Mode decoupled and sensorless cutting force monitoring based on multi-encoder

Cutting force monitoring is an important technology for tool condition monitoring. However, a high precision and wideband cutting force estimation, including cross-feed components, with a sensorless approach of the ball-screw-driven stage, is still challenging because of its multiple structural modes and non-linear friction. This study proposes a process monitoring technique that independently estimates the cutting force components in rigid body and in vibration mode coordinate systems, based on multi-encoder signals. In the rigid body mode, the cutting force components were estimated by extracting the static rigid-body motion. In the vibration mode, the cutting force was estimated by using the relative displacement, velocity, and acceleration between the motor and the table. The estimation accuracy of the cutting force in feed and cross-feed directions was evaluated through several end milling tests. In the rigid body mode, a temporal variation of the feed force components was observed. However, high-frequency variations irrelevant to the cutting force were included because of variations in motor current, which had position/rotation-dependent characteristics. On the other hand, in the vibration mode, it was possible to estimate both feed and cross-feed components with less than maximum static friction force, including high harmonics.