Leveraging Expert Demonstration Features for Deep Reinforcement Learning in Floor Cleaning Robot Navigation.

In this paper, a Deep Reinforcement Learning (DRL)-based approach for learning mobile cleaning robot navigation commands that leverage experience from expert demonstrations is presented. First, expert demonstrations of robot motion trajectories in simulation in the cleaning robot domain are collected. The relevant motion features with regard to the distance to obstacles and the heading difference towards the navigation goal are extracted. Each feature weight is optimized with respect to the collected data, and the obtained values are assumed as representing the optimal motion of the expert navigation. A reward function is created based on the feature values to train a policy with semi-supervised DRL, where an immediate reward is calculated based on the closeness to the expert navigation. The presented results show the viability of this approach with regard to robot navigation as well as the reduced training time.

Transient Thermomechanical Simulation of 7075 Aluminum Contraction around a SiO2 Microparticle.

One important challenge that faces the metallurgic industry turns around the constant increment in the mechanical resistance of certain finished products. Metallurgic advantages can be obtained from the inclusion of microparticles in metallic materials, but this inclusion involves complex challenges as the internal stress distribution can be modified. In this work, the simulation of a cooling sequence in 7075 aluminum with a SiO2 microparticle is presented. Two models of two-dimensional (2D) type were constructed in ANSYS®2019 with circular and oval shape microparticles located inside the aluminum. Both models were subjected to the same thermomechanical transient analysis to compare the remaining stress distributions around the microparticles after the thermal load and to observe the effect of the geometrical shape. The results show remaining stresses increased in the oval model as a consequence of the geometrical shape modification. After applying a tension load in the analyzed specimens, shear stress concentrations were observed with a higher magnitude around the covertex of the oval shape. The results can be very useful for the creation of materials with controlled remnant stress located in specific or desired locations in the matrix.

Análisis experimental del desgaste entre UHMWPE y acero inoxidable 316l empleados en la manufactura de prótesis coxofemorales / Experimental wear analysis of UHMWPE and stainless 316l used in the manufacturing of coxofemoral prosthesis

La causa más común de falla en prótesis coxofemorales es el aflojamiento entre los componentes que conforman el sistema, de manera específica la copa acetabular y la cabeza femoral. En esta investigación se presenta un análisis tribológico del desgaste en los componentes mencionados, ya que cuando las superficies en contacto se desgastan, la funcionalidad mecánica del sistema se compromete, debido al cambio de geometría de los mismos, dando como resultado un juego mecánico entre la copa y la cabeza. Los materiales considerados en este estudio son el polietileno de ultra elevado peso molecular (UHMWPE, por sus siglas en inglés) para la copa acetabular, y acero inoxidable 316L para la cabeza femoral. Esta combinación de materiales representa hoy en día la recomendación más usual por parte de los cirujanos para pacientes de la tercera edad. La tasa anual de desgaste se determinó de manera experimental y se cuantificó la cantidad de material desprendido durante el contacto. Se establecieron las condiciones de carga de forma analítica, considerando las que actúan sobre la cabeza femoral a lo largo del área de desgaste durante la marcha humana. Posteriormente, se realizó el análisis experimental de desgaste utilizando una máquina tribológica de configuración perno-sobre-disco (pin-on-disk), diseñada de manera específica para este estudio. Las pruebas para determinar la pérdida volumétrica de los componentes se realizaron bajo tres condiciones de operación: en seco, lubricada con agua destilada y lubricada con suero bovino. El marco experimental considerado consistió en pernos de UHMWPE sobre discos de acero inoxidable 316l simulando el desgaste equivalente a diez años de uso de la prótesis. Finalmente, de los resultados obtenidos se puede establecer que el desgaste y la cantidad de partículas desprendidas disminuyen considerablemente cuando se utiliza suero bovino como lubricante para replicar las condiciones reales de operación del sistema...

The most common cause of failure in coxofemoral prostheses is the loosening between the components of the system, namely the acetabular cup and the femoral head. In this work a tribologic analysis of wear suffered in the components is presented, due to when the surfaces in contact are worn, the mechanical function of the system is compromised as the wearing implies a change in the geometry of the components, thus in their dimensions, resulting on a looseness between the cup and the head. The materials considered in this study are Ultra High Molecular Weight Polyethylene (UHMWPE) for the cup and 316L Stainless Steel for the femoral head, which represent the surgeons choice for elderly patients. The annual wearing rate between these components was experimentally determined, as well as the amount of debris produced during contact. Firstly, the loading conditions were determined analytically considering those acting on the femoral head taking into consideration the wearing area during human walk. Secondly, the experimental analysis consisted in wearing tests using a tribology pin-on-disk machine, specifically built for this study. The tests to determine the volumetric loss of the components were performed under three different operational conditions: dry, lubricated with bovine serum and lubricated with destilated water. The experimental set up consisted on UHMWPE pins and 316L Stainless steel discs simulating the equivalent wear of ten years of usage of the prostheses. Lastly, the obtained results proved that using the bovine serum as lubricant the wear and debris of the components was significantly reduced when compared with other cases, being the dry scenario where more damage was produced. It is important to point out that the bovine serum was chosen to simulate the synovial fluid in which the system is embedded.