Team Peachy Keen:
Walker Renovation
Progress Report – Winter 2006
Adam Abshire
Natashia Baer
Sara Jennings
Paul Miller
Chelsea Stogsdill
Academic Advisor: Marshall Smith
Industry Advisor: Richard Klein
Sponsoring Company: Keen Mobility
ME 492
Executive Summary
There are two different walkers in the market today. A traditional walker and what is called a rollator. The traditional walker is comprised of grips to place your hands, and four adjustable legs for stability. Rollators add wheels for maneuverability, with the option to add a seat for sitting, a basket to hold personal items, and sometimes a cup holder for a beverage. Both are designed to fold onto themselves for easy storage.
A problem arises when users try to find a happy medium between the crude, traditional walker and the busy rollators. Users like the general shape of the rollators, but do not like how bulky they are. Users only like traditional walkers because they work. They provide mobility assistance but users complain that they are too boring and are in desperate need of an update. The blend of the traditional walker with the rollator is the goal for the Keen team walker renovation.
Table of Contents
Table of Contents 3
Introduction and Background information 4
Mission Statement 4
latest project planning document 5
final Product Design specifications 6
External Search 7-8
Internal Search 9-10
final design evaluation and selection 11
progress on detailed design 12-14
Conclusions and recommendations 15
Appendices 16-26
A: Project Detailed History 16
B: walker Use Learnings 17
C: Important Tips from Actual walker Users 18
D: Detailed Recent Progress: HOUSE OF QUALITY 19
E: Detailed External Search – Competing Solutions 20
F: Detailed Internal Search 21
G: Detailed Concept Evaluation 22-26
Introduction and Background Information
Walkers and rollators are essential for many people who have mobile challenges. The team is working with Keen Mobility to make activity a comfortable and enabling experience. Keen Mobility is an innovative company that manufactures and distributes medical devices that empower individuals by enabling them to be independent and mobile. Upon meeting with Keen, it became clear that there was a definite need for a walker renovation. The current walker, not to be confused with a rollator which commonly has wheels and a brake system, was not meeting the needs of the users. It was observed that the design was not ergonomically correct as it was hard for the user to maneuver, especially when the user had mobility impairments. The current rollator had the user bent over during use, putting unnecessary strain on their back. Just a few of the improved features of the renovated walker include many different height adjustments, more ergonomic for the user’s body, and even better looking!
There is a defined niche that the renovated walker fulfills among the various rollators and the original walker. The renovated walker will combine the aesthetic qualities of the rollators and the simplicity of use of the original walker.
Mission Statement
This team’s mission is to design and produce a more ergonomic walker that is adaptable to various customer needs. The walker is to be completed by June 2006 and will fulfill the needs of the elderly and those with mobility impairments. The constraints include being lightweight, inexpensive and incorporate Keen Mobility guidelines.
Latest Project Planning Document
An outline of the walker project with its deadlines is shown below. The graph is shown in monthly segments, with each block demonstrating a week. The blue blocks are objectives completed, and the green blocks are objectives currently in progress. A budget has been assigned to the project, with a grant from the National Collegiate Inventors & Innovators Alliance. A total of $4000 has been allocated for design, engineering and prototyping. By June 2006, a prototype will be created and the design with all analyses will be finalized.
Figure 1: Project plan
Final Product Design Specifications
The Product Design Specifications were determined by examining the results of the internal and external searches for customer needs. Many ideas were considered. Ultimately, after many meetings and revisions, the following criteria were determined to be the most critical to the design:
Ø Ease of Use
o Must be easy to fold, adjust easily to the user’s environment, and easily maneuverable.
Ø Safety
o Must be able to support the weight of the user without deflection, and the wheels must be a large enough diameter (5 inches) so that they will not get stuck in grates, cracks, etc..
Ø Ergonomic
o Will have ergonomic handles and shocks to increase comfort for long durations of use.
Ø Size & Shape
o Must be lightweight (under 10 lbs) and will have a 2” offset for the back feet to accommodate users with a wider gait.
Ø Cost
o Should be affordable to users with or without medical coverage (< $100).
Ø Aesthetics
o Will have various color options and sleek lines.
Ø Maintenance
o Will be easy to maintain with minimal upkeep.
External Search
An external search was conducted to find information concerning competing solutions, product related research, and design methods. There are many products in the medical industry, and in the walker-rollator division, various designs and accessories are available. Walkers are typically rigid, lightweight and rather ambulatory. Rollators are commonly bulky, with wheels, brakes and a seat, and on the expensive side. The walker renovation aim is to revise and implement the best features of each.
Walker Comparable
One product for comparison is the Invacare 6291A walker, shown in Figure 1. It follows the generic design of a walker, with legs folding in against the crossbar, with 6” height extensions. This particular walker weighs 5.5 pounds and costs $117. The features chosen to build upon were the lightweight Aluminum frame, extending legs, less expensive price, and the minimization of accessories.
Figure 2: Invacare 6291A
Rollator Comparable #1
The second comparable is the Invacare Rollator, shown in Figure 2. Its characteristics consist of 7” wheels, hand brakes, a seat, and a weight of 22 pounds. This rollator costs $514, which provided an extreme upper limit price. This rollator is difficult to fold, and barely fit in a car trunk. This also provided an extreme upper limit, with the goal of much smaller folded dimensions. The features taken from the Invacare Rollator were the comfort and long duration usage, its ergonomic handles, and provided opportunities to analyze characteristics we do not want, mainly heavy weight, high price and bad folding capabilities. Figure 3: Invacare Rollator
Rollator Comparable #2
The last design investigated in the external search is the Nova Cruiser Delight, shown in Figure 3. This rollator had an improved weight, 15.5 pounds, and improved price, $234. But again, the walker redesign will aim to exceed these features. This rollator uses 5” wheels, ergonomic handles, and telescoping extensions in the height, all characteristics to be improved upon in the redesign.
Figure 4: Nova Cruiser Delight
The walker-rollator industry has several needs not being met. There is currently no product in the 275-300 pound weight capacity range, which is one target for the redesign. Another current problem is the usage of tennis balls for feet. This feature will be greatly improved upon in the walker renovation. By combining the lightweight, inexpensive characteristics of a walker, with the comfortable, ergonomic, sleek features of a rollator, a new, valuable product will become available.
Internal Search
The team considered a number of rough designs that would satisfy the adjustability and foldability requirements. These proposed designs were rejected for a variety of reasons. Three ideas that showed early promise are presented here.
Tripod
This design would have featured a three footed walker with a lockable pivot located at the front wheel. Simply changing the angle of the arms would have allowed for changes in the width of the walker in a manner similar to the opening or closing of a giant pair of garden shears. The same mechanism could be used to fold the walker for storage. One problem was that if the arms change angle then so do the handles. That would have presented ergonomic difficulties for a person trying to grip those handles at an awkward angle. The proposed solution would have been some compensating angle adjustment located near the handles but that introduced complications and simplicity was one of the real appeals of Figure 5: Tripod
this design. A further, more serious problem was that tripod arrangements are less stable platforms for people relying on a walker for stability.
Stroller
The idea behind this design was to have both the cross-link and side arms supported by means of criss-crossing bars. The folding mechanism would be analogous to that of an umbrella stroller or a portable lawn chair. Adjustability would be achieved by providing intermediate stops so that the folding process could be done to any preset distance. The main down side to this design came from input provided from the nursing facility that the team Figure 6: Stroller
visited when conducting the external search. The care providers interviewed requested that nooks and crannies be kept to a minimum to make cleaning as easy as possible. They further noted that some of their clients were prone to getting food particles and other biological materials stuck into crevices, which posed a possible health risk. The stroller design would have introduced as many as seven open hinges and six sliders (or possibly slots), all of which provided potential for contamination.
Shopping Cart
The motivation behind this design was to get the supporting frame out of the way of a person’s feet so that they could walk freely. An added benefit would be that the user would have a mostly unobscured view and would be more able to minimize the mental awareness that they are using a mobility assistance device. There were two main reasons why this design was not pursued. First, it does little to facilitate the desired goals of adjustability and fold-ability in and of itself. Second, and more inconvenient, the location of the handles and feet virtually insures that the user would be off balance. Figure 7: Shopping cart
The center of gravity would necessarily be too far forward and people that required a more stable platform would be unable to comfortable use the device.
Final Design Evaluation and Selection
Many concepts for the features of the walker renovation were generated by the team and the advising company. Three existing products were used for the external search, and three internal designs were created, leading to the final design concept. In the design matrix shown below, evaluations of the features were used to compare each model. A short summary of each internal design is listed as well, with a complete, detailed description of each shown in Appendices H & I. The fact that the final design has a score of zero, compared with the other designs that had negatives scores, demonstrates that the final design exceeds its comparables.
Figure 8: Design Matrix
Figure 8: Design Matrix
(1) Tripod Design: Unstable and uncomfortable for user, first concept generated.
(2) Stroller Design: Excellent foldability, but did not provide a width extension.
(3) Shopping Cart Design: Unstable and not ergonomic.
Progress on Detailed Design
Many elements of the walker had to be revisited. The legs, feet, appeal, wheels, design results from finite element analysis, and the handles were all looked at again, once the initial designs exposed their flaws.
Keen Mobility insisted on implementing dampers, which they have previously designed, into the legs of the walker to alleviate common shock that might be applied to the body that is associated with operation of a walker. At first, they wanted all four legs to have dampers but were later found to create an unacceptable amount of instability. Finally, dampers in the front two legs were agreed upon. Figure 9: Internal Damper
The feet on most walkers are flat on the bottom. So, flat-bottomed feet were applied to the walker. Upon further research, the flat-bottomed feet caused more problems than they solved. Flat-bottomed feet created a lot of friction forcing the user to push rather robustly just to move, a lot of debris collects easily with flat-bottomed feet, and most surfaces are not perfectly Figure 10: Flat flat for the feet to work their best. A common, simple bottom foot fix is done by placing a modified tennis ball over the feet. The tennis balls reduce friction, and because of their spherical shape, operate well on most surfaces. Therefore, spherical-bottomed feet with a felt material replace the flat-bottomed feet.
Figure 11: Spherical bottom foot
A printed model of the walker was shown to Keen Mobility’s designers. The walker was very crude in appearance. The model consisted of many straight sections of tubing and small radius bends. This model is shown in Figure 12. Keen Mobility’s designers insisted on developing a “sexier” walker. The walker was described as cold, ambulatory, resembling a wheelchair, and needing to be more European in appearance.
The many straight sections of tubing and small radius bends were abandoned. However, the overall dimensions remained unchanged, the handles remain in their same places, and the legs created the same footprint as before. More graceful bends were applied to the walker as shown in Figure 13, to achieve the Figure 12: Ambulatory desired appearance.
version of the walker
Figure 13: Revised “sexy” version
Initially, the front wheels were fixed and were not free to rotate. The front wheels need to rotate freely to allow for easy maneuverability and steering. A simple change to casters in the front two wheels was applied to the walker.
Finite element analysis was applied to the walker and an unacceptable amount of stress and displacement was found. With 2024 T6 aluminum, a tube size of 1.0 inch OD and 0.125 inch wall thickness, a resultant Von Mises stress of 9.0 kpsi was found, and a displacement of 0.4 inch at the end of the handle where 150 pounds was applied. Assuming a 300 pound person, a safety factor of 4.78 was calculated. These results are in the ballpark of being acceptable but are still in need of further refinement. Several combinations of tube sizing and aluminum are currently being tested, and are still being formulated to arrive at the best possible solution.