JP2006036513A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To revise conveyance speed of paper and match a printing position in front of an image forming means irrespective of quality of paper to perform high quality printing. <P>SOLUTION: This image forming device 20 has a resist roller 2, a conveyance belt 3, the image forming means 7 for forming image on a paper 1 by corresponding to belt driving, and a speed difference detection means composed of a nip roller 12 following the belt and a nip roller encoder 24. The encoder 24 detects both of belt speed before conveying the paper 1 from the resist roller 2 and speed of the paper 1 conveyed from the resist roller 2, and a controller changes set speed of a resist roller driving means in accordance with difference between both speeds. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus capable of performing high-quality printing by adjusting a printing position by correcting a conveyance speed of a sheet before the sheet reaches an image forming unit without detecting the quality of the sheet. Is.

FIG. 6 is a diagram showing a configuration of an image forming apparatus proposed by the applicant of the present application.
An image is formed while conveying the sheets 1 one by one from the left to the right in FIG. A separation transport mechanism (not shown) for separating the sheets 1 from the sheet tray one by one and transporting them to the registration rollers 2 is provided on the left upstream side from the registration rollers 2. Correcting skew by hitting.

  The registration roller 2 is composed of a pair of rollers, and conveys the paper 1 to the belt conveyance surface 11 by registration roller driving means (not shown) using a motor capable of controlling the rotation speed.

  The conveyor belt 3 is an endless belt and is wound around three rollers (a driven roller 4, a driving roller 5, and a tension roller 6). Conveying belt driving means (not shown) having a motor is connected to the driving roller 5 and rotates the conveying belt 3 in the clockwise direction in the drawing at a constant speed. The driven roller 4 and the tension roller 6 rotate as the conveying belt 3 rotates. The number and arrangement of rollers for winding the belt may be changed depending on belt tension, belt skew performance, machine size, and the like. The number of rollers may be two or more, and the arrangement is not limited to the illustrated configuration and is arbitrary.

  Inside the conveyor belt 3, there is a fan (not shown) that conveys the sheet 1 together with the conveyor belt 3 while sucking the sheet 1 and holding it on the conveyance surface of the conveyor belt 3. However, the sheet 1 suction method of the transport belt 3 may be other suction means such as static electricity.

  The belt drive speed detection means of the conveyor belt 3 detects the conveyance movement amount of the paper 1 held and moved by the conveyance belt 3, and drives the image forming means 7 in accordance with the detected conveyance movement amount of the paper 1. Then, an image is formed on the paper 1. For detecting the amount of paper transport movement, belt drive speed detection means such as a rotary encoder (not shown) connected to an extension shaft of the rotation shaft of the drive roller 5 is used. Further, a similar rotary encoder may be attached to an extension shaft of the rotation shaft of another roller synchronized with the conveyance belt 3 such as the rotation shaft of the driven roller 4, or a slit is provided in the conveyance belt 3 and the belt of the conveyance belt 3 is detected by a sensor. The driving speed may be detected. In short, any means capable of detecting the belt driving speed of the conveying belt 3 may be used.

  The image forming unit 7 is configured so that an inkjet head capable of selectively ejecting ink of four colors of K (black), C (cyan), M (magenta), and Y (yellow) is sequentially placed above the conveyance surface of the conveyance belt 3. It arrange | positions in a contact state and prints by discharging each color to the paper 1 selectively one by one. In addition, an image forming apparatus such as a photosensitive drum in which the drum surface that is the printing surface and the conveyance surface of the paper 1 is in contact with the paper 1 may be any means that can form an image in conjunction with the movement of the conveyance belt 3. .

  The paper 1 printed on the transport surface of the transport belt 3 enters the paper discharge unit 9 through the separation claw 8 and the like, is transported by the paper discharge unit 9, is discharged to the discharge tray 10, and is stacked.

This image forming apparatus has a problem to be improved as described in the section “Problem to be Solved by the Invention” described later, and is a document describing a technique that can be considered to be partially related to this problem. The present applicant has recognized the following Patent Documents 1 and 2.
Japanese Patent Laid-Open No. 5-319609 Japanese Patent Laid-Open No. 2002-68520

  In order to form an appropriate image on the paper 1 on the transport surface 11 of the transport belt 3, it is necessary to perform printing corresponding to the transport of the transport belt 3. Therefore, if the paper 1 and the transport belt 3 are misaligned, the paper In some cases, a printing position shift with respect to 1 may cause a problem in printing. In particular, in the case of a color image forming unit in which the image forming unit 7 sequentially prints multiple colors on the paper 1 and the color changes according to the overlapping state of each color, the printing position deviation with respect to the paper 1 appears as color density unevenness. End up.

  The sheet conveyance linear velocity of the registration roller 2 has a difference due to tolerance (manufacturing variation) of the registration roller diameter, secular change (scraping or deterioration) due to long-term use, slip (surface condition of the sheet 1), and the like. Even if there is a difference between machines, if the registration roller linear velocity is set to be sufficiently higher than the linear velocity of the conveyance surface 11 of the conveyance belt 3, the leading edge of the sheet 1 is sucked by the conveyance belt 3. 6, in the case of plain paper with a low stiffness, tarmi occurs between the registration roller 2 and the conveyance belt 3 or between the registration roller 2 and the nip roller 12, the speed difference is absorbed, and the conveyance surface of the conveyance belt 3. 11 and the speed of the paper 1 match.

  However, in the case of the stiff paper 1 such as thick paper, it is difficult to cause the above-described tarmi, and the paper 1 slides on the transport surface 11 of the transport belt 3 by the speed difference between the registration roller 2 and the transport belt 3. The printing position was misaligned. In addition, after the trailing edge of the sheet 1 passes through the registration roller 2, the sheet 1 follows the speed of the conveying belt 3 and the printing position is aligned. The degree of overlap of each color changed, and the color density change was more conspicuous.

  As a countermeasure against such a printing position shift that occurs when the paper is thick, a distance between the registration roller 2 and the image forming unit 7 is widened, and the paper 1 is a drive system other than the conveying belt 3 during the image formation (the registration roller 2 and the like). It is also possible to adopt a configuration that does not receive the power from However, the machine itself or the housing for storing the machine is enlarged.

  Further, at the time of factory shipment or at the time of installing the printing machine, using a printed matter or a speed measuring device for each machine, the speed of the registration roller 2 is obtained so that the speed of the registration roller 2 and the conveyance surface 11 of the conveyance belt 3 is the same It is conceivable that the speed of the registration roller 2 is made the same as the speed of the transport surface 11 of the transport belt 3 by storing this in the control system and setting the stored speed regardless of the paper 1. However, such a method cannot cope with changes in the conveyance amount due to changes over time, such as the material of the conveyance belt 3 and the adhesion of paper dust, and causes problems even when printing plain plain paper that has not had problems. There is also a risk of doing.

  Further, a method of providing a means for detecting paper quality such as thick paper and setting the stored speed only when thick paper is detected is also conceivable. As a paper quality detection means, a method for manual setting by the user, a method for installing a sensor for detecting the paper thickness, a change amount of the paper tray for each printing (in the case of an elevator type paper feed stand, an elevator vertical movement amount for each printing) Change and weight change) can be considered, but the user's effort and cost increase can be considered, and it is impossible to cope with secular change.

  Note that the above-mentioned Patent Document 1 discloses a belt conveyance device provided with auxiliary torque applying means for applying rotational resistance to the speed detection roll in order to accurately measure the belt speed with a speed detection roll that rotates around the belt. However, it does not give suggestions for solving the above-described problems in the image forming apparatus having the above-described configuration.

  Further, the above-mentioned Patent Document 2 discloses a sheet conveying apparatus that detects the speed of a sheet by providing two sensors between an upstream conveying roller that conveys a sheet and a downstream conveying roller. This also does not give any suggestion for solving the above-described problem in the image forming apparatus having the above-described configuration.

  Accordingly, the present invention has been made in view of the above-described problems that cannot be solved by a conventionally known technique, and corrects the sheet conveyance speed before the sheet reaches the image forming unit without detecting the sheet quality. Accordingly, an object of the present invention is to provide an image forming apparatus that can perform high-quality printing by matching the printing positions.

  The image forming apparatus 20 of the present invention shown in FIGS. 1 and 4 does not detect the paper quality and increases the speed of the registration roller 2 with respect to the plain paper that has not caused the problem, thereby causing the problem to occur. In contrast, by correcting the speed of the registration roller 2, the image forming timing of the image forming unit 7 is matched with the conveyance of the paper 1 by the conveyance belt 3 so that high-quality printing can be performed. It is.

The image forming apparatus 20 described in claim 1 includes:
A registration roller 2 for conveying the paper 1, a registration roller driving means 21 for driving the registration roller 2,
A conveying belt 3 for conveying the sheet 1 conveyed from the registration roller 2 further downstream;
Conveying belt driving means 22 for driving the conveying belt 3;
A conveyor belt drive speed detecting means 23 for detecting a belt drive speed of the conveyor belt 3;
Image forming means 7 for forming an image on the paper 1 on the conveying belt 3 at a printing timing corresponding to the belt driving speed detected by the conveying belt driving speed detecting means 23;
By detecting both the belt movement speed before the sheet 1 is conveyed from the registration roller 2 and the sheet movement speed of the sheet 1 conveyed from the registration roller 2, the belt movement speed and the Speed difference detecting means 12 and 24 for detecting the speed difference of the paper moving speed are provided,
The set speed of at least one of the registration roller driving means 21 and the conveying belt driving means 22 is changed according to the speed difference detected by the speed difference detecting means 12, 24.

  If the configuration of claim 1 is further embodied, the conveying belt driving speed detecting means can be realized by a driving roller encoder 23 arranged on the shaft of the driving roller 5 for driving the conveying belt 3, and the speed difference detecting means is provided on the conveying belt 3. It can be realized by the nip roller 12 that can be driven by contacting the conveyor belt 3 and the nip roller encoder 24 arranged on the shaft thereof. Such a configuration can be realized even if the conveying belt driving speed by the conveying belt driving means 22 is varied in accordance with the speed difference between the belt moving speed detected by the speed difference detecting means 12 and 24 and the sheet moving speed. However, in practice, it is more preferable that the speed of the conveying belt 3 on which printing is performed is fixed as much as possible, and the sheet moving speed is varied under the control of the registration roller driving means 21.

  The image forming apparatus 20 according to claim 2 is the image forming apparatus 20 according to claim 1, wherein the speed difference detecting means is a roller (nip roller 12) that rotates following the conveying surface 11 of the conveying belt 3 in contact with the conveying surface 11. ).

  In addition to the roller, the speed difference detecting means according to claim 2 is a laser Doppler meter which is a laser reflection type speed measuring device using a Doppler phenomenon, or captures a specific range as an image every fixed period, A CCD that is a device for measuring a moving distance and a speed according to a change in (feature) can also be used. Further, since the roller (nip roller 12) as the speed difference detecting means preferably has a high surface friction, it is preferable to use a rubber having a high surface friction, a grid roller having fine irregularities formed by particles or processing on the surface, and the like. .

  The image forming apparatus 20 described in claim 3 is the image forming apparatus 20 according to claim 2, wherein the speed difference detecting means uses a speed measurement value obtained when the roller (nip roller 12) makes at least one rotation. And calculating the speed difference.

  If the roller (nip roller 12) is used as the speed detecting means as described in claim 2, the roller may be provided eccentrically, and in that case, the speed difference detecting means (nip roller encoder 24) measures. In the speed, speed unevenness occurs every one roller period. Further, since minute speed unevenness is also generated due to vibration or the like, the speed difference detecting means performs the measurement for one or more rotations of the roller as described in claim 3 to reduce the influence of the speed unevenness. It is desirable.

  The image forming apparatus 20 described in claim 4 is the image forming apparatus 20 according to claim 1, wherein the speed difference detected by the speed difference detecting means 12, 24 is determined by the belt driving speed and the belt movement. A speed ratio of the speed and a difference between the belt driving speed and the speed ratio of the paper moving speed, and at least one of the registration roller driving means 21 and the conveying belt driving means 22 depending on the difference in speed ratio. By changing one set speed, the sheet moving speed and the belt driving speed are matched.

  That is, it is desirable that the speed of the conveyor belt 3 be constant, but there may be some fluctuations depending on the sheet conveyance load and the performance of the driving means. The speed difference detected by the speed difference detecting means 12 and 24 may be used as long as there is a fluctuation that is practically no problem. However, as described in claim 4, the belt driving speed and the belt moving speed of the conveyor belt 3 are used. It is desirable that the sheet moving speed by the rotation of the registration roller 2 or the belt driving speed of the conveying belt 3 is made variable using the speed ratio of the above and the belt driving speed of the conveying belt 3 and the speed ratio of the sheet moving speed.

  According to a fifth aspect of the present invention, in the image forming apparatus 20 according to the first to fourth aspects, the speed difference detecting means 12, 24 is a roller in which the conveyance belt 3 is curved and wound ( It is characterized in that the surface of the conveyor belt 3 at a position away from the contact portion between the driven roller 4) and the conveyor belt 3 is detected.

  Specifically, as shown in FIG. 5 (enlarged sectional view of the conveyor belt 3 and the driven roller 4), the surface speed of the conveyor belt 3 varies depending on the location due to the thickness and expansion / contraction of the conveyor belt 3. In FIG. 5, the speed v <b> 1 on the outer peripheral surface side of the transport belt 3 wound around the driven roller 4 tends to be faster than the speed v <b> 3 of the transport surface 11 of the transport belt 3. It is desirable that the speed of the paper 1 (paper moving speed) sent from the registration roller 2 coincides with v3.

  As shown in FIG. 5, if the nip roller 12 serving as a speed difference detecting means used for speed difference measurement is arranged immediately above the axis of the driven roller 4 of the conveyor belt 3, it is affected by v1 when the belt moving speed is measured. End up. Therefore, the speed difference measurement by the nip roller 12 is performed by arranging the nip roller 12 at a position shifted from the contact point between the driven roller 4 wound around the conveyor belt 3 and the conveyor belt 3 to the downstream side (right direction indicated by a white arrow in FIG. 5). It is desirable to do this. Further, when a roller such as the nip roller 12 is used for speed difference measurement, the conveyance belt 11 is maintained so that the conveyance surface 11 of the conveyance belt 3 can be kept flat (the conveyance surface 11 of the conveyance belt 3 is not sunk by the nip roller 12). It is desirable to dispose the supporting roller 25 also below the 3.

  The image forming apparatus 20 according to a sixth aspect is the image forming apparatus 20 according to the first to fifth aspects, wherein the registration roller driving means 21 and the conveying belt driving means are detected according to detection results of the speed difference detecting means 12 and 24. Before changing at least one of the set speeds 22, the registration roller 2 is driven at a speed higher than that of the conveyor belt 3.

  As shown in FIG. 3, the registration roller speed is made lower than the conveyance belt conveyance surface speed, so it is not necessary to perform speed correction for plain paper with low stiffness (line (b)), and for thick paper with strong stiffness. Speed correction will not accelerate but only decelerate (line (c)). Therefore, the control is simplified if the setting is such that the registration roller 2 side becomes faster even if component tolerance or slip occurs.

  An image forming apparatus 20 according to a seventh aspect is the image forming apparatus 20 according to the first to sixth aspects, wherein the registration roller driving unit 21 and the registration roller driving unit 21 correspond to the speed difference detected by the speed difference detecting units 12 and 24. There is a storage means for storing the changed set speed in at least one of the conveying belt drive means 22, and after the next sheet passing, the registration roller drive means 21 at the changed set speed stored in the storage means. And at least one of the conveying belt driving means 22 is driven.

  The appropriate rotation speed of the registration roller 2 changes with the aging of the type and parts of the paper 1. Further, when printing is performed with the paper interval narrowed, if the registration roller 2 is too faster than the speed of the transport surface 11 of the transport belt 3, the leading edge of the next sheet catches up with the trailing edge of the previous sheet, and the sheet 1 overlaps. There may be a problem. However, in the invention described in claim 7, the speed difference between the registration roller 2 and the conveying belt 3 is detected, the proper speed of the registration roller 2 is obtained and stored, and the stored speed is used for the subsequent printing. Therefore, the related problem can be solved. In that case, if the stored value is used every time, the trouble of correcting the speed every time can be saved, and if the value stored by performing the speed correction every time is used, the speed correction range is reduced each time. The time spent on the paper is shortened, and it is possible to cope with subtle differences for each paper.

In the invention of claim 7, there are various methods for clearing and using the stored value, for example, the following (1) to (3). It is done.
(1) For the first printing start, the speed of the registration roller 2 (paper moving speed) is set to be higher than the speed of the conveying surface 11 of the conveying belt 3 (belt driving speed of the conveying belt 3), and the correction value is stored. The stored value is used for the second and subsequent sheets.
(2) For only the first sheet when the addition / replacement of the sheet 1 to the sheet tray is detected, the speed of the registration roller 2 is set to be higher than the speed of the transport surface 11 of the transport belt 3 and the correction value is stored. After that, the stored value is used.
(3) Speed correction is performed only at the time of printing when a predetermined time elapses, and the correction value is stored. Otherwise, the stored value is used and no speed correction is performed.

  According to the image forming apparatus 20 described in claim 1, the belt of the conveying belt 3 by the conveying belt driving unit 22 according to the difference between the belt moving speed detected by the speed difference detecting units 12 and 24 and the sheet moving speed. By varying the driving speed or the paper moving speed by the registration roller driving means 21, the image quality is always detected with respect to the movement of the paper 1 that is transferred from the registration roller 2 to the conveying belt 3 without detecting the paper quality. The image forming timing of the forming unit 7 can be matched, and high-quality printing can be performed.

  According to the image forming apparatus 20 described in claim 2, in addition to the effect of the image forming apparatus 20 according to claim 1, the speed difference detecting means 12, 24 is configured with a simple configuration that is low in cost and less likely to cause problems. it can.

  According to the image forming apparatus 20 described in claim 3, in addition to the effect of the image forming apparatus 20 according to claim 2, when the roller (nip roller 12) is used as the speed difference detecting means, the roller (nip roller 12). Even if the speed is decentered or minute speed unevenness occurs due to vibration or the like, the influence of the speed unevenness can be reduced in the measurement of the speed difference detecting means 12, 24.

  According to the image forming apparatus 20 described in claim 4, in addition to the effects of the image forming apparatus 20 according to claims 1 to 3, the belt driving speed of the conveying belt 3 is not constant, and the load of sheet conveying and the driving means Even if there is a slight variation due to the performance of the belt, the speed ratio between the belt driving speed and the belt moving speed and the speed ratio between the belt driving speed and the paper moving speed are detected, and the difference in both speed ratios is used to detect the registration roller 2. Since the sheet moving speed by the rotation or the belt driving speed by the conveying belt driving means 22 is varied, it is difficult to be adversely affected by these disadvantages.

  According to the image forming apparatus 20 described in claim 5, a portion where the speed of the conveyor belt 3 is stable even when the surface speed of the conveyor belt 3 varies depending on the location due to the thickness, expansion and contraction of the conveyor belt 3. Measurement can be performed with.

  According to the image forming apparatus 20 described in claim 6, in addition to the effects of the image forming apparatus 20 according to claims 1 to 5, the speed of the registration roller 2 is made faster than the speed of the transport surface 11 of the transport belt 3. Therefore, speed compensation is not necessary for plain paper with low stiffness, and speed compensation is not accelerated for thick paper with strong stiffness, so only the deceleration on the registration roller 2 side even if component tolerance or slippage occurs. If the setting is made faster, the control is simplified.

  According to the image forming apparatus 20 described in claim 7, in addition to the effects of the image forming apparatus 20 according to claims 1 to 6, the set speed of the registration roller driving unit 21 and the like is changed according to the speed difference. In this case, since this can be stored and saved, the conveyance speed of the paper 1 is set before the paper 1 reaches the image forming means 7 without detecting the paper quality of the paper 1 after the next paper pass. High-quality printing can be performed by correcting and matching the printing position. In that case, if the stored value is used every time, the trouble of correcting the speed every time can be saved, and if the value stored after performing the speed correction every time is used, the speed correction range is reduced each time. The time spent is shortened, and it is possible to cope with subtle differences between sheets.

1. Main Configuration of Image Forming Apparatus 20 of Present Embodiment Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.
FIG. 1 is a diagram showing an image forming apparatus 20 of the present embodiment (hereinafter referred to as this example). The same parts as those of the image forming apparatus previously proposed by the present applicant shown in FIG. 6 are denoted by the same reference numerals as those in FIG. 6, and the description thereof is omitted if necessary, or referring to FIG. Use the explanation.

  The image forming apparatus 20 of this example includes a pair of registration rollers 2 that convey the paper 1 and registration roller driving means 21 such as a motor (not shown) that drives the registration rollers 2. Next to the registration roller driving means 21, the driving roller 5, the driven roller 4, and the tension roller are used to convey the paper 1 conveyed from the registration roller 2 further downstream in the substantially same conveyance surface 11. 6 is provided with belt conveying means in which the conveying belt 3 is wound around. In the belt conveying means, a holding means for holding the paper 1 placed on the conveying surface 11 of the conveying belt 3 (the surface of the conveying belt 3) is provided. As the holding means, for example, a suction means for sucking and holding the sheet 1 from a plurality of holes provided in the conveyor belt 3, a gap between the plurality of conveyor belts 3, and an electrostatic adsorption means can be employed. is there. Conveying belt driving means 22 such as a motor for driving the driving roller 5 is linked to the driving roller 5 of the belt conveying means. Further, a separation claw 8 for separating the paper 1 from the conveyance belt 3 is sandwiched between the belt conveyance means at the front end side in the conveyance direction, and a belt type paper discharge unit 9 is provided. Is configured to transport the paper 1 peeled from the transport belt 3 and discharge the paper 1 onto a discharge tray 10 provided downstream of the paper discharge unit 9 for stacking and accumulation.

  An image forming means 7 is provided at a predetermined distance from the conveyor belt 3 on the side near the drive roller 5 at a substantially intermediate portion of the belt conveyor surface 11 of the conveyor belt. The image forming unit 7 sequentially applies an inkjet head capable of selectively ejecting ink of four colors of K (black), C (cyan), M (magenta), and Y (yellow) above the conveyance surface 11 of the conveyance belt 3. Are arranged in a non-contact state, and each color can be selectively and sequentially ejected onto the paper 1 for printing. Further, an image forming unit such as a photosensitive drum in which the peripheral surface of a drum that is also a printing surface and a paper conveyance surface contacts the paper can be employed as long as it can form an image in conjunction with the movement of the conveyance belt 3.

  Further, in this example, the driving roller 5 is provided with a conveying belt driving speed detecting means 23 for detecting the belt driving speed of the conveying belt 3. The conveyor belt drive speed detecting means 23 may be a drive roller encoder 23 for detecting the rotation of the drive roller 5 as shown in FIG. 1, or a drive motor as shown in FIG. It may be a belt drive motor encoder 26 provided on the shaft for detecting rotation. The image forming unit 7 is driven at a predetermined timing synchronized with the belt driving speed of the conveying belt 3 detected by the conveying belt driving speed detecting unit 23, and discharges ink onto the paper 1 held on the conveying belt 3. A desired color image can be formed.

  Further, in this example, a registration roller encoder 27 is provided in the registration roller 2 as a speed detection means for the paper 1 sent from the registration roller 2 for detecting the paper moving speed of the paper 1 sent by the registration roller 2. .

  Further, in this example, both the belt moving speed before the sheet 1 is conveyed from the registration roller 2 and the sheet moving speed of the sheet 1 conveyed from the registration roller 2 are detected, and both speeds are detected. Speed difference detection means 12 and 24 for detecting the difference are provided. The speed difference detecting means 12, 24 of this example is arranged at a position on the conveying belt 3 between the image forming means 7 and the driven roller 4, and is provided in contact with the conveying belt 3 so as to be driven. 12 and a nip roller encoder 24 arranged on the shaft thereof.

  That is, the image forming apparatus 20 of this example is different from the image forming apparatus shown in FIG. 6 in terms of speed measuring means for three rollers: a registration roller 2, a nip roller 12 as a roller constituting a speed difference detecting means, and a driving roller 5. Encoders 27, 24, and 23 are added, and the belt moving speed and registration before the sheet 1 arrives at the conveying surface 11 of the conveying belt 3 by the speed difference detecting means (nip roller 12 and nip roller encoder 24). The speed difference of the sheet moving speed by the roller 2 is measured, and the belt driving speed of the registration roller 2 (or the belt driving speed of the driving roller 5) before the sheet 1 reaches the image forming unit 7 according to the measurement result. Is corrected, and the speed of the conveying belt 3 and the speed of the paper 1 are combined to realize suitable printing.

2. Action or Principle of Image Forming Apparatus 20 of This Example The image forming apparatus 20 of this example is a speed between the belt moving speed before the sheet 1 arrives at the conveying surface 11 of the conveying belt 3 and the sheet moving speed by the registration roller 2. The difference is measured by the speed difference detecting means 12 and 24, and the belt driving speed of the registration roller 2 is corrected according to the result, so that the printing is optimized. The operation and principle will be described in detail below. To do.

  FIG. 2 shows a change in speed of the thick paper when a single thick paper is passed through the image forming apparatus 20 of this example. Before the leading edge of the sheet arrives at the nip roller 12 (before delivery), the nip roller 12 rotates with the conveying surface 11 of the conveying belt 3, so that the speed of the conveying surface 11 of the conveying belt 3 is the same. After the leading edge of the sheet arrives at the nip roller 12 (after delivery), the nip roller 12 rotates with the sheet 1, so that the speed of the registration roller 2 that conveys the sheet 1 is reached.

  In FIG. 2, the rotational speed of the nip roller 12 is increased after the delivery. This is a case where the rotational speed of the registration roller 2 is higher than the linear speed of the transport surface 11 of the transport belt 3. At this time, before the paper 1 arrives at the image forming apparatus 20, the speed of the registration roller driving means 21 (motor) that drives the registration roller 2 is corrected by the amount (ratio) of the nip roller 12 increased (ratio) ( If the speed is reduced, the speed of the paper 1 and the speed of the transport surface 11 of the transport belt 3 coincide with each other, and the printing is preferably performed.

  Further, since the belt moving speed may vary slightly due to the suction friction of the paper 1 being conveyed, the rotational speed of the nip roller 12 (belt moving speed) is equal to the rotational speed of the nip roller 12 (belt moving speed). Taking the ratio of the rotational speed of the driving roller 5 (belt driving speed of the conveyor belt 3) as a ratio, the rotational speed of the registration roller 2 (paper movement speed by the registration roller 2) is the rotation speed of the registration roller 2 (paper movement by the registration roller 2). Speed) and the rotation speed of the drive roller 5 (belt drive speed of the conveyor belt 3).

FIG. 3 is a graph showing the speed ratio (vertical axis) of the nip roller 12 and the driving roller 5 according to the speed ratio (horizontal axis) of the registration roller 2 and the driving roller 5 described above before paper delivery.
As shown in FIG. 3 (a), the nip / driving roller speed ratio before delivery indicates the rotational speed of the nip roller 12 before delivery, and conforms to the belt driving speed of the conveyor belt 3, so the rotational speed of the registration roller 2 Regardless.

  As shown in FIG. 3 (b), the nip / driving roller speed ratio after delivery when the low-stiff paper 1 is transported indicates the rotational speed of the nip roller 12 when plain paper or the like is passed. When the rotational speed of the roller 2 is slower than the belt driving speed of the conveying belt 3, the rotational speed of the nip roller 12 decreases before and after delivery. Further, when the rotation speed of the registration roller 2 is faster than the belt driving speed of the conveying belt 3, as shown by the dotted line in FIG. 1, tarmi is generated between the registration roller 2 and the nip roller 12. Is the same before and after delivery (the sheet 1 cannot be faster than the speed of the conveyor belt 3).

  As shown in FIG. 3 (c), the nip / driving roller speed ratio after delivery when transporting the stiff paper 1 indicates the rotational speed of the nip roller 12 when passing thick paper or the like, When the speed of the registration roller 2 is faster than the conveyance speed of the conveyance belt 3, no targing is generated between the registration roller 2 and the nip roller 12, and the nip roller 12 before and after delivery is proportional to the speed of the registration roller 2 before delivery. Speed will increase.

  The speed difference between the registration roller 2 and the conveyor belt 3 is detected based on the change in the rotational speed of the nip roller 12 before and after the delivery, and the speed of the registration roller 2 is corrected based on the detection result. Therefore, the linear velocity of the paper 1 (paper moving speed) and the linear velocity of the conveying surface 11 of the conveying belt 3 (belt driving speed of the conveying belt 3) can be matched.

  In other words, if there is a sufficient speed so that the rotation speed of the registration roller 2 is faster than the conveying belt driving speed even if there is a component tolerance, the “nip / driving roller speed after delivery when the paper is weak” In the case of “ratio”, there is no change in the rotational speed of the nip roller 12 before and after the delivery ((a) to (b) in FIG. 3), so that the paper tarmi is formed with almost no change in the rotational speed of the registration roller 2. Paper can be passed through.

  On the other hand, in the case of “nip / drive roller speed ratio after delivery for stiff paper”, the speed of the nip roller 12 increases before and after delivery ((a) to (c) in FIG. 3) as it is. However, as indicated by (d) in FIG. 3, the rotational speed of the registration roller 2 can be adjusted to the conveyance belt drive speed by reducing the speed of the registration roller 2 correspondingly.

  Such measurement of the difference in speed ratio and correction of the sheet moving speed of the registration roller 2 (or the belt driving speed of the driving roller 5) according to the measurement result are performed before the sheet 1 reaches the image forming means 7. By doing so, suitable printing can be realized by combining the speed of the conveying belt 3 and the speed of the paper 1.

  As shown by (e) in FIG. 3, when the speed of the registration roller 2 and the belt driving speed are the same, the nip roller / driving roller speed ratio does not change before and after the delivery of the paper 1.

3. Configuration of Control System of Image Forming Apparatus 20 of This Example FIG. 4 shows a configuration diagram of the control system of this example for realizing the speed control as described above.
The control device 30 is a CPU, DSP, ASIC, or the like that can perform motor control according to a signal, and also has functions such as a timer and storage means. The motors constituting the conveyor belt driving unit 22 and the registration roller driving unit 21 are feedback-controlled by the control device 30. That is, the belt drive motor encoder 26 and the registration roller encoder 27 measure the speed, and the measurement result is input to the control device 30 to perform arithmetic processing. The control device 30 performs the conveyance belt drive circuit 31 and the registration roller drive circuit. The motor driving voltage and current are varied via 32 to drive the motors constituting the conveyor belt driving means 22 and the registration roller driving means 21. The belt drive motor encoder 26 can be substituted for the drive roller encoder 23 as shown in FIG.

  Further, the sheet moving speed (or transport amount) in the registration roller 2 can be measured by a signal (number of pulses) from the registration roller encoder 27, and the control device 30 determines whether or not the sheet 1 has reached the nip roller 12. It is possible to detect whether the speed measurement by the nip roller encoder 24 is before or after the paper arrives (before and after the delivery).

  However, a sensor (not shown) may be provided in the vicinity of the nip roller 12 to detect before and after the delivery of the paper 1, and immediately after the paper 1 reaches the nip roller 12, as shown in FIG. Since the rotational speed of the sheet 1 vibrates and the speed fluctuation becomes severe, the timing before and after the delivery of the paper 1 may be detected by the timing at which the speed fluctuation becomes severe.

4). Description of Parts Corresponding to Configurations of Claims in Image Forming Apparatus 20 of This Example (1) Configurations of Example of Corresponding to Claim 1 Note that in the image forming apparatus 20 of this example, the nip roller 12 and the like Although the effect can be obtained even if the conveying belt driving speed by the conveying belt driving means 22 is varied in accordance with the speed difference detected in step 1, the speed of the conveying belt 3 on which printing is performed is as practical as possible. It is more preferable that the sheet moving speed is changed by the fixing and the control of the registration roller driving means 21.

(2) Concerning Configuration of This Example Corresponding to Claim 2 In addition to the combination of the nip roller 12 and the nip roller encoder 24, the speed difference detecting means is a laser that is a laser reflection type speed measuring device utilizing the Doppler phenomenon. A Doppler meter, a CCD that is a device that captures a specific range as an image at regular intervals, and measures a moving distance and a speed by changing the density (characteristic) of the image can also be used. However, if these devices are used, the cost of the device is increased and erroneous detection is caused by paper dust adhering to the lens. Therefore, it is more preferable that the nip roller encoder 24 is attached to the nip roller 12 as the speed difference detecting means. Further, since the nip roller 12 as the speed difference detecting means preferably has a high surface friction, it is preferable to use a rubber having a high surface friction, a grid roller having fine irregularities formed by particles or processing on the surface, and the like.

(3) About the configuration of this example corresponding to claim 3 Further, when the nip roller 12 is used as the speed difference detecting means as described above, the nip roller 12 may be provided eccentrically. In the speed measured by the nip roller encoder 24 as the speed difference detecting means, speed unevenness occurs every cycle of the roller. Further, since minute speed unevenness also occurs due to vibration or the like, the measurement of the speed difference detecting means 12 and 24 as described in claim 3 is effected by speed unevenness by performing for one or more rotations of the roller. It is desirable to reduce

(4) Concerning Configuration of This Example Corresponding to Claim 4 In the image forming apparatus 20 of this example, the conveying belt driving speed by the conveying belt driving means 22 is varied in accordance with the speed difference detected by the nip roller 12 or the like. However, as a speed difference to be actually detected, a speed ratio between the belt driving speed of the transport belt 3 and the belt moving speed and a speed ratio between the belt driving speed of the transport belt 3 and the paper moving speed are as follows. Used.

  That is, in the image forming apparatus 20 of the present example, it is desirable that the speed of the transport belt 3 is constant, but there may be some variation depending on the load of the paper transport and the performance of the driving unit. If the fluctuation does not affect the quality required for image formation, a speed difference obtained directly from the two speeds detected by the speed detecting means may be used. It is more desirable to make the rotation speed of the roller 2 variable.

(5) Configuration of this example corresponding to claim 5 In this example, in the configuration of the image forming apparatus 20, as described with reference to FIG. The conveyor belt 3 is arranged at a position away from the contact portion between the conveyor belt 3 and the driven roller 4 that is wound in a curved manner. However, such an arrangement provides the following advantages.
That is, as shown in FIG. 5, the surface speed of the conveyor belt 3 varies depending on the location due to the thickness and expansion / contraction of the conveyor belt 3. In FIG. 5, the speed v1 of the outer peripheral surface of the transport belt 3 on the driven roller 4 tends to be higher than the speed of the transport surface 11 of the transport belt 3 (the speed of the outer peripheral surface of the transport belt 3) v3. It is desirable that the speed of the paper 1 (paper moving speed) sent from the registration roller 2 coincides with v3.

  As shown in FIG. 5, if the nip roller 12 serving as a speed difference detecting means used for speed difference measurement is arranged immediately above the axis of the driven roller 4 of the conveyor belt 3, it is affected by v1 when the belt moving speed is measured. End up. Therefore, the speed difference measurement by the nip roller 12 is performed by disposing the nip roller 12 at a position shifted from the contact point between the driven roller 4 wound around the conveyor belt 3 and the conveyor belt 3 to the downstream side (right direction indicated by a white arrow in the drawing). It is desirable to do. Further, when a roller such as the nip roller 12 is used for speed difference measurement, the conveyance belt 11 is maintained so that the conveyance surface 11 of the conveyance belt 3 can be kept flat (the conveyance surface 11 of the conveyance belt 3 is not sunk by the nip roller 12). It is desirable to dispose the supporting roller 25 also below the 3.

(6) About the configuration of this example corresponding to claim 6 Further, as shown in FIG. 3, the speed of the registration roller 2 is made lower than the speed of the transport surface 11 of the transport belt 3, so that the waist is weak. For plain paper, the speed correction is not required (line (b)), and for thick paper, which is stiff, the speed correction does not accelerate but only decelerates (line (c)). Therefore, the control is simplified if the setting is such that the registration roller 2 side becomes faster even if component tolerance or slip occurs.

(7) Configuration of this Example Corresponding to Claim 7 In this example, in the configuration of the above-described control system, the registration roller driving means 21 of the registration roller driving means 21 according to the speed difference detected by the nip roller 12 or the like as speed difference detecting means. A new set speed is calculated and stored in the storage means in the control device 30, and the registration roller driving means 21 is driven at the changed set speed stored in the storage means after the next sheet passing. You may comprise.

  In that case, if the stored value is used every time, the trouble of correcting the speed every time can be saved, and if the value stored by performing the speed correction every time is used, the speed correction range is reduced each time. The time spent on the paper is shortened, and it is possible to cope with subtle differences for each paper.

Note that various methods such as the following 1) to 3) can be considered for clearing and using the stored values, and a corresponding effect can be obtained by using any method.
1) For the first printing start, the speed of the registration roller 2 (paper moving speed) is set to be higher than the speed of the conveying surface 11 of the conveying belt 3 (belt driving speed of the conveying belt 3), and the correction value is stored. The stored values are used for the second and subsequent sheets.
2) Only for the first sheet when the addition / replacement of the sheet 1 to the sheet tray is detected, the speed of the registration roller 2 is set to be higher than the speed of the transport surface 11 of the transport belt 3, and the correction value is stored. After that, the stored value is used.
3) Speed correction is performed only at the time of printing when a predetermined time elapses, and the correction value is stored. Otherwise, the stored value is used and no speed correction is performed.

5. Effects of Image Forming Apparatus 20 of this Example As described above, according to the image forming apparatus 20 of this example, there is no need to measure and set the waist strength of the paper 1 in advance, and machine variations and the like are preliminarily determined. There is no need to measure and store, and it is not necessary to increase the distance between the registration roller 2 and the image forming means 7 so that the sheet 1 does not receive the force from the registration roller 2 during image formation. It can cope with slight fluctuations in the belt drive speed without any problem, and automatically responds to the stiffness of the paper 1 with a compact configuration and the same control and setting, and the paper conveyance speed is adjusted to the image forming means 7 by the paper 1. Since correction can be made before reaching the printing position, there is an effect that it is possible to realize suitable printing by matching the printing position, and the effect is particularly great in multi-color printing and full-color printing.

FIG. 1 is a configuration diagram of an image forming apparatus 20 according to an embodiment of the present invention. FIG. 2 is a graph showing changes in rotational speeds of the registration roller 2 and the nip roller 12 before and after the sheet 1 is transferred from the registration roller 2 to the conveyance belt 3 in the image forming apparatus 20 according to the embodiment of the present invention. FIG. FIG. 3 is a graph showing a speed ratio (vertical axis) between the nip roller 12 and the driving roller 5 according to a speed ratio (horizontal axis) between the registration roller 2 and the driving roller 5 before paper delivery. FIG. 4 is a block diagram illustrating a configuration of a control system of the image forming apparatus 20 according to the embodiment of the present invention. FIG. 5 is an enlarged cross-sectional view in the vicinity of the driven roller 4 of the conveyance belt 3 in this example, and is a diagram for explaining a preferred position of the nip roller 12. FIG. 6 is a configuration diagram of the image forming apparatus 20 proposed by the applicant of the present application.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Paper 2 Registration roller 3 Conveyance belt 4 Driven roller 5 Drive roller 6 Tension roller 7 Image forming means 8 Separation claw 9 Paper discharge part 10 Discharge tray 11 Conveyance surface 12 Nip roller as speed difference detection means 20 Image forming apparatus 21 Registration roller drive Means 22 Conveying belt driving means 23 Driving roller encoder as conveying belt driving speed detecting means 24 Nip roller encoder as speed difference detecting means 25 Supporting roller 26 Belt driving motor encoder 27 Registration roller encoder 30 Controller 31 Conveying belt driving circuit 32 Resist Roller drive circuit

Claims (7)

A registration roller for conveying paper, a registration roller driving means for driving the registration roller,
A conveying belt for conveying the sheet conveyed from the registration roller further downstream;
A conveyor belt driving means for driving the conveyor belt;
A conveyor belt drive speed detecting means for detecting a belt drive speed of the conveyor belt;
Image forming means for forming an image on the paper on the conveyor belt at a printing timing corresponding to the belt driving speed detected by the conveyor belt driving speed detecting means;
By detecting both the belt movement speed before the sheet is conveyed from the registration roller and the sheet movement speed of the sheet conveyed from the registration roller, the belt movement speed and the sheet movement speed are detected. A speed difference detecting means for detecting a speed difference is provided,
An image forming apparatus, wherein a setting speed of at least one of the registration roller driving unit and the conveying belt driving unit is changed according to the speed difference detected by the speed difference detecting unit. The image forming apparatus according to claim 1, wherein the speed difference detecting unit includes a roller that rotates in contact with a conveyance surface of the conveyance belt. The image forming apparatus according to claim 2, wherein the speed difference detecting unit calculates the speed difference using a speed measurement value when the roller makes at least one rotation. The speed difference detected by the speed difference detecting means is a speed ratio between the belt driving speed and the belt moving speed, and a difference between the belt driving speed and the speed ratio between the paper moving speeds. The sheet moving speed and the belt driving speed are made to coincide with each other by changing a setting speed of at least one of the registration roller driving means and the conveying belt driving means according to the above. 3. The image forming apparatus according to 3. 2. The speed difference detecting unit detects a surface of the conveyor belt at a position away from a contact portion between a roller on which the conveyor belt is curved and wound and the conveyor belt. 5. The image forming apparatus according to 4. Before the setting speed of at least one of the registration roller driving unit and the conveyance belt driving unit is changed according to the detection result of the speed difference detection unit, the registration roller is driven at a higher speed than the conveyance belt. The image forming apparatus according to claim 1. Storage means for storing a set speed changed in at least one of the registration roller driving means and the conveying belt driving means in accordance with the speed difference detected by the speed difference detecting means;
7. After the next sheet is passed, at least one of the registration roller driving unit and the conveying belt driving unit is driven at the changed set speed stored in the storage unit. Image forming apparatus.

Images