JP2007230035A - Droplet ejection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a sheet adhere to a conveyer belt and carry out steady conveying, and to inhibit image quality degradation such as smudging, color mixture or the like by contact between a conveyer belt and a recording head. <P>SOLUTION: A conveyer belt 28 includes a dielectric layer 52 on a side of a front surface facing a recording head 32 and an electro-conductive layer 54 on a side of a rear surface. A sheet P is pushed against the conveyer belt 28 and charged with an electro static charge roll 36, and thereby electrostatic attraction of a sheet P to the conveyer belt 28 is carried out. A platen 60 is arranged to a rear surface of the conveyer belt 28, in the platen 60, a sinking comb-like electrode plate 62A and a sinking comb-like earth plate 62B are arranged in a nested shape with spacing, and a dielectric layer 66 is formed in an upper section of them. When power voltage is impressed to a sinking comb-like electrode plate 62A from a power source 68, charges of opposite polarity generate in a dielectric layer 66 on the sinking comb-like electrode plate 62A and the sinking comb-like earth plate 62B by polarization, charges having contrary polarity generate between the dielectric layer 66 and the electro-conductive layer 54, and thereby electrostatic attraction force generates between the conveyer belt 28 and the platen 60. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a droplet discharge device that includes a droplet discharge head that discharges droplets and a conveyance belt that holds a recording medium and conveys the recording medium to face the droplet discharge head.

  2. Description of the Related Art Conventionally, there is an ink jet recording apparatus as a liquid droplet ejecting apparatus that ejects liquid droplets from a plurality of nozzles and prints on a recording medium such as paper. The ink jet recording apparatus is small, inexpensive, and quiet. It has advantages and is widely available commercially. In particular, piezo inkjet systems that eject ink droplets by changing the pressure in the pressure chamber using piezoelectric elements and thermal inkjet recording devices that eject ink droplets by expanding the ink by the action of thermal energy are high-speed printing. It has many advantages such as high resolution.

  In such an ink jet recording apparatus, the charging member is charged with a conveying member such as a conveying belt or a conveying drum to generate an electrostatic adsorption force between the recording medium and the conveying member, and the recording medium is conveyed to the conveying member. To be electrostatically adsorbed. In this state, the recording medium is passed through the ink droplet ejection area of the recording head (droplet ejection head) to record an image on the recording medium. As a result, the uniformity of the distance between the recording medium and the nozzle surface of the recording head (hereinafter referred to as TD: Throw Distance) is increased, the accuracy of the ink droplet landing position on the recording medium is improved, and the image quality is improved.

  In recent years, the TD has been narrowed to 1 to 2 mm for the purpose of further improving the accuracy of the ink droplet landing position on the recording medium, that is, further improving the image quality. On the other hand, in order to improve the uniformity of TD, it is required to increase the electrostatic adsorption force between the recording medium and the conveying member, and the TD depends on the environmental change such as temperature and humidity and the type of the recording medium. In order to prevent the uniformity of the recording medium from deteriorating, it is required to further increase the electrostatic adsorption force between the recording medium and the conveying member.

  As a method for generating an electrostatic attraction force, for example, there is a method in which a recording medium is placed on a conveyance belt provided with a dielectric layer and charged from above the recording medium. Since the surface of the conveying belt has a high potential of several hundred to several kilovolts and the recording head is grounded in many cases, a potential difference is generated between the recording head and the conveying belt. Therefore, there is a possibility that the conveyance belt and the recording head are attracted and contacted by electrostatic force.

  When the conveyor belt comes into contact with the recording head, the conveyor belt is soiled with ink, the ink moves from one recording head to the other recording head via the conveyor belt, color mixing occurs, or foreign matter attached to the conveyor belt is removed from the nozzle. There arises a problem of mixing into the recording head. In particular, a system that uses a transparent ink (reaction liquid) that mixes with yellow (Y), magenta (M), cyan (C), and black (K) inks to cause an agglomeration reaction, mainly for the purpose of improving image quality. In a so-called two-liquid system or a system in which different color inks such as K and Y are mixed and reacted (a so-called inter-ink reaction system), ink aggregation, discoloration, and nozzle clogging occur in the recording head. It becomes impossible to recover.

  On the other hand, if the TD is widened, this problem can be avoided, but the landing accuracy of the ink droplets ejected from the recording head is lowered, and it becomes difficult to obtain high-quality recording. Although a method of suppressing the conveyor belt with a roll or a star wheel is also conceivable, printing disturbance due to ink offset occurs when passing over a recording medium.

  Further, a configuration is disclosed in which vibration of the conveyor belt is suppressed by sucking the conveyor belt to the side opposite to the recording head (see, for example, Patent Document 1). In the configuration described in Patent Document 1, a voltage is applied to the comb-like electrodes built in the conveyor belt, and electrostatic attraction is generated on both the front and back surfaces of the conveyor belt, whereby a recording medium is placed on the surface of the conveyor belt. At the same time, the back surface of the conveyance belt is sucked by a member disposed on the opposite side of the recording belt side of the conveyance belt as a belt suction member.

  Here, in order to continuously apply a high voltage to the electrodes built in the rotating conveyor belt, the electrodes are exposed along the belt rotating direction, and the power supply brush is rubbed against the exposed portions of the electrodes. However, high-voltage power supply is performed at the rubbing portion between the power supply brush and the electrode, so that electric discharge is likely to occur, and electromagnetic waves generated with the electric discharge become noise sources and cause malfunctions. . In addition, the occurrence of a spark at the rubbing portion between the power supply brush and the electrode damages the electrode and the power supply brush, and their lifespan is significantly shortened. There is also a problem that the direction of the electric force generated by the comb-like electrodes of the transport belt adversely affects the ink ejection direction, and the image is disturbed.

  As another configuration, an electrode is provided on a platen that guides a conveyance belt made of a single-layer elastomer, and a voltage is applied to the electrode to generate an electrostatic adsorption force between the recording medium and the conveyance belt. Has been disclosed (for example, see Patent Document 2).

However, in the configuration described in Patent Document 2, when the electrostatic adsorption force between the recording medium and the conveyance belt is increased, the adsorption force between the platen and the conveyance belt is also increased, and the conveyance belt is adsorbed to the platen. It will be so difficult to rotate. Even if the conveyor belt can be rotated, a large driving force is required to rotate the conveyor belt, resulting in an increase in the size of the apparatus. Conversely, if the suction force between the transport belt and the platen is reduced so that the transport belt rotates smoothly, the electrostatic suction force between the recording medium and the transport belt is reduced, and the suction force sufficient for transporting the recording medium. Cannot be obtained. Even if the platen surface is made of a low friction coefficient material, the adsorption force between the platen and the conveyor belt is very strong.
JP 2002-145474 A JP 2004-90533 A

  The present invention has been made in view of the above problems, and stably conveys a recording medium by a conveying member such as a conveying belt, prevents contact between the conveying member and a droplet discharge head, and provides a high-quality image. It is an object of the present invention to provide a droplet discharge device capable of forming the above.

  In order to achieve the above object, a liquid droplet ejection apparatus according to the first aspect of the present invention is provided with a liquid droplet ejection head that ejects liquid droplets from a nozzle, and is opposed to the liquid droplet ejection head. The suction side of the recording medium on the front side facing the droplet discharge head is a member having higher resistance than the back side, and a charge is supplied to the front side of the transport member, which is movably stretched by a support member. A recording medium attracting force generating means for attracting the recording medium to the transport member, a platen for guiding the back side of the transport member in the discharge region of the droplet discharge head, and a second electrode having a potential difference inside the platen. 1 electrode and 2nd electrode are alternately arrange | positioned to one direction, It has the conveyance member adsorption | suction force generation means which generate | occur | produces the adsorption | suction force for making the said conveyance member adsorb | suck to the said platen, It is characterized by the above-mentioned.

  According to the first aspect of the present invention, the conveying member is such that the suction side of the recording medium on the front side facing the droplet discharge head is a member having higher resistance than the back side, and the height of the conveying member is increased by the recording medium attracting force generating means. Charge is supplied to the resistance portion. As a result, the recording medium is electrostatically attracted to the surface side of the transport member. The transport member is movably stretched by the support member, and moves while being guided by the platen on the back surface side of the transport member in the discharge region of the droplet discharge head. In the platen, the first electrode and the second electrode having a potential difference are alternately arranged in one direction as the conveying member adsorption force generating means, and the conveying member is caused by the potential difference between the first electrode and the second electrode. Adsorption force is generated for adsorbing to the platen. Thereby, the back surface side of the transport member moves while being attracted to the platen, and the transport member is suppressed from being lifted from the platen. For this reason, image quality deterioration such as dirt and color mixing due to the conveyance member or the recording medium coming into contact with the droplet discharge head is suppressed. In addition, the distance (TD) between the conveying member and the droplet discharge head can be narrowed, thereby improving the landing accuracy of the droplet on the recording medium and further improving the image quality.

  According to a second aspect of the present invention, in the liquid droplet ejection device according to the first aspect, the transport member includes a first dielectric portion provided on the front surface side and a conductive portion provided on the back surface side. It is characterized by that.

  According to the second aspect of the present invention, the transport member includes the first dielectric portion on the front surface side and the conductive portion on the back surface side, and the charge is supplied from the first dielectric portion side by the recording medium attracting force generating means. Thus, the recording medium is electrostatically attracted to the first dielectric portion of the transport member. In addition, since the conductive portion can be conducted and maintained at a predetermined potential, the state of the electric charge of the first dielectric portion is stabilized and the electrostatic adsorption force of the recording medium is stabilized, so that the recording medium is lifted from the conveying member. It is suppressed.

  According to a third aspect of the present invention, in the droplet discharge device according to the first or second aspect, the platen is formed on a contact surface of the upper part of the first electrode and the second electrode with the conveying member. It has two dielectric parts.

  In the third aspect of the present invention, the second dielectric portion is provided on the contact surface of the first electrode and the second electrode on the conveying member, and the first electrode and the second electrode are alternately arranged in one direction. Polarization occurs in the second dielectric part due to the potential difference between the electrodes, and the charge is stably maintained. As a result, a stable electrostatic attraction force is generated between the transport member and the second dielectric portion, and lifting of the transport member from the platen is suppressed.

  According to a fourth aspect of the present invention, in the liquid droplet ejection apparatus according to the first aspect, the transport member includes a first dielectric portion provided on the front surface side, a third dielectric portion provided on the back surface side, And a conductive portion sandwiched between the first dielectric portion and the third dielectric portion.

  According to the fourth aspect of the present invention, the recording medium is electrostatically attracted to the transport member by supplying the charge from the recording medium attracting force generating means to the first dielectric portion on the surface side of the transport member. In addition, since the conductive portion of the transport member can be conducted and maintained at a predetermined potential, the state of the electric charge of the first dielectric portion is stabilized and the electrostatic adsorption force of the recording medium is stabilized. The floating of the is suppressed. In addition, due to the potential difference between the first electrode and the second electrode that are alternately arranged in one direction inside the platen, polarization occurs in the third dielectric portion on the back surface side of the transport member, and the charge is stably maintained. Thereby, an electrostatic attraction force is generated between the conveying member and the third dielectric portion, and the lifting of the conveying member from the platen is suppressed.

  According to a fifth aspect of the present invention, in the liquid droplet ejection apparatus according to any one of the first to fourth aspects, the transport member adsorption force generating means is configured to be the first electrode or the second electrode. One of the features is that it is grounded.

  In the invention according to claim 5, the conveying member adsorption force generating means is configured such that one of the first electrode or the second electrode is grounded and a voltage is applied to the other first electrode or the second electrode. A potential difference is generated between the first electrode and the second electrode. As a result, charges having different polarities are generated by polarization at the upper portions of the first electrode and the second electrode, and the electrostatic attraction force of the transport member is stabilized. For this reason, the lifting of the conveying member from the platen can be further suppressed.

  According to a sixth aspect of the present invention, in the liquid droplet ejection apparatus according to any one of the first to fifth aspects, the recording medium adsorbing force generating means comprises a charging roll that contacts the conveying member. The recording medium introduced into the conveying member is charged while being pressed against the conveying member.

  In the invention according to claim 6, the charging roll is in contact with the conveying member, and the recording medium introduced into the conveying member is charged while being pressed against the conveying member, whereby the recording medium is electrostatically attracted to the conveying member. The Thereby, the lifting of the recording medium from the conveying member is suppressed.

  According to a seventh aspect of the present invention, in the liquid droplet ejection apparatus according to any one of the first to sixth aspects, the surface potential sensor for measuring the surface potential of the transport member and the liquid droplet ejection head A position sensor that detects a distance between the transport member and the surface potential, a surface potential measured by the surface potential sensor, and a distance between the droplet discharge head and the transport member detected by the position sensor. A suction force determination unit that calculates a suction force between the member and the droplet discharge head, and a suction force of the transport member by the transport member suction force generation unit according to the suction force calculated by the suction force determination unit. And a variable suction force control means.

  According to the seventh aspect of the invention, the surface potential of the transport member is measured by the surface potential sensor, and the distance between the droplet discharge head and the transport member is detected by the position sensor. Then, the suction force determination unit calculates the suction force between the droplet discharge head and the transport member based on the surface potential of the transport member and the distance between the droplet discharge head and the transport member. The attracting force control means varies the attracting force of the conveying member by the conveying member attracting force generating means according to the attracting force calculated by the attracting force determining means. Thereby, the adsorption | suction force to the platen of a conveyance member is adjusted appropriately, and the raising of a conveyance member is suppressed further. Further, the adsorption force of the conveying member to the platen becomes too strong to prevent the movement of the conveying member.

  According to an eighth aspect of the present invention, in the liquid droplet ejection device according to the seventh aspect, when the suction force determining means determines that the transport member is lifted from the platen, the suction force control means is It is characterized by operating the conveying member adsorption force generating means.

  In the invention according to claim 8, when the suction force determining means determines that the transport member is lifted from the platen, the suction force control means operates the transport member suction force generating means. Thereby, the adsorption | suction force to the platen of a conveyance member can be generated only when it is assumed that a conveyance member floats from a platen. Thereby, the lifting of the conveying member is suppressed, and wear due to friction between the conveying member and the platen can be suppressed.

  According to a ninth aspect of the present invention, in the liquid droplet ejection device according to any one of the first to sixth aspects, the surface potential sensor that measures the surface potential of the transport member, and the surface potential sensor And control means for operating the conveying member suction force generating means when the measured value is higher than a preset potential.

  In the invention according to claim 9, the surface potential of the conveying member is measured by the surface potential sensor. The control means operates the conveying member suction force generating means when the measured value of the surface potential sensor is higher than a preset potential. As a result, when the surface potential of the transport member is high and is easily attracted to the recording head, it is possible to generate an attracting force of the transport member to the platen. For this reason, the lifting of the conveying member from the platen is suppressed.

  According to the present invention, a recording medium can be stably adsorbed by adsorbing to a conveyance member, contact between the conveyance member and a droplet discharge head can be prevented, and occurrence of image quality deterioration such as dirt and color mixing can be reduced. . Further, the distance (TD) between the transport member and the droplet discharge head can be narrowed, the droplet landing accuracy is improved, and a high-quality image can be formed.

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

  First, an overall configuration of an ink jet printer which is a droplet discharge device of the present invention will be outlined. FIG. 1 shows a schematic configuration of an inkjet recording apparatus 12 according to the first embodiment of the present invention.

  A paper feed tray 16 is provided in the lower part of the casing 14 of the ink jet recording apparatus 12, and the sheets P stacked in the paper feed tray 16 can be taken out one by one by a pickup roll 18. The taken paper P is transported by a plurality of transport roller pairs 20 constituting a predetermined transport path 22.

  Above the paper feed tray 16, an endless transport belt 28 as a transport member is stretched around a drive roll 24 and a driven roll 26. A recording head array 30 is disposed above the conveyor belt 28 and faces the flat portion 28F of the conveyor belt 28. This opposed area is an ejection area SE where ink droplets are ejected from the recording head array 30. The sheet P transported along the transport path 22 is held by the transport belt 28 and reaches the discharge area SE, and ink droplets corresponding to image information are attached from the recording head array 30 in a state of facing the recording head array 30. The

  In this embodiment, the recording head array 30 has a long shape in which the effective recording area is equal to or larger than the width of the paper P (the length in the direction orthogonal to the transport direction), and cyan (C) and magenta (M). , Yellow (Y), and black (K), four ink jet recording heads (hereinafter referred to as recording heads) 32 corresponding to the four colors are arranged along the transport direction, so that a full color image can be recorded. ing.

  Each recording head 32 is driven by a head drive circuit (not shown). The head drive circuit is configured to, for example, determine the ink droplet ejection timing and the ink ejection port (nozzle) to be used according to the image information, and send a drive signal to the recording head 32.

  The recording head array 30 may be stationary in a direction orthogonal to the transport direction. However, if the recording head array 30 is configured to move as necessary, an image with higher resolution can be obtained by multi-pass image recording. Or the failure of the recording head 32 is not reflected in the recording result.

  Four maintenance units 34 corresponding to the respective recording heads 32 are arranged on both sides of the recording head array 30. As shown in FIG. 2, when performing maintenance on the recording head 32, the recording head array 30 is moved upward, and the maintenance unit 34 moves into the gap formed between the conveyance belt 28 and enters. . Then, a predetermined maintenance operation (suction, wiping, capping, etc.) is performed while facing the nozzle surface.

  A separation plate 40 is disposed on the downstream side of the recording head array 30 and separates the paper P from the conveyance belt 28. The peeled paper P is transported by a plurality of discharge roller pairs 42 that constitute a discharge path 44 on the downstream side of the peeling plate 40, and is discharged to a paper discharge tray 46 provided on the top of the housing 14.

  A reverse conveyance path 23 for duplex printing is connected from the discharge path 44 to the conveyance path 22. When performing double-sided printing, the paper on which single-sided printing has been performed is transported from the discharge path 44 to the transport path 22 via the reverse transport path 23 and sent again onto the transport belt 28 to perform image recording. As described above, a series of image recording is performed.

  As shown in FIGS. 1 and 2, an ink tank 35 that stores ink of each color is disposed above the recording head array 30. Each recording head 32 is connected to each ink tank 35.

  As shown in FIG. 3, on the upstream side of each recording head 32, a charging roll 36 is disposed as a sheet attracting force generating unit. A power supply 38 for applying a DC voltage is connected to the charging roll 36. The charging roll 36 is driven while sandwiching the conveyance belt 28 and the paper P with the driven roll 26, and presses the paper P against the conveyance belt 28. The driven roll 26 is grounded as shown by reference numeral 39. By appropriately setting the DC voltage applied from the power supply 38, a predetermined potential difference is generated between the charging roll 36 and the driven roll 26, and the sheet P is charged and electrostatically attracted to the transport belt 28. it can.

  Further, the platen 60 is in contact with the back surface of the conveying belt 28 in the area facing each recording head 32. The platen 60 is disposed so as to be flush with the upper ends of the drive roll 24 and the driven roll, and the conveyor belt 28 slides on the platen 60 and moves.

As shown in FIGS. 4A and 4B, the platen 60 includes a comb-like electrode plate 62A as a first electrode of a belt adsorption force generating unit and a comb as a second electrode on an insulating layer 64. The toothed ground plate 62B is embedded in a nested state at intervals. A power source 68 for applying a DC voltage is connected to the comb-like electrode plate 62A. A dielectric layer 66 is formed on the upper portions of the comb-shaped electrode plate 62A and the comb-shaped ground plate 62B. The dielectric layer 66 is a layer for holding electric charges supplied from the comb-like electrode plate 62A for adsorbing the transport belt 28, and is formed of a resin material or the like. For example, polyethylene, polycarbonate, acrylic, or the like is used as the resin material. The dielectric layer 66 preferably has an electrical resistance of 10 ¹² to 10 ¹⁷ Ω · cm and a thickness of 0.5 to 1.0 mm.

  Further, the transport belt 28 is formed of two layers of a front-side (outer peripheral side) dielectric layer 52 facing the recording head 32 and a back side (inner peripheral side) conductive layer 54. The conductive layer 54 is disposed so as to slide with the dielectric layer 66 of the platen 60. Further, the conductive layer 54 is grounded as shown by reference numeral 39 by sliding with the driven roll 26.

The dielectric layer 52 is a layer for holding charges supplied from the charging roll 36 for electrostatically adsorbing the paper P, and is formed of a resin material, a rubber material, or the like. For example, polyimide, polyimide amide or the like is used as the resin material, and chloroprene rubber or the like is used as the rubber material. The dielectric layer 52 preferably has an electric resistance of 10 ⁷ to 10 ¹⁷ Ω · cm and a thickness of 10 to 200 μm. The conductive layer 54 is a layer for forming a stable electric field with charges supplied from the charging roll 36, and is formed of a metal material or the like. For example, Al, Cr, Ni or the like is used as the metal material. The conductive layer 54 preferably has an electrical property of 10 ⁻⁶ to 10 ⁶ Ω · cm and a thickness of 10 nm to 10 μm. By grounding the conductive layer 54, the charge distribution of the dielectric layer 52 is stabilized, and the adsorption force is stabilized. The conductive layer 54 may be formed on one surface of the dielectric layer 52 by a known method such as vapor deposition, sputtering, or conductive paste printing.

  In the present embodiment, the transport belt 28 has two layers of the dielectric layer 52 and the conductive layer 54, but the boundary between the dielectric material and the conductive material may not be clearly distinguished. A configuration in which the component ratios of the two materials are mixed while the two materials are mixed may be used.

  Next, the operation of the ink jet recording apparatus 12 will be described.

  As shown in FIG. 3, the charging roll 36 presses the paper P supplied on the transport belt 28 against the transport belt 28 with the driven roll 26. Then, a positive voltage is applied to the paper P by applying a DC voltage to the charging roll 36, and the paper P is electrostatically attracted to the dielectric layer 52 of the transport belt 28 as shown in FIG. 5. Further, an adsorption force Fh is generated between the recording head 32 and the paper P due to the negative charge of the recording head 32 and the positive charge of the paper P, but the electrostatic adsorption force (illustrated) between the paper P and the dielectric layer 52 is illustrated. The sheet P is electrostatically adsorbed to the dielectric layer 52 because it is stronger. At this time, the electric charge of the dielectric layer 52 is stabilized by the conductive layer 54 of the transport belt 28, and the sheet P can be stably electrostatically adsorbed, and the lifting of the sheet P can be suppressed.

  Further, as shown in FIG. 5, when a DC voltage is applied to the comb-shaped electrode plate 62A from the power source 68 (see FIG. 4B), a dielectric polarization phenomenon occurs in the dielectric layer 66 of the platen 60, resulting in a different polarity. The charge is excited, and is negative (indicated as “−” in FIG. 5) at the top of the comb-shaped electrode plate 62A, and positive (indicated as “+” in FIG. 5) at the top of the comb-shaped ground plate 62B. ) State. Then, it is considered that a charge opposite to the charge of the dielectric layer 66 of the platen 60 is generated in the region of the conductive layer 54 on the back of the transport belt 28. Accordingly, an adsorption force Fv is generated only between the platen 60 and the conductive layer 54 region of the conveyor belt 28, so that the electrostatic adsorption between the sheet P and the conveyor belt 28 due to the supply of charges from the charging roll 36. The conveying belt 28 can be electrostatically attracted to the platen 60 without disturbing the force.

However, as shown in FIG. 5, the adsorption force Fh between the recording head 32 and the paper P, the downward force Fo due to the tension of the conveyance belt 28, and the adsorption force Fv between the conveyance belt 28 and the platen 60. In relation to
Fv ≧ Fh-Fo
It is necessary to set the voltage to be applied to the comb-like electrode plate 62A so as to satisfy the condition and to generate the suction force Fv. Thereby, the lifting of the conveying belt 28 from the platen 60 is suppressed, and the occurrence of image quality deterioration such as contamination and color mixing due to contact between the conveying belt 28 and the paper P and the recording head 32 can be reduced.

  As shown in FIG. 6, when the conveying belt 28 is charged by the charging roll 36 (the state where there is no paper P), positive charge is held in the dielectric layer 52. Further, when a DC voltage is applied to the comb-like electrode plate 62A, charges of different polarities are excited by the dielectric polarization phenomenon in the dielectric layer 52 of the platen 60, and minus and comb-tooth are formed above the comb-like electrode plate 62A. The upper portion of the ground plate 62B is in a plus state. In the region of the conductive layer 54 of the transport belt 28, a charge opposite to the charge of the dielectric layer 66 of the platen 60 is generated. As a result, an attracting force Fv is generated between the conductive layer 54 of the transport belt 28 and the dielectric layer 66 of the platen 60, and the transport belt 28 is attracted to the platen 60 side.

At this time, as shown in FIG. 7, when there is no paper P and the charge is supplied to the transport belt 28, the transport belt 28 becomes a high potential, and the suction between the recording head 32 and the transport belt 28. The force Fh increases, and the conveyor belt 28 is lifted from the platen 60 and easily comes into contact with the recording head 32. Therefore, the suction force Fv between the conveyor belt 28 and the platen 60 is
Fv ≧ Fh-Fo
It is necessary to set to satisfy. Thereby, the lift of the conveyor belt 28 from the platen 60 can be suppressed.

  In the above embodiment, the configuration includes the comb-like electrode plate 62A to which a positive voltage is applied from the power source 68 and the grounded comb-like ground plate 62B. However, the present invention is not limited to this configuration. . For example, it may be configured to include a comb-shaped first electrode to which a positive voltage is applied from the power source 68 and a comb-shaped second electrode to which a negative voltage is applied from the power source. Further, the shape of the electrode is not limited to the comb, and the first electrode having a positive voltage and the second electrode having a negative voltage are alternately arranged in one direction, and the first electrode and the second electrode Any structure may be used as long as a potential difference is generated between the electrodes.

  In the above embodiment, the conveyor belt 28 has a two-layer structure including the upper dielectric layer 52 and the lower conductive layer 54, and the platen 60 is disposed above the comb-shaped electrode plate 62A and the comb-shaped ground plate 62B. Although the configuration includes the dielectric layer 66, the configuration is not limited to this configuration. For example, the transport belt includes three layers including an upper first dielectric layer, an inner conductive layer, and a lower third dielectric layer located above the comb-like electrode plate and the comb-like ground plate of the platen. It may be a structure. In this configuration, it is necessary to expose the end of the conductive layer in the width direction and bring the conductive member into contact with the ground. Even in such a configuration, the charge from the charging roll 36 is held in the first dielectric layer and the conductive layer is grounded, so that the state of the charge is stabilized (a stable adsorption force is obtained) and the second dielectric is obtained. It is possible to retain a charge having a polarity opposite to that of the comb-shaped electrode plate and the comb-shaped ground plate in the layer.

  The conveyor belt 28 is an example of a conveyor member, and a plate-like member can be used in addition to the belt.

  Next, an ink jet recording apparatus according to a second embodiment of the present invention will be described.

  In addition, the same code | symbol is attached | subjected to the same member as 1st Embodiment, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 8, in this ink jet recording apparatus, a surface potential meter 80 that measures the surface potential of the transport belt 28 on the downstream side in the movement direction from the charging roll 36 of the transport belt 28 and on the upstream side of the recording head 32. A position detection sensor 82 for detecting the position of the conveyor belt 28 is provided. A laser displacement meter is used as the position detection sensor 82, and the distance (TD) between the recording head 32 and the conveyance belt 28 is measured based on the detected position of the conveyance belt 28. Further, a control unit 84 to which signals from the surface electrometer 80 and the position detection sensor 82 are input is provided. In the control unit 84, based on the surface potential of the conveyor belt 28 measured by the surface potential meter 80 and the data of the position of the conveyor belt 28 detected by the position detection sensor 82, the control unit 84 determines between the conveyor belt 28 and the recording head 32. The suction force Fh is calculated, and the voltage applied to the power source 68 is controlled. As a result, the suction force Fv between the conveyance belt 28 and the platen 60 is varied.

  Here, if the suction force Fv between the conveyor belt 28 and the platen 60 is constantly generated, a strong frictional force is always applied to the sliding surface of the platen 60 of the conveyor belt 28, and the conveyor belt 28 is worn. Resulting in. Also, from the viewpoint of energy, it is useless to suck the conveyor belt 28 when the conveyor belt 28 is not lifted. Therefore, in the present embodiment, when the conveyance belt 28 is predicted to come into contact with the recording head 32, an adsorption force Fv between the conveyance belt 28 and the platen 60 is generated.

  FIG. 9 shows a flowchart for controlling the suction force Fv between the conveyor belt 28 and the platen 60.

  When printing is started, first, in step 100, the surface potential of the conveyor belt 28 is measured by the surface potential meter 80. In step 102, the distance (TD) between the conveyance belt 28 and the recording head 32 is measured by detecting the distance (position of the conveyance belt 28) between the conveyance belt 28 and the position detection sensor 82. In step 104, the attractive force Fh between the conveyance belt 28 and the recording head 32 is calculated based on the surface potential and TD. The adsorption force Fh is calculated by the following equation.

Fh = 1 / 2εS (Vo / d1) ²
Here, Fh is the electrostatic adsorption force [N] between the conveyance belt 28 and the recording head 32, ε is the dielectric constant of air, Vo is the charging potential [V] of the dielectric layer 52 of the conveyance belt 28, and d1 is the conveyance belt 28. The distance between the nozzles of the recording head 32 [mm] and S is the surface area [m ² ] of the conveying belt 28. The calculation of the adsorption force Fh will be described later using specific numerical values.

  Next, at step 106, it is determined whether or not the relationship between the suction force Fh between the conveyance belt 28 and the recording head 32 and the downward force Fo due to the tension of the conveyance belt 28 is Fh ≧ Fo. . Here, as shown in FIG. 8, when Fh is smaller than Fo, the conveyor belt 28 does not lift. On the other hand, as shown in FIG. 10, when Fh is larger than Fo, it is predicted that the conveyor belt 28 floats from the platen 60 and contacts the recording head 32.

Accordingly, when it is determined in step 106 that Fh ≧ Fo, in step 108, the suction force Fv between the conveyor belt 28 and the platen 60 is calculated. This adsorption force Fv is
Fv ≧ Fh-Fo
The condition is set. Next, in step 110, the voltage applied from the power source 68 is controlled based on the calculated adsorption force Fv. As a result, as shown in FIG. 11, an attracting force Fv between the conveyor belt 28 and the platen 60 is generated, and the lifting of the conveyor belt 28 from the platen 60 can be prevented.

  On the other hand, when it is determined in step 106 that Fh is smaller than Fo, in step 112, the voltage applied from the power source 68 is turned off, and the suction force Fv between the conveyor belt 28 and the platen 60 is not generated.

  Here, the control of the suction force Fv will be described using specific numerical values.

In this example, the downward force Fo due to the tension of the conveyor belt 28 is 0.3 N, and the potential threshold on the conveyor belt 28 is 1300V.
(A) Adsorption force during normal charging As shown in FIG. 8, during normal charging, even if the adsorption force of the platen 60 is not generated, the downward force Fo due to the tension of the conveyor belt 28 or the like can be obtained only with the adsorption force Fh. Therefore, the conveyor belt 28 does not move upward. Fh in the normal state is obtained.

For example, when Vo = 1000 [V], d1 = 1.5 mm, and S = 0.09 m ² ,
Fh = 1 / 2εS (Vo / d1) ² = 0.18 [N]
It becomes. Here, Fh is an electrostatic adsorption force between the conveyance belt 28 and the recording head 32, ε is a dielectric constant of air, Vo is a charging potential of the dielectric layer 52 of the conveyance belt 28, and d1 is a nozzle of the conveyance belt 28 and the recording head 32. The distance S is the surface area of the conveyor belt 28.

(B) Adsorption force Fh when the conveying belt 28 contacts the recording head 32
For example, when V1 = 1500 [V], d1 = 1.5 mm, and S = 0.09 m ² ,
Fh = 1 / 2εS (V1 / d1) ² = 0.40 [N]
It becomes. Further, since TD is effective in the square, when the conveying belt 28 moves in the direction of the recording head 32, the suction force Fh becomes stronger.

  Here, the downward force Fo due to the tension of the conveyor belt 28 is 0.3 N, and the potential threshold on the conveyor belt 28 is 1300 V (when 1300 V, Fh = 0.3 N, which is balanced with Fo). ing.

  According to the flowchart shown in FIG. 9, the measured value of the surface potential of the conveyor belt 28 is V = 1500V, and the measured value of TD is 1.5 mm. When the suction force Fh between the conveying belt 28 and the recording head 32 is calculated, as described above, Fh = 0.4N, and Fh ≧ Fo, that is, 0.4N ≧ 0.3N. For this reason, it is expected that the conveyor belt 28 is lifted when the conveyor belt 28 is at a high potential (1500 V). Then, when the adsorption force Fv = Vh−Fo between the conveyor belt 28 and the platen 60 is calculated, Fv = 0.4N−0.3N = 0.1N. Based on this, the suction force Fv of the conveyor belt 28 is turned ON, and a force of Fv = 0.1 N or more is generated by the platen 60.

  By such control, as shown in FIGS. 10 and 11, the suction force Fv between the transport belt 28 and the platen 60 can be generated only when the transport belt 28 and the recording head 32 are expected to contact each other. Therefore, wear of the conveyor belt 28 can be reduced and energy saving can be achieved.

  In FIG. 8, one surface electrometer 80 and one position detection sensor 82 are installed on the upstream side of the recording head 32, but a plurality of installations are more preferable. Further, by installing the recording heads 32 at a plurality of locations such as the front side and the back side of the recording heads 32, the surface potential and TD fluctuations of the transport belt 28 at each location can be measured. This can be reflected in the adsorption force Fv.

  Next, an ink jet recording apparatus according to a third embodiment of the present invention will be described.

  In addition, the same code | symbol is attached | subjected to the same member as 2nd Embodiment, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 12, in this ink jet recording apparatus, a surface potential meter 80 that measures the surface potential of the transport belt 28 on the downstream side in the movement direction from the charging roll 36 of the transport belt 28 and on the upstream side of the recording head 32. Is arranged. In addition, a control unit 120 that controls the voltage applied to the power supply 68 based on the surface potential measured by the surface potential meter 80 is provided.

  Here, if the suction force Fv between the conveyor belt 28 and the platen 60 is constantly generated, a strong frictional force is always applied to the sliding surface of the platen 60 of the conveyor belt 28, and the conveyor belt 28 is worn. Resulting in. Also, from the viewpoint of energy, it is useless to suck the conveyor belt 28 when the conveyor belt 28 is not lifted. Therefore, in the present embodiment, control is performed such that the suction force Fv between the conveyor belt 28 and the platen 60 is generated only when a higher potential is seen on the conveyor belt 28 than during normal use.

  As shown in FIG. 13, when printing is started, in step 130, the surface potential of the conveyor belt 28 is measured by the surface potential meter 80. Next, in step 132, it is determined whether or not the measured surface potential of the conveyor belt 28 is higher than a threshold value (for example, 1300 V). If it is determined that the measured surface potential is 1500 V, which is higher than the threshold value, the voltage applied from the power source 68 is turned ON in step 134, and the adsorption force Fv between the conveyor belt 28 and the platen 60 is set. generate. At this time, if Fv is generated, for example, it is set so that Fv = 0.3N. On the other hand, when it is determined that the measured surface potential is 1000 V, which is lower than a threshold value (for example, 1300 V), the voltage applied from the power source 68 is turned off in Step 134, and between the conveyor belt 28 and the platen 60. Is not generated.

  By such a control, the adsorption force Fv between the conveyor belt 28 and the platen 60 is generated only when a higher potential is seen on the conveyor belt 28 than during normal use, so the wear of the conveyor belt 28 is reduced. Both can save energy.

  In the above embodiment, the ink jet recording head 32 is used. However, a thermal method, a piezoelectric method, or the like is also applicable. As the ink, various inks such as water-based ink, oil-based ink, and solvent-based ink can be used. In the example shown in FIG. 1 and the like, the endless conveyance belt 28 is suspended from the drive roll 24 and the driven roll 26, but the number of rolls that support the conveyance belt 28 can be set as appropriate. is there.

  In the example shown in FIG. 1 and the like, an example of FWA corresponding to the paper width has been described. However, the inkjet recording head of the present invention is not limited to this, and a partial width array (PWA) having a main scanning mechanism and a sub-scanning mechanism. It can also be applied to the apparatus of

  In the example shown in FIG. 1 and the like, an image (including characters) is recorded on the paper P as a recording medium. However, the liquid droplet ejection head and the liquid droplet ejection apparatus of the present invention are not limited to this. Is not to be done. That is, the recording medium is not limited to paper, and the liquid to be ejected is not limited to ink. For example, it is industrially useful to create color filters for displays by discharging ink onto polymer films or glass, or to form bumps for component mounting by discharging solder in a welded state onto a substrate. The present invention can be applied to all droplet discharge heads and droplet discharge apparatuses used.

1 is a schematic configuration diagram illustrating an ink jet recording apparatus according to a first embodiment of the present invention. FIG. 2 is a schematic configuration diagram illustrating a state in which a maintenance unit has moved below a recording head in the inkjet recording apparatus illustrated in FIG. 1. FIG. 2 is a side view illustrating an outline of a printing unit in which a recording head and a conveyance belt of the ink jet recording apparatus illustrated in FIG. 1 face each other. (A) is sectional drawing of a conveyance belt and a platen, (B) is a block diagram which shows the comb-tooth-shaped electrode plate and comb-tooth-shaped earth board of a platen. FIG. 4 is a schematic configuration diagram illustrating a charge state when a sheet is present in a printing unit where a recording head and a conveyance belt face each other. FIG. 4 is a schematic configuration diagram illustrating a charge state when there is no paper in a printing unit where a recording head and a conveyance belt face each other. FIG. 6 is a schematic configuration diagram illustrating a state where the conveyance belt is lifted in a printing unit where the recording head and the conveyance belt face each other. It is a side view which shows the outline of the printing part with which the recording head and conveyance belt of the inkjet recording device which are 2nd Embodiment of this invention oppose. It is a figure which shows the flowchart when controlling the attraction | suction force between a conveyance belt and a platen. FIG. 6 is a schematic configuration diagram illustrating a state where the conveyance belt is lifted in a printing unit where the recording head and the conveyance belt face each other. FIG. 4 is a schematic configuration diagram illustrating a state in which an adsorption force between the recording head and the conveyance belt is generated in a printing unit where the recording head and the conveyance belt face each other. It is a side view which shows the outline of the printing part with which the recording head and conveyance belt of the inkjet recording device which are 3rd Embodiment of this invention oppose. It is a figure which shows the flowchart when controlling the attraction | suction force between a conveyance belt and a platen.

Explanation of symbols

12 Inkjet recording device (droplet ejection device)
24 Drive roll (support member)
26 Follower roll (support member)
28 Conveying belt (conveying member)
30 Recording head array 32 Recording head (droplet discharge head)
36 Charging roll (Recording medium adsorption force generating means)
38 Power supply 39 Earth (ground)
52 Dielectric layer (first dielectric part)
54 conductive layer 60 platen 62A comb-like electrode plate (first electrode, conveying member adsorption force generating means)
62B Comb-shaped earth plate (second electrode, conveying member adsorption force generating means)
64 Insulating layer 66 Dielectric layer (second dielectric part)
68 Power supply 80 Surface potential meter 82 Position detection sensor 84 Control unit 120 Control unit P Paper (recording medium)

Claims (9)

A droplet discharge head for discharging droplets from a nozzle;
Conveyance provided opposite to the droplet discharge head, the suction side of the recording medium on the front side facing the droplet discharge head is a member having higher resistance than the back side, and is movably stretched by a support member Members,
A recording medium adsorbing force generating means for supplying an electric charge to the surface side of the conveying member to adsorb the recording medium to the conveying member;
A platen for guiding the back side of the transport member in the discharge region of the droplet discharge head;
The first electrode and the second electrode having a potential difference inside the platen are alternately arranged in one direction, and a conveying member adsorbing force generating means for generating an adsorbing force for adsorbing the conveying member to the platen;
A droplet discharge apparatus comprising:   The droplet discharge device according to claim 1, wherein the transport member includes a first dielectric portion provided on a front surface side and a conductive portion provided on a back surface side.   3. The droplet discharge device according to claim 1, wherein the platen has a second dielectric portion on a contact surface of the upper part of the first electrode and the second electrode with the transport member. 4.   The transport member includes a first dielectric portion provided on the front surface side, a third dielectric portion provided on the back surface side, and a conductive portion sandwiched between the first dielectric portion and the third dielectric portion. The droplet discharge device according to claim 1.   5. The droplet discharge device according to claim 1, wherein one of the first electrode and the second electrode is grounded in the conveying member adsorption force generation unit. .   2. The recording medium attracting force generating means includes a charging roll that contacts the conveying member, and charges the recording medium introduced into the conveying member while pressing the recording medium against the conveying member. Item 6. The droplet discharge device according to any one of Items 5 to 5. A surface potential sensor for measuring the surface potential of the conveying member;
A position sensor for detecting a distance between the droplet discharge head and the transport member;
Based on the surface potential measured by the surface potential sensor and the distance between the droplet discharge head and the transport member detected by the position sensor, the adsorption force between the transport member and the droplet discharge head is calculated. Adsorption force determination means;
An attraction force control means for varying the attraction force of the transport member by the transport member attraction force generation means according to the attraction force calculated by the attraction force determination means;
The liquid droplet ejection apparatus according to claim 1, wherein   8. The liquid according to claim 7, wherein when the conveyance force determination unit determines that the conveyance member is lifted from the platen, the adsorption force control unit operates the conveyance member adsorption force generation unit. Drop ejection device. A surface potential sensor for measuring the surface potential of the conveying member;
Control means for operating the conveying member adsorption force generating means when the measured value of the surface potential sensor is higher than a preset potential;
The liquid droplet ejection apparatus according to claim 1, wherein

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