hexapod structures in surgical applications presented by sanjay shirke muhammad umer

Hexapod Structures in Surgical Applications

Presented by

Sanjay Shirke

Muhammad Umer

March 18, 2003Hexapod Structures in Surgical Applications

ME 250 - Precision Mechanism Design Shirke/Umer

The Hexapod - A Brief History of Design

1800’s –Mathematician Augustine Cauchy studies rigidity of polygons

1947 – Dr. Eric Gough applies the parallel kinematic platform to a tire testing machine developed working under Dunlop.

1962 – Klaus Cappel develops vibration equipment for Franklin Institute.

1965 – Stewart platform developed for aircraft simulation. 1995 – Frauhofer Institute in Stuttgart, Germany approaches

Physik Instrumente to develop the surgical robot.




Fig.1. 1949-2000 (a)The original Dunlop tire testing machine invented by Eric Gough, (b) The modern tire testing machine.

(a) (b)




Fig.2. 1965 -1970 (a)The original Stewart Platform for aircraft simulation, (b) later incorporating the design of an octahedral hexapod.

(a)

(b)




Fig.3. 6 DOF motion achieved through 6 strut linear actuators. The resulting rapid, submicron multi-axis translation and rotation makes the hexapod ideal for precision surgical applications.




Universal Joints - offer 2 rotational DoF

Linear Hydraulic Actuators - offer 2 DoF: 1 translation and 1 rotation

Source: Marks’ Standard Handbook for Mechanical Engineers



Hexapods – Engineering and Kinematic PrinciplesMobility – The Kutzbach Criterion:

n = 12 (struts) + 1(base) + 1(platform) = 14

c = 3 x 6 x 4 = 72

M = 6(14 – 1) – 72 = 6 DoF

j

iicnM

1

)1(6

Quantity Occurrences Constraints # DoF Description

6 Base: Yoke 1/ Yoke 2 Universal Joint 4 2 RR

6 Strut Lower end (Y2) / Strut upper end (Y3) 4 2 TR

6 Strut Upper end (Y3) / Platform Universal Joint (Y4) 4 2 RR



Hexapods – Engineering and Kinematic PrinciplesRange of Motion and

ResolutionModels M-800.11 M-800.12

Travel X [mm] ±35 ±64

Travel Y [mm] ±35 ±59

Travel Z [mm] ±14 ±26

Travel Theta-X/Theta-Y [°] ±8 ±20

Travel Theta-Z [°] ±25 ±45

Actuator stroke [mm] ±13 ±25

Resolution X/Y [µm] 1 2

Resolution Z [µm] 0.5 1

Resolution Theta-X/Theta-Y/Theta-Z [arcsec] 1 1.4

Fig 4. The Physik Instrumente M-800.11



Hexapods – Engineering and Kinematic Principles

Design Criteria Minimize mass and inertia for

maximum speed and acceleration.

Strut Operation – linear hydraulic actuators

Joint Design – Universal or Ball and Socket

Integrity tested with CAD, FEA, and laser vibrometery tools.



Is the Hexapod really worth it?

advantages Complete range of motion. High precision and

accuracy Computer visualization

tools High stiffness High load/weight ratio

limitations Friction Length of struts Dynamic thermal growth Calibration



Development of Surgical Applications

Hexapod vs. Nonapod Extra legs contain

redundant sensors Insures against failure

of standard measuring system

Reliability increase is of the essence



The future of Parallel Kinematics Minimize Friction, hysteresis, and backlash Improve material composition to limit thermal

growth Actuators – A future in the voice coil? Currently, applications are limited to endoscopy.

Incorporate use of scissors, forceps, balloon catheters and coagulation probes.

Endorse the use of a cockpit to create a “virtual surgery” environment

Expand to the fields of orthopedics, ear/nose/throat surgery, and ophthalmology.



Bibliography and References Avallone, E.A., Baumeister III, T., Marks’ Standard Handbook for

Mechanical Engineers 10th Edition, McGraw-Hill, New York, 1996 Hale, Layon C., “Principles and Techniques for Designing Precsion

Machines”, UCRL-LR-133066, Lawrence Livermore National Laboratory, 1999.

Smith, S.T., Chetwynd, D.G., Foundations of Ultraprecision Mechanism Design, Gordon and Breach Science Publishers, Switzerland, 1992.

“Low-Inertia Parallel-Kinematics Systems for Submicron Alignment and Handling” (http://www.parallemic.org/Reviews/Review012.html)

“Why Hexapods and Parallel Kinematics?” (http://www.hexapods.net/hexapod.htm)



Bibliography and References

“Six DOF Hexapod: Challenge of Design and Innovation” (http://biotsavart.tripod.com/hexapod.htm)

“Surgeon Navigates … from Operating Cockpit” (http://www.hoise.com/vmw/articles/LV-VM-05-98-17.html)

“History of the Universal Joint” (http://www.driveshafts.com/u-joint.html)

“M-850 Hexapod 6-Axis Parallel Kinematics Robot” (http://www.physikinstrumente.com/micropositioningsystems/8_4.html)

hexapod structures in surgical applications presented by sanjay shirke muhammad umer

Documents

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