Sealing has become a main application area because it demands a lot of manpower to encapsulate the spars and fasteners, and the materials in use don’t offer a long period of time to be dispensed. Blanchette said there is research on new automated cartridge dispensing methods and new materials using robotics, as well as the possibility of mixing materials on demand, as they are needed.
One example of a sealing operation is an aircraft wing assembly, where there are spars under the skin of the aircraft that provide structural integrity. The spars are used to attach the wing to the wing box. All of the connection points and fasteners on the wings that are exposed to the outside need to be sealed to prevent corrosion and leaking, since the wings are filled with fuel.
Robotic force sensor feedback
“What we’re hearing from aerospace customers is that they want robots to get smarter. One way that is happening is by mounting force sensors on the end effectors, which provides on-the-fly feedback to the robot controller,” Chris Kolb of Aerobotix Inc. told us. “This technology is now allowing the robot to change its original path in real time based on the force sensor feedback.”
A prototype robotic sanding tool from Aerobotix prepares to sand inside a combat aircraft inlet duct, using the integrated FANUC Force Sensor and ATI Quick Disconnect as part of the application force control solution.
Kolb said it’s now possible to take a sanding path for a known part, teach the path to a robot, and specify 1.6 kilograms of pressure on the sanding pad while operating. If the tooling changes or the part is moving, the application has a way to “fix” the path:
With the force sensor in the system looking for the 1.6 kilograms of pressure, the robot will automatically adjust to a flat wing that is in a horizontal presentation, for example, and seek down in the Z-axis to find that 1.6 kilograms while it is running the baseline path. To have the robot changing its kinematic path on-the-fly to achieve a process set point is incredible.
In the past, Kolb said the end effector might have used pneumatics to press down at a certain psi. The cylinders would use extra stroke to compensate if the part fell away from the program, and the end effector would have enough compliance to seek the part.
But with the force sensor end effector, the robot itself is seeking contact with the part and finely adjusting to maintain a set point within a couple tenths of a kilogram. The end result is increased application in tooling and parts by not needing a large number of programs, touch-offs, and frame shifts to locate the part in the robotic workspace. “We have used this technology in sanding applications, but there we see other processes like sanding or grinding using this technology to allow the robot to ‘feel’ the process and adjust like a human. But for the robot to change its path based on feedback is exciting technology,” said Kolb.
He said Aerobotix performed a test for a company that wanted to abrade the aluminum on a space launch vehicle fuel tank, and they had a big interest in process control. The challenge becomes how to abrade the tank with a Scotch-Brite pad mounted on an orbital sanding tool, and maintain control of the process if the tank is not perfectly round or always in the same location as the original program. But if the force sensor can feel the specified load, the robot will seek that load and report on how well it did.
Instead of a worker observing the process to make sure the aluminum is abraded properly, it should be possible to develop a solution using a specific speed, step over, and pressure (swapping the pad at a regular interval) to produce a very controllable output from the process. It’s very difficult to maintain quality in the process when the part or the tooling is moving around.