- 學位論文
廠內自動搬運車之微特徵視覺里程計定位系統
Visual Odometry Using Tiny Features for AGV Localization in Factory Environment
摘要
廠房的屋頂和牆壁阻絕衛星定位訊號，廠內的機台設備強烈干擾無線電波和磁場，本論文提出微特徵視覺里程計定位系統使自動搬運車可以在廠內環境順暢定位和導引。微特徵視覺里程計的攝影機採用主動光源朝向地面攝像，可以在單調的路面擷取微型特徵和深度的訊息，藉由匹配連續兩張影像中的特徵點達成估算位移和方向。微特徵視覺里程計採用尺度不變特徵轉換來擷取特徵點，並藉由瞬時旋轉中心推出車頭轉動的角度，路面顛頗引起的攝影機視野和尺度變動不會影響特徵點的匹配，因此位移和方向的估算準確度高又可靠，採用主動光源使自動搬運車無論在白天或晚上都可以工作。此微特徵視覺里程計定位系統安裝在一台實驗用的自動搬運車上，可以在主控電腦上規劃或變更行進路線，經過多種場景的測試，結果顯示八米的行進距離以內，定位和定向的準確度都可以符合廠內自動搬運車的需求，更長距離的行進可以利用基準標記系統消除累績的誤差，使自動搬運車可以在廠內長時間工作。
並列摘要
Navigation of automatic guided vehicles for transporting components inside a factory needs accurate estimates about vehicle’s position and orientation. The global positioning system fails to offer vehicle’s position in-door due to the structure of the building blocking the electromagnetic wave from the satellites. Electronic compass and radio positioning equipment are interfered severely by electromagnetic signals generated from electrical machines operating in the factory. This thesis presents a visual odometry which extracts tiny image features of the floor to estimate the displacement and orientation of the vehicle. The video camera which has an illuminating source points toward the floor to avoid disturbances resulted from reflection or shadow. We employ the scale-invariant feature transform algorithm to extract tiny image features from the image captured. Feature matching between two consecutive images enables using the triangulation method to calculate the displacement of the vehicle. Integrating the displacement data and using the rotating center of the vehicle lead to estimates of the position and orientation of the vehicle. The accuracy of estimates satisfies the requirements of AGV for factory use, and the result does not influenced by wheel slip or rough floor. Experiments under several scenarios show that path plan and modification can be achieved on the central control station. Position error is less than twenty centimeters for a path shorter than eight meters. For constant operations, the visual odometry needs a position-calibration system to eliminate accumulated errors.