Design Brief for the Development of the RehCycle Passive Exercise

Design Brief for the Development of the RehCycle Passive Exercise
Design Brief for the Development of the
RehCycle Passive Exercise Machine
Prepared for
RESNA Student Design Competition
Ali Al-Shaer
Eric Jacobsohn
Evan Jones
Rory Dougall
BCIT Mechanical Engineering Technology
Submitted on
April 11, 2016
Problem Statement
Cardiovascular exercise exclusively achieved through arm movements alone may result in a lower
cardiovascular output that may not be sufficient for improving health for people with mobility
impairments such as spinal cord injury (SCI). Arm Assisted Passive Leg Exercise (AAPLE) is one method
for greater exercise effects, with the passive movement of the legs increasing blood circulation and the
load on the cardiovascular system. AAPLE can be accomplished with an arm-leg bike by using the arms
to move the legs: transferring rotary motion on a hand crankset to a lower output shaft connected to
the user's feet via cranks and pedals. Movements of paralyzed lower limbs are also thought to be
beneficial for rehabilitation purposes.
Although certain AAPLE machines are available on the market for personal or clinical use, these
machines are very costly and are unaffordable for people living in developing world countries. They are
also typically large and costly for most home use scenarios in North America. For these reasons, an
economical and easy to build AAPLE bike - assembled with globally available parts and materials – has
been designed.
Ideally, the machine must also be easy to use by the user and/or caregiver. Current rehabilitation
exercise machines can be heavy or awkward to move, and are also difficult for the user to transfer into
as well as place and secure their legs onto without assistance. Most machines are also not usable
when lying down – a beneficial feature for early rehabilitation intervention during the acute care phase
of recovery. Thus, the rehabilitation version should allow for hospital bed use, and also be groundmounted so that a wheelchair can move next to it for use without needing to transfer.
Background
Many secondary negative effects experienced by a person with SCI are often overlooked. Some of the
secondary side effects include, but are not limited to, muscle atrophy, decreased bone density loss,
and a decrease in cardiovascular health which can lead to serious health issues such as heart attack
and stroke [1].
The typical cardiovascular exercise modality for people with SCI or other mobility impairments are
arm-only movements such as pushing a wheelchair or using a hand-cycle or arm ergometer. Two
newer methods are sometimes used for greater exercise benefits, although these methods are usually
only found in clinical settings. The first is passive leg exercise where the paralyzed limbs are moved in
common biomechanical ways either by the strength of other limbs or by a motor, with one example
being AAPLE machines. The second method builds on passive exercise by adding Functional Electrical
Stimulation (FES) to cause the muscles to fire in timed intervals to perform synchronized exercise
movements, thereby potentially providing an even greater cardiovascular stimulus. Unfortunately, FES,
in particular, is expensive, time consuming, and needs expert therapists to help administer.
The more cost effective and accessible option is AAPLE. Only a few AAPLE machines are currently
available on the market. These include the SCIFIT Inclusive Fitness Pro2, and the BerkelBike Fitness.
Neither of these machines offer supine use in bed. The YouBike offers supine use, although it has
limited resistance and flywheel features that make its use less smooth. Despite these machines allowing
passive exercise for the lower limbs, which is the main function of this design project, these products
also reveal the main concern with the current products on the market right now—cost. No options that
cost less than $2000 are believed to be currently available; this factor alone limits access to these
machines.
Methods and Solutions Considered
In order to address all the issues brought up in the problem statement, it was necessary to look at
designing from several different viewpoints. It became clear fairly quickly that there were two feasible
design approaches that could be used in conjunction with each other: designing components from the
ground up when needed, and utilizing existing bike parts.
Bike parts allow for the cost of the machine to be kept down by using readily available parts with
specific functions in the design. This will also result in easier repair should any of the bike components
break or wear out. In the cases where bike parts could not serve the function required, new
components were designed to fulfill said function. It is also thought that common 10 speed style
bicycle frames should be available in many developing countries; although other types of frames could
be used too if more these are found to be more common in different countries.
For every function of the exercise machine, many options were considered, putting special emphasis
on using bike parts and combining functions if possible. In this sense, it was decided to use regular
bicycle cranks and bottom brackets as the input interfaces at the hands and the feet. Due to the cost,
availability and ease of adjustability of length, bicycle chains were chosen over belts or linkages to
drive the machine.
For the resistance, using the original bicycle brake was considered, however it was found to be
impractical due the size constraints (having to ensure sufficient clearance for the wheel), wear, and
general effectiveness being poor due to mechanical friction limiting the inertial smoothing effect of the
flywheel. A resistance band was also thought to be an option, but it had many similar downfalls as the
bicycle brake. Ultimately it was decided to use an eddy current brake system, drawing inspiration from
various exercise machines and stationary bike trainers, due to its simple yet effective design.
Furthermore, an eddy current brake requires no input electricity and can be easily adjusted
mechanically with bicycle brake cables.
Final Approach and Design
The overall final approach for the design of the exercise machine is the combination of ground up
design and the integration of existing bike parts. The mechanical design assembly is shown in Figure 1.
The idea behind the design will lend itself to a ‘kit’ type of product that will include any specialized
components that were designed specifically for the machine. In theory, a customer will be able to
acquire a kit and from there, modify an existing bicycle to serve as an exercise machine. For bulkier
and heavier components, such as the base, that could prove difficult
or expensive to ship, detailed design plans could also be given in
order for the customer to fabricate these parts. This may be
particularly appealing in parts of the world where cost is even more
important. The custom components have been designed out of
materials that are easy to work with and do not require any special
fabrication machinery or tools. This means that should anything
break on the machine, it ought to be easily repairable or easily
replaced.
Using a generic bike frame, the geometry and various attachment
points of the frame were used to create an exercise machine that
functions correctly. By having the user’s feet rotate
about the bottom bracket (Fig. 2), and with the
designed hand crank linkage mechanism that attaches
to the head tube (Fig. 2) it was possible to create
enough space for the machine to be used
comfortably. At the rear dropouts of the bike (Fig. 3),
a bicycle hub will be used to mount a flywheel and the
eddy current resistance mechanism (Fig. 3). The
machine will be chain driven and purely mechanical (it
is completely user driven, no assistance is offered).
Figure 3 Main components of RehCycle machine in use from
wheelchair
The base is used to stabilize the machine and is
mounted on the chain stays of the frame (Fig. 3),
which creates a desirable rotation point when adjusting
the angle of the machine. Seat tubes and seat posts,
attached to the rear dropouts, add additional stability
and also lock the angle of the machine in place through
simple quick release mechanisms (Fig. 2).
Figure 1View of overall device clamped to
existing bicycle frame
Figure 2Pivot point along with rear hub assembly which houses
the resistance and flywheel
Figure 4 Eddy current brake mechanism
Referring to Figure 4, the eddy current brake
mechanism is shown as a fork holding magnets on
either side of an aluminum plate. This fork pivots to
adjust the overlap on an aluminum plate in which the
eddy current is induced to cause drag in the system.
This creates heat which is then mitigated with the
fan attached to the same axle. A gear shift lever is
placed for easy adjustment by the user.
A pin lock with several locking locations of the cranks was fabricated. This allows the user to lock the
foot pedals to ease them placing and securing their feet on the pedals. A simple orthotic boot and
Velcro straps is used to align the legs of the user and
secure them to the foot pedals (Fig. 5). But a cheap
plastic version would be able to be made for a
production version.
Outcome
Figure 5 Orthotic boot attached to bicycle pedals to align legs
The building and assembly of an alpha prototype was
completed on April 10, 2016. This has allowed for
verification that the overall design is functional and
working, in particular demonstrating that the design is
stiff enough to allow for full exertion during exercise.
We also demonstrated seated use in a
wheelchair, and exercise use when lying down
(Fig. 6). By locking the cranks in an appropriate
position, it was also demonstrated that a user
could easily strap their feet into the pedal boots.
More comprehensive physical testing of the
machine will be completed by the end of the
BCIT school year of May 20, 2016. This will
include testing by one of our faculty supervisors,
a person with SCI who uses a wheelchair. We
Figure 6 Use of machine lying down
anticipate he will be able to fully use the
machine independently, including mounting and securing his feet onto the footrests. The current alpha
prototype consists of the major components of the machine including: the steel base frame, pivots,
telescopic adjustment columns, bike frame, hand and foot cranks and pedals, and bicycle chains. Other
minor parts weren’t incorporated into this initial prototype by time of submission, such as the eddy
current brake.
Cost
One of the major themes of this project was maintaining a cost efficient product while not losing out
on effectiveness and performance, and this was a major challenge in the design process; in order to
maintain a low cost for the user of an AAPLE bike, common, globally available, mass produced parts
had to be chosen for the majority of the design. For this reason, custom parts were kept to a minimum
unless required, and then simple manufacturing methods were utilized. Lastly, materials used were
taken into consideration for both ease of assembly in different parts of the world and cost of shipping
related to unit weight. A cost breakdown of the expected prototype can be seen below in Table 1, with
the individual materials and parts itemized. Expected cost of a production version of this design can be
calculated in two ways. We are assuming a volume of 1000 units in this estimate. First, if a recycled
bicycle frame and fabrication in a developing world is available, an estimated cost is $178.97. In North
America, assuming labor cost of $30 per hour, and material to replace the bike frame, this would cost
$150. Multiplying by 3 would give an estimated retail price of $750.
Table 1 Approximate cost breakdown
Part
General fasteners, location devices, machining stock, and
pins
Barstock, extruded steel profiles, and flat plate
Supplier
Cost
McMaster
Metal Supermarket
Bottom Bracket Shell
Bushings and thrust washers
Nova Cycles Supply
Igus
Community Bike
Shop
Subtotal
$
$
$
4.25
$
Bicycle frame, cranks, pedals, and chain
5% Tax
Total
101.63
53.99
10.58
$
$
170.45
$
8.52
$
178.97
Significance
Evidence shows that AAPLE and other types of hybrid exercise can contribute to cardiovascular health
and overall health. For instance, one study of a single patient followed for 6 weeks showed that by
coupling upper body exercise with passive leg movement resulted in a much better cardiorespiratory
response than just upper body exercise alone [3]. Other advantages that AAPLE has over other forms of
exercise are: the small amount of time required for a person to get set up and exercising, and the ability
to use machines that don’t require “specialized parts” or expertise such as is needed with FES.
Hence, this project aimed to design an AAPLE machine that balances cost and effectiveness. Current
machines available in the market are prohibitively expensive for people with spinal cord injuries or
other impairments, certainly in developing countries and even to most home users in North America.
This project could lead to a low cost product that could be used to potentially offset some of the
secondary side effects of such injuries, improve people’s quality of life and health, and further promote
research on the benefits of passive leg exercise.
References and Acknowledgements
[1] Cragg, J. J., V. K. Noonan, A. Krassioukov, and J. Borisoff. 2013. "Cardiovascular Disease and Spinal
Cord Injury: Results from a National Population Health Survey." Neurology 81 (8): 723-728.
[2] Hasnan, N., N. Ektas, A. I. Tanhoffer, R. Tanhoffer, C. Fornusek, J. W. Middleton, R. Husain, and G.
M. Davis. 2013. "Exercise Responses during Functional Electrical Stimulation Cycling in
Individuals with Spinal Cord Injury." Medicine and Science in Sports and Exercise 45 (6): 11311138.
[3] West, C. R., K. D. Currie, C. Gee, A. V. Krassioukov, and J. Borisoff. 2015. "Active-Arm Passive-Leg
Exercise Improves Cardiovascular Function in Spinal Cord Injury: A Case Report." American
Journal of Physical Medicine & Rehabilitation / Association of Academic Physiatrists.
Links
SCIFIT Inclusive Fitness Pro 2:
http://www.scifit.com/product/ifi-pro2/
BerkelBike Fitness:
http://www.berkelbike.com/products/berkelbike-fitness/
YouBike:
http://www.youbike.co.nz/
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