JP2007331315A - Inkjet recorder and its controlling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a highly precise height detecting technique by using a simple optical sensor. <P>SOLUTION: The inkjet recorder carries out recording by delivering ink to a recording medium while moving a recording head with a plurality of nozzles back and forth by a carriage. The inkjet recorder comprises a detecting means which is carried on the carriage and detects a distance between the recording head and the recording medium, a calculating means which calculates an amount of variation of the distance in a recording region of the recording medium on the basis of the detected result of the distance, and a controlling means which controls an ink delivering timing of the recording head so as to correct a deviation from a target delivering position of the ink on the basis of the calculated amount of variation of the distance. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink jet recording technique for performing recording by discharging ink.

  Various recording apparatuses (hereinafter referred to as printers) for printing image data, such as a dot impact system, a thermal transfer system, and an electrophotographic system, have been devised, and ink jet printers are also widely used. An ink jet printer discharges ink from a recording head and performs printing in a non-contact manner, so that printing can be performed even on a recording medium with a poor surface condition, such as rough plain paper or cloth.

  The ink jet printer has a paper transport mechanism, a head scanning mechanism, a motor, a drive circuit, a head drive circuit, a data processing / control circuit, an operation / display circuit, a power supply circuit, and the like as a basic configuration, and is an electrophotographic system such as an LBP. The mechanism is simpler than that of a printer.

  In addition, the conventional inkjet printer has a large ink droplet size, and the effect of slight fluctuations on the image quality is small. However, with the recent demand for higher image quality, the droplet size has become smaller and more accurate. Is now required.

  One of the factors that hinders high accuracy is a variation in the distance between the recording head and the paper (hereinafter, the distance between the head paper). For example, when the distance between the head sheets fluctuates by 0.1 mm, the ink droplet landing (dot) position is shifted by 20 μm (bidirectional printing, CR (carriage) speed 40 inch / s, ink ejection speed 10 m / s). Calculated value). Therefore, when the droplet size is reduced, a slight deviation in the landing position greatly affects the print quality.

In order to solve the above-described problem, Patent Document 1 describes a technique for correcting the landing position of an ink droplet by controlling the ink ejection timing based on the fluctuation amount of the distance between head sheets.
JP-A-11-240146

  However, in order to detect the variation in the distance between the head sheets in Patent Document 1, a highly accurate detector is required, resulting in an increase in complexity and cost of the apparatus.

  The present invention has been made in view of the above problems, and an object of the present invention is to realize a technique capable of accurately measuring a distance between head sheets with a simple configuration by mounting an optical sensor on a carriage.

  Another object of the present invention is to realize a technology capable of improving the landing accuracy and the printing quality by controlling the ink ejection timing based on the variation amount of the distance between the head sheets measured with high accuracy.

  In order to solve the above problems and achieve the object, the present invention provides an inkjet recording apparatus that performs recording by ejecting ink onto a recording medium while reciprocally scanning a recording head having a plurality of nozzles with a carriage. A detection unit that is mounted on a carriage and detects a distance between the recording head and the recording medium, and a calculation that calculates a variation amount of the distance in a recording area of the recording medium based on the detection result of the distance. And control means for controlling the ink ejection timing of the recording head so as to correct the deviation of the ink from the target ejection position based on the calculated variation amount of the distance.

  The present invention also provides a control method for an ink jet recording apparatus that performs recording by ejecting ink onto a recording medium while reciprocally scanning a recording head having a plurality of nozzles with a carriage, and includes a detection unit mounted on the carriage. A detecting step for detecting a distance between the recording head and the recording medium; a calculating step for calculating a variation amount of the distance in a recording area of the recording medium based on the detection result of the distance; And a control step of controlling the ink ejection timing of the recording head so as to correct the deviation of the ink from the target ejection position based on the distance fluctuation amount.

  According to the present invention, the landing accuracy is improved by controlling the ink ejection timing based on the amount of variation in the distance between the head sheets measured with high accuracy, and ruled line deviation, color change, color deviation, and the like are reduced. Can do.

  Hereinafter, an embodiment according to the present invention will be described in detail with reference to the drawings.

  The embodiment described below is an example as means for realizing the present invention, and should be appropriately modified or changed according to the configuration of the apparatus to which the present invention is applied and various conditions. It is not limited to the embodiment.

  In the present embodiment, “print” is not only formed when significant information such as characters and figures is formed, but also manifested so that humans can perceive it visually. Whether or not. That is, a case where an image, a pattern, a pattern, or the like is widely formed on a recording medium or a medium is processed is also expressed.

  “Paper” is not only paper used in general printers, but also widely represents cloth, plastic film, metal plate, glass, ceramics, wood, leather, etc. that can accept ink. To do.

  Furthermore, “ink” should be interpreted widely as the definition of “print” above, and is applied on paper to form images, patterns, patterns, etc., or process paper, or process ink. Represents a liquid that can be subjected to Examples of the ink treatment include solidification or insolubilization of the colorant in the ink applied to the paper.

  Further, the “nozzle” is a generic term for an ejection port or a liquid passage communicating with the nozzle and an element that generates energy used for ink ejection unless otherwise specified.

[Schematic description of inkjet printer (FIG. 1)]
FIG. 1 is a perspective view showing an ink jet printer according to an embodiment of the present invention with an upper cover removed.

  As shown in FIG. 1, a manual insertion slot 88 is provided on the front surface of an inkjet printer (hereinafter referred to as printer) 2, and a roll paper cassette 89 that can be opened and closed to the front surface is provided below the manual insertion slot 88. As a result, a recording medium such as paper (hereinafter, paper) is supplied from the manual insertion slot 88 or the roll paper cassette 89 into the printer. The printer 2 includes an apparatus main body 94 supported by two leg portions 93, a stacker 90 for stacking discharged sheets, and an upper cover 91 that is transparent and can be opened and closed. Further, on the right side of the apparatus main body 94, an operation panel 12, an ink supply unit, and an ink tank are arranged.

  The printer 2 includes a transport roller 70 for transporting the paper in the arrow B direction (sub-scanning direction), and a carriage unit (hereinafter referred to as “reciprocating” in the width direction of the paper (arrow A direction, main scanning direction)). Carriage) 4 is provided. The printer 2 also includes a carriage motor (not shown) and a carriage belt 3 for reciprocating the carriage 4 in the direction of arrow A. In addition, the printer 2 supplies an ink jet recording head (hereinafter referred to as a print head) 11 mounted on the carriage 4 and a suction type for supplying ink and eliminating ink ejection defects due to clogging of ejection ports of the print head 11. And an ink recovery unit 9.

A print head 11 composed of six heads corresponding to six color inks is mounted on the carriage 4 in order to perform color recording on paper.
That is, the print head 11 ejects, for example, a K head that ejects K (black) ink, a C head that ejects C (cyan) ink, an M head that ejects M (magenta) ink, and a Y (yellow) ink. It is composed of a Y head. Further, the print head 11 includes an LC head that ejects LC (light color cyan) ink and an LM head that ejects LM (light color magenta) ink.

  As described above, after the sheet is conveyed to the predetermined recording start position by the conveyance roller 70, the operation of causing the carriage 4 to scan the print head 11 in the main scanning direction, and the operation of conveying the sheet by the conveyance roller 70 in the sub-scanning direction. Is repeated to record on the entire sheet.

  That is, the carriage 4 is moved in the direction of arrow A shown in FIG. 1 by the carriage belt 3 and a carriage motor (not shown), and recording is performed on the paper. When the carriage 4 is returned to the position before being scanned (home position), the sheet is conveyed in the sub-scanning direction (the direction of arrow B shown in FIG. 1) by the conveying roller. Thereafter, the carriage is scanned again in the direction of arrow A in FIG. 1 to record images, characters, etc. on the paper. When the above operation is repeated and the recording of one sheet is completed, the sheet is discharged into the stacker 90, and the recording for one sheet is completed.

[Description of Printer Control Circuit (FIG. 2)]
FIG. 2 is a block diagram showing a main control configuration of the printer shown in FIG.

  In FIG. 2, reference numeral 1 denotes a host device such as a personal computer (PC) that supplies image data, commands, and the like. The printer 2 receives image data, commands, parameters, an image processing LUT (lookup table), and the like from the PC 1 and records the received image data according to the commands, parameters, and image processing LUT.

  The PC 1 is a general one, has a keyboard and a display, and implements an interface with the user by application software, a printer driver dedicated to the printer, and dedicated printer control software (RIP or the like).

  A control unit 5 includes a CPU, an ASIC, a DMAC, a RAM, a ROM, and the like for controlling the entire printer 2. Reference numeral 4 denotes a carriage 4 on which the print head 11 is mounted, 6 denotes a carriage transport unit that reciprocates the carriage 4 in the main scanning direction, and 7 denotes a paper transport unit that moves the paper in the sub-scanning direction. Reference numeral 8 denotes a supply unit that supplies ink to the print head 11, and 9 denotes a recovery unit that recovers the print head 11 to a good state by performing surface cleaning, ink suction, ink droplet ejection, and the like of the print head 11. Reference numeral 10 denotes a power supply unit for supplying power to the print head 11 and the control unit 5 and other unit units. Reference numeral 12 denotes an operation panel unit having a display such as a key switch or LCD.

  In the present embodiment, although detailed drawings and descriptions of the mechanism unit are omitted, the printer 2 operates as a serial printer.

  In this embodiment, the print head 11 is detachable with respect to the carriage 4. The carriage 4 is an electrical contact, a joint portion such as a tube for supplying ink, a member for supporting and fixing the print head 11, and the carriage transport unit 6. And a connection part. The carriage 4 is supported by a rail (not shown) of the carriage transport unit 6 and is connected to a motor (not shown) of the carriage transport unit 6 by a timing belt (not shown) of the carriage transport unit 6. The carriage 4 reciprocates in the main scanning direction. Further, an encoder sensor (not shown) is mounted on the carriage 4, and an encoder linear scale (not shown) is provided in the main scanning direction inside the carriage transport unit 6, and the print head 11 mounted on the carriage 4. Can be detected and its moving speed can be controlled.

  The paper transport unit 7 controls the rotation of the transport roller 70 with a motor (not shown) and a rotary encoder (not shown) in order to move the paper in the sub-scanning direction.

  The ink supply unit 8 connects an ink tank (not shown) and the print head 11 with an ink tube or the like, and supplies ink from the ink tank to the print head. Further, a valve mechanism is provided in the middle of the ink tube, and ink leakage from the ink tube and the print head is prevented by closing the valve when the print head 11 is replaced or the ink tank is replaced. A motor is used as a drive source for moving the valve mechanism, and a photo interrupter is used as a position sensor to detect the open / closed state of the valve.

  The recovery unit 9 has a wiping mechanism for wiping the surface of the print head 11, a capping mechanism for sealing the surface of the print head with a member, and a suction pump mechanism for sucking ink from the nozzles of the print head 11. Further, the recovery unit 9 includes a motor that drives these mechanisms, a drive transmission mechanism, and a position sensor that detects the state of each part of the mechanism unit.

  The power supply unit 10 is turned on / off by an AC switch, a soft switch on the operation panel 12, and the like, and the control unit 5 is supplied with power of 3.3V and 5V as a logic power supply. Further, the power supply unit 10 supplies power of a voltage of 24 V to the actuators (motors, etc.) of each unit via the I / O control unit & driver unit 26 in the control unit. In addition, the head power of the print head 11 is supplied from the power supply unit 10 at a set voltage value via a head power control unit in the control unit.

  The control unit 5 includes a sequence control unit 21 that manages the overall operation, an image processing unit 22 that performs conversion processing from image data to recording data, and a timing control unit 23 that adjusts the timing of recording data in accordance with the operation of the printer 2. Prepare. Further, the control unit 5 is an I / O that performs interface and drive control with the head drive unit 24 that controls drive data, drive pulses, drive voltage, and the like of the print head 11, and sensors and actuators (motors, etc.) of the internal unit of the printer 2. O control unit & driver unit 25 and the like.

  The control unit 5 is physically a circuit board. The sequence control unit 21 is a CPU, a ROM that stores a control program for the CPU and various data, a RAM that is used as a work area for the CPU and stores various data, and an I / F unit that controls an interface with the PC 1 serving as a host device. Etc. The image processing unit 22, the timing control unit 23, and the head drive unit 24 are mainly configured by a memory such as an ASIC and a RAM, and the I / O control unit & driver unit 25 is an electric circuit such as a general-purpose LSI or a transistor. Composed.

  The image processing unit 22 converts the luminance image data (RGB color component data) from the PC 1 into density image data (K, C, M, Y, LC, LM components) corresponding to ink colors based on the image processing LUT. A color conversion processing unit 41 is provided. The image processing unit 22 also includes an output γ processing unit 42 that converts density image data from the color conversion processing unit 41 based on output γ characteristics of the printer. Further, the image processing unit 22 includes a binarization processing unit 43 that converts density image data (multi-value data) from the output γ processing unit 42 into binary image data.

  The timing control unit 23 sets the arrangement order of binary image data (raster direction (main scanning direction) order) corresponding to each ink color processed by the image processing unit 22 in the order (column column) of the print head 11 in the nozzle arrangement direction. An HV conversion unit 47 that converts in the direction (sub-scanning direction) is provided. In addition, the timing control unit 23 includes a memory unit 48 that stores image data converted in the column direction. Further, the timing control unit 23 controls the read timing from the memory unit 48 for each image data corresponding to each ink color according to the position and moving direction of the print head 11 and adjusts so that the recording by each ink does not shift. A registration adjustment unit 49 is provided.

[Detection of head-to-paper distance]
Next, a method for detecting the distance between the head sheets by the printer of this embodiment will be described.

  FIG. 3 is a view showing a carriage peripheral portion in the printer of the present embodiment.

  In FIG. 3, 51 is a platen, 52 is an optical sensor such as a reflective sensor, and 53 is paper. The optical sensor 52 is disposed on the downstream side (or upstream side or one side of the main scanning direction A) of the paper 53 in the carriage 4 in the conveyance direction (sub-scanning direction B). The conveyance roller 70 sequentially stores position information using the rotary encoder described above. Although the transport roller 70 and the paper 53 are slightly slipped, they basically operate in conjunction with each other. Therefore, the control unit 5 calculates the relative position (paper feed amount) of the paper 53 with respect to the print head 11 from the position information (direction and movement amount) of the transport roller 70.

  FIG. 4 is a schematic configuration diagram of the optical sensor of FIG.

  In FIG. 4, 54 is a light emitting LED, and 55 is a phototransistor. Light emitted from the light emitting LED 54 is reflected by the surface of the paper 53 and received by the phototransistor 55. When the distance between the paper 53 and the optical sensor 52 varies, the amount of light received by the phototransistor 55 changes. Therefore, the distance between the paper 53 and the optical sensor 52 can be detected by obtaining the change in the amount of light.

[Correction of landing position]
Next, a method for correcting the landing position using the distance between the head sheets using the optical sensor will be described.

  FIG. 5 is a flowchart showing the landing position correction processing based on the head sheet distance according to the present embodiment. The following steps are realized by the sequence controller 21 of the control unit 5 executing a program stored in the ROM when the printer is turned on.

Step5-1 (Detecting the entire height of the paper width)
The optical sensor 52 is used to detect the fluctuation amount of the head paper distance (or head platen distance, hereinafter also referred to as height) in the entire paper width (or printable area). Furthermore, in addition to the variation in the distance between the head sheets, the count value of the encoder sensor that detects the position of the carriage in the main scanning direction (the reference position is set to “0” and the count value increases in the direction away from the reference position). get. This count value may be averaged with a plurality of values in the main scanning direction of the carriage. Thereby, the storage capacity is reduced.

Step5-2 (Calculation of landing position)
The landing position deviation amount is calculated according to the following equation in accordance with the fluctuation amount of the head sheet distance over the entire sheet width.

Landing position deviation amount = head paper distance variation / ink ejection speed × carriage speed × bidirectional deviation For example, head paper fluctuation amount: 0.2 mm, ink ejection speed: 10 m / s, carriage speed: 40 inch / s Then, the landing position deviation amount = 0.2 / 1000/10 × 40 × 25.4 / 1000 × 2 = 0.00004064 m, that is, the deviation amount is about 40 μm.

  In addition, when the ink droplet size is 4 pl, the dot diameter on the paper is about 30 μm in diameter (although approximate depending on the distance between the paper and the head paper and the ink state).

  Visibility varies slightly from person to person, but it is generally said that if a half dot of ink droplets (15 μm in the case of the size exemplified here) is displaced, ruled line displacement or color change can be recognized. Yes.

Step5-3 (Correction of landing position over the entire paper width)
The ejection timing of the ink droplets by the head driving unit 24 is controlled so as to correct the landing position deviation calculated in Step 5-2.

  Here, correction for shifting the landing position will be described.

  6A and 6B are a plan view and a side view showing the positional relationship between the carriage and the paper when there is no landing position deviation, and FIG. 7 shows the positional relationship between the carriage and the paper when there is a landing position deviation. It is a top view (a) and a side view (b).

  6 and 7, reference numeral 62 denotes a landing target position, 63 denotes a landing position deviation amount when there is a convex step on the paper 53, and 64 denotes a head paper distance.

  As shown in FIG. 6, landing position adjustment (registration adjustment) is performed so that the landing position of the ink droplet matches the target landing position 62 in a state where there is no step on the paper 53.

  On the other hand, in the state where there is a step on the paper 53 as shown in FIG. 7, even if the registration adjustment is performed without the step, the landing position deviation occurs. The ruled line shift does not occur when there is no step in FIG. 6, but the ruled line shift occurs when there is a step as shown in FIG. 6 and 7 focus only on the ruled line deviation, the same can be said for the color change.

  FIG. 8 is a diagram for explaining the occurrence of a color change due to a landing position shift.

  In the state where there is no level difference in FIG. 8A, the ejected ink droplets 61 are arranged on the paper 53 at equal intervals, and the dots in the entire printing area are uniformly arranged, so that the color does not change.

  However, in the case where there is a step in FIG. 8B, the landing position is shifted in the main scanning direction A due to the step, and the dots in the entire print area are uniformly arranged even if the ink droplet ejection timing is controlled to be constant. This will cause a change in color.

  FIG. 9A is a plan view and FIG. 9B is a side view showing the positional relationship between the carriage and the paper when the ink droplet ejection timing is corrected to eliminate the landing position deviation.

  In FIG. 9, in order to correct the landing position deviation amount 63, the ejection timing of the ink droplets at the position of the carriage 4 with respect to the target landing position 62 is shifted based on the head sheet distance fluctuation amount (Step 5-1). 4 → 4 ′) and land at the target landing position 62. In this way, by performing the correction for shifting the ink droplet ejection timing using the fluctuation amount of the distance between the head sheets, the ruled line deviation can be eliminated as in the case where there is no step as shown in FIG.

Step5-4 (Execution judgment for each scan)
The amount of variation in the distance between the head sheets is detected every time the carriage is scanned, and it is determined whether it is necessary to correct the landing position. This is because, for example, when height fluctuation (cockling) or the like that occurs due to the effect of printing is corrected, it changes each time printing is continued. Because it is necessary to correct. Of course, it is not always necessary to perform every scan, and may be performed at regular intervals. In addition, when the distance between the head sheets varies due to the tolerance of the printer main body, it is not necessary to detect the amount of variation in the distance between the head sheets for each scan, and once at the time of paper setting (or once at the time of factory shipment). It is enough to do.

  Next, a method for detecting the distance between the head sheets according to the present embodiment will be described.

  FIG. 10 is a flowchart showing the processing for detecting the distance between head sheets according to the present embodiment.

  In this embodiment, since a small amount of variation in the distance between head sheets (hereinafter also referred to as a gap) is detected using a simple optical sensor 52 mounted on the carriage 4, the sensor is detected and adjusted at a specific position. Then, detection in the entire area and calibration of the output value are performed, and a desired amount of change in the distance between the head sheets is detected.

Step10-1 (reference plane detection)
FIG. 11 is a diagram illustrating a carriage, a sheet, and a reference position in the head sheet distance detection according to the present embodiment.

  In FIG. 11, 31 is a static gap detection position, and 32 is a gap height reference part (height reference plane). In FIG. 11, the optical sensor 52 is provided at one downstream side in the main scanning direction A and at a position where the sensor 52 passes through the gap height reference portion 32 in the scanning range of the carriage 4.

  The static gap detection position 31 is a position for detecting the carriage 4 in a stationary state in order to detect the gap. This position is not particularly formed with a marker or the like, and is a position where the distance between the head sheets is calibrated when the printer body is assembled.

  The gap height reference portion 32 is a position where a variation in height from the static gap detection position 31 is guaranteed, and is present at a position different from the paper conveyance path. FIG. 12 shows a cross section of the gap height reference portion, and the reference portion is provided with a plurality of surfaces having different heights.

  FIG. 13 is a diagram showing the relationship between the gap fluctuation and the output fluctuation of the optical sensor of this embodiment.

  In FIG. 13, reference numeral 33 denotes an assumed height fluctuation region that is assumed to be a detection range of the distance between head sheets.

  In the assumed height fluctuation region 33, the arrangement inside the sensor is determined so that the output fluctuation of the sensor keeps substantially linear.

  For example, the height reference plane is defined as “−0.3 mm” and “0.3 mm” when the static gap detection position 31 is “0 mm”.

  Within the range of the assumed height fluctuation region 33, the output fluctuation is kept substantially linear. For this reason, the output at the position of the height “−0.3 mm” is “0.4 (relative value)”, and the output at the position of “0.3 mm” is “0.6 (relative value)”. Then, for example, when the sensor output is “0.5 mm (relative value)”, the height can be detected as “0 mm”. In this way, by calibrating the sensor output in advance with the gap height reference plane 32, the height variation amount can be detected from the sensor output value.

  The reason why the gap height reference plane 32 is calibrated is to calibrate variations in the elements of the light emitting LED 54 and the phototransistor 55 constituting the sensor. The calibration on the reference surface 32 may be performed by adjusting the light emission amount on the light emitting side and adjusting the amplification degree on the light receiving side.

Step10-2 (Height detection at fixed position)
Here, height detection is performed at a fixed position (specific position) on the sheet.

  The fixed position is where the distance between the head sheets is calibrated when the printer body is assembled.

  The height detected at this fixed position is a value obtained by subtracting the thickness of the sheet from the distance between the head sheets assumed at the time of assembly.

  Since the thickness of the paper printed by the ink jet printer is almost small enough to be within 0.1 to 0.3 mm, it does not exceed the linear region of the sensor output variation shown in FIG. I can say that.

  On the other hand, since the reflectance varies depending on the paper, the output value varies depending on the amount of reflected light even if the height is the same.

  FIG. 14 is a diagram showing the relationship between the height fluctuation and output fluctuation of sheets having different reflectivities, 53a being the height fluctuation and output fluctuation of the sheet 53A having reflectance X, and 53b being the height of the sheet 53B having reflectance Y. Variation and output variation are shown respectively.

  For example, when the thicknesses of the sheets 53A and 53B are the same, and the height variation is “0 mm”, the output of the sheet 53A is “0.474” and the output of the sheet 53B is “0.158”. Although the absolute value of the output value on the paper differs for each paper, the output fluctuation ratio when the height fluctuates is the same.

  For example, when the height variation is “−0.2 mm”, the output of the paper 53A is “0.564” and the output of the paper 53B is “0.188”. The output fluctuation ratio when the height is changed to “−0.2 mm” is 0.564 / 0.474 = 1.19 for the paper 53A and 0.188 / 0.158 = 1.19 for the paper 53B. .

  That is, the output fluctuation ratio is the same regardless of the reflectance of the paper. This is because the output fluctuation ratio does not depend on the sheet surface state (the amount of reflected light) but depends on the aperture size of the LED light.

  Here, the setting of the specific position will be described.

  The specific position also serves as a reference for registration adjustment (nozzle position adjustment), and registration adjustment (particularly bidirectional registration adjustment) is performed in the vicinity of the specific position. Then, the discharge timing is corrected by the height variation based on the registration adjustment result.

Step10-3 (Gain setting for dynamic height detection)
Here, the output of the sensor is adjusted on the paper.

  The reason for adjusting the output of the sensor is to calibrate the difference between the reflected light amount of the reference surface on which the reference surface detection (Step 10-1) is performed and the reflected light amount of the paper (that is, the difference due to the paper). This is because, depending on the paper, the output fluctuation is large when the height fluctuation occurs, and the output may be saturated. The gain is set on the assumption that there is a height variation by the printer main body tolerance from the output at a specific position where the distance between the head sheets is known.

Step10-4 (Dynamic height detection)
Here, the height of the entire sheet is detected using the output adjustment result in Step 10-3, and the ratio between the output fluctuation and the static gap detection position 31 is calculated. Then, the fluctuation amount of the head sheet distance is calculated from the relationship between the calculated ratio, the height fluctuation obtained in advance, and the output fluctuation.

  FIG. 15 is a diagram showing the result of calculating the height fluctuation from the output fluctuation of the sensor. The horizontal axis is the paper width position, and the measurement result is obtained using a printer having a printable area (paper width) of 900 mm. Of the height variation on the vertical axis, the assumed tolerance of the printer body is about 500 μm.

[Second Embodiment]
Next, as a second embodiment, a method for calibrating the output result of the sensor in the entire print area of the paper using output values at at least two or more specific positions will be described.

  In the first embodiment, it is assumed that a region where the sensor height fluctuation and output fluctuation are approximately linear is used. This premise is substantially established with respect to the normally used paper thickness and the assumed main body tolerance when the thickness of the normal paper is about 0.1 to 0.3 mm.

  However, it is conceivable to use a non-linear region as the assumed height fluctuation region 33 when printing on a particularly thick paper (thickness exceeding 1 mm exists) such as board paper.

  In this way, when a non-linear region is used as the assumed height variation region 33, detection and adjustment of the sensor at a specific position, detection over the entire region, and calibration of the output value are performed, and a desired amount of variation in the distance between the head sheets A method for detecting this will be described with reference to the flowchart of FIG.

  In FIG. 16, the two steps described below are performed after the dynamic height detection (Step 10-4) in the flow of FIG.

Step16-1 (Height detection at fixed position 2)
The sensor output adjustment on the paper uses the same result as in Step 10-2.

  As the height of the second specific position, a position whose relative height fluctuation with the height of the first specific position is known is used. This position is realized, for example, by recording numerical values at a factory or by adjusting the printer body. In FIG. 17, reference numeral 34 denotes a second static gap detection position.

  Since the distance between the head sheets at each of the first and second specific positions must be different, the first height obtained in Step 10-2 (a known value at the time of shipment from the factory) is G1, this sequence The output value above is V1. Further, the second height obtained in Step 16-1 (a known value at the time of factory shipment) is G2, and the output value on this sequence is V2.

Step16-2 (Height fluctuation correction)
Using the first and second static gap detection results, the dynamic height detection result is multiplied by the following fluctuation to calculate the height fluctuation.

Each height fluctuation = each output fluctuation x (G1-G2) / (V1-V2) + (G2 * V1-G1 * V2) / (V1-V2)
The ejection timing is controlled using the dynamic height detection result calculated as described above.

  The above method is based on the premise that the distance between the head sheets and the output value of the sensor are at least monotonically increasing (or monotonically decreasing) even if they are not linear.

  The height detection at the second specific position is performed after Step 10-4, but the effect is the same if performed immediately after the first detection at Step 10-2.

[Third Embodiment]
Next, as a third embodiment, a method for determining whether or not there is an abnormality at height detection and performing correction based on the determination result will be described.

  Here, the abnormality is assumed, for example, when different printing is performed on the paper in advance, or when the paper is dirty or scratched.

  FIG. 18 is a diagram illustrating a height detection result when different printing is performed on the paper in advance.

  In FIG. 18, 45 indicates points before and after the abnormal value of the height detection result.

  If there is a print location on the paper at the time of dynamic height detection described above, the output value there changes significantly. This depends on the wavelength of the light emitting LED of the sensor and the light absorption characteristics.

  For this reason, when there is some abnormality such as a print location on the paper, a value remarkably different from the output fluctuation caused by the height fluctuation is detected. Therefore, the average value of the output values up to the position 45 immediately before the significant change in the output value is used for abnormality determination of height fluctuation. Here, it is assumed that there is no significant height fluctuation in a narrow region.

  In addition, since abnormality determination can be performed using the output fluctuation of the sensor, for example, when the abnormality is determined, the sheet may be conveyed again and detected again at a different position.

[Platen structure]
19A and 19B are views for explaining the structure of the platen. FIG. 19A is a cross-sectional view viewed from the downstream side in the paper transport direction, and FIG. 19B is an enlarged view of a part of FIG.

  In FIG. 19, reference numeral 106 denotes a base member of the platen 51. The platen 51 has a structure in which a plurality of members 101 to 105 are mounted on a base member 106. In other words, the platen 51 is arranged by arranging a plurality of members 101 to 105 on the base member 106 in the print head scanning direction. Further, FIG. 19A shows a state in which the paper 53 is conveyed on the platen 51, 31 is a static gap detection position, and 32 is a gap height reference member.

  In FIG. 19B, reference numeral 35 denotes a resist adjustment pattern.

  In FIG. 19B, the resist adjustment pattern 35 is recorded at a position corresponding to the upper portion of the member 102 on the paper 53 and avoiding the portion straddling the members 101 and 103. The position where the resist adjustment pattern 35 is recorded is a position where the static gap detection position 31 is included.

[Other Embodiments]
The embodiment according to the present invention has been described in detail using specific examples. However, the present invention can take an embodiment as a system, apparatus, method, program, storage medium (recording medium), or the like. is there. Specifically, the present invention may be applied to a system composed of a plurality of devices, or may be applied to an apparatus composed of a single device.

  It goes without saying that the object of the present invention can be achieved even if any part of the illustrated functional blocks and operations is realized by a hardware circuit or by software processing using a computer.

  Note that the present invention includes a case where the present invention is achieved by supplying a software program for realizing the functions of the above-described embodiments directly or remotely to a system or apparatus. In that case, a computer such as a system reads and executes the program code.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

1 is a perspective view showing an ink jet printer according to an embodiment of the present invention with an upper cover removed. FIG. 2 is a block diagram illustrating a main control configuration of the printer illustrated in FIG. 1. It is a figure which shows the carriage peripheral part in the printer of this embodiment. It is a schematic block diagram of the optical sensor of FIG. It is a flowchart which shows the correction process of the landing position based on the distance between head sheets by this embodiment. FIG. 5A is a plan view and FIG. 5B is a side view illustrating a positional relationship between a carriage and a sheet when there is no landing position deviation. FIG. 6 is a plan view (a) and a side view (b) showing a positional relationship between a carriage and a sheet when there is a landing position shift. It is a figure explaining the change of the color due to landing position deviation, and is a side view showing the positional relationship between ink droplets and paper when there is no landing position deviation (a) and there is a landing position deviation (b). FIG. 4A is a plan view and FIG. 4B is a side view illustrating a positional relationship between a carriage and a sheet when ink droplet ejection timing is corrected in order to eliminate landing position deviation. It is a flowchart which shows the detection process of the distance between head sheets by this embodiment. FIG. 5 is a diagram illustrating a carriage, a sheet, and a reference position in detecting a distance between head sheets according to the present embodiment. It is a figure which shows the cross section of a gap height reference | standard part. It is a figure which shows the relationship of the gap fluctuation | variation and output fluctuation | variation of the optical sensor of this embodiment. It is a figure which shows the relationship between the height fluctuation | variation of a paper with different reflectance, and an output fluctuation | variation. It is a figure which shows the result of having calculated height fluctuation | variation from the output fluctuation | variation of a sensor. 10 is a flowchart illustrating a process for detecting a distance between head sheets according to the second embodiment. It is a figure which shows each static gap detection position of the 1st time and 2 times by 2nd Embodiment. It is a figure which shows the height detection result when different printing was previously carried out on the paper. 2A and 2B are diagrams illustrating the structure of a platen, where FIG. 1A is a cross-sectional view viewed from the downstream side in the paper conveyance direction, and FIG.

Explanation of symbols

31 Static gap detection position 32 Gap height reference member 33 Assumed height fluctuation region 34 Static gap detection position (second time)
35 resist adjustment pattern 41 color conversion processing unit 42 output γ processing unit 43 binarization processing unit 47 HV conversion unit 48 memory unit 49 registration adjustment unit 51 platen 52 optical sensor 53 paper 54 LED for light emission
55 Phototransistor 61 Ink droplet 62 Target landing position 63 Landing position deviation amount 64 Head paper distance 70 Transport roller 88 Manual feed port 89 Roll paper cassette 90 Stacker 91 Upper cover 93 Leg portion 94 Main body 101 to 105 Platen component 106 Platen base member

Claims (11)

An inkjet recording apparatus that performs recording by ejecting ink onto a recording medium while reciprocally scanning a recording head having a plurality of nozzles with a carriage,
A detection means mounted on the carriage for detecting a distance between the recording head and the recording medium;
Calculation means for calculating a variation amount of the distance in a recording area of the recording medium based on the detection result of the distance;
An inkjet recording apparatus comprising: control means for controlling ink ejection timing of the recording head so as to correct a deviation from a target ejection position of ink based on the calculated variation amount of the distance.   Calibration means for calibrating the output of the detection means by using the detection result of the reference portion in which the distance from the platen arranged to face the recording head is adjusted in advance and the detection result of the specific position on the recording medium. The inkjet recording apparatus according to claim 1, comprising:   The calibration means uses the detection result of the reference means, the detection result of the specific position, and the detection result of the second specific position whose relative position with respect to the specific position is preset. The inkjet recording apparatus according to claim 2, wherein the output is calibrated. Means for comparing the detection result of the distance by the detection means with a specified value;
The inkjet recording apparatus according to claim 1, further comprising: a unit that determines whether the detection result is abnormal based on a comparison result with the specified value.   The inkjet recording apparatus according to claim 4, wherein the specified value is an average value of detection results obtained immediately before. The platen has a structure in which a plurality of members are mounted on a base member,
The inkjet recording apparatus according to claim 2, wherein the reference portion is provided on a base member. A control method for an ink jet recording apparatus that performs recording by ejecting ink onto a recording medium while reciprocally scanning a recording head having a plurality of nozzles with a carriage,
A detecting step of detecting a distance between the recording head and the recording medium by a detecting means mounted on the carriage;
A calculation step for calculating a fluctuation amount of the distance in a recording area of the recording medium based on the detection result of the distance;
And a control step of controlling the ink ejection timing of the recording head so as to correct the deviation of the ink from the target ejection position based on the calculated variation amount of the distance.   A calibration step of calibrating the output of the detection means using the detection result of the reference portion in which the distance to the platen disposed to face the recording head is adjusted in advance and the detection result of the specific position on the recording medium; 8. The method of claim 7, comprising:   The calibration step uses the detection result of the reference surface, the detection result of the specific position, and the detection result of the second specific position whose relative position with respect to the specific position is preset. The method of claim 8, wherein the output is calibrated. Comparing the detection result of the distance by the detection means with a specified value;
The method according to claim 7, further comprising: determining whether the detection result is abnormal based on a comparison result with the specified value.   The method according to claim 10, wherein the specified value is an average value of detection results obtained immediately before.

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