Newly developed walking apparatus for identification of obstructions by visually impaired people

Mitsuhiro Okayasu 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.6

In this work, two visual systems to help visually impaired people walk were developed: the first is a white cane with a non-contact detection system, and the second is a three-dimensional (3D) visual system. In place of the sense of sight, the sense of touch, either via vibration or of pins, can relay information on objects and obstacles around people. In a white cane non-contact detection system, two sets of ultrasonic sensors and vibrators, respectively, are employed to indicate the positions of both low- and high-level obstructions in front of the visually impaired person. When objects are detected by the sensor, the vibrator is strongly activated. In this system, the range of obstruction detection can be adjusted between 0.5 m and 5.5 m. By comparison, the 3D visual system uses two different components, an infrared camera sensor to detect obstructions and a tooling apparatus, incorporating a number of 1 mm diameter pins, by which their 3D shapes are derived. The pins are arranged in a 10×10 matrix and move longitudinally between the retracted and extended positions based on the depth data between the infrared sensor and the obstruction. Pins are elongated individually, so that each pin tip represents a specific area of the outer surface of the object. This tactile 3D image can provide effective object information.

Effects of cyclic loading on fatigue properties of austenite stainless steel

Mitsuhiro Okayasu,Hironobu Fukui 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.9

Fatigue properties of stainless steels have been investigated by various researchers. The present work examined fatigue properties undervarious cyclic loading conditions to determine the significant factors of loading condition to fatigue strength (se). From this approach,no clear frequency effects on the S-Nf relation were detected, but clear R-ratio effects were identified on fatigue strength. A higher R-ratioyielded higher se, and a clear correlation was observed between R-ratio and endurance limit. A different trend was observed for the S-Nfcurve when the stress value on the ordinate of the S-Nf relation was plotted using the maximum tensile stress (smax). However, the S-Nfcurves obtained overlaid each other when using stress amplitude (sa) instead of smax. Fatigue properties were analyzed further using severalrelations proposed previously, such as modified Goodman relation. In this case, the fatigue data obtained were clearly approximatedby an elliptical relation. Severe microstructural damage arising from plastic deformation was observed in the sample fractured under theR = −1 condition, where striation was a main failure mode. In contrast, no clear microstructural damages were observed in the samplesfractured at R = 0.1 even when a higher maximum tensile stress was applied (e.g., smax = 60% sUTS), where ripple-like failure was thedominant feature.

The effects of artificial asperities on crack closing behavior in quenched and tempered medium carbon steel

Mitsuhiro Okayasu,Zhirui Wang 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.10

To better understand the effect of an asperity on crack closure behavior, K-CMOD relations were examined using artificial asperity/wedge, inserted into the fatigue crack in a three point bending specimen made of a hardened medium carbon steel. Experimental results revealed that the unloading phase of the K vs. CMOD curve exhibited a concave shape if soft artificial asperity (Al alloy) was inserted,signifying acceleration in the CMOD decrease at zero applied load. This was mainly related to elastic and plastic deformation in the wedge material during the unloading process. On the contrary, the linear unloading portion of K vs. CMOD was obtained as hard asperity (high carbon steel) was employed, which specified deceleration in the CMOD decrease at zero applied load, where the only elastic deformation in the asperity was affected. From their unloading curves, the severity of crack closure or ?Keff value was found to be related to the strength of the asperity material. The values of ?Keff were examined in two different ways, e.g., (i) the remote displacement method and (ii) the adjusted compliance ratio method (ACR). The ?Keff value, measured using both approaches, decreases with increasing wedge strength, such as hardness and yield strength. The rate of reduction in <Keff was, however, changed depending on the manner of ?Keff examination, in which the ?Keff decreased at a higher rate for the compliance ratio method and at a lower rate for the remote displacement method. The reason for this is discussed in the present work.

The development of a visual system for the detection of obstructions for visually impaired people

Mitsuhiro Okayasu 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.10

In this paper, the author presents a new visual system that can aid visually impaired people in walking. The system provides object information (that is, shape and location) through the sense of touch. This visual system depends on three different components: (i) an infrared camera sensor that detects the obstruction, (ii) a control system that measures the distance between the obstruction and the sensor, and (iii) a tooling apparatus with small pins (φ1 mm) used in forming a three-dimensional shape of the obstruction. The pins, arranged on a 6×6 matrix, move longitudinally between the retracted and extended positions based on the distance data. The pin extends individually, while the pin tip reflects the object’s outer surface. The length of the pin from the base surface is proportional to the distance of the sensor from the obstruction. An ultrasonic actuator, controlled at a 15Hz frame rate, is the driving force for the pin movement. The tactile image of the 3D shape can provide information about the obstruction.

Mechanical and wear properties of Cu-Al-Ni-Fe-Sn-based alloy

Okayasu, Mitsuhiro,Izuka, Daiki,Ninomiya, Yushi,Manabe, Yuki,Shiraishi, Tetsuro Techno-Press 2013 Advances in materials research Vol.2 No.4

To obtain bronze with good mechanical properties and high wear resistance, a new bronze (CADZ) is proposed on the basis of various fundamental information. The CADZ consists of the elements Al10.5, Fe4.2, Sn3.7 and Ni3.1, and its design is based on Cu-Al10.5 alloy. The Cu-10.5%Al is very hard and brittle. To obtain the high material ductility of the Cu-10.5%Al alloy, an attempt was made to add a few percent of Sn. Moreover, to make high strength of the Cu alloy, microstructure with small grains was created by the proper amount of Fe and Ni (Fe/Ni = 0.89). The mechanical properties of the CADZ sample have been examined experimentally, and those were compared with commercial bronzes. The tensile strength and wear resistance of CADZ are higher than those for commercial bronzes. Although the ductility of CADZ is the lower level, the strain to failure of CADZ is about 2.0~5.0% higher than that for the Cu-Al10.5 alloy. Details of the microstructural effects on the mechanical properties in the CADZ sample were further discussed using various experimental results.

Effects of loading conditions on the fatigue failure characteristics in a polycarbonate

Okayasu, Mitsuhiro,Yano, Kei,Shiraishi, Tetsuro Techno-Press 2014 Advances in materials research Vol.3 No.3

In this study, fatigue properties and crack growth characteristics of a polycarbonate (PC) were examined during cyclic loading at various mean stress (${\sigma}_{amp}$) and stress amplitude (${\sigma}_{mean}$) conditions. Different S vs. N and da/dN vs. ${\Delta}K$ relations were obtained depending on the loading condition. The higher fatigue strength and the higher resistance of crack growth are seen for the PC samples cyclically loaded at the higher mean stress and lower stress amplitude due to the low crack driving force. Non-linear S - N relationship was detected in the examination of the fatigue properties with changing the mean stress. This is attributed to the different crack growth rate (longer fatigue life): the sample loaded at the high mean stress with lower stress amplitude. Even if the higher stress amplitude, the low fatigue properties are obtained for the sample loaded at the higher mean stress. This was due to the accumulated strain energy to the sample, where severe plastic deformation occurs instead of crack growth (plasticity-induced crack closure). Shear bands and discontinuous crack growth band (DGB) are observed clearly on the fracture surfaces of the sample cyclically loaded at the high stress amplitude, where the lower the ${\sigma}_{mean}$, the narrower the shear band and DGB. On the other hand, final fracture occurred instantly immediately after the short crack growth occurs in the PC sample loaded at the high mean with the low ${\sigma}_{amp}$, i.e., tear fracture, in which the shear bands and DGB are not seen clearly.

Microstructural characteristics in tough pitch copper for revealing the work hardening region

Okayasu, Mitsuhiro,Taki, Tatsuya,Takasu, Satoshi,Takeuchi, Shuhei,Shiraishi, Tetsuro Techno-Press 2012 Advances in materials research Vol.1 No.4

To reveal localized plastic deformation zones in a tough pitch copper, the etching characteristics of a copper sample have been examined. The etching was carried out on a sample surface using an etchant consisting of 25 ml nitric acid solution and 75 ml water. To clarify the plastic deformation zone, the sample deformed plastically was heated to between $250^{\circ}C$ and $300^{\circ}C$ before the etching process. This is due to a change of the microstructure and crystal orientation in the plastic deformation zone producing recrystallized small grains. In this case, the plastically deformed zone is severely etched, whereas the undeformed zone is only slightly etched. Identification of the details of the deformation zone from the etching is further discussed.

Effects of Sb, Sr, and Bi on the material properties of cast Al-Si-Cu alloys produced through heated mold continuous casting

Mitsuhiro Okayasu,Shuhei Takeuchi,Shaohua Wu,Toshihiro Ochi 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.3

Rare earth metals can create a fine eutectic Si structure in cast Al-Si 10.6 -Cu 2.5 (ADC12) alloys produced through heated mold continuous casting. Fine and spherical eutectic Si phases are created in the ADC12 alloys through the addition of Sr 0.04 , and fine lamellar eutectic Si phases are created through Sb and Bi addition. Crystal orientation on the face perpendicular to the casting direction is formed by [110];however, this uniform formation is collapsed in the ADC12 alloy with an increasing amount of Sr addition, such as Sr > 0.04%. The shape of the eutectic Si is statically analyzed, and the effects of the eutectic Si characteristics on the mechanical properties are examined experimentally. On the one hand, the mechanical properties of the ADC12-Sr alloy increase with increasing Sr content because of the fine eutectic Si, the randomly orientated crystal formation, and so on. On the other hand, the material ductility increases in the ADC12 alloy with increasing addition of Sb and Bi elements. A high fracture strain of approximately 14% is obtained for the ADC12-Bi1.5 alloy.

Infl uence of Strain Induced Martensite Formation of Austenitic Stainless Steel on Wear Properties

Yoon‑Seok Lee,Kazuki Ishikawa,Mitsuhiro Okayasu 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.3

In this study, the wear characteristics and behaviors of both AISI304 and AISI316 austenitic stainless steels were evaluatedunder the diff erent rotation speeds, using block-on-ring wear testing machine. From the microstructure analysis, at the fi rst,the transition of strain induced-martensite was observed in wear-aff ected region of both AISI304 and AISI316. It is consideredthat the interfacial friction stress between test block and ring may trigger the phase transformation of meta-stable γ-fccto ε/α′ martensite. Moreover, it is also observed that the amount of martensite increases with increasing rotation speed forboth AISI304 and AISI316. The thickness of transformed martensite was deeper in AISI304, compared to AISI316 at allrotation speed. It can be explained by that the existence of molybdenum in AISI316 increases stacking fault energy, whichcan retard nucleation and growth of strain induced-martensite. Furthermore, reverse transformation was also detected atsubsurface layer of both AISI304 and AISI316.