Research Papers

Digital Human Forward Kinematic and Dynamic Reliabilities

[+] Author and Article Information
James Yang

e-mail: james.yang@ttu.edu
Human-Centric Design Research Laboratory,
Department of Mechanical Engineering,
Texas Tech University,
Lubbock, TX 79409

1Corresponding author.

Contributed by the Design Automation Committee of ASME for publication in the Journal of Mechanical Design. Manuscript received October 29, 2012; final manuscript received April 4, 2013; published online xx xx, xxxx. Assoc. Editor: Matthew B Parkinson.

J. Mech. Des 135(7), 071008 (May 24, 2013) (10 pages) Paper No: MD-12-1565; doi: 10.1115/1.4024234 History: Received October 29, 2012; Revised April 04, 2013

Probabilistic methods have been applied to many problems in various fields of study. There are many distinct applications of probabilistic design in the biomechanics field, in particular. Traditionally, deterministic methods have been applied in digital human modeling (DHM). Transforming the deterministic approach of digital human modeling into a probabilistic approach is natural since there is inherent uncertainty and variability associated with DHM problems. Typically, deterministic studies in this field ignore this uncertainty or try to limit the uncertainty by employing optimization procedures. Often, inverse kinematics or dynamics techniques are introduced to point the system to the desired solution, or “best solution.” Due to the variability in the inputs, a deterministic study may not be enough to account for the uncertainty in the system. Probabilistic design techniques allow the designer to predict the likelihood of an outcome while also accounting for uncertainty, in contrast to deterministic studies. The purpose of this study is to incorporate probabilistic approaches to a deterministic DHM problem that has already been studied, analyzing human forward kinematics and dynamics. The problem is transformed into a probabilistic approach where the human forward kinematic and dynamic reliabilities are determined. The forward kinematic reliability refers to the probability that the human end-effector position (and/or orientation) falls within a specified distance from the desired position (and/or orientation) in an inverse kinematics problem. The forward dynamic reliability refers to the probability that the human end-effector position (and/or velocity) falls within a specified distance from the desired position (and/or velocity) along a specified trajectory in the workspace. The dynamic equations of motion are derived by the Lagrangian backward recursive dynamics formulation.

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Fig. 1

Twenty one DOF human model

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Fig. 2

Pregnant female pulling simulation

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Fig. 3

Forward kinematic reliability results for 100 sets of joint angles

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Fig. 4

PDF of the position error (first time step) of the forward kinematic reliability simulation

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Fig. 5

Forward dynamic reliability results for 100 time steps: In trial 2, the standard deviations, {στ,σL,σm,σIj}, of the input random variables, RVd={τ,L,m,Ij}, are double that of trial 1

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Fig. 6

PDFs of the position error (first time step) of the forward dynamic reliability simulations




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