JP4937023B2 - Sheet transport device - Google Patents

Description

  The present invention relates to a sheet conveying apparatus that conveys a sheet by electrostatic adsorption, and is used particularly in an image forming apparatus that forms an image by ejecting ink onto a sheet by a print head, and the sheet is held on a belt by electrostatic adsorption. The present invention relates to an electrostatic attraction type sheet conveying apparatus capable of producing a great effect in a sheet conveying apparatus having a function of conveying along a print head. In addition, in this application, a sheet shall mean a sheet-like printing medium, for example, a printing paper, a film, the sheet-like material wound by roll shape, cloth, etc.

  In an image forming apparatus that forms an image by discharging aqueous ink from a print head onto a sheet of paper, the paper on which the ink has been transferred swells and causes cockling. When double-sided printing or the like is performed by re-feeding such a sheet, the leading edge of the sheet may be lifted, and there is a high possibility that the sheet will collide with rollers or a print head on the conveyance path and cause a conveyance jam. .

  In order to solve such a problem, as a sheet conveying device used in the image forming apparatus as described above, it is considered effective to apply the principle of electrostatic attraction. A sheet conveying means as described in the above items 3 to 3 is known.

  As shown in FIGS. 4 to 5, the sheet conveying means disclosed in Patent Document 1 includes a pair of comb-like electrodes 100 and 101 that are nested together and connected to positive and negative potentials, respectively. The conveyance belt 102 made of a dielectric is configured to move above the electrodes. The conveying belt 102 is polarized by the positively or negatively charged comb-like electrodes 100 and 101 below the surface and charged, whereby the paper P on the conveying belt 102 can be adsorbed and conveyed.

  As shown in FIGS. 6 to 7, the sheet conveying means disclosed in Patent Document 2 has an electrode 202 embedded in a conveying belt 201. These electrodes 202 constitute a plurality of independent rectangular electrode groups whose longitudinal direction is a direction intersecting the transport direction, and are led out to both edges of the transport belt 201 alternately in the transport direction. The positive and negative brush-like charging members respectively disposed along both edges of the conveying belt 201 are alternately charged positively or negatively in the conveying direction. Can be sucked and conveyed.

As shown in FIG. 8, in the sheet conveying means disclosed in Patent Document 3, a charging roller 303 connected to an AC power source 302 is rotatably contacted to the lower surface of a conveying belt 301 made of an insulating material. The conveying belt 301 is alternately charged positively or negatively in the conveying direction, whereby the sheet on the conveying belt 301 can be adsorbed and conveyed.
JP 2004-90533 A JP 2000-247476 A JP 2003-103857 A

  However, according to the sheet conveying means of the comb electrode fixed type described in Patent Document 1, there is a problem that the conveying belt 102 is attracted to the comb electrodes 100 and 101, so that the conveying load is large and the power consumption increases. . Further, since the comb-like electrodes 100 and 101 charged alternately with positive and negative are fixed and the conveyor belt 102 moves with respect thereto, the comb-like electrodes 100 and 101 are moved as shown in FIG. Each positive or negative charged portion of the conveyor belt 102 polarized according to the potentials of the tooth-shaped electrodes 100 and 101 is adjacent to the comb-tooth shape by the movement of the conveyor belt 102 as schematically shown in FIG. The electrode 100, 101 is instantaneously opposed to a negative or positive potential, and a repulsive force is temporarily generated between the conveyor belt 102 and the comb-like electrodes 100, 101, which causes a resistance to the conveyance. End up. In this way, according to this sheet conveying means, the suction force is not stable, so the conveying speed of the conveying belt 102 is not stable, and if expressed in extreme terms, the movement mode of the conveying belt 102 becomes intermittent, and printing There was a problem that the print quality of the image deteriorated.

  According to the electrode belt-embedded sheet conveying means described in Patent Document 2, the conveying belt 201 is wound around a roller, but is also incorporated at a portion where the conveying belt 201 is bent by the roller. Since the electrode 202 itself does not bend, there is a problem that the conveyor belt 201 is easily deteriorated due to a large load. There is also a problem that the movement of the conveyor belt 201 becomes intermittent for the same reason as pointed out in the technique described in Patent Document 1. Further, since the conveyance belt 201 has a structure in which the electrode 202 is built in, the thickness of the conveyance belt 201 is relatively larger than that of the sheet conveyance means having other structures, and therefore, unevenness in thickness occurs particularly in the roller portion. As a result, the distance from the roller center to the surface of the conveyor belt 201 varies, and the conveyance speed on the surface of the conveyor belt 201 fluctuates. There is also a problem that the manufacturing process becomes complicated because the electrode 202 is built in the conveyor belt 201. Furthermore, there is a problem that the means (such as the brush-shaped charging member described above) for applying a voltage to the built-in electrode 202 from the outside of the conveyor belt 201 is complicated.

  According to the charging roller type sheet conveying means described in Patent Document 3, since the conveying belt 301 is charged by the charging roller 303, the conveying belt 301 charged by the charging roller 303 is adjacent immediately after leaving the charging roller 303. Since positive and negative charges start to cancel and disappear due to leakage, there is a problem that sufficient adsorption force may not be obtained in the case of long-distance conveyance or when the humidity is high. To cope with this problem, it is conceivable to increase the number of charging rollers 303 in contact with the conveying belt 301. However, simply increasing the number of charging rollers 303 cannot avoid an increase in cost, and a plurality of charging rollers 303 are arranged. However, since there is a high possibility that the printing surface of the paper is soiled, it cannot be arranged on the printing surface, and there is a problem that the actual roller arrangement is difficult. Furthermore, in the system in which the conveying belt 301 is charged by the charging roller 303, there is a problem that it is difficult to make the adsorption force locally variable.

  The present invention has been made in view of the above problems, and is used in a sheet conveying apparatus that conveys a sheet by electrostatic attraction, and in particular, an image forming apparatus that forms an image by ejecting ink onto a sheet with a print head. In a sheet conveying device that electrostatically adsorbs a sheet to a belt and conveys it along a print head, it is possible to realize a stable adsorption force and conveyance speed with a simple structure, hardly affected by humidity, and ink droplets due to the influence of an electric field Bends are unlikely to occur, and the power consumption is low due to a small transport load. The motor can be reduced in cost, and the potential is applied only to the minimum electrodes necessary for electrostatic adsorption of paper. An object of the present invention is to provide a sheet conveying apparatus that consumes less power even when there is no point.

The sheet conveying apparatus according to claim 1 is:
In a sheet conveying apparatus that conveys a sheet,
A dielectric layer is provided on the surface on the side where the sheet is conveyed, and a plurality of independent fixed electrodes that are arranged in the conveying direction of the sheet at intervals and are selectively given a first potential;
Driven by circulating in the sheet conveying direction relative to the dielectric layer of the fixed electrode, a second electric potential is applied, and a plurality of through holes through which lines of electric force from the fixed electrode pass are formed, and A transport belt made of a conductor on which a sheet is electrostatically adsorbed on the surface opposite to the fixed electrode;
Sheet position detecting means for detecting the position of the sheet on the conveyor belt;
A power supply device that selectively applies a first potential to the fixed electrode at a position corresponding to the position of the sheet detected by the sheet position detecting means;
It is characterized by having.

The sheet conveying apparatus according to claim 2 is:
In a sheet conveying device that is provided in an image forming apparatus that forms an image on a sheet by discharging ink from a plurality of print heads arranged at intervals to the sheet, and in which the sheet is conveyed along the print head,
A dielectric layer is provided on the surface on the side where the sheet is conveyed, and a plurality of independent fixed electrodes that are arranged in the conveying direction of the sheet at intervals and are selectively given a first potential;
Driven by circulating in the sheet conveying direction relative to the dielectric layer of the fixed electrode, a second electric potential is applied, and a plurality of through holes through which electric lines of force from the fixed electrode pass are formed , A transport belt made of a conductor on which a sheet is electrostatically adsorbed on the surface on the print head side opposite to the fixed electrode side ;
Sheet position detecting means for detecting the position of the sheet on the conveyor belt;
A power supply device that selectively applies a first potential to the fixed electrode at a position corresponding to the position of the sheet detected by the sheet position detecting means;
It is characterized by having.

The sheet conveying apparatus according to claim 3 is the sheet conveying apparatus according to claim 2 ,
The plurality of fixed electrodes are arranged at positions that do not face the print heads.

The sheet conveying apparatus according to claim 4 is the sheet conveying apparatus according to any one of claims 1 to 3,
The sheet position detecting means is provided at the entrance of the conveyor belt and detects the leading edge of the fed sheet, and the conveyor belt movement is provided on the conveyor belt and detects the amount of movement of the conveyor belt. It is constituted by an amount detection means, and a control means for calculating the position of the sheet on the conveyance belt by a signal from the sheet leading edge detection sensor and a signal from the conveyance belt movement amount detection means. .

The sheet conveying apparatus according to claim 5 is the sheet conveying apparatus according to any one of claims 1 to 3,
The sheet position detection means is provided at the entrance of the transport belt to detect the front end of the fed sheet, a signal from the sheet front end detection sensor, and a predetermined transport speed of the transport belt And a control means for calculating the position of the sheet on the conveyor belt.

The sheet conveying apparatus according to claim 6 is the sheet conveying apparatus according to any one of claims 1 to 3,
The sheet position detection means is a plurality of sheet detection sensors provided in the vicinity of each fixed electrode,
Control means for driving the power supply device to apply a first potential to each of the fixed electrodes corresponding to the sheet leading edge detection sensor while the sheet conveyed by the conveyance belt is detected by the sheet detection sensor. Is further provided.

The sheet conveying apparatus according to claim 7 is the sheet conveying apparatus according to any one of claims 1 to 3,
In the plurality of fixed electrodes existing below the sheet detected by the sheet position detecting means, the first potential is applied to the fixed electrodes on both sides sandwiching one or more fixed electrodes that do not apply the first potential. .

The sheet conveying apparatus according to claim 8 is the sheet conveying apparatus according to any one of claims 1 to 3,
The first potential is also applied to the fixed electrode that is adjacent to the fixed electrode that is the furthest in the sheet conveyance direction among the fixed electrodes that are in the position corresponding to the sheet and that is not in the position corresponding to the sheet It is characterized by doing.

  According to the sheet conveying apparatus described in claim 1, when the first potential is a positive potential and the second potential is 0 or a negative potential, 0 or a negative potential is always applied to the conveyance belt. However, the fixed electrode to which a positive potential is applied is only the fixed electrode at a position opposite to the sheet detected by the sheet position detecting means among the plurality of fixed electrodes. In the fixed electrode to which the first potential is applied, the dielectric layer is polarized by the positive potential and generates a positive charge on the surface thereof, and the electric lines of force thereby carry the zero or negative potential. Of the through-holes in the belt, it passes through the through-holes directly above the fixed electrode and reaches and penetrates the sheet placed on the surface of the conveyor belt, and polarizes it to generate positive and negative charges on the front and back surfaces. Therefore, the sheet is electrostatically adsorbed to the conveyance belt at or around the through hole portion adjacent to the fixed electrode of the conveyance belt. If the conveyance belt is moved along the fixed electrode, the fixed electrode that generates an adsorption force is also moved along with the movement of the sheet, and the sheet is conveyed while being electrostatically adsorbed on the conveyance belt.

  In this way, it is easy to apply a voltage to each electrode while having a simple structure, and it is possible to realize a stable suction force and a stable transport speed without unevenness, and a load on the transport belt can be reduced. It is possible to realize a sheet conveying apparatus that is not easily affected. Furthermore, since the electrodes are divided in the sheet conveyance direction, there is an effect that the conveyance load is reduced. Furthermore, the power consumption can be reduced in that the potential is applied only to the minimum fixed electrodes necessary for electrostatic attraction of the paper.

  According to the sheet conveying apparatus described in claim 2, in addition to obtaining the same effect as that of the invention according to claim 1, the conveying belt that adsorbs the sheet moves while being adsorbed to the fixed electrode. Since the sheet is conveyed, the distance between the print head and the sheet can be kept constant in the image forming apparatus, thereby obtaining the effect of improving the print quality.

  According to the sheet conveying device of the third aspect, each fixed electrode that is divided into a plurality of pieces and independently driven is disposed at a position that is not opposed to each print head, and therefore is ejected from the print head. The ink droplet is not affected by the electric field generated by the fixed electrode, and the flight bend does not occur.

As described above, according to the first to third aspects of the invention, the following effects (1) to (4) can be obtained.
(1) Simple structure It is a simple configuration in which the conveyor belt as the movable electrode of the second potential moves with respect to the fixed electrode of the first potential, and each electrode is independent, so that it is easy to assemble and manufacture. This is advantageous in terms of cost compared to a conventional electrostatic attraction type sheet conveying apparatus using comb-like electrodes or the like. Further, the positive and negative electrodes are arranged in a vertical relationship, and it is easy to set the interval between the two electrodes that determine the attractive force more easily and precisely.

(2) Easy application of voltage to each electrode For the wiring connected to each fixed electrode, the sheet position is detected by the sheet position detection means. A voltage can be applied only to a certain fixed electrode, and a voltage can be applied to a conductive conveyance belt, which is a movable electrode, by a roller connected to a predetermined potential, for example.

(3) Reduction of uneven transport speed Since the two types of positive and negative electrodes are divided into a fixed electrode and a transport belt as a movable electrode, the conventional electrostatic adsorption transport device with the built-in electrode in the transport belt is used. In comparison, since the thickness of the transport belt itself is small and there are few surface irregularities, it is possible to reduce uneven thickness, reduce uneven transport speed, and obtain good print image quality.

  Furthermore, there is no intermittent conveyance operation unlike the conventional electrostatic attraction type sheet conveyance device using a comb-like electrode or the like in which positive and negative electrodes are alternately arranged, and the conveyance belt moves smoothly. Therefore, it is possible to obtain good print image quality in this respect.

(4) Reduction of the load on the conveyor belt Since the through hole is formed in the conveyor belt as a movable electrode that moves relative to the fixed electrode, the contact area between both electrodes is reduced and the conveyor load is reduced.

  According to the sheet conveying apparatus described in claim 4, in the effect of the sheet conveying apparatus according to any one of claims 1 to 3, the sheet leading edge detection sensor detects the leading edge of the sheet, and from that time By detecting the moving amount of the conveying belt by the conveying belt moving amount detecting means, the current position of the sheet can be accurately detected. Thus, a positive potential can be applied only to the fixed electrode that is actually located at a position corresponding to the sheet among the plurality of fixed electrodes, and the sheet is attracted to the transport belt and transported.

  According to the sheet conveying apparatus described in claim 5, since the moving speed of the conveying belt is constant in the effect of the sheet conveying apparatus according to any one of claims 1 to 3, the sheet leading edge detection sensor If the leading edge of the sheet is detected, the current position of the sheet can be accurately detected based on the elapsed time from that point. Thus, a positive potential can be applied only to the fixed electrode that is actually located at a position corresponding to the sheet among the plurality of fixed electrodes, and the sheet is attracted to the transport belt and transported.

  According to the sheet conveying device described in claim 6, in the effect of the sheet conveying device according to any one of claims 1 to 3, in the vicinity of each fixed electrode as the sheet moves by the conveying belt. When each sheet detection sensor detects the leading edge of the sheet, the first potential is applied to the fixed electrode, so that the sheet is adsorbed to the conveyance belt and conveyed.

  According to the sheet conveying apparatus described in claim 7, in the effect of the sheet conveying apparatus according to any one of claims 1 to 3, the first potential is applied to all the fixed electrodes corresponding to the sheet. If the first potential is applied to both sides of the fixed electrode that does not apply the first potential instead of contributing to the adsorption of the sheet, at least there is no major problem in the conveyance of the sheet by the conveyance belt, and the power consumption is further reduced. can do.

  According to the sheet conveying apparatus described in claim 8, in the effect of the sheet conveying apparatus according to any one of claims 1 to 3, the position further advanced in the conveying direction from the leading edge of the conveyed sheet Since the first potential is also applied to the fixed electrode located in the sheet, the sheet can be sucked and conveyed by the conveying belt more smoothly.

1. First Embodiment An electrostatic attraction type sheet conveying apparatus 1 according to an embodiment of the present invention and an image forming apparatus 2 including the same will be described in detail with reference to FIGS. 1 to 3.
As shown in FIG. 1, in the image forming apparatus 2 of this example, a plurality of print heads 3 having different ink colors are arranged downward at a predetermined interval along the conveyance direction of the sheet S indicated by an arrow. The ink droplets can be ejected toward the sheet S conveyed below. In the example shown in the figure, four print heads 3 for ejecting inks of four colors of C (cyan), K (black), M (magenta), and Y (yellow) are installed.

  A sheet conveying apparatus 1 for conveying the sheet S along the print head 3 is disposed immediately below the print heads 3. First, a registration roller 4 and a driven roller 5 are provided adjacent to a sheet feeding mechanism (not shown) on the front side of the print head 3 in the conveyance direction, and the sheet S is supplied to the next sheet conveyance apparatus 1. ing.

  The sheet conveying apparatus 1 is disposed below the intermediate roller between the driven roller 6 on the upstream side in the conveying direction, the driving roller 8 provided on the downstream side in the conveying direction and interlocked to the driving source 7, and the driven roller 6 and the driving roller 8. The endless transport belt 10 is wound around the tension roller 9 and the transport belt 10 is circulated in the transport direction by the driving roller 8 while applying an appropriate tension to the transport belt 10 by the tension roller 9 biased downward. And can be moved. Of the conveyor belt 10 that is moved around the rollers 6, 8, and 9, a portion that moves horizontally adjacent to the print head 3 is a conveyance path of the sheet S.

  As shown in FIG. 2, the conveyor belt 10 is composed of a conductor 11 on the inner side (lower side in the drawing in contact with the driven roller 6), and a dielectric layer 12 is provided on the outer side (upper side in the drawing facing the print head 3). A two-layer structure is obtained. The dielectric 12 is a substance having a dielectric property superior to a conductivity and having an insulation property against a direct current, and examples thereof include a plastic.

  As shown in FIG. 2, the conductor 11 and the dielectric layer 12 are formed with a plurality of circular holes with the same inner diameter that pass through continuously at appropriate intervals. As will be described later, these through holes are formed in order to form an electric field in and around the sheet S on the transport belt 10. The holes of the dielectric layer 12 communicating with the through holes 13 are referred to as openings 14.

  The driven roller 6 has a conductive surface at least on its peripheral surface, and the peripheral surface is given a zero potential by grounding as shown in FIG. The device is connected to a high voltage power source 51 (power source device) controlled by means) and given a predetermined negative potential. Accordingly, the conductor 11 of the conveyor belt 10 that contacts the driven roller 6 is at 0 (ground) or a negative potential. That is, the conveyance belt 10 of this example is a movable electrode having 0 or a negative potential.

As shown in FIG. 1, a rectangular plate-like platen base 15 that supports the conveyance belt 10 is installed below the conveyance belt 10 in the conveyance path of the sheet S. The platen base 15 is made of an insulator, and a plurality (five in this example) of fixed electrodes 16 to which a positive potential is applied by being connected to a high voltage power supply 51 are embedded and installed at predetermined intervals. The fixed electrode 16 has a position not facing the print head 3, specifically, a position in front of the print head 3 (C) that is most upstream in the transport direction, and the four print heads 3 (C, K, M , Y) are arranged at three positions corresponding to the position of the print head 3 (Y) that is most downstream in the transport direction. As shown in FIG. 2, a dielectric layer 17 is provided on the surface of each fixed electrode 16 in order to prevent a short circuit due to contact with the transport belt 10.
In FIG. 2, the platen base 15 is not shown for convenience, and the function of the control device 50 that selectively applies the positive voltage of the high-voltage power supply 51 to each fixed electrode 16 is shown as a switch element.

  In the plurality of fixed electrodes 16, not all the fixed electrodes 16 are simultaneously given a positive potential. Each fixed electrode 16 is configured to selectively apply a positive potential individually. That is, as shown in FIG. 1, each fixed electrode 16 is connected to a high voltage power supply 51 by separate wiring, and when the high voltage power supply 51 is driven by the control device 50, each fixed electrode 16 is positively connected. Can be selectively applied. According to this example, by grasping the position of the sheet S conveyed by the conveyance belt 10, a positive potential is applied only to the fixed electrode 16 at the position corresponding to the sheet S, and the sheet S is conveyed to the conveyance belt 10. Can be efficiently adsorbed and held.

  In order to grasp the position of the sheet S conveyed by the conveying belt 10, the sheet conveying apparatus of the present example includes a sheet position detecting apparatus. The sheet position detecting device includes a sheet leading end detection sensor 20 that detects the leading end of the sheet S that is provided at the entrance of the conveying belt 10 and that is fed, an encoder (not shown) that is provided on the driving roller 8 of the conveying belt 10, and a sheet leading end. It has the control apparatus 51 which processes the signal sent from the detection sensor 20 and the encoder. The encoder functions as a conveyance belt movement amount detection unit that detects the movement amount of the conveyance belt 10 by detecting the rotation amount of the driving roller 8. The control device 51 calculates the position of the sheet S on the conveyance belt 10 based on the signal from the sheet leading edge detection sensor 20 and the encoder information (signal) from the encoder. Then, the control device 51 drives the high-voltage power supply 51 so as to apply a positive potential only to the fixed electrode 16 at a position corresponding to the calculated position of the sheet S (in this example, below the sheet S). can do.

Next, the principle of sheet suction in the above configuration will be described.
In FIG. 2 schematically showing the principle of sheet adsorption, the transport belt 10 is always given a potential of 0, but the fixed electrode 16 to which a positive potential is applied is applied to the sheet S among the plurality of fixed electrodes 16. Only the fixed electrodes 16 at the opposite positions. In the fixed electrode 16, the dielectric layer 17 is polarized by a given positive potential, and the surface thereof becomes a positive potential. Therefore, the electric lines of force from the fixed electrode 16 side are conveyed immediately above the fixed electrode 16. The belt 10 passes through the hole (through hole 13 and opening 14) through which the belt 10 penetrates and goes above the conveying belt 10, and passes through the sheet S placed on the surface of the conveying belt 10 from below to polarize it. The lines of electric force bend downward and penetrate the sheet S from above around the holes 13 and 14 of the conveyor belt 10 and polarize it to the opposite potential. Furthermore, the electric lines of force reach and penetrate the dielectric layer 12 of the conveyor belt 10 and polarize it.

As a result, as shown in FIG. 2, positive and negative charges opposite to each other are generated on the front and back surfaces of the sheet S and the dielectric layer 12, so that they are in a range adjacent to the fixed electrode 16 to which a positive potential is applied. The sheet S is electrostatically adsorbed to the dielectric layer 12 of the conveyance belt 10 in the vicinity of the through holes 13 and 14 of the conveyance belt 10 and the periphery thereof.
As shown in FIG. 2, such a phenomenon of dielectric polarization does not occur in the fixed electrode 16 to which a positive potential is not applied, and there is no sheet S to be adsorbed.

Next, the conveying operation of the sheet S based on the principle of sheet adsorption described above will be described.
In FIG. 1, when the sheet S passes between the registration roller 4 and the driven roller 5 and is fed to the conveyance start position of the conveyance belt 10, the sheet leading edge detection sensor 20 detects the leading edge of the sheet S and controls the detection signal. Send to device 50. Here, the control device 50 drives the drive source 7 to drive the conveyor belt 10, but the rotation state of the drive roller 8 that is rotated by the drive source 7 to move the conveyor belt 10 is determined by an encoder (not shown). It is detected and sent to the control device 50 as encoder information. Then, the control device 50 determines the amount of movement of the sheet S placed on the conveyance belt 10 from the timing at which the sheet leading edge detection sensor 20 provided at a predetermined position detects the leading edge of the sheet S and the amount of rotation of the driving roller thereafter. To calculate the current position. Based on the recognized position of the sheet S, the control device 50 drives and controls the high voltage power source 51 so as to apply a positive potential only to the fixed electrode 16 under the sheet S.

  FIG. 3 corresponds to the movement of the sheet S accompanying the movement of the conveying belt 10, and the fixed electrode 16 immediately below the moving sheet S is turned ON (a positive potential is applied), and the fixed electrode 16 that is not directly below the sheet S. FIG. 4 illustrates a state in which the sheet S is attracted to the transport belt 10 and transported by the control in which is turned off (a positive potential is not applied).

  First, in FIG. 1, the sheet S passes through the sheet leading edge detection sensor 20, is placed on the conveyance belt 10, and is sent to the destination by the movement of the conveyance belt 10. When the leading edge of the sheet S reaches the first fixed electrode 16 among the plurality of fixed electrodes 16, the control device 50 applies a positive potential to the fixed electrode 16 at that timing. The leading edge of the sheet S is adsorbed and held by the conveyance belt 10 according to the principle described above.

  Then, as shown in FIG. 3A, when the conveying belt 10 and the sheet S adsorbed thereto move and cover one after another on the fixed electrodes 16 arranged side by side, the control device 50 at that timing, A positive potential is sequentially applied to each fixed electrode 16 under the sheet S. The sheet S is conveyed while being adsorbed and fixed to the conveyance belt 10 in order from the leading edge at each position facing each fixed electrode 16.

  As shown in FIG. 3B, when the sheet S moves while being attracted and held by the conveying belt 10, the rear portion of the sheet S passes through the fixed electrode 16 through which the front end of the sheet S has passed first. Accordingly, the fixed electrodes 16 are not opposed to the sheet S, and the control device 50 sequentially turns off the positive potential applied to the fixed electrodes 16 in synchronization with the passage of the sheet S.

  Although not shown, when the sheet S moves while being attracted and held by the conveyance belt 10, the leading end portion of the sheet S passes through the last fixed electrode 16 in the conveyance direction so that there is no fixed electrode 16. Since the sheet is moved, the adsorption force by the fixed electrode 16 cannot be obtained in this portion, but the sheet S is conveyed in a state where the trailing end of the sheet S is adsorbed to the conveyance belt 10, so And is discharged to a paper discharge tray (not shown).

  Thus, in the sheet conveying apparatus 1 of the present example, the conveying belt 10 moves along the plurality of fixed electrodes 16 arranged at intervals, and each fixed electrode 16 is connected to the sheet S on the conveying belt 10. When facing each other, a predetermined potential is applied and the facing sheet S is attracted to the conveying belt 10. Therefore, if the conveying belt 10 is moved along the fixed electrode 16, the fixed electrode 16 that generates an attracting force is also moved with the movement of the sheet S, and the sheet S is electrostatically adsorbed on the conveying belt 10. The effect of being conveyed is obtained.

Next, the operation of image formation by the image forming apparatus 2 using the sheet conveying apparatus 1 of the present example described above will be described.
According to the image forming apparatus 2 of this example, the sheet S is supplied to the conveyance belt 10 driven by the driving roller 8, and the sheet S is conveyed along the conveyance direction while being sucked and held by the conveyance belt 10 as described above. If each print head 3 is driven at an appropriate timing according to the conveying speed to eject and deposit ink of each color on the sheet S, a desired color image can be formed on the sheet S. .

  According to the sheet conveying apparatus 1 of this example, although it is a simple structure, it is easy to apply a voltage to each electrode, and it is possible to realize a stable suction force and a stable conveying speed without unevenness. It is possible to realize a sheet conveying apparatus that requires less load and is not easily affected by humidity. Furthermore, since the electrodes are divided in the conveyance direction of the sheet S, there is an effect that the conveyance load is reduced, and the motor as the drive source 7 can be reduced in size by reducing the load, and the cost can be reduced. Furthermore, the power consumption can be reduced in that the potential is applied only to the minimum fixed electrode 16 necessary for electrostatic attraction of the sheet.

  According to the image forming apparatus 2 including the sheet conveying apparatus 1 of the present example, the conveying belt 10 that is a movable electrode of 0 or a negative potential moves with respect to the fixed electrode 16 to which a positive potential is applied corresponding to the sheet position. Because of this simple configuration, it is advantageous in terms of assemblability and manufacturing cost compared to a conventional electrostatic attraction type sheet conveying apparatus using comb-like electrodes. Further, the positive and negative electrodes are arranged in a vertical relationship, and it is easy to set the interval between the two electrodes that determine the attractive force more easily and precisely.

  A plurality of fixed electrodes 16 embedded in a single plate-like platen base 15 are arranged below the plurality of print heads 3, but these fixed electrodes 16 are not located immediately below the print head 3. The front and rear of each print head 3 are provided in the transport direction of the transport belt 10. Accordingly, the conveyance belt 10 on which the sheet S is placed moves under the print head 3 in a state where the sheet S is adsorbed by the two fixed electrodes 16 and 16 sandwiching the print head 3. Since the distance between the print head and the sheet S can be kept constant within the range where 3 is arranged, the print quality is improved.

  Each print head 3 is arranged so as to avoid the position of the fixed electrode 16, and there is no fixed electrode 16 below the print head 3, and ink droplets discharged downward from each print head 3 Since inconveniences such as flight bending due to an electric field are unlikely to occur, a good image quality can be obtained also in this respect.

  In addition, since the two types of positive and negative electrodes are divided into the fixed electrode 16 and the transport belt 10 as the movable electrode, as in the conventional electrostatic transport apparatus using comb-like electrodes charged alternately positive and negative Each of the positive and negative charged portions of the conveying belt polarized according to the potential of the comb-like electrode instantaneously opposes the adjacent comb-like electrode of the opposite potential due to the movement, thereby causing resistance in conveyance. There is no inconvenience, the conveyance is not intermittent, and the sheet S can be conveyed with a smooth operation. Therefore, it is possible to obtain a good print image quality also in this respect.

  Furthermore, the thickness of the conveyor belt 10 itself is small and the surface unevenness is small compared to a conventional electrostatic adsorption type conveyor device in which an electrode is incorporated in the conveyor belt. It is possible to reduce the speed unevenness and obtain a good print image quality also in this respect.

  Further, in this example, since the dielectric layer 12 is provided on the surface of the conveyor belt 10, it is possible to prevent an accident that a user accidentally touches the conductor 11 of the conveyor belt 10 during use or inspection. Can be safe. Even if the transport belt 10 does not have the dielectric layer 12, the sheet S and the dielectric layer 17 of the fixed electrode 16 facing the sheet S are polarized at opposite potentials in the portion of the hole 13 through the transport belt 10. Therefore, the electrostatic attraction force is ensured and the sheet S can be adsorbed to the conveyance belt 10.

  In this embodiment, the holes (through holes 13 and openings 14) are passed through the conveyance belt 10, but the holes are made of polyacetylene, polyparaphenylene, polyaniline, polythiophene, polypyrrole, polyacene, polyparaphenylene vinylene, or the like. A conductive polymer may be used.

  Next, other embodiments (Embodiments 2 to 5) of the present invention will be described. The same components as those in the first embodiment are referred to in the first embodiment, and are different from the first embodiment. Only the characteristic part will be mainly described. It should be noted that substantially the same effects as those of the first embodiment can be obtained by these second to fifth embodiments.

2. Second Embodiment A sheet conveying apparatus according to a second embodiment is configured to selectively apply a positive potential only to the fixed electrode 16 located at a position corresponding to the position of the sheet S. Although it is the same as that of the first embodiment in that the position needs to be detected, the configuration of the sheet position detection means is partially different from that of the first embodiment. That is, the sheet position detection means of this example has a sheet leading edge detection sensor 20 that is provided at the entrance of the conveyance belt 10 and detects the leading edge of the sheet S that is fed in. This is the same as in the first embodiment. is there. However, unlike the first embodiment, there is no rotary encoder, and the control device 50 that forms a part of the sheet position detection means conveys the signal based on the signal from the sheet leading edge detection sensor 20 and a predetermined conveyance speed of the conveyance belt 10. The position of the sheet S on the belt 10 is calculated. Even with such a configuration, the position of the sheet S can be detected, and the high voltage power supply 51 can be driven so as to apply a positive potential only to the fixed electrode 16 at the corresponding position accordingly.

3. Third Embodiment A sheet conveying apparatus according to a third embodiment is configured to selectively apply a positive potential only to the fixed electrode 16 located at a position corresponding to the position of the sheet S. Although it is the same as that of the first embodiment in that the position needs to be detected, the configuration of the sheet position detection unit is different from that of the first embodiment. That is, the sheet position detection means of this example is a plurality of sheet detection sensors provided in the vicinity of each fixed electrode 16. Further, while the sheet S conveyed by the conveyance belt 10 is detected by the sheet detection sensor, the sheet position detection unit is configured to apply a first potential to each fixed electrode 16 corresponding to the sheet detection sensor. The control device 50 as a unit is configured to drive a high voltage power supply 51. In addition, it is preferable to arrange | position each sheet | seat detection sensor in the position close | similar to the edge of the upstream of each fixed electrode 16, or a downstream. The vicinity of each fixed electrode 16 where each sheet detection sensor is installed is also the vicinity of each print head.

4). Fourth Embodiment In the first embodiment, a positive potential is applied to all the fixed electrodes 16 at positions corresponding to the position of the sheet S detected by the sheet position detecting means. That is, if there are three fixed electrodes 16 below the sheet S, a positive potential is applied to the three fixed electrodes 16 to adsorb as much area as possible of the sheet S. However, in such a case, a potential is not applied to the central fixed electrode 16, but a positive potential is applied to the two fixed electrodes 16, 16 on both sides thereof, and the portion of the sheet S facing the fixed electrode 16. Among them, even if the suction force reaches only both ends in the transport direction of the sheet S, it can be transported substantially without any problem, and the power consumption can be further reduced. That is, in the fourth embodiment, even if one or two fixed electrodes 16 that do not apply the first potential are continuously provided in the plurality of fixed electrodes 16 existing below the detected sheet S, the fixed electrodes If there are fixed electrodes 16 to which a positive potential is applied on both sides before and after sandwiching 16, the front end side and the rear end side of the sheet S are adsorbed in the conveyance direction, so that there is substantially no trouble in conveyance and power consumption is further increased It is characterized by being able to reduce.

5. Fifth Embodiment In the first embodiment, a positive potential is applied to the fixed electrode 16 below the sheet S detected by the sheet position detecting means. In this example, in addition to this, a positive potential is also given to the fixed electrode 16 that is adjacent to the front end of the sheet S in the conveyance direction of the sheet S and not originally under the sheet S. As a result, the leading edge of the sheet S can be reliably adsorbed and a more reliable transport operation can be performed without delaying the transport timing of the sheet S by the transport belt 10.

  The sheet conveying apparatuses according to the first to fifth embodiments described above are used as means for conveying the sheet S in the image forming apparatus including the print head that discharges ink to form an image on the sheet S. However, the present invention is not necessarily applied only to such an ink jet type image forming apparatus, and can be applied as, for example, a sheet conveying unit in a stencil printing apparatus, or image forming using other image forming principles. The present invention can also be applied to an apparatus or a printing apparatus, and is not limited to a sheet conveying unit of an image forming apparatus, and can be effectively used as a unit that can stably convey a sheet S corresponding to various industrial uses. Is.

1 is an overall configuration diagram of a first embodiment of the present invention. It is sectional drawing which shows the charging state etc. of each member in the conveyance belt vicinity of 1st Embodiment. It is sectional drawing which shows the principle of the sheet conveyance in 1st Embodiment. It is a top view of the comb-tooth electrode used with the conventional electrostatic conveyance type sheet conveying apparatus. It is sectional drawing which shows the charging state etc. of each member in the conveyance belt vicinity in the electrostatic conveyance type sheet | seat conveying apparatus using the conventional comb-tooth electrode. It is a front view of the conventional electrostatic conveyance type sheet conveying apparatus with a built-in electrode. It is a front view of the conventional electrostatic conveyance type sheet conveying apparatus with a built-in electrode. It is sectional drawing of the conveyance belt in the conventional electrostatic conveyance type sheet | seat conveyance apparatus with a built-in electrode. It is sectional drawing of the conveyance belt vicinity in the conventional charging roller type electrostatic conveyance type sheet conveying apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Sheet conveying apparatus 2 ... Image forming apparatus 3 ... Print head 10 ... Conveying belt 11 ... Conductor 12 ... Dielectric layer of conveying belt 13 ... Conductor through-hole 16 ... Fixed electrode 17 ... Dielectric layer of fixed electrode 20 ... Sheet tip detection sensor as sheet position detection device 50 ... Control device as control means 51 ... High voltage power supply as power supply device S ... Sheet

Claims (8)

In a sheet conveying apparatus that conveys a sheet,
A dielectric layer is provided on the surface on the side where the sheet is conveyed, and a plurality of independent fixed electrodes that are arranged in the conveying direction of the sheet at intervals and are selectively given a first potential;
Driven by circulating in the sheet conveying direction relative to the dielectric layer of the fixed electrode, a second electric potential is applied, and a plurality of through holes through which lines of electric force from the fixed electrode pass are formed, and A transport belt made of a conductor on which a sheet is electrostatically adsorbed on the surface opposite to the fixed electrode;
Sheet position detecting means for detecting the position of the sheet on the conveyor belt;
A power supply device that selectively applies a first potential to the fixed electrode at a position corresponding to the position of the sheet detected by the sheet position detecting means;
A sheet conveying apparatus comprising: In a sheet conveying device that is provided in an image forming apparatus that forms an image on a sheet by discharging ink from a plurality of print heads arranged at intervals to the sheet, and in which the sheet is conveyed along the print head,
A dielectric layer is provided on the surface on the side where the sheet is conveyed, and a plurality of independent fixed electrodes that are arranged in the conveying direction of the sheet at intervals and are selectively given a first potential;
Driven by circulating in the sheet conveying direction relative to the dielectric layer of the fixed electrode, a second electric potential is applied, and a plurality of through holes through which electric lines of force from the fixed electrode pass are formed , A transport belt made of a conductor on which a sheet is electrostatically adsorbed on the surface on the print head side opposite to the fixed electrode side ;
Sheet position detecting means for detecting the position of the sheet on the conveyor belt;
A power supply device that selectively applies a first potential to the fixed electrode at a position corresponding to the position of the sheet detected by the sheet position detecting means;
A sheet conveying apparatus comprising: The sheet conveying apparatus according to claim 2 , wherein the plurality of fixed electrodes are arranged at positions that do not face the print heads. The sheet position detecting means is provided at the entrance of the conveyor belt and detects the leading edge of the fed sheet, and the conveyor belt movement is provided on the conveyor belt and detects the amount of movement of the conveyor belt. An amount detection unit, and a control unit that calculates a position of the sheet on the conveyance belt based on a signal from the sheet leading end detection sensor and a signal from the conveyance belt movement amount detection unit. The sheet conveying apparatus according to any one of claims 1 to 3. The sheet position detection means is provided at the entrance of the transport belt to detect the front end of the fed sheet, a signal from the sheet front end detection sensor, and a predetermined transport speed of the transport belt 4. The sheet conveying apparatus according to claim 1, further comprising: a control unit that calculates a position of the sheet on the conveying belt. The sheet position detection means is a plurality of sheet detection sensors provided in the vicinity of each fixed electrode,
Control means for driving the power supply device to apply a first potential to each of the fixed electrodes corresponding to the sheet leading edge detection sensor while the sheet conveyed by the conveyance belt is detected by the sheet detection sensor. The sheet conveying apparatus according to claim 1, further comprising: In the plurality of fixed electrodes existing below the sheet detected by the sheet position detecting means, the first potential is applied to the fixed electrodes on both sides sandwiching one or more fixed electrodes to which the first potential is not applied. The sheet conveying apparatus according to any one of claims 1 to 3. The first potential is also applied to the fixed electrode that is adjacent to the fixed electrode that is the furthest in the sheet conveyance direction among the fixed electrodes that are in the position corresponding to the sheet and that is not in the position corresponding to the sheet. The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is a sheet conveying apparatus.

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