JP6668846B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device that fixes a toner image on paper.

  2. Description of the Related Art Conventionally, there is known an electrophotographic image forming apparatus including a fixing device for melting a transferred toner image by heating the toner and fixing the toner on a sheet. The fixing device has a heating element such as a halogen heater or a ceramic heater for melting the toner. The fused 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 fixing device of the heat fixing method consumes a large amount of electric power because the toner is heated, and thus is not suitable for power saving of the image forming apparatus.

  In order to solve the above-mentioned 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 sheet to fix the toner image on the sheet. This fixing device does not require a heat treatment for melting the toner as in the heat fixing method, has low power consumption, and is excellent in power saving. As a method of applying a fixing solution to a toner image, a method of applying a fixing solution to a toner image by electrostatic spraying is known (see Patent Document 1).

JP 2009-69256 A

  By the way, in the fixing method using the electrostatic spray, when the spray of the fixing liquid from the nozzle for spraying the fixing liquid is stopped and the fixing liquid adheres to the outer peripheral surface of the nozzle and remains, the normal spraying is performed at the next spraying start. May not be possible.

  Accordingly, an object of the present invention is to remove a fixing solution attached to an outer peripheral surface of a nozzle for spraying the fixing solution.

In order to solve the above-described problems, a fixing device according to the present invention includes a storage unit that stores therein a fixing liquid, and a nozzle 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 solution in the nozzle and a recording sheet conveyed at a position distant from the nozzle, and a pressure applying unit for applying pressure to the fixing solution And a control unit for controlling a voltage applied to the potential difference forming unit and a pressure applied to the fixing solution.
The control unit sets the pressure applied to the fixing solution by the pressure applying unit to a first pressure, and applies a voltage to the potential difference forming unit to spray the fixing solution from the nozzle toward the recording sheet. When the spraying process and the fixing spraying process are not performed, a voltage is applied to the potential difference forming unit while the pressure applying unit applies a second pressure smaller than the first pressure to the fixing solution. And a droplet removing process to be applied.

  According to this configuration, even when the fixing liquid adheres to the outer peripheral surface of the nozzle, the fixing liquid adhering to the outer peripheral surface of the nozzle can be removed by performing the droplet removal processing, so that the spraying is performed. When starting, a stable spray state can be obtained quickly.

  Further, in the above-described configuration, the control unit may be configured to perform the droplet removing process before performing the fixing spraying process.

  Further, in the above-described configuration, the second pressure may be equal to or lower than a meniscus pressure resistance.

  In the above-described configuration, the control unit may be configured to apply a voltage for a first time in the droplet removing process.

  Further, in the above-described configuration, after performing the voltage application for the first time in the droplet removing process, the control unit changes the pressure from the second pressure to the first pressure and starts the fixing spray process. It may be configured to do so.

  In the above-described configuration, the control unit may change the pressure from the second pressure to the first pressure when a state in which no current flows in the potential difference forming unit continues for a second time in the droplet removing process. The fixing spraying process may be started by changing the setting.

  Further, in the above-described configuration, the control unit may be configured to perform the droplet removing process based on an input of a print job.

  In the above-described configuration, the control unit may be configured not to perform the droplet removing process when a third time or more has elapsed from the end of the previous fixing spraying process.

  Here, the “third time” refers to a sufficiently long time for evaporating the fixing solution attached to the outer peripheral surface of the nozzle.

  According to this, if the third time or more has elapsed since the end of the previous fixing spraying process, the fixing liquid attached to the outer peripheral surface of the nozzle will not evaporate, and in this case, the droplet removing process will not be performed. Thus, power consumption can be suppressed.

  Further, the voltage applied to the potential difference forming section in the droplet removing process may be within a range of a voltage value in the fixing spraying process.

  Further, in the above-described configuration, the control unit may be configured to perform the droplet removing process when performing a purge process of discharging the fixing solution from the nozzle to the outside by pressure.

  According to this, the fixer adhering to the outer peripheral surface of the nozzle in the purging process can be satisfactorily removed by the droplet removing process.

  In the above-described configuration, the pressure applying unit may include a pump that pressurizes gas in the fixing head.

  In the above-described configuration, the potential difference forming section may include a first electrode that contacts the fixing solution, and a second electrode that faces the nozzle.

  ADVANTAGE OF THE INVENTION According to this invention, the fixing liquid adhering to the outer peripheral surface of the nozzle which sprays the fixing liquid can be removed.

1 is a diagram illustrating a laser printer including a fixing device according to an embodiment of the present disclosure. FIG. 3 is a diagram illustrating a fixing device in detail. FIG. 3A is a perspective view of the fixing head viewed from diagonally above, and FIG. 3B is a perspective view of the first fixing head viewed from diagonally below. FIG. 3 is a bottom view of the fixing head as viewed from below. 4 is a flowchart illustrating an operation of a control unit. FIGS. 7A to 7C are diagrams illustrating a state in which a fixing solution attached to an outer peripheral surface of a nozzle is removed. 9 is a flowchart illustrating an operation of a control unit according to a modification.

  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. Further, the up-down direction toward the paper surface is referred to as “up-down direction”.

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

  The feeder unit 3 includes a paper feed tray 31 that is detachably attached to a lower portion of the main body housing 2, and a paper feed mechanism 32 that feeds the paper SH 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 SH, and can be appropriately switched between stop and rotation by a control unit 100 described later.

  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, 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 light 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 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 for supplying the developing roller 61 are provided.

  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 onto 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 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 sheet SH is conveyed 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 sheet SH.

  The fixing device 7 is a device that fixes the toner image on the sheet SH by supplying the charged fixing liquid L to the toner image on the sheet SH 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 Rd for nipping and transporting the sheet SH discharged from the fixing device 7 to the downstream side are provided. The sheet SH transported by the downstream-side transport roller Rd is transported to the paper discharge roller R, and is discharged from the paper discharge roller R onto the paper discharge tray 21.

Next, the configuration of the fixing device 7 will be described in detail.
As shown in FIG. 2, the fixing device 7 includes a fixing head 71 for spraying the fixing liquid L toward the toner image on the sheet SH, a second electrode 72 for supporting the sheet SH under the fixing head 71, A pressurizing device 75 as an example of a pressure applying unit, a fixing liquid cartridge 76, a tank 77, and a control unit 100.

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 the solute, as an aliphatic monocarboxylic acid ester system, ethyl laurate, butyl laurate, isopropyl laurate, ethyl myristate, butyl myristate, isopropyl myristate, ethyl palmitate, butyl 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, alkylaryl sulfonates such as sodium dodecylbenzenesulfonate, alkyl sulfate salts such as sodium dodecyl sulfate, and polysulfates such as sodium polyethoxyethylene lauryl ether sulfate. Polyoxyethylene alkyl aryl ether sulfates such as sodium oxyethylene alkyl ether sulfate and sodium polyoxyethylene nonyl phenyl 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. 3A, the fixing head 71 is arranged in a staggered manner in the width direction, and has 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 arranged at substantially the same position in the front-rear direction, that is, in the transport direction of the sheet SH, and are spaced apart in the left-right direction, that is, in the width direction of the sheet SH. 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. That is, each of the fixing heads 71A to 71E (each of the housing portions 73) has the same shape and is configured separately. Further, the same number of nozzles N are provided in the same arrangement in each of the housing portions 73.

  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. 3B, the plurality of nozzles N in 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.

  More 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. 4, 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 disposed 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 disposed 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 in 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, a fixing head (for example, the first nozzle N1 on the leftmost side of the first fixing head 71A in the drawing) in the width direction of the predetermined fixing head and a 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 SH 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.

  The 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 SH1 of a plurality of types of sheets SH on which printing can be performed by the laser printer 1. It is formed with a width smaller than the width of the sheet SH1. 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 SH1. More specifically, the first fixing area A1 of the first fixing head 71A is formed to have a size equal to or larger than the width of the image forming area, which is the area where the image of the first sheet SH1 is formed, and It is arranged so that the entire width of the image forming area falls within the width of the area A1.

  In this embodiment, as shown in FIG. 4, the sheets SH1 to SH5 having different sheet widths are transported based on the left end. More specifically, a guide member (not shown) that contacts the left end of each of the sheets SH1 to SH5 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 (from the right end of the second sheet SH2 wider than the first sheet SH1). On the other side). More specifically, the right end of the second fixing area A2 of the second fixing head 71B is located at the same position as the right end of the image forming area of the second sheet SH2 or at a position to the right of the right end. The left end of the image forming area of the second sheet SH2 is substantially the same as the left end of the image forming area of the first sheet SH1. 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 to the image forming area of the second sheet SH2. 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 SH3 wider than the second sheet SH2. Specifically, the right end of the third fixing area A3 of the third fixing head 71C is located at the same position as the right end of the image forming area of the third sheet SH3 or at a position on the right side of the right end. The left end of the image forming area of the third sheet SH3 is located at substantially the same position as the left end of the image forming area of the first sheet SH1. As described above, the first fixing head 71A, the second fixing head 71B, and the third fixing head 71C are arranged, so that the first fixing head 71A, the second fixing head 71B, and the third fixing head 71C become the third fixing head 71C. The fixing liquid L can be sprayed on the image forming area of the sheet SH3.

  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 SH4 wider than the third sheet SH3. Specifically, the right end of the fourth fixing area A4 of the fourth fixing head 71D is arranged at the same position as the right end of the image forming area of the fourth sheet SH4 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 SH4 is substantially at the same position as the left end of the image forming area of the first sheet SH1. 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 SH4.

  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 SH5 wider than the fourth sheet SH4. Specifically, the right end of the fifth fixing area A5 of the fifth fixing head 71E is arranged at the same position as the right end of the image forming area of the fifth sheet SH5 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 SH5 is located at substantially the same position as the left end of the image forming area of the first sheet SH1. 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 SH5.

  Returning to FIG. 2, 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 the voltage application unit 120. The voltage applied to the first electrode 74 is preferably 1 kV to 10 kV.

  A pressure device 75 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 a pump 75A that pressurizes the air in each of the fixing heads 71A to 71E, and air from each of the fixing heads 71A to 71E. And a pressure reducing valve 75B for reducing the pressure by releasing the pressure. Each of the fixing heads 71A to 71E is provided with a pressure sensor SP (only one of them 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 forming a potential difference between the fixing solution L in the nozzle N and the sheet SH by coming into contact with the sheet SH, 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 sheet SH, 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 sheet SH is in a substantially zero potential state. For this reason, the fixing liquid L in the form of droplets flies toward the sheet SH due to the Coulomb force, and adheres to the sheet SH and the toner image.

  The first current sensor SB 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 first current sensor SB detects a current flowing through the first electrode 74 when the fixing liquid L is sprayed from the nozzle N onto the sheet SH, and outputs the detected value to the control unit 100. Here, even if 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 sheet SH, a current flows through the first electrode 74.

  The second current sensor SA is a sensor that detects a current flowing through the second electrode 72. The second current sensor SA detects a current flowing through the second electrode 72 when the fixing liquid L is sprayed from the nozzle N onto the sheet SH, and outputs the detected value to the control unit 100. Here, even if 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 second electrode 72 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 sheet SH, a current flows through the second electrode 72.

  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 solution L in the nozzle N and the sheet SH conveyed at a position away from the nozzle N. Department.

  The fixing liquid cartridge 76 is a cartridge in which the fixing liquid L is filled, and is configured to be detachable from the main housing 2. The fixing liquid cartridge 76 is connected to a tank 77 via a pipe 76A. The pipe 76A may be provided with a hydraulic pump for supplying the fixing liquid L from the fixing liquid cartridge 76 to the tank 77, a switching valve for switching between supplying and stopping the fixing liquid L, and the like.

  The tank 77 is provided in the main body housing 2 and is connected to the housing 73 of each of the fixing heads 71A to 71E via a plurality of pipes 77A. Each pipe 77A is provided with a hydraulic pump for supplying the fixing liquid L from the tank 77 to each of the fixing heads 71A to 71E, and a valve 77B for switching between supplying and stopping the fixing liquid L. The valve 77B is made of an insulating member.

  The control unit 100 includes a storage unit 110 including a RAM and a ROM, a voltage application unit 120 that applies a voltage to the first electrode 74, a CPU, an input / output circuit, and the like. The control unit 100 controls the pressurizing device 75 and controls the voltage applied to the first electrode 74 based on image data input from the outside and signals from the sensors SP, SA, and SB. have. More specifically, the control unit 100 individually controls the voltage applied to the fixing liquid L in each of the fixing heads 71A to 71E and the pressure applied to the fixing liquid L in each of the fixing heads 71A to 71E for each fixing head. It is configured as follows.

  Specifically, the control unit 100 performs a fixing spraying process of spraying the fixing liquid L from the fixing heads 71A to 71E toward the sheet SH to fix the toner image on the sheet SH, and a liquid spraying process on the outer peripheral surface of the nozzle N. And a droplet removing process for removing droplets. When performing the fixing spraying process, the control unit 100 sets the pressure P applied to the fixing liquid L to the first pressure P1, sets the pressure P applied to the fixing liquid L to the first pressure P1, and sets each first electrode The configuration is such that the voltage V applied to 74 is controlled based on the target spray amount ρ obtained based on the image data. Here, the target spray amount ρ is a target value of the fixing liquid L sprayed per unit area of the paper SH, and is set to a larger spray amount as the image density is higher. Further, the first pressure P1 is appropriately set, for example, by an experiment, a simulation, or the like.

  The control unit 100 executes the droplet removing process before performing the fixing spraying process. More specifically, the control unit 100 executes the droplet removing process from when a print job is input to when the fixing spraying process is executed.

  The controller 100 sets the pressure P applied to the fixing liquid L to a second pressure P2 smaller than the first pressure P1 and sets the voltage V applied to the fixing liquid L to a predetermined voltage Va in the droplet removing process. . Here, the predetermined voltage Va is a value within the range of the voltage value at the time of the fixing spray processing, and is appropriately determined by an experiment, a simulation, or the like. The higher the predetermined voltage Va, the more the fixing liquid L attached to the outer peripheral surface of the nozzle N can be scattered. Therefore, the predetermined voltage Va is set to the maximum voltage value in the range of the voltage value during the fixing spraying process. It is good to set. The second pressure P2 is a value within the range of 0 ≦ P2 <P1, and is appropriately determined by experiments, simulations, or the like so as to be equal to or lower than the meniscus withstand pressure.

Here, the meniscus pressure resistance refers to the maximum pressure at which the fixing liquid L can be held in the nozzle N when no voltage is applied to the fixing liquid L, and is expressed by the following equation (1). .
Pm = (4 · σ · cos θ) / d (1)
Pm: Meniscus pressure resistance σ: Surface tension of fixing liquid L θ: Contact angle d: Inner diameter (diameter) of tip of nozzle N

  That is, when a voltage higher than the meniscus pressure resistance is applied to the fixing liquid L in a state where no voltage is applied to the fixing liquid L, the fixing liquid L leaks from the tip of the nozzle N, and the pressure applied to the fixing liquid L is reduced. In the following case, the fixing liquid L is held in the nozzle N.

  In the droplet removing process, the control unit 100 changes the pressure P from the second pressure P1 to the first pressure P1 after applying the voltage V that becomes the predetermined voltage Va to the first electrode 74 for the first time T1. The fixing spraying process is started. Here, the first time T1 refers to a time required for removing the fixing liquid L adhered to the outer peripheral surface of the nozzle N by applying the predetermined voltage Va, and is appropriately set by an experiment, a simulation, or the like.

  When a print job is input, the control unit 100 determines whether or not a third time T3 or more has elapsed since the end of the previous fixing spraying process. Is configured not to perform. Here, the "third time T3" refers to a sufficiently long time for allowing the fixing liquid L attached to the outer peripheral surface of the nozzle N to evaporate spontaneously, and is appropriately set by experiments, simulations, or the like.

  Note that the third time T3 may be appropriately changed according to temperature, humidity, and the like. For example, the third time T3 may be set to a shorter time as the temperature is higher, or may be set to a shorter time as the humidity is lower.

  In addition, the control unit 100 determines that when the moisture of the fixing liquid L entering the tip of the nozzle N evaporates and the viscosity of the fixing liquid L increases (for example, when the fixing operation has not been performed for a certain period of time or the like). And a function of executing a purge process for discharging the fixing liquid L clogged at the tip of the nozzle N to the outside by pressure. In the purging process, for example, the control unit 100 presses the fixing solution L in the fixing heads 71A to 71E by driving the pump 75A without applying a voltage to the fixing solution L, so that the fixing solution Discharge L.

  When such a purging process is performed, the fixing liquid L easily adheres to the outer peripheral surface of the nozzle N. Therefore, in the present embodiment, the control unit 100 is configured to perform the droplet removing process even when the purge process is performed.

  Next, the operation of the control unit 100 will be described in detail with reference to FIG. The control unit 100 executes the process shown in FIG. 5 for each of the fixing heads 71A to 71E. Hereinafter, control of the first fixing head 71A will be described as a representative.

  As shown in FIG. 5, the control unit 100 first determines whether a print job has been input (S1). If it is determined in step S1 that a print job has been input (Yes), the control unit 100 determines whether the third time T3 has elapsed since the previous fixing spraying process (S2).

  If it is determined in step S2 that the third time T3 has not elapsed (No), the control unit 100 sets the pressure P applied to the fixing liquid L to a lower second pressure P2 (S3). Specifically, when the current pressure P is the same as the second pressure P2 in step S3, the control unit 100 maintains the pressure P at the second pressure P2 without controlling the pressurizing device 75. If the current pressure P is smaller than the second pressure P2 in step S3, the control unit 100 operates the pump 75A to increase the pressure P to the second pressure P2, and the current pressure P becomes the second pressure P2. If the pressure is higher than the pressure P2, the pressure reducing valve 75B is opened to reduce the pressure P to the second pressure P2, and then the pressure reducing valve 75B is closed.

  After step S3, the control unit 100 applies a predetermined voltage Va to the fixing liquid L (S4). Thus, the droplet removing process is started.

  After step S4, the control unit 100 determines whether or not the first time T1 has elapsed since the application of the predetermined voltage Va to the fixing liquid L, so that the fixing liquid L adhering to the outer peripheral surface of the nozzle N is reduced. It is determined whether or not it has been removed (S5). If it is determined in step S5 that the first time T1 has not elapsed (No), the control unit 100 returns to the process of step S3 and continues the droplet removing process. If it is determined in step S5 that the first time T1 has elapsed (Yes), the control unit 100 proceeds to the process in step S6.

  If it is determined in step S1 that a print job has not been input (No), the control unit 100 determines whether a purge process has been executed (S7). If it is determined in step S7 that the purging process has not been performed (No), the control unit 100 ends the control.

  If it is determined in step S7 that the purge process has been performed (Yes), the control unit 100 sets the flag F indicating that the purge process has been performed to 1 (S8), and then performs the droplet removal process (S3, S4). ). In step S6, the control unit 100 determines whether or not the flag F is 0, thereby determining whether or not the droplet removal processing has been executed in response to the input of the print job.

  If it is determined in step S6 that F = 0 (Yes), it means that a print job has been input, and the control unit 100 proceeds to the fixing spraying process (S9 to S11). If it is determined in step S6 that F = 1 (No), that is, if the print job has not been input, the control unit 100 proceeds to the fixing spraying process (S9 to S11) without changing the flag. F is returned to 0 (S13), and this control ends.

  Here, when returning the flag F to 0, the control unit 100 stops, for example, the application of the voltage in order to end the droplet removing process. Note that the pressure P after the end of the droplet removal processing, that is, the pressure P during standby, may be maintained at the second pressure P2 during the droplet removal processing, or may be a pressure value different from the second pressure P2. Good.

  If it is determined in step S2 that the third time T3 has elapsed (Yes), a state in which the fixing liquid L attached to the outer peripheral surface of the nozzle N has evaporated after a sufficiently long time has elapsed since the previous fixing spraying process. Therefore, the control unit 100 proceeds to the fixing spraying process (S9 to S11) without executing the droplet removing process (S3, S4).

  In step S9, the control unit 100 sets the target spray amount ρ based on the image corresponding to the first fixing head 71A based on the print data. After step S9, the control unit 100 changes the pressure P applied to the fixing liquid L in the first fixing head 71A from the second pressure P2 to the first pressure P1 (S10). More specifically, in step S10, the control unit 100 operates the pump 75A to increase the pressure P from the second pressure P2 to the first pressure P1.

  After step S10, the control unit 100 sets the voltage V to be applied to the first electrode 74 based on the target spray amount ρ, and applies the voltage V to the first electrode 74, so that the first fixing head 71A A fixing spraying process for spraying the fixing liquid L on the image on the paper SH is performed (S11). After step S11, the control unit 100 determines whether or not the fixing spray processing has been completed (S12).

  If it is determined in step S12 that the fixing spray process has not been completed (No), the control unit 100 returns to the process of step S11 and continues the fixing spray process. If it is determined in step S12 that the fixing spraying process has been completed (Yes), the control unit 100 stops applying the voltage and ends the present control. Note that the pressure P after the end of the fixing spraying process may be reduced to the second pressure P2 at the time of the droplet removing process, or may be reduced to a pressure value different from the second pressure P2.

Next, how the fixing liquid L adhered to the outer peripheral surface of the nozzle N is removed will be described with reference to FIGS.
As shown in FIG. 6A, after the end of the fixing spraying process or after the purging process, the fixing liquid L in the form of a droplet may adhere to the outer peripheral surface of the tip of the nozzle N in some cases. In this case, by performing the droplet removing process, an electric field is generated around the fixing liquid L attached to the outer peripheral surface of the tip end portion of the nozzle N due to the application of the voltage to the first electrode 74. As shown in FIG. 6B, the fixing liquid L is scattered. As a result, as shown in FIG. 6C, the fixing liquid L adhered to the outer peripheral surface at the tip of the nozzle N can be removed satisfactorily.

  In the droplet removing process, the pressure P applied to the fixing liquid L is set to the second pressure P2 lower than the first pressure P1 in the fixing spraying process. Is reduced. This suppresses the fixing liquid L from being pushed out from the opening of the nozzle N to the outer peripheral surface during the droplet removing process, so that the amount of the fixing liquid L on the outer peripheral surface of the nozzle N is amplified. The fixing liquid L can be removed from the outer peripheral surface of the nozzle N without satisfactorily.

According to the above, the following effects can be obtained in the present embodiment.
Even when the fixing liquid L adheres to the outer peripheral surface of the nozzle N, the fixing liquid L adhered to the outer peripheral surface of the nozzle N can be removed by executing the droplet removal processing. When starting, a stable spray state can be obtained quickly.

  If the third time T3 or more has elapsed since the end of the previous fixing spraying process, the droplet removal process is not performed, so that power consumption can be suppressed.

  Since the droplet removing process is performed after the purging process, the fixing liquid L attached to the outer peripheral surface of the nozzle N can be satisfactorily removed in the purging process.

  Note that the present invention is not limited to the above embodiment, but can be used in various forms as exemplified below. In the following description, members having substantially the same structure as those of the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted.

  In the above embodiment, the determination as to whether or not the fixing liquid L attached to the outer peripheral surface of the nozzle N has been removed is made by determining whether or not the first time T1 has elapsed. The present invention is not limited thereto, and may be performed by determining whether or not the state in which no current flows through the first electrode 74 has continued for the second time T2 or longer. Specifically, as shown in FIG. 7, a new step S21 may be provided instead of step S5 in the flowchart of FIG.

  In step S21, the control unit 100 determines whether or not the state in which the detection value is not output from the second current sensor SA continues for the second time T2 or longer. Specifically, the control unit 100 starts counting by the counter when the voltage V is set to the predetermined voltage Va in step S4, and before the count number of the counter reaches the count number corresponding to the second time T2. When the detection value is obtained from the second current sensor SA, the counter is reset to 0. Then, after resetting the count, the control unit 100 starts counting by the counter again. Then, when the count number of the counter is equal to or greater than the count number corresponding to the second time T2, the control unit 100 determines Yes in step S21.

  According to this, it is determined whether or not the state in which no current has flowed through the first electrode 74 has continued for the second time T2 or more, to determine whether or not the scattering of the fixing liquid L on the outer peripheral surface of the nozzle N has been completed. Can be accurately determined. Note that the second time T2 may be appropriately set by an experiment, simulation, or the like.

  In the above-described embodiment, the timing for performing the droplet removing process is set between the time when the print job is input and the time when the fixing spraying process is started and the time when the purge process is completed. However, the present invention is not limited to this. Any timing may be used as long as the processing is not being executed. For example, the droplet removal processing may be performed after the end of the fixing spray processing.

  In the above embodiment, the voltage V is maintained at the predetermined voltage Va in the droplet removing process. However, the present invention is not limited to this, and the voltage value may be changed in the droplet removing process.

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

  In the above-described 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 copier or a multifunction peripheral.

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

  In the above-described embodiment, the pressurizing device 75 having the pump 75A and the pressure reducing valve 75B is exemplified as a pressure applying unit that applies pressure to the fixing solution in the storage unit. However, the present invention is not limited to this. A device or the like that pressurizes or decompresses the liquid in each head using the above method may be used.

  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 thereto. May be small or large. That is, the fixing area may be defined by the width of the fixing liquid sprayed on the sheet in the front-rear direction and the left-right direction.

DESCRIPTION OF SYMBOLS 1 Laser printer 7 Fixing device 71 Fixing head 72 Second electrode 73 Housing 74 First electrode 75 Pressurizing device 100 Control unit L Fixing liquid N Nozzle SH Paper

Claims (12)

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 the developer image on the recording sheet;
A potential difference forming unit for forming a potential difference between the fixing solution in the nozzle and a recording sheet conveyed at a position away from the nozzle;
Pressure applying means for applying pressure to the fixing solution,
A control unit that controls a voltage applied to the potential difference forming unit and a pressure applied to the fixing solution,
The control unit includes:
A fixing spraying process in which the pressure applying unit applies a pressure to the fixing liquid as a first pressure and applies a voltage to the potential difference forming unit to spray the fixing liquid from the nozzle toward the recording sheet;
Droplets for applying a voltage to the potential difference forming unit in a state where the pressure applying unit applies a second pressure smaller than the first pressure to the fixing solution when the fixing spraying process is not being performed. And a removing device.   The fixing device according to claim 1, wherein the control unit performs the droplet removing process before performing the fixing spray process.   The fixing device according to claim 2, wherein the second pressure is equal to or less than a meniscus pressure resistance.   4. The fixing device according to claim 2, wherein the control unit applies a voltage for a first time in the droplet removal processing. 5.   The control unit may change the pressure from the second pressure to the first pressure and start the fixing spraying process after performing the voltage application for the first time in the droplet removing process. The fixing device according to claim 2.   The controller changes the pressure from the second pressure to the first pressure and changes the pressure to the fixing spray process when a state in which no current flows in the potential difference forming unit continues for a second time in the droplet removing process. The fixing device according to claim 2, wherein the fixing is started.   The fixing device according to claim 2, wherein the control unit performs the droplet removing process based on an input of a print job.   8. The method according to claim 2, wherein the control unit does not perform the droplet removal processing when a third time or more has elapsed from the end of the previous fixing spray processing. 9. Fixing device.   9. The fixing device according to claim 1, wherein a voltage applied to the potential difference forming unit in the droplet removing process is within a range of a voltage value during the fixing spraying process. 10. .   10. The method according to claim 1, wherein the control unit performs the droplet removing process when performing a purge process of discharging the fixing solution from the nozzle to the outside by pressure. 11. The fixing device as described in the above.   The fixing device according to claim 1, wherein the pressure applying unit includes a pump configured to pressurize a gas in the fixing head.   The fixing device according to claim 1, wherein the potential difference forming unit includes a first electrode that contacts the fixing solution, and a second electrode that faces the nozzle.

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