JP6299403B2 - Image forming apparatus, image forming system, and program - Google Patents

Description

  The present invention relates to an image forming apparatus, an image forming system, and a program.

  An ink jet image forming apparatus drives a nozzle of a recording head in accordance with image data, and forms an image on a printing medium such as recording paper by ejecting ink droplets from the nozzle. The recording head tends to have a large number of nozzles as the image quality is improved and the size of the apparatus is reduced.

  In this type of image forming apparatus, the mutual interference of the driven nozzles depends on the total number of nozzles driven at the same drive timing (within the same drive cycle) and the density of nozzles driven at the same drive timing. There arises a problem that characteristics such as ejection speed of ink droplets are unstable. Therefore, a technique for improving the image quality by solving such a problem of mutual interference between nozzles has been proposed (see, for example, Patent Document 1).

  The technique described in Patent Document 1 detects the total number of nozzles driven at the same drive timing and the density of nozzles driven at the same drive timing, and ejects ink droplets (ejection speed) according to the detection result. A correction amount for correcting is calculated. The drive waveform data is corrected at a correction rate corresponding to the correction amount, and the recording head is driven using the corrected drive waveform data, so that high-quality image formation can be performed.

  However, since the technique disclosed in Patent Document 1 is configured to correct the common drive waveform data prepared for the entire recording head or for each nozzle row, the correction can be performed with a fine granularity such as a nozzle unit. Can not. For this reason, an improvement for further improving the image quality by performing more accurate correction is desired.

  In order to solve the above-described problems, an image forming apparatus according to the present invention includes a recording head having a plurality of nozzles that eject droplets, and the total number of nozzles driven at the same drive timing based on input image data. A detection unit that detects the total number of drive nozzles and the number of continuous drive nozzles that are the number of nozzles in a continuous drive region in which nozzles driven at the same drive timing are continuous, and the total number of drive nozzles and the number of continuous drive nozzles A correction data generation unit that generates correction data based on the correction data, a correction unit that corrects input image data using the correction data, and the recording head according to the image data corrected by the correction unit And a head driving unit that drives the nozzles.

  According to the present invention, it is possible to accurately correct the influence of mutual interference of nozzles driven at the same drive timing, and to improve the image quality.

FIG. 1 is a perspective view illustrating the inside of the image forming apparatus according to the embodiment. FIG. 2 is a top view illustrating an internal mechanical configuration of the image forming apparatus according to the embodiment. FIG. 3 is a cross-sectional view of the recording head included in the image forming apparatus according to the embodiment along the short direction. FIG. 4 is a cross-sectional view along the longitudinal direction of the recording head provided in the image forming apparatus of the embodiment. FIG. 5 is a diagram schematically showing how the nozzles of the recording head are driven. FIG. 6 is a diagram illustrating the relationship between the number of nozzles that are driven simultaneously and the ejection speed of ink droplets ejected from the nozzles. FIG. 7 is a block diagram illustrating a hardware configuration example of the image forming apparatus according to the embodiment. FIG. 8 is a diagram illustrating the configuration of the drive wave generation circuit. FIG. 9 is a block diagram illustrating a configuration example of the recording head driver. FIG. 10 is a block diagram illustrating a functional configuration example of the image processing unit. FIG. 11 is a block diagram illustrating a configuration example of the correction calculation unit. FIG. 12 is a diagram illustrating the relationship between the image data and the synchronous clock signal input to the correction calculation unit, and the drive nozzles and non-drive nozzles of the recording head. FIG. 13 is a diagram illustrating an example of a correction table stored in the table storage unit. FIG. 14 is a flowchart showing a flow of a series of processes by the image processing unit. FIG. 15 is a schematic diagram conceptually showing image correction by the bicubic method. FIG. 16 is a block diagram illustrating a configuration example of an image forming system. FIG. 17 is a diagram illustrating a configuration example of a main part of an image forming apparatus including a line head type recording head.

  Hereinafter, an image forming apparatus, an image forming system, and a program according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  First, a mechanical configuration example of the image forming apparatus 1 of the present embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view showing the inside of the image forming apparatus 1 as seen through, and FIG. 2 is a top view showing the mechanical configuration inside the image forming apparatus 1.

  As shown in FIG. 1, the image forming apparatus 1 of the present embodiment includes a carriage 5 that reciprocates in the main scanning direction (the direction of arrow A in the figure). The carriage 5 is supported by a main guide rod 3 extending along the main scanning direction. The carriage 5 is provided with a connecting piece 5a. The connecting piece 5 a engages with the sub guide member 4 provided in parallel with the main guide rod 3 to stabilize the posture of the carriage 5.

  As shown in FIG. 2, four recording heads 6y, 6m, 6c, and 6k are mounted on the carriage 5. The recording head 6y is a recording head that discharges yellow (Y) ink. The recording head 6m is a recording head that discharges magenta (M) ink. The recording head 6c is a recording head that discharges cyan (C) ink. The recording head 6k is a plurality of recording heads that discharge black (Bk) ink. Hereinafter, the recording heads 6y, 6m, 6c, and 6k are collectively referred to as the recording head 6. The recording head 6 is supported by the carriage 5 such that the ejection surface (nozzle surface) faces downward (recording paper P side).

  A cartridge 7 for supplying ink to the recording head 6 is disposed at a predetermined position in the image forming apparatus 100. The cartridge 7 and the recording head 6 are connected by a pipe (not shown), and ink is supplied from the cartridge 7 to the recording head 6 through this pipe.

  The carriage 5 is connected to a timing belt 11 stretched between a driving pulley 9 and a driven pulley 10. The drive pulley 9 is rotated by driving the main scanning motor 8. The driven pulley 10 has a mechanism for adjusting the distance to the driving pulley 9 and has a role of applying a predetermined tension to the timing belt 11. The carriage 5 reciprocates in the main scanning direction when the timing belt 11 is fed by driving the main scanning motor 8. The movement of the carriage 5 in the main scanning direction is controlled based on an encoder value obtained when the encoder sensor 13 provided on the carriage 5 detects the mark on the encoder sheet (linear scale) 14 as shown in FIG. The

  Further, the image forming apparatus 1 of the present embodiment includes a maintenance mechanism 15 for maintaining the reliability of the recording head 6. The maintenance mechanism 15 performs cleaning and capping of the ejection surface of the recording head 6 and discharging unnecessary ink from the recording head 6.

  As shown in FIG. 2, a platen 16 is provided at a position facing the ejection surface of the recording head 6. The platen 16 is for supporting the recording paper P when ink is ejected from the recording head 6 onto the recording paper P. The recording paper P is nipped by a conveyance roller that is driven by a sub scanning motor (not shown), and is intermittently conveyed on the platen 16 in the sub scanning direction.

  The recording head 6 has a plurality of nozzles, ejects ink droplets (droplets) from the nozzles driven according to the image data toward the recording paper P on the platen 16, and ink droplets on the recording paper P Is attached to form an image on the recording paper P.

  Each of the mechanical elements constituting the image forming apparatus 1 of the present embodiment is disposed inside the exterior body 2. The exterior body 2 is provided with a cover member 2a that can be opened and closed. When maintenance of the image forming apparatus 1 or a jam occurs, the operation can be performed on each component provided inside the exterior body 2 by opening the cover member 2a.

  The image forming apparatus 1 according to the present embodiment intermittently conveys the recording paper P in the sub-scanning direction (the direction of arrow B in the figure), and while the conveyance of the recording paper P in the sub-scanning direction is stopped, the carriage 5 Are reciprocated in the main scanning direction. Then, by driving the nozzles of the recording head 6 according to the image data during the movement of the carriage 5, ink droplets are ejected from the nozzles of the recording head 6 onto the recording paper P on the platen 16. An image is formed (serial head method). The recording paper P is an example of a printing medium on which an image is formed, and the usable printing medium is not limited to paper.

  Next, details of the recording head 6 will be described with reference to FIGS. 3 and 4 are cross-sectional views of the recording head 6, FIG. 3 is a cross-sectional view taken along the short direction of the recording head 6, and FIG. 4 is the longitudinal direction of the recording head 6 (the direction in which the nozzles constituting the nozzle row are arranged). FIG.

  The recording head 6 includes a flow path plate 61 formed of, for example, a single crystal silicon substrate, a vibration plate 62 bonded to the lower surface of the flow path plate 61, and a nozzle plate 63 bonded to the upper surface of the flow path plate 61. On the nozzle plate 63, nozzles 65 for discharging ink droplets are formed. In addition, a pressure chamber 66 communicating with the nozzle 65, an ink supply port 67 for supplying ink to the pressure chamber 66, and the like are formed in the flow path plate 61. The diaphragm 62 is a member that is deformed by driving a piezoelectric element, which will be described later, and is formed with a thin part for facilitating deformation and a thick part that is joined to the piezoelectric element.

  On the lower surface side of the diaphragm 62, a piezoelectric element 70 that is a pressure generating means (actuator) for pressurizing ink in the pressurizing chamber 66 corresponding to each pressurizing chamber 66, and a base substrate that supports the piezoelectric element 70 71 and a frame member 72 are provided. A common liquid chamber 73 is formed in the frame member 72. The common liquid chamber 73 is a flow path through which the ink supplied from the cartridge 7 (see FIG. 1) passes, and communicates with the pressurizing chamber 66 provided for each nozzle 65 through the ink supply port 67.

  In the recording head 6 of the present embodiment, the piezoelectric member is subjected to slit processing by half-cut dicing, thereby supporting the piezoelectric element 70 corresponding to each pressurizing chamber 66 and the partition wall portion 61 a between the pressurizing chambers 66. The support post 74 is formed integrally. Note that the column portion 74 is made of the same material as the piezoelectric element 70, but does not displace because no drive voltage is applied, and functions as a column that supports the partition wall portion 61a.

  The piezoelectric element 70 includes, for example, a lead zirconate titanate (PZT) piezoelectric layer 81 having a thickness of 10 to 50 μm / layer, and an internal electrode layer 82 made of silver and palladium (AgPd) having a thickness of several μm / layer. Are alternately stacked. The internal electrode layer 82 is electrically connected alternately to the individual electrode 83 and the common electrode 84 which are end face electrodes (external electrodes) on the end face. In the recording head 6 of the present embodiment, for example, the pressurizing chamber 66 is contracted and expanded by expansion and contraction of the piezoelectric element 70 whose piezoelectric constant is d33. The piezoelectric element 70 is expanded when a driving signal is applied and charged, and contracts in the opposite direction when the electric charge charged in the piezoelectric element 70 is discharged.

  The end face electrode on one end face of the piezoelectric element 70 is divided for each piezoelectric element 70 to be an individual electrode 83, and the end face electrode on the other end face is integrated with the end face electrodes of the other piezoelectric elements 70 in all the piezoelectric elements 70. The conductive common electrode 84 becomes conductive.

  An FPC cable 85 is connected to the individual electrode 83 of the piezoelectric element 70. The FPC cable 85 is connected to a driving circuit (recording head driver) for selectively applying a driving waveform to each piezoelectric element 70. The common electrode 84 is connected to the ground (GND) electrode of the FPC cable 85.

  In the recording head 6 configured as described above, for example, when a drive waveform (pulse voltage of 10 to 50 V) is applied to the piezoelectric element 70, the piezoelectric element 70 is displaced in the stacking direction. Then, when the diaphragm 62 is deformed, the ink in the pressurizing chamber 66 is pressurized to increase the pressure, and an ink droplet is ejected from the nozzle 65.

  Thereafter, the ink pressure in the pressurizing chamber 66 decreases with the end of ink droplet ejection, and a negative pressure is generated in the pressurizing chamber 66 due to the inertia of the ink flow and the discharge process of the drive pulse. At this time, the ink supplied from the cartridge 7 flows into the common liquid chamber 73 and is filled into the pressure chamber 66 from the ink supply port 67. Thereafter, ink droplet ejection and ink filling are repeated by repeating the above operations.

  By the way, in the recording head 6 having the structure as described above, since the ink droplets are ejected by using the displacement of the piezoelectric element 70, the driving conditions of the adjacent nozzles 65 influence each other and the pressurizing chamber 66 is affected. The pressure of the ink becomes non-uniform and unstable, and so-called mutual interference problems such as the characteristics of the ink droplet ejection speed Vj differ for each nozzle 65 are likely to occur.

  Here, an example of mutual interference of the nozzles 65 will be described with reference to FIGS. 5 and 6. FIG. 5 is a diagram schematically showing how the nozzle 65 is driven. FIG. 5A shows an example in which only one nozzle 65 is driven (single drive), and FIG. 5B shows three adjacent nozzles. An example in which 65 is driven simultaneously (3ch drive) is shown, and (c) shows an example in which a large number of nozzles 65 are driven simultaneously (multi-drive). FIG. 6 is a diagram showing the relationship between the number of nozzles that are driven simultaneously (number of drive channels) and the ejection speed Vj of the ink droplets ejected from the nozzle 65 at the position indicated by the arrow in FIG. Here, the simultaneous driving means that they are driven at the same driving timing (within the same driving cycle).

  Referring to FIG. 6, it can be seen that the ink discharge speed Vj in the 3ch drive (b) is faster than the ink discharge speed Vj in the single drive (a). This is because the pressure escapes to the pressurizing chamber 66 of the nozzle 65 adjacent to the nozzle 65 being driven at the time of single driving, but this pressure relief is suppressed at the time of 3ch driving. On the other hand, in the multi-drive (c), since the effective excluded volume is reduced by lifting the entire flow path plate 61, the pressure in the pressurizing chamber 66 is reduced, and the ink droplet ejection speed Vj. Is slower than single drive.

  In addition to such structural factors, the ink droplet ejection speed Vj may vary due to electrical factors (load characteristics of the drive waveform). This is because the number of drive nozzles and the wiring length of the recording head 6 are replaced with equivalent circuits such as capacitance and inductance, so that the waveform output from the drive waveform generation circuit, which will be described later, fluctuates, and the ink droplet ejection speed This is because it affects Vj.

  Note that the above-described problem of mutual interference is not limited to the recording head 6 using the displacement of the piezoelectric element 70, and may occur in, for example, a thermal ink jet recording head. In a thermal ink jet recording head, bubbles are generated in the pressure chamber to pressurize the ink, so the partition that partitions the pressure chamber is deformed by the pressure applied by the bubble, and the pressure changes in the adjacent pressure chamber. Is generated. For this reason, a problem of mutual interference due to mechanical factors such as fluctuations in the ink droplet ejection speed Vj occurs as in the above-described example.

  In view of this, in the present embodiment, the above-described problem of mutual interference between nozzles is solved, the ejection characteristics of the nozzles are stabilized, and high-quality image formation can be performed. Specifically, the image forming apparatus 100 of the present embodiment is the same as the total number of drive nozzles that is the total number of nozzles driven at the same drive timing based on input image data (image data to be printed). The number of continuously driven nozzles, which is the number of nozzles in a continuous drive region where nozzles driven at the drive timing are continuous, is detected. Then, the input image data (image data to be printed) is corrected using the correction data generated based on the detected total number of drive nozzles and the number of continuous drive nozzles, and according to the corrected image data The nozzles of the recording head 6 are driven.

  Hereinafter, a specific configuration example of the image forming apparatus 1 that realizes such a function will be described. In this embodiment, as described above, the image forming apparatus 1 including the recording head 6 that ejects ink droplets by using the displacement of the piezoelectric element 70 is illustrated, but the problem of mutual interference of nozzles occurs. The present invention can also be effectively applied to an image forming apparatus provided with other possible recording heads, for example, the above-described thermal ink jet recording head.

  FIG. 7 is a block diagram illustrating a hardware configuration example of the image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 includes a main control board 100, a head relay board 200, and an image processing board 300.

  The main control board 100 includes a central processing unit (CPU) 101, a field-programmable gate array (FPGA) 102, a random access memory (RAM) 103, a read only memory (ROM) 104, and a non-volatile random access memory (NVRAM). 105, a motor driver 106, a drive waveform generation circuit 107, and the like are mounted.

  The CPU 101 controls the entire image forming apparatus 1. For example, the CPU 101 uses the RAM 103 as a work area, executes various control programs stored in the ROM 104, and outputs control commands for controlling various operations in the image forming apparatus 1. At this time, the CPU 101 controls various operations in the image forming apparatus 1 in cooperation with the FPGA 102 while communicating with the FPGA 102.

  The FPGA 102 includes a CPU control unit 111, a memory control unit 112, an I2C control unit 113, a sensor processing unit 114, a motor control unit 115, and a print head control unit 116.

  The CPU control unit 111 has a function of communicating with the CPU 101. The memory control unit 112 has a function of accessing the RAM 103 and the ROM 104. The I2C control unit 113 has a function of communicating with the NVRAM 105.

  The sensor processing unit 114 performs processing of sensor signals of various sensors 130. The various sensors 130 are generic names of sensors that detect various states in the image forming apparatus 1. In addition to the encoder sensor 13 described above, the various sensors 130 include a paper sensor that detects the passage of the recording paper P, a cover sensor that detects the opening of the cover member 2a, a temperature and humidity sensor that detects environmental temperature and humidity, and the recording paper P. A paper fixing lever sensor for detecting the operation state of the lever for fixing the ink, a remaining amount detecting sensor for detecting the remaining ink amount of the cartridge 7, and the like. The analog sensor signal output from the temperature / humidity sensor or the like is converted into a digital signal by an AD converter mounted on the main control board 100 or the like and input to the FPGA 102, for example.

  The motor control unit 115 controls various motors 140. The various motors 140 are generic names of motors included in the image forming apparatus 1. In addition to the main scanning motor 8 described above, the various motors 140 operate a sub-scanning motor for transporting the recording paper P in the sub-scanning direction, a paper feeding motor for feeding the recording paper P, and a maintenance mechanism 15. Maintenance motors and the like for.

  Here, a specific example of control by cooperation between the CPU 101 and the motor control unit 115 of the FPGA 102 will be described by taking operation control of the main scanning motor 8 as an example. First, the CPU 101 notifies the motor control unit 115 of the movement speed and distance of the carriage 5 together with an operation start instruction of the main scanning motor 8. Upon receiving this instruction, the motor control unit 115 generates a drive profile based on the information on the movement speed and the movement instruction notified from the CPU 101, and the encoder value supplied from the sensor processing unit 114 (the sensor signal of the encoder sensor 13). The PWM command value is calculated and output to the motor driver 106 while comparing with the value obtained by processing the above. When the predetermined operation is finished, the motor control unit 115 notifies the CPU 101 of the end of the operation. Here, the example in which the motor control unit 115 generates the drive profile has been described, but the CPU 101 may generate the drive profile and instruct the motor control unit 115. The CPU 101 also counts the number of printed sheets and counts the number of scans of the main scanning motor 8.

  The recording head control unit 116 passes the head drive data stored in the ROM 104 to the drive waveform generation circuit 107 and causes the drive waveform generation circuit 107 to generate a common drive waveform signal Vcom. The common drive waveform signal Vcom generated by the drive waveform generation circuit 107 is input to a recording head driver 210 described later mounted on the head relay substrate 200.

  Further, the recording head control unit 116 receives image data SD ′ after image processing from an image processing unit 310 (described later) provided on the image processing substrate 300, and each of the recording heads 6 is based on the image data SD ′. A mask control signal MN for selecting a predetermined waveform of the common drive waveform signal Vcom according to the size of the ink droplet ejected from the nozzle is generated. Then, the recording head control unit 116 transfers the image data SD ′, the synchronization clock signal SCK, the latch signal LT instructing to latch the image data, and the generated mask control signal MN to the recording head driver 210 ( (See FIG. 9).

  FIG. 8 is a diagram for explaining the configuration of the drive wave generation circuit 107. The drive waveform generation circuit 107 includes a DAC 121, a voltage amplification unit 122, and a current amplification unit 123, as shown in FIG. The head drive data transferred from the recording head control unit 116 is converted into an analog signal by the DAC 121 and is voltage amplified by the voltage amplification unit 122. The voltage-amplified driving waveform is input to the recording head driver 210 as a common driving waveform signal Vcom through a current amplifying unit 123 including a low impedance circuit including a SEEP circuit (NPN transistor and PNP transistor).

  The head relay substrate 200 is mounted on the carriage 5. As shown in FIG. 7, the recording head 6 and the recording head driver 210 are mounted on the head relay substrate 200. The recording head driver 210 drives the nozzles of the recording head 6 based on the common driving waveform signal Vcom input from the driving waveform generation circuit 107 and the image data SD ′ transferred from the recording head control unit 116, etc. Let the drops be ejected. 7 shows only one recording head driver 210, the recording head driver 210 exists for each recording head 6 mounted on the carriage 5 (mounted on the head relay substrate 200).

  FIG. 9 is a block diagram illustrating a configuration example of the recording head driver 210. As shown in FIG. 9, the recording head driver 210 includes a shift register 211, a latch circuit 212, a gradation decoder 213, a level shifter 214, and an analog switch 215.

  The shift register 211 receives the image data SD ′ and the synchronous clock signal SCK transferred from the recording head control unit 116. The latch circuit 212 latches each registration value of the shift register 211 by a latch signal LT transferred from the recording head control unit 116.

  The gradation decoder 213 decodes the value (image data SD ′) latched by the latch circuit 212 and the mask control signal MN, and outputs the result. The level shifter 214 converts the logic level voltage signal of the gradation decoder 213 to a level at which the analog switch 215 can operate.

  The analog switch 215 is a switch that is turned on / off by the output of the gradation decoder 213 given through the level shifter 214. The analog switch 215 is provided for each of the nozzles included in the recording head 6 and is connected to the individual electrode 83 of the piezoelectric element 70 corresponding to each nozzle. The analog switch 215 receives the common drive waveform signal Vcom from the drive waveform generation circuit 107. Therefore, the on / off of the analog switch 215 is switched according to the output of the gradation decoder 213 given through the level shifter 214, so that the piezoelectric waveform corresponding to each nozzle among the drive waveforms constituting the common drive waveform signal Vcom. The waveform applied to element 70 is selected. As a result, the size of the ink droplet ejected from the nozzle is controlled.

  As shown in FIG. 7, the image processing substrate 300 is provided with an image processing unit 310. The image processing unit 310 performs gradation processing for converting pixel values into density (luminance) for input image data, and converts the image data after gradation processing into a format corresponding to the recording head 6 of the serial head system. Rendering processing for conversion (data rearrangement) is performed, and image data SD (serial data) to be supplied to the recording head controller 116 is generated. In this embodiment, the image processing unit 310 detects the total number of drive nozzles and the number of continuous drive nozzles described above, generates correction data based on the detected total number of drive nozzles and the number of continuous drive nozzles, and uses the correction data. Thus, a function for correcting input image data is provided.

  FIG. 10 is a block diagram illustrating a functional configuration example of the image processing unit 310. As illustrated in FIG. 10, the image processing unit 310 includes an image I / F unit 311, a gradation processing unit 312, a frame memory 313, a rendering unit 314, a correction calculation unit 315, and a correction unit 316.

  The image I / F unit 311 receives image data to be printed and a synchronization clock signal SCK. Hereinafter, the image data input to the image I / F unit 311 is referred to as original image data in distinction from the image data KD and SD processed by the image processing unit 310. The original image data input to the image I / F unit 311 is transferred to the gradation processing unit 312 and temporarily stored in the frame memory 313. The synchronous clock signal SCK input to the image I / F unit 311 is passed to each unit in the image processing unit 310.

  The gradation processing unit 312 performs the above-described gradation processing on the original image data received from the image I / F unit 311, and passes the image data KD after the gradation processing to the rendering unit 314.

  The rendering unit 314 performs the above-described rendering process on the image data KD received from the gradation processing unit 312, and passes the rendered image data SD to the correction calculation unit 315.

  The correction calculation unit 315 detects the total number of drive nozzles and the number of continuous drive nozzles based on the image data SD and the synchronous clock signal SCK received from the rendering unit 314. Then, based on the detected total number of drive nozzles and the number of continuous drive nozzles, the correction calculation unit 315 has correction rates α1 to α192 for each nozzle of the recording head 6 (here, the number of nozzles of the recording head 6 is 192). Correction data including the generated correction data is generated, and the generated correction data is transferred to the correction unit 316. Details of a specific example of the correction calculation unit 315 will be described later.

  The correction unit 316 corrects the original image data temporarily stored in the frame memory 313 using the correction data received from the correction calculation unit 315. For example, the correction unit 316 reads the original image data from the frame memory 313 and multiplies the correction rates α1 to α192 for each nozzle included in the correction data for each pixel area of the original image data corresponding to the number of nozzles of the recording head 6. Thus, the original image data is corrected. A specific example of the process in which the correction unit 316 corrects the original image data will be described later.

  In the present embodiment, the gradation processing unit 312 performs gradation processing again on the original image data corrected by the correction unit 316, and the image data KD ′ after gradation processing is passed to the rendering unit 314. The rendering unit 314 performs rendering processing on the image data KD ′, and the rendered image data SD ′ is sent to the recording head control unit 116 of the FPGA 102.

  Next, a specific example of the correction calculation unit 315 will be described with reference to FIGS. 11 and 12. 11 is a block diagram illustrating a configuration example of the correction calculation unit 315. FIG. 12 illustrates the image data SD and the synchronization clock signal SCK input to the correction calculation unit 315, the driving nozzles of the recording head 6, and the non-printing conditions. It is a figure explaining the relationship with a drive nozzle.

  As shown in FIG. 11, the correction calculation unit 315 includes a detection unit 321, a correction data generation unit 322, and a table storage unit 323.

  The detection unit 321 detects the total number of drive nozzles and the number of continuous drive nozzles based on the image data SD and the synchronous clock signal SCK received from the rendering unit 314.

  As shown in FIG. 12, the image data SD input from the rendering unit 314 to the correction calculation unit 315 corresponds to the arrangement order of the nozzles in the recording head 6 and is at the H level for the driving nozzles and for the non-driving nozzles. This is serial data that becomes L level. The detection unit 321 counts the pulse width (the number of clocks in which the H level continues) of the image data SD, and holds the count value for each drive cycle of the recording head 6. Then, the detection unit 321 can detect the total number of drive nozzles by obtaining the total count value counted within one drive cycle of the recording head 6. For example, in the example of FIG. 12, one pulse of the image data SD corresponds to one nozzle, and the count value changes from 1 → 1 → 1 → 20 → 5. Therefore, the detection unit 321 detects 1 + 1 + 1 + 20 + 5 = 28 as the total number of drive nozzles, and outputs the total number of drive nozzles A (28).

  Further, the detection unit 321 counts the synchronization clock SCK for each driving cycle of the recording head 6, so that the position of the driving nozzle and the continuous driving region including the driving nozzle (the driving nozzle is continuous). The number of nozzles in the region) (the number of continuously driven nozzles) can be detected. For example, in the example of FIG. 12, the count values of the synchronous clock SCK corresponding to the continuous drive region in which 20 drive nozzles are continuous are 11 to 31. Therefore, the detection unit 321 detects that the 11th to 31st nozzles in the recording head 6 are the drive nozzles, and the number of continuous drive nozzles in that region is 20, and the number of continuous drive nozzles B (20, 11 to 31) are output. In the example of FIG. 12, the count value of the synchronous clock SCK corresponding to the continuous drive region in which five drive nozzles are continuous is 35 to 39. Therefore, the detection unit 321 detects that the 35th to 39th nozzles in the recording head 6 are the drive nozzles, and the number of continuous drive nozzles in that region is 5, and the number of continuous drive nozzles B (5, 35-39) is output.

  The correction data generation unit 322 generates correction data including a correction rate for each nozzle of the recording head 6 based on the total number A of drive nozzles detected by the detection unit 321 and the number B of continuous drive nozzles. The correction rate for each nozzle of the recording head 6 can be obtained by referring to a correction table stored in the table storage unit 323, for example.

  The table storage unit 323 stores, for example, a correction table in which a correction rate is determined with each of the nozzle position, the total number of drive nozzles, and the number of continuous drive nozzles in the recording head 6 as dimensions. This correction table is created through, for example, a prior verification experiment and stored in the table storage unit 323 in advance. FIG. 13 is a diagram illustrating an example of a correction table stored in the table storage unit 323. In FIG. 13, for the sake of convenience, the three-dimensional correction table stored in the table storage unit 323 is represented as a set of two-dimensional tables for each nozzle position (only the α11 table, the α12 table, and the α31 table are illustrated). ing.

  Note that the positive and negative correction rates corresponding to the nozzles at the same position are switched between the forward path and the backward path when the carriage 5 reciprocates in the main scanning direction, but a forward path correction table and a backward path correction table are prepared. The correction table referred to in the forward path and the return path may be switched, or the correction rate may be reversed in circuit between the forward path and the return path.

  For example, the correction data generation unit 322 refers to the correction table shown in FIG. 13 to determine the correction rate of each drive nozzle corresponding to the total number A of drive nozzles detected by the detection unit 321 and the number B of continuous drive nozzles. For example, in the example of FIG. 12, the detection unit 321 sends the correction data generation unit 322 the total number of drive nozzles A (28), the number of continuous drive nozzles B (20, 11 to 31), and the number of continuous drive nozzles B (5 , 35-39). The correction data generation unit 322 refers to, for example, the correction table illustrated in FIG. 13 for the 11th to 31st nozzles in the recording head 6 and corresponds to the total number of drive nozzles of 28 and the number of continuous drive nozzles of 20. Correction rates α11 to α31 are acquired. The correction data generation unit 322 refers to, for example, the correction table shown in FIG. 13 for each of the 35th to 39th nozzles arranged in the recording head 6, and sets the total number of drive nozzles to 28 and the number of continuous drive nozzles to 5. Corresponding correction factors α35 to α39 are acquired. It should be noted that the correction rate may be set to 1 because there is no need to correct the non-driven nozzles.

  As described above, the correction data generation unit 322 obtains correction rates α1 to α192 (when the number of nozzles of the recording head 6 is 192) for each nozzle of the recording head 6, and includes the correction rates α1 to α192 for each nozzle. Generate correction data. The correction data generated by the correction data generation unit 322 is passed to the correction unit 316. Then, the correction unit 316 corrects the original image data using the correction rates α1 to α192 for each nozzle, and the nozzles of the recording head 6 are driven according to the image data SD ′ obtained from the corrected original image data. Is done. Thereby, the problem of the mutual interference of the nozzles described above can be solved, the ejection characteristics of the nozzles can be stabilized, and high-quality image formation can be performed.

  The correction table illustrated in FIG. 13 is a table in which correction ratios are determined by using the nozzle position, the total number of drive nozzles, and the number of continuous drive nozzles in the recording head 6 as dimensions. May be the position of the area to which each nozzle belongs in the area of the recording head 6 that is divided in advance. For example, the recording head 6 is divided into three regions, ie, a region on one end side, a central region, and a region on the other end side, and each region corresponds to the total number of drive nozzles and the number of continuous drive nozzles. You may use the correction table of the structure which defined the correction factor. In this case, the same correction factor is given to the drive nozzles belonging to the same region, but the correction effect can be sufficiently expected. In this case, the table size can be reduced to reduce necessary memory resources.

  In the case where a plurality of print modes having different moving speeds of the carriage 5 (moving speeds of the recording head 6) can be specified, the above-described correction table is prepared for each print mode and stored in the table storage unit 323. Alternatively, a correction table corresponding to the designated print mode may be selected to obtain the correction rate for each nozzle. Examples of print modes in which the moving speed of the recording head 6 is different include a high-speed print mode in which priority is given to the print speed and a high-quality print mode in which priority is given to the image quality. When the correction rate is determined in accordance with such a printing mode, the original image data can be corrected so as to absorb the variation in the ejection characteristics of the nozzle due to the difference in the moving speed of the recording head 6. High-quality image formation can be performed.

  Further, the above-described correction table is prepared for each environmental temperature with different ink ejection speed Vj and stored in the table storage unit 323, and the correction table corresponding to the environmental temperature detected by the above-described temperature and humidity sensor is selected. Thus, the correction rate for each nozzle may be obtained. When configured in this manner, the original image data can be corrected so as to absorb the variation in the ejection characteristics of the nozzles due to the difference in the environmental temperature, and further high-quality image formation can be performed.

  Here, a processing procedure in the image processing unit 310 of the present embodiment will be described with reference to FIG. FIG. 14 is a flowchart showing a flow of a series of processing by the image processing unit 310.

  When the processing shown in the flowchart of FIG. 14 is started, first, the image I / F unit 311 inputs original image data (step S101). The original image data input by the image I / F unit 311 is transferred to the gradation processing unit 312 and temporarily stored in the frame memory 313 (step S102).

  Next, the gradation processing unit 312 performs gradation processing on the original image data received from the image I / F unit 311 and passes the image data KD after the gradation processing to the rendering unit 314 (step S103).

  Next, the rendering unit 314 performs a rendering process on the image data KD received from the gradation processing unit 312, and passes the rendered image data SD to the correction calculation unit 315 (step S104).

  Next, the detection unit 321 of the correction calculation unit 315 detects the total number of driving nozzles and the number of continuous driving nozzles based on the image data SD received from the rendering unit 314 and the synchronous clock signal SCK, and the total number of detected driving nozzles. The number of continuously driven nozzles is transferred to the correction data generation unit 322 (step S105).

  Next, the correction data generation unit 322 refers to the correction table stored in the table storage unit 323 based on the total number of drive nozzles and the number of continuous drive nozzles received from the detection unit 321, and the correction rate for each nozzle of the recording head 6. Is generated, and the correction data is transferred to the correction unit 316 (step S106).

  Next, the correction unit 316 reads the original image data temporarily stored in the frame memory 313 (step S107), and uses the correction data received from the correction calculation unit 315 to read the original image data read from the frame memory 313. Correction is performed (step S108). The original image data corrected by the correction unit 316 is transferred to the gradation processing unit 312 again.

  Next, the gradation processing unit 312 performs gradation processing on the original image data after correction received from the correction unit 316, and passes the image data KD ′ after gradation processing to the rendering unit 314 (step S109). .

  Next, the rendering unit 314 performs a rendering process on the image data KD ′ received from the gradation processing unit 312 (step S110), and the rendered image data SD ′ is sent to the recording head control unit 116 of the FPGA 102. Transfer (step S111). Thus, a series of processes shown in the flowchart of FIG.

  When the image data SD ′ is transferred from the image processing unit 310 to the recording head control unit 116 of the FPGA 102, the nozzles of the recording head 6 are driven by the recording head driver 210 in accordance with the image data SD ′. An image is formed on the recording paper P by ejecting the ink droplets.

  As described above, the image forming apparatus 1 according to the present embodiment detects the total number of drive nozzles and the number of continuous drive nozzles based on image data to be printed, and based on the detected total number of drive nozzles and the number of continuous drive nozzles. To generate correction data. Then, the image data to be printed is corrected using the correction data, and the nozzle of the recording head 6 is driven according to the corrected image data, thereby forming an image. Therefore, according to the image forming apparatus 1 of the present embodiment, it is possible to accurately correct the influence of the mutual interference of the nozzles of the recording head 6 and perform high-quality image formation.

  In particular, in the image forming apparatus 1 of the present embodiment, correction data including correction rates α1 to α192 for each nozzle of the recording head 6 is generated, and the original image data is corrected using the correction rates α1 to α192 for each nozzle. Therefore, the original image data can be corrected with high accuracy in units of one nozzle.

  Here, an example of a method for correcting the original image data will be described by taking as an example a case where correction of +0.6 dots is necessary for the pixel value n of a pixel in the original image data (when the correction rate is +0.6 dots). explain. This correction can be performed using, for example, an interpolation calculation method called a bicubic method. FIG. 15 is a schematic diagram conceptually showing image correction by the bicubic method.

When correction of +0.6 dots (d in FIG. 15) is necessary for the pixel value n of a pixel in the original image data, the pixel value n to be corrected and three neighboring pixel values (n−1) , N + 1, n + 2) into the following (1), the corrected pixel value n ′ can be obtained. That is, a pixel having the original image data is converted to +0... By the interpolation operation of the following equation (1) using the pixel value n to be corrected and the three neighboring pixel values (n−1, n + 1, n + 2). The pixel value n ′ when shifted by 6 dots can be obtained.
n ′ = W1 × (n−1) + W2 × n + W3 × (n + 1) + W4 × (n + 2) (1)

  The bicubic method is a technique known as a method for performing an interpolation operation on pixel values when an image is enlarged. For example, in the case of performing double density processing for enlarging an image twice in both the main scanning direction and the sub-scanning direction, the interpolation calculation according to the above equation (1) is performed with W1 = W4 = −0.125 and W2 = W3 = 0.625. As a result, the pixel value n ′ of a new sampling point at a position shifted by +0.5 dots from the pixel having the pixel value n can be obtained. Here, if the values of the coefficients W1 to W4 in the above equation (1) are changed, the pixel value at an arbitrary position can be obtained. That is, by changing the coefficients W1 to W4 according to the correction rate α (for example, +0.6 dots) for a certain pixel in the original image data, the pixel value when the pixel in the original image data is shifted by the correction rate α is obtained. be able to.

  This embodiment can be understood as shown below. That is, the image forming apparatus 1 according to the present embodiment includes a recording head 6 having a plurality of nozzles that eject ink droplets, and drive nozzles that are the total number of nozzles that are driven at the same drive timing based on input image data. Based on the detection unit 321 that detects the total number and the number of continuous drive nozzles that is the number of nozzles in a continuous drive region in which nozzles driven at the same drive timing are continuous, and the total number of drive nozzles and the number of continuous drive nozzles A correction data generation unit 322 that generates correction data, a correction unit 316 that corrects input image data using the correction data, and the recording head according to the image data corrected by the correction unit 316. And a recording head driver 210 that drives the six nozzles.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied with various modifications and changes in the implementation stage without departing from the scope of the invention. For example, in the above-described embodiment, the image processing board 300 is provided separately from the main control board 100, and the image processing unit 310 is mounted on the image processing board 300. A configuration realized by a program executed by the CPU 101 mounted on the main control board 100 may be used. In this case, a program for realizing the function of each unit in the image processing unit 310 is provided by being incorporated in advance in the ROM 104, for example. The CPU 101 uses the RAM 103 as a work area, reads this program from the ROM 104, and executes it. Thereby, the function of each unit in the image processing unit 310 is generated on the RAM 103.

  Further, the program for realizing the function of each unit in the image processing unit 310 may be provided by being recorded on a computer-readable recording medium in a file in an installable format or an executable format, for example. Good. In addition, a program for realizing the function of each unit in the image processing unit 310 may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network.

  Further, the function of each unit in the image processing unit 310 may be provided in, for example, the FPGA 102 mounted on the main control board 100.

  The function of the image processing unit 310 described above may be provided to an external computer (information processing apparatus) connected to the image forming apparatus. For example, an image forming system is known in which an information processing device called DFE (Digital Front End) is connected to an image forming apparatus, and in this DFE, preprocessing of image data given to the image forming apparatus and operation control of the image forming apparatus are performed. It has been. The DFE in this image forming system may have the function of the image processing unit 310 described above.

  FIG. 16 is a block diagram illustrating a configuration example of such an image forming system. The image forming system shown in FIG. 16 includes an image forming apparatus 400 and a DFE 500 connected to the image forming apparatus 400.

  The image forming apparatus 400 includes an engine 401, an operation display unit 402, an I / F unit 403, other I / F units 404, and the like, and these units are connected by a bus. The DFE 500 includes a CPU 501, a memory unit 502, an image processing unit 503, a communication I / F unit 504, an I / F unit 505, and the like, and these units are connected by a bus. The memory unit 502 includes a ROM 511, a RAM 512, a hard disk (HDD) 513, and the like.

  The image forming apparatus 400 and the DFE 500 are connected by an I / F unit 403 and an I / F unit 505. The image forming apparatus 400 operates the engine 401 based on the image data sent from the DFE 500 under the control of the DFE 500, and forms an image on the recording paper. The engine 401 performs image formation by an ink jet method, and includes a configuration corresponding to the recording head 6 and the recording head driver 210 of the image forming apparatus 1 described above. The operation display unit 402 includes various operation keys and a display such as an LCD (Liquid Crystal Display). Various operations necessary for the operation of the image forming apparatus 400 are performed by the operation keys. Various information notified to the user is displayed and output on the display. The other I / F unit 404 is used for connection of an expansion unit.

  The DFE 500 stores a control program for controlling the operation of the image forming apparatus 400 and necessary data in the ROM 511 or the HDD 513. The CPU 501 controls the operation of the image forming apparatus 400 based on a program in the ROM 511 or the HDD 513, whereby basic processing as the image forming apparatus 400 is executed.

  The communication I / F unit 504 is connected to a host PC or the like via a line such as a network, and receives image data that causes the image forming apparatus 400 to form an image. In addition, the image data received by the image processing unit 503 and the communication I / F unit 504 are subjected to various image processing necessary for image formation by the engine 401 of the image forming apparatus 400. The image processing unit 503 is provided with the function of the image processing unit 310 of the image forming apparatus 1 described above. Further, the function of the image processing unit 310 of the image forming apparatus 1 may be realized by the CPU 501 executing a program in the ROM 511 or the HDD 513.

  In the image forming system illustrated in FIG. 16, the operation of the image forming apparatus 400 is controlled by the DFE 500, but the image forming operation in the image forming apparatus 400 is autonomously controlled by the image forming apparatus 400. The configuration may be such that only preprocessing of data is performed.

  In the above-described embodiment, the image forming apparatus 1 including the serial head type recording head 6 has been described. However, the present invention can also be effectively applied to an image forming apparatus including a line head type recording head. is there.

  FIG. 17 is a diagram illustrating a configuration example of a main part of an image forming apparatus 600 including a line head type recording head. In the image forming apparatus 600 shown in FIG. 17, a plurality of recording heads 601 are connected in the main scanning direction so as to cover the entire width of the recording paper P as a whole. For this reason, the recording head 601 does not move in the main scanning direction.

  The recording head 601 is arranged and fixed with high accuracy with respect to the adjustment plate 602, and constitutes a line head for each ink color of yellow (Y), magenta (M), cyan (C), and black (Bk). Each line head is electrically connected to the drive control board 604 via a flat cable 603. The adjustment plate 602 is supported on the recording paper P with a predetermined gap so that the ejection surface (nozzle surface) of the recording head 601 faces the recording paper P to be conveyed.

  Each recording head 601 constituting the line head includes a piezoelectric element in the same manner as the recording head 6 described above, and the ink droplets are ejected from the nozzles by driving the piezoelectric element according to a common drive waveform signal or image data. An image is formed on the recording paper P by discharging. The drive control board 604 is provided with a head drive unit similar to the print head driver 210 described above, and the nozzles of the print head 601 are controlled by controlling the operation of the head drive unit according to the common drive waveform signal and image data. Ink droplets are ejected from. The image data used for the operation control of the head drive unit is image data corrected based on the total number of drive nozzles and the number of continuous drive nozzles, as in the image forming apparatus 1 described above. Note that in the image forming apparatus 600 including the line head type recording head, it is not necessary to rearrange the data in a serial type, so that the rendering process by the rendering unit 314 described above is unnecessary.

  In the image forming apparatus 600 including the line head type recording head, the image corrected based on the total number of driving nozzles and the number of continuous driving nozzles is the same as in the image forming apparatus 1 including the serial head type recording head 6 described above. By driving the nozzles of the recording head 601 according to the data, the influence of mutual interference between the nozzles of the recording head 601 can be accurately corrected, and high-quality image formation can be performed.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 6 Recording head 116 Recording head control part 210 Recording head driver 310 Image processing part 313 Frame memory 315 Correction calculating part 316 Correction part 321 Detection part 322 Correction data generation part 323 Table memory | storage part 400 Image forming apparatus 500 DFE
503 Image processing unit

JP 2013-199025 A

Claims (10)

A recording head having a plurality of nozzles for discharging droplets;
Based on the input image data, the total number of drive nozzles that is the total number of nozzles that are driven at the same drive timing, and the continuous drive nozzle that is the number of nozzles in the continuous drive region where nozzles that are driven at the same drive timing are continuous A detection unit for detecting the number;
A correction data generation unit that generates correction data based on the total number of drive nozzles and the number of continuous drive nozzles;
A correction unit that corrects input image data using the correction data;
An image forming apparatus comprising: a head drive unit that drives nozzles of the recording head in accordance with the image data corrected by the correction unit.   The image forming apparatus according to claim 1, wherein the correction data generation unit generates the correction data including a correction rate for each nozzle included in the recording head. A storage unit that stores a correction table in which a correction rate is determined with each of the position of the nozzle in the recording head, the total number of driving nozzles, and the number of continuous driving nozzles as dimensions;
The image forming apparatus according to claim 2, wherein the correction data generation unit obtains a correction rate for each nozzle of the recording head with reference to the correction table.   The image forming apparatus according to claim 3, wherein a position of the nozzle in the recording head is a position of an area to which each nozzle belongs in the area of the recording head divided in advance. The storage unit stores the correction table for each print mode in which the moving speed of the recording head is different,
The image forming apparatus according to claim 3, wherein the correction data generation unit obtains a correction rate for each nozzle of the recording head with reference to the correction table corresponding to the designated print mode. A temperature detection unit for detecting the environmental temperature;
The storage unit stores the correction table for each environmental temperature with different droplet discharge speeds,
The image forming apparatus according to claim 3, wherein the correction data generation unit obtains a correction rate for each nozzle of the recording head with reference to the correction table corresponding to the detected environmental temperature.   The image forming apparatus according to claim 1, wherein the recording head is a serial head type recording head.   The image forming apparatus according to claim 1, wherein the recording head is a line head type recording head. An image forming system including an image forming apparatus and an information processing apparatus connected to the image forming apparatus,
The image forming apparatus includes:
A recording head having a plurality of nozzles for discharging droplets;
A head driving unit that drives the nozzles of the recording head according to image data,
The information processing apparatus includes:
Based on the input image data, the total number of drive nozzles that is the total number of nozzles that are driven at the same drive timing, and the continuous drive nozzle that is the number of nozzles in the continuous drive region where nozzles that are driven at the same drive timing are continuous A detection unit for detecting the number;
A correction data generation unit that generates correction data based on the total number of drive nozzles and the number of continuous drive nozzles;
A correction unit that corrects input image data using the correction data, and
The image forming system, wherein the head driving unit drives the nozzles of the recording head in accordance with the image data corrected by the correcting unit. A program executed in an image forming apparatus comprising: a recording head having a plurality of nozzles for discharging droplets; and a head driving unit that drives the nozzles of the recording head according to image data,
In the image forming apparatus,
Based on the input image data, the total number of drive nozzles that is the total number of nozzles that are driven at the same drive timing, and the continuous drive nozzle that is the number of nozzles in the continuous drive region where nozzles that are driven at the same drive timing are continuous The ability to detect numbers and
A function of generating correction data based on the total number of drive nozzles and the number of continuous drive nozzles;
A program for correcting input image data using the correction data, and causing the head driving unit to drive the nozzles of the recording head according to the corrected image data.

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