Qunfei Zhao

An Effective Defect Inspection Method for LCD Using Active Contour Model

Visual defects in liquid crystal display images often appear as low contrast and blurry contour without distinct intensity difference from their surrounding region. Besides, the background is usually intensity inhomogeneity. All these properties make the machine vision inspection extremely hard. This paper presents an effective machine vision inspection method using a local active contour model to detect defects with different brightness levels as well as diverse sizes and shapes. A modified local binary fitting model which is robust to initial contour is developed to extract defect boundary. Meanwhile, a simple preprocessing scheme is given to compensate the drawback of the two-phase active contour model for detecting objects with wide brightness levels. Experimental results show that the presented method can detect various types of defects effectively and achieves high performance in terms of inspection accuracy (both precision and recall are higher than 0.99).

A Spatial Sound Localization System for Mobile Robots

In this paper, we described a robotic spatial sound localization system using four microphones arranged on the surface of a sphercial robot head. The four microphones, with three on the head center level and one on the top, provide spatial cues for sound elevation as well as azimuth. A weighted cross-correlation method based on the model of the precedence effect is used to calculate the time differences and suppress the influence of echoes. To integrate spatial cues of different microphone pairs, a mapping method from the correlation between different microphone pairs to a 2-D map corresponding to azimuth and elevation of sound sources was proposed. Experiments shows the system can provide the distribution of sound sources in azimuth-elevation space for sound sources, even concurrently in reverberant environments.

Robot Position Identification Using Specially Designed Landmarks

In this paper, we proposed a visual position calibration method using colored rectangle signboards for a mobile robot which is designed to work in a room environment. The rectangle signboards are placed in several known positions. By calculate the vanishing points in the image of the signboard, it is possible to obtain the relative direction and distance between the signboard and the robot by a single image. Experiments of position calibration were conducted. The results showed this method is effective and the errors between the set up positions and the experimental results were about 1.7 degrees and 3 cm when the distance to the signboards was set to 100 cm

Mobile Robot Position Identification with Specially Designed Landmarks

In this paper, we proposed a visual position calibration method using colored rectangle signboards for a mobile robot which is designed to work in a room environment. The rectangle signboards are placed in several known positions. Using Canny Algorithm to detect the edge of color area to calculate the vanishing points in the image of the signboard, it is possible to obtain the relative direction and distance between the signboard and the robot by a single image. Experiments of position calibration were conducted. The results showed this method is effective and the errors between the set up positions and the experimental results were about 1.5 degrees and 3 cm in an array position.

Robot Position Identification by Actively Localizing Sound Beacons

In this paper, we proposed a robot self position identification method by active sound localization. This method can be used for autonomous security robots working in room environments. A system using a AIBO robot equipped with two microphones and wireless network is constructed and is used for position identification experiments. Arrival time differences to the microphones of robot are used as localization cues. To overcome the ambiguity of front-back confusion, a three-head position measurement method was proposed. The robot position can be identified by the intersection of circles restricted by the azimuth differences to different speaker pairs. By localizing three or four speakers as sound beacons positioned on known locations, the robot can identify its self position with an average error of about 7 cm in a 2.5 times 3.0 m2 working space

Application of “human-in-the-loop” control to a biped walking-chair robot

This paper presents the research on stability for biped walking-chair robot with human-in-the-loop. The inherent properties of the biped system which is developed for the disable people to replace traditional wheelchairs are analyzed. Control of the robot for the gait and navigation is introduced. Posture stability computation method based on ZMP (zero moment point) theory is discussed. Some suggestions about the future research are also presented.

Robot navigation and sound based position identification

In this paper, we proposed a robot self position identification method by active sound localization. This method can be used for autonomous security robots working in room environments. A system using a AIBO robot equipped with two microphones and wireless network is constructed and is used for position identification experiments. Arrival time differences to the microphones of robot are used as localization cues. To overcome the ambiguity of front-back confusion, a three-head position measurement method was proposed. The robot position can be identified by the intersection of circles restricted by the azimuth differences to different speaker pairs. By localizing three or four speakers as sound beacons positioned on known locations, the robot can identify its self position with an average error of about 7 cm in a 2.5times3.0 m2 working space. A robot navigation experiment was conducted to demonstrate the effectiveness of the position identification system.

Spatial direction estimation for multiple sound sources in reverberation environment

In this paper, we propose spatial localization of multiple sound sources using a spherical robot head equipped with four microphones. We obtain arrival time differences using phase difference candidates. Based on the model of precedence effect, arrival temporal disparities obtained from the zero-crossing point are used to calculate time differences and suppress the influence of echoes in a reverberant environment. To integrate spatial cues of different microphone pairs, we use a mapping method from the correlation between different microphone pairs to a 3D map corresponding to azimuth and elevation of sound sources directions. Experiments indicate that the system provides the distribution of sound sources in azimuth-elevation localization, with the EA model even concurrently in reverberant environments.

Spatial localization of concurrent multiple sound sources

Based on the human auditory system for spatial localization theory, we proposed a spatial localization of multiple sound sources using a spherical robot head. Space sound vectors recorded by a microphone array with spatial configuration, are used to estimate the histograms of spatial arrival time difference vectors by solving the simultaneous equations in different frequency bands. The echo avoidance model based on precedence effect is used to reduce the interference of environment reverberations which provide the strong interference for phase vectors especially in small indoor environments. To integrate spatial cues of different microphone pairs, we propose a mapping method from the correlation between different microphone pairs to a 3D map corresponding to azimuth and elevation of sound sources directions. Experiments indicate that the system provides the distribution of sound source in azimuth-elevation localization, even concurrently in reverberant environments.