1. Field of the Invention
The present invention relates to an on-demand type inkjet recording device, and particularly to a high-speed inkjet recording device that records images using a plurality of nozzles.
2. Description of Related Art
An inkjet recording device provided with a recording head having a plurality of nozzles can record images at a high rate of speed and at a high density on recording medium due to the plurality of nozzles.
Such inkjet recording devices are categorized as continuous type or on-demand type devices. The on-demand type inkjet recording device, such as that disclosed in Japanese unexamined patent application publication No. 2002-273890, has a simpler construction than that of the continuous system. Therefore it is possible to dispose hundreds or thousands of nozzles to be disposed at a high density in the on-demand type inkjet recording device.
However, in such a multi-nozzle inkjet recording device, the ejection velocity and weight of ink droplets ejected from multiple nozzles tend to vary widely among nozzles. When the ejection velocity varies, the position at which ink droplets land on the recording medium also varies, leading to an obvious deterioration in image quality in lines of text, figures, tables, and the like. When the weight of the ink droplets varies, on the other hand, the surface area of the dots on the recording medium also varies, producing irregular densities in the image, particularly halftone images.
Therefore, multi-nozzle inkjet recording devices have been proposed for regulating the ejection velocity or ink droplet weight for each nozzle by making separate fine adjustments to the drive voltage waveform applied to the piezoelectric element or heating element of each nozzle.
For example, Japanese unexamined patent application publication No. HEI-9-11457 provides a multi-nozzle inkjet recording device having a plurality of drive waveform generators for generating desired drive voltage waveforms. In this multi-nozzle inkjet recording device, appropriate drive voltage waveforms are selected for each nozzle to achieve a desired ink droplet weight or ejection velocity, and the selected drive voltage waveform is applied to the nozzle from the corresponding drive waveform generator.
Further, Japanese unexamined patent application publication No. HEI-4-316851 provides a multi-nozzle inkjet recording device having a single drive waveform generator capable of generating a plurality of drive voltage waveforms. In this multi-nozzle inkjet recording device, since the same drive voltage waveform is applied to all nozzles simultaneously, it is not possible to eject ink simultaneously from all nozzles while applying individual drive voltage waveforms to each nozzle. Therefore, a time-division method is used to apply an appropriate drive voltage waveform sequentially to one nozzle at a time, obtaining the desired ink droplet weight or ejection velocity.
However, in the conventional multi-nozzle inkjet recording device described above, including a combination of Japanese unexamined patent application publication No. HEI-9-11457 and No. HEI-4-316851, it is not possible to perform calibration for both ejection velocity and ink droplet weight simultaneously Variations in the weight can increase when variations in velocity are suppressed, while variations in the velocity can increase when variations in weight are suppressed.
In view of the above-described drawbacks, it is an objective of the present invention to provide a multi-nozzle inkjet recording device capable of recording high-quality images by selectively emphasizing either precision in droplet ejection velocity or precision in ink droplet weight.
In order to attain the above and other objects, the present invention provides an inkjet recording device. The inkjet recording device includes a nozzle module, a switching unit, a waveform generating unit, an image recognizing unit and a pulse width modulating unit.
The nozzle module has a plurality of nozzles for ejecting ink droplets and a plurality of piezoelectric elements. Each piezoelectric element includes a common electrode and an individual electrode. The piezoelectric element is deformed when a potential difference is generated between the common electrode and the individual electrode. The nozzles is provided in one-to-one correspondence with the piezoelectric elements. Each nozzle ejects the ink droplet in accordance with deformation of the corresponding piezoelectric element.
The switching unit includes one terminal connected to the individual electrode and another terminal grounded. The switching unit is capable of opening and closing in response to a switch pulse. The opening duration of the switch unit is variable depending on the switch pulse. The waveform generating unit applies a drive voltage to the common electrodes of all the nozzles commonly.
The image recognizing unit determines an ejection condition of the ink droplet ejected from the nozzle while referring to ejection data indicating a type of each pixel to be recorded, and generates switch pulse width data that includes the ejection data and the ejection condition. The pulse width modulating unit generates the switch pulse based on the switch pulse width data.
The above and other objects, features and advantages of the invention will become more apparent from reading the following description of the preferred embodiments taken in connection with the accompanying drawings in which:
An inkjet-recording device according to a first embodiment of the present invention will be described while referring to
The inkjet-recording device 10 includes an inkjet head module (hereinafter referred to as a “head module”) 103, a paper conveying device 105, an inkjet head drive circuit (hereinafter abbreviated to “drive circuit”) 102, and an ink tank 104. A plurality (256 in the preferred embodiment) of nozzles 300 is arranged in a row in the head module 103. The paper conveying device 105 conveys a recording paper 106 in a paper conveying direction A (indicated by the arrow A in the drawing) orthogonal to the row of nozzles 300 while outputting paper position detection signals ENC that indicate paper positions, to the controller 20. The drive circuit 102 actuates the head modules 103 while transmitting a common drive voltage VCOM for all nozzles 300 and individual drive voltages VNOZ for each nozzle 300 in order to form an image on the recording paper 106. The ink tank 104 supplies ink to the head modules 103 via a pipe.
The controller 20 outputs a latch enable signal LE, a data clock pulse CLK, and ejection data DAT to the drive circuit 102. The latch enable signal LE is transmitted in synchronization with the paper position detection signal ENC in order to instruct start of forming of each line that configures a part of an image and is parallel to the row of nozzles 300. The latch enable signal LE according to the preferred embodiment is a short pulse signal of 10 KHz.
The ejection data DAT is serial data with respect to ejection from each of the nozzles 300 arranged in order of 1th to 256th nozzle 300. The ejection data DAT is “1” or “0”, where “1” represents ejection and “0” represents no ejection. The ejection data DAT is transmitted in synchronization with the data clock pulse CLK. The controller 20 begins transmitting the data clock pulse CLK and the ejection data DAT at the same instant of the transmitting of the latch enable signal LE. In the preferred embodiment, the data clock pulse CLK has a frequency of 5 MHz. Accordingly, 51.2 μs are required to transmit the 256 ejection data elements DAT for all of the nozzles 300.
When the latch enable signal LE is generated, 256 bits of ejection data DAT, that has one-to-one correspondence with 256 of the nozzles 300 for the first line (line 1) of an image being recorded, is transferred. After one line worth of data has been transferred, 256 bits of data for the next line is transferred when the latch enable signal LE is generated again. The ejection data DAT for subsequent lines are transferred in the same way.
The head module 103 will be described with reference to
Each nozzle 300 also includes a piezoelectric element 304. One part of the piezoelectric element 304 is fixed to the piezoelectric element fixing substrate 306 and another part of the piezoelectric element 304 is linked to the vibration plate 303 by an elastic material 309, such as a silicon adhesive. The piezoelectric element 304 includes a pair of signal input terminals 305a and 305b. The piezoelectric element 304 expands and contracts when a voltage difference is generated between the signal input terminals 305a and 305b, and remains in its original shape when a voltage is not applied. The support plate 313 reinforces the vibration plate 303.
For example, the vibration plate 303, restrictor plate 310, pressure chamber plate 311, and support plate 313 are made from stainless steel while the orifice plate 312 is constructed from a nickel material. The piezoelectric element fixing substrate 306 is formed of an insulating material, such as a ceramic or polyimide.
With this construction, ink supplied from the ink tank 104 (
Next, the drive circuit 102 will be described with reference to
The image recognizing device 201 converts 1 bit ejection data DAT for each nozzle to 8 bit switch pulse width data 202 for modifying each nozzle's variation. The switch pulse width data 202 are stored in the shift register 203 sequentially in synchronization with the data clock pulse CLK. When all of the switch pulse width data 202 for the 256 nozzles 300 have been accumulated in the shift register 203 and the latch enable signal LE is generated, the latch 204 latches all of the switch pulse width data 202 accumulated in the shift register 203 simultaneously in synchronization with the latch enable signal LE. Then, the switch pulse width data 202 latched by the latch 204 is input into the pulse width modulator 205. The pulse width modulator 205 converts the switch pulse width data 202 to a switch pulse 206, and the switch pulse width data 202 is outputted to the corresponding signal input 207a of the switch 207.
The upper side of each switch 207 is connected to the signal input terminal 305b of the corresponding nozzle 300, while the lower side is grounded. If a “1” is inputted into the signal input 207a, that is, if the switch pulse 206 is a “1”, the switch 207 closes. If a “0” is inputted into the signal input 207a, that is, if the switch pulse 206 is a “0”, the switch 207 is opened. Thus, the individual drive voltages VNOZ1-VNOZ256 are applied to the signal input terminals 305b of each nozzle 300. This will be described in greater detail below.
The waveform generator 208 generates a common drive voltage VCOM in synchronization with the latch enable signal LE. The common drive voltage VCOM is applied to the signal input terminals 305a of all the nozzles 300 commonly.
Next, the image recognizing device 201 will be described with reference to
The binary counter 401 generates nozzle addresses 402 while counting the data clock pulse CLK. The first nozzle address 402 is “0” that indicates the first nozzle 300, and the last nozzle address 402 is “255” that indicates the 256th nozzle 300. The binary counter 401 is cleared by the latch enable signal LE. The nozzle addresses 402 are outputted to the memory unit 403. Each nozzle address 402 corresponds to the ejection data DAT inputted into the memory unit 403 at same time.
The ejection data DAT inputted into the image recognizing device 201 is inputted into the memory unit 403 as the ejection data D33 in synchronization with the data clock pulse CLK. The ejection data DAT is also inputted into the flip flop 404a and the FIFO memory unit 405 in synchronization with the data clock pulse CLK.
The ejection data DAT inputted into the flip flop 404a is inputted to the memory unit 403 as the ejection data D32 in synchronization with the next data clock pulse CLK due to the storage function of the flip flop 404a. The ejection data DAT inputted into the flip flop 404a is also inputted to flip flop 404d. The ejection data DAT inputted into the flip flop 404d is also inputted to the memory unit 403 as the ejection data D31 in synchronization with the further next data clock pulse CLK.
The FIFO memory unit 405 can store 8 bit worth of the ejection data DAT and has an internal address counter that is reset to 0 by the latch enable signal LE. The FIFO memory 405 does not output the ejection data DAT inputted until 8 bit worth of the ejection data DAT corresponding to one line has been stored. When the ejection data DAT corresponding to one line has been stored in the FIFO memory unit 405, the FIFO memory unit 405 outputs ejection data DAT-1 in synchronization with the data clock pulse CLK in order stored. Since the FIFO memory unit 405 outputs data inputted before 8 bit, the ejection data DAT-1 corresponds to the previous line.
The ejection data DAT-1 is inputted to the memory unit 403 as the ejection data D23, D22 and D21 in the same manner of D33, D32 and D31. The ejection data DAT-1 is also inputted into the FIFO memory unit 407. The FIFO memory 407 outputs the ejection data DAT-2 to the memory unit 403 as D13, D12 and D11 in the same manner.
The ejection data D11-D33 obtained with this configuration indicates a region that is formed of a 3-by-3 (3×3) block of pixels in a recorded image as shown in
The ejection data D11-D33 are inputted all at once into the memory unit 403. The memory unit 403 generates switch pulse width data 202 for each nozzle 300 corresponding to the ejection data D22 that is a center of the region R. The memory unit 403 has stored switch pulse width table Tp for changing a flight condition, such as the quantity, of the ink droplet ejected from the nozzle 300 corresponding to the ejection data D22 in question. The switch pulse width table Tp has switch pulse width data 202 with respect to the ejection data D22 based on the condition of the ejection data D11-D33 for all the nozzles. The switch pulse width data Tp has been obtained from experiments.
The memory unit 403 judges the condition of the ejection data D22 based on the ejection data D11-D21 and D23-D33. Meanwhile, the memory unit 403 judges that the state of the ejection data D22 is which of (a) all of the ejection data D11-D33 are black dots (“1”), (b) the ejection data D22 is a black dot (“1”) though at least one of the ejection data D11-D21 and D23-D33 is a white dot (“0”), or (c) the ejection data D22 is a white dot (“0”) without reference to D11-D21 and D23-D33. Accordingly, it becomes that the memory unit 403 has stored switch pulse width table Tp that has the switch pulse width data 202 for each nozzle for each of (a), (b), (c) described above.
The ejection data elements D23, D22, and D21 in the current transfer are identical with the ejection data DAT-1 transferred from the controller 20 one line earlier due to the FIFO memory 405 (
The first through third nozzles (nozzle addresses 402=0-2) of the switch pulse width data 202 are “0” referring to the switch pulse width table Tp in
Next, the pulse width modulator 205 will be described with reference to
Next, the configuration of the waveform generator 208 will be described with reference to
Next, operations of the pulse width modulator 205 will be described for the fifth nozzle 300 (nozzle address 402=4) referring to
The magnitude comparator 701 is comparing the magnitudes of inputs A and B each time the binary comparator 702 is incremented. The magnitude comparator 701 outputs “1” to the signal input 207a as switch pulse 206 when the input A is larger than the input B, while outputting “0” to the signal input 207a as switch pulse 206 when the input A is smaller than the input B. The switch 207 closes when “1” is inputted into the signal input 207a, while the switch 207 is opened when “0” is inputted into the signal input 207a.
The waveform generator 208 also outputs the common drive voltage VCOM shown in
The waveform of the drive voltage V is a trapezoidal wave well known in the art. When the voltage V drops, the pressure chamber 302 expands, drawing the meniscus inside the nozzle hole 301. When the voltage V rises (the voltage difference is called as an ejection voltage Vf), the pressure chamber 302 contracts, causing the meniscus to move outward. Thus, an ink droplet is ejected. The ejection velocity v and droplet weight w of the ink droplet ejected from the nozzle 300 varies according to the ejection voltage Vf.
The “Tp1-v” through “Tp256-v” and the “Tp1-w” through “Tp256-w” stored in the memory unit 403 corresponds to the ejection voltage Vf-v and ejection voltage Vf-w for each nozzle.
In the preferred embodiment, it is possible to switch the priority for precision in droplet weight and precision in ejection velocity automatically for each pixel. Meanwhile, which of the precision in droplet weight or the precision in ejection velocity is determined based on the ejection data D11-D33 referring to the switch pulse width table Tp.
Since the ink droplet weight for each nozzle is fixed when printing a solid image (case (a)), it is possible to prevent streaks and other printing problems in the paper conveying direction A caused by irregularities in density. As a result, the quality of images can be improved. The quality of halftone images can similarly be improved by recording all dots in a halftone image at the same weight.
Since the ink droplet velocity for each nozzle is fixed when printing text or diagrams, such as graphs and tables (case (b)), it is possible to record high-quality images at a high rate of speed with no variation in the ejection positions.
Therefore, it is possible to achieve high quality printing of composite images.
Next, an ink ejection system according to a second embodiment of the present invention will be described with reference to
In the ink ejection system according to the second embodiment, as shown in
Pp=Pn sin θ
Although exaggerated in
The ink ejection system according to the second embodiment includes a drive circuit 1102 in place of the drive circuit 102, as shown in
If the switch pulse width data 1202 for all the nozzles 300 are inputted into the pulse width modular 205 simultaneously such as the first embodiment when the head modules 103 is slanted, a line is also formed slanted since the ejection data DAT is data with respect to the X-direction in
The latch 204 outputs a 256×8-bit latch output 1202 (switch pulse width data 202) for the 1st through 256th nozzles to the switching device 1200. Of this data, only 8 bits for the first nozzle (Tp1) is transferred to the pulse width modulator 205, while the remainder (255×8 bits) is inputted into the FIFO memory unit 2001. The FIFO memory unit 2001 outputs the remainder of the latch output 1202 for four lines earlier (255×8 bits) as output 2001′. Of this output data, only 8 bits for the 2nd nozzle (Tp2) is transferred to the pulse width modulator 205.
The remainder of the output 2001′ (254×8 bits) is inputted into the FIFO memory unit 2002. Hence, the FIFO memory unit 2002 outputs the remainder of the latch output 1202 for eight lines earlier as output 2002′. Of this output data, only 8 bits for the 3rd nozzle (Tp3) is transferred to the pulse width modulator 205.
After repeatedly performing this process, the final remainder (1×8 bits) is inputted into the FIFO memory unit 2255. Hence, the FIEO memory unit 2255 outputs the remainder of the latch output 1202 for 4×255 lines earlier (1×8 bits), which output is transferred to the pulse width modulator 205 as 8 bits for the 256th nozzle (Tp256).
Thus, each ink droplet ejected from each nozzle 300 is ejected while delayed so that the ink droplets ejected from all the nozzle 300 form a line in the X-direction. Accordingly, in the preferred embodiment, when the head module 103 is disposed at a slant in order to record at a desired resolution, the switching device 1200 can rearrange the switch pulse width data 202 in order to achieve the same effects obtained in the first embodiment described above.
While the invention has been described in detail with reference to specific embodiments thereof, it would be apparent to those skilled in the art that many modifications and variations may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims.
For example, although the switch pulse width data 202 in the preferred embodiments described above is 8 bits in size, the switch pulse width data 202 may be set to any number of bits. When the switch pulse width data 202 is less than 8 bits, memory units 1301 may be disposed in direct connection to the inputs A of the magnitude comparators 701 to convert the switch pulse width data 20 from n bits to 8 bits, as shown in
Further, while only one head module 103 was described in the first and second embodiments, a plurality of head modules 103 may be provided. Though the switch pulse width data 202 is generated based 3×3 blocks (D11-D33) in the preferred embodiment, more blocks may be referred to generate the switch pulse width data 202.
Number | Date | Country | Kind |
---|---|---|---|
P2004-219771 | Jul 2004 | JP | national |