Walker with Hand Haptic Interface for Spatial Recognition H.Hashimoto, A.Sasaki, Y.Ohyama and C.Ishii
Abstract — This paper presents a user-friendly hand force feedback system to recognize surrounding obstacles around the elderly to making walking safer. The system is implemented on a joystick mounted on a walker. The user is able to recognize the surrounding spatial information from the repulsive force generated as feedback on the joystick. The system is based on the generation of a virtual potential field that corresponds to the distance and direction to the obstacle is employed. Through the experimental results, it is found that the practice time of the user to learn basic operation of the system is sufficiently short. Furthermore, the user feels the sense of security while recognizing the surrounding information through the hand force feedback.
I.
INTRODUCTION
This paper presents a user-friendly hand force feedback system that allows the elderly to perceive obstacles around them and thus walk with greater safety. Japan has the world's highest percentage of elderly, approximately 26 percent of the population was over the age of 60 in 2004, and the rate will continue to increase for the next 20 years [1]. One of the most important factors determining the quality of life is the ability to move around independently. Not only is mobility crucial for daily living, but it is also essential for maintaining fitness and vitality. This emphasizes the importance of a pedestrian mobility aid that can enhance the quality of life. Our goal is assisting a user who has some basic physical, visible and mental abilities, but finds common action difficult or unsafe. That is, the technologies we are interested in enhance the user’s capabilities, not replace them. Our first target is to help the user walk independently without relying on a mobility support vehicle such as a robotic walker [2]-[6]. An important factor in pedestrian safety is how to announce the detection of an obstacle to the user. Earlier research on autonomous vehicles [3]-[5] focused on the autonomous avoidance under computer control and did not consider how to inform the user of the surrounding obstacles in any detail. Most just notified the user that there was an obstacle in a certain direction. In other research, voice messages were used to inform the user of obstacles [2]-[7]. Verbal instructions are not optimum since many of the elderly are hard of hearing, most environments are noisy, and illusory obstacles can be generated by insufficient information. Thus, H. Hashimoto, T.Sasaki and Y.Ohyama are with the School of Bionics, Tokyo University of Technology, Katakura, Hachioji, Tokyo, Japan (e-mail:
[email protected]) C.Ishii is with the Department of Basic Engineering in Global Environment, Kogakuin University, Nakano, Hachioji, Tokyo, Japan (e-mail:
[email protected]).
0-7803-9511-5/06/$20.00 ©2006 IEEE
it is necessary that the surrounding obstacle information be transmitted to the user as intuitively as possible. From the consideration above, this paper presents a user-friendly hand force feedback system. It enables the user to rapidly perceive surrounding obstacles which makes the user walk with ease. The key technique is the feedback established through a joystick. The system is based on a virtual potential field that is dependent on the distance and direction to the obstacle [7][8]. This field is translated into the appropriate repulsive force. Since the force is perceived by the hand, the user is able to know where the surrounding obstacles are. This paper is organized as follows. In Section II, we consider the technical problems of other methods for obstacle perception. Section III describes the proposed system. Section IV explains how the potential field is generated from obstacle information and converted into a force feedback. Section V demonstrates experiments on the passageway model and a field trial. Finally, conclusions are given in Section VI.
II.
EXAMPLE OF PERCEPTION PROBLEM
In the obstacle detection method in use common, the directional sensor such as supersonic or infrared sensors gather only the distance and the direction to the obstacle by corresponding to the vertical line on the sensor face. Such sensors are effective in use of autonomous navigation with computer, since the processing time of computer is fast and the sufficient dense steps in scanning is available. However, our goal is not the navigation by autonomous with computer, but by human perception, so the sufficient scanning steps is not used in our system. Under those conditions, the problem by using the approach to sensing obstacles and informing them to the user is explained in Fig.1. First the sensor detects the right wall as an object ((i) in Fig.1 ), it then turns scan in counter-clockwise direction to find (ii) and (iii). Due to the coarse scanning steps and the paucity of feedback information, the sensor can not find the exit passage. The user is not told of the exit which results in confusion and uncertainty. Consequently, the surrounding obstacle information should be notified to the user instantaneously at an appropriate level of detail without relying on visual interfaces. The following sections show how we overcame these problems.
311
III. SYSTEM CONFIGURATION The concept of the proposed hand force feedback system
AMC’06-Istanbul, Turkey
Distance accuracy Angular range Angular resolution Output response time
1 mm 180 deg 1.8 deg 180 ms for 180 deg
Fig.3. Obstacle detection sensor and its specificaions.
Fig. 1. Schematic representation of not finding the exit passage, since the sensor scans at discrete intervals sparsely. The real line with arrow indicates the sensor ray.
is shown in Fig. 2. Its obstacle detection sensor is based on an optical LED and the joystick provides the hand force feedback.
The sensor covers a wide angular range. The angular resolution on the sensor is 1.8 deg within range of 180 degs. And it only takes 180 msec for one complete scan, so more that five scans a second can be achieved. Taking into account of the velocity of user movement, these specifications enable real-time processing. Two motor drives inside the joystick (Fig. 4 (a)) impress a force on the stick so as to incline it as shown in Fig.4 (b). The angular displacement is limited to -30 deg to +30 deg, and the corresponding integer values for programming are 0 to 65536. The force, integer range is -10000 to +10000 in steps of one, can be adjusted by command through a USB port.
Fig.2. Concept design of hand force feedback system implemented on a walker.
When the user advances pushing the bar of the walker while gripping the joystick, the user is able to recognize the presence of obstacles by rotating the joystick. The repulsive force indicates the distance and direction to the obstacles. Thus, the system helps users walk by themselves safely by perceiving hand force, even if he is blind or visually impaired. The obstacle detection sensor shown in Fig.3 gives real-time updates of the surrounding environment.
Fig.4. Joystick with force feedback, and its specifications.
IV.
HAND FORCE FEEDBACK SYSTEM
A. Potential field according to obstacle The detection region of the sensor is a semicircle of radius R in xy-coordinates with the origin being the position of the sensor as shown in Fig. 5.
Effective detecting distance 3 m
312
B. Hand force feedback We define the virtual movement point (VMP) pa that travels from the origin to an arbitrary position in xy-coordinates, those positions are calculated by the inclination angles T xJ ,T yJ of the joystick which the user manipulate, i.e., pa
kax
ª kax T xJ º « J» ¬« kay T y ¼»
ª xa º «y » ¬ a¼
R J T max x
kay
,
J J where T max x , T max y
xy-coordinates Fig.5. Schematic representation of sensing obstacles.
The sensor measures n points per scan, and outputs distance {l1, l2, ... , ln} and angle { T1 , T 2 , …, T n } as the obstacle information. Let's define T i = R, if the sensor does not detect any obstacle on the scan line. We denote the position from the measurement point as follows pi
ª xi º «y » ¬ i¼
ªli cos Ti º « l sin T » i¼ ¬i
i
,
1, , n
(1)
The potential function is defined by
U i x, y
Ui
2 1 § 1 1 · °° K ¨ ¸ ® 2 © Ui U 0 ¹ ° 0 °¯
x xi
2
y yi
2
Ui d U 0
Ui ! U0
(5) R
(6)
J T max y
are the maximum angles around
respectively,
and
kax , kay
are
the
transformation coefficients from the angles to the position in xy-coordinates. When the VMP which is set by the user through the joystick is located in a potential field, the force feedback value f F proportional to intensity at the location is calculated as follows, fF
TF
k FU pa §T J tan 1 ¨ yJ ¨T © x
· ¸¸ ¹
(7) (8)
where k F is a gain parameter to adjust for the hand force. Consequently, f F is obtained by fF
(2)
ª f Fx º «f » ¬ Fy ¼
ª f F cos T F º « » ¬ f F sin T F ¼
(9)
The process mentioned above is explained as the block diagram in Fig.6. (3)
where K is a positive constant value, U 0 is a parameter to define the distance limit of the potential field influence. Both are design parameters used to adjust sensing level to detect obstacles and take into account the walking velocity. The upper bound of function U i x, y is set to a given constant positive value U max . An obstacle is described by a set of U i x, y , so the superposition property of potential fields that describe it is given by U x, y
n
¦U x, y i
(4)
i 1
where nis the number of the measurement points defined on each scan, i.e., n=180/1.8 =100. Next, we express how the intensity of the potential field is translated into the hand force.
Fig.6 Hand force feedback system.
As shown in Fig. 6, when the VMP pa is located into the potential field produced by the obstacle, the inclination angle of the joystick represents the distance and direction to the obstacle, and becomes the repulsive force that is perceived by the hand. Furthermore, the smoothness of the potential field gives the user a sense of security, since the hand force does not change rapidly or discontinuously.
313
V. EXPERIMENTAL RESULTS The effectiveness of the system in portraying obstacle was examined. First, the superposition property of the potential fields was examined for several configurations of the passage model. Second, we examined the efficiency with which a blindfolded user could learn to recognize the surrounding information in a real passage and to walk safely. A. Passage Model We used boxes to create several configurations of the passage model with obstacles (shaded areas) and the resulting potential fields were examined; the left and right figures in Fig.7 represent the overlooked passages and the corresponding potential fields, respectively. In the examination, the sensor was stationary at the designated point, and the blindfolded user answered whether the point was on (a) a straight passage, (b) a dead end, (c) a T junction, or (d) a crossing passage. The results showed that the system generated a smooth potential field for the obstacles and its intensity increased in proportion to the distance to the obstacle. Five healthy males participated in the experiments; all were blindfolded given only five minutes of practice time. The results are shown in Table.1.
Table 1 Results of recognition experiments for passage models.
User 1 2
Number of correct answers 12/12 8/12
3 4 5
11/12 12/12 12/12
Example of mis-answer (b)->(a), (b)->(a), (b)->(a), (c)->(d) (d)->(c)
Fig. 7. Passage models with obstacles (dashed line) and corresponding potential field.
The correct answer rate for all subjects and all arrangements was 91.6% . The results indicate that errors were due to front obstacles, not right or left ones. This suggests that users are more careful of right and left obstacles than those at the front. B. Field Trial We conducted a field trial of the prototype walker, see Fig.8. Fig. 8. Prototype the user-friendly walker be equipped with hand force feedback system to recognize surrounding obstacles around the blindfold userto walk safely.
The subject did not know the layout of the passage beforehand; it consisted of walls and pillar as the obstacles as 314
shown in Fig. 9.
Fig.9. Test passage.
The user advanced down the right side of the passage (Fig. 10(a)), while using the system. A subject who participated in the first evaluation was able to walk safely down the passage, scanning the environment in 1-2 sec bursts and sometimes stopping (Fig. 10 (b),(c)). Another trial used a narrow (90 cm) passageway. The subject had no problem in walking down this passage (Fig.11). After the field trial, the subject answered a questionnaire, the results of which confirmed that the subject was able to perceive obstacles and walk safely.
VI.
CONCLUSION AND DISCUSSION
We have proposed a hand force feedback system that allows users to perceive obstacles around the user. In field trials, a subject was able to walk safely down a narrow passageway that was only 90cm wide. Thus, this system can be used for supporting the elderly and the visually handicapped in daily life. Pre-experiments showed that the time needed to learn the basic operation of the joystick is sufficiently short. Furthermore, we confirmed, through questionnaires after the field trials that the subjects could feel a sense of security by being able to perceive the surrounding obstacles through the hand force. These results indicate that a walker equipped with the proposed system is very user-friendly. The prototype device describe here is still in an early stage of development, and we intend to downsize the walker to make it more practical.
REFERENCES [1] Database of Ministry of Health, Labour and Welfare in Japana, http://www.mhlw.go.jp/english/index.html
Fig.10 Walking experiment by blindfold user
[2] S.Dubowsky, F.Genot, S.Godding, H.Kozono, A.Skwersky and H.Y.Yu : PAMM - A Robotic Aid to the Elderly for Mobility Assistance and Monitoring: A "Helping-Hand" for the Elderly, IEEE International Conference on Robotics and Automation(ICRA), pp.570-576, 2000 [3] G.Wasson, J.Gunderson, S.Graves and R.Felder : An Assistive Robotic Agent for Pedestrian Mobility, International Conference on Autonomous Agents, Proc. of the fifth international conf. on Autonomous Agents, pp.169-173, 2001 [4] G.Wasson, P.Sheth, M.Alwan, K.Granata, A.Ledoux, C.Huang: User Intent in a Shared Control Framework for Pedestrian Mobility Aids, IEEE/RSJ Intr. Conf. on Intelligent Robotics and Systems(IROS), 2003 [5] A.J.Rentschler, R.A.Cooper, B.Blasch and M.L. Boninger : Intelligent walkers for the elderly: Performance
315
and safety testing of VA-PAMAID robotic walker, Journal of Rehabilitation Research & Development, Vol.40, No.5, pp.423-432, 2003 [6] S.Shoval, I.Ulrich and J.Borenstein : NavBelt and the GuideCane, IEEE Robotics & Automation Magazine, pp.9-20, 2003 [7] H.R.Everett : Sensors for Mobile Robots Theory and Application, A K Peters, Ltd, 1995 [8] O.Khatib : Real-Time Obstacle Avoidance for Manipulators and Mobile Robots, The Inter. Journal of Robotics Research, pp.90-98, 1986
Fig.11 Walking experiment for the narrowpassageway
316
