JP2013129081A - Printer, and ink return method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a problem due to presence of air in a supply channel.SOLUTION: A printer having an ink storage unit storing ink, a head unit discharging the ink to a medium, a supply channel to supply the ink from the ink storage unit to the head unit, and a controller carrying out a return process to return the ink in the supply channel to the ink storage unit, has an emptiness prevention liquid storage unit 401 storing an emptiness prevention liquid to prevent the supply channel from being emptied owing to carrying out of the return process. The controller returns the ink in the supply channel to the ink storage unit and makes the emptiness prevention liquid in the emptiness prevention liquid storage unit 401 flow into the supply channel in carrying out the return process.

Description

  The present invention relates to a printing apparatus and an ink return method.

  A printing apparatus including an ink storage unit that stores ink, a head unit that discharges ink to a medium, and a supply flow path for supplying ink from the ink storage unit to the head unit is already well known. In such a printing apparatus, a return process for returning the ink in the supply channel toward the ink storage unit may be executed.

JP-A-60-137655

  By the way, when the return process described above is executed, the inside of the supply flow path may become empty (that is, a state where air has entered). If the air is present in the supply flow path, the following problems may occur. For example, when the ink that has come into contact with the air dries and hardens, it becomes dust or causes clogging.

  This invention is made | formed in view of this subject, The place made into the objective is to suppress generation | occurrence | production of the problem by air existing in a supply flow path.

The main present invention is an ink storage unit for storing ink;
A head unit for discharging the ink onto a medium;
A supply flow path for supplying the ink from the ink storage unit to the head unit;
A controller for performing a return process for returning the ink in the supply flow channel toward the ink storage unit;
A printing device comprising:
An empty liquid storage unit for containing an empty liquid for preventing the inside of the supply flow path from becoming empty due to the execution of the return process;
When the controller executes the return process, the controller returns the ink in the supply flow path toward the ink storage unit, and the empty liquid in the empty liquid storage unit is returned to the supply flow path. A printing apparatus is characterized by being caused to flow.
Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

1 is a schematic diagram illustrating a configuration of an image recording apparatus 1. FIG. 1 is a block diagram illustrating a configuration of an image recording apparatus 1. FIG. 4 is a block diagram of a black ink supply unit 36. FIG. FIG. 5 is a block diagram showing a state of a black ink supply unit 36 immediately before a switching process is executed. FIG. 6 is a block diagram showing a state of a black ink supply unit 36 immediately before the return process is completed. FIG. 6 is a block diagram showing a state of a black ink supply unit 36 immediately before the switching process is completed. FIG. 10 is a block diagram of a black ink supply unit 36 according to a modification.

  At least the following will be made clear by the description of the present specification and the accompanying drawings.

An ink storage unit for storing ink;
A head unit for discharging the ink onto a medium;
A supply flow path for supplying the ink from the ink storage unit to the head unit;
A controller for performing a return process for returning the ink in the supply flow channel toward the ink storage unit;
A printing device comprising:
An empty liquid storage unit for containing an empty liquid for preventing the inside of the supply flow path from becoming empty due to the execution of the return process;
When the controller executes the return process, the controller returns the ink in the supply flow path toward the ink storage unit, and the empty liquid in the empty liquid storage unit is returned to the supply flow path. A printing apparatus characterized by being caused to flow.
According to such a printing apparatus, it is possible to suppress the occurrence of problems due to the presence of air in the supply flow path.

Further, the ink storage unit has a supply ink storage part and a return ink storage part,
The supply flow path is a flow path for supplying the ink from the supply ink reservoir to the head unit,
The return process may be a process of returning the ink in the supply flow channel toward the return ink reservoir.
In such a case, it is possible to avoid the inconvenience that the ink reservoir is full and the ink cannot be returned.

A plurality of the supply channels;
The head unit is composed of a plurality of sub head units,
Each of the plurality of supply flow paths supplies the ink to the sub head unit corresponding to each of the supply flow paths,
The controller may return the ink in each of the supply flow paths toward one return ink reservoir.
In such a case, the configuration of the printing apparatus is simplified.

Further, the return ink storage part is provided with a detection sensor for detecting the amount of the ink,
The controller may determine the end timing of the return process based on a detection result output by the detection sensor.
In such a case, the return process can be executed more reliably.

The ink storage unit includes a first ink storage unit that stores the first ink and a second ink storage unit that stores the second ink,
The head unit has a nozzle through which the first ink and the second ink can selectively pass, and the ink is ejected from the nozzle onto the medium.
The supply channel selectively supplies the ink to the head unit from either the first ink storage unit or the second ink storage unit,
The controller is
The first ink in the supply flow path is returned toward the first ink storage unit, and the empty prevention liquid in the empty prevention liquid storage unit is caused to flow into the supply flow path, and then the supply flow path By discharging the anti-empty liquid in the supply channel, and flowing the second ink in the second ink storage unit into the supply channel,
A switching process for switching the ink that passes through the nozzle from the first ink to the second ink,
It may be executed.
In such a case, there is a cost merit.

Next, an ink storage unit for storing ink;
A head unit for discharging the ink onto a medium;
A supply flow path for supplying the ink from the ink storage unit to the head unit;
Providing a printing device having:
The ink in the supply flow path is returned toward the ink storage unit, and an empty prevention liquid for preventing the supply flow path from being emptied by returning the ink flows into the supply flow path. And letting
An ink return method characterized by comprising:
According to such an ink return method, it is possible to suppress the occurrence of problems due to the presence of air in the supply flow path.

=== About Configuration Example of Image Recording Apparatus 1 ===
A configuration example of an image recording apparatus 1 (an ink jet printer in the present embodiment) as an example of a printing apparatus will be described with reference to FIGS. FIG. 1 is a schematic sectional view of the image recording apparatus 1. FIG. 2 is a block diagram of the image recording apparatus 1.
In the following description, when referring to “up and down direction” and “left and right direction”, the direction indicated by the arrow in FIG. 1 is used as a reference. In addition, the “front-rear direction” refers to a direction orthogonal to the paper surface in FIG.
In the present embodiment, a description will be given using a sheet wound in a roll shape (hereinafter referred to as a roll sheet (continuous sheet)) as an example of a medium on which the image recording apparatus 1 records an image.

  As shown in FIGS. 1 and 2, the image recording apparatus 1 according to the present embodiment includes a transport unit 20 and a transport path through which the transport unit 20 transports the roll paper 2 (in FIG. 1, the transport path is A feed unit 10, a platen 29, a take-up unit 90, and a take-up unit 90. The head unit 30 that performs image recording by discharging a plurality of types of ink in the image recording region R on the transport path, the ink supply unit 35, the carriage unit 40, the cleaning unit 43, the heater unit 70, and the platen 29 A blower unit 80 for sending air to the upper roll paper 2, and a controller 60 for controlling these units and controlling the operation as the image recording apparatus 1. It has a detector group 50, a.

  The feeding unit 10 feeds the roll paper 2 to the transport unit 20. The feeding unit 10 includes a winding shaft 18 around which the roll paper 2 is wound and rotatably supported, a relay roller 19 for winding the roll paper 2 fed from the winding shaft 18 and guiding the roll paper 2 to the transport unit 20; have.

  The transport unit 20 transports the roll paper 2 sent by the feeding unit 10 along a preset transport path. As shown in FIG. 1, the transport unit 20 includes a relay roller 21 that is positioned horizontally to the right of the relay roller 19, a relay roller 22 that is positioned obliquely downward to the right when viewed from the relay roller 21, and the relay roller 22. A first conveyance roller 23 located obliquely right above (as viewed from the platen 29 in the conveyance direction), and a steering unit (steering unit) 20a positioned between the relay roller 22 and the first conveyance roller 23, A second transport roller 24 positioned on the right side (downstream in the transport direction as viewed from the platen 29) as viewed from the first transport roller 23, a reversing roller 25 positioned vertically downward as viewed from the second transport roller 24, A relay roller 26 located on the right side when viewed from the reversing roller 25, a delivery roller 27 positioned above when viewed from the relay roller 26, It has.

The relay roller 21 is a roller that winds the roll paper 2 sent from the relay roller 19 from the left side and loosens it downward.
The relay roller 22 is a roller that winds the roll paper 2 sent from the relay roller 21 from the left side and conveys it obliquely upward to the right.

  The first transport roller 23 includes a first drive roller 23a driven by a motor (not shown), and a first driven roller 23b arranged to face the first drive roller 23a with the roll paper 2 interposed therebetween. have. The first transport roller 23 is a roller that pulls up the roll paper 2 slacked downward and transports it to the image recording region R facing the platen 29. The first conveyance roller 23 temporarily stops conveyance during a period in which image printing is performed on the portion of the roll paper 2 on the image recording region R. In addition, the conveyance amount of the roll paper 2 positioned on the platen 29 is adjusted by rotating the first driven roller 23b in accordance with the rotational drive of the first drive roller 23a by the drive control of the controller 60.

  As described above, the transport unit 20 has a mechanism for transporting the portion of the roll paper 2 wound between the relay rollers 21 and 22 and the first transport roller 23 by slacking it downward. The slackness of the roll paper 2 is monitored by the controller 60 based on a detection signal from a slack detection sensor (not shown). Specifically, when a portion of the roll paper 2 slackened between the relay rollers 21 and 22 and the first transport roller 23 is detected by the slack detection sensor, a tension of an appropriate magnitude is applied to the portion. Therefore, the transport unit 20 can transport the roll paper 2 in a relaxed state. On the other hand, when the portion of the roll paper 2 that has been loosened is not detected by the slack detection sensor, an excessive amount of tension is applied to the portion, so that the roll paper 2 is transported by the transport unit 20. It is temporarily stopped and the tension is adjusted to an appropriate magnitude.

  As shown in FIG. 1, the steering unit 20a is positioned on the conveyance path in an inclined state, and rotates to roll paper 2 in the width direction position (width direction (front-back direction shown in FIG. 1)) of the roll paper 2. This is for changing the position at which is located. That is, when the roll paper 2 is conveyed along the conveyance path, the tension applied to the roll paper 2 fluctuates due to an axial deviation or an assembly error of a relay roller or the like. The position may be displaced. The steering unit 20 a is for adjusting the position in the width direction of the roll paper 2.

  The second transport roller 24 includes a second drive roller 24a driven by a motor (not shown), and a second driven roller 24b disposed so as to face the second drive roller 24a with the roll paper 2 interposed therebetween. have. The second transport roller 24 is a roller that transports the portion of the roll paper 2 on which the image is recorded by the head unit 30 in the horizontal right direction along the support surface of the platen 29 and then transports it vertically downward. Thereby, the conveyance direction of the roll paper 2 is changed. The second driven roller 24b rotates as the second drive roller 24a is driven to rotate by the drive control of the controller 60, whereby a predetermined amount given to the portion of the roll paper 2 located on the platen 29 is obtained. Tension is adjusted.

The reversing roller 25 is a roller that wraps the roll paper 2 sent from the second conveying roller 24 from the upper left side and conveys it diagonally upward to the right.
The relay roller 26 is a roller that winds the roll paper 2 sent from the reversing roller 25 from the lower left side and conveys it upward.
The delivery roller 27 winds the roll paper 2 sent from the relay roller 26 from the lower left side and sends it to the take-up unit 90.

  As described above, the roll paper 2 moves sequentially through the rollers, whereby a transport path for transporting the roll paper 2 is formed. The roll paper 2 is intermittently transported along the transport path by the transport unit 20 in units of regions corresponding to the image recording regions R.

  The head unit 30 is for recording an image on a portion of the roll paper 2 located in the image recording region R on the transport path. In other words, the head unit 30 forms an image by ejecting ink from the nozzles onto the portion of the roll paper 2 that has been fed by the transport unit 20 into the image recording region R (on the platen 29) on the transport path. In the present embodiment, the head unit 30 has 15 heads 31.

  Each head 31 has a nozzle row in which nozzles are arranged in the row direction on the lower surface thereof. In this embodiment, each of the ink types (colors) such as yellow (Y), magenta (M), cyan (C), and black (K) has a nozzle row composed of a plurality of nozzles # 1 to #N. doing. The nozzles # 1 to #N in each nozzle row are linearly arranged in a crossing direction that intersects the transport direction of the roll paper 2 (that is, the crossing direction is the above-described row direction). Each nozzle row is arranged in parallel with a space between each other along the transport direction.

  Each nozzle # 1 to #N is provided with a piezo element (not shown) as a drive element for ejecting ink droplets. When a voltage having a predetermined time width is applied between the electrodes provided at both ends of the piezoelectric element, the piezoelectric element expands according to the voltage application time and deforms the side wall of the ink flow path. As a result, the volume of the ink flow path contracts according to the expansion and contraction of the piezo element, and the ink corresponding to the contraction is ejected from the nozzles # 1 to #N of the respective colors as ink droplets.

  Then, 15 such heads 31 are arranged in the intersecting direction (the row direction), thereby forming the head unit 30. Therefore, the head unit 30 has 15 × N nozzles for each ink type (color).

  In the present embodiment, the matte black (Mk) ink (corresponding to the first ink, hereinafter also referred to as the Mk ink) and the photo black (Pk) ink (corresponding to the second ink) from the nozzle corresponding to the black color. (Hereinafter also referred to as Pk ink) can be selectively ejected. That is, the head unit 30 is provided with 15 × N nozzles through which Mk ink and Pk ink can selectively pass. Therefore, the ink flow path in the head unit 30 for guiding the ink to each nozzle is also a common flow path for the Mk ink and the Pk ink (that is, this flow path is used for both the Mk ink and the Pk ink. Can pass through).

  The ink supply unit 35 is for supplying ink to the head unit 30 when the amount of ink in the head unit 30 decreases due to ink ejection by the head 31. The ink supply unit 35 will be described in detail later (a mechanism relating to switching between Mk ink and Pk ink will also be described here).

  The carriage unit 40 is for moving the head unit 30 (head 31). The carriage unit 40 is supported by a carriage guide rail 41 (indicated by a two-dot chain line in FIG. 1) extending in the transport direction (left-right direction) and reciprocally movable along the carriage guide rail 41 in the transport direction (left-right direction). A carriage 42 and a motor (not shown).

  The carriage 42 is provided with a head unit 30, that is, 15 heads 31. More specifically, the carriage 42 is divided into four sub-carriages (first sub-carriage to fourth sub-carriage), and each of the first sub-carriage to third sub-carriage has four heads 31. Three heads 31 are provided on the fourth sub-carriage.

  In other words, the fifteen heads 31 include four head groups (corresponding to a plurality of sub head units), that is, the first head group 302 to which the first head to the fourth head belong, and the fifth head to the eighth head. The second head group 304 belongs, the third head group 306 to which the ninth head to the twelfth head belong, and the fourth head group 308 to which the thirteenth head to the fifteenth head belong. The first head group 302 is the first sub-carriage, the second head group 304 is the second sub-carriage, the third head group 306 is the third sub-carriage, the fourth head group 308 is the fourth sub-carriage, Each is provided.

  The carriage 42 composed of four sub-carriages is integrated with a head unit 30 composed of four head groups (in other words, fifteen heads 31) by driving a motor (not shown) in the transport direction (left-right direction). ).

  The cleaning unit 43 (not shown in FIG. 1) is for cleaning the head 31. The cleaning unit 43 is provided at a home position (hereinafter referred to as HP, see FIG. 1), and has a cap (not shown), a suction pump 43a (see FIG. 3 and the like), and the like. When the head 31 (carriage 42) moves in the transport direction (left-right direction) and is positioned on the HP, a cap (not shown) comes into close contact with the lower surface (nozzle surface) of the head 31. When the suction pump 43a operates in such a state that the cap is in close contact, the ink in the head 31 is sucked together with the thickened ink and paper powder. In this way, the clogged nozzle recovers from the non-ejection state, thereby completing the head cleaning.

  A flushing unit 44 is provided between the HP and the platen 29 in the transport direction (left-right direction), and the head 31 (carriage 42) moves in the transport direction (left-right direction) to face the flushing unit 44. When the head 31 is positioned, the head 31 performs a flushing operation for performing flushing by ejecting ink from each nozzle belonging to the nozzle row.

  The platen 29 supports the part of the roll paper 2 located in the image recording region R on the conveyance path and heats the part. As shown in FIG. 1, the platen 29 is provided corresponding to the image recording area R on the conveyance path, and is an area along the conveyance path between the first conveyance roller 23 and the second conveyance roller 24. Is arranged. The platen 29 can heat the portion of the roll paper 2 by receiving supply of heat generated by the heater unit 70.

  The heater unit 70 is for heating the roll paper 2 and has a heater (not shown). This heater has a nichrome wire, and the nichrome wire is arranged inside the platen 29 so as to be at a fixed distance from the support surface of the platen 29. For this reason, when the heater is energized, the nichrome wire itself generates heat, and heat can be conducted to the portion of the roll paper 2 located on the support surface of the platen 29. Since this heater is configured by incorporating a nichrome wire in the entire area of the platen 29, heat can be uniformly conducted to the portion of the roll paper 2 on the platen 29. In the present embodiment, the portion of the roll paper 2 is uniformly heated so that the temperature of the portion of the roll paper 2 on the platen is 45 ° C. Thereby, the ink landed on the part of the roll paper 2 can be dried.

  The blower unit 80 is for sending wind to the roll paper 2 on the platen 29. The blower unit 80 includes a fan 81 and a motor (not shown) that rotates the fan 81. The fan 81 rotates to send wind to the roll paper 2 on the platen 29 and dry the ink landed on the roll paper 2. As shown in FIG. 1, a plurality of fans 81 are provided on an openable / closable cover (not shown) provided on the main body. Each fan 81 is positioned above the platen 29 when the cover is closed, and faces the support surface of the platen 29 (the roll paper 2 on the platen 29).

  The take-up unit 90 is for taking up the roll paper 2 (roll paper on which an image has been recorded) sent by the transport unit 20. This take-up unit 90 is fed from the relay roller 91 that is rotatably supported by the relay roller 91 for winding the roll paper 2 sent from the feed roller 27 from the upper left side and conveying it to the lower right side. And a take-up drive shaft 92 for taking up the roll paper 2.

  The controller 60 is a control unit for controlling the image recording apparatus 1. As shown in FIG. 2, the controller 60 includes an interface unit 61, a CPU 62, a memory 63, and a unit control circuit 64. The interface unit 61 is for transmitting and receiving data between the host computer 110 as an external device and the image recording apparatus 1. The CPU 62 is an arithmetic processing device for controlling the entire image recording apparatus 1. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like. The CPU 62 controls each unit by a unit control circuit 64 according to a program stored in the memory 63.

  The detector group 50 is for monitoring the situation in the image recording apparatus 1. For example, a rotary encoder that is attached to the above-described slack detection sensor and the conveyance roller and is used for controlling the conveyance of the roll paper 2. A paper detection sensor for detecting the presence or absence of the roll paper 2 being conveyed, a linear encoder for detecting the position of the carriage 42 (or head 31) in the conveyance direction (left and right direction), and the paper edge in the width direction of the roll paper 2 There are a paper edge position detection sensor for detecting the (edge) position, an ink sub-tank sensor and an empty liquid sub-tank sensor, which will be described later.

=== Regarding the Ink Supply Unit 35 ===
<<< Regarding Configuration Example of Ink Supply Unit 35 >>>
Next, the ink supply unit 35 will be described with reference to FIGS. 1 and 3. FIG. 3 is a block diagram of the black ink supply unit 36.

  As described above, the ink replenishment unit 35 is for replenishing (supplying) ink to the head unit 30 when the amount of ink in the head unit 30 decreases due to ink ejection by the head 31. .

  The ink supply unit 35 is provided for each ink color. That is, a yellow ink supply unit for supplying yellow ink, a magenta ink supply unit for supplying magenta ink, a cyan ink supply unit for supplying cyan ink, and a black ink supply For this purpose, a black ink supply unit 36 is provided.

  As described above, the matte black (Mk) ink and the photo black (Pk) ink can be selectively ejected from the nozzle corresponding to the black color. For this reason, the black ink supply unit 36 has a configuration different from the configuration of the ink supply units of other colors (while the configuration of the ink supply units of other colors is common). In the following description, the black ink replenishment unit 36 among the plurality of ink replenishment units 35 will be mainly described, and the ink replenishment units of the other colors will be described later only in the configuration difference from the black ink replenishment unit 36. .

  As shown in FIG. 3, the black ink supply unit 36 includes a cartridge 37 (that is, the ink cartridge 362 and the empty liquid cartridge 402), and a sub tank unit 38 (that is, a supply ink sub tank as an example of a supply ink storage unit). 365 and an ink sub-tank unit 364 as an example of an ink storage unit including a return ink sub-tank 366 as an example of a return ink storage unit, and an empty prevention liquid sub tank 404), and a flow path (passage) for ink and empty prevention liquid ), A number of valves for opening and closing the tube (in this embodiment, the valve is a solenoid valve, but is not limited to this), and a return pump 369 ( In this embodiment, the return pump 369 is a Is a Buponpu has to be not) for limitation, a. Note that the locations where the cartridge 37 and the sub tank unit 38 are installed are indicated by reference numerals 35 and 36 in FIG.

  The ink cartridge 362 contains ink to be supplied to the head unit 30. The ink cartridge 362 is configured to be detachable from the image recording apparatus main body. As the ink cartridge 362, an ink cartridge for Mk ink (Mk ink cartridge 362a) and an ink cartridge for Pk ink (Pk ink cartridge 362b) are provided.

  Further, as shown in FIG. 3, the ink cartridge 362 is connected via a tube (the tube is referred to as an IC-IST tube 370 for convenience) that connects the ink cartridge 362 and the ink sub tank unit 364 (supply ink sub tank 365). The ink sub tank unit 364 (supply ink sub tank 365) is connected.

  The ink sub tank unit 364 is for storing ink. As the ink sub tank unit 364, an Mk ink sub tank unit 367 (corresponding to the first ink storage unit) that stores Mk ink and a Pk ink sub tank that stores Pk ink. A unit 368 (corresponding to a second ink storage unit) is provided.

  Each ink sub tank unit 364 includes a supply ink sub tank 365 and a return ink sub tank 366. That is, the Mk ink sub tank unit 367 has a supply Mk ink sub tank 365a and a return Mk ink sub tank 366a, and the Pk ink sub tank unit 368 includes a supply Pk ink sub tank 365b and a return Pk ink sub tank. 366b. These ink sub tanks are fixed to the image recording apparatus main body. That is, unlike the ink cartridge 362, the ink sub-tank has a configuration that cannot be attached to and detached from the image recording apparatus main body.

  The supply ink sub tank 365 temporarily stores ink supplied from the ink cartridge 362 to the head unit 30. As described above, the supply ink sub-tank 365 is connected to the ink cartridge 362 via the IC-IST tube 370. As shown in FIG. A valve (the valve is referred to as an IC-IST valve 390 for convenience) is provided. Further, the supply ink sub-tank 365 is provided with an ink sub-tank sensor (not shown) that detects when the amount of ink in the supply ink sub-tank 365 becomes less than a threshold value.

When the controller 60 receives the detection signal from the ink sub-tank sensor and grasps that the amount of ink in the supply ink sub-tank 365 is less than the threshold, the closed IC-IST valve 390 is opened. Ink is supplied from the ink cartridge 362 to the supply ink sub tank 365. Thus, in the supply ink sub-tank 365, the amount of ink is controlled so that an amount of ink equal to or greater than the threshold is always present (stored).
Details of the return ink sub-tank 366 will be described later.

  Further, as shown in FIG. 3, the supply ink sub tank 365 is connected to the head unit 30 via four supply tubes that connect the supply ink sub tank 365 and the head unit 30. The four supply tubes (the first supply tube 372, the second supply tube 374, the third supply tube 376, and the fourth supply tube 378) are supplied to supply ink from the supply ink sub tank 365 to the head unit 30. Act as a road.

  That is, when image recording (printing) or the like is performed, ink is ejected from the head unit 30 (head 31), and ink in the head unit 30 (head 31) is consumed, the consumed ink is supplemented. As described above, the ink in the supply ink sub tank 365 flows into the head unit 30 (head 31) through the first supply tube 372 to the fourth supply tube 378.

  In addition, as already described, the head unit 30 according to the present embodiment has 15 heads 31, and the 15 heads 31 include four head groups, that is, the first head group 302 to the fourth head group. Although the head group 308 is provided, each of the four supply tubes is connected to each of the four head groups as shown in FIG. In other words, each of the four supply tubes supplies ink to the head group corresponding to each of the four supply tubes.

  That is, the first supply tube 372 is connected to the first head group 302 (first head to fourth head) and supplies ink to the first head to fourth head. The second supply tube 374 is connected to the second head group 304 (fifth head to eighth head), and supplies ink to the fifth head to eighth head. The third supply tube 376 is connected to the third head group 306 (the ninth head to the twelfth head) and supplies ink to the ninth head to the twelfth head. The fourth supply tube 378 is connected to the fourth head group 308 (the thirteenth head to the fifteenth head) and supplies ink to the thirteenth head to the fifteenth head.

  As is apparent from FIG. 1, the ink sub tank 365 for supply of the ink replenishing unit 35 and the head unit 30 are located far away from each other. Therefore, each of the first supply tube 372 to the fourth supply tube 378 is a very long tube, and the length thereof is 5 to 6 meters. As shown in FIG. 3, a cable bear 400 is provided for arranging the first supply tube 372 to the fourth supply tube 378, and the first supply tube 372 to the fourth supply tube 378 are connected to the cable bear 400. Is housed inside.

  Further, each of the first supply tube 372 to the fourth supply tube 378 (hereinafter, the first supply tube 372 will be described as an example, but the same applies to other supply tubes), as shown in FIG. An Mk ink supply channel 382 through which only ink flows, a Pk ink supply channel 384 through which only Pk ink flows, and a common supply channel 386 through which both Mk ink and Pk ink flow are provided, and these channels are connected upstream. Connection is made at section 388. The ink in the supply Mk ink sub-tank 365a passes through the Mk ink supply flow path 382, the upstream connection portion 388, and the shared supply flow path 386 of the first supply tube 372 in this order, and is thus head unit 30 (head 31). The ink in the supply Pk ink sub-tank 365b passes through the Pk ink supply channel 384, the upstream connection portion 388, and the common supply channel 386 of the first supply tube 372 in this order. Thus, it flows into the head unit 30 (head 31). That is, the first supply tube 372 selectively supplies ink to the head unit 30 from either the supply Mk ink subtank 365 a of the Mk ink subtank unit 367 or the supply Pk ink subtank 365 b of the Pk ink subtank unit 368.

  As described above, the Mk ink and the Pk ink can be selectively ejected from the nozzle corresponding to the black color of the head unit 30, but the Mk ink can be ejected from the nozzle (hereinafter referred to as Mk ejection for convenience). A switching process (which will be described in detail later) is required to switch from one to the other (referred to as a Pk discharge enabled state for the sake of convenience) and a state in which Pk ink can be discharged from the nozzles (hereinafter referred to as a Pk discharge enabled state). For example, in the switching process from the Mk dischargeable state to the Pk dischargeable state, conventionally, in the switching process, in order to fill the supply tube with Pk ink, it is present in the common supply flow path 386. The Mk ink to be discarded was discarded (specifically, discharged from the nozzle), and the Pk ink was caused to flow into the common supply channel 386. For this reason, the Mk ink is wasted.

  As a countermeasure against such inconvenience, in the present embodiment, the shared supply flow is not discarded without discarding the Mk ink existing in the shared supply flow path 386 during the switching process from the Mk discharge enabled state to the Pk discharge enabled state. In order to discharge the Mk ink from the path 386, the Mk ink in the supply tube is returned to the ink sub-tank unit 364 (to be described in detail later), and the Mk ink existing in the common supply channel 386 is backflowed. (Move the returned Mk ink in the next Mk dischargeable state (after switching to the next Mk dischargeable state) for printing. Used again). In order to realize such return processing, the black ink supply unit 36 according to the present embodiment is provided with a return ink sub-tank 366, a return pump 369, and the like.

  The return ink sub-tank 366 (that is, the return Mk ink sub-tank 366a for returning Mk ink and the return Pk ink sub-tank 366b for returning Pk ink) is for storing the ink returned by the return process. is there. As shown in FIG. 3, the return ink sub tank 366 includes the return ink sub tank 366 and four supply tubes (a first supply tube 372, a second supply tube 374, a third supply tube 376, and a fourth supply tube 378). Are connected to the four supply tubes via the upstream connection portion 388 (that is, the ink in each supply tube is one (common) return ink). It is to be returned to the sub tank 366).

  Each of the four supply tubes is provided with a return pump 369 for causing the ink in the supply tubes to flow backward. In the present embodiment, the return pump 369 is located between the upstream connection portion 388 and the cable bearer 400 as shown in FIG. When the return pump 369 is activated, the ink in the supply tube (shared supply flow path 386) and the return tube 379 flows backward and moves toward the return ink sub tank 366. Then, a part of the ink flows (returns) into the return ink sub tank 366.

  As described above, when the return process described above is executed during the switching process from the Mk dischargeable state to the Pk dischargeable state, the Mk ink existing in the shared supply flow path 386 flows backward, and the Mk ink is not discarded. However, air may enter the common supply flow path 386 in place of the Mk ink. In other words, there is a possibility that the common supply flow path 386 has a place where the supply flow path is empty. If the air is present in the common supply flow path 386, the following problem may occur. For example, when the ink that has come into contact with the air dries and hardens, it becomes dust or causes clogging.

  Therefore, in the present embodiment, when the return process is executed, the Mk ink in the supply tube is returned (not only returned) to the ink sub tank unit 364, and the empty prevention liquid flows into the supply tube. I try to let them. In order to realize this, the black ink replenishing unit 36 according to the present embodiment is provided with an empty liquid storage unit 401.

  The empty prevention liquid is a liquid for preventing the inside of the supply tube from becoming empty due to the execution of the return process, and any liquid may be used as long as it achieves such an object. In the present embodiment, the composition and physical properties are close to those of the ink, but the solvent component is not included in the solid content such as the pigment (for example, the pigment is removed from the ink) (therefore, the ink is used). Cost is also cheaper than ink).

  The empty prevention liquid storage unit 401 includes an empty prevention liquid cartridge 402, an empty prevention liquid sub tank 404, an injection tube 410, and the like.

The anti-empty liquid cartridge 402 contains an anti-empty liquid to be supplied to the supply tube. The empty liquid cartridge 402 is configured to be detachable from the image recording apparatus main body.
Further, as shown in FIG. 3, the empty liquid cartridge 402 is connected via a tube connecting the empty liquid cartridge 402 and the empty liquid sub-tank 404 (this tube is referred to as a VC-VST tube 406 for convenience). It is connected to the empty liquid sub tank 404.

  The air prevention liquid sub tank 404 temporarily stores the air prevention liquid supplied from the air prevention liquid cartridge 402 to the supply tube. The empty liquid sub-tank 404 is fixed to the image recording apparatus main body. That is, unlike the anti-empty liquid cartridge 402, the anti-empty liquid sub tank 404 has a configuration that cannot be attached to and detached from the image recording apparatus main body.

  In addition, the point that the empty prevention liquid sub tank 404 is connected to the empty prevention liquid cartridge 402 via the VC-VST tube 406 has already been described. As shown, a valve (the valve is referred to as a VC-VST valve 408 for convenience) is provided. Further, the empty liquid sub-tank 404 is provided with an empty liquid sub-tank sensor (not shown) that detects when the amount of the empty liquid in the empty liquid sub-tank 404 is less than a threshold value.

  When the controller 60 receives the detection signal from the empty liquid sub-tank sensor and recognizes that the amount of the empty liquid in the empty liquid sub-tank 404 is less than the threshold value, the closed VC-VST valve 408 is closed. Is opened so that the empty prevention liquid flows from the empty prevention liquid cartridge 402 into the empty prevention liquid sub-tank 404. Thus, in the empty prevention liquid sub-tank 404, the amount of the empty prevention liquid is controlled so that an amount of the empty prevention liquid equal to or greater than the threshold is always present (stored).

  Further, as shown in FIG. 3, the empty liquid sub-tank 404 includes an empty liquid sub-tank 404 and four supply tubes (first supply tube 372, second supply tube 374, third supply tube 376, fourth supply tube 378. ) To the four supply tubes (common supply flow path 386) via the four tubes (tubes for allowing the emptying liquid to flow into the supply tube; for convenience, referred to as the injection tube 410). Connected at 412.

  The downstream connection portion 412 is located in the vicinity of the head unit 30 as shown in FIG. Further, as is clear from FIG. 1, the empty liquid sub-tank 404 of the ink supply unit 35 and the head unit 30 are located far away from each other. Therefore, each of the four injection tubes 410 is a very long tube, and its length is 5 to 6 meters. As shown in FIG. 3, the four injection tubes 410 are also accommodated in the cable bear 400.

  Further, as shown in FIG. 3, each of the four upstream connecting portions 388 is provided with an upstream valve 389 (a member represented by four white circles in FIG. 3). Mk ink supply channel 382 that is a supply tube for Mk ink, Pk ink supply channel 384 that is a supply tube for Pk ink, a return tube 379 for Mk ink, and a return tube 379 for Pk ink It serves to connect any of the tubes with the common supply channel 386. Each of the four downstream connection parts 412 is provided with a downstream valve 414 (a member represented by two white circles in FIG. 3). The downstream valve 414 includes the head unit 30 and the injection tube 410. Any one of these is connected to the common supply channel 386. The specific operation of these valves will be clarified later.

  In the present embodiment, the ink replenishment unit 35 for colors other than black ink is not configured to selectively eject a plurality of types of ink. Therefore, each of the first supply tube 372 to the fourth supply tube 378 is not provided with the common supply flow path 386 or the upstream connection portion 388 described above, and the ink cartridge 362 and the supply ink sub-tank 365 are not provided. There is only one each. As a matter of course, members (return ink sub-tank 366, return pump 369, etc.) for realizing the return process and members (empty prevention liquid storage unit 401) for introducing the empty prevention liquid are also provided. Absent.

<<< Switching process >>>
Here, the process of switching the ink passing through the nozzle from one of the Mk ink and the Pk ink to the other, that is, the state in which the Mk ink can be ejected from the nozzle (hereinafter referred to as the Mk ejectable state for convenience) and the Pk ink in the nozzle 4 to 6, the switching process from the Mk dischargeable state to the Pk dischargeable state is taken as an example of the mutual switching process of the dischargeable state (hereinafter referred to as the Pk dischargeable state for convenience). explain. FIG. 4 is a block diagram showing a state of the black ink supply unit 36 immediately before the switching process is executed. FIG. 5 is a block diagram showing a state of the black ink supply unit 36 immediately before the return process is completed. FIG. 6 is a block diagram showing a state of the black ink supply unit 36 immediately before the switching process is completed.

  In the switching process, the behavior of the liquid (ink or anti-empty liquid) in the first supply tube 372 to the fourth supply tube 378 is not different for each supply tube. The first supply tube 372 will be described as an example. Therefore, in FIGS. 4 to 6, only the first supply tube 372 is described, and the description of the second supply tube 374 to the fourth supply tube 378 is omitted. Further, in order to make the drawing easy to understand, the illustration of the cartridge 37 is also omitted.

  Further, in order to show which liquid is present in the tube, the thickness of the tube is made thicker in FIGS. 4 to 6 than in FIG. The black portion in the tube indicates Mk ink, the shaded portion indicates Pk ink, and the spotted portion indicates the empty prevention liquid.

  As described above, FIG. 4 shows the state of the black ink supply unit 36 before the switching process is executed. At this time, as shown in FIG. 4, the upstream side valve 389 is in a state where the Mk ink supply flow path 382 is connected (in the figure, the black circle is connected, and the white circle is not connected). The downstream valve 414 is in a state where the head unit 30 is connected. That is, when the ink in the head unit 30 is consumed, the ink in the supply Mk ink sub tank 365a flows into the head unit 30 through the Mk ink supply channel 382 and the common supply channel 386. As shown in FIG. 4, Mk ink is present in the Mk ink supply channel 382, the common supply channel 386, and the head unit 30. Although not shown in the drawing, the head unit 30 (head 31) is located at the HP, and the cap is in close contact with the lower surface (nozzle surface) of the head 31.

  In this state, the controller 60 starts the switching process. First, the controller 60 executes the first step. That is, a return process for returning the Mk ink in the first supply tube 372 (shared supply flow path 386) toward the return Mk ink subtank 366a of the ink subtank unit 364 is executed, and at the time of executing the return process, the adjustment is performed. Thus, the empty prevention liquid in the empty prevention liquid storage unit 401 is caused to flow into the first supply tube 372 (common supply flow path 386).

  In the present embodiment, the controller 60 executes the following in order to realize such processing. First, the controller 60 performs valve switching. That is, as shown in FIG. 5, the upstream side valve 389 is switched to a state where the return tube 379 for Mk ink is connected, and the downstream side valve 414 is switched to a state where the injection tube 410 is connected.

  Next, the controller 60 operates the return pump 369 as shown in FIG. 5 (the upward arrow in the return pump 369 indicates “pump operation”). Then, as shown in FIGS. 4 and 5, the Mk ink in the common supply flow path 386 and the return tube 379 flows back to the return Mk ink sub-tank 366a and the empty prevention liquid storage unit 401 (specifically) Specifically, the empty prevention liquid in the injection tube 410) flows into the common supply flow path 386 (and the inflow empty prevention liquid also goes to the returning Mk ink sub tank 366a). Then, a part of the Mk ink flows (returns) into the return Mk ink sub tank 366a.

  Then, the controller 60 continues the operation of the return pump 369 until the empty prevention liquid toward the return Mk ink sub-tank 366a reaches the upstream connection portion 388 (the state where it has been reached is shown in FIG. 5). , The return process is terminated upon arrival. Although the method for detecting the arrival is not particularly limited, in this embodiment, focusing on the fact that the ink is opaque and the empty prevention liquid is transparent, a detection method using an optical sensor is used. Adopted. That is, the light emitting element emits light toward the transparent upstream connection portion 388, and the output of the light receiving element is different depending on whether ink is present in the upstream connection portion 388 and when the empty prevention liquid is present. The arrival is detected using.

  Next, the controller 60 executes the second step. That is, the empty prevention liquid in the first supply tube 372 (shared supply flow path 386) is discharged from the first supply tube 372, and the Pk ink in the Pk ink sub tank unit 368 (supply Pk ink sub tank 365b) is discharged. Flow into the first supply tube 372.

  In the present embodiment, the controller 60 executes the following in order to realize such processing. First, the controller 60 performs valve switching. That is, as shown in FIG. 6, the upstream side valve 389 is switched to a state where the Pk ink supply channel 384 is connected, and the downstream side valve 414 is switched to a state where the head unit 30 is connected.

  Next, as shown in FIG. 6, the controller 60 operates the suction pump 43a (the downward arrow in the suction pump 43a represents “pump operation”). Then, the Mk ink in the head unit 30 and the empty prevention liquid in the common supply channel 386 are sucked and discharged from the nozzle. Instead, the Pk ink flows into the head unit 30 and the common supply channel 386. Will be.

  Thus, when the ink in the head unit 30 is consumed, the ink in the supply Pk ink sub-tank 365b flows into the head unit 30 through the Pk ink supply channel 384 and the common supply channel 386. In this state, that is, as shown in FIG. 6, Pk ink is present in the Pk ink supply channel 384, the common supply channel 386, and the head unit 30, and the switching process is completed.

=== Effectiveness of Image Recording Apparatus 1 According to the Present Embodiment ===
As described above, the image recording apparatus 1 according to the present embodiment includes the ink sub tank unit 364 that stores ink, the head unit 30 that discharges ink to the roll paper 2, and the ink from the ink sub tank unit 364 to the head unit 30. A supply tube for supplying and a controller 60 for executing a return process for returning the ink in the supply tube toward the ink sub tank unit 364 are provided. The supply tube includes an empty liquid storage unit 401 that stores an empty liquid for preventing emptying of the supply tube due to the execution of the return process, and the controller 60 supplies the empty liquid when the return process is executed. The ink in the tube is returned toward the ink sub-tank unit 364, and the empty prevention liquid in the empty prevention liquid storage unit 401 is caused to flow into the supply tube.

  Therefore, as described above, when the return process is performed, air enters due to the flow of the anti-empty liquid into the supply tube (that is, the supply tube has a place where the supply tube is empty). ) Is appropriately prevented. Therefore, the occurrence of problems due to the presence of air in the supply tube (for example, problems in which ink that has come into contact with the air dries and hardens, causing dust or clogging) is suppressed. It becomes possible.

=== Other Embodiments ===
Although the above embodiment is mainly described for a printing apparatus, disclosure of an ink return method and the like is also included. The above-described embodiments are for facilitating understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

  In the said embodiment, although the roll paper 2 was mentioned as an example and demonstrated as a medium, it is not limited to this, For example, a cut paper, a film, and cloth may be sufficient.

  In the above embodiment, the head unit 30 has a plurality (15) of the heads 31. However, the present invention is not limited to this. For example, the head unit 30 may be composed of one head 31.

  In the above embodiment, the Mk ink and the Pk ink have been described as examples of the first ink and the second ink. However, the present invention is not limited to this, and other types of ink may be used. Good. The plurality of types of inks may not be the same type of ink such as Mk ink and Pk ink.

  In the above embodiment, the ink sub tank unit 364 includes the supply ink sub tank 365 and the return ink sub tank 366, and the supply tube supplies ink from the supply ink sub tank 365 to the head unit 30. The return process is a process of returning the ink in the supply tube toward the return ink sub-tank 366. That is, in the above embodiment, the return ink sub-tank is prepared separately from the supply ink sub-tank. However, the present invention is not limited to this.

For example, the ink may be returned toward the ink subtank for supply without providing a separate ink subtank for return (that is, there is no distinction between supply and return for the ink subtank).
However, the above embodiment is preferable in that it is possible to avoid the inconvenience that the ink sub tank is full and cannot be returned when the ink is returned to the supply ink sub tank.

  In the above embodiment, a plurality of supply tubes are provided, and the head unit 30 includes a plurality of head groups. Each of the plurality of supply tubes supplies ink to the corresponding head group, and the controller 60 The ink in each supply tube is returned toward one return ink sub tank 366. In other words, when the return ink sub tank 366 is provided, the return ink sub tank 366 is an ink sub tank common to a plurality of supply tubes.

However, the present invention is not limited to this. For example, as shown in FIG. 7, a return ink sub-tank 366 is provided for each of the plurality of supply tubes, and the controller 60 controls the ink in each supply tube. May be returned toward the corresponding return ink sub-tank 366.
However, the above embodiment is preferable in that the configuration of the image recording apparatus 1 becomes simple.

  The return ink sub-tank 366 is provided with a detection sensor for detecting the amount of ink, and the controller 60 determines the end timing of return processing based on the detection result output by the detection sensor. It is good as well.

  That is, in the above-described embodiment, as described above, a detection method using an optical sensor is employed as a method for determining the end timing of the return process. In other words, the light emitting element emits light toward the transparent upstream connection portion 388, and the output of the light receiving element is different when ink is present at the upstream connection portion 388 and when the empty prevention liquid is present. Was. However, in this method, if the image recording apparatus 1 is continuously used for a long period of time, the upstream side connection portion 388 is noticeably contaminated, which may cause an error in the output result of the optical sensor.

  However, if the controller 60 determines the end timing of the return process based on the detection result output by the detection sensor for detecting the amount of ink in the return ink sub-tank 366, such a problem is caused. Does not occur.

  As a specific example, when the empty prevention liquid reaches the upstream connection portion 388 (see FIG. 5), the amount of ink stored in the return ink sub-tank 366 is obtained in advance. Then, when the detection sensor detects this amount, the return process is terminated. In this way, the return process can be terminated when the empty prevention liquid reaches the upstream connection portion 388, as in the above embodiment. Further, since the above-described error does not occur, the return process can be executed more reliably.

  In the above embodiment, the ink sub-tank unit 364 includes the Mk ink sub-tank unit 367 for storing Mk ink and the Pk ink sub-tank unit 368 for storing Pk ink, and the head unit 30 has Mk ink and Pk ink. There is a nozzle that can selectively pass through, and ink is ejected from the nozzle onto the roll paper. The supply tube selectively selects ink from one of the Mk ink sub-tank unit 367 and the Pk ink sub-tank unit 368 to the head unit 30. The controller 60 returns the Mk ink in the supply tube toward the Mk ink sub-tank unit 367 and causes the empty prevention liquid in the empty prevention liquid storage unit 401 to flow into the supply tube, and then in the supply tube. Supply empty prevention liquid With discharged from over blanking, by flowing a Pk ink in Pk ink sub-tank unit 368 to the supply tube, switching processing for switching the ink to pass nozzle from Mk ink to Pk inks, it was decided to run. That is, in the above-described embodiment, in the so-called ink switching process, the ink in the supply tube is returned to the ink sub tank unit 364 and the empty prevention liquid in the empty prevention liquid storage unit 401 is caused to flow into the supply tube. It was.

  However, the present invention is not limited to this. In a scene different from the ink switching process, the ink in the supply tube is returned to the ink sub tank unit 364 and the empty prevention liquid in the empty prevention liquid storage unit 401 is supplied to the supply tube. There is a case where it is allowed to flow in, and such a case may be used.

  For example, the image recording apparatus 1 is provided with ink that tends to settle, such as white ink, and the white ink in the supply tube is used for the purpose of preventing the sedimentation from being accelerated when the white ink is not used. It may be possible to return to the sub tank unit 364 (the ink sub tank unit 364 is provided with a stirring member for stirring the ink) and to allow the empty prevention liquid in the empty prevention liquid storage unit 401 to flow into the supply tube. It is done. Even in such a case, problems due to the presence of air in the supply tube (for example, ink that has come into contact with the air dries and solidifies, resulting in dust or clogging. It is possible to suppress the occurrence of problems.

  However, in the case of the above-described embodiment, in addition to the effect of suppressing the occurrence of problems due to the presence of air in the supply tube, the following advantages are provided. desirable.

  This will be described with reference to FIGS. 4 to 6 again. Conventionally, when the ink switching process is executed (for example, when switching from Mk ink to Pk ink), the state shown in FIG. 4 is not passed through the state shown in FIG. (Without execution), the suction process was performed to shift to the state shown in FIG. In other words, when the ink switching process is executed, only the second step is performed without performing the first step described above. In such a case, the Mk ink in the common supply flow path 386 and the head unit 30 is discharged (discarded), as is apparent from a comparison of FIGS. 4 and 6. In contrast, in the present embodiment, the return process is performed in the ink switching process and the empty prevention liquid is allowed to flow into the supply tube during the return process (that is, the first step). As is apparent from comparison and reference 6, the Mk ink in the head unit 30 is discharged (discarded), but the Mk in the common supply channel 386 (this channel is very long as described above). The ink does not have to be discharged (discarded) (instead, the empty prevention liquid is discarded, but an inexpensive one can be used for the empty prevention liquid). That is, a cost merit arises.

1 image recording device, 2 roll paper,
10 Feeding unit, 18 winding shaft, 19 relay roller,
20 transport unit, 20a steering unit,
21 relay roller, 22 relay roller,
23 1st conveyance roller, 23a 1st drive roller, 23b 1st driven roller,
24 second conveying roller, 24a second driving roller, 24b second driven roller,
25 reversing roller, 26 relay roller, 27 delivery roller,
29 platens, 30 head units, 31 heads,
35 ink supply unit, 36 black ink supply unit,
37 cartridges, 38 sub tank units,
40 carriage unit, 41 guide rail, 42 carriage,
43 Cleaning unit, 43a Suction pump, 44 Flushing unit,
50 detector groups, 60 controllers, 61 interface units,
62 CPU, 63 memory, 64 unit control circuit,
70 heater unit, 80 blower unit, 81 fan,
90 winding unit, 91 relay roller, 92 winding drive shaft,
110 host computer,
302 First head group, 304 Second head group,
306 Third head group, 308 Fourth head group,
362 ink cartridge,
362a Mk ink cartridge, 362b Pk ink cartridge,
364 Ink sub tank unit, 365 Ink sub tank for supply,
365a Mk ink sub tank for supply, 365b Pk ink sub tank for supply,
366 Return ink sub tank,
366a Mk ink sub tank for return, 366b Pk ink sub tank for return,
367 Mk ink sub tank unit, 368 Pk ink sub tank unit,
369 return pump, 370 IC-IST tube,
372 first supply tube, 374 second supply tube,
376 Third supply tube, 378 Fourth supply tube,
379 return tube,
382 Mk ink supply channel, 384 Pk ink supply channel,
386 shared supply flow path, 388 upstream connection,
389 Upstream valve, 390 IC-IST valve, 400 Cableveyor,
401 empty prevention liquid storage unit, 402 empty prevention liquid cartridge,
404 air prevention liquid sub tank,
406 VC-VST tube, 408 VC-VST valve,
410 Injection tube, 412 Downstream connection part, 414 Downstream valve

Claims (6)

An ink storage unit for storing ink;
A head unit for discharging the ink onto a medium;
A supply flow path for supplying the ink from the ink storage unit to the head unit;
A controller for performing a return process for returning the ink in the supply flow channel toward the ink storage unit;
A printing device comprising:
An empty liquid storage unit for containing an empty liquid for preventing the inside of the supply flow path from becoming empty due to the execution of the return process;
When the controller executes the return process, the controller returns the ink in the supply flow path toward the ink storage unit, and the empty liquid in the empty liquid storage unit is returned to the supply flow path. A printing apparatus characterized by being caused to flow. The printing apparatus according to claim 1,
The ink storage unit has a supply ink storage part and a return ink storage part,
The supply flow path is a flow path for supplying the ink from the supply ink reservoir to the head unit,
The printing apparatus according to claim 1, wherein the return process is a process of returning the ink in the supply flow channel toward the return ink storage unit. The printing apparatus according to claim 2,
A plurality of the supply channels are provided,
The head unit is composed of a plurality of sub head units,
Each of the plurality of supply flow paths supplies the ink to the sub head unit corresponding to each of the supply flow paths,
The printing apparatus, wherein the controller returns the ink in each of the supply flow paths toward one return ink storage section. The printing apparatus according to claim 2 or 3,
The return ink reservoir is provided with a detection sensor for detecting the amount of the ink,
The printing apparatus, wherein the controller determines an end timing of the return process based on a detection result output from the detection sensor. The printing apparatus according to any one of claims 1 to 4,
The ink storage unit includes a first ink storage unit that stores the first ink and a second ink storage unit that stores the second ink,
The head unit has a nozzle through which the first ink and the second ink can selectively pass, and the ink is ejected from the nozzle onto the medium.
The supply channel selectively supplies the ink to the head unit from either the first ink storage unit or the second ink storage unit,
The controller is
The first ink in the supply flow path is returned toward the first ink storage unit, and the empty prevention liquid in the empty prevention liquid storage unit is caused to flow into the supply flow path, and then the supply flow path By discharging the anti-empty liquid in the supply channel, and flowing the second ink in the second ink storage unit into the supply channel,
A switching process for switching the ink that passes through the nozzle from the first ink to the second ink,
A printing apparatus that executes the printing apparatus. An ink storage unit for storing ink;
A head unit for discharging the ink onto a medium;
A supply flow path for supplying the ink from the ink storage unit to the head unit;
Providing a printing device having:
The ink in the supply flow path is returned toward the ink storage unit, and an empty prevention liquid for preventing the supply flow path from being emptied by returning the ink flows into the supply flow path. And letting
An ink return method characterized by comprising:

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