Force and Tactile Feedback

Authors: Corde Lane and Jerry Smith

The sense of touch is one of the most powerful learning tools that humans have. Whenever someone discovers something new, instinctively they want to hold it, poke at it, touch and feel it. Since, so much can be conveyed by the haptic senses, integrating them into a virtual environment would yield great rewards. However, the difficulty is great in dealing with the complex problems of creating such stimuli. Therefore no generic output tool exists that can be integrated easily into a virtual environment. Therefore the prototypes that do exist are used only in specific functions.

Force Feedback

Motion Platforms

The most common force feedback technique uses movable platforms. In many video game arcades there are games where one drives a vehicle like a motorcycle. The player sits on a seat and as they control the motorcycle, the seat reacts to give the rider a feeling of actually being on a motorbike. The seat will vibrate and move to one side as the player maneuvers around a curve. Although interesting, players rarely find this convincing.

Simulated Rides

Disney's Star Tours or the locally known attraction Days of Thunder at King's Dominion are simulated rides that use motion platforms to enhance visual cues of movement. These attractions strap people to a motion platform. A large screen depicts an action, like flying on an airplane or riding a speeding car. The motion platform actually moves to create an illusion of accelerating or turning. These simulation rides are engaging; however they are not interactive. The audience is just along for the ride.

Flight Simulators

The military uses motion platforms in their expensive flight simulators. Along with recreations of the control panels and high definition visual displays these simulators provide an interactive and engaging training program.

Force Feedback Devices

There are few commercially available force feedback output devices. This is due to the complexity of delivering force feedback. Since research in this area is not as intensive as with visual or auditory, there are few commercially available interfaces.

Portable Dextrous Master

The Portable Dextrous Master (PDM) is a force feedback system for delicate hand motions. It is design to be used with the VPL DataGlove. The DataGlove detects finger movement to the computer which then sends signals to the PDM which, in turn, supplies force feedback in the thumb, forfinger, and middle finger through piston-like cylinders mounted on ball joints. The entire unit attaches to the palm of the DataGlove.

GROPE-III (UNC)

The University of North Carolina (UNC) modified a mechanical controller for a robotic arm previously used in radioactive material handling. Motors were added to the Argonne remote manipulator (ARM). The motors would be activated by the virtual environment to create forces on the controller. UNC used this in their GROPE-III system to help chemist "feel" the attractive and resistive forces of molecules reacting and bonding to each other. The chemist could use the forces and torques to learn how to make new chemical compounds.

PER Force Handcontroller (Cybernet Systems)

The PER Force Handcontroller supplies six-degree-of-freedom force feedback much like the ARM (see GROPE-III). It is a hand feedback system that mounts to a desk or other flat surface. The operator may then grab a handle grip to use the system. Its main advantage over the ARM is its light weight and small size.

FRHC (University of Maryland)

A force reflective hand controller (FRHC) is being developed to control a robot arm. When the robot arm picks up an object or pushes something, those forces and torques are felt by the operator. The operator can now tell how much strain is placed on the robot's motors, gears, and structure. Also this controller gives the operator a partial sense of touch that the robot would have.

Exoskeleton (University of Utah)

At the University of Utah, an operator can strap their arm into a large 50 pound exoskeleton developed to deliver force feedback. The operator's arm and hand can move in 10 different ways at the same time. The computer constantly changes the force output of the motors and hydraulic actuators on the exoskeleton so that it can feel essentially weightless. However, when the operator touches something, the virtual forces become actual forces felt through the exoskeleton. They could feel the increasing resistance of compressing a virtual spring or their arm would stop hard when it reached a virtual wall.

Tactile Feedback Devices

TeleTact Glove (UK's Advanced Robotics Research Center and Airmuscle)

TeleTact offers force feedback and tactile feedback by using small airbags inside the lining of the TeleTact Glove. When worn, the user can feel the size, shape, and some texture of a virtual or remote object because the airbags quickly fill and deflate to provide touch sensation to the hand.

Begej Glove Controller (Begej Corp.)

The Begej Glove provides advanced tactile and force feedback to three fingers of the hand. It provides force feedback using and exoskeleton mechanism that provides the necessary resistance to movement. For tactile feedback, the Begej Glove uses what Begej Corporation calls taxels, arrays of small tactile display elements positioned an the pads of the fingers. The Begej Glove is currently still in research and is not commercially available.

TiNi Alloy Tactile Feedback System

Using shape-memory alloys, or memory metals, the TiNi Alloy TFS provides temperature tactile feedback. This feedback is displayed by heating the appropriate memory metal element positioned on the hand (probably in a glove). This product is still in research and is not commercially available.

Sandpaper System (MIT)

The Sandpaper System is a mouse like device that provides tactile sensations through the mouse by changing the bottom of the "mouse's" surface depending on the virtual surface it is passing over. This product is still in research and is not commercially available.

How To Get Involved

Learning about the sensors, electronics, and mechanics, can come from a variety of classes and work areas. Therefore education areas include how the human body reacts to forces, classes in biomechanics provide this knowledge.

References

Remis, S. J.; Nelson, D. K. "Force-Reflecting Interfaces to Telemanipulators Testing System (FITTS", Interim User's Guide; Interim rept. Jan 89- Dec 90.

Srinivassem, M. "Design Requirements for Force Reflecting Master Controllers", MIT, Cambridge, MA, 1992.

Human Interface Technology Laboratory