Takaaki Sarai

High-speed processing for obtaining three-dimensional distance image and its application

A high-speed method of 3-D distance acquisition based on the triangulation principle is presented. This method uses conventional devices such as a CCD camera, a laser emitting semiconductor, and scanning mirrors; however, new circuits have been developed for detecting the position of spot image on the CCD. This development enables the high speed measurement and reduces the cost of the apparatus. Experiments showed that the apparatus and the method gave the practical measuring accuracy and speed, and it was found that the system is useful for image recognition. This method can easily display the stereoscopic image and cross-sectional figure of the object body. The method of real time processing has also been developed with the view to apply the device to the range finders for robots and blind persons.<<ETX>>

Implant Failure of Titanium Versus Cobalt-Chromium Growing Rods in Early-onset Scoliosis.

Study Design. Retrospective case series of one institute database. Objective. To investigate the differences in the metallic strength of rods used for implant failure in the dual growing rod technique and evaluate clinical outcomes. Summary of Background Data. The dual growing rod technique in which implanted rods extend with the growth of the spine is a useful treatment for early onset scoliosis. However, many complications, particularly those associated with rods, exist. Especially, the implant failure of growing rod focused on metallic strength is unknown. Methods. Thirteen patients (42 lengthening surgeries) who underwent surgery by this technique at our hospital from 2007 were divided into a titanium rod plus titanium connector group (T group, n = 4, 26 lengthening surgeries) and cobalt-chromium rod plus titanium connection group (C group, n = 9, 16 lengthening surgeries). The incidence of implant failure and the site of fracture were retrospectively investigated. Results. Implant failure occurred in three patients in the T group, because of rod fracture in two patients and connector fracture in one. In the C group, implant failure occurred in six patients, because of rod fracture in one patient and connector fracture in seven. Fracture occurred twice in two patients. The rod fracture rate decreased with the use of cobalt-chromium rods but the rate of connector fracture increased. We performed a stress distribution analysis using the finite element method to clarify the mechanisms underlying implant failure in both groups. Regardless of the rod type, the greater load was placed on the distal rod. However, differences in the metallic strength caused the rod to fracture when titanium rods were used and connectors (weak metallic strength) to fracture when cobalt-chromium rods were used. Conclusion. Rod fractures occurred more commonly with titanium rods and connector fractures with cobalt-chromium rods. Level of Evidence: 4

Stress Analysis of Interphalangeal Joint during Compressive Impact Loading.

Propagation of the stress wave in a proximal interphalangeal joint during compressive impact loading was analyzed by the dynamic finite element method. The explicit method was used in the analysis and the distribution of stress at each step of the time was evaluated. The maximum principal stress is nearly equal to the minimum one in the articular cartilage and therefore the equivalent stress is very small. The equivalent stress and the principal stress fluctuate with the time in the subchondral bone of the middle phalanx. The concentration of stress is observed there and the maximum principal stress is positive, i.e., tension. The impulsive stress is absorbed when the stress wave travels through the articular cartilage. The relation between the equivalent stress and the impact velocity is dependent on the time and the stress is linearly related to the velocity in a short time after the impact.

X-ray Strain Analysis and Elastic Anisotropy of Textured Metals

ABSTRACT The stress and strain in each grain in a rolled steel during uniaxial elastic deformation were analyzed by the finite element method using a plane model of polycrystals, and the influence of texture on the elastic constants of the bulk specimen and that on the lattice strain in the grains reflecting X-rays were studied. The stress in a grain was affected by the restraint on it and by its shape. In the case of a model with elliptical grains, the mode of deformation was close to the condition of uniform local strain, and the influence of the restraint on the grains was small when the shape of the grains was prolate in the direction of the applied stress. On the other hand, the mode was close to the condition of uniform local stress, and the influence of the restraint was large when the shape was oblate. The elastic constants of the bulk specimen were affected by the texture, their values being dependent on the restraint condition of the grains and on the shape of grains. The lattice strain was not linearly related to sin2 Ψ for those metals with texture in X-ray stress measurements. The relationship between the lattice strain and sin2 Ψ was greatly affected by the texture, and the influence of the deformation behavior of polycrystals was small for the 211 reflection. In the sin2 Ψ diagram, the influences of the restraint and shape of grains were relatively small, and the results calculated by the present model are close to those of the uniform local stress model for the 310 reflection.

Microscopic deformation behavior and X-ray elastic constants in polycrystalline metals. Influence of grain shape.

The influence of the grain shape on the microscopic deformation of polycrystalline metals was studied analytically by the finite element method in the uniaxial elastic deformation. In the present analysis, a plane model of polycrystals was used and the elastic constants of the polycrystals and the X-ray elastic constants were also calculated. The stress in individual grains became uniform when the grain was oblate in the direction of the applied stress, while the strain became uniform when it was prolate. The stress at the region across the grain boundary changed with the crystal orientation and the shape of the grains, and it was closely related to the deformation of the grain. The elastic constant was affected by the shape of the grains, indicating that the anisotropic properties in the polycrystals arose from the elongated grains. The influence of the grain shape on the X-ray elastic constants S1, S2/2 was dependent on the diffraction plane. In the case of α-iron, the influence on S1 was small for the refection from the (211)planes.

MICROSCOPIC RESIDUAL STRESS IN METALS DEFORMED PLASTICALLY UNDER MULTI-AXIAL STRESS.

The microscopic and macroscopic residual stresses in metals deformed plastically under multi-axial stress are studied with the models of polycrystals. In the analysis, the Taylor model is adopted for the plastic deformation and the uniform stress and uniform strain models are used for the unloading process after the plastic deformation. The state of microscopic residual stress in a grain changes with the orientation of the crystal and it is much affected by the condition of yield stress in the plastic deformation. The microscopic residual stress is different from the macroscopic one. In the case where a compressive residual stress is observed macroscopically, there exists a tensile residual stress in a particular grain. The residual lattice strain is not linearly related to sin2 φ in X-ray stress measurement. The residual lattice strains measured by X-rays agree with the results analyzed by the Taylor model and the uniform stress model.