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Authors: Po-Er Hsu, Yeh-Liang Hsu, Jun-Ming Lu, Jerry, J.-H. Tsai, Yi-Shin Chen (2011-05-21); recommended: Yeh-Liang Hsu (2011-05-21).
Note: This paper is presented in the “1st Asia Pacific eCare and TeleCare Congress,” June 16-19, 2011, Hong Kong, China.

iRW: An Intelligent Robotic Wheelchair Integrated with Advanced Robotic and Telehealth Solutions

Abstract

With the global trend of aging, there has been a growing demand for human-friendly wheelchairs as mobility aids. In addition to the enhanced mobility and more comfortable use, people also expect a wheelchair to be the center of everyday living and health care. This paper describes the development of an intelligent robotic wheelchair (iRW) which integrates with advanced robotic and telehealth solutions. While most technologies required are readily available, the emphasis in this research is to properly adapt and integrate these technologies into the iRW to make it human desirable and business viable.

Following the requests of senior users and professional caregivers, the design needs of the iRW were defined. Various technologies were reviewed for the possibility of meeting those needs. The iRW is composed of a moving vehicle, the sensing/control module and the information/communication module to provide mobility aids and supports for everyday living and healthcare. Integrated with Mecanum wheels, the sensing/control module and a simplified indoor navigation system, the senior user can freely control the wheelchair in all directions or let the wheelchair move from site to site automatically. Besides, the Stewart platform with reduced degree-of-freedom and the ergonomically designed seat integrated with pressure sensors enable relaxed sitting with dynamic postures, as well as lifting and transfer assistance. Moreover, the telehealth system in the form of a digital photo frame serves as the platform of health care management and the information channel between the wheelchair user and the family or caregivers.

By carefully adapting the robotic and telehealth solutions, the iRW realizes enhanced mobility, improved safety and comfort, better environmental control, enriched information exchange, and stronger interpersonal communication. The iRW has good potential to help the senior user interact with the home environment more effectively and actively, while improving the quality of life of the elderly people.

Keyword: robotic wheelchair, indoor navigation, telehealth

1.       Introduction

Lower limb disability is one of the most common disabilities among elders, and wheelchair is the most common and important mobility aids. Electrical wheelchair is an option for users who cannot move themselves on a wheelchair. However, operating an electrical wheelchair is often difficult for users. Fehr et al. [2000] 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.

In recent years, research in electrical wheelchairs has been emphasizing on how to implement the sensing and judgment capabilities commonly seen on robots, so that the wheelchairs can perform autonomous behaviors to a certain extent in order to improve its usability. Miller and Slack [1995] first used the term “robotic wheelchair” in their research. They applied various sensing and navigation technologies often used in robotics and built two prototypes of robotic wheelchairs, which were able to assist users to pass through narrow paths while avoiding 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. [2001] developed robotic wheelchair MAid (Mobility Aid for Elderly and Disabled People) to support and transport users with limited motion skills and to provide them with a certain amount of autonomy and independence.

Man-machine collaborative control scheme is another important issue in the research of the robotic wheelchair [Katsura and Ohnishi, 2004; Galindo et al., 2006a]. Galindo et al. [2006b] developed a robotic wheelchair SENA to facilitate mobility of the disable people and users. They considered completely autonomous performance of a mobile robot within non-controlled and dynamic environments is not possible yet, due to different reasons including environment uncertainty, sensor/software robustness, limited robotic abilities, etc. 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 [1998] 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. [2002] 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. [2004] combined the capability of the user and the robotic wheelchair to design the collaborative scheme to reduce the operational load for the user.

Observing the elderly people living in nursing home or in the home environment, the wheelchair is the place where they spend the most time in everyday living for many senior users. Mobility is one of the fundamental requirements of the quality of life to senior users. In addition to providing mobility assistance, the wheelchair should also integrate and satisfy the needs in everyday living, healthcare, and social participation.

With the global trend of aging, there has been a growing demand for human-friendly wheelchairs as mobility aids. In addition to the enhanced mobility and more comfortable use, people also expect a wheelchair to be the center of everyday living and health care. This paper describes the development of an intelligent robotic wheelchair (iRW) which integrates with advanced robotic and telehealth solutions. While most technologies required are readily available, the emphasis in this research is to properly adapt and integrate these technologies into the iRW to make it human desirable and business viable.

Section 2 of the paper describes the needs and design concept of the iRW. Section 3, 4, and 5 describe technologies to achieve the functions in mobility, everyday living, and health care of the iRW, with emphasis on the discussion on how technologies be best used to support the needs. Finally Section 6 concludes the paper.

2.       The needs and design concept of the iRW

The iRW intends to redefine the wheelchair as the center of mobility, everyday living and healthcare of the senior users, based on the technologies of robotic wheelchairs. Figure 1 describes the overall design concept of the iRW developed in this study. Centered on the needs of the 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 iRW is composed of a moving vehicle, a sensing/control module, and an information/communication module, to provide the senior users three types of functions: mobility, everyday living, and healthcare. The iRW is expected to assist the senior users to interact with the environment more effectively, including physical interaction, environmental control, information exchange, and most importantly, interpersonal communication. The final aim is to enhance independence and social participation, and to improve the quality of life of the senior users.

Figure 1. Design concept of the iRW

In addition to the technical development, the design process of the iRW focused on answering the question: “How can technology be best used to support the needs of the aging society?” Following the “Design Thinking” proposed by IDEO CEO Tim Brown (Figure 2), the development of the iRW continuously focused on the simultaneous consideration of “human desirable, business viable, and technology feasible”.

des-fea-via-small

Figure 2. Design thinking [IDEO (http://www.ideo.com) CEO Tim Brown]

Figure 3 is the fishbone diagram of technologies used in the iRW. The needs collected in interviews with 17 experts and professional caregivers and questionnaires from 403 senior users were classified into needs in mobility, healthcare and everyday living. To answer the major needs, an animation movie of the iRW was made to describe the application scenario of the iRW. The animation movie was also used to confirm with the experts and professional caregivers on the application scenario of the iRW. Technical functions to be achieved were then identified.

Figure 3. The fishbone diagram of technologies of the iRW.

After these technical functions were defined, various technologies were reviewed for the possibility of meeting those technical functions. At this stage, the major consideration is whether the technologies are “business viable” on the iRW, such as the cost, reliability, and usability of the technology. The detail of technologies selected is described in the following sections.

3.       Technologies for mobility functions of the iRW

The iRW is designed for home or nursing home use, to be used mostly indoor or short-distance outdoor (such as taking a walk in the garden). Referring to Figure 3, nimble maneuver is required for the iRW should be able to move freely in home and nursing home environments. Autonomous behaviors are needed to reduce the operating load of the senior users. Schemes of collaborative control also need to be developed to make the iRW more convenient and easy to operate.

Most electrical wheelchairs are two-wheel drive, and cannot move sideways. Figure 4 shows the Mecanum-wheeled vehicle of the iRW for nimble maneuver in all directions. The 4 Mecanum wheels and motors are installed at the corners of the chassis. The outer ring of every Mecanum wheel has free rollers, which make a 45 degree angle with the wheel’s axis. A joystick controller is used to control the iRW to move forward/backward, sway right/left, and spin clockwise/counter clockwise. Table 1 shows the specifications of Mecanum wheeled vehicle of the iRW. The maximum forward speed of the iRW is set at 3km/h, which is close to walking speed of human, and the maximum backward and sideways speed is set at 1.5km/h.

Figure 4. Mecanum wheeled of the iRW

Table 1. Specifications of the Mecanum wheels and motors of the iRW

Item

Specification

L×W×H

800×610×300 mm

Forward speed

3 km/h (Max)

Backward, sideways, clockwise/counter clockwise speed

1.5 km/h

Mecanum wheel

10 inch

Voltage/Current of the motor

24V/3 (A, Max)

C-LiFePO4 Battery

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

Indoor navigation can be achieved by processing the “received signal strength indicator (RSSI)” from a carefully-designed wireless sensor network. We chose not to use this technology in the iRW because it is too costly to be practical to achieve the required navigation accuracy. Instead, a semi-autonomous indoor navigation is implemented using the concept similar to the automated guided vehicles (AGV) to reduce the operation load of senior users.

AGV is a mature technology which can follow the physical guide-paths and have the intelligence to perform actions. Early the guide-paths of the AGV were installed in the floor, and hence, some variants installed the guide-paths on the ceiling to reduce the floor modification and cost [Vis, 2006]. For the iRW, QR code (Quick Response code) landmarks are deployed on the ceilings as “virtual AGV track”. When the iRW is steered under the track, the camera on the iRW will capture and recognize the QR code. Subsequently, the information conveyed by the QR code can be interpreted so that the iRW follows the virtual AGV track to move to the specific stop, such as bed room, living room, kitchen, etc. The user then takes over to steer the iRW to the required location.

This semi-autonomous indoor navigation system aims to reduce the operating load of steering the iRW manually on a long path. It is inexpensive, flexible, and easy to implement. The QR code is a two-dimensional bar code system commonly used in various applications. Public domain software programs are available 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.

The camera installed on the iRW can also be used for tele-operation. Remote operator can help move the iRW when necessary. In addition, low-cost and reliable ultrasonic range-finding sensors are used to perform obstacle avoidance function 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 senior user. Advanced control interface such as voice control was considered in the development process. But we decided to stick with the traditional joystick and buttons to reduce the complexity of the control.

4.       Technologies for everyday living functions of the iRW

Referring to Figure 3, multiple degree-of-freedom (DOF) seat adjustment is required in the iRW to provide transfer assist and comfortable seating positions for various situations encountered in everyday living. The seat itself serves as the interface between the senior user and the iRW. Ergonomic seat design is also important for the senior user to sit on the iRW for a long period every day.

Stewart platform is a parallel robot which has advantages of high rigidity and high positioning accuracy comparing with the serial structure robots. The Stewart platform (Figure 5) is composed of a fixed base, a movable platform, and 6 variable length actuators connecting the fixed base and the movable platform. This is universal-prismatic-spherical mechanism has 6 DOFs, including heave, surge, sway, yaw, pitch, and roll.

On the iRW, a 4-axis Stewart platform is implemented to provide multiple DOF seat adjustment. Figure 6 shows the design concept of the seat adjustment mechanism integrating with the Macanum-wheeled vehicle of the iRW. As shown in Figure 6, the seat plate is the movable plate of the Stewart platform, and the L-shape structure of the chassis is the fixed plate of the Stewart platform. The number of variable length actuators is reduced from 6 to 4 because only 4 degrees of freedom, heave, surge, sway and pitch, are required for height adjustment, transfer assist, and sit-stand assist. Note that two variable length actuators are in tension and the other two are in compression. These variable length actuators also serve as structural members of the iRW. In order to increase the stability and safety, locking mechanism is designed to constrain the uncontrolled DOF, surge and sway of the seat. Table 2 shows specifications of the seat adjustment.

Figure 5. Stewart platform

Figure 6. 4-axis Stewart platform is implemented on the iRW

Table 2. Specifications of the seat adjustment mechanism

Item

Specification

Tensile force/ Thrust force/ Self-locking force of the variable length actuator

1200/1200/800 (Max, N)

Stroke of the variable length actuator

150 mm

Current of the variable length actuator

2.5 (A, Max)

Seat height adjustment range

460 ~ 345 mm

Seat sway adjustment range

150 mm

Seat pitch adjustment range

20° ~ -8°

A standard ergonomic seat design process was carried out to establish the dimensions and shape of the seat by referencing to the Anthropometric Data Book of people in Taiwan [Wang et al., 2002] and the human spine contour. However, in the prototyping stage, we decided to directly install a seat made by memory foam seat from an existing chair, considering the cost of fabricating a new seat. The memory foam can help relieve the body pressure for better comfort. The armrests are redesigned to be adjustable in height during transfer assist. Table 3 shows dimensions of the seat and armrests.

Table 3. Dimensions of the seat

Item

Specification

Item

Specification

Width of the seat

490 mm

Length of the seat

450 mm

Height of the seat back

525 mm

Height of the armrest

0 ~ 200 mm

Width of the armrest

100 mm

Length of the armrest

450 mm

5.       Technologies for the healthcare functions of the iRW

Referring to Figure 3, the iRW should provide a telehealth system with easy-to-wear, non-invasive devices for real time vital sign monitoring and long-term health care management for the senior users, their family and caregivers. In addition, function of preventing pressure ulcer is also important for the senior users who sit on the iRW for a long period of time every day.

The home telehealth system of the iRW is in the form of a “Care Delivery Frame (CDF)” (Figure 7). By integrating the home telehealth system and the remote photo sharing function 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, weather information, and even commercial ads can be provided through the use of the CDF. The CDF software is running independently on a pad PC, which can be installed and separated from the iRW when the senior user leaves the iRW. The four main functions of the CDF are described below:

(1)     Home telehealth

The basic function of CDF is based on the Distributed Data Server (DDS) of the decentralized home telehealth system [Hsu, 2007]. All technical functions of a home telehealth system are built in the CDF. Currently the vital sign sensors that can be connected to the CDF include the sphygmomanometer, the blood glucose meter, and the oximeter (for real time vital sign monitoring).

(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)

“Smartpad” is implemented on the seat of the iRW to sense the pressure during the senior user sitting on the iRW. Smartpad is a soft, comfortable, washable and low-cost pressure sensing unit. The structure of Smartpad is the multi-layers architecture which is composed of elastic fabric, conductive fabric, and foam. There is a linear relationship between the pressure and the resistance of the sensor pressure is applied on SmartPad. If the pressure distribution does not change in a while, the iRW will adjust the seating position to relieve the pressure to prevent pressure ulcer by controlling the 4-axis Stewart platform.

6.       Conclusion

This paper describes the development of an intelligent robotic wheelchair intending to redefine the wheelchair as the center of mobility, everyday living and healthcare of the senior users, based on the technologies of robotic wheelchairs. In addition to the technical development, the design process of the iRW focused on answering the question: “How can technology be best used to support the needs of the aging society?”

Figure 8 shows the first and second lab prototypes of the iRW. The first prototype is for realization of the various functions. Currently the second prototype is under user evaluation. By carefully adapting the robotic and telehealth solutions, the iRW realizes enhanced mobility, improved safety and comfort, better environmental control, enriched information exchange, and stronger interpersonal communication. The iRW has good potential to help the senior user interact with the home environment more effectively and actively, while improving the quality of life of the elderly people.

     

Figure 8. The prototypes of the iRW

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