Spring 2020 Design Prompt Overview

The UF Nonlinear Controls and Robotics (NCR) Group requests the complete design and construction of human lift and support harnesses by UF’s MAE Capstone Design program. These devices will provide user defined partial-to-full body weight support while automatically adjusting their vertical height to compensate for movement by the participant. The resulting devices will be broadly applicable in a variety of rehabilitative applications for individuals with neuromuscular disorders (ND’s) resulting in lower extremity movement disorders.

These systems will provide automated body weight support above a pre-existing motorized functional electrical stimulation (FES) elliptical stepping machine. This assistive exercise benefits people with ND’s who suffer impaired movement because it builds leg muscle strength, increases bone density, betters cardiovascular health, and improves limb mobility.

Motorized FES elliptical trainers are popular rehabilitation devices because they coordinate movement by the lower and upper extremities in a (partial) weight bearing configuration. Such devices provide an essential segue therapy for participants that are not yet capable of treadmill or over-ground walking. Yet, a critical barrier to motorized FES elliptical trainer therapy is transitioning a vulnerable participant with compromised movement and balance capabilities into the trainer. While patient lift systems exist, they are not capable of suspending a person at heights suitable for elliptical machine training while also providing interactive variable weight support. Therefore, two key functions of our participant lift and support harness are to

• Lift participants from their wheelchair, transport them to the elliptical trainer, and safely suspended them above the trainer during exercise and FES stimulation; and
• Maintain a controllable weight offset so the participant need only support a fraction of their total body weight during rehabilitation exercise.

This second function presents an added challenge because of the uncertain variable vertical translation that occurs during elliptical exercise, eliminating the possibility of suspending participants at a fixed height. Therefore, a key attribute of our lift and support harness is active offset weight control despite the user’s continuous motion. Additional novel features differentiating the proposed system from others include:

• Real-time adjustment of offset weight while the participant is exercising to increase/decrease difficulty
• Capacity for the participant to adjust the exercise load themselves without the need to add/remove weights
• Interoperability of one lift and support harness with many trainer types, including treadmills and ellipticals
• Ability to dynamically differentiate weight born by the participant’s right or left legs, which is beneficial for people with movement disorders resulting in bilateral asymmetric gait.

Customer Needs

The following is a list of product requirements for the Lift and Support Harness provided by the UF NCR Group.

“Must Have” Requirements

3. Must fit inside a medical or rehabilitation facility, taking into consideration
   3. Clearance through doors (when assembled)
   4. Loadbearing capacity of floors
   5. Floor footprint (during assembly and when assembled)
   6. Ceiling height (when assembled)
4. If powered, runs from 120 VAC electricity from a standard wall outlet with 15-amp breaker capacity
5. Allows the user to stand and exercise on a standard elliptical machine without interfering with the elliptical machine’s operation.
6. Supports the full weight of the user up to the full capacity of the elliptical machine
7. All design margins have an acceptable factor of safety
8. Includes a fail-safe system to catch the user, preventing a fall should the primary system fail
9. The user is lifted from the wheelchair and placed on the elliptical trainer at safe and comfortable speeds.
10. The system will prevent the suspended user from swinging and/or hitting the elliptical trainer or the wheelchair during transfers to/from the wheelchair or elliptical.
11. Allows the user to translate unencumbered in the vertical direction during exercise
12. Prevents the user from losing balance in a sagittal (backward or forward) fall
13. Prevents the user from losing balance in a transverse (left or right) fall
14. Lifts the user from a seated position (e.g., a wheelchair) to fully suspended
15. Moves the fully suspended user from their original location over a standard elliptical trainer
16. Holds the user suspended over the elliptical trainer while they are being strapped into the trainer
17. Accommodates user body sizes ranging from a 5% female to a 95% male
18. Once user is attached to the elliptical trainer slowly transitions to preset offset weight
19. Allows user to select offset weight to any value between 0% and 100% of their body weight
20. Can be mounted from structural members in walls or ceilings or can sit on the floor.
21. Provides continuous user-defined offset weight support for the user while the user is exercising
22. Offset weight support feels continuous to the user despite the repeating periodic motion of their exercise
23. Must provide pre-set weight offset over the full vertical, horizontal, and transverse range of the user’s motion during exercise
24. Is programmable (i.e., control parameters can be changed, or a more complex control routine added in software)
25. Has an intuitive user interface
26. Prototype cost for materials cannot exceed $4,000
27. Includes an emergency shut-off that can be actuated by the user or a nearby trainer that safely stops all motion while fully supporting the user’s weight
28. Includes an automatic force-based safety limit shutoff that shuts down the device if either 1) a maximum force on the lift is exceeded or 2) the lift experiences an unexpected rise in force magnitude or direction [e.g., it gets caught on something during motion].
29. Has a visual indicator easily seen by the user and a nearby trainer that shows when the system is on, what mode it is functioning in, and how much user weight is being offset
30. Has an operational lifetime that exceeds by three times the operational lifetime of a standard elliptical trainer
31. FES stimulation pad electrical connections must be accessible
32. Overall footprint of lift system plus elliptical trainer cannot exceed 2.43 m X 3.05 m (8’ X 10’)
33. The system cannot use rails, tracks, or other guides permanently mounted to the floor

“Try To Have” Requirements

1. Must be transportable (disassembled) in the trunk of a personal vehicle
2. Must be moveable when disassembled by one person (e.g., using a hand truck)
3. Must be moveable when assembled by two people (e.g., by team lift)