Game Development Reference
In-Depth Information Transmissions
It is preferable to place the heaviest motors near or on the fixed base of the robot to
reduce the apparent mass of the interface.
In these conditions, the actuation of the remote axes is carried out by rod or cable
transmissions. To optimise the position bandwidth, the reduction stages must then be
located at the level of the articulations to be used rather than at the level of the motors
(Townsend, 1988). Balancing
The user must not feel the weight of the robot gripper during the operation of a
force feedback interface. This presupposes that the robot is statically balanced. This
balancing can be obtained in various ways. The first solution consists of using the
motors of the robot to offset its weight, which requires the identification of its gravity
model. This solution presents the disadvantage of continuously stimulating the robot
actuators, which leads to their over-heating. In addition, the torque available for the
force feedback is reduced. Finally, the balancing stops as soon as the arm is switched
off (for example when the power is cut).
Passive balancing does not have these drawbacks. However, it requires the addition
of mechanical components (springs or counterweight). The simplest solution is the use
of counterweight.
In this paragraph, we provide a few representative examples of force feedback inter-
faces that are available in the market or developed in laboratories. There are so many
existing interfaces that this presentation cannot be exhaustive. It will also be limited
to the devices dedicated to Virtual Reality.
8.4.1 External reaction force feedback interfaces
The first force feedback interface category groups the interfaces with a fixed base.
Under these conditions, the operator is only in contact with the robot gripper and only
feels the force applied by it. We also refer to external reaction force feedback interfaces.
This type of interface generally helps to obtain a high-quality force feedback. The f ixed interfaces with serial structure
The majority of force feedback interfaces, like most of the manipulator-type robots,
have a serial structure. This type of structure, constituting interconnected segments
following a single kinematic chain, is easier to design and control. It also provides a
significant work space, mainly in rotation, which is quite favourable for numerous
applications. The best-known serial interface is PHANToM, initially designed in MIT
(Massie, 1993; Massie&Salisbury, 1994) and is presently manufactured andmarketed
by the American company, Sensable Technologies Inc. For the first time in the mid
90's, this interface revolutionised the field by offering a simple and efficient solution,
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