JP2012014062A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of wrinkle due to unstable attitude of a sheet entering a fixing nip for various kinds of paper.SOLUTION: A sheet on which a line pattern is projected in a width direction by a pattern projector 62 is conveyed to a fixing nip. A shape of the line pattern on the sheet is measured by an area sensor 61a to detect the out-of-plane deformation of the sheet. Further, a sheet tip position is detected by a sheet tip position sensor 61b. Based on the detection results, a predicted time difference in biting the left and right tips of the sheet is calculated to determine an adjustment amount of the fixing conditions such as a rotational speed of a fixing roller and a heating temperature of the fixing roller, and thereby the fixing conditions are changed to prevent occurrence of wrinkle.

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly to a technique for suppressing the occurrence of wrinkling of a recording sheet due to an unstable posture when the recording sheet comes into contact with a fixing nip.

  In an image forming apparatus using an electrophotographic system, a fixing device for fixing an unfixed toner image transferred onto a recording sheet is mounted. The fixing device fixes the toner image on the recording paper by passing the recording paper on which the toner image is transferred to a fixing nip portion formed by, for example, a fixing roller and a pressure roller. In this type of fixing device, the recording paper may be wrinkled during the fixing process.

FIG. 9 is a diagram showing a fixing roller described in Patent Document 1 as a prior art.
As a technique for dealing with the problem that wrinkles are generated on the recording paper during the fixing process, as shown in FIG. 9, the thickness of both ends of the elastic layer 42b of the fixing roller 42 that is rotationally driven by a drive motor is shown in FIG. There is described a fixing device in which the fixing roller 42 is thicker than the portion, and the shape of the fixing roller 42 is a so-called “reverse crown shape” whose central portion is smaller in diameter than both ends. By making the shape of the fixing roller 42 into an inverted crown shape, the peripheral speed of the end portion having a large outer diameter becomes faster than that of the central portion, and a force for pulling the recording paper in the fixing nip outward in the paper width direction acts. When the recording paper receives such a force pulling outward in the paper width direction, generation of wrinkles can be suppressed.

  However, in the prior art, it is not possible to obtain a sufficient effect on the wrinkles of the recording paper due to the unstable posture of the paper before entering the nip portion, and furthermore, one roller for a wide variety of paper types. It is difficult to suppress the generation of wrinkles by shape.

  The present invention has been made in view of the above problems, and an object of the present invention is to suppress the generation of wrinkles due to instability of the posture of the paper entering the fixing nip portion for a wide variety of paper types. A fixing device and an image forming apparatus are provided.

  In order to achieve the above object, the present invention provides the following fixing device and image forming apparatus.

  A fixing device according to the present invention includes a driving member that is rotationally driven by a driving source, and an opposing member that contacts the driving member and forms a fixing nip with the driving member. A leading edge position detecting means for detecting a leading edge position of the left and right edges of the recording paper near the entrance of the fixing nip, an out-of-plane deformation shape detecting means for detecting an out-of-plane deformation shape of the left and right edges, the leading edge position detecting means, Control means for controlling the drive speed of the drive member based on the detection result of the out-of-plane deformed shape detection means.

  An image forming apparatus according to the present invention includes the fixing device, and a storage unit that stores a control limit threshold value that is a difference in biting time for which the driving speed can be controlled for each type of recording paper. The means controls the driving speed when a biting time difference predicted based on detection results of the tip position detection means and the out-of-plane deformation shape detection means is less than the control limit threshold value. .

  According to the present invention, it is possible to suppress the generation of wrinkles due to instability of the posture of the paper entering the fixing nip portion for a wide variety of paper types.

1 is a diagram schematically illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a perspective view showing an intermediate transfer belt 20 of FIG. 1 and a mechanism related thereto. It is a schematic block diagram which shows the fixing device 40 and control block of FIG. It is a figure which shows the example of the threshold value table 66a and the correction value table 66b of FIG. FIG. 4 is a perspective view showing the periphery of the fixing nip of FIG. 3. (A) shows a fixing nip biting initial state when there is a difference in biting time at the leading end of the sheet, and (b) is a schematic diagram showing a state when wrinkles occur when there is a biting time difference at the leading end of the sheet. . FIG. 10 is a control flowchart for adjusting a paper leading edge biting time difference in the present embodiment. It is a block diagram of the out-of-sheet deformation shape detection means of the present embodiment. It is a figure which shows the conventional fixing roller.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram schematically showing a device configuration of a printer which is an example of an image forming apparatus according to the present embodiment. The image forming apparatus 1 shown in this figure is an electrophotographic color image forming apparatus capable of forming a full color image by adopting a tandem method, and includes four image forming units 10 (Y, M, C, Bk). The intermediate transfer belt 20 is juxtaposed along the upper running side. The intermediate transfer belt 20 will be described in detail later with reference to FIG.

  Each image forming unit 10 has the same configuration except for the color of the toner to be handled. In FIG. 1, only the leftmost yellow image forming unit 10Y has a reference numeral attached to a device constituting the unit. That is, each image forming unit 10 includes a photosensitive drum 11 as an image carrier. Around the photosensitive drum 11, a charging unit 12, a developing device 13, a cleaning device 14, and the like are arranged, and further, a primary transfer unit is configured inside the intermediate transfer belt 20 so as to face each photosensitive drum 11. A transfer roller 15 is provided. Further, in this example, each image forming unit is provided with an exposure unit. For example, an exposure unit 16 such as an LED is arranged between the charging unit 12 and the developing device 13 so that optical writing is possible. As the exposure means, it is possible to use an exposure apparatus common to each image forming unit, for example, a laser writing apparatus.

  A transfer roller 31, which is a transfer member, is disposed so as to be opposed to the transfer counter roller 32, which is one of the support members of the intermediate transfer belt 20 and functions as a backup member, with the intermediate transfer belt 20 interposed therebetween. In the drawing of the transfer roller 31, a registration roller pair 54 is disposed on the right side, and a conveyance belt 55 is disposed on the left side. A fixing device 40 is provided on the left side of the transport belt 55. This fixing device 40 is a belt fixing device having a fixing belt 43 stretched between a heating roller 41 as a heating means and a fixing roller 42, and the pressed roller 44 is pressed against the fixing roller 42 with the fixing belt 43 interposed therebetween. It is provided to do.

  In the lower part of the apparatus, a sheet feeding tray 50 for storing the sheet bundle P is disposed, and a pickup roller 51 and a separation feeding roller 52 are provided as sheet feeding means. Further, a conveyance roller 53 is disposed at an appropriate position in the sheet conveyance path indicated by a one-dot chain line in the drawing. Further, although not shown, a paper guide is provided as appropriate. In addition, a manual paper feed unit and a paper reversing unit can be provided as necessary. It is also possible to mount an image reading device (scanner), an automatic document feeder (ADF), or the like.

  An image forming operation in the image forming apparatus configured as described above will be briefly described.

  The photosensitive drum 11 of the image forming unit 10 is rotationally driven counterclockwise in the figure by a driving unit (not shown), and the surface of the photosensitive drum 11 is uniformly charged to a predetermined polarity by the charging unit 12. The charged photosensitive member surface is irradiated with scanning light from the exposure unit 16, thereby forming an electrostatic latent image on the photosensitive drum 11 surface. At this time, the image information exposed to each photosensitive drum 11 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. Each color toner is applied from the developing device 13 to the electrostatic latent image formed in this manner, and visualized as a toner image. Further, the intermediate transfer belt 20 is driven to run in the clockwise direction in the drawing, and the respective color toner images are sequentially transferred from the photosensitive drum 11 to the intermediate transfer belt 20 by the action of the primary transfer roller 15 in each image forming unit 10. In this way, the intermediate transfer belt 20 carries a full-color toner image on its surface. Note that a single color image can be formed using any one of the image forming units 10, or a two-color or three-color image can be formed using a plurality of image forming units. In the case of monochrome printing, image formation is performed using the rightmost black unit 10Bk in the drawing among the four image forming units.

  The residual toner adhering to the surface of the photosensitive drum 11 after transferring the toner image is removed from the surface of the photosensitive drum by the cleaning device 14, and then the surface is subjected to the action of a static eliminator (not shown) so that the surface potential is initially set. To prepare for the next image formation.

  On the other hand, the paper is fed from the paper feed tray 50 and is sent out toward the secondary transfer position by the registration roller 54 in timing with the toner image carried on the intermediate transfer belt 20. The toner image on the surface of the intermediate transfer belt is collectively transferred onto the sheet by the transfer roller 31 as the second transfer unit. The sheet on which the toner image has been transferred is sent to the fixing device 40 by the conveying belt 55, and when passing through the fixing device 40, the toner image is fused and fixed to the sheet by heat and pressure. The paper on which the toner image is fixed is discharged to a paper discharge tray (not shown).

FIG. 2 is a perspective view showing the configuration of the intermediate transfer belt 20.
As shown in this figure, the intermediate transfer belt 20 is stretched over a drive roller 21, a driven roller 22, an external stretching roller 23, a transfer counter roller 32, and a transfer guide roller 33. The drive roller 21 is driven by a motor 26. By being driven to rotate, the vehicle travels in the direction of arrow A in the figure. The driven roller 22 applies tension to the intermediate transfer belt 20 by a load applying unit (not shown), and generates a friction conveying force between the driving roller 21 and the intermediate transfer belt 20. As described with reference to FIG. 1, the photosensitive drums 11 of the respective color image forming units are arranged in parallel on the upper traveling side of the intermediate transfer belt 20 which is a belt stretching surface formed by the driving roller 21 and the driven roller 22. A transfer roller 15 as a primary transfer unit is disposed in the loop of the intermediate transfer belt 20 so as to face each photoconductor drum 11. A transfer roller 31 is disposed below the transfer counter roller 32 and is pressed against the transfer counter roller 32 with the intermediate transfer belt 20 interposed therebetween. A predetermined high voltage is applied to the transfer counter roller 32 from a transfer power source (not shown), and a transfer electric field is formed in the transfer nip with the transfer roller 31 that is electrically grounded. In addition, the transfer roller 31 conveys the sheet with a predetermined pressing force together with the transfer counter roller 32 and the intermediate transfer belt 20. Further, a transfer guide roller 33 is disposed on the back side of the intermediate transfer belt 20 and in the vicinity of the upstream side of the transfer counter roller 32 in the belt rotation direction. The transfer roller 30, the transfer counter roller 31 and the transfer guide roller 32 constitute a secondary transfer unit 30. As can be seen from FIG. 1, the transfer guide roller 33 is disposed slightly outside the straight line connecting the outer peripheral surfaces of the drive roller 21 and the transfer counter roller 32, and the intermediate transfer belt 20 is moved from the belt inner side to the outer side. It is provided at a position to push it out. Thereby, the arrangement relationship between the transfer facing roller 32 and the transfer roller 30 is sandwiched between the transfer nip formed by the transfer roller 30 and the transfer facing roller 32 after the intermediate transfer belt 20 is wound around the surface of the transfer roller 30, and The arrangement is such that the rear end portion of the paper with respect to the portion sandwiched in the transfer nip is brought close to the surface of the image carrier by the waist of the paper. Although not shown in FIG. 2, belt cleaning means 24 (FIG. 1) for cleaning the intermediate transfer belt 20 is disposed outside the belt between the transfer counter roller 32 and the external stretching roller 23, and the belt. A backing roller 25 (FIG. 1) corresponding to the cleaning blade of the cleaning means 24 is disposed inside the belt. The paper P is conveyed in the direction of arrow B in the figure, and after the posture of the paper is corrected by the registration roller pair 54, it is conveyed between the transfer roller 31 and the intermediate transfer belt 20, and the toner image on the intermediate transfer belt 20 is transferred. It is electrostatically transferred onto the paper.

FIG. 3 is a schematic configuration diagram showing the fixing device 40 and a control block diagram.
As described above, the fixing device 40 is a belt fixing device having the fixing belt 43 stretched between the heating roller 41 serving as a heating means and the fixing roller 42. The fixing device 40 is applied to the fixing roller 42 with the fixing belt 43 interposed therebetween. A pressure roller 44 is provided so as to be in pressure contact.

  The heating roller 41 as a heating means incorporates a heater 45 such as a halogen lamp in a hollow metal cored bar, and heats the fixing belt 43 from the inside by this radiant heat.

  The heating roller 41 is rotationally driven by a drive source (not shown), the fixing roller 42 is rotationally driven through the fixing belt 43, and the pressure-sensitive roller 44 is driven to rotate through the fixing nip. In other words, in the present embodiment, the fixing roller 42 functions as a driving member that transmits the driving force of the driving source to the sheet and applies a conveying force to the sheet, and the pressed roller 44 rotates following the fixing nip. It functions as an opposing member.

  An area sensor 61a and a pattern projector 62 are provided in the vicinity of the entrance of the fixing nip. The pattern projector 62 of the present embodiment uses a projector that projects a linear pattern in the paper width direction.

  The control unit 63 controls the entire apparatus, and various devices and sensors are connected. In the figure, only the devices and sensors related to the feature points of the present apparatus are shown. The control unit 63, which is a control unit, includes a CPU, a ROM, a RAM, and the like, and realizes functions of each unit by executing a predetermined program on hardware. As shown in the figure, the control unit 63 calculates an out-of-plane deformation shape in the width direction of the paper P at the entrance of the fixing nip from the output value of the area sensor 61a. That is, in the present embodiment, the control unit 63, the area sensor 61a, and the pattern projector 62 constitute an out-of-plane deformed shape detection unit.

  A paper leading edge position detection sensor 61b is provided in the vicinity of the entrance of the fixing nip. The paper leading edge position detection sensor 61b according to the present embodiment includes a light emitting element that illuminates the paper in the width direction of the paper and a light receiving unit that converts reflected light from the paper into a potential. When the sheet passes just below the sheet leading edge position sensor 61b, the leading edge position of the sheet can be detected from the change in the amount of light entering the light receiving unit without the sheet. Further, by arranging the paper leading edge position detection sensor across the paper width direction, the positions of the paper leading edges on the left and right sides of the paper can be known.

  In this embodiment, the out-of-plane deformed shape detecting unit and the paper leading edge position detecting unit are separately configured. However, the out-of-plane deformed shape detecting unit can also measure the paper leading end position and is configured by one element. It is also possible to do.

The control unit 63 is connected to a non-volatile memory 64 serving as a storage unit. The non-volatile memory 64 includes a reference biting time difference 65 obtained in advance by experiments and a threshold value of the biting time difference at which wrinkles occur. A threshold table 66a such as a control limit biting time difference, a correction value table 66b, and the like are stored.
FIG. 4 shows an example of the threshold value table 66a and the correction value table 66b.

  Here, the reference biting time difference 65 obtained in advance by experiment is the biting time difference for each condition because the paper flapping method at the entrance of the fixing nip changes depending on the paper path shape, paper type, and environment of the apparatus. Is stored as a reference value. Depending on the conditions, the reference value may reach the threshold value of the biting time difference at which wrinkles occur. In this case, the fixing drive control is performed when a printing instruction is input by the operator.

The control unit 63 controls the driving motor 67 to control the rotation speed of the fixing roller 42 and the power source 68 of the heater 45 to control the amount of fixing heat. Further, the control unit 63 is connected to a speaker 69 and a display unit 70 as notification means, and can control the speaker 69 and the display unit 70 to notify the user of predetermined information. Here, the predetermined information is, for example, an indication that the risk of jam is large.
Next, a method for evaluating the difference in biting time at the leading edge of the paper will be described.

FIG. 5 shows a geometrical arrangement of the paper conveyed to the fixing nip in an unstable posture.
The sheet P on which the toner image is formed by a transfer unit (not shown) is ideally conveyed in the plane indicated by the two-dot chain line in the figure, and is bitten by the fixing nip part to melt and fix the toner image on the sheet. Let However, the paper is often transported out of the ideal plane as shown in the figure due to flapping during the transport of the paper or curling of the paper.

  Since unfixed toner adheres to the paper immediately before the fixing nip, it is impossible to guide the paper flutter with the paper guide, and to prevent paper wrinkles due to such paper flutter. It has become a difficult event to do.

In the present embodiment, the leading end of the sheet ideal position P _L, P _R Karakara out by P _L ', the state became P _R, i.e., the sheet edge portion of the paper near side at a height h by two-dot chain line The state which deviated from the shown ideal position plane is shown. At this time, assuming that the front end of the sheet is in contact with the fixing roller 42, if the angle formed by the center positions N _L and P _L ′ in the width direction of the fixing nip is α, and the angle formed by the front end of the sheet and the ideal plane is θ, the sheet The difference in time during which the left and right ends of the leading end are caught in the fixing nip can be obtained as a difference in the conveyance path.

That is, the difference δ in the conveyance path between the left and right ends of the sheet front and the time difference Δt between the left and right ends of the sheet front with respect to the system of FIG.
δ = 2πRα− (R−h) tanα (1)
Δt = δ / v (2)
Can be obtained as

In this way, it is possible to predict the difference in the engagement time of the leading end of the sheet into the fixing nip from the measurement result of the out-of-plane deformation shape of the sheet. Furthermore, by taking into account the measurement result of the position of the leading edge of the paper, the biting time difference obtained as described above can be obtained with higher accuracy.
Next, a phenomenon in which wrinkles occur due to a difference in the biting time at the leading edge of the paper will be described.

FIG. 6 shows an out-of-plane deformation shape in the sheet width direction at the fixing nip.
As shown in FIG. 5, when the left end PL ′ of the leading edge of the sheet is deviated from the ideal sheet conveyance plane, as described above, a time difference between the leading edge of the sheet and the fixing nip occurs. Thus, a situation occurs in which a part of the front end of the sheet (only the right side in this embodiment) is caught in the fixing nip. At this time, the left side of the front end of the sheet is not yet caught in the fixing nip portion.

  With the rotation of the fixing roller, the paper is conveyed in the direction B in the figure, and the left side of the front edge of the paper is also caught in the two fixing nips. At this time, the area bitten first and the area bitten later As a result, an angle difference occurs in the direction of conveyance in the sheet surface, the sheet cannot maintain a planar shape, and undulation W1 occurs. As the paper is transported, the waviness of the paper increases, and finally wrinkles W2 are generated at the paper nip portion.

Therefore, in the present embodiment, the rotation speed of the fixing roller 42 is slowed down when the paper tip engagement time difference Δt predicted from the measurement result of the out-of-plane deformation shape and the paper front end position reaches a value that causes wrinkles. I have control. When the rotation speed of the fixing roller 42 becomes slow, the sheet P is pushed toward the fixing nip side by the conveying force from the transfer unit, and the leading end of the sheet (left side in this embodiment) that has not been caught in the fixing nip unit is also generated. It becomes caught in the fixing nip. In other words, it is possible to substantially reduce the biting time difference at the leading end of the sheet, thereby preventing wrinkles.

  In the case of thick paper with high paper rigidity, since the force to keep the paper in a flat shape is strong, the difference in biting time at the leading edge of the paper is large, and the waviness is reduced, and wrinkles are not caused. On the other hand, in the case of thin paper with low paper rigidity, since the force to keep the paper in a flat shape is weak, wrinkles are generated even with a slight difference in biting time at the front end of the paper. As described above, since the ease of wrinkling differs depending on the type of paper, the biting time difference at the leading end of the paper that begins to wrinkle differs depending on the type of paper. Therefore, in the present invention, the threshold value of the biting time difference in which wrinkles are generated for each paper type is held in the storage means such as the nonvolatile memory 64, and based on the measurement result of the deformed shape of the paper and the measurement result of the front end position of the paper. By referring to the calculated time difference between the leading edges of the paper, it is determined whether or not to perform control for preventing wrinkles.

  In addition, as the reduction amount of the rotation speed of the fixing roller is increased, it becomes possible to control the wrinkle-free state even with a large difference in the biting time at the leading end of the paper. A reduction amount of the rotation speed of the fixing roller is determined in advance, and is stored in a storage unit such as a memory as a correction value.

  However, since the change in the rotation speed of the fixing roller directly affects the fixability, there is a limit from the viewpoint of obtaining stable fixing quality even if the fixing temperature is changed according to the rotation speed of the fixing roller. Therefore, in the present invention, the limit at which stable fixing quality can be obtained is held in a storage means such as a memory as a control limit biting time difference, and if the biting time difference at the leading end of the paper exceeds this limit, This message is displayed to the user and the device is stopped to prevent paper jams caused by wrinkled defective prints and wrinkles, thereby preventing wasteful use of paper and wasteful time required for jam processing. Like to do.

FIG. 7 is a control flow chart for adjusting the paper leading edge biting time difference.
First, the control unit 63 specifies the paper type for measuring the out-of-plane deformation shape (S1). For specifying the paper type, for example, when the paper P is set in the paper feed tray, the user inputs information on the thickness and type of the paper P set in the paper feed tray, and the input information is stored in the nonvolatile memory 64. Remember.

  The control unit 63 can specify the paper type for measuring the out-of-plane deformation shape by reading the paper type information of the paper set in the paper feed tray 50 stored in the nonvolatile memory 64. Next, the control unit 63 projects the line pattern onto the sheet by the pattern projector 62 (S2), conveys the sheet irradiated with the line pattern to the fixing nip, and measures the shape of the line pattern by the area sensor 61a. Then, an out-of-plane deformed shape is detected (S3). Further, the paper front end position sensor 61b detects the paper front end position (S3).

  The control unit 63 calculates a paper leading edge biting time difference predicted from the detected out-of-plane deformed shape and the paper leading edge position, and a leading edge biting time difference control limit value corresponding to the paper type stored in the nonvolatile memory 64. Compare (S4). If the predicted paper tip biting time difference exceeds the control limit value, wrinkles cannot be avoided, so an alarm is issued by controlling the speaker and a message indicating that the risk of jamming is large is displayed. The device is displayed and stopped (S8).

  If the predicted paper leading edge biting time difference does not exceed the limit value (S4 / No), it is compared with the leading edge biting time difference control necessity threshold value corresponding to the paper type stored in the nonvolatile memory 64 (S5). ). If the predicted paper tip biting time difference is smaller than the control necessity threshold, wrinkles will not occur, so the fixing conditions for preventing wrinkles due to the paper tip biting time difference are not controlled, and the normal fixing conditions remain unchanged. Continue printing with.

  When the predicted paper leading edge biting time difference is larger than the control necessity threshold (S5 / No), the control unit 63 predicts the leading edge biting predicted from the correction value table 66b stored in the nonvolatile memory 64 and the measurement result. An adjustment amount of the fixing condition such as the rotation speed of the fixing roller and the temperature of the fixing roller is obtained from the time difference (S6), and the fixing condition is changed according to the obtained adjustment amount to avoid wrinkles (S7).

  Since the rigidity of the paper varies greatly depending on the environment, the above-described various limit values and threshold values differ depending not only on the paper type but also on the environment. Therefore, it is desirable that the above-described various limit value and threshold value tables are stored in a nonvolatile memory for each paper type and environment. Here, the environment mainly means a temperature and humidity environment.

FIG. 8 is a configuration diagram of the out-of-sheet deformation shape detecting means.
The sheet P is conveyed in the direction of arrow B through the nip formed by the fixing roller 42 and the pressed roller 44. The pattern projector 62 is arranged at a predetermined angle with respect to the recording surface of the paper P on the nip entering side, and irradiates the pattern LP over the entire width of the paper P near the nip entering side. Here, the angle at which the pattern projector 62 with the “predetermined angle” is arranged with respect to the recording surface of the paper P decreases as the measurement is close to perpendicular to the paper P, and increases when the angle is shallower. On the other hand, since it will be out of the measurement range with a slight deformation, about 45 ° is easy to handle.

  The area sensor 61 is arranged in a direction substantially perpendicular to the recording surface of the paper P on the pattern LP forming side of the paper P, and images the pattern LP formed on the paper P. When the sheet P has no deflection, the pattern LP is captured by the area sensor 61 as a straight line. However, when the sheet P is bent, the height of the sheet locally changes due to the undulation of the sheet. The pattern LP irradiated obliquely with respect to the recording surface of the paper P can be understood by the area sensor 61 as a distorted curve.

  Since it is known that when the amount of out-of-plane deformation of the paper increases and exceeds a predetermined value, wrinkles W are generated in the vicinity thereof, whether or not wrinkles occur by measuring the amount of out-of-plane deformation of the paper. Can be predicted. Further, the out-of-plane deformation amount of the paper P can be obtained from the output of the area sensor 61 by examining the relationship between the height of the paper and the position of the pattern LP in advance.

  In the present embodiment, the deformation shape of the sheet is measured over the entire width of the sheet. However, by arranging spot-like displacement measuring devices at positions corresponding to both ends in the width direction of the sheet to be passed, the cost of the sensor is increased. The same effect can be obtained while reducing the above.

  Hereinafter, the effect of this embodiment will be described.

  According to the present embodiment, since the front end position detecting means for detecting the front end position of at least the left and right ends of the recording paper in the vicinity of the fixing nip entrance is provided, the front end position detected by the front end position detecting means and the out-of-plane position are detected. Based on the predicted biting time difference calculated from the out-of-plane deformed shape detected by the deformed shape detecting means, it can be determined whether or not the recording paper is wrinkled.

The reason will be described below.
There may be a difference in the biting time to the fixing nip in the width direction of the paper due to flapping of the paper being conveyed or deformation of the paper. In this case, there is an angle difference in the direction of conveyance in the paper surface between the part that is bitten by the front of the paper and the part that is bitten by the back, and the paper does not maintain a flat shape and causes swell deformation. Develop. As described above, since there is a correlation between the difference in the paper biting time and the occurrence of the paper wrinkle, the occurrence of the wrinkle can be determined by measuring the difference in the paper biting time.

  In addition, according to the present embodiment, since the control unit that controls the driving member or the heating unit is provided based on the detection results of the tip position detection unit and the out-of-plane deformation shape detection unit, wrinkles are generated. Can be prevented.

  In other words, the fixing roller rotation speed is temporarily reduced based on the paper biting time difference predicted from the above measurement results, and the paper is pressed by the paper conveyance system arranged upstream of the fixing device. By reducing the difference in the time for which the paper is caught in the nip, the generation of paper wrinkles can be prevented.

  Further, the uniformity of the fixing property can be ensured by controlling the temperature of the fixing roller according to the driving speed of the fixing roller.

  Further, according to the present embodiment, the standard biting time difference and the threshold value of the biting time difference necessary for driving speed control are stored in the storage unit, and it is determined whether or not the fixing driving control is performed based on the threshold value. Therefore, unnecessary control is prevented.

  Furthermore, in the present embodiment, the storage means stores the biting time difference of the control limit that cannot be compensated by the drive speed control, and the control means checks whether the calculation result of the biting time difference has reached the control limit. If it is determined that it has reached, it is possible to prevent defective printing due to paper wrinkles and paper jamming defects by prohibiting the fixing operation.

  Further, in the present embodiment, since the above limit values are provided for various types of paper, appropriate control can be performed for each paper type, and stable printing can be realized for a wide range of paper types.

DESCRIPTION OF SYMBOLS 40 Fixing device 41 Heating roller 42 Fixing roller 43 Fixing belt 44 Pressurized roller 45 Heater 61a Area sensor 61b Paper leading edge position detection sensor 62 Pattern projector 63 Control unit 64 Non-volatile memory 69 Speaker 70 Display unit

JP 2005-195856 A

Claims (5)

A fixing device comprising: a driving member that is rotationally driven by a driving source; and an opposing member that contacts the driving member and forms a fixing nip with the driving member,
Leading edge position detecting means for detecting the leading edge positions of the right and left edges of the recording paper near the fixing nip entrance;
Out-of-plane deformation shape detection means for detecting the out-of-plane deformation shape at the left and right ends;
And a control unit that controls a driving speed of the driving member based on detection results of the tip position detection unit and the out-of-plane deformation shape detection unit. A heating means for heating the recording paper passing through the fixing nip;
The fixing device according to claim 1, wherein the control unit controls the heating unit based on the driving speed. Store the reference biting time difference obtained in advance by experiment at the left and right ends,
The control means is based on the stored reference biting time difference and the biting time difference predicted based on the detection results of the tip position detection means and the out-of-plane deformation shape detection means. The fixing device according to claim 1, wherein the fixing device is controlled. A fixing device according to any one of claims 1 to 3,
Storage means for storing a control limit threshold that is a biting time difference capable of controlling the driving speed for each paper type of recording paper,
The control means includes
An image forming apparatus that controls the driving speed when a difference in biting time predicted based on detection results of the tip position detection unit and the out-of-plane deformation shape detection unit is less than the control limit threshold value. . The storage means stores a control necessity threshold value which is a biting time difference that requires the driving speed control,
The control means includes
The driving speed is controlled when a biting time difference predicted based on detection results of the tip position detection means and the out-of-plane deformation shape detection means exceeds the control necessity threshold. 5. The image forming apparatus according to 4.

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