Virtual Reality
By: Sadwika Salain
Haptic aka Virtual Reality is a sense of touch caused by feedback force resulted from interaction with an object. Such interaction may form in three distinction; human to a real object, robot end effector with the real object or human and simulated object.
MA. Sinivasan (1997) subdivided haptic into three areas:
- Human haptics. In this area, haptic is used to study human sensing and manipulation through touch.
- Machine haptics. Haptic is involved in designing, constructing to either replace or augment human touch.
- Computer haptics. On this division, haptic is aimed at generating and rendering the touch and feel of virtual objects using algorithms and associated software.
Applications
Nowadays, haptic has wide range of use starting from study and research purposes, medical application, entertainment and the latest – communication.
In medical field, using haptic in Medical Simulations is prevalent. “Just as flight simulators are used to train pilots, the multimodal virtual environment system we have developed is being used in developing virtual reality based needle procedures and surgical simulators that enable a medical trainee to see, touch, and manipulate realistic models of biological tissues and organs.” MA. Sinivasan (Retrieved 20 November 2008).
This statement can be conceded easily as haptic does offer several benefits compared to those conventional techniques, such as:
- Risk-free
As it works on simulated-device – not the real patients – haptic application is risk-free learning method.
- Repeatable
The haptic device lets the student, practitioners and resident to repeat the process without any worrisome hurting someone etc. This repeatability will significantly improve the proficiency of the student, practicians or anyone who use this device. This repeatable simulation cannot be applied whenever the patients are human.
- Near-Real
Haptic is able to provide visual, physiological and tactile realism that mimic the real procedure.
- Various Scenario
Haptic is easily adjusted to highest and complex procedure that rarely happen in reality. This wide variety allows student, practical complex problem
- Comprehensive Learning
Along with the traditional training methods, haptic provide a comprehensive learning opportunity by combining multiple elements.
- Objective Assessment
- Effective for Certification
Haptic Rendering
Basic process of haptic simulation can briefly describe as below (Salisbury K, Conti F, 2004):
- Human Operator
Human operator operates the haptic device based on the guidance of video and audio on the computer screen. Regarding the way how the operator communicate to the system, he/she communicates reversibly to the haptic device, yet one way-communication to the screen as he/she just receives the command (no input can be made) from the screen.
- Video and Audio
- Simulation Engine
It is responsible to compute the virtual environment behaviour over time
- Video, Audio and Haptic Rendering
In this stage, the inputs are translated into computational processes using the rendering algorithms. THe outputs are virtual environment, sound, graphics, sound and force feedback.
- Haptic Device
It behaves either as a sensor or as a transducer. As a sensor, its task is to convert the input (e.g position and speed changes) into electrical signal that can be understood by the system. While, as a transducer, it is responsible for translating the electrical signal become mechanical signal i.e movement, sending feedback force, en so forth.
Basic Interaction of Haptic
- System architecture of haptic rendering can be subcategorised become three main parts; haptic rendering, simulation and visual rendering.
- Afterwards, haptic rendering is comprised of three processes; collision detection, force response and control algorithm
Haptic Rendering Architecture
- Collision Detection : It is an algorithm that detects collision between objects and avatars- virtual representation of the haptic interface. It determines about position, time and the strength of collision. In addition, it also defines the type of collision i.e penetration, indentation has occurred.
- Force Response :This algorithm is responsible for computing the force of interaction between object and avatar in the virtual environment. Force Response work based on the relative position of object in virtual environment and the extent of collision occurs. Its outputs are either force feedback or torque to be sent to the both simulation engine and control algorithm, as accurate as possible.
- Control Algorithm : This is a normalization process of inaccuracy or errors of forces occur at the Force-response stage. This inaccuracy is likely caused by hardware limitation of the haptic devices. The control algorithm works on the distinction between what is the ideal output should be and what the applicable force was.
Simulation Engine
The next stage after rendering process in simulation, held upon Simulation Engine. This process exerts the interactionforces resulted from the Force-Response algorithms, and then compute their effects in the virtualenvironment. A common servo rate that is used 1-kHz as it is able to deal with the stiffness of complex object (Salisbury K, Conti F, 2004).
Back-drive Inertia of Haptic Device
Inertia of the hapticdetermines the mass of the haptic. It is important that the haptic device havethe lowest inertia to increase the transparency of the device so that there is no extra force is introduced (MPB Technologies, XXXX).
Back–drivabilityis the ability to move the end-effector of the haptic in the workspace without opposition. The back-drivability of haptic devices are usually caused by friction in the motors and their transmissions.
Inertia back drivability is ability to move the end-effector of the haptic in the workspace without opposition caused by the mass of the device. We need to have the lowest back-drive inertia possible so that there are no feedback forcesproduced by the mass whenever there is no interaction to the avatar in the virtual world.
REFERENCES
MP Technologies, “How do you choose a haptic device?”, http://www.mpb-technologies.ca/mpbt/haptics/hand_controllers/freedom/resources/How_do_you_choose_a_haptic_device.pdf
Salisbury, K., Conti, F., and Barbagli, F., “Haptic Rendering: Introductory Concepts”, IEEE Computer Community, January/February 2004, pp. 24 – 32
Srinivasan, M.A. and Basdogan, C., “Haptics in Virtual Environments: Taxonomy, Research Status, and Challenges,” Computers and Graphics, vol. 21, no. 4, 1997, pp. 393-404.
Srinivasan, M.A, “What is Haptic?”, Paper Review, Laboratory for Human and Machine Haptics: The Touch Lab. Massachusetts Institute of Technology, Retrieved 20 November 2008, http://www.sensable.com/documents/documents/what_is_haptics.pdf
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