Julian P. Brooker, Paul M. Sharkey,
John P. Wann, Annaliese M. Ploy
Mechatronics, 9, 1999
Summary
Teleoperation
has an interesting potential, enabling human operators to perform delicate
physical manipulation without the requirement of physically being present where
the task is done, therefore it becomes fundamental to provide an obstructed and
natural viewpoint, in order obtain high performance and safety.
There is scientific proof
that proprioceptive information for hand localization may be biased by the
stereo-vergence typical of humans, therefore two possible solutions maybe
possible: using a stereographic display or using a helmet mounted display
containing separate lightweight image displays for each eye.
Using an helmet display
has the advantage of allowing the user to gaze around a scene without the use
of head movement being limited, while problems, in general for Teleoperation,
are related to low LCD screen resolution.
In designing a head
mounted display device, variables have to be kept into account: 1) the
inter-camera distance (ICD) and the inter-display distance (IDD) which have to
be matched to the observer’s inter-pupil distance (IPD); 2) the field of view
(FOV) of the camera configuration has to be the same of the FOV of the display
configuration.
In telepresence
environments high-quality binocular image of element in the near viewing field is
more important than a wide angled view of the distant viewing field, therefore
the FOV must be reduced together with the percentage of the overlap occurring
on an object in the near viewing field also decreases.
To obtain this result
cameras have to verge, a problem occurring in verging the two mounted cameras
is that the object viewed tends to be altered in humans view. We can computer d
(minimum distance at which the target is viewed) as: d = (p+w)/(2tan(a/2)),
where w is the target’s width, p is the IPD of the operator and a the
horizontal angle of view.
Solutions presented in the
case of camera verging could be involving tracking operator’s eyes so that the
camera geometry could be optimized to the situation, but the problem would be
moving screens and cameras synchronously, which involved multiple problems.
A solution may be using
electronic image translation, this would avoid use of mechanical moving parts,
horizontal image detection could be achieved with minimal additional image
processing hardware and the translation system is likely to be higher
performing than a mechanical one; the main problem would be that images may
appear deformed and LCD display may have low resolution, leading the authors to
finally opt for a mechanical display positioning.
Using a mechanical system
it has to be kept into account that displays have to face directly the pupil
and therefore rotate with it, infrared sensor are used for this purpose.
Potential problem are related to small movement the eye perform such as flicks,
drifts and tremors, it is demonstrated that a system capable of tracking all
this movements appears to be too sensible and therefore not being able to keep
a proper and sufficient track of the system.
The eye tracking apparatus
appears for each eye is located behind the half silvered mirror, for the
prototype make by the authors in this paper, the problem of size of the overall
system hasn’t been touched.
The control algorithm
works in an iterative process to tune the parameters of the PID controller, in
order to give damped responses on the camera axis.
Key Concepts
Virtual Reality
Key Results
The system has been tested
and allows to perform teleoperations with good quality and results, IDD and IPD
have to be calibrated to match the operator as well as the rotational centers.
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