Impact-cutting and regenerative chatter in robotic grinding

This paper presents a study on the dynamic behavior of a flexible robot performing a grinding process. The ultimate goal is to understand whether regenerative chatter is the source of divergent vibrations observed when machining with a compliant robot. An important nonlinear characteristic of the dynamic response of the system is found and is included in the conventional approach to chatter analysis. Robotic machining is represented by a SDOF model. The steady-state response of this model to external forces is found to be repetitive impacts. The existence of this process is justified theoretically without invoking any self-exciting regenerative effect. High-speed camera observations during operation confirm the existence of such a vibro-impact process. To investigate stability, the robotic holder’s dynamic equation is excited by a forcing function representing impulse forces during cutting impacts. Response to regenerative impact cutting forces is simulated. Zones of stable/unstable cutting were identified. This suggests that the regenerative mechanism may explain the onset of divergent vibrations in the application under study. Established regenerative chatter theory predicts an extensive stable cutting zone for a flexible robotic holder. A regenerative mechanism then would not be a probable source of instability. Considering that conventional analysis is based on linear responses, the existence of vibro-impact nonlinearity is illustrated and its effect is analyzed. This results in a more realistic stable cutting zone, better matching our experience.Copyright © 2011 by ASME