Design Objectives

ELM designs proposes the design of a wheelchair pressure sensor cushion that can be used as a teaching tool for wheelchair users from 15 to 70 years of age. The cushion will use auditory, visual, and sensory alarms to remind patients to perform 15±1-second pressure-relief exercises every 15±1 minutes; the frequent performance of these exercises plays a crucial role in avoiding pressure ulcers in wheelchair users. The main design objectives for this project are as follows:

1. The arrangement of sensors will accommodate two different methods of pressure relief exercises:
a.    Patients can completely lift themselves from the seat using their arms.
b.    Patients can lean forward and from side to side. This is usually performed by those unable to use their arms or who regularly experience muscle weakness.
2. The sensors will be designed to have variable modes of alert. Three alarms will be incorporated into the design: auditory, visual and sensory.
3. This product will be adaptable to different widths and lengths of wheelchair seats since it will be used by a variety of patients.


The arrangement of the sensors will accommodate different types of pressure-relief exercises.  Furthermore, since some of the patients may have some form of hearing disability, the auditory alarm included in the final design will be low-pitched, thus allowing it to be noticed more easily by hearing-impaired patients.  In addition to the auditory signal, the device will incorporate an optional visual alarm. To improve the practicality of the sensor cushion, the final design will also incorporate an option to disable the alarms. The sensor cushion will be placed underneath an existing wheelchair cushion such as the ROHO cushion.
 




Selecting Design Concepts

Selecting Design Concept
     Once the four alternative design concepts were generated, the preferred design was selected by assessing how well each idea met the customer’s needs and specifications.  A list of criteria was established, and each idea was evaluated objectively in Table 1:
Table 1:  Evaluation of Four Alternative Design Concepts based on Target Specifications

Design A Design B Design C Design D
Sensitivity to
depression of switches		 Only 5 switches-
low sensitivity		 High sensitivity-
may be over sensitive		 Good sensitivity Good Sensitivity
Cost Low cost Moderate Cost Moderate Cost Most Expensive
Weight Low weight  Most sensors –highest weight  Medium weight Low weight
Ease of Manufacture Simple design Simple design Simple design (slightly more complex than B) Complex design to manufacture
Waterproof Yes – can be sealed in thin covering Yes – can be sealed in thin covering Yes – can be sealed in thin covering Yes – can be sealed in thin covering
Pressure Relief Exercise 1:
leaning to side		 Fair – switches are large, so patient must lean significantly Excellent – switches are small and easily released Excellent – switches are small and easily released More information needed
Pressure Relief Exercise 2:
body suspension		 Good Good Good Good
Lifetime (durability) Good Poor - error in one sensor disrupts system Good More information needed

According to these evaluation results, Design C is the preferred concept.  This design will accommodate both pressure relieving exercises without being excessively sensitive to un-related pressure changes.  Furthermore, the parallel design of the sensors (the “zones”) means that a problem in one sensor will not necessarily disrupt the whole device, as would be the case with Design B.  Design D, while the most creative concept, is unfeasible at this time due to the high cost of piezoelectric devices.

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