Patent Application
20070126834
This disclosure relates to ink image printing machines or printers and, more particularly, to apparatus for preheating printing sheets, such as paper and transparency film, prior to ink printing on such sheets. Specifically, this disclosure relates to such a sheet heater assembly having air-bearing platelets for reducing stiction forces and friction between fed sheets and sheet-path defining plates of the heater.
Some conventional printer systems require printing sheets to be uniformly preheated prior to printing to provide an aesthetic and durable output. Typical heaters employ radiant or convective heat sources adjacent to the paper path and “upstream” of the print head. These existing heaters have several disadvantages. A lack of uniformity in heating can cause non-uniform printer output, and sheet warping or cockle. Examples of conventional sheet heaters or preheaters are disclosed in the following references:
U.S. Pat. No. 5,691,756 issued on Nov. 25, 1997 entitled “Printer media preheater and method” discloses a media preheater positioned in the media path of a printer and having a fixed heater and a movable plate array biased toward the heater such that printing media passing between the heater and the plate array is compressed therebetween and heated. The preheater may be positioned upstream of a print head and downstream of a media advancing mechanism in the media path. More than one plate may be provided in the plate array to accommodate non-planarity of the heater or the printing medium. The plate array may be a thermally massive element that contacts the heater when no media is present, thereby permitting the medium to be heated from both sides.
U.S. Pat. No. 5,856,650 issued on Jan. 5, 1999 entitled “Method of cleaning a printer media preheater” discloses a method of cleaning a media preheater that is positioned in the media path of a printer. The media preheater [a plate on plate type] has a fixed heater and a movable plate array biased toward the heater such that printer media passing between the plate array and the heater is compressed therebetween and heated. The preheater may be positioned upstream of a print head and downstream of a media advancing mechanism in the media path. More than one plate may be provided in the plate array to accommodate non-planarity of the heater or the printing media. The method elevates the temperature of the contact surface of the preheater to a cleaning temperature that is greater than the operating temperature and then passes a chase sheet over the surface to remove contamination from the preheater surface.
U.S. Pat. No. 6,048,059 issued on Apr. 11, 2000 entitled “Variable power preheater for an ink printer” discloses a preheater placed between a supply tray station and a print zone of an ink printer. Power to the preheater is varied so that the preheater is heated to a fist relatively high temperature during the time that the recording medium is advanced from the supply station to the print zone. When the recording medium enters the print zone, the medium is moved at a slower indexing speed, and the power to the preheater is reduced to a second level. The result is a more uniform application of preheat to the recording medium.
Conventional Plate On Plate (POP) preheaters as disclosed above, provide good heat transfer to the sheet being fed through the preheater. Unfortunately however, such conventional preheaters create significant drag on the sheet or paper undesirably resulting in feed reliability problems such as jams and sheet edge stubbing. Smudging of duplex or two-sided images and poor sheet registration are also other undesirable results.
Furthermore, in order to assure the good heat transfer mentioned above, the POP preheater and platelets must be extremely flat, and thus require tight tolerances and are therefore costly to make. A negative consequence of this flatness however, is the generation of a significant undesirable stiction (that is, the force required to cause one platelet in contact with the heater plate to begin moving away from the heater plate) between the platelets and the preheater. Such stiction is thought to be a combination of vanderwaals forces and vacuum created between the very flat surfaces, as the platelets are being open. It is believed that sheet jamming and stubbing occurs at the entrance to the preheater because the sheet upon entering the preheater must first overcome this stiction force.
Solid ink images will be transferred to the heater plate side of the paper or sheet. The platelets themselves become heated from contact with the heater plate and thus themselves also transfer heat to the sheet. The weight of the platelets also act to force the sheet being fed through the pre-heater down against the heater plate, thus dramatically increasing the heat transfer rate from the heater plate to the sheet. As such, during duplex or two-sided printing when e sheet with an ink image on a first side thereof is re-fed through the preheater, the already inked-side of the sheet, (now a back side) contacts and rubs against the platelets as it is fed through the preheater. During such rubbing, the coefficient of friction between the inked page of the sheet and the platelets (which is significantly higher than if the page was blank), undesirably causes the ink image on the page to smudge.
In accordance with the present disclosure, there has been provided an air bearing sheet heater assembly for heating a sheet in an ink imaging printer that includes (a) a heater plate including a heating element, and having a front side defining a first side of a sheet path through the heater assembly; (b) at least one movable platelet having a back surface 122, and an opposite front surface 124 facing the heater plate and defining a second side of the sheet path; and (c) an air bearing assembly mounted to the at least one platelet for creating an air bearing between the second side and the first side of the sheet path by pneumatically spacing the front surface 124 of the at least one movable platelet from the front side of the heater plate, thereby reducing stiction forces and friction along the sheet path through the air bearing sheet heater assembly.
The features and advantages of the disclosure will become apparent upon consideration of the following detailed disclosure, especially when it is taken in conjunction with the accompanying drawings in which:
Referring now to
The high-speed phase change ink image producing machine or printer 10 also includes a phase change ink delivery subsystem 20 that has at least one source 22 of one color phase change ink in solid form. Since the phase change ink image producing machine or printer 10 is a multicolor image producing machine, the ink delivery system 20 includes four (4) sources 22, 24, 26, 28, representing four (4) different colors CYMK (cyan, yellow, magenta, black) of phase change inks. The phase change ink delivery system also includes a melting and control apparatus (not shown) for melting or phase changing the solid form of the phase change ink into a liquid form. The phase change ink delivery system is suitable for then supplying the liquid form to a printhead system 30 including at least one printhead assembly 32. Since the phase change ink image producing machine or printer 10 is a high-speed, or high throughput, multicolor image producing machine, the printhead system 30 includes multicolor ink printhead assemblies and a plural number (e.g. four (4)) two 32, 34, of which are shown as of separate printhead assemblies. In order to achieve and maintain relatively high quality image productions by the printhead assembly.
As further shown, the phase change ink image producing machine or printer 10 includes a substrate supply and handling system 40. The substrate supply and handling system 40 for example may include sheet or substrate supply sources 42, 44, 46, 48, of which supply source 48 for example is a high capacity paper supply or feeder for storing and supplying image receiving substrates in the form of cut sheets 49 for example. The substrate supply and handling system 40 also includes a substrate or sheet heater or pre-heater assembly 100 in accordance with the present disclosure, (to be described in detail below). The phase change ink image producing machine or printer 10 as shown may also include an original document feeder 70 that has a document holding tray 72, document sheet feeding and retrieval devices 74, and a document exposure and scanning system 76.
Operation and control of the various subsystems, components and functions of the machine or printer 10 are performed with the aid of a controller or electronic subsystem (ESS) 80. The ESS or controller 80 for example is a self-contained, dedicated mini-computer having a central processor unit (CPU) 82, electronic storage 84, and a display or user interface (UI) 86. The ESS or controller 80 for example includes sensor input and control means 88 as well as a pixel placement and control means 89. In addition the CPU 82 reads, captures, prepares and manages the image data flow between image input sources such as the scanning system 76, or an online or a work station connection 90, and the printhead assemblies 32, 34. As such, the ESS or controller 80 is the main multi-tasking processor for operating and controlling all of the other machine subsystems and functions, including the air bearing sheet heater or pre-heater assembly 100 of the present disclosure.
In operation, image data for an image to be produced is sent to the controller 80 from either the scanning system 76 or via the online or work station connection 90 for processing and output to the printhead assemblies 32, 34. Additionally, the controller determines and/or accepts related subsystem and component controls, for example from operator inputs via the user interface 86, and accordingly executes such controls. As a result, appropriate color solid forms of phase change ink are melted and delivered to the printhead assemblies. Additionally, pixel placement control is exercised relative to the imaging surface 14 thus forming desired images per such image data, and receiving substrates are supplied by anyone of the sources 42, 44, 46, 48 and handled by means 50 in timed registration with image formation on the surface 14. Finally, the image is transferred from the surface 14 and fixedly fused to the copy sheet within the transfix nip 18.
Referring now to
As illustrated in
In accordance with the present disclosure, the air bearing sheet heater assembly 100 further includes an air bearing assembly 140 that is mounted to the at least one platelet 120A, 120B, 120C, 120D for creating an air bearing or thin film 150 of pressurized air between the second side and the first side of the sheet path 116 as illustrated in
As illustrated, the air bearing assembly 140 includes (a) a source 142 of pressurized air for producing and supplying pressurized air 143; (b) an air conduit assembly connecting the source 142 of pressurized air to the sheet path 116 portion through the air bearing sheet heater assembly 100; (c) a hole or port 127 formed through the at least one movable platelet 120A, 120B, 120C, 120D from the back surface 122 to, and through, the front surface 124 into the sheet path 116 portion; and (d) air flow control or regulating means 147, such as a voltage means or an air pressure regulator, for regulating at least a pressure of air 143 flowing through the conduit assembly into the sheet path 116 portion. In an embodiment thereof, the source 142 of pressurized air comprises a positive displacement pump.
Referring in particular to
Thus the air conduit assembly for each platelet 120A, 120B, 120C, 120D includes a flexible air tube 144 and a nozzle 149 sealingly connecting the flexible tube 144 through the air port or hole 127 in the at least one movable platelet 120A, 120B, 120C, 120D. Pressurized air 143 supplied into the sheet path 116 portion is vented to and through mainly an entrance opening E1 and an exit opening E2 of the sheet portion. Some such air is also vented through the gaps G1 between adjacent platelets.
Thus in accordance with the present disclosure, the air bearing sheet heater or pre-heater assembly 100 is capable creating an air bearing 150 between the heater plate 110, or sheet (when being fed), and the movable platelets 120. The pressurized air 143 is pumped into the sheet path 116 through the air port 127 near the center of each movable platelet 120A, 120B, 120C, 120D to create an air pressure of about 2.8 in-H2O (0.1 PSIG) between the heater plate 110 and such platelet. This is because the front surface 124 of each such platelet 120A, 120B, 120C, 120D is relatively flat, is impervious to air, and covers a significant distance in every direction from the air port 127 to its edges where the pressurized air is able to escape. The weight of each platelet 120A, 120B, 120C, 120D as mounted above the heater plate 110 is determined such that the about 2.8 in-H2O (0.1 PSIG) air pressure is sufficient to counter and overcome the weight of the platelet with fairly low volume flow rates of air.
As pointed out above, the pressurized air source for example is a positive displacement pump, and includes conventional means 147 for regulating the airflow and air pressure and comprise voltage regulators and valves. An air heater 141 may be included for separately warming the pressurized air being used, however, it has been found that the heat capacity of the air is relatively small in comparison to the total heat transfer rate of the heater, so that the air bearing 150 does not significantly impact thermal performance of the heater.
As shown, the platelets or platelet arrays are mounted above the heater plate 110, and each platelet 120A, 120B, 120C, 120D ordinarily (when the air bearing is not in operation) rests gravitationally on the portion of the heater plate below it. However, as illustrated in
When a sheet 49 is being fed through the sheet path 116 over the front side 112 of the heater plate, the thin film 150 of pressurized air 143 instead forms between the back or upper side of the sheet 49 and the front surface 124 of each platelet, and there acts as a fluid or air bearing 150 between the platelet and the sheet. It has been found that the air bearing 150 results in a much lower coefficient of friction between the sheet and the platelet. The reduced friction was found to be even more significant between the platelets and previously inked upper sides of sheets than blank sides of sheets. It was also found that the air gap and air bearing between the platelets and the heater plate completely eliminated stiction between the two, greatly improving sheet feed reliability.
Platelets are made of Aluminum, for example anodized or Nickel plated aluminum. Each sheet enters the preheater at ambient temperature of about 30° C., and exits at a temperature of about 60° C. It has also been found that the temperature of sheets exiting the heater assembly 100 at a given set point was slightly lower with unheated air turned on (as expected), than with such air off. However, the sheet temperature ranges (across and down the page), were equivalent with and without such air. It was further found that sheet stubbing and jam performance were also significantly improved by turning on the air bearing. For example, without the air bearing, the jam rate was 70% at 0.5 m/s, but with the air bearing, the jam rate was 0.0%.
As can be seen, there has been provided an air bearing sheet heater assembly for heating a sheet in an ink imaging printer that includes (a) a heater plate including a heating element, and having a front side defining a first side of a sheet path through the heater assembly; (b) at least one movable platelet having a back surface 122, and an opposite front surface 124 facing the heater plate and defining a second side of the sheet path; and (c) an air bearing assembly mounted to the at least one platelet for creating an air bearing between the second side and the first side of the sheet path by pneumatically spacing the front surface 124 of the at least one movable platelet from the front side of the heater plate, thereby reducing stiction forces and friction along the sheet path through The air bearing sheet heater assembly.
Accordingly, the spirit and broad scope of the appended claims is intended to embrace all such changes, modifications and variations that may occur to one of skill in the art upon a reading of the disclosure. All patent applications, patents and other publications cited herein are incorporated by reference in their pertinent part.
