1. Dahlin Control of a Wood Flake Conveyor Dryer
Robert Spring, P. Eng., CAP

2. Presenter Robert Spring, P.Eng, CAP
A specialist in heat energy and wood drying.
Interests include optimization, sensors and advanced controls.
Work experience in the mineral processing, pulping, paper-making and wood products industries.

3. Why Dry?

4. Conveyor Dryers – Transportation Delay
Transport Delay = 15 minutes
Energy Usage = 10,000 Households

5. Dryer Schematic

6. PID versus Dahlin - Simulations

7. “Not-dumb” Use of Information
Error
Past Move
Dead-time
Fixed Parameters

8. Design the Trajectory

9. Synthesis Steps – Model Identification
Process Gain
Process Time Constant
Dead-time
Control Time Interval

10. Synthesis Steps – Controller Implementation

11. Adaptive Dead-time

12. Bumpless Transfer and Anti-windup

13. Bumpless Transfer and Anti-windup

14. Feed-forward

15. Feed-forward

16. Disturbance Model
Time Constant
Gain
Dead-time

17. Feed-forward

18. Benefit of Feed forward - Simulations

19. Before and After Dahlin Control
σ=1.8%
σ=0.7%

20. PLC Implementation

21. Ladder Logic Sample

22. Structured Text Sample
// b*x(t) NewSpeed := Lambda *OldSpeed; // DelayAdj changes with the speed Index := DelayAdj; // Reference into stored vector of past speeds SpeedDelayedN := Speed_Time_Series[Index]; // (1-b)*x(t-n) NewSpeed := NewSpeed+(1.0-Lambda)*SpeedDelayedN;

23. Packaging as a Subroutine or Add-on

24. Conclusions – Dahlin Control
Suited for:
long dead-time
variable dead-time
feed-forward compensation
Simple to program (ladder logic or structured text)
Single tuning parameter

25. Result: Make Every Board the Same