Patent Grant
RE40775
This invention relates generally to printing control methods in which a media moves relative to a print source, and more particularly, to a method for controlling a drive shaft of a media roller.
For desktop printers, such as inkjet printers, a media sheet is picked from an input tray and moved along a media path into a print zone where characters, symbols or graphics are printed onto the media sheet. For scanning-type inkjet printers, the media sheet is fed incrementally as a printhead scans across the media sheet. Typically, the media sheet is moved by a linefeed distance between or during printing to a given line.
The media handling system for an inkjet printer includes a set of rollers which move a media sheet along a media path. The rollers are driven by a drive shaft, which in is driven by a drive motor. In many instances there is intermediary gearing for varying the motion of the rollers. A print controller controls the drive motor.
For printing from a desktop computer, a user typically issues a print command within an application program environment. A tile specified by the user then is downloaded to the printer for printing. Typically a printer driver handles the communication interface between the computer and the printer. For text printing a conventional print driver issues linefeed commands within a stream of character data so that the character data is printed in a desired visual format, (e.g., with desired margins and desired line spacing). The print controller controls timing for printing characters that achieve the desired format. Such timing is determined by the print driver commands, the data stream and fixed parameters. The fixed parameters are based upon a given physical configuration of a printer. Linefeed distance typically is based upon one or more of these fixed parameters for text, graphic and imaging processing. For example, for text printing the line spacing (e.g., 1, 1.5 or 2) is based upon the fixed linefeed parameter. This invention is directed to a method for adjusting the linefeed distance.
According to the invention, mean linefeed error for a print engine is determined and corrected. The print engine is configured to provide closed loop control over a drive shaft. The drive shaft rotates feed rollers which advance a media sheet along a media path. The print engine includes, among other components, a print controller, a drive motor, an encoder, and the drive shaft. The print controller issues signals to the drive motor for controlling the drive motor. The drive motor in turn rotates the drive shaft. The feed rollers are coupled to the drive shaft. The encoder detects the drive shaft position. Such position is fed back to the print controller to complete the closed loop control. The print controller is able to adjust the signal to the motor to control drive shaft movement.
One aspect of this invention is to correct linefeed errors that are not compensated for by the closed loop control of the drive shaft. A source of mean linefeed error in such a closed loop system is feed roller diameter variation. Although the closed loop system accounts for drive shaft position, the diameter of the feed rollers moving with the drive shaft may vary from printer to printer (and may vary over time). Differences in feed roller diameter cause a media to advance by a different amount for a given rotation of the drive shaft. In addition, variation in pinch roller force among printers cause different compression of the feed rollers. Thus, variation in pinch roller force also alters the diameter of the feed rollers, and in turn the media advance distance for a given rotation of the drive shaft.
According to one aspect of this invention, a test plot including several areas is printed. Each area is formed of the same image test pattern, but is printed at a different linefeed adjustment to compensate for mean linefeed error. The different adjustments are prescribed and span a typical compensation range for a given print engine model. The test plot is prescribed to be a test pattern which exhibits characteristics enabling a viewer to perceive the effects of linefeed error. In one embodiment the test pattern is a gray scale pattern. The different adjustment factors for the different areas of the test plot cause a banding artifact to occur. For example, white bands in an area of the plot indicate over-feeding. Dark bands in an area of the plot indicate under-feeding. The user picks the one of the test plot areas which the viewer perceives as having the highest quality (i.e., least or no banding). The linefeed adjustment factor corresponding to such test pattern area is used thereafter for normal printing.
According to another aspect of this invention, a user is able to run the calibration method at any time during the life of the printer to recalibrate the linefeed adjustment factor. Linefeed error is calibrated originally for each given print engine. Linefeed error also can be recalibrated per the user's discretion, per a manufacturer's suggested time interval, or per changes in the environment. It is desirable that a user be able to recalibrate the linefeed error at any time based upon the user's discretion. The manufacturer also may suggest a time interval to recalibrate based upon expected changes over the useful life of the printer. For example, the feed roller diameter may wear down over time. For some print engines this may not introduce a significant change in print quality, but for other high precision print engines even such change in diameter may adversely impact image quality.
According to another aspect of this invention, the print controller tracks the life of the feed rollers, (e.g., pages printed; linear distance printed). In one embodiment, the linefeed error adjustment factor is varied as a function of life of the rollers (e.g., pages printed; linear distance printed).
Changing the environment of the printer also may impact the roller diameter. For example, cooler temperature environments may cause less roller friction than higher temperature environments. A reduced roller friction may cause or alter slippage of the media during rotation of the rollers. Again as print quality standards are driven higher such slippage may not be tolerable. Accordingly, a user can recalibrate when operating in a different environment having a different temperature or humidity.
In an alternative embodiment, the method is used for calibrating swath height error. Swath height error is a variation between the outer distance (in the direction of media travel) among nozzles in a nozzle array of the printhead and the outer distance among dots printed by such nozzles. For example, a printhead having a 0.5 inch printing swath at the printhead surface which results in a 0.501 inch ink swath at the media sheet exhibits a 0.001 inch swath height error. Such error occurs, for example, when the media is not parallel to the printhead (i.e., the distance from a first nozzle to the media is different than from another nozzle to the media). As for the linefeed adjustment correction, a test plot having multiple areas is printed. Each area has the same test pattern, but is printed at a different swath height adjustment factor. Again the best adjustment is perceived by the viewer as the test pattern area with least or no banding. The swath height error adjustment is set to the value corresponding to the selected area of the test plot.
According to another aspect of this invention, the linefeed adjustment factor is varied for different media. Typically, a user is able to pick a paper setting for a document, file or image to be printed. For example, a user often is able to select among standard and non-standard stocks (e.g., weights, thicknesses) of media. Often the user can even pick among specialty media (e.g., photographic paper, transparencies, coated paper, envelopes, index cards, greeting cards, craft project media). In some printers a user can even define custom media, such as fabric, t-shirt transfer media, slide projector images, or lunch bags. The linefeed error may vary according to the media thickness and finish. Thickness directly relates to the media advance for a given rotation of the drive shaft. Finish impacts the linefeed error based upon the variation in friction of the finish. The impact on linefeed error can be computed as a variation relative to standard stock paper with a standard finish. When a user selects a given paper type or stock, the precomputed variation is combined with the calibrated mean linefeed error adjustment to come upon with an new linefeed adjustment to be used when printing such media. Alternatively, a calibration can be performed for any one or more paper stocks and finishes.
One advantage of the invention is that mean linefeed error for a specific printer is calibrated. Thus, manufacturing tolerances for a given printer model (e.g., roller diameter tolerances) which result in different mean linefeed error for different specimens of such model need not be as tight to achieve desired print quality. Another advantage is that calibration can be achieved using the naked eye without the need for separate, expensive measurement devices. Thus, the calibrations can be performed at home, in the office, or at low cost service centers. Another advantage is that the calibration can be reperformed over the life of the printer. An advantage of having a linefeed adjustment factor which varies as a function of the media type is that better print quality is achieved across a wider range of media types and weights.
A benefit of this calibration method is that image size is more accurately controlled. Previously, some printers have not allowed the printing region to span the entire page. A border area at the paper margins has been required to allow a distance for over-advances. Because the over-advancing is being reduced, the area allotted for the image can be increased for a given media size. In addition, better control of image size allows for more accurate reproduction of images because distortion from over-advancing and under-advancing is reduced or eliminated. These and other aspects and advantages of the invention will be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings.
Host Environment
As used herein the term computer includes any device or machine capable of accepting data, applying prescribed processes to the data, and supplying results of the processes.
The printer 14 includes a data interface 32, a print controller 34, memory 36, a print source 38 and a media handling subsystem 40. Typically a user works in a computing environment on the host system 10. During their work, the user may issue a print command to print out a file, document or image at the printer. Conventionally, the computer 12 includes a print driver stored in memory 24. The print driver includes code and data for implementing communication between the computer 12 and printer 14. When the user issues a print command, one of the variables specified with the command is a file, document, image or portion thereof to be printed. The print driver prepares the document, file, image or portion according to a given protocol as a print job and downloads the print job to the printer 14 via the computer's interface 26 and the printer's data interface 32. The print controller 34 stores the print job data in memory 36 and controls the printing operation. In particular the print controller 34 synchronizes the media handling system 40 and the print source 38 during printing. The print source 38 is, for example, an inkjet pen having a printhead and an array of nozzles. The media handling subsystem 40 picks a media sheet and moves the media sheet along a media path. By synchronizing the ejection of ink onto the media sheet with the movement of the media sheet, an image is printed onto the media sheet.
Media Handling and Control
The feed rollers 46 are mounted onto a drive shaft 52 and move with the drive shaft 52. Referring to
It is expected that the rollers 46 of each printer for a given printer model will have approximately the same diameter. However, as desired print quality increases, the tolerances for roller diameter may not be satisfactory to achieve the desired print quality. According to an aspect of this invention, mean linefeed error is determined and corrected so as to calibrate mean linefeed error for a given printer specimen (of a given printer model). Thus, even if two printer specimens 14 have slightly different roller diameters, the mean linefeed error can be calibrated for each specimen so as to print at the desired print quality. Such calibration can be performed in the factory and at times thereafter to account for changes in mean linefeed error caused by (i) wear of the roller 46, (ii) varied pressure applied to the roller 46 by the pinch roller 50, or (iii) different environmental conditions causing the roller 46 to exhibit different coefficients of surface friction. Differences in friction impact the amount of slippage of the media sheet 44 while driven by a roller 46. The coefficient of friction for the roller may vary as the roller 46 wears away and as the printer is operated in different environmental conditions. For example if the printer 14 is moved to a cooler working environment, then the coefficient of friction at the outer surface of the roller 46 may vary causing more slippage to occur. By recalibrating for the new environment, the printer 14 is able to achieve a desired/rated print quality.
Method for Calibrating Mean Linefeed Error
To account for difference in roller diameter from printer to printer a linefeed error adjustment parameter is defined for the specific printer. Such parameter is derive from a calibration process. Given the specific tolerances for the rollers 46 of a printer model, it is expected that the linefeed error adjustment will be within a known range of values. Values within such known range are stored in memory 36 of the printer 14. One of such values is to be selected during the calibration process to serve as the normal value for the linefeed error adjustment parameter.
To perform the calibration process, a user, such as an end user or technician, enters an appropriate command at a user interface. In an alternative embodiment the process is automatically commenced at a given time (e.g., at power up; after a prescribed interval of time; after a prescribed amount of use). For a user-initiated calibration process, the user interface is embodied at a control panel of the printer 14 or by the keyboard 18/mouse 20 and display 16 of the computer system 12. For a control panel embodiment, the user presses a dedicated button or makes a menu selection. For either embodiment of the user-initiated process, a command is generated at the print controller 34 to print out a test plot onto the media sheet 44. Similarly for the automatically started calibration process, a similar command as generated or the print controller 34 determines itself to commence the process.
The print controller 34 causes a test plot to be printed onto the media sheet 44 upon commencement of the calibration process. The test plot is a test pattern which is printed multiple times using different values for the linefeed error adjustment parameter. Such values are those values within the known range of values for the printer model which are stored (e.g., embedded) in memory 36.
With the test plot 80 printed out onto a media sheet 44, the operator is able to view the areas 82-90 and determine which area has the most desirable print quality. It is expected that the most desirable print quality corresponds to the area having no banding or the least banding. For the embodiment illustrated the third area 86 lacks banding. Thus, the operator selects the third area 86. In other exemplary calibration runs a different area may result in the best print quality. The operator inputs the choice of area with the best print quality via the user interface (e.g., the keyboard and/o mouse; or the printer control panel). Alteratively, the operator can terminate the process without calibration occurring, or the process can terminate automatically if the operator does not input a selection within a prescribed time period. Such alternatives are particularly beneficial for the embodiments in which the calibration process commences automatically.
When the operator enters a selection, the print controller 34 receives an indication of the selected area 86. The print controller 34 identifies the linefeed error adjustment parameter value that was used to print the test pattern in the selected area 86 and sets the normal value to such identified value. The normal value is stored in memory (e.g., memory 36; memory 24; or disk 30). Thereafter during normal print jobs, the linefeed error adjustment parameter is such normal value.
The media sheet for calibrating the normal value for the linefeed error adjustment parameter can be any media used by the printer 14. In a preferred embodiment the media sheet 44 used for calibration is a standard stock media of standard finish. In another preferred embodiment the media sheet 44 is the standard media predominantly used for such printer 14. In an alternative embodiment a media sheet supplied according to the manufacturer's specification is used for the calibration.
Adjustments to the Linefeed Error Adjustment Parameter
An operator is able to run the calibration process at any time during the life of the printer 14 to recalibrate the linefeed adjustment factor. Linefeed error is calibrated originally for each given printer specimen. Linefeed error also can be recalibrated per the user's discretion, per a manufacturer's suggested time interval, or per changes in the environment. It is desirable that a user be able to recalibrate the linefeed error at any time based upon the user's discretion. The manufacturer also may suggest a time interval to recalibrate based upon expected changes over the useful life of the printer. For example, the feed roller 46 diameter may wear down over time. For some printers this may not introduce a significant change in print quality, but for other high precision printers, even such change in diameter may adversely impact image quality.
Changing the environment of the printer also may impact the roller diameter. For example, cooler temperature environments may cause less roller friction than higher temperature environments. A reduced roller friction may cause or alter slippage of the media sheet 44 during rotation of the rollers 46. Again as print quality standards are driven higher such slippage may not be tolerable. Accordingly, an operator can recalibrate when operating in a different environment having a different temperature or humidity.
In some embodiments the normal value for the linefeed error adjustment parameter is varied over time or varied temporarily for a given print job. It is expected that over time the diameter of the rollers 46 may change due to wear and pressure from the pinch rollers 50. The change in roller diameter over time is determined empirically during development of a given printer model. Time in such case refers to the amount of printing done by the computer. This can be measured in linear feet that the rollers 46 rotate or number of revolutions of the drive shaft 52, or the number of pages printed, or another measure indicate of, or generally correlating to, wear on the roller 46. Whatever the measure, such measure is tracked during the life of the printer 14 to determine what the expected wear is on the rollers 46. More specifically, a factor for adjusting the normal value is applied. In some embodiments an original normal value is determined at the factory and permanently stored. A current normal value then is derived from this permanent value based upon the life of the printer. For example if rotations of the drive shaft is the measure and is tracked, then the normal value is derived from the permanent value and the current number of rotations of the drive shaft. Such update can occur with every print job or after a prescribed number of drive shaft rotations or upon request by an operator.
In another embodiment whenever an operator recalibrates the linefeed error adjustment parameter the current value of the life measure (e.g., drive shaft rotations) also is stored. When the current normal value is later updated automatically, the value is derived from the previously stored normal value and life measure value and the current life measure value. In such embodiment the permanent normal value may be used with the previously stored normal value and measure and the current measure to interpolate the new normal value.
A temporary value for the linefeed error adjustment parameter also is derived in some embodiments for the specific print job. For example, the linefeed error may vary according to the media thickness and finish. Thickness directly relates to the media advance for a given rotation of the drive shaft. Finish impacts the linefeed error based upon the variation in friction of the finish. The impact on linefeed error can be computed as a variation relative to standard stock paper with a standard finish. When a user selects a given paper type or stock, the precomputed variation is combined with the calibrated mean linefeed error adjustment parameter's normal value to come up with a temporary value to be used when printing such media. Alternatively, a calibration can be performed for any one or more paper stocks and finishes and a normal value stored for each such stock or finish.
Typically, a user specifies the media type for a print job from a menu listing of choices. Often a print driver allows the user to specify standard stock, card stock, or envelope stock. Stock typically refers to a weight or thickness of the media. Some printers also include choices for specialty paper, such as photography paper, glossy/coated paper, transparencies, envelopes, index cards, greeting cards, or craft project media. In some printers a user can even define custom media, such as fabric, t-shirt transfer media, slide projector images, or lunch bags. Factors for altering the normal value are derived during development of a print model and stored in the memory 36 for each media type or thickness or finish supported. When a print job is received the print controller determines the media type, thickness, or finish and adjusts the normal value to derive a temporary value for the linefeed error adjustment parameter for the current job. Such temporary value may be computed at the time of calibration and stored for the given media type, thickness or finish, or may be derived at run-time for each print job. According to one embodiment a temporary value is derived for a given media type as specified for the print job. According to another embodiment a temporary value is derived for a given media thickness specified for the print job. According to yet another embodiment a temporary value is derived for a given media finish as specified for the print job.
Swath Height Error Calibration
In some embodiment the calibration process alternatively or in addition, serves to calibrate a swath height error adjustment parameter. In particular, the calibration process corrects for the presence of both linefeed error and swath height error by deriving either or both of a swath height error adjustment factor or a linefeed error adjustment factor. Swath height error is a variation between the outer distance (in the direction of media travel) among nozzles in a nozzle array of the printhead and the outer distance among dots printed by such nozzles.
Mentonous and Advantageous Effects
One advantage of the invention is that mean linefeed error for a specific printer is calibrated. Thus, manufacturing tolerances for a given printer model (e.g., roller diameter tolerances) which result in different mean linefeed error for different specimens of such model need not be as tight to achieve desired print quality. Another advantage is that calibration is achieved using the naked eye without the need for separate, expensive measurement devices. Thus, the calibrations can be performed at home, in the office, or at low cost service centers. Another advantage is that the calibration can be reperformed over the life of the printer. An advantage of having a linefeed adjustment factor which varies as a function of the media type is that better print quality is achieved across a wider range of media types and weights.
A benefit of this calibration method is that image size is more accurately controlled. Previously, some printers have not allowed the printing region to span the entire page. A border area at the paper margins has been required to allow a distance for over-advances. Because the over-advancing is being reduced, the area allotted for the image can be increased for a given media size. In addition, better control of image size allows for more accurate reproduction of images because distortion from overadvancing and underadvancing is reduced or eliminated.
Although a preferred embodiment of the invention has been illustrated and described, various alternatives, modifications and equivalents may be used. For example, although only drive shaft having one or more rollers has been illustrated, other embodiments may include multiple drive shafts controlled in common through the drive motor and intermediary gear structures. In such embodiment the feedback signal 62 is generated by monitoring the position of one of the drive shafts with the linear encoder 60. In another alternative embodiment one or more sensors are included in the printer to detect the media type, media thickness and/or media stock. For example, an optical sensor is included in one embodiment for detecting transparencies. In another embodiment sensors detect the length and or width of the media sheet to determine the media size. A default media type then is looked up for the media size. This is particularly useful for detecting envelope media and postcard media. Therefore, the foregoing description should not be taken as limiting the scope of the inventions which are defined by the appended claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4653399 | Kuehfuss | Mar 1987 | A |
| 4734868 | DeLacy | Mar 1988 | A |
| 5321437 | Heeren | Jun 1994 | A |
| 5347369 | Harrington | Sep 1994 | A |
| 5439302 | Andou | Aug 1995 | A |
| 5592202 | Erickson | Jan 1997 | A |
| 5600350 | Cobbs | Feb 1997 | A |
| 5627572 | Harrington | May 1997 | A |
| 5717977 | Suzuki | Feb 1998 | A |
| 5889534 | Johnson | Mar 1999 | A |
| 6356358 | Kakutani et al. | Mar 2002 | B1 |
| Number | Date | Country |
|---|---|---|
| 5-096796 | Apr 1993 | JP |
| WO9845119 | Oct 1998 | WO |
| WO 98 54119 | Oct 1998 | WO |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09009320 | Jan 1998 | US |
| Child | 10279709 | US |
