Matrix Screw Test Station Team Synthes:
Outline Introduction Sponsor Background Introduction to the Matrix Screw Assembly overview Our testing station Project scope, realization of wants and metrics Concept Generation and Selection Station function breakdown Selected concept Subassembly overviews: chosen vs. rejected concepts Prototype Realization Assembly process Validation Testing Path forward
Sponsor Overview: Synthes International biomedical component producer, founded in Switzerland Philosophy of treating bone fractures using implants and fixtures Working with Dave Petersen, an automation engineer
Matrix Screws Basics Used in spine to hold rods Made from titanium 5-9mm diameters 27-108mm lengths Two body styles Body Collet Screw Matrix Screw
Testing the Matrix Screw Two main defects to test for Strong resistance to motion Screw can be dislodged from the body with an axial force Currently testing is performed by hand This test is subjective Body Collet Screw Matrix Screw
Assembly Overview Collet and body assembled Collet fastened inside body Part Storage Body Collet Screw Complete Matrix Screws Part arrival and removal Laser etching (labeling) Testing: Resistance to motion and security Screw inserted and pressed Currently the screws are manually assembled and tested Synthes is moving to an automated system
Project Scope Summary Testing: Resistance to motion and security Automated testing station for the screws Must measure force Be able to collect force/torque data to assist in future implementation Test that the screw is securely assembled (Axial Test) Successfully test screws of different lengths, diameters and body styles The purpose is to ensure quality through testing every size assembly in an objective, repeatable and quantifiable manner
Metrics Metric Measured By Target Value Size Area footprint (m) 0.5 x 0.6m Cycle Time Time to test a specimen 40 seconds Estimated Life Test until maintenance 6 Months Directions Tested # of directions tested 4 directions Accuracy Error between the calculated value and the actual value 0.05 Nm Precision Standard Deviation of samples 0.05 Nm Reliability Number of cycles before fault 1000 Tests before fault
Testing Process Analysis Indexing carousel rotates and brings screw to station Screw is moved to test platform Screw is gripped Screw is moved Screw s resistance to motion is measured Screw is engaged Screw is actuated Screw is returned to carousel Screw is Accepted/Rejected Rejection Notification method For now collect data Axial test is performed Axial testing apparatus Analysis reveals four essential subsystems in the testing process. The station needs systems to: 1. Move the part to and from test station 2. Perform resistance to motion test 3. Perform axial test 4. Clamp the part during the testing
Selected Concept Task Selected Concept 1. Translating the part Overhead track (blue) 2. Perform resistance to motion test Rotary testing (red) 3. Perform axial test Swing clamp (green) 4. Hold part during testing Clamping fixture (gold)
Overhead Track Assembly Rotary Table Linear Actuator Parallel Finger Gripper Rodless Cylinder Components MYB10G-300 Rodless Cylinder CQSKB16-30D Linear Actuator MSUA3-905 Rotary Table MHZ2-16C Parallel Finger Gripper Delrin/Titanium Fingers Supports Roller bearing Mounting plates Cantilevered supports Guide rail
Concept Selection: Overhead Track Due to the design of the carousel it was necessary to grip the part from above in order to remove it from the carousel. Concepts Considered Rack and Pinion Cable and Track Pneumatic Cylinder Rodless Cylinder
Testing Station: Detail View Testing System Clamp Body Grip Screw Actuate screw with rotational motion Torque sensor measures resistance to motion Overhead grip spins screw 90 o Repeat process
Concept Selection: Rotary Test Linear Test Actuation- Pneumatic Cylinder, Solenoid Interface- Cone, Hoop, U-Shape, Flat Rotational Test Actuation- Servo Motor, Stepper Motor Interface- Grip the screw
Axial Test Station: Detail View Axial Testing System Clamp Body Release overhead grip and return to initial position Apply downward force to the top of the screw with swing clamp
Concept Selection: Swing Clamp Concepts Considered Rotating Actuator from above Swing Clamp Grip Thread and Pull
Prototype Station Overhead Track Swing Clamp Rotary test
Problems During Assembly Misalignment Adding stops and shims Miscommunication of components Due to time issues components were changed Ambiguity in drawings from manufacturers of purchase components Augmenting transfer plates and fixtures
Other Steps in Assembly Wiring: sensors, power, PLC Pneumatics Coding: logic algorithm
Validation
Validation: Overhead Track With stop in place rodless cylinder goes from carousel to testing station with a consistent positioning Rotary table rotates only 90 o Gripper fingers are aligned with part properly, and can grip part in any orientation. Linear cylinder stroke length allows for both style bodies to be gripped
Validation: Testing Station The system can test screws from the smallest diameter to the largest, the shortest screws to the longest and both body styles. The swing clamp is aligned properly and the air pressure can be adjusted to provide the required force to dislodge a faulty part.
Testing Metric Measured By Target Value Testing Method Achieved Value Size Area footprint (m) 0.5 x 0.6m General Validation 0.45 x 0.45m Cycle Time Time to test a specimen 40 seconds Performance Timing 30 seconds Estimated Life Test until maintenance 6 Months Ongoing Ongoing Directions Tested # of directions tested 4 directions Performance Directions Tested 4 directions Accuracy Precision Reliability Error between the calculated value and the actual value Standard Deviation of samples Number of cycles before fault 0.05 Nm 0.05 Nm Performance Accuracy and Precision Performance Accuracy and Precision Ongoing* 0.001 Nm 1000 Ongoing Ongoing *Acquiring sufficient quantities of untested screws has proven difficult, however by testing the various components we are confident our prototype operates as expected.
Cost Analysis Other associated costs: Machining- in house Table, wiring box, wires Materials for machined parts Assistance from Synthes professionals Based on costs of the components as well as the other associated costs we estimate the total prototype cost to be about $10,000
Differences for Final Implementation Determining pass fail criteria for parts Modify the programming in the controller Non-rotating linear cylinder (overhead track) Resizing Components Rodless cylinder Clamping cylinder Integration with automated assembly system
Acknowledgements Special thanks for all of the invaluable help from Dave and others at Synthes, including: Kevin, Howard and Gerry And to Dr. Glancey and the Senior Design Staff