Multibody Modeling and Nonlinear Control of a Pantograph Scissor Lift Mechanism

In this paper, a new strategy for developing effective control policies suitable for guiding the motion of articulated mechanical systems that are described within the framework of multibody system dynamics is proposed. In particular, a scissor lift table having a pantograph topology is analytically modeled as a rigid multibody system by using a Lagrangian formulation. An operational approach is thus introduced in this investigation to design the control system that commands the motion of the lift table. In this vein, two dynamical models are developed in this investigation, namely a minimal coordinate multibody model and a redundant coordinate multibody model. While the minimal coordinate multibody model is used in the paper for the optimal design of a high-performing nonlinear controller, the redundant coordinate multibody model is employed to verify both the efficiency and the effectiveness of the control approach adopted in this work. More specifically, the nonlinear control system devised in this paper is based on the combination of an open-loop control architecture with a closed-loop control strategy. The open-loop control policy is determined by using a nonlinear quasi-static feedforward controller, whereas the closed-loop control action is obtained considering an error-based proportional-derivative feedback controller. With the use of both the pantograph scissor lift multibody models developed in this work, several numerical experiments are carried out in the paper, thereby demonstrating the readiness and the effectiveness of the control methodology proposed in this investigation.