• Anti-tip bar leg attached to a collar fitted with side plates with guiding grooves designed to provide stopping points to the tip system

• Addition of copper springs to solenoid system will allow the solenoid to return to the extended state when de-energized.

• A collar was designed to attach the anti-tip system to the wheelchair.

• Leg length determined by measuring the distance between the wheelchair axel and the ground while maintaining an angle designed to keep the tracking wheel flush against the ground at all times.

• Aluminum side plates are attached to the sides of the collar. Each plate has a custom designed groove through which the solenoid pins will travel.

• A 90 degree torsion spring of 42 in-lb force was attached to the anti-tip system via the shoulder bolt to provide resistance to the user and to bring the system back to the ground after wheeling off a curb.

• Solenoids are attached to U-brackets bolted to the anti-tip leg.

• Tipping measurements made and traced on side plates to determine slit locations for standard and hill settings. Side plate slits cut accordingly.

• Stress/strain and maneuverability tests performed to ensure safety and proper functionality of design. 

There are 3 settings:

• For standard setting: The solenoid associated with the larger groove will be in the extended position. The other solenoid will be retracted and disabled. This allows for a wide rage of motion for the leg while still adding support during the wheelie position

• For a hill: Both solenoids will be in the extended position. The solenoid associated with the smaller groove is the more important one for this setting as it limits the range of motion for added support on a hill

• For a curb: Both solenoids will be in the retracted state. This configuration allows for the leg to extend 90 degrees to enable the user to clear a curb of any height.

Smart Anti-Tip System for Manual WheelchairNick Burjek1, Andrew Dawson2, Austin Dirks1, Katie Gallup1, Harrison Lamons1

Advisor:Dr. Mark Richter – MAX mobility, Nashville, TN

Department of Biomedical Engineering1, Department of Mechanical Engineering2, Vanderbilt University, Nashville, TN

Background

Project Goals & Requirements

Safety Statistics

Design

Safety and Stress Analysis

Conclusion

Acknowledgements

Future Considerations

The current prototype meets our project requirements and goals in that it does not inhibit movement, allows the user a sense of security, and provides the user with a safe alternative to the current anti-tip devices on the market. Once testing of the device is complete, we can move into a larger market segment. The anti-tip device developed is fully functional and can be attached to any wheelchair provided the right collar dimensions. The current profit estimates per chair manufactured is $147.29, but varies based on the number of chairs produced in bulk. The success of the device in latter stages will depend on simplifying the design to reduce manufacturing costs and consequently reduce the end cost to the user as well as provide reliability and safety for the future.

Russell Rodriguez – MAX Mobility

• Solenoid pins are mounted on both sides of the leg facing opposite directions to provide the 3 settings: standard use, hill mode, and curb mode

• One side plate will have a larger slit to allow greater range of motion of the leg while the other will have a smaller slit to restrict the range of motion

The success of the initial and secondary designs is encouraging for the future development of the anti-tip device. While the device meets all project requirements, it may be simplified in the future to reduce cost and increase product practicality and capacity to be re-produced on the large-scale. Any manufacturing and redesign of the device will be handled by MAX Mobility.

Anti-Tip Device – Old vs. New

* Collar price estimated for bulk production. Collar price for one-time production was $225 for the cost of parts, specialization, and welding. Collar produced in bulk will raise profit margins for MAX Mobility or lower end cost to user.

Cost to Manufacture

Manual wheelchairs are traditionally outfitted with anti-tip bars; bars that protrude from the rear of the chair and prevent the user from flipping over.  The bars are very effective in preventing tips in situations such as inclines, drop-offs, and intentional wheelies.  However, while the traditional anti-tip bar is advantageous from a safety standpoint, it greatly hinders the mobility of the user.  The standard anti-tip bar may catch when moving on uneven terrain or off a curb.  It can also prevent the user from maneuvering in tight areas. Many beginner wheelchair users may feel unsafe and unstable in their wheelchair while trying to become comfortable with it. The problem remains however that these new users remove anti-tip mechanisms from their wheelchair because of hindered movement. Without these tip bars, a sense of security is lost. Therefore, our efforts are to develop an innovative anti-tip system that will maintain the functional safety of the current anti-tip bars but will not hinder the mobility of the user in performing common maneuvers and day-to-day obstacles.

• To develop a dynamic anti-tip support system for a manual wheelchair equipped with various settings depending on the user’s needs.

• The user shall have the ability to easily change the state of the tip bar via a toggle switch.

• The tip bar shall not hinder the movement of the user in any fashion.

• The system should allow the user to navigate hills, curbs, uneven terrain, perform controlled wheelies, and provide a sense of support.

• The system must allow the chair to be folded into the seat of a car.

• The system should be inexpensive and lightweight.

• In 2003 more than 100,000 wheelchair related injuries were treated in the ER

• Tipping and falling was the leading cause accounting for 65-80% of wheelchair injuries

• For children, who are often new, inexperienced wheelchair users, about 58% of these injuries were due to situations such as stairs, curbs, and ramps.

• These types of obstacles make wheelchair maneuvering difficult for new users who are not comfortable with engaging in a wheelie or tilting.

Current Device Function & Performance

Safety Features and Testing include the following:

• Should electrical components fail, wheelchair defaults to standard setting, preventing tipping

•Predicted battery life is 6 months with change recommended at least once per year to avoid failure

• The ultimate strength of the stainless steel pin = 75ksi > 15.8ksi

•The ultimate yield measured = 30 ksi >15.8 ksi

• U-brackets surrounding solenoid pins designed to restrict stress only to the pin.

Materials and Production Costs

Collar* 90.00

Solenoids 68.00

Lantern Battery 12.79

Toggle Switch 7.82

Torsion Springs 8.80

Shoulder Bolt 1.50

Wheel Castings 6.00

Hinge Mounts 7.80

Total Cost 202.71

Wholesale Cost 350.00

MSRP (End User Cost) 499.00

Total Profit 147.29

Over the past decade wheelchair injuries have drastically increased, almost doubling:

Target Market

Between 1.6 and 2.2 million Americans rely on wheelchairs for mobility. The target market for the device includes new users who are unfamiliar with the wheelie and other users who may be particularly concerned with safety such as children or elderly.

Old tip bars often impede user mobility and do not provide flexibility with varying terrains.

New design allows for 3 setting flexibility while maintaining within wheel parameters.