Laser Trackers Integrate with Automated Systems

A FARO Laser Tracker positions a robotic head during assembly-level drilling
Founded 1998, Plymouth, MI-based VRSI consists of highly experienced metrology and automation specialists, providing customers with expert services and unbiased technology evaluations. By offering customers state-of-the-art vision solutions for metrology, industrial robot guidance, and inspection, they typically work closely with measurement technology suppliers and automation companies to provide end-users with integrated assembly systems that can maintain high quality standards and close tolerances. They accomplish this by using in-process measurement to characterize sub-assembly variation and automatically compensate with flexible, intelligent automated final assembly processes.

By integrating dimensional measurement into automated manufacturing systems, VRSI measures the process itself in real-time, rather than measuring the part at the end of the process, ensuring every part, while being produced, is within tolerance.

Within the world of close tolerance, high-volume manufacturing, there is a pent up demand for more cost efficient and flexible automation systems. Mass produced industrial robots hold the tantalizing prospect of providing excellent value in these applications. However, volumetric accuracy and other dynamic characteristics that cannot compete with the heavy machines or hard tool-based manual drilling that is traditionally used in processes such as aerospace drilling, can limit their success.

In many high accuracy robotic processes, one approach is to measure the robot's motion very carefully, developing an enhanced kinematic model. This approach works well up to the point where dynamic effects such as thermal expansion, driveline backlash, and process forces – which cannot be accurately modeled – dominate the positional error. To break through this accuracy barrier, only in-process measurement with an external metrology system can guarantee dimensional performance.

VRSI's approach is to integrate closed-loop positional measurement into the process to bring the performance of commodity industrial robots up to aerospace standards. Previously, they evaluated some narrow-angle and single image photogrammetric and hybrid systems, but they found that only a laser tracker measuring multiple targets or using wide-angle triangulation could maintain very high accuracy over large volumes.

VRSI uses FARO laser trackers for dimensional certification because the devices provide the combination of compact size, high accuracy, and software support that VRSI needs to integrate positional measurement into automation processes. With software support in North America, and a mature software development kit (SDK), it has been easy to interface with the Tracker to automate the measurement functions as needed.

"VRSI has a strong culture of skepticism about dimensional accuracy claims, especially under the dynamic conditions of working on the production floor," says Michael Kleemann, principal engineer, VRSI. "We trust our Faro laser trackers to provide accurate and reliable data about the dimensional performance of our systems in the field."

Traditional methods of manually drilling an F-35 inlet ducts provided little room to work.VRSI also uses FARO measurement technology in metrology-guided robotic drilling applications. One example of VRSI's integration of laser trackers is their work involving the F-35 Joint Strike Fighter – working in partnership with Comau Inc. and Brown Aerospace, under a Small Business Innovation Research (SBIR) contract administered by the Air Force Research Laboratory (AFRL) and sponsored by the F-35 Joint Program Office (JPO), together with support from Northrop Grumman and Lockheed Martin. Through this work, VRSI developed the Inlet Duct Robotic Drilling (IDRD) system to automate the otherwise time-consuming and ergonomically challenging task of manually drilling F-35 inlet ducts from the inside out.

In this system, two industrial robots work in cooperation, reaching into the F-35's ducts from opposite ends. While one robot performs a process task – such as measuring datum features with the vision sensor, drilling holes with one of the drill heads, or measuring drilled holes with a probe head – the other robot holds a FARO laser tracker ION and provides closed-loop positional feedback in a global reference frame. VRSI software coordinates the robots and the laser tracker, and specialized dimensional control algorithms compensate for deviation of individual subcomponents in the assembly to ensure that both global (true position) and local (hole-to-edge) positional accuracy tolerances are maintained. The IDRD system is in production today producing F-35 center fuselages in Palmdale, CA, and ensures quality while significantly reducing process time – performing inlet duct drilling in a matter of hours rather than a matter of days.

Another example of VRSI's innovative use of laser trackers is the Robotic Applied Drilling System (RADS). Working in partnership with Electroimpact Inc., VRSI developed the RADS system as a Phase III extension of the IDRD project. RADS expands the capability of metrology-guided industrial robots to perform heavy assembly-level drilling over large volumes while meeting stringent global positional tolerances. Like IDRD, RADS uses a FARO Laser Tracker to register in-process the machine coordinates and provide closed-loop positional feedback. Enhanced control systems developed by Electroimpact allow the robots to drill, rapidly, certain sections of the aircraft, autonomously, with closed-loop feedback from the laser tracker used only for ultra-high tolerance patterns. Technology developed under the RADS project has already seen commercial success with numerous public and military robotic drilling applications.

Global and local positional accuracy tolerances are maintained with advanced metrology technology.Wing Overlap Robotic Drilling (WORD) is another example of VRSI's integration of technology into practical use. Working in partnership with KUKA, Zagar, and FARO, VRSI is currently developing a new innovative type of metrology guidance under the F-35 Affordable Accurate Robot Guidance (AARG) SBIR contract, administered by AFRL and sponsored by the JPO with support from Lockheed Martin and Northrop Grumman. The AARG system combines a FARO 2-axis pointing device with a VRSI-developed active target array and allows for extremely rapid and accurate six-degree-of-freedom measurement and correction of robotic position. VRSI's innovative approach turns the conventional photogrammetry equation on its head – leveraging the accuracy of the FARO device to concentrate the pixels of resolution where needed, at any given time, rather than spreading them over the entire work of volume. The result allows for much higher accuracy and much larger volumetric coverage than is currently possible with photogrammetric robot guidance systems.

"In each of these examples, FARO technology was integrated directly into the process," Kleemann says. "As you can see, bringing closed-loop dimensional measurement into an automated process not only ensures 100% quality, it also allows for lighter and more flexible automated machinery to perform high-precision tasks."

To optimize its return on investment in Laser Trackers, VRSI simultaneously uses them in multiple markets: direct integration in automated processes; field calibration, validation, and root-cause analysis of vision-guided automated processes; and contract dimensional certification of tooling and automation systems.

The VRSI approach of integrating closed-loop measurement with robotic automation allows light, commoditized machinery to perform tasks that were formerly only possible with large, purpose-built machines or with time-consuming manual processes. This innovative approach allows both automated and manual processes to be faster and more cost-efficient.

Faro Technologies Inc.
Lake Mary, FL
faro.com

VRSI
Plymouth, MI
vrs-inc.com