Introduction to Computer Haptics

Chris Harding charding@iastate.edu

Haptic (adj.) (from the Greek word haptesthai for to grasp or to touch) :related to the sense of touch.

Haptic Rendering:process of displaying synthetically generated 2D/3D haptic stimuli to the user

Graphical Rendering: process of displaying synthetically generated 2D/3D visual stimuli to the user

F

simulatedhapticprobe

Haptic Interface: device for touch interactions in real and virtual worlds

End-effector (pen, thimble, surgical instrument, …)

Motors, cables, actuators, position sensors, …

Human vs Machine Haptics:

Tactile Displays(skin)

Force feedback Displays(Kinesthetic: position)

Types of Haptic Devices

Machine Haptics:

Types of Haptic Devices

ActivePassive

keyboard, trackball, mice, etc.

Force

Types of Haptic Devices

Grounded Attached

combined Hulk strong – crush Coke

can !!

Applications

Haptic Feedback for Medical Simulation and

Training

VisualDisplay

HapticDisplay

force

molecule

Haptic Feedback forMolecular Simulation

Haptic Feedback for Crew Training

Haptic User Interface (HUI)

collected data

haptic display

Haptic Visualization

tangible data

Tangible Interfaces• buttons• dials• slider bars• folders• layers• force fields

Simulation ofrepair and

maintenance tasks

Haptic Feedback for CollaborativeEngineering Design

Applications

Integration of Vision and Touch

HapticThread

HapticInterface

HUMAN OPERATOR

VisualThread

VisualInterface

SharedDatabase

MotorTorques EncoderPositions

DISPLAYFORCE STATE

~1 kHz

DISPLAYVISUALS STATE

Images ~ 30 Hz

•Geometry•Color•Stiffness•Deformability

Point-based Haptic feedback Problem:

simulating the Human hand (22 DOF) and tactile sensations (skin pressure) is very difficult (impossible) to simulate

Need very fast update rates (~1000 Hz) Need Interface acceptable to everyday users Affordable, with API for non-haptic specialists

Solution (Enter the PHANtOM): Use only a single point (3DOF): point with stylus (direction vector) GHOST API, ReachIn API, OpenHL

Stylus Tip

Virtual Finger Tip

Haptic Rendering with a Force Display

CollisionDetection

CollisionResponse

Geometry

Material

Object Database

PositionOrientation

ContactInformation

Force

virtualwall

F = stiffness

* dist

void calculate_force (Vector &force) { float X, Y, Z, distance; float R = 20.0;

X = HIP[0]; Y = HIP[1]; Z = HIP[2]; distance = sqrt(X*X + Y*Y + Z*Z);

if(distance < R) //collision check { force[0] = X/distance * (R-distance); force[1] = Y/distance * (R-distance); force[2] = Z/distance * (R-distance);

}

}

F

R

distanceHIP Hand

point-object interaction

HIP = Haptic Interface Point: True (real world) position of stylus tipHand: always drawn outside the sphere

Assumption:Stiffness = 1.0

Haptic Rendering of 3D Objects via Proxy (point-object interaction)

Proxy (displayed position)

HIP (stylus tip: actual position!)

Spring with stiffness kF = k * d(Hooke’s Law)

d: Proxy to Tipdistance

(If in doubt: the visual sense will override the sense of touch …)

HIPt

HIPt-1 HIPt-2HIPt-3

v2

v3

v1

HIPt+1

IHIPt

IHIPt+1

d

HIPt+2

IHIPt+2

d

Haptic Rendering of Polygonal Surfaces

HIP = actual tip positionIHIP = Proxy point

actualshape

Haptic Display of Surface Details

Haptic smoothing of object surfacesding)(similar to Phong shag

Rendering of haptic textures Haptic rendering of surfaces with friction (

Directionof movement

Fn

Ff

Ft

Fuser displayedshape

Haptic Texturing

s

t

• image-based

• procedural

h(x,y,z)

two-stage mappingBier & Sloan, 1986

bump mapping

Blinn, 1978;Max and Becker, 1994

Force-Reflecting Deformable Models:

Haptic Sculpting/painting

Surgical Simulation

FF

Reachin Display Phantom + Reachin

Display + Reachin API 3D stereo via mirror Integrates 3D Vision with

haptics After calibration:

real stylus = virtual stylus Uses proxy method 3D haptic user interface

(HUI) API: define VRML

scenegraph with graphics and haptics properties

Sensable Omni Phantom New, “cheap” version of

phantom line Stiffness: 3 - 4 N Firewire port Windows, Linux (?) OpenHL API: (low-level

OpenGL-like haptics) Demo of virtual clay

sculpting (splodge?)

Conclusion

Point haptics: Reduction of hand to point Separate Update loop at 1000 Hz Same geometry as graphics but additional

haptic properties Improvements in tool based interaction:

Surgical simulation and training assembly/repair planning Virtual clay sculpting (art, rapid prototyping) Sculpting of subsurface layers (saltdome modelling)