Ben Cazzolato

John Costi

Boyin Ding

Richard Stanley

Hexapod Robot Control System for Biomechanics Testing

Ben S. Cazzolato, John Costi, Boyin Ding and Richard Stanley

Hexapod Robots (or Stewart Platforms) are used in many applications where precise six degree of freedom (6 DOF) position and motion control are required. A few of the industries using this design include aerospace, automotive, nautical, and machine tool technology. Hexapod Robots have been used to simulate flight, model a lunar rover, build bridges, aid in vehicle maintenance, design crane hoist mechanisms, position satellite communication dishes and telescopes, among other tasks.

A novel design of a Hexapod Robot is underway at the School of Computer Science, Engineering & Mathematics, Flinders University and the School of Mechanical Engineering, University of Adelaide, to enable complex 6 DOF testing of bones, joints, soft tissues, artificial joints and other medical/surgical devices. The project is being funded by funds awarded to Dr Costi from Foundation Daw Park, Repatriation General Hospital, The Health and Medical Research Fund, Department of Health, SA Government, and jointly by the School of Computer Science, Engineering & Mathematics and the Faculty of Science & Engineering, Flinders University. The University of Adelaide is providing in-kind support, primarily in the design of the controller and human-machine-interface. The current hexapod is based heavily on the very successful Hexapod developed at the UVM by Ian Stokes et al..

The system is comprised of the following:

• Six Aerotech BM Series Brushless Servo Motors to actuate the legs
• Six Aerotech Soloist Servo Amplifiers to drive the motors and provide some fault diagnostics
• The motors are coupled to Edrive Ballscrew Linear Actuators
• Linear encoders are employed (in conjunction with the rotary encoders in the servo motors) to ensure absolute positioning control
• An AMTI load cell provides load feedback for the 3 forces and 3 moments generated by the manipulator
• Control of the entire system is being implemented using National Instruments hardware and Labview. The system operates a host/target configuration using Labview RealTime. The majority of the high-level control functions are performed on the realtime PXI target. High speed control of the position or load servo loops are performed on FPGAs. The figure below shows the architecture of the control hardware.

Currently the mechanical design is being finalised to minimise compliance. A control system to operate the Hexapod Robot in six degrees of freedom under closed-loop position or load control is being developed. Successful dual-loop control has been achieved for each of the leg, and the global controller for the kinematics and trajectory generation is well underway. A user-friendly GUI to allow input of required testing parameters and logging of data is also underway.