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Goal

To create a 3D range finding device that could acquire data continuously while using a minimum of power for movement.

Prior State of the Art

Previous 3D adaptations of the SICK company’s 2D laser range finders have fallen into two categories. There have been units using large and high power motors to scan the lasers vertically quickly, allowing for scans during vehicle motion. Other units have used the same mechanical motion but with slower and smaller motors. With these units, scans can take several seconds to complete, so the vehicle must be stationary during scans.

Besides the tradeoff between speed and power, units of these varieties have a more severe limitation: laser point density is highest at the extremes of motion and lowest at the center of travel.

Solution

The solution to these design problems lay in an unusual design: continuous rotation By continuously rotating the laser about its forward direction we could drastically lower power consumption Our first generation unit spins at 1.5 Hz and uses less than 10 watts of power An additional advantage of this design is that the scan frequency is twice the rotation frequency, and we can capture an entire hemisphere of range data The point cloud is densest forward of the laser and becomes less dense as the points approach the edge of the scanned hemisphere We can also vary the point cloud density by changing the rotational velocity.

Challenges

The main challenge of this project was the extreme space and time constraints.

The vehicle on which the scanner was initially mounted limited the mechanism to a 2.5” depth because we did not want the laser to be the forward-most object In addition, we did not want the mechanism to increase the spinning laser’s swept volume.

Time from concept generation to delivered first generation unit was about 7 weeks This included custom part design, custom part fabrication, COTS part procurement, assembly, wiring, and testing.

After we built the first generation laser unit we developed a second module that added vision capability This second module holds two firewire cameras, power regulation electronics, a mini-itx computer, and a laptop hard drive.

Both of these units were designed to be used in harsh environments and can be sealed against water.