Fusing LSTM neural network and expanded disturbance Kalman filter for estimating external disturbing forces of ball screw drives

Monitoring external disturbing forces is of great significance for improving the control performance and interaction safety of ball screw drives. In consideration of the low cost in long-term use and the non-invasiveness to work space, estimating external disturbing forces using motor torque and motion states has been viewed as the solution that has great potential to be applied in real industry. However, the existing methods cannot efficiently establish accurate estimation models in a low-cost and general manner (i.e., not depend on specific work scenarios). To overcome this challenge, a novel hybrid-driven method that fuses Long Short-Term Memory (LSTM) Neural Network (NN) and Expanded Disturbance Kalman Filter (EDKF) is proposed. The motion state of the worktable is decoupled as the linear superposition of the outputs of two independent dynamic models, i.e., Ideal Dynamic Model (IDM) and Disturbance Dynamic Model (DDM). IDM predicts the motion state that is only driven by the motor torque, is modeled as an LSTM NN and trained by self-excitation experiments. DDM is equivalent to the disturbance transfer function and easily identified by impact tests. The motion state only driven by external disturbing forces is calculated by the predicted result of IDM and the monitored actual motion state, and then external disturbing forces are estimated by a DDM-based EDKF. The verifications in simulation and real environments both show that by the proposed method, accurate estimation models of external disturbing forces can be efficiently established through self-excitation experiments and impact tests.