Patent Grant
6935717
The present invention relates generally to printing mechanisms, such as inkjet printers or inkjet plotters. Printing mechanisms often include an inkjet printhead which is capable of forming an image on many different types of media. The inkjet printhead ejects droplets of colored ink through a plurality of orifices and onto a given media as the media is advanced through a printzone. The printzone is defined by the plane created by the printhead orifices and any scanning or reciprocating movement the printhead may have back-and-forth and perpendicular to the movement of the media. Conventional methods for expelling ink from the printhead orifices, or nozzles, include piezo-electric and thermal techniques which are well-known to those skilled in the art. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, the Hewlett-Packard Company.
In a thermal inkjet system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are individually addressable and energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. The inkjet printhead nozzles are typically aligned in one or more linear arrays substantially parallel to the motion of the print media as the media travels through the printzone. The length of the linear nozzle arrays defines the maximum height, or “swath” height of an imaged bar that would be printed in a single pass of the printhead across the media if all of the nozzles were fired simultaneously and continuously as the printhead was moved through the printzone above the media.
Typically, the print media is advanced under the inkjet printhead and held stationary while the printhead passes along the width of the media, firing its nozzles as determined by a controller to form a desired image on an individual swath, or pass. The print media is usually advanced between passes of the reciprocating inkjet printhead in order to avoid uncertainty in the placement of the fired ink droplets. If the entire printable data for a given swath is printed in one pass of the printhead, and the media is advanced a distance equal to the maximum swath height in-between printhead passes, then the printing mechanism may achieve its maximum throughput.
Often, however, it is desirable to print only a portion of the data for a given swath, utilizing a fraction of the available nozzles and advancing the media a distance smaller than the maximum swath height so that the same or a different fraction of nozzles may fill in the gaps in the desired printed image which were intentionally left on the first pass. This process of separating the printable data into multiple passes utilizing subsets of the available nozzles is referred to by those skilled in the art as “shingling,” “masking,” or using “print masks.” While the use of print masks does lower the throughput of a printing system, it can provide offsetting benefits when image quality needs to be balanced against speed. For example, the use of print masks allows large solid color areas to be filled in gradually, on multiple passes, allowing the ink to dry in parts and avoiding the large-area soaking and resulting ripples, or “cockle,” in the print media that a single pass swath would cause.
A printing mechanism may have one or more inkjet printheads, corresponding to one or more colors, or “process colors” as they are referred to in the art. For example, a typical inkjet printing system may have a single printhead with only black ink; or the system may have four printheads, one each with black, cyan, magenta, and yellow inks; or the system may have three printheads, one each with cyan, magenta, and yellow inks. Of course, there are many more combinations and quantities of possible printheads in inkjet printing systems, including seven and eight ink/printhead systems.
Each process color ink is ejected onto the print media in such a way that the drop size, relative position of the ink drops, and color of a small, discreet number of process inks are integrated by the naturally occurring visual response of the human eye to produce the effect of a large colorspace with millions of discernable colors and the effect of a nearly continuous tone. In fact, when these imaging techniques are performed properly by those skilled in the art, near-photographic quality images can be obtained on a variety of print media using only three to eight colors of ink. This high level of image quality depends on many factors, several of which include: consistent and small ink drop size, consistent ink drop trajectory from the printhead nozzle to the print media, and extremely reliable inkjet printhead nozzles which do not clog.
Unfortunately, however, there are many factors at work within the typical inkjet printing mechanism which may clog the inkjet nozzles, and inkjet nozzle failures may occur. For example, paper dust may collect on the nozzles and eventually clog them. Ink residue from ink aerosol or partially clogged nozzles may be spread by service station printhead scrapers into open nozzles, causing them to be clogged. Accumulated precipitates from the ink inside of the printhead may also occlude the ink channels and the nozzles. Additionally, the heater elements in a thermal inkjet printhead may fail to energize, despite the lack of an associated clogged nozzle, thereby causing the nozzle to fail.
Clogged or failed printhead nozzles result in objectionable and easily noticeable print quality defects such as banding (visible bands of different hues or colors in what would otherwise be a uniformly colored area) or voids in the image. In fact, inkjet printing systems are so sensitive to clogged nozzles, that a single clogged nozzle out of hundreds of nozzles is often noticeable and objectionable in the printed output.
It is possible, however, for an inkjet printing system to compensate for a missing nozzle by removing it from the printing mask and replacing it with an unused nozzle or a used nozzle on a later, overlapping pass, provided the inkjet system has a way to tell when a particular nozzle is not functioning. In order to detect whether an inkjet printhead nozzle is firing, a printing mechanism may be equipped with a low cost ink drop detection system, such as the one described in U.S. Pat. No. 6,086,190 assigned to the present assignee, Hewlett-Packard Company. The nozzle plate of a printhead is inherently near ground potential due to the power supply connections on the printhead. A conductive target may be placed a few millimeters below the nozzle plate, and a biasing voltage may be applied to the target, forming an electric field between the nozzle plate and the target. Upon firing an ink drop, as the ink drop begins to exit the nozzle, a charge accumulates on the protruding tip of the drop, due to the influence of the nozzle-plate-to-target electric field. When drop breakoff occurs, the drop retains this charge. When the drop contacts the target, a small current, in relation to the charge on the drop, is induced from the target to ground. The periodic flow of current from drops striking the target may be converted to a signal voltage by an amplifier which is AC-coupled to the target, and then an analog-to-digital converter may digitize the output signal for processing to determine if a nozzle or group of nozzles are working properly.
In practical implementation, however, this drop detection system has some limitations. Successive drops of ink, drying on top of one another quickly form stalagmites of dried ink which may grow toward the printhead. Since it is preferable to have the electrostatic sensing element very close to the printhead for more accurate readings, these stalagmites may eventually interfere with or permanently damage the printhead, adversely affecting print quality. Therefore, it is desirable to have a low cost and efficient method and mechanism for ink drop detection which is less susceptible to waste ink residue build-up.
While it is apparent that the printer components may vary from model to model, the typical inkjet printer 20 includes a chassis 22 surrounded by a frame or casing enclosure 24, typically of a plastic material. The printer 20 also has a printer controller, illustrated schematically as a microprocessor 26, that receives instructions from a host device, such as a computer, print server, or personal data assistant (PDA) (not shown). A screen coupled to the host device may also be used to display visual information to an operator, such as the printer status or a particular program being run on the host device. Printer host devices, such as computers and PDA's, their input devices, such as a keyboards, mouse devices, stylus devices, and output devices such as liquid crystal display screens and monitors are all well known to those skilled in the art.
A conventional print media handling system (not shown) may be used to advance a sheet of print media (not shown) from the media input tray 28 through a printzone 30 and to an output tray 31. A carriage guide rod 32 is mounted to the chassis 22 to define a scanning axis 34, with the guide rod 32 slideably supporting an inkjet carriage 36 for travel back and forth, reciprocally, across the printzone 30. A conventional carriage drive motor (not shown) may be used to propel the carriage 36 in response to a control signal received from the controller 26. To provide carriage positional feedback information to controller 26, a conventional encoder strip (not shown) may be extended along the length of the printzone 30 and over a servicing region 38. A conventional optical encoder reader may be mounted on the back surface of printhead carriage 36 to read positional information provided by the encoder strip, for example, as described in U.S. Pat. No. 5,276,970, also assigned to the Hewlett-Packard Company, the present assignee. The manner of providing positional feedback information via the encoder strip reader, may also be accomplished in a variety of ways known to those skilled in the art.
In the printzone 30, the media sheet is supported by paper path ribs 39 and receives ink from an inkjet cartridge, such as a black ink cartridge 40 and a color inkjet cartridge 42. The cartridges 40 and 42 are also often called “pens” by those in the art. The black ink pen 40 is illustrated herein as containing a pigment-based ink. For the purposes of illustration, color pen 42 is described as containing three separate dye-based inks which are colored cyan, magenta, and yellow, although it is apparent that the color pen 42 may also contain pigment-based inks in some implementations. It is apparent that other types of inks may also be used in the pens 40 and 42, such as paraffin-based inks, as well as hybrid or composite inks having both dye and pigment characteristics. The illustrated printer 20 uses replaceable printhead cartridges where each pen has a reservoir that carries the entire ink supply as the printhead reciprocates over the printzone 30. As used herein, the term “pen” or “cartridge” may also refer to an “off-axis” ink delivery system, having main stationary reservoirs (not shown) for each ink (black, cyan, magenta, yellow, or other colors depending on the number of inks in the system) located in an ink supply region. In an off-axis system, the pens may be replenished by ink conveyed through a conventional flexible tubing system from the stationary main reservoirs which are located “off-axis” from the path of printhead travel, so only a small ink supply is propelled by carriage 36 across the printzone 30. Other ink delivery or fluid delivery systems may also employ the systems described herein, such as “snapper” cartridges which have ink reservoirs that snap onto permanent or semi-permanent print heads.
The illustrated black pen 40 has a printhead 44, and color pen 42 has a tri-color printhead 46 which ejects cyan, magenta, and yellow inks. The printheads 44, 46 selectively eject ink to form an image on a sheet of media when in the printzone 30. The printheads 44, 46 each have an orifice plate with a plurality of nozzles formed therethrough in a manner well known to those skilled in the art. The nozzles of each printhead 44, 46 are typically formed in at least one, but typically a plurality of linear arrays along the orifice plate. Thus, the term “linear” as used herein may be interpreted as “nearly linear” or substantially linear, and may include nozzle arrangements slightly offset from one another, for example, in a zigzag arrangement. Each linear array is typically aligned in a longitudinal direction perpendicular to the scanning axis 34, with the length of each array determining the maximum image swath for a single pass of the printhead. The printheads 44, 46 are thermal inkjet printheads, although other types of printheads may be used, such as piezoelectric printheads. The thermal printheads 44, 46 typically include a plurality of resistors which are associated with the nozzles. Upon energizing a selected resistor, a bubble of gas is formed which ejects a droplet of ink from the nozzle and onto the print media when in the printzone 30 under the nozzle. The printhead resistors are selectively energized in response to firing command control signals delivered from the controller 26 to the printhead carriage 36. It is also possible to implement a page-wide printhead array which does not need to be reciprocated across the printzone 30.
Between print jobs, the inkjet carriage 36 moves along the carriage guide rod 32 to the servicing region 38 where a service station 48 may perform various servicing functions known to those in the art, such as, priming, scraping, and capping for storage during periods of non-use to prevent ink from drying and clogging the inkjet printhead nozzles.
The printer chassis 22 is illustrated as supporting an electrically biased absorbent electrostatic sensing element, or “electrically biased absorbent target” 50, in the printer's “inboard” region 52 located on the side of service station 48 near the printzone 30. The print carriage 36 may be moved along carriage guide rod 32 until printheads 44, 46 are positioned over the electrically biased absorbent target 50. Ink droplets may be fired onto the upper surface of electrically biased absorbent target 50 and detected according to the method described in U.S. Pat. No. 6,086,190, assigned to the Hewlett-Packard Company, the present assignee. Target 50 may be constructed by using a foam pad which is pretreated with a conductive solvent such as glycerol or polyethylene glycol (PEG). Other absorbent materials may similarly be selected depending on design or cost restraints, for example, the electrically biased absorbent target 50 could be constructed of polyurethane or a rigid and porous sintered plastic. Electrically biased sensing conductor 54 applies a biasing voltage to the target 50 while also connecting the target 50 to an electrostatic drop detect printed circuit board assembly (PCA) 56. The PCA 56 contains various electronics (not shown) for filtering and amplification of drop detection signals received from the target 50 via electrically biased sensing conductor 54. An additional electrical conductor 58 links the PCA 56 to controller 26 for drop detection signal processing. PCA 56 may be located in various locations inside of the printer 20 to accommodate design goals such as sharing PCA real estate with other circuitry, locating in the proximity of the target 50 to reduce signal noise effects, or to remove the PCA 56 from the vicinity of conductive ink residue and ink aerosol.
Electrically biased absorbent target 50 does not need a cleaning mechanism, so it is simple to construct and economical, and should prevent the build-up of ink residue stalagmites as ink droplets are fired onto the target 50 because the droplets can be absorbed into the target 50 and preferably kept in solution by the optional ink solvent present in the target 50. Electrically biased absorbent target 50 may be constructed in varying sizes to accommodate a portion of a printhead's 44, 46 nozzles, an entire printhead's 44, 46 nozzles, or even all of the nozzles for multiple printheads 44, 46. Additionally, electrically biased absorbent target 50 may be located in other locations below the plane defined by printheads 44, 46 as they are propelled by the printhead carriage 36 back and forth on carriage guide rod 32 along scanning axis 34. Examples of alternate locations for electrically biased absorbent target 50 include, for example, the “outboard region” 60 which is on the opposite side of printzone 30 from the service station 48, the servicing region 38, and “outside service station region” 62.
An electrically biased sensing conductor 54 may connect the non-contact target loop 76 to the drop detector PCA 56 as illustrated in
An electrically biased sensing conductor 54 may connect the non-contact electrically biased sensing plates 82 to the drop detector PCA 56 as illustrated in
Electrically biased conductor 86 provides a biasing voltage to the electrically biased loop 84. The voltage present on the electrically biased loop 84 creates an electric field between the electrically biased loop 84 and the ground plane present at the nozzle plate of the printhead 44. Selected printhead 44 nozzles may then be fired in response to commands from controller 26 to eject ink droplets 68 through the opening defined by electrically biased loop 84. As each droplet 68 begins to exit the printhead 44 nozzle, a charge accumulates on the protruding tip of the drop, due to the influence of the printhead 44 nozzle-plate-to-electrically biased loop 84 electric field. When drop breakoff occurs, the droplet 68 retains this charge. Droplet 68 passes through the opening defined by the electrically biased loop 84 and contacts conductive target 88. A sensing conductor 90 connects the target 88 to the drop detector PCA 56 as illustrated in
Electrically biased conductor 86 provides a biasing voltage to the electrically biased plates 92. The voltage present on the electrically biased plates 92 creates an electric field between the electrically biased plates 92 and the ground plane present at the nozzle plate of the printhead 44. Selected printhead 44 nozzles may then be fired in response to commands from controller 26 to eject ink droplets 68 through the electric field. As each droplet 68 begins to exit the printhead 44 nozzle, a charge accumulates on the protruding tip of the drop, due to the influence of the printhead 44 nozzle-plate-to-electrically biased plates 92 electric field. When drop breakoff occurs, the droplet 68 retains this charge. A sensing conductor 90 connects the target 88 to the drop detector PCA 56 as illustrated in
In each of the embodiments illustrated in
Various non-contact electrically biasing and sensing electrostatic drop detect target configurations, as well as absorbent target configurations have been illustrated with example embodiments to enable a low cost and efficient method and mechanism for ink drop detection which is less susceptible to waste ink residue build-up. Each of the target and electrically biasing element embodiments illustrated in
Non-contact electrically biasing and sensing electrostatic drop detect target configurations, as well as absorbent target configurations enable a printing mechanism to reliably and economically gather ink drop detection readings, without the need for a cleaning mechanism to clean the target surface, in order to provide users with consistent, high-quality, and economical inkjet output despite printheads 44, 46 which may clog over time. In discussing various components of the non-contact electrically biasing and sensing electrostatic drop detect target configurations, as well as absorbent target configurations, various benefits have been noted above.
It is apparent that a variety of other structurally equivalent modifications and substitutions may be made to construct non-contact electrically biasing and sensing electrostatic drop detect target configurations, as well as absorbent target configurations, according to the concepts covered herein depending upon the particular implementation, while still falling within the scope of the claims below.
This application is a divisional of: application Ser. No. 09/916,008 filed Jul. 25, 2001 now U.S. Pat. No. 6,769,756.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4484199 | Watanabe | Nov 1984 | A |
| 5160939 | Bajeux et al. | Nov 1992 | A |
| 6086190 | Schantz et al. | Jul 2000 | A |
| 6769756 | Su et al. | Aug 2004 | B2 |
| Number | Date | Country | |
|---|---|---|---|
| 20040056917 A1 | Mar 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09916008 | Jul 2001 | US |
| Child | 10666666 | US |
