The Challenge

The U.S. Air Force required a control system to rapidly teach complex trajectories required of a robot, equipped with paint stripping blast nozzle, when stripping paint off F-18 fighter aircraft. The control software was to allow the operator to dynamically modify process parameters such as strip rate. It was also to allow the operator to skip over sections or revisit them, "on-the-fly".

ACG solution

The ACG polishing module was developed specifically to accelerate the process of programming robots for polishing tasks. Using the software, the robotic system was polishing a newly taught door handle in two days. The user teaches a few control points manually and the software then generates a smooth continuous path that links all the control points together. Both arc and line motions are created automatically. Additionally B-spline curves are generated automatically from a few control points. 100 points can thus automatically generated from 10 taught control points. The system then allows the user to tweak these points, if necessary. The polishing software enables the user to customize the "stiffness" of the system for different work pieces, materials and abrasive wheels. 

As an extension to our polishing module ACG developed a four point ranging device to record the profile of sections of the aircraft. The operator is required to simply move the robot to define four corners of a rectangular area of interest. The range sensor and support software does the rest.
 
The software determines the curvature of each of the "sides" of the rectangle by directing the robot to move along the surface. Range data is monitored and the surface normalize computed. From this, smooth trajectories are generated for the robot to follow. The trajectories are a sequence of points with their associated process parameters. The operator can play back and edit these points. The points are stored as program files by the control software. The files contain all the data to run the paint stripping process.
 
During program execution, the paint stripping process is adjustable through the pendant control. The operator can also "fast-forward" or "rewind" to repeat or skip a section. Automated vision sensing has also been employed to automatically adjust the paint stripping rate. The software has been in production, stripping paint off F-18 aircraft . A more advanced version, complete with a Tele-robotic Interface and a CAD data interface was also developed by ACG and deployed. A variation of this system is also in operation at Schlage Lock, for robotic polishing of door handles and knobs.
 

Benefits

Rapid generation of the trajectories of motion significantly reduces the time and costs associated with robot programming. A  family of parts can be polished using the same software modules, with motion parameters being read from configuration files during system initialization. If the automation of a family of parts is of interest, our software driven approach is more cost effective and "reusable" than other more traditional, hardware intensive solutions.
 
Automated generation of the trajectories of motion significantly reduces the time and costs associated with robot programming. The ability to change process parameters during run time ensures that task requiring sensor driven real time path modification can be automated cost effectively. Paint Stripping is one such application: the aircraft skin geometry deviates from the CAD models and the system has to automatically adjust for this variation.