Haptic Technology

Topics: Virtual reality, Haptic technology, Wired glove Pages: 5 (1337 words) Published: February 26, 2010
1.1 What is *Haptics*?
Haptics refers to sensing and manipulation through touch. The word comes from the Greek ‘haptesthai’, meaning ‘to touch’. The history of the haptic interface dates back to the 1950s, when a master-slave system was proposed by Goertz (1952). Haptic interfaces were established out of the field of tele- operation, which was then employed in the remote manipulation of radioactive materials. The ultimate goal of the tele-operation system was "transparency". That is, an user interacting with the master device in a master-slave pair should not be able to distinguish between using the master controller and manipulating the actual tool itself. Early haptic interface systems were therefore developed purely for telerobotic applications. {draw:frame} {draw:frame}

Fig.2.1Basic architecture for a virtual reality application incorporating visual, auditory, and haptic feedback. • Simulation engine: • Visual, auditory, and haptic rendering algorithms: Compute the virtual environment’s graphic, sound, and force responses toward the user. • Transducers:

Convert visual, audio, and force signals from the computer into a form the operator can perceive. The human operator typically holds or wears the haptic interface device and perceives audiovisual feedback from audio (computer speakers, headphones, and so on) and visual displays (a computer screen or head-mounted display, for example). 2.2 System architecture for *haptic* rendering:

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Fig 2.2Haptic rendering divided into main three blocks
*S- contacts* occurring between an avatar at position X and objects in the virtual environment. Fd- *return* the ideal interaction force between avatar and virtual objects. Fr- Force to the user

1.Collision-detection algorithms detect collisions between objects and avatars in the virtual environment and yield information about where, when, and ideally to what extent collisions (penetrations, indentations, contact area, and so on) have occurred. 2.Force-response algorithms compute the interaction force between avatars and virtual objects when a collision is detected. This force approximates as closely as possible the contact forces that would normally arise during contact between real objects. Hardware limitations prevent haptic devices from applying the exact force computed by the force-response algorithms to the user. 3.Control algorithms command the haptic device in such a way that minimizes the error between ideal and applicable forces. The discrete-time nature of the haptic- rendering algorithms often makes this difficult. The force response algorithms’ return values are the actual force and torque vectors that will be commanded to the haptic device. Existing haptic rendering techniques are currently based upon two main principles: "point-interaction" or "ray-based". In point interactions, a single point, usually the distal point of a probe, thimble or stylus employed for direct interaction with the user, is employed in the simulation of collisions. The point penetrates the virtual objects, and the depth of indentation is calculated between the current point and a point on the surface of the object. Forces are then generated according to physical models, such as spring stiffness or a spring-damper model. In ray-based rendering, the user interface mechanism, for example, a probe, is modeled in the virtual environment as a finite ray. Orientation is thus taken into account, and collisions are determined between the simulated probe and virtual objects. Collision detection algorithms return the intersection point between the ray and the surface of the simulated object. *2.2.1 Computing contact-response forces*:

Humans perceive contact with real objects through sensors (mechanoreceptors) located in their skin, joints, tendons, and muscles. We make a simple distinction between the information these...
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