Patent Publication Number: US-9429909-B2

Title: Image forming apparatus

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. 2013-267521, filed on Dec. 25, 2013, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     This disclosure relates to an image forming apparatus using an electrophotographic process and is applicable to a copier, a printer, a facsimile machine, and a multifunction peripheral combining the functions of these apparatuses, and more particularly to an image forming apparatus capable of reducing power consumption in response to a demand for energy efficiency by collecting heat generated in the image forming apparatus, converting the heat into electrical energy, storing the electrical energy, and generating power with the stored electrical energy in a sleep state. 
     2. Related Art 
     A typical technology applicable to power generation using a heat-generating component of an image forming apparatus and cooling of the heat-generating component is, for example, a power generator that continuously and stably generates power using a thermoelectric conversion element. 
     SUMMARY 
     In one embodiment of this disclosure, there is provided an improved image forming apparatus that, in one example, includes a heat-generating component, a power generation device, a heat radiation device, a cooling device, a temperature detector, and a controller. The power generation device includes a thermoelectric element. The heat radiation device includes a first radiator plate interposed between the heat-generating component and a first surface of the thermoelectric element and a second radiator plate attached to a second surface of the thermoelectric element opposite the first surface. The temperature detector detects a temperature increase of the heat-generating component. The controller controls operations of the cooling device and the power generation device by operating the cooling device if the detected temperature increase reaches at least a predetermined threshold value, and causing the power generation device to generate power without operating the cooling device to cool the first heat radiator plate passively if the detected temperature increase falls below the predetermined threshold value. 
     In one embodiment of this disclosure, there is provided another improved image forming apparatus that, in one example, includes a heat-generating component, a power generation device, a heat radiation device, a cooling device, and a controller. The power generation device includes a thermoelectric element. The heat radiation device includes a first radiator plate interposed between the heat-generating component and a first surface of the thermoelectric element and a second radiator plate attached to a second surface of the thermoelectric element opposite the first surface. The cooling device cools the first radiator plate. The controller predicts a temperature increase of the heat-generating component from a control state of the image forming apparatus assumed to be related to the temperature increase. The controller controls operations of the cooling device and the power generation device by operating the cooling device if the predicted temperature increase reaches at least a predetermined threshold value, and causing the power generation device to generate power without operating the cooling device to cool the first heat radiator plate passively if the predicted temperature increase falls below the predetermined threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of this disclosure and many of the advantages thereof are obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a schematic diagram illustrating a basic configuration of a mechanical system of an image forming apparatus according to a first embodiment of this disclosure; 
         FIG. 2  is a schematic block diagram illustrating a basic configuration of a power supply system of the image forming apparatus illustrated in  FIG. 1 ; 
         FIG. 3  is a schematic block diagram illustrating a power generation and cooling system according to an existing example, which uses a heat-generating component of the image forming apparatus illustrated in  FIG. 1 ; 
         FIG. 4  is a schematic diagram illustrating the structure of the heat-generating component of the image forming apparatus illustrated in  FIG. 1 ; 
         FIG. 5  is a diagram illustrating the structure of a pressure roller illustrated in  FIG. 4 ; and 
         FIG. 6  is a diagram comparing power generation and consumption of the heat-generating component of the image forming apparatus according to the temperature increase between the power generation and cooling system of the existing example illustrated in  FIG. 3 , the power generation and cooling system of the first embodiment illustrated in  FIG. 5 , and a cooling system without a heat generation system. 
     
    
    
     DETAILED DESCRIPTION 
     In describing the embodiments illustrated in the drawings, specific terminology is adopted for clarity. However, this disclosure is not intended to be limited to the specific terminology so used, and it is to be understood that substitutions for each specific element can include any technical equivalents that have the same function, operate in a similar manner, and achieve a similar result. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, image forming apparatuses according to embodiments of this disclosure will be described. 
     A first embodiment of this disclosure will now be described. 
       FIG. 1  is a schematic diagram illustrating a basic configuration of a mechanical system of an image forming apparatus  1  according to the first embodiment of this disclosure. In the present embodiment, the image forming apparatus  1  is a digital multifunction peripheral having functions such as a copy function, a print function, a facsimile function. The functions are sequentially selectable with an application switch key of a later-described operation unit  40  in the image forming apparatus  1 . For example, the image forming apparatus  1  shifts to a copy mode upon selection of the copy function, a print mode upon selection of the print function, and a facsimile mode upon selection of the facsimile function. 
     Specifically, when the image forming apparatus  1  in  FIG. 1  is in the copy mode, an automatic document feeder (ADF)  2  sequentially feeds a bundle of documents to an image reader  3 , which then reads image information from the documents. A writing unit  4  serving as a writing device converts the read image information into optical information with an image processor. A photoconductor drum  6  in a printer unit  5  is uniformly charged by a charger and exposed with the optical information from the writing unit  4 , to thereby form an electrostatic latent image on the photoconductor drum  6 . A developing device  7  develops the electrostatic latent image on the photoconductor drum  6  to form a toner image. A transport belt  8  transports a transfer sheet (also referred to as a recording sheet or recording medium, for example) to transfer the toner image from the photoconductor drum  6  onto the transfer sheet. A fixing device  9  fixes the toner image on the transfer sheet. The transfer sheet is then discharged to the outside of the image forming apparatus  1 . 
       FIG. 2  is a schematic block diagram illustrating a basic configuration of a power supply system of the image forming apparatus  1 . As illustrated in  FIG. 2 , the image forming apparatus  1  includes, as a power supply system, a heat radiation device  300 , a cooling fan  26 , a temperature sensor  29 , and an input-output control unit  20 . The heat radiation device  300  includes an air-cooled first radiator plate  30  and a second radiator plate  31 . The first radiator plate  30  is interposed between a heat-generating component  22  and one surface of a thermoelectric element  32  serving as a power generation device. The second radiator plate  31  is attached to the other surface of the thermoelectric element  32 . 
     The cooling fan  26  serves as a cooling device that cools the first radiator plate  30 . The temperature sensor  29  serves as a temperature detector that detects a temperature increase of the heat-generating component  22 . The input-output control unit  20  (specifically, a later-described CPU  201 ) serves as a controller that controls the operations of the cooling fan  26  and the thermoelectric element  32 , specifically, operating the cooling fan  26  if the temperature increase detected by the temperature sensor  29  equals or exceeds a predetermined threshold value, and causing the thermoelectric element  32  to generate power without operating the cooling fan  26  to cool the first heat radiator plate  30  passively if the detected temperature increase is less than the predetermined threshold value. 
     The input-output control unit  20  is connected to an operation unit  40  and a personal computer (PC)  50 . The operation unit  40  is a so-called control panel (operation panel) provided to a typical multifunction peripheral (i.e., the image forming apparatus  1  in the present embodiment). The PC  50  is a typical computer that issues a print command to the image forming apparatus  1  via a network. The input-output control unit  20  includes a central processing unit (CPU)  201 , a communications interface  202 , an analog/digital (A/D) convertor  203 , an input-output (I/O) controller  204 . The A/D converter  203  converts analog values of temperature information received from an interior temperature sensor  28  and the temperature sensor  29  into digital values. The communications interface  202  receives print information from the operation unit  40  or the PC  50 . The I/O controller  204  controls input and output ports in accordance with commands from the CPU  201 . The CPU  201  performs arithmetic operations with input information. 
     As illustrated in  FIG. 2 , the communications interface  202  receives the print command from the operation unit  40  or the PC  50 . The print command includes image data to be printed, information about the number of prints to be produced, the type of sheets to be printed (e.g., plain paper or high-quality paper), the thickness of the sheets, and the print mode (e.g., color or monochrome, intensive print, and duplex print), and a variety of instructions concerning image formation. The CPU  201  recognizes the number of prints by extracting the information thereof from the print command. Further, the CPU  201  similarly recognizes the thickness of the sheets and the print mode by extracting the information thereof from the print command. As well as the controller, the CPU  201  also implements the functions of a print number detector, a sheet thickness detector, and a print mode recognition device, descriptions of which are deferred. 
     In the present embodiment, the thermoelectric element  32  is installed to the heat-generating component  22  with the air-cooled first radiator plate  30  interposed therebetween. Thermal energy discharged from the heat-generating component  22  and conducted to the thermoelectric element  32  through the first radiator plate  30  is converted into electrical energy by the thermoelectric element  32 . 
     The electrical energy generated by the thermoelectric element  32  is stored in a storage battery  34  via a direct-current/direct-current converter (DDC) charger  27 . If the DDC charger  27  is turned off, the thermoelectric element  32  and the DDC charger  27  are disconnected from each other, thus stopping power generation by the thermoelectric element  32 . The electrical energy stored in the storage battery  34  is supplied to a load  21  via a DDC discharger  24  and a switching circuit  23 . Since the present embodiment requires a power supply for operating the DDC charger  27 , the DDC discharger  24 , and the switching circuit  23 , a power supply line extending from a power supply unit (PSU)  25  connected to an alternating-current (AC) power supply  35  is connected to the switching circuit  23 . With this configuration, the switching circuit  23  switches, under the control of the input-output control unit  20 , between power from a main power supply based on AC power supplied from the PSU  25  and power generated by the thermoelectric element  32 , stored in the storage battery  34 , and discharged by the DDC discharger  24 , and supplies the selected power to the load  21 . 
     As well as the above-described control of the operations of the cooling fan  26  and the thermoelectric element  32  based on the temperature increase detected by the temperature sensor  29  attached to the heat-generating component  22 , the input-output control unit  20  performs other controls. For example, the input-output control unit  20  controls the operation of the cooling fan  26  based on an interior temperature detected by the interior temperature sensor  28  that detects the temperature of the interior of the image forming apparatus  1  as necessary. Further, the input-output control unit  20  controls the image forming apparatus  1  as a whole based on respective readings obtained from a variety of other sensors, and operates various respective units (functions) of the image forming apparatus  1  that serve as the load  21  in accordance with the operation mode. The input-output control unit  20  also controls the charging operation of the DDC charger  27  to the storage battery  34  and the discharging operation of the DDC discharger  24  from the storage battery  34 , and operates the DDC charger  27  to perform the charging operation when power generation using the heat-generating component  22  is available. 
       FIG. 3  is a schematic block diagram illustrating, as a comparative example, a power generation and cooling system according to an existing example, which uses the heat-generating component  22  of the image forming apparatus  1 . As illustrated in  FIG. 3 , in the power generation and cooling system according to the existing example using the heat-generating component  22 , the thermoelectric element  32  generates power with one surface thereof in contact with the heat-generating component  22  and the other surface thereof attached to an air-cooled radiator plate  33 . The input-output control unit  20  controls the operation of the cooling fan  26  to perform a cooling operation based on the temperature increase detected by the temperature sensor  29  attached to the heat-generating component  22 . 
     In this example, as the heat-generating component  22  operates and generates heat in the image forming apparatus  1 , the heat is transmitted to the thermoelectric element  32 , and the thermoelectric element  32  generates power. In this process, the heat transmitted to the thermoelectric element  32  is radiated into the air through the air-cooled radiator plate  33 . If the temperature increase of the heat-generating component  22  detected by the temperature sensor  29  is small, the heat-generating component  22  is unlikely to be destroyed by the increased temperature even if the cooling fan  26  is not operated. On the other hand, if the detected temperature increase is large owing to a continuous operation of the heat-generating component  22  in a certain use state of the image forming apparatus  1 , for example, the cooling performance is insufficient. To prevent the destruction of the heat-generating component  22 , therefore, it is necessary to operate the cooling fan  26  and apply cool air to heat radiation fins  36  and the body of the radiator plate  33  to enhance the cooling performance. 
     When power generation takes place in the thermoelectric element  32  in contact with the heat-generating component  22 , a high thermal resistance of the thermoelectric element  32  should be taken into account, as well as the cooling function of the heat-generating component  22 . Compared with a configuration not having the thermoelectric element  32  between the heat-generating component  22  and the radiator plate  33 , in the configuration having the thermoelectric element  32  between the heat-generating component  22  and the radiator plate  33  and including the cooling fan  26  having the same level of cooling performance as that of the configuration not having the thermoelectric element  32 , it is difficult to cool the heat-generating component  22  because of the thermal resistance of the thermoelectric element  32 . Therefore, the function of cooling the heat-generating component  22  is inhibited, and at worst elements in the heat-generating component  22  may be destroyed owing to the temperature increase. To prevent such destruction of the heat-generating component  22 , it is conceivable to increase the airflow volume of the cooling fan  26 . The increase of the airflow volume, however, entails a substantial increase in power necessary for the cooling operation, which is undesirable in view of the recent demand for energy efficiency. 
     In this disclosure, therefore, two types of radiator plates are provided, and cooling methods are switched in accordance with the use state of the image forming apparatus  1 . 
       FIG. 4  is a diagram illustrating the structure of the heat-generating component  22  of the image forming apparatus  1 . The fixing device  9  includes a fixing roller  91  and a pressure roller  92 , which are typically disposed in a casing  93 . A transfer sheet S passes between the fixing roller  91  and the pressure roller  92  that axially rotate. In this process, the transfer sheet S is heated by the fixing roller  91  and pressed against the pressure roller  92 , and thereby toner on the transfer sheet S is fused and fixed thereon. A temperature sensor  52  is disposed in the fixing device  9  to measure the temperature of the fixing roller  91 . The temperature sensor  52  may be employed as the temperature sensor  29  in  FIG. 2 . 
       FIG. 5  is a diagram illustrating details of the structure of the pressure roller  92  illustrated in  FIG. 4 . The first radiator plate  30 , the thermoelectric element  32 , and the second radiator plate  31  are provided to the pressure roller  92 . The following description is given on the assumption that, in the present embodiment, the heat-generating component  22  illustrated in  FIG. 2  corresponds to the fixing device  9 , more specifically to the pressure roller  92  that receives the heat from the fixing roller  91 . 
     The fixing roller  91  has a shaft including a heater. The heat generated by the heater is conducted to the pressure roller  92  from the fixing roller  91 . The pressure roller  92  has a rotary shaft formed of a heat pipe  95 . The heat conducted to the pressure roller  92  from the fixing roller  91  is further conducted to the heat pipe  95  and guided to the first radiator plate  30  by the heat pipe  94 . 
     The first radiator plate  30  is fixed to the heat pipe  95 , and thus rotates together with the heat pipe  95 . Although the first radiator plate  30  in the present embodiment has a circular shape, the shape of the first radiator plate  30  is not limited thereto. 
     The thermoelectric element  32  is disposed on a surface of the first radiator plate  30  opposite the surface facing the pressure roller  92 . The thermoelectric element  32  has a circular shape having a smaller diameter than that of the first radiator plate  30 . The diameter of the thermoelectric element  32 , however, may be determined to a desired value. Further, the thermoelectric element  32  may be a commonly used thermoelectric element. 
     The second radiator plate  31  is disposed on a surface of the thermoelectric element  32  opposite the surface facing the first radiator plate  30 . The second radiator plate  31  may be provided with heat radiation fins. 
     The thermoelectric element  32  has a function of converting the received heat into electricity. On the circumferential surface of the thermoelectric element  32 , a pair of electrodes  51   a  and  51   b  are disposed to extract the electricity from the thermoelectric element  32 . The electrodes  51   a  and  51   b  are connected to the DDC charger  27  illustrated in  FIG. 2 . 
     When the temperature of the fixing roller  91  is measured by the temperature sensor  29  (i.e., the temperature sensor  52 ), these temperature readings are supplied to the CPU  201 . When the increase in temperature of the fixing roller  91  equals or exceeds a predetermined threshold value, the CPU  201  drives the cooling fan  26 . Conversely, if the increase in temperature of the fixing roller  91  is less than the predetermined threshold value, the CPU  201  does not drive the cooling fan  26  but instead allows the first radiator plate  30  to cool passively, through so-called passive cooling. In this process, the thermoelectric element  32  generates power. 
     That is, the present embodiment employs two types of cooling methods; a method of cooling the first radiator plate  30  with the cooling fan  26  and a method of cooling the second radiator plate  31  through passive cooling. 
     If the temperature increase of the heat-generating component  22  according to the use state of the image forming apparatus  1  detected by the temperature sensor  29  is small and less than the predetermined threshold value, the temperature increase due to the heat generation is small enough not to cause the destruction of the heat-generating component  22 . Therefore, the input-output control unit  20  does not operate the cooling fan  26  but instead allows cooling of the heat generating component  22  only through passive cooling of the second heat radiator plate  31 . In this process, the heat from the heat-generating component  22  is conducted to the first radiator plate  30  having a high thermal conductivity and then is transmitted to the thermoelectric element  32 . The heat transmitted to the thermoelectric element  32  is passively cooled and radiated from the second radiator plate  31 . Since the cooling fan  26  is not operating during this process, the heat generation takes place in the thermoelectric element  32  with no need for power for operating the cooling fan  26 . The temperature increase of the heat-generating component  22  is less than the predetermined threshold value in, for example, the production of a small number of prints, which accounts for a large proportion of the operations of the image forming apparatus  1 . In such an operation, therefore, efficient heat generation takes place in the thermoelectric element  32  without the operation of the cooling fan  26 , i.e., without the consumption of power for the cooling operation. 
     If the temperature increase of the heat-generating component  22  according to the use state of the image forming apparatus  1  detected by the temperature sensor  29  is large and equal to or greater than the predetermined threshold value, the temperature increase due to the heat generation is large enough to raise the possibility of destroying the heat-generating component  22 . Therefore, the input-output control unit  20  operates the cooling fan  26  to actively apply the cool air from the cooling fan  26  to the first radiator plate  30 , to thereby radiate the heat from the heat-generating component  22  through the first radiator plate  30 . In the present configuration, the thermoelectric element  32  having a high thermal resistance is not interposed between the heat-generating component  22  and the first radiator plate  30 . Therefore, the installation of the thermoelectric element  32  does not increase the power for the cooling operation, thereby allowing efficient cooling. 
       FIG. 6  is a diagram comparing power generation and consumption of the heat-generating component  22  of the image forming apparatus  1  according to the temperature increase between the power generation and cooling system of the existing example illustrated in  FIG. 3 , the power generation and cooling system of the first embodiment illustrated in  FIG. 5 , and a cooling system without a heat generation system, which corresponds to charts E 1 , E 2 , and E 3 , respectively 
     In general, the production of a small number of prints accounts for a large proportion of the operations performed by the image forming apparatus  1  used in an office or the like. In such an operation, the image forming apparatus  1  shifts to a standby mode or a sleep mode after printing, and the flow of current to the heat-generating component  22  stops, halting the temperature increase of the heat-generating component  22 . In such production of a small number of prints, although the current temporarily flows through the heat-generating component  22  and increases the temperature thereof, the operating time of the image forming apparatus  1  is short due to the small number of prints. Consequently, the current flow stops before the temperature reaches the upper limit, thereby reducing the temperature. Due to the power generation by the thermoelectric element  32  during the repetition of such an operation, small power generation amounts accumulate, producing an energy saving effect. 
     In some cases, however, the image forming apparatus  1  produces a large number of prints. In this case, the current flows through the heat-generating component  22  for an extended time, increasing the temperature of the heat-generating component  22 . Then, if the cooling performance is surpassed by the temperature increase, the temperature of the elements in the heat-generating component  22  continues to increase, eventually exceeding the upper limit thereof and destroying the heat-generating component  22 . Forced cooling by the cooling fan  26  is necessary to prevent such an outcome, but the operation of the cooling fan  26  means an increase in power consumption. 
     As illustrated in  FIG. 6 , in the power generation and cooling system according to the existing example in chart E 1 , if the temperature increase of the elements in the heat-generating component  22  is small, the thermoelectric element  32  is capable of generating power while the heat of the heat-generating component  22  is radiated through the radiator plate  33 . If the temperature increase is thus small, the thermoelectric element  32  is capable of generating power without the operation of the cooling fan  26 , although the power generation amount is small. Accordingly, a predetermined power generation amount is obtained without power consumption for the cooling operation. 
     If the temperature increase is large, however, it is necessary to operate the cooling fan  26 . In this example, the thermoelectric element  32  having a high thermal resistance is interposed between the heat-generating component  22  and the radiator plate  33 , and thus the power consumption for the cooling operation is substantially increased compared with that in the cooling system without a heat generation system (i.e., without the thermoelectric element  32 ) in chart E 3 .  FIG. 6  illustrates that, when the temperature increase is large in this existing example, the thermoelectric element  32  generates approximately half the predetermined power generation amount with the power consumption for the cooling operation excluding the increment indicated by hatching. Without this increment in the power consumption for the cooling operation, the elements in the heat-generating component  22  are likely to be destroyed when the temperature increase is large. 
     On the other hand, in the heat generation and cooling system according to the first embodiment in chart E 2 , if the temperature increase of the elements in the heat-generating component  22  is small, the heat from the heat-generating component  22  is conducted to the first radiator plate  30  having a high thermal conductivity and then is transmitted to the thermoelectric element  32 . The heat transmitted to the thermoelectric element  32  is radiated from the second radiator plate  31  and passively cooled. Accordingly, the predetermined power generation amount is obtained from the power generation by the thermoelectric element  32 . Since the cooling fan  26  is not operating during this process, there is no power consumption for the cooling operation. 
     If the temperature increase is large, the cooling fan  26  is operated to actively apply the cool air to the first radiator plate  30 . Thereby, the heat of the heat-generating component  22  is radiated through the first radiator plate  30 . In the present embodiment, the cool air produced by the operation of the cooling fan  26  is used for the cooling operation. Unlike the heat generation and cooling system according to the existing example in chart E 1 , however, the thermoelectric element  32  having a high thermal resistance is not interposed between the heat-generating component  22  and the first radiator plate  30  in the present embodiment, and thus there is no increase in the power consumption for the cooling operation. When the temperature increase is large, therefore, the power consumption for the cooling operation, i.e., for the operation of the cooling fan  26  is approximately the same as that in the cooling system without a heat generation system (i.e., without the thermoelectric element  32 ) in chart E 3 . 
     A second embodiment of this disclosure will now be described. 
     According to the second embodiment, the image forming apparatus  1  does not include the temperature sensor  29  attached to the heat-generating component  22  to detect the temperature increase of the heat-generating component  22 . Instead, the input-output control unit  20  predicts the temperature increase of the heat-generating component  22  from the control state of the image forming apparatus  1 , which is assumed to be related to the temperature increase of the heat-generating component  22 . Further, the input-output control unit  20  controls the operations of the cooling fan  26  and the thermoelectric element  32  by operating the cooling fan  26  if the predicted temperature increase equals or exceeds a predetermined threshold value, and causing the thermoelectric element  32  to generate power without operating the cooling fan  26  to cool the first radiator plate  30  through passive cooling if the predicted temperature increase is less than the predetermined threshold value. 
     That is, in the image forming apparatus  1  according to the second embodiment, the input-output control unit  20  calculates the heat generation amount based on, for example, the amount of current flowing through the heat-generating component  22  and the length of time the current flow detected from the control state of the image forming apparatus  1 , and predicts the temperature increase based on the heat generation amount. The present embodiment obviates the need for installing the special temperature sensor  29  to the heat-generating component  22 , thereby achieving a reduction in cost. 
     A third embodiment of this disclosure will now be described. 
     The image forming apparatus  1  according to the third embodiment is an embodiment of the second embodiment. In the image forming apparatus  1  according to the third embodiment, the print number detector (i.e., the CPU  201 ) detects, as an example of the control state of the image forming apparatus  1 , the number of prints to be produced by the image forming apparatus  1 . The input-output control unit  20  predicts the temperature increase of the heat-generating component  22  based on the number of prints detected by the print number detector, and controls the operations of the cooling fan  26  and the thermoelectric element  32  in accordance with the predicted temperature increase. Specifically, the input-output control unit  20  operates the cooling fan  26  if the predicted temperature increase equals or exceeds a predetermined threshold value, and causes the thermoelectric element  32  to generate power without operating the cooling fan  26  to cool the first radiator plate  30  through passive cooling if the predicted temperature increase is less than the predetermined threshold value. 
     The image forming apparatus  1  according to the third embodiment obviates the need for installing the special temperature sensor  29  to the heat-generating component  22  similarly to the second embodiment, thereby achieving a reduction in cost. Further, the present embodiment allows the thermoelectric element  32  to generate power without the operation of the cooling fan  26  when the temperature of the heat-generating component  22  is not increased to the level at which the cooling by the cooling fan  26  is necessary, such as the production of a small number of prints, which accounts for a large proportion of the operations performed by the image forming apparatus  1 . Accordingly, an effect of allowing efficient power generation is also expected. 
     A fourth embodiment of this disclosure will now be described. 
     The image forming apparatus  1  according to the fourth embodiment is an embodiment variation of the second embodiment. In the image forming apparatus  1  according to the fourth embodiment, the sheet thickness detector (i.e., the CPU  201 ) that detects, as an example of the control state of the image forming apparatus  1 , the thickness of a sheet to be printed by the image forming apparatus  1 . The input-output control unit  20  predicts the temperature increase of the heat-generating component  22  based on the thickness of the sheet detected by the sheet thickness detector, and controls the operations of the cooling fan  26  and the thermoelectric element  32  in accordance with the predicted temperature increase. Specifically, the input-output control unit  20  operates the cooling fan  26  if the predicted temperature increase equals or exceeds a predetermined threshold value, and causes the thermoelectric element  32  to generate power without operating the cooling fan  26  to cool the first radiator plate  30  through passive cooling if the predicted temperature increase is less than the predetermined threshold value. 
     In the image forming apparatus  1  according to the fourth embodiment, the temperature increase is predictable based on the ON time of the heat-generating component  22  and the value of the current flowing through the heat-generating component  22  during the ON time, which are detected from the thickness of the sheet detected and output by the sheet thickness detector. The present embodiment therefore obviates the need for installing the special temperature sensor  29  to the heat-generating component  22  similarly to the second embodiment, thereby achieving a reduction in cost. 
     A fifth embodiment of this disclosure will now be described. 
     The image forming apparatus  1  according to the fifth embodiment is yet another variation of the second embodiment. In the image forming apparatus  1  according to the fifth embodiment, the print mode recognition device (i.e., the CPU  201 ) recognizes, as an example of the control state of the image forming apparatus  1 , a print mode of the image forming apparatus  1 . The input-output control unit  20  predicts the temperature increase of the heat-generating component  22  based on the print mode recognized by the print mode recognition device, and controls the operations of the cooling fan  26  and the thermoelectric element  32  in accordance with the predicted temperature increase. Specifically, the input-output control unit  20  operates the cooling fan  26  if the predicted temperature increase equals or exceeds a predetermined threshold value, and causes the thermoelectric element  32  to generate power without operating the cooling fan  26  to cool the first radiator plate  30  through passive cooling if the predicted temperature increase is less than the predetermined threshold value. 
     In the image forming apparatus  1  according to the fifth embodiment, the temperature increase is predictable based on the ON time of the heat-generating component  22  and the value of the current flowing through the heat-generating component  22  during the ON time, which are detected from the print mode (e.g., monochrome or color) recognized and output by the print more recognition device. The present embodiment therefore obviates the need for installing the special temperature sensor  29  to the heat-generating component  22  similarly to the second embodiment, thereby achieving a reduction in cost. 
     An image forming apparatus according to an embodiment of this disclosure includes a heat radiation device including a first radiator plate interposed between a heat-generating component and one surface of a thermoelectric element and a second radiator plate attached to the other surface of the thermoelectric element. Further, the image forming apparatus includes a controller that controls operations of a cooling device of the image forming apparatus and the thermoelectric element by operating the cooling device if a temperature increase of the heat-generating component detected by a temperature detector or predicted from a control state of the image forming apparatus assumed to be related to the temperature increase equals or exceeds a predetermined threshold value, and causing the thermoelectric element (i.e., a power generation device) to generate power without operating the cooling device to cool the first heat radiator plate passively if the detected or predicted temperature increase is less than the predetermined threshold value. 
     Even with the structure having the thermoelectric element installed to the heat-generating component, therefore, the image forming apparatus has a function of cooling the heat-generating component and generating power from the heat-generating component, while allowing efficient cooling of the heat-generating component without degrading the heat radiation performance of the heat-generating component or increasing the power consumption for a cooling operation. Consequently, the destruction of the heat-generating component due to degraded heat radiation performance is prevented. 
     The above-described embodiments are illustrative and do not limit this disclosure. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements or features of different illustrative and embodiments herein may be combined with or substituted for each other within the scope of this disclosure and the appended claims. Further, features of components of the embodiments, such as number, position, and shape, are not limited to those of the disclosed embodiments and thus may be set as preferred. It is therefore to be understood that, within the scope of the appended claims, this disclosure may be practiced otherwise than as specifically described herein.