Nonlinear Observer-Based Position Control of the Piston Stroke in a Plastic Molding Machine

Abstract

This paper presents a nonlinear sliding mode observer design for the position control of a hydraulic piston driving the movable platen of a plastic injection molding machine. Since the dynamical model describing the hydraulic force applied to the piston presents some static and dynamic nonlinearities due to the movable platen kinematic chain, linearization via nonlinear state feedback has been applied to guarantee asymptotic trajectory tracking. As the states are not readily available, they are derived with a nonlinear sliding mode observer. The control scheme has been tested on the 7th-order model of the real injection molding machine. Satisfactory results suggest the applicability of the proposed algorithm in this important industrial process.