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ADCATS CASE STUDY:

Investigating skew between LCD display and lens artwork affecting appearance and customer confidence. Detailed analysis approach, assembly review, model creation, constraints analysis, and tolerance calculation presented. Results and recommendations include methods for optimizing alignment.

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ADCATS CASE STUDY:

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  1. ADCATS CASE STUDY: Angular Variation in a Cellular Phone Display

  2. By: Kenneth W. Chase & Alan J. Mortensen BYU: January, 2001 Sponsored by and presented with permission from:

  3. The Problem: Skew between the LCD display and Lens artwork. Affects: • Appearance • Customer confidence in quality LCD Display 345-6789* Lens Artwork *numbers superimposed on image

  4. Analysis Approach • Review Assembly • Create Simplified Model • Analyze Constraints • Calculate Assembly Tolerance (skew) • Results and Recommendations Demonstrate 1-D Excel Solver

  5. Task 1: Review Assembly

  6. Assembly Photos: Front Case Lens Outside Inside Electronics Artwork (permanent decal) Gasket LCD PCB

  7. Assembly Photos: Front Case Lens Outside Inside Electronics Loose Artwork placement is process controlled Lens is held by adhesive Slot/Hole 2 Pins

  8. Display to Lens Artwork Assembly Graph:

  9. Task 2: Create Simplified Model

  10. Display to Lens Artwork Simplified Assembly Graph:

  11. Range of rotation determined by clearance 1-D Stack of angular variation between components Skew between Lens Artwork & Display No vector loop required because: There are no kinematic joints Only analyzing rotation Simplified Model:

  12. Task 3: Analyze Constraints Identify critical features controlling angular variation

  13. Features Analyzed: • Pin Positioning -Side-to-side relation -How far pins seat in holes • Interference between Gasket & Display -Could prevent proper seating of pins

  14. Pin Positioning: Process-Dependant Consideration < a) Deterministic angle b) Random angle Force Closed Assembly Random Location in Clearance **Cell PhoneApplication: Gasket fixes it in random position

  15. Pin Positioning: General Case • Side-to-side Consideration d2 > d1 P2 Contacts on Right d2 < d1 P2 Contacts on Left

  16. Pin Positioning:Hole vs. Slot 2 Pin / 2 Hole 2 Pin / Hole & Slot Nominal Position Extreme Position Angular Displacement

  17. Gasket/Display Interference: Requirements for pin self-alignment: • C1 > C2 • C3  0, before the gasket makes contact

  18. Gasket/Display Analysis: C6 C2

  19. Predicted range: -0.23 to +0.11 (RSS) • Gasket will sometimes not seat on display glass • Centering of pins affected by too much interference Gasket/Display Analysis: Interference between the Display & Gasket (*Negative value desired ) C2

  20. Predicted range: -0.96 to -0.62 (RSS) • Full pin diameter enters the hole before the gasket contacts Gasket/Display Analysis: Pin shoulder depth in hole when the gasket first seats C6

  21. Task 4: Calculate Assembly Tolerance (skew)

  22. Example: 2Pin/2Hole Equivalent Angle: Angular variation for each contributing process variation

  23. } Desired Skew limits:±0.78 º 2.70 assembly process quality level 3 limits from Tolerance:±0.87 º Angular Variation (3):

  24. +2.7 -2.7 ±2.7: 99.31% 6940 Angular Variation 3: +3 -3 %YieldRejects/million ±3: 99.73% 2700

  25. sasm sasm 6 Variation Defined: RSS: 6s: where Cpk = Cp(1-k)

  26. Angular Variation (6):

  27. Task 5: Results & Recommendations

  28. Angular Variation 6:

  29. Conclusions: • Tolerance analysis shows areas of concern • Possible redesign and tolerance allocation will allow improved results

  30. Advantages: • Gasket always seats with pins centered • Angular variation is decreased (clearance B<A) • No need to bottom out the pin in the hole Suggested Redesign: Present Design Suggested Redesign

  31. 1-D Analysis in Excel: • Enter inputs values and assembly specifications.

  32. 1-D Analysis in Excel: • Review Reports: Stack-Up, Assembly Quality

  33. 1-D Analysis in Excel: 3. The Assembly Distribution is automatically generated

  34. Questions?

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