Newsletter Volume 9 - 1st Quarter 2006
Active Human Response to a Vibration Environment
CONTENTS
Case Study: Active Human Response to a Vibration Environment.
Software: LifeMOD™ v2005.6.0 New Product Release!
Other News : MSC.Software veteran Brian Cheung appointed as vice president of marketing.
Publications: Journal Papers, Magazine Articles and Book Chapters
This issue presents a study on the active human response to a vibration environment. This study is based on ongoing work with our large commercial earth moving equipment partner, and is part of the ongoing research on Whole Body Vibration at the Virtual Soldier Research Program (VSR) at The University of Iowa (PI: Dr. Salam Rahmatalla, www.digital-humans.org).
We would like to announce that BRG has formed a new partnership with Vicon Peak to provide an integrated human modeling solution with motion capture technology. The Biomechanics Research Group's leading human modeling solution, LifeMOD™, with Vicon Peak MX Camera series, the leading in motion capture technology, are uniquely able to provide a state-of-the-art solution for medical device development, clinical rehabilitation, ride comfort, ergonomics, and sports performance applications. Through the newly formed partnership, Vicon Peak's 3D motion analysis systems will provide real-time, subject specific movement to plug-n-play with LifeMOD's human simulation.
This month's case study features a LifeMOD solution integrated with a Vicon Peak system to study human vibration in vehicles.
Contact BRG today at newsletter@lifemodeler.com for more information!
On the product development front, we are pleased to announce the release of LifeMOD™ Version 2005.6.0 with many new functions and features including a new scalable muscle geometry database for the entire body and scaling muscle graphics. We invite you to download a free trial version of the software; try out one of our 17 easy-to-follow tutorials and begin building physics-based human models today.
The staff at BRG is very pleased to announce the appointment of MSC.Software veteran Brian Cheung as vice president of marketing. Brian's group will continue to build a secure foundation of processes and mechanisms to sustain long lasting relationships with our customers and partners as well as to maintain LifeMOD as the de facto human modeling program in the world today.
CASE STUDY: ACTIVE HUMAN RESPONSE TO A
VIBRATION ENVIRONMENT
Introduction
Every day people are exposed to vibration in many ordinary activities such as riding in vehicles, working with vibrating machines, using power tools, etc. Severe or long-term exposure to vibration can affect comfort, safety and health of persons exposed. Since vibration is a common factor in the workplace, it is recognized as an occupation health hazard and should be treated as any other hazard such that it is controlled, eliminated or minimized.
In the construction and heavy mining equipment field, two types of human vibration are under investigation, whole body vibration and segmental vibration. Whole body vibration energy enters the body through a seat or the floor, it affects the entire body or a number of organs in the body. Segmental vibration exposure affects an organ, part or "segment" of the body.
Severity of vibration is determined by its magnitude, frequency, duration and direction. Each part of the human body has its own natural frequency of vibration, therefore the extent to which the human body is affected depends on the vibration frequency it is to which exposed.
To understand why human beings are more sensitive to some frequencies than to others, it is useful to consider the human body as having subsystems, where each subsystem has its own resonance frequency band and the interactions between subsystems are influenced by the body's position, for example, standing or sitting. Figure 1 displays a simplified human body subsystem classification with the resonance vibration frequency band for each.
Figure 1. Simplified human body subsystems and vibration frequency resonance band.
Human computer models can be developed to predict human subsystem vibration frequencies for a particular environment, a particular posture and particular interface configuration between the human and the environment. Computer models can also provide detailed information on the joint and muscle forces during the episode as well. By studying an active human model, or one which responds in an active way to the environment, information can be provided on human reaction and vibration adaptation or shielding.
In this study, a multi-axis vibration environment for an offroad heavy vehicle is examined using an active human model. This work is part of the ongoing research on Whole Body Vibration at the Virtual Soldier Research Program (VSR) at The University of Iowa (PI: Dr. Salam Rahmatalla, www.digital-humans.org).
Data for motion of the platform, the seat, and the body segments of the human test subject is collected using a video-based motion tracking system and used to develop a human model which responds to the vibration environment. The model is used to provide insight on human internal reactions, segment vibration frequencies and human adaptation to the vibration environment.
Data Collection
To study the human response to a vibratory environment of an offroad heavy vehicle, a human test subject was instrumented with retro-reflective markers used to track displacement data with a Vicon Peak motion capture system recording data at 100 hz.
A test cabin, complete with seat with suspension and driver controls, was used to simulate the actual vehicle under work loading conditions for periods of several minutes. The test cabin consisted of a 6 degree-of-freedom moving platform driven with data from the actual vehicle during a working activity. 3D Motion data was collected in separate files for the platform, the seat and the human subject. Figure 2 displays the instrumented testing platform, seat, controls and human test subject.
Figure 2. Test rig to simulate actual working conditions of the offroad heavy vehicle. The operator is rigged with photo reflective markers used to capture the motion during the exercise. Input to the rig is through a 6 DOF moving platform. (Courtesy of the University of Iowa, Virtual Soldier Research Program.)
Model Development
LifeMOD was used to develop a model of the operator used in the experiment. Forty seven specific body measurements were recorded from the operator and used in conjunction with the anthropometric library within LifeMOD to create the 19-segment human model, closely approximating the segment dimensions and mass properties of the operator.
A seat model complete with articulating rider controls was created and joined to a virtual model of the articulating platform. Contact forces were created between the human model and the seat, hands and the controls and the feet and the pedals. Figure 3 displays the model positioned in the vibration environment.
Figure 3. Simulation model complete with articulating platform, seat with suspension, 19-segment human model, and forces between the human model and the environment (seat, controls and foot pedals).
LifeMOD motion agents are automatically created at each reflective marker location from the data collection experiment. Motion agents are parts which will be driven using the recorded trajectory information from the experiment. Motion agents are created on the human model, the seat and the platform. Each motion agent spring forces is normalized to the relative accuracy of the specific reflective marker, thereby allowing for the most accurate reflective marker to contribute most to the model motion.
Figure 4. Motion agents are automatically created at the reflective marker locations in the experiment. They will drive the model to capture joint motion patterns to be used in a subsequent forward dynamics analysis.
With the human model created and positioned in the seat and the motion agents positioned at each reflective marker location, the model is now ready for inverse-dynamics analysis. During this dynamic simulation, the three-dimensional joint angles at each anatomical joint are recorded.
Next, the motion agents are removed from the human model, and proportional-derivative controllers are automatically generated by LifeMOD to create torques which drive the anatomical joints by minimizing the error between the desired angle and the instantaneous angle. With the torques now driving the joints, the model becomes an active human model.
For the active human simulation, the motion agents on the seat and the platform are still present and will be used to drive the seat and platform using the same data as in the previous simulation. With the motion agents removed from the human model, the human model will be free to bounce in the seat as well as to move via the joint torques.
Figure 5 summarizes the model building and simulation process.
Figure 5. Modeling process flow.
Results
Two types of model output were examined: the body segmental vibration and the active human response to the vibration. Figure 6 displays the input motion from the machine and the human model response via head and chest vibration patterns in the horizontal and vertical planes. From the plots it can be ascertained that the vibration frequencies for the head and chest are around 3 Hz and 1.5 Hz respectively, or far below the resonance frequencies displayed in figure 1.
Also, the graph indicates that the vibration frequencies of these body segments is much less that the input frequency of the driving platform indicating a large amount of damping or energy release between the platform and the body segments.
The question is: Other than the passive effects, how did the human actively shield his head from vibration and excessive motion?
Figure 6. Head and chest vibration in the horizontal and vertical planes.
To gain some insight into the human active vibration shielding, it is helpful to examine plots of the vertical plane velocity of the lower torso and the head, and relate these to neck torque function. (See Figure 6). It can be observed in this figure, that the pelvis velocity is of a greater magnitude than the head indicating a vibration damping effect or shielding by the human joint reactions. The trends indicate that when velocity of both segments changes, the neck torque peaks. This could represent a measure of anticipation of a rotational hyperextension.
This type of analysis was carried out in other planes and other joint combinations to characterize the human response to the environment from an internal reaction perspective.
Figure 7. Vertical plane neck torque compared to vertical plane head and pelvis velocities for a specific time slice of the simulation.
Conclusions
This study represents an ongoing effort into the study of active human response to vibration. This study will lead to efforts to characterize the response as an measure of comfort and chronic or acute injury potential. New techniques being developed for this project include new data collection methods and the development of specific modules to enhance LifeMOD's ability to support a general vibration environment.
SOFTWARE
The BRG is pleased to announce the release of LifeMOD™ version 2005.6.0. This new release makes state-of-the-art human modeling accessible to every investigator interested in the physics behind human motion. The release includes a new muscle parameters library which includes data on physiological cross sectional areas, maximum tissue stresses, etc. for each of the 212 muscles included in LifeMOD. These properties also scale based on the body size, weight, age and gender. In addition the user may affect the muscle output from 5 times normal to 0 (off) to perform muscle imbalance or weakened studies.
A new graphical animation feature has been introduced which allows for the scaling of the muscle graphics and joint graphics based on force and torque magnitudes.
A new generalized contact algorithm which permits general contact between any two surfaces has been introduced. This allows for sophisticated modeling of knee joints, as well as external contacts between the body and the environment.
Due to the tremendous response we received from our users for our "trainable" muscles, we have introduced several more muscle groups to ensure LifeMOD's position as the most powerful, versatile and ease-to-use full-body human modeling package available today.
This new version is a direct result from an ongoing and rigorous user dialogue, partnerships with our research community, and the inclusion of much functionality developed by our professional staff to solve the world's most demanding biomechanics issues. View Examples...
SERVICES
The Biomechanics Research Group Inc. is a service-based organization chartered to
empower customers to capture a level of ROI from their technology investment in ways
they have never imagined. We are committed to customer service, product excellence
and continuous improvement in everything we do. We provide training, modeling and
simulation expertise. Contact us for more information.
OTHER NEWS
The Biomechanics Research Group (BRG) and Vicon-Peak are announcing a global strategic partnership. Together, BRG's leading human modeling solution and Vicon's leadership in motion capture cameras represent a state-of-the-art solution for medical device development, clinical rehabilitation, ride comfort, sports performance, and more. The partnership will start with deeper product integration and bundled LifeMOD MX Camera solutions. The partnership will continue to look for ways in which the two companies can better support our customers. Contact BRG today for more information!
The staff at BRG would like announce the appointment of MSC.Software veteran Brian Cheung as vice president of marketing. Brian's group will continue to build a secure foundation of processes and mechanisms to sustain long lasting relationships with our customers and partners, as well as to maintain LifeMOD as the de facto human modeling program in the world today. Brian brings a wealth of global marketing experience including Global Industry Business Development manager for several markets at MSC.Software.
New book chapter: "Chapter 24: The Virtual Knee" in Total Knee Arthoplasty, Springer 2005. See PDF
New Publication: "Effect of Guided Knee Motion and High Flexion TKA on Kinematics, Implant Stresses, and Wear" American Academy of Orthopaedic Surgeons 2006 Annual Meeting See PDF
New Publication: "Modeling Alpine Skiing using LifeMOD" INSA Toulouse Presentation (in French) See PDF
Check out our new model repository! We would like to sincerely thank those who have contributed to the LifeMOD— body of knowledge. We pledge to do our best to expand the technical capabilities of LifeMOD while developing new ways to educate the community.
If you would like further information on our software and services, please contact us.
Copyright© 2006 LifeModeler, Inc.