Development of a generalized process-based observer for indirect monitoring of cutting force and tool vibration in milling

In machining processes, cutting forces and vibration measurements are essential to allow cutting process and tool conditions monitoring. Moreover, in order to get information about the quality of the milled part, the amplitude of the tool tip vibration would be very useful. Since both the measurements are extremely complicated especially in an industrial scenario, in this study, an in-process model-based estimator of cutting forces and tool tip vibration was designed and properly tested. Although in the specific literature some cutting force observers, based on Kalman’s filter theory, were developed, a general cutting force observer that is suitable for working in any cutting condition is still missing. Indeed, one of the limitations of the existing approaches is connected to the capability of estimating the cutting forces/vibrations even when the regenerative chatter affects the cutting. This drawback is mainly due to the fact that the model typically used for developing the observer considers only the machine dynamics, but it does not consider the coupling with the cutting process. In order to overcome this shortcoming, in this paper an observer based on a combined machine tool dynamics-cutting process model was conceived. In fact, even the contribution due to the regeneration phenomenon was considered in the observer development. The innovative observer was tested through simulations of stable and unstable cuttings. The estimating properties were compared to the ones achievable using the approach already adopted in the literature. The observed results confirmed the enhancement of the observer monitoring skills in milling operations affected by regenerative chatter