System Engineering Design

Pump Selection

Selecting the proper peristaltic pump is an important part of the engineering design process. To do this, the necessary pressure and flow rates were considered, while analyzing the properties of the the air that the pump would be interacting with. After performing a series of calculations the ideal flow rate was found, ranging from 800 - 2400 mL/min.

Subsystem Components

The overall system can be split up into four main subsystems: the pump, sensor suite, valves, and data acquisition. Each of these will interact with the other to deform the skin properly, complete the experiment, collect data and process for analysis. For further detail on pump selection visit the above section. Ported pressure sensors will be the main components of the sensor suite due to their sensitivity and ease of integration. A valve will be used to release the pressure from the skin after testing so it can relax to its original state. The DAQ subsystem will use an Arduino enabled board (such as the wemos R1) to collect and process data. Software design and data collection is a main focus for the following phases.

Overall System

The overall system design can be described by the block diagram shown in the figure below, along with the five stage process representing the inputs and the outputs of the system. The diagram to the left shows a brief overview of how all the subsystems would work together and be set up in a physical manner.

In addition to the system block diagram showing the transfer of information between the subsystems, the stage diagram can be revisited to gain a more complete understanding of how the subsystems interact.

INITIAL: Device is placed on the patient’s skin, initial conditions with no initial skin deformation.
IN PROGRESS: Activation of pump causes negative pressure buildup in cup and progression of skin deformation. Slow loading profile desired for accurate stress response.
FINAL: Skin deformation reaches 1mm, and seals off contact probe.
1. Pressure sensor (#1) records pressure in main line
2. Pressure sensor (#2) records internal cup pressure.
RELEASE: Valve release pressure, allowing skin to relax to undeformed state
1. Data acquisition subsystem gathers pressure data and calculates differential
2. Differential is used to calculate the mechanical properties of the skin, focusing on anisotropy.
END: Data collected, skin returned to initial state

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