Image forming apparatus

Abstract

To appropriately control temperature when performing printing on a plurality of sheets.SOLUTION: An image forming apparatus 1 comprises: a heat roller 36 that is heated by a heater 40; a back-up roller 37 that forms a nip part with the heat roller 36; a thermopile 42 that is arranged inside a paper feed area ARp and detects the temperature of the heat roller 36 when the heater 40 starts heating; and a printing control unit 50 that causes the heater 40 to apply heat on the basis of at least a first detection temperature that is a result of detection performed by the thermopile 42 to control the heat roller 36 to reach a target temperature. When performing printing on a plurality of sheets, the printing control unit 50 controls the timing to change the target temperature from a first temperature T1 when the heater 40 starts heating to a second temperature T2 lower than the first temperature T1 according to the first detection temperature.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, and is suitable for application to, for example, an electrophotographic printer. [Background technology]

[0002] Conventionally, a widely used image forming device (also called a printer) performs printing processing by forming a developer image using toner (also called a developer) in an image forming unit based on an image supplied from a computer device or the like, transferring the developer image to a medium such as paper, and then fixing the image by applying heat and pressure in a fixing unit.

[0003] As such an image forming device, one has been proposed in which a heater provided inside a fixing member such as a fixing belt or a heat roller in a fixing unit is heated, and the temperature of the fixing member is controlled by measuring the temperature of the central part of the fixing member in the longitudinal direction to control the heater (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Application No. 2020-194102 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in an image forming apparatus, it is sometimes difficult to properly control the temperature when printing a plurality of sheets after warming up the fixing unit.

[0006] The present invention has been made in consideration of the above points, and aims to propose an image forming apparatus that can properly control the temperature when printing multiple sheets. [Means for solving the problem]

[0007] In order to solve this problem, the image forming apparatus of the present invention is provided with a heating element heated by a heater, a pressure element forming a nip portion between the heating element and the heating element, a first temperature detection unit arranged within the paper passing area and detecting the temperature of the heating element when the heater starts heating, and a control unit that heats the heater based on at least a first detected temperature which is the detection result of the first temperature detection unit, and controls the heating element to reach a target temperature, and when printing multiple sheets, the control unit controls the timing for changing the target temperature from the first temperature when the heater starts heating to a second temperature lower than the first temperature according to the first detected temperature.

[0008] The present invention maintains fixability by quickly allowing the ends of the heating element to reach a target temperature in the early stages of printing multiple sheets, depending on the temperature of the heating element when the heater starts heating, while reducing power consumption by preventing the ends of the heating element from heating up more than necessary when multiple sheets have been printed repeatedly. [Effects of the Invention]

[0009] According to the present invention, in the early stages of printing multiple sheets, the end of the heating element is made to quickly reach the target temperature according to the temperature of the heating element when the heater starts heating, thereby maintaining fixability, and after printing multiple sheets, the end of the heating element is prevented from being heated more than necessary, thereby reducing power consumption. Thus, the present invention can realize an image forming apparatus that can perform appropriate temperature control when printing multiple sheets. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a left side view showing the configuration of the image forming apparatus. [Figure 2] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus. [Figure 3] 1A and 1B show the configuration of the fixing unit, where FIG. 1A is a front view and FIG. 1B is a left side view. [Figure 4] 10 is a flowchart showing a fixing control process procedure. [Figure 5]10 is a time chart showing changes in the thermopile detected temperature and the side thermistor detected temperature when the target temperature is not lowered. [Figure 6] 10 is a time chart showing changes in the thermopile detected temperature and the side thermistor detected temperature when the target temperature is lowered from the 11th sheet onward. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[0012] [1. Configuration of image forming device] As shown in FIG. 1, the image forming apparatus 1 is, for example, an electrophotographic printer that forms a monochrome image on a sheet of paper P by performing an image formation operation using a developer such as toner. Hereinafter, a position close to the paper cassette 3, or a direction toward the paper cassette 3, as viewed from an arbitrary position on the transport path W along which the sheet of paper P is transported, is referred to as "upstream." Also, a position close to the stacker 14 into which the sheet of paper P is discharged and stacked, or a direction toward the stacker 14, as viewed from an arbitrary position on the transport path W, is referred to as "downstream." Furthermore, the direction from upstream to downstream is referred to as "transport direction." Furthermore, the right end portion of FIG. 1 is the front of the image forming apparatus 1, and the following description defines the up-down, left-right, and front-rear directions when viewed from this front. The image forming apparatus 1 employs a so-called direct transfer system, i.e., a toner image as a developer image is directly transferred onto the sheet of paper P from a photosensitive drum 26 (described later) of an image forming unit 8 (described later).

[0013] The image forming apparatus 1 is controlled overall by a print control unit 50 (FIG. 2). This print control unit 50 has a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), I / O ports, timers, counters, etc. (not shown), and performs various processes by reading and executing predetermined programs. The image forming apparatus 1 also has a box-shaped housing 2 inside which are a paper cassette 3, a hopping roller 4, a paper feed roller 5, a transport roller 6, a registration roller 7, an image forming unit 8, a transfer unit 10, a fuser 11, and discharge rollers 12 and 13.

[0014] The paper cassette 3 is attached to the bottom of the housing 2 and accommodates a stack of multiple sheets of paper P. A hopping roller 4 is provided downstream of the paper cassette 3. The hopping roller 4 rotates while pressing against the surface of the paper P, separating the paper P one by one and sending it downstream along the conveying path W.

[0015] A paper feed roller 5 is provided downstream of the hopping roller 4. The paper feed roller 5 transports the paper P toward the transport roller 6. The transport roller 6 is provided downstream of the paper feed roller 5. The transport roller 6 transports the paper P toward the registration roller 7. The registration roller 7 is provided downstream of the transport roller 6. The registration roller 7 transports the paper P toward the image forming unit 8 provided downstream. When the paper P is transported, the leading edge of the paper P abuts against the registration roller 7, thereby correcting any skew of the paper P.

[0016] Downstream of the registration rollers 7, there is provided one image forming unit 8 corresponding to the color of the developer (for example, black (K) toner) used in the image forming apparatus 1. Hereinafter, the left-right direction perpendicular to the conveying direction of the paper P and the thickness direction perpendicular to the paper surface of the paper P will also be referred to as the conveying width direction.

[0017] The image forming unit 8 is made up of a toner cartridge 20, a developing device 21, and a print head 22. The toner cartridge 20 is disposed above the developing device 21, contains toner, and is configured to be detachable from the developing device 21. The developing device 21 is provided with a supply roller 24, a developing roller 25, a photosensitive drum 26, a charging roller 27, a developing blade 28, a cleaning blade 29, etc.

[0018] The print head 22 is an LED (Light Emitting Diode) head that is provided adjacent to the upper side of the photosensitive drum 26 and has multiple LED elements aligned in the left-right direction, and each LED element is turned on or off under the control of the print control unit 50. The print head 22 exposes the charged surface of the photosensitive drum 26 to light based on print data to form an electrostatic latent image.

[0019] The supply roller 24 supplies the toner contained in the toner cartridge 20 to the developing roller 25. The charging roller 27 uniformly charges the surface of the photosensitive drum 26. The developing blade 28 uniformly distributes a thin layer of toner on the developing roller 25. The developing roller 25 charges the toner and electrostatically attaches it to the electrostatic latent image formed on the photosensitive drum 26 to form a toner image. The photosensitive drum 26 carries the electrostatic latent image and also carries a toner image obtained by developing the electrostatic latent image with toner. The cleaning blade 29 scrapes off and removes toner remaining on the surface of the photosensitive drum 26.

[0020] In this configuration, the image forming unit 8 forms an electrostatic latent image on the surface of the photosensitive drum 26 by irradiating and exposing the surface of the photosensitive drum 26 with light using the LED head of the print head 22, and then forms a toner image on the surface of the photosensitive drum 26 by adhering toner supplied from the toner cartridge 20 to the electrostatic latent image.

[0021] In addition, a transfer unit 10 is provided below the image forming unit 8. The transfer unit 10 has a circular conveyor belt (not shown) that is provided so as to be able to move freely in the front-to-back direction along the conveyance path W, and a transfer roller 30 that is disposed below the photosensitive drum 26 and faces the conveyor belt, with the conveyor belt sandwiched between them. The transfer roller 30 charges the paper P to a polarity opposite to that of the toner as the paper P passes between the photosensitive drum 26 and the conveyor belt, thereby transferring the toner image formed on the photosensitive drum 26 to the paper P. In this way, the transfer unit 10 transfers a toner image of one color, black, onto the surface of the paper P, and then hands over the paper P with the transferred toner image to the fixing device 11.

[0022] The fixing device 11 applies heat and pressure to the toner image transferred onto the paper P transported from the image forming unit 8, thereby fixing the toner image onto the paper P, and also transports the paper P along the transport path W toward the discharge rollers 12.

[0023] Discharge rollers 12 are provided downstream of the fixing unit 11. The discharge rollers 12 transport the paper P toward discharge rollers 13 provided downstream. The discharge rollers 13 transport the paper P toward a stacker 14. In this way, the image forming apparatus 1 stacks the paper P, on which the toner image has been fixed, in the stacker 14 provided outside the housing 2.

[0024] An entrance sensor 32, a writing sensor 33, and a discharge sensor 34 are provided on the transport path W for the paper P to detect the presence or absence of paper P. The entrance sensor 32, the writing sensor 33, and the discharge sensor 34 detect the presence or absence of paper P on the transport path W and notify the print control unit 50 (FIG. 2). The entrance sensor 32 is provided upstream of the registration rollers 7, and its detection signal serves as a reference for adjusting the paper feed timing and the amount of paper P abutting the registration rollers 7 during continuous printing. The write sensor 33 is provided downstream of the registration rollers 7, and its detection signal serves as a reference for toner image formation, such as the exposure timing of the print head 22 and the timing of applying high voltage to the transfer roller 30. The discharge sensor 34 is provided downstream of the fixing unit 11, and a discharge sensor signal S2, which is the detection signal of the discharge sensor 34, serves as a reference for determining whether a series of image formation processes for the paper P have been completed. Specifically, the discharge sensor signal S2 is High while the paper P is detected, and is Low while the paper P is not detected.

[0025] [2. Configuration of the fixing unit] 1 and 3, the fixing unit 11 is broadly composed of a heat roller 36 arranged above the conveying path W and a backup roller 37 arranged below the conveying path W. The fixing unit 11 is generally surrounded by a housing. This housing is appropriately formed with holes and the like for allowing the paper P to pass along the conveying path W.

[0026] [2-1. Heat Roller Configuration] The heat roller 36 is a cylindrical roller with its central axis aligned in the left-right direction. The heat roller 36 has a multi-layer structure in which a cylindrical aluminum alloy or other base material is overlaid with a surface layer made of a fluororesin coating, such as PTFE (polytetrafluoroethylene) or PFA (perfluoroalkoxyalkane), or a tube made from such a coating. A heater 40 is provided inside the heat roller 36.

[0027] [2-2. Heater configuration] The heater 40 is a halogen heater that extends in the longitudinal direction (left-right direction). The heating portion, which generates heat when power is supplied, is not divided but is formed continuously from one end to the other end of the heater 40 in the longitudinal direction. The heater 40 is given an arbitrary heat distribution (i.e., a distribution of the ease of heat generation). In this embodiment, the heat distribution at both ends is set higher than the heat distribution at the center. This is because the end portions of the heater 40 lose heat more easily than the center portion of the heat roller 36, making it difficult for the temperature to rise. Specifically, the heater 40 is configured so that, when the heat distribution ratio at the center portion is 100%, the heat distribution ratio at both ends is set to, for example, 130%. The heater 40 is configured so that the center portion and both end portions switch 80 mm to the left of the center (center) in the left-right direction, and the center portion and both end portions switch 80 mm to the right of the center. That is, the heater 40 has a central area set from a position 80 mm to the left of the center to a position 80 mm to the right of the center, and two end areas set from a position 80 mm to the left of the center to the left end of the heat generating section, and another area set from a position 80 mm to the right of the center to the right end of the heat generating section.

[0028] The heater 40 has a heating area length L1, which is the length (i.e., width) of the heating element in the left-right direction, of 225 mm, corresponding to the vertical width of an A4 sheet of paper (210 mm). Therefore, the image forming apparatus 1 is set to be able to print up to the vertical width of an A4 sheet of paper. The area that the A4 sheet of paper Pa4 occupies in the transport width direction when it passes through the fixing device 11 is the paper passing area ARp. Furthermore, the area outside the paper passing area ARp in the transport width direction, where the paper P does not pass, is the non-paper passing area.

[0029] [2-3. Thermopile configuration] A thermopile 42 is installed outside the heat roller 36, slightly in front of (i.e., upstream of) it. The thermopile 42 is a non-contact optical temperature sensor that receives infrared light emitted from the surface of the heat roller 36, converts the amount of infrared light received into temperature, and generates an electrical signal corresponding to the surface temperature of the heat roller 36. This signal is supplied to the fixing controller 52 (FIG. 2) as a thermopile-detected temperature TO, which serves as a first detected temperature. The fixing controller 52 acquires the thermopile-detected temperature TO as the temperature of the heat roller 36 and controls the temperature of the heat roller 36 to a target temperature based on the thermopile-detected temperature TO. The thermopile 42 is installed at the center of the sheet passage area ARp in the longitudinal direction (transverse direction) of the heat roller 36. The thermopile 42 may be installed inside the fixing unit 11. However, in this case, an expensive sensor would be installed inside the fixing unit 11, which is a consumable item. Therefore, it is preferable to install the thermopile 42 inside the main body of the image forming apparatus 1 to reduce costs.

[0030] [2-4. Side thermistor configuration] Additionally, side thermistor 44L is located 110 mm to the left of the center of heater 40, and side thermistor 44R is located 110 mm to the right of the center of heater 40, both of which are positioned to abut against heat roller 36. Hereinafter, side thermistors 44L and 44R are collectively referred to as side thermistors 44, which serve as second temperature detection units. The resistance values ​​of side thermistors 44L and 44R change depending on the temperature of the heat roller 36 at which they abut. Therefore, they generate electrical signals corresponding to the temperature and supply these signals to the fuser control unit 52 (FIG. 2) as side thermistor-detected temperatures TL and TR, respectively, as second detected temperatures. In other words, side thermistor 44 detects the temperature of heat roller 36 itself and generates an electrical signal representing that temperature. This side thermistor 44 is positioned in a non-paper-passing area, which is located outside the paper-passing area ARp in the transport width direction. The fixing control unit 52 monitors the non-sheet passing area temperature based on the side thermistor detected temperatures TL and TR so that the temperature does not exceed the heat-resistant temperature.

[0031] [2-5. Backup Roller Configuration] On the other hand, backup roller 37, which serves as a pressure member, is formed in a cylindrical shape with its central axis aligned in the left-right direction, is rotatably supported by a support member (not shown), and is urged toward heat roller 36. Therefore, in fuser 11, backup roller 37 is pressed against heat roller 36, and a nip portion is formed between them to sandwich paper P conveyed from transfer unit 10 (FIG. 1). Fixer 11 applies heat and pressure to the toner image transferred onto paper P at the nip portion, thereby fixing the toner image to paper P.

[0032] [3. Operation of the fixing unit] In this configuration, the fixing unit 11 detects the temperature using the thermopile 42 and the side thermistor 44, and controls the power supplied to the heater 40 under the control of the fixing control unit 52 (FIG. 2), thereby controlling the heater 40 to a desired temperature. During printing, the fixing control unit 52 controls the fixing unit 11 mainly based on the temperature of the thermopile 42. Meanwhile, the fixing control unit 52 uses the side thermistor 44 mainly to detect alarm conditions, such as abnormal temperature rise in the heater 40 or excessive temperature rise in non-paper passing areas when printing on narrow media.

[0033] During printing, the fixing control unit 52 performs PID calculations based on the difference between the temperature detected by the thermopile 42 (thermopile detection temperature TO) and the target temperature determined according to the printing conditions every 100 ms, which is the temperature control period, to determine the duty value of the heater ON signal S1 (described later). The calculation formula for the duty value in the nth period is the following formula (1), which is a function of the deviation ε between the target temperature and the thermopile detection temperature TO. DUTY value (n)=Kp*ε+Ki*Σε+Kd*dε / dt+DutyMod(n-1) ε: Temperature deviation (target temperature - thermopile detection temperature TO) Kp: Proportional gain Ki: Integral gain Kd: Differential gain DutyMod(n-1): The remainder of the DUTY value that was not consumed in the previous control cycle

[0034] The fixing control unit 52 repeatedly determines whether the heater ON signal S1 is ON (High) if the DUTY value calculated by the formula (1) is equal to or greater than a predetermined threshold, the heater ON threshold, or whether the heater ON signal S1 is OFF (Low) if the DUTY value is less than the heater ON threshold.

[0035] [4. Control Configuration of Image Forming Apparatus] As shown in FIG. 4, the print control unit 50 is connected to the entrance sensor 32, the writing sensor 33, the discharge sensor 34, the thermopile 42, the side thermistor 44L, the side thermistor 44R, the print head 22, the high-voltage generating unit 54, the main motor 55, the discharge motor 56, and the heater control circuit 57, and in accordance with instructions from a higher-level device 58 such as a personal computer, analyzes, calculates, and determines the conditions for the information signals from each sensor and each unit, including the entrance sensor 32, the writing sensor 33, and the discharge sensor 34, and outputs operation instruction signals to each unit, thereby controlling the printing operation of the image forming apparatus 1.

[0036] Based on control from the print control unit 50, the high voltage generation unit 54 applies a high voltage (bias) to the image forming unit 8 and the transfer roller 30. The main motor 55 is a DC motor that drives each rotating body of the developing device 21, the hopping roller 4, the paper feed roller 5, the conveying roller 6, the registration roller 7, and the heat roller 36. The discharge motor 56 is a pulse motor that drives the discharge rollers 12 and 13.

[0037] The print control unit 50 also includes a paper-passing counter 51 and a fixing control unit 52. During continuous printing, the paper-passing counter 51 counts the number of sheets P passing through the discharge sensor 34, starting with the first page of print data containing multiple pages. The fixing control unit 52 receives output signals from the thermopile 42 and side thermistors 44L and 44R (i.e., thermopile-detected temperature TO, and side thermistor-detected temperatures TL and TR). Based on the thermopile-detected temperature TO, the fixing control unit 52 outputs a heater-ON signal S1 to a heater control circuit 57, which controls the heat roller 36 to a target temperature according to printing conditions such as paper thickness and paper width. The heater control circuit 57, which is comprised of a triac and a drive circuit, turns on / off the power supply to the heater 40 in response to the heater-ON signal S1 received from the fixing control unit 52.

[0038] [5. Fixing control process] Next, a fixing control process procedure RT1, which is a specific process procedure of the fixing control process in which the print control unit 50 controls the fixing unit 11, will be described using the flowchart shown in Fig. 4. In step SP1, the print control unit 50 waits until it receives print data from the higher-level device 58, and when it receives the print data, it proceeds to step SP2.

[0039] In step SP2, the print control unit 50 begins preparation for the printing operation, sets the target temperature to a first temperature T1 (e.g., 165°C), and proceeds to step SP3. In step SP3, the print control unit 50 detects the temperature of the heat roller 36, i.e., the thermopile-detected temperature TO and the side thermistor-detected temperatures TL and TR, to confirm the temperature distribution in the longitudinal direction of the heat roller 36, and proceeds to step SP4.

[0040] In step SP4, the print control unit 50 determines whether the thermopile detection temperature TO is equal to or greater than the first temperature threshold of 120°C (i.e., the thermopile detection temperature TO≧120°C). If a positive result is obtained, this indicates that a short time has passed since the end of the previous printing operation and the end temperature of the heat roller 36 is sufficiently high (i.e., a temperature that can easily reach the target temperature), and the print control unit 50 then proceeds to step SP5.

[0041] In step SP5, the print control unit 50 warms up the fixing unit 11 by starting the supply of electricity to the heater 40, and when the thermopile detection temperature TO reaches the first temperature T1, the print operation is started and the process proceeds to step SP6. Here, warming up the fixing unit 11 refers to control to start heating the heater 40 when starting the current print operation after the previous print operation has ended and the image forming apparatus 1 has stopped the rotation of the heat roller 36.

[0042] In step SP6, when the count of the number of sheets passed counter 51 reaches five, the print control unit 50 changes the target temperature from the first temperature T1 set at the start of printing to a second temperature T2 (for example, 160°C, which is 5°C lower than the first temperature T1 as a temperature drop), thereby lowering the target temperature from the start of printing for the sixth sheet onwards, and continues the printing operation by lowering the target temperature from the start of printing for the sixth sheet onwards, then proceeds to step SP13 and ends the fixing control processing procedure RT1.

[0043] On the other hand, if a negative result is obtained in step SP4, this indicates that a long time has passed since the end of the previous printing operation and the end temperature of the heat roller 36 is not sufficiently high, and the print control unit 50 then proceeds to step SP7. In step SP7, the print control unit 50 determines whether the thermopile detection temperature TO is equal to or greater than the second temperature threshold of 80°C and less than the first temperature threshold of 120°C (i.e., 80°C≦thermopile detection temperature TO<120°C). If a positive result is obtained here, this indicates that it is necessary to compare the temperature difference between the center and end of the heat roller 36, and the print control unit 50 then proceeds to step SP8.

[0044] In step SP8, the print control unit 50 determines whether the center-edge temperature difference, which is the temperature difference between the thermopile detection temperature TO and the side thermistor detection temperature TL (the thermopile detection temperature TO minus the side thermistor detection temperature TL), is less than the temperature difference threshold of 5°C (i.e., center-edge temperature difference < 5°C). If a positive result is obtained here, this indicates that the edge temperature of the heat roller 36 will reach the target temperature relatively easily, and the print control unit 50 proceeds to step SP9. Note that, due to the characteristics of the image forming apparatus 1 according to this embodiment, the side thermistor detection temperature TL is lower than the side thermistor detection temperature TR. Therefore, the print control unit 50 calculates the temperature difference between the thermopile detection temperature TO and the side thermistor detection temperature TL as the center-edge temperature difference.

[0045] In step SP9, the print control unit 50 warms up the fixing unit 11 by starting the supply of current to the heater 40, and starts the printing operation when the thermopile detection temperature TO reaches the first temperature T1, then proceeds to step SP10. In step SP10, the print control unit 50 changes the target temperature from the first temperature T1 set at the start of printing to the second temperature T2 when the number of sheets passed counter 51 counts seven, thereby lowering the target temperature from the start of printing for the eighth sheet onwards, and continues the printing operation with the target temperature lowered from the start of printing for the eighth sheet onwards, then proceeds to step SP13, and ends the fixing control processing procedure RT1.

[0046] On the other hand, if a negative result is obtained in step SP7, this indicates that the thermopile detected temperature TO is less than 80°C, so the temperature at the end of the heat roller 36 is low and a reasonable period of time is required to reach the target temperature, and in this case the print control unit 50 proceeds to step SP11. On the other hand, if a negative result is obtained in step SP8, this indicates that a reasonable period of time is required for the temperature at the end of the heat roller 36 to reach the target temperature, and in this case the print control unit 50 proceeds to step SP11.

[0047] In step SP11, the print control unit 50 warms up the fixing unit 11 by starting the supply of current to the heater 40, and starts the printing operation when the thermopile detection temperature TO reaches the first temperature T1, then proceeds to step SP12. In step SP12, the print control unit 50 changes the target temperature from the first temperature T1 set at the start of printing to the second temperature T2 when the number of sheets passed counter 51 counts 10 sheets, thereby lowering the target temperature from the start of printing for the 11th sheet and onwards, and continues the printing operation with the target temperature lowered from the start of printing, then proceeds to step SP13, and the fixing control processing procedure RT1 ends.

[0048] [6. Comparison of changes in thermopile detected temperature and side thermistor detected temperature] 5 shows the changes in the thermopile detection temperature TO and the side thermistor detection temperature TL when the image forming apparatus 1 starts cold, turns the heater ON signal S1 ON (High), starts heating the heater 40, and then, after the thermopile detection temperature TO reaches the first temperature T1 (165°C), which is the target temperature Tt, completing the warm-up, switches the heater ON signal S1 ON (High) or OFF (Low), and repeatedly prints on multiple sheets of paper P while maintaining the thermopile detection temperature TO. In the case of FIG. 5, the process of changing the target temperature Tt from the first temperature T1 to the second temperature T2 at the time the count number of passed paper counter 51 reaches the predetermined number in step SP6, SP10, or SP12 of the fixing control process procedure RT1 (FIG. 4) is not performed, and the target temperature Tt remains the first temperature T1. In the case of FIG. 5, although the temperature TL detected by the side thermistor reaches the target temperature around the time of printing the 11th sheet, the temperature TL detected by the side thermistor continues to rise overall as time passes.

[0049] In contrast, Fig. 6 shows the changes in the thermopile detection temperature T0 and the side thermistor detection temperature T1 when the image forming apparatus 1 controls the heater-ON signal S1 in a manner similar to that shown in Fig. 5, but changes the target temperature from the first temperature T1 to the second temperature T2 at time t1, just before the start of printing on the 11th sheet of paper P, as in step SP12 of the fixing control procedure RT1 (Fig. 4) of this embodiment, and continues printing. In Fig. 6, the side thermistor detection temperature T1 reaches the target temperature around time t1, which is when the 11th sheet is printed. Because the target temperature is changed from the first temperature T1 to the second temperature T2 at that time, the thermopile detection temperature T0 drops, and the rise in the side thermistor detection temperature T1 is suppressed. The limit temperature T1 shown in Figs. 5 and 6 indicates the lowest temperature at which stable fixing can be performed. If the thermopile detection temperature T0 falls below the limit temperature T1, problems may occur in the fixing operation.

[0050] [7. Effects, etc.] In the above configuration, when printing multiple sheets, the image forming apparatus 1 detects the temperature of the heat roller 36 before warming up, and controls the timing for changing the target temperature from the first temperature T1 at the start of heating of the heater 40 to a second temperature T2 lower than the first temperature T1, according to the thermopile detection temperature TO and the side thermistor detection temperature TL.

[0051] Specifically, when the thermopile detection temperature TO is equal to or higher than the first temperature threshold (120°C), the image forming device 1 determines that the time since the end of the previous printing operation is short and the end temperature of the heat roller 36 is sufficiently high, and when the number of sheets counted by the paper count counter 51 reaches five, the image forming device 1 lowers the target temperature from the first temperature T1 to the second temperature T2 and continues the printing operation.

[0052] Furthermore, when the thermopile detection temperature TO is equal to or greater than the second temperature threshold (80°C) and less than the first temperature threshold (120°C), and the central end temperature difference, which is the temperature difference between the thermopile detection temperature TO and the side thermistor detection temperature TL, is less than the temperature difference threshold (5°C), the image forming apparatus 1 determines that the end temperature of the heat roller 36 will reach the target temperature relatively easily, and when the number of sheets counted by the paper count counter 51 reaches the eighth sheet, which is more than five, the target temperature is lowered from the first temperature T1 to the second temperature T2, and the printing operation is continued.

[0053] Furthermore, when the thermopile detection temperature TO is less than the second temperature threshold (80°C) or the center-end temperature difference is equal to or greater than the temperature difference threshold (5°C), the image forming device 1 determines that the temperature at the end of the heat roller 36 is low and that a considerable period of time is required to reach the target temperature, and when the number of sheets passed counter 51 counts the eleventh sheet, which is more than eight, the target temperature is lowered from the first temperature T1 to the second temperature T2 and printing operation is continued.

[0054] In this way, when the image forming device 1 is performing multiple sheet printing (continuous printing) in which printing is performed on multiple sheets of paper P, the timing of lowering the target temperature from the first temperature T1 to the second temperature T2 after starting heating of the heater 40 is delayed so that the colder the end of the heat roller 36 is at the start of warm-up.

[0055] Therefore, even if the temperature of the end of the heat roller 36 is in various states when warm-up begins, the image forming device 1 can maintain fixability at the end of the paper P in the transport width direction by quickly making the end of the heat roller 36 reach the target temperature when the end of the heat roller 36 is not high at the beginning of printing multiple sheets, and can reduce power consumption by preventing the end of the heat roller 36 from heating up more than necessary and causing the temperature to rise when the end of the heat roller 36 becomes high after repeated printing on multiple sheets.

[0056] Furthermore, in the image forming apparatus 1 according to this embodiment, only one heater 40 is provided on the heat roller 36 of the fixing unit 11. This allows the image forming apparatus 1 to have a simpler configuration and lower costs compared to when multiple heaters 40 are provided on the heat roller 36. However, in the case of this type of image forming apparatus 1, it is not possible to provide multiple heaters 40 separately in the center and at the ends of the heat roller 36 and perform different heating controls.

[0057] In response to this, particularly during a cold start when the temperature at both ends of the heat roller 36 is lower than at the center, it may be possible to increase the target temperature for the thermopile detection temperature TO in order to raise the temperature at both ends of the heat roller 36. However, in this case, power consumption increases by the amount that the target temperature for the thermopile detection temperature TO is increased.

[0058] In contrast, even if the image forming device 1 has only one heater 40 on the heat roller 36 in the fixing device 11, it can maintain fixability in the early stages of printing multiple sheets, and when the end of the heat roller 36 becomes higher after repeated printing on multiple sheets, it can prevent the end of the heat roller 36 from heating up more than necessary, thereby reducing power consumption.

[0059] It is also conceivable that the image forming apparatus 1 could detect the thermopile-detected temperature TO during printing, rather than before the printing operation, and lower the target temperature at a predetermined timing. However, because the thermopile 42 is an optical temperature sensor, it has high responsiveness and accuracy in temperature detection. Furthermore, in the image forming apparatus 1, the thermopile-detected temperature TO may fluctuate somewhat significantly during printing as the heater 40 is turned on and off. For this reason, if the image forming apparatus 1 detects the thermopile-detected temperature TO during printing, it may not be able to accurately detect the thermopile-detected temperature TO, which fluctuates greatly, and therefore may not be able to properly control the temperature of the heat roller 36.

[0060] In response to this, image forming apparatus 1 detects the temperature of heat roller 36 when power is started to be supplied to heater 40, which is the timing before the start of printing operation, and determines in advance, before the start of printing operation, the timing for lowering the target temperature from first temperature T1 to second temperature T2. This allows image forming apparatus 1 to appropriately control the temperature of heat roller 36 without being affected by fluctuations in thermopile-detected temperature TO during printing operation.

[0061] According to the above configuration, the image forming apparatus 1 includes a heat roller 36 heated by a heater 40, a backup roller 37 that forms a nip portion between the heat roller 36, a thermopile 42 that is arranged within the paper passing area ARp and detects the temperature of the heat roller 36 when the heater 40 starts heating, and a print control unit 50 that heats the heater 40 based on at least a first detected temperature that is the detection result of the thermopile 42, and controls the heat roller 36 to reach a target temperature, and when printing multiple sheets, the print control unit 50 controls the timing for changing the target temperature from a first temperature T1 when the heater 40 starts heating to a second temperature T2 that is lower than the first temperature T1, according to the first detected temperature.

[0062] As a result, the fixing device 11 maintains fixability by quickly bringing the end of the heat roller 36 to the target temperature in the early stages of printing multiple sheets, depending on the temperature of the heat roller 36 at the start of warm-up, while reducing power consumption by preventing the end of the heat roller 36 from heating up more than necessary after multiple sheets have been printed.

[0063] 8. Other Embodiments In the above-described embodiment, the image forming apparatus 1 changes the target temperature from the first temperature T1 to the second temperature T2 when the count of the passed-sheet counter 51 reaches a predetermined number of sheets. However, the present invention is not limited to this. The image forming apparatus 1 may be provided with a time counting unit that counts the time since the start of the printing operation, and may change the target temperature from the first temperature T1 to the second temperature T2, for example, when the value counted by the time counting unit after the heater 40 starts heating reaches a predetermined value (i.e., when a predetermined time has elapsed since the heater 40 started heating). The image forming apparatus 1 may also change the target temperature from the first temperature T1 to the second temperature T2, for example, when the number of rotations of the heat roller 36 after the heater 40 starts heating reaches a predetermined value (i.e., when the heat roller 36 has rotated a predetermined number of times since the heater 40 started heating).

[0064] In the above-described embodiment, the image forming apparatus 1 changes the target temperature to the second temperature T2 by a temperature decrease amount from the first temperature T1 set at the start of printing when the number of sheets passed counter 51 counts five in step SP6 of the fixing control procedure RT1. However, the present invention is not limited to this. For example, the image forming apparatus 1 may decrease the target temperature from the first temperature T1 by 1°C to 164°C when the number of sheets passed counter 51 counts five, by another 1°C to 163°C when the number of sheets passed counts six, by another 1°C to 162°C when the number of sheets passed counts seven, by another 1°C to 161°C when the number of sheets passed counts eight, and by another 1°C to 160°C when the number of sheets passed counts nine. The same applies to steps SP10 and SP12 of the fixing control procedure RT1.

[0065] Furthermore, in the above-described embodiment, in steps SP6, SP10, and SP12 of the fixing control procedure RT1, the image forming apparatus 1 changes the target temperature to the second temperature T2 by decreasing the temperature decrease amount from the first temperature T1 set at the start of printing when the number of sheets passed counter 51 reaches a predetermined number. However, the present invention is not limited to this. The image forming apparatus 1 may set the target temperature to the first temperature T1, which is the temperature obtained by adding the absolute value of the temperature decrease amount to the second temperature T2, when the number of sheets passed counter 51 reaches a predetermined number, and change the target temperature to the second temperature T2 by subtracting the temperature decrease amount from the first temperature T1.

[0066] Furthermore, in the above-described embodiment, the image forming apparatus 1 measures the temperature of the heat roller 36 before the start of warm-up in step SP3 of the fixing control processing procedure RT1. However, the present invention is not limited to this, and the image forming apparatus 1 may measure the temperature of the heat roller 36 simultaneously with the start of warm-up or immediately after the start of warm-up.

[0067] Furthermore, in the above-described embodiment, the image forming apparatus 1 is designed so that the side thermistor detected temperature TL is lower than the side thermistor detected temperature TR in step SP8 of the fixing control procedure RT1, and therefore the temperature difference between the thermopile detected temperature TO and the side thermistor detected temperature TL is calculated as the central-edge temperature difference. However, the present invention is not limited to this. If the image forming apparatus 1 is designed so that the side thermistor detected temperature TR is lower than the side thermistor detected temperature TL, the image forming apparatus 1 may calculate the temperature difference between the thermopile detected temperature TO and the side thermistor detected temperature TR as the central-edge temperature difference. Furthermore, the image forming apparatus 1 may calculate the temperature difference between the thermopile detected temperature TO and the lower of the side thermistor detected temperatures TL and TR measured in step SP3 as the central-edge temperature difference.

[0068] Furthermore, in the above-described embodiment, the image forming apparatus 1 has been described as having a so-called heat roller type heating element in which the heater 40 is disposed inside the cylindrical heat roller 36. However, the present invention is not limited to this, and the image forming apparatus 1 may have a so-called fixing belt type heating element in which, for example, a planar heater is disposed inside a fixing belt made of a flexible cylindrical film.

[0069] Furthermore, in the above-described embodiment, the image forming apparatus 1 has been described as having the thermopile 42, a non-contact temperature sensor, disposed at the longitudinal center of the heat roller 36. However, the present invention is not limited to this, and the image forming apparatus 1 may have various other non-contact temperature sensors or various other contact temperature sensors disposed at the longitudinal center of the heat roller 36.

[0070] Furthermore, in the above-described embodiment, the image forming apparatus 1 has been described as having the thermopile 42 disposed at the center in the longitudinal direction of the heat roller 36. However, the present invention is not limited to this, and the image forming apparatus 1 may have the thermopile 42 disposed at various other positions within the paper passage area ARp in the longitudinal direction of the heat roller 36.

[0071] Furthermore, in the above-described embodiment, the image forming apparatus 1 is described as having the side thermistor 44 disposed in a non-paper passing area that is outside the paper passing area ARp in the transport width direction. However, the present invention is not limited to this, and the image forming apparatus 1 may have the side thermistor 44 disposed at least outside the thermopile 42 in the longitudinal direction of the heat roller 36.

[0072] Furthermore, in the above-described embodiment, the image forming apparatus 1 has been described as having a temperature drop amount of 5° C. However, the present invention is not limited to this, and the image forming apparatus 1 may have a temperature drop amount of various other values.

[0073] Furthermore, in the above-described embodiment, the present invention has been described as being applied to a so-called direct transfer type image forming apparatus 1 in which a toner image is directly transferred from the photosensitive drum 26 of the image forming unit 8 to the paper P. However, the present invention is not limited to this, and the present invention may also be applied to a so-called intermediate transfer type (or secondary transfer type) image forming apparatus in which toner images of each color are transferred from the photosensitive drum 26 of the image forming unit 8 to an intermediate transfer belt so as to be sequentially superimposed on top of each other, and the toner images are then transferred from this intermediate transfer belt to the paper P.

[0074] Furthermore, in the above-described embodiment, the present invention has been described as being applied to an image forming apparatus 1 that prints using a developer that uses a one-component development method. However, the present invention is not limited to this, and may also be applied to an image forming apparatus that prints using a developer that uses a two-component development method, in which a carrier and a toner are mixed and an appropriate amount of charge is imparted to the toner by utilizing friction between the carrier and the toner.

[0075] Furthermore, in the above-described embodiment, the present invention has been described as being applied to the image forming apparatus 1, which is a monochrome printer that has one image forming unit 8 corresponding to the color black and performs monochrome printing. However, the present invention is not limited to this, and may be applied to various image forming apparatuses, such as an image forming apparatus that is a color printer that has four image forming units corresponding to the colors yellow, magenta, cyan, and black and performs color printing, or an image forming apparatus that has three or less image forming units or five or more image forming units.

[0076] Furthermore, in the above-described embodiment, the present invention has been described as being applied to the image forming apparatus 1, which is a single-function printer. However, the present invention is not limited to this, and may be applied to image forming apparatuses having various other functions, such as an MFP (Multi Function Peripheral) that has the functions of a copier or facsimile machine. The present invention may also be applied to various electronic devices that form images on paper P using a developer by electrophotography.

[0077] Furthermore, the present invention is not limited to the above-described embodiment and other embodiments. That is, the scope of application of the present invention extends to embodiments in which the above-described embodiment and the other embodiments are combined in part or in whole. The scope of application of the present invention also extends to embodiments in which part of the configuration described in any of the above-described embodiment and other embodiments is extracted and used as part of the configuration of any of the above-described embodiment and other embodiments, or in which part of the extracted configuration is added to any of the above-described embodiment.

[0078] Furthermore, in the above-described embodiment, the image forming apparatus 1 is configured as an image forming apparatus using the heat roller 36 as a heating element, the backup roller 37 as a pressure element, the thermopile 42 as a first temperature detection unit, and the print control unit 50 as a control unit. However, the present invention is not limited to this, and the image forming apparatus may be configured using a heating element, pressure element, first temperature detection unit, and control unit having various other configurations. [Industrial Applicability]

[0079] The present invention can be used when printing an image on a medium using an electrophotographic image forming apparatus. [Explanation of symbols]

[0080] 1...image forming apparatus, 2...casing, 3...paper cassette, W...conveyance path, 4...hopping roller, 5...paper feed roller, 6...conveyance roller, 7...registration roller, 8...image forming unit, 10...transfer unit, 11...fuser, 12, 13...discharge roller, 14...stacker, 20...toner cartridge, 21...developing device, 22...print head, 24...supply roller, 25...developing roller, 26...photosensitive drum, 27...charging roller, 28...developing blade, 29...cleaning blade, 30...transfer roller, 32...entrance sensor, 33...write sensor, 34 ......Ejection sensor, 36......Heat roller, 37......Backup roller, 40......Heater, L1......Heat generating area length, 42......Thermopile, 44L, 44R......Side thermistor, 50......Printing control unit, 51......Paper count counter, 52......Fusing control unit, 54......High voltage generation unit, 55......Main motor, 56......Ejection motor, 57......Heater control circuit, 58......Host device, TO......Thermopile detected temperature, TL, TR......Side thermistor detected temperature, S1......Heater ON signal, S2......Ejection sensor signal, Tl......Limit temperature, Tt......Target temperature, T1......First temperature, T2......Second temperature.

Claims

1. a heating body heated by a heater; a pressure member that forms a nip portion between itself and the heating member; a first temperature detection unit disposed within a sheet passing area and configured to detect the temperature of the heating element when the heater starts heating; a control unit that controls the heater to heat the heater so that the heater reaches a target temperature based on at least a first detected temperature that is a detection result of the first temperature detection unit; and The control unit When printing a plurality of sheets, the timing for changing the target temperature from a first temperature at the start of heating of the heater to a second temperature lower than the first temperature is controlled in accordance with the first detected temperature. Image forming device.

2. The control unit When printing multiple sheets, if the first detected temperature is equal to or higher than a first temperature threshold, the target temperature is changed from the first temperature to the second temperature at an earlier timing than when the first detected temperature is lower than the first temperature threshold. The image forming apparatus according to claim 1 .

3. The control unit When printing multiple sheets, if the first detected temperature is lower than the first temperature threshold and equal to or higher than a second temperature threshold that is lower than the first temperature threshold, the target temperature is changed from the first temperature to the second temperature at an earlier timing than when the first detected temperature is lower than the second temperature threshold. The image forming apparatus according to claim 2 .

4. a second temperature detection unit disposed outside the first temperature detection unit in the longitudinal direction of the heating body, the second temperature detection unit detecting the temperature of the heating body when the heater starts heating; and The control unit When printing a plurality of sheets, the timing for changing the target temperature from the first temperature to the second temperature is controlled in accordance with the first detected temperature and a second detected temperature that is a detection result of the second temperature detection unit. The image forming apparatus according to claim 1 .

5. The control unit When printing a plurality of sheets, if a center-end temperature difference obtained by subtracting the second detected temperature from the first detected temperature is less than a temperature difference threshold, the target temperature is changed from the first temperature to the second temperature at an earlier timing than when the center-end temperature difference is equal to or greater than the temperature difference threshold. The image forming apparatus according to claim 4 .

6. the first temperature detection unit is disposed in the center of the sheet passing area, The second temperature detection unit is disposed outside the sheet passing area. The image forming apparatus according to claim 4 .

7. The printer further includes a sheet counting unit that counts the number of sheets of paper on which printing has been performed, The control unit When the value counted by the sheet number counter after the heater starts heating reaches a predetermined value, the target temperature is changed from the first temperature to the second temperature. The image forming apparatus according to claim 1 .

8. The printer further includes a time counting unit that counts the time from when the printing operation is started, The control unit When the value counted by the time counting unit after the heater starts heating reaches a predetermined value, the target temperature is changed from the first temperature to the second temperature. The image forming apparatus according to claim 1 .

9. The heater is formed without being divided from one end side to the other end side in the longitudinal direction. The image forming apparatus according to claim 1 .

10. the heating element is a heat roller, The heater is a halogen heater. The image forming apparatus according to claim 1 .

11. The first temperature detection unit is an optical sensor. The image forming apparatus according to claim 1 .

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