Auto Access
Project undertaken in course year 2022-23 with Volkswagen
Project Goal
Develop a system to deliver persons utilizing manual wheelchairs safely into and out of an autonomous commercial transportation vehicle and secures the person and their wheelchair into the vehicle as necessary for riding said vehicle without additional intervention from a human operator.
Project Motivation
There are currently 2.7 million manual wheelchair users in the United States, and current solutions for wheelchair securement in commercial vehicles require driver assistance. However, as autonomous vehicle technology emerges, there may be no driver to assist passengers with securement. As autonomous vehicle technology emerges, assistance-free and wheelchair-accessible ingress, egress, and securement for these vehicles must be considered.
Background
Autonomous level 5 technology is expected to take off as soon as 2030 according to field experts. Since no human assistance will be available with these vehicles, ingress/egress and securement systems for users of mechanical wheelchairs must be integrated. Volkswagen is currently developing its own level 5 autonomous vehcile, the Sedric, which will allow manual wheelchair users to seamlessly and safely get to their destination in the future.
High Priority Requirements
Users can enter and exit vehicle without assitance from another human
Users can operate securement, release, and emergency release mechanisms without further assistance from another human
A first time user can enter, exit, and secure themselves in under 40 seconds
Mechanisms can be operated with one hand
User can comfortably and easily enter the vehicle without mechanism deformation
Mechanisms hold for all weather and driving conditions
Mechanism shall secure the wheelchair without damaging it
Ingress/egress must follow ADA standards
Ethical Considerations
Economic Accessibility - to address this, the majority of our designs use readily available parts in standard sizes to prevent custom manufacturing costs
Internal Biases - none of the team members in our group uses a wheelchair on a daily basis, so we used ADA requirements and research on inclusive design to shape our design choices
Environmental impact - By working within the automotive industry, we hav to confront the environmental impact of vehicles. We did our part to reduce our impact u using almost entirely recyclable or scrap materials
Solution
We developed a solution for entry, exit and securement of a manual wheelchair user in a vehicle without assistance from a driver. Our solution consists of a four-bar actuated ramp for entry and exit, and a spring-loaded mechanism that attaches to the frame of the wheelchair for securement.
4-bar ramp mechanism
Stowed and deployed view of the ramp mechanism. The included drawer slides grant the ramp low-profile storage with versatile motion.
Securement
System used for securement of wheelchair in to vehicle. The cutaway shows the mechanism itself, and the upper image shows the wheelchair secured by the system as it grip onto the frame
CAD image of 4-bar
CAD rendering of one side of hte ramp mechanism. The arms have been spaced in such a way to avoid intersections during motion while remaining highly concealable.
CAD image of securement tooth
Internal mechanism of the securement. A simple compression spring pushes the tooth outward, and the backstop and casing prevent the wheelchair movements both backwards and horizontally.
Tooth FEA
Stress analysis of lateral load case using PLA material property data.
Ramp friction testing
Coefficient of friction test setup, showing the wet ramp surface, wheelchair, and phone used for angle measurement
Ramp deflection testing
Measuring the deflection of the ramp under measured load. A calipers are used as a depth gage.
Ramp deflection FEA
Analysis of a subsection of the initial ramp design, showing max stress at the center. These resulted in a deflection under 1.5mm, meeting requirements.
Ramp deflecton vs applied force
The ramp deflected a maximum of 1.3mm with 900 lb load, below the desired 1.5mm, meeting requirements. Results also agreed well with predicted, showing an R-sq of 0.923
User trials time to secure
8 first-time users performed the securement process, moving the wheelchair up the ramp and into the securement. All users were below 40s threshold.
Other testing conducted
Force required to actuate securement
Securement strength tests under axial and lateral loads
Ramp slope, compliance with ADA size requirements
Student team
Future Work
Incorporate ramp edges so wheelchair rolls smoothly onto the ramp
Update design for manufacturing - replace welds with bolts on tooth casings to housing sheets
Develop system that holds securement system to the vehicle
Implement guides on floor to help guide user in the wheelchair to the securement
Motorizing four-bar linkages
User trials with all these updates