Reaching and Grasping Reaching control synthetic human arm

Reaching and Grasping Reaching control synthetic human arm to reach for object or position in space while possibly avoiding obstacles Grasping Control synthetic hand fingers to simulate the supporting of an object Transporting Move object in space, move hand with object, and use IK to move arm along Rick Parent - CIS 681

Reaching: human-like What is “human-like”? Experiments: Planning happens in Cartesian space Not joint space Not muslce space Bell-shaped velocity curves Obstacle avoidance low curved sections Connected by highly curved sections Rick Parent - CIS 681

Reaching: inverse kinematics Inverse kinematics End-effector = hand No sense of “body” Hard to enforce joint limits Motions not necessarily human-like Most often used to enforce constraints once endeffector almost in correct position, e. g. , Foot on ground Hand at object Rick Parent - CIS 681

Human reach IKAN: http: //hms. upenn. edu/software/ik/ik. html Use analytic IK whenever possible Human motion uses pre-defined planar configurations Hand orientation determines plane Use wrist to position hand - independent from arm Rick Parent - CIS 681

Human reach Given body and goal First determine plane q 1 Solve for angles q 2 Orient hand Rick Parent - CIS 681

Obstacle Avoidance Path planning End effector Intermediate links Goal Obstacles Rick Parent - CIS 681

Obstacle Avoidance 1. Look for global optimal solution 2. “Reason” from starting position Greedy algorithm w/backtracking 3. Use precompiled known solutions Rick Parent - CIS 681

Obstacle Avoidance Genetic algorithm Search space of possible paths Evaluate path Collisions, joint limits, comfort Minimize: end-effect path length maximum acceleration jerk Rick Parent - CIS 681

Obstacle Avoidance Rick Parent - CIS 681

Obstacle Avoidance Rick Parent - CIS 681

Tool Manipulation Gravity Minimize torque? Orient tool for maximum comfort? Rick Parent - CIS 681

Strength Guided Motion P. Lee, S. Wei, J. Zhao, N. Badler, SIGGRAPH 90 “Moving a load to a specified position in space” Strongly influenced by Strength comfort Objective: “to find trajectories, both joint and end-effector, that a human-like linkage would traverse to complete a task. ” Rick Parent - CIS 681

Strength Guided Motion P. Lee, S. Wei, J. Zhao, N. Badler, SIGGRAPH 90 Comfort level: maximum torque ratio summed over entire body Perceived exertion: depends on Amount of strength required (perceived) Amount of strength available Rick Parent - CIS 681

Strength Guided Motion P. Lee, S. Wei, J. Zhao, N. Badler, SIGGRAPH 90 Each Do. F has two muscle groups: extension and flexion Each muscle group strength is modeled as a function of Body position Anthropometry Gender Handedness fatigue Etc. Rick Parent - CIS 681

Strength Guided Motion P. Lee, S. Wei, J. Zhao, N. Badler, SIGGRAPH 90 3 Components Condition monitor - current state Path Planning Scheme - IK plus headroom Rate Control Process - determines joint rates Motion Strategies Available torque Reducing moment Pull back Added joint, and jerk Rick Parent - CIS 681

Grasping Hand-object interaction Hand: ability for various configurations Object: lends itself to certain uses (affordances) Regrasping Multiple hand manipulation Rick Parent - CIS 681

Task Planning Simulate vision, memory to identify object in environment Plan path of figure through environment Position figure relative to workspace Use Do. Fs of figure including arm to reach object Configure hand relative to object to grasp it Use strength of figure to manipulate object Rick Parent - CIS 681