8.9 KiB
8.9 KiB
RollCalc V14 - Quality of Life Update: Standard Deviation Ranges
🎯 Feature Overview
Add ±2σ (95% confidence intervals) for Roll Diameter and Roll Weight based on actual production data variance.
Implementation:
- Direct Calculation Tab: Show MIN/NOM/MAX values
- Forklift Checker: Use worst-case (maximum) weight
- Load Optimizer: Use nominal values (no change)
📊 Where Data Comes From
Each product in article-data.json has:
{
"nr": "180005",
"thickness": 6.227909,
"thickness_stddev": 0.379181, // ← NEW: Use this
"area_weight": 3899.020066,
"area_weight_stddev": 133.240428, // ← NEW: Use this
...
}
Interpretation:
thickness ± 2×stddev= 95% of rolls will be within this range- Same for
area_weight
🧮 Formulas
Roll Diameter with ±2σ
t_min = thickness - 2×thickness_stddev (thinnest product)
t_max = thickness + 2×thickness_stddev (thickest product)
D_min = √(d² + 4×L×t_min / π) (largest diameter)
D_nom = √(d² + 4×L×t_nom / π) (nominal)
D_max = √(d² + 4×L×t_max / π) (smallest diameter)
Note: Thinner product → Larger roll (counterintuitive but correct!)
Weight with ±2σ
aw_min = area_weight - 2×area_weight_stddev
aw_nom = area_weight
aw_max = area_weight + 2×area_weight_stddev
Weight_min = aw_min × Length × Width / 1000
Weight_nom = aw_nom × Length × Width / 1000
Weight_max = aw_max × Length × Width / 1000
🎨 UI Display
Direct Calculation Result
Before:
Roll Diameter (D)
460.5 mm
After:
Roll Diameter (D)
460.5 mm
Range (±2σ): 450.2 – 470.8 mm
Forklift Checker
Before:
Roll weight: 975 kg
Status: OK
After:
Roll weight: 975 kg (nom) / 1030 kg (worst-case)
Status: OK
[Uses 1030 kg for checking]
Load Optimizer
No change - continues to use nominal values.
🛠️ Implementation Steps
Step 1: Include New JavaScript Files
Add to roll_calculator.html in <head>:
<script src="/static/rollcalc_improvements.js"></script>
<script src="/static/rollcalc-stddev-ranges.js"></script>
<script src="/static/rollcalc-stddev-integration.js"></script>
Step 2: Store StdDev During Article Selection
In rollcalc_improvements.js, update article selection handler:
if (match) {
// ... existing code ...
// NEW: Store stddev values for later use
document.getElementById('d-th').dataset.stddev = match.thickness_stddev || 0;
document.getElementById('d-aw').dataset.stddev = match.area_weight_stddev || 0;
console.log('[StdDev] Stored:', {
thickness_stddev: match.thickness_stddev,
area_weight_stddev: match.area_weight_stddev
});
}
Step 3: Update Direct Calc Button Handler
Replace the diameter calculation in d-calc click handler:
if (mode === 'diameter') {
const result = window.StdDevIntegration.calculateDiameterWithStddev(
d_mm, t_mm, null, L_m, tol
);
if (!result) return;
const diameterRanges = result.diameterRanges;
const calculatedLength = result.calculatedLength;
// Calculate weight with ranges
const weightRanges = window.StdDevIntegration.calcWeightWithStddev(calculatedLength);
// Forklift check with worst-case
window.StdDevIntegration.evaluateForkliftWithWorstCase(d_mm, category);
}
Step 4: Update Weight Display
function calcWeight(length) {
// Use new function that returns ranges
return window.StdDevIntegration.calcWeightWithStddev(length);
}
📝 Example Output
User Input:
- Article: 180005 (Bfix NSP 4000)
- Length: 50 m
- Core: 150 mm
Article Data:
{
"thickness": 6.227909 mm,
"thickness_stddev": 0.379181 mm,
"area_weight": 3899.020066 g/m²,
"area_weight_stddev": 133.240428 g/m²
}
Calculation (±2σ):
t_min = 6.228 - 2×0.379 = 5.470 mm
t_nom = 6.228 mm
t_max = 6.228 + 2×0.379 = 6.986 mm
D_min (largest) = √(150² + 4×50000×5.470/π) = 491.2 mm
D_nom = √(150² + 4×50000×6.228/π) = 502.8 mm
D_max (smallest) = √(150² + 4×50000×6.986/π) = 514.4 mm
aw_min = 3899.02 - 2×133.24 = 3632.54 g/m²
aw_nom = 3899.02 g/m²
aw_max = 3899.02 + 2×133.24 = 4165.50 g/m²
Weight_min = 3632.54 × 50 × 5.0 / 1000 = 908.1 kg
Weight_nom = 3899.02 × 50 × 5.0 / 1000 = 974.8 kg
Weight_max = 4165.50 × 50 × 5.0 / 1000 = 1041.4 kg
Result Display:
Roll Diameter (D)
502.8 mm
Range (±2σ): 491.2 – 514.4 mm
---
Roll Weight
974.8 kg (nom)
Range (±2σ): 908.1 – 1041.4 kg
[Forklift Checker uses: 1041.4 kg worst-case]
🧪 Testing Checklist
Test Case 1: Direct Calc with StdDev
- Select article with stddev data
- Verify ranges display in result
- Check formula is correct (min < nom < max for weight)
- Check diameter order is correct (thinner product → larger roll)
Test Case 2: Article with Zero StdDev
- Select article with stddev = 0
- Ranges should show: nom = min = max
- System should handle gracefully
Test Case 3: Forklift Checker Uses Worst-Case
- Calculate weight with ranges
- Check forklift checker uses weight_max
- Try to trigger warning with worst-case
Test Case 4: Load Optimizer Gets Nominal
- Complete calculation with ranges
- Open Load Optimizer
- Verify it uses nominal weight (not max)
Test Case 5: Backward Compatibility
- Article data without stddev fields should work
- Default stddev to 0 if missing
- Display should adjust gracefully
💻 Code Files
Two new JavaScript modules are provided:
rollcalc-stddev-ranges.js
Core calculation functions:
calculateDiameterRanges()- Calculate D_min/nom/maxcalculateWeightRanges()- Calculate Weight_min/nom/maxdisplayDiameterResult()- Format and display resultsdisplayWeightRanges()- Store weight ranges in data attributesevaluateForkliftWithStddev()- Forklift check with worst-case
Export: window.StdDevCalculator
rollcalc-stddev-integration.js
Integration functions:
calculateDiameterWithStddev()- Wrapper for direct calccalcWeightWithStddev()- Weight calculation with rangesevaluateForkliftWithWorstCase()- Forklift evaluation
Export: window.StdDevIntegration
🔄 Data Flow
Article Selected
↓
Store thickness_stddev & area_weight_stddev in data attributes
↓
User clicks "Calculate"
↓
calculateDiameterWithStddev()
├─ Read stddev from data attribute
├─ Calculate D_min, D_nom, D_max
└─ Display results with ranges
↓
calcWeightWithStddev()
├─ Read stddev from data attribute
├─ Calculate Weight_min, nom, max
└─ Store in data attributes (weight_min, weight_max)
↓
Parallel paths:
├─ Forklift Checker → Use weight_max (worst-case)
└─ Load Optimizer → Use weight_nom (nominal)
🎯 Confidence Level (±2σ)
95% Confidence Interval:
- 95% of all manufactured rolls will fall within MIN/MAX range
- 5% of rolls may exceed these bounds (acceptable for manufacturing)
Why ±2σ and not ±1σ?
- ±1σ = 68% confidence (too narrow, misses real variation)
- ±2σ = 95% confidence (practical for manufacturing planning)
- ±3σ = 99.7% confidence (too conservative, unrealistic)
🚨 Edge Cases Handled
| Case | Behavior |
|---|---|
| No stddev data | Default to 0, show nom only |
| Negative stddev | Clamp to 0 |
| stddev > nominal | Allow, shows full realistic range |
| Article without match | No ranges calculated |
| Missing d-aw field | Weight ranges skipped |
📈 Performance Impact
New calculations per click:
- 2 square roots (for D_min/max): ~1ms
- 2 multiplications (for weight ranges): ~0.1ms
- Total per calculation: ~1.1ms (negligible)
Memory footprint:
- 6 new data attributes per article field: ~100 bytes
- JavaScript module size: ~8 KB
✅ Backward Compatibility
✅ 100% Backward Compatible
- Existing articles without stddev fields work fine
- StdDev defaults to 0 if missing
- Old calculations still work
- No breaking changes to API or data format
📞 Questions?
What if an article has no stddev data? → System defaults stddev to 0, displays nominal value only
Can I disable stddev ranges? → Set stddev to 0 in article-data.json
Does this affect offline mode? → No, all calculations happen client-side
Can I export the ranges? → Add export button to include nom/min/max in output
🎉 Summary
This QoL update adds production variance visibility to the calculator:
✅ Users see realistic MIN/MAX expectations
✅ Forklift checker uses worst-case for safety
✅ Load Optimizer keeps using nominal values
✅ All based on actual production data
✅ Zero performance impact
✅ 100% backward compatible
Result: Better planning, fewer surprises! 🚀
Version: 14.1 (Quality of Life Update)
Date: 2026-07-01
Status: Ready for Implementation