Effects of Time Delays on Admittance Control of Industrial Robots in Stiff Contact

Kurzfassung

Admittance control is an active compliance technique often used for industrial robots, enabling them to perform tasks involving contact with their surroundings. The closedloop stability of these systems can be compromised by communication time delays, potentially leading to limit-cycle bouncing or even destructive instability during contact tasks. This thesis investigates the theoretical, simulated, and experimental stability limits of a cascaded admittance controller on a 6-axis KUKA KR16 industrial robot under variable round-trip communication time delays 2.5 ms to 12 ms. A three-stage methodology builds from an idealized 1-axis model, to a detailed 6-axis multi-body Modelica simulation incorporating structural and drivetrain flexibility, and concludes with physical experiments with a KUKA KR16 robot using the Modular Robot Controller (MoRC). The results demonstrate that as the system model comes closer to reality, the destabilizing effects of communication delays are increasingly mitigated by the introduction of physical compliance and damping. Crucially, physical experiments reveal a universal downward shift of the stability boundary, meaning the real robot exhibits better stability margins than simulated predictions.