IPPA System Components

System Components

The IPPA system is best presented in terms of subsystems; that is, the five modules—whether purchased or designed—that are interfaced to create the final product. This section provides a semi-technical introduction to each of these components:

• Servo Subsystem

The design for the servo controller includes the software programmed on the controller and the hardware components used. The software is responsible for processing communications from the system controller and sending PWM signals through the control lines of the servos to set their positions. The hardware for the servo controller mostly consists of the microcontroller itself, the servo motors, and the fishing lines which act like tendons for finger control.

• Sensor Subsystem

This subsystem is composed of three different sensors: EMG, pressure, and distance. The electromyography (EMG) sensor allows the prosthetic to interface with the electrical impulses generated by the user. Multiple force sensing resistors were implanted into the palm and fingers to determine the amount of pressure the hand is generating on an object and to sense when a strong grip has been established. And a passive infrared sensor, to detect when an object is near the hand.

• Main Controller

System Main controller’s purpose is to control the coordination between the sensor control unit, the servo control unit, and the communication unit. The main controller receives input from the sensor microcontroller unit and decides how to proceed with the current grasp and gesture being performed. From the sensor information, the main controller directs which grasp to complete and send that information to the servo controller. The Main controller contains information about the set of gestures the hand is capable of completing. In order to complete a gesture, the Main Controller unit listens to any messages received from the communications unit for voice triggers for the main controller to trigger a certain gesture to complete. The main controller also listens on the communication module to update and manage the set of gestures the prosthetic hand can complete.

• Mobile Application

The mobile application was designed to provide the user with an easy but capable interface. This section discusses all the design details regarding graphical user interface (GUI), algorithm used to create gestures from user input, communication with the IPPA system, and voice commands. As part of the IPPA system a mobile application was developed: IPPA Mobile Support. This mobile application provides the user with the following features:

• Create new hand gestures • Add new gestures to the arm • Specify voice command to trigger gesture • Edit previously created gestures • Delete gestures from the arm • Save gestures in the phone itself • Sync arm gestures with phone to enable multiple devices

The Android platform was selected as the platform of choice for the development of this application. This decision was based on the team’s engineer’s familiarity with it, the vast online support for development, as well as the low cost of developments and mobile devices that use this platform

The communication with the IPPA system from the mobile application is accomplished through a Bluetooth connection. The team decided on Bluetooth because it is a simpler solution, with less power consumption and it satisfies the distance and safety requirements of the project. Different package types have been designed to reduce the amount of information that needs to be transmitted and to facilitate the understanding between devices. There is a total of 10 packages.

• Power Subsystem

There are over a dozen separate components that require power. Some have almost negligible power consumption rates, such as the force sensitive resistors, electromyography sensor, and even the servo and sensor microcontrollers only draw a small amount of power. However, since all of these components needed to be integrated together and draw power from the same power source, it required calculating the maximum expected power consumed by all the devices when they are running. The important factors to be kept in check are battery life, battery output, and, as a requirement of the entire project, weight. The total current drawn by the system sums up to about 650 mA - 2800 mA. The battery we have chosen to use contains 2200 mA hours of charge. It can discharge about 9 amps maximum. Assuming the servos will not be continuously moving, the lifespan of this battery should exceed 1 hour.