1

Assessment of a simple obstacle detection device for the visually

impaired

Cheng-Lung Lee1*

, Chih-Yung Chen1, Peng-Cheng Sung

1 and Shih-Yi Lu

2

1Department of Industrial Engineering and Management, Chaoyang University of Technology,

No. 168, Jifeng E. Rd., Wufeng District, Taichung, 41349, Taiwan, R.O.C. 2School of Occupational Safety and Health, Chung Shan Medical University,

No. 110, Sec. 1, Jianguo N. Rd., 40201, Taiwan, R.O.C.

*Corresponding author. Tel: +886 4 23323000 ext 4458; fax: +886 4 23742327.

E-mail address: cllee@cyut.edu.tw

Postal address: Department of Industrial Engineering and Management, Chaoyang

University of Technology, No. 168, Jifeng E. Rd., Wufeng District, Taichung,

41349, Taiwan, R.O.C.

Abstract

A simple obstacle detection device, based upon an automobile parking sensor, was assessed

as a mobility aid for the visually impaired. A questionnaire survey for mobility needs was

performed at the start of this study. After the detector was developed, five blindfolded sighted

and fifteen visually impaired participants were invited to conduct travel experiments under

three test conditions: 1) using a white cane only, 2) using the obstacle detector only and 3)

using both devices. A post experiment interview regarding the usefulness of the obstacle

detector for the visually impaired participants was performed. The results showed that the

obstacle detector could augment mobility performance with the white cane. The obstacle

detection device should be used in conjunction with the white cane to achieve the best

mobility speed and body protection.

Keywords: Visually impaired; obstacle detection; travel aid.

1. Introduction

Mobility refers to one’s ability to identify the relation between their position and the objects

in the environment and then move independently, safely and efficiently (Kuyk et al. 2010).

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The most obvious problem faced by blind persons is moving around in their environment

without bumping into unexpected obstacles (Molton et al. 1998). Obstacle detection is thus

one of the major problems to be solved to ensure safe navigation. The white cane is the most

popular and traditional navigation aid for the visually impaired (Molton et al. 1998; Snaith et

al. 1998; Dakopoulos and Bourbakis 2010) in spite of modern technology-based devices

(Clark-Carter et al. 1986a; Schellingerhout et al. 2001). The white cane is the simplest,

cheapest and most reliable device thus far. It can be generally applied to detect static

obstacles on the ground, uneven surfaces, holes and stairs (Cardin et al. 2007). However, the

reach of the cane is limited (Yasumuro et al. 2003) and obstacles not located on the ground

are hardly detected.

A number of electronic travel aids (ETAs) for the visually impaired have been developed

for navigation and obstacle detection/avoidance. Dakopoulos and Bourbakis (2010) presented

a comparative survey among portable/wearable obstacle detection/avoidance systems for the

visually impaired. Cardin et al. (2007) also reviewed several obstacle detection devices

developed in the literature.

The common ETA features based upon new technologies in the literature may conclude

that information was gathered from the environment using sonar, laser scanner or stereo

camera vision. The user was generally informed through auditory and/or tactile sense (Cardin

et al. 2007; Dakopoulos and Bourbakis 2010). Other features and disadvantages of ETAs are

briefly summarized as follows. The signal processing of many novel ETAs usually required

complicated computer algorithms to provide more complete information about nearby

obstacles (Cardin et al. 2007; Sainarayanan et al. 2007). The sensors in some ETAs could

only detect obstacles on the ground just like the white cane. Other ETAs had more functional

body protection capabilities (e.g., shoulder protection, Cardin et al. 2007). Some ETAs were

small, light and handheld, e.g., Miniguide (Phillips, 1998), while other ETAs were bulky, e.g.,

Navbelt (Shoval et al. 1994) and GuideCane (Ulrich and Borenstein 2001), making them

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difficult to hold or carry when needed. Although some aids were portable, they still required

manual operation (e.g. Ghiani et al. 2009), making co-incident use of conventional aids

difficult or impossible (e.g. white canes). One or more cameras in some ETAs required

mounting on headgear (Sainarayanan et al. 2007) or the frame of eyeglasses for obstacle

capture (Meers and Ward 2005 cited Dakopoulos and Bourbakis 2010). Such devices may be

not accepted by some visually impaired individuals because they may feel cumbersome or

embarrassed to wear in public places. Some ETAs required extensive training periods (Snaith

et al. 1998). The relatively high cost of ETAs available in the market is a discouraging

feature.

To fill the detection gaps in the white cane and overcome the disadvantages of ETAs, a

compact size, lightweight, low-cost and simple detection feedback obstacle detection device

was developed and explored in this study. The prototype of this detector was developed and

evaluated using blindfolded sighted and visually impaired participants in travel experiments.

This study hypothesized that different travel aid devices would alter walking efficiency and

obstacle detection for visually impaired persons. The aims of this study were to compare ETA

walking efficiency and obstacle detection capability using both blindfolded sighted and

visually impaired participants under three test conditions.

2. Method

2.1 Survey of mobility needs

At the start of obstacle detector development a survey of visually impaired students was

conducted to determine their mobility needs in daily life. Participants were interviewed

individually using a constructed questionnaire. The data were then recorded by researchers.

The first part of the questionnaire contained the participant’s personal data which included

name, gender, age, educational level, blind or visually impaired condition, peripheral (side)

vision, awareness of light, colour vision and any other impairment. The second part asked for

travel experiences including daily activities, use of travel aids and obstacle collision

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experiences in the environment. Several discussions were held with teachers, who were blind

and teaching in the school, to modify the questions before the interview was performed. The

purpose of this study was clearly explained to the participants prior to the interview. Informed

consent to participate was obtained from the participants in this study.

Thirty one participants were junior high and senior high students from a school for the

visually impaired in Central Taiwan. The students had received at least six-month training in

orientation and mobility before joining this study. During the interview one student was

determined to have a learning disability, and thus, was eliminated from the study. A total of

30 valid participants included 15 junior high school students (aged 13-15, 9 males and 6

females) and 15 senior high school students (aged 16-19, 9 males and 6 females). As

self-reported during the interview, 25 students (83.3%) said they were blind and 5 classified

themselves as having low vision, 27 (90.0%) with congenital impairment and 3 with acquired

impairment.

All interviewed participants lived at school during the weekdays and could choose to

return home or stay at school during weekends and holidays. This study (including a survey

and an obstacle detection experiment) was approved by the Institutional Review Board for

Ergonomics Experiment of Chaoyang University of Technology.

2.2 Travel aid development

2.2.1 Obstacle detector

The obstacle detector developed in this study was based upon an automobile parking sensor,

consisting of 3 main modules; a sensing module with transmitting and receiving functions, a

processing module and a warning module. Table 1 shows the dimensions and photos of the

ultrasonic obstacle detector modules. The detector architecture is illustrated in Figure 1. The

detection system works by sending out ultrasonic pulses that are reflected back to the sensor

by obstacles within the sensor detection envelope. The reflected signals are processed by the

processing module, which in turn activates the warning buzzer to alert the user that there is an

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obstacle in the travel path.

The three detector modules were commercial electronic parts packed as a set used for

obstacle detection while car-parking. The default distance sensitivity setting of the sensor was

adjusted to a lower level for this study. Another detection system modification was made for

the detector power connection. A 12 Volt dry battery was sufficient for detector use by an

individual. A 12 Volt battery with 2Ah capacity was used to supply the experiment with

sufficient operational time during a day. The obstacle detector was small and lightweight, as

shown in Table 1. One sensing module was mounted on the participant’s body with the other

two modules placed in a small bag on a belt worn on the waist or in a pocket. Two sensors

were attached to the participant’s chest and waist, respectively, during the experiment. The

reason for this arrangement was to test if the detector could effectively detect obstacles not

located on the ground.

The sensor detection envelope was investigated in the laboratory before the detector was

assessed in the field. A high flat wooden board (height 245.4 cm, width 32.5 cm) and three

university students were employed to move around as targets for detection envelope

measurements. The mean age of these students was 27.0 yr/SD 2.6 yr; mean body height

165.6 cm/SD 4.6 cm; and mean body weight 60.3 kg/SD 10.8 kg. The test direction was

varied every 5° from the mid-saggital plane to the right and left sides. Each angle for each

target was tested twice. Another test for detection distance was performed at the university

campus after the laboratory test. The obstacles on the campus included the iron railings

outside a building and in an athletic field, the net in a volleyball court, the bonnet of sedans

and the stairways. An individual (stature 163.3 cm and body weight 68.4 kg) was asked to

wear a sensor on his chest (120.4 cm) in the test. A parking lot gate arm (7.5 cm in width)

was also tested in a parking lot by the individual with a sensor worn on his waist.

2.2.2 Evaluation of the Electronic Obstacle Detector

Two experimental stages were performed for obstacle detection evaluation in this study. Five

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blindfolded sighted participants (4 males and 1 female) who were graduate students at the

university were recruited to detect obstacles in a simulated environment. Fifteen visually

impaired participants (10 males and 5 females) were then invited to travel a real world

mobility route. The visually impaired participants included 5 junior high school students, 6

senior high school students and 4 teachers from a visually impaired school in Central Taiwan.

These participants were totally blind with no residual vision. Thirteen suffered from

congenital visual impairment. All visually impaired participants had received at least

six-month training in orientation and mobility prior to this study. Table 2 shows the

participants’ personal data and anthropometric measurements.

A corridor 30 meters long outside the laboratory at the university was used as a

simulated route for the first experimental stage. Nine obstacles existed in the corridor,

including 5 purposefully placed obstacles (1 bicycle, 2 chairs, and 2 overhanging cardboard

boxes) arranged in the middle of the corridor and 4 natural obstacles (2 shoe cabinets and 2

shelves) situated against the corridor walls. The positions of the purposefully placed obstacles

were changed for each test and each participant. No arrival time was recorded at each

checkpoint (i.e., the obstacle location) in this experimental stage and only the total time for

each test was recorded.

The route around the school campus travelled by visually impaired participants was used

for the second-stage test. The route shown in Figure 2 was determined based upon the

concern for the participant’s transportation safety when the experiment was proposed and

discussed with the school staff. Eight obstacles were placed in the 138 meter long route. The

purposefully placed obstacles consisted of 2 bicycles/motorcycles and 1 hanging cardboard

box. Their locations were varied for each test condition and each participant. Five natural

obstacles existed in the path, including a plant terrace, a tall tree, a pedestrian overpass, a

side-door and a tilted tree. Ten checkpoints in the path, shown in Figure 2, consisted of 3

locations on the pedestrian overpass and 7 locations at the other obstacles. The arrival time to

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each of these 10 checkpoints in the path was recorded for each test condition and each

participant.

Three experimental test conditions were completed by both blindfolded sighted and

visually impaired participants: 1) using a white cane only, 2) using the obstacle detector only

and 3) using both devices together. The test conditions were selected at random for each

participant in the experiment.

A collision prevention strategy regarding participant safety during the experiment was

stated as follows. A collision risk assessment was conducted to ensure the safety of

participants before the experiment was performed. A pilot test was performed by an

experimenter with and without a blindfold in order to observe the possible collisions before

and after the collision prevention was discussed and improved. The possible parts of

obstacles that might be collided with by the participant’s body during the experiment were

wrapped with foam instead of asking the participant to wear personal protective equipment

such as helmet and gloves. This was done because observing the participant’s behaviours

after obstacle collision was one of the major study purposes. Several instructions were given

to the participants before the experiment: (a) Participants had the possibility of body collision

with obstacles on the footpath during the experiment. Such obstacles were wrapped with

foam and might exist at ground, waist or head level. (b) Although measures to minimize the

risk for injury had been taken, participants could still suffer light impact with obstacles when

collisions occurred during the experiment. (c) An experimenter would follow the participant

on the path during the experiment to protect the participant from any injury. When an

orientation loss took place or before a harmful collision occurred the experimenter would

guide the participant with verbal warnings or/and hand(s). (d) Participants had the option to

withdraw from the experiment any time.

A clear explanation of the experimental objectives and procedures was given to ensure

no difficulties in operating the experimental aids by the participants A brief training period

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for both blindfolded sighted and visually impaired participants was provided to ensure

enough practice and familiarity with the tests before actual data were collected. A written

consent from each participant was obtained and the anthropometric data were measured. For

test conditions 2 and 3 (i.e., a detector included), two sensing modules were worn on each

participant's chest and waist to detect possible collisions by the head or waist. Both finish

time and collision frequency of three test conditions for each participant were recorded to

determine whether different test conditions resulted in differences in walking efficiency and

mobility safety. A warning sound was delivered to the participants by a buzzer. An

experimenter followed the participant on the footpath, could hear the warning sound and

record the participant’s behaviour during the experiment. Post experiment interviews

regarding the usefulness of the travel aids were carried out after the participant had completed

all three test conditions.

Finish time (FT) was defined as the time required for one participant to complete one

test condition. Collision frequency (CF) was considered only when participants collided

unintentionally with the obstacles. If the participants walked into and made contact with an

obstacle on the route with their white cane or when an alarm sounded and the participant

recognized that an obstacle lay ahead in test conditions 2 and 3, tentative actions were usually

taken by participants to try to determine the characteristics of the obstacles. Such behaviour

would be considered an intentional collision and was not counted in CF in this study.

2.2.3 Data Analysis

Finish time and collision frequency under three different test conditions from 5 blindfolded

sighted and 15 visually impaired participants were obtained in the experiment. Data were

analyzed using one-way ANOVA using SPSS 10.0 for Windows. When the main effect was

significant, a post hoc analysis using Duncan's new multiple range test was applied to

evaluate differences among test conditions. All significance levels were set at alpha =.05.

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3. Results

3.1 Mobility needs

The questionnaire results showed that 90.0% of the participants often used a white cane when

going out alone. Ninety percent of the visually impaired did not use white canes in familiar

environments such as school or home. The places visited most frequently included stores

(73%), relatives’/friends’ homes (50%), and restaurants (30%). Figure 3 shows four obstacle

types that the participants often collided with while navigating. Both the

automobile/motorcycle (70%) and piled item/protrusion (63%) obtained the highest obstacle

collision percentage. Figure 4 illustrates the body parts that were most often collided with

obstacles and expected to avoid obstacle-colliding. All participants expressed that they had

never used electronic travel aids before but would like to try if available. The low cost,

convenient aids were of greatest interest for all participants.

3.2 Experiment

3.2.1 Mobility Performance Data

Figure 5 shows the sensor detection envelopes obtained from two tests using a high flat

wooden board and three persons as targets in the laboratory. The farthest and shortest

detection distances were about 228 cm and 43 cm when the sensor was placed right ahead of

the wooden board (i.e., 0° in the figure) and at ±50° to the mid-sagittal plane of the person.

The sensor did not detect the wooden board or three persons at angle ranges beyond 50°. The

detection distance measured at the university campus after the laboratory test ranged from

72.5 to 152.3 cm for different obstacles, including iron railings, volleyball net, sedan bonnet

and stairways. A parking lot gate arm that protruded about the individual’s waist height (105

cm) could be detected.

Figures 6 and 7 show the finish time (FT) and collision frequency (CF) means obtained

from 5 blindfolded sighted and 15 visually impaired participants under the three test

conditions. The shortest finish time was found using the white cane plus detector test

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condition for both blindfolded sighted and visually impaired participants. The maximum

differences in FT among the visually impaired participants were 235.4 seconds using the

white cane only, 213.4 seconds using the detector only, and 156.9 seconds using both aids

together. The FT values varied markedly among the visually impaired participants under the

same test condition, however, such results were not found among the blindfolded sighted

participants. Table 3 shows the collision frequency and the obstacles collided with by both 5

blindfolded sighted and 15 visually impaired participants under the three test conditions. The

body parts that collided with the obstacles are also shown in the Table. The white cane only

usually failed to detect obstacles above the ground for both blindfolded sighted and visually

impaired participants, especially obstacles at head level. When the obstacle detector sensors

were placed on the upper parts of the participant’s body the CF values were reduced. No CF

values were obtained under the white cane plus detector condition for both blindfolded

sighted and visually impaired participants. The statistical analysis results revealed that both

finish time and collision frequency for the visually impaired participants showed significant

differences among the three test conditions (F(2, 42)=6.935, p=.002, and F(2, 42)=63.7,

p=.000). The Duncan's groupings for both FT and CF were then obtained by test condition

(α=.05) and present in Figures 6 and 7, respectively. Among the three test conditions, the test

using both devices produced the smallest FT. The test with the white cane only produced the

largest CF among the three conditions.

3.2.2 Post Experiment Interview

All blindfolded sighted participants stated that they did not feel confident in detecting

obstacles while using the detector only. For the other two test conditions they felt more

confident because the white cane was included. However, they all reported positive when the

detector was used in the experiment and agreed that the detector was useful in detecting

obstacles not located on the ground. The post experiment interview results for the visually

impaired participants are listed in Table 4. Eleven participants (73.4%) were satisfied or very

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satisfied with current detector prototype, and 12 (80.0%) were satisfied or very satisfied with

the prototype weight. Thirteen participants (86.7%) expressed that the travel aid was really

helpful to their mobility and their confidence in mobility could be enhanced (80.0%). In

response to questions about their preference for the devices used in this experiment, all

participants preferred to rely upon the white cane due to its reliability when only one device

could be chosen. However, using both devices would be their best choice if the obstacle

detector was available for use.

4. Discussion

4.1 Mobility needs

The questionnaire inquired into the participant’s vision status (total blindness and low vision),

light perception and colour vision. The visually impaired participants recruited for this study

were totally blind with no residual vision. The participants’ vision status was not reconfirmed

with eye examinations. Their answers to these questions were kept confidential. However,

there might be bias in the study survey results.

The participants were allowed to choose more than one answer (item) in the questionnaire

regarding the obstacle types that they often collided with. Seventy percent of the visually

impaired participants, shown in Figure 3, expressed that automobile/motorcycle was the most

common obstacle that they often collided with. Automobiles or motorcycles are allowed to be

parked on the roadside in Taiwan. Occasionally automobiles or motorcycles are illegally

parked on the sidewalk. Visually impaired persons therefore may easily meet and collide with

them while walking in the street. The participants were allowed to answer with more than one

body part that often collided with obstacles. The result shown in Figure 4 indicated that head

collisions (57%) occurred almost as often as leg collisions (60%). However, there are far

fewer head level obstacles than leg level obstacles in a natural environment. This might be

explained as follows. A head collision is a serious event and the participant was more likely

to remember head collision incidences than other body part collision incidences. The high

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rate of reported head collisions might simply reflect the long-lasting memory of painful head

collisions instead of the true frequency of head collision incidences. Therefore, the highest

desire was to avoid head collisions, which seemed to be a reasonable assessment, with the

highest percentage (50%) among body parts.

All participants agreed that the white cane could be used to detect static obstacles on the

ground and protect the lower body parts but protection gaps did exist. The white cane was

insufficient to protect the head, hands and waist while walking. Head collision was the

participant’s strongest desire to avoid. Additionally, the cost and ease-of-use of travel aids

were also a great concern. This motivated the development of a low cost electronic detector

with a warning for obstacles near the head and waist of the visually impaired.

The limitations of this survey were that the sample size was small, the participants were

young and their travel environment was restricted mostly to a school campus or several

limited sites that they frequently visited. Future surveys must collect larger samples with a

wide range of ages and visual impairment for further statistical analysis.

4.2 Evaluation of aids

The longest finish time (FT) was found in the test condition using only a detector for both

blindfolded sighted and visually impaired. All blindfolded sighted and visually impaired

participants had no previous experience using a detector and were observed to walk forward

slowly and carefully when using only the detector during the experiment. It was also found

that the mobility speed varied markedly among participants. An individual’s walking habit

partly accounted for the speed difference.

The shortest FT appeared in the condition where both devices were used together. The

body protection (for head, waist/hands, and legs) was also enhanced and the collision

frequency (CF) decreased. The mobility performance and body protection using both devices

used together were the highest in all test conditions. Using a detector only protected the

user’s body parts better than the white cane but was worse in mobility speed. The

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experimental results verified the study hypotheses. This is consistent with the results of

Snaith et al. (1998) and Cardin et al. (2007) that the white cane is a major mobility aid and

other aids can assist with the cane’s deficiency. The developed detector did augment the white

cane. Participants walking with both devices together would obtain more information about

obstacles ahead and their confidence in mobility might be increased. This finding could be

observed from the post experiment interview results, in which all participants expressed

positive comments for the presence of the detector. It should be noted that the benefit of using

the cane and the detector together only occurred in finish time, not in obstacle collision.

There was no significant difference in obstacle collision between the detector alone condition

and the white cane plus detector condition.

Visually impaired participants received mobility and orientation training prior to this study.

They could more easily adopt coping strategies and obtain more confidence with their

mobility needs. It was observed that they showed good navigation behaviour during the

experiment. However, the study results showed that visually impaired participants gained

greater finish times. The difference in finish time between visually impaired and blindfolded

sighted participants might result from the travel routes selected for the experiment. The route

around the school campus navigated by visually impaired participants was to some extent

complicated. There were 3 turning points, 1 pedestrian overpass, 1 plant terrace and 1

side-door on the route. This route was longer than that travelled by the blindfolded sighted

participants. Visually impaired participants sometimes deviated from the planned path during

the experiment and the actual travel distance became larger when an orientation loss took

place. However, path deviation and orientation loss were found in only a few instances for

blindfolded sighted participants because the test route was straight, flat and shorter.

Additionally, the blindfolded sighted participants usually waited at laboratory for the

experiment and basically knew the route and the obstacles before they were blindfolded.

Therefore, blindfolded sighted participants would have much shorter finish times. The

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preliminary test for the travel aid detection function (i.e., white cane and detector), observed

from blindfolded sighted participants, was the purpose for the first experimental stage.

Observing visually impaired participants’ behaviour during the experiment was the purpose

of the second stage. The navigation performance comparison between these two groups was

not the original experiment design in this study.

The detector developed in this study could not differentiate the characteristics of obstacles.

The warning sound simply raised the alertness level of the participant and prompted the

participant to take cautious actions. It was observed that the participants always moved with

their hand(s) raised forward and upward when the buzzer sounded under test conditions 2 and

3 (i.e., a detector included). They also swung their white cane vigorously when an obstacle

was detected by the white cane. They adopted these actions to determine what and where the

obstacles were. They then lowered their head or stooped down to avoid head collisions,

side-stepped away from an obstacle on the ground with hands touching or/and with the white

cane swinging. A loss of orientation usually occurred for most participants after they collided

with an obstacle during the experiment. Visually impaired persons should decrease their

walking speed to avoid an accidental collision. Additionally, they should be trained how to

solve the orientation loss problem while collisions happen during navigation.

The warning signal for the obstacles ahead was the only information provided by the

detector. This has been generally sufficient in most situations for the visually impaired to take

action and avoid possible collisions. The developed device was small in size and lightweight.

One or more sensing modules can be easily worn or attached to user body sites such as the

head, chest, waist, hand or other body part to detect obstacles. One advantage of the current

detection system is that it is hands free.

At the travel aid development stage pilot trials were performed to test the detection system

capabilities. The warning signal frequently sounded in trials with the original detection

system (i.e., without any sensor modification). It was observed that objects located a little

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farther on the side of the road and within the detection envelope might be detected by the

sensor. However, such objects did not obstruct the users’ movement. The sensor default

distance sensitivity setting was adjusted to a lower level. The detection system then worked

reasonably. This sensor adjustment avoided false alarms while walking and successfully met

the obstacle detection demands of this study.

The distance envelope obtained with the test using a wooden board as the target was larger

than that used by the sample individuals (Figure 5). This result was fair because more

reflected signals were received from the flat board by the ultrasonic sensor due to its smooth

surface. A certain amount of reflected signals occurred from an individual, however, these

signals became scattered and could not be received by the detector. This decreased the

effective detection distance. Furthermore, the detection distance varied for different obstacles

tested at the university campus after the laboratory test. It was found that the sensor distance

envelope could be affected by several factors such as the body movement while walking, the

individual’s clothing, the body sites where sensors were attached and the obstacle features

(e.g., dimensions, appearance, and surface roughness). Users should be aware that the sensor

detection distance is target and direction dependent.

The visually impaired participants were not told or did not ask about the nature and

number of obstacles appearing on the route as well as whether the same route was used for all

three tests during the experiment. Three test conditions were completed in random order by

each participant and the locations of the purposefully placed obstacles were varied in each

condition. The experimental results could be used to reasonably explore the usefulness and

make a comparison analysis of the tested devices. However, a familiar test environment

might lead to insufficient generalizability of the FT and CF results.

Eight obstacles were scattered over a 138-meter path with no two obstacles within the

detection envelop at the same time in this study. However, the participants were not told that

there was only one obstacle when the warning sounded. They always behaved as described

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above when an obstacle was detected. In a realistic environment the warning sound might be

continuous. If this occurs it is suggested that the user turn the detector off and use a white

cane or other suitable travel aid instead. This might be the limitation of using this detector.

The experimental results presented positive responses to the detector. However, detector

improvement is still needed. To enhance user convenience the detection device system should

be designed with a user-friendly interface and wireless function. A vibro-tactile feedback and

earphone function should also be provided to ensure the warning signals are received by users

who are deaf/blind or in a noisy environment. Furthermore, a global positioning system (GPS)

may be taken into account in detection system development to provide location information

for the visually impaired in outdoor navigation.

The current developed detector provides only information that a detected obstacle is in

front and nearby. If the actual position of the obstacle (i.e., appearing on the left side, right

side, upper level, or lower level of the user) can be provided the user may more easily take

correct action to avoid obstacle collision. Future work should be done regarding this

suggestion: 1) the feasibility of manufacturing such a detector prototype/product, 2)

experiments conducted for detection performance and 3) a training course for the user.

5. Conclusions

A compact, lightweight, simple detection feedback, easy-to-use, low-cost obstacle detection

device for the visually impaired was developed in this study. The results showed that the

developed detector could augment the user’s performance with a white cane. To achieve the

best mobility performance and body protection effect, the obstacle detection device should be

used in conjunction with the white cane.

Acknowledgements

The authors wish to thank the National Taichung Special Education School for the Visually

Impaired for their support and the participants for their time and patience in completing the

questionnaire survey and the experiment.

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References

Cardin, S., Thalmann, D. and Vexo, F., 2007. A wearable system for mobility improvement of

visually impaired people. Visual Comput. 23, 109-118.

Clark-Carter, B.D., Heyes, A.D. and Howarth, C.I., 1986a. The efficiency and walking speed

of visually impaired people. Ergonomics 29, 779-789.

Dakopoulos, D. and Bourbakis, N.G., 2010. Wearable obstacle avoidance electronic travel

aids from blind. IEEE Trans. Syst., Man Cybern. C, Appl. Rev. 40 (1), 25-35.

Ghiani, G., Leporini, B. and Paterno, F., 2009. Vibrotactile feedback to aid blind users of

mobile guides. J. Visual Lang. Comput. 20, 305-317.

Kuyk, T., Liu, L., Elliott, J. and Fuhr, P., 2010. Visual search training and obstacle avoidance

in adults with visual impairments. J. Visual Impair. Blind. 104 (4), 215-227.

Molton, N., Se, S., Brady, J.M., Lee, D. and Probert, P., 1998. A stereo vision-based aid for

the visually impaired. Image Vision Comput. 16, 251-263.

Phillips, G., 1998. The Miniguide ultrasonic mobility aid. GDP Research, South Australia.

online at http://www.gdp-research.com.au/minig_1.htm

Sainarayanan, G., Nagarajan, R. and Yaacob, S., 2007. Fuzzy image processing scheme for

autonomous navigation of human blind. Appl. Soft Comput. 7, 257-264.

Schellingerhout, R., Bongers, R.M.,Van Grinsven, R., Smitsman, A.W., and Van Galen, G.P.,

2001. Improving obstacle detection by redesign of walking canes for blind persons.

Ergonomics 44 (5), 513-526.

Shoval, S., Borenstein, J. and Koren, Y., 1994. Mobile Robot Obstacle Avoidance in a

Computerized Travel Aid for the Blind”, in Proceeding of the IEEE International

Conference on Robotics and Automation, San Diego, CA, 2029-2032.

Snaith, M., Lee, D. and Probert, P., 1998. A low-cost system using sparse vision for

navigation in the urban environment. Image Vision Comput. 16, 225-233.

Ulrich, I. and Borenstein, J., 2001.The GuideCane – applying mobile robot technologies to

18

assist the visually impaired people. IEEE Trans. Syst., Man Cybern. A, Syst., Humans 31

(2), 131-136.

Yasumuro, Y., Murakami, M., Imura, M., Kuroda, T., Manabe, Y. and Chihara, K., 2003.

E-cane with situation presumption for the visually impaired. In: N. Carbonell and C.

Stephanidis, ed. User Interfaces for All, LNCS 2615, Berlin Heidelberg: Springer-Verlag,

409-421.

19

Table 1. Dimensions and pictures of the electronic obstacle detector modules.

Table 2. Personal data and anthropometric measurements of 5 blindfolded sighted (BS) and

15 visually impaired (VI) participants in the experiment.

Table 3. Collision frequency (CF) and obstacles collided with by both 5 blindfolded sighted

and 15 visually impaired participants under three test conditions.

Table 4. Detector dimension, weight, mobility assistance and confidence satisfaction survey.

Values in parenthesis are the number of visually impaired participants.

20

Figure 1. The obstacle detector architecture which included three modules: a sensing module,

a processing module, and a warning module.

Figure 2. The route sketch for the visually impaired participants to travel in the second-stage

test.

Figure 3. Four obstacle types that participants mostly often collided with while walking.

Figure 4. The percentage of body parts that often collided with obstacles and most expected

to avoid collisions. Hands/waist is expressed together because the hands and waist are

usually at the same vertical level while walking.

Figure 5. Sensor detection envelopes obtained from two tests using a high flat wooden board

and three persons as targets.

Figure 6. Means and standard deviations of finish time (FT) and the Duncan’s new multiple

range test by test condition for both the visually impaired and blindfolded sighted

participants. Means with the same letter are not significantly different (α=.05).

Figure 7. Means and standard deviations of collision frequency (CF) and the Duncan’s new

multiple range test by test condition for both the visually impaired and blindfolded sighted

participants. Means with the same letter are not significantly different (α=.05).

21

Table 1. Dimensions and pictures of the electronic obstacle detector modules.

Module Dimension (mm) Weight (g) Photo

Processing module

(Control host)

Length×Width×Height

=95.2×57.0×25.8

74.8

Sensing module

(transmitting and

receiving unit)

Length×Width×Height

(Max.) =37.6.×24.2×15.4

16.6×2a

Warning module

(buzzer)

Diameter×Height=41.5×15.9 10.5

a: 2 sets of the sensing module were worn on the participant's chest and waist during the experiment.

22

Table 2. Personal data and anthropometric measurements of 5 blindfolded sighted (BS) and

15 visually impaired (VI) participants in the experiment.

Variable Age (yr) Stature

(cm)

Body weight

(kg)

Limb length

(cm)

Waist height

(cm)

Shoulder

height (cm)

Mean (SD)a

BS 31.2(2.8) 165.3(5.0) 62.1(6.5) 71.6(4.5) 92.5(3.7) 129.1(4.3)

VI 23.8(13.5) 161.3(6.9) 57.3(11.1) 68.6(6.4) 93.4(6.8) 128.4(5.8)

Range

BS 27.1-34.2 160.5-173.7 54.7-68.4 67.1-76.2 86.4-96.4 125.6-140.1

VI 13.7-51.4 149.8-172.3 45.0-74.6 56.4-79.3 80.4-109.4 119.5-139.4 a: SD indicates standard deviation

23

Table 3. Collision frequency (CF) and obstacles collided with by both 5 blindfolded sighted

and 15 visually impaired participants under three test conditions.

N Statusa Gender

b White cane Detector Both

d

CF Obstacle (body part)c CF Obstacle(body part) CF Obstacle(body part)

The blindfolded sighted participant

1 G M 2 box 1 (H), box 2 (H) 1 chair 1 (W) 0 0

2 G F 2 box 1 (H), box 2 (H) 0 0 0 0

3 G M 2 box 1 (H), box 2 (H) 0 0 0 0

4 G M 2 box 1 (H), box 2 (H) 1 chair 2 (W) 0 0

5 G M 2 box 1 (H), box 2 (H) 0 0 0 0

Mean 2 0.4 0

SD 0 0.5 0

Range 2 0-1 0

The visually impaired participant

1 T M 2 Box (H), tilted tree (H) 0 0 0 0

2 T F 2 Box (H), tilted tree (H) 0 0 0 0

3 T M 1 Tilted tree (H) 1 bike/motor 2 (W) 0 0

4 T M 0 0 0 0 0 0

5 S M 3 Bike/motor 1 (W), box

(H), tilted tree (H)

0 0 0 0

6 S M 2 Box (H), tilted tree (H) 1 bike/motor 2 (W) 0 0

7 S F 2 Box (H), tilted tree (H) 0 0 0 0

8 S F 2 Box (H), tilted tree (H) 1 bike/motor 2 (W) 0 0

9 S F 2 Box (H), tilted tree (H) 0 0 0 0

10 S F 2 Box (H), tilted tree (H) 0 0 0 0

11 J M 2 Box (H), tilted tree (H) 0 0 0 0

12 J M 2 Box (H), tilted tree (H) 1 bike/motor 1 (W) 0 0

13 J M 2 Bike/motor 2 (W),

tilted tree (H)

0 0 0 0

14 J M 2 Box (H), tilted tree (H) 0 0 0 0

15 J M 1 Box (H) 0 0 0 0

Mean 1.8 0.27 0

SD 0.7 0.5 0

Range 0-3 0-1 0

a G: graduate blindfolded sighted student; T: visually impaired teacher, S: senior high visually

impaired student, J: junior high visually impaired student; b M: male, F: female;

c The body site

collided by obstacles, H indicates head collision and W indicates waist collision. d

using both

white cane and detector in the experiment.

24

Table 4. Detector dimension, weight, mobility assistance and confidence satisfaction survey.

Values in parenthesis are the number of visually impaired participants.

Item Detector

dimension

Detector weight Mobility

assistance

Mobility

Confidence

Very satisfied 26.7% (4) 40.0% (6) 26.7% (4) 33.3% (5)

Satisfied 46.7% (7) 40.0% (6) 60.0% (9) 46.7% (7)

Acceptable 26.7% (4) 20.0% (3) 13.3% (2) 20.0% (3)

25

Buzzer

Warning Module

Control

host

Processing ModuleSensing Module

Obstacle

Transmitting

unit

Receiving

unit

Figure 1. The obstacle detector architecture which included three modules: a sensing module,

a processing module, and a warning module.

26

7.0 m 26.8 m (walking distance 33.4 m) 9.0 m

9.3

m4

1.3

m

11.2 m 20.4 m

4.5

m

S

F

12

3

4 5 6 7

8

9

10

2.2 m

Checkpoints:

Bike/motorcycle

Cardboard box

Plant terrace

Tall tree

Pedestrian overpass 1

Side-door

Bike/motorcycle

Tilted tree

1

F Finish pointS Start point

2

3

4

5

6

7

8

9

10

Turning point Check point

Pedestrian overpass 2

Pedestrian overpass 3

Figure 2. The route sketch for the visually impaired participants to travel in the second-stage

test

27

70%

63%

20%17%

0%

10%

20%

30%

40%

50%

60%

70%

80%

Automobile/

motorcycle

piled item/

protrusion

step Table/chair

Obstacle type

Subject

Figure 3. Four obstacle types that participants mostly often collided with while walking.

28

57%

40%

60%

50%

17%

33%

0%

10%

20%

30%

40%

50%

60%

70%

Head Hand/waist Leg

Body part

Subject

often collide with obstacles

mostly expect to avoid colliding

Figure 4. The percentage of body parts that often collided with obstacles and most expected

to avoid collisions. Hands/waist is expressed together because the hands and waist are usually

at the same vertical level while walking.

29

0

50

100

150

200

250

-60∘ -50∘ -40∘ -30∘ -20∘ -10∘ 0∘ 10∘ 20∘ 30∘ 40∘ 50∘ 60∘

Angle

Detection distance

Board

Man

Figure 5. Sensor detection envelopes obtained from two tests using a high flat wooden board

and three persons as targets.

30

A

301.0

A

52.1

A

333.0

A

79.4

B

257.7

B

44.1

0

50

100

150

200

250

300

350

400

Visually impaired Blindfolded normal

Participant

(s)

Cane

Detector

Both

Mean finish time

Figure 6. Means and standard deviations of finish time (FT) and the Duncan’s new multiple

range test by test condition for both the visually impaired and blindfolded sighted participants.

Means with the same letter are not significantly different (α=.05).

31

A

1.8

A

2.0

B

0.4B

0.3

0

0.5

1

1.5

2

2.5

3

Visually impaired Blindfolded normal

Participant

CaneDetectorBoth

Mean collision frequency

B

0.0

B

0.0

Figure 7. Means and standard deviations of collision frequency (CF) and the Duncan’s new

multiple range test by test condition for both the visually impaired and blindfolded sighted

participants. Means with the same letter are not significantly different (α=.05).