Dawei Tu

Generic nonsinusoidal fringe model and gamma calibration in phase measuring profilometry

Gamma distortion is a dominant error source of phase measuring profilometry. It makes a single frequency for the ideal sinusoidal waveform an infinite width of spectrum. Besides, the defocus of the projector-camera system, like a spatial low-pass filter, attenuates the amplitudes of the high-frequency harmonics. In this paper, a generic distorted fringe model is proposed, which is expressed as a Fourier series. The mathematical model of the harmonic coefficients is derived. Based on the proposed model, a robust gamma calibration method is introduced. It employs the multifrequency phase-shifting method to eliminate the effect of defocus and preserve the influence of gamma distortion. Then, a gamma correction method is proposed to correct the gamma distortion with the calibrated gamma value. The proposed correction method has the advantage of high signal-to-noise ratio. The proposed model is verified through experiments. The results confirm that the phase error is dependent on the defocus and the pitch. The proposed gamma calibration method is compared with the state of the art and proves to be more robust to pitch and defocus variations. After adopting the proposed gamma correction method, the phase precision is much enhanced with higher quality in the measured surfaces.

Fuzzy decoding in color coded structured light

Abstract. Decoding is a challenging and complex problem in a coded structured light system. In this paper, the decoding problem is modeled as matching two floating number sequences. Fuzzy window matching instead of hard window matching is proposed to determine the correspondence. In the proposed decoding method, the stripe edges are extracted using color edge detection after color correction has been conducted. Then, the stripe colors are identified through the use of a fuzzy c-means clustering algorithm on a color feature, which is only related to the spectral sensitivity of red, green, and blue sensors and the albedo of the surface. Finally, a fuzzy multistep matching method is proposed to find the correspondence, which aims to match the subsequences with the length less than the window width. In the experiments, fuzzy window matching is compared with hard window matching. No matter what local matching method is adopted, fuzzy window matching can achieve higher accuracies than hard window matching. The obtained point clouds and surfaces are also larger. When the multistep idea is added, the performance is enhanced.

Multi-initialized States Referred Work Parameter Calibration for Gaze Tracking Human-Robot Interaction

In order to adaptively calibrate the work parameters in the infrared-TV based eye gaze tracking Human-Robot Interaction (HRI) system, a kind of gaze direction sensing model has been provided for detecting the eye gaze identified parameters. We paid more attention to situations where the users head was in a different position to the interaction interface. Furthermore, the algorithm for automatically correcting work parameters of the system has also been put up by defining certain initial reference system states and analysing the historical information of the interaction between a user and the system. Moreover, considering some application cases and factors, and relying on minimum error rate Bayesian decision-making theory, a mechanism for identifying system state and adaptively calibrating parameters has been proposed. Finally, some experiments have been done with the established system and the results suggest that the proposed mechanism and algorithm can identify the system work state in multi- situations, and can automatically correct the work parameters to meet the demands of a gaze tracking HRI system.

Range image acquisition for machine vision

An optical 3-D imaging system for autonomous vehicle and mobile robot navigation is presented. The system is based on a phase comparison range finder using a 30-mW laser diode modulated at a 5-MHz frequency, and a scanning mechanism, consisting of a nodding mirror and an eight-faced polygon and providing 30 X 30-deg total view with only 0.5-deg instantaneous fields of view for the receiver optics. A Si-avalanche photodiode (APD) optoelectric detector and low-noise preamplifier can detect very low levels of returned energy. With an integrated MC4044 circuit for phase comparison, pixel range information can be represented by gray level on the high-resolution video monitor. A 3-D range image is obtained in the experiment, and a range accuracy of 0.08 m at 10 m outdoors in sunlight is achieved.

Eye moving behaviors identification for gaze tracking interaction

The correct identification of eye moving behaviors is an important foundation for a gaze tracking interaction system. After analyzing the characteristics of eye moving behaviors in gaze tracking human computer interaction, a kind of eye moving behaviors classified method has been presented, in light of the fact that blinks, saccades, and fixations successively take place in certain sequences, and a blink is usually the beginning action or end action for a saccade or a fixation sequence. In addition, there are some other contributions in this paper. Firstly, a blink recognition algorithm has been proposed with eye’s height-width aspect ratio and iris or eyelid edge fitting curvature. Secondly, taking the recognized blink as a starting point to calculate the mean and standard deviation of eye’s moving displacements in a certain period, and then identifying the saccades and fixations in terms of the calculated parameters. At last, some experiments have been done, and the results show that the proposed method, by considering the relationship between eye behaviors, can accurately classify blinks, saccades, and fixations, especially for large-scale saccades and long time fixations. Moreover, the present also provides a new reference for designing an accessible interface to reduce the impacts on the reliability caused by the randomness of eye movements.

ACT-R-typed human–robot collaboration mechanism for elderly and disabled assistance

This work aims to propose an innovative mechanism of human–robot collaboration (HRC) for mobile service robots in the application of elderly and disabled assistance. Previous studies on HRC mechanism usually focused on integrating decision-making intelligence of human beings by qualitative judgment and reasoning intelligence of robots by quantitative calculation. Instead, novelties of the proposed methodology include (1) constructing an HRC framework by taking reference from the Adaptive Control of Thought – Rational (ACT-R) human cognitive architecture; (2) establishing semantic webs of cognitive reasoning through human–robot interaction (HRI) and HRC to plan and implement complex tasks; and (3) realizing human–robot intelligence fusion by mutual encouragement, connect, and integration of modules of human, robot, perception, HRI, and HRC in the ACT-R architecture. Its technical feasibility is validated by some selected experiments within a “pouring” scenario. Further, although this study is oriented to mobile service robots, the modularized design of hardware and software makes its extensive use feasible in other types of service robots like smart rehabilitation beds, wheelchairs, and cleaning equipments.

Spy quantitative inspection with a machine vision light sectioning method

Machine vision light sectioning sensing is developed and expanded to the range of spy quantitative inspection for hole-like work pieces in this paper. A light beam from a semiconductor laser diode is converged into a line-shape by a cylindrical lens. A special compact reflecting-refracting prism group is designed to ensure that such a sectioning light is projected axially onto the inner surface, and to make the deformed line be imaged onto a CCD sensitive area. The image is digitized and captured into a computer by a 512×512 pixel card, and machine vision image processing methods such as thresholding, line centre detect and the least-squares method are developed for contour feature extraction and description. Two other important problems in such an inspection system are how to orientate the deep-going optical probe and how to bring the projected line into focus. A focusing criterion based on image position deviation and a four-step orientating procedure are put forward, and analysed to be feasible respectively. The experimental results show that the principle is correct and the techniques are realizable, and a good future for application in industry is possible.

Mechanism and experimental study on three-dimensional facula shaping in femtosecond laser micromachining

Abstract. Because of the laser beam waist and diffraction effect of the lens, the focal spot light field in femtosecond laser microprocessing has an ellipsoidal spatial distribution. This leads to the gap between two processing layers increasing along the axial direction, and the distribution density of processing points decreasing along the horizontal direction. This directly reduces the resolution of the microprocessing, and badly affects the machining accuracy and surface quality. We established a mathematical model for three-dimensional (3-D) laser beam shaping based on the Fresnel diffraction theory and designed a kind of four-ring complex amplitude transmittance phase plate by using a global optimization algorithm and genetic algorithm to simultaneously realize transverse and axial 3-D shaping. We numerically showed that the transverse and axial gains of the focal facula after 3-D shaping are 0.77 and 0.68, respectively, where the corresponding peak energy ratio is 0.36, the transverse and axial sidelobe energies are 0.28 and 0.62, respectively, and the defocusing amount is −0.08. We also constructed a confocal/two-photon microscope system to experimentally achieve a better shaping effect in the case of femtosecond laser fabrication at a point on the thin film of a photochromic material.

Head Behavior Detection Method Based on Optical Flow Theory

In order to make the intelligent virtual classroom distinguish out the rotation direction of the users head, a method for head behavior detection based on optical flow is proposed in this paper. Firstly, we select the key feature points of users facial area. Then we calculate the users head movement parameter through the data of feature points which have been recorded. Secondly, a kind of head direction sensing model has been provided for detecting the head identified parameters. Finally, according to the interaction mechanism of the interaction scenario, intelligent virtual classroom will respond to the users head movement based on the result of the head direction judgment. By online tests, the results show that the method is of high recognition rate and quick real-time.

Natural human-robot interaction for elderly and disabled healthcare application

Natural human-robot interaction plays an important role in effective nursing services system provided by service robots for the elderly and disabled people. This paper proposed a multimodal “human-robot integration” collaboration system, and set up a shared collaboration interface between human and service robot. Consequently, Users and service robots can naturally communicate and retrieve information from the collaborative interface with multimodality(e.g. head gesture, eye gaze) in an interactive dialogue approach. By this way, making the service robots fully understand humans intention, so they can collaborate and complete tasks well. Furthermore, some experiments were conducted, and the results suggest that it is effective to identify users intention in light of the advantage of different modalities, the shared collaboration interface can provide more information both from human and robots to improve the naturalness of human-machine collaboration. The proposed methods can provide a new way for exploiting human-service robots cooperation.