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, MD Department 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: 15 o C axis: ± 720 o 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, 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 System Maintain joint in Phosphate Buffered Saline during testing Use 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 laser 2.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 triangle ii.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 X Y Figure 7. Indentation probe testing human patella NIH HHMI