In this paper, we consider the convey-crane system, which can transport loads for industrial purposes. The stabilization problem of the desired convey-crane position is posed under uncertain mass inertia characteristics, incomplete measurements and an action of external disturbances. Based on the passivity property, the control law with linear and sigmoidal parts is constructed for the solution of the problem. It is shown that the using of sigmoidal function as a prelimit realization of sign-function provides disturbances invariance with the given accuracy. Moreover, sigmoidal function in feedback allows to provide transient responses that are close to aperiodic and to reduce the control resources and chattering effect due to its boundness and smoothness properties. We use the reduced order state observer with sigmoidal corrective action to estimate the speed of the convey-cranes by measuring its position. This observer does not require the knowledge of plant model and introduction of an model of external disturbances. Simulation results of a closed system with developed dynamic feedback are presented, which are compared with a classical PD-controller.