Exact Constraint Design Using Tolerance Analysis Methods Danny Smith Brigham Young University 15 June 2001 Special Acknowledgements to: ADCATS Research NSF Grant DMI ADCATS 2001

Presentation Outline  Background Constraint Analysis and Screw Theory Tolerance Analysis  Variation-based Constraint Analysis of Assemblies (VCAA) Method  Case Studies  Conclusion

ADCATS 2001 Why Analyze for Constraints?  Key Definitions: Degrees of Freedom Exact-constraint Overconstraint Underconstraint

ADCATS 2001 Common Assembly Problems  Overconstraint or Redundant DOF  Underconstraint or Idle DOF

ADCATS 2001 Current Constraint Methods  Kinematic Constraint Pattern Analysis [Blanding 1999]  Geometric Constraint Solving [Hoffmann and Vermeer 1995]  Screw Theory-Based Constraint Analysis [Adams 1998], [Konkar 1993], and [Adams and Whitney 2001]

ADCATS 2001 Screws – Twists and Wrenches Twist Wrench Please see [Adams and Whitney 2001] for details

ADCATS 2001 Fundamental Principles  Reciprocity of twists and wrenches  Screw coordinate representation  Virtual coefficient  Solve for twistmatrix and wrenchmatrix

ADCATS 2001 Screw Theory Steps 1. Locate mating features on assembly using transformation matrices. 2. Form Twist matrices for each mating feature 3. Use screw algorithms and linear algebra to solve for Resultant Twist and Resultant Wrench matrices Please see [Adams and Whitney 2001] for details

ADCATS 2001 DOF Analysis Example  Individual feature screw representation  Algorithms  Resultant Twistmatrix and Wrenchmatrix  Interpretation Taken From [Adams and Whitney 2001]

ADCATS 2001 Example (Cont.)  Assembly DOF and Constraint Solution Taken From [Adams and Whitney 2001]

ADCATS 2001 Tolerance Analysis Background  Dimensional, Kinematic, and Geometric Variation  Direct Linearization Method (DLM)  Vector Loops  Global Coordinate Method (GCM) Please see [Chase 1999] and [Gao 1993] for complete details

ADCATS 2001 Direct Linearization Method  Manufactured or Independent variables  Assembly or Dependent variables  Geometric Feature variables

ADCATS 2001 Vector Loops and GCM  A Matrix Independent Variable Sensitivity Matrix  B Matrix Dependent Variable Sensitivity Matrix  F Matrix Geometric Feature Variable Matrix  Sensitivities are determined by the GCM

ADCATS 2001 Development of the Variation-based Constraint Analysis of Assemblies (VCAA) Method  Variation analogies Velocity Force and moments  GCM connection  Employs screw theory  Solves for under- and overconstraints underconstraint information [B][B] overconstraint information [F][F]

ADCATS 2001 VCAA for Underconstraints [ B ] T column T joint i W intermediate-joint i W intermediate-part j T Resultant-part j DLM Tolerance Analysis Transpose and Switch Associate Dependent Variables to Joint Types Reciprocal Operation Reciprocal Operation Union Matrices For Each Part

ADCATS 2001 VCAA for Overconstraints DLM Tolerance Analysis Transpose [ F ] W column W jointi T intermediate-jointi T intermediate-part j or T intermediate-loop k W Resultant-part j or W Resultant-loop k Associate Geometric Feature Variables to Joint Types Reciprocal Operation Reciprocal Operation Union Matrices For Each Part or Loop

ADCATS 2001 Case Studies of VCAA  Case 1 - One-way Clutch Assembly in 2-D  Case 2 - Stacked Blocks Assembly in 2-D  Case 3 - Crank Slider Assembly in 3-D

ADCATS 2001 Case 1 - One-Way Clutch Assembly  Transmits torque in one rotational direction  Assembly formed from Roller, Hub, and Ring  Pressure Angle  1 is the key dimension

ADCATS 2001 Case 1 - Sensitivity Matrices  Sensitivity Matrices Calculated using GCM

ADCATS 2001 Case 1 - Underconstraint Analysis  Form Joint Twists for each joint from [B]  Perform intermediate steps See [Adams 1998]  Evaluate Resultant Twist for each part to identify underconstraint information

ADCATS 2001 Case 1 - Underconstraint Solution and Results  Resultant Twists for each part show any underconstrained degrees of freedom

ADCATS 2001 Case 1 - Overconstraint Analysis  Form Joint Wrenches for each joint from [F]  Perform intermediate steps See [Adams 1998]  Evaluate Resultant Wrench for each part to identify overconstraint information

ADCATS 2001 Case 1 - Overconstraint Solution and Results  Resultant Wrench for each set shows any overconstrained degrees of freedom

ADCATS 2001 Case 2 – Stacked Blocks Assembly  Theoretical assembly for tolerance analysis  Assembly formed from Base, Block, and Cylinder  Vertical placement A of cylinder is key dimension  Three Vector Loops needed

ADCATS 2001 Case 2 - Sensitivity Matrices  Sensitivity Matrices Calculated using GCM

ADCATS 2001 Case 2 - Sensitivity Matrices  Sensitivity Matrices Calculated using GCM

ADCATS 2001 Case 2 - Underconstraint Analysis  Form Joint Twists for each joint from [B]  Perform intermediate steps See [Adams 1998]  Evaluate Resultant Twist for each part to identify underconstraint information

ADCATS 2001 Case 2 - Underconstraint Solution and Results  Resultant Twists for each part shows any underconstrained degrees of freedom

ADCATS 2001 Case 2 - Overconstraint Analysis  Form Joint Wrenches for each joint from [F]  Perform intermediate steps See [Adams 1998]  Evaluate Resultant Wrench for each part to identify overconstraint information

ADCATS 2001 Case 2 - Overconstraint Solution and Results  Resultant Wrench for each set show any overconstrained degrees of freedom

ADCATS 2001 Case 3 – Crank Slider Assembly  Assembly formed from Base, Crank, Link, and Slider  Slider Position U is the key dimension  One Vector Loop needed

ADCATS 2001 Case 3 - Sensitivity Matrices  Sensitivity Matrices Calculated using GCM

ADCATS 2001 Case 3 - Sensitivity Matrices  Sensitivity Matrices Calculated using GCM

ADCATS 2001 Case 3 - Underconstraint Solution and Results  Resultant Twists for each part show any underconstrained degrees of freedom

ADCATS 2001 Case 3 - Overconstraint Solution and Results  Resultant Wrench for each set shows any overconstrained degrees of freedom

ADCATS 2001 Conclusions  VCAA Method connects Constraint Analysis and Tolerance Analysis  Based on Screw Theory and the Global Coordinate Method  The VCAA Method can extract twist and wrench matrices directly from the vector model  Can perform a constraint analysis and a tolerance analysis simultaneously

ADCATS 2001 Bibliography  Adams, Jeffrey D. Feature Based Analysis of Selective Limited Motion in Assemblies. Master of Science Thesis, Massachusetts: Massachusetts Institute of Technology,  Adams, Jeffrey D.; Whitney, Daniel E. “Application of Screw Theory to Constraint Analysis of Mechanical Assemblies Joined by Features.” In Journal of Mechanical Design: Transactions of the ASME, Vol. 123, pp , March  Blanding, Douglass L. Exact Constraint: Machine Design Using Kinematic Principles. New York: ASME Press,  Chase, Kenneth W. Dimensioning & Tolerancing Handbook, ed. Paul J. Drake, Jr., New York: McGraw Hill, “Multi_Dimensional Tolerance Analysis.”, 1999.

ADCATS 2001 Bibliography (cont.)  Chase, Kenneth W.; Gao, Jinsong; Magelby, Spencer; Sorensen, Carl. “Including Geometric Feature Variations in Tolerance Analysis of Mechanical Assemblies.” In IIE (Institute of Industrial Engineers) Transactions, Chapman & Hall Ltd., pp. 795_807, 10 Oct  Gao, Jinsong; Chase, Kenneth; Magleby, Spencer. “Generalized 3-D Tolerance Analysis of Mechanical Assemblies with Small Kinematic Adjustments.” In IIE (Institute of Industrial Engineers) Transactions, Chapman & Hall Ltd, pp. 367_377, 4 April  Gao, Jinsong; Chase, Kenneth; Magleby, Spencer. “Global Coordinate Method for Determining Sensitivity in Assembly Tolerance Analysis” in Proceedings of the ASME International Mechanical Engineering Conference and Exposition, Anaheim, California, 1998

ADCATS 2001 Bibliography (cont.)  Gao, Jinsong. Nonlinear Tolerance Analysis of Mechanical Assemblies. A Doctor of Philosophy Dissertation, Provo, Utah: Brigham Young University, August  Hoffmann, Christoph; Vermeer, Pamela. Computing in Euclidean Geometry (2 nd Edition), ed. Du, Ding-Zhu; Hwang, Frank, Singapore: World Scientific Publishing Co. Pte. Ltd., “Geometric Constraint Solving in U 2 and U 3.”, pp ,  Konkar, Ranjit. Incremental Kinematic Analysis and Symbolic Synthesis of Mechanisms. Doctor of Philosophy Dissertation, Palo Alto, California: Stanford University, June  Konkar, Ranjit; Cutkosky, M. “Incremental Kinematic Analysis of Mechanisms.” In Journal of Mechanical Design, Vol. 117, pp , December 1995.

ADCATS 2001 Bibliography (cont.)  Roth, Bernard. “Screws, Motors, and Wrenches that Cannot be Bought in a Hardware Store.” In Robotics Research, Chapter 8, pp ,  Waldron, K. J. “The Constraint Analysis of Mechanisms.” In The Journal of Mechanisms, Volume 1, pp Great Britain: Pergamon Press, 1966.