Active Disturbance Rejection Control based on Generalized Proportional Integral Observer to Control a Bipedal Robot with Five Degrees of Freedom

An Active Disturbance Rejection Control based on Generalized Proportional Integral observer (ADRC with GPI observer) was developed to control the gait of a bipedal robot with five degrees of freedom. The bipedal robot used is a passive point feet which produces an underactuated dynamic walking. A virtual holonomic constraint is imposed to generate online smooth trajectories which were used as references of the control system. The proposed control strategy is tested through numerical simulation on a task of forward walking with the robot exposed to external disturbances. The performance of ADRC with GPI observer strategy is compared with a feedback linearization with proportional-derivative control. A stability test consisting on analyzing the existence of limit cycles using the Poincaré's method revealed that asymptotically stable walking was achieved. The proposed control strategy effectively rejects the external disturbances and keeps the robot in a stable dynamic walking

Robust compound control of dynamic bipedal robots

This paper presents a robust compound control strategy to produce a stable gait in dynamic bipedal robots under random perturbations. The proposed control strategy consists of two interactive loops: an adaptive trajectory generator and a robust trajectory tracking controller. The adaptive trajectory generator produces references for the robot controlled joints without a-priori knowledge of the terrain features and minimizes the effects of disturbances and model uncertainties during the gait, particularly during the support-leg exchange. The trajectory tracking controller is a non-switching robust multivariable generalized proportional integral (GPI) controller. The GPI controller rejects external disturbances and uncertainties faced by the robot during the swing walking phase. The proposed control strategy was evaluated on the numerical model of a five-link planar bipedal robot with one degree of under-actuation, four actuators, and point feet. The results showed robust performance and stability under external disturbances and model parameter uncertainties on uneven terrain with uphills and downhills. The stability of the gait was proven through the computation of a Poincaré return map for a hybrid zero dynamics with uncertainties (HZDU) model, which shows convergence to a bounded neighborhood of a nominal orbital periodic behavior

Hybrid disturbance rejection control of dynamic bipedal robots

This paper presents a disturbance rejection control strategy for hybrid dynamic systems exposed to model uncertainties and external disturbances. The focus of this work is the gait control of dynamic bipedal robots. The proposed control strategy integrates continuous and discrete control actions. The continuous control action uses a novel model-based active disturbance rejection control (ADRC) approach to track gait trajectory references. The discrete control action resets the gait trajectory references after the impact produced by the robot’s support-leg exchange to maintain a zero tracking error. A Poincaré return map is used to search asymptotic stable periodic orbits in an extended hybrid zero dynamics (EHZD). The EHZD reflects a lower-dimensional representation of the full hybrid dynamics with uncertainties and disturbances. A physical bipedal robot testbed, referred to as Saurian, is fabricated for validation purposes. Numerical simulation and physical experiments show the robustness of the proposed control strategy against external disturbances and model uncertainties that affect both the swing motion phase and the support-leg exchange

Automatic Stabilization of a Riderless Bicycle using the Active Disturbance Rejection Control Approach

[ES] Este trabajo propone una estrategia de Control por Rechazo Activo de Perturbaciones (ADRC), usando observadores extendidos de perturbación, para estabilizar una bicicleta en movimiento, sin conductor y con una velocidad de avance variable. Aunque la bicicleta tiene una dinámica inestable y no lineal alrededor de su posición vertical, que puede modelarse como un sistema Lineal de Parámetros Variantes (LPV) dependientes de la velocidad, el diseño del controlador usa un modelo simplificado de parámetros concentrados invariantes en el tiempo y una velocidad nominal constante. El esquema ADRC agrupa las discrepancias entre el modelo simplificado y la planta, junto con las perturbaciones externas en una señal aditiva unificada, que es estimada a través del observador y realimentada mediante una ley de control lineal para rechazarla. La efectividad de la estrategia es validada mediante una co-simulación entre ADAMS y MATLAB, la cual exhibe un alto desempeño y robustez sobre un modelo dinámico virtual de la bicicleta, sometida a perturbaciones externas severas y variaciones de parámetros.[EN] This work proposes an ADRC (Active Disturbance Rejection Control) strategy by disturbance extended observers to stabilize a moving riderless bicycle with a variant forward speed. Although the bicycle has an unstable and non-linear dynamics when in its upright position, which can be modeled as a LPV (Linear-Parameter-Varying) system that depends on the forward speed, a simplified time-invariant and lumped-parameter model, with an nominal constant forward speed is used in the controller design. ADRC scheme groups discrepancies between the simplified model and the plant, with external disturbances into an equivalent additive unified disturbance signal at input, which is estimated via the observer and rejected through a linear control law. The effectiveness of this strategy is validated by a co-simulation between ADAMS and MATLAB, which exhibits a high performance and robustness in a virtual dynamic model of the bicycle, submitted to severe external disturbances and parameter variations. Baquero-Suárez, M.; Cortes-Romero, J.; Arcos-Legarda, J.; Coral-Enriquez, H. (2017). Estabilización Automática de una Bicicleta sin Conductor mediante el Enfoque de Control por Rechazo Activo de Perturbaciones. Revista Iberoamericana de Automática e Informática industrial. 15(1):86-100. https://doi.org/10.4995/riai.2017.8832OJS86100151Ai-Buraiki, O., Thabit, M. B., Jun 2014. Model Predictive Control Design Approach for Autonomous Bicycle Kinematics Stabilization. In: 22nd Mediterranean Conference of Control and Automation (MED). pp. 380-383. https://doi.org/10.1109/MED.2014.6961401Bickford, D., Davison, D. E., May 2013. Systematic Multi-Loop Control for Autonomous Bicycle Path following. In: 2013 26th IEEE Canadian Conference on Electrical and Computer Engineering (CCECE). pp. 1-5. https://doi.org/10.1109/CCECE.2013.6567714Brizuela, J., Astorga, C., Zavala, A., Pattalochi, L., Canales, F., Dec 2016. State and Actuator Fault Estimation Observer Design Integrated in a Riderless Bicycle Stabilization System. fISAg Transactions 61, 199-210.Canudas deWit, C., Tsiotras, P., 1999. Dynamic Tire Friction Models for Vehicle Traction Control. In: Proceedings of the 38th IEEE Conference on Decision and Control. Vol. 4. pp. 3746-3751. https://doi.org/10.1109/CDC.1999.827937Cerone, V., Andreo, D., Larsson, M., Regruto, D., Oct 2010. Stabilization of a Riderless Bicycle, A Linear-Parameter-Varying Approach [applications of control]. Control Systems, IEEE 30 (5), 23-32. https://doi.org/10.1109/MCS.2010.937745Cortés Romero, J., Luviano Juárez, A., Álvarez Salas, R., Sira Ramírez, H., Aug 2010. Fast Identification and Control of an Uncertain Brushless DC Motor Using Algebraic Methods. In: 12th International Power Electronics Congress (CIEP). pp. 9-14. https://doi.org/10.1109/CIEP.2010.5598844Cortés Romero, J., Ramos, G., Coral Enriquez, H., Aug 2014. Generalized Proportional Integral Control for Periodic Signals under Active Disturbance Rejection Approach. ISA Transactions 53 (6), 1901-1909. https://doi.org/10.1016/j.isatra.2014.07.001Emaru, T., Tsuchiya, T., Dec 2005. Research on Estimating Smoothed Value and Differential Value by using Sliding Mode System. IEEE Transactions on Robotics and Automation 21 (6), 391-402.Gao, B., Junpeng Shao, Xiaodong Yang, Nov 2014. A Compound Control Strategy Combining Velocity Compensation with ADRC of Electroydraulic Position Servo Control System. ISA Transactions 53 (6), 1910-1918. https://doi.org/10.1016/j.isatra.2014.06.011Goldstein, H., 1953. Classical Mechanics, 3rd Edition. Addison-Wesley, Ch. 5, pp. 184-188.Gordon Wilson, D., Jim Papadopoulos, 2004. Bicycling Science, 3rd Edition. The MIT Press, Ch. 8, pp. 263-310.Hwang, C.-L., Hsiu-Ming Wu, Shih, C.-L., May 2009. Fuzzy Sliding Mode Underactuated Control for Autonomous Dynamic Balance of an Electrical Bicycle. IEEE Transactions on Control Systems Technology 17 (3), 658-670. https://doi.org/10.1109/TCST.2008.2004349Jin, H., Yang, D., Liu, Z., Zang, X., Li, G., Zhu, Y., Dec 2015. A Gyroscope-Based Inverted Pendulum with Application to Posture Stabilization of Bicycle Vehicle. In: 2015 IEEE International Conference on Robotics and Biomimetics (ROBIO). pp. 2103-2108. https://doi.org/10.1109/ROBIO.2015.7419084Kooijman, J. D. G., Meijaard, J. P., Papadopoulos, J. M., Ruina, A., Schwab, A. L., 2011. A Bicycle can be Self-Stable without Gyroscopic or Caster Effects. Science 332 (6027), 339-342. https://doi.org/10.1126/science.1201959Kooijman, J. D. G., Schwab, A. L., Meijaard, J. P., May 2008. Experimental Validation of a Model for the Motion of an Uncontrolled Bicycle. Multibody System Dynamics 19 (1), 115-132. https://doi.org/10.1007/s11044-007-9050-xLam, P. Y., Sep 2011. Gyroscopic Stabilization of a Kid-Size Bicycle. In: 2011 IEEE 5th International Conference on Cybernetics and Intelligent Systems (CIS). pp. 247-252. https://doi.org/10.1109/ICCIS.2011.6070336Lewis, F. L., Popa, L. X. D., 2008. Optimal and Robust Estimation, with an Introduction to Stochastic Control Theory, 2nd Edition. CRC Press, Ch. 3, pp. 151-204.Limebeer, D. J. N., Sharp, R. S., Oct 2006. Bicycles, Motorcycles, and Models. IEEE Control Systems 26 (5), 34-61. https://doi.org/10.1109/MCS.2006.1700044Meijaard, J., Papadopoulos, J. M., Ruina, A., Schwab, A., 2007. Linearized Dynamics Equations for the Balance and Steer of a Bicycle: a Benchmark and Review. Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 463 (2084), 1955-1982. https://doi.org/10.1098/rspa.2007.1857Michini, B., Sean Torrez, 2007. Autonomous Stability Control of a Moving Bicycle. Tech. rep., Massachusetts Institute of Technology, USA, 77 Massachusetts Ave, Rm 33-336 - Cambridge MA 02139.Neimark, J. I., N. A. Fufaev, 2004. Translations of Mathematical Monographs. In: Dynamics of Nonholonomic Systems. Vol. 33. American Mathematical Society, Ch. 6, pp. 330-373.Nenner, U., Linker, R., Gutman, P.-O., 2010. Robust Feedback Stabilization of an Unmanned Motorcycle. Control Engineering Practice 18 (8), 970-978. https://doi.org/10.1016/j.conengprac.2010.04.003Papadopoulos, J. M., 1987. Bicycle Steering Dynamics and Self-stability: A Summary Report on Work in Progress. Cornell bicycle research project, Cornell University, Ithaca, NY.Schwab, A., Meijaard, J., Papadopoulos, J., 2005a. Benchmark Results on the Linearized Equations of Motion of an Uncontrolled Bicycle. Journal of Mechanical Science and Technology 19 (1), 292-304. https://doi.org/10.1007/BF02916147Schwab, A. L., J. P. Meijaard, Papadopoulos, J. M., Aug 2005b. A Multibody Dynamics Benchmark on the Equations of Motion of an Uncontrolled Bicycle. In: Proceedings of the Fifth EUROMECH Nonlinear Dynamics Conference. pp. 511-521.Schwab, A. L., Meijaard, J. P., May 2013. A Review on Bicycle Dynamics and Rider Control. Vehicle System Dynamics 51 (7), 1059-1090. https://doi.org/10.1080/00423114.2013.793365Schwab, A. L., Meijaard, J. P., Kooijman, J. D. G., Aug 2012. Lateral Dynamics of a Bicycle with a Passive Rider Model: Stability and Controllability. Vehicle System Dynamics 50 (8), 1209-1224. https://doi.org/10.1080/00423114.2011.610898Srivastava, S., Pandit, V., 2016. A PI/PID Controller for Time Delay Systems with Desired Closed Loop Time Response and Guaranteed Gain and Phase Margins. Journal of Process Control 37, 70-77. https://doi.org/10.1016/j.jprocont.2015.11.001Åström, K. J., Hägglund, T., 1995. PID Controllers: Theory, Design, and Tuning, 2nd Edition. ISA, Ch. 3, pp. 80-92.Åström, K. J., Klein, R. E., Lennartsson, A., Aug 2005. Bicycle Dynamics and Control: Adapted Bicycles for Education and Research. IEEE Control Systems 25 (4), 26-47. https://doi.org/10.1109/MCS.2005.1499389Su, Y. X., Zheng, C. H., Dong Sun, Duan, B. Y., Aug 2005. A Simple Nonlinear Velocity Estimator for High-Performance Motion Control. IEEE Transactions on Industrial Electronics 52 (4), 1161-1169. https://doi.org/10.1109/TIE.2005.851598Sun, B., Zhiqiang Gao, Oct 2005. A DSP-based Active Disturbance Rejection Control Design for a 1-Kw H-bridge DC-DC Power Converter. IEEE Transactions on Industrial Electronics 52 (5), 1271-1277. https://doi.org/10.1109/TIE.2005.855679Tanelli, M., Schiavo, F., Savaresi, S. M., Ferretti, G., Oct 2006. Object-Oriented Multibody Motorcycle Modelling for Control Systems Prototyping. In: IEEE International Conference on Control Applications. pp. 2695-2700.Whipple, F., 1899. The Stability of the Motion of a Bicycle. Quart. J. Pure Appl. Math. 30 (120), 312-348.Yuanyuan, F., Runjia, D., Yuping, X., 2017. Steering Angle Balance Control Method for Rider-Less Bicycle Based on ADAMS. Springer Singapore, Singapore, Ch. 1, pp. 15-31

Major histocompatibility complex associations of ankylosing spondylitis are complex and involve further epistasis with ERAP1

Ankylosing spondylitis (AS) is a common, highly heritable, inflammatory arthritis for which HLA-B*27 is the major genetic risk factor, although its role in the aetiology of AS remains elusive. To better understand the genetic basis of the MHC susceptibility loci, we genotyped 7,264 MHC SNPs in 22,647 AS cases and controls of European descent. We impute SNPs, classical HLA alleles and amino-acid residues within HLA proteins, and tested these for association to AS status. Here we show that in addition to effects due to HLA-B*27 alleles, several other HLA-B alleles also affect susceptibility. After controlling for the associated haplotypes in HLA-B, we observe independent associations with variants in the HLA-A, HLA-DPB1 and HLA-DRB1 loci. We also demonstrate that the ERAP1 SNP rs30187 association is not restricted only to carriers of HLA-B*27 but also found in HLA-B*40:01 carriers independently of HLA-B*27 genotype

Sensing and Tactile Artificial Muscles from Reactive Materials

Films of conducting polymers can be oxidized and reduced in a reversible way. Any intermediate oxidation state determines an electrochemical equilibrium. Chemical or physical variables acting on the film may modify the equilibrium potential, so that the film acts as a sensor of the variable. The working potential of polypyrrole/DBSA (Dodecylbenzenesulfonic acid) films, oxidized or reduced under constant currents, changes as a function of the working conditions: electrolyte concentration, temperature or mechanical stress. During oxidation, the reactive material is a sensor of the ambient, the consumed electrical energy being the sensing magnitude. Devices based on any of the electrochemical properties of conducting polymers must act simultaneously as sensors of the working conditions. Artificial muscles, as electrochemical actuators constituted by reactive materials, respond to the ambient conditions during actuation. In this way, they can be used as actuators, sensing the surrounding conditions during actuation. Actuating and sensing signals are simultaneously included by the same two connecting wires

Proteomic Analysis of Fusarium solani Isolated from the Asian Longhorned Beetle, Anoplophora glabripennis

Wood is a highly intractable food source, yet many insects successfully colonize and thrive in this challenging niche. Overcoming the lignin barrier of wood is a key challenge in nutrient acquisition, but full depolymerization of intact lignin polymers has only been conclusively demonstrated in fungi and is not known to occur by enzymes produced by insects or bacteria. Previous research validated that lignocellulose and hemicellulose degradation occur within the gut of the wood boring insect, Anoplophora glabripennis (Asian longhorned beetle), and that a fungal species, Fusarium solani (ATCC MYA 4552), is consistently associated with the larval stage. While the nature of this relationship is unresolved, we sought to assess this fungal isolate's ability to degrade lignocellulose and cell wall polysaccharides and to extract nutrients from woody tissue. This gut-derived fungal isolate was inoculated onto a wood-based substrate and shotgun proteomics using Multidimensional Protein Identification Technology (MudPIT) was employed to identify 400 expressed proteins. Through this approach, we detected proteins responsible for plant cell wall polysaccharide degradation, including proteins belonging to 28 glycosyl hydrolase families and several cutinases, esterases, lipases, pectate lyases, and polysaccharide deacetylases. Proteinases with broad substrate specificities and ureases were observed, indicating that this isolate has the capability to digest plant cell wall proteins and recycle nitrogenous waste under periods of nutrient limitation. Additionally, several laccases, peroxidases, and enzymes involved in extracellular hydrogen peroxide production previously implicated in lignin depolymerization were detected. In vitro biochemical assays were conducted to corroborate MudPIT results and confirmed that cellulases, glycosyl hydrolases, xylanases, laccases, and Mn- independent peroxidases were active in culture; however, lignin- and Mn- dependent peroxidase activities were not detected While little is known about the role of filamentous fungi and their associations with insects, these findings suggest that this isolate has the endogenous potential to degrade lignocellulose and extract nutrients from woody tissue

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)

Meeting abstrac