Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-10-15
2003-04-29
Nguyen, Lamson (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S014000
Reexamination Certificate
active
06554388
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to an improvement to a printing apparatus that forms an image using a plurality of exposure elements and more particularly relates to a method for improving uniformity of output prints from such a printing apparatus.
BACKGROUND OF THE INVENTION
The difficulty of achieving uniform density output from a printer is a well-known problem in the printer art. Non-uniformity is particularly noticeable with high-quality color printers, where it is important to be able to faithfully reproduce subtle changes in shading and gradation or flat fields having the same density. Non-uniform response of a printhead causes unacceptable anomalies such as streaking and banding, which can easily render a print useless, or at least disappointing, for its intended audience.
Factors that contribute to printer non-uniformity vary, depending on the specific printing technology. With a thermal printhead, for example, where resistive print elements are linearly aligned along a writing surface, slight mechanical irregularities or additive mechanical tolerance variability can cause some elements to be more effective in transferring heat than others. With a printhead that scans optically, such as a CRT printhead, optical aberrations or fringe effects can mean that light power is less effectively distributed at the extreme edges of the scan pattern than it is in the center of a scan line. In a photofinishing system that uses an array of light-emitting elements, such as a Micro Light Valve Array (MLVA) in the Noritsu model QSS-2711 Digital Lab System, manufactured by Noritsu Koki Co., located in Wakayama, Japan, individual elements in the array may vary in the intensity of light emitted.
Achieving printer uniformity for high-performance printers used, for example, as photofinishing systems, graphic arts image-setters, and color proofing systems, can be particularly complex. Due to customer expectations for quality, the problem of printing apparatus non-uniformity is especially acute in the photofinishing arts. In photofinishing, the continued development of digital solutions for image scanning and printing of photographic-quality images make the problem of achieving print uniformity particularly important. To complicate the task of achieving uniformity among printers used in photofinishing, these printing apparatus may include components provided by more than one manufacturer. Companies specializing in different aspects of the photofinishing process provide exposure apparatus, development apparatus, scanning devices, film and paper, and consumable development chemicals needed in the process. In order to design a complete photofinishing printing apparatus, a systems integrator may create a system by combining preferred components and consumables from a number of vendors. In many cases, vendor companies providing the various components and consumables may even be, at least in part, competing against one another. From the perspective of a supplier of one or more components, it is advantageous to be able to provide a printing apparatus subsystem that can maintain or improve image quality with minimal dependency on other subsystems. From the alternate perspective of an integrator of components, it is advantageous to be able to purchase a necessary component or consumable from a photofinishing manufacturer as a “black box”, where no proprietary information on internal components or operation is needed or provided. Instead, in order to integrate a component or consumable into a photofinishing printing apparatus, a systems integrator only needs access to information on performance and external operation for those components.
As one relatively complex type of printer, a conventional printing apparatus used for digital photofinishing typically comprises the key subsystems shown in FIG.
1
. Here, a printing apparatus is generally numbered
10
. The data path for printing apparatus
10
is represented by solid arrowed line B. A digital image source
12
provides input image data. Digital image source
12
could be, for example, a color scanner. An image data manager
14
performs digital manipulation and processing of the input image data from digital image source
12
. Image data manager
14
is a computer, which may be a Windows or UNIX platform, for example, specially configured for its imaging function. Image data manager
14
comprises the necessary CPU, disk storage, and memory components for processing an image and providing the image data at its output.
As the printing engine of printing apparatus
10
, an image forming assembly
22
comprises a printhead
16
and support circuitry, including a transfer element
36
, an optional transport mechanism
28
(where printhead
16
includes moving parts or scanning components), and a drive electronics assembly
26
that controls the amount of energy applied to transfer element
36
. A system controller
30
provides control logic and processing functions for image forming assembly
22
components. Printhead
16
creates an image by applying energy from transfer element
36
onto a receiver substrate
18
. For typical apparatus of this type, receiver substrate
18
is photosensitive print paper. For such a typical system, transfer element
36
applies light energy to expose the paper. Alternate combinations of receiver substrate
18
and transfer element
36
are possible, however, such as using a colorant that is applied directly to receiver substrate
18
(for example, ink) or a colorant donor material. For inkjet printing, transfer element
36
provides colorant directly, where the amount of colorant transfer is modulated by varying the amount of heat exposure energy applied to inkjet nozzles. For printing apparatus
10
using colorant donor imaging technology, transfer element
36
can apply light or heat exposure energy to a donor material (not shown) to transfer colorant to receiver substrate
18
. For any type of printing apparatus
10
, dashed line A represents the travel path of receiver substrate
18
from a receiver supply
24
through image forming assembly
22
. A processor
20
provides any necessary processing of receiver substrate
18
in order to provide a completed output print
38
. For photofinishing printing apparatus
10
that uses photosensitive silver-halide chemistry, processor
20
uses a series of chemicals (for example, bleach, fixer, and developer) that develop the latent image exposed by printhead
16
onto receiver substrate
18
. For printing apparatus
10
using a donor colorant, processor
16
may transfer colorant from a receiver substrate
18
onto paper stock, with optional addition of a lamination layer.
Referring again to
FIG. 1
, it is instructive to note that conventional approaches for non-uniformity correction are directed to internal adjustments that are made to components within image forming assembly
22
. For some types of printing apparatus
10
, a sensor
58
is provided in order to measure a characteristic of transfer element
36
. Sensor
58
feedback then goes to image forming assembly
22
to adjust the behavior of drive electronics assembly
26
. Dotted line C represents this feedback path using sensor
58
. For other types of printing apparatus
10
, a scanning device
60
, such as a scanner or densitometer, is employed to obtain measurements from output print
38
. Data from scanning device
60
is then directed to image forming assembly
22
to adjust the behavior of drive electronics assembly
26
. Dotted line D represents this alternate feedback path using scanning device
60
measurements. It is instructive to note that, when using the feedback path indicated by dotted line D, density data is obtained from output print
38
. Image forming assembly
22
must perform some further conversion of this feedback density data to data values actually used by printhead
16
to control exposure.
The disclosures of the following patents illustrate conventional approaches for non-uniformity correction as applied for various types of printheads
16
:
U.S. Pat. No. 5,546
Barnick William M.
Narayan Badhri
Wong Victor C.
Blish Nelson Adrian
Nguyen Lamson
Stewart Jr. Charles W.
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