Image forming apparatus having temperature detection member and temperature correction unit

An image forming apparatus is provided. The image forming apparatus includes an apparatus main unit; a detected unit that is placed in the apparatus main unit; a temperature detection member that is provided out of contact with the detected unit in the apparatus main unit for detecting a temperature of the detected unit; a change member for changing a state of an air current in the apparatus main unit; and a temperature correction unit for correcting a value relevant to the temperature detected by the temperature detection member based on change of the state of the air current by the change member.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2008-019567, which was filed on Jan. 30, 2008, the disclosure of which is herein incorporated by reference in its entirety.

TECHNICAL FIELD

Apparatuses consistent with the present invention relate to an image forming apparatuses such as an electro-photographic color printer.

BACKGROUND

Japanese unexamined patent application publication No. JP-A-2007-163884 describes a related art image forming apparatus. The related art image forming apparatus such as an electro-photographic color printer is provided with a fixing unit for fixing toner transferred to a sheet onto the sheet. The fixing unit includes a heating roller and a pressing roller placed in a press state against the heating roller. The sheet with toner transferred thereto is conveyed through the nip between the heating roller and the pressing roller. While the sheet passes between the heating roller and the pressing roller, the toner is fixed onto the sheet by heating and pressing.

To control the fixing temperature, the fixing unit is provided with a temperature sensor for detecting the surface temperature of the heating roller or the pressing roller. For example, a fixing unit in the related art image forming apparatus has a noncontact thermistor placed at a predetermined distance from the surface of a pressing sensor. Output of a heater provided in the pressing roller is controlled so that the temperature detected by the noncontact thermistor becomes a predetermined target fixing temperature.

SUMMARY

However, the related art image forming apparatus has a few disadvantages. For example, the temperature detected by the noncontact thermistor may deviate from the actual temperature of the surface of the pressing roller. If the temperature deviates, the actual temperature of the surface of the pressing roller deviates from the target fixing temperature and a problem of a curl of a sheet caused by overheating, a fixing failure caused by heat shortage, etc., occurs.

Exemplary embodiments of the present invention address the above disadvantages and other disadvantages not described above. However, the present invention is not required to overcome the disadvantages described above, and thus, an exemplary embodiment of the present invention may not overcome any of the problems described above.

Accordingly, it is an aspect of the present invention to provide an image forming apparatus capable of precisely acquiring the actual temperature of a detected unit based on the detected temperature of a noncontact temperature detection member.

According to an exemplary embodiment of the present invention, there is provided an image forming apparatus comprising: an apparatus main unit; a detected unit that is placed in the apparatus main unit; a temperature detection member that is provided out of contact with the detected unit in the apparatus main unit for detecting a temperature of the detected unit; a change member for changing a state of an air current in the apparatus main unit; and a temperature correction unit for correcting a value relevant to the temperature detected by the temperature detection member based on change of the state of the air current by the change member.

1. General Configuration of Printer

FIG. 1is a sectional side view to show a printer as an example of an image forming apparatus of the first exemplary embodiment of the present invention.

A printer1is a tandem color printer. In a main casing2as an example of an apparatus main unit, four process cartridges3are placed in parallel corresponding to colors of black, yellow, magenta, and cyan. Each of the process cartridges3can be placed in and detached from the main casing2in a state in which a top cover4of the top face of the main casing2is opened.

Each of the process cartridges3has a drum cartridge7for holding a photoconductive drum5and a scorotron charger6and a developing cartridge9for holding a developing roller8, the developing cartridge9detachably placed in the drum cartridge7. The surface of the photoconductive drum5is uniformly charged by the scorotron charger6and then is selectively exposed by an LED provided in an LED unit10. Accordingly, an electrostatic latent image based on image data is formed on the surface of the photoconductive drum5. The electrostatic latent image is visualized by toner carried on the developing roller8and a toner image is formed on the surface of the photoconductive drum5.

A sheet P is housed in a sheet feeding cassette11placed on the bottom of the main casing2. The sheets P housed in the sheet feeding cassette11are conveyed one at a time onto a conveying belt12as an example of a belt by various rollers. The conveying belt12is placed facing the four photoconductive drums5from below. The sheet P conveyed onto the conveying belt12passes through the nip between the conveying belt12and each of the photoconductive drums5in sequence as the conveying belt12runs. When the toner image on the surface of the photoconductive drum5faces the sheet P, it is transferred onto the sheet P by a transfer bias applied to a transfer roller13. The transfer rollers13are placed facing the photoconductive drums5in a one-to-one correspondence with each other across the conveying belt12.

The upstream side in the conveying direction of the sheet P by the conveying belt12is assumed to be the front of the printer1, and the left and the right in the printer1are applied when the printer1is viewed from the front.

The sheet P with the toner image transferred thereto is conveyed to a fixing unit14, which then fixes the toner image onto the sheet P by heating and pressing. Specifically, the fixing unit14includes a heating roller15as an example of a heating member of a detected member and a pressing roller16brought into press contact with the heating roller15from below. The heating roller15includes a metal pipe having a surface coated with a fluorocarbon resin and a halogen lamp17(seeFIG. 2) inserted into the metal pipe for heating. The pressing roller16has a metal roller shaft covered with a rubber material. While the sheet P passes through the nip between the heating roller15and the pressing roller16, the toner image is fixed onto the sheet P by heating and pressing.

The sheet P with the toner image fixed thereonto is discharged onto a sheet discharge tray18formed on the top face of the top cover4or is discharged onto a rear cover tray19as an example of a change member of a guide member attached to the back (rear) of the main casing2. The rear cover tray19is provided as it can be opened and closed between a state in which it is inclined to the back of the main casing2and forms an opening20at the back of the main casing2and a state in which it extends along the back of the main casing2and closes the opening20. The inner face of the rear cover tray19forms a part of a sheet discharge path of the sheet P proceeding toward the sheet discharge tray18in a state in which the rear cover tray19is closed. Therefore, the sheet P conveyed from the fixing unit14is discharged onto the sheet discharge tray18in a state in which the rear cover tray19is closed. On the other hand, the sheet P conveyed from the fixing unit14is discharged onto the rear cover tray19in a state in which the rear cover tray19is opened.

The rear cover tray19is formed in a base end part (lower end part of the rear cover tray19in a state in which the rear cover tray19is closed) with a plurality of intake ports21shaped like slits to take outside air into the main casing2.

The printer1is provided with an exhaust air duct22for exhausting hot air from the fixing unit14above the fixing unit14. The exhaust air duct22has an inlet23opened downward in front of the heating roller15. A fan24(seeFIG. 2) is provided in the exhaust air duct22. When the fan24is driven, an atmosphere in the proximity of the fixing unit14is sucked into the exhaust air duct22through the inlet23and is exhausted through the exhaust air duct22to the outside of the main casing2. As the atmosphere is exhausted, the air outside the main casing2flows through the intake ports21into the main casing2. The air flowing into the main casing2flows toward the inlet23of the exhaust air duct22by the action of the fan24. Accordingly, in the main casing2, an air current from the intake ports21through the proximity of the heating roller15to the inlet23is formed as indicated by an open arrow inFIG. 1.

The printer1also includes a manual tray25as an example of a sheet feed tray. The manual tray25is provided as it can be opened and closed between a state in which it is inclined to the front of the main casing2and forms an opening26at the front of the main casing2and a state in which it extends along the front of the main casing2and closes the opening26. If a command to feed a sheet from the manual tray25is given in a state in which the manual tray25is opened and a sheet P is placed on the manual tray25, the sheets P on the manual tray25are conveyed one at a time onto the conveying belt12.

2. Control System of Printer

FIG. 2is a block diagram to show a control system of the printer.

The printer1includes a controller30implemented as a microcomputer containing a CPU, RAM, ROM, etc. The printer1also includes a noncontact temperature sensor27as an example of a temperature detection member for detecting the surface temperature of the heating roller15, a rear cover switch28for detecting opening/closing of the rear cover tray19, and a fixing motor29for driving the heating roller15. The noncontact temperature sensor27is placed out of contact with the heating roller15with a spacing above the heating roller15, as shown inFIG. 1. The rear cover switch28is provided in association with the rear cover tray19. For example, the switch is turned on in a state in which the rear cover tray19is closed; the switch is turned off in a state in which the rear cover tray19is opened. Detection signals of the noncontact temperature sensor27and the rear cover tray19are input to the controller30.

The halogen lamp17, the fan24, and the fixing motor29are connected to the controller30for controlling the components.

The controller30substantially includes a temperature correction unit30A for correcting the temperature detected by the noncontact temperature sensor27(detected temperature) The temperature correction unit30A is a function processing unit implemented as software as the CPU executes a program stored in the ROM.

The noncontact temperature sensor27has a resistance element whose resistance value changes in response to the radiation amount from the heating roller15, and a given voltage is applied to the resistance element from a power supply. Thus, if the radiation amount from the heating roller15changes, the amount of a current flowing through the resistance element changes. The noncontact temperature sensor27outputs the current flowing through the resistance element as a detection signal, for example. The temperature correction unit30A calculates the temperature (detected temperature) from the detection signal output by the noncontact temperature sensor27and corrects the calculated detected temperature (temperature data) as described below. In the first exemplary embodiment, the detected temperature is an example of a value relevant to the temperature detected by the temperature detection member.

3. Temperature Correction

FIG. 3is a graph to describe temperature correction executed by the temperature correction unit30A.

In the state in which the rear cover tray19is closed, an air current from the intake ports21through the proximity of the heating roller15to the inlet23of the exhaust air duct22is formed in the main casing2as previously described with reference toFIG. 1. When the rear cover tray19is opened, the opening20is formed in the rear of the main casing2and thus an air current from the opening20through the proximity of the heating roller15to the inlet23of the exhaust air duct22is formed in the main casing2. At this time, the air current is stronger than the air current formed when the rear cover tray19is closed.

As the strength of the air current passing through the proximity of the heating roller15changes, the strength of the air current passing between the heating roller15and the noncontact temperature sensor27changes accordingly and thus the detected temperature of the noncontact temperature sensor27changes. Specifically, as shown inFIG. 3, when the rear cover tray19is closed, the air current is relatively weak and thus the detected temperature of the noncontact temperature sensor27is relatively close to the actual temperature of the surface of the heating roller15; when the rear cover tray19is opened, the air current is relatively strong and thus the detected temperature of the noncontact temperature sensor27is relatively away from the actual temperature of the surface of the heating roller15.

Then, the temperature correction unit30A corrects the detected temperature of the noncontact temperature sensor27based on change in the state of the air current formed in the main casing2. Specifically, the temperature correction unit30A sets a temperature correction coefficient based on on/off of the rear cover switch28and multiplies the detected temperature of the noncontact temperature sensor27by the setup temperature correction coefficient, thereby correcting the detected temperature of the noncontact temperature sensor27so as to match the actual temperature of the surface of the heating roller15. Here, the temperature correction unit30A may add the temperature correction coefficient to the detected temperature instead of multiplying the detected temperature by the temperature correction coefficient. If the rear cover tray19is closed and the rear cover switch28is on, the deviation of the detected temperature of the noncontact temperature sensor27from the actual temperature of the surface of the heating roller15is relatively small and thus the temperature correction coefficient (correction amount) is set to a relatively small value. On the other hand, if the rear cover tray19is opened and the rear cover switch28is off, the deviation of the detected temperature of the noncontact temperature sensor27from the actual temperature of the surface of the heating roller15is relatively large and thus the temperature correction coefficient (correction amount) is set to a relatively large value.

The controller30controls output of the halogen lamp17so that the post-corrected detected temperature becomes the predetermined target fixing temperature based on the detected temperature of the noncontact temperature sensor27after corrected by the temperature correction unit30A. Accordingly, the temperature of the surface of the heating roller15can be set to the target fixing temperature. Thus, good fixing of the tone image onto the sheet P can be accomplished without introducing a problem of a curl of the sheet P caused by overheating, a fixing failure caused by heat shortage, etc. Consequently, a high-quality image can be formed on the sheet P.

As described above, the noncontact temperature sensor27for detecting the temperature of the heating roller15is placed out of contact with the heating roller15in the main casing2. The main casing2is provided with the rear cover tray19for guiding and receiving the sheet P with the toner image fixed thereto by the heating roller15. The rear cover tray19is provided as the position of the rear cover tray19can be changed between the open position and the closed position. When the rear cover tray19is set to the open position, the opening20is formed in the rear of the main casing2and when the rear cover tray19is set to the closed position, the opening20is closed by the rear cover tray19. Thus, the position of the rear cover tray19is changed between the open position and the closed position, whereby the opening20is opened and closed and accordingly the state of the air current formed in the main casing2is changed.

The temperature detected by the noncontact temperature sensor27is corrected by the temperature correction unit30A based on the position of the rear cover tray19. Thus, the actual temperature of the heating roller15can be precisely acquired based on the detected temperature of the noncontact temperature sensor27regardless of change in the state of the air current accompanying the position change of the rear cover tray19.

5. Second Exemplary Embodiment

A printer1is provided with a fan24for forcibly exhausting air in a main casing2to the outside as shown inFIG. 2. The capability of the fan24is changed by a controller30substantially including a fan capability change unit30B indicated by a dashed line inFIG. 2. For example, the capability of the fan24is set to weak in a sleep state in which the image formation operation of the printer1is not performed; the capability of the fan24is set to strong during the image formation operation. When the capability of the fan24is changed, the exhaust air current amount from the inside of the main casing2to the outside changes and accordingly the state of the air current passing through the proximity of a heating roller15is changed. That is, if the capability of the fan24is enhanced (set to strong), the exhaust air current amount from the inside of the main casing2to the outside increases and the air current passing through the proximity of the heating roller15becomes strong. On the other hand, if the capability of the fan24is lowered (set to weak), the exhaust air current amount from the inside of the main casing2to the outside decreases and the air current passing through the proximity of the heating roller15becomes weak.

As the strength of the air current passing through the proximity of the heating roller15changes, the strength of the air current passing between the heating roller15and a noncontact temperature sensor27changes accordingly and thus the detected temperature of the noncontact temperature sensor27changes.

Then, a temperature correction unit30A may set a temperature correction coefficient based on strong/weak of the capability of the fan24(for example, based on capability control of the fan24by the fan capability change unit30B) and may multiply the detected temperature of the noncontact temperature sensor27by the setup temperature correction coefficient, thereby correcting the detected temperature of the noncontact temperature sensor27so as to match the actual temperature of the surface of the heating roller15. When the capability of the fan24is set to weak, the temperature correction coefficient is set to a relatively small value. On the other hand, when the capability of the fan24is set to strong, the temperature correction coefficient is set to a relatively large value. (This means that in the state in which the capability of the fan24is set to strong, the correction amount of the detected temperature in the temperature correction unit30A becomes large as compared with the state in which the capability of the fan24is set to weak.)

Accordingly, the actual temperature of the heating roller15can be precisely acquired based on the detected temperature of the noncontact temperature sensor27regardless of change in the state of the air current accompanying change of the capability of the fan24.

6. Third Exemplary Embodiment

A main casing2is provided with a manual tray25for feeding a sheet P into the main casing2so that the position of the manual tray25can be changed between an open position and a closed position. When the manual tray25is set to the open position, an opening26is formed in the main casing2and when the manual tray25is set to the closed position, the opening26is closed by the manual tray25. Thus, the position of the manual tray25is changed between the open position and the closed position, whereby the opening26is opened and closed and accordingly the state of the air current formed in the main casing2is changed.

Then, a detection signal of a manual tray switch31to detect open/closed of the manual tray25may be input to a controller30, as indicated by a dashed line inFIG. 2. The manual tray switch31is provided in the proximity of the front of the main casing2in association with of the manual tray25. The manual tray switch31is turned on in a state in which the manual tray25is closed; the manual tray switch31is turned off in a state in which the manual tray25is opened.

A temperature correction unit30A may set a temperature correction coefficient based on on/off of the manual tray switch31and may multiply the detected temperature of a noncontact temperature sensor27by the setup temperature correction coefficient, thereby correcting the detected temperature of the noncontact temperature sensor27so as to match the actual temperature of the surface of a heating roller15. If the manual tray25is closed and the manual tray switch31is on, the temperature correction coefficient is set to a relatively small value. On the other hand, if the manual tray25is opened and the manual tray switch31is off, the temperature correction coefficient is set to a relatively large value.

Accordingly, the actual temperature of the heating roller15can be precisely acquired based on the detected temperature of the noncontact temperature sensor27regardless of change in the state of the air current accompanying opening/closing of the manual tray25.

Sheets P differ in heat capacity according to the thickness. If the thickness of the sheet P is relatively large (if the sheet P is a cardboard), it takes time in fixing a toner image onto the sheet P as compared with the case where the thickness of the sheet P is relatively small (if the sheet P is ordinary paper). Thus, a speed control unit30C (indicated by a dashed line inFIG. 2) substantially included in a controller30may control driving of a fixing motor29to change the rotation speed of a heating roller15in response to the thickness of the sheet P. That is, if the sheet P is a cardboard, the rotation speed of the heating roller15may be relatively decreased; if the sheet P is ordinary paper, the rotation speed of the heating roller15may be relatively increased.

When the rotation speed of the heating roller15is changed, the conveying speed of the sheet P changes in the fixing unit14and accordingly the state of the air current formed in a main casing2(in the proximity of the heating roller15) is changed. That is, when the rotation speed of the heating roller15is increased, the air current passing through the proximity of the heating roller15becomes strong. On the other hand, when the rotation speed of the heating roller15is decreased, the air current passing through the proximity of the heating roller15becomes weak.

As the strength of the air current passing through the proximity of the heating roller15changes, the strength of the air current passing between the heating roller15and a noncontact temperature sensor27changes accordingly and thus the detected temperature of the noncontact temperature sensor27changes.

Then, a temperature correction unit30A may set a temperature correction coefficient based on the rotation speed of the heating roller15(for example, based on drive control of the fixing motor29by the speed control unit30C) and may multiply the detected temperature of the noncontact temperature sensor27by the setup temperature correction coefficient, thereby correcting the detected temperature of the noncontact temperature sensor27so as to match the actual temperature of the surface of the heating roller15. When the rotation speed of the heating roller15is high, the temperature correction coefficient is set to a relatively large value. On the other hand, when the rotation speed of the heating roller15is low, the temperature correction coefficient is set to a relatively small value.

Accordingly, the actual temperature of the heating roller15can be precisely acquired based on the detected temperature of the noncontact temperature sensor27regardless of change in the state of the air current accompanying change of the rotation speed of the heating roller15.

In a printer1, there is a fear of causing a sheet P to bend along the peripheral surface of a heating roller15or a pressing roller16, namely, causing a sheet curl to occur depending on the pressing state of the sheet P, etc., by the heating roller15and the pressing roller16as an example of a pressing member. Thus, the pressing roller16may be provided so as to be able to make a relative move to the heating roller15(able to make position change) as indicated by a dashed line inFIG. 1and the position of the pressing roller16relative to the heating roller15is changed in response to the state of the sheet curl (state in which the toner transfer face of the sheet P is bent like a convex or a concave), thereby making it possible to correct the sheet curl.

When the position of the pressing roller16relative to the heating roller15is changed, the conveying passage of the sheet P is changed in the proximity of the heating roller15and accordingly the state of the air current formed in a main casing2(in the proximity of the heating roller15) is changed.

Then, a detection signal of a pressing roller position sensor32for detecting the position of the pressing roller16may be input to a controller30as indicated by a dashed line inFIG. 2. The pressing roller position sensor32is implemented as a micro switch, for example. When the pressing roller16is at a position indicated by a solid line inFIG. 1, the pressing roller position sensor32is turned on; when the pressing roller16is at a position indicated by a dashed line inFIG. 1, the pressing roller position sensor32is turned off.

A temperature correction unit30A may set a temperature correction coefficient based on the position of the pressing roller16(for example, based on on/off of the micro switch) and may multiply the detected temperature of a noncontact temperature sensor27by the setup temperature correction coefficient, thereby correcting the detected temperature of the noncontact temperature sensor27so as to match the actual temperature of the surface of the heating roller15.

Accordingly, the actual temperature of the heating roller15can be precisely acquired based on the detected temperature of the noncontact temperature sensor27regardless of change in the state of the air current accompanying change of the position of the pressing roller16.

When a monochrome image is formed, a toner image is formed only on a black photoconductive drum5and is not formed on a yellow, magenta, or cyan photoconductive drum5. Thus, it is desirable that the yellow, magenta, and cyan photoconductive drums5should be brought out of contact with a conveying belt12to prevent consumption of the photoconductive drums5as an example of an image formation member. To do this, a contact-noncontact mechanism33for bringing the yellow, magenta, and cyan photoconductive drums5into and out of contact with the conveying belt12may be provided as indicated by a dashed line inFIG. 1in a main casing2. InFIG. 1, to prevent complication of the drawing, only the state in which one (magenta) photoconductive drum5is brought out of contact with the conveying belt12is indicated by a dashed line.

When the position of each photoconductive drum5is changed, the state of the air current formed in the main casing2is changed accordingly.

Then, a detection signal of a drum sensor34for detecting the position of the photoconductive drum5may be input to a controller30as indicated by a dashed line inFIG. 2. A temperature correction unit30A may set a temperature correction coefficient based on the position of each photoconductive drum5(for example, based on the detection result of the drum sensor34) and may multiply the detected temperature of a noncontact temperature sensor27by the setup temperature correction coefficient, thereby correcting the detected temperature of the noncontact temperature sensor27so as to match the actual temperature of the surface of the heating roller15.

Accordingly, the actual temperature of the heating roller15can be precisely acquired based on the detected temperature of the noncontact temperature sensor27regardless of change in the state of the air current accompanying change of the position of each photoconductive drum5.

10. Applying of the Invention to Other Types of Image Forming Apparatus

The invention has been described by taking as an example the case where the noncontact temperature sensor27outputs a current flowing through the resistance element as a detection signal, the temperature correction unit30A calculates the temperature (detected temperature) from the detection signal output by the noncontact temperature sensor27and corrects the calculated detected temperature, thereby calculating the actual temperature of the heating roller15. However, the temperature correction unit30A may correct the detection signal output by the noncontact temperature sensor27and may calculate the actual temperature of the heating roller15based on the post-corrected signal. In this case, the detection signal output by the noncontact temperature sensor27is an example of a value relevant to the temperature detected by the temperature detection member.

The noncontact temperature sensor27may find the temperature value responsive to the current flowing through the resistance element (the resistance value of the resistance element) and may output a data signal representing the temperature value (temperature data). In this case, the temperature correction unit30A corrects the temperature data represented by the data signal output by the noncontact temperature sensor27, thereby calculating the actual temperature of the heating roller15.

In the embodiment described above, the noncontact temperature sensor27outputs the current flowing through the resistance element as a detection signal. However, a given current may be allowed to flow into the resistance element and the noncontact temperature sensor27may output the value of a voltage applied to the resistance element as a detection signal.

That is, when a given current is allowed to flow into the resistance element, if the radiation amount from the heating roller changes, the voltage of the resistance element changes and thus the voltage value can be adopted as a detection signal.

Although the tandem color printer1has been described, the invention can also be applied to a color printer of intermediate transfer type for transferring a toner image for each color from each image carrier to an intermediate transfer belt and then transferring the toner images from the intermediate transfer belt to a sheet in batch.

The invention can also be applied to a monochrome printer.

As described above, there is provided an image forming apparatus including an apparatus main unit; a detected unit being placed in the apparatus main unit; a temperature detection member being provided out of contact with the detected unit in the apparatus main unit for detecting a temperature of the detected unit; a change member for changing the state of an air current in the apparatus main unit (in other words, affecting change in the state of the air current); and a temperature correction unit for correcting a value relevant to the temperature detected by the temperature detection member based on change of the state of the air current by the change member.

For example, if the temperature detection member outputs a signal responsive to the temperature of the detected unit (detected temperature), the temperature correction unit may correct the signal output from the temperature detection member or may correct temperature data generated to represent the temperature from the output signal of the temperature detection member.

Also, according to one of the exemplary embodiments, the detected unit is a heating member for fixing a developer image onto a record sheet, the change member is a guide member being provided in the apparatus main unit so that the position of the member can be changed for guiding the record sheet with the developer image fixed thereonto by the heating member in a direction responsive to the position of the member, and the temperature correction unit corrects the value relevant to the temperature detected by the temperature detection member based on the position of the guide member.

Also, according to one of the exemplary embodiments, the guide member is formed as a part of the apparatus main unit and is provided as the position of the guide member can be changed between an open position for forming an opening in the apparatus main unit and a closed position for closing the opening.

Also, according to one of the exemplary embodiments, the image forming apparatus further includes a fan being provided in the apparatus main unit for forcibly exhausting air in the apparatus main unit to the outside and a fan capability change unit for changing the capability of the fan, wherein the change member is the fan, and wherein the temperature correction unit corrects the value relevant to the temperature detected by the temperature detection member based on the capability of the fan.

Also, according to one of the exemplary embodiments, the change member is a sheet feed tray being provided as the position of the sheet feed tray can be changed between an open position for forming an opening in the apparatus main unit and a closed position for closing the opening for feeding a record sheet into the apparatus main unit when the sheet feed tray is at the open position, and the temperature correction unit corrects the value relevant to the temperature detected by the temperature detection member based on the position of the sheet feed tray.

Also, according to one of the exemplary embodiments, the image forming apparatus further includes a heating roller being provided in the apparatus main unit for fixing a developer image onto a record sheet and a speed control unit for controlling the rotation speed of the heating roller, wherein the detected unit is the heating roller, wherein the change member is the heating roller, and wherein the temperature correction unit corrects the value relevant to the temperature detected by the temperature detection member based on the rotation speed of the heating roller.

Also, according to one of the exemplary embodiments, the image forming apparatus further includes a fixing unit being provided in the apparatus main unit for fixing a developer image onto a record sheet, the fixing unit including a heating member and a pressing member placed facing the heating member and provided as the position of the pressing member relative to the heating member can be changed, wherein the detected unit is the heating member, wherein the change member is the pressing member, and wherein the temperature correction unit corrects the value relevant to the temperature detected by the temperature detection member based on the position of the pressing member.

Also, according to one of the exemplary embodiments, the image forming apparatus further includes a belt being provided in the apparatus main unit for conveying a record sheet and a plurality of image formation members being provided so as to be able to be brought into and out of contact with the belt for forming an image on the record sheet conveyed by the belt, wherein the change member is the image formation member, and wherein the temperature correction unit corrects the value relevant to the temperature detected by the temperature detection member based on the position of each of the image formation members.

Also, according to one of the exemplary embodiments, an intake port for taking outside air into the apparatus main unit is formed in the apparatus main unit, and the image forming apparatus further includes an exhaust air dust having an inlet in the apparatus main unit for allowing air accepted through the inlet to circulate, wherein the inlet is placed at a position for allowing an air current to be formed from the intake port through the detected unit to the inlet.

According to one of the exemplary embodiments, the temperature detection member for detecting the temperature of the detected unit is provided out of contact with the detected unit in the apparatus main unit. The image forming apparatus is also provided with the change member for changing the state of an air current in the apparatus main unit. The value relevant to the temperature detected by the temperature detection member is corrected based on change of the state of the air current by the change member. Thus, the actual temperature of the detected unit can be precisely acquired based on the detected temperature of the noncontact temperature detection member regardless of change of the state of the air current by the change member.

According to one of the exemplary embodiments, the guide member for guiding the record sheet with the developer image fixed thereonto by the heating member is provided in the apparatus main unit so that the position of the guide member can be changed. When the position of the guide member is changed, the guide direction of the record sheet by the guide member changes and accordingly the state of the air current formed in the apparatus main unit (in the proximity of the heating member) is changed. The temperature correction unit corrects the value relevant to the temperature detected by the temperature detection member based on the position of the guide member. Thus, the actual temperature of the heating member of the detected unit can be precisely acquired based on the detected temperature of the noncontact temperature detection member regardless of change in the state of the air current accompanying the position change of the guide member.

According to one of the exemplary embodiments, the guide member is provided as the position of the guide member can be changed between the open position and the closed position. If the guide member is placed at the open position, an opening is formed in the apparatus main unit; if the guide member is placed at the closed position, the opening is closed by the guide member. Thus, the position of the guide member is changed between the open position and the closed position, whereby the opening is formed and closed and accordingly the state of the air current formed in the apparatus main unit is changed.

According to one of the exemplary embodiments, the fan for forcibly exhausting air in the apparatus main unit to the outside is provided in the apparatus main unit. The fan capability change unit changes the capability of the fan. When the capability of the fan is changed, the exhaust air current amount from the inside of the apparatus main unit to the outside changes and accordingly the state of the air current formed in the apparatus main unit is changed. The temperature correction unit corrects the value relevant to the temperature detected by the temperature detection member based on the capability of the fan. Thus, the actual temperature of the detected unit can be precisely acquired based on the detected temperature of the noncontact temperature detection member regardless of change in the state of the air current accompanying change of the capability of the fan.

According to one of the exemplary embodiments, the sheet feed tray for feeding a record sheet into the apparatus main unit is provided as the position of the sheet feed tray can be changed between the open position and the closed position. If the sheet feed tray is placed at the open position, an opening is formed in the apparatus main unit; if the sheet feed tray is placed at the closed position, the opening is closed by the sheet feed tray. Thus, the position of the sheet feed tray is changed between the open position and the closed position, whereby the opening is formed and closed and accordingly the state of the air current formed in the apparatus main unit is changed. The temperature correction unit corrects the value relevant to the temperature detected by the temperature detection member based on the position of the sheet feed tray. Thus, the actual temperature of the detected unit can be precisely acquired based on the detected temperature of the noncontact temperature detection member regardless of change in the state of the air current accompanying the position change of the sheet feed tray.

According to one of the exemplary embodiments, the heating roller for fixing a developer image onto a record sheet is provided in the apparatus main unit. The speed control unit controls (changes) the rotation speed of the heating roller in response to the thickness of the record sheet, for example. When the rotation speed of the heating roller is changed, the conveying speed of the record sheet changes and accordingly the state of the air current formed in the apparatus main unit (in the proximity of the heating roller) is changed. The temperature correction unit corrects the value relevant to the temperature detected by the temperature detection member based on the rotation speed of the heating roller. Thus, the actual temperature of the heating roller of the detected unit can be precisely acquired based on the detected temperature of the noncontact temperature detection member regardless of change in the state of the air current accompanying change of the rotation speed of the heating roller.

According to one of the exemplary embodiments, the fixing unit for fixing a developer image onto a record sheet is provided in the apparatus main unit. The fixing unit includes the heating member and the pressing member. The pressing member is placed facing the heating member and is provided as the position of the pressing member relative to the heating member can be changed. When the position of the pressing member relative to the heating member is changed, the conveying passage of the record sheet is changed in the proximity of the heating member and accordingly the state of the air current formed in the apparatus main unit (in the proximity of the heating member) is changed. The temperature correction unit corrects the value relevant to the temperature detected by the temperature detection member based on the position of the pressing member relative to the heating member. Thus, the actual temperature of the heating member of the detected unit can be precisely acquired based on the detected temperature of the noncontact temperature detection member regardless of change in the state of the air current accompanying change of the position of the pressing member.

According to one of the exemplary embodiments, the belt for conveying a record sheet and a plurality of image formation members for forming an image on the record sheet conveyed by the belt are provided in the apparatus main unit. The image formation members are provided so as to be able to be brought into and out of contact with the belt. For example, when a color image is formed on a record sheet, all image formation members are placed at positions where they come in contact with the belt. On the other hand, when a monochrome image is formed on a record sheet, to suppress consumption of the image formation members, preferably other image formation members than the image formation member for forming a black image are brought out of contact with the belt. When the position of each of the image formation members is changed, the state of the air current formed in the apparatus main unit is changed accordingly. The temperature correction unit corrects the value relevant to the temperature detected by the temperature detection member based on the position of each of the image formation members. Thus, the actual temperature of the detected unit can be precisely acquired based on the detected temperature of the noncontact temperature detection member regardless of change in the state of the air current accompanying change of the position of each of the image formation members.

According to one of the exemplary embodiments, the intake port for taking outside air into the apparatus main unit is formed in the apparatus main unit. The inlet of the exhaust air dust is placed in the apparatus main unit. An air current from the intake port through the detected unit to the inlet is formed in the apparatus main unit, and the air reaching the inlet circulates through the exhaust air dust. Since the air current passes through the detected unit, if the change member changes the state of the air current, the detected temperature of the temperature detection member fluctuates. The temperature correction unit corrects the value relevant to the temperature detected by the temperature detection member based on the position of each of the image formation members. Thus, the actual temperature of the detected unit can be precisely acquired based on the detected temperature of the noncontact temperature detection member regardless of change in the state of the air current accompanying change of the position of each of the image formation members.

According to one of the exemplary embodiments, an air current sensor configured to detect a state of an air current in the main casing2is further provided, and the controller30corrects the detected temperature of the noncontact temperature sensor27based on a detection of the air current sensor.

Further, “correcting the detected temperature of the noncontact temperature sensor” also includes a meaning of correcting a control signal for the heater, the control signal being based on the detected temperature of the noncontact temperature sensor.