Master s Thesis: Real-Time Object Shape Perception via Force/Torque Sensor

Transcription

1 S. Rau TAMS-Oberseminar 1 / 25 MIN-Fakultät Fachbereich Informatik Master s Thesis: Real-Time Object Shape Perception via Force/Torque Sensor Current Status Stephan Rau Universität Hamburg Fakultät für Mathematik, Informatik und Naturwissenschaften Fachbereich Informatik Technische Aspekte Multimodaler Systeme

2 S. Rau TAMS-Oberseminar 2 / 25 Table of Contents 1. Motivation Personal Interest Explore Environment Goal 2. Setup Hardware setup Tools 3. Heuristic 4. Approaches

3 Personal Interest... Motivation Setup Heuristic Approaches...raised by the TAMS Masterproject Intelligent Robotics... and IROS S. Rau TAMS-Oberseminar 3 / 25

4 S. Rau TAMS-Oberseminar 4 / 25 Explore Environment Importance of grasping objects Identifying object before grasping Good exploration yields good manipulation Methods: Vision,..., haptic exploration Haptic exploration is suitable in exploration scenarios with low visibility conditions as underwater, in foggy environments, with bad lighting conditions.

5 S. Rau TAMS-Oberseminar 5 / 25 Goal Model the shape of objects with force and torque sensor data Generate 3D model later used for: collision planning, grasping/manipulation, deburring...

6 S. Rau TAMS-Oberseminar 6 / 25 Hardware Setup - Mitsubishi PA-10 6-DOF - Sunrise M3207 F/T-Sensor - Drill chuck - Sphere fixed at/as the tip

7 S. Rau TAMS-Oberseminar 7 / 25 Tools ROS Simplifications for programming with robots Extensive use of tf package Reflexxes Motion Libraries Force and torque sensor readings OctoMap FK/IK solver for the PA10 provided by Norman Hendrich PA10_reflexxes ROS package provided by Norman Hendrich

8 Setup OctoMap 3D mapping framework based on octrees OctoMap library implements 3D occupancy grid mapping approach RViz display plugins octomap.github.io [HWB + 13] S. Rau TAMS-Oberseminar 8 / 25

9 S. Rau TAMS-Oberseminar 9 / 25 Setup Reflexxes Motion Libraries Real time (online) motion control New motions are calculated within one low-level control cycle (typically within one millisecond or less). [Krö11]

10 General Heuristic The end effector moves along x-axis and reacts in z-axis direction when force is encountered. y x z z x S. Rau TAMS-Oberseminar 10 / 25 x

11 S. Rau TAMS-Oberseminar 11 / 25 Approach 1 z x

12 S. Rau TAMS-Oberseminar 12 / 25 Approach 1

13 S. Rau TAMS-Oberseminar 13 / 25 Approach 2 z x 4cm

14 S. Rau TAMS-Oberseminar 14 / 25 Approach 2

15 S. Rau TAMS-Oberseminar 15 / 25 Approach 3 z x 4cm

16 S. Rau TAMS-Oberseminar 16 / 25 Approach 3

17 S. Rau TAMS-Oberseminar 17 / 25 Problems with Approaches 1-3 Risk of unwanted collision between object and PA10 Static >4cm parameter Slow execution of change in orientation The risk of collision between object and a link of a robotic arm without force sensitivity hardly preventable. New approach: Make >4cm vanish Aim for smooth movement execution along object

18 S. Rau TAMS-Oberseminar 18 / 25 Approach 4 - End effector link orientation is -F - Tip of robotic arm remains at contact location F F y F F x The rotation of the appropriate joint needs to be calculated.

19 S. Rau TAMS-Oberseminar 19 / 25 Approach 4 Put sphere as new tip Set frame in center of sphere Same orientation as last joint frame -> Z-axis points in same direction

20 S. Rau TAMS-Oberseminar 20 / 25 Approach 4 Procedure to calculate the rotation to make Z-axis point in -F direction: 1. Find acting point on sphere 2. Find rotation quaternion for appropriate joint 1.) x Fx/norm(F ) P = y = r Fy/norm(F ) z Fz/norm(F ) r = Radius of sphere F = Force vector acting on sphere P y F z

21 S. Rau TAMS-Oberseminar 21 / 25 Approach 4 2.) Find rotation quaternion for appropriate joint: 1. Rotation axis v = a b 2. Rotation angle θ = acos(norm(a) norm(b)) 3. Rotation matrix: Rodriguez rotation formula R = I + (sin θ)k + (1 cos θ)k 2 4. Extract quaternion from R a = (0, 0, 1) b = acting point on sphere K = cross-product-matrix of v I = 3x3 identity matrix 2 1 F

22 S. Rau TAMS-Oberseminar 22 / 25 Approach 4

23 S. Rau TAMS-Oberseminar 23 / 25 Approach 4 Heuristic to move along Object on y-axis: Force normal to tangent Use tangent in desired direction F y T y F F x T T x

24 S. Rau TAMS-Oberseminar 24 / 25 Approach 4 z 3 2 y 4 1 in -y direction: 1. : 2. : 3. : 4. : in y direction: 4. : 3. : 2. : 1. :

25 S. Rau TAMS-Oberseminar 25 / 25 References [HWB + 13] Armin Hornung, Kai M. Wurm, Maren Bennewitz, Cyrill Stachniss, and Wolfram Burgard. OctoMap: An efficient probabilistic 3D mapping framework based on octrees. Autonomous Robots, Software available at [Krö11] Torsten Kröger. Opening the door to new sensor-based robot applications the reflexxes motion libraries. In Robotics and Automation (ICRA), 2011 IEEE International Conference on, pages 1 4. IEEE, 2011.