DESIGN OF PROSTHETIC HAND

ABSTRACT

To design and develop a prosthetic hand which is controlled by human hand gestures. The prosthetic hand is made up of levers controlled by servo motors acting as the actuation system. The system is controlled wirelessly using Arduino as the embedded controlling unit.

DESIGN COMPONENTS

ACTUATION SYSTEM

The actuation system is either a mechanical . electrical or a electo-mrchanical systems used to produce the required action or movements.

 SERVO MOTORS

 To fully understand how the servo works, you need to take a look under the hood. Inside there is a pretty simple set-up: a small DC motor, potentiometer, and a control circuit. The motor is attached by gears to the control wheel. As the motor rotates, the potentiometer's resistance changes, so the control circuit can precisely regulate how much movement there is and in which direction.

When the shaft of the motor is at the desired position, power supplied to the motor is stopped. If not, the motor is turned in the appropriate direction. The desired position is sent via electrical pulses through the signal wire. The motor's speed is proportional to the difference between its actual position and desired position. So if the motor is near the desired position, it will turn slowly, otherwise it will turn fast. This is called proportional control. This means the motor will only run as hard as necessary to accomplish the task at hand, a very efficient little guy.

Servos are controlled by sending an electrical pulse of variable width, or pulse width modulation (PWM), through the control wire. There is a minimum pulse, a maximum pulse, and a repetition rate. A servo motor can usually only turn 90 degrees in either direction for a total of 180 degree movement. The motor's neutral position is defined as the position where the servo has the same amount of potential rotation in the both the clockwise or counter-clockwise direction. The PWM sent to the motor determines position of the shaft, and based on the duration of the pulse sent via the control wire; the rotor will turn to the desired position. The servo motor expects to see a pulse every 20 milliseconds (ms) and the length of the pulse will determine how far the motor turns.

Servo motor

ELECTRONICS SYSTEM

ARDUINO UNO

Arduino is a single-board microcontroller to make the use of electronics in multidisciplinary projects more accessible. The hardware consists of an open-source hardware board designed around an 8-bit Atmel AVR microcontroller, or a 32-bit Atmel ARM. The software consists of a standard programming language compiler and a boot loader that executes on the microcontroller.

Arduino uno

This is the new Arduino Uno R3. In addition to all the features of the previous board, the Uno now uses an ATmega16U2 instead of the 8U2 found on the Uno (or the FTDI found on previous generations). This allows for faster transfer rates and more memory. No drivers needed for Linux or Mac (inf file for Windows is needed and included in the Arduino IDE), and the ability to have the Uno show up as a keyboard, mouse, joystick, etc. The Uno R3 also adds SDA and SCL pins next to the AREF. In addition, there are two new pins placed near the RESET pin. One is the IOREF that allow the shields to adapt to the voltage provided from the board. The other is a not connected and is reserved for future purposes. The Uno R3 works with all existing shields but can adapt to new shields which use these additional pins.

Arduino is an open-source physical computing platform based on a simple i/o board and a development environment that implements the Processing/Wiring language. Arduino can be used to develop stand-alone interactive objects or can be connected to software on your computer (e.g. Flash, Processing, MaxMSP). The open-source IDE can be downloaded for free (currently for Mac OS X, Windows, and Linux).

BLUETOOTH MODULE

Bluetooth is a wireless technology standard for exchanging data over short distances (using short-wavelength microwave transmissions in the ISM band from 2400–2480 MHz from fixed and mobile devices, creating personal area networks (PANs) with high levels of security. Created by telecom vendor Ericsson in 1994, it was originally conceived as a wireless alternative to RS-232 data cables. It can connect several devices, overcoming problems of synchronization.

    A master Bluetooth device can communicate with a maximum of seven devices in a piconet (an ad-hoc computer network using Bluetooth technology), though not all devices reach this maximum. The devices can switch roles, by agreement, and the slave can become the master.

                   

Bluetooth HC-05

BATTERIES

The power source for the prosthetric hand is provided by the lithium-polymer batteries. LiPo battery can be found in a single cell (3.7V) to in a pack of over 10 cells connected in series (37V). A popular choice of battery for any is always a Lipo which can give a better efficient power supply .

LIPO BATTERY

    These are very slim, extremely light weight batteries based on the new Polymer Lithium Ion chemistry. This is the highest energy density currently in production. Each cell outputs a nominal 3.7V at 1000mAh! Comes terminated with a standard 2-pin JST-PH connector - 2mm spacing between pins. These batteries require special charging. Do not attempt to charge these with anything but a specialized Lithium Polymer charger.

GLOVE GESTURE HAND

COMPONENTS NEEDED

FLEX SENSOR

FLEX SENSOR

Flex sensors are sensors that change in resistance depending on the amount of bending on the sensor. They convert the bend into electrical resistance-more the bend , more the electrical resistance. They are usually in the form of thin strips of 1inch to 5 inches long that vary in resistance. They can be made uni-directional or bi-directional.

They are analog resistors and they work as variable analog voltage dividers. Inside the flex sensors are carbon resistive elements within a thin flexible substrate. More carbon means less resistance. When the substrate is bent, it produces resistance according to the bend radius.

GLOVES

GLOVES

Gloves are used for covering the hand which is fitted with the flexi sensors for transmitting the bending movements to the prosthetic hand . It converts our gestures into a suitable actuation in the prosthetic hands.

 CONDUCTIVE CLOTH

Conductive cloth

This is a conductive knit fabric for use in e-textiles. It is silver-plated nylon that is stretchy in both directions. It is highly conductive with a surface resistivity of < 1 ohm/sq. This is a great add-on to any LilyPad project. Medtex 130 Ag Nylon stretch. It is a bit thinner than our Medtex 180.

 CONDUCTIVE THREAD

CONDUCTIVE THREAD

Conductive thread is a creative way to connect various electronics onto clothing. This thread can carry current for power and signals. While not as conductive as traces on a printed circuit board (PCB), this thread makes wearable clothing 'wearable'!

This thread is stainless steel making it extremely tarnish resistant. This thicker 6-ply thread gives it the ability to conduct much more power. It is often laid on a fabric and then held in place with a over-stitch (sometimes called acouching stitch) of non-conductive machine sewable thread.

Once again the Arduino PRO and a Bluetooth module are used here for the wireless connectivity between the controller boards for controlling the action of the servo motors.

Fabrication:

The Mechanical hand is fabricated using card boards, Corrugated pipes and nylon thread. Servo motors are attached at the base and connected to the nylon thread. The servos are connected to the arduino uno which uploaded with a firmware. The glove is attached with flex sensors and connected to the Arduino uno analog pins. The mechanical hand is controlled directly using arduino uno first. Then the wireless communication is enabled.

 Working video:

                                                              Gesture controlled Prosthetic hand

          

The wireless control of the prosthetic hand is on the progress and will be updated in the next post !