SKA Conference 2009Design of a Hexapod for the Phased Experimental
Demonstrator
MSc Mechatronic Engineering Mr. Frank Janse van Vuuren
Stellenbosch University Supervisor: Dr. Y. Kim
Co-Supervisor: Prof. K. Schreve
OBJECTIVE
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Objective Design a Hexapod mount to position a 3.69 m antennae at
the PED (Phased Experimental Demonstrator).
The PED is used as a testbed for the KAT project and also used to educate and train students.
Project Activities : Model Simulation Controller Design Construct a scale model Programme a Graphical User Interface Verify the performance capabilities
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Hexapod Mount (Stewart Platform)Positioning mechanism
consisting of base and platform.
Linear actuator legs. Leg lengths change length to
alter the orientation of the platform.
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Figure 1: Stewart Platform [1]
Stewart_Platform_up_down_2.wmv
AlternativeAlt-Azimuth Mount is currently widely used in telescopic positioning.
Advantages of the Hexapod Mount:High Load Carrying capacityHigh StiffnessPrecise positioning Accuracy
DisadvantagesSmall workspaceComplex controlSingularities
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Figure 2: Altitude- Azimuth Mount [2] (top) Figure 3: Hexapod Mount [3] (bottom)
Presentation Overview1. Dynamics2. Hexapod Model3. Controller4. Graphical User Interface (GUI)5. Testing6. PED Hexapod
6Hexapod
ModelController GUI Testing
PED Hexapod
Dynamics
Dynamic Forces
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fti,z
fti,y
fti,x
Bi
Ti
e2
e1
di
fbi,y
fbi,xfbi,z
x
y
z
m2gC (piston)
m1gC (cylinder)
B1
B2 B3
B4
B5B6
T1
T4
T2 T3
T5
T6
x y
z
u v
wmT
m2
m1
Dynamics Controller GUI TestingPED
HexapodHexapod
Model
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4-100
0
100
200
300
400
500
time (s)
Forc
e (N
)
Total Force
F1F2
F3
F4
F5F6
Base Joint
8Hexapod
ModelController GUI Testing
PED Hexapod
Dynamics
Plain Spherical Bearing Bush
Housing
Angular Range
Platform Joint
9Hexapod
ModelController GUI Testing
PED Hexapod
Dynamics
10Hexapod
ModelController GUI Testing
PED Hexapod
Dynamics
Model Design
Manufactured Components
11Hexapod
ModelController GUI Testing
PED Hexapod
Dynamics
Platform Joint
12Hexapod
ModelController GUI Testing
PED Hexapod
Dynamics
Linear Drive
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EncoderMotor Housing
Hexapod Model
Controller GUI TestingPED
HexapodDynamics
14Hexapod
ModelController GUI Testing
PED Hexapod
Dynamics
Hexapod Model
15Hexapod
ModelController GUI Testing
PED Hexapod
Dynamics
Controller Program FlowController PCBController Schematics
GUI Programme Flow
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Initialize program
Connect to Controller
Send Data to Controller
Controller
Connected?
Data Received
?
Display Data
USER INPUTS
Set Leg Lengths
Read Leg Lengths
Calibrate
Enable Legs
Stop
Wait for Controller
Data or User Input
Controller Busy?
GUI
Hexapod Model
Controller TestingGuiPED
HexapodDynamics
Hexapod Model System
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Controller
HexapodPower Source
Computer
Hexapod Model
Controller GUI TestingPED
HexapodDynamics
Error Radius
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X-bus Sensor Controller
Orientation Sensor
Hexapod Model
Controller GUI TestingPED
HexapodDynamics
Simulation ResultsTesting Apparatus
19Hexapod
ModelController GUI Testing
PED Hexapod
Dynamics
Parameter ValueError Radius Due to Encoder Resolution >0.028°
Maximum Speed 3.7°/s
Maximum Viewing Angle 120°
Cost Estimation R160 000
PED Hexapod
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Future WorkConstruction of PED HexapodPED Hexapod used as a research tool to
develop singularity free tracking algorithms
References
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1. Tsai, Lung-Wen. Robot Analysis: the mechanics of serial and parallel manipulators. NY : John Wiley & Sons, 1999. 0-471-32593-7.
2. Jangan, Manisha. Giant Metrewave Radio Telescope. [Online] January 20, 2005. [Cited: June 18, 2008.] http://www.gmrt.ncra.tifr.res.in/.
3. Kingsley, Jeffrey S., Martin, Robert N. and Gasho, Victor L. A Hexapod 12m Antenna Design Concept for the MMA. Taipei : s.n., 1997.
Questions?
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Thank You