Note
This technote is a work-in-progress.
1 Abstract¶
This technote reports the data analysis M2 no-back driving for the axial and tangent actuators. The tests have been conducted at the Level 3 and the test case formulation and execution can be found here:
Axial actuators: https://jira.lsstcorp.org/secure/Tests.jspa#/testCase/LVV-T2873
Tangent actuators: https://jira.lsstcorp.org/secure/Tests.jspa#/testCase/LVV-T1784
The Jupiter Notebook scripts of the data analysis can be found here:
TBW ADD GitHub links
The Jupiter Notebook script used for the test execution on the axial actuators can be found here: https://github.com/lsst-sitcom/notebooks_vandv/blob/develop/notebooks/tel_and_site/subsys_req_ver/m2/m2_functional_verification/LVV-T1784-no_back_driving.ipynb The tangent actuators do not require any test script since the M2 surrogate wieght is used as an equivalent applied force close to the closed-loop maximum force limit.
2 Requirements to be verified¶
LTS-146-REQ-0084-V-02 3.3.1.4 GRAVITATIONAL ORIENTATION OFF-TELESCOPE - M2 LSST Re-verification LTS-146-REQ-0084-V-03 3.3.1.8 NO BACK-DRIVING - M2 LSST Re-verification
3 Axial actuators¶
The no-back driving behaviour of the axial actuators has been tested in two configurations: with the M2 surrogate facing downward and the M2 weight pulling the actuators, and with the M2 surrogate facing upward with the M2 weight pushing the actuators. The axial actuators have been tested subdividing the 72 actuators in 8 groups of 12 actuators each. Within each group to avoid excessive stress on the actuators, half of them (6 units) have been pushed towards the positive force limit value (444N) and the other half was pushed towards the negative force limit value (-444N) as shown in Figure 1. The force to be applied is estimated by retrieving a statistics of the axial actuator measured forces from the EFD and their oscillations as follows:
The test script deliberately keeps a contingeny (430N instead of 444N) to avoid triggering any faults for maximum force limits in closed-loop.
Figure 1. Map of the 72 axial actuators. Of each tested group made of 12 actuators, half of them (large yellow circles) are pushed towards the positive force limit value (444N) and the other half (small blue circles) towards the negative force limit value (-444N) which is not achieved in absolute value because all the actuators have non-zero force controlled by the force balance to distribute the load of the M2 surrogate weight.
Once the applied force is commanded the force is held for approximately 30 sec before cutting the M2 cell power by pushing the Estop button. This window is needed to acquire a reliable measurement of the measured forces and RBP as measured by the IMS before the power cut to compare with the same quantities following the power cut. This comparison is the core of the no-back driving test. Figure 2 shows the drops of the motor current following the push of the Estop.
Figure 2. The motor current of the M2 cell drops to zero following the E-stop push.
The typical profile of the measured forces before and after the commanded force (orange) and the Estop push (green) is reported in Figure 3.
Figure 3. The profile of the measured forces from 12 axial actuators with the highlighted times of the commanded applied force (orange) and the Estop push (green).
The measured forces from 12 axial actuators before (blue) and after (orange) the Estop push are shown in Figure 4.
Figure 4. Profiles of the measured forces from 12 axial actuators before (blue) and after (orange) the Estop push.
To get a reliable proof of the no-back driving behaviour of the axial actuators we look at the motor encoder position after the Estop push. A null angular coefficient of the linear fit of the motor encoder position proves that the actuators do not back drive and verifies the requirement LTS-146-REQ-0084-V-03 3.3.1.8 NO BACK-DRIVING - M2 LSST Re-verification. The typical motor encoder position and fit are shown in Figure 5.
Figure 5. Linear fit (dashed line) of the motor encoder position (yellow) from 12 axial actuators after the Estop push.
GROUP 1 |
GROUP 2 |
GROUP 3 |
GROUP 4 |
GROUP 5 |
GROUP 6 |
GROUP 7 |
GROUP 8 |
|---|---|---|---|---|---|---|---|
2.3e-16 |
-8.2e-16 |
-9.3e-16 |
-4.4e-16 |
5.4e-17 |
2.7e-16 |
5.5e-06 |
3.3e-17 |
-1.4e-16 |
1.2e-16 |
7.7e-07 |
-6.9e-17 |
-6.7e-18 |
1.4e-16 |
-2.0e-16 |
-1.7e-17 |
5.8e-08 |
8.7e-17 |
-3.6e-18 |
-5.5e-17 |
1.7e-18 |
3.8e-16 |
-5.7e-16 |
2.6e-16 |
3.5e-16 |
-9.8e-21 |
-8.7e-17 |
-1.9e-06 |
-6.7e-18 |
-6.8e-17 |
6.5e-17 |
-4.1e-17 |
7.3e-18 |
-1.9e-20 |
4.6e-07 |
8.8e-07 |
-1.3e-17 |
9.5e-17 |
-4.3e-17 |
-4.9e-17 |
-1.3e-16 |
9.8e-21 |
-5.8e-16 |
-6.1e-16 |
1.1e-16 |
8.7e-16 |
-3.4e-16 |
-6.6e-17 |
5.8e-16 |
-1.8e-16 |
-5.8e-16 |
-2.8e-16 |
1.1e-16 |
3.0e-16 |
-5.7e-17 |
9.9e-17 |
3.5e-16 |
-4.4e-17 |
-1.7e-16 |
-2.2e-16 |
1.3e-16 |
3.4e-17 |
1.4e-17 |
2.1e-18 |
-8.0e-16 |
-3.6e-18 |
2.5e-17 |
-1.4e-17 |
2.2e-16 |
4.3e-16 |
-3.4e-16 |
2.0e-16 |
2.9e-16 |
1.2e-16 |
-5.8e-16 |
-5.5e-17 |
2.7e-17 |
1.1e-16 |
2.8e-06 |
6.6e-17 |
5.8e-17 |
-6.6e-17 |
-8.7e-17 |
-1.7e-16 |
2.7e-17 |
2.7e-17 |
1.8e-18 |
5.2e-19 |
7.9e-19 |
5.8e-17 |
-1.7e-16 |
-3.0e-16 |
5.4e-17 |
5.9e-16 |
-4.6e-16 |
-6.6e-17 |
GROUP 1 |
GROUP 2 |
GROUP 3 |
GROUP 4 |
GROUP 5 |
GROUP 6 |
GROUP 7 |
GROUP 8 |
|---|---|---|---|---|---|---|---|
1.3e-16 |
0 |
-7.2e-17 |
2.4e-17 |
-1.7e-16 |
-1.5e-16 |
-4.3e-16 |
5e-16 |
-3.4e-06 |
6.4e-17 |
-2.5e-06 |
3.2e-17 |
-8.9e-18 |
-2.6e-17 |
-1.6e-16 |
2.6e-17 |
-2e-16 |
-7.7e-17 |
-6.8e-07 |
1.5e-07 |
0 |
-9.2e-06 |
-2.4e-16 |
2.1e-16 |
-7e-07 |
3.1e-21 |
-5.7e-17 |
7e-06 |
-8.5e-08 |
-3.1e-16 |
-3.2e-16 |
1.5e-16 |
-5.7e-17 |
6.3e-21 |
-1.7e-16 |
1.1e-16 |
2.8e-17 |
-5.1e-17 |
-2.1e-16 |
6.2e-17 |
-8.5e-17 |
-3.1e-21 |
-2.9e-17 |
4.8e-17 |
4.2e-17 |
0 |
1.3e-17 |
7.3e-17 |
-2.3e-16 |
9.7e-18 |
-5.7e-17 |
8e-17 |
-2e-16 |
2e-16 |
-2.1e-16 |
1.7e-16 |
-2.8e-16 |
5.2e-17 |
-3.4e-16 |
-3.1e-07 |
-1.4e-16 |
-5.1e-17 |
-2e-17 |
1.2e-16 |
-1.7e-16 |
1.2e-16 |
-8.6e-17 |
4.8e-17 |
-4.2e-07 |
-5.1e-17 |
-3.3e-17 |
-1e-16 |
-4.3e-17 |
1e-16 |
-3.6e-18 |
5.6e-17 |
0 |
-1e-16 |
-2.9e-07 |
-2.3e-17 |
-1.7e-16 |
5.2e-17 |
0 |
1.6e-16 |
-1.7e-16 |
-5.1e-17 |
1.3e-17 |
5e-06 |
-2.1e-06 |
2.1e-16 |
-1.4e-16 |
-1.6e-17 |
2.8e-17 |
2.6e-17 |
-2.4e-06 |
-6.2e-17 |
During the power cut the RBP is monitored using the IMS to verify that its position does not change when the M2 cell is unpowered. See Figure 6 for the trend of the 6 degrees of freedom.
Figure 6. Behaviour of the 6 degrees of freedom of the M2 surrogate RBP as monitored by the IMS.
This check verifies the requirement LTS-146-REQ-0084-V-02 3.3.1.4 GRAVITATIONAL ORIENTATION OFF-TELESCOPE - M2 LSST Re-verification by proving that the mirror support system safely supports the M2 mirror for any orientation of the M2 cell relative to the gravity vector, from 0 degrees (zenith) to 90 degrees (horizon), while the M2 Cell Assembly is powered on or off.
IMS DoF |
Command Time |
eStop |
|---|---|---|
GROUP1 |
Command Time |
eStop |
x |
-5.57 +/- 0.02 |
-5.6 +/- 0.00 |
y |
4.19 +/- 0.04 |
4.2 +/- 0.00 |
z |
10.58 +/- 0.01 |
1.1e+01 +/- 0.10 |
xRot |
4.88 +/- 0.00 |
4.9 +/- 0.01 |
yRot |
1.60 +/- 0.00 |
1.6 +/- 0.01 |
zRot |
0.44 +/- 0.00 |
0.44 +/- 0.00 |
GROUP2 |
Command Time |
eStop |
x |
-3.70 +/- 0.07 |
-3.7 +/- 0.00 |
y |
1.74 +/- 0.05 |
1.7 +/- 0.00 |
z |
29.47 +/- 0.06 |
2.9e+01 +/- 0.03 |
xRot |
15.88 +/- 0.01 |
1.6e+01 +/- 0.00 |
yRot |
2.87 +/- 0.01 |
2.9 +/- 0.00 |
zRot |
0.28 +/- 0.01 |
0.27 +/- 0.00 |
GROUP3 |
Command Time |
eStop |
x |
-7.42 +/- 0.00 |
-7.4 +/- 0.00 |
y |
3.03 +/- 0.00 |
3.0 +/- 0.00 |
z |
6.18 +/- 0.03 |
6.2 +/- 0.01 |
xRot |
2.41 +/- 0.00 |
2.4 +/- 0.00 |
yRot |
4.68 +/- 0.01 |
4.7 +/- 0.00 |
zRot |
0.41 +/- 0.00 |
0.41 +/- 0.00 |
GROUP4 |
Command Time |
eStop |
x |
-6.84 +/- 0.04 |
-7.0 +/- 0.00 |
y |
2.31 +/- 0.00 |
2.3 +/- 0.00 |
z |
5.25 +/- 0.01 |
5.2 +/- 0.00 |
xRot |
0.80 +/- 0.01 |
0.83 +/- 0.00 |
yRot |
3.59 +/- 0.02 |
3.5 +/- 0.00 |
zRot |
0.39 +/- 0.00 |
0.38 +/- 0.00 |
GROUP5 |
Command Time |
eStop |
x |
-7.92 +/- 0.00 |
-7.9 +/- 0.01 |
y |
1.88 +/- 0.00 |
1.9 +/- 0.02 |
z |
3.48 +/- 0.04 |
3.5 +/- 0.02 |
xRot |
-0.67 +/- 0.01 |
-0.68 +/- 0.00 |
yRot |
2.81 +/- 0.00 |
2.8 +/- 0.00 |
zRot |
0.43 +/- 0.00 |
0.43 +/- 0.00 |
GROUP6 |
Command Time |
eStop |
x |
-7.15 +/- 0.08 |
-7.2 +/- 0.03 |
y |
2.17 +/- 0.01 |
2.2 +/- 0.05 |
z |
3.24 +/- 0.03 |
3.2 +/- 0.00 |
xRot |
-1.70 +/- 0.00 |
-1.7 +/- 0.00 |
yRot |
0.47 +/- 0.01 |
0.47 +/- 0.00 |
zRot |
0.46 +/- 0.00 |
0.45 +/- 0.00 |
GROUP7 |
Command Time |
eStop |
x |
-6.67 +/- 0.00 |
-6.7 +/- 0.00 |
y |
1.73 +/- 0.00 |
1.7 +/- 0.00 |
z |
3.06 +/- 0.05 |
3.1 +/- 0.05 |
xRot |
-3.05 +/- 0.01 |
-3.1 +/- 0.01 |
yRot |
-0.37 +/- 0.00 |
-0.38 +/- 0.00 |
zRot |
0.44 +/- 0.00 |
0.44 +/- 0.00 |
GROUP8 |
Command Time |
eStop |
x |
-5.92 +/- 0.00 |
-5.9 +/- 0.00 |
y |
1.30 +/- 0.00 |
1.3 +/- 0.00 |
z |
4.27 +/- 0.04 |
4.2 +/- 0.04 |
xRot |
-2.99 +/- 0.01 |
-3.0 +/- 0.00 |
yRot |
-3.08 +/- 0.01 |
-3.1 +/- 0.01 |
zRot |
0.36 +/- 0.00 |
0.36 +/- 0.00 |