JP5404323B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus typified by a copying machine, a printer, a printing machine, and the like, and more particularly, to an image forming apparatus that performs skew correction using one side of a transfer material to be conveyed as a reference side.

  When a transfer material such as paper is transported in an image forming apparatus, the skew or misalignment of the transfer material that occurs during transport is caused by poor delivery to the transport jam or the downstream transport roller, or printing on the surface of the transfer material. If it is performed, problems such as a decrease in printing accuracy are caused. For this reason, the conventional image forming apparatus is provided with some type of skew feeding correcting means. Generally, by providing the skew feeding correcting means immediately before the image is transferred onto the surface of the transfer material, the position of the transfer material and the image is determined. Matching is performed with higher accuracy. Specifically, the registration device 65 provided immediately before the secondary transfer unit in the image forming apparatus 60 shown in FIG. 1 corresponds to this.

  There are several types of registration apparatuses, and representative ones include an oblique registration method, an active registration method, and a shutter registration method.

  The skew feeding registration type apparatus is configured to abut a reference feeding roller pair disposed at an angle with respect to a transfer material conveyance direction and a reference side of the transfer material conveyed by the skew feeding roller pair. An abutting reference member is provided. The reference side in the skew correction is a side in the transport direction (side side). Also, in the active registration type apparatus and the shutter registration type apparatus, the reference side in the skew correction is the side in the width direction (top side). Therefore, high accuracy is required to perform skew correction using the reference side, and in particular, the inclination of the reference side is an important factor because it greatly affects the margin when an image is formed on a transfer material. . In order to improve the accuracy of the skew feeding correction, as a conventional image forming apparatus, for example, an image forming apparatus using the skew feeding registration method, an apparatus in which the angle of the abutting reference member is variable is known. This conventional image forming apparatus attempts to minimize the relative inclination relationship between the transfer material and the image by adjusting the angle of the abutting reference member (see, for example, Patent Documents 1 and 2).

JP 2003-63695 A JP 2003-66661 A

  However, the factors that actually affect the relative inclination relationship between the transfer material and the image include not only the accuracy of parallelism and perpendicularity of the abutting reference member but also the cutting accuracy of the transfer material itself. In the registration method using one side of the transfer material as a reference side, it is assumed that the transfer material is cut at a right angle. However, in reality, there are many transfer materials with low squareness accuracy. This is because, in addition to the accuracy of the cutting machine, the fiber orientation in the transfer material varies, so that the expansion and contraction due to changes in temperature and humidity are not uniform.

  FIG. 5 is a diagram illustrating an example of a result of transferring an image to a transfer material having a bad perpendicularity. In the figure, it is assumed that the transport direction is the arrow F direction, and the lower side is the reference side for skew correction, that is, the side that is abutted against the abutting reference member. At this time, in the transfer material in which the tip side is at an angle α ° (> 90 °) with respect to the reference side as in the illustrated example, the tip margins on the upper side and the lower side in the width direction are not uniform. In particular, when the adjustment of the inclination of the abutting reference member is performed with a transfer material having a good squareness as in the conventional image forming apparatus, all the cutting accuracy is not uniform in the width direction of the leading edge margin. Since it appears, it is conspicuous as a poor image quality.

  In addition, the problem of the perpendicularity of the transfer material may not be sufficiently solved even if the angle of the abutting reference member is once adjusted because the individual variations of the transfer material are large. Even if the angle adjustment of the abutting reference member is performed every time the type of transfer material or the use environment (temperature and humidity) of the image forming apparatus changes, until the optimum angle is determined in the conventional image forming apparatus described above. It is necessary to repeat trial and error by the test print. Therefore, it becomes a work which requires time and effort depending on circumstances. Furthermore, when printing on both sides of the transfer material, even the trial and error operation is substantially difficult.

  The present invention has been made paying attention to this point, and provides an image forming apparatus capable of preventing the right and wrong of the transfer material from being unevenly concentrated on the non-reference side margins. For the purpose.

  It is another object of the present invention to provide an image forming apparatus capable of realizing registration control that takes into consideration the influence of variations in the cutting accuracy of a transfer material, including during double-sided printing.

  In order to achieve the above object, an image forming apparatus according to claim 1, wherein a printing unit that prints an image on a conveyed rectangular transfer material, and one side of the transfer material as a reference side, at least the reference Detection means for detecting a non-reference edge which is another side adjacent to the reference edge, and a first calculation for calculating an angle α ° formed by the non-reference edge and the reference edge detected by the detection means And an angle at which the reference side is rotated in order to correct the shape of a rectangular image margin having the non-reference side as one side, which is assumed to occur when | 90 ° −α ° | ≠ 0. A second calculating unit that calculates an angle β ° satisfying 0 <β ° <| 90 ° −α ° |, and the reference side is the angle β ° calculated by the second calculating unit. The front of the image so that the shape of the image margin rotates in a direction closer to a square. And a correction means for correcting the skew of the transfer material.

  According to the present invention, at least two sides of the transfer material, the reference side and the non-reference side, are detected, so even if the transfer material is skewed during conveyance, the reference side and the non-reference side are formed. The angle α ° can be calculated. Further, an angle β ° that is an angle for rotating the reference side and satisfies 0 <β ° <| 90 ° −α ° | is calculated, and the shape of the image margin is more the same for the reference side by the angle β °. Since the skew correction of the transfer material is performed so that it rotates in the direction approaching the shape, even if the cutting accuracy of the transfer material, specifically, the perpendicularity is bad, it occurs on the non-reference side of the skew correction It is possible to make the non-uniformity of the image margin to be conspicuous.

  In addition, if it is possible to select whether or not to perform skew correction, it is possible to selectively obtain the effect of skew correction only for printed matter in which the non-uniformity of the image margin causes a fatal quality defect. It becomes.

1 is a diagram showing an outline of an internal structure of an image forming apparatus according to a first embodiment of the present invention. It is a top view of the conveyance part containing the registration apparatus in FIG. It is a figure which shows an example of the structure which detects the external shape of a transfer material with an area sensor. It is a figure which shows an example of the structure which detects the external shape of a transfer material with a line sensor. It is a figure which shows an example of the nonuniform margin produced when an image is printed on the transfer material with a bad perpendicularity. FIG. 6 is a diagram illustrating an example of a result of correcting the non-uniform margin of FIG. 5. FIG. 2 is a block diagram showing a system configuration necessary for realizing a skew correction method for a transfer material. It is a flowchart which shows the procedure of the control processing which CPU in FIG. 7 performs. FIG. 6 is a top view of a conveyance unit including a registration device included in an image forming apparatus according to a second embodiment of the present invention. It is a figure which shows another example of the structure which detects the external shape of a transfer material with an area sensor. It is a figure which shows an example of the nonuniform margin produced when an image is printed on the transfer material with a bad perpendicularity. It is a figure which shows an example of the result of having corrected the nonuniform margin of FIG. FIG. 10 is a top view of a conveyance unit including a registration device included in an image forming apparatus according to a third embodiment of the present invention.

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

(First embodiment)
FIG. 1 is a diagram showing an outline of the internal structure of the image forming apparatus according to the first embodiment of the present invention. In this embodiment, an electrophotographic color image forming apparatus is employed. In the figure, an image forming apparatus 60 is a so-called intermediate transfer tandem type image forming apparatus in which four color image forming portions are arranged side by side on an intermediate transfer belt.

<Transfer material transfer process>
In FIG. 1, the transfer material S is stacked and stored on the bottom plate 62 in the transfer material storage 61, and is fed by the paper feeding unit 63 at the timing of image formation. The transfer material S is a rectangular copy paper having a predetermined size (for example, A4 size). In addition, as the paper feed unit 63, either a method using frictional separation by a paper feed roller or the like, or a method using separation / adsorption by air can be employed. In the present embodiment, the latter is used.

  The transfer material S sent out by the paper supply unit 63 passes through a transport path 64 a included in the transport unit 64 and is transported to the registration device 65. The transfer material S is subjected to skew correction and timing correction by the registration device 65 and then sent to the secondary transfer unit. The secondary transfer portion is a toner image transfer nip portion to the transfer material S, which is constituted by an opposing secondary transfer inner roller 603 and secondary transfer outer roller 66, and has a predetermined pressure and an electrostatic load bias. As a result, the toner image is adsorbed on the transfer material S.

<Image creation process>
The image forming unit 613 mainly includes a photoconductor 608, an exposure device 611, a developing device 610, a primary transfer device 607, a photoconductor cleaner 609, and the like. An exposure device 611 is driven on the basis of image information on a photoreceptor 608 whose surface is uniformly charged in advance by the charging device and rotates in the direction of arrow m in the figure, and a latent image is appropriately passed through a reflection mirror 612 and the like. Is formed. The electrostatic latent image formed on the photoconductor 608 is visualized as a toner image on the photoconductor 608 through toner development by the developing device 610. Thereafter, an electrostatic load bias is applied by the primary transfer device 607, and the toner image is transferred onto the intermediate transfer belt 606. Thereafter, the untransferred toner remaining without being transferred onto the photoreceptor 608 is collected by the photoreceptor cleaner 609.

  In the illustrated example, the image forming unit 613 includes four sets of yellow (Y), magenta (M), cyan (C), and black (Bk).

  The intermediate transfer belt 606 is stretched by rollers such as a driving roller 604, a tension roller 605, and a secondary transfer inner roller 603, and is driven to rotate in the direction of arrow n in the drawing. The toner images are transferred onto the intermediate transfer belt 606 by the Y, M, C, and Bk image forming units 613 to form a full-color toner image and conveyed to the secondary transfer unit.

<Process after secondary transfer>
A full-color toner image is transferred onto the transfer material S at the secondary transfer portion, and then the transfer material S is transported to the fixing device 68 by the pre-fixing transport portion 67. The fixing device 68 melts and fixes the toner image on the transfer material S by applying a predetermined pressing force by an opposing roller or belt or the like and generally a heating effect by a heat source such as a heater. The transfer material S on which the image is fixed in this way is discharged as it is onto the paper discharge tray 600 by the branch conveyance device 69 or is conveyed to the reverse conveyance device 601 when double-sided image formation is required. When double-sided image formation is required, the transfer material S sent to the reverse conveyance device 601 is conveyed to the double-sided conveyance device 602 after the front and rear ends are switched by a switchback operation. After that, the transfer unit 64 joins from the refeed path 64b of the transport unit 64 at the same timing as the transfer material of the subsequent job transported from the paper feeder 61, and is similarly sent to the secondary transfer unit. Note that the image forming process on the back surface (second surface) is the same as the image forming process on the front surface (first surface) described above, and a description thereof will be omitted.

  Here, as described above, the image forming apparatus 60 uses the switchback method to invert the transfer material S. However, since the leading edge and the trailing edge of the transfer material S are switched at the time of switchback, in this embodiment, a side registration whose position does not change between the front side and the back side can be used as a reference side for skew correction. The method is adopted.

<Slope feeding registration method>
FIG. 2 is a top view of the conveyance unit including the registration device 65. In the same figure, the conveyance direction is the direction of arrow F, and it is divided from the upstream side into a pre-registration conveyance unit, a skew feeding registration unit, and a slide unit. In the illustrated example, a belt conveyance system is used as the pre-registration conveyance unit.

  The transfer material S is carried on a conveying belt 4 stretched around the belt driving roller 1 and the belt driven roller 3 and conveyed in the direction of arrow F by the belt driving motor 5. The transfer material S is held by a suction force by a suction fan 6 provided on the back side of the conveyance belt 4. The pre-registration conveyance unit may be configured using a general conveyance roller pair. However, in the present embodiment, an area sensor in which elements are two-dimensionally arranged is used as means for detecting the perpendicularity of the transfer material S, and the pre-registration conveyance unit can be imaged in a relatively wide area from above. The conveyor belt system that can eliminate the need for the conveyor guide is used.

  The skew feeding registration portion is mainly configured by a movable guide 8, a pair of skew feeding rollers 9a to 9c and a front movable unit in which the abutting reference member 10 is integrated, and a fixed guide 11. In the image forming apparatus 60 according to the present embodiment, the image forming and conveying reference is a center reference determined at the center in the width direction. The front movable unit is configured to be movable in the width direction by the slide drive motor 60d to an optimum standby position corresponding to the size of the transfer material S to be conveyed. Here, the optimum standby position means a position obtained by adding an abutment distance D to the end position Ps in the width direction of the image (or transfer material S) defined by the center reference. This is an offset measure for reliably transferring the transfer material S without colliding with the inlet side end of the abutting reference member 10 because the transfer material S conveyed on the center reference varies in the width direction during conveyance. is there. Therefore, the transfer material S whose skew has been corrected along the abutting reference member 10 is in a state of being shifted by the distance D by abutting in the width direction with respect to the image position. Further, the abutting reference member 10 receives a moment due to the tensile force of the biasing member 12 with respect to the rotation center Rc in the clockwise direction, and is positioned by being biased by the cam surface of the angle adjusting cam 13. Is decided. The phase of the cam surface of the angle adjustment cam 13 is controlled by the angle adjustment motor 14.

  The pair of inclined feeding rollers 9a to 9c are arranged to be inclined at a predetermined angle with respect to the transport direction F so as to generate a transport force toward the abutting reference member 10. Here, when the skew feeding by the skew feeding roller pairs 9a to 9c is started, it is necessary to consider that the upstream pre-registration conveyance unit does not inhibit the skew feeding. As shown in FIG. 2, in the present embodiment, the suction shutter 16 is closed using the detection signal of the oblique feed sensor 15 as a trigger. As a result, when the oblique feeding by the most upstream oblique feeding roller pair 9a is started, the suction effect by the suction fan 6 is blocked, and the binding force of the transfer material S can be reduced.

  The slide part is mainly composed of a conveyance guide 17, a registration roller 7, a registration drive motor 18, a slide motor 150, a pre-registration sensor 19, and a post-registration sensor 100. The registration roller 7 is supported and driven so that it can slide in the width direction. The registration roller 7 sandwiches the transfer material S by the slide motor 150 in order to align the position of the transfer material S offset by the distance D in the width direction with the image position on the intermediate transfer belt 606 (see FIG. 1). Slide in the width direction while transporting. When performing this slide movement, it is necessary to release at least the nip of the upstream feeding roller pairs 9a to 9c. The release timing of the nip is triggered by a transfer signal S passing signal from the pre-registration sensor 19. As controlled. On the other hand, the passage signal of the transfer material S obtained by the post-registration sensor 100 is used as a trigger for adjusting the arrival timing of the downstream secondary transfer outer roller 66 (see FIG. 1). When the secondary transfer outer roller 66 starts to convey the transfer material S, the registration roller 7 releases the nip and slides back to the standby position in the width direction again.

<Squareness detection unit>
As described above, in this embodiment, means for detecting the perpendicularity of the transfer material S conveyed in the pre-registration conveyance unit is provided. As a specific detection means, for example, an area sensor 50 typified by a complementary metal oxide semiconductor (CMOS) sensor is used. As shown in FIG. 3, the area sensor 50 is arranged so that the transfer material S carried on the transport belt 4 can be imaged from above. Specifically, the pre-registration conveyance unit is irradiated by the light source 41, and the reflected light is appropriately imaged on the element of the area sensor 50 by the imaging lens 51. Thereby, a relatively wide range (for example, the detection area A1 in FIG. 2) is imaged, and the outer shape of the transfer material S is captured. If the area sensor 50 is used as a perpendicularity detecting means in this way, two adjacent sides of the transfer material S can be detected simultaneously, so that the angle (squareness) formed by the two sides can be accurately and easily determined. Furthermore, it is possible to cope with various sizes of the transfer material S whose outer shape should be captured by one detection means. Further, there is an advantage that even if the transfer material S is conveyed in a skewed state, it can be detected without any problem.

  As the detection means, a line sensor in which elements are arranged one-dimensionally as shown in FIG. 4 can be used. In this case, in order to detect at least two sides of the reference side and the non-reference side in parallel, it is necessary to arrange two line sensors 110a and 110b in the width direction and two line sensors 111a and 111b in the transport direction. The pre-registration conveyance unit may be a general conveyance roller pair 112 and a conveyance guide 113 (for convenience of explanation, the upper guide is omitted in FIG. 4). However, since the interval between the two line sensors in the width direction and the conveyance direction must be set according to the transfer material of the minimum size, conversely, when detecting the transfer material of the maximum size, it is compared with the length of the side. The line interval is narrow, which causes a decrease in the S / N of the detected inclination. In order to avoid this, either one of the line sensors (for example, the line sensors 110b and 111b) is configured to be movable in the width direction and the conveyance direction, or the lines can be accommodated to a transfer material of a typical size. This will increase the number of sensors. As a result, a detection network close to the area sensor 50 as described in FIGS. 2 and 3 is configured.

<Target angle of reference side>
The correction amount β ° (angle β °) is calculated from the angle α ° between the reference side and the non-reference side detected by the detection means (in this embodiment, the area sensor 50), and the target angle of the reference side is corrected. And the method of determining will be described. Originally, as shown in FIG. 2, the abutting reference member 10 in the oblique registration method is positioned on a reference line Sx perpendicular to the width direction reference line Sy which is also a reference at the time of image formation.

  For example, when a transfer material having a leading edge (non-reference edge) of an angle α ° (> 90 °) with respect to the reference edge as shown in FIG. 5 is conveyed, both ends on the reference edge side are used in the oblique registration method. The image margin lengths Bc and Bd in FIG. Here, the image margin means a region between a region where an image on the transfer material is to be transferred and each side of the transfer material. However, the non-reference side is inclined by (α−90) ° with respect to the width direction. Accordingly, there is a difference between the lengths of the image margins Ba and Bb at both ends on the non-reference side side due to poor cutting accuracy. That is, the amount of the image margin on the near side and the amount of the image margin on the back side in the width direction are different. Such a difference in the amount of image margin is visually conspicuous in the case of a printed material such as a large poster, which causes a problem as poor quality. Therefore, in the present embodiment, the difference in the amount of image margin due to the cutting accuracy of the transfer material is dispersed so as not to be concentrated on one side. Then, the correction amount β ° for the most effective dispersion is obtained as follows.

  As shown in FIG. 5, when the length of the long side of the transfer material S is L and the length of the short side is W, the margin amount difference generated at the leading end side is

It becomes. Now, a reference line Sx ′ obtained by rotating the reference line Sx shown in FIG. 2 by the correction amount β ° in the clockwise direction with respect to the rotation center Rc is determined, and one of the margin amount differences Ba−Bb is shown in FIG. Consider that the part is divided into the margin amount difference on the reference side side. At this time, the most visually conspicuous dispersion method is a method of equalizing the margin amount difference generated at the ends of two sides having different lengths. That is, in FIG.

It is. Therefore,

A correction amount β ° that satisfies the above is determined, and a new reference line Sx ′ that defines this as a target angle of the reference side is determined. Note that equation (1) is an equation described for α> 90 °. On the other hand, when α <90 °, the same idea as when α> 90 °,

And a new reference line Sx ′ having the target angle of the reference side as a target angle may be determined. Here, the position of the rotation center Rc is not limited to that shown in FIG. However, it is considered desirable to provide the rotation center Rc at the end portion on the registration roller 7 side because the margin amounts Bb and Bc can be dispersed without greatly changing.

  In this way, by detecting the angle α ° formed between the reference side and the non-reference side of the transfer material, it is possible to determine the reference line Sx ′ that makes the margin amount difference visually inconspicuous. Further, if an area sensor is used as the detecting means for the angle α °, the angle α ° can be directly detected. Therefore, the transfer material S has the detection of the angle α ° and the determination of the reference line Sx ′ during the conveyance. It is also possible to correct the influence of the variation factor.

<Control action>
FIG. 7 is a block diagram showing a system configuration necessary to realize the above-described correction method for the transfer material S. As shown in the figure, the image forming apparatus 60 includes a CPU 60a, a detection unit 60b, a correction target angle adjustment unit 60c, a slide drive motor 60d, and a memory 60e. The CPU (arithmetic control unit) 60a detects the reference side and the non-reference side of the transfer material S from the detection unit 60b typified by an area sensor, for example. Then, the angle α °, the correction amount β °, the correction direction thereof, and the like are calculated, and the control target value adjustment unit 60c that adjusts the angle of the reference line Sx ′ that is the correction target is supplied with a control value corresponding to the correction amount β °. Issue a command. Further, the CPU 60a stores various calculated values in the memory 60e as necessary.

  FIG. 8 is a flowchart showing a procedure of control processing executed by the CPU 60a. As shown in the figure, first, the CPU 60a detects the reference side and the non-reference side of the transfer material S via the detection unit 60b (step S1). Next, the CPU 60a calculates an angle α ° formed from the detected two sides (step S2), and determines whether α ≠ 90 ° (step S3). As a result of this determination, when α ≠ 90 °, that is, when α = 90 °, there is no need to obtain the skew correction reference line Sx ′, and the CPU 60a ends this control process. On the other hand, when α ≠ 90 °, the CPU 60a determines whether or not the reference side for skew correction is a side side (step S4). Since the oblique registration method employed by the registration device 65 corresponds to this, the CPU 60a calculates the correction amount β ° and the correction direction based on the equation (1) or (2). Here, the correction amount β ° and the correction direction are calculated based on the expression (1) when the angle α ° calculated in step S2> 90 ° (step S6), and when the angle α ° <90 °. In addition, it is calculated based on the above equation (2) (step S7).

  The CPU 60a calculates the phase of the angle adjustment cam 13 corresponding to the correction amount β ° calculated in this way, converts it to the number of drive pulses of the angle adjustment motor 14, and gives a control command for driving the angle adjustment motor 14. Output (step S11). As a result, the skew correction is performed by the reference line Sx ′ reflecting the cutting accuracy (| 90 ° −angle α ° |) of the transfer material S.

  When the skew correction is performed, the CPU 60a uniformly drives the slide drive motor 60d by the amount of the contact D (step S17). The above process is a process for printing on one side of a single transfer material. If a single-sided print job is designated, the process is basically terminated (step S16 → end).

  On the other hand, when the double-sided print job is designated, the CPU 60a returns the transfer material S again for printing the second side based on the correction direction and the correction amount β ° calculated in step S6 or S7. A skew correction reference line Sx ′ is calculated. Specifically, regardless of the double-sided inversion method (in this embodiment, the switchback inversion method), the relative inclination relationship (that is, the perpendicularity) between the reference side and the non-reference side calculated in step S2 is the first side. On the second side, the sign is reversed. That is, as shown in step S18, −β °, in which the magnitude of the correction amount is kept as it is and the correction direction is reversed, is calculated as a value defining the reference line Sx ′ at the time of printing the second side. Generally, in a print job, an ID number is assigned to each transfer material, and the relationship between the first and second surfaces of the same transfer material can be identified and matched. Therefore, the value calculated in step S18 is also stored in the memory 60e as information accompanying this ID number (step S19). Thus, when returning to print the second side again, the CPU 60a performs drive control of the angle adjustment motor 14 based on the correction value −β ° (step S11).

  As described above, according to this embodiment, it is not necessary to perform a trial-and-error adjustment operation including a case of a double-sided print job, and it is easy to perform highly accurate registration considering the cutting accuracy of the transfer material. Can be done.

  Note that the control process of FIG. 8 may be installed in the image forming apparatus 60 as one of the print mode functions. For example, a user interface is constructed on the operation screen of the image forming apparatus 60 so that the operator can select a print mode in which this control process can be turned on / off. Then, the operator turns off this control process when printing with a high character ratio that is not concerned with the margin difference, whereas when printing a poster sample with a high photo ratio to a large size such as 13 inches × 19 inches, This control process is turned on. Thereby, the calculation of the correction amount β ° and the control of the angle adjustment motor 14 can be suppressed to the minimum necessary, and the calculation load and power load applied to the CPU 60a can be reduced.

(Second Embodiment)
Next, an image forming apparatus according to a second embodiment of the present invention will be described. The internal structure of the image forming apparatus of this embodiment is basically the same as that of the image forming apparatus of the first embodiment, that is, the one shown in FIG. Therefore, descriptions of the image forming process and the transfer material conveyance process are omitted. The image forming apparatus according to the present embodiment employs an active registration type registration apparatus that is excellent in media adaptability because it is not necessary to contact the reference side of the transfer material S.

<Active registration method>
FIG. 9 is a top view of the transport unit including the registration apparatus of the present embodiment. In the figure, the conveyance direction is the direction of arrow F, and is divided into a pre-registration conveyance unit, a skew feeding correction unit, and a slide unit from the upstream side. Since the pre-registration conveyance unit uses a belt conveyance method in the same manner as the pre-registration conveyance unit of the first embodiment, detailed description thereof is omitted.

  The skew correction unit mainly includes a conveyance guide 20, skew correction motors 21a and 21b, two pairs of skew correction roller pairs 22a and 22b, tip detection line sensors 23a and 23b, and side detection line sensors. 24. Each skew correction roller pair 22a and 22b is arranged on the same axis in the width direction, and performs the skew correction by driving the transfer material S at an independent transport speed. Here, the conveyance drive of the transfer material S is performed by the skew correction motors 21a and 21b rotating and driving the skew correction roller pairs 22a and 22b independently. The tip detection line sensors 23a and 23b are arranged parallel to the reference axis Sx in the transport direction and symmetrical with respect to the transport center. The side detection line sensor 24 is arranged in parallel with the reference axis Sy in the width direction.

  The transfer material S that has been conveyed to the skew correction unit is detected at two points by the tip detection line sensors 23a and 23b, and the skew amount is measured. The CPU (arithmetic control unit) 60a calculates a rotational speed difference that cancels the skew amount, and controls driving of the skew correction motors 21a and 21b so as to be the rotational speed difference. For example, the CPU 60a reduces the number of rotations of the preceding skew correction motor, and performs drive control with the goal that the detection levels of both the tip detection line sensors 23a and 23b become equal. The transfer material S that has been subjected to skew correction in this way is conveyed to a registration roller 7 described later. At this time, the position of the transfer material S in the width direction is detected by the side detection line sensor 24, and it is determined how much the transfer material S is deviated from the image position on the intermediate transfer belt 606 (see FIG. 1). .

  In FIG. 9, the line sensor is used for tip detection so that the rotational speed can be controlled while continuously determining the skew correction degree. However, a configuration in which a plurality of general optical sensors are arranged may be used. In addition, although a pair of skew correction motors is provided, a configuration in which a plurality of pairs are provided to perform skew correction in stages may be employed. When skew correction by the skew correction roller pair 22a and 22b is started, it is necessary to consider that the upstream pre-registration conveyance unit does not disturb the correction operation. For this reason, the suction shutter 16 is closed in the same manner as in FIG. 2 using as a trigger the level at which the signal levels of the tip detection line sensors 23a and 23b can reach the skew correction roller pair 22a and 22b.

  The slide portion mainly includes a conveyance guide 17, a registration roller 7, a registration drive motor 18, a slide motor 150, and a post-registration sensor 100. The registration roller 7 is supported and driven so that it can slide in the width direction. That is, the registration roller 7 is slid by the slide motor 150 while the transfer material S is nipped and conveyed in a direction matching the image position on the intermediate transfer belt 606 by the width direction deviation detected by the side detection line sensor 24. . When performing this sliding movement, it is necessary to release at least the nip between the upstream skew correction roller pair 22a and 22b. The timing for releasing the nip is controlled by using a passing signal of the transfer material S by the side detection line sensor 24 as a trigger. Further, the passage signal of the transfer material S by the post-registration sensor 100 is used as a trigger for adjusting the arrival timing of the downstream secondary transfer outer roller 66 (see FIG. 1). When the secondary transfer outer roller 66 starts to convey the transfer material S, the registration roller 7 releases the nip and slides back to the standby position in the width direction again.

<Squareness detection unit>
In the present embodiment, similarly to the first embodiment, in order to detect the perpendicularity of the transfer material S conveyed by the pre-registration conveyance unit, for example, an area sensor 50 represented by a CMOS sensor is provided. ing. As for the detection region, as shown in FIG. 10, a transparent small window portion 40 may be provided to detect only one corner portion of the transfer material S. In this case, the pre-registration conveyance unit can be configured using a general conveyance roller pair 112 and a conveyance guide 113 as in the illustrated example, and the optical system can be configured small because the detection area is narrow. However, in the system in which the leading edge is used as the reference edge as shown in FIG. 9, if the leading edge region of the transfer material S can be detected over the entire width, the angles of the two corners can be calculated simultaneously, and finer control is possible. Can be done. Therefore, here, a configuration capable of detecting a relatively wide area as shown in FIG. 3 is adopted, and for example, a region A1 shown in FIG. 9 is detected.

  Further, for example, if the arrangement configuration can be detected by enlarging the region A2 including the skew correction portion, the functions of the tip detection line sensors 23a and 23b and the side detection line sensor 24 can be replaced by the area sensor 50. That is, in this configuration, these line sensors 23a, 23b and 24 can be dispensed with. In particular, if an area sensor that can be read for each block, such as a CMOS sensor, is used, the detection area A2 is divided into a squareness detection block, a skew detection block, and a side position detection block. Can be detected with the required resolution.

<Target angle of reference side>
A method of correcting and determining the target angle of the reference side by calculating the correction amount β ° from the angle α ° formed by the reference side and the non-reference side detected by the detection means (in this embodiment, the area sensor 50). explain. Originally, as shown in FIG. 9, the detection signal difference between the tip detection line sensors 23a and 23b in the active registration system is such that the width direction reference line Sy and the tip side (reference side) of the transfer material S are parallel. “0” is set.

  For example, when a transfer material in which a side side (non-reference side) forms an angle α ° (> 90 °) with respect to a reference side as shown in FIG. Image margin lengths Ba and Bb are substantially equal. However, the non-reference side with respect to the transport direction is inclined by (α−90) °. Accordingly, there is a difference between the image margin lengths Bc and Bd at both ends on the non-reference side side due to poor cutting accuracy. As a result, the non-uniformity of the image margin is noticeable visually. Therefore, in this embodiment, the non-uniformity of the image margin due to the cutting accuracy of the transfer material is dispersed so as not to be concentrated on one side. Then, the correction amount β ° for the most effective dispersion is obtained as follows.

  As shown in FIG. 11, when the length of the long side of the transfer material S is L and the length of the short side is W, the difference in the amount of blank space generated at both ends of the front end side is

It becomes. As can be seen from the above formula, the registration device with the tip side as the reference side as in the present embodiment has a longer maximum non-reference side length, so even a transfer material cut at the same angle is not. The margin amount difference generated on the reference side becomes large.

  Now, a reference line Sy ′ obtained by rotating the reference line Sy shown in FIG. 9 in the counterclockwise direction by the correction amount β ° is defined, and a part of the margin amount difference Bd−Bc as shown in FIG. Consider distributing the difference in the margin amount on the side. At this time, the most visually conspicuous dispersion method is a method of equalizing the margin amount difference generated at the ends of two sides having different lengths. That is, in FIG.

It is. Therefore,

A correction amount β ° that satisfies the above is determined, and a new reference line Sy ′ having the target angle of the reference side as a target angle is determined. Equation (3) is an equation described for α> 90 °. On the other hand, when α <90 °, the same idea as when α> 90 °,

A correction amount β ° that satisfies the above is determined, and a new reference line Sy ′ having the target angle of the reference side as a target angle may be determined.

  In this way, by detecting the angle α ° formed between the reference side and the non-reference side of the transfer material, it is possible to determine the reference line Sy ′ that makes the margin amount difference most visually inconspicuous. Further, if an area sensor is used as the detecting means for the angle α °, the angle α ° can be directly detected. Therefore, the transfer material S has the detection of the angle α ° and the determination of the reference line Sy ′ during the conveyance. It is also possible to correct the influence of the variation factor.

  In the present embodiment, as described above, by detecting the detection region A1 or A2, the angles of the two corners of the transfer agent can be detected simultaneously. As the angle α ° that is substituted into the equation (3) or (4), the correction angle β ° that more effectively disperses the margin amount difference is obtained by using the one of the two angles having the lesser squareness. be able to.

<Control action>
Hereinafter, control processing executed by the image forming apparatus 60, particularly the CPU 60a, will be described with reference to the system of FIG. 7 and the flowchart of FIG.

  For example, the CPU 60a detects the reference side and the non-reference side of the transfer material S from the detection unit 60b typified by an area sensor. Then, the angle α °, the correction amount β °, the correction direction, and the like are calculated, and the calculated values are reflected in a predetermined difference between the detection signals of the tip detection line sensors 23a and 23b that are correction targets. That is, the predetermined difference is set to “0” in the initial state, but when the correction amount β ° is calculated, the timing of the detection signals of the tip detection line sensors 23a and 23b is equivalent to β °. A change is made so that the shifted state becomes the skew correction completed state. In addition, when the detection area is the area A2 in FIG. 9, the position shift in the width direction of the transfer material S can be simultaneously detected by the detection unit 60b. Therefore, the CPU 60a calculates the number of drive pulses corresponding to this positional deviation, and outputs a control value command including the number of drive pulses to the slide drive motor 60d that moves the registration roller 7 in the width direction. Further, the CPU 60a stores various calculated values in the memory 60e as necessary.

  In FIG. 8, first, the CPU 60a detects the reference side and the non-reference side of the transfer material S via the detection unit 60b (step S1). Next, the CPU 60a calculates an angle α ° formed from the detected two sides (step S2), and determines whether α ≠ 90 ° (step S3). As a result of this determination, when α ≠ 90 °, that is, when α = 90 °, there is no need to obtain the skew correction reference line Sy ', so the CPU 60a ends this control process. On the other hand, when α ≠ 90 °, the CPU 60a determines whether or not the reference side for skew correction is a side side (step S4). The active registration method employed by the registration apparatus according to the present embodiment does not correspond to this, and therefore the CPU 60a calculates the correction amount β ° and the correction direction based on the equation (3) or (4). . Here, the correction amount β ° and the correction direction are calculated based on the equation (3) when the angle α ° calculated in step S2> 90 ° (step S9), and when the angle α ° <90 °. In addition, it is calculated based on the equation (4) (step S10).

  The CPU 60a calculates the detection timing difference between the tip detection line sensors 23a and 23b corresponding to the correction amount β ° calculated in this way, and changes the threshold value for determining the skew correction completion state (step S11). As a result, the skew correction is performed by the reference line Sy ′ reflecting the cutting accuracy (| squareness−angle α ° |) of the transfer material S. When the skew correction is performed, the CPU 60a determines whether or not the skew feeding registration method is adopted (step S12). As described above, since the active registration method is employed in the present embodiment, the CPU 60a detects the position in the width direction of the transfer material S again via the detection unit 60b (step S13). The CPU 60a calculates the positional deviation in the width direction of the transfer material S from the detected position in the width direction, and converts this positional deviation in the width direction into the number of pulses of the slide drive motor 60d (step S14). Further, the CPU 60a outputs a control value command including the number of drive pulses to the slide drive motor 60d (step S15). The above process is a process for printing on one side of a single transfer material. If a single-sided print job is designated, the process is basically terminated (step S16 → end).

  On the other hand, when the double-sided print job is designated, the CPU 60a returns the transfer material S again for printing the second side based on the correction direction and the correction amount β ° calculated in step S9 or S10. A skew correction reference line Sy ′ is calculated. Specifically, regardless of the double-sided inversion method (in this embodiment, the switchback inversion method), the relative inclination relationship (that is, the perpendicularity) between the reference side and the non-reference side calculated in step S2 is the first side. On the second side, the sign is reversed. That is, as shown in step S18, −β °, in which the magnitude of the correction amount is kept as it is and the correction direction is reversed, is calculated as a value defining the reference line Sy ′ at the time of printing the second side. Generally, in a print job, an ID number is assigned to each transfer material, and the relationship between the first and second surfaces of the same transfer material can be identified and matched. Therefore, the value calculated in step S18 is also stored in the memory 60e as information accompanying this ID number (step S19). Thus, when returning for printing the second surface again, the CPU 60a changes the detection timing difference between the tip detection line sensors 23a and 23b based on the correction value −β ° (step S11).

  In this embodiment, the active registration method using the tip side as a reference side has been described as an example. However, in the active registration method, if the side for detecting the skew of the transfer material is set as a side side, the side A method using the side as a reference side can also be easily adopted. In that case, in addition to the switchback inversion method, a configuration in which the reference side does not change between the front surface and the back surface of the transfer material can be employed. When this configuration is adopted, the equation (1) or (2) described in the first embodiment may be applied to the correction amount β ° (step S6 or S7 is executed). Alternatively, if the leading edge is used as a reference edge as in this embodiment, if the reversal method for both sides is a so-called spiral reversal method, the reference edge does not change between the front and back surfaces of the transfer material. Can be more desirable.

(Third embodiment)
Next, an image forming apparatus according to a third embodiment of the present invention will be described.

  The internal structure of the image forming apparatus of this embodiment is basically the same as that of the image forming apparatus of the first embodiment, that is, the one shown in FIG. Therefore, descriptions of the image forming process and the transfer material conveyance process are omitted. The image forming apparatus according to the present embodiment employs a shutter registration type registration apparatus that has the simplest configuration and is excellent in cost merit.

<Shutter registration method>
FIG. 13 is a top view of the transport unit including the registration apparatus of the present embodiment. In the figure, the conveyance direction is the direction of arrow F, and is divided into a pre-registration conveyance unit, a skew feeding correction unit, and a registration roller unit from the upstream side. Since the pre-registration conveyance unit uses a belt conveyance method in the same manner as the pre-registration conveyance unit of the first embodiment, detailed description thereof is omitted.

  The skew correction unit mainly includes a conveyance guide 30, a pre-shutter sensor 31, a shutter member 32, and a shutter motor 33 that opens and closes the shutter member 32. Control of the opening / closing operation of the shutter member 32 is performed by phase control of an eccentric cam (not shown) provided on the shaft of the shutter motor 33. Further, the actuator used for opening and closing the shutter member 32 may be a solenoid as well as a motor.

  The front end of the transfer material S conveyed to the skew correction unit is detected by the pre-shutter sensor 31, the shutter motor 33 is driven at a predetermined timing, and the shutter member 32 is closed so as to block the conveyance path. . As a result, the leading end side of the transfer material S comes into contact with the shutter member 32 and is pushed by the upstream conveying belt 4. However, since the vicinity of the upstream side of the shutter member 32 is a region where the suction effect of the suction fan 6 does not reach, it is a loop space G that bends and absorbs the pushed-in portion. Therefore, even the transfer material S that has been conveyed obliquely is pushed in such a way that the front end side is parallel to the shutter member 32. The transfer material S whose skew has been corrected in this way is conveyed to the downstream registration roller section by driving the shutter motor 33 again and opening the shutter member 32. The skew correction unit is unitized, and is supported in the transport unit shown in FIG. 13 so that the alignment of the unit can be changed. Specifically, a moment acts on the unit stage 34 supporting the unit in the clockwise direction with respect to the rotation center Rc by the urging member 35, and the moment is received by the cam surface of the angle adjusting cam 36. Is decided. Further, the phase of the cam surface of the angle adjusting cam 36 can be arbitrarily changed by the angle adjusting motor 37.

  The registration roller portion is mainly composed of a conveyance guide 17, a registration roller 7, a registration driving motor 18, a pre-registration sensor 19, and a post-registration sensor 100. The passing signal of the transfer material S by the post-registration sensor 100 is used as a trigger for adjusting the arrival timing of the downstream secondary transfer outer roller 66 (see FIG. 1). Then, the rotational speed of the registration drive motor 18 is appropriately controlled so that the timing of the image on the intermediate transfer belt 606 (see FIG. 1) and the transfer material coincide. Note that, as described in the first and second embodiments, the registration roller 7 may be configured to be slidable in the width direction, and more accurate image alignment may be performed.

<Squareness detection unit>
Also in the present embodiment, as in the first or second embodiment, an area sensor 50 represented by, for example, a CMOS sensor is used to detect the perpendicularity of the transfer material S conveyed by the pre-registration conveyance unit. have. Since the shutter registration system is a system in which the front end side of the transfer material S is used as a reference side, as described in the second embodiment, each of the two corners of the transfer material S can be detected simultaneously. 3 is used. As a detection area, an area A1 shown in FIG. 9 is detected.

<Target angle of reference side>
Originally, as shown in FIG. 13, the shutter member 32 in the shutter registration system is in an initial state where the abutting surface is parallel to the reference line Sy. Therefore, the idea regarding the correction amount β ° is the same as that in the second embodiment. For this reason, the reference line Sy ′ that most effectively disperses the non-uniformity of the image margin due to the cutting accuracy of the transfer material is determined from the correction amount β ° calculated based on the formula (3) or (4). To do.

<Control action>
Hereinafter, control processing executed by the image forming apparatus 60, particularly the CPU 60a, will be described with reference to the system of FIG. 7 and the flowchart of FIG. For example, the CPU 60a detects the reference side and the non-reference side of the transfer material S from the detection unit 60b typified by an area sensor. Then, an angle α °, a correction amount β °, a correction direction thereof, and the like are calculated, and a command for a control value corresponding to the correction amount β ° is issued to the correction target angle adjustment unit 60c that adjusts the angle of the reference line serving as a correction target. put out. Further, the CPU 60a stores various calculated values in the memory 60e as necessary.

  In the shutter registration method, since the reference side is not the side side, the same processing as in the second embodiment is followed from step S4 in FIG. However, the control command value in step S11 is the number of drive pulses of the angle adjustment motor 37, and is a value obtained by converting the correction amount β ° into the phase of the angle adjustment cam 36.

  As described above, even in the shutter registration method, the non-uniformity of the image margin due to the cutting accuracy of the transfer material can be dispersed so as to be visually inconspicuous.

7: Registration roller 8: Movable guide 9: Skew feed roller pair 10: Abutting reference member 21 ... Skew correction motor 22 ... Skew correction roller pair 23 ... Tip Detection line sensor 24 ... side detection line sensor 32 ... shutter member 50 ... area sensor 65 ... registration device 613 ... image forming unit S ... transfer material Sx ... transport Direction reference line Sy ... Width direction reference line

Claims (11)

Printing means for printing an image on a rectangular transfer material that has been conveyed;
A detection means for detecting a non-reference side that is at least one side adjacent to the reference side and the reference side, with one side of the transfer material as a reference side;
First calculation means for calculating an angle α ° between the reference side detected by the detection means and the non-reference side;
An angle at which the reference side is rotated in order to correct the shape of a rectangular image margin having the non-reference side as one side, which is assumed to occur when | 90 ° −α ° | ≠ 0, Second calculating means for calculating an angle β ° satisfying 0 <β ° <| 90 ° −α ° |
Correction means for correcting the skew of the transfer material so that the reference margin rotates in the direction closer to the square by the angle β ° calculated by the second calculation means. An image forming apparatus comprising the image forming apparatus.   The image forming apparatus according to claim 1, further comprising a selection unit that selects whether to perform skew correction by the correction unit. The detecting means detects another non-reference side adjacent to the reference side;
The first calculating means calculates two angles formed by the detected reference side and two non-reference sides, and calculates a value of the calculated two angles that is less perpendicular to the angle α °. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The printing means is capable of printing images on both sides of the transfer material,
When a job for printing an image on both sides of the transfer material is selected, the second calculation means calculates the angle β ° calculated for the front surface of the transfer material as −β ° for the back surface of the transfer material. The image forming apparatus according to claim 1, wherein the image forming apparatus is calculated as follows.   The detection unit includes a two-dimensional image sensor that detects an outer shape of a transfer material being conveyed, and the reference side and the non-reference side are detected by the image sensor. An image forming apparatus according to claim 1.   The detection means includes a plurality of line sensors arranged at predetermined intervals in the width direction and the conveyance direction of the transfer material, and the line sensor detects the reference side and the non-reference side. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The reference side is one side in the same direction as the transfer direction of the transfer material,
The second calculation means calculates the angle β ° when the length of the long side of the transfer material is L and the length of the short side is W.

The image forming apparatus according to claim 1, wherein the image forming apparatus is calculated as a value satisfying the above. The reference side is a tip side when the transfer material is conveyed,
The second calculation means calculates the angle β ° when the length of the long side of the transfer material is L and the length of the short side is W.

The image forming apparatus according to claim 1, wherein the image forming apparatus is calculated as a value satisfying the above.   The correction means includes an abutting reference member for abutting a reference side of the transfer material, and a conveying direction of the transfer material so as to generate a conveying force toward the abutting reference member with respect to the transfer material. A pair of skew feeding rollers disposed at a predetermined angle with respect to the sheet, and the transfer material is conveyed by the skew feeding roller pair and abutted against the abutting reference member. The image forming apparatus according to claim 1, wherein correction is performed, and an angle of the abutting reference member is changed by the angle β °.   The correction means includes a plurality of skew correction roller pairs that are arranged on the same axis in the width direction of the transfer material and perform skew correction by driving the transfer material at independent transfer speeds. The image forming apparatus according to claim 1, wherein a conveyance speed of each skew correction roller pair is controlled so that the transfer material is skew-corrected by the angle β °.   The correction means includes a shutter member that abuts the leading edge in the conveyance direction of the transfer material, and performs skew correction by forming a loop in the transfer material in a state where the transfer material is abutted against the shutter member. The image forming apparatus according to claim 1, wherein an angle of the shutter member is changed by the angle β °.

Images