2-DOF Control of a Fire-Rescue Turntable Ladder

Modern fire-rescue turntable ladders are build to be in lightweight of construction to increase their maximum operation velocities, maximum length, and outreach. Hence, the truss structure of the ladder set provides a limited stiffness and is subject to bending oscillations in the various modes. To damp these oscillations with its hydraulic drives, a 2-degree-of-freedom control is proposed in this paper. The feedforward control is based on the differential flatness of a simple multibody system by only considering the fundamental oscillations. Using Euler-Bernoulli beam theory, the dominant modes of oscillation are taken into account during feedback control design. The model parameters are assumed discontinuous but piecewise constant over the ladder length while the cage at the free end is accounted for by dynamic boundary conditions. Based on the analytical form of the eigenfunctions the modal representation of the system is derived. It is used to design a feedback controller and to merge the measurement information of the gyroscope with the measurements of the strain gauges. The proposed control approach allows for damping of the dominant modes and for asymptotically stabilizing the system around a reference trajectory. An important demand on the proposed approach is to derive a control law which accounts for the low computational power of the ladder's microcontroller. The proposed control concept is implemented in fixed-point arithmetic on the control unit running the turntable ladders made by the market leader IVECO Magirus Brandschutztechnik GmbH. Measurement results from the IVECO Magirus DLK55CS validate the performance of the proposed control concept on a ladder already in production.