DAVID SLS-2 Tutorial

Transcription

1 DAVID SLS-2 Tutorial

2 Overview The DAVID SLS-2 system consists of calibration plates, a tripod, a projector, a camera, and software. It uses a technology called Structured Light Scanning (SLS) to measure the distance between the light source (a projector in this case) and the physical object being scanned. After a setup and calibration procedure, the projector beams known light patterns onto an object. The camera reads these patterns distortions, and the software converts these into surfaces. The physical object is then rotated to capture a number of scans that is sufficient to create a 3D representation of the object, color included (if desired), which can be exported in a variety of formats. Before You Start Why Scan? 3D scanning can be useful in a number of contexts: Performing dimensional analysis Generating 3D models for FEA/CFD analysis Reverse engineering Reproducing existing objects (via additive manufacturing or machining) Repairing a damaged object Archiving a digital copy of a physical object Most commonly in the PRL, students will use the FDM, ProJet, or Ultimaker II to reproduce objects scanned using the DAVID scanner. For objects not easily reproducible by hand in CAD, 3D scanning is an excellent option. How Long Does It Take? The time it takes to scan an object can vary widely depending on its size/complexity/surface properties. Setup and calibration can take minutes or more, particularly if an object is mostly symmetrical or has a troublesome surface finish but there will be more on those two points later! Each scan will only take a few seconds, but there will be multiple passes (and associated reorientation of the object) required to scan every part of an object s surface. Fusing the scans together can be tricky, and the time this takes can vary from just a few minutes to half an hour or more. 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 2

3 Our Setup Tripod The tripod is set up with the projector and camera, which should not be removed. Both the camera and projector are adjustable along the red railing. Calibration Plates The calibration plates and fixtures live to the side of the table, next to the computer on the left. These plates are made of glass and thus are extremely fragile. Treat them with extreme care! The fixtures are designed to hold the plates exactly 90 degrees from one another. These black fixtures slip off very easily. 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 3

4 Backdrop The background against which you place your object is critically important. The background needs to be as black and as matte as possible, or else there is risk of unwanted data being collected in the scans anything colored or reflective will appear. This isn t necessarily a huge deal, but it can be tedious to manually remove a lot of unwanted artifacts. The black fabric we currently have hanging in the corner works well as a backdrop and should be used in most cases. Technical Specs Size of objects to be scanned: 60mm 500mm ( ) Resolution: 0.1% of scanned object size (down to.06mm) Scanning time: a few seconds per scan Mesh density: Up to 1,200,000 vertices per scan Export formats: STL (most common), OBJ, PLY 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 4

5 Object Preparation The best objects to scan are: Bounded by the specified mm in any dimension Matte, not shiny Opaque, not translucent/transparent Asymmetrical, with abundant scan alignment features If this sounds like your object, you will have minimal prep to do! If not, check the recommendations below: If your object is too small or too large Go ahead and give it a try anyway and let us know how it goes! Small objects will scan with limited resolution this may or may not be an issue for you. Large objects require a bit of a different setup, so come grab a TA for help. If your object is shiny/reflective or not fully opaque If coloring the object is not an option, you may be able to rescue the scan by coating your object with a fine layer of talcum/baby powder. You can find this in the drawer please take this outside if you choose to use it. Reflective surfaces will distort the input to the software, and the camera won t pick up any translucency. This is a limitation of the SLS technology, which relies on a projected image being read by a camera. If your object is mostly symmetrical Symmetrical objects are difficult to scan because in knitting the scans together, there are no obvious features to align, so the software struggles to interpret where in space each scan belongs. To combat this, we can exploit the scanner s color capabilities and make alignment marks with various writing implements on the surface of your object. It may take several iterations before you figure out how many marks you need and where to place them, but it makes scanning an otherwise un-scannable object possible. 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 5

6 Scanning Getting Started To begin: 1. Turn on the projector 2. Take the lens cap off of the camera 3. Fire up the DAVID 3 program on the desktop If all goes well, you should see the projected pattern and some curious squiggly lines in a grid in the software s main view. You re doing it right! 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 6

7 Hardware Setup In the left hand panel, Hardware Setup should be the topmost section, expanded by default. Type à DAVID SLS-2 Screen ID à 2 Camera à DAVID CAM, and leave the resolution settings alone Enable Texturing à Check the Enable Texturing box if you d like to capture color data. This is important if you ve drawn alignment features on your object! Calibration **IMPORTANT: The calibration plates are glass and extremely fragile. The top and bottom fixtures slip off very easily** The default configuration of the calibration plates gives you 3 different background options identical patterns but different sizes: 30mm, 60mm, and 120mm. You want to select a background that is slightly larger than the object itself. The object should fit comfortably within the bounds of the pattern, but it shouldn t be dwarfed by the pattern bounds, either. 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 7

8 Object is too small JUST RIGHT! Object is too large You will likely need to elevate your object to center it within the pattern. Use objects that will be invisible in the scan something matte black. All 6 large dots need to be visible to the camera when you calibrate, so take care not to obscure these or crop them out. Your object will be removed from the scene during calibration make sure the camera could see them if your object weren t there. Your chosen calibration pattern should fill the camera s view. elevated joint 6 dots Back your object up so that it s very close to the joint between the calibration plates. Adjust the tripod so that the live image is centered at that joint between plates and the camera is looking down slightly at the object. Move the tripod so that your object fills as much of the viewport as possible - you ll need to physically move the tripod or object forward or backward to do this because there is no zoom on the camera. **More of your object s pixels on the screen means higher file resolution!** 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 8

9 Next, adjust the focus of the projector so the focus is on the joint between the calibration plates. (You may need to remove your object from the scene to do this.) Then, slide the camera so that the object is centered on the computer screen. Adjust the camera s exposure (back knob on the camera) so that the red sine waves on the computer screen are situated comfortably within the blue borders. Sliding the camera Loosening the set screws to adjust the rings 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 9

10 TOO LIGHT Waves attenuated JUST RIGHT! Waves centered TOO DARK Waves too small Play around with this until you get the best setting, with minimal flatlining and cutoffs. After setting the exposure, use the front knob to adjust the focus, getting the center vertical lines as crisp as possible on your object. The rest will be blurry that s fine! Then, LOCK THE SET SCREWS! If these are accidentally jostled during scanning, you ll need to start again. At this point, don t move or touch the tripod, camera, or projector! 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 10

11 You re now ready to run a calibration pass. Remove your object (and any elevation props you ve needed to add) from the scene. In the Calibration menu, select V3 Pattern and enter the scale of the background you re using. (This is the only way the software will know how large your object is, so it s critical to get this right!) Then, hit Calibrate the software will run through a series of flashes and patterns, which will take a few seconds. You ll end up with a checkerboard pattern exactly aligned with the calibration points. 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 11

12 Capturing a Scan **Note: Sometimes at this point something funky happens and the live view of the camera goes away. We think this is a software bug definitely not your fault! If this happens to you, go back up to the Hardware menu, deselect the DAVID camera, and then re-select it. You should now see the screen update live. You re working in the Structured Light panel now, and your pretty checkerboard will go away. For most scans, you shouldn t need to make any changes to any of the settings, unless you don t want to scan any color data in that case, deselect the Auto Grab Texture checkbox. Click on Quality for the best quality scan (this gives you the best file resolution and doesn t actually take any longer than doing Default or Speed scans, oddly). CAREFULLY remove the calibration plates from the scene and put them in their holster to the left of the scanning computer. These are precision glass plates, and the scanning setup is useless without them in pristine condition. Treat them well! Place your object and any necessary elevating objects back into the scene right where it all was before. You want it in the middle of the view and in focus. 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 12

13 If it s not in focus, DO NOT move the tripod or make any adjustments to the camera/projector move your object forward or backward on the table. Re-check the red sine waves if anything looks cropped, adjust the projector brightness slider in the software. You re now ready to scan. Click Start to capture a scan. This should take just a few seconds. There are a few options for post-filtering, if your scan is missing lots of data. Adjust the Quality Check parameter to see your scan change on the fly. A lower quality setting will include more scan data. A value of 0.2 works well in most cases. Once you re happy with it, click Add to List to accept the scan. (You can always remove it later.) Quality Check =.2 Quality Check =.5 Aligning Scans The rest of the process will repeat as follows: you ll clean up the scan you just took, align it to the other scans (if necessary), physically rotate your object, and repeat the scanning & alignment process until you have captured your whole object. 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 13

14 In the Shape Fusion mode, the whole workspace will change. Click and hold the left mouse button to pan around, and click and hold the right mouse button to rotate your scan. You ll use the tools in the Cleaning section up at the top of the screen to select and delete any stray bits that have been scanned inadvertently or scanned poorly. Poor scan data manifests as very jagged edges and usually corresponds to the outer extents of a scan that would be best captured from another viewing angle. 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 14

15 Jagged edges Stray bits When you re happy with your scan, click back into the Structured Light panel. Rotate your object so there will still be some overlap with the previous scan as much new surface area as possible. Take another scan, and repeat the same cleanup process. Click the eye icon to hide your previous scan(s) while you clean up your new scan. Now, you re ready to align the scans. 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 15

16 In the Shape Fusion panel, select Free and then the Contact Pair Selection checkbox. Click the eye icon next to your old scan to make it visible again. Then, click the Align Scans button. You ll then click on the same feature in both scans this will help the software be more efficient at aligning the two surfaces. After a few seconds, you should see the result! Click on the various icons in the Visibility panel to change the view to something you like. It can be distracting to have the object s texture visible when aligning because the lighting can be different depending on the angle the object was scanned. Repeat the process of rotating your object (yes, you ll also need the bottom and top of whatever it is you re scanning!), taking scans, cleaning it up, and aligning the new scans. It s far easier to align your new scan with your already aligned previous scans as you go, as it can be overwhelming to have to align many individual scans all at once. To group previous scans together, select them from the right hand list, right click, and select Combine Scans. If you re unhappy with a scan, select it from the list and click the minus icon. As you go, you ll discover which angles you need to scan to complete the coverage. 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 16

17 Missing coverage When you re happy with your coverage, click the Fuse button this will fuse all of your scans together into one solid. If you want to close gaps between scans (recommended in most cases!) check the Close Holes checkbox. This can take a couple of minutes depending on how many scans you have to fuse. You can then save your result (by hitting Save ) or make adjustments to your previous scans even take new ones to fill in any gaps. This is an iterative process! 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 17

18 Finishing Up You can save your fused result as.obj,.ply, or.stl. Save as.stl if your goal is to 3d print your result. Congratulations! You re done! 7 July 2015 v1.0 DAVID SLS-2 Tutorial Page 18