Improving digital human modelling for proactive ergonomics in design

This paper presents the need to improve existing digital human models (DHMs) so they are better able to serve as effective ergonomics analysis and design tools. Existing DHMs are meant to be used by a designer early in a product development process when attempting to improve the physical design of vehicle interiors and manufacturing workplaces. The emphasis in this paper is placed on developing future DHMs that include valid posture and motion prediction models for various populations. It is argued that existing posture and motion prediction models now used in DHMs must be changed to become based on real motion data to assure validity for complex dynamic task simulations. It is further speculated that if valid human posture and motion prediction models are developed and used, these can be combined with psychophysical and biomechanical models to provide a much greater understanding of dynamic human performance and population specific limitations and that these new DHM models will ultimately provide a powerful ergonomics design tool.     

Creating and retargetting motion by the musculoskeletal human body model

Recently, optimization has been used in various ways to interpolate or retarget human body motions obtained by motion-capturing systems. However, in such cases, the inner structure of a human body has rarely been taken into account, and hence there have been difficulties in simulating physiological effects such as fatigue or injuries. In this paper, we propose a method to create/retarget human body motions using a musculoskeletal human body model. Using our method, it is possible to create dynamically and physiologically feasible motions. Since a muscle model based on Hill's model is included in our system, it is also possible to retarget the original motion by changing muscular parameters. For example, using the muscle fatigue model, a motion where a human body gradually gets tired can be simulated. By increasing the maximal force exertable by the muscles, or decreasing it to zero, training or displacement effects of muscles can also be simulated. Our method can be used for biomechanically correct inverse kinematics, interpolation of motions, and physiological retargetting of the human body motion.     

Improving digital human modelling for proactive ergonomics in design

This paper presents the need to improve existing digital human models (DHMs) so they are better able to serve as effective ergonomics analysis and design tools. Existing DHMs are meant to be used by a designer early in a product development process when attempting to improve the physical design of vehicle interiors and manufacturing workplaces. The emphasis in this paper is placed on developing future DHMs that include valid posture and motion prediction models for various populations. It is argued that existing posture and motion prediction models now used in DHMs must be changed to become based on real motion data to assure validity for complex dynamic task simulations. It is further speculated that if valid human posture and motion prediction models are developed and used, these can be combined with psychophysical and biomechanical models to provide a much greater understanding of dynamic human performance and population specific limitations and that these new DHM models will ultimately provide a powerful ergonomics design tool.     

Reducing musculoskeletal disorders among computer operators: comparison between ergonomics interventions at the workplace

Typing is associated with musculoskeletal disorders (MSDs) caused by multiple risk factors. This control study aimed to evaluate the efficacy of a workplace intervention for reducing MSDs among computer workers. Sixty-six subjects with and without MSD were assigned consecutively to one of three groups: ergonomics intervention (work site and body posture adjustments, muscle activity training and exercises) accompanied with biofeedback training, the same ergonomics intervention without biofeedback and a control group. Evaluation of MSDs, body posture, psychosocial status, upper extremity (UE) kinematics and muscle surface electromyography were carried out before and after the intervention in the workplace and the motion lab. Our main hypothesis that significant differences in the reduction of MSDs will exist between subjects in the study groups and controls was confirmed (χ² = 13.3; p = 0.001). Significant changes were found in UE kinematics and posture as well. Both ergonomics interventions effectively reduced MSD and improved body posture.

Practitioner Summary: This study aimed to test the efficacy of an individual workplace intervention programme among computer workers by evaluating musculoskeletal disorders (MSDs), body posture, upper extremity kinematics, muscle activity and psychosocial factors were tested. The proposed ergonomics interventions effectively reduced MSDs and improved body posture.     

A memory-based model for planning target reach postures in the presence of obstructions

Existing posture prediction and motion simulation models generally lack the capability of simulating human obstruction avoidance during target reach. This compromises the utility of digital human models for ergonomics, as many design problems involve interactions between humans and obstructions. To address this problem, this paper presents a novel memory-based posture planning (MBPP) model, which plans reach postures that avoid obstructions. In this model, the task space is partitioned into small regions called cells. For a given human figure, each cell is linked to a memory that stores various alternative postures for reaching the cell. When a posture planning problem is given in terms of a target and an obstruction configuration, the model examines postures belonging to the relevant cell, selects collision-free ones and modifies them to exactly meet the hand target acquisition constraint. Simulation results showed that the MBPP model is capable of rapidly and robustly planning reach postures for various scenarios.     

Computerized task risk assessment using digital human modeling based Job Risk Classification Model

Different from the classical ergonomics analysis, Virtual Interactive Design methodology relies on manikin movements in virtual environment. This platform has been implemented by researchers to accomplish static ergonomic analyses including Rapid Upper Limb Assessment, NIOSH lifting equation and Static Strength Prediction. However, considering only static posture information limits the capacity of ergonomics analysis. In this study, the methodology of performing dynamic ergonomics analysis based on this Virtual Interactive Design platform is proposed. This environment allows velocity and angular velocity of specified body segments/joints calculated for designed tasks to be used to assess the corresponding risk levels based on Job Risk Classification Model. The motion calculation is completed based on the captured interaction between human participants and virtual workplace/mockup. To evaluate the validity and reliability of this upgraded platform, potential errors are analyzed by comparing outputs from several designed experimental conditions.     

基于舒适度最大化的人体运动控制

在分析人体自身运动反馈控制机理的基础上,引入舒适度作为人体运动控制的性能指标函数,提出了一种基于舒适度最大化的人体运动控制算法．该算法综合考虑了运动学、动力学以及人体工效学等因素,避免了单纯从动力学方面求解带来的虚拟人体动画所隐含的力量冲突,提高了仿真结果的真实性和合理性．最后,用实验验证了文中算法的有效性．该算法为设计安全舒适的人体动作和作业提供了一定的参考依据．     

The interacting effects of forearm rotation and exertion direction on male and female wrist strength

The accurate estimation of wrist strength is an important component of ergonomics task evaluation, as a vast majority of occupational tasks involve use of the hands to generate forces and moments. The purpose of this study was to examine the interacting effects of forearm rotation (pronation/supination) and wrist exertion direction on strength at the wrist joint in males and females. A total of 24 male and female participants performed maximum isometric wrist exertions while maintaining a non-deviated wrist posture (no flexion/extension or radial/ulnar deviation) and an open hand. Maximum wrist moments were obtained in combinations of three forearm rotations (90° pronation, neutral, 90° supination) and four exertion directions (flexion, extension, radial and ulnar deviation). A greater effect of forearm rotation was observed for males, as strength in the neutral forearm posture was significantly different than pronated and supinated postures in 5 of 8 comparisons. For females, both wrist flexion and extension strengths were higher in neutral, compared to supinated forearm postures. The findings of this study suggest that wrist strength does depend on forearm rotation, and this interaction between axes needs to be accounted for in future strength capability estimates.Relevance to industryThis study shows that wrist strength estimates, currently used by ergonomics software packages in industry, can be improved to more accurately reflect the actual wrist strength capabilities of workers during hand-intensive tasks.     

An assessment of the realism of digital human manikins used for simulation in ergonomics

In this study, the accuracy of the joint centres of the manikins generated by RAMSIS and Human Builder (HB), two digital human modelling (DHM) systems widely used in industry for virtual ergonomics simulation, was investigated. Eighteen variously sized females and males were generated from external anthropometric dimensions and six joint centres (knee, hip and four spine joints) were compared with their anatomic locations obtained from the three-dimensional reconstructed bones from a low-dose X-ray system. Both RAMSIS and HB could correctly reproduce external anthropometric dimensions, while the estimation of internal joint centres location presented an average error of 27.6 mm for HB and 38.3 mm for RAMSIS. Differences between both manikins showed that a more realistic kinematic linkage led to better accuracy in joint location. This study opens the way to further research on the relationship between the external body geometry and internal skeleton in order to improve the realism of the internal skeleton of DHMs, especially for a biomechanical analysis requiring information of joint load and muscle force estimation.

Practitioner summary: This study assessed two digital human modelling (DHM) systems widely used in industry for virtual ergonomics. Results support the need of a more realistic human modelling, especially for a biomechanical analysis and a standardisation of DHMs.     

Evaluation of upper-limb body postures based on the effects of back and shoulder flexion angles on subjective discomfort ratings, heart rates and muscle activities

A possible limitation of many ergonomics checklists that evaluate postures is an independent evaluation of each body segment without considering the coordination between body segments and resulting in the under-/over-estimation of body postures. A total of 20 men were selected to evaluate the effects of shoulder and back flexion angles on the upper-limb muscle activities, subjective discomforts and heart rates. Interesting findings were obtained from the coordination between back flexion angles and shoulder flexion angles. At a back flexion angle of 45°, the discomfort and heart rates were the least at a shoulder flexion angle of 45°. The %MVC also showed a similar trend. It could be inferred that the 0° shoulder flexion angle would be a natural posture, when the back flexion angle is 0°, whereas 45° shoulder flexion might be a more natural posture when the back flexion angle is 45°. STATEMENT OF RELEVANCE: This study evaluated the effects of back and shoulder flexion angles on subjective as well as objective measures. The findings of this study considered the coordination between two body flexion angles and could be used to improve the accuracy of existing ergonomics evaluation methods for body postures.     

What do we mean by a ‘working posture’?

Abstract

No clear definition of ‘posture’ can be found in ergonomics literature. It may be regarded as the configuration of the body's head, trunk and limbs in space or as a ‘quasistatic biomechanical alignment’ (Rohmert and Mainzer 1986), depending on whether the particular context in which it is used is anatomical or biomechanical. The functional aspects of posture are highlighted by the definition of a ‘position adopted because it is appropriate for the task being performed’ (Corlett 1981). Yet, in any work situation, functional, geometric, and biomechanical aspects are as integral to the concept of posture as they are to the consequences for performance and comfort. A simple task posture model, describing the relationships between the various factors which influence working postures, is presented as an aid to workplace design, and two examples are given to show how the model can be applied to die demands of particular types of task. An analysis is also made of the factors involved in the exertion of force, including physiological, environmental, personal, and task factors, in order to give a better understanding of the influences of task and workplace on strength capability.     

人机任务仿真中虚拟人行为建模及仿真实现

提出一种采用高级智能对象(ASO)的建模方法,实现虚拟人的行为建模。首先, 引入 ASO 的概念,对交互特征中的交互元素、交互部位及对象动作进行定义,并对交互动作进 行分类;其次,提出了对象驱动方法,解决由虚拟对象作为主动体动作而导致的虚拟人作为被 动体的运动计算问题,实现对象以交互特征为主的建模;最后,根据人机任务需要对虚拟人的 基本行为动作进行分析,选择常用的 4 种基本动作,对其进行定义并进行动作组合,给出以交 互元素为主的位姿、手型的计算方法,实现了行为建模并进行仿真实现,解决了任务仿真中的 交互量大问题,使仿真结果具有重用性。并以飞机装配的手工铆接仿真为例对方法进行验证。     

Contact Modeling and Identification of Planar Somersaults on the Trampoline

This paper presents an extensive study on the trampoline-performed planar somersaults. First, a multibody biomechanical model of the trampolinist and the recurrently interacting trampoline bed are developed, including both the motion equations and the determination of joint reactions. The mathematical model is then identified –the mass and inertia characteristics of the human body are estimated, and the stiffness and damping characteristics of the trampoline bed are measured. By recording the actual somersault performances the motion characteristics of the stunts, i.e. the time variations of positions, velocities and accelerations of the body parts are also obtained. Finally, an inverse dynamics formulation for the system designated as an under-controlled system, is developed. The followed inverse dynamics simulation results in the torques of muscle forces in the joints that assure the realization of the actual motion. The reaction forces in the joints during the analyzed evolutions are also determined. Using the kinematic and dynamics characteristics, the nature of the stunts, the way the human body is maneuvered and controlled, can be studied.     

Evaluation of upper-limb body postures based on the effects of back and shoulder flexion angles on subjective discomfort ratings,heart rates and muscle activities

A possible limitation of many ergonomics checklists that evaluate postures is an independent evaluation of each body segment without considering the coordination between body segments and resulting in the under-/over-estimation of body postures. A total of 20 men were selected to evaluate the effects of shoulder and back flexion angles on the upper-limb muscle activities, subjective discomforts and heart rates. Interesting findings were obtained from the coordination between back flexion angles and shoulder flexion angles. At a back flexion angle of 45°, the discomfort and heart rates were the least at a shoulder flexion angle of 45°. The %MVC also showed a similar trend. It could be inferred that the 0° shoulder flexion angle would be a natural posture, when the back flexion angle is 0°, whereas 45° shoulder flexion might be a more natural posture when the back flexion angle is 45°.

Statement of Relevance: This study evaluated the effects of back and shoulder flexion angles on subjective as well as objective measures. The findings of this study considered the coordination between two body flexion angles and could be used to improve the accuracy of existing ergonomics evaluation methods for body postures.     

基于少量关键序列帧的人体姿态识别方法

针对传统人体姿态识别数据采集易受环境干扰、难以解决人体运动姿态的相似性和 人体运动执行者的特征差异性等问题,提出一种基于少量关键序列帧的人体姿态识别方法。首先 对原有运动序列进行预选,通过运动轨迹取极值的方法构造初选关键帧序列,再利用帧消减算法 获取最终关键帧序列;然后对不同人体姿态分别建立隐马尔科夫模型,利用 Baum-Welch 算法计 算得到初始概率矩阵、混淆矩阵、状态转移矩阵,获得训练后模型;最后输入待测数据,应用前 向算法,得到对于每个模型的概率,比较并选取最大概率对应的姿态作为识别结果。实验结果表 明,该方法能够有效的选取原始运动序列的关键帧,提高人体姿态识别的准确性。     

A memory-based model for planning target reach postures in the presence of obstructions

Existing posture prediction and motion simulation models generally lack the capability of simulating human obstruction avoidance during target reach. This compromises the utility of digital human models for ergonomics, as many design problems involve interactions between humans and obstructions. To address this problem, this paper presents a novel memory-based posture planning (MBPP) model, which plans reach postures that avoid obstructions. In this model, the task space is partitioned into small regions called cells. For a given human figure, each cell is linked to a memory that stores various alternative postures for reaching the cell. When a posture planning problem is given in terms of a target and an obstruction configuration, the model examines postures belonging to the relevant cell, selects collision-free ones and modifies them to exactly meet the hand target acquisition constraint. Simulation results showed that the MBPP model is capable of rapidly and robustly planning reach postures for various scenarios.     

CCPE: Methodology for a Combined Evaluation of Cognitive and Physical Ergonomics in the Interaction between Human and Machine

Evaluation methods of today often focus on cognitive ergonomics (such as mental workload or usability) or physical ergonomics (such as physical workload or body posture). This article describes an analytical methodology of a joint systematic search for potential deficiencies in the human–machine interaction; such as high physical and mental workload, use errors, usability problems, and physical ergonomic errors. The purpose with the joint search is to achieve a more holistic evaluation approach and make the evaluation cost more effective than when using separate evaluation methods for cognitive and physical ergonomic aspects. The methodology is task‐based, which makes it possible to use both with focus on the device design, as in development projects; as well as with focus on the procedure, in the operative organization. © 2012 Wiley Periodicals, Inc.     

Action recognition from only somatosensory information using spectral learning in a hidden Markov model

Human action classification is fundamental technology for robots that have to interpret a human’s intended actions and make appropriate responses, as they will have to do if they are to be integrated into our daily lives. Improved measurement of human motion, using an optical motion capture system or a depth sensor, allows robots to recognize human actions from superficial motion data, such as camera images containing human actions or positions of human bodies. But existing technology for motion recognition does not handle the contact force that always exists between the human and the environment that the human is acting upon. More specifically, humans perform feasible actions by controlling not only their posture but also the contact forces. Furthermore these contact forces require appropriate muscle tensions in the full body. These muscle tensions or activities are expected to be useful for robots observing human actions to estimate the human’s somatosensory states and consequently understand the intended action. This paper proposes a novel approach to classifying human actions using only the activities of all the muscles in the human body. Continuous spatio-temporal data of the activity of an individual muscle is encoded into a discrete hidden Markov model (HMM), and the set of HMMs for all the muscles forms a classifier for the specific action. Our classifiers were tested on muscle activities estimated from captured human motions, electromyography data, and reaction forces. The results demonstrate their superiority over commonly used HMM-based classifiers.     

Kinematic and electromyographic differences between mouse and touchpad use on laptop computers

Background

Numerous studies have compared the postures and muscular activities induced by the various input devices available. To the authors' knowledge, no studies have yet compared upper body posture and movement, sEMG activity and muscle co-contractions induced by use of a mouse or of a touchpad.

Objective

The aim of this study was to compare posture, joint excursion and sEMG activity when using a laptop equipped with a mouse or a touchpad.

Methods

Trunk and upper arm posture, ranges of motion and muscle activities were measured in ten subjects during two standardized tasks.

Results

Mouse use induced larger shoulder abduction than touchpad use. On the other hand, when a touchpad was used, the upper arm joints were bound and fixed to a greater extent than during mouse use. Touchpad users are forced to maintain a more static posture. The upper arm electromyography results clearly indicate that touchpad use requires more stabilization than mouse use.

Conclusion

Motor tasks executed by means of the mouse allow a greater range of motions and reduce the biomechanical stress thanks to the greater postural mobility, even though the posture is less neutral. The results of our study tend to suggest that an external mouse should be preferred to the touchpad by frequent users of laptops.

Relevance to industry

This study is a suggestion for IT companies to give customers information of possible advantages using an external mouse. Furthermore our data highlight the importance of providing a mouse to all laptop users in order to reduce biomechanical risks.     

Nonlinear inverse optimization approach for determining the weights of objective function in standing reach tasks

This paper presents a nonlinear inverse optimization approach to determine the weights for the joint displacement function in standing reach tasks. This inverse optimization problem can be formulated as a bi-level highly nonlinear optimization problem. The design variables are the weights of a cost function. The cost function is the weighted summation of the differences between two sets of joint angles (predicted posture and the actual standing reach posture). Constraints include the normalized weights within limits and an inner optimization problem to solve for joint angles (predicted standing reach posture). The weight linear equality constraints, obtained through observations, are also implemented in the formulation to test the method. A 52 degree-of-freedom (DOF) human whole body model is used to study the formulation and visualize the prediction. An in-house motion capture system is used to obtain the actual standing reach posture. A total of 12 subjects (three subjects for each percentile in stature of 5th percentile female, 50th percentile female, 50th percentile male and 95th percentile male) are selected to run the experiment for 30 tasks. Among these subjects one is Turkish, two are Chinese, and the rest subjects are Americans. Three sets of weights for the general standing reach tasks are obtained for the three zones by averaging all weights in each zone for all subjects and all tasks. Based on the obtained sets of weights, the predicted standing reach postures found using the direct optimization-based approach have good correlation with the experimental results. Sensitivity of the formulation has also been investigated in this study. The presented formulation can be used to determine the weights of cost function within any multi-objective optimization (MOO) problems such as any types of posture prediction and motion prediction.