05-07-2013, 03:40 PM
Redesign of the Rollator’s Parking Brake System
Redesign of the Rollator’s.pdf (Size: 583.2 KB / Downloads: 35)
Abstract
A large concern for the elderly is forgetting to engage the parking mechanism on the rollator before using it as
a seat or for support. Interviews and research indicate that the elderly are prone to falling because of the
dependence on memory to activate the rollator’s parking mechanism and also the inability of the current rollator
to effectively park when the braking mechanism is engaged. The design project focuses on creating a rollator that
will brake by default and thus will eliminate the need for users to rely on memory to activate the parking
mechanism. The first iteration of the design is based on the concept of a pin-lock braking system that is activated
by the top frame of the rollator. The second and final iteration of the design replaces the pin-lock with a chainlock.
Based on another round of customer feedback, the next generation of the rollator will replace the chain-lock
with a ratchet gear lock.
Introduction
Home safety is an important aspect of life for the elderly, and the SYDE 361 design project aimed to address the
current challenges within this area. Research and interviews indicated that fall prevention is currently the most
pressing issue amongst the elderly. It was found that falling while walking is the second leading cause (29%) of
hospitalization in all ages and accounts for 62% of hospitalization among seniors in Canada [1].
Within the current state of art, rollators, forearm crutches and canes were three solutions evaluated against
cost, feasibility and limitations. The group found that the rollator is the most frequently used assistive device for
the elderly but is limited in serving mobility purposes due to its bulkiness and inflexible structure. Thus, the
problem statement focused on improving the current design of the rollator to accommodate everyday mobility
requirements around the home.
Problem definition
Based upon user feedback and group discussion, the problem statement can be described as follows:
The current rollator is unable to remain completely immobile while users attempt to sit down on it after activating
the parking mechanism, leading to numerous falls amongst the elderly. In addition, the use of the parking feature
is dependent on user memory but the user population is mainly elderly individuals with degrading memory
capabilities. The design should address the reliance on user memory to immobilize the rollator and improve the
current wheel locking mechanism, thus reducing the number of incidents related to falling due to unlocked and
ineffective brakes.
Concept generation, selection and testing
As discussed earlier in the report, users of the rollator are forgetting to engage the parking mechanism on the
rollator before using the rollator as a seat or for support.
To address these user needs, concepts were brainstormed that emulated different parking mechanisms on other
devices such as bicycle brakes, airport luggage cart brakes, pin-lock mechanisms, seat activated brakes, motion
sensor locks, button activated brakes, and spring-loaded casters. The advantages and disadvantages of the
brainstormed ideas were then passed through a screening process, which resulted in three key ideas: default
braking mode from an airport luggage cart, pin locks and the handle bars from current rollators.
Parking mechanism
The parking mechanism consists of a gear fixed to the axle of the wheel and an interlocking chain mounted on a
track along the leg of the wheel. A steel wire connects the chain to the top frame. During the default parking
state, the steel wire is slack and the interlocking chain fits with the teeth of the gear preventing motion due to the
rigidity of the frame housing the chain. When the steel wire becomes taut, the chain frame slides up along the
track compressing a spring and unlocking the chain from the gear which allows motion of the wheel. When the
steel wire becomes slack again, the compressed spring pushes the chain back onto the teeth of the gear thus
parking the rollator.
Top frame
The top frame redesign of the rollator represents three main functionalities – default parking, differentiation
between movement and support, and self-parking during non-use. Through these three functionalities, the needs
of the user surrounding being intuitive, immobile during parking, and requiring less strength are addressed.
The slot and pin mechanism allows for the three functionalities. In the default state where the pin is at the right
side of the slot and the frame is parallel to the ground, the steel wire connected to the parking brake is slack thus
exhibiting default parking.
Mathematical Analysis
During the building of the prototype, it was discovered that due to construction irregularities and human error, the
friction in the horizontal pin-slot was greater than anticipated, resulting in difficulties for the top frame to slide
back to its default locking position automatically. Therefore a deflector lever with a spring was added to the frame
(Figure 11) to overcome the friction forces. The spring has a maximum stretch length of 5 cm and thus will
generate a pulling force of 10 N in the direction of the lever. This force will be used for all subsequent analysis of
the deflector lever for worst case scenarios. Mathematical analysis was done on the rotation and sliding
mechanisms of the top frame.
Conclusion
The redesign of the rollator’s parking brake mechanism was successful overall. As mentioned throughout the
report, users felt that the idea of having the rollator brake by default is an excellent solution to the frequent
problem of falling when forgetting to apply parking brakes. Although positive feedback is promising, feedback
was also received on how the redesign can be improved for the next generation. The group also faced scheduling
conflicts during the final stretch of the design project and was unable to construct all of the planned changes. In
particular, the prototype did not have a cable that connected top frame of the rollator to the chain-lock braking
mechanism. As a result of this missing link, the new design was not able to directly demonstrate how the chainlock
brakes would be activated or deactivated as a result of the different actions that the top frame can make. This
was, however, only a minor shortcoming as the group was still able to demonstrate the braking mechanism by
showing how the chain would lock and unlock with a manual force applied by the hand. These shortcomings can
easily be addressed in the next design iteration which the group is considering to pursue in the near future.