May 22, 2003
An affordable and elegantly simple new rapid prototyping system from Germany was the most exciting new product at this year’s Society of Manufacturing Engineers rapid prototyping conference and exposition. The manufacturer, Envisiontec, calls its system the Perfactory (short for personal factory).
|The Perfactory builds parts by shining visible light on resin. Layers are exposed from below by a DLP projector, and the part grows from the top down.|
Like stereolithography machines, the Perfactory builds parts by curing layers of liquid photopolymer. Unlike stereolithography systems, however, which use expensive lasers guided by precision optics, the Perfactory employs an off-the-shelf digital projector to solidify entire layers of resin with visible light. Delivering impressive resolution and building speed and requiring virtually no calibration or maintenance, the Perfactory could be the machine that takes high accuracy rapid prototyping off the shop floor and into the design office.
Stereolithography machines build parts by solidifying layers on the surface of a vat of liquid resin and then lowering a part into the basin as it grows. Instead of a deep tank, the Perfactory uses a clear glass tray to hold only about three millimeters of liquid resin. The resin is exposed to an image of the layer projected through the glass from below. The glass is coated with a proprietary substance to keep the solidified resin from sticking to it. Once a layer is cured, the growing part, attached to an overhead gantry, is raised away from the glass and new resin is allowed to flow beneath it. Then the part is lowered into the thin pool of liquid resin until it is a single layer-thickness from the bottom of the glass tray (0.025mm to 0.1mm [0.001-0.003 inches], and the process is repeated. Each layer takes only eight to ten seconds to build. Once parts are complete, they require no further post-curing. The build rate is approximately 0.75 inches per hour.
Digital Light Processing (DLP)
The key to the system is a digital light processing (DLP) projector developed by Texas Instruments. At the heart of TI's technology is an optical semiconductor chip with an array of 1.5 million microscopic mirrors. These tiny mirrors tilt back and forth independently up to 5,000 times per second, operating as optical switches to project high-resolution images. Texas Instruments introduced digital light processing technology commercially in 1996 and since then has come to dominate the digital projection business. Currently DLP projectors can be purchased for as little as $1,500.
Parts built by the Perfactory look like stereolithography parts. When built with the minimum layer thickness -- 0.001 inches (0.25mm) -- little stair-stepping is evident. On all the Perfactory parts we’ve seen, the detail is excellent.
- Operational unknowns
The full article is available for a fee at CADCAMNet.