Hello! Thank you for coming to see my presentation
My name is Chaeyong Park, and I am a graduate student at POSTECH, South Korea.
I’m going to talk about our paper,
“Augmenting Physical Buttons with Vibrotactile Feedback for Programmable Feels.”
This work was done with my collaborator Jinhyuk Yoon, Seungjae Oh, and my advisor Seungmoon Choi.
Physical buttons are one of the most effective, efficient, and pervasive user interfaces,
which are widely used in the world.
They provide physical affordance, as well as natural and pronounced haptic feedback.
However, a physical button presents the same feedback all the time.
So, it is not easy to use physical buttons for a programmable interface.
Other type, virtual buttons, displayed on the touchscreen with additional vibration,
offer advantages of adaptability.
but they lack the physical affordance and clear haptic feedback.
To improve this drawback, some researchers modulate the kinesthetic response of a physical button
by adding a force actuator.
But, this system is complex and needs a large the cost.
Also, there is another approach,
which augments the feel of a physical button by adding a vibration based on Haptic augmented reality.
Here, the haptic augmented reality presents mixed sensations
combined with both the real haptic sensations and additional artificial haptic feels
and its concept is similar to the visual AR.
When the user operates the physical button, the user feels the original force response,
as well as an overlaid vibration, based on this concept.
However, none of the works reported physical or perceptual evaluation results on the augmentation.
Therefore, in this paper, we expand the idea by designing many vibration-augmented physical buttons.
Then, we explore the vast design space of the augmented buttons
to acquire fundamental knowledge on their perceptual characteristics,
and present structured and detailed analysis on the perceptual attributes of click sensations.
This is the overall design of our vibration augmented button.
We use a linear mechanical switch, which does not include a buckling response.
We also use a vibrotactile actuator and put them all into a 3D printed housing.
Then a user feels the vibration-augmented sensations on the physical button.
For vibrotactile augmentation, we designed 40 vibration waveforms
by varying vibration frequency, amplitude, and envelope.
For frequency, we selected four values
to cover the entire range
mediated by the two rapidly adapting mechanoreceptive neural channels
called RA 1 and PC channel.
For the envelope, we designed five envelope functions.
In general, key compression takes about 30ms, and the entire operation is finished in less than 100ms.
So, we choose three rectangular envelopes with different durations,
and the other two have the same duration of 100ms, which decay exponentially with different rates.
We choose two values to make an area of the slow-decaying envelope is half of the rectangular envelope,
and that of the fast-decaying envelope is a quarter of the rectangular one.
Lastly, we use two levels of amplitude, full and half.
These are examples of our augmentation technique.
Here we visualize the effects using measured acceleration and force profiles.
The next section shows two user experiments
to investigate the perceptual properties of the augmented button.
The first experiment is to estimate a perceptual space,
and the second experiment is to project perceptual dimensions into the perceptual space.
In this experiment, we wanted to estimate a perceptual space
that visualizes the relationships between many physical and augmented buttons.
We used the 40 vibration-augmented buttons
7 physical buttons without any external vibrotactile feedback.
All augmented buttons are based on the linear physical button #41,
and the button #41 is the physical button itself without vibration.
Button #42 requires a smaller force than the base button,
and button #43 and #44 deliver a buckling sensation.
Also, membrane switches with different stiffness are used.
The last button, the tact switch, has a unique and strong click feel.
To compare the similarity between button click sensations, we used the cluster sorting method.
In this method, the participants compared the feel of all buttons
and grouped them into a given number of clusters based on their perceptual similarity.
And then, we calculated the pairwise dissimilarity score of button feel
and applied Multi-Dimensional Scaling analysis with the score to find the perceptual space.
The perceptual space is a Euclidean space that visualizes relationships
between the feel of the button based on perceptual similarity.
As a result, the 47 buttons are widely spread across at the 2D perceptual space.
The base button #41 is represented with a star,
and the distance between two points means
the perceptual dissimilarity between the two corresponding buttons.
Interestingly, even though the button #8 is an augmented button
the dissimilarity score between button #8 and #41
is greater than that between the physical buttons, #41 and #47.
According to the results of clustering analysis
the augmented button and the physical buttons are classified into four groups
The base physical button and other linear buttons anchored the green group.
Also, there are augmented buttons, which are characterized by high frequency and low-energy envelope.
In the red group, the augmented buttons have low frequency and low-energy envelope.
From this group, we can see that adding the vibration, shown in the page
creates a similar sensation to mild buckling.
Also, those augmented buttons can convey a soft rubbery feel.
In the blue group, there is a physical button #46, which gives a highly-stiff rubbery feel,
and augmented buttons with low frequency and high-energy envelope.
Through the results, the augmented button with low frequency vibration creates a rubbery feel
and the energy envelope affects the stiffness of the button sensation.
The last group, yellow, has no physical buttons.
Thus, vibration-augmented buttons with high frequency and high-energy envelope deliver unique feels
which are quite distinguished from the 7 physical buttons.
To analyze the effects of each design variable, we can also show the centroids of each variable.
From the results, vibration frequency and envelope have critical effects.
More detailed, changing vibration frequency moves the centroid from the right to the left,
and the envelope has a similar effect by translating the centroid vertically.
Interestingly, envelope shape and amplitude are much less important.
In the second experiment, we tried to figure out a coordinate frame
that can explain the point distribution of the perceptual space with linguistically meaningful words.
We selected ten words consisting of seven bipolar adjectives with opposing meanings
and three unipolar semantic words for material properties.
After that, participants rated the subjective sensations of each button using sliders.
We projected each word to a line in the perceptual space using multiple linear regression.
Each line represents a perceptual axis for the button feel,
and each button position can be projected to the axis to recover the extent of the button’s sensation with the word.
For example, button #8 gives a hard, sticky, and blunt feel.
and the button #20 gives a sharp, shallow, and light feel.
Since the perceptual space is 2D
finding two primary perceptual dimensions is sufficient to represent all the buttons using coordinates.
To this end, we choose two lines
that have High R^2 value and are presented with mutually orthogonal axes.
Thus, we recommend sharp-blunt and soft-hard
as the two main perceptual dimensions for characterizing the perception of the buttons.
Using the primary perceptual dimensions, we can obtain the tendency similar to the experiment 1
which is related to vibration frequency or energy of envelope.
Also, we can label the perceptual properties of the four button groups using the two dimensions.
The percept of each button can be represented by its coordinates (b, h)
where b is the button position projected to the sharp-blunt axis
and h is the button position in the soft-hard axis.
We can understand the perceptualrelations between various augmented buttons,
and this is similar to the HSV model for color perception and representation.
For detailed description of the other dimensions, you can find them in our paper.
In this section,
we introduce many interaction scenarios with simple and easy vibration augmented buttons.
First, we can design context-dependent buttons
to deliver more immersive and engaging experiences for entertainment.
For example, when we play a game the gamepad can give a bumpy feel on uneven ground
depending on the context.
Also, in a soccer game, providing different click sensations
during attack or defense state may enable the user to be aware of the current context.
For electronic devices, augmented buttons can present the state of the system
by providing different key-press feedback according to the state.
For instance, the feedback can be soft, smooth, and light for calls from a beloved someone.
Also, because touch is a very effective modality for affective interfaces
we can customize button click sensations for each driver in a car.
Finally, augmented feedback can be associated with immediate system responses to the user.
For example, when an error occurs during key-pressing
the augmented button can give different feedback
as a notification of error with auditory and visual effects.
Finally, we suggest major design guidelines of effective augmentation for physical buttons.
First, the feel of the vibration-augmented button is well expressed in 2-dimensional perceptual space
with the two perceptual dimensions of sharp-blunt and soft-hard.
Second, the vibration frequency is a critical design variable for the feel of a button.
Using a high frequency makes the button feel sharper, and a low frequency makes blunter.
Third, the energy of a vibration determined by envelope shape and duration
is another primary design variable.
Augmentation with a high-energy envelope increases the hardness
while a low-energy envelope increases the softness.
Next, Envelope shape and vibration amplitude make no noticeable difference in haptic augmentation.
So, we can use simple patterns without complex computational cost.
Last, the augmented button renders a similar sensation to a real physical button
that exhibits material properties or a buckling effect.
From our observations, for the base linear physical button
haptic augmentation with vibrotactile feedback is a very effective technique
in expanding button click sensations.
This is the end of my talk.
Thank you for watching it.