Development of a Dynamic Biomechanical Model for Load Carriage: Phase 4, Part C4: User's Manual for the Standardized Protocol of Mapping Skin Contact Pressure Using the Standardized Load Distribution Mannequin PDF Download

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Languages : en
Pages : 42

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The Dynamic Biomechanical Model (DBM) requires input about pack geometry and the material property response of the load carriage suspension interface to resolve the forces acting on the body. Since there is extensive redundancy in applied forces (i.e., shoulder straps, load lifter straps, hip stabilizer straps and waist belt and skin contact pressure), it is not possible to describe the mechanical characteristics of pack components as combinations of linear and/or non linear springs and linear and/or non linear dampers unless a standardized protocol is used to determine the limit values that should be placed on specific straps in the model. The purpose of this report is to describe the common pack protocol on the Load Distribution Mannequin that will be followed when establishing these limit values for the DBM. The rationale for using the static Load Distribution Mannequin is that forces can be partitioned into upper and lower body forces, it is easier to control strap force inputs than with the Load Carriage Simulator and dynamic forces follow a similar profile to static measures expect that amplitudes and phase shifts are likely. (DBM model is calibrated for these conditions using the LC Simulator). This report describes the protocol for the baseline testing of backpacks on the Standardized Load Distribution Mannequin (SLDM). The protocol describes three different configurations: isolated shoulder, isolated waist belt and combined shoulder and waist belt.

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Languages : en
Pages : 32

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A variety of pressures mapping technologies have been used to assess contact pressures between human tissues and solid flat surface materials. However, research on the accuracy, repeatability, and creep for these technologies is limited. Three commonly used technologies were evaluated for accuracy, repeatability, and creep on a flat surface under highly controlled laboratory conditions. The systems tested included a resistive ink technology known as the F-scan F-socket (Tekscan Incorporated), a piezoresistive technology known as the FSA seat mat (Vista Medical, Limited), and a capacitance technology known as the XSENSOR seat mat (XSENSOR Technology Corporation). Loads between 9.392 kg and 19.627 kg were placed on each sensor using three standardized protocols: an incremental, a low threshold and a creep protocol. The XSENSOR(Registered) and FSA pressure measurement systems were superior to the F Scan system in terms of accuracy, although the XSENSOR was more accurate than the other two systems at low threshold pressures. The main drawback of each system at this time is the long settling time needed to get more accurate data due to creep. This needs to be corrected within the software of each system. For use in human load carriage, there will need to be adjustments in amplitude and creep characteristics.

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Languages : en
Pages : 23

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Soldiers, who transport equipment by foot, experience dynamic pressures as a result of personal load carriage equipment. To understand how these dynamic pressures affect soldier tolerance and performance, pressure measurement equipment must be able to accurately and repeatable measure changing applied pressures to the skin. Two modern pressure measurement systems with potential for application on human subjects were examined in this study: a piezoresistive technology by Vista Medical, Ltd., and a capacitance system by XSENSOR Technology Corporation. Each system was tested to determine the accuracy and repeatability to highly controlled, standardized dynamic loading. To examine pressure sensor performance, each pressure sensor was cyclically loaded by an Instron 5500 R using a standardized protocol in each sensor's calibration range. Results showed the XSENSOR had showed better accuracy compared to the FSA, since the XSENSOR measured a force that was 64% of the peak force applied to the sensor; whereas the FSA measured a force that was 49% of the actual applied force. Further, the XSENSOR showed better repeatability for peak forces (1.3% coefficient of variation) compared to the FSA (20.8% coefficient of variation). Results suggest that both systems have poor accuracy in comparison to the Instron; however, the low coefficient of variation for the XSENSOR means that an algorithm could be built to correct for the slow response time of the system. Further research is required to improve the accuracy and repeatability of the XSENSOR for dynamic research applications.

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Languages : en
Pages : 39

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Soldiers experience pressure as a result of their personal load carriage system acting on the shoulder and back. As such, an experimental measurement tools must be able to accurately and repeatability measure pressures on these curved surfaces. The purpose of this study was to examine pressure measurement systems on curved surfaces resembling the shoulders and the hips. To accomplish this, a method developed by Hadcock (2002) that resolves normal force vectors into vertical and horizontal components was used to test the validity using two different pressure measurement technologies: the XSENSOR X36 model by XSENSOR Technology Corporation and the F Scan (F socket series) model by Tekscan Incorporated. The testing jigs used in this study were a cylindrical shape for the shoulder and an elliptical shape for the hips. Under ideal test conditions, results showed that the XSENSOR had a 2% accuracy error on the shoulder and 4% accuracy on the hip, which is notably better than the 72% accuracy error on the shoulder model and 53% accuracy error for the hip model found for the F Scan. The F Scan errors were due primarily to working at the low end of the sensor's range and bending the mylar around a 114 mm diameter cylinder that induces a preload on the sensels.

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Languages : en
Pages : 52

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The purpose of this DRDC dynamic biomechanical model research program is to improve the understanding of human load carriage capabilities and to understand the effects of load carriage design features on human health and mobility. This research is directed at creating a method of determining several of the biomechanical factors to be used as inputs to the Load Conditions Limit model as described in DRDC report# W7711-0-7632-01 entitled "Proposed Long Range Plan for a Research and Development Program of Dynamic Load Carriage Modeling." In the current study, a 3D solid model was split into an upper and lower torso coupled with a rigid join located at the location of the spine at the L3/L2 height. Acceleration histories of subjects wearing packs were previously recorded during human trials. Acceleration of a person was numerically integrated and used to drive the motion of the Dynamic Biomechanical Model (DBM) torso. Torso accelerations for a wide range of activities were recorded and can be used to drive these models, creating an excellent data base for many human and pack motions for current and future modeling of human motions. This technique of capturing and generating motions is applicable to many situations where an envelope of human motion and body accelerations needs to be tested to ensure equipment does not cause excessive dynamic loading on the soldier. Piecewise linear dynamic, static and creep material response models were developed for typical backpack materials. In addition, a piecewise linear model of the dynamic stress strain response for the Clothe the Soldier shoulder strap assembly was developed. The model estimates reaction forces and moments on the lumbar spine and the total shoulder reaction force. The model also calculates the distribution of force to the upper and lower torso and the total contact force.

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Languages : en
Pages : 74

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Part A of Phase I of the contract was to develop the instrumentation so that a dynamic biomechanical model could be developed. The specific objectives were: (a) to develop Fastrak(TM) software for relative pack person motion, (b) construct smaller strap force gauges, (c) build and calibrate a moment of inertia platform, (d) modify the Load Carriage compliance tester to automate two degrees of freedom and (e) create a full body mapping of mannequin. This report describes the purposes and outputs available from the pack person motion, describes the development, construction, calibration and protocol for use of smaller strap sensors and the moment of inertia platform, and the development and steps involved in modifying the LC compliance tester and the mannequin mapping. For the most part, tasks were developmental and construction based with no data analyses, other than to confirm the accuracy and precision of the instrumentation. This report deals only with Part A consisting of five sub parts of the contract. Part B involved changing the technical manuals based on the upgrades stated within this report. Part C of this contract is under separate cover and was to develop a long range plan and budget for dynamic biomechanical modeling. Part D was to assist with the NATO HFM Specialist Meeting entitled "Soldier Mobility: Innovations in Load Carriage System Design and Evaluation" held on 27-29 June 2000. Part D is described by the NATO RTO MP 56 Technical Proceedings Report entitled: "Soldier Mobility: Innovations in Load Carriage System Design and Evaluation."

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Category :
Languages : en
Pages : 297

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Languages : en
Pages : 98

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Soldier operational performance is impacted by a number of factors including physiological workload, the biomechanical effects of equipment used in the field, demographics and soldier readiness. The specific objectives of the work reported here are to identify components of a load carriage limit (LCL) equation specifically related to the physiological workload and biomechanical effects, and to further the development of a dynamic biomechanical model (DBM) for load carriage. The ultimate goal of this research program is to develop and fully validate an LCL equation, which includes all relevant factors and which can be used to predict the operational effectiveness of soldiers in the field. Data were collected in a previous contract on 10 physically fit male subjects. In the DBM development, a skin layer with appropriate properties was created for the torso model and the modeling of all relevant pack components that form the person-to-pack interface has been completed. Stress analyses, in the equilibrium state, for the skin layer, and the shoulder strap and waist belt contact regions were done. A library of material properties for biological (skin on the back, skin toughened, skin over bone) and pack materials, both individually and in combination, has been compiled. Completion of the DBM will entail validating the motion and stress response of the DBM against existing test data, improving the user interface, and adding an output format that will provide the biomechanical factor for input into the LCL equation.

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Languages : en
Pages : 33

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The overall purpose of this is to improve the understanding of human load carriage capabilities. Earlier phases of the dynamic biomechanical model have lead to a new modeling approach that treats the pack person interface as a dynamic suspension system. In the current study, both 2D and 3D dynamic modeling software packages were selected to permit multiple models of the pack person suspension characteristics. The selected software both permit full user control of model geometry, inertial properties, have extensive libraries of existing dynamic elements for modeling constraints, allow the user to construct complex constraint equations and allow the user to input complex forcing functions. For both the 2D and 3D models, two types of dynamic tests were conducted to determine the impulse response and the natural frequencies. For the 2D model, the impulse response test showed typical results for a mildly under damped system with the amplitude ratio plot showing a modest peak at approximately 8 Hz, higher than the estimated natural frequency of 4.8 Hz. On the other hand, the impulse response test for the 3D model gave a vertical displacement typical of an over damped system and an amplitude ratio plot with several resonant frequencies at approximately 2.5 Hz and again at 5 Hz. With the damping reduced by a factor of 100, there were some initial oscillations of the system followed by a slow decay in the vertical position and as expected, the minimally damped 3D model displayed a dominant natural frequency at approximately 5 Hz. Overall, the 2D model required much higher damping coefficients to bring about a pack displacement pattern similar to that of the 3D model. In addition, the 3D model behaviour was more consistent with the physical system. The next stage in model development is to integrate a waist belt model (Hadcock, 2002) being developed separately into the 3D model.

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Languages : en
Pages : 117

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In previous studies, two biomechanical models were developed that used pack and person geometry as well as pack mass to determine the reaction forces on the body. One problem has been determining the pack-person interface forces using Tekscan(TM) pressure sensors on rounded surfaces such as the shoulder and waist. The goal of this study was to determine design factors that affect force distribution of the backpack waist belt. A human-sized symmetrical lower torso (SLT) was created. A method of calculating the directional coordinates of applied forces was developed in order to understand the reactions between pack and person. Tekscan(TM) Sensors were used to measure the surface pressures between the torso and the waist belt. These were converted to normal force measures based on the mathematical coordinates of each sensel. Calibration factors, a factor of effective sensel area and a frictional coefficient for the in situ orientation of each sensor were calculated and used for the calculation of the directional forces. Then, using sites on the waist belt, known forces were applied and the resulting directional forces correlated moderately well with the known applied forces (19%). The pressure distributions of three waist belts were compared and the design features were examined to account for differences in distribution. The distributions were compared to results of the previous biomechanical models and determined to be too complex to be resolved with the simplified hoop stress theory. The study determined the importance of waist belt design, frictional force from belt tightening, and influence of load in understanding the force distribution of a waist belt. It is recommended that each pack and load condition be tested using this approach if one wishes to use the waist strap force gauge to determine compressive forces on the lumbar spine and on the hips.