Collision-free walking in cluttered environments is still an open issue for humanoids. Most current approaches use heuristics with large safety margins to plan the robot's motion. That way, the ...chance of collisions can be greatly reduced but the robot movements are artificially limited. In this context, we extend our framework for motion generation and whole-body collision-avoidance by an on-line predictive kinematic parameter evaluation and optimization: we propose to evaluate the parameter set describing the walking pattern by integrating the full kinematic model of the robot. Initial parameter sets, which are kinematically infeasible due to kinematic limits or collisions, can be identified and adapted before the motion is executed. Starting with a feasible solution, the parameter set is optimized using a gradient method. Since the method is applied before each step, while the robot is executing the previous step, it is very reactive to changes in the environment or in the user input. The optimization method is not limited to a specific walking pattern representation, but it is applicable to different representations. We want to emphasize its suitability for real-time control. The optimization can be stopped if it exceeds a predetermined time budget. In that case, an executable but suboptimal result is used. The method is presented with simulation results obtained with our multi-body simulation. We have also validated the real-time performance in experiments with our humanoid Lola.
Real-time 3D collision avoidance for biped robots Hildebrandt, Arne-Christoph; Wittmann, Robert; Wahrmann, Daniel ...
2014 IEEE/RSJ International Conference on Intelligent Robots and Systems,
2014-Sept.
Conference Proceeding
Odprti dostop
The ability to avoid collisions is crucial for locomotion in cluttered environments. It is not enough to plan collision-free movements in advance when the environment is dynamic and not precisely ...known. We developed a new method which generates locally optimized trajectories online during the feedback control in order to dynamically avoid obstacles. This method successfully combines a local potential field method with a heuristic based on height and width of an obstacle to avoid collisions. The program's main feature is the integration of obstacles into the framework designed for self-collision avoidance presented in 1 and the collisions avoidance in task-space. We show experimental results validating the method.
This paper presents a new real-time walking pattern generator that calculates center of mass trajectories from footstep locations. Key features are the calculation of reference torque patterns by ...quadratic programming and the solution of the equations of motion by spline collocation. Fast real-time planning is combined with offline optimisation of free parameters based on a comprehensive simulation of the closed loop system to automatically generate optimally tuned walking controllers. The effectiveness of the proposed method is shown using a dynamics simulation of the robot JOHNNIE.
This paper describes a real-time walking control system developed for the biped robots JOHNNIE and LOLA. Walking trajectories are planned on-line using a simplified robot model and modified by a ...stabilizing controller. The controller uses hybrid position/force control in task space based on a resolved motion rate scheme. Inertial stabilization is achieved by modifying the contact force trajectories. The paper includes an analysis of the dynamics of controlled bipeds, which is the basis for the proposed control system. The system was tested both in forward dynamics simulations and in experiments with JOHNNIE.
Regulation of the stability of p53 is key to its tumor-suppressing activities. mdm2 directly binds to the amino-terminal region
of p53 and targets it for degradation through the ubiquitin-proteasome ...pathway. The coactivator protein TAF II 31 binds to p53 at the amino-terminal region that is also required for interaction with mdm2. In this report, we demonstrate
that expression of TAF II 31 inhibits mdm2-mediated ubiquitination of p53 and increases p53 levels. TAF II 31-mediated p53 stabilization results in activation of p53-mediated transcriptional activity and leads to p53-dependent growth
arrest in fibroblasts. UV-induced stabilization of p53 coincides with an increase in p53-associated TAF II 31 and a corresponding decrease in mdm2-p53 interaction. Non-p53 binding mutant of TAF II 31 fails to stabilize p53. Our results suggest that direct interaction of TAF II 31 and p53 not only mediates p53 transcriptional activation but also protects p53 from mdm2-mediated degradation, thereby
resulting in activation of p53 functions.
To simplify the development of new trajectories for a humanoid robot with many joints, the ability to check for potential collisions is crucial. More importantly, to enable on line generation of ...general motions, such as whole-body-motion, collision avoidance must be employed, which is usually more challenging. In this paper, a model-based and efficient on-line distance calculation between links of the robot is proposed. To avoid collisions the results are projected into the null space term of the inverse-kinematics which is based on the redundancy resolution framework of LIEGEOIS. Additionally, a novel method to reduce the vertical angular momentum for a walking biped robot which uses the arm motion is proposed. It reduces the vertical angular momentum of the walking robot especially for larger steps. Since the method also works in the null-space, it can easily be combined with the proposed collision avoidance scheme. Finally, results for the proposed methods from simulations and experiments with the robot Lola are shown.
Pushing, soft ground contact and other unknown large disturbances can cause humanoid robots to fall. In order to face such problems, an accurate and fast model of the robot is necessary to estimate ...the state at a certain time in the future using only current measurements. We approximate the robot by a three-mass model with two degrees of freedom. Unilateral compliant contacts and a closed-loop control similar to the one used on the real robot are included additionally. Utilizing this model it is possible to predict the robot's behavior and calculate compensating motions for different disturbance cases. Furthermore, it is possible to integrate the estimation results into the real-time control system of our biped LOLA. Simulation and experimental results demonstrate the effectiveness and the advantages of the proposed method.
Key to p53 ability to mediate its multiple cellular functions lies in its stability. In the present study we have elucidated the mechanism by which Mdm2 regulates p53 degradation. Using in vitro and ...in vivo ubiquitination assays we demonstrate that Mdm2 association with p53 targets p53 ubiquitination. Exposure of cells to UV-irradiation inhibits this targeting. Mdm2 which is deficient in p53 binding failed to target p53 ubiquitination, suggesting that the association is essential for Mdm2 targeting ability. While mdm2-p53 complex is found in non-stressed cells, the amount of p53-bound mdm2 is decreased after UV-irradiation, further pointing to the relationship between mdm2 binding and p53 level. Similar to Swiss 3T3 cells, the dissociation of mdm2-p53 complex was also found in UV-treated Scid cells, lacking functional DNA-PK, suggesting that DNA-PK is not sufficient for dissociating mdm2 from p53. Together our studies point to the role of Mdm2, as one of p53-associated proteins, in targeting p53 ubiquitination.
Zusammenfassung
Der Beitrag gibt einen Überblick der Forschung an voll aktuierten, humanoiden Laufmaschinen. Neben einer allgemeinen Einführung wird ein kurzer Abriss der Geschichte humanoider ...Roboter gegeben. Die bekanntesten Systeme werden nach Forschungszentren gegliedert vorgestellt. Aufbauend auf einer kurzen Einführung zu grundlegenden Aspekten der Dynamik des zweibeinigen Gehens werden die am weitesten verbreiteten Strategien zur Laufregelung dargestellt. Am Ende des Artikels wird auf einige offene Fragestellungen eingegangen.
Abstract
This paper surveys research on fully actuated humanoid walking machines. After a general introduction we briefly review the history of humanoid robots. We present the most prominent examples of current biped robots. Following a brief introduction of basic aspects of the dynamics of biped robots we review popular walking control methods. A brief review of open research questions concludes the paper.
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