Typewriting machines – Carriage or carriage-moving or movement-regulating mechanism – Carriage-feed mechanism
Reexamination Certificate
1998-03-17
2002-10-08
Hirshfeld, Andrew H. (Department: 2854)
Typewriting machines
Carriage or carriage-moving or movement-regulating mechanism
Carriage-feed mechanism
C400S320000, C400S352000, C347S033000
Reexamination Certificate
active
06461064
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of wide format color digital printing systems, and in particular to an improved drum-based ink jet printer having a novel service station for precisely cleaning and storing a plurality of marking elements associated with ink emitting print heads. The present invention finds use in the digital printing and imaging industry where successful repeatable printing requires precise placement of dots on print substrates including paper, vinyl, film, and other print substrates of varying thickness that typically include emulsion coatings thereon to promote consistent interaction with printing media marking materials such as ink, toner, or various printing compounds.
BACKGROUND OF THE INVENTION
The present invention relates to an improved apparatus for supporting, driving, maintaining, and operating print heads coupled to a carriage across a printing media so that ink droplets may be placed thereon to reproduce text and images with precision. Prior art mechanisms for driving a print carriage typically utilize a belt and pulley actuated mechanism or helical gear attached to the print carriage. These prior art carriage mounting and drive systems are known to cause errors in printed output.
Prior art print head rail members for large format print engines further encounter limitations due simply to the length and mass of a typical rail, carriage drive means, and carriage assembly as well as mechanical control difficulties related to precisely controlling all the specifications and tolerances during manufacturing and installation. A phenomena described as “tolerance stacking” contributes a significant component of error in an assembly process wherein at least two precision machining events occur at differing times on the same assembly or same time for different assemblies. In relation to a carriage assembly for a large format print engine, such tolerance stacking occurs at a number of discrete points of manufacture. For example, a carriage typically precisely supports at least one, and oftentimes several, print heads, a portion of the circuitry for such print heads, and all intervening means for driving the carriage assembly upon a guideway or track in a highly controlled manner (e.g., belts, pulleys, gears, encoders, motors, etc.). Thus, machining portions of subassemblies to arrive at an exact location of the print head(s) relative to: other print head(s), the printing medium, and the rail assembly can all contribute positional error relative to a design criteria possessing rigorous tolerance specifications. Prior art carriages typically couple to opposing sides of a single rail and often include a driving force to both impart axial motion and to constrain movement of the carriage. The inventors believe that using an attachment point for driving a carriage causes errors in the locations of ink droplets on the paper as described hereinbelow.
Additional problems with prior ink jet head configurations involve the mounting of the print head for accurate placement and movement across the printed image. The rail structure for the print head must adequately support the print head not only over the entire printed image, but also for any cleaning, maintenance, and temporary storage of the print heads. It is common to provide a zone, away from the printing medium within which to “park” the print head to perform auxiliary “service” functions, this zone is commonly known as a service station. These auxiliary functions may include manipulating the carriage, certain calibration functions, cleaning and capping of the print heads. To accommodate the park zone, the support system, or rails, must support the head over a distance greater than the width of the printing medium. For example, printers handing printing medium about 36 inches wide may have rails about 48 inches long.
Accurate placement and movement of the print head becomes more and more difficult as the length of the print scan (i.e., the width of the image) increases. Most prior ink jet printers over about 17 inches wide employ either a two-rail structure, or a single-rail and outrigger structure, for head carriage X-directional travel. Both of these techniques provide two separate and independently adjustable support points for the carriage. Multiple support systems were used on wide format printers because it was believed that a single rail could not provide adequate support and stability for the print head over a large distance. Multiple support systems were utilized to provide a wider support base for the print head and carriage to lessen the effect of any stability problems, as well as to provide additional strength to lessen rail flexing problems. Vibration problems may occur if the print head undergoes movement with respect to the rail structure. The print head may slightly rotate or shake about an axis parallel to the rails, causing the print head placement with regard to the paper surface to be inaccurate. Alternatively, the print head may slightly rotate or shake from side to side on the rails, perhaps due to the direction of print head travel.
Dual support systems have not proven to be altogether feasible for graphics quality large format printing because it is generally difficult to maintain parallelism of the supports across the entire width of the large format media and oftentimes either more or less than three discrete points constrain the carriage. More particularly, each support introduces positional error, resulting in non-parallel guide paths for the carriage. Further, prior art two-rail systems employ a pair of circular rails, with the print head mounted on a carriage which is in turn mounted on the rails. The carriage is generally supported by circular sets of ball bearings wrapped around each of the circular rails. Non-parallelism of the rails introduces vibration through the ball bearings to the carriage, often causing instantaneous horizontal velocity errors. If the supports are not parallel, the rollers on the carriage will bind or have excess freedom at particular locations along the rails, and cause further stability and vibration problems. If bending of the rails occurs and the railings are not maintained completely straight, errors occur in positioning the print head. Additional problems occur due to the space that the rails take up, interfering with the transfer of electronics and ink from the printer housing to the print head. It will be appreciated that these problems are magnified as the length of the rail or rails becomes greater, as in large-format printing. Accordingly, a print head configuration is desired which will avoid these various problems.
Furthermore, such prior art carriage and drive systems typically are not designed for in-field replacement with minimum personnel and requiring a minimum amount of service time. In fact, due to the obvious competing design objectives of mechanical positional accuracy and field replacement convenience, the inventors are aware of only one other such rail system offering similar design benefits as the present invention. The inventors refer to U.S. Pat. No. 5,592,202, issued Jan. 7, 1997 and titled “Ink Jet Printer Rail Assembly” which application is commonly assigned with the present invention to ColorSpan Corporation (formerly known as LaserMaster Corporation) of Eden Prairie, Minn. 55344. In the application cited, a single rail pivotably attaches to at least one end of a print engine chassis so that the carriage riding thereon may be removed for field service and replacement. The benefits of such a system relate to diminished down-time, reduced required service, and efficient repairs, thereby reducing the overall cost of ownership involved in operating one or more large format digital print engines.
Prior art digital printing systems typically operate by moving a print medium transverse to an articulated imaging print head. The print head frequently includes a plurality of discrete imaging elements suitably arranged in a pattern wherein one or more linearly aligned sets of ink emitting nozzles, or jets, dispo
Anderson Kerry Ray
Bloom Gregg Michael
Hanson Michael David
Leonard Benjamin Patrick
Carmody & Torrance LLP
Chau Minh
Hirshfeld Andrew H.
LandOfFree
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