ActiveBelt: Belt-type Wearable Tactile Display
for Directional Navigation
Koji Tsukada1 and Michiaki Yasumura2
1

Graduate School of Media and Governance, Keio University, 5322 Endo Fujisawa,
Kanagawa 252-8520, Japan,
tsuka@sfc.keio.ac.jp,
http://mobiquitous.com/index-e.html
2
Faculty of Environmental Information, Keio University,
yasumura@sfc.keio.ac.jp.

Abstract. In this paper we propose a novel wearable interface called“ActiveBelt” that enables users to obtain multiple directional information with the tactile sense. Since the information provided by the tactile
sense is relatively unobtrusive, it is suited for daily use in mobile environments. However, many existing systems don’t transmit complex information via the tactile sense. Most of them send only simple signals, suchas vibration in cellular phones. ActiveBelt is a novel belt-type wearable
tactile display that can transmit directional information. We have developed prototype systems and applications, evaluated system performanceand usability, and demonstrated the possibility of practical use.

1

Introduction

As positioning technologies such as GPS (Global Positioning System) have become popular and widely used, many researchers have developed location-aware
information systems in mobile environments using positioning technologies[3][14][24]. Moreover, in Japan, some cell phone companies have provided locationaware information services, such as “eznavigation”[7] by KDDI.
While there are many applications for these location-aware information services, one of the most popular applications is navigation[11]. For example, “eznavigation” provides an application called “GPS Map” that can display a fairly
accurate map of the current location in a few seconds using GPS and informationof base stations. These navigation systems look useful at ﬁrst glance. However,users often have diﬃculty matching geographical information on maps to thereal world. For example, people often get lost in a large exhibition even if they
have a map of it. Moreover, some people are not good at reading maps.
Since these problems result from a diﬃculty to match geographical information on 2D maps to the real world, we can address the problems by providing
suitable directional information to a destination. For example, when a person
gets lost in a large exhibition, it’s very helpful for someone to tell her/him what
the correct direction to her/his destination is.

In this paper we propose a novel belt-type wearable interface called “ActiveBelt” that enables users to obtain directional information via the tactile sense.
First, we describe properties of tactile displays and belt-type devices.
1.1

Types of Display in Mobile Environments

Three types of display used in mobile and wearable computing are: visual displays, auditory displays, and tactile displays. Each of these types of display has
advantages and disadvantages. The visual display can transmit vast quantities
of information quickly, but it prevents visual attention being directed to othertasks. For example, a user often has diﬃculty looking at a display of a cell
phone while walking. The Auditory display is more easily used with other tasks.
However, the auditory display can conﬂict with other sounds in the surrounding
environment. For example, it is diﬃcult for users to use the auditory display invery noisy or silent environments. The tactile display is limited in the amountof information it can transmit. However, it’s easiest for users to use the tactile
display with other tasks, and so it is suited for daily use in mobile environment.
In this paper we focus on the tactile display as a display type that is well
suited to mobile use.
1.2

Types of Forms of Wearable Interfaces

As shown in Table 1, many researchers proposed various forms of wearable interfaces such as glasses, gloves, watches, rings, shoes, vests, pendants, caps, earrings,
and so on. We have focused on a belt-type device since the shape of a belt seems
suited to transmitting directional information via the tactile sense. Since a belt
is worn around the user’s torso, it can provide directional information only byactivating vibrators. Moreover, since many people usually wear belts, they don’t
need to wear additional devices. In addition, although many researchers in wearable computing used belts for attaching computers and batteries, the possibilityof belts for input/output interfaces has not received much attention. Because of
these considerations, we chose a belt-type device.

2

ActiveBelt

2.1

Concepts

In this section we describe the concepts of the ActiveBelt. The main concepts of
the ActiveBelt are as follows:
1. Tactile display that enables users to intuitively obtain directional information
2. Belt-type wearable device optimized for mobile use
3. Suited for various applications, especially for location-aware information services.

Table 1. Typical products and research projects of wearable interfaces classiﬁed bytheir forms
Forms

Typical products and research projects

glasses MicroOptical[13], Poma[17]gloves 5DTDataGlove[1], CyberGlove[6], Ubi-Finger[25]watches Whisper[10]rings
FingeRing[9], GSR rings[16]shoes Expressive Footwear[15], GSR Shoes[16]vestsTactual Wearable Display[23]pendants GesturePendant[21]capsWearable American Sign Language[22]earrings The Blood Volume Pressure earring[16]Fig. 1. Basic Concept of ActiveBelt

First, the ActiveBelt can enable users to intuitively obtain directional information in the real world simply by activating vibrators. Since a user can easily
match this tactile information to directions in the real world, the ActiveBelt cantransmit eﬀective information via the tactile sense.
Second, the ActiveBelt doesn’t require the user to wear or carry yet anotherdevice, since it attaches vibrators in a typical belt worn by many people in daily
life. In addition, since people usually wear belts outside, ActiveBelt is well suited
to use in mobile environments.
Third, the ActiveBelt can be used for a variety of applications and especiallyfor location-aware information services like navigation systems.

2.2

Device Architecture

In this section, we describe the device architecture of the ActiveBelt. The ActiveBelt consists of two sensors (a direction sensor and a GPS) to detect a user’s
location and orientation, multiple vibrators to transmit tactile information, anda microcomputer to control these devices (Fig. 1). The vibrators are attachedthroughout a belt at regular intervals.

2.3

Sensitivity of the Torso to Vibration

In this section, we discuss the sensitivity of the torso to the vibration. According
to van Erp[26], the resolutions of the torso are as follows: In the abdominal area,
the resolution has a roughly 0.4 cm jnd(just noticeable diﬀerence) interval at
the center, and a 1.2 cm interval at the sides. In the back, the resolution is lesssensitive about a 1.8 cm interval at the center, and about a 3.0 cm interval at thesides. These results show that the resolutions of a torso are fairly good. Moreover,Yamamoto[30] reported that people can distinguish horizontal direction fairly
accurately based on vibration to their torsos.
Thus, the resolutions of a torso are fairly good, and people can tell horizontal
direction with vibration. This suggests that the ActiveBelt may help navigation
using vibration to indicate the direction to take at each point in time.
2.4

Numbers of Vibrators to be Used

Human sensitivity allows for the use of a relatively large number of vibrators
around the torso. However, too many vibrators may generate problems, such asincreases in power consumption, complications of cables, needs for more I/O of
microcomputers, and so on.
To avoid these problems, we used eight vibrators. These vibrators and cables
can be easily attached inside a belt, and controlled using a microcomputer.

3

Development

3.1

Prototype

We developed a prototype ActiveBelt system based on the above concepts. The
prototype system consists of four components: (1)ActiveBelt hardware, (2)aGPS, (3)a directional sensor, and (4) a microcomputer (Fig. 2). Fig. 3 shows
the system architecture of the ActiveBelt. Next, we explain each component of
the prototype system.
Belt-type hardware We developed the ﬁrst prototype of the ActiveBelt in
the form of a typical belt adjusted using a buckle (Fig. 4). We attached eightvibrators (FM23A by TPC) and LEDs 3 in the belt. The diameter of the FM23A
is about 18 mm, and the thickness is about 3 mm. We attached four vibrators in
the center of the abdomen, in the center of the back, and the left and right sides
close to the hips. We also attached four other vibrators in each midway between
two of the ﬁrst four vibrators.
The frequencies of each vibrator change with voltages, such as 33Hz at 0.3
V, 40Hz at 0.6V, 55Hz at 0.8V, and 77Hz at 1.2V. Thus, we can control the3

LEDs are turned on and oﬀ in sync with vibrators. We used LEDs to check thestates of the ActiveBelt.

Fig. 2. Prototype system of ActiveBelt (1. ActiveBelt hardware, 2. GPS, 3. directional
sensor, 4. microcomputer)Fig. 3. System architecture of ActiveBelt

strength of vibrators by changing the voltages4 . For human skin, the most sensitive frequency band is between 200 Hz and 250Hz. We used a less sensitivefrequency band between 33Hz and 77Hz in the prototype system. We focused onusing cheap and easily obtainable vibrators this time. Other vibrators may be
used in later research.
We adjusted the length of the belt to the waist size of one of the authors.
The distance between the vibrators was 9.75cm on average (±0.25cm), and thewhole length of the belt was about 78.0cm. It was diﬃcult for many users towear this prototype, since the mapping between vibrators and directions was
modiﬁed when a user adjusted the length of the belt to her/his waist.
To solve this problem, we developed a universal-size ActiveBelt ver.2 thatconsists of leather parts in which vibrators are attached and elastic rubber parts
4

Since energies change with frequencies in general, people feel stronger vibration in ahigh frequency.

Fig. 4. Hardware of ActiveBelt ver.1

Fig. 5. Hardware of ActiveBelt ver.2 (universal-size)

ﬁt to the size of the user’s waist (Fig. 5). While the whole length of the belt
is about 75.0 cm, a wide range of users with waist circumference less than 98.0
cm can wear the belt without breaking the correspondences between vibratorsand directions (Fig. 7）. We have wired each vibrators loosely in considerationof elasticity of rubber parts (Fig. 6).
Directional Sensor and GPS The directional sensor consists of a geomagnetic
sensor (TMC3000NF by NEC Tokin) and an acceleration sensor (ADXL202E by
Analog Devices)(Fig. 8). We used the geomagnetic sensor to detect the orientation of a user. The output voltages of the geomagnetic sensor are converted
to digits with 10 bit A/D converters in a microcomputer. The accuracy of thegeomagnetic sensor for detecting directions is about ±1.5 degree. We used theacceleration sensor to detect horizontal angles. We considered using the acceleration sensor for calibrating the horizontal angles of the geomagnetic sensor,
since the geomagnetic sensor must keep its position horizontal to detect precise
directions. However, through simple experiment, we found that humans can eas-Fig. 6. Wiring inside of universal-size ActiveBelt

Fig. 7. Example of wearing universal-size ActiveBelt

ily keep the position of their waist horizontal even when they walk on ascentsof about 30 degrees. In addition, perfect precision is not needed. Consequently,
we don’t modify the outputs of the geomagnetic sensor in the current prototype
system.
We used the IPS-5100G (by Sony) as a GPS. The IPS-5100G transmits output signals to the microcomputer as serial data, and the microcomputer extracts
latitudes and longitudes from the data. We used spherical trigonometry to calculate a relative direction and distance to a destination.
Microcomputer and Surrounding Circuit We used a microcomputer (PIC
18F452 by MicroChip) to control the sensors and vibrators. The functions of
the microcomputer are as follows: (1) controlling vibrators and LEDs based on
input data from sensors, and (2) communicating with host PC/PDA. For theﬁrst function, the microcomputer controls the vibrators and LEDs with a D/Aconverter (AD7304 by Analog Devices). Since we can easily control output voltages using the D/A converter, we can control the frequencies of the vibrators

Fig. 8. Circuit board of direction sensor

and the brightness of the LEDs smoothly 5 . For the second function, the microcomputer communicates with the host PC/PDA via RS-232C. Users can register
the latitude and longitude of a destination with the host PC/PDA.
3.2

Applications

In this section, we discuss applications of the ActiveBelt. We propose four applications: (1) FeelNavi for human navigation systems, (2) FeelSense for locationaware information services, (3) FeelSeek for search of lost properties, (4)FeelWave
for entertainment.
FeelNavi FeelNavi is an application of navigation using tactile information.
Users can intuitively reach destinations by walking toward the direction of vibration. In the prototype system, a user registers the latitude and longitudeof her/his destination with a host PC/PDA. The ActiveBelt then activates the
speciﬁed vibrator, based on the current position and orientation of the user (Fig.
9). We express a distance to a destination using pulse intervals of vibration.
When a user comes nearer to the destination, the pulse intervals of vibration
become shorter.
FeelSense As mentioned before, many researchers and companies have developed location-aware information services. Most of these existing systems usedvisual displays. Although the visual display has an advantage that it can transmit
vast quantities of information quickly, this approach is sometimes unsatisfactory
for users. Moreover, location-aware information services are expected to extend
rapidly in the near future. For these reasons, we should consider new approaches
that are more convenient for users.
5

The voltage range we used was between 0V and 1.2V. We could activate vibrators
by raising the voltage above 0.3V.

Fig. 9. Basic concept of FeelNavi

FeelSense is an always-active tactile display with which users can detect
location-aware information while walking around a town. As shown in Fig. 10,
users register interesting categories in advance. When they come near to relevant
location-aware information, the ActiveBelt activates speciﬁed vibrators based ona user’s position and orientation, and the location of the target information. For
example, they can easily ﬁnd shops of interest such as boutiques or restaurants.

FeelSeek Recently, RFID (Radio Frequency Identiﬁcation) tags have become
smaller and cheaper, and they are expected to be attached in various commodities[29]. Moreover, a real-world reminder system using proximity information isa useful application in ubiquitous environments[12]. In such a situation, it isuseful to attach RFID tags to valuables such as wallets and cell phones, and totell users immediately if they leave their valuables behind.
FeelSeek is an application to remind users of valuables left behind, and tonavigate users toward those valuables. As shown in Fig. 11, when the RFID
tagged object moves away from the RFID reader attached on the belt, the ActiveBelt activates all vibrators to remind a user of it. Then, she/he inputs a
trigger information if she/he want to search it. Finally, the ActiveBelt calculatesa brief position of the item using records of GPS, and navigates the user to it.

FeelWave FeelWave is an application to amuse users with rhythmic vibrationin sync with music (Fig. 12). For example, since ActiveBelt can transmit tactile
information in all direction, it can be used as a stereophonic tactile display withstereophonic music. In addition, the ActiveBelt may be used as new expressive
medium such that it transmits rhythmic vibrations to members of an audiencein sync with a turntable played by a DJ.

Fig. 10. Basic concept of FeelSense

4

Evaluation

We have evaluated the eﬀectiveness of the ActiveBelt using the universal-size
prototype system. As mentioned above, in the application of a human navigation
system called FeelNavi, we express the direction to a destination by activatinga speciﬁc vibrator and express the distance by controlling pulse intervals of vibration. In this evaluation, we examined whether subjects can recognize changesof direction, and pulse intervals of vibration, both in a standing state and in awalking state. We selected six test subjects who had never used the ActiveBelt
before. Their ages ranged between 21 and 30.
4.1

Methods

The subjects wore the universal-size ActiveBelt and a wireless RS-232C transceiver.
The experimenter controlled the direction and interval of vibration with a PDA
and a wireless RS-232C transceiver(Fig. 13). The experimenter activated only
one vibrator at a time, and kept the strength of vibration at about 77Hz. The
period of each evaluation was about 15 minutes.
There were two postural conditions in the study: standing, and walking. In
the standing condition, the experimenter controlled the direction of vibration
and asked the subjects to indicate the direction orally or with gestures.We usedfour pulse intervals of vibration, that is, 250msec (125msec On, 125msec Oﬀ),
500msec (250msec On, 250msec Oﬀ), 1000msec (500msec On, 500msec Oﬀ),
and 1680msec (840msec On, 840msec Oﬀ). In the walking condition, the experimenter controlled the direction of vibration and asked the subjects to turn tothe direction of vibration. We used the same four pulse intervals of vibration as
described above.

Fig. 11. Basic concept of FeelSeek

The experimenter observed the behaviors of subjects during each condition.
After each condition, the experimenter asked them questions to obtain theirsubjective feedbacks about changes in direction and pulse intervals signalled by
the vibration. At the end of the evaluation, the experimenter asked each of them
about their impressions of the prototype system including what problems theyexperienced.
4.2

Results

In the standing condition, all subjects were able to recognize all changes in
the four pulse intervals. For changes in direction, ﬁve subjects were able to tell
direction to a fair degree of accuracy within about one second. We asked thesubjects “Can you diﬀerentiate the eight directions in each pulse interval?”.
Five subjects said they could easily tell the diﬀerence amongst all directions for
all intervals. On the other hand, one subject said that he could easily recognize
four directions (front, back, left, and right) in all intervals, but could not easily
recognize the other four directions. This diﬃculty may have resulted from his
waist being very thin (about 67cm). Since the belt did not ﬁt with his waist, theActiveBelt was not able to transmit enough tactile information.
In the walking condition, the behaviors of the subjects were quite diﬀerent
for each pulse interval. In the case when the pulse intervals were 1680msec and1000msec, when the experimenter changed a direction of vibration, all subjects
walked for one or two more steps, stopped for a moment, and then turned toFig. 12. Basic concept of FeelWave

the direction of vibration. When questioned, they said that they were able torecognize the changes in vibration while walking, and that they were able torecognize the direction if they stopped for a moment. For the pulse intervals of
500msec, all subjects sometimes failed to recognize the change of vibration. Two
subjects said that they were not able to feel vibration in this range. When thepulse intervals were 250msec, all subjects said that they were not able to feelvibration.
Finally, we summarize the impressions that subjects reported about the prototype system.
1. Vibration on the back is perceived to be weaker than vibrations on theabdomen. (5 / 6)
2. For practical use, it is more desirable that the vibrators are activated only
when users get lost than that they are always activated. (2 / 6)
3. For practical use, eight vibrators are not necessarily needed, and four vibrators are good enough. (3 / 6)
4.3

Consideration

Based on the above results, we discuss current problems and propose improvements needed for practical use of the ActiveBelt.
Providing Direction When standing, almost all subjects were able to recognize directions within about one second. When walking, and for the pulseintervals of more than 1000msec, all subjects recognized changes of vibration
within two steps, stopped only for a moment, and then turned to the direction

Fig. 13. Prototype system used in the evaluation. left: a subject, upper right: a microcomputer and surrounding circuit, lower right: a controller for the experimenter (1. adirectional sensor, 2.a wireless RS-232C transceiver)of vibration. Thus, we conﬁrmed that the ActiveBelt can navigate users to thetarget direction using vibration both when standing and when walking.
Indicating Distance In FeelNavi, we indicated distance to a destination using
pulse intervals of vibration. When standing, all subjects were able to recognizechanges in the four pulse intervals. However, when walking, they often failed
to recognize vibration with a pulse less than 500msec. We will examine otherexpressions of distance, along with the pulse intervals.
Navigating In oral interviews, we received interesting feedbacks about navigation. First, some subjects said that it is more desirable that the vibrators areactivated only when users get lost than that they are always activated. Thisapproach looks similar to behaviors that people pick up and look at maps only
when they get lost.
Some subjects said that they thought four vibrators were good enough fornavigation. However, we think it is useful to attach eight or more vibrators, sincehigher resolutions are useful for versatile applications and for error correction.

5

Discussion

Most existing human navigation systems in mobile environments apply visualdisplays, that is, they plot users’ positions and orientations on 2D displays of
PDAs or cell phones. We discuss here the diﬀerences between visual navigation
systems and the belt-type tactile navigation system described in this paper.
The merits of visual navigation systems are as follows:(1) visual navigation
systems can easily transmit complex information such as the layout of buildings

near the destination and a detailed route to it, and (2)they usually provide input
interfaces, so users can easily use them interactively.
The merits of the belt-type tactile navigation system are as follows: (1)thebelt-type tactile navigation system is convenient to use when walking since it
doesn’t occupy users’ visual or auditory senses, (2)users can intuitively recognize
directions to their destinations even when the they are not good at reading maps,and (3)it can navigate users to their destinations even in bad conditions such as
in heavy fog or deep night, or with no landmarks near locations of users, since
it doesn’t depend on visual landmarks in the surrounding environment.
Each system, visual and tactile, has its own merits. We will improve oursystem by combining the merits of visual and tactile navigation systems.

6

Related Work

Other research on human navigation systems and location-aware information
services includes Walk Navi[14], Augument-able Reality[19], Touring Machine[8],Cyberguide[3], and Space Tag[24]. Various applications with location-aware information have been proposed, and most of the associated systems used visualdisplays.
A cell phone equipped with a GPS and a directional sensor[2] can display amap of a user’s position, and rotate the map in sync with the orientation of thecell phone. This approach is interesting in helping users to match 2D maps andreal world using directional information.
Research has been carried out on wearable tactile interfaces such as Cyber
Touch, Tactual Wearable Display and GentleGuide. Cyber Touch[6] can generatetactile feedbacks of objects in virtual world, using six vibrators attached on
gloves. Tactual Wearable Display[23] attached a matrix of vibrators to the back ofa vest, and tried to transmit directions and other information. It also proposed aninteresting tactile system using cognitive characteristics of the tactile sense suchas apparent movement 6 . GentleGuide[4] proposed a tactile navigation system
via two bracelets. It outputs three commands, left, right, and stop(activate bothbracelets). In the meanwhile, our approach used a belt-type tactile display, andcan enable users to obtain directional information more intuitively with thetactile sense.
There is research on tactile displays in aircrafts cockpits[18][20][27]. These
research projects used vest-type tactile displays to provide pilots with navigation information. Brewster proposed a sophisticated conceptual framework fortactile displays and information presentation[5]. This approach is interesting in
discussing many parameters used for designing tactile displays.
Waist Measure Belt[28] is a unique belt-type wearable device. A user caneasily measure her/his waist-size only by wearing it which contains a digital
6

When a user is stimulated on two point of her/his skin alternatively in a speciﬁed
interval, she/he feels continuous stimulations as if a small animal is hopping between
the two points.

measuring scale. It is interesting in proposing an application of health monitoring
using a belt-type device.

7

Conclusion

We have proposed a novel belt-type wearable interface called “ActiveBelt” thatenables users to obtain multiple directional information with the tactile sense.
We developed prototype systems, and evaluated the possibilities for practicaluse. When we solve the problems of the current prototype systems, we believethat ActiveBelt will become a useful and intuitive navigation system. We are also
examining other applications for entertainment and location-aware information
services.

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