Virtual human simulation integrated into virtual reality applications is
mainly used for virtual representation of the user in virtual environment or
for interactions between the user and the virtual avatar for cognitive tasks.
In this paper, in order to prevent musculoskeletal disorders, the integration
of virtual human simulation and VR application is presented to facilitate
physical ergonomic evaluation, especially for physical fatigue evaluation of a
given population. Immersive working environments are created to avoid expensive
physical mock-up in conventional evaluation methods.

The paper presents a methodology for the enhanced stiffness analysis of
parallel manipulators with internal preloading in passive joints. It also takes
into account influence of the external loading and allows computing both the
non-linear "load-deflection" relation and the stiffness matrices for any given
location of the end-platform or actuating drives.

The paper focuses on the enhanced stiffness modeling of robotic manipulators
by taking into account influence of the external force/torque acting upon the
end point. It implements the virtual joint technique that describes the
compliance of manipulator elements by a set of localized six-dimensional
springs separated by rigid links and perfect joints.

It was shown recently that parallel manipulators with several inverse
kinematic solutions have the ability to avoid parallel singularities [Chablat
1998a] and self-collisions [Chablat 1998b] by choosing appropriate joint
configurations for the legs. In effect, depending on the joint configurations
of the legs, a given configuration of the end-effector may or may not be free
of singularity and collision.

This paper introduces a methodology to analyze geometrically the
singularities of manipulators, of which legs apply both actuation forces and
constraint moments to their moving platform. Lower-mobility parallel
manipulators and parallel manipulators, of which some legs do not have any
spherical joint, are such manipulators. The geometric conditions associated
with the dependency of six Pl\"ucker vectors of finite lines or lines at
infinity constituting the rows of the inverse Jacobian matrix are formulated
using Grassmann-Cayley Algebra.

The paper proposes a new calibration method for parallel manipulators that
allows efficient identification of the joint offsets using observations of the
manipulator leg parallelism with respect to the base surface. The method
employs a simple and low-cost measuring system, which evaluates deviation of
the leg location during motions that are assumed to preserve the leg
parallelism for the nominal values of the manipulator parameters. Using the
measured deviations, the developed algorithm estimates the joint offsets that
are treated as the most essential parameters to be identified.

This paper discusses the utility of using simple stiffness and vibrations
models, based on the Jacobian matrix of a manipulator and only the rigidity of
the actuators, whenever its geometry is optimised. In many works, these
simplified models are used to propose optimal design of robots. However, the
elasticity of the drive system is often negligible in comparison with the
elasticity of the elements, especially in applications where high dynamic
performances are needed.