171 research outputs found
Estimating Lower Limb Kinematics using a Lie Group Constrained EKF and a Reduced Wearable IMU Count
This paper presents an algorithm that makes novel use of a Lie group
representation of position and orientation alongside a constrained extended
Kalman filter (CEKF) to accurately estimate pelvis, thigh, and shank kinematics
during walking using only three wearable inertial sensors. The algorithm
iterates through the prediction update (kinematic equation), measurement update
(pelvis height, zero velocity update, flat-floor assumption, and covariance
limiter), and constraint update (formulation of hinged knee joints and
ball-and-socket hip joints). The paper also describes a novel Lie group
formulation of the assumptions implemented in the said measurement and
constraint updates. Evaluation of the algorithm on nine healthy subjects who
walked freely within a m room shows that the knee and hip
joint angle root-mean-square errors (RMSEs) in the sagittal plane for free
walking were and , respectively, while
the correlation coefficients (CCs) were and ,
respectively. The evaluation demonstrates a promising application of Lie group
representation to inertial motion capture under reduced-sensor-count
configuration, improving the estimates (i.e., joint angle RMSEs and CCs) for
dynamic motion, and enabling better convergence for our non-linear
biomechanical constraints. To further improve performance, additional
information relating the pelvis and ankle kinematics is needed.Comment: 6 pages. arXiv admin note: text overlap with arXiv:1910.0091
Robust Learning-Based Incipient Slip Detection using the PapillArray Optical Tactile Sensor for Improved Robotic Gripping
The ability to detect slip, particularly incipient slip, enables robotic
systems to take corrective measures to prevent a grasped object from being
dropped. Therefore, slip detection can enhance the overall security of robotic
gripping. However, accurately detecting incipient slip remains a significant
challenge. In this paper, we propose a novel learning-based approach to detect
incipient slip using the PapillArray (Contactile, Australia) tactile sensor.
The resulting model is highly effective in identifying patterns associated with
incipient slip, achieving a detection success rate of 95.6% when tested with an
offline dataset. Furthermore, we introduce several data augmentation methods to
enhance the robustness of our model. When transferring the trained model to a
robotic gripping environment distinct from where the training data was
collected, our model maintained robust performance, with a success rate of
96.8%, providing timely feedback for stabilizing several practical gripping
tasks. Our project website:
https://sites.google.com/view/incipient-slip-detection
Peripheral Nerve Activation Evokes Machine-Learnable Signals in the Dorsal Column Nuclei
The brainstem dorsal column nuclei (DCN) are essential to inform the brain of tactile and proprioceptive events experienced by the body. However, little is known about how ascending somatosensory information is represented in the DCN. Our objective was to investigate the usefulness of high-frequency (HF) and low-frequency (LF) DCN signal features (SFs) in predicting the nerve from which signals were evoked. We also aimed to explore the robustness of DCN SFs and map their relative information content across the brainstem surface. DCN surface potentials were recorded from urethane-anesthetized Wistar rats during sural and peroneal nerve electrical stimulation. Five salient SFs were extracted from each recording electrode of a seven-electrode array. We used a machine learning approach to quantify and rank information content contained within DCN surface-potential signals following peripheral nerve activation. Machine-learning of SF and electrode position combinations was quantified to determine a hierarchy of information importance for resolving the peripheral origin of nerve activation. A supervised back-propagation artificial neural network (ANN) could predict the nerve from which a response was evoked with up to 96.8 ± 0.8% accuracy. Guided by feature-learnability, we maintained high prediction accuracy after reducing ANN algorithm inputs from 35 (5 SFs from 7 electrodes) to 6 (4 SFs from one electrode and 2 SFs from a second electrode). When the number of input features were reduced, the best performing input combinations included HF and LF features. Feature-learnability also revealed that signals recorded from the same midline electrode can be accurately classified when evoked from bilateral nerve pairs, suggesting DCN surface activity asymmetry. Here we demonstrate a novel method for mapping the information content of signal patterns across the DCN surface and show that DCN SFs are robust across a population. Finally, we also show that the DCN is functionally asymmetrically organized, which challenges our current understanding of somatotopic symmetry across the midline at sub-cortical levels
Tactile Sensors for Friction Estimation and Incipient Slip Detection - Toward Dexterous Robotic Manipulation:A Review
Humans can handle and manipulate objects with ease; however, human dexterity has yet to be matched by artificial systems. Receptors in our fingers and hands provide essential tactile information to the motor control system during dexterous manipulation such that the grip force is scaled to the tangential forces according to the coefficient of friction. Likewise, tactile sensing will become essential for robotic and prosthetic gripping performance as applications move toward unstructured environments. However, most existing research ignores the need to sense the frictional properties of the sensor-object interface, which (along with contact forces and torques) is essential for finding the minimum grip force required to securely grasp an object. Here, we review this problem by surveying the field of tactile sensing from the perspective that sensors should: 1) detect gross slip (to adjust the grip force); 2) detect incipient slip (dependent on the frictional properties of the sensor-object interface and the geometries and mechanics of the sensor and the object) as an indication of grip security; or 3) measure friction on contact with an object and/or following a gross or incipient slip event while manipulating an object. Recommendations are made to help focus future sensor design efforts toward a generalizable and practical solution to sense, and hence control grip security. Specifically, we propose that the sensor mechanics should encourage incipient slip, by allowing parts of the sensor to slip while other parts remain stuck, and that instrumentation should measure displacement and deformation to complement conventional force, pressure, and vibration tactile sensing
Conventional in vivo irradiation procedures are insufficient to accurately determine tumor responses to non-uniform radiation fields
A comparison of magnetic resonance imaging and neuropsychological examination in the diagnostic distinction of Alzheimer’s disease and behavioral variant frontotemporal dementia
The clinical distinction between Alzheimer's disease (AD) and behavioral variant frontotemporal dementia (bvFTD) remains challenging and largely dependent on the experience of the clinician. This study investigates whether objective machine learning algorithms using supportive neuroimaging and neuropsychological clinical features can aid the distinction between both diseases. Retrospective neuroimaging and neuropsychological data of 166 participants (54 AD; 55 bvFTD; 57 healthy controls) was analyzed via a Naïve Bayes classification model. A subgroup of patients (n = 22) had pathologically-confirmed diagnoses. Results show that a combination of gray matter atrophy and neuropsychological features allowed a correct classification of 61.47% of cases at clinical presentation. More importantly, there was a clear dissociation between imaging and neuropsychological features, with the latter having the greater diagnostic accuracy (respectively 51.38 vs. 62.39%). These findings indicate that, at presentation, machine learning classification of bvFTD and AD is mostly based on cognitive and not imaging features. This clearly highlights the urgent need to develop better biomarkers for both diseases, but also emphasizes the value of machine learning in determining the predictive diagnostic features in neurodegeneration
Current Preclinical Testing of New Hip Arthroplasty Technologies Does Not Reflect Real-World Loadings: Capturing Patient-Specific and Activity-Related Variation in Hip Contact Forces
Background: Total hip replacement (THR) implants are routinely tested for their tribological performance through regulatory pre-clinical wear testing (e.g. ISO-14242). The standardized loading conditions defined in these tests consist of simplified waveforms, which do not specifically represent in vivo loads in different groups of patients. The aim of this study was to investigate, through musculoskeletal modelling, patient-specific and activity-related variation in hip contact forces (HCFs) in a large cohort of THR patients during common activities of daily living (ADLs).
Methods: 132 THR patients participated in a motion-capture analysis while performing different ADLs, including walk, fast walk, stair ascent and descent (locomotor); sit-to-stand, stand-to-sit, squat and lunge (non-locomotor). HCFs were then calculated using the AnyBody Modelling System and qualitatively compared across all activities. The influence of gender on HCFs was analysed through statistical parametric mapping (SPM) analysis.
Results: Systematic differences were found in HCF magnitudes and individual components in both locomotor and non-locomotor ADLs. The qualitative analysis of the ADLs revealed a large range and a large variability of forces experienced at the hip during different activities. Significant differences in the three-dimensional loading patterns were observed between males and females across most activities.
Conclusions: THR patients present a large variability in the forces experienced at the hip joint during their daily life. The inter-patient variation might partially explain the heterogeneity observed in implant survival rates. A more extensive pre-clinical implant testing standard, under clinically relevant loading conditions has been advocated to better predict and avoid clinical wear problems
Deletion of parasite immune modulatory sequences combined with immune activating signals enhances vaccine mediated protection against filarial nematodes
<p>Background: Filarial nematodes are tissue-dwelling parasites that can be killed by Th2-driven immune effectors, but that have evolved to withstand immune attack and establish chronic infections by suppressing host immunity. As a consequence, the efficacy of a vaccine against filariasis may depend on its capacity to counter parasite-driven immunomodulation.</p>
<p>Methodology and Principal Findings: We immunised mice with DNA plasmids expressing functionally-inactivated forms of two immunomodulatory molecules expressed by the filarial parasite Litomosoides sigmodontis: the abundant larval transcript-1 (LsALT) and cysteine protease inhibitor-2 (LsCPI). The mutant proteins enhanced antibody and cytokine responses to live parasite challenge, and led to more leukocyte recruitment to the site of infection than their native forms. The immune response was further enhanced when the antigens were targeted to dendritic cells using a single chain Fv-αDEC205 antibody and co-administered with plasmids that enhance T helper 2 immunity (IL-4) and antigen-presenting cell recruitment (Flt3L, MIP-1α). Mice immunised simultaneously against the mutated forms of LsALT and LsCPI eliminated adult parasites faster and consistently reduced peripheral microfilaraemia. A multifactorial analysis of the immune response revealed that protection was strongly correlated with the production of parasite-specific IgG1 and with the numbers of leukocytes present at the site of infection.</p>
<p>Conclusions: We have developed a successful strategy for DNA vaccination against a nematode infection that specifically targets parasite-driven immunosuppression while simultaneously enhancing Th2 immune responses and parasite antigen presentation by dendritic cells.</p>
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