The peculiarity of offshore cranes, i. e. cranes based on ships or drilling platforms, is not only a significant motion of their base, but also the taut-slack phenomenon. Under some circumstances a rope can temporarily go completely slack, while a moment later, the force in the rope can increase to nominal or even higher value. Periodic occurrence of such phenomena can be damaging to the supporting structure of the crane and its driver. In the paper, mathematical models of offshore cranes that allow for analysis of the taut-slack phenomenon are presented. Results of numerical calculations show that the method of load stabilization proposed by the authors in their earlier works can eliminate this problem.

In order for a quadruped robot to be able to move on wheels while keeping its platform in horizontal position, and to walk, the kinematic system of its limbs should be so designed that each of the wheels has at least four degrees of freedom. Consequently, the designed system will have many DOFs and many controlled drives. This paper presents a novel solution in which, thanks to a suitable limb kinematic system geometry, the number of drives for the robot travel function, i.e. travelling on an uneven surface with the robot platform kept horizontal, has been reduced by four which are used only for walking. The robot structure, the required geometry of the limb links and the driving torque characteristics are presented. Moreover, an idea of the control system is sketched. Finally, selected results of the tests carried out on the robot prototype are reported.

A backward tucked somersault from the standing position is analyzed in this study. The used computations were based on a three-dimensional model of the human body defined in natural coordinates. The net torques and internal reactions occurring at the ankle, knee, hip, upper trunk-neck and neck-head joints were obtained by inverse dynamics. The achieved results confirmed the significant loads at the joints at the beginning of the landing phase and revealed the way the analyzed stunt was controlled. It was also shown that the natural coordinates provide a useful environment for modeling spatial biomechanical structures.

The paper presents selected methods used for estimation the unknown geometrical parameters of a spatial mechanism model, used to describe the position and orientation of the end-effector, for example the coordinates of the center points of spherical joints, link dimensions etc. These data are necessary when dealing with computer simulation of any mechanism. The parameters are estimated based on coordinate measurements of selected points, located on the real mechanism links, using a portable manipulator with serial structure composed of 6 revolute joints and a spherical probe, but other techniques of acquiring point coordinates are applicable as well. The described methods can be used in the cases of a disassembled link, an assembled mechanism and redundant data sets. The methods are characterized by accuracy and robustness in the presence of different levels of noise, stability with respect to degenerate data sets, and low computation time. Special attention is paid to the case when the wanted parameters are hard to measure directly. Numerical examples are presented dealing with 5-link mechanism used to guide front wheels of a car.

In this work, a novel approach to designing an on-line tracking controller for a nonholonomic wheeled mobile robot (WMR) is presented. The controller consists of nonlinear neural feedback compensator, PD control law and supervisory element, which assure stability of the system. Neural network for feedback compensation is learned through approximate dynamic programming (ADP). To obtain stability in the learning phase and robustness in face of disturbances, an additional control signal derived from Lyapunov stability theorem based on the variable structure systems theory is provided. Verification of the proposed control algorithm was realized on a wheeled mobile robot Pioneer–2DX, and confirmed the assumed behavior of the control system.

Cranes belong to underactuated mechanical systems, an important subclass of nonlinear control systems typified by fewer control inputs than the degrees of freedom. The usual performance goal of a crane is to execute a desired motion of the load, specified by as many outputs as the control inputs. The challenging task of inverse simulation study, in which control of the underactuated system subject to execute the partly specified motion is determined, is usually formulated in independent variables. In this paper, a dependent variable formulation is motivated and developed. Compared to the independent variable formulation, the use of dependent variables leads to much simpler governing equations, and their effective number is reduced. The developed formulation is illustrated by a simulation model of an overhead crane executing a rest-to-rest maneuver of the load along a specified curvilinear trajectory.

Moving with the wheelchair can be a serious problem, especially when the obstacle occurs on its way. An alternative solution would be to equip the wheelchair with appropriate mechanical device, thanks to that it becomes possible to overcome barriers such as kerbs or doorsteps. In this paper, the authors present an idea of mechanism overcoming barriers by the wheelchair. Type and geometrical synthesis have been presented. The mechanism is modelled in a multibody computer analysis system and sample simulation research results are reported.

Parallel computers are becoming more available. The natural way to improve computational efficiency of multibody simulations seems to be parallel processing. Within this work we are trying to estimate the efficiency of parallel computations performed using one of the commercial multibody solver. First, the short theoretical outline is presented to give the overview of modeling issues in multibody dynamics. Next, the experimental part is demonstrated. The series of dynamics analyses are carried out. The test mechanisms with variable number of bodies are used to gather the performance results of the solver. The obtained data allow for estimating the number of bodies which are sufficient to gain benefits from parallel computing as well as their level. The parallel processing profits are taken into account in the case of contact forces present in the system. The performance benefits are indicated, when the multilink belt chain is simulated, in which contact forces are included in the model.

The paper presents a spatial model of the satellite antenna with an arbitrary number of flexible arms. Such a system is an example of an open kinematic chain with a tree-like structure. The modification of the rigid finite element method is used to discretise flexible links. The equations of motion are derived from the Lagrange equations and the motion of the system is described using joint coordinates and homogenous transformations. Numerical simulations have been carried out to analyse how the method of extending the arms influences the dynamics of the system.