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The ATLAS experiment has planned a major upgrade in view of the enhanced luminosity of the beam delivered by the Large Hadron Collider (LHC) in 2021. As part of this, the trigger at Level-1 based on calorimeter data will be upgraded to exploit fine-granularity readout using a new system of Feature Extractors (three in total), which each uses different physics objects for the trigger selection. The...
To cope with the enhanced luminosity of the beam delivered by the Large Hadron Collider (LHC) in 2020, the “A Toroidal LHC ApparatuS” (ATLAS) experiment has planned a major upgrade. As part of this, the trigger at Level1 based on calorimeter data will be upgraded to exploit fine-granularity readout using a new system of Feature Extractors, which each use different physics objects for the trigger selection...
In this paper, we present an under-actuated model of human walking, comprising only a soleus muscle and flexion/extension monoarticular hip muscles. The remaining muscle groups of the human leg are modeled using quasi-passive, series-elastic clutch elements. We hypothesize that series-elastic clutch units spanning the knee joint in a musculoskeletal arrangement can capture the dominant mechanical...
A transtibial amputee does not have a functional gastrocnemius muscle, which affects the knee as well as the ankle joint. In this investigation, we developed a transtibial prosthesis comprising an artificial gastrocnemius mechanism as well as a powered ankle-foot device. A pilot study was conducted with a bilateral transtibial amputee walking at a self-selected speed. The trial compared muscle electromyography...
Recent humanoid control investigations have emphasized the importance of controlling whole-body angular momentum throughout a movement task. For typical movement tasks, such as normal walking, such controllers minimize fluctuations in angular momentum about the center of mass (CM). This minimization is consistent with observed behavior of humans for such tasks. However, there are cases where such...
In this paper, we study the mechanical behavior of leg muscles and tendons during human walking in order to motivate the design of economical robotic legs. We hypothesize that quasi-passive, series-elastic clutch units spanning the knee joint in a musculoskeletal arrangement can capture the dominant mechanical behaviors of the human knee in level-ground walking. Since the mechanical work done by the...
Human locomotion involves a number of different complex activities. Humanoid robots, if they are expected to work in a human environment, should be expected to navigate obstacles and transients as well as, or better than a human being. Turning is one aspect of human walking that is poorly understood from the perspective of biomechanics and robotics. It is an important task comprising a large percentage...
The majority of commercial prosthetic knees are passive in nature and therefore cannot replicate the positive mechanical work exhibited by the natural human knee in early and late stance. In contrast to traditional purely dissipative prosthetic knees, we propose a biomimetic active agonist-antagonist structure designed to reproduce both positive and negative work phases of the natural joint while...
In this paper we describe the design and preliminary evaluation of an energetically-autonomous powered knee exoskeleton to facilitate running. The device consists of a knee brace in which a motorized mechanism actively places and removes a spring in parallel with the knee joint. This mechanism is controlled such that the spring is in parallel with the knee joint from approximately heel-strike to toe-off,...
This paper presents the mechanical design, control scheme, and clinical evaluation of a novel, motorized ankle-foot prosthesis, called MIT Powered Ankle-Foot Prosthesis. Unlike a conventional passive-elastic ankle-foot prosthesis, this prosthesis can provide active mechanical power during the stance period of walking. The basic architecture of the prosthesis is a unidirectional spring, configured...
The ground reaction force (GRF) and the zero moment point (ZMP) are important parameters for the advancement of biomimetic control of robotic lower-limb prosthetic devices. In this document a method to estimate GRF and ZMP on a motorized ankle-foot prosthesis (MIT Powered Ankle-Foot Prosthesis) is presented. The method proposed is based on the analysis of data collected from a sensory system embedded...
Although the potential benefits of a powered ankle-foot prosthesis have been well documented, no one has successfully developed and verified that such a prosthesis can improve amputee gait compared to a conventional passive-elastic prosthesis. One of the main hurdles that hinder such a development is the challenge of building an ankle-foot prosthesis that matches the size and weight of the intact...
In this paper, we seek to understand how leg muscles and tendons work mechanically during walking in order to motivate the design of efficient robotic legs. We hypothesize that a robotic leg comprising only knee and ankle passive and quasi-passive elements, including springs, clutches and variable-damping components, can capture the dominant mechanical behavior of the human knee and ankle during level-ground...
The capability of muscle to produce mechanical work under periodic motions has been traditionally estimated using the workloop technique. We extend this method by allowing a pair of antagonist muscles to interact against a common load with non-zero admittance. We present an experimental approach to measuring the work done by a two-muscle system and show preliminary data. A complimentary problem is...
In this investigation we put forth a simple model to quantify the capacity of series elasticity to increase peak power output from an actuator. Using a linear bandwidth limited force source, we show how series spring stiffness and source stroke length effect power output to an inertial load. We show that an appropriate spring constant increases the peak power delivered to the inertial load over a...
Although below-knee prostheses have been commercially available for some time, today's devices are completely passive, and consequently, their mechanical properties remain fixed with walking speed and terrain. A lack of understanding of the ankle-foot biomechanics and the dynamic interaction between an amputee and a prosthesis is one of the main obstacles in the development of a biomimetic ankle-foot...
Metabolic studies have shown that there is a metabolic cost associated with carrying load. Several leg exoskeletons have been developed by various groups in an attempt to augment the load carrying capability of the human. Previous research efforts have not fully exploited the passive dynamics of walking and have largely focused on fully actuated exoskeletons that are heavy with large energy requirements...
We present a model structure and a method for identifying the dynamics of electrically stimulated muscle. The model structure is sufficiently rich to describe a wide set of muscle behavior. It consists of (i) an input static nonlinearity representing the muscle's recruitment properties, (ii) a linear dynamical system representing the contraction dynamics, (iii) an output static nonlinearity representing...
The aim of this study was to examine the ankle joint during level walking, stair ascent, and stair descent to determine models for use in the design of prosthetic and orthotic systems. Ten healthy subjects were asked to walk (1) across a level walkway, (2) up, and (3) down an instrumented stairway. Sagittal plane kinematic and kinetic data were analyzed to obtain ankle biomechanics during the stance...
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