Prediction of Workpiece Location Due to Fixture-Induced Error

Transcription

1 Predition of Workpiee Loation Due to Fixture-Indued Error Anand Raghu: Graduate Student Dr. Shreyes Melkote: Faulty Advisor IAB Meeting for PMRC Otober 29 th, 2002

2 Outline: Projet goal Prior work Model omponents Model integration Loators Base Workpiee Hydrauli Clamps Initial results Basi Fixturing sheme Summary and next steps

3 Projet goal: Fixtures are a ritial omponent of the manufaturing system, they serve to repeatedly and uniquely loate and hold a workpiee. Fixture indued errors suh as: Clamp, loator, workpiee bulk deformation Loator and workpiee geometry error Clamping sequene, all effet workpiee fixturing error. Our goal is to model these error soures to better understand their effet on the final position and orientation of the workpiee Appliation: - Fixture design - Tool path and assembly trajetory planning/orretion - Tolerane alloation

4 Prior Work: Author Primary fous Limitation DeMeter Salisbury DeVor Melkote Simoltaneous solution with loator error Sequential solution with loator & wrkp error Modeling of effet of lamping sequene Loalized ontat deformation model Rigid workpiee and loator, no lamping effets Rigid workpiee and loator, no lamping effets Error in loator or workpiee geometry not modeled No bulk deformation of system, workpiee position not effeted Our model s limitations: -Prismati workpiees loating sheme (an be extended with modifiations) -Limited lamping loations -Re-run FEA to generate flexibility influene oeffiients

5 Model omponents: workpiee plaement - Uses sequential positioning - Motion through series of translations and rotations 1 2 1: ontat primary datum plane 3 Not in line with other two on the plane Top view of fixture 2: ontat seondary datum plane Side view of fixture 3: ontat tertiary datum plane Side view of fixture

6 Bulk deformation model: workpiee - Simple model in ANSYS to determine flexibility influene oeffiients - Points are onstrained at base orners of workpiee Clamping fore 3 DOF onstraints δ1 δ 2 δ 3 = F F F ij : flexibility influene oeffiient Basi model Flexibility influene oeffiient matrix for a 3 DOF system

7 Bulk deformation model: lamp and loator Clamp bending: (beam model) Fixture layout (top view) F lamp F tangential F lamp F lamp F axial Loator bending: (short stubby beam model) F tangential

8 Loal deformation and lamping sequene Loalized deformation model developed by Satyanarayana and Melkote Clamping sequene model By Chandra and DeVor Wrk p Wrk p Contat deformation (S. Sathyanarayana thesis, 2001) Wrk p

9 Model integration Input onditions Determine deformation magnitudes Sum geometri and deformation error Initial onditions Clamping fores Workpiee geometry Loator positions Clamping positions Deformation alulation: Minimization of system energy method Error modeling: E total = E geometry + E deformation Determine final position and orientation of workpiee

10 Initial results Workpiee dimensions x, 12 units y, 12 units z, 2 units Poi nt Coor di nat e Point 1 (4, 4, 0) Point 2 (16, 16, 2) Perent error Perent error omparison to hand alulation Jayaram New Model KEY Case 1 Translation A Point 1 Case 2 Translation A Point 2 Case 3 Translation B Point 1 Case 4 Translation B Point 2 Case 5 Translation C Point 1 Case 6 Translation C Point 2 Case 7 Translation D Point 1 Case 8 Translation D Point 2 Case 9 Rotation A Point 1 Case 10 Rotation A Point Case Number

11 Summary and next steps - Presentation of goal - Desription of model and omponents - Model integration - Initial results Next steps: - Generate alternative flexibility influene oeffiients - Integration of entire model - Validation through experimental testing

12 Questions