Showing papers by "Oliver Sawodny published in 2003"

A cascaded tracking control concept for pneumatic muscle actuators

Abstract: Pneumatic muscles are interesting in their use as actuators in robotics, because they have a high power/weight ratio, a high tension force and a long durability. However, their physical model is highly nonlinear. In this paper a nonlinear control strategy is presented. The main objective is to control a trolley, which is driven by an artificial muscle to follow a reference path. The cascaded control, which is presented here is based on a physical model of an experimental setup. The inner loop is responsible for the force control, which cancels the nonlinearities of the system and ensures therefore a linear input/output behavior. The outer control loop consists of a feedforward and an observer based feedback controller. In addition the observer is extended with a disturbance observer in order to compensate model errors. Measurement results show the efficiency of the presented control strategy.

Anti-sway system for boom cranes based on an optimal control approach

Abstract: For the operation of boom cranes a significant high level of experience is needed to achieve a large amount of handled containers. Therefore, automation systems with anti-sway abilities for boom cranes were developed to increase the handling rate especially for inexperienced crane operators. In the paper, an optimal control approach is presented as an alternative to feedback control systems. After deriving the nonlinear dynamic model, the anti-sway problem is formulated as a nonlinear constrained optimal control problem. The numerical solution method for this optimal control problem is presented. The results are illustrated at measurements for the harbour mobile crane LIEBHERR LHM400.

Control design for the rotation of crane loads for boom cranes

Abstract: This paper handles the control of flexible link robot systems. Since in the considered case a manipulator for grabbing containers is suspended on two ropes, torsional oscillation occurs changing the position of the manipulator. A control strategy, which consists of feedforward and disturbance observer based feedback control implemented on boom cranes to assure an accurate tracking of the manipulator along a reference path is shown. The system parameters like rope length, moment of inertia of the load and its mass are changed frequently during the crane operation. Therefore the controller is fully adaptive due to the varying system parameters. Measurement results show the efficiency of the presented control strategy implemented on a harbor mobile crane LIEBHERR LHM 400.

Model Based Trajectory Control of an Overhead Travelling Crane

Abstract: Until now, most papers concerning control of overhead travelling cranes have only focussed on position control of the translational degrees of freedom, see for example [1], [3], [4], and [5]. With more advanced robotic applications envisaged, however, there is a demand for both trajectory control in six degrees of freedom and active damping of the weakly damped load oscillations due to the rope suspension [2]. Hence, a model based trajectory control is presented for an overhead travelling crane that has been upgraded with an orientation unit providing three additional axes. Starting from a central multibody model, decentralised design models are derived for each crane axis. By this, couplings between the axes are identified and appear as disturbance inputs in these decentralised design models. Each decentralised axis controller consists of linear state feedback, feedforward control, and observer based disturbance compensation and is derived in symbolic form. This allows for an adaptation of the complete control structure employing the gain scheduling technique with respect to varying system parameters like rope length and load mass. Couplings between the crane axes are compensated by feedforward control, whereas the e.ects of nonlinear friction forces are counteracted by combination of feedforward control and disturbance estimation. Experimental results, taken at a 5 t - bridge crane, show the bene.ts of the proposed control scheme as regards control performance and steady-state accuracy.