Patent Publication Number: US-8977154-B2

Title: Image forming device

Description:
This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2010-102424 filed on Apr. 27, 2010, the contents of which are incorporated herein by reference in its entirety. 
     BACKGROUND 
     Apparatuses and methods consistent with the present disclosure relate to an image forming device that has a fixing unit for thermally fixing a developer on a recording sheet. 
     There has been a known control for a time interval up to starting paper feeding after receiving a printing command so that a heating roller in a fixing unit can reach its optimum fixing temperature when a recording sheet reaches the fixing unit. For example, in one of related arts, when a heater is ON for a predetermined time, the temperature increase rate of a detection temperature detected by a temperature sensor is calculated, and the time interval is controlled based on the temperature increase rate. 
     SUMMARY 
     However, according to the above configuration, if the printing command is output in a state where the temperature drops from the fixing temperature to a stand-by temperature, the temperature increase rate cannot be calculated. Thus, the recording sheet cannot be transported at a suitable timing, and it is difficult to carry out the fixing process at a suitable fixing temperature. 
     Thus, an object of an aspect of the disclosure is to provide an image forming device that can carry out the fixing process on the recording sheet at a suitable fixing temperature, even when the printing command is output in a state where the temperature drops from the fixing temperature to the stand-by temperature. 
     An aspect of the disclosure provides the following arrangements: 
     An image forming device comprising: 
     a fixing unit configured to thermally fix a developer on a recording sheet; 
     a control unit configured to control temperature to maintain the fixing unit at one of a fixing temperature and a stand-by temperature lower than the fixing temperature; and 
     a transport unit configured to transport the recording sheet to the fixing unit, 
     wherein, if the temperature of the fixing unit is dropping from the fixing temperature to the stand-by temperature, and a printing command is received, the control unit controls the transport unit so as to set, based on information relating to the current temperature of the fixing unit, a stand-by time to wait before starting to transport the recording sheet after the printing command is received as a second time interval, which is longer than a first time interval at the time the temperature of the fixing unit is the fixing temperature. 
     An image forming device comprising: 
     a fixing unit configured to thermally fix a developer on a recording sheet; 
     a control unit configured to control temperature to maintain the fixing unit at one of a fixing temperature and a stand-by temperature lower than the fixing temperature; and 
     a transport unit configured to transport the recording sheet to the fixing unit, 
     wherein the control unit controls the transport unit so as to set a stand-by time to wait before starting to transport the recording sheet after the printing command is received as a first time interval if the temperature of the fixing unit is a first temperature lower than the fixing temperature and higher than the stand-by temperature and a printing command is received, and 
     wherein the control unit controls the transport unit so as to set the stand-by time as a second time interval longer than the first time interval if the temperature of the fixing unit is a second temperature lower than the first temperature and higher than the stand-by temperature and the printing command is received. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view that shows a laser printer as an example of an image forming device according to an embodiment. 
         FIG. 2  is an explanatory diagram that shows a temperature change of a heating roller after turning a power source of a laser printer ON. 
         FIG. 3  is a flow chart that shows an operation of a control unit. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENT 
     The Whole Configuration of Laser Printer 
     An exemplary embodiment will be described in detail with reference to appropriate drawings, 
     As shown in  FIG. 1 , a laser printer  1  as an example of the image forming device includes a feeder portion  4  for supplying a paper  3  as an example of a recording sheet into a device main body  2 , an image forming portion  5  for forming an image on the supplied paper  3  or the like. 
     The feeder portion  4  includes a paper feeding tray  6  which is mounted on a bottom portion in the device main body  2  in an attachable and detachable manner, and a paper pressing plate  7  which is provided in the paper feeding tray  6 . Furthermore, the feeder portion  4  includes a paper feeding roller  8  and a paper feeding pad  9  provided in an upper part of an end portion of the paper feeding tray  6 , and paper powder grasping rollers  10  and  11  provided in a downstream side of a transport direction of the paper  3  with respect to the paper feeding roller  8 . Moreover, the filter portion  4  includes a resist roller  12  provided in a downstream side with respect to the paper powder grasping rollers  10  and  11 . 
     Moreover, in the feeder portion  4  configured as above, the papers  3  within the paper feeding tray  6  approach the paper feeding roller  8  side via the paper pressing plate  7 , are delivered by the paper feeding roller  8  and the paper feeding pad  9 , pass through the respective rollers  10  to  12  and then are transported to the image forming portion  5  one by one. 
     The image forming portion  5  includes a scanner portion  16 , a process cartridge  17 , a fixing unit  18  or the like. 
     The scanner portion  16  is provided on an upper portion in the device main body  2  and includes a laser light emitting portion (not shown), a polygon minor  19  that is rotated and driven, lenses  20  and  21 , and reflectors  22 ,  23  and  24  or the like. Moreover, in the scanner portion  16 , a laser beam is irradiated on a surface of a photosensitive drum  27  of the process cartridge  17  through a path shown by dotted lines in the drawing at a high speed. 
     The process cartridge  17  is arranged on a lower part of the scanner portion  16  and can be attached to and detached from the device main body  2 . Moreover, the process cartridge  17  is constituted by a developing cartridge  28  and a drum cartridge  51 . 
     The developing cartridge  28  includes a developing roller  31 , a layer thickness restriction blade  32 , a supply roller  33  and a toner hopper  34 . 
     The drum unit  51  includes a photosensitive drum  27 , a charger  29  and a transfer roller  30 . 
     In the process cartridge  17 , the surface of the rotating photosensitive drum  27  is charged by the charger  29  and then is exposed by the high speed scanned laser beam from the scanner portion  16 . As a result, the electric potential of the exposed surface of the photosensitive drum  27  is lowered, whereby an electrostatic latent image based on the image data is formed on the surface of the photosensitive drum  27 . 
     Next, the toner within the developing cartridge  28  is supplied to the electrostatic latent image on the surface of the photosensitive drum  27  by the rotating developing roller  31 , whereby the toner image is formed on the surface of the photosensitive drum  27 . Thereafter, the paper  3  is transported between the photosensitive drum  27  and the transfer roller  30 , whereby the toner image on the surface of the photosensitive drum  27  is transferred onto the paper  3 . 
     In addition, in the present embodiment, a transport unit  50  for transporting the paper  3  to the fixing unit  18  is constituted by the above-mentioned feeder portion  4 , the photosensitive drum  27  and the transfer roller  30 . Furthermore, on the outer surface of the device main body  2 , an environmental temperature sensor  60  is provided for detecting an environmental temperature outside the device main body  2 , i.e., an environmental temperature of the fixing unit. 
     &lt;Structure of Fixing Unit&gt; 
     The fixing unit  18  is for thermally fixing the toner onto paper  3 , and includes a halogen heater HH as an example of a heat source, a heating roller  41 , a pressurization roller  42 , and a thermistor TH as an example of a fixing temperature sensor. 
     The halogen heater HH is arranged inside the cylindrical heating roller  41  and heats the heating roller  41  from the inside thereof. Moreover, the halogen heater HH is suitably controlled by a control unit  100  described later in detail. 
     The heating roller  41  is a metallic member formed in approximately a cylindrical shape, and is rotatably supported by the device main body  2 . Moreover, the heating roller  41  is configured to rotate by a driving force from a driving device (not shown) driven with a control signal from the control unit  100 . In addition, the heating roller  41  may be formed in an aluminum cylinder member and circumferential surface of the aluminum cylinder member may be coated by PTFE. 
     The pressurization roller  42  is pressed to the heating roller  41  by a spring (not shown), and comes into contact with the heating roller  41 . In addition, the pressurization roller  42  may be formed of a urethane rubber provided around a core metal and circumferential surface of the urethane rubber may be covered with a PTFE tube. 
     The thermistor TH is configured to detect a detection temperature of the heating roller  41 , and is provided near the downstream side of a nip portion where the peripheral surface of the heating roller  41  contacts the peripheral surface of the pressurization roller  42 . Data of the detection temperature detected by the thermistor TH is output to the control unit  100 . 
     Moreover, in the fixing unit  18  configured in this manner, the heating roller  41  is heated by the halogen heater HH, whereby, when the paper  3  passes between the heating roller  41  and the pressurization roller  42 , the toner image is fixed on the paper  3 . Thereafter, the paper  3  is transported to the paper discharging passage  44  by the transport roller  43 . In addition, the paper  3  transported to the paper discharging passage  44  is discharged onto the paper discharging tray  46  by the paper discharging roller  45 . 
     &lt;Configuration of Control Unit&gt; 
     Next, a configuration of the control unit  100  will be described. 
     The control unit  100  has a CPU, a ROM, a RAM or the like, and is configured to perform the reception of a printing command and a printing data, and the control of the feeder portion  4 , the image forming portion  5  or the like according to a program. 
     The control unit  100  is configured to selectively carry out a known control to maintain the detection temperature of the heating roller  41  at a fixing temperature Tf (see  FIG. 2 ) used for fixing the toner image on the paper  3  and at a stand-by temperature Ts upon setting the laser printer  1  to the stand-by state. 
     The control unit  100  is further configured to control the transport unit  50  to set, based on the detection temperature, a stand-by time to wait until starting to transport the first paper  3  from the paper feeding tray  6  after printing command is received. In detail, the control unit  100  controls the transport unit  50  to set the stand-by time as a first time interval G 1  when the detection temperature is the fixing temperature Tf. 
     Herein, the stand-by temperature Ts is a temperature lower than the fixing temperature Tf. In case that the current detection temperature is the stand-by temperature Ts and the stand-by time is set as the first time interval G 1 , the detection temperature will not reach the fixing temperature Tf by a timing when the first paper  3  reaches the fixing unit even if the halogen heater HH is turned ON when printing command is received even accounting for increment of the detection temperature. 
     Furthermore, the control unit  100  is configured to control the fixing unit  18  so as to turn OFF the halogen heater HH at timing t 1  when the detection temperature initially reaches the fixing temperature Tf after the power source of the laser printer  1  is turned ON, thereby lowering the detection temperature to the stand-by temperature Ts. 
     Moreover, the control unit  100  is configured to carry out the unique control in accordance with the present embodiment, when the detection temperature of the heating roller  41  detected by the thermistor TH is dropping from the fixing temperature Tf to the stand-by temperature Ts at a timing when the printing command is received. Specifically, the control unit  100  controls the transport unit  50  to set the stand-by time as a second time interval G 2  longer than the first time interval G 1  based on the detection temperature at a timing when the printing command is received while the detection temperature is dropping from the fixing temperature Tf to the stand-by temperature Ts. 
     More specifically, the control unit  100  controls the transport unit  50  to set the stand-by time as the first time interval G 1  if the detection temperature is between the fixing temperature Tf and a recoverable temperature Tc at a timing when the printing command is received while the detection temperature is dropping from the fixing temperature Tf to the recoverable temperature Tc. The control unit  100  further controls the transport unit  50  to set the stand-by time as the second time interval G 2  if the detection temperature is between the recoverable temperature Tc and the stand-by temperature Ts at a timing when the printing command is received while the detection temperature is dropping from the recoverable temperature Tc to the stand-by temperature Ts. 
     Herein, the recoverable temperature Tc is a temperature between the fixing temperature Tf and the stand-by temperature Ts and is closer to the fixing temperature Tf than the stand-by temperature Ts. In case that the current detection temperature is the recoverable temperature Tc and the stand-by time is set as the first time interval G 1 , the detection temperature will become above the fixing temperature Tf at a timing when the first paper  3  reaches the fixing unit if the halogen heater HH is turned ON when printing command is received. 
     Moreover, when the control unit  100  controls the fixing unit  18  to maintain the detection temperature at the stand-by temperature Ts, the control unit  100  further controls the transport unit  50  to set the stand-by time as a third time interval G 3  longer than the second time interval G 2 . 
     Furthermore, the control unit  100  changes the stand-by time so that, as the environmental temperature detected by the environmental sensor  60  becomes lower, the stand-by time is longer. 
     As mentioned above, the control unit  100  carries out the control, whereby, as shown in  FIG. 2 , in a state where the detection temperature is dropping from the fixing temperature Tf to the recoverable temperature Tc (timing t 2  to t 3 ), the stand-by time is set to the first time interval G 1 . 
     In addition, during a term from timing t 1  when the halogen heater HH is turned OFF to timing t 2  when the temporarily increased detection temperature has dropped to the fixing temperature Tf which is a target temperature, the stand-by time is set as the first time interval G 1 . 
     Furthermore, during a term from timing t 3  to timing t 4  when the detection temperature has further dropped to the stand-by temperature Ts, the stand-by time is set as the second time interval G 2  longer than the first time interval G 1 . Furthermore, after the timing t 4  the stand-by time is set as the third time interval G 3  longer than that of the second time interval G 2 . 
     Hereinafter, a control of the control unit  100  will be described in detail with reference to  FIG. 3 . 
     As shown in  FIG. 3 , the control unit  100  determines whether or not the detection temperature tends to drop by comparing the previous value of the detection temperature with the current value thereof (S 1 ). If it is determined that the detection temperature tends to drop in step S 1  (Yes), then the control unit  100  determines whether or not the printing command is received (S 2 ). 
     If the printing command is not received in step S 2  (No), the control unit  100  finishes the main control. If the printing command is received in step S 2  (Yes), the control unit  100  determines whether or not the detection temperature is higher than the recoverable temperature Tc (S 3 ). 
     If the detection temperature is higher than the recoverable temperature Tc in step S 3  (Yes), the control unit  100  sets the stand-by time as the first time interval G 1  (S 4 ). If the detection temperature is equal to or less than the recoverable temperature Tc in step S 3  (No), then the control unit  100  determines whether or not the detection temperature is higher than the stand-by temperature Ts (S 5 ). 
     If the detection temperature is higher than the stand-by temperature Ts in step S 5  (Yes), the control unit  100  sets the stand-by time as the second time interval G 2  (S 6 ). If the detection temperature is equal to or less than the stand-by temperature Ts in step S 5  (No), the control unit  100  sets the stand-by time as the third time interval G 3  (S 7 ). 
     After setting the stand-by time in step S 4 , in step S 6  or step S 7 , the control unit  100  corrects the stand-by time based on the environmental temperature detected by the environmental temperature sensor  60  (S 8 ). Specifically, for example, a plurality of correction values is stored in a memory portion as a map depending on a plurality of environmental temperatures so that, as the environmental temperature becomes lower, the stand-by time is longer. The control unit  100  can determine the correction value by using the map based on the environmental temperature, thereby correcting the stand-by time in accordance with the determined correction value. 
     After step S 8 , the control unit  100  carries out printing control based on the corrected stand-by time (S 9 ). Herein, the printing control is a known control, and the driving of the transport unit  50 , turning ON of the halogen heater HH, the exposure control for the scanner portion  16  or the like are carried out. Moreover, a driving start timing of the transport unit  50  during printing control is suitably set depending on the corrected stand-by time. 
     That is, in the printing control, the control unit  100  starts the driving of the transport unit  50  after elapse of the corrected stand-by time in response to receiving the printing command. As a result, the paper feeding is started at the suitable timing depending on the time intervals G 1 , G 2  and G 3 , even in a case where the detection temperature tends to drop. Therefore, when the paper  3  reaches the fixing unit  18 , the detection temperature has reliably reached to the fixing temperature Tf. 
     In addition, in a case where the detection temperature does not tend to drop (S 1 ; No), the control unit  100  finishes the main control and carries out the known control depending on respective cases. Specifically, in the case of carrying out the control of maintaining the detection temperature at the fixing temperature Tf, the stand-by time is set as the first time interval G 1 . In the case of carrying out the control of maintaining the detection temperature at the stand-by temperature Ts, the stand-by time is set as the third time period G 3 . 
     In addition, in a case where the detection temperature tends to rise, for example, the stand-by time may be determined by a method disclosed in the related art. 
     As described above, it is possible to obtain the following effect in the present embodiment. 
     Even in a case where the printing command is output while the detection temperature drops from the fixing temperature Tf to the stand-by temperature Ts, it is possible to perform the fixing process on the paper  3  at a suitable fixing temperature Tf. 
     While the detection temperature is between the fixing temperature Tf and the recoverable temperature Tc (step S 3 ; Yes), the paper  3  is transported with the first time interval G 1  used for regular printing operation (step S 4 ). Thus, it needs not to wait to start printing between timings t 2  and t 3 . 
     If the stand-by time were set as the second time interval G 2  when the detection temperature is between the fixing temperature Tf and the recoverable temperature Tc, which is between timings t 2  and t 3 , the stand-by time would be too long and a phenomenon in which the detection temperature exceeded greatly beyond the fixing temperature Tf might occur. 
     When the detection temperature is at the stand-by temperature Ts, the stand-by time is set at the time interval G 3  longer than the second time interval G 2 , which is set in a case where the detection temperature tends to drop. Therefore, at the stand-by temperature Ts lower than temperature during its drop tendency time, it is possible to transport the paper  3  at a suitable timing, thereby performing the fixing process on the paper  3  at the suitable fixing temperature Tf. 
     The stand-by time may be corrected so that the stand-by time is longer as the environmental temperature becomes lower. Therefore, even when the environmental temperature is changed, it is possible to perform the fixing process in the paper  3  at the suitable fixing temperature Tf. 
     In addition, the present invention is not limited to the above-mentioned embodiment but can be practiced in various formations as described below. 
     In the above-mentioned embodiment, the temperature information detected by the thermistor TH is used as information relating to the temperature of the fixing unit  18 , but the present embodiment is not limited thereto. For example, the time information including the elapsed time after turning the heat source of the fixing unit OFF may be used as the information relating to the temperature of the fixing unit  18 . 
     Specifically, as shown in  FIG. 2 , if elapsed time from the timing t 1  when the halogen heater HH is turned OFF is a first elapsed time α (α≦t 3 −t 1 ), the stand-by time may be set as the first time interval G 1 . If the elapsed time is a second elapsed time β (t 3 −t 1 &lt;β≦t 4 −t 1 ), the stand-by time may be set as the second time interval G 2 . If the elapsed time is a third elapsed time γ (γ&gt;t 4 −t 1 ), the stand-by time may be set as the third time interval G 3 . Furthermore, the stand-by time may be set in accordance with elapsed time from timing of power ON of the laser printer  1 . 
     In the above-mentioned embodiment, the present invention was applied to the laser printer  1 , but the present invention is not limited thereto. The present invention can be applied to other kind of image forming devices, for example, a copier, a multi-function device or the like. 
     In the above-mentioned embodiment, the paper  3  may be a thick paper, a postcard, a thin paper, or an OHP sheet. 
     In the above-mentioned embodiment, the fixing unit  18  may include has a cylindrical fixing film instead of the heating roller  41 . 
     Furthermore, the transport unit may further include an additional transport roller disposed between the fixing unit and the photosensitive drum. Furthermore, in a color printer, a transport unit may include a paper transport belt. 
     The above-mentioned embodiment may be applied to a state where the temperature is dropping from the fixing temperature Tf after printing. 
     In the state where the detection temperature of the fixing unit  18  is dropping from the fixing temperature Tf to the recoverable temperature Tc, the stand-by time may be set as a time interval longer than the first time interval G 1  but shorter than the second time interval G 2 . 
     At the stand-by temperature Ts, the stand-by time may be set as the second time interval G 2 . 
     The environmental sensor  60  may be disposed at a position outside of the fixing unit  18  but inside the device main body  2  so as to detect the temperature inside the device main body  2 . 
     It may be determined that the detection temperature of the foxing unit  18  tends to drop if a predetermined time has been elapsed after turning the laser printer  1  ON. 
     The stand-by time may be corrected in accordance with a predetermined calculation equation based on the environmental temperature. 
     Instead of the halogen heater HH, IH (Induction Heating) heater or a heating resistor may be used.