What's your vision?
Industrial Technology invited SICK UK's product manager for imaging and measurement systems, Neil Sandhu, to look at a technology evolution which has developed to offer the most versatile vision choices that automation engineers have seen.
There are two sides to the machine vision coin: One is the hardware, encompassing a wide range of technologies for different applications. The other is the software and algorithms which process and interpret the signal data. Developments in processing power and inter-device communications have helped industry to exploit the advances in both. But as new technologies and applications proliferate, how do users keep pace? How do they know which vision technology is best for any given application?
Vision applications date back nearly a century. The earliest examples are thought to be the colour sorters used in the nuts, seeds and grain industries in the USA in the early 1930s. They provided a simple, automated quality-check of colour changes, using filters and the newly-developed photomultiplier technology. Since that time, different technologies developed, initially in parallel, and now in combination, to provide vision-based applications that the pioneers of those early days might have found hard to imagine.
While cameras were slowly being adopted during the 20th Century for specialised industrial uses, other light-based devices were also being developed and applied to vision-related functions.
The widespread uptake of barcode technology in the 1980s and 1990s drove an explosion in light technologies. Now, PinPoint LED lighting, with a minimal central spot, can deliver a high-resolution non-laser light source. These light sources are ideal for a wide range of vision applications, particularly those requiring 1D sensing where the use of more expensive laser technologies is difficult to justify against the benefit. Integrated, reliable LED lighting and sensors are now capable of detecting and assessing difficult products and materials, such as transparent plastics and foil packaging with near-perfect success rates. Based on PinPoint LEDs, the Inspector I40 (below left) from SICK, for example, uses UV filters to be able to detect the photoluminescence in some transparent medical plastics.
Since the invention of the laser in 1960, less expensive and more compact lasers have enhanced and increased multiplicity of control and presence applications, including position, distance measurement and machine safety. In the 21st Century, options have widened with the advent of scanning laser sensors. Aided by software advances, they can now detect shapes in 2D and compare them to pre-set profiles. Applications such as automated, driverless vehicles are causing excitement, alongside more prosaic uses such as inspecting cut and formed timber shapes for furniture or for the volume measurement and traceability of parcels in courier delivery operations. Camera-based vision developed slowly 1980s and into the 1990s and still required direct human monitoring and intense lighting. But in this century, more sensitive optical sensing and progress in digital control and processing have enabled more autonomous operation.
Vision cameras became 'smart' with the advent of on-board computing power and lasers starting to be used alongside them. The combination enabled new methods of quality-checking profiles and shapes in 2D and 3D, as well as triangulation to measure position, for example on a conveyor belt. These advances paved the way for a series of 2D and 3D cameras, such as the ground-breaking IVC-3D smart cameras, and the multi-scanning ColorRanger from SICK. Aided by high-performance software, this new breed of smart vision camera can integrate a wide variety of tasks on high-speed moving production lines from inspecting complex shapes and orientation, to colour and code reading.
Software and algorithm advances can now facilitate real-time control to match high production line speeds. So, for example, real-time reading and verification can be carried out simultaneously for barcodes and alpha-numeric characters by a single device - for example the SICK Lector 620 OCR - to provide unprecedented quality and traceability advantages for products such as perishable foods and pharmaceuticals.
In the field of robotics, 3D vision-guided applications have always been a 'holy grail'. Now the latest technologies are bringing new levels of affordability and productivity for manufacturers. By combining 3D and 2D measurements, the SICK ScanningRuler (above) offers unique new features to support fast and accurate picking of random machined parts piled in stillages, bins and baskets. With a built-in laser light source, the imaging technology is resistant to ambient light changes and provides reliable measurements despite varying surface characteristics and part colours.
A single ScanningRuler can generate a complete 3D image of the content contained within the volumetric area associated with a US or Euro pallet. Incorporating a fixed laser with a rotating mirror, the camera sweep-scans the volumetric area producing a 3D measuring image of all parts with their x/y/z points in millimetres and an accurate 2D overlay which enables part identification against known profiles. The combined image can be processed by image-handling software and tell the robot arm where to start gripping.
The ScanningRuler image produced can be used to direct the robot's gripping arms to select the uppermost part in a pile at its optimum gripping position and deposit it on, for example, a conveyor line or a tray.
Up to now this task could only be done by having a fixed camera and moving the heavy bin under it, or moving the camera which shortens the camera life. Often the only effective solution has been using human labour, risking problems of repetitive stress and strain.
So machine vision has developed into a broad range of options and advanced applications. Its true power can be harnessed when it is combined with complementary technologies and integrated through factory-wide communications platforms.
There simply is no one-size-fits-all technology. Not laser, or camera; it's likely to be a combination. Manufacturers and suppliers with a wide grasp of these technologies can offer customers solutions best tailored to their specific requirements. Users should always seek advice.
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