QP-based Adaptive-Gains Compliance Control in Humanoid Falls

International audienceWe address the problem of humanoid falling with a decoupled strategy consisting of a pre-impact and a postimpact stage. In the pre-impact stage, geometrical reasoning allows the robot to choose appropriate impact points in the surrounding environment and to adopt a posture to reach them while avoiding impact-singularities and preparing for the postimpact. The surrounding environment can be unstructured and may contain cluttered obstacles. The post-impact stage uses a quadratic program controller that adapts on-line the joint proportional-derivative (PD) gains to make the robot compliant-to absorb impact and post-impact dynamics, which lowers possible damage risks. This is done by a new approach incorporating the stiffness and damping gains directly as decision variables in the QP along with the usually-considered variables of joint accelerations and contact forces. Constraints of the QP prevent the motors from reaching their torque limits during the fall. Several experiments on the humanoid robot HRP-4 in a full-dynamics simulator are presented and discussed

Fall Prediction and Controlled Fall for Humanoid Robots

Humanoids which resemble humans in their body structure and degrees of freedom are anticipated to work like them within infrastructures and environments constructed for humans. In such scenarios, even humans who have exceptional manipulation, balancing, and locomotion skills are vulnerable to fall, humanoids being their approximate imitators are no exception to this. Furthermore, their high center of gravity position in relation to their small support polygon makes them more prone to fall, unlike other robots such as quadrupeds. The consequences of these falls are so devastating that it can instantly annihilate both the robot and its surroundings. This has become one of the major stumbling blocks which humanoids have to overcome to operate in real environments. As a result, in this thesis, we have strived to address the imminent fall over of humanoids by developing different control techniques. The fall over problem as such can be divided into three subissues: fall prediction, controlled fall, and its recovery. In the presented work, the first two issues have been addressed, and they are presented in three parts. First, we define what is fall over for humanoids, different sources for it to happen, the effect fall over has both on the robot and to its surroundings, and how to deal with them. Following which, we give a brief introduction to the overall system which includes both the hardware and software components which have been used throughout the work for varied purposes. Second, the first sub-issue is addressed by proposing a generic method to predict the falling over of humanoid robots in a reliable, robust, and agile manner across various terrains, and also amidst arbitrary disturbances. The aforementioned characteristics are strived to attain by proposing a prediction principle inspired by the human balance sensory systems. Accordingly, the fusion of multiple sensors such as inertial measurement unit and gyroscope (IMU), foot pressure sensor (FPS), joint encoders, and stereo vision sensor, which are equivalent to the human\u2019s vestibular, proprioception, and vision systems are considered. We first define a set of feature-based fall indicator variables (FIVs) from the different sensors, and the thresholds for those FIVs are extracted analytically for four major disturbance scenarios. Further, an online threshold interpolation technique and an impulse adaptive counter limit are proposed to manage more generic disturbances. For the generalized prediction process, both the instantaneous and cumulative sum of each FIVs are normalized, and a suitable value is set as the critical limit to predict the fall over. To determine the best combination and the usefulness of multiple sensors, the prediction performance is evaluated on four different types of terrains, in three unique combinations: first, each feature individually with their respective FIVs; second, an intuitive performance based (PF); and finally, Kalman filter based (KF) techniques, which involve the usage of multiple features. For PF and KF techniques, prediction performance evaluations are carried out with and without adding noise. Overall, it is reported that KF performs better than PF and individual sensor features under different conditions. Also, the method\u2019s ability to predict fall overs during the robot\u2019s simple dynamic motion is also tested and verified through simulations. Experimental verification of the proposed prediction method on flat and uneven terrains was carried out with the WALK-MAN humanoid robot. Finally, in reference to the second sub-issue, i.e., the controlled fall, we propose two novel fall control techniques based on energy concepts, which can be applied online to mitigate the impact forces incurred during the falling over of humanoids. Both the techniques are inspired by the break-fall motions, in particular, Ukemi motion practiced by martial arts people. The first technique reduces the total energy using a nonlinear control tool, called energy shaping (ES) and further distributes the reduced energy over multiple contacts by means of energy distribution polygons (EDP). We also include an effective orientation control to safeguard the end-effectors in the event of ground impacts. The performance of the proposed method is numerically evaluated by dynamic simulations under the sudden falling over scenario of the humanoid robot for both lateral and sagittal falls. The effectiveness of the proposed ES and EDP concepts are verified by diverse comparative simulations regarding total energy, distribution, and impact forces. Following the first technique, we proposed another controller to generate an online rolling over motion based on the hypothesis that multi-contact motions can reduce the impact forces even further. To generate efficient rolling motion, critical parameters are defined by the insights drawn from a study on rolling, which are contact positions and attack angles. In addition, energy-injection velocity is proposed as an auxiliary rolling parameter to ensure sequential multiple contacts in rolling. An online rolling controller is synthesized to compute the optimal values of the rolling parameters. The first two parameters are to construct a polyhedron, by selecting suitable contacts around the humanoid\u2019s body. This polyhedron distributes the energy gradually across multiple contacts, thus called energy distribution polyhedron. The last parameter is to inject some additional energy into the system during the fall, to overcome energy drought and tip over successive contacts. The proposed controller, incorporated with energy injection, minimization, and distribution techniques result in a rolling like motion and significantly reduces the impact forces, and it is verified in numerical experiments with a segmented planar robot and a full humanoid model

Transcranial Direct Current Stimulation (tDCS) to Improve Lower Limb Motor Recovery Following Stroke: A Review and Study Proposal

Strokes are the result of restricted blood flow to particular areas of the brain classified by their cause. The neural damage they cause are of growing concern as the number of young adults experiencing strokes has increased by 11% in the last decade. Following stroke, there is an imbalance of inhibitory and excitatory neuronal activity, and disruption of neural networks. These changes lead to neuronal death and loss of synaptic connections that, depending on which part of the brain is affected, result in behavioral deficits such as weakness, limb hemiparesis, and loss of coordination, as well as speech and cognitive impairments. However, this loss of function can be partly recovered due to neuroplastic processes. Non-invasive brain stimulation (NIBS) is an approach that involves implanting electrodes into targeted areas of the brain which are connected to an implantable pulse generator on the skin that delivers chronic electric pulse. There are different forms of stimulation, but one with some established success in improving upper and lower limb mobility, as well as some cognitive symptoms, is transcranial direct current stimulation (tDCS). For the treatment of stroke, tDCS aims to increase excitability of the lesioned areas to improve contralesional mobility. While past research has focused on stimulating well established motor regions, such as the cerebellum, motor cortex, and basal ganglia, sensory systems also play a key role in sending information through the ascending dorsal column medial lemniscal pathway, posterior and anterior spinocerebellar tracts, and spinoreticular tracts. Here is a review of the current research on the integration of sensory and motor information in order to carry out desired movement, a discussion about how these networks are being targeted by tDCS after stroke to help patients regain lower limb movement, and finally, a proposed study in which improvements in balance, gait, and postural stability after anodal tDCS continue up to a year post-treatment in chronic ischemic stroke patients

Custom-Made Helmet Fabrication for Occupational Therapists Treating Patients with Traumatic Brain Injury

Soldiers within the Veteran\u27s Administration who have sustained a traumatic brain injury (TBI) were the focus of this project. Reports showed a growing number of soldiers have returned from Iraq with head injuries, including cranial and brain defects (Defense and Veterans Brain Injury Center, 2007). Symptoms individuals with TBI commonly exhibit include dizziness, balance problems, sleep problems, excessive fatigue, headaches, and difficulties with cognitive processes. Other symptoms associated with a TBI are blurred vision, ringing in the ears, and bad tastes in the mouth (National Institute of Neurological Disorders and Stroke, 2007). The purpose of this project was to develop a cranial helmet that would be custom-fit to the individual who has sustained a TBI to protect his or her cranium during the healing process to prevent a secondary TBl or additional complications. A literature review was conducted using PubMed, CINAHL, and electronic organizational resources to identify existing occupational therapy resources pertaining to the fabrication process of custom-made helmets. Information was also obtained from textbooks, seminars, and library searches. Limited resources existed for the use of custom-made helmets in the area of adult TBI. Instead, we used research literature regarding the fabrication of helmets for children with cranial defects to guide the development of our project. The helmet was designed incorporating the client\u27s values and interests. A mold of the individuals head was created with plaster around which we formed materials in Custom-made Helmet for Patients with Traumatic Brain Injury subsequent steps. The helmet was comprised of insulated foam used for protection and comfort. Thermoplastic splinting material was then formed on top of the foam to create the shell of the helmet. The helmet had four quadrants for air circulation to allow cool air along the head. A chin strap was added to support the helmet in place. An accompanying manual was also designed to guide the fabrication of the helmet. For the purpose of the scholarly project, time and financial aspects, this fabricated prototype is the first step in the development of the helmet. The final product will need extensive testing from competent engineers to ensure the safety of the clients using the helmet

ACUTA Journal of Telecommunications in Higher Education

In This Issue President\u27s Message Business Relationship Management: Does Your organization Need It? Predict Your organization\u27s ICT Future by Making lt Happen Safeguarding Campus Networks in an loT World What the Year 2020 Holds tor the Digital Campus Collaborating for Success The Campus of the Future: 2020 and Beyond The lnternet of Things, Higher Education, and lT: How Do We Fit ln? 201 6 institutional! Excellence Awar

Enhanced stiffness modeling of manipulators with passive joints

The paper presents a methodology to enhance the stiffness analysis of serial and parallel manipulators with passive joints. It directly takes into account the loading influence on the manipulator configuration and, consequently, on its Jacobians and Hessians. The main contributions of this paper are the introduction of a non-linear stiffness model for the manipulators with passive joints, a relevant numerical technique for its linearization and computing of the Cartesian stiffness matrix which allows rank-deficiency. Within the developed technique, the manipulator elements are presented as pseudo-rigid bodies separated by multidimensional virtual springs and perfect passive joints. Simulation examples are presented that deal with parallel manipulators of the Ortholide family and demonstrate the ability of the developed methodology to describe non-linear behavior of the manipulator structure such as a sudden change of the elastic instability properties (buckling)

Interventions for reducing sedentary behaviour in people with stroke

BACKGROUND: Stroke survivors are often physically inactive as well as sedentary,and may sit for long periods of time each day. This increases cardiometabolic risk and has impacts on physical and other functions. Interventions to reduce or interrupt periods of sedentary time, as well as to increase physical activity after stroke, could reduce the risk of secondary cardiovascular events and mortality during life after stroke. OBJECTIVES: To determine whether interventions designed to reduce sedentary behaviour after stroke, or interventions with the potential to do so, can reduce the risk of death or secondary vascular events, modify cardiovascular risk, and reduce sedentary behaviour. SEARCH METHODS: In December 2019, we searched the Cochrane Stroke Trials Register, CENTRAL, MEDLINE, Embase, CINAHL, PsycINFO, Conference Proceedings Citation Index, and PEDro. We also searched registers of ongoing trials, screened reference lists, and contacted experts in the field. SELECTION CRITERIA: Randomised trials comparing interventions to reduce sedentary time with usual care, no intervention, or waiting‐list control, attention control, sham intervention or adjunct intervention. We also included interventions intended to fragment or interrupt periods of sedentary behaviour. DATA COLLECTION AND ANALYSIS: Two review authors independently selected studies and performed 'Risk of bias' assessments. We analyzed data using random‐effects meta‐analyses and assessed the certainty of the evidence with the GRADE approach. MAIN RESULTS: We included 10 studies with 753 people with stroke. Five studies used physical activity interventions, four studies used a multicomponent lifestyle intervention, and one study used an intervention to reduce and interrupt sedentary behaviour. In all studies, the risk of bias was high or unclear in two or more domains. Nine studies had high risk of bias in at least one domain. The interventions did not increase or reduce deaths (risk difference (RD) 0.00, 95% confidence interval (CI) ‐0.02 to 0.03; 10 studies, 753 participants; low‐certainty evidence), the incidence of recurrent cardiovascular or cerebrovascular events (RD ‐0.01, 95% CI ‐0.04 to 0.01; 10 studies, 753 participants; low‐certainty evidence), the incidence of falls (and injuries) (RD 0.00, 95% CI ‐0.02 to 0.02; 10 studies, 753 participants; low‐certainty evidence), or incidence of other adverse events (moderate‐certainty evidence). Interventions did not increase or reduce the amount of sedentary behaviour time (mean difference (MD) +0.13 hours/day, 95% CI ‐0.42 to 0.68; 7 studies, 300 participants; very low‐certainty evidence). There were too few data to examine effects on patterns of sedentary behaviour. The effect of interventions on cardiometabolic risk factors allowed very limited meta‐analysis. AUTHORS' CONCLUSIONS: Sedentary behaviour research in stroke seems important, yet the evidence is currently incomplete, and we found no evidence for beneficial effects. Current World Health Organization (WHO) guidelines recommend reducing the amount of sedentary time in people with disabilities, in general. The evidence is currently not strong enough to guide practice on how best to reduce sedentariness specifically in people with stroke. More high‐quality randomised trials are needed, particularly involving participants with mobility limitations. Trials should include longer‐term interventions specifically targeted at reducing time spent sedentary, risk factor outcomes, objective measures of sedentary behaviour (and physical activity), and long‐term follow‐up