BACKGROUND• Biomechanical properties of cartilage vary

throughout joint surface• Manual positioning & testing of each site is time-

consuming• Proposed Robotic Mechanical Testing System

(RMTS) incorporates a 6-DOF robotic platform to automate testing

• Indentation testing non-destructively characterizes mechanical properties of cartilage on joints

OBJECTIVES• Design an automated positioning system to allow

high throughput mechanical testing• Outfit robotic platform for mechanical testing• Incorporate modular design that can be used for

future applications

HARDWARE DESIGN

ROBOTIC MECHANICAL TESTING SYSTEM (RMTS)Meena Siddiqui, Sahil D Patel, Bradley C Hansen, Johnny C Tam, Cynzia X Fan

Won C Bae, PhD, Robert L Sah, MD, ScD, Graeme M. Bydder, MDDepartment of Bioengineering, University of California-San Diego

ACKNOWLEDGMENTS Calit2 Undergraduate Research Scholarship

Figure 1. RMTS concept design showing the major sub-systems.

• Specifications:• Weight: 800 lbs• Dimensions: Ø 36”, Height 24”• Platform capacity: 220 lbs• Accuracy: ± .002”• Repeatability: .001”• Working volume

• X,Y,Z: 4”• A,B axis: 15o

• C axis: ± 720o

2. Computer • Coordinate movement of robot, indentor, and laser• Acquire and analyze laser and indentor data• Various algorithms were designed to coordinate

movement of robot with the indentor, using data from the laser system

September 21, 2007

3. HYDRATION CONTAINMENT

4. LASER 5. INDENTOR

7. FRAME

2. COMPUTER

6. HYDRATION

1. ROBOT

7. Frame• House robot, laser, and hydration system• Provide attachments for modular subsystems• Support forces generated by the robotic platform with minimal deflection

6. Hydration SystemMaintain joint in Phosphate Buffered Saline during testingUse spray nozzle to minimize fluid volume & leakage of fluid

5. Indenting System• Apply displacement and measure force to determine mechanical stiffness• Develop active indentation system with actuator and force transducer to allow use of various probe tips • Align sample via robotic platform

4. Laser Scanning System• Obtain 3D geometric data of the cartilage surface on the joint• Measure displacements as robotic platform moves sample

• Robot Calibration Procedure Using a Laser:1. Find distance vs. volt ratio, and range of laser2. Measure translation (X, Y, Z), set up laser along

axis of motion, record at 5mm increments

3. Measure rotation (A, B, C), calculate angle of motion by:i. Representing motion with isosceles triangleii. Using law of cosines: to determine input angle α

LASER

Design Goals

Protect Platform

Fit many clamps

Fit on robot

Not affect accuracy

Resist corrosion

3. Hydration Containment System • Adapter 1: ¾” thick aluminum, ½-13 counterbores, 3/8-16 taps, self-sealing hex bolts• Basin: Anodized aluminum 16” baking pan• Adapter 2: ¾” stainless steel, 3/8-16 counterbores, ¼-20 taps, T-slots, O-ring grooves

Figure 5. Sectional view of adapters and basin assembled w/ bolts

INDENTOR

PATELLA

1.R1000 Robot• Assist laser scanning system by providing translation of sample• Align joint surface perpendicular to indentation

probe• Robot calibration necessary to examine 6DOF precision, accuracy and backlash of R1000

Figure 2. R1000 robot

PLATFORM

• Test plans:• Insert cobalt chloride moisture strips inside O-ring grooves• Blue to pink with water contact

Figure 4.18” Adapter 1 (left)10” Adapter 2 (right)

PLATFORM

Figure 3. Calibration set-up

XY

Figure 7. Indentation probe testing human patella

• NIH

• HHMI