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Robo arm final 2 (2)
a tour of new features
AIM OF THE PROJECT
• The main aim of our project is to build a
robotic arm that can grip or pick things
• We have implemented the robotic arm that
can be controlled by gesture commands. We
have proposed a simple algorithm for hand
ROBO ARM & DEGREE OF FREEDOM
• A robotic arm is a
with similar functions to
a human arm.
• It has about the same
number of degree of
freedom as in human
MAKING OF ROBOTICS ARM AT A GLANCE
The movement of the human arm is sensed by accelerometer
The accelerometer generates an analog voltage accordingly.
The movement of fingers is sensed by flex sensors which causes a
change in the resistance
An impedance follower is used to convert the resistance to
The analog voltages are then digitized using an A/D converter .
It is then sent to the microcontroller.
Microcontroller differentiates all data of X-axis, Y-axis & Z-axis.
These data are used to generate PWM signal for corresponding
The data from flex sensor are used to drive a motor driver
This motor driver drives the DC motor of the gripper part
To build a gestures control robotics arm
We have technical details for every step of the way
HOW THE GESTURES CAN BE
& Flex Sensors
• The movement of the human arm is
sensed by accelerometer.
• The accelerometer generates an
analog voltage accordingly.
• Analog voltage passes through a
Mode of operation
The 3-axis accelerometer
to the right arm is used
to recognize gestures
The robot moves along the X,
Y and Z axes separately.
the robot in the X direction,
the user should move the
accelerometer along the X axis,
keeping it in the horizontal.
Recognition of gestures
When the arm is moved in the
positive X direction (X+) initially
the value of acceleration x a
increases because the arm begins
to move and then, when the arm
begins to slow the positive value
of x a is converted to a negative
value. This point ( a 0 x = ) marks
the point of maximum speed. The
acceleration a y remains near to
zero and z a remains near to one
because the accelerometer is held
horizontally (acceleration due to
For our project a ±1.5g, ±6g three-axis low g micro machined
accelerometer (MMA7361L) has been used
The MMA7361L is a low power, low profile capacitive
micro machined accelerometer featuring signal conditioning
, a 1-pole low pass filter, temperature compensation,
self-test, 0g-Detect which detects linear free fall,
and g-Select which allows for the selection between 2 sensitivities.
Zero-g offset and sensitivity are factory set
and require no external devices.
•The MMA7361L includes a Sleep Mode
that makes it ideal for handheld battery powered electronics.
For gripping mechanism, flex sensors are used on two fingers i.e forefinger and
Flex sensors are sensors that change in resistance depending on the amount of
bend on the sensors.
They convert the change in bend to electrical resistance-the more the bend, the
more the resistance value
Inside the flex sensor are carbon resistive elements within a thin
More carbon means less resistance.
When the substrate is bent the sensor produces a resistance
output relative to the bend radius-the smaller the radius, the higher
the resistance value
Analysis, Calculate and Making decision
HUMAN TO MCU INTERFACE
• The analog
voltage is then
digitized using an
A/D converter .
• It is then sent to
unique 8 bit digit
code for different
axis and different
The microcontroller used for the
project is Atmega8(L).
ADC7..6 (TQFP andQFN/MLF
Package Only)-In the TQFP and
QFN/MLF package, ADC7..6 serve as
analog inputs to the A/D
converter.These pins are powered
from the analog supply and serve as
10-bit ADC channels.
The ATmega8 on the board comes
pre-loaded with a bootloader
program, which can be used to burn
your project’s HEX files on the
microcontroller directly via the USB
connector without any separate
HOW DOES THE CIRCUIT WORK ?
•The Port B of the microcontroller
is set for the output. Reference
voltage is at AVcc.
•The ADC converts an analog input
voltage to a 8-bit digital value
through successive approximation..
•The ADC is enabled by setting the
ADC Enable bit, ADEN in ADCSRA.
•The ADC generates a 10-bit result
which is presented in the ADC Data
Registers, ADCH and ADCL.
•A single conversion is started by
writing a logical one to the ADC
Start Conversion bit, ADSC. This bit
stays high as long as the conversion
is in progress and will be cleared by
hardware when the conversion is
Activating the accelerometer:
first remains at
•A positive high
signal sent to SL
through PB4 pin of
MCU to activate
Initializing PWM for driving motors: •The Timer/Counter (TCNT1),
Output Compare Registers
(OCR1A/B), and Input Capture
Register(ICR1) are all 16-bit
•The double buffered Output
Compare Registers (OCR1A/B)
are compared with the
Timer/Counter value at all time.
The result of the compare can
be used by the waveform
generator to generate a PWM or
variable frequency output on
the Output Compare Pin
•The 16bit timer/counter1
(TCNT1) is set for fast PWM
mode. The time period is set at
20ms. The Timer/Counter can
be clocked internally, via the
prescalar. Prescalar value is set
at 64 division factor
•For output PB1 and PB2 are
MCU TO MECHANICAL PART INTERFACE
• The 8 bit data is then
sent to be compared
with registers of Timer1.
• Content of OCR1A &
OCR1B are compared
with ICR1 and PWM
signals are generated.
Collect data and Follow instructions
WORKING OF MECHANICAL PART
• Motors are used for joint
• The base consists of a servo
• The elbow consists of a
servo motor allowing
up/down movement of the
• The grip consists of a d.c.
motor allowing to grip a
What makes a Servo
Servo motors are constructed out of basic DC
motors, by adding:
• some gear reduction
• a position sensor for the motor shaft
• an electronic circuit that controls the
It is a
closed servomechanism that
uses position feedback to
control its motion and final
The input to its control is
some signal, either analogue
or digital, representing the
position commanded for the
The motor is paired with
some type of encoder to
provide position and speed
How do servo
motors work ?
Servos are controlled by sending an
electrical pulse of variable width, or pulse
width modulation (PWM), through the
There is a minimum pulse, a maximum
pulse, and a repetition rate.
Servo motors can usually only turn 90
degrees in either direction for a total of 180
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
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. For example, a 1.5ms pulse will make
the motor turn to the 90-degree position.
Shorter than 1.5ms moves it to 0 degrees,
and any longer than 1.5ms will turn the
servo to 180 degrees,
Dc motor which is driven by a motor driver
(L293D) is used for the gripper part.
The L293D is designed to provide bidirectional
drive currents of up to 600-mA at voltages from 4.5
V to 36 V.
gg The bent in fingers
is indicated by the
change in resistance
which in turn drives
the dc motor
attached to the
As the motor
rotates the gripper
closes in thus
grabbing the object
The arm is made with
balsa wood. The wood
pieces are carefully cut
according to the
measurements and then
they are put together to
form the structure of the
Why we need ROBOTICS ARM???
. The robotic arm can be designed to perform any desired task
such as welding, gripping, spinning etc.
. The space shuttle Remote Manipulator System have multi
degree of freedom robotic arms
. In various industrial or home applications
. In medical science: soft tissue manipulation, needle insertion,
suturing, and cauterization.
of doing multiple tasks
MOBILITY & NAVIGATION-
mobile,able to move under their
own power & navigation systems
accelerometers used for
shoulder,elbow & wrist movement
allowing circular & angular
information about its environment
back to a remote “safe” location
making decisions about the task it
Robots help people with tasks that would be
difficult, unsafe, or boring for a real person to do
alone. To conclude, robotic arm, is probably the
most mathematically complex robotic part one
could ever build.
Our deepest thanks to our mentor, Mrs Antara
Mukherjee, for helping us out and guiding us
with her valuable suggestions and support.