DOOMBA ME 4451: Robotics December 14, 2010 Dr. Harvey ... - helix

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Initial Plan For the Doomba project the primary objective was to create a mobile robot capable of tracking a human in a dynamic environment. The only variable to be inputted by the user would be a specific distance to maintain from the target. The robot, in this case the iRobot Create with a webcam, would then calculate the angle and distance to the target from image processing, determine the necessary movements to reorient itself, then execute those movements to arrive at the specified distance and a zero degree angle difference (i.e. directly facing the target). Figure 1 below is a graphical representation of these operations. d 0ᵒ θᵒ d + x 2 0ᵒ d 1 Figure 1: Physical representation of tracking and subsequent reorientation To accomplish this overall task, three operations would have to be accomplished. First the system would have to be manually calibrated to the environment, second the camera would have to locate the subject of tracking, and third the locations obtained from the tracking would have to be transformed in to robotic movements. Initially this sequence of operations was to be completed using live human tracking algorithms and real time video. Real time tracking was accomplished using the Simulink block set, unfortunately Simulink would not communicate with the Create and we were forced to switch from video tracking to image grabbing using Matlab. Switching to Matlab as the processing platform reduced the speed of image analysis but the overall theme of the project was maintained. 1
To accomplish human tracking in Matlab, the target to be tracked had to wear two green circles spaced 9” center to center apart. Using the calibration functions we would manually choose the tracked colors from an image grab. After calibrating the system Matlab would grab images from the video and perform a series of image filters to select the chosen target color, calculate the properties of the image, filter out noise, determine which objects were circular, and output the coordinates of the two desired circle centroids. Finally, a function would take these centroid locations and calculate the angle and distance to the target, based on camera specific parameters. These measurements would be compared against the desired distance to maintain, and the current orientation, and the appropriate robot motions would be executed using the Create Toolbox functions. This process would then repeat after every move allowing the robot to follow a target. Robot Kinematics The bulk of the project revolved around image processing and very minor robot kinematics were incorporated into the final product with the exception of the movements preformed by the iRobot. The only parameters given to the robot were distance and angle changes needed to maintain proper orientation to the target. These commands were executed using turnAngle and travelDist. Supplying the rotation angle and the distance difference between the current and desired locations to these two functions, allowed us to effectively relocate the robot without extensive code or calculations. Although inelegant, it was the simplest solution to the kinematics issue, and removed the need to focus our energy on this problem. After achieving reasonable image processing results, we invested some time in writing the code necessary to solve the velocity kinematics for the robot in order to use smoother motions to arrive at the final destination. To do this we calculated the change in x, y, and angle θ, from one frame to the next. Dividing these values by the processing time between frames gave us their rates of change. Using these values a reverse velocity kinematics analysis could be preformed to calculate the turning speed of each wheel. The equation for this is shown below. 2
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DOOMBA ME 4451: Robotics December 14, 2010 Dr. Harvey ... - helix

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