Patent Application
20080239014
The present invention contains subject matter related to Japanese Patent Application JP 2007-090861 filed in the Japanese Patent Office on Mar. 30, 2007, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a liquid discharging head and a liquid discharging apparatus which include a common passage member that defines a common passage communicating with all liquid chambers in a head chip and which discharge liquid from the liquid chambers by driving energy generating elements in the head chip so as to apply a discharging force to the liquid in the liquid chambers. More particularly, the present invention relates to a technique of smoothly removing bubbles from the liquid in the common passage.
2. Description of the Related Art
In an inkjet printer as an example of a liquid discharging apparatus, a recording sheet is conveyed to a liquid discharging head, and ink (liquid) is discharged for printing on the recording sheet by driving a heating resistor (energy generating element) in an ink chamber (liquid chamber) of a head chip that constitutes the liquid discharging head. In this inkjet printer, it is necessary to stably supply ink stored in an ink cartridge to the ink chamber of the head chip.
Water-based ink and oil-based ink can be discharged. Particularly when water-based ink is used, air dissolved in the ink sometimes form bubbles, for example, because of a temperature change, or air taken from the outside sometimes remains as bubbles in the ink. If these bubbles accumulate near the head chip, the flow of ink to the ink chamber is hindered, and sufficient ink supply is difficult during printing. For this reason, the bubbles in the ink disturb the ink discharging direction and change the ink discharging amount.
Ink is discharged by the application of a discharging force from the heating resistor in the head chip to the ink in the ink chamber. If a bubble exists in the ink, it weakens the ink discharging force because of gas compressibility, and disturbs the ink discharging direction. Further, if the bubble in the ink is expanded in accordance with the installation environment of the inkjet printer, the temperature change due to ink discharging (driving of the heating resistor), or the change in atmospheric pressure, the ink in the ink chamber is sometimes unintentionally discharged from the nozzle.
In order to overcome the above problems due to the existence of bubbles in the ink, various technologies for removing bubbles from the ink have been proposed. For example, in the case of a line printer which performs printing corresponding to the width of the recording sheet with nozzles arranged over the length corresponding to the width of the recording sheet, the number of prints is large and good durability is necessary. For this reason, bubbles near the head chip are removed from the ink by being circulated together with the ink by a transfer means such as a pump.
In this bubble removing method, bubbles can be removed with the flow of ink in the common passage communicating with all ink chambers of the head chip. That is, ink is ejected from an outlet of a buffer tank (common passage member) that defines the common passage while supplying ink from an inlet of the buffer tank, so that bubbles are removed from the common passage together with the ink.
However, in order to move bubbles, the flow velocity of ink flowing near the ink chamber of the head chip is required to be somewhat high. Therefore, in order to transfer the ink at the flow velocity, it is necessary to use a high-rate pump. Conversely, when a low-rate pump is used, the capacity of the ink chamber is reduced in order to move the bubbles by increasing the flow velocity of ink near the ink chamber. However, the number of bubbles does not vary in accordance with the capacity of the ink chamber. As the capacity of the ink chamber decreases, the influence of bubbles relatively increases.
Accordingly, in a bubble removing technique disclosed in Japanese Unexamined Patent Application Publication No. 2002-144576, a ceiling surface of a common passage defined by a buffer tank is inclined and the buoyancy of bubbles is divided by the inclination to produce a force component in the moving direction so that the bubbles can easily move even when the flow velocity of ink is relatively low.
Unfortunately, in the technique disclosed in the above-described publication, the bubbles are sometimes adsorbed on the ceiling surface of the common passage, and stay thereat. This makes it difficult to sufficiently remove the bubbles. Further, if the inclination of the ceiling surface is increased to reliably move the bubbles, the capacity of the common passage increases. As a result, the size of the pump increases.
Accordingly, it is desirable to reliably move bubbles even with a low-rate pump and to smoothly remove bubbles from liquid (ink) in a common passage.
A liquid discharging head according to an embodiment of the present invention includes a head chip including a plurality of energy generating elements configured to discharge liquid, and liquid chambers provided around the corresponding energy generating elements; and a common passage member configured to define a common passage communicating with all the liquid chambers in the head chip. The liquid is discharged from the liquid chambers by driving the energy generating elements so as to apply a discharging force to the liquid in the liquid chambers. The common passage member includes an inlet through which the liquid is supplied to the common passage, and an outlet through which the liquid is ejected from the common passage. The common passage includes a ceiling surface having a groove extending from the inlet toward the outlet.
A liquid discharging apparatus according to another embodiment of the present invention includes the above-described liquid discharging head, and transfer means configured to transfer the liquid from the inlet toward the outlet of the common passage member.
In the above embodiments, the common passage member includes the inlet through liquid is supplied to the common passage, and the outlet through which the liquid is ejected from the common passage. The ceiling surface of the common passage has the groove extending from the inlet toward the outlet. For this reason, even when bubbles contained in the liquid in the common passage are brought into contact with the ceiling surface by the buoyancy, since the ceiling surface is kept in a water retention state by the groove, it does not adsorb the bubbles. This allows the bubbles to move easily.
According to the embodiments of the present invention, since the ceiling surface of the common passage is kept in a water retention state by the groove and bubbles are not adsorbed to the ceiling surface. Therefore, bubbles contained in the liquid can easily move even when they are brought into contact with the ceiling surface by the buoyancy. For this reason, even when a low-rate pump is used, the bubbles reliably move, and can be smoothly removed from the liquid in the common passage.
An embodiment of the present invention will be described below with reference to the drawings.
In the following embodiment, a color inkjet printer (line printer 1) that discharges inks (liquids) of four colors, Y (yellow), M (magenta), C (cyan), and K (black) will be described as an example of a liquid discharging apparatus according to the present invention. A line head 10 used in the line printer 1 corresponds to the liquid discharging head in the present invention.
As shown in
The line head 10 can perform printing corresponding to the width of the largest recording sheet supplied from the sheet trays 2a, 2b, and 2c. In contrast to a serial-head printer that performs printing by moving a serial head in the width direction of the recording sheet, the line printer 1 does not use any device for moving the line head 10. This can reduce vibration and noise, and can markedly increase the print speed.
Ink can be supplied to the line head 10 by a “head integrated method” in which ink to be supplied is provided in the head, and a “head separate method” in which ink is supplied from the outside. In this embodiment, the line printer 1 adopts a head separate method, and includes an ink cartridge 13 provided separate from the line head 10. The ink cartridge 13 separately stores four color inks Y, M, C, and K, and can be easily loaded in and unloaded from the line printer 1. For this reason, when ink in the ink cartridge 13 is completely consumed, the ink cartridge 13 can be quickly replaced with a new one.
A pump 11 (corresponding to the transfer means in the present invention) is provided between the line head 10 and the ink cartridge 13 via a subtank 12 (corresponding to the pressure adjustment unit in the present invention). By driving the pump 11, ink is supplied from the ink cartridge 13 to the line head 10 with a predetermined pressure.
In order to perform printing with this line printer 1, one recording sheet 8 is selectively conveyed from any of the sheet trays 2a, 2b, and 2c by the conveying unit 3, and is placed on the print table 4. The maintenance unit 5 is separated from the line head 10 so as to expose the ink discharging surface of the line head 10. Color printing is performed by discharging color inks from the line head 10 while moving the recording sheet 8 on the print table 4. After printing, the recording sheet 8 is moved by the output table 6 and is stocked in the output tray 7.
As shown in
In this way, the line head 10 includes the four head modules 20 (Y, M, C, and K), and four color inks Y, M, C, and K are supplied thereto from subtanks 12 that store the inks. That is, the subtanks 12 (Y, M, C, and K) are respectively connected to the head modules 20 (Y, M, C, and K) via supply tubes 81 (Y, M, C, and K). Therefore, four color inks are supplied from the subtanks 12 (Y, M, C, and K) to the line head 10 by driving the corresponding pumps 11 (Y, M, C, and K).
The four color inks supplied to the line head 10 not only are discharged onto the recording sheet 8 placed on the print table 4, but also are circulated. That is, the color inks from the line head 10 return to the subtanks 12 (Y, M, C, and K) via ejection tubes 82 (Y, M, C, and K), switch valves 15 (Y, M, C, and K), first communication tubes 16 (Y, M, C, and K), the pumps 11 (Y, M, C, and K), and second communication tubes 17 (Y, M, C, and K). Color inks consumed by discharging are replenished from the ink cartridges 13 (Y, M, C, and K) to the subtanks 12 (Y, M, C, and K) via connecting tubes 18 (Y, M, C, and K), the switch valves 15 (Y, M, C, and K), the first communication tubes 16 (Y, M, C, and K), the pumps 11 (Y, M, C, and K), and the second communication tubes 17 (Y, M, C, and K).
As shown in
In the head chip 60, a barrier layer 63 is stacked on a semiconductor substrate 61, and the nozzle sheet 64 having nozzles 65 is bonded to the barrier layer 63. A plurality of heating resistors 62 (corresponding to the energy generating element in the present invention) are deposited at regular intervals in one direction on the semiconductor substrate 61. The semiconductor substrate 61, the barrier layer 63, and the nozzle sheet 64 surround the heating resistors 62 so as to define ink chambers 66 (corresponding to the liquid chamber in the present invention). The ink chambers 66 respectively have apertures communicating with a common ink passage 24. Ink is supplied to the ink chambers 66 through the apertures.
The semiconductor substrate 61 is formed of, for example, silicone, glass, or ceramics. The heating resistors 62 are deposited on one surface of the semiconductor substrate 61 by a micro fabrication technology for fabricating semiconductors and electronic devices. The heating resistors 62 are electrically connected to an external circuit via a conductor portion (not shown) provided on the semiconductor substrate 61.
The barrier layer 63 is provided on the surface of the semiconductor substrate 61 having the heating resistors 62. That is, the barrier layer 63 is patterned on a portion of the semiconductor substrate 61 excluding the vicinities of the heating resistors 62 in the following manner. First, photosensitive resin is applied on the entire upper surface of the semiconductor substrate 61, and is exposed via a photomask having a predetermined pattern by an exposure apparatus using light having the best wavelength band for exposure. The exposed photosensitive resin is then developed with a predetermined developing liquid, and an unexposed portion is removed. The semiconductor substrate 61, the heating resistors 62, and the barrier layer 63 constitute the head chip 60.
The nozzle sheet 64 is formed by, for example, electroforming using Ni (nickel). A plurality of nozzles 65 are arranged in the nozzle sheet 64. The head chip 60 (the semiconductor substrate 61, the heating resistors 62, and the barrier layer 63) is precisely positioned so that the nozzles 65 are aligned with the heating resistors 62, that is, so that the nozzles 65 oppose the heating resistors 62. Further, the head chip 60 is bonded onto the nozzle sheet 64 with the barrier layer 63 facing downward.
Therefore, the ink chambers 66 of the head chip 60 are defined by the semiconductor substrate 61, the barrier layer 63, and the nozzle sheet 64 so as to surround the heating resistors 62, as shown in
The ink chambers 66 respectively have apertures on the lower right side in
If there is a bubble in the ink chamber 66, as shown in
As shown in
The head module 20 includes a head chip 60 and a buffer tank 21 (corresponding to the common passage member in the present invention) for discharging ink. Unlike the structure shown in
The buffer tank 21 forms a common passage 24 (see
The inlet 22 of the buffer tank 21 is connected to a supply tube 81 through which ink in the subtank 12 is supplied to the buffer tank 21. The outlet 23 of the buffer tank 21 is connected to an ejection tube 82 through which the ink is ejected from the buffer tank 21. The ejection tube 82 is connected to the pump 11 via a circulation-side section 15a of a switch valve 15 and a first communication tube 16, and the pump 11 is connected to the subtank 12 via a second communication tube 17. The subtank 12 is provided with a communication valve 14 that allows the interior of the subtank 12 to communicate with the atmosphere. A supply-side section 15b of the switch valve 15 is connected to a connecting tube 18 that supplies ink stored in the ink cartridge 13.
In order to supply ink from the subtank 12 to the buffer tank 21 in the line printer 1, the supply-side section 15b of the switch valve 15 is closed and the circulation-side section 15a is opened, as shown in
When the pump 11 is driven in this state, air in the buffer tank 21 and air from nozzles 65 (see
When the ink is supplied to the buffer tank 21 in this way, the nozzles 65 of the head chip 60 are closed by the ink, and no more air enters the nozzles 65. For this reason, the pressure in the subtank 12 does not increase further, but is in equilibrium. Since ink supply from the subtank 12 to the buffer tank 21 is thereby completed, the head chip 60 is allowed to discharge ink.
In order to perform printing by discharging ink from the head chip 60, the circulation-side section 15a of the switch valve 15 is closed, the supply-side section 15b is opened, and the communication valve 14 is opened. By driving heating resistors 62 (see
When the subtank 12 runs short of ink because of ink discharging from the head chip 60, ink can be added to the subtank 12 by driving the pump 11 while exerting little influence on ink discharging of the head chip 60. That is, ink in the ink cartridge 13 is supplied into the subtank 12 via the connecting tube 18, the supply-side section 15b of the switch valve 15, the first communication tube 16, the pump 11, and the second communication tube 17 by driving the pump 11.
An ink-amount measuring device (not shown) is attached to the subtank 12, and outputs an ink-amount limit signal when the level of ink in the subtank 12 reaches a predetermined ink level. When the control unit (not shown) receives this limit signal, it issues a command to the pump 11. According to the command, the pump 11 automatically stops, and the addition of ink to the subtank 12 is completed. This ink supply to the subtank 12 is also automatically performed when the subtank 12 is empty of ink, for example, when the line printer 1 is first started.
Therefore, a predetermined amount of ink is constantly stored in the subtank 12, and the ink is stably supplied to the head module 20. This allows the line printer 1 to achieve high-quality printing. In order to maintain the high quality, it is necessary to sufficiently remove bubbles from the ink.
In the line printer 1, bubbles are removed from the ink by circulating the ink. For that purpose, the circulation-side section 15a of the switch valve 15 is opened, the supply-side section 15b is closed, and the communication valve 14 is opened. By opening the communication valve 14, the entire ink circulation path is brought into a state in which the pressure is fixed in accordance with the ink level in the subtank 12.
When the pump 11 is driven in this state, the ink is supplied from the subtank 12 to the common passage 24 (see
In the line printer 1, ink containing bubbles is thus circulated by driving the pump 11, as shown by the arrows in
As shown in
Bubbles produced in the common passage 24 rise because of buoyancy. Although the bubbles are going to stick on the ceiling surface of the common passage 24, the ceiling surface has a plurality of grooves 25, and ink is retained in the grooves 25 by capillary action. For this reason, even if the bubbles attempt to stick on the ceiling surface of the common passage 24, the sticking force of the bubbles is seriously reduced, because the ink retained in the grooves 25 lies between the bubbles and the ceiling surface.
The grooves 25 are provided to form steps, and a down-pointing triangular portion at the top is provided between the grooves 25. Therefore, even when the bubbles touch the ceiling surface of the common passage 24 near the grooves 25, they touch only edges of the grooves 25. Therefore, the contact areas between the bubbles and the grooves 25 are small, and this reduces the sticking force. As a result, bubbles in the ink in the common passage 24 easily move not only in the upward direction, but also in the right-left direction.
When ink is circulated so that ink is supplied to this common passage 24 from the inlet 22 and is ejected from the outlet 23, bubbles move toward the outlet 23 with the flow of the ink even when the flow velocity of the ink is low, since the sticking force of the bubbles to the ceiling surface of the common passage 24 is small. Finally, the bubbles are ejected together with the ink from the outlet 23. The bubbles in the ejected ink are removed at the subtank 12 (see
As shown in
On ceiling surfaces of the passage chambers 34a, 34b, and 34c of the common passage 34, a plurality of grooves 35a, 35b, and 35c extend from the inlet 32 toward the outlet 33. For this reason, when ink is supplied (circulated) from the inlet 32, a bubble in the passage chamber 34a moves along the groove 35a with the flow of the ink, and enters the next passage chamber 34 beyond the partition wall 36a. Thus, the bubble is removed from the ink in the passage chamber 34a.
The bubble entering the passage chamber 34b does not sink down, but moves along the groove 35b. Then, the bubble is combined with a bubble originally existing in the passage chamber 34b into a larger bubble, and enters the next passage chamber 34c beyond the partition wall 36b. For this reason, the bubble is also removed from the ink in the passage chamber 34b.
Further, the bubble entering the passage chamber 34c is combined with a bubble originally existing in the passage chamber 34c into an even larger bubble, and moves along the groove 35c. The bubble is then ejected together with the ink from the outlet 33. As a result, bubbles are ejected from all the passage chambers 34a, 34b, and 34c, and are removed at a subtank 12 (see
As shown in
On ceiling surfaces of the passage chambers 44a, 44b, and 44c of the common passage 44, a plurality of grooves 45a, 45b, and 45c extend from the inlet 42 toward the outlet 43. The grooves 45a, 45b, and 45c are similarly inclined upward from the inlet 42 toward the outlet 43.
In the line head 40, the grooves 45a, 45b, and 45c are thus inclined upward from the inlet 42 toward the outlet 42, and the entrance side of each of the passage chambers 45a, 45b, and 45c is lower than the exit side thereof. For this reason, even when bubbles rise because of buoyancy and touch the grooves 45a, 45b, and 45c, the buoyancy is divided by the inclination of the grooves 45a, 45b, and 45c. Consequently, a force component heading from the entrance side of each of the passage chambers 44a, 44b, and 44c toward the exit side is produced.
While the bubbles can easily move by the effect of the grooves 45a, 45b, and 45c, they are even more easily ejected from the passage chambers 44a, 44b, and 44c not only by the circulation of ink, but also by the force components produced by the inclinations of the grooves 45a, 45b, and 45c. Even when the line printer 1 is inclined, for example, because of the installation condition, bubbles can be easily ejected as long as the inclination is within the height difference between both ends of each of the grooves 45a, 45b, and 45c.
Alternatively, an inclined groove may extend through the entire common passage 44, instead of forming a groove in each of the passage chambers 44a, 44b, and 44c. However, when the grooves 45a, 45b, and 45c are inclined, as in the line head 40 of the third embodiment, a height difference can be formed between the entrance side and the exit side of each of the passage chambers 44a, 44b, and 44c. This provides a high ratio of the length and the height difference, and increases the force component produced by the inclination.
As shown in
When ink is supplied (circulated) from the inlet 42a of the first buffer tank 41a, a bubble in ink in the buffer tank 41a moves with the ink flow, and is ejected from the outlet 43a. The ink ejected from the outlet 43a and containing the bubble passes through the connecting tube 51, and enters the second (N-th=second) buffer tank 41b from the inlet 42b. The bubble in the ink is combined with a bubble originally existing in the buffer tank 41b into a larger bubble. The bubble is then ejected together with the ink from the outlet 42b.
Therefore, bubbles in the ink are ejected from both the buffer tanks 41a and 41b, and are removed at the subtank 12 (see
In the line printer 1 according to the embodiment (the line head 10 of the first embodiment, the line head 30 of the second embodiment, the line head 40 of the third embodiment, the line head 50 of the fourth embodiment), a plurality of grooves 25 (35a to 35c, 45a to 45c) are provided in the ceiling surface of the common passage 24 (34, 44) defined by the buffer tank 21 (31, 41). Therefore, bubbles in the ink smoothly move and can be easily removed from the common passage 24 (34, 44). This can prevent the bubbles in the ink from adversely affecting ink discharging.
By connecting the buffer tanks 21 (31, 41) including the grooves 25 (35a to 35c, 45a to 45c) in series, the line printer 1 can perform printing on larger recording sheets 8. Further, since the grooves 45a to 45c are inclined, a similar bubble removing effect can be obtained even when the line printer 1 is inclined, for example, because of the installation condition.
While the embodiments of the present invention has been described above, the present invention is not limited to the above embodiments. For example, the following various modifications can be made.
(1) While four grooves 25 are provided on each of the right and left sides of the ceiling surface of the common passage 24 so as to form steps in the line head 10 according to the first embodiment, the number and shape of the grooves 25 are not limited thereto. While the common passage 44 is divided into three passage chambers 44a, 44b, and 44c by the two partition walls 46a and 46b of the buffer tank 41 in the line head 30 according to the second embodiment, the number of partition walls is not limited thereto. Further, while the two (N=2) buffer tanks 41a and 41b are connected in series in the line head 50 according to the fourth embodiment, it is satisfactory as long as the number N of buffer tanks is more than or equal to two.
(2) While the inkjet line printer 1 in the embodiments includes the line head 10 having the length corresponding to the print width, the present invention is not limited to this printer, but is widely applied to other liquid discharging apparatuses for discharging various kinds of liquids. For example, the present invention is also applicable to a liquid discharging apparatus that discharges dye onto goods.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2007-090861 | Mar 2007 | JP | national |
