Visual control of autonomous mobile robot based on self-organizing model for pattern learning

This article proposes a self-organizing model for pattern learning together with an application to an autonomous mobile robot system. The self-organizing model consists of a processing rule prescribed and a memory part being blank at the initial stage. To an input signal, the model searches for a similar signal in the memory, and recalls its related information. If the information accompanied with the input signal differs from the recalled information, the model adds the new information to the memory. It influences the subsequent operations. Thus, the model constructs successively a data-base in a self-organizing way. This model can universally learn and reproduce any pattern of input-output response desired. Two principal functions in autonomous movement, i.e., position identification and obstacle avoiding movement were realized based on the self-organizing model. Furthermore, a camera type autonomous mobile robot system for indoor was made up. The size of the robot is about 0.7 × 0.7 × 0.7 m, and the weight is about 30 kg. The speed of movement is less than 3 km/h. A small computer that has a 16 bit microprocessor and a 1 Mbyte RAM controls the motion of the robot with an extended C language.     

Joint-space orthogonalization and passivity for physical interpretations of dextrous robot motions under geometric constraints

A principle of ‘joint-space orthogonalization’ is proposed as an extended notion of hybrid (force and position) control for robot manipulators under geometric constraints. The principle realizes the hybrid control in a strict sense by letting position feedback signals be orthogonal in joint space to the contact force vector whose components exert at corresponding joints. This orthogonalization is executed via a projection matrix computed in real-time from a Jacobian matrix of the constraint equation in joint coordinates. To show the important role of the principle in control of robot manipulators, two basic set-point control problems are analysed. One is a hybrid PID control problem for robot manipulators under geometric endpoint constraint and another is a coordinated control problem of two arms. It is shown that passivity properties of residual dynamics of robots follow from the introduction of a quasi-natural potential and the joint-space orthogonalization. Various stability problems of PID-type feedback control schemes without compensating for the gravity force and with or without use of a force sensor are discussed from passivity properties of robot dynamics with the aid of the hyper-stability theory.     

Microstructural Development of Natural Hydroxyapatite Originated from Fish-Bone Waste through Heat Treatment

The morphologic and microstructural development of natural fish bone through heat treatment is examined in view of fish-waste management and as a possible route for hydroxyapatite ceramics. Fish bone heated at temperatures ≤1300°C maintains a porous structure, with a sintered wall and a major crystalline phase of hydroxyapatite. Fish-originated ceramics are potentially useful as bioactive media as well as for environmentally compatible materials.     

Hydride Anion Substitution Boosts Thermoelectric Performance of Polycrystalline SrTiO3 via Simultaneous Realization of Reduced Thermal Conductivity and High Electronic Conductivity

The development of environmentally benign thermoelectric materials with high energy conversion efficiency (ZT) continues to be a long-standing challenge. So far, high ZT has been achieved using heavy elements to reduce lattice thermal conductivity (κ_lat). However, it is not preferred to use such elements because of their environmental load and high material cost. Here a new approach utilizing hydride anion (H⁻) substitution to oxide ion is proposed for ZT enhancement in thermoelectric oxide SrTiO₃ bulk polycrystals. Light element H⁻ substitution largely reduces κ_lat from 8.2 W/(mK) of SrTiO₃ to 3.5 W/(mK) for SrTiO_3−xH_x with x = 0.216. The mass difference effect on phonon scattering is small in the SrTiO_3−xH_x, while local structure distortion arising from the distributed Ti−(O,H) bond lengths strongly enhances phonon scattering. The polycrystalline SrTiO_3−xH_x shows high electronic conductivity comparable to La-doped SrTiO₃ single crystal because the H⁻ substitution does not form a grain boundary potential barrier and thus suppresses electron scattering. As a consequence, SrTiO_3−xH_x bulk exhibits maximum ZT = 0.11 at room temperature and the ZT value increases continuously up to 0.22 at T = 657 K. The H⁻ substitution idea offers a new approach for ZT enhancement in thermoelectric materials without utilizing heavy elements.     

Coalition structure generation in cooperative games with compact representations

This paper presents a new way of formalizing the coalition structure generation problem (CSG) so that we can apply constraint optimization techniques to it. Forming effective coalitions is a major research challenge in AI and multi-agent systems. CSG involves partitioning a set of agents into coalitions to maximize social surplus. Traditionally, the input of the CSG problem is a black-box function called a characteristic function, which takes a coalition as input and returns the value of the coalition. As a result, applying constraint optimization techniques to this problem has been infeasible. However, characteristic functions that appear in practice often can be represented concisely by a set of rules, rather than treating the function as a black box. Then we can solve the CSG problem more efficiently by directly applying constraint optimization techniques to this compact representation. We present new formalizations of the CSG problem by utilizing recently developed compact representation schemes for characteristic functions. We first characterize the complexity of CSG under these representation schemes. In this context, the complexity is driven more by the number of rules than by the number of agents. As an initial step toward developing efficient constraint optimization algorithms for solving the CSG problem, we also develop mixed integer programming formulations and show that an off-the-shelf optimization package can perform reasonably well.     

Strain-Dependent Dynamic Properties of Remolded Sand-Clay Mixtures

A series of undrained cyclic torsional simple shear tests using hollow cylindrical torsional shear apparatus was carried out to investigate the dynamic shear moduli and damping properties of clayey specimens with various sand contents and plasticity indices. The clayey soils used were collected from various sites along the coast of west Japan. Among these clayey soils, a clay sample with intermediate plasticity and another with high plasticity were mixed with silica sand at different proportions in order to examine the dynamic properties of sand-clay mixtures. In addition, experiments were carried out on undisturbed and remolded natural clay specimens with various plasticities. The effects of plasticity, loading frequency and confining pressure on the strain dependent normalized shear modulus and damping ratio were examined. Based on the results, empirical correlations for predicting the normalized shear modulus and damping ratio of remolded sand-clay mixtures at various shear strain levels were proposed.     

Internal Friction in Metaphosphate Glasses

The internal friction of metaphosphate glasses was measured as a function of temperature by a free torsional vibration method. In the high-temperature region metaphosphate glasses (MO/P₂O₅=l)for which M=Ca, Sr, or Ba exhibit high-temperature peaks in plots of internal friction vs temperature, whereas for M =Mg or Zn this peak is missing.     

A relationship between electrical conductivity and photodegradation in styrene-butadiene copolymer/multi-wall carbon nanotube composite

An effect of photodegradation on electrical conductivity of a styrene-butadiene copolymer (SBR)/multiwall carbon nanotube (MWNT) composite was studied with a TiO₂/polyethylene oxide/methyl linoleate paint photocatalyst under UV and/or visible light irradiation. An oxidative etching of impurities on the MWNT surface was caused by the UV or visible light irradiation, leading to an increase of quality of MWNT. On the other hand, the photocatalyst addition caused the degradation of MWNT structure. A relationship between the electrical conductivity and MWNT content showed that the MWNT dispersity in a SBR was superior to that in a polystyrene (PS). In addition, the PS addition to SBR matrix caused MWNT aggregation. The electrical conductivity decrease of the MWNT composite was due to electrical percolation structure loss caused by the photocatalyst under the visible light irradiation, and its rate depended on the MWNT dispersity. The PS molecular weight change behavior with the photocatalyst was consistent with the electrical conductivity one of the SBR/MWNT. The photocatalyst ability was estimated from the electrical conductivity of the SBR/MWNT.     

Mechanical and Thermal Properties of β'-Sialon Prepared by a Slip Casting Method

Various mechanical and thermal properties of β'-sialon ceramics, Si_6–zAl_zO_zN_8–z, prepared from aqueous slurries by a slip casting method were investigated as a function of Z values from 0 to 4. In the present study, Si_6–zAl_zO_zN_8–z occurred in the β'-sialon crystalline phase only near Z = 1. The maximum values for bending strength and fracture toughness, 660 MPa and 5.7 MPa·m^1/2, respectively, were obtained at Z = 0.5. The thermal expansion coefficient exhibited its lowest value, 3.4 × 10⁻⁶· T⁻¹ , at Z = 0.5. In view of the present results, β'-sialon, Si_6–zAl_zO_zN_8–z (Z = 0.5–1), prepared by a slip casting method using aqueous slurries could be adopted, with no problem, for refractory parts.