A bio‐inspired approach for regulating and measuring visco‐elastic properties of a robot arm

This work focuses on interaction control of robot manipulators in unstructured environments, with special regard for situations of unpredictable contact/noncontact transitions. It is basically addressed to those environments where a high level of robot adaptability is required and no information on the geometry of the environment is available. By pointing out the main limitations of standard interaction control schemes in managing situations of contact/noncontact transitions, this paper proposes a new control solution that is inspired by the biological model of motor control in voluntary movements. It consists of a combination of a feedforward loop and a proportional‐derivative plus gravity compensation control in the feedback loop. The control law is named coactivation‐based compliance control in the joint space since a unique function, called coactivation function, is evaluated for regulating robot visco‐elasticity in an unpredictably variable environment. It resumes the mechanism of adjustable visco‐elastic properties acting on the agonist and antagonist muscles of a human arm. The work also proposes a methodology for evaluating performance of interaction control schemes that is based on stiffness graphical representation through ellipses. The method replicates the experimental setup used in neuroscience to measure stiffness in human limbs. It is regarded as a powerful tool for evaluating robot behavior over space and time, since it allows both a visual representation of stiffness variation during motion and a quantitative measure of robot performance. It is shown how the method can be used to evaluate a control scheme and how it can provide indications to improve a control law. In this paper, an application to the standard compliance control in the joint space and the coactivation‐based compliance control is presented. © 2005 Wiley Periodicals, Inc.     

Eye Tracking in Image Sequences by Competitive Neural Networks

An automatic algorithm is presented for the eye tracking within face image sequences. It is based on the property of local Gabor filters to efficiently determine the location of eyes in face images. The proposed algorithm is implemented by a competitive neural network, that locates and tracks the eyes in a reliable manner as shown by experimental results.     

Nanocluster evolution in Ge ion implanted Ta2O5 layers

Ion implantation-induced nanoclusters were synthesized in reactive sputtered Ta₂O₅ films by Ge⁺ implantation and subsequent annealing. The effects of ion fluence and post-implantation thermal treatment on the kinetics of the nanoclustering were investigated. Ge⁺ ions with energy of 40 keV and fluences of 5 × 10¹⁵, 1 × 10¹⁶ and 5 × 10¹⁶ cm^− 2 were implanted in the Ta₂O₅ layers at room temperature. The samples were thermally treated by rapid thermal annealing in vacuum at 700 °C and 1000 °C for 30, 60 and 180 s. Structural studies of all samples were done by Cross-sectional Transmission Electron Microscopy in diffraction and phase contrast mode. Under optimized conditions (high implantation fluence, subsequent annealing) nanoclusters are formed around the projected ion range of the implanted Ge⁺ ions. The structure of the implanted Ta₂O₅ matrix changes from amorphous to orthorhombic when the annealing was performed at 1000 °C. Although the Ta₂O₅ matrix crystallizes, no evidence is obtained for crystallization of the embedded nanoclusters even after annealing at 1000 °C.     

Tilting angle and water slippage over hydrophobic coatings

Hydrophobic coatings, such as octadecyltrichlorosilane or n-alkyl monolayers, enhance the slippage of liquids on solid walls. For a given alkyl chain length, the main structural parameter for homogeneous coatings is the tilt angle between coating molecules and the surface normal. In this paper, ab initio calculations are used to calculate the equilibrium configuration of coating molecules, showing that the tilt angle easily changes from 0° to 30° depending on the specific head group binding the solid substrate. These values are used to set up classical molecular dynamics of water slippage over the coatings using different water models (Transferable Intermolecular Potential 3 point (TIP3P), Transferable Intermolecular Potential 4 point (TIP4P) and TIP4P/2005). The slippage is found to be robust with respect to the coating tilting, while a slight dependence on the water model is observed.