Patent Publication Number: US-6714229-B2

Title: Image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus which takes outside air into a housing to cool down the inside thereof. 
     2. Background Arts 
     In an image forming apparatus such as a printer, a copy machine, a facsimile and the like, there are provided many parts in a housing some of which generate heat. In a color thermal printer in which a thermal head makes tightly contact with a color thermo-sensitive recording paper for thermal recording, for example, a greatest amount of heat is generated from an optical fixing lamp. The fixing lamp fixes the thermal coloring layer of the color thermo-sensitive recording paper. When the bulb temperature of the fixing lamp increases too much, the efficiency of fixing decreases due to decrease in an amount of light emitted therefrom. In the thermal head, a heat element generates heat to form pixels on the thermo-sensitive recording paper, so that the recording density of the color pixels is varied as the temperature of the thermal head increases. Therefore, it is necessary to control the temperature inside the housing of the color thermal printer. 
     There is known an image forming apparatus which can efficiently cool down the inside of the housing. The image forming apparatus has a duct for discharging the heat inside of the housing into the outside, and a fan for generating airflow inside the duct. Japanese Patent Laid-Open Publication No. 2000-305439, for example, discloses an image forming apparatus having plural discharge fans installed inside a duct in series. A louver of the duct is connected to the inside and outside of a housing. The discharge fans discharge heat generated inside the housing with outside air from a discharge opening connected to the outside of the housing. An image forming apparatus, disclosed by Japanese Patent Laid-Open Publication No. 08-220952, further blows the outside air sucked from the outside of the housing on a heat source to cool it down. 
     In an image forming apparatus with plural heat sources, as described in Japanese Patent Laid-Open Publications No. 06-059549 and 2002-023571, a duct is so disposed inside the housing as to pass the vicinity of each heat source. An opening is formed in the duct at a position so as to face each heat source. A discharge fan installed inside the duct discharges heat generated from the heat sources into the outside of the housing. 
     In the above image forming apparatuses, however, dust in the outside air is sucked thereinto with the outside air. The dust tends to cause smudges on a recording paper, so that a print image is adversely affected. For this reason, the image forming apparatuses according to Japanese Patent Laid-Open publications No. 08-220952 and 2002-023571 further comprise an air filter provided inside the duct to eliminate the dust. In these image forming apparatuses, it is possible to prevent degradation in the print image, because the dust in the outside air does not get into the apparatus. 
     When the air filter disposed inside the duct is clogged with the dust, however, an amount of airflow rapidly decreases. Cooling effect inside the housing extremely becomes worse. Thus, the air filter needs troublesome maintenance, in other words, needs to be exchanged at regular intervals. 
     In the image forming apparatus according to Japanese Patent Laid-Open publication No. 2002-023571, a switch valve is provided in some of plural discharge openings disposed in a discharge path. Since the switch valve opens and closes in accordance with the clogging of the air filter, it is possible to prevent decrease in the amount of the airflow for discharging. In this image forming apparatus, air filtered by the air filter passes through the discharge openings. Accordingly, in a case where the air filter heavily clogs, the airflow cannot be generated in the discharge path even if the switch valve is opened. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an image forming apparatus which can cool the inside of a housing even when an air filter clogs. 
     To achieve the above object, an image forming apparatus with a housing according to the present invention comprises a duct provided in the housing, an air filter, an inside inlet, and a cooling fan. The duct has at least one outside inlet opened to the outside of the housing, and at least one discharge opening provided in the housing. The air filter is disposed between the outside inlet and the discharge opening. The inside louver sucks inside air in the housing. The cooling fan is disposed in front of the discharge opening of the housing. The air filter filters outside air sucked into the duct, to prevent dust from getting into the housing. The cooling fan releases mixed air, which includes the outside air entered from the outside inlet and passing through the duct, and the inside air entered from the inside inlet, into the housing, for the purpose of circulating the air inside the housing. 
     The inside inlet may be a gap formed between the discharge opening and a cooling fan, or may be at least one opening formed in a sidewall of the duct. The opening is formed between the air filter and the cooling fan. 
     The cooling fan blows the mixed air on a part generating heat to cool it. 
     A suction fan may be provided in the vicinity of the outside inlet. The suction fan forcefully takes the outside air into the duct through the outside inlet. 
     The suction fan may be disposed between the outside inlet and the air filter. 
     The operation of the cooling fan and the suction fan is so controlled by a common controller that the cooling fan and the suction fan rotate in the same timing. 
     According to the present invention, the air circulates inside a housing even when an air filter clogs, because the image forming apparatus is provided with an inside inlet for sucking inside air in the housing. The air is blown on a part generating heat in the housing, so that it is possible to cool the inside of a housing even when an air filter clogs. It is also possible to contribute to reduction in cost of the image forming apparatus, as the number of the controllers decrease. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become apparent from the following detailed descriptions of the preferred embodiments when read in association with the accompanying drawings, which are given by way of illustration only and thus do not limit the present invention. In the drawings, the same reference numerals designate like or corresponding parts throughout the several views, and wherein: 
     FIG. 1 is a schematic view showing the structure of a color thermal printer; 
     FIG. 2 is an explanatory view showing airflow during printing; 
     FIG. 3 is an explanatory view showing airflow when an air filter clogs; 
     FIG. 4 is a graph showing variation in temperature of an ultraviolet lamp when the air filter clogs; and 
     FIG. 5 is an explanatory view showing airflow in a color thermal printer according to another embodiment, when an air filter clogs. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring to FIG. 1, a color thermal printer  2  uses a recording paper roll  4  wound with continuous color thermo-sensitive recording paper  3  as a recording medium. A paper magazine  5  having lightproof construction contains the recording paper roll  4 . The paper magazine  5  is set in a paper feed section  7 , which is provided in the front surface of a housing  6  of the color thermal printer  2 . 
     A feed roller unit  9  for advancing and retracting the color thermo-sensitive recording paper  3  is attached inside the paper magazine  5 . A capstan roller and a pinch roller constitute the feed roller unit  9 . Upon setting the paper magazine  5  in the paper feed section  7 , the capstan roller is electrically or mechanically connected to the color thermal printer  2 , and the operation of the capstan roller is controlled by the printer  2 . The color thermo-sensitive recording paper  3  drawn from the paper magazine  5  is carried along an approximately U-shaped carrying path provided inside the housing  6 . 
     The color thermo-sensitive recording paper  3 , as is well known, has a cyan thermo-sensitive coloring layer, a magenta thermo-sensitive coloring layer, and a yellow thermo-sensitive coloring layer formed on a base in this order from underneath. Since the yellow thermo-sensitive coloring layer, being a top layer, has the highest heat sensitivity, the yellow thermo-sensitive coloring layer develops a color of yellow with low heat energy. Since the cyan thermo-sensitive coloring layer, being a bottom layer, has the lowest heat sensitivity, the cyan thermo-sensitive coloring layer develops a color of cyan with high heat energy. The yellow thermo-sensitive coloring layer loses its color developing capability when near-ultraviolet rays of 420 nm are irradiated thereto. The magenta thermo-sensitive coloring layer develops a color of magenta with intermediate heat energy between the yellow thermo-sensitive coloring layer and the cyan thermo-sensitive coloring layer, and loses its color developing capability when ultraviolet rays of 365 nm are irradiated thereto. 
     On the carrying path of the color thermo-sensitive recording paper  3 , a yellow printing station  11 , a magenta printing station  12 , and a cyan printing station  13  are disposed at predetermined intervals. The yellow printing station  11  includes a carry roller set  15 , a thermal head  16 , and a platen roller  17 . The carry roller set  15  carries the color thermo-sensitive recording paper  3  in a paper advancing direction. The thermal head  16  is pressed to contact with the color thermo-sensitive recording paper  3  to develop the yellow thermo-sensitive coloring layer. The platen roller  17  rotates in accordance with the carry of the color thermo-sensitive recording paper  3 , with nipping the color thermo-sensitive recording paper  3  with the thermal head  16 . 
     The carry roller set  15  comprises a capstan roller rotated by a stepping motor, and a pinch roller nipping the color thermo-sensitive recording paper  3  with the capstan roller. 
     The thermal head  16  is provided with a heating element array in which a lot of heating elements are linearly arranged. In printing, the heating element array is pressed to contact with the color thermo-sensitive recording paper  3  on the platen roller  17 . When the heating element array generates heat, the heat energy therefrom develops the yellow thermo-sensitive coloring layer of the color thermo-sensitive recording paper  3 . 
     The magenta printing station  12  and the cyan printing station  13  are provided with carry roller sets  18  and  21 , thermal heads  19  and  22 , and platen rollers  20  and  23 , respectively. The structure of the magenta printing station  12  and the cyan printing station  13  is the same as that of the yellow printing station  11 , so detailed description is omitted. 
     A yellow fixing device  25  is disposed between the yellow printing station  11  and the magenta printing station  12 . A magenta fixing device  26  is disposed between the magenta printing station  12  and the cyan printing station  13 . The yellow fixing device  25 , which fixes the yellow thermo-sensitive coloring layer of the color thermo-sensitive recording paper  3 , comprises plural ultraviolet lamps  28  for radiating the near-ultraviolet rays the emission peak of which is 420 nm, and an approximately box-shaped lamp house  29  for containing the ultraviolet lamps  28 . The ultraviolet lamp  28  is in the shape of a bar extending to the widthwise direction of the color thermo-sensitive recording paper  2 . 
     Referring to FIG. 2, the lamp house  29  is provided with an irradiation opening  29   a  which is formed in the surface opposite to the color thermo-sensitive recording paper  3 . The ultraviolet lamps  28  irradiate the color thermo-sensitive recording paper  3  with the ultraviolet rays through the irradiation opening  29   a . A transparent guide plate  31  is fitted into the irradiation opening  29   a . The guide plate  31 , made out of transparent materials such as glass and acrylic, allows the ultraviolet rays to pass through. A cooling opening  29   b , into which airflow for cooling flows, is formed in the surface opposite to the irradiation opening  29   a , of the lamp house  29 . 
     The magenta fixing device  26  is provided with a lamp house  34  and a guide plate  35 . The lamp house  34  has ultraviolet lamps  33  for radiating the ultraviolet rays the emission peak of which is 365 nm, an irradiation opening  34   a , and a cooling opening  34   b . The structure of the lamp house  34  and the guide plate  35  is the same as that of the yellow fixing device  25 , so detailed description is omitted. 
     An ejection slit  37  as the lowest reaches of the carrying path is provided in the upper portion of the front wall of the housing  6 . A cutter  38  for cutting the continuous color thermo-sensitive recording paper  3  is provided at inside of the ejection slit  37 . The printed color thermo-sensitive recording paper  3  cut by the cutter  38  into a predetermined size is ejected through the ejection slit  37 . 
     On the backward of the color thermal printer  2 , a duct  40  is disposed on the top wall of the housing  6  in such a manner as to face downward. The duct  40  has a louver  41  (referring to FIG. 2) as an outside inlet formed in the top wall of the housing  6  to take in outside air, a first discharge opening  42  disposed in the vicinity of the yellow fixing device  25 , and a second discharge opening  43  disposed in the vicinity of the magenta fixing device  26 . 
     A suction axial flow fan  45  for taking outside air into the duct  40 , and an air filter  46  for filtering the taken outside air are installed inside of the louver  41  in the duct  40 . The suction axial flow fan  45  is so disposed near the louver  41  as to efficiently take the outside air into the housing  6 . The air filter  46  has a filtering member folded in the shape of pleats. Since the surface area of the filtering member is large, it is possible to use the air filter  46  for the long term without clogging up. The positions of the suction axial flow fan  45  and the air filter  46  may be changed. 
     A first axial flow fan  49  for cooling is disposed between the first discharge opening  42  and the yellow fixing device  25 . A second axial flow fan  50  for cooling is disposed between the second discharge opening  43  and the magenta fixing device  26 . The first and second axial flow fans  49  and  50  blow the filtered outside air flowing into the duct  40  into the yellow and magenta fixing devices  25  and  26 , respectively. 
     The first axial flow fan  49  is disposed in front of the first discharge opening  42  of the duct  40  with keeping a gap CL 1  as an inlet for inside air. When the outside air is not sucked through the louver  41  due to the clogging of the air filter  46 , or when an amount of sucked air is extremely decreased, as shown in FIG. 3, air is supplied to the first axial flow fan  49  through the gap CL 1 , in order to circulate the air inside the housing  6 . The second axial flow fan  50  is disposed in front of the second discharge opening  43  with keeping a gap CL 2  having the same function as the gap CL 1 . The size of the gap between the discharge openings and the axial flow fan is determined with considering the static pressure of the axial flow fan. Accordingly, steep increase in temperature of the installed parts is prevented, because the air circulates inside the housing  6  even when the air filter clogs up. It is possible to prevent degradation in the image quality of a print due to insufficient fixing, and increase in time of the print. 
     According to the present invention, the air is circulated inside the housing  6  by the first and second axial flow fans  49  and  50  for cooling, even when the air filter  46  clogs up. Thus, it is unnecessary to separately control the suction axial flow fan  45  and the first and second axial flow fans  49  and  50 , on the contrary, they may be controlled in the same timing. In this case, a common controller  52  and driver  53  can control the rotation of the suction axial flow fan  45  and the first and second axial flow fans  49  and  50 , so that it is possible to contribute to cost reduction. 
     The operation of the above color thermal printer  2  will be hereinafter described. Upon starting the print, the controller  52  rotates the suction axial flow fan  45  and the first and second axial flow fans  49  and  50  via the driver  53 . Each of the axial flow fans  45 ,  49  and  50  may start rotating at the same time as the power-on of the color thermal printer  2 , or may start rotating when the measured temperature of the yellow fixing device  25  and the magenta fixing device  26  exceeds a predetermined value. 
     Referring to FIG. 2, the suction axial flow fan  45  takes the air outside of the housing  6  into the duct  40  through the louver  41 . The outside air flowing into the duct  40  is filtered by the air filter  46  to eliminate a foreign object like dust. The filtered outside air flowing through the duct  40  is released from the first and second discharge openings  42  and  43  by the static pressure of the first and second axial flow fans  49  and  50 . 
     The first axial flow fan  49  blows the outside air released from the first discharge opening  42  into the lamp house  29  through the cooling opening  29   b  of the yellow fixing device  25 , for the purpose of cooling the ultraviolet lamps  28 . The second axial flow fan  50  blows the outside air released from the second discharge opening  43  into the lamp house  34  through the cooling opening  34   b  of the magenta fixing device  26 , for the purpose of cooling the ultraviolet lamps  33 . 
     The feed roller unit  9  carries the color thermo-sensitive recording paper  3 , drawn out from the recording paper roll  4 , along the carrying path of the color thermal printer  2 . In the yellow printing station  11 , the carry roller set  15  carries the color thermo-sensitive recording paper  3  at a constant speed in the paper advancing direction. While doing so, the thermal head  16  nips the color thermo-sensitive recording paper  3  with the platen roller  17 , to print the yellow image on the yellow thermo-sensitive coloring layer. 
     In order to fix the yellow thermo-sensitive coloring layer, the yellow fixing device  25  irradiates the color thermo-sensitive recording paper  3 , on which the yellow image is printed, with the near-ultraviolet rays having the emission peak of 420 nm. An amount of light emitted from the ultraviolet lamps  28  does not decrease, because the first axial flow fan  49  cools the yellow fixing device  25 . 
     The color thermo-sensitive recording paper  3  with the fixed yellow thermo-sensitive coloring layer is sent to the magenta printing station  12 . In the magenta printing station  12 , the thermal head  19  prints the magenta image on the magenta thermo-sensitive coloring layer, while the carry roller set  18  carries the color thermo-sensitive recording paper  3  at a constant speed in the paper advancing direction. 
     In order to fix the magenta thermo-sensitive coloring layer, the magenta fixing device  26  irradiates the color thermo-sensitive recording paper  3 , on which the magenta image is printed, with the ultraviolet rays having the emission peak of 365 nm. An amount of light emitted from the ultraviolet lamps  34  does not decrease, because the second axial flow fan  50  cools the magenta fixing device  26 . 
     Then, the color thermo-sensitive recording paper  3  is sent to the cyan printing section  13 . The thermal head  22  prints the cyan image on the cyan thermo-sensitive coloring layer. The color thermo-sensitive recording paper  3  on which three primary color images are printed is cut by the cutter  38 , and is ejected from the ejection slit  37  out of the housing  6 . 
     When the printing operation as described above is carried out for the long terms, the air filter  46  comes to be clogged up with the dust in the outside air. In a conventional color thermal printer which takes in air only from an air filter, an amount of air supplied from a suction axial flow fan decreases when the air filter clogs. Accordingly, as shown in FIG. 4, the bulb temperature of ultraviolet lamps suddenly increases after the clogging of the air filter. Decrease in an amount of light emitted from the ultraviolet lamps, due to increase in the bulb temperature thereof, causes defect in fixing an image and delay in fixing time. 
     In the present invention, however, the gaps CL 1  and CL 2  are provided between the first discharge opening  42  and the first axial flow fan  49 , and between the second discharge opening  43  and the second axial flow fan  50 , respectively. When suction resistance increases due to the clogging of the air filter  46 , as shown in FIG. 3, the air inside of the housing  6  is supplied to the first and the second axial flow fans  49  and  50  through the gaps CL 1  and CL 2 . Accordingly, as shown in FIG. 4, the temperature of the yellow fixing device  25  and the magenta fixing device  26  is prevented from increasing. 
     The gaps CL 1  and CL 2  as the inlets are provided in the vicinity of the first and second axial flow fans  49  and  50 . Therefore, it is possible to efficiently use the air blow power of the first and second axial flow fans  49  and  50 . The yellow fixing device  25  and the magenta fixing device  26  are so disposed in the lower reaches of airflow by the first and second axial flow fans  49  and  50 , as to be cooled down effectively. If the clogged air filter  46  is exchanged with a new one, as shown with a broken line of FIG. 4, the bulb temperature of the ultraviolet lamps is lowered to an appropriate value. 
     In the above embodiment, the gaps CL 1  and CL 2  are provided as the inlets. However, as shown in FIG. 5, plural openings  60  may be formed in the wall of the duct  40  as the inlets. The openings  60  are formed between the air filter  46  and the first discharge opening  42 , and between the air filter  46  and the second discharge opening  43 . Since the air at various locations inside of the housing  6  is sucked into the duct  40 , it is possible to further improve the circulatory efficiency of the air inside of the housing  6 . Both the gaps CL 1  and CL 2  and the openings  60  may be provided as the inlets. 
     The above embodiment uses the color thermo-sensitive recording paper  3  with triple layer structure having the cyan, magenta, and yellow thermo-sensitive coloring layers. However, for example, a color thermo-sensitive recording paper with quadruple layer structure may be used. The color thermo-sensitive recording paper with the quadruple layer has a black thermo-sensitive coloring layer in addition to the three coloring layers described above. 
     The suction axial flow fan  45  and the first and second axial flow fans  49  and  50 , which rotate in the same timing in the above embodiment, may rotate independently. In this case, the rotation of the suction axial flow fan  45  may stop in response to the clogging, detected by an airflow sensor provided inside the duct  40 . 
     The axial flow fans are used in the above embodiment, but a sirocco fan, a cross flow fan, or the like may be used. 
     In the above embodiment, the color thermal printer is three-head one-path type. The present invention, however, maybe applied to a one-head three-path type of color thermal printer, which prints color images with reciprocating the recording paper. 
     In the above embodiment, the present invention is applied to the color thermal printer. The present invention, however, may be applied to a dye sublimation type printer and a wax-transfer type printer with color ink sheets of yellow, magenta, and cyan, a printer with a toner cartridge, an image forming apparatus such as a copying machine, a facsimile and the like, a machine containing a part which generates heat. 
     Although the present invention has been described with respect to the preferred embodiment, the preset invention is not to be limited to the above embodiment but, on the contrary, various modifications will be possible to those skilled in the art without departing from the scope of claims appended hereto.