JP2013082538A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reliably eliminate skew, and prevent noise from being generated due to an increase in sagging, when intermediate rollers are stopped after a sheet reaches a pair of registration rollers.SOLUTION: The image forming apparatus includes: an image forming part; a pair of registration rollers configured to deliver a sheet to the image forming part in accordance with formation of an image; the rotating bodies configured to convey the sheet toward the pair of registration rollers; an upstream detector for detecting the sheet reaching the pair of registration rollers. The rotating bodies stop when a predetermined sag formation period elapses after the upstream detector detects the arrival of the sheet. The pair of registration rollers are suspended at the time when the arrival of the sheet is detected. When the rotating bodies stop after the lapse of the sag formation period, the pair of registration rollers perform a sag eliminating operation, that is, temporarily rotate and stop, then, after the sag eliminating operation, the rotating bodies and the pair of registration rollers simultaneously start to rotate to convey the sheet to the image forming part.

Description

  The present invention relates to an image forming apparatus such as a printer, a multi-function machine, a copier, and a facsimile machine including a registration roller pair to be sent out after bending the paper and a rotating body that conveys the paper toward the registration roller pair.

  The image forming apparatus forms an image on a sheet being conveyed while conveying the sheet. If the distance between the sheets is too tight, it may cause jamming or hinder image formation at an appropriate position of the sheet. Further, it is necessary to control (adjust) the interval between sheets before reaching the image forming unit that performs image formation. Therefore, in many cases, a registration roller pair is provided toward the image forming unit to feed paper at the timing of image formation, and the paper spacing is adjusted before the registration roller pair.

  An example of such an image forming apparatus is described in Patent Document 1. Specifically, Patent Document 1 discloses a sheet feeding unit that feeds a sheet, a registration unit that performs a registration operation on a sheet at a predetermined registration operation timing, and a sheet conveyance unit that conveys the fed sheet to the registration unit. And sheet feeding means, registration means, and control means for controlling each of the sheet conveyance means, and the sheet conveyance means (pre-registration roller pair 106) is a sheet detection means (detecting sheet conveyance time interval). An image forming apparatus that includes a determination sensor 109) and that controls the sheet feeding unit, the registration unit, and the sheet conveyance unit based on the conveyance time interval is described. In this configuration, a sheet detection unit is provided upstream of a portion (sheet conveyance unit) that conveys a sheet between the registration roller pair and the sheet feeding unit to check a gap between sheets. When the paper gap is not secured, the pre-registration roller pair 106 is stopped to adjust the paper gap (see Patent Document 1: Claim 1, paragraph 0047, etc.).

JP 2001-213548 A

  In general, a rotating body (intermediate roller pair, “pre-registration roller pair 106” in Patent Document 1) that transports paper fed from a paper feed roller toward a pair of registration rollers is provided in a paper transport path of the image forming apparatus. May be provided. Further, in order to make the timing of feeding the paper to the image forming unit, a sensor (registration sensor) for detecting the arrival and passage of the paper to the registration roller pair is usually provided in the vicinity of the registration roller pair.

  Then, in order to adjust the image forming position on the paper and adjust the gap between the paper, the intermediate roller pair may be temporarily stopped and the paper may be temporarily fastened by the registration roller pair. Thereafter, the sheet conveyance to the image forming unit is resumed by the rotation of the registration roller pair and the intermediate roller pair.

  For example, in Patent Document 1, a sensor (intermediate sensor, “determination sensor 109” in Patent Document 1) provided upstream of the intermediate roller pair (pre-registration roller pair 106 in Patent Document 1) in the paper conveyance direction is provided. Then, the paper interval is detected before reaching the registration roller pair. If the paper interval is short, the intermediate roller pair is stopped to adjust the paper interval.

  However, in such a configuration, it is essential to provide a sensor (intermediate sensor) on the upstream side of the intermediate roller pair. Then, there is a problem that the manufacturing cost of the image forming apparatus is high. In addition, the conveyance distance from the paper feeding unit to the pair of registration rollers may be relatively short, and there may be no space for installing the intermediate sensor.

  Therefore, an intermediate sensor may not be used (not provided). When the intermediate sensor is not provided in this way, the registration sensor detects the arrival of the paper to the registration roller pair, confirms that the paper is being transported properly, and adjusts the image formation position on the paper. In order to adjust the gap between the sheets, the intermediate roller pair is temporarily stopped.

  Here, the registration roller pair may have a function of correcting the skew (skew) of the paper. Specifically, when the sheet arrives, the registration roller pair is stopped. As a result, the leading edge of the reached paper is abutted against the resist roller pair in the stopped state. Then, for example, the intermediate roller continues to convey the sheet and creates a sheet deflection. Along the axial direction of the pair of registration rollers, the elasticity of the sheet of which the leading end of the sheet is bent. Thereby, the skew of the paper is corrected.

  When the intermediate sensor is not used, the pair of intermediate rollers may be stopped in order to secure a gap between the sheets after detecting the sheet with the registration sensor and creating the deflection.

  However, when the intermediate roller pair is stopped, the time until the intermediate roller pair stops varies for various reasons (the time until the stop is different each time). In many cases, ON / OFF control of rotation of the intermediate roller pair is performed using a clutch capable of controlling connection and release. In addition, variations in the time required to connect and release the clutch may cause variations in time until the intermediate roller pair stops. In addition, inertia, the wear state of the intermediate roller pair, the type of paper, and the like may cause variations in the time until the intermediate roller pair stops.

  If the stop of the intermediate roller pair is delayed due to variations in the time until the intermediate roller pair stops, the amount of deflection of the paper increases. In this case, the sheet may come into contact with the conveyance path and make a sound (noise may be generated). Accordingly, it is conceivable that the intermediate roller pair is stopped quickly (the time for creating the deflection is reduced) in anticipation of an increase in the amount of deflection of the sheet.

  However, if there is no delay in stopping the pair of intermediate rollers or if there is a variation in the direction in which the stop is accelerated, the sheet cannot be flexed appropriately as necessary, and the skew may not be eliminated. As described above, there is a trade-off relationship between appropriate and reliable cancellation of skew and the prevention of noise. Therefore, if the intermediate roller pair is stopped after the sheet reaches the registration roller pair, there is a problem in that it is impossible to achieve both the generation of noise and the reliable elimination of skew. This problem is particularly noticeable in an image forming apparatus (an image forming apparatus having a large number of printed sheets per unit time, a so-called high speed machine) having a high paper conveyance speed.

  The present invention has been made in view of the above-mentioned problems of the prior art, and when the intermediate roller pair is stopped after the paper reaches the registration roller pair without having an intermediate sensor, the skew is reliably eliminated. It is an object to prevent the generation of noise due to an increase in the amount of bending.

  An image forming apparatus according to claim 1 is provided on an upstream side of the image forming unit with respect to an image forming unit that forms an image on a sheet, and the image forming unit is configured to form an image toward the image forming unit. A registration roller pair that feeds out the sheet, a rotating body that conveys the sheet toward the registration roller pair, and an upstream side that is provided upstream of the registration roller pair and detects arrival of the sheet to the registration roller pair The rotating body includes a detector, and the rotating body stops when the predetermined deflection creation time is rotated from the paper arrival detection by the upstream detector, and the registration roller pair is stopped at the time of paper arrival detection. When the rotating body stops after the bending creation time rotation, the rotating body performs a bending canceling operation that stops after rotating temporarily, and the rotating body and the registration roller pair are After resolving, it was decided to carry the sheet toward the image forming unit to start rotating simultaneously.

  According to this configuration, the registration roller pair is in a state of being stopped at the time of paper arrival detection. The rotating body and the registration roller pair start to rotate at the same time after the deflection eliminating operation, and convey the paper toward the image forming unit. As a result, the rotating body is bent and rotated for the creation time, and the sheet is sufficiently bent, so that the skew is reliably eliminated. Then, after the sheet is bent to eliminate the skew, the registration roller pair is operated by the bend eliminating operation with the rotation of the rotating body to convey the sheet a little. Therefore, even when the rotation of the rotating body is delayed due to variations in the time until the rotating body stops, it is possible to prevent the sheet from being bent as much as noise is generated due to contact of the sheet with the conveyance path.

  According to a second aspect of the present invention, in the first aspect of the present invention, the arrival of a sheet fed from the pair of registration rollers is provided between the pair of registration rollers and the sheet conveyance path of the image forming unit. Including the downstream detection body, the image forming unit starts image formation based on the paper arrival detection by the downstream detection body.

  The registration roller pair is rotated by the deflection eliminating operation and stopped. In addition, the conveyance amount of the registration roller pair in the deflection elimination operation may vary. Accordingly, the time from the start of conveyance from the registration roller pair to the arrival of the image forming position on the paper in the image forming unit may vary. Therefore, according to this configuration, the image forming unit starts image formation based on the paper arrival detection by the downstream detector. As a result, when the registration roller pair and the rotating body are rotated after the bend elimination operation, the image formation is started based on a certain standard, so the image is formed at an accurate position of the paper regardless of the position of the paper. can do. The image forming unit may start image formation triggered by detection of paper arrival by the downstream detector, or start image formation after a predetermined time has elapsed from detection of paper arrival by the downstream detector. Also good.

  According to a third aspect of the present invention, in the invention of the first or second aspect, the registration roller pair has a range equal to or less than a sheet conveyance amount in the rotation of the rotation body during the deflection creation time in the deflection elimination operation. The paper is transported by the transport amount.

  According to this configuration, the registration roller pair conveys the sheet with a conveyance amount in a range equal to or less than the sheet conveyance amount in the rotation of the rotation time of the rotating body in the bending elimination operation. Thereby, for example, the sheet can be prevented from being conveyed more than necessary as the sheet is stretched in the bend elimination operation.

  According to a fourth aspect of the present invention, in the first to third aspects of the present invention, the rotating body is predetermined as a space between the sheet reached by the upstream detection body and the preceding sheet should be secured. Only when it is detected that the distance is smaller than the required paper interval, the paper is detected by the upstream side detection body, and when the bend creation time is rotated, the registration roller pair is substantially synchronized with the rotation of the rotary body. The bending elimination operation was performed.

  According to this configuration, the rotating body is upstream only when it is detected that the space between the paper reached by the upstream side detection body and the previous paper is smaller than the required paper space that is determined in advance to be secured. When the bend creation time is rotated from the detection of the arrival of the paper by the side detection body, it stops, and the registration roller pair performs the bend elimination operation substantially in synchronization with the stop of the rotation body. As a result, an operation for securing the paper gap and an operation for avoiding noise generation are performed only when the paper gap is to be secured.

  According to a fifth aspect of the present invention, in the fourth aspect of the invention, the rotating body is detected by the upstream detector to detect that the space between the preceding paper and the paper that has reached is greater than the required paper space. The rotation continues even if the deflection creation time rotates from the paper arrival detection by the upstream detector, and the registration roller pair rotates when the deflection creation time elapses from the paper arrival detection by the upstream detector. It started and the said bending elimination operation | movement was not performed.

  According to this configuration, when the upstream detection body detects that the space between the preceding paper and the reached paper is greater than or equal to the required paper, the rotating body creates a deflection from the paper arrival detection by the upstream detection body. The registration roller pair continues to rotate even if it rotates for a period of time, and when the deflection creation time elapses from the detection of the arrival of the sheet by the upstream side detection body, the registration roller pair starts to rotate and does not perform the deflection elimination operation. As a result, if the necessary sheet space is ensured, the sheet conveyance and image formation are performed without stopping the rotating body. Therefore, the image forming speed (printing speed) can be increased, and the productivity of the image forming apparatus can be improved.

  As described above, according to the present invention, when the rotating body is stopped after the sheet reaches the pair of registration rollers, the skew can be appropriately and reliably eliminated. In addition, the generation of noise due to an increased amount of deflection is prevented. Accordingly, it is possible to achieve both the elimination of appropriate skew and the prevention of noise generation due to an increase in the amount of bending.

It is a model section left side view showing a schematic structure of a printer. 2 is a block diagram illustrating an example of a hardware configuration of a printer. FIG. FIG. 5 is a block diagram illustrating an example of a portion that conveys a sheet toward an image forming unit. It is explanatory drawing for demonstrating creation of the bending of a paper. It is a timing chart which shows an example of operation when stopping a pair of intermediate rollers in a printer concerning an embodiment. 6 is a flowchart illustrating an example of a flow of sheet conveyance control. It is a timing chart for demonstrating operation | movement when stopping the intermediate roller pair in the conventional paper conveyance.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. In the following description, an electrophotographic digital printer 100 is taken as an example of the image forming apparatus. However, each element such as configuration and arrangement described in each embodiment does not limit the scope of the invention and is merely an illustrative example.

(Outline of image forming apparatus)
First, the printer 100 according to the embodiment will be described with reference to FIG. FIG. 1 is a schematic cross-sectional left side view showing a schematic structure of the printer 100.

  As shown in FIG. 1, an operation panel 101 is provided on the upper front side of the printer 100. The operation panel 101 includes a liquid crystal display unit 102 that displays the status of the printer 100 and various messages. The operation panel 101 turns on and off in accordance with a key 103 for setting various functions of the printer 100 (for example, paper size setting for printing) and the state of the printer 100 (during job execution, error occurrence, etc.). An indicator 104 or the like is also provided.

  As shown in FIG. 1, the paper feeding unit 1 is disposed below the inside of the main body of the printer 100. The paper feed unit 1 includes a cassette 11 that can be inserted and removed. A plurality of sheets P can be stacked on the cassette 11. A paper feed roller 12 is provided in the paper feed unit 1. The paper feed roller 12 is in contact with the uppermost paper P and is driven to rotate. By driving the paper feed roller 12, the paper P used for printing is sent out from the cassette 11 one by one.

  The conveyance path 2 is connected downstream of the sheet feeding unit 1 in the sheet conveyance direction. The transport path 2 transports the paper P supplied from the paper feed unit 1 toward the image forming unit 5. In the conveyance path 2, a winding portion 21, an intermediate roller pair 3 (corresponding to a rotating body), and a registration roller pair 4 are arranged in this order from the upstream side.

  First, the whispering part 21 includes a pair of rollers. The separating unit 21 prevents double feeding (feeding out two or more sheets P from the paper feeding unit 1). The upper roller 22 on the upper side of the winding unit 21 is driven to rotate in a direction to feed the paper P toward the image forming unit 5, and the lower roller 23 on the lower side rotates in a direction to send the paper P back to the paper feeding unit 1. The lower roller 23 returns the double-fed paper P to the paper feeding unit 1. Thereby, the double feed of the paper P is eliminated.

  The intermediate roller pair 3 conveys the paper P toward the registration roller pair 4 and the image forming unit 5. The registration roller pair 4 corrects the skew of the paper P (details will be described later). Then, the registration roller pair 4 measures the timing with the toner image formed in the image forming unit 5 and sends the paper P to the image forming unit 5.

  Note that the printer 100 according to the present embodiment includes a downstream side of the intermediate roller pair 3 and an upstream side for detecting the arrival and passage of paper to the registration roller pair 4 on the upstream side and in the vicinity of the registration roller pair 4. A sensor 61 (corresponding to an upstream detection body) is provided. For example, the upstream sensor 61 is used to detect the arrival and passage of the paper P in the vicinity of the registration roller pair 4 and to measure the distance between the paper P that has reached the registration roller pair 4 and the previous paper P. .

  Further, a downstream sensor 62 (corresponding to a downstream detector) is provided downstream of the registration roller pair 4 and upstream of the image forming unit 5 (photosensitive drum 51 and transfer roller 55). For example, it is used for detecting the leading edge of the paper P sent out from the registration roller pair 4 and taking the start timing of image formation (toner image formation) in the image forming unit 5.

  Next, toner image formation in the image forming unit 5 will be described. The image forming unit 5 is provided with a photosensitive drum 51 that rotates at a predetermined speed and carries a toner image. The charging unit 52 charges the photosensitive drum 51 to a constant potential. The exposure unit 53 irradiates the photosensitive drum 51 with the laser light L based on image data transmitted from the computer 200 (see FIG. 2) or the like to the printer 100 or setting data for printing, and performs scanning and exposure. Do. Thereby, an electrostatic latent image is formed on the photosensitive drum 51. The developing device 54 supplies toner to the electrostatic latent image. Thereby, the toner image is developed. A transfer roller 55 is provided below the photosensitive drum 51. The transfer roller 55 is in pressure contact with the photosensitive drum 51. The toner image is transferred onto the paper P at the nip between the transfer roller 55 and the photosensitive drum 51. When the toner image and the paper P enter the nip, a transfer voltage is applied to the transfer roller 55. As a result, the toner image is transferred to the paper P.

  A fixing unit 7 a is provided downstream of the image forming unit 5 in the sheet conveyance direction. The fixing unit 7a heats and presses the paper P on which the toner image is transferred. The fixing unit 7a of the present embodiment includes a heating roller 72 having a built-in heating element 71 and a pressure roller 73 that presses against the heating roller 72 to form a nip. The paper P carrying the unfixed toner image is sent to the fixing unit 7a, and the paper P enters the nip. As a result, the toner is melted and fixed on the paper P by heating and pressing.

  The fixed sheet P is guided to the discharge conveyance path 7b. The discharge conveyance path 7b feeds the fixed (printed) paper P upward and discharges it to the uppermost discharge tray 74 of the main body. Note that the discharge conveyance path 7 b is provided with a conveyance roller pair 75 and a discharge roller pair 76 that rotate and convey the paper P toward the discharge tray 74.

(Hardware configuration of printer 100)
Next, a hardware configuration of the printer 100 according to the embodiment will be described with reference to FIG. FIG. 2 is a block diagram illustrating an example of a hardware configuration of the printer 100 according to the embodiment.

  As shown in FIG. 2, the printer 100 according to the present embodiment includes a main control unit 8 inside. The main control unit 8 performs overall control, communication control, and image processing, and controls each unit of the printer 100. For example, the main control unit 8 is a substrate including a CPU 81, an image processing unit 82, and the like.

  The main control unit 8 is connected to the storage unit 83. The storage unit 83 is a combination of nonvolatile and volatile storage devices such as ROM, RAM, flash ROM, and HDD. For example, the storage unit 83 stores a control program, control data, and the like for the printer 100. The CPU 81 is a central processing unit, and controls and calculates each unit of the printer 100 based on a control program and setting data stored in the storage unit 83.

  The image processing unit 82 is a circuit including an ASIC, an image processing RAM, and the like. The image processing unit 82 performs various image processing such as enlargement, reduction, density conversion, data format conversion, and the like on the image data in accordance with the setting. Then, the image processing unit 82 sends the image data after the image processing to the exposure unit 53. The exposure unit 53 receives this image data, performs scanning and exposure, and forms an electrostatic latent image on the photosensitive drum 51.

  The main control unit 8 is connected to the operation panel 101. The main control unit 8 recognizes an input made on the operation panel 101. Further, the main control unit 8 recognizes the input content by the key 103. Further, the main control unit 8 controls display by the liquid crystal display unit 102 and the indicator 104 on the operation panel 101. For example, when an error such as a jam occurs, the main control unit 8 turns on the indicator 104 to display that an error has occurred.

  The main control unit 8 is connected to the I / F unit 84. The I / F unit 84 communicates with a computer 200 (for example, a personal computer or a server) that is a transmission source of print data including image data to be printed and setting data for printing via a network or a cable. It is a communication interface. The printer 100 performs printing based on image data from the computer 200 input to the I / F unit 84 and setting data for printing. The data received by the I / F unit 84 includes, for example, data relating to print settings such as data specifying a paper size used for printing.

  An engine control unit for controlling a part related to image formation in the printer 100 (including the engine unit 90, for example, the sheet feeding unit 1, the conveyance path 2, the image forming unit 5, the fixing unit 7a, and the discharge conveyance path 7b). 9 is provided in the cabin. In addition, the control unit may be configured in a form in which the main control unit 8 and the engine control unit 9 are combined into one instead of separate the engine control unit 9 and the main control unit 8.

  The engine control unit 9 includes an engine CPU 91, a memory 92, a time measuring unit 93, and the like in order to control the operation of each part included in the engine unit 90 during printing. The engine CPU 91 is an arithmetic processing device that performs calculations and processing based on programs and data in the memory 92. The memory 92 is a ROM or RAM that stores control programs and data related to image formation. The timer 93 measures time related to control, such as the time between sheets. Note that the timing can also be performed by the engine CPU 91.

  The engine control unit 9 controls the operation of each unit of the engine unit 90 so that image formation is appropriately performed based on a control program and control data related to printing in the memory 92. In the present embodiment, an example in which an engine control unit 9 that specially controls a part that performs image formation is provided separately from the main control unit 8 is described. However, the engine control unit 9 and the main control unit 8 are integrated. The main control unit 8 may be assigned the function and processing of the engine control unit 9.

  The engine control unit 9 supplies paper P by turning on / off motors and the like that rotate various rotating bodies in the paper feeding unit 1, the conveyance path 2, the image forming unit 5, the fixing unit 7a, and the discharge conveyance path 7b. Perform paper transport control. The engine control unit 9 performs control related to printing by performing toner image formation control in the image forming unit 5 and fixing temperature control in the fixing unit 7a.

(Conveying paper toward the image forming unit 5)
Next, with reference to FIG. 3, details of a portion that conveys the sheet toward the image forming unit 5 in this embodiment will be described. FIG. 3 is a block diagram illustrating an example of a portion that conveys the sheet toward the image forming unit 5.

  As shown in FIG. 3, for example, the engine control unit 9, the sheet feeding unit 1, the conveyance path 2, the conveyance motor M <b> 1, the upstream sensor 61, and the downstream sensor are included in a part that is involved in sheet conveyance toward the image forming unit 5. 62 etc. are provided.

  The sheet feeding unit 1 is provided with a sheet feeding roller electromagnetic clutch 120 that transmits a driving force to the sheet feeding roller 12. When an instruction for printing (toner image formation) is given to the operation panel 101, the paper P used for printing is supplied by the paper feed roller 12 and the electromagnetic clutch 120 for the paper feed roller.

  The conveyance path 2 is provided with a registration roller electromagnetic clutch 41 that transmits a driving force to the registration roller pair 4. The registration roller pair 4 and the registration roller electromagnetic clutch 41 constitute a registration unit that feeds the paper P toward the image forming unit 5 in time with toner image formation.

  The transport path 2 is provided with an intermediate roller electromagnetic clutch 31 that transmits driving force to the intermediate roller pair 3. The intermediate roller pair 3 and the intermediate roller electromagnetic clutch 31 constitute an intermediate conveyance unit that conveys the paper P toward the registration roller pair 4 (registration unit) and generates deflection.

  The transport motor M <b> 1 is a drive source for rotating the registration roller pair 4, the intermediate roller pair 3, and the paper feed roller 12. The engine control unit 9 rotates the transport motor M1 so that the registration roller pair 4, the intermediate roller pair 3, and the paper feed roller 12 transport the paper P at a predetermined speed. Further, the transport motor M1 is connected to an electromagnetic clutch 120 for a feed roller, an electromagnetic clutch 41 for a registration roller, and an electromagnetic clutch 31 for an intermediate roller through a plurality of gears (not shown), and driving force is transmitted to each clutch. Is done.

  The engine control unit 9 turns on / off transmission of driving force from the transport motor M1 to the paper feed roller 12 by switching between connection and release of the magnetic clutch 120 for paper feed roller. Thereby, the engine control unit 9 controls ON / OFF of the rotation of the paper feed roller 12.

  When the feed roller 12 is rotated, the engine control unit 9 turns on (couples) the feed roller electromagnetic clutch 120 while rotating the transport motor M1. As a result, the paper feed roller 12 rotates. On the other hand, when stopping the paper feed roller 12, the engine control unit 9 stops the transport motor M1 or turns off (opens) the paper feed roller electromagnetic clutch 120. Thereby, the paper feed roller 12 is kept in a stopped state.

  The engine control unit 9 turns on / off transmission of driving force from the conveyance motor M1 toward the registration roller pair 4 by switching between connection and release of the electromagnetic clutch 41 for registration rollers. Thereby, the engine control unit 9 controls ON / OFF of the rotation of the registration roller pair 4.

  When rotating the registration roller pair 4, the engine control unit 9 turns on (couples) the registration roller electromagnetic clutch 41 while rotating the transport motor M <b> 1. As a result, the registration roller pair 4 rotates. On the other hand, when stopping the registration roller pair 4, the engine control unit 9 stops the transport motor M <b> 1 or turns off (opens) the registration roller electromagnetic clutch 41. Thereby, the registration roller pair 4 is kept in a stopped state.

  Further, the engine control unit 9 turns on / off transmission of driving force from the transport motor M1 toward the intermediate roller pair 3 by switching between connection and release of the electromagnetic clutch 31 for the intermediate roller. Thereby, the engine control unit 9 controls ON / OFF of the rotation of the intermediate roller pair 3.

  When rotating the intermediate roller pair 3, the engine control unit 9 turns on (connects) the intermediate roller electromagnetic clutch 31 while rotating the transport motor M <b> 1. Thereby, the intermediate roller pair 3 rotates. On the other hand, when stopping the intermediate roller pair 3, the engine control unit 9 stops the transport motor M <b> 1 or turns off (opens) the intermediate roller electromagnetic clutch 31. Thereby, the intermediate roller pair 3 is maintained in a stopped state.

  Further, as shown in FIG. 3, for example, the outputs of the upstream sensor 61 and the downstream sensor 62 relating to paper conveyance are input to the engine control unit 9.

  The upstream sensor 61 and the downstream sensor 62 are, for example, optical sensors. As the optical sensor, a reflective optical sensor including a light emitting unit that emits light toward the conveyance path 2 and a light receiving unit that receives the light reflected by the paper P can be used. Further, as the optical sensor, a transmissive optical sensor provided with an actuator that moves in contact with the paper P conveyed between the light emitting unit and the light receiving unit can be used. For example, in the transmission type optical sensor, when the paper P does not reach or pass, the actuator blocks the light from the light emitting portion to the light receiving portion, and when the paper P reaches or passes, the position of the actuator changes and the light receiving portion to the light receiving portion. The light reaches, and the output changes. As long as the arrival and passage of the paper can be detected, the sensor is not limited to the optical sensor, and other types of sensors may be used.

  In this way, the upstream sensor 61 and the downstream sensor 62 switch the output (output voltage value) when the presence of the paper P is detected and when it is not detected. The outputs of the upstream sensor 61 and the downstream sensor 62 are input to the engine control unit 9.

  The engine control unit 9 determines whether the sheet P has reached the registration roller pair 4 or has reached the sheet P by the output of the upstream sensor 61 (for example, switching from High to Low and High → Low and Low → High). You can recognize whether you have passed or are passing.

  Further, the engine control unit 9 detects the time from the passage of the rear end of the previous paper P to the detection of arrival of the next paper P to the registration roller pair 4 (detection of arrival of the upstream sensor 61) The time between the sheets of paper P can be measured. For example, the timer unit 93 (or the engine CPU 91) of the engine control unit 9 measures the time between sheets. The interval between sheets can be grasped as “time”, or can be grasped as “length” by multiplying the interval between sheets by a predetermined sheet conveyance speed.

  Further, the engine control unit 9 causes the sheet P to reach the installation position of the downstream sensor 62 by the output from the downstream sensor 62 (for example, by switching from High to Low and from High to Low and Low to High). It can be recognized whether the arrived paper P has passed or is passing. The engine control unit 9 causes the image forming unit 5 to start image formation (toner image formation) for one page based on the detection of the leading edge of the paper P by the downstream sensor 62. For example, specifically, exposure of the photosensitive drum 51 by the exposure unit 53 is started.

(Create deflection of paper P)
Next, the creation of the deflection of the paper P in the printer 100 according to the embodiment will be described with reference to FIG. FIG. 4 is an explanatory diagram for explaining the bending of the paper P.

  Specifically, FIG. 4 shows, from the left, the intermediate roller pair 3, the upstream sensor 61, the registration roller pair 4, the downstream sensor 62, and the image forming unit 5 (the photosensitive drum 51 and the transfer roller 55). 3 is a diagram schematically illustrating a sheet conveyance path from 3 to the image forming unit 5. FIG. For the sake of convenience, in FIG. 4, the sheet conveyance path is shown in a straight line, with the vertical positions of the intermediate roller pair 3, the registration roller pair 4, and the image forming unit 5 being substantially the same position. Further, in FIG. 4, for the sake of convenience, the distance between the intermediate roller pair 3 and the registration roller pair 4 and the distance between the registration roller pair 4 and the image forming unit 5 are shown as being substantially the same.

  In the printer 100 according to the present embodiment, the engine control unit 9 causes the intermediate roller pair 3 to convey the paper while deflecting the paper P while abutting the paper P against the registration roller pair 4. Therefore, the creation of the deflection of the paper P in the printer 100 of this embodiment will be described with reference to FIG.

  The engine control unit 9 rotates the intermediate roller pair 3 to convey the paper P supplied from the paper feeding unit 1 toward the registration roller pair 4. Then, the engine control unit 9 recognizes that the leading edge of the paper P that has passed through the intermediate roller pair 3 is detected by the upstream sensor 61 based on the output of the upstream sensor 61. In other words, the engine control unit 9 recognizes that the paper P has reached the upstream sensor 61 based on the output of the upstream sensor 61.

  When the paper P reaches the upstream sensor 61, the engine control unit 9 puts the registration roller pair 4 in a stopped state. Then, the engine control unit 9 continues the sheet conveyance for at least the deflection creation time in the intermediate roller pair 3 while the registration roller pair 4 is stopped. The bending creation time is a time for rotating the intermediate roller pair 3 in order to obtain a necessary bending amount (conveyance amount).

  As a result, the leading edge of the paper P hits the registration roller pair 4. Then, due to the elasticity of the bent paper P, the leading edge of the paper P follows the nip of the registration roller pair 4. As a result, even if the paper P is skewed (even if it is conveyed in an oblique state), the skew is corrected.

(Operation when the intermediate roller stops)
Next, an example of the operation when stopping the pair of intermediate rollers in the paper conveyance of the printer 100 according to the present embodiment will be described with reference to FIGS. 5 and 7. FIG. 5 is a timing chart illustrating an example of an operation when stopping the intermediate roller in the printer 100 according to the present embodiment. FIG. 7 is a timing chart for explaining the operation when stopping the pair of intermediate rollers in the conventional sheet conveyance.

  2. Description of the Related Art Conventionally, in an image forming apparatus, after a sheet arrives, the sheet is sent out after waiting for the sheet by a pair of registration rollers for a time longer than the time required for creating the deflection of the sheet. For example, if the required amount of paper between the sheets cannot be secured, a jam may occur where the front and rear sheets overlap. Further, if the necessary paper interval Δ1 is not secured and the arrival at the image forming unit 5 is too early, the image (toner image) may not be transferred to an appropriate position in the paper. When a sensor for detecting the arrival of paper is not provided in the vicinity of the intermediate roller pair, the paper interval is confirmed using a sensor provided in the vicinity of the registration roller pair. Specifically, after the paper reaches the registration roller pair, the intermediate roller pair is stopped, and the paper feed by the registration roller pair is delayed to secure the space between the papers.

  Here, with reference to FIG. 7, for example, an example of the operation of the conventional image forming apparatus when the intermediate roller pair is stopped and the sheet is made to wait by the registration roller pair in order to secure a sheet interval will be described. The conventional image forming apparatus is described as having a registration sensor, a registration roller electromagnetic clutch corresponding to the registration roller pair, and an intermediate roller electromagnetic clutch corresponding to the intermediate roller near the upstream side of the registration roller pair. To do.

  First, the uppermost chart in FIG. 7 shows the output of a sensor (registration sensor) provided near the registration roller pair. In this example, High of the registration sensor indicates a state where the presence of paper is detected. Low of the registration sensor indicates that no paper is detected.

  In FIG. 7, the middle chart shows signals for instructing connection and release of the intermediate roller electromagnetic clutch. For example, High indicates connection (rotates the intermediate roller pair), and Low indicates release (intermediate roller pair is stopped).

  Further, the lowermost chart in FIG. 7 shows a signal for instructing connection and release of the electromagnetic clutch for the registration roller. For example, High indicates connection (rotates the registration roller pair) and Low indicates release (stops the registration roller pair).

  First, in order to cause the sheet to abut against the registration roller pair and bend, a signal for stopping the registration roller pair is output (time t02) after detection of the trailing edge of the sheet (time t01). When the arrival of the next sheet is detected (time t03), the sheet is bent by a predetermined conveyance amount (after rotating for a predetermined characteristic time) to bend the sheet, and then the intermediate roller pair Is output (time t04).

  When it is time to feed the paper, such as when the necessary paper space Δ1 is secured, a signal for rotating the registration roller pair and the intermediate roller pair is output (time t05).

  Here, conventionally, at time t04, a signal for stopping the pair of intermediate rollers is output, and the electromagnetic clutch for intermediate rollers opens the clutch in response to this signal. In general, the electromagnetic clutch has a variation in response time. Even when the clutch is released, the intermediate roller pair continues to rotate with some inertia.

  Therefore, the stop of the intermediate roller pair may be delayed after outputting a signal for stopping the intermediate roller pair. If the stop of the intermediate roller pair is delayed, the sheet P is bent too much, and the sheet may come into contact with the conveyance path (guide plate for guiding the sheet conveyance), and noise may be generated. On the other hand, if the stop timing of the intermediate roller pair is advanced in order to avoid such noise, there is a high possibility that the sheet cannot be bent so that the skew can be eliminated. Therefore, in the printer 100 of the present embodiment, it is possible to eliminate the difficulty of both avoiding noise and reliably bending the paper P.

  Specifically, the operation when stopping the intermediate roller 3 in the printer 100 of the present embodiment will be described with reference to FIG.

  First, in FIG. 5, the three charts from the top (the charts (1) to (3)) are timing charts showing the operation in the conveyance path 2 when the space between the sheets is more than necessary. is there. Of the charts in FIG. 5, the uppermost chart (1) shows an example of the output of the upstream sensor 61. Of the respective charts in FIG. 5, the second chart (2) from the top shows signals instructing connection and release of the intermediate roller electromagnetic clutch 31 output from the engine control unit 9. Of the charts in FIG. 5, the third chart (3) from the top shows a signal instructing connection and release of the registration roller electromagnetic clutch 41 output from the engine control unit 9.

  Further, in FIG. 5, the lower three charts (the charts (4) to (6)) are the ones on the conveyance path 2 when the intermediate roller pair 3 is stopped for the purpose of securing a gap between sheets. It is a timing chart which shows operation. The third chart (4) from the bottom of each chart in FIG. 5 shows an example of the output of the upstream sensor 61. Of the respective charts in FIG. 5, the second chart (5) from the bottom shows signals instructing the connection and release of the intermediate roller electromagnetic clutch 31 output from the engine control unit 9. Of the charts in FIG. 5, the bottom chart (6) shows a signal instructing connection and release of the registration roller electromagnetic clutch 41 output by the engine control unit 9.

  Further, in the charts (1) and (4) in FIG. 5, High indicates a state in which the upstream sensor 61 detects the presence of the paper P. Low indicates that the upstream sensor 61 has not detected the presence of the paper P. The charts (2) and (5) in FIG. 5 show the output states of signals that the engine control unit 9 instructs the intermediate roller electromagnetic clutch 31 to be connected and released. For example, High indicates connection (intermediate roller pair 3 is rotated), and Low indicates release (intermediate roller pair 3 is stopped). The charts (3) and (6) in FIG. 5 show the output states of signals that the engine control unit 9 instructs the registration roller electromagnetic clutch 41 to be connected and released. For example, High indicates connection (registration roller pair 4 is rotated), and Low indicates opening (registration roller pair 4 is stopped).

  First, the operations of the intermediate roller pair 3 and the registration roller pair 4 when a sufficient paper space is secured will be described using the charts (1) to (3) in FIG.

  First, in the printer 100 of the present embodiment, the engine control unit 9 recognizes the paper interval (time) by counting the time from when the upstream sensor 61 detects the passage of the rear end of the previous sheet to the detection of the arrival of the next sheet. For example, the predetermined paper interval that should be secured is about several hundred milliseconds (for example, 300 ms). The interval between papers that should be secured in advance varies depending on the model. Also, the paper interval that is predetermined as to be secured is stored in, for example, the memory 92 and referred to by the engine control unit 9. Since the paper transport speed is predetermined, the engine control unit 9 multiplies the time from the detection of the trailing edge of the previous paper P to the detection of the next paper arrival by the predetermined paper transport speed. The interval between sheets may be recognized as the length.

  First, as shown in the chart of FIG. 5A, the engine control unit 9 detects and recognizes passage of the trailing edge of the sheet based on the output of the upstream sensor 61 (time t11). Thereafter, in order to cause the paper P to abut against the registration roller pair 4 and bend, the engine control unit 9 outputs a signal for stopping the registration roller pair 4 (time t12) as shown in the chart of FIG. 5 (3). .

  Then, as shown in the chart of FIG. 5A, the engine control unit 9 detects and recognizes the arrival of the next sheet at the registration roller pair 4 (upstream sensor 61) based on the output of the upstream sensor 61. (Time t13). The interval from t11 to t13 is a time indicating the interval between sheets. In the charts of FIGS. 5 (1) to 5 (3), the engine control unit 9 recognizes that the necessary paper interval is secured because the paper interval is equal to or greater than the predetermined required paper interval Δ1.

  Then, the engine control unit 9 causes the intermediate roller pair 3 to carry the sheet P by a predetermined conveyance amount in order to bend the paper P (rotate only for a predetermined bending creation time). Thereafter, the engine control unit 9 outputs a signal for connecting the registration roller electromagnetic clutch 41 (time t14) because the necessary paper interval Δ1 is secured. Thereby, the engine control unit 9 rotates the registration roller pair 4. As shown in the chart (2) in FIG. 5, when the necessary paper interval Δ1 is secured, the engine control unit 9 feeds the paper P from the registration roller pair 4 without stopping the intermediate roller pair 3.

  Next, using the charts (4) to (6) in FIG. 5, the intermediate roller pair 3 is stopped for a reason such that a sufficient space between the sheets is not secured, and the sheet P is moved to the registration roller pair 4. Next, the operation of the registration roller pair 4 and the like when standing by will be described.

  First, as shown in the chart of FIG. 5 (4), the engine control unit 9 detects and recognizes passage of the trailing edge of the paper based on the output of the upstream sensor 61 (time t21). Thereafter, in order to cause the sheet P to abut against the registration roller pair 4 and bend it, the engine control unit 9 sends a signal for stopping the registration roller pair 4 as shown in the chart of FIG. 5 (6). 41 (time t22).

  Then, as shown in the chart (4) of FIG. 5, the engine control unit 9 detects and recognizes the arrival of the next sheet at the registration roller pair 4 (upstream sensor 61) based on the output of the upstream sensor 61. (Time t23). The interval from t21 to t23 is a time indicating the interval between sheets. In the case of the charts of FIGS. 5 (4) to (6), the engine control unit 9 recognizes that the required paper interval Δ1 is not secured because the paper interval is smaller than the predetermined required paper interval Δ1. Then, it is determined that the sheet P needs to be waited by the registration roller pair 4.

  Then, the engine control unit 9 causes the intermediate roller pair 3 to carry a predetermined amount of conveyance from the arrival of the next sheet to the registration roller pair 4 (upstream sensor 61) in order to bend the sheet P. (Rotate for a predetermined deflection creation time). After that, the engine control unit 9 outputs a signal for opening the intermediate roller electromagnetic clutch 31 because the sheet P is bent as much as necessary (time t24). Thereby, the engine control unit 9 stops the intermediate roller pair 3.

  At this time, as described above, due to variations in the time required to open the intermediate roller electromagnetic clutch 31, the intermediate roller pair 3 may not stop immediately in response to the fall of the signal for opening the intermediate roller electromagnetic clutch 31. is there. In other words, the stop of the intermediate roller pair 3 may be delayed. As a result, the amount of bending of the paper P becomes excessive, and the paper P may come into contact with the transport path 2 and make a sound.

  Therefore, in order to prevent the sheet P from being squeezed due to excessive bending, when the registration roller pair 4 waits for the sheet P, the engine control unit 9 synchronizes the signal for opening the intermediate roller electromagnetic clutch 31 with the output, A signal for connecting the roller electromagnetic clutch 41 is output (time t24). The output time point of the signal for releasing the intermediate roller electromagnetic clutch 31 and the output time point of the signal for connecting the registration roller electromagnetic clutch 41 may not coincide with each other.

  Thereafter, the engine control unit 9 outputs a signal for opening the registration roller electromagnetic clutch 41 (time t25). As described above, the engine control unit 9 temporarily rotates the registration roller pair 4 in order to eliminate the bending (bending elimination operation, t24 to t25). In this deflection elimination operation, the engine control unit 9 temporarily rotates the registration roller pair 4 in a range in which the conveyance amount of the registration roller pair 4 is less than or equal to the conveyance amount of the intermediate roller pair 3 at the deflection creation time.

  When the necessary paper interval Δ1 is secured, the engine control unit 9 outputs a signal for connecting the intermediate roller electromagnetic clutch 31 and the registration roller electromagnetic clutch 41 (time t26). Thereby, the engine control unit 9 rotates the intermediate roller pair 3 and the registration roller pair 4 to convey the paper P toward the image forming unit 5.

(Flow of paper transport control)
Next, an example of the flow of paper conveyance control according to the present embodiment will be described based on FIG. FIG. 6 is a flowchart illustrating an example of the flow of paper conveyance control. In this description, an example in which a plurality of pages are continuously printed will be described.

  First, the start of FIG. 6 is the time when the engine control unit 9 recognizes the arrival of the first page of paper P on the registration roller pair 4 based on the output of the upstream sensor 61 by the start of the print job. Although not directly included in this flow, when a plurality of pages are continuously printed, the paper feeding unit 1 feeds the paper P at a predetermined timing. Basically, when a plurality of pages are continuously printed, the intermediate roller pair 3 does not stop, and the sheet conveying operation toward the registration roller pair 4 is continued.

  Then, the engine control unit 9 rotates the registration roller pair 4 to send the first page of paper P from the registration roller pair 4 to the image forming unit 5 to execute printing of the first page (step # 1). Thereafter, the paper P is discharged to the discharge tray 74 through the image forming unit 5 and the fixing unit 7a.

  Then, the engine control unit 9 recognizes the rear end passage of the previous paper P based on the output of the upstream sensor 61 (step # 2). Then, the engine control unit 9 controls the registration roller electromagnetic clutch 41 to stop the registration roller pair 4 (step # 3).

  Next, the paper of the next page is conveyed by the paper feeding by the paper feeding unit 1 and the rotation of the intermediate roller pair 3, and the engine control unit 9 performs registration rollers for the next paper P based on the output of the upstream sensor 61. The arrival at the pair 4 (upstream sensor 61) is detected (step # 4).

  The engine control unit 9 confirms whether the measured paper interval (time) is equal to or greater than a predetermined required paper interval Δ1 (required paper interval time) (step # 5). In other words, the engine control unit 9 checks whether or not the necessary paper interval Δ1 is secured (step # 5).

  If the necessary paper interval Δ1 is secured (Yes in step # 5), the engine control unit 9 causes the intermediate roller pair 3 to create a deflection (step # 6). Then, the engine control unit 9 controls the registration roller electromagnetic clutch 41 and the intermediate roller electromagnetic clutch 31 to rotate the registration roller pair 4 and the intermediate roller pair 3 so as to feed the paper P from the registration roller pair 4 ( Step # 7). For example, the engine control unit 9 rotates the registration roller pair 4 when a predetermined deflection creation time elapses after detection of the arrival of the sheet at the upstream sensor 61. Thereby, the produced | generated bending amount becomes substantially equal in each page, and it can be set as the appropriate bending amount.

  Then, the downstream sensor 62 detects the leading edge of the paper P by the rotation of the registration roller pair 4 (step # 8). When the downstream sensor 62 detects the leading edge of the paper P, the engine control unit 9 causes the image forming unit 5 to start forming a toner image (step # 9). In other words, the image forming unit 5 starts toner image (image) formation based on the detection of the leading edge of the paper P by the downstream sensor 62 (step # 9). As a result, regardless of whether or not the sheet P protrudes from the registration roller pair 4, toner image formation is started based on a certain point in time, and blurring of the image forming position of the sheet P can be eliminated. Thereafter, the paper P is discharged to the discharge tray 74 through the image forming unit 5 and the fixing unit 7a.

  Then, the engine control unit 9 confirms whether or not printing of all pages has been completed (step # 10). If printing of all pages has not been completed (No in step # 10), the flow returns to step # 2. On the other hand, when the printing of all pages is completed, the engine control unit 9 causes the respective units of the print engine unit 90 to sequentially stop the printing operation, and this flow ends (step # 11 → end).

  On the other hand, if the necessary paper interval Δ1 is not secured (No in Step # 5), the engine control unit 9 rotates the intermediate roller pair 3 for a predetermined deflection creation time, for example, to create a deflection (Step S5). # 12). Then, the engine control unit 9 controls the intermediate roller electromagnetic clutch 31 to stop the intermediate roller pair 3 (step # 13).

  Further, the engine control unit 9 controls the registration roller electromagnetic clutch 41 to temporarily rotate the registration roller pair 4 so as to perform a deflection eliminating operation (step # 14). Then, the engine control unit 9 controls the registration roller electromagnetic clutch 41 to stop the registration roller pair 4 (step # 15).

  Then, the engine control unit 9 confirms whether the measured paper interval (time) is equal to or greater than a predetermined required paper interval Δ1 (required paper interval time) over time (step # 16). If the necessary paper interval Δ1 is not secured (No in step # 16), the flow returns to step # 15. On the other hand, if the necessary paper interval Δ1 is ensured (Yes in step # 16), the flow proceeds to step # 7, the feeding of the paper P from the registration roller pair 4 is started, and printing is performed.

  In this way, the image forming apparatus (for example, the printer 100) according to the embodiment is provided on the upstream side in the paper conveyance direction with respect to the image forming unit 5 that forms an image on the paper P, and the image forming unit 5 A registration roller (registration roller pair 4) that feeds the paper P toward the part 5 in accordance with image formation, a rotating body (intermediate roller pair 3) that conveys the paper P toward the registration roller, and upstream of the registration roller Including an upstream detector (upstream sensor 61) for detecting paper arrival at the registration roller, and the rotating body rotates for a predetermined deflection creation time from detection of paper arrival by the upstream detector. Then, it stops, and the registration roller is in a stopped state at the time of paper arrival detection, and when the rotating body stops after the bending creation time rotation, it temporarily rotates. It performs a deflection resolving to stop the rotating body and the resist roller, after the deflection resolving, start rotating simultaneously, to convey the sheet P toward the image forming unit 5.

  As a result, the rotating body (intermediate roller pair 3) is rotated for the bending time to sufficiently bend the paper P, so that the skew is reliably eliminated. Then, after the sheet P is bent to eliminate skew, the registration roller (registration roller pair 4) operates to slightly convey the sheet P as the rotating body stops, due to the bending cancellation operation. Therefore, even if the rotation of the rotating body is delayed due to variations in the time until the rotating body stops, it is possible to prevent the sheet P from being bent as much as noise is generated due to contact of the paper P with the conveyance path 2 or the like.

  Further, the registration roller (registration roller pair 4) is rotated and stopped by the deflection eliminating operation. In addition, the conveyance amount of the registration roller in the bending elimination operation may vary. Accordingly, the time from the start of conveyance from the registration roller to the arrival of the image forming position on the paper P in the image forming unit 5 may vary. Therefore, the image forming apparatus (for example, the printer 100) according to the embodiment is provided between the registration roller and the sheet conveyance path of the image forming unit 5, and a downstream detector (detecting the arrival of the sheet sent from the registration roller) Including the downstream sensor 62), the image forming unit 5 starts image formation based on the paper arrival detection by the downstream detector. Thus, when the registration roller and the rotating body (intermediate roller pair 3) are rotated after the deflection eliminating operation, image formation is started based on a certain standard. An image can be formed at an accurate position. The image forming unit 5 may start image formation triggered by detection of paper arrival by the downstream detector, or start image formation after a predetermined time has elapsed from detection of paper arrival by the downstream detector. May be.

  Further, the registration roller (registration roller pair 4) conveys the sheet P by a conveyance amount within a range equal to or less than the sheet conveyance amount by the rotation of the rotating body (intermediate roller pair 3) during the deflection generation time in the deflection elimination operation. Thereby, for example, the sheet P can be prevented from being conveyed more than necessary as the sheet P is stretched in the bend elimination operation.

  In addition, the rotating body (intermediate roller pair 3) has a predetermined paper interval Δ1 that is determined in advance as a space between the paper P reached by the upstream detector (upstream sensor 61) and the previous paper P should be secured. Only when it is detected that the rotation is smaller than the detection of the arrival of the sheet by the upstream detection body, the rotation is stopped and the registration roller (registration roller pair 4) is stopped substantially in synchronization with the stop of the rotation body. I do. As a result, an operation for securing the paper gap and an operation for avoiding noise generation are performed only when the paper gap is to be secured.

  Further, when the rotating body (intermediate roller pair 3) detects that the interval between the preceding sheet P and the arrived sheet P is equal to or more than the necessary sheet interval Δ1 by the upstream side detection body (upstream side sensor 61), The rotation continues even if the deflection creation time is rotated from the paper arrival detection by the upstream detector, and the registration roller (registration roller pair 4) starts rotating when the deflection creation time has elapsed from the paper arrival detection by the upstream detector. The bend elimination operation is not performed. As a result, if the necessary sheet interval Δ1 is ensured, the sheet conveyance and image formation are performed without stopping the rotating body. Therefore, the image forming speed (printing speed) can be increased, and the productivity of the image forming apparatus (for example, the printer 100) can be improved.

  Next, another embodiment will be described. In the above-described embodiment, the example in which the engine control unit 9 recognizes the gap between sheets based on the output of the upstream sensor 61 and performs rotation control of the registration roller pair 4 and the intermediate roller pair 3 has been described. However, instead of the engine control unit 9, the main control unit 8 or another control circuit may recognize the gap between the sheets and control the rotation of the registration roller pair 4 and the intermediate roller pair 3.

  Moreover, in this embodiment, the example which stops the intermediate roller pair 3 was demonstrated. However, when the distance between the registration roller pair 4 and the paper feed roller 12 is short and the intermediate roller pair 3 is not provided, the paper feed roller 12 may be stopped to secure the space between the papers.

  Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention.

  The present invention is applicable to an image forming apparatus including a registration roller pair that feeds a sheet by bending it and an intermediate roller.

100 Printer (image forming apparatus) 3 Intermediate roller pair (rotating body)
4 Registration roller pair 5 Image forming part 61 Upstream sensor (upstream detector)
62 Downstream sensor (downstream detector) P Paper Δ1 Required paper space

Claims (5)

An image forming unit for forming an image on paper;
A pair of registration rollers that are provided upstream of the image forming unit in the paper conveyance direction, and that feeds the paper toward the image forming unit in accordance with image formation;
A rotating body that conveys paper toward the pair of registration rollers;
Provided upstream of the registration roller pair, and includes an upstream detector for detecting the arrival of paper to the registration roller pair,
When the rotating body rotates for a predetermined deflection creation time from the paper arrival detection by the upstream detector,
The registration roller pair is in a state of being stopped at the time of paper arrival detection, and when the rotating body stops after the bending creation time rotation, performs a bending canceling operation to stop after temporarily rotating,
The image forming apparatus, wherein the rotating body and the registration roller pair simultaneously start rotation after the deflection eliminating operation and convey the sheet toward the image forming unit. A downstream detector that is provided between the registration roller pair and a sheet conveyance path of the image forming unit and detects arrival of the sheet fed from the registration roller pair;
The image forming apparatus according to claim 1, wherein the image forming unit starts image formation based on paper arrival detection by the downstream detector.   3. The registration roller pair according to claim 1, wherein the pair of registration rollers conveys a sheet with a conveyance amount in a range equal to or less than a sheet conveyance amount in rotation of the rotator during the deflection creation time. The image forming apparatus described The upstream detection body is only detected when it is detected that the space between the sheet reached by the upstream detection body and the previous sheet is smaller than the required paper space that is determined in advance to be secured. Stops when the deflection creation time rotates from the paper arrival detection by
4. The image forming apparatus according to claim 1, wherein the registration roller pair performs the bending elimination operation substantially in synchronization with the stop of the rotating body. 5. The rotating body detects the deflection creation time from the paper arrival detection by the upstream detector when it is detected by the upstream detector that the interval between the preceding paper and the reached paper is not less than the required paper. Even if it rotates, it continues to rotate,
5. The image forming apparatus according to claim 4, wherein the registration roller pair starts rotating and does not perform the deflection elimination operation when the deflection creation time elapses after the paper arrival detection by the upstream side detection body. .

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