scholarly journals Energetic Consequences of Series and Parallel Springs in Lower-Extremity Powered Prostheses

2019 ◽  
Author(s):  
Matt Carney ◽  
Hugh Herr
Keyword(s):  
Lower Extremity ◽  
Mechanical Design ◽  
Minimum Energy ◽  
Optimization Procedure ◽  
Spring Stiffness ◽  
Cost Of Transport ◽  
Stair Ascent ◽  
Trade Offs ◽  
Negative Effect ◽  
System Equations

We present electric energetic consequences for mechanical design trade-offs in lower-extremity powered prostheses. There are four main hardware components commonly implemented in these devices that can be tuned to achieve desired performance: motor, reduction ratio N, series spring stiffness Ks, and parallel spring stiffness Kp. The allowed joint range of motion is a fifth parameter that can also drastically change energy consumption. We apply a kinematically clamped analysis to the system equations to map the electric cost of transport (COT) for knee and ankle level-ground walking, in addition to ankle stair ascent and descent. We also utilize an optimization procedure to identify minimum energy hardware configurations. The energy map provides insight into consequences of variance from optimal parameters. Our results support the contribution of the series elastic element for improved power output. Parallel stiffness can provide up to 8% improvements in walking with minimal negative effect with varied terrain, and a varying ankle transmission ratio can similarly improve COT by 8% from level-ground to stair ascent. Limited dorsiflexion can further improve COT by 30%. These observations can provide the designer clarity to how design decisions modulate hardware performance.

Load Distribution of Parallel Springs With Random Length and Stiffness

1987 ◽  
Vol 109 (4) ◽  
pp. 402-406 ◽  
Author(s):  
Go¨ran Gerbert ◽  
Jacques de Mare´
Keyword(s):  
Uniform Distribution ◽  
Load Distribution ◽  
Simple Formula ◽  
Mechanical Design ◽  
Numerical Results ◽  
Maximal Length ◽  
Major Influence ◽  
Length Variation ◽  
Spring Stiffness ◽  
Failure Risk

There are many applications in mechanical design where load distribution is modelled with parallel springs. Here random variation in spring length and spring stiffness is considered. Length variation is assumed to be the major influence and the case with uniform distribution is analyzed in detail. Small variations in spring stiffness are included. Numerical results are given. A simple formula is presented which gives the maximal length deviation as a function of the number of springs. The formula is based on a 10 percent failure risk which is a common number in practical mechanical design.

scholarly journals Stability of Optimal Closed-Loop Cleaning Scheduling and Control with Application to Heat Exchanger Networks under Fouling

Processes ◽  
2020 ◽  
Vol 8 (12) ◽  
pp. 1623
Author(s):  
Federico Lozano Santamaria ◽  
Sandro Macchietto
Keyword(s):  
Heat Exchanger ◽  
Closed Loop ◽  
Operating Cost ◽  
Optimization Procedure ◽  
Loop Model ◽  
Loop Scheduling ◽  
Loop Optimization ◽  
Trade Offs ◽  
Heat Exchanger Networks ◽  
And Control

Heat exchanger networks subject to fouling are an important example of dynamic systems where performance deteriorates over time. To mitigate fouling and recover performance, cleanings of the exchangers are scheduled and control actions applied. Because of inaccuracy in the models, as well as uncertainty and variability in the operations, both schedule and controls often have to be revised to improve operations or just to ensure feasibility. A closed-loop nonlinear model predictive control (NMPC) approach had been previously developed to simultaneously optimize the cleaning schedule and the flow distribution for refinery preheat trains under fouling, considering their variability. However, the closed-loop scheduling stability of the scheme has not been analyzed. For practical closed-loop (online) scheduling applications, a balance is usually desired between reactivity (ensuring a rapid response to changes in conditions) and stability (avoiding too many large or frequent schedule changes). In this paper, metrics to quantify closed-loop scheduling stability (e.g., changes in task allocation or starting time) are developed and then included in the online optimization procedure. Three alternative formulations to directly include stability considerations in the closed-loop optimization are proposed and applied to two case studies, an illustrative one and an industrial one based on a refinery preheat train. Results demonstrate the applicability of the stability metrics developed and the ability of the closed-loop optimization to exploit trade-offs between stability and performance. For the heat exchanger networks under fouling considered, it is shown that the approach proposed can improve closed-loop schedule stability without significantly compromising the operating cost. The approach presented offers the blueprint for a more general application to closed-loop, model-based optimization of scheduling and control in other processes.

The Berkeley Lower Extremity Exoskeleton

2005 ◽  
Vol 128 (1) ◽  
pp. 14-25 ◽  
Author(s):  
H. Kazerooni ◽  
R. Steger
Keyword(s):  
Lower Extremity ◽  
Control Algorithm ◽  
Local Area Network ◽  
Control Method ◽  
Local Area ◽  
Area Network ◽  
System Sensitivity ◽  
Trade Offs ◽  
Control Schemes ◽  
Definition Of

The first functional load-carrying and energetically autonomous exoskeleton was demonstrated at the University of California, Berkeley, walking at the average speed of 1.3m∕s(2.9mph) while carrying a 34kg(75lb) payload. Four fundamental technologies associated with the Berkeley lower extremity exoskeleton were tackled during the course of this project. These four core technologies include the design of the exoskeleton architecture, control schemes, a body local area network to host the control algorithm, and a series of on-board power units to power the actuators, sensors, and the computers. This paper gives an overview of one of the control schemes. The analysis here is an extension of the classical definition of the sensitivity function of a system: the ability of a system to reject disturbances or the measure of system robustness. The control algorithm developed here increases the closed-loop system sensitivity to its wearer’s forces and torques without any measurement from the wearer (such as force, position, or electromyogram signal). The control method has little robustness to parameter variations and therefore requires a relatively good dynamic model of the system. The trade-offs between having sensors to measure human variables and the lack of robustness to parameter variation are described.

Prediction of the Lower Extremity Muscle Forces During Stair Ascent and Descent

2008 ◽  
Author(s):  
Ali Selk Ghafari ◽  
Ali Meghdari ◽  
Gholam Reza Vossoughi
Keyword(s):  
Lower Extremity ◽  
Inverse Dynamics ◽  
Sagittal Plane ◽  
Optimization Technique ◽  
The Elderly ◽  
Plantar Flexors ◽  
Stair Ascent ◽  
Lower Extremity Muscle ◽  
Anatomical Classification ◽  
Muscle Groups

An inverse dynamics musculoskeletal model of the lower extremity was combined with an optimization technique to estimate individual muscular forces and powers during stair ascent and descent. Eighteen Hill-type musculotendon actuators per leg were combined into the eleven functional muscle groups based on anatomical classification to drive the model in the sagittal plane. Simulation results illustrate the major functional differences in plantar flexors of the ankle and extensors of the knee and hip joints during ascent and descent. The results of this study not only could be employed to evaluate the rehabilitation results in the elderly but also could be used to design more anthropometric assistive devices with optimum power consumption.

scholarly journals The Effects of Land-Use Change/Conversion on Trade-Offs of Ecosystem Services in Three Precipitation Zones

2021 ◽  
Vol 13 (23) ◽  
pp. 13306
Author(s):  
Qiang Feng ◽  
Siyan Dong ◽  
Baoling Duan
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Piecewise Linear ◽  
Land Use Changes ◽  
Spatial Differentiation ◽  
Mean Annual Precipitation ◽  
Water Yield ◽  
Trade Off ◽  
Trade Offs ◽  
Negative Effect

Revealing the spatial differentiation of ecosystem service (ES) trade-offs and their responses to land-use change along precipitation gradients are important issues in the Loess Plateau of China. We selected three watersheds called Dianshi (300 mm < MAP (mean annual precipitation) < 400 mm), Ansai (400 mm < MAP < 500 mm), and Linzhen (500 mm < MAP < 600 mm). A new ES trade-off quantification index was proposed, and quantile regression, piecewise linear regression, and redundancy analysis were used. The results were as follows. (1) Carbon sequestration (TC) and soil conservation (SEC) increased, but water yield (WY) decreased in the three watersheds from 2000 to 2018. (2) The effect of forests on trade-offs was positive in three watersheds, the main effect of shrubs was also positive, but the negative effect appeared in the TC-WY trade-off in Ansai. Grassland exacerbated trade-offs in Dianshi, whereas it reduced trade-offs in Ansai and Linzhen. These effects exhibited respective trends with the quantile in the three watersheds. (3) There were threshold values that trade-offs responded to land-use changes, and we could design land-use conversion types to balance ESs. In general, the water consumption of grass cannot be ignored in Dianshi; shrubs and grass are suitable vegetation types, and forests need to be restricted in Ansai; more forests and shrubs can be supported in Linzen due to higher precipitation, but the current proportions of forests and shrubs are too high. Our research contributes to a better understanding of the response mechanisms of ES trade-offs to land-use changes.

scholarly journals Digital Control for V/Stol Powerplants

1980 ◽  
Author(s):  
E. S. Eccles
Keyword(s):  
Control System ◽  
Digital Control ◽  
Mechanical Design ◽  
Digital Control System ◽  
Control Approach ◽  
Trade Offs ◽  
Control Configuration ◽  
Vtol Aircraft

The author describes the evolution of his company’s digital control approach to the Pegasus engine as applied to a single engined VTOL aircraft. The paper describes the digital control system being built by Dowty and Smiths Industries Controls Limited (DSIC). The design is based on extensive engine evaluation of different control configuration with electronic and hydromechanical back-up system. The paper describes the mechanical design, installation on the engine and the cooling of the system including the choice of basic packaging concept. It also discusses the rationale for the particular choice of back-up system and the reliability/safety of flight trade-offs involved.

scholarly journals Robotic Parking Technology for Congestion Mitigation and Air Quality Control Around Park & Rides

2021 ◽  
Author(s):  
Mahdi Yoozbashizadeh ◽  
Forouzan Golshani
Keyword(s):  
Intelligent Control ◽  
Mechanical Design ◽  
Robotic Platform ◽  
Transit Systems ◽  
The Public ◽  
Overall Design ◽  
Suburban Areas ◽  
Parking Management ◽  
Current Design ◽  
Negative Effect

A lack or limited availability for parking may have multiple consequences, not the least of which is driver frustration, congestion, and air pollution. However, there is a greater problem that is not widely recognized by the public, namely the negative effect on the use of transit systems due to insufficient parking spaces close to key transit stations. Automated parking management systems, which have been successfully deployed in several European and Japanese cities, can manage parking needs at transit stations more effectively than other alternatives. Numerous studies have confirmed that quick and convenient automobile access to park-and-ride lots can be essential to making public transit competitive with the automobile in suburban areas. Automated parking systems use a robotic platform that carries each vehicle to one of the locations in a custom designed structure. Each location is designed compactly so that considerably more vehicles can be parked in the automated garages than the traditional parking lots. Central to the design of these systems are three key technologies, namely: 1. Mechanical design and the operation of vehicle transfer, i.e., the robotic platform 2. Structural and architectural requirements to meet safety and earthquake standards, among other design imperatives, 3. Automation and intelligent control issues as related to the overall operation and system engineering. This article concerns the first technology, and more specifically the design of the robotic platform for vehicle transfers. We will outline the overall design of the robot and the shuttle, followed by a description of the prototype that was developed in our laboratories. Subsequently, performance related issues and scalability of the current design will be analyzed.

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