perception of mobile device vibrations -...

Perception of

Mobile Device Vibrations

Korea HCI Conference 2009

Haptics Tutorial

Haptics and Virtual Reality Laboratory

POSTECH

Seungmoon Choi, Ph. D.

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Overview

(Very) Basics of Vibrotactile Perception

Physical Characteristics

Absolute Detection Thresholds

Perceived Intensity

Perceptual Space

Perceptually Transparent Rendering

Graphical Authoring Tools

2KHCI 2009. Haptics Tutorial�1�6�8�9

(VERY) BASICS OF

VIBROTACTILE PERCEPTION


Pathway of Tactile Perception


Approaches in Perception Research

Psychophysics

– What are the smallest stimulus intensities that the human skin can sense

for various stimulus conditions?

– How does perceived stimulus magnitude increases as stimulus intensity

increases?

Neurophysiology

– What organs in the skin sense tactile stimuli?

– How is the sensed information transmitted to the brain?

– What parts of the brain processes the information?

Methods from both fields are often used together


Mechanoreceptors


Mechanoreceptor Characteristics

7

Merkel DiskMeissner

Corpuscle

Ruffini

Cylinder

Pacinian

Corpuscle

Location

Border between

the epidermis and

the dermis

Just below the

epidermisIn the dermis

Deeper in the

dermis

Frequency

Range0.3 – 3 Hz 3 – 40 Hz 15 – 400 Hz 10 – 500 Hz

Perceiving

PropertyPressure Flutter Stretching Vibration

Receptive

Field SizeSmall Small Large Large

Sensory

AdaptationSA1 RA1 SA2 RA2

Neural

ChannelNP III NP I NP II PC

KHCI 2009. Haptics Tutorial�1�6�9�4

PHYSICAL

CHARACTERISTICS


Vibration Motor

9

Widely used as a vibration actuator for mobile devices

Structure of a coin-type vibration motor


I/O Characteristics

Input

– Voltage applied to a vibration

motor

Output

– Sinusoidal vibration with correlated

amplitude and frequency

– Vibration direction is omni-

directional

10

Cellular phone used in the study


Vibration Example

11

Vibration acceleration (v=2.5V) Power spectrum (v=2.5V)


Vibration Frequency and Amplitude

12

Voltage vs. Frequency Voltage vs. Acceleration Amplitude


Vibration Amplitude and Power

Consumption

13

Voltage vs. Position Amplitude Voltage vs. Power


Voice Coil Actuator

Consists of a coil and an iron core.

Coil moves in a magnetic field produced by a permanent magnet and

intensified by an iron core.

The coil is usually attached a movable load.

Frequency and amplitude of vibration are independent.

Applications

The diaphragm of an audio speaker

The read-write head of a computer disk drive.

14

<Voice Coil Structure>


Example VBW32 (Tactaid)

Consists of coil and magnet mounted on the flat spring.

Controlled by AC signals.

Frequency range: 250Hz nominal.

Amplitude range: 50dB above detection threshold.

Transient response: 5ms.

<VBW32> <Structure of VBW32>

15KHCI 2009. Haptics Tutorial

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Characteristics of Voice Coil Actuator

16

Can provide a tactile waveform of an arbitrary shape.

The range of usable frequency and amplitude is fairly limited.


Frequency Response Example

17

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

100 125 150 175 200 225 250 275

테이블 손-약하게

손-강하게

Frequency (Hz)

Frequency Response (Z축)

Linear voice-coil actuator used in the

haptic phoneKHCI 2009. Haptics Tutorial

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ABSOLUTE DETECTION

THRESHOLDS


Related Concepts

Absolute Detection Thresholds (AL)

– The stimuli intensity that is barely perceivable

– Corresponds to “zero” in the perceptual dimension

Sensation Level (SL)

– A measure that indicates how large a signal is

compared to its detection threshold

19

)(

)(log20 LevelSensation

vAL

vApos


Apparatus

A vibration motor or a

voice-coil motor cannot

be used for measuring

ALs.

The shaker system can

create vibrotactile

stimuli in a wide

dynamic range.

20

Mini-Shaker System


Measured ALs


Sensation Levels – Vibration Motor


PERCEIVED INTENSITY

•


Related Concepts

Perceived magnitude (intensity)

– The magnitude of sensation perceived by the observer from a proximal stimulus

Psychophysical magnitude function

– A relationship between stimulus intensity and judged perceived magnitude

Absolute magnitude estimation

– A subjects tells a number of stimulus intensity without any standard stimulus (modulus).


Psychophysical Magnitude Function

Measured with the Cellular Phone

25

The increasing pattern well matches to that of the SL curve.


Power Consumption vs. Perceived

Magnitude


Psychophysical Magnitude Function

Measured with the Shaker


Comparison of Perceived Inteisty

Between Cellular Phone and Shaker

28

Cellular Phone

Mini-Shaker


Comparison of Perceived Intensity

Between Voice Coil Actuator and Shaker


PERCEPTUALLY

TRANSPARENT RENDERING

•


Related Concepts

Perceptually Transparent Rendering

Can we do this for vibration rendering in a

mobile device with perceived magnitude as a

target perceptual variable?31KHCI 2009. Haptics Tutorial

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Inverse of Psychophysical

Magnitude Function

32

xey 984.17436.0


Pairwise Discriminability of Vibrations

Driven with Two Voltages

Averages of All Levels

Averages of Adjacent Levels

Only


34

Thank you!

Questions and comments can be addressed to:

-Seungmoon Choi, Ph.D., [email protected]

More information is at http://hvr.postech.ac.kr.


mailto:[email protected]

http://hvr.postech.ac.kr/

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