Patent Application
20070068560
The present invention relates generally to inkjet printing systems employed during flat panel display formation, and is more particularly concerned with apparatus and methods for cleaning inkjet print heads.
The flat panel display industry has been attempting to employ inkjet printing to manufacture display devices, in particular, color filters. However, inkjet print heads used in inkjet printing may become filled with ink, clogged, coated, or otherwise rendered unsuitable for use in an inkjet printing process. Conventional methods for cleaning inkjet print heads involve a manual wiping process. This process often includes bringing inkjet print heads offline and away from a clean production environment, is slow and may damage or shift a print head from a desired print position. Accordingly, improved methods and apparatus for cleaning an inkjet print head are desired.
In certain aspects of the invention, a method for cleaning a nozzle plate of an inkjet print head is provided. The method includes positioning a cleaning medium proximate the inkjet print head, determining a pressure for a pressure roller to apply against the cleaning medium, contacting the cleaning medium with the pressure roller with the determined pressure, and moving the cleaning medium relative to the inkjet print head so as to clean the inkjet print head.
In other aspects of the invention, an apparatus for inkjet print head cleaning is provided. The apparatus includes a cleaning station adapted to provide a location to support an inkjet print head during cleaning, a pressure roller adapted to move a cleaning medium proximate to the cleaning station, and a biasing mechanism coupled to the pressure roller and adapted to move the pressure roller against the cleaning medium during cleaning of the inkjet print head at the cleaning station.
In yet other aspects of the invention, a system for inkjet print head cleaning is provided. The system includes an inkjet head cleaning module with a feed roller adapted to supply a cleaning medium, a take up roller adapted to receive the cleaning medium from the feed roller, a tension roller adapted to tension the cleaning medium as it is supplied from the feed roller to the take up roller, and a pressure roller adapted to move the cleaning medium supplied from the feed roller to the take up roller proximate to an inkjet print head so as to clean the inkjet print head.
Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings.
The present invention provides methods and apparatus for inkjet print head cleaning. According to the present invention, a pressure roller may cause a movable cleaning medium to contact or nearly contact the nozzle plate of an inkjet print head, thus wiping the nozzle plate clean. For example, the moving cleaning medium may be positioned close to the nozzle plate so as to remove (e.g., wick) liquid ink adhered to the nozzle plate without contacting the nozzle plate. The moving cleaning medium may also be brought into contact with the nozzle plate by the pressure roller to wipe liquid ink from and/or scrape away any unwanted material on the nozzle plate. In one or more embodiments, pressure applied by the pressure roller to cause the cleaning medium to contact the nozzle plate may be sufficient to draw off or scrape off any material residue on the nozzle plate, but insufficient to cause misalignment of the print head or structural damage to the nozzle plate. Note that a nozzle plate may be “wiped” using the cleaning medium by passing the cleaning medium close to the nozzle plate and/or by contacting the nozzle plate with the cleaning medium.
The pressure roller may be adjustable about a central axis to maintain a substantially parallel planar relationship between the nozzle plate and the cleaning medium. In some embodiments, one or more adjustment rollers may be utilized to adjust an approach angle and/or departure angle of the cleaning medium with respect to the nozzle plate. For example, the approach angle and departure angle may be optimized to bring the cleaning medium into a substantially parallel planar relationship with the nozzle plate while preventing the cleaning medium from abrading a leading edge of the nozzle plate. In the same or other embodiments, the cleaning medium may be spooled between a feed roller and a take up roller and/or may be tensioned via a tension roller. In addition, the tension roller, adjustment roller, and pressure roller may be independently adjustable such that the cleaning medium may be positioned for optimal wiping. In such embodiments, the tension roller, adjustment roller, and pressure roller may be monitored and adjusted either manually or automatically (e.g., by a control mechanism or mechanisms).
The cleaning medium 104 may be moved proximate to the nozzle plate 114 by a pressure roller 118. Pressure roller 118 may include shaft encoder 120 to measure the rotational velocity of the pressure roller 118, which may be converted to a speed of the cleaning medium 104. The other rollers of the cleaning system 100 may be similarly configured. Cleaning medium 104 may then be passed over an idle roller 124 before being spooled on a take up roller 126, which may be driven by a take up motor 128. The cleaning system 100 may also include a controller 130 coupled to any of feed roller 102, feed motor 106, tension roller 108, tension roll sensor 110, adjustment roller 112, pressure roller 118, shaft encoder 120, idle roller 124, take up roller 126, take up motor 128, or any other part of cleaning system 100.
A cleaning medium breakage sensor 132 may be employed in the system 100 adjacent cleaning medium 104 to determine whether the cleaning medium 104 is damaged and/or broken during cleaning; and a feed roller empty sensor 134 may be disposed adjacent feed roller 102 to determine whether the feed roller 102 is empty or about to be empty. The cleaning medium sensor 132 and/or feed roller empty sensor 134 also may be coupled to the controller 130.
In the exemplary embodiment of
The cleaning medium 104 may be any material suitable for use in wiping the nozzle plate 114 or other surface of a print head 116, such as a particle free medium, and may contain a cleaning fluid (e.g., water or solvent) suitable for cleaning inkjet print heads. For example, the cleaning medium 104 may be 100% non-woven polyester, such as SatWipes C3 Wiper manufactured by Contec, Inc. of Spartanburg, SC. In some embodiments a solvent (e.g., PGMEA (propylene glycol methyl ether acetate), acetone, etc.) or other cleaning fluid may be sprayed (e.g., via a spray nozzle) or otherwise deposited onto the cleaning medium 104. In the same or other embodiments, the cleaning fluid may be deposited directly onto the inkjet print head 116.
In some embodiments, the tension roller 108 may be formed from Teflon® and/or aluminum and have a diameter of about one inch, although other materials and/or sizes may be used. The tension of the cleaning medium 104 may be measured via the tension sensor 110. This information may be relayed to controller 130. The relative position and angle of tension roller 108 may be adjusted based on the determined tension (e.g., manually or automatically, such as under direction of the controller 130) to achieve a desired tension of the cleaning medium 104. In at least one embodiment, tension of the cleaning medium 104 may be approximately 50 to 1000 grams, although any appropriate tension may be used. In the same or alternative embodiments, tension may be determined in part by measuring motor torque of feed motor 106 and/or take-up motor 128.
The adjustment roller 112 may be adjustable so as to change the angle of approach A, illustrated in
In at least one embodiment, the adjustment roller 112 may be formed from Teflon® and/or aluminum and have a diameter of about one inch. Other adjustment roller materials and/or sizes may be used.
In some embodiments, the position of the adjustment roller 112 may be adjustable (e.g., by adjustment of a supporting block (not shown)) to compensate for tension variations resulting from changes in the geometry of the cleaning medium 104 path over the tension roller 108 as the roll of cleaning medium 104 is transferred from the feed roller 102 to the take up roller 126. In the same or alternative embodiments, the position of the adjustment roller 112 may also be adjustable to compensate for variations in the thickness of cleaning medium 104 or any offset in the position of inkjet print head 116. Additionally, the position of the adjustment roller 112 may be adjustable to improve clearance so that inkjet print head 116 may be moved to a parking station (not shown) when the print head is not in use. In an exemplary embodiment, with the adjustment roller 112 set to about a two degree approach angle and the pressure roller 118 retracted away from the cleaning station 116A, a clearance of approximately 2.3 mm, less cleaning medium 104 thickness, may be provided for the inkjet print head 116 to pass en route to the parking station (not shown).
During the cleaning operation, inkjet print head 116 may be located at the cleaning station 116A. The cleaning station 116A may be capable of housing a single inkjet print head 116, a row of inkjet print heads 116, an array of inkjet print heads 116, or any other suitable amount and/or arrangement of inkjet print heads 116. In an exemplary embodiment, cleaning station 116A may be a structure adapted to hold an inkjet print head or heads 116 in a particular location. Inkjet print heads 116 may be mounted to a rail (not shown) and may be moved into position at the cleaning station 116A. In other embodiments, the cleaning station 116A may be a space (e.g., gap, door, window, etc.) in a wall surrounding part or all of inkjet print head cleaning system 100.
The pressure roller 118 may be biased toward the nozzle plate 114 using a spring loaded assembly or similar biasing mechanism (as described further below with reference to biasing mechanism 204 in
Idle roller 124 may be used to guide cleaning medium 104 and adjust the departure angle of the cleaning medium 104 with respect to the nozzle plate 114 (in a manner similar to how adjustment roller 112 adjusts approach angle). Idle roller 124 may also be used to adjust a tension in cleaning medium 104, and may be of a similar size and material as the adjustment roller 112 (although other sizes and/or materials may be used). The idle roller 124 may be stationary and adjustable in position.
As stated, cleaning medium 104 may be wrapped onto take up roller 126 after use in the inkjet print head cleaning system 100. Take up roller 126 may be driven by take up motor 128. Take up motor 128 may be a belt driven motor, although any other suitable motor may be used. Take up roller 126 may be of a similar size and material as feed roller 102, although other sizes and/or materials may be used.
The controller 130 may be operably connected to the feed motor 106, take up motor 128, tension sensor 110, or any other part of the cleaning system 100. Controller 130 may be any suitable computer or computer system, including, but not limited to, a mainframe computer, a minicomputer, a network computer, a personal computer, and/or any suitable processing device, component, or system. Likewise, the controller 130 may comprise a dedicated hardware circuit or any suitable contribution of hardware and software.
In at least one embodiment, the controller 130 may monitor feed roll size, torque, and/or rotational speed, take up roll size, torque, and/or rotational speed, cleaning medium tension, cleaning medium distance traveled, and/or cleaning media speed. Controller 130 may utilize this information to control the various attributes and components of the system 100 so as to ensure a functional cleaning process. For example, in an exemplary embodiment, controller 130 may monitor tension, speed, and the distance traveled of the cleaning medium 104 as well as the size of the cleaning medium rolled onto feed roll 102 and take up roll 126. As tension is measured by tension sensor 110, this information may be used by the controller 130 to adjust the speed of the feed motor 106 or take up motor 128 (e.g., to keep an approximately constant tension on cleaning medium 104). As the speed of the cleaning medium 104 is monitored, the speeds of both the take up motor 106 and feed motor 128 may be adjusted (e.g. to keep the cleaning medium 104 traveling at an approximately constant speed). Similarly, information about the cleaning medium 104 distance traveled and the size of the cleaning medium 104 rolls on feed roll 102 and take up roll 126 may be used to determine and/or adjust the take up motor 106 speed and feed motor 128 speed (e.g., to affect cleaning medium speed and/or tension). In another embodiment, the speed and distance traveled of the cleaning medium 104, the feed motor 106 torque, and the size of the cleaning medium 104 rolls on feed roll 102 and take up roll 126 may be known, measured, and/or adjustable by controller 130. Cleaning medium 104 speed may be used by the controller 130 to adjust take up motor 128 speed. Feed motor 106 torque may be used by the controller 130 to adjust feed motor 106 torque. Similarly, the diameter of the cleaning medium 104 on either or both of the feed roller 102 and the take-up roller 126 may be used in conjunction with a measured motor torque on either or both of the feed motor 106 and the take-up motor 128 by the controller 130 to control the cleaning medium 104 tension. The motor torque of the feed motor 106 and/or the take-up motor 128 may be inversely proportional to the measured cleaning medium 104 diameter when cleaning medium 104 tension is kept constant.
Cleaning medium breakage sensor 132 is adapted to determine a defect in the cleaning medium 104. In a preferred embodiment, breakage sensor 132 may be disposed between the tension roller 108 and adjustment roller 118 although other locations may be used. In some embodiments, breakage sensor 132 may be an optical sensor that detects the presence or absence of the cleaning medium 104 (e.g., via reflection or a through beam) or may be any other suitable sensor or device. For example, the breakage sensor 132 may include a light beam source 132a and a detector 132b that only detects a light beam from the light beam source 132a when the clean medium 104 is not present or improperly positioned between the light beam source 132a and detector 132b. Absence of the cleaning medium 104, or a change in the transmission characteristics through the cleaning medium 104, may indicate a defect (e.g., breakage of the cleaning medium 104, improper cleaning medium type, etc.) Feed roller empty sensor 134 may be disposed adjacent feed roller 102 and be adapted to monitor the roll size of cleaning medium 104 on the feed roller 102. For example, the feed roller empty sensor 134 may include a light source adapted to transmit a light beam toward a detector (not shown) that detects the light beam only if the diameter of cleaning medium 104 on the feed roller 102 is below a predetermined size (e.g., indicating the feed roller 102 is or is about to be empty). Other feed roller empty sensors may be used including, for example, a sensor that measures the weight of the feed roller 102 to determine the amount of cleaning medium 104 on the feed roller 102 or a reflected ultrasound or laser sensor. As cleaning medium 104 pays out during a cleaning process, the roll size (diameter) may be monitored to prevent running out of cleaning medium 104 during the cleaning process. In one embodiment, a feed roller empty sensor 134 may be mounted perpendicular to the feed roller 102.
If a designated cleaning medium 104 roll-change point is desired, a discrete-output sensor may be used, such as the light source/detector embodiment described above. In another embodiment, the feed roller empty sensor 134 may be adapted to measure how much cleaning medium 104 has been payed out by the feed roller 102 and configured and/or programmed with a specific distance which corresponds to a low supply condition, at which point the output of the feed roller empty sensor 134 changes state. If a continuous inventory is desired, an analog-output sensor may be used. Feed roller empty sensor 104 may be taught a distance which corresponds to the full roll, and a distance to the empty roll. As the cleaning medium 104 pays out, the sensor may send an analog signal that is scaled to represent the shrinking size of the roll. Any other suitable sensor may be used.
Feed roller empty sensor 134 may also be used to measure a diameter of the cleaning medium 104 mounted on feed roller 102. The diameter of the cleaning medium 104 may be used by the controller 130 to control tension of the cleaning medium 104.
Pressure roller 202 may house shaft encoder 206. In alternative embodiments, shaft encoder 206 may be operably connected to pressure roller 202, but may reside outside of the roller housing. Controller 130 (shown in
In operation, pressure roller 202 may be operable to apply pressure against the cleaning medium 104 and move the cleaning medium 104 in proximity of cleaning station location 210A, which may house the inkjet print head 210.
An example of a commercially available print head suitable for use with the present invention is the model SX-128, 128-Channel Jetting Assembly manufactured by Spectra, Inc. of Lebanon, NH. This particular jetting assembly includes two electrically independent piezoelectric slices, each with sixty-four addressable channels, which are combined to provide a total of 128 jets. The print head includes a number of nozzles which are arranged in a single line, at approximately 0.020″ distance between nozzles. Other print heads with differently sized nozzles may also be used.
The biasing mechanism 204 may be any mechanism or structure capable of moving the pressure roller 202 (e.g., spring arm, spring bias, or the like). Biasing mechanism 204 may be operable to move pressure roller 202 in proximity of the nozzle plate 214 of inkjet print head 210, which is located at the cleaning station 210A. In some embodiments, the pressure exerted against the cleaning medium 104 by the pressure roller 202 or the “pressure roller load” (or the load on biasing mechanism 204) may be set by extension of a spring 204a against an arm 204b. In an alternative embodiment, the load on biasing mechanism 204 may be set by a compression spring (not shown). Any other suitable method for adjusting load on biasing mechanism 204 may be used. Some of the load may offset the weight of pressure roller 202 and biasing mechanism 204. The roller load may be set by extension of the spring. In an alternative embodiment, roller load may be set by compression of the spring. The pressure roller load results in the pressure roller 202 contacting the cleaning medium 104 and applying a desired pressure on the nozzle plate 214. In a preferred embodiment, a spring rate of approximately 9 g/mm may be used to allow an accurate load setting, although any appropriate and/or practible spring rate may be used. The pressure roller load may be set by adjustment of the spring to compensate for changes in cleaning medium 104 tension and approach angle. In the same or alternative embodiments, the pressure roller load may be set to compensate for variations in cleaning medium 104 thickness.
As stated, pressure roller 202 may be limited in movement by up limit 208. Up limit 208 may be any suitable limiting device which will prevent pressure roller 202 from unwanted or excessive contact with inkjet print head 210. In a preferred embodiment, up limit 208 may be set approximately 0.1 mm past the point where pressure roller 202 would contact nozzle plate 214. The up limit 208 may be used to set an initial position for pressure roller 202 and setting of the roller load. Up limit 208 may be set at any appropriate point conducive to the pressure roller 202 diameter, inkjet print head 210 position, or any other factor which may affect the pressure roller 202 contact point.
Pressure roller 202 may be further limited in movement by down limit 212. Down limit 212 may be any suitable limiting device which will prevent pressure roller 202 from contacting other parts of system 100. Down limit 212 may a hard stop, spring return type, or any other suitable limiter.
Pressure roller 202 may house shaft encoder 206. Shaft encoder 206 may be operable to determine a rotational velocity of the pressure roller 202 and convert the rotational velocity to a cleaning medium 104 velocity. Alternatively, shaft encoder 206 may determine a rotational velocity of the pressure roller 202 and relay this information to controller 130. In alternative embodiments, shaft encoder 206 may be operably connected to pressure roller 202, but may reside outside of the roller housing.
Controller 130 (shown in
Turning to
In step 306, ink remaining in the inkjet print head 210 may be purged. To purge ink from the print head 210, the inkjet print head may force any remaining ink inside the inkjet print head 210 out of the inkjet print head via any suitable method. This may include, for example, jetting ink or air through the inkjet print head 210. In one or more embodiments, ink or air may be jetted through the inkjet print head 210 using a pulse of duration of about 0.5 seconds, although any other pulse widths may be used. In an exemplary embodiment, inkjet print head 210 may purge between approximately three and six cubic centimeters of ink per cycle. Inkjet print head 210 may be purged onto cleaning medium 104 at cleaning station 210A or at a parking station (not shown).
In step 308, cleaning medium 104 may be moved. Moving cleaning medium 104 may include rotating feed roller 102 so as to dispense cleaning medium 104 from the feed roller 102 and rotating take up roller 126 so as to re-spool used cleaning medium 104 onto the take up roller 126. Any appropriate cleaning medium 104 speed may be employed. In an exemplary embodiment, cleaning medium 104 may be moved at a speed of approximately 10-150 mm/s.
During step 308, the speed of the cleaning medium 104 also may be adjusted. For example, adjustment of a cleaning medium 104 speed may be made by first determining a current cleaning medium speed. The current cleaning medium speed may be determined by measuring a tension of the cleaning medium, a distance traveled by the cleaning medium, comparing a first feed roll size to a second feed roll size, comparing a first take up roll size to a second take up roll size, any combination thereof, or the like. Any other suitable method may be used to determine speed of the cleaning medium 104. The current cleaning medium speed may then be adjusted, for example, by adjusting a feed roller rotational speed, a take up roller rotational speed, a cleaning medium tension, or any combination thereof. Any other suitable method may be used to adjust cleaning medium 104 speed. A feed roller 102 rotational speed may be adjusted by adjusting the motor speed of feed motor 106. Similarly, a take up roller 126 rotational speed may be adjusted by adjusting the motor speed of take up motor 128.
In step 310, pressure roller 202 may be moved against cleaning medium 104 proximate to nozzle plate 214. This may cause any liquid ink remaining on nozzle plate 214 to be wicked or drawn off the nozzle plate 214 onto cleaning medium 104. For example, pressure roller 202 may be moved via biasing mechanism 204 or any suitable method and/or device. The pressure roller 202 may be moved incrementally (e.g., so as to continually adjust pressure roller 202 position, such as based on feedback from controller 130); or pressure roller 202 may be moved in a single step to a predetermined position.
In step 312, pressure roller 202 may be moved against cleaning medium 104 so as to cause cleaning medium 104 to contact the surface of nozzle plate 214 and wipe away any remaining ink. In at least one embodiment, pressure exerted by cleaning medium 104 may be sufficient to scrape away any ink from the nozzle plate 214, but insufficient to cause damage to and/or mis-alignment of the inkjet print head 210. The biasing mechanism 204 or any other device may be employed to move the pressure roller 202 (e.g., manually or under control of the controller 130).
In step 314, pressure roller 202 may be moved away from inkjet print head 210, causing cleaning medium 104 to be moved away from nozzle plate 214. For example, pressure roller 202 may be moved away via biasing mechanism 204 or any suitable method and/or device. The pressure roller 202 may be moved incrementally away from inkjet print head 210 (e.g., by continually adjusting pressure roller 202 position, such as based on feedback from controller 130); or, the pressure roller 202 may be moved away from inkjet print head 210 in a single step to a predetermined position.
In step 316, ink may be pre-jetted from inkjet print head 210. Pre-jetting ink may cause ink to be jetted from the inkjet print head 210 after cleaning and before returning to a print process. Ink may be pre-jetted onto cleaning medium 104 at cleaning station 210A or may be pre-jetted at a parking station (not shown).
The method ends at step 318.
The foregoing description discloses only exemplary embodiments of the invention; modifications of the above disclosed methods and apparatus which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For instance, although the above example methods are described with reference to only one adjustment roller 112 and one idle roller 124 as described above with reference to
Accordingly, while the present invention has been disclosed in connection with specific embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.
