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 Steve Dai, Haptics Purdue October 21, 2008

Haptics Overview Sample applications BMW mice I-drive vibrating gaming call alert controllers 3D Design & Interaction medical training Braille displays Steve Dai, Haptics Purdue October 21, 2008

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 Steve Dai, Haptics Purdue October 21, 2008

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 Steve Dai, Haptics Purdue October 21, 2008

Haptics Overview Receptors Light SOUND TOUCH Steve Dai, Haptics Purdue October 21, 2008

Haptics for Mobile Devices 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 Steve Dai, Haptics Purdue October 21, 2008

Haptics for Mobile Devices 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 Steve Dai, Haptics Purdue October 21, 2008

Haptics for Mobile Devices 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) Steve Dai, Haptics Purdue October 21, 2008

Haptics for Mobile Devices 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 Steve Dai, Haptics Purdue October 21, 2008

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 Steve Dai, Haptics Purdue October 21, 2008

Localized Piezo Haptics The challenge “Morphing” keypad = Display? Lack of keyclick feedback for key press Sample photo placement ROKR E8 ModeShiftTM keypad Steve Dai, Haptics Purdue October 21, 2008

Localized Piezo Haptics 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 Steve Dai, Haptics Purdue October 21, 2008

Localized Piezo Haptics 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 Steve Dai, Haptics Purdue October 21, 2008

Haptics Characterization 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 Steve Dai, Haptics Purdue October 21, 2008

Haptics Characterization 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) Steve Dai, Haptics Purdue October 21, 2008

Haptics Characterization 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 Steve Dai, Haptics Purdue October 21, 2008

Haptics Characterization 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 Steve Dai, Haptics Purdue October 21, 2008

Haptics Characterization 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 Steve Dai, Haptics Purdue October 21, 2008

Haptics Characterization 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 Steve Dai, Haptics Purdue October 21, 2008

Haptics Characterization 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 Steve Dai, Haptics Purdue October 21, 2008

Haptics Characterization “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 Steve Dai, Haptics Purdue October 21, 2008

Haptics Characterization 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 Steve Dai, Haptics Purdue October 21, 2008

Haptics Characterization 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 Steve Dai, Haptics Purdue October 21, 2008

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 Steve Dai, Haptics Purdue October 21, 2008

Haptics Characterization 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 Steve Dai, Haptics Purdue October 21, 2008 Two springs?

Haptics Characterization 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 Steve Dai, Haptics Purdue October 21, 2008

Haptics Characterization 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 Steve Dai, Haptics Purdue October 21, 2008

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 Steve Dai, Haptics Purdue October 21, 2008

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 Steve Dai, Haptics Purdue October 21, 2008

Backup slides Steve Dai, Haptics Purdue October 21, 2008

Haptics Characterization 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 Steve Dai, Haptics Purdue October 21, 2008

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

by Steve Dai

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