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 31.01.2017
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
Personal Interest... Motivation Setup Heuristic Approaches...raised by the TAMS Masterproject Intelligent Robotics... and IROS 2015. S. Rau TAMS-Oberseminar 3 / 25
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.
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...
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
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
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
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]
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
S. Rau TAMS-Oberseminar 11 / 25 Approach 1 z x
S. Rau TAMS-Oberseminar 12 / 25 Approach 1
S. Rau TAMS-Oberseminar 13 / 25 Approach 2 z x 4cm
S. Rau TAMS-Oberseminar 14 / 25 Approach 2
S. Rau TAMS-Oberseminar 15 / 25 Approach 3 z x 4cm
S. Rau TAMS-Oberseminar 16 / 25 Approach 3
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
S. Rau TAMS-Oberseminar 18 / 25 Approach 4 - End effector link orientation is -F - Tip of robotic arm remains at contact location 1 2 3 F F y F F x The rotation of the appropriate joint needs to be calculated.
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
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
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
S. Rau TAMS-Oberseminar 22 / 25 Approach 4
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
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. :
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, 2013. Software available at http://octomap.github.com. [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.