Range Sensing Based Autonomous Canal Following Using a Simulated Multi-copter. Ali Ahmad

Transcription

1 Range Sensing Based Autonomous Canal Following Using a Simulated Multi-copter Ali Ahmad MS Student of Electrical Engineering Laboratory for Cyber Physical Networks and Systems LUMS School of Science & Engineering Lahore, Pakistan WFAR8

2 Problem Statement To simulate a canal shape in Gazebo. Quad copter simulation equipped with laser scanner & plugins to move around. Calculation of center point of canal using the laser scanner data. Generation of center points along the movement of quad copter. Guiding quad rotor over the center of canal.

3 Canal Design The canal design is done in GoogleSketchup & then imported into Gazebo. Some images are shown below. Few hurdles are also visible in the canal.

4 Quad copter & Scanner Model In this project Hector Quad rotor model is used. Gazebo world file is created by merging the hector quad rotor model & our canal model. Hokoyo laser scanner is mounted on the quad rotor. Laser Scanner position is adjusted at 60 degrees from the x- axis of the quad rotor in order to point the laser beam a little ahead of the quad rotor.

5 Flow chart of program Start Nodes Scan the surface (Get scan data) Convert scan data into (x,y) coordinate from (r,ø) Calculate the center Move forward or turn

6 Scanning Curve & Calculating Center For simplicity, scan data is converted from (r,ø) to the rectangular coordinate system (x,y). We have assumed that the height of the quad rotor remains fixed so the z- dimension part is ignored while transformation of scans.

7 Scanning Canal & Calculating Center For a scan, slope is calculated between the successive points of a laser scan. The points representing sides of canal will have some slope nearly equal & opposite. This slope & sign of slope is used for calculating the center point of the canal.

8 Scanning Canal & Calculating Center Since the canal is assumed to be very symmetrical, so algorithm was tested by adding some sensor noise. Results are shown below. Gaussian Noise added (Mean=0, Std_Dev=0.01): Green Points are the center points

9 Scanning Canal & Calculating Center Gaussian Noise added (Mean=0, Std_Dev=0.08): Green Points are the center points

10 Refining the Trajectory After calculating center, quad rotor has to move along the calculated center points. Control can be done by moving one by one on to the successive center points. For good stability & higher speeds, a smooth curve has to be generated through these center points. B ezier curve can be used to generate smooth trajectory. Basic expression for a linear & quadratic Bezier curve is given below. Here Pi are the control points of the curve, in our case these are center points. Ref: Trajectory Planning and Lateral Control for Agricultural Guidance Applications, Patrick Fleischmann, Tobias F ohst and Karsten Berns, Robotics Research Lab, Department of Computer Science, University of Kaiserslautern, Kaiserslautern, Germany

11 Refining the Trajectory After getting the guidance points (center point of canal), a curve representing the trajectory is drawn. It is shown in figure below. In this project, we have used a 5-point Bezier curve. Green points are center points, Red line is the trajectory.

12 Guiding the Quad rotor To move forward and steer left/right, linear velocity in x-direction and angular motion yaw are required. Proportional controls & Stanley controls are used for guiding the quad rotor left or right according to the center. It is assumed here that the quad rotor is moving at a fixed height.

13 Guiding the Quad rotor A general control diagram is showing how linear & lateral controls are being used to control the quad rotor. Error is calculated between the trajectory point & the point ahead seen by the quad copter. Velocity controller varies the velocity proportionally according to the error. Lateral control is done according to the angular difference between trajectory & look ahead point.

14 Guiding the Quad rotor The quad copter was simulated over the canal as shown below, the bottom figure shows the trajectory it followed over the whole simulated canal.

15 Simulation Video Video 1 Video 2

16 Implementation of Algorithm On Actual Quad Rotor (Future Work) The whole simulation project has to be transferred to an actual quad rotor on an actual canal. A small LUMS campus is currently used for this purpose. Scans are taken by Laser scanner (Hokoyu) & then the center calculation method has been applied to resultant scan. Some results are shown below.

17 Scanning Canal Using Laser Scanner Few Scan Results

18 Sensing Canal Using Laser Scanner

19 Scanning Canal Using Laser Scanner Some commonly used methods for Laser Scan Processing & Segmentation: Corner detection in a laser scan is more used in obstacle avoidance methods. Inscribed Angle method is used to detect corner. Line or circle fitting methods are also used for finding walls or round obstacles. As the previously used method was not very robust & had uncertainty in calculating the center so I am working on a more better way to find extract center point. The bed & sides of actual canals are not very smooth in actual as it is in the canal shown so RANSAC is used for finding the bed & sides. Some results are shown below.

20 Scan Results Input Point Cloud of Laser Scan Output Point Cloud of line segments.

21 References Trajectory Planning and Lateral Control for Agricultural Guidance Applications, Patrick Fleischmann, Tobias F ohst and Karsten Berns, Robotics Research Lab, Department of Computer Science, University of Kaiserslautern, Kaiserslautern, Germany Automatic Steering Methods for Autonomous Automobile Path Tracking, Jarrod M. Snider, Robotics Institute Carnegie Mellon University Pittsburgh, Pennsylvania. 2D Feature Extraction in Sensor Coordinates for Laser Range Finder, UniversitiTeknologi Malaysia, UTM Skudai. Fast Line, Arc/Circle and Leg Detection from Laser Scan Data in a Player Driver, Institute of Systems and Robotics - ISR, University of Coimbra, Portugal, Centre for Intelligent Systems - CSI, University of Algarve, Portugal

22 Questions??

23 Thank You