Human Tactile Sensing & Sensors: From Receptors to Robotics, Exercises of Nursing

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Tactile Sensing

From Humans to Humanoids

Authors: Allen, Patel, Tandon, Dahiya, Metta, Valle, and Sandini

Human Tactile Sensing

“The human sense of touch deals with the spatiotemporal perception of external

stimuli through a large number of receptors that are distributed all over the body

with various density.” – Dahiya et al

This “distribution” of receptors primarily involves:

1. Mechanoreceptors (pressure/vibrations)

2. Thermoreceptors (temperature)

3. Nocioreceptors (damage/pain)

Human Tactile Mechanoreceptors A. In the human hand the submodalities of touch are sensed by four types of mechanoreceptors. Specific tactile sensations occur when distinct types of receptors are activated. Firing of all four receptors produces the sensation of contact with an object. Selective activation of Merkel cells and Ruffini endings produces sensations of steady pressure on the skin above the receptor. When the same patterns of firing occur only in Meissner's and Pacinian corpuscles, the tingling sensation of vibration is perceived. B. Location and other spatial properties of a stimulus are encoded by the spatial distribution of the population of activated receptors. Each receptor fires action potentials only when the skin close to its sensory terminals is touched, ie, when a stimulus impinges on the receptor's receptive field. The receptive fields of mechanoreceptors—shown as red areas on the finger tip—differ in size and response to touch. Merkel cells and Meissner's corpuscles provide the most precise localization of touch, as they have the smallest receptive fields and are also more sensitive to pressure applied by a small probe. Ruffini's end organs detect tension deep in the skin. Meissner's corpuscles detect changes in texture (vibrations around 50 Hz) and adapt rapidly. Pacinian corpuscles detect rapid vibrations (about 200–300 Hz). Merkel's discs detect sustained touch and pressure. Hair follicle receptors are located in hair follicles and sense position changes of hairs.

Types of Signal in Human Touch Sensing Basis of Classification :  Type of Signal Frequency of Signal

A grid of Tactels

A Thermal Image formed by a Tactel

Tactile sensing: Methods of transduction  Usually an array of discrete sensing elements.  Sensing elements can be many types:  Resistive: strain gauge, piezoresistive.  Capacitive  Piezoelectric  & others like (magnetic, optical, conductive rubber, ultrasonic)

Different Sensor Types and Materials

Sensor Types

• Resistive Sensor
• Tunnel Effect Sensor
• Capacitive Sensor
• Optical Sensor
• Ultrasonic Sensor
• Magnetic Sensor
• Piezoelectric Sensor

Materials

• Rubber
• Fluids
• Gels
• Sponges
• Pastes

Applications :  Manipulation : Grasp force control; contact locations and kinematics; stability assessment.  Exploration : Surface texture, friction and hardness; thermal properties; local features.  Response : Detection and reaction to contacts from external agents.

The Design for a Robotic Tactile Sensing System

1. Varied and distributed receptors

2. Correlation between size and sensitivity for sensors

3. High range of sensitivity-measure contact & normal

4. Ability to detect dynamic and static contact

5. Quick Response, little hysteresis

6. Preprocessing within sensors

7. Flexible shape, curved surfaces

What’s the recipe???

Links of Interest

• http://www.iinuu.eu/en/wisdom/human-body-and-nature/what-human-hand-tells
• http://www.nicehdwallpaper.com/wp-content/uploads/2013/06/Beautiful-butterfly-in-robot-hand-hd-wallpaper.jpg
• http://ndpbluenote.com/2012/11/14/steamed-chicken/robot-human-hand-2/
• http://kin450-neurophysiology.wikispaces.com/Cutaneous+Receptor
• http://www.ib.cnea.gov.ar/~redneu/2013/BOOKS/Principles%20of%20Neural%20Science%20- %20Kandel/gateway.ut.ovid.com/gw2/ovidweb.cgisidnjhkoalgmeho00dbookimagebookdb_7c_2fc~28.htm
• http://stock-clip.com/video-footage/knuckles/
• http://www.baseballplayamerica.com/page1.html
• http://what-when-how.com/nursing/the-nervous-system-structure-and-function-nursing-part-4/
• http://joelcollyer.tumblr.com/post/1681280433/twitter-bots
• http://www.iff.fraunhofer.de/en/business-units/robotic-systems/technologies/tactile-sensor-systems.html
• http://www.gasgoo.com/auto-products/electricity-electronics-298/1226244.html