UWE Bristol Engineering showcase 2015

Kaya Sinclair
BEng Robotics
Project Supervisor
Dr Alexander Lenz:
A 3 D.O.F Spherical Joint with Absolute Position Sensing
Novel Method
Using a camera mounted in the joint
to track LEDs mounted in the socket
to provide a unique position of the
socket relative to the ball.
Software
Python and Open CV
Using Blob Detection methods to
track LEDs. Algorithms developed to
calculate rotations about X, Y and Z
axis.
Camera
ELP-USBFHD01ML180
Fisheye lens camera with multiple
resolutions & frame rates.
38mm x 38mm
Spherical Joint
The Joint was designed using 3D
CAD software and 3D printed.
LEDs
Red, Blue and Green
2.0mm x 1.2mm x 1.1mm
Mounted in base of socket
Lens Calibration
Due to the fisheye lens used,
calibration was completed to adjust
for distortion in the camera.
Testing
Testing apparatus was designed and
manufactured.
Testing was completed with a
accuracy of one degree, over 360
degrees in the Z axis, and over 80
degrees in the X and Y axis.
Results
Testing proved the feasibility of the
new method proposed. Aims of the
project were successfully met.
Z axis
Error Range: -2.71 to -2.04 degrees
X axis
Error Range: -2.35 to 1.4 degrees
Y axis
Error Range: -2.35 to 1.4 degrees
Speed
25 Frames a second
Further Work
• Creating a stable testing rig
• Redesign joint to keep camera in
a fixed position, and rotate the
LEDs
• Use a more opaque material for
3D printing, to prevent light
bleeding into the joint
• Optimise software algorithms to
improve speed of software
• Find or manufacture a smaller
camera to reduce size of joint.
Project summary
There is a growing desire for multiple degree
of freedom joints, particularly for use in
humanoid robotics. This project has
developed a new method for absolute
position sensing in a 3 D.O.F. spherical joint,
suitable for use in low budget applications
Project Objectives
• Design, manufacture and implement a
new absolute position sensing method for
a 3 DOF spherical Joint
• Test the new method to an accuracy of 1
degree
• Prove the feasibility of the new absolute
sensing method
Project Conclusion
The new method of absolute position sensing
is feasible, although there are plenty of
further improvements to be made to the
system.
Spherical Rotations about all three axis have
been tested to 1 degree, with no significant
deviations that could not be solved with
better testing methods, improved software or
improved hardware.
Rotations about the X and Y axis have a
maximum error of between approximately 1.4
and -2.35 degrees, and rotations about the
axis have a maximum error of between 2.71
and -2.04 at the highest resolution. The
sampling rate of the spherical joint software
runs at approximately 25 frames per second.