Our design for a machine that can see and measure things is based on the principles of structured light, an optical method for 3-D scanning. It works by projecting a known pattern of pixels — often grids or horizontal bars — on an object and then detecting distortions of the patterns with a camera or sensor. Image processing and triangulation algorithms then convert these distortions into a 3-D “point cloud” that can be used to extrapolate the shape of the object, or render it as a CAD model.
What that means is that the dimensions of any object—including surface area, volume, and feature size—can be extracted. Machines can see and measure objects.
And if a machine can measure shapes, it can print them The structured light approach is also making its way into 3D printing through a technique called photo-polymerization – as light selectively hardens resin in a pool, the printed object emerges, much like the robotic villain in “Terminator 2,” rising from a metallic puddle.
New applications for structured light appear every day. A clever one is in forensics. Instead of using tape to extract and “flatten” a fingerprint, police now use 3D photography to flatten and analyze the print digitally, which saves time.
The DLP LightCrafter 6500 sold by Texas Instruments is a rather capable — high performance, flexible — evaluation module made for experimenting with structured light applications that require “high resolution, optical throughput and brightness at a competitive price point,” says the company. It allows you to format and sequence light patterns through a graphical user interface and to sync with cameras, sensors, or other peripheral devices.
At the heart of DLP LightCrafter 6500 is the Digital Micro-mirror Device (DMD), the digital light switch invented in 1987 by Larry Hornbeck of Texas Instruments. On the surface of a DMD chip is a rectangular array of hundreds of thousands of microscopic mirrors, cleverly printed with a MEMS process so that they can rotate by a few degrees. By controlling—individually — the rotation of the micro-mirrors, incident light can be reflected in different directions.
Detailed features of the evaluation module can be found here.
A fascinating demonstration of the principles of the DMD can be found in this video by our favorite geek, Ben Krasnow, the Applied Science guy.