VRSI Integrates Laser Trackers into Automated Systems

Application measures processes in real-time so parts are within tolerance as they are produced

Published: Wednesday, July 20, 2011 - 11:15

Variation Reduction Solutions Inc. (VRSI) is an independent integrator of machine vision and applied metrology technologies for automated manufacturing. The company focuses on achieving disruptive gains in assembly-process accuracy and efficiency through the innovative application of measurement technology and data automation.

Founded in 1998, VRSI (www.vrs-inc.com) is based in Plymouth, Michigan. The VRSI team consists of experienced metrology and automation specialists, and provides customers with expert services and unbiased technological evaluations. It offers customers vision solutions for metrology, industrial robot guidance, and inspection. VRSI works 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. The company accomplishes this by using in-process measurement to characterize subassembly variation and automatically compensate with flexible, intelligent automated final-assembly processes.

The problem

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. This ensures that every part is within tolerance as it is being produced.

Within the world of close-tolerance, high-volume manufacturing, there is a 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, they are limited by volumetric accuracy and other dynamic characteristics that can’t compete with the heavy machines or hard tool-based manual drilling that is traditionally used in processes such as aerospace drilling (see figure 1).

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Figure 1: Many drilling tasks in aerospace manufacturing are inaccessible to robots.

In many robotic processes that require high accuracy, one approach is to measure the robot’s motion very carefully and develop 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.

Figure 2: Closed-loop positional measurement bridges the gap between robotic capabilities and aerospace standards.

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 (see figure 2). Previously, the company evaluated some narrow-angle and single image photogrammetric and hybrid systems, but found that only a laser tracker measuring multiple targets or using wide-angle triangulation could maintain very high accuracy over large volumes.

Solution

VRSI uses FARO Laser Trackers for dimensional certification because of their high accuracy, portability, reliability, and FARO’s excellent customer support. These devices provide the combination of compact size, high accuracy, and software support that VRSI needs to integrate positional measurement into automation processes. With FARO software support available in North America and a mature software development kit, 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 at VRSI. “We trust our FARO Laser Trackers to provide accurate and reliable data about the dimensional performance of our systems in the field.”

VRSI uses FARO measurement technology in metrology-guided robotic drilling applications. One example is VRSI’s work involving the F-35 Joint Strike Fighter. Working in partnership with Comau Inc. and Brown Aerospace under a Small Business Innovation Research contract administered by the Air Force Research Laboratory and sponsored by the F-35 Joint Program Office, along with support from Northrop Grumman and Lockheed Martin, VRSI developed the innovative 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.

Figure 3: Two robots work in tandem to drill F-35 Joint Strike Fighter inlet ducts.

In this system, two industrial robots work in cooperation, reaching into the F-35’s ducts from opposite ends (see figure 3). 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 (i.e., 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, California, and ensures quality while significantly reducing process time. Inlet duct drilling is performed 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 rapidly drill 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.

Wing overlap robotic drilling (WORD) is another example of VRSI’s integration of technology into practical use (see figure 4). Working in partnership with KUKA, Zagar, and FARO, VRSI is currently developing an innovative metrology guidance under the F-35 Affordable Accurate Robot Guidance Small Business Innovation Research contract, administered by the Air Force Research Laboratory and sponsored by the Joint Program Office with support from Lockheed Martin and Northrop Grumman. The Affordable Accurate Robot Guidance system combines a next-generation FARO two-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.

Figure 4: An example of wing overlap robotic drilling (WORD)

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 they are 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,” says Kleemann. “As you can see, bringing closed-loop dimensional measurement into an automated process not only ensures 100-percent quality; it also allows for lighter and more flexible automated machinery to perform high-precision tasks.”

Return on investment

To optimize its return on investment in FARO 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 approach allows both automated and manual processes to be done faster and more cost-efficiently.

About The Author

FARO

FARO develops and markets computer-aided coordinate measurement and imaging devices and software. FARO’s portable equipment permits high-precision 3-D measurement, imaging, and comparison of parts and compound structures within production and quality assurance processes. The devices are used for inspecting components and assemblies, production planning, 3-D documentation, as well as for investigation and reconstruction of accident sites or crime scenes, and to generate digital scans of historic sites. Principal products include the FaroArm, the FARO Laser Tracker ION, FARO Laser ScanArm, FARO Laser Scanner, FARO Gage, and the CAM2 family of advanced CAD-based measurement and reporting software.