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AuthorsPo-Er Hsu (2013-01-28); recommended: Yeh-Liang Hsu (2013-02-10).
Note: This article is the Chapter 1 of Po-Er Hsu’s doctoral thesis “Development of an intelligent robotic wheelchair as the center of mobility, health care, and daily living of older adults.”

Chapter 1. Introduction

Over the past decades, the rapidly aging society has brought an increasing demand for living support and healthcare. The ageing process of older adults results in declined functional status and decreased mobility, which affects their level of self-care and independence. Mobility is a crucial aspect regarding one’s living independence. It is sensitive to changes in health and psychological status and is one of the most crucial factors determining one’s functional capacity [Celler et al., 1995; Heikkinen, 1998]. Limited mobility is associated with a deterioration of health and functional impairment in older adults [Folden et al., 1990].

To facilitate mobility, people with disability frequently employ mobility assistive technology (MAT) such as canes, walkers, manual wheelchairs (MWCs), power wheelchairs (PWCs), and scooters, etc [Souza et al., 2010]. Many older adults who have multiple and complex physical and cognitive impairments use wheelchairs as a primary means of mobility [Wang, 2011]. A wheelchair is the most common and important aid for older adults. Nineteen percent of older adults 65 years or older use wheelchairs, and they are the majority (57.5 percent) of manual wheelchair users [NCHS, 2004]. Moreover, approximately 50 percent of older adults in Canadian institutions use wheelchairs for mobility [Shields, 2004].

This chapter first discusses the design issues in mobility assistance and seat adjustment of the wheelchair. A patent analysis is also presented to explore the current trend of power wheelchair development. The emerging field of “robotic wheelchair” is then introduced. Finally, the purpose of this research, to develop an intelligent robotic wheelchair for older adults, is presented.

1.1      Design issues in mobility assistance of the wheelchair

Unlike common transportation devices, movement of the wheelchair is slow, short, and is discontinuous. Sonenblum et al. [2008] collected 25 non-ambulatory, full-time power wheelchair users’ wheelchair usage data in 395 days. They found that the users spent 10.8 ± 2.9 hours daily sitting on the wheelchair, and they moved the wheelchair in less than ten percent of the time. The median of “mobility bouts” which is used to represent transition numbers between activities was 110 times a day. Tolerico et al. [2007] studied the usage of manual wheelchairs for daily living in the home. They concluded that wheelchair users spent 8.3 ± 3.3 hours daily sitting on the wheelchair, and the average operating speed was 0.79 ± 0.19 m/s. The maxima period and distance of continued movement were 2.9 ± 1.4 min and 215.6 ± 119.8 m. Many other researches on wheelchair usage had similar findings, as summarized in Table 1-1.

Table 1-1. The survey of researches of the wheelchair usage



et al. [2002]


et al. [2003]


et al. [2007]

Sonenblum et al.[2008]

Karmarkar et al. [2011]






26 / 13





46.8 ± 13.3

43 (median)

62.5±5.7 / 66.9±7.5








Using Time (hours/day)

About 20


8.3 ± 3.3

10.8 ± 2.9


Speed (m/s)

About 0.3

0.44 ± 0.09

0.79 ± 0.19


0.64 ± 0.13 / 0.7 ± 0.3


Maxima period of continued movement




2.9 ± 1.4


2.5 ± 1.9 /

4.2 ± 2.8


Maxima distance of continued movement




215.6 ± 119.8


182.2 ± 190.4 / 344.1 ± 324.9



PWC / Home

MWC / Home

MWC / Home



Older adults with difficulties self-propelling manual wheelchairs, which can be attributed to physical capacity declined or overexertion, may benefit from power wheelchairs [Curtis et al., 1999; Algood et al., 2005]. However, the maneuverability and accessibility of power wheelchairs can also be a major problem for older adults.

About one third of wheelchair and scooter users reported that they have accessibility problems outside the home in a survey of wheeled mobility devices usage in the United States [Kaye et al., 2000]. The wheelchair users often expressed problems related to environmental access (e.g., door widths and passageways that are too narrow, inaccessible bathrooms, obstructed travel, and transportation) and the hardware of manual/power wheelchairs (e.g., manual wheelchairs that are too heavy to push or maneuver and power wheelchairs that are too wide or complicated to use) [Berry et al., 1996; Meyers et al., 2002; Chaves et al., 2004]. Fehr et al. [2000] surveyed 200 practicing clinicians in a variety of clinics, residential treatment facilities, and rehabilitation hospitals. Forty percent of the patients who received power wheelchair training thought that the power wheelchair was difficult or impossible to maneuver. Nearly half of the patients unable to control a power wheelchair by conventional methods would benefit from an automated navigation system, according to their clinicians. Further, Koontz et al. [2010] used four maneuverability trials, as shown in Figure 1-1, to evaluate 109 manual wheelchairs, 89 power wheelchairs, and 15 scooters recently. They concluded that many wheelchairs were unable to access the public place where the turning space was limited. They suggested that revision of the ADAAG guidelines was necessary to improve access to a space within the built environment.

Figure 1-1. Four maneuverability trials

1.2      Design issues in seat adjustment of the wheelchair

In addition to providing mobility assistance, seat adjustment design is of crucial importance in a wheelchair. The wheelchair user makes direct contact with the seat, which serves as the interface between the user and the wheelchair, for much of a given day. Souza et al. [2010] examined 50 journal articles on mobility assistive technology (MAT) and concluded that electric wheelchairs should be considered not only as providing mobility for advanced stages but as mobility assistive technology that can be integrated with an adjustable seating system to reduce fatigue.

To enable functional independence for older adults who use a wheelchair, their posture and comfort should be considered. Redford [1993] reviewed studies specifically concerned with seating and wheeled mobility for older adults, and concluded that these users would benefit from matching of mobility to function, cheaper and more effective cushions, more modular seating systems, and better lifting and transfer. Among the considerations in wheelchair seat design, pressure management received the most attention. Sitting-acquired pressure ulcers are a significant healthcare problem for wheelchair users. Various seating designs have been proposed for maintaining tissue viability while the user is in the wheelchair. For example, air cells with pressure sensors to monitor the pressure distribution on the buttock are often utilized to provide timely adjustment of the shape of the seat cushion to relieve concentrated pressure [Henderson et al., 1994; Burns and Betz, 1999; Chugo et al., 2011]. “Dynamic seating” on the wheelchair, in which a power-operated seat adjustment mechanism would allow the user to maintain proper posture, was also proposed [Graf et al., 1995].

Tilt-in-space, backrest recline, and seat elevation are the most clinician-prescribed seat adjustment functions of electric wheelchairs to facilitate posture change and/or assist activities of daily living (ADL) for users [Paralyzed Veterans of America, 2000; Trefler et al., 2001]. Ding et al. [2008] surveyed the real-life usage of powered seating functions among wheelchair users during their daily activities. Results showed that subjects accessed tilt-in-space, backrest recline, and seat elevation 19 ± 14 times, 12 ± 8 times, and 4 ± 4 times per day, respectively. Further, of the time participants spent in a wheelchair, 39.3% ± 36.5% was in the tilted or reclined positions. Lacoste et al. [2003] interviewed 40 participants at home and reported that 97.5 percent used the powered tilt-in-space and/or recline function in a given day and that 70 percent used the functions primarily to rest, relax, increase comfort, and decrease pain.

Many studies have been conducted to evaluate seat pressures at different angles of the tilt-in-space function in laboratory settings. Sprigle et al. [1997] found that the tilt-in-space function reduced static seating pressure significantly, which was a key factor in pressure ulcer prevention. In addition, many laboratory-based studies suggested that large tilt-in-space angles can be used to manage seating pressure to reduce the risk of pressure ulcers [Henderson et al., 1994; Stinson et al., 2002]. Aissaoui et al. [2001] concluded that the maximum pressure reduction at ischial tuberosities was at 45° of tilt-in-space.

In addition to providing seating comfort and pressure management, the seat elevation function for wheelchair users is considered medically necessary [Cooper et al., 2004; RESNA, 2005]. The seat elevation feature can help wheelchair users accomplish mobility-related ADL, such as performing transfers and reaching objects at different heights to preserve upper-limb functions and to achieve eye contact in social situations.

A search of related patents indicated that most seat adjustment functions for wheelchairs applied linkage mechanisms [Cerreto et al., 2012; Chuang, 2011; Wu et al., 2009]. Additionally, some linkage mechanisms were implemented with actuators or motors to provide multiple degrees of freedom (DOF) in seat adjustment. Bae and Moon [2008] designed a wheelchair seat mechanism, as shown in Figure 1-2, using four actuators to achieve the forward/backward tilting, elevation, and standing motions. The seat mechanism is composed of four independent adjustment mechanisms, each of which is driven by an actuator. Wada [2008] used a linear drive unit to develop a chair tilting system for the climbing wheelchair to maintain the angle between the seat and the floor. Lee et al. [2011] developed a seat adjustment mechanism that is integrated with the frame of the wheelchair to increase stability by shifting the center of gravity. The mechanism also provided a tilt-in-space function. Koontz et al. [2010] evaluated 109 manual wheelchairs, 89 electric wheelchairs, and 15 scooters for maneuverability. They concluded that the angles produced by the tilt-in-space and recline functions lengthen electric wheelchairs and therefore increase the space needed for maneuvering. Weight and complexity of the wheelchair is also increased with the multiple-DOF seat adjustment functions.

Figure 1-2. Wheelchair seat mechanism

Transfer activities mainly determine the degree of independence attainable by wheelchair users in daily living. Among all transfer activities, sitting pivot transfer (SPT) is the most commonly used [Finley et al., 2005; Perry et al., 1996; Bromley, 1998; Somers, 2001]. The basic steps of SPT are moving the buttocks toward the edge of the initial surface, placing the feet in a stable position, and leaving one hand on the initial surface (trailing) while placing the other hand on the target surface (leading). The arms are used to push up from the initial surface and pivot the body on the feet, swinging and landing the buttocks onto the target surface [Koontz et al., 2011]. However, proper transfer technique may not be sufficient when wheelchair users encounter height differences and gap crossing between wheelchair and target surface [Forslund et al., 2006].

Few studies have examined the development of a transfer assist function of a wheelchair. Khatchadourian et al. [1994] used robotic technologies to develop a mobile robot molded into a forklift for users to perform transfer activities. The user uses a beacon to position the mobile robot close to him or her. Then, the user can apply force to the support arms of the lifting mechanism to relocate himself or herself into the mobile robot to finish the transfer activities. Bostelman and Albus [2008] built a “Home Lift, Position and Rehabilitation (HLPR) Chair”, as shown in Figure 1-3, to provide independent mobility and transfer activities assist for the user in the indoor environment. However, the size (1,450×580×1,780 mm in mobility configuration, 1,450×580×2,410 mm in full lifted configuration) and weight (136 kg) of the HLPR chair may make it impractical for the home.

Figure 1-3. Home Lift, Position and Rehabilitation (HLPR) Chair

1.3      Patent analysis

A patent search from the United States Patent and Trademark Office (USPTO) database is conducted to explore the current trend of power wheelchair development. Using “wheelchair”, “electric”, “power” and “motor” as the key words, 637 patents were retrieved. Table 1-2 summarizes the patent search strategy. The complete patent analysis (in Chinese) is in Appendix.

Table 1-2. Patent search strategy


The United States


1976/01/01 to 2012/07/01


Abstract, Description/Specification, International Classification



Key words

“wheelchair”, “electric”, “power”, “motor”

Search query

ICL/A61$ AND ABST/((power$ OR electric$) OR motor) AND wheelchair

Figure 1-4 shows the technology life cycle (TLC) based on the patent and assignee number. The TLC can be used to analyze the technological development phase. There are four phases: “research and development phase”, “ascent phase”, “maturity phase”, and “decline phase”. Figure 1-5 is the technology life cycle drawn from the power wheelchair patents in USPTO. Comparing Figure 1-5 with Figure 1-4, the technological development of the power wheelchair is in the decline phase.

Figure 1-4. Technology life cycle (TLC) of the patent development

Figure 1-5. Technology life cycle of the United States

International Patent Classification (IPC) is used to classify the patents according to different technologies. Table 1-3 lists the top five IPCs among all patents in power wheelchairs. Note that a patent may belongs to more than one IPC. From this IPC ranking, technology development of power wheelchair focuses on motors, parts and accessories, and facilitating the access of power wheelchairs.

Table 1-3. International Patent Classification of the power wheelchair





Chairs or personal conveyances specially adapted for patients or disabled persons, e.g. wheelchairs



Chairs or personal conveyances specially adapted for patients or disabled persons, e.g. wheelchairs / Motor-driven



Chairs or personal conveyances specially adapted for patients or disabled persons, e.g. wheelchairs / Parts, details or accessories



Ambulance aspects of vehicles; Vehicles with special provisions for transporting patients or disabled persons, or their personal conveyances, e.g. for facilitating access of, or for loading, wheelchairs



Transfer using ramps, lifts or the like


Table 1-3 is the top five citations of power wheelchair patents. The citation number can represent the relative importance of the patent. In this list, U.S. Patent 5,435,404 describes a suspension mechanism to enhance the stability and to reduce the size of the power wheelchair, as shown in Figure 1-6. U.S. Patent 5,575,348 also describes a power wheelchair suspension system which was no anti-tip caster wheels. The adjustable center of gravity mechanism also provided the user an adjustable seat and seatback. U.S. Patent 4,634,941 describes a power wheelchair control method which is pertained to feedback speed control. U.S. Patent 4,634,941 describes a six-wheel power wheelchair chassis to increase the maneuverability.

Table 1-3. Citations of power wheelchair patents

U.S. Patent number

Citation number


Application date

Publish date



Powered mobility chair for individual





Electric wheelchair with improved control circuit





Power-assisted wheelchair





Wheeled chassis





Powered wheelchair with adjustable center of gravity and independent suspension



Figure 1-6. A suspension mechanism

In addition to develop suspensions, control methods, and chassis of wheelchair, Staodyn, Inc. designes a power-assisted wheelchair to help the user propel the wheelchair himself / herself. The power-assist is provided by an electrical power unit that includes a motor for driving each main wheel of the manual wheelchair, as shown in Figure 1-7. The electrical power unit is removable so that the user can remove the unit and fold the manual wheelchair. Following this new design concept, Yamaha develops some power-assisted wheelchair by using a light and small motor, recently. Figure 1-8 is the Yamaha’s product of power-assisted wheelchair, JWII.

Figure 1-7. Power-assist wheelchair and electrical power unit

Figure 1-8. Power-assist wheelchair Yamaha JWII

1.4      Robotic wheelchair

Miller and Slack [1995] first used the term “robotic wheelchair”. 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. Simpson [2005] reviewed many recent studies on the development of “smart wheelchairs” that can perform some autonomous behaviors for mobility assistance, such as obstacle avoidance and navigation.

Automatic navigation is one of the major research issues in robotic wheelchair, since mobility assistance is the fundamental function of a wheelchair. Prassler et al. [2001] developed robotic wheelchair MAid (Mobility Aid for Elderly and Disabled People), as shown in Figure 1-9, to support and transport users with limited motor skills. The system provides functions ranging from fully autonomous navigation in an unknown crowded environment such as a railway station to partially autonomous local maneuvers such as passing through narrow doorways. Cruz et al. [2011] proposed a landmark based navigation system and an obstacle avoidance strategy for robotic wheelchairs. In their system, every landmark was composed of a segment of metallic path and a RFID tag. All landmarks were detected by inductive sensors and identified by a RFID reader.


Figure 1-9. Robotic wheelchair MAid

Man-machine collaborative control scheme, which addresses how a human and a robot collaborate to perform tasks and to achieve goals [Fong et al., 1999], is another important issue of the research in robotic wheelchairs [Katsura and Ohnishi, 2004; Galindo et al., 2006a; Holzapfel, 2008; Urdiales et al., 2011; 2010; Braga et al., 2011]. There is no supervisor in the collaborative control scheme, the user and the robotic wheelchair exchange information and resolve differences together. The robotic wheelchair is more like a partner to help the user find good solutions when there are problems [Fong, 1999]. Galindo et al. [2006b] developed a robotic wheelchair SENA to facilitate mobility of the disable people and older adults. 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.

1.5      Purpose of this research

This thesis presents the development of the “intelligent Robotic Wheelchair” (iRW), which intends to redefine the wheelchair as the center of mobility, daily living, and healthcare of older adults. Figure 1-10 illustrates the overall design concept of the iRW. The core of the iRW is a collaborative control designed specifically for older adults’ declining abilities in perception, motor control, and cognition. Technically, the iRW is composed of an omni-directional vehicle, a multiple degree-of-freedom (DOF) seat adjustment mechanism, and an information/communication module. The iRW is intended to enhance the usability of wheelchair to increase the independent living and social participation for the older adult, and therefore improve their quality of life.

Figure 1-10. Design concept of the iRW

Figure 1-11 is the current prototype of the iRW. The omni-directional vehicle of the iRW uses four Mecanum wheels to facilitate movement in all directions, including moving sideways, and with zero radius of rotation. The iRW requires much less space than do general electric wheelchairs in turning and sideway maneuvers. Based on this omni-directional vehicle, mobility assistance functions are design for three different operators: the wheelchair user, caregivers, and the iRW itself performing autonomous behaviors. Five operation modes, all mutually exclusive, are developed: obstacle avoidance, joystick mode, handlebar mode, teleoperation, and indoor navigation. Man-machine collaborative control is reflected in the assignment of priorities to the three operators.

The multiple-DOF seat adjustment mechanism is intended to increase the independence of the wheelchair user, while maintaining a concise structure, light weight, and intuitive control interface. This four-axis Stewart platform is capable of the motions of heaving, pitching, and swaying to provide seat elevation, tilt-in-space, and sideways movement functions. The geometry and types of joints of this mechanism are carefully arranged so that only one actuator needs to be controlled, enabling the wheelchair user to adjust the seat by simply pressing a button. The seat is also equipped with soft pressure-sensing units to provide pressure management by adjusting the seat mechanism once continuous and concentrated pressure is detected.

The information/communication module is in the form of an App running on a tablet mounted on the armrest of the iRW. Connected to blood pressure and blood glucose meters, the tablet serves as the platform for tele-healthcare management. Through caring messages, timely reminders, and photos sent by remote family members and caregivers, the tablet is also the communication channel for the wheelchair user [Chen at al., 2011]. This thesis focuses on the technical development and user evaluation of the mobility assistance functions and the multiple-DOF seat adjustment mechanism of the iRW.

Figure 1-11. Current prototype of the iRW

The thesis is organized as follows. Chapter 2 describes the mobility assistance design of the iRW. Chapter 3 presents the technological details of the indoor navigation function of mobility assistance design. The seat adjustment design based on the Stewart platform is then introduced in Chapter 4. Chapter 5 describes the usability assessment of the iRW. Finally , Chapter 6 concludes this thesis.


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