JP2013099866A - Image forming apparatus, pattern position detecting method, image forming system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus by which a position of a test pattern can be accurately decided even though a diameter of light is longer than a line width.SOLUTION: The image forming apparatus reading the test pattern of a plurality of lines formed in a recording medium 150 and adjusting a discharge timing of liquid droplets has a reading means 30 having a light emitting means irradiating light to the recording medium and a light receiving means receiving reflected light from the recording medium, a pattern data storing means 618 storing the pattern data of the test pattern, a test pattern printing means reading out the pattern data and forming the test pattern in the recording medium, an intensity data storing means 525 storing the intensity data of the reflected light which the light receiving means receives from a scanning position of the light while the light moves on the test pattern, and a position detecting means 616 deciding the scanning position of a changing ratio data on which attention is focused at the center position of the lines in the case the arrangement of the plurality of changing ratio data before and behind the changing ratio data on which attention is focused is generally point symmetry.

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).

  Fig.1 (a) is an example of the figure explaining adjustment of a landing position. When spot light irradiated by a light emitting element (for example, 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. If the sheet material is a highly reflective paper such as white, when the light scans the test pattern, the light is absorbed by the ink relative to when the solid portion is moved. If the reflected light received by the light receiving element is expressed as a voltage, as shown in the figure, the voltage when the spot light is superimposed on the test pattern is much lower than the voltage when scanning a plain part other than the test pattern. To do. The edge position of the test pattern can be determined by analyzing the region where the voltage rapidly decreases.

  FIG. 1B is a diagram showing the relationship between the spot light and the size of 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). In a spot light and a sheet material having a general wavelength, the reflected light of the spot light may decrease as the overlapping area of the light and the test pattern increases. Therefore, in order to determine the edge position from the voltage drop region as shown in FIG. 1A, the spot diameter d = the line width L of the test pattern or the spot diameter d <the line width L of the test pattern. It is preferable.

  However, if the spot diameter d ≦ the line width L of the test pattern has to be satisfied, there is a problem in that a large amount of ink is used to increase the line width L. Although d ≦ L can also be satisfied by reducing the spot diameter, the improvement of the light emitting element brings about an increase in cost.

  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 even if the diameter of the spot light is longer than the line width.

  The present invention relates to an image forming apparatus that reads a test pattern formed by ejecting droplets onto a recording medium and adjusts the ejection timing of the droplets, and includes a light emitting unit that irradiates the recording medium with light and the recording medium A reading means having a light receiving means for receiving reflected light from the light, a pattern data storage means for storing pattern data of a test pattern, and a test pattern printing means for reading the pattern data and forming a test pattern on the recording medium. A relative moving means for moving the recording medium or the reading means at a constant speed so that the light moves on a plurality of lines constituting the test pattern, and while the light is moving through the test pattern, 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; and the intensity Focusing on the change rate data of the overlap area of the light and the line obtained from the data, the change rate focused when the arrangement of a plurality of change rate data before and after the focused change rate data is substantially point symmetric Position determining means for determining the scanning position of data at the center position of the line.

  It is possible to provide an image forming apparatus capable of accurately determining the position of the test pattern even when the diameter of the spot light is longer than the line width.

It is an example of the figure explaining adjustment of a landing position in the past. FIG. 5 is an example of a diagram illustrating a method for determining a line center position when spot diameter d> line width L 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. It is an example of the figure which shows typically the structure for a droplet position shift sensor to detect the line center position of a test pattern. It is an example of the figure explaining the outline of the determination of the conventional edge position. It is an example of the figure explaining the determination method of the conventional edge position. FIG. 5 is an example of a diagram illustrating a signal waveform when spot diameter d> line width L; 6 is an example of a diagram illustrating a method for determining a line center position by a discharge timing correction unit 616. FIG. It is an example of the figure explaining the process of a data point. It is an example of the figure explaining determination of the line position of the test pattern of spot diameter d> line width L by the conventional line position determination method. It is a figure which shows an example of the relationship between the color of a line, and line width. 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 a flowchart figure which shows an example of the procedure in which a correction process execution part correct | amends a droplet discharge timing. 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.

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

FIG. 2 is an example of a diagram illustrating a method for determining the line center position in the case of “spot diameter d> line width L of test pattern”. Spot light scans one line at a constant speed from left to right. Due to the shape of the line and the spot light, when the spot light begins to overlap with the line, the overlap area increases rapidly, and when the spot light finishes overlapping with the line, the overlap area decreases rapidly.

  On the other hand, while the center of gravity of the spot light is overlapped with the center of the line (line center position), the change in the overlap area is small, but it should be slowly changing from increasing to decreasing. The reflected light from the test pattern is smaller as the overlapping area of the line and spot light is larger and smaller as it is smaller. Therefore, if the intensity of the reflected light is monitored, the timing at which the center of gravity of the spot light passes the line center position is detected. . Therefore, the position of the spot light when the rate of increase in the intensity of the reflected light changes from positive to negative (when the area increase rate ΔS changes from positive to negative) is the line position (in this case, the line center position). .

  In this embodiment, the position where the area increase rate ΔS changes from positive to negative is determined based on the two x-intercepts of the regression line of the data points before and after that. A method for obtaining the line center position will be described in detail later.

  While the center of gravity of the spot light scans near the center of the line, the rate of change of the overlapping area is small, so the intensity of the reflected light also changes slowly. For this reason, the position where the area increase rate ΔS changes from positive to negative is easily stabilized. Therefore, even in a situation where spot diameter d> line width L of the test pattern (hereinafter simply referred to as “line width L”), the position of the line can be determined with high accuracy.

[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 droplet position deviation sensor 30 for detecting landing position deviation (reading a test pattern) is mounted. The droplet position deviation sensor 30 reads a test pattern for detecting a 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 this droplet displacement sensor 30 is for the recording head 21, another droplet displacement sensor 30 is mounted in parallel with the recording heads 22-24 in order to adjust the droplet discharge timing of the recording heads 22-24. Is preferred. Further, if the carriage 5 is equipped with a mechanism for sliding the droplet position deviation sensor 30 so as to be in parallel with the recording heads 22 to 24, the liquid in the recording heads 22 to 24 can be obtained by using one droplet position deviation sensor 30. Drop ejection 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 droplet 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 line center 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. The recording heads 21 to 24 have a switch for each nozzle, and the recording heads 21 to 23 have a size specified at the position of the sheet material 150 specified by the print data by being turned on / off based on a 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 drive unit 316 drives a paper discharge motor 134 that drives a roller for discharging the printed sheet material 150 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 processing for forming a test pattern on the sheet material, and performs light emission drive control for causing the light emitting element of the droplet displacement 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 droplet position deviation sensor 30 to detect the line center position of the test pattern. FIG. 6 is a view of the recording head 21 and the droplet displacement sensor 30 of FIG. 4 as viewed from the right side plate 4.

  The droplet position deviation sensor 30 includes 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 droplet position deviation sensor 30 facing the platen 40 is shielded from the outside by a lens 405. Thus, the droplet position deviation sensor 30 is packaged and can be distributed alone.

In the droplet 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 the spot diameter is related to the detection accuracy of the edge of the test pattern, the line center position can be detected with sufficiently high accuracy even in the mm order if the line center position of the present embodiment is obtained. 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 droplet position deviation sensor 30. Specifically, the CPU 301 sets a PWM value for driving the light emitting element 402 of the droplet 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 driven. Is provided to 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 (sensor detection voltage) 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 determining the line position (line center position) of the test pattern and comparing it with the appropriate distance between the two lines.

  The correction processing execution unit 526 includes an ejection timing correction unit 616, a test pattern printing unit 617, and a pattern data storage unit 618. The test pattern printing unit 617 forms a test pattern stored in the pattern data storage unit 618 on a sheet material. The test pattern is read by the circuit of FIG. 6 and the like, and the detected voltage data is stored in the shared memory 525.

  The ejection timing correction unit 616 determines the line center position from the detected voltage data. Then, based on the distance between the lines, a correction value of the droplet discharge timing when driving the recording head 21 so as to eliminate the landing position deviation is calculated, and the calculated correction value of the droplet discharge timing is used as a head drive control unit. 312 is 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.

[Determination of line position]
<Determination of conventional line position>
FIG. 7 is an example of a diagram for explaining the outline of determination of a conventional line position. Numbers I to V in FIG. 7A indicate the passage of time, and the lower the spotlight, the longer the passage of time.
Time I: Spot light and test pattern are not superimposed.
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 are not superimposed.

  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 a relationship between the times II and IV, the edge position can be determined with high accuracy.

  FIG. 7B shows an example of the detection voltage of the light receiving element, FIG. 7C shows an example of the absorption area (the overlapping area of the spot light and the test pattern), and FIG. 7D shows the absorption of FIG. 7C. An example of the increase rate of the absorption area obtained by differentiating the area is shown. In FIG. 7D, equivalent information can be obtained even if the output waveform of FIG. 7B is differentiated. Further, the absorption area is calculated from the detection voltage, for example, but does not need to be an absolute value. Therefore, the absorption area in FIG. 7C is obtained by subtracting the detection voltage in FIG. 7B 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. 7 (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 be determined with high accuracy.

  FIG. 8 is an example of a diagram for explaining a conventional edge position determination method. FIG. 8A shows a schematic diagram of the detection voltage, and FIG. 8B shows an enlarged view of the detection voltage. The approximate value of the inflection point can be obtained experimentally by the discharge timing correction unit 616 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 detected voltage becomes substantially the same constant value (4 [V] described later) in an area without a 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 detected voltage data between the points P1 and P2, and an intersection point between the regression line L1 and the intermediate value Vc of the upper and lower threshold values 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 threshold values is calculated as an intersection point C2. Since the intersection C1 and the intersection C2 are edge positions of one line, the center of the intersections C1 and C2 is the line center position.

  Thereafter, the ejection timing correction unit 616 obtains the line center positions of the plurality of lines, and calculates the difference between the ideal distance between the two lines of the test pattern and the 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.

<Determination of the line position of this embodiment>
The ejection timing correction unit 616 of the present embodiment can determine the line position with high accuracy when the spot diameter d> the line width L. In this method, the line center position can be determined directly.

FIG. 9 is an example of a diagram illustrating a signal waveform when spot diameter d> line width L. In FIG.
9A shows the relative position of the line and the spot diameter, FIG. 9B shows the absorption area at each relative position, FIG. 9C shows the detection voltage at each relative position, and FIG. d) indicates the area increase rate ΔS at each relative position. Note that the absorption area in FIG. 9B is calculated, for example, by converting a decrease in the detection voltage into an increase in the overlapping area. If the waveform is known, it need not be an absolute value. Each graph is displayed so that the relative positions of the line and the spot diameter are the same.

  In FIG. 9, the spot diameter is moved relative to the line for convenience, but the relative position of both is the same as in FIG. 7 (however, in the case of a line head, the spot diameter is the line as shown in FIG. 9). Appears to be moving against.)

In FIG. 9A, I to III are numbers for indicating typical relative positions.
I: The left edge of the line matches the left edge of the spot light
II: The center of the line coincides with the center (center of gravity) of the spot light
III: The right edge of the line matches the right edge of the spot light
Compared with the case where d = L, the area occupied by the line in the spot light is small, so that the detection voltage increases as a whole including the minimum value (the spot light is not easily absorbed). When the detection voltage of the minimum value is large, the amplitude of the detection voltage can not take a sufficient value range, and it becomes difficult to include an inflection point in the threshold area. Or it becomes difficult to obtain an inflection point.

  It is not impossible to increase the amplitude of the detection voltage by some correction process (for example, by making the minimum value correspond to zero and linearly correcting the detection voltage from zero to 4V). However, as shown in FIG. 9D, the area increase rate ΔS changes abruptly in the vicinity of the edge. This indicates that the change in the detection voltage is large, and even if the amplitude is increased by linear correction, the error of the line position becomes large due to this rapid fluctuation.

  On the other hand, in the graph of the area increase rate ΔS in FIG. 9D, the “slope near the line center” is not only small but also stable. Therefore, if the line center position is determined using the data near the line center, the calculated value can be expected to have a small error.

FIG. 10 is an example of a diagram illustrating a method for determining the line center position by the ejection timing correction unit 616. The method for calculating the line center position is as follows, for example. The outline of the calculation method of this embodiment is as follows: “A focus is placed on the detection signal, a predetermined number of data is extracted in the vertical direction of the target value, and a regression curve of data above the target value and a regression curve of data below the target value. Is determined to be the inflection point. ” The left and right data centering on the target value at this time are closest to point symmetry.
(1) Pay attention to the area increase rate ΔS one by one in the detection order. Note that the data of interest may be sampled every predetermined number. The calculation time can be shortened by reducing the points of interest.
(2) A predetermined number of data points (data of area increase rate ΔS) are extracted in the vertical direction of the target value.
(3) A regression curve Line-U of data above the target value is obtained. The X-intercept of Line-U is obtained.
(4) A regression curve Line-D of data below the target value is obtained. The X intercept of LINE-D is calculated | required, respectively.
(5) The absolute value of the difference between the two X-intercepts is obtained and stored in association with the value of interest.

  When the absolute value of the difference between the two X-intercepts is small, it can be said that the degree of coincidence between the two regression lines Line-U and Line-D is high. Therefore, it is possible to determine that the point of interest having the smallest absolute value of the difference between the two X-intercepts is the inflection point (= Xn).

  As a method for calculating the degree of coincidence between two regression lines, the degree of coincidence can also be obtained by inclination. However, compared with the case where the degree of coincidence is obtained by the slope, the method using the x-intercept of the regression line can amplify a slight difference in the slope by the length of the regression line. That is, the difference between the two regression lines appears greatly. For this reason, in the calculation processing of software or hardware, the degree of coincidence is calculated by comparison with the decimal point. However, in the x-intercept comparison, only the integer value is compared (or the number of digits is required even if the decimal point is required). Less is enough). Since the calculation load is reduced, it becomes possible to take more points of interest and increase the number of data in the vertical direction of the values of interest, and the feature is that inflection points can be detected with higher accuracy. ing.

  Thereby, the detection accuracy of the line center position is also increased, and the correction accuracy of the discharge timing can be improved. Even under the condition of spot diameter d> line width L, a stable line center position can be calculated while suppressing variations, and the correction accuracy of ejection timing can be improved.

  Strictly speaking, the line center position is a position where the area change rate ΔS becomes zero, but has the same significance as the minimum value of the detection voltage and the maximum value of the overlapping area. Further, when the y intercepts of the two regression lines are compared, since the difference between the y intercepts is small if the slopes are approximately the same, the y intercepts may be compared.

Further, in the above (2) and (3), data points may be processed.
FIG. 11A is an example of a diagram for schematically explaining exclusion of data points as one of the processing of data points. (2) The predetermined number of data points in (3) refers to all data in a range where the area change rate ΔS is relative to the target value. The ejection timing correction unit, for example, excludes data that has greatly increased or decreased from all data points within a certain range with respect to the target value, or excludes data for every predetermined number of points. In the former method, data points having large variations can be excluded.

  FIG. 11B is an example of a diagram illustrating the data point averaging process. The ejection timing correction unit performs a filtering process (averaging process) on a predetermined number of data points. For example, a moving average process for obtaining an average value for every three data points and an average process for replacing three data points with one average value are performed. A simple average process is preferable to a process that excludes data points because a large number of data is used. Further, the processing is easier than the processing of excluding data that has greatly increased or decreased.

<Relationship between Spot Light Diameter d and Line Width L>
As described above, if spot diameter d = line width L or spot diameter d <line width L, a conventional line position determination method can be applied. However, even when the spot diameter d> the line width L, the conventional line position determination method may be applicable.

  FIG. 12 is an example for explaining the determination of the line position of the test pattern in which the spot diameter d 1> the line width L by the conventional line position determination method. 12A shows the relationship between the spot diameter d and the line width L, FIG. 12B shows an example of the detection voltage of the light receiving element, FIG. 12C shows an example of the absorption area, and FIG. An example of the increase rate of the absorption area obtained by differentiating the absorption area in FIG.

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

  However, in the conventional method, if the detection voltage data in the vicinity of 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, if the spot diameter d 1 is not extremely larger than the line width L, the line position can be accurately identified by the conventional line position determination method even if spot diameter d> line width L.

  In other words, the line position determination method of this embodiment is effective when d / 2 ≧ L (the line width L is equal to or less than half the spot diameter d).

  The lower limit of the line width L is affected by the wavelength of light emitted from the light emitting element, the line color, the performance of the light receiving element, and the like. Since the ink consumption can be reduced as the line width is narrower, the line width is preferably, for example, one pixel. However, in reality, with a line width of one pixel, even if the spot light is absorbed, the light receiving element cannot detect a decrease in reflected light due to the absorption. For example, in FIG. 9B, the absorption area S remains S = 0 and is only a constant value. In FIG. 9C, the detection voltage is only 4V constant. In FIG. 9D, ΔS = It is only 0 constant.

  Further, even if the wavelength of light emitted from the light emitting element is constant, the reflection intensity varies depending on the color of the line, and the reflection intensity varies depending on the wavelength of light emitted from the light emitting element even if the color of the line is the same. For this reason, it can be said that it is difficult to generally specify the lower limit of the line width L. In addition, as the line width L is shorter, the influence of the line color becomes smaller.

  Therefore, it can be said that it is difficult to uniformly specify the lower limit of the line width L. For this reason, for example, the lower limit of the line width L is defined as a width that allows the light receiving element to detect the absorption of the spot light by the test pattern. For example, the line width L when the minimum value of the detection voltage is smaller than the value of the plain portion of the sheet material (4 V in the figure) by, for example, a predetermined value (for example, 3 to 10%) is the lower limit of the line width L. .

  In addition, since there are many cases where the droplet position deviation sensor 30 mounted on the image forming apparatus is one type, the wavelength of the light emitted from the light emitting element is constant. Therefore, even if the line colors are different, it is also effective to make the line width variable depending on the line color so that the minimum value of the detection voltage becomes the identification degree in order to achieve the same accuracy in determining the line center position. It is.

  FIG. 13 is a diagram illustrating an example of the relationship between the line color and the line width. The black line width is LK, the cyan line width is LC, the yellow line width is LY, and the magenta line width is LM. In the figure, LK <LC <LM <LY, but may vary depending on the wavelength of light emitted from the light emitting element. Thus, by adjusting the line width for each color of the line, it becomes easy to bring the minimum value close regardless of the ink color.

  If the minimum value becomes constant, the waveform of the area increase rate ΔS shown in FIG. 9D tends to have a similar shape even if the line color is different. Even if the ejection timing correction unit 616 performs a common line position determination operation on different color lines, it is possible to suppress the occurrence of a minute error due to the color difference. For example, even if the “threshold value symmetric with respect to ΔS = 0” is set to a constant value common to KCYM, a minute error due to a difference in color is unlikely to occur. Even if the line width is the same for K, C, Y, and M, the “threshold value that is symmetrical with respect to ΔS = 0 as a center” is set to a constant value common to K, C, Y, and M. There is no denial.

[In the case of a line type image forming apparatus]
In this embodiment, the serial type image forming apparatus 100 shown in FIGS. 3 and 4 has been described as an example. However, the line type image forming apparatus 100 can 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. In the sensor fixing bracket 170, the droplet position deviation sensors 30 are arranged by the number of heads. That is, one droplet position deviation sensor 30 is disposed so as to at least partially overlap one recording head 180 in the main scanning direction. Further, one droplet 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. Similarly to the serial type image forming apparatus 100, the line center 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 disposing the droplet position deviation sensor 30.

[Operation procedure]
FIG. 15A 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. 15B 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 droplet 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, thereby providing the driving circuit 513. Drives the light emitting element 402 to emit light (S21).

  The intensity signal detected by the light receiving element 403 of the droplet position deviation 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 at S22), the process of FIG. 15B ends. 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. 15A, 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 (S3). As a result, a test pattern of spot light diameter d> line width L can be formed. 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 line center position of the test pattern from the detected voltage data, and corrects the landing position deviation of the droplet (S4). 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 of the present embodiment determines the line position using the detection voltage near the line center even if the test pattern of the line narrower than the spot light diameter d is formed. The error of the calculated value can be reduced. As a result, the droplet discharge timing can be adjusted 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. 16 is an example of a diagram schematically illustrating an image forming system 500 including the image forming apparatus 100 and the server 200. In FIG. 16, the same parts as those in FIG. 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. 16, 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. 17 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 from the storage device 57 and executes the RAM 53 as a working memory. This program performs the following processing.

  The RAM 53 serves as a work memory (main storage memory) for temporarily storing necessary data, and the ROM 52 stores BIOS, initially set data, a bootstrap loader, 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 is distributed in a state recorded in the storage medium 320 or downloaded from the server 200 (not shown).

  FIG. 18 is an example of a functional block diagram of the image forming system 500. The correction processing execution unit 526 of the image forming apparatus 100 includes only the test pattern printing unit 617 and the pattern data 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 pattern data 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 discharge timing correction unit 616. Since the function of the ejection timing correction unit 616 is the same as that of the first embodiment, description thereof is omitted.

  In the image forming system 500, the image forming apparatus transmits detected voltage data stored in the shared memory 525 to the server 200. The server-side ejection timing correction unit 616 calculates a correction value for the droplet ejection 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. 19 is an example of a flowchart illustrating an operation procedure of the image forming system 500. As shown in the figure, the server 200 performs S4 of FIG. 15, and the image forming apparatus 100 forms a test pattern and acquires detection voltage data.

  In addition, since the image forming apparatus 100 and the server 200 communicate with each other, the image forming apparatus 100 newly performs a process of transmitting detection voltage data in step S3-1 and a process of receiving a correction value of a droplet discharge timing in S3-2. To do.

  On the other hand, the server 200 receives the detected voltage data in S3-3. Then, after calculating the correction value of the droplet discharge timing in S4, a process of transmitting the correction value of the droplet discharge timing to the image forming apparatus 100 is newly performed in S5.

  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 Droplet 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 printing unit 618 Pattern data storage unit

JP 2008-229915 A

Claims (10)

An image forming apparatus that reads a test pattern formed by discharging droplets on a recording medium and adjusts the discharge timing of the 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 test pattern data;
Test pattern printing means for reading the pattern data and forming a test pattern on the recording medium;
Relative moving means for moving the recording medium or the reading means at a constant speed so that the light moves on a plurality of lines constituting the test pattern;
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;
Focusing on the change rate data of the overlap area of the light and the line obtained from the intensity data, the change focused on when the arrangement of a plurality of change rate data before and after the focused change rate data is substantially point symmetric Position determining means for determining the scanning position of rate data at the center position of the line;
An image forming apparatus comprising:   The position determining means calculates intercepts of two regression curves respectively obtained from a predetermined number of change rate data before the change rate data of interest and a predetermined number of change rate data after, The image forming apparatus according to claim 1, wherein the scanning position where the change rate data focused when the intercept is closest is determined as a center position of the line.   3. The image forming apparatus according to claim 2, wherein when the change rate data is plotted on the y-axis with the scanning position as the x-axis, the intercept is an x-intercept or a y-intercept.   The image forming apparatus according to claim 2, wherein the position determination unit focuses on change rate data every predetermined number.   The position determining means, after determining the change rate data of interest, averages the change rate data before and after the change rate data of interest for each predetermined number, and obtains a regression curve from the averaged change rate data. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 1, wherein a diameter of light formed on the recording medium by the light emitting unit is longer than a line width of the line. The pattern data stored in the pattern data storage means has a line width where the minimum value of the intensity data is about the same even if the line color is different.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The position detecting means calculates a distance between the center position of the first line and the center position of the second line adjacent to the first line;
Adjusting the droplet discharge timing based on a difference between the distance and a predetermined appropriate distance;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. 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;
Pattern data storage means for storing pattern data of test patterns, and pattern position detection of an image forming apparatus that reads a test pattern formed by ejecting droplets onto a recording medium and adjusts the ejection timing of the droplets A method,
A test pattern printing unit reading the pattern data to form a test pattern on the recording medium;
A step of moving the recording medium or the reading unit at a constant speed so that the relative movement unit moves the light on a plurality of lines constituting the test pattern;
Acquiring the 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, and storing the intensity data in the intensity data storage means;
When the position determining means pays attention to the change rate data of the overlapping area of the light and the line obtained from the intensity data, and the arrangement of a plurality of change rate data before and after the noticed change rate data is substantially point symmetric Determining the scan position of the change rate data of interest as the center position of the line;
A pattern position detection method comprising: An image forming system that reads a test pattern formed by discharging droplets on a recording medium and adjusts the discharge timing of the 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 printing means for reading pattern data and forming a test pattern on the recording medium;
Relative moving means for moving the recording medium or the reading means at a constant speed so that the light moves on a plurality of lines constituting the test pattern;
An image forming apparatus comprising:
Pattern data storage means for storing test pattern data;
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;
Focusing on the change rate data of the overlap area of the light and the line obtained from the intensity data, the change focused on when the arrangement of a plurality of change rate data before and after the focused change rate data is substantially point symmetric Position determining means for determining the scanning position of rate data at the center position of the line;
An image forming system comprising:

Images