1. Field of the Invention
The present invention relates to a printing apparatus and a temperature detection method. Particularly, the present invention relates to a temperature detection method of detecting the temperature in an inkjet printhead while scanning the printhead in a printing apparatus which mounts the printhead.
2. Description of the Related Art
These days, a printing apparatus typified by a printer is prevalent, and is required to attain high-speed printing, high-resolution printing, and low-noise operation as a general trend. An inkjet printing apparatus is widely prevailing as an inexpensive product which meets these requirements. In the inkjet method, ink droplets are discharged from the orifice of a printhead so that they adhere to a printing medium such as paper, thereby printing. Hence, the inkjet method can not only relatively easily attain, for example, high-speed printing, but also relatively stably print an image on the printing medium with little ink nonuniformity because printing is performed while the printhead and the printing medium do not contact with each other.
The arrangement of an inkjet printhead (to be simply referred to as a printhead hereinafter) and a method of driving it will be described herein with reference to
Therefore, a data signal having a total of 20 bits including a printing data signal having 16 bits d0 to d15 corresponding to 16 nozzles, and a signal having 4 bits BLE0 to BLE3 indicating the driving block numbers is transferred from the printing apparatus main body to the printhead for each block. Transfer data H_DATA is transferred using the two edges of a pulse signal having a transfer clock H_CLK, and a latch signal H_LAT of the transfer data is sent. A heat enable signal H_ENB for driving each heater is also sent.
In this case, nozzle columns are assumed to be driven in the order of driving blocks “0” to “15”, for the sake of descriptive convenience. Therefore, first, transfer data H_DATA are serially transferred in synchronism with a transfer clock H_CLK, and sequentially held in the shift register 401 in the printhead. Next, the transfer data H_DATA are latched by the latch circuit 402 in accordance with a data latch signal H_LAT. Of the latched, 20-bit transfer data signal, 4 bits are decoded by the decode circuit 403 to generate a block enable signal, so a predetermined block enable signal, printing data signal, and heat enable signal are input to each AND gate. Only when these three signals input to each AND circuit are all valid, a transistor corresponding to this AND circuit is turned on to drive a corresponding heater, thereby discharging ink.
At the timing at which driving block “0” is actually driven, data is transferred to driving block “1”. This operation is repeated to drive 256 heaters corresponding to 16 driving blocks. Then, ink is continuously discharged with respect to the direction in which the printhead is scanned, thereby forming an image in the scanning region.
In a printhead which discharges ink using a heater, the ink discharge amount is known to change with a change in head temperature and, more specifically, ink temperature. When the ink discharge amount changes, dots having different diameters are formed by ink droplets adhering on the printing medium, resulting in a density difference albeit very small. In the case of serial printing, this density difference occurs from the printing start position in the direction in which the printhead is scanned to the printing end position in this direction, as shown in
When, for example, a set of printing data have the same value, ideally no density difference occurs from the printing start position to the printing end position, as shown in
Hence, to suppress such a change in ink discharge amount due to a rise in head temperature, Japanese Patent Laid-Open No. 5-31905, for example, proposes an approach of applying a double-pulse to the printhead in one ink discharge operation and controlling, for example, the pulse width of the pre-pulse (performing its preheat control). This pulse control is based on the head temperature, so the temperature in the printhead is obtained by employing an arrangement, as shown in
In the arrangement shown in
In such an arrangement, to print with higher image quality, pulse control for driving the printhead is desirably performed in real time in response to a change in head temperature as much as possible. However, when the printhead 302 and the printing apparatus main body 301 are connected to each other via a flexible cable, the signal output from the head temperature sensor 310 suffers from crosstalk due to, for example, a data transfer clock, a transfer data signal, a latch signal, and a heat enable signal. As a result, induced noise is mixed with the signal output from the head temperature sensor 310, thus making it difficult to obtain a precise head temperature during printing scanning of the printhead.
To solve this problem, a method as disclosed in Japanese Patent Laid-Open No. 2002-264305, for example, has conventionally been proposed. That is, a sample-hold signal is provided to each of a plurality of printheads mounted in a printing apparatus to discriminate based on the sample-hold signal whether or not a driving pulse is applied to each printhead, upon detecting the temperature in the printhead. By outputting temperature measurement data to the printing apparatus main body at the timing at which a driving pulse is applied to none of the printheads, the temperature is obtained free of the influence of crosstalk resulting from a control signal.
Since the above-mentioned prior art method obtains the temperature at the timing at which a driving pulse is applied to none of the plurality of printheads, the temperature can actually be obtained at three timings shown in
Accordingly, the present invention is conceived as a response to the above-described disadvantages of the conventional art.
For example, a printing apparatus and a temperature detection method according to this invention are capable of precisely obtaining the temperature in a printhead free of the influence of a signal transferred to the printhead, without slowing down the printing speed.
According to one aspect of the present invention, there is provided a printing apparatus comprising: a printhead including a plurality of printing elements and a temperature sensor; a driving unit configured to divide the plurality of printing elements into a plurality of blocks to print on a printing medium and perform division driving of the plurality of printing elements for each block; an A/D converter configured to A/D-convert an analog temperature data signal output from the temperature sensor; a division unit configured to divide one printing period of the printhead, which is determined by a driving frequency of the printhead, into an active period required for the division driving, and an inactive period required for A/D conversion by the A/D converter; a transfer unit configured to transfer a signal required to drive the printhead to the printhead in the active period; and a reading unit configured to read a digital signal obtained by A/D-converting, by the A/D converter, the temperature data signal output from the printhead in the inactive period.
According to another aspect of the present invention, there is provided a temperature detection method for a printing apparatus which includes a printhead including a plurality of printing elements and a temperature sensor, and divides the plurality of printing elements into a plurality of blocks to print on a printing medium while performing division driving of the plurality of printing elements for each block, comprising: dividing one printing period of the printhead, which is determined by a driving frequency of the printhead, into an active period required for the division driving and an inactive period required for an A/D converter to A/D-convert an analog temperature data signal output from the temperature sensor; transferring a signal required to drive the printhead to the printhead in the active period; and reading a digital signal obtained by A/D-converting, by the A/D converter, the temperature data signal output from the printhead in the inactive period.
The invention is particularly advantageous since one printing period is divided into an active period in which a driving signal of a printhead is transferred and an inactive period in which no driving signal of the printhead is transferred, and a head temperature signal is obtained in the inactive period, thus making it possible to precisely obtain the head temperature free of the influence of crosstalk resulting from the driving signal. The invention is also advantageous since the active period and the inactive period are specified from the driving frequency of the printhead, thereby obtaining the temperature in the printhead with neither an influence on the printing speed nor a slowdown in printing speed.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
An exemplary embodiment 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 include 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, the term “printing element” is a generic term used to refer to an element which produces energy for an orifice, a liquid channel which communicates with it, and ink discharge.
As shown in
Also, in the printing apparatus, four ink cartridges 3a, 3b, 3c, and 3d which store magenta (M), cyan (C), yellow (Y), and black (K) inks, respectively, are mounted on the carriage 2, as shown in
At the time of printing, a printing medium 12 such as a printing paper sheet is fed via a paper feed mechanism (not shown), it is conveyed to the printing position by a conveyance roller 4, and ink is discharged from the printhead 1 onto the printing medium 8 at this printing position, thereby printing. Reference symbol F denotes the direction in which the printing medium 8 is conveyed. A plurality of nozzles are provided, as shown in
Note that the printhead 1 adopts the inkjet method of discharging ink utilizing thermal energy. Hence, the printhead 1 includes electrothermal transducers (heaters). This electrothermal transducer is provided in correspondence of each orifice, and a pulse voltage is applied to a corresponding electrothermal transducer in accordance with a printing signal, thereby heating and discharging ink from a corresponding orifice.
Referring to
Reference numeral 105 denotes a driving timing control unit which performs position and speed control in the direction in which the printhead 1 is scanned, timing control for generating printing data, and timing control for driving the printhead 1, based on an externally input encoder signal. Reference numeral 106 denotes a motor control unit which drives the carriage motor that scans the carriage 2 mounting the printhead 1, based on a timing signal generated by the driving timing control unit 105. Reference numeral 107 denotes a head control unit which performs, for example, transfer control of printing data transferred to the printhead 1, distributed drive control and heat pulse control for head driving, and temperature acquisition timing control.
Reference numeral 108 denotes a head temperature detection unit which obtains an output from an A/D converter 109 at a predetermined timing based on a timing signal input from the head control unit 107. The temperature in the printhead 1 is obtained by amplifying, by an amplifier (AMP) 110, an analog output from a temperature sensor 111 in the printhead 1, inputting the amplified analog signal to the A/D converter 109, and reading, by the CPU 101, the value of a digital signal obtained by A/D conversion.
In this embodiment, one column period is equally divided by the sum of the number of driving blocks and the number of blocks corresponding to the time required to obtain the temperature, thereby defining an active period in which a head control signal is driven, and an inactive period in which no head control signal is driven. In the inactive period, a head temperature acquisition timing is generated to obtain the head temperature.
Referring to
Reference numeral 203 denotes a driving block count register serving as a setting resister which sets the number of blocks used to drive one column. The value set in the driving block count register 203 is uniquely determined by the printhead 1. Reference numeral 204 denotes a period management block which generates one column period using a specific number of division blocks by referring to the driving block count register 203, based on the signals H_WIN and H_LAT input from the driving timing control unit 105, and the setting of the division block count register 201. The period management block 204 manages one column period by dividing it into the period in which the printhead 1 is driven (the number of driving blocks), and the period in which the printhead 1 is not driven (the number of blocks obtained by subtracting the number of driving blocks from the number of division blocks). Reference numerals 205a to 205d denote driving block counters which manage the active period and the inactive period for each nozzle column; and 206a to 206d, data transfer blocks which control transfer of printing data for each nozzle column based on the information provided by the driving block counters 205a to 205d, respectively.
Reference numeral 207a to 207d denote heat pulse generation blocks which control heat enable signals for each nozzle column based on the information provided by the driving block counters 205a to 205d, respectively. Reference numeral 208 denotes an A/D reception timing control block which performs timing control for controlling temperature acquisition in the inactive period based on the information provided by the period management block 204. Reference numeral 209 denotes an A/D trigger generation block which generates a trigger signal for triggering the A/D converter 109 to perform A/D conversion, and that for DMA-transferring data from the A/D converter 109, based on a timing signal from the A/D reception timing control block 208. Reference numeral 210 denotes an A/D value storing register which stores data received from the A/D converter 109. Reference numeral 211 denotes a DMA controller which DMA-transfers temperature data stored in the A/D value storing register 210 to the temperature acquisition data storage area of the RAM 103 using a signal input from the A/D trigger generation block 209 as a trigger.
This inactive period is sufficient to allow the A/D converter 109 to perform A/D conversion. However, if the driving frequency of the printhead 1 changes, the number of blocks to be assigned to the inactive period must change as well, so the number of divisions and the number of blocks to be assigned to the inactive period are set in the register to make them variable.
In this embodiment, “18” is set in the division block count register 201, and “16” is set in the driving block count register 203. The period division block 202 obtains one column period from an input encoder signal, and equally divides this column period into 18 blocks to generate a signal H_LAT, in accordance with the setting of the division block count register 201. The period management block 204 divides one column period having 18 blocks into an active period corresponding to 16 blocks and an inactive period corresponding to two (2) blocks with reference to nozzle column C based on the signals H_WIN and H_LAT for each nozzle column, and manages it. Note that this management is not limited to the above-mentioned values, and a modification in which 18 blocks are divided into an active period corresponding to 17 blocks and an inactive period corresponding to one block may also be adopted.
At this time, a signal AD_ENB is asserted in the inactive period. Since no head control signal is driven in the period in which the signal AD_ENB is asserted, head temperature data can be detected free of the influence of noise. The values obtained by the driving block counters 205a to 205d in each nozzle column are incremented in the period in which a corresponding signal H_WIN is asserted, but are not updated in the period in which the signal AD_ENB is asserted because the latter period is an inactive period. The data transfer blocks 206a to 206d and heat pulse generation blocks 207a to 207d transfer neither data nor a driving control signal to the printhead 1 in the inactive period in which the signal AD_ENB is asserted.
Two methods of obtaining the head temperature in the inactive period will be described next with reference to
According to the first method, A/D conversion is executed by triggering the A/D converter 109 to perform A/D conversion only in an inactive period.
An arrangement which generates an interrupt signal so that the CPU 101 reads the value stored in the A/D value storing register 210 may be adopted, as a matter of course.
According to the second method, only a temperature data signal obtained by executing temperature measurement in an inactive period is received while always executing A/D conversion.
According to this embodiment, the above-mentioned first and second methods employ an arrangement which performs mode setting by register setting of the head temperature detection unit.
The first and second methods can also be executed in combination, as shown in
According to the above-mentioned embodiment, a temperature data signal from the temperature sensor of the printhead can be input to the printing apparatus main body at the timing at which neither a data signal nor a control signal is transferred to the printhead. Therefore, in a flexible cable which connects the printhead and the printing apparatus main body to each other, no noise derived from crosstalk generated upon signal transfer is mixed with a temperature data signal, thus allowing temperature control with high accuracy.
Also, by dividing one column period into blocks larger in number than division driving blocks by only a small number (two in this embodiment), and setting an operation of inputting a temperature data signal in the period between successive data signal transfer operations for each column, the temperature data signal can be obtained without slowing down the printing speed.
Another embodiment will be described next.
The full-line inkjet printhead 14 includes nozzles, the number of which corresponds to the width of the printing medium 8, as shown in
As a supplement to the description with reference to
As a supplement to the description with reference to
For example, a value which divides one raster period can be set in the division block count register 201. The division block count register 201 is referred to so as to divide one raster period, thereby generating a synchronization signal in the block period. Also, the printing start position and printing end position in the direction in which the printing medium is conveyed are set in the printing region setting register 212. The number of blocks used to drive one raster is set in the driving block count register 203.
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. 2010-285169, filed Dec. 21, 2010, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2010-285169 | Dec 2010 | JP | national |