1. Field of the Invention
The present invention relates to a print element substrate including a plurality of print element arrays in which different numbers of print elements are arrayed, an inkjet printhead, and a printing apparatus.
2. Description of the Related Art
A printhead which prints on a printing medium by discharging ink according to a thermal inkjet method includes, as print element building elements in the printhead, heaters formed from heat generation elements. Drivers for driving heaters, and logic circuits for selectively driving the drivers in accordance with print data are formed on a single element substrate of the printhead.
The resolution of thermal inkjet type color inkjet printing apparatuses is increasing year by year. Along with this, the orifice arrangement density of a printhead is set to discharge ink in the range of a resolution of 600 dpi to resolutions of 900 dpi and 1,200 dpi. There is known a printhead having orifices at such high density.
Demand has arisen for reducing graininess at a halftone portion or highlight portion in a gray image and color photo image. To meet this demand, the size of an ink droplet (liquid droplet) discharged to form an image was about 15 pl several years ago, but is recently decreasing to 5 pl and then 2 pl year after year in a printhead which discharges color ink.
A high-resolution printhead in which orifices for discharging small ink droplets are arranged at high density satisfies a user need for high-quality printing when printing a high-quality color graphic image or photo image. However, when not high-resolution printing but high-speed printing is required in, for example, printing a color graph in a spreadsheet, the above-mentioned printhead may not meet the demand for high-speed printing because printing with small ink droplets increases the number of print scan operations.
To achieve even high-speed printing, there has been proposed a printhead which discharges small ink droplets for high-quality printing and large ink droplets for high-speed printing. There have also been known a printhead in which a plurality of heaters are arranged for one orifice to change the discharge amount by these heaters, and a printhead in which a plurality of orifices having different discharge amounts are arranged in one element substrate.
Element substrates having a plurality of orifices for discharging different amounts of ink include an element substrate in which an orifice array (small-droplet orifice array) of orifices for discharging small ink droplets, and an orifice array (large-droplet orifice array) of orifices for discharging large ink droplets are juxtaposed. To achieve high-quality printing at high speed by this element substrate, there is proposed an element substrate in which the orifice arrangement density of a small-droplet orifice array is higher than that of a large-droplet orifice array. An example of this element substrate is one having a large-droplet orifice array in which 600 orifices are arranged per inch (arrangement density is 600 dpi), and a small-droplet orifice array in which 1,200 orifices double in number are arranged per inch (arrangement density is 1,200 dpi).
To stably discharge ink, a stable voltage needs to be applied to heaters. When all heaters are driven concurrently, a large current flows, and the voltage greatly drops owing to the wiring resistance. To solve this, there is a time-divisional driving method of dividing a plurality of heaters on an element substrate into a plurality of blocks, and sequentially driving heaters for the respective blocks time-divisionally to stably discharge ink. Examples of this element substrate are arrangements disclosed in the U.S. Pat. Nos. 6,409,315, 6,474,790, 5,754,201, 6,137,502, and 6,966,629, and Japanese Patent Laid-Open No. 2002-374163.
Recent inkjet printing apparatuses discharge small ink droplets to print a high-quality image. At the same time, these inkjet printing apparatuses need to increase the print speed. Simply forming the same image requires the same ink amount. Thus, if the discharged ink droplet is downsized to decrease the discharged ink amount to ½, the print speed simply decreases to ½.
To discharge the same ink amount in the same time in order to prevent a decrease in print speed, the number of heaters needs to be doubled. If the number of heaters is doubled without changing the heater arrangement density, the size of an element substrate in which heaters are arranged increases double or more. In addition to the increase in element substrate size, this also increases the size of the printhead which moves at high speed in the printing apparatus, the size of the printing apparatus, and vibrations and noise. To prevent these, the heater arrangement density needs to be increased.
To print at high speed, a printhead having orifices for discharging large ink droplets is more advantageous than one having only orifices for discharging small ink droplets. Recent inkjet printing apparatuses adopt a printhead having an element substrate in which a small-droplet orifice array and large-droplet orifice array are juxtaposed. These inkjet printing apparatuses achieve both high-speed printing and high-quality printing by selectively driving orifices for discharging small ink droplets and those for discharging large ink droplets. However, to implement both high-speed printing and high-quality printing, the numbers of orifices and heaters integrated on the element substrate need to be increased.
An element substrate in which the orifice arrangement density of a small-droplet orifice array is higher than that of a large-droplet orifice array will be described. As this element substrate, an element substrate including a large-droplet orifice array at an arrangement density of 600 dpi and a small-droplet orifice array with a double number of orifices at a double arrangement density of 1,200 dpi, which are arranged on a single substrate, will be exemplified. In this element substrate, when printing one pixel by one bit, the number of heaters directly equals the number of bits of print data. The data amount necessary for the orifice array at the arrangement density of 1,200 dpi is double the data amount necessary for the orifice array at the arrangement density of 600 dpi.
As an example of the time-divisional driving method, the time-divisional counts of respective orifice arrays on an element substrate are sometimes set equal to each other. Since a common clock is used within the element substrate, the clock frequency is the same. For this reason, the data transfer speed is proportional to the number of bits in a shift register used to transfer data. Data is transferred for each orifice array, so the time taken for data transfer differs between a high-density orifice array and a low-density orifice array. For example, assume that the number of bits in a shift register corresponding to an orifice array made up of a relatively small number of orifices is 6 bits (4 bits for print data and 2 bits for block control data). Also assume that the number of bits in a shift register corresponding to an orifice array made up of a relatively lager number of orifices is 10 bits (8 bits for print data and 2 bits for block control data). In this case, even the data transfer speed for the 6-bit shift register is limited by that for the 10-bit shift register. Therefore, the 6-bit shift register transfers data at 6/10 of the original data transfer speed.
There is also a method of increasing the frequency of a clock for transferring print data in order to print at high speed. In general, the clock is supplied from the printing apparatus main body to the printhead. The printhead which moves during printing, and the printing apparatus main body are connected by a relatively long cable such as a flexible cable. Since this cable contains plural signal lines and current supply lines, noise is readily superposed on signals transmitted through the cable. The inductance component of the cable delays the rise and fall of the pulse waveform (distorted waveform). This becomes non-negligible because, as the clock cycle shortens, the ratio of fluctuations becomes relatively high. Thus, the printhead may malfunction. When a signal is transmitted using a high-frequency clock, the cable may function as an antenna to generate radiation noise. The radiation noise may cause the malfunction of a peripheral device.
Accordingly, the present invention is conceived as a response to the above-described disadvantages of the conventional art.
For example, a print element substrate including a plurality of print element arrays in which print elements are arranged at different arrayed densities according to this invention is capable of suppressing a decrease in the driving speed of a high-density print element array and efficiently transferring data to each print element.
According to one aspect of the present invention, preferably, there is provided a print element substrate comprising: a first print element array having a plurality of print elements; a second print element array having a plurality of print elements; a first driving circuit which divides the plurality of print elements included in the first print element array into a predetermined number of groups and time-divisionally drives print elements belonging to each group; a second driving circuit which divides the plurality of print elements included in the second print element array into a number of groups larger than the predetermined number of groups, and time-divisionally drives print elements belonging to each group; a first shift register circuit which holds data for driving the print elements belonging to the first print element array; a second shift register circuit and a third shift register circuit which divide a plurality of groups forming the second print element array into at least a first group set and a second group set, and hold data for driving the print elements belonging to each group set; and a signal line which transfers an externally input signal to each of the first shift register circuit, the second shift register circuit, and the third shift register circuit.
According to another aspect of the present invention, preferably, there is provided an inkjet printhead, having the above print element substrate, for printing by discharging ink.
According to still another aspect of the present invention, preferably, there is provided a printing apparatus having a carriage to which the above inkjet printhead can be attached.
The invention is particularly advantageous since data can be transferred to each print element efficiently in an element substrate including a plurality of print element arrays in which print elements are arranged at different arrayed densities.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Exemplary embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.
In this specification, the terms “print” and “printing” not only include the formation of significant information such as characters and graphics, but also broadly includes the formation of images, figures, patterns, and the like on a print medium, or the processing of the medium, regardless of whether they are significant or insignificant and whether they are so visualized as to be visually perceivable by humans.
Also, the term “print medium” not only includes a paper sheet used in common printing apparatuses, but also broadly includes materials, such as cloth, a plastic film, a metal plate, glass, ceramics, wood, and leather, capable of accepting ink.
Furthermore, the term “ink” (to be also referred to as a “liquid” hereinafter) should be extensively interpreted similar to the definition of “print” described above. That is, “ink” includes a liquid which, when applied onto a print medium, can form images, figures, patterns, and the like, can process the print medium, and can process ink. The process of ink includes, for example, solidifying or insolubilizing a coloring agent contained in ink applied to the print medium.
Furthermore, an element substrate (substrate for a printhead) in the description not only includes a simple substrate made of a silicon semiconductor, but also broadly includes an arrangement having elements, wires, and the like.
The expression “on a substrate” not only includes “on an element substrate”, but also broadly includes “on the surface of an element substrate” and “inside of an element substrate near its surface”. The term “built-in” in the invention not only includes “simply arrange separate elements on a substrate”, but also broadly includes “integrally form and manufacture elements on an element substrate by a semiconductor circuit manufacturing process or the like”.
<Inkjet Printing Apparatus>
A printing apparatus capable of mounting a printhead including an element substrate according to the present invention will be explained.
In the inkjet printing apparatus (to be also simply referred to as a printing apparatus hereinafter) shown in
The carriage 102 is guided and supported reciprocally along guide shafts 103, which elongates in a main scanning direction, provided to the printing apparatus main body. A carriage motor 104 drives the carriage 102 via a driving mechanism including a motor pulley 105, associate pulley 106, and timing belt 107. Further, the carriage motor 104 controls the position and movement of the carriage 102. The carriage 102 includes a home position sensor 130. When the home position sensor 130 on the carriage 102 passes through the position of a shielding plate 136, it can detect the position.
An auto sheet feeder (ASF) 132 feeds printing media 108 such as a printing paper or a plastic thin film separately one by one as a feed motor 135 rotates a pickup roller 131 via a gear. As a conveyance roller 109 rotates, the printing medium 108 is conveyed (sub-scanned) via a position (printing portion) facing the orifice surface of the head cartridge H1000. The conveyance roller 109 rotates via a gear as a conveyance motor 134 rotates. When the printing medium 108 passes through a paper end sensor 133, the paper end sensor 133 determines whether the printing medium 108 has been fed, and finalizes the start position upon paper feed. The paper end sensor 133 is also used to detect the actual position of the trailing end of the printing medium 108 and finally detect the current print position from the actual position of the trailing end.
A platen (not shown) supports the lower surface of the printing medium 108 to form a flat printing surface at the printing portion. In this case, the head cartridge H1000 mounted on the carriage 102 is held so that the orifice surface extends downward from the carriage 102 and becomes parallel to the printing medium 108 between the pair of two conveyance rollers.
The carriage 102 supports the head cartridge H1000 so that the orifice arrangement direction of the printhead coincides with a direction perpendicular to the scanning direction of the carriage 102. The head cartridge H1000 discharges liquid from orifice arrays to print.
<Control Arrangement>
A control arrangement for executing printing control of the above-described inkjet printing apparatus will be explained.
Referring to
The operation of this control arrangement will be explained. When a print signal is input to the interface 1700, it is converted into print data between the gate array 1704 and the MPU 1701. Then, the motor drivers 1706 and 1707 are driven. At the same time, the printhead 3 is driven in accordance with the print data sent to the head driver 1705, thereby printing.
<Head Cartridge>
<Element Substrate>
An element substrate according to the present invention will be explained.
Referring to
The clock input terminal 1107 receives clocks CLK by the number of bits of print data stored in the shift register 1104. Data is transferred to the shift register 1104 in synchronism with the leading edge of the clock CLK. Print data DATA for turning on/off each heater 1101 is input from the print data input terminal 1106.
An element substrate in which the number of bits of print data stored in the shift register 1104 is equal to that of heaters and that of power transistors for driving heaters will be explained for descriptive convenience. Pulses of the clock CLK are input by the number of heaters 1101, and the print data DATA is transferred to the shift register 1104. Then, the latch signal LT is input from the latch signal input terminal 1108, and the latch circuit 1103 latches print data corresponding to each heater. The switch 1109 is turned on for an appropriate time. Then, a current flows through the transistor 1102 and heater 1101 via the power supply line 1105 in accordance with the ON time of the switch 1109. The current flows into the GND line 1110. At this time, the heater 1101 generates heat necessary to discharge ink, and the orifice of the printhead discharges ink in correspondence with print data.
A time-divisional driving method for an element substrate which drives heaters using a shift register in which the number of bits is smaller than that of heaters will be explained with reference to
For example, when dividing all the heaters of a single heater array into N (N=2n: n is a positive integer) blocks and driving them time-divisionally (in N time division), every N adjacent heaters in a single heater array belong to one group. Assume that the heater array includes m groups (the total number of heaters of this heater array is N×m). Data input to the shift register 1104 are block control data for selecting a block, and print data for the block. In
A decoder 1203 receives block control data, and each AND circuit 1201 receives a block selection signal which is generated by the decoder 1203 on the basis of the block control data. The AND circuit 1201 builds the driving circuit of the heater 1101. The AND circuit 1201 is arranged in correspondence with each heater 1101. The number of bits of block control data necessary for N-time-divisional driving is n. Hence, m-bit print data and n-bit block control data are input from the print data input terminal 1106. Thus, the number of bits in the shift register 1104 and latch circuit 1103 is (n+m) bits. In this element substrate, to drive all the heaters of a hater array once, the gate array 1704 inputs, N times, (n+m)-bit data formed from print data and block control data. A heater driving signal in one-to-one correspondence with a heater is generated based on a print data signal based on the print data, a block selection signal based on the block control data, and a heat enable signal input from a heat enable signal input terminal 1202. The generated heater driving signal drives a corresponding heater.
<Method of Manufacturing Element Substrate and Printhead>
A method of manufacturing an element substrate according to the present invention and a printhead including the element substrate will be explained for a part associated with the present invention.
To supply ink to each orifice 1132, an ink supply port 1121, which is a long groove-like through hole with a surface inclined from the lower surface to upper surface of the element substrate, is formed by anisotropic etching using the crystal orientation of the Si wafer.
The element substrate having this structure can build a head cartridge by connecting the ink supply port 1121 and a channel member for guiding ink to the ink supply port 1121, and combining them with a container which stores ink. Particularly when the head cartridge is configured by combining containers which store inks of a plurality of colors, and element substrates for the respective colors, color printing can be performed using this head cartridge.
<Driving Circuit in Element Substrate>
Several embodiments of a heater array and shift register in the element substrate according to the present invention will be explained below in detail.
Element substrates in the following embodiments are those for an inkjet printhead. In these element substrates, a plurality of heater arrays each including a plurality of heaters are arranged along the ink supply port 1121. More specifically, each element substrate includes a heater array (first print element array) made up of a relatively large number of heaters serving as print elements, and a heater array (second print element array) made up of a relatively small number of heaters as printing elements. In the following embodiments, both the number of heaters (number of print elements) and the heater arrayed density differ between heater arrays to clarify features of the present invention. However, the present invention is also applicable to a case where the heater arrayed density is equal and only the number of heaters differs between heater arrays.
The element substrates shown in
In the element substrates shown in
Each heater array in the element substrates of
The element substrate according to the first embodiment shown in
In the element substrate of the first embodiment, a heater array in which heaters are arranged at low density includes four groups G0, G1, G2, and G3 each made up of four adjacent heaters, as shown in
Two shift registers are arranged in correspondence with the heater array in which heaters are arranged at high density. One shift register is arranged in correspondence with the heater array in which heaters are arranged at low density. The printhead includes signal lines each having a terminal 1106 for inputting data. The printhead uses a common clock signal line 1107. The shift register is configured by successively arraying circuit elements with the same arrangement by the number of data bits to be stored. A circuit which corresponds to one data signal and is configured by successively arraying circuit elements with the same arrangement will be defined as a shift register circuit.
Next, a latch circuit 1103c shown in
In the element substrate, a driving circuit (not shown) for each heater array receives a print data signal based on print data and a block selection signal based on block control data. The shift register corresponding to the heater array in which heaters are arranged at low density holds 6 bits, as shown in
Each of the shift registers 1104a and 1104b corresponding to the heater array in which heaters are arranged at high density holds 5 bits, as shown in
A decoder 1203b receives the block control data B0 and B1, generates control data of 4 bits, and outputs them to the respective groups. In accordance with the control data, one heater is selected from the four heaters of each group.
That is, two shift register circuits are arranged for a high-density heater array, and include independent data signal lines.
The data generation unit 1800 generates print data D0 to D7 of 8 bits used in the heater array. Although not described in detail, the data generation unit 1800 generates column binary data when data buffered in the print buffer are raster multilevel data. The data generation unit 1800 buffers the generated data (print data D0 to D7 and block control data B0 and B1) in a buffer 1800A. A latch circuit 1802 latches the block control data B0 and B1 among the buffered data.
Latch circuits 1803 and 1804 latch the print data D0 to D7. More specifically, the latch circuit 1803 latches the print data D5 to D7, and the latch circuit 1804 latches the print data D0 to D4. A data coupling unit 1801 couples outputs from the latch circuits 1802 and 1803. The data coupling unit 1801 holds a total of 5 bits: the print data D5 to D7 and block control data B0 and B1.
The transfer unit 1900 includes a transfer buffer 1900A which buffers data to be transferred to the shift register 1104a, and a transfer buffer 1900B which buffers data to be transferred to the shift register 1104b. Each of the transfer buffers 1900A and 1900B transfers 5-bit data. This arrangement generates data to be transferred to the printhead.
This arrangement contributes to reducing the difference between the number of data bits held in one shift register circuit corresponding to a heater array in which heaters are arranged at low density, and the number of data bits held in each of two shift register circuits corresponding to a heater array in which heaters are arranged at high density. It is also possible to make, equal to each other, the number of data bits held in two shift register circuits corresponding to a heater array in which heaters are arranged at high density, and the number of data bits held in one shift register circuit corresponding to a heater array in which heaters are arranged at low density.
The data transfer speed difference becomes smaller as the numbers of data bits held in all shift register circuits come closer to each other. This prevents an excessively low data transfer speed to a heater array in which heaters are arranged at high density, compared to a data transfer speed to a heater array in which heaters are arranged at low density. In the first embodiment, one of two shift register circuits corresponding to the heater array in which heaters are arranged at high density holds block control data. The other shift register circuit holds not block control data but only print data.
The element substrate in
In the element substrate of the second embodiment, as for a heater array in which heaters are arrayed at high density, the arrangement positions of terminals for inputting print data and block control data, and those of shift registers with respect to the heater array in the element substrate are different from those in the element substrate of the first embodiment. In the element substrate of the first embodiment, terminals for inputting print data and block control data, and shift registers are arranged at one end of the element substrate in the longitudinal direction (print element-arrayed direction of the print element array). To the contrary, in the element substrate of the second embodiment, terminals for inputting print data and block control data, and shift registers are arranged at the two ends of the print element array. For example, shift registers 1104a and 1104b are arranged at the two ends of a heater array L1. Each shift register has an independent data input line, similar to the first embodiment.
In the element substrate of the second embodiment, two shift registers corresponding to a heater array in which heaters are arrayed at high density are not 5-bit shift registers. One shift register is a 4-bit shift register which holds 4 bits out of 8-bit print data. The other shift register is a 6-bit shift register which holds 4-bit print data and 2-bit block control data.
The element substrate in the second embodiment prevents a decrease in data transfer speed to a heater array in which heaters are arranged at high density. Further, the element substrate is downsized by increasing the layout efficiency of the element substrate. In an element substrate employing the time-divisional driving method, as many print data signal lines as groups run from a shift register to a heater array. Thus, the element substrate in the second embodiment requires a wiring area for laying out eight print data signal lines for a heater array in which heaters are arranged at high density. In the element substrate of the second embodiment, eight print data signal lines are divided into two each for four adjacent groups. The two sets each of four lines are respectively connected to shift registers arranged at the two ends of the element substrate in the longitudinal direction. In this manner, a wiring area required for eight print data signal lines substantially fall within that required for four lines. One shift register further holds 2-bit block control data. As a result, the wiring area of print data signal lines which connect a heater array and a shift register decreases. This contributes to decreasing the interval between ink supply ports 1121. Particularly, this results in decreasing the area of an element substrate having many ink supply ports.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2008-122773, filed May 8, 2008, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2008-122773 | May 2008 | JP | national |
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