The hand-eye system calibration, aiming to achieve the relationship between the robot hand and vision sensor mounted on it, is an important technique in the robot applications, involving automatic 3D measurement, visual serving, sensor placement planning, etc. Generally, the key issue of hand-eye calibration is equivalent to solving the homogeneous transformation matrix X from the equation of the form AX=XB. In this paper, we develop an accurate hand-eye calibration method by establishing a global objective function, in which the errors of camera calibration and robot movements have been considered. It is constructed based on the minimizing the projection error from the target benchmarks to the camera retina plane at all robot motions. The experimental results prove that the proposed algorithm can accurately solve the hand-eye calibration problem. Meanwhile, we set up an automatic 3D measurement system based on a robot and a rotary table, and developed a calibration scheme for the system to achieve the multi-view and fully automatic 3D data acquisition by using a fringe projection 3D sensor.
At present, fringe projection profilometry has also been limited with a trade-off between speed and accuracy. For achieving high accuracy measurement, phase-shifting and phase-unwarpping operations will always be used for phase correspondence, however, the phase-unwrapping processing does not contribute to improve the phase accuracy, but just to distinguish phase steps. For futher reducing the projection pattern for phase-unwarpping, we propose a novel method for phase corresponding in bi-cameras system without phase unwrapping. Phase-to-3D mapping structures are utilized to obtain the candidate correspondences and eliminate the ambiguties with wrapped phase, which is implemented efficiently without time-comsuming phase correspondence searching. The experiments on both static and dynamic scenes are perfomed to verify its capability of 120 fps 3D reconstructing speed by overlapped using 3-step phase-shifting pattern.
The propagation characteristics of shock waves generated under hypervelocity impact (HVI) (an impact velocity leading to the case that inertial forces outweigh the material strength, usually on the order over 1 km/s) and guided by plate-like structures were interrogated. A hybrid numerical modeling approach, based on the Smoothed-Particle Hydrodynamics (SPH) and Finite Element Method, was developed, to scrutinize HVI scenarios in which a series of aluminum plates, 1.5- mm, 3-mm and 5-mm in thickness, was considered to be impacted by an aluminum sphere, 3.2-mm in diameter, at an initial velocity of 3100 m/s, 3050 m/s and 2490 m/s, respectively. The meshless nature of SPH algorithm circumvented the inefficiency and inaccuracy in simulating large structural distortion associated with HVI when traditional finite element methods used. The particle density was particularly intensified in order to acquire wave components of higher frequencies. With the developed modeling approach, shock waves generated under concerned HVI scenarios were captured at representative gauging points, and the signals were examined in both time and frequency domains. The simulation results resembled those from earlier experiment, demonstrating a capability of the developed modeling approach in canvassing shock waves under HVI. It has been concluded that in the regions near the impact point, the shock waves propagate with higher velocities than bulk waves; as propagation distance increases, the waves slow down and can be described as fundamental and higher-order symmetric and anti-symmetric plate-guided wave modes, propagating at distinct velocities in different frequency bands. The results will facilitate detection of orbital debris-induced damage in space vehicles.