Fall 2016 Prosthetic Hand – Finger Flexion Prototype

Electronics and Control Engineer – Younis Al-Kharusi

Table of Contents

Prototype Assembly

The goal of the first prototype was to demonstrate movement of one 3-D printed finger.

Using .stl files provided by the “Tact Hand”, linked, CAD files for a single finger were developed by the Manufacturing and Design Engineer of the group, Wilson Mach. Wilson Mach was able to assemble the finger in a similar fashion, resulting in the finger shown to the right.

Figure 1: Finger 3-D Print – Version 1

The next step was to attach a motor and controller to the finger in order to control the 3-D printed unit.

An SG90 servo was mounted at the bottom of the bending face of the finger. Then, a string was attached from the middle of the finger to the servo to facilitate the flexion motion. Next, the SG90 and a potentiometer was connected to an Arduino Leonardo.

In order to demonstrate flexion ability and proof of concept, the built-in example “Knob”, located under servos, was used to program the Arduino. The flexion in the finger is controlled using variable resistance from the potentiometer.

A video of the flexion process is provided below for clarity and convenience.

Anticipated Changes for Future

From this prototype, a few changes will be made immediately to the design.

  1. The SG90 servo will be replaced by an ESCAP 16 DC motor, driven by TB6612FNG dual motor drivers.
  2. The string connection between the motor and finger will be located within the finger rather than outside of the finger.
  3. Flex sensors or a button panel for foot-control will be used to control the hand wirelessly instead of use of the potentiometer.

Improvements To Be Made

In order to improve the prototype for the future, the elastic rubber band that promotes return from flexion could be placed within the finger rather than outside of it. Otherwise, it could be replaced using a spring and such associated mechanisms. Finally, integrating ball bearings at the joints would reduce friction and increase efficiency of the hand as well.