photoconductor drum 7Y is irradiated with a laser beam LY for yellow image. The photoconductor drum 7M is irradiated with a laser beam LM for a magenta image, the photoconductor drum 7C is irradiated with a laser beam LC for a cyan image, and the photoconductor drum 7K is irradiated with a laser beam LM for a black image. The laser beam LK is irradiated.

  For the paper 2 conveyed by the conveyance belt 3, following the transfer of the yellow toner image in the image processing unit 1Y, the transfer of the magenta toner image in the image processing unit 1M, and the transfer of the cyan toner in the image processing unit 1C. The transfer of the toner image and the transfer of the black toner image in the image processing unit 1K are performed, and the paper 2 on which the transfer is completed is separated from the transport belt 3 and sent to the fixing device 13, where the fixing process of the toner image is performed. Done.

  At a position below the conveyor belt 3 and in the vicinity of the driven roller 5, it is arranged in a direction (main scanning direction) orthogonal to the moving direction (sub-scanning direction) of the conveyor belt 3 so as to face the surface of the conveyor belt 3. Three sensors 14, 15, 16 are arranged. These sensors 14, 15, and 16 are used as sensors for detecting the alignment marks 17 formed in the image processing units 1Y, 1M, 1C, and 1K and transferred onto the conveyor belt 3, and one of them is used. The two sensors 14 are used as sensors for detecting the density adjustment marks 18 (see FIG. 10) formed in the image processing units 1Y, 1M, 1C, and 1K and transferred onto the conveyor belt 3.

  Slightly downstream of the sensors 14, 15, 16 along the moving direction of the conveyor belt 3, a belt cleaner 19 for cleaning the alignment mark 17 and the density adjustment mark 18 transferred onto the conveyor belt 3 is provided. Have been.

  As shown in FIG. 9, the alignment mark 17 is formed at a position on the conveyor belt 3 facing each of the sensors 14, 15, 16 and is a linear mark (horizontal line mark) parallel to the main scanning direction. ) And a line-shaped mark (oblique line mark) obliquely inclined with respect to the horizontal line mark. These alignment marks 17 are read by the sensors 14, 15, and 16, and the calculation of the amount of shift of the image for each color, the calculation of the amount of correction for eliminating the shift, and the execution command of the correction are performed according to the read result. The control is performed by a control unit (not shown) including the main CPU. (1) It is caused by an error between the axes of the photosensitive drums 7Y, 7M, 7C, 7K provided in the image processing units 1Y, 1M, 1C, 1K. (2) misalignment caused by unevenness in the main scanning direction of the photosensitive drums 7Y, 7M, 7C, and 7K provided in the image processing units 1Y, 1M, 1C, and 1K; (3) Main scanning registration deviation caused by deviation of the image writing position, (4) Magnification deviation caused by scanning line length being different for each color, and (5) Magnification in the main scanning direction is partially It can be occurring errors to adjust the magnification error deviation deviation causes, to align the image by eliminating the deviation between the colors of the image. Note that only the two sensors 14 and 16 may be used if only the positional deviation adjustments (1) to (4) are performed.

  As shown in FIG. 10, the density adjustment mark 18 is formed at a position facing the sensor 14 on the transport belt 3 and is formed as an image in which the density is changed to a plurality of levels for each color and gradation is obtained. ing. The density adjustment mark 18 is read by the sensor 14, the density value is calculated for each color, the correction amount relating to the density is calculated, and a correction effective command is performed by the control unit in accordance with the read result. Can be controlled.

  Conventionally, the detection of the density adjustment mark 18 for adjusting the image density of each color is performed using the sensor 14 which detects the alignment mark 17 for the alignment between the images of each color. A specific procedure for detecting the use mark 17 and the density adjustment mark 18 is as follows.

  First, an alignment mark 17 is formed and transferred onto the conveyor belt 3, and the alignment mark 17 is detected by using the sensors 14, 15, and 16. After the detection, the alignment mark 17 is detected by the belt cleaner 19. Clean. After the cleaning, the density adjustment mark 18 is formed and transferred onto the conveyor belt 3, the density adjustment mark 18 is detected by the sensor 14, and after the detection, the density adjustment mark 18 is cleaned by the belt cleaner 19.

  That is, after the formation, transfer, detection, and cleaning of the alignment marks 17 are completed, the formation, transfer, detection, and cleaning of the density adjustment marks 18 are performed. It takes time until the operation of the density adjustment is completed, and the operation efficiency of the image forming operation is deteriorated.

  SUMMARY OF THE INVENTION It is an object of the present invention to reduce the time required for the alignment of the images of each color and the density adjustment of the images of each color, and to increase the efficiency of the image forming operation.

  The invention according to claim 1 includes an endless belt that is driven to rotate, a plurality of image processing units that are arranged along the moving direction of the endless belt to form images of different colors, and A plurality of alignment sensors arranged in a direction orthogonal to a moving direction, and configured to detect alignment marks of each color formed by the image processing unit and transferred onto the endless belt, and In a color image forming apparatus configured to perform alignment of images of respective colors formed by the image processing unit according to a detection result of an alignment sensor, the alignment sensor is orthogonal to a moving direction of the endless belt. Are arranged on the same straight line at two positions on both the left and right ends in the direction of the endless belt, and are arranged at equal intervals, and the detection area in the direction orthogonal to the moving direction of the endless belt is A position between the alignment sensors that does not overlap with the detection area of the alignment sensor, which is arranged on the same straight line as the two alignment sensors, formed by the image processing unit, A density adjustment sensor for detecting a density adjustment mark transferred onto the endless belt is provided, and the density of an image formed by the image processing unit is adjusted according to the detection result of the density adjustment sensor. .

  Therefore, a positioning sensor for detecting the alignment mark transferred on the endless belt and a density adjusting sensor for detecting the density adjustment mark formed on the endless belt are separately provided, and Since the alignment sensor and the density adjustment sensor are arranged at positions where the detection areas in the direction orthogonal to the direction of movement of the endless belt do not overlap, detection of the alignment mark by the alignment sensor and density adjustment are performed. The detection of the density adjustment mark by the image sensor can be performed in parallel, and the alignment of each color image performed based on the detection result of the alignment mark and the detection based on the detection result of the density adjustment mark can be performed. The time required for completing the density adjustment of each color image can be shortened, thereby improving the work efficiency of the image forming operation. It can be.

  According to a second aspect of the present invention, in the color image forming apparatus according to the first aspect, the alignment mark and the density adjustment mark do not overlap in a direction orthogonal to a moving direction of the endless belt. When forming the alignment mark and the density adjustment mark, there is provided means for controlling the timing of forming the mark so that the formation of the other mark is started before the cleaning of one mark is completed. .

  Therefore, the detection of the alignment mark by the alignment sensor and the detection of the density adjustment mark by the density adjustment sensor can be performed with little time interval between the detections. It is possible to reduce the time required until the alignment of the images of each color performed based on the detection result of the mark and the density adjustment of the image of each color performed based on the detection result of the mark for density adjustment are completed. Thus, the work efficiency of the image forming work can be improved.

  According to a third aspect of the present invention, in the color image forming apparatus according to the first aspect, the alignment mark and the density adjustment mark overlap in a direction orthogonal to a moving direction of the endless belt.

  Therefore, the detection of the alignment mark by the alignment sensor and the detection of the density adjustment mark by the density adjustment sensor can be performed in parallel, and the image of each color is performed based on the detection result of the alignment mark. And the time required to complete the density adjustment of each color image based on the detection result of the density adjustment mark can be shortened, thereby improving the work efficiency of the image forming operation. it can.

  According to a fourth aspect of the present invention, in the color image forming apparatus according to any one of the first to third aspects, the alignment sensor and the density adjustment sensor are arranged on a single substrate.

  Therefore, since the alignment sensor and the density adjustment sensor use the same substrate, component management for the sensor is facilitated, and component cost for the sensor is reduced.

  According to the first aspect of the invention, the detection of the alignment mark by the alignment sensor and the detection of the density adjustment mark by the density adjustment sensor can be performed in parallel, and the detection of the alignment mark can be performed. It is possible to shorten the time required until the alignment of the image of each color performed based on the result and the density adjustment of the image of each color performed based on the detection result of the density adjustment mark are completed. Efficiency can be increased.

  According to the second aspect of the invention, the detection of the alignment mark by the alignment sensor and the detection of the density adjustment mark by the density adjustment sensor can be performed with little time interval between the detection. The time required until the alignment of each color image performed based on the detection result of the alignment mark and the density adjustment of each color image performed based on the detection result of the density adjustment mark is completed. Therefore, the working efficiency of the image forming operation can be improved.

  According to the third aspect of the invention, the detection of the alignment mark by the alignment sensor and the detection of the density adjustment mark by the density adjustment sensor can be performed in parallel, and the detection of the alignment mark can be performed. It is possible to shorten the time required until the alignment of the image of each color performed based on the result and the density adjustment of the image of each color performed based on the detection result of the density adjustment mark are completed. Efficiency can be increased.

  According to the fourth aspect of the present invention, since the positioning sensor and the density adjusting sensor use the same substrate, component management for the sensor is facilitated, and component cost for the sensor can be reduced.

  A first embodiment of the present invention will be described with reference to FIGS. Since the basic structure of the color image forming apparatus is the same as that of the conventional example described with reference to FIGS. 7 to 10, the overall structure of the color image forming apparatus will be described with reference to FIGS. The same parts as those described in FIGS. 7 to 10 are denoted by the same reference numerals, and description thereof is omitted (the same applies to the following embodiments). FIG. 1 is an explanatory view showing an arrangement state of a position adjustment sensor and a density adjustment sensor. FIG. 2 is a position adjustment mark and a density adjustment mark transferred onto a transport belt and a position adjustment sensor for detecting those marks. FIG. 3 is a timing chart showing the timing of a writing area signal in the sub-scanning direction between the alignment mark and the density adjustment mark of each color, and FIG. 4 is a timing chart of the color image forming apparatus. FIG. 2 is a block diagram illustrating an electrical hardware configuration.

  As described with reference to FIG. 7, the color image forming apparatus includes a conveying belt 3 which is located below the endless belt 3 and near the driven roller 5 so as to face the surface of the conveying belt 3. Three alignment sensors 14, 15, 16 arranged in a direction (main scanning direction) orthogonal to the three movement directions (sub-scanning direction) and one density adjustment sensor 20 are arranged. . These alignment sensors 14, 15, 16 and the density adjustment sensor 20 are mounted on a single substrate 21. The position adjustment sensors 14, 15, 16 are arranged at equal intervals, and the density adjustment sensor 20 has a detection area between the position adjustment sensors 14, 15 in the direction orthogonal to the moving direction of the transport belt 3. It is arranged at a position that does not overlap the detection areas of the alignment sensors 14 and 15.

  Here, the electrical hardware configuration and functions of the color image forming apparatus will be described with reference to FIG. The signal obtained from the alignment sensor 14 is amplified by the AMP 22, the frequency component higher than the required frequency is cut off by the filter 23, and the signal is converted from analog data to digital data by the A / D converter 24. The sampling of data is controlled by the sampling control unit 25, and the sampling rate is 20 KHz in the present embodiment. The sampled data is sequentially stored in the FIFO memory 26. Although only the signal obtained from one alignment sensor 14 has been described here, the signals obtained from the other alignment sensors 15 and 16 and the density adjustment sensor 20 are processed similarly.

  After the detection of the alignment marks 17 is completed, the data stored in the FIFO memory 26 is loaded into the CPU 29 and the RAM 30 via the data bus 28 via the I / O port 27, and various displacement amounts are calculated. Is performed. As a process based on a signal from the density adjustment sensor 20, an arithmetic process for density adjustment is performed.

  On the other hand, the ROM 31 stores various programs including programs for calculating various deviation amounts and density adjustment. The address bus 32 specifies a ROM address, a RAM address, and various input / output devices.

  Further, the CPU 29 monitors the detection signal from the sensor 14 (15, 16, 20) at an appropriate timing, so that even if the light emitting portions of the transport belt 3 and the sensor 14 (15, 16, 20) are deteriorated, etc. The light emission amount is controlled by the light emission amount control unit 33 so that the detection can be performed reliably, so that the level of the light receiving signal from the sensor 14 (15, 16) is always constant.

  Further, the CPU 29 has means for setting the timing of starting the formation of the alignment marks 17 and the density adjustment marks 18 on the writing control board 34, and the timing is transferred onto the transport belt 3. As shown in FIG. 2, the alignment mark 17 and the density adjustment mark 18 are set so as to overlap in a direction (sub-scanning direction) orthogonal to the moving direction of the transport belt 3.

  Further, the CPU 29 sets the writing control board 34 based on the correction amount obtained from the detection result of the alignment mark 17 to change the frequency based on the change of the main / sub resist and the magnification error. The write control board 34 is provided with a device capable of setting the output frequency very finely, for example, a clock generator using a VCO (voltage controlled oscillator) for each color including the reference color.

  Further, the CPU 29 sets the laser exposure power for the write control board 34 based on the image density condition obtained from the detection result of the density adjustment sensor 20, and also controls the bias control section via the I / O port 27. For 35, the developing bias and the charging bias are set.

  In such a configuration, in this color image forming apparatus, the alignment sensors 14, 15, 16 and the density adjustment sensor 20 are arranged along the sub-scanning direction, and the alignment sensors 14, 15, 16 The density adjustment sensor 20 and the density adjustment sensor 20 are arranged at positions where the detection areas in the direction orthogonal to the moving direction of the transport belt 3 do not overlap. For this reason, as shown in FIG. 2, the alignment marks 17 and the density adjustment marks 18 transferred on the conveyor belt 3 are overlapped in a direction orthogonal to the moving direction of the conveyor belt 3, and these alignment marks are aligned. The detection of the mark 17 for density and the mark 18 for density adjustment can be performed in parallel by the alignment sensors 14, 15, 16 and the sensor 20 for density adjustment, respectively.

  FIG. 3 shows the timing of the write area signal in the sub-scanning direction between the alignment mark 17 and the density adjustment mark 18 for each color. 17 and the density adjusting mark 18 are formed and transferred. However, such control is possible on the assumption that the density adjustment mark 18 of each color for density adjustment is formed by changing the laser power or the lighting duty (PWM value). Become.

  Therefore, the detection of the alignment mark 17 and the detection of the density adjustment mark 18 can be performed in parallel, and the alignment of the image of each color performed based on the detection result of the alignment mark 17 and the density adjustment The time until the density adjustment of each color image based on the detection result of the use mark 18 is completed can be shortened, and the time to wait the user until the image alignment and the image density adjustment are completed can be shortened. Therefore, the work efficiency of the image forming work can be improved.

  Further, in this color image forming apparatus, since the alignment sensors 14, 15, and 16 and the density adjustment sensor 20 are disposed on one substrate 21, the substrate 21 is shared and a plurality of sensors 14 are provided. , 15, 16, and 20 can be handled as one part, which facilitates the management of the parts related to the sensors 14, 15, 16, 20 and reduces the cost related to the sensors 14, 15, 16, 20. .

  In the present embodiment, the transport belt 3 that sucks and transports the sheet 2 is described as an example of the endless belt. However, the intermediate transfer belt is used as the endless belt, and the alignment mark is formed on the intermediate transfer belt. Alternatively, a mark for density adjustment may be transferred and detected by a sensor.

  Next, a second embodiment of the present invention will be described with reference to FIGS. The basic structure of the color image forming apparatus according to the present embodiment is the same as that of the color image forming apparatus according to the first embodiment. 5 is that the marks 17 do not overlap in the direction orthogonal to the moving direction of the conveyor belt 3 as shown in FIG. However, before the cleaning of the density adjustment marks 18 transferred onto the transport belt 3 by the belt cleaner 19 is completed, the transfer of the alignment marks 17 onto the transport belt 3 is started. The timing for starting the formation of these alignment marks 17 and density adjustment marks 18 is determined by the CPU 29 performing settings on the write control board 34 based on a program.

  In such a configuration, as a method of adjusting the density of an image, there is a method of changing the developing bias of the density adjusting mark 18 of each color gradation in a stepwise manner. When such a method is adopted, if the alignment mark 17 and the density adjustment mark 18 are formed simultaneously as shown in FIG. 2, the density of the alignment mark 17 also changes due to a change in the developing bias. As a result, erroneous detection may be caused at the time of detection by the alignment sensors 14, 15, and 16. Therefore, as shown in FIG. 5, first, the density adjustment mark 18 is formed, and then the alignment mark 17 is formed so that the formation timings do not overlap. This makes it possible to stably form the alignment mark 17 with a constant value of the developing bias.

  The formation of the density adjustment marks 18 and the alignment marks 17 is performed on the conveyor belt 3 before the cleaning of the density adjustment marks 18 transferred onto the conveyor belt 3 by the belt cleaner 19 is completed. Since the transfer of the alignment mark 17 is started, the density adjustment of the image of each color performed based on the detection result of the density adjustment mark 18 and the detection result of the alignment mark 17 are performed. It is possible to reduce the time required until the alignment of the image of each color to be performed is completed, and it is possible to enhance the efficiency of the image forming operation.

  FIG. 6 shows the timing of the writing area signal in the sub-scanning direction between the density adjusting mark 18 and the positioning mark 17 of each color, and writing is valid at the L level for each color. In the area shown in (1), the density adjustment mark 18 is formed, and in the area shown in (2), the alignment mark 17 is formed. Further, in the inactive period between the area (1) and the area (2), optimal setting of image density adjustment such as setting of a developing bias, a charging bias, and a laser exposure power is performed.

FIG. 3 is an explanatory diagram illustrating an arrangement state of a positioning sensor and a density adjustment sensor in the color image forming apparatus according to the first embodiment of the present invention. FIG. 4 is an explanatory diagram showing a registration mark and a density adjustment mark transferred on a conveyance belt, and a registration sensor and a density adjustment sensor that detect the marks; 5 is a timing chart showing the timing of a writing area signal in the sub-scanning direction for the alignment mark and the density adjustment mark for each color. FIG. 2 is a block diagram illustrating an electrical hardware configuration of the color image forming apparatus. FIG. 7 shows a registration mark and a density adjustment mark transferred on a conveyance belt in a color image forming apparatus according to a second embodiment of the present invention, and a registration sensor and a density adjustment sensor for detecting those marks; FIG. 5 is a timing chart showing the timing of a writing area signal in the sub-scanning direction of the density adjustment mark and the alignment mark of each color. FIG. 9 is a schematic diagram illustrating the entire structure of a conventional color image forming apparatus. It is a perspective view which shows a part. FIG. 4 is an explanatory diagram illustrating a positioning mark transferred onto a conveyance belt and a sensor that detects the mark. FIG. 4 is an explanatory diagram illustrating a density adjustment mark transferred on a conveyance belt and a sensor that detects the mark.

Explanation of reference numerals

1Y, 1M, 1C, CK Image processing unit 3 Endless belt 14, 15, 16 Positioning sensor 17 Positioning mark 18 Density adjusting mark 20 Density adjusting sensor 21 Substrate

Claims (4)

An endless belt driven to rotate, a plurality of image processing units arranged along the moving direction of the endless belt to form images of different colors, and arranged in a direction orthogonal to the moving direction of the endless belt And a plurality of alignment sensors for detecting alignment marks of each color formed by the image processing unit and transferred onto the endless belt, according to a detection result of the alignment sensor. A color image forming apparatus configured to perform alignment of images of respective colors formed by the image processing unit.
The positioning sensors are arranged at equal intervals on two identical straight lines at both left and right ends in a direction orthogonal to the moving direction of the endless belt,
The detection area in the direction orthogonal to the direction of movement of the endless belt is a position between the alignment sensors that does not overlap with the detection area of the alignment sensor, and is located on the same straight line as the two alignment sensors. A density adjustment sensor for detecting a density adjustment mark formed by the image processing unit and transferred onto the endless belt, and provided in accordance with a detection result of the density adjustment sensor. A color image forming apparatus, wherein the density of an image formed by an image processing unit is adjusted. The alignment mark and the density adjustment mark do not overlap in a direction orthogonal to the direction of movement of the endless belt, and when forming the alignment mark and the density adjustment mark, one of the 2. The color image forming apparatus according to claim 1, further comprising means for controlling the timing of forming the mark so that the formation of the other mark is started before the cleaning of the mark is completed. The color image forming apparatus according to claim 1, wherein the alignment mark and the density adjustment mark overlap in a direction orthogonal to a moving direction of the endless belt. The color image forming apparatus according to claim 1, wherein the alignment sensor and the density adjustment sensor are arranged on a single substrate.

Images