Online Modeling of the CNC Engraving System With Dead-Zone Input Nonlinearity

This article is concerned with modeling of a class of permanent-magnet-synchronous-motor-based drive systems with dead-zone input nonlinearity. The experimental testing method based on recursive least squares (RLS) is combined with the mechanism analysis method based on physical laws. With the structure of the analytical model first determined by the mechanism analysis method, an online RLS-based data-driven method is then exploited to obtain the unknown parameters of the analytical model. Since the unknown parameters are decoupled in the proposed method, all parameter estimates are available. An auxiliary model and a variable forgetting factor are constructed to ensure the high accuracy and the fast convergence of the proposed method, respectively. Besides, the asymptotic convergence property of the proposed method is analyzed, and the upper bound of the parameter estimation error is also presented. The effectiveness of the proposed method is verified by simulations and experiments on a self-designed computer numerical control engraving system.

I. Introduction

Multispindle computer numerical control (CNC) engraving machine is a typical multi-input multi-output (MIMO) nonlinear system, which is commonly driven by permanent magnet synchronous motors (PMSMs). Such a PMSM-based driven system has been widely used in advertisement, woodworking, furniture and handcraft industry, etc., due to its high processing efficiency and low-cost technology. The past decades have witnessed the great development in theoretical analysis and controller design for MIMO nonlinear systems [1]–[6]. However, it can be found that most of the existing results depend on the system model, and the model-based controllers [4]–[6] tend to have a better performance in practical applications. Moreover, most of the existing results on fault diagnosis [7]–[11] of PMSM-based drive systems are also model based. Therefore, it is of practical value to develop effective modeling methods for PMSM-based drive systems, such as CNC engraving machines.