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Mobility Assistive Technologies

Mobility impairment is the most prevalent type of disability in the United States and the third most common in Canada. Several diseases lead to mobility disability, and among those are injuries to the spinal cord, with a high prevalence of occurrence Spinal cord injury (SCI), has various consequences such as motor and/or sensory deficits, often including partial or complete impairment with walking. As a result, assistive technologies have been developed and used to help affected people maintain their independence and/or improve their functional mobility to perform activities of daily living. For example, wheelchairs, passive or active orthoses, crutches, canes, and walking frames are used to improve the mobility of people with disabilities. In our lab, we are specifically focused on the development of control strategies to improve the functionality of power-assisted wheelchairs and powered orthoses (exoskeletons).


Developing Control Strategies to Mitigate Injury after Falling Backward with a Lower Limb Exoskeleton

Powered lower limb exoskeletons (LLEs) are wearable robotic aids that provide mobility assistance for people with mobility impairments. Despite their advanced design, LLEs are still far from being effective assistive devices that can be used to perform activities of daily living. The main challenge in the operation of a LLE is to ensure that balance is maintained. However, maintaining an upright stance is not always achievable and regardless of the quality of user skill and training, inevitably falls will occur. Currently, there is no control strategy developed or implemented in LLEs that help reduce the user’s risk of injury in the case of an unexpected fall.

In this research, an optimization methodology was developed and used to create a safer strategy for exoskeletons falling backward in a simulation environment. Due to the data available regarding the biomechanics of human falls, the optimization methodology was first developed to study falls with simulation parameters characteristic of healthy people. The resulting optimal fall strategy in this study had similar kinematic and dynamic characteristics to the findings of previous studies on human falls. Rapid knee flexion at the onset of the fall, and knee extension prior to ground contact are examples of these characteristics. Following this, the optimization methodology was extended to include the characteristics of an exoskeleton. The results revealed that the hip impact velocity was reduced by 58% when the optimal fall strategy was employed compared to the case where the exoskeleton fell with locked joints. It was also shown that in both cases of optimal human and human-exoskeleton falls, the models contacted the ground with an upright trunk with a near-zero trunk angular velocity to avoid head impact. These results achieved the research goal of developing an effective safe fall control strategy. This strategy was then implemented in a prototype exoskeleton test device. The experimental results validated the simulation outcomes and support the feasibility of implementing this control strategy. Future studies are needed to further examine the effectiveness of applying this strategy in an actual LLE.

Principal Investigators

Dr. Jaimie Borisoff, Research Director at BCIT, Principle Investigator at ICORD
Dr. Mike Van der Loos, Associate Professor, Department of Mechanical Engineering, UBC

Researchers

Mahsa Khalili

Collaborators

Dr. Ian Mitchell, Professor, Computer Science Department, UBC


Implementation of Safe Fall Control Strategies in Half-Scale Lower Limb Exoskeleton Models

Our first exoskeleton prototype consisted of a model of a triple-link inverted pendulum and a control system, designed and fabricated by an undergraduate Engineering Physics student team at UBC (Jan-April 2016). The mechanical test setup characterized a half-plane and half-scale model of a human body. Three joints of the triple-link inverted pendulum replicated the motion of the hip, knee, and ankle joints. Similar to the three-link model of a human fall, the hip and knee joints of the inverted pendulum were actuated and the ankle was a passive joint. The hip and knee joint angles were read through the actuator’s encoder and the ankle joint angle was read by a potentiometer that was installed at the joint. The controller was programmed to start the safe fall control strategy once the ankle angle passed beyond a specified angle. Therefore, the ankle angle sensor was constantly monitored subsequent to the initialization of the hip and knee joints. When the ankle angle exceeded the specified limit, the position control strategy was activated to control the hip and knee joint angles throughout the fall.
Large deviations were observed between the experimental and optimal values of the joints angular velocity throughout the fall duration. This is mainly due to hardware and software limitations of this prototype.
To address the abovementioned issues and to further improve controller performance a second prototype was built by an undergraduate Mechanical Engineering student team at BCIT (Jan-April 2017). The second prototype includes a scaled and adjustable exoskeleton with the same actuation setup as the first prototype and will execute the fall routine, as well as a release mechanism to zero the system and initiate the fall. Currently, we are working on implementing the developed safe fall strategy in this prototype.

Capstone Teams

UBC, ENPH: Todd Darcie, Oliver Gadsby, Bryan Pawlina, Saman Shariat Jaffari

BCIT, MECH: Mila Karanovic, Victor Chen, Amin Askari

Past Interns and Volunteers

Jessica Bo (UBC, MECH), Carter Fang (UBC, MECH), Florian Denkmeier (MITACT Intern)


Evaluating the Personal Autonomy of Wheeled Mobility Assistive Device Users

Autonomy of wheeled mobility assistive device (WMAD) users has a direct impact on their life satisfaction and participation in life activities. Therefore, it is crucial to consider and address the autonomy-related needs and challenges of WMAD users. To achieve this goal, it is important to know the most influential contributing factors to autonomy and their importance to WMAD users. At the same time, it is crucial to recognize the impact of each factor on different users and in different contexts of device use (e.g., when performing different activities and in different environments). This study aims to identify and prioritize how certain features of WMADs, such as speed and maneuverability, influence the personal autonomy of users in different contexts.

This study will survey community-dwelling participants who independently use a manual wheelchair, power wheelchair or scooter at least some of the time. It will utilize an online survey examining the influence of 14 specific WMAD features on participation in five contexts. Contexts include mobility in the outdoor built environment, the natural environment, the indoor built environment, homes, and transportation. Quantitative data will be presented using descriptive statistics and open-ended questions will be analyzed using content analysis.

Principal Investigators

Dr. Jaimie Borisoff, Research Director at BCIT, Principle Investigator at ICORD
Ben Mortenson, Associate Professor, Department of Occupational Science & Occupational Therapy, UBC

Researchers

Mahsa Khalili
Chelsea Jonathan (MOT, UBC)
Nicole Hacking (MOT, UBC)


Developing Control Strategies to Improve the Performance of Power-Assisted Wheelchairs

The use of wheeled mobility assistive devices (WMADs) provides benefits and impose some restrictions on users that directly influence their autonomy. Currently, there is a need for a new generation of mobility assistive technologies that can provide a more balanced sense of autonomy for users to significantly improve their quality of life and life satisfaction. The identified gaps between autonomy-related needs of WMAD users and the solutions offered by existing devices can be reduced through a user-centered approach in conjunction with an autonomy-based design framework. Taking into account the advantages provided by power-assist devices, we hypothesize that adoption of a modular-based approach can further improve the individualized aspects of autonomy-related design components. This can potentially improve the autonomy-related factors in different contexts of mobility assistive device use. This hypothesis is supported by preliminary results of previous research, discussing the potential advantages of pushrim-activated power-assisted wheelchairs (PAPAWs) to improve the autonomy of both manual and power wheelchair users.

Despite the identified potential of PAPAWs to improve autonomy, the current design of existing power-assist devices hasn’t significantly changed the life satisfaction of users. Some of the challenges related to the use of PAPAWs are:

  • Coordinating the pushes on each wheel to achieve a smooth drive while wheeling on straight/circular roads or on different surfaces and terrains
  • Safety and controllability on steep declines
  • Stopping and reversing the wheeling direction
  • Design and functional characteristics of PAPAWs such as battery life and width and weight of the chair
  • User-device interaction such as assembling/disassembling the wheels
Our research objective to improve the autonomy of future power-assisted wheelchairs by developing adaptive-shared-control algorithms to improve user-device interaction and provide optimal assistance based on the need and intention of the use. Our second research objective is to use multiple add-ons that can be optimally integrated within mobility assistive devices to increase the accessibility of various terrains and surfaces.

Principal Investigators

Dr. Jaimie Borisoff, Research Director at BCIT, Principle Investigator at ICORD
Dr. Mike Van der Loos, Associate Professor, Department of Mechanical Engineering, UBC

Researchers

Mahsa Khalili

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