Patent Application
20080298831
This disclosure relates to imaging devices having rollers heated with multiple heaters and, more particularly, to imaging devices having image receiving members that are heated with different heaters.
Imaging devices use a variety of marking materials to generate a physical image of an electronic image. The materials include, for example, aqueous ink, melted ink and toner. The marking material may be ejected onto or developed on an image receiving member. For example, electronic image data may be used to generate a latent image on a photoreceptor belt and then the latent image is developed with toner material in a development station. With aqueous ink or melted ink, a print head ejects the melted ink onto an image receiving member. The firing of the ink jets in the print head to deposit the material on the image receiving member is manipulated by a print head controller using electronic image data.
Once the marking material is deposited onto an image receiving member, the image may be transferred or transfixed to an image media. For example, a sheet or web of image media may be moved into a nip formed between the image receiving member and a transfix or fuser roller so the image may be transferred to the image media. The movement of the image media into the nip is synchronized with the movement of the image on the image receiving member so the image is appropriately aligned with and fits within the boundaries of the image media. The pressure within the nip helps transfix or fuse the marking material onto the image media.
The image receiving member is typically heated to improve compatibility of the image receiving member with the inks deposited on the member. The image receiving member may be, for example, an anodized and etched aluminum drum. Within the drum, a heater reflector may be mounted axially within the drum. A heater is located at approximately each end of the reflector. The heater reflector remains stationary as the drum rotates. Thus, the heaters apply heat to the inside of the drum as the drum moves past the heaters on the reflector. The reflector helps direct the heat towards the inside surface of the drum. Each of the heaters is coupled to a controller. The controller is also coupled to temperature sensors located near the outside surface of the drum. The controller selectively operates the heaters to maintain the temperature of the outside surface within an operating range.
Differences in temperatures of the components interacting during a print cycle cause thermal gradients to appear sometimes across the outside surface of the image drum. For example, the controller operates the heaters in an effort to maintain the temperature of the outside surface in a range of about 55 degrees Celsius, plus or minus 5 degrees Celsius. The ink that is ejected onto the print drum has a temperature of approximately 110 to approximately 120 degrees Celsius. Thus, images having areas that are densely pixilated, may impart a substantive amount of heat to a portion of the print drum. Additionally, the drum experiences convective heat losses as the exposed surface areas of the drum lose heat as the drum rapidly spins in the air about the drum. Also, the contact of the recording media with the print drum also affects the surface temperature of the drum For example, paper placed in a supply tray has a temperature roughly equal to the temperature of the ambient air. As the paper is retrieved from the supply tray, it moves along a path towards the transfer nip. Typically, this path includes a media pre-heater that raises the temperature of the media. These temperatures may be approximately 40 degrees Celsius. Thus, when the media enters the transfer nip, areas of the print drum having relatively few drops of ink on them are exposed to the cooler temperature of the media. Consequently, densely pixilated areas of the print drum are likely to increase in temperature, while more sparsely covered areas are likely to lose heat to the passing media. These differences in temperatures result in thermal gradients across the print drum
Efforts have been made to control the thermal gradients across a print drum for the purpose of maintaining the surface temperature of the print drum within the operating range. Simply controlling the heaters is insufficient because the ejected ink may raise the surface temperature of the print drum above the operating range even though the heater in that region is off. To provide cooling, a fan has been added at one end of a print drum The print drum is open at each flat end of the drum. To best provide cooling, the fan is located outside the print drum and is oriented to blow air from the end of the drum at which the fan is located to the other end of the drum where it is exhausted. The fan is electrically coupled to the controller so the controller activates the fan in response to one of the temperature sensors detecting a temperature exceeding the operating range of the print drum. The air flow from the fan eventually cools the overheated portion of the print drum and the controller deactivates the fan.
While the fan system described above works for maintaining the temperature of the drum within an operating range, it possess some inefficiencies. Specifically, inefficiency arises when the surface portion of the print drum at which the air flow is exhausted has a higher temperature than the surface area near the end at which the fan is mounted. In response to the higher temperature detection, the controller activates the fan. As the cooler air enters the drum, it absorbs heat from the area near the fan that is within operating range. This cooling may result in the controller turning on the heater for that region to keep that area from falling below the operating range. Even though the air flow is heated by the region near the fan and/or the heater in that area, it still is able to cool eventually the overheated area near the drum end from which the air flow is exhausted. Nevertheless, the energy spent warming the region near the fan and the additional time required to cool the overheated area with the warmed air flow from the fan adds to the operating cost of the printer. Therefore, more efficient cooling of the print drum would be useful.
To address the issues arising from inefficiency in cooling overheated areas of an image receiving member in a printer, a system for cooling a portion of an image receiving member has been developed. The image receiving member cooling system includes an image receiving member having a first end and a second end, a first heater mounted within the image receiving member for heating the image receiving member in the vicinity of the first end, a second heater mounted within the image receiving member for heating the image receiving member in the vicinity of the second end, a first temperature detector located proximate the first end of the image receiving member, a second temperature detector located proximate the second end of the image receiving member, a fan mounted at one end of the image receiving member, and a controller electrically coupled to the first and the second temperature detectors and the fan, the controller for activating the fan to move air from the end at which a higher temperature is detected past the other end.
A method implemented by the thermal gradient control system helps ensure a more uniform distribution of temperature across the image receiving member. The method includes detecting a temperature at a first portion of a heated image receiving member being greater than a temperature threshold, detecting a temperature at a second portion of the heated image receiving member being less than the temperature threshold, and directing air flow from the first portion of the heated image receiving member past the second portion. The directing of the air flow may include the control of two separate fans or the control of a single bidirectional fan.
The image drum 10 includes a heat reflector 30 into which a heater 34 is mounted. The reflector 30 and heater 34 remain fixed as drum 10 rotates past the heater 34. The heater 34 generates heat that is absorbed by the inside surface of the drum 10 to heat the image receiving drum as it rotates past the heater. Although the heater 34 is shown as being located so it heats the inside surface of the drum, it may also be located externally of the drum to heat the external surface. A cooling system for the drum 10 includes a hub 38 that is preferably centered about the longitudinal center line of the image drum 10. A fan 40 is mounted outboard of the hub 38 and oriented to direct air flow through the drum. A temperature sensor 48 is located proximate the outer surface of the drum 10 to detect the temperature of the drum surface as it rotates.
In more detail, the drum 10 may be, for example, an aluminum drum that has been anodized and etched. Other image receiving members, however, may be used with the cooling system disclosed herein. Each end of the drum 10 may be open with a hub 38 and spokes 36 as shown in
A cross-sectional view of the drum 10 through the center of the hub 38 is shown in
Fan 40 is a bi-directional fan. That is, the direction of rotation for the fan blade 44 may be controlled by an appropriate signal to the fan. When the blade 44 rotates in one direction, air flows from fan 44 through the drum 10 for exhausting at end 64. When the blade 44 rotates in the opposite direction, air flows from end 64 for exhausting at end 60. In a similar manner, fan 40 may be a DC fan and the polarity of the supply voltage to the fan determines the direction of fan blade rotation and the direction of the air flow through the drum 10. Thus, a bi-directional fan and DC fan provide two directions of air flow through the drum 10 with a single fan. The advantage of a bi-directional fan is that the blade of such fans is shaped so the air flow is approximately the same regardless of the direction in which the blade is turning. A DC muffin fan does not necessarily have a fan blade that produces the same air flow in each direction. Consequently, air flow in one direction may be greater than air flow in the other direction.
In another embodiment, a second fan is mounted at the second end 64. The second fan is mounted outboard of the end 64 and is oriented to direct air flow into the drum 10 for exhaustion at end 60. In this embodiment, the two fans may be single direction fans that are independently controlled. When the first fan is activated to provide air flow from end 60 to end 64, the second fan remains off. When the second fan is activated to provide air flow from end 64 to end 60, the first fan remains off. Of course, both fans may also be bi-directional fans or DC fans. In this arrangement, when the first fan is controlled to move air from end 60 to end 64, the second fan is operated in the direction that also pulls air from end 60 to end 64. Similarly, the two bidirectional fans maybe operated simultaneously to move air from end 64 to end 60 for exhaustion.
A block diagram for the cooling system is shown in
The reader may ascertain from the above description that the cooling system disclosed herein usually moves air from the warmer end of the print drum to the cooler end. Although the warmer end may initially heat the cooler end, the flow of the warmer air away from the warmer end eventually reduces the temperature at the warmer end without causing the heater at the cooler end to activate. Thus, energy is conserved as operation of both a heater and a fan is avoided. This is an improvement over previously known systems in which movement of air from the cooler end to the warmer end may result in the heater being activated at the cooler end while the fan continues to run.
In another embodiment, the temperature comparators maybe implemented in a temperature comparator circuit. An exemplary temperature comparator circuit is shown in
The controller may be configured to operate one or two fans in a manner that improves the efficiency of the drum cooling process over processes previously known. An exemplary method of operation for a controller configured to read temperature values from the temperature signals is shown in
Those skilled in the art will recognize that numerous modifications can be made to the specific implementations described above. Therefore, the following claims are not to be limited to the specific embodiments illustrated and described above. The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
