Locomotion Interfaces - Human Walking in Virtual Environments - page 205

impossible to implement, because a very large number of linear actuators would be
required to cover the surface of the torus-shaped treadmills and control signal for
each actuator must be transmitted wirelessly.
The best approach to the simulation of uneven surfaces is a foot-pad-based loco-
motion interface presented in the next section.
9.4 Foot Pad
9.4.1 Related Works in Foot-Pad-Based Locomotion Interface
A foot-pad-based locomotion interface uses a platform to apply displacements to
each foot. The simplest way to realize this type of locomotion interface is via a
pedaling device. In the battlefield simulator of NPSNET project, a unicycle-like
pedaling device is used for locomotion in the virtual battlefield ([ 22 ]). A player of
the system changes direction by twisting his/her waist. The OSIRIS, simulator for
night-vision battle utilizes a stair stepper device ([ 18 ]). The device was as same as
that used in athletic gyms. A player of the system changes direction by controlling
a joystick or twisting at the waist.
In another work, two large manipulators driven by hydraulic actuators were de-
veloped at University of Utah and used to realize a locomotion interface. These
manipulators are attached to feet of a walker. The device is named BiPort ( http://
www.sarcos.com ) . The manipulators can simulate the viscosity of a virtual ground
surface. A similar device developed at the Cybernet Systems Corporation uses two
3 DOF motion platform for the feet [ 21 ]. These devices, however, have not been
evaluated or applied to VE simulation.
Schmidt et al. developed a “Haptic Walker” solution which comprises two pro-
grammable foot platforms with permanent foot-machine contact [ 24 ]. It is applied
to gait rehabilitation.
9.4.2 Gait Master
As was discussed in the first section, the third issue in locomotion interface is pre-
sentation of uneven surfaces. Locomotion interfaces are often applied for simulation
of buildings or urban spaces. Those spaces usually include stairs. A walker should be
provided with a sense of climbing up or going down those stairs. Some applications
of locomotion interfaces, such as training simulators or entertainment facility, rough
terrain should be presented.
The presentation of virtual staircases was tested at the early stage of the Virtual
Perambulator project [ 9 ]. When the walker is climbing up a stair, the forward foot