Game Development Reference
In-Depth Information
From a user's point of view , note that these are sensorimotor thus bidirectional
interfaces; there are two possible use cases:
The user voluntarily acts on the virtual environment, which in return, gives him
force feedback, that is either of a relatively high intensity to curb or block his hand
movement or to make him feel variable forces, in relation with the action that he
carries out on an object (for example, deformable object);
The virtual environment acts on the user's hand, independent of his behaviour
(for example, when an object falls on the subject's hand, the fall is not caused
by the behaviour of the user). Presently, the simulation of the second case in VR
applications is rarer as this case is generally less crucial than the interactions of
the subject in the virtual environment.
It can be said that, in the first case, we use the motor capacity of the interface more
(sensori-MOTOR interface) and in the second case, we use the sensory capacity of the
interface more (SENSORI-motor interface). This is to be varied with respect to the
applications where these two capacities can be used. Note that, basically, it is always
necessary to refer to the “Perception, Decision, Action'' loop for the subject: where do
the causes come from (the subject? the virtual environment?) and, vice versa, what are
the effects?
From a control point of view , we can classify them into two main categories:
Those that measure movement and provide force. These interfaces are called inter-
faces in impedance. They generally have low inertia and are completely reversible,
i.e. it is possible to control force in open loop. The Phantom interfaces from Sens-
able (Massie & Salisbury, 1994) and Virtuose from Haption belong to this type.
These interfaces are used to generate low forces;
Those that measure force and provide movement. They are qualified admittance
interfaces. They generally have high inertia and are not reversible. A force sensor
however helps to measure the force provided by the user on the device so as to
make it reversible (and transparent) by command (Whitney, 1987; De Schutter
et al., 1997; Carignan &Cleary, 2000). We can thus use industrial robots as haptic
devices (Clover et al., 1997). These interfaces are used to generate high forces.
The haptic interface can be defined as anything that exists between the human oper-
ator and the virtual environment (Adams & Hannaford, 1999). This includes the
haptic device, the algorithms managing the command and analogue-digital and digital-
analogue conversions. We can consider this haptic interface as a system that facilitates
the exchange of energy between the virtual world and the operator. Broadly speak-
ing, the virtual environment is an interactive simulation. This can come from an exact
reproduction of the physical appearance of the real world, as well as animations where
the forces to be felt by the user have a particular sense, which do not necessarily have
physical significance. These environments can thus be very varied, but we can classify
them into two categories:
The environment can operate in impedance, by accepting speed and/or positions,
and generating forces according to a certain physical model;
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