Final Poster (PowerPoint) - Clemson University

filercaliforniaMechanics

Nov 14, 2013 (3 years and 6 months ago)

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The Tendril


Matthew Bennink

Clemson University

Advisor: Dr. Ian Walker

SURE 2006

Introduction


The

Tendril

is

a

continuum

robot

designed

for

in
-
space

inspection
.

The

term

minimally

invasive

is

applied

to

it,

meaning

that

it

is

simply

there

to

observe

and

not

much

else
.

Inspired

by

biology,

the

Tendril

gets

its

name

for

the

climbing

plant

tendrils

often

found

in

gardens
.

It

can

also

be

compared

to

a

snake,

tentacle,

or

worm
.

There

are

devices

very

similar

to

the

Tendril

that

exist,

but

they

are

very

mechanical

in

operation

and

require

the

user

to

manipulate

them,

while

the

Tendril

is

operated

through

a

workstation

of

some

sort,

allowing

it

to

be

controlled

remotely
.

Assembly


This version of the Tendril was built in Clemson’s
Square
-
D Laboratory in the Fluor Daniel building. All the
parts were shipped from NASA, and therefore, they are
equivalent to the original parts used.







A slight modification was made with regard to the motors.
Due to time constraints, it was decided to use an existing
motor setup to control this Tendril. The operation is very
similar, but it does cause a small problem, specifically
with getting the right tension in the cables.







Also, NASA’s Tendril has a camera mounted at the tip.
There is a joystick connected to their Tendril, allowing a
user to maneuver the Tendril by looking out of the tip
through the camera. Sometime soon, it would be very
beneficial if Clemson’s Tendril could be connected to a
joystick, since this will be the better method of operation
at the moment.







Kinematics


Kinematics is defined to be the relationship between
joint (internal) variables and task (external) variables, at
position and velocity levels. NASA produced a set of
preliminary equations which match up to the ideal case.
However, when experiments were run, the results were
not as expected. NASA have since then changed their
kinematics equations, but only to manipulate one joint.
The kinematics currently used reflect the initial results
from NASA, but both joints may be operated, just not
together. The initial kinematics equations are as follows:



M
1

= El*cos(Az)



M
2

= El*sin(Az)

where El is the elevation desired, and Az is the azimuth
desired. A more complex set of equations will allow for
the zero azimuth to be set, and also allow for a
proportionality constant which converts the degrees into
an encoder value. This set is as follows:



M
1

= El*cos(Az + offset)*k



M
2

= El*sin(Az + offset)*k

where offset is the offset used to define zero azimuth and
k is the proportionality constant. M
3

and M
4

have similar
equations, but the Az is offset an additional 45 degrees.


Conclusion


Due to the very recent assembly of the Tendril, very
little time has been spent experimenting with the
kinematics problem. However, there has been some
success, and a demo will show just how far it has come.
Given a bit more time and energy, the Tendril will soon
be well understood, and then expanded upon. Future
work with the Tendril involves making it longer and
thinner while even adding a few more bending segments.



Thanks to:

National Aeronautics and Space Administration /







Johnson Space Center

Software


QNX Neutrino was the real
-
time operating system
used with the Tendril. The QMotor software package
was the main piece of software used to control the
Tendril. This software proved invaluable, as the only
thing left up to the user is the implementation of the
control loop and the setup of a few control parameters.