tailieunhanh - Advances in Service Robotics Part 2

Tham khảo tài liệu 'advances in service robotics part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 18 Service Robots To grasp objects the robot should interact with its environment. For example it should perceive where the desired object is. If there is a camera on the robot on same height as humans eyes are the robot cannot recognize objects which are far from the robot. General web camera specification is insufficient to see far objects. We put the web-camera on the back of the hand so that it can see the object closer and move its position during searching objects. Even if there are no objects on the camera screen the robot can try to find the object by locating its end effecter to another position. Placing the camera on the hand is more useful than placing it on the head. One problem occurs if one camera is used. It is that the distance from camera to object is hard to calculate. Therefore vision system roughly estimates the distance and compensates the distance by using ultrasonic sensors. Fig. 20 shows the robot arm with a web-camera and an ultrasonic sensor. Object recognition system We use Scale-Invariant Feature Transform to recognize objects 1999 . SIFT uses local features of input image so it is robustness to scale rotation and change of illuminations. Closed-loop vision system needs not only robust but also speed. Therefore we have implemented basic SIFT algorithm and customized it for our robot system for speed up. Fig. 21 shows example of our object recognition system. Fig. 21. Example of object recognition. Unfortunately the robot has just one camera on the hand so it is not able to estimate exact distance like when using stereo vision. Therefore more specific distance for the object database is required to calculate the distance using only one camera. When we make the object database the robot should know the distance from the object to the camera. Then we calculate the distance comparing the area of object and the size of the database. The size of the object is inversely proportional to the square of the distance. Fig. 22 shows the