Patent Application
20110228005
This invention relates generally to imaging and, more particularly, to a printhead plate having priming holes to allow freedom of nozzle placement and reduced purge volume in an ink jet print head.
In order to properly prime an inkjet printhead (during initial filling, after de-priming, or due to air ingestion), the incoming ink must displace all the air in the ink cavity, because residual air bubbles create a condition in the system that disrupts jetting. Instead of the generated pressure pulse being used to create drops, a large portion of it is absorbed by the volume change of air bubbles. This places extra constraints on the nozzle placement, because all of the air must escape before the liquid reaches the nozzle and blocks the nozzle. If, for example, the ink cavity is long and narrow, the nozzle would have to be placed near the very distant end, or else an air bubble will be trapped at the dead end. Typically, this location of the nozzle is not the optimal position for the nozzle. Also, if the nozzle is placed in a position where clearing the air out is difficult, large purge masses are required to get out all of the air. Large purge masses waste expensive ink, thereby making the nozzle position undesirable.
It would, therefore, be desirable to facilitate the purging of air from the internal ink path without interfering with optimal nozzle placements.
According to various embodiments, the present teachings include a nozzle plate for an ink jet printhead.
The nozzle plate includes nozzle holes through which ink is ejected, the nozzle holes positioned at a distance anywhere in the nozzle plate; and a priming hole, distinct from and of a smaller diameter than the nozzle holes, the priming hole positioned at a position in the nozzle plate to purge air from an ink cavity of the jet print head.
Additional advantages of the invention will be set forth in part in the description which follows, and in part will be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.
It should be noted that some details of the figures have been simplified and are drawn to facilitate understanding of the embodiments rather than to maintain strict structural accuracy, detail, and scale.
Reference will now be made in detail to the present embodiments (exemplary embodiments), examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown, by way of illustration, specific exemplary embodiments in which the present teachings may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present teachings. The following description is, therefore, merely exemplary.
As shown in
The carriage type printer can have a printhead having a single die assembly or several die assemblies abutted together for a partial width size printhead. Because both single die and multiple-die partial width printheads function substantially the same way in a carriage type printer, only the printer with a single die printhead will be discussed. The only difference, of course, is that the partial width size printhead will print a larger swath of information. The single die printhead, containing the ink channels and nozzles, can be sealingly attached to a disposable ink supply cartridge, and the combined printhead and cartridge assembly is replaceably attached to a carriage that is reciprocated to print one swath of information at a time, while the recording medium is held stationary. Each swath of information is equal to the height of the column of nozzles in the printhead. After a swath is printed, the recording medium P is stepped a distance at most equal to the height of the printed swath, so that the next printed swath is contiguous or overlaps with the previously printed swath. This procedure is repeated until the entire image is printed.
As shown in
In the print head 200, the membrane 260 can be an electrostatically actuated diaphragm, in which the membrane 260 is controlled by an electrode 262.
The nozzle plate 250 is located above electrostatically actuated membrane 260, forming a fluid pressure chamber 252 between the nozzle plate 250 and the membrane 260. Nozzle plate 250 has nozzle 270 formed therein. Fluid 280 is fed into this fluid pressure chamber 252 from a fluid reservoir (not shown). The fluid pressure chamber 252 can be separated from the fluid reservoir by a check valve to restrict fluid flow from the fluid reservoir to the fluid pressure chamber. The membrane 260 is initially pulled-down by an applied voltage or current. Fluid 280 fills in the volume created by the membrane deflection.
When a bias voltage or charge is eliminated, the membrane 260 relaxes, increasing the pressure in the fluid pressure chamber 252. As the pressure increases, fluid 280 is forced out of the nozzle 270 formed in the nozzle plate 250, as discrete fluid drops 282. For constant volume or constant drop size fluid ejection, the membrane 260 can be actuated using a voltage drive mode, in which a constant bias voltage is applied between the parallel plate conductors that form the membrane and the conductor.
The membrane 260 is typically formed using standard polysilicon surface micromachining, where the polysilicon structure that is to be released is deposited on a sacrificial layer that is finally removed. Electrostatic forces between deformable membrane 260 and conductor 262 deform the membrane.
The nozzle plate 350 of
In
Because the priming holes 290 are so much smaller than the nozzles 270 (ideally as small as the technology will allow), surface tension of the meniscuses is so high that the priming hole 290 will not jet or weep. The pressure at which a nozzle weeps is the inverse of the hole diameter, and the priming holes can be made to be from about 5 to about 10 times smaller than a diameter of the nozzles. Because there is little net flow through the priming holes 290 (they don't jet), they are unlikely to completely clog. However, redundant priming holes can be added as insurance.
The priming holes 290 can be made at the same time as the nozzles 270, so there is no extra cost associated with the priming holes at the manufacturing stage. Although the priming holes 290 are depicted as substantially vertical, they can also be tapered, as can occur during formation. An additional benefit is that the priming holes 290 generally make it easier to purge air out of the system, thereby decreasing the purge of ink the significant cost associated with expelling unnecessary ink. For both silicon and laser-etched nozzles, the addition of priming holes would only require an additional feature drawn on a mask.
The silicon nozzle plate 250 can include priming holes 290 having a diameter of from about 10 to about 15 μm in diameter. Priming holes 290 and nozzles 270 can be placed in many different positions along the length of the nozzle plate 250. With the one or more exemplary priming holes 290, the print head can prime easily regardless of the nozzle position and the priming holes have no impact on jetting of ink through the nozzle 270.
By way of example, moving a nozzle 270 from about 5% to about 20% away from an end of the nozzle plate 250, and therefore from an inner end of the fluid chamber 252, can cause a maximum drop speed to increase by about three times. This optimal positioning of the nozzle 270 can also cause the optimal pulse width to drop by up 2 microseconds (from 9 to 7 microseconds), allowing for higher frequency jetting of ink.
Because priming the device is achieved by the priming holes 290, the nozzle 270 can be positioned anywhere in the nozzle plate 250. For example, when there are corners in a fluid chamber 252 that gather air, large amounts of ink must be forced through the system to get enough turbulent flow to displace those air bubbles, or to dissolve the bubbles back into the ink. By allowing air to escape easily through the priming holes 290, substantially less ink will be required, reducing the purge mass and saving the customer money.
While the invention has been illustrated with respect to one or more implementations, alterations and/or modifications can be made to the illustrated examples without departing from the spirit and scope of the appended claims. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular function. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” The term “at least one of” is used to mean one or more of the listed items can be selected.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein. For example, a range of “less than 10” can include any and all sub-ranges between (and including) the minimum value of zero and the maximum value of 10, that is, any and all sub-ranges having a minimum value of equal to or greater than zero and a maximum value of equal to or less than 10, e.g., 1 to 5. In certain cases, the numerical values as stated for the parameter can take on negative values. In this case, the example value of range stated as “less than 10” can assume values as defined earlier plus negative values, e.g. −1, −1.2, −1.89, −2, −2.5, −3, −10, −20, −30, etc.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
