Patent Publication Number: US-10761462-B2

Title: Energy savings in an image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of application Ser. No. 16/574,139 filed on Sep. 18, 2019, which is a Continuation of application Ser. No. 16/228,997 filed on Dec. 21, 2018, now U.S. Pat. No. 10,459,381, which is a Divisional of application Ser. No. 15/708,378 filed on Sep. 19, 2017, now U.S. Pat. No. 10,197,956, the entire contents of both of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to energy savings in an image forming apparatus and methods related thereto. 
     BACKGROUND 
     In the related art, there are image forming apparatuses that cause a toner image to be fixed on an image formation medium (hereinafter referred to as a “sheet”) using a fixation roller and a pressurization roller that is pressure-contacted with the fixation roller. In this case, a fixation roller and a pressurization roller are rotated with the sheet being squeezed between the fixation roller and the pressurization roller, and thus heat of the fixation roller is transferred to the sheet. With the heating by the fixation roller, the toner image is fixed to the sheet. In this case, the image forming apparatus controls a temperature of the fixation roller, and rotation speeds of the fixation roller and the pressurization roller, in such a manner that the toner image is suitably fixed on the sheet. 
     On the other hand, for the purpose of saving energy, image forming apparatuses are being developed that transition to an operation mode for low power if a state of the image forming apparatus satisfies a predetermined condition. A state where the image forming apparatus operates in a low power mode is hereinafter referred to as a “sleep state”. However, if the image forming apparatus is in the sleep state for a predetermined time or longer, there is a likelihood that transformation will occur between a pressure contact portion between the pressurization roller and the fixation roller. This is because the pressurization roller that is hardened by the heat of the fixation roller is left unattended (naturally cooled) and thus is hardened in a state of being pressure-contacted with the fixation roller. This transformation is generally referred to as a creep, and is known to be a cause of the occurrence of various defects in the image forming apparatus and printed sheets produced by the image forming apparatus. 
     In the related art, although research is conducted on the technology of reducing the number of defects that occur due to this creep, suppression of strange sounds of a drive unit, which occur when the fixation roller is rotated have not yet been achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external appearance diagram illustrating an example of an entire configuration of an image forming apparatus according to a first embodiment. 
         FIG. 2  is a diagram illustrating an outline of a fixation unit in the image forming apparatus according to the first embodiment. 
         FIG. 3  is a diagram illustrating a specific example of creep that occurs in a pressurization roller according to the first embodiment. 
         FIGS. 4A and 4B  are diagrams for in more detail describing the principle of occurrence of a collision sound according to the first embodiment. 
         FIG. 5  is a diagram illustrating a specific example of a functional configuration of the image forming apparatus according to the first embodiment. 
         FIG. 6  is a diagram illustrating a specific example of a relationship between a temperature and hardness of the pressurization roller in the image forming apparatus according to the first embodiment. 
         FIG. 7  is a diagram illustrating a specific example of a relationship between a control temperature of a fixation roller and the size of the creep that occurs in the pressurization roller in the image forming apparatus according to the first embodiment. 
         FIG. 8  is a diagram illustrating a specific example of a relationship between the hardness of the pressurization roller and the cooling time in the image forming apparatus according to the first embodiment. 
         FIG. 9  is a flowchart illustrating a flow for control of the fixation unit according to the first embodiment. 
         FIG. 10  is a flowchart illustrating the flow for the control of the fixation unit according to the first embodiment. 
         FIG. 11  is a diagram illustrating a specific example of a functional configuration of an image forming apparatus according to a second embodiment. 
         FIG. 12  is a flowchart illustrating a flow for control of a fixation unit according to a second embodiment. 
         FIG. 13  is a flowchart illustrating the flow for the control of the fixation unit according to the second embodiment. 
         FIG. 14  is a flowchart illustrating the flow for the control of the fixation unit according to the second embodiment. 
         FIG. 15  is a flowchart illustrating the flow for the control of the fixation unit according to the second embodiment. 
         FIG. 16  is a three-dimensional diagram illustrating a specific example of a configuration of an image forming apparatus according to a third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An image forming apparatus according to the embodiment has a fixation member, a pressurization member, a heat source, a drive unit, a measurement unit, and a control unit. The pressurization member is pressure-contacted with the fixation member. The heat source heats the fixation member. The drive unit provides a drive force to the fixation member. The measurement unit measures the time that elapses after the image forming apparatus itself ends certain image forming processing until the image forming apparatus itself receives an instruction to perform next image forming processing. The control unit causes the heat source to start to heat the fixation member, as an operation that is to be prepared before performing the next image forming processing, according to reception of the instruction for performing. If the elapsed time does not exceed a predetermined threshold, the control unit causes the drive unit to start to drive the fixation member after a temperature of the fixation member reaches a first control temperature. If the elapsed time exceeds the predetermined threshold, the control unit causes the drive unit to start to drive the fixation member after the temperature of the fixation member reaches a second control temperature that is higher than the first control temperature. 
     The image forming apparatus according to the embodiment will be described above with reference to the drawings. 
     First Embodiment 
       FIG. 1  is an external appearance diagram illustrating an example of an entire configuration of an image forming apparatus  100  according to a first embodiment. The image forming apparatus  100  is, for example, a multi-function machine. The image forming apparatus  100  includes a display  110 , a control panel  120 , a printing unit  130 , a sheet accommodating unit  140 , and an image reading unit  200 . The image forming apparatus  100  forms an image on a sheet using a developing agent such as a toner. The sheet, for example, is a sheet of paper or a label. The sheet may be any material, on a surface of which the image forming apparatus  100  can form an image. 
     The display  110  is an image display device, such as a liquid crystal display or an organic electro luminescence display (EL) display. Displayed on the display  110  are various pieces of information relating to the image forming apparatus  100 . 
     The control panel  120  has a plurality of buttons. A user operation is performed on the control panel  120 . The control panel  120  outputs a signal in accordance with the operation that is performed by a user, to a control unit of the image forming apparatus  100 . It is noted that the display  110  and the control panel  120  may be configured to be integrated into a touch panel. 
     The printing unit  130  forms an image on a sheet, based on image information that is generated by the image reading unit  200 , or image information that is received through a communication path. For example, with the following processing, the printing unit  130 , for example, forms an image. An image forming module of the printing unit  130  forms an electrostatic latent image on a photosensitive drum based on the image information. The image forming module of the printing unit  130  forms a visible image by causing the developing agent to be adhered to the electrostatic latent image. As a specific example of the developing agent, there is a toner. A transfer module of the printing unit  130  transfers the visible image on a sheet. A fixation unit of the printing unit  130  causes the visible image to be fixed to the sheet by performing heating and pressurization on the sheet. It is noted that the sheet on which the image is formed may be a sheet that is accommodated in the sheet accommodating unit  140 , and be a sheet that is fed by human fingers. 
     The sheet accommodating unit  140  accommodates a sheet that is used for image formation in the printing unit  130 . 
     The image reading unit  200  reads reading-target image information as light and darkness. The image reading unit  200  records the image information that is read. The image information that is recorded may be transmitted to other information processing apparatus through a network. The recorded image information may be image-formed by the printing unit  130  on a sheet. 
       FIG. 2  is a diagram illustrating an outline of a fixation unit in the image forming apparatus  100  according to the first embodiment. The fixation unit includes a pressurization roller  300  and a fixation roller  400 . The exertion of a force (hereinafter referred to as a “pressure contact force”) in an arrow direction by a pressurization mechanism that is not illustrated pressure-contacts the pressurization roller  300  to the fixation roller  400 . The fixation roller  400  has a heater, such as a halogen lamp, inside, and is heated by heat that is emitted by the heater. A sheet is squeezed between the fixation roller  400  and the pressurization roller  300 , and the fixation roller  400  transports the sheet by being rotated in cooperation with the pressurization roller  300 . The fixation roller  400  pressurizes and heats an abutting surface of a sheet that is fed between the fixation roller  400  itself and the pressurization roller  300 , and thus causes a toner image to be fixed to the sheet. 
     It is noted that the larger the abutting surface, the higher the efficiency with which the pressurization roller  300  and the fixation roller  400  can cause the toner image to be fixed. For this reason, in order to broaden the abutting surface, in most cases, a surface of the pressurization roller  300  is formed using an elastic material, such as rubber that is hardened in the vicinity of a fixation temperature. Furthermore, the fixation roller  400  has a surface layer  402  that is formed using a cored-bar layer  401  made of metal and a resin material, such as polytetrafluoroethylene (PFA) in order to efficiently transfer the heat, which is emitted by the heater, to a surface thereof. 
       FIG. 3  is a diagram illustrating a specific example of a creep that occurs in the pressurization roller  300  according to the first embodiment.  FIG. 3  is an example of the creep p that occurs if the pressurization roller  300  in a state that is illustrated in  FIG. 2  is cooled. In this manner, the cooling of the pressurization roller  300  in a state where the fixation roller  400  is pressure-contacted causes a creep P to occur in an abutting portion. An increase in a temperature of the pressurization roller  300  causes the creep P to disappear, but it takes time for the temperature of the pressurization roller  300  to reach a necessary temperature. For this reason, in a situation where a sufficient temperature is not reached, when the pressurization roller  300  is rotated, a situation occurs where the pressure contact force causes the rotation of the fixation roller  400  to be accelerated. Accordingly, teeth of a gear (hereinafter referred to as a “drive gear”) that cause the fixation roller  400  to be driven and teeth of a gear on the fixation roller  400  side collide, and a strange sound (hereinafter referred to as “collision sound”) occurs. 
       FIGS. 4A and 4B  are diagrams for in more detail describing the principle of the occurrence of the collision sound according to the first embodiment. A drive gear G 1  that is illustrated in  FIGS. 4A and 4B  is a drive unit that provides a rotation force to the fixation roller  400 . As illustrated in  FIG. 4A , the rotation of the drive gear G 1  in a state of being engaged with a gear G 2  that is connected to a rotation shaft of the fixation roller  400  provides the rotation force in an arrow direction to the fixation roller  400 . At this time, as described above, the pressure contact force is applied to the pressurization roller  300 . For this reason, when a transition occurs from a state in  FIG. 4A , in which the fixation roller  400  and the pressurization roller  300  are brought into contact with a portion other than a creep portion, to a state in  FIG. 4B , in which the fixation roller  400  and the pressurization roller  300  are brought into contact with the creep portion, there occurs a situation where the pressurization roller  300  is pushed into the fixation roller  400  side as long a distance as the pressurization roller  300  is recessed due to the creep and where the rotation of the pressurization roller  300  is temporarily accelerated. Accordingly, the rotation of the fixation roller  400  is accelerated as well, and the fixation roller  400  is temporarily rotated at a higher speed than the drive gear G 1 . As a result, the teeth of the gear G 2  progress, while being rotated as great an idle as backlash, and collides with the teeth of the drive gear G 1  that precedes the gear G 2 . At that time, high-volume collision sound occurs. For example, when 50 or more minutes elapse until next image forming processing is performed after certain image forming processing is ended, in some cases, the collision sound occurs at the time of re-driving the fixation roller  400 . It is noted that in the drawings, as one example of the drive unit, one drive gear G 1  is illustrated, but in the fixation roller  400 , power of a motor is transmitted through several gears. For this reason, it is considered that a backlash distance is increased as much as the number of involved gears and thus that high-volume collision sound occurs. 
     The occurrence of the collision between the teeth of gears is not preferable not only in terms of operation of the apparatus, but also because the collision sound is undesired sound for the user. According to a situation where the creep occurs, the image forming apparatus  100  according to the embodiment has a configuration in which rotation operation of the pressurization roller  300  and heating operation of the fixation roller  400  are controlled. Specifically, the image forming apparatus  100  according to the embodiment can suppress the collision between the teeth of the gears by not causing the pressurization roller  300  to be rotated in a situation where the creep occurs. Furthermore, the image forming apparatus  100  according to the embodiment can cause the creep to be disappeared in a shorter time by controlling a temperature and rotation speed of the fixation roller  400 . 
       FIG. 5  is a diagram illustrating a specific example of a functional configuration of the image forming apparatus  100  according to the first embodiment. The image forming apparatus  100  includes a central processing unit (CPU), a memory, an auxiliary storage device, and the like that are connected to each other through a bus and executes a program. With execution of the program, the image forming apparatus  100  functions as an apparatus that includes the display  110 , the control panel  120 , the printing unit  130 , the sheet accommodating unit  140 , and the image reading unit  200 . It is noted that all portions, or one or several of each function of the image forming apparatus  100  may be realized using a piece of hardware, such as application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a field programmable gate array (FPGA). The program may be recorded in a computer-readable recording medium. For example, the “computer-readable recording medium” refers to a portable medium, such as a flexible disk, a magneto-optical disk, a ROM, and a CD-ROM, and a storage device, such as a hard disk, that is built into the computer system. The program may be communicated through an electric telecommunication line. 
     The fixation unit of the printing unit  130  includes the pressurization roller  300 , the fixation roller  400 , and a drive unit  131 . The drive unit  131  is a drive unit that provides a rotation force to the fixation roller  400 . For example, the drive unit  131  is configured with the drive gear G 1  that is illustrated in  FIG. 4 , a motor that is a power source thereof, and the like. The operation of the drive unit  131  is controlled by a control unit  153 . 
     The temperature measuring unit  151  measures the temperature of the fixation roller  400 . A temperature measuring unit  151  outputs temperature information indicating the measured temperature to the control unit  153 . It is noted that the temperature of the pressurization roller  300  correlates with the temperature of the fixation roller  400  that heats the pressurization roller  300 . Therefore, based on the temperature of the fixation roller  400 , it is also possible that the temperature of the pressurization roller  300  is measured. A sleep time measuring unit  152  measures the time (hereinafter referred to as the “sleep time”) that elapses from when an image forming apparatus to which the sleep time measuring unit  152  itself belongs to is in a sleep state. The sleep time measuring unit  152  outputs information indicating the measured sleep time (hereinafter referred to as “time information”) to the control unit  153 . 
     The control unit  153  (one example of an estimation unit and a control unit) controls each functional unit in such a manner that an apparatus to which the control unit  153  belongs functions as an image forming apparatus. The control unit  153  controls operation of the fixation unit in such a manner that the collision sound due to the creep does not occur in the image forming processing. Specifically, the control unit  153  acquires the temperature information and the time information from the temperature measuring unit  151  and the sleep time measuring unit  152 , respectively. Based on the sleep time that is indicated by the acquired time information, the control unit  153  estimates the presence or absence of the creep in the pressurization roller  300 . Furthermore, based on the presence or absence of the estimated creep, the control unit  153  controls the operation of the fixation unit. 
     More specifically, based on the sleep time, the control unit  153  avoids the occurrence of the collision sound by controlling the temperature of and the number of rotations of the pressurization roller  300 . The control unit  153  controls the temperature of the pressurization roller  300  by operating control temperature of the fixation roller  400 , and controls the number of rotations of the pressurization roller  300  by operating the output of the drive unit  131 . A method of controlling the fixation unit will be described in detail below. 
       FIG. 6  is a diagram illustrating a specific example of a relationship between the temperature and hardness of the pressurization roller  300  in the image forming apparatus  100  according to the first embodiment. The horizontal axis in  FIG. 6  represents the temperature of the pressurization roller and the vertical axis represents the hardness. As illustrated in  FIG. 6 , it is understood that the higher the temperature, the hardness of the pressurization roller  300  decreases. 
       FIG. 7  is a diagram illustrating a specific example of a relationship between the control temperature of the fixation roller  400  and the size of the creep (hereinafter referred to as an “amount of creep”) that occurs in the pressurization roller  300  in the image forming apparatus  100  according to the first embodiment.  FIG. 7  illustrates the amount of creep that results after 72 hours elapse after the heating of the fixation roller  400  is stopped. The horizontal axis in  FIG. 7  represents the control temperature of the fixation roller  400  at a point in time when the heating is stopped, and the vertical axis represents the amount of creep. As illustrated in  FIG. 7 , it is understood that the higher the control temperature at the point in time when the heating is stopped, the larger the amount of creep. 
       FIG. 8  is a diagram illustrating a specific example of a relationship between the hardness of the pressurization roller  300  and the cooling time in the image forming apparatus  100  according to the first embodiment. The horizontal axis in  FIG. 8  represents the cooling time, and the vertical axis represents the hardness of the pressurization roller  300  that results after the pressurization roller  300  is naturally cooled over a period of cooling time that is represented by the horizontal axis. The relationship that is illustrated in  FIG. 8  is obtained based on the relationship that is illustrated in  FIGS. 6 and 7 . 
     From  FIG. 8 , it is understood that the hardness of the pressurization roller  300  is 44 degrees over the cooling time period of 50 minutes. At this point, for example, if the hardness of the pressurization roller  300  is equal to or smaller than 44 degrees, it is assumed that the occurrence of the collision sound can be avoided. In this case, the control unit  153  can estimate whether or not the collision sound occurs, depending on determining whether or not the sleep time is equal to or more than 50 minutes. 
     If the sleep time is less than 50 minutes, if the image forming processing occurs, the control unit  153  can cause the fixation roller  400  to begin to rotate immediately, and thus can cause fixing processing to be quickly performed. On the other hand, if the sleep time is less than 50 minutes, if the image forming processing occurs, the control unit  153  starts to heat the fixation roller  400 , and waits for the fixation roller  400  to start to be rotated until the temperature of the pressurization roller  300  reaches a temperature at which the occurrence of the collision sound can be avoided. 
       FIGS. 9 and 10  are flowchart illustrating a flow for control of the fixation unit according to the first embodiment.  FIGS. 9 and 10  illustrate downstream processing of the image forming processing and upstream processing before a next image forming processing is performed. At this point, stopping the heater that heats the fixation roller  400  and stopping the motor that causes the drive unit  131  to be driven are described as the downstream processing. First, the control unit  153  powers off the heater (ACT  101 ) and stops the heating of the fixation roller  400 . The control unit  153  causes a power source such as the motor to stop (ACT  102 ) and causes the operation of the drive unit  131  to stop. When the performing of the downstream processing is finished, the control unit  153  causes the apparatus, to which the control unit  153  itself belong, to transition to the sleep state. 
     According to the transition of the apparatus to which the control unit  153  itself belongs to the sleep state, the sleep time measuring unit  152  starts to measure the sleep time (ACT  103 ). The control unit  153  determines whether or not an instruction to perform various types of processing is input into the apparatus to which the control unit  153  itself belongs (ACT  104 ). For example, the instruction for performing is input through the control panel  120 . The control unit  153  determines the presence or absence of the input of this instruction for performing based on input information that is output from the control panel  120 . 
     If the instruction for performing is not input (NO in ACT  104 ), the control unit  153  repeatedly performs ACT  104  until the instruction for performing is input. On the other hand, if the instruction for performing is input (YES in ACT  104 ), the control unit  153  determines whether or not the instruction for performing, which is input, is an instruction to perform the image forming processing (hereinafter referred to as an “image formation instruction”) (ACT  105 ). If an instruction to perform processing other than the image forming processing is input (NO in ACT  105 ), the control unit  153  controls the performance of the processing other than the image forming processing (ACT  106 ) and returns the processing in ACT  104 . 
     On the other hand, if the image formation instruction is input (YES in ACT  105 ), the control unit  153  determines whether or not the sleep time exceeds a predetermined threshold (ACT  107 ). At this point, the predetermined threshold is set as the time that the hardness of the pressurization roller  300  takes to reach the hardness at which the collision sound occurs after (previous) image forming processing is ended. For example, in the case of an example in  FIG. 8 , a threshold of the sleep time is set to 50 minutes. 
     If the sleep time does not exceed the threshold (NO in ACT  107 ), the control unit  153  performs first temperature control (ACT  108 ). The first temperature control is processing that increases and decreases the temperature of the fixation roller  400  up to the first control temperature. Specifically, the first control temperature is a minimum temperature (hereinafter referred to as a “preparatory-run start temperature”) at which a preparatory run can be started. 
     Generally, the image forming apparatus performs the upstream processing that causes the fixation roller  400  to be rotated in a prepared manner, as an operation in preparation for the fixing processing before performing the image forming processing. Generally, the upstream processing is referred to as a preparatory run. The preparatory run is started after the temperature of the fixation roller  400  reaches a predetermined preparatory-run start temperature. Generally, the preparatory-run start temperature is set to be a temperature that is lower than the fixation temperature (for example, approximately 140° C.). It is noted that at a point in time when ACT  106  is performed, the image forming apparatus  100  is in a sleep state, the temperature of the fixation roller  400  is lower than the first control temperature. For this reason, the control unit  153  powers on the heater, and causes processing, which heats the fixation roller  400 , to be started. It is noted that the preparatory run is described as a first preparatory run (a first preparatory run operation) in order to be distinguished from a second preparatory run that will be described below. 
     When the fixation roller  400  starts to be heated, the control unit  153  determines whether or not the temperature reaches the first control temperature (ACT  109 ). If the first control temperature is not reached (NO in ACT  109 ), the control unit  153  repeatedly performs ACT  109  until the temperature of the fixation roller  400  reaches the first control temperature. On the other hand, if the first control temperature is reached (YES in ACT  109 ), the control unit  153  causes the first preparatory run to be started (ACT  110 ). 
     On the other hand, in ACT  107 , if the sleep time exceeds a threshold (YES in ACT  107 ), the control unit  153  performs a second temperature control (ACT  111 ). The second temperature control is processing that causes the temperature of the fixation roller  400  to be increased up to the second control temperature. Specifically, the second control temperature is a temperature at which the hardness of the pressurization roller  300  is the hardness at which the occurrence of the collision sound can be avoided. Generally, the second control temperature is a temperature that is higher than the fixation temperature. For example, examples in  FIGS. 6 and 8  illustrate that, if the temperature of the pressurization roller  300  is equal to or higher than approximately 40° C., the hardness of the pressurization roller  300  is equal to or lower than 44 degrees. In this case, after the temperature of the fixation roller  400  reaches the second control temperature, the control unit  153  maintains such a state for a predetermined time, and thus causes the temperature of the pressurization roller  300  to be increased up to 40° C. or higher. 
       FIG. 11  is a diagram illustrating a specific example of a relationship between an occurrence situation of the collision sound and the second control temperature if the preparatory run is started at a point in time at which three hours elapse from when certain image forming processing is ended.  FIG. 11  illustrates the occurrence situation of the collision sound during each of the times (0 seconds, 4 seconds, 8 seconds, and 12 seconds) for which the fixation roller  400  is maintained to be at the second control temperature. In  FIG. 11 , “x” indicates that the collision sound occurs, “4” indicates that the collision sound occurs somewhat less often, and “0” indicates that the collision sound at a non-negligible level occurs. 
     At this point, if the permitted time (hereinafter referred to as the “permission time”) that the fixation roller  400  takes to start the preparatory run after the second control temperature is reached is 0 seconds, the second control temperature is set to 200° C. Furthermore, if the permission time is 0 seconds and the collision sound occurs somewhat less often, the second control temperature may be set to 180° C. Furthermore, if the permission time is 4 seconds, the second control temperature may be set to 180° C. In this manner, the second control temperature may be set based on a level at which the collision sounds occur, the permission time that takes for the preparatory run to be started, or the like. 
     The description is provided with reference back to FIG.  10 . With the second temperature control, the image forming apparatus  100  is in a state where, although the fixation roller  400  is caused to be rotated, the collision sound does not occur. 
     The control unit  153  determines whether or not the temperature of the fixation roller  400  reaches the second control temperature (ACT  112 ). If the temperature does not reach the second control temperature (NO in ACT  112 ), the control unit  153  repeatedly performs ACT  112  until the temperature reaches the second control temperature. On the other hand, if the temperature reaches the second control temperature (YES in ACT  112 ), the control unit  153  performs the first temperature control (ACT  113 ). At this point in time, the temperature of the fixation roller  400  is the second control temperature that is higher than the first control temperature. For this reason, the control unit  153  powers off the heater, and waits until the temperature of the fixation roller  400  is decreased to be the first control temperature. Furthermore, when the temperature of the fixation roller  400  is decreased to be the first control temperature, the control unit  153  repeatedly powers on and off the heater, and thus keeps the temperature of the fixation roller  400  adjusted to the first control temperature. 
     When the temperature of the fixation roller  400  reaches the first control temperature, the control unit  153  causes the second preparatory run (a second preparatory run operation) to be started (ACT  114 ). In the second preparatory run, the fixation roller  400  is caused to be rotated at a lower rotation speed than in the first preparatory run. Accordingly, the likelihood that the collision sound will occur when the fixation roller  400  is rotated can be further decreased. It is noted that in order to reduce nonuniformity in the temperature of the pressurization roller  300 , time (that is, time for driving the fixation roller  400 ) at which the second preparatory run is performed is desirably set to be lengthened within a permissible range. When the second preparatory run is finished, the control unit  153  instructs each functional unit to start the image forming operation (ACT  115 ). 
     The image forming apparatus  100  according to the first embodiment, which is configured in this manner, controls a timing at which the fixation roller  400  starts to be rotated, according to the presence or absence of the creep that is estimated based on the length of the sleep time, and thus it is possible that the collision sound is suppressed from occurring at the time of the image forming processing. 
     Second Embodiment 
       FIG. 11  is a diagram illustrating a specific example of a functional configuration of an image forming apparatus  100   a  according to a second embodiment. The image forming apparatus  100   a  is different from the image forming apparatus  100  according to the first embodiment in that instead of the sleep time measuring unit  152 , a torque measuring unit  154  is included and that instead of the control unit  153 , a control unit  153   a  is included. The other functional units are the same as those of the image forming apparatus  100  according to the first embodiment. For this reason, the same functional units are given the same reference numerals as in  FIG. 5 , and descriptions thereof are omitted. 
     The torque measuring unit  154  measures torque (one example of a load) of the pressurization roller  300  (or the fixation roller  400 ). The torque measuring unit  154  outputs torque information indicating the measured torque to the control unit  153   a.    
     The control unit  153   a  (one example of an estimation unit and a control unit) acquires the temperature information and the torque information from the temperature measuring unit  151  and the torque measuring unit  154 , respectively. Based on the torque that is indicated by the acquired torque information, the control unit  153   a  estimates the presence or absence of the creep in the pressurization roller  300 . As described above, with the rotation of the fixation roller  400 , the creep portion reaches the abutting surface in contact with the pressurization roller  300 , the rotation of the pressurization roller  300  is temporarily accelerated with the pressure contact force. For this reason, torque of the pressurization roller  300  is increased. The control unit  153   a  measures a change in this torque, and thus can estimate the presence or absence of the creep and can detect an endpoint of the creep. Furthermore, based on a position of the detected endpoint of the creep and an amount of rotation of the fixation roller  400 , the control unit  153   a  can estimate a next timing at which the creep reaches the abutting surface. Based on the presence or absence of the creep that is identified in this manner, the control unit  153   a  controls the operation of the fixation unit. 
       FIGS. 12, 13, 14, and 15  are charts illustrating a flow for control of the fixation unit according to the second embodiment. At this point, processing that is the same as that according to the first embodiment is given the same reference numeral as in  FIGS. 9 and 10 , and thus a description thereof is omitted. 
     After performing the first temperature control, in order to detect the creep, the control unit  153   a  causes the fixation roller  400  to be rotated temporarily (ACT  201 ). The control unit  153   a  acquires the torque information that results while the rotation of the fixation roller  400  is in progress, from the torque measuring unit  154 . Based on the acquired torque information, the control unit  153   a  determines whether or not the torque exceeds a predetermined threshold (ACT  202 ). If the torque does not exceed the threshold (NO in ACT  202 ), the control unit  153   a  returns to the control in ACT  110 , and causes the first preparatory run to be started. 
     On the other hand, if the torque exceeds the threshold (YES in ACT  202 ), the control unit  153   a  causes the fixation roller  400  to be rotated until the detected creep again reaches the abutting surface (ACT  203 ). When the creep again reaches the abutting surface, the control unit  153   a  returns to the control in ACT  110  and performs the second temperature control. 
     The image forming apparatus  100   a  according to the second embodiment, which is configured in this manner measures the torque that results when the fixation roller  400  is caused to be rotated temporarily, and detects the presence or absence of the creep based on the measured torque. After measures the torque, the image forming apparatus  100   a  causes the first or second preparatory run to be started. That is, the image forming apparatus  100   a  can obtain the occurrence situation of the creep more precisely than in the first embodiment in which the presence or absence of the creep is estimated based on the cooling time. For this reason, it is possible that the image forming apparatus  100   a  more efficiently suppresses the collision sound from occurring. 
     It is noted that, in each embodiment described above, if the occurrence of the creep is estimated, the control unit  153  (or  153   a ) is described as causing the temperature of the fixation roller  400  to be increased up to the second control temperature and then to be decreased up to the first control temperature, and thereafter causing the preparatory run to be started, but in this case, if the temperature of the fixation roller  400  is decreased to at least a ready temperature (one example of a third control temperature) or lower, the control unit  153  may cause the preparatory run to be started without the need to necessarily decease the temperature of the fixation roller  400  up to the first control temperature. At this point, the ready temperature is a temperature at which it is possible that the fixing processing is started. Generally, the ready temperature is set to be a temperature that is somewhat lower than the fixation temperature which is equal to or higher than the first control temperature. The image forming apparatus keeps the temperature of the fixation roller  400 , which results after the preparatory run is finished to the ready temperature, and thus it is possible that the image forming apparatus, when instructed to perform the image forming processing, causes the temperature of the fixation roller  400  increase up to the fixation temperature in a short time. Accordingly, the high-speed image forming processing can be realized. 
     Third Embodiment 
     An image forming apparatus  100   b  according to a third embodiment is different from the image forming apparatuses according to the first and second embodiments in that a stopper  132  is further included which prevents the pressurization roller  300  from being recessed into the fixation roller  400  due to the cooling over a long period of time. 
       FIG. 16  is a three-dimensional diagram illustrating a specific example of a configuration of the image forming apparatus  100   b  according the third embodiment. For example, the stopper  132  is configured to be one portion of the pressurization mechanism that provides the pressure contact force to the pressurization roller  300 . An example in FIG.  16  is an example in which the stopper  132  is connected to a support portion B that supports a shaft A of the pressurization roller  300 . In this case, with the pressurization mechanism, a pressure contact force is applied in an arrow direction to an indication portion B, and thus the pressure contact force is exerted on the shaft A through a connection portion. Accordingly, the pressure contact force is provided to the pressurization roller  300 . The stopper  132  is fixed to a position that, at a point of contact P 2 , is in contact with a surface of the fixation roller  400 . Accordingly, because a position of the pressurization roller  300  is also fixed by the stopper  132 , the pressurization roller  300  can be prevented from being recessed into the fixation roller  400  by a longer distance than is necessary. 
     According to at least one embodiment described above, the control unit is provided that controls a timing at which the preparatory run is started, based on the cooling time for the pressurization roller  300  or the torque of the fixation roller  400 , and thus it is possible that the collision sound which occurs in the image forming processing is sufficiently suppressed. 
     It is noted that in the image forming apparatus that causes the toner with two rotators, the fixation roller that has a cored bar inside and the pressurization roller that has the elastic layer, to be fixed, if the pressurization roller that has a small diameter for miniaturization of the apparatus is used, the amount of creep is easily increased. According to the embodiments described above, even if the pressurization roller that has a small diameter is used in this manner, the collision sound can be effectively suppressed. 
     It is noted that the fixation roller  400  is one example of the fixation member. Furthermore, the pressurization roller  300  is one example of the pressurization member. If the fixation member and the pressurization member are drive members that are pressure-contacted and come into contact with each other and are mechanism which, when driven, has the likelihood that a strange sound will occur due to the creep that occurs in an abutting portion, no limitation to aspects of rollers is imposed. Furthermore, a halogen lamp that includes the fixation roller  400  inside is one example of the heat source. No heat source that heats the surface of the fixation roller  400  is limited to the halogen lamp. 
     Furthermore, the drive gear G 1  that provides the rotation force to the fixation roller  400  is one example of the drive unit. Furthermore, the rotation force that is provided by the drive gear G 1  to the fixation roller  400  is one example of the drive force. No drive unit that provides the drive force to the fixation member (or the pressurization member) according to an aspect of the fixation member (or the pressurization member) is limited to an aspect of the gear. 
     Furthermore, the sleep time is one example of the elapsed time. If the elapsed time is the time for which the pressurization member is cooled, the elapsed time is not limited to the sleep time. For example, the elapsed time may be the time that the image forming apparatus takes to be powered on after powered off. 
     In this embodiment, ‘decoloring’ means to make it difficult to recognize a color of an image formed on an image receiving member after the image is formed on the image receiving member by a recording material which has different color from the color of the image receiving material. The color of recording material may be achromatic color including black or white, not limiting to chromatic color. And in the following embodiment, decoloring the image’ means ‘erasing the image’. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms: furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.