Chris Reilly

The purpose of this research is to develop hardware (and supporting software) capable of transmitting touch from tactile sensors on inanimate/prosthetic objects to the skin via haptic feedback.

Background

The ability to quickly and easily transmit information has revolutionized the world we live in.  Cheap, networked digital computers have exponentially increased the amount of information available to a very large, globally connected population.  The digital computing revolution comes at the tail end of a centuries-long expansion of information sharing: starting with the development of written language, followed by the advent of the mechanical printing press, there has been a steady push towards technology that encourages the creation and sharing of text, image and sound-based information.  The new fluidity with which just about anyone can view, create and share this information over the internet has dramatically lowered the costs of collaborative problem-solving.  The Apache HTTP server software project is just one example of a community-driven software project, programmed by a network of volunteers from all over the world, that now runs almost 60% of all the servers on the internet.

It’s not a coincidence that digital communication consists only of visual/aural media; methods of communication based on text, image, and sound existed long before their respective digital versions.  Handwriting, painting, music and song have all flourished in large part because they are easily abstracted and embodied: on paper, on canvas, in vinyl, in human memory, etc.  It should come as no surprise, then, that such mature formats have been easily ported into the digital realm.  The power of digital media based on hearing and sight is clear, but it begs the question: what more could be accomplished, communicated and experienced if the same ease of creation and distribution were applied to other senses, such as touch?

Unmediated touch defines a broad range of human experience: basic information about physical environments, inter-personal communication and physical/sexual intimacy are all centered around touch.  Creating digital hardware and software that enables a mediated experience of touch, one that allows for transmission of touch over distance, as well as abstraction of touch between input and output, offers the possibility of extending and enhancing the way touch-based information is created, distributed and used.  Just as digital imaging technology allows one to visually experience remote or synthetic spaces, digital touch transmission technology could allow a user to feel a remote or synthetic object, the ability to extend the body, through touch, into both the physical and abstract/virtual worlds.  Further, touch transmission technology could offer enhanced sensory experiences tailored for the blind or visually impaired (a sort of hyper-braille) or for prosthetics users.

Technical Challenges

Touch interaction offers a much more intuitive way of interacting with computer interfaces when compared to established methods such as text input.  Some interactive systems already offer feedback based on touch: for example, the pilot controls on large airliners use vibrating motors to mimic the warning sensations that would normally be felt on a simpler plane; or the vibrating controllers included with many video game consoles.  Additionally, many digital devices are being developed that offer touch input interfaces, such as the touchscreen on an iPhone.

Compared to real, unmediated touch, these technologies offer only a fraction of a full sensory experience. One major challenge of both tactile sensing and haptic feedback technology is abstracting touch into a codified, transmissible format; this is due in part to the multifaceted properties of the sense of touch.  The list below is by no means exhaustive or scientific, but represents at least a starting point for framing the complexity of touch:

Components of touch

• Temperature (hot/warm/cold)
• Texture (wet/dry/slippery)
• Pressure
• Movement
• Spatial location

In most of the technology mentioned above, only one or two of these components are addressed at the same time, and over a narrower range than human touch is fully capable of sensing.  Sensing, transmitting and outputting all the component parts of touch presents daunting technical challenges.  Below are cursory outlines of several sensors that could address some components of touch input, as well as actuators for haptic feedback:

Touch Sensors
Sensor Type	Measures	Flexible	Pros	Cons
Capacitive Sensing	Touch proximity, position	Yes	Fast, responsive.	More expensive, interference from water.
Resistive Sensing	Touch proximity, position	Unsure	Accurate.	May require stylus.
Piezoresistors	Force/pressure	Yes	Cheap.	Not incredibly accurate

Haptic Feedback Actuators
Type	Pros	Cons
Vibration w/ motor		High power consumption, mechanical wear.
Ionic Electroactive Polymer	Low voltage requirements.	Need to maintain wetness.
Dielectronic Electroactive Polymer	Holds displacement under current.	Require very high activation voltage (but low power).
Acoustic Radiation Pressure	Physical contact not required.	Difficult to reproduce precise sensations w/out large array of actuators.

Informational Resources

• DIY Pressure Sensor
• Capacitive Tactile Sensors
• General Haptic Technology Info
• Haptik Open-source hardware abstraction layer for haptik devices.
• Electroactive polymers
• Acoustic radiation pressure
• Audio-based tactile feedback
• Position Papers for Key Issues in Sensory Augmentation