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Design Summary
Design Summary
The final design is an inflatable balloon that sits on top of the patients chest, supporting the tracheostomy tube. Air flow is electrically controlled through the use of a two DC motor pump/vacuum system. Force detection is measured through a force sensing resitor (FSR) stuck to a typical foam dressing at the typical pressure ulcer site.
The entire system runs on an Arduino Pro Mini and controller board designed to implement an automatic mode — based on force sensor feedback — and an electrical manual mode using physical buttons. A stopcock valve is also integrated into the airflow tubing schematic to allow for manual mechanical air input.
Animated gif Illustrating the Functionality of the System
Inflatable Balloon
Inflatable Balloon
The inflation balloon is made entirely out of silicone since it is a soft comfortable material, medically approved, easy to mold, and biodegradable. The balloon is designed to have a nominal height of 2 cm without inflation, which was determined through the use of multiple MRI scans of real-life patients. It has an inflation height of up to 4cm and a pressure maximum of 3.5 psi.
The balloon support is made using mold release and a 3D printed mold to create a fully homogeneous design. More images and videos on the balloon's fabrication can be found on the Photos and Videos page.
Airflow Schematic
Airflow Schematic
The airflow circuit is comprised of two DC motor pumps, a solenoid switch valve, and a stopcock valve. The two DC motors work inversely, one pumping air into the balloon and the other sucking air out. Both motors run independently and never at the same time. The solenoid valve allows electrical control of the airflow, making the balloon only dependent on the pump or vacuum. The stopcock valve was incorporated into the system to allow manual control from the user using a hand pump. It also works as a physical fail safe in case the balloon become over inflated and endangers the patient.
Image taken from Tekscan website
Force Sensing Resistor
Force Sensing Resistor
The Tekscan FlexiForce force sensing resistor is a piezoelectric resistor that can determine forces felt on its sensing area. It is a flat 0.0008-inch-thick sensor that has an absolute zero, require no initial force to gather readings. Tacky tape is used to provide a stable surface for the sensor to stick onto and allows users to place the sensor onto foam dressing at various locations. The circuitry revolved around processing the sensor utilizes a low-pass op amp circuit to process and amplify clean voltage outputs.
PCB Design and Control System
PCB Design and Control System
The PCB is designed to allow user input through the use of buttons. The device is simple, allowing the user to be able to do only a select number of actions. This includes inflating, deflating, emergency stop, and switching between automatic and manual control. The PCB is also designed to drive the 2 DC motor pumps and power the solenoid valve. Due to the power level that these components, each driver circuit utilizes a transistor to regulate power directly from the power source with Arduino microcontroller input.
In the current model of the device, a breadboard is used in place of the PCB design. Current designs are being drafted and manufactured for another iteration.
Temporary testing stage of system
Final design of breadboard controller
Controller Housing
Controller Housing
The controller housing protects all the electrical components of the device in one central housing unit. Operation is simple, since all the complex controls are hidden from the user and protected from exterior damages. The housing is made with comfortable soft buttons and a hanging mechanism that can be attached to the side of a patient’s bed. This is vital since the casing must protect the airflow circuit from possible blockages and clogs.
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