Patent Application
20090060556
The present application relates generally to an image forming device, and more specifically to regulating the output voltage of a high voltage power supply in the image forming device.
The electrophotography process used in some image forming devices, such as laser printers and copiers, utilizes electrical potentials between components to control the transfer and placement of toner. These electrical potentials create attractive and repulsive forces that promote the transfer of charged toner to desired areas while ideally preventing transfer of the toner to unwanted areas. For instance, during the process of developing a latent image on a photoconductive surface, toner particles may be deposited onto latent image features (e.g., corresponding to text or graphics) on the photoconductive surface having a lower surface potential than the charged particles.
The image forming device may include four image forming units associated with four colors: cyan, magenta, yellow, and black. Each image forming unit includes an optical source that is scanned to produce a latent image on the charged surface of the photoconductive unit. Each image forming unit may also include a transfer roller charged to an opposite polarity than the photoconductive unit. The transfer rollers may require a separate power supply capable of adjusting an output voltage.
As new and/or updated models of image forming devices are developed, it may be advantageous to reuse a power supply from a previous model to lower costs and decrease engineering resource needs. However, new models often include higher print speed and print quality than their predecessors, which may dictate the need for higher transfer voltages. The higher transfer voltages may tax or even exceed the output of the power supplies of the previous models, limiting the ability to reuse these power supplies.
The embodiments disclosed herein are directed to methods and devices for a control system to regulate the output voltage of a high voltage power supply (HVPS) in an image forming device. In one embodiment, the HVPS comprises at least two voltage sources connected in series. A print engine controller is configured to disable at least one of the voltage sources when a voltage draw of a load exceeds a maximum differential voltage of the at least two voltage sources. In one embodiment, the HVPS is a component of an existing circuit design, and the control system modifies the existing circuit design for use in an alternate application.
The embodiments disclosed herein are directed to methods and devices for a control system to regulate the output voltage of a high voltage power supply (HVPS) in an image forming device. In one embodiment, the HVPS comprises at least two voltage sources connected in series. A print engine controller is configured to disable at least one of the voltage sources when a voltage draw of a load exceeds a maximum differential voltage of the at least two voltage sources. In one embodiment, the HVPS is a component of an existing circuit design, and the control system modifies the existing circuit design for use in an alternate application.
The HVPS control system may be implemented in a device such as the image forming device 10 generally illustrated in
Within the image-forming device housing 102, the image-forming device 10 includes one or more removable developer cartridges 116, photoconductive units 12, developer rollers 18 and corresponding transfer rollers 20. The image forming device 10 also includes an intermediate transfer mechanism (ITM) belt 114, a fuser 118, and exit rollers 120. Additionally, the image-forming device 10 includes a print engine controller 80 comprising controllers, microprocessors, DSPs, or other stored-program processors (not specifically shown in
Each developer cartridge 116 may include a reservoir containing toner 32 and a developer roller 18. Each developer roller 18 is adjacent to a corresponding photoconductive unit 12, with the developer roller 18 developing a latent image on the surface of the photoconductive unit 12 by supplying toner 32. In a typical color image forming device, three or four colors of toner—cyan, yellow, magenta, and optionally black—are applied successively (and not necessarily in that order) to an ITM belt 114 or to a media sheet 106 to create a color image. Correspondingly,
The operation of the image forming device 10 is conventionally known. Upon command from control electronics, a single media sheet 106 is “picked,” or selected, from the media tray 104 while the ITM belt 114 moves successively past the image forming units 50. As described above, at each photoconductive unit 12, a latent image is formed thereon by optical projection from the imaging device 16. The latent image is developed by applying toner to the photoconductive unit 12 from the corresponding developer roller 18. The toner is subsequently deposited on the ITM belt 114 as it is conveyed past the photoconductive unit 12 by operation of a transfer voltage applied by the transfer roller 20. The media sheet 106 is fed to a secondary transfer nip 122 where the image is transferred from the ITM belt 114 to the media sheet 106 with the aid of a transfer roller 130. The media sheet proceeds from the secondary transfer nip 122 along media path 38. The toner is thermally fused to the media sheet 106 by the fuser 118, and the sheet 106 then passes through the exit rollers 120 onto an output tray 124.
The representative image forming device 10 shown in
The latent image thus formed on the photoconductive unit 12 is then developed with toner 32 from the developer roller 18, on which is adhered a thin layer of toner 32. The developer roller 18 is biased to a potential −V2 that is intermediate to the surface potential −V1 of the discharged latent image areas 28 and the surface potential −V3 of the undischarged areas not to be developed 30. As is well known in the art, the photoconductive unit 12, developer roller 18 and toner 32 may be charged alternatively to positive voltages.
In this manner, the latent image on the photoconductive unit 12 is developed by the toner 32, which is subsequently transferred to the media sheet 106 by the positive voltage +V4 of the transfer roller 20. Alternatively, the toner 32 developing an image on the photoconductive unit 12 may be transferred to an ITM belt 114 and subsequently transferred to the media sheet 106 at a second transfer location (not shown in
In addition to charging the photoconductive unit 12, a charge may be supplied to each of the transfer rollers 20. In one embodiment, the function of the transfer rollers 20 necessitates that the power supply 70 include the capability to output both positive and negative voltages with respect to a system ground. In one embodiment as illustrated in
The output voltage range of the circuit illustrated in
As illustrated in
There are at least two methods to disable the fixed output voltage source 72. In one embodiment, the fixed output voltage source 72 is shut off. The output voltage when no load is applied across the terminals T1, T2, as described above, is the output voltage of the adjustable voltage source 71. However, when a load is applied, the output voltage is equal to the output voltage of the adjustable voltage source 71 minus a voltage drop across a resistance of the disabled fixed output voltage source 72. As illustrated schematically in
In another embodiment, the output of the fixed output voltage source 72 is regulated to 0V, rather than shutting off the voltage source 72. This embodiment may allow the fixed output voltage source 72 to overcome the voltage drop from the resistance R1 of the disabled fixed outpur voltage source 72. However, because both voltage sources 71, 72 affect a net output tolerance, the HVPS to HVPS transfer voltage accuracy for a given pulse-width modulation and load may be worse than with the previous embodiment. Additionally, regulating the output of the fixed output voltage source 72 may require additional control logic not needed with the previous embodiment.
Another consideration when increasing the voltage output of existing circuit designs is maintaining proper creepage and clearance distances. Electrical devices are designed with a separation between conductive components for safety considerations. Among other factors, this electrical isolation is a function of the voltage being carried by the components. In simple terms, the higher the voltage, the greater the required separation between components. This separation may be accomplished by spacing apart the conductive components and/or placing a layer of insulating material over one or more of the components. Breakdown of the electrical isolation may occur through air (clearance) or along a surface (creepage). For example, the surface of insulating materials within an electrical device may become at least partially conductive due to deposits from exposure to chemicals, humidity, and air pollution. Humidity and pollution may increase the conductivity of air surrounding electrical components.
Creepage distance is defined as the distance between two electrical conductors along the surface of an insulating material (e.g., the measured distance takes into account topological features of the insulating material between the conductors). The required creepage distance increases as the voltage carried by the conductors increases. Therefore, minimum creepage distance requirements may be re-evaluated if the voltage stress across terminals T1 and T2 increases when an existing circuit design is modified for another use.
Clearance is defined as the straight line distance between two conductors through air (e.g., the minimum distance through air between the conductors that does not intersect a solid surface). Like creepage, the minimum clearance distance is a function of the voltage carried by the conductors and increases with increasing voltage. As described above, the voltage stress between the terminals T1, T2 is the same before and after implementing the control system, and the clearance distance may not have to be re-evaluated.
As illustrated in
As used herein, the terms “having”, “containing”, “including”, “comprising”, and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.
The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.
