full Paper - Nguyen Dang Binh

In 1991, Wellner proposed for the first time the concept
of a digital desk [3, 4], which enables users to seamlessly
handle both digital and physical objects on the desk by using
a conventional video projector and CCD camera. Leibe
proposed the Perspective Workbench [5] that is additionally
equipped with infrared illumination lamps and infrared
CCD cameras to import the object’s shadows to reproduce its
shape digitally. The Enhanced Desk and Augmented Desk
[6, 7] by Koike were also equipped with an infrared camera
to capture the user’s hand motion as command input. The
Smart Skin [8] by Rekimoto was equipped with a unique array
of sensors to detect the user’s hands motion on a table
without cameras. The sensor used an electric capacitance
meter that was affected by user’s body, and many sensors
were embedded under the desk. In all these systems, the virtual
environment image is projected onto a common physical
desk where the visual channels acts simultaneously as
input/output device. Other studies have tried to introduce
the force feedback information not only for replacing the
conventional input devices but also for introducing novel
output devices. In fact Dennerlein and Yang [9] suggested
that the addition of force-feedback can improve operator’s
performance, and it potentially reduces the musculoskeletal
loading caused by the use of the mouse, which may be a
possible risk factor for chronics musculoskeletal disorders
of the upper extremity. Then, some mouse-like devices with
a force feedback mechanism were developed to reduce such
load. Ramstein’s Pantograph [10] employed a 2-DOF parallel
link mechanism. Kelly proposed the Magic Mouse [11]
using a 2-DOF linear DC motor. There are also commercial
products such as the penCAT/Pro (Haptic Technologies
Inc. [12]) and the haptic mouse (FEELit mouse) patented by
Immersion [13] and Logitech [14]. In most of all these devices,
the motion range is quite limited and even if they are
able of exerting force feedback, mental load is not reduced
and visual and haptic information is not co-located. The term
co-location has been used to describe a haptic and a visual
display that is calibrated such that visual and haptic coordinate
systems are coincident. This means that the user can
visually perceive an object in the same position in space as
the haptic simulation [15, 16]. This criterion simplifies the
required human perception process and facilitates its natural
integration for allowing fast reflexive motor responses to
the haptic stimuli. In fact, as it was presented in our previous
research [17], which implemented a planar 2-DOF haptic
interface with non-colocated haptic and visual information
[18], when users must perform higher-level cognitive
tasks, in that case Japanese Handwriting, the operator’s performance
can be significantly affected when the visual and
haptic information is not coincident. Also Ware and Rose
[19] noted that co-location between the hand and the virtual
workspace improved performance in tasks involving object
rotation. Up to now, few systems have been designed to
provide co-located haptic/visual information to the operator.
Reach-In [20] for example, integrates a 3D graphic system
with a PHANToM device [21, 22]. Another example is the
Massimo Bergamasco / Future trends and Applications, Education
31
DaVinci system [23], which offers a collocated teleoperation
environment able to lead surgical instruments to be remotely
controlled through images obtained from optical sensors and
presented by means of a system based on fixed screens. Although
both systems described above allow users to interact
with 3D environments, the limitation of the number of contact
points and the complexity of the images displayed may
demand a high level of skills for processing all the information.
In fact, such systems are used only by specialists (i.e.
doctors, designers, etc.) restricting the access to this technology.
Furthermore, the need of special requirements for
visualizing the 3D images and for providing the haptic information
increases considerably the cost of such systems
and the workspace required for placing the whole system.
On the other hand, some solutions for integrating 2D systems
have been proposed. Brederson proposed the Virtual
Haptic Workbench [24], which integrates a PHANToM with
a planar screen. Although the dimension of the workspace is
quite big, the system requires a complicate calibration procedure.
Moreover, the complexity of the haptic interface does
not match with the requirements of the visualization system
(2D). A different solution is based on linear induction motors
fixed under the desk, which produce forces on a metallic
plate fixed to the user’s finger or to the end part of the tool
[25, 26]. The disadvantage of this solution is that the visibility
of the graphical system can be obstructed by the operator’s
arm. In fact the projector is not under the desk but is
above user’s head.
2. DESIGN GUIDELINES
Two types of design guidelines have been employed during
the preliminary definition of the system: qualitative and performance
guidelines. According to qualitative guidelines the
device had to show ergonomic features, which make the use
of the system very comfortable. These guidelines have regarded:
the workplace, the quality of the visual feedback,
the aesthetics of the system, and the modality of interaction.
Another very important guideline was the reduction of mental
load during the use of the device. The system design and
control allow the user to feel and control haptic interaction
just below his fingertips, while directly viewing the effects
of his actions on the computer screen (co-location). Specific
state of the art analyses [29] have verified that co-location
greatly enhances the user performances in HCI while reducing
the mental load of the interaction. The haptic device has
therefore to be calibrated in order to collimate the position
of the usage tool (end-effector), with the pointer within the
computer screen. The accuracy provided in design, has to
ensure that the sensitivity of the system is far beyond the
pixel resolution of the screen. These guidelines have steered
the main design choices of the system: the presence of the
haptic interface has to minimally interfere with the visual
feedback in fact it was decided to make use of transparent
materials for building; all cables and connections has to be
hidden to the user; the device has to offer the possibility of
c­ The Eurographics Association 2005.