Tactile sensor
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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 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 sensors 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. 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 lamination, bolted joints, fuel cells 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.
Robots 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>Fleer, S.; Moringen, A.; Klatzky, R. L.; Ritter, H. (2020). "Learning efficient haptic shape exploration with a rigid tactile sensor array, S. Fleer, A. Moringen, R. Klatzky, H. Ritter". PLOS ONE. 15 (1): e0226880. doi:10.1371/journal.pone.0226880. PMC 6940144. PMID 31896135.</ref><ref>"Attention-Based Robot Learning of Haptic Interaction, A. Moringen, S. Fleer, G. Walck, H. Ritter" (PDF). doi:10.1007/978-3-030-58147-3_51. S2CID 220069113. {{cite journal}}: Cite journal requires |journal= (help)</ref>[better source needed] 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] Some methods for simultaneous localization and mapping are based on tactile sensors.<ref>Fox, Charles, et al. "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">Dahiya, R.S.; Metta, G.; Valle, M.; Sandini, G. (2010). "Tactile Sensing—From Humans to Humanoids – IEEE Journals & Magazine". IEEE Transactions on Robotics. 26 (1): 1–20. doi:10.1109/TRO.2009.2033627. S2CID 14306032.</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">Shimojo, M.; Namiki, A.; Ishikawa, M.; Makino, R.; Mabuchi, K. (2004). "A tactile sensor sheet using pressure conductive rubber with electrical-wires stitched method – IEEE Journals & Magazine". IEEE Sensors Journal. 4 (5): 589–596. doi:10.1109/JSEN.2004.833152. S2CID 885827.</ref> lead zirconate titanate (PZT), polyvinylidene fluoride(PVDF), PVDF-TrFE,<ref name="A1">Dahiya, Ravinder S.; Cattin, Davide; Adami, Andrea; Collini, Cristian; Barboni, Leonardo; Valle, Maurizio; Lorenzelli, Leandro; Oboe, Roberto; Metta, Giorgio; Brunetti, Francesca (2011). "Towards Tactile Sensing System on Chip for Robotic Applications – IEEE Journals & Magazine". IEEE Sensors Journal. 11 (12): 3216–3226. doi:10.1109/JSEN.2011.2159835. S2CID 11702310.</ref> FET,<ref name="A2">Piezoelectric oxide semiconductor field effect transistor touch sensing devices</ref> and metallic capacitive sensing<ref>Dobie, Gordon (7 May 2021). "PPS Capacitive Sensors". PPS. Retrieved 7 May 2021.</ref><ref>Dobie, Gordon (7 May 2021). "SingleTact Capacitive Tactile Sensors".</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>Baeckens, Simon; Wainwright, Dylan K.; Weaver, James C.; Irschick, Duncan J.; Losos, Jonathan B. (2019). "Ontogenetic scaling patterns of lizard skin surface structure as revealed by gel-based stereo-profilometry". Journal of Anatomy. 235 (2): 346–356. doi:10.1111/joa.13003. ISSN 1469-7580. PMC 6637707. PMID 31099429.</ref><ref>Wainwright, Dylan K.; Lauder, George V.; Weaver, James C. (2017). "Imaging biological surface topography in situ and in vivo". Methods in Ecology and Evolution. 8 (11): 1626–1638. Bibcode:2017MEcEv...8.1626W. doi:10.1111/2041-210X.12778. ISSN 2041-210X. S2CID 89811965.</ref> The Samsung ``See-through-your-skin (STS) sensor uses a semi-transparent gel to produce combined tactile and optical imaging.<ref>Hogan, Francois (5 January 2021). "Seeing Through Your Skin: Recognizing Objects With a Novel Visuotactile Sensor". PPS. Retrieved 11 October 2021.</ref>
Strain gauge rosettes
Strain gauges rosettes are constructed from multiple strain gauges, 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">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>Evans, Mathew H.; Fox, Charles W.; Pearson, Martin; Prescott, Tony J. (August 2010). Tactile Discrimination Using Template Classifiers: Towards a Model of Feature Extraction in Mammalian Vibrissal Systems. From Animals to Animats 11, 11th International Conference on Simulation of Adaptive Behavior. Paris, France.</ref> through more advanced fingertip-like sensors,<ref name="C">Fishel, Jeremy A.; Santos, Veronica J.; Loeb, Gerald E. (2008). "A robust micro-vibration sensor for biomimetic fingertips". A robust micro-vibration sensor for biomimetic fingertips – IEEE Conference Publication. pp. 659–663. doi:10.1109/BIOROB.2008.4762917. ISBN 978-1-4244-2882-3. S2CID 16325088.</ref><ref name="D">"Development of a tactile sensor based on biologically inspired edge encoding - IEEE Conference Publication". ieeexplore.ieee.org. June 2009. pp. 1–6.</ref><ref name="E">Cassidy, Andrew; Ekanayake, Virantha (2006). "A biologically inspired tactile sensor array utilizing phase-based computation". A biologically inspired tactile sensor array utilizing phase-based computation – IEEE Conference Publication. pp. 45–48. doi:10.1109/BIOCAS.2006.4600304. ISBN 978-1-4244-0436-0. S2CID 5774626.</ref> to complete skin-like sensors as on the latest iCub[citation needed]. 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-hardware, enabling enthusiasts and hobbyists to experiment with an otherwise expensive technology.<ref name="D1">"Building It – TakkTile". 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">"Exhor/bathtip". GitHub.</ref>
See also
- Tactile technology
- List of sensors
- Pressure measurement
- Sensitivity
- Touch sensor
- Transducer
- Tactile imaging
