Re-read disturbance identification section

index.org

@@ -491,26 +491,26 @@ These FRF will be used to compare the dynamics of the multi-body model with the
 <<sec:identification_disturbances>>
 
 ** Introduction                                                      :ignore:
-In this section, we wish to list and identify all the disturbances affecting the system.
+In this section, all the disturbances affecting the system are identified and quantified.
 
-Note that here we are not much interested by low frequency disturbances such as thermal effects and static guiding errors of each positioning stage.
-This is because the frequency content of these errors will be located in the controller bandwidth and thus will be easily compensated by the nano-hexapod.
+Note that the low frequency disturbances such as static guiding errors and thermal effects are not much of interest here, because the frequency content of these errors will be located way inside the controller bandwidth and thus will be easily compensated by the nano-hexapod.
 
-The problem are on the high frequency disturbances.
-In the following sections, we consider:
-- the ground motion
-- vibrations of each stage, due either to their control systems or their motion
+The main challenge is to reduce the disturbances containing high frequencies, and thus efforts are made to identify these high frequency disturbances such as:
+- Ground motion (Section [[sec:ground_motion]])
+- Vibration introduced by control systems (Section [[sec:stage_vibration_control]])
+- Vibration introduced by the motion of the spindle and of the translation stage (Section [[sec:stage_vibration_motion]])
 
+A noise budgeting is performed in Section [[sec:open_loop_noise_budget]], the vibrations induced by the disturbances are compared and the required control bandwidth is estimated.
 
-https://tdehaeze.github.io/meas-analysis/
-Open Loop Noise budget: https://tdehaeze.github.io/nass-simscape/disturbances.html
+The measurements are presented in more detail in [[https://tdehaeze.github.io/meas-analysis/][this]] document and the open loop noise budget is done in [[https://tdehaeze.github.io/nass-simscape/disturbances.html][this]] document.
 
 ** Ground Motion
 <<sec:ground_motion>>
 
-The ground motion can easily be estimated using an inertial sensor with sufficient sensitivity.
+Ground motion can easily be estimated using an inertial sensor with sufficient sensitivity.
 
 To verify that the inertial sensors are sensitive enough, a Huddle test has been performed (Figure [[fig:geophones]]).
+The details of the Huddle Test can be found [[https://tdehaeze.github.io/meas-analysis/huddle-test-geophones/index.html][here]].
 
 #+name: fig:geophones
 #+caption: Huddle Test Setup
@@ -526,20 +526,21 @@ The low frequency differences between the ground motion at ID31 and ID09 is just
 ** Stage Vibration - Effect of Control systems
 <<sec:stage_vibration_control>>
 
-Control system of each stage has been tested
+The effect of the control system of each micro-station's stage is identified.
 
-Each motor are turn off and then on.
-The goal is to see what noise is injected in the system due to the regulation loop of each stage.
+To do so, one geophone is located at the sample's location which another is located on the granite.
+The feedback loop of each stage is turned on and off, and the vibrations level of the sample with respect to the granite is measured.
+Note that here no stage is performing motion, just the disturbances introduced by the feedback loops are identified.
 
+It is shown that these local feedback loops have little influence on the sample's vibrations except the Spindle that introduced a sample's vertical motion at 25Hz.
 
 Complete reports on these measurements are accessible [[https://tdehaeze.github.io/meas-analysis/2018-10-15%20-%20Marc/index.html][here]] and [[https://tdehaeze.github.io/meas-analysis/disturbance-control-system/index.html][here]].
 
-25Hz vertical motion when the *Spindle* is turned on (even when not rotating).
-
 ** Stage Vibration - Effect of Motion
 <<sec:stage_vibration_motion>>
 
-We consider here the vibrations induced by the scans of the translation stage and rotation of the spindle.
+*** Introduction                                                    :ignore:
+We consider here the vibrations induced by *scans of the translation stage* and *rotation of the spindle*.
 
 Details reports are accessible [[https://tdehaeze.github.io/meas-analysis/disturbance-ty/index.html][here]] for the translation stage and [[https://tdehaeze.github.io/meas-analysis/disturbance-sr-rz/index.html][here]] for the spindle/slip-ring.
 
@@ -554,17 +555,18 @@ The setup for the measurement of vibrations induced by rotation of the Spindle a
 #+caption: Measurement of the sample's vertical motion when rotating at 6rpm
 [[file:figs/rz_meas_errors.gif]]
 
-A geophone is fixed at the location of the sample and we measure the motion:
-- without rotation
-- when rotating at 6rpm using the slip-ring motor
+A geophone is fixed at the location of the sample and the motion is measured:
+- without any rotation
+- when rotating at 6rpm using only the slip-ring motor
 - when rotating at 6rpm using the spindle motor synchronized with the slip-ring motor
 
-The obtained Power Spectral Density of the sample's absolute velocity are shown in Figure [[fig:sr_sp_psd_sample_compare]].
+The obtained Power Spectral Densities of the sample's absolute velocity are shown in Figure [[fig:sr_sp_psd_sample_compare]].
 
 We can see that when using the Slip-ring motor to rotate the sample, only a little increase of the motion is observed above 100Hz.
 
 However, when rotating with the Spindle (normal functioning mode):
-- a very sharp peak at 23Hz is observed. Its cause has not been identified yet
+- a very sharp peak at 23Hz is observed.
+  Its cause has not been identified yet
 - a general large increase in motion above 30Hz
 
 #+name: fig:sr_sp_psd_sample_compare
@@ -572,7 +574,7 @@ However, when rotating with the Spindle (normal functioning mode):
 [[file:figs/sr_sp_psd_sample_compare.png]]
 
 #+begin_important
-  Some investigation should be performed on the Spindle to determine where does this 23Hz motion comes from.
+  Some investigation should be performed to determine where does this 23Hz motion comes from and why such high frequency motion is introduced by the spindle's motor.
 #+end_important
 
 *** Translation Stage
@@ -580,9 +582,9 @@ However, when rotating with the Spindle (normal functioning mode):
 :UNNUMBERED: t
 :END:
 
-The same setup is used (a geophone is located at the sample's location and another on the granite).
+The same setup is used: a geophone is located at the sample's location and another on the granite.
 
-We impose a 1Hz triangle motion with an amplitude of $\pm 2.5mm$ on the translation stage (Figure [[fig:Figure_name]]), and we measure the absolute velocity of both the sample and the granite.
+A 1Hz triangle motion with an amplitude of $\pm 2.5mm$ is sent to the translation stage (Figure [[fig:Figure_name]]), and the absolute velocities of the sample and the granite are measured.
 
 #+name: fig:Figure_name
 #+caption: Y position of the translation stage measured by the encoders
@@ -598,17 +600,22 @@ This could be a problem if this is shown to excite the metrology frame of the na
 [[file:figs/ty_z_time.png]]
 
 The Amplitude Spectral Densities of the measured absolute velocities are shown in Figure [[fig:asd_z_direction]].
-We can see many peaks starting from 1Hz showing the large spectral content probably due to the triangular reference of the translation stage.
+The ASD contains any peaks starting from 1Hz showing the large spectral content of the motion which is probably due to the triangular reference of the translation stage.
+
+#+begin_important
+  A smoother motion for the translation stage (such as a sinus motion, of a filtered triangular signal) could help reducing much of the vibrations.
+
+  We should also note that away from the rapid change of velocity, the sample's vibrations are much reduced.
+  Thus, if the detector is only used in between the triangular peaks, the vibrations are expected to be much lower than those estimated.
+#+end_important
 
 #+name: fig:asd_z_direction
 #+caption: Amplitude spectral density of the measure velocity corresponding to the geophone in the vertical direction located on the granite and at the sample location when the translation stage is scanning at 1Hz
 [[file:figs/asd_z_direction.png]]
 
-#+begin_important
-  A smoother motion for the translation stage (such as a sinus motion) could probably help reducing much of the vibrations produced.
-#+end_important
+** Open Loop noise budgeting
+<<sec:open_loop_noise_budget>>
 
-** Sum of all disturbances
 We can now compare the effect of all the disturbance sources on the position error (relative motion of the sample with respect to the granite).
 
 The Power Spectral Density of the motion error due to the ground motion, translation stage scans and spindle rotation are shown in Figure [[fig:dist_effect_relative_motion]].
@@ -620,32 +627,30 @@ We can see that the ground motion is quite small compare to the translation stag
 [[file:figs/dist_effect_relative_motion.png]]
 
 The Cumulative Amplitude Spectrum is shown in Figure [[fig:dist_effect_relative_motion_cas]].
-It is shown that the motion induced by translation stage scans and spindle rotation are in the micro-meter range.
+It is shown that the motion induced by translation stage scans and spindle rotation are in the micro-meter range for frequencies above 1Hz.
 
 #+name: fig:dist_effect_relative_motion_cas
 #+caption: Cumulative Amplitude Spectrum of the motion error due to disturbances
 [[file:figs/dist_effect_relative_motion_cas.png]]
 
-We can also estimate the required bandwidth by seeing that $10\ nm [rms]$ motion is induced by the perturbations above 100Hz.
+From Figure [[fig:dist_effect_relative_motion_cas]], required bandwidth can be estimated by seeing that $10\ nm [rms]$ motion is induced by the perturbations above 100Hz.
 
 This means that if the controller compensate all the motion errors below 100Hz (ideal case), 10nm [rms] of motion will still remain.
 
-From that, we can conclude that we will probably need a control bandwidth to around 100Hz.
+From that, it can be concluded that control bandwidth will have to be around 100Hz.
 
 ** Better estimation of the disturbances
 All the disturbance measurements were made with inertial sensors, and to obtain the relative motion sample/granite, two inertial sensors were used and the signals were subtracted.
 
-This is not perfect as using only one geophone on the sample and one on the granite do not permit to separate the translations and the rotations.
+This is not perfect as using only one geophone on the sample and one on the granite do not permit to separate translations and rotations.
 
-An alternative could be to position a reference object at the sample location and to use the X-ray to measure its motion.
+An alternative could be to position a small calibrated sphere at the sample location and to use the X-ray to measure its motion while performing translation scans and spindle rotations.
 
-The detector requirement would be:
-- Sample frequency above $400Hz$
-- Resolution of $\approx 100nm$ (to be discussed)
+The detector requirement would need to have a sample frequency above $400Hz$ and a resolution of $\approx 100nm$ (to be discussed).
 
 ** Conclusion
 #+begin_important
-Main disturbance sources have been identified.
+Main disturbance sources have been identified (ground motion, vibrations of the translation stage and the spindle).
 These disturbances will then be included in the multi-body model.
 
 
@@ -653,7 +658,7 @@ Other disturbance sources were not estimated such as cable forces and acoustic d
 If heavy/stiff cables are to be fixed to the sample, this should be quantified and included in the model.
 
 
-Having better estimation of the disturbances would allows to more precisely estimate the attainable performances.
+A better estimation of the disturbances would allow a more precise estimation the attainable performance.
 This should however not change the conclusion of this study nor significantly change the nano-hexapod design.
 #+end_important