Patent Publication Number: US-8989617-B2

Title: Printer internal climate control

Description:
BACKGROUND 
     Temperature and humidity can affect the performance of commercial and industrial printers. It may be desirable in some printing environments to actively control the temperature and humidity in the printer to improve print quality and to prolong the life of some of the printer components. 
    
    
     
       DRAWINGS 
         FIG. 1  is a block diagram illustrating one example of a new printer internal climate control system. 
         FIG. 2  illustrates one type of printer in which examples of the new climate control system may be implemented, 
         FIG. 3  illustrates one example of a climate control system such as might be used in the printer of  FIGS. 2 . 
         FIG. 4  is a block diagram illustrating one example for the bypass in the climate control systems shown in  FIGS. 1 and 3 . 
         FIG. 5  is a block diagram illustrating one example for the humidifier in the climate control systems shown in  FIGS. 1 and 3 . 
     
    
    
     The same part numbers are used to designate the same or similar parts throughout the figures. 
     DESCRIPTION 
     A new climate control system for digital printing presses and other printers has been developed to help maintain desirable temperature and humidity conditions inside the printer while reducing the level of airborne contaminants in the printer environment. In one example of the new climate control system, warmer air from the printing area is treated to remove environmental contaminants by cooling the air to condense out contaminants in the incoming air stream. The treated air is reheated to the desired temperature before returning to the printing area. The system utilizes an economizer that exchanges heat between the warmer, untreated incoming air and the cooler, treated outgoing air to simultaneously pre-cool the untreated air and reheat the treated air, thus reducing the energy needed to clean and reheat the air. A bypass allows some of the cool, treated air to be diverted around the economizer to help regulate the temperature of the outgoing air. In this example, the system also includes a humidifier to selectively introduce clean water into the treated air stream as needed to maintain the desired humidity of the air returning to the printing area. 
     “Cleaner” air and “dirtier” air are used in this document to describe relatively lesser or greater amounts of a contaminant in the air. 
     Referring now to the block diagram of  FIG. 1 , one example of a new printer climate control system  10  includes a first, economizer heat exchanger  12 , a second heat exchanger  14 , a humidifier  16  and a bypass  18 . Economizer heat exchanger  12 , which exchanges heat between the warmer incoming air and the cooler outgoing air without mixing the two air streams, is also sometimes referred to in this document as an air-to-air heat exchanger. As described in more detail below with reference to the example shown in  FIG. 3 , the components of system  10  are arranged along an air flow path  20  extending from an intake  22  for receiving warmer, dirtier air from a printing area of the printer to an exhaust  24  for returning cooler, cleaner air to the printing area. In the embodiment shown in  FIG. 1 , climate control system  10  also includes a fan  26  for moving air along flow path  20 . 
     In operation, the warmer, dirtier incoming air passes through first heat exchanger  12  where it is cooled by cooler, cleaner outgoing air. The now cooler but still untreated incoming air then passes through second heat exchanger  14  where it is cooled to a predetermined dew point temperature corresponding to a desired level of contaminants remaining in the air that will be returned to the printing area. For example, the ink and toner used in some printing processes generate unwanted vapors, sometimes referred to as “VOCs” (volatile organic compounds), VOC contaminants may be removed by cooling the air in second heat exchanger  14  sufficiently to condense contaminant vapors. The dew point temperature selected to reduce contaminant levels will also establish the maximum level of humidity for the air leaving second heat exchanger  14 . The liquid condensate is removed from second heat exchanger  14  for disposal or recycling. 
     With continued reference to  FIG. 1 , having been treated to remove contaminants, the cool, cleaner air from second heat exchanger  14  moves past or through humidifier  16 . Humidifier  16  adds water selectively, as needed, to increase the humidity in the outgoing air stream to the desired level. Outgoing air passes through air-to-air first heat exchanger  12  where it is heated by the warmer incoming air. Some of the cool, treated air is diverted selectively past first heat exchanger  12  though bypass  18 , as needed, to adjust the temperature of the return air to the desired level. 
     Climate control system  10  may also include a filter or other suitable de-mister  28  for removing liquid droplets from the air downstream from second heat exchanger  14 . In some operating conditions for a climate control system  10 , the air stream downstream from second heat exchanger  14  may contain a fog or mist of residual contaminants. Under these operating conditions, it may be desirable to include a de-mister  28  to help prevent any such residual contaminant droplets from returning to the printing area. 
       FIG. 2  illustrates one type of a printer  30  in which examples of the new climate control system may be implemented.  FIG. 3  illustrates one example of a climate control system  10  for use in printer  10 . Printer  30  shown in  FIG. 2  uses a liquid electro-photographic (LEP) printing process to form images on paper or other print media. LEP printer  30  is one example of a printer that can benefit from the use of a climate control system  10  ( FIG. 3 ) to lower VOC levels and to help maintain the desired temperature and humidity in the printer&#39;s internal operating environment. 
     Referring to  FIG. 2 , printer  30  includes a media feed unit  32  with multiple media input trays  34 ,  36 , and  38 . Sheets of a print medium are fed from stacks  34 ,  36 , and  38  to a printing area  40  in the print engine  42  from which they emerge as printed sheets conveyed to an output stacker  44 . Although printing area  40  and print engine  42  are enclosed during printing operations, the forward part of the printer enclosure is omitted in  FIG. 2  to show printing area  40  and print engine  42 . 
     Print engine  42  includes a charging device  46  for charging the surface of a photoconductive drum  48 . A photo imaging device  50  exposes selected areas of drum  48  to light in the pattern of the desired printed image. A thin layer of liquid toner is applied to the patterned drum  48  through a series of developer units  52  to develop the latent image on drum  48  into a toner image. The toner image is transferred from drum  48  to the outside surface of an intermediate transfer member  54 . The toner image is then transferred to the print medium as the print medium passes through a nip between intermediate transfer member  54  and a pressure roller  56 , VOCs generated as toner carrier fluid evaporates off intermediate transfer member  54  are evacuated to a cooling cabinet  58  housing climate control system  10  at the back of printer  30 . 
     Referring now to  FIG. 3 , hot, “dirty” air from printing area  40  ( FIG. 2 ) is evacuated to climate control system  10  in cabinet  58  through intake  22 , for example at the urging of a suction blower  26 . Air with a comparatively high concentration of VOCs from printing area  40  may reach intake  22  at about 42° C., for example. The warmer, untreated incoming air passes through air-to-air heat exchanger  12  to heat the cooler, treated outgoing air as described above with reference to  FIG. 1 . Thus, the warmer incoming air is cooled as it passes through first heat exchanger  12 , for example to about 33° C. 
     The now cooler but still untreated air then passes through second heat exchanger  14  where it is cooled to a predetermined dew point temperature corresponding to a desired level of VOCs remaining in the air that will be returned to print engine  42  ( FIG. 2 ). In one example for an LEP printing press  30 , the level of VOCs may be reduced to about 200 ppm by cooling the incoming air to about 10° C. at second heat exchanger  14 . The liquid condensate containing water and toner carrier fluid that collects in second heat exchanger  14  is removed for recycling or disposal. 
     In the example shown in  FIG. 3 , an optional de-misting filter  28  is included in the flow path downstream from second heat exchanger  14  to remove droplets that may form as fog in the cool air exiting second heat exchanger  14 . For LEP printing applications, if a de-mister  28  is used, it is expected that de-mister  28  will be located as far as possible from second heat exchanger  14 . Any droplets of carrier fluid remaining in the air flow downstream from second heat exchanger  14  tend to stick to one another and become larger, and thus easier to filter, farther from heat exchanger  14 . 
     The cool air from second heat exchanger  14  moves past a humidifier  16  to first heat exchanger  12 . Humidifier  16  and heat exchanger  12  control the humidity and temperature of the air returning to print engine  42  through exhaust  24 . Humidifier  16  adds water selectively, as needed, to increase the humidity in the outgoing air stream to the desired level. Outgoing air then passes through air-to-air first heat exchanger  12  where it is heated by the warmer incoming air. Some of the cool, treated air is diverted selectively past first heat exchanger  12  though bypass  18 , as needed, to adjust the temperature of the return air to the desired level, In one example for an LEP printer, the outgoing air at exhaust  24  should have a relative humidity of about 38% at a temperature of about 23° C. This temperature and humidity condition at climate control system exhaust  24  allows the air to reach printing area  40  ( FIG. 2 ) at the desired operating conditions, for example about 30% relative humidity at about 27° C. 
       FIG. 4  is a block diagram illustrating one example for bypass  18  in system  10 . Referring to  FIG. 4 , bypass  18  includes an air flow conduit  60  bypassing heat exchanger  12 , a flow control valve  62 , and a thermostat or other suitable control mechanism  64  operatively connected between the outgoing air flow and flow control valve  62 . Thermostat  64  automatically adjusts the position of valve  62  based on the temperature of the outgoing air to control the flow of cool air through bypass conduit  60 , and maintain the desired temperature of air returning to the print engine. 
       FIG. 5  is a block diagram illustrating one example for humidifier  16  in system  10 . Referring to  FIG. 5 , humidifier  16  includes an atomizer  66  connected to a water reservoir  68  and a source of pressurized air  70 . Humidifier  16  also includes an air flow control valve  72  and a humidistat or other suitable control mechanism  74  operatively connected between the outgoing air flow and flow control valve  72 . Humidistat  74  automatically adjusts the position of valve  72  based on the humidity of the outgoing air to control the amount of water sprayed into the flow of air through second heat exchanger  14 , and maintain the desired humidity of air returning to the print engine. 
     Locating humidifier  16  upstream from heat exchanger  12  as shown in  FIG. 3  may be desirable in some printing environments to help ensure the water droplets will vaporize fully into the outgoing air stream, and thus minimize the risk of any water droplets reaching the print engine. However, in other printing environments it may be suitable to locate humidifier  16  downstream from heat exchanger  12 . 
     The examples shown in the figures and described above illustrate but do not limit the invention. Other examples, embodiments and implementations are possible. Therefore, the foregoing description should not be construed to limit the scope of the invention, which is defined in the following claims.