Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2003-01-29
2004-11-16
Nguyen, Thinh (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S019000
Reexamination Certificate
active
06817690
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a printing apparatus and voltage control method, and more particularly, to a printing apparatus mounting a DC power source for driving an inkjet printhead on a head carriage substrate and a voltage control method.
BACKGROUND OF THE INVENTION
Conventionally, two types of printing apparatuses are known: A thermal transfer method type, and an inkjet method type, the latter involving the discharge of ink onto paper or some other printing medium so as to form text or images. Inkjet printing apparatuses, which are widely used as data output means such as printers, copiers, facsimile machines and the like, print by discharging ink while moving the relative positions of the printing medium and the inkjet printhead. As a result, controlling the relative speeds of the inkjet printhead and the printing medium, as well as controlling the timing of the ink discharge and stabilizing the supply of power to the printhead are crucial determinants of the quality of the final printed output.
Inkjet printing apparatuses are broadly divided into two types, depending on the shape of the inkjet printhead being used: the so-called serial type, and the full-line type. Of these, the serial type, which is the more widely used, prints by discharging ink while moving the inkjet printhead.
In addition, among printheads that discharge ink, there are those that use the action of a piezoelectric transducer to discharge the ink and those that use instantaneous film-boiling of the ink to discharge the ink. Those printheads that boil to discharge the ink send an electric current to a heater provided adjacent to an ink flow path at an ink discharge orifice and utilize the thermal energy generated by the current to boil the ink so as to provide the discharge energy.
In order to maintain the quality of the printed data, it is important to maintain a stable supply of energy with which to discharge the ink and further to ensure that the ink is discharged under uniform conditions so as to obtain ink droplets of uniform size and shape. However, in printing, the duty ratio changes depending on the print data, so the number of heaters activated simultaneously at any given time varies as well. As a result, the drive conditions fluctuate due to voltage fluctuations caused by differences in current output by the power source and drop voltage differences caused by resistance in the power supply sub-system.
Conventionally, such ink discharge control is executed in such a way as to satisfy stable discharge conditions by refining the accuracy of the power supply output voltage and by reducing the loss along the power supply sub-system.
In order to facilitate an understanding of the present invention, a description is first given of the DC/DC converter that supplies power to the printhead in an arrangement related to this invention.
FIG. 11
is a block diagram of a voltage control circuit that forms a part of a DC/DC converter carefully studied as an example when this invention was made. Note that this example is not well-known to an ordinarily skilled person in this art.
As shown in
FIG. 11
, an input voltage (V
in
) to the DC/DC converter that is supplied from a power supply unit (not shown in the diagram) is input to a switching element
201
. A DC output converted by the switching element
201
and a diode
209
is output via an inductor
202
and is supplied as output voltage (VH-b) to the printhead, which is the load. A first condenser
203
is coupled to the DC side of the switching element
201
and a second condenser
204
is coupled to the AC side of the switching element
201
, with the inductor
202
and the second condenser
204
forming a smoothing circuit
205
.
The output voltage signal (VH-b) detected at the output terminal of the smoothing circuit
205
is divided by a first resistance R
1
and a second resistance R
2
at a voltage control circuit
206
and input to the negative (−) terminal of a differential amplifier
207
that forms the voltage control circuit
206
and is used for feedback control. An output signal (V ref′) from the differential amplifier
207
that inputs both the electric potential achieved by voltage-dividing the reference voltage (V ref) by a third resistance R
3
and a fourth resistance R
4
and the divided voltage of the above-described output voltage signal (VH-b) becomes the output signal of the voltage control circuit
206
, and controls the switching element
201
through a PMW gate drive circuit
208
so as to execute constant voltage control.
It should be noted that a fifth resistance R
5
and a condenser C
1
connected between the inverted terminal and the output terminal of the differential amplifier
207
are one example of a phase compensation circuit.
As thus described, the output voltage signal (VH-b) is feedback controlled so as to provide stable output voltage in the face of the output current fluctuations caused by changes in the number of nozzles simultaneously driven on the printhead which is the load.
In order to cope with recent technological advances, by which faster computers have made it easier to achieve image output of color image processing as well as image output from high-resolution digital cameras, inkjet printing apparatuses used as output apparatuses have had to simultaneously provide improved picture quality as well as faster printing speeds. Faster printing speeds can be achieved by increasing the ink discharge frequency and increasing the number of nozzles discharged simultaneously, and both faster printing speed and improved picture quality are achieved by increasing the volume of ink discharged per unit of time in droplet increments.
However, an examination of increasing the number of nozzles that simultaneously or substantially simultaneously discharge as a way of increasing printing speed reveals that, of those nozzles readied for simultaneous discharge, the necessity of discharging ink changes according to the image to be printed at that time. Thus, for example, whereas printing an entire page black requires that all the nozzles that can discharge ink actually do so, images with a low duty rate such as tables and the like require ink discharge from only a portion of all available nozzles.
As described above, when serial printing types of inkjet printheads print, that is, discharge ink, such printing is carried out using heat generated by the flow of an electric current through a heater.
With such an ink discharge method, the current required also increases proportionally to the increase in the number of nozzles that discharge ink simultaneously. Yet the required current is not always constant and uniform but varies continuously depending on the data sent to the printhead in proportion to the number of nozzles discharging ink.
In other words, depending on the image data transmitted from an external device, at an inkjet printing apparatus that forms an image, pattern or pattern character on a printing medium, the volume of ink droplets discharged per unit of time is determined by the amount of image data transmitted from the external device, and similarly, the amount of electric power consumed by the printhead is determined by the amount of image data per unit of time.
That is, the greater the amount of image data per unit of time, the greater the number of nozzles put into a state in which they are capable of generating a simultaneous ink discharge and the greater the amount of power consumed by the printhead. Conversely, the smaller the amount of image data per unit of time, the smaller the number of nozzles that simultaneously discharge ink and the smaller the amount of power consumed by the printhead. Similarly, the electric current that the DC/DC converter should deliver to the printhead is determined in proportion to the number of nozzles that are to simultaneously discharge ink.
<Problems to be Solved in a Power Source>
Next, in order to further facilitate an understanding of the present invention, a description is given of the power source that supplies electrical po
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Huffman Julian D.
Nguyen Thinh
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