JP2011206974A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming an image with high accuracy in a constitution which forms the image by delivering ink droplets from a linear head on paper supported to a drum.SOLUTION: At every one rotation of a rotating drum 1, a first carriage 7a and a second carriage 7b are moved in the main scanning direction, and print heads 9 arranged on the respective carriages deliver ink droplets to perform print with a high resolution. When the delivering of ink droplets on the leading paper P1 is finished by the print head 9a of the first carriage 7a at the upstream side in the rotating direction of the rotating drum 1, even if the print head 9b of the second carriage 7b performs the delivering of the ink droplets, the first carriage 7a is moved to move the print head 9a to a processing starting position SP, and the delivering of the ink droplets to the next paper P2 is started.

Description

  The present invention includes a control unit that forms an image by ejecting ink droplets from a linear print head as the drum rotates with respect to a recording medium supported on the outer periphery of the drum, and the control unit includes the print head. Among the dots formed on the recording medium by the ejection of ink droplets from the nozzles, the ink droplets are ejected from the nozzles to the intermediate region of the set length in the sub-scanning direction with the width of adjacent dots in the main scanning direction. The present invention relates to an image forming apparatus that forms a resolution image.

  As an image forming apparatus configured as described above, Patent Document 1 describes a line type ink jet recording apparatus in which an ink jet recording head (2) is arranged around a transfer drum (1). In Patent Document 1, the recording head (2) is moved at a recording pitch (p) shorter than the nozzle pitch (h) in the head moving direction (main scanning direction) of the recording head (2), and the transfer drum (1). A control mode is described in which recording is performed at a recording pitch (q) shorter than the nozzle pitch (h) in the rotation direction.

  In Patent Document 1, since the two recording pitches (p) and (q) are 1/4 of the nozzle pitch (h), the resolution is improved by rotating the transfer drum (1) 16 times.

  In Patent Document 2, when forming an image on a plurality of recording media provided with a linear head on a carriage and supported on the outer surface of the drum, a plurality of drums are rotated (multi-pass) as in Patent Document 1, A high-resolution image is formed by ejecting ink droplets onto a predetermined recording medium while the position of the linear head in the main scanning direction is set during rotation. Then, after such an image is formed, a control form is described in which ink droplets are ejected onto the next recording medium and recording is started. Further, Patent Document 2 describes that when recording on the previous recording medium is completed and recording on the next recording medium is started, the carriage is moved between the recording media.

JP-A-6-122195 JP 2006-69177 A

  The linear head is opposed to the print medium provided in the drum, and the linear head is moved in the main scanning direction every time the drum rotates once, so that a high quality image can be printed at a relatively high speed. have.

  However, when the carriage having the linear head is moved in the main scanning direction, the longer the dimension of the linear head in the main scanning direction, the more the weight is increased. Because of the influence of inertia, the accuracy of the ink droplet landing position on the recording medium is likely to be lowered, and there is room for improvement.

  Further, as described in Patent Document 2, an image is formed by multipass on one of a plurality of recording media supported by a drum, and after the formation of this image, image formation on the next recording medium is performed. In the case of starting the printing, it is necessary to set the print head at the image formation start position after the ejection of ink to the previous recording medium is completed. Therefore, when considering the moving time of the print head, a predetermined distance between the previous recording medium and the next recording medium is required, and the entire length in the circumferential direction of the drum cannot be effectively used. there were.

  An object of the present invention is to rationally configure an image forming apparatus capable of forming an image with high accuracy in a configuration in which an image is formed by ejecting ink droplets from a linear head onto paper supported on a drum.

A feature of the present invention is that it includes a control unit that forms an image by ejecting ink droplets from a linear print head as the drum rotates with respect to a recording medium supported on the outer periphery of the drum. Ink droplets are ejected from the nozzles to the intermediate region of the set length in the sub-scanning direction with the width of adjacent dots in the main scanning direction among the dots formed on the recording medium by ejecting ink droplets from the nozzles of the print head. An image forming apparatus for forming a high resolution image,
A plurality of carriages are provided in a positional relationship that does not interfere with each other when moving in the main scanning direction, and the print head is provided on each carriage,
When forming the high-resolution image, the control unit moves the carriages of the plurality of print heads in the main scanning direction for each rotation of the drum to set ink droplets in the intermediate area in a state where the discharge positions are set. In addition to controlling ejection, the carriage of the print head that has finished ejecting ink droplets to the intermediate region is allowed to operate independently.

According to this configuration, since the print head is provided for each of the plurality of carriages, the plurality of carriages can be independently driven even when the print head is moved in the main scanning direction, and each carriage is driven. Even if the actuator has a small capacity, the starting speed can be increased, and the dynamic inertia acting at the time of stopping can also be suppressed. In addition, since it is possible to independently move a plurality of print heads that have finished ejecting ink droplets to the intermediate region, it is possible to retract the print head and move it to a position to start the next print. Become.
As a result, it is possible to form an image with high accuracy in a configuration in which ink is ejected from a linear head onto a paper supported on a drum, and at the same time, a plurality of print heads can be sequentially moved from one that has finished printing. A possible image forming apparatus was constructed.

According to the present invention, when the control unit includes a plurality of groups of the recording media on the drum to form an image, the control unit ejects ink droplets from the plurality of print heads to the previous group of recording media. After the image formation is completed, the processing order is set so as to form an image by ejecting ink droplets from the plurality of print heads to the next group of recording media,
The control unit uses the print head, which has finished forming an image by ejecting ink droplets to the recording medium of the previous group, among the plurality of print heads to form an image in the next group according to the processing order. The carriage may be controlled so as to start moving to a processing start position that is a starting point of image formation on a group of recording media.

  According to this, when viewed from the direction along the axis of the drum, the plurality of carriages are arranged in a region along the circumferential direction of the drum. For this reason, the print head that has finished forming an image by ejecting ink droplets to the recording medium of the previous group among the plurality of print heads starts to move to the processing start position for the recording medium of the next group. Thus, the carriage is controlled. As a result, even when ink droplets continue to be ejected by other print heads, the print head that has finished forming an image by ejecting ink droplets is set at the processing start position, so that the next recording medium can be printed according to the processing order. You can start printing. Therefore, it is possible to form an image on the recording medium of the next group without setting a long interval (interval in the circumferential direction of the drum) between the recording medium of the previous group and the recording medium of the next group. Thus, it is possible to realize image formation that effectively utilizes the entire length of the drum in the circumferential direction.

  In the present invention, the processing start positions are set at both ends of the carriage movement region, and the control unit moves the print head to one side along the main scanning direction in order to form the high-resolution image. When an image has been formed by ejecting ink droplets onto the recording medium of the previous group, the print head is moved to the start position at the end in the moving direction, and the print head is moved from the start position to the other side. The carriage may be controlled so as to start image formation on the recording medium of the next group in accordance with the processing order by moving.

  According to this, the print head that has finished forming an image by ejecting ink droplets by moving the print head to one side along the main scanning direction to form a high-resolution image is moved to the processing start position at the moving end on this one side. The image formation on the recording medium of the next group can be started by moving the print head to the first position, and the image formation can be started quickly without moving the print head in the reverse direction (the direction of the original processing start position).

It is a vertical side view of an inkjet printer. It is a cross-sectional top view of an inkjet printer. It is a top view which shows the moving structure of a carriage. It is a perspective view which shows a carriage and a print head. It is a schematic diagram which shows arrangement | positioning of a print head. It is a block circuit diagram of a control system. It is a figure which shows a round strip and a sensor unit. It is a figure which shows the flow of the signal in a control unit. It is a figure which shows arrangement | positioning of the dot formed in an intermediate | middle area | region. 6 is a flowchart of a print processing routine in a high resolution mode. It is a conceptual diagram which shows continuously the relative positional relationship of the paper supported by the rotating drum, and two carriages.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an ink jet printer 100 constituting an embodiment of an image forming apparatus according to the present invention.

(Schematic configuration of inkjet printer)
The ink jet printer 100 includes a rotary drum 1 capable of supporting a paper P as a cut sheet-like recording medium on an outer peripheral surface in a casing C, and the rotary drum 1 being driven to rotate about a lateral axis X1. Motor M1, a discharge unit 6 that discharges fine ink droplets onto paper P (an example of a recording medium) supported on the rotating drum 1, and a control unit that drives and controls each member 50.

  The inkjet printer 100 is connected to an operation station 200 having an order information processing unit via a LAN cable or the like, and a print job sent from the operation station 200 is sent to the control unit 50 as shown in FIG. A print job input processing unit 51 that sequentially stores image data, an image data storage unit 52 that stores image data acquired from the operation station 200, a print management unit 53 that manages printing (image formation), and at the time of printing A head control unit 54 that performs control to operate the print head 9 in the main scanning direction and a nozzle control unit 55 that performs control to eject ink from the nozzles of the print head 9 based on the print image are provided.

  The rotating drum 1 is rotatably supported with respect to the housing C by a shaft 1s arranged coaxially with the shaft core X1. A motor M1 that rotationally drives the rotary drum 1 serves as a transport mechanism that moves the paper P in the sub-scanning direction relative to the discharge unit 6 by rotation.

  The rotating drum 1 includes a metal drum body 3 and a resin electrostatic adsorption sheet 2 attached over substantially the entire circumference of the outer peripheral surface of the drum body 3. Inside the drum body 3, a high-voltage power supply device 4 for generating an electrostatic adsorption force on the electrostatic adsorption sheet 2 is installed. The low voltage power is supplied from the outside of the casing C to the high voltage power supply device 4 through a slip ring SR provided at the outer end of the shaft 1s.

  As shown in FIG. 2, the electrostatic suction sheet 2 is composed of a plurality of suction sheets that are divided from each other along the axis X1. The electrostatic adsorption sheet 2 is divided into a plurality of pieces in the direction of the axis X1. The electrostatic adsorption sheet 2 is formed by insert molding a thin conductive mesh material (not shown) inside a resin sheet. The conductive mesh material is connected to the corresponding high-voltage power supply device 4 via a lead wire (not shown) that passes through a small through hole formed on the outer periphery of the rotary drum 1. The electrostatic adsorption sheet 2 is fixed to the outer peripheral surface of the rotary drum 1 with an adhesive or the like.

  In the rotary drum 1, when the high voltage power supply device 4 is driven by the control unit 50, a high voltage (for example, around 2000 volts) is applied to the conductive mesh material, so that the surface of the electrostatic adsorption sheet 2 is charged with static electricity. Thus, the paper P can be electrostatically attracted. The electrostatic attraction sheet 2 is configured such that the charging polarity of the electrostatic attraction sheet 2 can be set to either + or − in accordance with a command from the control unit 50. Basically, the general paper P is effectively adsorbed regardless of the polarity of the electrostatic adsorbing sheet 2.

(Configuration of discharge unit)
The discharge unit 6 prints an image on the paper P by discharging ink droplets onto the surface of the paper P supported by the rotary drum 1 at a timing synchronized with the peripheral speed of the rotary drum 1 rotated by the motor M1. (Form. As shown in FIGS. 1, 3, and 4, the discharge unit 6 has two carriages 7a and 7b that are arranged adjacent to each other along the circumferential direction of the rotary drum 1. An ink jet print head 9 in which various nozzles are formed is provided.

  Hereinafter, of the two carriages 7a and 7b, the upstream side (right side in FIG. 3) in the rotational direction of the rotary drum 1 is referred to as the first carriage 7a, and the downstream side in the rotational direction (left side in FIG. 3). This is referred to as a second carriage 7b, and a generic name for these is referred to as a carriage 7. Among the print heads 9, the one provided on the first carriage 7 a is referred to as a first print head 9 a, the one provided on the second carriage 7 b is referred to as a second print head 9 b, and these print heads are collectively referred to as the print head. 9.

  The carriage 7 is supported by a pair of guide shafts 8 supported by the housing C so as to be movable in the main scanning direction. The first carriage 7a and the second carriage 7b are arranged in a positional relationship that does not interfere with each other when moving in the main scanning direction, and are independently provided by the motor Ma and the motor Mb supported corresponding to the housing C. It is possible to move in the main scanning direction by the transmission mechanism 10 provided between the motors Ma and Mb and the first carriage 7a and the second carriage 7b so as to be driven. The transmission mechanism 10 includes, for example, a pair of pulleys 10 a that are spaced apart in the main scanning direction, and a timing belt 10 b that is wound between these pulleys 10 a, and one end of the timing belt 10 b is a part of the carriage 7. Fixed to the part.

  As shown in FIG. 3, the carriage 7 is scanned by a transmission mechanism 10 at a scanning position SP for forming an image on the paper P supported by the rotary drum 1 by the print head 9, and the print head 9 is scanned from the rotary drum 1 to the main scan. It is configured to be movable between home positions HP spaced apart in one direction. The positions of the two carriages 7 in the main scanning direction can be individually controlled by the control unit 50. The scanning position SP shown in FIG. 3 is a position where the print head 9 is set in the standard resolution mode. In the high resolution mode, as shown in FIG. 11, a processing start position SP that is the starting point of printing (image formation) is set at both ends in the main scanning direction, and from one processing start position SP to the other processing start position SP. Control for moving the print head 9 in the direction is performed.

  As shown in FIG. 4, an ink jet print head 9 is disposed on the lower surface of the carriage 7. As the print head 9, four types of print heads, a cyan print head 9C, a magenta print head 9M, a yellow print head 9Y, and a black print head 9K, are provided for each of the four colors CMYK. . Each color print head 9 is composed of two print heads 9 that are displaced in a staggered manner in the main scanning direction. As a result, each carriage 7 includes a total of eight print heads 9. The ink consumed by each print head 9 is appropriately replenished through the tube 12 from the ink bottle 11 of each color arranged in the housing C.

  One print head 9 is configured as a linear head in which nozzles of the same color are arranged linearly at a pitch of 150 dpi along the main scanning direction. Further, the two print heads 9 of the same color arranged in a staggered pattern are mainly composed of nozzles of two print heads 9 adjacent in the main scanning direction, as shown in FIG. 5 illustrating the cyan print head 9C. They are arranged apart from each other at an interval (about 1.7 mm) corresponding to 150 dpi in the scanning direction.

  Therefore, as illustrated in FIGS. 3 and 4, the relative positional relationship is set so that the nozzles of the first carriage 7 a and the second carriage 7 b have an interval corresponding to 150 dpi in the main scanning direction. By discharging ink droplets from the print head 9 without moving the carriage 7 in the main scanning direction during one rotation of the rotary drum 1, the resolution in the main scanning direction can be achieved with respect to the A4 size paper P. A 150 dpi image can be printed. A mode for printing an image of 150 dpi is referred to as a standard resolution mode.

  The ink jet printer 100 has a standard resolution by controlling the first carriage 7a and the second carriage 7b in the main scanning direction and controlling the ejection timing of ink droplets from the nozzles while rotating the rotary drum 1 a plurality of times. A high-resolution image of 300 to 600 dpi can be printed by ejecting ink droplets in the middle region of dots in the mode.

  Such processing for forming an image at a high resolution is referred to as a high resolution mode. For example, when an image is formed at a high resolution of 600 dpi, dots for forming an image in the standard resolution mode as shown in FIG. An image is formed with 16 dots in the intermediate area between the two, and each time the rotary drum 1 rotates, the print head 9 is set to a position where ink drops are discharged to the intermediate area, and ink drops are discharged from the nozzles. This discharge is continuously performed until the rotary drum 1 rotates 16 times.

  The intermediate area is an area having a set length in the sub-scanning direction with the width of adjacent dots (dots indicated by hatching) formed on the paper P along the main scanning direction in the standard resolution mode. Specifically, when dots are formed by ejecting ink droplets onto paper P in the standard resolution mode as shown in the figure, the interval between adjacent dots in the main scanning direction becomes the main pixel pitch Xs that matches the nozzle pitch. The sub-pixel pitch Ys is such that the dot interval in the sub-scanning direction is equal to the nozzle pitch. A rectangular area having the main pixel pitch Xs and the subpixel pitch Ys as one side is an intermediate area. The subpixel pitch Ys does not need to match the main pixel pitch Xs, and an arbitrary value can be adopted.

(Configuration of sensor unit)
A thin strip-shaped round strip RS is attached to one end of the outer peripheral surface of the rotating drum 1 over the entire circumference. As shown in FIG. 7, a scale image S whose shape changes in a sawtooth shape at a set interval Sp in the circumferential direction of the rotary drum 1 and one reference image T for specifying a reference position are formed on the round strip RS. ing. In particular, the scale image S is formed so as to divide the entire circumference of the rotary drum 1 into integers at the set interval Sp. A sensor unit SU that optically acquires these is arranged in the vicinity of the outer periphery of the rotating drum 1. Further, the sensor unit SU is supported by the casing C with a position set so as to be close to the print head 9 in the circumferential direction of the rotary drum 1 (when viewed in the direction along the axis X1).

  The sensor unit SU irradiates light from a light source module (not shown) to the scale image S and the reference image T of the round strip RS, and receives the irradiated light by the photo sensor module (not shown). Can be used. In this rotation detection unit, as the scale image S, a plurality of lines, a plurality of dots, or the like may be formed on the outer periphery of the rotating drum 1 at set intervals. Further, the sensor unit SU may be provided with a separate sensor for detecting the reference image T so that only the scale image S is detected and the reference image T is detected by a sensor different from the sensor unit SU. Furthermore, the detection system for specifying the reference position may be configured separately using a photo interrupt type sensor or the like. Further, as the sensor unit SU, the light beam from the light source module (not shown) is irradiated to the scale image S and the reference image T formed on the round strip made of a transparent material, and the light beam transmitted through the round strip is irradiated to the photo sensor module (not shown). You may use the transmission type thing received by illustration.

  The rotation detection unit is used to detect the outer peripheral position of the rotary drum 1 with high accuracy in order to land the ink droplets by the discharge unit 6 with respect to the predetermined outer peripheral position of the rotary drum 1 driven and rotated by the motor M1. .

  The sensor unit SU outputs a scale detection signal every time the scale image S is detected during rotation of the rotary drum 1 (intermittent output), and outputs a reference detection signal every time a reference image is detected. In addition, the print management unit 53 (see FIG. 8) integrates the scale detection signal to function as an incremental encoder, and the integrated value obtained in this way is a sub-value of the rotary drum 1 and the discharge unit 6. This is information for specifying the positional relationship in the scanning direction.

(Configuration of fixing unit)
Note that radical ultraviolet curable ink is used as the ink discharged from the discharge unit 6, and as shown in FIG. 1, a part of the vicinity of the outer peripheral surface of the rotary drum 1 is discharged onto the paper P. A fixing unit 20 for irradiating the ultraviolet curable ink with ultraviolet rays is disposed. The fixing unit 20 includes a housing 21 that houses the ultraviolet light source UL, and a slit 21a that extends linearly in parallel with the axis X1 is formed in a part of the housing 21.

  As the ultraviolet light source UL, a high-pressure mercury lamp or a fluorescent tube can be used, but the ultraviolet light source UL uses an ultraviolet LED. Further, the ultraviolet light from the ultraviolet light source UL is irradiated toward the outer peripheral surface of the rotating drum 1 through the slit 21a. The control unit 50 uses a predetermined algorithm based on the image data being printed and the characteristics of the paper P, and the ultraviolet light source UL for a necessary period determined in accordance with the rotational speed of the rotating drum 1 and the position of the paper P being sucked. Lights up. It should be noted that a shutter for controlling the irradiation of ultraviolet rays from the ultraviolet light source UL can be freely opened and closed, and the control mode can be set so that the shutter is opened when the irradiation of ultraviolet rays is required.

  In the housing C, a paper supply unit 22 for supplying unprocessed paper P to the outer peripheral surface of the electrostatic adsorption sheet 2 of the rotary drum 1 and a paper P for which printing has been completed are collected from the rotary drum 1. The print collection unit 26 is provided.

(Configuration of paper supply unit)
The paper supply unit 22 includes a paper magazine 24 installed at one lower end of the rotary drum 1 and a supply roller 25 for discharging the paper P one by one from a stack of unprocessed paper P stored in the paper magazine 24. And. A motor (not shown) for rotationally driving the supply roller 25 is also driven and controlled by the control unit 50. When a sheet of paper P is fed by the supply roller 25 to a state where it protrudes sideways from the paper magazine 24 by a predetermined length, the leading end of the paper P is statically placed at a predetermined position on the outer peripheral surface of the rotating electrostatic chucking sheet 2. Subsequently, the sheet is electroadsorbed, and subsequently, feeding by the supply roller 25 is executed at a speed synchronized with the peripheral speed of the electrostatic attraction sheet 2. Finally, the entire paper P is adsorbed to the electrostatic attraction sheet 2. By repeating this series of procedures, the rotating drum 1 of the ink jet printer 100 employs a size that can support up to three sheets of A4 size paper P at the same time.

(Configuration of print collection unit)
The print collection unit 26 includes a collection rocking body 27 that is swingably disposed around the horizontal axis X2 at the other lower end of the drum body 3, and a print stocker that can store a large number of processed paper P. 30. A plurality of vertical grooves 3D are formed on the outer periphery of the drum body 3 in the circumferential direction, and the recovery rocking body 27 includes a claw portion 27a extending along the vertical groove 3D on the outer periphery of the opposed rotating drum 1, and a claw portion 27a. It has a guide portion 27b that smoothly extends downward in a circular arc shape from the radially outer surface, and a collection roller pair 28 that is disposed at the other end of the guide portion 27b.

  The recovery rocking body 27 has a retracted posture in which the claw portion 27a is sufficiently separated from the outer peripheral surface of the drum main body 3 by the motor M4 supported by the casing C, and the vertical groove 3D ( The posture can be freely changed between the recovery posture that has entered (see FIG. 2). The collection roller pair 28 is configured to be rotationally driven by a motor M5 supported by the collection rocking body 27.

  When the control unit 50 finishes the printing by the discharge unit 6 and the fixing process by the fixing unit 20 on the paper P supported by the drum body 3, the recovery rocking body at an appropriate timing synchronized with the rotational phase of the rotating drum 1. 27 is switched to the collection posture. By this switching, the claw portion 27a of the recovery rocking body 27 enters the longitudinal groove 3D of the drum body 3 just before the front end of the corresponding paper P, so the paper P is pulled away from the outer peripheral surface of the drum body 3 by the claw portion 27a. Then, it is guided by the guide portion 27 b and sent to the nip of the collection roller pair 28 that has already started rotating, and is discharged into the print stocker 30 by the collection operation of the collection roller pair 28.

  When a plurality of papers P are simultaneously supported on the rotary drum 1, the interval between the leading end of the paper P that is scheduled to be collected first after the image forming process is completed and the trailing end of another adjacent paper P is determined as follows: The paper P is adsorbed in a state of being largely separated from other intervals between the papers P. By supporting the plurality of papers P in a separated state in this way, it is required for the timing at which the claw portions 27a of the recovery rocking body 27 enter the vertical groove 3D of the drum body 3 just before the front end of the corresponding paper P. The accuracy is relatively low.

[Control configuration]
The control unit 50 generates a print image corresponding to the resolution from the image data stored in the image data storage unit 52 (the process of this processing is not described), and detects the outer peripheral position of the rotary drum 1 by the rotation detection unit. At the same time, by ejecting ink droplets corresponding to the detected outer peripheral position in the print image, printing in the standard resolution mode and printing in the high resolution are realized. In particular, when printing is performed while supporting a plurality of papers P on the rotating drum 1, after the printing of one sheet (an example of one group) is finished, the next sheet (an example of a group) of paper P is completed. The processing order is set to perform printing. An outline of a configuration for realizing the control is shown in FIG.

  The control unit 50 includes the print management unit 53 that receives the scale detection signal and the reference detection signal from the sensor unit SU. Further, an address counter 63 for receiving a count signal from the print management unit 53 is provided, and an address specifying means 64 for specifying a print target address of the print image by the signal from the address counter 63 and acquiring density data (luminance data). And a print buffer 65 for storing density data (luminance data) output from the address specifying means 64. The print buffer 65 obtains a timing signal from the print management unit 53 and outputs density data to the nozzle control unit 55.

  The control unit 50 includes the head control unit 54 that acquires the head position signal from the print management unit 53 and sets the position of the print head 9 in the main scanning direction. A resolution setting unit 66 for setting information is provided, and a paper position acquisition unit 67 for giving the position of the paper P to the print management unit 53 is provided.

  The print target address of the print image Px designated by the address designation means 64 by the signal from the address counter 63 is information for designating a line-shaped area along the main scanning direction, and the density data of this line-shaped area The address designation means 64 separates the data into those corresponding to the group of nozzles, and the print buffer 65 separates them into areas corresponding to a plurality of nozzles of each print head 9 and stores them.

  The print image Px has a bitmap structure corresponding to the resolution set by the resolution setting unit 66 for the four colors CMYK of the image data acquired by the image data storage unit 52.

  Although not shown in the drawing, there are four sets of the address counter 63, the address designating unit 64, the print buffer 65, and the nozzle control unit 55 corresponding to the four colors of CMYK, and output from the print management unit 53 to the print buffer 65. As many timing signal output lines as the number of nozzles formed in the print head 9 are provided. Timing signals are output to the respective output lines with a time lag based on the rotational speed of the rotary drum 1. The

  The nozzle control unit 55 functions as a driver for driving each nozzle, and outputs power proportional to the density data from the print buffer 65 so as to eject ink drops of an amount corresponding to the density data. Function.

  The head controller 54 operates the carriages 7a and 7b in the main scanning direction by controlling the motors M2 and M3. In the inkjet printer 100, when printing is performed at a resolution of 150 dpi, the carriages 7a and 7b (print head 9) are fixed at the scanning position SP shown in FIG. Further, when printing at a high resolution, the print head 9 is moved in the main scanning direction every time the rotary drum 1 makes one rotation based on information from the resolution setting means 66 as described later. The ink droplets ejected by the ink are landed on the intermediate region.

  The print management unit 53, the head control unit 54, the nozzle control unit 55, the address counter 63, the address designation unit 64, the resolution setting unit 66, and the paper position acquisition unit 67 are configured by software. However, these may be configured by hardware, and a part of these may be configured by hardware to be configured by a combination of hardware and software.

(Print sequence)
In the ink jet printer 100, the paper P is supported on the outer periphery of the rotating drum 1 by supplying the paper P from the paper supply unit 22 while maintaining the outer periphery of the rotating drum 1 at a high potential. The end position of the paper P supported in this way is optically acquired by the paper position acquisition means 67 and associated with the print start timing. When printing in the standard resolution mode, each carriage 7 is held at a predetermined position by the head controller 54, and after reaching the print start timing, a scale detection signal from the sensor unit SU is printed. Input to the unit 53. The print management unit 53 outputs a count signal synchronized with the scale detection signal to the address counter 63, and the address designating unit 64 designates a print target address from the print image Px, and density data (luminance data for one line in the main scanning direction). ) And is stored (saved) separately in the storage area corresponding to the number of nozzle groups of the print head 9 in the print buffer 65.

  The density data stored in the print buffer 65 in this way is output to the nozzle control unit 55 in synchronization with a timing signal given to each group from the print management unit 53. As a result, the nozzle controller 55 ejects ink droplets from each nozzle to the paper P with power proportional to the density data, and an image is printed on the paper P by this ejection. The ink droplets ejected in this way are cured by the ultraviolet rays irradiated by the fixing unit 20 and collected by the print collection unit 26 in the print stocker 30.

  As described above, since the nozzles are divided into a plurality of groups, in the control in which the address designating unit 64 designates the density information (luminance information) of the pixels arranged in the main scanning direction from the print image Px, the sub-group of each group is designated. A time difference is set to the timing for reading out density data by the timing corresponding to the distance in the scanning direction.

  In the inkjet printer 100, when printing in the high resolution mode, a plurality of groups of papers P are supported on the rotating drum 1, and the interval D between the groups (interval in the circumferential direction of the rotating drum 1). Control that can be shortened. In the following description, it is assumed that one group includes one sheet of paper P. However, for example, two or three sheets of paper P may be supported as one group on the rotary drum 1 for printing.

  That is, as shown in the flowchart of FIG. 10 and the conceptual diagram of FIG. 11, for example, an outline of image printing in a state where the rotary drum 1 is provided with two papers P1 and P2 will be described as an initial operation. 2, two sheets of paper P are supplied from the paper supply unit 22 to the rotating drum 1. The positional relationship between the two sheets of paper P1 and P2 is acquired by the paper position acquisition unit 67 and given to the print management unit 53, and the image data to be printed on the two sheets of paper P is converted into a print image Px. It is saved (Step # 101).

  In parallel with such control, the first print head is set by setting the first carriage 7a and the second carriage 7b at one processing start position SP (left side in the figure) as shown in FIG. 9a and the second print head 9b are arranged in a parallel posture, and each time the rotary drum 1 rotates, the two carriages 7 are equal to the other side (the right side in the figure) as shown in FIG. 11B. By moving the sheet by the amount, the printing process for the first paper P1 is started in the form of performing the process of ejecting ink droplets to the intermediate area described above (steps # 102 and # 103). In particular, when the two carriages 7 are moved to the other side in this way, the first carriage 7a is moved first, as shown by the white arrow in FIG. 11B, and then the second carriage 7b. The order of movement is set to move.

  In this printing process, the rotating drum 1 rotates in the direction indicated by the arrow in FIG. 11 (in FIG. 11, the outer periphery of the rotating drum 1 moves from the bottom to the top). In addition, since the print head 9 of the first carriage 7a is located on the upstream side in the rotation direction of the rotary drum 1, the process of ejecting ink droplets onto the paper P1 is the process of the print head 9 of the second carriage 7b. Exit earlier.

  In this print process, when the print process is executed at a high resolution of 600 dpi, as described above, the paper P has a rectangular area having the main pixel pitch Xs and the sub-pixel pitch Ys as one side as shown in FIG. As a middle region, 16-dot ink droplets are ejected into this middle region.

  In this way, when it is determined that the image on the paper P1 has been printed (formed) by discharging the ink droplets of the first print head 9a, the image is printed (formed) on the next paper P2 in accordance with the processing order. Therefore, at the timing of the determination, the first carriage 7a is moved and set to the other processing start position SP (right side in the figure) as shown in FIG. 11C, and ink droplets are ejected onto the second paper P2. It shifts to the state that enables. When the second print head 9b continues to eject ink on the first sheet P at the timing when the first print head 9a moves to the other processing start position SP in this way. The position of the second print head 9b is maintained.

  In this way, with the first print head 9a set to the other processing start position SP, the second paper P is in a position where ink droplets can be ejected from the print head 9a as shown in FIG. 11 (d). When it reaches, the first print head 9a discharges ink droplets to start printing (steps # 104 to # 106).

  Immediately after the printing process is started by the first print head 9a, as shown in FIG. 11D, the printing process by the second print head 9b is also finished, and the second carriage 7b is moved to the other ( When the second paper P2 reaches a printable position, the second print head 9b discharges ink droplets and starts printing (# on the right side in the figure). 107- # 109 steps).

  That is, the printing process is performed in such a manner that the carriage 7 is moved in the forward direction when printing the first paper P1, and the carriage 7 is moved in the reverse direction when printing the second paper P2. Done. Therefore, when printing is performed by moving the carriage 7 in the reverse direction, the line-shaped density data designated by the address designation means 64 from the print image Px is rearranged in an order corresponding to the moving direction of the print head 9. Saved in the print buffer 65.

  As described above, when printing is performed with the two carriages 7 as described above, the two carriages 7 are moved to one side (left side in the figure) every time the rotating drum 1 makes one rotation, so that the above-described intermediate is performed. A print process is performed on the second sheet of paper P2 in a form in which the process of ejecting ink droplets onto the area is performed. When the image formation is completed, the first carriage 7a and the second carriage 7b are set at one of the process start positions SP (left side in FIG. 11), and the process is completed (Steps # 110 and # 111).

  When three sheets of paper P are supported on the rotating drum 1, the same processing as # 104 to # 106 is executed after the processing of # 109.

  By performing such processing, for example, the carriage is moved until the ejection of all ink droplets necessary for printing on the first paper P is completed as in the configuration in which the print head 9 is provided in a single carriage. Unlike those that cannot, the print processing by the first print head 9a provided in the first carriage 7a is possible even before the ejection of all ink droplets necessary for printing on the first paper P1 is completed. The distance D between the two papers P is set to a short dimension so that the entire length of the rotating drum 1 in the circumferential direction can be used effectively.

  In this flowchart, the print processing in the state where two sheets (two groups) of paper P are supported on the rotating drum 1 has been described. However, the number of sheets of the paper P is three or more (three or more groups). In this way, the interval between three or more papers P can be made short.

[Operations and effects of the embodiment]
As described above, since the plurality of carriages 7 are provided with the print heads 9, even when the print heads 9 are moved in the main scanning direction, the carriages 7 can be driven by motors Ma and Mb having relatively small capacities. In addition, it is possible to increase the speed immediately after start-up, and to suppress the vibration caused by the dynamic inertia that acts at the time of stop, so that the image quality is not deteriorated.

  In addition, when the first print head 9a and the second print head 9b have finished printing an image by ejecting ink droplets onto the first paper P1 by the first print head 9a, the first print head 9a and the second print head 9b. The first carriage 7a supporting 9a is further moved in the direction of the moving end to set the processing start position SP for the second paper P2. Thus, even when the second print head 9b continues to eject ink droplets to the first paper P1, ink droplets from the first print head 9a supported by the first carriage 7a in accordance with the processing order. Printing can be started on the second paper P2 by ejection. When printing a high-resolution image, the print head 9 is moved in a predetermined direction in the main scanning direction, so that the influence of backlash in the transmission system that moves in the main scanning direction is suppressed.

  For this reason, even if the interval between the previous paper P and the next paper P (interval in the circumferential direction of the rotating drum) is not set long, it is possible to form an image on the next paper P, and Image formation using the entire length in the direction is realized.

  In particular, in the present invention, a configuration in which three or more carriages 7 are provided and the print head 9 is provided for each carriage 7 may be employed. In such a case, each carriage 7 is operated at a higher speed. At the same time, dynamic inertia is suppressed to enable high-precision printing.

  The high resolution is not limited to 600 dpi, and may be arbitrarily set. Regardless of the resolution, control is performed to move the carriage 7 in the main scanning direction every time the rotating drum 1 makes one rotation, thereby realizing high-precision printing.

  INDUSTRIAL APPLICABILITY The present invention can be used in an image forming apparatus in which a recording medium is provided on a rotary drum and printing is performed by ejecting ink droplets from a print head provided on a carriage each time the drum rotates to increase resolution. .

1 drum (rotating drum)
7 Carriage 9 Print head 50 Control unit P Recording medium (paper)
SP processing start position X1 Rotation axis (axis)

Claims (3)

A control unit that forms an image by ejecting ink droplets from a linear print head as the drum rotates with respect to a recording medium supported on the outer periphery of the drum is provided. A high-resolution image is formed by ejecting ink droplets from the nozzles to an intermediate area of the set length in the sub-scanning direction with the width of adjacent dots in the main scanning direction among the dots formed on the recording medium by ejecting ink droplets An image forming apparatus that
A plurality of carriages are provided in a positional relationship that does not interfere with each other when moving in the main scanning direction, and the print head is provided on each carriage,
When forming the high-resolution image, the control unit moves the carriages of the plurality of print heads in the main scanning direction for each rotation of the drum to set ink droplets in the intermediate area in a state where the discharge positions are set. An image forming apparatus that performs ejection control and permits independent operation of a carriage of a print head that has finished ejecting ink droplets to the intermediate region. When the control unit includes a plurality of groups of the recording media on the drum and forms an image, the control unit forms an image by ejecting ink droplets from the plurality of print heads on the recording medium of the previous group. After finishing, the processing order is set to form an image by ejecting ink droplets from the plurality of print heads to the next group of recording media,
The control unit uses the print head, which has finished forming an image by ejecting ink droplets to the recording medium of the previous group, among the plurality of print heads to form an image in the next group according to the processing order. The image forming apparatus according to claim 1, wherein the carriage is controlled so as to start moving to a processing start position that is a starting point of image formation on a group of recording media.   The processing start positions are set at both ends of the carriage movement area, and the control unit moves the print head to one side along the main scanning direction to form the high resolution image. When the image formation is completed by ejecting ink droplets on the recording medium, the print head is moved to the start position at the end in the moving direction, and the print head is moved from the start position to the other side. The image forming apparatus according to claim 2, wherein the carriage is controlled to start image formation on a recording medium of a next group according to the processing order.

Images