Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2000-02-15
2003-05-27
Vo, Peter (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S829000, C029S846000, C400S112000, C400S113000
Reexamination Certificate
active
06568071
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to registration references for the print head of a high resolution laser or ink-jet printer or a plotter, and in particular to method of manufacturing a true-dimension optical encoder strip for a wide-format printer or plotter manufactured using known imagesetting devices.
2. Description of the Prior Art
Printers and plotters utilizing a wide variety of technologies are well known to the art. The term “printers” is used herein generically referring to color and monochromatic (black-and-white) laser printers, inkjet printers, and plotters, unless a particular distinction between these types of devices is specifically called for or noted. In general, many printers and plotters operate using substantially similar or interchangeable technology and components, but are utilized in different applications. Those of skill in the art readily appreciate these distinctions or limitations, and the relative advantages or disadvantages of the corresponding technologies.
Many commercial and personal printers have resolutions of 300 dots per inch (dpi) or greater, with 600 dpi and 1200 dpi becoming standard within recent years. Resolutions of greater than 2000 dpi can be achieved on some high end personal printers, and are conventional for professional printers, typesetting machines, and photoduplicating or photolithography machines.
It is readily appreciated that such printers require great precision and uniformity in the ability to repeatably position the print head. Variations in this precision result in compression or expansion along individual lines of an image, or in elements which lack clarity or definition at the desired dot resolution. Variations between lines will result in abnormally dithered or skewed portions of images, or other irregularities in print quality or clarity. In many graphic images for personal or even professional use, these minor variations will not be readily detectable by normal visual inspection in most applications unless a particular screen pattern or color separation is involved which produces a cascade effect and creates visible distortions throughout larger portions of the total image. By comparison, this lack of precision cannot be tolerated for computer-aided design (CAD) applications. In the case of high resolution or enhanced resolution printers for professional applications, precise print head placement is required to achieve the expected dot resolution of the device over the entire width of the image. Because high resolution images in large formats can be very expensive and slow to produce, plotters are more frequently utilized in applications where a large format image is created (often composed of significant “white space”), but exact accuracy is expected in line weights and the spacing between individual lines, the curvature or length of lines, and the density of image elements.
As such, providing an accurate linear reference to uniformly and repeatably determine the registration or placement of a print head is indispensable for printers and plotters. Many such devices rely on encoder strips which ideally have a multiplicity of discrete markings, equally spaced from one another but without corresponding dimensional references such as inches or points relative to the terminal ends of the encoder strip. A sensor such as an optical emitter/detector is mounted on or near the print head or carriage, and produces a digital or analog signal pulse as the sensor passes and detects each marking. A count of the signal pulses is used to calculate the position of the print head relative to one of the terminal ends of the encoder strip, or to the last reference position of the print head.
However, in practice the uniformity or precision in the spacing and weight of markings on an encoder strip is very much less than ideal. This is due primarily to limitations in the fabrication processes which result in inaccurate registration references.
FIGS. 1 and 2
illustrate a prior art encoder strip having an irregular spacing defect or “banding” defect. A distance between adjacent registrations marks
16
varies across the length of the encoder strip. As further discussed herein, the “banding” defect may result from limitations of the imagesetter's control and software systems.
Encoder strips fabricated from a polymer sheet or film such as Mylar® are also known. The markings on these polymer film encoder strips may be imprinted in a variety of ways, however the ultimate accuracy of the encoder strip is limited by the precision of the imprinting process or apparatus. Very high resolutions for imprinting encoder strips can be achieved using a device such as a laser imagesetter designed for electronic tooling, printed circuit board (PCB) fabrication, and wafer photoetching processes. Such imaging systems may be of either planar and drum design. Planar imaging systems, such as disclosed in U.S. Pat. No. 4,841,656, are types of imaging systems which have a planar surface for receiving a substrate. An optical exposure head is located on a movable gantry apparatus and is rastered above the substrate during exposure. Drum imaging systems, which may be of external or internal drum design, have a cylindrical drum surface portion receiving a substrate. A reflected or directed light beam is advanced across the substrate surface during exposure. Examples of such drum imaging systems are disclosed in U.S. Pat. Nos. 5,841,567 and 5,828,501.
A fundamental flaw has existed in the manufacture of encoder strips used for wide format printers. This deficiency is the result of reliance by those of skill in the art on traditional “lines per inch” standards for calculating and controlling image resolution. For example, one inch (1″) of encoder strip imprinted for 300 dpi basic (physical) resolution would have an alternating pattern of 150 lines and 150 intervening spaces. However, each line and each space would be one three-hundredths of an inch ({fraction (1/300)}″) in width. Converting this to decimal form, each line (or space) would have a width of 0.00333333 . . . inches, wherein the row of threes in the decimal would repeat infinitely. For suitable precision, the encoder strip would need to be imprinted using a device that provided accuracy to six decimal places, whereas most available devices default to only four or less decimal places of accuracy. As a result of the inherent limitations of the imagesetter to maintain accuracy across the entire length of the film, variations in the distance between adjacent registrations of the encoder strip results. These variations are often manifested as visual “banding”, defects, as illustrated in
FIGS. 1 and 2
.
The industry has attempted to address this inherent deficiency in several different ways. One method is to use a high resolution imagesetting device to generate a master imprinted on glass (or another permanent material), and using a contact photoprinting process to reproduce encoder strips from that master. This is a relatively slow process, and care must be taken to prevent dust or other contaminants from affecting the contact print. The conventional process of contact printing from a master can lead to loss in image quality, which adversely affects the accuracy or precision of the encoder strip. For wide format encoder strips, the equipment for and corresponding complexity of producing the master can increase the ultimate cost of the encoder strips, and it is necessary to produce a unique master for each version of an encoder strip.
Another method is to imprint markings having only thirty-three thousandths of an inch (0.0033″) width and spacing, rounded down from the corresponding infinite decimal. The result is 150 lines and 150 spaces which extend along a total distance of 0.99″ for each inch of encoder strip—or 99% of the total length of the encoder strip—for a 1% initial error factor overall. The encoder strip is then mounted by stretching the material to its full 100% length and pinning the opposing ends in plac
Hansel Bryan L.
Hansel Donald C.
Hansel Gregory A.
Johnson Jeffrey J.
Boswell Alan M.
Encoder Science Technologies LLC
Gray Plant Mooty Mooty & Bennett, P.A.
Vo Peter
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