  Boom cranes are among the most common material handling systems due to their
simple design. Some boom cranes also have an auxiliary jib connected to the
boom with a flexible joint to enhance the maneuverability and increase the
workspace of the crane. Such boom cranes are commonly called knuckle boom
cranes. Due to their underactuated properties, it is fairly challenging to
control knuckle boom cranes. To the best of our knowledge, only a few
techniques are present in the literature to control this type of cranes using
approximate models of the crane. In this paper we present for the first time a
complete mathematical model for this crane where it is possible to control the
three rotations of the crane (known as luff, slew, and jib movement), and the
cable length. One of the main challenges to control this system is how to
reduce the oscillations in an effective way. In this paper we propose a
nonlinear control based on energy considerations capable of guiding the crane
to desired sets points while effectively reducing load oscillations. The
corresponding stability and convergence analysis is proved using the LaSalle's
invariance principle. Simulation results are provided to demonstrate the
effectiveness and feasibility of the proposed method.
