Northrop Grumman selected Electroimpact to provide an articulated arm robotic drilling system for drilling and countersinking highly
curved high-strength metallic production aircraft panels at their St. Augustine, FL site. The size and complex contours that make up
the OML of the product demand the automation cover a large volume and be capable of high articulation. An off-the-shelf 6-axis robot
is utilized to which Electroimpact added absolute secondary feedback and integrated a single CNC to control the entire automation system.
For a robot, the secondary encoders added to each axis output reduce backlash to negligible magnitudes. With highly descriptive kinematics,
the accurate robot exhibits positioning accuracy on par with custom machine tools. On-part precision is maintained even with external forces
(e.g. one-sided clamping, drill thrust) and within the working volume on-part accuracy was validated to be less than 0.010.
A single multi-function end effector contains all the tools required to perform drilling and countersinking, hole inspection, automated
vision-based feature recognition, one-sided clamp pressure, and auto-normalization. For roughly 90% of the product the sub-processes
used include clamp up, normalization, drill/CSK, and hole inspection. Processes involving the vision system are used when features
exist at the location already (holes, temporary fasteners). The majority of final holes and countersinks are drilled in one step from
blank. In the end all holes are drilled and inspected in their full size condition using the robot.
Offline programs and simulation of the drilling process are generated in the CATIA environment. Prior to dry running the programs,
the programmer is able to interrogate the 3D engineering assembly, associated fastener meta data, and observe the automation movement
during a programmed process, check for collisions, and validate efficient robot motion and poses. To bridge the gap between CAD and
the physical environment, the precise location of the jig relative to the robot’s coordinate frame is determined by automatically
registering on tooling spheres surrounding the product with a spindle-mounted wireless touch probe.