JP2009056746A - Image forming device and method for correcting impact position deviation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a problem that, when a pattern for detecting impact position deviation is formed on a conveyor belt, an irregular state of recording head nozzles prevents a correct pattern from being formed and causes reduction in the accuracy for detecting the pattern and the accuracy for correcting the impact position deviation. <P>SOLUTION: A recording head 24 for discharging droplets is mounted on a carriage 23 to form an image on a sheet 12 to be conveyed. A pattern 400 for detecting impact position deviation (a reference pattern 400a and a pattern 400b to be measured) is formed on a conveyor belt 31. Each of the patterns 400a and 400b is read by a pattern reading sensor 401 mounted on the carriage 23. When the impact position deviation of the droplets from the recording head 24 is corrected based on the reading result, the pattern 400 is formed after performing blank discharge from the recording head 24 for forming the pattern 400. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a recording head that discharges droplets and a method for correcting the landing position of a droplet discharged from the recording head.

  As an image forming apparatus such as a printer, a facsimile machine, a copying machine, and a multifunction machine of these, for example, a recording head composed of a liquid discharge head (droplet discharge head) that discharges liquid droplets of a recording liquid (liquid) is used. (Hereinafter also referred to as “paper”, the material is not limited, and a recording medium, a recording medium, a transfer material, recording paper, etc. are also used synonymously.) In some cases, the ink is attached to a sheet to form an image (recording, printing, printing, and printing are also used synonymously).

  In the present application, “image forming apparatus” means an apparatus that forms an image by discharging liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc. "Image formation" means not only giving images with meanings such as characters and figures to the medium, but also giving images without meaning such as patterns to the medium (simply ejecting droplets). It also includes a textile printing device, a device for forming metal wiring, and the like. The “ink” is not particularly limited as long as it is a liquid capable of forming an image.

  In such a liquid ejection type image forming apparatus, in particular, when a carriage equipped with a recording head for ejecting liquid droplets is reciprocated to perform printing in both forward and backward directions, the printed image is a ruled line. In such a case, there is a problem that the displacement of the ruled line is likely to occur on the forward path and the return path. In addition, there is a problem in that color misregistration easily occurs when different colors are superimposed.

  For this reason, in general, in an inkjet recording apparatus or the like, a test chart for adjusting the landing position deviation is output, and the user selects and inputs an optimum value, and adjusts the discharge timing based on the input result. However, there are individual differences in how to read the test chart, and it is possible that a data entry error may occur due to unfamiliarity with the operation. It is done.

Thus, conventionally, Patent Document 1 describes that a test pattern is formed and the test pattern is read by a sensor.
JP-A-2005-262813

In Patent Document 2, a test pattern is formed on a print medium or a belt, the test pattern is read by a sensor, and an optical sensor detection of a uniform surface state provided on the medium surface adjacent to the pattern is obtained from the obtained sensor output. It is described that the detection accuracy is improved by removing the level fluctuation of the light reception output signal in the region and reducing the disturbance.
JP 2005-67093 A

Patent Document 3 describes that a test pattern is formed on a recording sheet and the test pattern is read by a sensor.
JP 2004-314361 A

In addition, in Patent Document 4, a print start point mark indicating the print start position of the next plurality of lines in the main scan is recorded on the transport belt mechanism, and the next plurality of print heads are printed based on the print start point mark. It describes that the print start position of the line is positioned.
JP 2003-218683 A

Patent Document 5 describes that the phase of fluctuations in the periodic torque of the transport roller is stored, and if there is a deviation of a predetermined amount or more, the motor-off signal timing is corrected to improve the sub-scanning stop position accuracy. .
JP 2006-272892 A

  However, as described above, when a test pattern is formed on a conveyance belt or a medium and read by a sensor, for example, depending on the combination of the color of the conveyance belt and the color of the ink, the color difference is small, so it is difficult to read accurately. is there. Therefore, in order to accurately perform color detection, a configuration such as detection using a light source whose wavelength is changed for each color is necessary, and in practice, in the conventional technology, a test pattern is formed on the transport belt, This cannot be read accurately.

  For example, when the transport belt is an electrostatic adsorption belt and is formed of an insulating layer on the front surface and a middle resistance layer on the back surface, and carbon is kneaded to obtain conductivity of the middle resistance layer Since the color on the appearance of the belt is black, even if it is attempted to detect a pattern only by reflection by color, it cannot be distinguished from black ink, and the pattern cannot be detected.

  Therefore, the present applicant first forms a pattern composed of independent ink droplets on a pattern forming member having water repellency, and takes advantage of the characteristic that the ink droplets become hemispherical, and emits light of a single wavelength. It has been proposed to detect the position of the pattern and to detect the positional deviation accurately by irradiating the ink droplets and detecting the attenuation amount of the regular reflection light amount due to the pattern being formed.

  In addition, even if the pattern for detecting droplet landing position deviation is formed on the transport belt in this way so that the pattern can be read accurately, the state of the nozzles of the recording head at the time of pattern formation is uneven. Then, there is another problem that variations occur in the formed pattern and an accurate pattern cannot be detected.

  The present invention has been made in view of the above-described other problems, and improves the pattern formation accuracy by aligning the ejection state of the recording head during pattern formation, and improves the pattern detection accuracy and the landing position deviation correction accuracy. Objective.

  In order to solve the above problems, an image forming apparatus according to the present invention includes a pattern forming member in which an image is formed on a transported recording medium by mounting a recording head for ejecting droplets on a carriage. Further, a pattern forming unit for forming a pattern for detecting landing position deviation, a pattern reading unit for reading each pattern, and a landing position deviation of a droplet from the recording head based on a reading result of the pattern reading unit. A configuration is provided that includes a correcting unit and a unit that performs idle ejection from the recording head that forms the pattern before the pattern is formed.

  Here, the landing position deviation detection pattern may be composed of a plurality of independent droplets. In this case, the pattern reading means includes a light emitting means for irradiating the landing position deviation detection pattern with light, and a light receiving means for receiving regular reflection light from the landing position deviation detection pattern; it can. Further, it is possible to adopt a configuration in which the droplets ejected in the idle cannot be read by the pattern reading unit.

  Further, the idle ejection pattern formed of the idle ejected droplets may have a line shape. In this case, it is possible to adopt a configuration in which the idle ejection pattern composed of the droplets that are ejected idle is disposed obliquely with respect to the landing position deviation detection pattern. In addition, the blank ejection pattern composed of the droplets ejected in the blank can be a solid pattern in which the droplets are not independent.

  Further, when the landing position deviation correction is performed, the idle ejection operation before image formation is not performed.

  The landing position deviation correction method according to the present invention is a method for correcting the landing position of a droplet discharged from a recording head, and before forming a landing position deviation detection pattern on a pattern forming member, Based on the pattern reading result, the step of performing idle ejection from the recording head for forming a pattern, the step of forming the pattern for detecting the landing position deviation on the pattern forming member, the step of reading each pattern, and the pattern reading result And the step of correcting the deviation of the landing position of the droplets from the recording head.

  According to the image forming apparatus according to the present invention and the landing position deviation correction method according to the present invention, before the pattern for landing position deviation detection is formed, idle ejection is performed from the recording head that forms the pattern. In addition, the discharge state of the recording head that performs pattern formation can be made uniform, pattern formation accuracy is improved, and pattern detection accuracy and landing position deviation correction accuracy are improved.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. An outline of an example of an image forming apparatus according to the present invention that implements the landing position deviation correction method according to the present invention will be described with reference to FIGS. 1 is a schematic configuration diagram showing the overall configuration of the image forming apparatus, FIG. 2 is an explanatory plan view of an image forming unit and a sub-scanning conveying unit of the apparatus, and FIG. 3 is an explanatory side view showing a partially transmissive state. It is.

  This image forming apparatus includes an image forming unit (means) 2 for forming an image while conveying a sheet and a sub-scanning conveying unit (means) 3 for conveying a sheet inside the apparatus main body 1 (enclosure). And the like, and a sheet 5 is fed one by one from a sheet feeding unit (means) 4 including a sheet feeding cassette provided at the bottom of the apparatus body 1, and the sheet 5 is fed by the sub-scanning conveying unit 3 to the image forming unit 2. The image forming unit 2 ejects liquid droplets onto the paper 5 while forming (recording) a desired image while conveying it at a position opposite to the image forming unit 2, and then forms it on the upper surface of the apparatus main body 1 through the paper discharge conveying unit (means) 7. The paper 5 is discharged onto the discharged paper discharge tray 8.

  The image forming apparatus also has an image reading unit (scanner) for reading an image above the discharge tray 8 above the apparatus main body 1 as an input system for image data (print data) formed by the image forming unit 2. Part) 11. The image reading unit 11 includes a scanning optical system 15 including an illumination light source 13 and a mirror 14 and a scanning optical system 18 including mirrors 16 and 17. The scanned document image is read as an image signal by the image reading element 20 disposed behind the lens 19, and the read image signal is digitized and subjected to image processing to print the image-processed print data. be able to.

  Here, as shown in FIG. 2, the image forming unit 2 of the image forming apparatus holds the carriage 23 in a cantilevered manner with a guide rod 21 and a guide rail (not shown) so as to be movable in the main scanning direction. In 27, movement scanning is performed in the main scanning direction via a timing belt 29 spanned between the driving pulley 28A and the driven pulley 28B.

  Here, as shown in FIG. 2, the image forming section 2 of the image forming apparatus includes a carriage guide (guide rod) 21 that is a main guide member horizontally mounted between the front side plate 101F and the rear side plate 101R and the rear side. A guide stay 22 which is a slave guide member provided on the stay 101B side holds the carriage 23 so as to be movable in the main scanning direction, and a timing belt 29 spanned between the driving pulley 28A and the driven pulley 28B by the main scanning motor 27. Through the main scanning direction.

  On the carriage 23, recording heads 24k1 and 24k2 each composed of two droplet discharge heads for discharging black (K) ink, cyan (C) ink, magenta (M) ink, and yellow (Y). A total of five droplet ejection heads, recording heads 24c, 24m, and 24y each composed of one droplet ejection head that ejects ink (when not distinguishing colors and collectively referred to as “recording head 24”), are included. A shuttle type is mounted, in which the carriage 23 is moved in the main scanning direction, and droplets are ejected from the recording head 24 while the paper 5 is fed in the paper transporting direction (sub-scanning direction) by the sub-scanning transport unit 3. Yes.

  In addition, a sub tank 25 is mounted on the carriage 23 in order to supply a recording liquid of a required color to each recording head 24. On the other hand, as shown in FIG. 1, recording liquid containing black (K) ink, cyan (C) ink, magenta (M) ink, and yellow (Y) ink from the front of the apparatus main body 1 to the cartridge mounting portion 26A. Each color ink cartridge 26 can be detachably mounted, and ink (recording liquid) is supplied from each color ink cartridge 26 to each color sub-tank 25 via a tube (not shown). The black ink is supplied from one ink cartridge 26 to the two sub tanks 25.

  The recording head 24 uses a piezoelectric element as a pressure generating means (actuator means) for pressurizing the ink in the ink flow path (pressure generation chamber) to deform the vibration plate that forms the wall surface of the ink flow path. A so-called piezo type that discharges ink droplets by changing the volume in the flow channel, or discharges ink droplets with a pressure generated by heating the ink in the ink flow channel using a heating resistor to generate bubbles. The so-called thermal type, the diaphragm that forms the wall surface of the ink flow path and the electrode are placed opposite to each other, and the diaphragm is deformed by the electrostatic force generated between the vibration plate and the electrode, thereby the ink flow path inner volume It is possible to use an electrostatic type or the like that discharges ink droplets by changing the above.

  Further, a linear scale 128 having a slit formed between the front side plate 101F and the rear side plate 101R along the main scanning direction of the carriage 23, and a transmission type photo for detecting the slit of the linear scale 128 on the carriage 23. An encoder sensor 129 made up of sensors is provided, and the linear scale 128 and the encoder sensor 129 constitute a linear encoder that detects the movement of the carriage 23.

  Further, on one side of the carriage 23, a reading means (detection) constituted by a reflection type photosensor including a light emitting means and a light receiving means for reading a landing position deviation detection pattern (referred to as an adjustment pattern) according to the present invention. A pattern reading sensor 401, and an adjustment pattern for detecting a landing position deviation formed on the conveyor belt 31 is read by the pattern reading sensor 401 as will be described later. Further, on the other side surface of the carriage 23, a sheet material detection sensor (tip detection sensor) 330, which is a sheet material detection means for detecting the leading edge of the conveyed member to be conveyed, is provided.

  Further, a maintenance / recovery mechanism (device) 121 for maintaining and recovering the state of the nozzles of the recording head 24 is disposed in a non-printing area on one side of the carriage 23 in the scanning direction. The maintenance / recovery mechanism 121 is a cap member for capping each nozzle surface 24a of the five recording heads 24, and includes one suction cap 122a that also serves as a moisture retention, and four moisture retention caps 122b to 122e. A wiper blade 124, which is a wiping member for wiping the nozzle surface 24a of the recording head 24, and an idle ejection receiver 125 for performing idle ejection are disposed. Further, an idle discharge receptacle 126 for performing idle discharge is disposed in the non-printing area on the other side of the carriage 23 in the scanning direction. Openings 127 a to 127 e are formed in the idle discharge receptacle 126.

  As shown in FIG. 3, the sub-scanning conveyance unit 3 is a driving roller for conveying the paper 5 fed from below by changing the conveyance direction by approximately 90 degrees and facing the image forming unit 2. An endless transport belt 31 laid between the transport roller 32 and a driven roller 33 which is a tension roller, and a charging means to which a high voltage as an alternating voltage is applied from a high voltage power source in order to charge the surface of the transport belt 31 The charging roller 34, the guide member 35 that guides the conveyance belt 31 in the opposed region of the image forming unit 2, and the holding member 136 are rotatably held, and the sheet 5 is conveyed at a position facing the conveyance roller 32. The pressure rollers 36 and 37 that are pressed against the belt 31, the guide plate 38 that presses the upper surface side of the paper 5 on which the image is formed by the image forming unit 2, and the paper 5 on which the image is formed are conveyed to the conveyor belt 31. And a separation claw 39 for al separation.

  The conveyance belt 31 is configured to circulate in the sheet conveyance direction (sub-scanning direction) when the conveyance roller 32 is rotated via the timing belt 132 and the timing roller 133 by a sub-scanning motor 131 using a DC brushless motor. is doing. For example, as shown in FIG. 4, the transport belt 31 is made of a pure resin material that is not subjected to resistance control, for example, a surface layer 31A that is a sheet adsorbing surface formed of ETFE pure material, and the same material as the surface layer 31A. Although it has a two-layer structure with a back layer (medium resistance layer, earth layer) 31B subjected to resistance control by carbon, it is not limited to this, and a one-layer structure or a structure of three or more layers may be used.

  Further, between the driven roller 33 and the charging roller 34, a cleaning means for removing paper dust and the like adhering to the surface of the conveyor belt 31 from the upstream side in the moving direction of the conveyor belt 31 is brought into contact with the surface of the conveyor belt 31. Mylar (paper dust removing means) 191 made of a PET film as an abutting member, a brush-shaped cleaning brush 192 that also abuts on the surface of the conveyor belt 31, and a static elimination brush 193 for removing charges on the surface of the conveyor belt 31 Has

  Further, a high-resolution code hole 137 is attached to the shaft 32a of the transport roller 32, and an encoder sensor 138 that is a transmission type photosensor that detects a slit 137a formed in the code wheel 137 is provided. The encoder sensor 138 constitutes a rotary encoder.

  The paper feeding unit 4 is detachable from the apparatus main body 1 and separates the paper 5 in the paper feeding cassette 41 one by one from the paper feeding cassette 41 which is a storing means for stacking and storing a large number of papers 5. A sheet feeding roller 42 and a friction pad 43 for feeding out and a registration roller pair 44 for registering the sheet 5 to be fed are provided.

  The paper feed unit 4 includes a manual feed tray 46 for stacking and storing a large number of sheets 5, a manual feed roller 47 for feeding the sheets 5 from the manual feed tray 46 one by one, and the apparatus main body 1. On the lower side, an optional paper feed cassette and a vertical transport roller 48 for transporting the paper 5 fed from the duplex unit are provided. Members for feeding the paper 5 to the sub-scanning conveying unit 3 such as the paper feeding roller 42, the registration roller 44, the manual feeding roller 47, and the vertical conveying roller 48 are a paper feeding made of an HB type stepping motor via an electromagnetic clutch (not shown). The motor (drive means) 49 is rotationally driven.

  The paper discharge transport unit 7 includes three transport rollers 71a, 71b, 71c (referred to as “transport roller 71” when not distinguished) and the paper 5 separated by the separation claw 39 of the sub-scan transport unit 3 and this. Spurs 72a, 72b, 72c (also referred to as "spurs 72") facing the, and a reversing roller pair 77 and a reversing discharge roller pair 78 for reversing the sheet 5 and feeding it to the discharge tray 8 face down. I have. Also,

  Further, in order to perform manual sheet feeding, as shown in FIG. 1, a single sheet feeding tray 141 can be opened and closed with respect to the apparatus main body 1 on one side of the apparatus main body 1 (can be turned over). In the case of manually feeding one sheet, the one-sheet manual feed tray 141 is lowered to the position indicated by the phantom line. The sheet 5 manually fed from the one-sheet manual sheet feeding tray 141 is guided by the upper surface of the guide plate 110 and linearly between the transport roller 32 and the pressure roller 36 of the sub-scan transport section 3 as it is. Can be plugged in.

  On the other hand, a straight discharge tray 181 is provided on the other side of the apparatus main body 1 so as to be openable and closable (can be opened and lowered) in order to discharge the sheet 5 on which the image has been formed straight up face up. By opening (turning over) the straight paper discharge tray 181, the paper 5 sent out from the paper discharge conveyance unit 7 can be discharged linearly to the straight paper discharge tray 181.

Next, an outline of the control unit of the image forming apparatus will be described with reference to the block diagram of FIG.
The control unit 300 retains data even when the power of the apparatus is shut off, the CPU 301, the ROM 302 that stores programs executed by the CPU 301 and other fixed data, the RAM 303 that temporarily stores image data and the like. Control of the entire apparatus, including a non-volatile memory (NVRAM) 304 and an ASIC 305 that processes various signal processing and rearrangement of image data and other input / output signals for controlling the entire apparatus. A main control unit 310 is also in charge of controlling the formation of the adjustment pattern, the detection of the adjustment pattern, and the adjustment (correction) of the landing position according to the present invention.

  The control unit 300 is interposed between the host side and the main control unit 310 and generates an external I / F 311 for transmitting and receiving data and signals, and head data generation for controlling the recording head 24. Main drive for driving a head drive control unit 312 including a head driver (actually provided on the recording head 24 side) composed of an array conversion ASIC and the like, and a main scanning motor 27 for moving and scanning the carriage 23. A drive unit (motor driver) 313, a sub-scanning drive unit (motor driver) 314 for driving the sub-scanning motor 131, a paper feed driving unit 315 for driving the paper feed motor 49, and a paper discharge unit 7. A paper discharge drive unit 316 for driving a paper discharge motor 79 that drives each roller, an AC bias supply unit 319 for supplying an AC bias to the charging belt 34, and others Although not shown, a recovery system drive unit for driving a maintenance / recovery motor that drives the maintenance / recovery mechanism 121, a double-sided drive unit that drives the double-sided unit when a double-sided unit is installed, and various solenoids (SOL) are driven. A solenoid drive unit (driver) for driving, a clutch drive unit for driving electromagnetic cracks and the like, and a scanner control unit 325 for controlling the image reading unit 11.

  In addition, the main control unit 310 inputs various detection signals such as an environmental sensor 234 that detects the temperature and humidity (environmental conditions) around the conveyor belt 31. It should be noted that detection signals from other sensors (not shown) are also input to the main control unit 310, but are not shown. The main control unit 310 also captures necessary key inputs and outputs display information with the operation / display unit 327 including various keys such as a numeric keypad and print start key provided on the apparatus main body 1 and various displays. Do.

  The main control unit 310 receives an output signal from a photosensor (encoder sensor) 129 that constitutes the linear encoder that detects the carriage position described above, and the main control unit 310 receives the main signal based on the output signal. By driving and controlling the sub-scanning motor 27 via the scanning drive unit 315, the carriage 23 is reciprocated in the main scanning direction. The main control unit 310 receives an output signal (pulse) from a photosensor (encoder sensor) 138 that constitutes a rotary encoder that detects the amount of movement of the conveyor belt 31 described above. The conveyance belt 31 is moved via the conveyance roller 32 by drivingly controlling the sub-scanning motor 131 via the sub-scan driving unit 314 based on the output signal.

  In addition, the main control unit 310 performs processing for forming an adjustment pattern on the conveyance belt 31 and performs light emission driving control for causing the light emission means of the pattern reading sensor 401 mounted on the carriage 23 to emit light with respect to the formed adjustment pattern. Then, the output signal of the light receiving means is input to read the adjustment pattern, the landing position deviation amount is detected from the read result, and the droplet ejection timing of the recording head 24 is made to eliminate the landing position deviation based on the landing position deviation amount. The control which correct | amends to is performed. Details of this will be described later.

  The image forming operation in the image forming apparatus configured as described above will be briefly described. The rotation amount of the conveyance roller 32 that drives the conveyance belt 31 is detected, and the sub-scanning motor 131 is driven and controlled in accordance with the detected rotation amount. In addition, a high voltage of positive and negative rectangular waves, which is an alternating voltage, is applied from the AC bias supply unit 319 to the charging roller 34, whereby positive and negative charges are applied to the transport belt 31 in the transport direction of the transport belt 31. On the other hand, it is alternately applied in a band shape, and charging is performed on the conveying belt 31 with a predetermined charging width to generate an unequal electric field.

  Therefore, the sheet 5 is fed from the sheet feeding unit 4 and is fed between the transport roller 32 and the first pressure roller 36, and an unequal electric field is generated by forming positive and negative charges. When the paper 5 is fed onto the conveying belt 31, the paper 5 is instantly polarized in accordance with the direction of the electric field, and is attracted onto the conveying belt 31 by the electrostatic adsorption force, and is conveyed along with the movement of the conveying belt 31.

  Then, the sheet 5 is intermittently conveyed by the conveyance belt 31 and recording liquid droplets are ejected from the recording head 24 onto the sheet 5 stopped while moving the carriage 23 in the main scanning direction to record an image. (Printing), the front end side of the paper 5 to be printed is separated from the transport belt 31 by the separation claw 39, sent to the paper discharge transport unit 6, and discharged to the paper discharge tray 7.

  During printing (recording) standby, the carriage 23 is moved to the maintenance / recovery mechanism 121 side, and the nozzle surface of the recording head 24 is capped by the cap 122, and the nozzles are kept in a wet state. To prevent. Further, the recording liquid is sucked from the nozzle in a state where the recording head 24 is capped with the suction and moisture retention cap 122a, and a recovery operation for discharging the thickened recording liquid and bubbles is performed. By this recovery operation, the nozzle surface of the recording head 24 is recovered. Wiping is performed by the wiper blade 124 in order to clean and remove the ink adhering to the ink. In addition, a blank ejection operation is performed in which ink that is not related to printing is ejected toward the blank ejection receiver 125 before recording is started or during recording. Thereby, the stable ejection performance of the recording head 24 is maintained.

  Next, a portion related to the droplet landing position deviation correction control in this image forming apparatus will be described with reference to FIGS. 6 is a block diagram for functionally explaining the droplet landing position deviation correction unit, and FIG. 7 is an explanatory diagram for explaining the droplet landing position deviation correction operation.

  First, as shown in FIGS. 7 and 8, the carriage 23 has a landing position deviation detection pattern (an adjustment pattern, a test pattern) formed on a conveyance belt 31 that is a water repellent member that is a pattern forming member. The detection pattern etc. are also used synonymously.) A pattern reading sensor 401 which is a reading means for detecting 400 is provided. As shown in FIG. 8, the adjustment pattern 400 means the whole composed of at least a reference pattern 400a and a measured pattern 400b.

  The pattern reading sensor 401 receives light-emitting elements 402 that emit light to the adjustment pattern 400 on the transport belt 31 arranged in a direction orthogonal to the main scanning direction, and regular reflection light from the adjustment pattern 501. A light receiving element 403 that is a light receiving means is held in a holder 404 and packaged. A lens 405 is provided at the exit and entrance of the holder 404.

  Note that the light emitting element 402 and the light receiving element 403 in the pattern reading sensor 401 are arranged in a direction orthogonal to the scanning direction of the carriage 23 as shown in FIG. Thereby, the influence on the detection result by the movement speed fluctuation | variation of the carriage 23 can be reduced. Further, as the light emitting element 402, a relatively simple and inexpensive light source such as an infrared region such as an LED or visible light can be used. Further, the spot diameter (detection range, detection area) of the light source is a detection range in the order of mm in order to use an inexpensive lens without using a high-precision lens.

  The adjustment pattern formation / reading control unit 501 scans the carriage 23 on the conveyance belt 31 in the main scanning direction and discharges droplets from the recording head 24 which is a droplet discharge unit via the droplet discharge control unit 502. Thus, a linear reference pattern 400a composed of a plurality of independent droplets 500 and a pattern to be measured 400b (these are collectively referred to as an adjustment pattern 400) are formed.

  The adjustment pattern formation / reading control unit 501 controls the pattern reading sensor 401 to read the adjustment pattern 400 formed on the conveyance belt 31. In this adjustment pattern reading control, the light emitting element 402 of the pattern reading sensor 401 is driven to emit light while moving the carriage 23 in the main scanning direction, and the adjustment pattern 400 on the conveyor belt 31 is irradiated with the light emitted from the light emitting element 402. Let

  The pattern reading sensor 401 irradiates the adjustment pattern 400 on the conveyor belt 31 with the light emitted from the light emitting element 402, so that the regular reflection light reflected from the adjustment pattern 400 is incident on the light receiving element 403. The detection signal corresponding to the amount of regular reflection light received from the adjustment pattern 400 is output from the adjustment pattern 400 and input to the landing position deviation amount calculation means 503 of the landing position correction means 505.

  The landing position deviation amount calculation means 503 of the landing position correction means 505 detects the position of the adjustment pattern 400 based on the output result of the light receiving element 403 of the pattern reading sensor 401 and detects the deviation amount relative to the reference position (droplet landing position deviation amount). ) Is calculated. The landing position deviation amount calculated by the landing position deviation amount calculation unit 503 is given to the ejection timing correction amount calculation unit 504, and the discharge timing correction amount calculation unit 504 eliminates the landing position deviation amount. Calculates the correction amount of the discharge timing when the recording head 24 is driven, and sets the calculated discharge timing correction amount in the droplet discharge control means 502. Thereby, when the recording head 24 is driven, the droplet discharge control means 502 corrects the discharge timing based on the correction amount and then drives the recording head 24, so that the deviation of the droplet landing position is reduced.

  Further, the pre-pattern formation idle discharge control means 506 is provided from the recording head 24 used for forming the adjustment pattern 400 via the droplet discharge control means 502 before the adjustment pattern 400 is formed by the pattern formation / reading means 501. Causes empty discharge to occur.

  Here, the pattern formable area is an area that is free from scratches, dirt, cloudiness, and the like on the conveyor belt 31 and can be read with high accuracy even when the adjustment pattern 400 is formed (a normal surface state area). It is.

Here, the formation of the pattern 400 and its detection principle will be described with reference to FIGS.
First, as shown in FIG. 9B, a pattern 400 is formed with a plurality of independent ink droplets 500 on the conveyance belt 31 (the ink droplets 500 are hemispherical when landed). Here, as shown in FIG. 11, when the light from the light emitting element 402 is irradiated on one ink droplet 500, when the incident light 601 hits the ink droplet 500, the ink droplet 500 has a rounded gloss. Since it is the surface, most of the light is diffusely reflected light 602 and only a small amount is detected as regular reflected light 603.

  In this case, the surface of the conveyor belt 31 (belt surface) is glossy, and when the light from the light emitting element 401 is irradiated, it is easy to return regular reflection light. In the case where scanning is performed by irradiating light from the light emitting element 402 of the reading sensor 401 including the pattern 400 composed of the plurality of ink droplets 500, light is diffused on the surface of the hemispherical and glossy ink droplet 500. In the portion of the pattern 400, the amount of the regular reflection light 603 decreases, and the output (sensor output voltage So) of the light receiving element 403 that receives the regular reflection light 603 becomes relatively small.

  Therefore, the position of the pattern 400 formed on the transport belt 31 can be detected based on the sensor output voltage So of the reading sensor 401.

  On the other hand, as shown in FIG. 10B, when the ink droplets are adjacently connected to each other on the conveyor belt 31, the upper surface of the connected ink droplet 500 becomes flat (flat). As a result, the specularly reflected light 603 increases, and the sensor output voltage So becomes an output value substantially the same as that of the surface of the conveyor belt 31 as shown in FIG. Becomes difficult. Even if the ink droplets stick together, scattered light is generated at the ends of the connected ink droplets. However, since the range is extremely limited, the detection is difficult. The viewing area (area to be detected) must be narrowed down, and there is a risk of reacting to noise factors such as a slight scratch or dust on the surface of the conveyor belt 31, resulting in a decrease in detection accuracy and reliability of detection results. Will drop.

  As shown in FIG. 12, since the ink droplets 500 are dried over time, the gloss is lost from the surface and further gradually flattened from the hemispherical shape, so that the range and the ratio in which the specular reflection light 603 is generated are diffused. The amount of light increases relatively with respect to the reflected light 602, and cannot be distinguished from the reflected light from the surface of the conveyor belt 31. Accordingly, when the regular reflection light 603 is received by the light receiving element 403, as shown in FIG. 13, the sensor output voltage So approaches the output voltage when the reflected light from the surface of the conveyor belt 31 is received as time passes. Therefore, it is preferable to detect the pattern 400 after the pattern 400 is formed and before the ink droplets 500 become flat, because the detection accuracy decreases with the passage of time.

  In this way, the pattern is detected by discriminating the portion of the output from the light receiving means that receives the specularly reflected light from the ink droplet where the specularly reflected light is attenuated, so that it can be detected with high accuracy. it can. In this case, the pattern 400 is preferably composed of a plurality of independent droplets in the detection area of the pattern reading sensor 401. Furthermore, it is preferable that the ink droplets are dense (the area between the droplets is smaller than the droplet adhesion area in the detection region).

  Here, standing on the peculiar properties of droplets, as a member for forming a pattern, by forming a pattern composed of a plurality of independent droplets on a water-repellent transport belt, The pattern can be detected with high accuracy by changing the amount of received regular reflected light, and as a result, the gap deviation can be detected with high accuracy.

Next, different examples of the position detection process of the pattern 400 formed on the conveyor belt 31 and the distance calculation process between the patterns 400a and 400b will be described with reference to FIGS.
In the first example shown in FIG. 14, when the reference patterns 400a and 400b are formed on the conveyor belt 31 as shown in FIG. 14A, these are read in the pattern scanning sensor in the sensor scanning direction (carriage main scanning direction). When reading is performed by scanning 401, the sensor output voltage So falling in the reference pattern 400a and the measured pattern 400b is obtained from the output result of the light receiving element 403 of the pattern reading sensor 401, as shown in FIG. .

  Therefore, by comparing the sensor output voltage So with a predetermined threshold value Vr, a position where the sensor output voltage So is lower than the threshold value Vr can be detected as an edge of the reference pattern 400a and the measured pattern 400b. At this time, the area centroid of the area surrounded by the threshold value Vr and the sensor output voltage So (the portion shown by hatching in the drawing) can be calculated, and the area centroid can be set as the center of the patterns 400a and 400b. By using, errors due to minute fluctuations in the sensor output voltage can be reduced.

  In the second example shown in FIG. 15, a sensor output voltage So as shown in FIG. 15A is obtained by scanning the reference pattern 400a and the measured pattern 400b similar to those in the first example with the pattern reading sensor 401. It is done. An enlarged view of the falling portion of the sensor output voltage So is shown in FIG.

  Here, the falling portion of the sensor output voltage So is searched in the direction indicated by the arrow Q1 in FIG. 15B, and the point where the sensor output voltage So falls below (below) the lower limit threshold Vrd is stored as the point P2. . Next, the point P2 is searched in the direction of the arrow Q2, and the point where the sensor output voltage So exceeds the upper limit threshold value Vru is stored as the point P1. Then, the regression line L1 is calculated from the output voltage So between the points P1 and P2, and the intersection point between the regression line L1 and the intermediate value Vrc of the upper and lower threshold values is calculated using the obtained regression line equation as the intersection point C1. . Similarly, a regression line L2 is calculated for the rising portion of the sensor output voltage So, and an intersection point between the regression line L2 and the intermediate value Vrc of the upper and lower threshold values is calculated as an intersection point C2. Then, a line center C12 is calculated from (intersection C1 + intersection C2) / 2 from an intermediate point between the intersection C1 and the intersection C2.

  In the third example shown in FIG. 16, as shown in FIG. 16A, a reference pattern 400a and a pattern to be measured 400b formed on the transport belt 31 are formed as in the first example, and these are subjected to main scanning. By scanning the pattern reading sensor 401 in the direction, a sensor output voltage (photoelectric conversion output voltage) So as shown in FIG. 16B is obtained.

  At this time, for example, processing for removing harmonic noise with an IIR filter is performed, then quality evaluation (detection of missing, unstable, surplus) of the detection signal is performed, and a slope portion near the threshold Vr is detected to obtain a regression curve. calculate. Then, intersection points a1, a1, b1, and b2 between the regression curve and the threshold value Vr are calculated (actually calculated by a position counter), and an intermediate point A between the intersection points a1 and a2 and an intermediate point B between the intersection points b1 and b2 are obtained. Calculate.

Next, a minimum unit (also referred to as a basic pattern) for detecting a landing position deviation constituting the adjustment pattern 400 in the image forming apparatus will be described with reference to FIG.
As described above, in the landing position deviation correction method in this image forming apparatus, a line-shaped pattern is formed in the direction perpendicular to the feed direction in the feed direction of the transport belt with the reference print head (color), and the other print heads A similar line pattern is formed at a predetermined interval (color), and the distance from the reference head is calculated (measured).

  Here, as a basic pattern for each minimum item, as shown in FIG. 17A, a measurement target formed by the recording head 24k2 with reference to the reference pattern FK1 formed by the recording head 24k1 in the forward path (first scan). The pattern for detecting the landing position deviation of the pattern FK2, and the pattern to be measured formed by the recording head 24k2 with reference to the reference pattern BK1 formed by the recording head 24k1 during the return path (second scan) as shown in FIG. A pattern for detecting the deviation of the landing position of BK2, formed by the recording heads 24c, 24m, and 24y with reference to the reference pattern FK1 formed by the recording head 24k1 in the forward path (third scan) as shown in FIG. Detect landing position deviation of measured pattern FC, FM, FY of each color (C, M, Y) As shown in FIG. 4D, the reference colors FK1 formed by the recording head 24k1 at the time of the return path (fourth scan) are used as references for the respective colors (C, M, and C) formed by the recording heads 24c, 24m, and 24y. Y) The pattern to be measured FC, FM, and the pattern for detecting the deviation of the landing position of FY, and the four types of patterns as the block pattern (basic pattern) for each minimum basic item, various detection contents can be obtained by combining these block patterns. Configure the resulting adjustment pattern.

  In particular, since the above-described image forming apparatus includes the two recording heads 24k1 and 24k2 for discharging black, not only the landing position deviation in bidirectional printing of one recording head but also the two recording heads 24k1. Therefore, there is also a pattern for detecting the landing position deviation of the pattern FK2 formed by the recording head 24k2 with reference to the pattern FK1 formed by the recording head 24k1.

Next, a monochrome ruled line shift adjustment pattern and a color color shift adjustment pattern based on this block pattern will be described with reference to FIGS.
The ruled line deviation adjustment pattern 400B shown in FIG. 18 includes a return path pattern BK1, a forward path pattern FK1, and an interval determined based on the position of the pattern FK1 in the reference direction (outward path) (with the pattern K1 as a reference pattern). By printing the return path pattern BK2 (these are the patterns to be measured), the landing position deviation with respect to the pattern K1 as the reference pattern is detected from the position information of these patterns FK1, BK1, FK1, and BK2. can do. The sensor scanning direction (reading direction) shows an example in which reading is performed in only one direction.

  The color misregistration adjustment patterns 400C1 and 400C2 shown in FIGS. 19A and 19B are respectively provided at regular intervals with respect to a reference color (here, the pattern FK1 by the recording head 24k1 is a reference pattern). Color patterns FY, FM, and FC (these are patterns to be measured) are printed, and the landing positions of the patterns FK1 and FY, FK1 and FM, and FK1 and FC are detected, whereby each color for the reference pattern FK1 is detected. The landing position can be detected. The sensor scanning direction (reading direction) shows an example in which reading is performed in only one direction.

Next, a specific example of forming the adjustment pattern will be described with reference to FIG.
First, as shown in FIG. 2, the scanning direction of the carriage 23 is a direction from the apparatus back side to the apparatus front side, and a direction from the apparatus front side to the apparatus back side is a return path direction. Assume that the recording heads 24c, 24k1, 24k2, 24m, and 24y are arranged in this order from the downstream side (the front side of the apparatus).

  In this example, the ruled line position deviation adjustment patterns 400B1 and 400B2 are formed on both ends of the conveyance belt 31, and the color deviation adjustment patterns 400C1 and 400C2 are formed in the central portion of the conveyance belt 31. That is, in this example, a plurality of block patterns are arranged within the width of the print area in the direction orthogonal to the feeding direction of the conveyor belt. At this time, since the printing is directly performed on the conveyance belt 31, the arrangement is made except for a portion having a large unevenness on the belt surface (particularly where the separation claw 39 for separating the recording medium is in contact with the conveyance belt 31). Like to do.

  Then, reading by the pattern reading sensor 401 is performed for each of the adjustment patterns 400B and 400C and then performed a plurality of times. In this case, the reading direction can be read multiple times in one direction (same direction), or read multiple times in both directions.

Therefore, the droplet landing position deviation adjustment (correction) processing executed by the main control unit 310 will be described with reference to the flowchart of FIG. 21 and the explanatory diagram of FIG.
When this processing is entered, the conveyor belt 31 is cleaned as preprocessing 1, and the pattern reading sensor 401 is calibrated as preprocessing 2, and the pattern reading sensor 401 (light emitting element) scanned by the carriage 23 is scanned. 402, the output of the light emitting element 402 is adjusted so that the output level of regular reflection of the light receiving element 403) is a constant value on the surface of the conveyor belt 31.

  Thereafter, droplets are ejected from each recording head 24 while scanning the carriage 23 in the main scanning direction to form a pattern to be formed in the forward path of the adjustment pattern 400, and then each recording head while performing backward scanning. A droplet is discharged from 24 to form a pattern to be formed in the return path of the adjustment pattern 400.

  At this time, before the adjustment pattern 400 is formed by forward scanning, as shown in FIG. 22A, the recording head 24 that forms the adjustment pattern 400 is ejected idle (the pattern formed by this idle ejection is This is referred to as “empty ejection pattern 410”). Similarly, before forming the adjustment pattern 400 by forward scanning, as shown in FIG. 22B, the recording head 24 that forms the adjustment pattern 400 is ejected idle. As a result, since the state (discharge state) of the nozzles of the recording head 24 used for forming the adjustment pattern 400 is aligned before the adjustment pattern 400 is formed, the landing position accuracy of the droplets for pattern formation is improved, and the pattern Formation accuracy is improved, and pattern detection accuracy and landing position deviation correction accuracy are improved.

  Thereafter, in a state where the light emitting element 402 of the pattern reading sensor 401 emits light, the carriage 23 scans in the main scanning direction to read the adjustment pattern 400, and the landing position is determined based on the output of the light receiving element 403 of the pattern reading sensor 401. The amount of deviation of the droplet landing position is calculated from the distance between the patterns detected.

  Then, it is determined whether or not the reading value obtained by the pattern reading sensor 401 is normal. If it is normal, it is determined whether or not N readings are to be performed. Return to. That is, here, reading in the forward direction is repeated N times. When N readings are completed, the correction value of the print ejection timing is calculated from the shift amount obtained by correcting the shift amount (reciprocal shift amount) between the forward path and the return path of the carriage 23 by the paper thickness. The print discharge timing is corrected by the correction value of the droplet discharge timing. Thereafter, as post-processing, cleaning for cleaning the surface of the conveyor belt 31 is performed.

  If the reading value by the pattern reading sensor 401 is not normal, it is determined whether or not the retry is the first time. If the retry is the first time, the adjustment pattern 400 is read again. If the retry is not the first time, the retry is performed. If the number of retries is not n, the process returns to the formation process of the adjustment pattern 400. When the number of retries is n, the cleaning of cleaning the surface of the conveyor belt 31 is performed as post-processing. Implement and move to error handling.

  In this way, on the conveyance belt having water repellency as a pattern forming member, it is composed of a plurality of independent droplets, consisting of a reference pattern consisting of a block pattern for each minimum item for detecting landing position deviation and a pattern to be measured The adjustment pattern is formed, and the adjustment pattern is irradiated with light to receive regular reflection light from the adjustment pattern to read the adjustment pattern. Based on the adjustment pattern read result, the droplets discharged from the recording head By correcting the landing position, it is possible to detect the landing position of the liquid droplet with high accuracy with a simple configuration and to correct the liquid droplet landing position deviation with high accuracy.

Here, different examples of the blank ejection pattern formed by performing blank ejection from the recording head 24 before pattern formation will be described with reference to FIGS.
The empty ejection pattern 410 may be a pattern (droplet aggregate) that cannot be read by the pattern reading sensor 401. For example, in the example shown in FIG. 23, the idle ejection pattern 410A is formed by forming lines with a width of one or several drops in the main scanning direction at intervals. Changes in the sensor output voltage So due to, and is not detected as a pattern.

  In the example shown in FIG. 24, the idle ejection pattern 410B is an example in which a line having a width of one drop or several drops is arranged obliquely with respect to the adjustment pattern 400. Such a pattern is also not detected as a pattern because there is little change in the sensor output voltage So due to specular reflection light.

  In the example shown in FIG. 25, the idle ejection pattern 410C is formed in a solid shape instead of an independent droplet. As described above, the pattern reading sensor 401 receives specularly reflected light from an independent droplet and detects the pattern based on the attenuation of the received light amount. Thus, if the pattern is a solid pattern, the reflection from the transport belt 31 is detected. It is indistinguishable from light, and the change in the sensor output voltage So due to specularly reflected light from the pattern reading sensor 401 is small and is not detected as a pattern.

  As described above, idle ejection is performed from the recording head 24 in the landing position deviation correction process, so that it is not necessary to perform idle ejection before image formation when the image forming operation is subsequently shifted, thereby reducing ink consumption. can do.

  Further, if the landing position deviation correction process is performed under the temperature and humidity conditions, it is possible to manage the pre-pattern printing empty discharge amount and reduce wasteful ink consumption.

Next, as another embodiment of the present invention, a case where the present invention is applied to a line type image forming apparatus will be described with reference to FIG.
In this case, the recording head 824 is composed of a line-type liquid discharge head having a length (a length in which a plurality of nozzles are arranged) corresponding to almost the entire width of the image forming area with respect to the conveyance belt 31. A line type pattern reading sensor 901 for reading the adjustment pattern 400 on the upper side is arranged.

  Also in this case, before the adjustment pattern 400 is formed, the recording head 824 that forms the pattern 400 is subjected to idle ejection (the idle ejection pattern 401 is formed), whereby the nozzle state (ejection state) of the recording head 824 is changed. Therefore, the landing position accuracy of the droplets for pattern formation is improved, the pattern formation accuracy is improved, and the pattern detection accuracy and the landing position deviation correction accuracy are improved.

  In this case as well, as shown in FIGS. 27A to 27C, the empty discharge pattern 400 that cannot be read by the pattern reading sensor 901, as shown in FIGS. In other words, the blank ejection pattern 410A having a width of one or several drops, the blank ejection pattern 410B arranged in an oblique direction with respect to the adjustment pattern 400, or a plurality of droplets are not independent. A solid idle ejection pattern 410C can be formed.

  In addition, the structure regarding pattern formation in the said embodiment is applicable also when using not only a conveyance belt but the sheet material which has water repellency.

1 is a schematic configuration diagram illustrating an overall configuration of an example of an image forming apparatus to which the present invention is applied. FIG. 2 is an explanatory plan view of an image forming unit and a sub-scanning conveyance unit of the apparatus. It is front explanatory drawing similarly shown in a partially transmissive state. It is a cross-sectional explanatory view showing an example of a conveyor belt. It is a block diagram explaining the outline | summary of a control part similarly. FIG. 3 is a block explanatory diagram functionally showing a portion related to droplet landing position detection and droplet landing position correction in the apparatus. It is explanatory drawing similarly provided for the description. It is explanatory drawing of a pattern reading sensor. It is explanatory drawing with which it uses for description of the formation of the pattern in a conveyance belt, and the detection principle. It is explanatory drawing with which it uses for description of the pattern in a comparative example. It is explanatory drawing which shows a mode that the light from the droplet used for description of the principle of pattern detection diffuses. It is explanatory drawing which shows a mode that light spreads similarly, when a droplet is planarized. It is explanatory drawing with which it uses for description of the relationship between the elapsed time from droplet landing similarly and a sensor output voltage change. It is explanatory drawing with which it uses for description of the 1st example of an adjustment pattern position detection process. It is explanatory drawing with which it uses for description of the 2nd example of an adjustment pattern position detection process. It is explanatory drawing with which it uses for description of the 3rd example of an adjustment pattern position detection process. It is explanatory drawing with which a block pattern (basic pattern) is demonstrated. It is explanatory drawing of a ruled line deviation adjustment pattern. It is explanatory drawing of a color shift adjustment pattern. It is explanatory drawing with which it uses for description of the formation position of an adjustment pattern. It is a flowchart with which it uses for description of a droplet landing position shift correction process. It is explanatory drawing with which it uses for description of the idle discharge before the pattern formation in the process. It is explanatory drawing explaining an example of the idle ejection pattern which cannot be read with a pattern reading sensor. It is explanatory drawing explaining the other example of an empty discharge pattern similarly. It is explanatory drawing explaining the other example of an empty discharge pattern similarly. FIG. 10 is a plan view for explaining a line type image forming apparatus as still another embodiment of the present invention. It is explanatory drawing explaining the example from which the same empty discharge pattern which cannot be read with a pattern reading sensor similarly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Apparatus main body 2 ... Image formation part 3 ... Sub-scanning conveyance part 4 ... Paper feed part 5 ... Paper (recording medium)
DESCRIPTION OF SYMBOLS 6 ... Paper discharge conveyance part 8 ... Paper discharge tray 7 ... Image reading part 23 ... Carriage 24 ... Recording head 27 ... Main scanning motor 31 ... Conveyance belt 32 ... Conveyance roller 131 ... Sub-scanning motor 400 ... Adjustment pattern 401 ... Pattern reading sensor (Reading means)
402 ... Light emitting element 403 ... Light receiving element 500 ... Liquid droplet (ink droplet)
501 ... Adjustment pattern formation / reading control means 502 ... Droplet discharge control means 503 ... Landing position deviation amount calculation means 504 ... Discharge timing correction amount calculation means 505 ... Landing position correction means 506 ... Empty discharge control means before pattern formation

Claims (9)

In an image forming apparatus in which a recording head for discharging droplets is mounted on a carriage and an image is formed on a recording medium to be conveyed.
Pattern forming means for forming a pattern for detecting landing position deviation on the pattern forming member;
Pattern reading means for reading each pattern;
Means for correcting a landing position deviation of a droplet from the recording head based on a reading result of the pattern reading means;
An image forming apparatus comprising: a unit that performs idle ejection from the recording head that forms the pattern before the pattern is formed.   The image forming apparatus according to claim 1, wherein the landing position deviation detection pattern includes a plurality of independent droplets.   3. The image forming apparatus according to claim 2, wherein the pattern reading unit receives light from the landing position deviation detection pattern and receives regular reflection light from the landing position deviation detection pattern. And an image forming apparatus.   4. The image forming apparatus according to claim 1, wherein the droplets that are ejected idle cannot be read by the pattern reading unit.   The image forming apparatus according to claim 1, wherein the idle ejection pattern formed of the droplets ejected idle is a line.   6. The image forming apparatus according to claim 5, wherein the idle ejection pattern constituted by the idle ejected droplets is arranged obliquely with respect to the landing position deviation detection pattern. .   5. The image forming apparatus according to claim 1, wherein the idle ejection pattern formed by the idle ejected droplets is a solid pattern in which the droplets are not independent. .   8. The image forming apparatus according to claim 1, wherein when the landing position deviation correction is performed, an idle ejection operation before image formation is not performed. A method of correcting the landing position of a droplet discharged from a recording head,
Before forming a landing position deviation detection pattern on the pattern forming member, causing the recording head to form the pattern to perform idle ejection;
Forming the landing position deviation detection pattern on the pattern forming member;
Reading each of the patterns;
And a step of correcting a landing position deviation of a droplet from the recording head based on the pattern reading result.

Images