JP2017209909A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that is configured to have a function of performing control so that the number of times of memory access is reduced by making data amounts of memory access executed once as large as possible.SOLUTION: The image forming device, which comprises a plurality of recording heads which can form linear images of a plurality of colors extending in a main scanning direction respectively and outputs image data of each color to each of the plurality of recording heads to form a color image, comprises: memorizing means which memorizes the image data for each color; correction value setting means which sets correction values corresponding to mutual displacement amounts of the plurality of recording heads; and control means which controls the recording means on the basis of the set correction values by the correction value setting means and shifts the image data and then outputs the data to the recording heads. The control means shifts a plurality of dots as one body collectively when shifting the image data.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a color printer, image data is stored in a memory so that color misregistration does not occur even when holding positions of a plurality of recording heads are shifted or tilted. When data is written to or read from the memory, correction is performed so as to cancel the color misregistration by finely switching the memory address (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 9-188000

  However, in the conventional image forming apparatus, address switching frequently occurs when the width of the partition in the memory corresponding to the correction unit is reduced in order to improve the correction accuracy to cancel the color misregistration. Instead of reducing the amount of data that is read from and written to the memory in a single memory access, the number of accesses increases.

  For this reason, for example, when a memory such as SDRAM, which is not good at random access, is used as the memory, there is a problem that the time required for the access becomes long and the printing speed is hindered.

  On the other hand, for example, when a memory that is good at random access such as SRAM is used as the memory, the time required for access does not become long, but if a memory having the same capacity as a memory that is not good at random access is to be mounted. There was a problem that the cost would be high.

  The present invention provides an image forming apparatus having a function of solving the above-described conventional problems and controlling the amount of data for one memory access to be as large as possible to reduce the number of memory accesses. With the goal.

  For this purpose, the image forming apparatus of the present invention includes a plurality of recording heads each capable of forming a plurality of line-shaped images extending in the main scanning direction, and each of the plurality of recording heads has image data of each color. Is a correction value setting for setting a correction value according to the mutual displacement amount of the recording means and the storage means for storing the image data for each color And control means for controlling the storage means based on the correction value set by the correction value setting means and shifting the image data to output to the recording head. The control means shifts the image data. In this case, a plurality of dots are moved together as a lump.

  According to the present invention, in the image forming apparatus, an increase in memory access time can be prevented and a printing speed can be improved without using a high-cost memory that is good at random access.

FIG. 3 is a block diagram illustrating a configuration of a control unit of the color recording apparatus according to the embodiment of the present invention. 1 is a schematic configuration diagram of a color recording apparatus according to an embodiment of the present invention. 1 is a partially cutaway perspective view showing a color image forming unit in an embodiment of the present invention. It is explanatory drawing which shows the test pattern in embodiment of this invention. It is a figure explaining the operation | movement which correct | amends the shift | offset | difference and inclination shift | offset | difference of the subscanning direction in embodiment of this invention. 4 is a flowchart showing an operation of the memory access control circuit in the embodiment of the present invention. It is a block diagram which shows the circuit of the memory in embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 2 is a schematic configuration diagram of a color recording apparatus according to an embodiment of the present invention, and FIG. 3 is a partially cutaway perspective view showing a color image forming unit according to the embodiment of the present invention.

  In the figure, reference numeral 10 denotes a color recording apparatus as an image forming apparatus, for example, a printer, a facsimile machine, a copying machine, or a multifunction machine having the functions of a printer, a facsimile machine, and a copying machine. Any type of image forming apparatus may be used as long as it can form an image on a recording medium 37 such as printing paper by using various image forming methods such as a printing method and a thermal transfer method. In the present embodiment, the case where the color recording apparatus 10 is a so-called tandem color electrophotographic printer will be described.

  In the color recording apparatus 10, the first to fourth printing mechanisms P1 to P4 serving as four recording heads corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (B). P4 is arranged in order from the upstream side to the downstream side in the conveyance direction of the recording medium 37. Each of the first to fourth printing mechanisms P1 to P4 is an electrophotographic LED (light emitting diode) printing mechanism, and the toner color as a developer to be used is different, but the configuration is substantially the same. It is what you have.

  Each of the first to fourth printing mechanisms P1 to P4 includes an image forming unit 12, an LED head 13 that exposes the photoreceptor 16 according to image data, and a developer image formed by the image forming unit 12, that is, a toner. A transfer roller 14 for transferring an image to the recording medium 37 is provided.

  The image forming unit 12 includes a photosensitive member 16 that rotates about a shaft 15 in a direction indicated by an arrow a, a charging roller 17 that uniformly charges the surface of the photosensitive member 16, and a developing unit 18. Prepare. The developing unit 18 of the first printing mechanism P1 stores yellow (Y) toner, the developing unit 18 of the second printing mechanism P2 stores magenta (M) toner, and the developing unit of the third printing mechanism P3. 18 contains cyan (C) toner, and the developing unit 18 of the fourth printing mechanism P4 contains black (B) toner.

  The developing unit 18 includes a developing roller 18a, a developing blade 18b, a sponge roller 18c, and a toner that are rotatable rotating members as a developer carrier for developing an electrostatic latent image by attaching toner to the photosensitive member 16. A tank 18d is provided. Then, the toner supplied from the toner tank 18d passes through the sponge roller 18c, reaches the developing blade 18b, is thinned on the peripheral surface of the developing roller 18a, and reaches the contact surface with the photoreceptor 16. When the toner is thinned, the toner is rubbed strongly against the developing roller 18a and the developing blade 18b and is triboelectrically charged. In this embodiment, the toner is triboelectrically charged to a negative polarity. The developing roller 18a is made of a semiconductive rubber material. The sponge roller 18c conveys an appropriate amount of toner to the developing blade 18b. When the toner runs out, new toner can be supplied by replacing the toner tank 18d.

  The LED head 13 includes a substrate 13a on which an LED array (not shown) and a drive IC that drives the LED array are mounted, a Selfoc lens array 13b that collects light from the LED array, and the like. The LED array is caused to emit light corresponding to the image data to be exposed to expose the surface of the photoreceptor 16, and an electrostatic latent image is formed on the surface of the photoreceptor 16. Toner on the peripheral surface of the developing roller 18a adheres to the electrostatic latent image by electrostatic force, and a toner image is formed. The yellow image data of the color image data is input to the LED head 13 of the first printing mechanism P1, and the magenta image data of the color image data is input to the LED head 13 of the second printing mechanism P2. Cyan image data of the color image data is input to the LED head 13 of the third printing mechanism P3, and black image data of the color image data is input to the LED head 13 of the fourth printing mechanism P4. .

  The image forming unit 12 of the first printing mechanism P1, the image forming unit 12 of the second printing mechanism P2, the image forming unit 12 of the third printing mechanism P3, and the image forming unit 12 of the fourth printing mechanism P4 are arranged in the case 50. As shown in FIG. 3, the color image forming unit 25 is integrally formed as shown in FIG. Reference numerals 28 and 29 shown in FIG. 2 are positioning members for positioning the color image forming unit 25 in the color recording apparatus 10. As described above, the color image forming unit 25 can be attached to and detached from the color recording apparatus 10.

  As shown in FIG. 3, a window hole 50 a corresponding to each LED head 13 is opened in the case 50 of the color image forming unit 25. The case 50 is provided with guide pin holes 50b and 50c corresponding to the LED heads 13 so that the LED heads 13 can be positioned with respect to the color image forming unit 25.

  The carrier belt 19 is made of a high-resistance semiconductive plastic film, is formed in a seamless endless shape (infinite track shape), and is wound around the driving roller 20, the driven roller 21, and the tension roller 22. ing. The resistance value of the carrier belt 19 is such that the recording medium 37 can be electrostatically attracted to the carrier belt 19, and when the recording medium 37 is separated from the carrier belt 19, the static electricity remaining on the carrier belt 19 is natural. It is in a range that can be neutralized.

  The drive roller 20 is connected to a motor 64 described later, and is rotated in the direction indicated by the arrow b by the motor 64. As a result, the carrier belt 19 transports the recording medium 37 downstream in the transport direction. Further, the tension roller 22 is urged in a direction indicated by an arrow c by a spring member (not shown), whereby a tension is always applied to the carrier belt 19. The carrier belt 19 is disposed so as to move between each photoconductor 16 and each transfer roller 14 so that the upper surface portion 19 a faces the photoconductor 16. In this embodiment, the photoconductor 16 and the transfer roller 14 are in contact with the carrier belt 19. A cleaning blade 24 made of flexible rubber or plastic material is pressed against the driven roller 21 with the carrier belt 19 interposed therebetween. As a result, the tip of the cleaning blade 24 is brought into pressure contact with the carrier belt 19, and residual toner adhering to the upper surface portion 19 a of the carrier belt 19 is scraped off to the waste toner tank 23.

  Further, a paper feeding mechanism 30 is provided in the color recording apparatus 10 on the lower right side in FIG. The paper feed mechanism 30 includes a paper storage cassette, a hopping mechanism, and a registration roller. The paper storage cassette includes a recording medium storage box 31, a push-up plate 32, and a pressing means 33. The hopping mechanism includes a discriminating means 34, a spring 35, and a paper feed roller 36. The recording medium 37 is guided by the guides 38 and 39 by the hopping mechanism and reaches the pair of registration rollers 40 and 41.

  The recording medium 37 stored in the recording medium storage box 31 is urged upward by the pressing means 33 via the push-up plate 32 and pressed against the paper feed roller 36. Further, the discriminating means 34 is urged by a spring 35 and pressed against the paper feed roller 36. In this state, when a paper feed roller 36 driven by a motor 63 described later rotates in the direction indicated by the arrow e, the recording medium 37 sandwiched between the paper feed roller 36 and the discriminating means 34 is fed out. The fed recording medium 37 is guided by the guides 38 and 39 and reaches the registration rollers 40 and 41. Further, when the registration rollers 40 and 41 driven by the motor 64 rotate in the direction indicated by the arrow f, the recording medium 37 is guided to the carrier belt 19.

  A charger 42 is provided above the carrier belt 19 between the registration rollers 40 and 41 and the first printing mechanism P1. The charger 42 charges the recording medium 37 conveyed by the paper feeding mechanism 30 and electrostatically attracts it to the upper surface portion 19 a of the carrier belt 19. A photo interrupter 70 that detects the leading end of the recording medium 37 is provided on the front side of the charger 42 in the conveyance direction of the recording medium 37.

  Further, a static eliminator 43 is provided above the carrier belt 19 in the vicinity of the driven roller 21. The static eliminator 43 neutralizes the recording medium 37 that has been attracted and conveyed by the carrier belt 19, releases the electrostatic adsorption state by the carrier belt 19, and facilitates separation of the recording medium 37 from the carrier belt 19. It is. A photo interrupter 71 that detects the rear end of the recording medium 37 is provided on the downstream side of the static eliminator 43 in the conveyance direction of the recording medium 37.

  Further, a guide 44 and a fixing device 45 are provided on the downstream side of the static eliminator 43 in the conveyance direction of the recording medium 37. The fixing device 45 is transferred onto the recording medium 37 from the surface of the photosensitive member 16 when the recording medium 37 conveyed by being attracted to the carrier belt 19 passes between the photosensitive member 16 and the transfer roller 14. The apparatus fixes a toner image to a recording medium 37, and includes a heat roller 46 that heats toner on the recording medium 37, and a pressure roller 47 that presses the recording medium 37 together with the heat roller 46. A downstream side of the fixing device 45 in the transport direction of the recording medium 37 is a discharge port 48, and a discharge stacker 49 is provided outside the discharge port 48. The printed recording medium 37 discharged from the discharge port 48 is placed on the discharge stacker 49.

  Next, the configuration of the control unit of the color recording apparatus 10 will be described.

  FIG. 1 is a block diagram showing a configuration of a control unit of a color recording apparatus according to an embodiment of the present invention.

  Here, symbols Y, M, C, and B correspond to the first printing mechanism P1, the second printing mechanism P2, the third printing mechanism P3, and the fourth printing mechanism P4, respectively. It shows that there is. And when each member corresponding to the 1st printing mechanism P1, the 2nd printing mechanism P2, the 3rd printing mechanism P3, and the 4th printing mechanism P4 is explained individually, numerals Y, M, C corresponding to each color and In the case where B is given and the members are described in an integrated manner, the symbols Y, M, C and B are not given.

  In the figure, reference numeral 51 denotes a control circuit as control means, which includes an arithmetic unit such as a microprocessor and controls the operation of the entire color recording apparatus 10. The control circuit 51 supplies SP bias power supplies 52Y, 52M, 52C and 52B for supplying power to the sponge rollers 18c of the developing devices 18 of the first to fourth printing mechanisms P1 to P4, and the developing rollers 18a of the developing devices 18 respectively. DB bias power supplies 53Y, 53M, 53C and 53B for supplying power, charging power supplies 54Y, 54M, 54C and 54B for supplying power to the charging rollers 17 of the first to fourth printing mechanisms P1 to P4, and the first ˜ It is connected to transfer power supplies 55Y, 55M, 55C and 55B for supplying electric power for charging the transfer rollers 14 of the fourth printing mechanisms P1 to P4. The control circuit 51 is connected to a charging power source 56 for supplying charging power to the charger 42 and a neutralizing power source 57 for supplying high voltage power for neutralization to the neutralizer 43. Each of the above power supplies is on / off controlled according to an instruction from the control circuit 51.

  Further, the control circuit 51 is connected to printing control circuits 58Y, 58M, 58C and 58B corresponding to the first to fourth printing mechanisms P1 to P4, respectively. The print control circuits 58Y, 58M, 58C and 58B receive image data from the memories 59Y, 59M, 59C and 59B as storage means, respectively, and according to instructions from the control circuit 51, each LED head 13 The exposure time of the LED head 13 is controlled to control the formation of an electrostatic latent image on the surface of each photoconductor 16. The memories 59Y, 59M, 59C and 59B include a RAM 59a described later, and store image data received from an external device (not shown) via the interface unit 60. The interface unit 60 separates image data received from an external device (for example, a host computer) by color, yellow image data to the memory 59Y, magenta image data to the memory 59M, and cyan image data to the memory. The image data of black is stored in the memory 59B.

  A fixing device driver 61 is connected to the control circuit 51 and drives a heater (not shown) disposed in the heat roller 46 so as to keep the temperature of the heat roller 46 in the fixing device 45 constant.

  A motor driving circuit 62 connected to the control circuit 51 includes a motor 63 that drives and rotates the paper feed roller 36, registration rollers 40 and 41, and first to fourth printing mechanisms P1 to P4. The photosensitive member 16, the charging roller 17, the developing roller 18a, the sponge roller 18c, the transfer roller 14, the driving roller 20, and the motor 64 that rotates the heat roller 46 are driven to rotate. The rollers rotated by the motor 64 are connected to each other by a gear, a belt, etc. (not shown).

  Reference numeral 65 denotes a sensor receiver driver connected to the control circuit 51, which drives the photointerrupters 70 and 71, receives their output waveforms, and transmits them to the control circuit 51.

  Reference numeral 66 denotes an EEPROM connected to the control circuit 51, which stores a shift correction amount array Offset [] for correcting a color shift caused by inclination in the main scanning direction, the sub-scanning direction, and the mounting state of the LED head 13 for each color. This is a non-volatile memory. Recording of the deviation correction amount array Offset [] to the EEPROM 66 and reading from the EEPROM 66 are performed by the control circuit 51.

  74 is a timing generator connected to the control circuit 51 and includes a programmable counter or the like, and generates a line signal Ls described later. The line signal Ls is transmitted to each circuit of the control unit as necessary.

  Reference numeral 75 denotes a memory access control circuit serving as a correction value setting unit connected to the control circuit 51. The memory access size size and address offset Aoffset when the memories 59Y, 59M, 59C, and 59B read image data. And calculate. The memory access control circuit 75 performs control to increase the access size as much as possible in order to reduce the number of memory accesses. The memory access control circuit 75 receives the line signal Ls from the timing generator 74, and outputs the memory access size size, the address offset Aoffset, and the memory access activation pulse RSstart to the memories 59Y, 59M, 59C and 59B. Output.

  A test pattern generation circuit 77 connected to the control circuit 51 generates test pattern image data described later. The test pattern image data is transmitted to the memories 59Y, 59M, 59C, and 59B via the interface unit 60 according to an instruction from the control circuit 51, and further transmitted to the print control circuits 58Y, 58M, 58C, and 58B. Thereby, a test pattern can be printed.

  Next, the operation of the color recording apparatus 10 in the present embodiment will be described. First, a printing operation that is an operation for forming a toner image on the recording medium 37, specifically, a color printing operation for forming a color toner image will be described.

  When a power supply (not shown) of the color recording apparatus 10 is turned on, the control circuit 51 executes a predetermined initial setting and then reads the deviation correction amount array Offset [] from the EEPROM 66 and stores it in the working memory in the memory access control circuit 75. Remember. Subsequently, the control circuit 51 drives the fixing device driver 61 to warm up until the temperature of the heat roller 46 in the fixing device 45 reaches a predetermined temperature. Note that the control circuit 51 performs control so that the temperature of the heat roller 46 is always kept constant.

  When the temperature of the heat roller 46 reaches a predetermined temperature, the control circuit 51 drives the motor 64 via the motor drive circuit 62, rotates the drive roller 20, drives the carrier belt 19, and moves the arrow d. Move in the direction shown. When the carrier belt 19 is moved by a distance slightly longer than one round, the control circuit 51 stops the motor 64 and stops driving the carrier belt 19. As a result, residual toner and dust adhering to the upper surface portion 19 a of the carrier belt 19 are scraped off by the cleaning blade 24 and stored in the waste toner tank 23.

  As described above, the initial setting of the color recording apparatus 10 is completed, and the control circuit 51 waits for image data to be transmitted from the external apparatus via the interface unit 60.

  When image data transmitted from an external device such as a host computer is received via the interface unit 60, the control circuit 51 issues an instruction to the interface unit 60 and the memories 59Y, 59M, 59C, and 59B. In accordance with the instruction, the interface unit 60 separates the received image data for each color, and stores the image data for each color in the memories 59Y, 59M, 59C, and 59B for each color. That is, yellow image data is stored in the memory 59Y, magenta image data is stored in the memory 59M, cyan image data is stored in the memory 59C, and black image data is stored in the memory 59B.

  As a result, the memory 59Y, 59M, 59C, and 59B store image data of each color for one page printed on the recording medium 37, respectively.

  Next, an operation for printing image data on the recording medium 37 from this state will be described.

  The control circuit 51 drives the motor 63 via the motor drive circuit 62 and rotates the paper feed roller 36. By the rotation of the paper feed roller 36, only one recording medium 37 stored in the recording medium storage box 31 is unwound and conveyed to the guides 38 and 39. The control circuit 51 controls the motor drive circuit 62 so that the recording medium 37 is transported slightly longer than the distance at which the leading edge of the recording medium 37 reaches the registration rollers 40 and 41.

  Thereby, the leading end of the recording medium 37 is pressed slightly between the registration rollers 40 and 41 to be slightly bent. Due to this bending, the skew of the recording medium 37 is corrected.

  Subsequently, the control circuit 51 drives the motor 64 via the motor drive circuit 62, and the registration rollers 40 and 41, the photosensitive member 16, the charging roller 17, and the developing roller of the first to fourth printing mechanisms P1 to P4. 18a, sponge roller 18c, transfer roller 14, drive roller 20, and heat roller 46 of fixing unit 45 are rotated. At the same time, in order to apply a voltage to the charging roller 17, the developing roller 18a, and the sponge roller 18c of the first to fourth printing mechanisms P1 to P4, the control circuit 51 includes charging power sources 54Y, 54M, 54C and 54B, The DB bias power supplies 53Y, 53M, 53C and 53B, and the SP bias power supplies 52Y, 52M, 52C and 52B are turned on.

  As described above, the surface of the photosensitive member 16 of the first to fourth printing mechanisms P1 to P4 is uniformly charged by the charging roller 17, and the sponge roller 18c and the developing roller 18a of the first to fourth printing mechanisms P1 to P4 are predetermined. Charged to a high voltage.

  Subsequently, the control circuit 51 issues a command to the memory 59Y that stores the yellow image data, and causes the yellow image data for one line to be transmitted from the memory 59Y to the print control circuit 58Y of the first printing mechanism P1. . The print control circuit 58Y converts the image data transmitted from the memory 59Y into a form that can be transmitted to the LED head 13 of the first printing mechanism P1 according to a command from the control circuit 51, and the LED head. 13 to send. The LED head 13 emits light from the LED array corresponding to the transmitted image data, and forms an electrostatic latent image for one line corresponding to the image data on the surface of the charged photoreceptor 16.

  In this way, the yellow image data transmitted from the memory 59Y for each line is successively converted into an electrostatic latent image on the surface of the photosensitive member 16, and the yellow image data corresponding to the length in the sub-scanning direction. When the electrostatic latent image is formed, the exposure ends. The yellow toner supplied from the developing roller 18a adheres to the surface of the photoreceptor 16 on which the electrostatic latent image is formed. As the photoconductor 16 rotates, the electrostatic latent images are successively developed with yellow toner.

  When the leading edge of the recording medium 37 conveyed by the carrier belt 19 reaches between the photosensitive member 16 and the transfer roller 14, the control circuit 51 turns on the transfer power supply 55Y of the first printing mechanism P1. . As a result, the yellow toner image on the surface of the photoreceptor 16 is electrically transferred onto the recording medium 37 by the transfer roller 14. As the photosensitive member 16 rotates, yellow toner images are successively transferred onto the recording medium 37, and a yellow toner image for one page is transferred onto the recording medium 37.

  Thus, the transfer of the yellow toner image onto the recording medium 37 by the first printing mechanism P1 is completed. When the rear end of the recording medium 37 reaches between the photosensitive member 16 and the transfer roller 14, the control circuit 51 controls the transfer power supply 55Y, the charging power supply 54Y, and the SP bias power supply 52Y of the first printing mechanism P1. The DB bias power supply 53Y is turned off.

  The carrier belt 19 is continuously driven, and the recording medium 37 conveyed by the carrier belt 19 moves from the first printing mechanism P1 to the second printing mechanism P2. Then, the magenta toner image is transferred onto the recording medium 37 by the second printing mechanism P2. The operation of forming a magenta toner image and transferring it to the recording medium 37 is the same as the operation of forming the yellow toner image and transferring it to the recording medium 37, and a description thereof will be omitted.

  Further, the carrier belt 19 is continuously driven, and the recording medium 37 transported by the carrier belt 19 moves from the second printing mechanism P2 to the third printing mechanism P3. Then, the cyan toner image is transferred onto the recording medium 37 by the third printing mechanism P3. The operation of forming the cyan toner image and transferring it to the recording medium 37 is the same as the operation of forming the yellow and magenta toner images and transferring them to the recording medium 37, and the description thereof is omitted. To do.

  Further, the carrier belt 19 is continuously driven, and the recording medium 37 conveyed by the carrier belt 19 moves from the third printing mechanism P3 to the fourth printing mechanism P4. Then, the transfer of the black toner image onto the recording medium 37 is performed by the fourth printing mechanism P4. The operation of forming the black toner image and transferring it to the recording medium 37 is the same as the operation of forming the yellow, magenta, and cyan toner images and transferring them to the recording medium 37. Is omitted.

  As described above, the toner images of the respective colors are transferred onto the recording medium 37 in an overlapping manner.

  Thereafter, the recording medium 37 is conveyed by the carrier belt 19 and reaches the static eliminator 43. Here, the control circuit 51 turns on the neutralization power source 57 and neutralizes the recording medium 37. As a result, the recording medium 37 is easily separated from the carrier belt 19, separated from the carrier belt 19 above the driven roller 21, and guided to the fixing device 45 by the guide 44. When the recording medium 37 is separated from the static eliminator 43, the control circuit 51 turns off the static elimination power source 57.

  The recording medium 37 sent to the fixing device 45 is conveyed while being sandwiched from both sides by a heat roller 46 that has already reached a fixing temperature and a pressure roller 47 that is in pressure contact with the heat roller 46. As a result, the toner image is fixed on the recording medium 37.

  When the fixing of the toner image is completed, the recording medium 37 is discharged out of the color recording apparatus 10 from the discharge port 48 and placed on the discharge stacker 49. The discharge of the recording medium 37 is notified to the control circuit 51 when the photo interrupter 71 detects the rear end of the recording medium 37. When the control circuit 51 determines that the ejection of the recording medium 37 has been completed, the control circuit 51 stops the motor 64 via the motor drive circuit 62.

  In each of the first to fourth printing mechanisms P1 to P4, the charging power supply 54, the SP bias power supply 52, the DB bias power supply 53, and the transfer power supply 55 are turned off when the transfer of the toner image is completed. The

  As described above, the color printing operation of the color recording apparatus 10 is executed.

  As described above, the color recording apparatus 10 according to the present embodiment includes a plurality of first to fourth printing mechanisms P1 to P4 that can respectively form a plurality of line-shaped images extending in the main scanning direction. A color image is formed by outputting image data of each color to each of the first to fourth printing mechanisms P1 to P4. Here, the color recording apparatus 10 includes a memory 59 that stores image data for each color, and a memory access control that sets correction values according to the amounts of misalignment between the plurality of first to fourth printing mechanisms P1 to P4. A control circuit 51 for controlling the memory 59 based on the correction value set by the memory access control circuit 75 and shifting the image data to output to the first to fourth printing mechanisms P1 to P4. In 51, when the image data is shifted, a plurality of dots are collectively moved.

  Next, an operation for correcting a color shift that occurs in color printing of the color recording apparatus 10 will be described. First, a test pattern for detecting a color misregistration state will be described.

  FIG. 4 is an explanatory diagram showing a test pattern in the embodiment of the present invention.

  When receiving an instruction from an external device such as a host computer, the control circuit 51 issues an instruction to the test pattern generation circuit 77 to generate a test pattern as shown in FIG. To be written in the memory 59. The color recording apparatus 10 forms a color image of the test pattern on the recording medium 37. Specifically, the control circuit 51 transmits the image data of the test pattern stored in the memory 59 to the print control circuits 58Y, 58M, 58C, and 58B, executes the above-described color printing operation, and performs the test. Print the pattern.

  In the figure, straight lines H1, H2, H3, and H4 indicate the LED head 13 when the recording medium 37 is sandwiched between the photosensitive member 16 and the transfer roller 14 in each of the first to fourth printing mechanisms P1 to P4. All the dots (W dots) of one line of the LED array are emitted to simultaneously form an electrostatic latent image on the photosensitive member 16, and the electrostatic latent image is developed with each color toner to form a toner image. , A line in the main scanning direction obtained by transferring the toner image to the recording medium 37 by the transfer roller 14 and fixing the toner image by the fixing device 45.

  Originally, the straight line H1 is a yellow horizontal line printed by the first printing mechanism P1, the straight line H2 is a magenta horizontal line printed by the second printing mechanism P2, and the straight line H3 is printed by the third printing mechanism P3. The straight line H4 is a black horizontal line printed by the fourth printing mechanism P4. From the straight lines H1 to H4 of the respective colors, the attachment errors (distance and inclination) of the first to fourth printing mechanisms P1 to P4 can be known.

  In the example shown in the drawing, when the yellow straight line H1 printed by the first printing mechanism P1 is selected as the reference line, the straight line H2 is separated from the straight line H1 by a distance L2, and is inclined to the right by ΔL2. I understand that Similarly, it can be seen that the straight line H3 is separated from the straight line H1 by a distance L3 and inclined to the left shoulder by ΔL3, and the straight line H4 is separated from the straight line H1 by a distance L4 and rises to the left shoulder. ΔL4 can be seen to be inclined. Thereby, it is possible to know the distances and inclinations of the second, third, and fourth printing mechanisms P2, P3, and P4 with respect to the first printing mechanism P1.

  V1 shown in the figure is a line printed continuously by causing only the leftmost dot of the LED head 13 of the first printing mechanism P1 to emit light. The difference ΔW2 between the line V1 and the left end of the straight line H2 indicates that the second printing mechanism P2 is shifted to the right (upward in the drawing) by ΔW2 with respect to the first printing mechanism P1. Further, it can be seen that the third printing mechanism P3 is shifted to the right by ΔW3 with respect to the first printing mechanism P1 due to the difference ΔW3 between the line V1 and the left end of the straight line H3. Further, the difference ΔW4 between the line V1 and the left end of the straight line H4 indicates that the fourth printing mechanism P4 is shifted leftward (downward in the drawing) by ΔW4 with respect to the first printing mechanism P1.

  As described above, by mounting the test pattern as shown in the figure, it is possible to know the amount of attachment displacement of the first to fourth printing mechanisms P1 to P4.

  The values of L2, L3 and L4, ΔL2, ΔL3 and ΔL4 (including information on rising and rising shoulders) and ΔW2, ΔW3 and ΔW4 are stored in the EEPROM 66, and further, a control circuit If 51 reads these values from the EEPROM 66 and stores them in the working memory, and corrects the mounting displacement amounts of the first to fourth printing mechanisms P1 to P4 based on these values, the color misregistration is eliminated.

  In the figure, Wp is the printing width (number of dots) in the main scanning direction, and ΔW1 dot is a non-printing dot for the first printing mechanism P1 (yellow).

  Next, an operation for correcting the attachment displacement amount of the first to fourth printing mechanisms P1 to P4 will be described using the displacement amount shown in FIG. 4 as an example. First, an operation for correcting a deviation in the main scanning direction will be described.

  The first printing mechanism P1 performs printing so that printing is performed by emitting only Wp dots of image data stored in the memory 59Y after emitting one line of ΔW1 dots in the LED array of the LED head 13. It is controlled by the control circuit 58Y. Also, the second printing mechanism P2 emits only one line of (ΔW1-ΔW2) dots in the LED array of the LED head 13, and then causes only the Wp dots of the image data stored in the memory 59M to emit light. Control is performed by the print control circuit 58M to perform printing. Further, the third printing mechanism P3 causes one line of (ΔW1-ΔW3) dots in the LED array of the LED head 13 to emit light, and then causes only the Wp dots of the image data stored in the memory 59C to emit light. Control is performed by the print control circuit 58C so as to perform printing. Furthermore, after the fourth printing mechanism P4 emits one line of (ΔW1 + ΔW4) dots in the LED array of the LED head 13, it prints only the Wp dots of the image data stored in the memory 59B. Is controlled by the print control circuit 58B.

  As described above, the print start position in the main scanning direction by the first to fourth printing mechanisms P1 to P4 can be adjusted within one dot.

  Next, an operation for correcting a shift in the sub-scanning direction and a tilt shift will be described.

  FIG. 5 is a diagram for explaining an operation for correcting a shift in the sub-scanning direction and a tilt shift in the embodiment of the present invention. In the figure, (a) is an explanatory view showing the arrangement of image data on a memory, (b) is an explanatory view showing an exposure method of image data when rising right, and (c) is an exposure of image data when rising left. It is explanatory drawing which shows a method.

When the second printing mechanism P2 is inclined by θ2 = sin ⁻¹ (ΔL2 / W) with respect to the first printing mechanism P1, as shown by the straight line H2 shown in FIG. 4, the LED head of the second printing mechanism P2 When the image data is transmitted to 13 and printed as it is, the image is printed with an inclination of θ2 with respect to the image data printed by the first printing mechanism P1. Therefore, it is necessary to correct the tilt deviation. W is the number of dots for one line of the LED array of the LED head 13.

  First, an operation for correcting a tilt deviation when the LED head 13 of the second printing mechanism P2 is tilted upward with respect to the straight line H1 like the straight line H2 will be described.

  Here, the number of print dots in the width direction of the recording medium 37 is set to Wp = 640 dots for easy understanding. The inclination amount is 3 dots.

  Further, one square in FIG. 5A showing the arrangement of the image data on the memory 59 (more specifically, a later-described RAM 59a provided in the memory 59) has a size of Unit = 64 dots = 8 bytes. Inclination deviation correction is performed collectively with this unit (one square) as one section. Here, for convenience of explanation, it is assumed that the one section corresponds to one address (address). FIG. 5A is a diagram showing the arrangement of the stored image data on the memory 59, and the numbers in each square indicate the addresses of the sections of the memory 59. The image data is stored in order in each address of the memory 59. In the example shown in FIG. 5A, white background data is written in addresses 0 to 19 of the memory 59, the first line of image data is stored in the addresses 20 to 29, and the second line of image data is the next. The third line of image data is stored at addresses 40-49.

  In FIG. 5B, the image data arranged on the memory 59 as shown in FIG. 5A is exposed by the LED head 13 of the second printing mechanism P2 inclined upward to the right, It is a figure explaining the method of performing printing. As described above, the LED head 13 is inclined by 3 dots with respect to the print dot width Wp = 640 dots. The LED head 13 emits light from the LED array, exposes the first line of the image data, performs printing, and then corresponds to the movement of the recording medium 37 in the sub-scanning direction. In the first and third lines, printing is performed by exposing line by line.

  In this state, the image data of the first line (addresses 20 to 29) indicated by the oblique lines in FIG. 5A is 1 of the LED head 13 of the second printing mechanism P2, as shown in FIG. 5B. If printing is performed at the positions indicated by the oblique lines in the second line, the second line, and the third line, the line printed by the second printing mechanism P2 is the straight line H1 and one dot printed by the first printing mechanism P1. It will match with the error within. The selection of the positions indicated by the oblique lines in the first line, the second line, and the third line of the LED head 13 as shown in FIG. 5B is a target section when the image data is read from the memory 59. This can be easily realized by accessing the memory 59 by adding an offset (as shown in the lower part of FIG. 5B) obtained from the deviation amount to the address.

  Next, how to obtain the deviation correction amount array Offset [] indicating the deviation amount of the target section will be described.

  In the example shown in FIG. 5B, the tilt deviation amount of the entire LED head 13 is ΔW = 3, and the number of partitions serving as a correction unit is the access-target final partition position Wlast + 1 = 10. . Therefore, the amount of inclination deviation per section is ΔW / (Wlast + 1) = 0.3, and the calculation is shifted by 0.3 dots for each section.

  Since the LED head 13 rises to the right, if Offset [0] in the leftmost section is determined to be 0, Offset [1] in the adjacent section becomes 0.3, which is 0.3 plus 0. If the following value is rounded down, it becomes 0. Offset [2] is 0 by rounding off the value after 0.6 decimal point of 0.3 obtained by adding 0.3 to 0.3 which is the value of Offset [1]. Similarly, Offset [3] becomes 0 by rounding off the value after 0.9 decimal point of 0.9 obtained by adding 0.3 to 0.6 which is the value of Offset [2]. Note that Offset [4] becomes 1 by rounding off the value after the decimal point of 1.2 obtained by adding 0.3 to 0.9 which is the value of Offset [3]. Similarly, Offset [5] and [6] are set to 1, and Offset [7], [8], and [9] are set to 2.

  Next, an operation for correcting the tilt deviation when the LED head 13 of the third printing mechanism P3 is tilted to the left with respect to the straight line H1 like the straight line H3 will be described. Note that description of points that are the same as those in the case of rising to the right is omitted, and here, a method of obtaining the shift correction amount array Offset [] in the example illustrated in FIG.

  Since the LED head 13 rises to the left, if the Offset [9] in the rightmost section is determined to be 0, the Offset [8] in the adjacent section will be 0.3, which is 0.3 plus 0, which is a value after the decimal point. If it is truncated, it becomes 0. Offset [7] is 0 by rounding off the value after 0.6 decimal point of 0.3 obtained by adding 0.3 to 0.3 which is the value of Offset [8]. Similarly, Offset [6] becomes 0 by rounding off the value after 0.9 decimal point of 0.9 obtained by adding 0.3 to 0.6 which is the value of Offset [7]. Note that Offset [5] becomes 1 by rounding off the value after the decimal point of 1.2 obtained by adding 0.3 to 0.9 which is the value of Offset [6]. Similarly, Offset [4] and [3] are set to 1, and Offset [2], [1], and [0] are set to 2.

  In this way, Offset [] can be obtained regardless of whether the inclination of the LED head 13 rises right or left. Note that the obtained Offset [] is stored in the EEPROM 66.

  By shifting the read address of the image data stored in the memory 59 using the above Offset [], the relationship between the line position of the image data in the specific section and the line position of the LED head 13 can be shifted in section units. It becomes possible. As a result, the color shift between the first printing mechanism P1 and the second to fourth printing mechanisms P2 to P4 can be corrected within one line.

  Next, the operation of the memory access control circuit 75, which is a circuit for obtaining the address offset Aoffset, which is a signal for instructing the address shift amount when performing memory access, and the memory access size size at one time from Offset [] will be described. To do.

  FIG. 6 is a flowchart showing the operation of the memory access control circuit in the embodiment of the present invention.

  First, when a power supply (not shown) of the color recording apparatus 10 is turned on, in step S1, the control circuit 51 determines the data size Unit of each partition, the maximum memory access size SIZEmax, the access target final partition position Wlast, and the shift correction amount array Offset. [0. . . Wlast].

  Specifically, the control circuit 51 performs initial setting of the memory access control circuit 75 as part of the initial setting of the color recording apparatus 10. Here, the data size Unit of each section is the data size of one section, which is a unit for correcting the tilt deviation. The maximum memory access size SIZEmax is the maximum access data size that can be read / written (read and written) from the memory 59 at a time, and is determined mainly by the size of a buffer memory (not shown) provided in the interface unit 60. . Note that the maximum memory access size SIZEmax needs to be at least twice as large as the unit. Here, it is assumed that SIZEmax = 8. Further, the access target final section position Wlast matches the number obtained by subtracting 1 from the number of sections for inclination deviation correction. It is assumed that the deviation correction amount array Offset [] of each section has already been calculated and stored in the EEPROM 66.

  Subsequently, in step S <b> 2, the memory access control circuit 75 determines whether to start line transfer of the memory 59. Specifically, when the printing operation is started by the control circuit 51 and the timing generator 74 starts to generate the line signal Ls, the memory access control circuit 75 receives the line signal Ls, and every time the line signal Ls is received. In addition, the memory access control signal for the line is generated. Then, when the line transfer of the memory 59 is started, the process proceeds to step S3, and when the line transfer of the memory 59 is not started, the operation is repeated.

  In step S3, the memory access control circuit 75 sets initial values, sets the access size size = Unit, and sets the access target section target = 0. Specifically, the memory access control circuit 75 that has received the line signal Ls initializes variables in order to generate a line access control signal. That is, initialization is performed by setting the size size for accessing the memory 59 at a time as unit, setting the target indicating the partition of interest in the current calculation process to 0, and setting the address offset Aoffset read from the memory 59 to 0. Note that according to the example shown in FIG. 5, size = 1.

  Subsequently, in step S4, the memory access control circuit 75 determines whether or not size = SIZEmax or target = Wlast or Offset [target] ≠ Offset [target + 1]. Specifically, the memory access control circuit 75 determines whether or not to execute memory access based on the current access size size and the address offset Aoffset. Then, when size is equal to the maximum access data size SIZEmax to the memory 59, when the target section target is the last section Wlast, or when the shift correction amount Offset [target] of the target section target is one right next to the target section target If the deviation correction amount Offset [target + 1] of the sections does not match, the access size cannot be increased any more, and the process proceeds to step S6 to activate the memory access. Otherwise, the process proceeds to step S5.

  In step S5, the memory access control circuit 75 sets size = size + Unit, target = target + 1, and returns to step S4. Specifically, since it is already known that the deviation correction amounts Offset [] of two adjacent sections are the same, the memory access control circuit 75 performs a process of combining the memory accesses of the two sections into one. That is, processing for adding the data size Unit of one section to the memory access size size is performed. Then, the memory access control circuit 75 adds 1 to the target in order to move the partition of interest to the partition on the right, and returns to step S4 to loop.

According to the example shown in FIG. 5B, in the first loop, when target = 0,
size (= 1) ≠ SIZEmax (= 8),
target (= 0) ≠ Wlast (= 9),
Offset [target] (= 0) = Offset [target + 1] (= 0)
Therefore, the process proceeds to step S5 to repeat the loop.

And in the next loop where size = 2 and target = 1,
size (= 2) ≠ SIZEmax (= 8),
target (= 1) ≠ Wlast (= 9),
Offset [target] (= 0) = Offset [target + 1] (= 0)
Therefore, the process moves to step S5 and the loop is repeated.

  Even when target = 2, the loop is repeated.

Next, in the loop where target = 3,
size (= 4) ≠ SIZEmax (= 8)
target (= 3) ≠ Wlast (= 9),
Offset [3] (= 0) ≠ Offset [4] (= 1)
Therefore, the loop is temporarily interrupted here, and the process proceeds to step S6.

  In step S <b> 6, the memory access control circuit 75 outputs a memory access activation pulse together with size and Offset [target]. Specifically, the memory access control circuit 75 outputs a memory access start pulse to the memory 59 while outputting the access size size (= 4) and the address offset Aoffset (= 0). The address offset Aoffset outputs Offset [target].

  Subsequently, in step S7, the memory access control circuit 75 determines whether or not target = Wlast. Specifically, the memory access control circuit 75 determines whether or not the partition target currently focused on is the final partition Wlast. If target = Wlast, the process proceeds to step S9. Otherwise, the process proceeds to step S8.

  In step S8, the memory access control circuit 75 sets size = Unit, target = target + 1, and returns to step S4. Specifically, if it is determined in step S7 that target ≠ Wlast, since the currently targeted partition target is not the final partition Wlast, the memory access control circuit 75 initializes size to “Wunit” in step S8. 1 is added to target to move to the next partition. Then, returning to step S4, if steps S4 to S8 are repeated one or more times, and finally target = Wlast, it means that the memory access has been completed up to the final section of one line, so the process proceeds to step S9. .

  In step S9, the memory access control circuit 75 determines that the line transfer of the memory 59 is completed, and returns to step S2. Specifically, if it is determined in step S7 that target = Wlast, the memory access has been completed up to the final partition of one line, so the memory access control circuit 75 returns to step S2 and starts transferring the next line. Wait for a request.

  According to the example shown in FIG. 5B, when target = 3, 6 and 9, the process reaches step S7. When target = 3 and 6, the process returns to step S4 via step S8, and when target = 9, step S9 is reached. The process returns to step S2.

  As described above, three memory access activation pulses are output to the memory 59 for convenience. As memory access settings corresponding to the respective activation pulses, the first one is size = 4, Aoffset = 0, and the second one is size =. 3, Aoffset = 1, the third is size = 3, and Aoffset = 2 is output.

Next, a flowchart will be described.
Step S1 The control circuit 51 determines the data size Unit of each partition, the maximum memory access size SIZEmax, the access target final partition position Wlast, and the shift correction amount array Offset [0. . . Wlast].
Step S2: The memory access control circuit 75 determines whether or not to start line transfer of the memory 59. When the line transfer of the memory 59 is started, the process proceeds to step S3. When the line transfer of the memory 59 is not started, the operation is repeated.
Step S3: The memory access control circuit 75 sets an initial value, sets the access size size = Unit, and sets the access target section target = 0.
Step S4: The memory access control circuit 75 determines whether or not size = SIZEmax or target = Wlast or Offset [target] ≠ Offset [target + 1]. If size = SIZEmax or target = Wlast or Offset [target] ≠ Offset [target + 1], the process proceeds to step S6, and if size = SIZEmax or target = Wlast or Offset [target] ≠ Offset [target + 1], the process proceeds to step S6. .
Step S5 The memory access control circuit 75 sets size = size + Unit, and set target = target + 1, and returns to Step S4.
Step S6: The memory access control circuit 75 outputs a memory access activation pulse together with size and Offset [target].
Step S7: The memory access control circuit 75 determines whether or not target = Wlast. If target = Wlast, the process proceeds to step S9, and if not target = Wlast, the process proceeds to step S8.
Step S8 The memory access control circuit 75 sets size = Unit and target = target + 1 and returns to Step S4.
Step S9: The memory access control circuit 75 returns to step S2 when the line transfer of the memory 59 is completed.

  Next, the memory operation will be described. First, an operation of writing and storing image data received from an external device via the interface unit 60 in the memory 59 will be described.

  FIG. 7 is a block diagram showing a memory circuit in the embodiment of the present invention.

  In the present embodiment, the memory 59 includes a RAM 59a, an address selector 59b, an adder 59c, an address latch 59d, a subtractor 59e, an OR unit 59f, and a multiplier 59g, as shown in the figure.

  The write start address (address) of the image data to the RAM 59a is determined after the inclination of the LED head 13 is calculated. That is, if the inclination of the LED head 13 is ΔL2 dots with respect to the line width W (the number of dots for one line of the LED array of the LED head 13), the number of inclined dots ΔL with respect to the printing width Wp in the main scanning direction. ΔL = ΔL2 * Wp / W. This calculation is performed by the control circuit 51 after the control circuit 51 reads the information stored in the EEPROM 66. The address (ΔL−1) * Wp is the write start address in the RAM 59a.

  In the example shown in FIG. 5B, since Wp = 640 and ΔL = 3, the address 20 is the write start address. The control circuit 51 prefills 0 data from address 0 to address 19 in advance. When the interface unit 60 receives image data from the external device, the interface unit 60 sequentially writes the image data from the 20th address. In the example shown in FIG. 5B by such a data writing operation, “0” is written in the addresses 0 to 19, and the image data of the first line received by the interface unit 60 is the address 20. The image data of the second line is written in the addresses 30 to 39, and the image data of each line is sequentially written and stored in each address.

  Next, an operation for reading image data stored in the memory 59 will be described.

  Here, based on the example shown in FIG. 5B, an operation of reading and printing the image data written and stored in the RAM 59a as described above will be described. In this case, the image data transmitted to the LED head 13 may be read as shown in FIG. That is, the image data of the first line may be read out in the order of addresses 20, 21, 22, 23, 14, 15, 16, 7, 8, and 9 in the RAM 59a and transmitted to the print control circuit 58.

  First, since the read start address is the address 20, the control circuit 51 outputs the address 20 to the address selector 59b as the read start address before starting printing. Further, the control circuit 51 outputs 10 which is the offset amount of the address per line to the multiplier 59g.

  In this state, when the start signal St is output from the control circuit 51 to the timing generator 74, the timing generator 74 outputs the line signal Ls to the address selector 59b and the OR unit 59f. The address selector 59b outputs the address 20 as the read start address to the input part of the address latch 59d at the timing when the line signal Ls is received.

  The line signal Ls is output to the address latch 59d as a latch timing signal via the OR unit 59f. The address latch 59d latches and outputs address = 20 at the timing of receiving the latch timing signal. The output address = 20 is input to the adder 59c.

  Further, the line signal Ls is also output to the control circuit 51. The control circuit 51 starts outputting the start address of the next line, that is, the address 30 as the read start address at the timing of receiving the line signal Ls. However, since it is blocked by the address selector 59b at this time, the address 30 as the start address of the next line output from the control circuit 51 is the operation of the memory 59 until the next line signal Ls is output. Will not be affected.

  After that, the memory access control circuit 75 that has received the line signal Ls performs the operation described in the flowchart of FIG. 6 to calculate the access size and the address offset. The first time, 4 is added as the access size to the adder 59c and the RAM 59a. And 0 as an address offset is output to the multiplier 59g, and at the same time, a start pulse is output to the OR unit 59f and the RAM 59a.

  Then, when the RAM 59a receives the activation pulse, the RAM 59a performs memory access according to the address 20-0 * 10 = 20 as the output of the subtractor 59e and 4 as the access size. The image data up to the address 23 is accessed at once, and the image data from the address 20 to the address 23 is output to the print control circuit 58.

  The start pulse is used as the latch timing of the address latch 59d via the OR unit 59f. At this time, the address latch 59d is accessed with 20 as the output of the address latch 59d calculated by the adder 59c. Since the sum 24 with the size 24 is input via the address selector 59b, the output of the address latch 59d is updated to 24.

  In this way, when the first memory access is completed for the image data on the first line, the memory access is shifted to the second memory in the same procedure.

  In the second memory access, the output of the address latch 59d is updated to 24, and the access size and address offset output from the memory access control circuit 75 are 3 and 1, respectively. Therefore, the RAM 59a performs memory access according to the address 24-1 * 10 = 14 as the output of the subtractor 59e and 3 as the access size, and as a result, the image data from the address 14 to the address 16 are simultaneously obtained. Access is performed, and the image data from the address 14 to the address 16 is output to the print control circuit 58.

  The output of the address latch 59d is updated to 24 + 3 = 27.

  In the third memory access, the output of the address latch 59d is updated to 27, and the access size and address offset output from the memory access control circuit 75 are 3 and 2, respectively. Therefore, the RAM 59a performs memory access according to the address 27-2 * 10 = 7 as the output of the subtractor 59e and 3 as the access size, and as a result, the image data from the address 7 to the address 9 are processed at a time. Access is performed, and the image data from address 7 to address 9 is output to the print control circuit 58.

  As described above, the image data of the first line of the LED head 13 stored in the memory 59 can be read out by three memory accesses.

  The reading of the image data for the second and subsequent lines of the LED head 13 is the same as the reading of the image data for the first line except that the read start address output from the control circuit 51 is different for each line. Is omitted.

  The image data read in this way is transmitted to the LED head 13 line by line and printed one after another. Then, when the last line of image data is printed, the operation of reading out the image data ends.

  As described above, when the LED heads 13 of the second to fourth printing mechanisms P2 to P4 are attached to the LED head 13 of the first printing mechanism P1, the mounting is inclined to the right shoulder or the left shoulder. However, by operating the read start address and the access size of the RAM 59a, the color shift can be adjusted with an error within one dot.

  As described above, in the present embodiment, the memory access control circuit 75 controls the address for reading image data from the memory 59 and the memory access size, and collects image data at a plurality of addresses, that is, a plurality of dots as a lump. Since the shift is performed collectively, it is possible to reduce the number of memory accesses required for correcting the tilt shift between the colors. In other words, the memory accesses of the continuous sections having the same color misregistration correction value are combined into one transfer, and control is performed so as to reduce the number of memory accesses by setting the data amount of one memory access as large as possible.

  As a result, it is possible to shorten the memory access time when reading image data, and it is possible to realize a high printing speed even when the same speed storage element is used. It can be realized. In other words, it is possible to prevent an increase in the memory access time and improve the printing speed without using a high-cost storage element that is good at random access.

  In the present embodiment, the case where the color recording apparatus 10 is a color electrophotographic printer that uses the LED head 13 as an exposure unit has been described. However, a color electrophotographic printer that uses a laser as the exposure unit, The present invention can also be applied to an ink jet color printer.

  The present invention is not limited to the above-described embodiment, and various modifications can be made based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

  The present invention can be used in an image forming apparatus.

10 Color Recording Device 51 Control Circuit 59, 59Y, 59M, 59C, 59B Memory 75 Memory Access Control Circuit P1 First Printing Mechanism P2 Second Printing Mechanism P3 Third Printing Mechanism P4 Fourth Printing Mechanism

Claims (5)

Image forming apparatus comprising a plurality of recording heads capable of forming a plurality of line-shaped images extending in the main scanning direction, and forming a color image by outputting image data of each color to each of the plurality of recording heads Because
Storage means for storing the image data for each color;
Correction value setting means for setting a correction value according to the mutual displacement amount of the plurality of recording heads;
Control means for controlling the storage means based on the correction value set by the correction value setting means and shifting the image data to output to the recording head,
The control means shifts the plurality of dots as a whole when shifting the image data. The image forming apparatus according to claim 1, wherein the control unit switches a plurality of dots as a whole by switching an address and a read size for reading image data from the storage unit. The image forming apparatus according to claim 1, wherein the control unit shifts a plurality of consecutive dots having the same correction value and having the same correction value as a lump. 3. The image forming apparatus according to claim 2, wherein the shift amount is an inclination amount, and the read size is a size capable of collecting a plurality of dots having the same shift amount in the sub-scanning direction as a lump. The image forming apparatus according to claim 2, further comprising a buffer memory that temporarily stores image data read from the storage unit, wherein the read size does not exceed a data size that can be stored in the buffer memory. .

Images