Event-Based Haptics

Günter Niemeyer

Stanford Telerobotics Labhttp://telerobotics.stanford.edu

Adding High-Frequency Playbackto make virtual feel real

2Telerobotics Lab

Exploration: Static or Dynamic?

(LaMotte, 2000; Kontarinis and Howe, 1998; Lawrence et al., 2000)

Press?

Stiffness

or Tap!!

x

F&

&

x

F

∆Rate-hardness

3Telerobotics Lab

Very Dynamic!

Tapping

Firm Grip

Soft Grip

up to

~ 1000 Hz

4Telerobotics Lab

Today’s Haptics = NERF World

Need HF!

5Telerobotics Lab

Classic Haptics: Control like Robot

Compute forces every servo cycle (closed-loop feedback)

MotionForce

Ke

F = - Ke xm

6Telerobotics Lab

Why not realistic?

Kcontrol

Fuser

mdevice

o Frequency content from CL poles:mass ↔ stiffness

ω = √ K/m

o Typical K = 1000 N/mm = 100 g = 0.1 kg

ω = √ 10,000 = 100 rad/sec= 16 Hz

7Telerobotics Lab

• High gain K = 4,000,000 N/m• Amplifiers ~ 10,000 Hz• Servo rate ~ 10,000 Hz• Encoders ~ 4,000,000 lines/rev

To make it “real”… YIKES!

o Generate frequency content1000 Hz >60x improvement

Fcol∆encK =

Robot with µm and sub-ms resolution…

8Telerobotics Lab

o We

• Position >1 mm

• Move <10 Hz

• React >100 ms

o But

• Sense force up to 1000 Hz!

o Asymmetric!

Detect Event Signatures

Would we want to?

9Telerobotics Lab

Event-Based Haptics

Event = Impact, Transition

Open-loop playback ofcharacteristic force profile

POW!M

F = - Ke xm + Fevent(t,vin)

= +

10Telerobotics Lab

o Superimpose HFover PD (LF)

o Uncontrolled< 50 … 100 ms

o Library of transientsfor velocity andmaterial

o Momentum cancellation

Event-Based Haptics (cont’d)

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User Testing

o 12 objects (3 real, 9 virtual)

o 16 subjects

12Telerobotics Lab

Acceleration Matching

=Fwood

Fmotorastylus astylus

Fwood ≠ Fmotor

astylus = astylus

13Telerobotics Lab

Acceleration Matching

o Invert model to match stylus accelerations

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vin

o Library by velocity vin

Event-Based “Signature” Libraries

Can approximate as:

Decaying Sinusoids(Okamura et al.)

Pulses(Salcudean et al.)

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o Classic PD = Foam, Event-Based = Real

Event-Based Haptics “feels real”

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Surface Feature = Micro-Tap

vinFdown

o Flight phase (no contact force)o Fdown vin Fpeak

Fsurface

t

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Micro Steps...Classic: Event-Based: POW! Real:

18Telerobotics Lab

o Open-loop HF playback →More real, more information

o Surface features ≈ micro-taps

o Parameterized libraries

o Easier computation(lower servo rates)

Event-Based is GOOD ☺

Fdown

19Telerobotics Lab

o Students:Jesse HwangMichael WilliamsKatherine KuchenbeckerJonathan Fiene

Acknowledgements / Questions?

o Funding:NSF Career IIS-0547672Stanford OTL Award