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?

22

Thank You