Game Development Reference
In-Depth Information
the palm of the hand and the fingers. The contact surface between the hand and
the object is significant but the movement of the fingers is limited;
Precision grips: These grips are used for considerations of sensitivity and dexterity.
The object is grasped with fingers. The contact surface is less significant but there
is an increased freedom of movement.
There are a large number of precision and power grips. These different types of
grips are adapted to the various types of objects that a person can grasp. The robot
grippers used most commonly on the force feedback interfaces are either a handle or a
pen that approximately correspond to the objects manipulated in the real environment.
The posture and the type of grip must be considered at the same time as they
jointly influence the abilities of the user. Thus, for example, in case of work that
requires precision we can use a support for the wrist or elbow and a precision grip.
For more generic work, we can use a seated or standing posture that makes it possible
to use full arm movements and a precision or power grip (by using the palm of the
hand). Finally, we can work with both hands for work that requires force to be applied,
while for work in large spaces, we can move using the interface. Work space and position resolution
Work space : A haptic interface is considered to be transparent when it does not disturb
the movements of the users. However, it is advisable to limit its travel to approximately
a third of the maximum target values of the users, so that that they always work in a
comfortable manner without forcing their articulations. This limitation should how-
ever not be too large so as to ensure that the users can occasionally make movements
of greater amplitude.
This particularly holds true for orientations. In fact, experience shows that rota-
tion movements are generally less frequent than translation movements. It is thus less
disturbing that the interfaces make it possible for the users to reach extreme con-
figurations in orientation. Taking into account all these constraints and based on
the information regarding the amplitudes of movements from the workstation stan-
dards (AFNOR, 1982), the compendiums of physiology or ergonomics (Daams, 1994;
Kapandji, 2002), and the experience acquired on the existing systems, we recommend
a work space with the following specifications:
40 wrist placed;
5 to 10 cm on the side and
75 elbow placed;
15 to 25 cm on the side and
80 seated;
30 to 40 cm on the side and
90 standing.
(and a larger space if the user needs to move)
40 to 60 cm on the side and
These figures correspond to the useful work space of the operator, i.e. the work space
where the user can work comfortably. These values are evidently given as a rough guide
as there is a strong variability between individuals mainly depending on age, sex, size
and build.
Position resolution : The hand is a bidirectional organ. It helps to move objects and
to measure their displacements, at the same time. We will now make a distinction with
respect to position resolution: The motor resolution, which is the smallest movement
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