Patent Publication Number: US-9835992-B2

Title: Image forming apparatus for setting standby temperature of a fixing device of the image forming apparatus, method for controlling image formation, and recording medium

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. §119(a) to Japanese Patent Application No. 2015-101013, filed on May 18, 2015, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to an image forming apparatus, a method for controlling image formation, and a non-transitory recording medium. 
     Description of the Related Art 
     An image forming apparatus is known that includes a fixing device maintained at a predetermined temperature until the image forming apparatus receives an instruction to start image formation. For example, in a time-saving mode, the fixing device is heated and maintained at a standby temperature until the start of image formation in order to shorten a time period taken for image formation compared with a normal mode. In response to receiving an instruction to form an image in such standby state, a heater, which is provided with the fixing device, heats the fixing device to a predetermined fixing temperature with power from a power supply. The standby temperature is set so that it does not cause fixing failure even when the voltage of the power supply is at a lower limit according to a product standard. 
     SUMMARY 
     An image forming apparatus includes a fixing device and a processor. The fixing device fixes an image formed on a recording medium at a fixing temperature. The fixing device includes a heater to heat the fixing device with power from a power supply. The processor detects a voltage value of the power supply, sets a standby temperature of the fixing device based on the detected voltage value of the power supply, and controls operation of the heater to heat the fixing device from the standby temperature to the fixing temperature in response to receiving an instruction for forming an image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein: 
         FIG. 1  illustrates a schematic view of an image forming apparatus according to an exemplary embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating a hardware configuration to detect a voltage value of a power supply in the image forming apparatus of  FIG. 1 ; 
         FIG. 3  is a block diagram illustrating a hardware configuration of the image forming apparatus of  FIG. 1 ; 
         FIG. 4  is a block diagram illustrating a functional configuration of the image forming apparatus of  FIG. 1 ; 
         FIG. 5  is a flowchart illustrating an operation of controlling temperature of a fixing device of the image forming apparatus of  FIG. 1 ; 
         FIG. 6  is a view illustrating an example of a conversion table according to an embodiment of the present invention; 
         FIG. 7  is a graph illustrating variation in temperature of the fixing device of the image forming apparatus of  FIG. 1 ; 
         FIG. 8  is a block diagram illustrating a hardware configuration to detect a voltage value of a power supply in the image forming apparatus of  FIG. 1  according to another embodiment of the present invention; 
         FIG. 9  is a flowchart illustrating an operation of controlling temperature of a fixing device of the image forming apparatus according to still another embodiment of the present invention; 
         FIG. 10  is a flowchart illustrating an operation of controlling temperature of a fixing device of the image forming apparatus according to still another embodiment of the present invention, and 
         FIG. 11  is a flowchart illustrating an operation of controlling temperature of a fixing device of the image forming apparatus according to still another embodiment of the present invention. 
     
    
    
     The accompanying drawings are intended to depict example embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DESCRIPTION OF THE EMBODIMENTS 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     In describing example embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the present disclosure is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. 
     Hereinafter, a description is given of an image forming apparatus, a method for controlling image formation, and a non-transitory recording medium according to several exemplary embodiments of the present invention. 
     An image forming apparatus  1  according to the following embodiments may be any apparatus as long as it forms an image using a fixing device. Examples of such an image forming apparatus  1  include a printer, a facsimile, a copier, or a multifunction peripheral (MFP) having multiple functions such as a printer function, a copier function, a scanner function, and a facsimile function. The image forming apparatus  1  according to the following embodiments operates on power from a power supply  25  ( FIG. 2 ). 
     Hereinafter, a description is given of embodiments of the image forming apparatus  1  that supports an electrophotography system as an example. 
       FIG. 1  illustrates a schematic view of the image forming apparatus  1  according to an exemplary embodiment. 
     As illustrated in  FIG. 1 , the image forming apparatus  1  is a tandem printer, including an intermediate transfer belt  2 , a plurality of image forming units (electrophotographic processors)  3 Y,  3 M,  3 C, and  3 BK, which are disposed side by side along the intermediate transfer belt  2 , and a writing unit  4 . The intermediate transfer belt  2  is an endless belt, which is stretched over a drive roller  5  and a driven roller  6 . A driver actuates the drive roller  5  to rotate. In accordance with the rotation of the drive roller  5 , the intermediate transfer belt  2  rotates. 
     The image forming units  3 Y,  3 M,  3 C, and  3 BK are disposed side by side along a conveyance direction of the intermediate transfer belt  2 , and respectively form toner images of different colors on the surface of the intermediate transfer belt  2 . The writing unit  4  irradiates the image forming units  3 Y,  3 M,  3 C, and  3 BK with exposure light rays corresponding to image data of different colors, (e.g., light beams  7 Y,  7 M,  7 C, and  7 BK) to write electrostatic latent images of respective colors onto the image forming units  3 Y,  3 M,  3 C, and  3 BK. The image forming units  3 Y,  3 M,  3 C, and  3 BK are substantially similar in configuration with one another. Accordingly, a description is given of the image forming unit  3 Y as an example. Elements and configurations included in the image forming unit  3 Y are denoted by the suffix—Y, whereas the corresponding elements or configurations included in the image forming units  3 M,  3 C, and  3 BK are denoted by the suffix—M, C, and BK, respectively. 
     The image forming unit  3 Y includes an image bearer  8 Y, a charging device  9 Y, a developing device  10 Y, and a discharging device  11 Y, which are disposed around the outer circumference of the image bearer  8 Y. In this example, the image bearer  8 Y is a photoconductor having a drum shape. In advance of image formation, the charging device  9 Y uniformly charges the outer circumferential surface of the image bearer  8 Y in the dark. The writing unit  4  irradiates the charged outer circumferential surface of the image bearer  8 Y with the light beam  7 Y, which corresponds to an image of yellow color, to form an electrostatic latent image on the surface of the image bearer  8 Y. The developing device  10 Y develops the electrostatic latent image with yellow toner to form a visible yellow toner image on the surface of the image bearer  8 Y. A transfer device  12 Y transfers the toner image formed on the image bearer  8 Y onto the intermediate transfer belt  2  at a first transfer position, where the image bearer  8 Y contacts with the intermediate transfer belt  2 . After this transfer of the toner image to the intermediate transfer belt  2 , a cleaner removes residual toner on the outer circumferential surface of the image bearer  8 Y. Subsequently, the discharging device  11 Y discharges the image bearer  8 Y. 
     The intermediate transfer belt  2  rotates while carrying the toner image transferred thereonto such that the toner image moves to the image forming unit  3 M. The image forming unit  3 M forms a magenta toner image on the surface of the image bearer  8 M, and transfers the magenta toner image onto the surface of the intermediate transfer belt  2  such that the magenta toner image is overlaid on the yellow toner image. In substantially the same manner, the image forming unit  3 C transfers a cyan toner image formed on the surface of the image bearer  8 C onto the surface of the intermediate transfer belt  2 . The image forming unit  3 BK also transfers a black toner image formed on the surface of the image bearer  8 BK onto the surface of the intermediate transfer belt  2  in substantially the same manner. Thus, the toner images of four different colors are transferred onto the surface of the intermediate transfer belt  2 , overlaid one atop the other so that a colored toner image is formed on the surface of the intermediate transfer belt  2 . 
     The image forming apparatus  1  further includes a feed roller  13 , a pair of separation rollers  14 , and a sheet tray  15 . The feed roller  13  rotates to convey a sheet  16  accommodated in sheet tray  15  in cooperation with the separation rollers  14 , in accordance with the rotation and movement of the intermediate transfer belt  2 . The sheet  16  is an example of a recording medium, which is a medium on which an image is to be formed. Examples of the recording medium may include a recording paper, a recording sheet, and a recording material. The sheet  16  is conveyed to a second transfer position, where the sheet is brought into contact with the intermediate transfer belt  2 , such that the toner image formed on the surface of the intermediate transfer belt  2  is transferred onto the sheet  16 . After this transfer of the toner image onto the sheet  16 , the sheet passes through a fixing device  20 , which fixes the toner image to form (print) the colored image on the sheet  16 . The sheet having the printed image thereon is ejected to the outside of the image forming apparatus  1 . 
     The fixing device  20  fixes the toner image on the sheet  16 , and includes a pair of rollers (i.e., a fixing roller  21  and a pressure roller  22 ), a thermistor  23 , and a thermostat  24 . The fixing roller  21  and the pressure roller  22  are disposed side by side. The pressure roller  22  presses the fixing roller  21  with a predetermined pressure. The thermistor  23  is an example of a temperature detector that detects a temperature of the fixing roller  21 . In this example, thermistor  23  detects a surface temperature of the fixing roller  21 . The thermistor  23  further outputs a temperature reading of the fixing roller  21  to a control unit  33  ( FIG. 3 ) of the image forming apparatus  1 . 
     The thermostat  24  is an example of a heating device that heats the fixing roller  21 . The thermostat  24  heats a heater with power from the power supply  25  to cause the heater to heat the fixing roller  21 . The thermostat  24  is also an example of an adjuster that adjusts the temperature (surface temperature) of the fixing roller  21 . The thermostat  24  controls the passage of electric current through the heater to adjust and maintain the temperature of the fixing roller  21 . The control unit  33  ( FIG. 3 ) of the image forming apparatus  1  causes the thermostat  24  to control the temperature of the fixing roller  21  based on the temperature of the fixing roller  21  detected by the thermistor  23 . 
     While forming an image, the thermostat  24  heats the fixing roller  21  to maintain the fixing roller  21  at a predetermined temperature. A driver such as a drive motor rotates the fixing roller  21  and the pressure roller  22  to cause the sheet  16  to pass through between the fixing roller  21  and the pressure roller  22 . While the sheet passes through between the fixing roller  21  and the pressure roller  22 , the pressure roller  22  pressurizes the sheet  16  and the fixing roller  21  heats the sheet  16  to fix an image (toner image) on the sheet  16 . The fixing device  20  is thus heated by power from the power supply  25 , which is provided outside the image forming apparatus  1 , to apply heat to the sheet  16 . Further, the fixing device  20  heats the toner image formed on the sheet  16  to fix the image on the sheet  16  with heat. 
     Hereinafter, a description is given in detail of an operation of controlling the temperature of the fixing device  20  by the image forming apparatus  1 . 
     In response to receiving an instruction to select the time-saving mode from a user, the image forming apparatus  1  causes the thermostat  24  to maintain the temperature of the fixing device  20  at a predetermined standby temperature. In this example, the thermostat  24  maintains the temperature of the fixing roller  21  at the standby temperature. In the time-saving mode, it takes less time for the image forming apparatus  1  to form an image than it does in a normal mode. The image forming apparatus  1  receives an instruction to select the time-saving mode through an input to a control panel provided with the image forming apparatus  1 . The standby temperature is a temperature of the fixing device  20  in a standby state, where the image forming apparatus waits for the start of image formation. 
     In the time-saving mode, the thermostat  24  heats the fixing device  20  to maintain the temperature of the fixing device  20  at the standby temperature. The image forming apparatus  1  and the fixing device  20  keeps waiting for receiving an instruction to form an image in such standby state. In response to receiving the instruction to form an image during the standby state, the image forming apparatus  1  causes the thermostat  24  to heat the fixing device  20  such that the temperature of the fixing device is raised up to a predetermined fixing temperature, which is higher than the standby temperature. Because, in the time-saving mode, the fixing device  20  is heated and maintained in advance at the standby temperature, a time period taken for heating the fixing device  20  up to the fixing temperature is shortened. Accordingly, it takes less time for the image forming apparatus  1  to form an image than it does in a normal mode. In this example, the image forming apparatus  1  determines the standby temperature of the fixing device  20  based on a voltage value of the power supply  25 , and controls the temperature of the fixing device  20  according to the determination result. 
       FIG. 2  is a block diagram illustrating a configuration to detect the voltage value of the power supply  25  in the image forming apparatus  1 . 
     As illustrated in  FIG. 2 , the image forming apparatus  1  includes an alternating current (AC) to direct current (DC) converter  30 , which is connected to the power supply  25 , an analog to digital (A/D) converter  31 , and a processor  32 . The power supply  25  is a commercial AC power supply as a main power supply, which supplies power to the image forming apparatus  1 . The AC-DC converter  30  is a power supply device that converts AC power to DC power. The AC-DC converter  30  converts AC power supplied from the power supply  25  to DC power, which is suitable for use by the image forming apparatus  1 , to convert an AC voltage value to a DC voltage value. 
     The A/D converter  31  measures the DC voltage value, which is converted from the AC voltage value by the AC-DC converter  30 , and converts the measured DC voltage value to digital data. Further The A/D converter  31  outputs the digital data, which is converted from the DC voltage value, to the processor  32 . The processor  32  is implemented by, for example, a micro processing unit (MPU) or a central processing unit (CPU) that carries out various arithmetic and logical operations. The processor  32  also constitutes a part of the control unit  33  of the image forming apparatus  1  and carries out arithmetic and logical operations of controlling operation of the image forming apparatus  1 . 
       FIG. 3  is a block diagram illustrating configurations of the control unit  33  of the image forming apparatus  1  and some elements or devices of the image forming apparatus  1  that are connected to the control unit  33 . 
     As illustrated in  FIG. 3 , the control unit  33  includes the processor  32 , a read only memory (ROM)  34 , and a random access memory (RAM)  35 . The ROM  34  stores therein various programs including a program executed by the processor  32 . The RAM  35  temporarily stores data used by the processor  32  when carrying out arithmetic and logical processing or information processing. The control unit  33  is connected to the fixing device  20  and a memory  36 , and controls operation of the image forming apparatus  1 . The memory  36  is implemented by, for example, a storage device such as a hard disk drive (HDD). The control unit  33  and the processor  32  each acquires data from the memory  36 , and carries out various operations based on the data acquired from the memory  36 . 
     The image forming apparatus  1  includes various units as described below that implement various functions, which are implemented by the processor  32  of the control unit  33 , when executing according to the program stored in the ROM  34  using the RAM  35  as a work area. For example, the processor  32  of the control unit  33  executes the program stored in the ROM  34  to implement a temperature control unit  37  ( FIG. 4 ), which controls operation of the thermostat  24  of the fixing device  20  to change the temperature of the fixing device  20 . Specifically, the temperature control unit  37  controls operation of the thermostat  24  to change the temperature of the fixing device  20  to the fixing temperature, at which the image is fixed on the sheet  16 , or to the standby temperature, which is lower than the fixing temperature. Further, the processor  32  of the control unit  33  detects the AC voltage value supplied from the power supply  25  based on the DC voltage value acquired from the A/D converter  31  (see FIG.  2 ). In this example, the processor  32  detects an actual value of the voltage or a maximum value of the voltage as the AC voltage value. 
     For example, the control unit  33  (the processor  32 ) acquires, from the memory  36 , a voltage value conversion table that stores a relation between the DC voltage values and the AC voltage values. The control unit  33  acquires the AC voltage value that is associated with the DC voltage value acquired from the A/D converter  31  based on the obtained voltage value conversion table to detect the voltage value supplied from the power supply  25 . Alternatively, the control unit  33  may acquire, from the memory  36 , a relational expression that represents a relation between the DC voltage value and the AC voltage value. The control unit  33  calculates the AC voltage value from the DC voltage value acquired from the A/D converter  31  using the obtained relational expression. Thus, the AC-DC converter  30 , the A/D converter  31 , and the processor  32  of the control unit  33  constitute an example of a voltage value detection unit  38  ( FIG. 4 ) that detects the voltage value of the power supply  25 . 
       FIG. 4  is a block diagram illustrating a functional configuration of a part of the image forming apparatus  1 . 
     As illustrated in  FIG. 4 , the image forming apparatus  1  includes a standby temperature setting unit  39 , in addition to the temperature control unit  37  and the voltage value detection unit  38 , which are described above. The standby temperature setting unit  39  sets the standby temperature of the fixing device  20  based on the voltage value detected by the voltage value detection unit  38 . Specifically, the controller  33  causes the processor  32  to perform an operation as described below of setting of the standby temperature to implement the standby temperature setting unit  39 . 
       FIG. 5  is a flowchart illustrating an operation of controlling the temperature of the fixing device  20 . Specifically, the flowchart illustrates an operation of controlling the temperature of the fixing device  20  in the time-saving mode. 
     As illustrated in  FIG. 5 , when the image forming apparatus  1  is turned on (S 101 ), the voltage value detection unit  38  detects the AC voltage value of the power supply  25  (S 102 ). The standby temperature setting unit  39  changes the setting of the standby temperature from a predetermined reference standby temperature based on the detected voltage value of the power supply  25  to set the standby temperature of the fixing device  20 . Specifically, the standby temperature setting unit  39  determines whether to change the setting of the standby temperature of the fixing device  20  from the predetermined reference temperature based on the detected voltage value of the power supply  25 . When the standby temperature setting unit  39  determines that the setting of the standby temperature is to be changed, the standby temperature setting unit  39  acquires a change amount of the standby temperature based on the detected voltage value of the power supply  25 . In other words, the processor  32  as the standby temperature setting unit  39  executes the program stored in the ROM  34  to perform the operation of determining whether to change the setting of the standby temperature and the operation of acquiring the change amount of the standby temperature. 
     In this exemplary embodiment, the reference standby temperature of the fixing device  20  corresponds to a lower limit of the voltage value (referred to as a “lower voltage limit” hereinafter) of the power supply  25 . The reference standby temperature is an upper limit of the standby temperature of the fixing device  20  in the standby state. The lower voltage limit of the power supply  25  and the reference standby temperature each is set in advance and stored in the memory  36 . The standby temperature setting unit  39  compares the detected voltage value of the power supply  25  with the lower voltage limit. Based on the comparison result, the standby temperature setting unit  39  determines whether to change the setting of the standby temperature of the fixing device  20  to a lower value from the reference standby temperature. In other words, the processor  32  executes the program stored in the ROM  34  to perform the operation of comparing the voltage value of the power supply  25  with the lower voltage limit and the operation of determining whether to change the setting of the standby temperature based on the comparison result. 
     Specifically, the standby temperature setting unit  39  compares the detected voltage value of the power supply  25  with the lower voltage to determine whether the voltage value of the power supply  25  is close to the lower voltage limit. More specifically, the standby temperature setting unit  39  determines whether a voltage difference, which is obtained by subtracting the lower voltage limit from the voltage value of the power supply  25 , is less than a predetermined acceptable value. When the standby temperature setting unit  39  determines that the voltage difference is less than the predetermined acceptable value, the standby temperature setting unit  39  determines that the voltage value of the power supply  25  is close to the lower voltage limit (S 103 : YES). The acceptable value of the voltage difference is set in advance and stored in the memory  36 . 
     When the standby temperature setting unit  39  determines that the voltage value of the power supply  25  is close to the lower voltage limit (S 103 : YES), the standby temperature setting unit  39  does not change the setting of the standby temperature of the fixing device  20  from the predetermined reference standby temperature (S 104 ). In contrast, when the standby temperature setting unit  39  determines that the voltage difference is greater than or equal to the predetermined acceptable value, the standby temperature setting unit  39  determines that the voltage value of the power supply  25  is not close to the lower voltage limit (S 103 : NO). Based on such determination result, the standby temperature setting unit  39  sets the standby temperature of the fixing device  20  to a temperature that is lower than the reference standby temperature (S 105 ). With the operation as described above, the standby temperature setting unit  39  sets the standby temperature of the fixing device  20 . 
     After S 105 , the image forming apparatus  1  starts forming an image, or the fixing device  20  transitions to the standby state in which the fixing device  20  keeps waiting for the start of image formation (S 106 ). In a case where the image forming apparatus  1  starts forming an image at S 106 , the image forming units  3 Y,  3 M,  3 C, and  3 BK starts forming an image on the sheet  16 . Further, the thermostat  24  heats the fixing device  20  up to the fixing temperature with power supplied from the power supply  25  so that the unfixed toner image formed on the sheet  16  is fixed on the sheet  16  with heat of the fixing device  20 . In a case where the fixing device is kept in the standby state at S 106 , the thermostat  34  heats the fixing device  20  up to the standby temperature, and maintains the temperature of the fixing device  20  at the standby temperature. More specifically, at S 106 , the thermostat  34  heats the fixing device  20  up to the reference standby temperature corresponding to the lower voltage limit, when the standby temperature setting unit  39  does not change the setting of the standby temperature of the fixing device  20  at S 104 . In contrast, at S 106 , the thermostat  34  heats the fixing device  20  up to the standby temperature that is changed from the reference standby temperature, when the standby temperature setting unit  39  changes the setting of the standby temperature at S 105 . 
     The temperature of the fixing device  20  is maintained at the standby temperature that is set at S 104  or S 105  until the start of image forming. In response to receiving the instruction to form an image during such standby state, the image forming apparatus  1  causes the thermostat  24  to heat the fixing device  24  up to the fixing temperature from the standby temperature such that the unfixed toner image formed on the sheet  16  is fixed onto the sheet  16  with heat of the fixing device  20 . When the image formation ends, the thermostat  24  changes the temperature of the fixing device  20  to the standby temperature. Then, the fixing device  20  again keeps waiting for the start of image formation at the standby temperature. The temperature control unit  37  controls operation of the thermostat  24  to change the temperature of the fixing device  20  to the fixing temperature, at which the fixing device  20  fixes the image on the sheet  16 , or to the standby temperature, at which the fixing device  20  is kept in the standby state. Further, the standby temperature setting unit  39  acquires the change amount of the standby temperature corresponding to the voltage value of the power supply  25  based on a predetermined conversion table. The standby temperature setting unit  39  sets the standby temperature of the fixing device  20  based on the acquired change amount of the standby temperature. 
       FIG. 6  is a view illustrating an example of the conversion table used by the stand by temperature setting unit  39  for acquiring the change amount of the standby temperature according to an embodiment of the present invention. In the example illustrated in  FIG. 6 , a standard of a power supply voltage of the image forming apparatus  1  is 90V or more and 110V or less. The upper voltage limit is 110V while the lower voltage limit is 90V. In the conversion table illustrated in  FIG. 6 , N-M (except for 109-110) represents N or more and less than N. 109-110 represents 109 or more and 110 or less. 
     As illustrated in  FIG. 6 , the conversion table defines the change amount of the standby temperature corresponding to the voltage value of the power supply  25 , and represents a relation between the voltage value of the power supply  25  and the change amount of the standby temperature. Specifically the conversion table stores pieces of data, which are combinations of the voltage value of the power supply  25  and the change amount of the standby temperature. The conversion table is set in advance and stored in the memory  36 . For example, when the voltage value of the power supply  25  is 90V, the standby temperature setting unit  39  does not change the setting of the standby temperature from the reference standby temperature based on the determination indicating that the voltage value of power supply  25  is close to the lower voltage limit. Accordingly, in the conversion table, the voltage value of 90-91V is associated with the change amount of 0.0 degree Celsius. In contrast, when the voltage value of the power supply  25  is 91V or more, the change amounts of the standby temperature are set in accordance with the voltage values of the power supply  25 . The higher the voltage value, the greater is the change amount of the standby temperature. 
     The standby temperature setting unit  39  acquires the conversion table from the memory  36  to convert the voltage value of the power supply  25  to the change amount of the standby temperature based on the conversion table. Thus, the standby temperature setting unit  39  acquires the change amount of the standby temperature corresponding to the voltage value of the power supply  25 . The standby temperature setting unit  39  changes the setting of the standby temperature from the reference standby temperature based on the acquired changed amount of the standby temperature. In this example, the standby temperature setting unit  39  subtracts the change amount from the reference standby temperature to set the standby temperature of the fixing device  20  at a temperature that is lower than the reference standby temperature. 
       FIG. 7  is a graph illustrating variation in the temperature of the fixing device  20  of the image forming apparatus  1  according to an embodiment of the present invention. The graph includes two examples of the temperature variation, which are represented by R 1  and R 2 , respectively. Further, the graph also illustrates a dashed line F that represents a comparative example of the temperature variation resulting from a temperature control according to a typical fixing device. In  FIG. 7 , the graph shows a temperature and a time period in vertical and horizontal axes respectively. 
     As illustrated in  FIG. 7 , in the comparative example (F), the standby temperature of the typical fixing device is set to T 2  only, which corresponds to the lower voltage limit, such that no fixing failure occurs even when the voltage of the power supply is a lower voltage limit according to a product standard. Accordingly, in the comparative example, the fixing device may consume a larger amount of power than is necessary in the standby state (V 1 ). 
     Specifically, in the comparative example, the fixing device keeps waiting in the standby state (V 1 ) for the start of image formation at the standby temperature T 2 , and the heating of the fixing device is started at K 1  such that the temperature of fixing device is raised up to the fixing temperature T 3 . However, the voltage value of the power supply is often greater than the lower voltage limit of a product standard. Accordingly, in such a case where the voltage value of the power supply is close to a power rating (100V, for example), the temperature of the fixing device reaches the standby temperature T 3  before image fixing is started at K 2 . The fixing device is maintained at the fixing temperature T 3  during a time period V 2  until the fixing of image is started at K 2 . As a result, in the comparative example, a larger amount of power than necessary may be consumed in order to keep the temperature of the fixing device at the fixing temperature T 3 . 
     In contrast, the image forming apparatus  1  according to this exemplary embodiment detects the voltage value of the power supply  25 , and performs the operation of controlling the temperature of the fixing device  20  based on the detected voltage value. Specifically, as in the example represented by R 1 , in a case where the voltage value of the power supply  25  is relatively low (90V, for example, which is the lower voltage limit), the standby temperature of the fixing device  20  is set to T 2 , which is relatively high and corresponds to the reference standby temperature. Accordingly, the fixing device  20  is kept in the standby state (V 1 ) at the standby temperature T 2 . Then, in response to the start of image formation, the heating of the fixing device  20  is started at K 1  such that the temperature of the fixing device  20  is raised up to the fixing temperature T 3 . The fixing device  20  is heated from the standby temperature T 2  for a heating time period and at a heating speed, each corresponding to the voltage value of the power supply  25 . The temperature of the fixing device  20  reaches the fixing temperature T 3  at the same time or nearly the same time of the start of image formation (K 2 ). 
     Further, as in the example represent by R 2 , in a case where the voltage value of the power supply  25  is higher than the lower voltage limit (100V, for example), the standby temperature of the fixing device  20  is set to T 1 , which is lower than the reference standby temperature. In other words, the setting of the standby temperature of the fixing device  20  is changed to a lower temperature from the reference standby temperature based on the voltage value of the power supply  25 . The fixing device  20  is kept in the standby state (V 1 ) at the standby temperature T 1 . Then, in response to the start of image formation, the heating of the fixing device  20  is started at K 1  such that the temperature of the fixing device  20  is raised up to the fixing temperature T 3 . The fixing device  20  is heated from the standby temperature T 1  for a heating time period and at a heating speed, each corresponding to the voltage value of the power supply  25 . The temperature of the fixing device  20  reaches the fixing temperature T 3  at the same time or nearly the same time of the start of image formation (K 2 ). Accordingly, an excessive consumption of power is suppressed for keeping the temperature of the fixing device at the standby temperature T 1  during the standby state (V 1 ) and for heating the fixing device  20  up to the fixing temperature T 3 . 
     As described heretofore, according to this exemplary embodiment, the fixing device  20  of the image forming apparatus  1  is kept in the standby state at the standby temperature corresponding to the voltage value of the power supply  25 . Accordingly, excessive consumption of power by the fixing device  20  is suppressed. Further, the change amount of the standby temperature is acquired based on the voltage value of the power supply  25 . Accordingly, the standby temperature of the fixing device  20  is set accurately. Furthermore, the change amount of the standby temperature is converted from the voltage value of the power supply  25  based on the conversion table. Accordingly, the standby temperature of the fixing device  20  is set in a relatively simple manner. Furthermore, the AC-DC converter  30  converts the AC voltage value of the power supply  25  to the DC voltage value to enable the A/D converter  31  to detect the voltage value of the power supply  25  in a relatively simple manner and accurately in accordance with the resolution of the A/D converter  31 . 
     Hereinafter, a description is given of the image forming apparatus  1  according to another exemplary embodiment of the present invention. The image forming apparatus  1  according to the following exemplary embodiment is substantially similar in configuration to the information processing apparatus  1  according to the exemplary embodiment described above, and produces similar effects. Accordingly, a description of elements, members, components, or operations that are same as those of the exemplary embodiment described above will be omitted below. In the drawings and description of the following exemplary embodiments, the same reference numbers are allocated to elements (members or components) having the same function or shape as those of the exemplary embodiment described above. 
     In this exemplary embodiment, the standby temperature setting unit  39  ( FIG. 4 ) acquires the change amount of the standby temperature corresponding to the voltage value of the power supply  25  based on a predetermined relational expression in place of the conversion table as illustrated in  FIG. 6 . The standby temperature setting unit  39  determines the standby temperature of the fixing device  20  based on the acquired change amount of the standby temperature. The relational expression indicates the change amount of the standby temperature corresponding to the voltage value of the power supply  25 . Based on the relational expression, the voltage value of the power supply  25  is converted to the change amount of the standby temperature. The relation expression is set in advance and stored in the memory  36 . 
     In this exemplary embodiment, the standby temperature setting unit  39  subtracts the lower voltage limit from the voltage value of the power supply  25  to obtain the voltage difference. Then, the standby temperature setting unit  39  multiplies the obtained voltage difference by a predetermined coefficient to obtain the change amount of the standby temperature. Accordingly, the relational expression is as follows:
 
Change amount of standby temperature=(Voltage value of power supply−Lower voltage limit)*Coefficient
 
     Thus, based on the above relational expression, the change amount (degree Celsius) of the standby temperature is calculated. The standby temperature setting unit  39  acquires the relational expression from the memory  36 , and uses the relational expression to calculate the change amount from the voltage value of the power supply  25 . 
     In other words, the processor  32  of the image forming apparatus  1  executes the program stored in the ROM  34  to perform the operation of calculating the change amount of the standby temperature based on the voltage value of the power supply  25 . The standby temperature setting unit  39  changes the setting of the standby temperature from the reference standby temperature based on the acquired changed amount of the standby temperature. In this example, the standby temperature setting unit  39  subtracts the change amount from the reference standby temperature to set the standby temperature of the fixing device  20 . The calculation of the change amount of the standby temperature using the relational expression makes it possible to change the setting of the standby temperature of the fixing device  20  in a relatively simple manner. 
     In addition, the standby temperature setting unit  39  compares the voltage value of the power supply  25  with the standard of the voltage value (e.g., the upper voltage limit and the lower voltage limit). When the comparison result indicates that the voltage value of the power supply  25  is greater than or equal to the lower voltage limit and less than or equal to the upper voltage limit, the standby temperature setting unit  39  calculates the change amount of the standby temperature using the relational expression. The coefficient of the relational expression is determined, for example, by experiment, and is set depending on different models or types of the image forming apparatus  1 . The relational expression is either linear or non-linear. 
       FIG. 8  is a block diagram illustrating a configuration to detect the voltage value of the power supply  25  in the image forming apparatus  1  according to still another exemplary embodiment of the present invention. 
     In this exemplary embodiment, as illustrated in  FIG. 8 , the image forming apparatus  1  includes the AC-DC converter  30 , which is connected to the power supply  25 , a comparator  40 , and the processor  32 . The comparator  40  is implemented by, for example, a comparison circuit that compares the DC voltage value, which is converted by the AC-DC converter  30 , with a predetermined reference voltage value to determine whether the DC voltage value is greater than the reference voltage value. 
     The image forming apparatus  1  causes the comparator  40  to determine whether the voltage value of the power supply  25  is close to the lower voltage limit. In addition, the image forming apparatus  1  causes the comparator  40  to compare the DC voltage value with a plurality of the reference voltage values to determine the voltage value of the power supply  25 . The determination result is output to the processor  32 . The processor  32  uses the determination result to perform the operation for changing the setting of the standby temperature of the fixing device  20 . The reference voltage values of the comparator  40  are set in advance to correspond the voltage values set in the conversion table ( FIG. 6 ), for example. The comparator  40  makes it possible to detect the voltage value of the power supply  25  in a relatively simple manner without the A/D converter  31  provided with the image forming apparatus  1 . 
       FIG. 9  is a flowchart illustrating an operation of controlling the temperature of the fixing device  20  according to still another exemplary embodiment of the present invention. 
     In this exemplary embodiment, as illustrated in  FIG. 9 , when the image forming apparatus  1  is turned on, or, when the image forming apparatus  1  transitions from a sleep mode (S 201 ), the voltage value detection unit  38  detects the AC voltage value of the power supply  25  (S 202 ). Subsequently, the processor  32  compares the voltage value of the power supply  25  with a predetermined threshold to determine whether the voltage value of the power supply  25  satisfies a predetermined condition of the threshold. When the determination result indicates that the voltage value of the power supply  25  does not satisfy the predetermined condition of the threshold, the processor  32  stops image formation by the image forming apparatus  1 . 
     In other words, the processor  32  of the image forming apparatus  1  executes the program stored in the ROM  34  to perform the operation of determining whether the voltage value of the power supply  25  satisfies a condition of the threshold of the voltage value and the operation of stopping image formation based on the determination result. When the processor  32  determines that the voltage value of the power supply  25  satisfies the predetermined condition of the threshold, the standby temperature setting unit  39  changes the setting of the standby temperature of the fixing device  20  from the reference standby temperature based on the voltage value of the power supply  25 . Any desired value may be set as the threshold of the voltage value of the power supply  25  in accordance with a product standard or a nominal voltage value. For example, the upper voltage limit and the lower voltage limit are set as the threshold. In this example, the processor  32  determines whether the voltage value of the power supply  25  is greater than or equal to the upper voltage limit and whether the voltage value of the power supply  25  is less than or equal to the lower voltage limit. 
     In this exemplary embodiment, the processor  32  determines whether the voltage value of the power supply  25  is within a range between the two thresholds, e.g., the lower voltage limit and the upper voltage limit (S 203 ). When the voltage value of the power supply  25  is greater than the upper voltage limit, or, when the voltage value of the power supply  25  is less than the lower voltage limit, the processor  32  determines that the voltage value of the power supply  25  is not within a range between the two thresholds (S 203 : NO). Based on such determination result, the processor  32  stops image formation by the image forming apparatus  1  (S 204 ). Further, the processor  32  displays an image or video indicating that the image formation is stopped or a warning about the voltage value on, for example, the control panel of the image forming apparatus  1  (S 205 ). 
     When the processor  32  determines that the voltage value of the power supply  25  is within a range between the two thresholds (S 203 : YES), the standby temperature of the fixing device  20  is set by substantially similar operations as those of S 102  to S 105  of  FIG. 5  (S 206 ). After S 205 , the image forming apparatus  1  starts forming an image, or the fixing device  20  keeps waiting for the start of image formation at the standby temperature (S 207 ). As described heretofore, according to this exemplary embodiment, an operation of forming an image is stopped based on the voltage value of the power supply  25 . This prevents the image forming apparatus  1  from malfunctioning. 
       FIG. 10  is a flowchart illustrating an operation of controlling the temperature of the fixing device  20  according to still another exemplary embodiment of the present invention. 
     In this exemplary embodiment, as illustrated in  FIG. 10 , when the image forming apparatus  1  is turned on (S 301 ), the standby temperature of the fixing device  20  is set by substantially similar operations as those of S 102  to S 105  of  FIG. 5 . Subsequently, a temperature measurement device provided with the image forming apparatus  1  measures ambient temperature of the image forming apparatus  1 . In addition, the measurement device outputs a measurement result, i.e., the measured ambient temperature, to the controller  33  of the image forming apparatus  1 . The measurement device is implemented by, for example, a temperature sensor or a thermistor. The ambient temperature of the image forming apparatus  1  is the temperature of air in adjacent areas of the image forming apparatus  1 . 
     The processor  32  of the image forming apparatus  1  compares the measured ambient temperature with a predetermined temperature to determine whether the ambient temperature of the image forming apparatus  1  is lower than or equal to the predetermined temperature (S 302 ). The predetermined temperature to be compared with the ambient temperature is a reference temperature of the ambient temperature, which is set in advance and stored in the memory  36 . The processor  32  compares the ambient temperature with the predetermined temperature to determine whether to change the setting of the standby temperature of the fixing device  20  from the reference standby temperature based on the comparison result. When the processor  32  determines that the setting of the standby temperature is to be changed based on the comparison result, the processor  32  changes the setting of the standby temperature to adjust the standby temperature of the fixing device  20  in accordance with the ambient temperature. In other words, the processor  32  of the image forming apparatus  1  executes the program stored in the ROM  34  to perform the operation of adjusting the standby temperature of the fixing device  20  based on the ambient temperature of the image forming apparatus  1 . 
     When the processor  32  determines that the ambient temperature is lower than or equal to the reference temperature (S 302 : YES), the processor  32  does not change the setting of the standby temperature from the standby temperature set with the substantially similar operations as those of S 102  to S 105  of  FIG. 5  (S 303 ). After S 305 , the image forming apparatus  1  starts forming an image, or the fixing device  20  keeps waiting for the start of image formation at the standby temperature (S 304 ). In contrast, in a case where the ambient temperature is higher than the reference temperature, a rate of rise in the temperature of the fixing device  20  when heated increases. Accordingly, when the processor  32  determines that the ambient temperature is higher than the reference temperature (S 302 : NO), the processor  32  sets the standby temperature of the fixing device  20  to a temperature that is lower than the standby temperature that is preset with the substantially similar operations as those of S 102  to S 105  of  FIG. 5 . 
     Specifically, the processor  32  acquires a predetermined change amount of the standby temperature from the memory  36 , and lowers the preset standby temperature by the change amount to adjust the standby temperature. Thus, the processor  32  sets the standby temperature, which is a temperature up to which the fixing device is to be heated and maintained in the standby state, to a temperature that is lower than the standby temperature that is preset with the substantially similar operations as those of S 102  to S 105  of  FIG. 5  (S 305 ). After S 305 , the image forming apparatus  1  starts forming an image, or the fixing device  20  keeps waiting for the start of image formation at the standby temperature (S 306 ). As described heretofore, according to this exemplary embodiment, the setting of the standby temperature of the fixing device  20  is adjusted in accordance with the ambient temperature of the image forming apparatus  1 . 
       FIG. 11  is a flowchart illustrating an operation of controlling the temperature of the fixing device  20  according to still another exemplary embodiment of the present invention. 
     In this exemplary embodiment, as illustrated in  FIG. 11 , when the image forming apparatus  1  is turned on (S 401 ), the processor  32  of the image forming apparatus  1  detects a status of the voltage value detection unit  38  to determine whether the voltage value detection unit  38  is in failure (S 402 ). For example, the processor  32  determines that the voltage value detection unit  38  is in failure, when the voltage value of the power supply  25  that is detected by the voltage value detection unit  38  is fixed at the upper voltage limit or the lower voltage limit due to open circuit faults or short circuit faults. 
     When the processor  32  determines that the voltage value detection unit  38  is not in failure (S 402 : NO), the standby temperature of the fixing device  20  is set by substantially similar operations as those of S 102  to S 105  of  FIG. 5  (S 403 ). After S 403 , the image forming apparatus  1  starts forming an image, or the fixing device  20  keeps waiting for the start of image formation at the standby temperature (S 404 ). In contrast, when the determination result indicates that the voltage value detection unit  38  is in failure, the processor  32  of the image forming apparatus  1  prevents the standby temperature setting unit  39  from changing the setting of the standby temperature from the reference standby temperature. In other words, the processor  32  executes the program stored in the ROM  34  to perform the operation of determining whether the voltage value detection unit  38  is in failure and the operation of preventing the standby temperature setting unit  39  from changing the setting of the standby temperature. 
     When the processor  32  determines that the voltage value detection unit  38  is in failure (S 402 : YES), the standby temperature setting unit  39  does not change the setting of the standby temperature from the reference standby temperature (S 405 ). After S 405 , the image forming apparatus  1  starts forming an image, or the fixing device  20  keeps waiting for the start of image formation at the standby temperature (S 406 ). As described heretofore, according to this exemplary embodiment, the operation of changing the setting of the standby temperature is canceled in response to the failure of the voltage value detection unit  38 . 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the disclosure of the present invention may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. 
     Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), digital signal processor (DSP), field programmable gate array (FPGA), and conventional circuit components arranged to perform the recited functions.