JP2022006977A - Recording device and method for controlling recording device - Google Patents

Abstract

To suppress densities of ink in a circulation passage from increasing, while reducing amounts of wasted ink.SOLUTION: A recording deice comprises: a tank; a recording head that has an ejection port that ejects ink and a pressure chamber that is filled with ink and performs recording by ejecting ink while performing reciprocating scanning; a supply passage through which ink is supplied from the tank to the recording head; and control means that controls preliminary ejection from the recording head. The recording head has a first liquid chamber having a connected part with the supply passage, a second liquid chamber communicating with the first liquid chamber through the pressure chamber, and a volume varying part that varies volumes of the second liquid chamber. The control means executes the preliminary ejection at a timing after recording operation in one scanning by the recording head is finished and before circulation of ink in the recording head that occurs by reciprocating scanning performed by the recording head is started.SELECTED DRAWING: Figure 10

Description

The present invention relates to a recording device and a method for controlling the recording device.

There is a so-called serial type inkjet recording device in which a recording operation is performed by repeating movement of a recording head in the main scanning direction and transfer of a recording medium. Patent Document 1 describes an inkjet head having a collection side ink chamber, a supply side ink chamber, and an ink circulation device in a serial type inkjet recording apparatus. In Patent Document 1, the collection side ink chamber, the supply side ink chamber, and the ink circulation device are integrally formed above the inkjet head with the inkjet head. It is described that the ink circulation device includes an ink circulation pump and a pressure sensor, and drives the ink circulation pump to circulate ink between ink chambers through a nozzle.

Japanese Unexamined Patent Publication No. 2016-52769

The technique described in Patent Document 1 has an ink circulation device integrally formed with an inkjet head, and a large number of parts such as an ink circulation pump and a pressure sensor are used in the ink circulation device. Therefore, if an attempt is made to circulate the ink in the vicinity of the nozzle by using the technique described in Patent Document 1, there is a possibility that the configuration of the recording head may be complicated or the control of the apparatus may be complicated. Further, although it is possible to eliminate the thickening of the ink in the vicinity of the ejection port by circulating the ink in the vicinity of the ejection port, the thickening of the ink gradually progresses in the circulation path.

It is an object of the present invention to reduce the amount of waste ink and suppress an increase in the concentration of ink in the circulation path by moving the ink in the vicinity of the ejection port with a simple configuration in the inkjet recording apparatus.

The recording device according to one aspect of the present invention has a tank for accommodating ink, a discharge port for ejecting ink, and a pressure chamber filled with ink, and records by ejecting ink while reciprocating scanning. A recording device including a head, a supply flow path for supplying ink from the tank to the recording head, and a control means for controlling preliminary ejection from the recording head, wherein the recording head is the supply flow path. It has a first liquid chamber having a connection portion with the ink chamber, a second liquid chamber communicating with the first liquid chamber via the pressure chamber, and a variable volume portion for changing the volume of the second liquid chamber. The control means is at a timing after the recording operation of one scan by the recording head is completed and before the ink circulation in the recording head started due to the reciprocating scanning of the recording head. It is characterized by carrying out the preliminary discharge.

According to the present invention, in the inkjet recording apparatus, by moving the ink in the vicinity of the ejection port with a simple configuration, it is possible to suppress an increase in the density of the ink in the circulation path while reducing the amount of waste ink.

It is a schematic perspective view which shows the appearance of a recording apparatus. It is a figure which shows the ink path from an ink tank to a recording head. It is a block diagram which shows the outline of the control composition of a recording apparatus. It is a figure explaining the liquid chamber in a recording head. It is sectional drawing of the recording head. It is a figure explaining the inertial force with the movement of a carriage. It is a figure which shows the change of the ejection speed with respect to the length of the non-ejection time during a recording operation. It is a conceptual diagram explaining the ink concentration change in the vicinity of a ejection port. It is a figure for quantifying and explaining the ink concentration change. It is a flowchart explaining the preliminary discharge sequence. It is a timing chart to which the preliminary discharge control is applied. It is a timing chart which shows the comparative example. It is a conceptual diagram which shows the effect of the concentrated ink discharge. It is a figure which shows the time passage of the average ink density | concentration of the whole ink supply system. It is a conceptual diagram which shows the relationship between the preliminary discharge timing and a scanning width. It is a figure explaining the relationship between the recording mode, the preliminary discharge timing, and the number of preliminary discharge shots.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. It should be noted that the following embodiments do not limit the present invention, and not all combinations of features described in the present embodiments are essential. The same configuration will be described with the same reference numerals.

In addition, in this specification, "record" is not only the case of forming significant information such as characters or figures, but also significant and unintentional. In addition, regardless of whether or not it is manifested so that it can be visually perceived by humans, when an image, pattern, pattern, etc. is widely formed on a recording medium, or when the recording medium is processed. It shall be represented.

The term "ink" (sometimes referred to as "liquid") should be broadly construed as in the definition of "recording" above. Therefore, by being applied onto the recording medium, an image, a pattern, a pattern, or the like is formed, the recording medium is processed, or the ink is processed (for example, coagulation or insolubilization of the colorant in the ink applied to the recording medium). It shall represent the liquid that can be provided to.

The term "recording medium" refers not only to paper used in general recording equipment, but also to a wide range of materials such as cloth, plastic film, metal plate, glass, ceramics, wood, and leather that can accept ink. It shall be.

<< First Embodiment >>
In the present embodiment, the recording operation is performed by repeating the movement of the recording head in the main scanning direction and the transfer of the recording medium in the direction intersecting the main scanning direction (hereinafter referred to as the sub-scanning direction), that is, so-called serial. A formula inkjet recording device will be described. Then, in the inkjet recording device (hereinafter, simply referred to as a recording device), a mode of moving the ink in the vicinity of the ejection port will be described.

First, the background of the requirement to move the ink in the vicinity of the ejection port will be briefly described. The recording head of the recording device is configured to eject ink from the ejection port by driving an energy generating element (recording element) arranged in the pressure chamber. As a method of applying energy, an electric heat conversion element (heater), a piezoelectric element, or the like can be used. The ink filled in the pressure chamber is ejected from the ejection port by driving the energy generating element.

If the ink is not ejected from the ejection port during the recording operation for a long time, the evaporation component of the ink evaporates at the meniscus, which is the interface between the ink and the outside air at the ejection port. Therefore, the density and viscosity of the ink in the vicinity of the ejection port become high, and the ejection port is likely to be clogged. In order to suppress such a phenomenon, in general, in a serial type recording device, when the recording head is reciprocated, ink is ejected from the ejection port outside the recording range of the recording medium, and the ink is ejected in the vicinity of the ejection port. A process is performed to eject ink whose characteristics have changed. This process is called a preliminary discharge process (or flushing process). The preliminary discharge process is executed once for every few round trips, once for each round trip when higher image quality is required, and at the maximum, once for each of the outward route and the return route. Such a preliminary discharge process lowers the recording speed and causes an extra recording time. In addition, ink that is not used for recording images is consumed.

In this embodiment, an example of moving ink in the vicinity of the ejection port from the ejection port will be described. As a result, it is possible to suppress the evaporation of the evaporation component of the ink in the vicinity of the ejection port, so that it is possible to suppress the thickening of the ink in the vicinity of the ejection port without performing the preliminary ejection process frequently. In the present embodiment, the ink in the vicinity of the ejection port is moved by utilizing the characteristics of the serial type recording head. More specifically, an example of moving the ink in the vicinity of the ejection port by utilizing the pressure fluctuation generated in the tube communicating with the recording head during the reciprocating scanning of the recording head will be described. That is, an example of suppressing thickening of the ink near the ejection port with a simple configuration without providing a circulation mechanism such as a pump for moving the ink near the ejection port will be described. Further, since the thickened ink near the ejection port is diffused in the recording head, the ink density (viscosity) in the recording head gradually increases. Therefore, in the present embodiment, an example in which the increase in the ink density in the recording head is suppressed by performing the preliminary ejection process at an appropriate timing according to the movement of the ink in the vicinity of the ejection port due to the reciprocating scanning of the recording head. explain.

<Appearance of recording device>
FIG. 1 is a schematic perspective view showing the appearance of the recording device 100 in the present embodiment. The recording device 100 has a recording head 101. The recording head 101 has a plurality of ejection ports arranged, and can eject ink of a different color for each row of ejection ports. The recording head 101 communicates with the ink tank 103 via a supply tube 102 that functions as a supply flow path. The ink tank 103 is fixedly installed at a predetermined position of the recording device 100. Ink of each color is supplied from the ink tank 103 to the ejection port row of each ink color of the recording head 101 via the supply tube 102 for each color. When the ink is ejected from the ejection port, the ink is supplied from the ink tank 103 to the recording head 101.

The recording head 101 is detachably mounted on the carriage 104. The carriage 104 reciprocates along the guide shaft 107 in the main scanning direction of the coordinate axis X during the recording operation. The recording head 101 moves in the main scanning direction integrally with the carriage 104 as the carriage 104 moves. The recording medium 105 is conveyed by the transfer roller 106 in the sub-scanning direction in the coordinate axis Y direction. In the standby state when the recording operation is not performed, the discharge port of the recording head 101 is capped by the cap 108. The position where the discharge port of the recording head 101 is capped by the cap 108 is the standby position of the recording head 101.

The carriage 104 reciprocates along the X direction together with the recording head 101. Specifically, the carriage 104 is movably supported along a guide shaft 107 arranged along the X direction and is fixed to an endless belt (not shown) that moves substantially parallel to the guide shaft 107. .. The endless belt reciprocates by the driving force of the carriage motor (CR motor), thereby reciprocating the carriage 104 in the X direction.

<Ink path>
FIG. 2 is a schematic view of the recording device 100 viewed from the + Y direction in FIG. FIG. 2 shows the path of ink for one color from the ink tank 103 arranged at a fixed position of the main body of the apparatus to the recording head 101.

The ink supply system 203 including the ink tank 103 has a hollow tube 204 and a buffer chamber 205, and is held and fixed at a predetermined position of the recording device 100 main body. The supply tube 102 is used as an ink flow path. The supply tube 102 is connected to the ink supply system 203 via an on-off valve 202 that can be opened and closed. The supply tube 102 is made of a flexible material, and can supply ink to the recording head 101 while reciprocating the carriage 104 in the X direction. The supply tube 102 can be connected to the recording head 101 at an arbitrary position of the recording head 101. Further, the supply tube 102 is arranged so as to have a section substantially parallel to the moving direction of the carriage 104. Details will be described later. The arrangement of the supply tubes 102 shown in FIGS. 1 and 2 is an example, and is not limited to this.

Next, a method of supplying ink from the ink tank 103 will be described. The ink tank 103 is detachably mounted on the recording device 100 main body. The ink tank 103 is connected to the supply tube 102 by a hollow tube 204. The supply tube 102 includes an on-off valve 202 that can open and close the flow path. The on-off valve 202 is configured to open when the power of the recording device 100 is turned on and to close when the power is turned off. That is, the on-off valve 202 is in the open state when the recording operation is being performed. The on-off valve 202 may be closed even after the power is turned on, and the on-off valve 202 may be opened when a recording command is input to the recording device 100. The ink tank 103 is connected by a thin tube 206 so as to communicate with the buffer chamber 205. The connection position between the ink tank 103 and the thin tube 206 is substantially below the ink tank 103, similar to the connection position between the ink tank 103 and the hollow tube 204. The buffer chamber 205 is connected by a thin tube 206 similar to the hollow tube 204 so as to communicate with the ink tank 103. While the buffer chamber 205 is connected to the ink tank 103, it is connected to the communication pipe 207 for opening to the atmosphere. As a result, the internal pressure of the ink tank 103 and the atmospheric pressure are balanced. The thin tube 206 that connects the buffer chamber 205 and the ink tank 103 has a structure in which the flow path is sufficiently narrow so as to communicate the ink tank 103 and the buffer chamber 205 and minimize the ink evaporation in the ink tank 103. Is made up of.

<Block diagram>
FIG. 3 is a block diagram showing an outline of a control configuration of the recording device 100 of the present embodiment. The CPU 301 reads the program that controls the system control stored in the ROM 302 into the RAM 312 and executes it, and controls the entire system according to the executed program. The RAM 312 is used as a work area for temporarily storing programs and input data required for processing executed by the CPU 301.

Further, the CPU 301 controls the operation of the cleaning unit 304, the transport unit 303, and the like. The transfer unit 303 controls the drive of the transfer roller 106. Further, the CPU 301 controls the recording operation of the recording head 101 through the drive circuit 307, the binarization circuit 308, and the image processing unit 309. The image processing unit 309 performs predetermined image processing on the input color image data to be recorded. The image processing unit 309 executes data conversion for mapping the color gamut reproduced by the input image data of each RGB color component into the color gamut reproduced by the recording device, for example. Based on the converted data, the image processing unit 309 performs processing to obtain CMYK component density data, which is color separation data corresponding to the combination of inks that reproduce the colors indicated by each data, and the color separation data decomposed into each color. Gradation conversion is performed for each of.

The binarization circuit 308 performs halftone processing or the like on the multi-value density image data converted by the image processing unit 309, and then converts it into binary data (bitmap data). The drive circuit 307 executes the ink ejection operation by the recording head 101 according to the binar data obtained by the binarization circuit 308 and the like. The CPU 301 controls the recording medium 105 to be conveyed by the transfer unit 303 in correspondence with the recording operation of the recording head 101, and the image is recorded on the recording medium 105.

<Recording head liquid chamber>
FIG. 4 is a diagram illustrating a liquid chamber in the recording head 101. FIG. 4A is a schematic cross-sectional view of the recording head 101 of the present embodiment. Each discharge port 401 is arranged in the depth direction of the paper surface. A heater 407 is arranged as an energy generating element in the pressure chamber 408 inside the recording head 101. Foaming occurs by applying pulsed electric power to the heater 407, and ink droplets are ejected from the ejection port 401.

The recording head 101 has two liquid chambers, a first liquid chamber 402 and a second liquid chamber 403, which sandwich the discharge port 401. The first liquid chamber 402 is a liquid chamber connected to the supply tube 102. The second liquid chamber 403 is a liquid chamber located on the opposite side of the first liquid chamber 402 with respect to the discharge port 401. The first flow path 404 is a flow path connecting each discharge port 401 and the first liquid chamber 402. The second flow path 405 is a flow path connecting each discharge port 401 and the second liquid chamber 403.

The second liquid chamber 403 includes a variable volume portion 406. The volume variable portion 406 is a member capable of changing the volume in the liquid chamber. In FIG. 4A, the variable volume portion 406 includes a bellows-shaped telescopic member 411 and a liquid chamber wall 410 to which the telescopic member 411 is joined and movable by the telescopic member 411. FIG. 4B is a diagram showing an example in which the configuration of the volume variable portion 406 is different from the example shown in FIG. 4A. In FIG. 4B, the variable volume portion 406 is a rubber-like telescopic member 412.

As shown in FIGS. 4A and 4B, the variable volume portion 406 uses a mechanism that expands and contracts in response to pressure or a flexible member. For example, when pressure is applied from the first liquid chamber 402 to the second liquid chamber 403, the volume variable portion 406 changes, and the volume of the second liquid chamber 403 is expanded. As a result, the ink that fluctuates due to the reciprocating scan can be temporarily stored in the second liquid chamber 403 without overflowing from the ejection port 401.

FIG. 5 is a cross-sectional perspective view of the recording head 101 as seen from the surface on which the discharge port 401 is formed. Each discharge port 401 is arranged in a row. The first flow path 404 and the second flow path 405 are arranged for each discharge port 401. The first liquid chamber 402 and the second liquid chamber 403 extend along the discharge port row. That is, the ink in the first liquid chamber 402 can pass through the first flow path 404, pass through each discharge port 401, and then pass through the second flow path 405 and join in the second liquid chamber 403. The recording head 101 has inks of a plurality of colors, and a plurality of rows of ejection ports 401 are arranged.

<Explanation of inertial force due to movement of carriage>
FIG. 6 is a diagram illustrating an inertial force associated with the movement of the carriage 104. The recording head 101 connected to the ink tank 103 by the supply tube 102 is integrated with the carriage 104 and reciprocates left and right in the X-axis direction of FIG. 1, which is the main scanning direction. That is, in FIG. 6, the carriage 104 reciprocates left and right. The reciprocating motion of the carriage 104 may be performed during the recording operation or may be performed when the recording operation is not performed.

FIG. 6A is a schematic diagram of the arrangement of the supply tube 102 when the carriage 104 moves to the left end side in the main scanning direction. The left end side is the side in the + X direction in FIGS. 1 and 6 (a), and is the left end side in the paper surface of FIG. 6 (a). When the carriage 104 accelerates / decelerates on the left end side in the main scanning direction, an inertial force is generated in the ink in the supply tube 102. Specifically, as shown in FIG. 6A, the ink in the region R1 (the region that moves with the movement of the carriage 104) in the supply tube 102 is inertial in the direction toward the left side of FIG. 6A. Force is generated. The inertial force acting on the region R1 in the supply tube 102 is generated in the direction from the recording head 101 to the ink tank 103 when viewed from the entire flow path. As described above, the on-off valve 202 is in an open state, and the ink tank 103 communicating with the supply tube 102 is open to the atmosphere. Therefore, when the inertial force is generated as shown in FIG. 6 (a), the ink flows in the direction from the second liquid chamber 403 to the first liquid chamber 402 as shown in FIG. 6 (b).

FIG. 6 (c) is a schematic view of the arrangement of the supply tube 102 when the carriage 104 moves to the right end side in the main scanning direction. The right end side is the side in the −X direction in FIGS. 1 and 6 (c), and is the right end side on the paper surface of FIG. 6 (c). When the carriage 104 accelerates / decelerates on the right end side in the main scanning direction, an inertial force is generated in the ink in the supply tube 102. Specifically, as shown in FIG. 6 (c), the ink in the region R2 (the region that moves with the movement of the carriage 104) in the supply tube 102 is inertial in the direction toward the right side of FIG. 6 (c). Force is generated. The inertial force acting on the region R2 in the supply tube 102 is generated in the direction from the ink tank 103 to the recording head 101 when viewed from the entire flow path. That is, pressure due to inertial force is applied in the direction from the first liquid chamber 402 to the second liquid chamber 403 in the recording head 101. In the present embodiment, as shown in FIG. 6D, the volume variable portion 406 expands the volume of the second liquid chamber 403 and can accommodate the ink that has flowed by pressurization. Therefore, the ink does not leak from the discharge port 401 due to the pressurization, but flows from the first liquid chamber 402 to the second liquid chamber 403.

As described with reference to FIGS. 6 (a) to 6 (d), the carriage 104 performs acceleration / deceleration scanning at the left and right ends, so that the ink reciprocates in the vicinity of the ejection port 401. That is, it is possible to move the ink in the vicinity of the ejection port 401 without using a circulation pump or the like.

In addition, in FIGS. 6A to 6D, an example in which the supply tube 102 is crawled into a substantially J-shape connected so as to lie down the J-shape has been described. Further, an example has been described in which the crawling direction of the supply tube 102 does not change depending on whether the carriage is moved to the left end side or the right end side. Further, FIG. 6 shows an example in which the supply tube 102 is connected to the first liquid chamber 402 so as to wrap around from the left side of the figure in the vicinity of the connection portion between the first liquid chamber 402 and the supply tube 102. There is. Here, the inertial force acts on the ink in the supply tube 102 (R1 shown in FIG. 6A or R2 shown in FIG. 6C) that moves with the movement of the carriage 104. Therefore, if the crawling direction of the entire supply tube 102 does not change when the carriage is moved, the ink is the same regardless of which direction the supply tube 102 is connected to the first liquid chamber 402 near the connection portion. It will move in the direction.

<Explanation of ink movement>
Next, a phenomenon caused by the movement of ink near the ejection port 401 will be described. As described above, the evaporation component of the ink evaporates at the meniscus, which is the interface between the ink of the ejection port 401 and the outside air. The higher the temperature of the ink, the more the evaporation component of the ink is likely to evaporate. Further, the evaporation component of the ink is more likely to evaporate as the humidity of the outside air is lower. As described above, the characteristics of the ink in the vicinity of the ejection port 401 may change, the ejection accuracy may deteriorate, or the ejection port 401 may be clogged to cause ejection defects.

In order to recover the ejection port 401 in which the ink having changed characteristics is retained, it is required to replace the ink retained in the ejection port 401 with the ink having no changed characteristics. Ink with changed characteristics has a high viscosity and density, the ejection speed is slower than that of normal ink ejection, and the landing position on the recording medium deviates from the desired landing position, which causes deterioration of the image quality of the recorded image. Become. Further, changes in the volume of the ejected ink and high recording densities also cause deterioration in the image quality of the recorded image. Therefore, in order to maintain the desired ink ejection, it is required to move the ink whose characteristics have changed due to evaporation at the meniscus in the vicinity of the ejection port 401 from the vicinity of the ejection port 401 (at least the meniscus portion).

In the present embodiment, as described above, the ink in the vicinity of the ejection port 401 moves with the reciprocating movement of the carriage 104, so that the ink thickened in the vicinity of the ejection port 401 does not thicken. It will be alleviated by mixing with.

FIG. 7 shows the change in the ejection speed with respect to the length of the non-ejection time during the recording operation. In FIG. 7, the ejection speeds were actually measured in the case where the flow due to the inertial force was generated in the vicinity of the ejection port 401 at regular intervals (ink moving state) and in the case where no flow was generated (ink stationary state). It is the figure which showed the result. The measurement is performed by using a discharge observation jig capable of applying an arbitrary drive pulse and continuously discharging at a constant frequency with the recording head 101 fixed. The ejected droplets are photographed with strobes with different emission delays, and the difference in the positions of the droplets is converted into the velocity. When there is no ink flow in the vicinity of the ejection port 401, the ink in the vicinity of the ejection port 401 evaporates when the non-ejection time becomes long, so that the ejection speed suddenly slows down. It becomes a state (see the dotted line in FIG. 7). On the other hand, in the recording device 100, when the ink reciprocates in the vicinity of the ejection port 401 due to the reciprocating scanning of the carriage 104, the progress of evaporation of the ink staying in the vicinity of the ejection port 401 is suppressed. Therefore, it is possible to maintain a normal discharge state without a decrease in the discharge speed (see the solid line in FIG. 7).

As described above, in the present embodiment, when the carriage 104 performs acceleration / deceleration scanning at the left and right ends, the ink flows in the vicinity of the ejection port 401, so that the change in the ink characteristics can be suppressed. By utilizing the reciprocating movement of the carriage 104, which is a characteristic of the serial type, it is possible to move the ink in the vicinity of the ejection port 401 without using a circulation pump or the like. Further, by moving the ink in the vicinity of the ejection port 401, it is possible to suppress the change in the characteristics of the ink. Hereinafter, using the pressure fluctuation in the tube due to the reciprocating movement (reciprocating scanning) of the carriage 104 to circulate the ink in the vicinity of the ejection port and suppress the ejection failure is referred to as a self-circulation method.

The recording device 100 described in this embodiment can be applied to any serial recording device. In the case of a recording device that records a large-sized recorded object such as large-format printing, the time required for reciprocating motion becomes long, so that the characteristics of the ink in the vicinity of the ejection port 401 that is not used for ejection are likely to change. Therefore, it is more effective to use the self-circulation method for a large recording device.

When the self-circulation method is used, when the thickening ink near the ejection port continues to be diffused into the circulation flow path in the recording head by the reciprocating scanning of the carriage 104, the concentration (viscosity) of the ink in the circulation flow path gradually increases. It gets higher. Therefore, in the present embodiment, an example of suppressing an increase in the ink density in the recording head by performing the preliminary ejection process at an appropriate timing in accordance with the self-circulation method will be described. Preliminary ejection generally includes a first method in which the recording head is temporarily stopped at a predetermined position to eject a predetermined amount of ink, and as described above, the recording head is moved outside the recording medium without stopping. There is a second method in which preliminary ejection is performed at a predetermined position. In this embodiment, an example of performing preliminary discharge in this second method will be described.

<Characteristics of changes in ink concentration near the ejection port>
Next, the characteristics of the ink concentration change in the vicinity of the ejection port 401 will be described with reference to FIGS. 8 and 9. FIG. 8 is a diagram showing a cross section in the vicinity of the ejection port 401, and is a conceptual diagram illustrating a change in ink concentration in the vicinity of the ejection port 401 in the present embodiment. 8 (a) to 8 (e) show the recording head 101 from 0.1 seconds to 1. The progress of ink concentration up to 0 seconds is intermittently shown. FIG. 8A shows a state at a time when 0.1 seconds have elapsed after the preliminary discharge operation, and shows a state in which the time axis elapses from FIG. 8B to FIG. 8E. ing. The components constituting the ink in the present embodiment include a coloring material component, a solvent component, an ejection assisting agent component, and moisture. In FIG. 8, among them, the color material concentration of the color material component in the ink is shown as a representative. The ink viscosity that leads to ejection failure shall be approximately proportional to the distribution of the ink colorant density. In FIG. 8, the white portion represents the color material density of 1.0 times, and the black portion represents the color material density of 1.5 times.

First, the water in the ink evaporates from the meniscus interface of the ejection port 401, and the ink flows from the first flow path 404 and the second flow path 405 accordingly. As a result, when a concentration gradient is generated in the coloring material and the solvent in the flow path, a diffusion phenomenon occurs so as to cancel the concentration gradient. By this evaporation, advection, and diffusion, a color material concentration gradient in the ink is formed.

By the way, looking at the cross-sectional view after 0.1 seconds shown in FIG. 8A, although the colorant concentration on the surface of the discharge port 401 rapidly increases, the first flow path 404 and the second flow path It can be seen that it has not spread by 405. On the other hand, looking at the cross-sectional view after 1.0 second shown in FIG. 8 (e), the increase in the colorant concentration of the discharge port 401 has slowed down, and conversely, the first flow path 404 and the second flow path 405 have slowed down. The phenomenon of diffusion to is becoming dominant. This is because the amount of water contained in the meniscus of the discharge port 401 decreases due to evaporation, and the evaporation rate decreases.

FIG. 8 (f) shows a cross section of the vicinity of the ejection port 401 immediately after the operation of moving the ink in the vicinity of the ejection port 401 in response to the reciprocating scanning of the recording head 101 (carriage 104) as described in the present embodiment. Is shown. As described above, as a result of the dynamic pressure fluctuation of the supply tube 102 occurring in the acceleration / deceleration region due to the reciprocating movement of the recording head 101, the volume variable portion 406 of the recording head is deformed, and the ink in the vicinity of the ejection port 401 Movement and diffusion are occurring. At this time, the ink moving speed instantly reaches 10 mm / sec to 20 mm / sec, and the circulation flow path near the discharge port 401 except for the vicinity of the surface end of the discharge port 401, which is a stagnation portion of the circulation flow path. The colorant concentration and the solvent concentration are almost constant.

FIG. 9 is a diagram for quantifying and explaining the change in ink concentration in FIG. FIG. 9A is a view showing a cross section in the vicinity of the discharge port 401, similarly to FIG. For the sake of explanation below, as shown in FIG. 9A, the positions in the flow path from the discharge port 401 to the first flow path 404 are referred to as positions Z1 to Z10. The position Z1 is the position Z1 on the surface of the meniscus. The higher the number, the farther away from the meniscus interface. Since the structure near the discharge port 401 is symmetrical, only one side will be described for simplification.

9 (b) is a graph showing the changes in ink concentration in FIGS. 8 (a) to 8 (f). The horizontal axis of FIG. 9B is a depth direction (Z direction) position in the discharge port, and indicates positions Z1 to Z10. On the vertical axis, the initial color material concentration such as immediately after the preliminary discharge operation is ρ0, and the color material concentration at positions Z1 to Z10 when the non-discharge time has elapsed by t [seconds] is ρ [t], and the color material concentration ratio is set. It is a plot of ρ [t] / ρ0. For example, the color material concentration ratio ρ [t] / ρ0 for 0.1 seconds shown in FIG. 8A is 1 at positions Z2 to Z10 deeper than the position Z1. According to the graph shown in FIG. 9B, it can be seen that the colorant density is highest on the nozzle surface (that is, position Z1) and decays exponentially in the Z direction. The solvent concentration and viscosity distribution show the same tendency.

The positions Z1 to Z10 in the ejection port substantially match the ejection amount of one drop of ink. That is, in 0.1 seconds corresponding to the time when the thickening ink is generated at the position Z1 (the time when the colorant density ratio exceeds 1), if one drop (also referred to as one shot) of the ink liquid is ejected, the thickening of the ink is achieved. It will be resolved. That is, since the thickening ink is discharged to the outside by the preliminary ejection, the thickening of the ink is eliminated. Similarly, in 0.3 seconds, which corresponds to the time when the thickening ink is generated at the position Z2, the thickening of the ink is canceled by two ink droplets. Similarly, if 5 ink droplets are ejected at position Z5 (0.3 seconds), 7 ink droplets are ejected at position Z7 (0.7 seconds), and 10 ink droplets are ejected at position Z10 (1.0 seconds). The thickening of the ink is eliminated.

<Flow chart of preliminary discharge sequence>
FIG. 10 is a flowchart illustrating a preliminary discharge sequence according to the present embodiment. The control process shown in FIG. 10 is realized by the CPU 301 executing a program stored in the ROM 302 of the recording device 100. The process shown in FIG. 10 is executed when the CPU 301 receives a record command. Alternatively, it may be executed by a controller (not shown) that controls the recording head 101. The process of FIG. 10 is shown by extracting the process related to the preliminary discharge sequence, and the description of the record control process is omitted. The symbol "S" in the description of each process in FIG. 10 means a step in the flowchart.

In S1001, the recording device 100 determines whether it is the preliminary discharge execution timing. In the present embodiment, the state of “after recording” for one scan and “before deceleration” of the carriage 104 is determined as the preliminary discharge execution timing. One scan corresponds to one-way scanning when recording is performed in both directions when the carriage 104 reciprocates.

As described above, in the self-circulation method, a circulating flow is generated in the vicinity of the discharge port 401 by acceleration / deceleration due to the fluctuation of the carriage speed. In other words, during recording and scanning at a constant speed, no circulating flow is generated, and the ink density is increased at the ejection port 401 that is not used for recording. Therefore, in the present embodiment, preliminary ejection is performed after the completion of the recording scan and at the timing "before deceleration" of the carriage 104, that is, in a state where a strong gradient of ink density is generated in the vicinity of the ejection port. .. Then, as described with reference to FIG. 8, the ink is ejected in order from the portion near the surface of the ejection port 401, which has a particularly high ink density. On the other hand, when a circulating flow is generated in the vicinity of the ejection port 401 due to the acceleration due to the fluctuation of the carriage speed, the ink having an increased density is diffused in the recording head 101. For this reason, preliminary ejection is performed at the timing before deceleration of the carriage 104, concentrated ink is ejected, and then a circulating flow is generated near the ejection port by a self-circulation method to generate ink in the vicinity of the ejection port and in the recording head. It is possible to suppress an increase in the concentration of ink. Further, the number of preliminary discharges (preliminary discharge amount) at this time can be smaller than that in the case where the self-circulation method is not used.

If it is determined in S1001 that the pre-discharge execution timing (after the completion of the recording scan and before the "deceleration" of the carriage 104) is determined, the process proceeds to S1002, and if not, the process proceeds to S1006.

In S1002, the recording device 100 determines whether the elapsed time from the previous preliminary discharge execution is equal to or longer than the threshold value. Even if it is determined in S1001 that the timing of the processing of S1002 is suitable for performing preliminary ejection, if the time elapsed from the previous preliminary ejection is short, for example, because the image width is short, the preliminary ejection is performed. This is because discharge may not be necessary. Any value can be set as appropriate for the threshold value, but as an example, it is set to 0.5 seconds. If it is determined in S1002 that the elapsed time from the previous preliminary discharge execution is equal to or longer than the threshold value, the process proceeds to 1003, and if not, the process proceeds to S1006.

In S1003, the recording device 100 determines whether or not it is a preliminary ejection possible position. This is because there is a position where preliminary discharge cannot be performed as the main body device configuration. Further, depending on the device configuration, preliminary ejection may be possible on one end side of the carriage in the scanning direction, and preliminary ejection may not be possible on the other end side. In S1003, it is determined whether the position of the recording head 101 at the present time is a position where preliminary ejection is possible, and if it is a position where preliminary ejection is possible, the process proceeds to S1004, and if not, the process proceeds to S1006. If No is determined in S1003, the head position may be moved to the nearest spare discharge port as necessary.

In S1004, the recording device 100 determines the number of preliminary discharges. The recording device 100 is determined by using at least one of, for example, the elapsed time since the previous preliminary ejection, the environmental temperature, the environmental humidity, and the ink temperature of the recording head. Moreover, you may make a comprehensive decision using all of these. In this example, assuming that the number of ink shots required to discharge the concentrated ink generated at that time is 10 in the maximum non-ejection time of 1.0 second, the number of preliminary shots is determined to be 2. The number of shots is not limited to the above.

Next, in S1005, the recording device 100 performs preliminary ejection. That is, the preliminary discharge process is performed at the position determined by S1003 at the execution timing determined by S1001 and S1002 with the number of shots determined by S1004. After that, the process proceeds to S1006.

In S1006, the recording device 100 determines whether the recording is finished, and if the recording is finished, the process of this flowchart is finished, and if the recording is not finished, the process returns to S1001 and the process is repeated.

<Timing chart of this embodiment>
FIG. 11 is a timing chart to which the preliminary discharge control in the present embodiment is applied. 11 (a) to 11 (d) show the carriage speed, the carriage acceleration, the inertial force caused by the fluctuation of the tube dynamic pressure, and the ink circulation speed in the nozzle, respectively. Since the X direction in FIG. 1 is positive, a negative sign can be taken. FIG. 11 shows an example in which the preliminary discharge is executed at the timing “before deceleration” of the carriage, which is determined by the preliminary discharge sequence described with reference to FIG. As described above, the recording operation is performed when the speed is constant. The preliminary discharge is performed after the recording operation and before the deceleration. As shown in FIGS. 11 (b) to 11 (d), since the preliminary discharge is performed before the deceleration, the preliminary discharge is performed before the circulation by the self-circulation method is performed.

<Timing chart of comparative example>
FIG. 12 is a timing chart showing a comparative example. FIG. 12 is also an example in which the self-circulation method is applied. However, this is an example in which the execution timing of the preliminary discharge operation is set to "after acceleration" and "before recording" of the carriage, not before deceleration of the carriage. That is, the execution timing of the preliminary discharge in S1001 of the preliminary discharge sequence described with reference to FIG. 10 is set to "after acceleration" and "before recording" of the carriage. Others are the same as the example described with reference to FIG. Generally, in an inkjet recording device, a preliminary ejection operation is performed while scanning "after acceleration" and "before recording" of this carriage. However, when this preliminary ejection timing is applied to the self-circulation method, the ejection efficiency of the concentrated ink deteriorates. The timing after the end of acceleration and the end of deceleration of the carriage is after the circulation flow is generated in the discharge port due to the inertial force. Therefore, as shown in FIG. 8 (f), the gradient of the ink density in the vicinity of the ejection port is almost lost and becomes uniform. Therefore, even if the preliminary ejection is performed at the timing shown in FIG. 12, the effect of ejecting the concentrated ink is low. Even when the preliminary ejection is performed during the acceleration operation or the deceleration operation, the degree of the ejection effect of the concentrated ink is the same as in FIG.

FIG. 13 is a conceptual diagram showing the effect of concentrated ink ejection depending on the execution timing of preliminary ejection. The graph of FIG. 13 is an excerpt from FIG. 9B showing the “ink density distribution with a concentration time of 1.0 second” as the condition of the present embodiment. This is because, for example, the time required for one scan is 1.0 second, and the preliminary discharge is executed because the discharge is not performed in the immediately preceding recording scan. Preliminary discharge is performed in 1.0 second. Therefore, as a condition of this embodiment, "ink density distribution with a concentration time of 1.0 second" is extracted and displayed. On the other hand, as a condition of the comparative example, "ink density distribution immediately after circulation" is extracted and displayed from FIG. 9B. This is because the condition of the above-mentioned comparative example is that the preliminary ejection is performed at the timing after the acceleration / deceleration of the carriage, so that the ink density distribution immediately after the circulation is followed.

The region 1301 of FIG. 13 shows the region of the concentrated ink discharged when two preliminary ejections are performed at the timing of performing the preliminary ejection of the present embodiment. The average ink density of the ejected ink is 1.25 times. On the other hand, in the comparative example, in the comparative example, in the comparative example, when the circulation flow is generated by the deceleration operation of the carriage after the elapsed time of 1.0 second, the concentrated ink in the vicinity of the nozzle is averaged, and then two preliminary ejections are performed. Shows the area of the concentrated ink discharged. The average ink density of the ejected ink is 1.11 times. That is, when the same self-circulation method is used to perform preliminary ejection for the same number of shots, it is possible to eject ink having a higher ink concentration by performing preliminary ejection at the timing of performing preliminary ejection in the present embodiment. can.

FIG. 14 is a diagram showing the passage of time of the average ink density of the entire ink supply system when the preliminary ejection operation according to the present embodiment and the preliminary ejection operation according to the comparative example are continued. Here, the ink supply system indicates a systematic route from the ink tank 103 to the recording head 101. The horizontal axis of FIG. 14 is the elapsed time, and the vertical axis is the average ink density of the entire ink supply system. If the number of preliminary discharges in the preliminary discharge operation according to the present embodiment and the preliminary discharge operation according to the comparative example are the same, the preliminary discharge of the present embodiment in which the preliminary discharge is performed before circulation is better. Efficient concentration ink discharge. Therefore, it is possible to suppress an increase in the ink density of the entire ink supply system. Further, when the goal is to suppress the increase curve of the ink density of the entire ink supply system to the same level, the preliminary ejection operation according to the present embodiment has a smaller number of preliminary ejections than the comparative example. The increase curve of ink density can be suppressed to the same level.

In addition, an example in which the preliminary discharge operation of the present embodiment is performed before the deceleration of the carriage as the timing before the circulation operation has been described. However, the timing may be any time before the circulation operation, and for example, the preliminary discharge operation before the acceleration of the carriage may be performed. As described above, the ejection efficiency of the concentrated ink is high by performing the preliminary ejection before deceleration, but even when the preliminary ejection is performed before the acceleration, the concentrated ink is compared with the preliminary ejection after the acceleration of the carriage. The emission efficiency of the ink can be increased.

The effect of reducing waste ink by performing preliminary ejection before such acceleration / deceleration operation is an effect peculiar to the self-circulation method described in the present embodiment. For example, when constant circulation is carried out using a power source such as a pump, the ink density gradient in the vicinity of the ejection port is basically almost constant. Therefore, even if the execution timing of the preliminary discharge is changed, it is difficult to obtain the effect as described above. Further, in the recording method of the general serial scan method, which is not the self-circulation method, the effect of nozzle circulation due to the fluctuation of dynamic pressure is almost nonexistent. Therefore, even if the execution timing of the preliminary discharge is changed, the effect as described above cannot be obtained.

That is, the effect of increasing the ejection efficiency of the concentrated ink is immediately before the circulation occurs in the supply system in which the circulation near the ejection port occurs at the local timing such as the dynamic pressure fluctuation, as in the self-circulation method. This is a peculiar effect when pre-discharge is carried out.

The deceleration operation of the carriage in this embodiment is not limited to the trapezoidal speed profile as shown in FIG. 11A. For example, a speed profile such as an upper triangle shape includes a deceleration operation that starts deceleration slowly. Further, the execution timing of the preliminary discharge does not have to be limited to before the carriage starts deceleration in a strict sense. For example, even after the carriage deceleration starts but before it is completely stopped, the self-circulation operation continues, and the effect of reducing waste ink exists. It can also be combined with preliminary discharge before or during the acceleration operation of the carriage, if necessary. For example, it may be possible to suppress the final amount of waste ink by setting the preliminary ejection timing to one shot immediately before acceleration and two shots immediately before deceleration. Further, the number of preliminary ejections and the preliminary ejection timing may be changed according to the ink type, head temperature, environmental temperature, environmental humidity, and the like. For example, the faster the evaporation rate, the higher the head temperature, the higher the environmental temperature, or the lower the environmental humidity, the higher the number of pre-discharges or the frequency of pre-discharges may be. Further, as a measure against ink concentration in the entire supply system, in addition to the preliminary ejection of the second method described in the present embodiment, the preliminary ejection of the first method described above may be performed on the cap. Further, it may be appropriately combined with a suction recovery operation or the like.

As described above, in the present embodiment, the preliminary discharge is performed before the circulation by the acceleration / deceleration operation of the carriage in the self-circulation method. Therefore, by moving the ink near the ejection port with a simple configuration, the thickening of the ink near the ejection port is suppressed while reducing the amount of waste ink, and the increase in the concentration of the ink in the circulation path is suppressed. can do.

<< Second Embodiment >>
In this embodiment, an example of changing the preliminary discharge timing and the number of shots according to the recording mode will be described. Since the basic configuration and the method of the self-circulation method in the recording device 100 of the present embodiment are the same as the examples described in the first embodiment, the description thereof will be omitted. Hereinafter, the description will be given focusing on the differences from the first embodiment.

FIG. 15 is a conceptual diagram showing the relationship between the preliminary discharge timing and the scanning width in the present embodiment. A recording head 101 fixed on a carriage 104 (not shown in FIG. 15) records on a recording medium 105, and scans back and forth while performing preliminary ejection on preliminary ejection ports 110 arranged at the left and right ends. The recording operation is being carried out.

FIG. 15A is an explanatory diagram in which preliminary ejection is performed during the acceleration operation of the carriage. FIG. 15B is an explanatory diagram in which preliminary ejection is performed before the deceleration operation of the carriage, as described in the first embodiment. As shown in FIGS. 15 (a) and 15 (b), the scanning width of the carriage in FIG. 15 (b) is larger than that in FIG. 15 (a). The reason for this is that, as described in the first embodiment, in order to carry out the preliminary discharge before circulation, the preliminary discharge is performed while passing through the preliminary discharge port 110 at a substantially constant speed. In other words, it is controlled so that the deceleration operation is started only after passing through the preliminary discharge port 110. As described in the first embodiment, the preliminary ejection before deceleration of the carriage requires a small number of shots, so that there is an advantage that waste ink can be reduced, but as shown in FIG. 15, the scanning width becomes large. .. Therefore, the entire recording time may become long. Therefore, it may not be suitable for a recording mode that requires high-speed recording.

Therefore, in the present embodiment, the preliminary discharge timing and the number of shots are changed according to the recording mode. FIG. 16 is a diagram illustrating the relationship between the recording mode, the preliminary discharge timing, and the number of preliminary discharge shots. As shown in FIG. 16, in the recording mode in which the image quality is prioritized and the short recording time is not required, the preliminary discharge timing is set to “before deceleration” and the number of preliminary discharge shots is suppressed to two. That is, the control as described in the first embodiment is performed.

On the other hand, in the recording mode in which the speed is prioritized and the recording time is required to be short, the preliminary discharge timing is set to "accelerating". As a result, the scanning width can be shortened as shown in FIG. 15 (a). As a result, the entire recording time can be shortened. However, as described in the first embodiment, in the self-circulation method, when the preliminary ejection is performed during acceleration, the efficiency of waste ink ejection is lowered. Therefore, as shown in FIG. 16, the number of preliminary discharges may be increased to about 10 as necessary. As shown in FIG. 16, the number of preliminary discharges in the mode in which the image quality is prioritized may be set to be equal to or larger than the number of preliminary ejections in the mode in which the recording time is prioritized. Although FIG. 16 shows “accelerating”, it may be “decelerating”. Further, as another method of discharging waste ink, the preliminary ejection of the first method may be collectively performed on the cap after the recording is completed, or a suction operation or the like may be used in combination as necessary.

As described above, according to the present embodiment, the preliminary discharge timing and the number of shots are changed according to the recording mode. As a result, in the case of the mode in which the recording speed is prioritized, the increase of the concentrated ink can be suppressed while the recording speed is maintained. In the mode in which the recording speed is not prioritized (or the mode in which the image quality is prioritized), the increase in the concentrated ink can be suppressed while suppressing the amount of waste ink.

<< Other Embodiments >>
In the first embodiment and the second embodiment described above, the example in which the recording head 101 and the ink tank 103 are connected by one tube has been described, but the recording head 101 and the ink tank 103 are connected by two tubes. May be connected. That is, the ink tank 103 and the recording head 101 are connected by the first tube and the second tube, the first tube is connected to the first liquid chamber 402 in the recording head 101, and the second tube is in the recording head 101. It may be configured to be connected to the second liquid chamber 403 of the above. By forming the first tube and the second tube in a symmetrical crawling configuration, as described in the first embodiment, an ink circulation flow is generated in response to the reciprocating movement of the carriage to generate an ink circulation flow in the vicinity of the ejection port. Ink can be moved. In addition, by changing the flow path resistance between the first tube and the second tube, the ink moves in one direction according to the reciprocating movement of the carriage, so that the ink is circulated between the ink tank and the recording head. Can be done.

Alternatively, one tube connected to the ink tank branches into two tubes in the middle, one of the two branched tubes is connected to the first liquid chamber 402, and the other is connected to the second liquid chamber 403. It may be configured to be connected to.

The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

101: Recording head 104: Carriage 401: Discharge port 404: First flow path 405: Second flow path

Claims (11)

A tank that holds ink and
A recording head that has a discharge port for ejecting ink and a pressure chamber filled with ink, and ejects ink while scanning reciprocatingly for recording.
A supply flow path for supplying ink from the tank to the recording head,
A control means for controlling the preliminary discharge from the recording head, and
It is a recording device equipped with
The recording head is
A first liquid chamber having a connection portion with the supply flow path and
A second liquid chamber communicating with the first liquid chamber via the pressure chamber,
A volume variable portion that changes the volume of the second liquid chamber,
Have,
The control means said that the control means is after the recording operation of one scan by the recording head is completed, and at the timing before the ink circulation in the recording head started due to the reciprocating scanning of the recording head. A recording device characterized by performing preliminary ejection. The first aspect of the present invention is characterized in that the control means performs the preliminary ejection after the recording operation of one scan by the recording head is completed and at the timing before the recording head decelerates. Recording device. The first aspect of the present invention is characterized in that the control means performs the preliminary ejection after the recording operation of one scan by the recording head is completed and at a timing before the recording head accelerates. Recording device. Claims 1 to 3 are characterized in that the number of shots of ink ejected by the preliminary ejection is determined based on at least one of the ink type, the temperature of the recording head, the environmental temperature, and the environmental humidity. The recording device according to any one of the above. The recording device according to any one of claims 1 to 4, wherein the control means changes the timing at which the preliminary discharge is performed according to the recording mode. When the recording mode is a mode in which image quality is prioritized or a mode in which recording speed is not prioritized, the control means is after the recording operation of one scan by the recording head is completed, and the ink circulation is performed. The recording device according to claim 5, wherein the preliminary discharge is performed at a timing before the start. The recording device according to claim 5 or 6, wherein the control means performs the preliminary discharge during acceleration of the recording head when the recording mode is a mode in which the recording speed is prioritized. The recording device according to any one of claims 1 to 7, wherein the control means changes the number of shots discharged by the preliminary discharge according to a recording mode. The control means is
When the recording mode is a mode in which image quality is prioritized or a mode in which recording speed is not prioritized, the number of shots discharged by the preliminary discharge is set as the first number of shots.
The eighth aspect of the present invention is characterized in that, when the recording mode is a mode in which the recording speed is prioritized, the number of shots discharged by the preliminary discharge is set to a second number of shots equal to or higher than the first number of shots. The recording device described. The recording device according to any one of claims 1 to 9, wherein the control means performs the preliminary discharge while causing the recording head to perform reciprocating scanning. A tank that holds ink and
A recording head that has a discharge port for ejecting ink and a pressure chamber filled with ink, and ejects ink while scanning reciprocatingly for recording.
A supply flow path for supplying ink from the tank to the recording head,
A control means for controlling the preliminary discharge from the recording head, and
Equipped with
The recording head is
A first liquid chamber having a connection portion with the supply flow path and
A second liquid chamber communicating with the first liquid chamber via the pressure chamber,
A volume variable portion that changes the volume of the second liquid chamber,
It is a control method of a recording device having
The preliminary ejection is performed after the recording operation of one scan by the recording head is completed and at the timing before the circulation of ink in the recording head started due to the reciprocating scanning of the recording head. A method for controlling a recording device, which comprises a process.

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