Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1997-07-28
2002-06-25
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06409315
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substrate for use of the ink jet recording head of an ink jet recording apparatus that forms droplets by discharging liquid from orifices. The invention also relates to a head using such substrate.
2. Related Background Art
With respect to an ink jet recording head of the kind, an ink jet recording method, such as disclosed in the specification of Japanese Patent Laid-open Application No. 54-51837, is to cause thermal energy to act upon liquid for obtaining the power source for discharging liquid. This is the characteristic aspect of the method that differs from the other types of ink jet recording methods. In other words, the recording method disclosed in the specification of the Laid-Open Application described above, liquid is heated by the application of thermal energy and is caused to bubble. The force generated by the bubbles as they expand, causes droplets of liquid to be ejected out through orifices arranged at the leading end of the recording head unit. These ejected droplets impinge upon and adhere to a recording member and thereby record information on the recording medium.
A recording head which operates according to the recording method described above is generally provided with several orifices through which the liquid is discharged. Such head also includes as part of its structure a liquid discharging unit which contains heat activating portions, which connects with the orifice. In the heat activating portions thermal energy acts upon the liquid therein and causes droplets to be ejected through the orifices as described above. In the heat activating portions there are provided heat generating resistive layers that form electrothermal transducing elements which generate thermal energy; upper layers are provided to protect the heat generating resistive layers from ink. In addition lower layers are provided under the heat generating resistive layers to accumulate heat.
Also, in the specification of Japanese Patent Laid-open Application No. 57-72867, it has been proposed to incorporate an element for driving heat generating resistors on a substrate in order to minimize the numbers of required electrodes pads.
FIG. 12
is a plan view which shows an example of a conventional recording head substrate structure having electric power wiring arranged on a substrate together with heat generating resistors.
The example shown in
FIG. 12
is a substrate used for a so-called edge shooter type ink jet recording head where liquid is discharged in the direction substantially in parallel with the heat generating surface of heat generating resistors (in the right-hand direction in FIG.
12
).
In the example of
FIG. 12
, a heat generating resistive layer and electrode layer are provided on a silicone substrate. Then, by means of photolithographic technique, heat generating elements
71
and pads
73
for use of external fetch electrodes are formed. The size of each heat generating resistor
71
is 150 pm×30 &mgr;m. Eight resistors are provided at a pitch of 200 &mgr;m.
Subsequently, a protection layer is formed over the resistive and electrode layer. Then by means of a photolithographic technique, a common electrode
72
and electrode pads
73
are formed over the protective layer. Through holes
74
are provided in the common electrode
72
by making holes on a fetching unit of common electrode. The common electrode
72
and its electrode pads
73
are formed from an aluminum layer which is subjected to a photolithographic and etching technique to shape a common electrode
72
and an electrode pad
75
extending therefrom which is used for external fetching.
In the conventional recording head thus structured, each of the electrode pads
73
is connected via through holes and associated electrodes with one end of each heat generating resistor
71
, while the other end of each heat generating resistor is connected with the common electrode
72
by way of associated ones of the through holes
74
for its shareable use. Thus, heat is generated when voltage is applied across the electrodes
73
and
75
.
Each of the heat generating elements
71
is separated and covered by the walls (not shown) which are arranged between and over them to form associated liquid flow paths. Liquid supplied into the flow paths is discharged from each of the orifices (not shown) by the force of expanding bubbles which are formed in the liquid by heat generated by the associated heat generating elements.
A large number of electrode pads are required to receive electric power which is supplied from an external source through each of the electrode pads. In order to maximize printing speed, a large number of heat generating resistors should be provided. It frequently happens that many of these several heat generating resistors must be driven simultaneously. When driving many heat generating resistors at the same time, a large amount of current must be supplied to the ink jet head.
The driving of an ink jet head which uses thermal energy to discharge ink by bubbling is different from the driving of a thermal head. To produce a good bubbling effect, the electrical current pulses which are applied to the heat generating resistors should be as short as possible. Accordingly, the electrical current in these pulses is increased. Thus, even if the electric power wiring which transmits these current pulses is arranged with a low resistance, there is still a problem encountered in that the quality of printed images becomes inferior. This is due to impediments, such as the inability to effectuate normal bubbling or disabled bubbling, because the voltage which causes each current pulse is caused to drop by an amount which corresponds to the product of the difference that takes place in the electric current when only one heat generating resistor is driven and when many of them are driven at the same time. Also the resistive value of the electric power wires further contributes to this voltage drop because this inevitably results in a reduction of the voltage applied to the heat generating resistors when several of them are driven at a time.
The above described problems can be appreciated from the following description in which the specific numerical values are given. When thirty-two heat generating resistors, each having a resistance of 1 &OHgr;, are driven together and arranged with the driving current of 0.2 A for each with a heat generating resistor, the total current flow is 32×0.2 or 6.4 A. When one of the resistors is driven along the total current flow is 1×0.2 or 0.2 A; so that the difference in total current flow when one of them is driven and when all of them at the same time, is 6.2 A.
When the driving voltage is set at 20 V, which is 1.3 times the bubbling voltage 15.3 V, the driving voltage 13.8 V, which is 20 V—such reduced voltage of 6.2 V, is lower than the bubbling voltage of 15.3 V. As a result, bubbling becomes impossible. In order to avoid this event, the applied voltage should be raised. However, if the applied voltage is raised, each of the heat generating resistors receives a greater voltage when each of them is driven individually. Therefore, the life of heat generating resistors is made shorter inevitably.
In convention practice each driving cycle is divided into several time increments and different groups of the heat generating resistors are driven in each time increment. Under the present circumstances, however, driving should be carried out at a high frequency in order to enhance the printing speed. Thus, the driving cycle should be as short as possible. However, the driving cycle duration is dependent primarily on the response capability of the driving element. It is difficult, because of the limited response capability of the driving element, to make the width of the driving pulse small and therefore only a limited number of driving pulses can be generated during each cycle. As a result, the number of time divisions cannot be increased any more.
Also, conceivably, it may be possible by
Barlow John
Brooke Michael S
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