Positioning device for outdoor mobile robots using optical sensors and lasers

We propose a novel method for positioning a mobile robot in an outdoor environment using lasers and optical sensors. Position estimation via a noncontact optical method is useful because the information from the wheel odometer and the global positioning system in a mobile robot is unreliable in some situations. Contact optical sensors such as computer mouse are designed to be in contact with a surface and do not function well in strong ambient light conditions. To mitigate the challenges of an outdoor environment, we developed an optical device with a bandpass filter and a pipe to restrict solar light and to detect translation. The use of two devices enables sensing of the mobile robot’s position, including posture. Furthermore, employing a collimated laser beam allows measurements against a surface to be invariable with the distance to the surface. In this paper, we describe motion estimation, device configurations, and several tests for performance evaluation. We also present the experimental positioning results from a vehicle equipped with our optical device on an outdoor path. Finally, we discuss an improvement in postural accuracy by combining an optical device with precise gyroscopes.     

Molecular valve consisting of poly(acrylic acid) gel

A molecular valve, consisting of poly(acrylic acid) gel-coated Au mesh, was developed based on volume change of the gel in response to cation concentration. The valve closed when concentration of cations such as H⁺, Na⁺, K⁺, Ca²⁺, Cu²⁺, or Al³⁺ was low, whereas opened upon increase in its concentration. The valve re-closed when water was flowed. The concentration where the valve opens was found to increase in the order of Al³⁺, Ca²⁺, and Na⁺ (2 × 10⁻⁴, 5 × 10⁻⁴, and 6 × 10⁻³ M, respectively). The response to Cu²⁺ ion showed similar behaviour, but the opening concentration was ca. 2 × 10⁻⁴ M, which is lower than that of Ca²⁺ ion. The valve appeared to close over the pH range from 3 to 12, whereas to open below and above it. The fastest response time to open the valve (less than 1 min) was obtained for a solution of pH 1–2. The valve showed repeatability at least 25 cycles upon successive loading of a solution of pH 2 and water. Effects of anions and pressure were also studied.     

A multilevel PWM strategy suitable for high‐voltage motor direct drive systems with consideration of the adverse effect of dead time

Recently, high‐voltage motor direct drive systems have been put to practical use, and various multilevel PWM strategies have also been proposed. This paper describes a multilevel PWM strategy [our group calls it the Carrier Phase Selection Method (CPS)] that has the lowest line voltage harmonic distortion in order to prevent the degradation of high‐voltage motor winding insulations. This method takes the adverse effect of dead time into consideration, and it controls the shift direction of a carrier phase. Therefore, a favorable output waveform without instantaneous voltage surges is achieved even if the line voltage level changes. Moreover, the switching transitions across all switching devices are well‐balanced, so the utilization of inverter unit cells is equalized. This is an important factor when designing the entire system. Based on simulation and experimental results, it is shown that this CPS method is particularly effective in high‐voltage motor direct drive systems. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(2): 77–88, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20474     

Morphology of nanoholes formed in silicon by wet etching in solutions containing HF and H2O2 at different concentrations using silver nanoparticles as catalysts

Holes with diameters of tens of nanometers were bored in Si(1 0 0) in aqueous solutions containing hydrofluoric acid and hydrogen peroxide utilizing silver nanoparticles as catalysts. The holes grew deeply in the [1 0 0] direction when the concentration of hydrogen peroxide was about 0.18 M. In addition to these vertical holes, holes were generated horizontal to the surface in the 〈1 0 0〉 directions near the surface of the sample. We found that the silver particles making the deep holes in the [1 0 0] direction were more spherical than those making the horizontal holes near the surface. These results indicate that the shape of the silver particles is an important factor controlling the direction of the holes. When the hydrogen peroxide concentration was increased to 1.8 M, as well as the vertical and horizontal holes, a microporous layer was formed on the top surface region. On the other hand, when the hydrogen peroxide concentration was lowered to 0.0018 M, holes did not show any preference for growing direction and were crooked. Even in HF solutions that did not contain hydrogen peroxide, holes were generated at a very slow rate in random directions if the solutions contained oxygen.     

Direct observation of internal structure in spray-dried yttria-doped zirconia granule

Spray-dried yttria-doped zirconia granules were made transparent by immersion in a liquid and the internal structure was characterized using an optical microscope. This unique technique was found to be applicable for this system by using an immersion liquid with appropriate refractive index, and it enabled observation of the internal structure to be made over the entire volume of granules, in clear contrast to conventional SEM observation. Distinct features, which were considered to be agglomerates, were found in the granules. This was supported by SEM observation.     

Microstructure Control of Sintered Porous Yttria-Stabilized Zirconia as a Durable Thermal Shielding Material

The microstructure of a thermal shielding material affects its thermal conductivity and mechanical property. In this study, the effects of the sintering temperature and the polymethyl methacrylate powder as a pore-former on the microstructure of a sintered porous yttria-stabilized zirconia (YSZ), which is used as a durable thermal shielding material, were investigated. It became clear that the microstructure of the sintered YSZ could be controlled by the particle size and the amount of the pore-former and the sintering temperature. The effect of the yttria amount in the YSZ on the microstructure was also clarified.     

Analysis and application of theoretical gain curves to the design of multi-quantum-well lasers

Gain/current curves for a single quantum well are calculated. The optimum well number, cavity length, threshold current, and current density of multi-quantum-well (MQW) lasers are derived in terms of this gain curve. The limiting performance of MQW lasers is found to be better than that of graded refractive index (GRIN) lasers, assuming comparable efficiencies and spontaneous emission linewidths. The optimum threshold current for an MQW laser with a 7 μm cavity and 90 percent facet reflectivity issim50 muA/μm.     

Adsorption of bovine serum albumin to a polymer brush prepared by atom-transfer radical polymerization in a porous inorganic membrane

Protein adsorption was performed by a polymer brush prepared by atom-transfer radical polymerization (ATRP) to a porous inorganic membrane. The porous inorganic membrane, Shirasu Porous Glass made from silica, was modified with a halogen-containing compound to bind the active species for the polymerization. Glycidyl methacrylate was polymerized from the halogen compound by ATRP for a prescribed time, and subsequently chemically modified. The progression of the chemical modification allowed the membrane to lower the phosphate-buffer flux of the porous membrane due to the attachment of the polymer brush. Bovine serum albumin (BSA), as a model protein, was adsorbed at 12 mg per gram of the membrane in permeating BSA solution through the polymer-brush-attached porous membrane.