MXPA06008673A - High precision feed particularly useful for uv ink jet printing on vinyl - Google Patents

Abstract

An apparatus (30, 40, 50) and a method of ink jet printing are disclosed that use a system for feeding a substrate longitudinally relative to a support area and a system for moving a printhead parallel to the direction of substrate feed. hldexing between transverse scan rows of a printhead (20) is carried out initially by the substrate feed system (16) and the actual feed distance is ineasured using an encoder or other substrate position measurement device (26). A controller (25) determines the amount of any error that occurs between the actual and the desired feed distances. The controller (25) then sends signals to move the printhead (20) to compensate for any error in the feed system feed. Compensating adjustments are then made to the next subsequent substrate indexing step so that the printhead tends to move back toward its home or zeroed position with its next correction and does not walk away from this home position as a result of cumulative movements. For printers that have bridges (17) moveable relative to the machine frame (11) on which the printhead (20) is carried, printhead motion is achieved by moving the bridge, for example, by actuating alinear servo bridge motion system (31). For fixed bridge roll-to-roll printers, the printhead (20) can be caused to shift longitudinally on the bridge (17) to make the correcting movements.

Description

HIGHLY PRECISION FEED PARTICULARLY USEFUL FOR PRINTING BY JET OF UV INK ON VINYL This application claims the benefit of United States Provisional Application Serial No. 60 / 540,933, filed on January 30, 2004, expressly incorporated herein by reference.

FIELD OF THE INVENTION This invention relates to ink jet printing, and more particularly, to the longitudinal adjustment of a print head with respect to a substrate between transverse explorations of the print head.

BACKGROUND OF THE INVENTION The use of inkjet printing in wide-format applications is expanding. In wide-format ink jet printing, rigid panel substrates or flexible roll-to-roll tapes are supported with respect to an ink jet print head. The print head typically prints moving transversely to the substrate in a printing station where the substrate is supported, to print a row of an image on the substrate. The print head moves through the substrate on a bridge that extends transversely through the substrate at the printing station, carrying the print head on a carriage that is movable on the bridge. Said row of the image is typically formed of a plurality of dotted lines jetted from a plurality of corresponding nozzles on the printhead. A complete image is formed by printing a plurality of said rows side by side in a scanning movement by adjusting the print head longitudinally with respect to the substrate. Traditionally, there has been no relative movement between the print head and the substrate during transverse movement of the print head on the substrate when printing a row of the image. However, between the printing of each row of the image, longitudinal adjustment of the substrate is carried out with respect to the print head. This adjustment can be achieved by moving the substrate longitudinally on its support, or by moving the bridge relative to the support. A printing system that provides both types of longitudinal movement is described in the U.S. patent. No. 6,012,403, expressly incorporated herein by reference. The relative movement between the print head and the substrate in the longitudinal direction, ie, perpendicular to the printing movement of the transverse row of the print head, requires that the adjustment distance be achieved with sufficient precision to avoid visible artifacts in the printhead. the printed image caused by tolerances in the lengths of the adjustment steps between the printing of the cross lines of points of adjacent rows. The degree of precision required depends, in addition to the resolution requirements of the particular application, on the nature of the ink being jetted and the physical properties of the substrate. For example, the much larger format printing is for posters, flags and signs that are printed on vinyl substrate tapes, either by roll-to-roll or roll-to-sheet procedures. Traditionally, these substrates have been printed with solvent-based inks that form spots that stretch a little on the vinyl substrate before drying. This scattering of points tends to forgive longitudinal feeding errors of several thousandths of an inch (or its corresponding conversion in cm). However, this dispersion of points limits the resolution of the image being printed and the overall quality of the image. The advantages in wide-format inkjet printing have resulted from the use of inks that are cured by exposure to ultraviolet light. These ultraviolet light curable inks can produce superior images in many applications, and can print on some substrates over which other inks can not. In addition, ultraviolet light curable inks do not have some of the occupational and environmental disadvantages of some other inks. Examples of inkjet printing with UV ink are described in the U.S. Patents. Nos. 6,312,123; 6,467,898; 6,523,921 and 6,702,438, and in PCT publications WO02 / 078958 and WO02 / 18148, expressly incorporated herein by reference. The advantages of UV inks over solvent based inks and other inks include, for example, less dot scattering, particularly over substrates such as vinyl. This property of UV inks can provide higher resolution. However, the higher resolution may reveal artifacts such as those caused by adjustment tolerances or feeding between the scanning rows of the print head. The human eye can detect, for example, defects smaller than 25.4 microns. This has created problems with roller-fed substrates, particularly smooth low-absorbency substrates, which can occur when dot scattering is minimal. Coil printers are particularly prone to longitudinal feeding errors that have been difficult to control. Cumulative tolerances in the control linkages, potential slippage of the substrate on the rollers, and other mechanical limitations, have produced errors that are difficult to predict when trying to longitudinally adjust a belt, in particular a belt of highly flexible material. Attempts to improve the accuracy of the fit between the print head and the substrate have focused on the feed controls. Attempts have been made, for example, to use a signal encoder to measure the actual feed of the substrate relative to the bridge of the print head. The use of a signal encoder in a closed loop control of the substrate feed control has only been moderately successful due to a lack of "stiffness" in the control loop. The use of a signal encoder to read the results of an adjustment step and feed the results back to the control to make a subsequent correction, has presented other problems. When signals of error of signal encoders have been received by controllers of the feeding system after a longitudinal feeding step, it takes time to make a post-feeding correction, delaying the scanning of the transverse print head. In addition, the feeding step with correction is also prone to error, which may require another corrective movement. In addition, the error may indicate that the substrate has been fed too far, requiring a negative correction step, or a backward movement of the tape. Not all machines are capable of executing reverse movements of a substrate tape, and many of those that can reverse substrate feeding can not do so accurately or efficiently. As a result, deliberate sub-feeding of the tape has been attempted. Underfeeding the tape increases the likelihood that a correction is needed, and increases the overall probable number of corrections that need to be made. As a result of these difficulties, high-quality inkjet printing with UV ink on smooth substrates has not been performed in most applications where the above problems occur.

Accordingly, there is a need for a form that increases the precision in the relative longitudinal feed between the print heads and the substrates, in particular smooth substrates such as vinyl, and in particular when printing with UV inks.

BRIEF DESCRIPTION OF THE INVENTION A primary objective of the present invention is to provide increased precision in the imparting of relative movement of a substrate with respect to the transverse path of an ink jet print head. In accordance with the principles of the present invention, a compound feed system imparts relative movement of a substrate with respect to the transverse path of an ink jet print head. These and other objects and advantages of the present invention will be more readily apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective diagram of an ink jet printing system of the prior art.

Figure 2 is a perspective diagram, similar to Figure 1, illustrating one embodiment of an ink jet printing system that describes principles of the present invention. Figure 3 is a perspective diagram, similar to Figure 2, illustrating an alternative embodiment of an ink jet printing system that describes principles of the present invention. Figure 4 is a perspective diagram, similar to Figure 2, illustrating another alternative embodiment of an ink jet printing system that describes principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION In Figure 1, an inkjet printing apparatus 10 of the prior art is illustrated. The apparatus 10 includes a frame 11 having a support plane 12 of the substrate on which a substrate 15 is supported. The substrate 15 is illustrated as a strip of material that is fed longitudinally from a supply roll 13 thereof, along the frame 11 and on the support plane 12, by one or more series of feed rollers 14 which are mounted to rotate on the frame 11. A drive motor 16, which may be a drive servomotor, advances the substrate 15 past a bridge 17, which is fixed to the frame 11, and on which a carriage is mounted. 18 which moves on bridge 17 in a direction transverse to that of the feed. The carriage 18 has mounted thereon one or more ink jet printing heads 20, which carries them transversely through the frame 11. The carriage 18 is moved through the bridge 17 by a linear servomotor 19 carried by the bridge 17 and the carriage 18. The print heads 20 include nozzles (not shown), which are directed from the carriage 18 toward the support plane 12 to pressurize an ink jet onto a substrate 15 when it is supported on the substrate. plane 12. A controller 25 operates the print heads to synchronize the ejection of the ink jet onto the substrate with the position of the print heads relative to the substrate, to produce an image according to a programmed design. The controller 25 also controls the motor 16 which moves the substrate 15 longitudinally with respect to the frame 11, and the motor 21 which moves the carriage 18 transversely across the bridge 17. The apparatus 10 is also provided with a signal encoder 26, which it is mounted on the frame 11 at a point near the static bridge 17 and has a detection wheel 27, approximately 15.24 cm in diameter, meshing with the substrate 15 and producing a measurement signal in response to the movement of the substrate 15 with respect to the bridge 17. This measurement signal is sent to the controller 25, which in response to the substrate supply measurement signal, sends a feed adjustment signal to the motor 16. The motor 16 makes a feed adjustment to the substrate 15. In the prior art, said adjustment has not been totally satisfactory in the elimination of power failure artifacts.

In Figure 2, a printing apparatus 30 is illustrated in accordance with one embodiment of the present invention. The apparatus 30 has certain elements that are the same as the elements of the apparatus 10 of Figure 1, the elements of which are listed in a similar manner. In addition, the apparatus 30 includes a feeding system having the characteristics of the apparatus of the U.S. patent. No. 6,012,403, wherein the bridge 17 is mounted to move longitudinally on the frame 11. This movement is provided by linear servomotors 31 carried by the bridge 17 and the frame 1. A controller 35 having the functions described for the controller is provided. 25 of the above apparatus 10, with additional functions including the ability to control the motors 31 to move the bridge 17 relative to the frame 11 in a longitudinal direction. As such, the controller 35 can fix the substrate 15 longitudinally with respect to the print head 20 keeping the bridge 17 static with respect to the frame 11 and moving the substrate 15 longitudinally with respect to the frame 11, or keeping the substrate 15 static with respect to the frame 11 and moving the bridge 17 relative to the frame 11, or by a combination of the movements of the bridge 17 and the substrate 15 with respect to the frame 11. Accordingly, the motors 16 and 31 can be energized alternatively or in combination by the controller 35. The experience has shown that the longitudinal adjustment of the print head 20 with respect to the substrate 15 that is made with the movement of the bridge 17 on the frame 11 by the motor 31, can be much more precise than the adjustment made with the movement of the substrate 15 to the frame 11 by the motor 16. However, there are applications where the feeding of the substrate 15 onto the frame 11 by activ The motor 16 has advantages, in particular where large images are printed on a continuous substrate tape. In accordance with the present invention, a signal encoder 26 or other position feedback and measurement device is configured and mounted on the apparatus 30 in such a way as to accurately measure the actual distance that the belt 15 is fed in response to the drive. of the motor 16 in response to a control setting signal of the controller 25. In the embodiment of FIG. 2, the position measuring device is in the form of a signal encoder or resolution device 26, and is mounted at a point fixed on the frame 11 near the normal rest site of the bridge 17 in the apparatus 30. The signal encoder 26 is rectified or is otherwise sufficiently accurate to measure the actual feed distance with an accuracy corresponding to the adjustment accuracy desired. For example, if adjustment precision of 0.00127 cm is desired to avoid printing artifacts, the position measuring device should be configured to read the actual feed distance to at least 0.00127 cm, and preferably 0.000635 cm. The controller 35 is programmed such that, when the substrate 15 is powered by motor 16, the movement of the substrate 15 is measured by the signal encoder 26, the controller 35 receives the measurement signal from the signal encoder 26, calculates any feeding error, and send a correction signal to the motor 31. In this way, the motor 31 moves the bridge 17 to move the print head 20 a longitudinal distance that compensates for any error in the feeding of the substrate 15 by the motor 16. Said movement of the bridge 17 by the engine 31 can be carried out with precision, typically of the order of +/- 5 microns. As a result, the feed correction can be made accurately and quickly during the time that the printhead carriage is reversing the direction facing the substrate side 15 between scans of the printheads resulting in the printing of rows of the printhead. image on the substrate 15. Further in accordance with the present invention, any error correction made by the movement of the bridge 17 by the motor 31 is subtracted from the next adjustment movement signaled by the controller 35 towards the motor 16. For example, if an X correction is made by moving the bridge 17 which is added in the longitudinal forward direction, the next feed distance of the substrate 15 is reduced by the amount X. If the correction was made in the inverse longitudinal direction, then X is added to the next feed distance of the substrate 15. This avoids that the bridge 17 moves progressively longitudinally along the frame 11 and that the end of its journey finally arrives. Figure 3 illustrates an ink jet printing apparatus 40 in accordance with another embodiment of the invention, wherein the bridge 17 is static on the frame 11. In the apparatus 40, the print head 20 is provided with a small amount. capacity of movement in the longitudinal direction on the cart 18. This capacity of movement needs to be only a few thousandths of an inch (or its corresponding conversion in cm). It can be implemented by providing a slidable assembly 41 for the print head 20 on the carriage 18 that provides a small amount of longitudinal travel of the print head. A cam 42 can be provided for the movement of the print head on this assembly which is driven by a servomotor 43. In operation, the controller 35 sends the correction signal to the servomotor 43, in the same way as it was sent to the servomotor. 31 in the previous 30 mode. This mode can easily be adapted to existing coil printing machines that have fixed bridges. Figure 4 illustrates an ink jet printing apparatus 50 according to another embodiment of the invention, in a signal encoder or resolution device 26 that is fixed to the bridge 17, to move with the bridge 17 rather than being static with respect to the frame 11. It is more likely that this positioning of the position measuring device accurately measures the actual movement of the tape 15 beyond the print head, despite the position of the bridge 17. In the apparatus 50, the The output of the position measuring device is the actual distance moved by the tape with respect to the last position of the print head 20.

Although in the illustrations the position feedback and measurement device is schematically shown as a signal encoder or resolution device, those skilled in the art will appreciate that other devices that accurately measure the distance moved by the tape 12 can be used. The invention has been described in the context of examples of modalities. Those skilled in the art will appreciate that additions, deletions, and modifications can be made to the features described herein, without departing from the principles of the present invention. Therefore, the following is claimed:

Claims (19)

NOVELTY OF THE INVENTION CLAIMS

1. - A method of adjusting a substrate with respect to a print head between transverse print scans of the print head, the method comprising: adjusting the substrate to move the substrate longitudinally an additional distance; to measure the real distance moved by the substrate during the adjustment, and to determine from the measurement the difference between the real distance moved by the substrate and the additional distance; and in response to the difference, adjust the longitudinal position of the print head.

2. The method according to claim 1, further characterized in that the adjustment of the substrate is carried out by moving a feed element a predetermined amount to move the substrate longitudinally the additional distance through a printing station.

3. The method according to claim 1, further comprising scanning transversely with the print head in the adjusted longitudinal position.

4. The method according to claim 1, further characterized in that it comprises scanning transversely with the print head in the adjusted longitudinal position; then, further adjust the substrate longitudinally the additional distance modified by the amount that the longitudinal position of the print head was adjusted.

5. The method according to claim 1, further characterized in that the measurement of the real distance moved by the substrate includes measuring the distance with respect to a fixed frame of a printing machine.

6. The method according to claim 1, further characterized in that the measurement of the real distance moved by the substrate includes measuring the distance with respect to the longitudinal position of the print head.

7. An ink jet printing method, comprising: printing by ink jet, with a printhead in a printing station, a first row of an image transversely through a substrate that is static in a station of impression; then, feeding the substrate longitudinally through the printing station in response to a feed signal from a controller that is representative of a given feed distance, and measuring the actual distance that the substrate moves longitudinally when it is fed in this way; then, calculate, as a correction distance, the difference between the determined feed distance and the actual measured distance; then, move the print head longitudinally the correction distance; then, ink jet another row of the image transversely across a substrate, with the substrate being static in a printing station.

8. The method according to claim 7, characterized in that it comprises: further feeding the substrate longitudinally through the printing station in response to a power supply signal of the controller, the power signal being representative of a certain power distance minus the calculated correction distance.

9. The method according to claim 7, further characterized in that after printing the additional row of the image, move the print head longitudinally to bring the print head to a reference position; further feeding the substrate longitudinally through the printing station in response to a power signal from the controller that is representative of the determined feed distance less the calculated correction distance and the set distance.

10. The method according to any of the preceding claims, further characterized in that the adjustment includes moving the print head longitudinally in the direction of the adjustment when the additional distance is greater than the actual distance and is in a direction opposite to the direction of the adjustment when the additional distance is less than the actual distance.

11. - The method according to any of the preceding claims, further characterized in that the ink jet printing is carried out with the print head moving transversely across a bridge, and the print head is moved longitudinally by moving the bridge with respect to to a fixed frame.

12. The method according to any of the preceding claims, further characterized in that the ink jet printing is carried out with the print head moving transversely through a bridge, and the print head is moved longitudinally moving the print head. print head relative to the bridge.

13. An ink jet recording apparatus, comprising: a frame; a bridge that extends transversely through the frame and defines a printing station; a movement system configured to move the print head longitudinally relative to the frame; a feeding system configured to advance a substrate longitudinally through the printing station; a printhead movable transversely across the bridge to print a row of the image through the substrate at the printing station; an operable controller for activating the feeding system for performing a movement of adjustment of the substrate longitudinally through the printing station; an operable tape position measuring device for measuring and communicating to the controller a signal corresponding to a real distance moved by the substrate during the adjustment movement; and the controller being operable to activate the movement system, to move the print head longitudinally a distance corresponding to the difference between the actual distance moved by the substrate during the adjustment movement and a predetermined distance.

14. The apparatus according to claim 13, further characterized in that the bridge is movable longitudinally relative to the frame by movement; and the controller is operable to activate the movement system to move the bridge longitudinally with respect to the frame, in order to move the print head longitudinally the distance corresponding to the difference between the actual distance moved by the substrate during the adjustment movement. and a predetermined distance.

15. The apparatus according to claim 14, further characterized in that the movement system includes a linear servomotor having a stator extending longitudinally fixed to the frame, and a frame fixed to the bridge and responsive to the controller.

16. The apparatus according to claim 13, further characterized in that the print head is movable longitudinally relative to the bridge by movement; and the controller is operable to activate the movement system to move the print head longitudinally relative to the bridge, to thereby move the print head longitudinally the distance corresponding to the difference between the actual distance moved by the substrate during the movement of adjustment and a predetermined distance.

17. The apparatus according to any of claims 13 to 16, further characterized in that the device for measuring the position of the tape includes a signal encoder sensitive to the movement of the substrate with respect to it.

18. The apparatus according to any of claims 13 to 17, further characterized in that the device for measuring the position of the tape is fixed to the frame.

19. The apparatus according to any of claims 13 to 17, further characterized in that the device for measuring the position of the tape is fixed to the bridge. SUMMARY OF THE INVENTION An apparatus 30, 40, 50 and an inkjet printing method are described which use a system for feeding a substrate longitudinally with respect to a support area, and a system for moving a print head parallel to the direction of substrate feeding; the adjustment between transverse scan rows of a print head 20 is initially carried out by the substrate feed system 16, and the actual feed distance is increased by using a signal encoder or other measuring device 26 for the position of the substrate a controller 25 determines the amount of any error that occurs between the actual and desired feed distances; the controller 25 then sends signals to move the print head 20 to compensate for any errors in the feeding of the supply system; compensation adjustments are then made to the next step of adjusting the subsequent substrate, so that the print head tends to move back to its initial position or zero with its next correction and does not move away from its initial position as a result of cumulative movements.; for printers having movable bridges 17 with respect to the frame 11 of the machine on which the print head 20 is carried, the movement of the print head is achieved by moving the bridge, for example, by actuating a system of servomotors 31 of linear bridge; for fixed bridge roller-roller printers, the print head 20 can be made to change longitudinally on the bridge 17 to make the correction movements. 18B P06 / 1270F