134,230 research outputs found
New results in feedback control of unsupported standing in paraplegia
No full textThe aim of this study was to implement a new approach to feedback control of unsupported standing and to evaluate it in tests with an intact and a paraplegic subject. In our setup, all joints above the ankles are braced and stabilizing torque at the ankle is generated by electrical stimulation of the plantarflexor muscles. A previous study showed that short periods of unsupported standing with a paraplegic subject could be achieved. In order to improve consistency and reliability and to prolong the duration of standing, we have implemented several modifications to the control strategy. These include a simplified control structure and a different controller design method. While the reliability of standing is mainly limited by the muscle characteristics such as reduced strength and progressive fatigue, the results presented here show that the new strategy allows much longer periods (up to several minutes) of unsupported standing in paraplegia
Feedback control of unsupported standing
No full textThis paper presents the results of continuing work on feedback control of unsupported standing in paraplegia. Our experimental setup considers a situation in which all joints above the ankle are braced, and stabilising torque at the ankle is generated by stimulation of the plantarflexors. A previous study showed that short periods of unsupported standing with paraplegic subjects could be achieved. In order to improve consistency and reliability of unsupported standing we are currently investigating several modifications to the control strategy. The paper reports progress towards this goal
Design of feedback controllers for paraplegic standing
No full textThe development, implementation and experimental evaluation of feedback systems for the control of the upright posture of paraplegic persons in standing is described. While the subject stands in a special apparatus, stabilising torque at the ankle joint is generated by electrical stimulation of the paralysed calf muscles of both legs using surface electrodes. This allows the subject to stand without the need to hold on to external supports for stability- this is termed 'unsupported standing'. Sensors in the apparatus allow independent measurement of left and right ankle moments together with measurement of the inclination angle. A nested loop structure for control of standing is implemented, where a high-bandwidth inner loop provides control of the ankle moments, while the angle controller in the outer loop regulates the inclination angle. A number of important modifications to a control strategy which was previously tested with both neurologically intact and paraplegic subjects are presented. The new strategy is described, and an experimental evaluation with intact subjects is reported. The experimental results show that the control system for unsupported standing performs reliably, and according to the design formulation. There aa-e a number of design choices, appropriate to different situations, and the practical effect of each is clear. This allows easy 'tuning' during an experimental session. This is important since the complete design procedure, from muscle dynamics identification to control design, has to be carried out as quickly as possible while the subject is standing in the apparatus. A number of recommendations are made regarding the preferred design choices for control of unsupported standing
Control of body position of a stick insect standing on uneven surfaces
No full textCruse H, Riemenschneider D, Stammer W. Control of body position of a stick insect standing on uneven surfaces. Biological Cybernetics. 1989;61(1):71-77
Rehabilitation robot cell for multimodal standing-up motion augmentation
No full textThe paper presents a robot cell for multimodal standing-up motion augmentation. The robot cell is aimed at augmenting the standing-up capabilities of impaired or paraplegic subjects. The setup incorporates the rehabilitation robot device, functional electrical stimulation system, measurement instrumentation and cognitive feedback system. For controlling the standing-up process a novel approach was developed integrating the voluntary activity of a person in the control scheme of the rehabilitation robot. The simulation results demonstrate the possibility of “patient-driven” robot-assisted standing-up training. Moreover, to extend the system capabilities, the audio cognitive feedback is aimed to guide the subject throughout rising. For the feedback generation a granular synthesis method is utilized displaying high-dimensional, dynamic data. The principle of operation and example sonification in standing-up are presented. In this manner, by integrating the cognitive feedback and “patient-driven” actuation systems, an effective motion augmentation system is proposed in which the motion coordination is under the voluntary control of the user
Nonlinear modeling of FES-supported standing-up in paraplegia for selection of feedback sensors
No full textThis paper presents analysis of the standing-up manoeuvre in paraplegia considering the body supportive forces as a potential feedback source in functional electrical stimulation (FES)-assisted standing-up. The analysis investigates the significance of arm, feet, and seat reaction signals to the human body center-of-mass (COM) trajectory reconstruction. The standing-up behavior of eight paraplegic subjects was analyzed, measuring the motion kinematics and reaction forces to provide the data for modeling. Two nonlinear empirical modeling methods are implemented-Gaussian process (GP) priors and multilayer perceptron artificial neural networks (ANN)-and their performance in vertical and horizontal COM component reconstruction is compared. As the input, ten sensory configurations that incorporated different number of sensors were evaluated trading off the modeling performance for variables chosen and ease-of-use in everyday application. For the purpose of evaluation, the root-mean-square difference was calculated between the model output and the kinematics-based COM trajectory. Results show that the force feedback in COM assessment in FES assisted standing-up is comparable alternative to the kinematics measurement systems. It was demonstrated that the GP provided better modeling performance, at higher computational cost. Moreover, on the basis of averaged results, the use of a sensory system incorporating a six-dimensional handle force sensor and an instrumented foot insole is recommended. The configuration is practical for realization and with the GP model achieves an average accuracy of COM estimation 16 /spl plusmn/ 1.8 mm in horizontal and 39 /spl plusmn/ 3.7 mm in vertical direction. Some other configurations analyzed in the study exhibit better modeling accuracy, but are less practical for everyday usage
Free-Standing Two-Dimensional Single-Crystalline InSb Nanosheets
No full textGrowth
of high-quality single-crystalline InSb layers remains challenging
in material science. Such layered InSb materials are highly desired
for searching for and manipulation of Majorana Fermions in solid state,
a fundamental research task in physics today, and for development
of novel high-speed nanoelectronic and infrared optoelectronic devices.
Here, we report on a new route toward growth of single-crystalline,
layered InSb materials. We demonstrate the successful growth of free-standing,
two-dimensional InSb nanosheets on one-dimensional InAs nanowires
by molecular-beam epitaxy. The grown InSb nanosheets are pure zinc-blende
single crystals. The length and width of the InSb nanosheets are up
to several micrometers and the thickness is down to ∼10 nm.
The InSb nanosheets show a clear ambipolar behavior and a high electron
mobility. Our work will open up new technology routes toward the development
of InSb-based devices for applications in nanoelectronics, optoelectronics,
and quantum electronics and for the study of fundamental physical
phenomena
A decision theory approach to standing order procurement of NASA reports
No full textExplains various package deal procurement methods including standing order method for library documents. Enumerates different standing order services of NTIS for technical reports. Describes the NASA information system. Discusses and analyses the economy of NASA FS service by applying decision theory approach and considering the various costs as well as saving aspects/advantages. Explains the non-economic factors to be considered in evaluating such a service. Suggests ways of making NASA FS service more beneficial to the library of ISRO Satellite Centre (ISAC)
Predicting the vibration discomfort of standing passengers in transport
No full textIt has previously been assumed that the vibration discomfort of standing people can beestimated using the same procedures developed from for seated people. In this thesis, thediscomfort of standing people exposed to vibration was investigated to improve understandingof the mechanisms responsible for discomfort and construct a model that may be usedto predict the discomfort of standing railway passengers.The first of five experiments using the method of magnitude estimation and 6-s periodsof vibration investigated how the discomfort of standing subjects exposed to fore-and-aft,lateral, and vertical sinusoidal vibration depends on the frequency of vibration. From thejudgements of 12 subjects at each of the 16 preferred one-third octave centre frequenciesfrom 0.5 to 16 Hz, frequency weightings were constructed for each direction. For verticalvibration, the weighting was similar to that recommended in standards, but the weightingsfor fore-and-aft and lateral vibration differed from that previously assumed. Horizontalvibration caused loss of balance at frequencies less than about 3 Hz, and it caused discomfortin the legs at higher frequencies. Vertical vibration caused discomfort in the upper body. Toadjust the frequency weightings according to differences in sensitivity between directions,the second experiment with 12 subjects compared the discomfort caused by 4-Hz sinusoidalvibration in the fore-and-aft, lateral, the vertical directions. It was found that sensitivitywas greater for fore-and-aft vibration than lateral vibration at frequencies less than 4 Hzand weightings were determined to assist the evaluation vibration in all three directions.The third experiment investigated the extent to which postural supports used by standingtrain passengers (vertical bar, shoulder support, and back support) affect discomfort causedby fore-and-aft and lateral vibration in the range 0.5 to 16 Hz. Supports that created anew path for the transmission of vibration to the upper-body increased discomfort over therange 4 to 16 Hz.The fourth experiment investigated how the root-mean-square method, the basic evaluationmethod in current standards but known to underestimate the discomfort caused bymotions containing occasional peaks, could be modified for the evaluation of non-sinusoidalvibration. Using 1-Hz and 8-Hz random vibrations with a range of crest factors it was foundthat the discomfort of standing subjects was better predicted with an exponent around 3,rather than an exponent of 2 implicit in r.m.s. averaging. The final experiment determineda method for predicting the discomfort of tri-axial vibration. The cube root of the sumof the cubes of the discomfort caused by the single-axis components gave good estimatesof the total discomfort for both 1-Hz and 4-Hz tri-axial vibration. Since it was found inthe first experiment that the discomfort was generally proportional to the acceleration atthe power 0.7. these results suggest that the root-sum-of-squares of the accelerations givesgood estimates of the total discomfort for tri-axial vibration .The results of all experiments were combined in an empirical model for predicting thediscomfort of standing people exposed to 6-s periods of vibration. It is concluded that thereare two distinctly different mechanisms responsible for vibration discomfort when standing:postural instability and body vibration. Postural instability is dominant with horizontalvibration at frequencies less than about 3 Hz, whereas body vibration is dominant withvertical vibration and with horizontal vibration at frequencies greater than about 3 Hz.The discomfort of standing people is similar to the discomfort of seated people for verticalvibration, but fundamentally different with horizontal vibration due to postural instabilityat low frequencies and vibration attenuation in the legs at higher frequencie
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