Toyz & Kidz

LEGO 3d: The Lego Scanner

These nifty device convert the rotation movement of a motor into a linear movement. The result is the scanner pictured above.

Lego 3d Scanner

It’s very slow, as you’ll see in his video , but regardless it’s pure coolness. Many parts have a clear geometric structure and are relatively easy to create, but parts like the frog pictured above have no defined geometric shape and are very difficult to model. Full setup with the laptop gathering data. The complete scanner, showing all modules.The probe module (red/yellow) moves the probing needle back and forth as well as up and down. When the probe needle touches the object, the location of the contact point is recorded. The object module (white/blue) is able to move back and forth the object and rotate it. The carrier bears a turntable, driven by a second motor through a worm gear. Note the use of two stacked turntables to avoid wobble caused by mechanical play. Though the scanner as shown uses 4 motors, only 3 are needed at the same time for a given style of scan.

Lego 3d Scanner

Short video of 3D scanner I made using Lego Mindstorms.

The needle is mounted on an axle that is maintained by a very slightly taught rubber band. When the needle touches the object, the axle goes back a little and a black and a white pin joiners move in front of the light sensor. This allows detection of the contact with very little force applied on the object (so the object is not punched by the needle!). Though reasonably rigid, the needle carriage assembly bends when a regular stiff cable is used. This assembly is used to attach the modules together. It can be easily modified to adapt to various sizes of scanned objects. The modules configured in polar scan setup. The acquired points in these area have low precision and must be deleted before assembly. No damage on the part: pressure is so low that there is no needle marks, and rubbing with alcohol after scan easily removes glue. After doing a lot of back and forth moves (during a scan the probe shuttles several thousands times!) the zero of the encoder does not correspond to the same mechanical position of the shaft. Depending on the scan parameters, this issue is barely noticeable or make the scan useless. The scanning process is very slow, several hours for a small part!

After the scan is completed, use a text editor to clean-up the log file (remove console output before and after scan) and save it with. obj file extension. At the send of setup, all useless functions are erased from memory, making room for scan function. The triangular mesh will not show till you choose an appropriate display mode (flat lines, circled in red).

We now clean-up the mesh of unneeded parts, mainly background. In addition to background, try to remove areas where needle direction was almost tangent with the surface of the object (since the needle slips in these areas, dot coordinates are very imprecise. Note that selection operates on all triangles under the cursor, even hidden back faces.

We are now going to align properly all parts of the scan. Meshlab has automatic alignment functions, but they don’t seem to work properly here, probably because there is little overlap between the various files. It will be used to anchor the frog on top. Transform” has a close and freeze button that would do both operations, but it is clumsy to use in relative mode, since it applies the transformation once more before freezing. Frog side is now correctly oriented, but not properly placed.

You can now align the frog side with the brick.

Note that if you forget to press the control key you will rotate the layer, which is not desired here. Note that you can save only one layer at a time. The brick is no longer needed, select it in the layer dialog and press the “-” button. A second movement module allows the object being scanned to move around and rotate, meaning the scanner can operate completely independently of human control. Essentially, a manual stop-motion technique is used. An object is placed in a the bowl and milk is added to come halfway up.

You need to flip the model to scan the other side, but this is a great low tech and effective hack. Objects to be scanned are placed on top of a small platform against two surfaces that create a reference for the software doing the scanning. The models produced are surprisingly accurate and great for modeling some of the rounder objects you’d like to add to your lego collection.

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