Patent Application
20080225065
The invention relates generally to handling sheets of media through a printing apparatus and more particularly to registering an image onto media of the printing apparatus.
A media handling subsystem transports a media sheet through a printing apparatus, such as a computer printer, fax machine or copy machine, for imaging. A media sheet is picked from a stack, typically in a tray, then moved along a media path using drive rollers. Along the media path, the media sheet is positioned relative to an imaging mechanism, such as an ink or toner cartridge or printhead, which forms character and/or graphic markings on the media sheet.
For drum based printers, for example, a sheet is fed to the rotating drum by a sheet feeder, and a vacuum captures it and rolls it on to the drum. In scanning-carriage printing systems, such as inkjet printers for example, printheads are typically mounted on a carriage that is moved back and forth across the print media. As the printheads are moved across the print media, the printheads are activated to deposit or eject ink droplets onto the print media to form text and images. The print media is generally held substantially stationary while the printheads complete a “print swath”, typically an inch or less in height; the print media is then advanced between print swaths. The need to complete numerous carriage passes back and forth across a page has meant that such printers have typically been significantly slower than some other forms of printers, such as laser printers, which can essentially produce a page-wide image.
The ink ejection mechanisms of inkjet printheads are typically manufactured in a manner similar to the manufacture of semiconductor integrated circuits. The print swath for a printhead is thus typically limited by the difficulty in producing very large semiconductor chips or “die”. Consequently, to produce printheads with wider print swaths, other approaches are used, such as configuring multiple printhead dies in a printhead module, such as a “page wide array”. Print swaths spanning an entire page width, or a substantial portion of a page width, can allow inkjet printers to better compete with laser printers in print speed.
One type of printing system utilizes multiple printhead modules that each print a substantial portion of a page width; the modules are on carriages that need to be accurately positioned such that visible print defects are not introduced where the separately-printed portions of the page meet.
In order to ensure accurate media or image registration of the printing system, the print engine needs to correlate reference coordinates in both the drum spin or media advance direction (e.g. X-direction) as well as in the carriage motion direction (e.g. Y-direction). Such reference coordination is needed to register the media according to required print margins (e.g. 2 millimeter (mm) print margin). Furthermore, the print engine needs to know where the media is loaded onto the drum relative to the carriages so as to know where to move the carriages and when to trigger the start of printing.
In a basic form a method of calibrating image registration onto a sheet of media of a printer comprises: determining a first relative distance between a first sensor for sensing advancement of a sheet of media onto an imaging surface and a printhead of a carriage along a first axis, by performing measurements on the printer; determining a second relative distance between a second sensor movable along a second axis and the printhead by performing measurements on the printer; determining a third relative distance between the first and second sensors by performing measurements on the printer; and adjusting imaging of a sheet of media advanced onto an imaging surface of the printer and sensed by the first sensor using the first, second and third relative distances.
Understanding of the present invention will be facilitated by consideration of the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which like numerals refer to like parts and:
The following description of the preferred embodiments is merely by way of example and is in no way intended to limit the invention, its application, or uses.
Apparatus 10 includes an imaging mechanism 20 for printing images on media sheets while they are supported by drum 30. The media sheets may take the form of sheets of paper, transparencies or any other substrate suitable for having images printed thereon. Mechanism 20 may take the form of a monochrome and/or color printing mechanism, and incorporate one or more print cartridges (such as cartridges that incorporate ink or toner) and/or one or more print carriages 22, 24 that carry one or more printheads or print nozzles, such as ink-jet pen print bodies, all by way of non-limiting example only. Printheads 18 comprise printheads configured to dispense imaging material, such as ink, upon the medium held by drum 30. In one embodiment, printheads 18 comprise piezo electric printheads. In another embodiment, printheads 18 comprise thermal inkjet printheads. As shown by
According to an embodiment of the present invention, drum 30 may be suitable for advancing media sheets of different sizes past imaging mechanism 20 in different modes. In such a case, drum 30 may be configured to have a different number of media sheet imaging facets in the different modes. As shown in
Apparatus 10 includes a media handling system 40 that transports media sheets along path 5 to drum 30, and in the illustrated embodiment, receives media sheets from drum 30. The media handling system includes a plurality of drive rollers (not shown), each akin to an elastomeric “tire”. The driver rollers are typically grouped about a rotating shaft (not shown). Each shaft is typically driven by a motor responsively to a media transport controller.
The media handling system picks media sheets from stacks of one or more media sheets supported by input trays. Media sheets picked from the trays are fed along media path 5 through the print apparatus 10 to receive printed markings by imaging mechanism 20.
Referring now to
Still referring to
In an exemplary embodiment, memory 74 contains or stores at least one table 74a having data entries. According to an embodiment of the present invention, each data entry is indicative of a drum 30 position and at least one associated action, or event. At least some of the actions or events have associated subroutines that may be executed by or at the request of the controller upon occurrence or detection thereof. Such actions, for example, include printhead firing, paper positioning, carriage positioning, and the like. Processor 77 further operates to control sensors 100 and 200 (
Referring again to
According to an embodiment of the present invention, sensor 100 may take the form of an optical sensor. Accordingly, sensor 100 may incorporate a light source and a light detector. Exemplary light sources include a photo-emitter, LED, laser diode, super luminescent diode and fiber optic source. Exemplary light detectors include a photo-detector, charged couple device and photodiode. The light source is oriented to emit a light beam onto drum 30. The light detector is aligned to detect light emitted from the source, either directly or after being reflected by the media, for example. Other types of detectors, such as one or more flag sensors, may be used as sensor 100.
As further shown in
For purposes of explanation only, the illustrated embodiment of
In an exemplary embodiment, and still referring to
Referring now to the simplified flow diagram of
In one configuration, the first sensor 100 performs leading edge detection of the advancing media sheet in the X-direction. In response to the edge detection the encoder position associated with the drum is latched and reported to controller 70 (block 420) using corresponding electronics (not shown). Controller 70 includes in its table in memory 74 the encoded drum positions for firing the printheads 18 for imaging the media. According to an aspect of the present invention, controller 70 retrieves calibrated distance data (e.g. previously stored relative distance data) corresponding to the relative measured distance between the first sensor 100 and the printheads in the X-direction (block 430) and adjusts the firing position at which the printheads are to fire onto the media based on the detected encoded position of the media engaging the drum and the retrieved distance between the first sensor and the printhead (block 440).
For example, controller 70 has a given pen or printhead (e.g. printhead 1) scheduled to fire at a given drum encoder position such as position 10,300. The relative distance D1 in encoder position units between the first sensor 100 and printhead 1 is calibrated beforehand (e.g. off-line) and stored. By knowing D1 (e.g. 300 encoder units) and further knowing the distance from the first sensor to the drum (e.g. assume 2 encoder units), controller 70 thus expects first sensor 100 to detect the media sheet at (10,300)−(300)−(2)=9,998. If, however, the first sensor 100 detects the media at latched encoder position 9,970 (indicating the media is being applied to the drum earlier than scheduled), the controller 70 operates to recalculate when the first printhead should start firing using the detected information and calibration data, to correctly place the image in the X-direction. In this example, the printhead 1 firing position would be adjusted to (9,970)+(300)+(2)=10,272 encoder drum position.
For purposes of discussion, it is understood that the measured distance from the first sensor to printhead 1 is an ideal logical, such that all printheads are aligned and relative offsets are obtained for corresponding printheads. In similar fashion, it is understood that the offset distance between the first sensor and the drum is known or compensated for as part of the edge detection encoder latching or controller readout.
In any event, X registration calibration by measuring the distance between the first sensor 100 and a given printhead (e.g. the first printhead) is performed statically (e.g. offline) and the value stored in memory.
Referring now to the flow diagram of
Operation continues by positioning the movable second sensor 200 to be at the same vertical position as the first sensor 100, which is stationary (block 660). This may be accomplished by again moving the carriage 22 with which sensor 200 is coupled so as to properly position second sensor 200 to be in vertical alignment with first sensor 100. A sheet of media is loaded onto the drum (block 670) and a leading edge of the sheet media is detected (block 680) by first sensor 100 as the sheet advances to the drum. The encoded position associated with the detection is latched/recorded (block 685) (e.g. EP D). The leading edge of the sheet media is also detected (block 690) by the second sensor 200 as the sheet continues to advances about the drum. The encoded position associated with this detection is also latched/recorded (block 695) (e.g. EP F).
The relative distance D3 from the first sensor 100 to second sensor 200 is then calculated (block 700) using D3=(EP D)−(EP F) based on the corresponding recorded encoder positions (block 685, 695). The relative distance D4 from the first sensor 100 to the print head 18 is then calculated (block 710) by adding the magnitudes of the relative distances D2 and D3 from block 655 and block 700.
In accordance with another aspect of the present invention, registration in the Y-direction may be performed in accordance with the flow diagram of
As shown in block 730 the second sensor 200 then measures the side edge of the sheet media. This is accomplished by scanning the carriage such that the carriage is slewed off sheet and the sensor cannot see the media and then slewing the carriage until the side edge of the media sheet is detected. For each page, the measured distance between sensor 200 and the first printhead and the sensor measured paper side edge position is used to calculate where to place the carriages for printing operations.
In one embodiment, this distance may be calculated by loading a sheet onto the drum and printing a test pattern onto the sheet. Once the test pattern is applied to the sheet of media, rotate the drum a predetermined amount and stop the drum at a position such that the second sensor 200 can detect the pattern as the carriage is moved along the Y-axis. In one configuration, the carriage is slewed to a rearward position and then moved until sensor 200 detects the pattern along the side edge of the media sheet. At this point the difference between where the pattern was detected by the second sensor and where the carriage printhead printed the pattern is determined and carriage placement determined (block 740).
The calibration system and method of the present invention enables an image to be accurately printed on a sheet of media in the presence of unit to unit variance in physical distances between sensors and carriages as well as variance in the load position of each page. Furthermore, the calibration process can be implemented as part of automatic pen alignment (APA) activities without impacting the overall time for pen alignment processing. Still further, the prestored process for X-Y calibration may be utilized as part of field service processes to re-calibrate media registration after parts (such as sensor 100, sensor 200, carriage or drum encoder devices, for example) have been repaired or replaced.
The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
