Patent Application
20060120738
The present invention relates to a system and method of preventing image transfer or “offsetting” between sheets of media such as plastic substrate or similar unconventional media with a layer of plastic on the outer surface such as transparencies or labels, in the output bin of a printing device. More particularly, the present invention relates to a system and method of limiting the amount and rate of energy accumulation in a stack of media by allowing more cooling time in the output bin of a printing device by controlling a combination of factors, which may include fuser temperature, media process speed and interval time between copies. This provides a lower temperature of the media stack as a whole and/or lower temperatures between the interface of, e.g., two transparencies as they are stacked. The lower temperature achieved may therefore be, e.g., below that temperature in which bonding can occur between media, e.g. plastic films on the backside of one transparency and the printer toner on the frontside of another transparency.
Image forming apparatus and devices such as a copying machine, a printer or a facsimile machine may use an electrophotographic system to heat and fuse a developer image that has been transferred from an image bearing body to a sheet of media, such as paper or a transparency resin sheet, and “fix” the image to a surface of the sheet. The transferring body may comprise nip rolls or a belt assembly. These devices preferably operate at high speeds to produce multiple copies rapidly. In doing so, a significant amount of heat energy is transferred to the sheet media as the fuser for the toner being transferred may operate in the range of about 130° C. to about 220° C. depending on the media transit speed and the nature of toner being transferred. The result is an accumulation of heat energy in the output bin of the apparatus as the media sheets are stacked.
With transparency media, which may be comprised of one or more layers of thermoplastic in sheet form, more heat is absorbed than plain paper. The higher thermal capacitance of transparencies may: (a) allow more energy to be “piled” into a stack of transparencies in the output bin; and/or (b) make an abnormally high temperature interface even between only two transparencies printed.
A problem in image quality may arise as multiple transparencies stack up in the printer output bin, as the heat from the fuser process accumulates and may cause the transferred toner to become “sticky” and adhere somewhat to the backside of the previous transparency which it rests against in the stack. Also, with the high thermal capacitance of transparencies even two sheets printed alone may be very hot when touching each other in the output bin. This may result in a residual image (offset) that appears on the backside of the earlier-copied sheet and/or voided areas in the toner image printed on the front side of the more recently copied sheet.
What is therefore needed is a process and a system that can adjust media variables such as process speed and fuser temperature to limit the rate of energy accumulated and allow more cooling time in a stack of media, e.g. transparencies, to below an energy/temperature threshold level and which will provide adequate fusing of the toner yet substantially prevent residual image transfer or “offsetting”.
What is also needed is a control algorithm which upon recognition of the type of media being processed initiates a process protocol to effectively control the accumulation of heat in the output bin or other collection location or will allow sufficient time or pause between as little as two media sheets, e.g. transparencies, such that a targeted interface temperature is not exceeded and bonding between the plastic film and toner does not occur in the stack.
It is thus an object of the present invention to provide a system and method of limiting the amount of media energy accumulated, or pausing sufficiently (e.g., increase in interpage gaps or even slow down of the rate of media transport) to allow cooling between the sheet-to-sheet interface of 2 or more media sheets in a stack output bin of a printer or like device.
It is a further object of the present invention to provide a control algorithm for controlling the heat accumulated in a stack of printed transparencies below a critical threshold level such that offsetting is substantially prevented.
It is further object of the present invention to provide a system and a method to reduce the rate of energy accumulated in a stack, or allow more time between even two printed sheets such as printed transparencies by, among other things, reducing the process speed of the media moving through the printing apparatus optionally in concert with reducing the fuser temperature when, e.g., transparencies are printed, to provide more cooling time yet still provide adequate fusing of the toner.
It is a still further object of the present invention to include an interval or pause time in the printing sequence as another technique of adjusting media throughput to prevent accumulation of energy in the output bin from exceeding a critical threshold value and to allow the energy accumulated in the output bin to dissipate.
These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show an embodiment in accordance with the present invention.
The present invention is directed at a system and method of controlling print quality on media by controlling the amount of energy accumulated in the output bin or collection device of the printer device and substantially preventing “offsetting”.
In one embodiment, the present invention relates to a method of controlling the accumulation of heat in stacked sheets of media in a printing or copying device, the device having a collection location for collection of a plurality of media sheets, wherein the sheets of media include toner images, and a fixing device to fix the toner images on said media at a selected temperature. The method includes the steps of providing in the printing or copying device a control system wherein the control system identifies media for printing or copying at a selected fuser temperature and adjusts the fuser temperature for selected media. The controller may then assign a rate of movement of media in the printing or copying device for selected media such that the accumulation of heat in a plurality of sheets of media is controlled not to exceed a condition where the toner on the plurality of sheets of media at the collection location will transfer as between said sheets.
In another embodiment, the present invention relates to a method of controlling the accumulation of heat in stacked sheets of media in a printing or copying device, the device having a collection location for collection of a plurality of media sheets and wherein the sheets of media include toner images, and a fixing device to fix said toner images on the media at a selected temperature. The method includes the steps of providing in the printing or copying device a control system wherein the control system identifies media for printing or copying at a selected fuser temperature and lowers said fuser temperature for selected media and sets a throughput rate based on said media type. The control system then may assign a rate of movement of media in the printing or copying device for selected media relative to the set throughput rate such that the accumulation of heat in a plurality of sheets of said media is controlled not to exceed a condition where said toner on the plurality of sheets of media at the collection location will transfer as between said sheets.
In another embodiment, the present invention relates to a method of controlling the accumulation of heat in stacked sheets of media in a printing or copying device, the device having a collection location for collection of a plurality of media sheets wherein the sheets of media include toner images. The method includes the steps of identifying a temperature where the toner on a plurality of sheets of media at the collection location will transfer as between the sheets and monitoring a temperature of said plurality of sheets at said collection location. The method then includes incorporating in the printing or copying device a control system wherein the control system assigns a rate of movement of media in the printing or copying device such that the accumulation of heat in a plurality of sheets of the media at the collection location is controlled not to exceed the temperature where the toner on said plurality of sheets of media will transfer as between said sheets.
In another embodiment, the present invention relates to a method of controlling the accumulation of heat in stacked sheets of media in a printing or copying device, the device having a collection location for collection of a plurality of media sheets, wherein the sheets of media include toner images, and a fixing device to fix toner images on the media at a selected temperature. The method includes the steps of providing in the printing or copying device a control system wherein said control system identifies media for printing or copying at a selected fuser temperature. The control system may then assign a rate of movement of media in the printing or copying device for selected media such that the accumulation of heat in a plurality of sheets of said media at the collection location is controlled not to exceed a condition where said toner on the sheets of media will transfer as between said sheets.
In another embodiment, the present invention relates to a system for controlling the accumulation of heat in a plurality of sheets of media in a printing or copying device, wherein the sheets of media include toner images, and a fixing device to fix the toner images on the media at a selected temperature. The device also has a collection location for collection of one or a plurality of media sheets. The device includes a controller which is capable of setting a throughput rate and fuser temperature for the media based upon the media type, and which controller identifies a maximum sheet count for the media. The controller is also capable of identifying whether or not the printer or copying device has output a number of media sheets equal to the maximum media sheet count, at which point the controller is capable of assigning a rate of movement of media in the printing or copying device for selected media. This assignment is such that the accumulation of heat in a plurality of sheets of media at the collection location is controlled not to exceed a condition where toner will substantially transfer as between the sheets.
Printing or copying an image onto a substrate such as high thermal capacitance media, such as a transparent resin sheet, is typically accomplished by fixing a loose powder toner using heat onto the surface of the media in an electrophotographic process. In electrophotography, a latent image is created on the surface of an insulating, photoconducting material by selectively exposing an area of the surface to light. A difference in electrostatic density is created between the areas on the surface exposed and those unexposed to the light. The latent electrostatic image is developed into a visible image by electrostatic toners which contain pigment components and thermoplastic components. The toners, which may be liquids or powders, are selectively attracted to the photoconductor's surface, and either exposed or unexposed to light, depending upon the relative electrostatic charges on the surfaces of the photoconductor, the development electrode and the toner. The photoconductor may be either positively or negatively charged, and the toner system similarly may contain negatively or positively charged particles.
A sheet of paper or intermediate transfer medium is given an electrostatic charge opposite that of the toner and then passed close to the photoconductor's surface, pulling the toner from the photoconductor's surface onto the paper or intermediate medium in the pattern of the image developed from the photoconductor's surface. A set of fuser rolls or belts, under heat, melts and fixes the toner to the paper or medium surface subsequent to transfer, producing the printed image.
After the image is transferred to the paper or other recording medium, it goes to the fuser where the medium is moved through a nip where it is heated and pressed. This melts the thermoplastic portion of the toner, causing it to bond to the medium, thereby fixing the image onto the surface.
The process of fixing the image therefore involves coalescing and binding the toner image to a plastic or paper substrate or other media. For transparencies, the plastic substrate may be a polyester, polyamide, ionomer or other resin, or combinations or laminates thereof. In the case of labels, the labels may comprise a paper or plastic substrate with a polymer film coating. A fuser system typically supplies the heat to the toner. The fuser system may employ two rollers in nip relation through which the media sheet or transparency passes for fusing. Heat may be provided by a halogen lamp placed inside one or both of the rolls. Alternatively, the fuser may be a belt fuser employing a polyimide or metal belt wrapped over a ceramic or other low thermal capacity heater. The belt is typically pressed against a silicon-coated backup roll to form a nip.
A representative electrophotographic device, suitable for use in the present invention, is shown in
The media feed section (10) includes a feed tray (11), a feed roller (12), a paper separating friction plate (13), a pressure spring (14), a media detection actuator (15), a media detection sensor (16), and a control circuit (17).
Upon receiving a print instruction, the sheets of recording media (1) placed in the media feed tray 11 (or in the case of the present invention, transparent resin sheets or any similar media with relatively high thermal capacitance as compared to paper) may be fed one-by-one into the printer by operation of the printer feed roller (12), the media separating friction plate (13) and the pressure spring (14). As the fed sheet of recording media (1) pushes down the media detection actuator (15), the media detection sensor (16) outputs an electrical signal instructing commencement of printing of the image. The control circuit (17), initiated by operation of the paper detection actuator (15) transmits an image signal to a laser diode light-emitting unit (31) of the laser scanning section (30) so as to control on/off of the light-emitting diode.
The laser scanning section (30) may include the laser diode light-emitting unit (31), a scanning mirror (32), a scanning mirror motor (33), and reflecting mirrors (35, 36 and 37). The scanning mirror (32) may be rotated at a constant high speed by the scanning mirror motor (33). In other words, laser light (34) scans in a vertical direction to the paper surface of
The image-forming device (20) includes the photosensitive body (21), a transfer roller (22), a charging member (23), a developing roller (24), a developing unit (25), and a cleaning unit (26). The surface charge of the photosensitive body (21), charged in advance by the charging member (23), is selectively discharged by the laser light (34). An electrostatic latent image is thus formed on the surface of the photosensitive body (21). The electrostatic latent image is visualized by the developing roller (24), and the developing unit (25). Specifically, the toner supplied from the developing unit (25) is adhered to the electrostatic latent image on the photosensitive body (21) by the developing roller (24) so as to form the toner image.
Toner used for development is stored in the developing unit (25). The toner contains coloring components (such as carbon black for black toner) and thermoplastic components. The toner, charged by being appropriately stirred in the developing unit (25), adheres to the above-mentioned electrostatic latent image by an interaction of the developing bias voltage applied to the developing roller (24) and an electric field generated by the surface potential of the photosensitive body (21), and thus conforms to the latent image, forming a visual image on the photosensitive body (21). The toner typically has a negative charge when it is applied to the latent image, forming the visual image.
Next, the sheet of recording media (1) transported from the feed section (10) is transported downstream while being pinched by the photosensitive body (21) and the transfer roller (22). The media (1) arrives at the transfer nip in timed coordination with the toned image on the photosensitive body (21). As the sheet of recording media (1) is transported downstream, the toner image formed on the photosensitive body (21) is electrically attracted and transferred to the sheet of recording media (1) by an interaction with the electrostatic field generated by the transfer voltage applied to the transfer roller (22). Any toner that still remains on the photosensitive body (21), not having been transferred to the sheet of recording media (1), is collected by the cleaning unit (26).
Thereafter, the sheet of recording media (1) is transported to the fixing device (50). In the fixing device (50), an appropriate temperature and pressure are applied while the sheet of recording media (1) is being pinched by moving through the nip formed by a pressure roller (51) and the fixing roller or belt (52) that is maintained at an elevated temperature. The thermoplastic components of the toner are melted by the fixing roller (52) and fixed to the sheet of recording media (1) to form a stable image. The sheet of recording media (1) is then transported and ejected out of the printer by the printer transport rollers (41, 42) and into the output bin (60) where it may be stacked, one sheet (referenced as 1′) of media upon another.
The fixing belt on the fixing roller is generally an endless belt or tube formed from a low thermal mass and durable material having good parting properties and preferably a thickness of not more than about 100 μm, more preferably not more than about 70 μm. Preferred belts are made from a polyimide film. The belt may have an outer coating of, for example, a fluororesin or Teflon® material to optimize release properties of the fixed toner from the belt. Such fuser belts are well-known in the art.
A heater (54), generally a ceramic heater, is placed on the inside surface of the belt and the outside surface of the belt forms a fusing nip with the back-up roller (51) at the location of the heater. Put another way, the heater (54) and the back-up roller (51) form the nip, with the fuser belt (52) interposed between them. Each sheet carrying the toner travels through this nip [i.e., between the fuser belt (52) and the back-up roller (51)] and the toner is fixed on the sheet through the combination of applied heat, the time the page is in the fuser nip, and pressure. Typically, the pressure between the fuser belt (52) and the back-up roller (51) at the fuser nip is from about 5 to about 30 psi. While the fuser belt (52) may be driven itself, often this is not the case. Generally, the back-up roller (51) is rotated and it is the friction between the surface of the back-up roller (51), and the printed sheet and ultimately the surface of the fuser belt (52), which causes the fuser belt (52) to rotate.
The backup or pressure roller (51) is generally cylindrical in shape. It is made from or is coated with a material that has good release and transport properties for the recording media (1). The backup roller (51) is sufficiently soft so as to allow it to be rotated against the fuser belt (52) to form a nip through which the printed sheets travel. By going through this nip, printed sheets are placed under pressure and the combined effects of this pressure, the time the sheet is in the nip, and the heat from the fuser belt (52) acts to fix the toner onto the media. A preferred material for use in forming the backup roller (51) is silicone rubber. The roller typically has an aluminum core with a silicone rubber layer molded or adhesively bonded onto its surface. This roller may also have a fluoropolymer (e.g., Teflon®) sleeve or coating. The backup roller may be essentially hollow, having a metallic core, an outer metallic shell surrounding and essentially concentric with the core, and ribs between the core and the outer shell.
With heat from the fuser system heater (54) being transferred to each sheet of media, as successive copies are printed, the sheets of media (1′) stack up in the output bin 60 and the heat of fusing is accumulated. With two or more sheets stacked together, where such sheets have relatively high thermal capacitance, the toner may become sticky, or begin to remelt, and may transfer, at least partially, to an overlying sheet in the stack. The result is often reduced quality of the printed image as a residual image (offset) may be formed on the backside of the overlying sheet and corresponding toner “voids” created in the printed image of the underlying sheet in the stack. The present invention addresses such accumulation of heat and potential for offset as noted above, by identifying and controlling one or more of the process parameters which cause such problem to occur.
A preferred embodiment of the present invention is illustrated in the flow chart given in
Accordingly, in the broad context of the present invention, is has been found that transparencies with toner will stick to one another when above a certain temperature threshold limit when stacked in the output bin of a printer or copier. It has been found that, e.g., stacked transparencies, made from polyester, polyamide, ionomer or other resins, with toner which are at or above a temperature of about 100-105° C., will tend to attach to one another when removed from the output bin due to sticking of the toner between transparency sheets. Therefore, in a particularly preferred embodiment, the present invention recognizes that for toner that has a melting temperature Tm (toner), the temperature of the transparencies in the output bin may be regulated such that they avoid approaching within about 10-15° C. of a toner thermal softening transition, such as Tm (toner) and/or exceeding Tm (toner). The Tm of toner may be about 100-110° C.
Exemplary system operation in accordance with the present invention, as shown in
To initiate printing, the printer controller determines at decision point 82 whether the media type is a transparency or other media (paper, etc.). In the broad context of the present invention, the detection of whether the media may be a transparency can be accomplished by manually inputting such information to the printer or copier, and or providing an automatic detection means to determine whether or not the media is, e,g., a paper or plastic transparency.
If the decision is no, that the media is not a transparency, the controller at action 84 clears the transparency counter. If the decision is yes, that the media is indeed a transparency, the controller at action 86 increases the transparency count by one unit. At 88 the system then monitors whether or not the transparency count is less than a selected maximum amount that was determined to provide a heat build-up in the output bin for a given printer or copier output bin. In such regard, it has been found that offset and sticking of toner on stacked transparencies may occur in certain printers when only as few as 2-3 transparencies are stacked in the output bin after printing at a rated speed.
In such regard, attention is directed to
Returning then to
If the decision is that the count equals the predetermined maximum allowable count, then action 90 sets a pause for the transparency stack cooling flag. For instance, the device may then be rendered inoperable for about 30 seconds or other appropriate time period to allow the heat to dissipate from the stack. If the decision is yes, (that is the count is less) then action 92 is to send a “print ready” to the raster image processor (RIP) and printing will proceed.
Expanding upon the above, it should be noted that in the case of the exemplary transparency printing rate of 16 pages per minute, the rate can be further reduced by one of several options to reduce such rate to, e.g., about 8 pages per minute, which would represent a reduction of 50%. For example, while the rate can be reduced by implementing a complete pause command to the system, it can be appreciated that the rate of transport of the media can itself be reduced, or optionally, the gap time (GT) between printing successive sheets of media can be increased. Accordingly, the rate of movement of media may be reduced 5-500%, and all incremental values therebetween, by any one or more of such optional procedures.
In the event that the number of transparencies is fewer than a predetermined maximum, the printer completes the printing of the transparencies while remaining under the predetermined maximum amount. Then, at decision 94 the printer controller determines whether there is a new print request, and if yes, the action is to repeat the above described process by again determining the type of media (action 76), etc.
Alternatively, as alluded to above, if the decision at 88 is no, and the system invokes a pause, the print engine goes to standby as indicated at 96. As shown in
At 104 the system checks whether the transparency stack cooling timer has indeed finally reached an appropriate pause time for the transparencies to cool so that printing may continue without offset. If the system has paused for a sufficient time to cool, the system will then clear the transparency stack cooling timer at 106, clear the transparency counter at 108, and check the status for the presence of a pause on the transparency stack cooling flag. If yes, the system sends a print ready to the RIP and clears the pause for the transparency stack cooling flag and then checks whether the power saver timeout has expired as shown at 116. Alternatively, if no, the system directly checks whether the power saver timeout has expired, again at 116.
Turning then to 116, if the power saver timeout has expired, the system proceeds to power saver mode at 118 it repeats blocks 106-114 noted above followed by decision 122 as to whether to not there is a new print request. If no, the system keeps checking for the presence of a new print request. If there is a new print request, the system directs back up to set the throughput rate based on media type at 76, etc. Alternatively, if the power saver timeout has not expired, the system monitors for a new print request at 124, and if yes, proceeds back to 76, etc., and if no, proceeds to 98, etc.
In this manner, the device is controlled via the algorithm, as shown in
It should also be appreciated that the functionality described herein for the embodiments of the present invention may be implemented by using hardware, software, or a combination of hardware and software, either within the printer or copier or outside the printer copier, as desired. If implemented by software, a processor and a machine readable medium are required. The processor may be of any type of processor capable of providing the speed and functionality required by the embodiments of the invention. Machine-readable memory include any media capable of storing instructions adapted to be executed by a processor. Some examples of such memory include, but are not limited to, read-only memory (ROM), random-access memory (RAM), programmable ROM (PROM), erasable programmable ROM (EPROM), electronically erasable programmable ROM (EEPROM), dynamic RAM (DRAM), magnetic disk (e.g., floppy disk and hard drive), optical disk (e.g. CD-ROM), and any other device that can store digital information. The instructions may be stored on medium in either a compressed and/or encrypted format. Accordingly, in the broad context of the present invention, and with attention to
It will be appreciated that any specific values given herein are illustrative with regard to the limits of this invention. As those of skill in the art will appreciate, operation involves interaction of, e.g., heating and cooling of media which may vary in characteristics, and final values may be readily obtained experimentally and may vary depending on all the physical factors of a particular printing or copying device. The illustrations shown in the present application are therefore only intended to be illustrative of the present invention and not limiting thereof. The full scope of the present invention is defined by the following claims and equivalents thereof.
