Authors: Yeh-Liang Hsu, Po-Er Hsu, Jun-Ming Lu, Jerry J.-H. Tsai, Yi-Shin
Chen, Chau-Heng Tu, Chia-Hung Lu, Yan-Wei Chen, Ju-An Wang(2010-11-21); recommended:
Yeh-Liang Hsu (2010-12-01).
Note: This paper was presented at the “International Forum for Disability
Prevention & the 4th Forum for the Development of Work on
Disability in China,” Peking University, Beijing, China, December, 2010.
Reinventing the wheelchair -- Development of an intelligent
robotic wheelchair for the senior users
In this study, an
intelligent robotic wheelchair (iRW) is
developed with the intention to redefine the wheelchair as the center of
mobility, everyday living and healthcare of the senior users. The objective is
to enhance the independence and social participation of the senior users, as
well as improving their quality of life. The iRW is composed of a moving vehicle, a sensing and control module
and an information/communication module to provide the senior users with three main
functions: mobility, everyday living, and healthcare. Integrated with Mecanum
wheels, navigation system, the Stewart platform, the ergonomically designed
seat and the telehealth system, the iRW
is expected to provide improved safety and comfort, better environmental
control, enriched information exchange, and stronger interpersonal
communication. By enabling the senior users to interact with the environment
more effectively and actively, it has good potential to prevent transitions
from mobility impairment to disability.
Keywords: robotic wheelchair,
Mecanum wheel, indoor navigation, home telehealth system, Stewart platform,
Over the past
decades, the rapidly aging society has brought an increasing demand for living
support and healthcare. In the mean time, social participation of the elderly
is also of great concern. In addition to providing an environment with improved
comfort and safety, researchers and practitioners are also attempting to prevent
transitions from impairment to disability. Regarding this issue, accessibility
limitations can be a key factor that influences the effect of impairment leading
to disability. Generally, an elderly person with mobility impairment
necessitates the use of a wheelchair. If he/she is not able to operate the
wheelchair freely, the health condition may become even worse and severely
curtails the social life. Mended de Leon et al.  reported that significant
cross-sectional associations can be found between social engagement and
disability, with more socially engaged older adults reporting less disability.
In other words, promotion of social engagement may be important for the
prevention of disability. For these reasons, it is essential to provide the
elderly with good mobility in the everyday living.
For the elderly with mobility impairment, a wheelchair is the
most common and important aid. Electrical
wheelchair is an option for senior users who cannot move themselves on a
wheelchair. However, operating an electrical wheelchair is often difficult for senior
users. Fehr et al.  surveyed 200 people with severe disabilities who were
trained for operating electrical wheelchairs. Ten percent of the testers thought electrical
wheelchairs cannot satisfy their living requirement and 40 percent could not
use electrical wheelchairs to move to where they wanted. Although this survey is
for disable people, the usability of electrical wheelchairs can also be a major
problem for senior users. To solve this problem, many studies focus on the
development of wheelchairs
that can perform autonomous behaviors to a certain extent in order to improve its usability.
Miller and Slack  first used the term “robotic
wheelchair” in their research. They applied various sensing and navigation
technologies that are often used in robotics and built two prototypes of
robotic wheelchairs, which were able to assist users to pass through narrow paths
and avoid obstacles. Automatic navigation is one of the
major research issues in robotic wheelchair, since mobility assist is the fundamental
function of a wheelchair. Prassler et al.  developed robotic wheelchair MAid
(Mobility Aid for Elderly and Disabled People) to support and transport senior
users with limited motion skills and to provide them with a certain amount of autonomy
man-machine collaborative control scheme is another important issue of the
research on robotic wheelchair [5, 6]. Galindo et al.  developed a robotic
wheelchair SENA to facilitate mobility of the disable people and senior users.
They presented the design and implementation of the human-robot-integration
idea into SENA, which permits a person to extend/improve the autonomy of the
whole system by participating at all levels of the robot operation, from
deliberating a plan to executing and controlling it. Bourhis and Agostini 
considered collaboration between the users and robotic wheelchairs will improve
the efficiency of navigation tasks. They classified the collaborative
relationship into behavior model, man supervisor, and robot supervisor, and implemented
the collaborative control strategy in their robotic wheelchair VAHM. Takahashi
et al.  developed a robotic wheelchair in which the user can use body
posture to control forward/backward motion by sensing the change of user’s
center of gravity. Katsura et al.  combined the capability of the user and the
robotic wheelchair to design the collaborative scheme to reduce the operational
load for the user.
functions in mobility assistance, such as navigation and man-machine collaborative
control, will be the keys in the future developments of robotic wheelchairs. However,
the wheelchair can be more than just a vehicle for mobility assistance for the
senior users. In fact, the wheelchair is probably the place that many senior
users spend the most time with in their everyday lives. It can play an
important role as the interface between the senior users and all aspects of
their daily lives.
describes an an on-going research project in the Gerontechnology Research
Center in Yuan Ze University, Taiwan in developing an intelligent robotic
wheelchair (iRW), which intends to redefine the wheelchair as the center of mobility, everyday
living and healthcare of the senior users. Figure 1 illustrates the overall design concept of the iRW. On
the basis of the needs of senior users, the core of the iRW is a user interface
designed specifically for the senior users’ declining ability
in perception, motor control and cognition. The objective
is to enhance the independence and social participation of the elderly, as well
as improving their quality of life.
Figure 1. Design concept
of the iRW
The iRW is composed of a moving vehicle, a
sensing and control module and an information/communication module to provide
the senior users with three main functions: mobility, everyday living, and
healthcare. Integrated with the Mecanum wheels, the navigation system, the
Stewart platform, the ergonomically designed seat and the telehealth system,
the iRW is expected to provide
improved safety and comfort, better environmental control, enriched information
exchange, and stronger interpersonal communication. By enabling the senior users
to interact with the environment more effectively and aggressively, it has good
potential to prevent transitions from mobility impairment to disability.
2. Design concept of
The three main functions planned for the iRW are described as follows:
The iRW is designed for home and nursing home
use, mostly being used indoor or short-distance outdoor (such as taking a walk
in the garden). The iRW employs a Mecanum-wheeled vehicle
which can move in any
direction for nimble maneuver.
The iRW also realizes autonomous movements by implementing functions including
indoor navigation, obstacle avoidance, and dynamic route planning. Schemes of collaborative
control are also developed to make it more convenient and easier to use in home
and nursing home environments.
(2) Everyday living
The iRW applies Stewart platform to design a versatile
seat mechanism with multiple degrees of freedom in seat adjustments to provide transfer
assist and comfortable seating positions to the senior user for various situations
encountered in everyday living. Interacting with the wireless sensor network constructed
in the home or nursing home environment, the iRW provides the senior user with convenient environmental control. The information and communication
module in the form of a digital photo frame embedded in iRW also
provides a channel of information exchange and
interpersonal communication with the nursing staff and the family.
The iRW provides an easy-to-wear, non-invasive
device for blood oxygenation measurement. Other physiological signals such as
heart rate and respiration rate can be also captured in terms of real time
monitoring. Combining with the information and communication module embedded in
the digital photo frame, a home telehealth system is thus integrated with the iRW.
Figure 4 is the appearance of the prototype for the iRW. Basically the iRW is a “chair within a chair”. The vehicle (Figure 2 left) is
basically a robot in the form of a chair to provide mobility assistance to the
senior users. The elegant lines of Chinese traditional fauteuil are embedded in
the vehicle to soften the mechanical feeling of the robot. The seat fixed on
the vehicle integrates all usability functions and provides an interface
between the senior users to the vehicle. In addition to considerations in
ergonomics, the shape of the seat is also designed to create a feeling of
affectionate embrace to the senior users (Figure 2 right).
Appearance planned for the iRW
progress of the various systems of iRW
will be described in the following sections, including mobility assistance,
seat design, seat adjustment mechanism, and home telehealth system.
assistance is the basic function of the iRW.
Nimble maneuverability is of the highest priority so that the iRW can be used in the crowded indoor home
environment. For this reason, the moving vehicle of the iRW consists of four Mecanum-wheels that are designed by Swiss
inventor Bengt Ilon. As shown in Figure 3, the outer ring of the Mecanum wheel
has free rollers in a 45-degree angle toward the axis. The vehicle can move in
all directions by controlling the direction of rotation of the four Mecanum
wheels. In our design, the moving vehicle of iRW can go forward/backward, shift right/left, and rotate clockwise/counterclockwise
by operating the joystick.
Figure 3. The Mecanum wheel and application on a
We did not
implement complete automatic navigation function in the iRW because the cost is rather high to achieve the required
accuracy. Moreover, complete autonomy may not be proper for the iRW. Instead, a semi-autonomous indoor navigation
based on recognizable landmarks is implemented. On the basis of the concept
similar to the automated guided vehicles (AGV), it helps to reduce the
operation load of senior users with reasonable cost. Landmarks are deployed on
the ceilings as “virtual AGV track”. When iRW
is steered under a landmark, the camera on the iRW will capture and recognize the landmark. Subsequently, the information
conveyed by the landmark can be interpreted, and then the iRW follows the virtual AGV track to move to the specific location,
such as bed room, living room, kitchen, etc. This semi-autonomous indoor navigation
system is inexpensive, flexible, and easy to implement. The QR code (Quick
Response code), a two-dimensional bar code system commonly used in various
applications, is adopted as the recognizable landmarks in this system. By using
the software programs for generating and recognizing QR codes, the user can generate
and print out the QR code landmarks and easily deploy the virtual AGV track in
the home environment.
In addition, ultrasonic
range-finding sensors are used to perform the low-cost and reliable function of
obstacle avoidance in the iRW. When an obstacle is detected within a specific
distance from the iRW, iRW simply stops all autonomous
behaviors and handed the control back to the user.
Ergonomic seat design
In the use of iRW, the user makes direct contact with
the seat, which serves as the interface between the user and the wheelchair.
Thus, in addition to the enhanced mobility, it is also important to design a
comfortable seat for the user to sit on for a long period every day. From the
ergonomic perspective, there are four basic requirements for a comfortable
Fitting the size
user usually spends a long time sitting on the wheelchair every day, improperly
fitted seat may cause discomfort and lead to pain or other health problems. The
human body is of great diversity and complexity. Thus, the key to good fitness
is based on accurate measurements. By referencing the Anthropometric Data Book
of the Chinese people in Taiwan
, the key dimensions of the seat are determined according to corresponding
body dimensions of the elderly, such as sitting height, hip breadth, buttock to
popliteal length, and elbow height. The objective in the current stage is to
provide an average-sized seat that fits around fifty percent of the population.
Nevertheless, it is rather difficult to find an ideal size that fits all. Thus,
for the next stage, we aim to improve the fitness by providing extreme designs
for large-sized and small-sized users. Ultimately, the adjustable design will
be realized in the final stage to make all users further satisfied with exact
fit and great comfort.
Fitting the shape
spine consists of four regions, including cervical spine (neck), thoracic spine
(trunk), lumbar spine (lower back), and sacrum (sitting bone). When properly
aligned and balanced, the thoracic spine region has a slightly convex or kyphotic
curve, while there is a slightly concave or lordotic curve in the cervical and
lumbar spine regions. These natural S-shaped curves need to be maintained to keep
the back and spine relaxed and thus free of pressure and pain. When a person
changes the posture from standing to sitting, the lumbar spine region may turn
into a kyphotic curve. As the person attempts to restore the balance, it will increase
the pressure on the intervetrabral discs and generate higher muscle activity,
which usually leads to pain and discomfort.
to help maintain the natural curves and reduce body discomfort while sitting,
the seat needs to be designed to provide good support to the spine. In other
words, the contour of the seat pan and backrest has to fit the shape of human
spine. Again, by referencing the anthropometric database , the curves of
the contour are determined based on related body dimensions, including height
from the seventh cervical vertebra to sitting plane, height from scapula to
sitting plane, height from the fifth lumbar vertebra to the sitting plane, and
Supporting the weight
sitting, the body weight is mainly supported by the hip and the two legs. For a
long period of use, the pressure applied to the hip is usually too high and
thus cause poor blood circulation, which may lead to skin disorders such as
pressure sores. Thus, the body weight needs to be further distributed to other
body parts by giving additional supports. To achieve this goal, the seat of iRW is provided with the backrest, headrest,
and armrests to help relieve the body pressure for better comfort. Besides, the
raised edges on both lateral sides are adopted for not only supporting the
weight but also enhancing the stability and safety.
Fitting the task
types of task, the required muscles are different and thus cause the change of
body postures. It is the same in the use of a wheelchair. The angle between the
seat pan and the backrest needs to be flexible to fit the task. For example, the
user has to sit upright for reading or writing, while leaning backward is
recommended for resting. In the development of iRW, this is enabled by the use of the Stewart platform. The
details will be discussed in the next section.
requirements, the seat for iRW was
ergonomically designed as shown in Figure 4. In addition to the well-fitting
size and shape, the seat is equipped with adjustable armrests and headrest to
give good support. The control panel can be installed on either left- or
right-hand side, depending on the user’s handness. Moreover, a working table
can be attached to the armrests if it is required. Other accessories, such as
the Care Delivery Frame (described in the next section) and camera for
navigation and communication, can be placed on the working table.
Figure 4. The seat for iRW
Seat adjustment mechanism
The iRW applies the Stewart platform to
design a versatile seat mechanism with multiple degrees of freedom in seat
adjustments for various situations encountered in everyday living. One goal is
to meet the ergonomic requirement of “fitting the task.” Besides, it enables
the transfer assists which allows the user to move from the wheelchair to the bed
is a parallel structure robot which has the advantages of high stiffness and
high positioning accuracy compared to the serial structure robots. The geometry
of this parallel robot, as illustrated in Figure 5, is composed of a fixed
base, a movable platform, and six variable length actuators connecting the
fixed base and the movable platform. This is a 6 degrees-of-freedom
universal-prismatic-spherical mechanism, including heave, surge, sway, yaw,
pitch, and roll.
Figure 5. Schematic diagram and degrees-of-freedom
of parallel robot
required in transfer assist and changing seating positions, the seat mechanism of
iRW needs only four degrees-of-freedom
including heave, surge, sway, and pitch. As shown in the conceptual sketch of
the first iRW prototype in Figure 6,
the seat mechanism of iRW uses a four-axis Stewart platform. The
Mecanum-wheeled vehicle serves as the fixed plate, while the seat is the
movable plate. In order to enhance the stability of the seat, a locking-mechanism
is designed to constrained uncontrolled degree of freedoms (surge and sway) of
the seat. Table 1 shows the functions and specifications of the seat adjustment
mechanism of the iRW prototype.
Figure 6. The iRW
prototype uses a four-axis Stewart platform in the seat mechanism
Table 1. Functions and specifications of the seat
mechanism of the iRW prototype
Adjustment of comfort
Height of the seat
(Distance from the bottom of the seat to the
Highest position: 498mm
Initial position: 433mm
Lowest position: 368mm
Adjustment of transfer assist
Back/hip pressure variability
24V, 9.6Ah, 402×133.5×71.5 (mm, L×W×H), 3.4 kg
Home telehealth system
telehealth system of the iRW is embedded
in the digital photo frame called “Care Delivery Frame (CDF)”. By integrating
the home telehealth system and the remote photo sharing service of a digital
photo frame, the iRW aims to create a
unique information channel for senior users who are not familiar with the
computers and the Internet. In addition to the monitoring of health status,
children or caregivers can deliver care to the elderly with warm messages and
thoughtful reminders displayed on the CDF. Further, they can share their
feelings, joy, and life experience with the elderly by means of digital photos
and video clips. Moreover, the daily news, useful information, and even
commercial ads can be provided through the use of CDF. The CDF software is running independely on a pad PC, which can be
installed and seperated from the iRW
when the senior user leaves the iRW. Figure
7 illustrates the four main functions of CDF:
function of CDF is based on the Distributed Data Server (DDS) of the
decentralized home telehealth system . All technical functions of a home
telehealth system are built in the CDF. Currently the vital sign sensors that
can be connected to CDF include sphygmomanometer, blood glucose meter, and oximeter.
Remote photo sharing
provides a platform for children and caregivers to upload photos and videos
clips remotely, and to manage the display sequence and timing on the CDF for
the senior users who are not living together with them.
Caring messages and reminders
and caregivers can send warm caring messages and thoughtful reminders displayed
on the CDF to the elderly.
Entertainment and life information
with information service companies, CDF can also be a platform to display
information such as weather forecast and shopping discounts, as well as music
and other entertainment information.
Figure 7. The four main functions of the Care
Delivery Frame (CDF)
Figure 8 presents
the first prototype of the iRW, which
is in a skeleton form constructed by aluminum extrusions. This prototype is
currently under intensive testing and evaluation. After the functional tests and
seat design are completed, a field test of the iRW will be conducted in a nursing home to get feedbacks from the
senior users for further improvements in its usability.
Figure 13. The first prototype of iRW
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