Evaluation of upper body kinematics and muscle activity during milking attachment task

The objective of the study was to evaluate the effects of udder height on upper body kinematics and muscle activity during a simulated attachment task in a parallel parlor set up, and the effects of udder access method (back or side) on the task biomechanics. Twenty males performed the task under conditions that simulated three udder heights and two udder access methods. The muscular load and kinematics during the task confirmed that milking is a physically demanding task. Trunk flexion angle increased with decreasing udder height, and the erector spinae activation was higher when the udder was below shoulder height compared to at or above. Compared to accessing the udder from side of the cow (herringbone parlor style), accessing from behind (Parallel parlor style) was associated with lower trunk flexion, greater shoulder horizontal adduction, lower shoulder elevation, and greater anterior deltoid activation. Milking in herringbone parlor style and with the udder at or above shoulder level may help reduce strain on the trunk/neck.     

Sex-specific effects of muscle fatigue on upper body kinematics and discomfort during a repetitive point task performed on a sit-stand stool

When performing repetitive work-like tasks while standing, people may develop leg discomfort and adapt their whole-body motion to arm fatigue. How these responses are affected when working while sitting on a sit-stand stool is unknown. Asymptomatic young adults (N = 29, 15 females) performed a repetitive pointing task sitting on a sit-stand stool, while whole-body kinematics was recorded. Results showed no leg discomfort increase with fatigue. The upper body leaned more backwards and towards the non-reaching side. Variability increased at the seat (p = 0.002), shoulder (p = 0.001) and elbow (p = 0.005) but was preserved at wrist (p = 0.058) and endpoint (p = 0.088). Participants who were more fatigable increased seat variability (males, p = 0.01) or seat range of motion (females, p = 0.022) after fatigue. The sit-stand stool contributed to the response to arm fatigue, although females and males developed different strategies. The maintained endpoint variability and leg discomfort suggest that the sit-stand stool could be recommended as an alternate workstation with minimal disruption to work performance or worker discomfort.     

Estimating joint kinematics of a whole body chain model with closed-loop constraints

Computer simulation and optimal control requiring actual joint kinematics and based on the definition of a chain model become more used in biomechanics for studying the musculo-skeletal coordination or optimizing the performance. For this purpose, numerical optimization methods using a chain model have been developed and showed promising results to estimate joint kinematics for open-loop movements. The aim of this study was to exhaustively compare the type of method and closed-loop constraint with four criteria: (i) reconstruction quality, (ii) loop closure respect, (iii) regularity of joint kinematics, and (iv) computational time. Five algorithms were tested to estimate the whole body joint kinematics of 10 elite athletes paddling an ergometer: global optimization (GO) without closed-loop constraints, with soft closed-loop constraints and with strict closed-loop constraints, and Kalman filter (KF) without closed-loop constraints and with soft closed-loop constraints. Each athlete was modelled using a personalized 17-segment 42-degree of freedom chain model. Input data were measured by a 10-camera motion capture system sampled at 250 Hz. ANOVAs were performed on the four criteria to identify differences between the five algorithms. Marker residuals were slightly increased by about 2–3 mm using GO under strict constraints and KF with soft constraints. Closed-loop errors were five times reduced when introducing constraints (10 to 2 mm). KF algorithms gave significantly smoother joint kinematics than the three GO algorithms. Computational time was largely increased by introducing closed-loop constraints in GO algorithm (from 21 to 200 ms per frame) while it remained unchanged in KF algorithm (about 60 ms per frame). To conclude, KF with soft constraints represents the best compromise between the four criteria.     

Improvement of a neural network-based motion generator with bimanual coordination for upper limb prosthesis

We propose to redesign a neural network used as a motion generator with bimanual coordination for upper limb prosthesis in order to improve its learning capability. We assumed that the wearer of the prosthesis was a unilateral amputee. In our previous work, we proposed a prosthesis control system using a neural network that learned bimanual coordination in order to implement smooth motion with both hands. However, the previously proposed system has the problem that a neural network cannot generate the desired motion of the prosthesis in special cases. The reason is that the motion generator calculates the desired posture of the prosthesis from the current posture of the healthy arm only, regardless of the current posture of the prosthesis. We propose to use the current posture of both the healthy arm and the prosthesis as neural network inputs in order to solve this problem. In this article, we show that a single neural network whose input was the current posture of both arms could learn the relationships of the coordinated motions of holding boxes of different sizes, and the newly proposed system can calculate the desired motion of the prosthesis in special cases through computer simulations.     

Kinematic compatibility between the body and a mock spacesuit during basic upper body motions

In this study, a novel conceptual method was tested to study the kinematic mismatch between the body motion of an occupant with respect to a rigid suit. It was hypothesized that differences between body and suit motion would require extra body movement to achieve the desired suit motion. To quantify the mismatch in kinematics, mock upper body suits with an open structure were used in conjunction with a marker-based motion capture system. A 3D motion modeling software was used to determine the range of motion of the suit and body segments of nine participants performing seven basic arm and trunk motions. In general, range of motion of the body segment was found to be higher than the corresponding suit segment range of motion. Differences in range of motion of up to 21.3% were found between corresponding body and suit segments, and significance was found in five of the seven motions.     

Evaluation of five steering input devices in terms of muscle activity,upper body kinematics and steering performance during heavy machine simulator driving

Work related upper body musculoskeletal symptoms and disorders constitute a major problem for operators of heavy machinery. Steering input devices mediate risk factors of upper body musculoskeletal disorders. Little research has been conducted to compare the multiple commercially available steering input devices in a multi-faceted approach. The present study evaluated five commonly used steering input devices (conventional steering wheel, fast steering wheel, miniature steering wheel, first-order joystick and second-order joystick) in terms of muscle activity, upper body kinematics and steering performance during heavy machine simulator driving. Fifteen healthy males novice to operation of heavy machinery completed five laps on a simulated track with each steering input device. Results showed a generally lower muscle activity when using the joysticks. The conventional and fast steering wheel increased mean wrist and shoulder flexion/extension angles and participants spent more time in wrist flexion/extension angles corresponding to moderate and poor comfort levels. An increased elbow protonation angle was found for the three steering wheels compared to the joysticks. The conventional steering wheel showed slowest track completion time and was subjectively ranked worst. The first-order joystick was ranked highest but also showed the highest amount of steering reversal rates, posing a risk of increased repetitiveness. Overall, the second-order joystick is considered superior ergonomically compared to the other steering input devices evaluated. However, all evaluated steering input devices exceeded muscle activity and/or joint angle recommendations.Relevance to the industry: Compared to steering wheels, joystick steering showed reduced muscular activity and less awkward joint postures, suggesting a reduced risk of developing musculoskeletal disorders in the long term. However, the results warrant efforts to further develop joystick steering resulting in a reduction of exposure level beyond the existing solutions.     

Improving virtual reality navigation tasks using a haptic vest and upper body tracking

Haptic feedback is an important component of immersive virtual reality (VR) applications that is often suggested to complement visual information through the sense of touch. This paper investigates the use of a haptic vest in navigation tasks. The haptic vest produces a repulsive vibrotactile feedback from nearby static virtual obstacles that augments the user spatial awareness. The tasks require the user to perform complex movements in a 3D cluttered virtual environment, like avoiding obstacles while walking backwards and pulling a virtual object. The experimental setup consists of a room-scale environment. Our approach is the first study where a haptic vest is tracked in real time using a motion capture device so that proximity-based haptic feedback can be conveyed according to the actual movement of the upper body of the user.User study experiments have been conducted with and without haptic feedback in virtual environments involving both normal and limited visibility conditions. A quantitative evaluation was carried out by measuring task completion time and error (collision) rate. Multiple haptic rendering techniques have also been tested. Results show that under limited visibility conditions proximity-based haptic feedback generated by a wearable haptic vest can significantly reduce the number of collisions with obstacles in the virtual environment.     

Partial least squares-based human upper body orientation estimation with combined detection and tracking

This paper deals with the problem of estimating the human upper body orientation. We propose a framework which integrates estimation of the human upper body orientation and the human movements. Our human orientation estimator utilizes a novel approach which hierarchically employs partial least squares-based models of the gradient and texture features, coupled with the random forest classifier. The movement predictions are done by projecting detected persons into 3D coordinates and running an Unscented Kalman Filter-based tracker. The body orientation results are then fused with the movement predictions to build a more robust estimation of the human upper body orientation. We carry out comprehensive experiments and provide comparison results to show the advantages of our system over the other existing methods.     

零售商温和不公平厌恶下的回购合约与渠道协调

以不公平厌恶效用函数作为一个温和不公平厌恶零售商的决策准则,研究采用回购合约协调供应链的问题.对于合约参数的不同取值,分析回购合约定价对零售商公平状况及其最优订购决策的影响,给出达到供应链协调的回购合约,并用数值算例对结果进行进一步讨论.研究发现,存在两种协调供应链的回购合约定价规则.第一种与零售商为公平中性时的协调供应链的回购合约定价规则相同,回购定价区间只与零售商不利不公平的厌恶程度有关;另一种定价规则的利润分配总是公平的,其具体形式依赖于需求的分布及公平的利润分配比例.     

Estimating the angular velocity of a rigid body moving in the plane from tangential and centripetal acceleration measurements

Two methods are available for the estimation of the angular velocity of a rigid body from point-acceleration measurements: (i) the time-integration of the angular acceleration and (ii) the square-rooting of the centripetal acceleration. The inaccuracy of the first method is due mainly to the accumulation of the error on the angular acceleration throughout the time-integration process, which does not prevent that it be used successfully in crash tests with dummies, since these experiments never last more than one second. On the other hand, the error resulting from the second method is stable through time, but becomes inaccurate whenever the rigid body angular velocity approaches zero, which occurs in many applications. In order to take advantage of the complementarity of these two methods, a fusion of their estimates is proposed. To this end, the accelerometer measurements are modeled as exact signals contaminated with bias errors and Gaussian white noise. The relations between the variables at stake are written in the form of a nonlinear state-space system in which the angular velocity and the angular acceleration are state variables. Consequently, a minimum-variance-error estimate of the state vector is obtained by means of extended Kalman filtering. The performance of the proposed estimation method is assessed by means of simulation. Apparently, the resulting estimation method is more robust than the existing accelerometer-only methods and competitive with gyroscope measurements. Moreover, it allows the identification and the compensation of any bias error in the accelerometer measurements, which is a significant advantage over gyroscopes.     

Changes in gait kinematics and posture with the use of a front pack

The objective of this study was to determine if posture during gait can be affected by position of the load. It was hypothesized that the front pack would result in postural changes in the gait cycle, compared to a similarly loaded backpack. Thirteen healthy adults, free of any injury, volunteered to participate in this study. Two dimensional video data were collected at 50 Hz using a MacReflex video system. A backpack and a front pack were compared using loads of 10 and 15% of body weight. Markers were placed on the ear, acromion, greater trochanter and lateral joint line of the knee, lateral malleolus and fifth metatarsophalangeal joint. Data were collected while the participants walked at 0.75 stride/s. The data were used to calculate joint angles and displacements during each gait cycle. There was a significant difference noted in angles of the hip flexion, with the backpack condition demonstrating a greater flexion in each stride than either the control or front pack. Both backpack and front pack conditions demonstrated a significant change in neck motion compared to the control condition. The results of the position analysis over time also revealed an increase in the forward head position when participants were wearing the backpack compared to either the control or the front pack condition. It was concluded that the use of a front pack results in a more upright posture in gait, when compared to a backpack carrying the same load.     

Changes in gait kinematics and posture with the use of a front pack

The objective of this study was to determine if posture during gait can be affected by position of the load. It was hypothesized that the front pack would result in postural changes in the gait cycle, compared to a similarly loaded backpack. Thirteen healthy adults, free of any injury, volunteered to participate in this study. Two dimensional video data were collected at 50 Hz using a MacReflex video system. A backpack and a front pack were compared using loads of 10 and 15% of body weight. Markers were placed on the ear, acromion, greater trochanter and lateral joint line of the knee, lateral malleolus and fifth metatarsophalangeal joint. Data were collected while the participants walked at 0.75 stride/s. The data were used to calculate joint angles and displacements during each gait cycle. There was a significant difference noted in angles of the hip flexion, with the backpack condition demonstrating a greater flexion in each stride than either the control or front pack. Both backpack and front pack conditions demonstrated a significant change in neck motion compared to the control condition. The results of the position analysis over time also revealed an increase in the forward head position when participants were wearing the backpack compared to either the control or the front pack condition. It was concluded that the use of a front pack results in a more upright posture in gait, when compared to a backpack carrying the same load.     

Rigid body dynamics with a scalable body,quaternions and perfect constraints

In this paper, we present a formulation of the quaternion constraint for rigid body rotations in the form of a standard perfect bilateral mechanical constraint, for which the associated Lagrangian multiplier has the meaning of a constraint force. First, the equations of motion of a scalable body are derived. A scalable body has three translational, three rotational, and one uniform scaling degree of freedom. As generalized coordinates, an unconstrained quaternion and a displacement vector are used. To the scalable body, a perfect bilateral constraint is added, restricting the quaternion to unit length and making the body rigid. This way a quaternion based differential algebraic equation (DAE) formulation for the dynamics of a rigid body is obtained, where the 7×7 mass matrix is regular and the unit length restriction of the quaternion is enforced by a mechanical constraint. Finally, the equations of motion in the form of a DAE are linked to the Newton–Euler equations of motion of a rigid body. The rigid body DAE formulation is useful for the construction of (energy) consistent integrators.     

Model building and location problem solving in a plane with forbidden gaps

Problems of optimal object location in a plane outside rectangular forbidden gaps are considered. Objects under location are connected with one another and with the objects, located in the same plane. The criteria are the minimization of maximal weighted distance or total cost of the links between objects. A model building procedure of integer linear programming of the problems above for rectangular metric is given. Solution algorithms are briefly described. The outcomes of a numerical experiment are given.     

A position/force control for a robot finger with soft tip and uncertain kinematics

We consider the position and force regulation problem for a soft tip robot finger in contact with a rigid surface under kinematic and dynamic parametric uncertainties. The reproducing force is assumed to be related to the displacement through a nonlinear function whose characteristics are unknown, but both the actual displacement and force can be directly measured. Kinematic uncertainties concern the rigid surface orientation and the contact point location. Kinematic parameters involved in the contact point location concern the length from the last joint to the contact point and the rest of the link lengths in the general case. An adaptive controller with a composite update parameter law is proposed, and the asymptotic stability of the force and estimated position errors under dynamic and kinematic uncertainties is shown for the planar case. Simulation results for a three‐degrees‐of‐freedom planar robotic finger are presented. © 2002 Wiley Periodicals, Inc.     

Optimal design of a 2-DOF parallel manipulator with actuation redundancy considering kinematics and natural frequency

In this paper, a planar 2-DOF parallel manipulator with actuation redundancy is proposed and the optimal design considering kinematics and natural frequency is presented. The stiffness matrix and mass matrix are derived, and the structural dynamics is modeled. The natural frequency is obtained on the basis of dynamic model. Based on the kinematic performance, the range for link length is given. Then, considering the natural frequency, the geometry is optimized. The natural frequency is simulated and compared with the corresponding non-redundant parallel manipulator. The designed redundant parallel manipulator has desired kinematic performance and natural frequency and is incorporated into a 4-DOF hybrid machine tool.     

Ordering and returns handling decisions and coordination in a supply chain with demand uncertainty

We develop a newsvendor model to study the retailer's order quantity, the manufacturer's returns handling strategy, and channel coordination. The manufacturer chooses one of two returns handling strategies: manufacturer handling or retailer handling under the coordinated and decentralized scenarios, respectively. Under the coordinated scenario, we find that when consumer's returns handling cost under manufacturer handling or the manufacturer's returns handling cost is small, consumer returns should be handled by the manufacturer. Under the decentralized scenario, when the retailer's returns handling cost or the consumer's returns handling cost under retailer handling is low, the manufacturer will choose manufacturer handling; both the manufacturer and the retailer may be better off using manufacturer handling (a win–win situation). The impact of the returns handling strategy on the retailer's ordering quantity largely depends on its effect on the consumer's returns handling cost. Finally, we also design buyback contracts to coordinate the supply chain and find that both wholesale price and buyback price under manufacturer handling are higher than those under retailer handling.     

Studies on a micro turbine device with both journal- and thrust-air bearings

This paper presents design, fabrication, analysis and test of a silicon-based micro turbine device that is driven by compressed air. To improve the motion stability at high rotational speed, the turbine device employs an enhanced micro air bearing system that includes both journal air bearing and thrust air bearings. The double-sides dynamic thrust air bearings are designed to support the rotor from both its top and bottom sides. The top thrust air bearing employs pump-in spiral groove configuration, and the bottom bearing uses pump-out spiral groove configuration. The dynamic journal air bearing is formed by a plain circular trench with a short journal length (L) and a narrow radial clearance (C). The critical aspect ratio (L/C) over 20:1 is realized through an optimized fabrication process. The micro turbine device has been fabricated, integrated and tested. During the test, the turbine device demonstrated stable operations at a rotational speed of 14,700 rpm.     

考虑风险容忍度的双渠道绿色供应链运营决策及协调研究

针对双渠道绿色供应链,在考虑各方不同风险容忍度的基础上,构建以制造商为主导的供应链博弈模型,利用均值方差法分析集中式决策和批发价格契约下参与方的运营决策和期望利润,并设计协调契约.研究发现:在批发价格契约下,产品绿色度与制造商风险容忍度正相关,与零售商风险容忍度无关;最优零售价格均与双方风险容忍度正相关,且线上价格基准系数与直销价格负相关,与零售价格正相关;当绿色产品对消费者需求影响较大时,零售商的期望利润与制造商风险容忍度正相关.带有转移支付的反向收益共享与成本分担组合契约可实现双渠道绿色供应链的协调.