Design and Control Challenges for a Surgical Radiographic Imaging System Tim Elmore Orthopaedic Biomechanics Laboratory Department of Mechanical & Aerospace Engineering University of Florida

The Motivation What surgeons can see… What surgeons want to see… http://www.theploughhundon.co.uk/steak%20tuesday.jpg http://www.flickr.com/photos/stanfordmedicine/3660598599/

The Motivation Current O-arm technology remains in sterile field, giving surgeon limited access to patient The standard in industry … Over 100 ft3 total volume!

The Motivation Existing project development… Gator-Ray ! + =

Design Challenges for Surgical GatoRay Kinematic DOF Obstacles Reach Accuracy Kinetic Payload mass Velocity/Acceleration Bearing life 5 degrees of freedom OR table, surgeons, equipment Under OR table to lateral view +/- 1mm, +/-1 deg 30-60kg (65-130lbs) 0.25m/s, 2.5m/s^2 1,500,000 cycles (100/day, 40yr)

Mitsubishi PA10-6CE Specifications Six Degree-of-Freedom Robot Arm 3-phase AC Brushless Servo Motors Harmonic Drive Transmissions Manufacturer Specified Positional Repeatability of ±0.1mm AND Joint Resolver Accuracy = ±0.44 arc min (0.0073º) 10kg payload limit

Mitsubishi PA10-6CE Specifications This payload would result in a 700% overload!

Alternative Manipulators Panasonic VR-032 Robot Axes: 6 Payload: 32 kg H-Reach: 1866 mm Repeatability: ±0.15 mm Robot Mass: 580 kg Mounting: floor, ceiling Disadvantages: Size Mass EE rotations are translation dependent Cost ($20,000 used) Table Height: 32 inches/810mm

Alternative Manipulators Parallel Manipulators Degrees of Freedom: 6 Payload: high (>30kg) Repeatability: good (<1mm) Robot Mass: low (<200 kg) Disadvantage: Limited rotation angles Limited translations

Alternative Manipulators Ballscrew/Rotary tables Degrees of Freedom: 1 per table Payload: high (>100kg) Repeatability: good (<1mm) Robot Mass: low (<200 kg) Advantages: Each axis is customizable Mass supported by frame, not torque

The Proposed System (v0.1) X-Ray Source Undertable Robot

The Proposed System (v1.0) PA-10 X-Ray Sensor X-Ray Source Under table Robot

The Proposed System (v1.0) X-Ray Source Z Y X Undertable Robot

The Proposed System (v1.0)

Design Goals for Surgical GatoRay Kinematic 5 DOF (3 translation, 2 rotation) Reach around table into lateral view Displacement: 3 translation, 2 rotation Accuracy 0.2mm/axis, 1mm total Kinetic 30-60kg payload 0.5m/sec velocity, 5m/sec2 acceleration 1,500,000 cycles at 30kg load

Kinematics By inspection, task space dependencies: Rx = f(xjs,Θzjs) Ry = f(yjs,Θzjs) Rz = f(zjs) Θx = f(Θxjs) Θz = f(Θxjs, xjs, yjs) Z Y X

Kinematics

Kinetics Motor choices Servo Stepper Pros: torque, speed Cons: size, price, control Stepper Pros: size, price, control Cons: torque, speed

Kinetics Servo Control Input Output Stepper Control Input Output

Stepper Motors

Stepper Motors 125kg horizontal payload 30kg vertical payload time