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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

Abstract

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, ergonomic design.

1.    Introduction

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. [1] 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. [2] 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 [3] 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. [4] 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 and independence.

Beside navigation, man-machine collaborative control scheme is another important issue of the research on robotic wheelchair [5, 6]. Galindo et al. [7] 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 [8] 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. [9] 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. [10] combined the capability of the user and the robotic wheelchair to design the collaborative scheme to reduce the operational load for the user.

Advanced 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.

This paper 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 iRW

The three main functions planned for the iRW are described as follows:

(1)  Mobility

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.

(3)  Healthcare

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).

Figure 2. Appearance planned for the iRW

The current 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.

3.    Mobility assistance

Mobility 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 wheelchair [http://car.pege.org/2006-ever-monaco/wheel-chair.htm]

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.

4.    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 seat:

(1)     Fitting the size

Since the 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 [10], 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.

(2)     Fitting the shape

The human 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.

Attempting 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 [10], 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 lumbar depth.

(3)     Supporting the weight

While 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.

(4)     Fitting the task

For varied 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.

Combining these 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

5.    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 or reversely.

Stewart platform 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

Considering adjustments 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

Function

Specification

Moving vehicle

forward speed

40cm/s

Backward/sway/rotate speed

10cm/s

Adjustment of comfort

Height of the seat

(Distance from the bottom of the seat to the ground)

Highest position: 498mm

Initial position: 433mm

Lowest position: 368mm

Adjustment of transfer assist

Stand assist

+15°(Pitch)

Back/hip pressure variability

+15°~ -15°(Pitch)

Transfer assist

130mm (left/right)

C-LiFePO4 Battery

24V, 9.6Ah, 402×133.5×71.5 (mm, L×W×H), 3.4 kg

6.    Home telehealth system

The home 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:

(1)     Home telehealth

The basic function of CDF is based on the Distributed Data Server (DDS) of the decentralized home telehealth system [11]. 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.

(2)     Remote photo sharing

CDF 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.

(3)     Caring messages and reminders

Children and caregivers can send warm caring messages and thoughtful reminders displayed on the CDF to the elderly.

(4)     Entertainment and life information

Collaborating 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)

7.    Conclusion

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

Reference

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[3]     Miller, D., Slack, M., 1995. “Design and testing of a low-cost robotic wheelchair prototype,” Autonomous Robots, v. 2, pp. 77-88.

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