JP2012166566A - Method for controlling printing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printing apparatus that strikes a balance between print throughput and print quality with high-dimension.SOLUTION: A controller includes a memory for storing information regarding at least one rotation of a conveyance roller by correlating the information a first acquisition unit (rotary encoder) acquires and the information a second acquisition unit (direct sensor) acquires as correction data. The controller reads the correction data corresponding to rotation information the first acquisition unit acquires from the memory, and corrects at least one of drive control of a print head and drive control of the roller. The correction data are different based on when printing is performed on a first surface or a second surface.

Description

  The present invention relates to a printing apparatus that conveys a sheet and performs printing.

  Patent Document 1 discloses a printing apparatus that directly measures the speed of a sheet surface with a speed sensor and controls the ink ejection timing of a print head. FIG. 8 is a simplified diagram of the printing apparatus disclosed in FIG. The sheet 500 wound in a roll is conveyed by the upstream conveying roller pair 501 and the downstream conveying roller pair 502 and printed by the print head 503. Between the upstream conveying roller pair 501 and the print head 503, a speed sensor 504 (laser Doppler sensor) that directly measures the moving speed of the sheet is disposed. The drive control timing of the print head 503 is corrected according to the conveyance speed measured by the speed sensor 504, and high-quality printing is realized.

JP 2009-6655 A

  In the field of mass printing such as a print laboratory, how to increase the printing speed while maintaining the image quality is a problem. In addition, in consideration of bookbinding such as a photo book, there is an increasing demand for printing on both sides of a sheet.

  In the apparatus of Patent Document 1, a plurality of images can be sequentially printed on one side of a continuous sheet, but printing on both sides of the sheet is not considered at all. In double-sided printing, the coefficient of friction of the sheet surface that contacts the conveying roller changes between printing on the first side of the sheet and printing on the second side, and particularly when ink is applied, the coefficient of friction of the sheet surface changes greatly. As a result, in the second side printing after the first side printing, the degree of slip between the conveyance roller and the sheet surface changes, and the sheet conveyance state differs even when the same driving force is applied. Therefore, if the same correction is performed at the time of printing the first side and the second side by the method as in Patent Document 1, the image on the second side is different from the original size, and the image size on the front and back sides is different. It will not match.

  Further, the laser Doppler sensor used in the apparatus disclosed in Patent Document 1 temporarily stores measured information, performs signal processing, and outputs a result on the principle of measurement. For this reason, the detection delay required for complicated signal processing becomes rate-determining, and it may be difficult to increase the printing speed (sheet moving speed) by preventing the real-time correction control from being speeded up.

  In view of the recognition of the above problems, a first object of the present invention is to provide a technique capable of accurately printing an image on both sides of a sheet and capable of duplex printing with high print throughput.

In the apparatus disclosed in Patent Document 1, a speed sensor is disposed between the upstream conveying roller and the print head. Since the speed sensor (laser Doppler sensor) requires a large installation space, the distance between the conveyance roller and the print head is increased accordingly. For this reason, when the sheet is introduced, the leading end of the sheet floats up from the conveyance roller to the print head, and the possibility that the nozzle of the most upstream print head contacts the leading end of the sheet increases. In order to suppress this, it is necessary to make the distance between the speed sensor and the print head as small as possible. However, as the speed sensor and the print head come closer, the problems listed below become more apparent.
(1) Within the time from the measurement position of the speed sensor to the most upstream print head, there is a high possibility that it will not be possible to complete the calculation by the speed sensor and control the ink ejection timing in time. Since this problem increases as the sheet conveying speed increases, it is difficult to improve the printing speed.
(2) When the print area of the print head approaches the measurement position of the speed sensor, cockling (local sheet lifting) that occurs when the sheet absorbs ink immediately after printing affects the measurement position. The possibility increases. If the sheet floats at the measurement position of the sensor, it causes a measurement error.
(3) When the print head and the speed sensor are close to each other and there is no shielding object therebetween, ink mist (fine ink droplets) that is generated and scattered when ink is ejected from the print head is likely to adhere to the speed sensor. The speed sensor (laser Doppler sensor) has a light emitting part and a light receiving part. If ink mist adheres to the light emitting part or the light receiving part, the detection signal level is lowered, and stable measurement cannot be performed.

  In view of the above problems (1) to (3), the second object of the present invention is to achieve both high speed of sheet conveyance and measurement accuracy of the speed sensor at a high level, and high printing even during long-term operation. It is to provide a method that can maintain the quality.

  An embodiment of the present invention is a control method of a printing apparatus capable of performing double-sided printing on a first surface and a second surface of a sheet with a printing unit, and the sheet is conveyed by a roller provided with a driving force, Correction information corresponding to the information indicating the rotation phase acquired along with the rotation of the roller is acquired when acquiring information indicating the rotation phase of the rotating roller and printing on the first surface and the second surface. Is used to correct at least one of the control of the printing unit and the driving control of the roller, and the correction data used for correction when printing on the first surface and the printing on the second surface In this case, the correction data used for correction is different.

  According to the present invention, a printing apparatus that achieves both high print quality and high print throughput can be realized.

Schematic showing the internal configuration of the printing device Block diagram of control unit Diagram for explaining the operation in single-sided print mode and double-sided print mode Detailed configuration diagram of the print unit Graph showing change in sheet conveyance error due to conveyance Flow chart showing operation sequence in single-sided print mode Flow chart showing operation sequence in duplex printing mode Schematic diagram of conventional example

  Hereinafter, an embodiment of a printing apparatus using an inkjet method will be described. The printing apparatus of this example uses a long and continuous sheet (a continuous sheet longer than the length of a repeated printing unit (referred to as one page or unit image) in the conveyance direction), and is used for both single-sided printing and double-sided printing. It is a compatible high-speed line printer. For example, it is suitable for the field of printing a large number of sheets in a print laboratory or the like. In this specification, even if a plurality of small images, characters, and blanks are mixed in the area of one print unit (one page), what is included in the area is collectively referred to as one unit image. . That is, the unit image means one print unit (one page) when a plurality of pages are sequentially printed on a continuous sheet. The length of the unit image varies depending on the image size to be printed. For example, the length in the sheet conveyance direction is 135 mm for the L size photograph, and the length in the sheet conveyance direction is 297 mm for the A4 size.

  The present invention can be widely applied to printing apparatuses such as printers, multifunction printers, copiers, facsimile machines, and various device manufacturing apparatuses. The printing process may be any system such as an inkjet system, an electrophotographic system, a thermal transfer system, a dot impact system, or a liquid development system. The present invention is not limited to print processing, and can be applied to a sheet processing apparatus that performs various processing (recording, processing, coating, irradiation, reading, inspection, etc.) on a continuous sheet. In this case, a processing head for performing processing other than printing is used instead of the print head.

  FIG. 1 is a schematic cross-sectional view showing the internal configuration of the printing apparatus. The printing apparatus according to the present embodiment is capable of duplex printing on the first surface of the sheet and the second surface on the back side of the first surface, using the sheet wound in a roll shape. Inside the printing apparatus, there are roughly a sheet supply unit 1, a decurling unit 2, a skew correction unit 3, a printing unit 4, an inspection unit 5, a cutter unit 6, an information recording unit 7, a drying unit 8, a reversing unit 9, and a discharge unit. Each unit includes a transport unit 10, a sorter unit 11, a discharge unit 12, and a control unit 13. A sheet is conveyed by a conveyance mechanism including a roller pair and a belt along a sheet conveyance path indicated by a solid line in the drawing, and is processed in each unit. Note that at an arbitrary position in the sheet conveyance path, the side close to the sheet supply unit 1 is referred to as “upstream”, and the opposite side is referred to as “downstream”.

  The sheet supply unit 1 is a unit for holding and supplying a continuous sheet wound in a roll shape. The sheet supply unit 1 can store two rolls R <b> 1 and R <b> 2, and is configured to selectively pull out and supply a sheet. The number of rolls that can be stored is not limited to two, and one or three or more rolls may be stored. Moreover, if it is a continuous sheet | seat, it will not be restricted to what was wound by roll shape. For example, the continuous sheet | seat provided with the perforation for every unit length may be return | folded and laminated | stacked for every perforation, and may be accommodated in the sheet | seat supply part 1. FIG.

  The decurling unit 2 is a unit that reduces curling (warping) of the sheet supplied from the sheet supply unit 1. The decurling unit 2 uses two pinch rollers for one driving roller, and curls the sheet by curving and passing the sheet so as to give the curl in the opposite direction, thereby reducing the curl.

  The skew correction unit 3 is a unit that corrects skew (inclination with respect to the original traveling direction) of the sheet that has passed through the decurling unit 2. The sheet skew is corrected by pressing the sheet end on the reference side against the guide member.

  The printing unit 4 is a unit that forms an image by performing a printing process on the conveyed sheet from above with the print head 14. That is, the print unit 4 is a processing unit that performs a predetermined process on the sheet. The printing unit 4 also includes a plurality of conveyance rollers that convey the sheet. The print head 14 has a line type print head in which an inkjet nozzle row is formed in a range that covers the maximum width of a sheet that is supposed to be used. The print head 14 has a plurality of print heads arranged in parallel along the transport direction. In this example, there are seven print heads corresponding to seven colors of C (cyan), M (magenta), Y (yellow), LC (light cyan), LM (light magenta), G (gray), and K (black). . The number of colors and the number of print heads are not limited to seven. As the inkjet method, a method using a heating element, a method using a piezo element, a method using an electrostatic element, a method using a MEMS element, or the like can be adopted. Each color ink is supplied from the ink tank to the print head 14 via an ink tube.

  In the printing unit 4, a direct sensor 20 is provided upstream of the print head 14 to acquire information related to the sheet moving state (moving speed and moving distance) by directly measuring the sheet surface at a predetermined measurement position. . Further, a mark reader 122 is provided for reading a mark formed on the sheet by the print head 14 from the back side of the measurement position. Details of the direct sensor 20 and the mark reader 122 will be described later.

  The inspection unit 5 optically reads the inspection pattern or image printed on the sheet by the printing unit 4 using a scanner, and inspects the nozzle state of the print head, the sheet conveyance state, the image position, etc., and the image is printed correctly. This is a unit for determining whether or not. The scanner has a CCD image sensor and a CMOS image sensor.

  The cutter unit 6 is a unit including a mechanical cutter that cuts a printed sheet into a predetermined length. The cutter unit 6 also includes a plurality of conveyance rollers for sending out the sheet to the next process.

  The information recording unit 7 is a unit that records print information (unique information) such as a print serial number and date in a non-print area of the cut sheet. Recording is performed by printing characters and codes using an inkjet method, a thermal transfer method, or the like. A sensor 23 for detecting the leading edge of the cut sheet is provided on the upstream side of the information recording unit 7 and the downstream side of the cutter unit 6. That is, the sensor 23 detects the edge of the sheet between the cutter unit 6 and the recording position by the information recording unit 7, and the information recording unit 7 controls the timing of information recording based on the detection timing of the sensor 23.

  The drying unit 8 is a unit for heating the sheet printed by the printing unit 4 and drying the applied ink in a short time. Inside the drying unit 8, hot air is applied at least from the lower surface side to the passing sheet to dry the ink application surface. The drying method is not limited to the method of applying hot air, and may be a method of irradiating the sheet surface with electromagnetic waves (such as ultraviolet rays and infrared rays).

  The sheet conveyance path from the sheet supply unit 1 to the drying unit 8 is referred to as a first path. The first path has a U-turn shape between the printing unit 4 and the drying unit 8, and the cutter unit 6 is located in the middle of the U-turn shape.

  The reversing unit 9 is a unit for temporarily winding a continuous sheet that has been printed on the front (front) surface when performing double-sided printing, and reversing the front and back. The reversing unit 9 is a path (loop path) (referred to as a second path) from the drying unit 8 through the decurling unit 2 to the printing unit 4 for supplying the sheet that has passed through the drying unit 8 to the printing unit 4 again. It is provided on the way. The reversing unit 9 includes a winding rotary body (drum) that rotates to wind the sheet. The continuous sheet that has been printed on the surface and has not been cut is temporarily wound around the winding rotary member. When the winding is completed, the winding rotary member rotates in the reverse direction, and the wound sheet is supplied to the decurling unit 2 and sent to the printing unit 4. Since this sheet is turned upside down, the printing unit 4 can print on the back side. More specific operation of duplex printing will be described later.

  The discharge conveyance unit 10 is a unit for conveying the sheet cut by the cutter unit 6 and dried by the drying unit 8 and delivering the sheet to the sorter unit 11. The discharge conveyance unit 10 is provided in a route (referred to as a third route) different from the second route in which the reversing unit 9 is provided. In order to selectively guide the sheet conveyed on the first path to one of the second path and the third path, a path switching mechanism having a movable flapper is provided at a branch position of the path.

  The sorter unit 11 and the discharge unit 12 are provided on the side of the sheet supply unit 1 and at the end of the third path. The sorter unit 11 is a unit for sorting printed sheets for each group as necessary. The sorted sheets are discharged to the discharge unit 12 including a plurality of trays. In this way, the third path has a layout that passes below the sheet supply unit 1 and discharges the sheet to the opposite side of the printing unit 4 and the drying unit 8 across the sheet supply unit 1.

  The control unit 13 is a unit that controls each unit of the entire printing apparatus. The control unit 13 includes a CPU, a storage device, a control unit (control unit) including various control units, an external interface, and an operation unit 15 that is input and output by a user. The operation of the printing apparatus is controlled based on a command from a host device 16 such as a host computer connected to the control unit or the control unit via an external interface.

  FIG. 2 is a block diagram showing the concept of the control unit 13. A control unit (range surrounded by a broken line) included in the control unit 13 includes a CPU 201, a ROM 202, a RAM 203, an HDD 204, an image processing unit 207, an engine control unit 208, and an individual unit control unit 209. A CPU 201 (central processing unit) controls the operation of each unit of the printing apparatus in an integrated manner. The ROM 202 stores programs executed by the CPU 201 and fixed data necessary for various operations of the printing apparatus. The RAM 203 is used as a work area for the CPU 201, used as a temporary storage area for various received data, and stores various setting data. The HDD 204 (hard disk) can store and read programs executed by the CPU 201, print data, and setting information necessary for various operations of the printing apparatus. The operation unit 15 is an input / output interface with a user, and includes an input unit such as a hard key and a touch panel, and an output unit such as a display for presenting information and a sound generator. For example, a display with a touch panel is used, and the operation status, printing status, maintenance information (remaining ink amount, remaining sheet amount, maintenance status, etc.) of the apparatus are displayed to the user. The user can input various information from the touch panel.

  A dedicated processing unit is provided for units that require high-speed data processing. An image processing unit 207 performs image processing of print data handled by the printing apparatus. The color space (for example, YCbCr) of the input image data is converted into a standard RGB color space (for example, sRGB). Various image processing such as resolution conversion, image analysis, and image correction is performed on the image data as necessary. Print data obtained by these image processes is stored in the RAM 203 or the HDD 204. The engine control unit 208 performs drive control of the print head 14 of the print unit 4 according to print data based on a control command received from the CPU 201 or the like. The engine control unit 208 also controls the transport mechanism of each unit in the printing apparatus. The engine control unit 208 includes a nonvolatile memory that stores correction data, which will be described later. The individual unit control unit 209 includes a sheet supply unit 1, a decurling unit 2, a skew correction unit 3, an inspection unit 5, a cutter unit 6, an information recording unit 7, a drying unit 8, a reversing unit 9, a discharge conveyance unit 10, and a sorter unit. 11 and a sub-control unit for individually controlling each unit of the discharge unit 12. The control unit 13 receives detection signals from a rotary encoder 19, a direct sensor 20, and other sensors described later. The individual unit control unit 209 controls the operation of each unit based on a command from the CPU 201. The external interface 205 is an interface (I / F) for connecting the control unit to the host device 16 and is a local I / F or a network I / F. The above components are connected by the system bus 210.

  The host device 16 is a device serving as a supply source of image data for causing the printing apparatus to perform printing. The host device 16 may be a general-purpose or dedicated computer, or a dedicated image device such as an image capture having an image reader unit, a digital camera, or a photo storage. When the host device 16 is a computer, an OS, application software for generating image data, and a printer driver for the printing device are installed in a storage device included in the computer. Note that it is not essential to implement all of the above processing by software, and a part or all of the processing may be realized by hardware.

  Next, the basic operation during printing will be described. Since the printing operation differs between the single-sided printing mode and the double-sided printing mode, each will be described.

  FIG. 3A is a diagram for explaining the operation in the single-sided print mode. The sheet supplied from the sheet supply unit 1 and processed by the decurling unit 2 and the skew feeding correction unit 3 is printed on the front surface (first surface) by the printing unit 4. An image (unit image) having a predetermined unit length in the conveyance direction is sequentially printed on a long continuous sheet to form a plurality of images side by side. The printed sheet passes through the inspection unit 5 and is cut for each unit image in the cutter unit 6. The cut sheet is recorded with print information on the back side of the sheet by the information recording unit 7 as necessary. Then, the cut sheets are conveyed one by one to the drying unit 8 and dried. Thereafter, the sheet is sequentially discharged and stacked on the discharge unit 12 of the sorter unit 11 via the discharge conveyance unit 10. On the other hand, the sheet left on the print unit 4 side by cutting the last unit image is sent back to the sheet supply unit 1, and the sheet is wound on the roll R1 or R2. Thus, in single-sided printing, the sheet passes through the first path and the third path and is processed, and does not pass through the second path.

  FIG. 3B is a diagram for explaining the operation in the duplex printing mode. In double-sided printing, the back (second side) print sequence is executed after the front (front) side (first side) print sequence. In the first front surface print sequence, the operation in each unit from the sheet supply unit 1 to the inspection unit 5 is the same as the one-sided printing operation described above. The cutter unit 6 is conveyed to the drying unit 8 as a continuous sheet without performing a cutting operation. After the ink is dried on the surface in the drying unit 8, the sheet is guided to the path (second path) on the reversing unit 9 instead of the path (third path) on the discharge conveyance unit 10 side. In the second path, the sheet is wound around the winding rotary body of the reversing unit 9 that rotates in the forward direction (counterclockwise direction in the drawing). When all of the scheduled printing on the surface is completed in the printing unit 4, the trailing edge of the print area of the continuous sheet is cut by the cutter unit 6. With reference to the cutting position, the continuous sheet on the downstream side (printed side) in the conveying direction is wound up to the rear end (cutting position) of the sheet by the reversing unit 9 through the drying unit 8. On the other hand, at the same time as the winding, the continuous sheet remaining on the upstream side in the conveying direction (on the printing unit 4 side) with respect to the cutting position is not supplied to the decurling unit 2 at the sheet leading end (cutting position). 1 and the sheet is wound on roll R1 or R2. By this rewinding, collision with the sheet supplied again in the following back surface printing sequence is avoided.

  After the above-described front surface print sequence, the back surface print sequence is switched. The winding rotary body of the reversing unit 9 rotates in the opposite direction (clockwise direction in the drawing) to that during winding. The end of the wound sheet (the trailing edge of the sheet at the time of winding becomes the leading edge of the sheet at the time of feeding) is fed into the decurling unit 2 along the path of the broken line in the figure. In the decurling unit 2, the curl imparted by the winding rotary member is corrected. That is, the decurling unit 2 is provided between the sheet supply unit 1 and the printing unit 4 in the first path and between the reversing unit 9 and the printing unit 4 in the second path, and functions as a decal in any path. It is a common unit. The sheet whose front and back sides are reversed is sent to the printing unit 4 through the skew correction unit 3 and printed on the back side of the sheet. The printed sheet passes through the inspection unit 5 and is cut into predetermined unit lengths set in advance in the cutter unit 6. Since the cut sheet is printed on both sides, recording by the information recording unit 7 is not performed. Cut sheets are conveyed one by one to the drying unit 8, and sequentially discharged and stacked on the discharge unit 12 of the sorter unit 11 via the discharge conveyance unit 10. As described above, in duplex printing, a sheet passes through the first path, the second path, the first path, and the third path in this order.

  Next, the printing unit 4 in the printer having the above configuration will be described in more detail. FIG. 4 is a configuration diagram of the printing unit 4. In the printing unit 4, the sheet S is conveyed in the direction of arrow A in the figure by three types of roller pairs, a first roller pair, a second roller pair, and a third roller pair. The first roller pair is a roller pair including a conveying roller 101 having a driving force and a pinch roller 102 that is driven to rotate. The second roller pair indicates each roller pair (seven sets) including a plurality of conveying rollers 103a to 103g having a driving force and a plurality of pinch rollers 104a to 104g that are driven to rotate. The third roller pair is a roller pair including a conveying roller 105 having a driving force and a pinch roller 106 that is driven to rotate. The transport roller 101 is provided with a rotary encoder 19 (first acquisition unit) for detecting the rotation state of the roller.

  In the print area 110 downstream of the first conveying roller pair, seven line type print heads 14a to 14g corresponding to the respective colors are arranged along the sheet conveying direction. The line type print heads 14a to 14g and the pinch rollers 104a to 104g are alternately arranged one by one. Platens 112a to 112g are provided at positions facing the print heads 14a to 14g, respectively, and support the sheet S. At each of the opposed positions of the print heads 14a to 14g, the sheet S is nipped on both upstream and downstream sides by a pair of rollers and supported by a platen, so that the sheet conveyance behavior is stabilized. In particular, when a sheet is first introduced, the leading end of the sheet passes through a plurality of nip positions in a short cycle, so that floating of the leading end of the sheet is suppressed and stable sheet introduction is performed.

  The direct sensor 20 (second acquisition unit) is a non-contact optical sensor that directly acquires information on the movement state (movement speed or movement distance) of the sheet from the sheet by directly measuring the sheet surface. A measurement position 111 is between the nip position of the first roller pair and the nip position of the third roller pair. The direct sensor 20 measures the sheet surface (the back side of the print surface) at the measurement position 111 to acquire information on the sheet movement state. Since the direct sensor 20 is disposed on the back side of the sheet S, ink mist generated from the print head 14 during printing is blocked by the sheet S, and deterioration in detection performance due to ink mist adhering to the sensor is suppressed. The direct sensor 20 may also be arranged on the surface side of the sheet. In the present embodiment, two direct sensors 20 are provided along the sheet width direction. By providing two direct sensors 20 in the sheet width direction, even when the conveyance speed of the conveyed sheet S differs at two measurement positions (there is a skew movement), the behavior of the sheet can be accurately measured. Can do. Furthermore, even if one of the direct sensors 20 becomes impossible to measure, the other sensor can be backed up, improving the reliability. The number of direct sensors 20 may be three or more, or only one.

  In this example, the direct sensor 20 is a laser Doppler sensor. The laser Doppler sensor is a speed sensor that measures a moving speed and a moving distance by irradiating a moving surface with a laser and capturing a Doppler shift. Since the measurement principle of a more detailed configuration of the laser Doppler sensor is widely known in the above-mentioned Patent Document 1 (Japanese Patent Laid-Open No. 2009-6655) and other documents, description thereof is omitted here.

  The direct sensor 20 may be a non-contact optical sensor other than a laser Doppler sensor. For example, there is a type of direct sensor using an image sensor (CCD image sensor or CMOS image sensor). This type of direct sensor acquires a plurality of image data by imaging a sheet surface that is moved by a fixed image sensor at different timings in time series. Then, the moving state (moving distance, moving speed) of the sheet is acquired by comparing the image data with a technique such as pattern matching. As another form of the direct sensor 20, a contact-type direct sensor in which the sensor surface physically contacts the surface of the sheet S may be used.

  The sheet S supplied from the sheet supply unit 1 is nipped at a predetermined nip position and conveyed in the order of the third roller pair, the first roller pair, and the second roller pair. The conveyance path from the first roller pair to the third roller pair is a straight line. The straight line here is not limited to a strict straight line, but includes a form that is almost a straight line.

The conveying force with which each roller pair conveys a sheet is set so as to satisfy the relationship of the following Expression 1.
First roller pair> Second roller pair> Third roller pair (Formula 1)

  The conveying force of the roller pair is determined by the nip force of the pinch roller. This is because the slip between the sheet and the roller surface is less likely to occur as the nip force increases. The nip force is determined by the spring pressure of a spring that presses the pinch roller against the conveying roller. In this example, the spring pressure of the pinch roller 102 of the first roller pair is 20 kgf, the total spring pressure of the seven pinch rollers 104a to 104g of the second roller pair is 4 kgf, and the spring pressure of the pinch roller 106 of the third roller pair is 1 kgf. . With this relationship, the dominant force of the first roller pair is the largest in terms of sheet conveyance accuracy. Therefore, if the focus is on improving the conveyance control accuracy of the first roller pair among the rollers, the sheet as a whole Conveyance accuracy is improved.

About the conveyance speed (peripheral speed of a conveyance roller) of each roller pair, it sets so that the relationship of following Formula 2 may be satisfy | filled.
Second roller pair> First roller pair> Third roller pair (Formula 2)

  The transport roller 105 of the third roller pair is provided with a torque limiter on the same axis. The torque limiter restricts transmission of force due to slippage when a rotational torque exceeding a predetermined set value is applied. Since the conveyance roller 105 has a slightly lower conveyance speed than the conveyance roller 101, the torque limiter of the conveyance roller 105 is activated during conveyance, and the conveyance roller 105 is slightly decelerated. For this reason, even if the conveying roller 105 has a slight eccentricity or uneven roller shape, the overall sheet conveying accuracy is hardly affected.

  Due to the relationship between the transport force (formula 1) and the transport speed (formula 2) as described above, almost no slip occurs at the nip position (between the transport roller 101 and the sheet S) of the first roller pair as the main transport means. . At each nip position of the second roller pair (between the conveying rollers 103a to 103g and the sheet S), a slip due to a speed difference occurs. At the nip position of the third roller pair (between the conveying roller 105 and the sheet S), a slip due to the speed difference occurs, and the torque limiter operates on the conveying roller 105. By satisfying the above relationship, the first roller pair determines the overall conveyance speed. Further, the sheet S is given a weak tension between any pair of rollers, and local sheet lifting is prevented from occurring. Therefore, in the print area 110, the distance between each print head 14 and the sheet S is kept constant, and high print accuracy is maintained. Further, even at the measurement position 111 of the direct sensor 20, the distance between the direct sensor 20 and the sheet S is kept constant, and high measurement accuracy is maintained.

  The control unit of the control unit 13 controls the ink ejection timing (drive control timing) of each nozzle of each of the print heads 14a to 14g based on the information regarding the sheet conveyance state measured and acquired by the direct sensor 20. The ink discharge timing is basically controlled based on the measurement value (detection pulse count) of the rotary encoder 19 provided on the transport roller 101. However, when the transport roller 101 has a slight eccentricity or when a slight slip occurs between the transport roller 101 and the sheet S, the measured value of the rotary encoder 19 and the transport speed of the sheet S (or An error occurs during the transport distance. Since the direct sensor 20 directly measures the movement state of the sheet surface, the direct sensor 20 can acquire information on the conveyance speed (or conveyance distance) of the sheet S with higher accuracy than the rotary encoder 19. By obtaining the difference between the measurement value of the direct sensor 20 and the measurement value error of the rotary encoder 19, error information is obtained. However, if the direct sensor measurement is performed in real time during printing, the detection delay required for complicated signal processing becomes rate limiting, and it may be difficult to increase the printing speed (sheet moving speed). Therefore, in the present embodiment, correction data is acquired in advance and stored in the memory of the engine control unit 208, and the correction value is controlled by reading the value in the memory during printing. That is, the error information stored in the memory is read to control the ink ejection timing (the timing of the drive pulse signal given to each nozzle) in the print heads 14a to 14g. A slight conveyance error due to the conveyance roller 101 can be corrected on the timing of print formation by the print head, thereby achieving both high quality printing and high speed printing.

  It should be noted that the measurement result of the direct sensor 20 may be fed back to the sheet conveyance control and the conveyance error may be corrected and controlled together with the correction of the print formation timing or without the correction of the print formation timing. In the sheet conveyance correction control, at least the conveyance speed of the conveyance roller 101 of the first roller pair is corrected so as to correct the conveyance error. Preferably, the conveyance speed of the second roller pair and the third roller pair is also changed. That is, the control unit performs correction control by storing correction data for correcting at least one of print head drive control and roller drive control in a memory in advance based on information acquired by the direct sensor 20. . Although the present invention includes both forms, the form of correcting the recording timing of the print head is preferable if high speed is to be pursued. When the correction data is fed back to the rotation speed control of the conveyance roller 101, the command value is given to the rotation speed control of the motor of the conveyance roller drive source, and the drive motor is slightly changed to the target rotation speed. Cause a time lag. On the other hand, if feedback is made to the print timing of the print head, there is almost no time lag compared to the conveyance speed control, so that higher-speed correction control can be performed.

  FIG. 5 is a graph showing a change in conveyance error associated with sheet conveyance based on the relationship between detection outputs of the rotary encoder 19 and the direct sensor 20. The horizontal axis represents the transport distance, and the vertical axis represents the sheet transport error (the transport amount error with respect to the designed value). The coordinate 0 position on the horizontal axis is the origin position of the encoder, and the number of pulses of the rotary encoder 19 is the unit on the horizontal axis. The pulse interval continuously output by the rotary encoder 19 during conveyance corresponds to a predetermined unit moving distance in design. The rotational phase is obtained from the two pieces of information of the origin and the pulse number count value (= rotation amount) therefrom.

  During measurement, every time the rotary encoder 19 counts up by one pulse during conveyance, the amount of movement of how much the sheet has actually moved is directly within the time period before the generation timing of the previous pulse. It is detected by the sensor 20. The solid line in the graph of FIG. 5 is obtained by plotting the difference (sheet conveyance error) between the detected value of the direct sensor 20 and a predetermined unit moving distance in design. As can be seen from the figure, the sheet conveyance error fluctuates in an equal cycle according to the conveyance distance, and conveyance unevenness occurs. This is a phenomenon that occurs because the rotation axis of the transport roller 101 is eccentric from the original center position. That is, even if the conveying roller is rotated at an equiangular speed, if there is an eccentricity, the peripheral speed (= sheet conveying speed) of the portion where the conveying roller is in contact with the sheet fluctuates periodically, which causes uneven conveyance. In the graph of FIG. 5, the conveyance error of the direct sensor output curve (solid line) is shifted in the negative direction as a whole. This is because a slight slip occurs between the conveyance roller 101 and the sheet, and the actual conveyance distance becomes smaller than the original conveyance distance. FIG. 5 shows an example in which the outer periphery of the transport roller 101 is a perfect circle. However, if the transport roller 101 is not a perfect circle due to a manufacturing error or the like, the local increase / decrease is further increased by a periodic increase / decrease. It becomes a complicated graph curve with a typical error added.

  In consideration of the characteristics of FIG. 5, at least each plot value (conveyance error) during the rotation of the conveyance roller 101 is associated with the count value (rotation phase) of the encoder pulse from the origin 0 on a one-to-one basis. Is stored in the memory of the engine control unit 208 as correction data.

  As an alternative, the output value of the direct sensor 20 itself is associated with the count value of the encoder pulse from the origin 0 on a one-to-one basis instead of the error in the transport amount with respect to the design value, and is stored as correction data in the form of a data table. You may make it memorize. Alternatively, the sheet conveyance error may be converted into a discharge timing shift time (necessary correction amount) and stored in the memory as correction data in the form of a data table. In any case, the control unit corresponds to the information acquired by the first acquisition unit (rotation phase) and the information acquired by the second acquisition unit (sheet conveyance error, direct sensor output value, or ejection timing shift time). In addition, control is performed so that the correction data is stored in the memory. By referring to the data table of this correction data, an appropriate correction value according to the rotation phase can be acquired.

  When a pulse motor is used as the drive source for the transport roller 101, the number of drive pulses corresponds to the transport distance. The first acquisition unit detects the rotation state of the transport roller 101 with the rotary encoder 19, but the rotation information of the transport roller 101 may be acquired from the drive pulse of the pulse motor.

<Single-sided print mode>
Next, the operation sequence in the single-sided print mode will be described with reference to the flowchart of FIG. In step S100, the sequence is started. In step 101, the user selects a roll (roll 1 or roll R2) to be used in the sheet supply unit 1. Since the coefficient of friction between the sheet and the conveying roller 101 varies depending on the type, thickness, or size of the sheet, the optimum correction data can vary depending on the sheet used.

  In step S102, initial correction data corresponding to the roll to be used is set in the memory of the engine control unit 208. As the initial correction data, if there is no roll replacement or roll switching after the previous one-sided printing, the correction data set last time is set as it is. The memory for storing the correction data is a rewritable nonvolatile memory, and the stored contents of the memory are retained even when the printing apparatus is turned off. Therefore, even if the power is turned off after the previous printing, the previous correction data remains without being erased. If the roll is changed, the roll is switched, or double-sided printing is performed after the previous single-sided printing, the correction data is re-acquired and the initial correction data is set while actually transporting the sheet prior to printing. To do. In this case, measurement by the direct sensor 20 and the rotary encoder 19 is performed in a section of at least one rotation of the transport roller 101, and the correction data is stored in the memory of the engine control unit 208. Even for an unknown sheet, optimum correction data can be set by measuring the sheet.

  In step S103, the selected sheet is supplied from the sheet supply unit 1. In step S104, the printing operation is started. In step S105, a plurality of images are sequentially printed on the first surface of the sheet using the correction data stored in the memory. Using the correction data stored in the memory, the ink ejection timing (drive timing) of each line head is corrected. Based on the number of output pulses of the rotary encoder 19 from the origin, the correction data stored in association with the number of pulses is read from the memory. Based on the read correction data, the ink ejection timing of each line head is shifted from the original timing so that the ink landing position on the sheet approaches the ideal position. In the example of FIG. 5, the error is −20 μm at the position of the transport distance A. For example, when the transport speed v is 100 mm / s, the ink discharge timing is delayed by 0.02 / 100 = 0.0002 [seconds]. Control may be performed as follows. As a result, for the prints after the second job, it is possible to form an image with very high accuracy regardless of the eccentricity and shape accuracy of the transport roller 101. In this way, the control unit corrects the recording timing of the print head based on the correction data stored in the memory corresponding to the information (rotation phase) acquired by the first acquisition unit at the time of printing. Control to print.

  In step S106, new correction data is reacquired at a predetermined timing during the printing operation. The predetermined timing will be described later. The direct sensor 20 and the rotary encoder 19 are measured at least in a section corresponding to one rotation of the transport roller 101. The measurement results of the rotary encoder 19 and the direct sensor 20 are compared. The rotational phase of the conveyance roller 101 acquired by the rotary encoder 19 and the movement information acquired by the direct sensor 20 are associated with each other and temporarily stored in the memory as correction data.

  As the printing apparatus is used, there is a case where the conveyance roller is worn and the mounting accuracy is changed to change the optimum correction data. In consideration thereof, in step S106, the correction data is reacquired at a predetermined timing to update the contents of the memory. The predetermined timing is a timing once for a predetermined number of sheets when printing a plurality of images sequentially. Since there is little possibility that the optimum correction data changes for each unit image, for example, the correction data is reacquired once every time several tens to several hundreds of images are continuously printed. When updating the contents of the memory, either overwrite the previous data with new data, write the new data in another storage area while leaving the previous data, and change the reference address. Form may be sufficient.

  In step S107, a difference between the correction data reacquired in step S106 and the existing correction data is obtained. The correction data for one rotation of the roller are compared with each other to obtain a difference value in each rotation phase, and the maximum difference value is defined as the difference here. It is determined whether the obtained difference is larger than a predetermined first threshold value (Yes) or not (No). If the determination is yes, the process proceeds to step S20, and if the determination is no, the process proceeds to step S110.

  In step S20, it is determined whether the difference is larger than a predetermined second threshold value that is larger than the first threshold value (Yes) or not (No). If the determination is yes, the process proceeds to step S112, and if the determination is no, the process proceeds to step S109.

  In step S109, the contents of the memory are updated to new correction data acquired by re-acquisition. In step S 110, the sheet is cut by the cutter unit 6 for each printed unit image, and the cut sheet is discharged to the discharge unit 12. In step S111, it is determined whether or not all the plurality of images to be printed on the first surface have been printed (Yes) or not (No). If the determination is Yes, the process proceeds to step S115. If the determination is No, the process returns to step S105, and the same processing is repeated.

  If the process proceeds to step S112 as determined in step S20, single-sided printing is interrupted in step S112. In a succeeding step S113, it is determined whether the difference is larger than a predetermined third threshold value that is larger than the second threshold value (Yes) or not (No). When the determination is Yes, the process proceeds to step S114, and when the determination is No, the process proceeds to step S115.

  In step S114, it is determined that a jam has occurred in the sheet conveyance, and a message indicating that a jam has occurred and user maintenance is required is displayed on the operation unit 15. When a jam occurs, even if the conveying roller 101 rotates, the sheet slips and the sheet is not actually conveyed or only slightly moved. Therefore, the difference between the values acquired by the rotary encoder 19 and the direct sensor 20 increases. That is, the re-acquired correction data (the correction amount at each rotation phase) shows a large value, and the difference from the existing correction data also becomes a large value. The third threshold value is used to determine the difference value. If the difference value does not exceed the third threshold value, which is larger than the second threshold value, the jam does not occur, but the conveyance accuracy deteriorates for some reason, and high-precision printing cannot be guaranteed. Therefore, the printing operation is interrupted in step S112.

  In step S115, the continuous sheet is cut at a position behind (upstream) the last printed image. In step S116, an unused sheet remaining on the upstream side of the cutting position is fed back to the sheet feeding unit 1 (back feed).

  In step S117, new correction data is reacquired while the sheet is back-fed. The acquisition method is the same as that described in step S106. In order to acquire correction data more reliably, the sheet conveyance speed of back feed is made smaller than the sheet conveyance speed during printing. Since the back feed is an operation after printing is completed, even if the speed is lowered, the overall print throughput is not affected. Instead of re-acquiring correction data while back-feeding, the memory contents may be updated with the latest correction value already acquired during the back-feed period.

  In step S118, a difference between the correction data reacquired in step S117 and the existing correction data is obtained. It is determined whether the obtained difference is greater than a predetermined first threshold (Yes) or not (No). If the determination is Yes, the process proceeds to step S119. If the determination is No, step S119 is skipped and the sequence is terminated. If the difference is small, there is a possibility that only an error has been picked up and the reliability is low, so step S119 is skipped.

  In step S119, the contents of the memory are updated to new correction data acquired by re-acquisition. Since the memory is non-volatile, the contents are retained even when the apparatus is turned off and used in the next printing operation. Then, the sequence ends.

  In the above-described operation sequence of the single-sided printing mode, it is preferable to control so that the sheet conveyance speed at the time of obtaining correction data is lower than usual. If the conveyance speed is low, the signal processing of the direct sensor 20 is more time-consuming, so that the processing capability of the signal processing system may be small. In order to further improve the print throughput, steps S107 to S109 and steps S112 to S114 may be omitted in the operation sequence of FIG. In this case, the correction data is set twice, that is, the initial setting in step S102 and the initial data update in step S119.

<Double-sided print mode>
Next, the double-sided print mode will be described. In double-sided printing, the coefficient of friction of the sheet surface that is in contact with the conveying roller changes between the first-side printing and the second-side printing that follows. In the first side printing, the conveyance roller 101 having the most control over the overall conveyance accuracy contacts the second surface of the sheet to which no ink is applied. In the subsequent second side printing, the conveying roller 101 contacts the first side on which the sheet is reversed and ink is applied to change the friction coefficient. Depending on the type of sheet, the friction coefficient between the first surface and the second surface may be different in the first place regardless of whether ink is applied to the sheet. Further, the curl direction of the sheet is different between the first side print and the second side print, and the contact area with the conveying roller 101 differs depending on the curl direction. For these reasons, the first sheet print and the second sheet print have different sheet conveyance states even when the same driving force is applied by changing the degree of slip between the conveyance roller 101 and the sheet surface. Therefore, the optimum correction data is different between the first side print and the second side print. In order to solve this problem, in the present embodiment, control is performed so that correction data used for correction differs between when printing on the first surface and when printing on the second surface.

  FIG. 7 is a flowchart showing an operation sequence in the duplex printing mode. In step S200, the sequence is started. In step S101, the user selects a roll (roll 1 or roll R2) to be used in the sheet supply unit 1.

  In step S202, initial correction data corresponding to the roll to be used and suitable for printing the first surface is set in the memory of the engine control unit 208. As the initial correction data, if there is no roll replacement or roll switching after the previous printing, the correction data set last time is set as it is. If the roll is changed, the roll is switched, or single-sided printing is performed after the previous double-sided printing, the correction data is re-acquired and the initial correction data is set while actually transporting the sheet prior to printing. To do.

  In step S203, the selected sheet is supplied from the sheet supply unit 1. In step S204, the printing operation on the first surface in duplex printing is started.

  In step S205, a plurality of images are sequentially printed on the first surface of the sheet using the correction data stored in the memory. A specific correction method is the same as that described in step 105. In step S206, new correction data is acquired at a predetermined timing.

  In step S207, it is determined whether correction data needs to be updated (Yes) or not (No). The determination method is the same as described in step S107 to step S114. If the determination is Yes, the process proceeds to step S208, and the correction data is updated in step S208. If the determination is No, step S208 is skipped and the process proceeds to step S209.

  In step S208, it is determined whether all of the plurality of images to be printed on the first surface have been printed (Yes) or not (No). If the determination is Yes, the process proceeds to step S210. If the determination is No, the process returns to step S205 and the same process is repeated.

  In step S210, the printing operation on the first surface is finished, and the continuous sheet is cut at a position behind (upstream) the last printed image. In step S211, all the sheets on the downstream side of the cutting position are wound around the reversing unit 9. At the same time, the unused sheet left on the upstream side of the cutting position is sent back to the sheet supply unit 1.

  In step 212, initial correction data corresponding to the roll to be used and suitable for printing the second surface is reset in the memory. As described above, the correction data used for correction differs between the first side print and the second side print. As the initial correction data, if there is no roll replacement or roll switching after the previous double-sided printing, the correction data set in the previous second-side printing is set as it is. If the roll is changed, the roll is switched, or single-sided printing is performed after the previous double-sided printing, the correction data is re-acquired and the initial correction is made while actually transporting the sheet prior to the second-side printing. Set the data.

  In step S213, the winding rotary member of the reversing unit 9 rotates reversely, and the temporarily wound sheet is fed again toward the printing unit 4 in a state where the front and back sides are reversed. In step S214, the printing operation on the second surface in duplex printing is started.

  In step S215, a plurality of images are sequentially printed on the second surface of the sheet using the correction data stored in the memory. A specific correction method is the same as that described in step 105. In step S215, new correction data is acquired at a predetermined timing.

  In step S217, it is determined whether correction data needs to be updated (Yes) or not (No). The determination method is the same as in step S207. If the determination is Yes, the process proceeds to step S218, and the correction data in the memory is updated in step S218. If the determination is No, step S218 is skipped and the process proceeds to step S219.

  In step S219, the sheet is cut by the cutter unit 6 for each printed unit image, and the cut sheet is discharged to the discharge unit 12. In step S220, it is determined whether or not all of the plurality of images to be printed on the first surface have been printed (Yes) or not (No). If the determination is Yes, the process proceeds to step S221. In step S221, the printing operation for the second surface is terminated, and the sequence is terminated if there is no subsequent processing. When judgment is No, it returns to step S215 and repeats the same process.

  In the operation sequence of the duplex printing mode described above, it is preferable to control the sheet conveyance speed at the time of obtaining correction data so as to be smaller than the conveyance speed at the time of printing. If the conveyance speed is low, the signal processing of the direct sensor 20 is more time-consuming, so that the processing capability of the signal processing system may be small. In order to further improve the print throughput, steps S206 to S208 in the first side printing and steps S216 to S218 in the second side printing may be omitted in the operation sequence of FIG. In this case, the correction data is set twice in the initial setting in step S202 for the first side printing and the initial setting in step S212 for the second side printing.

  According to the printing apparatus of the present embodiment, correction data corresponding to the rotation information acquired by the first acquisition unit at the time of printing is read from the memory, and at least one of print head drive control and sheet conveyance control is corrected. . Then, control is performed so that the correction data used for correction differs between when printing on the first side and when printing on the second side. As a result, a printing apparatus capable of accurately printing images on both sides of the sheet and capable of duplex printing with high print throughput is realized.

  In addition, when a plurality of images are printed on a continuous sheet and an unused sheet is sent back to the sheet supply unit, correction data is re-acquired and the contents of the memory are updated as necessary. Appropriate correction data is acquired at an appropriate timing and stored in the memory, so that it is possible to perform double-sided printing that balances print throughput and print quality at a high level.

In addition, the printing apparatus according to the present embodiment includes a first roller pair that nips a sheet on the upstream side of the print head, a second roller pair that nips a sheet on the downstream side of the print head, and an upstream side of the first roller pair. And a third roller pair for nipping the sheet. The arrangement relationship is provided with a direct sensor for measuring the sheet surface at a measurement position between the nip position of the first roller pair and the nip position of the third roller pair. With this configuration, the following effects can be obtained.
(1) The distance between the first roller pair and the print head can be reduced. For this reason, when the sheet is introduced, the leading edge of the sheet floats while reaching the print head from the first pair of rollers, and the possibility that the nozzle of the most upstream print head contacts the leading edge of the sheet can be reduced.
(2) Since the distance between the direct sensor and the print head is large, the calculation with the direct sensor is completed and the ink ejection timing is controlled from the measurement position of the direct sensor to the most upstream print head. You can earn enough time. In other words, the sheet conveyance speed can be increased to improve the printing speed. (3) Since the distance between the direct sensor and the print head is large and the first roller pair is arranged between the direct sensor and the print head, the cockling that occurs when the sheet absorbs ink immediately after printing reaches the measurement position. Preventing influence.
(4) Since the distance between the direct sensor and the print head is large, and the first roller pair and the sheet are arranged as a shield, the ink mist generated and scattered when ink is ejected from the print head Is reduced from adhering to the direct sensor. For this reason, the direct sensor can maintain high measurement accuracy even during operation for a long period of time, and can maintain high print quality.

4 Print unit 13 Control unit 19 Rotary encoder (corresponding to the first acquisition unit)
20 Direct sensor (corresponding to the second acquisition unit)

Claims (5)

A printing apparatus control method capable of performing double-sided printing on a first side and a second side of a sheet by a printing unit,
The sheet is conveyed by a roller given a driving force,
Obtaining information indicating the rotational phase of the rotating roller;
When printing on the first surface and the second surface, using the correction data corresponding to the information indicating the rotational phase acquired with the rotation of the roller, the control of the printing means and the driving of the roller Corrects at least one of the controls,
The method of controlling a printing apparatus, wherein the correction data used for correction when printing on the first surface is different from the correction data used for correction when printing on the second surface.   The correction data is obtained based on information indicating a moving state of a sheet acquired by using a direct sensor that measures a sheet surface for at least one rotation of the roller. 2. A method for controlling a printing apparatus according to 1.   The method according to claim 2, wherein the correction data is stored in a storage unit, and is updated at a predetermined timing when the printing apparatus is used.   A first sheet and a second roll, each of which is a continuous sheet wound in a roll shape, are held and selectively supplied for printing, and the correction data is respectively applied to the first roll and the second roll. The method of controlling a printing apparatus according to claim 1, wherein the printing apparatus is prepared correspondingly. 5. The rotation phase according to claim 1, wherein the rotation phase is acquired based on an output of a rotary encoder that detects a rotation state of the roller or a signal that controls a motor that applies a driving force to the roller. The printing apparatus according to any one of the above.

Images