Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings.
A print head 105 is detachably attached to a carriage 104 that moves along a guide shaft 103. The print head 105 ejects, while moving in the main scanning direction, ink droplets through a plurality of ejection openings based on a printing signal. As a result, the print medium 102 is printed in an amount corresponding to one print scanning operation. After the print scanning operation has performed the print medium 102 is transported in the sub-scanning direction in an amount corresponding to the printing width of the print head 105. By alternately repeating such print scanning operation and transportation, an image is sequentially formed on the print medium 102.
It is noted that ink ejected from the print head 105 is supplied from an ink supply apparatus (not shown) fixed in the apparatus. Although not shown, the apparatus also includes a print medium supply means for supplying a not-yet-printed print medium 102 to the pair of paper feed rollers 101 and a print medium discharge means for discharging a printed print medium. Furthermore, a recovery means for performing a maintenance processing of the print head 105 and a preparatory auxiliary means for example are also preferred in order to stably provide an effect of the present invention. These means may include, for example, a capping means for capping an ejection opening face of a print head, a cleaning means for cleaning such as foreign matters at a discharge opening face, a means for pressurizing or sucking the interior of the ejection opening, or a means for receiving ink ejected in a preparatory manner.
A print medium generally may be a plain paper or a paper exclusively used for an ink jet printer but also may be, for example, a sheet made of a different material (e.g., OHP sheet, compact disc). Furthermore, in the case of a DNA chip manufacture apparatus or a display manufacture apparatus using an ink jet printing method, a substrate consisting of an appropriate material corresponds to a print medium in the present invention.
A host apparatus 704 connected to the printing apparatus from outside is a supply source of image data. The host apparatus 704 may be a computer that prepares data for printing (e.g., image) or performs a processing for example and also may be a reading unit for reading image for example. Image data, a command, a status signal or the like is transferred between the host apparatus 704 and the CPU 700 via an interface (I/F) 701.
A head driver 709 is a driver that drives, based on print data for example, an electrothermal conversion body (heater) of the print head 105. The head driver 709 has: a shift register for arranging print data to correspond to a position of an electrothermal conversion element; a latch circuit for latching with an appropriate timing; and a logic circuit element for operating the electrothermal conversion element in synchronization with a drive timing signal.
The print head 105 includes obtaining means 708 for obtaining a temperature of ink near the heater (a temperature sensor for detecting the temperature of ink, for example) and a sub heater 707 for heating the print head until an appropriate temperature is reached. The sub heater 707 is provided for a temperature adjustment purpose in order to provide a stabilized ink ejection characteristic. The sub heater 707 may be formed on a substrate of a print head together with an electrothermal conversion element or also may be attached to a body of the print head 105. The obtaining means 708 may be a configuration obtaining temperature information of ink inside of the print head instead of the temperature information of ink mentioned above.
A carriage motor driver 711 is a motor for driving a carriage motor 710 that provides a transfer force of the carriage 104. A conveying motor driver 713 is a driver for driving a conveying motor 712 that provides a power to rotate the paper feed rollers 101.
The following section will describe a driving control method as a characteristic of the present invention.
When the heater is driven based on any of the tables, an ink ejection volume substantially linearly uprise with a rate of about 0.4(P1)/10 degrees to the temperature T (detected temperature). Specifically, when a driving control is performed based on only one table, an ink ejection volume rises by about 0.4 pl with an increase of a detected temperature of 10 degrees. According to the printing apparatus of this embodiment, it was confirmed that a very small problematic image is caused if fluctuation of an in ejection volume is equal to or lower than 0.2 pl. Based on this, this embodiment has prepared a plurality of pulse tables different in an ink ejection volume of about 0.2 Pl for a single temperature so that these pulse tables are switched whenever the detected temperature T increases by 5 degrees. When such a PWM control is employed and the detected temperature T gradually rises from T1, a table switching is performed to draw a locus as shown by the thick arrow. By doing this, an ink ejection volume can be maintained within a control range width (from about 4.5 pl to 4.7 pl) regardless of the detected temperature T.
When the PWM control is performed with a fixed driving voltage, the temperature T at which a preheat pulse width is 0 is an upper limit of a controllable temperature. For example, when a driving voltage Vop is 20.5V, 60 degrees is an upper limit of a controllable temperature. Thus, this embodiment prepares, in addition to the five tables tb11 to tb15 having a driving voltage of 20.5V, new PWM control tables tb21 to tb26 having a driving voltage of 24.0V to further uprise the upper limit of a controllable temperature.
In this case, with regards to a temperature close to a temperature at which a driving voltage is switched (60 degrees), two tables (tb11 and tb26) are prepared to correspond to two driving voltages (20.5V and 24.0V) and a region is provided at which PWM driving control ranges are overlapped so that any of the driving voltages can be used.
The existence of such an overlapped region is a characteristic of the present invention. It is effect of the invention that, when a temperature covered by an overlapped region is detected, a convenient table can be selected from among the tables.
Generally, a head temperature tends to be increased during a print scanning operation. Thus, when Tmax>60 degrees is determined at the Step S702, the head may have a temperature exceeding 60 degrees during the subsequent print scanning operation with a high probability, even when the head at the previous print scanning operation has a temperature equal to or lower than 60 degrees. In such a case, when a driving voltage at the start of a print scanning operation is set as Vop1 (i.e., 20.5V), a voltage must be changed during a print scanning operation. However, when an overlapped region with a certain amount is provided at a temperature close to the switching temperature 60 degrees as in this embodiment, a driving voltage of Vop2 (i.e., 24.0V) can be set even when the then detected temperature is lower than 60 degrees. Even when the subsequent print scanning causes a head temperature exceeding 60 degrees, an ink ejection volume can be controlled without changing the driving voltage.
Although the above section has determined a driving voltage for the subsequent print scanning operation based on the highest temperature Tmax detected during the previous print scanning, a driving voltage can be determined in consideration of various parameters. For example, a temperature rise can be predicted based on the number of ink ejections during the subsequent print scanning to determine, based on the predicted result, a driving voltage for the subsequent print scanning. In this case, the number of dot (or data amount) may be counted in advance.
By the PWM driving control in two steps as described above, the printing apparatus of this embodiment can control an ink ejection volume within a range of the detected temperature T of 35 degrees<T<75 degrees (see
In this embodiment, a print head is heated by the sub heater 709 when the detected temperature T has a relation of T<35 degrees and no printing operation is performed until T≧35 degrees are established. However, a method for heating a print head is not limited to this. For example, another method also may be used in which the respective heaters are applied with a short pulse not causing ink ejection to heat ink. When the detected temperature T has a relation T>75 degrees on the other hand, a printing operation is stopped immediately to wait for a relation of T<75 degrees.
Hereinafter, the second embodiment of the present invention will be described. The second embodiment also uses the ink jet printing apparatus shown
Generally, in a print head including a plurality of chips, a different temperature is detected among each chip depending on an ejecting frequency of each chip.
In such a case, when a driving voltage is set based on the flowchart described with reference to
It is noted that, although the above embodiment has prepared two types of PWM tables as shown in
As described above, by setting a further wider overlapped region of different PWM driving control ranges, a PWM control (head driving control) can be more appropriately realized when a difference in the detected temperature between chips is significant or when a temperature change between print scanning operations is different among chips. Even when a significant temperature change width is anticipated in a single print scanning operation, a PWM control by the same driving voltage can be realized in the single print scanning. In other words, even when a temperature change is significant in the print scanning, the time at which a driving voltage is switched can be reduced.
In addition,
Although the above embodiment has described a control of an ink ejection volume by two PWM controls based on two driving voltages of Vop1 of 20.5V and Vop2 of 24.0V, the present invention also can be applied to a PWM driving control based on three or more driving voltages. In this case, the overlapped region as described above is preferably provided in each of a plurality of regions for which a driving voltage is switched.
Although the above embodiment has described a driving pulse having a so-called double pulse shape, the invention also can be applied to a single pulse or one table also can include a double pulse and a single pulse.
In the above embodiment, different threshold values also can be used for a switching from Vop1 to VoP2 and a switching from Vop2 to Vop1.
By providing an overlapped region to two PWM control ranges as shown in
Although the above embodiment has exemplarily described the serial-type ink jet printing apparatus in which a main scanning by a print head and the transportation of a print medium are alternately performed to form an image, the present invention is not limited to such an embodiment. The present invention also can be applied to a full line type ink jet printing apparatus in which nozzles of a print head are arranged in accordance with a printing width of a print medium. The full line type ink jet printing apparatus prints an image for one page by ejecting ink from the respective nozzles of the print head with a predetermined frequency while transporting a print medium in a sub-scanning direction. Thus, by assuming that one print scanning operation of the above-described serial type printing apparatus corresponds to a print operation for one page by the full line type printing apparatus, the pulse table shown in
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. 2006-157664, filed Jun. 6, 2006, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
---|---|---|---|
2006-157664 | Jun 2006 | JP | national |