Moving Ahead With MR. ROAM
Quite often, the biggest benefit of a consumer electronics device is its mobility. Unfortunately, the biggest drawback of an industrial electronic machine—such as a robot—is often its lack of mobility.
Since 2009, the Southwest Research Institute (SwRI) has been working to change that. Based in San Antonio, TX, SwRI is an independent applied engineering and physical sciences research and development organization.
“Today’s industrial robots usually serve a broad range of small- and medium-scale applications,” says Paul Hvass, senior research engineer at the Southwest Research Institute. “However, scaling up these systems is often prohibitive because of cost, limited accuracy or inability to access complex structures and parts.”
To expand robotics for large-scale applications, SwRI developed a mobile manipulator demonstration system called MR ROAM. The title is short for Metrology Reference ROving Accurate Manipulator. Hvass says a larger MR ROAM will initially be used to remove coatings from cargo or passenger aircraft. However, the system also offers manufacturers the potential to assemble large-scale parts, perform welding operations, and create rapid prototypes from relatively soft materials like foam or wood.
“The accuracy of industrial robots is largely determined by the error stack-up through each joint and link from a ground reference to the robot’s end-effector,” says Hvass. “For MR ROAM, a large-scale metrology system replaces this physical link with a signal-based link to ground reference. The system makes it safe for the robot to do maintenance tasks around the aircraft.”
MR ROAM has been developed in two phases, both funded through SwRI’s Internal Research and Development program. Phase one took place in 2009. MR ROAM 1 featured a Vicon metrology motion capture system, a Robai Cyton Alpha robot arm (with seven degrees of freedom) and a Pioneer AT3 skid steer platform.
Numerous empirical tests were conducted to quantify the repeatability and accuracy of the system when stripping paint from an isolated jet wing. The robot arm’s end-effector accuracy was computed at 20-millimeter waypoint intervals along a curved 3D path, but proved inadequate. This led to a second phase of development beginning in 2011.
Phase two took place in 2011. MR ROAM 2 featured a Motoman Yaskawa SIA-20 robot arm (with seven degrees of freedom), a customized omnidirectional platform by Vehicle Technologies Inc. and a Nikon Metrology iGPS system for 6 degree-of-freedom position and orientation feedback. Basic integration was done during the first six months. System calibration and control-algorithm testing took place in the third quarter, followed by data analysis in the fourth quarter.
Analysis of tracking data from the iGPS indicated that the system had a positional accuracy of less than 0.5 inch and a repeatability of 0.25 inches in the direction of travel, and 0.125 inches in the other two directions, according to calculations from ISO standard 9283. The system maintained a standard deviation of less than 0.25 inch in all coordinate directions.
What’s next for MR ROAM? Hvass says the there are multiple follow-up programs in the early stages of development for depainting both commercial and military aircraft.