A Method of Adaptive Control of an Overhead Crane with Direct Tracking of the Load Movement

Abstract

The paper proposes a method of automated control of an overhead crane aimed at direct tracking of horizontal movement of the load at a set height to the designated position under the conditions of continuous a priori uncertainty of the load parameters and external disturbances. The latter include wind effects, friction changes in the crane trolley movement, etc. The approach replaces two conventional problems: tracking of the crane trolley movement to a set position and damping of angular oscillations of the load. In addition, the proposed control method is based on an adaptive control approach with an identifier and an implicit reference model using simplified adaptation conditions. The latter are reduced to the requirement of convergence of the identification residual at applying an algorithm for continuous identification and the selection in a certain range of constant evaluation of the control coefficient. The said evaluation is chosen sufficiently large in its absolute value to provide the largest margin of stability of the closed control system in amplitude with the required quality of control. In order to implement continuous parametric identification, it is proposed to apply recursive least squares method with a forgetting factor. The reference model is chosen in the form of an oscillatory link with an eigenfrequency not exceeding that of a controlled object with a fixed base and falling within an experimentally set range. For closer definition of the reference eigenfrequency, an evaluation of the load suspension length with an accuracy of at least 30 % is required. The simplest algorithm for obtaining such an estimate is proposed. It is based on the average velocity of the vertical movement of the load, which is generally approximately known. The paper proposes a simple algorithm for obtaining such an evaluation and provides the results of model studies of the efficiency of the proposed adaptive control system on the basis of the performance of the developed experimental overhead crane unit, taking into account the characteristics of standard data sensors and drives. The proposed method has demonstrated its high efficiency in a wide range of loads and disturbance conditions. It can serve as a basis for development of functional control systems for any type of cranes for moving suspended loads.