Leader steering method is a new concept of guidance and control for multi-lift slung-load transport system. The multi-lift slung-load transport system is a system in which multiple lifting vehicles connected with a load are transported in cooperation of the vehicles. In this case, the load moves and swings by hanging on the wires and affects the movement of the vehicles again. The leader steering method sets one vehicle as a leader and the others as porters. Only the leader can measure the position information of the system and calculate the guidance command accordingly, while the porters determine the control technique according to the change of the wire connected to the load. That is, when the leader pulls the connection wire in a specific direction, the porter moves in accordance with the pace.
For effective modeling of this system, Udwadia-Kalaba Equation (UKE), which is easy to reflect constraints, was used. UKE is a powerful modeling tool that can reflect changes in constraints. In this study, leader steering method is proposed as an efficient design method for the multi-lift slung-load transport system.
Firstly, a leader steering method using PID controller is proposed. It adopts way point passing method and control method through tuning of PID gains of leader and porters by guidance modes such as linear translation, turn, up and down. It is confirmed that the leader steering method is applicable through some simulations.
However, there is a limitation in that the stability of the system cannot be guaranteed with PID controller. Sliding mode controller (SMC) for nonlinear multiple input and multiple output (MIMO) systems is applied as follows: Defining sliding surfaces, dividing inputs for one-to-one matching to output, estimating non-measurable states, and designing control law based on Lyapunov approach. It can also be seen through simulations that the leader steering system achieves the purpose effectively.