Patent Grant
8911044
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2011-000121, filed on Jan. 4, 2011, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to an inkjet recording apparatus comprising a multi-drop-type inkjet head, and a recording method thereof.
An ink jet recording apparatus which forms a color image on a white ground uses color inks, such as a black ink (K), a cyan ink (C), a magenta ink (M), and an yellow ink (Y), and a white ink. A white ground is formed on a print surface of a recording medium with the white ink, and thereafter, a color image is formed.
The color image formed by the ink jet recording apparatus improves more in quality as coverage of the print surface with the white ink increases. Therefore, the ink jet recording apparatus is devised to raise the coverage. For example, a number of print scans for the white ink is increased to be greater than the other color inks. Otherwise, a number of heads for the white ink is increased to be greater than the other color inks.
However, if the number of times for which scanning is performed to print the white ink is increased to be greater than the other color inks, image formation requires a long time. If the number of heads for the white ink is increased to be greater than for the other color inks, a total number of heads increases so that the whole apparatus becomes large. Further, product costs and maintenance costs increase also. Therefore, there are demands for an inkjet recording apparatus and a recording method which can solve problems described above.
In general, according to one embodiment, an inkjet recording apparatus includes: a plurality of inkjet heads of a multi-drop method, each of which controls a diameter of each ink dot formed on a recording medium by changing a number of ink drops to sequentially eject; a first controller; and a second controller. The first controller controls ejection of ink drops from a first inkjet head for ejecting a first ink for which print resolution is required, among the plurality of inkjet heads, in a manner that the number of ink dots formed in a main scanning direction as a printing direction during relative movement between the recording medium and the inkjet heads is great, and that the number of ink drops ejected for each one of the ink dots is small. The second controller controls ejection of ink drops from a second inkjet head for ejecting a second ink for which coverage over a recording surface of the recording medium is required, among the plurality of inkjet heads, in a manner that the number of ink dots formed in the main scanning direction is small, and that the number of ink drops ejected for each one of the ink dots is great.
Hereinafter, embodiments of an inkjet recording apparatus and a recording method will be described with reference to the drawings.
The embodiments relate to application to an inkjet recording apparatus 1 in which a white ground is formed on a print surface of a recording medium, and a color image is formed on the ground.
The inkjet recording apparatus 1 conveys a recording medium 2 in the sub-scanning direction Y by a conveyor mechanism (not shown) which is driven by a conveyor motor 21 as a drive source. The recording medium 2 is not limited to any particular material, thickness, or size insofar as image formation is available by the inkjet recording apparatus 1.
The inkjet recording apparatus 1 comprises a head carriage 12 on which five inkjet heads 11A, 11B, 11C, 11D, and 11E are mounted. The head carriage 12 is attached to a carriage belt 13. The carriage belt 13 is wound between a pair of pulleys 14A and 14B which are respectively provided at one end side and the other end side along the main scanning direction. The pulley 14A at the one end side is fixed to a rotary shaft of a carriage motor 22 which can rotate in regular and reverse directions. Therefore, the carriage belt 13 reciprocally moves in the main scanning direction X according to regular or reverse rotation of the carriage motor 22. Further, the head carriage 12 is reciprocally moved, energized by reciprocal movement of the carriage belt 13.
When the head carriage 12 reciprocally moves, the inkjet recording apparatus 1 makes individual of the inkjet heads 11A to 11E selectively discharge ink drops. In this manner, the inkjet recording apparatus 1 forms an image of ink dots on a recording surface of the recording medium 2.
Each of the inkjet heads 11A to 11E employs a multi-drop method. The multi-drop method controls diameters of dots formed on the recording medium 2 by changing the number of ink drops ejected from each of the inkjet heads 11A to 11E.
Among the inkjet heads 11A to 11E, the head 11A is a head for a black ink (K) (hereinafter referred to as black head 11A). The head 11B is a head for a cyan ink (C) (hereinafter referred to as cyan head 11B). The head 11C is a head for a magenta ink (M) (hereinafter referred to as magenta head 11B). The head 11D is a head for yellow ink (Y) (hereinafter referred to as yellow head 11D). The head 11E is a head for white ink (W) (hereinafter referred to as white head 11E).
Print resolution is required for the black, cyan, magenta, and yellow color inks (K, C, M, and Y). These inks are referred to as first inks. Coverage over a recording surface of the recording medium 2 is required for the white ink (W). Such an ink is referred to a second ink.
The inkjet recording apparatus 1 further comprises head drive circuits 23A, 23B, 23C, 23D, and 23E respectively for the inkjet heads 11A to 11E, and a printer controller 24.
The printer controller 24 is connected to a host computer 3 such as a personal computer through an interface. The printer controller 24 controls the conveyor motor 21, carriage motor 22, and head drive circuits 23A to 23E, based on print data supplied form the host computer 3. Under control of the printer controller 24, the inkjet recording apparatus 1 forms a color image according to the print data on a print surface of the recording medium 2.
The printer controller 24 comprises a first controller 31 and a second controller 32.
The first controller 31 controls individuals of the inkjet heads 11A, 11B, 11C, and 11D which emits the first inks (K, C, M, and Y), in the following manner. Specifically, the first controller 31 controls ejection of inks from individuals of the inkjet heads 11A, 11B, 11C, and 11D so as to increase the number of ink dots formed in the main scanning direction, and to decrease the number of ink drops ejected for each one of the ink dots.
The second controller 32 controls the inkjet head 11E which ejects the second ink (W) in the following manner. Specifically, the second controller 31 controls ejection of an ink from the inkjet head 11E so as to decrease the number of ink dots formed in the main scanning direction X, and to increase the number of ink drops ejected for each one of the ink dots.
The CPU 41 forms a controller body. The ROM 42 stores fixed data such as a program. The RAM 43 has a region to temporarily store variable data.
The communication interface 44 receives print data transmitted from the host computer 3 in accordance with preset communication protocols. The CPU 41 analyzes the print data received through the communication interface 44, and prepares the print data for each of the inkjet heads 11A to 11E.
The I/O port 45 electrically connects the head drive circuits 23A to 23E. The CPU 41 transmits print data and control signals respectively corresponding to the inkjet heads 11A to 11E, to the drive circuits 23A to 23E through the I/O port 45. The control signals comprise a shift clock signal and a latch pulse signal and a timing pulse signal.
The first motor driver 46 drives the conveyor motor 21 in accordance with a command from the CPU 41. The second driver 47 drives the carriage motor 22 in accordance with a command from the CPU 41.
The CPU 41 performs, as the first controller 31 and second controller 32, controls by appropriately using regions of the RAM 43, based on the program stored in the ROM 42.
The head drive circuits 23A to 23E have the same configurations as each other, and a main part thereof is shown in
The head drive circuits 23A to 23E each comprise a shift register 51, a latch circuit 52, an output control circuit 53, and a drive pulse generator circuit 54. The shift register 51 connects to the latch circuit 52. The latch circuit 52 connects to the output control circuit 53. The output control circuit 53 connects to the drive pulse generator circuit 54.
The drive pulse generator circuit 54 connects to the inkjet heads 11A to 11E.
The shift register 51 stores print data supplied from the printer controller 24, sequentially shifting the print data in synchronization with a shift clock signal.
The latch circuit 52 latches the print data stored in the shift register 51, based on a latch pulse signal supplied from the printer controller 24.
The output control circuit 53 outputs the print data latched by the latch circuit 52 to the drive pulse generator circuit 54 in synchronization with a timing pulse signal supplied from the printer controller 24.
The drive pulse generator circuit 54 converts the print data supplied from the output control circuit 53 into drive pulse signals, and outputs the signals to the inkjet heads 11A to 11E.
The inkjet heads 11A to 11E have the same configurations as each other, and main parts thereof are shown in
In the inkjet heads 11A to 11E each, a first piezoelectric member 62 is joined to an upper surface on a front side of a base board 61, and a second piezoelectric member 63 is joined to the first piezoelectric member 62. In the inkjet heads 11A to 11E each, the first piezoelectric member 62 and the second piezoelectric member 63 are joined, polarized in mutually opposite directions along thickness directions. Further, the inkjet heads 11A to 11E each are provided with a large number of grooves 68 extended from front ends of the joined piezoelectric members 62 and 63 toward rear ends thereof. The grooves 68 are provided at constant intervals in parallel. The grooves 68 each have an open front ends and a rear end inclined up.
In the inkjet heads 11A to 11E, electrodes 69 are provided on sidewalls and a bottom surface of each of the grooves 68. Further, the inkjet heads 11A to 11E are provided with lead electrodes 70 respectively extended from the electrodes 69, e.g., from the rear ends of the grooves 68 toward the rear upper surface of the second piezoelectric member 63.
In the inkjet heads 11A to 11E, upper parts of the grooves 68 are respectively closed by a ceiling plate 64, and front ends of the grooves 68 are closed with an orifice plate 65. The ceiling plate 64 internally comprises a common ink chamber 71 on a rear side. In the inkjet heads 11A to 11E each, nozzles 72 for ejecting an ink are formed by the grooves 68 surrounded between the ceiling plate 64 and the orifice plate 65. The nozzles 72 are also referred to as ink chambers. In the inkjet heads 11A to 11E each, ink ejection ports 73 are opened at positions of the orifice plate 65 opposed to the grooves 68.
In the inkjet heads 11A to 11E each, a printed board 75 where a conductive pattern 74 is formed is joined to an upper surface of a rear part of the base board 61. In the inkjet heads 11A to 11E each, a drive IC 76 is mounted on the printed board 75. Each drive IC 76 is connected to the conductive pattern 74. The conductive pattern 74 is connected, by wire bonding, to the lead electrodes 70 through the leads 77. The drive IC 76 forms the head drive circuits 23A to 23E.
Next, operation principles of the inkjet heads 11A to 11E configured as described above will be described with reference to
As shown in
When time t1 is reached upon elapse of the regular segment Ta, the head drive circuits 23A to 23E each apply a predetermined negative voltage (−Vs) to the electrode corresponding to the nozzle 72a. Then, elapse of the preparation segment T1 is awaited. When the negative voltage (−Vs) is applied, the sidewalls 78a and 78b on two sides of each nozzle 72a deform outside so as to expand the volume of the nozzle 72a, and reach a state as shown in
When time t2 is reached upon elapse of the preparation segment T1, the head drive circuits 23A to 23E continue to apply the negative voltage (−Vs) to the electrodes 69 corresponding to the nozzles 72a until the sustained segment Tb further elapses. During this time, the nozzles 72a, 72b, and 72c maintain a state as shown in
When time t3 is reached upon elapse of the sustained segment Tb, the head drive circuits 23A to 23E return to 0 V, the voltage applied to the electrodes 69 corresponding to the nozzles 72a. Further, elapse of the ejection segment T2 is awaited. When the applied voltage becomes zero, the walls 78a and 78b on two sides of each nozzle 72a are restored into a regular state, and return into the state as shown in
When time t4 is reached upon elapse of the ejection segment T2, the head drive circuits 23A to 23E apply the predetermined positive voltage (+Vs) to the electrode 69 corresponding to the nozzles 72a. Further, elapse of the post-processing segment T3 is awaited. When the positive voltage (+Vs) is applied, the walls 78a and 78b on two sides of each nozzle 72a deform inside so as to contract the volume of the nozzle 72a, and reach a state as shown in
When time t5 is reached upon elapse of the post-processing segment T3, the head drive circuits 23A to 23E return again to 0 V, the voltage applied to the electrodes 69 corresponding to the nozzles 72a. In response to the applied voltage returned to zero, the walls 78a and 78b on two sides of each nozzle 72a are restored into the regular state. That is, the nozzles 72a, 72b, and 72c each return to the state as shown in
The head drive circuits 23A to 23E supply the electrodes 69 of the nozzles 72a with the drive pulse signal having the conduction waveform shown in
Next, gradation printing according to the multi-drop method will be described with reference to
Specifically, the head drive circuits 23A to 23E each repeatedly output the drive pulse voltage having the conduction waveform as shown in
Though four to six gradations are not shown, the number of ink drops increases depending on the number of gradations. The volume of ink which penetrates the recording medium 2 increases accordingly.
Thus, in the gradation printing according to the multi-drop method, a relationship between the number of ink drops to eject and the print density changes linearly. Accordingly, excellent gradation printing can be achieved by controlling the number of ink drops to eject, depending on the number of drive pulses.
Hence, the nozzles 72 are divided into three groups of n, n−1, and n+1. Specifically, supposing that a nozzle 72a belongs to group n, division is performed in a manner that a nozzle 72b adjacent to the nozzle 72a on one side belongs to group n−1, and a nozzle 72c adjacent to the nozzle 72a on the other side belongs to group n+1.
The head drive circuits 23A to 23E supply the drive pulse signal to the electrodes 69 of the nozzles 72a at timings shifted respectively for the groups, as shown in
If a delay time between one another of the groups is Td, a cycle time Tc required for three-division driving at the time of the maximum seven gradations is expressed by expression (1) below.
Tc=(Tt×7+Td)×3 (1)
A drive frequency F is an inverse number of the cycle time Tc, and is therefore expressed by expression (2) below.
F=1/(Tt×7+Td)×3 (2)
Operation principles of the inkjet heads 11A to 11E according to the multi-drop method have been described above.
Meanwhile, the inkjet heads 11A to 11E used in the first embodiment can be driven by maximum drive frequencies, as values shown in Table 1, depending on ink ejection volumes.
That is, an ink ejection volume is 6 pL when print data is 1 Hex (hexadecimal), i.e., when the basic drive waveform shown in
Thus, the inkjet heads 11A to 11E have a feature that the drive frequency can be increased as the number of drops to eject decreases. By utilizing this feature, the inkjet heads 11A, 11B, 11C, and 11D which eject the color inks (K, C, M, and Y), and the inkjet head 11E which ejects the white ink, according to the first embodiment are controlled, in the first embodiment, as shown in
That is, the inkjet heads 11A, 11B, 11C, and 11D form an image according to print data by ejecting ink drops 81 one after another (6 pL) at a high resolution of 12,000 dpi in the main scanning direction X at a speed of 28,000 dots per second. Such ejection control is performed by the first controller 31.
In contrast, the inkjet head 11E which ejects the white ink (W) forms an image as a ground by sequentially emitting six ink drops 81 (36 pL) at low resolution of 300 dpi in the main scanning direction at a speed of 7,000 dots per second. Such ejection control is performed by the second controller 32.
Resolution in the sub-scanning direction is the same 1,200 dpi as when the color inks (K, C, and Y) are ejected.
As is apparent from
Therefore, the inkjet recording apparatus 1 according to the first embodiment achieves an effect of increasing coverage of the white ink (W) over a print surface of a recording medium, without reducing the print speed.
According to the second embodiment, an image is formed by ejecting, at most, two ink drops 81 for from each of inkjet heads 11A, 11B, 11C, and 11D which respectively eject color inks (K, C, M, and Y). Hardware part of an inkjet recording apparatus 1 is the same as that in the first embodiment. Therefore,
In the second embodiment, as shown in
In contrast, an inkjet head 11E which ejects a white ink (W) forms an image as a ground by sequentially emitting nine ink drops (54 pL) at low resolution of 300 dpi in the main scanning direction X at a speed of 4,175 dots per second. Such ejection control is performed by a second controller 32.
Resolution in the sub-scanning direction is the same 1,200 dpi as when the color inks (K, C, M, and Y) are ejected.
The resolution in the main scanning direction X, drive frequencies of the inkjet heads 11A, 11B, 11C, 11D, and 11E, ejection volumes of the ink drops 81, moving speeds of the inkjet heads 11A, 11A, 11B, 11C, 11D, and 11E in the main scanning direction X, and ejection volumes of the ink drops 81 when the resolution in the main scanning direction X is 300 dpi are as shown in Table 3 for the color inks (K, C, M, and Y) and white ink (W).
As is apparent from
Therefore, the inkjet recording apparatus 1 according to the second embodiment can also achieve the same operation and effect as according to the first embodiment.
The foregoing embodiments have exemplified application to the inkjet recording apparatus 1 on which five inkjet heads 11A, 11B, 11C, 11D, and 11E are mounted. However, the number of heads is not limited to five. The embodiments are applicable to any inkjet recording apparatus insofar as, at least, two or more inkjet heads which employ first and second inks are mounted on the inkjet recording apparatus wherein print resolution is required for the first ink, like a color ink, and coverage over a recording medium is required for the second ink, like a white ink.
Although the foregoing embodiments use a white ink (W) as the second ink, the second ink is not limited to this ink. For example, the embodiments are applicable to an inkjet recording apparatus in which a second ink is an ink for overcoating an image formed by color inks as first inks (K, C, M, and Y) on a recording surface of a recording medium 2.
Similarly, the embodiments are also applicable to an inkjet recording apparatus in which a second ink is an ink for undercoating an image formed by color inks as first inks (K, C, M, and Y) on a recording surface of a recording medium 2.
The embodiments are still also applicable to an inkjet recording apparatus which prints first and second inks on a circuit board wherein the first ink for which resolution is required is used for circuit symbols and the second ink for which coverage is required is a resist ink.
In the inkjet recording apparatuses 1 according to the foregoing embodiments, the inkjet heads 11A to 11E are arrayed in the main scanning direction X and are mounted on the head carriage 12. Further, by reciprocally moving the head carriage 12 along the main scanning direction X, an image is formed on a recording surface of the recording medium 2 which moves in the sub-scanning direction Y. However, the embodiments are also applicable to an inkjet recording apparatus in which a plurality of line heads are arrayed along a conveying direction of the recording medium 2.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
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