Acquiring general material appearance with hand-held consumer RGB-D cameras is difficult for casual users, due to the inaccuracy in reconstructed camera poses and geometry, as well as the unknown lighting that is coupled with materials in measured color images. To tackle these challenges, we present a novel technique for estimating the spatially varying isotropic surface reflectance, solely from color and depth images captured with an RGB-D camera under unknown environment illumination. The core of our approach is a joint optimization, which alternates among solving for plausible camera poses, materials, the environment lighting and normals. To refine camera poses, we exploit the rich spatial and view-dependent variations of materials, treating the object as a localization-self-calibrating model. To recover the unknown lighting, measured color images along with the current estimate of materials are used in a global optimization, efficiently solved by exploiting the sparsity in the wavelet domain. We demonstrate the substantially improved quality of estimated appearance on a variety of daily objects.
With the development of the aviation industry, the performance requirements of materials for aviation large-scale structural parts are getting higher and higher. Ti-6554 alloy is the material of choice for aviation large-scale structural parts, but its forming process window is narrow and its microstructure is sensitive to process parameters, which affects the performance of the alloy. By adjusting the existing hot deformation process, it is of great significance to improve the properties of the alloy. Hot compression tests of Ti-6554 alloy were carried out at temperatures of 715–840 °C and strain rates of 0.001–1 s−1. The results show that the flow stress and peak stress increased significantly with the increase of strain rate. At the same strain rate, the strain required for the stress to reach the peak point is smaller with the temperature increases. When the deformation temperature is below the phase transition point, the volume fraction and size of primary α phase gradually decrease with the increase of deformation temperature, while when the temperature is above the phase transition point, with the increase of deformation temperature, β grains grow up gradually, and the grain boundary bending effect is more obvious. The hyperbolic-sine Arrhenius constitutive equation was established. The correlation coefficient between experimental data and model calculated data reached 0.994. It indicates that the stress constitutive model proposed in this study can accurately reflect the stress characteristics of Ti-6554 alloy. Based on the dynamic material model, the processing maps of the alloy were established. The optimum hot deformation parameters range of the alloy was determined by analyzing the processing maps: the deformation temperature range of 800–830 °C, the strain rate range of 0.001–0.01 s−1. Through the analysis of the processing maps, the instability regions in the process of cross-phase forging can be effectively avoided, and the performance of the forging can be effectively improved.
Purpose
The purpose of this paper is to put forward a rolling assistant robot with two rolling modes, and the multi-mode rolling motion strategy with path planning algorithm, which is suitable to this multi-mode mobile robot, is proposed based on chessboard-shaped grid division (CGD).
Design/methodology/approach
Based on the kinematic analysis and motion properties of the mobile parallel robot, the motion strategy based on CGD path planning algorithm of a mobile robot with two rolling modes moving to a target position is divided into two parts, which are local self-motion planning and global path planning. In the first part, the mobile parallel robot can move by switching and combining the two rolling modes; and in the second part, the specific algorithm of the global path planning is proposed according to the CGD of the moving ground.
Findings
The assistant robot, which is a novel 4-RSR mobile parallel robot (where R denotes a revolute joint and S denotes a spherical joint) integrating operation and rolling locomotion (Watt linkage rolling mode and 6R linkage rolling mode), can work as a moving spotlight or worktable. A series of simulation and prototype experiment results are presented to verify the CGD path planning strategy of the robot, and the performance of the path planning experiments in simulations and practices shows the validation of the path planning analysis.
Originality/value
The work presented in this paper is a further exploration to apply parallel mechanisms with two rolling modes to the field of assistant rolling robots by proposing the CGD path planning strategy. It is also a new attempt to use the specific path planning algorithm in the field of mobile robots for operating tasks.
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