Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-04-23
2001-06-19
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C400S313000, C400S328000
Reexamination Certificate
active
06247785
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
FIELD OF INVENTION
This invention relates generally to a positioning assembly for a print head drive mechanism in an imaging apparatus and, more specifically, to a positioning assembly that reduces positional variances to improve ink drop placement accuracy.
BACKGROUND OF THE INVENTION
Ink-jet printing systems commonly utilize either a direct printing or an offset printing architecture. In a typical direct printing system, ink is ejected from jets in the print head directly onto the final receiving medium. In an offset printing system, the print head jets the ink onto an intermediate transfer surface, such as a liquid layer on a drum. The final receiving medium is then brought into contact with the intermediate transfer surface and the ink image is transferred and fused into the medium.
In many direct and offset printing systems, the print head moves relative to the final receiving medium or the intermediate transfer surface in two dimensions as the print head jets are fired. Typically, the print head is translated along an X-axis while the final receiving medium/intermediate transfer surface is moved perpendicularly along a Y-axis. In this manner, the print head “scans” over the print medium and forms a dot-matrix image by selectively depositing ink drops at specific locations on the medium.
In a typical offset printing architecture, the print head moves in an X-axis direction that is parallel to the intermediate transfer surface as a drum supporting the surface is rotated. Typically, the print head includes multiple jets configured in a linear array to print a set of scan lines on the intermediate transfer surface with each drum rotation. Precise placement of the scan lines is necessary to meet image resolution requirements and to avoid producing undesired printing artifacts, such as banding and streaking. Accordingly, the Xaxis (head translation) and Y-axis (drum rotation) motions must be carefully coordinated with the firing of the jets to insure proper scan line placement.
Prior ink jet printers have utilized various implementations of a lead screw mechanism to impart X-axis movement to a print head. An exemplary patent that discloses a lead screw positioning mechanism is U.S. Pat. No. 4,613,245 for DEVICE FOR CONTROLLING THE CARRIAGE RETURN OF A LEAD SCREW DRIVEN PRINTING HEAD (the '245 patent).
Prior lead screw print head drive mechanisms can introduce positional errors due to component imperfections and system inaccuracies. These imperfections and inaccuracies may include irregularities in drive system components, thread imperfections, axial misalignments and similar component and manufacturing-related variations. In a lead screw mechanism, these sources of positional error tend to be manifested in cyclical repetitions that correspond to the characteristics and gear ratios of the drive system componentry. In printing architectures that generate images using scan lines, these positional errors can introduce undesirable white space between adjacent scan lines and produce other printing artifacts that reduce image quality.
These positional errors can be controlled to some degree by the use of precision components and control systems in the drive mechanism and associated positioning assemblies. However, such precision components and control systems are more expensive and often more time-intensive to manufacture and assemble.
Accordingly, what is needed is a low cost, low complexity lead screw drive mechanism and positioning assembly for a print head that provides improved positional accuracy and overcomes the drawbacks of prior systems.
SUMMARY OF THE INVENTION
It is an aspect of the present invention to provide a lead screw drive mechanism and positioning assembly for a print head that overcome the drawbacks of prior systems.
It is another aspect of the present invention to provide a lead screw drive mechanism and positioning assembly that minimize positional offsets due to imperfections in drive system components and control systems.
It is a feature of the present invention that the thread pitch of the lead screw is calibrated to the spacing between adjacent jets in the print head to reduce positional offsets.
It is another feature of the present invention that the angular positions of the driving motor and the driven gear that is coupled to the lead screw are substantially equal for any pair of adjacent scan lines.
It is another feature of the present invention to provide a positioning assembly that constrains translational motion of the print head in the direction of a preload force.
It is an advantage of the present invention that the lead screw drive mechanism and positioning assembly provide improved ink drop placement accuracy to eliminate white space between adjacent pixel columns.
It is another advantage of the present invention that the positioning assembly is essentially non-extensible in an X-axis direction but freely pivotable in a direction perpendicular to the X-axis.
It is another advantage of the present invention that the lead screw drive mechanism and the positioning assembly are simple, low cost and reliable mechanisms.
To achieve the foregoing and other aspects, features and advantages, and in accordance with the purposes of the present invention as described herein, a print head drive mechanism and cooperating positioning assembly are provided. In one embodiment, the print head drive mechanism comprises a lead screw that is coupled to the print head and extends through the threaded hub of a gear. The gear is driven by a stepper motor through a pinion. A support cylinder extends from one face of the gear and includes a tapered nose that seats within a recess in a brace. The brace cooperates with two spaced apart legs to form a positioning assembly that is essentially non-extensible in an X-axis direction but freely pivotable in a direction perpendicular to the X-axis. The thread pitch of the lead screw matches the jet spacing in the print head to minimize positional offsets due to component irregularities and misalignments. In another embodiment, the print head is coupled to at least one nut that is translated by a lead screw, with the lead screw having a thread pitch that matches the jet spacing in the print head.
Still other aspects of the present invention will become apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of this invention, simply by way of illustration of one of the modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments and its several details are capable of modifications in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. And now for a brief description of the drawings.
REFERENCES:
patent: 3945481 (1976-03-01), Lindberg
patent: 4613245 (1986-09-01), Ikeda et al.
patent: 5389958 (1995-02-01), Bui et al.
patent: 5488396 (1996-01-01), Burke et al.
patent: 5625390 (1997-04-01), Burke et al.
patent: 5734393 (1998-03-01), Eriksen
patent: 5818497 (1998-10-01), Kerr et al.
U.S. application No. 08/757,366, filed Nov. 27, 1996, PN 5,949452.
Jensen James B.
Jones Brent R.
Knierim David L.
Barlow John
Moore Charles F.
Stephens Juanita
Xerox Corporation
LandOfFree
Positioning assembly for drive mechanism does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Positioning assembly for drive mechanism, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Positioning assembly for drive mechanism will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2487877