Linear positioners drive ink jets

By Control Engineering Staff February 1, 2006

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When most people hear the term “ink jet” they think of an inexpensive color printer. Yet ink-jet technology has a much wider range of uses.

As a branch of digital fabrication, it is used in producing passive and active electronics, in biomedicine, pharmacology, micro-optics, and stereolithography, and in many other applications. In electronics, it is used in the production of rigid and flexible printed circuits, for printing legends, and for applying solder masks. It’s even being used with conductive “inks” to create lines, pads, and interconnects for short-run-production and prototype electronics.

Ink-jet technology also is used for fabricating electronic displays. It is—or soon will be—used to print color filters for liquid crystal displays (LCD), displays using organic light emitting diodes (OLED), and organic thin-film transistors (TFT). Other optics applications include lenses and light pipes for lasers and optical computing chips.

Ink-jet technology also is being used to create three-dimensional objects and structures, including lattices for growing biological tissue, such as bone and skin.

With such an enormous range of applications and materials, it is not surprising that process development challenges manufacturers. Critical parameters include ink chemistry and properties, print head design (thermal or piezoelectric), morphology, and substrate properties, to name a few.

Several types of equipment are used in process development, including visualization systems, which use microscopes, cameras, and image capture to study the behavior of print heads, fluids, and substrates under simulated operating conditions.

A web-press development system is used when the expected substrate is flexible. It moves paper, or other flexible media, past fixed print heads and is used in ink development, ink/substrate interaction analysis, image quality evaluation, and print head sustainability and reliability testing.

For working with rigid or flexible substrates, the development system of choice is the printing and deposition system, used to develop production processes and produce sample output for evaluating fluid and substrate properties. Precise motion control of components is necessary to isolate characteristics of print head, fluid, and substrate dependencies.

Imaging Technology International (iTi) designs and builds all three types of development systems, production ink jet systems, and related material handling equipment, and provides integration services.

The main printing and deposition system is the XY Materials Deposition System (XYMDS, see photo), used by industrial users, ink developers, and print head suppliers for developing ink-jet-based production processes and jet-able fluids, and analyzing the interaction between fluids and solid substrates. In XYMDS, a rigid or flexible substrate is scanned under a stationary set of print heads. The system accommodates substrates ranging from 6 x 6 in. (152 x 152 mm) to 12 x 12 in. for four fluid printing, and up to 16 x 16 in. (406 x 406 mm) for single fluid printing. Scanning can be in raster or vector modes.

The system produces samples for studying process speed, order of lay-down, resolution, and fluid-to-fluid and fluid-to-substrate interaction. In addition, curing or drying devices can be adapted. XYMDS integrates with multiple print-head vendors to provide a precise, reliable, and easily maintained system for analyzing UV inks, printing inks, electronic materials, and/or biological fluids and solid substrates.

System design
In developing an XYMDS, iTi engineers needed to integrate a controller from National Instruments and other motion control functions into a high-level software architecture. They then presented XYMDS as a network device in a production and laboratory environment, using the encoder as a synchronizing data clock for position- and velocity-specific processes and using the stages in a vector trajectory for ink-jet material deposition.

At the heart of the XYMDS is an X-Y stage that provides speeds to 1.0 m/sec, acceleration of 5 G, positional repeatability of

National Instruments’ PCI 7342 two-axis servo-motor controller provides linear interpolation for multi-axis movement; it also features 32 bits of digital I/O capability for high-speed capture and RTSI bus for real-time synchronization.
For XYMDS axis-drives, Mark Einarson, territory manager at Western Technology, local distributor for Parker Daedal, helped choose the slides for the axes, and recommended Parker’s 400LXR series linear servo motor tables and a pair of Parker Daedal Aries drives (see photos).

The application used a Parker Daedal 406LXR linear-servo-motor table for the X axis and a 404LXR for the Y axis. These are slotless, brushless linear-servo motor/square-rail bearing-positioners with high strength, extruded aluminum bodies with magnetically retained protective seals. They are powered by one rail of high-energy rare-earth magnets. Load bearing members provide heavy load and moment capacity, dynamic stiffness and precise straightness and flatness of travel. An integral linear encoder provides non-contact positional feedback with selectable resolutions from 0.1-5.0

Einarson says the application required positioning accuracy and repeatability, which the 400LXR series provides. “They are able to take these complete actuators that are enclosed and also mounted in an X-Y configuration right from the factory,” says Einarson, “put the actuators into their machine, and they have their motion.”

Another advantage of the 400LXR series, Einarson continues, is that they are enclosed. “They have a strip seal that seals them up so if the user gets any ink or a spill of something then it doesn’t get into the mechanical working of the actuator.”

Motion, interface software
System software runs on a standard PC running in a Microsoft Windows environment. iTi developed the software for the motion control, interfaced that with the nozzle layout geometry of the print heads, and coordinated the two, to put each droplet in the right place at the right time. iTi also provided a user interface to make it convenient for process development, writing most of it in C++, with a few parts in N400LXR series NI LabView.

iTi’s 2.0 version of XYMDS uses lighter platens to allow higher speeds and better acceleration. This unit uses a Parker 6K multiaxis motion controller.

A redesigned platen removed some weight to boost speed and eliminate errors caused by vibration or motion; part of the challenge was to provide a mechanical platform stable enough for these stages. Bill Demyanovich, chief iTi engineer, designed an extruded box aluminum frame that would support the 3-in. thick piece of granite under the stages. Isolating electronics below the granite has reduced the possibility of vibration and prevented unwanted movement. With several hours of running, some systems with X-Y tables actually can vibrate across a room.

Ross Mills, Ph.D., founder, chairman and chief technology officer, Imaging Technology International.

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About the author
Ross N. Mills is chairman of the board and the chief technical officer of imaging Technology international (iTi) Corp. He received his Ph.D. and MS in Engineering Science from the University of California at Berkeley and his BS in Aerospace Engineering from the University of Texas at Austin. Since 1978, he has worked as a research, development, and manufacturing engineer in both staff and management capacities in the areas of piezoelectric and thermal ink jet printers and electrophotographic printers for IBM, Lexmark International, and Topaz Technologies, as well as iTi. In 1992, he founded iTi Corp. in Boulder, Colo., as an ink jet consulting and development firm, and as an integration facility for advanced applications in ink jet and imaging technology. Mills has 12 patents in this field and he is the inventor of iTi’s proprietary Esijet technology.