Training of Procedural Tasks Through the Use of Virtual Reality and Direct Aids - Virtual Reality and Environments - page 55

2. The simulation thread validates the motion requested by the trainee according to the task,
for example: detecting collisions of the model in movement, simulating an operation or
constraining the motion of trainees along a specific path, etc.
3. The rendering thread updates the graphical rendering of the virtual scene, sends the
requested audio feedback at each time, processes the commands of the trainees (i.e.
making a zoom in, rotating the view, etc.) entered by the keyboard or the switches of
the haptic device and controls the training process.
Fig. 6. Multi-thread solution implemented in the IMA-VR system.
The main components of the new training system are:
• Graphics Rendering Module : it loads and displays the virtual scenario from a VRML file.
Each object is represented by a triangle mesh and a transformation matrix. This module
also includes some features to simulate the visual deformation of flexible objects as cables.
• Haptic Rendering Module: it analysis the collisions between the user and the scene
for exploration tasks and between the object in movement and the rest of the objects
for manipulation tasks. This module also supports two haptic devices working
simultaneously to simulate bi-manual operations.
• Operation Simulator: it simulates some of the most common operations of a
assembly/disassembly task such as: insert/remove a component in/from another one,
align two components along an axis, etc.
• Virtual Fixtures Module :theterm virtual fixture is used to refer to a task dependent aid
(visual, audio or haptic aid) that guides the motion and actions of users. This module
provides both visual and haptic fixtures. Examples of visual fixtures are: changing the
color of a virtual object, making a copy of an object and displaying it in a specific position,
rendering auxiliary virtual elements such as arrows, trajectories, reference planes, points,
etc. The output of the haptic fixtures is rendered in the form of forces dependent on the type
of fixture: e.g. trainees can receive forces in order to constraint their hand-motion along
a specific path or just attraction/repulsion forces with different levels of force and areas
of influence (a surrounding area of a object or the whole-working space). This library of
virtual fixtures is the basis of most of the training strategies provided by the system.