Publikation
Flatness Based Control of an Industrial Robot Joint Using Secondary Encoders
Jonas Weigand; Nigora Gafur; Martin Ruskowski
In: Robotics and Computer-Integrated Manufacturing, Vol. 68, Pages 1-13, Elsevier BV, 1/2021.
Zusammenfassung
Due to their compliant structure, industrial robots without precision-enhancing measures are only to
a limited extent suitable for machining applications. Apart from structural, thermal and bearing de1formations, the main cause for compliant structure is backlash of transmission drives. This paper
proposes a method to improve trajectory tracking accuracy by using secondary encoders and applying
a feedback and a flatness based feed forward control strategy. For this purpose, a novel nonlinear,
continuously differentiable dynamical model of a flexible robot joint is presented. The robot joint is
modeled as a two-mass oscillator with pose-dependent inertia, nonlinear friction and nonlinear stiff2ness, including backlash. A flatness based feed forward control is designed to improve the guiding
behaviour and a feedback controller, based on secondary encoders, is implemented for disturbance
compensation. Using Automatic Differentiation, the nonlinear feed forward controller can be com3puted in a few microseconds online. Finally, the proposed algorithms are evaluated in simulations and
experimentally on a real KUKA Quantec KR300 Ultra SE.