Design and validation of a pediatric gait assistance exoskeleton system with fast non-singular terminal sliding mode controller.

Existing exoskeletons for pediatric gait assistance have limitations in anthropometric design, structure weight, cost, user safety features, and adaptability to diverse users. Additionally, creating precise models for pediatric rehabilitation is difficult because the rapid anthropometric changes in children result in unknown model parameters. Furthermore, external disruptions, like unpredictable movements and involuntary muscle contractions, add complexity to the control schemes that need to be managed. To overcome these limitations, this study aims to develop an affordable stand-aided lower-limb exoskeleton specifically for pediatric subjects (8-12 years, 25-40 kg, 128-132 cm) in passive-assist mode. The authors modified a previously developed model (LLESv1) for improved rigidity, reduced mass, simplified motor arrangement, variable waist size, and enhanced mobility. A computer-aided design of the new exoskeleton system (LLESv2) is presented. The developed prototype of the exoskeleton appended with a pediatric subject (age: 12 years old, body mass: 40 kg, body height: 132 cm) is presented with real-time hardware architecture. Thereafter, an improved fast non-singular terminal sliding mode (IFNSTSM) control scheme is proposed, incorporating a double exponential reaching law for expedited error convergence and enhanced stability. The Lyapunov stability warrants the control system's performance despite uncertainties and disturbances. In contrast to fast non-singular terminal sliding mode (FNSTSM) control and time-scaling sliding mode (TSSM) control, experimental validation demonstrates the effectiveness of IFNSTSM control by a respective average of 5.39% and 42.1% in tracking desired joint trajectories with minimal and rapid finite time converging errors. Moreover, the exoskeleton with the proposed IFNSTSM control requires significantly lesser control efforts than the exoskeleton using contrast FNSTSM control. The Bland-Altman analysis indicates that although there is a minimal mean difference in variables when employing FNSTSM and IFNSTSM controllers, the latter exhibits significant performance variations as the mean of variables changes. This research contributes to affordable and effective pediatric gait assistance, improving rehabilitation outcomes and enhancing mobility support.

Robust LQR-Based Neural-Fuzzy Tracking Control for a Lower Limb Exoskeleton System with Parametric Uncertainties and External Disturbances.

The design of an accurate control scheme for a lower limb exoskeleton system has few challenges due to the uncertain dynamics and the unintended subject's reflexes during gait rehabilitation. In this work, a robust linear quadratic regulator- (LQR-) based neural-fuzzy (NF) control scheme is proposed to address the effect of payload uncertainties and external disturbances during passive-assist gait training. Initially, the Euler-Lagrange principle-based nonlinear dynamic relations are established for the coupled system. The input-output feedback linearization approach is used to transform the nonlinear relations into a linearized state-space form. The architecture of the adaptive neuro-fuzzy inference system (ANFIS) and used membership function are briefly explained. While varying mass parameters up to 20%, three robust neural-fuzzy datasets are formulated offline with the joint error vector and LQR control input. Thereafter, to deal with external interferences, an error dynamics with a disturbance estimator is presented using an online adaptation of the firing strength matrix. The Lyapunov theory is carried out to ensure the asymptotic stability of the coupled human-exoskeleton system in view of the proposed controller. The gait tracking results for the proposed control scheme (RLQR-NF) are presented and compared with the exponential reaching law-based sliding mode (ERL-SM) controller. Furthermore, to investigate the robustness of the proposed control over LQR control, a comparative performance analysis is presented for two cases of parametric uncertainties and external disturbances. The first case considers the 20% raise in mass values with a trigonometric form of disturbances, and the second case includes the effect of the 30% increment in mass values with a random form of disturbances. The simulation runs have shown the promising gait tracking aspects of the designed controller for passive-assist gait training.

Initial default among diagnosed sputum smear-positive pulmonary tuberculosis patients in Andhra Pradesh, India.

BACKGROUND: Under the Indian Revised National TB Control Programme (RNTCP), smear-positive pulmonary tuberculosis (PTB) patients not confirmed as starting treatment are reported as 'initial defaulters'. SETTING: Twenty districts of Andhra Pradesh State, India. OBJECTIVE: To evaluate reasons for treatment non-initiation in smear-positive PTB patients diagnosed and reported as initial defaulters by the NTP. DESIGN: A cross-sectional survey conducted of all reported initial defaulters during the period July-September 2006. RESULTS: Of 1304 reported initial defaulters, 619 (47.5%) had been placed on treatment, having been incorrectly reported due to poor documentation of patients referred for treatment in the same district or whose treatment initiation was delayed until the subsequent quarter. Of the 685 (4.5% of the total diagnosed) who were confirmed initial defaulters, 350 (51%) were untraceable, 152 (22%) had died before treatment initiation, 38 (5.5%) were treated privately, 93 (13.5%) had other reasons (e.g., refusal of treatment, chronic case, etc.) and no data were available for 52 (8%). CONCLUSIONS: Nearly 5% of smear-positive PTB patients diagnosed in the study period were confirmed as not having initiated treatment under the RNCTP. Improvements in address recording may assist efforts to retrieve these patients for treatment. Additional evaluations are needed of improved counselling of TB suspects to prevent initial default, and of reasons for death before treatment initiation.

Tuberculosis 'retreatment others': profile and treatment outcomes in the state of Andhra Pradesh, India.

SETTING: The Government of India's Revised National Tuberculosis Control Programme (RNTCP), Andhra Pradesh, South India. OBJECTIVES: To study the basic characteristics and treatment outcomes of tuberculosis (TB) patients classified as 'retreatment others' and compare their treatment outcomes with smear-positive retreatment TB cases (relapse, failure, and treatment after default [TAD]). DESIGN: Retrospective record and report review of a patient cohort (n = 1237) registered as 'retreatment others' under the RNTCP from July to September 2008. RESULTS: Of 1009 patient records of 'retreatment others' reviewed, 674 (67%) were males, 892 (88%) were aged 15-64 years, 847 (84%) were pulmonary sputum smear-negative, 843 (84%) had unknown human immunodeficiency virus (HIV) status and 55 (5.5%) were HIV-positive. All patients were treated with the RNTCP intermittent (thrice weekly) retreatment regimen. Eighty per cent were successfully treated (cured plus treatment completed). Successful outcomes were higher in females (84%), in patients with extra-pulmonary TB (87%) and in HIV-negative patients (87%). The treatment outcomes were significantly better for 'retreatment others' (P < 0.05) than among the sputum smear-positive retreatment cases (78% for relapses, 59% for failures and 73% for TAD). CONCLUSIONS: 'Retreatment others' were predominantly sputum smear-negative TB, with significantly better treatment outcomes than among smear-positive retreatment patients. Future studies may assess the accuracy of the diagnoses and factors contributing to the occurrence of 'retreatment others'.