JP5919771B2 - Image forming apparatus, pattern position detecting method, and image forming system - Google Patents

Description

  The present invention relates to an image forming apparatus that reads a test pattern of a plurality of lines formed on a recording medium and adjusts a droplet discharge timing.

  There is known an image forming apparatus that forms an image by discharging droplets onto a sheet material such as paper (hereinafter, referred to as a liquid discharge type image forming apparatus). Liquid discharge type image forming apparatuses can be roughly classified into serial type and line head type. In the serial image forming apparatus, the recording head reciprocates at right angles to the paper feeding direction (in the main scanning direction) while repeating paper feeding to form an image on the entire paper. In the line head type image forming apparatus, the nozzles are arranged to be approximately the same length as the maximum paper width, and the nozzles in the line head discharge the liquid droplets when the paper is sent and the liquid droplets are discharged. Form.

  However, it is known that in a serial type image forming apparatus, when a single ruled line is formed in both directions of the forward path and the return path, positional deviation of the ruled line is likely to occur in the forward path and the return path. Also, in line head type image forming apparatuses, it is known that a line parallel to the paper feed direction is likely to appear if there is a nozzle whose landing position steadily shifts due to nozzle processing accuracy or mounting errors. Yes.

  For this reason, an adjustment function for adjusting the landing position of a droplet may be mounted on a liquid ejection type image forming apparatus (see, for example, Patent Document 1). In Patent Document 1, a water-repellent member having water repellency is composed of a reference pattern composed of a plurality of independent droplets and a plurality of independent droplets ejected under ejection conditions different from the reference pattern. Reading means comprising a pattern forming means for forming the measured patterns side by side in the scanning direction of the recording head, a light emitting means for irradiating each pattern with light, and a light receiving means for receiving specularly reflected light from each pattern And a correction unit that measures the distance between the patterns based on the reading result of the reading unit and corrects the droplet discharge timing of the recording head based on the measurement result. Has been.

  However, it is necessary to adjust the ejection timing for each ink color (for each nozzle). However, since the intensity of reflected light varies depending on the color, there are the following problems.

  FIG. 1A is an example of a diagram schematically illustrating a light receiving element that reads a black test pattern. When the spot light irradiated by the LED scans the test pattern in the direction of the arrow, reflected light corresponding to the density at the scanning position of the spot light is detected by the light receiving element. As is well known, light is well absorbed by a black object. For example, if the sheet material is white and the test pattern is black, the spot light when the test pattern is scanned is not easily reflected. If the reflected light received by the light receiving element is represented by a detection voltage, as shown in the figure, the detection voltage when the spot light is superimposed on the test pattern is significantly lower than the detection voltage when scanning other than the test pattern. .

  FIG. 1B is an example of an enlarged view showing a change in voltage obtained from a black test pattern. The horizontal axis is, for example, time or spot light scanning position. The elongated circle indicates a region where the voltage changes rapidly. It is presumed that the edge of the line constituting the test pattern is in this region. For example, when the detected voltage indicates an inflection point, it is determined that the center of gravity of the spot light is scanning the edge of the test pattern.

  FIG. 1C schematically shows an example of a light-receiving element that reads a black and magenta test pattern, and FIG. 1D shows an enlarged change in voltage obtained from the black and magenta test pattern. It is an example of the figure shown. The minimum value of the detection voltage reflected from the magenta line is larger than that of black.

  In other words, if the light emitting element has a single wavelength but the line color of the test pattern is different, the intensity of the reflected light when the spot light passes through the line changes depending on the color. It is difficult to accurately obtain the distance between the test patterns. More specifically, even if the inflection point of the detection voltage obtained from the black line is correctly obtained, it is difficult to correctly obtain the inflection point of the detection voltage obtained from the magenta line. This is because the image forming apparatus sets the inflection point calculation range in advance with respect to the detection voltage. In magenta, since the inflection point does not enter this calculation range, the error of the obtained edge position becomes large.

  Mounting the light emitting elements corresponding to the respective colors on the image forming apparatus so that the signal waveforms when passing the test pattern are the same results in an increase in cost, and it is necessary to prepare mounting spaces corresponding to the number of light emitting elements. Give rise to

  In view of the above problems, an object of the present invention is to provide an image forming apparatus that can accurately determine the position of a test pattern from the waveform of reflected light even if the ink color of the test pattern is different.

In view of the above problems, the present invention provides an image forming apparatus that reads a test pattern composed of a plurality of lines formed on a recording medium and adjusts the discharge timing of the liquid droplets, and emits light to the recording medium. And a reading means having a light receiving means for receiving reflected light from the recording medium, a pattern data storage means for storing pattern data for forming the test pattern, and a test pattern is formed by reading the pattern data A test pattern forming unit that moves the recording medium or the reading unit at a relatively constant speed, and the light receiving unit moves from the scanning position of the light while the light is moving through the test pattern. Intensity data storage means for storing intensity data of the received reflected light, and before being included within a lower limit from a predetermined upper limit A position detecting means for detecting a position of the line subjected to line position determination calculation the intensity data, wherein the test pattern forming means, at least the ejection timing of the color of the line drop out before Symbol plurality of lines A test pattern formed from a first droplet discharged from a nozzle to be adjusted and a second droplet different from the first droplet is formed.

  It is possible to provide an image forming apparatus that can accurately determine the position of a test pattern from the waveform of reflected light even if the ink color of the test pattern is different.

It is an example of the figure which illustrates typically the light receiving element which reads a test pattern. It is an example of the figure explaining the outline of the formation method of a test pattern. 1 is an example of a schematic perspective view of a serial type image forming apparatus. It is an example of the figure explaining the operation | movement of a carriage in detail. 2 is an example of a block diagram of a control unit of the image forming apparatus. FIG. FIG. 2 is an example of a diagram schematically illustrating a configuration for a print position deviation sensor to detect an edge of a test pattern. It is an example of a functional block diagram of a correction processing execution unit It is a figure which shows an example of a spot light and a test pattern. It is a figure which shows an example of a spot light and a test pattern. It is an example of the figure explaining the identification method of an edge position. It is a figure which shows an example of the increase rate of an absorption area and an absorption area, respectively. It is an example of the figure explaining the diameter of a spot light, and the line width of a test pattern. It is an example of the figure explaining the diameter of a spot light, and the line width of a test pattern. FIG. 2 is an example of a diagram schematically illustrating a head arrangement and a test pattern of a line type image forming apparatus. It is an example of the figure which shows the test pattern at the time of forming the test pattern of each color by a single color. It is a figure which shows an example of the test pattern in which the background pattern of the ink color Y with a small reflection intensity of a different color was overlapped with the ink color M with a high reflection intensity. FIG. 6 is an example of a diagram for explaining in more detail a magenta test pattern and a detection voltage when the reflection intensity reducing ink is yellow. FIG. 5 is an example of a diagram for explaining in more detail a magenta test pattern and a detection voltage when the reflection intensity reducing ink is black; FIG. 6 is an example of a diagram schematically showing a magenta test pattern and a detection voltage when the ink for reducing reflection intensity is a plurality of colors. It is a flowchart figure which shows an example of the procedure in which a correction process execution part correct | amends a droplet discharge timing. It is a figure which respectively shows an example of the detection voltage with an unstable amplitude, and the detection voltage after an amplitude correction | amendment. It is an example of the functional block diagram of a correction process execution part (Example 2). It is a figure which shows an example of the measurement result of n times scanning. It is an example of the figure explaining a synchronous process. It is an example of the figure explaining filter processing. It is an example of the figure explaining n times scanning. It is an example of the figure explaining a synchronous process. It is an example of the figure explaining Vsg and Vp. It is a figure which shows an example of the output waveform of pattern measurement data, and an example of the output waveform of blank sheet measurement data, respectively. It is an example of the figure which illustrates typically the detection voltage z obtained from x 'and y'. It is a flowchart figure which shows an example of the procedure which a correction process execution part correct | amends a signal. It is an example of the flowchart figure explaining the process of a correction process execution part. 1 is an example of a diagram schematically illustrating an image forming system having an image forming apparatus and a server. 2 is a diagram illustrating an example of a hardware configuration diagram of a server and an image forming apparatus. FIG. 1 is an example of a functional block diagram of an image forming system. FIG. 3 is an example of a flowchart illustrating an operation procedure of the image forming system.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 2 is an example for explaining the outline of the test pattern forming method of the present embodiment. FIG. 2A shows an example of a detection voltage having a different minimum value due to a difference in ink color. Since the light emitting element has a single wavelength, the intensity of the reflected light when the spot light passes on the line changes depending on the color of the line of the test pattern (hereinafter, the test pattern and the lines constituting the test pattern) Will be explained without distinction.) For this reason, the position (voltage value) of the inflection point differs greatly depending on the color.

  In view of this, the image forming apparatus according to the present exemplary embodiment forms a background pattern in an overlapping manner when an ink color (for example, magenta) test pattern in which the inflection point does not fall within the calculation range due to high reflection intensity.

  The background pattern can only be formed with a discharge density that does not fall within the inflection point calculation range with the ink alone (condition 1). This is because if the detection voltage of the background pattern alone falls within the inflection point calculation range, it cannot be distinguished whether the inflection point is due to the background pattern or the magenta. Further, the background pattern reflects the spot light together with the test pattern, so that the background pattern has a drawing density such that the inflection point falls within the calculation range (Condition 2).

  FIG. 2B shows a test pattern in which a background pattern is superimposed on a magenta test pattern and its detected voltage. The background pattern is formed by, for example, yellow large droplets or black small droplets. There are no restrictions on the color combinations of the test pattern and the background pattern. This is because a background pattern that satisfies the conditions 1 and 2 can be formed by adjusting the drawing density of the background pattern.

  In the figure, large yellow droplets are formed as a background pattern. Therefore, as shown in the drawing, even for magenta having a high reflection intensity, the background pattern can absorb light and the reflection intensity can be included in the inflection point calculation range. Therefore, the inflection points of the respective colors can be brought close to each other, and the detection accuracy of the test pattern position can be improved.

[Configuration example]
FIG. 3 shows an example of a schematic perspective view of the serial type image forming apparatus 100. The image forming apparatus 100 is supported by the main body frame 70. A guide rod 1 and a width guide 2 are spanned in the longitudinal direction of the image forming apparatus 100, and a carriage 5 is held on the guide rod 1 and the sub guide 2 so as to be able to reciprocate in the arrow A direction (main scanning direction). Yes.

  In the main scanning direction, an endless belt-like timing belt 9 is stretched around a driving pulley 7 and a pressure roller 15, and a part of the timing belt 9 is fixed to the carriage 5. Further, the drive pulley 7 is driven to rotate by the main scanning motor 8, whereby the timing belt 9 moves in the main scanning direction, and the carriage 5 also reciprocates in conjunction with it. The timing belt 9 is tensioned by a pressure roller 15, and the timing belt 9 can drive the carriage 5 without sagging.

  The image forming apparatus 100 also includes a cartridge 60 that supplies ink and a maintenance mechanism 26 that maintains and cleans the recording head.

  The sheet material 150 is intermittently conveyed in the arrow B direction (sub-scanning direction) by a roller (not shown) on the platen 40 below the carriage 5. The sheet material 50 may be a recording medium to which droplets can adhere, such as plain paper such as paper, glossy paper, film, and electronic substrate. The carriage 5 moves in the main scanning direction for each conveyance position of the sheet material 150, and a recording head mounted on the carriage 5 discharges droplets. When the discharge is finished, the sheet material 150 is conveyed again, and the carriage 5 moves in the main scanning direction to discharge the droplets. By repeating this, an image is formed on the entire surface of the sheet material 150.

  FIG. 4 is an example of a diagram for explaining the operation of the carriage 5 in more detail. The guide rod 1 and the sub guide 2 are stretched between the left side plate 3 and the right side plate 4, and the carriage 5 holds the guide rod 1 and the sub guide 2 slidably by the bearing 12 and the sub guide receiving portion 11. , And can be moved in the directions of arrows X1 and X2 (main scanning direction).

  The carriage 5 includes recording heads 21 and 22 that discharge black (K) droplets and recording heads 23 and 24 that discharge ink droplets of cyan (C), magenta (M), and yellow (Y). Has been. The recording head 21 is arranged because black is often used, and can be omitted.

  As the recording heads 21 to 24, a piezoelectric element is used as a pressure generating means (actuator means) for pressurizing ink in the ink flow path (pressure generating chamber), and a diaphragm that forms the wall surface of the ink flow path is deformed. The so-called piezo type that discharges ink drops by changing the volume in the ink flow path, and discharges ink drops with pressure by heating the ink in the ink flow path using a heating resistor to generate bubbles A so-called thermal type or a diaphragm that forms the wall surface of the ink flow path and an electrode are arranged opposite to each other, and the diaphragm is deformed by an electrostatic force generated between the vibration plate and the electrode, whereby the ink flow path An electrostatic type that discharges ink droplets by changing the internal volume can be used.

  The main scanning mechanism 32 that moves and scans the carriage 5 is disposed on one side in the main scanning direction, the drive pulley 7 that is rotationally driven by the main scanning motor 8, and the other side in the main scanning direction. And a timing belt 9 wound around between the driving pulley 7 and the pressure roller 15. The pressure roller 15 is tensioned outward (in a direction away from the drive pulley 7) by a tension spring (not shown).

  A part of the timing belt 9 is fixedly held by a belt holding unit 10 provided on the back side of the carriage 5, and the carriage 5 is pulled in the main scanning direction as the timing belt 9 moves endlessly.

  Further, an encoder sheet 41 is arranged along the main scanning direction of the carriage 5, and the position of the carriage 5 in the main scanning direction is read by reading the slit of the encoder sheet 42 by the encoder sensor 42 provided on the carriage 5. Can be detected. When the carriage 5 is present in the recording area of the main scanning area, the sheet material 150 is intermittently moved in the arrow Y1 and Y2 directions (sub-scanning direction) perpendicular to the main scanning direction of the carriage 5 by a paper feed mechanism (not shown). Be transported.

  In the image forming apparatus 100 according to the present embodiment described above, the recording heads 21 to 24 are driven according to the image information while moving the carriage 5 in the main scanning direction and intermittently feeding the sheet material 150. A desired image can be formed on the sheet material 150 by ejecting the droplets.

  On one side surface of the carriage 5, a print position deviation sensor 30 for detecting a deviation in the landing position (reading a test pattern) is mounted. The print position deviation sensor 30 reads a test pattern for detecting the landing position formed on the sheet material 150 by a light receiving element constituted by a light emitting element such as an LED and a reflective photosensor.

  Since the print position deviation sensor 30 is for the recording head 21, it is preferable to mount another print position deviation sensor 30 in parallel with the recording heads 22 to 24 in order to adjust the droplet discharge timing of the recording heads 22 to 24. . If the carriage 5 is equipped with a mechanism for sliding the print position deviation sensor 30 so as to be in parallel with the recording heads 22 to 24, the single print position deviation sensor 30 can eject droplets from the recording heads 22 to 24. The timing can be adjusted. Alternatively, even when the image forming apparatus 100 sends the sheet material 150 in the reverse direction, the droplet discharge timings of the recording heads 22 to 24 can be adjusted by the single print position deviation sensor 30.

  FIG. 5 is an example of a block diagram of the control unit 300 of the image forming apparatus 100. The control unit 300 includes a main control unit 310 and an external I / F 311. The main control unit 310 includes a CPU 301, a ROM 302, a RAM 303, an NVRAM 304, an ASIC 305, and an FPGA (Field Programmable Gate Array) 306. The CPU 301 executes a program 3021 stored in the ROM 302 to control the entire image forming apparatus 100. In addition to this program 3021, the ROM 302 stores fixed data such as initial values and control parameters. The RAM 303 is a working memory that temporarily stores programs, image data, and the like, and the NVRAM 304 is a non-volatile memory that holds data such as setting conditions while the apparatus is powered off. The ASIC 305 performs various signal processing and rearrangement on the image data, and controls various engines. The FPGA 306 processes input / output signals for controlling the entire apparatus.

  The main control unit 310 controls the entire apparatus and controls related to test pattern formation, test pattern detection, landing position adjustment (correction), and the like. As will be described later, in this embodiment, the CPU 301 mainly executes the program 3021 stored in the ROM 302 to detect the edge position. However, part or all of the processing may be performed by an LSI such as the FPGA 306 or the ASIC 305.

  The external I / F 311 is a communication device for communicating with other devices connected to the network, a bus and a bridge for connecting to the USB and IEEE1394, and sends data from the outside to the main control unit 310. The external I / F 311 outputs the data generated by the main control unit 310 to the outside. A removable storage medium 320 can be attached to the external I / F 311, and the program 3021 is distributed in a state stored in the storage medium 320 or via an external communication device.

  The control unit 300 includes a head drive control unit 312, a main scanning drive unit 313, a sub-scanning drive unit 314, a paper feed drive unit 315, a paper discharge drive unit 316, and a scanner control unit 317. The head drive control unit 312 controls the presence / absence of ejection of each of the recording heads 21 to 24, the droplet ejection timing and the ejection amount when ejecting. The head drive control unit 312 has an ASIC for head data generation array conversion for controlling the drive of the recording heads 21 to 24 (head driver), and based on the print data (dot data subjected to dither processing), A drive signal indicating the presence / absence of a droplet and the size of the droplet is generated and supplied to the recording heads 21 to 24. Each of the recording heads 21 to 24 has a switch for each nozzle, and the recording heads 21 to 23 have a size designated at the position of the sheet material 150 designated by the print data by being turned on / off based on the drive signal. Land the droplet. The head driver of the head drive control unit 312 may be provided on the recording heads 21 to 24 side, or the head drive control unit 312 and the recording heads 21 to 24 may be integrated. The illustrated configuration is an example.

  A main scanning drive unit (motor driver) 313 drives a main scanning motor 8 that moves and scans the carriage 5. The main controller 310 is connected to the encoder sensor 42 that detects the carriage position described above, and the main controller 310 detects the position of the carriage 5 in the main scanning direction based on the output signal. Then, the carriage 5 is reciprocated in the main scanning direction by drivingly controlling the main scanning motor 8 via the main scanning driving unit 313.

  A sub-scanning driving unit (motor driver) 314 drives a sub-scanning motor 132 for feeding paper. An output signal (pulse) from the rotary encoder sensor 131 that detects the amount of movement in the sub-scanning direction is input to the main control unit 310, and the main control unit 310 detects the paper feed amount based on this output signal, By driving and controlling the sub-scanning motor 132 through the scanning drive unit 314, the sheet material is fed through a conveyance roller (not shown).

  A paper feed driver 315 drives a paper feed motor 133 that feeds a sheet material from a paper feed tray. The paper discharge driving unit 316 drives a paper discharge motor 134 that drives a roller for discharging the sheet material 150 on which an image is formed onto the platen. The paper discharge drive unit 316 may be substituted by the sub-scanning drive unit 314.

  The scanner control unit 317 controls the image reading unit 135. The image reading unit 135 optically reads a document and generates image data.

  The main control unit 310 is connected to an operation / display unit 136 including various keys such as a numeric keypad and a print start key and various displays. The main control unit 310 receives a key input operated by the user via the operation / display unit 136, displays a menu, and the like.

  Although not shown in the drawings, a recovery drive unit for driving a maintenance recovery motor that drives the maintenance mechanism 26, a solenoid drive unit (driver) for driving various solenoids (SOL), a clutch for driving electromagnetic cracks, etc. You may have a drive part. In addition, detection signals from various other sensors (not shown) are also input to the main control unit 310, but are not shown.

  The main control unit 310 performs a process of forming a test pattern on the sheet material, and performs light emission drive control for causing the light emitting element of the print misregistration sensor 30 mounted on the carriage 5 to emit light with respect to the formed test pattern. Then, the output signal of the light receiving element is acquired, the reflected light of the test pattern is electrically read, the landing position deviation amount is detected from the read result, and the droplet ejection of the recording heads 21 to 24 is further performed based on the landing position deviation amount. Control is performed to correct the timing so that the landing position deviation is eliminated.

[Correction of landing position deviation]
FIG. 6 is an example of a diagram schematically illustrating a configuration for the print position deviation sensor 30 to detect the edge position of the test pattern. FIG. 6 is a view of the recording head 21 and the print position deviation sensor 30 of FIG. 4 as viewed from the right side plate 4.

  The print position deviation sensor 30 has a light emitting element 402 and a light receiving element 403 arranged in a direction orthogonal to the main scanning direction. The arrangement of the light emitting element 402 and the light receiving element 403 may be reversed. The light emitting element 401 projects spot light, which will be described later, onto the test pattern 400, and the light receiving element 403 receives light reflected by the sheet material 150, reflected light from the platen 40, and other scattered light. The light emitting element 402 and the light receiving element 403 are fixed to the inside of the housing, and the surface of the printing position deviation sensor 30 facing the platen 40 is shielded from the outside by a lens 405. As described above, the print position deviation sensor 30 is packaged and can be distributed alone.

  In the print position deviation sensor 30, the light emitting element 402 and the light receiving element 403 are arranged in a direction orthogonal to the scanning direction of the carriage 5 (arranged in parallel in the sub-scanning direction). Thereby, the influence on the detection result by the movement speed fluctuation | variation of the carriage 5 can be reduced.

  The light emitting element 402 is, for example, an LED, and the peak emission wavelength is 563 nano [m] corresponding to green. In addition, the light receiving element 403 has a peak light receiving sensitivity wavelength of 560 nanometers according to the light emitting element. The reason why such a wavelength is adopted is that the ink color of the test pattern is mainly K, M, and C, but the reflection intensity of both the M and C inks becomes small (is easily absorbed), and the wavelength is 560 nanometers [m. ] For the periphery. For this reason, when the ink color is other than the above (K, M, C), the wavelength of the light emitting element 402 may be designed if necessary.

  Further, the spot diameter formed by the light emitting element 402 is in the order of mm in order to use an inexpensive lens without using a highly accurate lens. Although this spot diameter is related to the edge detection accuracy of the test pattern, the edge position can be detected with sufficiently high accuracy even in the mm order if the edge position is obtained in the present embodiment. However, it is possible to make the spot diameter smaller.

  The CPU 301 starts the landing position deviation correction at a predetermined timing. This timing is specified, for example, when the user gives an instruction to correct landing position deviation from the operation / display unit 136, and because the light emitting element 402 emits light before the ink is ejected by the CPU 301, and the intensity of reflected light at that time is less than a predetermined value. The timing at which the sheet material 150 is determined, the temperature and humidity at the time of the last landing position deviation correction are stored, and the timing at which it is determined that either the temperature or the humidity has deviated by more than a threshold value, periodically (every day, Weekly, monthly, etc.).

  The formation of the test pattern will be described. The CPU 301 instructs the main scanning control unit 313 to reciprocate the carriage 5 and the head drive control unit 312 to discharge droplets using a predetermined test pattern as print data. The main scanning control unit 313 causes the carriage 5 to reciprocate in the main scanning direction with respect to the sheet material 150, and the head drive control unit 312 ejects droplets from the recording head 21, so that at least two or more independent members are used. A test pattern including a line is formed.

  Further, the CPU 301 performs control for reading the test pattern formed on the sheet material 150 by the print position deviation sensor 30. Specifically, the CPU 301 sets a PWM value for driving the light emitting element 402 of the printing position deviation sensor 30 in the light emission control unit 511, and the output of the light emission control unit 511 is smoothed by the smoothing circuit 512, and the driving circuit. 513. The drive circuit 513 drives the light emitting element 402 to emit light, and the spot light is irradiated from the light emitting element 402 to the test pattern of the sheet material 150. The light emission control unit 511, the smoothing circuit 512, the drive circuit 513, the photoelectric conversion circuit 521, the low-pass filter 522, the A / D conversion circuit 523, and the correction processing execution unit 526 are mounted on the main control unit 310 or the control unit 300. ing. The shared memory 525 is, for example, the RAM 303.

  By irradiating the test pattern on the sheet material with the spot light from the light emitting element 402, the reflected light reflected from the test pattern enters the light receiving element 403. The light receiving element 403 outputs an intensity signal of the reflected light to the photoelectric conversion circuit 521. Specifically, the photoelectric conversion circuit 521 photoelectrically converts the intensity signal and outputs this photoelectric conversion signal to the low-pass filter circuit 522. The low-pass filter circuit 522 outputs a photoelectric conversion signal to the A / D conversion circuit 523 after removing high-frequency noise. The A / D conversion circuit 523 A / D converts the photoelectric conversion signal and outputs the signal to a signal processing circuit (FPGA) 306. The signal processing circuit (FPGA) 306 stores in the shared memory 525 detection voltage data (detection voltage and detection voltage data are used without distinction), which is a digital value of the A / D converted detection voltage. The intensity data storage means in the claims corresponds to, for example, the shared memory 525.

  The correction processing execution unit 526 reads the detection voltage data stored in the shared memory 525, corrects the landing position deviation, and sets it in the head drive control unit 312. That is, the correction processing execution unit 526 calculates the landing position deviation amount by detecting the edge position of the test pattern and comparing it with the appropriate distance between the two lines.

  The correction processing execution unit 526 calculates a correction value of the droplet discharge timing when driving the recording head 21 so that the landing position deviation is eliminated, and sends the calculated correction value of the droplet discharge timing to the head drive control unit 312. Set. Accordingly, when the recording head 21 is driven, the head driving control unit 312 corrects the droplet discharge timing based on the correction value and then drives the recording head 21, thereby reducing the landing position deviation of the droplet. be able to.

  FIG. 7 is an example of a functional block diagram of the correction process execution unit 526. The correction process execution unit 526 includes a test pattern formation unit 617, an ejection timing correction unit 616, and a pattern data storage unit 618. The test pattern forming unit 617 forms a test pattern for each color (for each recording head 22 to 24) on a sheet material. The ejection timing correction unit 616 corrects the droplet ejection timing based on the landing position deviation amount obtained from the edge position of the test pattern. Details of these processes will be described later.

The pattern data storage unit 618 stores pattern data of a test pattern for each color ink and a background pattern. Since there are no restrictions on the combination of the test pattern and background pattern colors, various combinations are possible. In the present embodiment, a single color background pattern may include a plurality of colors of ink. In the pattern data storage unit 618, combinations of test patterns and background patterns are determined in advance.
Magenta test pattern: magenta + yellow background pattern
Magenta + black background pattern
Magenta + yellow + black background pattern [spot light position and edge position]
Next, the relationship between the spot light and the edge position will be described with reference to FIGS.
FIG. 8 is a diagram illustrating an example of the spot light and the test pattern. The spot light moves so as to cross a plurality of lines (one line in the figure) constituting the test pattern at a constant speed (constant speed). The speed of crossing may be variable, but is constant during the crossing. Since the sheet material such as paper is moved in the longitudinal direction of the line by paper feeding, the spot light moves diagonally across the line, but the edge position specifying method is the same even if the sheet material stops. . In the spot light of a general wavelength and the sheet material, the reflected light of the spot light may decrease as the overlapping area of the test pattern increases.

  In FIGS. 8 and 9, the spot diameter d = the line width L of the test pattern. Actually, the spot light becomes a slight ellipse, but since the ellipse has a long axis parallel to the test pattern, the shape of the spot light hardly affects the accuracy of the edge position.

FIG. 9 is an example of a diagram illustrating a specific outline of the edge position according to the present embodiment. Numbers I to V in FIG. 9A indicate the passage of time, and the lower the spotlight, the longer the passage of time.
Time I: Spot light and test pattern do not overlap.
Time II: Half of the spot light is superimposed on the test pattern. At this moment, the reduction rate of the reflected light becomes the largest (the overlapped area changes most positively in unit time).
Time III: The entire spot light is superimposed on the test pattern. At this moment, the intensity of the reflected light becomes the smallest.
Time IV: Half of the spot light is superimposed on the test pattern. At this moment, the increase rate of the reflected light becomes the largest (the overlapping area changes most negatively per unit time).
Time V: The spot light passes through the test pattern, and the spot light and the test pattern do not overlap.

  It is time II and IV that the center of gravity of the spot light coincides with the edge position of the line of the test pattern. Therefore, if it can be detected from the reflected light that the spot light and the line have the relationship between the times II and IV, the edge position can be specified with high accuracy.

  FIG. 9B shows an example of the detection voltage of the light receiving element, FIG. 9C shows an example of the absorption area (the overlapping area of the spot light and the test pattern), and FIG. 9D shows the absorption of FIG. 9C. An example of the increase rate of the absorption area obtained by differentiating the area is shown. In FIG. 9D, equivalent information can be obtained even if the output waveform of FIG. 9B is differentiated. Moreover, although the absorption area is calculated from the detection voltage, for example, it does not have to be an absolute value. Therefore, the absorption area in FIG. 9C is obtained by subtracting the detection voltage in FIG. 9B from the predetermined value. A waveform similar to is obtained.

  As described above, the decrease rate of the reflected light becomes the largest at time II (the overlapping area changes most positively in unit time), and the increase rate of the reflected light becomes the largest at time IV (superimposition). Area changes most negatively per unit time). As shown in FIG. 9 (d), the point at which the increase rate changes from an increasing trend to a decreasing trend is coincident with time II, and the point at which the increase rate changes from a decreasing trend to an increasing trend is at time IV Is consistent with

  A point that changes from an increasing tendency to a decreasing tendency or vice versa is a point where the bending direction changes in a curved line on a plane, that is, an inflection point. From the above, if the output signal indicates an inflection point, the spot light coincides with the edge position of the test pattern. Therefore, if the inflection point is detected with high accuracy, the edge position can also be specified with high accuracy.

[Identification of edge position]
FIG. 10 is an example of a diagram illustrating a method for specifying an edge position. FIG. 10A is a schematic diagram of the detection voltage, and FIG. 10B is an enlarged view of the detection voltage. The approximate value of the inflection point can be obtained experimentally by the correction processing execution unit 526 or the developer. As described above, for example, the inflection point is a position where the detected voltage and the absorption area are differentiated and the inclination is closest to zero.

  The upper limit threshold value Vru and the lower limit threshold value Vrd of the detection voltage are determined in advance so that this inflection point is included. As will be described later, the CPU 301 calibrates the output of the light emitting element 402 and the sensitivity of the light receiving element 403 so that the detection voltage becomes substantially the same constant value (4 [V] described later) in an area where there is no test pattern. By correcting the drawing density according to the present embodiment, the maximum value of the detection voltage can be set to substantially the same constant value, so that an inflection point is included between the upper limit threshold value Vru and the lower limit threshold value Vrd.

  The discharge timing correction unit 616 searches for the falling portion of the detected voltage in the direction indicated by the arrow Q1, and stores the point where the detected voltage is equal to or lower than the lower limit threshold Vrd as the point P2. Next, the point P2 is searched in the direction of the arrow Q2, and the point where the detected voltage exceeds the upper limit threshold value Vru is stored as the point P1.

  Then, a regression line L1 is calculated using a plurality of detection voltage data between the points P1 and P2, and an intersection point between the regression line L1 and the upper and lower threshold intermediate value Vc is calculated as an intersection point C1.

  Similarly, the discharge timing correction unit 616 searches the rising portion of the detected voltage in the direction indicated by the arrow Q3, and stores the point where the detected voltage is equal to or higher than the lower limit threshold Vru as the point P4. Next, a search is made from the point P4 in the direction indicated by the arrow Q4, and the point where the detected voltage is equal to or lower than the upper threshold value Vrd is stored as the point P3.

  Then, a regression line L2 is calculated using a plurality of detected voltage data between the points P3 and P4, and an intersection point between the regression line L2 and the intermediate value Vc of the upper and lower thresholds is calculated as an intersection point C2. Since the intersection point C1 and the intersection point C2 are edge positions of one line, the center of the intersection points C1 and C2 is a line center.

  Thereafter, the ejection timing correction unit 616 calculates line centers of a plurality of lines, and calculates a difference between an ideal distance between two lines of the test pattern and a distance between the line centers. Since this difference is a deviation of the actual line position from the ideal line position, it becomes the landing position deviation amount. The discharge timing correction unit 616 calculates a correction value for correcting the timing (droplet discharge timing) for discharging a droplet from the recording head 21 based on the calculated landing position deviation amount, and uses the correction value as the head drive control unit 312. Set to. As a result, the head drive control unit 312 drives the recording head 21 at the corrected droplet discharge timing, so that landing position deviation is reduced.

[Cause of reduced accuracy]
As described above, when an edge is detected using detection voltage data between the upper threshold and the lower threshold, the edge cannot be detected unless at least an inflection point is included between the upper threshold and the lower threshold. The width formed by the upper threshold and the lower threshold (two thresholds) is hereinafter referred to as a “threshold region”. The threshold region is based on the detection voltage, but can also be defined by the absorption area corresponding to the detection voltage.

  FIG. 11 is a diagram illustrating an example of an absorption area and an increase rate of the absorption area. If there is an inflection point in the threshold area A of FIG. 11, the ejection timing correction unit 616 can detect the edge position with high accuracy as described in FIG.

  On the other hand, if there is an inflection point in the threshold area B of FIG. 11, the ejection timing correction unit 616 cannot detect an accurate edge position even if a regression line is obtained from the A threshold area. Further, if it is known that the inflection point is in the B threshold area, the discharge timing correction unit 616 can obtain the regression line by moving the threshold area from A to B. If the position is greatly shifted, there is a possibility that the curve of the detection voltage or the absorption area is deformed. For example, if the discharge timing correction unit 616 obtains a regression line from a threshold region where the slope of the curve has increased, the intersections C1 and C2 may also be greatly shifted. In the lower diagram of FIG. 11, the width of the position including the vicinity of the vertex can be estimated in a sufficiently narrow range in the threshold area A, whereas the inflection point (in the threshold area B in FIG. 11) is estimated in the B threshold area. This is indicated by the fact that the width of the position including the vicinity is difficult to estimate in a narrow range.

  Therefore, when the amplitude of the detected voltage fluctuates so that the inflection point does not enter the threshold area A, the edge position is specified from the threshold area A, or the inflection point itself is obtained and the threshold area is moved to move the edge position. It can be seen that determining is not preferred.

  Therefore, the correction processing execution unit 526 of the present embodiment changes the droplet drawing density so that the light receiving element 403 detects the same detection voltage even if the colors are different, thereby changing the position of the inflection point ( (Voltage value) enters the threshold region. Thereby, the edge position can be detected with high accuracy.

[Spot light diameter and test pattern line width]
In FIG. 8, the spot diameter d = the line width L of the test pattern, but the edge position can be detected even if “spot diameter d> the line width L of the test pattern” or “spot diameter d <the line width L of the test pattern”. It is.

  FIG. 12A shows an example of the spot light and the test pattern in the relationship of the spot diameter d> the line width L of the test pattern. Here, it is assumed that “d / 2 <L <d”. 12B shows an example of the detection voltage of the light receiving element, FIG. 12C shows an example of the absorption area, and FIG. 12D shows the increase rate of the absorption area obtained by differentiating the absorption area of FIG. An example is shown respectively.

  Since the spot diameter d> the line width L of the test pattern means that the spot light and the test pattern do not completely overlap, as is apparent from the increase rate of the absorption area in FIG. When the right edge of the light passes the test pattern, the absorption area starts to decrease, and the increase rate decreases rapidly.

  However, in the present embodiment, if the detection voltage data near the inflection point is obtained, the intersections C1 and C2 can be obtained, so the diameter d of the spot light only needs to be d / 2 <L. That is, it is sufficient that the spot diameter d 1 is not extremely larger than the line width L of the test pattern.

  FIG. 13A shows an example of the spot light and the test pattern in the relationship of spot diameter d <line width L of the test pattern. FIG. 13 (b) shows an example of the detection voltage of the light receiving element, FIG. 13 (c) shows an example of the absorption area, and FIG. 13 (d) shows the increase rate of the absorption area obtained by differentiating the absorption area of FIG. 13 (c). An example is shown respectively.

  Since the spot diameter d <the line width L of the test pattern means that the state in which the spot light and the test pattern are completely superimposed continues, as shown in FIGS. A region having a constant absorption area is generated. Moreover, as shown in FIG.13 (d), the area | region where the increase rate of an absorption area becomes zero arises. After that, when the right end of the spot light gets over the test pattern, the absorption area starts to decrease, and the increase rate gradually decreases (the decrease rate increases).

  In such a case, similarly to FIG. 8, the detection voltage data near the inflection point is sufficiently obtained, so that the ejection timing correction unit 616 can sufficiently obtain the intersections C1 and C2.

[In the case of a line type image forming apparatus]
In this embodiment, the serial type image forming apparatus 100 of FIGS. 3 and 4 has been described as an example. However, the line type image forming apparatus 100 can also correct the landing position deviation amount by the same method. The line type image forming apparatus 100 will be briefly described.

  FIG. 14 is an example of a diagram for schematically explaining the head arrangement and the test pattern of the line type image forming apparatus 100. The head fixing bracket 160 is fixed so as to be spanned from end to end in the main scanning direction orthogonal to the sheet material conveyance direction. In the head fixing bracket 160, recording heads 180 of KCMY ink are arranged from the upstream side over the entire area in the main scanning direction. The recording heads 180 for each color are arranged in a staggered manner so that the ends overlap. By doing so, droplets with sufficient resolution are ejected even at the end of the recording head 180, so that it is not necessary to dispose one recording head 180 over the entire region in the main scanning direction, and an increase in cost can be suppressed. Note that one recording head 180 may be arranged in the entire region in the main scanning direction for each ink color, or the overlapping region in the main scanning direction of the recording head 180 for each color may be made longer.

  A sensor fixing bracket 170 is fixed downstream from the head fixing bracket 160 so as to be spanned from end to end in the main scanning direction orthogonal to the sheet material conveyance direction. The sensor fixing bracket 170 has as many print position deviation sensors 30 as the number of heads. That is, one print position deviation sensor 30 is arranged so as to at least partially overlap one print head 180 in the main scanning direction. Further, one printing position deviation sensor 30 has a pair of light emitting element 402 and light receiving element 403. The light emitting element 402 and the light receiving element 403 are arranged in parallel substantially in the main scanning direction.

  The image forming apparatus 100 having such a form forms each line constituting the test pattern so that the longitudinal direction of the line is parallel to the main scanning direction. When correcting landing position deviation of droplets of other colors based on K, the image forming apparatus 100 forms a K line and an M line, a K line and a C line, and a K line and a Y line. To do. Then, similarly to the serial type image forming apparatus 100, the edge position of the CMYK test pattern is detected, and the droplet discharge timing is corrected based on the positional deviation amount.

  As described above, also in the line type image forming apparatus 100, the landing position deviation can be corrected by appropriately arranging the print position deviation sensor 30.

[Background pattern]
15 and 16 are examples of diagrams for explaining the background pattern. First, FIG. 15 shows a test pattern when the test patterns of the respective colors are formed with a single color. The image forming apparatus forms test patterns for all the colors that can be ejected by the recording heads 21 to 24 (the test patterns of light colors may be omitted) and adjusts the ejection timing. (Black) and M (magenta) test patterns are illustrated.

  A detection voltage (output waveform) when the light receiving element 403 receives reflected light from the test pattern is shown below the test pattern. K and M are formed with the same drawing density (in the example, main scanning 600 × sub scanning 300 dpi). Since the drawing density is the same, the detection voltage is affected by the reflection intensity of the ink color. That is, black K has a low reflection intensity and thus a minimum value, but magenta M has a high reflection intensity and thus the minimum value does not decrease. “−” Intersecting the waveform indicates an inflection point, but the inflection point position does not approach in black and magenta, and the inflection point position does not enter the threshold area in magenta. For this reason, the accuracy of the position of the test pattern is lowered.

  FIG. 16 shows an example of a background pattern of the ink color yellow Y having a low reflection intensity, which is formed over the test pattern of the ink color magenta M having a high reflection intensity. In black and magenta, since the reflection intensity of magenta is larger, yellow droplets are ejected so as to overlap the magenta line.

A color such as yellow with respect to magenta is referred to as ink for reducing reflection intensity. The background pattern with the reflection intensity reducing ink is not limited in color (reflection intensity) as long as the following conditions are satisfied.
Condition 1) The background pattern has a drawing density that is less than the drawing density that does not enter the threshold region by itself.
Condition 2) The drawing density of the background pattern is such that the inflection point that did not enter the threshold area by the test pattern alone has a reflection intensity enough to enter the threshold area (for example, the reflection intensity decreases by the arrow ΔM in FIG. 15) Have an effect).

  By discharging the background pattern of the ink for decreasing the reflection intensity on magenta, the light of the light emitting element is absorbed and the minimum value can be reduced.

  Note that the general four-color ink for reducing reflection intensity of yellow, black, cyan, and magenta can form a background pattern that satisfies the conditions 1 and 2. This is because the background pattern can be formed with the drawing density of the reflection intensity just before entering the threshold region of Condition 1 for any color. If the ink color has a high reflection intensity such as yellow, the drawing density may be increased. If the ink color has a low reflection intensity such as black, the drawing density may be decreased.

<When the reflection intensity reducing ink is yellow>
FIG. 17 is an example of a diagram for explaining detection voltages of a magenta test pattern and a background pattern when the reflection intensity reducing ink is yellow.

  FIG. 17A schematically shows a yellow background pattern and a detection voltage. Even if only the yellow background pattern is formed and the light receiving element reads the reflected light, the inflection point of the detection voltage does not enter the threshold region. Further, the downward peak of the detection voltage is ΔM (only the yellow background pattern is formed on the sheet material 150, and the difference in reflection intensity between the portion where the yellow background pattern is formed and the portion of the sheet material 150 where there is no droplet) ). Thus, by setting the drawing density of the ink for reducing reflection intensity in advance, it is possible to prevent the detection accuracy of the magenta line position, which is the original test pattern color, from being affected.

  FIG. 17B is an example of a diagram schematically showing black and magenta test patterns and detection voltages as in the prior art. As described above, since the inflection point of the black detection voltage is in the threshold region, the detection accuracy of the line edge is stable. However, the inflection point of the magenta detection voltage is out of the threshold region, and it is expected that the detection accuracy of the edge of the magenta line will be lowered. If the inflection point of magenta becomes comparable to the inflection point of black, the inflection point of magenta is also included in the threshold area. The fact that the inflection point of magenta and the inflection point of black are approximately the same means that the minimum value of the black detection voltage and the minimum value of the magenta detection voltage are approximately the same. In this case, the difference between the inflection point of magenta and the inflection point of black and ΔM are approximately the same. In addition, since the inflection point of the magenta detection voltage only needs to be included in the threshold area, the difference between the inflection point of magenta and the inflection point of black and ΔM need not be the same. That is, ΔM may be slightly smaller than the difference between the magenta inflection point and the black inflection point.

  FIG. 17C is an example of a diagram schematically showing detection voltages of the magenta test pattern and the yellow background pattern of the present embodiment. A yellow droplet is superimposed on a magenta droplet as a background pattern. In addition to magenta, the reflection intensity reducing ink absorbs light from the light emitting element, so that the minimum value of the detection voltage obtained from the reflected light of magenta is sufficiently small, and the inflection point is in the threshold region. Therefore, by forming the background pattern so as to overlap the test pattern, it is possible to accurately detect the edge position of the test pattern having a high reflection intensity.

  In FIG. 17C, the magenta and yellow droplets do not overlap, but this is for explanation, and the droplets may be ejected in a superimposed manner. Since the light from the light emitting element passes through the superimposed droplets, a combined value of the reflection intensities of the two color droplets is obtained. In addition, since the light from the light emitting element passes through the superimposed droplets, the background pattern is discharged before (down) or after (up) the color pattern that is the detection target of the edge position. Also good. Since there is a degree of freedom in the order of ejection, the pattern of the background pattern and the test pattern can be ejected in either the forward path or the backward path of the recording head.

  Further, it is preferable that the background pattern is formed larger than the color pattern that is the detection target of the edge position in consideration of the deviation of the ejection position. In this case, it is not necessary to accurately form a test pattern color pattern in the center of the reflection intensity reducing ink. In other words, if the background pattern is made larger, the entire test pattern is included in the background pattern, so that precise alignment is unnecessary. If the pattern of the same color as the background pattern and the test pattern has the same size and is not precisely aligned, the edge position cannot be detected accurately at the portion where the pattern of the same color as the test pattern protrudes.

<When the reflection intensity reducing ink is black>
FIG. 18 is an example of a diagram for explaining detection voltages of a magenta test pattern and a background pattern when the reflection intensity reducing ink is black.

  FIG. 18A schematically shows a black background pattern and a detection voltage. As in the case of yellow, even when only the black background pattern is formed and the light receiving element reads the reflected light, the inflection point of the detection voltage does not enter the threshold region. Let the downward peak of the detection voltage be ΔM.

  FIG. 18B is the same as FIG. The inflection point of the black detection voltage is included in the threshold area, but the inflection point of the magenta detection voltage is out of the threshold area. ΔM is the same as that in FIG.

  FIG. 18C is an example of a diagram schematically showing detection voltages of the magenta test pattern and the black background pattern of the present embodiment. A black background pattern is superimposed on a magenta test pattern. In addition to magenta, black ink absorbs light from the light emitting element, so that the minimum value of the detection voltage obtained from the reflected light of magenta is sufficiently small, and the inflection point is in the threshold region. Therefore, the edge position of the test pattern having a high reflection intensity can be accurately detected by discharging the background pattern so as to overlap the ink of the test pattern.

  As shown in the figure, when the ink for reducing reflection intensity is black, the droplets are smaller than when it is yellow. This is because black has a lower reflection intensity than yellow. However, the size of the droplets of the background pattern may be such that the detection voltage of the test pattern does not fit in the threshold area (more specifically, the minimum value of the detection voltage is larger than the upper limit of the threshold area), and the ink liquid Drop size can be adjusted.

  Regardless of the ink for lowering reflection intensity, the function of the background pattern can be satisfied by reducing the size of the droplets and increasing the number of droplets accordingly. Therefore, as the background pattern, if the drawing density is such that the inflection point of the detected voltage does not fit in the threshold area even if it is read alone, the inflection point of the detected voltage read together with the test pattern fits in the threshold area. Good.

<In the case of multiple colors of ink for reducing reflection intensity>
FIG. 19 is an example of a diagram schematically showing detection voltages of a magenta test pattern and a background pattern when the reflection intensity reducing ink has a plurality of colors.

  FIG. 19A schematically shows a background pattern composed of two colors, yellow and black, and a detection voltage. Even when only the yellow and black patterns are formed and the light receiving element reads the reflected light, the inflection point of the detection voltage does not enter the threshold region. Let the downward peak of the detection voltage be ΔM.

  FIG. 19 (b) is the same as FIG. 17 (b). The inflection point of the black detection voltage is included in the threshold area, but the inflection point of the magenta detection voltage is out of the threshold area. ΔM is the same as that in FIG.

  FIG. 19C is an example of a diagram schematically showing detection voltages of a magenta test pattern and a black and yellow background pattern of the present embodiment. Yellow and black droplets are superimposed on the magenta pattern as a background pattern. In addition to magenta, the reflection intensity reducing ink absorbs light from the light emitting element, so that the minimum value of the detection voltage obtained from the reflected light of magenta is sufficiently small, and the inflection point is in the threshold region.

  Thus, the background pattern need not be formed of a single color. Further, the background pattern does not have to be two colors or less, and may include three or more colors (for example, further adding a cyan pattern) ink for reducing reflection intensity.

In the above description, magenta is used as the ink color of the test pattern, and the ink color of the background pattern is yellow or / and black. However, there are innumerable other combinations. When the test pattern ink color is cyan, the background pattern is black, magenta, magenta, and black. When the test pattern ink color is yellow, the background pattern is black, cyan, cyan, and black. (It is preferable to reduce the drawing density.)
Pattern data storage unit 618 stores experimentally obtained pattern data (a combination of test pattern ink color pattern data and background pattern ink color pattern data).

[Operation procedure]
FIG. 20A is a flowchart illustrating an example of a procedure in which the correction processing execution unit 526 corrects the droplet discharge timing.

  First, the CPU 301 instructs the main control unit 310 to start landing position deviation correction. In response to this instruction, the main control unit 310 drives the sub-scanning motor 132 via the sub-scanning driving unit 314 to convey the sheet material 150 to just below the recording head 21 (S1).

  Next, the main control unit 310 drives the main scanning motor 27 via the main scanning drive unit 313 to move the carriage 5 onto the sheet material 150 and receive light from the light emitting element at a specific location on the sheet material 150. The element is calibrated (S2).

  FIG. 20B is an example of a flowchart for explaining the process of S2. The calibration is a process of adjusting the light amount of the light emitting element so that the detection voltage of the light emitting element is adjusted within a desired range (for example, adjusted within a range of 4V ± 0.4 [V]).

  The CPU 301 sets a PWM value for driving the light emitting element 402 of the print position deviation sensor 30 in the light emission control means 511, smoothes it by the smoothing circuit 512, and then gives it to the driving circuit 513, whereby the driving circuit 513 The light emitting element 402 is driven to emit light (S21).

  The intensity signal detected by the light receiving element 403 of the printing position misalignment sensor 30 is stored in the shared memory 525, and the CPU 301 checks whether it has a desired voltage value (S22).

  If the desired voltage value is reached (OK in S22), the process in FIG. If the desired voltage value is not reached (No in S22), the CPU 301 changes the PWM value (S23) to readjust the light amount.

  Returning to FIG. 20A, the main control unit 310 moves the carriage 5 via the main scanning drive motor 27 without moving the paper while keeping the sub-scanning position of the sheet material 150 as it is. Then, the head drive control unit 312 drives the recording heads 21 to 24 using the pattern data stored in the pattern data storage unit 618 (S6). Thereby, a test pattern on which the background pattern is superimposed is formed on the sheet material. For example, when the correction processing execution unit 526 adjusts the landing position deviation of magenta based on black, a test pattern in which black and magenta lines are alternately formed is formed. The same applies to other colors.

  Next, the ejection timing correction unit 616 detects the edge position of the test pattern from the detected voltage data, and corrects the landing position deviation of the droplet (S12). That is, the ejection timing correction unit 616 calculates the landing position deviation amount by comparing the distance between the lines with the appropriate distance, calculates the correction value of the droplet ejection timing so as to eliminate the landing position deviation, and the head drive control unit 312 is set.

  As described above, the image forming apparatus according to the present exemplary embodiment superimposes the background pattern having a color different from the ink color of the pattern to be detected at the edge position so that the reflection intensity becomes the same for each ink color. Thereby, the position of the inflection point can be brought close even if the ink colors are different, and the edge position can be detected with high accuracy. As a result, the droplet discharge timing can be adjusted with high accuracy.

  In Example 1, the minimum value of the detection voltage is made small by superimposing the ink for reducing the reflection intensity on the ink color having the high reflection intensity, so that the inflection point enters the threshold region. However, the ink color and its reflection intensity are not the only factors that disturb the position of the inflection point.

[Cause of reduced accuracy]
As described with reference to FIG. 10, when an edge is detected using detection voltage data between the upper threshold value and the lower threshold value, an edge is detected if at least an inflection point is not included between the upper threshold value and the lower threshold value. It cannot be detected.

  FIG. 21A shows an example of a detection voltage with unstable amplitude, and FIG. 21B shows an example of a detection voltage after amplitude correction. The detection voltage as shown in FIG. 21A is generally not obtained. However, when the print position deviation sensor 30 reads a test pattern formed on the sheet material 150 having a high transmittance such as a tracing paper, the transparency of the paper It is known that the amplitude of the detection voltage varies due to unevenness (transmission variation), amplification of the sensitivity of the light receiving element, and the like. As shown in the figure, when the amplitude becomes unstable, the inflection point deviates from the threshold region. If the correction processing execution unit 526 obtains the intersection points C1 and C2 while maintaining the original threshold region, the intersection points C1 and C2 are obtained from the detection voltage that does not include the inflection point, so the edge position is not accurate. .

  On the other hand, as shown in FIG. 21B, the inflection points can be included in the threshold region and concentrated near the center of the threshold region by bringing the maximum value of the amplitude close to each other. become. Therefore, in this embodiment, an image forming apparatus capable of adjusting the ejection timing using the test pattern of Embodiment 1 and correcting the amplitude of the detection voltage even with a special sheet material will be described.

  In the present embodiment, a tracing paper is described as an example, but the same problem occurs if the sheet material 150 has a high transmittance. For example, when the plain paper other than the tracing paper is sufficiently thin, the edge position detection method of this embodiment is effective. Therefore, the droplet discharge timing correction processing of the present embodiment is not limited to the sheet material 150 having a specific material, type, and thickness. Also, it can be applied to plain paper having a sufficient thickness.

  FIG. 22 is an example of a functional block diagram of the correction processing execution unit 526 of the present embodiment. In FIG. 22, the description of the same parts as those in FIG. 7 is omitted. The correction processing execution unit 526 of the present embodiment includes a pre-printing preprocessing unit 611, a post-printing preprocessing unit 612, a synchronization processing unit 613, a pattern non-existence exclusion processing unit 614, an amplitude correction processing unit 615, and an ejection timing correction unit 616. Have The pre-printing pre-processing unit 611 performs pre-processing on the detection voltage data before the test pattern is formed, and the post-printing pre-processing unit 612 performs pre-processing on the detection voltage data after the test pattern is formed. The synchronization processing unit 613 synchronizes (matches) the detection voltage data before and after the test pattern is formed. The pattern non-existence exclusion processing unit 614 subtracts Vp described later from the detected voltage data. The amplitude correction processing unit 615 generates a detection voltage z for calculating the edge position by performing amplitude correction processing.

(Signal correction)
Hereinafter, detection signal correction of the detection voltage of this embodiment will be described. The signal correction of this embodiment is
-It has two corrections: pattern non-existence exclusion processing and amplitude correction processing.

In addition, preprocessing is required for signal correction. Therefore, the processing procedure is as follows.
(1) Preprocessing (2) Signal correction (2-1) Pattern non-existence exclusion processing, (2-2) Amplitude correction processing <Preprocessing>
Hereinafter, preprocessing will be described. Preprocessing can be divided into preprocessing A and preprocessing B. The pre-processing A is configured by the following processing on the detection voltage data in the blank state (background) before the test pattern is formed.
・ Pretreatment A
(i) n scans
(ii) Synchronous processing
(iii) Averaging
(iv) Filter processing Pre-processing B is configured by the following processing on detected voltage data after test pattern formation in which the drawing density is changed for each ink color.
・ Pretreatment B
(i) n scans
(ii) Synchronous processing
(iii) Averaging <Pretreatment A>
・ Pretreatment A- (i)
FIG. 23 is a diagram illustrating an example of a measurement result of n scans of A- (i). Prior to the n-th scanning, the n-time scanning unit performs sensor calibration on the sheet material (ex, plain paper, tracing paper). The n-time scanning unit requests the CPU 301 so that the detection voltage of the reflected light detected by the light receiving element and finally converted by the A / D conversion circuit 523 becomes a certain constant value. The CPU 301 performs feedback control so that the detected voltage falls within a certain range. For example, if the detection voltage is greater than 4.4 [V], the light emission amount of the light emission control means 511 is reduced, and if the detection voltage is less than 4.0 [V], the light emission amount of the light emission control means 511 is increased. As shown in FIGS. 23A and 23B, the sensor voltage comes into the range of 4.0 to 4.4 [V] by the sensor calibration. Sensor calibration may be performed by PI control or PID control in which the target value is set to 4.0 to 4.4V. The n-time scanning unit obtains n pieces of detection voltage data as shown in FIGS. Note that the shared memory 525 used by the pre-printing preprocessing unit 611 or a predetermined area of the shared memory 525 corresponds to the first intensity data storage unit in the claims.

・ Pretreatment A- (ii)
FIG. 24 is an example of a diagram illustrating the synchronization process A- (ii). Although the detection voltage data is detected even when the spot light scans other than the sheet material 150, only the detection voltage obtained from the sheet material 150 is necessary. Therefore, the synchronization unit aligns the start of the n detection voltage data with the paper edge of the sheet material 150.

  Since the detection voltage data of n times is started from the end of the paper, the synchronization unit detects that the detection voltage data first exceeds the threshold as the end of the sheet 150. The detection voltage data to be averaged is data after the threshold value is exceeded (detection voltage data exceeding the threshold value is handled as the first data). When the target value of sensor calibration is 4.0 [V], the threshold is about 3.5 to 3.9 [V] which is slightly smaller than that.

  In addition to such a synchronization method, detection voltage data is stored in correspondence with position information in the main scanning direction detected by the encoder sensor 42, and the n pieces of detection voltage data are synchronized by matching the position information. Also good.

・ Pretreatment A- (iii)
Next, the n pieces of detection voltage data have n pieces of detection voltage data for each position with the paper edge of the sheet 150 as a reference position in the scanning direction (position is zero). This position is the position of the carriage 5 detected by the encoder sensor, but corresponds to the position of the center of gravity of the spot light in a one-to-one relationship. That is, the averaging unit calculates an average of n detection voltage data for each barycentric position.

・ Pretreatment A- (iv)
FIG. 25 is an example of a diagram illustrating the filtering process. The filter processing unit filters the average value of the detected voltage data for each barycentric position averaged by the averaging unit. Specifically, m pieces of data before and after the detection voltage data of interest (m including the data of interest) are extracted, and an average is calculated. As a result, measurement noise is reduced, and deviation of detected voltage data that cannot be synchronized by the synchronization process can be reduced.

  In FIG. 25, the solid line waveform is detection voltage data before filtering, and the dotted line waveform is detection voltage data after filtering. The detected voltage data before the filter processing is affected by the resolution of the A / D conversion circuit 523 and shows a step-like variation, but it can be seen that it becomes gentle by the filter processing.

<Test pattern formation>
The test pattern forming unit 617 forms the test pattern stored in the pattern data storage unit 618 as described in the first embodiment. That is, in the case of magenta, a test pattern in which two patterns of magenta and, for example, yellow are superimposed is formed.

<Pretreatment B>
・ Pretreatment B- (i)
FIG. 26 is an example of a diagram illustrating n-time scanning of B- (i). In FIG. 26A, a test pattern is formed on the sheet material 150 that has been scanned n times in A- (i). FIG. 26B shows a waveform of detected voltage data when the light receiving element receives reflected light from the sheet material 150 on which the test pattern is formed. The n-time scanning unit acquires such data n times. The shared memory 525 used by the pre-printing preprocessing unit 612 or a predetermined area of the shared memory 525 corresponds to the first intensity data storage unit in the claims.

・ Pretreatment B- (ii)
FIG. 27 is an example of a diagram illustrating the synchronization process. The upper part schematically shows detection voltage data before synchronization, and the lower part schematically shows detection voltage data after synchronization. Unlike the formation of test data, after the formation of test data, the waveforms can be made uniform by matching the maximum values and the minimum values of the n detection voltage data. There are several methods for matching the maximum values and the minimum values of the waveform data as shown in FIG. 21 (although it is difficult to match them completely).

  A relatively simple method is to align the start of the n detection voltage data with the paper edge of the sheet material 150 as in A- (ii). If the test pattern is formed at the same position with respect to the paper edge, the maximum value and the minimum value of the plurality of detection voltage data can be aligned at the same position.

  Similarly to A- (ii), the detected voltage data is stored in correspondence with the position information in the main scanning direction detected by the encoder sensor 42, and the position information is matched to synchronize the n pieces of detected voltage data. You may take it.

  In addition, the synchronization unit can determine the position of the n detection voltage data so that the shift of the n detection voltage data is minimized while shifting the position of the n detection voltage data.

・ Pretreatment B- (iii)
The averaging unit calculates the average of the synchronized n detection voltage data. Since the n detection voltage data includes n detection voltage data for each position, the averaging unit calculates an average of the n detection voltage data for each barycentric position.

<Signal correction processing>
The synchronization processing unit 613 performs synchronization processing before signal correction. The synchronization processing unit 613 performs detection voltage data before the test pattern formation subjected to the preprocessing of A- (i) to (iv) and the test pattern subjected to the preprocessing of B- (i) to (iii). The paper edges of the detection voltage data after formation are aligned.

  Similar to A- (ii), the alignment is performed by setting the detected voltage data that first exceeds the threshold value as the first data. Hereinafter, for the sake of explanation, detection voltage data before test pattern formation is referred to as blank sheet measurement data Vsg2, and detection voltage data after test pattern formation is referred to as pattern measurement data Vsg1.

Hereinafter, the signal correction process will be described.
(2-1) Pattern Non-existence Exclusion Process The pattern non-existence exclusion process performs a process of reducing the detection voltage independent of the pattern from the detection voltage Vsg. Specifically, Vp is subtracted from Vsg. Thereby, the detection voltage resulting from other than the sheet material 150 can be eliminated.

FIG. 28 is an example of a diagram illustrating Vsg and Vp. Factors contributing to the detection voltage of the light receiving element will be described. Most of the light received by the light receiving element is reflected light of the light emitted from the light emitting element to the sheet material. The reflected light is reflected by the reflection of the sheet material and the plate-like member (hereinafter referred to as platen) under the sheet. Minutes included. In addition to the reflected light, light such as aerial scattered light and background radiation is also received by the light receiving element. These are defined as follows.
Vsg: All detection voltages of light received by the light receiving element
Vp: Reflected light due to light that cannot be absorbed even at the part where the test pattern is formed, scattered light in the air, detection voltage due to dark output
Vs: Detection voltage to be detected Vsg in FIG. 28 is a waveform of a detection voltage when a test pattern is formed. In Vsg, the reflected light is lowered at the portion where the test pattern is formed, because the test pattern absorbs light. However, Vp in FIG. 19 is also output at the portion where the test pattern is formed. This is the detection voltage Vp that does not vary with the formation of the test pattern.

  For this reason, after the test pattern is formed, the minimum value of the detection voltage can be considered to be due to the absence of the pattern that is not absorbed by the ink. Therefore, in this embodiment, the minimum voltage Vp at the time of pattern reading is the detection voltage due to the absence of the pattern. .

  Here, the case of a single color test pattern has been described as an example, but the present processing can also be applied to a case of a plurality of color test patterns. In that case, the minimum value in the test pattern of the color that absorbs the most spot light is Vp. In this case, although the voltage that cannot be excluded remains in the test pattern portions of other colors, the position detection accuracy is improved even if some voltage remains.

  Accordingly, if Vp is subtracted from the pattern measurement data Vsg1 and the blank paper measurement data Vsg2, detection voltages other than those reflected from the ink can be excluded. Thereby, the dispersion | variation in the minimum value of the waveform output at the time of a light receiving element reading a test pattern is reduced.

The pattern non-existence exclusion processing unit 614 calculates the following.
x ′ = Vsg1−Vp
y '= Vsg2-Vp
FIG. 29A shows an example of an output waveform of pattern measurement data, and FIG. 29B shows an example of an output waveform obtained by subtracting Vp from the pattern measurement data. As can be seen from a comparison between FIGS. 29A and 29B, it can be seen that the pattern measurement data is reduced as a whole by about 1 [V] by the pattern non-existence exclusion process.

  FIG. 29C shows an example of an output waveform of blank sheet measurement data, and FIG. 29D shows an example of an output waveform obtained by subtracting Vp from the blank sheet measurement data. As can be seen from a comparison between FIGS. 29C and 29D, it can be seen that the blank sheet measurement data is reduced as a whole by about 1 [V] by the pattern non-existence exclusion process.

(2-2) Amplitude correction processing Since x ′ and y ′ are detected voltage data at the same scanning position by the synchronization processing, x ′ and y ′ become equal when the spot light scans a place where there is no test pattern. When scanning the place where the pattern is, x ′ becomes substantially zero. This means that x ′ is a detection voltage by reflected light detected without being absorbed by the test pattern with y ′ as a reference (maximum) at a certain position. That is, even if the variation caused by the transmittance of the sheet material varies from position to position, x ′ increases at the position where the variation increases the detection voltage (the position where y ′ is large), and the position where the variation reduces the detection voltage ( At a position where y ′ is small, x ′ is also small.

  In other words, this indicates that the variation caused by the position included in x ′ can be appropriately corrected by proportional correction of “x ′ / y ′”.

FIG. 30 is an example of a diagram schematically illustrating the detection voltage z obtained from x ′ and y ′. In FIG. 30A, x ′ and y ′ are displayed so as to overlap each other, and in FIG. 30B, the detected voltage z and a fixed value are displayed. Since x ′ / y ′ represents how much x ′ including a change in a position is included when y ′ is used as a reference, if an appropriate fixed value is determined as an amplitude, “ Detection voltage data having a constant amplitude can be acquired by “fixed value × x ′ / y ′”. Assuming that this detection voltage is z, from the above, the detection voltage z after amplitude correction processing is
z = fixed value × (x ′ / y ′)
Can be expressed as

  The detection voltage z is a detection voltage with a constant amplitude at which the fluctuation caused by the position of the sheet material is eliminated and the test pattern portion is minimized and maximized on a white background.

  Based on the above concept, the amplitude correction processing unit 615 calculates “fixed value × (x ′ / y ′)”. x ′ and y ′ have already been obtained, and the fixed value is a value obtained by subtracting Vp from the maximum value (for example, 4 [V]) of the detection voltage obtained by sensor calibration. And y 'also because Vp is reduced).

  From the above, the amplitude correction processing unit 615 can obtain a detection voltage z having a constant amplitude as shown in FIG. Thereafter, the discharge timing correction unit 616 determines the intersection points C1 and C2 as edge positions from the detection voltage z as described above. The inflection points can be concentrated near the center of the threshold area by the pattern nonexistence exclusion process and the amplitude correction process.

  The fixed value may be a value obtained by subtracting Vp from the average value or median value of Vsg2 correlated with the local maximum value. In addition, since the amplitude of the detection voltage is constant regardless of the number of fixed values, it can be changed on the assumption that the threshold area is adjusted.

[Operation procedure]
FIG. 31 is a flowchart illustrating an example of a procedure in which the correction processing execution unit 526 performs signal correction.

  First, the CPU 301 instructs the main control unit 310 to start landing position deviation correction. In response to this instruction, the main control unit 310 drives the sub-scanning motor 132 via the sub-scanning driving unit 314 to convey the sheet material 150 to just below the recording head 21 (S1).

  Next, the main control unit 310 drives the main scanning motor 27 via the main scanning drive unit 313 to move the carriage 5 onto the sheet material 150 and receive light from the light emitting element at a specific location on the sheet material 150. The element is calibrated (S2). Since the process of S2 is the same as that of Example 1, description is abbreviate | omitted.

  Next, the n-time scanning unit of the pre-printing pre-processing unit 611 moves the carriage 5 to the home position, performs n-time scanning before test pattern formation, and stores n detection voltage data in the shared memory 525 ( S3a).

  FIG. 32B is an example of a flowchart for explaining the process of S3. First, the CPU 301 turns on the light emitting element (S31).

  Next, the photoelectric conversion circuit 521 and the like start taking in the detection voltage data (S32). When the capturing is started, the main scanning driving unit 313 moves the carriage 5 by the main scanning driving motor 27 (S33). That is, while the carriage 5 moves, the photoelectric conversion circuit 521 and the like take in the detection voltage data. Data sampling is, for example, 20 kHz (50 μs interval).

  When the carriage 5 reaches the end portion of the image forming apparatus, the photoelectric conversion circuit 521 and the like finish taking in the detection voltage data (S34). The main control unit 310 stores a series of detection voltage data in the shared memory 525. The main control unit 310 stops the carriage 5 at the home position (S35).

  The CPU 301 confirms whether or not the detection voltage data has been read n times a predetermined number of times. If it has been completed, the process proceeds to the next step S5, and if not, the detection voltage data reading process in S3. Is performed again (S4).

  Next, the pre-printing preprocessing unit 611 reads the detected voltage data before forming the test pattern, which has been read a predetermined number of times stored in the shared memory 525, executes preprocessing, and stores the data in the RAM 303 (S5). The contents of the pre-processing in S5 are shown in FIG.

  Next, the main control unit 310 moves the carriage 5 through the main scanning drive motor 27 without moving the paper while keeping the sub-scanning position of the sheet material 150 as it is, and the head drive control unit. 312 uses the pattern data stored in the pattern data storage unit 618 to drive the recording heads 21 to 24 to discharge droplets (S6). Thereby, a test pattern for adjusting landing position deviation is formed on the sheet material.

  Next, the n-time scanning unit of the post-printing pre-processing unit 612 moves the carriage 5 to the home position, performs n-time scanning after the test pattern is formed, and stores n pieces of detection voltage data in the shared memory 525 ( S3b).

  The CPU 301 confirms whether or not the detection voltage data has been read n times a predetermined number of times. If completed, the process proceeds to the next step S8, and if not completed, the pattern data reading process of S3 is performed again. Perform (S7).

  Next, the post-printing pre-processing unit 612 reads the detection voltage data read a predetermined number of times stored in the shared memory 525, performs pre-processing, and stores the data in the RAM 303 (S8). The contents of the pre-processing at S8 are shown in FIG.

  Next, the synchronization processing unit 613 reads the pre-processed blank sheet measurement data and pattern measurement data from the RAM 303, and performs alignment by synchronization processing (S9).

  Next, the pattern non-existence exclusion processing unit 614 obtains Vp from the minimum value of the pattern measurement data, and subtracts Vp from the blank sheet measurement data and the pattern measurement data, respectively (S10).

  Next, the amplitude correction processing unit 615 performs amplitude correction processing using the formula “z = fixed value × (x ′ / y ′)” to generate a detection voltage z (S11). As a result, detection voltage data in which the inflection point is included in the threshold region is obtained.

  The ejection timing correction unit 616 detects the edge position based on the detection voltage z, and corrects the landing position deviation of the droplet (S12). That is, the ejection timing correction unit 616 calculates the landing position deviation amount by comparing the distance between the lines with the appropriate distance, calculates the correction value of the droplet ejection timing so as to eliminate the landing position deviation, and the head drive control unit 312 is set.

  As described above, the image forming apparatus 100 according to the present embodiment forms a test pattern in which a background pattern is superimposed on an ink color having a high reflection intensity. Further, the position of the inflection point can be accommodated in the threshold region by correcting the detection voltage so that the amplitude of the detection voltage becomes substantially constant even for a sheet material having a high transmittance. Therefore, the edge position can be obtained with high accuracy, and the landing position deviation of the droplet can be corrected with high accuracy.

  In this embodiment, an image forming system in which a non-sheet reflection exclusion process and an amplitude correction process are performed by a server instead of an image forming apparatus will be described.

  FIG. 33 is an example of a diagram schematically illustrating an image forming system 500 including the image forming apparatus 100 and the server 200. 33, the same parts as those in FIG. 4 are denoted by the same reference numerals, and the description thereof is omitted. The image forming apparatus and the server 200 are connected via a network 201. The network 201 is an in-house LAN, a WAN connecting the LANs, the Internet, or a combination of these.

  In the image forming system 500 as shown in FIG. 33, the image forming apparatus 100 forms a test pattern and scans the test pattern using a print position deviation sensor, and the server 200 calculates a correction value for the droplet discharge timing. Accordingly, the processing load on the image forming apparatus 100 can be reduced, and the function for calculating the correction value of the droplet discharge timing can be integrated in the server 200.

  FIG. 34 is a diagram illustrating an example of a hardware configuration diagram of the server 200 and the image forming apparatus 100. The server 200 includes a CPU 51, a ROM 52, a RAM 53, a storage medium mounting unit 54, a communication device 55, an input device 56, and a storage device 57 that are mutually connected by a bus. The CPU 51 reads an OS (Operating System) and a program 570 from the storage device 57, and executes them using the RAM 53 as a working memory. This program performs the following processing.

  The RAM 53 is a working memory (main storage memory) for temporarily storing necessary data, and the ROM 52 stores BIOS, initially set data, a bootstrap rotor, and the like. The storage medium mounting unit 54 is an interface for mounting a portable storage medium 320.

  The communication device 55 is called a LAN card or an Ethernet (registered trademark) card, and is connected to the network 201 to communicate with the external I / F 311 of the image forming apparatus 100. Note that at least the IP address or domain name of the server 200 is registered in the image forming apparatus 100.

  The input device 56 is a user interface that accepts various user operation instructions such as a keyboard and a mouse. A touch panel or a voice input device can be used as the input device.

  The storage device 57 has a nonvolatile memory such as an HDD (Hard Disk Drive) or a flash memory as an entity, and stores an OS, a program, and the like. The program 570 is distributed in a state recorded in the storage medium 320 or downloaded from the server 200 (not shown).

  FIG. 35 is an example of a functional block diagram of the image forming system 500. The correction processing execution unit of the image forming apparatus 100 has only n scanning units before and after printing, a test pattern forming unit 617, and a test pattern storage unit 618, and the server has the remaining functions. A function on the server side is referred to as a correction processing calculation unit 620. The shared memory 525 may be included in the server 200, or both the server 200 and the image forming apparatus 100 may include the shared memory 525. Further, the test pattern storage unit 618 may be on the server side, and the image forming apparatus 100 may download it from the server 200 or a server (not shown).

  The correction processing calculation unit 620 includes a synchronization unit before printing, an averaging unit, a filter processing unit, a synchronization unit after printing, an averaging unit, a synchronization processing unit 613, a pattern non-existence exclusion processing unit 614, and an amplitude correction processing unit. 615 and a discharge timing correction unit 616. Since the function of each block is the same as that of the first embodiment, description thereof is omitted.

  In the image forming system 500, the n-time scanning unit on the image forming apparatus side transmits n data before printing and after printing to the server 200. The server-side correction processing calculation unit 620 performs a pattern non-existence exclusion process and an amplitude correction process to calculate a correction value for the droplet discharge timing. Since the server 200 transmits the correction value of the droplet discharge timing to the image forming apparatus 100, the head drive control unit 312 can change the discharge timing.

  FIG. 36 is an example of a flowchart showing an operation procedure of the image forming system 500. 26, the server 200 performs S5 and S8 to S12 in FIG. 26, and the image forming apparatus 100 performs other processes necessary for n scans before and after printing.

  Since the image forming apparatus 100 and the server 200 communicate with each other, the image forming apparatus 100 transmits n scan results before printing in step S4-1, and n scan results after printing in step S7-1. Is newly performed. Further, the image forming apparatus 100 newly performs a process of receiving the correction value of the droplet discharge timing in S7-2.

  On the other hand, the server 200 newly performs a process of transmitting the droplet discharge timing correction value to the image forming apparatus 100 in S13 after S12.

  In this way, just by changing the place where the processing is performed, the image forming system 500 can correct the droplet discharge timing with high accuracy while suppressing the influence from the characteristics of the sheet material as in the first embodiment. Can do.

DESCRIPTION OF SYMBOLS 1 Guide rod 2 Sub guide 5 Carriage 7 Drive pulley 8 Main scanning motor 9 Timing belt 21-24 Recording head 30 Print position shift sensor 41 Encoder sheet 42 Encoder sensor 100 Image forming apparatus 200 Server 301 CPU
310 Main control unit 312 Head drive control unit 313 Main scan drive unit 314 Sub scan drive unit 402 Light emitting element 403 Light receiving element 500 Image forming system 525 Shared memory 526 Correction processing execution unit 611 Pre-printing preprocessing unit 612 Post printing preprocessing unit 613 Synchronization processing unit 614 Pattern non-existence exclusion processing unit 615 Amplitude correction processing unit 616 Discharge timing correction unit 617 Test pattern formation unit 618 Pattern data storage unit 620 Correction processing calculation unit

JP 2008-229915 A

Claims (10)

An image forming apparatus that reads a test pattern composed of a plurality of lines formed on a recording medium and adjusts the discharge timing of droplets,
A reading means having a light emitting means for irradiating the recording medium with light and a light receiving means for receiving reflected light from the recording medium;
Pattern data storage means for storing pattern data for forming the test pattern;
A test pattern forming means for reading the pattern data and forming a test pattern;
Relative moving means for moving the recording medium or the reading means at a relatively constant speed;
Intensity data storage means for storing intensity data of the reflected light received by the light receiving means from the scanning position of the light while the light is moving through the test pattern;
Position detecting means for performing a line position determination calculation on the intensity data included within a lower limit from a predetermined upper limit, and detecting the position of the line,
The test pattern forming means includes:
At least one color of the line is formed from a different second droplet from the first droplet and said first liquid droplets ejected nozzle trying to adjust the ejection timing of the droplet of the previous SL plurality of lines Forming a test pattern,
An image forming apparatus.   The image forming apparatus according to claim 1, wherein the minimum values of reflected light reflected by the plurality of lines constituting the test pattern are substantially the same. When only the second droplet pattern is ejected to the recording medium, the minimum value of the intensity data of the reflected light acquired by the light receiving unit from the recording medium does not fall below the predetermined upper limit. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The test pattern forming means includes the second droplet pattern having a wider area than the first droplet pattern, and the entire first droplet pattern is the second droplet pattern. Forming the one- color line to be inside,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The test pattern forming unit discharges the second droplet pattern after discharging the first droplet pattern to form the line.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The test pattern forming means discharges the first droplet pattern after discharging the second droplet pattern to form the one- color line .
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. If only the formation pattern of the the recording medium the second droplet, and formed part of the pattern of the second droplet, the difference of the intensity data of the portion having no liquid droplets of the recording medium,
Wherein among the plurality of lines included in the test pattern, wherein the minimum value of the intensity data and the minimum value of the smallest line, only the pattern of the first droplet is obtained from the recording medium discharged is the difference the same level as the minimum value of the intensity data,
The image forming apparatus according to claim 5 . Second intensity data storage means for storing second intensity data of the reflected light received from the light scanning position by the light receiving means before the test pattern is formed;
After the test pattern is formed, the test pattern a first storing the first intensity data of the reflected light which the light receiving means has received when the light is moved in the scanning position and the same scanning position Intensity data storage means;
Subtraction processing means for subtracting a value comparable to the minimum value of the first intensity data from each of the first intensity data and the second intensity data;
And signal correction means for calculating a ratio of said first intensity data for the subtracted processed second intensity data, align the maximum value of the first intensity data in a constant,
The image forming apparatus according to claim 1, wherein the image forming apparatus includes: A reading means having a light emitting means for irradiating the recording medium with light and a light receiving means for receiving the reflected light from the recording medium;
Wherein the pattern data storing means for storing the pattern data for forming a test pattern consisting of a plurality of lines formed on the recording medium, has, by reading a plurality of test pattern lines formed on the recording medium, A pattern position detection method for an image forming apparatus for adjusting the discharge timing of droplets,
A test pattern forming unit reads the pattern data to form a test pattern;
A relative moving means moving the recording medium or the reading means at a relatively constant speed;
Storing the intensity data of the reflected light received from the scanning position of the light in the intensity data storage means while the light is moving through the test pattern;
A position detecting means, performing a line position determination operation on the intensity data included within a lower limit from a predetermined upper limit, and detecting the position of the line,
In the step of forming the test pattern, the test pattern forming means, the first liquid droplet and said nozzle at least one color line is trying to adjust the ejection timing of the droplet of the previous SL plurality of lines are discharged A pattern position detection method, comprising: forming a test pattern formed from a second droplet different from one droplet . An image forming system that reads a test pattern composed of a plurality of lines formed on a recording medium and adjusts the discharge timing of droplets,
A reading means having a light emitting means for irradiating the recording medium with light and a light receiving means for receiving reflected light from the recording medium;
Test pattern forming means for forming a test pattern;
Relative moving means for moving the recording medium or the reading means at a relatively constant speed;
An image forming apparatus having
Intensity data storage means for storing intensity data of the reflected light received by the light receiving means from the scanning position of the light while the light is moving through the test pattern;
Pattern data storage means for storing pattern data for forming the test pattern;
Position detecting means for performing a line position determination calculation on the intensity data included within a lower limit from a predetermined upper limit, and detecting the position of the line,
The test pattern forming means includes:
At least one color of the line is formed from a different second droplet from the first droplet and said first liquid droplets ejected nozzle trying to adjust the ejection timing of the droplet of the previous SL plurality of lines An image forming system characterized by forming a test pattern.

Images