Industrial Robots – The Metrology Solution Of The Future?

Part 1

The Fourth Industrial Revolution is under way. An explosion in the installation of Industrial Robots is occurring as manufacturing industry automates production operations, enhancing flexibility and efficiency of manufacturing processes. All part of the migration path toward the digital factory.

It is estimated the population of Industrial Robots will increase from about 1.8 million at the end of 2016 to 3 million by 2020 representing an average annual growth rate of 14 percent. Since 2016, the largest installation base of Industrial Robots has been in China. In 2020, this will amount to almost 1 million units with an estimated 1.9 million robots in operation across all of Asia; almost equal to the globally installed base of robots in 2016.

USA Robot numbers are closely monitored by the Association for Advancing Automation who reported that for the first nine months of 2017, 25,936 Robots valued at approximately $1.496 billion were shipped in North America, the highest level ever recorded, representing a growth of 18% in units over the 2016.

As manufacturing industry takes-up Robotic Automation what about part inspection and quality control?

In an automated flexible manufacturing world part quality must become much more integral into the manufacturing process whether it be probing integrated into CNC machine-tools or the comprehensive Robotic Inspection of car bodies during the fabrication and assembly process.

The 6 axis Industrial Robot was developed to provide repeatable process actions at which they perform exceptionally well. Robotic Metrology solutions however require accuracy as well as repeatability if they are to provide fully traceable results for upstream/downstream actionable data.

The first Industrial Robots ventured onto vehicle assembly lines almost two decades ago with single laser-line scanning mounted sensors that were capable of measuring a number of individual, deemed critical, features in process. These early technology implementations used comparative gauging techniques to provide process control monitoring. Correlation with off-line Coordinate Measuring Machines (CMM) data was always an issue and ongoing calibration against a certified ‘golden part’ problematic.

Today sensor technology has moved on from the limitations offered by the original single laser-line scanners with many new technologies entering the market capable of digitally scanning complete parts providing full geometrical knowledge in short time periods. Most of these next generation smart sensor solutions are too heavy to be carried by the traditional CMM and require more dexterity from the mover as line of site becomes a bigger issue with optical metrology sensors.

Manufacturing metrology in the digital factory should be capable of determining all manufactured errors and communicate immediately with the process to provide real-time corrections replacing the traditional ‘Tailgate Measurement’ process of inspecting parts upon their competition (typically using a CMM) which adds additional costs and risks scrapping a whole batch of parts that were made before errors were identified. Final inspection will still be a regulatory requirement in some industries necessitating continued CMM verification albeit part conformance should be high due to the measurements and controls applied during the production process.

If the Robotic Coordinate Measuring Machine (RCMM) is to find its way into the production process and provide CMM data (absolute accuracy)  Robot accuracy must be considerably improved. The 6 axis robot was never designed for the metrology application and with the current market uptake the robot industry has little appetite to develop a true metrology Robot at this current time as metrology still remains a niche application. The acquisition by ABB of Spanish metrology company NUB3D in early 2017 is the first indication of metrology being ‘in-play’ for Robot companies.

The traditional CMM offers outstanding repeatability and accuracy while the Robot today offers adequate repeatability for some metrology applications and very limited accuracy. The CMM frame is designed deliberately stiff, unlike robot arms, adding to Robot metrology issues. In addition thermal behaviors of the orthogonal CMM has been deeply studied over past years with various thermal compensation solutions existing to accommodate CMM installations on the production floor. The thermal expansion of the Robot arm becomes ever more critical for Robotic metrology applications to take hold.

Various calibration methods are being adopted today to ‘off-the-shelf’ 6 axis Industrial Robots to improve or negate robot inaccuracies when used in automated metrology solutions:

  • Calibration and error mapping of robot at predetermined joint positions in space
  • Dynamic tracking of robots with real-time error compensation
  • Photogrammetry solutions eliminating robot metrology from part inspection results

The 6 axis portable arm CMM (PCMM) has made huge inroads into industry performing an admirable role in providing accurate production measurements and has proven itself as a carrier of laser scanning sensors albeit not as accurately as a traditional CMM.

Metrologic showcased Cobotic Inspection with its i-robot universal metrology software at the Control Exhibition last year on a Collaborative Robot with Optical Scanner mounted on an AGV demonstration “roaming” inspection of the future.

Is the market awaiting the arrival of a Metrology Robot? – a CNC version of the PCMM. The Collaborative Metrology Robot offers one possible solution since it does not require the expensive and cumbersome safety-fences demanded by the classic Industrial Robot. With today’s high resolution optical encoder technology, complex error mapping algorithms and demands from manufacturing surely it is just a matter of time before a purpose developed RCMM enters the market. High accuracy Medical Robots already exist so the leap to an Industrial Metrology Robot seems a migration path technologically already within reach.

For sure given the number of Robots now being applied to metrology application the Robot is playing an increasing role in automating metrology processes; the automated metrology technology is evolving at a fast pace and in the next few years we could witness the emergence of a whole new generation of robotic metrology solutions.

Part 2 of this article exploring Robot Metrology will be published in coming days.