57 research outputs found
Evolutionary Curriculum Training for DRL-Based Navigation Systems
In recent years, Deep Reinforcement Learning (DRL) has emerged as a promising
method for robot collision avoidance. However, such DRL models often come with
limitations, such as adapting effectively to structured environments containing
various pedestrians. In order to solve this difficulty, previous research has
attempted a few approaches, including training an end-to-end solution by
integrating a waypoint planner with DRL and developing a multimodal solution to
mitigate the drawbacks of the DRL model. However, these approaches have
encountered several issues, including slow training times, scalability
challenges, and poor coordination among different models. To address these
challenges, this paper introduces a novel approach called evolutionary
curriculum training to tackle these challenges. The primary goal of
evolutionary curriculum training is to evaluate the collision avoidance model's
competency in various scenarios and create curricula to enhance its
insufficient skills. The paper introduces an innovative evaluation technique to
assess the DRL model's performance in navigating structured maps and avoiding
dynamic obstacles. Additionally, an evolutionary training environment generates
all the curriculum to improve the DRL model's inadequate skills tested in the
previous evaluation. We benchmark the performance of our model across five
structured environments to validate the hypothesis that this evolutionary
training environment leads to a higher success rate and a lower average number
of collisions. Further details and results at our project website.Comment: Robotics: Science and System
Hierarchical Experience-informed Navigation for Multi-modal Quadrupedal Rebar Grid Traversal
This study focuses on a layered, experience-based, multi-modal contact
planning framework for agile quadrupedal locomotion over a constrained rebar
environment. To this end, our hierarchical planner incorporates
locomotion-specific modules into the high-level contact sequence planner and
solves kinodynamically-aware trajectory optimization as the low-level motion
planner. Through quantitative analysis of the experience accumulation process
and experimental validation of the kinodynamic feasibility of the generated
locomotion trajectories, we demonstrate that the experience planning heuristic
offers an effective way of providing candidate footholds for a legged contact
planner. Additionally, we introduce a guiding torso path heuristic at the
global planning level to enhance the navigation success rate in the presence of
environmental obstacles. Our results indicate that the torso-path guided
experience accumulation requires significantly fewer offline trials to
successfully reach the goal compared to regular experience accumulation.
Finally, our planning framework is validated in both dynamics simulations and
real hardware implementations on a quadrupedal robot provided by Skymul Inc
Fabrication and properties of zirconia/hydroxyapatite composite scaffold based on digital light processing
Zirconia and hydroxyapatite(HA) are two typical implant materials, which have the advantages of excellent mechanical strength and good biological activity respectively. It was found that composite material had good biocompatibility and mechanical strength compared to the single material.
In this paper, the porous scaffolds of ZrO2/HA composite were formed by digital light processing (DLP) technology and their performance were evaluated. Cell experiments showed that the addition of HA had a positive effect on cell proliferation and differentiation. Mechanical tests showed that the composite scaffold with 10 wt% HA had the best compressive capacity due to the pinning and bridging effect of a small amount of HA grains. When scaffolds were immersed in the simulated body fluid (SBF), the compressive strengths of the composite scaffolds decreased within the first 14 days and gradually increased after 14 days. The reason for this phenomenon was the degradation of calcium phosphate components and the deposition of apatite. By the 28th day, the compressive strengths of all the composite scaffolds increased to over 20 MPa, close to that of the zirconia scaffolds during the same period (25 MPa). The compressive strengths of all scaffolds met the requirement of cancellous bone during the entire soaking period, and the composite scaffolds have potential application value in bone repair
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