Omnidirectional treadmill

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US Army Research Lab's ODT with CAVE Graphics

An omnidirectional treadmill, or ODT, is a device that allows a person to perform locomotive motion in any direction. The ability to move in any direction is how these treadmills differ from their basic counterparts (that only permit unidirectional locomotion). Omnidirectional treadmills are employed in immersive virtual environment implementations to allow unencumbered movement within the virtual space through user self-motion.

Advantages to pairing an ODT with an immersive virtual environment include:

Natural navigational movement of the system user within the enclosure while still providing context cues which simulate physical traversal through the virtual terrain

Reverting immersive navigation tasks from hand-based (mouse, joystick) to mentally hard-wired whole body (leg) based

Enhancing immersion by providing a whole-body experience that begins at the soles of the feet and ends at the top of the head

Facilitating whole-body haptic interaction

1 History
2 Future directions and discussion
3 Related efforts
4 Potential uses
5 References
6 External links

[edit] History

First Generation ODT

Although the concept of an omni-directional walking surface parallels the history of virtual reality technology, it wasn't until 1997 that one was successfully constructed. US Army's STRICOM (now PEO-STRI) funded the first ODT. After lengthy testing, the device ultimately found a home at the Army Research Lab, Human Engineering Research Directorate (HRED). The patent for this device (No. 5562572) was issued in the US to David E. E. Carmein on October 8, 1996.^[1]

This unit employed a belt made from plastic, toothed rollers. It employed mechanical tracking using a body harness, and included provisions for pneumatically powered, full-body force feedback for haptic and force display. The photo at right shows this unit with its first mechanical tracking arm.

At the University of Tsukuba VR Lab, Dr. Hiroo Iwata's group independently conceived and built a belt-based ODT in 1999. It had individual treadmill segments each powered by its own servomotor. It is known as the Torus Treadmill because, as with all treadmills of this class, the active surface forms a flattened torus.

In 2003 the Department of Computer Science and Information Engineering at Tamkang University in Taiwan built a passive treadmill surface comprised of balls constrained within a concave walking surface. It relies on the users energy to move the balls during walking, and a waist harness to provide counterforce. This design is quite similar to the virtual space navigation device described in Michael Crichton's book, Disclosure.

The CyberWalk Project began in 2005 through a European Commission funded collaboration of several universities. Their first design, like Tamkang University, relied on a bed of rotating balls. Unlike TU's design, CyberWalk's Cybercarpet actively powers the balls by rotating a standard linear treadmill underneath. A prototype has been produced which was big enough to evaluate the behaviour under conditions of normal walking.

Cyberwalk

A second-generation, belt-based ODT was funded and developed through a US Army contract in 2003. A video of this design in operation is available on YouTube, and a photo of the installed unit is shown above.

In 2007 another omnidirectional platform was released by the Cyberwalk project: The Cyberwalk itself. It also uses belts which form a torus and claims to be sizeable by its architecture without limitations. It was designed and built by the Institute for Applied Mechanics of the Technische Universität München by Martin Schwaiger. The whole system will be implemented in the Cyberneum^[2] in Tübingen, Germany.

[edit] Future directions and discussion

Natural navigation employing the ODT has two fundamental, parallel paths. One path seeks to create the holodeck of Star Trek fame, the other seeks a lower cost, more restricted device. The holodeck vision is that of a large active surface upon which the immersant is able to walk freely and unfettered. The second approach employs a harness for tracking, and optionally provides whole-body force feedback.

Both approaches have their advantages and disadvantages. Without a harness, the ODT user is able to accelerate away from center of the surface. The system must recognize this using a variety of sensing means, and gently accelerate the user back towards the center. Keeping the forces that return the user to center below the human sensing threshold is the main challenge with these systems. The larger the active surface, the easier it is to control using this means.

With a harness, the user is kept on center mechanically, and the surface area can be made much smaller. But actions such as rolling are not possible. On the plus side, a harness can provide body forces such as inertia or slope display. In addition, the harness may provide lifting force to simulate free-body flight. And the well-defined user space makes interaction with outside haptic devices feasible.

[edit] Related efforts

Several alternative whole-body human-computer interfaces exist. The VirtuSphere permits a person to walk on the inside surface of a large, hollow ball. Like the Tamkang University's device, the VirtuSphere is passive. It requires user energy input to start and stop sphere rotation.

Walking- or stepping-in-place as a substitute for real walking was researched by Slater, Steed, and Usoh, at the University of London, in 1993. More recently, the US Navy's VIRTE project employed walk-in-place as a substitute for real walking. A similar approach by the Southwest Research Institute uses a walking pad.

Besides an ODT, the University of Tsukuba VR Lab has built numerous prototypes of various natural navigation walking devices. These have included rollers on shoes combined with a waist harness and the CirculaFloor, a group of smart tiles that arrange themselves to recycle from the rear of an active surface to the front.

Numerous references to walking interfaces for virtual reality environments exist in the US Patent Office database. Most of these have not been reduced to practice.