JP2008164919A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus capable of suppressing displacement of image forming positions by a plurality of image forming means even when a recording medium with low flexibility is used.
In a second mode for performing printing on a recording medium with low flexibility (S101: YES), the image forming apparatus passes through a supply unit on the upstream side of the image forming unit. Up to (S107: NO), the conveyance speed in the image forming unit is increased, so an image is formed at an image formation start timing earlier than the standard and at a scanning interval shorter than the standard (S105). Thereafter, when the recording medium finishes passing through the supply unit (S107: YES), the conveyance speed in the image forming unit returns to the reference conveyance speed, and thus an image is formed at a standard scanning interval (S109).
[Selection] Figure 2

Description

  The present invention relates to an image forming apparatus.

  Conventionally, as an image forming apparatus for forming an image by an electrophotographic method, a recording medium is conveyed from a supply unit to an image forming unit to form an image, and further, the recording medium is conveyed to a fixing unit. What is fixed on a recording medium is known (for example, see Patent Document 1). In this type of image forming apparatus, each of the above units plays a role as a conveying unit that conveys a recording medium.

  By the way, when the recording medium is transported from the upstream side to the downstream side in the transport direction by the plurality of transport means, if the transport speed on the downstream side is larger, the transport medium is connected between the upstream side and the downstream side. And the recording medium is pulled. In such a state, excessive tension may act on the recording medium or the conveyance speed may become unstable, which may adversely affect image quality.

For this reason, in general, this type of image forming apparatus is often designed such that the conveying means on the downstream side has a lower conveying speed than the conveying means on the upstream side.
Thus, if the downstream transport speed is low, even if the recording medium is sandwiched between the transporting means between the upstream side and the downstream side, at least the recording medium is not pulled. Further, the recording medium is transported from the upstream side more than the transport amount by the downstream transport means. If the recording medium is somewhat bent between the upstream side and the downstream side, the recording medium is upstream and downstream side. The speed difference of the conveyance speed is absorbed.

Accordingly, both the upstream side and downstream side conveying means can convey the recording medium at the designed conveying speed.
JP-A-2005-104645

  However, some of the recording media used in the image forming apparatus are less likely to bend in comparison with standard recording media (for example, cut paper that is commercially available as copy paper, printer paper, etc.). . As a specific example, a thick paper thicker than a standard cut paper or a plastic film harder than paper usually has low flexibility and is difficult to bend.

  When such a low-flexibility recording medium is used, even if the recording medium is transported from the upstream transport means more than the transport amount by the downstream transport means, the recording medium is between the upstream side and the downstream side. Will not bend sufficiently. Therefore, it is impossible to absorb the difference in transport speed between the upstream side and the downstream side, and as a result, the recording medium cannot be transported at the transport speed as designed in the upstream or downstream transport means. There was.

  More specifically, if the clamping force by the upstream conveying unit is relatively strong, the upstream conveying unit sends out the recording medium even if the recording medium is not bent. It will be forced into being pushed into. For this reason, in such a situation, the transport speed in the downstream transport unit may be higher than expected.

  When such a situation occurs between the supply unit and the image forming unit, the conveyance speed becomes higher than expected in the image forming unit corresponding to the downstream side conveyance unit. For this reason, when an image is formed by a plurality of image forming means, even if the image is transferred to a recording medium at a designed timing, the image is generated by each of the plurality of image forming means because the conveyance speed is higher than expected. There has been a problem that the formation position is shifted and the image quality is adversely affected.

  On the contrary, if the clamping force by the downstream transport unit is relatively strong, the recording medium is not forced to be pushed into the downstream transport unit, and the recording medium does not bend. The recording medium cannot be sent downstream. For this reason, in such a situation, the transport speed in the upstream transport unit may be lower than expected.

  When such a situation occurs between the image forming unit and the fixing unit described above, the conveyance speed becomes lower than expected in the image forming unit corresponding to the upstream conveyance unit. Therefore, when an image is formed by a plurality of image forming means, even if the image is transferred to the recording medium at the designed timing, the image is respectively transferred by the plurality of image forming means because the conveyance speed is lower than expected. There has been a problem that the formation position is shifted and the image quality is adversely affected.

  In other words, whether the conveyance speed in the image forming unit becomes larger or smaller than expected depends on whether the image forming unit is simultaneously with the upstream conveyance unit (for example, supply unit) or the downstream side conveyance unit (for example, fixing unit). Varies depending on whether the structure is in a state of sandwiching.

  However, in any structure, the essence of the problem that the image forming position by each of the plurality of image forming units is shifted due to the conveyance speed by the image forming unit not being as designed is the same. .

  The present invention has been made to solve the above-described problems, and an object of the present invention is to suppress the shift of the image forming position by each of a plurality of image forming units even when a recording medium with low flexibility is used. An object is to provide a possible image forming apparatus.

Hereinafter, the configuration employed in the present invention will be described.
First, an image forming apparatus of the present invention described below includes a plurality of image forming units that each form an image on a recording medium and convey the recording medium at a reference conveying speed, and the reference conveying speed. An upstream conveying means for conveying the recording medium to the image forming means side at a higher upstream conveying speed, a first mode for forming an image on a standard recording medium, and the standard Controlling the plurality of image forming units in correspondence with any one of a plurality of operation modes including at least a second mode for forming an image on a recording medium having a lower flexibility than a recording medium. And when the control unit performs the control in the second mode, the next image forming unit forms the image after one image forming unit starts forming the image. Time to start , And controls so as to be shorter than the case of performing the control in the first mode.

  In the image forming apparatus configured as described above, when a recording medium with low flexibility is used, the recording medium pushed out by the upstream conveying unit is pushed into the image forming unit without much bending. Therefore, the conveyance speed of the recording medium by the image forming unit is higher than the reference conveyance speed.

  However, in such a state, if the operation mode of the image forming apparatus is set to the second mode, the timing at which each of the plurality of image forming units starts to form an image on the recording medium is the first mode. It will be faster than the case. Accordingly, even when the recording medium is conveyed early, the timing of forming an image on the recording medium is advanced accordingly, so that the shift of the image forming position by a plurality of image forming means is suppressed. Can do.

  By the way, when the image forming apparatus of the present invention is displaced to a predetermined position, the recording medium entering the image forming means has a cross-sectional shape orthogonal to the conveyance direction of the recording medium being convex. In this case, the control means may perform the control in the second mode when the movable member is displaced to the predetermined position.

  In the image forming apparatus configured as described above, when a recording medium with high flexibility is used, the flexibility of the recording medium is lowered by displacing the movable member to a predetermined position. be able to. Therefore, it is possible to prevent the recording medium from being wrinkled or the image quality from being deteriorated due to excessive bending of the recording medium.

  In addition, when the flexibility of the recording medium is lowered by the movable member, the operation mode of the image forming apparatus is set to the second mode, and each of the plurality of image forming units starts forming an image on the recording medium. The timing is earlier than in the first mode.

  Therefore, even when the recording medium is transported early because the flexibility of the recording medium is reduced by the movable member, the timing for forming an image on the recording medium is adjusted accordingly. It is possible to reduce the shift of the image forming position.

  In the image forming apparatus according to the aspect of the invention, when the control unit performs the control in the second mode, each of the image forming units is performed while the recording medium passes through the upstream transport unit. The scanning interval may be shorter than the scanning interval in the first mode.

  According to the image forming apparatus configured as described above, the scanning interval of each image forming unit is shorter than the scanning interval in the first mode while the recording medium passes through the upstream conveying unit. Distortion of an image formed on a recording medium can be suppressed.

  That is, when the recording medium conveyance speed becomes faster than expected, if the image formation position shift is suppressed by increasing the timing for forming an image on the recording medium, the image quality can be improved accordingly. If image distortion is suppressed by the above configuration, the image quality is further improved. More specifically, with the above-described configuration, it is possible to prevent the image formed on the recording medium from becoming long in the sub-scanning direction and improve the image quality.

  Furthermore, in the image forming apparatus according to the present invention, when the control unit performs the control in the second mode, the image forming unit is configured so that the rear end of the recording medium passes through the upstream conveying unit and then the image forming unit. The scanning interval may be the same as the scanning interval in the first mode.

  According to the image forming apparatus configured as described above, after the recording medium passes through the upstream conveying unit, the scanning interval of each image forming unit becomes the same as the scanning interval in the first mode. Distortion of the image formed thereon can be suppressed.

  That is, after the recording medium passes through the upstream conveying means, the recording medium conveying speed returns to the reference conveying speed. Therefore, even in such a state, if the scanning interval of each image forming unit is kept shorter than the scanning interval in the first mode, the image formed on the recording medium is shortened in the sub-scanning direction. .

  In this regard, with the above-described configuration, if the scanning interval of each image forming unit is the same as the scanning interval in the first mode after the recording medium has passed through the upstream conveying unit, an image formed on the recording medium can be obtained. Shortening in the sub-scanning direction can be prevented, and the image quality can be further improved.

  The image forming apparatus according to the present invention, which will be described next, includes a plurality of image forming units each forming an image on a recording medium and conveying the recording medium at a reference conveying speed, and the image forming unit side. A downstream transport means for transporting the recording medium transported from the recording medium at a downstream transport speed smaller than the reference transport speed, and a first mode for forming an image on a standard recording medium, And the plurality of images corresponding to one of a plurality of operation modes including at least a second mode for forming an image on a recording medium having lower flexibility than the standard recording medium. Control means for controlling the forming means, and when the control means performs control in the second mode, the next image forming means starts after one image forming means starts forming the image. Start forming the image The time until the, and controls so as to be longer than the case of performing the control in the first mode.

  In the image forming apparatus configured as described above, when a recording medium with low flexibility is used, the recording medium sent out by the image forming sending unit is not much even if pressed against the downstream conveying unit. Without bending, the extrusion from the image forming means is prevented. Therefore, the conveyance speed of the recording medium by the image forming unit is smaller than the reference conveyance speed.

  However, in such a state, if the operation mode of the image forming apparatus is set to the second mode, the timing at which each of the plurality of image forming units starts to form an image on the recording medium is the first mode. It will be slower than the case. Therefore, even if the conveyance by the image forming unit is completed later, the timing for forming an image on the recording medium is also delayed in accordance with that, so that the shift of the image forming position by the plurality of image forming units is suppressed. be able to.

  Further, the image forming apparatus of the present invention to be described next includes a plurality of image forming units each forming an image on a recording medium and conveying the recording medium at a reference conveying speed, and the image forming unit side A downstream transport means for transporting the recording medium transported from the recording medium at a downstream transport speed smaller than the reference transport speed, and a first mode for forming an image on a standard recording medium, And the plurality of images corresponding to one of a plurality of operation modes including at least a second mode for forming an image on a recording medium having lower flexibility than the standard recording medium. Control means for controlling the forming means, and when the control means performs the control in the second mode, each image formation is performed while the recording medium passes through the downstream conveying means. The scanning interval of the means, Serial characterized by longer than the scanning interval in the first mode.

  According to the image forming apparatus configured as described above, the scanning interval of each image forming unit is longer than the scanning interval in the first mode while the recording medium passes through the downstream transport unit. Distortion of an image formed on a recording medium can be suppressed.

  That is, when the conveyance speed of the recording medium becomes slower than expected, the image quality can be improved by suppressing the shift of the image forming position, but the image quality can be improved even if the distortion of the image is suppressed. be able to. More specifically, with the above-described configuration, it is possible to prevent the image formed on the recording medium from being shortened in the sub-scanning direction and improve the image quality.

In addition, the image forming apparatus of the present invention preferably includes an operation mode setting unit that allows a user to arbitrarily set the first mode or the second mode.
With such an image forming apparatus, the user can arbitrarily set the operation mode, and the shift of the image forming position by the plurality of image forming units can be suppressed.

Next, embodiments of the present invention will be described with specific examples.
(1) First Embodiment First, a first embodiment will be described.

[Schematic structure of image forming apparatus]
FIG. 1 is a longitudinal sectional view showing a schematic structure of the image forming apparatus 1.
The image forming apparatus 1 is an apparatus that forms an image on a recording medium by electrophotography, and is generally called a laser printer. The image forming apparatus 1 includes a supply unit 3, an image forming unit 5, a fixing unit 7, and the like.

  The supply unit 3 is a portion that supplies a recording medium such as cut paper, and is fed by a pair of conveyance rollers 11 (corresponding to an example of an upstream conveyance unit in the present invention) on the end side in the conveyance direction of the supply unit 3. A recording medium is supplied to the image forming unit 5.

  The image forming unit 5 includes four sets of image forming mechanisms 13K, 13Y, 13M, and 13C (corresponding to an example of the image forming unit in the present invention) corresponding to the respective colors of black, yellow, magenta, and cyan, a conveyance belt 15, and the like. It has.

  Each of the image forming mechanisms 13K, 13Y, 13M, and 13C includes a photoconductor, and an electrostatic latent image is formed on the photoconductor by scanning the photoconductor with a laser scanner. Then, the latent image is developed by the toner in each of the image forming mechanisms 13K, 13Y, 13M, and 13C, and the developed toner image is transferred to the recording medium conveyed by the conveyance belt 15. Yes.

  The fixing unit 7 sandwiches the recording medium onto which the toner image has been transferred between a heating roller 17 and a pressure roller 19 (corresponding to an example of a downstream side conveying unit in the present invention), and applies heating and pressure. Thus, the toner image is fixed to the recording medium.

  In addition, a pre-registration sensor 21 is provided near the conveyance path between the supply unit 3 and the image forming unit 5, and near the conveyance path between the image forming unit 5 and the fixing unit 7. A paper discharge sensor 23 is provided. Each of the pre-registration sensor 21 and the paper discharge sensor 23 is a contact type sensor that switches from off to on in accordance with the contact with the recording medium. When the recording medium passes through the place where each sensor is disposed, The presence of the recording medium can be detected.

[Characteristics of image forming apparatus and control for correcting the characteristics]
Next, characteristics of the image forming apparatus 1 and control for correcting the characteristics will be described.

  In the image forming apparatus 1, the supply unit 3 (conveying roller pair 11) and the image forming unit 5 (the image forming mechanism 13 </ b> K and the conveying belt 15) are designed such that the supplying unit 3 has a higher conveying speed. Yes.

  This is to prevent excessive tension from acting on the recording medium even when the recording medium is sandwiched between the supply unit 3 side and the image forming unit 5 side. As described above, when the conveyance speed on the image forming unit 5 side is reduced, the recording medium is conveyed from the supply unit 3 side by a larger amount than the conveyance amount by the image forming unit 5.

  Here, when the recording medium is conveyed from the supply unit 3 side more than the conveyance amount by the image forming unit 5, the conveyance speed in the image forming unit 5 changes due to the flexibility of the recording medium. There is.

  Specifically, when a standard recording medium 25 having relatively high flexibility is used, the recording medium 25 bends considerably between the supply unit 3 and the image forming unit 5. Therefore, with the occurrence of this bending, the difference in the conveyance speed between the supply unit 3 and the image forming unit 5 is absorbed, and the conveyance speed in the image forming unit 5 becomes the speed assumed at the time of design. Hereinafter, the transport speed as designed in the image forming unit 5 is referred to as a reference transport speed.

  On the other hand, when a recording medium 27 (for example, a plastic film such as cardboard or an OHP sheet) having a lower flexibility than the standard recording medium 25 is used, the recording medium between the supply unit 3 and the image forming unit 5 is used. The deflection of the recording medium 27 is not as great as that of the recording medium 25 (see FIG. 1).

  However, even if the recording medium 27 is difficult to bend, the supply unit 3 sends out the recording medium 27. As a result, the recording medium 27 is forced into the image forming unit 5 without being bent. Become.

  Therefore, the conveyance speed of the recording medium 27 in the image forming unit 5 is larger than the reference conveyance speed. That is, since the difference in the conveyance speed between the supply unit 3 and the image forming unit 5 cannot be absorbed by the degree of bending of the recording medium 27, the conveyance speed in the image forming unit 5 increases.

  When the conveyance speed in the image forming unit 5 is increased in this way, when image formation is performed by each of the four sets of image forming mechanisms 13K, 13Y, 13M, and 13C on the assumption that the conveyance speed is the reference conveyance speed, A shift occurs in the image forming position between the four sets of images. In addition, each image is distorted.

  Specifically, when the conveyance speed of the recording medium 27 in the image forming unit 5 is higher than the reference conveyance speed, for example, the recording medium 27 that has passed through the first image forming mechanism 13K is later than the assumed timing. Passes the image forming mechanism 13Y at an early timing.

  Therefore, even if image formation by the image forming mechanism 13Y is started on the premise that the recording medium 27 is conveyed at the reference conveyance speed, the images formed by the image forming mechanisms 13K and 13Y should originally match. A slight deviation occurs in the reference position (origin). The same slight deviation occurs between the images formed by the image forming mechanisms 13Y and 13M, and also occurs between the images formed by the image forming mechanisms 13M and 13C.

  Therefore, the slight deviation as described above is accumulated between the images formed by the image forming mechanisms 13K and 13C located at the farthest positions, and the deviation width is maximized.

  In addition to the above-described displacement between images, when image formation is performed by each of the image forming mechanisms 13K, 13Y, 13M, and 13C on the assumption that the conveyance speed of the recording medium 27 is the reference conveyance speed, Each image is distorted. Specifically, when an image is formed over the same time as the reference transport speed even though the transport speed of the recording medium 27 is somewhat high, the distance from the image formation start position to the end position increases. Each image becomes longer in the sub-scanning direction.

  Therefore, in this image forming apparatus 1, by performing control to change the image formation start timing when the conveyance speed in the image forming unit 5 becomes the reference conveyance speed and when it becomes larger than the reference conveyance speed. , Suppress the shift between images. Further, the distortion of each image is suppressed by performing control for changing the scanning interval in the sub-scanning direction.

  Hereinafter, these controls will be described based on the flowchart of FIG. Note that the processing shown in FIG. 2 is processing corresponding to one recording medium when a print command is given to the image forming apparatus 1.

  When this process is started, the control unit included in the image forming apparatus 1 first determines whether or not to print in the second mode (S101). In the present embodiment, the image forming apparatus 1 is configured such that the operation mode is switched to the first mode or the second mode when the user performs an operation mode switching operation on an operation panel (not shown). The mode switching may be configured so that it can be remotely set from a PC or the like connected to the image forming apparatus 1.

  Among these operation modes, the first mode is a mode corresponding to the case where the standard recording medium 25 is used, and the second mode is a coverage with lower flexibility than the standard recording medium 25. This mode corresponds to the case where the recording medium 27 is used.

  When it is determined in the processing of S101 that printing is not in the second mode (that is, the user has set the first mode) (S101: NO), the standard image formation start timing and the standard scanning interval Then, an image is formed (S103), and the processing shown in FIG.

  Here, the standard image formation start timing is between images formed by the four sets of image forming mechanisms 13K, 13Y, 13M, and 13C when the conveyance speed in the image forming unit 5 is the reference conveyance speed. This is a timing at which no deviation occurs in the image forming position.

  The standard scanning interval means that images formed by the image forming mechanisms 13K, 13Y, 13M, and 13C are not distorted in the sub-scanning direction when the conveyance speed in the image forming unit 5 is the reference conveyance speed. It is a scanning interval. In this embodiment, the standard scanning interval is about 40 μm (in the case of resolution 600 dpi).

  On the other hand, in the process of S101, when it is determined that printing is performed in the second mode (that is, the user has set the second mode) (S101: YES), first, image formation start timing earlier than the standard and An image is formed at a scanning interval shorter than the standard (S105).

  In the present embodiment, in the process of S105, the image formation start timing by the image forming mechanism 13M is advanced by about 20 μm (corresponding to 0.5 lines at a resolution of 600 dpi). In addition, the image formation start timing by the image forming mechanism 13C is advanced by about 40 μm (corresponding to one line at a resolution of 600 dpi). Further, the scanning interval in each of the image forming mechanisms 13K, 13Y, 13M, and 13C is made shorter than the standard scanning interval.

  In the process of S105, the image forming start timing is controlled only for the image forming mechanisms 13M and 13C as described above because the deviation width with respect to the image forming position by the image forming mechanism 13K is larger than that of the image forming mechanism 13Y. This is because the influence on image quality is correspondingly great.

  On the contrary, the image forming mechanism 13Y has a smaller shift width with respect to the image forming position by the image forming mechanism 13K than the image forming mechanisms 13M and 13C, and even if this shift is corrected, the influence on the image quality is small. However, the image formation start timing is not corrected. However, it goes without saying that the image formation start timing may be controlled so that the deviation width with respect to the image forming position by the image forming mechanism 13K is corrected for all of the image forming mechanisms 13Y, 13M, and 13C.

  Note that the control for advancing the image formation start timing is realized by performing a control for advancing the scan start timing by the laser scanner when forming an electrostatic latent image on the photoreceptor provided in each of the image forming mechanisms 13M and 13C. Further, the control for reducing the scanning interval to be shorter than the standard scanning interval is realized by performing control for increasing the scanning speed by the laser scanner.

  The process of S105 as described above is continued while the recording medium 27 passes through the supply unit 3 (S107: NO), and when the recording medium 27 finishes passing through the supply unit 3 (S107: YES), the process proceeds to S109. If the process proceeds to S109, an image is formed at a standard scanning interval (S109), and the process shown in FIG. 2 ends.

  The reason why the process of S105 is switched to the process of S109 is that the conveyance speed in the image forming unit 5 is initially higher than the reference conveyance speed and then becomes the reference conveyance speed. The transport speed in the image forming unit 5 is initially higher than the reference transport speed because the recording medium 27 is sandwiched between the supply unit 3 side and the image forming unit 5 side as described above. This is because the recording medium 27 to be sent out is forcibly pushed into the image forming unit 5.

  On the other hand, the conveyance speed in the image forming unit 5 thereafter becomes the reference conveyance speed when the end of the recording medium 27 is separated from the supply unit 3 side and is conveyed only by the conveyance force acting from the image forming unit 5 side. Because it becomes.

  Therefore, the timing at which the processing at S105 is switched to the processing at S109 by the processing at S107 is the timing at which the end of the recording medium 27 is separated from the supply unit 3 side. In this embodiment, this timing is a timing at which a predetermined time has elapsed after the start edge of the recording medium 27 is detected by the pre-registration sensor 21.

  The predetermined time is determined according to the sheet length (length in the sub-scanning direction) of the recording medium 27 accommodated in the supply unit 3. As for the specific time, the time corresponding to the recording medium 27 of various sizes is measured in advance by an actual machine and stored in a nonvolatile memory provided in the control unit of the image forming apparatus 1. In the process of S107, the time corresponding to the size of the recording medium 27 accommodated in the supply unit 3 is read from the nonvolatile memory and used for the determination.

  In the present embodiment, the pre-registration sensor 21 is on the downstream side of the conveyance path with respect to the conveyance roller pair 11. For this reason, the timing at which the end of the recording medium 27 is separated from the supply unit 3 side is measured by the elapsed time after the start edge of the recording medium 27 is detected by the pre-registration sensor 21. If there is a sensor on the upstream side of the path, the sensor can detect the passage of the end of the recording medium 27 and measure the timing at which the end of the recording medium 27 moves away from the supply unit 3 side.

[Effect of the first embodiment]
According to the image forming apparatus 1 described above, when the operation mode is set to the second mode, the image formation start timing by the image forming mechanisms 13M and 13C is earlier than in the first mode. Accordingly, even if the recording medium 27 with low flexibility is conveyed early, the timing for forming an image on the recording medium 27 is advanced accordingly, so that a plurality of image forming mechanisms 13K, 13Y, 13M, and 13C. It is possible to suppress the deviation of the image forming position due to the above.

  In the image forming apparatus 1, when the operation mode is set to the second mode, the image forming mechanisms 13K, 13Y, 13M, and the like are processed by the process of S105 while the recording medium 27 passes through the supply unit 3. The scanning interval of 13C is shorter than the scanning interval in the first mode. Therefore, distortion of images formed by the image forming mechanisms 13K, 13Y, 13M, and 13C can be suppressed.

Further, in the image forming apparatus 1, when the operation mode is set to the second mode, after the trailing end of the recording medium 27 passes the supply unit 3, each image forming mechanism 13K, 13Y, 13M, The scanning interval of 13C is the same as the scanning interval in the first mode. Therefore, even after the rear end of the recording medium 27 passes through the supply unit 3, distortion of images formed by the image forming mechanisms 13K, 13Y, 13M, and 13C can be suppressed.
(2) Second Embodiment Next, a second embodiment will be described. In the second and subsequent embodiments, although a part of the configuration is different from the first embodiment, there are many common parts. Therefore, in the following description, the differences from the first embodiment are mainly described. Detailed description will be made with respect to the common parts with the same reference numerals as in the first embodiment, and detailed description thereof will be omitted.

[Schematic structure of image forming apparatus]
FIG. 3 is a longitudinal sectional view showing a schematic structure of the image forming apparatus 31.
The image forming apparatus 31 includes a supply unit 3, an image forming unit 5, a fixing unit 7, and the like. These are all the same as those in the first embodiment. Further, as a configuration different from the first embodiment, a front guide 33 and a movable central rib 35 (corresponding to an example of a movable member in the present invention) are provided near the entrance side of the image forming unit 5. .

  The movable central rib 35 is provided so as to be movable up and down in the direction indicated by the double-ended arrows in FIG. 4A. When the movable central rib 35 is lowered, the movable central rib 35 projects downward from the lower surface of the front guide 33, and FIG. As shown in the figure, the recording medium 25 is in contact with the recording medium 25.

  As shown in FIG. 5A and FIG. 5B, a mechanism for moving the movable central rib 35 up and down is not shown. The linear cam 39 is driven by an actuator and slides.

  As the linear cam 39 slides, the gap between the linear cam 39 and the front guide 33 expands (see the upper side of FIG. 5A and FIG. 5B), and the gap decreases. Displacement to a position (see the lower side of FIG. 5A and FIG. 5B). Further, the movable central rib 35 is biased by a spring (not shown) and is always in a state of trying to rotate in the upward direction.

  For this reason, when the linear cam 39 is displaced to a position where the gap is enlarged, the movable central rib 35 is rotated in the upward direction by a force received from a spring (not shown) and is not projected to the lower surface side of the front guide 33. It will be stored. On the other hand, when the linear motion cam 39 is displaced to a position where the gap is reduced, the movable central rib 35 is rotated downward by a force received from the linear motion cam 39 side, and is lower than the lower surface of the front guide 33. Protruding state.

  As described above, when the movable central rib 35 protrudes downward from the lower surface of the front guide 33, the recording medium 25 passing through this position abuts on the movable central rib 35 and moves in the transport direction. The cross-sectional shape orthogonal to the shape is deformed into a downward convex shape (see FIG. 4B).

  When the shape of the recording medium 25 is deformed as described above, the recording medium 25 is less flexible with respect to bending deformation in a direction in which the curvature of the cross-sectional shape parallel to the transport direction is increased. It becomes difficult to deform in the direction. That is, by projecting the movable central rib 35, the flexibility of the recording medium 25 can be reduced.

  With such a configuration, the flexibility of the recording medium 25 is reduced. If the recording medium 25 is too flexible, the recording medium 25 is moved into the image forming unit 5 when the recording medium 25 enters the image forming unit 5. This is because the tip may be bent or a skew may occur. In this respect, if the movable central rib 35 is provided, the flexibility of the recording medium 25 can be reduced, and therefore the recording medium 25 can be smoothly entered into the image forming unit 5.

  However, when the flexibility of the recording medium 25 is lowered, the recording medium 27 with low flexibility is used even when the standard recording medium 25 having relatively high flexibility is used. As in the case, the conveyance speed in the image forming unit 5 is larger than the reference conveyance speed.

  Therefore, in the second embodiment, when the movable central rib 35 is not projected, printing is performed in the first mode described in the first embodiment, and the movable central rib 35 is projected. Is configured to perform printing in the second mode described in the first embodiment.

  Specifically, when the user performs an operation for projecting the movable central rib 35 on an operation panel (not shown) or the like, the operation mode of the image forming apparatus 31 is linked to the second mode. It is comprised so that it may switch to. With this configuration, when the movable central rib 35 is protruded, printing in the second mode is performed. Therefore, as described in the first embodiment, displacement between images and distortion of each image are prevented. Can be suppressed.

  Note that the specific processing executed in the image forming apparatus 31 is exactly the same as the processing described based on the flowchart of FIG. 2 in the first embodiment, and thus the description thereof is omitted here.

[Effects of Second Embodiment]
According to the image forming apparatus 31 described above, the movable central rib 35 can be protruded to reduce the flexibility of the recording medium 25, so that the leading end of the recording medium 25 is introduced into the image forming unit 5. Can be prevented from being bent or skewed.

  In addition, when the flexibility of the recording medium 25 is lowered, the operation mode is switched to the second mode in conjunction therewith. Accordingly, as in the first embodiment, the image formation start timing by the image forming mechanisms 13M and 13C is earlier than that in the first mode, so that the image forming position shifts by the plurality of image forming mechanisms 13K, 13Y, 13M, and 13C. Can be suppressed.

Further, in the image forming apparatus 31, when the operation mode is the second mode, the scanning intervals of the image forming mechanisms 13K, 13Y, 13M, and 13C are controlled by the processing of S105 and S109. Therefore, distortion of images formed by the image forming mechanisms 13K, 13Y, 13M, and 13C can be suppressed.
(3) Third Embodiment Next, a third embodiment will be described.

[Schematic structure of image forming apparatus]
FIG. 6 is a longitudinal sectional view showing a schematic structure of the image forming apparatus 41.
The image forming apparatus 41 includes a supply unit 3, an image forming unit 5, a fixing unit 7, and the like. These are functionally the same as those in the first embodiment.

  However, the image forming apparatus 41 according to the third embodiment has a characteristic that the conveyance speed in the image forming unit 5 varies depending on the degree of bending of the recording medium between the image forming unit 5 and the fixing unit 7. This is different from the first and second embodiments. Hereinafter, characteristics of the image forming apparatus 41 and control for correcting the characteristics will be described.

[Characteristics of image forming apparatus and control for correcting the characteristics]
In this image forming apparatus 41, the image forming unit 5 has a higher conveying speed in the image forming unit 5 (the image forming mechanism 13C and the conveying belt 15) and the fixing unit 7 (the heating roller 17 and the pressure roller 19). Designed to be

  This is to prevent excessive tension from acting on the recording medium even when the recording medium is sandwiched between the image forming unit 5 side and the fixing unit 7 side. In this way, when the conveyance speed on the fixing unit 7 side is designed to be smaller than the conveyance speed on the image forming unit 5 side, the recording medium is larger than the conveyance amount by the fixing unit 7 from the image forming unit 5 side. It will be transported.

  Here, when the recording medium is conveyed from the image forming unit 5 side more than the conveyance amount by the fixing unit 7, the conveyance speed in the image forming unit 5 changes due to the flexibility of the recording medium.

  Specifically, when a standard recording medium 25 having relatively high flexibility is used, the recording medium 25 can be bent correspondingly between the image forming unit 5 and the fixing unit 7. Therefore, with the occurrence of this bending, the difference in the conveyance speed between the image forming unit 5 and the fixing unit 7 is absorbed, and the conveyance speed in the image forming unit 5 becomes the speed assumed at the time of design. Hereinafter, the transport speed as designed in the image forming unit 5 is referred to as a reference transport speed.

  On the other hand, when a recording medium 27 (for example, a plastic film such as a cardboard or an OHP sheet) having a lower flexibility than the standard recording medium 25 is used, the recording medium between the image forming unit 5 and the fixing unit 7 is used. The deflection of the recording medium 27 is not as great as that of the recording medium 25 (see FIG. 6).

  Therefore, the feeding from the image forming unit 5 is hindered, and the conveyance speed of the recording medium 27 in the image forming unit 5 is smaller than the reference conveyance speed. That is, since the difference in the conveyance speed between the image forming unit 5 and the fixing unit 7 cannot be absorbed by the degree of bending of the recording medium 27, the conveyance speed in the image forming unit 5 decreases.

  As described above, when the conveyance speed in the image forming unit 5 is reduced, when the image formation is performed by each of the four sets of image forming mechanisms 13K, 13Y, 13M, and 13C on the assumption that the conveyance speed is the reference conveyance speed, A shift occurs in the image forming position between the four sets of images. In addition, each image is distorted.

  Specifically, when the conveyance speed of the recording medium 27 in the image forming unit 5 is lower than the reference conveyance speed, for example, the recording medium 27 that has passed through the first image forming mechanism 13K is later than the assumed timing. It passes through the image forming mechanism 13Y at a late timing.

  Therefore, even if image formation by the image forming mechanism 13Y is started on the premise that the recording medium 27 is conveyed at the reference conveyance speed, the images formed by the image forming mechanisms 13K and 13Y should originally match. A slight deviation occurs in the reference position (origin). The same slight deviation occurs between the images formed by the image forming mechanisms 13Y and 13M, and also occurs between the images formed by the image forming mechanisms 13M and 13C.

  Therefore, the slight deviation as described above is accumulated between the images formed by the image forming mechanisms 13K and 13C located at the farthest positions, and the deviation width is maximized.

  In addition to the above-described displacement between images, when image formation is performed by each of the image forming mechanisms 13K, 13Y, 13M, and 13C on the assumption that the conveyance speed of the recording medium 27 is the reference conveyance speed, Each image is distorted. Specifically, when an image is formed over the same time as the reference transport speed even though the transport speed of the recording medium 27 is somewhat slow, the distance from the image formation start position to the end position decreases. Each image becomes shorter in the sub-scanning direction.

  Therefore, in this image forming apparatus 41, by performing control to change the image formation start timing when the conveyance speed in the image forming unit 5 becomes the reference conveyance speed and when it becomes larger than the reference conveyance speed. , Suppress the shift between images.

  However, in the third embodiment, control for suppressing distortion of each image is not performed. If the control for suppressing the distortion of each image is not performed, the distortion of the image is of course not corrected, but the shift between the images caused by the distortion of the image is suppressed, so that the image quality is correspondingly improved accordingly. be able to.

  Hereinafter, the control in the third embodiment will be described based on the flowchart of FIG. Note that the processing shown in FIG. 7 is processing corresponding to one recording medium when a print command is given to the image forming apparatus 41.

  When this process is started, the control unit included in the image forming apparatus 41 first determines whether or not to print in the second mode (S201). The first mode is a mode for using a standard recording medium 25, and the second mode is a mode for using a recording medium 27 that is less flexible than the standard recording medium 25. This is the same as in the first embodiment. The configuration for switching between these operation modes may be the same as that in the first embodiment.

  When it is determined in the process of S201 that printing is not in the second mode (that is, the user has set the first mode) (S201: NO), the standard image formation start timing and the standard scan interval Then, an image is formed (S203), and the processing shown in FIG.

  Here, the standard image formation start timing is between images formed by the four sets of image forming mechanisms 13K, 13Y, 13M, and 13C when the conveyance speed in the image forming unit 5 is the reference conveyance speed. This is a timing at which no deviation occurs in the image forming position.

  The standard scanning interval means that images formed by the image forming mechanisms 13K, 13Y, 13M, and 13C are not distorted in the sub-scanning direction when the conveyance speed in the image forming unit 5 is the reference conveyance speed. It is a scanning interval. In this embodiment, the standard scanning interval is about 40 μm (in the case of resolution 600 dpi).

  On the other hand, if it is determined in the process of S201 that printing is performed in the second mode (that is, the user has set the second mode) (S201: YES), the image formation start timing later than the standard and the standard Images are formed at scanning intervals (S205). Note that when the process of S205 is finished, the process shown in FIG.

  In the present embodiment, in the processing of S205, the image formation start timing by the image forming mechanism 13M is delayed by about 20 μm (corresponding to 0.5 lines at a resolution of 600 dpi). In addition, the image formation start timing by the image forming mechanism 13C is delayed by about 40 μm (corresponding to one line at a resolution of 600 dpi).

  In the process of S205, the reason for controlling the image formation start timing for only the image forming mechanisms 13M and 13C as described above is that the deviation width with respect to the image forming position by the image forming mechanism 13K is an image as in the first embodiment. This is because it is larger than the forming mechanism 13Y. However, as in the first embodiment, the image formation start timing may be corrected for the image forming mechanism 13Y.

  Note that the control for delaying the image formation start timing is realized by performing control for delaying the scan start timing by the laser scanner when forming an electrostatic latent image on the photoconductor provided in each of the image forming mechanisms 13M and 13C.

[Effect of the third embodiment]
According to the image forming apparatus 41 described above, when the operation mode is set to the second mode, the image formation start timing by the image forming mechanisms 13M and 13C is delayed as compared with the case of the first mode. Accordingly, even when the recording medium 27 with low flexibility is conveyed late, the timing for forming an image on the recording medium 27 is delayed accordingly, so that the plurality of image forming mechanisms 13K, 13Y, 13M, The shift of the image forming position due to 13C can be suppressed.

  In the following, further details regarding the suppression of the shift between images in the third embodiment will be described. In the third embodiment, when the recording medium 27 with low flexibility is used and the control in the second mode is not performed, the recording medium 27 is the reference until the recording medium 27 reaches the fixing unit 7. It is transported at the transport speed. Therefore, with respect to images formed by the plurality of image forming mechanisms 13K, 13Y, 13M, and 13C, no shift occurs between the images, and no distortion of each image occurs.

  Accordingly, regarding the image formed on the recording medium 27 before the recording medium 27 reaches the fixing unit 7 out of the entire image formed on the recording medium 27, there is a deviation between the images as described above. It does not occur and distortion of each image does not occur.

  On the other hand, after the time when the recording medium 27 reaches the fixing unit 7, the recording medium 27 is transported at a speed lower than the reference transport speed. Therefore, distortion occurs in each image regarding images formed by the plurality of image forming mechanisms 13K, 13Y, 13M, and 13C.

  Further, the length in the sub-scanning direction of the portion where the distortion occurs (a portion of the image) varies depending on the relationship between the positions of the plurality of image forming mechanisms 13K, 13Y, 13M, and 13C and the transport direction. Specifically, the image formed by the image forming mechanism 13K has the shortest length of the distortion portion, and the image formed by the image forming mechanism 13C has the longest length of the distortion portion. The difference in the length of the portion where the distortion occurs appears as a shift between images on the end side of the recording medium 27.

  That is, regarding the image formed on the recording medium 27 after the recording medium 27 reaches the fixing unit 7 among the entire images formed on the recording medium 27, each image is distorted. Due to the fact that the length of the portion where the image is generated varies from image to image, a shift occurs between the images.

  Under such a background, in the control in the second mode, the distortion of each image itself is not corrected, the image formation start timing by the image forming mechanisms 13M and 13C is controlled, and the image by the image forming mechanisms 13M and 13C is controlled. Only the formation position is shifted.

  When such control is performed, the distortion of each image itself is not corrected, but the shift between the images that has occurred on the end side in the entire image formed on the recording medium 27 is reduced. Of course, since the image formation start position is shifted without correcting the distortion of each image itself, the image at the start end of the recording medium 27 (the recording medium 27 is not transferred to the fixing unit 7) that originally had no deviation between the images. Even in an image formed on the recording medium 27 before reaching, a certain amount of deviation occurs.

However, when the control in the second mode is not performed, a large shift occurs only at the end side of the recording medium 27, whereas the control of the recording medium 27 is performed when the control in the second mode is performed. A small deviation occurs on both the start and end sides. Therefore, the deviation width visible to the user is reduced, and the image quality is improved.
(4) Fourth Embodiment Next, a fourth embodiment will be described. In the fourth embodiment, in the image forming apparatus 41 having exactly the same characteristics as the third embodiment, control different from the third embodiment is performed as control for correcting this characteristic. Therefore, in the following description, only control different from the third embodiment will be described in detail.

[Control for correcting characteristics of image forming apparatus]
The process shown in FIG. 8 is a process executed corresponding to one recording medium when a print command is given to the image forming apparatus 41.

  When this process is started, the control unit included in the image forming apparatus 41 first determines whether to print in the second mode (S301). The first mode is a mode for using a standard recording medium 25, and the second mode is a mode for using a recording medium 27 that is less flexible than the standard recording medium 25. This is the same as in the first embodiment. The configuration for switching between these operation modes may be the same as that in the first embodiment.

  If it is determined in the processing of S301 that printing is not in the second mode (that is, the user has set the first mode) (S301: NO), the standard image formation start timing and the standard scanning interval Then, an image is formed (S303), and the processing shown in FIG.

  Here, the standard image formation start timing is between images formed by the four sets of image forming mechanisms 13K, 13Y, 13M, and 13C when the conveyance speed in the image forming unit 5 is the reference conveyance speed. This is a timing at which no deviation occurs in the image forming position.

  The standard scanning interval means that images formed by the image forming mechanisms 13K, 13Y, 13M, and 13C are not distorted in the sub-scanning direction when the conveyance speed in the image forming unit 5 is the reference conveyance speed. It is a scanning interval. In this embodiment, the standard scanning interval is about 40 μm (in the case of resolution 600 dpi).

  On the other hand, when it is determined in step S301 that printing is performed in the second mode (that is, the user has set the second mode) (S301: YES), the standard image formation start timing and An image is formed at a standard scanning interval (S305).

  The process of S305 is continued until the recording medium 27 reaches the fixing unit 7 (S307: NO), and when the recording medium 27 reaches the fixing unit 7 (S307: YES), the process proceeds to S309. .

  The reason why the process of S305 is switched to the process of S309 is that the conveyance speed in the image forming unit 5 is initially the reference conveyance speed and then becomes slower than the reference conveyance speed. As described in the third embodiment, the conveyance speed in the image forming unit 5 is reduced in the middle. As described in the third embodiment, the recording medium 27 is sandwiched between the image forming unit 5 side and the fixing unit 7 side. This is because the delivery from the machine is hindered.

  Therefore, the timing at which the processing at S305 is switched to the processing at S309 by the processing at S307 is the timing at which the starting end of the recording medium 27 reaches the fixing unit 7 side. In this embodiment, this timing is a timing at which a predetermined time has elapsed after the start edge of the recording medium 27 is detected by the pre-registration sensor 21 or the paper discharge sensor 23.

  If the process proceeds to S309, an image is formed at a scanning interval longer than the standard (S309). In the processing of S309, the scanning interval in each of the image forming mechanisms 13K, 13Y, 13M, and 13C is made longer than the standard scanning interval. Note that when the process of S309 is completed, the process illustrated in FIG.

[Effect of Fourth Embodiment]
According to the image forming apparatus 41 described above, if the operation mode is set to the second mode, the image forming mechanisms 13K, 13Y, 13M, and 13C are processed by the process of S305 until the recording medium 27 reaches the fixing unit 7. This scanning interval is the same as the scanning interval in the first mode. Further, after the recording medium 27 reaches the fixing unit 7, the scanning interval of each of the image forming mechanisms 13K, 13Y, 13M, and 13C is made shorter than the scanning interval in the first mode by the process of S309. .

Accordingly, with respect to images formed by the image forming mechanisms 13K, 13Y, 13M, and 13C, it is possible to suppress displacement between images and distortion of each image.
(5) Modifications The embodiment of the present invention has been described above. However, the present invention is not limited to the specific embodiment described above, and can be implemented in various other forms.

  For example, in the above-described embodiment, the conveyance speed in the image forming unit 5 is affected by the supply unit 3 (first and second embodiments), and is affected by the fixing unit 7 (third and fourth embodiments). ) Have been described as separate embodiments, but these may be combined.

  For example, the conveyance speed in the image forming unit 5 is initially increased due to the influence of the supply unit 3, and then reaches the reference conveyance speed until the recording medium is separated from the supply unit 3 until reaching the fixing unit 7. An apparatus that is slower than the reference transport speed due to the influence of 7 can be considered. In this case, the configuration of the first embodiment and the configuration of any one of the third and fourth embodiments may be employed in combination.

  In the above-described embodiment, the configuration in which the operation mode is switched is a configuration in which the user switches the operation mode. However, the operation mode in either the first mode or the second mode corresponding to the type of each recording medium in advance. It may be configured to switch the operation mode automatically based on the information of the recording medium to be used when the user performs an operation for starting printing in advance.

1 is a longitudinal sectional view illustrating a schematic structure of an image forming apparatus according to a first embodiment. 6 is a flowchart illustrating processing executed by the image forming apparatus according to the first embodiment. FIG. 6 is a longitudinal sectional view illustrating a schematic structure of an image forming apparatus according to a second embodiment. FIG. 9 is an enlarged view of the vicinity of a movable central rib provided in the image forming apparatus according to the second embodiment. FIG. 9 is an operation explanatory diagram of a movable central rib included in the image forming apparatus of the second embodiment. FIG. 6 is a longitudinal sectional view showing a schematic structure of an image forming apparatus according to third and fourth embodiments. 10 is a flowchart illustrating processing executed by the image forming apparatus according to the third embodiment. 10 is a flowchart illustrating processing executed by an image forming apparatus according to a fourth embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,31,41 ... Image forming apparatus, 3 ... Supply part, 5 ... Image forming part, 7 ... Fixing part, 11 ... Pair of conveyance rollers, 13C, 13K, 13M, 13Y ..Image forming mechanism 15... Conveying belt 17. Heating roller 19. Pressure roller 21. Pre-registration sensor 23. Recording medium, 33 ... front guide, 35 ... movable central rib, 37 ... rotating shaft, 39 ... linear motion cam.

Claims (7)

A plurality of image forming means each forming an image on a recording medium and conveying the recording medium at a reference conveying speed;
An upstream conveying means for conveying the recording medium to the image forming means side at an upstream conveying speed greater than the reference conveying speed;
A first mode for forming an image on a standard recording medium, and a second mode for forming an image on a recording medium that is less flexible than the standard recording medium A control unit that controls the plurality of image forming units in correspondence with any one of a plurality of operation modes including at least:
When the control unit performs the control in the second mode, a time period from when one image forming unit starts forming the image to when the next image forming unit starts forming the image is determined. The image forming apparatus is controlled so as to be shorter than the control in the first mode. A movable member that, when displaced to a predetermined position, deforms the recording medium that enters the image forming unit into a shape in which a cross-sectional shape perpendicular to the conveyance direction of the recording medium is convex;
The image forming apparatus according to claim 1, wherein the control unit performs the control in the second mode when the movable member is displaced to the predetermined position. When the control unit performs the control in the second mode, the scanning interval of each of the image forming units is set in the first mode while the recording medium passes through the upstream transport unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is shorter than the scanning interval. When the control unit performs the control in the second mode, the scanning interval of each image forming unit is set in the first mode after the trailing edge of the recording medium passes through the upstream transport unit. The image forming apparatus according to claim 3, wherein the scanning interval is the same. A plurality of image forming means each forming an image on a recording medium and conveying the recording medium at a reference conveying speed;
A downstream transport unit that transports the recording medium transported from the image forming unit side at a downstream transport speed smaller than the reference transport speed;
A first mode for forming an image on a standard recording medium, and a second mode for forming an image on a recording medium that is less flexible than the standard recording medium And a control unit that controls the plurality of image forming units in correspondence with any one of a plurality of operation modes including:
When the control unit performs the control in the second mode, a time period from when one image forming unit starts forming the image to when the next image forming unit starts forming the image is determined. The image forming apparatus is controlled so as to be longer than when the control is performed in the first mode. A plurality of image forming means each forming an image on a recording medium and conveying the recording medium at a reference conveying speed;
A downstream transport unit that transports the recording medium transported from the image forming unit side at a downstream transport speed smaller than the reference transport speed;
A first mode for forming an image on a standard recording medium, and a second mode for forming an image on a recording medium that is less flexible than the standard recording medium And a control unit that controls the plurality of image forming units in correspondence with any one of a plurality of operation modes including:
When the control unit performs the control in the second mode, the scanning interval of each of the image forming units is set in the first mode while the recording medium passes through the downstream transport unit. An image forming apparatus characterized in that it is longer than the scanning interval. The image forming apparatus according to claim 1, further comprising: an operation mode setting unit that allows a user to arbitrarily set the first mode or the second mode. apparatus.

Images