Abstract:
A printing device includes a print media advancement subsystem for providing accurate and timely print media advancement in the printing device. The print media advancement subsystem includes a vacuum chamber for generating a vacuum force through a platen for holding a print media stationary. In response to receiving a print media advance signal from a controller in the printing device, a sealing plate forming a side of the vacuum chamber is removed from the vacuum chamber. When the sealing plate is removed, the vacuum chamber is substantially open to the atmosphere, causing the vacuum chamber to pressurize. The pressurization of the vacuum chamber results in removal of the vacuum force from the print media, allowing the print media to advance along the top surface of the platen with minimal friction.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention is generally related to printing devices. More particularly, the invention is related to a vacuum control mechanism for improving print media advancement in a printing device.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is known to use a vacuum induced force to adhere a sheet of print media to a surface in a printing device. For example, a vacuum may be used for holding a sheet of print media temporarily to a platen (e.g., a print media hold-down surface used in a printing device). In a printing device implementation, typically the platen is used either to transport cut-sheet print media to a printing station of a printing device (e.g., printer, photocopier, facsimile, and the like) and/or to hold the print media at the printing station while images are formed at the printing area (e.g., the print zone) of the printing device. Such vacuum hold-down systems are a relatively common, economical technology to implement commercially and can improve throughput specifications.  
           [0003]    One universal problem, particularly pertinent in the adaptation of a vacuum hold-down system used in a printing device, is related to print media advancement. When print media advances through a print zone, friction is created between the print media and the platen. The resulting friction can decrease line feed accuracy, which can result in the misalignment of the print media through the print zone and inferior print quality.  
           [0004]    A conventional technique for minimizing friction on the platen includes switching a vacuum fan, which generates the vacuum force in a vacuum chamber for holding the print media against the platen, on and off. By switching the vacuum fan off when print media is advancing through a print zone, friction between the print media and the platen is reduced. However, the period of time to pressurize/depressurize a vacuum chamber can have a magnitude in the tens of seconds, which drastically increases printing times. For example, the vacuum fan can typically operate at approximately 9000 rpm to generate the vacuum force. When the fan is switched off, it may continue to spin at a high rpm for a period of time. This increases the time to pressurize the vacuum chamber, and increases print times. Therefore, the throughput of the printing device may be drastically reduced. The period of time to depressurize the chamber when the vacuum fan is switched on may also result in a drastic reduction of throughput for the printing device.  
           [0005]    Another conventional technique utilizes two accumulation vacuum chambers having two different vacuum levels (e.g., one chamber having the pressure of the atmosphere and one having a higher pressure for providing more vacuum force to hold down the print media). A switch connects a main vacuum chamber underneath the platen to one of the two accumulation chambers, depending on whether the print media needs to advance or be secured in the print zone. However, the main chamber underneath the platen still needs to pressurize/depressurize depending on which of the two accumulation chambers are connected to the main chamber through the switch. The period of time to pressurize/depressurize the main chamber is dependent on the size of the accumulation chamber connected to the main chamber. Typically, an accumulation chamber is at least twice as large as the main chamber. The use of accumulation chambers may increase the size of the printing device and the cost of the printing device.  
         SUMMARY OF THE INVENTION  
         [0006]    In an embodiment of the invention, a method is provided for controlling print media advancement in a printing device. The method comprises steps of substantially sealing a vacuum chamber; depressurizing the vacuum chamber to generate a vacuum force for holding a print media; substantially opening the vacuum chamber to pressurize the vacuum chamber; and advancing the print media.  
           [0007]    In another embodiment of the invention a printing device is provided that comprises a vacuum control mechanism for controlling a vacuum force applied to a print media. The vacuum control mechanism is configured to substantially open and close a vacuum chamber to control the vacuum force applied to the print media.  
           [0008]    In still another embodiment of the invention, a print media advancement subsystem in a printing device is provided. The print media advancement subsystem comprises a vacuum chamber including a U-shaped vacuum guide, a platen covering the U-shaped vacuum guide and forming the top of the vacuum chamber, and a sealing plate forming a side of the vacuum chamber. The sealing plate is removable to substantially open and substantially seal the vacuum chamber. A vacuum force is applied through the platen to a print media supported by a top surface of the platen when the vacuum chamber is substantially sealed, and the vacuum force is substantially removed from the print media when the vacuum chamber is substantially open.  
           [0009]    The print media advancement subsystem further comprises a control mechanism connected to the sealing plate and configured to remove the sealing plate from the vacuum chamber in response to receiving a print media advance signal from a controller in the printing device.  
           [0010]    In comparison to known prior art, certain embodiments of the invention are capable of achieving certain aspects. For example, certain embodiments provide a print media advancement system that can reduce the cost and size of conventional systems and provide accurate paper advancement that minimizes paper misalignment during printing and increases print quality. Also, certain embodiments provide a robust mechanism that can increase the life of the printing device. Those skilled in the art will appreciate these and other advantages and benefits of various embodiments of the invention upon reading the following detailed description of a preferred embodiment with reference to the below-listed drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The present invention is illustrated by way of example and not limitation in the accompanying figures in which like numeral references refer to like elements, and wherein:  
         [0012]    [0012]FIG. 1 illustrates an exemplary system employing principles of the invention;  
         [0013]    FIGS.  2 A-B illustrate an exemplary vacuum control mechanism employing principles of the invention;  
         [0014]    [0014]FIG. 3 illustrates an embodiment of a vacuum control mechanism; and  
         [0015]    [0015]FIG. 4 illustrates an exemplary method employing principles of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that these specific details need not be used to practice the present invention. In other instances, well known structures, interfaces, and processes have not been shown in detail in order not to unnecessarily obscure the present invention.  
         [0017]    [0017]FIG. 1 illustrates an exemplary printing device system  100 . The system  100  includes a controller  105  connected to multiple subsystems  115 - 117 . The controller  105  is also connected to a memory  120  and a host device  130 .  
         [0018]    The controller  105  may be configured to provide control logic for the system  100  (e.g., the functionality for a printer). In this respect, the controller  105  may possess a microprocessor, a micro-controller, an application specific integrated circuit, and the like. The controller  105  may be interfaced with the memory  120  that is configured to provide storage of a computer software that provides the functionality for the system  100 . The memory  120  may also be configured to store maintenance information for each subsystem. The memory  120  may be implemented as a combination of volatile and non-volatile memory, such as dynamic random access memory (“RAM”), EEPROM, flash memory, and the like.  
         [0019]    The system  100  may be connected to the host device  130  (e.g., personal computer, server, personal digital assistant, and the like) through an I/O interface  125 . The I/O interface  125  is configured to provide a communication channel between the host device  130  and the controller  105 . The I/O interface  125  may conform to protocols, such as RS-232, parallel, small computer system interface, universal serial bus, etc. The system  100  may include a standalone device, however, that is not connected to a host device.  
         [0020]    The controller  105  is connected to the subsystem  115 , which is a print media advancement subsystem  115 . The print media advancement subsystem  115  includes a vacuum control mechanism (VCM)  135 . The VCM  135  receives print media advancement control signals from the controller  105  for controlling the amount of vacuum force applied to a print media (e.g., paper or other conventional print media). For example, the VCM  135  receives a print media advance signal from the controller  105 . Then, the VCM  135  removes the vacuum force applied to the print media to allow the print media to advance freely to the next subsystem in the system  100 . Then, the VCM  135  applies sufficient vacuum force to the print media to prevent movement of the media, for example, in the print zone during printing.  
         [0021]    Subsystems  116  and  117  include conventional subsystems in a printing device (e.g., ink drop subsystem, print media output subsystem, and the like). The system  100  includes three subsystems  115 - 117  for illustration purposes, and it will be apparent to one of ordinary skill in the art that the system  100  may include as many subsystems as necessary to facilitate printing.  
         [0022]    FIGS.  2 A-B illustrate the VCM  135  in two different positions to facilitate print media advancement control in the system  100 . FIG. 2A illustrates the VCM  135  in the open position, where no vacuum force is provided to a print media. A vacuum chamber  202  is created by a platen  204  forming the top of the vacuum chamber  202  and being supported by a U-shaped vacuum guide  206 . The vacuum guide  206  is supported by a beam  208 . The VCM  135  includes a sealing plate control mechanism  220 , which includes a sealing plate  222  connected to a linear solenoid switch  224  via a piston  226 . The piston  226  is supported by a linear ride  228 , which provides accurate linear travel for the piston  226 . Left and right wings  231  and  232  may optionally be connected to the sealing plate  222  if an additional pull-out force is needed, but are not required for this embodiment. A vacuum fan  240  is connected to the vacuum chamber  202  for generating a vacuum in the vacuum chamber  202 .  
         [0023]    In an exemplary embodiment, the solenoid switch  224  receives print media advance signals from the controller  105 , which causes the solenoid switch  224  to move the sealing plate  222  in a linear motion away from the vacuum chamber  202 . For example, when the solenoid switch  224  receives a print media advance signal, the piston  226  retracts. This causes the sealing plate  222  to travel linearly away from the vacuum chamber  202 , and the vacuum chamber  202  becomes pressurized because it is substantially open to the atmosphere (i.e., air flows into the vacuum chamber). When the vacuum chamber  202  is open, such as shown in FIG. 2A, the vacuum force applied against a print media (not shown) supported by the platen  204  is removed. Instead, the vacuum force is generated at the opening of the vacuum chamber  202 , as illustrated by the vacuum flow  240 . Then, the print media can advance with minimal friction against the platen  204 .  
         [0024]    [0024]FIG. 2B illustrates the sealing plate control mechanism  220  in a closed position, where a vacuum force is applied to a print media supported by the platen  204 . For example, when the solenoid switch  224  does not receive a print media advance signal, the solenoid switch  224  applies pressure to the piston  226 , such that the sealing plate  222  is sealed against a side surface of the vacuum guide  206  and a side surface of the platen  204 . For example, the sealing plate  222  moves linearly towards the vacuum chamber  202  on the linear ride  228  to close the vacuum chamber  202 . When the sealing plate  222  is sealed against the side surfaces of the vacuum guide  206  and the platen  204 , a vacuum force is generated on a print media through orifices  210  in the platen  204 , as illustrated by the vacuum flow  240 . The vacuum force keeps the print media stationary on the platen  204 , and can be applied, for example, in a print zone during printing or in other areas where it is necessary to keep the print media stationary.  
         [0025]    In one embodiment, the solenoid switch  224  employs a conventional linear slide technology that functions to slide the piston  226  along the linear ride  228 . For example, the solenoid switch  224  maintains the sealing plate  222  in the position shown in FIG. 2B, such that the vacuum chamber is closed. When the solenoid switch receives a print media advance signal from the controller  105 , the linear slide technology retracts the piston  226 . This results in the sealing plate  222  being removed from the vacuum chamber  202 , and the vacuum chamber is open. The solenoid switch may pulse the piston  226  to allow the vacuum chamber  202  to be momentarily open. This allows enough time for the print media to advance along the top surface of the platen  204  with minimal friction.  
         [0026]    In another embodiment, shown in FIG. 3, the sealing plate  222  includes wings  231  and  232 , which are spaced, parallel supports. The wings  231  and  232  support springs  254  and  256  respectively. The springs  254  and  256  are connected to pins  260  and  262  extending upwards from the beam  208 . The spring  256  and the pin  262  are hidden from view and are connected to the wing  232  and positioned similarly to the spring  254  and the pin  260  connected to the wing  231 . When the solenoid switch  224  is not applying force on the sealing plate  204  to seal the vacuum chamber  202 , the springs function to move the piston  226  and the sealing plate  222  away from the vacuum chamber. It will be apparent to one of ordinary skill in the art that a single spring and pin may be used if the spring maintains enough force to linearly slide the piston away from the vacuum chamber  202 .  
         [0027]    In this embodiment, the solenoid switch  224  continually forces the sealing plate  222  against the vacuum chamber  202 , such that the vacuum chamber  202  generates a vacuum force, such as illustrated in FIG. 2B. When the solenoid switch  224  receives a print media advance signal from the controller  105 , the solenoid switch  224  momentarily removes the force from the piston  226 . The springs  254  and  256  cause the piston  226  to retract, and the vacuum chamber  202  opens momentarily, as illustrated in FIG. 2A. The print media may then advance along the top surface of the platen  204  with minimal friction.  
         [0028]    [0028]FIG. 4 illustrates an exemplary method  400  employing principles of the present invention. In step  405 , the vacuum chamber  202  is substantially sealed. For example, the solenoid switch  224  applies force to the sealing plate  222  via the piston  226 , such that the sealing plate  222  seals the vacuum chamber  202 .  
         [0029]    At step  410 , the vacuum chamber  202  is depressurized. For example, the vacuum fan  240  is connected to the vacuum chamber  202 . The vacuum fan  240  may be continually running. When the vacuum chamber  202  is sealed, the vacuum chamber automatically depressurizes, creating a vacuum within the vacuum chamber  202 .  
         [0030]    At step  415 , when the vacuum chamber  202  is depressurized, a vacuum force (e.g., the vacuum flow  240 , shown in FIG. 2B) is generated on print media through the platen  204 . For example, a sheet of print media rests on the top surface of the platen  204 . A vacuum force is generated through the orifices  210  in the platen  204  to hold the sheet of print media in a substantially stationary manner.  
         [0031]    At step  420 , the VCM  135  receives a print media advance signal from the controller  105 . For example, the solenoid switch  224  receives the print media advance signal from the controller  105 .  
         [0032]    At step  425 , the vacuum chamber  202  is substantially open to the atmosphere. For example, the solenoid switch  224  retracts the piston  226 , which causes the sealing plate  222  to travel linearly away from the vacuum chamber  202 . Then, the vacuum chamber  202  is substantially open to the atmosphere.  
         [0033]    In another embodiment (shown in FIG. 3), the solenoid switch  224  continually applies a force to the piston  226 , which causes the sealing plate  222  to close and seal the vacuum chamber  202 . When the solenoid switch  224  receives the print media advance signal, the solenoid switch  224  releases the force applied to the piston  226 . Then, the springs  254  and  256  cause the sealing plate  222  to travel linearly away from the vacuum chamber  202 . Then, the vacuum chamber  202  is substantially open to the atmosphere.  
         [0034]    At step  430 , the vacuum force is released from the print media on the top surface of the platen  204 . For example, when the vacuum chamber  202  is opened, such as shown in FIG. 2A, the vacuum chamber  202  substantially instantly pressurizes (e.g., in less than 0.1 seconds), and the vacuum flow shifts from the platen (e.g., the vacuum flow  240 ) to outside the vacuum chamber (e.g., the vacuum flow  230 ).  
         [0035]    At step  435 , the print media advances from the top surface of the platen  204 . Because, the vacuum force is released from the print media on the top surface of the platen  204 , the print media may easily advance with minimal friction against the platen  204 . Furthermore, the print media may advance almost immediately after the VCM  135  receives the print media advance signal, because of the minimal period of time required to pressurize the vacuum chamber  202 .  
         [0036]    After step  435 , the method  400  may return to step  405 . For example, the VCM  135  may pulse, such that the vacuum chamber  202  momentarily opens and closes upon receipt of a print media advance signal from the controller  105 .  
         [0037]    While this invention has been described in conjunction with the specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. For example, conventional switches, other than a solenoid switch may be used in the VCM  135 . Also, it will be apparent to one of ordinary skill in the art that control mechanism  220  may be comprised of other mechanisms that are functional to open and close a vacuum chamber. Also, the controller  105  may transmit more than one control signal to the VCM  135 . For example, the controller  105  may transmit a print media advance signal to the VCM  135 , which causes the vacuum chamber  202  to be opened. Then, the VCM  135  may continue to keep the vacuum chamber  202  open until the VCM  135  receives a print media hold signal from the controller  105 . Then, the VCM  135  seals the vacuum chamber  202 . These and other changes that may be made without departing from the spirit and scope of the invention.