Dr. K's Canes (Stanford University)

Harpreet K. Sangha

Abstract

Dr.  K, age 86, currently uses a four-wheeled walker, when walking and standing, to improve balance and stability. Though content with how well his walker performs, Dr. K is not impressed with its size and weight, and he desires a lightweight, compact substitute for his walker that is convenient to transport and store. Team Quadruped sought to improve an initial prototype (see below) by creating an adjustable angle between the forearm segment and the bottom member, forming better rests for and connections to Dr. K’s forearms, and allowing for varying height of the bottom member[1].

Different designs were considered for each feature and design feedback was solicited from mechanical engineer Doug Schwandt and occupational therapist (OT) Deborah T. Kenney. Ultimately, the team prototyped a lightweight design that provides Dr. K an improved forearm segment and the ability to adjust the angle between the top and bottom cane components.

Introduction

Figure 1

For balance and stability, while walking, standing, and negotiating stairs, Dr. K requires some external support. Dr. K, a Stanford University Professor Emeritus, currently uses a four-wheeled walker, similar to the one in figure 1. Dr. K’s usage of a four-wheeled walker indicates that he does not load-bear on the walker as  “[four-wheeled walkers] are best for higher functioning patients who walk long distances and require minimal weight bearing” (Van Hook). While his walker functions well, he is dissatisfied with its size and weight. In general, walkers are large and bulky and thus not ideal for storage and portability.

Though they are lightweight and occupy minimal space, canes do not resolve Dr. K’s issues with his walker. Canes assist in balance, but also double as load-bearing devices, a function not needed for Dr. K (Van Hook). Additionally, Dr. K finds traditional canes limiting. In using ordinary canes for balance, he loses function of his hands for other tasks as the canes require constant usage of both hands. In other words, the canes do not connect to the arms in an ideal way for Dr. K.

In summary, Dr. K seeks a streamlined mechanical solution that matches his four-wheeled walker in function, but, unlike his walker, is lightweight and compact.

Objective

Figure 2

In 2009, engineer Doug Schwandt created the first working prototype for “Dr. K’s Canes” using PVC tubing and fittings and tape (see Figure 2). Dr. K was extremely content with the general look, feel, and performance of the first prototype.

The objective of Team Quadruped was to build a second prototype that enhanced the initial prototype through three additional features. The desired features in order of decreasing priority were: i) angle between bottom member and the forearm segment (see Figure 3) should be adjustable so that Dr. K can find his optimal angle(s) through experimentation, ii) the forearm segment should better adapt to Dr. K’s forearms, and iii) the bottom member should be of adjustable height to allow Dr. K to use his canes to negotiate stairs and tailor the cane height to his personal comfort.

Design Criteria

A conversation with Dr. K revealed that since the device does not need to support his weight, a low-weight material, such as graphite composite, could be used for final construction. Additionally, he indicated that using the canes, he wants to mimic quadruped gait, which is a stable configuration for low speed walking.  Research shows that “normal quadruped crawl favored by most animals for very low speed locomotion” is the “unique optimum gait with maximum static stability” of “all the entire theoretically possible quadruped gait” (McGhee).  The fact that Dr. K sought a quadruped gait further illustrates why a design based on standard canes would not have been a good fit.

Figure 3

Dr. K desired the ability to adjust the angle between the bottom member that is in contact with the ground and the forearm segment (see Figure 3).  He felt that the ability to adjust the angle would enable him to customize the cane to his personal preferences. Doug Schwandt recommended that the angle adjust in increments of about 5° to a maximum angle of 35° from the “vertical”[2]. However, Team Quadruped conjectured that the option to surpass 35° or have negative angles (with respect to the “vertical”) could potentially assist with efficiently storing the device. In addition, Angelo Szychowski, a student in the Engineering 110 course, proposed that negative angles might also prove helpful in ascending or descending stairs. Professor Drew Nelson suggested just providing the option to select between two pre-determined angles. Since there wasn’t an analytical way to determine “the perfect angle”, the project resolved to provide Dr. K with the ability to change the angle by at least 35° with respect to the “vertical”, as indicated in figure 3.

Figure 4

The first prototype did not include a well working interface between Dr. K’s forearms and the corresponding segments on the canes (see Figure 4). While the Velcro straps on the first prototype hinted towards the desired function, the second iteration needed to designate the place for Dr. K to rest his forearms using cuffs or troughs as markers.  In addition, handgrips needed to be added to allow Dr. K to grip the canes.

To negotiate stairs and to customize to personal preferences, Dr. K wanted the length of member that is in contact with the ground to be adjustable. To climb stairs, he would decrease the height of his canes according to the height of the steps and likewise, to walk downstairs, he would increase the height. Dr. K also had not found an optimal cane height using the initial prototype and wanted to try different lengths before settling on the “default” height.

Design Considerations for Overall Configuration

Potential Design 1, whose profile is shown in figure 5, deviated from the initial prototype in its overall configuration. The bottom segment extended above the adjustable angle junction to provide a different place for the handgrip, and a trough was implemented as the forearm rest. The change in the location of the handgrip was motivated by a suggestion from Mike Norell, a prosthetist and orthotist. Norell felt that the position and orientation of the forearm on the initial prototype may provoke Carpal tunnel syndrome with extended usage.

Potential Design II, whose profile is shown in figure 6, retained the general overall configuration of the initial prototype, however it suggested a different arm placement. With this design, the forearm would rest on the slanted forearm segment, while the upper arm would lock into a cuff.

Potential Design III, profiled in figure 7, was similar to Potential Design I. However, in this design, the trough was placed on the forearm segment of the cane. This design also allowed for the usage of a cuff, similar to the one pictured in figure 7, instead of a trough.

Figure 5

Figure 6

Figure 7

Figure 8

In addition to rests for his forearms, Dr. K needed comfortable grips for his hands. The initial prototype used horizontal handgrips (see Figure 8). A vertical handgrip, similar to the one shown in Figure 8, was considered as an alternative for the horizontal handgrip.

The team experimented with a potential ratchet mechanism for changing the angle.  Though this mechanism would have allowed for multiple angles, it was difficult to operate in its original form as it required opening a dial lock using a Phillips screwdriver. If the team had been able to streamline the opening and closing mechanism, the ratchet mechanism would have been a strong candidate to use for providing angle adjustability.

Figure 9

Another design that was considered to allow different angles was based on the pin-and-hole mechanism that is often used on crutches to allow for varying height (see Figure 9). In this design, a special part called the Connector would be used to join the upper segment to the bottom segment, and the bottom segment could be locked into nine different positions on the Connector. In this design, each notch or position corresponded with a different angle measure between the bottom angle and the forearm segment.

To provide adjustability in height, the team considered borrowing the pin-and-hole mechanism that is found commonly on adjustable crutches, for it is a reliable, tested, and secure way to change height.

Methods

The team met with Deborah Kenney, an occupational therapist, and evaluated each design from an occupational therapy point-of-view. In short, Kenney felt that the adjustable angle and the varying height features presented enormous safety risks.  As an occupational therapist, she was not “ready to buy into” any of the proposed designs and for safety reasons, she warned against using moving parts in the canes.

However, Dave Jaffe, the course instructor, recommended that team continue exploring improvements to the initial design configuration, as recommended by Dr. K. In assembling the final design, the team consulted Doug Schwandt on the feasibility and practicality of each design, while keeping in mind the recommendations of Dr. K.

The overall configuration of the canes was carried over from the initial prototype primarily because Dr. K was extremely pleased with the initial configuration and did not express that as an area for improvement. Furthermore, a reason why a configuration change was originally proposed was because of a concern expressed about the arm orientation and position. However, Deborah Kenney did not express any concern about the arm placement and its orientation.

Based on Dr. K’s recommendations, a horizontal grip (as opposed to the vertical grip) and a cuff (as opposed to a trough) were implemented in the final design. Dr. K was satisfied with the horizontal grip on the initial prototype. One possible explanation for why he may have preferred a horizontal grip is because the resting or the natural orientation of one’s hand is horizontal. For personal reasons, Dr. K was biased towards a Canadian cuff.

The angle adjustability feature was one of the more difficult features to resolve for the cane design. Several factors were considered in choosing the pin-and-hole mechanism as the final mechanism. The pin-and-hole mechanism provides a secure joint, has an intuitive user interface, and the mechanism is mechanically simple.

Wherever possible, an effort to minimize the weight of the canes was made, e.g. through decreasing part thicknesses to reduce the amount of material used or integrating unrelated parts, such as the handgrip and the angle adjustable part.

Results

Figure 10

The final cane prototype is pictured in figure 10. Briefly, the prototype features an adjustable angle feature and an interface for Dr. K’s hands and forearms. Given its weight and structural integrity, 6061-T6 Aluminum was selected as the main material for construction.

The adjustable angle feature functions in increments of 10° and allows for a wide range of angles. With respect to the “vertical” indicated in figure 3, the angle can be changed by 40° in both directions. In other words, the angle between the forearm segment and the bottom segment has a maximum at 115° and a minimum at 40°.

But, with assistance, Dr. K is able to use the current prototype to experiment with various angles. Preliminary testing showed that he appreciated having the ability to change the angle and he preferred narrower angles. It appears that further, extensive testing will help him determine his optimal angle(s). Accordingly, a future prototype will only need to have the ability to oscillate between his preferred angle choices. If the range of possible angles that are desired is limited, automating the angle changing mechanism may be more feasible. Once selected, a desired angle is held steady using a ball-detent clevis pin, see figure 11. The use of the ball-detent clevis pin ensures that a desired angle is locked. However, an unreasonable amount of force is required in inserting and pulling out the clevis pin because of the stiffness of the spring used within the ball-detent clevis pin. While other types of clevis pins or even ball-detent clevis pin from different manufacturers could be explored, those solutions wouldn’t decrease the level to which the current  process of the changing the angle is “manual”. Given his eyesight impairment, Dr. K might experience a difficult time independently operating the current angle changing mechanism.

Figure 11

There is a notch on the Connector that assists in conveniently storing the device and makes the device extremely portable. When the bottom member is locked at this position, the height of the canes is significant reduced (see Figure 12). While at an eatery for breakfast, Dr. K used this feature to store the canes in entirety under his dining table. Without this feature, the canes would have extended outside of the table’s perimeter and posed a potential tripping risk. Additionally, during transport, this feature allowed the team to house the canes on the backseat of a car, which would not have been easily possible with a 4-wheeled walker

Figure 12

The horizontal handgrip is well integrated with the Connector. Though originally the handle grip was meant to be mounted separately, the fact that it was combined with another part was a fortuitous consequence of the shape of the Connector. The diameter and the length of the handgrip allow Dr. K to comfortably place three fingers. The shape of the handle bar is tubular and the material used is Delrin. In designing the handgrip for future iterations, an ergonomic analysis should be performed.

The cuffs for the canes were borrowed from forearm crutches. The cuff material is malleable and it is possible to adjust them to the girth of Dr. K’s forearms. Despite cuff adjustment, Dr. K still didn’t feel “buckled in enough”. In order to achieve a more sealed connection between his forearms and the canes, Dr. K expressed a desire for straps that he can wrap around his forearms.

In general, Dr. K was content with the second iteration of the canes and found them as “a step in the right direction”. He was most content with the ability to adjust the angle and the weight of the canes. Limited by his eyesight, he was unable to critically analyze the cane design, or in other words he didn’t provide feedback or comment on how the various parts of the canes connected to and functioned with each other.

Costs associated with prototyping the device amounted to about $250. If the canes were to be launched as a product, the prototyping cost is not an accurate measure of the final manufacturing cost. The team estimates that the canes could be produced for less than $50, which is nearly half the retail value of a standard 4-wheeled walker.

Discussion

With limited time in the quarter, the team was not able to address the safety concerns with the adjustable features raised by Deborah Kenney. With the third iteration, it will be sensible to consider the cane design from an occupational therapy perspective alongside the engineering point-of-view

It may turn out that upon experimenting with the adjustable angle and the adjustable height in the second prototype, Dr. K will discover an optimal angle and height, which subsequently may eliminate the need for adjustable height and angle features in future iterations.  In going forward and in the long run, Dr. K’s Cane Project should aim for a solution that finds common ground between the fewest number of moving and adjustable parts and Dr. K’s desires.

If however Dr. K still finds the need for multiple angles, then it will be important to automate the angle changing process. The team deems the current mechanism as “too manual” and not consistent with the idea of universal design.  Additionally, the first and second cane prototypes were largely built with natural intuition. But, in the near future, it will be important to perform a strength or stress analysis to estimate expected loading on the cane while it supports the user and to estimate safety factors of the various components as such an analysis will help in forming a robust design for the canes.

Acknowledgements

Team Quadruped is thankful to the following for their support and unmatched advice: Dave Jaffe,  Doug Schwandt, Paul Noonan, Dr. K, Deborah Kenney, and Mike Norell.

References

McGhee, Robert, and Frank, A.A. “On the stability properties of quadruped creeping gaits.” Mathematical Biosciences (2002). Print.

Van Hook, Frederick, Demonbreun, Dale, and Weiss, Barry. “Ambulatory Devices for Chronic Gait Disorders in the Elderly.” American Family Physician (2003). Print.

Stanford News Article

[1]There is a position, which is labeled as the “vertical” in this paper, of the bottom member on the current prototype that is perpendicular to the ground.