Print head apparatus capable of temperature sensing

Details Print head apparatus capable of temperature sensing Print head apparatus capable of temperature sensing

2001-08-28

2003-10-21

Nguyen, Judy (Department: 2853)

Incremental printing of symbolic information

Ink jet

Controller

C347S017000, C347S060000, C347S185000

Reexamination Certificate

active

06634731

ABSTRACT:

This application incorporates by reference Taiwanese application Serial No. 89117550, filed on Aug. 29, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to an apparatus for temperature sensing and heating, and more particularly to an apparatus for temperature sensing and heating for use in a print head.
2. Description of the Related Art
Over the years, electronic related industries progress as the technology advances. For various electronic products, such as computer systems, computer peripherals, appliances and office machines, their functions and appearances are improved greatly as well. For example, in the 1980s, impact-type dot matrix printers and monochrome laser printers were pre-dominant. Later in the 1990s, monochrome inkjet printers and color inkjet printers became popular for common uses while color laser printers were available for professional uses. For common end users who do not print documents frequently, they would probably select color inkjet printers after considering the printing quality and price. People with sufficient budgets would probably purchase a monochrome laser printer. Since the price and quality are critical to the users' choices, printer vendors aggressively develop their products so that the products have lower cost and better quality so as to increase popularity and profits of their products. Therefore, developers are focusing on how to improve the performance of products under limited cost.
Most inkjet printers now use bubble inkjet print head or piezo-electrical inkjet print head to spray ink droplets onto a sheet of medium, such as paper, for printing. The bubble inkjet print head includes a heating device, ink, and nozzles. The heating device is to heat the ink to create bubbles until the bubbles expand enough to burst so that ink droplets are fired onto the sheet of paper through the nozzles, forming dots on the sheet of paper. Varying the concentration and locations of the droplets can form wide range of different texts and graphics on the paper.
The quality of printing is closely related to the resolution provided by the printers. Currently, entry-level color printers provide a maximum resolution of 720 by 720 dot per inch (dpi) or 1440 by 720 dpi. Higher resolution requires finer size of the droplets. The size of the droplets is related to the cohesion of the droplets. For instance, for droplets having identical amount of ink, those droplets with greater cohesion may have a smaller range of spread when they fall onto the paper, resulting in clearer and sharper printing quality. On the other hand, those droplets with smaller cohesion may have a greater range of spread when they fall onto the paper, resulting in a poorer printing quality. Thus, cohesion of the droplets affects the printing quality. In common bubble inkjet printing technique, if it is required to eject ink droplets by a specific nozzle, the heating device associated with the nozzle is first enabled to heat the ink so as to generate bubbles in the chamber associated with the nozzle. The viscosity of the ink decreases as the temperature of the ink rises. If the heating process is not well controlled and the ink is overheated, the viscosity of the ink becomes lower than a normal level and the cohesion of the droplets is reduced, resulting in a degraded printing quality. In addition, if the chamber contains insufficient ink or the ink droplet is not fired properly, the temperature of the ink in the chamber will exceed the normal level, resulting in the viscosity of the ink being lower than the normal. In addition, if a nozzle is frequently fired, the ink in the chamber associated with the nozzle will have higher temperature and lower viscosity than the ink in the chamber associated with other nozzles. All these conditions cause the viscosity of the ink to be unstable, and thus affecting the printing quality. Therefore, accurately monitoring and controlling the temperature of the ink in the chamber is the key to the improvement in the ink jet printing quality.
FIG. 1A
is a block diagram illustrating the conventional control of an inkjet printer. The inkjet printer
10
includes a driving module
11
and a print head module
15
. The driving module
11
includes a controller
12
and a driver circuit
13
. The print head module
15
includes an array of inkjet ejector
16
and a temperature sensing device
17
. For the printing of data onto a sheet of paper, the controller
12
, in response to the data, drives the driver circuit
13
so that the driver circuit
13
sends selection signals
14
to the array of inkjet ejectors
16
. In the array of inkjet ejectors
16
, selected heating devices such as a heating device
19
shown in
FIG. 1B
heat up according to selection signals
14
so that ink droplets are ejected onto the paper through the nozzles of the array of inkjet ejectors
16
.
FIG. 1B
is a sectional view illustrating the array of inkjet ejectors
16
shown in
FIG. 1A
along with the heating device
19
and a nozzle
18
. The heating device
19
is mounted in close proximity to the nozzle
18
, and is used for heating the ink in the chamber
21
in order to create a bubble
20
. The ink in the chamber
21
is heating up until the pressure in the chamber
21
forces the bubble
20
to burst and a droplet of ink is ejected from the nozzle
18
. The ejected ink droplet then forms a spot on the sheet of paper.
Further, in order to monitor the temperature of the nozzles, a temperature sensing device
17
, such as a thermal resistor, is arranged near a portion of nozzles of the array of inkjet ejectors
16
. The measured temperature data from the temperature sensing device
17
is fed back to the controller
12
for the control of the temperature.
In the following, it is to describe how to select heating devices according to selection signals
14
so that ink droplets are ejected from the nozzles.
FIG. 2
is a circuit diagram illustrating the array of inkjet ejectors
16
in FIG.
1
A. The array of inkjet ejectors
16
includes an M×N two-dimensional array of circuit elements. Each of the circuit elements is formed by a resistor R coupled with a transistor Q, and is associated with one of the nozzles. Besides, the selection signals
14
are selectively applied to the circuit units to create bubbles and cause ink droplets to be ejected for the formation of marks on the sheet of paper. When one of the selection signals
14
is selectively applied to the circuit element to cause the transistor Q conduct, the resistor R generates heat for the ink of the chamber
21
to cause a ink droplet to be ejected from the nozzle
18
. In other words, the resistor R is used as the heating device for heating the ink of the chamber. In addition, for the reduction of the number of signals, the selection signals can be composed of row signals and column signals. In
FIG. 2
, X
a
denotes one row signal of the selection signals
14
while Y
b
denotes one column signals of the selection signals
14
, where a=1, 2, . . . , M and b=1, 2, . . . , N. For the sake of brevity, this notation will be used in the following of the specification. For instance, when the row signal X
1
and column signal Y
1
are active and fed to the array of ink ejectors
16
, the transistor Q
11
conducts and thus the resistor R
11
produces heat so that a droplet of ink is ejected from the associated nozzle. Likewise, when the row signal X
M
and column signal Y
N
are active and fed to the array of ink ejectors
16
, the transistor Q
MN
conducts and thus the resistor R
MN
produces heat so that a droplet of ink is ejected from the associated nozzle. In this way, according to the row and column signals of selection signals
14
, the nozzles indicated by selection signals
14
can be accurately enabled for printing.
FIG. 3
are comparative graphs of measured temperature of the nozzles in the same structure as in
FIG. 1B
versus the time as the nozzles are in a normal case and in an abnormal case. In the normal case, the temperature of the nozzle

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