JP5054458B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming equipment comprising a recording head for ejecting liquid droplets.

  As an image forming apparatus such as a printer, a facsimile machine, a copying apparatus, and a multifunction machine of these, for example, a liquid ejection apparatus including a recording head composed of a liquid ejection head (droplet ejection head) that ejects liquid droplets of a recording liquid (liquid) As a liquid while transporting a medium (hereinafter also referred to as “paper”, but the material is not limited, and a recording medium, a recording medium, a transfer material, recording paper, etc. are also used synonymously). The recording liquid (hereinafter referred to as ink) is attached to a sheet to form an image (recording, printing, printing, and printing are also used synonymously).

  The image forming apparatus means an apparatus for forming an image by discharging a liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc. This 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, forming a printing device and metal wiring. It also includes a device to perform. The liquid is not particularly limited as long as it is a liquid that can form 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.

Therefore, as described in Patent Document 1, conventionally, a reference nozzle selected from among a plurality of ink nozzles as ink ejection portions formed on a print head of a printing apparatus and a nozzle to be inspected arbitrarily selected are used. When printing is performed with the intention of forming an assumed inspection pattern composed of a plurality of line-like patterns that are alternately printed at regular intervals, the ink ejection direction of the inspection target nozzle matches the specified direction. A print control unit for instructing printing of the actually obtained execution test pattern on the print medium and at least the execution test pattern are printed for comparison control of the density with the ideal test pattern to be formed. A light-emitting unit that emits irradiation light to the print medium; and the reflected light reflected on the surface of the print medium is received and detected, and the inspection pattern An optical sensor having a light receiving unit that converts and generates a light receiving output signal having a value corresponding to the intensity of the reflected light that reflects the print density of light, and a light receiving output obtained by scanning the execution inspection pattern with the optical sensor Some include a pass / fail determination unit that compares a signal value with a predetermined determination threshold and determines pass / fail of the ink ejection direction of the inspection target nozzle.
JP-A-2005-262813

Further, as described in Patent Document 2, the print operation state determination print pattern is provided on the surface of the print medium (belt) adjacent to the pattern from the light reception output signal obtained as a result of detection by the optical sensor. There is one that improves the detection accuracy by removing the level fluctuation of the light reception output signal in the detection region of the optical sensor having a uniform surface state to reduce the disturbance.
Japanese Patent Laying-Open No. 2005-067093

As described in Patent Document 3, the nozzle position deviation amount is measured and recorded in advance in a data table for each speed profile for driving the carriage, and the nozzle position deviation amount at the carriage position at each printing timing is recorded at the time of printing. There is also a type that corrects the printing timing by reading out from the data table, calculating the deviation of the printing timing from this and the carriage speed at each ink ejection position.
JP 2003-062985 A

In addition, although not directly related to landing position deviation correction, as described in Patent Document 4, it is obtained from a detected image composed of a chromatic index and brightness detected from a printed image and an image signal of the image to be printed. There is a technique in which a color difference ΔE is calculated from the obtained reference data including a chromatic index and brightness, and density unevenness of a detected image is detected based on the color difference ΔE. In addition, as described in Japanese Patent Application Laid-Open No. H10-228707, there is a technique in which the positional deviation is corrected by changing the conveyance amount.
JP 2005-297287 A JP 2005-272892 A

  By the way, the carriage mounted with the recording head in the image forming apparatus is moved and scanned through a timing belt stretched between a driving pulley and a driven pulley by rotation of a motor, for example. Even when the carriage is moved at a constant speed, the carriage moving speed (carriage speed) varies depending on the resonance frequency of the carriage.

  Therefore, as described in Patent Documents 1 and 2 described above, when an optical sensor that reads a pattern is mounted on the carriage in order to correct the landing position deviation, the pattern reading result by the optical sensor is changed due to a change in the carriage speed. There is a problem in that variations occur and accurate landing position deviation correction cannot be performed.

  In other words, the carriage drive control is performed using a linear encoder, but in order to perform pattern detection at “position (distance)” using the same encoder signal as the carriage drive control, a carriage drive motor control circuit is used. Since it is necessary to synchronize (link) the optical sensor output processing circuit for pattern detection with a high-cost configuration, pattern detection may be performed by simple time measurement using a timer or the like. preferable.

  In this case, if the carriage movement speed fluctuates, the movement speed of the optical sensor will fluctuate, and if the distance between patterns is measured by simple time measurement, the measurement time will vary and the exact landing position Deviation correction cannot be performed.

  Further, in the configuration described in Patent Document 3, it is necessary to measure and record the speed profile as many as the number of carriage driving speeds, and to read and correct the amount of nozzle position deviation from the data table for all print data. Has a problem that a high-spec configuration is required and the cost is increased.

  The present invention has been made in view of the above problems, and an object of the present invention is to reduce the influence of fluctuations in carriage speed as much as possible and to correct landing position deviation with high accuracy at low cost. .

In order to solve the above problems, an image forming apparatus according to claim 1 of the present invention provides:
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 moving the carriage and ejecting droplets from the recording head to form a reference pattern for landing position correction and a pattern to be measured on the pattern forming member;
A reading unit mounted on the carriage and reading each pattern formed on the pattern forming member;
Means for calculating and correcting a landing position deviation of the droplet of the recording head from a distance between the reference pattern and the pattern to be measured based on a reading result of the reading unit;
The pattern forming means detects a change in a fluctuation period of the moving speed of the carriage and changes an interval between the reference pattern and the pattern to be measured ;
The carriage moving speed when forming and reading the pattern is different from the carriage moving speed during printing .

By the present invention lever, it made to reduce as much as possible the influence of the velocity fluctuation of the key Yarijji to allow the correction of the landing position shift with high accuracy at a low cost.

  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.

  Also, on one side surface of the carriage 23 is a reading means (detecting means) constituted by a reflection type photosensor including a light emitting means and a light receiving means for detecting landing position deviation (reading an adjustment pattern) according to the present invention. A certain reading sensor (DRES sensor) 401 is provided, and this pattern reading sensor 401 reads an adjustment pattern for detecting the landing position formed on the conveyance belt 31 as 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. 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 corrects 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. 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. FIG. 6 is a block diagram for functionally explaining the droplet landing position deviation correction unit, and FIG. 7 is a block diagram schematically showing a functional flow of the droplet landing position deviation correction operation.

  First, as shown in FIGS. 7 and 8, the carriage 23 has a landing position deviation correction adjustment pattern (test pattern, detection pattern) formed on a conveyance belt 31 that is a water repellent member that is a pattern forming member. A pattern reading sensor 401 which is a reading means for detecting 400 is provided. 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 reciprocally in the main scanning direction with respect to the conveyance belt 31 and instructs the droplets via the droplet discharge control unit 502 when the landing position deviation correction is instructed. A droplet-shaped adjustment pattern 400 (400B1, 400B2, 400C1, 400C1, etc.) as shown in FIG. Form. The adjustment pattern formation / reading control unit 501 is constituted by the CPU 301 of the main control unit 310 and the like.

  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. This adjustment pattern reading control is performed by driving the light emitting element 402 of the pattern reading sensor 401 to emit light while moving the carriage 23 in the main scanning direction. Specifically, as shown in FIG. 7, the CPU 301 of the main control unit 310 sets a PWM value for driving the light emitting element 402 of the pattern reading sensor 401 in the light emission control unit 511, and the output of this light emission control unit 511. Is smoothed by the smoothing circuit 512 and applied to the driving circuit 513, so that the driving circuit 513 drives the light emitting element 402 to emit light, and the emitted light from the light emitting element 402 with respect to the adjustment pattern 400 on the conveyance belt 31. Is irradiated.

  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. Specifically, as shown in FIG. 7, the output signal from the light receiving element 403 of the pattern reading sensor 401 is photoelectrically converted by a photoelectric conversion circuit 521 included in the main control unit 310 (not shown in FIG. 5). Sensor output voltage data obtained by removing noise from the photoelectric conversion signal (sensor output voltage) by the low-pass filter circuit 522, A / D converting by the A / D conversion circuit 523, and A / D converting by the signal processing circuit (DSP) 524. Is stored in the shared memory 525.

  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.

  Specifically, as shown in FIG. 7, each adjustment pattern 400 (for example, the sensor output voltage So shown in FIG. 7A stored in the shared memory 525 is stored in the shared memory 525 by the processing algorithm 526 executed by the CPU 301. The center position (point A) of one line pattern is set to “400a”), the amount of deviation of the actual landing position by the head relative to the reference position (reference head) is calculated, and the print ejection timing is calculated from the amount of deviation. The correction amount is calculated, and this correction amount is set in the discharge control means 502.

Here, the adjustment pattern 400 will be described with reference to FIG.
First, the principle of landing position detection (pattern detection) in this image forming apparatus will be described. A state in which light from a droplet diffuses when light is irradiated onto the droplet (hereinafter referred to as “ink droplet”) will be described with reference to FIG.
As shown in FIG. 10, when incident light 601 strikes an ink drop 500 that has landed on the landing member 600 (in the landed state, the ink drop is hemispherical), the ink drop 500 has a rounded glossy surface. Therefore, most of the light is diffusely reflected light 602 and only a small amount is detected as regular reflected light 603. However, as shown in FIG. 11, 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 rate in which the specular reflection light 603 is generated diffuses. It becomes relatively large with respect to the reflected light 602. Therefore, when the regular reflection light 603 is received by the light receiving element 403, as shown in FIG. 12, the sensor output voltage decreases with time, and the detection accuracy decreases with time.

Next, detection of the position of the ink droplet 500 constituting the adjustment pattern 400 (exactly one pattern) will be described with reference to FIG.
It is assumed that the surface (belt surface) of the conveyor belt 31 is glossy and easily returns specularly reflected light when irradiated with light from the light emitting element 401. For this reason, in FIG. 13B, in the region of the surface of the conveyance belt 31 where the ink droplet 500 has not landed, the incident light 601 from the light emitting element 401 is almost regularly reflected on the belt surface, so that regular reflection is performed. As the amount of light 603 increases, the output (sensor output voltage) of the light receiving element 403 that receives the specularly reflected light 603 relatively increases as shown in FIG.

  On the other hand, in the region where the ink droplets 500 are independent and densely landed in FIG. 13B, the light is diffused on the surface of the hemispherical and glossy ink droplet 500, so that regular reflection is performed. As shown in FIG. 13A, the amount of light 603 decreases, and the output (sensor output voltage) of the light receiving element 403 that receives the specularly reflected light 603 becomes relatively small. “Dense” refers to a state in which the area between the ink droplets 500 is smaller than the area (attachment area) of the region where the ink droplets 500 land within a predetermined detection region.

  On the other hand, as shown in FIG. 14B, when the ink droplets are adjacently connected to each other on the conveyance 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 has 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.

  Therefore, the landing position of the ink droplet can be detected by determining the portion of the output from the light receiving means that receives the regular reflected light from the ink droplet, where the regular reflected light is attenuated. In order to detect the landing position of the ink droplets with high accuracy, the adjustment pattern (adjustment pattern) 400 is composed of a plurality of independent droplets in the detection region of the pattern reading sensor 401, and is densely packed. (The area between the droplets is small relative to the adhesion area of the droplets in the detection region), and a simple configuration of light emitting means and light receiving means by forming such an adjustment pattern Thus, the adjustment pattern (droplet landing position) can be detected with high accuracy.

  Here, standing on the unique properties of droplets, it is composed of a plurality of independent droplets on a water-repellent transport belt as a member that forms an adjustment pattern. By forming an adjustment pattern in which the area between the droplets is smaller than the area, the adjustment pattern can be detected with high accuracy by the change in the amount of specularly reflected light received from the adjustment pattern. The positional deviation can be adjusted (corrected).

Next, different examples of position detection processing (reading processing) of the adjustment pattern 400 formed on the conveyance belt 31 will be described with reference to FIGS. 15 to 17.
In the first example shown in FIG. 15, as shown in FIG. 15A, a line-shaped reference pattern 400k1 is formed on the transport belt 31 by, for example, the recording head 24k1, and the line-shaped measured pattern 400k2 is formed by the recording head 24k2. Form. Then, by scanning this with the pattern reading sensor 401 in the sensor scanning direction (carriage main scanning direction), the reference pattern 400k1 is obtained from the output result of the light receiving element 403 of the pattern reading sensor 401 as shown in FIG. The sensor output voltage So falling at the measured pattern 400k2 is obtained.

  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 400k1 and the measured pattern 400k2. At this time, the area centroid of the area surrounded by the threshold value Vr and the sensor output voltage So (the part shown by hatching in the drawing) can be calculated, and the area centroid can be set as the center of the patterns 400k1 and k2. By using, errors due to minute fluctuations in the sensor output voltage can be reduced.

  In the second example shown in FIG. 16, a sensor output voltage So as shown in FIG. 16A is obtained by scanning the reference pattern 400k1 and the measured pattern 400k2 similar to those in the first example by 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 of the arrow Q1 in FIG. 16B, 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, the line center C12 is referred to at (intersection C1 + intersection C2) / 2 from an intermediate point between the intersection C1 and the intersection C2.

  In the third example shown in FIG. 17, as shown in FIG. 17A, a linear reference pattern 400k1 is formed on the transport belt 31 by using, for example, the recording head 24k1, as in the first example, and the recording head A pattern to be measured 400k2 is formed using 24k2, and this is scanned by the pattern reading sensor 401 in the main scanning direction, whereby a sensor output voltage (photoelectric conversion output voltage) So as shown in FIG. 17B is obtained. .

  At this time, in the processing algorithm 525 described above, processing for removing harmonic noise is performed by an IIR filter, and then the quality of the detection signal is evaluated (whether it is missing, unstable, or surplus), and an inclined portion near the threshold Vr is detected. To calculate a regression curve. Then, the intersection points a1, a1, b1, and b2 between the regression curve and the threshold value Vr are calculated (actually, the calculation is performed by an ASIC: a position counter configured by an application specific integrated circuit), and an intermediate point A between the intersection points a1 and a2. Then, an intermediate point B between the intersection points b1 and b2 is calculated, and a distance L (measured as time as will be described later) between the intermediate point A and the intermediate point B is calculated. Thereby, an intermediate position between the reference pattern 400k1 and the measured pattern 400k2 is detected.

  Therefore, the amount of deviation in actual printing is obtained by multiplying the difference between the ideal distance between the recording head 24k1 and the recording head 24k2 and the time corresponding to the calculated distance L by the moving speed of the pattern reading sensor 401. Is obtained. Therefore, based on the obtained deviation amount, a correction value for correcting the timing of ejecting droplets from the recording heads 24k1 and 24k2 (droplet ejection timing) is calculated, and the correction value is set in the ejection control unit 502. As a result, the ejection control unit 502 drives the head at the corrected droplet ejection timing, so that the positional deviation is reduced.

Next, a block pattern (also referred to as a basic pattern) for each minimum item 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. 18A, a measurement target formed by the recording head 24k2 with reference to a 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 a deviation in the landing position of BK2, formed by recording heads 24c, 24m, and 24y with reference to a reference pattern FK1 formed by 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, the monochrome ruled line shift adjustment pattern and the color color shift adjustment pattern based on this block pattern will be described with reference to FIGS. 19 and 20. FIG.
The ruled line deviation adjustment pattern 400B shown in FIG. 19 includes a return path pattern BK1, a forward path pattern FK1, and a forward path pattern FK1, at intervals determined with reference to the position of the pattern FK1 in the reference direction (outward path). 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. 20A and 20B are each at regular intervals with respect to a reference color (here, the pattern FK1 by the recording head 24k1 is a reference pattern). The color patterns FY, FM, and FC (these are the 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, so that each color with respect to 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.

A droplet landing position deviation adjustment (correction) process executed by the main control unit 310 will be described with reference to FIG.
Maintenance and recovery of the recording heads 24k1 and 24k2 using black ink is performed (K1 or K2). Cleaning is completed, cleaning is performed after the device is left for a predetermined time, and the temperature change amount of the environmental temperature is greater than or equal to a predetermined value. Sometimes this droplet landing position deviation adjustment process is started.
Then, as the preprocessing 1, the conveyance belt 31 is cleaned, and as the preprocessing 2, the pattern reading sensor 401 is calibrated, and the pattern reading sensor 401 (light emitting element 402, light receiving element 403) scanned by the carriage 23 is used. The output of the light emitting element 402 is adjusted so that the output level of the regular reflection becomes a constant value on the surface of the conveyor belt 31.

  Thereafter, droplets are ejected from the respective recording heads 24 while scanning the carriage 23 in the main scanning direction, and a pattern (reference number) to be formed in the forward path of the adjustment pattern (adjustment pattern 400) described with reference to FIG. Then, a droplet is ejected from each recording head 24 while performing backward scanning, and is formed in the backward path of the adjustment pattern (adjustment pattern 400) described in FIG. A power pattern (a pattern in which “B” is added to the code) is formed.

  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, a reference pattern comprising a block pattern for each minimum item, which is composed of a plurality of independent liquid droplets and detects landing position deviation, on a conveyance belt which is a water repellent member having water repellency as a pattern forming member. An adjustment pattern composed of a pattern to be measured is formed, light is applied to the adjustment pattern, regular reflection light from the adjustment pattern is received, the adjustment pattern is read, and the recording head is read based on the adjustment pattern reading result. By correcting the landing position of the discharged droplet, the landing position of the droplet can be detected with high accuracy with a simple configuration, and the deviation of the droplet landing position can be corrected with high accuracy.

Next, reduction in pattern detection variation due to fluctuations in the moving speed of the carriage will be described.
As described above, in order to perform the position (distance) detection using the same encoder signal as the carriage driving control by the pattern reading sensor 401 using the reference pattern and the pattern to be measured, the carriage driving motor control circuit and the pattern reading sensor 401 are used. Therefore, it is necessary to synchronize (link) the sensor output processing circuit.

  Therefore, in the present invention, the time from when the pattern reading sensor 401 reads the reference pattern until the pattern to be measured is read, and the landing position deviation is detected by the difference between the measured time and the regular time. If the movement speed of the carriage 23 fluctuates, the movement speed of the pattern reading sensor 401 fluctuates, resulting in variations in measurement time.

  First, the outline of the present invention will be described with reference to FIGS. FIG. 23 shows an example of fluctuations in the moving speed of the carriage 23. The change in carriage speed at each carriage position (main scanning direction position) obtained from the encoder signal from the linear encoder (encoder sensor 129) is shown in FIG. Shows the carriage speed at each carriage position measured using a laser Doppler, and FIG. 25 shows the result of frequency analysis of a part of the speed data obtained from the linear encoder.

  From these, it can be seen that a high frequency sine fluctuation occurs in the carriage speed. And also from the frequency analysis result shown in FIG. 25, it turns out that the specific frequency protrudes extremely. In the example shown in FIG. 25, since high peaks are recognized at 75 Hz and 230 Hz, the pitch between the reference pattern and the pattern to be measured (referred to as “pattern pitch”) constituting the adjustment pattern 400 for correcting the landing position deviation is referred to as this. By associating with either one, it is possible to simply halve the influence of the carriage linear speed fluctuation (movement speed fluctuation) on the reading result by the pattern reading sensor 401 (one of the two peaks is canceled). .

First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 26 is an explanatory diagram illustrating an example of a change in carriage speed with respect to time, and FIG. 27 is an explanatory diagram illustrating setting of a pattern pitch with respect to a change in carriage speed.
As shown in FIG. 26, when scanning of the carriage 23 is started, the carriage 23 moves to the constant speed area (constant speed area) through the acceleration area and is moved at a constant speed. As described, the carriage speed in the constant speed region also varies. Here, the variation period Tc of the carriage speed is, for example, constant.

  At this time, the speed of the pattern reading sensor 401 mounted on the carriage 23 also fluctuates due to fluctuations in the carriage speed, and therefore the detection position of the adjustment pattern 400 is inevitably affected.

  That is, as shown in FIG. 27A, when the carriage speed fluctuates at the fluctuation period Tc, as shown in the comparative example of FIG. 27B, the pattern pitch Pp1 between the reference pattern 400a and the measured pattern 400b. Is about 2 to 5 times the carriage fluctuation period Tc (Pp1 = 2.5Tc), the pitch between the reference pattern 400a read by the pattern reading sensor 401 and the pattern to be measured 400b (this is referred to as "detection pitch" or "reading pitch"). “)” Is detected by the measurement time between patterns, and therefore, it deviates from the actual pattern pitch Pp1 depending on the amplitude of the carriage speed fluctuation component.

  Therefore, as shown in the embodiment of FIG. 27C, by setting the pattern pitch Pp0 between the reference pattern 400a and the measured pattern 400b to an integral multiple of the carriage fluctuation period Tc (for example, 4 times, Pp0 = 4Tc), Even if the amplitude of the carriage speed fluctuation fluctuates, it is canceled during one period, and the pitch between the reference pattern 400a and the pattern to be measured 400b read by the pattern reading sensor 401 (this is referred to as “detection pitch” or “reading pitch”). ")" Is less affected by the magnitude of the amplitude of the carriage speed fluctuation component, and the deviation from the actual pattern pitch Pp0 is reduced.

  That is, the pattern pitch (distance) of the adjustment pattern for correcting the landing position deviation is associated with the carriage speed fluctuation period Tc, in other words, set to an integral multiple of the carriage speed fluctuation period Tc, thereby outputting the optical sensor (pattern reading sensor). The carriage speed fluctuation component to the “distance between the reference pattern and the pattern to be measured” calculated from the above can be canceled (removed).

Next, a second embodiment of the present invention will be described with reference to the flowchart shown in FIG.
In the first embodiment described above, the description has been made on the assumption that the variation period Tc of the carriage speed is constant. However, the variation period Tc of the carriage speed actually changes. Therefore, in this embodiment, when the carriage speed fluctuation period (fluctuation frequency) changes for some reason, the pattern pitch of the adjustment pattern 400 for correcting the landing position deviation is changed accordingly.

  That is, referring to FIG. 28, when entering the adjustment pattern setting process for positional deviation correction, it is determined whether or not the carriage speed fluctuation period Tc has changed, and when the carriage speed fluctuation period Tc has not changed, A predetermined initial value pattern pitch is called and a transition is made to the landing position deviation correction mode. When the carriage speed fluctuation period Tc is changed, the predetermined initial value pattern pitch is corrected, and then the landing position deviation correction mode is set. Migrate to

  As described above, when the carriage speed fluctuation period Tc changes, the pattern pitch set in advance based on the carriage speed fluctuation period Tc is corrected, so that the pattern pitch can be accurately obtained even when the carriage speed fluctuation period Tc changes. Can be detected.

Next, a third embodiment of the present invention will be described with reference to the flowchart shown in FIG.
Here, a pattern reading sensor 401 (optical sensor) for landing position deviation correction or a temperature / humidity sensor for detecting environmental conditions (temperature, humidity) is provided in the carriage 23 on which the sensor 401 is mounted. The pattern pitch is corrected accordingly.

  In other words, referring to FIG. 29, when the adjustment pattern setting process for correcting misalignment is entered, for example, it is determined whether or not the detected temperature is equal to or higher than a predetermined set temperature (X ° C.), and the detected temperature is not higher than the set temperature. Sometimes, a predetermined initial value pattern pitch is called and the mode shifts to the landing position deviation correction mode. When the detected temperature is equal to or higher than the set temperature, the predetermined initial value pattern pitch is corrected, and then the landing position deviation correction mode is set. Migrate to

  As described above, when the environmental condition changes, the pattern pitch can be detected with high accuracy even when the environmental condition changes by correcting the pattern pitch set in advance based on the carriage speed fluctuation period Tc. .

Next, a fourth embodiment of the present invention will be described with reference to the flowchart shown in FIG.
Here, the state of the main scanning mechanism (motor, timing belt, pulley, etc.) that causes the carriage 23 to perform main scanning changes as the usage time of the apparatus and the cumulative number of printed sheets (total number of printed sheets, number of sheets to pass) increase. Since the speed fluctuation frequency (fluctuation period) may change, the pattern pitch is corrected according to changes over time.

  That is, referring to FIG. 30, when the adjustment pattern setting process for misregistration correction is entered, for example, whether or not the cumulative number of printed sheets (or other time-dependent elements as described above) is greater than or equal to a predetermined set number. When the accumulated number of printed sheets is not equal to or greater than the set number, the pattern pitch of a predetermined initial value is called, and the mode shifts to the landing position deviation correction mode. After the pattern pitch is corrected, the mode shifts to the landing position deviation correction mode.

  In this way, by correcting the pattern pitch set in advance based on the carriage speed fluctuation period Tc according to the temporal condition, the pattern pitch can be detected with high accuracy even when the temporal condition changes.

Next, a fifth embodiment of the present invention will be described with reference to the flowchart shown in FIG.
Here, a frequency analysis circuit for performing frequency analysis (FFT) is provided on an arithmetic circuit for a signal from a linear encoder provided as means for monitoring the carriage speed, and a pattern corresponding to the sequentially measured carriage speed fluctuation frequency is provided. The pitch is corrected.

  That is, referring to FIG. 31, the main scanning (pre-operation) of the carriage 23 is executed at a predetermined carriage speed for positional deviation correction, the linear encoder signal is acquired (speed sample data acquisition), and the frequency analysis circuit Then, the carriage speed fluctuation is analyzed (detection of the carriage speed fluctuation period), and a peak having a predetermined frequency or higher is extracted. Then, the peak having the maximum speed fluctuation width is selected, the pattern pitch is calculated, and the landing position deviation correction mode is entered.

  In this way, by detecting the variation period of the carriage speed and setting the pattern pitch according to the detection result, the pattern pitch can always be detected with high accuracy.

Next, a sixth embodiment of the present invention will be described with reference to FIGS. 32 and 33. FIG.
Here, FIG. 32A shows a carriage speed (linear speed) used in a normal printing operation (operation for recording an image on a sheet) (this is referred to as “carriage speed A during normal printing”). In the carriage speed A during normal printing, the fluctuation amplitude is small and the rise and fall are smooth as shown in FIG. 5B, but there are a plurality of speed fluctuation frequencies during constant speed movement. The effect of association with the pattern pitch is weak. The carriage linear speed during normal printing is generally required to be a constant speed in consideration of productivity. Since the ink droplet ejection timing is triggered by an encoder signal such as a linear scale, there is a characteristic that the influence of the speed fluctuation is small.

  On the other hand, the carriage speed (linear speed) (referred to as “carriage speed B”) shown in FIG. 33A is large in fluctuation amplitude, but has one kind of speed fluctuation frequency (fluctuation period) during constant speed movement. However, it is easy to associate with the pattern pitch.

  Therefore, by setting the pattern pitch when forming the adjustment pattern 400 based on the carriage speed B and performing the pattern reading by the pattern reading sensor 401 at the carriage speed B, high-precision reading can be performed. Become.

Next, a seventh embodiment of the present invention will be described with reference to FIG. FIG. 34 is a plot of signal positions obtained from the sensor when the same pattern is read while moving the sensor at different carriage speeds.
In order to increase the resolution of the output signal from the optical sensor constituting the pattern reading sensor 401, the pattern position can be detected with higher accuracy when the carriage speed (linear speed) is lower. That is, as shown in FIG. 34, when the carriage speed is relatively large (fast) and when the carriage speed is relatively small (slow), the latter has higher resolution (distance).

  Therefore, by making the carriage speed when reading the pattern slower than the carriage speed during normal printing, high-precision reading is possible.

Next, an eighth embodiment of the present invention will be described with reference to FIG. 33 described above.
When the pattern pitch is set to an integral multiple of the carriage speed fluctuation period, the effect of canceling the carriage speed fluctuation component is higher when the speed fluctuation period protrudes like the carriage speed B described above and there is no other protruding frequency. Become. Therefore, the landing position deviation correction is performed at a carriage speed at which the speed fluctuation cycle is stable (there is a single peak protruding in the frequency analysis).

Next, a ninth embodiment of the present invention will be described with reference to the flowchart shown in FIG.
The variation in the carriage speed varies to some extent from machine to machine. Therefore, the carriage speed fluctuation is measured in advance for each device, and the pattern pitch is individually set for each device.

  For example, as shown in FIG. 35, a carriage pre-operation is executed at a carriage speed for correcting misalignment, a linear scale (linear encoder) signal is acquired (acquisition of speed sample data), and within the carriage movable range based on the acquired speed data. The speed fluctuation period is analyzed (for pattern arrangement position determination), the speed fluctuation frequency within the carriage movable range is analyzed (for pattern pitch determination), and the pattern pitch of the landing position deviation correction pattern is determined.

Next, a tenth embodiment of the present invention will be described with reference to FIG. FIG. 36A shows an example of a profile of the carriage speed fluctuation in the carriage movable area, and FIG. 36B shows the frequency analysis result in the area B of FIG.
Within the movable range of the carriage 23, the carriage speed fluctuation profile varies depending on the carriage position as shown in FIG. In the example shown in FIG. 36, the area A is an area where the amplitude of the carriage speed fluctuation is relatively smaller than the other areas, and the area B is an area where the carriage speed fluctuation period is relatively stable. .

  Therefore, the adjustment pattern 400 can be arranged in the region A where the amplitude of the carriage speed fluctuation is relatively small. Alternatively, the adjustment pattern 400 can be arranged in the region B where the carriage speed fluctuation period is relatively stable. In this manner, by setting the position where the adjustment pattern is arranged according to each device, it is possible to perform landing position deviation correction with higher accuracy.

Next, an eleventh embodiment of the present invention will be described with reference to FIG.
As described above, since the adjustment pattern 400 is a pattern composed of independent droplets, the width of the adjustment pattern 400 (width in the main scanning direction) is associated with the carriage speed variation period, so that each pattern according to the calculation algorithm is used. The accuracy of center value calculation is improved. For example, when the carriage speed fluctuates with the period Tc as shown in FIG. 37A, the width of the pattern constituting the adjustment pattern 400 is set to N × Tc (N = N =) as shown in FIGS. The center position calculation accuracy is improved by setting it to an integer of 1 or more. On the other hand, when the pattern width is 2.5 Tc, for example, as shown in FIG. As a result, the pattern width largely fluctuates, and the detection accuracy of the center position decreases.

Next, a twelfth embodiment of the present invention will be described with reference to FIGS.
The output signal of the optical sensor constituting the pattern reading sensor 401 is generally an analog output, and binary determination is often performed by providing a threshold value in a circuit on the apparatus main body side. By adjusting the threshold value that can be individually set by the circuit on the apparatus main body side, the pattern width dimension of the adjustment pattern 400 can be associated with the carriage speed fluctuation period.

  For example, when the carriage speed fluctuates as shown in FIG. 38 (a), when the sensor output voltage shown in FIG. 38 (b) is obtained, as shown in FIG. The pattern width to be detected becomes longer than the threshold value D, and at the threshold value D, the pattern width to be detected becomes shorter than the carriage speed fluctuation period Tc. Therefore, by performing binary determination of the sensor output voltage with the threshold C, it is possible to detect with the same pattern width as the carriage speed fluctuation period Tc.

  As in the eleventh and twelfth embodiments, the pattern pitch is set to an integral multiple of the carriage speed fluctuation period, and the pattern width or the threshold for detecting the pattern is also set to an integral multiple of the carriage speed fluctuation period. Thus, higher landing position deviation correction can be performed.

  In the above embodiment, the example in which the pattern forming member is a conveyance belt that is a water repellent member is described. However, a sheet material having water repellency can be used separately.

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. FIG. 6 is a block explanatory diagram functionally showing a specific example of a portion related to droplet landing position detection and droplet landing position correction. It is explanatory drawing explaining the example of an adjustment pattern. It is explanatory drawing of a pattern reading sensor. 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. FIG. 6 is a schematic explanatory diagram for explaining the adjustment pattern. It is typical explanatory drawing with which it uses for description of the adjustment pattern which concerns on a comparative example. 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 adjustment pattern position detection processing. 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 it uses for description of a block pattern. 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 explaining a droplet landing position shift adjustment (correction) process. It is explanatory drawing of an example of the carriage speed fluctuation | variation in each carriage position obtained from the encoder signal. It is explanatory drawing which shows an example of the carriage speed fluctuation | variation in each carriage position similarly measured using the laser Doppler. It is explanatory drawing which shows the result of having analyzed the frequency of a part of speed data obtained from the encoder signal of FIG. It is explanatory drawing which shows an example of the change of the carriage speed with respect to time with which it uses for description of 1st Embodiment of this invention. It is explanatory drawing explaining the setting of the pattern pitch similarly with respect to a carriage speed fluctuation | variation. It is a flowchart with which it uses for description of 2nd Embodiment of this invention. It is a flowchart with which it uses for description of 3rd Embodiment of this invention. It is a flowchart with which it uses for description of 4th Embodiment of this invention. It is a flowchart with which it uses for description of 5th Embodiment of this invention. It is explanatory drawing which shows an example of the carriage speed (linear speed) used by normal printing operation | movement used for description of 6th Embodiment of this invention, and a speed fluctuation. It is explanatory drawing which shows an example of the carriage speed (linear speed) similarly used for pattern formation and a detection, and a speed fluctuation. It is explanatory drawing which shows an example of the relationship between the carriage speed used for description of 7th Embodiment of this invention, and the reading position of a sensor output voltage. It is a flowchart with which it uses for description of 9th Embodiment of this invention. It is explanatory drawing which shows an example of the change of the carriage speed within the carriage movable range for description of 10th Embodiment of this invention. It is explanatory drawing which shows the example from which a carriage speed fluctuation | variation period and pattern width differ for description of 11th Embodiment of this invention. It is explanatory drawing which shows the relationship between the carriage speed provided for description of 12th Embodiment of this invention, and the threshold value of a sensor output voltage. It is explanatory drawing which similarly shows the relationship between a sensor output voltage threshold value and pattern width.

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 ejection control means 503 ... Landing position deviation amount calculation means 504 ... Discharge timing correction amount calculation means 505 ... Landing position correction means

Claims (8)

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 moving the carriage and ejecting droplets from the recording head to form a reference pattern for landing position correction and a pattern to be measured on the pattern forming member;
A reading unit mounted on the carriage and reading each pattern formed on the pattern forming member;
Means for calculating and correcting a landing position deviation of the droplet of the recording head from a distance between the reference pattern and the pattern to be measured based on a reading result of the reading unit;
The pattern forming means detects a change in a fluctuation period of the moving speed of the carriage and changes an interval between the reference pattern and the pattern to be measured;
An image forming apparatus, wherein a movement speed of a carriage when forming and reading the pattern is different from a movement speed of a carriage during printing. 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 moving the carriage and ejecting droplets from the recording head to form a reference pattern for landing position correction and a pattern to be measured on the pattern forming member;
A reading unit mounted on the carriage and reading each pattern formed on the pattern forming member;
Means for calculating and correcting a landing position deviation of the droplet of the recording head from a distance between the reference pattern and the pattern to be measured based on a reading result of the reading unit;
The pattern forming means detects a change in a fluctuation period of the moving speed of the carriage and changes an interval between the reference pattern and the pattern to be measured;
An image forming apparatus, wherein a carriage moving speed when reading the pattern is slower than a carriage moving speed during printing. 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 moving the carriage and ejecting droplets from the recording head to form a reference pattern for landing position correction and a pattern to be measured on the pattern forming member;
A reading unit mounted on the carriage and reading each pattern formed on the pattern forming member;
Means for calculating and correcting a landing position deviation of the droplet of the recording head from a distance between the reference pattern and the pattern to be measured based on a reading result of the reading unit;
The pattern forming means detects a change in a fluctuation period of the moving speed of the carriage and changes an interval between the reference pattern and the pattern to be measured;
An image forming apparatus, wherein the pattern is read at a carriage moving speed at which a fluctuation cycle of the carriage moving speed is constant. 4. The image forming apparatus according to claim 1, wherein an interval between the reference pattern and the pattern to be measured is changed based on an environmental condition. 5. The image forming apparatus according to claim 1, wherein an interval between the reference pattern and the pattern to be measured is changed based on a cumulative number of printed sheets. The image forming apparatus according to any one of claims 1 to 5, comprising means for frequency analyzing the encoder signals from the linear encoder for detecting the speed and position of the carriage, and detects the fluctuation component of the moving speed of the carriage An image forming apparatus, wherein an interval between the reference pattern and the pattern to be measured is changed. The image forming apparatus according to any one of claims 1 to 6, the image forming apparatus, characterized in that the amplitude of fluctuation of the moving speed of the carriage to form the respective patterns in a relatively small area. The image forming apparatus according to any one of claims 1 to 7, the image forming apparatus, wherein a width of each pattern is set based on the period of change in the moving speed of the carriage.

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