3D imaging developments
01 May 2012
There can be no doubt that the use of 3D imaging for volumetric comparisons, volume measurements and bin picking of random parts is now a very real and growing part of the industrial vision market. Suzanne Gill reports on the developments in 3D imaging and asks whether the technology can offer real benefits.
VisionPro 3D from Cognex
A market study undertaken by the VDMA (Verband Deutscher Maschinen und Anlagenbau - German Engineering Federation) indicated that, while the revenue from 3D optical systems was about 10% of that of 2D systems, 3D growth rates are higher, indicating that it is becoming more significant.
John Haddon, technical consultant to the UK Industrial Vision Association (UKIVA) explains more about 3D imaging developments: “While extrapolations from 2D imaging to produce pseudo 3D measurements have been possible for many years, the emergence of processors capable of handling the computational overhead required for 3D cloud datasets at production line speeds has been the key to establishing true 3D measurement techniques. 3D vision technology is a now a credible alternative to 3D contact measurement and metrology.”
The fact that many UKIVA members now offer the cameras, software and/or structured light sources needed for 3D imaging and measurement is a good indication of the growing importance of the technique. This view is endorsed by many members of the UKIVA management committee, whose companies have been involved in a diverse range of 3D applications in the food, automotive, packaging, pharmaceutical and transport industries.
Ian Alderton, of Alrad Imaging said: “We have been involved in a number of transport-related 3D measurement projects, and there is no doubt that given the choice, most engineers would prefer to get genuine 3D information rather than an extrapolated 2D representation.” Paul Wilson from Scorpion Vision reports an increased use of 3D robot vision in the automotive and pharmaceutical industries, where 100% inspection is critical. He said: “Using 3D robot vision to pick unordered parts enables manufacturers to save a lot of time and resources shifting or organising parts in the manufacturing process or feeding robots and machines with parts.”
Julie Busby from MultiPix Imaging commented: “ 3D imaging is providing automated inspection solutions for both simple and complex objects which previously were not being inspected and/or required very time consuming and highly expensive manual interaction. By understanding the 3D techniques available today, you can normally assess very quickly its suitability for use and whether it offer advantages over other inspection methods.” Mark Williamson of STEMMER IMAGING agrees. He said: “3D machine vision can solve many difficult problems and may also solve many of the same inspections as a 2D system. However, the reality is that 3D adds more data and more complexity, so 2D still very much has its place.
What is the difference
Explaining the difference between 2D and 3D vision systems, Thomas Nepstad, international product marketing manager, PC vision, at Cognex, said: “In a 2D system a single camera accumulates the reflected light of an object into pixels. These pixels are used by vision tools to calculate the quality or integrity of a part or do identification tasks. The values of the pixels will vary, depending on the light or part presentation. This pixel value variation made many vision systems unstable or they only worked when the parts were perfectly presented.”
The answer to this was to develop systems which do not look at pixels, but at geometries of the object to be inspected. This empowered integrators and machine builders to build more cost-efficient machines. However, 2D systems still limited the objects to be more or less in a known presentation plane. To overcome this, one needs to move into a 3D world.
How does 3D work? Nepstad explains: “Basically, a 3D image formation system maps the surface of an object into a set of X/Y/Z positions. A collection of these positions is called point cloud. The tools to do inspections are no longer image inspection, but rather point cloud processing tools. There are different techniques to create the point clouds. The most common one is using structured light such as laser stripes or fringe pattern projectors. The goal of any 3D image formation is to get as many good points as possible. Depending on part and production conditions the user has to choose the appropriate solution.”
So, why would a user choose to employ a 3D vision solution if there is no simple 3D image formation available? “It is the nature of the information contained in the point cloud. Basically an object can be shown to a 3D iterated function system (IFS) in any orientation and any features such as expected geometries or defect are always the same. It is a matter of understanding where the basic location of the object is in the point cloud. Then is very simple to calculate any deviations which map into good or bad. In an ideal world, one would drop a CAD representation of a part into a system and the system would automatically do all inspections/measurements regardless of part presentation/conditions,” said Nepstad.
Nepstad believes that every market can benefit from 3D. “Applications where parts need to be picked from a rack, tray, conveyor belt or even from the bin are finding more successful installations. The benefits for the user is cost reduction through simplified robot end effectors and less cost in part presentation. Other areas are food, where volume and shape of products are of interest.”
Patrick Schwarzkopf, head of the VDMA specialist department Machine Vision, has also been observing developments in the 3D sector very closely. He recently reported: "In the component sector, for example with cameras, we are seeing increasingly smaller designs with higher resolutions and less energy consumption." He has also identified changes in the area of lighting: "Many new applications already use the ultraviolet or infrared spectrum. As a result, machine vision systems can now work reliably unobstructed by ambient light."
Many of these developments will be displayed at AUTOMATICA 2012 in Munich, Germany, from 22 to 25 May. We are told the event will play host to around 30 companies from the machine vision sector.
LMI Technologies is a specialist in 3D measurement sensors and has contributed some major development efforts in the field of 3D sensor technology and machine vision in factory automation. It has provided solutions for many automotive applications with rugged sensors and algorithms developed specifically for the industry. Applications include integrated 3D sensors, mounted into robots for door inspections, and underbody inspection.
In sawmill applications, manufacturers of wood products have also employed 3D scanning and vision capabilities to optimise the value recovery of logs. The industry has used some form of scanning since the 1970s, but technology advances have now resulted in the industry being able to take advantage of high end 3D scanning, together with colour vision.
With the continued development of 3D imaging technology such as the introduction of 3D smart cameras, some would say that 3D is the future. While industrial 3D imaging is certainly not a gimmick, it should be used only where it is applicable and needed.
Industry is already making real, practical use of 3D vision technology. The current indications of growth, together with the technological developments suggest that, for the right applications, 3D vision could take off in a big way.
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