TECHWATCH tm: The Print Engine That Could

Digital press and copier makers sometimes hobble faster-running models to produce slower versions sold at lower price points. But can you goose a top-speed digital engine to go even faster? We've run across a dry toner electrophotographic press for which this could be the case.

Kodak recently debuted the NexPress S3000, a 4- and 5-color digital press with systems inside that let it run 20% (3,000 sph) faster than the NexPress 2500. Five areas adjusted to allow this performance-enhancing uptick—front end processing, writing heads, paper-flow mechanics, dry ink control and fusing—hold potential for even faster models. Data from the S3000 NexStation V front end hardware is processed on new version 10.0 software, and uses entirely new and scalable architecture. Its image data path was designed to render images to print surfaces at speeds even faster than the press requires, so the system takes advantage of the advances in workstation performance. A new internal data path supports these higher data rates.

The NexStation V front end now uses two dual-core processors. It is the first and only existing production-color digital press running Adobe native PDF Print Engine. So the same file process architecture used in Acrobat and Creative Suite to build files now prints them, rendered natively throughout the workflow, eliminating the need to flatten transparent artwork. The breakthrough with this end-to-end workflow is a common file technology that generates, preview and prints. Previous digital systems hit a speed bump in file workflow, slowing down as they translate files from formats used in premedia into separate languages the printers understand.

Kodak employs an LED (light emitting diode) to quickly generate latent images on the NexPress photoreceptor cylinder. Comparable to offset plate images, these charged images attract and hold toner in high-quality color patterns. The size and density of pixels to be printed are a function of exposure. Kodak lines up its LEDs in a linear array: a row of flickering lights with lenses and constant adjustment and power controls that form outstanding printed images.

To appreciate the challenge, and the imaging power of NexPress's eight-bit depth output, realize that it delivers 256 gray levels for each pixel, in each of the color separations printed. Running the math for a print resolution of 600×600 dpi shows the writing heads must deliver an output capacity of 14,284,828 levels per square centimeter of printed space. Kodak patented this high information capacity printing process. (See GAM May 2006, p.44.)

To juice up the NexPress, engineers knew that much of the original head design was robust and could handle the increased thermal load required to write more frequently. Low thermal-expansion ceramics, as well as dynamic temperature-compensated LED drivers, are incorporated to better transfer heat from the head and minimize image shifting due to thermal expansion.

The S3000 writing head runs with a new data-electronics interface, pumping two gigabits of picture per second. (Think of this as the plasma engine that allows the StarTrek Enterprise spaceship to attain warp speed.)

SWIFT (Smart Writer Interface Technology) enables high-speed data transmission and allows continuous error-checking for image-data integrity. The S3000 writing head also contains a built in soft-core processor that manages internal functions, optimizing the data path image-data transfer at maximum speeds.

Based on my assessment, the NexPress writing head architecture may have the highest bandwidth in the industry. There is no doubt this will allow Kodak to deliver images even faster, far exceeding the S3000's demands. We should expect to see further speed increases.

Faster digital presses mean heavier volumes of paper transport and faster-running mechanical components. Adjustments were made across the press for more powerful motors, heavier-duty driver boards and more electrical power where higher current driving would be needed.

An area of particular interest is the dry toner delivery, because it must be transferred, applied, removed and recycled 20% faster. Dancing electrostatically charged toner particles don't always behave. (These challenges compare to ink misting on high- speed presses.) Properly applying the dry ink to the latent image on the photoreceptor cylinder required nifty engineering.

Rather than engineer a new toner for these demands, Kodak solved its toner delivery problems by applying an additional electronic charge, generating a magnetic field that pulls excess developer back to its proper receptacle after it escapes the Dry Ink station. This also lays the groundwork for the NexPress S3000 to deliver magnetically MICR toner used in check printing.

Fusing toner to paper while increasing press speeds is no trivial matter. (GAM Sept. '07, p.19). As paper moves faster and faster in a digital press, dwell time for fusing shrinks. So the S3000 fuser delivers greater levels of heat energy to the substrate—and without overheating nearby components. Kodak improved release by adapting the air knife for optimal performance at the higher speed. It also improved the fuser roller temperature control so resulting image appearance is more consistent throughout each print run.

The NexPress S3000 prints at full rated speed for all weights of stock. So fusers must deliver the heaviest of cover stock (350 gsm) applying the heaviest of toner coverage areas.

It is most likely that we will see the OEM increasing even further its toner coverage area and density for the NexPress. This will result in even deeper colors and saturations, as well as extend the clear toner scuff-resistance and decorative overcoating delivered from the fifth unit. Thicker matte and gloss coatings will also increase the depth of Kodak's digital water-marking.

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