Forward dynamics based realistic animation of rigid bodies

This paper presents a new methodology for model and control of the motion of an (articulated) rigid body for the purposes of animation. The technique uses a parameter optimization method for forward dynamic simulation to obtain a good set of values for the control variables of the system. We model articulated rigid bodies using a moderate number of control nodes, and we linearly interpolate control values between adjacent pairs of these nodes. The interpolated control values are used to determine the forces/torques for the body actuators. We can control total motion duration time, and the control is more flexible than in any other dynamics based animation techniques. We employ a parameter optimization, (or nonlinear programming) method to find a good set of values for the control nodes. We extend this method by using a musculotendon skeletal model for the human body instead of the more commonly used robot model to provide more accurate human motion simulations. Skeletal and musculotendon dynamics enable us to do the human body animation more accurately than ever because the muscle force depends on the geometry of a human as well as on differential kinematic parameters. We show various levels of motion control for forward dynamics animation: ranging from piecewise linear forces/torques control for joints to muscle activation signal control for muscles to generate highly nonlinear forces/torques. This spectrum of control levels provides various nonlinear resulting motions to animators to allow them to achieve effective motion control and physically realistic motion simultaneously. Because our algorithms are heavily dependent on parameter optimization, and since the optimization technique may have difficulty finding a global optimum, we provide a modified optimization method along with various techniques to reduce the search space size. Our parameter optimization based forward dynamic animation and musculotendon dynamics based animation present the first use of such techniques in animation research to date.     

Multibody simulation of the musculoskeletal system of the human hand

This paper presents a numerical model of the forward multibody dynamics of the human hand. This model forms the basic foundation in the development of a five-fingered anthropomorphic hand prosthesis. The model is composed of two parts: a model for the rigid-body dynamics of the bone and joint structure of the human hand using the modified articulated-body algorithm for tree structures, and a model to represent the action the muscles tendons present in the hand. The resulting nonlinear model takes as input the actuation of each muscle and outputs the movements of the joints of the hand. This model will be used in the development of a nonlinear controller for the prosthesis and in its testing before being applied into the prosthesis prototype.     

Modeling and computational issues in the inverse dynamics simulation of triple jump

The triple jump is a demanding field event consisting of an approach run, and then followed by a hop, a bound, and a jump. The three consecutive takeoffs are executed at high speed, during which a jumper must absorb extremely large impact forces. The purpose of this paper is to develop an effective formulation for the inverse dynamics simulation of all the jump phases separately. A planar model of the jumper is used, composed of 14 rigid segments connected by 13 hinge joints, and actuated by muscle forces in the lower limbs and resultant muscle torques in the upper body joints. The equations of motion of the model are obtained using a projective technique, allowing for effective assessment of the ground reactions as well as muscle forces and joint reaction forces in the lower limbs. Some numerical results of the inverse dynamics simulation of a triple jump are reported.     

Relaxed individual control of skeletal muscle forces via physical human–robot interaction

This study develops a relaxed formulation of a method for controlling individual muscle forces using exoskeleton robots. Past studies have developed a muscle-force control method with very strict limitations on the conditions. These conditions will be removed, and the problem will be reformulated as a constrained optimization of several parameters. The optimization algorithm recognizes when a solution to the muscle control problem cannot be exactly realized, and finds the solution that minimizes the mean errors of the individual muscles between expected and desired muscle activation. This is demonstrated in a computer simulation of human arm dynamics and compared against the prior method to demonstrate its wider applicability. In addition, the control method is extended to resolve issues associated with a nonideal exoskeleton with incomplete torque application to the joints. A quasi-optimized motor-task that minimizes the errors in target muscles and nontarget muscles can be obtained. This paper presents theoretical analysis, simulation, and experimental results on the performance of the relaxed individual muscle control.     

Analysis of the musculoskeletal system of the hand and forearm during a cylinder grasping task

Musculoskeletal disorders of the hand are mostly due to repeated or awkward manual tasks in the work environment and are considered a public health issue. To prevent their development, it is necessary to understand and investigate the biomechanical behavior of the musculoskeletal system during the movement. In this study a biomechanical analysis of the upper extremity during a cylinder grasping task is conducted by using a parameterized musculoskeletal model of the hand and forearm. The proposed model is composed of 21 segments, 28 musculotendon units, and 20 joints providing 24 degrees of freedom. Boundary conditions of the model are defined by the three-dimensional coordinates of 43 external markers fixed to bony landmarks of the hand and forearm and tracked with an optoelectronic motion capture system. External marker positions from five healthy participants were used to test the model. A task consisting of closing and opening fingers around a cylinder 25 mm in diameter was investigated. Based on experimental kinematic data, an inverse dynamics process was performed to calculate output data of the model (joint angles, musculotendon unit shortening and lengthening patterns). Finally, based on an optimization procedure, joint loads and musculotendon forces were computed in a forward dynamics simulation. Results of this study assessed reproducibility and consistency of the biomechanical behavior of the musculoskeletal hand system.     

Influence of selected modeling and computational issues on muscle force estimates

Knowledge of muscle forces and joint reaction forces during human movement can provide insight into the underlying control and tissue loading. Since direct measurement of the internal loads is generally not feasible, non-invasive methods based on musculoskeletal modeling and computer simulations have been extensively developed. By applying observed motion data to the musculoskeletal models, inverse dynamic analysis allow to determine the resultant joint torques, transformed then into estimates of individual muscle forces by means of different optimization procedures. Assessment of the joint reaction forces and other internal loads is further possible. Comparison of the muscle force estimates obtained for different modeling assumptions and parameters in the model can be valuable for the improvement of validity of the model-based estimations. The present study is another contribution to this field. Using a sagittal plane model of an upper limb with a weight carried in hand, and applying the data of recorded flexion and extension movement of the upper limb, the resultant muscular forces are predicted using different modeling assumptions and simulation tools. This study relates to different coordinates (joint and natural coordinates) used to built the mathematical model, muscle path modeling, muscle decomposition (change in number of the modeled muscles), and different optimization methods used to share the joint torques into individual muscles.     

Modeling and simulation of powered hip orthosis by pneumatic actuators

In this study, a simulation model for a powered hip orthosis (PHO) with air muscles to predict the gait of paraplegics is presented which can be used as a design tool for hip orthoses. Before simulation, mathematical models for a human dummy with an orthosis and a pneumatic muscle actuator were generated. For the air muscle, coefficients required were obtained by static and dynamic experiments of the air muscle and experiments for the valve controlling the air pressure. The computation was conducted on the ADAMS package together with MATLAB. Computer simulation of the flexion of hip joints by the pneumatic muscle results in similar values to those from gait analysis. With the development of a simulation model for a PHO, the gait simulation model using pneumatic muscles can be used to analyze and evaluate the characteristics and efficiency of a PHO by setting the input and boundary conditions.     

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.     

手部运动计算机仿真的实现

根据手部自身的物理特性和生理特性,采用分层技术,严格按照手部解剖学,先建立其骨骼模型,在此基础上形成肌肉模型,最后在肌肉模型上附加一层皮肤。这样,骨骼运动引起肌肉的变形,随着皮肤也跟着发生相应的变化,使虚拟手模型无论从形状上还是运动上都能达到更高程度的逼真效果。     

气动机器人多指灵巧手——ZJUT Hand

总结了现有灵巧手的缺点,例如结构复杂、难以控制等,并在此基础上提出了一种新型的气动驱动多指灵巧手,命名为ZJUT Hand.基于一种新型的气动柔性驱动器FPA,设计了气动刚柔性弯曲关节及侧摆关节;在此基础上给出了一种4自由度气动拟人手指;为了获得较高的模块化集成度,将5个完全相同的手指装配在拟人手掌上,构成具有5个手指、20个自由度的ZJUT Hand的本体结构;采用仿生学优化方法确定ZJUT Hand的结构参数,并对其本体结构进行了抓持仿真实验.仿真结果表明:ZJUT Hand能够对圆柱、长条形、球形等典型形状的物体实现抓持,并能够模拟人手实现对捏、夹持、勾拉等复杂拟人手形.详细设计了ZJUT Hand的力/位传感系统.完成了ZJUT Hand的抓取实验,结果表明:ZJUT Hand能够对典型形状目标物体实现稳定抓取.最后,简单总结了ZJUT Hand的特色之处.     

A multibody biomechanical model of the upper limb including the shoulder girdle

The aim of this work is to propose a robust musculoskeletal model of the upper limb to serve as the basis for the study of different types of shoulder pathologies, including the use of anatomical or reverse prostheses. The multibody biomechanical model is defined by seven rigid bodies constrained by the sternoclavicular, acromioclavicular, and glenohumeral joints, each modeled as a three d.o.f. spherical joint; the humeroulnar and radioulnar joints, each modeled as one d.o.f. hinge joint; and the scapulothoracic articulation, modeled by two holonomic constraints that allow the scapula to glide over the thorax. The muscle system includes 21 muscles described by 37 individual segments using the obstacle-set method. The muscle contraction dynamics is represented by the Hill-type muscle model, being the activation of each muscle unknown. The muscle force sharing is a redundant problem in which an optimization technique is applied to find the muscle activations, and the corresponding muscle forces, by minimizing an objective function that represents muscle energy consumption. The fulfillment of the equations of motion of the biomechanical model are enforced and the stability of the glenohumeral joint and the scapulothoracic articulation is also imposed, thus providing two sets of constraints for the optimal problem. The validation of the model is carried out by comparing the results from an acquired motion, the abduction of the arm, with available data in the literature and with EMG data.     

虚拟人骨骼结构的多刚体系统建模方法研究

提出了一种虚拟人骨骼结构的多刚体系统模型,可有效地克服DH表示法只能适用于单链结构的缺陷．首先通过合理的简化与假设,给出了一种16关节、39自由度的虚拟人简化模型;然后将该虚拟人模型抽象成为一个各肢体间通过机械转动铰相连的多刚体系统;最后引入树模型与低序体阵列来表达虚拟人的骨骼结构．分析结果表明,文中方法除能够自然地表达虚拟人的复杂分支结构外,还可以容易地实现虚拟人模型的任意分辨率扩展,并具备递归计算的优点,具有广泛的适用性。     

Design optimization with respect to ergonomic properties

This paper introduces the idea of engineering design optimization with respect to ergonomic properties. The optimization is based on a detailed inverse dynamic analysis of the motion and forces of the human body. The problem of muscle recruitment calculation in inverse dynamics is introduced and solved via a min/max optimality criterion. The implementation of this criterion in the body modelling system AnyBody is described, and the use of the system is demonstrated on the sample problem of designing a hand saw. We conclude that the methodology is applicable but dependent on anthropometrically accurate body models.     

基于OPENGL的人体姿态数据仿真

依据人体的关节连接体层次结构,将各肢体抽象为简单的刚性几何实体,构建了人体骨骼模型,通过定义人体坐标和肢体局部坐标及其相互间的变换,描述了人体骨骼模型中各关节之间的相对位置和姿态的变化.详细论述了应用D-H方法分析人体上肢运动模型的方法,最后利用VC++构建了基于OpenGL技术的虚拟人体运动程序.该应用程序可以在虚拟环境中载入、驱动并显示一个三维虚拟人.它能够灵活的利用采集得到人体运动数据驱动虚拟人,可以应用于医学仿真、智能人机交互等领域.     

A non-linear model of shape and motion for tracking finger spelt American sign language

This work presents a piecewise linear approximation to non-linear Point Distribution Models for modelling the human hand. The work utilises the natural segmentation of shape space, inherent to the technique, to apply temporal constraints, which can be used with CONDENSATION to support multiple hypotheses and discontinuous jumps within shape space. This paper presents a novel method by which the one-state transitions of the English Language are projected into shape space for tracking and model prediction using an HMM like approach. The paper demonstrates that this model of motion provides superior results to that of other tracking approaches.     

基于个性和OCC的机器人情感建模研究

机器人不仅要具有简单的机械作业和逻辑推理能力，还应当具有类似人类的情感能力．本文将个性与情绪、情感、理解、表达相结合，采用OCC模型作为评价标准，建立了符合人类情感规律的、可用于情感机器人的情感模型。通过一个应用上述模型的虚拟人情感交互系统．验证了此模型可以很好的对人类的情感进行仿真．可以应用于情感机器人和人性化计算机、游戏等许多领域。     

基于分类特征提取的手部动作识别方法的研究及应用

提出一种基于分类特征提取的手部动作识别方法,该方法通过自适应的混合高斯模型构建背景模型,使用背景减除法并充分利用人体手部肤色信息分割出人体手部区域,结合手部关节、骨骼特征及肤色信息估算手部关节点位置,构建三维手部骨架模型,然后提取手部各关节角度、位置信息并利用隐马尔柯夫(HMM)模型对其所表示的动作进行训练识别。     

Real-time scheduling by parallel and distributed simulation over IP Multicast

Scheduling optimization of manufacturing processes becomes more and more important. Complex models with a lot of constraints cause a higher computational effort of the simulation. Optimization cycles of heuristic optimization algorithms like genetic algorithms or local search strategies can easily be scheduled in parallel. But recurrent requirements are the distribution of the model, the interchange of the parameters and results. The IP Multicast architecture is an ideal platform for distributing model data over the network. It reduces the network overhead for sending the model to different clients and simplifies also the initial setup between client and server. The client and the server are able to find each other automatically by preconcerted multicast channels. The developed test implementation is designed to work with the simulation system simcron MODELLER and will be used to handle typical optimization tasks like the weekly demand plan of a back-end process or optimal batch sizes for burn-in ovens. It is also suitable for educational purposes and we use it in practical courses where students learn more about factory scheduling. The system offers a high reusability for any operating sequence optimization problem in electronic or semiconductor manufacturing industry, as well as in other fields.     

一种基于改进UKF的3D人手跟踪算法

将手指作为基本处理对象，对UKF（unscented Kalman filter）算法进行改进，并利用它对当前手指各关节进行预测；以预测值作为初值，用局部搜索技术对误差较大的关节用改进的UKF算法重新进行预测，直到该手指在像平面上的投影轮廓和图像轮廓之间的距离图满足指定的精度为止．该算法以状态变量量测值的获取作为突破口，解决现有算法中跟踪精度过分依赖于3D人手模型精度的问题．实验结果表明，该算法具有较强的处理局部自遮挡问题能力，对3D人手模型的不精确性也具有更好的鲁棒性．     

Fatigue evaluation in maintenance and assembly operations by digital human simulation in virtual environment

Virtual human techniques have been used a lot in industrial design in order to consider human factors and ergonomics as early as possible, and it has been integrated into VR applications to complete ergonomic evaluation tasks. In order to generalize the evaluation task in VE, especially for physical fatigue evaluation, we integrated a new fatigue model into a virtual environment platform. Virtual Human Status is proposed in this paper in order to assess the difficulty of manual handling operations, especially from the physical perspective. The decrease of the physical capacity before and after an operation is used as an index to indicate the difficulty level. The reduction of physical strength is simulated in a theoretical approach on the basis of a fatigue model in which fatigue resistances of different muscle groups were regressed from 24 existing maximum endurance time models. A framework based on digital human modeling technique is established to realize the comparison of physical status. An assembly case in airplane assembly is simulated and analyzed under the framework in VRHIT experiment platform. The endurance time and the decrease of the joint moment strengths are simulated. The experimental result in simulated operations under laboratory conditions confirms the feasibility of the theoretical approach: integration of virtual human simulation into virtual reality for physical fatigue evaluation.