Design and verification of a parallel elastic robotic leg.

This paper presents the design and experimental verification of a parallel elastic robotic leg mechanism that aims to capture the dynamics of the linear mass-spring-damper model. The mechanism utilizes a wrapping cam mechanism to linearize the non-linear force resulting from the elongation of the parallel elastic element. Firstly, we explain the desired dynamics of the mass-spring-damper model, including the impact transitions, and the design of the wrapping cam mechanism. We then introduce a system identification procedure to estimate the parameters of the leg mechanism corresponding to the dynamic model. The estimated parameters are tested with a cross-validation approach to evaluate the mechanism's performance in tracking the desired model. The experimental results show that the passive dynamics of the mechanism resemble the linear model as intended. Thus, the robot provides a basis for using parallel elastic actuation while using model-based controllers that benefit the analytic solutions of the linear model.

Efficient bipedal locomotion on rough terrain via compliant ankle actuation with energy regulation.

Legged locomotion enables robotic platforms to traverse on rough terrain, which is quite challenging for other locomotion types, such as in wheeled and tracked systems. However, this benefit-moving robustly on rough terrain-comes with an inherent drawback due to the higher cost of transport in legged robots. The ultimate need for energy efficiency motivated the utilization of passive dynamics in legged locomotion. Nevertheless, a handicap in passive dynamic walking is the fragile basin of attraction that limits the locomotion capabilities of such systems. There have been various extensions to overcome such limitations by incorporating additional actuators and active control approaches at the expense of compromising the benefits of passivity. Here, we present a novel actuation and control framework, enabling efficient and sustained bipedal locomotion on significantly rough terrain. The proposed approach reinforces the passive dynamics by intermittent active feedback control within a bio-inspired compliant ankle actuation framework. Specifically, we use once-per-step energy regulation to adjust the spring precompression of the compliant ankle based on the liftoff instants-when the toe liftoffs from the ground-of the locomotion. Our results show that the proposed approach achieves highly efficient (with a cost of transport of 0.086) sustained locomotion on rough terrain, withstanding height variations up to 15% of the leg length. We provide theoretical and numerical analysis to demonstrate the performance of our approach, including systematic comparisons with the recent and state-of-the-art techniques in the literature.

The Effects of Clinical and Home-based Physiotherapy Programs in Secondary Head and Neck Lymphedema.

OBJECTIVES/HYPOTHESIS: To determine the effects of complex decongestive physiotherapy (CDP) and home programs on external lymphedema, staging of lymphedema, fibrosis, and three-dimensional (3D) surface scanning and volume evaluation in head and neck lymphedema. STUDY DESIGN: A prospective randomized controlled study. METHODS: Twenty-one patients were randomly divided into three groups: CDP (n:7), home program (n:7), and control (n:7). Assessment methods were applied at baseline and 4 weeks later for all groups. MD. Anderson Cancer Center Head and Neck Lymphedema Protocol was implemented to evaluate head and neck external lymphedema, staging of lymphedema, and fibrosis. A 3D scanner and a software were used to determine and calculate the volume of the head and neck region via 3D surface scanning. Head and neck external lymphedema and fibrosis assessment criteria were performed to evaluate visible soft tissue edema and the degree of stiffness. RESULTS: The severity and volume of lymphedema decreased in the CDP program group (P < .05). Besides, external lymphedema and fibrosis at submental region were decreased in both CDP program and home program groups (P < .05). CONCLUSIONS: While the benefits of home program are limited, a CDP program may be more effective in the management of lymphedema and fibrosis in patients diagnosed with head and neck cancer. The clinical trial registration number: NCT04286698, date: 02/25/2020, retrospectively registered. LEVEL OF EVIDENCE: 4 Laryngoscope, 131:E1550-E1557, 2021.

Approximate analytical solutions to the double-stance dynamics of the lossy spring-loaded inverted pendulum.

This paper introduces approximate time-domain solutions to the otherwise non-integrable double-stance dynamics of the 'bipedal' spring-loaded inverted pendulum (B-SLIP) in the presence of non-negligible damping. We first introduce an auxiliary system whose behavior under certain conditions is approximately equivalent to the B-SLIP in double-stance. Then, we derive approximate solutions to the dynamics of the new system following two different methods: (i) updated-momentum approach that can deal with both the lossy and lossless B-SLIP models, and (ii) perturbation-based approach following which we only derive a solution to the lossless case. The prediction performance of each method is characterized via a comprehensive numerical analysis. The derived representations are computationally very efficient compared to numerical integrations, and, hence, are suitable for online planning, increasing the autonomy of walking robots. Two application examples of walking gait control are presented. The proposed solutions can serve as instrumental tools in various fields such as control in legged robotics and human motion understanding in biomechanics.

Stride-to-stride energy regulation for robust self-stability of a torque-actuated dissipative spring-mass hopper.

In this paper, we analyze the self-stability properties of planar running with a dissipative spring-mass model driven by torque actuation at the hip. We first show that a two-dimensional, approximate analytic return map for uncontrolled locomotion with this system under a fixed touchdown leg angle policy and an open-loop ramp torque profile exhibits only marginal self-stability that does not always persist for the exact system. We then propose a per-stride feedback strategy for the hip torque that explicitly compensates for damping losses, reducing the return map to a single dimension and substantially improving the robust stability of fixed points. Subsequent presentation of simulation evidence establishes that the predictions of this approximate model are consistent with the behavior of the exact plant model. We illustrate the relevance and utility of our model both through the qualitative correspondence of its predictions to biological data as well as its use in the design of a task-level running controller.