Human motion simulation for vehicle and workplace design

Digital Human Models (DHMs) are fast becoming an effective tool for performing proactive ergonomics analysis and design. DHM software, such as Jack, SAFEWORK, RAMSIS, SAMMIE, and the UM 3DSSP, are meant to assist a designer early in a product development process, when he or she is attempting to improve the physical design of vehicle interiors and manufacturing workplaces. To become even more effective in meeting such a goal, it is proposed that future DHMs must include valid posture and motion prediction models for various populations. It is argued in this article that existing posture and motion prediction models now used in DHMs must be based on real motion data to assure validity for complex dynamic task simulations. It is further proposed that if valid human posture and motion prediction models are developed, these can be combined with psychophysical and biomechanical models to provide a very powerful tool for predicting dynamic human performance and population specific limitations. © 2007 Wiley Periodicals, Inc. Hum Factors Man 17: 475–484, 2007.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/56152/1/20087_ftp.pd

Development of computerized human static strength simulation model for job design

This article describes the development of models to predict population static strengths and low back forces resulting from common manual exertions in industry. The resulting biomechanical models are shown to be valid for their intended purposes, but limitations still exist. In particular, they are meant to aid in evaluating very slow or static exertions, such as when carefully lifting, pushing, or pulling on heavy objects, but do not allow dynamic exertions to be simulated. It is shown that use of these models in the early design of workplaces and equipment is dependent on the use of computerized homonoids and behavioral-based inverse kinematic algorithms in conjunction with CAD systems. © 1997 John Wiley & Sons, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/35211/1/3_ftp.pd

Predicting Foot Positions for Manual Materials Handling Tasks

Copyright © 2005 SAE International For many industrial tasks (push, pull, lift, carry, etc.), restrictions on grip locations and visibility constrain the hand and head positions and help to define feasible postures. In contrast, often the foot locations are minimally constrained and an ergonomics analyst can choose several different stances in selecting a posture to analyze. Also, because stance can be a critical determinant of a biomechanical assessment of the work posture, the lack of a valid method for placing the feet of a manikin with respect to the task compromises the accuracy of the analysis. To address this issue, foot locations and orientations were captured in a laboratory study of sagittal plane and asymmetric manual load transfers. A pilot study with four volunteers of varying anthropometry approached a load located on one of three shelves and transferred the load to one of six shelves. The data illustrate foot placements and behaviors that depend on pickup heights, the use of one or two hands to grasp the object, and the participantsʼ body dimensions. Two distinct pickup and delivery strategies were observed. Split stance, with one foot in front of the other, was markedly more frequent than parallel stance with the feet side by side. A statistical model was developed to predict foot placements at load pickup. This study confirms the importance of this topic and provides the basis for the much more comprehensive study that is now underway

A biomechanical evaluation of five lifting techniques

Five lifting methods which cover the range of techniques recommended by various back schools have been biomechanically analysed with a static sagittal-plane computer model. The analysis was performed with two load-types (compact and bulky) and three weights in the hands (44 N, 222 N and 400 N). The methods were compared in terms of predicted L5/S1 disc compression, low-back ligament strain and strength requirements at the shoulders, L5/S1, hip and knee joints. In general the method entailing a squat posture, straddle foot stance and flat back (oriented as when standing erect) yielded lower compressions, ligament strains and overall strength requirements than the other methods.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26237/1/0000317.pd

Some biomechanical aspects of the carpal tunnel

Previously presented evidence indicates that carpal tunnel syndrome is related to compression of the median nerve inside the carpal tunnel. Biomechanical arguments in which the extrinsic finger flexor tendons inside the carpal tunnel are characterized as a frictionless pulley-belt mechanism are presented to show quantitatively how wrist size, wrist position and hand position affect forces on the tendons and their adjacent structures.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23744/1/0000716.pd

An investigation of the relationship between displacements of the finger and wrist joints and the extrinsic finger flexor tendons

Several investigators have developed biomechanical models of finger flexor tendon displacements during pinching or gripping exertions of hands. Landsmeer has developed the most comprehensive set of models for this purpose. This paper describes experiments in which various sized cadaver hands were used to statistically evaluate the Landsmeer models. In so doing, the effects of hand and wrist anthropometry are included. The results indicate that the tendons displace in relation to joint positions as described by that Landsmeer model in which the tendon is depicted as sliding over the curved articular surface of the proximal bone of the joint. Joint thickness effects were found to modify the parameters in the model as intuitively expected. An empirical prediction model of the anthropometric effects was developed. Further, the tendon displacements for various wrist orientations were expressed empirically for the first time and were shown to be consistent with expected anatomical considerations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22712/1/0000267.pd

Validation of a biodynamic model of pushing and pulling

Pushing and pulling during manual material handling can increase the compressive forces on the lumbar disc region while creating high shear forces at the shoe-floor interface. A sagittal plane dynamic model derived from previous biomechanical models was developed to predict L5/S1 compressive force and required coefficients of friction during dynamic cart pushing and pulling. Before these predictions could be interpreted, however, it was necessary to validate model predictions against independently measured values of comparable quantities. This experiment used subjects of disparate stature and body mass, while task factors such as cart resistance and walking speed were varied. Predicted ground reaction forces were compared with those measured by a force platform, with correlations up to 0.67. Predicted erector spinae and rectus abdominus muscle forces were compared with muscle forces derived from RMS-EMGs of the respective muscle groups, using a static force build-up regression relationship to transform the dynamic RMS-EMGs to trunk muscle forces. Although correlations were low, this was attributed in part to the use of surface EMG on subjects of widely varied body mass. The biodynamic model holds promise as a tool for analysis of actual industrial pushing and pulling tasks, when carefully applied.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29656/1/0000745.pd

Effects of Pacing When Using Material Handling Manipulators

Common manipulator-assisted materials handling tasks were performed in a laboratory simulation at self-selected and faster (paced) speeds. The effects of pacing on peak hand forces, torso kinematics, spine moments and forces, and muscle antagonism were determined, along with any influences of several task variables on these effects. The faster trials were performed 20% more rapidly than the self-paced trials. It was found that (a) achieving this level of performance required 10% higher hand forces and 5%-10% higher torso moments, (b) consistent torso postures and motions were used for both speed conditions, and (c) the faster trials resulted in 10% higher spine forces and 15% higher levels of lumbar muscle antagonism. On whole, these results suggest a higher risk of musculoskeletal injury associated with performance of object transfers at faster than self-selected speeds with and without a manipulator. Further analysis provided evidence that the use of manipulators involves higher levels of motor coordination than do manual tasks. Several implications regarding the use of material handling manipulators in paced operations are discussed. Results from this investigation can be used in the design, evaluation, and selection of material handling manipulators.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67067/2/10.1518_001872099779591240.pd

Simulating Reach Motions

Modeling normal human reach behavior is dependent on many factors. Anthropometry, age, gender, joint mobility and muscle strength are a few such factors related to the individual being modeled. Reach locations, seat configurations, and tool weights are a few other task factors that can affect dynamic reach postures. This paper describes how two different modeling approaches are being used in the University of Michigan Human Motion Simulation Laboratory to predict normal seated reaching motions. One type of model uses an inverse kinematic structure with an optimization procedure that minimizes the weighted sum of the instantaneous velocity of each body segment. The second model employs a new functional regression technique to fit polynomial equations to the angular displacements of each body segment. To develop and validate these models, 38 subjects of widely varying age and anthropometry were asked to perform reaching motions while seated in simulated vehicle or industrial workplace. Between 48 and 72 reaches were required of each subject, for a total of over 7000 reaches. During these motions a Qualysis motion capture system was combined with an Ascension Technology Corporation Flock of Birds system to record the movements of each person's torso, shoulders, arm, forearm and hand. The paper discusses how the models differ in construction and performance, and how our existing biomechanical models can be linked to the new kinematic models for improved dynamic ergonomic evaluations. Ongoing research being conducted on human motion simulations at the University of Michigan's HUMOSIM Laboratory also is described

Isometric and isokinetic back and arm lifting strengths: Device and measurement

This study was conducted to measure isometric (static) and isokinetic (dynamic) back and arm lifting strengths at 20, 60 and 100 cm s-1 of young adults. Ten male and ten female volunteers without a history of back pain participated. The isokinetic lifting task was achieved by designing and fabricating a servo controlled motorized dynamic strength tester (DST). A regression analysis and analysis of variance was carried out on the strength data. The peak static strength values were significantly greater from the peak dynamic strength values. The peak dynamic strength was inversely related to the speed of motion. There were significant differences between the dynamic strengths at different stages of lift.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27450/1/0000490.pd