View source for Tactile sensor

{{primary sources|date=October 2021}}

[[File:USkin Sensor Integration.png|alt=a high-density 3-axis tactile sensing in a thin, soft, durable package, with minimal wiring. Integrating uSkin on the Allegro hand provides it with the human sense of touch.|thumb|uSkin Sensor by XELA Robotics, a high-density 3-axis tactile sensor in a thin, soft, durable package, with minimal wiring.]]
[[File:TactileHeadImage.png|alt=A PPS tactile sensor system (TactileHead) designed to quantify the pressure over a human head.|thumb|A PPS tactile sensor system (TactileHead<ref>{{Cite web|last=Dobie|first=Gordon|date=7 May 2021|title=TactieHead|url=https://pressureprofile.com/body-pressure-mapping/head-pressure-mapping}}</ref>) designed to quantify the pressure distribution over the face and head.   Useful to optimise the ergonomic design of headgear and eyewear.]]
{{Use dmy dates|date=May 2021}}
[[File:SynTouch BioTac.jpg|thumb|right|The SynTouch BioTac,<ref name="F">{{cite web|url=http://www.syntouchllc.com/Technology/TechnologyOverview.php|title=Sensor Technology – SynTouch, Inc.|website=www.syntouchllc.com|date=6 October 2020 }}</ref> a multimodal tactile sensor modeled after the human fingertip]]

A '''tactile sensor''' is a device that measures information arising from physical interaction with its environment. Tactile sensors are generally modeled after the biological sense of [[cutaneous receptor|cutaneous touch]] which is capable of detecting stimuli resulting from mechanical stimulation, temperature, and pain (although pain sensing is not common in artificial tactile sensors). Tactile [[sensor]]s are used in [[robotics]], [[computer hardware]] and [[security systems]]. A common application of tactile sensors is in [[touchscreen]] devices on [[mobile phones]] and [[computing]].

Tactile sensors may be of different types including [[piezoresistive]], [[piezoelectric]], optical, capacitive and elastoresistive sensors.<ref name="A4">. Tactile sensors also come in the form of pressure indicating films that reveal pressure distribution and magnitude between contacting surfaces by virtue of an immediate and permanent color change. These pressure indicating films are one-time use sensor that capture the maximum pressure they were exposed to. Pressure indicating films are activated by chemical reaction and are non-electronic sensors.  [https://www.springer.com/engineering/robotics/book/978-94-007-0578-4 Robotic Tactile Sensing – Technologies and System]</ref>

==Uses==
Tactile sensors appear in everyday life such as elevator buttons and lamps which dim or brighten by touching the base. There are also innumerable other applications for tactile sensors of which most people are never aware.

Sensors that measure very small changes must have very high sensitivities. Sensors need to be designed to have a small effect on what is measured; making the sensor smaller often improves this and may introduce other advantages. Tactile sensors can be used to test the performance of all types of applications. For example, these sensors have been used in the [[manufacturing]] of [[automobiles]] (brakes, clutches, door seals, [[gasket]]), [[Battery (electricity)|battery]] lamination, bolted joints, [[fuel cell]]s etc.

[[Tactile imaging]], as a medical imaging modality, translating the sense of touch into a digital image is based on the tactile sensors. Tactile imaging closely mimics manual palpation, since the probe of the device with a pressure [[sensor array]] mounted on its face acts similar to human fingers during clinical examination, deforming soft tissue by the probe and detecting resulting changes in the pressure pattern.

[[Robot]]s designed to interact with objects requiring handling involving precision, [[dexterity]], or interaction with unusual objects, need sensory apparatus which is functionally equivalent to a human's tactile ability. Tactile sensors have been developed for use with robots.<ref>{{cite journal|title=Learning efficient haptic shape exploration with a rigid tactile sensor array, S. Fleer, A. Moringen, R. Klatzky, H. Ritter |year=2020 |doi=10.1371/journal.pone.0226880 |pmid=31896135 |doi-access=free |last1=Fleer |first1=S. |last2=Moringen |first2=A. |last3=Klatzky |first3=R. L. |last4=Ritter |first4=H. |journal=PLOS ONE |volume=15 |issue=1 |pages=e0226880 |pmc=6940144 }}</ref><ref>{{cite journal|url=https://link.springer.com/content/pdf/10.1007%2F978-3-030-58147-3_51.pdf|title=Attention-Based Robot Learning of Haptic Interaction, A. Moringen, S. Fleer, G. Walck, H. Ritter |doi=10.1007/978-3-030-58147-3_51 |s2cid=220069113 }}</ref>{{better source needed|date=October 2021}} Tactile sensors can complement visual systems by providing added information when the robot begins to grip an object. At this time vision is no longer sufficient, as the mechanical properties of the object cannot be determined by vision alone. Determining weight, texture, [[stiffness]], [[center of mass]], [[coefficient of friction]], and [[thermal conductivity]] require object interaction and some sort of tactile sensing.
 
Several classes of tactile sensors are used in robots of different kinds, for tasks spanning collision avoidance and manipulation.{{citation needed|date=July 2019}} Some methods for [[simultaneous localization and mapping]] are based on tactile sensors.<ref>Fox, Charles, et al. "[http://eprints.whiterose.ac.uk/108430/1/fox_icra12.pdf Tactile SLAM with a biomimetic whiskered robot]." 2012 IEEE International Conference on Robotics and Automation. IEEE, 2012.</ref>

==Pressure sensor arrays==
Pressure sensor arrays are large grids of tactels. A "tactel" is a 'tactile element'. Each tactel is capable of detecting normal forces. Tactel-based sensors provide a high resolution 'image' of the contact surface. Alongside spatial resolution and force sensitivity, systems-integration questions such as wiring and signal routing are important.<ref name="A0">{{cite journal|title=Tactile Sensing—From Humans to Humanoids – IEEE Journals & Magazine|journal=IEEE Transactions on Robotics|volume=26|issue=1|pages=1–20|doi=10.1109/TRO.2009.2033627|year=2010|last1=Dahiya|first1=R.S.|last2=Metta|first2=G.|last3=Valle|first3=M.|last4=Sandini|first4=G.|s2cid=14306032 |url=https://zenodo.org/record/3435623}}</ref> Pressure sensor arrays are available in [[thin-film]] form. They are primarily used as analytical tools used in the [[manufacturing]] and [[R&D]] processes by engineers and technicians, and have been adapted for use in robots. Examples of such sensors available to consumers include arrays built from [[conductive rubber]],<ref name="A">{{cite journal|title=A tactile sensor sheet using pressure conductive rubber with electrical-wires stitched method – IEEE Journals & Magazine|journal=IEEE Sensors Journal|volume=4|issue=5|pages=589–596|doi=10.1109/JSEN.2004.833152|year=2004|last1=Shimojo|first1=M.|last2=Namiki|first2=A.|last3=Ishikawa|first3=M.|last4=Makino|first4=R.|last5=Mabuchi|first5=K.|s2cid=885827 }}</ref> [[lead zirconate titanate]] (PZT), [[polyvinylidene fluoride]](PVDF), PVDF-TrFE,<ref name="A1">{{cite journal|title=Towards Tactile Sensing System on Chip for Robotic Applications – IEEE Journals & Magazine|journal=IEEE Sensors Journal|volume=11|issue=12|pages=3216–3226|doi=10.1109/JSEN.2011.2159835|year=2011|last1=Dahiya|first1=Ravinder S.|last2=Cattin|first2=Davide|last3=Adami|first3=Andrea|last4=Collini|first4=Cristian|last5=Barboni|first5=Leonardo|last6=Valle|first6=Maurizio|last7=Lorenzelli|first7=Leandro|last8=Oboe|first8=Roberto|last9=Metta|first9=Giorgio|last10=Brunetti|first10=Francesca|s2cid=11702310 }}</ref> [[Field-effect transistor|FET]],<ref name="A2">[http://apl.aip.org/resource/1/applab/v95/i3/p034105_s1 Piezoelectric oxide semiconductor field effect transistor touch sensing devices]</ref> and metallic [[capacitive sensing]]<ref>{{Cite web|last=Dobie|first=Gordon|date=7 May 2021|title=PPS Capacitive Sensors|url=https://www.pressureprofile.com|access-date=7 May 2021|website=PPS}}</ref><ref>{{Cite web|last=Dobie|first=Gordon|date=7 May 2021|title=SingleTact Capacitive Tactile Sensors|url=https://www.singletact.com}}</ref> elements.

==Optically-based tactile sensors==
Several kinds of tactile sensors have been developed that take advantage of camera-like technology to provide high-resolution data.
A key exemplar is the Gelsight technology first developed at MIT which uses a camera behind an opaque gel layer to
achieve high-resolution tactile feedback.<ref>{{Cite journal|last1=Baeckens|first1=Simon|last2=Wainwright|first2=Dylan K.|last3=Weaver|first3=James C.|last4=Irschick|first4=Duncan J.|last5=Losos|first5=Jonathan B.|date=2019|title=Ontogenetic scaling patterns of lizard skin surface structure as revealed by gel-based stereo-profilometry|journal=Journal of Anatomy|language=en|volume=235|issue=2|pages=346–356|doi=10.1111/joa.13003|issn=1469-7580|pmc=6637707|pmid=31099429}}</ref><ref>{{Cite journal|last1=Wainwright|first1=Dylan K.|last2=Lauder|first2=George V.|last3=Weaver|first3=James C.|date=2017|title=Imaging biological surface topography in situ and in vivo|journal=Methods in Ecology and Evolution|language=en|volume=8|issue=11|pages=1626–1638|doi=10.1111/2041-210X.12778|bibcode=2017MEcEv...8.1626W |s2cid=89811965 |issn=2041-210X|doi-access=free}}</ref>  The Samsung ``See-through-your-skin'' (STS) sensor uses a semi-transparent gel to produce combined tactile and optical imaging.<ref>{{Cite web|last=Hogan|first=Francois|date=5 Jan 2021|title=Seeing Through Your Skin: Recognizing Objects With a Novel Visuotactile Sensor|url=https://openaccess.thecvf.com/content/WACV2021/html/Hogan_Seeing_Through_Your_Skin_Recognizing_Objects_With_a_Novel_Visuotactile_WACV_2021_paper.html|access-date=11 October 2021|website=PPS}}</ref>''

==Strain gauge rosettes==
Strain gauges rosettes are constructed from multiple [[strain gauge]]s, with each gauge detecting the force in a particular direction. When the information from each strain gauge is combined, the information allows determination of a pattern of forces or torques.<ref name="B">[http://www.schunk.com/schunk_files/attachments/FT-Nano_43_EN.pdf Data sheet for Schunk FT-Nano 43, a 6-axis force torque sensor]</ref>

==Biologically inspired tactile sensors==
A variety of biologically inspired designs have been suggested ranging from simple whisker-like sensors which measure only one point at a time <ref>{{cite conference |url=https://www.researchgate.net/publication/221116457 |title=Tactile Discrimination Using Template Classifiers: Towards a Model of Feature Extraction in Mammalian Vibrissal Systems |last1=Evans |first1=Mathew H. |last2=Fox |first2=Charles W. |last3=Pearson |first3=Martin |last4=Prescott |first4=Tony J. |date=August 2010 |location=Paris, France |conference=From Animals to Animats 11, 11th International Conference on Simulation of Adaptive Behavior}}</ref> through more advanced fingertip-like sensors,<ref name="C">{{cite book|title=A robust micro-vibration sensor for biomimetic fingertips – IEEE Conference Publication|pages=659–663|doi=10.1109/BIOROB.2008.4762917|chapter=A robust micro-vibration sensor for biomimetic fingertips|year=2008|last1=Fishel|first1=Jeremy A.|last2=Santos|first2=Veronica J.|last3=Loeb|first3=Gerald E.|isbn=978-1-4244-2882-3|s2cid=16325088 }}</ref><ref name="D">{{cite web|url=https://ieeexplore.ieee.org/document/5174720 |title=Development of a tactile sensor based on biologically inspired edge encoding - IEEE Conference Publication|pages=1–6|author=|date=June 2009|website=ieeexplore.ieee.org}}</ref><ref name="E">{{cite book|title=A biologically inspired tactile sensor array utilizing phase-based computation – IEEE Conference Publication|pages=45–48|doi=10.1109/BIOCAS.2006.4600304|chapter=A biologically inspired tactile sensor array utilizing phase-based computation|year=2006|last1=Cassidy|first1=Andrew|last2=Ekanayake|first2=Virantha|isbn=978-1-4244-0436-0|s2cid=5774626 }}</ref> to complete skin-like sensors as on the latest [[iCub]]{{Citation needed|date=January 2022}}. Biologically inspired tactile sensors often incorporate more than one sensing strategy. For example, they might detect both the distribution of pressures, and the pattern of forces that would come from pressure sensor arrays and strain gauge rosettes, allowing [[two-point discrimination]] and force sensing, with human-like ability.

Advanced versions of biologically designed tactile sensors include [[vibration]] sensing which has been determined to be important for understanding interactions between the tactile sensor and objects where the sensor slides over the object. Such interactions are now understood to be important for human tool use and judging the texture of an object.<ref name="C"/> One such sensor combines force sensing, vibration sensing, and heat transfer sensing.<ref name="F"/>

==DIY and open-hardware tactile sensors==
Recently, a sophisticated tactile sensor has been made [[Open-source hardware|open-hardware]], enabling enthusiasts and hobbyists to experiment with an otherwise expensive technology.<ref name="D1">{{cite web|url=http://www.takktile.com/main:plans|title=Building It – TakkTile|website=www.takktile.com}}</ref> Furthermore, with the advent of cheap optical cameras, novel sensors have been proposed which can be built easily and cheaply with a 3D printer.<ref name="D2">{{cite web|url=https://github.com/Exhor/bathtip|title=Exhor/bathtip|website=GitHub}}</ref>

==See also==
* [[Tactile technology]]
* [[List of sensors]]
* [[Pressure measurement]]
* [[Sensitivity (electronics)|Sensitivity]]
* [[Touch sensor]]
* [[Transducer]]
* [[Tactile imaging]]

==References==
{{Reflist}}

==External links==
* [http://www.soton.ac.uk/~rmc1/robotics/artactile.htm Automation and Robotics]
* [http://library.thinkquest.org/C0126120/tactile.htm Tactile/Touch and Resistive Based Sensors]

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[[Category:Transducers]]