Patent Application
20070024668
An exemplary embodiment of this application relates to an ink jet printer having a translating print bar with spaced print heads thereon that print on a rotating image receiving surface. More particularly, the exemplary embodiment relates to an ink jet printer having a translating print bar with a plurality of equally spaced print heads thereon. Each of the print heads eject ink droplets onto the surface of a rotating image receiving cylindrical surface as the print bar is translated to produce barber pole shaped swaths of an image on the cylindrical surface. After multiple passes of the cylindrical surface past the translating print bar, a complete image is printed thereon. The cylindrical surface may be a recording medium, such as paper, held on a drum or an intermediate transfer drum.
Droplet-on-demand ink jet printing systems eject ink droplets from print head nozzles in response to pressure pulses generated within the print head by either piezoelectric devices or thermal transducers, such as resistors. The ejected ink droplets are propelled to specific locations on a recording surface, commonly referred to as pixels, where each ink droplet forms a spot thereon. The print heads have arrays of droplet ejecting nozzles and a plurality of ink containing channels, usually one channel for each nozzle, which interconnect an ink reservoir in the print head with the nozzles.
In a typical piezoelectric ink jet printing system, the pressure pulses that eject liquid ink droplets are produced by applying an electric pulse to the piezoelectric devices, one of which is typically located within each one of the ink channels. Each piezoelectric device is individually addressed to cause it to bend or deform and pressurize the volume of liquid ink in contact therewith. When a voltage pulse is applied to a selected piezoelectric device, a quantity of ink is displaced from the ink channel and a droplet of ink is mechanically ejected from the nozzle associated with that piezoelectric device. Just as in thermal ink jet printing, the ejected droplets are propelled to pixel targets on a recording surface to form an image of information thereon. The respective channels from which the ink droplets were ejected are refilled by capillary action from an ink supply. For an example of a piezoelectric ink jet printer, refer to U.S. Pat. No. 6,739,690 or U.S. Pat. No. 3,946,398.
The problem of ink drying time and paper cockling are widely recognized issues when printing high coverage areas with aqueous based inks, particularly when printing color images. The problem of drying time and paper cockling is substantially reduced when solid ink printers are used and their print heads eject droplets of melted ink onto the recording surface, where the melted ink droplets solidify immediately. Improvements in image quality and latitude are obtained when the print head ejects droplets of melted ink onto an intermediate surface, such as, for example, the surface of an intermediate transfer drum, that has a release agent coating thereon. Once the image is formed on the intermediate transfer drum, the image is then transferred to a recording medium, such as paper. The transfer is generally conducted in a nip formed by the rotating intermediate transfer drum surface and a rotatable pressure roll. The pressure roll may be heated or the recording medium may be pre-heated prior to entry in the transfixing nip. As a sheet of paper is transported through the nip, the fully formed image is transferred from the intermediate transfer drum surface to the sheet of paper and concurrently fixed thereon. This transfer technique of using the combination of heat and pressure at a nip to transfer and fix the image to a recording medium passing through the nip is usually referred to as “transfixing,” a well known technology.
Conventionally, there are two classes of multi-pass ink jet printing architectures; viz., one using a partial width print head for scanning and the other using a full width print head for scanning. Partial width print heads generally require that the print head remain stationary while printing a swath of image during each pass of a recording medium held on a rotating drum or a rotating intermediate transfer drum. After each swath of image is printed, the print head is stepped a distance at most equal to the width of the printed swath on the recording medium or surface of the intermediate transfer drum. The printing and stepping continues until the complete image has been printed. In contrast, the full width array print heads remain stationary as the recording medium or intermediate transfer drum is rotated there past. The full width array print heads offer advantages over partial width scanning arrays, for there is no need for a scanning carriage to travel a large distance and, since there is no stepping required, there is no loss of printing productivity that is associated with print head stepping.
Some current solid ink jet type printers generally use multiple passes of a full width print head having low nozzle densities to print on a rotating intermediate transfer drum. By utilizing a single full width array print head, but of limited nozzle density, the full width array print head is required to translate only a small distance along the length of the intermediate transfer drum for each pass of the intermediate transfer drum. Such an architecture is efficient in that it allows for image printing with little lost of printing productivity, except, of course, for the subsequent transfer step upon completion of the printed image.
The full width print head of such known ink jet printers may print pixel columns of information circumferentially on the intermediate transfer drum. After each printed pixel column, the full width print head may be stepped axially to the drum axis for printing subsequent adjacent columns until the entire image is completed. Some printing productivity is lost during the required print head stepping.
Print heads having piezoelectric devices suitable for solid ink printing may now be available in small dies or MEMS devices with high nozzle densities, such as, for example, nozzle arrays capable of printing 400 to 450 spots per inch (spi). However, a difficulty is encountered when trying to take advantage of this high density printing capability in a low cost office printer. For example, a full width print head composed of abutted dies or MEMS devices with nozzles spaced for printing at 400 to 450 spi, would have increased printing speed and resolution. However, the large increase in the number of nozzles required for a full width print head would also reduce print head reliability and greatly increase the print head cost. Accordingly, the trade off of using a full width print head having high density nozzle arrays in a solid ink jet printer instead of a more reliable, lower resolution full width print head is much less desirable when cost and reliable are a factor.
In one known solid ink jet printer, the transfixing roll is spaced from the intermediate transfer drum and is moved to produce a nip with the intermediate drum only after the complete image has been printed on the intermediate drum and the intermediate transfer drum is stopped. Before the nip is formed, the leading edge of a recording medium is transported into the transfixing nip region. Therefore, the transfixing roll engages the leading edge of the recording medium and sandwiches it between the transfixing roll and the intermediate drum. Once the nip is formed, the transfixing roll and intermediate drum are rotated to transport the recording medium through the transfixing nip and concomitantly transfixing the image to it. Conversely, the transfixing roll is disengaged from the trailing edge of the recording medium before the recording medium leaves the transfixing nip.
Examples of ink jet printers having full width array print heads and/or an intermediate transfer drum from which printed images are transferred to a recording medium at a transfixing station are disclosed below.
U.S. Pat. No. 5,099,256 discloses a thermal ink jet printer having a translatable multicolor printhead and a rotatable intermediate drum with a film forming silicone polymer layer on the outer surface thereof. The drum surface is heated to dehydrate the aqueous based ink droplets deposited thereon from the printhead at a first location. The drum is rotated and the dehydrated droplets are transferred from the drum to a recording medium at a transfer station positioned adjacent the drum at a second location.
U.S. patent application Ser. No. 11/040,040, filed Jan. 21, 2005, discloses an ink jet printer having a print head that moves in a two dimensional direction across the surface of a moving intermediate drum or belt. During the printing process, the print head is concurrently moved in a first direction at a velocity equal to the velocity and direction of the intermediate surface and in a second direction that is perpendicular to the first direction. This two dimensional movement of the print head causes the ink droplets to print swaths of information across the intermediate surface that are perpendicular to the first direction. Downstream from the print head, the printed information is transferred and fixed to a recording medium as it is transported through the transfixing nip at the transfixing station.
U.S. patent application Ser. No. 10/974,768, filed Oct. 28, 2004 (Attorney Docket No. A3079-US-NP), discloses an ink jet printer having a print head, intermediate drum, and transfixing station. Test images are formed on the inter-document space or blank portions of the intermediate drum by those nozzles of the print head that are most likely to be defective. Thus, the time and ink required to form the test images with nozzles unlikely to be defective is not wasted. The test images printed by the potentially defective nozzles are tested using an image sensor.
U.S. patent application Ser. No. 11/120,343, filed May 3, 2005 (Attorney Docket No. 20040643-US-NP), discloses an ink jet printer having an intermediate transfer drum that rotates past a print head and a downstream transfixing station. The transfixing station has separate simplex and duplex operating modes. A movable transfixing roll at the transfixing station forms a nip with the intermediate transfer drum with different timing relationships as the recording medium approaches the nip, depending upon whether the image to be transfixed is a simplex or duplex print.
U.S. Pat. No. 4,829,324 discloses a large width array thermal ink jet print head that is assembled from generally identical print head sub-units. The sub-units eject ink droplets from nozzles on a side edge thereof and are generally referred to as edge shooters. The sub-units are aligned and bonded end-to-end on a strengthening substrate. U.S. Pat. No. 5,198,054 discloses a process for fabricating a page width print head from small edge shooter type print head sub-units. U.S. Pat. No. 5,160,945 discloses a page width thermal ink jet print head that is assembled from fully functional roof shooter type print head sub-units. The sub-units are fixedly mounted on an edge of a structural bar to minimize print head warping. A passageway in the structural bar edge provides the ink supply to each of the print head sub-units.
U.S. Pat. No. 5,257,043 discloses a large width array of individual thermal ink jet print head sub-units on a support bar. A series of the print head sub-units are spaced apart from each other by equal distances on both sides of the support bar. The series on each side of the support bar are in a staggered relationship to each other. Each print head sub-unit is mounted so that it can be replaced. U.S. Pat. No. 5,221,397 discloses a full width array thermal ink jet print head assembled from print head sub-units. The print head sub-units are assembled in an alignment fixture and then a structural bar is aligned and bonded to the assembled sub-units before the full width array print head assembly is removed from the alignment fixture.
According to aspects illustrated herein, there is provided an ink jet printer having a cylindrical, image-receiving surface rotated about its axis and a translatable print bar mounted adjacent and parallel thereto. The print bar has equally spaced, identical print heads mounted along the length of the print bar. The print heads eject ink droplets onto the rotating image receiving surface as the print bar is translated relative thereto, thereby printing swaths of information thereon in a barber pole fashion. Each print head has an array of nozzles with a predetermined length. The spacing between print heads on the print bar are equal to integer multiples of the length of a nozzle array as measured between nozzle arrays. The print bar may be translated the distance of from an integer divisor of the nozzle array length up to the distance of one nozzle array length during each revolution of the image-receiving surface. Thus, each print head prints a barber pole shaped swath of image on the image-receiving surface. The print head spacing on the print bar along with the desired image resolution in terms of spots per inch determines the number of drum revolutions required for completing the printed image. The cylindrical surface may be a receiving medium, such as paper, held on a cylindrical member or an intermediate transfer drum. Once the complete image is formed, the recording medium is removed from the drum or a movable transfixing roll is brought into contact with the intermediate transfer drum to form a transfixing nip through which a recording medium is transported.
In one aspect of the exemplary embodiment, there is provided a method of printing by an ink jet printer of the type having a print bar and a rotary image receiving member, comprising: providing a cylindrical image receiving surface having an axis; providing an elongated print bar adjacent said drum and parallel to said image receiving surface; equally spacing high resolution print heads in at least one row along said print bar, each of said print heads having an array of droplet ejecting nozzles that extend for a predetermined length, said print head spacing being integer multiples of a distance equal to said nozzle array length as measured between nozzle arrays of said print heads; rotating said image receiving surface about its axis; translating said elongated print bar in a direction parallel to said axis of said image receiving surface and at a speed capable of moving said print bar a predetermined distance during each revolution of said image receiving surface; and ejecting ink droplets from said print heads on said translating print bar onto said rotating image receiving surface, so that a swath of image information is printed on said image receiving surface in a barber pole fashion by each print head during each revolution of the image receiving surface.
An exemplary embodiment of this application will now be described, by way of example, with reference to the accompanying drawings, in which like reference numerals refer to like elements, and in which:
For a general understanding of an ink jet device, such as, for example, a solid ink jet printer in which the features of the exemplary embodiment of this application are incorporated, reference is made to
The memory 26 may include, for example, any appropriate combination of alterable, volatile or non-volatile memory, or non-alterable or fixed memory. The alterable memory, whether volatile or non-volatile, can be implemented using any one or more of static or dynamic RAM, a disk drive, a writeable or re-writeable optical disk and disk drive, a hard drive, flash memory or the like. Similarly, the non-alterable or fixed memory can be implemented using any one or more of ROM, PROM, EPROM, EEPROM, an optical ROM, such as CD-ROM or DVD-ROM disk, and disk drive or the like. It should also be appreciated that the controller 24 and/or memory 26 may be a combination of a number of component controllers or memories all or part of which may be located outside the printer 10.
The solid ink jet printer 10 shown in
With continued reference to
While the print heads 14 on the print bar 12 are printing, the print bar is concurrently translated a small distance during each revolution of the intermediate transfer drum 16. The translation range of the print bar during one rotation of the intermediate transfer drum is from an integer divisor of the nozzle array length A to a complete length A of one nozzle array. If less than a nozzle array length is used for the print bar translation during one revolution of the intermediate transfer drum, more passes or revolutions would be required of the intermediate transfer drum 16 to complete an image thereon. However, a translation of less than one nozzle array length by the print bar 12 per revolution of the intermediate transfer drum 16 would proportionally increase the printing resolution by providing more spots or lines per inch. For example, if a plurality of print heads, each having a nozzle array length of 0.1 inches, is spaced along a print bar with a spacing of two nozzle array lengths (0.2 inches) between nozzle arrays that have a density of 400 nozzles per inch, then the image would be completely printed in three passes with a resolution of 400 spi, when the print bar is translated 0.1 inches (one nozzle array length) during each revolution of the intermediate transfer drum. However, if this print bar is translated only 0.05 inches (a nozzle array length integer divisor of 2) during each revolution of the intermediate transfer drum, the image would be completely printed in six passes with a resolution of 800 spi. The translation of the print bar 12, while the print heads 14 thereon are printing on a rotating intermediate transfer drum 16, produces the images printed thereon in the form of barber pole shaped swaths 36 of ink images (see
As shown in
Referring again to
The rotation or rolling of both the intermediate transfer drum 16 and transfixing roll 17, as shown by arrows 27,28 respectively, not only transfix the images onto the recording medium, but also assist in transporting the recording medium through the nip 19 formed between them. This transporting assistance by the rolling intermediate transfer drum 16 and transfixing roll 17 is especially needed after the trailing edge of the recording medium 21 leaves the recording medium transport 22.
Once an image is transferred from the intermediate transfer drum 16 and transfixed to a recording medium 21, the transfixing roll 17 is moved away from the intermediate transfer drum and the intermediate transfer drum continues to rotate. Under the control of the controller 24, any residual ink left on the intermediate transfer drum is removed by well-known drum maintenance procedures at a maintenance station, not shown. Also, periodic applications of release agent (not shown), such as, for example, silicone oil, are applied to the surface of the intermediate transfer drum by the release agent applicator 20, under control of the controller 24, prior to subsequent printing of images on the intermediate transfer drum by the print heads 14 on print bar 12. Typically, the release agent applicator 20 includes a container 29 of release agent (not shown) and a resilient porous roll 30 rotatably mounted in the container and in contact with the release agent. The porous roll 30 is periodically moved into and out of temporary contact With the rotating intermediate drum to coat the surface thereof as needed by the controller 24, as indicated by arrow 31.
In
The print bar 12, sparsely populated with print heads 14, is shown with the print heads aligned in a single row. The print heads 14 could also be staggered rather than being in a single row along the length of the print bar 12. The spacing between the print heads 14 shown in
In
The print bar 12 of
In
Modern solid ink print head designs, such as, for example, MEMS devices, are able to pack more and more droplet ejecting nozzles in their nozzle arrays, leading to high spi densities and higher productivity printing. However, a difficulty is encountered when trying to take advantage of this high pixel density in an office class printer. The large increase in the number of nozzles in a full width array print head also increases the likelihood of nozzle failure, so reliability decreases and, of course, the huge increase in print head cost makes a full width array print head with high nozzle density less desirable. This forces the compromise of either using partial width print heads having high density nozzle arrays in the office class printer, and thus suffer the loss of printing productivity during stepping of the partial width print head as well as the acceleration/deceleration time loss inefficiencies, or continuing to use low density nozzle arrays for full width array print heads in the office class printer.
In
The recording medium 21 is wrapped around and held onto the outer surface of the cylindrical drum 53 by any suitable means (not shown), such as, for example, by electrostatic attraction or by a vacuum. As described with reference to
In the same manner as in ink jet printer 10,, the ink supply 51 is connected to an ink distribution system (not shown) on the print bar 12. The ink distribution system and electrical drive circuitry (not shown) are located at any convenient place on the print bar 12. Each of the print heads 14, as discussed above, is only a die or body containing ink flow channels with associated piezoelectric devices and the array of nozzles connected to the channels. The main difference between ink jet printer 52 and ink jet printer 10 is that the print heads 14 of printer 52 print images directly on a recording medium 21 attached to the cylindrical drum 53, while the print heads 14 of ink jet printer 10 print images on the intermediate transfer drum 16 and the images must subsequently be transferred to a recording medium 21.
In
In summary, the exemplary embodiment of this application solves the above-described dilemma of meeting cost requirements of the office printer with desired higher printing resolutions by taking advantage of the capabilities of the high density nozzle array print heads, based, for example, on the MEMS technology. In the exemplary embodiment, a full width print head is formed by sparsely populating a print bar with small identical, high nozzle density print heads that are spaced apart by multiples of the length of the print head's nozzle array. The print bar is moved a distance in the range of an integer divisor of the nozzle array length up to one whole nozzle array length (or printed swath width) during each revolution of the intermediate transfer drum. Thus, each print head 14 on the print bar 12 prints a swath 36 of information on the intermediate transfer drum 16 in a barber pole fashion. The number of passes of the rotatable intermediate transfer drum 16 required to print a complete image thereon is determined by the spacing of the print heads 14 and the amount of print bar 12 advance.
By sparsely populating the high density print heads, such as MEMS devices, on a full width print bar, the print bar would act in many respects just as a conventional low density full width print bar, but would offer higher printing productivities. Accordingly, the goal of the exemplary embodiment is achieved by providing a low cost, high efficiency, high-density printing printer having a low complexity barber pole multipass architecture. In addition, such an exemplary embodiment of a print bar could potentially be used for retrofitting into existing office class printers, thereby upgrading those printers from low resolution printers to high resolution printers.
It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
