Lateral Transfer Assist Robot (LTAR): Development of a proof-of-concept prototype

1. Introduction

People with mobility disability often use a wheelchair as a means of transport. According to previous studies, 6.1% of American and 4.6% of Canadian elderly individuals use a wheelchair [1, 2]. Although a wheelchair is crucial for mobility, it has two main disadvantages, especially when using it at home.

First, wheelchairs are associated with issues related to transferring. Numerous accidents occur during transfer to and from the wheelchair. Previous studies have reported that the frequency of transfers for wheelchair users is 14–18 times per day [3, 4]. A study revealed that for wheelchair users, approximately 55% of falls occurred during transfers, and 1.2% of falls resulted in fractures [5]. Most wheelchair-related injuries among those aged ⩾ 65 years occurred at home or in an institution or hospital [6]. In addition, transfer tasks cause musculoskeletal issues in those who assist with transfers as well as in wheelchair users themselves. Wheelchair users who have paraplegia rely heavily on the upper extremities for mobility and transfers, eventually resulting in structural or physiological joint degeneration [7]. Cross-sectional studies have reported that 60–100% of long-term wheelchair users experience shoulder pain [8, 9] that is mostly related to wheelchair-related activities [10]. In addition, assisting with daily transfers was reported as a risk factor for back injury in healthcare workers [11], and the annual prevalence of musculoskeletal injury in healthcare personnel has been reported to exceed 20% [12, 13].

Another disadvantage of wheelchair use in the home involves the difficulty in positioning the wheelchair appropriately for transfer within a narrow indoor space. This “space problem” is evident particularly in Asian countries. For example, in Japan, standard wheelchairs are constructed in accordance with the Japanese Industrial Standard (JIS) with a width of 630 mm or less and a minimum turning radius of 750 mm. However, the average size of a Japanese apartment is only approximately 45 square meters [14], and furniture, such as beds, dining tables, and home appliances, further restrict the movable space, while the average size of a living space in Europe and the United States is about 80 m 2 —1.8 times that in Japan. Regarding the transfer assistance device, a few devices have been developed [15, 16]. However, these devices are too large for home use, especially in Asian homes.

To overcome these two disadvantages of standard wheelchair use in homes, we developed a new robot, named the Lateral Transfer Assist Robot (LTAR). In this study, we described the design and key function of this newly developed robot, Furthermore, the effectiveness and usability of the robot was preliminary examined in healthy adults.

2. Methods

We developed the LTAR, which is the first robot that supports lateral transfers in a narrow space. We further preliminarily examined the effectiveness and usability in healthy adults. Using the LTAR, participants could perform lateral transfer and required significantly less vertical movement than when using the standard wheel chair, where participants are required to perform the getting-up transfer.

There have been reports on several transfer assist robots. Grindle et al. reported about the Robotic Assisted Transfer Device, which aids the transfer of people with disabilities to and from their electric powered wheelchair onto other surfaces. The device has a mechanical arm on the electric powered wheelchair and can be used for fully dependent transfers, where the person being transferred is in a sling and weight is completely on the robot [15]. Bostelman et al. reported the Home Lift, Position and Rehabilitation (HLPR) chair that provides mobility and lift for patient transfer. The HLPR chair was built on an off-the-shelf forklift. The forklift includes a U-frame base with two passive casters in the front and an actively steered and forward driven rear wheel. By turning the chair installed in the forklift by 180 degrees, it is possible for the passenger to turn to the transfer target without standing [16]. Development of these devices has been promoted in consideration of the risk of falls during transfer. However, the concept of these devices appears to be different from ours. These devices fully support the transferring, while our device helps the user’s transferring. From the view point of rehabilitation, staying as active as possible is very important for disabled people. Furthermore, these devices are too large for home use. Compared to those previously reported, the LTAR enables a safe lateral transfer and can be used in confined spaces including typical Asian apartment homes.

As established by Burkman et al. in the study of people who mainly use manual wheelchairs, the greatest concern was the size of the device limiting the places where the device could be used [22]. Because the mechanum wheels enable omnidirectional movement and save space, this feature is considered an effective space-saving approach and better for indoor use. The turning radius the JIS standard wheelchair is 750 mm, while the LTAR achieved a turning radius of 550 mm. This reduction in the turning radius is advantageous in moving within a narrow living spaces and corridors Japanese houses. Another advantage of this device is that it has sufficient speed for indoor use with a maximum velocity of 4.2 km/h, while suppressing the turning radius.

Some problems associated with this prototype include seat height adjustment and maneuvering with the joystick. Regarding seat height adjustment, although the current version can memorize three height patterns, it lacks versatility. The user cannot adjust the seat height well. Since the technology of a seat height position sensor has been developed, incorporation of this type of sensor should be considered for the next prototype. In addition, the questionnaire indicates that improvement in the easiness of operability is necessary. In particular, maneuvering with the three-axis joystick was difficult. The prototype’s joystick was 20 mm tall, and the size might be too difficult for elderly individuals to handle. Based on the results of the study, we are planning to improve the robot especially in terms of operability and demonstrate the practicality of the device by evaluating the ease of use for real wheelchair users.