Time-optimal motion planning and control of an electrohydraulically actuated toggle mechanism

The aim of this paper is to significantly reduce the cycle time of an injection molding machine by operating its clamping unit with minimum time. Therefore, a two-step control concept is presented. First, time-optimal trajectories are planned with respect to the kinematic and dynamic restrictions of the toggle mechanism. Formulating the time-optimal problem as a linear program allows the consideration of nonconstant velocity and acceleration limits as well as jerk constraints for the actuating piston. Second, a nonlinear control scheme based on feedback linearization is introduced to guarantee the time-optimal movement of the toggle mechanism. The proposed nonlinear controller possesses a cascade structure and considers the different modes of the clamping unit's hydraulic system as well as the clamping force build-up of the clamping unit. The simulation and measurement results presented in the paper show significant improvements compared to an existing open-loop control concept. (C) 2007 Elsevier Ltd. All rights reserved.