JP5693202B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus for transferring a toner image carried on an image carrier onto a recording material by using an electrophotographic technique such as a copying machine or a laser printer. Specifically, the present invention relates to an image forming apparatus having a transfer belt for transferring and conveying a recording material.

  In an electrophotographic apparatus in which a recording material is carried and conveyed by a transfer belt stretched by a plurality of rollers, the recording material on the transfer belt is electrostatically attracted to the transfer belt as it passes through the transfer nip portion.

  However, if the stiffness of the recording material is weak, the recording material cannot be separated from the transfer belt only by using the curvature of the separation roller as the separating tension member for stretching the transfer belt and the stiffness of the recording material. That is, the recording material remains stuck to the transfer belt at the position of the separation roller, resulting in separation failure. Therefore, as a configuration in which the transfer belt is waved at the separation position, there is a method in which a projection is uniformly formed on the surface of the separation roller on which the transfer belt is stretched to separate the recording material (Patent Document 1). By using such a configuration, waviness can be formed on the transfer belt at the separation position, but a large tension is always applied locally to the transfer belt. As a result, transferability becomes unstable due to resistance unevenness due to local wear of the transfer belt.

  Patent Document 2 discloses a method for reducing wear due to deformation while deforming a sheet carrying a recording material for separating the recording material. Patent Document 2 describes a configuration in which rollers are provided as push-up means that can move to a position where the transfer sheet is pushed up from the inside and a position where the transfer sheet is not pushed up. In the method described in Patent Document 2, the recording material is separated by pushing up the transfer sheet with a roller, and the transfer sheet is not pushed up while the recording material is not separated.

JP-A-9-015987 JP-A-5-119636

  When such a configuration is applied to the transfer belt, the transfer belt is locally pushed up by a roller during the separation step from the transfer member that transfers the toner image to the recording material on the transfer belt to the downstream side in the recording material conveyance direction. It becomes the structure which arrange | positions the raising means which can be. When the stiffness of the recording material such as thin paper is weak, the recording material is swelled by conveying the recording material while the transfer belt is locally pushed up, and the strength of the recording material during the separation process is increased. Can be bigger.

  However, there is a case where the recording material is left in the recording material container and the first recording material is wound. The wrapping of the recording material is suppressed by imparting rigidity to the leading end of the recording material while the push-up means pushes up the transfer belt. However, when the push-up member is retracted from the transfer belt, the leading edge of the recording material starts to curl. If the timing at which the push-up member retreats from the transfer belt is set in accordance with the timing at which the leading edge of the recording material is separated from the transfer belt, the timing at which the leading edge of the recording material being conveyed begins to curl after being separated from the transfer belt. As a result, the recording material may be conveyed toward the fixing device with the curl at the leading end of the recording material being large.

In order to solve the above problems, an image forming apparatus of the present invention includes an image carrier that carries a toner image,
Formed on the image carrier on a recording material accommodating portion for accommodating a recording material, a movable belt member for carrying and conveying the recording material conveyed from the recording material accommodating portion, and a recording material carried and conveyed by the belt member A transfer member for electrostatically transferring the toner image formed thereon, and a local protrusion in the width direction of the belt member, and the inner side of the belt member downstream of the transfer member in the conveyance direction of the recording material A push-up member that pushes up from the side, a pre-fixing guide that is disposed downstream of the belt member in the recording material conveyance direction and guides the conveyed recording material, and is downstream of the belt member in the recording material conveyance direction. are arranged from the fixing front guide on the side on the upstream side, the separation after the guide for the belt member to guide at the guide surface and the separated recording material is guided by the pre-fixing guide An image forming apparatus having a fixing unit that fixes a toner image on a recording material at a nip portion. The push-up member pushes up the belt member to separate the recording material, and the push-up member pushes up the belt member. A first mode for maintaining the state of the recording material until the leading edge of the recording material reaches the pre-fixing guide; and the push-up member pushes up the belt member to separate the recording material, and the push-up member moves the belt member the operation of saving the pushed state, that the leading edge of the recording material having an execution unit for executing a second mode in which before reaching the pre-fixing guide even after having reached the post-separation guide Features.

  According to the present invention, when the recording material is separated by being pushed up, even the first recording material can be prevented from curling the tip of the recording material after being separated from the transfer belt.

It is a figure explaining an image forming apparatus. It is a figure explaining operation | movement of a separation assistance apparatus. It is a figure explaining the structure of a separation auxiliary device. It is a block diagram of a control circuit. 10 is a flowchart of the operation of the separation assisting device during a single print job. 6 is a flowchart of the operation of the separation assisting device during a continuous print job.

(First embodiment)
(Image forming device)
The configuration and operation of the image forming apparatus according to the present exemplary embodiment will be described with reference to FIG.

  Reference numerals 1Y, 1M, 1C, and 1k denote photosensitive drums as image carriers, which are driven to rotate in the direction of arrow A. The surface is uniformly charged to a predetermined voltage by charging devices 2Y, 2M, 2C and 2k. The charged photosensitive drum surface is exposed by exposure devices 3Y, 3M, 3C, and 3k including a laser beam scanner to form an electrostatic latent image. The output of the laser beam scanner is turned on / off based on the image information, whereby an electrostatic latent image corresponding to the image is formed on each photosensitive drum. The developing devices 4Y, 4M, 4C, and 4k contain yellow (Y), magenta (M), cyan (C), and black (k) toners of chromatic color toner, respectively. A predetermined voltage is applied to the developing device, and the above-described electrostatic latent images are developed as they pass through the developing devices 4Y, 4M, 4C, and 4k, and are respectively developed on the photosensitive drums 1Y, 1M, 1C, and 1k. A toner image is formed. In the present embodiment, a reversal development method is used in which toner is attached to the exposed portion of the electrostatic latent image for development.

  The toner images formed on the photosensitive drums 1Y, 1M, 1C, and 1k are primarily transferred onto the intermediate transfer belt 6 by the corresponding primary transfer rollers 5Y, 5M, 5C, and 5k. In this way, four color toner images are transferred onto the intermediate transfer belt 6 in a superimposed manner.

  The intermediate transfer belt 6 is disposed so as to be in contact with the surface of the photosensitive drum 1 and is stretched by stretching rollers 20, 21, 22 as a plurality of stretching members in the direction of arrow G to 250-. It is designed to rotate at 300 mm / sec. In the present embodiment, the tension roller 20 is a tension roller that controls the tension of the intermediate transfer belt 6 to be constant. The tension roller 22 is a driving roller for the intermediate transfer belt 6.

  The transfer belt 24 that carries and transports the recording material is a belt member that is stretched by stretching rollers 25, 26, and 27 as a plurality of stretching members and is movable in the direction of arrow B at 250 to 300 mm / sec. As the transfer belt 24, an appropriate amount of carbon black as an antistatic agent is contained in a resin such as polyimide and polycarbonate, or various rubbers, the volume resistivity is 1E + 9 to 1E + 14 [Ω · cm], and the thickness is 0.07 to 0.00. What is set to 1 [mm] is used. Further, as the transfer belt 24, an elastic body having a Young's modulus measured by a tensile test method (JIS K 6301) of 0.5 MPa or more and 10 MPa or less is used.

  By using a member having a Young's modulus of 0.5 MPa or more in the tensile test of the transfer belt 24, the belt can be sufficiently rotated and driven. On the other hand, by using a member capable of sufficiently elastic deformation of 10 MPa or less, the recording material P is effectively swelled by the separation assisting device 40 described later, and the recording material from the transfer belt 24 is more effective. P separation can be achieved. In addition, since the member that can be sufficiently elastically deformed easily undergoes a relaxation phenomenon of the member when the amount of deformation is reduced from the deformed state, it is possible to reduce the wear of the transfer belt 24 by the separation assisting device 40. become. 26 bends the transfer belt 24 along its own curvature, and functions as a separation stretching roller that separates the recording material when the separation assisting device 40 is not used.

  The recording material is stored separately for each type of recording material in a cassette (recording material storage unit) (not shown). When the supply start signal is output, the recording material P is transported from the cassette by a roller (not shown) based on the supply start signal and guided to the registration roller 8. The registration roller 8 temporarily stops the recording material P and supplies the recording material P to the transfer belt 24 in synchronization with the toner image on the intermediate transfer belt 6 being conveyed.

  On the downstream side in the recording material conveyance direction (in the direction of arrow B) from the registration roller 8, a transfer nip N that faces the intermediate transfer belt stretching roller 21 and transfers the toner image to the recording material carried on the transfer belt 24. A secondary transfer roller 9 is disposed as a transfer member for forming the. When the recording material is conveyed to the transfer nip N, a secondary transfer voltage having a polarity opposite to that of the toner is applied to the secondary transfer roller 9, whereby the toner image on the intermediate transfer belt 6 is batched onto the recording material P. Is transferred electrostatically. The secondary transfer voltage is controlled at a constant voltage. The voltage value of the constant voltage is determined according to the current required for transfer. The current required for secondary transfer varies in the range of about 30 to 60 A depending on factors such as the dry state of the recording material, the environment, and the amount of toner to be transferred.

  The secondary transfer roller 9 is composed of an elastic layer of ion conductive foam rubber (NBR rubber) and a cored bar. The outer diameter is 24mm, the roller surface roughness Rz is 6.0-12.0 (μm), the resistance is N / N (23 ° C, 50% RH), and the transfer roller is 1E + 5 to 1E + 7Ω with 2kV applied. ing. A secondary transfer high-voltage power supply 13 with a variable supply bias is attached to the secondary transfer roller 9.

  The recording material P separated from the transfer belt 24 after the transfer passes through the guide surface of the post-separation guide 29, and is arranged on the downstream side of the post-separation guide 29 in the recording material conveyance direction and guides the pre-fixing guide 29 to the fixing device 60. Then, it is conveyed to the fixing device 60. The recording material is nipped by the fixing nip portion in the fixing device 60, and the toner image is fixed on the recording material by a heating and pressing process. After the toner image is fixed, the recording material P is discharged out of the machine.

(Configuration of separation assist device)
As a means for pushing up the transfer belt 24 in order to assist the separation from the transfer belt 24, the recording material is separated by pushing up the transfer belt 24 locally at a position between the secondary transfer roller 9 and the separation stretching roller 26. A separation assisting device 40 is provided that is deformed by deformation. When the separation assisting device 40 pushes up the transfer belt, the transfer belt is in a state where local irregularities are formed in the width direction, as shown in FIG.

  In the present embodiment, as shown in FIG. 1A, the separation assisting device 40 is disposed on the inner surface of the transfer belt 24 on the downstream side of the secondary transfer unit and on the upstream side of the separation stretching roller 26 in the recording material conveyance direction. Placed on the side. A separating tension roller 26 is disposed. A post-separation guide 29 for guiding the separated recording material to the fixing device 60 on the guide surface is disposed further downstream than the separation tension roller 26.

  2A and 2B show the detailed configuration and operation of the separation assisting device 40. FIG. The separation assisting device 40 includes a separation assisting roller 41 that is a separating member, a roller frame 42 that rotatably supports the separation assisting roller 41, and a roller swinging central shaft 43 that serves as a swinging center of the separation assisting roller 41. Further, a roller driving gear 44 for swinging the separation auxiliary roller 41 around the roller swinging central shaft 43, a motor drive transmission gear 45 for transmitting a driving force to the roller driving gear 44, and a drive source A motor 46 is provided. The rotational motion of the motor 46 is transmitted to the roller drive gear 44 by the motor drive transmission gear 45. Here, since the bearing is provided between the roller drive gear 44 and the roller swing center shaft 43, the roller swing center shaft 43 is not affected by the rotational drive by the motor 46 and does not move. ing.

  FIG. 2A shows a retreat position where the separation auxiliary roller 41 is separated from the transfer belt 24 and the separation auxiliary roller 41 is retreated from the pushed-up position. FIG. 2B shows a push-up position where the separation auxiliary roller 41 abuts against the inner surface of the transfer belt 24 and pushes up the transfer belt 24 locally. The separation auxiliary roller 41 is pushed up in the Y1 direction from the roller retraction position shown in FIG. 2 (a) by the predetermined amount of forward rotation of the motor 46 around the roller swinging central shaft 43 as shown in FIG. 2 (b). Can move to position. Further, by a predetermined amount of reverse rotation of the motor 46, the separation assist roller 41 can move from the pushed-up position in FIG. 2B in the Y2 direction and move to the retracted position shown in FIG. That is, the separation assisting roller 41 performs such a swinging motion by forward and reverse rotation.

  Separation auxiliary roller 41 made of ethylene-propylene rubber (EPDM), outer diameter is 6 to 10 mm, width is 5 to 15 mm. When such a separation assisting roller 41 pushes up the transfer belt 24, a local protrusion is formed on the transfer belt 24 in the width direction. Here, the width direction is a direction perpendicular to the moving direction of the moving belt surface.

  In the state of FIG. 2A, the distance from the separation auxiliary roller 41 to the separation stretching roller 26 is 4 to 8 mm. In the state of FIG. 2B, the separation auxiliary roller 41 has the belt surface of the transfer belt 24 on the inner surface. From the side, it is pushed up 6 mm from the planar state of FIG. Of course, the value is not intended to be limited to this value, and may be set as appropriate within a range of about 3 to 10 mm. In this embodiment, the separation auxiliary roller 41 is separated from the transfer belt 24 at the retracted position in FIG. 2A. However, the separation auxiliary roller 41 is attached to the transfer belt 24 so as not to deform the transfer belt 24 at the retracted position. It may be lightly touching.

  The separation effect of the recording material by the separation assisting device 40 will be described. Since the secondary transfer roller 9 applies a charge having a polarity opposite to that of the toner to the inner surface of the transfer belt 24, the recording material is adsorbed to the transfer belt 24 after the transfer nip N. Further, a recording material with low rigidity such as thin paper is easily deformed. For these reasons, as shown in FIG. 1B, the recording material is warped along the local deformation in the width direction generated in the transfer belt 24 by pushing up. As a result, the cross-sectional secondary moment of the recording material, that is, the strength of the recording material is increased. Even when the recording material is thin, such as thin paper, an effective separation effect can be obtained for separating the recording material.

  The separation auxiliary roller 41 included in the separation auxiliary device 40 may be one in the region through which the recording material passes. However, in this case, the range in which the recording material undulates in the width direction of the recording material becomes narrow. In order to wave the recording material in the width direction, it is preferable that a plurality of recording materials exist in the width direction within a range in which the recording material passes.

  As shown in FIG. 3, in the present embodiment, three auxiliary separation rollers 41 are provided in the width direction. The distance L2 between the adjacent separation assist rollers 41 is 125 mm. An interval L3 between the separation auxiliary rollers 41 at both ends is 250 mm. The separation assist roller 41 in the central portion is arranged so that the recording material of any width is positioned at the substantially central portion of the recording material conveyed so that the center in the width direction substantially coincides with a common reference line. ing. In particular, when a thin A-size recording material having a size of 297 mm in the width direction is conveyed, three places are pushed up with respect to the A4-sized recording material. This is effective for further improving the separability of the A4 size recording material.

  Further, in the present embodiment, the distance from the protrusion formation position where the separation auxiliary roller 41 forms a protrusion on the transfer belt to the pre-fixing guide is smaller than the recording material having the smallest size in the conveyance direction of the recording material used in the image forming apparatus. Is set to be shorter. As a result, even if the recording material having the smallest size in the transport direction is transported, the strength of the recording material is maintained to be increased by the separation auxiliary roller until the leading end of the recording material reaches the pre-fixing guide 61. It has a configuration that can.

(Control of separation auxiliary device 40)
The operation position of the separation assisting device 40 is controlled by the separation assist control circuit 50. FIG. 4 shows the relationship of this control. The control of the operation position signal of the separation assisting device 40 is based on the basis weight information of the recording material P specified by the user, the recording material leading edge position information obtained based on the recording material feed timing of the registration roller pair 8 and the recording material conveyance speed. based on. The control unit 50 includes a CPU, a ROM, and a RAM. Information from the operation unit 102 by which the user operates the image forming unit is input to the control unit 50. The operation timing of the registration roller 8 is input to the control unit 50. Information on the secondary transfer current value from the secondary transfer high-voltage power supply is input to the control unit 50. The control unit 50 controls the operation of the motor of the auxiliary separation device 40.

The basis weight is a unit indicating the weight per unit area (g / m ² ) and is generally used as a value indicating the thickness of the recording material.

In the present embodiment, the following two patterns are stored in advance in the ROM.
When the recording material has a basis weight of 40 g / m ² or less, the separation auxiliary roller 41 is positioned at the push-up position, and the transfer belt 24 is locally projected in the width direction. Separation of the recording material from the transfer belt 24 is performed by forming a local protrusion by pushing up.
When the recording material is larger than the basis weight of 40 g / m ² , the separation auxiliary roller 41 is located at the retracted position. The separation assist roller 41 is separated from the transfer belt 24 at the retracted position. The recording material is separated from the transfer belt 24 by using the curvature of the stretching roller 26.

  That is, an operation mode of pushing up the separation assist roller 41 with respect to a recording material having a specific basis weight (first basis weight) is executed. In addition, for the recording material having the second basis weight larger than the first basis weight, the operation mode of separating the recording material by the stretching roller 26 is executed without performing the operation of pushing up the separation assist roller 41.

  The basis weight may be input by the user using the operation unit 102 or may be input to the storage unit that stores the recording material, and based on the basis weight information input to the image forming apparatus. Thus, the control unit 50 determines the operation of the separation assisting device 40.

(Control timing of separation auxiliary roller)
(Single print job)
A flowchart of operation control of the separation assisting device 40 in the case of a single print job will be described with reference to FIG.

When started (S01), the basis weight information of the recording material set by the user through the user operation unit 102 is read (S02). It is determined whether the basis weight is greater than 40 g / m ² (S03). If the basis weight of the recording material is greater than 40 g / m ^{2 in} S03, the separation auxiliary roller 41 ends with being placed in the retracted position (S13). When the basis weight of the recording material P set by the user is 40 g / m ² or less, in order to separate the recording material having a small stiffness from the transfer belt 24, the transfer belt 24 is pushed up by the separation auxiliary roller 41 to locally protrude. The operation to form is required. When the basis weight of the set recording material P is 40 g / m ² or less, the image forming apparatus for the number of printing sheets of the recording material is started before starting a job for forming an image on the recording material stored in the selected cassette. It is determined whether or not the cumulative number since the start has reached a predetermined number (15) (S04). If the number of prints for the number of recording materials stored in the selected cassette before the start of the job for forming an image on the recording material has reached a predetermined number, the recording material It is determined that there is no wrap around and it is determined whether the recording material has reached a predetermined position (S05). The predetermined position is a position upstream of the separation auxiliary roller 41 in the recording material conveyance direction, and the separation auxiliary roller 41 pushes up the transfer belt 24, and the leading end of the recording material is pushed up by the separation auxiliary roller 41. Set to complete before reaching position. The position of the recording material can be determined by detecting the elapsed time after the recording material passes the registration roller and the recording material conveyance speed, or by arranging a detection member for detecting the passage of the recording material. Judgment is based on the detection method. When it is determined that the predetermined position has been reached, the separation assist roller 41 is moved in the Y1 direction and is placed at the pushed-up position where the transfer belt 24 is pushed up (S06). On the transfer belt 24 deformed by the separation auxiliary roller 41, the recording material P is swelled to increase the strength, and before the transfer belt 24 reaches the region in contact with the stretching roller 26. , Separated from the transfer belt 24. Next, it is determined whether or not the leading end position of the recording material P has reached the guide surface of the post-separation guide 29 (S07). Note that the position of the recording material can be determined by detecting the elapsed time after the recording material passes the registration roller and the recording material conveyance speed, or by arranging a detection member for detecting the passage of the recording material. Judgment is based on the method of detecting When the recording material has reached the guide surface of the guide 29 after separation, it is determined that separation has been performed. Before the leading edge of the recording material reaches the pre-fixing guide 61, the separation assist roller 41 moves to the retracted position (S12), and the process ends (S13).

  On the other hand, in S04, when the total number of recording materials printed in the selected cassette after starting up the image forming apparatus has not reached the predetermined number (15), the recording material has been stored in the selected cassette. It is determined that the recording material has winding folds. Therefore, it is necessary to lengthen the period during which the separation auxiliary roller 41 pushes up the transfer belt 24 in order to suppress the winding of the recording material with the winding. Before starting the job for forming an image on the recording material in S04, the cumulative number of images after the start of the image forming apparatus for the number of recording materials stored in the selected cassette has reached a predetermined number (15). If it is determined that the recording material is not, it is determined in S08 whether the recording material has reached a predetermined position. The predetermined position is a position upstream of the separation auxiliary roller 41 in the recording material conveyance direction, and the separation auxiliary roller 41 pushes up the transfer belt 24, and the leading end of the recording material is pushed up by the separation auxiliary roller 41. Set to complete before reaching position. If it is determined that the predetermined position has been reached, the separation assist roller 41 is moved in the Y1 direction and is placed at the pushed-up position where the transfer belt 24 is pushed up (S09). After the leading edge of the recording material reaches the guide surface of the guide 29 after separation (S10), it is determined in S11 whether or not the leading edge of the recording material has further reached the downstream pre-fixing guide 61. If the leading edge of the recording material has reached the pre-fixing guide 61 in S11, it is determined that the recording material is not sufficiently stuck during conveyance before fixing. Before the leading edge of the recording material reaches the pre-fixing guide 61 and before the fixing nip, the separation assist roller 41 moves to the retracted position (S12). Then, the process ends (S13). The reason why the auxiliary separation roller 41 moves to the retracted position after reaching the fixing nip after the leading edge of the recording material reaches the pre-fixing guide 61 will be described. This is because if the auxiliary separation roller 41 performs the retreat operation after reaching the fixing nip on the recording material, the orientation of the recording material may change due to the retraction operation and the recording material may be wrinkled.

  As described above, in the present embodiment, a predetermined number of sheets since the start of the image forming apparatus for the number of prints of the recording material stored in the selected cassette before starting a job for forming an image on the recording material. If not, the mode (first mode) in which the separation auxiliary roller 41 is retracted from the pushed-up position to the retracted position after the leading edge of the recording material reaches the pre-fixing guide 61 is executed. The reason for this will be described. When thin paper is left in the cassette, the moisture absorption state changes between the front surface and the back surface. As a result, there is a possibility that some of the thin papers placed in the cassette may be wound from the top and become wrinkled. When a recording material with such a winding wrinkle is conveyed, if the timing at which the separation auxiliary roller 41 is retracted from the transfer belt 24 is set in accordance with the timing at which the leading edge of the recording material is separated from the transfer belt 24, the transfer The timing at which the leading edge of the recording material being conveyed begins to curl after being separated from the belt 24 is advanced. As a result, the recording material may be conveyed toward the fixing device 60 with the curl at the leading end of the recording material being large. Therefore, in the present embodiment, when the cumulative number of sheets of the recording material stored in the selected cassette after starting up the image forming apparatus has not reached the predetermined number, the separation auxiliary roller 41 is moved from the pushed-up position to the retracted position. A mode (first mode) in which the timing of retreating is after the leading edge of the recording material reaches the pre-fixing guide 61 is executed. As a result, even when the recording material has a winding wrinkle, the separation auxiliary roller 41 pushes up the transfer belt 24, thereby imparting rigidity to the leading end of the recording material, and the recording material after the separation is wound. It is suppressed.

  In the present embodiment, as described above, the total number of prints of the number of prints of the recording material stored in the selected cassette is predetermined before starting a job for forming an image on the recording material. When the number of sheets has reached the number, the timing at which the separation auxiliary roller 41 is retracted from the pushed-up position to the retracted position is a mode in which the leading edge of the recording material reaches the post-separation guide 29 and before reaching the pre-fixing guide 61. (Second mode) is executed. As a result, the abrasion of the transfer belt 24 caused by the separation auxiliary roller 41 pushing up the transfer belt 24 can be suppressed.

  By the way, there is a case where the cassette is opened from when the user turns on the power supply of the image forming apparatus to start up the image forming apparatus and when image formation is started, and a new recording material is replenished to the cassette from above. In this case, since the new recording material is stacked on the cassette from above, the recording material that is not wound is conveyed. In other words, the operation of extending the period during which the separation auxiliary roller 41 pushes up the transfer belt 24 becomes unnecessary. Therefore, in the present embodiment, when the cassette is opened after the user turns on the power of the image forming apparatus and starts up the image forming apparatus until image formation starts, the number of prints of the recording material accommodated in the cassette It is determined that there is no wrinkle of the recording material regardless of whether the cumulative number after starting the image forming apparatus reaches a predetermined number (15). That is, the operation timing at which the separation auxiliary roller 41 is retracted from the transfer belt 24 is set after the leading edge of the recording material reaches the post-separation guide 29 and before reaching the pre-fixing guide 61. In FIG. 5, even if it is determined in S04 that the total number of recording materials printed in the cassette after starting up the image forming apparatus has not reached the predetermined number (15), the process does not proceed to S08 but S05. It becomes the flow which advances to

  On the other hand, there is a case where the cassette is not opened after the user turns on the power of the image forming apparatus and starts up the image forming apparatus until image formation starts. In this case, it is determined that a new recording material has not been replenished in the cassette. Since the upper recording material placed in the cassette has a winding wrinkle, it is necessary to increase the period during which the separation auxiliary roller 41 pushes up the transfer belt 24. That is, when the cassette is not opened after the user turns on the power of the image forming apparatus and starts up the image forming apparatus and the image formation starts, the image forming apparatus of the number of prints of the recording material accommodated in the cassette Whether or not there is a wrinkle of the recording material is determined based on whether or not the cumulative number of images after starting up reaches a predetermined number (15). If the cassette is not opened after the user turns on the power of the image forming apparatus and starts up the image forming apparatus, the image forming apparatus is started up with the number of prints of the recording material stored in the cassette. In the case where the cumulative number of sheets has reached the predetermined number (15 sheets), the timing of the retracting operation is set before reaching the pre-fixing guide 61 after the leading edge of the recording material reaches the post-separation guide 29. The If the total has not reached the predetermined number (15), the timing of the retreat operation is set after the leading edge of the recording material reaches the pre-fixing guide 61. That is, control is performed according to the flowchart of FIG.

In the present embodiment, it is configured to determine whether or not the cumulative total after starting the image forming apparatus for the number of prints of the recording material accommodated in the selected cassette has reached 15, but is limited to this value. Not intended. What is necessary is just to set according to the number of recording materials with winding.
In addition, the present embodiment has a configuration without a winding amount sensor. However, a winding amount sensor for detecting the winding amount of the recording material is provided, and switching between the first mode and the second mode is based on the detection result. You may go. In this case, the second mode may be performed when the amount of wrapping detected by the sensor is smaller than a predetermined value, and the first mode may be performed when the amount is greater than the predetermined value.
In addition, a recording unit that records the time when the recording material is left in the recording material container may be provided, and the switching between the first mode and the second mode may be performed based on the time when the recording material is left.

(Continuous print job)
A flowchart for controlling the separation auxiliary roller 41 when n sheets (n ≧ 2) of recording materials are continuously conveyed will be described with reference to FIG.

  The flow from S01 to S07 is the same as that for a single print job. If it is determined in S07 that the leading end position of the recording material P has reached the guide surface of the guide 29 after separation, it is determined that the recording material has been separated from the transfer belt 24. The separation auxiliary roller 41 moves to the retracted position before reaching the pre-fixing guide 61 (S08). If it is determined in S09 that image formation (secondary transfer) on the last n sheets of recording materials has been completed, the process ends (S18). If it is determined in S09 that image formation of the last n recording materials has not been completed, the process returns to S05 to determine whether or not the next recording material has reached a predetermined position.

  As described above, in this embodiment, before starting a job for forming an image on a recording material, the cumulative number after starting up the number of image forming apparatuses for the selected cassette has already reached a predetermined number. In this case, the push-up state between the recording materials is temporarily turned off. The retraction operation timing is set before the leading edge of the recording material reaches the pre-fixing guide 61. As a result, the period during which the transfer belt 24 is pushed up between the recording materials can be shortened to prevent the transfer belt 24 from being worn.

  On the other hand, in S04, before starting a job for forming an image on a recording material, a predetermined number (15) of the total number since the image forming apparatus for the number of recording materials printed in the selected cassette is started up. If the recording material has not reached the number of sheets, it is determined that the recording material accommodated in the selected cassette has a winding wrinkle. Therefore, it is necessary to lengthen the period during which the separation auxiliary roller 41 pushes up the transfer belt 24 in order to suppress the winding of the recording material with the winding. In S04, before starting a job for forming an image on a recording material, the total number of sheets after the start of the image forming apparatus for the number of recording materials stored in the selected cassette is set to a predetermined number (15). If it is determined that the number has not been reached, then in S10, the total number of prints after starting up the image forming apparatus for the selected cassette is predetermined for the kth sheet (2 ≦ k ≦ n−1) in the middle of the job. It is determined whether or not the number (15) has been reached. In S10, for the selected cassette, it is determined that the total number of printed sheets after starting up the image forming apparatus does not reach the predetermined number (15) at the kth sheet (2 ≦ k ≦ n−1) in the job. Then, it is determined that all n recording materials in the job are wound and wrinkled. In this case, it is necessary to lengthen the period during which the separation auxiliary roller 41 pushes up the transfer belt 24 after separation, in order to suppress winding wrinkles during conveyance for all n recording materials. In S11, it is determined whether the first recording material conveyed first reaches the predetermined position. The predetermined position is a position upstream of the separation auxiliary roller 41 in the recording material conveyance direction, and the separation auxiliary roller 41 pushes up the transfer belt 24. The leading edge of the first recording material is the separation auxiliary roller 41. Is set to complete before reaching the position pushed up by. When it is determined that the predetermined position has been reached, the separation assist roller 41 is moved in the Y1 direction and is placed at the pushed-up position where the transfer belt 24 is pushed up (S12). Thereafter, the separation auxiliary roller 41 is held at a push-up position where the transfer belt 24 is pushed up. In S13, it is determined whether or not the leading end of the nth recording material conveyed last has reached the guide surface of the guide 29 after separation. If the leading edge of the recording material has reached the post-separation guide 29 in S13, it is determined that the sprinkling of the recording material after separation has been sufficiently suppressed. Before reaching the fixing nip after the leading edge of the recording material reaches the pre-fixing guide 61, the separation assist roller 41 moves to the retracted position (S14). Then, the process ends (S18).

  In the continuous print mode in which images are continuously formed on a plurality (n sheets) of recording materials, there are cases in which all of the n recording materials are wound with wrinkles. In order to suppress winding wrinkles during conveyance of all n recording materials, it is necessary to lengthen the period during which the separation auxiliary roller 41 pushes up the transfer belt 24 for all n recording materials. However, the interval between the recording materials may be as small as 50 mm. In this case, the pushed-up state is maintained until the leading edge of the recording material reaches the pre-fixing guide 29, the separation auxiliary roller 41 pushed up between the recording materials is retracted, and then the separation roller is moved between the same recording materials. It is difficult to push up. Therefore, in the present embodiment, in the continuous print mode in which images are continuously formed on a plurality (n sheets) of recording materials, when all the n recording materials have winding creases, the recording materials are separated. The auxiliary roller 41 is continuously pushed up.

  On the other hand, in S10, it is determined that the total number of printed sheets after starting up the image forming apparatus for the selected cassette reaches the predetermined number (15) at the kth sheet (2 ≦ k ≦ n−1) in the job. Then, it is determined that the recording material from the first sheet to the kth sheet has a winding wrinkle, and the recording material from the (k + 1) th sheet to the nth sheet has no wrinkle. That is, for the first to kth recording materials, it is necessary to lengthen the period during which the separation auxiliary roller 41 pushes up the transfer belt 24, but for the k + 1st to nth recording materials, It is not necessary to lengthen the period during which the separation auxiliary roller 41 pushes up the transfer belt 24. In S10, it is determined that the total number of printed sheets after starting up the image forming apparatus for the selected cassette reaches the predetermined number (15) at the kth sheet (2 ≦ k ≦ n−1) in the job. In S15, it is determined whether the first recording material conveyed first reaches the predetermined position. The predetermined position is a position upstream of the separation auxiliary roller 41 in the recording material conveyance direction, and the separation auxiliary roller 41 pushes up the transfer belt 24. The leading edge of the first recording material is the separation auxiliary roller 41. Is set to complete before reaching the position pushed up by. If it is determined that the predetermined position has been reached, the separation assist roller 41 is moved in the Y1 direction and is placed at the pushed-up position where the transfer belt 24 is pushed up (S16). Thereafter, the separation auxiliary roller 41 is held at a push-up position where the transfer belt 24 is pushed up. In S17, it is determined whether or not the leading edge of the (k + 1) th recording material has reached the guide surface of the guide 29 after separation. If the leading edge of the (k + 1) th recording material reaches the post-separation guide 29 in S17, it is determined that the (k + 1) th recording material has been separated, and in S08, the separation auxiliary roller 41 is moved to the retracted position. . Thereafter, when it is determined in S09 that image formation on the nth recording material is completed, the process ends in S18. If it is determined in S09 that image formation on the nth recording material has not been completed, it is determined in S05 whether or not a predetermined position of the recording material has been reached.

  As described above, in the present embodiment, the total number of printed sheets after the image forming apparatus is started up for the selected cassette is the predetermined number (15 sheets) at the kth sheet (2 ≦ k ≦ n−1) in the job. When it is determined that the separation auxiliary roller 41 has reached, the separation auxiliary roller 41 is kept pushed up until the leading edge of the (k + 1) th recording material reaches the guide 29 after separation.

  That is, with respect to the 1st to kth recording materials with winding wrinkles, the pushed-up state is maintained until the leading end of the recording material reaches the pre-fixing guide 61. As a result, it is possible to suppress the leading edge of the recording material from being wound after being separated from the transfer belt 24. For the (k + 1) th and subsequent recording materials, the timing of the retreat operation is set before the leading edge of the recording material reaches the post-separation guide 29 and before the pre-fixing guide 61. As a result, it is possible to suppress the transfer belt 24 from being worn due to the transfer belt 24 being pushed up.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Primary charging device 3 Exposure apparatus 4 Developer 5 Primary transfer roller 6 Intermediate transfer belt 8 Registration roller 9 Secondary transfer roller 11 Drum cleaning device 12 Belt cleaning device 13 Secondary transfer high voltage power supply 20 Intermediate transfer belt tension Roller (tension roller)
21 Intermediate transfer belt stretching roller (opposing roller for secondary transfer roller 9)
22 Intermediate transfer belt stretcher roller (drive roller)
24 Transfer Belt 25 Transfer Belt Stretch Roller 26 Transfer Belt Stretch Roller 27 Transfer Belt Stretch Roller (Tension Roller)
29 Recording material guide 31 Transfer belt cleaning device 40 Separation auxiliary device 50 Control unit 60 Fixing device 61 Pre-fixing guide P Recording material A Rotating direction of photosensitive drum B Rotating direction of transfer belt G Rotating direction of intermediate transfer belt N Secondary transfer portion

Claims (6)

An image carrier for carrying a toner image;
A recording material accommodating portion for accommodating the recording material;
A movable belt member that carries and conveys the recording material conveyed from the recording material container;
A transfer member for electrostatically transferring a toner image formed on the image carrier to a recording material carried and conveyed by the belt member;
A push-up member that forms a local protrusion in the width direction of the belt member, and pushes up the belt member on the downstream side of the transfer member in the recording material conveyance direction from the inner surface side;
A pre-fixing guide that is disposed downstream of the belt member in the recording material conveyance direction and guides the conveyed recording material;
A post-separation guide for guiding the recording material separated from the belt member by a guide surface, which is disposed downstream of the belt member in the recording material conveyance direction and upstream of the pre-fixing guide;
Fixing means for fixing a toner image to a recording material guided by the pre-fixing guide at a nip portion;
In an image forming apparatus having
A first mode in which the push-up member pushes up the belt member to separate the recording material and maintains the state in which the push-up member pushes up the belt member until the leading end of the recording material reaches the pre-fixing guide. And the push-up member pushes up the belt member to separate the recording material and the push-up member retreats from the state of pushing up the belt member after the leading end of the recording material reaches the post-separation guide. A second mode performed before reaching the pre-fixing guide;
An image forming apparatus having an execution unit for executing the above . The execution unit has reached the predetermined number of images formed on the recording material in the recording material storage unit from the start of the image forming apparatus to before starting a job for forming an image on the recording material. 2. The method according to claim 1, wherein if there is not, the first mode is executed for the job, and the second mode is executed for the job when the cumulative number has reached the predetermined number. The image forming apparatus described in 1. The recording material container is configured to be openable to replenish the recording material,
The execution unit executes the first mode when the recording material storage unit is not opened during a period from when the image forming apparatus is started up to when image formation is started. 3. The image forming apparatus according to claim 1, wherein the second mode is executed when the recording material container is opened. 4. In the first mode, in the job for forming an image on only one recording material, the execution unit retreats from the state in which the push-up member pushes up the belt member. The image forming apparatus according to claim 1, wherein the image forming apparatus is performed before reaching the position. In the job in which images are continuously formed on a plurality of recording materials, the execution unit maintains the state in which the push-up member pushes up the belt member between the recording materials in the first mode, and performs the retreat. 5. The image forming apparatus according to claim 1, wherein the operation is performed before the leading end of the last recording material reaches the nip portion after reaching the pre-fixing guide. 6. The execution unit accumulates the number of images formed after starting the image forming apparatus on the recording material in the recording material container in the middle of a job for forming images on a plurality of recording materials continuously. When the predetermined number of sheets is reached, the state in which the push-up member pushes up the belt member is maintained until the tip of the (k + 1) th recording material reaches the post-separation guide, and the retreating operation is performed. 5. The image forming apparatus according to claim 1, which is performed after the k + 1th recording material reaches the post-separation guide and before the pre-fixing guide. 6.

Images