# Tutorial Review on Space Manipulators for Space Debris Mitigation
## 12 The Nature of Dexterity and Tactility
Piezoelectric film can detect only dynamically changing forces and slip similar to Pacinian corpuscles in human skin; to measure static forces, resistive or capacitative measurements are required. Force sensing provides information on pressure for shape and hardness determination, piezoelectric dynamic vibration sensors provides information on texture and slip, while fast response thermocouples provides information on thermal conductivity. Pain was recorded as an overload in all three sensors. Thermal feedback was provided through a Peltier effect heat pump, texture/slip and pressure feedback was provided by increasing temperatures towards the thermal design limit of 50 \({}^{\circ}\)C. The system revealed that operators gave 90% correct identification of surfaces after only 10 min of training. Active touch sensing using multifingered hands may be used to acquire 3D scene information by manipulating and detecting changes in the environment [293]. Complete haptic feedback for handling compliant and slippery material requires force feedback for pressure information and tactile imaging for the extraction of shape [273]. Conductive silicone rubber impregnated by carbon particles may be employed as a tactile sensor in measuring applied force through resistance change. Slippage direction and extraction of shape from an array of such tactile \"taxels\" may be enabled by neural networks. This can provide the basis for elastomeric artificial skin. Artificial skin comprising 2D arrays of taxels affords highly sophisticated robotic control strategies [294] including the implementation of tactile maps [295]. Active tactile sensing with multiple fingers mounted with arrays of tactels enables the construction of 3D scenes of the touched surface [293]. Superquadratics can be fitted to the grasp shape through the shape parameters. Electronic skin with embedded pressure and temperature sensors may be based on flexible organic thin-film transistors which can stretch without altering the substrate's conductive properties [296]. Inkjet printing can apply circuitry patterns of conducting thin films--nanowires--with organic transistor-based amplifiers onto a substrate. Tactility is inherently multisensory which invites consideration of multisensory fusion. Multiple sensor data affords greater accuracy than single sensor data but measurement data between sensors must be correlated. Bayesian inferencing provides a principled means for combining multisensory data probabilistically. [PERSON] rule computes a posteriori probability of a hypothesis given its a priori probability and the conditional probability of an observation given that hypothesis. Dempster-Shafer theory of evidential reasoning extends Bayesian probability by overcoming some of its shortcomings at the cost of higher computational complexity. We can assume that for a robot manipulator and its finger configuration, tracking its changing pose \((q,\dot{q})\) is of paramount importance and multiple sensors provide indirect measurements of this changing pose. We are not aware of any work examining sensor fusion of multiple sensor modalities relating to tactility but propose that it is an area that should be developed. Assuming that tactility fusion is a variation on robot pose fusion, a discrete linear system model with state \(x(k)\) of pose, input \(u(k)\) with process noise \(w(k)\) and measurement output \(z(k)\) with measurement noise \(v(k)\) has a state space form:  
\[x(k)=A(k)x(k-1)+B(k)u(k)+w(k) \tag{146}\]  
\[z(k)=H(k)x(k)+v(k) \tag{147}\]  
Process and measurement noise are independent and Gaussian with covariance \(Q(k)\) and \(R(k)\) respectively. In the case of multiple sensors, there is more than one measurement equation. The Kalman filter is a recursive Bayesian method that generates an optimal solution to mean square error in the presence of Gaussian noise [297]. The Kalman filter has been the most commonly used approach on spacecraft for merging attitude determination sensors for spacecraft attitude estimation so it has an extensive space pedigree.