This document describes work done on closed-loop motor position control for the ERIS project at the Very Large Telescope (VLT). It discusses: 1. Developing direct motor control and control with a grating wheel to an accuracy of 2 arcseconds. 2. Testing open-loop and closed-loop control schemes using resolver and autocollimator feedback. Closed-loop control achieved better precision. 3. Estimating the gear ratio between the motor and grating wheel through homing procedures and revolution counting. 4. Developing position control loops in LabVIEW and PLC software to control the motor and grating wheel to sub-2 arcsecond precision over full and half paths

1. Closed-loop Motor Position Control at
arcsecond precision for the ERIS Project
at VLT (Very Large Telescope)
AMR AWAD
STUDENT NUMBER: 840804
8/12/2016
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2. Agenda
1. About Max Planck Institute for Extraterrestrial Physics and the Project (ERIS)
2. Introduction to the Master Thesis Contribution
3. The Project Setup
4. Direct Motor Control
5. Motor Control with the Grating wheel
6. Conclusion
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3. Agenda
1. About Max Planck Institute for Extraterrestrial Physics and the Project (ERIS)
2. Introduction to the Master Thesis Contribution
3. The Project Setup
4. Direct Motor Control
5. Motor Control with the Grating wheel
6. Conclusion
8/12/2016
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4. Max Planck Institute for Extraterrestrial
Physics (MPE)
 MPE research fields and approach
• modern astrophysics and space plasma research
 MPE instruments
• Above the dense Earth (Satellites)
• Ground-based observatories (Telescopes)
 Electronic group
• Structure (developing, engineering and workshop)
• Developing concept  Engineering  Constructing 
Testing  Commissiong
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5. ERIS Project
 ERIS: Enhanced Resolution Infrared Spectrometer
 SPIFFI instrument at VLT
• SPIFFI: SPectrometer for Infrared Faint Field Imaging
• VLT: Very Large Telescope
 About the telescope physical measurement
• Near InfraRed (NIR) Imaging
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6. Agenda
1. About Max Planck Institute for Extraterrestrial Physics and the Project (ERIS)
2. Introduction to the Master Thesis Contribution
3. The Project Setup
4. Direct Motor Control
5. Motor Control with the Grating wheel
6. Conclusion
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7. Grating Wheel
 holds four gratings for the different wavelength
bands (J, H, K, High Resolution J/H/K)
 Accuracy of 2 arcsec
 Setup notes:
• First functional tests of the Grating-Wheel mechanism
without Gratings have been done.
• Turns ration is not precisely defined
• Test setup does not have Indyctosyn
Motor+
Resolver
Inductosyn Gear
Gratings
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8. Agenda
1. About Max Planck Institute for Extraterrestrial Physics and the Project (ERIS)
2. Introduction to the Master Thesis Contribution
3. The Project Setup
4. Direct Motor Control
5. Motor Control with the Grating wheel
6. Conclusion
8/12/2016
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9. Project Block diagram
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10. Agenda
1. About Max Planck Institute for Extraterrestrial Physics and the Project (ERIS)
2. Introduction to the Master Thesis Contribution
3. The Project Setup
4. Direct Motor Control
5. Motor Control with the Grating wheel
6. Conclusion
8/12/2016
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11. Problem definition
Motor Control Problem
Rated Torque
Micro-stepping
(512 micro-steps
test)
Open loop Closed loop
Position control
Resolver feedback
Resolver and
Autocollimator
feedback 8/12/2016
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12. Test setups (1)
1. Motor axis slot to fix the lever to the motor
2. Lever
3. Weight
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 Translation motion
 Reflected light position changes in Y AND Z with the
mirror motion
 Moving light focus in an arc
 Theoretically covers 610 Micro-steps
 Practically  Moving dot (Reflected light)!
4. Mirror carrying structure
5. Mirror’s reflexive surface
Y
Z

13. Test setups (2)
 Rotation motion
 Reflected light position changes in Z with the mirror
motion
 Moving light focus in a line
 Theoretically covers 9 Micro-steps
 Practically  less degrees of freedom but easier for
control
 Practically  same pattern like the grating wheel
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1. Motor axis slot to fix the lever to the motor
2. Lever
3. Weight
4. Mirror carrying structure
5. Mirror’s reflexive surface
Y
Z

14. Load torque characteristics
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 Aluminium lever:
M [mNm] = 67.836 [mm]* 0.5778 [N]
+m [kg]*9.81*(95 [mm] –a [mm])
 Vanadium lever:
M [mNm] = 56.73 [mm]* 1.0546 [N]
+m [kg]*9.81*(95 [mm] –a [mm])
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15. Results for Motor: 42.200.2,5
Lever Weight a [mm] M [mNm] Max_Y Min_Y Range_Y
Al
without N.A 39.1956 104.5 100 4.5
Al
72.01 46.4352148 121.7 111.2 10.5
61.03 49.8928278 -147.3 -156.6 9.3
50.01 53.3630368 -348.9 -370.8 21.9
39.09 56.8017557 -240.7 -251.8 11.1
28 60.2940078 182.8 168.1 14.7
VA
71.99 59.8271891 97.1 66.2 30.9
61.01 69.6722305 260.5 246.7 13.8
50.02 79.5262381 -104.3 -133.2 28.9
39.01 89.3981785
VA
without N.A 59.8275 83.1 77.2 5.9
Al
72 67.070181 151.7 132.5 19.2
55.02 72.4172 3.7 -10.8 14.5
41.5 76.6746615 13.6 7.2 6.4
27 81.240726 34.3 22.6 11.7
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16. Problem definition
Motor Control Problem
Rated Torque
Micro-stepping
(512 micro-steps
test)
Open loop Closed loop
Position control
Resolver feedback
Resolver and
Autocollimator
feedback 8/12/2016
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17. 512 Micro-stepping test (Open loop)
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 ssd
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 Load Torque:
40, 50, 60, 65, 70 [mNm]
 Reduced Current:
500, 1000,1500, 2000, 2500
[mA]
 Statistical approach

18. 512 Micro-stepping test (Closed loop)
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 ssd
18
 Load Torque:
40, 50, 60, 65, 70, 80 [mNm]
 Reduced Current:
Minimum reduced current
(Bisection approach in
equation roots finding)
500, 1000,1500, 2000, 2500
[mA]
 Statistical approach

19. 512 Micro-stepping application
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LabVIEW TWINCAT 3 (Tc2_MC2)
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20. Sample result: Open loop, 40 [mNm], 2500
[mA] (Current/ Torque)
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 Motor cycles:
• 128 up  256 down  128 up
 Holding Torque Equation:
τℎ𝑜𝑙𝑑 = 𝐾 𝐼 𝑎
2
+ 𝐼 𝑏
2
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21. Sample result: Closed loop, 40 [mNm],
1000 [mA] (Current/ Torque)
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 Motor cycles:
• 128 up  256 down  128 up
 Holding Torque Equation:
τℎ𝑜𝑙𝑑 = 𝐾 𝐼 𝑎
2
+ 𝐼 𝑏
2

22. Sample result: Position diagram
Open loop vs. Closed loop
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23. Sample result: Position Error diagram
Open loop vs. Closed loop
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24. 8/12/2016
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RMS Error (Open loop, Motor: 33.200.2,5)

25. 8/12/2016
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RMS Error (Closed loop, Motor: 33.200.2,5)

26. Maximum Load Torque Motor: 33.200.2,5
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27. Problem definition
Motor Control Problem
Rated Torque
Micro-stepping
(512 micro-steps
test)
Open loop Closed loop
Position control
Resolver feedback
Resolver and
Autocollimator
feedback 8/12/2016
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28. Position control loop
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 Setpoint scale:
 10: 350 °
 OPC UA (Realtime problem)
 PLC blocks update
 Enable/ Disable time

29. Position control loop with two sensors
(fine tuning)
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 Setpoint scale:
• 10: 350 °
 Sensors reading normalization
to avoid abrupt control action at
the transition point

30. Position control loop application
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31. Sample result: Kp= 0.0001,
Enable time = 20 [ms], Disable time= 50 [ms]
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32. Agenda
1. About Max Planck Institute for Extraterrestrial Physics and the Project (ERIS)
2. Introduction to the Master Thesis Contribution
3. The Project Setup
4. Auxiliary Tools
5. Direct Motor Control
6. Motor Control with the Grating wheel
7. Conclusion
8/12/2016
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33. Problem definition
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Grating wheel control problem
Homing Gear ratio
Micro-stepping
(512 micro-steps
test)
Open loop Closed loop
Position control
LabVIEW via OPC
UA
PLC control

34. Motor referencing procedure
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1. Initial position
2. Reference switch latch detection
3. Motor stop
4. Travelling backwards
5. Signal synchronization (omitted)
6. Reference switch release detection
7. Stop at Home Position

35. Motor referencing results
 Mechanical response of the
limit switch
 Central limit theory
 Normal distribution
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36. Problem definition
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Grating wheel control problem
Homing Gear ratio
Micro-stepping
(512 micro-steps
test)
Open loop Closed loop
Position control
LabVIEW via OPC
UA
PLC control

37. Gear ratio estimation
 Homing  one complete  Homing at the new reference
 Counting the number of revolutions made by the motor
(LabVIEW interface with the absolute 16 bit encoder)
 Statistical approach of the gear ratio estimation
 Estimated gear ratio = 2097.142
 Calculated Variance= 0.273731
 Calculate standard deviation = 0.523193
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38. Problem definition
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Grating wheel control problem
Homing Gear ratio
Micro-stepping
(512 micro-steps
test)
Open loop Closed loop
Position control
LabVIEW via OPC
UA
PLC control

39. 512 Micro-stepping test (Open loop)
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 Load Torque:
Grating Wheel
 Reduced Current:
250, 500, 750, 1000,1500,
2000, 2500 [mA]

40. 512 Micro-stepping test (Closed loop)
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 Load Torque:
Grating Wheel
 Reduced Current:
250, 500, 750, 1000,1500,
2000, 2500 [mA]

41. Sample result: Position diagram at 2500 [mA]
Open loop vs. Closed loop
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42. Sample result: Position Error diagram at
2500 [mA] Open loop vs. Closed loop
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43. Sample result: Resolver vs Autocollimator at
2500 [mA] Open loop vs. Closed loop
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44. Sample result: Resolver vs Autocollimator
Offset- Open loop vs. Closed loop
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45. Problem definition
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Grating wheel control problem
Homing Gear ratio
Micro-stepping
(512 micro-steps
test)
Open loop Closed loop
Position control
LabVIEW via OPC
UA
PLC control

46. Position control loop (LabVIEW via OPC)
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47. Position control loop (PLC)
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48. Sample result: Full path
Error < 0.02 [arcsec] (grating wheel side)
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49. Sample result: Half path
Error < 0.02 [arcsec] (grating wheel side)
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50. Agenda
1. About Max Planck Institute for Extraterrestrial Physics and the Project (ERIS)
2. Introduction to the Master Thesis Contribution
3. The Project Setup
4. Auxiliary Tools
5. Direct Motor Control
6. Motor Control with the Grating wheel
7. Conclusion
8/12/2016
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51. Conclusion
 Control achieved in open and closed loop (2 [arcsec] precision)
 OPC UA real time limitation
 Feedback from the grating wheel side is much better  Inductosyn
 Limit switch changing with better preciseness to be used with the Inductosyn
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52. Thank You!
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