Image forming apparatus and control method

Abstract

This prevents damage to the temperature detection sensor due to ion migration and enables accurate detection of the temperature of the fixing section. [Solution] The image forming apparatus 1 includes heaters 33 and 34 for heating the fixing unit 30, a temperature detection sensor 36 for detecting the temperature of the fixing unit 30, and a control unit 35 that controls the heaters 33 and 34 based on the temperature detected by the temperature detection sensor 36, and also controls the power supply to the temperature detection sensor 36. The control unit 35 cuts off the power supply to the temperature detection sensor 36 when transitioning to a power-saving mode that involves stopping the heaters 33 and 34.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and a control method.

Background Art

[0002] An image forming apparatus such as an MFP (Multifunction Peripheral) includes a fixing unit that fixes an image on a sheet. The fixing unit includes a heater, and the image is fixed on the sheet by performing heat treatment and pressure treatment on the sheet on which the image is formed. In this type of image forming apparatus, when switched to the non-fixing control state, a technique has been proposed to cut off the power supply to other sensors used during image formation execution except for the fixing control sensor and the heating temperature sensor (for example, Patent Document 1).

[0003] However, in this conventional technology, the power supply to the fixing control sensor and the heating temperature sensor is continued in the non-fixing control state. That is, since it is in the non-fixing state, although the heater of the fixing unit is stopped, the power supply to the fixing control sensor and the heating temperature sensor is continued.

[0004] When the heater of the fixing unit stops, the temperature of the fixing unit gradually decreases. Along with this, water droplets due to condensation may occur around the fixing unit. And the water droplets may adhere to the temperature detection sensor. When water droplets adhere to the temperature detection sensor in the energized state, ion migration occurs, and there is a possibility that the sensor wiring may be short-circuited or disconnected. If the sensor wiring is short-circuited or disconnected, the temperature detection sensor cannot accurately detect the temperature of the fixing unit. Therefore, the image forming apparatus cannot normally perform temperature control of the fixing unit.

[0005] Problems caused by ion migration can also occur when the power is turned on. For example, when switching from power-saving mode back to normal power supply, water droplets may adhere to the temperature sensor. If power is supplied to the heater and the temperature sensor simultaneously in this state, ion migration may occur, potentially causing a short circuit or disconnection of the sensor wiring. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-163039 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] This invention was made to solve the above-mentioned conventional problems. Specifically, the purpose of this invention is to provide an image forming apparatus and control method that prevents damage to the temperature detection sensor due to ion migration and enables accurate detection of the temperature of the fixing section. [Means for solving the problem]

[0008] To achieve the above objective, the invention according to claim 1 is an image forming apparatus comprising: a heater for heating a fixing section; a temperature detection sensor for detecting the temperature of the fixing section; and a control unit that controls the heater based on the temperature detected by the temperature detection sensor and controls the supply of power to the temperature detection sensor, wherein the control unit cuts off the supply of power to the temperature detection sensor when transitioning to a power-saving mode that involves stopping the heater.

[0009] The invention according to claim 2 is characterized in that, in the image forming apparatus of claim 1, the control unit determines whether or not there are water droplets in the temperature detection sensor when the heater is restarted upon returning from the power saving mode, and if it determines that there are water droplets, it cuts off the power supply to the temperature detection sensor.

[0010] The invention according to claim 3 is an image forming apparatus according to claim 2, characterized in that the control unit restarts power to the temperature detection sensor when it determines that there are no water droplets when the heater is restarted.

[0011] The invention according to claim 4 is an image forming apparatus according to claim 2, further comprising a temperature measuring unit that measures the temperature of the fixing unit at a position different from the temperature detection sensor, wherein the control unit, when it determines that there are water droplets when the heater is restarted, controls the heater based on the temperature measured by the temperature measuring unit.

[0012] The invention according to claim 5 is characterized in that, in the image forming apparatus of claim 4, a coating material is applied to the detection unit of the temperature measuring unit.

[0013] The invention according to claim 6 is characterized in that, in the image forming apparatus of claim 4, the control unit, when it determines that there are no water droplets after returning from the power saving mode, resumes power supply to the temperature detection sensor and switches from control based on the temperature measured by the temperature measuring unit to control based on the temperature detected by the temperature detection sensor.

[0014] The invention according to claim 7 is an image forming apparatus according to any of claims 2 to 6, further comprising a humidity sensor for detecting humidity, wherein the control unit determines the presence or absence of water droplets based on the humidity detected by the humidity sensor.

[0015] The invention according to claim 8 is an image forming apparatus according to any of claims 2 to 6, wherein the control unit determines the presence or absence of water droplets in the temperature detection sensor based on the elapsed time since the heater was stopped.

[0016] The invention according to claim 9 is an image forming apparatus according to claim 1, characterized in that the control unit resumes power supply to the temperature detection sensor after a predetermined time has elapsed since the heater was restarted following the return from the power saving mode.

[0017] The invention according to claim 10 is a control method for an image forming apparatus comprising a heater for heating a fixing section and a temperature detection sensor for detecting the temperature of the fixing section, characterized in that it comprises a heater control step for controlling the heater based on the temperature detected by the temperature detection sensor, and a power supply control step for cutting off the power supply to the temperature detection sensor when transitioning to a power-saving mode that involves stopping the heater.

[0018] The invention according to claim 11 is a control method according to claim 10, further comprising a determination step of determining the presence or absence of water droplets in the temperature detection sensor when the heater is restarted upon recovery from the power saving mode, wherein the power supply control step is configured to cut off power to the temperature detection sensor if it is determined in the determination step that water droplets are present.

[0019] The invention according to claim 12 is a control method according to claim 11, wherein the energization control step is characterized in that, if it is determined in the determination step that there are no water droplets, the energization to the temperature detection sensor is resumed.

[0020] The invention according to claim 13 is a control method according to claim 11, wherein the image forming apparatus further comprises a temperature measuring unit that measures the temperature of the fixing unit at a position different from the temperature detection sensor, and the heater control step is characterized in that, if it is determined in the determination step that there are water droplets, the heater is controlled based on the temperature measured by the temperature measuring unit.

[0021] The invention according to claim 14 is the control method according to claim 13, wherein in the energization control step, when it is determined in the determination step that there is no water droplet after the return from the power saving mode, the energization to the temperature detection sensor is restarted, and in the heater control step, the control based on the temperature measured by the temperature measurement unit is switched to the control based on the temperature detected by the temperature detection sensor.

[0022] The invention according to claim 15 is the control method according to any one of claims 11 to 14, wherein the image forming apparatus further includes a humidity sensor for detecting humidity, and in the determination step, the presence or absence of water droplets is determined based on the humidity detected by the humidity sensor.

[0023] The invention according to claim 16 is the control method according to any one of claims 11 to 14, wherein in the determination step, the presence or absence of water droplets in the temperature detection sensor is determined based on the elapsed time since the heater was stopped.

[0024] The invention according to claim 17 is the control method according to claim 10, wherein in the energization control step, the energization to the temperature detection sensor is restarted after a predetermined time has elapsed since the restart of the driving of the heater accompanying the return from the power saving mode.

Advantages of the Invention

[0025] According to the present invention, the energization to the temperature detection sensor is cut off when shifting to the power saving mode accompanied by the stop of the heater. Therefore, in the power saving mode in which the heater is stopped, the progress of ion migration in the temperature detection sensor can be prevented, and the breakage of the temperature detection sensor can be prevented. As a result, the temperature detection sensor can accurately detect the temperature of the fixing unit.

Brief Description of the Drawings

[0026] [Figure 1] It is a diagram showing a configuration example of an image forming apparatus. [Figure 2] This diagram shows the internal configuration of the fixing unit. [Figure 3] This figure shows an example of a control circuit that controls the power supply to a temperature detection sensor. [Figure 4] This flowchart shows an example of the processing procedure performed by the control unit. [Figure 5] This flowchart shows an example of a processing procedure for determining the presence of water droplets based on the elapsed time since switching to power-saving mode. [Figure 6] This flowchart shows an example of a processing procedure that waits for a predetermined time to elapse when resuming from power-saving mode. [Modes for carrying out the invention]

[0027] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. In the embodiments described below, elements common to all are denoted by the same reference numerals, and redundant explanations of these elements will be omitted.

[0028] Figure 1 is a conceptual diagram showing an image forming apparatus 1, which is one embodiment of the present invention. This image forming apparatus 1 is configured as an MFP and has multiple functions such as scanning, printing, and copying.

[0029] The image forming apparatus 1 has a scanner unit 2 at the top of the apparatus body 1a and a printer unit 4 at the bottom of the apparatus body 1a. The scanner unit 2 operates when a job related to scanning or copying is executed, and optically reads the image of a document set by the user to generate image data. The printer unit 4 operates when a job related to printing or copying is executed, and forms and outputs an image on a sheet such as printing paper. The image forming apparatus 1 also has an operation panel 3 on the front side of the apparatus body 1a that can be operated by the user. The operation panel 3 is a user interface that displays a screen that can be operated by the user and accepts user input. For example, the operation panel 3 includes a display unit such as a color liquid crystal display and an operation unit such as touchscreen keys.

[0030] Figure 1 shows the internal structure of the printer unit 4. The printer unit 4 is equipped with a main control unit 7 that comprehensively controls the operation of the image forming apparatus 1. The main control unit 7 comprehensively controls the execution of jobs in the image forming apparatus 1. For example, in the case of a print job, the main control unit 7 controls the operation of the printer unit 4 to form an image on a sheet and output it. The main control unit 7 also controls the power state of the image forming apparatus 1. For example, when the main power switch is switched from off to on, the main control unit 7 starts the image forming apparatus 1 in normal power supply mode. Normal power supply mode is a state in which power is supplied to each part of the image forming apparatus 1. Furthermore, when the time during which the image forming apparatus 1 is not used in normal power supply mode reaches a predetermined time, the main control unit 7 switches the power mode from normal power supply mode to power saving mode. Power saving mode is a power mode that reduces power consumption by supplying power to only a part of the image forming apparatus 1 and cutting off the power supply to other parts. When the main control unit 7 is in power-saving mode and receives a job to be executed by the image forming apparatus 1, it returns from power-saving mode to normal power supply mode and starts a warm-up operation to execute the job.

[0031] The printer unit 4 also includes a paper feed and transport unit 10 and an image forming unit 20. When the received job is a print job, the main control unit 7 operates the paper feed and transport unit 10 and the image forming unit 20 to form an image on the sheet and output it.

[0032] The paper feed and transport unit 10 feeds sheets 9 from one of the multiple paper trays 10a, 10b, and 10c, and transports the sheets 9 along a transport path 13 formed inside the printer unit 4. Each paper tray 10a, 10b, and 10c is provided with a pickup roller 11 and a paper feed roller 12. The paper feed and transport unit 10 drives the pickup roller 11 and paper feed roller 12 provided on one of the paper trays specified by the user, and feeds the sheets 9 toward the transport path 13. The paper feed and transport unit 10 transports the sheets 9 that have been sent toward the transport path 13 along the direction of arrow F1.

[0033] The transport path 13 is equipped with a sheet detection unit 14, a timing roller 15, a secondary transfer roller 16, a fixing unit 17, and an discharge roller 18.

[0034] The sheet detection unit 14 is installed at a predetermined position in the transport path 13 and detects the sheet 9 as it passes through that predetermined position. For example, the sheet detection unit 14 has the function of a media sensor and can detect the type of sheet 9, such as its thickness and basis weight. The detection result from the sheet detection unit 14 is output to the main control unit 7. The main control unit 7 controls the fixing temperature in the fixing unit 17, etc., based on the type of sheet 9 detected by the sheet detection unit 14.

[0035] The timing roller 15 is composed of a pair of rollers. The timing roller 15 is a roller that adjusts the timing for feeding the sheet 9 to the secondary transfer position by the secondary transfer roller 16. When the leading edge of the sheet 9 fed from the paper trays 10a, 10b, and 10c reaches the position of the timing roller 15, the paper feed transport unit 10 temporarily stops transporting the sheet 9. Then, the paper feed transport unit 10 drives the timing roller 15 in accordance with the timing when the image that has been primary transferred to the intermediate transfer belt 22 in the image forming unit 20 is transported to the secondary transfer position, and transports the sheet 9 toward the secondary transfer roller 16.

[0036] The sheet 9, fed out by the timing roller 15, has its image transferred to it as it passes the secondary transfer position by the secondary transfer roller 16. The sheet 9 with the image transferred to it is then transported to the fixing unit 17.

[0037] The image forming unit 20 includes image forming units 21Y, 21M, 21C, and 21K corresponding to yellow (Y), magenta (M), cyan (C), and black (K), respectively, and an intermediate transfer belt 22.

[0038] The image forming unit 21Y is a unit that forms an image of a color corresponding to Y. The image forming unit 21Y comprises an image carrier 25 composed of a photosensitive drum and the like, a charger 26, an exposure unit 27, and a developer unit 28. The image carrier 25 has a photosensitive layer on the surface of a cylindrical body and rotates in a predetermined direction (clockwise). The charger 26, exposure unit 27, and developer unit 28 are arranged around the image carrier 25. The charger 26 charges the surface of the image carrier 25 to a predetermined charge. The exposure unit 27 exposes the surface of the charged image carrier 25 based on image data included in the print job, thereby forming an electrostatic latent image on the surface of the image carrier 25. The developer unit 28 supplies toner to the surface of the image carrier 25 and develops the electrostatic latent image with toner. As a result, an image (toner image) corresponding to the image data is formed on the surface of the image carrier 25.

[0039] The other image forming units 21M, 21C, and 21K have the same configuration as image forming unit 21Y, differing only in the color of the toner supplied to the image carrier 25. In other words, multiple image forming units 21Y, 21M, 21C, and 21K, each with the same configuration, are arranged horizontally at predetermined intervals.

[0040] The intermediate transfer belt 22 is an endless belt positioned above the image forming units 21Y, 21M, 21C, and 21K. The intermediate transfer belt 22 is stretched over a drive roller 23 positioned opposite the secondary transfer roller 16 and a driven roller 24 positioned at a predetermined distance from the drive roller 23. As the drive roller 23 is rotated counterclockwise, the intermediate transfer belt 22 moves in a circular motion in the direction indicated by arrow F2. The intermediate transfer belt 22 contacts the secondary transfer roller 16 at the position of the drive roller 23.

[0041] Inside the intermediate transfer belt 22, primary transfer rollers 29 are provided at positions facing each image forming unit 21Y, 21M, 21C, and 21K. The primary transfer rollers 29 are operated by applying a predetermined voltage while the intermediate transfer belt 22 is pressed against the image carriers 25 of each image forming unit 21Y, 21M, 21C, and 21K, thereby primary transferring the image (toner image) formed on the image carriers 25 to the intermediate transfer belt 22. Each image forming unit 21Y, 21M, 21C, and 21K performs primary transfer, sequentially superimposing the Y, M, C, and K images onto the intermediate transfer belt 22. As a result, a color image is formed on the surface of the intermediate transfer belt 22. The image transferred to the intermediate transfer belt 22 is then secondary transferred to the sheet 9 at the position of the secondary transfer roller 16.

[0042] The fixing unit 17 applies heat and pressure to the sheet 9 on which the image has been formed, thereby fixing the image to the sheet 9. The fixing unit 17 has, for example, a heating roller and a pressure roller, and the sheet 9 is heated and pressured at the nip between the heating roller and the pressure roller. The surface temperature of the heating roller is heated and controlled to a temperature suitable for the type of sheet 9. The sheet 9 on which the image has been fixed in the fixing unit 17 is discharged via the discharge roller 18 to the output tray 6 located at the top of the printer unit 4.

[0043] Figure 2 shows the internal configuration of the fixing unit 17. The fixing unit 17 comprises a fixing section 30, a control section 35, a temperature detection sensor 36, a temperature measurement section 37, and a humidity sensor 38. The fixing section 30 applies heat treatment and pressure treatment to the sheet 9. The fixing section 30 has a heating roller 31 and a pressure roller 32. The heating roller 31 and the pressure roller 32 extend in a direction perpendicular to the conveying direction of the sheet 9. The fixing section 30 presses the pressure roller 32 against the heating roller 31 with a predetermined pressing force to form a nip section. This nip section extends in the longitudinal direction of the heating roller 31 and the pressure roller 32. The sheet 9 on which the image is formed passes through the longitudinal center of the nip section, and is subjected to heat treatment and pressure treatment as it passes through the nip section.

[0044] Furthermore, the heating roller 31 may also heat the fixing belt stretched across its surface. The fixing belt is stretched between a mounting member located opposite the pressure roller 32 and the heating roller 31, and moves in a circulating manner. In this case, the pressure roller 32 presses against the surface of the fixing belt at the position of the mounting member, forming a nip portion.

[0045] Inside the heating roller 31 are heaters 33 and 34, which are composed of halogen lamp heaters or the like. For example, heater 33 is provided along the entire length of the heating roller 31, heating the entire heating roller 31 from the inside. In contrast, heater 34 is provided in the center of the heating roller 31 in the length direction, heating only the central part of the heating roller 31 from the inside.

[0046] The temperature detection sensor 36 is positioned opposite the heating roller 31 and detects the surface temperature of the heating roller 31. For example, the temperature detection sensor 36 has a detection unit on which an infrared sensor is mounted, and this detection unit is exposed facing the surface of the heating roller 31. Therefore, the temperature detection sensor 36 can detect the surface temperature of the heating roller 31 with high accuracy. In addition, the temperature detection sensor 36 is positioned below the heating roller 31 and is installed so as not to be affected by the heat circulating above the heating roller 31.

[0047] Furthermore, the detection part of the temperature detection sensor 36 is not provided with a protective film or the like to prevent water droplets from adhering to it. Therefore, when the heaters 33 and 34 stop and the temperature of the fixing unit 30 decreases, water droplets may adhere to the detection part of the temperature detection sensor 36. If the temperature detection sensor 36 is energized under conditions where water droplets may adhere, ion migration may occur, potentially causing a short circuit or disconnection of the sensor wiring.

[0048] The temperature measuring unit 37 measures the surface temperature of the heating roller 31 in order to detect temperature unevenness along the longitudinal direction of the heating roller 31. For example, the temperature measuring unit 37 is located above the heating roller 31 and comprises a central temperature measuring unit 37a and an end temperature measuring unit 37b. The central temperature measuring unit 37a is positioned opposite the longitudinal center of the heating roller 31 and measures the temperature of the central part of the heating roller 31. The end temperature measuring unit 37b is positioned opposite the longitudinal end of the heating roller 31 and measures the temperature of the end of the heating roller 31. The detection units of the central temperature measuring unit 37a and the end temperature measuring unit 37b are equipped with non-contact thermistors and measure the surface temperature of the heating roller 31 non-contact. In addition, a coating material (protective film) such as polyimide with high insulating properties is applied to the detection unit composed of a non-contact thermistor. Therefore, the central temperature measuring unit 37a and the end temperature measuring unit 37b are configured so that water droplets do not adhere to the detection unit, and ion migration due to water droplets does not occur.

[0049] The humidity sensor 38 is located, for example, near the temperature detection sensor 36 and detects the humidity inside the fixing unit 17. The humidity sensor 38 may also be a sensor that detects the amount of moisture (water vapor) inside the fixing unit 17.

[0050] The control unit 35 controls the temperature of the fixing unit 30 in the normal energization mode. Specifically, the control unit 35 controls the surface temperature of the heating roller 31 to a predetermined target temperature by driving the heaters 33 and 34 to light up based on the surface temperature of the heating roller 31 detected by the temperature detection sensor 36. This control is performed as a heater control step by the control unit 35.

[0051] When no print job is running in normal power-on mode, the target temperature of the heating roller 31 is set to a standby temperature lower than the temperature during print job execution. Therefore, when no print job is running in normal power-on mode, the control unit 35 drives the heaters 33 and 34 so that the temperature detected by the temperature detection sensor 36 becomes the standby temperature.

[0052] In contrast, when a print job is executed in normal power-on mode, the target temperature of the heating roller 31 is set to the fixing temperature corresponding to the type of sheet 9. This fixing temperature is higher than the standby temperature mentioned above. When a print job is executed, the control unit 35 obtains the fixing temperature corresponding to the type of sheet 9 from the main control unit 7. The control unit 35 then drives and controls the heaters 33 and 34 so that the temperature detected by the temperature detection sensor 36 becomes the fixing temperature corresponding to the type of sheet 9.

[0053] Furthermore, when a print job is executed, the control unit 35 acquires the central temperature and edge temperature of the heating roller 31 measured by the temperature measuring unit 37, and detects temperature unevenness in the longitudinal direction of the heating roller 31. As described above, the sheet 9 on which the image is formed passes through the center of the nip portion of the fixing unit 30. Therefore, heat is easily absorbed from the central part of the heating roller 31 by the sheet 9, while heat is not easily absorbed from the edges by the sheet 9. Consequently, when a print job is executed, the temperature at the edges of the heating roller 31 tends to be higher than that at the center. The control unit 35 detects such temperature unevenness. For example, if it detects that the temperature at the edges of the heating roller 31 has become higher than that at the center, the control unit 35 stops the heater 33 that heats the entire heating roller 31 and drives the heater 34 that heats only the central part of the heating roller 31 to light up. This eliminates temperature unevenness in the longitudinal direction of the heating roller 31.

[0054] Furthermore, when the control unit 35 switches from the normal power supply mode to the power-saving mode, it stops the heaters 33 and 34. In other words, the control unit 35 reduces the power consumption of the fixing unit 17 by stopping the operation of the heaters 33 and 34 when switching to the power-saving mode. Therefore, when the image forming apparatus 1 switches to the power-saving mode, the temperature of the fixing unit 30 gradually decreases.

[0055] The control unit 35 is connected to the power supply circuit 8 of the image forming apparatus 1 and controls the power supply to the temperature detection sensor 36. Figure 3 shows an example of a control circuit that controls the power supply to the temperature detection sensor 36. The control unit 35 comprises a CPU 40, a regulator 41, and a resistor 42. The CPU 40 controls the temperature of the heating roller 31 described above by executing a predetermined program, and also controls the power supply to the temperature detection sensor 36 by driving the regulator 41. The CPU 40 is connected to the regulator 41 via a signal line 43. The signal line 43 is pulled up to a predetermined voltage via the resistor 42. The regulator 41 is, for example, a low-dropout regulator, which steps down the voltage supplied from the power supply circuit 8 to generate a stable output voltage. The regulator 41 supplies its output voltage to the temperature detection sensor 36, operating the temperature detection sensor 36.

[0056] When an enable signal is input from the CPU 40 via signal line 43, the regulator 41 performs the operation described above, generating an output voltage and supplying it to the temperature detection sensor 36. Conversely, when a disable signal is input from the CPU 40 via signal line 43, the regulator 41 stops its operation and does not output an output voltage. Therefore, the CPU 40 can switch the power supply state to the temperature detection sensor 36 by switching the signal output to the regulator 41 between the enable signal and the disable signal. The power supply control of the temperature detection sensor 36 by the control unit 35 is performed as a power supply control step.

[0057] When the main power switch of the image forming apparatus 1 is switched from off to on and the image forming apparatus 1 starts up in normal power supply mode, the control unit 35 drives the heaters 33 and 34 and performs a warm-up operation of the fixing unit 30 so that the surface temperature of the heating roller 31 reaches the standby temperature. At this time, the control unit 35 starts supplying power to the temperature detection sensor 36 and operates the temperature detection sensor 36. Therefore, when performing the warm-up operation, the control unit 35 can drive and control the heaters 33 and 34 based on the temperature detected by the temperature detection sensor 36.

[0058] However, if the temperature detection sensor 36 is left powered on while there is a possibility that water droplets are adhering to its detection part, ion migration may progress, potentially damaging the sensor wiring. Therefore, the control unit 35 prevents the temperature detection sensor 36 from remaining powered on when there is a possibility that water droplets are adhering to it. Specifically, in such a situation, the control unit 35 outputs a disable signal to the regulator 41 to cut off power to the temperature detection sensor 36.

[0059] Furthermore, when the control unit 35 transitions from normal power supply mode to power-saving mode, it cuts off the power supply to the temperature detection sensor 36. In other words, the control unit 35 cuts off the power supply to the temperature detection sensor 36 when transitioning to power-saving mode, which involves stopping the heaters 33 and 34. In power-saving mode, the heaters 33 and 34 are stopped, so the temperature of the fixing unit 30 gradually decreases. At this time, condensation may occur inside the fixing unit 17, and water droplets may adhere to the detection part of the temperature detection sensor 36. If power is continued to be supplied to the temperature detection sensor 36 in such a state, ion migration may occur, potentially damaging the sensor wiring. To prevent this, the control unit 35 cuts off the power supply to the temperature detection sensor 36.

[0060] Figure 4 is a flowchart showing an example of a processing procedure by the control unit 35, and is a flowchart of the processing procedure for controlling the power supply to the temperature detection sensor 36. This processing is mainly performed by the CPU 40 of the control unit 35 and starts when the main power switch of the image forming apparatus 1 is switched from off to on.

[0061] When power is turned on, the control unit 35 performs a startup process for the CPU 40 (step S10). Once the CPU 40 starts up, the control unit 35 starts powering the temperature detection sensor 36 in conjunction with starting to drive the heaters 33 and 34 to light up (step S11). As a result, the control unit 35 starts driving and controlling the heaters 33 and 34 based on the surface temperature of the heating roller 31 detected by the temperature detection sensor 36.

[0062] When the main power switch is turned on, there is a possibility that water droplets may be attached to the temperature detection sensor 36. Therefore, the control unit 35 obtains the humidity inside the fixing unit 17 detected by the humidity sensor 38 (step S12). Based on that humidity, the control unit 35 makes a determination as to whether or not there may be water droplets attached to the temperature detection sensor 36 (step S13). For example, if the humidity obtained from the humidity sensor 38 is above a predetermined value, the control unit 35 determines that there may be water droplets attached to the temperature detection sensor 36. On the other hand, if the humidity obtained from the humidity sensor 38 is below a predetermined value, the control unit 35 determines that there is no possibility of water droplets being attached to the temperature detection sensor 36.

[0063] If there is a possibility that water droplets are attached to the temperature detection sensor 36 (YES in step S14), the control unit 35 cuts off the power supply to the temperature detection sensor 36 (step S15). At this time, the control unit 35 does not stop the operation of the heaters 33 and 34. Therefore, the surface temperature of the heating roller 31 gradually rises due to the operation of the heaters 33 and 34.

[0064] The control unit 35 cuts off power to the temperature detection sensor 36 and then acquires humidity again from the humidity sensor 38 (step S16). Based on this humidity, the control unit 35 makes a water droplet determination again (step S17) and determines whether or not there is a possibility of water droplets adhering to the temperature detection sensor 36 (step S18). If there is a possibility of water droplets adhering (YES in step S18), the control unit 35 returns to step S16. The control unit 35 then repeatedly executes the processes from steps S16 to S18. At this time, since the heaters 33 and 34 are still running, the temperature inside the fixing unit 17 gradually rises. Consequently, the humidity inside the fixing unit 17 gradually decreases. Therefore, the control unit 35 waits while repeating the processes from steps S16 to S18 until it determines that there is no possibility of water droplets adhering.

[0065] When the control unit 35 is performing the water droplet detection process PA, which repeats steps S16 to S18, it cannot control the heaters 33 and 34 using the temperature detection sensor 36. Therefore, when the water droplet detection process PA is being performed, the control unit 35 controls the heaters 33 and 34 based on the temperature measured by the temperature measuring unit 37. This prevents the surface temperature of the heating roller 31 from becoming excessively hot.

[0066] If the water droplet detection process PA determines that no water droplets are attached to the temperature detection sensor 36 (NO in step S18), the control unit 35 resumes power supply to the temperature detection sensor 36 (step S19). Since no water droplets are attached to the temperature detection sensor 36, ion migration will not occur even if power supply to the temperature detection sensor 36 is resumed. Therefore, the control unit 35 can prevent damage to the temperature detection sensor 36.

[0067] The control unit 35 switches the control of heaters 33 and 34 when it resumes power supply to the temperature detection sensor 36. That is, the control unit 35 switches from control based on the temperature measured by the temperature measuring unit 37 to control based on the temperature detected by the temperature detection sensor 36. The temperature detection sensor 36 can detect the surface temperature of the heating roller 31 with higher accuracy than the temperature measuring unit 37. Therefore, the control unit 35 can control the surface temperature of the heating roller 31 with high accuracy by controlling heaters 33 and 34 based on the temperature detected by the temperature detection sensor 36.

[0068] Subsequently, the control unit 35 returns to step S12. The control unit 35 obtains humidity from the humidity sensor 38 (step S12) and performs a water droplet determination (step S13). In this water droplet determination, it is determined that there are no water droplets. Then the control unit 35 proceeds to step S20.

[0069] If the control unit 35 determines that there are no water droplets (NO in step S14), it determines whether the image forming apparatus 1 should switch from normal power supply mode to power saving mode (step S20). If the normal power supply mode continues (NO in step S20), the control unit 35 waits until it is time to switch to power saving mode.

[0070] If the normal power supply mode continues, the control unit 35 continues to control the heaters 33 and 34 based on the temperature detected by the temperature detection sensor 36. For example, when no print job is running in the normal power supply mode, the control unit 35 controls the heaters 33 and 34 so that the surface temperature of the heating roller 31 becomes the standby temperature. Also, for example, when a print job is running in the normal power supply mode, the control unit 35 controls the heaters 33 and 34 so that the surface temperature of the heating roller 31 becomes the fixing temperature according to the type of sheet 9.

[0071] When the control unit 35 determines that it is transitioning from the normal power supply mode to the power-saving mode (YES in step S20), it cuts off the power supply to the temperature detection sensor 36 (step S21). In power-saving mode, the heaters 33 and 34 are stopped from driving. Therefore, the control unit 35 cuts off the power supply to the temperature detection sensor 36 to prevent the temperature detection sensor 36 from remaining powered while water droplets due to condensation are attached to it. This prevents ion migration of the temperature detection sensor 36 from progressing in power-saving mode.

[0072] Subsequently, the control unit 35 waits until it is time to return from power-saving mode to normal power supply mode (step S22). When it returns from power-saving mode to normal power supply mode, the control unit 35 resumes driving control of heaters 33 and 34. Also, when returning from power-saving mode (YES in step S22), the control unit 35 obtains humidity from humidity sensor 38 (step S23). Then, based on that humidity, the control unit 35 makes a water droplet determination again (step S24) and determines whether or not there is a possibility of water droplets adhering to temperature detection sensor 36 (step S25). If there is a possibility of water droplets adhering (YES in step S25), the processing by the control unit 35 returns to step S23. The control unit 35 then repeatedly executes the processing from steps S23 to S25. At this time, since the driving of heaters 33 and 34 has been resumed, the temperature inside the fixing unit 17 gradually rises. Accordingly, the humidity inside the fixing unit 17 gradually decreases. Therefore, the control unit 35 waits while repeating the process from step S23 to S25 until it determines that there is no possibility of water droplets being present.

[0073] When the control unit 35 is performing the water droplet detection process PB, which repeats steps S23 to S25, it cannot control the heaters 33 and 34 using the temperature detection sensor 36. Therefore, when the water droplet detection process PB is being performed, the control unit 35 controls the heaters 33 and 34 based on the temperature measured by the temperature measuring unit 37. This prevents the surface temperature of the heating roller 31 from becoming excessively hot.

[0074] If the water droplet detection process PB determines that no water droplets are attached to the temperature detection sensor 36 (NO in step S25), the control unit 35 resumes power supply to the temperature detection sensor 36 (step S26). Since no water droplets are attached to the temperature detection sensor 36, ion migration does not occur even when power is resumed to the temperature detection sensor 36. Therefore, the temperature detection sensor 36 is not damaged by the power supply.

[0075] As the control unit 35 resumes power supply to the temperature detection sensor 36 (step S26), it switches the control of the heaters 33 and 34. That is, the control unit 35 switches from control based on the temperature measured by the temperature measuring unit 37 to control based on the temperature detected by the temperature detection sensor 36. The temperature detection sensor 36 can detect the surface temperature of the heating roller 31 with higher accuracy than the temperature measuring unit 37. Therefore, the control unit 35 can control the surface temperature of the heating roller 31 with high accuracy by controlling the heaters 33 and 34 based on the temperature detected by the temperature detection sensor 36.

[0076] Subsequently, the control unit 35 returns to step S20 and repeats the process described above. Therefore, when transitioning to a power-saving mode that involves stopping the heaters 33 and 34, the control unit 35 cuts off the power supply to the temperature detection sensor 36. Furthermore, when returning from power-saving mode, the control unit 35 resumes power supply to the temperature detection sensor 36, provided that no water droplets are attached to the temperature detection sensor 36. This process is repeatedly executed.

[0077] As described above, the image forming apparatus 1 of this embodiment is configured to cut off power to the temperature detection sensor 36 when transitioning to a power-saving mode that involves stopping the heaters 33 and 34. Therefore, the image forming apparatus 1 can prevent ion migration of the temperature detection sensor 36 from progressing in the power-saving mode.

[0078] Furthermore, when the image forming apparatus 1 restarts operation of the heaters 33 and 34 upon returning from power-saving mode, it performs a determination step to determine the presence or absence of water droplets on the temperature detection sensor 36. If it determines in this determination step that water droplets are present, the image forming apparatus 1 continues to cut off power to the temperature detection sensor 36. Therefore, the image forming apparatus 1 can prevent ion migration of the temperature detection sensor 36 from progressing immediately after returning from power-saving mode.

[0079] Incidentally, in the above embodiment, a humidity sensor 38 is provided in the fixing unit 17, and the control unit 35 determines whether or not there is a possibility of water droplets adhering to the temperature detection sensor 36 based on the humidity detected by the humidity sensor 38. However, the control unit 35 can also determine the possibility of water droplet adhesion based on information other than the humidity detected by the humidity sensor 38. For example, when the control unit 35 transitions from the normal power supply mode to the power saving mode, it starts counting the elapsed time and continues this counting operation in the power saving mode. Then, when it returns from the power saving mode to the normal power supply mode, the control unit 35 determines the possibility of water droplet adhesion based on the elapsed time since transitioning to the power saving mode.

[0080] Figure 5 is a flowchart showing an example of a processing procedure for determining the presence of water droplets based on the elapsed time since switching to power-saving mode. The flowchart in Figure 5 shows a processing procedure that replaces the processing procedure from steps S20 to S26 in the flowchart of Figure 4.

[0081] When the control unit 35 starts processing based on the flowchart in Figure 5, it determines whether the image forming apparatus 1 should switch from normal power supply mode to power saving mode (step S30). If it switches to power saving mode (YES in step S30), the control unit 35 starts counting the elapsed time (step S31). That is, the control unit 35 starts counting the elapsed time since switching to power saving mode. In addition, as the control unit 35 switches to power saving mode in which the heaters 33 and 34 are stopped, it cuts off the power supply to the temperature detection sensor 36 (step S32). This prevents ion migration of the temperature detection sensor 36 from progressing in power saving mode.

[0082] Subsequently, the control unit 35 waits until it is time to return from power-saving mode to normal power supply mode (step S33). When returning from power-saving mode to normal power supply mode, the control unit 35 resumes drive control of heaters 33 and 34. Also, when returning from power-saving mode (YES in step S33), the control unit 35 acquires the elapsed time during counting (step S34). Based on the acquired elapsed time, the control unit 35 makes a determination as to whether or not there is a possibility of water droplets adhering to the temperature detection sensor 36 (step S35). For example, if the elapsed time since switching to power-saving mode is longer than a predetermined time, the temperature inside the fuser unit 17 has fallen below the predetermined temperature, and there is a possibility that water droplets have adhered to the temperature detection sensor 36. On the other hand, if the elapsed time since switching to power-saving mode is less than the predetermined time, the temperature inside the fuser unit 17 is still at a high temperature above the predetermined temperature, and there is no possibility of water droplets adhering to the temperature detection sensor 36. Therefore, the control unit 35 determines whether or not the elapsed time since switching to power-saving mode is longer than a predetermined time.

[0083] If there is a possibility of water droplets being present (YES in step S36), the control unit 35 returns to step S34. The control unit 35 then repeatedly executes the processes from steps S34 to S36. At this time, since the heaters 33 and 34 are restarted, the temperature inside the fixing unit 17 gradually rises. Consequently, the humidity inside the fixing unit 17 gradually decreases. Therefore, the control unit 35 waits while repeating the processes from steps S34 to S36 until it determines that there is no possibility of water droplets being present. At this time, the control unit 35 controls the heaters 33 and 34 based on the temperature measured by the temperature measuring unit 37.

[0084] On the other hand, if the control unit 35 determines that no water droplets are attached to the temperature detection sensor 36 (NO in step S36), it resumes power supply to the temperature detection sensor 36 (step S37). Since no water droplets are attached to the temperature detection sensor 36, ion migration does not occur even when power is resumed to the temperature detection sensor 36. Therefore, the temperature detection sensor 36 is not damaged by the power supply. Also, as described above, when the control unit 35 resumes power supply to the temperature detection sensor 36 (step S37), it switches the control of heaters 33 and 34. After that, the processing by the control unit 35 returns to step S30.

[0085] Thus, the control unit 35 may determine the possibility of water droplet adhesion based on the elapsed time since switching to power-saving mode. In this case, it is not necessary to provide a humidity sensor 38 on the fixing unit 17.

[0086] Furthermore, when the control unit 35 returns from power-saving mode to normal power supply mode, it may wait for a predetermined time to elapse without determining the possibility of water droplet adhesion, and then resume power supply to the temperature detection sensor 36 after the predetermined time has elapsed.

[0087] Figure 6 is a flowchart showing an example of a processing procedure that waits for a predetermined time to elapse when returning from power-saving mode. The flowchart in Figure 6 shows a processing procedure that replaces the processing procedure from steps S20 to S26 in the flowchart of Figure 4.

[0088] When the control unit 35 starts processing based on the flowchart in Figure 6, it determines whether the image forming apparatus 1 should switch from normal power supply mode to power saving mode (step S40). If it switches to power saving mode (YES in step S40), the control unit 35 cuts off the power supply to the temperature detection sensor 36 (step S41). This prevents ion migration of the temperature detection sensor 36 from progressing in power saving mode.

[0089] Subsequently, the control unit 35 waits until it is time to return from power-saving mode to normal power supply mode (step S42). When returning from power-saving mode to normal power supply mode, the control unit 35 resumes drive control of heaters 33 and 34. Also, when returning from power-saving mode (YES in step S42), the control unit 35 starts time measurement (step S43).

[0090] When the system returns from power-saving mode to normal power-on mode, there is a possibility that water droplets may be attached to the temperature detection sensor 36. Therefore, the control unit 35 waits until a predetermined time has elapsed after restarting the drive control of the heaters 33 and 34 (step S44). The predetermined time is set in advance as the time required for the water droplets attached to the temperature detection sensor 36 to evaporate after restarting the drive of the heaters 33 and 34. Therefore, during the period until the predetermined time has elapsed, the temperature detection sensor 36 will be free of water droplets. While the control unit 35 is waiting until the predetermined time has elapsed, it controls the heaters 33 and 34 based on the temperature measured by the temperature measuring unit 37.

[0091] Then, after a predetermined time has elapsed (YES in step S44), the control unit 35 resumes power supply to the temperature detection sensor 36 (step S45). At this time, since no water droplets are attached to the temperature detection sensor 36, ion migration does not occur even when power is resumed to the temperature detection sensor 36. Therefore, the temperature detection sensor 36 is not damaged by the power supply. In addition, upon resuming power supply to the temperature detection sensor 36 (step S45), the control unit 35 controls the heaters 33 and 34 based on the temperature detected by the temperature detection sensor 36. After that, the processing by the control unit 35 returns to step S40.

[0092] Thus, the control unit 35 may be configured to wait for a predetermined time before resuming power supply to the temperature detection sensor 36 when returning from power-saving mode. In this case, it is not necessary to provide a humidity sensor 38 in the fixing unit 17.

[0093] Preferred embodiments of the present invention have been described above. However, the present invention is not limited to those described in the above embodiments, and various modifications are applicable.

[0094] For example, in the above embodiment, the image forming apparatus 1 is configured as an MFP and has multiple functions such as scanning, printing, and copying. However, the image forming apparatus 1 is not limited to being configured as an MFP. For example, the image forming apparatus 1 may be a printer equipped only with a printing function. [Explanation of Symbols]

[0095] 1. Image forming apparatus 8 Power circuit 17 Fixing Unit 30 Fixing section 31 Heating rollers 32 Pressure Rollers 33,34 Heater 35 Control Unit 36 Temperature detection sensors 37 Temperature measurement section 38 Humidity Sensor

Claims

1. A heater that heats the fixing section, A temperature detection sensor for detecting the temperature of the fixing section, A control unit that controls the heater based on the temperature detected by the temperature detection sensor and also controls the supply of power to the temperature detection sensor, Equipped with, The image forming apparatus is characterized in that the control unit cuts off the power supply to the temperature detection sensor when transitioning to a power-saving mode that involves stopping the heater.

2. The image forming apparatus according to claim 1, characterized in that the control unit determines whether or not there are water droplets in the temperature detection sensor when the heater is restarted upon returning from the power saving mode, and if it determines that there are water droplets, it cuts off the power supply to the temperature detection sensor.

3. The image forming apparatus according to claim 2, characterized in that the control unit restarts power to the temperature detection sensor when it determines that there are no water droplets when the heater is restarted.

4. A temperature measuring unit that measures the temperature of the fixing part at a position different from the temperature detection sensor. Furthermore, The image forming apparatus according to claim 2, characterized in that, when the control unit determines that there are water droplets when the heater is restarted, it controls the heater based on the temperature measured by the temperature measuring unit.

5. The image forming apparatus according to claim 4, characterized in that a coating material is applied to the detection section of the temperature measuring section.

6. The image forming apparatus according to claim 4, characterized in that, if the control unit determines that there are no water droplets after returning from the power saving mode, it resumes power supply to the temperature detection sensor and switches from control based on the temperature measured by the temperature measuring unit to control based on the temperature detected by the temperature detection sensor.

7. A humidity sensor that detects humidity. Furthermore, The image forming apparatus according to any one of claims 2 to 6, characterized in that the control unit determines the presence or absence of water droplets based on the humidity detected by the humidity sensor.

8. The image forming apparatus according to any one of claims 2 to 6, characterized in that the control unit determines the presence or absence of water droplets in the temperature detection sensor based on the elapsed time since the heater was stopped.

9. The image forming apparatus according to claim 1, characterized in that the control unit resumes power supply to the temperature detection sensor after a predetermined time has elapsed since the heater was restarted following the return from the power saving mode.

10. A heater that heats the fixing section, A temperature detection sensor for detecting the temperature of the fixing section, A control method for an image forming apparatus comprising, A heater control step that controls the heater based on the temperature detected by the temperature detection sensor, A power supply control step that cuts off power to the temperature detection sensor when transitioning to a power-saving mode that involves stopping the heater, A control method characterized by having the following features.

11. A determination step is taken to determine the presence or absence of water droplets in the temperature detection sensor when the heater is restarted following a return from the power-saving mode. It further possesses, The control method according to claim 10, characterized in that the power supply control step cuts off power to the temperature detection sensor if it is determined in the determination step that water droplets are present.

12. The control method according to claim 11, characterized in that the current supply control step resumes supplying power to the temperature detection sensor if it is determined in the determination step that there are no water droplets.

13. The image forming apparatus is A temperature measuring unit that measures the temperature of the fixing part at a position different from the temperature detection sensor. Furthermore, The control method according to claim 11, characterized in that the heater control step controls the heater based on the temperature measured by the temperature measuring unit when it is determined in the determination step that water droplets are present.

14. The power supply control step, if it is determined in the determination step that there are no water droplets after returning from the power saving mode, restarts power supply to the temperature detection sensor. The control method according to claim 13, characterized in that the heater control step switches from control based on the temperature measured by the temperature measuring unit to control based on the temperature detected by the temperature detection sensor.

15. The image forming apparatus is A humidity sensor that detects humidity. Furthermore, The control method according to any one of claims 11 to 14, characterized in that the determination step determines the presence or absence of water droplets based on the humidity detected by the humidity sensor.

16. The control method according to any one of claims 11 to 14, characterized in that the determination step determines the presence or absence of water droplets in the temperature detection sensor based on the elapsed time since the heater was stopped.

17. The control method according to claim 10, characterized in that the power supply control step resumes power supply to the temperature detection sensor after a predetermined time has elapsed since the heater was restarted following the return from the power saving mode.

Images