Abstract:
An electrophotographic marking device includes a xerographic marking module and an environmental control module which controls temperature and relative humidity inside the marking module. The environmental module has a main plenum chamber and a divided or split plenum chamber to create and supply two air streams with different temperatures and/or different humidities and/or different airflow volumes and/or airflow rates to a marking engine. A primary air stream plenum chamber is closed loop controlled by input from one or more temperature and/or humidity sensors in the xerographic module. A secondary air stream plenum chamber is open loop controlled by means of one or more temperature and/or humidity sensors in one or mode developer housings. Heating of the secondary air stream is achieved by heat generated in the developer housing(s) and/or one or more heaters distinct from the developer unit elements. The system achieves balanced, thermodynamically adjusted, air flows.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     The invention concerns maintaining suitable environmental conditions within a marking device.  
         [0003]     2. Description of Related Art  
         [0004]     U.S. Pat. No. 5,481,339 to DeCock et al. discloses an air conditioner device for an electrostatographic printer using environmental control. An air conditioning device is provided that has filters for removing dust and ozone from air leaving the environment of the image-producing station. DeCock et al. also provide a heat exchanger and a humidifier for adjusting the temperature and humidity of air leaving the environment of the image producing station, and an inlet manifold for introducing a stream of conditioned air into the environment of the image producing station. In one embodiment, the development station has an additional channel serving as an inlet for introducing a low speed stream of separately conditioned air to achieve an appropriate micro-climate, in which the temperature and relative humidity are different from the air-conditioned environment in the printer cabinet to obtain optimum development results. This embodiment is operated with a common air inlet provided at the top of the marking cabinet.  
         [0005]     U.S. Pat. No. 5,634,176 to Ayash et al. discloses an electrophotographic marking machine which has an air manifold system which supplies air flow to a plurality of machine components and which supports a component of the plurality of machine components.  
         [0006]     U.S. Pat. No. 5,689,766 to Hollar et al. discloses an apparatus for maintaining a desired ambient condition about an electrophotographic marking module. An air flow source supplies air to an electrophotographic module chamber and sensors respond to the amount of air flow to control the air flowing from the air source.  
         [0007]     U.S. Pat. No. 5,878,305 to Suzumura et al. discloses a liquid developing type of electrophotographic printer having a circulation means to take out and return gas generated in the printer casing, a gas cooling and solvent recovery means provided midway on the recirculation means to lower the gas concentration, means to detect the temperature and humidity of the gas in the casing, and a gas heating means downstream of the gas cooling and solvent recovery means to adjust the humidity of gas to be returned to the casing.  
         [0008]     U.S. Pat. No. 6,621,554 to Ayash et al. discloses a method and apparatus to control the atmosphere in a xerographic control module of an image forming device so that the dew point is not reached. Parameters controlled within a xerographic chamber include air pressure, temperature and humidity. Both open and closed loop recirculation systems are disclosed.  
         [0009]     U.S. Pat. No. 6,334,033 to Ayash et al. discloses an ambient atmospheric pressure compensation controller for a pressurized copying device.  
       SUMMARY OF THE INVENTION  
       [0010]     Environmentally controlled marking engines have difficulty maintaining airflow balance between main print engine chamber air flow and developer housing and charger airflow streams.  
         [0011]     The systems and methods of this invention provide an environmental module in which airflow balance is maintained for different components of a marking engine, such as, for example, overall main marking engine unit airflow and developer and/or charging sub-unit airflow streams in the sense that a predetermined ratio of the volume of air per unit time in each of two airstreams is maintained. Moreover, because the thermodynamic characteristics of the air flows, including temperature and moisture content of the air flows is adjusted to desired values using a common plenum, a thermodynamic adjustment of the airflows is also achieved.  
         [0012]     The systems and methods of the invention provide an environmental unit which supplies separate air streams with different characteristics, such as, for example, temperature, pressure and moisture content, to a marking engine.  
         [0013]     In various exemplary embodiments of the systems and methods of the invention provide an environmental unit that supplies one air stream to a marking engine unit and another air stream to developer housings and/or charging sub-units of the marking engine.  
         [0014]     In various exemplary embodiments of the systems and methods of the invention provide an environmental unit/module which creates separate air streams using one or more split plenum arrangements.  
         [0015]     In various exemplary embodiments of the systems and methods of the invention provide an environmental unit/module which creates a plurality of separate airstreams each of which may have different values of air pressure, flow velocity, moisture content, temperature and pressure.  
         [0016]     In various exemplary embodiments of the systems and methods of the invention provide an environmental unit/module which creates a plurality of separate airstreams in which the values of air pressure, flow velocity, temperature and pressure may be varied.  
         [0017]     In various exemplary embodiments of the systems and methods of the invention provide an environmental unit/module which creates and/or regulates one or more of the temperature, moisture content, flow rate and air pressure of a plurality of different airstreams in two separate plenum chambers.  
         [0018]     In various exemplary embodiments of the systems and methods of the invention provide an environmental unit/module which creates a plurality of separate airstreams two or more of which may use separate blowers.  
         [0019]     The systems and methods of the invention provide an environmental unit/module which creates a plurality of separate airstreams formed from a single plenum air stream using two or more separate plenum chambers.  
         [0020]     The systems and methods of the invention provide an environmental unit/module which creates a plurality of separate airstreams formed from a single plenum air stream using two or more separate plenum chambers.  
         [0021]     The systems and methods of the systems and methods of the invention provide a marking engine and/or reproduction system which includes an environmental unit/module having characteristics described above. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     Various exemplary embodiments of this invention will be described in detail, with reference to the following figures, wherein:  
         [0023]      FIG. 1  is a schematic elevational view of an illustrative xerographic marking machine which has its environment controlled by an environmental unit;  
         [0024]      FIG. 2  is a three-dimensional or perspective view of an environmental unit according to the invention;  
         [0025]      FIG. 3  is a cross-sectional view of the plenum of the environmental unit of  FIG. 2 ;  
         [0026]      FIG. 4  is a perspective view of a second embodiment of an environmental unit according to the invention;  
         [0027]      FIG. 5  is another perspective view of the environmental unit of  FIG. 4  showing airflow direction in the unit;  
         [0028]      FIG. 6  is a block diagram schematically showing a marking machine and an associated environmental unit/module;  
         [0029]      FIG. 7  is a block diagram of a control system according to this invention; and  
         [0030]      FIG. 8  is a block diagram of elements of a controller portion of the control system of this invention. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0031]     The present invention will hereinafter be described in connection with a number of exemplary embodiments thereof. It will be understood that it is not intended to limit the invention to the exemplary embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents that may be included within the spirit and scope of the invention.  
         [0032]     For a general understanding of the features of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate identical elements. It will become evident from the following discussion that the balanced separate air stream systems and methods of the present invention are equally well suited for use in a wide variety of marking machines and are not necessarily limited in their application to the exemplary embodiments depicted herein.  
         [0033]     Turning now to  FIG. 1 , there is illustrated a xerographic marking machine, such as an image-on-image machine  8 . The marking machine  8  for example employs a photoreceptor  10  in the form of a belt having a photoconductive surface layer  11  on an electroconductive substrate  13 . It is understood that the photoreceptor  10  equally can be in the form of a drum, in which case the belt-entraining rollers, described below, would not be needed. Photoreceptor belt  10  is supported for movement in the direction indicated by arrow  12 , for advancing sequentially through various xerographic process stations. As shown, the belt is entrained about a drive roller  14  and two tension rollers  16  and  18 . Drive roller  14  is operatively connected to a drive motor  20  for effecting movement of the belt through the xerographic stations.  
         [0034]     With continued reference to  FIG. 1 , a portion of belt  10  first passes through charging station M where a corona generating device, indicated generally by the reference numeral  22 , charges the photoconductive surface of belt  10  to a relatively high, and substantially uniform potential. For purposes of example, the photoreceptor is negatively charged, however it is understood that the present invention could be useful with a positively charged photoreceptor, by correspondingly varying the charge levels and polarities of the toners, recharge devices, and other relevant regions or devices involved in the image-on-image color image formation process, as will be hereinafter described.  
         [0035]     Next, the charged portion of photoconductive surface is advanced through an imaging station BB. At imaging station BB, the uniformly charged belt  10  is exposed to a laser based output scanning device  24  which causes the charge retentive surface to be discharged in accordance with the output from the scanning device  24 . Preferably the scanning device is a laser. Raster Output Scanner (ROS). Alternatively, the ROS could be replaced by other exposure devices, for example, a light lens system. Due to the exposure, an electrostatic latent image is recorded on the photoconductive surface of the photoreceptor belt  10 .  
         [0036]     At a first development station CC, a magnetic brush developer unit, indicated generally by the reference numeral  26 , advances developer material  31  into contact with the electrostatic latent image on the photoreceptor belt  10 . Developer unit  26  has a plurality of magnetic brush roller members. These magnetic brush rollers transport negatively charged dry toner material of a first color, such as black, to the latent image for development thereof. A power supply (not shown) electrically biases developer unit  26 .  
         [0037]     At a recharging station DD, a pair of corona recharge devices  36  and  37  adjust the voltage level of both the toned and untoned areas on the photoconductive surface to a substantially uniform level. A power supply is coupled to each of the electrodes of the corona recharge devices  36  and  37 . Recharging devices  36  and  37  substantially eliminate any voltage difference between toned areas and bare untoned areas, as well as reduce the level of residual charge remaining on the previously toned areas, so that subsequent development of different color toner images is effected across a uniform development field.  
         [0038]     A second exposure or imaging device  38  is then used to selectively discharge the photoreceptor on toned areas and/or bare areas. This records a second electrostatic latent image on the photoconductive surface. A negatively charged developer material  40 , for example, yellow color toner, develops the second electrostatic latent image. The toner is contained in a developer unit  42  disposed at a second development station EE and is transported to the second latent image recorded on the photoconductive surface by a donor roll. A power supply (not shown) electrically biases the developer unit  42  to develop this latent image with the negatively charged toner particles  40 .  
         [0039]     At a second recharging station FF, a pair of corona recharge devices  51  and  52  adjust the voltage level of both the toned and untoned areas on the photoconductive surface to a substantially uniform level. A power supply is coupled to the electrodes of corona recharge devices  51  and  52 . The recharging devices  51  and  52  substantially eliminate any voltage difference between toned areas and bare untoned areas, as well as reduce the level of residual charge remaining on the previously toned areas so that subsequent development of different color toner images is effected across a uniform development field.  
         [0040]     A third latent image is recorded on the photoconductive surface by exposure/imaging device  53 . This image is developed using a third developer material  55  contained in a developer unit  57  disposed at a third development station GG. An example of a suitable third developer material is magenta. Suitable electrical biasing of the developer unit  57  is provided by a power supply, not shown.  
         [0041]     At a third recharging station HH, a pair of corona recharge devices  61  and  62  adjust the voltage level of both the toned and untoned areas on the photoconductive surface to a substantially uniform level. The recharging devices  61  and  62  substantially eliminate any voltage difference between toned areas and bare untoned areas as well as to reduce the level of residual charge remaining on the previously toned areas, so that subsequent development of different color toner images is effected across a uniform development field.  
         [0042]     A fourth latent image is created using exposure/imaging device  63 . The fourth latent image is formed on both bare areas and previously toned areas of the photoreceptor that are to be developed with the fourth color image. This image is developed, for example, using a cyan developer material  65  contained in developer unit  67  at a fourth development station II. Suitable electrical biasing of the developer unit  67  is provided by a power supply, not shown.  
         [0043]     The dry developer material cases and developer units  42 ,  57 , and  67  may be of the type known in the art which do not interact, or are only marginally interactive with previously developed images. For examples, a DC jumping development system, a powder cloud development system, and a sparse, non-contacting magnetic brush development system are each suitable for use in an image-on-image color development system.  
         [0044]     In order to condition the toner for effective transfer to a substrate, a negative pre-transfer corotron member  50  negatively charges all toner particles to the required negative polarity to ensure proper subsequent transfer.  
         [0045]     A sheet  48  of material to be marked is, advanced, in the direction of arrow  58 , to transfer station JJ by a sheet feeding apparatus, not shown. Preferably, the sheet feeding apparatus includes a feed roll contacting the uppermost sheet of a stack of copy sheets. The feed rolls rotate so as to advance the uppermost sheet from stack into a chute which directs the advancing sheet  48  into contact with photoconductive surface of belt  10  in a timed sequence so that the toner powder image developed thereon contacts the advancing sheet  48  at transfer station JJ.  
         [0046]     Transfer station JJ includes a transfer corona device  54  which sprays positive ions onto the backside of sheet  48 . This attracts the negatively charged toner powder images from the belt  10  to sheet  48 . A detack corona device  56  is provided for facilitating stripping of the sheets from belt  10 .  
         [0047]     After transfer, the sheet  48  continues to move onto a conveyor (not shown) which advances the sheet to fusing station KK. Fusing station KK includes a fuser assembly, indicated generally by the reference numeral  60 , which permanently affixes the transferred powder image to sheet  48 . Preferably, fuser assembly  60  comprises a heated fuser roller  64  and a backup or pressure roller  68 . The sheet  48  passes between fuser roller  64  and backup roller  68  with the toner powder image contacting fuser roller  64 . In this manner, the toner powder images are permanently affixed to sheet  48 . After fusing, a chute, not shown, guides the advancing sheet  48  to a catch tray, not shown, for subsequent removal from the marking machine by the operator.  
         [0048]     After the sheet  48  is separated from photoconductive surface of belt  10 , the residual toner carried on the photoconductive surface is removed therefrom. The toner is removed at cleaning station LL using a cleaning brush structure, including a flicker bar  108 , contained in a housing  66 .  
         [0049]     The xerographic marking machine  8  includes the balanced airflow system of the present invention. Electrostatic Voltmeters (ESV) are utilized within xerographic machines to control the photoreceptor charging voltage, voltage increases of a charging, device, and the charge level of charged area images on the photoreceptor. Similar electrostatic measurement devices are also used in xerographic machines for generating a modified electrical signal in proportion to an electrostatic potential present on a surface. Such a device may include a sensor for producing a signal representative of the electrostatic potential on the surface. The marking machine  8  may also contain an impulse air ejector cleaning system (not shown), such as, for example, the system disclosed in commonly assigned U.S. Pat. No. 5,862,439, the subject matter which is hereby incorporated by reference in its entirety. The balanced airflow system and methods of the invention and the various other machine functions described above are generally managed and regulated by a controller or electronic control subsystem (ESS)  90 , preferably in the form of a programmable microprocessor. The microprocessor controller  90 , connected for example by means (not shown) to environmental module  200 , provides electrical command signals for operating all of the machine subsystems.  
         [0050]     A first exemplary embodiment of an environmental unit  200  using two cooling air flows is shown in  FIGS. 2 and 3 . In the environmental unit  200  shown in  FIG. 2 , air returning from the marking engine  8  of  FIG. 1  flows through duct  209  into main flow plenum portion  210 , where it is conditioned by including, for example, an ozone filter  272  and a HEPA filter  273  shown in  FIG. 4 . Reference is made to commonly assigned U.S. Pat. No. 5,170,211 which discloses use of a HEPA filter to remove particulates and contaminating gas from input air to a marking engine corona device and to remove harmful corona-generated effluents from the output, the disclosure of which is incorporated in its entirety herein by reference. The air is conditioned by cooling it by an evaporator  211  and by subsequently heating it by heater  212 . Cooling the air in an evaporator allows moisture removal from the return air stream. Subsequent heating by heaters  212  is .used to bring the temperature of the primary air stream to, or substantially to, the operating temperature of the xerographic cavity of the marking device  8 . The secondary air stream is typically heated using a separate heater to control the secondary air stream to a set point which differs from the primary air stream set point. In other exemplary embodiments, the air may be heated before it is cooled.  
         [0051]     The air is then passed directly, or indirectly through a transition plenum section  210 , to plenum section  213 , which has two compartments or chambers  220  and  230  separated by a dividing wall  215 . Plenum chamber  220  is the primary air flow plenum chamber through which most of the conditioned air is drawn by primary blower  225  to supply the conditioned air to marking engine module  8 . In one exemplary embodiment, primary blower  225  supplies primary air to the marking engine module  8  at about 220 cubic feet per minute (CFM) and at about 77° F. plus or minus 3° F. A heater unit  212  is provided in the primary air flow plenum  220  to heat the air to the desired temperature.  
         [0052]     Plenum chamber  230  is the secondary air flow chamber through which a relatively smaller amount of air is drawn by secondary blower  235 . As shown in  FIG. 1 , this secondary air is directed to developer units CC, DD, EE, GG, II and/or charging units AA, DD, FF and HH by secondary blower  235 . In one exemplary embodiment, secondary blower  235  supplies secondary air to the aforementioned developer and/or charging units at about 80 cubic feet per minute exiting the environmental unit  200  at a maximum temperature of about 55° F. In the exemplary embodiment of the marking engine module shown in  FIG. 1 , because there are four developer units, the conditioned flow reaching each unit is approximately 20 cubic feet per minute (CFM). The temperature of the secondary air flow may be adjusted by providing a separate heater in the secondary air flow path, and/or by using the heat generated by the developing units CC, EE, GG, and II.  
         [0053]     In the exemplary embodiment shown in  FIGS. 2 and 3 , the primary plenum chamber  220  and the secondary plenum chamber  230  are coextensive and separated along their entire depth by a dividing wall or divider  215 .  
         [0054]      FIG. 4  shows a second exemplary embodiment of the environmental unit  200  according to this invention. In this second exemplary embodiment, an ozone filter  272  and a HEPA (High Efficiency Particulate Air) filter  273  are located in the main airflow plenum  210 . An air conditioner evaporator coil unit  211  is located in the primary air flow plenum chamber  220  and a heater unit  212  is located in the primary air flow plenum  220 . In this second embodiment, the secondary air flow plenum chamber  230  is separated from the primary air flow plenum  220  by a wall  215  that forms two sides of the secondary air flow plenum chamber  230 . A condensate collection and drip pan  280 , which also functions as an air flow diverter for air entering the main plenum chamber  210  from inlet such  209 , is located in a position to separate the main plenum chamber  210  from the primary air flow chamber  220 .  
         [0055]      FIG. 5  shows airflow directions in the second exemplary embodiment using arrows. Air from the marking engine enters the main flow plenum chamber  210  via duct  209 , and is diverted by the condensate collector and drip pan  280  to pass through filters  272  and  273  and through air conditioner evaporator  211  and heater  212  to main blower  225  to duct  140  (shown in  FIGS. 1 and 6 ) to the marking engine module  8 . Also, as shown in  FIG. 5 , air is drawn by secondary air flow blower  235  from main plenum chamber  210  through secondary air flow plenum chamber  230  to the developer and charging units in marking machine  8 .  
         [0056]     Temperature sensors may be placed in suitable locations in the overall system.  FIGS. 1 and 6  show temperature sensor  81  located in the primary air flow inlet duct  140  for marking machine  8 . A temperature sensor  85  is located in the primary air flow return duct  144 . A temperature sensor  84  is located in the marking engine module  8 .  FIG. 6  shows a temperature sensor  83  in the main return manifold  146 , a temperature sensor  82  in the main air flow plenum chamber  210 , a temperature sensor  87  in the primary air flow plenum chamber  220  and a temperature sensor  86  in the secondary air flow plenum chamber  230 .  
         [0057]     Moisture content sensors, in the form of absolute or relative humidity sensors, may also be placed in suitable locations in the overall marking system.  FIG. 1  shows a humidity sensor  91  located in the primary air flow inlet duct  140  for marking machine  8 . A humidity sensor  92  is located in the marking engine module  8 . A humidity sensor  95  is located in the primary air flow return duct  144 .  FIG. 6  shows a humidity sensor  93  in the main air flow plenum chamber  210 , a humidity sensor  94  in the primary air flow plenum chamber  220 , a humidity sensor  96  in the secondary air flow plenum chamber  230 , and a humidity sensor  97  in the main return manifold  146 .  
         [0058]     One purpose of providing the temperature and moisture content sensors is to permit the system to condition the primary and secondary air flows to provide optimum environmental conditions for operation of the marking engine. In various exemplary embodiments of the systems and methods of the invention, this environmental control provides and maintains secondary air flow to the aforementioned developer and/or charging units at about 80 cubic feet per minute exiting the environmental unit  200  at a maximum temperature of about 55° F., and provides and maintains primary air flow to the marking engine module  8  at about 77° F. plus or minus 3° F.  
         [0059]      FIG. 7  shows one exemplary embodiment of a control system  300  usable to maintain the temperature and humidity characteristics of the primary and secondary air flowing through in the marking engine module  8 , including the developing and charging units therein, to desired values to achieve maintain the developer units within a desired temperature and humidity range. As shown in  FIG. 7 , the control system includes a controller  310  connected via a link  322  to relative humidity sensors  91 - 97 , a link  332  to temperature sensors  81 - 87 , a link  362  to air conditioner (evaporator) unit  211 , a link  372  to heater unit  212 , a link  342  to primary air flow blower unit  225 , and a link  352  to secondary air flow blower unit  235 . The controller  310  receives signals from the relative humidity and temperature sensors and processes the signals to control the blower units  225  and  235 , the air conditioner unit  211  and heater unit  212  to maintain air temperature and relative humidity in portion  8  within desired ranges, such as the ranges described above. In various exemplary embodiments, heating of the secondary air stream may be achieved using heat generated in the developer housing(s) and/or using one or more heaters distinct from the heater unit(s).  
         [0060]     Moreover, with reference to U.S. Pat. No. 6,621,554, incorporated by reference, above, the system may be provided with air intake actuators and exhaust valve actuators to provide make-up air and/or otherwise alter the characteristics of the air flow in the system to achieve desired operational characteristics of the marking device.  
         [0061]      FIG. 8  shows in greater detail one exemplary embodiment of the controller  310 . As shown in  FIG. 8 , the controller  310  includes an I/O interface  311 , a memory  312 , a temperature and humidity processing circuit  313 , a circulation loop control circuit  314 , an air conditioning and blower control circuit  315 , and a temperature and humidity value comparing circuit  316 , interconnected by a data control bus  319 . The interface  311  connects to the links  322 ,  332 ,  342 ,  352 ,  362  and  372  and to the data/ control bus  319  to transmit data and control signals to and from the control units  313 - 316  and/or memory  312  of the controller  310 .  
         [0062]     The controller  310  may be implemented on a programmed general purpose computer. However, the controller  310 , and any of the separate circuits therein, can also be implemented on a special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit elements, an ASIC or other integrated circuit, a digital signal processor, a hardwired electronic or logic circuit such as a discrete element circuit, a programmable logic device such as a PLD, PLA, FPGA or PAL, or the like. In general, any device capable of implementing a finite state machine that is in turn capable of implementing the control functions referred to above can be used to implement the invention. The links  322 - 372  can be implemented by any known or later developed device or system for connecting the controller  310  to the components  320 - 370 . In general, the links  322 - 372  can be any known or later developed connection system or structure usable to connect the controller  310  to the components  320 - 370 .  
         [0063]     The memory  312  preferably implemented using static or dynamic RAM. However, the memory  312  can also be implemented using a floppy disk and disk drive, a writable optical disk and disk drive, a hard drive, flash memory or any other known or later developed alterable volatile or non-volatile memory device or system.  
         [0064]     In operation, signals from the temperature sensors  81 - 86  and humidity sensors  91 - 96  are received by controller  310  through the interface  311 . These signals are sampled by the temperature and humidity processing circuit  313  to determine the temperature and humidity of the air in marking engine module  8 , and in the developer and charging units in module  8 . These values are forwarded to a temperature and humidity value comparing circuit  316  where they are compared. The air conditioner blower and heater control circuit  315  is then used to adjust the air conditioner unit  211 , heater unit  212 , primary air flow blower  225 , and secondary airflow blower unit  235 , based on the comparisons of those values, to achieve desired temperature and humidity and flow rates of the air flow in the primary and secondary air flow paths.  
         [0065]     In one exemplary embodiment, the system supplies about 220 CFM air to the marking engine module  8 , which may also be referred to as a Xerographic cavity  8 , to control it at 77° F.+/−3° F. and the system supplies about 80 CFM air to a developer cooling manifold  142  to supply about 20 CFM to each of the four developing units, and supply secondary air to the developer and charging units at a maximum temperature of about 55° F. to provide sufficient cooling to the developer housings to maintain the units, including a developer trim bar below about 90° F. Air is also supplied to each of the charging units. It should be understood that these temperatures may be varied depending on the characteristics of the marking engine components. Reference is made to U.S. Patent U.S. Pat. No. 5,155,444 for details of a developer trim bar, the subject matter of which is hereby incorporated by reference in its entirety.  
         [0066]     While this invention has been described in conjunction with the exemplary embodiments set forth above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be, made without departing from the spirit and scope of the invention.