Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-04-26
2003-06-24
Nguyen, Thinh (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S014000, C347S197000
Reexamination Certificate
active
06582045
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a printing apparatus and to a method of controlling printing in the printing apparatus. More particularly, the invention relates to an ink-jet printing apparatus for ejecting ink by utilizing thermal energy, and to a method of controlling printing by the printing apparatus.
BACKGROUND OF THE INVENTION
In a printer of the type which uses an ink-jet printhead to print images by ejecting ink, non-uniformity in the size of the ejected ink droplets leads to a decline in the quality of the printed image, which can also result from an attendant unevenness in density. Therefore, in order to perform high-quality printing, it is desirable that the size of the ink droplets be held constant at all times.
With a printhead of the type which causes ink to foam by heating the ink within the printhead so that the ink is ejected by the pressure produced, droplets of a constant size can be ejected by forming bubbles of a constant size.
If the energy introduced to a heater within the printhead is too low, the jetting of the ink may become unstable. If too much energy is introduced, the heater elements may deteriorate and burn out. In an arrangement where the ink is heated by a heater, therefore, it is vital that the amount of heat produced by the heater be held constant.
A heater board on which heater elements are formed is fabricated through a semiconductor manufacturing process. The circuit that drives these heater elements also is formed on the heater board through the same manufacturing process. The resistance value of a heater element fabricated by semiconductor film-forming techniques varies from one heater board to another depending upon the manufacturing lot. As a consequence, even if the voltage applied to the heater is constant, the heater driving electrical energy introduced to the heater will differ depending upon the resistance value of the heater when the resistance value exhibits the above-mentioned variation. In order for the energy introduced to the heater to be held constant irrespective of this disparity in the resistance value of the heater, it is required that the energy of the heat evolved be adjusted based upon the length of time over which current is passed through the heater.
The specification of Japanese Patent Application Laid-Open No. 10-95116 proposes means which corrects for this variation in heater resistance from one heater board to another. Specifically, a heater board on which a heater element is formed is provided with an element for sensing a variation in the resistance value of the heater, the information acquired from the sensing element is extracted, and a correction is applied by adjusting the driving pulse width, which is a condition of the driving signal applied to the printhead from the printer proper. As a result, the amount of heat evolved by the heater is rendered constant.
To deal with the higher density of driving elements, recent printhead heater boards are fabricated by a CMOS semiconductor manufacturing process in which the process steps are reduced to enable a reduction in cost. In accordance with this process, heaters and MOS transistors are serially connected and the MOS transistors are controlled so as to turn on the desired heaters. In this case, ON resistance, which is the value of resistance when a MOS transistor is turned on, also usually exhibits a variation on the order of several tens of percent.
In a case where a heater board is formed on a semiconductor wafer, the number of chips that can be manufactured from a single wafer can be increased by reducing the area of the heater board, thereby making it possible to raise the yield of manufacture. In terms of lowering cost, therefore, a MOS transistor of small area is preferred.
The ON resistance value of the MOS transistor should be sufficiently small in comparison with the resistance value of the heater in order to suppress the influence of resistance-value variation on energy applied to the heater. Lowering the ON resistance involves enlarging the gate width of the transistor, however, as a result of which the transistor occupies a greater area on the heater board. A transistor having such an area that will reduce the ON resistance value sufficiently is difficult to form on a heater board if it is desired to achieve the reduction in cost mentioned above. If the ON resistance value of a MOS transistor serially connected to a heater exhibits variation, the voltage drop across the MOS transistor will fluctuate and so will the voltage impressed upon the heater. If the resistance value of the heater exhibits variation, then the energy applied to the heater will fluctuate in similar fashion.
The specification of Japanese Patent Application Laid-Open No. 10-95116 proposes a method of sensing a variation in the ON resistance of a MOS transistor. A method of measuring the resistance value of a heater and the ON resistance of a MOS transistor according to this proposal is performed as set forth below.
As shown in the equivalent circuit of
FIG. 3
, a driving element fabricated with the same design and through the same process as those of a driving element provided on a heater board is disposed as an ON-resistance measurement element on individual heater boards constituting printheads. The ON-resistance measurement element is driven by a signal from a device external to the head, the ON resistance value is calculated from the relationship between applied current and measured voltage, and pulse width, which is a driving condition, is varied using a table that is set up beforehand on the side of the device. If this arrangement is adopted, the energy applied to an electrothermal transducer can be rendered constant from one head to another. If the energy is constant between heads, a uniform printing performance is obtained between heads and printing yield rises. This also eliminates rapid burn-out ascribable to deterioration of the heater element due to application of excessive energy. The end result is enhanced printhead reliability.
The ON resistance value generally is low (approximately 10&OHgr;). Accordingly, there are cases where the measurement precision (S/N ratio) of the ON-resistance measurement element, which serves as the driving element whose design is the same as that of the driving element of the electrothermal transducer, is unsatisfactory. In such case, however, it is possible to use an ON-resistance measurement element whose design is altered so as to improve measurement precision. It is required in such case that the relative value of amount of variation be kept unchanged. In the case of an NMOS transistor, this can be dealt with by changing the gate width.
As set forth in the specification of Japanese Patent Application Laid-Open No. 10-95116, it is also possible to adopt an arrangement in which an element for sensing a variation in sheet resistance value is fabricated on a heater board on which an electrothermal transducer is formed, with this element being provided along with the above-mentioned ON-resistance measurement element, as shown in FIG.
4
. Here two lines usually are required, namely a signal line from the ON-resistance measurement element and a signal line from the element that senses the variation in sheet resistance value. However, it is preferable to adopt an arrangement in which the signal line from the ON-resistance measurement element and the signal line from the sensing element are connected within the heater board so that a single signal line will suffice. Specifically, an arrangement should be adopted in which the signal line from the ON-resistance measurement element and the signal line from the sensing element are connected in parallel, as illustrated in FIG.
4
. By applying a certain signal, e.g., a clock selection signal, to the ON-resistance measurement element, the ON-resistance measurement element, namely the driving element, is turned on and off, whereby the ON resistance of the driving element and the sheet resistance of the electrothermal transducer can be extracted at a single external output termi
Canon Kabushiki Kaisha
Dudding Alfred E
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Thinh
LandOfFree
Printing apparatus and printing control method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Printing apparatus and printing control method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Printing apparatus and printing control method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3124127