Transfer Device Project | Isidora Mack's site

Reimagining Independent Transfers in the Home

This device is a compact lift system that enables wheel chair users by standing and pivoting to another location independently. This project was conducted over three months and sponsored by Elevated LLC who submitted for patent.

A project by Isidora Mack, Isabella Kemling, Rebekah Gatz, and Mathew Brown. University of Minnesota, 2023.

SKILLS DEVELOPED

Led user interviews with PTs and OTs to define biomechanical requirements
Designed and fabricated lifting subsystem
Modeled 4-bar linkage to determine actuator force requirements
Specified actuator capable of 1762 lb peak force

BACKGROUND

Existing Transfer Devices

Hoyer Lift

Sera Steady

EZ Stand

Research

In observing the process of how a person naturally stands, wefound that:

when standing up, an individual leans forward to center their weight over their feet and
they then push upward with their legs to rise. The device will need to move with this motion to ensure balance.

Interviews were conducted with physical therapists, occupational therapists, and the target user group on best practices for assisting with standing and pivoting. User needs include:

The ability to complete transfer process without straining/pulling on the shoulders
Balance and stability throughout the process.
A device that adapts to the natural standing and pivoting motions

Standing

Pivoting

Diagram showing how a caregiver helps an individual transfer using a gait belt

Problem Statement

For many wheelchair users, the most dangerous moment of the day isn't mobility, it’s transfer. Moving from a wheelchair to a toilet, bed, or chair often requires a caregiver. Existing lift systems are large, expensive, and typically require a second person to operate them. For users who are otherwise independent, this single dependency can determine whether they are able to live alone. The goal was to design an affordable, compact device that would allow a user to safely transfer from wheelchair to commode independently within the spatial constraints of a home bathroom.

This was not just a lifting problem.
It was a biomechanics, stability, footprint, and usability problem.

Frames from a video of someone standing. Insights are that the user leans forward, then begins rising and a shin rest is needed to prevent tipping forward.

Key Design Constraints

The system had to:

Complete connection and transfer in under 5 minutes
Supports a 50% of the weight of a user (up to 300 lb)
Powered via standard 15A wall outlet
Lifting the user from the trunk not the arms to prevent injury
Allow donning and doffing without obstruction

IDEATION

Rough sketches of some initial ideas and sources of inspiration for potential designs.

A Pugh Matrix (below) was used to evaluate and narrow down lift mechanisms, considering factors such as cost, power density, feasibility, safety, and overall viability. A hydraulic / linear-electric actuator configuration with a 4-bar mechanism provided the best balance of force capacity, compactness, and stability.

DESIGN

Free body diagram/4 bar

Dimensions for finding actuator specs

Actuator Specifications

Physical prototyping was invaluable for designing the lifting mechanism; I used PVC pipes to roughly determine the lift arm dimensions. The handle height should feel comfortable, and the gait belt attached to the arm should pull upward and slightly forward.

The first sketch below illustrates the lifting system as a 4-bar mechanism as well as a free body diagram. The primary forces include actuation force and the user’s weight acting at point A.

The other sketch shows the distance of each force from the pivot point and distance that point A moves vertically. Using this information, the minimum specifications for an actuator were determined.

Stroke Length: 4.8 inches

Required Actuator Force (statics): 750.3 lbs

Required Actuator Force (acceleration): 1762 lbs

First Design

Our first prototype design revealed several issues:

Footprint was too large for standard bathrooms
Gait belt attachment was positioned too close to the user’s face
Manufacturing complexity was high
Stability conflicted with portability
Shin rest should be contoured to around the legs to increase support

A major design tension emerged: Modularity vs. stability. Making the device easily disassemblable risked structural rigidity during lift. We prioritized structural integrity in the final configuration.

FINAL DESIGN

The final design features lockable, kick down wheels for simple transport, a smaller footprint, a 2-point attachment system to support the user, and an arm that angles more upward to pull vertically. The controls are located in the middle of the handle where the user can easily operate with their thumb. The overall design is meant to look aesthetically sleek. The clients were happy with this design and submitted it for patent (patent # US-20240358570-A1).

Future Improvements

Further improvement of this design would include user testing with the target demographic to collect feedback. The UI would also need to be improved so that even those without fine motor skills can easily control the device. This beta prototype would need to be scaled for distribution through designing for manufacturing. Finally, stability could be improved throughout the product to reliably lift a user up to 300lbs.