Wednesday, November 30, 2011

Scanners and Shiny Stuff

Have you heard it? Have you felt it?
...the glaring silence when people talk about scanning a shiny object?
Sometimes the response is to jump quickly to questions of accuracy on parts that AREN'T shiny...
Sometimes the response is to jump quickly to a can of white powder spray...
Sometimes the response is to ignore the topic completely and hope it doesn't appear again...
None of the above responses are particularly flattering for the customer or the 3D metrology company. 
We've all seen the data: the glaringly high outliers, the strange reflections in the data, discontinuous data, the lack of data altogether, the high levels of noise, and the incomplete data coverage across the scanner's field of view.
But now it's time to write a rulebook on shiny objects. These are the "laws" that govern the 3D metrology of shiny objects.
Rule 1 - Scanning a shiny object will NEVER be as accurate as scanning a non-shiny one. As a rule of thumb, expect an order of magnitude up to several orders of magnitude of difference. This is because the "feature finding uncertainty" (whether a fringe, line, or pattern) shoots way up due to the specularity of the surface, and diffraction.
Rule 2 - A camera-projector setup that relies on cameras and projectors in fixed locations relative to a moving (non-fixed) part will suffer from severe systemic errors (several orders of magnitude of difference relative to a non-shiny part). Unfortunately, this setup applies to all "head" style scanners on the market -- which represents the vast majority of all 3D scanners. The pathological error in the case of fixed-camera-projector systems is known as multipath -- the phenomenon whereby the projected light reflects from one surface onto another, resulting in a "path" of light that takes "multiple" routes due to reflection.
Rule 3 - Scanning a shiny object MUST take place in a completely dark room/enclosure. The signal-to-noise requirements for shiny parts are much more demanding than non-shiny parts, and therefore complete blackness is necessary.
The 3 rules above necessarily indicate that when scanning shiny objects, a highly-conservative design in terms of accuracy must be employed, the light source must remain fixed with the part (as opposed to fixed with the cameras), and a dark environment must be built. Unfortunately, this is not the kind of 3D scanner that you will find at trade shows, and therefore most customers have never seen a working 3D scanner that can successfully scan shiny objects.
On a side note, some companies have advertised scanners that are "better at shiny objects," but this is generally a marketing angle rather than based on the laws of physics. The kinds of errors caused by shiny surfaces are not well-addressed by the claims of these companies, and by and large, the systems are not successful for high-accuracy work. For high-accuracy work, the 3 rules above must be observed. The reason these companies may advertise these claims is because, at a surface-finish level (i.e. surface porosity and microreflection level), some approaches are superior, however, they are useless for the large, dominant errors associated with shiny surfaces. In other words, solving a small problem does not solve the large one.

On a second side note, we have seen techniques to "mask out" portions of the projection to try to minimize multipath.  This is a valid technique, but it is not a catch-all.  It requires careful selection/deselection of very specific portions of the surface, and therefore requires very skilled operators.   
To measure shiny surfaces every time, no matter the surface, corners, or the shape, the three rules above must be upheld. 

Thursday, November 10, 2011

The 10-Year 3D Metrology Purchasing Cycle

The world of 3D Metrology capital equipment looks something like this:

Year 1 - 2: a company discovers an opportunity to apply 3D metrology to solve a problem
Year 2-3: the company researches various options, technologies, and solutions, and identifies the "best" one, often through a series of tests and product demonstrations.
Year 3-4: the company requests a budget for the equipment by justifying the Return on Investment (ROI) against the capital cost
Year 4-5: the company receives the budget, and places an order for the equipment. The equipment is delivered within several months, unpacked, set up, and training takes place.
Year 5-6: the company starts using and testing the 3D metrology equipment, and ramps up on its use. They work through issues, perform tests, and start on the path of becoming an "expert" in its use.

THEN, SOMETHING AMAZING HAPPENS (year 6-7) -- either the equipment works, or it doesnt. If it works, then the customer's use of the equipment meets the ROI, and all is good. The company is able to continue its use, and possibly purchase additional systems to further improve productivity. But if it doesn't work or if it "kind of" works (i.e. it doesn't work), then the ROI is not met.

If it doesn't work, then in many cases the technology itself is blamed as "not being ready" or perhaps the project is shifted to a different department, or perhaps the measurement equipment is re-purposed to another task, and the company continues to try to find a new solution (since the original problem has not yet been solved). They go back to Year 1, and the next system is not purchased until several years later. This means that the company does not have an opportunity to solve the problem the 2nd time until 10 years after the original opportunity was identified. Hopefully, this time around they pick the correct technology, or the cycle extends even longer.

But what almost never happens is that if the technology doesn't work, the company asks the 3D metrology company for a refund so they don't have to wait 5 more years for their next budget. We believe this is wrong. We believe that if the 3D metrology equipment does not meet its specification to realize the ROI, then the 3D metrology company should refund the purchase price.

In addition, we are taking additional steps to assist companies in solving their 3D metrology needs the right way, the first time. How are we doing this?
1) By charging the lowest possible price for the equipment, i.e. delivering the highest-perfoming system at the lowest possible price (through innovative system design --there are numerous examples of our approach saving significant money for customers), and therefore improving the ROI multiple, and reducing the size of the budget required for the purchase (and therefore hopefully accelerating the budget cycle); and

Choose wisely.