二维直线运动平台几何误差建模与数字化分析

针对二维直线运动平台的定位精度受到绕X、Y、Z三个方向转动产生的角位移误差和沿着这三个方向的线位移误差的影响,采用一种基于三维模型的数字化方法对这些几何误差进行分析。通过参考坐标系和齐次变换矩阵建立二维直线运动平台几何误差运动学模型,并基于误差模型对运动平台的各项几何误差进行分配、计算和合成。基于以上误差分配原则对运动平台使用的导轨提出形位公差要求。通过上述工作,在虚拟样机设计阶段能对所设计结构几何误差进行预测,为后续精密运动的设计提供可靠的参考。     

企业发展中存在的八大误区

介绍企业在发展中存在的八大误区为:(1)企业越大越好;(2)发展越快越好;(3)集体决策优于个人决策;(4)多元化经营可降低风险;(5)什么赚钱干什么;(6)成功带来更大的成功;(7)好产品代表一切;(8)从产品经营到资本运营.     

Suboptimal robust synthesis for MIMO plant under coprime factor perturbations

Suboptimal robust synthesis for MIMO nominal system under coprime factor perturbations is considered in classical and non-classical statements. In the classical statement, weights of perturbations and upper bound on magnitude bounded exogenous disturbance are assumed to be known to controller designer. Suboptimal synthesis within ε tolerance is reduced to the solution of log₂(1/ε) standard mixed sensitivity problems of ℓ₁ optimization. In the non-classical statement, the upper bounds on perturbations and exogenous disturbance are to be estimated from measurement data and suboptimal synthesis is reduced to the solution of 1/ε mixed sensitivity problems.     

Uniting Local and Global Controllers with Robustness to Vanishing Noise

We consider control systems for which we know two stabilizing controllers. One is globally asymptotically stabilizing, the other one is only locally asymptotically stabilizing but for some reason we insist on using it in a neighborhood of the origin. We look for a uniting control law being equal to the local feedback on a neighborhood of the origin, equal to the global one outside of a larger neighborhood and being a globally stabilizing controller. We study several solutions based on continuous, discontinuous, hybrid, time-varying controllers. One criterion of the selection of a controller is the robustness of the stability to vanishing noise. This leads us in particular to consider a kind of generalization of Krasovskii trajectories for hybrid systems. Date received: November 29, 1999. Date revised: August 7, 2000.     

Aberrant driving behaviour: errors and violations

The present study was a replication of the research of Reason et al. (1990). Its aim was to confirm the distinction between driving errors and violations in a Western Australian driving population. Sixty-one male drivers and 74 female drivers completed a questionnaire containing items on driver demographics, driving penalties incurred, driving convictions and accident history and driver behavioural aberrations drawn from the Driver Behaviour Questionnaire (DBQ). In agreement with Reason et al. factor analysis revealed three factors; in the present study these were general errors, dangerous errors, and dangerous violations. Young drivers committed more dangerous errors and dangerous violations than older drivers. Females reported more dangerous errors than males. Males reported more dangerous violations than females. Drivers who reported a high level of road exposure and those who reported having been convicted for speeding reported more dangerous violations. Differences in the results of the two studies can largely by accounted for by differences in the representation of age and gender in the two populations studied.     

Learning from errors in a driving simulation: effects on driving skill and self-confidence

Two experiments investigated the effect of making errors during training (error training) on a driving simulator versus learning from examples of errors (guided error training) on driving skill and confidence. Experiment 1 indicated that compared with errorless learning (where participants drove through a training run not designed to elicit errors), error training led to significantly better transfer to driving tests that were analogous to those situations encountered in training and more effective use of strategies for coping with a novel driving situation. Error training also reduced self-confidence in driving skill at the end of training relative to errorless learning. Experiment 2 provided weak evidence of the superiority of guided error training over errorless learning (where the driver in the video did not make any errors) on analogous tests, and no evidence of transfer to a novel test. Furthermore, guided error training did not influence self-confidence in driving skill. The potential value of driving simulators in providing active processing during driver training is discussed, along with the effects of passive and active exposure to errors on driver confidence.     

A critical appraisal of javelin high speed cinematography results using a computer flight simulation program

Abstract

Errors in javelin release parameters obtained from high-speed film analysis of real throws have been quantified in order to assess the accuracy of studies that assume a rigid body javelin model when measuring human performance characteristics. Human digitizing errors and the inadequate rigid body javelin model represent increments of up to 6 m in range as predicted by a computer flight simulation program. These errors result from difficulties in digitizing blurred javelin coordinates caused by large release speeds and javelin flutter. Errors in release-pitch rate are as high as 27·0%. Digital filtering methods tend to underestimate transiational and angular speeds such that errors in previous literature represent simulated range increments of up to 29 m. This is owing to the filtering methods interpreting high frequency flutter as noise. It is concluded that present methods in javelin film analysis are inadequate for measuring absolute values of release parameters and need to be revised. Accurate quantification is essential before simulation programs can be used in a human performance perspective.     

‘Actions not as planned’ in military air-traffic control

Observations were made of the errors made by eight air-traffic controllers over two periods each of 2½ hours. Errors were classified using a recently devised classification of motor-program errors (Reason 1979) and all the controllers were observed under three conditions of workload, and performing two ostensibly similar air-traffic tasks.

More errors were found with increasing workload, but only in one of the tasks This was interpreted in terms of the pacing and time stress inherently imposed in that task. The assessment of error incidence seems a good candidate as a non-intrusive measure of workload. Analysis of errors in terms of Reason's typology showed no interaction with any of the other variables.

The association of errors with the use of particular pieces of equipment demonstrated ergonomic deficiencies which may have otherwise remained unnoticed It seems that error auditing may also be a useful investigative technique in ergonomic assessment.     

Can self-estimates of body weight and height be used in place of measurements for college students?

A study was conducted to determine how accurately college students can estimate their height and body weight. Four hundred and sixty-nine students (136 females and 333 males) completed a short questionnaire eliciting self-estimates of height and weight, frequency and recency of measuring them, age, and gender. Immediately afterwards, their height and weight were measured. Three hundred and forty-nine subjects were told that they would be measured later; the others were not told that they would be measured. Analysis of the data revealed relatively small absolute errors of estimation (1.00—3.54%); both males and females overestimated height and underestimated weight; females estimated weight less accurately and height more accurately than males; and knowing that one's estimation would be checked by measurement produced slightly more accurate estimations. Simple self-estimates of height and weight are accurate enough to be used in place of measurements.     

Modernization of the Driver Behaviour Questionnaire

IntroductionThe current study builds on previous versions of the Driver Behaviour Questionnaire (DBQ) by incorporating a larger sample of driving behaviors targeting inattention, distraction, aggressive driving, and health related to aging. The goals of this study were to determine if the resulting factor structure was consistent with a more contemporary view of unsafe driving behaviors, and to determine whether scores on the factors could predict self-reported collisions and police citations.MethodsThe instrument was given to a sample of 3295 drivers ranging in age from 19 to 80+ years old. It was divided in two sections, the first to provide demographic information and driving history data and the second containing 105 driver behavior questions.ResultsAn exploratory factor analysis resulted in a 65-item scale organized in four factors. The factors were labeled tentatively as Inattention Errors, Age-Related Problems, Distraction and Hurry, and Aggressive Violations. Regression analyses showed that the factors were predictors of self-reported, at-fault collisions and police citations.Practical implicationsThe factor scores found in this research are consistent with a useful theoretical framework for understanding unsafe driver actions, and demonstrate some potential to identify several individual difference variables that predict self-reported collisions and citations.