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 employed in applications where sensing physical interaction is required, including robotics, computer hardware and even security systems. One of the most common implementations of tactile sensors are touch screen devices used widely in mobile phones and computing.

Tactile sensors are generally known and can be grouped into a number of different types depending upon their construction; the most common groups are piezoresistive, piezoelectric, capacitive and elastoresistive sensors.[1]

Uses[edit]

Tactile sensors are often in everyday objects such as elevator buttons and lamps which dim or brighten by touching the base. There are also innumerable 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 noted to be used in the manufacturing of automobiles (brakes, clutches, door seals, gasket), battery lamination, bolted joints, fuel cell, etc.

In robots designed to interact with objects requiring handling involving: precision, dexterity, or interaction with unusual objects it becomes increasingly necessary to provide sensory apparatus which is functionally equivalent to the various sensors which human workers are naturally endowed. Tactile sensors have been developed for use with robots. Tactile sensors can complement visual systems by providing information at the time contact is made between a gripper of the robot and an object being gripped. At this time vision is no longer sufficient, as the mechanical properties of the object cannot be determined by vision alone. Determining weight, 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:

Pressure Sensor Arrays[edit]

Pressure sensor arrays are large grids of tactiles. A tactile is a ‘tactile element’. Each tactel is capable of detecting normal forces. The advantage of tactel based sensors is that they 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.[2] Pressure sensor arrays are often available in thin-film form. They are primarily used as analytical tools used in the manufacturing and R&D processes by engineers and technician, but have been adapted to be used in robots. Examples of such sensors available to consumers include arrays built from conductive rubber,[3] lead zirconate titanate (PZT), polyvinylidene fluoride(PVDF), PVDF-TrFE,[4] FET,[5] and metallic capacitive sensing elements.

Strain Gauge Rosettes[edit]

Strain gauges rosettes are constructed from multiple [strain gauge]s, where each are responsible for detecting the force or torque in a particular direction. The advantage of strain gauges is that when the information from each individual strain gauge is combined, the information allows determination of a pattern of forces or torques.[6]

Biologically Inspired Tactile Sensors[edit]

A variety of biologically inspired designs have been suggested,.[7][8][9] One characteristic of biologically inspired tactile sensors is that they 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. Hence, the advantage of a biologically designed tactile sensor is able to perform multiple types of sensing, e.g. two-point discrimination and force sensing both 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.[7] One such sensor combines force sensing, vibration sensing, and heat transfer sensing.[10]

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