Image formation apparatus

Abstract

To perform normal image formation without affecting a recording material in an image formation apparatus that performs conveyance to a secondary transfer position using a plurality of driving sources.SOLUTION: A recording material has a length such that the recording material is conveyed by a registration roller 221 in a state where a trailing end of the recording material has not passed through a reversing roller pair 230. When the recording material is conveyed by the registration roller 221 and the reversing roller pair 230, a sheet feeding conveyance control unit 330 performs second control before performing first control. In the first control, conveyance of the recording material is continued. In the second control, the sheet feeding conveyance control unit 330 controls a sheet feeding motor 332 and a fixing motor 352 so as to decelerate the conveyance speed of the recording material or stop conveyance of the recording material upstream of a registration sensor 222 in a conveyance direction. In the second control, the sheet feeding conveyance control unit 330 controls the sheet feeding motor 332 and the fixing motor 352 so as to accelerate the conveyance speed of the recording material upstream of the registration sensor 222 in the conveyance direction.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, for example, an image forming apparatus using an electrophotographic process or the like.

Background Art

[0002] In an image forming apparatus (for example, a copier or a printer) using an intermediate transfer member, a toner image is formed on a photosensitive drum (image carrier) by a developing roller, and this toner image is primarily transferred to the intermediate transfer member. Thereafter, the toner image on the intermediate transfer member is batchwise secondarily transferred onto a recording material such as paper, and the recording material on which the toner image has been transferred is passed through a fixing device, whereby an image is formed on the recording material. In such an image forming apparatus, due to the loading amount in the cassette, the carry-out amount by the leading sheet, the wear state of the paper feed roller, the type of the medium (recording material), etc., there is variation in the timing of reaching the secondary transfer position after feeding the recording material into the image forming apparatus.

[0003] In Patent Document 1, the following control is performed. In order to align the image transferred to the intermediate transfer member with the leading edge of the recording material, the time difference between the leading edge of the recording material and the image is detected at the timing when the leading edge of the recording material is detected by a conveyance sensor (hereinafter, a registration sensor) disposed upstream in the conveyance direction from the secondary transfer unit. Then, before reaching the secondary transfer roller, the conveyance speed of the recording material is accelerated, decelerated, or temporarily stopped so as to eliminate the detected time difference, thereby improving the transfer accuracy. Hereinafter, such control is referred to as conveyance speed control.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In an image forming apparatus, when a recording material having a size such that conveyance up to the secondary transfer position is performed by a plurality of conveyance rollers with different drive sources and the recording material is conveyed across the plurality of conveyance rollers is used, the following problems occur. That is, when one drive source is stopped and the other drive source is driven in the conveyance speed control, the recording material may be damaged.

[0006] The present invention has been made under such circumstances, and in an image forming apparatus that performs conveyance up to the secondary transfer position with a plurality of drive sources, an object thereof is to perform normal image formation without affecting the recording material.

Means for Solving the Problems

[0007] In order to solve the above-described problems, the present invention includes the following configuration.

[0008] (1) A first conveying means for conveying a recording material, a first driving means for driving the first conveying means, a second conveying means for conveying the recording material, the second conveying means being provided upstream of the first conveying means in the conveying direction of the recording material, a second driving means for driving the second conveying means, the second driving means being different from the first driving means, an intermediate transfer member on which a toner image transferred from a photosensitive drum is carried, a transfer means configured to transfer the toner image on the intermediate transfer member to the recording material at a transfer position, a detection means for detecting the recording material, the detection means being provided upstream of the transfer position in the conveying direction, and a control means configured to perform a first control in response to the leading end of the recording material reaching the detection means, the control means being configured to control the first driving means to accelerate or decelerate the conveying speed of the recording material in the first control. An image forming apparatus comprising: the recording material having a length such that the recording material is conveyed by the first conveying means in a state where the trailing end of the recording material has not passed through the second conveying means; and when the recording material is conveyed by the first conveying means and the second conveying means, the control means performs a second control before performing the first control, in the first control, the conveying of the recording material is continued, and in the second control, the control means controls the first driving means and the second driving means to decelerate the conveying speed of the recording material upstream of the detection means in the conveying direction, or to stop the conveying of the recording material, and in the second control, the control means controls the first driving means and the second driving means to accelerate the conveying speed of the recording material upstream of the detection means in the conveying direction. An image forming apparatus characterized by that.

Effect of the Invention

[0009] According to the present invention, in an image forming apparatus that conveys to a secondary transfer position using a plurality of drive sources, image formation can be performed normally without affecting the recording material.

Brief Description of the Drawings

[0010]

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Best Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of the features described in the embodiments are essential for the solution means of the invention.

[0012] <Reference Example 1> FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 200 according to Reference Example 1. FIG. 1(a) shows a schematic configuration diagram of the entire image forming apparatus 200, and FIG. 1(b) shows an enlarged configuration diagram of one process cartridge which is an image forming means among the entire image forming apparatus 200. However, the components, dimensions, arrangements, etc. in the embodiment should be appropriately changed and do not limit the scope of the present invention.

[0013] (Overall Configuration of Image Forming Apparatus) With reference to FIG. 1, the overall configuration of the image forming apparatus 200 will be described. FIG. 1 schematically shows a cross-sectional view of the schematic configuration of the image forming apparatus 200 according to Reference Example 1, and each configuration is shown in a simplified manner.

[0014] The image forming apparatus 200 according to Reference Example 1 includes a plurality of process cartridges 201 configured to be detachable. The process cartridge 201 is formed by a developing unit 202 and a photosensitive drum unit 203. The photosensitive drum unit 203 includes a photosensitive drum 204 which is an image carrier for an electrostatic latent image, a charging roller 205 which is a charging means for charging the photosensitive drum 204, and a cleaning blade 206 which is a cleaning means for the photosensitive drum 204.

[0015] In the image forming apparatus 200, a transfer roller 211 is installed at a position facing the photosensitive drum 204 in order to transfer the toner image on the photosensitive drum 204 to an intermediate transfer belt 213 which is an intermediate transfer member. Regarding the transfer rollers 211a, 211b, 211c, 211d in FIG. 1(a), the subscripts a to d of the reference numerals represent different colors (for example, yellow, magenta, cyan, black, etc.).

[0016] The photosensitive drum unit 203 is provided with a cleaning blade 206 for cleaning the toner remaining on the photosensitive drum 204 without being transferred to the intermediate transfer belt 213. Further, a developing unit 202 is attached around the photosensitive drum 204. In the developing unit 202, a developing roller 207 as a developing means, a supply member 208, and a developing blade 209 as a regulating member are arranged.

[0017] The developing roller 207 is a roller for carrying the toner as a developer and developing the electrostatic latent image formed on the surface of the photosensitive drum 204 with the carried toner. The supply member 208 is a member arranged around the developing roller 207 for supplying and stripping the toner to the developing roller 207. The developing blade 209 is a regulating member for regulating the supplied toner to a predetermined toner amount.

[0018] The toner images formed on each photosensitive drum 204 are transferred from each photosensitive drum 204 onto the intermediate transfer belt 213 (on the intermediate transfer member), and a full-color image is formed on the intermediate transfer belt 213 (primary transfer).

[0019] The toner image formed on the intermediate transfer belt 213 is transferred by a secondary transfer roller 212 as a transfer means to a recording material R that is conveyed in synchronization (secondary transfer). Hereinafter, the position where the toner image on the intermediate transfer belt 213 is transferred to the recording material R by the secondary transfer roller 212 is referred to as the secondary transfer position (transfer position) or the secondary transfer portion.

[0020] The unfixed toner transferred onto the recording material R (on the recording material) is fixed to the recording material R by applying pressure and heat when passing through the fixing device 214. The fixing device 214 has a heater 226 and is provided downstream of a resist roller 221 and the secondary transfer position, which will be described later, in the conveyance direction of the recording material R.

[0021] An exposure unit 215 for forming an electrostatic latent image corresponding to image data on the charged photosensitive drum 204 is attached to the image forming apparatus 200. The image forming apparatus 200 is attached with a power source (not shown) for applying a predetermined voltage to each of the charging roller 205, the developing roller 207, the developing blade 209, the supply member 208, and the transfer roller 211.

[0022] The control unit 241 controls the driving of the process cartridge 201 and the fixing device 214, voltage control, transfer timing to the recording material R, etc., and includes an engine control unit 302 described later. The control unit 241 is connected to a controller (not shown) and receives information obtained by converting the print image size and the color of the image into laser emission as a print command in response to a print instruction from the user.

[0023] The image forming apparatus 200 includes an operation display unit 251. The operation display unit 251 is provided with various known input means for the user to input various information and various known display means for displaying various information. For example, the user can use the operation display unit 251 to set the paper size and paper type (plain paper, thin paper, thick paper, etc.) of the recording material R for printing.

[0024] For example, the engine control unit 302 described later determines that the recording material R is a long paper based on the information input from the operation display unit 251. The engine control unit 302 can also determine whether the recording material R is a long paper based on the output signal of a registration sensor 222 or a discharge sensor 233 described later. Note that information indicating that the recording material R is a long paper may be input from an external device connected to the image forming apparatus 200 by wire or wirelessly.

[0025] (Description of the image forming operation) The exposure unit 215 that exposes the charged photosensitive drum 204 performs exposure on the photosensitive drum 204 in the main scanning direction using a laser beam according to the image data. The exposure in the main scanning direction is performed in synchronization with the timing in the sub-scanning direction. As a result, an electrostatic latent image is formed on the photosensitive drum 204. Here, the portion where the image is formed on the photosensitive drum 204 (hereinafter referred to as the image forming portion) becomes the bright potential. Note that the main scanning direction refers to the direction of the rotation axis of the photosensitive drum 204, and the sub-scanning direction refers to the rotational movement direction of the photosensitive drum 204, that is, the direction orthogonal to the rotation axis direction.

[0026] The developing roller 207 attached to the developing unit 202 carries toner as a developer, contacts the photosensitive drum 204 during image formation, and develops the electrostatic latent image with the toner. Since the development is performed by the potential difference between the bright potential and the developing roller 207, a predetermined developing voltage is applied to the developing roller 207. The developing roller 207 rotates in the direction opposite to the photosensitive drum 204, and its surface speed rotates with a speed difference with respect to the surface speed of the photosensitive drum 204. Charge assisting agents such as silica and titanium oxide are used as external additives for the toner, and the fluidity and chargeability of the toner are controlled by the external additives. The toner image developed on the photosensitive drum 204 is sent to the contact portion (primary transfer portion) between the intermediate transfer belt 213 and the photosensitive drum 204 and transferred onto the intermediate transfer belt 213. A predetermined transfer voltage is applied to the transfer roller 211 by a power source (not shown) so that a predetermined potential difference is generated between the transfer roller 211 and the photosensitive drum 204.

[0027] The toner that has not been transferred by the primary transfer unit is removed by the cleaning blade 206. The cleaning blade 206 is attached so as to face the rotation direction of the photosensitive drum 204 (that is, in the counter direction). By bringing the cleaning blade 206 into contact with the photosensitive drum 204 with an appropriate contact pressure in the counter direction, the remaining toner can be steadily removed from the photosensitive drum 204. The removed toner is stored in the waste toner storage chamber 216. By removing the toner by cleaning, the photosensitive drum 204 can be charged again by the charging roller 205 with no toner or the like on its surface.

[0028] By repeating such steps, a toner image can be formed on the intermediate transfer belt 213. Then, toner images of respective colors are sequentially superimposed on the intermediate transfer belt 213 from a plurality of process cartridges to form a superimposed full-color image. The full-color image is transferred to a recording material R that is conveyed in synchronization by the secondary transfer roller 212.

[0029] (Explanation of the conveyance operation of the recording material) The paper feed unit 217 is a paper feed cassette as a recording material storage means for storing the recording material R, particularly for storing the recording paper on which an image is to be formed. When feeding paper from the paper feed unit 217, the pickup roller 219 driven by a drive source (not shown) is driven, causing the bottom plate 220 to rise and pushing up the recording material R installed in the paper feed unit 217. The uppermost sheet of the pushed-up recording material R comes into contact with the pickup roller 219, and is separated and fed one by one by the rotation of the pickup roller 219, and is conveyed to the registration roller 221 which is the first conveyance means. The recording material R fed from the paper feed unit 217 is conveyed by the registration roller (first roller) 221 driven by a paper feed motor (first motor) 332 described later.

[0030] The recording material R is conveyed to the secondary transfer unit so that the leading edge of the image coincides with the leading edge of the recording material R, based on the timing when the arrival of the leading edge of the recording material R is detected by the resist sensor 222 using the conveyance speed control described later. The resist sensor 222 is provided upstream of the secondary transfer unit in the conveyance direction and functions as a detection means for detecting the recording material R. The resist sensor 222 can detect the timing when the conveyance of the recording material R by the resist roller 221 is started (the timing when the leading edge of the recording material R reaches the resist roller 221).

[0031] In the secondary transfer unit, the toner image is transferred from the intermediate transfer belt 213 to the recording material R. Thereafter, the recording material R with the unfixed toner image transferred thereon is sent to the fixing device 214. The fixing device 214 fixes the secondarily transferred visible image (toner image) to the recording material R. The fixing device 214 includes a fixing roller 223 that heats the recording material R and a pressure roller 224 for pressing the recording material R against the fixing roller 223. The fixing roller 223 and the pressure roller 224 of the fixing device 214 are arranged so as to be rotatable in the direction of the arrow by a fixing motor (second motor) 352 described later. A heater 226 is built into the fixing roller 223. Thereby, the recording material R holding the visible image is conveyed by the fixing roller 223 and the pressure roller 224, and the melted toner is fixed to the recording material R by applying heat and pressure.

[0032] The discharge roller pair 227 rotates by a fixing motor 352 described later and discharges the recording material R after the visible image is fixed by the fixing device 214 to the stacking unit 228. The above is the operation when printing on only the first side of the recording material R (hereinafter referred to as single-sided printing) or when printing on both the first side of the recording material R and the second side which is the opposite side of the first side (hereinafter referred to as double-sided printing) is completed.

[0033] (Explanation of the inversion path) The image forming apparatus 200 of Reference Example 1 is capable of performing double-sided printing in which images are formed on the first surface (also referred to as the front surface) and the second surface (also referred to as the back surface) opposite to the first surface of the recording material R. The reversing unit includes a flapper 229, a pair of reversing rollers 230 including a reversing roller (second roller) which is the second conveying means, and pairs of conveying rollers 231, 232 including a conveying roller (first roller) which is the first conveying means. The pairs of conveying rollers 231, 232 are provided in the double-sided conveying path.

[0034] The flapper 229 changes the conveying path of the recording material R that has passed through the fixing roller 223 and the pressure roller 224. The flapper 229 is configured to be switchable by a reversing solenoid 345, which will be described later, to either the direction of the pair of discharge rollers 227 or the direction of the pair of reversing rollers 230.

[0035] The fixing motor 352 can rotate the reversing roller of the pair of reversing rollers 230 in the direction of drawing the recording material R into the reversing unit, or rotate it so as to convey the drawn recording material R in the direction of the pair of conveying rollers 231. The fixing motor 352 can rotate the reversing roller of the pair of reversing rollers 230 in a first direction and a second direction opposite to the first direction. The switching of the rotation direction of the pair of reversing rollers 230 is configured to be interlocked with the movement of the flapper 229.

[0036] The pairs of conveying rollers 231, 232 are configured to be able to convey the recording material R that has passed through the fixing device 214 in the direction of the secondary transfer roller 212. The pair of discharge rollers 227, the pair of reversing rollers 230, the fixing device 214, the pickup roller 219, the registration roller 221, and the pairs of conveying rollers 231, 232 are supplied with driving force by a drive source (paper feed motor 332, fixing motor 352). The pair of discharge rollers 227, the pair of reversing rollers 230, and the fixing device 214 are driven by the fixing motor 352. The pickup roller 219, the registration roller 221, and the pairs of conveying rollers 231, 232 are driven by the paper feed motor 332.

[0037] Further, the reversing unit includes a duplex clutch 343 described later, and the pair of conveying rollers 231 and 232 disposed on the duplex conveying path are rotated or stopped by the duplex clutch 343.

[0038] (Description of the conveyance of the recording material R in the reversing unit) The conveyance operation of the reversing unit includes reversing the conveyance direction and conveying from the reversing path to the registration roller 221. In the reversing operation of the conveyance direction, the reversing unit drives a reversing solenoid 345 that changes the position of the flapper 229 based on the timing when the leading end of the recording material R reaches the discharge sensor 233. The reversing unit changes the conveyance direction of the recording material R after visible image fixing by the fixing device 214 and guides the recording material R to the pair of reversing rollers 230. The reversing unit stops the reversing solenoid 345 based on the timing when the trailing end of the recording material R passes the discharge sensor 233, changes the rotation direction of the pair of reversing rollers 230, and conveys the recording material R in the direction of the reversing path.

[0039] In the conveyance from the reversing path to the registration roller 221, the reversing unit drives the duplex clutch 343 to supply a driving force to the pair of conveying rollers 231 and 232 to rotate them, and performs the conveyance speed control (first control) described later when the registration sensor 222 detects the recording material R. In the conveyance speed control for the recording material R conveyed from the reversing path, when the stop control is selected once, the duplex clutch 343 is stopped and the supply of the driving force to the pair of conveying rollers 231 and 232 on the reversing path is stopped.

[0040] (Description of the functional block diagram) FIG. 2 is a functional block diagram related to the engine control unit 302 of a laser printer as the image forming apparatus 200. Hereinafter, the functional blocks related to the conveyance control of the recording material R during printing will be described. The controller unit 301 can communicate with the host computer 300 and the engine control unit 302. When the controller unit 301 receives (inputs) print data from the host computer 300, it expands the print data and converts it into image data for image formation. Then, based on the image data, video signals for exposure of four colors for exposure are generated.

[0041] When the generation of the video signal is completed, the controller unit 301 instructs the video interface unit 310 of the engine control unit 302, which serves as a control means, to start printing. The engine control unit 302 incorporates a ROM (Read Only Memory), a RAM (Random Access Memory), includes a microcomputer (not shown) having a microprocessor as a CPU (Central Processing Unit), and a timer (not shown). The engine control unit 302 exchanges information with the controller unit 301 through serial communication and performs the control described below based on the information received from the controller unit 301.

[0042] When the video interface unit 310 receives a print start instruction from the controller unit 301, it transmits the print start instruction to the image formation control unit 320 of the engine control unit 302. Based on the received print start instruction, the image formation control unit 320 activates various actuators and starts the preparation for image formation. When the preparation for image formation is complete, the image formation control unit 320 notifies the controller unit 301 of the completion of image formation preparation via the video interface unit 310. When the controller unit 301 receives the completion of image formation preparation, it transmits a video signal to the video interface unit 310. The image formation control unit 320 performs image formation based on the video signal received by the video interface unit 310.

[0043] The paper feed and conveyance control unit 330 of the engine control unit 302 includes a paper feed unit 217, a drive unit 3302 for the paper feed motor 332, a leading edge detection unit 3303 for the recording material, a conveyance speed control unit 3304 for the paper feed motor 332, and a calculation unit 3305 for calculating the control timing of the conveyance speed. Based on the print start timing received by the image formation control unit 320, the pickup roller 219 is rotated by the pickup solenoid 333 and the paper feed motor 332, which is the first driving means, included in the paper feed and conveyance unit 303. As a result, the recording materials R stacked in the paper feed unit 217 are separated and fed one by one. Thereby, the paper feed and conveyance control unit 330 sends out the recording material R toward the registration sensor 222. The leading edge detection unit 3303 for the recording material detects that the fed recording material R has reached the registration sensor 222.

[0044] The calculation unit 3305 calculates the conveyance speed and the conveyance speed control timing at the timing when the leading end of the recording material R reaches the registration sensor 222. The method for calculating the conveyance speed and the conveyance speed control timing will be described later. The conveyance speed control unit 3304 of the paper feed motor 332 controls the speed of the paper feed motor 332 by the drive unit 3302 of the paper feed motor 332 at the conveyance speed control timing calculated by the calculation unit 3305, so as to align the image leading end and the recording material leading end in the secondary transfer unit. The paper feed conveyance control unit 330 controls the paper feed motor 332 to control the conveyance speed of the recording material R in response to the leading end of the recording material R reaching the registration sensor 222, so that the toner image on the intermediate transfer belt 213 is transferred to the recording material R at the secondary transfer position. Specifically, the paper feed conveyance control unit 330 performs conveyance speed control (S1 described later), which is the first control for accelerating or decelerating the paper feed motor 332 or stopping the conveyance of the recording material R.

[0045] The fixing conveyance control unit 350 of the engine control unit 302 includes a conveyance speed control unit 3502 of the fixing motor 352 and a drive unit 3501 of the fixing motor 352. The fixing conveyance control unit 350 controls the fixing motor 352, which is the second drive means of the fixing conveyance unit 305, based on the print start timing of the image forming control unit 320, and conveys the recording material R by the fixing roller 223 and the discharge roller pair 227 using the fixing motor 352 as a drive source.

[0046] Based on the printing start timing of the image forming control unit 320, the reverse conveyance control unit 340 of the engine control unit 302 controls the duplex clutch 343 and the reverse solenoid 345 based on the detection timings of the discharge sensor 233 and the duplex sensor 342 of the reverse unit 304. Thereby, the reverse conveyance control unit 340 controls the reverse and discharge of the recording material R. The reverse conveyance control unit 340 controls the reverse solenoid 345 to switch the rotation direction of the reverse roller pair 230 having the fixing motor 352 as a drive source, and switches the conveyance path of the recording material R by the flapper 229 to the reverse unit or the stacking unit 228. Also, the conveyance roller pairs 231 and 232 have the paper feed motor 332 as a drive source, and can switch the stop and drive of the conveyance roller pairs 231 and 232 by controlling the duplex clutch 343.

[0047] (Conveyance Speed Control When Conveying Long Paper Duplex) Next, the conveyance speed control when printing long paper duplex will be described with reference to FIGS. 3 and 4. Conveyance speed control is control in which when the leading edge of the recording material R is detected by the registration sensor 222, the motor is accelerated, decelerated, or temporarily stopped to control the conveyance speed of the recording material R, and the leading edge of the recording material R and the leading edge of the image on the intermediate transfer belt 213 are aligned at the secondary transfer unit. FIG. 3 is a timing chart of the conveyance speed control for aligning the leading edge of the recording material R and the leading edge of the image by performing acceleration and deceleration of the motor. FIG. 4 is a timing chart of the conveyance speed control for aligning the leading edge of the recording material R and the leading edge of the image by temporarily stopping the motor.

[0048] In FIGS. 3 and 4, (i) shows the timing of commands transmitted or received by the controller unit 301. (ii) shows the timing of commands transmitted or received by the engine control unit 302. (iii) shows the timing of the image on the intermediate transfer belt 213 (400). (iv) shows the control state of the paper feed conveyance control unit 330 (paper feed on the front side, waiting for inversion, reverse conveyance on the back side, waiting for paper feed, etc.). (v) shows the output signal of the registration sensor 222 (low level or high level) (410), and (vi) shows the output signal of the discharge sensor 233 (low level or high level) (420). (vii) shows the state of the inversion solenoid 345 (430), indicating stop at the low level and drive at the high level. (viii) shows the speed of the paper feed motor 332 (440). Note that the speed of the paper feed motor 332 can take values such as V0 (441), V1 (442), V2 (443), etc. between the maximum speed and the minimum speed of the paper feed motor 332. The horizontal axis indicates time.

[0049] Note that the long paper in this configuration is defined as a recording material R with a length Ls equal to or greater than the distance from the inversion roller pair 230 to the registration sensor 222 on the inversion path. However, the length at which problems occur varies depending on the device configuration. That is, when the length of the recording material R is equal to or greater than the distance from the registration sensor 222 to the second conveyance means (second roller) driven by the second driving means (second motor), the recording material R is long paper.

[0050] The engine control unit 302 determines whether the recording material R is long paper based on information input from the operation display unit 251 or information received from the controller unit 301. The engine control unit 302 can also determine whether the recording material R is long paper based on the output signals of the registration sensor 222 or the discharge sensor 233. Also, sensors other than the registration sensor 222 and the discharge sensor 233 can be used to determine whether it is long paper. In this case, while performing single-sided printing on the recording material R, the engine control unit 302 can measure the length of the recording material R with the registration sensor 222 or the discharge sensor 233 and determine whether the recording material is long paper. That is, the image forming apparatus 200 has a sensor for detecting the length of the recording material, and it can be said that the registration sensor 222 or the discharge sensor 233 is a part of it.

[0051] In the present embodiment, as the sensor for detecting the recording material R, sensors such as the registration sensor 222 and the discharge sensor 233, which have a contact member that moves in contact with the recording material R and a detection unit for detecting the movement of the contact member, can be used. The detection unit can detect the movement of the contact member by optically detecting the contact member or the detected part that moves in conjunction with the contact member.

[0052] FIG. 5 shows the configuration of the registration sensor 222 in the present embodiment. The registration sensor 222 has a contact part 222a that moves in contact with the recording material R, a detected part 222b, and a detection unit 222c that detects the movement of the contact part 222a by detecting the movement of the detected part 222b. The contact part 222a and the detected part 222b are attached to the rotation axis 321a of the driven roller 321 that contacts the registration roller 221.

[0053] In addition, the contact part 222a of the registration sensor 222 in the present embodiment contacts the recording material R and has a function of correcting skew. A plurality of contact parts (shutters) 222a are provided in the direction of the rotation axis of the registration roller 221. The contact part 222a contacts the recording material R before the leading end of the recording material R reaches the nip part of the registration roller pair (registration roller 221 and driven roller 321) and has a function of correcting skew. As the contact part 222a is pushed and moved by the leading end of the recording material R, the recording material R with corrected skew is conveyed by the registration roller pair, and the registration sensor 222 detects the leading end of the recording material R. In the conveyance direction of the recording material R, the registration sensor 222 and the registration roller 221 are arranged immediately before the secondary transfer position. Note that, as the sensor for detecting the recording material R, a sensor that optically detects the recording material R or a sensor that adopts other methods can also be used.

[0054] (Transport speed control: acceleration and deceleration) Using the timing chart of Fig. 3, the transport speed control for aligning the leading edge of the recording material R with the leading edge of the image by performing acceleration and deceleration of the paper feed motor 332 when transporting a long sheet of paper will be described. First, the controller unit 301 transmits a print start command 401 to the engine control unit 302. When the engine control unit 302 receives the print start command 401, it starts print preparation and instructs the paper feed transport control unit 330 to start paper feed preparation.

[0055] Next, when the preparation for image formation is complete, the engine control unit 302 instructs the controller unit 301 to start image formation instruction 402. When the controller unit 301 receives the image formation start instruction 402, it starts transmitting the video signal, and the engine control unit 302 starts image formation (403) based on the received video signal. The image (400) generated by the image formation control unit 320 enters the secondary transfer unit after a predetermined time has elapsed. On the other hand, after starting the paper feed of the recording material R, the paper feed transport control unit 330 continues to transport the recording material R at speed V0 (441). The paper feed transport control unit 330 starts detecting the leading edge of the recording material R with the registration sensor 222 (411) based on the image formation start timing (403) of the image formation control unit 320. The speed V0 is the speed at which the recording material R is transported in the secondary transfer unit, and hereinafter will be referred to as the transfer execution speed V0.

[0056] Thereafter, the paper feed conveyance control unit 330 starts conveyance speed control (acceleration and deceleration) (413) at the timing (412) when the leading edge of the recording material R reaches the registration sensor 222. The paper feed conveyance control unit 330 calculates the following amounts in order to make the leading edge of the recording material R enter the secondary transfer unit in synchronization with the leading edge of the image. That is, the paper feed conveyance control unit 330 calculates a leading amount S1 (444), which is the distance by which the recording material R precedes the image, from the difference between the distance from the leading edge of the recording material R to the secondary transfer roller 212 and the distance from the leading edge of the image to the secondary transfer roller 212. As shown in FIG. 3 (viii), in the graph of time and speed, the leading amount S1 is represented by the area of a trapezoid. The paper feed conveyance control unit 330 determines a speed V1 (442) for delaying the conveyance of the recording material R by the calculated leading amount S1 (444) and a timing (445) for returning to the transfer execution speed V0 (441) in the secondary transfer unit. Since the recording material R is leading, the speed V1 is slower than the transfer execution speed V0 (V1 < V0).

[0057] Here, the recording material R leading means a state where if the conveyance of the recording material R is continued as it is, the recording material R reaches the secondary transfer position at a timing earlier than the toner image on the intermediate transfer belt 213. Conversely, the case where the toner image on the intermediate transfer belt 213 reaches the secondary transfer position at a timing earlier than the arrival of the recording material R is called the image leading. In addition, when the recording material R is leading, control for advancing the timing at which the toner image transferred onto the intermediate transfer belt 213 is formed can also be considered. However, since it may take time to develop the print data, and ultimately the recording material R will lead in this case, the conveyance speed of the recording material R is decelerated or temporarily stopped. The paper feed conveyance control unit 330 drives the paper feed motor 332, which is the drive source of the registration roller 221 holding the recording material R, at the determined speed V1 and timing (445). Thereby, the leading edge of the image and the leading edge of the recording material R are made to coincide, and the machine waits until the paper is fed again from the reverse path (414).

[0058] Next, the engine control unit 302 starts the image formation on the back surface (405) at an arbitrary timing after the completion of the image formation (404), similar to the front surface. As described in the recording material conveyance operation in FIG. 1 and the recording material conveyance control during inversion, after the transfer to the recording material R, the image is fixed on the recording material R by the fixing device 214. Based on the timing 421 when the leading edge of the recording material R reaches the discharge sensor 233, the inversion solenoid 345 (430) is driven (431) to change the conveyance direction of the recording material R to the direction of the inversion roller pair 230.

[0059] Thereafter, based on the timing 422 when the trailing edge of the recording material R passes through the discharge sensor 233, the inversion solenoid 345 (430) is stopped (432), the rotation direction of the inversion roller pair 230 is changed, and the conveyance through the inversion path is performed. During the conveyance through the inversion path, at the timing 415 when the leading edge of the recording material R reaches the registration sensor 222 (410), the paper feed conveyance control unit 330 starts the conveyance speed control (acceleration / deceleration) again (416). Similar to the conveyance speed control for the first-sided image, the paper feed conveyance control unit 330 calculates the leading amount S2 (446) of the recording material R. The paper feed conveyance control unit 330 calculates the speed V2 (443) for delaying the conveyance of the recording material R and the timing (447) for returning to the transfer execution speed V0 (441). The paper feed conveyance control unit 330 performs the conveyance speed control to align the timing between the leading edge of the recording material R and the image leading edge. Since the recording material R is leading, the speed V2 is slower than the transfer execution speed V0 (V2 < V0). The paper feed conveyance control unit 330 then waits for the feeding of the subsequent recording material R (417). In the above description, as an example, the case where the recording material R leads the image (400) and the conveyance speed control for delaying the recording material R is described. However, when the image leads, the conveyance speed control for accelerating the conveyance of the recording material R is performed. That is, the paper feed conveyance control unit 330 calculates a speed faster than the transfer execution speed V0 and the timing for returning to the transfer execution speed V0.

[0060] (Conveyance speed control: once stopped) Next, using the timing chart of FIG. 4, a case where the motor is temporarily stopped to align the leading edge of the recording material R with the leading edge of the image when transporting a long sheet of paper will be described. Since the control of the first side (front surface) and the basic control operations are the same as those in FIG. 3, the parts different from FIG. 3 will be described here.

[0061] Due to a delay or the like of the print start command 406 from the controller unit 301, when image formation starts later by the amount of time 407 than in FIG. 3 (405), the recording material R leads the image by the amount of time 407 elapsed. In such a case, even when the motor is set to the lowest speed controllable by the conveyance speed control, there may be a situation where the leading of the recording material R cannot be eliminated. Therefore, it becomes impossible to eliminate the leading of the recording material R only by the acceleration and deceleration of the motor.

[0062] In that case, the paper feed conveyance control unit 330 needs to perform the following operations. That is, at the timing (415) when the registration sensor 222 detects the leading edge of the recording material R, in order to align the timing of the leading edge of the recording material R with the leading edge of the image, the motor is temporarily stopped to stop the conveyance of the recording material R. Then, by advancing only the conveyance of the leading edge of the image, the leading of the recording material R is eliminated. The motor is redriven at the timing when the leading edge of the image reaches the refeed position 418 and is made to enter the secondary transfer unit.

[0063] Here, the fixing motor 352 is also the drive source of the fixing device 214. The fixing motor 352 needs to continue driving the fixing device 214 in order to ensure the temperature required for the fixing operation. If the fixing motor 352 is stopped and then redriven, a certain amount of time is required until the temperature required for the fixing operation is ensured.

[0064] As described above, since the resist sensor 222 is disposed immediately before the secondary transfer position, the distance between the resist sensor 222 and the fixing device 214 is short. When the fixing motor 352 is stopped with the leading end of the recording material R reaching the resist sensor 222, the recording material R may reach the fixing device 214 before the temperature required for the fixing operation is secured when driven again. Therefore, when the leading end of the recording material R reaches the resist sensor 222, the driving of the fixing motor 352 is continued. Further, in the present embodiment, when the fixing motor 352 is driven, the inversion roller pair 230 is configured to always be driven in conjunction.

[0065] When the recording material R is once stopped to eliminate the lead of the recording material R, if a long sheet is used as the recording material R, the following problems occur. As shown in FIG. 6, when the paper feed motor 332 is stopped, the resist roller 221 and the conveyance roller pairs 231 and 232 among the rollers sandwiching the recording material R stop. On the other hand, the fixing motor 352 cannot be stopped, and the inversion roller pair 230 continues to convey the recording material R toward the inside of the apparatus, causing the recording material R to become bellows-shaped (accordion-shaped) and the recording material R to be damaged.

[0066] (Control of Reference Example 1) In Reference Example 1, in the case of the example of FIG. 6, the timing at which the conveyance speed from the inversion path to the resist sensor 222 and the timing at which the speed returns to the speed before the change are determined at the timing when the inversion solenoid 345 is stopped. As a result, in the conveyance speed control when the leading end is detected by the resist sensor 222, the leading amount of the recording material R can be reduced to an amount that can be eliminated by the acceleration and deceleration of the motor, and the conveyance can be continued without stopping the paper feed motor 332 and the fixing motor 352.

[0067] That is, according to the control of Reference Example 1, after the leading end of the recording material R as a long sheet to be double-sided printed reaches the resist sensor 222, when the above-described first control is performed, while the acceleration and deceleration of the conveyance of the recording material R are executed, the recording material R is not stopped. That is, the conveyance of the recording material R is continued.

[0068] In Reference Example 1, when the recording material R is a predetermined recording material having a length such that the rear end of the recording material R is conveyed by the resist roller 221 without passing through the pair of reversing rollers 230, the following control is performed. This control is executed when the predetermined recording material is actually conveyed by the pair of reversing rollers 230 and the resist roller 221 (that is, when double-sided printing is performed). Before performing the first control described above, the paper feed conveyance control unit 330 performs a second control (S3 described later) to decelerate the conveyance speed of the predetermined recording material upstream in the conveyance direction from the resist sensor 222 or to stop the conveyance of the predetermined recording material. As an example of the predetermined recording material, in Reference Example 1, it is a long sheet. Note that the predetermined recording material can also be defined as a recording material having a length such that the front end of the recording material R can reach the resist roller 221 while the rear end of the recording material R has not passed through the pair of reversing rollers 230.

[0069] FIG. 7 is a timing chart when the control of Reference Example 1 is applied in the case described in FIG. 4. (i) to (vii) in FIG. 7 are the same as (i) to (vii) in FIGS. 3 and 4. FIG. 7(viii) shows the speeds of the paper feed motor 332 and the fixing motor 352. Since the control of the first side (front side) and the basic control operations are the same as those in FIGS. 3 and 4, the parts different from FIGS. 3 and 4 will be described here.

[0070] When the reversing solenoid 345 is stopped (432) and the conveyance of the recording material R starts in the direction of the resist sensor 222 using the reversing path at timing 604, the paper feed conveyance control unit 330 performs the following calculation. For an image, a predetermined position before the secondary transfer position is referred to as a position corresponding to the leading edge detection of the resist sensor 222. The distance between the predetermined position and the secondary transfer position corresponds to the distance from the leading edge detection position by the resist sensor 222 to the secondary transfer unit. The paper feed conveyance control unit 330 calculates the leading amount S3 (601) of the recording material R with respect to the image from the difference between the distance from the position of the leading edge of the recording material R to the leading edge detection position of the resist sensor 222 and the distance from the position of the leading edge of the image to the position corresponding to the leading edge detection of the resist sensor 222. Hereinafter, the position of the leading edge of the recording material R may be referred to as the paper leading edge position, and the position of the leading edge of the image may be referred to as the image leading edge position.

[0071] The paper feed conveyance control unit 330 calculates a speed V3 (602) for delaying the conveyance of the recording material R by a leading amount S3 (601) and a timing (603) for returning to the transfer execution speed V0 (441) before the change. Since the recording material R is leading, the speed V3 is slower than the transfer execution speed V0 (V3 < V0). Also, in FIG. 7(viii), V3 < V2, but the speed V3 does not necessarily become V3 < V2 depending on the conditions.

[0072] At this time, the long paper as the recording material R is sandwiched by the reversing roller pair 230 driven by the fixing motor 352. For this reason, in addition to the paper feed motor 332, the speed of the fixing motor 352 is also changed to V3 (602) and V0 (441) (640). Then, the speed of the paper feed motor 332 is changed from the transfer execution speed V0 (441) to the speed V3 (602) (604).

[0073] Thereafter, after a predetermined time has elapsed (603), the conveyance speed control unit 3304 of the paper feed motor 332 returns the speed of the paper feed motor 332 from the speed V3 (602) to the transfer execution speed V0 (441). That is, after the second control is performed and before the first control is performed, the engine control unit 302 controls the paper feed motor 332 and the fixing motor 352 so that the conveyance speed of the recording material R becomes the transfer execution speed V0. As a result, compared to the case where the control for canceling the leading amount S3 is not performed, the leading amount of the recording material R becomes smaller because the image leading edge reaches a further position, and it becomes possible to select acceleration / deceleration instead of a momentary stop of the motor when performing conveyance speed control. Thereafter, at the timing (415) when the leading edge of the recording material R reaches the registration sensor 222, the conveyance speed control (first control) (FIG. 3) for performing acceleration / deceleration of the motor, which was described in FIGS. 3 and 4, is performed to align the leading edge of the recording material R and the image leading edge.

[0074] Note that the operation of conveying the recording material R at the speed V3 is basically performed when the recording material R precedes the image. Therefore, in many cases, the speed V2 of the paper feed motor 332 after the recording material R reaches the registration sensor 222 is set to be lower than the transfer execution speed V0. However, as a result of delaying the arrival of the recording material R at the registration sensor 222, there may be a case where the image precedes the recording material R. In this case, the speed V2 of the paper feed motor 332 after the recording material R reaches the registration sensor 222 is set to be higher than the transfer execution speed V0.

[0075] Also, when the recording material R is not a long sheet, with the front end of the recording material R in contact with the registration sensor 222, the rear end of the recording material R is separated from the inversion roller pair 230. In this case, even if the paper feed motor 332 is stopped and the fixing motor 352 is driven with the front end of the recording material R reaching the registration sensor 222, the recording material R will not be damaged. Therefore, when the recording material R is not a long sheet, it is not necessary to perform the above-described control.

[0076] In the image forming apparatus 200 according to the present embodiment, the first conveying means driven by the paper feed motor 332 includes a plurality of first rollers (the registration roller 221, the conveying rollers of the conveying roller pairs 231, 231). Among these, the conveying rollers of the conveying roller pair 231 are one of the plurality of first rollers and are arranged adjacent to the inversion rollers of the inversion roller pair 230.

[0077] The inversion roller pair 230 conveys the recording material R such that a part of the recording material R protrudes outside the housing of the image forming apparatus 200. Further, the inversion roller pair 230 is arranged at the position farthest from the registration sensor 222 in the inverted conveying direction when the conveying direction of the recording material R that has passed through the fixing device 214 is inverted and double-sided printing is performed.

[0078] As a result, when a recording material R having a length such that it separates from the inversion roller pair 230 when the front end of the recording material R reaches the registration sensor 222 is used, in the first control, it is allowed to stop the conveyance.

[0079] (Transport speed control of Reference Example 1) Next, among the controls described with reference to FIG. 7, the control from stopping the reverse solenoid 345 (604) to starting the transport speed control (415) after starting the transport of the recording material R to the reverse path will be described with reference to FIG. 8.

[0080] In step (hereinafter referred to as S) 101, the paper feed transport control unit 330 determines whether the length L of the recording material R is equal to or greater than the threshold value Ls of the length of the recording material R. If in S101 the paper feed transport control unit 330 determines that the length L of the recording material R to be actually transported is less than the length threshold value Ls of the recording material R, the process ends. In this case, when the leading edge of the recording material R reaches the leading edge detection position of the registration sensor 222, the recording material R is not sandwiched between the pair of reverse rollers 230 operated by the fixing motor 352. Therefore, the transport operation is not decelerated, and the transport continues at the same speed. On the other hand, if in S101 the paper feed transport control unit 330 determines that the length L of the recording material R is equal to or greater than the threshold value Ls, the process proceeds to S102. In this case, when the leading edge of the recording material R reaches the leading edge detection position of the registration sensor 222, the recording material R is sandwiched between the pair of reverse rollers 230 operated by the fixing motor 352.

[0081] In S102, the paper feed transport control unit 330 obtains the time from the current paper leading edge position to the leading edge detection position of the registration sensor 222 and the time from the current image leading edge position to the position corresponding to the leading edge detection of the registration sensor 222. The paper feed transport control unit 330 calculates the leading amount S3 of the recording material R with respect to the image by obtaining the difference between them.

[0082] In S103, the paper feed transport control unit 330 determines whether the leading amount S3 obtained in S102 is equal to or greater than the upper limit leading amount threshold value Ss. Here, the upper limit leading amount threshold value Ss is the leading amount that can be eliminated when the motor is driven at the slowest controllable speed and the driving speed of the motor is returned at the slowest timing in the case of performing motor acceleration and deceleration in the transport speed control.

[0083] As described with reference to FIG. 6, when the leading amount of the recording material R is large at the timing when the leading end of the recording material R reaches the position of the resist sensor 222 and the leading of the recording material R cannot be eliminated even by performing acceleration / deceleration control of the motor, conveyance speed control of once stopping or decelerating is performed.

[0084] In S103, when the paper feed conveyance control unit 330 determines that the leading amount S3 is smaller than the leading amount threshold value Ss, the paper feed conveyance control unit 330 does not perform a decelerated conveyance operation, continues conveyance at the current speed, and ends the process. On the other hand, in S103, when the paper feed conveyance control unit 330 determines that the leading amount S3 is equal to or greater than the leading amount threshold value Ss, the process proceeds to S104. In this case, the conveyance speed of the recording material R is decelerated to perform a conveyance operation.

[0085] In S104, the paper feed conveyance control unit 330 calculates the deceleration amount of the necessary conveyance rollers from the leading amount S3 of the recording material R. As described with reference to FIG. 7, the paper feed conveyance control unit 330 calculates the speed V3 for delaying the recording material R and the timing (603) for returning to the original transfer execution speed V0 from the leading amount S3 of the recording material R with respect to the image. In S105, the paper feed conveyance control unit 330 decelerates the paper feed motor 332 and the fixing motor 352. Note that the control of the fixing motor 352 is performed by the fixing conveyance control unit 350, and the same applies to the following reference examples and embodiments. As described with reference to FIG. 7, the paper feed conveyance control unit 330 changes the speeds of the paper feed motor 332 and the fixing motor 352 to a speed for delaying the recording material R, for example, the speed V3.

[0086] In S106, the paper feed conveyance control unit 330 determines whether or not the deceleration section has ended. If it is determined that the deceleration section has not ended, the process returns to S106. If it is determined that the deceleration section has ended, the process proceeds to S107. That is, in this determination, the paper feed conveyance control unit 330 checks the timing (603) for returning from the speed V3 for delaying the recording material R obtained in S104 to the original transfer execution speed V0. The deceleration section is the section from 604 to 603 in FIG. 7(viii). In S107, the paper feed conveyance control unit 330 returns the paper feed motor 332 and the fixing motor 352 to the transfer execution speed V0 before the process of S105 is performed, and ends the process.

[0087] Based on the above, the speed of the motor from the inversion start position of the recording material to the tip detection position of the resist sensor 222 and the timing to return the speed of the motor are determined to convey the inversion path. As a result, the lead of the recording material R at the timing when the tip is detected by the resist sensor 222 is eliminated, and by using the acceleration and deceleration of the motor in the conveyance speed control, in other words, without once stopping the motor, the tip of the recording material and the tip of the image can be aligned. Further, when the recording material R is not a long sheet, control may be performed to once stop the recording material R downstream of the resist sensor 222. Note that Reference Example 1 does not limit the invention according to the claims, and not all of the features described in Reference Example 1 are essential for the solution means of the invention.

[0088] In this way, when the formation of the toner image by each cartridge is started (FIG. 4 405), the paper feed conveyance control unit 330 obtains the leading distance by which a predetermined recording material leads the toner image based on the difference between the first time and the second time. Here, the first time is the time until the tip of the recording material R is detected by the resist sensor 222. The second time is the time when the image reaches a predetermined position (a position corresponding to the tip detection of the resist sensor 222) upstream of the secondary transfer position in the moving direction of the intermediate transfer belt 213. The distance between the predetermined position and the secondary transfer position corresponds to the distance from the resist sensor 222 to the secondary transfer position. The paper feed conveyance control unit 330 obtains the first speed (V3) of the paper feed motor 332 and the fixing motor 352 and the timing (603) to return to the second speed (transfer execution speed V0) before performing the second control based on the obtained leading distance. As described above, according to Reference Example 1, in an image forming apparatus that conveys to the secondary transfer position using a plurality of drive sources, image formation can be normally performed without affecting the recording material.

[0089] <Reference Example 2> In Reference Example 1, when the start of image formation on the second side (back side) was delayed, the conveyance speed from the inversion path to the resist sensor 222 and the timing to return to the conveyance speed before the change were determined and controlled. Thereby, a method of performing acceleration and deceleration of the paper feed motor 332 and the fixing motor 352 in the conveyance speed control when the leading edge of the recording material R was detected by the resist sensor 222 was described.

[0090] However, if the start of image formation is further delayed, the following situation may occur. Even when the conveyance control is performed by lowering the conveyance speed to the lower limit by the control of Reference Example 1, when the leading edge is detected by the resist sensor 222, the leading of the leading edge of the paper with respect to the position of the leading edge of the image may not be eliminated, and the conveyance speed control may once select to stop.

[0091] Also, when the fixing motor 352, which is the drive source of the inversion roller pair 230, is stopped, it is necessary to also stop the temperature control of the fixing. Therefore, when the conveyance speed control described above once selects to stop and the fixing motor 352 is stopped, the fixing temperature control is also stopped in the same manner. That is, the heating operation of the heater 226 of the fixing device 214 is stopped. As a result, the temperature of the fixing device 214 decreases. After that, when the fixing motor 352 is driven again to resume the temperature control, if the distance from the leading edge detection position of the resist sensor 222 of the recording material R to the entry into the fixing device 214 is short, only the time for conveying that distance can be secured as the time for performing the temperature control. That is, since the recording material R reaches the fixing device 214 before the temperature of the fixing device 214 reaches a fixable temperature, there is a possibility that the toner image cannot be properly fixed on the recording material R.

[0092] Therefore, in view of such a situation, in Reference Example 2, when the leading edge of the recording material R reaches an arbitrary position upstream in the conveyance direction from the resist sensor 222, the conveyance is stopped, the leading of the leading edge of the paper with respect to the position of the leading edge of the image is eliminated, and then the conveyance is resumed to the resist sensor 222. At this time, the position where the recording material R is stopped is determined so that the temperature of the fixing device 214 can reach a fixable temperature by the time the conveyance of the recording material R is resumed and the recording material R reaches the fixing device 214.

[0093] When the control of Reference Example 2 is performed, since the leading edge of the recording material R has been resolved at the timing when the leading edge is detected by the resist sensor 222, the leading edge position of the paper and the leading edge position of the image can be adjusted by using the acceleration and deceleration of the paper feed motor 332 in the conveyance speed control.

[0094] That is, in Reference Example 2, when the recording material R precedes the toner image even if the first speed is set to the slowest speed among the speeds of the paper feed motor 332 and the fixing motor 352 in the second control described in Reference Example 1, the paper feed conveyance control unit 330 performs the following control. The paper feed conveyance control unit 330 performs a third control (hereinafter referred to as a temporary stop control of the fixing drive) described later to stop the conveyance of the recording material R before the leading edge of the recording material R reaches the resist sensor 222.

[0095] (Control when temporarily stopping the fixing drive) FIG. 9 is a timing chart when the control of Reference Example 2 is applied in a case where the start of image formation is further delayed than the situation assumed in Reference Example 1. FIGS. 9(i) to (viii) are the same as the figures shown in FIGS. 7(i) to (viii). FIG. 9(ix) shows the state 710 (during temperature control (fixing impossible), fixing possible, stopped, etc.) of the fixing device 214. Since the basic control operation is the same as that of Reference Example 1 described in FIG. 7, the same events are denoted by the same reference numerals, and here, the parts different from FIG. 7 will be described.

[0096] When the start of image formation on the back surface of the recording material R is delayed (405) due to a delay in the print start command 701 from the controller unit 301 or the like, the leading edge amount is determined by comparing the leading edge position of the image and the leading edge position of the paper at the timing (704) when the conveyance of the recording material R to the inversion path is started. Here, the difference between the timing 702 of the start of image formation at which the leading edge amount becomes 0 and the timing (405) at which the image formation is actually started is taken, and the image formation delay time 703 is determined. In order to cancel the leading edge of the recording material R for the image formation delay time 703 generated due to the delay in the start of image formation, a conveyance stop time 705 for the same time as the image formation delay time 703 is determined.

[0097] Next, in response to also stopping the fixing motor 352, the conveyance stop time 705 minutes is set, and the temperature of the fixing device 214 that decreases when the temperature control of the fixing device 214 is stopped is calculated. When the temperature control is restarted during the re-driving of the fixing device 214 (fixing motor 352), the time 706 until the temperature reaches a temperature at which toner can be fixed is determined. Note that the amount by which the temperature of the fixing device 214 drops (the drop amount) between when the temperature control is stopped and when re-driving occurs, and the time 706 until it becomes possible to fix after the temperature control is restarted do not necessarily have to be values calculated and obtained by the engine control unit 302. For example, values determined in advance by experiments or the like may be stored in the storage unit of the engine control unit 302, and the engine control unit 302 may use the values stored in the storage unit.

[0098] Thereafter, in order to secure the time 706 minutes described above for the recording material R to enter the fixing device 214, the following control is performed. Here, the conveyance of the recording material R to the fixing device 214 is performed at the transfer execution speed V0 (441), and it is assumed that during conveyance speed control, it is performed at the maximum speed V4 (V4 > V0) (707) of the paper feed motor 332 and the fixing motor 352. In this case, the timing 708 upstream of the fixing device 214 (hereinafter referred to as the conveyance stop timing) is determined for the distance by which the recording material R is conveyed during the time 706. In the example shown in FIG. 9, in the conveyance speed control, the recording material R is conveyed at the maximum speed V4 greater than the transfer execution speed V0, in other words, the conveyance of the recording material R is accelerated, but it is not limited to this. In the conveyance speed control, there may be a case where deceleration is performed as shown by 446 in FIG. 7 (viii) of Reference Example 1.

[0099] The recording material R is conveyed to the inversion path at the transfer execution speed V0, and at the timing when the leading end of the recording material R reaches the conveyance stop timing 708, the fixing motor 352 and the paper feed motor 332 are stopped, and it is waited for the conveyance stop time 705 to elapse. When the conveyance stop time 705 has elapsed, the fixing motor 352 and the paper feed motor 332 are re-driven, the conveyance of the recording material R is restarted at the transfer execution speed V0, and conveyance is performed until the leading end of the recording material R is detected by the registration sensor 222.

[0100] At the timing (415) when the resist sensor 222 detects the leading edge of the recording material R, the leading of the recording material R is eliminated by the control to stop the recording material R upstream of the resist sensor 222 in the conveyance direction. Therefore, when performing the conveyance speed control (first control) described with reference to FIG. 3, it is possible to align the leading edge position of the paper and the leading edge position of the image without temporarily stopping the driving of the paper feed motor 332 and the fixing motor 352, in other words, without temporarily stopping the conveyance of the recording material R.

[0101] (Conveyance speed control process when temporarily stopping the fixing drive) With reference to FIG. 10, the once-stop control of the fixing drive when temporarily stopping to eliminate the leading of the recording material R between starting the conveyance of the recording material R to the inversion path and starting the conveyance speed control, which was described with reference to FIG. 9, will be explained. In S801, the paper feed conveyance control unit 330 determines whether the length L of the recording material R is greater than or equal to the threshold value Ls based on the information acquired from the controller unit 301 or the operation display unit 251. If the paper feed conveyance control unit 330 determines in S801 that the length L of the recording material R is less than the threshold value Ls, it does not perform the once-stop control of the fixing drive and ends the process. If the paper feed conveyance control unit 330 determines in S801 that the length L of the recording material R is greater than or equal to the threshold value Ls, it proceeds with the process to S802 in order to perform the once-stop control of the fixing drive.

[0102] In S802, the paper feed conveyance control unit 330 obtains the time required for the recording material R to be conveyed at the transfer execution speed V0 from the current paper leading edge position to the secondary transfer position, and the time required for the toner image on the intermediate transfer belt 213 to be conveyed from the current image leading edge position to the secondary transfer position. The paper feed conveyance control unit 330 calculates the leading amount S of the recording material R with respect to the image by taking the difference between the two obtained times. Note that since the image leading edge position cannot be determined before the start of image formation, the paper feed conveyance control unit 330 obtains the time from the current point in time until the next image formation is performed and secondary transfer is carried out, and calculates the leading amount S based on this time.

[0103] At S803, the paper feed conveyance control unit 330 calculates the conveyance stop time T1 (705 in Fig. 9(ix)) described above in order to cancel the leading amount S obtained at S802. At S804, the paper feed conveyance control unit 330 calculates the amount by which the temperature of the fixing device 214 decreases when the conveyance stop time T1 (705) during which the fixing roller 223 stops and the temperature control also stops has elapsed. The paper feed conveyance control unit 330 calculates the time T2 (the time 706 described above) (the time from the re-driving of the fixing unit to when the fixing becomes possible) for recovering the temperature decrease amount.

[0104] At S805, when the paper feed conveyance control unit 330 drives the fixing motor 352 for the time T2 (706) calculated at S804, it calculates the distance D by which the recording medium R is conveyed at the transfer execution speed V0. The paper feed conveyance control unit 330 obtains the position upstream by the distance D on the conveyance path from the timing when the recording medium R enters the fixing device 214, and determines the conveyance stop timing 708 at which it reaches the position upstream by the distance D from the current leading edge position of the sheet. At this time, if the time T2 cannot be ensured unless it stops at a position upstream of the current leading edge position of the sheet, in Reference Example 2, the paper feed conveyance control unit 330 determines that the leading of the recording medium R cannot be canceled and appropriate toner image fixing cannot be performed. Then, the paper feed conveyance control unit 330 notifies the controller unit 301 to that effect.

[0105] At S806, the paper feed conveyance control unit 330 determines whether it has reached the conveyance stop timing 708 calculated at S805 by referring to the timer. If it determines that it has not reached the conveyance stop timing 708, the process returns to S806. At S806, when the paper feed conveyance control unit 330 determines that it has reached the conveyance stop timing 708, the process proceeds to S807. At S807, the paper feed conveyance control unit 330 stops the driving of the paper feed motor 332 and the fixing motor 352 in order to stop the conveyance of the recording medium R.

[0106] With S808, the paper feed and conveyance control unit 330 determines whether or not the conveyance stop time T1 calculated in S803 has elapsed by referring to a timer. If, in S803, the paper feed and conveyance control unit 330 determines that the conveyance stop time T1 has not elapsed, the process returns to S808. If, in S808, the paper feed and conveyance control unit 330 determines that the conveyance stop time T1 has elapsed, the process proceeds to S809. In S809, the paper feed and conveyance control unit 330 resumes driving the paper feed motor 332 and the fixing motor 352 and returns to the speed (for example, the transfer execution speed V0) before stopping in S807. Note that in Reference Examples 1 and 2, in the section where conveyance speed control (acceleration / deceleration control) is not performed, the conveyance of the recording material R is set to the transfer execution speed V0, but it is not limited thereto. The conveyance speed of the recording material R in the section where conveyance speed control is not performed may be determined according to the image forming conditions between the maximum speed (V4) and the minimum speed of the paper feed motor 332 and the fixing motor 352.

[0107] As described above, in Reference Example 2, conveyance is stopped so that the leading edge of the recording material stops at an arbitrary position upstream in the conveyance direction from the registration sensor 222, and after eliminating the leading of the recording material, it is conveyed again to the registration sensor 222. Thereby, the leading of the recording material R at the timing when the leading edge of the recording material is detected by the registration sensor 222 is eliminated, and the leading edge position of the paper and the leading edge position of the image can be aligned using the acceleration / deceleration of the motor in the conveyance speed control. Note that Reference Examples 1 and 2 do not limit the invention according to the claims, and not all of the features described in the embodiments are essential for the solution means of the invention.

[0108] In this way, the paper feeding and conveyance control unit 330 obtains a stop time for stopping the conveyance of a predetermined recording material based on the difference between the first time and the second time. The first time is the time until the leading edge of the recording material R is detected by the registration sensor 222. The second time is the time when an image reaches a predetermined position upstream of the secondary transfer position in the moving direction of the intermediate transfer belt 213. The distance between the predetermined position and the secondary transfer position corresponds to the distance from the registration sensor 222 to the secondary transfer position. The paper feeding and conveyance control unit 330 obtains the temperature of the heater that decreases during the stop time based on the obtained stop time, and obtains a recovery time until the temperature of the heater before the decrease is restored based on the obtained temperature. The paper feeding and conveyance control unit 330 determines the timing (708 in FIG. 10) at which the paper feeding motor 332 and the fixing motor 352 in the above-described third control are stopped so that a predetermined recording material reaches the fixing device 214 after the recovery time has elapsed. As described above, according to Reference Example 2, in an image forming apparatus that conveys the recording material R to the secondary transfer position using a plurality of drive sources, image formation can be normally performed without affecting the recording material.

Example

[0109] In Reference Example 1 and Reference Example 2, when image formation is delayed (407 in FIG. 7, 703 in FIG. 9), the conveyance speed from the inversion path to the registration sensor 222 and the timing to return to the conveyance speed before the change are determined to control the conveyance of the recording material R. As a result, in the conveyance speed control when the leading edge of the recording material R is detected by the registration sensor 222, the paper feeding motor 332 and the fixing motor 352 are decelerated or stopped to eliminate the leading of the recording material R. Then, in the conveyance speed control when the leading edge is detected by the registration sensor 222, a method of reducing the leading amount of the recording material R to an amount that can be eliminated by the acceleration and deceleration of the motor has been described.

[0110] However, when the recording material R is longer than the length of the formed image in the conveyance direction of the image, there are the following problems. That is, the timing to stop the reverse solenoid 345 is delayed by the difference between the length of the recording material R and the length of the image. For this reason, the image precedes the recording material R, and it is impossible to eliminate the leading of the image by decelerating or stopping the paper feed motor 332 and the fixing motor 352 as in the control of Reference Example 1.

[0111] Therefore, in view of such a situation, in the first embodiment, when it is found that the image precedes the recording material R at the timing to stop the reverse solenoid 345, the following control is performed. Before performing the first control described above, the paper feed conveyance control unit 330 accelerates the conveyance speed of a predetermined recording material from the transfer execution speed V0 upstream of the registration sensor 222 in the conveyance direction.

[0112] When the control of the first embodiment is implemented, since the leading of the image has been eliminated at the timing when the leading end is detected by the registration sensor 222, it is possible to align the leading end position of the paper and the leading end position of the image by using the acceleration and deceleration of the paper feed motor 332 in the conveyance speed control. That is, in the first embodiment, when the toner image (image) precedes the recording material R, the paper feed conveyance control unit 330 performs the following control. The paper feed conveyance control unit 330 determines the conveyance speed so as to accelerate a predetermined recording material before the leading end of the recording material R reaches the registration sensor 222.

[0113] (Control of the First Embodiment) FIG. 11 is a timing chart when the control of the first embodiment is applied when the image precedes the recording material R. FIGS. 11(i) to (viii) are the same as the figures shown in FIGS. 7(i) to (viii). Since the basic control operations are the same as those of Reference Example 1 described with reference to FIG. 7, the same events are denoted by the same reference numerals, and here, the parts different from FIG. 7 will be described.

[0114] When the length of the recording material R in the conveyance direction is longer than the length of the specified image in the conveyance direction from the controller unit 301, etc., and the image precedes the recording material R, the paper feed conveyance control unit 330 makes the following determination. That is, the paper feed conveyance control unit 330 compares the leading edge position of the paper and the leading edge position of the image at the timing (901) of starting the conveyance of the recording material R to the reverse path, and determines the leading amount S4 (605) of the image with respect to the recording material R. The paper feed conveyance control unit 330 calculates the speed V3 (602) for accelerating the conveyance of the recording material R by the leading amount S4 (605) and the timing (603) to return to the previous transfer execution speed V0 (441). Since the image is preceding, the speed V3 is higher than the transfer execution speed V0 (V3 > V0).

[0115] After the paper feed conveyance control unit 330 determines the speed V3 (602) and the timing (603) to return to the transfer execution speed V0 (441), it changes the speeds of the paper feed motor 332 and the fixing motor 352 to the speed V3 (602) in the same manner as in Reference Example 1 (901).

[0116] Thereafter, after a predetermined time has elapsed (603), the conveyance speed control unit 3304 of the paper feed motor 332 returns the speed of the paper feed motor 332 from the speed V3 (602) to the transfer execution speed V0 (441). As a result, compared to the case where control for eliminating the leading amount S4 of the image is not performed, the leading edge of the recording material R advances to a position where the leading amount of the image becomes smaller, and acceleration and deceleration of the motor can be selected instead of a momentary stop of the motor when performing conveyance speed control. Thereafter, the paper feed conveyance control unit 330 performs the conveyance speed control (first control) for accelerating and decelerating the motor, which was described in FIGS. 3 and 4, at the timing (415) when the leading edge of the recording material R reaches the registration sensor 222, and aligns the leading edge of the recording material R and the leading edge of the image.

[0117] (Conveyance speed control process in the case of Embodiment 1) Using FIG. 12, the control for accelerating the conveyance speed of the recording material R to eliminate the leading of the image from the start of the conveyance of the recording material R to the start of the conveyance speed control, which was described in FIG. 11, will be described.

[0118] In S1001, the paper feeding and conveyance control unit 330 obtains the time from the current leading edge position of the paper to the leading edge detection position of the registration sensor 222, and the time from the current leading edge position of the image to the position corresponding to the leading edge detection of the registration sensor 222. The paper feeding and conveyance control unit 330 obtains the difference between them and calculates the leading amount S4 of the image with respect to the recording material R.

[0119] In S1002, the paper feeding and conveyance control unit 330 determines whether the leading amount S4 obtained in S1001 is greater than or equal to the upper limit leading amount threshold Ss. Here, the upper limit leading amount threshold Ss is the leading amount that can be eliminated when the motor is driven at the upper limit speed controllable in the conveyance speed control and the driving speed is returned at the slowest timing.

[0120] In S1002, when the paper feeding and conveyance control unit 330 determines that the leading amount S4 is smaller than the leading amount threshold Ss, it does not perform an accelerated conveyance operation, continues the conveyance at the current speed, and ends the process. On the other hand, in S1002, when the paper feeding and conveyance control unit 330 determines that the leading amount S4 is greater than or equal to the leading amount threshold Ss, it advances the process to S1003. In this case, the paper feeding and conveyance control unit 330 accelerates the conveyance speed of the recording material R and performs a conveyance operation.

[0121] In S1003, the paper feeding and conveyance control unit 330 calculates the acceleration amount of the necessary conveyance rollers from the leading amount S4 of the recording material R obtained in S1001. As described with reference to FIG. 11, the paper feeding and conveyance control unit 330 calculates the speed V3 for advancing the recording material R and the timing (603) to return to the original transfer execution speed V0 from the leading amount S4 of the image with respect to the recording material R. In S1004, the paper feeding and conveyance control unit 330 performs acceleration of the paper feeding motor 332 and the fixing motor 352. As described with reference to FIG. 11, the paper feeding and conveyance control unit 330 changes the speeds of the paper feeding motor 332 and the fixing motor 352 to the speed for advancing the recording material R, for example, the speed V3.

[0122] At S1005, the paper feed conveyance control unit 330 determines whether the acceleration period has ended. If it determines that the acceleration period has not ended, the process returns to S1005. If it determines that the acceleration period has ended, the process proceeds to S1006. That is, in this determination, the paper feed conveyance control unit 330 checks the timing (603) to return from the speed V3 for advancing the recording material R obtained at S1003 to the original transfer execution speed V0. The acceleration period is the period from 901 to 603 in Fig. 11 (viii). At S1006, the paper feed conveyance control unit 330 returns the paper feed motor 332 and the fixing motor 352 to the transfer execution speed V0 before the process of S1004 is performed, and ends the process.

[0123] As described above, in the first embodiment, the speed of the motor from the reverse start position of the recording material to the tip detection position of the registration sensor 222 and the timing to return the speed of the motor are determined, and the recording material is conveyed through the reverse path. Thereby, the leading of the image at the timing when the tip of the recording material R is detected by the registration sensor 222 is eliminated. After the tip of the recording material R is detected by the registration sensor 222, the acceleration and deceleration (first control) of the motor are used in the conveyance speed control. In other words, the tip of the recording material and the tip of the image can be aligned without once stopping the motor. Further, when the recording material R is not a long sheet, control may be performed to once stop the recording material R downstream of the registration sensor 222. Note that the first embodiment does not limit the invention according to the claims, and not all of the features described in the embodiment are essential for the solution means of the invention.

[0124] As described above, according to the first embodiment, in an image forming apparatus that conveys to the secondary transfer position using a plurality of drive sources, normal image formation can be performed without affecting the recording material.

Embodiment

[0125] In Reference Example 1, Reference Example 2, and Embodiment 1, the conveyance speed from the inversion path to the resist sensor 222 and the timing to return to the conveyance speed before the change were determined and controlled. That is, before the leading edge of the recording material R was detected by the resist sensor 222, the paper feed motor 332 and the fixing motor 352 were decelerated or accelerated. Thereby, the leading of the recording material R or the leading of the image was eliminated, and in the conveyance speed control (first control) when the leading edge of the recording material R was detected by the resist sensor 222, the method of reducing the leading amount of the recording material R or the leading amount of the image to an amount that can be eliminated by the acceleration and deceleration of the motor was described.

[0126] However, when the transfer execution speed V0, which is the conveyance speed of the recording material R in the section where the conveyance speed control (acceleration and deceleration control) is not performed, is close to the maximum speed V4 of the paper feed motor 332 and the fixing motor 352, there are the following problems. For example, in the control of Embodiment 1, it is assumed that the conveyance speed (transfer execution speed V0) is increased to the maximum speed V4 and the conveyance control is performed. Even in such a case, when the leading edge of the recording material R is detected by the resist sensor 222, the leading of the image leading edge with respect to the paper leading edge position cannot be eliminated, so there may be a case where the leading edge of the recording material R and the image leading edge cannot be aligned at the secondary transfer position.

[0127] Also, when the transfer execution speed V0, which is the conveyance speed of the recording material R in the section where the conveyance speed control (acceleration and deceleration control) is not performed, is close to the minimum speed V5 of the paper feed motor 332 and the fixing motor 352, there are the following problems. For example, in the control of Reference Example 1, it is assumed that the conveyance speed (transfer execution speed V0) is decreased to the minimum speed V5 and the conveyance control is performed. Even in such a case, when the leading edge of the recording material R is detected by the resist sensor 222, the leading of the paper leading edge with respect to the image leading edge position cannot be eliminated, so there may be a case where a stop is once selected in the conveyance speed control.

[0128] Therefore, in view of such a situation, in the second embodiment, the paper feed conveyance control unit 330 performs the following control (fourth control). The paper feed conveyance control unit 330 compares the speed difference between the original transfer execution speed V0 (441) and the maximum speed V4 of the paper feed motor 332 and the fixing motor 352, and the speed difference between the original transfer execution speed V0 (441) and the minimum speed V5 of the paper feed motor 332 and the fixing motor 352. As a result of comparing the two speed differences, when the transfer execution speed V0 is close to the maximum speed V4, the paper feed conveyance control unit 330 does the following. That is, the paper feed conveyance control unit 330 changes the image formation start timing so that the conveyance speed V3 from the reverse path to the resist sensor 222 can be determined to be a conveyance speed between the transfer execution speed V0 and the minimum speed V5.

[0129] On the other hand, as a result of comparing the two speed differences, when the transfer execution speed V0 is close to the minimum speed V5, the paper feed conveyance control unit 330 does the following. That is, the paper feed conveyance control unit 330 changes the image formation start timing so that the conveyance speed V3 from the reverse path to the resist sensor 222 can be determined to be a conveyance speed between the transfer execution speed V0 and the maximum speed V4.

[0130] By implementing the control (fourth control) of the second embodiment, the conveyance speed of the recording material R from the reverse path to the resist sensor 222 can be determined to be between the maximum speed V4 and the minimum speed V5 of the paper feed motor 332 and the fixing motor 352.

[0131] (When the transfer execution speed V0 is close to the maximum speed V4) FIG. 13 is a timing chart when the control of the second embodiment is applied in the case where the original transfer execution speed V0 (441) is close to the maximum speed V4 (1101) of the paper feed motor 332 and the fixing motor 352 in the cases described in the reference example 1 and the first embodiment. Since the basic control operations are the same as those in the reference example 1 and the first embodiment described in FIGS. 7 and 11, the same events are denoted by the same reference numerals, and here, the parts different from FIGS. 7 and 11 will be described.

[0132] The paper feed conveyance control unit 330 compares the difference 1103 and the difference 1104 at the timing of the image formation start instruction 402 on the front surface (first surface) (the timing of the start of toner image formation). Here, the difference 1103 is the difference between the original transfer execution speed V0 (441) and the maximum speed V4 (1101) of the paper feed motor 332 and the fixing motor 352. The difference 1104 is the difference between the original transfer execution speed V0 (441) and the minimum speed V5 (1102) of the paper feed motor 332 and the fixing motor 352. In the case of FIG. 13, the difference 1104 from the minimum speed V5 (1102) is larger than the difference 1103. Therefore, the paper feed conveyance control unit 330 determines the timing of the image formation start instruction 709 to be the time 1105 from the timing of the image formation start instruction 402 on the front surface so that the speed V3 (602) can be made smaller than the original transfer execution speed V0 (441). This time 1105 is determined according to the image formation conditions so as to be an arbitrary time such that the recording material R precedes the image at the timing 432 when the reverse solenoid 345 is stopped.

[0133] Thereafter, the paper feed conveyance control unit 330 conveys the recording material, and determines the timing (603) to return from the speed V3 (602), which is smaller than the transfer execution speed V0 (441), to the original transfer execution speed V0 (441) at the timing 432 when the reverse solenoid 345 is stopped. Thereafter, the paper feed conveyance control unit 330 changes (604) the speeds of the paper feed motor 332 and the fixing motor 352 to the speed V3 (602) and performs the control described in Reference Example 1. As described above, when the transfer execution speed V0 is close to the maximum speed V4, the speed V3 for eliminating the leading amount S3 is determined between the transfer execution speed V0 and the minimum speed V5 (V5 < V3 < V0).

[0134] (When the transfer execution speed V0 is close to the minimum speed V5) FIG. 14 is a timing chart when the control of Example 2 is applied in the case where the original transfer execution speed V0 (441) is close to the minimum speed V5 of the paper feed motor 332 and the fixing motor 352 in the cases described in Reference Example 1 and Example 1. Since the basic control operations are the same as those described in FIG. 13, the same events are denoted by the same reference numerals, and only the parts different from FIG. 13 will be described here.

[0135] The paper feed and conveyance control unit 330 compares the difference 1103 and the difference 1104 at the timing of the image formation start instruction 402 on the front surface (first surface). Here, the difference 1103 is the difference between the original transfer execution speed V0 (441) and the maximum speed V4 (1101) of the paper feed motor 332 and the fixing motor 352. The difference 1104 is the difference between the original transfer execution speed V0 (441) and the minimum speed V5 (1102) of the paper feed motor 332 and the fixing motor 352. In the case of FIG. 14, the difference 1103 from the maximum speed V4 (1101) is larger than the difference 1104. Therefore, the paper feed and conveyance control unit 330 determines the timing of the image formation start instruction 709 to be the time 1201 from the timing of the image formation start instruction 402 on the front surface so that the speed V3 (602) can be made larger than the original transfer execution speed V0 (441). This time 1201 is determined according to the image formation conditions so as to be an arbitrary time such that the image precedes the recording material R at the timing 432 for stopping the reverse solenoid 345.

[0136] Thereafter, the paper feed and conveyance control unit 330 conveys the recording material, and determines the timing (603) to return from the speed V3 (602), which is higher than the transfer execution speed V0 (441), to the original transfer execution speed V0 (441) at the timing 432 for stopping the reverse solenoid 345. Thereafter, the paper feed and conveyance control unit 330 changes (604) the speeds of the paper feed motor 332 and the fixing motor 352 to the speed V3 (602), and performs the control described in the first embodiment. As described above, when the transfer execution speed V0 is close to the minimum speed V5, the speed V3 for eliminating the leading amount S3 is determined between the transfer execution speed V0 and the maximum speed V4 (V0 < V3 < V4).

[0137] (Image formation timing determination process in the case of the second embodiment) Using FIG. 15, the determination process of the image formation timing on the back surface (second surface), which was described with reference to FIGS. 13 and 14, will be described. At S1301, the paper feed and conveyance control unit 330 determines whether the length L of the recording material R is greater than or equal to the threshold value Ls of the length of the recording material.

[0138] In S1301, when the paper feed conveyance control unit 330 determines that the length L of the recording material is less than the threshold value Ls of the length of the recording material, the process ends. In this case, it is determined that the recording material R is not of a length that can be sandwiched by the reversing roller pair 230 operating with the fixing motor 352 even if it is conveyed to the resist sensor 222. On the other hand, in S1301, when the paper feed conveyance control unit 330 determines that the length L of the recording material R is greater than or equal to the threshold value Ls, the process proceeds to S1302. In this case, it is determined that the recording material R is of a length that can be sandwiched by the reversing roller pair 230 operating with the fixing motor 352 when it is conveyed to the resist sensor 222.

[0139] In S1302, the paper feed conveyance control unit 330 calculates the difference Vdmax (= V4 - V0) and the difference Vdmin (V0 - V5). Note that the difference Vdmax is the difference between the transfer execution speed V0 and the maximum speed V4 (upper limit) of the paper feed motor 332 and the fixing motor 352, and corresponds to the difference 1103 described above. Also, the difference Vdmin is the difference between the transfer execution speed V0 and the minimum speed V5 (lower limit) of the paper feed motor 332 and the fixing motor 352, and corresponds to the difference 1104 described above.

[0140] In S1303, the paper feed conveyance control unit 330 compares the difference Vdmax and the difference Vdmin calculated in S1302. In S1303, when the paper feed conveyance control unit 330 determines that Vdmax > Vdmin, the process proceeds to S1304. This corresponds to the situation described in FIG. 14. In S1304, the paper feed conveyance control unit 330 advances the image formation timing by the difference (Ld - Lds) between the length Ld of the image and the threshold value Lds of the length of the image, and ends the process. Here, the threshold value Lds of the length of the image is the same length as the threshold value Ls of the length of the recording material described above.

[0141] As a result, the image will be in a state of leading the recording material R at the timing of calculating the leading amount of the recording material and the image, and the paper feed conveyance control unit 330 selects a speed faster than the original transfer execution speed V0 as the conveyance speed V3 of the reverse path. Note that, as an example, the amount of advancing the image formation timing is the difference between the length Ld of the image and the length threshold Lds, but it is not limited to this. The image formation timing may be determined according to the image formation conditions as long as it is such that a speed faster than the original transfer execution speed V0 is selected as the conveyance speed V3 of the reverse path.

[0142] On the other hand, when the paper feed conveyance control unit 330 determines in S1303 that Vdmax ≦ Vdmin, the process proceeds to S1305. This corresponds to the situation described with reference to FIG. 13. In S1305, the paper feed conveyance control unit 330 delays the image formation timing by the difference (Lmax - Ld) between the maximum printable size Lmax and the length Ld of the image, and ends the process. The maximum printable size Lmax is the length in the conveyance direction of the largest recording material R that can be printed by the image forming apparatus 200.

[0143] As a result, the recording material R will be in a state of leading the image at the timing of calculating the leading amount of the recording material and the image, and the paper feed conveyance control unit 330 selects a speed slower than the original transfer execution speed V0 as the conveyance speed V3 of the reverse path. Note that, as an example, the amount of delaying the image formation timing is the difference between the maximum printable size Lmax and the length Ld of the image, but it is not limited to this. The image formation timing may be determined according to the image formation conditions as long as it is such that a speed slower than the original transfer execution speed V0 is selected as the conveyance speed V3 of the reverse path. The control of S1304 or S1305 described above corresponds to the fourth control.

[0144] As described above, in the second embodiment, based on the transfer execution speed V0, the image formation timing on the back surface is changed. As a result, the conveyance speed V3 of the inversion path for canceling the leading of the recording material R or the image can be determined within the range of the maximum speed V4 and the minimum speed V5 of the paper feed motor 332 and the fixing motor 352. Further, when the image formation timing cannot be changed due to image formation conditions or the like and the image formation is delayed, the control (third control) of the reference example 2 may be performed. Note that the second embodiment does not limit the invention according to the claims, and not all of the features described in the embodiment are essential for the solution means of the invention.

[0145] As described above, according to the second embodiment, in an image forming apparatus that conveys to the secondary transfer position by a plurality of drive sources, image formation can be normally performed without affecting the recording material.

[0146] The disclosure of the present embodiment includes the following configurations. (Configuration 1) A first conveyance unit that conveys a recording material, A first drive unit that drives the first conveyance unit, A second conveyance unit that conveys the recording material, the second conveyance unit being provided upstream of the first conveyance unit in the conveyance direction of the recording material, A second drive unit that drives the second conveyance unit, the second drive unit being different from the first drive unit, An intermediate transfer body on which a toner image transferred from a photosensitive drum is carried, A transfer unit configured to transfer the toner image on the intermediate transfer body to the recording material at a transfer position, A detection unit that detects the recording material, the detection unit being provided upstream of the transfer position in the conveyance direction, A control unit configured to perform first control in response to the leading end of the recording material reaching the detection unit, the control unit controlling the first drive unit to accelerate or decelerate the conveyance speed of the recording material in the first control, An image forming apparatus comprising: The recording material has a length such that the recording material is conveyed by the first conveying means while the rear end of the recording material has not passed through the second conveying means, and when the recording material is conveyed by the first conveying means and the second conveying means, the control means performs second control before performing the first control, and the conveyance of the recording material is continued in the first control. In the second control, the control means controls the first driving means and the second driving means so as to decelerate the conveyance speed of the recording material upstream of the detection means in the conveyance direction, or stop the conveyance of the recording material. In the second control, the control means controls the first driving means and the second driving means so as to accelerate the conveyance speed of the recording material upstream of the detection means in the conveyance direction. An image forming apparatus characterized by that. (Configuration 2) Further comprising an image forming means for forming a toner image on the intermediate transfer body, including the photosensitive drum. Based on the leading distance by which the recording material precedes the toner image, the control means obtains a first speed of the first driving means and the second driving means in the second control, and a timing for returning from the first speed to a second speed. The image forming apparatus according to Configuration 1, characterized in that. (Configuration 3) In the second control, when the recording material precedes the toner image even if the first speed is the slowest speed among the speeds of the first driving means and the second driving means, the control means stops the first driving means and the second driving means so as to stop the conveyance of the recording material before the leading end of the recording material reaches the detection means. The image forming apparatus according to Configuration 2, characterized in that it performs third control. (Configuration 4) Having a heater, provided downstream of the transfer position, and comprising a fixing device for fixing the toner image on the recording material. The first conveying means is a first roller provided upstream of the transfer position and for conveying the recording material. The first driving means is a first motor for driving the first roller. The second conveying means is a second roller for conveying the recording material that has passed through the fixing device to the transfer position, The second driving means is a second motor that drives the fixing device and the second roller, and is configured to rotate the second roller in a first direction and a second direction opposite to the first direction, The fixing device is the image forming apparatus according to Configuration 3, characterized in that the temperature of the heater decreases while the driving by the second motor is stopped. (Configuration 5) The first conveying means includes a plurality of the first rollers, and one of the plurality of the first rollers is arranged adjacent to the second roller in the conveying direction, which is the image forming apparatus according to Configuration 4. (Configuration 6) The control means includes a stop time for stopping the conveyance of the recording material, obtains a recovery time until the temperature of the heater that has decreased during the stop time recovers to the temperature before the decrease, The image forming apparatus according to Configuration 4, characterized in that the timing for stopping the first driving means and the second driving means in the third control is determined so that the recording material reaches the fixing device after the recovery time has elapsed. (Configuration 7) having a heater, provided downstream of the transfer position, and including a fixing device for fixing the toner image on the recording material, The first conveying means is a first roller provided upstream of the transfer position and configured to convey the recording material, The first driving means includes a first motor that drives the first roller, The second conveying means is a second roller for conveying the recording material that has passed through the fixing device to the transfer position, The second driving means is a second motor that drives the fixing device and the second roller, and is configured to rotate the second roller in a first direction and a second direction opposite to the first direction, which is the image forming apparatus according to Configuration 1. (Configuration 8) The first conveying means includes a plurality of the first rollers, and one of the plurality of the first rollers is arranged adjacent to the second roller in the conveying direction, in the image forming apparatus according to Configuration 7. (Configuration 9) The detection means includes a contact portion that contacts the recording material to correct skew, in the image forming apparatus according to any one of Configurations 1 to 8. (Configuration 10) When the conveying speed of the recording material at the transfer position is defined as the transfer speed, the conveying speed of the recording material when the second control is performed is slower than the transfer speed, in the image forming apparatus according to any one of Configurations 1 to 9. (Configuration 11) The control means controls the first driving means and the second driving means so that the recording material is conveyed at the transfer speed after the second control and before the first control is performed, in the image forming apparatus according to Configuration 10. (Configuration 12) When the control means determines the first speed by the second control, the control means performs a fourth control of accelerating from the second speed to the first speed by advancing the formation start timing of the toner image by the image forming means, or decelerating from the second speed to the first speed by delaying the formation start timing of the toner image by the image forming means, in the image forming apparatus according to Configuration 2. (Configuration 13) It has a heater, is provided downstream of the transfer position, and includes a fixing device that fixes the toner image on the recording material. The first conveying means is a first roller that is provided upstream of the transfer position and conveys the recording material. The first driving means is a first motor that drives the first roller. The second conveying means is a second roller for conveying the recording material that has passed through the fixing device to the transfer position. The second driving means is a second motor that drives the fixing device and the second roller, and is configured to rotate the second roller in a first direction and a second direction opposite to the first direction. The image forming apparatus according to Configuration 12, wherein the fixing device is configured such that the temperature of the heater decreases while the drive by the second motor is stopped. (Configuration 14) The image forming apparatus according to Configuration 13, wherein the first conveying means includes a plurality of the first rollers, and one of the plurality of the first rollers is disposed adjacent to the second roller in the conveying direction.

Explanation of Signs

[0147] 213 Intermediate transfer belt 221 Registration roller 222 Registration sensor 230 Inversion roller pair 330 Paper feed conveyance control unit 332 Paper feed motor 352 Fixing motor

Claims

1. A first conveying means for conveying a recording material; A first driving means for driving the first conveying means; A second conveying means for conveying the recording material, the second conveying means being provided upstream of the first conveying means in the conveying direction of the recording material; A second driving means for driving the second conveying means, the second driving means being different from the first driving means; An intermediate transfer member on which a toner image transferred from a photosensitive drum is carried; A transfer means configured to transfer the toner image on the intermediate transfer member to the recording material at a transfer position; A detection means for detecting the recording material, the detection means being provided upstream of the transfer position in the conveying direction; A control means configured to perform first control in response to the leading end of the recording material reaching the detection means, wherein in the first control, the control means controls the first driving means to accelerate or decelerate the conveying speed of the recording material; An image forming apparatus comprising: The recording material has a length such that the recording material is conveyed by the first conveying means while the rear end of the recording material has not passed through the second conveying means, and when the recording material is conveyed by the first conveying means and the second conveying means, the control means performs second control before performing the first control, and the conveyance of the recording material is continued in the first control; In the second control, the control means controls the first driving means and the second driving means to decelerate the conveying speed of the recording material upstream of the detection means in the conveying direction, or to stop the conveyance of the recording material; An image forming apparatus, wherein in the second control, the control means controls the first driving means and the second driving means to accelerate the conveying speed of the recording material upstream of the detection means in the conveying direction.

2. Further comprising an image forming means including the photosensitive drum for forming a toner image on the intermediate transfer member; The control means obtains a first speed of the first driving means and the second driving means in the second control and a timing to return from the first speed to a second speed based on a leading distance by which the recording material precedes the toner image. The image forming apparatus according to claim 1.

3. In the second control, when in the third control, even if the first speed is the slowest among the speeds of the first driving means and the second driving means and the recording material still precedes the toner image, the control means stops the first driving means and the second driving means so as to stop the conveyance of the recording material before the leading end of the recording material reaches the detection means. The image forming apparatus according to claim 2, characterized in that.

4. It has a heater, is provided downstream of the transfer position, and includes a fixing device for fixing the toner image on the recording material. The first conveyance means is a first roller provided upstream of the transfer position for conveying the recording material. The first driving means is a first motor for driving the first roller. The second conveyance means is a second roller for conveying the recording material that has passed through the fixing device to the transfer position. The second driving means is a second motor for driving the fixing device and the second roller, and is configured to rotate the second roller in a first direction and a second direction opposite to the first direction. The fixing device is characterized in that the temperature of the heater decreases while the driving by the second motor is stopped. The image forming apparatus according to claim 3.

5. The first conveyance means includes a plurality of the first rollers, and one of the plurality of the first rollers is arranged adjacent to the second roller in the conveyance direction. The image forming apparatus according to claim 4, characterized in that.

6. The control means determines a stop time for stopping the conveyance of the recording material, Obtains a recovery time until the temperature of the heater that has decreased during the stop time recovers to the temperature before the decrease, The image forming apparatus according to claim 4, characterized in that the timing for stopping the first driving means and the second driving means in the third control is determined so that the recording material reaches the fixing device after the recovery time has elapsed.

7. It has a heater, is provided downstream of the transfer position, and includes a fixing device for fixing the toner image on the recording material. The first conveyance means is a first roller provided upstream of the transfer position for conveying the recording material. The first driving means includes a first motor for driving the first roller. The second conveyance means is a second roller for conveying the recording material that has passed through the fixing device to the transfer position. The second driving means is a second motor that drives the fixing device and the second roller, and is configured to rotate the second roller in a first direction and a second direction opposite to the first direction. The image forming apparatus according to claim 1, characterized in that.

8. The first conveying means includes a plurality of the first rollers, and one of the plurality of the first rollers is disposed adjacent to the second roller in the conveying direction. The image forming apparatus according to claim 7, characterized in that.

9. The detection means includes a contact portion that contacts the recording material and corrects skew. The image forming apparatus according to any one of claims 1 to 8, characterized in that.

10. When the conveyance speed of the recording material at the transfer position is defined as the transfer speed, the conveyance speed of the recording material when the second control is performed is slower than the transfer speed. The image forming apparatus according to claim 1, characterized in that.

11. The control means controls the first driving means and the second driving means so that the recording material is conveyed at the transfer speed after the second control is performed and before the first control is performed. The image forming apparatus according to claim 10, characterized in that.

12. When the control means determines the first speed by the second control, the control means accelerates from the second speed to the first speed by advancing the timing of forming the toner image by the image forming means, or delays the timing of forming the toner image by the image forming means. A fourth control for decelerating from the second speed to the first speed is performed. The image forming apparatus according to claim 2, characterized in that.

13. Having a heater, provided downstream of the transfer position, and comprising a fixing device for fixing the toner image on the recording material, The first conveying means is a first roller provided upstream of the transfer position and configured to convey the recording material, The first driving means is a first motor that drives the first roller, The second conveying means is a second roller for conveying the recording material that has passed through the fixing device to the transfer position, The second driving means is a second motor that drives the fixing device and the second roller, and is configured to rotate the second roller in a first direction and a second direction opposite to the first direction, The fixing device is characterized in that the temperature of the heater decreases while the driving by the second motor is stopped. The image forming apparatus according to claim 12, characterized in that.

14. The first conveying means includes a plurality of the first rollers, and one of the plurality of the first rollers is arranged adjacent to the second roller in the conveying direction, according to the image forming apparatus according to claim 13.

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