An Integrated Design for a Myoelectrically-Based Writing Module for a Controlled Prosthesis

canolaokahumpkaElectronics - Devices

Nov 2, 2013 (3 years and 9 months ago)


An Integrated Design for a
Based Writing
Module for a Controlled Prosthesis


Andres Herrera, Malek Adjouadi, and Melvin Ayala

Center for Advanced Technology and Education

Florida International University


Malek Adjouadi


Research Objectives

Design and implementation of a writing module

Integration with a myoelectrical
based gripper as a
potential prosthetic device

Help amputees recover some of their writing abilities

Important Issues

Advancements in prostheses technology => prosthetics
with greater functionality, performance, durability, and
cosmetic appearance

highly advanced materials and electronics not yet

copying the functionality of the hand is too difficult

Task of writing: challenging communication endeavor,
only appreciated when one attempts to automate it in


To create a support system for a writing module that is
designed to translate muscular activity into written
characters by integrating (a) a mechanical system, (b) an
electrical system and (c) software

Mechanical Implementation

A rail
actuated module is proposed

Actuation mechanism: a device to slide the
writing tip along the rail generated axis

A writing algorithm is integrated to the
mechanical system to write the characters and
to accommodate changes in the writing surface

Fig. 1:
Complete rail actuated system showing
perpendicular rails, motors, and sensors

Mechanical Implementation

Electrical Implementation

The electrical system captured the real time
electromyogram (EMG) bio
potentials of the

After the acquisition of the EMG signals, they
are processed into useful data for the

The microcontroller outputted instructions to the
motors; either to write a character or to open and
close the gripper for grasping tasks

Electrical Implementation


Capture system is similar to those used in current

It had an added electrode (connected to the ground of
the main circuit) to distinguish between the writing and
the grasping task.

Advantages of having an extra electrode:

It stabilizes the system and the overall capturing

It prevents undesired offsets in the signals or
electrical interference (noise, light sources,
microwave signals).

Electrical Implementation (Contd)

Electrodes: connected to the surface of the skin
to measure the bio
potential difference among
the targeted muscle groups.

Instrumentation amplifiers: connected to the
electrodes to reject common mode signals
between them, and to amplify differential mode
in the bio
potential measurements.

signals are differentiated, amplified, and rectified
to be used as control signals.

Electrical Implementation (Contd)

Writing application realized by a

User can perform upgrades and updates to the

User can customize their writing module

detailed information such as name, signature
and address can be associated with simple
codes. Therefore, the amputee would avoid
the need to input a code for each character.

Fig. 3:
Overall System Circuitry

Software Implementation

Writing module assembler code: written in an infinite loop.

Software will constantly check for bio
potential input for grasping
task (a must to guarantee functionality on demand).

Writing task would also be accounted for in every cycle of the loop,
but only addressed when needed.

Characters are inputted by utilizing coding schemes.

Software Implementation


Coding Schemes:

Coding schemes: best option for an amputee to be able to input a
request for a character.

coding schemes entered by moving the remaining muscle.

Amputee can enter a binary code that can easily be learned.

Distinction between ON and OFF positions relates directly to
myoelectric bio

Dynamic codes have the same function as Morse code.

Dynamic codes have a fixed length. 6
bit code scheme is
recommended as the minimal selected value because the entire
English alphabet can be represented with 26 characters.

Simulation and Testing

Fig. 4: Entering code 01111 by

hand movements to request writing
the word “CATE”

Simulation and Testing (Contd)

Fig. 5: Module while writing the word “CATE”. In
this experiment, module is being held by hand
instead of a prosthesis.

Demo of the writing device in action will be shown at the
end of the presentation.

Simulation and Testing


Experiment 1: Simulation of a seven segment display
(simplest way to obtain a character)

Fig. 6:
First character written by the module

Simulation and Testing (Contd)

Experiment 2: Writing the word CATE by entering
associated binary code (01111)

Fig. 7:
Word "CATE" written without
retractable electromagnetic writing


There were connecting lines between the characters.

Simulation and Testing


Experiment 3: Writing the word CATE

Connecting lines between the characters are removed
by using the retractable electromagnetic writing tip.

Fig. 8:
Word "CATE" written using

retractable electromagnetic writing tip

Conclusions and Recommendations

Groundwork for future integration of a writing
module for current prostheses.

Retractable tip produced an acceptable level of
accuracy accomplished.

To increase accuracy and detail of printed
characters: use micro
stepper motors, high
precision mechanics, and lightweight polymers.

To accurately reflect real position: use of a
feedback system.

Bigger size memory bank: for the
implementation of more characters