Accurate Inline Tracked Robot Measurements Pace Automotive Production

Author: Steve Shickell – NMS 3D UK Sales and Marketing Manager

Automating Metrology started more than 2 decades ago with programmable tactile coordinate measuring machines (CMM). The CMM, which was designed for stable and temperature-controlled quality control rooms, typically not installed near the production area, were specifically tasked with measuring completed components to check if they met specification.

The introduction of the CMM was a major step forward for most manufacturers and quickly became the standard and overruling quality ‘stamp’ of approval, albeit seen as an unnecessary evil, as the CMM could stop parts leaving the factory, or even worse render them as scrap straining relationships between quality assurance and production operations.

Looking at Metrology for Automotive Body in White (BIW) we immediately hit a problem with CMM speed and throughput, as in higher volume car production the shear amount of inspection overwhelms the idea of measuring every part or even every vehicle and the accepted CMM technique is rendered too slow and typically doesn’t provide the density of data required for today’s ever challenging car body panel shapes and features.

In past years other technologies have been employed that partly address the CMM speed issue with Industrial Robot mounted gauging sensors being employed in-process. These solutions typically zero in on a few deemed critical features which are monitored inside the production line. These robot systems however only answer part of the issue as they are typically dependent upon the repeatability of the Robot for accuracy.

Today automotive tolerances are getting tighter and the importance of the complete vehicle geometry being evaluated means that relative measurements can’t replace a CMM, so when an error triggers an issue, the production line has to stop and often a car body is take off-line to a CMM for verification which can be extremely time consuming and expensive.

The desire of major Automotive OEM’s is for Absolute Inline Measurement Systems which are able to datum into the Cars Reference Point System (RPS) and capture as many key characteristics as possible within the ‘Takt Time’ of the production process. Takt Time’ can be 25 Minutes for a luxury car and as little as 55 seconds for a mass-produced vehicle. Required accuracy must be comparable to a Sheet Metal CMM, and in order to meet the ‘Takt Time’ the process must be fully automated; Robotics with fast data acquisition sensors are currently the only option.

NMS (Non-Contact Measurement Systems) have pioneered such a solution which stemmed from a collaboration partnership with a key automotive customer in Slovakia.  The customer had previously invested heavily in Laser Scanning, and typically were using Leica Laser Trackers with T-Scan Laser Scanners for Manual Inspection of BIW Structures and Panels. Following extensive testing they were satisfied with the overall ease of use and accuracy of the tested system and requested NMS to support them in a project taking this technology to the production line replacing manual scanning with Robotic automated scanning.

From this initial project NMS has developed a whole suite of Non-Contact Measurement Systems including the Inline DUO System able to capture 200 Key Features in around 35 Seconds and aligned to the Car line Coordinate System. The system uses smart tooling and Leica Absolute Laser Trackers and Reflectors for the RPS Alignment which also aligns each Absolute Tracker to each other. Two seven axis Robots mounted with Leica T-Scan 5 Laser Scanners can both scan up to 210,000 points per second, without the need of time consuming photogrammetry targets, scale bars, calibration blocks and plates.

Both independent Laser Trackers with T-Scan have an accuracy of UL = +/- 0.06mm providing specification accuracy comparable to a dual arm CMM with adjustable wrists and extension probes.

The NMS solution is also ideally suited to the harsh environment of a Welding Production Line with an IP 54 Dust and Moisture Rating and operational temperature range of 0o to 40oC making these Metrology systems a perfect match for an automotive BIW inspection solution. NMS Inline Measurement Technology has become widely accepted within many major Automotive OEMs and their supply chain.

Key benefits include the amount of data that is output; welding line engineers can capture issues within the latency of only one vehicle, and in addition have the ability to provide a ‘quality stop’ for example if spot welds are missing or if the key characteristics are outside their tolerance. Importantly the data received is so informative that it provides actionable information and root cause analysis instantly to quality and maintenance engineers so that they can rectify issues and optimize production and quality.

Although the investment of an Inline NMS Robotic Solution maybe higher in comparison to an inline gauging system, with its comparable accuracy to a Sheet Metal CMM the combined cost is far less. The end result is much more valuable and therefore the main reason why automotive customers are investing heavily in this technology.

Many major automotive OEM’s are now aiming to phase out Sheet Metal CMM’s in favour of automated metrology systems so NMS are continuing to develop new products and solutions to help customers continuously improve their quality and efficiency.

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