JP7363104B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus including a fixing section that fixes a developer image to a sheet.

Conventionally, a fixing device includes a main heater that heats the center of the heating roller, a sub-heater that heats the end of the heating roller, a first temperature sensor that detects the temperature of the center of the heating roller, and a temperature of the end of the heating roller. There is known a device that includes a second temperature sensor that detects temperature and a control unit that controls each heater (see Patent Document 1). In this technique, the control unit controls the output of each heater so that the temperature detected by each temperature sensor becomes a predetermined fixing temperature during printing.

Japanese Patent Application Publication No. 2005-257902

By the way, when printing continues, heat is accumulated in the end portion of the heating roller through which the paper does not pass, and the temperature of the end portion increases. In this case, the temperature detected by the second temperature sensor becomes high, and the control unit lowers the output of the sub-heater, which lowers the temperature of the part of the edge where the paper passes, causing a problem of fusing failure in that part. arise.

Therefore, an object of the present invention is to suppress fixing failures at the ends of the heating roller (heating section).

In order to solve the above problems, an image forming apparatus according to the present invention includes a process section that forms a developer image on a sheet, a fixing section that fixes the developer image on the sheet, and a control section.
The fixing unit includes a heating unit that heats the sheet, a main heater that heats a center portion of the heating unit in the width direction of the sheet more strongly than an edge portion, and a main heater that heats the edge portion of the heating unit in the width direction of the sheet. a sub-heater that heats more strongly than the center portion; a first temperature detection portion that detects the temperature of the center portion of the heating portion; and a second temperature detection portion that detects the temperature of the end portion of the heating portion. Be prepared.
The control unit controls energization of the main heater so that a first temperature detected by the first temperature detection unit becomes a first target temperature when fixing the sheet, and controls energization of the main heater to detect the second temperature. The energization to the sub-heater is controlled so that the second detected temperature detected at the second target temperature becomes the second target temperature, and the energization amount Ds to the sub-heater per unit time is determined relative to the energization amount Dm per unit time to the main heater. When the ratio Ds/Dm becomes smaller than a predetermined threshold value, the output of the sub-heater is increased.

For example, during continuous printing, if heat is accumulated in the area where the sheet does not pass through (heat is not taken away by the sheet) among the edges of the heating section, the second detected temperature detected by the second temperature detection section becomes the second target temperature. It becomes difficult to drop from around the temperature. In this case, the amount of electricity supplied to the sub-heater per unit time tends to decrease, and the temperature of the sheet passage area at the end of the heating section tends to decrease. On the other hand, in the above-mentioned configuration, the output of the sub-heater is increased when the ratio Ds/Dm becomes smaller than a predetermined threshold value, thereby preventing the temperature of the sheet passage area at the end of the heating section from becoming too low. Therefore, it is possible to suppress the occurrence of fixing defects.

Further, the control unit may raise the second target temperature to a predetermined temperature when the ratio Ds/Dm becomes smaller than the predetermined threshold.

Further, the control unit adjusts the second target temperature so that when the ratio Ds/Dm becomes smaller than the predetermined threshold, the ratio Ds/Dm falls within a predetermined range larger than the predetermined threshold. May be changed.

Further, the image forming apparatus according to the present invention includes a process section that forms a developer image on a sheet, a fixing section that fixes the developer image on the sheet, and a control section.
The fixing unit includes a heating unit that heats the sheet, a main heater that heats a center portion of the heating unit in the width direction of the sheet more strongly than an edge portion, and a main heater that heats the edge portion of the heating unit in the width direction of the sheet. a sub-heater that heats more strongly than the center portion; a first temperature detection portion that detects the temperature of the center portion of the heating portion; and a second temperature detection portion that detects the temperature of the end portion of the heating portion. Be prepared.
The control unit controls energization of the main heater so that a first temperature detected by the first temperature detection unit becomes a first target temperature when fixing the sheet, and controls energization of the main heater to detect the second temperature. The energization to the sub-heater is controlled so that the second detected temperature detected by the sub-heater becomes the second target temperature, and when the amount of energization Ds per unit time to the sub-heater becomes smaller than a predetermined value, the sub-heater Increase the output of

For example, during continuous printing, if heat is accumulated in the area where the sheet does not pass through (heat is not taken away by the sheet) among the edges of the heating section, the second detected temperature detected by the second temperature detection section becomes the second target temperature. It becomes difficult to drop from around the temperature. In this case, the amount of electricity supplied to the sub-heater per unit time tends to decrease, and the temperature of the sheet passage area at the end of the heating section tends to decrease. On the other hand, in the above-described configuration, the output of the sub-heater is increased when the amount of current Ds per unit time to the sub-heater becomes smaller than a predetermined value, so that the temperature of the sheet passage area at the end of the heating section is increased. It is possible to prevent the temperature from becoming too low, and it is possible to suppress the occurrence of fixing failure.

Further, the control unit may raise the second target temperature to a predetermined temperature when the energization amount Ds becomes smaller than the predetermined value.

Further, when the energization amount Ds becomes smaller than the predetermined value, the control unit may control the ratio Ds of the energization amount Ds per unit time to the sub-heater to the energization amount Dm per unit time to the main heater. The second target temperature may be changed so that /Dm falls within a predetermined range.

Furthermore, in the case of continuously printing a plurality of sheets, the control unit may maintain the second target temperature after raising the second target temperature until the continuous printing is completed.

Furthermore, when the second target temperature is increased in the previous print job, the control unit may lower the second target temperature in accordance with the elapsed time from the end of the previous print job.

According to this, the second target temperature is lowered according to the elapsed time since the end of the previous print job, so the second target temperature used in the next print job is lowered according to the heat storage status at the end of the heating section. You can set it to an appropriate value.

Further, in the main heater, the output at the end portions in the width direction is 10% or more and less than 50% of the output at the center portion, and the sub heater is configured such that the output at the center portion in the width direction is less than the output at the end portions. It may be 30% or more and 60% or less of the output.

Further, the second temperature detection section may be located outside the printing range in the width direction.

In this configuration, the second temperature detection section easily detects the temperature of the region of the end portion of the heating section where the sheet does not pass, and the above-described problem is likely to occur, so the above-described energization process is particularly effective.

According to the present invention, it is possible to suppress fixing failures at the ends of the heating section.

FIG. 1 is a diagram showing a laser printer according to the present embodiment. It is a figure showing the composition around a heating part. It is a graph showing the output of each heater. FIG. 3 is a block diagram showing the configuration of a control section. It is a flowchart which shows energization processing. It is a flowchart which shows the 2nd target temperature setting process. It is a figure which shows the 2nd target temperature setting table. It is a time chart showing an example of changes in each temperature and the amount of energization during continuous printing. It is a flow chart which shows the energization processing concerning the 1st modification. It is a figure showing the 2nd target temperature setting table concerning the 1st modification. It is a flow chart which shows the energization processing concerning the 2nd modification. It is a flow chart which shows the energization processing concerning the 3rd modification.

Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

As shown in FIG. 1, a laser printer 1 is an example of an image forming apparatus that forms an image on a sheet S, and includes a supply section 3, a process section PR, a fixing section 8, and a control section within a main body housing 2. 100.

The supply section 3 is a mechanism for supplying the sheet S to the process section PR, and is provided in the lower part of the main body casing 2. The supply section 3 includes a supply tray 31 that accommodates the sheets S, a sheet pressing plate 32, and a supply mechanism 33. The supply mechanism 33 includes a pickup roller 33A, a separation roller 33B, a first conveyance roller 33C, and a registration roller 33D. In the supply section 3, the sheet S in the supply tray 31 is brought to a pick-up roller 33A by a sheet pressing plate 32, and is sent to a separation roller 33B by the pick-up roller 33A. The sheet S is separated into one sheet by the separation roller 33B, and is transported by the first transport roller 33C. The registration roller 33D aligns the leading edge of the sheet S and then transports the sheet S toward the process section PR.

The process section PR has a function of forming a developer image on the sheet S. The process section PR includes an exposure device 4 and a process cartridge 5.

The exposure device 4 is disposed in the upper part of the main body housing 2, and includes a laser light source (not shown), a polygon mirror, a lens, a reflecting mirror, etc., which are shown without reference numerals. In the exposure device 4, the surface of the photoreceptor drum 61 is exposed by scanning the surface of the photoreceptor drum 61 with laser light based on image data emitted from a laser light source.

The process cartridge 5 is disposed below the exposure device 4 and is removable from the main body casing 2 through an opening created when a front cover 21 provided on the main body casing 2 is opened. The process cartridge 5 includes a drum unit 6 and a developing unit 7.

The drum unit 6 includes a photosensitive drum 61, a charger 62, and a transfer roller 63. The developing unit 7 is detachable from the drum unit 6 and includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, a developer storage section 74 that stores developer, and an agitator 75. There is.

In the process cartridge 5, the surface of the photoreceptor drum 61 is uniformly charged by the charger 62 and then exposed to laser light from the exposure device 4, thereby forming an image on the photoreceptor drum 61 based on the image data. A latent image is formed. Further, the developer in the developer storage section 74 is supplied to the developing roller 71 via the supply roller 72 while being agitated by the agitator 75, and as the developing roller 71 rotates, the developing roller 71 and the layer thickness regulating blade 73 and is carried on the developing roller 71 as a thin layer with a constant thickness.

The developer carried on the developing roller 71 is supplied from the developing roller 71 to the electrostatic latent image formed on the photoreceptor drum 61 . As a result, the electrostatic latent image is visualized, and a developer image is formed on the photoreceptor drum 61. Thereafter, the sheet S supplied from the supply unit 3 is conveyed between the photoreceptor drum 61 and the transfer roller 63, so that the developer image formed on the photoreceptor drum 61 is transferred onto the sheet S. .

The fixing unit 8 is a device that fixes the developer image on the sheet S, and is disposed downstream of the process cartridge 5 in the conveyance direction of the sheet S. The fixing section 8 includes a heating section 81 that heats the sheet S, and a pressure section 82 that sandwiches the sheet S between the heating section 81 and the heating section 81 .

The heating unit 81 is a rotatable cylindrical heating roller made of metal or the like. Inside the heating section 81, a main heater H1 and a sub-heater H2 are provided. The pressure section 82 is a rotatable pressure roller, and has an elastic layer made of elastically deformable rubber or the like on its surface. In the fixing section 8, the sheet S to which the developer image has been transferred is conveyed between the heating section 81 and the pressing section 82, so that the developer image is thermally fixed onto the sheet S. The sheet S on which the developer image is thermally fixed is discharged onto the discharge tray 22 by the second conveyance roller 23 and discharge roller 24 .

As shown in FIG. 2, the main heater H1 is a halogen lamp, and is configured to heat the center portion 81A in the width direction of the heating portion 81 more strongly than the one end portion 81B and the other end portion 81C in the width direction. . Here, the width direction of the heating section 81 refers to the direction along the rotational axis of the heating section 81, and means the same direction as the width direction perpendicular to the conveyance direction on the surface of the sheet S. Moreover, the center part 81A in the width direction of the heating part 81 is a range including the center in the width direction of the heating part 81, and the one end part 81B in the width direction of the heating part 81 is the edge 81D on the one end side of the heating part 81. and the center portion 81A. The other end portion 81C in the width direction of the heating portion 81 is a range between the edge 81E on the other end side of the heating portion 81 and the center portion 81A.

The main heater H1 includes a glass tube H11 and a filament H12 provided within the glass tube H11. In the filament H12, the light emitting parts are concentrated at the center portion in the width direction compared to each end portion in the width direction.

The sub-heater H2 is a halogen lamp, and is configured to heat one end 81B and the other end 81C of the heating section 81 more strongly than the center 81A. The sub-heater H2 includes a glass tube H21 and a filament H22 provided within the glass tube H21. In the filament H22, the light emitting parts are concentrated at each end in the width direction compared to the center part in the width direction.

As shown by the solid line in FIG. 3, the output of the main heater H1 has a distribution in which the output is highest at the center in the width direction and gradually decreases toward both ends in the width direction. Thereby, in the main heater H1, the heating ability for the central portion 81A of the heating section 81 is greater than the heating ability for the one end portion 81B and the other end portion 81C. As shown by the broken line, the output of the sub-heater H2 has a distribution in which both ends in the width direction are higher than the center. As a result, the sub-heater H2 has a heating ability for the one end 81B and the other end 81C of the heating section 81 that is greater than the heating ability for the central portion 81A. The range where the output of the main heater H1 is maximum and the range where the output of the sub-heater H2 is maximum are set so as not to overlap.

In the present embodiment, the boundaries between the central portion 81A of the heating section 81 and each end portion 81B, 81C are positions P1, P2 where the magnitude relationship of the output of the sub-heater H2 with respect to the output of the main heater H1 is reversed.

The output of the one end 81B and the other end 81C of the main heater H1 is 10% or more and 50% or less of the output of the central part 81A, and the output of the central part 81A of the sub-heater H2 is the same as that of the one end 81B and the other end. It is 30% or more and 60% or less of the output of the section 81C. These numerical values are the average output at the center (per predetermined width) and the average output at the ends (per predetermined width).

Note that the heaters H1 and H2 used in this laser printer 1 have specified specifications, and the specifications are determined by a predetermined detection method. As a method for detecting the output of each of the heaters H1 and H2, for example, there is a method in which an optical sensor that detects the light from the heater is placed a predetermined distance away from the heater, and the amount of light is detected. Here, the predetermined distance is the distance from the heater to the inner peripheral surface of the heating section 81.

Returning to FIG. 2, the fixing section 8 further includes a first temperature detection section TS1 and a second temperature detection section TS2. The first temperature detection section TS1 is a sensor that detects the temperature of the central portion 81A of the heating section 81 in the width direction. The first temperature detection section TS1 is located closer to the center portion 81A than one end portion 81B or the other end portion 81C. In other words, the distance from the first temperature detection part TS1 to the center part 81A is smaller than the distance from the first temperature detection part TS1 to the one end part 81B or the other end part 81C.

The first temperature detection portion TS1 is shifted toward the other end portion 81C with respect to the center in the width direction of the heating portion 81, that is, the conveyance center FC. The first temperature detection section TS1 is not in contact with the heating section 81. Specifically, the first temperature detection section TS1 is arranged at a distance from the outer circumferential surface of the heating section 81.

The second temperature detection section TS2 is a sensor that detects the temperature of one end 81B of the heating section 81 in the width direction. The second temperature detection section TS2 is located closer to the one end portion 81B than the center portion 81A. In other words, the distance from the second temperature sensing portion TS2 to the one end portion 81B is smaller than the distance from the second temperature sensing portion TS2 to the central portion 81A.

Specifically, the second temperature detection unit TS2 is located outside the printing range GR of the sheet S. Specifically, in this embodiment, the second temperature detection section TS2 is located outside the width SL of the sheet S. That is, the second temperature detection section TS2 is arranged in a region of the one end portion 81B through which the sheet S does not pass (hereinafter also referred to as "non-passage region R1"). The second temperature detection section TS2 is in contact with the non-passage region R1 of the one end portion 81B.

Note that as the first temperature detection section TS1 and the second temperature detection section TS2, for example, a non-contact type thermistor can be used for the first temperature detection section TS1, and a contact type thermistor can be used for the second temperature detection section TS2. can.

A sheet sensor SA that detects the presence or absence of the sheet S is provided on the upstream side of the fixing section 8 in the conveyance direction. The sheet sensor SA is located within the width SL of the sheet S and within the range of one end 81B of the heating section 81 in the width direction. In other words, the sheet sensor SA is arranged in a region of the one end portion 81B through which the sheet S passes (hereinafter also referred to as "passing region R2"). Note that the sheet sensor SA can be configured to include, for example, a lever that rotates when it comes into contact with the sheet S, and an optical sensor that detects the rotation of the lever.

As shown in FIG. 4, the control unit 100 includes an ASIC 110, a first energization circuit 120, and a second energization circuit 130. The ASIC 110 includes a CPU 111, a first heater controller 112, and a second heater controller 113. The first energizing circuit 120 is a circuit including a switching circuit that switches the input AC voltage between a energizing state and a non-energizing state, and is connected to the main heater H1 and the first heater controller 112. The second energizing circuit 130 is a circuit including a switching circuit that switches the input AC voltage between a energized state and a non-energized state, and is connected to the sub-heater H2 and the second heater controller 113.

The CPU 111 is implemented as a function within the ASIC 110. The CPU 111 outputs a target temperature command value that is the target temperature of the main heater H1 to the first heater controller 112.

The first heater controller 112 is a function or circuit built into the ASIC 110, and controls the first energization circuit 120 so that the first detected temperature Tα at the first temperature detection unit TS1 becomes the target temperature command value. By doing so, the main heater H1 is energized. Specifically, the first heater controller 112 determines the duty ratio of the AC voltage to be energized to the main heater H1 based on the difference between the first detected temperature Tα and the target temperature command value, and performs the first energization at the determined duty ratio. Feedback processing for controlling the circuit 120 is performed. The duty ratio is determined by proportional control such that the larger the value obtained by subtracting the first detected temperature Tα from the target temperature command value, the closer it becomes to 100%. Note that when the first detected temperature Tα is larger than the target temperature command value, the duty ratio is 0%. Further, the determined duty ratio is output to the CPU 111, and the CPU 111 calculates the amount of current Dm per unit time to the main heater H1 based on the duty ratio.

Further, the CPU 111 outputs a target temperature command value that is the target temperature of the sub-heater H2 to the second heater controller 113.

The second heater controller 113 is a function or circuit built into the ASIC 110, and controls the second energization circuit 130 so that the second detected temperature Tβ at the second temperature detection section TS2 becomes the target temperature command value. By doing so, the sub-heater H2 is energized. Specifically, the second heater controller 113 determines the duty ratio of the AC voltage that is energized to the sub-heater H2 based on the difference between the second detected temperature Tβ and the target temperature command value, and operates the second energized circuit at the determined duty ratio. A feedback process is performed to control 130. The duty ratio is determined by proportional control such that the larger the value obtained by subtracting the second detected temperature Tβ from the target temperature command value, the closer it becomes to 100%. Note that when the second detected temperature Tβ is larger than the target temperature command value, the duty ratio is 0%. Further, the determined duty ratio is output to the CPU 111, and the CPU 111 calculates the amount of current Ds per unit time to the sub-heater H2 based on the duty ratio.

Note that the feedback processing performed by the first heater controller 112 or the second heater controller 113 may be implemented in a chip outside the ASIC 110, or may be executed by the CPU.

The control unit 100 has a function of executing a first energization process, a second energization process, an end output increase process, and a second target temperature setting process. In the first energization process, when fixing the sheet S, the main heater is heated so that the first detected temperature Tα detected by the first temperature detection unit TS1 becomes the first target temperature Tt1, which is the target temperature command value of the main heater H1. This is a process for controlling energization to H1. The second energization process is performed when fixing the sheet S to the sub-heater H2 so that the second detected temperature Tβ detected by the second temperature detection unit TS2 becomes the second target temperature Tt2, which is the target temperature command value of the sub-heater H2. This process controls the energization of the

During the execution of the first energization process and the second energization process, the end output increase process is performed by increasing the ratio Ds/Dm of the energization amount Ds per unit time to the sub-heater H2 to the energization amount Dm per unit time to the main heater H1. This is a process of increasing the output of the sub-heater H2 when the value becomes smaller than a predetermined threshold value A. Specifically, when the ratio Ds/Dm becomes smaller than the predetermined threshold A, the control unit 100 increases the output of the sub-heater H2 by increasing the second target temperature Tt2 to a predetermined temperature (Tf+3α).

Here, Tf is the initial value of the second target temperature Tt2. Note that Tf and 3α may be appropriately determined by experiment, simulation, or the like.

After raising the second target temperature Tt2 to a predetermined temperature (Tf+3α) during printing, the control unit 100 maintains the second target temperature Tt2 at the predetermined temperature (Tf+3α) until printing is completed. Therefore, after raising the second target temperature Tt2 during continuous printing, the control unit 100 maintains the second target temperature Tt2 until the continuous printing ends.

The second target temperature setting process is a process that is executed after the end of the previous print job when the second target temperature Tt2 is raised in the previous print job, and is performed according to the elapsed time TM from the end of the previous print job. , is a process of lowering the second target temperature Tt2. Specifically, in the second target temperature setting process, the control unit 100 gradually lowers the second target temperature Tt2 based on the second target temperature setting table and the elapsed time TM shown in FIG. When the target temperature Tt2 reaches the initial value Tf, the second target temperature setting process ends.

Next, the operation of the control section 100 will be explained in detail.
Upon receiving the print command, the control unit 100 executes the energization process shown in FIG. 5 . In the energization process, the control unit 100 first detects the temperatures of the center portion 81A and one end portion 81B of the heating portion 81 using the first temperature detection portion TS1 and the second temperature detection portion TS2 (S1).

After step S1, the control unit 100 executes a first energization process to control energization to the main heater H1 so that the first detected temperature Tα at the first temperature detection unit TS1 becomes the first target temperature Tt1. (S2). After step S2, the control unit 100 executes a second energization process to control energization to the sub-heater H2 so that the second detected temperature Tβ at the second temperature detection unit TS2 becomes the second target temperature Tt2 ( S3).

After step S3, the control unit 100 determines whether the ratio Ds/Dm of the amount of energization Ds per unit time to the sub-heater H2 to the amount Dm of energization per unit time to the main heater H1 is smaller than a predetermined threshold A. Make a judgment (S4). If it is determined in step S4 that Ds/Dm<A (Yes), the control unit 100 sets the second target temperature Tt2 to the predetermined temperature (Tf+3α) (S5).

After step S5, or if the determination is No in step S4, the control unit 100 determines whether printing has ended (S6). If it is determined in step S6 that printing has not been completed (No), the control unit 100 returns to the process in step S1. If it is determined in step S6 that printing has ended (Yes), the control unit 100 turns off the power to each of the heaters H1 and H2 (S7), and ends this process.

If the end portion output increase process (S5) was executed in the previous print job, the control unit 100 executes the second target temperature setting process shown in FIG. 6 . In the second target temperature setting process, the control unit 100 first determines whether the second target temperature Tt2 is higher than the initial value Tf (S11).

If it is determined in step S11 that Tt2>Tf (Yes), the control unit 100 sets the second target temperature according to the elapsed time TM from the end of the previous print job and the second target temperature setting table of FIG. A temperature Tt2 is set (S12). Specifically, when the elapsed time TM is less than the first threshold value TM1, the control unit 100 maintains the second target temperature Tt2 at the predetermined temperature (Tf+3α).

When the elapsed time TM is greater than or equal to the first threshold TM1 and less than the second threshold TM2, the control unit 100 sets the second target temperature Tt2 to the second target temperature Tt2 (=Tf+3α) when TM<TM1. ) is set to a temperature (Tf+2α) lower by α. When the elapsed time TM is greater than or equal to the second threshold TM2 and less than the third threshold TM3, the control unit 100 sets the second target temperature Tt2 to the second target temperature Tt2 (when TM1≦TM<TM2). The temperature (Tf+α) is set to be lower by α than Tf+2α). When the elapsed time TM is equal to or greater than the third threshold value TM3, the control unit 100 sets the second target temperature Tt2 to the initial value Tf.

After step S12, the control unit 100 determines whether there is a print command (S13). If it is determined in step S13 that there is no print command (No), the control unit 100 returns to the process of step S11. If it is determined that there is a print command in step S13 (Yes), or if it is determined that Tt2>Tf is not satisfied in step S11 (No), the control unit 100 ends this process.

Next, an example of the operation of the control unit 100 will be described in detail with reference to FIG. 8. In the following description, it is assumed that the second target temperature Tt2 is set to the initial value Tf before receiving the print command (before time t1).

As shown in FIG. 8, upon receiving the printing command (time t1), the control unit 100 performs the first energization process and the first energization process so that each detected temperature (Tα, Tβ) becomes each target temperature (Tt1, Tt2). 2 Execute the energization process. Specifically, the control unit 100 increases the amount of current (Dm, Ds) to the heaters H1 and H2 at an early stage when the difference between the detected temperature and the target temperature is large, and thereafter when the difference between the detected temperature and the target temperature is small. As the temperature increases, the amount of current (Dm, Ds) applied to the heaters H1 and H2 is decreased. After the detected temperature reaches the target temperature, the control unit 100 controls the amount of current (Dm, Ds) to be applied to the heaters H1 and H2 at substantially constant values in order to maintain the detected temperature near the target temperature.

Specifically, in the process of maintaining the detected temperature near the target temperature, the control unit 100 slightly moves the energization amount (Dm, Ds) up and down by feedback control. As a result, during printing, the temperature of the main heater H1 is maintained near the first target temperature Tt1, and the temperature of the sub-heater H2 is maintained near the second target temperature Tt2 (=Tf).

When printing a plurality of sheets S continuously, heat accumulates in a non-passing region R1 through which the sheets S do not pass among the end portions 81B of the heating section 81 shown in FIG.

When the second detected temperature Tβ becomes higher than the second target temperature Tt2 by a predetermined value or more due to heat accumulation in the non-passing region R1, the control unit 100 lowers the amount of electricity Ds to be applied to the sub-heater H2 by the second energization process (at the time t2-t3). However, when heat is accumulated in the non-passing region R1, a situation occurs in which the second detected temperature Tβ is difficult to fall from around the second target temperature Tt2 even if the amount of electricity Ds to the sub-heater H2 is reduced.

When such a situation occurs, the control unit 100 lowers the energization amount Ds much lower than usual, so that the temperature of the passage area R2 of the end portion 81B of the heating unit 81 through which the sheet S passes is lowered. There is a possibility that Tx (two-dot chain line) may become too low, and there is a possibility that poor fixing may occur.

In this embodiment, when Ds/Dm<A due to a decrease in the energization amount Ds (time t3), the control unit 100 increases the second target temperature Tt2 from the initial value Tf to a predetermined temperature (Tf+3α). As a result, the second target temperature Tt2 becomes higher than the second detected temperature Tβ, so the control unit 100 increases the amount of current Ds applied to the sub-heater H2 by the second energization process (times t3 to t4). Then, the temperature Tx of the passing region R2 increases in accordance with the increase in the amount of current Ds, so that the occurrence of fixing failure is suppressed.

When printing is completed (time t5), the control unit 100 sets each of the energization amounts Dm and Ds to zero. When the elapsed time TM from the end of printing becomes equal to or greater than the first threshold value TM1 (time t6), the control unit 100 lowers the second target temperature Tt2 by α from the previous value and sets it to the temperature (Tf+2α).

When the elapsed time TM becomes equal to or greater than the second threshold value TM2 (time t7), the control unit 100 lowers the second target temperature Tt2 by α from the previous value and sets it to temperature (Tf+α). When the elapsed time TM becomes equal to or greater than the third threshold value TM3 (time t8), the control unit 100 lowers the second target temperature Tt2 by α from the previous value and sets it to the initial value Tf. Note that if a printing command is received during the period from time t5 to t8, that is, before the second target temperature Tt2 is returned to the initial value Tf, the control unit 100 prints a print command that is different from the second target temperature Tt2 at that time, that is, the initial value Tf. The value is used in the second energization process in the next print job.

According to the above, the following effects can be obtained in this embodiment.
Since the output of the sub-heater H2 is increased when Ds/Dm<A, it is possible to prevent the temperature Tx of the passing region R2 at one end 81B of the heating section 81 from becoming too low, and to prevent fixing failure from occurring. Can be suppressed.

According to this, the second target temperature Tt2 is lowered according to the elapsed time TM from the end of the previous print job, so that the second target temperature Tt2 used in the next print job is set at one end 81B of the heating section 81. An appropriate value can be set according to the heat storage situation in the non-passing region R1.

Note that the present invention is not limited to the embodiments described above, and can be utilized in various forms as exemplified below. In the following description, members having substantially the same structure as those in the embodiment described above are denoted by the same reference numerals, and the description thereof will be omitted.

Since the problem due to heat accumulation in the non-passing region R1 occurs during continuous printing, the end output increasing process may be executed using the number of printed sheets S as a control parameter. Specifically, for example, when the number of sheets printed on the sheet S is a predetermined number or more, the end output increase process is executed, and when the number of prints on the sheet S is less than the predetermined number, the end output increase process is executed. does not need to be executed. Note that in the embodiment, since the number of prints on the sheet S is not used as a control parameter, it is possible to appropriately control sheets having different heat capacities.

In the embodiment described above, the edge output increasing process is always executed regardless of the width of the sheet S, but the present invention is not limited to this. For example, when the sheet passes the edge of the heating section, If the edge output increasing process is executed and the sheet does not pass through the edge of the heating section, the edge output increasing process may not be executed. Note that whether or not the sheet passes the edge of the heating section may be determined based on the signal from the sheet sensor SA mentioned above, or it may be determined based on the sheet size specified in the printing command. Alternatively, the determination may be made based on the position of a sheet guide that is movable according to the sheet size.

In the embodiment described above, the second target temperature Tt2 was raised to the predetermined temperature (Tf+3α) in the end output increasing process, but the present invention is not limited to this. For example, as shown in FIG. 9, in the end output increase process (S21), the energization amount ratio Ds/Dm is within a predetermined range (A<Ds/Dm<B) larger than the predetermined threshold value A. The second target temperature Tt2 may be increased.

Specifically, the process in FIG. 9 includes a new process in step S21 in place of step S5 in the process in FIG. 5, and the other processes are the same as the process in FIG. If the control unit 100 determines that Ds/Dm<A in step S4 of the process in FIG. 9 (Yes), it changes the second target temperature Tt2 so that A<Ds/Dm<B (S21).

Also in this embodiment, since the output of the sub-heater H2 increases as the second target temperature Tt2 increases, it is possible to suppress fixing failures at the ends 81B and 81C of the heating section 81. Note that in this embodiment, unlike the embodiment described above, the second target temperature Tt2 is set to an arbitrary value according to the ratio Ds/Dm of the amount of energization, so the second target temperature setting table as shown in FIG. use.

If the elapsed time TM from the end of the previous print job is less than the first threshold TM1, the control unit 100 changes the second target temperature Tt2 to the second target temperature Tt2 (set at the end of the previous print job). (hereinafter also referred to as "temperature Te at the end of printing"). When the elapsed time TM is greater than or equal to the first threshold value TM1 and less than the second threshold value TM2, the control unit 100 sets the second target temperature Tt2 to a value obtained by subtracting β from the temperature Te at the end of printing (Te - β). and the initial value Tf, whichever is larger.

When the elapsed time TM is greater than or equal to the second threshold TM2 and less than the third threshold TM3, the control unit 100 sets the second target temperature Tt2 to a value obtained by subtracting 2β from the temperature Te at the end of printing (Te-2β). and the initial value Tf, whichever is larger. When the elapsed time TM is equal to or greater than the third threshold value TM3, the control unit 100 sets the second target temperature Tt2 to the initial value Tf.

In the embodiment described above, the output of the sub-heater H2 is increased when the ratio Ds/Dm of the energization amount becomes larger than the predetermined threshold value A, but the present invention is not limited to this. For example, the control unit 100 may increase the output of the sub-heater H2 when the amount of current Ds per unit time to the sub-heater H2 becomes smaller than a predetermined value Dth.

In this case, as shown in FIG. 11, instead of step S4 in the process of FIG. 5, a process (S31) for determining whether the energization amount Ds is smaller than a predetermined value Dth may be provided. . Note that the end output increasing process performed after satisfying Ds<Dth may be a process of setting the second target temperature Tt2 to a predetermined temperature (Tf+3α) as shown in FIG. 11, or a process as shown in FIG. The second target temperature Tt2 may be gradually raised so that A<Ds/Dm<B.

Note that the end output increasing process is not limited to the method of changing the second target temperature Tt2 as described above, but may be any process that increases the output of the sub-heater H2. For example, the output of the sub-heater may be increased by setting the parameter to be compared with the second target temperature in the second energization process to be a value obtained by subtracting a predetermined value from the second detected temperature.

In the embodiment described above, the present invention is applied to the laser printer 1, but the present invention is not limited thereto, and the present invention may be applied to other image forming apparatuses, such as copying machines and multifunction peripherals.

The process section is not limited to one using a laser beam, a photoreceptor drum, etc. as in the above embodiment, but may also be one using a light source such as an LED, a belt-shaped photoreceptor, or the like.

In the embodiment described above, a heating roller is used as an example of the heating section, but the present invention is not limited thereto, and the heating section can be, for example, a plate-shaped nip member heated by a heater, or a combination of a nip member and a pressure section. It may also be a fixing belt sandwiched between the two.

In the embodiment, a pressure roller is used as an example of the pressure section, but the present invention is not limited thereto, and the pressure section may be, for example, a pressure belt.

In the embodiment, a halogen lamp is used as an example of the heater, but the present invention is not limited thereto, and the heater may be a solid heating element such as a carbon heater.

In the embodiment, a thermistor is used as an example of the temperature detection section, but the present invention is not limited to this, and any sensor that detects temperature may be used.

In the embodiment, the first temperature detection section TS1 is not in contact with the heating section 81, but the present invention is not limited thereto, and the first temperature detection section may be in contact with the heating section. Further, the second temperature detection section may be made non-contact with the heating section.

In the embodiment, the second temperature detection section TS2 is arranged outside the width SL of the sheet S, but the present invention is not limited thereto. For example, the second temperature detection section TS2 is arranged outside the width SL of the sheet S. In addition, it may be arranged outside the printing range GR.

Furthermore, the elements described in the embodiments and modified examples described above may be implemented in any combination.

1 Laser printer 8 Fixing section 81 Heating section 81A Center section 81B One end section 100 Control section A Predetermined threshold Dm Amount of current Ds Amount of current H1 Main heater H2 Sub heater PR Process section S Sheet TS1 First temperature detection section TS2 Second temperature detection section Tt1 First target temperature Tt2 Second target temperature Tα First detected temperature Tβ Second detected temperature

Claims (10)

a process section that forms a developer image on the sheet;
a fixing unit that fixes the developer image on the sheet;
comprising a control unit;
The fixing section is
a heating section that heats the sheet;
a main heater that heats a central portion of the heating section in the width direction of the sheet more strongly than the end portions;
a sub-heater that heats the end portion of the heating section in the width direction more strongly than the center portion;
a first temperature detection section that detects the temperature of the central portion of the heating section;
a second temperature detection section that detects the temperature of the end portion of the heating section;
The control unit includes:
When fixing the sheet, the amount of electricity Dm per unit time to the main heater is changed from the first target temperature so that the first temperature detected by the first temperature detection section becomes the first target temperature. The duty ratio of the AC voltage applied to the main heater is controlled so as to approach 100% as the value obtained by subtracting the first detected temperature is larger, and the second detected temperature detected by the second temperature detection section is set to a second target temperature. The duty ratio of the AC voltage applied to the sub-heater approaches 100% as the value obtained by subtracting the second detected temperature from the second target temperature increases the amount of current Ds applied to the sub-heater per unit time. control to,
An image forming apparatus characterized in that the output of the sub-heater is increased when a ratio Ds/Dm of the energization amount Ds to the energization amount Dm becomes smaller than a predetermined threshold value. The image forming apparatus according to claim 1, wherein the control unit raises the second target temperature to a predetermined temperature when the ratio Ds/Dm becomes smaller than the predetermined threshold. The control unit changes the second target temperature so that when the ratio Ds/Dm becomes smaller than the predetermined threshold, the ratio Ds/Dm falls within a predetermined range larger than the predetermined threshold. The image forming apparatus according to claim 1, characterized in that: a process section that forms a developer image on the sheet;
a fixing unit that fixes the developer image on the sheet;
comprising a control unit;
The fixing section is
a heating section that heats the sheet;
a main heater that heats a central portion of the heating section in the width direction of the sheet more strongly than the end portions;
a sub-heater that heats the end portion of the heating section in the width direction more strongly than the center portion;
a first temperature detection section that detects the temperature of the central portion of the heating section;
a second temperature detection section that detects the temperature of the end portion of the heating section;
The control unit includes:
When fixing the sheet, the amount of electricity Dm per unit time to the main heater is changed from the first target temperature so that the first temperature detected by the first temperature detection section becomes the first target temperature. The duty ratio of the AC voltage applied to the main heater is controlled so as to approach 100% as the value obtained by subtracting the first detected temperature is larger, and the second detected temperature detected by the second temperature detection section is set to a second target temperature. The duty ratio of the AC voltage applied to the sub-heater approaches 100% as the value obtained by subtracting the second detected temperature from the second target temperature increases the amount of current Ds applied to the sub-heater per unit time. control to,
An image forming apparatus characterized in that the output of the sub-heater is increased when the energization amount Ds becomes smaller than a predetermined value. The image forming apparatus according to claim 4, wherein the control unit raises the second target temperature to a predetermined temperature when the energization amount Ds becomes smaller than the predetermined value. When the energization amount Ds becomes smaller than the predetermined value, the control unit controls a ratio Ds/Dm of the energization amount Ds per unit time to the sub-heater to the energization amount Dm per unit time to the main heater. The image forming apparatus according to claim 4, wherein the second target temperature is changed so that the second target temperature is within a predetermined range. 2. The control unit maintains the second target temperature after raising the second target temperature until the continuous printing is completed when a plurality of sheets are continuously printed. The image forming apparatus according to claim 2 or claim 5. 2. The control unit, when the second target temperature is increased in the previous print job, lowers the second target temperature according to the elapsed time from the end of the previous print job. 2. The image forming apparatus according to claim 5 or claim 7. The main heater has an output at the ends in the width direction that is 10% or more and 50% or less of the output at the center,
The sub-heater according to any one of claims 1 to 8, wherein the output at the center portion in the width direction is 30% or more and 60% or less of the output at the end portions. Image forming device. 10. The image forming apparatus according to claim 1, wherein the second temperature detection section is located outside a printing range in the width direction.

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