Study on Positioning Control Algorithm for Stacker Cranes.

Abstract

Recently, many types of automatic logistics systems have been developed in order to meet various requirements. A stacker crane functions as a key component in the automatic warehouse system and is required to move quickly with minimum residual vibration. The driving motor is controlled by the controller which cannot control its speed in low speed region. So, in the last stage of motion control, the motor is driven at the lowest controllable speed and is stopped by the mechanical and electric brake. In this paper, we consider the problem of how to realize the best residual vibration settling characteristics for the horizontal motion axis by the optimization of three proposed braking parameters (creep velocity, creep motion distance, delay time between electric braking and mechanical braking). This research led to the following conclusion and proposal. (1) The optimal onset timing of the mechanical braking is the time when the phase of the acceleration at the upper part of the crane reaches 90∼180°. (2) We proposed "soft braking control" which means that electric braking is applied earlier than mechanical braking and reduced the settling time 70% compared with the case which used only mechanical braking.