Abstract:
An image forming apparatus according to an aspect of the invention includes: a media sensor that detects a type of a recording paper; a development unit configured to develop an image on the recording paper; a pair of rollers that fixes the image on the recording paper by nipping the recording paper bearing the image developed in the development unit and forcing the recording paper to pass by; a main heater that heats the pair of rollers by passing a current therethrough when the recording paper passes by; and an auxiliary heater that selectively heats at least one of the pair of rollers by passing a current therethrough when the recording paper passes by the pair of rollers in a case where the media sensor detects that the weight per unit of the recording paper or the thickness of the recording paper is equal to or greater than a specific value.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    (1) Field of the Invention 
         [0002]    The present invention relates to an image forming apparatus, such as a copying machine, a printer, and an MFP (Multi Function Peripherals), and more particularly, to an improvement of a heat fusing device for an image in the visible form. 
         [0003]    (2) Description of the Related Art 
         [0004]    For an MFP, media onto which are printed color images have been increasing. Taking print media of paper alone as an example, various types of paper that differ in thickness or the like are used. The types of paper are normally divided by the basic weight indicating a weight per a specific area (unit: g/m 2 ), and for example, papers that fall within the ranges of 64 to 105, 106 to 163, 164 to 209, 210 to 256, and 257 to 300 are referred to as plain papers, thick papers  1 , thick papers  2 , thick papers  3 , and thick papers  4 , respectively. These basic weights depend on the density and the thickness of papers, and given that the density of papers is almost constant, then the basic weights are proportional to the thickness. 
         [0005]    When the thickness of papers varies with the types of papers as described above, optimal print conditions to achieve a satisfactory print image vary as well. Generally, when the thickness of papers is increased, the fixing temperature of an image in the visible form drops abruptly, and when fixing is performed on the images at the same temperature, a wait-stop occurs due to poor fixing and a drop in temperature, which makes it impossible to achieve a satisfactory print image. Hence, in order to achieve a satisfactory print image, it becomes necessary to determine the type of papers used for printing. 
         [0006]    In order to identify the types of papers, the user used to input the thickness and the basic weight on the screen displayed on the control panel of the MFP, and the fixing of the image in the visible form is controlled and a paper carrying rate is controlled according to the thickness and the basic weight of papers thus inputted. 
         [0007]    The user, however, is rarely aware of the thickness of papers or the like except when he sets print papers in the print paper accommodating cassette. Hence, papers of wrong type are set often and the user fails to obtain a satisfactory print image, which results in a waste of print papers. 
         [0008]    As is disclosed in JP-A-2004-126328, there is an image forming apparatus, in which plural temperature detecting elements are provided to a heating member to determine the type of a recording material according to a difference of temperatures detected by the temperature detecting elements, and the fixing temperature is set according to the determination result. However, because plural temperature detecting elements are required and the fixing temperature is changed in response to a difference of the temperatures thereof, there are problems that it takes a time to reach an optimal fixing temperature, the mechanism becomes complex, and so forth. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The invention was devised in view of the problems in the related art as discussed above, and therefore provides an image forming apparatus having an image fixing device capable of changing the fixing temperature or the like in response to the type of papers and thereby achieving a satisfactory print image swiftly. 
         [0010]    In an aspect of the invention, an image forming apparatus is provided, which includes: a media sensor that detects a type of a recording paper by one of a weight per unit and a thickness of the recording paper; a development unit configured to develop an image on the recording paper; a pair of rollers that fixes the image on the recording paper by nipping the recording paper bearing the image developed in the development unit and forcing the recording paper to pass by; a main heater that heats the pair of rollers by passing a current therethrough when the recording paper passes by; and an auxiliary heater that selectively heats at least one of the pair of rollers using an auxiliary power supply when the recording paper passes by the pair of rollers by passing a current therethrough in a case where the media sensor detects that one of the weight per unit of the recording paper and the thickness of the recording paper is equal to or greater than a specific value. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a view showing the configuration of an image forming apparatus according to one embodiment of the invention; 
           [0012]      FIG. 2  is a view showing the flowchart used to describe operations of the image forming apparatus shown in  FIG. 1 ; 
           [0013]      FIG. 3  is a view showing the flowchart used to describe operations in the case of a copy mode or a print mode in an example when the invention is applied to an MFP; and 
           [0014]      FIG. 4  is a view showing the flowchart used to describe operations in the case of the print mode. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    Hereinafter, embodiments of the invention will be described with the use of the drawings. 
       First Embodiment 
       [0016]      FIG. 1  is a view showing the configuration of one embodiment when the invention is applied to an MFP. 
         [0017]    The MFP  10  is formed of a system control unit  11  that controls the entire apparatus, a scanner unit  12 , a facsimile unit  13 , and an engine control unit  14  controlled by the system control unit, a control panel  15  that sends a control signal to the system control unit  11 , a media sensor  18  that detects the paper type of a recording paper  17  or the like, an image generation unit  19  that generates an image, a development unit  20  that develops the image generated in the image generation unit  19  on a recording paper  17 , a fixing device  25  composed of a heat roller  22  having a main heater  21   a  inside and a press roller  24  having a main heater  21   b  and an auxiliary heater  23  inside, an auxiliary power supply device  26  that controls ON and OFF actions of the auxiliary heater  23  upon receipt of a signal relating to the paper type from the media sensor  18 , an AC power supply  27 , and an ON and OFF heating control unit  28  that is connected to the AC power supply  27  and controls heating of the main heaters  21   a  and  21   b.    
         [0018]    A device connected to the MFP  10  from the outside, for example, a personal computer  29 , is connected to the system control unit  11  of the MFP  10 . The auxiliary power supply device  26  includes an auxiliary power supply that passes a current through the auxiliary heater  23  when auxiliary heating is necessary, a charge and discharge circuit, and a control circuit for these components. 
         [0019]    As the main heater  21   a  enclosed in the heat roller  22 , for example, a halogen lamp of about 900 W is used. As the main heater  21   b  provided inside the press roller  24 , for example, a halogen lamp of about 300 W is used. As the auxiliary heater  23 , for example, a halogen lamp of about 500 W is used. The auxiliary power supply and the ON and OFF control heating control unit  28  convert an alternating current to a direct current and pass a direct current through these halogen lamps. The auxiliary heater  23  may be provided inside the heat roller  22 . A heating method in the fixing device is not limited to a method of having the heater inside the roller, and a fixing portion may be heated by means of induction heating (IH). 
         [0020]    The MFP  10  has at least three modes: a copy mode, a facsimile mode, and a print mode. In the copy mode, it is able to capture an image from the scanner unit  12 , generate the image in the image generation unit  19 , develop the image on a recording paper  17  in the development unit  20 , and fix the image in the fixing device  25 . In the facsimile reception mode, it is able to take in a facsimile signal sent from the outside into the facsimile unit  13 , reproduce an image in the image generation unit  19 , develop the image on a recording paper  17  in the development unit  20 , and discharge the recording paper  17  to the outside after the developed image is fixed in the fixing device  25 . In a facsimile transmission mode, it is able to scan a transmission original document in the scanner unit  12  first, then convert the image into a facsimile signal, and transmit the facsimile signal to the outside via the facsimile unit  13 . 
         [0021]    In the print mode, it is in a mode in which, for example, a display image on the personal computer  29  connected to the MFP is printed. After an image signal of the personal computer  29  is taken into the image generation unit  19  via the system control unit  11  of the MFP  10 , the image signal is sent to the development unit  20 , and the image is developed on a recording paper  17  in the development unit  20 . Thereafter, the recording paper  17  is sent to the fixing device  25  for the developed image to be fixed thereon and discharged to the outside. 
         [0022]    The control on these modes is inputted as the user selects, for example, icons of the copy mode, the facsimile mode, and the print mode displayed on the control panel, and control signals of these modes are sent to the system control unit  11  for the processing desired by the user to be performed. 
         [0023]    The engine control unit  14  has the capability to perform mechanical control chiefly using motors, such as scan on original documents in the scanner unit  12 , feeding of recording papers  17 , rotational control of the heat roller  22  and press roller  24  in the fixing device  25 . Overall control on the engine control unit  14 , the scanner unit  12 , and the facsimile unit  13  is performed by the system control unit  11 . 
         [0024]    The fixing device  25  performs heat fixing by nipping the recording paper  17  bearing the image developed on the recording paper  17  between the heat roller  22  and the press roller  24 . The heat roller  22  is heated by passing a current through the main heater  21   a  provided inside thereof, and the press roller  24  is heated by passing a current through the main heater  21   b  and the auxiliary heater  23  provided inside thereof. A current is passed through the main heater  21   a  inside the heat roller  22  and the main heater  21   b  inside the press roller  24  by converting an alternating current to a direct current through the ON and OFF control by the ON and OFF heating control unit  28 . 
         [0025]    Meanwhile, a current is passed through the auxiliary heater  23  inside the press roller  24  by the auxiliary power supply  26  connected thereto. 
         [0026]    The media sensor  18  determines the paper type of the recording paper  17 , and determines as being the plain paper, the thick paper  1 , the thick paper  2 , the thick paper  3 , or the thick paper  4  by the weight per unit, for example, the basic weight described above. 
         [0027]    Besides the foregoing, the media sensor  18  is able to determine the paper type using a magnetic sensor, or a distance measuring sensor that detects a paper thickness by measuring rotations of the roller that feeds the recording paper and a moving distance in that instance. 
         [0028]    Operations of the MFP of this embodiment will now be described with the use of the flowchart of  FIG. 2 . Initially, in a case where the mode of the MFP  10  is switched to either the copy mode or the print mode, in Step S 201 , the media sensor  18  determines the paper type of the recording paper  17  from the weight per unit. In subsequent Step S 202 , whether the weight per unit of the recording paper  17  is equal to or greater than a specific value, that is, whether the recording paper  17  is the thick paper  2 , the thick paper  3 , or the thick paper  4 , is detected from the detection result. In a case where the recording paper  17  is the thick paper  2  (164 to 209 g/m 2 ) or thicker, the auxiliary power supply of the auxiliary power supply device  26  is switched ON in Step S 203 . When the auxiliary power supply comes ON, a direct current passes through not only the main heater  21   b  but also the auxiliary heater inside the press roller  24 . 
         [0029]    Printing is executed in subsequent Step S 204 . More specifically, the image is fixed as the recording paper  17 , on which the image has been developed in the development unit  20 , passes through a space between the heat roller  22  and the press roller  24  in the fixing device  25 . In this instance, when the recording paper  17  is the thick paper  2  or thicker as described above, a current passes through not only the main heater  21   b  but also the auxiliary heater  23  inside the press roller  24 , which stabilizes the fixing temperature at the time of image fixing. 
         [0030]    Meanwhile, in a case where the recording paper  17  is determined as being the plain paper or the thick paper  1  by the media sensor  18  in Step S 202 , the flow proceeds to Step S 205  to switch OFF the auxiliary power supply of the auxiliary power supply device  26 . Thereafter, the recording paper  17  bearing the image developed in the development unit  20  is inserted into a space between the heat roller  22  and the press roller  24  in the fixing device  25  for the image to be fixed thereon (Step S 204 ). 
         [0031]    In this instance, a current passes through the main heater  21   b  inside the press roller  24  but no current passes through the auxiliary heater  23 . 
         [0032]    As has been described, in a case where the recording paper  17  is the plain paper (basic weight of 64 to 105 g/m 2 ) or the thick paper  1  (basic weight of 106 to 163 g/m 2 ), the auxiliary heater  23  goes OFF. In a case where the recording paper is the thick paper  2  (basic weight of 164 to 209 g/m 2 ) or thicker, the auxiliary heater  23  comes ON to stabilize the fixing temperature of the image, which makes it possible to achieve a satisfactory fixed image. 
         [0033]    The ON and OFF control on the auxiliary heater  23  may be performed by determining whether the basic weight is that of the thick paper  1  or thinner or by determining whether the basic weight is that of the thick paper  2  or thicker. 
       Second Embodiment 
       [0034]    A second embodiment of the invention will now be described. An MFP used in this embodiment is almost the same as the apparatus shown in  FIG. 1 .  FIG. 3  shows the flow of the processing when the apparatus is resumed from a preheat state or resumed from a sleep state.  FIG. 4  shows the flow of the processing during the printing. 
         [0035]    Initially, when the apparatus is resumed from the preheat state or resumed from the sleep state, the temperature of the image fixing portion of the fixing device  25  is detected in Step S 301  of  FIG. 3  to detect whether this temperature is equal to or higher than a specific value. In a case where the temperature of the image fixing portion is equal to higher than the specific value, the auxiliary power supply is switched OFF in Step S 302 . 
         [0036]    When the temperature of the image fixing portion is equal to or higher than the specific value in Step S 301 , because the warming-up will end shortly, there is no need to raise the heating temperature using the auxiliary heater  23 . Hence, the auxiliary power supply is not switched ON. 
         [0037]    Meanwhile, in a case where the temperature of the image fixing portion of the fixing device  25  has not reached the specific value in Step S 301 , whether the mode of the MFP  10  is the copy mode is determined in subsequent Step S 303 . When the mode is switched to the copy mode, it is assumed that the user stands nearby the MFP and wishes to make copies as soon as possible. It is therefore necessary to switch ON the auxiliary power supply. However, in the mode other than the copy mode, the auxiliary power supply is switched OFF in Step S 302  because there is no such a need. 
         [0038]    Through an input from the control panel  15 , the user is able to make settings as to whether the auxiliary power supply is switched ON or OFF when any mode from the copy mode, the facsimile mode, and the print mode is selected. Even in a case where the settings have been made with the print mode, when a connection is established with the personal computer  29 , it is possible to set the MFP  10  to the print mode from the personal computer. 
         [0039]    In subsequent Step S 304 , when the power supply stays ON by the settings of the weekly timer being used, because the MFP  10  is not used immediately, the flow proceeds to Step S 302  to switch OFF the auxiliary power supply. 
         [0040]    In subsequent Step S 305 , it is detected whether the paper type of the recording paper  17  is the thick paper  2  or thicker, that is, any one of the thick paper  2 , the thick paper  3 , and the thick paper  4 . This detection is made by the media sensor  18 , and when the recording paper  17  is not equal to the thick paper  2  or thicker, that is, the plain paper or the thick paper  1 , the auxiliary power supply of the auxiliary power supply device  26  is switched OFF in Step S 302 . Hence, no current passes through the auxiliary heater  23 . 
         [0041]    In Step S 306 , a charge capacity of the auxiliary power supply is detected to detect whether it is possible to supply power to the auxiliary power supply. When power can be supplied to the auxiliary power supply, the flow proceeds to Step S 307  to switch ON the auxiliary power supply. However, in a case where power cannot be supplied to the auxiliary power supply in Step S 306  even when it is preferable to switch ON the auxiliary power supply under the conditions up to Step S 305 , the auxiliary power supply is switched OFF in Step S 302 . 
         [0042]    Either the auxiliary power supply is switched OFF in Step S 302  or the auxiliary power supply is switched ON in Step S 307 , after which the image fixing on the recording paper is performed as needed. 
         [0043]    Operations of the MFP  10  during the printing will now be described with the use of  FIG. 4 . In Step S 401 , it is detected by the media sensor  18  whether the paper type of the recording paper  17  is the thick paper  2  or thicker, that is, any one of the thick paper  2 , the thick paper  3 , or the thick paper  4 . When the paper type of the recording paper  17  is the thick paper  2  or thicker, the flow proceeds to Step S 402  to switch ON the auxiliary power supply of the auxiliary power supply device  26  to start printing. 
         [0044]    In subsequent Step S 403 , when the size of the recording paper  17  is found to be large, for example, an A-3 size or a long paper having a length of 1200 mm, the flow also proceeds to Step S 402  to switch ON the auxiliary power supply. In subsequent Step S 404 , it is detected whether the second surface is being printed after the first surface is printed in duplex printing. In the case of the printing on the first surface, the auxiliary power supply is switched ON. However, in the case of the printing on the second surface, because the recording paper has been heated, the auxiliary power supply is switched OFF. 
         [0045]    In Step S 405 , whether the number of papers to be printed inputted in advance is equal to or greater than a specific number, for example,  100 , is detected. When the number of papers is equal to or greater than the specific number, the flow proceeds to Step S 402  to start developing and fixing of the image after the auxiliary power supply is switched ON. The purpose of this configuration is to avoid the occurrence of poor fixing resulting from a drop of the fixing temperature when the number of papers to be printed becomes larger. 
         [0046]    In subsequent Step S 406 , whether the setting inputted in advice is color copy printing is detected, and in the case of color copy printing, the auxiliary power supply is switched ON and developing and fixing of the image are performed in Step S 402 . 
         [0047]    This is because the fixing performance is high for monochrome copying whereas the fixing performance is insufficient in color coping and fixing can be performed more satisfactorily when the auxiliary power supply is switched ON. When the setting is found not to be the color printing, that is, the setting is found to be the monochrome printing, in Step S 406 , developing and fixing of the image is performed after the auxiliary power supply is switched OFF in Step S 407 . 
         [0048]    The embodiment above described a case where the invention is applied to an MEP having three modes: the copy mode, the facsimile mode, and the print mode. It should be appreciated, however, that the invention is also applicable to an MFP having these three modes or an MFP having four or more capabilities. 
         [0049]    The embodiment above described a case where the paper type is determined by the weight per unit, that is, the basic weight, and the paper type includes five types: plain paper, thick paper  1 , thick paper  2 , thick paper  3 , and thick paper  4 . In the invention, however, the paper type is not limited to five types and the weight may be detected in any other unit. The invention is also applicable to a case where the paper type is determined by the thickness of recording papers using the distance measuring sensor besides the weight. It is also possible to determine the paper type by a magnetic sensor. 
         [0050]    In the embodiment above, the auxiliary heater is provided inside the press roller. However, it may be provided inside the heat roller or it may be provided inside both the press roller and the heat roller. 
         [0051]    According to the embodiment, the auxiliary power supply can be switched ON and OFF in a fine-tuned manner under various conditions. Hence, it is possible to achieve an MFP that is able to perform fixing satisfactorily while being capable of not only shortening a stand-by time but also saving power. 
         [0052]    In addition, in the invention, because the auxiliary power supply is controlled to be merely switched ON and OFF and does not need complex control, for example, to raise the fixing temperature of the roller appropriately, an image forming apparatus of a simple configuration can be achieved. In a case where the power supply of the auxiliary power supply is a rechargeable battery, it is possible to reduce the number of charging operations and to shorten a charging time, which can in turn extend the life time of the auxiliary power supply. Further, it is possible to reduce power consumption of the MFP. 
         [0053]    The embodiment above described a case where the invention is applied to an MFP. The invention, however, is also applicable to a copying machine, a printer, a facsimile machine, and so forth. 
         [0054]    It should be appreciated that the invention is not limited to the embodiment described above, and various modifications are possible within the scope of the technical idea of the invention.