JP6752621B2 - Image forming device - Google Patents

Description

The present invention relates to, for example, an image forming apparatus capable of forming an image on a recording material such as a copier or a printer adopting an electrophotographic method or a facsimile.

Conventionally, in an image forming apparatus such as an electrophotographic apparatus and an electrostatic recording apparatus, a latent image formed on an image carrier is developed and made into a visible image, and this visible image (toner image) is used as a recording material to apply electrostatic force. Transfer using pressure. Then, by fixing the transferred image by heat and pressure, the image is recorded and formed on the recording material.

The applicant has previously proposed the image forming apparatus of Patent Document 1. In this image forming apparatus, a loop detection sensor for detecting the loop degree of the recording material is provided between the transfer position (transfer device) and the fixing position (fixing device), and the fixing device is based on the detection result of the loop degree. Acceleration / deceleration control is performed by the motor control unit. This prevents the recording material from being pulled between the transfer position and the fixing position, and at the same time, the loop of the recording material generated by the speed difference between the transfer position and the fixing position does not exceed a certain level. I have to.

That is, loop control is performed while making the predetermined transfer speed of the fixing device slower than the transfer transfer speed so that image defects due to pulling of the recording material between the transfer position and the fixing position do not occur. This control controls the rotation speed of the motor so as to keep the transfer speed of the recording material constant while the average transfer speed is slower than the transfer transfer speed so as to absorb the speed fluctuation due to the thermal expansion of the fixing roller of the fixing device. ing.

Japanese Unexamined Patent Publication No. 10-97154

The present invention relates to further improvement of the above-mentioned prior art. That is, in the loop control of the prior art, after the rear end of the recording material is removed from the transfer position, the actual speed of the recording material cannot be known due to the speed fluctuation due to the thermal expansion of the fixing roller. Therefore, it is necessary to secure a loop space in the downstream transport path for fixing so that there is no damage to the recording material or image defects due to a speed mismatch with the transport roller downstream of the fixing. In addition, since the transfer rollers cannot be brought close to each other in order to secure a spare space, it is not possible to transfer a recording material having a short length in the transfer direction, so that the length of the transferable paper is restricted.

The present invention provides an image forming apparatus that improves this point. That is, recording material damage and image defects due to rubbing of the transport path are suppressed, and recording material transport control without recording material damage and image defects even if the pitch between rollers is shortened for transporting recording materials with a short transport direction. It is an object of the present invention to provide an image forming apparatus having a fixing transfer speed control that can be performed.

A typical configuration of the image forming apparatus according to the present invention for achieving the above object is a toner image on the recording material from the side of the image carrier carrying the unfixed toner image by sandwiching and transporting the recording material. Is located on the downstream side of the transfer nip portion in the transport direction of the recording material, and the recording material transferred from the transfer nip portion is sandwiched and conveyed to fix the toner image on the recording material. The fixing nip portion, the transport nip portion located downstream of the fixing nip portion in the transport direction of the recording material and sandwiching and transporting the recording material transported from the fixing nip portion, the transfer nip portion and the fixing nip portion. When the recording material is transported between the transfer nip portion and the fixing nip portion, the transfer nip portion and the transfer nip portion and the transfer nip portion are provided due to a difference in transfer speed between the transfer nip portion and the fixing nip portion. A loop detection unit that detects a state of a first loop amount and a state of a second loop amount larger than the first loop amount with respect to the loop of the recording material generated between the fixing nip portion, and the loop detection unit. The control unit has a control unit that changes the transport speed of the fixing nip portion so that the loop falls within a predetermined amount range based on the detection information, and the control unit has the fixing in the state of the first loop amount. From the rotation speed of the transfer speed control motor of the nip portion and its operating time, and the rotation speed of the transfer speed control motor of the fixing nip portion and its operating time in the state of the second loop amount, the transfer of the fixing nip portion is performed. After the average speed of the recording material is obtained and the rear end of the recording material passes through the transfer nip, the transfer speed of the fixing nip portion is switched to the average speed and the transfer speed of the transfer nip portion is switched. ..

According to the present invention, it is possible to provide an image forming apparatus having a fixing transfer speed control capable of performing recording material transfer control without recording material damage or image defects.

It is a main part figure of the image forming apparatus of an Example. It is a schematic block diagram of the image forming apparatus of an Example. It is a perspective view of the main part of the fixing device in the image forming apparatus of an Example. It is a block diagram of the control part system which performs fixing speed control. It is a flowchart which shows the operation state of the fixing speed control.

Next, a specific example (Example) of the embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples.

<< Example 1 >>
[Image forming device]
FIG. 2 is a schematic configuration diagram of an image forming apparatus 50 having a fixing device 40 that controls the fixing speed in this embodiment. FIG. 1 is an enlarged view of a main part of FIG. FIG. 3 is a perspective view of a main part of the fixing device 40. FIG. 4 is a block diagram of the control system.

The image forming apparatus 50 is a tandem-intermediate transfer type laser beam printer using an electrophotographic process. The printer 50 uses a full-color or monocolor image corresponding to print data (electrical image data) input from the host device 600 connected to the printer control unit 300 (FIG. 4: hereinafter referred to as a CPU) as a recording medium. It can be formed on the recording material P and output.

The CPU 300 is a control means that comprehensively controls the operation of the printer 50, and exchanges electrical information with the host device 600 and the printer operation unit 700. Further, the CPU 300 controls processing of electrical information signals input from various process devices and sensors, processing of command signals to various process devices, predetermined initial sequence control, predetermined image formation sequence control, and the like. The host device 600 is a personal computer, a network, an image reader, a facsimile, or the like.

Recording material (hereinafter referred to as paper) P is a sheet-like member capable of forming a toner image, and specific examples thereof include plain paper, resin sheets that are substitutes for plain paper, thick paper, and sheets for overhead projectors. There is. Further, in the following description, up and down means up and down in the direction of gravity. The upstream side and the downstream side are the upstream side and the downstream side in the paper transport direction.

UY, UM, UC, and UBk are four electrophotographic imaging units for forming toner images of Y (yellow) color, M (magenta) color, C (cyan) color, and Bk (black) color, respectively. is there. Each image forming unit U has a photosensitive drum (first image carrier: hereinafter referred to as a drum) 1, a charger 2, a developing device 3, a primary transfer roller 4, and a drum cleaner 5. Reference numeral 6 denotes a laser scanner unit as an exposure device for the drum 1 of each image forming unit U.

Toner images of Y color, M color, C color, and Bk color are formed on the drum 1 in each image forming unit U, respectively. Since the principle and operation of image formation by the electrophotographic process in each image formation unit U are known, the description thereof will be omitted. The toner images of the above colors are predeterminedly superimposed on the rotating intermediate transfer belt (second image end time body: hereinafter referred to as a belt) 8 in the intermediate transfer unit 7 from the drum 1 of each image formation unit U. Primary transcription. As a result, a toner image in which four colors are superimposed is formed on the belt 8.

On the other hand, the paper feed roller 11 is driven at a predetermined control timing, and the paper P is fed out one by one from the paper feed cassette 10, enters the transport path 12 after feeding, is conveyed from the bottom to the top, and is fed to the resist roller pair 13. Is done. The resist roller pair 13 temporarily receives the tip end portion of the paper P. As a result, when the paper P is skewed, the skew is corrected and the posture is corrected to a straight position.

Then, the resist roller pair 13 specifies the paper P to the secondary transfer portion (transfer portion: transfer nip portion) 15 which is the pressure contact portion between the belt 8 and the secondary transfer roller 14 in synchronization with the toner image on the belt 8. It is sent at the control timing of. The secondary transfer roller 14 presses against the secondary transfer opposed roller 9, which is one of the plurality of suspension members of the belt 8, with a predetermined pressing force via the belt 8 and is in contact with the belt 8 as a secondary transfer unit. 15 is formed. The paper P is sandwiched and conveyed by the secondary transfer unit 15 and receives the batch secondary transfer of the unfixed toner image of the four-color superimposed on the belt 8.

The paper P leaving the secondary transfer section 15 is separated from the belt 8 and passes through the pre-fixing transport path 16 and is introduced into the fixing device (fixing section) 40 from bottom to top. Then, it is sandwiched and conveyed by the fixing nip portion N which is a pressure contact portion between the fixing roller 100 which is a pair of rotating bodies and the pressure roller 101. As a result, the unfixed toner image on the paper (on the recording material) is heated and pressurized and fixed as a fixed image. The paper P leaving the fixing nip portion N is sent upward from the fixing device 40.

Then, in the single-sided printing mode (single-sided image forming mode), the paper P leaving the fixing device 40 is sandwiched between the paper ejection rollers pair (conveying nip portion) 17 and is sandwiched between the paper ejection rollers 18 and the paper ejection tray 19 from the paper ejection port 18. Is discharged as single-sided printed matter.

In the double-sided printing mode (double-sided image forming mode), the one-sided printed paper P exiting the fixing nip portion N is sandwiched between the paper ejection rollers 17 and placed on the paper ejection tray 19 from the paper ejection port 18. It will be sent out. Then, when the rear end of the paper P reaches the inversion point 20 on the upstream side of the paper ejection roller pair 17, the rotation of the paper ejection roller pair 17 is driven by the forward rotation of the solid line arrow in FIG. Can be switched to the reverse rotation drive of the broken line arrow. Further, the flapper 21 is switched from the first posture shown by the solid line in FIG. 1 to the second posture shown by the broken line.

As a result, the one-sided printed paper P is switchback-conveyed by the reverse rotation-driven paper ejection roller pair 17, and is introduced into the double-sided transport path 22 by the flapper 21 in the second posture. The paper P is conveyed from top to bottom on the double-sided transfer path 22, and is reintroduced in a state of being inverted with respect to the transfer path 12 after feeding on the predetermined upstream side of the resist roller pair 13. The paper ejection roller pair 17 is returned to the forward rotation drive after the rear end portion of the paper P which has been switched back and conveyed has passed. Further, the flapper 21 is returned to the first posture after the rear end portion of the paper P that has been switchback-conveyed has passed.

Then, the paper P that has been turned upside down from the double-sided transport path 22 and reintroduced into the transport path 12 after being fed is subjected to an image formation on the other side through the same process as in the single-sided printing mode, and is used as a double-sided printed matter. It is discharged on 19.

The portion composed of the switchback operation of the paper ejection roller pair 17 and the flapper 21 is an example of the reversing means. Further, in the present embodiment, the paper P is inverted by the output roller pair 17, but in order to increase the productivity of printing, an inversion portion or a plurality of output portions are provided to provide a paper ejection roller. Inversion may be performed at a place other than vs. 17. Further, although the image forming apparatus 50 of this embodiment is an intermediate transfer method using the belt 8 as an intermediate transfer body, a method of directly transferring the toner image from the drum 1 of each image forming unit U to the paper P may be used. ..

[Jam detection and jam processing]
A paper detection sensor is provided in the transport path as a means for detecting the state of the paper P being transported through the transport path. With reference to FIGS. 1 and 2, 200, 210, and 201 are a registration sensor (resist sensor), an internal paper discharge sensor, and a paper discharge sensor, respectively, as paper detection sensors.

The registration sensor 200 is arranged in a transport path portion between the resist roller pair 13 and the secondary transfer unit 15 in the transport path 12 after feeding, and detects the presence or absence of paper in the transport path portion. The internal paper discharge sensor 210 is arranged in a transport path portion between the fixing nip portion N and the upper outlet in the fixing device 40, and detects the presence or absence of paper in the transport path portion. The paper discharge sensor 201 is arranged in a transport path portion between the paper discharge roller pair 17 and the paper discharge port 18, and detects the presence or absence of paper in the transport path portion.

Paper presence / absence detection signals from the sensors 200, 210, and 201 are input to the CPU 300. The CPU 300 detects the paper jam in the transport path according to the detection signals input from the sensors 200, 210, and 201, and controls the printer operation.

For example, when the paper P is being conveyed along the transport path, the on-time of any of the sensors is longer than the specified time in the sequence, or the arrival at any of the sensors is delayed from the specified time in the sequence. It is determined that the paper P is jammed somewhere (jam has occurred). Then, the CPU 300 urgently stops the operation of the printer 50 based on the detection signal so that the paper jam state does not progress. That is, the drive unit of each roller of the printer 50 is stopped, and the display unit (not shown) of the operation unit 700 or the host device 600 is displayed to urge the user to perform jam processing.

For the purpose of removing the jammed paper P, the device main body 50A of the printer 50 is provided with a door 80 that can be opened and closed with the hinge 90 as the center of rotation. In FIG. 2, the door 80 is opened from the device main body 50A by tilting and rotating to the right in the figure around the hinge 90 as shown by the alternate long and short dash line from the closed state with respect to the device main body 50A. Can be. On the contrary, it can be raised and rotated to return to the closed state.

Inside the door 80, one guide member (on the right side in the drawing) constituting the transport path 12 after paper feeding, one roller (on the right side in the drawing) forming the resist roller pair 13, the secondary transfer roller 14, and before fixing. A transport path 16, a double-sided transport path 22, and the like are arranged. Therefore, when the door 80 is opened, the transport paths other than the fixing device 40 are opened between the transport path 12 and the paper ejection roller pair 17 after feeding. As a result, the jammed paper can be easily removed.

[Fixing device]
The fixing device 40 includes a fixing roller 100 and a pressure roller 101, which are a pair of rotating bodies, for heating and pressure-fixing the toner image on the paper. The fixing roller 100 is a hollow cylindrical body, and a heating member 106 for heating the fixing roller 100 is provided inside. The fixing roller 100 forms an elastic layer of a rubber material having high thermal conductivity by superimposing it on a base layer of a tubular metal core, and forms a release layer of fluororesin on the surface. In this embodiment, the roller outer diameter is φ25 mm, the base layer is an iron material with a thickness of 0.5 mm, the elastic layer is a silicone rubber with a thermal conductivity of 1.0 W / m · K, and the release layer is a PFA with a thickness of 30 μm. It is a tube.

The pressure roller 101 forms an elastic layer of a flexible rubber material on the outside of a shaft member made of a cylindrical material such as iron or aluminum, and covers the surface of the elastic layer with a release layer of fluororesin. In this embodiment, an aluminum tube having a roller outer diameter of φ25 mm, a shaft member having an outer diameter of φ10 mm and a wall thickness of 3 mm is used, the elastic layer has a wall thickness of 3 mm, silicone rubber having an asker hardness of 64 °, and the release layer has a thickness of 50 μm. It is a PFA tube.

The heating member 106 is a halogen heater (hereinafter referred to as a heater). The heating member 106 has a basic configuration of a glass tube, a filament portion provided inside the glass tube, and a feeding portion at one end of the glass tube, and the filament in the heat generating region of the filament portion is wound to be long and close to each other. It is a heater with a low heat capacity whose heat generation region rises when energized. In this embodiment, the glass tube is φ6 and the filament is a tungsten material.

With reference to FIG. 3, the pressure roller 101 is rotatably supported on one end side and the other end side between the support members 110a and 110b on the respective sides via bearings 103a and 103b. One end side and the other end side of the fixing roller 100 are rotatably supported between the pressure levers 111a and 111b on the respective sides via bearings 102a and 102b.

The support member 110a and the pressure lever 111a on the one end side, and the support member 110b and the pressure lever 111b on the other end side are pivotally attached to the shafts 112a and 112b, respectively. The support member 110a and the pressure lever 111a on the one end side, and the support member 110b and the pressure lever 111b on the other end side respectively pull the shafts 112a and 112b in the pulling direction by the pressing force of the pressure springs 113a and 113b, respectively. It is rotationally urged to the center.

As a result, the fixing roller 100 and the pressurizing roller 101 are pressed against each other with a predetermined pressing force to form a fixing nip portion N having a predetermined width with respect to the paper transport direction a. The pressing force in this embodiment is 100N on one end side and 200N on the total pressing force.

With reference to FIG. 1, the fixing device 40 has an inlet guide 104 on the upstream side of the fixing nip portion N, and an outlet guide 105 and an outlet on the downstream side of the fixing nip portion N in order to assist the transfer of the paper P. An opposing guide 107 is provided.

The fixing roller 100 and the pressurizing roller 101 are rotationally driven by a fixing drive mechanism including a fixing motor 403 (FIG. 4: transport speed control motor). Further, the fixing roller 100 is heated by energizing the heating member 106. The surface temperature of the fixing roller 100 is detected by a roller temperature detecting member (temperature sensor: not shown), and the detected temperature information is input to the CPU 300. The CPU 300 controls the power supplied to the heating member 106 to control the temperature of the fixing roller 100 so that the surface temperature of the fixing roller 100 is raised and maintained at a predetermined temperature based on the input detection temperature information.

In this fixing device state, the paper P carrying the unfixed toner image is introduced into the fixing nip portion N from the side of the secondary transfer portion 15, and is sandwiched and conveyed. As a result, the unfixed toner image on the paper P is heated and pressurized and fixed as a fixed image. The paper P leaving the fixing nip portion N is conveyed to the downstream side.

The outlet guide 105 is provided with an internal paper discharge sensor flag 211, an internal paper discharge sensor flag spring 212, and the internal paper discharge sensor 210. The internal paper discharge sensor flag 211 includes a sheet portion 211a and a sensor portion 211b. The sheet portion 211a is arranged straddling the outlet facing guide 105 and the outlet facing guide 107 so as to block the transport path on the downstream side of the fixing nip portion N, and the urging force of the internal paper discharge sensor flag spring 212 toward the outlet facing guide 107. It is provided with.

The sensor unit 211b is arranged so that the detection unit of the internal paper discharge sensor 210 provided inside the exit guide 105 can be detected. The detection unit of the internal paper discharge sensor 210 receives the light emitted from the light emitting element (not shown) by the light receiving element (not shown), emits an off signal in that state, and emits an on signal when the light is blocked. It is a so-called photo interrupter sensor that emits light. The detection means that the sensor unit 211b of the internal paper discharge sensor flag 211 blocks and does not block light by the detection unit of the internal paper discharge sensor 210, so that the detection output (light shielding = on, non-shading = off) is performed.

These components are housed in the fixing frame 130 and the fixing cover 131 and integrated into a unit, and the fixing device 40 is a unit that can be attached to and detached from the device main body 50A of the printer 50.

In this embodiment, the internal output sensor flag 211 is detected by the photo interrupter sensor, but the sensor flag may not be used and the detection may be performed by an optical sensor that directly detects the conveyed state of the paper P.

[Transport path before fixing]
Next, the configuration around the paper transport path 16 from the secondary transfer section 15 to the fixing nip section N will be described with reference to FIG. Since the pre-fixing transport path 16 between the secondary transfer portion 15 and the fixing nip portion N is not provided with a roller, a belt, or the like for transporting the paper P, the secondary transfer portion 15 and the fixing nip portion N The distance between them is set to be shorter than the shortest length of paper P that can be used for the printer 50.

A pre-fixing transfer path 16 is provided between the secondary transfer unit 15 and the fixing nip portion N for the purpose of feeding the paper P transferred from the secondary transfer unit 15 to the fixing nip portion N while assisting the transfer posture. There is. The pre-fixing transport path 16 is provided with a loop sensor flag 221, a loop sensor flag spring 222, and a loop sensor 220 as loop detection units for the paper P.

When the paper P is conveyed across the secondary transfer portion 15 and the fixing nip portion N, the secondary transfer portion 15 and the fixing nip portion N are caused by the difference in transfer speed between the transfer secondary transfer portion 15 and the fixing nip portion N. A loop of paper P occurs between the two. The loop detection units 220, 221 and 222 are in a state of a first loop amount (loop cancellation state: a state in which the loop is shallow) and a state of a second loop amount larger than the first loop amount (loop) with respect to the loop. Formation state: state where the loop is deep) Ld is detected.

The loop sensor flag 221 includes a seat portion 221a and a sensor portion 221b. The sheet portion 221a projects into the pre-fixing transport path 16 so as to come into contact with the paper P being transported at approximately the middle between the secondary transfer portion 15 and the fixing nip portion N, and the loop sensor flag is maintained in that state. It is provided with an urging force by a spring 222. The sensor unit 221b is arranged so that the detection unit of the loop sensor 220 provided inside the transport path 16 before fixing can be detected. The standby position is a state provided with the urging force of the loop sensor flag spring 222.

The loop sensor 220 uses a photo interrupter sensor like the internal paper discharge sensor 210, and the sensor unit 221b of the loop sensor flag 221 blocks or does not block light by the detection unit of the loop sensor 220, so that a detection output ( Shading = on, non-shading = off). In FIG. 1, 221on indicates the loop sensor flag on output position, and 221off indicates the loop sensor flag off output position. Based on the detection information of the loop detection unit, the CPU 300 changes the transport speed of the fixing nip unit so that the loop of the paper P generated between the secondary transfer unit 15 and the fixing nip unit N falls within a predetermined amount range ( Loop control).

In this embodiment, the loop sensor flag 221 is detected by the photo interrupter sensor, but it may be detected by an optical sensor that directly detects the conveyed state of the paper P without using the sensor flag.

Further, in the present embodiment, the position of the loop sensor 220 is substantially in the middle of the transport path 16 before fixing, but it may be provided anywhere as long as it comes into contact with the paper P and can detect the loop of the paper P.

[Control circuit and control operation]
Next, the control circuit and the control operation of the printer 50 will be described with reference to FIG. The printer 50 is provided with a CPU 300 as a control means (control unit) for controlling an image forming operation, a ROM 301 that stores a program executed by the CPU 300 in advance, and a RAM 302 that stores variables and the like of the program executed by the CPU 300. There is.

The ROM 301 stores the size and type of the paper P, which is a condition for forming an image. Further, the ROM 301 is selectively based on the detection results from the image forming color mode, the single-sided or double-sided image forming (printing) mode, the temperature / humidity detecting member (not shown), the roller temperature detecting member (not shown), and the like. The control condition table that guides the image formation conditions is stored. Further, the ROM 301 stores control conditions such as the rotation speed of the motor according to the image formation mode.

Among the control conditions stored in the ROM 301, the RAM 302 stores conditions that need to be changed by the user or maintenance, variables used for various controls, and calculated values in the RAM 302, and stores rewritable setting values according to the situation. Has been done.

Next, the configuration and control operation of each motor of the printer 50 will be described. The transport motor 401 is a motor that mainly transports the paper P, and drives and rotates the rollers that transport the paper P, such as the paper feed from the paper feed cassette 10 and the registration roller pair 13. An electromagnetic clutch (not shown) or the like is used for a gear train (not shown) for drive transmission, and each roller is rotated at a timing to convey the paper P. Basically, the paper P is driven and rotated so as to have a constant transport speed, but acceleration / deceleration control may be performed as necessary.

The image-creating motor 402 is a motor that mainly forms an image and conveys a toner image to the secondary transfer unit 15. The image-forming motor 402 drives and rotates the drum 1 of each image-forming unit U and the developer transfer screw (not shown) in the developing device 3. Further, the secondary transfer opposing roller 9 as the drive roller of the belt 8, the primary transfer roller 4 of each image forming unit U, and the secondary transfer roller 14 are driven and rotated. The motor 402 is a motor responsible for image formation, and is rotationally controlled so as to create and convey a toner image at a constant speed with extremely high accuracy.

The exposure motor 400 is a motor that mainly creates a latent image, and is housed in the laser scanner unit 6. The unit 6 has a semiconductor laser (not shown) that lights up based on image data corresponding to each color of Y, M, C, and Bk. Further, it has a rectangular polygon mirror (not shown) for forming a latent image on the drum 1 of each image forming unit U by deflecting and scanning the laser light (not shown) emitted from each of the semiconductor lasers. The exposure motor 400 drives and rotates the square polygon mirror. Although a semiconductor laser is used in this embodiment, an exposure apparatus such as LED lighting control may be used.

The fixing motor 403 mainly drives and rotates the fixing roller 100 and the pressurizing roller 101 to convey the paper P heated and pressurized by the fixing nip portion N downstream. Since the outer diameters of the fixing roller 100 and the pressure roller 200 change due to the heat of the heating member 106, the transfer speed of the paper P by the fixing nip portion N changes even if the rotation of the fixing motor 403 is constant. Therefore, the fixing motor 403 is one of the control means for controlling the fixing speed.

The paper ejection motor 404 mainly drives the paper ejection roller pair 17, and as described above, when the paper P is ejected to the paper ejection tray 19, it rotates in the normal direction and switches the paper P to the double-sided transport path 22. It rotates in the reverse direction during back transportation.

Each of the motors 401 to 404 uses a pulse motor, a DC servo motor, or the like, and it is possible to control the rotation speed at a rate of a few percent of commas.

[Fixing transfer speed control]
Next, the details of the operation at the time of image formation for performing the fixing and conveying speed control (controlling the conveying speed of the sandwiching and conveying of the paper P in the fixing nip portion N) will be described. FIG. 5 is a flowchart showing an operating state of fixing and conveying speed control.

When the CPU 300 receives the print data from the host device 600 and converts it into image data, the CPU 300 issues an image drawing start instruction (step S1). Based on this, a rotation start instruction is issued to the transfer motor 401, the image drawing motor 402, and the exposure motor 400, and each motor starts rotating at a predetermined rotation speed stored in the ROM 301 via the drive circuit 303 (S2). ..

In the paper P transporting process, as described above, the paper P starts feeding from the paper feed cassette 10 (S8), is fed one by one, is fed to the resist roller pair 13, and temporarily stops the transport motor 401. Then, the paper P stands by at the resist roller pair 13.

In the image forming process, the image forming motor 402 rotates so that the speed of the belt 8 is driven at a constant speed Vs. The exposure motor 400 starts rotating in each image forming unit U so that the latent image writing speed of the drum 1 after the start of exposure substantially matches the intermediate transfer belt speed Vs. The substantially matching speed is calculated by the CPU 300 based on the reading result of the speed stabilization control patch (not shown) on the belt 8 before image formation, and the speed is set according to the conditions recorded in the ROM 301. In this embodiment, for example, the belt speed Vs is set to 220 mm / sec.

In the fixing device 40, when the surfaces of the fixing roller 100 and the pressure roller 101 reach a predetermined temperature stored in the ROM 301 by the heating member 106, the fixing motor is instructed to stand by for fixing and heating (S3: YES). Start rotating 403 (S4). The fixing motor 403 is rotated at the rotation speed Rm stored in the ROM 301 so that the fixing transfer speed at this time is Vm (S5). In this embodiment, for example, the fixing transfer speed Vm is set to 220 mm / sec, which is substantially the same as the belt speed Vs, and the rotation speed Rm is set to 2000 rpm.

The paper ejection motor 404 starts rotating in accordance with the start of rotation of the fixing motor 403 (S4), and the speed of the paper ejection roller pair 17 is driven so as to rotate at the paper ejection transport speed Vex. The paper ejection transfer speed Vex is driven to rotate at a speed slower than the belt speed Vs. At this time, the output motor 404 is rotated so that the rotation speed of the output motor 404 is the rotation speed Rex stored in the ROM 301.

In this embodiment, for example, the rotation speed Resp of the paper ejection motor 404 is 1800 rpm when the paper ejection transport speed Vexp, which substantially matches the belt speed Vs, is 220 mm / sec. Further, the paper discharge transfer speed Vex is set to 213.4 mm / sec, which is 97% of the belt speed Vs, and the rotation speed Rex of the paper discharge motor 404 is set to 1746 rpm.

Here, the reason why the paper discharge transfer speed Vex is slower than the speed of the belt speed Vs is that the paper P tends to be pulled while the paper P is nipped by both the fixing nip portion N and the paper discharge roller nip portion of the fixing device 40. This is to prevent the image from being disturbed during the fixing process. The relationship with the average transfer speed of the fixing device 40 needs to be as follows.

Belt speed Vs> Fixed transfer speed average value> Paper discharge transfer speed Vex
The start timing of each motor is not limited to the embodiment. For example, it may be the timing when the print data is received, and if it is in the standby state in advance, it is necessary to change the start timing according to the state.

Next, when the CPU 300 receives the fixing heating standby (S3: YES) from the fixing device 40 and the image drawing start standby due to the start of motor rotation (S6: YES), an image drawing start permission signal is issued (S7). Then, an exposure start signal 500 (FIG. 4) is output, and a latent image is started to be created on the drum 1 in each image forming unit U (S9). Then, after the toner image formed on the drum 1 begins to be transferred to the belt 8, a signal from the CPU 300 issues a refeeding start instruction, and the resist roller pair 13 is rotationally driven to start feeding the paper P (S10). ).

The signal is output at the secondary transfer unit 15 at the timing so that the image on the belt 8 and the tip image position of the paper P are appropriately transferred. The appropriate tip image position is, for example, an image position such that an appropriate paper tip margin is, for example, 4 mm when an image is written from the tip of the image writing area.

Here, the paper length detection will be described. The tip of the paper P fed from the resist roller pair 13 reaches the registration sensor 200 by the start of re-feeding (S10), and the registration sensor 200 detects that the paper is on (S12: YES), so that the paper length detection is started (S12: YES). S14). After that, the rear end of the paper passes through the resist roller pair 13 and the registration sensor 200, and the registration sensor 200 detects off (S16: YES), so that the paper length detection ends (S18). The CPU 300 calculates (acquires) the length of the paper P on which the paper is conveyed from the passing time from on to off of the registration sensor 200 and the belt speed Vs.

For example, when the belt speed Vs is 220 mm / sec and the passing time is 1.35 seconds, the passing length is 297 mm, which is substantially the same as the vertical length of A4 according to the standard size stored in the ROM 301. , A4 vertical paper is judged. The calculation formula is as follows.

Belt speed Vs (mm / sec) × Passing time of registration sensor 200 (sec)
= Passing length (mm)
In this embodiment, the paper length is detected by the register sensor 200, but when the paper P is set in the paper cassette 10, the length may be detected by the position of the paper regulation plate in the paper cassette 10.

Next, the paper P sent out from the resist roller pair 13 reaches the secondary transfer unit 15 at the tip of the paper and is conveyed toward the fixing device 40 while performing the secondary transfer step. Here, before the paper P passes through the secondary transfer unit 15 and enters the fixing nip portion N of the fixing device 40, the fixing motor 403 is interrupted by the elapse of Ti for a predetermined time from the exposure start signal 500 (S11: YES). The speed is changed so that the rotation speed becomes the rotation speed Ri stored in the ROM 301. That is, the fixing transfer speed is switched from the fixing transfer speed Vm to the fixing transfer speed Vi (S13).

The fixing transfer speed Vi is slightly slower than the belt speed Vs. In this embodiment, for example, the fixing transfer speed Vi is set to 98% of the belt speed Vs, 215.6 mm / sec, and the rotation speed Ri of the fixing motor 403 is set to 1960 rpm. The reason why the fixing transfer speed Vi is made slower than the belt speed Vs is that the paper P tends to be pulled immediately after being nipped by both the secondary transfer unit 15 and the fixing nip portion N of the fixing device 40, and the secondary transfer is performed. This is to avoid disturbing the image.

Here, the fixing transfer speed is switched to the fixing transfer speed Vi before the tip of the paper rushes into the fixing nip portion N of the fixing device 40. However, the fixing transfer speed Vm at the start of rotation of the fixing motor 403 may be set to the same speed as Vi and the speed switching may not be performed, or the setting value may be the same for switching.

The predetermined time Ti from the exposure start signal 500 is calculated as follows. If it is a color image,
(A) The distance A from the exposure position of Y (yellow) to the nip position (primary transfer position) of the primary transfer roller 4 on the drum 1 in the image forming unit UY.
(B) The distance from the nip position of the primary transfer roller 4 in the image forming unit UY to the nip position of the primary transfer roller 4 in the image forming unit UBk is the distance B.
(C) The distance from the nip position of the primary transfer roller 4 of the image forming unit UBk to the position of the secondary transfer unit 15 is the distance C.
(D) The distance D from the secondary transfer unit 15 to an arbitrary position between the fixing nip portion N of the fixing device 40
And It is calculated by the distance [A + B + C + D] obtained by adding these four distances and the belt speed Vs at that time. The distances A, B, and C are fixed distances in the printer configuration and are stored in the ROM 301. The distance D is stored in the ROM 302 so that it can be changed as needed.

For example, in this embodiment, the distances A, B, C, and D are calculated as the following set values, respectively. The distance A is such that the primary transfer nip is 180 degrees from the exposure position and the drum diameter is φ20, and φ20 × π × 180 ÷ 360 = 31.416 mm. The distance B is a drum pitch of 85 mm between the image-forming units U, and 85 × 3 = 255 mm between the four colors. The distance C is 60 mm. The distance D is a distance at which the speed can be switched to Vi before the paper P rushes into the fixing nip portion N, and the distance from the secondary transfer portion 15 to the fixing nip portion N of the fixing device 40 is 100 mm, which is approximately in the middle. .. That is, it was set to 50 mm.

Therefore, the distance from the exposure position to the speed switching position [A + B + C + D] = 396.416 mm. The belt speed Vs is 220 mm / sec, and the predetermined time Vs is 1.802 seconds. The calculation formula is as follows.

From the exposure position Speed switching position (mm) ÷ Belt speed Vs (mm / sec) = Predetermined time In the case of black-and-white image image formation, the primary from the (black) exposure position on drum 1 in the image formation unit UBk. The distance to the nip position (primary transfer position) of the transfer roller 4 is defined as the distance A. This is the same as the distance A in the case of image formation of the color image. It is calculated by the distance [A + C + D] obtained by adding the distance A, the distance C, and the distance D, and the belt speed Vs at that time. The storage in ROM 301 and ROM 302 is the same as described above.

For example, this embodiment is calculated as the following design values. The distance A is 31.416 mm, which is the same as the distance A. The distance C and the distance D are the same as the distance C and the distance D, respectively.
The distance is 60 mm and the distance is 50 mm. It is as follows when it is calculated by the same calculation formula as above. The distance from the exposure position to the speed switching position [A + C + D] = 141.416 mm, the belt speed Vs is 220 mm / sec, and the predetermined time Vs is 0.643 seconds.

Next, the paper tip reaches the fixing nip portion N of the fixing device 40, and the paper P is conveyed toward the paper ejection roller pair 17 while performing the fixing step. Here, when the tip of the paper P exceeds the fixing nip portion N of the fixing device 40, the fixing speed control starts the loop control mode by interrupting the elapse of a predetermined time Ts from the exposure start signal 500 (S15: YES). (S17).

The fixing transfer speed in the loop control mode is selectively switched according to the detection state of the loop sensor 220 obtained in conjunction with the paper P contacting the loop sensor flag 221 to operate the loop sensor flag 221. Here, the loop control mode is started after the paper tip exceeds the fixing nip portion N of the fixing device 40, but the setting may be made before the paper tip enters the fixing nip portion N of the fixing device 40. As described above, the setting may be such that the paper P forms a loop after the paper tip has entered the fixing nip portion N of the fixing device 40.

The detection state of the loop sensor 220 and the fixing transfer speed in the loop control mode will be described below. When the detection state of the loop sensor 220 is turned on (S19: YES), the loop sensor flag 221 is pushed by the paper P to approach the pre-fixing transport path 16 and the inlet guide 104, and the loop sensor flag is turned on and the output position is set. It was when it became 221 on. The paper P is in the loop forming state Ld (FIG. 1), and is switched to a fixing transfer speed Vh faster than the belt speed Vs in order to eliminate the loop (S22). The fixing motor 403 is rotated so that the rotation speed of the fixing motor 403 at this time becomes the rotation speed Rh stored in the ROM 301.

In this embodiment, for example, the fixing transfer speed Vh is set to a speed of 222.2 mm / sec, which is 101% of the belt speed Vs, and the rotation speed Rh of the fixing motor 403 is set to 2020 rpm.

When the detection state of the loop sensor 220 is turned off (S19: NO), the loop sensor flag 221 is returned to the standby position by the paper P, and the paper P moves away from the pre-fixing transport path 16 and the inlet guide 104. As a result, the loop sensor flag is off and the output position is 221 off. The paper P is in the loop elimination state Ls (FIG. 1), and is switched to a fixing transfer speed Vl slower than the belt speed Vs in order to form a loop (S21). The fixing motor 403 is rotated so that the rotation speed of the fixing motor 403 at this time becomes the rotation speed Rl stored in the ROM 301.

In this embodiment, for example, the fixing transfer speed Vl is set to 209.0 mm / sec, which is 95% of the belt speed Vs, and the rotation speed Rl of the fixing motor 403 is set to 1900 rpm.

During the loop control mode, as described above, the overloop of the paper P and the paper P between the secondary transfer unit 15 and the fixing nip portion N are performed while changing the rotation speed of the fixing motor 403 and switching the fixing transfer speed. Image defects in the secondary transfer unit 16 due to tension are prevented from occurring. That is, the fixing and conveying speed is controlled so that the posture of the paper P is conveyed while forming a loop between the loop forming state Ld and the loop eliminating state Ls.

The rotation speed calculation process of the fixing motor 403 in the loop control mode will be described below. In the loop control mode, as described above, the rotation speed of the fixing motor 403 is changed to switch the fixing transfer speed to a plurality of speeds, but at the same time, the calculation process (acquisition) for calculating the average speed of the fixing transfer speed is performed. In addition, the calculation result is further calculated and used for the paper discharge transfer speed.

That is, the CPU 300 has a fixing nip based on the rotation speed of the fixing motor 403 and its operating time in the state Ls of the first loop amount and the rotation speed and its operating time of the fixing motor 403 in the state Ld of the second loop amount. Acquire the average speed of the transport speed of the part. Then, this is reflected in the transport speed of the fixing nip portion N and the paper ejection nip portion 17.

Specifically, when the paper P is conveyed at a fixing transfer speed Vh faster than the belt speed Vs, the rotation time (operating time) TRh at the rotation speed Rh of the fixing motor 403 is integrated. Further, when the paper P is conveyed at a fixing transfer speed Vl slower than the belt speed Vs, the rotation time (operating time) TRl at the rotation speed Rl of the fixing motor 403 is integrated. The following calculation is executed by the CPU 300 from the rotation speed and the integration result.

Calculation formula of average rotation speed Rave [(rotation speed Rh x rotation time TRh) + (rotation speed Rl x rotation time TRl)] ÷
(Rotation time TRh + Rotation time TRl) = Average rotation speed Rave
Next, from the above results, the speed ratio α of the belt speed Vs and the fixing transfer speed is calculated. At this time, since the calculation is the rotation speed of the fixing motor 403, the fixing motor rotation speed Rm when the fixing transfer speed Vm at a speed substantially matching the belt speed Vs is used as the calculation base.

Calculation formula of speed ratio α Average rotation speed Rave ÷ fixing motor rotation speed Rm = speed ratio α
Next, from the above results, the rotation speed Rexo of the paper ejection motor 404 having the paper ejection transport speed Vexo corresponding to the fixing transport speed Vo of the average rotation speed Rave of the fixing motor 403 is calculated. At this time, in a state where the paper P is nipped by both the fixing nip portion N of the fixing device 40 and the nip portion of the paper ejection roller pair 17, the paper P tends to be pulled so as not to disturb the image during the fixing process. .. Therefore, the coefficient β stored in the RAM 302 is multiplied so that the paper ejection transport speed Vexo is slower than the fixing transport speed Vo. Further, the rotation speed Resp of the paper discharge motor 404 having a paper discharge transfer speed Vexp that substantially matches the belt speed Vs that is the reference speed is calculated as the reference speed.

Calculation formula of the number of revolutions Rexo of the paper ejection motor 404 Exp. × Speed ratio α × coefficient β = number of revolutions Rexo
As a result of the above three calculations, the average rotation speed Rave, the speed ratio α, and the rotation speed Rexo are stored in the RAM 302 so as to be rewritable for each calculation.

In this embodiment, for example, the following design values are calculated as an example of a state in which a plurality of sheets of paper P are continuously conveyed.

Calculation of average rotation speed Rave rotation speed Rh = 2020 rpm (belt speed Vs x 101%)
Rotation time TRh = 300 msec
Rotation speed Ri = 1900 rpm (belt speed Vs x 95%)
Rotation time TRi = 200msec
[(2020 x 300) + (1960 x 200)] ÷ (300 + 200)
= 1972 rpm
Calculation of speed ratio α 1972 ÷ 2000 = 0.986%
Calculation of rotation speed Rexo of paper ejection motor 404 Coefficient β = 0.99
1800 x 0.986 x 0.99 = 1746.36 rpm
In this example, in a certain state, the following is calculated and stored in the RAM 302.

Fixing transfer speed Vh = Belt speed Vs x 98.6%
Average rotation speed of fixing motor 403 Rave = 1972 rpm
Rotation speed of paper ejection motor 404 Rexo = 1746.36 rpm
The predetermined time Ts from the exposure start signal 500 is calculated by the following.

In the case of image formation of a color image, it is calculated by the distance [A + B + C + E] obtained by adding the distance A, the distance B, the distance C, and the following distance E, and the belt speed Vs at that time. The distance E is a distance from the secondary transfer unit 15 to an arbitrary position beyond the fixing nip portion N of the fixing device 40. Similarly, the distances A, B, and C are fixed distances in the printer configuration and are stored in the ROM 301. The distance E is stored in the ROM 302 so that it can be changed as needed.

For example, this embodiment is calculated as the following design values. The distance A is 31.416 mm as described above, the distance B is 255 mm as described above, and the distance C is 60 mm as described above. The distance E was set to 110 mm, which was slightly longer than the distance E from the secondary transfer unit 15 to the fixing nip portion N of the fixing device 40.

It is as follows when it is calculated by the same calculation formula as above. The distance from the exposure position to the speed switching position [A + B + C + E] = 456.416 mm, the belt speed Vs is 220 mm / sec, and the predetermined time Vs is 2.075 seconds.

Further, in the case of image formation of a black-and-white image, it is calculated by the distance [A + C + E] obtained by adding the distance A, the distance C, and the distance E, and the belt speed Vs at that time. The storage in ROM 301 and ROM 302 is the same as described above.

For example, this embodiment calculates the following design values. The distance A was 31.416 mm as described above, the distance C was 60 mm as described above, and the distance E was 110 mm as described above. It is as follows when it is calculated by the same calculation formula as above. The distance from the exposure position to the speed switching position [A + C + E] = 2011.416 mm, the belt speed Vs is 220 mm / sec, and the predetermined time Vs is 0.915 seconds.

Next, in the paper P, the rear end of the paper reaches the secondary transfer unit 15, the secondary transfer step is completed, and the rear end of the paper is discharged from the secondary transfer unit 15. Here, when the rear edge of the paper exceeds the secondary transfer unit 15, the loop control mode is terminated by interrupting the elapse of the predetermined time Te from the exposure start signal 500 (S23: YES) (S24). Then, the fixing transfer speed is switched to the fixing transfer speed Vo (S25). The rotation speed of the fixing motor 403 at this time is calculated by the above, and the fixing motor 403 is rotated so as to be the average rotation speed Rave stored in the RAM 302.

In synchronization with the switching of the fixing transport speed, the paper discharge transport speed is switched to the paper discharge transport speed Vexo (S26). The rotation speed of the fixing motor 403 at this time is calculated by the above, and the paper ejection motor 404 is rotated so as to be the rotation speed Rexo stored in the RAM 302.

Here, the fixing transfer speed is switched to the fixing transfer speed Vo when the rear end of the paper exceeds the secondary transfer unit 15, but the following settings may be used. That is, if the paper P forms a loop, the paper P is not pulled by the fixing nip portion N of the fixing device 40 and only the loop is eliminated. Therefore, the fixing transport is performed before the rear end of the paper exceeds the secondary transfer portion 15. It may be set to switch to the speed Vo.

The predetermined time Te from the exposure start signal 500 is calculated by the following. In the case of image formation of a color image, the distance [A + B + C + L + F] obtained by adding the distance A, the distance B, the distance C, the paper length L, and the following distance F, and the belt speed Vs at that time are used. It is calculated. The paper length L is a standard size length stored in the ROM 301 based on the paper length detection result. The distance F is the distance from the secondary transfer unit 15 to an arbitrary position. Similarly, the distances A, B, and C are fixed distances in the printer configuration and are stored in the ROM 301. The distance F is stored in the ROM 302 so that it can be changed as needed.

For example, this embodiment is calculated as the following design values. The distance A is 31.416 mm as described above, the distance B is 255 mm as described above, and the distance C is 60 mm as described above. The paper length L is 297 mm per A4 vertical size paper P. The distance F was set to a position of 10 mm at which the rear end of the paper was discharged from the secondary transfer unit 15 and slightly advanced.

It is as follows when it is calculated by the same calculation formula as above. From the exposure position, the speed switching position [A + B + C + L + F] = 653.416 mm, the belt speed Vs is 220 mm / sec, and the predetermined time Vs is 2.970 seconds.

Further, in the case of image formation of a black-and-white image, it is calculated by the distance [A + C + L + F] obtained by adding the distance A, the distance C, the paper length L, and the distance F, and the belt speed Vs at that time. The storage in ROM 301 and ROM 302 is the same as described above.

For example, this embodiment calculates the following design values. The distance A is 31.416 mm as described above, the distance C is 60 mm as described above, the paper length L is 297 mm as described above, and the distance F is 10 mm as described above.

It is as follows when it is calculated by the same calculation formula as above. The speed switching position from the exposure position is [A + C + L + F] = 398.416 mm, the belt speed Vs is 220 mm / sec, and the predetermined time Vs is 1.811 seconds.

Next, if the device is not in image formation and the paper P is the final image drawing paper (S27: NO), the paper P passes through the fixing device 40 and the output roller pair 17 and is discharged to the output tray 19. At this time, the paper ejection of the paper ejection sensor 201 is detected without switching between the fixing transport speed and the paper ejection transport speed while maintaining the fixing transport speed Vo and the paper ejection transport speed Vexo (S20: YES). When the image drawing is completed (S28), the rotation of each motor is stopped (S29).

Next, a case where there is a secondary printing paper when the rear end of the paper reaches the secondary transfer unit 15, the secondary transfer step is completed, and the rear end of the paper is ejected from the secondary transfer unit 15 will be described. During continuous paper transport, the average speed is acquired for each paper P transport, and is reflected in the transport speed of the fixing nip portion N and the paper discharge nip portion 17 for each paper (recording material).

Specifically, when the fixing transfer speed is switched to the fixing transfer speed Vo, if image formation is in progress (S26: YES), the fixing transfer speed control repeats the sequence from the exposure start signal 500 of the next printing paper P. (S9). That is, the sequence of the next printing paper P is operated in parallel with the sequence of the preceding printing paper P. This means that the fixing transfer speed is similarly controlled regardless of whether the next printing paper P is the paper transfer from the paper feed cassette 10 or the paper transfer from the double-sided transfer path 22 in the case of double-sided printing. ..

The paper discharge transport speed at this time maintains the paper discharge transport speed Vexo at the time of pre-passing, and maintains the speed until it is rewritten by the calculation at the time of loop control on the next printing paper. In the case of continuous paper passing, the process is repeated for each paper, and every time the rear end of the paper reaches the secondary transfer unit 15, the fixing transfer speed Vo and the paper discharge transfer speed Vexo are continuously updated.

As described above, the fixing transfer speed during actual transfer is calculated from the loop control state of the fixing transfer speed control. Then, after the rear end of the paper reaches the secondary transfer unit 16, the fixing transfer speed and the paper discharge transfer speed are synchronized. Further, the speed calculation is continuously performed every time the paper is passed. As a result, it is possible to cope with the transport speed of the paper P due to the change in the outer diameter due to the heating of the fixing roller 100 and the pressure roller 101. Therefore, it is possible to provide an image forming apparatus having a fixing transport speed control capable of shortening the roller pitch for paper transport and small size paper transport without paper damage or image defects in the paper ejection path.

In this embodiment, the fixing device 40 is provided with a pair of rotating bodies, a fixing roller 100 and a pressure roller 101, but the fixing method is not limited to this fixing method. For example, a belt method may be used on the fixing member side or the pressurizing member side, or a fixing method by electromagnetic induction heating may be used. Further, the integration of the rotation time of the fixing motor 403 is used for the calculation of the average speed of the fixing transfer speed. However, the ON time and the OFF time of the loop sensor 220 may be used without this limitation. That, CPU 300 includes a rotating speed of the first loop of the state Ls of the detection time and the fixing motor 403 at that time, the detection time and the rotational speed Toka et of the fixing motor 403 at the time of the second loop of states Ld, Obtain the average transfer speed of the fixing nip. Then, it is reflected in the transport speed of the fixing nip portion N and the paper ejection nip portion 17.

Further, the distance between the secondary transfer unit 15 and the fixing nip portion N of the fixing device 40 is set to be shorter than the shortest length of paper P that can be used in the device, but the distance is not limited to this. For example, both the secondary transfer unit 15 and the fixing nip portion N of the fixing device 40 are provided with rollers, belts, etc. for transporting the paper P between the secondary transfer unit 15 and the fixing nip portion N of the fixing device 40. The control may be performed only when the paper P having a length of the paper P is conveyed.

Further, in the present embodiment, the fixing transfer speed control unit and the paper discharge transfer speed control unit are separated from each other, and feedback control is performed to synchronize the speeds of the respective units, but this is not the case. For example, even when the paper ejection unit has a fixed speed ratio to the fixing unit in the same drive unit in which the fixing and conveying speed control unit has the same drive unit, the fixing and conveying speed is set to be a set value that approximates the fixed speed. Therefore, the feedback control of only the fixing transfer speed may be performed.

50 ... Image forming apparatus, 1 ... First image carrier (photosensitive drum), 8 ... Second image carrier (intermediate transfer belt), P ... Recording material, 15 ... Transfer nip, N・ ・ Fixing nip part, 17 ・ ・ Conveying (paper ejection) nip part, Ls ・ ・ First loop amount state, Ld ・ ・ Second loop amount state, 220, 222, 222 ・ ・ Loop detection part, 300 ... Control unit, 403 ... Transport speed control motor for fixing nip

Claims (4)

A transfer nip that transfers the toner image from the side of the image carrier that carries the unfixed toner image by sandwiching and transporting the recording material to the recording material, and
A fixing nip portion located downstream of the transfer nip portion in the transport direction of the recording material, sandwiching and transporting the recording material transported from the transfer nip portion to fix a toner image on the recording material, and a fixing nip portion.
A transport nip portion located downstream of the fixing nip portion in the transport direction of the recording material and sandwiching and transporting the recording material transported from the fixing nip portion.
When the recording material is conveyed between the transfer nip portion and the fixing nip portion and the recording material is conveyed between the transfer nip portion and the fixing nip portion, the transfer nip portion and the fixing nip portion are conveyed. A loop that detects the state of the first loop amount and the state of the second loop amount larger than the first loop amount with respect to the loop of the recording material generated between the transfer nip portion and the fixing nip portion due to the speed difference. With the detector
It has a control unit that changes the transport speed of the fixing nip unit so that the loop falls within a predetermined amount range based on the detection information of the loop detection unit.
The control unit includes the rotation speed of the transfer speed control motor of the fixing nip portion in the state of the first loop amount and its operating time, and the transfer speed control motor of the fixing nip portion in the state of the second loop amount. The average speed of the transfer speed of the fixing nip portion is obtained from the number of rotations and the operating time thereof, and after the rear end of the recording material passes through the transfer nip, the transfer speed of the fixing nip portion is set to the average speed. An image forming apparatus characterized by switching and switching the transport speed of the transport nip portion . When continuous recording material conveying performs acquisition of the average speed for each transport of the recording material, to reflect the conveying speed of the conveying nip portion and the fixing nip portion for each recording medium in claim 1, wherein The image forming apparatus described. A transfer nip that transfers the toner image from the side of the image carrier that carries the unfixed toner image by sandwiching and transporting the recording material to the recording material, and
A fixing nip portion located downstream of the transfer nip portion in the transport direction of the recording material, sandwiching and transporting the recording material transported from the transfer nip portion to fix a toner image on the recording material, and a fixing nip portion.
A transport nip portion located downstream of the fixing nip portion in the transport direction of the recording material and sandwiching and transporting the recording material transported from the fixing nip portion.
When the recording material is conveyed between the transfer nip portion and the fixing nip portion and the recording material is conveyed between the transfer nip portion and the fixing nip portion, the transfer nip portion and the fixing nip portion are conveyed. A loop that detects the state of the first loop amount and the state of the second loop amount larger than the first loop amount with respect to the loop of the recording material generated between the transfer nip portion and the fixing nip portion due to the speed difference. With the detector
It has a control unit that changes the transport speed of the fixing nip unit so that the loop falls within a predetermined amount range based on the detection information of the loop detection unit.
The control unit has a detection time of the state of the first loop amount, a rotation speed of the transport speed control motor of the fixing nip part at that time, a detection time of the state of the second loop amount, and the fixing nip at that time. rpm Toka et conveyance speed control motor parts, obtains the average speed of the conveying speed of the fixing nip portion, after the trailing edge of the recording material has passed through the transfer nip, the average conveyance speed of the fixing nip portion An image forming apparatus characterized by switching to a speed and switching the transport speed of the transport nip portion . According to claim 3 , when the recording material is continuously transported, the average speed is acquired for each recording material and is reflected in the transport speed of the fixing nip portion and the transport nip portion for each recording material. The image forming apparatus described.