Teletaction - Tactile Sensing and Displays - page 201

Length - perception is more accurate in vision than in haptics, especially in the youngest
subjects [96]. In the haptic modality, the results observed in the literature are very vari-
able. To understand them, the different methodologies used in the various studies will be
examined.
Localization - perception is more accurate in vision than in haptics [97]. As for the
study of length perception, the different approaches used for studying this type of haptic
perception will be presented.

10.5.3 Perception of Texture
In a wider sense, all physical properties defining a surface's micro-structure are included
in the term 'texture,' including roughness, hardness, and elasticity [71] although only
roughness, and to a lesser extent hardness, have been studied.
Tactile texture perception is as efficient as visual perception, and sometimes even sur-
passes it for the extremely fine textures of abrasive papers (ranging from 1000 to 6000
grit, according to standard norms).

10.5.4 Control of Haptic Interfaces
In contact tasks involving finite impedances, either displacement or force can be viewed as
being the control variable, with the other being a display variable, depending on the control
algorithms employed. However, consistency among free-band motions and contact tasks
is best achieved by viewing the position and motion of the band as the control variable,
and the resulting net force vector and its distribution within the contact regions as the
display variables.
The concept of teleoperation has evolved to accommodate not only manipulation at a
distance, but manipulation across barriers of scale and in VEs, with applications in many
areas. Furthermore, the design of high-performance force-feedback teleoperation masters
has been a significant driving force in the development of novel electromechanical or 'hap-
tic' computer-user interfaces that provide kinesthetic and tactile feedback to the computer
user. Since haptic interfaces/teleoperator masters must interact with an operator and a real
or virtual dynamic slave that exhibits significant dynamic uncertainty, including sometimes
large and unknown delays, the control of such devices possess significant challenges.
The teleoperation controller should be designed with the goal of ensuring stability
for an appropriate class of operator, and environment models, as well as satisfying an
appropriately defined measure of performance, usually termed as transparency.
A commonly used teleoperation system model, with five interacting subsystems, is
shown in Figure 10.8 [98, 99]. The master manipulator, controller, and slave manipulator

Human Master Controller Slave Environment

Figure 10.8 Teleoperation system model