To achieve high accuracy advanced signal processing is required. J. Dargahi, S. Sokhanvar, S. Najarian, and S. Arbatani. The suction module consists of four layers the base layer, the spacer layer to introduce gaps between the base and the suction layers, the suction layer with suction holes, and the enclosure layer to establish proper contact boundary with an object and to reduce air leaks. With a proper arrangement, this feature can be turned into an advantage and the POSFET device can be made multifunctional—capable of detecting both dynamic contact forces and the contact temperature. Again there are numerous examples to illustrate this technique. Broadly defined, capacitance is the ability of a capacitor to store electrical charge. Additionally, sensor probe was characterized for machine tool with a computer numerical controlled tool with respect to various parameter setting such as silicone cylinders (1.58–4.75 mm), at varying subcutaneous depth (1–5 mm) with sliding speed (0.5–21 mm/s) and range of indentation depths (0–8 mm). Figure 4.20.  reported a skin-inspired, highly stretchable sensor with conformable matrix networks (SCMNs), based on a structured polyimide network, as shown in Figure 5. Change in resistance of semi-conductive materials (b) The balloon tactile displays were mounted directly onto the da Vinci master control for thumb and index finger (adapted with permission from Ref. The spinothalamic pathway is part of the anterolateral system, and it transmits information to the thalamus about temperature and pain, while the dorsal column-medial lemniscus pathway transmits vibration, pressure, and shared position information from mechanoreceptors to the CNS [40, 41]. One of the first results of this approach is described in Ref. Tactile sensors are used either to extract shape information on the basis of touch or to provide haptic feedback to the operator of manipulators as for instance in surgery. Figure 5(d) shows the spatial pressure achieved before and after 300% expansion of the SCMN, enabling it to identify position and pressure load and estimate the size of the loading object. The detection of small defects requires waves with a correspondingly short wavelength and therefore a much higher frequency compared to applications in air, typically in the MHz range. By measuring these parameters over a relevant frequency range, various liquid properties can be deduced or evaluated. , presenting a system based on ToF in the z-direction and spatial scanning using an x–y table, and  (2D angular scanning). (Source: Engel et al., 2003a,b). Piezoresistive elastomers belong to the first tactile sensors in robot grippers [23,24]. #U1505251, #U1713219, and #71531004) funded by the National Natural Science Foundation of China. For instance, Ohtsuka et al. In addition to minimizing the utilization of space, the marriage of transducer and electronics results in better force resolution, spatial resolution, and signal-to-noise ratio. Where acoustic damping (see Section 9.1.3) is an unwelcome effect in most of the applications discussed so far, this property of sound can be used to identify, monitor, or determine particular properties of a material. The thickness of polymer film depends on the solution concentration, spinner’s speed, and time of spinning. Various alternative schemes have been investigated aiming at increased effectiveness of this solution and reduction of electronic complexity, for instance in Refs [30–32]. At least one company offers such pressure-sensitive devices, which can also be used for the construction of tactile sensors . In the following, the most recent advances of tactile technologies in MIS are briefly summarized. Either the objects move relative to fixed transducers, or the transducers are moving relative to a fixed object. Thus, having a replica in intelligent machines that have been developed for robotic surgery remains a thing of focus in the world today. Schostek et al. These problems are solved using a set of transmitters and/or receivers at known relative positions and proper signal processing. The 8×8 taxels are defined by the crossing points of the fibers. The sensor comprised of a composite material (multi-walled carbon nanotubes dispersed in polydimethylsiloxane (PDMS)) and liquid metal interconnects. Gray, “Preparation, characterization and micromolding of multi-walled carbon nanotube polydimethylsiloxane conducting nanocomposite polymer,”, Z. Wu, Z. Chen, X. As an example, a 2.5 μm thick PVDF-TrFE polymer film can be deposited by spin coating a 10% solution at 3000 rpm for 30 s (Dahiya et al., 2008). The idea of mimicking the sense-of-touch capacities of by human skin has motivated the use of fully stretchable organic electrochromic devices (ECDs) which can be fabricated with reduced consumption power and can be integrated with highly tunable resistive pressure sensing. When negative pressure is applied, the air between the suction layer and the object will be sucked out to create vacuum thus increasing the contact grip. To our knowledge, no fully nanoscience based tactile sensor has yet been produced. This analogy, between POSFET touch sensing device and the mechanoreceptors in the skin, is shown in Figure 4.4. Our sense of touch is crucial for object recognition and manipulation. In order to determine object size and ship, the software uses logarithm based on the opening angle of the forceps and pressure profile. 5. Figure 4.22. The adaptation rates can be separated into two main groups: slow adapting (S) units and rapid adapting units (RA), also known as fast adapting (FA) units. The robot enables measuring accurate tactile motion and feedback, due to the role of MR in mimicking the human fingertip with various materials. Gao et al. This system was the first complete tactile system known to be applied to commercial robotic surgical system; it is used to evaluate the direct tactile feedback in robotic surgery. One of the most common classification methods is by the source of neural inputs which may be cutaneous, kinesthetic, or haptic [22–25]. Not only is the bulk resistivity a proper sensing parameter, but it is also possible to utilize the surface resistivity of such materials. The dermis layer, which is located under the epidermis, transmits nerve information from thermal, mechanical, and chemical stimuli. Moreover, sensors were attached to the main controller manipulators in order not to interfere with arm or tool motion and measure acceleration signals and then transfer it to the main receiving unit (MRU). Herein, a template‐method is used to synthesize the hierarchical structure of MOF hybrid array (MHA) on copper mesh (MHA@Mesh) for flexible sensor.  designed another acceleration feedback system named by vibrotactile feedback for the da Vinci system (Verro-touch). (2002) proposed a large area force sensor fabricated by sandwiching semi-conductive film in between screen-printed traces of Ag-filled thermoplastic polymer. Typical approaches for resistive-metal based sensors involve a flexible array of tactile sensors with each sensory element consisting of piezoresistive metal capable of sensing stress/shear forces (Engel et al., 2003b; Hwang et al., 2007). Figure 4.6. An important aspect of tactile sensors based on resistive sheets is the selection and readout of the individual pressure points (taxels). 4.20) contains a large grid based on capacitive sensing. However, in many applications the resolution requirements are not severe. These promote durability and an excellent pressure sensitivity of 0.06 kPa−1. Effects of different parameters on the sensing performance of a soft capacitor fiber are also studied. Furthermore, DNN-based e-skin showed high performance in pressure sensitivity and high spatial resolution (0.78 ± 0.44 mm) for position recognition . Polymer-based tactile sensors, on the other hand, are more flexible, not limited by dimensions, and chemically resistant (Liu, 2007). Additionally, thin soft strips are attached to the modules as extensions and loops to facilitate easy mounting over the rigid hand. Tactile sensors are used in robotics, computer hardware and security systems. Each element contains one piezoresistor. Optical tactile sensors have a wide range application for compliance , roughness sensing , shear, and vertical stress [74–76]. The stiffness palpation method proposed in can distinguish vein from surrounding tissue. Cross-talk between the sensing elements poses a problem for these kinds of sensors. While the tendons control the overall gripping motion and the orientation of the hand, the soft layers provide contact modulation to improve the grip. (2004) reported fabrication of flexible tactile sensing array using a conductive rubber capable of sensing pressure-related deformations. The sensing electrodes were obtained by winding copper electrodes around nylon fibres. An often overlooked aspect is mechanical crosstalk between adjacent taxels, due to the stiffness of the elastic layer or an additional protective layer. The first part is a rigid tendon-driven modular anthropomorphic gripper which acts as a skeleton for the whole device (Fig. As described later in this section, the POSFET devices on the tactile sensing chips are realized by depositing a piezoelectric polymer, PVDF-TrFE (Polyvinylidene Fluoride—Trifluoroethylene), on the gate area of a MOS transistor (Dahiya et al., 2009a, 2011, 2013, 2014; Adami et al., 2012);. , the signals are relayed to the master handles of the system. Different types of materials used for tactile sensing includes silicon-based piezoresistive (Beebe et al., 1995; Kane et al., 2000) or capacitive sensors (Gray and Fearing, 1996; Leineweber et al., 2000), and polymer-based piezoelectric, capacitive or piezoresistive sensors (Kolesar and Dyson, 1995; Reston and Kolesar, 1990). Vibration measurements (example: a vibrating cantilever, phase detection of an 80 kHz sound wave ), Seam tracking (example: short-range scanning with a MHz piezoelectric transducer with focusing surface ), Respiratory air flow (example: two CW waves from piezoelectric transducers, with slightly different frequencies ), Liquid level (example: in bottles, 220 kHz piezoelectric sensors, burst mode ; as an acoustic resonator ), Go/no-go decision on product quality (example: quality of foundry pieces; signature imaging and Artificial Neural Network (ANN) for identification ; defect detection in food can production line: same method, according to Fig.  presented a low-cost, single-use probe that is mounted in RMIS for localizing subcutaneous structure like blood vessel and tumors. The tactile feedback in the system was evaluated by 16 novices and 4 experts peg transfer tasks, as reported by King et al. . One of the first sound-based tactile matrix sensors is described in Ref. tactile sensor is developed, on the basis of the concept of applying two sensors with considerably different stiffnesses to soft tissue for compliance detection, to demonstrate the ability of this concept in detecting the stiffness of a soft tissue independently on the applied displacement between the sensor and the tissue. Scanning can be performed in various ways. Tactile sensors in medical surgery have already been applied in a variety of surgical robotic tools. The skin has been regarded as the largest sensory system with which human surgical experts can carry out different intelligent tasks such as surgery. 4 shows a schematic of artificial tactile skin and the arrangement of the spiral electrodes. Mechanoreceptors in the human skin collect different information by neural afferents, which transmit information to the brain. The overall dimension of the initial version of this tactile sensing array was 1.5 cm × 1.5 cm, with each POSFET touch sensing device on the array designed to be 1 mm × 1 mm in size—ensuring human-like spatial acuity. However due to the continuous nature of the resistivity of the sheet, the selected taxel resistance is shunted by resistances of all other taxels, as can be seen in the model of the tactile sensor given in Fig. (2007) reported an experimental design and a theoretical model of an endoscopic tooth-like tactile sensor capable of measuring compliance of a contact tissue/object. The sensor is aimed at to improve minimally invasive surgeries but its potential in helping robots grip sensitive objects is very attractive even if the sensor cannot inform on the direction of pressure. It must also be miniature and might need to be disposable. Thus, flexible tactile sensors are a promising development due to their ability to mimic the transduction mechanism of human skin. The modules are arranged such that the suction module comes over the link of the rigid hand whereas the inflation module comes over the joint (Fig. This results in accumulation of charge carriers at the surface of the semiconductor—according to the polarization direction. The pressure sensor with a diaphragm configuration utilized a Wheatstone bridge circuit, which allowed it to achieve high performance with a fast time-response (90 ms), high resolution (sub-100 Pa), high sensitivity (0.0835 kPa−1), linearity, and temperature self-compensation. Robotics; Computer hardware; Security system; Touch screen devices on mobile phone; Computing; Advantages of Tactile Sensor. They can be found in elevator buttons, mobile phone touch screens, as well as in robotics. Later, Kim et al. developed a piezoelectric tactile sensor able to locate small, barely-visible nodules during minimally invasive thoracoscopic surgery . However, pressure sensitivity still needs to be improved to detect low pressure range and external stress. Human skin is an active sensory system which protects our bodies from injury, dehydration, radiation, and toxic substances in the external environment by tactile sensation of stimuli . L. Li, Z. Lou, W. Han, and G. Shen, “Flexible in-plane microsupercapacitors with electrospun NiFe2O4nanofibers for portable sensing applications,” Nanoscale, vol. A snapshot of the binary images, obtained from the normalized response of various taxels, is also shown in Figure 4.6(c). Chou et al. Crosstalk and phantom images are reduced by actively guarding the nonselected rows and columns, thus zeroing the potential over all nonselected taxels. The extended gate approach brings the sensor and conditioning electronics closer, and hence, the overall response is better than the conventional approach—where the sensor and conditioning electronics are placed apart. ). They still receive much attention from designers of robots intended for human-like capabilities, in particular soft gripping (see, for example, Fig. Various alternative schemes have been investigated aiming at increased effectiveness of this solution and reduction of electronic complexity, for instance in Refs. In addition, optical tactile sensors exhibit many potential applications which require the features of portability and flexibility [77, 78]. A typical problem to be overcome in this approach is to obtain image data that are position and orientation invariant. Individual taxels are addressed by selecting the corresponding row and column, for instance by applying a reference voltage on the column electrode and measuring the current through the selected row electrode. A Si3N4/SiO2 double layer is used as a gate dielectric. Yeow, in Biosensors and Bioelectronics, 2011. Furthermore, this evaluation included tool contact acceleration feedback via audio. The pressure sensitive part of each taxel consists of the two crossing areas between row and column. When piezoelectric polymer is polarized along thickness and the mechanical stress is also applied along this direction, the mechanical stress T3, the electric field E3, and the electric displacement D3 are related as (Dahiya et al., 2009c,d; Dahiya, 2015): Figure 4.4. Most popular is the row–column readout, accomplished by a line grid of highly conductive electrodes on either side of the elastomer, making right angles and thus defining the pressure points of the sensor matrix (Figure 4.21A). The most common techniques currently being employed for tactile transduction are based on piezoresistive, capacitive, optical, piezoelectric, and triboelectric tactile sensing methods (TESM). The PVDF sensors are mechanically durable, have a wide bandwidth response, and are self-powered. Using ultrasound concludes this chapter grip and the arrangement of the seven DOF can be used to better. 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