Image forming apparatus

Abstract

To accurately control a sheet conveyance speed of a fixing unit to reduce occurrence of an image defect.SOLUTION: An image forming apparatus comprises: an image forming unit that conveys a sheet while forming an image on the sheet; a fixing unit that conveys, while heating, the sheet on which the image is formed by the image forming unit to fix the image to the sheet; a first driving unit that drives to rotate the fixing unit; a first detection unit that detects the sheet conveyed by the fixing unit; and a control unit that controls the number of rotations of the first driving unit to a set number of rotations. The control unit changes the set number of rotations (RPz+1) on the basis of a first detection time (TFOFFz-TFONz) during which the first detection unit detects the sheet and a length of the sheet (LPAPz).SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to an image forming apparatus including a fixing unit that heats a sheet to fix an image.

Background Art

[0002] For example, in image forming apparatuses such as printers, copiers, and multifunction peripherals, there is a type that transfers a toner image to a sheet at a transfer unit and heats and presses the sheet at a fixing unit to fix it, such as a laser beam printer. In such an image forming apparatus, even if the rotation speed of the motor is controlled to be constant due to thermal expansion of the drive roller of the fixing unit, the conveyance speed of the sheet changes. For this reason, there is a risk that the sheet may be pulled between the transfer unit and the fixing unit, or excessive deflection (so-called loop) may occur, resulting in image defects such as image elongation and image contamination. For this reason, a method has been proposed in which the distance (loop amount) from a sensor of a sheet between the transfer unit and the fixing unit is measured by an infrared reflection type distance sensor, and the conveyance speed of the sheet in the fixing unit is adjusted (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the case of measuring the loop amount as in the above Patent Document 1, since the loop amount reflects the cumulative result in the past sheet conveyance, the result does not appear unless the sheet is conveyed for a certain period of time. Therefore, it is difficult to change the rotation speed of the motor with high precision in a short period of time. In recent years, in particular, the miniaturization of products has advanced, the distance between the transfer unit and the fixing unit has become smaller, and it has become necessary to make the formed loop smaller. As a result, with the method of Patent Document 1, the control is not in time, and there is a risk that the sheet is pulled between the transfer unit and the fixing unit, or the deflection (so-called loop) becomes excessive, resulting in image defects. Further, in an image forming apparatus that attempts to convey the sheet at the same speed without forming a loop between the transfer unit and the fixing unit, there is also a problem that the method of Patent Document 1 cannot be used in the first place.

[0005] Therefore, an object of the present invention is to provide an image forming apparatus capable of accurately controlling the conveyance speed of the sheet in the fixing unit and reducing the occurrence of image defects.

Means for Solving the Problems

[0006] One aspect of the present invention includes an image forming unit that conveys a sheet while forming an image on the sheet, a fixing unit that conveys the sheet while heating the sheet on which the image is formed by the image forming unit and fixes the image on the sheet, a first driving unit that rotationally drives the fixing unit, It is arranged at a distance downstream of the fixing unit in the sheet conveyance direction, a first detection unit that detects the sheet conveyed by the fixing unit, and a control unit that controls the rotation speed of the first driving unit to a set rotation speed. The control unit By subtracting the separation distance between the fixing unit and the first detection unit from the length of the sheet, the when the first detection unit detects the sheet The measured distance by which the sheet is conveyed by the conveying force of the fixing unit is calculated, the separation distance is used to calculate the separation distance conveyance time during which the sheet is conveyed, the separation distance conveyance time is subtracted from the first detection time when the first detection unit detected the sheet to calculate the measured time during which the sheet is conveyed by the fixing unit, the measured distance is divided by the measured time to calculate the conveyance speed of the fixing unit, and according to the conveyance speed of the fixing unit, the changes the set rotation speed. The image forming apparatus is characterized by this.

[0007] One aspect of the present invention includes an image forming unit that conveys a sheet while forming an image on the sheet, a fixing unit that conveys the sheet while heating the sheet on which the image is formed by the image forming unit and fixes the image on the sheet, a first driving unit that rotationally drives the fixing unit, a first detection unit that detects the sheet conveyed by the fixing unit, A deflection detection unit that is arranged between the image forming unit and the fixing unit in the sheet conveyance direction and detects the deflection of the sheet; the rotation speed of the first driving unit To control A control unit to be controlled A control unit that executes loop control to form a deflection in the sheet while the sheet is nipped and conveyed by the image forming unit and the fixing unit and includes, and the control unit In the loop control, when the deflection detection unit does not detect the deflection of the sheet, it is controlled to be a first rotation speed that is smaller than the reference rotation speed by a first predetermined amount, and when the deflection detection unit detects the deflection of the sheet, it is controlled to be a second rotation speed that is larger than the reference rotation speed by a second predetermined amount. When the loop control is executed on the first sheet, the first detection unit Based on both the first detection time when the first sheet was detected and the rotation speed of the first driving unit by the loop control while the first sheet was being detected by the first detection unit, the reference rotation speed in the second sheet conveyed after the first sheet is changed, and an image forming apparatus characterized by this.

Advantages of the Invention

[0008] According to the present invention, the conveyance speed of the sheet in the fixing unit can be controlled with high precision, and the occurrence of image defects can be reduced.

Brief Description of the Drawings

[0009]

Figure 1

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Figure 14

Mode for Carrying Out the Invention

[0010] <First Embodiment> Hereinafter, a first embodiment, which is one mode for carrying out the present invention, will be described.

[0011] [Schematic of the Image Forming Apparatus] First, the schematic configuration of the image forming apparatus 100 will be described with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view showing the image forming apparatus according to the first embodiment. The image forming apparatus 100 shown in FIG. 1 is a monochrome electrophotographic (laser beam method) printer having a plurality of paper feed cassettes. Note that the image forming apparatus is not limited to a printer, and may be, for example, a copier, a facsimile apparatus, a printing machine, or the like. Further, the image forming apparatus is not limited to performing monochrome printing, and may be capable of color printing.

[0012] As shown in FIG. 1, the image forming apparatus 100 generally includes a sheet feeding unit 100A, a sheet conveying unit 100B, an image forming unit 100C, a fixing unit 100D, and a sheet discharging unit 100E. Further, in the image forming apparatus 100, a registration sensor 106 configured by, for example, an optical sensor or the like and detecting a sheet is disposed upstream of the image forming unit 100C in the sheet conveying direction. Also, in the image forming apparatus 100, a fixing discharge sensor 115 configured by, for example, an optical sensor or the like and detecting a sheet is disposed downstream of the fixing unit 100D in the sheet conveying direction.

[0013] In the image forming apparatus 100, a loop sensor 114 as a deflection detection unit for detecting a deflection (loop) of the sheet 101 is disposed between the image forming unit 100C and the fixing unit 100D in the sheet conveying direction. The loop sensor 114 has, for example, a flag member biased by a spring or the like, and is configured to detect no loop when the flag member is pressed by the sheet 101, and to detect a loop when the flag member protrudes into the conveyance path without being pressed by the sheet 101.

[0014] The sheet feeding unit 100A includes a paper feed cassette 102 that stores a plurality of sheets of paper 101 and a paper feed roller 103 that feeds the paper 101. When a CPU 201 (see FIG. 2) described later receives a print job, the sheet feeding unit 100A separates the sheets of paper 101 stored and supported in the paper feed cassette 102 one by one by the paper feed roller 103 and feeds them toward the image forming unit 100C.

[0015] The sheet conveying unit 100B includes a paper feed conveying roller 104 and a pair of registration rollers (hereinafter referred to as "registration rollers") 105. The sheet conveying unit 100B conveys the sheet 101 fed from the sheet feeding unit 100A to the image forming unit 100C in synchronization with the toner image formed by the image forming unit 100C described later by the registration rollers 105.

[0016] The image forming unit 100C includes an optical unit 107, a process cartridge 108, and a transfer roller 110. The process cartridge 108 is provided with a photosensitive drum 109 as an image carrier that carries a toner image. The photosensitive drum 109 is rotationally driven by a main motor 205 (see FIG. 2) as a second driving unit, and the conveyance speed of the paper 101 is controlled. A CPU 201 (see FIG. 2), which will be described later, generates an image signal from the received print job, and irradiates the photosensitive drum 109 with laser light based on the image signal from the optical unit 107 in accordance with the position of the paper 101 detected by the registration sensor 106. Thereby, an electrostatic latent image is drawn on the photosensitive drum 109. The electrostatic latent image drawn on the photosensitive drum 109 is developed with toner by the developing unit of the process cartridge 108, and a toner image is formed on the photosensitive drum 109. Then, in a transfer nip N1 formed by the photosensitive drum 109 and the transfer roller 110, the toner image is transferred onto the paper 101 to form an image, and the paper 101 is conveyed at the rotation speed of the photosensitive drum 109.

[0017] The fixing unit 100D includes a fixing unit 111 having a fixing sleeve 112 that is a driven roller and a fixing pressure roller 113 that is a driving roller. The fixing sleeve 112 incorporates a fixing heater (not shown) as a heat source. On the other hand, the fixing pressure roller 113 is disposed opposite to the fixing sleeve 112 so as to be pressed against the fixing sleeve 112, and forms a fixing nip N2 between the fixing sleeve 112. The fixing pressure roller 113 is rotationally driven by a fixing motor 206 (see FIG. 2), and the conveyance speed of the paper 101 is controlled. The fixing sleeve 112 is driven to rotate by the rotational drive of the fixing pressure roller 113. When the paper 101 onto which the toner image has been transferred is conveyed to the fixing unit 111 by the photosensitive drum 109, the fixing unit 111 heats and presses the paper 101 to fix the toner image onto the paper 101, and the paper 101 is conveyed at the rotation speed of the fixing pressure roller 113.

[0018] The sheet discharge unit 100E has a pair of fixing and paper discharge rollers 116, a paper discharge conveyance roller 117, and a paper discharge roller 118 as a conveyance unit downstream of the fixing unit. Further, a stacking unit 119 for stacking the discharged paper 101 is formed on the upper surface of the image forming apparatus 100. After the paper 101 that has passed through the fixing unit 100D is confirmed by the fixing paper discharge sensor 115 to have no winding jam inside the fixing unit 111, it is further conveyed downstream in the sheet conveyance direction by the fixing paper discharge roller 116. Then, the paper 101 is further conveyed downstream in the sheet conveyance direction by the paper discharge conveyance roller 117 and the paper discharge roller 118, discharged outside the image forming apparatus 100, and stacked on the stacking unit 119.

[0019] Note that the fixing paper discharge roller 116 is also rotationally driven by a fixing motor 206 (see FIG. 2) described later. The conveyance force (the nipping force of the paper 101) of the pair of fixing paper discharge rollers 116 is configured to be smaller than the conveyance force (the nipping force of the paper 101) of the fixing sleeve 112 and the fixing pressure roller 113 of the fixing unit 111. In other words, the conveyance force of the fixing unit 100D (fixing unit 111) is larger than the conveyance force of the fixing paper discharge roller 116, and when the paper 101 is conveyed across the fixing unit 100D and the fixing paper discharge roller 116, the paper 101 is not pulled by the fixing paper discharge roller 116. Further, the conveyance speed of the paper 101 of the fixing paper discharge roller 116 is configured to be equal to or lower than the conveyance speed of the paper 101 of the fixing unit 100D by a transmission mechanism (not shown) that transmits the rotation of the fixing motor 206 to the fixing pressure roller 113 and the fixing paper discharge roller 116.

[0020] Incidentally, since the outer diameter of the fixing pressure roller 113 expands or contracts due to heat, the conveyance speed of the sheet 101 in the fixing unit 100D (fixing unit 111) may not be constant. Particularly when the length of the sheet 101 in the sheet conveyance direction is long, heat is absorbed by the sheet 101 and the heat from the fixing heater in the fixing sleeve 112 is not transmitted to the fixing pressure roller 113, and the outer diameter of the fixing pressure roller 113 contracts. On the other hand, for example, when cleaning is performed in the image forming unit 100C or when the fixing property is improved, if the interval between the sheets 101 (so-called intersheet) becomes long while the fixing temperature control is being performed, the temperature of the fixing pressure roller 113 rises and the outer diameter of the fixing pressure roller 113 expands. Therefore, it is necessary to monitor the detection result of, for example, the loop sensor 114 and adjust the driving speed of the fixing pressure roller 113 so that the sheet 101 does not get stuck between the fixing unit 111 and the photosensitive drum 109. The details of this control will be described later.

[0021] [Control System of Image Forming Apparatus] Next, the configuration of the control system of the image forming apparatus 100 according to the first embodiment will be described with reference to FIG. 2. FIG. 2 is a block diagram showing the control system of the image forming apparatus according to the first embodiment.

[0022] As shown in FIG. 2, the image forming apparatus 100 is provided with a CPU 201 as a control unit, and a ROM 202, a RAM 203, and an external communication interface unit 204 are connected to the CPU 201 so as to be able to transmit and receive signals. Further, each unit of the image forming unit 100C, the fixing paper discharge sensor 115, the loop sensor 114, the registration sensor 106, the fixing motor 206, and the main motor 205 are connected to the CPU 201 so as to be able to transmit and receive signals.

[0023] The CPU 201 can read the program stored in the ROM 202 and execute the control of each process, which will be described in detail later, according to the content thereof, and execute all the processes of the image forming apparatus 100. In the present embodiment, it is described that only one CPU 201 is mounted, but a configuration in which a plurality of CPUs (control units) are mounted and each control is executed in a shared manner may be employed. Note that the CPU 201 uses the RAM 203 to temporarily store data during the execution of each process.

[0024] The CPU 201 receives a print job from an external computer (not shown) or the like through the external communication interface unit 204 and temporarily stores the print job in the RAM 203. Then, a printing operation is performed according to the content of the print job stored in the RAM 203.

[0025] To perform the printing operation, the CPU 201 operates each part of the main motor 205, the fixing motor 206, and the image forming unit 100C. The main motor 205 transmits a driving force to the paper feed roller 103, the paper feed conveyance roller 104, the registration roller 105, and the photosensitive drum 109 to drive them. Also, the fixing motor 206 transmits a driving force to the fixing pressure roller 113, the fixing paper discharge roller 116, the paper discharge conveyance roller 117, and the paper discharge roller 118 to drive them.

[0026] That is, when performing the printing operation, the CPU 201 detects the position of the sheet 101 based on the input signals (detection results) of the registration sensor 106 and the fixing paper discharge sensor 115. Then, the CPU 201 appropriately controls the main motor 205, the fixing motor 206, the image forming unit 100C, the fixing unit 100D, etc. according to the position of the sheet 101, forms an image on the sheet 101, and conveys it to the outside of the machine.

[0027] [Explanation of the Position of the Sheet and Various Symbols During the Printing Operation] Next, with reference to FIGS. 3 and 4, the position of the sheet 101 during the printing operation and various symbols used in the present embodiment will be described. FIG. 3(A) is a diagram showing a state where the leading edge of the sheet has entered the registration sensor. FIG. 3(B) is a diagram showing a state where the leading edge of the sheet has entered the fixing unit. FIG. 3(C) is a diagram showing a state where the trailing edge of the sheet has passed through the registration sensor. FIG. 4(A) is a diagram showing a state where the leading edge of the sheet has entered the fixing and discharging sensor. FIG. 4(B) is a diagram showing a state where the trailing edge of the sheet has passed through the transfer unit. FIG. 4(C) is a diagram showing a state where the trailing edge of the sheet has passed through the fixing unit. FIG. 4(D) is a diagram showing a state where the trailing edge of the sheet has passed through the fixing and discharging sensor. In the following description, although there are some figures in which a plurality of sheets 101 are drawn, the description will be given only for the preceding sheet 101.

[0028] First, various symbols will be described below. L DR : The distance between the photosensitive drum 109 and the registration sensor 106 L PD : The distance between the fixing pressure roller 113 and the photosensitive drum 109 L FP : The distance between the fixing and discharging roller 116 and the fixing pressure roller 113 L PAPn : The sheet length of the n-th page 2r Pn : The diameter of the fixing pressure roller 113 of the n-th page 2r F : The diameter of the fixing and discharging roller 116 V R : The sheet conveyance speed of the registration roller 105 and the photosensitive drum 109 V Fn : The sheet conveyance speed of the fixing and discharging roller 116 of the n-th page

[0029] FIG. 3(A) shows the timing when the leading edge of the sheet 101 enters the registration sensor 106. At this time, since the sheet 101 is being conveyed by the registration roller 105, the sheet conveyance speed is V Ris constant. FIG. 3(B) shows the timing when the leading edge of the sheet 101 reaches the fixing nip N2 (see FIG. 1) between the fixing sleeve 112 and the fixing pressure roller 113. At this time, the sheet 101 is upstream in the conveyance direction (toward the registration roller 105) from the transfer nip N1 (see FIG. 1) between the photosensitive drum 109 and the transfer roller 110, and the sheet conveyance speed is V R and is conveyed. FIG. 3(C) shows the timing when the trailing edge of the sheet 101 passes through the registration sensor 106. At this time, the sheet 101 is upstream in the conveyance direction from the transfer nip N1, similarly to FIGS. 3(A) and 3(B), and the sheet conveyance speed is V R and is conveyed. Also, since the sheet conveyance speed is constant at V R from the time when the registration sensor 106 turns ON until it turns OFF, the length L PAPn of the n-th page can be calculated from this time.

[0030] FIG. 4(A) shows the timing when the leading edge of the sheet 101 enters the fixing discharge sensor 115. At this time, the sheet 101 is upstream in the conveyance direction from the transfer nip N1, similarly to FIGS. 3(A), 3(B), and 3(C), and the sheet conveyance speed is V R and is conveyed. However, the fixing unit 111 may change the rotation speed (rotational speed) of the fixing motor 206 during the conveyance of the sheet 101, and due to the fact that the diameter 2r Pn of the fixing pressure roller 113 expands and contracts due to heat, the conveyance speed of the sheet 101 may not be constant.

[0031] FIG. 4(B) shows the timing when the trailing edge of the sheet 101 passes through the transfer nip N1. At this time, the leading edge of the sheet 101 has reached the fixing discharge roller 116, but the sheet conveyance speed of the sheet 101 is determined by the rotation speed of the fixing motor 206 and the diameter 2r Pn of the fixing pressure roller 113 throughout the entire area. This is because, as described above, the conveyance force of the fixing unit 111 is stronger than that of the fixing discharge roller 116, and the sheet conveyance speed of the fixing discharge roller 116 is faster than the sheet conveyance speed of the fixing unit 111.

[0032] Figure 4(C) shows the timing when the trailing edge of the sheet 101 exits the fixing nip N2. From this timing, the sheet 101 is not affected by the fixing unit 111, and the sheet conveyance speed is determined by the fixing discharge roller 116. Therefore, the sheet 101 is conveyed at the sheet conveyance speed V Fn . Since the fixing discharge roller 116 is driven by the fixing motor 206, as will be described in detail later, by changing the rotation speed of the fixing motor 206, the sheet conveyance speed V Fn will also vary.

[0033] Figure 4(D) shows the timing when the trailing edge of the sheet 101 exits the fixing discharge sensor 115. At this time, the sheet 101 is similarly conveyed at the sheet conveyance speed V Fn . During the period from Figure 4(C) to Figure 4(D), by keeping the rotation speed of the fixing motor 206 constant, it is possible to easily calculate the timing when the trailing edge of the sheet 101 shown in Figure 4(C) exits the fixing unit 111 from the timing when the fixing discharge sensor 115 turns OFF.

[0034] [Control of the printing operation according to the first embodiment] Subsequently, with reference to FIGS. 5 to 9, the control of the printing operation according to the first embodiment will be described. FIG. 5 is a flowchart showing the main process according to the first embodiment. FIG. 6 is a flowchart showing the determination process for starting sheet conveyance according to the first embodiment. FIG. 7 is a flowchart showing the detection process for the sheet length according to the first embodiment. FIG. 8 is a flowchart showing the detection process for the optimum rotation speed of the fixing motor according to the first embodiment. FIG. 9 is a flowchart showing the calculation process for the rotation speed of the fixing motor according to the first embodiment.

[0035] Note that FIG. 5 is a flowchart showing the main process as the overall operation from when the image forming apparatus 100 is powered on until it is powered off. In the figure, "A" indicates that they are connected. FIG. 6 is a sub-flowchart showing the determination process for starting paper conveyance in the main process of FIG. 5, FIG. 7 is a sub-flowchart showing the detection process for the paper length in the main process, and FIG. 8 is a sub-flowchart showing the details of the detection process for the optimum rotation speed of the fixing motor in the main process. Further, FIG. 9 is a sub-flowchart showing the details of the calculation process for the rotation speed of the fixing motor in the detection process of the optimum rotation speed. Also, assuming that each of these processes is executed by the CPU 201 as a control unit, the following description will be given.

[0036] (Standby state process) First, the standby state process from step S1 to step S3 will be described. When the power is turned on, the CPU 201 checks whether a power switch (not shown) is pressed (S1). If the power switch (not shown) is pressed (Yes in S1), the CPU 201 turns off the power and ends the process. If the power switch (not shown) is not pressed (No in S1), the CPU 201 executes the process of receiving a print job via the external communication interface unit 204 (S2). When a print job is received, the CPU 201 stores the content of the print job in the RAM 203.

[0037] Next, the CPU 201 checks whether a print job is stored in the RAM 203 (S3). If no print job is stored (No in S3), the process returns to the process of checking whether the power switch (not shown) is pressed (S1). If a print job is stored in the RAM 203 (Yes in S3), the process proceeds to step S4.

[0038] (Pre-print process) Next, the pre-print processing from step S4 to step S10 will be described. When a print job is stored in the RAM 203 in the standby state processing described above (Yes in S3), the CPU 201 starts initializing variables for which areas are allocated in the RAM 203 to be used for printing. The contents to be initialized are as follows. · Set the variable "previous registration sensor reading value" to OFF (S4). · Set the variable "previous fixing and paper discharge sensor reading value" to OFF (S5). · Set the variables "x" to 1, "y" to 1, and "z" to 1 (S6). Note that the variable "x" is the paper feed page number, the variable "y" is the page number for paper length detection performed by the registration sensor 106, and the variable "z" is the page number for the fixing motor optimum rotation speed detection process performed by the fixing and paper discharge sensor 115.

[0039] Subsequently, the CPU 201 sets the target rotation speed of the main motor 205 to the rotation speed at which the paper conveyance speed V R is achieved by the registration roller 105 and the photosensitive drum 109, and starts driving the main motor 205 (S7). Subsequently, the CPU 201 calculates the fixing motor rotation speed R Pz as the optimum rotation speed of the first drive unit for the first page, and stores the value in the variable "R P1 " for which an area is allocated in the RAM 203 (S415). The optimum fixing motor rotation speed R PZ (R P1 ) is set to the value at which the fixing pressure roller 113 achieves the paper conveyance speed V R at room temperature (23°C). Note that the variable "R P1 " is for storing the optimum fixing motor rotation speed for the first page. Then, the CPU 201 sets the target rotation speed of the fixing motor 206 to the value of the variable "R P1 " for which an area is allocated in the RAM 203, and starts driving the fixing motor 206 (S9). Subsequently, the CPU 201 turns on a fixing heater (not shown) (S10).

[0040] (During printing processing) Next, the printing process from step S11 to step S15 will be described. After the pre-printing process is completed, specifically, the CPU 201 performs a determination process for starting paper conveyance (S11), which will be described in detail later. By performing this determination process for starting paper conveyance, the sheets 101 corresponding to the number of pages of the print job stored in the RAM 203 can be fed from the paper feed cassette 102 at a predetermined interval and conveyed to the image forming unit 100C.

[0041] Subsequently, the CPU 201 performs image drawing processing (S12). That is, a toner image corresponding to the content of the print job is formed on the photosensitive drum 109, and a process of transferring the toner image onto the sheet 101 is performed. Next, the CPU 201 performs a paper length detection process (S13), which will be described in detail later. By performing this paper length detection process, the paper length of the fed sheet 101 is calculated.

[0042] Next, the CPU 201 performs a detection process for the optimum rotation speed of the fixing motor (S14), which will be described in detail later. By performing this detection process for the optimum rotation speed of the fixing motor, the current appropriate rotation speed of the fixing motor 206 can be calculated and applied to the printing of the next page.

[0043] Then, the CPU 201 checks whether the printing of all pages has been completed (S15). If the printing of all pages has not been completed yet (No in S15), the process returns to the determination process for starting paper conveyance (S11), which is the first process in the printing process, to continue the printing operation. If the printing of all pages has been completed (Yes in S15), the process proceeds to step S16 to end the printing process.

[0044] (Post-printing process) Next, the post-print processing from step S16 to step S18 will be described. When the printing of all pages is completed, the CPU 201 turns off the fixing heater (not shown) (S16). Further, the CPU 201 also turns off the main motor 205 and the fixing motor 206 (SS17, S18). And finally, the CPU 201 deletes the print job stored in the RAM 203 (S19). Thereby, the post-print processing is terminated, and the process returns to the confirmation (S1) that the power switch (not shown), which is the start of the standby state processing, is pressed.

[0045] (Judgment Process for Starting Paper Feeding) Next, the details of the judgment process for starting paper feeding in step S11 will be described. When the CPU 201 starts the judgment process for starting paper feeding, it feeds and conveys the paper 101 corresponding to the number of pages of the print job stored in the RAM 203 from the paper feed cassette 102 at predetermined intervals. Also, in this process, it operates on the premise that the variable 'x' for which an area is allocated in the RAM 203 is initialized in the above pre-print processing (see S6 in FIG. 5).

[0046] As shown in FIG. 6, when the CPU 201 starts the process of judging the start of paper feeding, it first checks whether there is a page in the print job stored in the RAM 203 that is the same as the value of the variable 'x' (S21). If there is no page that is the same as the value of the variable 'x' (No in S21), the CPU 201 ends the judgment process for starting paper feeding.

[0047] If there is a page that is the same as the value of the variable 'x' (Yes in S21), the CPU 201 checks whether the value of the variable 'x' is 1 (S22). This is for starting paper feeding and conveyance unconditionally in the case of the first page. And when the value of the variable 'x' is other than 1 (No in S22), the CPU 201 checks whether the current time is equal to or greater than the addition result of the variable 'T PICK ' of the paper feeding and conveyance start time one page before stored in the RAM 203 and the paper feeding interval T BTWN and also performs the check (S23). Note that the paper feeding interval T BTWNthe distance between the leading sheet 101 and the trailing sheet 101 is the distance L as the separation distance between the fixing discharge roller 116 and the fixing pressure roller 113 FP is a fixed value that can be ensured more.

[0048] When neither of the conditions in steps S22 and S23 is satisfied (No in S22 and No in S23), the CPU 201 ends the process of determining the start of paper conveyance. On the other hand, when either one of the conditions is satisfied (Yes in S22 or Yes in S23), the CPU 201 drives the paper feed roller 103 by pulling a paper feed solenoid (not shown) for a predetermined time to start paper conveyance (S24). Subsequently, the CPU 201 adds 1 to the value of the variable 'x' (S25), and updates the variable 'T PICK ' of the start time of paper feed and conveyance one page before to the current time (S26). Thus, the CPU 201 ends the process of determining the start of paper conveyance.

[0049] (Paper length detection process) Subsequently, the details of the process of determining the start of paper conveyance in step S13 above will be described. This paper length detection process is a process of calculating the paper length of the paper 101 based on the ON / OFF timing of the registration sensor 106 and the paper conveyance speed, and storing the result in the area allocated in the RAM 203. Note that this process operates on the premise that the variable 'y' and the variable 'previous registration sensor reading value' for which areas are allocated in the RAM 203 are initialized in the pre-printing process of FIG. 5 (see S5 and S6).

[0050] As shown in FIG. 7, when the CPU 201 starts the paper length detection process, first, the CPU 201 compares the value of the variable 'previous registration sensor reading value' with the result read by the current registration sensor 106 (S31). As a result of the comparison, if they are the same (that is, when there is no change in the signal of the registration sensor 106) (No in S31), the CPU 201 updates the variable 'previous registration sensor reading value' with the result read by the current registration sensor 106 (S37), and ends the paper length detection process.

[0051] On the other hand, when the comparison result in step S31 is different (that is, when there is a change in the signal of the registration sensor 106) (Yes in S31), the CPU 201 checks whether the result read by the registration sensor 106 is ON (S32). When the read result of the registration sensor 106 is ON (that is, when the registration sensor 106 changes from OFF to ON) (Yes in S32), the CPU 201 stores the current time in the variable 'T RONy ' in the RAM 203 for which an area has been allocated (S33). Note that the variable 'T RONy ' stores the ON time of the registration sensor 106 on the page of the value of the variable 'y'. Subsequently, the CPU 201 updates the variable 'previous registration sensor read value' with the result read by the current registration sensor 106 (S37), and ends the paper length detection process.

[0052] Also, when the result read by the registration sensor 106 in step S32 is not ON (that is, when it changes from ON to OFF) (No in S32), the CPU 201 stores the current time in the variable 'T ROFFy ' in the RAM 203 for which an area has been allocated (S34). Note that the variable 'T ROFFy ' stores the OFF time of the registration sensor 106 on the page of the value of the variable 'y'.

[0053] Next, the CPU 201 stores the paper length of the page with the value of the variable 'y' in the variable 'L PAPy ' in the RAM 203 for which an area has been allocated (S35). The paper length is calculated by the formula "V R ×(T ROFFy -T RONy )". That is, the paper conveyance speed V R of the photosensitive drum 109 which is the conveyance speed of the image forming unit, and the time (T ROFFy -T RONy ) as the second detection time from the ON of the registration sensor 106 to the OFF of the registration sensor (see FIGS. 3(A) to 3(C)) are multiplied. Thereby, the length of the paper 101 is calculated. Subsequently, the CPU 201 adds 1 to the value of the variable 'y' (S36). Then, the CPU 201 updates the variable 'previous registration sensor read value' with the result read by the current registration sensor 106 (S37), and ends the paper length detection process.

[0054] (Detection Process of Optimal Rotation Speed of Fixing Motor) Next, the details of the detection process of the optimal rotation speed of the fixing motor in step S14 will be described. This detection process of the optimal rotation speed of the fixing motor calculates the optimal rotation speed as the set rotation speed of the fixing motor 206 based on the ON / OFF timing (sheet detection result) of the fixing paper discharge sensor 115 and the paper length, and stores the result in the area allocated to the RAM 203. In this process, it operates on the premise that the variable 'z' and the variable 'previous fixing paper discharge sensor reading value' allocated areas in the RAM 203 are initialized in the pre-printing process (see S5 and S6 in FIG. 5).

[0055] As shown in FIG. 8, when the CPU 201 starts the detection process of the optimal rotation speed of the fixing motor, it first compares the value of the variable 'previous fixing paper discharge sensor reading value' with the result read by the current fixing paper discharge sensor 115. If the comparison result is the same (that is, when there is no change in the signal of the fixing paper discharge sensor 115) (No in S41), the CPU 201 updates the variable 'previous fixing paper discharge sensor reading value' with the result read by the current registration sensor 106 (S48). Then, the detection process of the optimal rotation speed of the fixing motor ends.

[0056] On the other hand, when the comparison result is different in step S41 (that is, when there is a change in the signal of the fixing paper discharge sensor 115) (Yes in S41), the CPU 201 checks whether the result read by the fixing paper discharge sensor 115 is ON (S42). When the read result of the fixing paper discharge sensor 115 is ON (that is, when the fixing paper discharge sensor 115 changes from OFF to ON) (Yes in S42), the CPU 201 stores the current time in the variable 'T FONz ' allocated an area in the RAM 203 (S43). The variable 'T FONz ' stores the ON time of the fixing paper discharge sensor 115 for the page with the value of the variable 'z'. Subsequently, the CPU 201 updates the variable 'previous fixing paper discharge sensor reading value' with the result read by the current fixing paper discharge sensor 115 (S48) and ends the paper length detection process.

[0057] Also, when the result read by the fixing paper discharge sensor 115 in step S42 is not ON (that is, when the fixing paper discharge sensor 115 changes from ON to OFF), the CPU 201 allocates an area in the RAM 203 to the variable 'T' for storing the current time. FOFFz '. FOFFz The variable 'T' stores the OFF time of the fixing paper discharge sensor 115 for the page with the value of the variable 'z'.

[0058] Next, the CPU 201 performs a calculation process for the fixing motor rotation speed, which will be described in detail later (S45). By performing this calculation process for the fixing motor rotation speed, the optimum rotation speed of the fixing motor for the next page can be obtained. Subsequently, the CPU 201 adds 1 to the value of the variable 'z' (S46). Further, the CPU 201 updates the rotation speed of the fixing motor to the value of the variable 'R'. Pz '. Pz The variable 'R' stores the optimum rotation speed of the fixing motor for the page with the value of the variable 'z'. Then, the CPU 201 updates the variable 'previous fixing paper discharge sensor reading value' with the result read by the current fixing paper discharge sensor 115 (S47), and ends the detection process for the optimum rotation speed of the fixing motor.

[0059] (Calculation process for the fixing motor rotation speed) Next, the details of the calculation process for the fixing motor rotation speed in step S45 will be described. This calculation process for the fixing motor rotation speed calculates the optimum rotation speed of the fixing motor for the next page and stores the result in the area allocated in the RAM 203. In this calculation process for the fixing motor rotation speed, it operates on the premise that the variable 'z' with an area allocated in the RAM 203 is initialized in the pre-printing process of FIG. 5 (see S6).

[0060] As shown in FIG. 9, when the CPU 201 starts the calculation process for the fixing motor rotation speed, first, it calculates the paper conveyance speed V of the fixing paper discharge roller 116 for the page with the value of the variable 'z' allocated in the RAM 203. Fz Fz The calculation formula for the paper conveyance speed V FZ is "V F×R Pz ×gr F 」 is. This "gr F 」 is the gear ratio of a gear (not shown) that transmits the rotation of the fixing motor 206 to the fixing discharge roller 116, and is a fixed value specific to the model. That is, by multiplying the diameter of the fixing discharge roller 116, the rotation speed R Pz of the fixing motor, and the gear ratio gr F , the paper conveyance speed V Fz of the fixing discharge roller 116 is calculated.

[0061] Next, the CPU 201 calculates the paper conveyance time T FPz as the conveyance time of the separation distance from the fixing unit 111 to the fixing discharge roller 116 (S52). The calculation formula for the paper conveyance time T FPz is "T FPz = L FP ÷ V Fz ". That is, the distance L FP (separation distance) between the fixing unit 111 and the fixing discharge roller 116 is divided by the paper conveyance speed V Fz of the fixing discharge roller 116 calculated above. Thereby, the paper conveyance time T FPz for the paper 101 (the rear end thereof) to be conveyed from the fixing unit 111 to the fixing discharge roller 116 is calculated.

[0062] Subsequently, the CPU 201 calculates the average paper conveyance speed V Pz of the fixing unit 111 (S53). The calculation formula for the average paper conveyance speed V Pz is "V Pz = (L PAPz - L FP ) ÷ ((T FOFFz - T FONz ) - T FPz )". That is, the paper length L PAPz of the paper 101 detected in step S13 above is subtracted by the distance L FP between the fixing unit 111 and the fixing discharge roller 116, and the distance (L PAPz - L FP ) as the measured distance conveyed by the conveyance force of the fixing unit 111 is calculated. The distance (L PAPz - L FP) is the state shown in Fig. 4(C) from the state shown in Fig. 4(A). Then, the time (T FOFFz -T FONz )(that is, the first detection time during which the sheet was detected) is subtracted from the paper conveyance time T FPz conveyed by the conveyance force of the fixing and discharging roller 116. That is, the time ((T FOFFz -T FONz )-T FPz ) as the measurement time conveyed by the conveyance force of the fixing unit 111 is calculated. This means that the time from the state shown in Fig. 4(A) to the state shown in Fig. 4(D) is subtracted by the time from the state shown in Fig. 4(C) to the state shown in Fig. 4(D), that is, the time from the state shown in Fig. 4(A) to the state shown in Fig. 4(C) is calculated. And the distance (L PAPz -L FP ) conveyed by the conveyance force of the fixing unit 111 is divided by the time ((T FOFFz -T FONz )-T FPz ) conveyed by the conveyance force of the fixing unit 111 to calculate the average paper conveyance speed V Pz of the fixing unit 111. In short, the calculation formula in step S53 removes the conveyance by the fixing and discharging roller 116 from the conveyance detected by the fixing and discharging sensor 115, and calculates the average paper conveyance speed V Pz by the conveyance of the fixing unit 111. This average paper conveyance speed V Pz is ultimately the actual conveyance speed.

[0063] Next, the CPU 201 calculates the diameter 2r Pz of the fixing pressure roller 113 when the paper 101 is conveyed by the fixing unit 111 of the page with the value of the variable 'z' (S54). The calculation formula for the diameter 2r Pz is '2r Pz =V Pz ÷(π×R Pz ×gr P )'. This 'gr P ' is the gear ratio of a gear (not shown) that transmits the rotation of the fixing motor 206 to the fixing pressure roller 113 and is a fixed value specific to the model. That is, the above calculated average paper conveyance speed VPz is divided by the value obtained by multiplying the number π of pi and the rotation speed R of the fixing motor (before change) when the sheet 101 is conveyed Pz by the gear ratio gr F to calculate the diameter 2r of the fixing pressure roller 113 Pz . Note that the calculated diameter 2r Pz is the average value of the diameters

[0064] Subsequently, the CPU 201 calculates the optimal rotation speed of the fixing motor for the next page and stores it in the variable 'R Pz+1 ' in the area allocated to the RAM 203 (S55). The calculation formula for the optimal rotation speed of the fixing motor for the next page is "R Pz+1 = V PID ÷ (π × 2r Pz × gr P )". This variable 'R Pz+1 ' stores the value of the variable 'z' + the optimal rotation speed of the fixing motor on the first page. Also, V PID is the paper conveyance speed at which the fixing unit 111 does not pull the sheet 101 being conveyed by the photosensitive drum 109, and basically has the same value as the paper conveyance speed V R of the registration roller 105 and the photosensitive drum 109. That is, based on the calculated diameter 2r R of the fixing pressure roller 113, the optimal rotation speed R PID of the fixing motor is calculated so that the paper conveyance speed by the fixing pressure roller 113 is the same as the paper conveyance speed V Pz of the photosensitive drum 109 (= V Pz+1 ). Thus, the CPU 201 finishes the calculation process of the rotation speed of the fixing motor. Note that the optimal rotation speed R Pz+1 calculated in this way is set as the rotation speed R Pz (set rotation speed) of the fixing motor for the next page (see S45 to S47).

[0065] [Summary of the First Embodiment] As described above, in this first embodiment, from the conveyance result of the sheet 101 on this page, the diameter 2r PzCalculate it and change (correct) it so that the rotation speed of the fixing motor on the next page becomes optimal. In short, in the first embodiment, the optimal fixing motor rotation speed is calculated and changed (corrected) based on the time when the fixing paper discharge sensor 115 detects the paper 101 and the length of the paper 101. As a result, for example, the paper conveyance speed by the fixing pressure roller 113 can be controlled with higher precision than controlling the fixing motor rotation speed based on the detection result of the loop sensor 114, and the occurrence of image defects such as image elongation and image smudging can be reduced.

[0066] In particular, after the leading edge of the paper 101 on the next page reaches the fixing unit 111 (see FIG. 3(B)), at least until the trailing edge of the paper 101 passes through the transfer nip N1 (see FIG. 4(B)), the changed fixing motor rotation speed R Pz+1 is controlled so as to be. Thereby, the pulling and excessive bending of the paper 101 between the image forming unit 100C and the fixing unit 100D are reduced, and the occurrence of image defects can be reduced.

[0067] Furthermore, after the leading edge of the paper 101 reaches the fixing nip N2 (see FIG. 3(B)), until the trailing edge of the paper 101 passes through the fixing paper discharge sensor 115, the fixing motor rotation speed is set (changed) to the changed fixing motor rotation speed R Pz+1 is controlled so as to be. And after the trailing edge of the paper 101 passes through the fixing paper discharge sensor 115, the change (correction) of the fixing motor rotation speed is performed. By controlling in this way, the average paper conveyance speed V Pz can be calculated with high precision, that is, the diameter 2r Pz of the fixing pressure roller 113 can be calculated with high precision. Therefore, the paper conveyance speed by the fixing pressure roller 113 can be controlled with high precision.

[0068] <Second Embodiment> Next, a second embodiment in which the first embodiment is partially modified will be described with reference to FIGS. 10 to 14. FIG. 10 is a flowchart showing the main processing according to the second embodiment. FIG. 11 is a flowchart showing the fixing loop control according to the second embodiment. FIG. 12 is a flowchart showing the detection process of the average rotation speed of the fixing motor according to the second embodiment. FIG. 13 is a flowchart showing the detection process of the optimum rotation speed of the fixing motor according to the second embodiment. FIG. 14 is a flowchart showing the calculation process of the rotation speed of the fixing motor according to the second embodiment.

[0069] In the above first embodiment, the paper conveyance speed V by the fixing pressure roller 113 PZ is the same as the paper conveyance speed V of the photosensitive drum 109 R and the fixing motor rotation speed R Pz is set to a constant rotation speed. However, for example, when the outer diameter of the fixing pressure roller 113 fluctuates during the conveyance of the paper 101, particularly when the paper conveyance speed V of the fixing pressure roller 113 PZ becomes faster than the paper conveyance speed V of the photosensitive drum 109 R there is a risk of causing a tension in the paper 101. Therefore, in the second embodiment, a fixing loop control for forming a bend (loop) in the paper 101 between the image forming unit 100C and the fixing unit 100D is executed. Further, when the fixing loop control is executed, since the paper conveyance speed V of the fixing pressure roller 113 PZ is not constant, the average is calculated in the calculation of the paper conveyance speed V PZ , that is, in the calculation process of the fixing motor rotation speed.

[0070] Hereinafter, each process in the second embodiment will be described in detail. In each process, the description of the same process as in the first embodiment will be omitted. First, the standby process from step S1 to step S3 and the pre-print process from step S4 to step S10 in FIG. 10 are the same as those in the first embodiment, so the description will be omitted.

[0071] (Printing Process in the Second Embodiment) The printing process from step S11 to step S15 according to the second embodiment will be described. The determination process for starting paper conveyance in step S11, the image drawing process in step S12, and the paper length detection process in step S13 are the same as those in the first embodiment (see FIGS. 5, 6, and 7).

[0072] Next, in step S101, in this second embodiment, as will be described in detail later, the average rotation speed R of the fixing motor PAVE is detected. As a result, the average value of the rotation speed of the fixing motor 206 during the period when the fixing paper discharge sensor 115 is ON can be obtained, and even when the rotation speed of the fixing motor 206 changes during paper conveyance, the optimum rotation speed can be calculated.

[0073] Subsequently, in step S14, in this second embodiment, using the average rotation speed R of the fixing motor PAVE a detection process for the optimum rotation speed of the fixing motor, which will be described in detail later, is performed. As a result, the current appropriate rotation speed of the fixing motor 206 can be calculated and applied to the printing of the next page. Note that this detection process for the optimum rotation speed of the fixing motor is almost the same as the content of FIG. 8, but the calculation formula used in the calculation process (S45) of the fixing motor rotation speed is slightly different (see FIGS. 9 and 14).

[0074] Next, in this second embodiment, the fixing loop control in step S102 is executed. This fixing loop process switches the rotation speed of the fixing motor 206 according to the value of the loop sensor 114. As a result, even when the outer diameter of the fixing pressure roller 113 fluctuates during the conveyance of the paper 101, it is possible to reduce the occurrence of image elongation, image contamination, etc.

[0075] Then, the CPU 201 checks whether the printing of all pages has been completed (S15). If the printing of all pages has not been completed yet (No in S15), it returns to the paper conveyance start determination (S11), which is the first process during printing, and continues the printing operation. If the printing of all pages has been completed (Yes in S15), in order to end the printing process, it proceeds to the post-printing processes from step S16 to step S19. Since this post-printing process is the same as that in the first embodiment, its description is omitted.

[0076] (Fixing loop process) The fixing loop control is a control that is executed during the period when the sheet 101 straddles (is nipped between) at least both the fixing unit 111 and the photosensitive drum 109 (see FIGS. 3(B) to 4(B)). In this fixing loop control, the rotation speed of the fixing motor 206 is switched to be faster or slower than the optimal fixing motor rotation speed R PZ which is the basis, with the aim of reducing image elongation and image contamination.

[0077] In the second embodiment, during the period when the rear end of the sheet 101 is between the photosensitive drum 109 and the fixing paper discharge sensor 115 (see FIGS. 4(B) to 4(D)), the rotation speed of the fixing motor 206 is controlled to be constant at the set fixing motor rotation speed R Pz Specifically, during the period from when the rear end of the sheet 101 exits the fixing unit 111 until it exits the fixing paper discharge sensor 115, the rotation speed of the fixing motor 206 is made constant at the fixing motor rotation speed R Pz so that the time can be calculated with high precision. Therefore, in the calculation process of the fixing motor rotation speed described later, the time during which the sheet 101 was conveyed by the conveying force of the fixing unit 111 can be calculated with high precision, and the optimal fixing motor rotation speed R PZ+1 can be calculated with high precision.

[0078] Also, in this fixing loop process, it operates on the premise that the variables 'y' and 'z' for which areas are allocated in the RAM 203 are initialized in the pre-printing process of FIG. 10 (see S6). Also, the variable 'TRONz 』(the time when the registration sensor 106 is turned on), variable 『T ROFFz 』(the time when the registration sensor 106 is turned off), variable 『R Pz 』(the number of rotations of the fixing motor) operate on the premise that their values are set in advance.

[0079] As shown in FIG. 11, when the CPU 201 starts the fixing loop process, first, it checks that the leading edge of the sheet 101 is downstream of the fixing unit 111. For this purpose, the CPU 201 checks whether the registration sensor 106 is ON or the value of the variable 『z』 is 1 (S81), and whether the current time is "T RONz +( (L DR + L PD ) ÷ V R )」 or more (S82). That is, in this step S82, after the registration sensor 106 is turned on, the time it takes for the leading edge of the sheet 101 to travel from the registration sensor 106 to the fixing unit 111 at the sheet conveyance speed V R is calculated. If the registration sensor 106 is not ON (No in S81), or the current time is less than "T RONz +( (L DR + L PD ) ÷ V R )」 (No in S82), the CPU 201 overwrites the target rotation speed of the fixing motor 206 with the value of the variable 『R Pz 』 (S88). Then, the CPU 201 ends the fixing loop process.

[0080] When the registration sensor 106 is ON and the current time is "T RONz +( (L DR + L PD ) ÷ V R )」 or more (Yes in S81, Yes in S82), the CPU 201 determines that the trailing edge of the sheet 101 is upstream of the photosensitive drum 109. Therefore, the CPU 201 checks whether the value of the variable 『y』 is the same as the value of the variable 『z』 (S83). If the value of the variable 『y』 is different from the value of the variable 『z』 (No in S83), the CPU 201 checks whether the current time is "T ROFFz +(L DR ÷ V R) Check whether it is as follows (S84). That is, in this step S84, after the registration sensor 106 is turned off, the trailing edge of the sheet 101 calculates the time it takes to travel from the registration sensor 106 to the fixing unit 111 at the sheet conveyance speed V R and proceeds.

[0081] Note that during the period when the trailing edge of the sheet 101 is between the photosensitive drum 109 and the fixing unit 111, it is not necessary to keep the rotation speed of the fixing motor 206 constant at the fixing motor rotation speed R Pz . Therefore, in step S84, the value to be compared with the current time is not "T ROFFz +(L DR ÷V R )", but it may be changed to "T ROFFz +((L DR +L PD )÷V R )".

[0082] If the value of the variable 'y' is the same as the value of the variable 'z', or the current time is "T ROFFz +(L DR ÷V R )" or less (Yes in S84), it is determined that the sheet 101 is in the execution period of the fixing loop control. During the execution period of the fixing loop control, the CPU 201 checks the value of the loop sensor 114 (S85) and sets the rotation speed of the fixing motor 206 according to the result.

[0083] That is, when the loop sensor 114 is ON (that is, when the loop sensor 114 detects a predetermined amount of deflection) (Yes in S85), the value obtained by adding the value of the variable 'R Pz ' and the first predetermined speed α is set as the target rotation speed of the fixing motor 206 (S86). The first predetermined speed α is a fixed correction value such that image contamination of the sheet 101 does not occur even if the outer diameter of the fixing pressure roller 113 fluctuates. That is, the rotation speed of the fixing motor is set to the first rotation speed R PZ +α which is faster than the optimal rotation speed R PZ of the base fixing motor by the first predetermined speed α. Then, the CPU 201 ends the fixing loop process.

[0084] On the other hand, when the loop sensor 114 is not ON (i.e., when the loop sensor 114 does not detect a predetermined amount of deflection) (No in S85), the value obtained by subtracting the second predetermined speed β from the target rotation speed of the fixing motor 206 by the value of the variable "R" Pz 』 is set (S87). The second predetermined speed β is a fixed correction value such that the image elongation of the sheet 101 does not occur even if the outer diameter of the fixing pressure roller 113 fluctuates. That is, the rotation speed of the fixing motor is set to the second rotation speed R PZ -β which is slower than the optimal fixing motor rotation speed R PZ serving as a base by the second predetermined speed β. Then, the CPU 201 ends the fixing loop control.

[0085] After that, when the value of the variable "y" is different from the value of the variable "z" and the current time exceeds "T" ROFFz +(L DR ÷V R ) (No in S84), that is, the trailing edge of the sheet 101 has passed the photosensitive drum 109. Therefore, the CPU 201 overwrites the target rotation speed of the fixing motor 206 with the value of the variable "R" Pz 』 (S88), that is, makes the sheet conveyance speed by the fixing pressure roller 113 constant. Then, the CPU 201 ends the fixing loop control.

[0086] (Detection process of average rotation speed of fixing motor) Next, the details of the detection process of the average rotation speed of the fixing motor in the above step S101 (see FIG. 10) will be described. The detection process of the average rotation speed of the fixing motor obtains the average value of the rotation speed of the fixing motor 206 during the period when the fixing paper discharge sensor 115 is ON. As an acquisition method, during the period when the fixing paper discharge sensor 115 is ON, the target rotation speed of the fixing motor 206 is integrated at intervals of the average speed sampling time T SMPL (for example, 50 ms or less), and finally the integrated value is divided by the number of samples to obtain it. This average speed sampling time T SMPLSet it to a value such that the error in the average rotation speed of the fixing motor to be obtained is sufficiently small. Note that the variable "previous fixing paper ejection sensor reading value" for which an area is allocated in the RAM 203 operates on the premise that it is initialized in the pre-print processing of FIG. 10 (see S5). Also, it operates on the premise that the value is updated in the detection process of the optimum rotation speed of the fixing motor, which will be described in detail later.

[0087] As shown in FIG. 12, when the CPU 201 starts the detection process of the average rotation speed of the fixing motor, it checks whether the value of the variable "previous fixing paper ejection sensor reading value" is the same as the current reading value of the fixing paper ejection sensor 115 (whether there is a change in the signal) (S61). If the value of the variable "previous fixing paper ejection sensor reading value" is different from the current reading value of the fixing paper ejection sensor 115 in step S61 (if there is a change in the signal) (Yes in S61), the CPU 201 first checks whether the reading value of the fixing paper ejection sensor 115 is ON (S62).

[0088] If the reading value of the fixing paper ejection sensor 115 is ON (when the fixing paper ejection sensor 115 is turned ON) (Yes in S62), the CPU 201 sets the target rotation speed of the current fixing motor 206 to the variable "R SUM " allocated an area in the RAM 203 (S63). Subsequently, the CPU 201 sets 1 to the variable "CNT" allocated an area in the RAM 203 (S64), and further updates the variable "T SUM " allocated an area in the RAM 203 to the current time (S65). Then, the CPU 201 ends the detection process of the average rotation speed of the fixing motor.

[0089] On the other hand, in step S61 above, if the value of the variable "previous fixing paper ejection sensor reading value" is the same as the current reading value of the fixing paper ejection sensor 115 (No in S61), the CPU 201 checks whether the reading value of the paper ejection sensor is ON (S67). Subsequently, the CPU 201 checks whether the current time is "T SUM + T SMPL " or more (S68). If the fixing paper ejection sensor 115 is not ON, or the current time is "T SUM + T SMPLIf it is less than (No in S67 or No in S68), the CPU 201 ends the detection process of the average rotation speed of the fixing motor.

[0090] If the fixing paper discharge sensor 115 is ON and the current time is "T SUM + T SMPL " or more (Yes in S67 and Yes in S68), the CPU 201 adds the target rotation speed of the current fixing motor 206 to the variable 'R SUM '. That is, during the period when the fixing paper discharge sensor 115 is ON, the target rotation speed of the fixing motor 206 is cumulatively integrated at intervals of the average speed sampling time T SMPL (predetermined time interval) (S69). Subsequently, the CPU 201 adds 1 to the value of the variable 'CNT' (S70), and further updates the variable 'T SUM ' to the current time (S71). Then, the CPU 201 ends the detection process of the average rotation speed of the fixing motor.

[0091] After that, if the value of the variable 'previous reading value of the fixing paper discharge sensor' is not the same as the current reading value of the fixing paper discharge sensor 115 (there is a change in the signal) (Yes in S61), and it is assumed that the reading value of the fixing paper discharge sensor 115 has become OFF (No in S62). That is, when the fixing paper discharge sensor 115 is turned OFF, the CPU 201 sets the result of "R PAVE ÷ CNT" to the variable 'R SUM ' allocated an area in the RAM 203 (S66). As a result, the variable 'R SMPL ' cumulatively integrated at intervals of the average speed sampling time T SUM ' is divided by the number of integrations, and the average rotation speed R PAVE of the fixing motor is calculated. Then, the CPU 201 ends the detection process of the average rotation speed of the fixing motor.

[0092] In the detection process of the average rotation speed of the fixing motor described above, the average value of the target rotation speed of the fixing motor 206 is calculated. However, for example, using a rotation speed sensor or the like, the actual rotation speed of the fixing motor 206 may be monitored and the average value thereof may be used. Further, the detection process of the average rotation speed of the fixing motor does not necessarily have to be performed by the CPU 201, and for example, it may be configured to obtain the average rotation speed of the fixing motor 206 by another means such as a signal processing board of the rotation speed sensor.

[0093] (Detection Process of Optimal Rotation Speed of Fixing Motor) The detection process of the optimal rotation speed of the fixing motor according to the second embodiment is the same as the detection process of the optimal rotation speed of the fixing motor according to the first embodiment (see FIGS. 13 and 8). However, only the calculation content executed in the calculation process of the rotation speed of the fixing motor in step S45 is different (see FIGS. 14 and 9).

[0094] (Calculation Process of Rotation Speed of Fixing Motor According to Second Embodiment) The calculation process of the rotation speed of the fixing motor according to the second embodiment calculates the optimal rotation speed of the fixing motor on the next page and stores the result in the area allocated by the RAM 203. Note that this process operates on the premise that the variable 'z' for which an area is allocated in the RAM 203 is initialized in the pre-printing process (S6) of FIG. 10.

[0095] As shown in FIG. 14, when the CPU 201 starts the calculation process of the rotation speed of the fixing motor, first, the paper conveyance speed V of the fixing discharge roller 116 on the page of the value of the variable 'z' for which an area is allocated in the RAM 203 Fz is calculated (S51). Next, the CPU 201 calculates the paper conveyance time T from the fixing unit 111 to the fixing discharge roller 116 FPz . Further, the CPU 201 calculates the average paper conveyance speed V of the fixing unit 111 Pz . Note that the processes in steps S51 to S53 are the same as the calculation process of the rotation speed of the fixing motor shown in FIG. 9 in the first embodiment.

[0096] Next, the CPU 201 calculates the average rotation speed R of the fixing motor 206 when the sheet 101 is conveyed by the conveying force of the fixing unit 111 of the page with the value of the variable 'z'. PDz (S201). The average rotation speed R PDz is calculated by the formula "R PDz = (((T FOFFz - T FONz ) × R PAVE ) - (T FPz × R Pz )) ÷ ((T FOFFz - T FONz ) - T FPz )". That is, during the time when the fixing discharge sensor 115 is ON, it multiplies by the average rotation speed R PAVE of the fixing motor during the period of fixing loop control. Also, during the time when the rear end of the sheet 101 is conveyed from the fixing unit 111 to the fixing discharge sensor 115, it multiplies by the constant rotation speed R PZ of the fixing motor. Further, it subtracts the latter from the former, and calculates the integration of the rotation speed of the fixing motor during the period when the sheet 101 is conveyed by the conveying force of the fixing unit 111 (see FIGS. 3(B) to 4(C)) ((T FOFFz - T FONz ) × R PAVE ) - (T FPz × R Pz ). Then, it divides by the time ((T FOFFz - T FONz ) - T FPz ) when the sheet 101 is conveyed by the conveying force of the fixing unit 111 to calculate the average rotation speed R PDz .

[0097] Next, the CPU 201 calculates the diameter 2r of the fixing pressure roller 113 when the sheet is conveyed by the fixing unit 111 of the page with the value of the variable 'z'. Pz (S202). The calculation formula for the diameter 2r Pz is '2r Pz = V Pz ÷ (π × R PDz × gr P )'. That is, in the first embodiment, with a constant rotation speed R Pz of the fixing motor, the diameter 2r Pzis calculated (see S54 in FIG. 9). In contrast, in the second embodiment, the average rotation speed R of the fixing motor 206 calculated as described above PDz and the diameter 2r of the fixing pressure roller 113 Pz are calculated.

[0098] Then, in the same manner as in the first embodiment, the CPU 201 determines the diameter 2r of the fixing pressure roller 113 Pz Based on this, the optimum fixing motor rotation speed R for the next page PZ+1 is calculated and stored as a variable "R Pz+1 " in the area allocated to the RAM 203 (S55). Then, the CPU 201 ends the process of calculating the fixing motor rotation speed.

[0099] [Summary of the Second Embodiment] As described above, also in this second embodiment, from the conveyance result of the sheet 101 of the current page, the diameter 2r of the fixing pressure roller 113 Pz is calculated and changed (corrected) so that the fixing motor rotation speed for the next page becomes optimal. In short, in this first embodiment, based on the time when the fixing paper ejection sensor 115 detects the sheet 101 and the length of the sheet 101, the optimal fixing motor rotation speed is calculated and changed (corrected). Thereby, for example, compared to controlling the fixing motor rotation speed based on the detection result of the loop sensor 114, the paper conveyance speed by the fixing pressure roller 113 can be controlled with high precision, and the occurrence of image defects such as image elongation and image contamination can be reduced.

[0100] Also, in the present embodiment, since the fixing loop control is performed while the sheet 101 straddles the fixing unit 111 and the photosensitive drum 109, further reduction of image elongation and image contamination can be achieved. Also, by performing this fixing loop control, the rotation speed of the fixing motor will fluctuate. However, while the fixing paper ejection sensor 115 is ON, the average rotation speed R of the rotation speed of the fixing motor 206 acquired at intervals of the average speed sampling time T SMPL is calculated. Then, based on this, the diameter 2r of the fixing pressure roller 113 PDz is calculated. And based on that, the diameter 2r of the fixing pressure roller 113 PzCalculate it, thereby obtaining the fixing motor rotation speed R PZ+1 Calculate. Thus, even if the fixing motor rotation speed fluctuates, the optimal fixing motor rotation speed R PZ+1 on the next page can be calculated with high precision.

[0101] Note that the other configurations, operations, and effects in the second embodiment are the same as those in the first embodiment described above, and thus the description thereof is omitted.

[0102] <Possibility of other embodiments> Note that in the first embodiment, when calculating the average paper conveyance speed V Pz of the fixing unit 111, it is not calculated from when the trailing edge of the paper 101 exits the fixing unit 111 until it exits the fixing discharge sensor 115 (see FIGS. 4(C) to 4(D)). That is, the paper length L PAPz of the paper 101 minus the distance L FP between the fixing unit 111 and the fixing discharge roller 116. Also, the time from when the fixing discharge sensor 115 is turned ON until it is turned OFF (T FOFFz -T FONz ) minus the paper conveyance time T FPz conveyed by the fixing discharge roller 116. Then, the average paper conveyance speed V Pz of the fixing unit 111 is calculated from the subtracted distance and time. However, simply dividing the paper length L PAPz of the paper 101 by the time from when the fixing discharge sensor 115 is turned ON until it is turned OFF (T FOFFz -T FONz ) to calculate the average paper conveyance speed V Pz of the fixing unit 111 is also acceptable. In this case, it will also include the calculation from when the trailing edge of the paper 101 exits the fixing unit 111 (see FIG. 4(C)) until it exits the fixing discharge sensor 115 (see FIG. 4(D)). However, the paper conveyance speed V FZ by the fixing discharge roller 116 is only slightly slower than the average paper conveyance speed V Pz of the fixing unit 111, and the distance L PAPz between the fixing unit 111 and the fixing discharge roller 116 with respect to the paper length LFP is also small. Therefore, even if this part is included in the calculation target, the error is slight.

[0103] Also, in the second embodiment, when calculating the average rotation speed R of the fixing motor PAVE , it is calculated while the fixing paper discharge sensor 115 is ON (see FIGS. 4(A) to 4(D)). However, from the time when the trailing edge of the paper 101 exits the fixing unit 111 until it exits the fixing paper discharge sensor 115 (see FIGS. 4(C) to 4(D)), the rotation speed R of the fixing motor PZ is constant. Therefore, when calculating the average rotation speed R of the fixing motor PAVE , this period may not be set as the calculation target period.

[0104] Also, in the first and second embodiments, the diameter 2r of the fixing pressure roller 113 Pz is calculated, and based on this, the optimum rotation speed R of the fixing motor Pz+1 is calculated. However, for example, if a value for increasing or decreasing the current rotation speed R of the fixing motor is calculated from the ratio between the calculated average paper conveyance speed V of the fixing unit 111 Pz and the target paper conveyance speed V PID , the optimum rotation speed R of the fixing motor Pz can also be obtained. Also, for example, if a value for increasing or decreasing the current rotation speed R of the fixing motor is calculated from the ratio between the calculated average rotation speed R of the fixing motor Pz+1 and the rotation speed of the fixing motor corresponding to the target paper conveyance speed V PAVE , the optimum rotation speed R of the fixing motor PID can also be obtained. Therefore, even without calculating the diameter 2r of the fixing pressure roller 113 Pz , the optimum rotation speed R of the fixing motor Pz+1 can be obtained. Pz Pz+1 Pz+1 can be obtained.

[0105] Also, in the first and second embodiments, the average paper conveyance speed V of the fixing unit 111 Pz is calculated, and based on this, the optimum rotation speed R of the fixing motor Pz+1The one that calculates has been described. However, the average paper conveyance speed V of the fixing unit 111 Pz does not have to be calculated. For example, the time (T FOFFz -T FONz ) from when the fixing paper discharge sensor 115 is turned ON until it is turned OFF, the paper length L PAPz , and the optimal fixing motor rotation speed R Pz+1 are prepared as a table. Then, referring to the table from these values, the optimal fixing motor rotation speed R Pz+1 may be obtained.

[0106] Also, in the first and second embodiments, the paper conveyance speed V of the next page PID is made the same as the paper conveyance speed V of the photosensitive drum 109 R , and the optimal fixing motor rotation speed R Pz+1 is obtained and described. However, for example, in order to cause the paper 101 to bend between the fixing unit 111 and the photosensitive drum 109, the paper conveyance speed V of the next page PID may be set to a speed slower than the paper conveyance speed V of the photosensitive drum 109 R .

[0107] Also, in the first embodiment, the calculation result of the optimal fixing motor rotation speed R Pz+1 is calculated from the average paper conveyance speed V of the fixing pressure roller 113 on the previous page Pz and described. Also, in the second embodiment, the calculation result of the optimal fixing motor rotation speed R Pz+1 is calculated from the fixing motor average rotation speed R of the previous page PAVE and described. However, when the paper length L of the paper 101 PAPz is long, the heat of the fixing pressure roller 113 is absorbed by the paper 101, and the diameter 2r of the fixing pressure roller 113 Pz may become small. On the contrary, when the interval (between papers) between the previous page and the next page is wide, the fixing pressure roller 113 is heated, and the diameter 2r of the fixing pressure roller 113 Pz may become large. Therefore, the optimal fixing motor rotation speed R Pz+1When calculating [[ID=]], a correction value may be multiplied or added in consideration of the deviation amount from these heat balances.

[0108] Also, in the first and second embodiments, an example has been described in which the fixing paper discharge sensor 115 is used as the first detection unit to detect the sheet 101 conveyed by the fixing unit 111. However, the present invention is not limited to this, and any sensor may be used as long as it can detect the sheet 101 conveyed by the fixing unit 111, and it may be arranged upstream of the fixing unit 111 in the conveyance direction.

[0109] Also, in the first and second embodiments, an example has been described in which the length of the sheet 101 is detected using the registration sensor 106. However, the present invention is not limited to this, and any sensor may be used as long as it can detect the passing time of the sheet 101, and it may be arranged at any location in the image forming apparatus. Further, a sensor that can directly measure the length of the sheet 101 may be used. Also, the length of the sheet 101 may be, for example, the length obtained from the sheet size information set by an external computer, an operation panel, or the like.

[0110] Also, in the first and second embodiments, an example has been described in which the toner image is directly transferred from the photosensitive drum 109 to the sheet 101. However, the present invention is not limited to this, and a configuration in which the toner image is first transferred to an image carrier such as an intermediate transfer belt and then secondarily transferred to the sheet may also be acceptable.

[0111] The present disclosure can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and having one or more processors in a computer of the system or apparatus read and execute the program. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

Description of Reference Numerals

[0112] 100…Image forming apparatus / 100C…Image forming unit / 100D…Fixing unit / 101…Paper (sheet) / 106…Registration sensor (second detection unit) / 109…Photosensitive drum (image carrier) / 112…Fixing sleeve (driven roller) / 113…Fixing pressure roller (driving roller) / 114…Loop sensor (bending detection unit) / 115…Fixing paper discharge sensor (first detection unit) / 116…Fixing paper discharge roller (fixing downstream conveyance unit) / 201…CPU (control unit) / 205…Main motor (second driving unit) / 206…Fixing motor (first driving unit) / 2r Pn …Diameter / L FP …Distance (separation distance) / L PAPz …Paper length (length of sheet) / R PAVE …Average rotational speed of fixing motor (average rotational speed) / R PZ …Rotational speed of fixing motor (rotational speed of first driving unit) / R PZ +α…First rotational speed / R PZ -β…Second rotational speed / R PZ+1 …Set rotational speed / T FPz …Time (separation distance conveyance time) / T SMPL …Average speed sampling time (predetermined time interval) / V Pz …Average paper conveyance speed (actual conveyance speed) / V R …Paper conveyance speed (conveyance speed of image forming unit) / α…First predetermined speed / β…Second predetermined speed

Claims

1. An image forming unit that conveys a sheet while forming an image on the sheet, A fixing unit that conveys the sheet while heating the sheet on which the image has been formed by the image forming unit to fix the image on the sheet, A first driving unit that rotationally drives the fixing unit, A first detection unit that is disposed downstream of the fixing unit in the sheet conveyance direction and detects the sheet conveyed by the fixing unit, A control unit that controls the rotation speed of the first driving unit to a set rotation speed, and includes: The control unit: By subtracting the separation distance between the fixing unit and the first detection unit from the length of the sheet, calculates the measured distance that the sheet has been conveyed by the conveying force of the fixing unit since the first detection unit detected the sheet, Calculates the separation distance conveyance time during which the sheet is conveyed for the separation distance, Subtracts the separation distance conveyance time from the first detection time when the first detection unit detected the sheet to calculate the measured time that the sheet has been conveyed by the fixing unit, Divides the measured distance by the measured time to calculate the conveyance speed of the fixing unit, Changes the set rotation speed according to the conveyance speed of the fixing unit, An image forming apparatus characterized by the above.

2. The fixing unit includes a driving roller and a driven roller that is driven by the driving force of the driving roller, The control unit calculates the diameter of the driving roller from the conveyance speed of the fixing unit and the set rotation speed before the change, and changes the set rotation speed according to the diameter of the driving roller, The image forming apparatus according to claim 1, characterized by the above.

3. The control unit controls the rotation speed of the first driving unit to be the set rotation speed set from when the leading end of the sheet reaches the fixing unit until at least the trailing end of the sheet passes through the image forming unit, and then changes the set rotation speed, The image forming apparatus according to claim 2, characterized by the above.

4. The control unit controls the rotation speed of the first driving unit to be the set rotation speed set from when the leading end of the sheet reaches the fixing unit until the trailing end of the sheet passes through the first detection unit, and after the trailing end of the sheet passes through the first detection unit, changes the set rotation speed, The image forming apparatus according to claim 3, characterized by the above.

5. The fixing unit includes a driving roller and a driven roller that is driven by the driving force of the driving roller, The control unit: While the first detection unit is detecting the sheet, calculates the average rotation speed of the rotation speed of the first driving unit acquired at predetermined time intervals, Calculate the diameter of the drive roller from the conveyance speed of the fixing unit and the average rotation speed, and change the set rotation speed according to the diameter of the drive roller. The image forming apparatus according to claim 1, characterized in that.

6. Comprising a deflection detection unit that detects the deflection of the sheet between the image forming unit and the fixing unit. When the control unit does not detect the deflection of the sheet by the deflection detection unit from when the leading end of the sheet reaches the fixing unit until the trailing end of the sheet passes through the image forming unit, the control unit controls the rotation speed of the first drive unit to be a first rotation speed that is slower than the set rotation speed by a first predetermined speed. When the deflection detection unit detects the deflection of the sheet, the control unit controls the rotation speed of the first drive unit to be a second rotation speed that is faster than the set rotation speed by a second predetermined speed, and then changes the set rotation speed. The image forming apparatus according to claim 5, characterized in that.

7. The control unit controls the rotation speed of the first drive unit to be the set rotation speed from when the trailing end of the sheet passes through the image forming unit until the trailing end of the sheet passes through the first detection unit, and changes the set rotation speed after the trailing end of the sheet passes through the first detection unit. The image forming apparatus according to claim 6, characterized in that.

8. The control unit changes the set rotation speed so that the conveyance speed of the fixing unit becomes the same as the conveyance speed of the image forming unit. The image forming apparatus according to claim 1, characterized in that.

9. Comprising a second detection unit that is disposed upstream of the image forming unit in the sheet conveyance direction and detects the sheet. The control unit calculates the length of the sheet based on the second detection time when the second detection unit detected the sheet and the conveyance speed of the image forming unit. The image forming apparatus according to claim 1, characterized in that.

10. Comprising a fixing downstream conveyance unit that is disposed downstream of the fixing unit in the sheet conveyance direction, conveys the sheet with a conveyance speed faster than that of the fixing unit and a conveyance force weaker than that of the fixing unit. The image forming apparatus according to claim 1, characterized in that.

11. The fixing downstream conveyance unit is rotationally driven by the first drive unit. The image forming apparatus according to claim 10, characterized in that.

12. The image forming unit has an image carrier that carries a toner image to be transferred to the sheet. Comprising a second drive unit that rotationally drives the image carrier. The image forming apparatus according to claim 1, characterized in that

13. An image forming unit that conveys a sheet while forming an image on the sheet, A fixing unit that conveys the sheet while heating the sheet on which the image has been formed by the image forming unit to fix the image on the sheet, A first driving unit that rotationally drives the fixing unit, A first detection unit that detects the sheet conveyed by the fixing unit, A deflection detection unit that is disposed between the image forming unit and the fixing unit in the sheet conveyance direction and detects the deflection of the sheet, A control unit that controls the rotational speed of the first driving unit, and executes loop control to form a deflection in the sheet while the sheet is nipped and conveyed by the image forming unit and the fixing unit, The control unit is In the loop control, when the deflection detection unit does not detect the deflection of the sheet, it controls to a first rotational speed that is smaller than a reference rotational speed by a first predetermined amount, and when the deflection detection unit detects the deflection of the sheet, it controls to a second rotational speed that is larger than the reference rotational speed by a second predetermined amount, When the loop control is executed for the first sheet, based on both the first detection time when the first sheet is detected by the first detection unit and the rotational speed of the first driving unit by the loop control while the first sheet is detected by the first detection unit, the reference rotational speed in the second sheet conveyed after the first sheet is changed, An image forming apparatus characterized in that

14. The control unit changes the reference rotational speed in the second sheet conveyed after the first sheet based on the rotational speed of the first driving unit acquired at predetermined time intervals while the first sheet is detected by the first detection unit, The image forming apparatus according to claim 13, characterized in that

15. The first detection unit is disposed downstream in the sheet conveyance direction from the fixing unit, The control unit controls the rotational speed of the first driving unit to the reference rotational speed while the rear end of the sheet is being conveyed between the fixing unit and the first detection unit, The image forming apparatus according to claim 13, characterized in that

16. The control unit controls the rotational speed of the first driving unit to the reference rotational speed while the rear end of the sheet is being conveyed between the image forming unit and the first detection unit, The image forming apparatus according to claim 13, characterized in that

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