Xerox Scientist Describes Experiments To Optimize Printheads For Solid Ink Printers

Xerox Corporation's next generation of solid ink printheads is being designed through a "rapid prototyping" process that will speed development, increase product quality and may yield useful information for other industries that need to control the behavior of fluids on a micro scale, according to a Xerox scientist.

In a talk being given at PhAST 2006, John Andrews, a principal scientist at Xerox Research Center Webster in Webster, N.Y., will discuss "Laser Rapid Prototyping for Designed Experiments in Microfluidics." The annual conference, sponsored by the Optical Society of America, presents the latest breakthroughs in laser applications, systems and technologies.

Andrews reported on experiments in which he systematically varied the size and shape of a printhead nozzle - with an opening one-tenth the diameter of a human hair - and other parts of the fluid delivery structure in order to optimize the placement of ink droplets that the printhead squirts onto paper to form images. He used rapid prototyping, a process that integrates Xerox's modeling and simulation expertise with laser micromachining, to produce functioning printheads having desirable performance characteristics. That reduced the time required to produce the prototype devices to a matter of hours or days compared with as much as two months if done by conventional methods.

Andrews used a laser to micromachine - or drill - a number of inkjet nozzles, each with a slightly different shape. By testing the droplet shapes resulting from the various openings, he found that he could use the nozzle plate thickness and the shape of the nozzle's barrel to predict how fast the droplet would travel.

The results from experiments will enable systems engineers to pick a nozzle design that produces the performance characteristics desired for the system they are planning. In addition to inkjet printers, other applications where a liquid must be forced through a tiny opening include spraying materials for biological analyses and DNA testing, testing for the presence of chemical agents, shooting droplets of solder to bond chips to a circuit board, and constructing three-dimensional wax parts models by "printing" them.

"Nozzle properties are important," Andrews concludes, "because the nozzle is the last interface between the liquid pool and the air. Nozzle shape controls the speed and direction at which the drop travels as well as its size."

Andrews' research using laser micromachining for rapid prototyping will lead to faster development of next-generation solid ink printheads at lower cost. Introduced more than 15 years ago, Xerox's exclusive solid ink technology is an affordable option for businesses looking to add color to their documents and has become a competitive force in the industry. Solid ink creates brilliant prints on a wide range of media, is easy to use and produces 90 percent less waste than laser printing.

Rapid prototyping one of the reasons Xerox is able to quickly bring to market new marking systems that are smarter, smaller, simpler and speedier.

A Chat with John Andrews
John R. Andrews is a principal scientist in Xerox Corporation's Xerox Research Center Webster in Webster, N.Y. He is currently project leader for advanced piezo inkjet printhead technology. He has a doctorate in chemistry from Stanford University and joined Xerox in 1982. During his career at Xerox, Andrews has done research supporting both xerographic marking and inkjet marking technologies and has worked in research and in a business division.

Q: How do fluids on a micro scale behave differently from fluids in, say, a garden hose?
A: Microfluidic structures have features with sizes of on the order of 1/10 the diameter of a hair up to the size of a coffee stirrer. Blood capillaries are biological microfluidic structures.
With such small dimensions, flow resistance can be much larger than in larger structures so that more force is required to cause the fluid to flow. The small dimensions also mean that surface tension (capillary-driven flow) can be very important where there are interfaces that include air-liquid-solid interfaces.

Q: What are some of the challenges in inkjet printhead design?
A: Having a high efficiency for the actuator (the microscopic engine that causes the fluid to move) is very important for performance and cost. Developing a design that can tolerate small variations in dimensions of the jet and still make drops nearly identical to the other jets in the printhead is critical to having good image quality.

Q: What is rapid prototyping?
A: Rapid prototyping is a collection of methods that can be used to make functional parts that can be tested to verify that a design meets the requirements of the application. The term "rapid" in rapid prototyping indicates that methods are used to make the prototypes that are quicker to implement than a standard mass production method. One familiar means of rapid prototyping could be computer numerical control (CNC) machining of a part that might normally be mass produced using injection molding. Some laser micromachining can be considered a form of CNC machining where the steel bit is replaced with a laser beam.

Q: How does Xerox use laser rapid prototyping in inkjet technology development?
A: Xerox is using laser rapid prototyping for microfluidic studies and in prototyping and production for electrical interconnect components for its solid inkjet printers. One key advantage of laser prototyping is the flexibility in changing initial designs and the ability to try systematic variations of fluid and electrical interconnect to understand the design performance trade-offs. One of the reasons for the rapidity and flexibility in prototyping is that the design is largely a matter of computer control. By simple changes to a computer program, the design can be changed. Another factor is the feature resolution and accuracy of the laser cutting compared to many of the more common prototyping and production methods. In many cases, if laser prototyping can produce the components needed, it is an advantageous production method as well for both cost and quality.