Directing Physically Based (and Physical) Interactions
Animating Dexterous Motions How can we easily animate the starfish’s escape? • Appearance of intelligent motion • Believable physical interaction with the glass box • Dynamic, fun actions • Animation tools accessible to anyone
Animating Dexterous Motions Videos created by two novice users using our system.
Background: Classical Approaches • Motion Capture • Not available for leaping starfish! • Traditional Keyframing • Keyframing complex dynamic interactions is hard • Physically based simulation • Great for passive objects • Difficult to create “intelligent” motions • Physically based controllers / Physically based optimization • How do we build a controller or objective function for this task? • No reference motions are available
Factors that appear to contribute to human motion selection Lillian Y. Chang and Nancy S. Pollard, “Pre -Grasp Interaction for Object Acquisition in Difficult Tasks,” forthcoming book chapter
Background: Better Alternatives • Operational space / task space control • Great concept, and we will use it Sentis and Khatib • Direct control of physically based systems • Goal: a more general animation system, motivated by demonstrations Laszlo, van de Panne, and Fiume like these! • We found that a variety of control modalities are needed and can be incorporated easily van de Panne
Ski Stunt Simulator
What Control Modes are Intuitive?
User Interface Example
Interface Modes Manipulate Bones • Drag a bone to control its motion • direct control of head position • Constrain a bone to a fixed position / orientation • constrain base to orientation shown
Interface Modes Manipulate Center of Gravity • Drag the CG of the lamp in a tightly controlled manner to keep it balanced • Drag the CG of the starfish abruptly to create a jump • Drag the CG of the donut in a free form manner to create the desired animation
Interface Modes Manipulate Character Root Orientation • Drag a special rotation widget for 3D rotational motions
Interface Modes Manipulate Joints • Keyframe a leaping action for the worm • Set and maintain joint limits • Run a passive controller for a soft landing • How? Set a single desired configuration and low stiffness
Interface Modes Previewing • Observe the effect of maintaining current command for a given period of time
Interface Modes Speed up, slow down, advance, back up the simulation • Trial and error to learn the character dynamics and achieve desired result
Animating Dexterous Motions Our observation: Different control modes are needed at different times to create animations sophisticated enough to tell a story Our solution: Put a variety of control modes into the animators hands and make them as intuitive as possible
Overview of Our System Results: Compute muscle forces User Interface: for the character to best Real-time, trial achieve the user’s goals and error (e.g., Jump like this!) Character model: Coarse volumetric model -> fast simulation Junggon Kim and Nancy S. Pollard, Fine surface detail for “Direct Control of Simulated Non -Human appearance, contacts Characters,” IEEE CG&A, 2011 and collision
Interface Modes Under the Hood The user is placing a variety of constraints on the character’s motion How do we determine how the character should behave, in a physically realistic manner, to best meet those constraints?? Our only “lever” is accelerations or torques that must be applied at the character’s joints to advance the simulation Algebra on the equations of motion? Complex, local-minimum prone, prioritized optimization??
Interface Modes Under the Hood Most quantities we care to measure or control have a locally linear relationship to joint accelerations and joint torques Evangelos Kokkevis, Practical Physics for Articulated Characters, Game Developer's Conference 2004.
Example: Bone Constraints Express bone constraint as a linear function of joint accelerations: Bone accelerations when joint accelerations Straightforward are zero Desired bone differentiation of accelerations equations of motion Obtaining desired bone accelerations:
Interface Modes Under the Hood (1) Express all constraints as a linear function of joint accelerations: (2) Solve a Quadratic Program to obtain joint accelerations: (3) Use these accelerations for the next timestep to advance the simulation
Final Demos
Realistic Physical Behavior? http://www.youtube.com/watch?v=a-1AiExU3Vk Huai-Ti Lin, Tufts Biomimetic Devices Laboratory
Notes Constraint priorities: Mouse drags are satisfied after everything else Contact modeling : “hallucinate” constraints to account for pushoff forces Objective functions: minimize joint accelerations, torques, or velocities Speed: Simulations are real-time or better; users preferred 3X-8X slower Ease of use: Starfish escape animations created by novices in minutes
What Control Modes are Intuitive?
References http://www.cs.cmu.edu/~junggon/ Junggon Kim and Nancy S. Pollard, “Fast Junggon Kim and Nancy S. Pollard, “Direct Control of Simulated Non -Human Simulation of Skeleton-Driven Deformable Characters,” IEEE CG&A, 2011 Body Characters,” ACM ToG, 2011 http://www.cs.cmu.edu/~junggon/
Sticky Finger Manipulation With a Multi-Touch Interface Ken Toh MS Thesis
Motivation • User interaction is a key feature in most graphical and robotic applications. Manipulating virtual cloth Teleoperating a robot with a multi-fingered hand Sticky Finger Manipulation With a Multi-Touch Interface 28
Motivation • Traditional User Input Devices are effective for many simple high-level interaction tasks.. On/off Up, down, left, right Common user input devices with simple command spaces Sticky Finger Manipulation With a Multi-Touch Interface 29
Motivation • Dexterous manipulation of simulated/real world objects with high DOFs can however be quite awkward to achieve with these existing input devices Realistic cloth tearing requires more than a single cursor to execute A panel of buttons is not the most intuitive interface for dexterous tele-manipulation Sticky Finger Manipulation With a Multi-Touch Interface 30
Motivation • Key Question: Can we design an intuitive user interface that allows us to feel natural when manipulating objects by proxy, almost as though we are interacting with them directly? Sticky Finger Manipulation With a Multi-Touch Interface 31
Cloth Manipulation: Modes Creation Mode Sticky-Finger Mode Cut Mode Sticky Finger Manipulation With a Multi-Touch Interface 32
Sticky Fingers for Cloth Manipulation Underlying cloth particles within radius of each active fingertip center are stuck to that finger and moves with it Sticky Finger Manipulation With a Multi-Touch Interface 33
Sticky-finger Lifting • User activates toggle which changes the plane of control from the x-z plane to x-y plane. Sticky Finger Manipulation With a Multi-Touch Interface 34
Pinch-lifting • Automatic detection of pinch event when two finger touches are close together. Sticky Finger Manipulation With a Multi-Touch Interface 35
Cloth Simulation Model A mesh of particles connected by bend, shear and stretch constraints Sticky Finger Manipulation With a Multi-Touch Interface 36
Verlet Integration • Key: Position-based dynamics essential because we need to stick particles kinematically to fingers (ie. modify positions directly) Sticky Finger Manipulation With a Multi-Touch Interface 37
Iterative Constraint Satisfaction x 2 r x 1 • Must handle cases with stuck fingers Correction vector Case (a): x 1 and x 2 not stuck Case (b): x 1 stuck, x 2 not stuck Case (c): if both are stuck, both = 0 Sticky Finger Manipulation With a Multi-Touch Interface 38
Tearing • Sticky finger pins down relevant particles and constraints, allowing unconstrained regions to elongate and eventually tear. Finger size matters too. Sticky Finger Manipulation With a Multi-Touch Interface 39
Cutting Similar to tearing but in a more controlled fashion Sticky Finger Manipulation With a Multi-Touch Interface 40
Direct Cloth Manipulation
Robotic Telemanipulation Goal: intuitive interactive control of dexterous manipulation for a robot arm / hand system • Remote dexterous manipulation • Scripting new behaviors • Learning from demonstration
What is available? Master-slave systems: Origami with the DaVinci surgical robot http://www.youtube.com/watch?v=x9Bjs99A0k0
What is available? Glove interfaces for dexterous hand control: Cyberglove interface http://www.youtube.com/watch?v=jOnp2M5qibs&feature=player_detailpage TVO: Doing the Dirty Work: Robots for Hire on the NASA Robonaut
What is available? Glove interfaces for dexterous hand control: Cyberglove interface http://www.youtube.com/watch?v=_R40j64C7t8 Video from Shadow Robot Company
Recommend
More recommend
