Touch-down and take-off characteristics of the long jump performance of world level above- and below-knee amputee athletes

The aims of this study were to establish the take-off characteristics of long jump performance of disabled amputee athletes, and to establish to what extent amputee athletes conform to a model of performance defined for elite able-bodied athletes. The jumps of 8 male below-knee (trans-tibial) and 8 male above-knee (trans-femoral) amputee athletes who competed in the finals of the long jump at the 1998 World Disabled Championships were recorded in the sagittal plane on video (50 Hz). Approach speed was measured using a laser Doppler system. The best jump for each athlete was digitized, and kinematic data from the key instants of touch-down (TD), maximum knee flexion (MKF) and take-off (TO) were obtained. Amputees demonstrated a lower approach speed and jumped less far than able-bodied athletes although below-knee amputees performed better than above-knee amputees. For each amputee group there was a significant (p < 0.05) linear relationship between approach speed and distance jumped. With the exception of their slower horizontal speed and greater negative vertical speed at touch-down, below-knee amputees demonstrated characteristics of technique that were similar to elite able-bodied long jumpers. Above-knee amputees at touchdown had a more upright trunk, smaller hip and knee angles and consequently a smaller leg angle. This was attributed to the difficulty of taking off on the last stride on the prosthetic limb. Consequently, above-knee amputees were less able to gain vertical velocity during the compression (TD-MKF) phase, but were able to compensate for this by using a greater hip range of motion during the extension (MKF-TO) phase. It was concluded that below-knee amputees displayed the same basic jumping technique as elite able-bodied long jumpers, but above-knee amputees did not. These findings have implications for the training and technical preparation of amputee long jumpers.     

Touch-down and take-off characteristics of the long jump performance of world level above- and below-knee amputee athletes

The aims of this study were to establish the take-off characteristics of long jump performance of disabled amputee athletes, and to establish to what extent amputee athletes conform to a model of performance defined for elite able-bodied athletes. The jumps of 8 male below-knee (trans-tibial) and 8 male above-knee (trans-femoral) amputee athletes who competed in the finals of the long jump at the 1998 World Disabled Championships were recorded in the sagittal plane on video (50 Hz). Approach speed was measured using a laser Doppler system. The best jump for each athlete was digitized, and kinematic data from the key instants of touch-down (TD), maximum knee flexion (MKF) and take-off (TO) were obtained. Amputees demonstrated a lower approach speed and jumped less far than able-bodied athletes although below-knee amputees performed better than above-knee amputees. For each amputee group there was a significant (p < 0.05) linear relationship between approach speed and distance jumped. With the exception of their slower horizontal speed and greater negative vertical speed at touch-down, below-knee amputees demonstrated characteristics of technique that were similar to elite able-bodied long jumpers. Above-knee amputees at touchdown had a more upright trunk, smaller hip and knee angles and consequently a smaller leg angle. This was attributed to the difficulty of taking off on the last stride on the prosthetic limb. Consequently, above-knee amputees were less able to gain vertical velocity during the compression (TD-MKF) phase, but were able to compensate for this by using a greater hip range of motion during the extension (MKF-TO) phase. It was concluded that below-knee amputees displayed the same basic jumping technique as elite able-bodied long jumpers, but above-knee amputees did not. These findings have implications for the training and technical preparation of amputee long jumpers.     

Energetic versus sthenic optimality criteria for gymnastic movement synthesis

Dynamic synthesis of human movements raises the question of the selection of a suitable performance criterion able to generate proper dynamic behaviors. Two quite different criteria are likely to be appropriate candidates: the minimum effort cost (or sthenic criterion) and the minimum energy cost. The paper is aimed at clarifying the dynamic effects of these two fundamental criteria when considering movements executed with liveliness as they are in gymnastic. It is well known that the former cost generates movements with smooth dynamics. A special attention is devoted to the latter. The optimal control theory shows that minimizing the energy consumption results in actuating inputs of bang-off-bang type producing momentum impulses. When achieving dynamic synthesis, this criterion makes necessary to account for bounds set on driving torques. Moreover, when dealing with one-sided contacts, as in floor handstands, the unilaterality of contact forces must be explicitly accounted for since it tends to be infringed by impulsive efforts.Numerical simulations of these formal properties are carried out using a parametric optimization technique, and considering the raising phase of floor handstands. It is shown that the energetic criterion tends to generate movements which exhibit similarities with their real counterpart performed by an expert gymnast. Conversely, the sthenic criterion produces movements quite different. But, a salient fact is that these ones proved to be easier to perform by young beginners. As a result, they could help to coach novice gymnasts.     

A comparison of hand and foot movement times

Three experiments are reported in which a comparison is made between the times for movement of the hand and the foot. Both ballistic and visually-controlled movements were studied. It was found that execution time for foot movements is generally about twice as long as that for the equivalent arm movement. The times for foot movements were described well by the Welford, Norris and Shock modification of Fitts' Law for visually-controlled movements and, for ballistic movements, by the square-root-of-amplitude equation found by Hoffmann for arm movements.     

Investigations of the influence of the laser texture design in the hard disk landing zone on the dynamic characteristics of Pico slider during contact take-off

 A good laser texture design in hard disk landing zone can significantly reduce the slider-disk contact force, contact time and contact frequency during a slider's contact start and stop process. In this paper a numerical investigation was conducted on the effects of laser texture properties, disk topography and slider design on the dynamic characteristics of a Pico slider during its take-off in the landing zone. Factors considered in this study are bump  height, bump diameter, bump density, slider crown, spin acceleration, and waviness. The slider contact take-off process was simulated with various values of those factors, and the results were analyzed through comparing the contact frequency, contact force, contact time, and take-off speed. The simulation results show that a regular take-off is not a continuous contact process, but composed of periodical contact bursts, and the time duration of each group of contact bursts is about the same. It has been found that some of the laser texture properties can significantly influence the slider's take-off characteristics. Properly choosing laser texture design parameters can reduce the impacts between slider and bumps during the take-off process. Received: 25 September 2001/Accepted: 7 May 2002     

Dynamic obstacle avoidance for real-time character animation

This paper proposes a novel method to control virtual characters in dynamic environments. A virtual character is animated by a locomotion and jumping engine, enabling production of continuous parameterized motions. At any time during runtime, flat obstacles (e.g. a puddle of water) can be created and placed in front of a character. The method first decides whether the character is able to get around or jump over the obstacle. Then the motion parameters are accordingly modified. The transition from locomotion to jump is performed with an improved motion blending technique. While traditional blending approaches let the user choose the transition time and duration manually, our approach automatically controls transitions between motion patterns whose parameters are not known in advance. In addition, according to the animation context, blending operations are executed during a precise period of time to preserve specific physical properties. This ensures coherent movements over the parameter space of the original input motions. The initial locomotion type and speed are smoothly varied with respect to the required jump type and length. This variation is carefully computed in order to place the take-off foot as close to the created obstacle as possible. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Simulation of rowing in an optimization context

Competitive rowing requires efforts close to the physiological limits, where oxygen consumption is one main aspect. The rowing event also incorporates interactions between the rower, the boat and oars, and water. When the intention is to improve the performance, all these properties make the sport interesting from a scientific point of view, as the many variables influencing the performance form a complex optimization problem. Our aim was to formulate the rowing event as an optimization problem where the movement and forces are completely determined by the optimization, giving at least qualitative indications on good performance. A mechanical model of rigid links was used to represent rower, boat and oars. A multiple phase cyclic movement was simulated where catch slip, driving phase, release slip and recovery were modeled. For this simplified model, we demonstrate the influence of the stated mathematical cost function as well as a parameter study where the optimal performance is related to the planned average boat velocity. The results show qualitatively good resemblance to expected movements for the rowing event. An energy loss model in combination with case specific properties of rower capacities, boat properties, and rigging was required to draw qualitative practical conclusions about the rowing technique.     

Eye movement as a mediator of the relationships among time pressure,feedback, and learning performance

The goal of this study is to examine the effects of time pressure and feedback on learning performance, as mediated by eye movement. Time pressure is one of main causes of human error in the workplace. Providing participants with feedback about their performance before task completion has been shown to reduce human error in diverse domains. Since both time pressure and feedback induce motivation, which is closely related to attention, we measured participants' eye movements to trace their attention and information acquisition coupled with a visual display. Time-to-deadline (long and short) and the presence of feedback were the independent factors used while measuring participants’ performance and eye movements as they learned new information about the subject of project management and answered multiple-choice questions via self-paced online learning systems. Using structural equation modeling, we found a mediating effect of eye movement on the relationships among time-to-deadline, feedback, and learning performance. Insufficient time-to-deadline accelerated the number of fixations on the screen, which resulted in longer task completion times and increased correct rates for participants learning about project management. The models in this study suggest the possibility of predicting performance from eye movement under time-to-deadline and feedback conditions. The structural equation model in the study can be applied to online and remote learning systems, in which time management is one of the main challenges for individual learners.     

Dynamic Modeling and Analysis of the Human Jumping Process

Humanoid robots have recently been the subject of many new and interesting fields both in robotics research and industry. The wide variety of their applications in civic and hostile environments demand developing approperiate theoretical models for analysis. A dynamical model was developed to study the human jumping process, and the effect of factors like joint speeds and hand motion in jumping. An experiment was designed and setup to compare the theoretical model with experimental observations. Time histories of vertical force, mass center velocity and driving torques were also obtained. Using dynamical equations, the effect of joint speeds on the maximum values of these quantities is discussed. It was shown that reducing the joint speeds of a body could lead to an unsuccessful jump in which the body would not enter the flight phase. An increase in speed reduced the take-off time (the time necessary for the body to leave the ground) and increased the body's linear velocity at take-off, as well as the maximum value of driving torques. Effect of hand motion was also investigated through suppressing motion of the shoulder and elbow. It was observed that hand motion had an improving effect on the body's linear velocity. Although speed of joints did not show to have a great influence on most joint torques, those at the shoulder and elbow were observed to be more sensitive to it.     

On the dynamic version of the minimum hand jerk criterion

This paper is concerned with the problem of trajectory formation of humanlike reaching movements. First, we review conventional criteria of optimality adopted in robotics and computational neuroscience for the prediction of reaching movements and formulate a dynamic version of the minimum hand jerk criteria. We call it a minimum driving force change criterion and check its performance for the free‐space movements. Next, we test the performance of the new criterion for the movements where the human hand is geometrically constrained by the external environment, and for the movements with flexible objects. The main feature of these movements is that the hand velocity profiles are not always bell shaped. Our simulations and initial experimental results show that the minimum driving force change criterion can roughly capture this feature and, therefore, can be a reasonable candidate for modeling of humanlike reaching movements. © 2005 Wiley Periodicals, Inc.     

A correlation between the Fukuma-Matsubara and circle criteria for the determination of jump resonance

Jump resonance is a particular type of discontinuity, the absence of which may be predicted by using one form of the circle criterion. Another method of determining presence or absence of jump resonance is due to Fukuma and Matsubara [1]. These two methods are compared after rederiving the Fukuma-Matsubara criterion using different bounds on the nonlinearity. The Fukuma-Matsubara criterion is found to yield a critical region inside the critical circle. Furthermore, an example is given in which the Fukuma-Matsubara criterion predicts the gain needed to produce jump resonance.     

Ballistic movements on data-entry keypads

Research to date on movement times on data-entry keypads has assumed that the movements are made under visual control [Drury, C.G., Hoffmann, E.R., 1992. A model for movement times on data-entry keyboards. Ergonomics 35, 129-147; Hoffmann, E.R., Tsang, K.T., Mu, A., 1995. Data-entry keyboard geometry and keying movement times. Ergonomics 38 (5), 940-950; Silfverberg, M., MacKenzie, I.S., Korhonen, P., 2000. Predicting text entry speed on mobile phones. In: Proceedings of the ACM Conference on Human Factors in Computing Systems - CHI 2000. ACM, New York, pp. 9-16]. This is often not the case; where the value of Fitts’ Index of Difficulty is low, it is likely that movements will be made ballistically. A survey of commonly used keypads on devices such as mobile phones and ATMs shows that there is a need to study movement times when these ID values are less than those for which movements are likely to be made under visual control [Gan, K.-C., Hoffmann, E.R., 1988a. Geometrical conditions for ballistic and visually-controlled movements. Ergonomics 31, 829-839]. A series of experiments on simulated and real keypads indicates that the ballistic form of movement is generally valid and may be modelled by a modification of the ballistic movement time model of Hoffmann [1981. An ergonomics approach to predetermined motion time systems. In: Australian Institute of Industrial Engineers, Proceedings, Ninth National Conference, pp. 33-47] and of Gan and Hoffmann [1988a. Geometrical conditions for ballistic and visually-controlled movements. Ergonomics 31, 829-839l; 1988b. Sequential ballistic movement. Ergonomics 31 (10), 1421-1436]. A model is developed for the time to complete sequences of number entries containing up to 5 numbers. In this model, the movement times are related to the square-root of the sum of the movement amplitudes.

Relevance to industry

Many industrial applications require the use of keypads for data entry. Movements may be made ballistically or visually controlled, depending on the geometry of the keypad. As the time for data entry is dependent on geometry, a model for time taken is necessary for predicting human performance.     

Assistant force compensation for hand movement of patients by using exogenous signals and/or neurophysiological signals

Because functional diseases of the brain can cause disabilities related to human movement control, a compensation method was developed for improving the performance of hand movements. The compensation for human hand movements can be carried out by adding an assistant force that is generated from artificial equipment attached to a human arm. From the experiment on visual target tracking, it was found that the tracking trajectory was adequately represented by a dynamic model of the motion of an articulated industrial robot arm, and the different abilities for movement control among healthy people and patients were classified by different model parameters as position loop gain, velocity loop gain, and response delay. Dynamic force compensation was approached by considering the different control features of the patients. The effectiveness of the proposed compensation method was verified in a simulation study on an actual industrial robot arm. A human-machine interface, e.g., a brain-computer interface (BCI), for realizing the control of artificial equipment to compensate for human hand movements is also presented and discussed.     

基于高精度相频同步的节点端无损切换技术研究

随着网络化高精度固定节点时频同步技术的发展,需要对簇节点端多输入信号进行处理。针对簇节点端多输入信号同源多路径的特性,为了提升系统的稳健性,提出了一种信号无损切换的方法,兼顾了开关的隔离度和切换速度;实现了主备路信号ps量级的同步精度,有效抑制了切换过程中的相位跳变,并对不同条件下的主备路相位同步精度、系统无损切换性能进行了仿真实验。仿真结果表明,提出的方案显著提升了主备路相位同步精度,有效抑制了切换过程中产生的相位跃变,验证了不同条件对系统精度的影响,对节点端无损切换乃至信号融合方面具有很大的借鉴意义。     

Effects of movement speed and predictability in human–robot collaboration

Human–robot collaboration (HRC) is characterized by a spatiotemporal overlap between the workspaces of the human and the robot and has become a viable option in manufacturing and other industries. However, for companies considering employing HRC it remains unclear how best to configure such a setup, because empirical evidence on human factors requirements remains inconclusive. As robots execute movements at high levels of automation, they adapt their speed and movement path to situational demands. This study therefore experimentally investigated the effects of movement speed and path predictability of an industrial collaborating robot on the human operator. Participants completed tasks together with a robot in an industrial workplace simulated in virtual reality. A lower level of predictability was associated with a loss in task performance, while faster movements resulted in higher‐rated values for task load and anxiety, indicating demands on the operator exceeding the optimum. Implications for productivity and safety and possible advancements in HRC workplaces are discussed.     

FFT计算菲涅尔衍射相位的跳变与矫正研究

采用傅里叶变换算法计算菲涅尔衍射相位时,在相位未解包裹的情况下,接收面上提取的相位分布曲线会出现跳变,如果进行解包裹,必然会导致错误的结果。研究发现用傅里叶变换算法进行衍射计算导致接收面上相位跳变的原因,是因为快速傅里叶变换（FFT）对矩阵标注索引的方式与离散傅里叶变换（DFT）有所区别,从而导致计算结果的相位与真实相位有差异。本文提出在FFT运算前后分别进行一次倒谱的方法矫正这种相位跳变,并仿真利用单次FFT进行二维矩孔的菲涅尔衍射,用2次倒谱矫正接收面上的相位跳变,结果证明了该矫正方法的可行性。     

A method of evaluating VDT screen layout by eye movement analysis

Abstract

The method for evaluating VDT screen layout by eye movements is studied. When the subjects read from the VDT screen, the change in their line of sight was measured by their eye movements. The measured eye movement patterns were divided into the sequential and rereading processes. When related to these characteristics, the performance of subjects was found to be good when the sequential process predominated over the rereading process. The eye movement pattern was shown to change with screen layout. The eye movement pattern proved effective in determining that tabular format is more legible than textual format. This confirmed the usefulness of the method of evaluating VDT screen layout by the eye movement pattern.     

A method of evaluating VDT screen layout by eye movement analysis.

The method for evaluating VDT screen layout by eye movements is studied. When the subjects read from the VDT screen, the change in their line of sight was measured by their eye movements. The measured eye movement patterns were divided into the sequential and rereading processes. When related to these characteristics, the performance of subjects was found to be good when the sequential process predominated over the rereading process. The eye movement pattern was shown to change with screen layout. The eye movement pattern proved effective in determining that tabular format is more legible than textual format. This confirmed the usefulness of the method of evaluating VDT screen layout by the eye movement pattern.     

Head movements during two computer work tasks assessed by accelerometry

We investigated whether potential differences in head inclinations and accelerations for two highly similar computer work tasks could be detected using (1) a triaxial accelerometer and (2) a simulated uniaxial accelerometer.Ten subjects’ head movements were registered with a triaxial accelerometer system for two similar document-management tasks at their work place: a fully electronic document-management task and one also involving paper documents.In situations where head movements were small, a triaxial accelerometer was able to discriminate between the different degrees of static work of the neck in terms of range of head inclinations and accelerations. A difference in head acceleration was also found by using a simulated uniaxial accelerometer. Thus, in terms of head movement and for work similar to this office work, potential dynamic differences in observationally similar work tasks can be investigated by using a triaxial accelerometer. For acceleration alone, a uniaxial accelerometer can also be used.