Mechatronics Learning Studio
Wireless Robotic Hand
Trang
Cung, Clarine Chan and Robin Bourge, Department of Mechanical
Engineering, University of Ottawa
The goal of this project is to take the motion
of a human hand and simulate it by a robotic hand. This
will hopefully help us later to develop a hand rehabilitation
device for those who have hand injuries. Strokes,
osteoarthritis and tendinitis can lead to hand disabilities in
adults. A significant amount of stroke survivors suffer from
weakness on one side of the body, leaving them with impaired
hand function. By replicating the motion of a human hand with a
robotic hand, one can take principals of this design and apply
the ideas to a hand rehabilitation device.
Implementation
The design is to convert the bending motion of
flex sensors into rotational motion of servomotors that are
controlled by flex sensors. The servomotors will act as
actuators to pull and release fish tackle, which is used to
control the motion of the robotic fingers.
Advantages
The wireless robotic hand could potentially be
used as a surgical device. The surgeon will be able to control
its movement using the glove, and the robotic hand performs
surgery on the patient. Precisely the robotic hand replicates
every movement the surgeon makes. The robotic hand can be built
in a microscopic size where it can easily fit through very small
incisions, which can potentially minimize scarring, of the
patient. Furthermore, it can provide the surgeon with
unprecedented control in a minimally invasive environment, and
is more hygienic and thus reduces the chances of postoperative
infections.
Additionally, the wireless robotic hand could be
found useful in environments where it is dangerous for humans.
In space or places such as hazardous radioactive environments is
where the robotic hand would be useful.
Flex Sensors
Flex sensors are used to
convert the flexing motion of the fingers into rotational motion
of the servo motors. The flex sensors used for the design are
4.5 inches long, which allows it to cover each finger. The flex
sensors are sewed onto the glove. As the flex sensor bends,
this increases its resistance. This change in resistance is the
signal that is sent to the servomotors. These flex sensors were
soldered onto wires for simpler use. A 15k
resistor was also placed in series with each flex sensor in
order to protect it. The flex sensors were powered by the 5V
pin on the Arduino.
Wireless Communication
To allow wireless communication between the two
Arduinos, two Xbee modules are used. The Xbee radio allows
wireless communication between microcontrollers such as Arduinos,
computers, and any system that has a serial port. The Xbee that
we used were XBee 1mW Trace Antenna - Series 1 (802.15.4). The
Xbee radios were configured using X-CTU to ensure their settings
allowed them to communicate with each other. In order to attach
the Xbee radio directly onto the Arduinos, we used Xbee
shields. Thus two XBees were required; one for each Arduino.
Microcontroller
Two Arduino Uno Atmega 328 were used. One
Arduino takes the signals from the flex
sensors and transmits this signal to the other Arduino which
contains the servomotors. The Arduino which contains the
servomotors is programmed to receive the signal and convert the
signal into a rotating motion of the servo motors. The higher
the resistance on the flex sensor, the more the servos will
turn. The Arduinos are programmed using the Arduino software.
Servomotors
The servomotors used for this
design is the standard sized Hitec HS-422. It operate at a
voltage of 4.6-6.0V and is able to turn 180
.
The servomotors pull on the fish wire which causes the robotic
hand to flex. The servomotors were powered by the 5V from the
Arduino. The maximum amount of torque that these servos are
able to generate is 56.93 oz-in.
Battery
Two 9-V batteries are used to power each arduino.
The Robotic Hand
Pin joint mechanical parts was as the main frame
of the fingers, we decided to use bicycle chains which allows
the fingers to have natural full range of motion. These linkages
are set into a spring which allows the fingers to return to
their resting position when the line is loosened. The bicycle
chain design pin joints were prevented from turning at all but 2
joints to create the jointed motion of actual fingers. The size
and length of the fingers and palm for our project is very
similar to the size of an average human hand.
Moreover, to combine all the fingers together to
form a hand, we used 2 aluminum metal sheet and sandwiched the
fingers using screws. Screws that were used to fix the fingers
double as points for the strings to bend around. This minimizes
the tangling of the wire. The robotic hand is also very
lightweight, durable, and portable/compact due to the materials
used and the way it is constructed.
