Stiffening the human foot with a biomimetic exotendon

Shoes are generally designed protect the feet against repetitive collisions with the ground, often using thick viscoelastic midsoles to add in-series compliance under the human. Recent footwear design developments have shown that this approach may also produce metabolic energy savings. Here we test an alternative approach to modify the foot–ground interface by adding additional stiffness in parallel to the plantar aponeurosis, targeting the windlass mechanism. Stiffening the windlass mechanism by about 9% led to decreases in peak activation of the ankle plantarflexors soleus (~ 5%, p < 0.001) and medial gastrocnemius (~ 4%, p < 0.001), as well as a ~ 6% decrease in positive ankle work (p < 0.001) during fixed-frequency bilateral hopping (2.33 Hz). These results suggest that stiffening the foot may reduce cost in dynamic tasks primarily by reducing the effort required to plantarflex the ankle, since peak activation of the intrinsic foot muscle abductor hallucis was unchanged (p = 0.31). Because the novel exotendon design does not operate via the compression or bending of a bulky midsole, the device is light (55 g) and its profile is low enough that it can be worn within an existing shoe.

Sequential Compression Device Adherence is Low in Hospitalized Antepartum Patients

Objective This study was aimed to describe sequential compression device (SCD) adherence and its associations with SCD education in hospitalized antepartum women. Study Design This study included antepartum, nonlaboring women admitted from 2016 to 2018, 1 year before and after an SCD education intervention. SCD use was assessed through the Kendall SCD 700 series compliance meter, which tracks the time the SCD machine takes within the monitoring interval. Recruitment occurred after 60 to 80 hours of monitoring, at which time a patient survey was completed. SCD use was the percentage of time the machine was on during monitoring. Mann–Whitney U and Chi-square tests were used to compare associations between SCD use, education, and pharmacologic prophylaxis. Results Among 125 recruited women, 123 provided adherence data, 69 before and 54 after the education. Median SCD use was 17.3% before and 20.7% after (p = 0.71). Pharmacologic prophylaxis use was similar between the two periods and was not associated with SCD use. Among 121 surveys, the most common reason as to why SCDs were not worn was prevention of walking (52/121 [43.0%]). Conclusion Using a novel monitoring technique, we found low-SCD use among antepartum inpatients, which was neither affected by education nor concurrent pharmacologic prophylaxis. Improving mobility with SCDs may improve use in this population. Key Points

Towards the Exploitation of Physical Compliance in Segmented and Electrically Actuated Robotic Legs: A Review Focused on Elastic Mechanisms

Physical compliance has been increasingly used in robotic legs, due to its advantages in terms of the mechanical regulation of leg mechanics and energetics and the passive response to abrupt external disturbances during locomotion. This article presents a review of the exploitation of physical compliance in robotic legs. Particular attention has been paid to the segmented, electrically actuated robotic legs, such that a comparable analysis can be provided. The utilization of physical compliance is divided into three main categories, depending on the setting locations and configurations, namely, (1) joint series compliance, (2) joint parallel compliance, and (3) leg distal compliance. With an overview of the representative work related to each category, the corresponding working principles and implementation processes of various physical compliances are explained. After that, we analyze in detail some of the structural characteristics and performance influences of the existing designs, including the realization method, compliance profile, damping design, and quantitative changes in terms of mechanics and energetics. In parallel, the design challenges and possible future works associated with physical compliance in robotic legs are also identified and proposed. This article is expected to provide useful paradigmatic implementations and design guidance for physical compliance for researchers in the construction of novel physically compliant robotic legs.

The Effect of Wing-Motor Connection Mechanism on the Payload Capacity of Flapping Flight Hovering Robots

In this paper, we study the effect of the wing to motor connection mechanism on generated lift in flapping wing hovering robots. We also propose a series compliance mechanism for the wing to motor connection and compare its performance against the existing mechanisms. In the first mechanism, the wing is directly connected to the motor with no compliance attached to the wing or motor. The second mechanism has a compliance in parallel to the wing while it, the wing, is directly connected to the motor. This mechanism resembles the well-known spring-mass system in which a spring is in parallel to the motor force, and the inertia of the wing and motor move together. The possibility of producing resonance with this mechanism is a great advantage that increases the produced lift around the resonant flapping frequency. Our proposed mechanism, the third mechanism, is inspired by the existence of tendons and muscles in animal wings. Therefore, there is an elastic spring (tendon) exist between the motor (muscle) and the wing. In this wing-motor mechanism, one end of the spring (or compliance) is connected to the wing and the other end is connected to the motor. We construct trajectory optimization to find the maximum lift production in each mechanism given the geometrical and physical limitations. The results show that the series and parallel compliance mechanisms have the potential to produce more lift with respect to the non compliance mechanism. Moreover, the series compliance mechanism can produce the highest lift depending on the inertia distribution between the wing and the motor.

Effect of Parallel Compliance on Stability of Robotic Hands With Series Elastic Actuators

Compliance is a key requirement for safe interactions with the environment for any robot. It has been well established that the human body exploits various arrangements of compliance such as series compliance (musculo-tendon units) and parallel compliance (joint capsules and ligament complex) to achieve robust and graceful interaction with the environment. Mechanical compliance can be similarly arranged in robotic joints in series or parallel to actuators. The effects of such arrangements on the closed loop properties of robotic joints such as stability, disturbance rejection and tracking performance have been analyzed separately, but their combined effects have not been studied. We present a detailed analysis on the combined effects of series and parallel arrangements of compliance on low inertia robotic joints. Our analysis shows the stability limitations of achievable joint stiffness due to series compliance and the subsequent increase in the stable upper limit of achievable joint stiffness by addition of parallel compliance. We provide guidelines towards designing compliance to improve the stability and performance of low-inertia robotic joints, which can be applied to the improvement of robotic hands performing grasping and manipulation tasks. We validate our analysis by means of an experimental platform and discuss the various characteristics and the effects of both arrangements of compliance on robotic hands.