Haptics for Mobile Devices

Haptics for Mobile
Communication Devices
Steve Dai, Device Technology, Motorola

Outline

Haptics Overview

Haptics for Mobile Devices

Localized Piezo Haptics

Haptics Characterization

Summary

Steve Dai, Haptics Purdue October 21, 2008

Haptics Overview

Definition: tactile feedback, more specifically active
feedback

Dominant Types of Active Feedback

Vibrotactile
Vibration sensed by nerves in the skin current focus

Kinesthetic
Sensations associated with body position, movement, or weight sensed by the nerves
in muscles, tendons, or joints


Haptics Overview

Sample applications

BMW
mice I-drive

vibrating
gaming call alert
controllers

3D Design &
Interaction

medical training Braille displays


Haptics Overview

Comparison with other senses

Neurons “Data” rate Temporal
(bits/s) Acuity

Touch ~106 102 5 ms

Hearing ~104-105 104 0.01 ms

Sight ~106 106-109 25 ms

Lynette Jones, MIT


Haptics Overview

Frequency Dependence of Perception

SIGHT: 540 THz SOUND: 20~20,000 Hz TOUCH: 20~1000 Hz

Minimum audible=threshold
Fletcher-Munson curves, 1933
Verrillo-RT. Subjective Magnitude
Functions for Vibrotaction. IEEE
Transactions on Man-Machine Systems
MMS-11(1): 19-24. (1970


Haptics Overview

Receptors
Light SOUND TOUCH



Why haptics?

“Data” rate Temporal Human to
(bits/s) Acuity device Input

Touch – 102 5 ms
fingertip
Audio – voice 104 0.01 ms

Sight – eye 106-109 25 ms


Value to users

FUNCTION SAMPLE USE CASES HAPTICS REQUIREMENTS

Vibe alert Simple vibration or patterns
Increasing Complexity

Notification
Confirma- Key press Short click-like response
tion status change Low latency
Localized preferred over global?
Amusement Base boost Rich variety of haptic contents
Entertain- Touchscreen UI event Visual/audio synchronization
ment Gaming “Essential but unnoticed” haptics

Communi- Sensorial Standards and infrastructure
cation communication “Hapton” capable phones



Global vs. Localized haptics
Global: vibrates the entire device
(phone)

Samsung F700 Samsung LG Voyager
Mot A1000 RAZR2 Mot & SCH-W559 Anycall 2008 (2008)
(2004) (2007) Krave (2007)
(2008)

Localized: vibration is localized to
an input surface (keypad, display)

ROKR E8 (2008)


Actuation Technologies

Global Localized

USE CASE &
IMPLEMENTATION
Rotary Linear Linear F Reactor Piezo

VIBE ALERT YES YES NO NO NO
KEYPRESS OK OK GOOD GOOD EXLT
ADVANCED HAPTICS LMTD LMTD OK LMTD EXLT
INTEGRATION NO NO LO LO MOD
COMPLEXITY


POKR E8 Haptics
The review

“This new type of haptics really
works, and quite well. The effect is
best described as "spooky". It
works so well that if Motorola had
told us it had real keys under the
surface - and wasn't a touch
keypad at all - we would have
believed them and never doubted
it…. ”

Eric Lin, Eric M. Zeman and Rich Brome
January 7, 2008
www.phonescoop.com


The challenge

“Morphing” keypad
= Display?

Lack of keyclick
feedback for key press
Sample photo placement

ROKR E8 ModeShiftTM keypad


The solution

Direct bonding of piezo Proof-of-concept
element on phone
chassis behind keypad

Shrinkage/expansion of
piezo under electrical
field translates to
“buckling” motion of
keypad Force
haptics to fingertip sensing
resistor


Why piezo?

Popple switch Optimized DC Optimized linear Piezoelectric
rotary motor motor actuator

Typical Popple Click (Press Only) Immersion VibeTonz vs. Click Linear Motor with Reverse Drive vs. Popple Click Piezo Actuator vs. Click

15 15 5

10 10
2.0 4.0 Popple Click Popple Click Popple Click

Acceleration (g) - Popple
Time (ms) Linear (Rev. Drive) Piezo Actuator
VibeTonz 5 5
Acceleration (g)

5

0 0

-5 5
-5

-10
MARGINAL -10
GOOD BEST
-15 5
-15
0 10 20 30 40 50 60 0 10 20 30 40 50 60
0 10 20 30 40 50 60 0 10 20 30 40 50
Time (ms) Time (ms)
Time (ms) Time (ms)

Global

Localized


What to measure for a keyclick?
Virtual tapping study (J Feine, Stanford Univ,
Haptics2006)
– Haptic simulations of tapping on a hard object
feels most real when hand acceleration
produced by virtual contact are matched to
those of contact with real object

Key click profile
– Push and release acceleration pulses 2.0
Time (ms)
4.0

– Each pulse: <5 ms, 40~100 g Accel_pp

Impact other than acceleration needs to be
further studied


Passive vibrotactile

Acceleration Comparizon Displacement Comparizon
0.6 10
SSRC SSRC
0.5
Average 8 Average

Dsiplacement (μ m)
Mountcastle
Acceleration (g)
Threshold

0.4
Mountcastle 6 1972
0.3 1972
4
0.2

0.1 2

0.0 0
0 100 200 300 400 0 100 200 300 400
Frequency (Hz) Frequency (Hz)
12 300
Comfort range

Max_g Max_d
10 Min_g
250
Min_d

Displacement ( μ m)
8 200
Accel_pp (g)

6 150

4 100

2 50

0 0
0 100 200 300 400 500 0 100 200 300 400 500

Frequency (Hz) Frequency (Hz)


Click threshold and comfort level

Test setup

Subjects control test processes
Up/down key to adjust voltage level
Space bar to register the desired voltage level

6 data points for each wave setting, 3 runs
starts from low and other 3 runs from high

Alternated test sequence on threshold and
comfort level for counter balance

Total 12 test subjects

12 levels at 2 dB a step


Waveforms and resultant acceleration profiles:
Step, sin300_1, sin300_2, sing150_1 and sing 150_2 generated in Audition
250 step w ave 250 Sin300_1 w ave 250 Sin300_2 w ave 250 Sin150_1 w ave 250 Sin150_2 w ave
200 200 200 200 200
150 150 150 150 150
Voltage (v)

Voltage (v)

Voltage (v)

Voltage (v)

Voltage (v)
100 100 100 100 100
50 50 50 50 50
0 0 0 0 0
-50 -50 -50 -50 -50
-0.005 0 0.005 0.01 0.015 0.02 -0.005 0 0.005 0.01 0.015 0.02 -0.005 0 0.005 0.01 0.015 0.02 -0.005 0 0.005 0.01 0.015 0.02 -0.005 0 0.005 0.01 0.015 0.02
Tim e (s) Tim e (s) Tim e (s) Tim e (s) Tim e (s)

15 step w ave p-p acceleratoin 15 15 15 15
sin300_1 w ave p-p acceleratoin sin300_2 w ave p-p acceleratoin sin150_1 w ave p-p acceleratoin sin150_2 w ave p-p acceleratoin
10 10 10 10 10
Acceleration (g)

Acceleration (g)

Acceleration (g)

Acceleration (g)

Acceleration (g)
5 5 5 5 5
0 0 0 0 0
-5 -5 -5 -5 -5
-10 -10 -10 -10 -10
-15 -15 -15 -15 -15
-0.005 0 0.005 0.01 0.015 0.02 -0.005 0 0.005 0.01 0.015 0.02 -0.005 0 0.005 0.01 0.015 0.02 -0.005 0 0.005 0.01 0.015 0.02 -0.005 0 0.005 0.01 0.015 0.02
Tim e (s) Tim e (s) Tim e (s) Tim e (s) Tim e (s)

Audio signal (Vpp = 0 ~ 2 V) to
20x piezo amplifier for threshold (max Vpp ~ 40 V)
100x Kepco voltage amplifier for comfort level (max Vpp ~ 200 V)
Wave forms played at both press and release of FSR


Click threshold 3
Threshold Acceleration

95% CI High
95% CI Low
Step wave

Threshold Accele_pp (g)
2 Mean
Accel_pp ~ 2 g
Single pulse? 1

Frequency effect 0
Step Sin150_1 Sin150_2 Sin300_1 Sin300_2
Accel_pp ~ 0.39 g at 150_1 Hz, Haptics
Accel_pp ~ 0.71 g at 300_1 Hz Vpp
20
95% CI High
Number of wave

Threshold Voltage (V)
15 95% CI Low
Mean
Accel_pp ~ decreases at double waves
10

Drive voltage 5

Voltage lower in double waves drive 0
Voltage lower as frequency goes up Step Sin150_1 Sin150_2 Sin300_1 Sin300_2
Haptics


Click “Comfort” Level Com fort Acceleration Level
25
95% CI High

Comfort Accele_pp (g)
Similar acceleration and voltage 20
95% CI Low
Mean
profiles as threshold 15

10

Frequency effect 5

Accel_pp ~ 3.2 g at 150_1 Hz, 0
Step Sin150_1 Sin150_2 Sin300_1 Sin300_2
Accel_pp ~ 6.7 g at 300_1 Hz Haptics

Com fort Voltage Level
Number of wave 150
95% CI High

Comfort Level Voltage (V)
Accel_pp ~ decreases at double 95% CI Low
100 Mean
waves
50
Drive voltage
Voltage lower in double waves drive 0
Voltage lower as frequency goes up Step Sin150_1 Sin150_2 Sin300_1 Sin300_2
Haptics


single, double waves and vibrotactile
1 2 …. Vibrotactile, 250 ms, 37~75 waves
wave waves Piezo Thunder Mini shaker

Threshold Sin150 0.39 0.25 0.03 0.03
Accel_pp (g) Sin300 0.71 0.51 N/A 0.12
Threshold Sin150 4.3 2.8 0.33 0.32
displ* (μm) Sin300 2.0 1.4 N/A 0.32

1 2 …. Vibrotactile, 250 ms, 37~75 waves
wave waves Piezo Thunder Mini shaker
Comfort level Sin150 3.21 2.04 0.12 ~0.9 0.92 ~ 5.37
Accel_pp (g) Sin300 6.71 4.48 N/A 3.2 ~ 10.3
Comfort level Sin150 35.4 22.5 4.6 ~ 34.5 10.2 ~ 60.4
displ* (μm) Sin300 18.5 12.4 N/A 8.8 ~ 28.5

Lower acceleration and displacement for multiple waves


“Comfort” vs threshold levels

Accel_Cmf/Accel_Thr In dB (=20*log(Cmf/Thr))
Step 8.79 18.9
Sin150_1 8.29 18.4
Sin150_2 8.02 18.1
Sin300_1 9.44 19.5
Sin300_2 8.76 18.8

For current interactive click feedback test, the comfort level is
approximately 18~19 dB over threshold. The ratio is appx a constant, and
is independent of the wave forms, frequency and number of pulses


Issues of existing in-line test fixture
Fixture Hand

Frequency response

200 g wt on linear slider
Good tool for production line with good R&R

Discrepancy of fixture vs hand
Magnitude of pk-pk acceleration
Trend of frequency response


Literature -- human finger study

Multiple joints, muscles/tendons to actuate finger
Biomimetic finger: use SMA for actuation
* Vishalini Bundhoo and Edward J. Park, “Design of an Artificial Muscle Actuated Finger towards Biomimetic Prosthetic
Hands”, IEEE, 2005


Haptics Characterization Rapid transient measurement
Literature – fingertip

Model
F (t ) = m&& + bx(t ) + kx(t )
x &
Findings
• Mass m: ~ 6 g
• Stiffness k: up linearly with force
• Damping b: large zero-f value, up linearly with force
* A. Haijun and R. Howe, “Identification of the mechanical impedance at the human
finger tip”, J Biomechanical Eng, Vol 119, P 109, Feb 1997

Internal Study -- finger impedance vs frequency
Model
Z(ω ) = F(ω ) x& (ω ) = (mω − k ω )j + b

16
14
12
|Z|, N-s/m

10
8
6
4
2
0
0 100 200 300 400 500 600
Frequency, Hz

2-spring system? 1 DOF?
• Both response to lower frequency
• One dominates at higher frequency
* C Fu and M Oliver, “Direct Measurement of Index Finger Mechanical
Impedance at Low Force”, World Haptics 2005

Two springs?

Improved test fixture – proof of concept
1 DOF
wt
Poron
A-meter
Probe

Phone

Springs

Schematic
• 2-spring system “Primitive” fixture
– Arm • stainless steel = spring 1
– probe • 200 g weigh: F @ contact ~ g
• 1 DOF at the joint • Accelerometer: MS ACH-01
• Weight and position to • Poron: Rogers 4790-92-15125-04 cellular
reach 150~200 g at the urethane foam, 3 mm, = spring 2
probe • Probe: Al block + screw with round tip


Results – Finger Press vs Fixture

Fairly good tracking
at 200, 250 and 300
Hz, nearly 1:1

Good tracking at all
voltage levels

Slightly off at 150 Hz

Overall the tracking is
very much improved
over the existing
inline test fixture


Summary

Haptics is an essential functionality of mobile devices

Proper developed haptics could greatly enhance device
usability

Piezoelectric enabled localized haptics can provide a
nearly true keyclick experience

Haptics characterization is critical for technology
development


Challenges

Haptics characterization
– Understanding of the physical parameter space responsible for a
wide range of tactile sensations that can be communicated from
a mobile device to the human hand and/or the wrist
– Provide psychophysical evidence for the design of tactile
patterns to be used with mobile devices

Haptics implementation
– Touchscreen solutions
– Novel UI enabled or enhanced by haptics in conjunction with
visual and audio effects


Backup slides


Voltage – Acceleration Calibration
Threshold Calibration Comfort Level Calibration
10 50
y = 0.216x - 0.033
Step R2 = 0.9996 Step y = 0.212x - 0.7498
sin150_1 sin150_1 R2 = 0.9986
8 40
Sin150_2 Sin150_2
Acceleration p-p (g)

Acceleration p-p (g)
sin300_1 sin300_1
6 Sin300_2 30 Sin300_2
Linear (Step) Linear (Step)

4 20

2 10

0 0
0 10 20 30 40 50 0 50 100 150 200 250
Voltage (v) Voltage (v)

• Observation
– Good linearity between Vpp to piezo and Accel_pp in all driving waveforms
• For sinusoidal wave, Accel ~ ω2*Displ ~ ω2*V
– Consistent slopes in both low and high voltage ranges
– Parameters from linear curve fitting are used to calculate the actual Accel_pp


ACTUATORS

Multi-Function Transducer (MFT)

FOR SOUND

TOP PLATE COIL PROTECTOR1 DIAPHRAGM SUSPENSION FRAME

PROTECTOR2 MAGNET POLE PIECE SUSPENSION SPACER
FOR VIBRATION

Microelectronics & Physical Sciences Research

Haptics for Mobile Devices

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