JP2012148471A - Flow path unit, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate sedimentation in a branch flow path that branches from the main flow path to the downstream side and connects to the discharge unit.SOLUTION: The flow path unit is a circulating type flow path unit of discharge liquid that supplies the discharge liquid to a plurality of discharge units that have the drive elements to discharge the discharge liquid from a nozzle, includes: a tank to store the discharge liquid; a main flow path that is an upstream side flow path that transports the discharge liquid from the tank to the discharge unit; an upstream side pipe that constitutes the upstream side flow path that has a branch flow path that branches from the main flow path to the down stream side and connects to the discharge unit; a down stream side pipe that constitutes the down stream side flow path and collects from the discharge unit, the discharge liquid not discharged from the nozzle; a pump that circulates the discharge liquid to the circulation flow path that includes the tank, the upstream side pipe, the discharge unit and the downstream side pipe; and a control part that controls output of the pump so that the flow rate of the discharge liquid in the branch flow path is higher than the prescribed value.

Description

  The present invention relates to a circulation type flow path unit that supplies a discharge liquid to a plurality of discharge units having a drive element that discharges the discharge liquid from a nozzle, and an image forming apparatus that includes the discharge unit and the flow path unit.

  2. Description of the Related Art Conventionally, an image forming apparatus having a circulation type flow path for a discharge liquid is known. For example, Patent Document 1 describes that a pump for circulating ink in a flow path is operated every predetermined time.

JP 2005-103841 A

It is conceivable that the circulation channel is composed of a plurality of pipes having various shapes. Even if the pump is operated every predetermined time, if the flow rate of the pump at the time of operation is the same, there is a case where sedimentation cannot be sufficiently eliminated depending on the pipe. In particular, the shape of the branch flow path branched downstream from the main flow path and connected to the discharge unit is likely to be complicated, and sedimentation is likely to occur due to a decrease in the flow rate.
An object of the present invention is to eliminate sedimentation in a branch channel that branches from a main channel downstream and is connected to a discharge unit.

  In order to solve the above problems, a circulation type flow path unit of the present invention includes a tank for storing discharge liquid, and an upstream flow path for transferring discharge liquid from the tank to the discharge unit, the main flow path and the main flow path An upstream pipe that constitutes an upstream flow path having a branch flow path that branches from the downstream to the downstream and that connects to the discharge unit, and a downstream flow that collects the discharge liquid that has not been discharged from the nozzle from the discharge unit to the tank A pump that circulates the discharge liquid in a circulation flow path constituted by a downstream pipe that constitutes the path, a tank, an upstream pipe, a discharge unit, and a downstream pipe, and a flow rate of the discharge liquid in the branch flow path that exceeds a predetermined value And a control unit for controlling the output of the pump.

  The branch flow path of the upstream flow paths is a flow path that is branched into a plurality of downstream sides from the main flow path and connected to a plurality of discharge units, and when sedimentation occurs in the upstream flow path including the branch flow path, The discharge liquid with a non-constant concentration is discharged from the discharge unit, or the sediment is retained and solidified to cause clogging in the flow path, resulting in a decrease in print quality. Focusing on the flow velocity of the branch flow channel as in the present invention, the sedimentation in the branch flow channel can be eliminated by controlling the output of the pump so that the flow velocity becomes a predetermined value or more. Therefore, the predetermined value is designed to have a flow rate that can eliminate sedimentation in the branch flow path. The value of the predetermined value may be different depending on the cross-sectional area of the flow path (the area of the cross section perpendicular to the direction in which the discharge liquid is transferred), the type of the discharge liquid, and the like.

Further, in the present invention, the control unit may increase the output of the pump from the execution of printing so that the flow velocity becomes a predetermined value or more at the time of non-printing.
The flow path unit of the present invention has two types of pump functions: a pump function by a pump and a pump function by a driving element (the discharge liquid moves in the flow path when the discharge liquid is discharged from the nozzle). When non-printing is performed, that is, when the discharge liquid is not discharged from the nozzle, the pump function by the drive element does not operate. Therefore, by increasing the output of the pump from when printing is performed, it is possible to control the flow velocity in the branch flow path to be a predetermined value or more when non-printing is performed.

Furthermore, in the present invention, the predetermined value may be a flow rate in the branch flow path when dots are recorded on the print medium at a predetermined printing speed and a predetermined recording density with the pump stopped.
The printing speed means the area of a region to be printed per unit time. The predetermined printing speed may be a maximum speed that can be realized by the image forming apparatus, an average speed, or the like. The recording density can be defined by the size of ink droplets and the number of dots per unit area. The predetermined recording density may be a maximum density that can be realized by the image forming apparatus or an average density.

Furthermore, in the present invention, the branch channel may have a smaller cross-sectional area than the main channel.
If the cross-sectional area is smaller than the main flow path, the branch flow path is more likely to be clogged than the main flow path, but in the present invention, the flow speed of the branch flow path is controlled to be equal to or higher than the predetermined value. Can be prevented.

Furthermore, in the present invention, the discharge unit may be provided with a cap that presses the nozzle surface in close contact with the nozzle surface in which the nozzle opening is formed. In that case, the control unit may increase the output of the pump when the nozzle surface is pressed by the cap than when the nozzle surface is not pressed.
When the nozzle surface is pressed by the cap, the discharge liquid does not leak from the nozzle even at a flow rate that generates a pressure that exceeds the meniscus limit. The flow rate can be increased. The above-described content means that the pressure is higher than a predetermined value both when pressed and when not pressed, and when the pressure is further pressed, the flow velocity of the branch flow path is made faster than when not pressed.

The present invention is also established as an invention of an image forming apparatus including the discharge unit and the flow path unit.
By providing the discharge unit and the flow path unit described above, it is possible to provide an image forming apparatus in which sedimentation is eliminated in the flow path and sediment is less likely to stay.

In the above image forming apparatus, the tank, the discharge unit, the upstream side pipe, the downstream side pipe, and the pump are provided for each type of the discharge liquid, and correspond to the discharge liquid whose use frequency is the first frequency. The output of the pump to be used may be larger than the output of the pump corresponding to the discharged liquid whose second usage frequency is higher than the first frequency.
The frequency of use may vary depending on the type of discharge liquid. The lower the frequency of use of the discharge liquid, the less the movement of the discharge liquid in the flow path, and the easier it is for the solid component having a higher specific gravity contained in the discharge liquid to settle. Therefore, by setting the output of the discharge liquid pump having a low use frequency (first frequency) higher than the output of the discharge liquid pump having a high use frequency (second frequency), sedimentation can be more reliably eliminated. . It should be noted that both the first frequency ink and the second frequency ink satisfy the fact that the flow velocity of the branch flow path is equal to or higher than a predetermined value, and further change the flow velocity according to the use frequency. means.

In the image forming apparatus, the cross-sectional area of the branch flow path corresponding to the discharge liquid whose use frequency is the first frequency is the same as that of the branch flow path corresponding to the discharge liquid whose use frequency is the second frequency. It may be smaller than the area.
If the flow rate (volume / time) is the same, the flow velocity varies depending on the cross-sectional area of the flow path. The smaller the cross-sectional area of the channel, the faster the flow velocity. Therefore, the use frequency is low by making the cross-sectional area of the branch flow path of the discharge liquid that is low in use frequency (first frequency) smaller than the cross-sectional area of the branch flow path of the discharge liquid that is high in use frequency (second frequency). The flow rate of the discharge liquid in the branch flow path can be increased, and sedimentation can be more reliably eliminated.

1 is a block diagram showing an image forming apparatus according to a first embodiment. (2A) and (2B) are schematic views showing a discharge unit according to the first embodiment. The graph for demonstrating the flow velocity concerning 1st embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the corresponding component in each figure, and the overlapping description is abbreviate | omitted.

1. First Embodiment FIG. 1 is a schematic diagram showing main components of an inkjet printer 1 as an image forming apparatus according to a first embodiment of the present invention. The ink jet printer 1 includes a control unit 10, an ink tank 21, a discharge unit 22, an upstream side pipe 23, a downstream side pipe 24, and a pump 25. The ink tank 21, the discharge unit 22, the upstream side pipe 23, and the downstream side pipe 24 are provided for each type of ink (discharge liquid), and those corresponding to one ink are collectively referred to as a flow path hereinafter. Called Set 20. A plurality of discharge units 22 are provided in one flow path set 20. The control unit 10 includes a CPU, a RAM, and a ROM (not shown), and controls a piezo element (drive element), a pump, and a cap, which will be described later, by the CPU executing a control program stored in the ROM.

  As described above, the flow path set 20 includes the ink tank 21, the plurality of discharge units 22, the upstream pipe 23, the downstream pipe 24, and the pump 25. The upstream pipe 23 constitutes an upstream flow path, and the upstream flow path has an upstream main flow path 23a and an upstream branch flow path 23b. The upstream main flow path 23 a is connected to the ink tank 21. The upstream branch flow path 23 b is a flow path branched from the upstream main flow path 23 a to the downstream side, and is connected to the plurality of discharge units 22. The cross-sectional area of the upstream branch flow path 23b (the cross-sectional area perpendicular to the ink transfer direction) is smaller than the cross-sectional area of the upstream main flow path 23a.

  The upstream main channel 23a is a channel having a section for transferring ink in the horizontal direction in order to supply ink to the plurality of ejection units 22 arranged in the horizontal direction. The upstream branch flow path 23b branches vertically downward from the upstream main flow path 23a, and there is also a section in the upstream branch flow path 23b where ink is transferred in the horizontal direction until it is connected to the ejection unit 22. To do.

The downstream pipe 24 constitutes a downstream channel, and the downstream channel has a downstream main channel 24a and a downstream branch channel 24b. Each of the plurality of discharge units 22 is connected to the downstream branch flow path 24b. Each downstream branch flow path 24 b joins the downstream main flow path 24 a, and the downstream main flow path 24 a is connected to the ink tank 21. The cross-sectional area of the downstream branch flow path 24b is smaller than the cross-sectional area of the downstream main flow path 24a. The ink that has not been ejected from the ejection unit 22 is again collected in the ink tank 21 via the downstream flow path. That is, in this embodiment, the ink is circulated in order to prevent a solid component that is a solid component contained in the ink and has a specific gravity greater than the liquid component constituting the ink from settling in the flow path. A circulation channel is configured. The pump 25 can suck ink from the ink tank 21 and transfer the ink to the upstream main flow path 23a to circulate the ink in the flow path. The pump 25 can change the output, that is, the flow rate according to the control of the control unit 10.
The control unit 10, the ink tank 21, the upstream side pipe 23, the downstream side pipe 24, and the pump 25 correspond to a flow path unit.

  In the present embodiment, the cross-sectional area of the upstream main flow path 23a is molded so as to be the same regardless of the type of ink (flow path set 20). Similarly, the upstream branch flow path 23b is the same regardless of the type of ink. The cross-sectional area of the downstream main flow path 24a is the same for all inks, and the cross-sectional area of the downstream branch flow path 24b is also the same for all inks.

  2A and 2B are schematic views of the discharge unit 22. A common ink chamber 225 is formed in the discharge unit 22, and the common ink chamber 225 is connected to the upstream branch flow path 23b and the downstream branch flow path 24b. A plurality of nozzles 221 are formed in the discharge unit 22, and each nozzle 221 forms an opening in the nozzle surface 220. The piezo element 222 and the ink chamber 223 are provided for each nozzle 221. Each ink chamber 223 is connected to a common ink chamber 225. The upstream flow path, the common ink chamber 225, the ink chamber 224, and the downstream flow path are filled with ink supplied from the ink tank. When a driving voltage pulse is applied to the piezo element 222, the piezo element 222 is mechanically deformed, the ink filled in the ink chamber 223 is pressurized and depressurized, and an ink droplet is ejected from the nozzle 221.

  When the discharge unit 22 discharges ink droplets, ink is sucked from the ink tank 21 and ink is also sucked from the ink tank 21 by the pump 25 to transfer the ink to the upstream main flow path. The discharge unit 22 is provided with a cap 226. The cap 226 is in close contact with the nozzle surface 220 and presses the nozzle surface 220 when the inkjet printer 1 is not printing (for example, during an initialization operation or a maintenance operation) (see FIG. 2B). Each flow path set 20 is provided with a mechanism (not shown) for pressing the nozzle surface 220 with the cap 226 and separating the cap 226 from the nozzle surface 220 and returning it to the retracted position. The cap mechanism can perform the above-described operation in accordance with a control signal from the control unit 10.

  FIG. 3 is a graph showing the relationship between the ink flow velocity in the upstream branch flow path 23b and the pump 25 or the piezo element 222 contributing to the flow velocity. As described above, the upstream branch flow path 23b has a section for transferring ink in the horizontal direction. Depending on the flow velocity, the ink components may settle in the flow path, causing clogging. The upstream branch flow path 23b is narrower than the upstream main flow path 23a, and has a more complicated shape than the upstream main flow path 23a due to a curved portion. Therefore, the upstream branch flow path 23b is more easily clogged than the upstream main flow path 23a. If clogging occurs in the upstream flow path, ink cannot be supplied to the discharge unit 22 and print quality is degraded. For this reason, it is important to prevent clogging of the flow path in the upstream flow path (especially the upstream branch flow path 23b that is likely to be clogged because its cross-sectional area is smaller than the upstream main flow path 23a and its shape tends to be complicated) (Even if the downstream channel is clogged, ink can be ejected).

  Therefore, in the present embodiment, paying attention to the flow velocity in the upstream branch flow path 23b, the control unit 10 controls the output of the pump 25 so that the flow velocity in the upstream branch flow path 23b at the time of non-printing is equal to or higher than a predetermined value. . Specifically, data defining the correspondence between the information given to the pump 25 and each scene in order to obtain each flow rate shown in FIG. 3 is stored in advance in the ROM or the like, and the control unit 10 uses the data. The output of the pump 25 is controlled in each scene. Examples of information to be given to the pump 25 include a voltage value and the number of rotations of a rotating body provided in the pump. In the present embodiment, the predetermined value refers to the flow velocity of the upstream branch flow path 23b during reference printing (see FIG. 3). The reference printing refers to recording dots on a printing medium at a predetermined printing speed and a predetermined recording density with the output of the pump 25 stopped. Even when the pump function of the pump 25 is stopped, ink is sucked from the ink tank 21 to the upstream channel by ejecting ink droplets from the piezo element 222.

  For example, if the inkjet printer 1 is a line printer, the printing speed is such that dots are formed by ink supplied from one ink tank 21 at a predetermined recording density in an area having a predetermined length in the conveyance direction of the print medium. It is defined as a value obtained by dividing the aforementioned predetermined length by the time of the case. The recording density is defined by the size (ejection amount) of ink droplets ejected from the nozzles 221 and dpi. The predetermined printing speed may be a maximum speed that the inkjet printer 1 can realize in terms of performance, or may be an average speed, for example. Also, the predetermined recording density may be the highest density that can be realized by the ink jet printer 1 or an average density.

  In the present embodiment, the reference printing refers to printing at the fastest printing speed and the highest density that can be realized by the inkjet printer 1 and printing so that an area of an arbitrary area is filled with one ink color. The flow velocity in the upstream branch flow path 23b during the standard printing is set to a predetermined value Vb. The flow velocity in the upstream branch flow path 23b is obtained by, for example, radiating a microwave that penetrates the pipe to the pipe of the upstream branch flow path 23b and measuring the moving speed of the particles in the ink liquid. Can do. Alternatively, the flow rate per unit time can be acquired using a flow rate sensor, and the flow velocity can be acquired from the flow rate and the cross-sectional area of the upstream branch flow path 23b.

  At the time of normal printing with respect to the reference printing, for example, as shown in FIG. 3, the ink moves in the flow path by the pump function of the piezo element 222 and the pump function of the pump 25 as an auxiliary. Since the amount ejected by the print image data is not constant during normal printing, the flow rate of the upstream branch flow path 23b can also be changed by only the pump function of the piezo element. Therefore, the control unit 10 compensates the non-constant flow rate caused by the discharge operation of the piezo element variably with the pump function of the pump 25 so that the average flow rate of the upstream branch flow path 23b becomes the predetermined value Vb. The pump 25 is controlled. As a result, the average flow velocity of the upstream branch flow path 23b can be set to the predetermined value Vb even during normal printing.

  When printing is not performed (for example, when initialization is performed before normal printing is started or when maintenance is performed, ink droplets are not ejected from the nozzles 221), ink droplets are ejected from the nozzles 221. The controller 10 operates the pump 25 in order to circulate the ink in the flow path without discharging the ink. In addition, when non-printing is performed, the nozzle surface 220 is covered and pressed by the cap 226 and the case where it is not pressed is divided. The controller 10 controls the output of the pump 25 so that the flow velocity in the upstream branch flow path 23b is equal to or higher than the predetermined value Vb both when not pressed and when pressed. At the time of non-pressing, the control unit 10 controls the output of the pump 25 so that the flow velocity is in a range not less than the predetermined value Vb and not exceeding the meniscus limit of the nozzle 221. At the time of pressing, the nozzle surface 220 is pressed by the cap 226, so that the control unit 10 can further increase the pump output and increase the flow rate of the upstream branch flow path 23b compared to when the nozzle surface 220 is not pressed. That is, the flow rate can be set to a pressure exceeding the meniscus limit during pressing. As described above, when non-printing is performed, the flow rate of the upstream branch flow path 23b is increased to be equal to or higher than the predetermined value Vb when printing is performed, so that sedimentation of components contained in the ink can be eliminated and sedimentation can be prevented. Moreover, since the flow velocity can be increased at the time of pressing than at the time of non-pressing, sedimentation can be more easily eliminated than that at the time of non-pressing.

  Further, the frequency of ink use varies depending on the type of ink. In the present embodiment, the control unit 10 outputs the output of the pump 25 corresponding to the ink whose usage frequency is the first frequency of the pump 25 corresponding to the ink whose second usage frequency is higher than the first frequency. The output is controlled to be larger than the output. For example, assume that black ink and yellow ink are used more frequently. When the cap is pressed during non-printing, the controller 10 controls the yellow ink pump 25 so that the flow rate of the yellow ink upstream branch channel 23b is higher than the flow rate of the black ink upstream branch channel 23b. The output is controlled to be larger than the output of the black ink pump 25. In this case as well, both pumps 25 are controlled so that the flow velocities of the upstream branch flow paths 23b for both black and yellow inks are equal to or higher than the predetermined value Vb. Thus, by making the output of the pump 25 variable according to the frequency of use, sedimentation in the flow path can be more efficiently eliminated and sedimentation can be prevented.

2. Other Embodiments The technical scope of the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the scope of the present invention. For example, in the above-described embodiment, the configuration in which the cross-sectional area of the upstream branch flow path 24b is the same for all inks has been described. However, the upstream branch flow path 23b corresponding to the ink whose use frequency is the first frequency is described. The cross-sectional area may be smaller than the cross-sectional area of the upstream branch flow path 23b corresponding to the ink whose use frequency is higher than the first frequency (the number of branch flow paths is the same for each ink). And). If the flow rate is the same, the smaller the cross-sectional area, the faster the flow rate. Therefore, for example, when it is known in advance that yellow ink is used less frequently than black ink, the cross-sectional area of the upstream branch flow path 23b for yellow ink is the cross-sectional area of the upstream branch flow path 23b for black ink. Mold each ink tube to be smaller (however, the inner diameter of the tube and the lower limit of the cross-sectional area must be taken into account, such as the inner diameter of the tube being several times the diameter of the largest particle contained in the ink) There). As a result, even if the output of the pump 25 is the same, the flow speed of the upstream branch flow path 23b for yellow ink can be made faster than that for the black ink. Of course, in this case as well, the output of the pump 25 may be variable.

In the above-described embodiment, the configuration in which the output of the pump 25 for each ink is changed according to the use frequency of the ink has been described. However, the output of the pump 25 may be changed according to the leaving time. That is, the control unit 10 may increase the output of the pump 25 as the ink is left for a long time without being circulated in the flow path. For example, the control unit 10 can obtain the time for which each ink is left by providing a function of counting the elapsed time from the date and time (time) when the ink droplets are finally discharged or the pump 25 is operated.
In addition, since the ease of sedimentation, the ease of solidification, and the like differ depending on the type of ink (the type of solvent and color material), the output of the pump 25 is more suitable for inks that are easily settled or solidified. It may be increased to increase the flow rate.

  In the above embodiment, examples of non-print execution include the initialization operation before normal printing and the maintenance operation. However, the present invention is not limited thereto. Among multiple inks, for example, if there is ink that is not used (ink that has not ejected ink droplets) even when the printer as a whole is printing, non-printing is performed for that unused ink The control unit 10 may increase the output of the pump 25 as the state.

  In the above-described embodiment, the output of the pump 25 is controlled by dividing the non-printing time into the non-pressing time and the non-pressing time. However, the cap 226 always presses the nozzle surface 220 during non-printing time. If it is the structure to perform, it is not necessary to make variable the output of the pump 25 at the time of non-printing execution by the presence or absence of the cap 226.

In the above-described embodiment, the configuration in which both the pump function of the pump 25 and the pump function of the piezo element 222 act during normal printing has been described. However, the pump function of the pump 25 may be stopped during normal printing. Good.
The drive element is not limited to a piezo element as long as it can eject ink like from a nozzle.

  1: Inkjet printer (image forming apparatus), 10: control unit, 20: flow path set, 21: ink tank (tank), 22: discharge unit, 23: upstream pipe, 23a: upstream main flow path, 23b: upstream Side branch flow path, 24: downstream pipe, 24a: downstream main flow path, 24b: downstream branch flow path, 25: pump, 220: nozzle surface, 221: nozzle, 222: piezo element, 223: ink chamber, 225 : Common ink chamber, 226: Cap

Claims (8)

A circulation type flow path unit for discharge liquid to be supplied to a plurality of discharge units having drive elements for discharging discharge liquid from nozzles,
A tank for storing the discharge liquid;
An upstream flow path for transferring the discharge liquid from the tank to the discharge unit, the flow path including a main flow path and a branch flow path branched from the main flow path to the downstream side and connected to the discharge unit An upstream pipe constituting the path;
A downstream pipe constituting a downstream flow path for collecting the discharge liquid not discharged from the nozzle from the discharge unit to the tank;
A pump that circulates the discharge liquid in a circulation flow path constituted by the tank, the upstream pipe, the discharge unit, and the downstream pipe;
A control unit for controlling the output of the pump so that the flow rate of the discharge liquid in the branch flow path is equal to or higher than a predetermined value;
A flow path unit comprising: The control unit increases the output of the pump from that at the time of printing so that the flow rate is equal to or higher than the predetermined value at the time of non-printing.
The flow path unit according to claim 1. The predetermined value is a flow rate in the branch flow path when dots are recorded on a print medium at a predetermined printing speed and a predetermined recording density with the pump stopped.
The flow path unit according to claim 1 or 2. The branch channel has a smaller cross-sectional area than the main channel,
The channel unit according to any one of claims 1 to 3. The discharge unit is provided with a cap that presses the nozzle surface in close contact with the nozzle surface in which the nozzle opening is formed,
The control unit increases the output of the pump when the nozzle surface is pressed by the cap than when not pressed.
The flow path unit according to any one of claims 1 to 4.   An image forming apparatus provided with the said discharge unit and the flow-path unit in any one of Claims 1-5. The tank, the discharge unit, the upstream pipe, the downstream pipe, and the pump are provided for each type of the discharge liquid,
The output of the pump corresponding to the discharge liquid whose use frequency is the first frequency is larger than the output of the pump corresponding to the discharge liquid whose second use frequency is higher than the first frequency. ,
The image forming apparatus according to claim 6. The cross-sectional area of the branch flow path corresponding to the discharge liquid whose usage frequency is the first frequency is the cross-sectional area of the branch flow path corresponding to the discharge liquid whose usage frequency is the second frequency. Smaller,
The image forming apparatus according to claim 7.

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