Printing device and printing method

Abstract

To stably discharge ink by suppressing the variation in the output of a circulation pump 93 in the printing start.SOLUTION: An idle operation is executed before a time t1. Over the time before and after the shift to a printing start operation from the idle operation, while continuing supply of ink to a recovery sub-tank 92 from a main tank 95, the supply amount of the ink is increased with the lapse of the time to support the start of ink discharge from a discharge head H. Namely, ink supply to the recovery sub-tank 92 by a supply pump 962 is already executed before the printing start, and the ink supply amount is increased to support the start of ink discharge.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a printing technique for printing an image on a printing medium by ejecting ink from nozzles of an ejection head. [Background technology]

[0002] Patent Document 1 describes a printing device that includes a supply subtank that stores ink to be supplied to the ejection head and a recovery subtank that stores ink recovered from the ejection head, and that circulates the ink through a circulation path that returns the ink recovered from the supply subtank to the recovery subtank via the ejection head. This printing device sends ink from the supply subtank to the recovery subtank via the ejection head by generating a negative pressure difference between the supply subtank and the recovery subtank. Furthermore, a circulation pump provided between the recovery subtank and the supply subtank returns ink from the recovery subtank to the supply subtank. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-44823 Summary of the Invention [Problem to be solved by the invention]

[0004] In such a printing device, when ink is ejected from the ejection head upon the start of image printing, the amount of ink circulating in the circulation path decreases. This decrease in ink can be addressed by starting the supply of ink from a buffer tank connected to the collection sub-tank or the supply sub-tank. However, the effects of starting the ink supply from the buffer tank, in addition to the effects of starting the ink ejection from the ejection head, can cause large fluctuations in the output of the circulation pump, which can make the ink ejection unstable at the start of printing.

[0005] SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems, and has as its object to suppress fluctuations in the output of the circulation pump at the start of printing, thereby enabling stable ink ejection. [Means for solving the problem]

[0006] A printing device according to the present invention includes a discharge head having nozzles for discharging ink, a supply sub-tank for storing ink to be supplied to the discharge head, a recovery sub-tank for storing ink recovered from the discharge head, a supply pipe connecting the supply sub-tank to the discharge head through a flow path and for sending the ink supplied from the supply sub-tank to the discharge head, a recovery pipe connecting the discharge head to the flow path and for sending the ink recovered from the discharge head to the recovery sub-tank, a return pipe connecting the flow path between the recovery sub-tank and the supply sub-tank through a flow path and for sending the ink stored in the recovery sub-tank to the supply sub-tank, and a pipe provided on the return pipe for sending ink from the recovery sub-tank to the supply sub-tank, thereby returning the ink recovered in the recovery sub-tank from the supply sub-tank via the discharge head to the supply sub-tank. the inkjet recording head includes a circulation pump, a buffer tank for storing ink, a recovery pump provided in a pipe connecting the supply sub-tank and the buffer tank through a flow path and sending ink from the supply sub-tank to the buffer tank, a supply pump provided in a pipe connecting the buffer tank and the recovery sub-tank through a flow path and sending ink from the buffer tank to the recovery sub-tank, and a control unit that performs image printing by ejecting ink from nozzles of an ejection head onto the printing medium, and the control unit controls the recovery pump and the supply pump to perform idle operation before the start of image printing so that the supply pump supplies ink from the buffer tank to the recovery sub-tank at an idle supply amount, and the recovery pump recovers ink from the supply sub-tank to the buffer tank at an idle recovery amount, In response to the start of image printing, the recovery pump and the supply pump are controlled so that the amount of ink that the supply pump supplies from the buffer tank to the recovery sub-tank is increased over time from the idle supply amount, and the amount of ink that the recovery pump recovers from the supply sub-tank to the buffer tank is reduced over time from the idle recovery amount, thereby executing a print start operation.

[0007] The printing method of the present invention is a printing method for printing an image on a printing medium by ejecting ink from nozzles of an ejection head onto the printing medium, and includes a step of performing an idle operation before the start of image printing while performing ink circulation in which ink recovered from a supply subtank via the ejection head to a recovery subtank is returned to the supply subtank by a circulation pump, and a step of performing a print start operation in response to the start of image printing while performing ink circulation, wherein in the idle operation, ink is supplied to the recovery subtank at an idle supply amount by a supply pump that sends ink from a buffer tank to the recovery subtank, and ink is recovered to the buffer tank at an idle recovery amount by a recovery pump that sends ink from the supply subtank to the buffer tank, and in the print start operation, the amount of ink supplied to the recovery subtank by the supply pump is increased over time from the idle supply amount, and the amount of ink recovered by the recovery pump from the supply subtank is decreased over time from the idle recovery amount.

[0008] According to the present invention (printing apparatus and printing method) configured as described above, an idle operation is performed before image printing begins, and a print start operation is performed in response to the start of image printing. During the idle operation, the supply pump supplies ink to the recovery subtank at an idle supply rate, while the recovery pump recovers ink to the buffer tank at an idle recovery rate. In other words, the idle operation allows ink to be supplied from the buffer tank to the recovery subtank even before image printing begins. During this operation, the ink supplied to the recovery subtank returns to the buffer tank via the supply subtank, preventing excessive ink from being stored in the recovery subtank and supply subtank. Furthermore, during the print start operation, the supply pump increases the amount of ink supplied to the recovery subtank from the idle supply rate over time, while decreasing the amount of ink recovered from the supply subtank from the idle recovery rate over time. This allows ink to continue being supplied from the buffer tank to the recovery subtank over time, both before and after the transition from the idle operation to the print start operation, and this ink supply rate increases over time to accommodate the start of ink ejection from the ejection head. In other words, in this invention, the supply pump supplies ink to the recovery subtank before printing starts, and the ink supply amount is increased when ink ejection starts, thereby suppressing fluctuations in the output of the circulation pump at the start of printing and enabling stable ink ejection.

[0009] The printing device may also be configured so that the increase in the amount of ink supplied from the buffer tank to the recovery sub-tank by the supply pump at the start of printing is greater than the decrease in the amount of ink recovered by the recovery pump from the supply sub-tank to the buffer tank. With this configuration, fluctuations in the output of the circulation pump at the start of printing can be suppressed, and the amount of ink required for printing an image can be reliably supplied to the recovery sub-tank.

[0010] The printing device may also be configured such that the control unit controls the recovery pump so that the amount of ink recovered by the recovery pump from the supply sub-tank to the buffer tank is reduced to zero during the print start operation. This configuration contributes to ensuring that the amount of ink required for image printing is supplied to the recovery sub-tank.

[0011] The printing device may also be configured so that the circulation pump sends an amount of ink from the recovery subtank to the supply subtank via the return pipe during idle operation and print start operation, the amount of ink corresponding to the difference between the amount of ink stored in the supply subtank and the amount of ink stored in the recovery subtank. With this configuration, the amounts of ink stored in the supply subtank and the recovery subtank can be appropriately managed throughout idle operation and print start operation.

[0012] The present invention is particularly suitable for printing devices whose ejection heads eject white ink. This means that white ink tends to be used in large quantities when printing an image. Therefore, when printing an image, a large amount of ink needs to be supplied from the buffer tank to the collection subtank, which can significantly affect the output fluctuations of the circulation pump. By applying the present invention, it is possible to suppress the output fluctuations of the circulation pump at the start of printing and stably eject white ink. [Effects of the Invention]

[0013] As described above, according to the present invention, it is possible to suppress fluctuations in the output of the circulation pump at the start of printing, and to eject ink stably. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a front view schematically showing a printing system equipped with an example of a printing device according to the present invention. [Figure 2] FIG. 2 is a diagram schematically illustrating the configuration of a discharge head and an ink supply mechanism that supplies ink to the discharge head. [Figure 3]FIG. 2 is a block diagram showing the electrical configuration of the printing apparatus. [Figure 4] 6 is a timing chart showing the time variation of the flow rates of a circulation pump, a recovery pump, and a supply pump based on ink supply control. [Figure 5] FIG. 4 is a table showing circulation modes executed in ink supply control. [Figure 6A] 10 is a flowchart showing an example of an execution sequence of a circulation mode in a modified example of ink supply control. [Figure 6B] 10 is a flowchart showing an example of an execution sequence of a circulation mode in a modified example of ink supply control. [Figure 6C] 10 is a flowchart showing an example of an execution sequence of a circulation mode in a modified example of ink supply control. DETAILED DESCRIPTION OF THE INVENTION

[0015] Fig. 1 is a front view showing a schematic diagram of a printing system equipped with an example of a printing device according to the present invention. In Fig. 1, in order to clarify the positional relationship of each part of the device, an XYZ coordinate system is shown, in which the horizontal direction in which the coating device 2, printing device 3, and drying device 4 constituting the printing system 1 are arranged is defined as the X direction, the horizontal direction perpendicular to the X direction is defined as the Y direction, and the vertical direction is defined as the Z direction.

[0016] This printing system 1 applies coating, printing, and drying processes to a long strip of printing medium M while transporting the printing medium M roll-to-roll from a payout roll 11 to a take-up roll 12. That is, a coating device 2 applies a coating liquid to the printing medium M. Then, a printing device 3 applies ink of each color to the printing medium M using an inkjet method to print an image. Furthermore, a drying device 4 dries the ink that has adhered to the printing medium M. The printing medium M is made of a film such as OPP (oriented polypropylene) or PET (polyethylene terephthalate). However, the material of the printing medium M is not limited to film and may be paper or the like. Such a printing medium M is flexible. In the following, the recording surface on which an image is printed of both sides of the printing medium M will be referred to as the front surface M1, and the surface opposite the front surface M1 will be referred to as the back surface M2.

[0017] The coating device 2 has a pan 21 that stores a liquid primer (coating liquid), a gravure roller 22 that is partially immersed in the primer stored in the pan 21, and a conveying unit 23 that conveys the print medium M. The coating device 2 has a coating area where the gravure roller 22 contacts the print medium M conveyed by the conveying unit 23 from below, and the conveying unit 23 conveys the print medium M along the coating area while facing the surface M1 of the print medium M downward. Meanwhile, the gravure roller 22 supplies the primer to the coating area by rotating while holding the primer on its circumferential surface. In this way, the primer supplied by the gravure roller 22 is applied to the surface M1 of the print medium M in the coating area. Furthermore, in the coating area, the traveling direction of the print medium M and the rotation direction of the circumferential surface of the gravure roller 22 are opposite. In other words, the primer is applied to the print medium M using a so-called reverse kiss method. Then, the transport unit 23 transports the printing medium M from the coating device 2 to the printing device 3 while facing the surface M1 of the printing medium M coated with the primer upward.

[0018] The printing device 3 comprises a housing 31, a color printing unit 32 arranged within the housing 31, a white printing unit 33 arranged above the color printing unit 32 within the housing 31, and a transport unit 34 that transports the printing medium M using multiple rollers arranged within the housing 31.

[0019] The color printing unit 32 has a plurality of (four) head units 321 arranged in the direction of travel of the printing medium M above the printing medium M transported by the transport unit 34. Each head unit 321 has a plurality of ejection heads, and ejects different color inks from nozzles of the ejection heads facing from above onto the surface M1 of the printing medium M passing below it using an inkjet method. An ink supply mechanism is also provided that supplies color ink to the ejection heads of the head unit 321 for each color. That is, a color image is printed on the surface M1 of the printing medium M by the color inks ejected from the nozzles of the ejection heads while the ink supply mechanism supplies the color inks to the ejection heads of the head unit 321. Here, color ink means inks other than white, and includes inks such as cyan, magenta, yellow, and black.

[0020] The white printing unit 33 also has a single head unit 331 arranged above the printing medium M transported by the transport unit 34. The head unit 331 has multiple ejection heads, and ejects white ink from nozzles of the ejection heads facing from above onto the surface M1 of the printing medium M passing below it using an inkjet method. An ink supply mechanism is also provided that supplies white ink to the ejection heads of the head unit 331. That is, while the ink supply mechanism supplies white ink to the ejection heads of the head unit 331, a white image is printed on the surface M1 of the printing medium M using the white ink ejected from the nozzles of the ejection heads. The configuration and operation of the ink supply mechanism will be described in detail later.

[0021] Although not shown in Figure 1, two types of drying units are provided inside the housing 31 of the printing device 3. One is a pre-drying unit that dries the color inks that have been applied to the surface M1 of the printing medium M by the color printing unit 32. The other is an upper drying unit that dries the white ink that has been applied to the surface M1 of the printing medium M by the white printing unit 33.

[0022] The drying device 4 dries the ink adhering to the surface M1 of the printing medium M transported from the printing device 3. The drying device 4 has a housing 41 (drying oven). In addition, rollers 42, 43, and 46 are arranged on one side in the X direction (left side in FIG. 1) of the housing 41, and air turn bars 44 and 45 are arranged on the other side in the X direction (right side in FIG. 1). This forms a roughly S-shaped transport path when viewed from the Y direction, and the printing medium M is transported along this transport path. During this transport, the ink adhering to the surface M1 of the printing medium M is dried. Then, the printing medium M that has been dried is transported out of the drying device 4 and taken up by the take-up roll 12.

[0023] 2 is a diagram schematically illustrating the configuration of a discharge head and an ink supply mechanism that supplies ink to the discharge head. This ink supply mechanism 9 is provided for each of the multiple head units 321 and the single head unit 331 described above, but here, only one ink supply mechanism 9 will be described. Each of the multiple head units 321 and the single head unit 331 is provided with multiple discharge heads H, and more specifically, the multiple discharge heads H are provided in parallel between a supply sub-tank 91 and a recovery sub-tank 92 provided in the ink supply mechanism 9. However, here, the description will be given while showing only one discharge head H.

[0024] As shown in FIG. 2, the ejection head H has a housing Ha, and multiple nozzles N are arranged and open at the bottom of the housing Ha. Inside the housing Ha, multiple cavities Hb are provided, each communicating with the multiple nozzles N, and an ink supply chamber Hc is provided, communicating with the multiple cavities Hb. Ink supplied from the ink supply chamber Hc is stored in the cavities Hb. A piezoelectric element provided in the cavity Hb pushes the ink out of the cavity Hb, causing the ink to be ejected from the nozzle N communicating with the cavity Hb. Note that the specific method for ejecting ink does not necessarily have to be a piezoelectric element-based method; a thermal method for heating the ink may also be used. An ink inlet Hd and an ink outlet He are provided at the top of the ejection head H. Ink flows from an ink supply mechanism 9 into the ink supply chamber Hc through the ink inlet Hd and then flows out of the ink supply chamber Hc to the ink supply mechanism 9 through the ink outlet He.

[0025] The ink supply mechanism 9 includes a supply subtank 91 connected to the ink inlet Hd via a supply pipe 91a, and a recovery subtank 92 connected to the ink outlet He via a recovery pipe 92a, and ink is stored in both the supply subtank 91 and the recovery subtank 92. The supply subtank 91 and the recovery subtank 92 are both located above the ejection head H. The ink supply mechanism 9 also includes a return pipe 93a that connects the recovery subtank 92 to the supply subtank 91, and a circulation pump 93 that is located midway along the return pipe 93a and sends ink from the recovery subtank 92 to the supply subtank 91. In other words, the circulation pump 93 can send ink along a first path Ca from the recovery subtank 92 through the return pipe 93a to the supply subtank 91. The ink supply mechanism 9 also includes a filter 931 disposed midway along the return pipe 93a between the circulation pump 93 and the supply sub-tank 91, and a degasser 932 disposed between the filter 931 and the supply sub-tank 91. The filter 931 removes solid matter from the ink flowing through the first path Ca, and the degasser 932 removes gas from the ink flowing through the first path Ca.

[0026] Furthermore, the ink supply mechanism 9 includes a supply-side pressure generating unit 941 (hereinafter referred to as the "pressure generating unit 941") that applies a negative pressure P1 to the supply subtank 91. The pressure generating unit 941 includes a pressure tank (not shown) and a pressure transmission pipe 941a. One end of the pressure tank is connected to the pressure tank, and the other end is disposed so as to face the atmosphere inside the supply subtank 91. The pressure generating unit 941 generates a negative pressure P1 inside the pressure tank by exhausting gas from the pressure tank, and applies the negative pressure P1 to the supply subtank 91 via the pressure transmission pipe 941a. Meanwhile, gas (air) accumulates above the ink surface in the supply subtank 91. That is, ink is stored below the gas-liquid interface in the supply subtank 91, and gas exists above the gas-liquid interface. Therefore, the pressure generating unit 941 applies a negative pressure P1 to the gas-liquid interface in the supply subtank 91.

[0027] The ink supply mechanism 9 also includes a recovery-side pressure generating unit 942 (hereinafter referred to as the "pressure generating unit 942") that applies a negative pressure P2 lower than the negative pressure P1 to the collection subtank 92. The pressure generating unit 942 includes a pressure tank (not shown) and a pressure transmission pipe 942a that is connected at one end to the pressure tank and at the other end to the atmosphere in the collection subtank 92 and transmits the pressure generated in the pressure tank to the collection subtank 92. The pressure generating unit 942 exhausts gas from the pressure tank to generate negative pressure P2 inside the pressure tank and applies it to the collection subtank 92 via the pressure transmission pipe 942a. Meanwhile, gas (air) accumulates above the ink surface in the collection subtank 92. That is, in the collection subtank 92, ink is stored below the gas-liquid interface and gas exists above the gas-liquid interface. Therefore, the pressure generating unit 942 applies a negative pressure P2 to the gas-liquid interface in the collection sub-tank 92.

[0028] Thus, the negative pressure P2 applied to the recovery subtank 92 is lower than the negative pressure P1 applied to the supply subtank 91. The difference between the negative pressures P2 and P1 causes ink to flow along a second path Cb from the supply subtank 91 through the supply pipe 91, via the ink supply chamber Hc of the ejection head H, and through the recovery pipe 92a to the recovery subtank 92. The ink that has flowed into the recovery subtank 92 along the second path Cb is returned to the supply subtank 91 by the circulation pump 93 along a first path Ca from the recovery subtank 92 through the return pipe 93a to the supply subtank 91. In this way, the ink circulates along a circulation path (second path Cb+first path Ca) that runs from the supply subtank 91 through the ejection head H to the recovery subtank 92 and then back to the supply subtank 91.

[0029] The ink supply mechanism 9 includes a main tank 95, which can store a larger amount of ink than the supply subtank 91 and the recovery subtank 92. The ink supply mechanism 9 also includes a pipe 951 that connects the main tank 95 and the supply subtank 91 through a flow path, and a pipe 952 that connects the main tank 95 and the recovery subtank 92 through a flow path. In other words, the main tank 95 communicates with the supply subtank 91 via the pipe 951, and with the recovery subtank 92 via the pipe 952.

[0030] Furthermore, the ink supply mechanism 9 includes a recovery pump 961 attached to the pipe 951 between the main tank 95 and the supply subtank 91 to recover ink from the supply subtank 91 to the main tank 95, and a supply pump 962 attached to the pipe 952 between the main tank 95 and the recovery subtank 92 to supply ink from the main tank 95 to the recovery tank 92. Therefore, the recovery pump 961 recovers ink from the supply subtank 91 to the main tank 95 via the pipe 951, and the supply pump 962 supplies ink from the main tank 95 to the recovery subtank 92 via the pipe 952.

[0031] The ink supply mechanism 9 also includes a valve 953 attached to the pipe 951 between the recovery pump 961 and the supply subtank 91, and a valve 954 attached to the pipe 952 between the supply pump 962 and the recovery subtank 92. Therefore, by opening the valve 953, the main tank 95 and the supply subtank 91 can be communicated with each other, while by closing the valve 953, the main tank 95 and the supply subtank 91 can be isolated from each other. Furthermore, by opening the valve 954, the main tank 95 and the recovery subtank 92 can be communicated with each other, while by closing the valve 954, the main tank 95 and the recovery subtank 92 can be isolated from each other.

[0032] In the ink supply mechanism 9 configured as described above, by operating the recovery pump 961 and the supply pump 962 with the valves 953 and 954 open, ink flows along a third path Cc from the supply subtank 91 through the piping 951, via the main tank 95, and through the piping 952 to the recovery subtank 92. Furthermore, the ink that has flowed into the recovery subtank 92 along the third path Cc is returned to the supply subtank 91 by the circulation pump 93 along the first path Ca. In this way, the ink circulates along a circulation path (third path Cc+first path Ca) from the supply subtank 91 through the piping 951, via the main tank 95, and through the piping 952 to reach the recovery subtank 92, and then back to the supply subtank 91 through the return piping 93a.

[0033] Furthermore, the ink supply mechanism 9 includes a liquid level sensor 971 provided in the supply subtank 91 and a liquid level sensor 972 provided in the recovery subtank 92. The liquid level sensor 971 detects the liquid level of ink stored in the supply subtank 91, and the liquid level sensor 972 detects the liquid level of ink stored in the recovery subtank 92. These liquid level sensors 971, 972 can be configured with various level switches, for example, float type, electrode type, or capacitance type.

[0034] 3 is a block diagram showing the electrical configuration of the printing device. As shown in FIG. 3, the printing device 3 includes a control unit 100 that controls the entire device, and a storage unit 110 that stores various data and programs. The control unit 100 may be implemented by a processor such as a CPU (Central Processing Unit) or an FPGA (Field-Programmable Gate Array). The storage unit 110 can be configured with a storage device such as a gate array (Gate Array). The storage unit 110 is configured with a hard disk drive (HDD) or a solid state drive (SSD), and stores image data Dp that indicates an image to be printed on the printing medium M. The control unit 100 then prints the image indicated by the image data Dp onto the printing medium M (image printing) by ejecting ink from the nozzles N of the ejection head H based on the image data Dp.

[0035] Furthermore, the control unit 100 controls the output of the circulation pump 93 based on the detection values ​​of the liquid level sensors 971 and 972. Specifically, the control unit 100 controls the output of the circulation pump 93 in accordance with the difference between the liquid level in the supply subtank 91 detected by the liquid level sensor 971 and the liquid level in the recovery subtank 92 detected by the liquid level sensor 972, thereby sending ink from the recovery subtank 92 to the supply subtank 91 via the return pipe 93a. This makes it possible to reduce the difference between the liquid level in the supply subtank 91 and the liquid level in the recovery subtank 92.

[0036] The control unit 100 also controls the flow rate of ink sent by the recovery pump 961 from the supply sub-tank 91 to the main tank 95 via the pipe 951 (i.e., the liquid feed rate of the recovery pump 961), and also controls the flow rate of ink sent by the supply pump 962 from the main tank 95 to the collection sub-tank 92 via the pipe 952 (i.e., the liquid feed rate of the supply pump 962). Here, the liquid feed rate is the amount of ink fed per unit time. Furthermore, the control unit 100 controls the negative pressure P1 applied to the supply sub-tank 91 by the pressure generation unit 941 and the negative pressure P2 applied to the collection sub-tank 92 by the pressure generation unit 942.

[0037] In the above configuration, the circulation pump 93 adjusts the amount of ink sent from the recovery subtank 92 to the supply subtank 91 in accordance with the difference between the liquid level in the supply subtank 91 and the liquid level in the recovery subtank 92. This reduces the difference in liquid level between the supply subtank 91 and the recovery subtank 92. However, because the first path Ca, through which the circulation pump 93 sends ink via the return pipe 93a, forms a circulation path together with the second path Cb via the ejection head H, fluctuations in the pressure (output) that the circulation pump 93 applies to the ink to send it are transmitted to the second path Cb of the ejection head H, which can affect the ejection of ink from the nozzles N. To address this issue, a third path Cc is provided to send ink from the supply subtank 91 to the main tank 95 via the pipe 951 and from the main tank 95 to the recovery subtank 92 via the pipe 952. This third path Cc forms a circulation path together with the first path Ca. This reduces output fluctuations from the circulation pump 93, allowing ink to be ejected smoothly from the nozzles N. In particular, in this embodiment, in order to suppress fluctuations in the output of the circulation pump 93 that accompany the start of image printing, the recovery pump 961 and the supply pump 962 are operated based on the following ink supply control.

[0038] FIG. 4 is a timing chart showing an example of temporal changes in the flow rates of the circulation pump, recovery pump, and supply pump based on ink supply control. In this timing chart, the horizontal axis represents time, and the vertical axis represents the flow rates of the circulation pump 93, recovery pump 961, and supply pump 962. In the figure, the dashed line represents the flow rate of the circulation pump 93, the dashed-dotted line represents the flow rate of the supply pump 962, and the dashed-two-dotted line represents the flow rate of the recovery pump 961. In the figure, the flow rates Fl, Fo, and Fh are all greater than zero, and the flow rate Fh is greater than the flow rates Fl and Fo. Note that the flow rate Fh is at least twice the flow rate Fl and at least twice the flow rate Fo. However, the ratio of the flow rate Fh to the flow rate Fl or the flow rate Fo is not limited to this example. The flow rates Fo and Fl are approximately equal, but the flow rate Fo is slightly greater than the flow rate Fl. The operation shown in this timing chart is executed by the control unit 100 controlling the circulation pump 93, recovery pump 961, and supply pump 962. In particular, the flow rate of the recovery pump 961 can be switched between at least two stages: zero and flow rate Fo (on flow rate), and the flow rate of the supply pump 962 can be switched between at least three stages: zero, flow rate Fl (low flow rate), and flow rate Fh (high flow rate).

[0039] Specifically, the operation of the timing chart shown in Fig. 4 is obtained as a result of executing the control of Fig. 5 and Figs. 6A to 6C. Here, Fig. 5 is a diagram showing, in table form, each circulation mode executed in ink supply control. Figs. 6A to 6C are flowcharts showing an example of the execution sequence of the circulation mode of Fig. 5, in particular Fig. 6A shows the flow before image printing starts, Fig. 6B shows the flow immediately after image printing starts, and Fig. 6C shows the flow during image printing.

[0040] 5, the liquid level sensor 972 detects the liquid level of the ink stored in the recovery subtank 92 in four levels: Low, Mid, High, and Ovf. Specifically, the liquid level sensor 972 outputs Low if the liquid level is below a threshold Tl, outputs Mid if the liquid level is equal to or greater than the threshold Tl but less than Tm which is higher than the threshold Tl, outputs High if the liquid level is equal to or greater than the threshold Tm but less than Th which is higher than the threshold Tm, and outputs Ovf if the liquid level is equal to or greater than the threshold Th. Similarly, the liquid level sensor 971 detects the liquid level of the ink stored in the supply subtank 91 in four levels: Low, Mid, High, and Ovf.

[0041] 5, in the "circulation pump 93" column, "maintain" indicates an operation to maintain the output of the circulation pump 93, "increase" indicates an operation to increase the output of the circulation pump 93 by a fixed value, "decrease" indicates an operation to decrease the output of the circulation pump 93 by a fixed value, and "zero" indicates an operation to set the output of the circulation pump 93 to zero. In the "supply pump 962" column, "On(Fh)" indicates an operation to set the flow rate of the supply pump 962 to flow rate Fh, "On(Fl)" indicates an operation to set the flow rate of the supply pump 962 to flow rate Fl, and "Off" indicates an operation to set the flow rate of the supply pump 962 to zero. In the "recovery pump 961" column, "On(Fo)" indicates an operation to set the flow rate of the recovery pump 961 to flow rate Fo, and "Off" indicates an operation to set the flow rate of the recovery pump 961 to zero.

[0042] As shown in Figure 5, when the liquid level in the recovery sub-tank 92 detected by the liquid level sensor 972 is low and the liquid level in the supply sub-tank 91 detected by the liquid level sensor 971 is low, the circulation pump 93 maintains the flow rate (i.e., does not change it), the supply pump 962 delivers liquid at a flow rate Fh, and the recovery pump 961 stops (circulation mode D1).

[0043] When the liquid level in the recovery sub-tank 92 detected by the liquid level sensor 972 is Mid and the liquid level in the supply sub-tank 91 detected by the liquid level sensor 971 is Low, the circulation pump 93 increases the flow rate, the supply pump 962 delivers liquid at a flow rate Fh, and the recovery pump 961 stops (circulation mode D2).

[0044] When the liquid level in the recovery sub-tank 92 detected by the liquid level sensor 972 is High and the liquid level in the supply sub-tank 91 detected by the liquid level sensor 971 is Low, the circulation pump 93 increases the flow rate, the supply pump 962 delivers liquid at a flow rate Fl, and the recovery pump 961 stops (circulation mode D3).

[0045] When the liquid level in the recovery sub-tank 92 detected by the liquid level sensor 972 is Low and the liquid level in the supply sub-tank 91 detected by the liquid level sensor 971 is Mid, the circulation pump 93 reduces the flow rate, the supply pump 962 delivers liquid at a flow rate Fh, and the recovery pump 961 stops (circulation mode D4).

[0046] When the liquid level in the recovery sub-tank 92 detected by the liquid level sensor 972 is Mid and the liquid level in the supply sub-tank 91 detected by the liquid level sensor 971 is Mid, the circulation pump 93 maintains the flow rate, the supply pump 962 delivers liquid at a flow rate Fl, and the recovery pump 961 delivers liquid at a flow rate Fo (circulation mode D5).

[0047] When the liquid level in the recovery sub-tank 92 detected by the liquid level sensor 972 is High and the liquid level in the supply sub-tank 91 detected by the liquid level sensor 971 is Mid, the circulation pump 93 increases the flow rate, the supply pump 962 delivers liquid at a flow rate Fl, and the recovery pump 961 delivers liquid at a flow rate Fo (circulation mode D6).

[0048] When the liquid level in the recovery sub-tank 92 detected by the liquid level sensor 972 is low and the liquid level in the supply sub-tank 91 detected by the liquid level sensor 971 is high, the circulation pump 93 reduces the flow rate, the supply pump 962 delivers liquid at a flow rate Fl, and the recovery pump 961 delivers liquid at a flow rate Fo (circulation mode D7).

[0049] When the liquid level in the recovery sub-tank 92 detected by the liquid level sensor 972 is Mid and the liquid level in the supply sub-tank 91 detected by the liquid level sensor 971 is High, the circulation pump 93 reduces the flow rate, the supply pump 962 delivers liquid at a flow rate Fl, and the recovery pump 961 delivers liquid at a flow rate Fo (circulation mode D8).

[0050] When the liquid level in the recovery sub-tank 92 detected by the liquid level sensor 972 is High and the liquid level in the supply sub-tank 91 detected by the liquid level sensor 971 is High, the circulation pump 93 reduces the flow rate, the supply pump 962 delivers liquid at a flow rate Fl, and the recovery pump 961 delivers liquid at a flow rate Fo (circulation mode D9).

[0051] When the liquid level in the supply sub-tank 91 detected by the liquid level sensor 971 is Ovf, the circulation pump 93, the supply pump 962, and the recovery pump 961 are all stopped (circulation mode D10).

[0052] When the liquid level in the recovery sub-tank 92 detected by the liquid level sensor 972 is Ovf, the circulation pump 93, the supply pump 962, and the recovery pump 961 are all stopped (circulation mode D11).

[0053] 4 is obtained as a result of mainly executing circulation modes D1 to D8 according to the liquid levels detected by the liquid level sensors 972 and 971. Note that circulation modes D9 to D11 are provided to deal with emergencies when there is an excess of ink in the collection sub-tank 92 or the supply sub-tank 91.

[0054] 4, preparations for printing an image are made during the period from time t0 to time t2, and image printing is performed during the period from after time t2 to time t8. That is, during the period from after time t2 to time t8, ink is ejected from the nozzles N of the ejection head H, but during the period before time t2 and the period after time t8, ink is not ejected from the nozzles N of the ejection head H. Furthermore, throughout the period shown in this timing chart, ink is sent through the second path Cb due to the difference between the negative pressures P1 and P2, and one of the circulation modes D1 to D8 is executed depending on the detection values ​​of the liquid level sensors 971 and 972.

[0055] The period before time t0 is an idle period during which the printer waits for image printing to be performed. During this idle period, ink is not ejected from the nozzles N of the ejection head H, and therefore ink is not consumed. In this state, ink is circulated through the circulation path (Cb+Ca) of the second path Cb and the first path Ca, and the circulation path (Cc+Ca) of the third path Cc and the first path Ca. As a result, there are repeated cycles in which there is more ink in the supply subtank 91 than in the collection subtank 92, and vice versa.

[0056] 6A, in the former situation, circulation modes D7 and D8 are executed (steps S101, S107, and S108), and the amount of ink sent from the recovery subtank 92 to the supply subtank 91 is reduced while the ink is collected from the supply subtank 91 to the main tank 95, thereby bringing the liquid level in the supply subtank 91 closer to Mid from High. In a situation between the former and latter, circulation mode D5 is executed (steps S102 and S106), and the ink flow rate in each circulation path is maintained, thereby stabilizing the liquid levels in the supply subtank 91 and the recovery subtank 92 at Mid. In the latter situation, circulation modes D6 and D3 are executed (steps S103 and S104), and the amount of ink sent from the recovery subtank 92 to the supply subtank 91 is increased, bringing the liquid level in the recovery subtank 92 closer to Mid from High. Alternatively, circulation mode D2 is executed (step S105), and the amount of liquid sent from the recovery sub-tank 92 to the supply sub-tank 91 is increased while liquid is sent from the main tank 95 to the recovery sub-tank 92 at a flow rate Fh, thereby stabilizing the liquid level in the supply sub-tank 91 at Mid.

[0057] 6A, control is performed to balance the liquid levels in the supply sub-tank 91 and the recovery sub-tank 92 at Mid. As a result, during the idle period, the idle operation described below is performed.

[0058] As shown in the idle period (before time t0) in FIG. 4, during idle operation, the recovery pump 961 recovers ink from the supply subtank 91 to the main tank 95 at a flow rate Fo, and the supply pump 962 supplies ink from the main tank 95 to the recovery subtank 92 at a flow rate Fl. This causes ink to be transported through the third path Cc. Furthermore, ink is transported through the second path Cb at a flow rate corresponding to the difference between the negative pressure P1 in the supply subtank 91 and the negative pressure P2 in the recovery subtank 92. Furthermore, the circulation pump 93 operates in accordance with the detection values ​​(liquid levels) of the liquid level sensors 971 and 972, as described above. Specifically, as shown in FIG. 4, the flow rate of the circulation pump 93 fluctuates between zero and a flow rate Fc1 (greater than the flow rate Fo and the flow rate Fl) that is greater than zero. This causes ink to circulate through a circulation path (Cc+Ca) made up of the third path Cc and the first path Ca, and a circulation path (Cb+Ca) made up of the second path Cb and the first path Ca.

[0059] 6B , the state changes from a stable state (step S201) in which the liquid levels in the supply subtank 91 and the collection subtank 92 are balanced at Mid and the circulation mode D5 is executed, through an unstable state (steps S202 to S205) in which the liquid levels in the supply subtank 91 and the collection subtank 92 fluctuate greatly and the circulation modes D2, D6, D3, and D6 are executed, to a stable state (steps S206 and S207) in which the liquid levels in the supply subtank 91 and the collection subtank 92 are balanced at Mid and the circulation modes D5 and D6 are repeated. 6C , as ink is ejected from the nozzles N, much of the ink that flowed from the supply subtank 91 into the ink supply chamber Hc stops flowing into the recovery subtank 92, so the system transitions from a stable state (steps S206 and S207) in which circulation modes D5 and D6 are repeatedly executed to steps S301 and S302 in which circulation modes D1 and D2 are executed, and ink is sent from the main tank 95 to the recovery subtank 92 at a flow rate Fh. Then, as the liquid levels in the supply subtank 91 and the recovery subtank 92 stabilize near Mid, circulation modes D2, D5, and D4 are executed (steps S303 to S305).

[0060] Thus, with the start of preparation for printing an image, the flow rate of the circulation pump 93 begins to increase at time t1. That is, as shown in FIG. 4, the flow rate of the circulation pump 93 increases from flow rate Fc1 to flow rate Fc2 from time t1 to time t2 (after time t1). Also, at time t2 (after time t1), the circulation pump 93 reaches flow rate Fc2 and when the flow rate stabilizes, the print start operation begins. That is, as shown in FIG. 4, in this print start operation, the supply pump 962 increases the amount of ink supplied from the main tank 95 to the recovery sub-tank 92 from flow rate F1 over time, while the recovery pump 961 decreases the amount of ink recovered from the supply sub-tank 91 to the main tank 95 from flow rate F0 over time. Specifically, at time t3 (after time t2), the flow rate of the supply pump 962 begins to increase. That is, as shown in FIG. 4, the flow rate of the supply pump 962 increases from flow rate F1 to flow rate Fh from time t3 to time t5 (before time t6). After time t5, the supply pump 962 supplies ink at a flow rate Fh.

[0061] At time t4 (after time t3), the flow rate of the recovery pump 961 begins to decrease. That is, as shown in Figure 4, the flow rate of the recovery pump 961 decreases from flow rate Fo to zero from time t4 to time t7 (after time t6).

[0062] In this way, the supply pump 962 fulfills the function of replenishing ink consumed as ink is ejected from the nozzles N. This ink replenishment is performed by transitioning from circulation mode D5 or D6 to circulation mode D2, as shown in FIG. 6C. That is, the supply pump 962 responds to ink replenishment by increasing the amount of ink supplied by the liquid supply that has already been performed, rather than starting liquid supply from a stopped state. Therefore, the ink supply amount can be increased relatively smoothly without causing large pressure fluctuations that accompany starting the pump. As a result, it is possible to avoid a situation in which the output of the circulation pump 93 fluctuates unstably due to an increase in the amount of ink supplied.

[0063] Also, when printing is completed and time t9 arrives, the control unit 100 controls the pressure generating unit 941 and the pressure generating unit 942 to return the pressure difference between the negative pressure P1 applied from the pressure generating unit 941 to the supply sub-tank 91 and the negative pressure P2 applied from the pressure generating unit 942 to the state during idle operation.

[0064] Note that the timing of each step in the print start operation is not limited to this example. For example, time t2 when the increase in the flow rate of the circulation pump 93 ends and time t3 when the increase in the flow rate of the supply pump 962 begins may occur simultaneously, or time t2 may occur after time t3. Furthermore, time t5 when the increase in the flow rate of the supply pump 962 ends and time t7 when the decrease in the flow rate of the recovery pump 961 ends may occur simultaneously, or time t5 may occur after time t7.

[0065] In this way, the print start operation corresponds to the ejection of ink from the nozzles N by increasing the amount of ink supplied to the circulation path (Cb+Ca) of the second path Cb and the first path Ca. Note that between time t6 and time t8, the flow rate of the supply pump 962 oscillates between flow rate Fh and flow rate Fl. This is because circulation modes D2, D4, and D5 are selectively executed depending on the detection values ​​of the liquid level sensors 971 and 972 (steps S303 to S305). Furthermore, as the print start operation is executed, the flow rate of the circulation pump 93 stabilizes at flow rate Fc2, which is greater than flow rate Fc1. Then, when image printing is completed at time t8, ink ejection is stopped and the above-mentioned idle operation is executed.

[0066] According to the embodiment described above, an idle operation is performed before time t1, and a print preparation operation is performed from time t1 to time t2. Thereafter, when the flow rate of the circulation pump 93 becomes constant, a print start operation is performed (after time t2). During the idle operation, the supply pump 962 supplies ink to the recovery subtank 92 at a flow rate Fl (idle supply rate), while the recovery pump 961 recovers ink into the main tank 95 (buffer tank) at a flow rate Fo (idle recovery rate). In other words, the idle operation causes ink to be supplied from the main tank 95 to the recovery subtank 92 before image printing begins. At this time, the ink supplied to the recovery subtank 92 returns to the main tank 95 via the supply subtank 91, preventing excessive amounts of ink from being stored in the recovery subtank 92 and the supply subtank 91. Furthermore, during the print start operation after time t2, the supply pump 962 increases the amount of ink supplied to the collection subtank 92 from the flow rate Fl (idle supply amount) over time, while the recovery pump 961 decreases the amount of ink recovered from the supply subtank 91 from the flow rate Fo (idle recovery amount) over time. This allows ink to continue being supplied from the main tank 95 to the collection subtank 92 before and after the transition from idle operation to print start operation, while increasing the amount of ink supplied over time to accommodate the start of ink ejection from the ejection head H. In other words, in this embodiment, the supply of ink to the collection subtank 92 by the supply pump 962 is already performed before printing starts, and the start of ink ejection is accommodated by increasing the amount of ink supplied. This suppresses fluctuations in the output of the circulation pump 93 at the start of printing, enabling stable ink ejection.

[0067] Furthermore, at the start of printing, the increase in the amount of ink supplied to the recovery subtank 92 by the supply pump 962 (=Fh-Fl) is greater than the decrease in the amount of ink recovered from the supply subtank 91 by the recovery pump 961 (=Fo-0). With this configuration, it is possible to reliably supply the amount of ink required for image printing to the recovery subtank 92 while suppressing output fluctuations of the circulation pump 93 at the start of printing.

[0068] Furthermore, during the print start operation, the control unit 100 reduces to zero the amount of ink that the recovery pump 961 recovers from the supply subtank 91. This configuration helps ensure that the amount of ink required for image printing is supplied to the recovery subtank 92.

[0069] Furthermore, during idle operation and print start operation, the circulation pump 93 sends an amount of ink from the recovery subtank 92 to the supply subtank 91 that corresponds to the difference between the amount of ink stored in the supply subtank 91 and the amount of ink stored in the recovery subtank 92. With this configuration, the amounts of ink stored in the supply subtank 91 and the recovery subtank 92 can be appropriately managed during idle operation and print start operation.

[0070] Furthermore, it is particularly suitable to perform the above-described idle operation and print start operation for supplying ink to the ejection head H that ejects white ink. That is, white ink tends to be used in large quantities when printing an image. Therefore, when image printing begins, a large amount of ink needs to be supplied from the main tank 95 to the recovery sub-tank 92, which can have a significant impact on fluctuations in the output of the circulation pump 93. In response to this, by applying the above-described operations to the ejection head H that ejects white ink, fluctuations in the output of the circulation pump 93 at the start of printing can be suppressed, enabling stable ejection of white ink.

[0071] In the embodiment described above, the printing device 3 corresponds to an example of the "printing device" of the present invention, the supply sub-tank 91 corresponds to an example of the "supply sub-tank" of the present invention, the supply pipe 91a corresponds to an example of the "supply pipe" of the present invention, the recovery sub-tank 92 corresponds to an example of the "recovery sub-tank" of the present invention, the supply pipe 92a corresponds to an example of the "recovery pipe" of the present invention, the circulation pump 93 corresponds to an example of the "circulation pump" of the present invention, the return pipe 93a corresponds to an example of the "return pipe" of the present invention, the main tank 95 corresponds to an example of the "buffer tank" of the present invention, the recovery pump 961 corresponds to an example of the "recovery pump" of the present invention, the supply pump 962 corresponds to an example of the "supply pump" of the present invention, the control unit 100 corresponds to an example of the "control unit" of the present invention, the flow rate Fl corresponds to an example of the "idle supply amount" of the present invention, the flow rate Fo corresponds to an example of the "idle recovery amount" of the present invention, the ejection head H corresponds to an example of the "ejection head" of the present invention, and the nozzle N corresponds to an example of the "nozzle" of the present invention.

[0072] The present invention is not limited to the above-described embodiment, and various modifications other than those described above are possible without departing from the spirit of the present invention. For example, the ink supply control shown in Figures 4 to 6C may be performed on the ejection head H that ejects white ink, but not on the ejection heads H that eject color inks.

[0073] Furthermore, in the print start operation, it is not necessary to reduce the flow rate of the recovery pump 961 to zero, but it may be reduced from the flow rate Fo to a flow rate greater than zero.

[0074] In the above description, the valves 953 and 954 are always open. However, it is also possible to appropriately perform operations such as closing the valve 953 after a certain time has elapsed since the output of the recovery pump 961 was set to zero, or closing the valve 954 after a certain time has elapsed since the output of the supply pump 962 was set to zero.

[0075] Also, it is not necessarily necessary to provide the valve 953 or the valve 954. Furthermore, the filter 931 or the degasser 932 can also be omitted as appropriate.

[0076] Furthermore, the magnitude relationship between the flow rates Fl and Fo may be reversed, or the flow rates Fl and Fo may be the same.

[0077] Furthermore, the configuration for sending ink from the supply sub-tank 91 to the recovery sub-tank 92 via the ejection head H is not limited to the configuration using the negative pressures P1 and P2 described above, and for example, a positive pressure may be applied to the supply sub-tank 91. [Industrial Applicability]

[0078] The present invention is applicable to all printing techniques that print images by ejecting ink. [Explanation of symbols]

[0079] 3...Printing device 91...Supply subtank 91a...Supply piping 92...Recovery subtank 92a...Recovery piping 93...Circulation pump 93a...Return pipe 95...Main tank (buffer tank) 961...Recovery pump 962...Supply pump 100...Control unit Fl...Flow rate (idle supply amount) Fo...Flow rate (idle recovery amount) H...Discharge head N...Nozzle

Claims

1. an ejection head having nozzles for ejecting ink; a supply sub-tank that stores ink to be supplied to the ejection head; a collection sub-tank for storing ink collected from the ejection head; a supply pipe that connects the supply sub-tank and the ejection head through a flow path and sends ink supplied from the supply sub-tank to the ejection head; a collection pipe that connects the ejection head and the collection sub-tank through a flow path and sends the ink collected from the ejection head to the collection sub-tank; a return pipe that connects the collection sub-tank and the supply sub-tank through a flow path and sends ink stored in the collection sub-tank to the supply sub-tank; a circulation pump provided in the return pipe, which sends ink from the recovery sub-tank to the supply sub-tank, thereby returning the ink recovered from the supply sub-tank to the recovery sub-tank via the ejection head to the supply sub-tank; a buffer tank for storing ink; a recovery pump provided in a pipe connecting the supply sub-tank and the buffer tank, for sending ink from the supply sub-tank to the buffer tank; a supply pump provided in a pipe connecting the buffer tank and the collection sub-tank, for sending ink from the buffer tank to the collection sub-tank; a control unit that executes image printing by ejecting ink from the nozzles of the ejection head onto a printing medium to print an image on the printing medium; Equipped with The control unit before the start of the image printing, the recovery pump and the supply pump are controlled to perform an idle operation so that the supply pump supplies ink from the buffer tank to the recovery sub-tank at an idle supply amount, while the recovery pump recovers ink from the supply sub-tank to the buffer tank at an idle recovery amount; in response to the start of image printing, the recovery pump and the supply pump are controlled so that the amount of ink that the supply pump supplies from the buffer tank to the recovery sub-tank increases over time from the idle supply amount, while the amount of ink that the recovery pump recovers from the supply sub-tank to the buffer tank decreases over time from the idle recovery amount, thereby executing a print start operation; A printing apparatus in which the flow rate of the circulation pump is increased to a predetermined flow rate before the supply pump starts to increase the amount of ink supplied from the buffer tank to the recovery sub-tank.

2. 2. The printing device according to claim 1, wherein, during the print start operation, an increase in the amount of ink supplied from the buffer tank to the recovery sub-tank by the supply pump is greater than a decrease in the amount of ink recovered from the supply sub-tank to the buffer tank by the recovery pump.

3. 3. The printing apparatus according to claim 1, wherein the control unit controls the recovery pump so as to reduce the amount of ink recovered by the recovery pump from the supply sub-tank to the buffer tank to zero during the print start operation.

4. 4. A printing device according to claim 1, wherein the circulation pump sends an amount of ink corresponding to the difference between the amount of ink stored in the supply sub-tank and the amount of ink stored in the recovery sub-tank from the recovery sub-tank to the supply sub-tank via the return pipe during the idle operation and the print start operation.

5. 5. The printing device according to claim 1, wherein the ejection head ejects white ink.

6. A printing method for printing an image on a printing medium by ejecting ink from nozzles of an ejection head onto the printing medium, comprising: a step of performing an idle operation before the start of the image printing while performing ink circulation in which ink recovered from the supply sub-tank via the ejection head into the recovery sub-tank is returned to the supply sub-tank by a circulation pump; a step of executing a print start operation in response to the start of the image printing while executing the ink circulation; Equipped with In the idle operation, ink is supplied to the recovery sub-tank at an idle supply amount by a supply pump that sends ink from a buffer tank to the recovery sub-tank, and ink is recovered into the buffer tank at an idle recovery amount by a recovery pump that sends ink from the supply sub-tank to the buffer tank, In the print start operation, the amount of ink that the supply pump supplies to the recovery sub-tank is increased over time from the idle supply amount, while the amount of ink that the recovery pump recovers from the supply sub-tank is decreased over time from the idle recovery amount; A printing method in which the flow rate of the circulation pump is increased to a predetermined flow rate before the supply pump starts to increase the amount of ink supplied from the buffer tank to the recovery sub-tank.

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