Patent Publication Number: US-8538285-B2

Title: Printer and fusing system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application relates to commonly assigned, copending U.S. application Ser. No. 12/768,824, filed Apr. 28, 2010, entitled: “PRINTER AND FUSING METHOD”) hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     This invention relates to methods and appparatii that are used to appropriately fuse electrophotographic toner. 
     BACKGROUND OF THE INVENTION 
     In conventional electrophotography, it is known to imagewise apply toner particles in piles on a receiver to form a toner image. The toner image is the fused to form a permanent image that is bound to the receiver. In color electrophotography, fusing is also used to enable two or more colors of toner to mix to form a combination color. Accordingly, proper fusing of electrophotographic toner is essential to the formation of high quality electrophotographic images. 
     While other types of fusing exist, such as those that involve the use of solvents or pressure differentials, fusing is typically achieved by heating the toner in a toner image to a temperature that is higher than a glass transition temperature of the toner. There are several key variables that impact the effectiveness of such thermal toner fusing. These include the rate at which energy can be supplied by all sources to heat the toner during fusing, the amount of exposure time during which the energy can be applied for the purpose of fusing, the rate at which the energy can be absorbed and transferred by a given unit of the thickness of toner without causing damage to the toner, the toner piles formed on the receiver, and the amount of ambient pressure applied to the toner pile during exposure. 
     These variables can be combined in a variety of ways to achieve a fusing solution. One variable that is generally held fixed in determining a fusing solution is the stack height of the toner pile on the receiver. Typically, the stack height is controlled to be within a predefined range. This reduces the cost of images printed using the toner and also reduces the number of variables that must be managed when determining a fusing solution. Further, the use of relatively consistent toner pile thickness across a toner image allows all of the other fusing variables to be set once and maintained at a steady state. Typically toner stack heights are maintained in a range of less than about 20 μm. 
     Various conventional technologies are known that are adapted to thermally fused toner piles that have such managed stack heights. In one example of contact fusing, known as hot roller fusing, a receiver having a toner image applied thereto is passed between a nip and a heated roller or belt. Heat and pressure are applied to the toner image and receiver causing the toner to heat to a temperature at or above the glass transition temperature of the toner. U.S. Pat. No. 6,577,840, entitled “Method and Apparatus for Image Forming Capable of Effectively Performing an Image Fixing Process”, issued to Hachisuka et al. on Jun. 10, 2003 shows one example of a heated roller type fuser while U.S. Pat. No. 7,630,677, entitled “Image Heating Apparatus”, issued to Osada et al. on Dec. 8, 2009 shows one example of heated belt fuser. 
     Similarly, various forms of non-contact fusing are known that can cause a toner to be heated. U.S. Pat. No. 7,630,674 entitled “Method and Arrangement for Fusing Toner Images to a Printing Material” shows one example of this. 
     Combinations of contact fusing and non-contact fusing are also known. For example, U.S. Pat. No. 6,909,871 entitled “Method and Device for Fusing Toner Onto a Substrate” shows a combination of microwave and pressure roller heating to achieve a fusing solution to allow fusing to occur in during abbreviated exposure times in order to enable high rates of printing. 
     Recently, it has become popular to provide toner images having portions with high toner stack heights such as those that include for example and without limitation stack heights that are on the order of 50 μm to 500 μm. An advantage of such high toner stack heights is that they can be used to form projections from a surface of an image that can impart a three dimensional look and/or feel to an image. This extra dimension, is provided by a contrast in toner stack heights which can range from a conventional stack height to, as noted above, stack heights of up to 500 μm. 
     Conventional fusing technologies however are not easily applied to the purpose of fusing toner images having toner piles that have high toner stack heights. In part, this is because the rate at which thermal energy can be transferred to and into a unit of toner is such that only a conventional toner pile thickness can be fully fused during a fusing operation that is performed at desirable and commercially profitable commercial printing speeds. In part this is also because of the extent of the variability in toner stack heights within the toner image. 
     This problem is not easily solved in general and in particular where fusing is to be performed at production speeds. If insufficient energy is applied during the short time periods allotted for fusing at high production speeds, incomplete fusing can occur. Incomplete fusing can cause mechanical defects to arise in the printed images such as incomplete bonding of the toner pile to the receiver. This can lead to full or partial separation of the toner pile from the receiver resulting in an unacceptable image. Similarly, incomplete fusing can introduce weaknesses in the resultant toner pile such as pockets of unfused dry toner that can cause fracture of the toner itself, color mixing problems, gloss variations or partial separation of the toner powder from the receiver. 
     However, markedly increasing the amount of energy applied during a fusing step creates other problems in image formation. For example, as is described in commonly assigned U.S. Pat. Pub. No. 2009/014948 entitled “Enhanced Fuser Offset Latitude Method” filed by Cahill et al., on Dec. 18, 2007 using high temperatures for example on a roller type fuser can cause image artifacts. Such artifacts occur when toner that is in contact with a hot roller transitions to a glass transition temperature of the toner before toner that is closer to the receiver makes this transition. This can cause a portion of the toner to adhere to and contaminate the heated roller or other rollers associated with a fuser and can cause a variety of unwanted artifacts in an image. Similarly, as noted in the &#39;671 patent, in non-contact fusing such as microwave increased energy can create artifacts such as blister formation of the toner on the receiver. 
     For these reasons, a fusing solution must be managed so that sufficient energy is transferred to a toner during a fusing process to allow fusing to occur and so that the artifacts created by applying too much energy during a short period of are not created. 
     It will be appreciated that reaching such a solution is made more difficult by the increased energy load that must be delivered to heat a thick toner pile to ensure full fusing during the short fusing process allowed during printing. It will also be appreciated that there are inherent limitations on the rate at which toner can transfer energy through a toner pile without creating the aforementioned hot offset problems. 
     What is needed is a system that can thoroughly fuse toner images having toner piles with toner stack heights that are greater than about 50 μm. 
     SUMMARY OF THE INVENTION 
     A system and printer are provided for fusing toner on a receiver medium having a toner pile that extends at least about 50 μm above a receiver. In one aspect, a system has a first energy source to apply a first energy to raise a temperature of a first portion of the toner pile to a range of elevated temperature levels below a glass transition temperature of the toner and a second energy source to apply a second energy to raise a temperature of a second portion of the toner pile above the glass transition temperature and to allow the second portion to transfer energy to the first portion. The second energy is provided at a level that allows the transferred energy to raise the temperature of the first portion from the range of elevated levels to a range of temperatures above the glass 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a system level illustration of one embodiment of an electrophotographic printer; 
         FIG. 2  is a view of one embodiment of a fuser during a fusing operation; 
         FIG. 3  shows a flow diagram for one embodiment of a method for printing and fusing; 
         FIG. 4  is an elevational cross section view of a segment of a high stack height toner pile; 
         FIG. 5  is a view of the embodiment of  FIG. 2  during a fusing operation; 
         FIG. 6  shows a flow diagram for an embodiment of a method for printing and fusing; 
         FIG. 7  shows a view of an embodiment of a fuser; 
         FIG. 8  shows a view of an embodiment of a fuser and; 
         FIG. 9  shows another embodiment of a method for fusing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a system level illustration of an electrophotographic printer  20 . In the embodiment of  FIG. 1 , electrophotographic printer  20  has an electrophotographic print engine  22  that deposits toner  24  to form a toner image  25  in the form of a patterned arrangement of toner stacks. The toner image can include any patternwise application of toner  24  and can be mapped according data representing text, graphics, photo, and other types of visual content, as well as patterns that are determined based upon desirable structural or functional arrangements of the applied toner  24 . 
     Toner  24  is a material or mixture that contains toner particles, and that can form an image, pattern, or coating when electrostatically deposited on an imaging member including a photoreceptor, photoconductor, electrostatically-charged, or magnetic surface. As used herein, “toner particles” are the marking particles used in an electrophotographic print engine  22  to convert an electrostatic latent image into a visible image. Toner particles can also include clear particles that can provide for example a protective layer on an image or that impart a tactile feel to the printed image. 
     Toner particles can have a range of diameters, e.g. less than 8 μM, on the order of 10-15 μm, up to approximately 30 μm, or larger. When referring to particles of toner  24 , the toner size or diameter is defined in terms of the median volume weighted diameter as measured by conventional diameter measuring devices such as a Coulter Multisizer, sold by Coulter, Inc. The volume weighted diameter is the sum of the mass of each toner particle multiplied by the diameter of a spherical particle of equal mass and density, divided by the total particle mass. Toner  24  is also referred to in the art as marking particles or dry ink. 
     Typically, receiver  26  takes the form of paper, film, fabric, metalicized or metallic sheets or webs. However, receiver  26  can take any number of forms and can comprise, in general, any article or structure that can be moved relative to print engine  22  and processed as described herein. 
     Returning again to  FIG. 1 , print engine  22  can be used to deposit one or more applications of toner  24  to form toner image  25  on receiver  26 . A toner image  25  formed from a single application of toner  24  can, for example, provide a monochrome image. 
     A toner image  25  formed from more than one application of toner  24 , (also known as a multi-part image) can be used for a variety of purposes, the most common of which is to provide toner images  25  with more than one color. For example, in a four toner image, four toners having subtractive primary colors, cyan, magenta, yellow, and black, can be combined to form a representative spectrum of colors. Similarly, in a five toner image various combinations of any of five differently colored toners can be combined to form other colors on receiver  26  at various locations on receiver  26 . That is, any of the five colors of toner  24  can be combined with toner  24  of one or more of the other colors at a particular location on receiver  26  to form a color different than the colors of the toners  24  combined at that location. 
     In the embodiment that is illustrated, a primary imaging member (not shown) such as a photoreceptor is initially charged. An electrostatic latent image is formed by image-wise exposing the primary imaging member using known methods such as optical exposure, an LED array, or a laser scanner. The electrostatic latent image is developed into a visible image by bringing the primary imaging member into close proximity to a development station that contains toner  24 . The toned image on the primary imaging member is then transferred to receiver  26 , generally by pressing receiver  26  against the primary imaging member while subjecting the toner to an electrostatic field that urges the toner to receiver  26 . The toner image  25  is then fixed to receiver  26  by fusing. 
     In the embodiment of  FIG. 1 , print engine  22  is illustrated as having an optional arrangement of five printing modules  40 ,  42 ,  44 ,  46 , and  48 , also known as electrophotographic imaging subsystems arranged along a length of receiver transport  28 . Each printing module delivers a single application of toner  24  to a respective transfer subsystem  50  in accordance with a desired pattern as receiver  26  is moved by receiver transport  28 . Receiver transport  28  comprises a movable surface  30 , positions that moves receiver  26  relative to printing modules  40 ,  42 ,  44 ,  46 , and  48 . Surface  30  comprises an endless belt that is moved by motor  36 , that is supported by rollers  38 , and that is cleaned by a cleaning mechanism  52 . 
     After toner image  25  is formed on receiver  26 , receiver  26  is moved by receiver transport  28  to fuser  60 .  FIG. 2  shows one embodiment of fuser  60 . In this embodiment, fuser  60  comprises a fuser receiver transport  62  that carries toner image  25  and receiver  26  past a first energy source  64  that provides, a first energy  66  that heats a first portion  68  of a toner pile  70  on receiver  26  and a second energy source  72  that provides a second energy  74  that heats a second portion  76  of toner pile  70 . 
     First energy source  64  can comprise any known energy source that can convey a first energy  66  to cause a first portion  68  of toner pile  70  to be heated above an initial temperature range. In the embodiment shown in  FIG. 2 , first energy source  64  is illustrated in the example form of a microwave heater that applies first energy  66  by providing microwave energy that heats receiver  26  such that receiver  26  generates heat  78  that heats first portion  68  of toner pile  70 . In another example embodiment, first energy source  64  can comprise a heater that applies a first energy  66  in the form of heat that can be transferred by way of radiation, conduction, convection or any other known heat transfer mechanism into or within first portion  68 . 
     Second energy source  72  can comprise any known energy source that can convey a second energy  74  to cause a second portion  76  of toner pile  70  to be heated. In the embodiment shown in  FIG. 2 , second energy source  72  is illustrated in the example form of a heated roller  77  that cooperates with a support roller  79  and a pressure control system  80  to provide heat and pressure to transfer thermal energy directly to second portion  76  of toner pile  70 . Pressure control system  80  can comprise any mechanical structure that can provide an amount of pressure between heated roller  77  and support roller  79  when a toner pile  70  and receiver  26  are situated therebetween. In other embodiments, second energy source  72  can include but is not limited to a heater that generates heat that can be transferred for example by way of radiation, conduction, convection, or any other known heat transfer mechanism into or within second portion  76 . 
     In the embodiment of  FIG. 2 , an optional actuator  81  is provided that can cooperate with a embodiment of pressure control system  80  such as a spring tensioning system (not illustrated) to vary the amount of pressure applied between heated roller  77  and support roller  79 . 
     Referring again to  FIG. 1 , electrophotographic printer  20  is operated by a controller  82  that controls the operation of print engine  22  including but not limited to each of the respective printing modules  40 ,  42 ,  44 ,  46 , and  48 , receiver transport  28 , receiver supply  32 , transfer subsystem  50 , to form a toner image  25  on receiver  26  and to cause fuser  60  to fuse toner images  25  on receiver  26  in accordance with the methods claimed herein. 
     Controller  82  operates electrophotographic printer  20  based upon input signals from a user input system  84 , sensors  86 , a memory  88  and a communication system  90 . User input system  84  can comprise any form of transducer or other device capable of receiving an input from a user and converting this input into a form that can be used by controller  82 . For example, user input system  84  can comprise a touch screen input, a touch pad input, a 4-way switch, a 6-way switch, an 8-way switch, a stylus system, a trackball system, a joystick system, a voice recognition system, a gesture recognition system or other such systems. Sensors  86  can include contact, proximity, magnetic, or optical sensors and other sensors known in the art that can be used to detect conditions in electrophotographic printer  20  or in the environment-surrounding electrophotographic printer  20  and to convert this information into a form that can be used by controller  82  in governing printing and fusing. Memory  88  can comprise any form of conventionally known memory devices including but not limited to optical, magnetic or other movable media as well as semiconductor or other forms of electronic memory. Memory  88  can be fixed within electrophotographic printer  20 , removable from electrophotographic printer  20  at a port, memory card slot or other known means for temporarily connecting a memory  88  to an electronic device. Memory  88  can also be connected to electrophotographic printer  20  by way of a fixed data path or by way of communication system  90 . 
     Communication system  90  can comprise any form of circuit, system or transducer that can be used to send or receive signals to memory  88  or external devices  92  that are separate from or separable from direct connection with controller  82 . Communication system  90  can connect to external devices  92  by way of a wired or wireless connection. In certain embodiments, communication system  90  can comprise a circuitry that can communicate with such separate or separable device using a wired local area network or point to point connection such as an Ethernet connection. In certain embodiments, communication system  90  can alternatively or in combination provide wireless communication circuits for communication with separate or separable devices using a Wi-Fi or any other known wireless communication systems. Such systems can be networked or point to point communication. 
     External devices  92  can comprise any type of electronic system that can generate wireless signals bearing data that may be useful to controller  82  in operating electrophotographic printer  20 . For example and without limitation, an external device  92  can comprise what is known in the art as a digital front end (DFE), which is a computing device that can be used to provide images and or printing instructions to electrophotographic printer  20 . 
     An output system  94 , such as a display, is optionally provided and can be used by controller  82  to provide human perceptible signals for feedback, informational or other purposes. Such signals can take the form of visual, audio, tactile or other forms. 
       FIG. 3  shows a first embodiment of a method for operating electrophotographic printer  20  to print and fuse an image having a toner pile with a stack height above 50 microns. As is shown in the embodiment of  FIG. 3 , a printing process begins when controller  82  receives print order information including image data and optionally job instructions (step  100 ). The print order information can be supplied for example from memory  88 , communication system  90  or user input system  84 . The image data can be supplied in any known form including but not limited to a digital image. Similarly, the job instructions can take any form and can, for example, without limitation, take the form of instructions as to which media to use, finishing instructions, preferred toner materials and the like. In some circumstances, the print order information can be in the form of a digital image having print imager information in the form of image metadata. 
     Controller  82  then converts the print order information into printing instructions which are sent to print engine  22 , receiver transport  28 , receiver supply  32  and which cause toner  24  to be applied in various amounts and in particular locations to receiver  26  to yield, in combination, a superimposed image that corresponds to the image data for the image to be printed and the printing instructions (step  102 ). In some cases, this will require that controller  82  determines a set of color separation images and/or a clear toner image. In other cases, the digital image data provided to controller  82  can, for example, be provided from the color separation images that are generated by an external device  92  such as a computer known as a digital front end (DFE) and provided to electrophotographic printer  20  for example from memory  88  or communication system  90 . 
     Where one of the electrophotographic printing modules  40 ,  42 ,  44 ,  46 , or  48  has clear toner  24  available, controller  82  can provide instructions to the printing module having the clear toner available causing the printing module to deposit the clear toner  24  to form, for example, images having a uniform layer of clear toner material for protective, decorative, or to form various visual effects or that can be created by selective application of such a clear donor material. 
     In the embodiment illustrated in  FIG. 1 , fifth electrophotographic printing module  48  is provided with a clear toner (i.e. one lacking pigment) for application to receiver  26  and can be operated by controller  82  to form toner piles having stack heights that are greater than about 50 microns. In certain embodiments such clear toner  24  can comprise toner particles that have, for example, a diameter between 15 μm and 30 μm. In other embodiments the diameter of the particles in toner  24  can be for example between 20 μm and 30 μm. 
       FIG. 4  (not to scale) illustrates a cross section of a toner pile  70  to formed on receiver  26  during a single pass through the five modules, with printing module  48  apply clear toner  128  in a manner that creates high toner stack heights. In this illustration, five applications of toner  120 ,  122 ,  124 ,  126 , and  128  have been transferred, in registration to receiver  26  to form a five component image. Here, printing module  48  has applied a clear toner  128  to form a toner pile  70  having a toner stack height (T) for example on the order of 50 to 500 μm. The stack height T can be produced by selectively building up layer upon layer of toner  24  having particles of a standard general average mean volume weighted diameter of less than 9 μm, where for example each layer has a lay down coverage of 0.4 to 0.5 mg/cm 2 . 
     Alternatively, several layers of the standard size particles of toner  24  can be selectively covered by clear toner particles of a larger general average median volume weighted diameter of 12-30 μm. Here, the particles of toner  24  are clear (i.e., not pigmented) and have a lay down coverage of at least 2 mg/cm 2 . Using small marking particles for the non-raised image is preferred because it allows for high quality images even when the large clear particles are deposited on top. 
     The deposition of the clear toner can also be controlled by using a Fourier series to mathematically map the stack height of the toner piles forming toner image  25 . In this manner, controller  82  can generate the electrostatic latent image corresponding to the clear toner deposition by controlling the exposure, which is, itself, programmed to vary the exposure according to the Fourier series. 
     The high toner stack heights can be used, for example, to impart a background texture to an image, as described in U.S. Pat. No. 7,468,820, entitled “Profile Creation for Texture Simulation with Clear Toner” issued to Ng et al. on Dec. 23, 2008 and U.S. Publication 2009/0297970, entitled “Toner Composition for Preventing Image Blocking”, filed by Tyagi et al. on May 4, 2009. That is, using variable data, for example, from a database having any of a plurality of background texture, can be formed on an image by selective application of toner stack heights greater than about 50 μm; provide the appearance of a painter&#39;s canvas, an acrylic painting, a basketball (pigskin), sandstone, sandpaper, cloth, carpet, parchment, skin, fur, or wood grain. The resultant texture is preferably periodic, but can be random or unique. It is also preferable to create textures with a low frequency screening algorithm. Using variable data, in this way to provide patterns of high toner stack heights enables every printed page to contain unique information, with its own particular tactile feel. In order to improve reproduction of the colors in areas containing raised image effect, it may be desirable to build a new color profile based on the raised information. 
     Typically, a clear toner is applied on top of a color image to form a three-dimensional texture. It should be kept in mind that texture information corresponding to the clear toner image plane need not be binary. In other words, the quantity of clear toner called for, on a pixel by pixel basis, need not only assume either 100% coverage or 0% coverage; it may call for intermediate “gray level” quantities, as well. 
     In an area of the toner image  25  to be covered with a clear toner for three-dimensional texture, the color may change due to the application of the clear toner. For this approach, two color profiles are created. The first color profile is for 100% clear toner coverage on top and the second color profile is for 0% clear toner coverage on top. On a pixel by pixel basis, proportional to the amount of coverage called for in the clear toner image plane, a third color profile is created, and this third color profile interpolates the values of the first and second color profiles. Thus, a blending operation of the two color profiles is used to create printing values. In a preferred embodiment, a linear interpolation of the two color profile values corresponding to a particular pixel is performed. It is understood, however, that some form of non-linear interpolation may be used instead. This technique is especially useful when the spatial frequency of the clear toner texture is low. 
     The second approach may be used when the spatial frequency of the clear toner texture is high. In such case, only one color profile may be needed for that textured image. One option is to simply use the ICC color profile of the original system for all textures, i.e., the ICC color profile that assumes there is no clear toner. In such case, we simply accept the fact that the appearance of the colored image will change a bit since the absolute color will differ from the calibrated color. However, there will not be an observable color difference within a uniform color region, even though the color is not quite accurate. A second option is to build a new ICC color profile with that particular three-dimensional clear toner texture surface. In this manner, the macro “color accuracy” problem is corrected, while the color artifact from pixel-to-pixel is not noticeable. Furthermore, a library of such texture-modified ICC color profiles may be built up over time for use whenever an operator wishes to add a previously defined texture to a profile, as discussed above. In implementing such a method controller  82  can, for the second approach, automatically invoke just one of these two options, or may instead display a choice of the two options to an operator, perhaps with one of the options being the default. 
     After a toner image  25  having high toner piles is created, controller  82  causes receiver  26  to be forwarded for fusing. In the embodiment of  FIG. 1 , controller  82  does this by causing receiver transport  28  to move receiver  26  to fuser  60  such that receiver  26  is passed fuser receiver transport  62 . 
     As is shown in  FIGS. 2 and 3 , controller  82  then causes receiver  26  to be moved proximate to first energy source  64  such that first energy source  64  can apply a first energy  66  to raise a temperature of a first portion  68  of toner pile  70 . Controller  82  causes first energy source  64  to apply energy to first portion  68  of toner pile  70  to raise the temperature of first portion  68  to a range of elevated temperature levels that is below a glass transition temperature of the toner (step  106 ). Accordingly, as receiver  26  is moved from first energy source  64  the first portion  68  has substantially no toner  24  that is above the glass transition temperature. However, the amount of energy required to cause the first portion  68  to move into the range of glass transition temperatures is substantially lower than the amount of energy that would be required to cause the first portion  68  to heat from an ambient temperature range into range of the glass transition temperatures. Controller  82  then causes fuser receiver transport  62  to move receiver  26  to a position proximate to the second energy source  72 . 
     As is shown in  FIG. 5 , controller  82  then causes second energy source  72  to apply a second energy  74  to raise the temperature of the second portion  76  of toner pile  70  (step  108 ). 
     In this embodiment, the amount of energy applied to the second portion  76  of the toner pile  70  is determined to achieve two results: to allow second portion  76  to transfer sufficient energy into first portion  68  to cause the first portion  68  to heat from the range of elevated temperature levels to a range of temperatures above the glass transition temperature and to bring the temperature of the second portion  76  above the glass transition temperature of the toner, such that the first portion  68  and the second portion  76  are in a glassy state for a common period of time. 
     Both first energy  66  and second energy  74  are selected so that neither first energy  66  nor the second energy  74  is applied in an amount or at a rate that causes toner  24  to become damaged. The range of elevated temperatures is preferably as close to the glass transition temperature as can be achieved within a fusing exposure time and without causing damage or premature fusing of toner  24  in first portion  68 . 
     In certain embodiments, it may be useful for electrophotographic printer  20  to provide a uniform production rate for images having high toner stack heights as well as conventional toner stack heights. This will of course require that there be a generally consistent exposure time for fusing. In this regard, in certain embodiments, an electrophotographic printer  20  can use one of the first energy source and the second energy source to fuse toner on a receiver having a toner stack with toner stack heights that are below 50 microns during a first range of exposure times. To match this production rate, the first energy and second energy are applied so that the range of temperatures of the first portion and the second portion can be raised to the glass transition temperature to fuse high toner stack heights within the first range of exposure times. 
     In the embodiment of fuser  60  illustrated in  FIGS. 2 and 5 , first energy source  64  applies first energy  66  at a first surface  67  of toner pile  70  and the second energy source  72  applies the second energy  74  at a second, opposing surface  75  of toner pile  70 . This can help to reduce the risk that portions of the toner in toner pile  70  will become overheated. 
     As is shown in  FIGS. 2 and 5  second energy source  72  comprises a heated roller  77  and support roller  79  cr g a nip through which a toner pile  70  that forms part of a toner image  25  on receiver eatin  26  is passed. As toner pile  70  passes between heated roller  77  and support roller  79  pressure and heat are applied thereto to fuse toner pile  70 . To protect the integrity of toner pile  70  during fusing, the heated roller  77  is formed from thick soft thermally conductive elastomers having smooth lower surface energy materials on an outer surface thereof. As is illustrated in  FIG. 5  the thick soft thermally conductive elastomers conform to the toner pile  70  so as to avoid damaging the toner pile  70 . In this regard the elastomers used on heated roller  77  will have a thickness that is sufficient to conformally receive a toner pile  70  having a stack height about 50 μm to 500 μm. Any known low surface energy materials can be used for the outer surface of heated roller  72 . 
     To further protect toner pile  70 , the optional pressure control system  80  can be used to reduce pressure between heated roller  77  and the support roller  79  during the fusing of toner piles  70  having stack heights that are about 50 μm or more. In the embodiment that is illustrated in  FIGS. 2 and 5 , pressure control system  80  comprises a spring tensioning system (not illustrated) with a conventional mechanical adjustment that is driven by an optional actuator  81  which, for example, can comprise a motor that is appropriately linked to pressure control system  80 . 
     It will be appreciated that not every image fused by fuser  60  will have an image recorded thereon that has toner piles with stack heights on the order of 50 μm. Accordingly, for energy conservation and other efficiency considerations, it is useful to provide an electrophotographic printer  20  that has the capability to adjust the fusing process to provide an appropriate fusing solution for fusing toner piles having conventional toner stack heights as well as toner piles having toner stack heights that are greater than about 50 μm. 
     As is shown in the flow diagram of  FIG. 6 , controller  82  optionally can be adapted to adjust the fusing process based upon whether the print order information calls for images that have toner stack heights that are greater than about 50 μm. As is shown in  FIG. 6 , in this embodiment, controller  82  receives a print order information (step  100 ) and converts the print order information into printing instructions (step  102 ) in a manner that is consistent with what is disclosed above. However, controller  82  is further adapted to determine whether a particular receiver has toner with stack heights that are within a range of toner stack heights that can be fused using only one of the first energy source and the second energy source during an available fusing exposure period (step  103 ). In the embodiment that is illustrated, controller  82  makes this determination based upon whether the printing instructions require toner stack heights to be above 50 μm. If the controller determines that the printing instructions do call for such stack heights, then controller  82  can execute steps  104 ,  106  and  108  as is generally described above. 
     However, when controller  82  determines that the printing instructions do not require the formation of toner stack heights that are at least around 50 μm, controller  82  uses the printing restrictions to cause toner to be delivered to receiver  26  according to printing instructions and without a toner pile having a stack height that is greater than 50 μm (step  105 ). Controller  82  then causes one of the first energy source and second energy source to be deactivated during fusing operations (step  107 ) such as by cutting off the power the unused toner energy source or by sending instructions causing the energy source to deactivate. Accordingly energy is applied from only one source of energy to fuse images of this type. Alternatively, as shown in  FIG. 7 , electrophotographic printer  20  can include fuser receiver transport  62  having a first flow path  130  for receivers having toner  24  with toner stack heights that are below about 50 μm that by-passes one of the energy sources, and a second flow path  132  for receivers having toner with toner stack heights that are above about 50 um and that do not bypass either energy source (step  107 ). Here energy is applied from only one source of energy to fuse images of this type (step  109 ). In such an embodiment, a flow actuator  134  can be used for directing receiver  26  between the first flow path  130  and the second flow path  132 , and controller  82  can operate flow actuator  134  to direct a receiver along the first flow path  130  or the second flow path  132  based on whether receiver  26  has a toner piles  70  with a stack height that is above about 50 μm. 
     In still another embodiment, first energy source  64  can be adapted to apply sufficient energy to first portion  68  to allow the first portion  68  to partially heat the second portion  76  so that the second energy  74  begins heating second portion  76  at a temperature that is above an initial temperature of the toner  24 . This will reduce the amount of energy required of second energy  74  as compared to an amount of energy that second energy  74  would be required to apply to an unheated second portion  76 . 
     In other embodiments, first energy source  64  and second energy source  72  can take any of a variety of forms. For example, in the embodiment of  FIG. 8 , first energy source  64  takes the form of a microwave system for heating receiver  26 , while second energy source  72  takes the form of a flash fusing system. In still other embodiments, first energy source  64  or second energy source  72  can comprise, for example and without limitation, radiant heat fusers, hot air impingement fusers, and/or inductive heaters. To protect the toner pile  70 , first energy source  64  will typically be a non-contact type energy source. 
     As shown in  FIG. 9 , another embodiment, the printing method comprises transferring patterned applications of toner onto a receiver including toner piles having toner stack heights that are at least about 50 μm (step  140 ). This can be done generally as described above. 
     A initial portion of the toner piles is then heated to a range of elevated temperatures that is below a glass transition temperature of the toner (step  142 ). The initial portion can be heated in a single step or process for multiple steps. 
     A remaining portion of the toner piles is then heated to cause the remaining portion of the toner piles to heat the initial portion from the range of elevated temperatures to a range of temperatures above the glass transition temperature and to heat the remaining portion of the toner piles to the range of temperatures above the glass transition temperature (step  144 ). 
     In certain embodiments, the heating of the initial portion can apply a heat to a first surface of the toner piles while the heating of the remaining portion applies heat to a second surface of the toner piles with the second surface being opposite from the first surface. In other embodiments, the heating of one of the portions can be performed by conforming a heated surface to the toner piles and transferring heat from the conforming surface into the toner piles. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           20  printer 
           22  print engine 
           24  toner 
           25  toner image 
           26  receiver 
           28  receiver transport 
           30  surface 
           32  receiver supply 
           36  motor 
           38  rollers 
           40  printing module 
           42  printing module 
           44  printing module 
           46  printing module 
           48  printing module 
           50  transfer subsystem 
           52  cleaning mechanism 
           60  fuser 
           62  fuser receiver transport 
           64  first energy source 
           66  first energy 
           67  first surface 
           68  first portion 
           70  toner pile 
           72  second energy source 
           74  second energy 
           75  second surface 
           76  second portion 
           77  heated roller 
           78  heat 
           79  support roller 
           80  pressure control system 
           81  actuator 
           82  controller 
           84  input system 
           86  sensors 
           88  memory 
           90  communication system 
           92  external devices 
           100  receive print order step 
           102  convert step 
           103  determining step 
           104  form toner image step 
           105  print step 
           107  bypass/disable step 
           108  apply second energy step 
           109  fuse with one fuser step. 
           120  first application of toner 
           122  second application of toner 
           124  third application of toner 
           126  fourth application of toner 
           128  fifth application of toner 
           130  first flow path 
           132  second flow path 
           134  flow actuator 
           140  transfer toner step 
           142  heat initial portion step 
           144  heat remaining portion step