Portable 3D Optical Measurement Systems 08-02-2008
Optical Vision Based Measurement Systems Provide an Alternative to Articulated Arm CMM's with Real User Advantages
The portable articulated arm measurement system that has delivered a high level of affordability and portability for three dimensional shop floor measurement today faces strong new competition from an alternative optically based technology that is finding favour in an expanding range of applications.
Optical based three-dimensional measurement systems from US, German, French and Swiss companies were recently presented at “Control”, a leading European metrology exhibition held in Sinsheim, Germany. After intensive international research and development in this field, the range of off the shelf systems available indicates a new level of maturity in the technology that offers practical and competitive measurement solutions for many industrial requirements, and a fast growing list of high profile customers around the world.
Two generic types of 3D vision based measurement systems are available, being those that use a measurement probe and those that directly measure a work-piece without physically contacting the part.
Probe based vision systems utilise a measurement stylus or laser scanning head similarly to an articulated arm or a manual CMM to deliver versatile measurement capabilities. Their most striking feature is that the probe is not mechanically connected. Instead, its position is determined by a remote vision receiver, typically comprising infrared transmitters and cameras or photocells that instantaneously identify and locate the probe position by automation of the traditional triangulation process known as photogrammetry. Advanced systems use radio communication so that the hand-held probe is wireless as well as mechanically connection free.
According to Antonio Mendes Nazare, Marketing Manager of leading developer ActiCM in France “we have worked on perfecting this technology for more than 18 years, but what has made the system really competitive in the general industrial market is the improvements in digital imaging and computing speeds now widely available since about 4 years now. What is really exciting for our users is that the performance and features of the system are more software than hardware based, so a system investment today faces ongoing performance upgrades rather than performance deterioration through mechanical wear and tear like our traditional competitors.”
Non-contact optical systems use a similar type of vision receiver, but rather than identifying the position of a measurement probe, these systems use sophisticated digital image processing techniques to directly interrogate the surface geometry of a component from different angles to rapidly and accurately acquire high resolution data of the surface shape as well as to automatically identify and measure the size and position of specific surface features.
According to Mark Viala, Engineering Director at ActiCM, “the system has already proven to deliver more than a ten fold reduction in inspection times for complex parts such as automotive stampings, body-in-white and composite aerospace components, with comparable levels of uncertainty to the CMM. This provides big efficiency gains for manufacturers as well as a very rich store of recorded data.”
3D vision systems offer many advantages including a high level of portability of the light-weight systems, excellent ergonomics of the wireless and connection free probes and a large measurement volume that is unobstructed by the measurement system itself. The powerful ability to simultaneously track both the probe and reference targets placed directly on the work-piece in real time is ingeniously applied by ActiCM to avoid the need for rigid mounting of either the part or the vision receiver, and even allows the geometry changes of an object in motion to be tracked at high speed.
Systems from different manufacturers offer a variety of workspace volume configurations, measurement characteristics, accuracy levels and system features. Manufacturers claim to provide competitive accuracies and costs for the measurement of parts ranging from small and intricate mouldings or castings up to parts and assemblies over 10 metres in length.
ActiCM in France is a leading manufacturer of both probe based and non-contact vision measurement systems and is represented in Australia by IS Tecnik, a distributor of advanced measurement systems,
Paul Frecker, General Manager, IS Tecnik 7th July 2007