Haptic Interaction

The CREATE project involves two kind of haptic interaction:

• Fine surface exploration, that allows to feel the shape and surface details of the objects accurately;
• Object Manipulation, that allows to get the sense of weight and inertial properties of the objects.

Haptic rendering is managed by a software module, implemented between the following components:

• An high performance Force Rendering component, capable of rendering fine interaction with complex shaped 3D objects and based on state of art haptic rendering techniques (Force Shading, Static/Dynamic Friction, Texture Rendering);
• A PBM (Physical Based Model) engine, based on Rigid Body Dynamics capable of simulating physic behaviour of several objects and replicating physical effect on the haptic interface.

In order to grant the best compromise between system performance and haptic rendering quality, two kind of model are used for each object of the Virtual Environment:

• Haptic Model: a high complexity 3D model, provided with haptic properties like tactile friction and stiffness, and surface description
• Physical Model: a low complexity 3D model, mass, inertial and bouncing properties, inter-object friction, etc…

The geometric models of the bodies for the haptic rendering must be very detailed to supply a realistic tactile feeling of the objects surfaces. The bodies are complex polygonal (e.g. triangles specified in Vrml format) meshes that describe a lot of objects details, allowing operation like grasping and contour following.

Each CREATE scenario is modelled as a Rigid Body System, where objects are Rigid Bodies, optionally connected through mechanical constraints.
During application execution the whole physical environment evolves through the interaction between bodies and the external input management (such as HI manipulation), under the control provided by an Ordinary Differential Equation (ODE) integrator, that must grant high performances and system stability. To simulate a physical environment is necessary to provide a geometry model of the involved objects. The more this model is detailed, the more the PBM engine works in a realistic way, because it’s able to accurately determine collisions contacts between objects and correctly manage responses and equilibrium conditions.
The CREATE PBM-engine works with simple types of objects like cube, parallelepiped, cylinder and sphere that can be translated and rotated in space and rigidly interconnected. So each body in the scenario environment is decomposed in simpler objects that approximate the original bodies.