JP6627589B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device that fixes a developer image on a recording sheet by supplying a fixing solution to the developer image on the recording sheet by electrostatic spraying.

2. Description of the Related Art Conventionally, there has been known an electrophotographic image forming apparatus including a fixing device for melting a transferred toner image by heating the toner to fix the toner on paper. The fixing device has a heating element such as a halogen heater or a ceramic heater for melting the toner. The melted toner is pressed against the paper and fixed on the paper. Such fixing devices are widely used because of their high fixing speed and good image quality. However, an image forming apparatus using such a heat fixing type fixing device consumes a large amount of power due to heating of the toner, and thus is not suitable for power saving of the image forming apparatus.
In order to solve the above problem, there is an image forming apparatus including a fixing device that applies a fixing solution that dissolves or swells the toner to the toner on the paper and fixes the toner image on the paper. This fixing device does not require a heat treatment for melting the toner as in the heat fixing method, consumes low power, and is excellent in power saving. As a method of applying the fixing solution to the toner image, a method of applying the fixing solution to the roller surface and applying the fixing solution on the roller to the toner image, or a method of applying the fixing solution to the toner image in a non-contact manner by a sprayer or the like. Are known (see Patent Document 1).
A fixing device that applies a fixing liquid by a roller has a structure in which a roller and a toner image are in contact with each other. Therefore, it is known that such a fixing device has a problem that an unfixed toner image moves (offsets) to the roller side when the roller contacts the toner image. On the other hand, a fixing device using a sprayer can apply a fixing solution to a toner image in a non-contact manner, and thus has an advantage that offset does not occur.

JP 2009-69256 A

  However, in the related art, an appropriate control for spraying the fixing liquid onto the recording sheet has not been studied.

  SUMMARY OF THE INVENTION It is an object of the present invention to provide a fixing device capable of performing a control capable of appropriately spraying a fixing liquid onto a recording sheet.

In order to solve the above-described problem, a fixing device according to the present invention includes a storage unit that stores a fixing liquid therein, and a communication unit that communicates with the storage unit and sprays the fixing liquid toward a developer image on a recording sheet. A potential difference forming unit for forming a potential difference between a fixing head having a nozzle, the fixing solution in the nozzle, and a recording sheet conveyed at a position distant from the nozzle; A control unit for controlling the voltage.
The control unit is configured to apply a voltage to the potential difference forming unit such that the fixing liquid is sprayed from the nozzle before the leading end of the recording sheet reaches the fixing region.

  According to this configuration, the fixing liquid is sprayed from the nozzle before the leading end of the recording sheet reaches the fixing area. Therefore, when switching from a state in which the fixing liquid is not sprayed to a state in which the fixing liquid is sprayed, a droplet-shaped dropping liquid from the nozzle is formed. The fixer can be prevented from adhering to the recording sheet.

  Further, the control unit is configured to apply a voltage to the potential difference forming unit such that the fixing liquid is sprayed from the nozzle after the leading end of the recording sheet passes between the photosensitive member and the transfer member. May be.

  Further, in the standby state, the control unit sets the voltage to a first voltage that does not spray the fixing liquid from the nozzle, and performs a predetermined timing before the leading edge of the recording sheet reaches the fixing area in the printing control. The voltage may be configured to be a second voltage higher than the first voltage.

  According to this, before the leading end of the recording sheet reaches the fixing area, the voltage is increased from the first voltage to the second voltage. Therefore, when the first voltage is switched to the second voltage, the droplet-shaped fixing liquid that drops from the nozzle is discharged. Adhesion to the recording sheet can be suppressed.

  In addition, the control unit sets the voltage before the developer image on the recording sheet reaches the fixing area to a voltage at which the developer can be fixed, and a third voltage higher than the second voltage. It may be configured to be a voltage.

  According to this, for example, as compared with a mode in which the first voltage is changed to the third voltage at once before the leading end of the recording sheet reaches the fixing area, the second voltage smaller than the third voltage is applied before the third voltage is applied. Therefore, power consumption can be reduced.

  Further, when a plurality of developer images are arranged on a predetermined recording sheet at a distance from each other in the transport direction of the recording sheet, the control unit may control the developer image on the predetermined recording sheet to pass through the fixing area. After that, when the time until the next developer image on the predetermined recording sheet reaches the fixing area is equal to or more than a first threshold, the voltage is set to be smaller than the third voltage, and The fourth voltage may be configured to be higher than the first voltage.

  According to this, the voltage is set to the fourth voltage smaller than the third voltage until the next developer image reaches the fixing region, so that power consumption can be suppressed.

  Note that the fourth voltage may have the same value as the second voltage.

  In addition, the control unit is configured such that a time from when the developer image on the predetermined recording sheet passes through the fixing area to when the next developer image on the predetermined recording sheet reaches the fixing area is the first time. If it is less than the threshold, the voltage may be maintained at the third voltage.

  According to this, the spray state when the next developer image is fixed can be stabilized.

  Further, the control unit may be configured to set the voltage to the first voltage after the developer image located on the most upstream side in the transport direction on the recording sheet has passed through the fixing area.

  According to this, wasteful power consumption between a predetermined recording sheet and the next recording sheet (hereinafter, also referred to as “between sheets”) can be suppressed.

  The controller may be configured such that the time from when the developer image on the recording sheet on the most upstream side in the transport direction passes through the fixing area to when the leading edge of the next recording sheet reaches the fixing area is less than a second threshold value. In this case, the voltage may be set to a value higher than the first voltage after the most upstream developer image passes through the fixing area.

  For example, when the conveying speed is increased, the time from when the upstreammost developer image passes through the fixing area to when the leading edge of the next recording sheet reaches the fixing area may be extremely short. In this case, if the voltage is set to the first voltage and switching from the first voltage to the second voltage is performed between the sheets, there is a possibility that the fixing liquid dropped from the nozzle adheres to the next recording sheet. On the other hand, in such a case, by setting the voltage between the sheets to a value larger than the first voltage, it is possible to suppress dripping that occurs when switching from the first voltage to the second voltage. The fixer can be prevented from adhering to the recording sheet.

  The control unit is configured to calculate a relational expression between a current flowing through the potential difference forming unit and a voltage applied to the potential difference forming unit in a standby state, and determine the second voltage based on the relational expression. May be.

  According to this, the second voltage can be set to an appropriate voltage.

  In the case where a pressure applying unit that applies pressure to the fixing solution is provided, the control unit may be configured to maintain the pressure applied to the fixing solution constant during printing control.

  When a plurality of the fixing heads are provided in the width direction of the recording sheet, the control unit may be configured to individually control a voltage applied to the fixing liquid in each of the fixing heads.

  According to this, since a plurality of fixing heads are individually controlled, useless spray can be suppressed.

  The fixing area may be set for each of the plurality of fixing heads.

  If the control unit determines that the developer image does not exist in a predetermined area within a predetermined width in the image forming area of the predetermined recording sheet, the control unit determines whether the developer image is present in the predetermined fixing head corresponding to the predetermined area. Is configured to be maintained at the first voltage after the predetermined timing and while the predetermined recording sheet passes through a fixing area corresponding to the predetermined fixing head. May be.

  According to this, when the developer image is not present in the predetermined area of the image forming area, the fixing liquid is not sprayed from the fixing head corresponding to the predetermined area, so that it is possible to suppress unnecessary spraying of the fixing liquid. Can be.

  The plurality of fixing heads include a first fixing head that sprays a fixing liquid on a first recording sheet, and a second fixing head that is adjacent to the first fixing head on one side in the width direction. A third fixing head adjacent to the second fixing head on one side in the width direction, wherein the first fixing head and the second fixing head have a second fixing head wider than the first recording sheet. The first fixing head, the second fixing head, and the third fixing head can spray the fixing liquid on the recording sheet, and the fixing liquid can be sprayed on the third recording sheet wider than the second recording sheet. May be configured to be sprayable.

  According to this, by controlling each fixing head according to the difference in the width of the recording sheet, it is possible to suppress unnecessary spraying of the fixing liquid.

  Note that the width of the first fixing head is smaller than the width of the first recording sheet, and the second fixing head is located on the other side of the one end in the width direction of the second recording sheet. The third fixing head may be disposed on the other side of the third recording sheet from the one end in the width direction of the third recording sheet.

  According to this, each fixing head can be reduced in size.

  Further, the second voltage may be a voltage at which the developer can be fixed.

  The potential difference forming section may include a first electrode which is in contact with the fixing solution and is capable of applying a voltage to the fixing solution, and a second electrode facing the nozzle.

  According to the present invention, it is possible to appropriately spray the fixing liquid on the recording sheet.

FIG. 1 is a diagram illustrating a laser printer according to an embodiment of the present invention. FIG. 3A is a perspective view of the fixing head as viewed obliquely from above, and FIG. 3B is a perspective view of the first fixing head as viewed obliquely from below. FIG. 3 is a bottom view of the fixing head as viewed from below. FIG. 4 is a diagram showing a relational expression between a current flowing through a second electrode and a voltage applied to the first electrode. It is a flowchart which shows the process which sets each time in a preparation state. 5 is a flowchart illustrating voltage control in a standby state. 6 is a flowchart illustrating voltage control in print control. 9 is a timing chart showing timings of changing voltages applied to a first fixing head, a third fixing head, and a fifth fixing head, corresponding to the leading edge of a sheet or each position of an image. FIG. 7 is a diagram illustrating a state where a voltage applied to each fixing head is switched, from a state before the first sheet reaches each fixing head to a state where the second image on the first sheet passes through the second fixing head. It is a figure (a)-(h) shown. FIGS. 7A to 7C are diagrams illustrating a state in which a voltage applied to each fixing head is switched, and are views (a) to (a) illustrating a state in which a second image passes through a first fixing head to a fourth image passes through a fifth fixing head; f).

  Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, first, the overall configuration of the laser printer will be described, and then the features of the present invention will be described in detail.

  In the following description, the directions will be described in the directions shown in FIG. That is, in FIG. 1, the right side as viewed in the drawing is “front side”, the left side as viewed in the drawing is “rear side”, the back side as viewed in the drawing is “right side”, and the near side as viewed in the drawing is “left side”. I do. In addition, the vertical direction toward the paper surface is referred to as “vertical direction”.

  As shown in FIG. 1, the laser printer 1 includes a main body housing 2, a feeder unit 3 for feeding a sheet P as an example of a recording sheet, and an image forming unit 4 for forming an image on the sheet P. And a control unit 100.

  The feeder unit 3 includes a paper feed tray 31 detachably attached to a lower portion of the main body housing 2, and a paper feed mechanism 32 that feeds the paper P in the paper feed tray 31 toward the image forming unit 4. ing. The paper feed mechanism 32 includes a paper feed roller 32A, a separation roller 32B, a separation pad 32C, a paper dust removal roller 32D, and a registration roller 32E. The registration roller 32E is a roller for aligning the leading end position of the sheet P, and can be appropriately switched between stop and rotation by the control unit 100.

  The image forming unit 4 is housed in the main body housing 2 and mainly includes a scanner unit 5, a process cartridge 6, a transfer roller TR as an example of a transfer member, and a fixing device 7.

  The scanner unit 5 is provided at an upper part in the main body housing 2 and includes a laser emitting unit (not shown), a polygon mirror, a lens, a reflecting mirror, and the like. The scanner unit 5 irradiates a laser beam onto a surface of a photosensitive drum 61 as an example of a photosensitive member described later by high-speed scanning.

  The process cartridge 6 is detachable from the main housing 2. The process cartridge 6 includes a photosensitive drum 61 on which an electrostatic latent image is formed, a charger (not shown), a toner storage unit 62 that stores toner as an example of a developer, and a photosensitive drum that stores the toner in the toner storage unit 62. A supply roller 63 and a developing roller 64 are provided to supply the toner to 61.

  In the process cartridge 6, a charger (not shown) uniformly charges the surface of the rotating photosensitive drum 61. The scanner unit 5 emits a laser beam to the surface of the photosensitive drum 61 and exposes the surface of the photosensitive drum 61 to form an electrostatic latent image on the surface of the photosensitive drum 61 based on image data.

  Next, the developing roller 64 driven to rotate supplies the toner to the electrostatic latent image on the photosensitive drum 61 to form a toner image on the surface of the photosensitive drum 61. Thereafter, when the paper P is transported between the photosensitive drum 61 and the transfer roller TR, the toner image carried on the surface of the photosensitive drum 61 is drawn to the transfer roller TR and transferred onto the paper P.

  The fixing device 7 is a device that fixes the toner image on the sheet P by supplying the charged fixing liquid L to the toner image on the sheet P by electrostatic spraying. The configuration of the fixing device 7 will be described later in detail.

  Downstream of the fixing device 7, a pair of downstream transport rollers 81 for nipping and transporting the sheet P discharged from the fixing device 7 to the downstream side is provided. The paper P transported by the downstream transport roller 81 is transported to a paper discharge roller R, and is discharged onto the paper discharge tray 21 from the paper discharge roller R.

Next, the configuration of the fixing device 7 will be described in detail.
The fixing device 7 includes a fixing head 71 for spraying the fixing liquid L toward the toner image on the sheet P, and a second electrode 72 that supports the sheet P below the fixing head 71.

As the fixing liquid L, a liquid in which a solute for dissolving the toner is dispersed in a solvent having a high dielectric constant can be used in order to perform good electrostatic spraying and to perform fixing. Safe water can be used as the solvent having a high dielectric constant. That is, in the present embodiment, the toner is dissolved by a type in which a solute for dissolving the toner is dispersed in water, that is, a so-called oil-in-water emulsion. That is, a fixing solution in which a solute insoluble or hardly soluble in water as a solvent is dispersed in water is used. As a solute, as an aliphatic monocarboxylic ester, ethyl laurate, butyl laurate, isopropyl laurate, ethyl myristate, butyl myristate, isopropyl myristate, ethyl palmitate, butyl palmitate, isopropyl palmitate, fat As an aliphatic dicarboxylic acid ester system, diethyl succinate, dibutyl succinate, an aliphatic tricarboxylic acid ester system, o-acetyl citrate triethyl, o-acetyl citrate tributyl, an aliphatic dicarboxylic acid dialkoxyalkyl system, diethoxyethyl succinate, Dibutoxyethyl succinate, ethylene carbonate and propylene carbonate can be used as the carbonate type. These solutes have a function of softening the toner.
Further, a surfactant may be added in order to form an emulsion well, and as the surfactant, an anionic surfactant, a cationic surfactant, or a nonionic surfactant can be used. Examples of anionic surfactants include higher fatty acid salts such as sodium laurate, alkyl aryl sulfonates such as sodium dodecylbenzenesulfonate, alkyl sulfate salts such as sodium dodecyl sulfate, and polysulfates such as sodium polyethoxyethylene lauryl ether sulfate. Polyoxyethylene alkylaryl ether sulfates such as sodium oxyethylene alkyl ether sulfate and sodium polyoxyethylene nonylphenyl ether sulfate can be used. As the cationic surfactant, aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts, and imidazolinium salts can be used. As nonionic surfactants, polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene alkyl phenyl ethers such as polyoxyethylene nonyl phenyl ether, sorbitan higher fatty acid esters such as sorbitan monolaurate, Use of polyoxyethylene sorbitan higher fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene higher fatty acid esters such as polyoxyethylene monolaurate, and sucrose fatty acid esters such as sucrose laurate ester Can be.

  As shown in FIG. 2A, the fixing heads 71 are arranged in a staggered manner in the width direction, and have a first fixing head 71A, a second fixing head 71B, a third fixing head 71C, a fourth fixing head 71D, and a fifth fixing head. It has a head 71E. The first fixing head 71A, the third fixing head 71C, and the fifth fixing head 71E are disposed at substantially the same position in the front-rear direction, that is, in the transport direction of the sheet P, and are spaced apart in the left-right direction, that is, in the width direction of the sheet P. Are located. The second fixing head 71B is arranged on the upstream side of the first fixing head 71A and the third fixing head 71C in the transport direction, and has a central portion in the width direction between the first fixing head 71A and the third fixing head 71C in the width direction. It is located between them. The fourth fixing head 71D is arranged on the upstream side of the third fixing head 71C and the fifth fixing head 71E in the transport direction, and has a central portion in the width direction between the third fixing head 71C and the fifth fixing head 71E in the width direction. It is located between them.

  The first fixing head 71A includes a storage unit 73 that stores the fixing liquid L therein, a plurality of nozzles N that communicate with the storage unit 73, and sprays the fixing liquid L toward the toner image. A first electrode 74 for applying a voltage to the fixing liquid L in the nozzle N. Since the other fixing heads 71B to 71E have substantially the same configuration as the first fixing head 71A, the members forming the other fixing heads 71B to 71E include the members forming the first fixing head 71A. The same reference numerals are given and the description will be appropriately omitted.

  The accommodation portion 73 is a rectangular insulating container that is long in the width direction, and has an upper wall 73A, a front wall 73B, a rear wall 73C, a left wall 73D, a right wall 73E, and a lower wall 73F. As shown in FIG. 2B, the plurality of nozzles N of each of the fixing heads 71A to 71E protrude downward from the lower wall 73F of the housing portion 73, and gradually decrease in diameter toward the lower side. ing. The plurality of nozzles N are arranged in the width direction and are arranged in the transport direction.

  Specifically, the plurality of nozzles N constitute a first staggered array group U1 and a second staggered array group U2 arranged in the transport direction. As shown in FIG. 3, the first staggered array group U1 includes a plurality of first nozzles N1 arranged at regular intervals in the width direction and a plurality of first nozzles N1 arranged at regular intervals in the width direction. The first nozzle N1 and the second nozzle N2 are alternately arranged on one side and the other side in the transport direction from one side in the width direction to the other side.

  In addition, each second nozzle N2 is arranged between two first nozzles N1 in the width direction. The shape connecting two adjacent first nozzles N1 in the width direction and the second nozzle N2 arranged between the two first nozzles N1 is an equilateral triangle or an isosceles triangle. Further, the shape connecting two adjacent second nozzles N2 in the width direction and the first nozzle N1 arranged between the two second nozzles N2 is also an equilateral triangle or an isosceles triangle.

  The second staggered array group U2 has the same structure as the first staggered array group U1. In the present embodiment, the nozzle pitch (the shortest distance between the outer diameters of adjacent nozzles) may be set in a range from 1 mm to 14 mm.

  Further, two fixing heads adjacent in the width direction (for example, the first fixing head 71A and the second fixing head 71B) are arranged so that the respective accommodation portions 73 overlap when viewed from the transport direction. Specifically, the minimum pitch (for example, the pitch between the first nozzle N1 and the second nozzle N2) in the width direction of the plurality of nozzles N in a predetermined fixing head (for example, the first fixing head 71A) is Da. I have. On the other hand, from the nozzle N on the most one side in the width direction of the predetermined fixing head (for example, the first nozzle N1 on the leftmost side of the first fixing head 71A in the drawing), the fixing head ( For example, the distance Db to the nozzle N on the other side in the width direction of the second fixing head 71B (for example, the first nozzle N1 on the rightmost side of the second fixing head 71B in the drawing) is smaller than the minimum pitch Da.

  That is, the fixing areas A1 to A5 (areas where the fixing liquid L is sprayed onto the sheet P by the nozzles N of the fixing heads 71A to 71E) set for each of the fixing heads 71A to 71E are viewed from the transport direction. The fixing heads 71A to 71E are arranged so as to overlap each other. In the present embodiment, the fixing areas A1 to A5 of the fixing heads 71A to 71E will be described as having the same shape, size, and position as the lower surface of each storage unit 73 for convenience.

  More specifically, the first fixing area A1 where the fixing liquid L is sprayed from the first fixing head 71A is transported to the second fixing area A2 where the fixing liquid L is sprayed from the second fixing head 71B. Seen from the direction. The fifth fixing area A5, which is an area where the fixing liquid L is sprayed from the fifth fixing head 71E, is viewed from the transport direction to the fourth fixing area A4 which is an area where the fixing liquid L is sprayed from the fourth fixing head 71D. overlapping.

  A third fixing area A3, which is an area where the fixing liquid L is sprayed from the third fixing head 71C, overlaps the second fixing area A2 and the fourth fixing area A4 when viewed from the transport direction. By arranging the fixing heads 71A to 71E in this manner, it is possible to suppress generation of a region where the fixing liquid L is not sprayed between the fixing heads 71A to 71E.

  The first fixing head 71A is a head for spraying the fixing liquid L onto the narrowest first sheet P1 of a plurality of types of sheets P on which printing can be performed by the laser printer 1. It is formed with a width smaller than the width of the sheet P1. The first fixing head 71A is disposed on the inner side in the left-right direction than the left and right ends of the first sheet P1. More specifically, the first fixing area A1 of the first fixing head 71A is formed to have a size that is equal to or larger than the width of the image forming area where the image of the first sheet P1 is formed. It is arranged so that the entire width of the image forming area falls within the width of the area A1.

  In the present embodiment, as shown in FIG. 3, sheets P1 to P5 having different sheet widths are transported based on the left end. Specifically, a guide member (not shown) that contacts the left end of each of the sheets P1 to P5 and guides the left end is provided in the main body housing 2.

  The second fixing head 71B is adjacent to the first fixing head 71A on the right side (one side in the width direction), and is on the left side of the right end of the second sheet P2 wider than the first sheet P1 ( On the other side). Specifically, the right end of the second fixing area A2 of the second fixing head 71B is arranged at the same position as the right end of the image forming area of the second sheet P2 or at a position on the right side of the right end. The left end of the image forming area of the second sheet P2 is substantially the same as the left end of the image forming area of the first sheet P1. As described above, by disposing the first fixing head 71A and the second fixing head 71B, the first fixing head 71A and the second fixing head 71B move the fixing liquid L with respect to the image forming area of the second sheet P2. Can be sprayed.

  The third fixing head 71C is adjacent to the second fixing head 71B on the right side, and is disposed on the left side of the right end of the third sheet P3 wider than the second sheet P2. Specifically, the right end of the third fixing area A3 of the third fixing head 71C is arranged at the same position as the right end of the image forming area of the third sheet P3 or at a position on the right side of the right end. Note that the left end of the image forming area of the third sheet P3 is located at substantially the same position as the left end of the image forming area of the first sheet P1. As described above, by disposing the first fixing head 71A, the second fixing head 71B, and the third fixing head 71C, the first fixing head 71A, the second fixing head 71B, and the third fixing head 71C are in the third position. The fixing liquid L can be sprayed on the image forming area of the sheet P3.

  The fourth fixing head 71D is adjacent to the third fixing head 71C on the right side, and is disposed on the left side of the right end of the fourth sheet P4 wider than the third sheet P3. Specifically, the right end of the fourth fixing area A4 of the fourth fixing head 71D is disposed at the same position as the right end of the image forming area of the fourth sheet P4 or at a position on the right side of the right end. Note that the left end of the image forming area of the fourth sheet P4 is located at substantially the same position as the left end of the image forming area of the first sheet P1. As described above, by disposing the fixing heads 71A to 71D, the fixing heads 71A to 71D can spray the fixing liquid L onto the image forming area of the fourth sheet P4.

  The fifth fixing head 71E is adjacent to the fourth fixing head 71D on the right side, and is disposed on the left side of the right end of the fifth sheet P5 wider than the fourth sheet P4. Specifically, the right end of the fifth fixing area A5 of the fifth fixing head 71E is located at the same position as the right end of the image forming area of the fifth sheet P5 or at a position on the right side of the right end. Note that the left end of the image forming area of the fifth sheet P5 is located at substantially the same position as the left end of the image forming area of the first sheet P1. By arranging the fixing heads 71A to 71E as described above, the fixing heads 71A to 71E can spray the fixing liquid L onto the image forming area of the fifth sheet P5.

  Returning to FIG. 1, the first electrode 74 is an electrode for applying a voltage to the fixing solution L in the storage unit 73 to generate an electric field at the tip of each nozzle N. The first electrode 74 is provided so as to penetrate the upper wall 73 </ b> A from the top to the bottom of the storage unit 73, and the lower end is disposed in the fixing liquid L in the storage unit 73 and contacts the fixing liquid L, and the upper end Are connected to the control unit 100 having a voltage application unit (not shown). The voltage applied to the first electrode 74 is preferably 1 kV to 10 kV.

  A pressure device 75 as an example of a pressure applying unit is connected to each of the fixing heads 71A to 71E. The pressurizing device 75 is a device that applies pressure to the fixing liquid L in each of the fixing heads 71A to 71E, and includes a pump that pressurizes the fixing liquid L by feeding the fixing liquid L into each of the fixing heads 71A to 71E, And a pressure reducing valve for reducing the pressure by allowing the fixing liquid L to escape from the inside of 71E. Further, each of the fixing heads 71A to 71E is provided with a pressure sensor SP (only one is shown) for detecting the pressure of the fixing liquid L in each of the fixing heads 71A to 71E.

  The second electrode 72 is an electrode for contacting the sheet P to form a potential difference between the fixing liquid L in the nozzle N and the sheet P, and from the tip of each nozzle N of each of the fixing heads 71A to 71E. The fixing heads are arranged below the fixing heads 71A to 71E so as to be separated by a predetermined distance. Here, the predetermined distance is a distance larger than the thickness of the paper P, and is set to a distance at which electrostatic spraying can be suitably performed by an experiment, a simulation, or the like.

  The second electrode 72 is grounded. Note that the second electrode 72 does not necessarily need to be grounded. For example, a voltage lower than the voltage applied to the first electrode 74 may be applied to the second electrode 72. The second electrode 72 forms an electric field with the tip of the nozzle N.

  When a voltage is applied to the first electrode 74, an electric field is formed in a space near the tip of the nozzle N. Since the fixing liquid L is supplied to the tip of the nozzle N by the pressurizing device 75, the second electrode 72 forms an electric field with the fixing liquid L at the tip of the nozzle N. Then, at the tip of the nozzle N, the fixing liquid L is pulled by the electric field to form a so-called Taylor cone. Fine liquid droplets are generated by tearing off the fixing liquid L from the tip of the Taylor cone.

  The droplet-like fixing liquid L sprayed from the nozzle N is positively charged. On the other hand, the paper P is in a substantially zero potential state. For this reason, the fixing liquid L in the form of droplets flies toward the paper P due to the Coulomb force and adheres on the paper P and the toner image.

  The current sensor SA is a sensor that indirectly detects a current flowing through the fixing liquid L by detecting a current flowing through the first electrode 74, and is provided corresponding to each first electrode 74. The current sensor SA detects a current flowing through the first electrode 74 when the fixing liquid L is sprayed onto the paper P from the nozzle N, and outputs the detected value to the control unit 100. Here, even when a voltage is applied to the first electrode 74, when the fixing liquid L is not sprayed from the nozzle N, no current flows to the first electrode 74 and the fixing liquid L is sprayed from the nozzle N. That is, when the charged fixing liquid L moves from the nozzle N to the paper P, a current flows through the first electrode 74.

  The first electrode 74 and the second electrode 72 configured as described above form a potential difference for forming a potential difference between the fixing liquid L in the nozzle N and the sheet P conveyed at a position away from the nozzle N. Department.

  The control unit 100 includes a storage unit 110 including a RAM, a ROM, and the like, a CPU, an input / output circuit, and the like, and performs control based on image data input from the outside and signals from the sensors SP and SA. It has a function of controlling the device 75 and controlling the voltage applied to the first electrode 74.

  Specifically, the control unit 100 is configured to maintain a constant pressure applied to the fixing liquid L in each of the fixing heads 71A to 71E based on information from the pressure sensor SP during printing control. The pressure applied to the fixing liquid L is, for example, a state in which the interface with the air of the fixing liquid L at the tip of the nozzle N is concave toward the fixing liquid L when no voltage is applied to the first electrode 74. Such a predetermined pressure value can be set. Here, when the pressure is small, the interface of the fixing liquid L at the tip of the nozzle N has a substantially hemispherical shape concave toward the fixing liquid L. When the pressure is gradually increased from this state, the interface becomes Moving outward, the shape gradually approaches a flat surface, and when the pressure is further increased, the interface moves further outward and becomes a substantially hemispherical shape that gradually projects outward. ing. When the interface has a shape close to a plane, the surface area is minimized. The larger the surface area of the interface, the more easily the fixing liquid L at the tip of the nozzle N dries and the more the tip of the nozzle N may be clogged.

  The control unit 100 is configured to individually control the voltage applied to the fixing liquid L in each of the fixing heads 71A to 71E. Specifically, in the standby state, the control unit 100 sets the voltage V applied to each first electrode 74 of each of the fixing heads 71A to 71E to the first voltage V1 of a magnitude such that the fixing liquid L is not sprayed from the nozzle N. In the control, at a predetermined timing before the leading edge of the sheet P reaches the fixing areas A1 to A5, the voltage V is set to the second voltage V2 higher than the first voltage V1 for each of the fixing heads 71A to 71E. have. In other words, the control unit 100 determines that the leading edge of the sheet P has reached the first position that is separated from the fixing areas A1 to A5 by a predetermined first distance D1 (see FIGS. 9B and 9C) upstream. In other words, when the distance from the leading edge of the sheet P to each of the fixing areas A1 to A5 becomes the first distance D1, the voltage V is increased for each of the fixing heads 71A to 71E by the second voltage larger than the first voltage V1. V2 function.

  The first voltage V1 can be set to a voltage value larger than 0. For example, when the pressure is set to the predetermined pressure value as described above, the fixing liquid L at the tip of the nozzle N is applied by applying a voltage. The voltage value can be set such that the surface area of the interface with the air is smaller than the maximum value (for example, the minimum value). The second voltage V2 is less than the desired spray amount, but can be set to a voltage value at which spraying is being performed.

  More specifically, the control unit 100 is configured to calculate a relational expression between the current flowing through the second electrode 72 and the voltage applied to the first electrode 74 in the standby state, and determine the second voltage V2 based on the relational expression. Have been. More specifically, as shown in FIG. 4, in the standby state, the control unit 100 first applies the voltage applied to each first electrode 74 such that the value of the current detected by the current sensor SA becomes the first current value Ia. Control V. Then, the first measured voltage Va when the detected value of the current becomes the first current value Ia is stored together with Ia.

  Next, the control unit 100 controls the voltage V applied to each first electrode 74 such that the detected value of the current becomes the second current value Ib different from the first current value Ia. Then, the control unit 100 stores the second measured voltage Vb when the detected value of the current becomes the second current value Ib, together with Ib.

  Thereafter, the control unit 100 calculates a relational expression indicating the relation between the current and the voltage as shown in FIG. 4 based on each of the measured voltages Va and Vb and each of the current values Ia and Ib. Then, the control unit 100 obtains a voltage (intercept) when the current becomes 0 from the relational expression, sets this voltage as the second voltage V2, and sets a value smaller than the second voltage V2 as the first voltage V1. Set.

  The control unit 100 executes the above-described calculation of the relational expression when a predetermined condition is satisfied in the standby state. Here, the predetermined condition may be any condition that indicates that the environment such as temperature may have changed. For example, as a predetermined condition, a predetermined specified time has elapsed since the previous printing control was terminated, or a temperature difference between a temperature detected by a temperature sensor (not shown) and a temperature at the time of calculating the previous relational expression was determined. It is possible to set that the amount becomes equal to or more than a predetermined amount, that a fixing liquid cartridge (not shown) for supplying the fixing liquid L to the fixing head 71 is replaced, and the like.

  The predetermined timing for switching the voltage V from the first voltage V1 to the second voltage V2 is set to a timing after the leading edge of the paper P has passed between the photosensitive drum 61 and the transfer roller TR. Note that the predetermined timing is a time when a predetermined first time (a time corresponding to each sheet P) has elapsed from a time serving as a predetermined starting point. The time serving as the predetermined starting point may be, for example, the time at which the sheet feeding is started by the sheet feeding roller 32A, or the time at which the conveyance of the sheet P once stopped by the registration roller 32E is restarted. Alternatively, the time may be the time when the passage of the leading edge of the sheet P is detected by a sheet passing sensor (not shown) provided upstream of the fixing device 7 and downstream of the registration roller 32E.

  Further, the predetermined timing depends on the distance from an initial position (for example, the position of the paper passing sensor) serving as a predetermined starting point to the above-described first position, and the transport speed of the paper P. In this case, it may be appropriately changed according to the transport speed. Specifically, the above-described first time may be calculated as distance / transport speed. In the following description, a plurality of predetermined timings for switching the voltage V from the first voltage V1 to the second voltage V2 will be described as a plurality of first times t1.

  The control unit 100 sets the voltage V to a voltage at which the toner can be fixed before the toner image (hereinafter, also referred to as “image”) on the sheet P reaches each of the fixing areas A1 to A5. In addition, the third voltage V3 is configured to be higher than the second voltage V2. In other words, the control unit 100 controls the second area D2 separated from the fixing areas A1 to A5 by a predetermined second distance D2 (a distance shorter than the first distance D1; see FIGS. 9D and 9E). When the image reaches the position, that is, when the distance between the image and each of the fixing areas A1 to A5 becomes the second distance D2, the voltage is increased for each of the fixing heads 71A to 71E by a voltage higher than the second voltage V2. It has a function of setting three voltages V3.

  Here, the third voltage V3 is set to a voltage value that is large enough to spray the amount of the fixing liquid L necessary for fixing the image. Therefore, the control unit 100 first sets a target supply amount of the fixing liquid L according to, for example, the image density, and sets a target current value Ix as shown in FIG. 4 according to the target supply amount. Then, the control unit 100 sets the third voltage V3 based on the target current value Ix and the relational expression of FIG.

  The timing before each image arrives at each of the fixing areas A1 to A5 is a predetermined second time (time corresponding to each image and each of the fixing areas A1 to A5) from the above-described predetermined starting point. Is the time when has elapsed. In the following description, a plurality of timings for switching the voltage V from the second voltage V2 to the third voltage V3 will be described as a plurality of second times t2.

  The control unit 100 also arranges a plurality of images corresponding to the fixing areas A1 to A5 (images that fall within the widths of the fixing areas A1 to A5) on a predetermined sheet P in the transport direction, and When the distance between the two images is larger than the third distance D3 (see FIG. 8) which is relatively short, the voltage V is changed to the third voltage V3 after the downstream image of the two has passed through the fixing region. To the second voltage V2. That is, when the control unit 100 determines that the distance between the two images G2 and G3 corresponding to the first fixing area A1 is larger than the third distance D3, for example, as illustrated in FIG. When G2 passes through the first fixing area A1, the voltage V is switched from the third voltage V3 to the second voltage V2. In other words, when the time until the next image G3 reaches the first fixing area A1 after the second image G2 has passed through the first fixing area A1 is equal to or more than the first threshold, the control unit 100 V is switched from the third voltage V3 to the second voltage V2.

  For example, when the control unit 100 changes the voltage applied to the first electrode 74 from the third voltage V3 to the second voltage V2, the first threshold is changed to the second voltage V2 after starting the control for changing the voltage. It is the time to stabilize and can be determined experimentally. The distance D3 can be obtained from the paper transport speed and the first threshold.

  In addition, the control unit 100 arranges a plurality of images corresponding to the respective fixing areas A1 to A5 on the predetermined sheet P in the transport direction, and a third distance D3 in which the distance between two images among the plurality is short to some extent. (See FIG. 8) In the following cases, a function is provided for recognizing two images as one image. That is, when the control unit 100 determines that the distance between the two images G1 and G2 corresponding to the first fixing area A1 is equal to or less than the third distance D3, for example, as illustrated in FIG. 8, the two images G1 and G2 Is recognized as one image, the third voltage V3 is maintained without dropping the voltage V between the two images G1 and G2. In other words, when the time until the next second image G2 reaches the first fixing area A1 after the image G1 passes through the first fixing area A1 is less than the first threshold, the control unit 100 V is maintained at the third voltage V3.

  Further, the control unit 100 changes the voltage V from the third voltage V3 to the first voltage when the most upstream image (for example, G3) on the predetermined sheet P in the transport direction passes through the fixing area (for example, A1). It has a function of changing to V1 or the second voltage V2. More specifically, for example, if the distance from the rear end of the image G3 on the most upstream side of the predetermined paper P to the leading end of the next paper P is larger than the fourth distance D4, the control unit 100 After the image G3 has passed through the first fixing area A1, the voltage V is switched from the third voltage V3 to the first voltage V1. In other words, the control unit 100 determines that, for example, the time from when the most upstream image G3 of the predetermined sheet P passes through the first fixing area A1 to when the leading edge of the next sheet P reaches the first fixing area A1. If the value is larger than the second threshold, the voltage V is switched from the third voltage V3 to the first voltage V1 after the image G3 on the most upstream side has passed through the first fixing area A1.

  For example, when the control unit 100 changes the voltage applied to the first electrode 74 from the third voltage V3 to the first voltage V1, the control unit 100 changes the voltage to the first voltage V1 after starting the control to change the voltage. It is the time to stabilize and can be determined experimentally. The distance D4 can be obtained from the paper transport speed and the second threshold.

  Further, the control unit 100 determines whether the next sheet P does not exist for the image on the most upstream side corresponding to the predetermined fixing area, or when the image corresponding to the predetermined fixing area does not exist on the next sheet P. Also, the voltage V is switched from the third voltage V3 to the first voltage V1 after the image on the most upstream side has passed through the fixing area. Specifically, for example, on the next sheet P conveyed subsequent to the predetermined sheet P on which the most upstream image G3 corresponding to the first fixing area A1 is formed, the image corresponding to the first fixing area A1 is formed. If no image exists, the control unit 100 switches the voltage V from the third voltage V3 to the first voltage V1 after the image G3 has passed through the first fixing area A1.

  Note that the timing at which each image on the most upstream side where the distance from the leading end of the next sheet P is larger than the fourth distance D4 passes through each of the fixing areas A1 to A5, the time when the next sheet P does not exist, or the next time The timing at which the images on the most upstream side where no images are present on the paper P pass through the respective fixing areas A1 to A5 is a predetermined fourth time from the above-mentioned predetermined starting point (the respective images and the respective fixing areas A1 to A5). (Time corresponding to A5). In the following description, a plurality of timings for switching the voltage V from the third voltage V3 to the first voltage V1 will be described as a plurality of fourth times t4.

  Further, for example, when the distance from the rear end of the fourth image G4 on the most upstream side of the predetermined paper P to the front end of the next paper P is equal to or less than the fourth distance D4, the control unit 100 After the fourth image G4 on the side passes through the fifth fixing area A5, the voltage V is switched from the third voltage V3 to the second voltage V2. In other words, the control unit 100 determines, for example, the time from when the most upstream image G4 of the predetermined sheet P passes through the fifth fixing area A5 to when the leading edge of the next sheet P reaches the fifth fixing area A5. If it is equal to or less than the second threshold, the voltage V is switched from the third voltage V3 to the second voltage V2 after the image G4 on the most upstream side has passed through the fifth fixing area A5.

  Note that the timing at which each image on the most upstream side, in which the distance from the leading edge of the next sheet P is equal to or less than the fourth distance D4, passes through each of the fixing areas A1 to A5 is a predetermined time from the above-described predetermined starting point. This is the time when the third time (time corresponding to each image and each fixing area A1 to A5) has elapsed. In the following description, a plurality of timings for switching the voltage V from the third voltage V3 to the second voltage V2 will be described as a plurality of third times t3.

  When the control unit 100 determines that the image does not exist in the predetermined area corresponding to the predetermined fixing area (for example, A3) in the image forming area of the predetermined sheet P, the control unit 100 determines the predetermined area corresponding to the predetermined area. The voltage V applied to the fixing liquid L in the fixing head (for example, 71C) is changed to the first voltage after the first time t1 and while the predetermined sheet P passes through the fixing area corresponding to the predetermined fixing head. It is configured to maintain the voltage V1. That is, since there is no image within the width of the third fixing area A3 in the image forming area of the sheet P on the left side of the drawing shown in FIG. 8, the control unit 100 controls the third fixing head 71C in this case. The first time t1 (that is, the timing of switching from the first voltage V1 to the second voltage V2) is not set. Thus, the voltage V applied to the third fixing head 71C is maintained at the first voltage V1 while the sheet P on the left side in the drawing passes through the third fixing area A3.

  The distances D1 to D4, the times t1 to t4, the voltages V1 to V3, and the like are appropriately set by experiments, simulations, and the like.

  Next, the operation of the control unit 100 will be described in detail. The control unit 100 executes the flowcharts shown in FIGS. 5 to 7 for each of the fixing heads 71A to 71E. In the following description, control of the first fixing head 71A will be described as a representative. The flowchart illustrated in FIG. 5 illustrates a process of setting the times t1 to t4 in the preparation state immediately before performing the fixing control. The flowchart shown in FIG. 6 shows voltage control in a standby state, and the flowchart shown in FIG. 7 shows voltage control in print control. The flowchart shown in FIG. 6 is repeatedly executed in the standby state, and the flowchart shown in FIG. 7 is executed repeatedly in the print control.

  Here, the fixing control refers to control from the start of spraying the fixing liquid L on the first sheet P image in the print command to the end of spraying on the last sheet P image. The preparation state refers to a state from the time when the printing instruction is received to the time when the spraying of the image of the first sheet P is started. The standby state refers to a state in which the power of the laser printer 1 is ON and no print command is received.

  As shown in FIG. 5, when the control unit 100 receives a print command in a standby state (START), first, based on print data, an image corresponding to the first fixing head 71A (hereinafter, also referred to as a “target image”). .) Is determined (S1). If it is determined in step S1 that the target image does not exist (No), the control unit 100 ends this control.

  If it is determined in step S1 that there is a target image (Yes), the control unit 100 sets two target images having an image interval equal to or less than the third distance D3, that is, two target images with a short image interval, as one target image. (S2). In the following description, the number of the plurality of target images set in step S2 is k, and an arbitrary target image among the first to k-th target images is referred to as “target image m”.

  After step S2, the control unit 100 sets a plurality of second times t2 which are timings for switching the voltage V from the second voltage V2 to the third voltage V3 for each target image m (S3). After step S3, the control unit 100 determines whether the target image m is the last image on the sheet P, that is, whether it is the most upstream image (S4).

  If it is determined in step S4 that the target image m is not the most upstream image (No), the control unit 100 increases the voltage V from the third voltage V3 to the second voltage for each target image m that is not the most upstream image. A plurality of third times t3, which are timings for switching to V2, are set (S5). In other words, after the processing of step S4: No → S5, after the target image m on the same sheet P other than the most upstream side has fallen out of the first fixing area A1, the voltage V is changed from the third voltage V3 to the third voltage V3. It can be reduced to two voltages V2.

  If it is determined in step S4 that the target image m is the most upstream image (Yes), the control unit 100 determines whether or not the next sheet P exists for the corresponding most upstream target image m. It is determined (S9). If it is determined in step S9 that the next sheet P does not exist with respect to the target image m (Yes), the control unit 100 proceeds to step S7, in which the corresponding most upstream target image m, that is, the last For the target image k, a fourth time t4 which is a timing for switching the voltage V from the third voltage V3 to the first voltage V1 is set. That is, when the target image m is the last target image k, that is, when the spraying on the last target image k is completed, the voltage V is changed to the standby state through the process of step S9: Yes → S7. The voltage is returned to the first voltage V1.

  When it is determined in step S9 that the next sheet P exists for the target image m (No), the control unit 100 determines the distance from the rear end of the most upstream target image m to the front end of the next sheet P. Is longer than the fourth distance D4 (S6). If it is determined in step S6 that the distance is longer than the fourth distance D4 (Yes), the control unit 100 changes the voltage V for each corresponding most upstream target image m from the third voltage V3 to the first voltage V1. A plurality of fourth times t4, which are the timings for switching to (S7). That is, through the process of step S6: Yes → S7, the time from when the uppermost stream target image m passes through the first fixing area A1 until the leading edge of the next sheet P reaches the first position is obtained. In the case of a relatively long time, the voltage V can be reduced from the third voltage V3 to the first voltage V1 to reduce power consumption.

  If it is determined in step S6 that the distance is equal to or less than the fourth distance D4 (No), the control unit 100 determines whether the target image m + 1 exists on the sheet P next to the corresponding target image m on the most upstream side. It is determined whether or not it is (S8). If it is determined in step S8 that the target image m + 1 does not exist on the next sheet P (Yes), the control unit 100 proceeds to step S7 and performs the fourth process for each corresponding target image m on the most upstream side. Time t4 is set. That is, through the processing of step S8: Yes → S7, if the target image m + 1 does not exist on the next sheet P, that is, it is necessary to spray the fixing liquid L onto the next sheet P with the first fixing head 71A. If not, the voltage V is maintained at the first voltage V1 from when the most upstream target image m passes through the first fixing area A1 until at least the next sheet P passes through the first fixing area A1. Thus, power consumption can be reduced.

  If it is determined in step S8 that the target image m + 1 exists on the next sheet P (No), the process proceeds to step S5, and a third time t3 is set for each corresponding target image m. In other words, if the distance from the rear end of the uppermost stream target image m to the front end of the next sheet P is short, ie, the fourth distance D4 or less, through the processing of step S6: No → S8: No → S5 By changing the voltage V from the third voltage V3 to the second voltage V2, the voltage V is changed from the first voltage V1 to the first voltage V1 between the sheets (between the predetermined sheet on which the target image m is formed and the next sheet). There is no need to switch to two voltages V2.

  Here, when the voltage V is switched from the first voltage V1 to the second voltage V2, a phenomenon may occur in which the fixing liquid L drops from the nozzle N as droplets. Further, in a case where the distance from the rear end of the most upstream target image m to the leading edge of the next sheet P is short, which is equal to or less than the fourth distance D4, for example, if the transport speed is increased, the most upstream target image m becomes the first In some cases, the time from when the sheet P exits the fixing area A1 to when the leading edge of the next sheet P reaches the first fixing area A1 may be extremely short. In this case, if the voltage V is set to the first voltage V1 after the target image m has passed through the first fixing area A1, and the first voltage V1 is switched from the first voltage V1 to the second voltage V2 between sheets, the fixing voltage dropped from the nozzle N is fixed. The liquid L may adhere to the next sheet P. On the other hand, when the distance is as short as the fourth distance D4 or less, the voltage V is maintained at the second voltage V2 between the sheets, thereby suppressing dripping that occurs when switching from the first voltage V1 to the second voltage V2. Therefore, it is possible to prevent the droplet-like fixing liquid L from adhering to the paper P.

  After step S7 or after step S5, for each sheet P including the target image m, the control unit 100 sets a plurality of first times t1 that are timings for switching the voltage V from the first voltage V1 to the second voltage V2. After setting (S10), the control is terminated.

  As shown in FIG. 6, when the power of the laser printer 1 is turned on (START), the control unit 100 determines whether or not a predetermined condition is satisfied, thereby determining whether or not the environment may have changed. A determination is made (S21). When it is determined in step S21 that the predetermined condition is satisfied, that is, that the environment may have changed (Yes), the control unit 100 sets the voltage V to the current values Ia and Ib as shown in FIG. And the relational expression is calculated (S22).

  After step S22, the control unit 100 sets the first voltage V1 and the second voltage V2 from the relational expression (S23). After step S23 or when determining No in step S21, the control unit 100 sets the voltage V to the first voltage V1 (S24), and ends the control. Accordingly, in the standby state, basically, voltage V is set to first voltage V1.

  As shown in FIG. 7, when the control unit 100 receives a print command (START), first, a time t based on a time serving as a predetermined starting point, that is, a time counted up from a time serving as a predetermined starting point. It is determined whether or not t has reached the first time t1 (S31). If t = t1 in step S31 (Yes), the control unit 100 sets the voltage V to the second voltage V2 (S32). Specifically, in step S32, the control unit 100 increases the voltage V from the first voltage V1 to the second voltage V2.

  If t = t1 is not satisfied in step S31 (No), the control unit 100 determines whether the time t has reached the second time t2 (S33). If t = t2 in step S33 (Yes), the control unit 100 sets the voltage V to the third voltage V3 (S34). Specifically, in step S34, the control unit 100 increases the voltage V from the second voltage V2 to the third voltage V3.

  If t = t2 is not satisfied in step S33 (No), the control unit 100 determines whether the time t has reached the third time t3 (S35). If t = t3 in step S35 (Yes), the control unit 100 sets the voltage V to the second voltage V2 (S36). Specifically, in step S36, the control unit 100 reduces the voltage V from the third voltage V3 to the second voltage V2.

  If t = t3 is not satisfied in step S35 (No), the controller 100 determines whether or not the time t has reached the fourth time t4 (S37). If t = t4 in step S37 (Yes), the controller 100 sets the voltage V to the first voltage V1 (S38). Specifically, in step S38, the control unit 100 reduces the voltage V from the third voltage V3 to the first voltage V1.

  If t = t4 is not satisfied in step S37 (No), or after steps S32, S34, S36, and S38, the control unit 100 determines whether the print control has been completed (S39). If the print control has not been completed in step S39 (No), the control unit 100 returns to the process of step S31. If the print control has been completed in step S39 (Yes), the control unit 100 ends this control.

Next, an example of the control will be described with reference to FIGS.
FIG. 8 is a diagram illustrating the time axis of the timing chart in correspondence with the position, and illustrates the control of the first fixing head 71A, the third fixing head 71C, and the fifth fixing head 71E as a representative. Note that, for the second fixing head 71B, since the target image has the same size and arrangement as the target images G1 to G3 for the first fixing head 71A, substantially the same control as the first fixing head 71A is performed. Is For the fourth fixing head 71D, since the target image has the same size and arrangement as the target images G4 to G7 for the fifth fixing head 71E, substantially the same control as the fifth fixing head 71E is performed. Is In the following description, for convenience, the target images G1 to G7 are sequentially referred to as a first image G1, a second image G2, a third image G3, a fourth image G4, a fifth image G5, a sixth image G6, and a seventh image. Also referred to as image G7.

First, control of the first fixing head 71A will be described with reference to FIG.
As shown in FIG. 8, at a first time t1 when the distance from the leading edge of the first sheet P in the print control to the first fixing area A1 becomes the first distance D1, the control unit 100 sets the first voltage in the standby state. The voltage V set to V1 is increased to the second voltage V2. At the second time t2 when the distance from the leading edge of the first image G1 of the first sheet P to the first fixing area A1 becomes the second distance D2, the control unit 100 changes the voltage V from the second voltage V2 to the third voltage. Increase to voltage V3.

  Since the interval between the two images G1 and G2 is equal to or less than the third distance D3, the control unit 100 determines that the second image G2 is in the first fixing state after the leading end of the first image G1 reaches the first fixing area A1. The voltage V is maintained at the third voltage V3 until passing through the area A1. At the third time t3 when the second image G2 passes through the first fixing area A1, the control unit 100 decreases the voltage V from the third voltage V3 to the second voltage V2. More specifically, since the second image G2 does not correspond to the most upstream image, the control unit 100 changes the voltage V from the third voltage V3 after the rear end of the second image G2 has passed through the first fixing area A1. The voltage is reduced to the second voltage V2.

  Thereafter, the control unit 100 similarly increases the voltage V from the second voltage V2 to the third voltage V3 at the second time t2 set for the third image G3 on the most upstream side. At a fourth time t4 when the third image G3 on the most upstream side passes through the first fixing area A1, the control unit 100 reduces the voltage V from the third voltage V3 to the first voltage V1. Specifically, since there is no image corresponding to the first fixing area A1 on the sheet P next to the first sheet P on which the third image G3 on the most upstream side is formed, the control unit 100 sets the voltage V to The third voltage V3 is reduced to the first voltage V1.

Next, control of the third fixing head 71C will be described.
Since there is no image corresponding to the third fixing head 71C on the first sheet P, the control unit 100 does not set the first time t1 for the first sheet P. Thus, even when the distance from the leading edge of the first sheet P to the third fixing area A3 is the first distance D1, the control unit 100 maintains the voltage V at the first voltage V1 in the standby state. I do.

  Since there are images G5 and G6 corresponding to the third fixing head 71C on the next sheet P, the control unit 100 sets the first time t1 for the next sheet P. Thus, at the first time t1 when the distance from the leading edge of the next sheet P to the third fixing area A3 becomes the first distance D1, the control unit 100 changes the voltage V from the first voltage V1 to the second voltage V2. Raise to

  Thereafter, similarly to the control of the first fixing head 71A, the voltage V is increased from the second voltage V2 to the third voltage V3 at the second time t2, and the voltage V is increased from the third voltage V3 to the first voltage at the fourth time t4. Lower to V1. Note that since the interval between the images G5 and G6 is also equal to or less than the third distance D3, the control unit 100 maintains the voltage V at the third voltage V3 between the images G5 and G6.

Finally, control of the fifth fixing head 71E will be described.
At a first time t1 when the distance from the leading edge of the first sheet P to the fifth fixing area A5 becomes the first distance D1, the control unit 100 changes the voltage V set to the first voltage V1 in the standby state. Increase to the second voltage V2. At the second time t2 when the distance from the leading end of the fourth image G4 of the first sheet P to the fifth fixing area A5 becomes the second distance D2, the control unit 100 changes the voltage V from the second voltage V2 to the third voltage t3. Increase to voltage V3.

  Here, since the image corresponding to the fifth fixing area A5 on the first sheet P is only one of the fourth images G4, the fourth image G4 corresponds to the most upstream image. Since the distance from the rear end of the fourth image G4 to the front end of the next sheet P is equal to or less than the fourth distance D4, the control unit 100 determines at the third time when the fourth image G4 passes through the fifth fixing area A5. At t3, the voltage V is reduced from the third voltage V3 to the second voltage V2 without lowering to the first voltage V1.

  As a result, the voltage is maintained between the time when the fourth image G4 on the first sheet P passes through the fifth fixing area A5 and the time when the fifth image G5 on the next sheet P reaches the position immediately before the fifth fixing area A5. V is maintained at the second voltage V2. Thereafter, similarly to the control of the first fixing head 71A, the voltage V is increased from the second voltage V2 to the third voltage V3 at the second time t2, and the voltage V is increased from the third voltage V3 at the fourth time t4. The voltage is reduced to the first voltage V1. Note that since the intervals between the images G5, G6, and G7 are each equal to or less than the third distance D3, the control unit 100 maintains the voltage V at the third voltage V3 between the images G5, G6, and G7.

Next, how the voltage V applied to each of the fixing heads 71A to 71E is switched will be described with reference to FIGS.
As shown in FIGS. 9A and 9B, when the leading edge of the first sheet P reaches a position upstream of the second fixing area A2 and the fourth fixing area A4 by a first distance D1, the second sheet P is moved to the second position. Each voltage V applied to the second fixing head 71B and the fourth fixing head 71D switches from the first voltage V1 to the second voltage V2.

  As shown in FIG. 9C, when the leading edge of the first sheet P reaches a position upstream of the first fixing area A1, the third fixing area A3, and the fifth fixing area A5 by a first distance D1. The voltages V applied to the first fixing head 71A and the fifth fixing head 71E are switched from the first voltage V1 to the second voltage V2. Since the first sheet P has no image corresponding to the third fixing head 71C, the voltage V applied to the third fixing head 71C is maintained at the first voltage V1.

  As shown in FIG. 9D, when the first image G1 corresponding to the second fixing head 71B reaches a position upstream of the second fixing area A2 by a second distance D2, the second fixing head 71B. Is switched from the second voltage V2 to the third voltage V3. As shown in FIG. 9E, when the first image G1 corresponding to the first fixing head 71A reaches a position upstream of the first fixing area A1 by a second distance D2, the first fixing head 71A. Is switched from the second voltage V2 to the third voltage V3.

  As shown in FIG. 9F, when the fourth image G4 corresponding to the fourth fixing head 71D reaches a position away from the fourth fixing area A4 by a second distance D2 upstream, the fourth fixing head 71D. Is switched from the second voltage V2 to the third voltage V3. As shown in FIG. 9G, when the fourth image G4 corresponding to the fifth fixing head 71E reaches a position upstream of the fifth fixing area A5 by a second distance D2, the fifth fixing head 71E. Is switched from the second voltage V2 to the third voltage V3.

  As shown in FIG. 9H, when the second image G2 leaves the second fixing area A2, the voltage V applied to the second fixing head 71B switches from the third voltage V3 to the second voltage V2. As shown in FIG. 10A, when the second image G2 leaves the first fixing area A1, the voltage V applied to the first fixing head 71A switches from the third voltage V3 to the second voltage V2.

  Thereafter, at the timing when the distance between the third image G3 corresponding to each of the fixing heads 71A and 71B and each of the fixing areas A1 and A2 becomes the above-described second distance D2, FIGS. 10B and 10C. As shown, each voltage V applied to each of the fixing heads 71A and 71B switches from the second voltage V2 to the third voltage V3. As shown in FIG. 10D, when the third image G3 passes through the second fixing area A2, the voltage V applied to the second fixing head 71B switches from the third voltage V3 to the first voltage V1. That is, since there is no image corresponding to the second fixing area A2 on the next sheet P, the voltage V applied to the second fixing head 71B switches from the third voltage V3 to the first voltage V1. Similarly, the voltage V applied to the first fixing head 71A also changes from the third voltage V3 to the first voltage V1 when the third image G3 passes through the first fixing area A1, as shown in FIG. Switch to.

  As shown in FIG. 10E, when the fourth image G4 corresponding to the fourth fixing head 71D passes through the fourth fixing area A4, the voltage V applied to the fourth fixing head 71D changes from the third voltage V3 to the third voltage V3. Switching to two voltages V2. That is, since the distance between the fourth image G4 and the leading end of the next sheet P is equal to or less than the fourth distance D4, the voltage V applied to the fourth fixing head 71D switches from the third voltage V3 to the second voltage V2. Similarly, the voltage V applied to the fifth fixing head 71E also changes from the third voltage V3 to the second voltage V2 when the fourth image G4 passes through the fifth fixing area A5 as shown in FIG. Switch to.

  8 to 10, the control of each of the fixing heads 71A to 71E for the widest fifth sheet P5 has been described. However, the above-described control is similarly performed for sheets P1 to P4 of other widths. . However, when the control is performed on the sheets P1 to P4 having other widths, the fixing head (for example, the fifth fixing head 71E for the fourth sheet P4) which is out of the width of the image forming area of the sheet is used. Is maintained at the first voltage V1 during the printing control.

  More specifically, for example, when print control is performed on the fourth sheet P4, there is no target image corresponding to the fifth fixing head 71E that is out of the width of the image forming area of the fourth sheet P4. In the process shown in FIG. 6 for No., it is determined No in step S1. As a result, since the times t1 to t4 for changing the voltage V are not set for the fifth fixing head 71E, the voltage applied to the fifth fixing head 71E is maintained at the first voltage V1 during the printing control. You.

According to the above, the following effects can be obtained in the present embodiment.
Since the voltage is increased from the first voltage V1 to the second voltage V2 before the leading edge of the paper P reaches the fixing areas A1 to A5, a droplet-shaped drop from the nozzle N when switching from the first voltage V1 to the second voltage V2. The fixer L can be prevented from adhering to the paper P.

  Since the second voltage V2 is smaller than the third voltage V3 before the third voltage V3 is applied, the first voltage is changed to the third voltage at a stretch before the leading edge of the sheet P reaches the fixing areas A1 to A5, for example. Power consumption can be reduced as compared with the embodiment.

  Since the voltage is reduced from the third voltage V3 to the second voltage V2 between the images G2 and G3 having a long image interval, the power consumption is lower than in the case where the voltage is maintained at the third voltage V3 between the images G2 and G3, for example. Can be suppressed.

  Since the voltage is maintained at the third voltage V3 between the images G1 and G2 whose image intervals are short, the spray state when the second image G2 following the first image G1 is fixed can be stabilized.

  Since the voltage is reduced to the first voltage V1 after the third image G3 on the most upstream side has passed through the first fixing area A1, wasteful power is consumed between the first sheet P and the next sheet P. Can be suppressed.

  After the fourth image G4 on the most upstream side passes through the fifth fixing area A5, the voltage is set to the second voltage V2 without lowering to the first voltage V1, so that the liquid drops from the fifth fixing head 71E between sheets. Can be suppressed.

  Since the second voltage V2 is determined based on the relational expression calculated in the standby state, the second voltage V2 can be set to an appropriate value according to the environment.

  Since the plurality of fixing heads 71A to 71E arranged in the width direction are individually controlled, for example, when the image corresponding to the third fixing head 71C does not exist on the sheet P, the third fixing head 71C is set to the non-operation state. Thus, useless spray from the third fixing head 71C can be suppressed.

  Since each of the fixing heads 71A to 71E is controlled in accordance with the difference in the width of the paper P, for example, when printing control is performed on the narrowest first paper P1, it corresponds to the image forming area of the first paper P1. The fixing heads 71 </ b> B to 71 </ b> E, which are not to be operated, are brought into a non-operating state, so that it is possible to suppress unnecessary spraying of the fixing liquid L from the fixing heads 71 </ b> B to 71 </ b> E.

  The width of the first fixing head 71A is made smaller than the width of the first sheet P1, and the other fixing heads 71B to 71E are configured to have a small width so as not to protrude outside the width of the corresponding sheets P2 to P5. Therefore, the size of each of the fixing heads 71A to 71E can be reduced, and the size of the fixing device 7 can be reduced.

  The present invention is not limited to the above-described embodiment, and can be used in various forms as exemplified below.

  In the above embodiment, when the distance between two images is larger than the third distance D3, the voltage V is changed to the second voltage V2 (a voltage value at which Taylor cone starts to be generated), but the present invention is not limited to this. However, any voltage value may be used as long as it is lower than the third voltage V3 and higher than the first voltage V1.

  In the embodiment, when the distance from the rear end of the fourth image G4 on the most upstream side to the leading end of the next sheet P is equal to or less than the fourth distance D4, the fourth image G4 on the most upstream side is fixed by the fifth fixing. After passing through the region A5, the voltage V is set to the second voltage V2. However, the present invention is not limited to this, and any voltage value may be used as long as the value is higher than the first voltage V1. Good.

  In the above-described embodiment, in the printing control, the voltage V is once increased from the first voltage V1 in the standby state to the second voltage V2, and then is increased to the third voltage V3 for fixing. It is not limited. For example, before the leading edge of the paper P reaches the fixing area, the voltage V may be increased from the first voltage V1 to the third voltage V3 at a stretch.

  In the above-described embodiment, the first electrode 74 is disposed inside the housing 73. However, the present invention is not limited to this. For example, the nozzle and the housing may be formed of a conductive member such as a metal to form the nozzle or the housing. May be applied. In this case, the nozzle or the housing to which the voltage is applied functions as a first electrode. Further, in this case, by moving the plurality of conductive housing portions apart from each other or by providing an insulating member between the housing portions, the movement of electric charge between the housing portions may be blocked. Good. Alternatively, the housing may be formed of a non-conductive member such as resin, the nozzle may be formed of a conductive member such as metal, and a voltage may be applied to the nozzle. In this case, the nozzle functions as a first electrode.

  In the above embodiment, the present invention is applied to the laser printer 1, but the present invention is not limited to this, and the present invention may be applied to other image forming apparatuses, for example, a copying machine or a multifunction peripheral.

  In the above embodiment, the recording sheet is a sheet P such as a thick sheet, a postcard, a thin sheet, or the like. However, the present invention is not limited to this, and may be, for example, an OHP sheet.

In the above embodiment, the photosensitive drum 61 is exemplified as the photosensitive member, but the present invention is not limited to this, and may be, for example, a belt-like photosensitive member.
In the above embodiment, the transfer roller TR is exemplified as the transfer member. However, the present invention is not limited to this, and the transfer member may be any one to which a transfer bias is applied, such as a conductive brush or a conductive leaf spring. .

  In the above embodiment, the pressurizing device 75 having a pump and a pressure reducing valve is exemplified as the pressure applying means. However, the present invention is not limited to this. For example, a cylinder or the like that pressurizes or depressurizes the air in each head. There may be.

  In the above-described embodiment, the fixing head 71 is configured by five fixing heads 71A to 71E, but the present invention is not limited to this, and may be configured by one fixing head, or two to four or six or more. May be constituted.

  In the above embodiment, the processing in steps S2 and S6 is determined based on the distance, but the present invention is not limited to this, and may be determined based on time.

  In the above embodiment, the voltage is applied in the standby state. However, the present invention is not limited to this, and the voltage need not be applied in the standby state.

  In the above-described embodiment, the fixing regions A1 to A5 have the same shape, size, and position as the lower surface of the storage unit 73 for convenience of description. However, the present invention is not limited to this. May be small or large. That is, the fixing area may be defined by the width of the sprayed fixing liquid on the sheet in the front-rear direction and the left-right direction.

7 Fixing Device 71 Fixing Head 72 Second Electrode 73 Housing 74 First Electrode 100 Control Unit L Fixing Solution N Nozzle P Paper

Claims (18)

An accommodating section for accommodating the fixing liquid therein, and a fixing head having a nozzle communicating with the accommodating section and spraying the fixing liquid toward a developer image on a recording sheet;
A potential difference forming unit for forming a potential difference between the fixing liquid in the nozzle and a recording sheet conveyed at a position away from the nozzle;
A control unit that controls a voltage applied to the potential difference forming unit,
The fixing device is characterized in that the control unit is configured to apply a voltage to the potential difference forming unit so that the fixing liquid is sprayed from the nozzle before the leading end of the recording sheet reaches the fixing region.   The control unit is configured to apply a voltage to the potential difference forming unit such that the fixing liquid is sprayed from the nozzle after the leading end of the recording sheet passes between the photosensitive member and the transfer member. The fixing device according to claim 1, wherein: The control unit includes:
In the standby state, the voltage is a first voltage of a magnitude that does not spray the fixing liquid from the nozzle,
3. The print control according to claim 1, wherein the voltage is set to a second voltage higher than the first voltage at a predetermined timing before the leading edge of the recording sheet reaches the fixing area. Fixing device.   Before the developer image on the recording sheet reaches the fixing area, the control unit changes the voltage to a voltage at which the developer can be fixed and to a third voltage higher than the second voltage. The fixing device according to claim 3, wherein:   In the case where a plurality of developer images are arranged on the predetermined recording sheet at a distance from each other in the transport direction of the recording sheet, the control unit may determine whether the developer image on the predetermined recording sheet has passed through the fixing area. When the time until the next developer image on the predetermined recording sheet reaches the fixing area is equal to or greater than a first threshold, the voltage is set to be smaller than the third voltage, and The fixing device according to claim 4, wherein the fourth voltage is higher than the voltage.   The fixing device according to claim 5, wherein the fourth voltage has the same value as the second voltage.   The controller may be configured such that the time from when the developer image on the predetermined recording sheet passes through the fixing area to when the next developer image on the predetermined recording sheet reaches the fixing area is less than the first threshold value. 7. The fixing device according to claim 5, wherein the voltage is maintained at the third voltage.   8. The control device according to claim 3, wherein the control unit sets the voltage to the first voltage after the developer image on the recording sheet on the most upstream side in the transport direction passes through the fixing area. 9. The fixing device according to claim 1.   The controller is configured such that the time from when the developer image on the recording sheet on the most upstream side in the transport direction passes through the fixing area to when the leading edge of the next recording sheet reaches the fixing area is equal to or less than a second threshold value. 9. The fixing device according to claim 8, wherein in the case, the voltage is set to a value higher than the first voltage after the developer image on the most upstream side passes through the fixing area.   The control unit calculates a relational expression between a current flowing through the potential difference forming unit and a voltage applied to the potential difference forming unit in a standby state, and determines the second voltage based on the relational expression. The fixing device according to claim 3. A pressure applying means for applying pressure to the fixing solution,
The fixing device according to any one of claims 3 to 10, wherein the control unit maintains a pressure applied to the fixing solution constant during printing control. The fixing head is provided in a plurality in the width direction of the recording sheet,
The fixing device according to claim 3 , wherein the control unit individually controls a voltage applied to a fixing solution in each of the fixing heads.   The fixing device according to claim 12, wherein the fixing area is set for each of the plurality of fixing heads.   When the control unit determines that the developer image does not exist in a predetermined area within a predetermined width of the image forming area of the predetermined recording sheet, the control unit fixes the developer in a predetermined fixing head corresponding to the predetermined area. The voltage applied to the liquid is maintained at the first voltage after the predetermined timing and while the predetermined recording sheet passes through a fixing area corresponding to the predetermined fixing head. Item 14. The fixing device according to Item 13. The plurality of fixing heads,
A first fixing head for spraying a fixing solution on the first recording sheet;
A second fixing head adjacent to the first fixing head on one side in the width direction;
A third fixing head adjacent to the second fixing head on one side in the width direction,
The first fixing head and the second fixing head are capable of spraying a fixing liquid onto a second recording sheet wider than the first recording sheet,
13. The fixing device according to claim 12, wherein the first fixing head, the second fixing head, and the third fixing head are capable of spraying a fixing liquid onto a third recording sheet wider than the second recording sheet. The fixing device according to any one of claims 1 to 14. A width of the first fixing head is smaller than a width of the first recording sheet;
The second fixing head is disposed on the other side of the one end of the second recording sheet in the width direction,
16. The fixing device according to claim 15, wherein the third fixing head is disposed on the other side of the third recording sheet from the one end in the width direction.   The fixing device according to claim 3, wherein the second voltage is a voltage at which the developer can be fixed. The potential difference forming section,
A first electrode capable of applying a voltage to the fixer in contact with the fixer;
A second electrode facing the nozzle;
The fixing device according to any one of claims 1 to 17, further comprising:

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