Intelligent fall prevention shoes using camera based line-laser obstacle detection system
Date Issued
2014
Date
2014
Author(s)
Yang, Chi-Yun
Abstract
In aging society nowadays, fall down of elders is a serious social problem. According to the data of CDC (Centers for Disease Control and Prevention), in death cases of injuries, half death cases result from unintentional falls. Besides, the medical costs with regard to falls reach up to 30 billion US dollars per year in the US. Also, because the decline of physical and reaction abilities of elders, elders tend to fall especially. As a result, designing an automated system to prevent falls from happening or send alarms for help after falls happened becomes a critical problem in the development of technologies recent years.
Scientists and Engineers have dedicated to develop technologies to prevent falls, including wearable devices and ambience devices, these devices has various application and their pros and cons. In this thesis, a camera-based line-laser obstacle detection system is proposed. Before elders kick on obstacles to fall, this system can emit alarm messages to mention them and then reach the goal to prevent falls, to prevent the damage on the bodies and the negative impacts to the mind of elders, finally to save medical costs of the whole society. Because elders spend most of their time at home or in nursing homes, most fall cases occur indoors. Therefore, the proposed line-laser obstacle detection system is designed mainly for indoor applications.
The camera based line-laser obstacle detection system cast its line-laser on a horizontal plane which has a specific height to the ground. And then the system uses a camera which has an angle to the plane to extract the line-laser pattern. Under this system configuration, when the depth of obstacles in front of the system changes, the extracted line-laser pattern in the image will have disparities. This system uses the characteristic of disparities to detect the distance of obstacles from the system.
In real implementation, system will be triggered when users step on the ground or when users raise the foot at max height during a gait cycle. This enables the system to detect obstacles on the ground or higher obstacles. In our method, differences between frames are utilized to determine the trigger time of our line-laser obstacle detection system. After the system was triggered, the captured frame will be filtered with a median filter first, and then the line-laser pattern on the image will be extracted. At the same time, an intensity threshold is used to separate the line-laser pattern from background in order to get a better line-laser pattern extraction result.
On the extracted line-laser pattern, the deviation between the present pixel and the last pixel is utilized to classify each pixel to the cluster which denotes a specific obstacle, and a deviation threshold is set to implement image segmentation. And then a tangent line with a specific threshold on histogram is used to distinguish clusters which denote obstacles from clusters which come from noise. Last, we implement homography matrix to transform the coordinate on the image into the coordinate on the detection plane. Therefore, the depth and the width of each obstacle can be calculated to judge how dangerous this obstacle is. If any obstacle is too dangerous, an alarm message will be emitted to prevent elders from falling.
Among algorithms of line-laser obstacle detection system, some parameters and thresholds of the system need to be determined. As a result, some experiments are designed to suggest suitable parameters and thresholds for system operation. Furthermore, a validation of homography which computes the distance between obstacles and the system is carried out. The result shows that the error of homography distance computation can fulfill the need of obstacle detection.
Keywords: Obstacle detection, line-laser, homography, disparity, image segmentation
Subjects
跌倒
障礙物偵測
線雷射
homography
disparity
影像分割
Type
thesis
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