The unobtainable ideal would be for the laser line to be exactly one pixel thick across our field of view with no laser speckle causing dropouts in the measurement. This would result in a perfect measurement with no noise. This is unobtainable, however, so the best we can do is minimize line thickness and speckle as much as possible.

The original laser delivered with the camera was a standard SNF model laser. Results were not as consistent as was desired and we researched alternatives. It turns out there is a version of the same SNF model laser with a narrow line thickness option. Swapping the laser dramatically improved our measurement quality with no other changes to the system.

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The Ranger came with a Fujinon 35mm lens which focused sharply in the center of the field of view. However there was significant blur near the edges. (The CMOS sensor on the Ranger is 15.4mm diagonal. That exceeds the specification of most common machine vision lenses.)

I tried a Tamron 35mm lens, and achieved better results, but there was still blur on the edges.

A Tamron 50mm lens worked better than the 35, but I moved my camera position back almost 3 inches to get the same field of view. My application is very space constrained and this is undesirable.

I remembered a presentation at a PPT vision seminar by Patrick McKenna, a Machine Vision Solutions Engineer from Edmund Optics. He talked about Edmund’s Double Gauss lenses. So I gave Patrick a call, and ordered the 35mm focusable Double Gauss lens. (Despite ordering after 5 pm, I still got it the next day, one of the things I love about Edmund.)

The Double Gauss lens did exactly what Patrick said it would. The image focused sharper than ever in the middle, and was just as sharp at the edges.

Here’s my data for a 1 inch Field of View. (The Sick Ranger has a 9.5 micron pixel size.) lp/mm is Line Pairs per Millimeter.

Fujinon 35mm: Center of field: 8.0 lp/mm, edge: 5.04 lp/mm

Tamron 35mm: Center of field: 8.98 lp/mm, edge: 8.0 lp/mm

Tamron 50mm: Center of field: 14.3 lp/mm, edge: 11.3 lp/mm

Edmund Double Gauss: Center of field: 16 lp/mm, edge: 16 lp/mm

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A recent NASA Invention of the Year was a hand-held, battery-operated scanner that they use to create surface maps of shuttle tile damage.

The same high-speed 3D scanner technology can also be used for longer range 3D measurements. NASA is investigating using this method for Rover Navigation and in-flight shuttle inspection with a system mounted on the robotic arm.

DMC has experience using the structured light approach for 3D vision applications. In one application we created a low-cost system for measuring parcel size using a stationary camera and movable laser line to scan the field of view. We performed all of the calculations on an embedded PC running Linux. Another application applies the Sick Ranger, an off-the-shelf 3D camera that uses the structured light principal, to measure dimensions of an aerospace part.

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The camera images a laser line from an out-of-plane location and processes the line position and shape as 3D points. The difference is that while the others process the line directly in the camera and transfers only a single line of height information, Matrox transfers the raw image to the processor and computes the 3D points there.

Consequently, the Matrox solution doesn’t have the blazing speed produced by the others. But it can be implemented on a Matrox Iris smart camera running MIL 9.0 for less than half the system cost.

The Iris solution can still exceed 100 frames per second at 640X480, and better than 20 frames per second at 1280X960.

See the system this week at the Robot and Vision Show.

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This device is a 64X48 pixel distance sensor. It operates by the time of flight principle. A pulse of light infra-red light is emitted by the device which bounces off of an object in the field of view and returns to the device through a lens.

Each pixel measures the time required for the light to make the round trip. By this way, it produces a 3D image of the object in front of it. The unit can be configured to output calculated quantities like max height, or volume.

It can also output the entire distance array through a TCP/IP connection. In addition to its capabilities, its list price is amazing at only $2100!

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Now, a couple of integrated and factory-calibrated units are on the market which offer a great head-start to a successful 3D scanning application.

SICK | IVP Ruler E

The SICK | IVP Ruler E is the integrated and calibrated version of the Sick Ranger product line.

Specs:

• 13 varieties available
• 1536 pixel profile width max
• 10,000 fill profiles per second
• Interface: Gigabit Ethernet
• Application Software: API’s provided for .Net, C, C++. LabVIEW API in beta.

Micro-Epsilon scanCONTROL

The Micro-Epsilon scanCONTROL is a new integrated and factory calibrated scanner.

Specs:

• 8 varieties available
• 1024 pixel profile width max
• 250 full profiles per second. (Up to 4000 for partial profiles)
• Interface: FireWire, RS232
• Application Software: API provided for C++, LabVIEW
• Works with the NI Compact Vision System
• For 2810 model, built in calculations are included for typical measurements of groove and bead applications, reducing custom programming.

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