# Haptic Stylus and Empirical Studies on Braille, Button, and Texture Display

Authors: Ki-Uk Kyung; Jun-Young Lee; Junseok Park
Journal: Journal of Biomedicine and Biotechnology
 (2008)

---

## Abstract

This paper presents a haptic stylus interface with a
built-in compact tactile display module and an impact module
as well as empirical studies on Braille, button, and texture
display. We describe preliminary evaluations verifying the
tactile display's performance indicating that it can
satisfactorily represent Braille numbers for both the normal
and the blind. In order to prove haptic feedback capability of
the stylus, an experiment providing impact feedback mimicking
the click of a button has been conducted. Since the developed
device is small enough to be attached to a force feedback
device, its applicability to combined force and tactile
feedback display in a pen-held haptic device is also
investigated. The handle of pen-held haptic interface was
replaced by the pen-like interface to add tactile feedback
capability to the device. Since the system provides
combination of force, tactile and impact feedback, three
haptic representation methods for texture display have been
compared on surface with 3 texture groups which differ in
direction, groove width, and shape. In addition, we evaluate
its capacity to support touch screen operations by providing
tactile sensations when a user rubs against an image displayed
on a monitor.


---

## Body

## 1. Introduction

Researchers have proposed a diverse range of haptic interfaces for more
realistic communication methods with computers. Force feedback devices, which have attracted
the most attention with their capacity to physically push and pull a user's
body, have been applied to game interfaces, medical simulators, training
simulators, and interactive design software, among other domains [1]. However,
compared to force feedback interfaces, tactile displays have not been deeply studied.
It is clear that haptic applications for mobile devices, such as PDAs, mobile
computers, and mobile phones, will have to rely on tactile devices. Such a
handheld haptic system will only be achieved through the development of a fast,
strong, small, silent, safe tactile display module, with low heat dissipation
and power consumption. Furthermore, stimulation methods reflecting human
tactile perception characteristics should be suggested together with a device.A number of researchers have proposed tactile display systems. In order to
provide tactile sensation to the skin, work has looked at mechanical,
electrical, and thermal stimulation. Most mechanical methods involve an array
of pins driven by linear actuation mechanisms such as solenoids, piezoelectric actuators, or pneumatic actuators. An
example is the “Texture Explorer,” developed by Ikei and Shiratori [2]. This 2×5 flat pin array is composed of piezoelectric actuators and
operates at a fixed frequency (−250 Hz) with maximum amplitude of 22 μm. Summers and Chanter [3] developed a broadband tactile
array using piezoelectric bimorphs and reported empirical results for stimulation
frequencies of 40 Hz and 320 Hz with the maximum displacement of 50 μm. Since the aforementioned
tactile displays may not result in sufficiently deep skin indentation, Kyung et
al. [4] developed a 5×6 pin-array
tactile display which has a small size, long travel, and high bandwidth.
However, this system requires a high input voltage and a high power controller.
As an alternative to providing normal indentation, Hayward and Cruz-Hernandez [5] and Luk et al. [6] have focused on the
tactile sensation of lateral skin stretch and designed a tactile display device
which operates by displaying distributed lateral skin stretch at frequencies of
up to several kilohertz. However, it is arguable that the device remains too
large (and high voltage) to be realistically integrated into a mobile device.
Furthermore, despite work investigating user performance on cues delivered by
lateral skin stretch, it remains unclear whether this method is capable of
displaying the full range of stimuli achievable by presenting an array of
normal forces.Konyo et al. [7] used an electroactive
polymer as an actuator for mechanical stimulation. Poletto and Van Doren developed
a high-voltage electrocutaneous stimulator with small electrodes [8]. Kajimoto
et al. [9] developed a nerve
axon model based on the properties of human skin and proposed an electrocutaneous
display using anodic and cathodic current stimulation. Unfortunately, these
tactile display devices sometimes involve user discomfort and even pain.We can imagine a haptic device providing both force and tactile feedback
simultaneously. Since Kontarinis and Howe
applied vibration feedback to a teleoperation in 1995 [10], some research works
have had interests in combination of force and tactile feedback. Akamatsu and MacKenzie [11] suggested a computer mouse
with tactile- and force feedback-increased usability. However, the work dealt
with haptic effects rather than precisely controlled force and tactile stimuli.
In 2004, Kammermeier et al. combined
a tactile actuator array providing spatially distributed tactile shape display
on a single fingertip with a single-fingered kinesthetic display and verified
its usability [12]. However, the size of the tactile display was not small enough
to practically use the suggested mechanism. As more practical design, Okamura et
al. designed a 2D tactile
slip display and installed it into the handle of a force feedback device [13].
Recently, in order to provide texture sensation with precisely controlled force
feedback, a mouse fixed on 2DOF mechanism was suggested [14]. A small pin-array
tactile display was embedded into a mouse body and it realized texture display
with force feedback. More recently, Allerkamp et al. developed a compact
pin-array and they tried to realize the combination of force feedback and
tactile display based on the display and vibrations [15]. However, in previous
works, the tactile display itself is quite small but its power controller is
too big to be used practically. Our work in this paper deals with this issue as
one of applications of our system.In the area of human tactile perception, Johansson and Vallbo [16] and
Johnson and Phillips [17] have studied human mechanoreceptors and their function
in connection with tactile perception and the anatomical structure of glabrous
skin such as the palm or finger pad. Verrillo et al. have suggested a four-channel
model of vibrotaction which shows the variation of the displacement
(indentation depth) threshold to frequency [18]. Also, studies have measured the
sensation magnitude of thresholds as a function of frequency of vibration [18, 19].
The previous physiological research shows that humans have four types of
mechanoreceptors for tactile sense and that each type responds in a specific
band of frequency. Therefore, frequency characteristics should be given careful
consideration in the design of a tactile display device and stimulation method.In this paper, we propose a
compact tactile display module which can be embedded into small devices and a
pen-type haptic interface providing impact and distributed pressure. In Section2, the design parameters and
structure of the proposed tactile display module are described in detail. In Section
3, the implementation of a pen-like haptic interface including the tactile
display module and impact generator is presented. In Section 4, we evaluate performance of this system, which
we term the “Ubi-Pen II.” In Section 5,
performance of a force and tactile feedback interface adopting the suggested
pen-like interface is described. Finally,
in Section 6, we discuss possible applications of the proposed system including image
display on a touch screen.


## 2. Compact Tactile Display Module

### 2.1. Design of a Tactile Display Module

In order to make a tactile display module, actuator
selection is the first and dominant step. The actuator should be small, light,
safe, silent, fast, powerful consume modest amounts of power and emits little heat. Recently, we
developed
a small tactile display using a small ultrasonic linear motor [20]. We here briefly
describe its operation principle and mechanism.The basic structure and driving principle of the actuator
are described in Figure1. The actuator is composed of a transducer, a shaft,
and a moving element. The transducer is composed of two piezoelectric ceramic
disks and elastic material membranes. The convex motion of the membranes causes
lift in the shaft of the motor. The fast restoring concave motion overcomes the
static frictional force between the moving element and the shaft, and it makes
the moving element maintain its position. The displacement “A” of one cycle is
submicrometer scale, and the
rapid vibration of the membrane at a frequency of 45 kHz (ultrasonic range)
causes rapid movement of the moving element. The diameter of the transducer is
4 mm and its thickness is 0.5 mm. The thrusting force of the actuator is greater
than 0.2 N and the maximum speed of the moving element is around 30 mm/sec. In order
to minimize the size of the tactile display module, the actuators were
arranged as shown in Figure 2. Essentially, this figure shows the arrangement
of two variations on the actuators—each with different shaft lengths. This
design minimizes the gap between actuators. Another feature is that the
elements previously described as “moving” are now stationary and
fixed together, causing the shafts to become the elements which move when the
actuators are turned on. This minimizes the size of the contact point with a user's
skin (to the 1 mm diameter of the shaft), while maintaining the mechanical
simplicity of the system.Figure 1
Operation principle of an actuator.Figure 2
The implemented tactile display module.


### 2.2. Implementation

From the design specification described in Section2.1, the prototype of
the tactile display module has been implemented as shown in Figure 2. In order
to embed the module in a pen, we constructed only a 3×3 pin array. However, it
should be noted that the basic design concept is fully extensible; additional
columns and rows can be added without electrical interference or changes in pin
density. The shaft itself plays the role of tactor and has a travel of 1 mm. The
distance between two tactors is 3.0 mm. Since the actuators operate in the ultrasonic
range, they produce little audible noise. The average thrusting force of each
actuator exceeds 0.2 N, sufficient to deform the skin with an indentation of 1 mm [21]. The total size of the module is 12×12×12 mm and its weight is 2.5 g. Since
the maximum speed of a pin is around 30 mm/sec, the bandwidth of the tactile display is approximately 20 Hz when used with a
maximum normal displacement of 1 mm. If the normal displacement is lower
than 1 mm, the bandwidth could be increased.


## 2.1. Design of a Tactile Display Module

In order to make a tactile display module, actuator
selection is the first and dominant step. The actuator should be small, light,
safe, silent, fast, powerful consume modest amounts of power and emits little heat. Recently, we
developed
a small tactile display using a small ultrasonic linear motor [20]. We here briefly
describe its operation principle and mechanism.The basic structure and driving principle of the actuator
are described in Figure1. The actuator is composed of a transducer, a shaft,
and a moving element. The transducer is composed of two piezoelectric ceramic
disks and elastic material membranes. The convex motion of the membranes causes
lift in the shaft of the motor. The fast restoring concave motion overcomes the
static frictional force between the moving element and the shaft, and it makes
the moving element maintain its position. The displacement “A” of one cycle is
submicrometer scale, and the
rapid vibration of the membrane at a frequency of 45 kHz (ultrasonic range)
causes rapid movement of the moving element. The diameter of the transducer is
4 mm and its thickness is 0.5 mm. The thrusting force of the actuator is greater
than 0.2 N and the maximum speed of the moving element is around 30 mm/sec. In order
to minimize the size of the tactile display module, the actuators were
arranged as shown in Figure 2. Essentially, this figure shows the arrangement
of two variations on the actuators—each with different shaft lengths. This
design minimizes the gap between actuators. Another feature is that the
elements previously described as “moving” are now stationary and
fixed together, causing the shafts to become the elements which move when the
actuators are turned on. This minimizes the size of the contact point with a user's
skin (to the 1 mm diameter of the shaft), while maintaining the mechanical
simplicity of the system.Figure 1
Operation principle of an actuator.Figure 2
The implemented tactile display module.


## 2.2. Implementation

From the design specification described in Section2.1, the prototype of
the tactile display module has been implemented as shown in Figure 2. In order
to embed the module in a pen, we constructed only a 3×3 pin array. However, it
should be noted that the basic design concept is fully extensible; additional
columns and rows can be added without electrical interference or changes in pin
density. The shaft itself plays the role of tactor and has a travel of 1 mm. The
distance between two tactors is 3.0 mm. Since the actuators operate in the ultrasonic
range, they produce little audible noise. The average thrusting force of each
actuator exceeds 0.2 N, sufficient to deform the skin with an indentation of 1 mm [21]. The total size of the module is 12×12×12 mm and its weight is 2.5 g. Since
the maximum speed of a pin is around 30 mm/sec, the bandwidth of the tactile display is approximately 20 Hz when used with a
maximum normal displacement of 1 mm. If the normal displacement is lower
than 1 mm, the bandwidth could be increased.


## 3. Implementation of Haptic Stylus

The styli have
become common tools for interacting with mobile communication devices. In the
area of haptics, Lee et al. [22]
suggested a haptic pen which could provide a sense of contact based around a
touch sensor and a solenoid. It could generate a feeling corresponding to
clicking a button.In order to
support richer stylus-based tactile cues, we embedded our tactile display
module into a pen-like prototype. We termed these kinds of devices the Ubi-Pen
and intend it for use as an interface to VR, for the blind, to represent
textures, and as a symbolic secure communication device [20]. In our previous
version, a small vibrator was installed at the tip of the pen. However, since
the vibrator's temporal response is slow, it causes time delay between signal
and activation. Although it was effective, it was not realistic.In this
research, instead of a typical vibrator, we installed an impact generator in
the head of the pen to provide a sense of contact (see Figure3). We named this
version the Ubi-Pen II. We suggest that it could be used generally as the stylus
of a mobile communication device, which provides realistic and interactive haptic
cues such as buttons during operation of OS.Figure 3
The prototype of the Ubi-Pen II.Figure4 shows
an operation principle of the impact generator. There is a mass inside the generator
and electromagnetic force induced by electric signal that makes the mass move along a
longitudinal axis of the case. This generator is generally used as a kind of
linear vibrator and we otherwise use it as an impact generator. The generator
is arranged along a longitudinal axis of the stylus housing. When a rising
signal is applied to the generator, the mass moves up fast and it collides with
the upper side. When a falling signal is applied to the generator, the mass
moves down fast and it collides with the bottom side. The response time of the
mass movement is within
milliseconds scale.Figure 4
Operation principle of an impact generator.


## 4. Evaluation of Performance

### 4.1. Braille Display of the Tactile Display Module

A common method to evaluate the performance of
tactile displays is to test user's performance at recognizing specific patterns
[2, 4]. We use Braille as a stimulus set to conduct such a test. Specifically,
we conducted a study involving the presentation of the Braille numbers 0–9 on
the Ubi-Pen.Figure5 shows the experimental Braille patterns. Subjects were required to hold the pen such that the tip of their index finger rested over the pin-array part of tactile display module. In our previous
work, the test was conducted for the normal people and there was small
observations for the blind [20]. In this paper, the Braille display test bas
been conducted for the normal and the blind.Figure 5
Braille patterns for the experiment.After setup stage, we conducted a study on
recognition rate of the 10 numeric digits in the Braille character set. As these can be displayed on only four pins, we mapped them
to the corner pins on our tactile display module. We chose to do this as our
user-base was composed of sighted Braille novices. We used three different stimulation
frequencies: 0, 2, and 5 Hz. (Pins move up
and maintain static position at the 0 Hz.)  Pins
movement was synchronized. We presented 60
trials in total, each number at each frequency, twice. All presentations were
in a random order, and subjects were not advised about the correctness of their
responses. 10 subjects
participated in the experiment. The Braille stimuli were generated continuously and changed as soon as
the subject respond using the graphic user interface. There were 2-minute breaks after
every 20 trials.Two blind people have participated in the same
experiment and the visual guidance in the experiment has been replaced by the
speech guidance of experimenter. For all stimuli, they responded exactly and
quickly. The Braille expert usually read more than 100 characters [23], and the
blind subjects responded
that they do not feel any difficulties to read the Braille numbers.  Since the duration of
each trial was shorter than 1-2 seconds and they answer in the form of
speech, we could not measure the duration exactly.Moreover, 4 neighborhood pins have been
presented again with identical procedure for the blind people; and they
responded more quickly since the gap of pins was more familiar with them. Duration
of each trial was always shorter than 1 second.Table1 shows the summary of experimental
results. Although normal subjects were novice in using the tactile display, the
average percentage of correct answers exceeded 80 percent. The confusions come
from the relatively low tactile sensitivity of the novices compared with the
sensitivity of the blind. Since the various analysis of the tactile display for
the blind is another interesting topic, this will be investigated in our future
work.Table 1
Experimental results.
Normal subjectsBlind subjectsAverage percentage of
correct answers80.83100Average duration of each
trial (sec)5.241∼2Craig's research shows the blind people have
extraordinary capability to recognize the vibrotactile patterns at very high
frequencies [23]. It might be true that specialized people recognize
vibrotactile patterns without respect to frequencies. However, spatial acuity
of human tactile perception is a function of the vibration frequency; and we
need to determine the best frequency for the tactile pattern display using the
developed device. Our previous work shows spatial acuities are better at the
range of the Merkel's disk and Meisner's corpuscle [4]. From the comparisons
at the frequency range of 0∼560 Hz, the sensitive range of the Merkel's disk,
1–3 Hz, was the best frequency for the pattern perception since the
mechanoreceptor is mainly related to the sense of surface pattern and
distributed pressure [18]. Before conducting the experiment, we needed to look
at the frequency bands of peripheral tactile neural responses. There are four
mechanoreceptors in the glabrous skin of the palm and fingertip regions.
Meissner's corpuscles and Merkel's discs are located in the upper layers, and
Ruffini endings and Pacinian corpuscles are located more deeply. These
receptors are divided into the following two classes according to their rate of
adaptation: the slowly adapting afferent receptors and the rapidly adapting
afferent receptors. The slowly adapting afferent receptors comprise Merkel's
discs (SA I) and the Ruffini endings (SA II), while the rapidly adapting
afferent receptors comprise Meissner's corpuscles (RA I) and the Pacinian
corpuscles (RA II). The four mechanoreceptors each have different functions [16, 18].
The SA I afferents respond to quasistatic deformations of the skin, such as
force or displacement in the frequency range of 0.4–3 Hz. These
receptors play an important role in detecting spatial structures in static
contact, such as an edge or a bar. The size of Merkel's receptor is small and
shows very high innervation density at the tip of index finger. The SA II
afferent receptors provide a neural image related to the direction of the skin
being stretched. SA Type II fibers produce a buzz-like sensation in the
frequency range of 100–500 Hz. The RA I
afferent receptors, which have a frequency range of 2–40 Hz, detect
dynamic deformations of the skin such as the sensation of flutter. The RA I
afferent receptors are about four times more sensitive than the SA I afferent
receptors; in addition, RA I shows best sensitivity in the frequency range of
25–40 Hz. The RA II afferent receptors, which have a frequency response in the
range of 40–500 Hz, are the
most sensitive to vibration amplitude and are particularly known to serve as
detectors of acceleration or vibration. Previous anatomic study shows the size
of Pacinian corpuscles to be bigger than the other mechanoreceptors located
deeper within the skins, and their innervation density is low [24]. Therefore,
it is to be expected that their spatial acuity would be poor. (However, in some
cases [23], good spatial resolution may be observed at frequencies expected to
activate Pacinian corpuscles.) Based on these findings, we found that humans were more
sensitive at a frequency band of 1–3 Hz in tactile pattern discrimination that
they are at surrounding frequencies [4]. This is due to the structure of our
neural mechanism for sensing tactile pattern. One part is easily activated by
this frequency band. Therefore, we hypothesized that stimuli delivered in that
frequency range would outperform those outside it. This was brought out by
asking subjects about their impressions of the cues, and 8 of the 10 subjects
suggested that some frequencies were easier to detect than others.However, as shown in Table2, there is no
difference among the percentage of correct answers according to frequencies.
Investigating in more detail, we turned to task completion time. Average
duration of a trial was 5.98 seconds at the 0 Hz, 4.42 seconds at the 2 Hz, and
5.24 seconds at 5 Hz. Thus, the average duration of a trial is decreased at the 2-Hz
frequency. Although, inconclusive, we suggest this indicates that subjects
found the sensations delivered at this frequency to be easier to detect. In
this section, the performance of the tactile display module has been verified. Especially,
its capability of displaying Braille for the blind was proved. In addition, an
appropriate stimulating frequency has been investigated.Table 2
Percentage of correct answers according to frequencies.
0 Hz2 Hz5 HzAverage percentage of correct
answers79.981.982.7Standard deviation18.612.39.2Here, we have some issues to be discussed. As mentioned
previously, since the blind people are familiar with rubbing surface to read
the Braille, we are not sure that stimulation of 2 Hz is effective for the
blind. In fact, after they participated in the experiments, they commented that
static display was easier to discriminate than vibrational stimuli. We have to
consider user's familiarity when we design tactile stimuli.


### 4.2. Simulation of Button Pressing Sense

One of the most
frequent complaints when using a touch screen is ambiguity about whether a
screen tap has resulted in a successful button press. Researchers have proposed
that there is a touch screen providing active touch feedback to address this
issue [25]. In a previous version of the Ubi-Pen, there is a short-term
vibration feedback for notifying button clicking [20]. In a different manner,
the Ubi-Pen II also possesses the ability to produce a click-like sensation
with an impact generator.As shown in Figure6, button pressing is
composed of 3 steps. The first step is increasing pressing force. The second
step is button pressed state after sudden falling down when the pressing force
is greater than a threshold. The third step is releasing the button with an
abrupt rising up. We do not have to consider the first step since it naturally
occurs on a touch screen. The touch screen
itself provides a function of button pressing with a threshold pressure; and
the keys of the second and the third steps are sudden change of movement. Because
the sudden change is a kind of impact, we can simulate the second and the third
steps with our haptic stylus including an impact generator. As shown in Figure
6, the falling down collision of the mass inside the generator gives effect of
the button pressing. The rising up collision of the mass provides sense of the
button releasing to users.Figure 6
Procedure of button pressing sense.Here we test the effectiveness of this feature.
We presented subjects with a simple calculator interface, shown in Figure7.
They had to enter each of the 6 equations shown on the right of the screen.
Each equation was randomly presented and haptic feedback was also randomly
provided in half the trials. Subjects had to calculate every equation twice
until they obtained the correct answer to each. This calculator displayed only
the results of calculations, not the figures entered. In this study, we
measured task completion time.Figure 7
Calculator and presented equations.The experimental results in Table3 show
that the clicking sense feedback of the Ubi-Pen II decreased the length of time
to enter the calculations. The major influence of the click sensation was to
add self confidence to users, and this contributed to the production of fewer
errors and the reduced duration of the calculations. We asked each participant
about the effectiveness of clicking sense feedback and they all agreed that clicking
sense feedback gives self confidence and reality. Additionally, we had a chance
demonstrating the Ubi-Pen II at an IT exhibition show and 145 of 160 visitors agreed
that proposed scheme provide users with reality of a button. From this test,
the effectiveness of the Ubi-Pen's button pressing feedback has been verified.Table 3
Effectiveness button pressing sense feedback.
Average duration of calculationStandard deviationWithout haptic feedback14.04 (sec)2.62With haptic feedback10.66 (sec)2.15


## 4.1. Braille Display of the Tactile Display Module

A common method to evaluate the performance of
tactile displays is to test user's performance at recognizing specific patterns
[2, 4]. We use Braille as a stimulus set to conduct such a test. Specifically,
we conducted a study involving the presentation of the Braille numbers 0–9 on
the Ubi-Pen.Figure5 shows the experimental Braille patterns. Subjects were required to hold the pen such that the tip of their index finger rested over the pin-array part of tactile display module. In our previous
work, the test was conducted for the normal people and there was small
observations for the blind [20]. In this paper, the Braille display test bas
been conducted for the normal and the blind.Figure 5
Braille patterns for the experiment.After setup stage, we conducted a study on
recognition rate of the 10 numeric digits in the Braille character set. As these can be displayed on only four pins, we mapped them
to the corner pins on our tactile display module. We chose to do this as our
user-base was composed of sighted Braille novices. We used three different stimulation
frequencies: 0, 2, and 5 Hz. (Pins move up
and maintain static position at the 0 Hz.)  Pins
movement was synchronized. We presented 60
trials in total, each number at each frequency, twice. All presentations were
in a random order, and subjects were not advised about the correctness of their
responses. 10 subjects
participated in the experiment. The Braille stimuli were generated continuously and changed as soon as
the subject respond using the graphic user interface. There were 2-minute breaks after
every 20 trials.Two blind people have participated in the same
experiment and the visual guidance in the experiment has been replaced by the
speech guidance of experimenter. For all stimuli, they responded exactly and
quickly. The Braille expert usually read more than 100 characters [23], and the
blind subjects responded
that they do not feel any difficulties to read the Braille numbers.  Since the duration of
each trial was shorter than 1-2 seconds and they answer in the form of
speech, we could not measure the duration exactly.Moreover, 4 neighborhood pins have been
presented again with identical procedure for the blind people; and they
responded more quickly since the gap of pins was more familiar with them. Duration
of each trial was always shorter than 1 second.Table1 shows the summary of experimental
results. Although normal subjects were novice in using the tactile display, the
average percentage of correct answers exceeded 80 percent. The confusions come
from the relatively low tactile sensitivity of the novices compared with the
sensitivity of the blind. Since the various analysis of the tactile display for
the blind is another interesting topic, this will be investigated in our future
work.Table 1
Experimental results.
Normal subjectsBlind subjectsAverage percentage of
correct answers80.83100Average duration of each
trial (sec)5.241∼2Craig's research shows the blind people have
extraordinary capability to recognize the vibrotactile patterns at very high
frequencies [23]. It might be true that specialized people recognize
vibrotactile patterns without respect to frequencies. However, spatial acuity
of human tactile perception is a function of the vibration frequency; and we
need to determine the best frequency for the tactile pattern display using the
developed device. Our previous work shows spatial acuities are better at the
range of the Merkel's disk and Meisner's corpuscle [4]. From the comparisons
at the frequency range of 0∼560 Hz, the sensitive range of the Merkel's disk,
1–3 Hz, was the best frequency for the pattern perception since the
mechanoreceptor is mainly related to the sense of surface pattern and
distributed pressure [18]. Before conducting the experiment, we needed to look
at the frequency bands of peripheral tactile neural responses. There are four
mechanoreceptors in the glabrous skin of the palm and fingertip regions.
Meissner's corpuscles and Merkel's discs are located in the upper layers, and
Ruffini endings and Pacinian corpuscles are located more deeply. These
receptors are divided into the following two classes according to their rate of
adaptation: the slowly adapting afferent receptors and the rapidly adapting
afferent receptors. The slowly adapting afferent receptors comprise Merkel's
discs (SA I) and the Ruffini endings (SA II), while the rapidly adapting
afferent receptors comprise Meissner's corpuscles (RA I) and the Pacinian
corpuscles (RA II). The four mechanoreceptors each have different functions [16, 18].
The SA I afferents respond to quasistatic deformations of the skin, such as
force or displacement in the frequency range of 0.4–3 Hz. These
receptors play an important role in detecting spatial structures in static
contact, such as an edge or a bar. The size of Merkel's receptor is small and
shows very high innervation density at the tip of index finger. The SA II
afferent receptors provide a neural image related to the direction of the skin
being stretched. SA Type II fibers produce a buzz-like sensation in the
frequency range of 100–500 Hz. The RA I
afferent receptors, which have a frequency range of 2–40 Hz, detect
dynamic deformations of the skin such as the sensation of flutter. The RA I
afferent receptors are about four times more sensitive than the SA I afferent
receptors; in addition, RA I shows best sensitivity in the frequency range of
25–40 Hz. The RA II afferent receptors, which have a frequency response in the
range of 40–500 Hz, are the
most sensitive to vibration amplitude and are particularly known to serve as
detectors of acceleration or vibration. Previous anatomic study shows the size
of Pacinian corpuscles to be bigger than the other mechanoreceptors located
deeper within the skins, and their innervation density is low [24]. Therefore,
it is to be expected that their spatial acuity would be poor. (However, in some
cases [23], good spatial resolution may be observed at frequencies expected to
activate Pacinian corpuscles.) Based on these findings, we found that humans were more
sensitive at a frequency band of 1–3 Hz in tactile pattern discrimination that
they are at surrounding frequencies [4]. This is due to the structure of our
neural mechanism for sensing tactile pattern. One part is easily activated by
this frequency band. Therefore, we hypothesized that stimuli delivered in that
frequency range would outperform those outside it. This was brought out by
asking subjects about their impressions of the cues, and 8 of the 10 subjects
suggested that some frequencies were easier to detect than others.However, as shown in Table2, there is no
difference among the percentage of correct answers according to frequencies.
Investigating in more detail, we turned to task completion time. Average
duration of a trial was 5.98 seconds at the 0 Hz, 4.42 seconds at the 2 Hz, and
5.24 seconds at 5 Hz. Thus, the average duration of a trial is decreased at the 2-Hz
frequency. Although, inconclusive, we suggest this indicates that subjects
found the sensations delivered at this frequency to be easier to detect. In
this section, the performance of the tactile display module has been verified. Especially,
its capability of displaying Braille for the blind was proved. In addition, an
appropriate stimulating frequency has been investigated.Table 2
Percentage of correct answers according to frequencies.
0 Hz2 Hz5 HzAverage percentage of correct
answers79.981.982.7Standard deviation18.612.39.2Here, we have some issues to be discussed. As mentioned
previously, since the blind people are familiar with rubbing surface to read
the Braille, we are not sure that stimulation of 2 Hz is effective for the
blind. In fact, after they participated in the experiments, they commented that
static display was easier to discriminate than vibrational stimuli. We have to
consider user's familiarity when we design tactile stimuli.


## 4.2. Simulation of Button Pressing Sense

One of the most
frequent complaints when using a touch screen is ambiguity about whether a
screen tap has resulted in a successful button press. Researchers have proposed
that there is a touch screen providing active touch feedback to address this
issue [25]. In a previous version of the Ubi-Pen, there is a short-term
vibration feedback for notifying button clicking [20]. In a different manner,
the Ubi-Pen II also possesses the ability to produce a click-like sensation
with an impact generator.As shown in Figure6, button pressing is
composed of 3 steps. The first step is increasing pressing force. The second
step is button pressed state after sudden falling down when the pressing force
is greater than a threshold. The third step is releasing the button with an
abrupt rising up. We do not have to consider the first step since it naturally
occurs on a touch screen. The touch screen
itself provides a function of button pressing with a threshold pressure; and
the keys of the second and the third steps are sudden change of movement. Because
the sudden change is a kind of impact, we can simulate the second and the third
steps with our haptic stylus including an impact generator. As shown in Figure
6, the falling down collision of the mass inside the generator gives effect of
the button pressing. The rising up collision of the mass provides sense of the
button releasing to users.Figure 6
Procedure of button pressing sense.Here we test the effectiveness of this feature.
We presented subjects with a simple calculator interface, shown in Figure7.
They had to enter each of the 6 equations shown on the right of the screen.
Each equation was randomly presented and haptic feedback was also randomly
provided in half the trials. Subjects had to calculate every equation twice
until they obtained the correct answer to each. This calculator displayed only
the results of calculations, not the figures entered. In this study, we
measured task completion time.Figure 7
Calculator and presented equations.The experimental results in Table3 show
that the clicking sense feedback of the Ubi-Pen II decreased the length of time
to enter the calculations. The major influence of the click sensation was to
add self confidence to users, and this contributed to the production of fewer
errors and the reduced duration of the calculations. We asked each participant
about the effectiveness of clicking sense feedback and they all agreed that clicking
sense feedback gives self confidence and reality. Additionally, we had a chance
demonstrating the Ubi-Pen II at an IT exhibition show and 145 of 160 visitors agreed
that proposed scheme provide users with reality of a button. From this test,
the effectiveness of the Ubi-Pen's button pressing feedback has been verified.Table 3
Effectiveness button pressing sense feedback.
Average duration of calculationStandard deviationWithout haptic feedback14.04 (sec)2.62With haptic feedback10.66 (sec)2.15


## 5. Combination of Force Feedback and Texture Feedback

### 5.1. System and Experimental Design

Currently, the PHANToM
is the most widely used haptic interface. It has force feedback capabilities
and it provides a stylus-like handle interface [26]. Here we replace its handle
with the Ubi-Pen II to add tactile feedback capability to the device. Since the
Ubi-Pen provides both impact and texture stimuli, this allows us to compare the
effectiveness of various haptic stimulation methods.In our previous experiment, the previous
version of the Ubi-Pen provided texture feedback and vibration feedback [20].
However, we reported that vibration potentially had problems in aspect of
control. The stylus is replaced by the Ubi-Pen II in this experiment. We conduct
similar experiment here, but we observe the effectiveness of impact feedback on
texture display. As shown in Figure 8, the proposed pen-like interface was
attached to the handle of a force feedback device (model: PHANToM Omni). In
order to test performance of the system, we designed a virtual tangible object.
The virtual object is a box and its stiffness is 2 kN/m. (The task in this experiment
does not require high interaction force.) The widths are 75 mm (300 pixels) and
67.5 mm (270 pixels). The upper surface of the box has a texture derived from texture
mapping an image and a user explores only upper surface. In order to use the
image as a texture, this test provides a symbolic pointer in the shape of a
square, with a size of 15×15 pixels. A user can load any gray-scale image. As
shown in Figure 9, when the user touches an image on the box with the
integrated interface, the area of the cursor is divided into 9(= 3×3) subcells
and the average gray value of each cell is calculated. Then, this averaged gray
value is converted to the intensity of the stimuli displayed on each pin of the
tactile display.Figure 8
Force and tactile feedback interface.Figure 9
Methodology of texture display according to the stimulation method.In this interaction, the stiffness of the box is
represented by the PHANToM force feedback device. However, the texture on the
surface can be represented in 3 ways. The first is through force feedback presented
by the PHANToM since we can feel texture by probe scanning. The second is texture
feedback by the Ubi-Pen since the pin's movement can display surface roughness.
The third is the Ubi-Pen's impact feedback since such stimuli could facilitate
the recognition of obstacles when rubbing a surface. We compared all the 3 possible
stimulation methods in this experiment as shown in Figure9. As mentioned
above, the area of virtual cursor is divided into 9 cells each with an
individual gray value. However, while the tactile display inside the pen
interface has 9 spatially distributed stimulators, the impact and force
feedback interface both have only one interaction point. Therefore, force
feedback and impact feedback use only the center value.In case of force feedback, the gray value is
converted into the height of pattern and its highest value is 1 mm. In case of
tactile feedback, the gray value is converted into the normal displacement of
each pin and the maximum displacement is 1 mm. When we use a pin-array-based
tactile display, representing resolution of the tactile display is determined by the resolution of the
pin-array. Thus, only tactile
display with high density pin-array is the solution of the high-resolution
display. In order to make up this
limitation, we derived an idea that the tactile display plays a role of
a texture magnifier. As shown in Figure10, size of the tactile display is 2.4 times bigger than the symbolic pointer. This
kind of skill may decrease reality in aspect of size, but it is a useful tip to
convey texture information to a user precisely when we use a low-density
pin-array.Figure 10
Methodology of pattern display.In case of impact feedback, haptic cues
indicate change of region while the pointer across over the texture pattern.
When the pointer moves inside texture area, the mass rises up and a user
recognizes a ridge of the pattern. When the pointer escapes texture area and
the gray value decreases under a threshold value, the mass falls down and the
user experiences sudden drop-like feeling. This kind of stimulation may not precisely
represent projected shapes of textures that could be effective to display surface
patterns.In order to compare the performance of all
stimulation methods, we prepared 3 groups of tactile patterns. Figure11(a) shows
5 image samples from group I which differ in the direction of the gratings they
feature. The size of each image was 300×270 pixels. Figure 11(b) shows image
samples from group II which contains
grooves of varying widths. A user feels horizontal gratings while rubbing the surfaces.
In order to discriminate these patterns, the tactile stimuli must be integrated
with movements on the plane. Figure 11(c) shows 5 image samples from group III,
each of which shows different shapes. Discriminating among these patterns will
require precise and accurate integration of the tactile cues with the movements
on the surface. Feeling distributed pressure (as with the pin array display)
may help users to discern the surfaces.Texture samples.
(a)(b)(c)Ten subjects participated in the experiment. In
each trial, one of the five images from one of the groups was texture mapped on
the upper surface of a virtual box. However, the graphical representation was
hidden, and only a blank surface displayed. When the user touched and rubbed the surface of the
object, the gray values of the image were conveyed to the haptic interface. They
were then required to state which texture was present. The subjects have shown all images patterns through another
screen in order to make their choice. All
texture images in a group were presented 4 times at random and the order of
test group was also randomly selected. The user felt the stiffness of the box
by force feedback, but there were three conditions for representing texture: force
feedback, tactile feedback, and impact feedback. In order to prevent practice
effects, the order of the stimulation method was also randomized. Finally,
sounds produced during the interaction may affect recognition performance, so
participants were required to wear noise cancelling headphones (Bose,
QuietComfort2).


### 5.2. Performance and Discussion

Table4 shows
experimental results for the force feedback case in the form of a confusion
matrix. Likewise, Tables 5 and 6, respectively, show the experimental results
for tactile and impact feedback. In case of force feedback, average percentages
of correct answers are 86.5% for group I, 73.5% for group II, and 60.5% for
group III. In case of tactile feedback, average percentages of correct answers
are 97.5% for group I, 91.5% for group II, and 80.5% for group III. In case of
impact feedback, average percentages of correct answers are 83.5% for group I,
81.5% for group II, and 61.0% for group III.  Figure 12 shows the mean durations of trials
in each condition. The experimental results for force feedback and tactile
feedback are similar to the previous paper's results [20]. This confirms that both previous and
new experimental results are reliable. In case of impact feedback, since impact
plays a role of cue to notifying change of texture, experimental results are a
bit similar to the case of vibration feedback previously observed.Table 4
Experimental results for force feedback (%).
Force feedback12345Group I195.02.5—2.5—2—75.05.012.57.537.55.085.02.5—4——5.095.0—515.02.5——82.5Group II182.52.57.57.5—22.567.5—12.517.5312.510.075.0—2.54—12.5—82.55.052.520.05.012.560.0Group III155.015.012.517.5—222.560.015.0—2.5325.07.555.012.5—47.55.010.067.510.057.515.0—12.565.0Table 5
Experimental results for tactile feedback (%).
Tactile feedback12345Group I1100.0————2—100.0———3——97.52.5—4——7.592.5—5———2.597.5Group II195.0—2.52.5—2—100.0———3—7.592.5——4———97.52.55—22.5—5.072.5Group III160.017.512.510.0—210.090.0———35.0—95.0——4——7.582.510.0510.0——15.075.0Table 6
Experimental results for impact feedback (%).
Impact feedback1.02.03.04.05.0Group I185.0—5.0—10.025.090.05.0——3——85.010.05.04—10.015.075.0—57.5—10.0—82.5Group II195.05.0———25.085.0—5.05.032.510.082.55.0—4——5.085.010.05—25.010.05.060.0Group III155.025.0—15.05.0210.060.010.015.05.0310.0—70.010.010.0415.05.015.055.010.055.05.015.010.065.0Figure 12
Duration of each trial.The texture samples assigned in group I can be discriminated
by detecting the direction of the gratings. Users can recognize the direction
from the position of the interaction point and the direction in which they rub.
In this case, there is no substantial difference between force feedback and impact
feedback. However, tactile display provides line load to the finger along the
gratings. As shown in Tables4, 5, and 6 as well as Figure 12, this makes human
recognize direction of the gratings more correctly and quickly.For group II, the images can be discriminated
by the variations in the spacing between the ridges. However, the spatial
resolution of the human arm is not sufficient to reliably detect variations on
the scale of millimeters
whereas the skin sense allows discrimination of submillimeter gaps [17]. In addition, pattern
display by force feedback inherently results in movement of the arm and even
stick slip vibration, factors which may disturb discrimination of gap
variation. Therefore, as shown in Table 4, the percentage of correct answers
for force feedback is lower than in the other conditions. A good example is
that users experienced difficulty discriminating between sample 2 and sample 5.
In the case of the tactile feedback, the narrow gaps are discriminated though the
skin. This shows the best performance. In the case of the impact feedback, the
participants typically rubbed the surface at a constant speed and felt the frequency
of the stimulation. This technique was also effective.As mentioned in Section5.1, in order to
recognize shape of a pattern, the tactile stimuli must be accurately integrated
with movements on the plane. However, arm movements do not guarantee the high spatial
resolution required for this. For example, when sample 3 of group III was
presented, users found it hard to discern it from the other samples; but, in
case of the tactile feedback, the distributed pressure cues enabled them to
make more accurate choices.If the tactile display had more pins, it might
show better performance. However, over all the tests, the haptic device combined with
the built-in compact tactile display showed satisfactory results. Impact
feedback was also reasonably effective in texture display with force feedback.


## 5.1. System and Experimental Design

Currently, the PHANToM
is the most widely used haptic interface. It has force feedback capabilities
and it provides a stylus-like handle interface [26]. Here we replace its handle
with the Ubi-Pen II to add tactile feedback capability to the device. Since the
Ubi-Pen provides both impact and texture stimuli, this allows us to compare the
effectiveness of various haptic stimulation methods.In our previous experiment, the previous
version of the Ubi-Pen provided texture feedback and vibration feedback [20].
However, we reported that vibration potentially had problems in aspect of
control. The stylus is replaced by the Ubi-Pen II in this experiment. We conduct
similar experiment here, but we observe the effectiveness of impact feedback on
texture display. As shown in Figure 8, the proposed pen-like interface was
attached to the handle of a force feedback device (model: PHANToM Omni). In
order to test performance of the system, we designed a virtual tangible object.
The virtual object is a box and its stiffness is 2 kN/m. (The task in this experiment
does not require high interaction force.) The widths are 75 mm (300 pixels) and
67.5 mm (270 pixels). The upper surface of the box has a texture derived from texture
mapping an image and a user explores only upper surface. In order to use the
image as a texture, this test provides a symbolic pointer in the shape of a
square, with a size of 15×15 pixels. A user can load any gray-scale image. As
shown in Figure 9, when the user touches an image on the box with the
integrated interface, the area of the cursor is divided into 9(= 3×3) subcells
and the average gray value of each cell is calculated. Then, this averaged gray
value is converted to the intensity of the stimuli displayed on each pin of the
tactile display.Figure 8
Force and tactile feedback interface.Figure 9
Methodology of texture display according to the stimulation method.In this interaction, the stiffness of the box is
represented by the PHANToM force feedback device. However, the texture on the
surface can be represented in 3 ways. The first is through force feedback presented
by the PHANToM since we can feel texture by probe scanning. The second is texture
feedback by the Ubi-Pen since the pin's movement can display surface roughness.
The third is the Ubi-Pen's impact feedback since such stimuli could facilitate
the recognition of obstacles when rubbing a surface. We compared all the 3 possible
stimulation methods in this experiment as shown in Figure9. As mentioned
above, the area of virtual cursor is divided into 9 cells each with an
individual gray value. However, while the tactile display inside the pen
interface has 9 spatially distributed stimulators, the impact and force
feedback interface both have only one interaction point. Therefore, force
feedback and impact feedback use only the center value.In case of force feedback, the gray value is
converted into the height of pattern and its highest value is 1 mm. In case of
tactile feedback, the gray value is converted into the normal displacement of
each pin and the maximum displacement is 1 mm. When we use a pin-array-based
tactile display, representing resolution of the tactile display is determined by the resolution of the
pin-array. Thus, only tactile
display with high density pin-array is the solution of the high-resolution
display. In order to make up this
limitation, we derived an idea that the tactile display plays a role of
a texture magnifier. As shown in Figure10, size of the tactile display is 2.4 times bigger than the symbolic pointer. This
kind of skill may decrease reality in aspect of size, but it is a useful tip to
convey texture information to a user precisely when we use a low-density
pin-array.Figure 10
Methodology of pattern display.In case of impact feedback, haptic cues
indicate change of region while the pointer across over the texture pattern.
When the pointer moves inside texture area, the mass rises up and a user
recognizes a ridge of the pattern. When the pointer escapes texture area and
the gray value decreases under a threshold value, the mass falls down and the
user experiences sudden drop-like feeling. This kind of stimulation may not precisely
represent projected shapes of textures that could be effective to display surface
patterns.In order to compare the performance of all
stimulation methods, we prepared 3 groups of tactile patterns. Figure11(a) shows
5 image samples from group I which differ in the direction of the gratings they
feature. The size of each image was 300×270 pixels. Figure 11(b) shows image
samples from group II which contains
grooves of varying widths. A user feels horizontal gratings while rubbing the surfaces.
In order to discriminate these patterns, the tactile stimuli must be integrated
with movements on the plane. Figure 11(c) shows 5 image samples from group III,
each of which shows different shapes. Discriminating among these patterns will
require precise and accurate integration of the tactile cues with the movements
on the surface. Feeling distributed pressure (as with the pin array display)
may help users to discern the surfaces.Texture samples.
(a)(b)(c)Ten subjects participated in the experiment. In
each trial, one of the five images from one of the groups was texture mapped on
the upper surface of a virtual box. However, the graphical representation was
hidden, and only a blank surface displayed. When the user touched and rubbed the surface of the
object, the gray values of the image were conveyed to the haptic interface. They
were then required to state which texture was present. The subjects have shown all images patterns through another
screen in order to make their choice. All
texture images in a group were presented 4 times at random and the order of
test group was also randomly selected. The user felt the stiffness of the box
by force feedback, but there were three conditions for representing texture: force
feedback, tactile feedback, and impact feedback. In order to prevent practice
effects, the order of the stimulation method was also randomized. Finally,
sounds produced during the interaction may affect recognition performance, so
participants were required to wear noise cancelling headphones (Bose,
QuietComfort2).


## 5.2. Performance and Discussion

Table4 shows
experimental results for the force feedback case in the form of a confusion
matrix. Likewise, Tables 5 and 6, respectively, show the experimental results
for tactile and impact feedback. In case of force feedback, average percentages
of correct answers are 86.5% for group I, 73.5% for group II, and 60.5% for
group III. In case of tactile feedback, average percentages of correct answers
are 97.5% for group I, 91.5% for group II, and 80.5% for group III. In case of
impact feedback, average percentages of correct answers are 83.5% for group I,
81.5% for group II, and 61.0% for group III.  Figure 12 shows the mean durations of trials
in each condition. The experimental results for force feedback and tactile
feedback are similar to the previous paper's results [20]. This confirms that both previous and
new experimental results are reliable. In case of impact feedback, since impact
plays a role of cue to notifying change of texture, experimental results are a
bit similar to the case of vibration feedback previously observed.Table 4
Experimental results for force feedback (%).
Force feedback12345Group I195.02.5—2.5—2—75.05.012.57.537.55.085.02.5—4——5.095.0—515.02.5——82.5Group II182.52.57.57.5—22.567.5—12.517.5312.510.075.0—2.54—12.5—82.55.052.520.05.012.560.0Group III155.015.012.517.5—222.560.015.0—2.5325.07.555.012.5—47.55.010.067.510.057.515.0—12.565.0Table 5
Experimental results for tactile feedback (%).
Tactile feedback12345Group I1100.0————2—100.0———3——97.52.5—4——7.592.5—5———2.597.5Group II195.0—2.52.5—2—100.0———3—7.592.5——4———97.52.55—22.5—5.072.5Group III160.017.512.510.0—210.090.0———35.0—95.0——4——7.582.510.0510.0——15.075.0Table 6
Experimental results for impact feedback (%).
Impact feedback1.02.03.04.05.0Group I185.0—5.0—10.025.090.05.0——3——85.010.05.04—10.015.075.0—57.5—10.0—82.5Group II195.05.0———25.085.0—5.05.032.510.082.55.0—4——5.085.010.05—25.010.05.060.0Group III155.025.0—15.05.0210.060.010.015.05.0310.0—70.010.010.0415.05.015.055.010.055.05.015.010.065.0Figure 12
Duration of each trial.The texture samples assigned in group I can be discriminated
by detecting the direction of the gratings. Users can recognize the direction
from the position of the interaction point and the direction in which they rub.
In this case, there is no substantial difference between force feedback and impact
feedback. However, tactile display provides line load to the finger along the
gratings. As shown in Tables4, 5, and 6 as well as Figure 12, this makes human
recognize direction of the gratings more correctly and quickly.For group II, the images can be discriminated
by the variations in the spacing between the ridges. However, the spatial
resolution of the human arm is not sufficient to reliably detect variations on
the scale of millimeters
whereas the skin sense allows discrimination of submillimeter gaps [17]. In addition, pattern
display by force feedback inherently results in movement of the arm and even
stick slip vibration, factors which may disturb discrimination of gap
variation. Therefore, as shown in Table 4, the percentage of correct answers
for force feedback is lower than in the other conditions. A good example is
that users experienced difficulty discriminating between sample 2 and sample 5.
In the case of the tactile feedback, the narrow gaps are discriminated though the
skin. This shows the best performance. In the case of the impact feedback, the
participants typically rubbed the surface at a constant speed and felt the frequency
of the stimulation. This technique was also effective.As mentioned in Section5.1, in order to
recognize shape of a pattern, the tactile stimuli must be accurately integrated
with movements on the plane. However, arm movements do not guarantee the high spatial
resolution required for this. For example, when sample 3 of group III was
presented, users found it hard to discern it from the other samples; but, in
case of the tactile feedback, the distributed pressure cues enabled them to
make more accurate choices.If the tactile display had more pins, it might
show better performance. However, over all the tests, the haptic device combined with
the built-in compact tactile display showed satisfactory results. Impact
feedback was also reasonably effective in texture display with force feedback.


## 6. Application of the Ubi-Pen II

### 6.1. Image Display on Touch Screen

As shown in Figure13,
the Ubi-pen mouse enables tactile pattern display when the scheme described in Section
5.1 is applied to the image on a touch screen. In order to verify texture
display performance of the Ubi-Pen, the image samples from Section 5 were
reused. One of five images from one of the groups was displayed on the screen,
but hidden from the participant. Instead, the visual representation was of a
blank square the same size as the image. When a user rubs against this square,
the gray values from the image are presented to the tactile display on the
Ubi-Pen. The experimental results are shown in Table 7 and these data verify
that the Ubi-Pen and image display scheme are effective. This scheme can be applied to
educational programs for children or interactive drawing software. In the
future, this kind of technology could be the basis of a virtual interactive
shopping mall.Table 7
Experimental results.
Percentage of correct answersDuration of a trial (second)S1S2S3S4S5Ave./Std.Group197.592.585.095.092.510.7/2.9Group292.510077.597.575.013.4/4.0Group362.577.580.072.595.020.6/10.7Figure 13
Tactile image display on a touchscreen.


### 6.2. Medical Applications

One possible application
of the combination of force and tactile feedback is a palpation medical
simulator. Palpation is a kind of diagnosis based on pressure and pressure
distribution. Therefore, when we develop a haptic palpation simulator, both force
and tactile display interface are required. Kim et al.
[27] proposed a palpation simulator based on this structure. However, their
tactile display was somewhat cumbersome. The use of our tactile display or the
Ubi-Pen might enhance the usability of this system; and there have been many
other studies for haptic medical simulators which required a compact tactile
display for more realistic and effective skin sense feedback.


### 6.3. Additional Applications

As tested in Section4.1, one of the most practical uses of our compact tactile display is Braille
display. In particular, it can realize a highly portable Braille display. However,
we need to conduct more precise evaluations before construction such a system.Finally, the tactile display module could be
installed in new mobile communication devices as well as PDAs and mobile
computers.


## 6.1. Image Display on Touch Screen

As shown in Figure13,
the Ubi-pen mouse enables tactile pattern display when the scheme described in Section
5.1 is applied to the image on a touch screen. In order to verify texture
display performance of the Ubi-Pen, the image samples from Section 5 were
reused. One of five images from one of the groups was displayed on the screen,
but hidden from the participant. Instead, the visual representation was of a
blank square the same size as the image. When a user rubs against this square,
the gray values from the image are presented to the tactile display on the
Ubi-Pen. The experimental results are shown in Table 7 and these data verify
that the Ubi-Pen and image display scheme are effective. This scheme can be applied to
educational programs for children or interactive drawing software. In the
future, this kind of technology could be the basis of a virtual interactive
shopping mall.Table 7
Experimental results.
Percentage of correct answersDuration of a trial (second)S1S2S3S4S5Ave./Std.Group197.592.585.095.092.510.7/2.9Group292.510077.597.575.013.4/4.0Group362.577.580.072.595.020.6/10.7Figure 13
Tactile image display on a touchscreen.


## 6.2. Medical Applications

One possible application
of the combination of force and tactile feedback is a palpation medical
simulator. Palpation is a kind of diagnosis based on pressure and pressure
distribution. Therefore, when we develop a haptic palpation simulator, both force
and tactile display interface are required. Kim et al.
[27] proposed a palpation simulator based on this structure. However, their
tactile display was somewhat cumbersome. The use of our tactile display or the
Ubi-Pen might enhance the usability of this system; and there have been many
other studies for haptic medical simulators which required a compact tactile
display for more realistic and effective skin sense feedback.


## 6.3. Additional Applications

As tested in Section4.1, one of the most practical uses of our compact tactile display is Braille
display. In particular, it can realize a highly portable Braille display. However,
we need to conduct more precise evaluations before construction such a system.Finally, the tactile display module could be
installed in new mobile communication devices as well as PDAs and mobile
computers.


## 7. Conclusion

This paper presents
the Ubi-Pen II, a pen-like haptic interface with a built-in compact
tactile display and an impact module, as well as empirical studies on Braille, button,
and texture display. Its performance is verified in a series of preliminary
evaluations which indicate that it can satisfactorily represent
tactile patterns and provide impact feedback. The compact tactile display can represent Braille patterns
and the impact feedback provides an effective button pressing sense which can
increase user confidence. Furthermore, we investigated its applicability to combined
force and tactile feedback interfaces in a haptic device with a pen-like end
effecter. Force feedback, tactile feedback, and impact feedback have been
compared for texture display. Of these three, combining tactile feedback with
force feedback showed enhanced performance. Finally, we evaluated the Ubi-Pen
II's capacity to support touch screen operations by providing tactile cues when
a user rubs an image displayed on a monitor.Future work involves improving the performance
and usability of the Ubi-Pen II. To make the interface a stand-alone system, a
processor and power controller should be embedded into the pen. The future
version will be an interactive wireless interface; and more psychophysical and
physiological studies will be involved in the next experiment for the Braille
and texture display.



---

*Source: 369651-2008-02-06.xml*