Coaching Mascot for broad-jumping: Multi-criterial optimization of the arm trajectories for Mascot’s hopping locomotion

After a cruise phase of four years, Mascot will land on the asteroid 1999JU3. Due to the complex interaction of the lander with the terrain in low-gravity environments, a certain orientation of Mascot after descent cannot be achieved directly. Thus the mobility unit developed in the DLR Robotics and Mechatronics Center enables Mascot to upright into the nominal position and to relocate by hopping motion. As the dependence of the desired jumping trajectory on the trajectory of the mobility eccentric arm is complex, a suitable trajectory cannot be determined beforehand. As even parabolic flight campaigns do not allow for sufficiently long low-gravity phases, it is also not possible to define the trajectories based on measurements. Additionally the zero or low gravity phase during parabolic flights needs to be quite precise. Thus Mascot’s multibody dynamics model is used to check a priori created trajectories. Therefore the model has been verified using both parabolic flight campaigns as well as high precision reaction force measurements in order to determine the applicable frequency range the model is able to reproduce. These comparisons have shown, that the range important for jumping is covered by the model and only higher frequency structural vibrations are not covered yet. As contact dynamics between the lander and the asteroid are crucial to cover the post-impact behaviour, the ground contact has been modeled as an elasto-plastic surface based on the currently available but yet limited knowledge on 1999JU3. Applying the aforementioned model to multi-criterial optimization enables to systematically search for suitable trajectories in an automated process. Using the optimization framework MOPS (Multi-Objective Parameter Synthesis) developed by DLR Institute of System Dynamics and Control it is possible to find global optima for the trajectories using evolutionary strategies. The objectives for this optimization are specifically defined for the hopping scenario. Due to the micro-gravity environment it is also crucial to keep the upwards velocity safely below the escape speed. By using the multi-criterial approach it can be always maintained that Mascot’s escape velocity is never reached and minimized, while also improving performance and reliability of the hopping locomotion. As the evolutionary algorithms usually need a certain number of individuals to find optima, these numerous simulations can be used in order to further investigate the complex low-gravity interaction of the lander and the asteroid. Using these preliminary sets of training data, Mascot’s short mission phase can be supported and enhanced by the deeper insight into the dynamic interaction between lander and Asteroid

Screw-driven locomotion into regolith simulants

The aim of the Thesis is the creation of the analytical model describing the dynamics of the screw-driven mechanism used for locomotion into regolith. The model is intended for the existing prototype of the device which was created primarily for the application in the planetary exploration field. It is based on the available methods of the modeling of devices for subsurface exploration in agreement with the appropriate laws of soil mechanics. In the beginning the idea of the planetary exploration is introduced with the emphasis on the significance of the subsurface locomotion devices. After that, the different solutions from the literature are described together with mathematical tools used for their modeling. Next, the dynamical model is formulated together with the precise mathematical description of all of its components. In the section that follows the results of model validation are presented using the measurement data obtained with the usage of an existing testbed. In the end an example of model’s application in the optimization algorithm is presented, in order to obtain a screw with the most optimal performance

Damage imaging in thin-walled structures using guided ultrasonic waves

W pracy przedstawiono nowatorską technikę badań nieniszczących struktur cienkościennych bazującą na estymacji lokalnej liczby falowej ultradźwiękowych fal prowadzonych. Technika bazuje na punktowym wzbudzeniu fal ultradźwiękowych i rejestracji odpowiedzi drganiowych na siatce punktów w obszarze zainteresowania z wykorzystaniem skanującego wibrometru laserowego. Wzbudzenie może być zrealizowane bezkontaktowo za pomocą impulsu lasera, bądź kontaktowo za pomocą przetwornika piezoelektrycznego. Praca omawia podstawy teoretyczne metody oraz jej zastosowania praktyczne. Skuteczność działania omawianej metody zilustrowano na przykładzie jednorodnej płyty aluminiowej oraz niejednorodnej warstwowej płyty kompozytowej.In this paper we present a novel nondestructive testing technique for platelike structures, using the local wavenumber estimation of ultrasonic guided waves. The technique is based on the excitation of ultrasonic waves and measuring the full-field response on a grid of points in the area of interest with a scanning laser vibrometer. The excitation can be realized using a non-contact laser pulse or a piezoelectric transducer. The paper discusses theoretical background of the technique and its practical applications. The efficacy of the proposed approach is demonstrated on a homogeneous aluminum plate and an inhomogeneous layered composite plate