Cutting Force Estimation Using Feed Motor Current Signatures In Milling

Milling force is an important signal representing the machining process status. Thetechnology of high-precision milling force monitoring is the prerequisite and foundationof intelligent machining system. Compared to the direct monitoring way usingdynamometer, the indirect method using motor current to estimate milling force is moreconvenient at a lower cost. At the same time, it is more favorable to be widely used inmodern industry.The existing way of milling force estimation using motor current is available only formilling force estimation in the constant speed milling process. The accuracy is extremelypoor when it is used to estimate dynamic milling force in multi-axis simultaneous millingprocess. For the purpose of high-accuracy milling force estimation, this thesis analyzedthe key technologies and designed the whole technical research route and set up theexperiment system.For the disturbance of nonlinear friction on the motor current, this thesis analyzedrolling friction’s characterization in the feed system, and pointed out the discrepancies ofthe classical LuGre model both in the pre-slide regime and the macro-slide regimecompared with experiments’results. After in-depth analysis, we found the weak-points ofthe LuGre model, and built a modified model suitable for friction in the feeding system.This model was verified on two different machining tools.For the disturbance of mechanical inertia on the motor current, this thesis used modelreference adaptive technology combined with Landau iterative algorithm to identify themoment of inertia in the feeding system. The influence of the key parameter, adaptive rate,was analyzed, and optimized values of adaptive rate under different accelerations wereworked out. The effectiveness of this method in identifying inertia was verified in theexperiment.The existing method used a linear mapping way to calculate milling force from motorcurrent, but the accuracy is very poor when it is used to estimate dynamic milling force.This thesis proposed a new nonlinear mapping way depending on the frequency of themilling force. To verify the effectiveness and accuracy of the milling force estimating methodproposed in this thesis, many experiments were accomplished in different machiningparameters. Both the constant-speed milling process and multi-axis simultaneous millingprocesses were researched applying this method. The experiments showed that thismethod can curtail the estimation error in fifty percent compared with the formerestimating ways.