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(termite:48779): GLib-WARNING **: 10:35:19.170: GChildWatchSource: Exit status of a child process was requested but ECHILD was received by waitpid(). See the documentation of g_child_watch_source_new() for possible causes.
(termite:336077): GLib-WARNING **: 15:08:41.789: GChildWatchSource: Exit status of a child process was requested but ECHILD was received by waitpid(). See the documentation of g_child_watch_source_new() for possible causes.

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@ -14,6 +14,8 @@
#+STARTUP: overview
#+OPTIONS: toc:2
#+LATEX_CLASS: cleanreport
#+LATEX_CLASS_OPTIONS: [conf, hangsection, secbreak]
@ -21,6 +23,15 @@
#+LATEX_HEADER: \newcommand{\authorLastName}{Dehaeze}
#+LATEX_HEADER: \newcommand{\authorEmail}{dehaeze.thomas@gmail.com}
#+LATEX_HEADER_EXTRA: \makeatletter
#+LATEX_HEADER_EXTRA: \preto\Gin@extensions{gif,}
#+LATEX_HEADER_EXTRA: \DeclareGraphicsRule{.gif}{png}{.png}{\noexpand\Gin@base.png}
#+LATEX_HEADER_EXTRA: \preto\Gin@extensions{png,}
#+LATEX_HEADER_EXTRA: \DeclareGraphicsRule{.png}{pdf}{.pdf}{\noexpand\Gin@base.pdf}
#+LATEX_HEADER_EXTRA: \makeatother
#+LATEX_HEADER: \addbibresource{ref.bib}
#+PROPERTY: header-args:latex :headers '("\\usepackage{tikz}" "\\usepackage{import}" "\\import{$HOME/Cloud/tikz/org/}{config.tex}")
#+PROPERTY: header-args:latex+ :imagemagick t :fit yes
#+PROPERTY: header-args:latex+ :iminoptions -scale 100% -density 150
@ -34,7 +45,11 @@
#+PROPERTY: header-args:latex+ :post pdf2svg(file=*this*, ext="png")
:END:
* Introduction :ignore:
* Introduction
:PROPERTIES:
:UNNUMBERED: t
:END:
In this document are gathered and summarized all the developments done for the design of the Nano Active Stabilization System.
This consists of a nano-hexapod and an associated control architecture that are used to stabilize samples down to the nano-meter level in presence of disturbances.
@ -59,6 +74,10 @@ Based on that, an optimal choice of the nano-hexapod stiffness is made (Section
Finally, using the optimally designed nano-hexapod, a robust control architecture is developed.
Simulations are performed to show that this design gives acceptable performance and the required robustness (Section [[sec:robust_control_architecture]]).
#+begin_export html
This report is also available as a <a href="./index.pdf">pdf</a>.
#+end_export
* Introduction to Feedback Systems and Noise budgeting
<<sec:feedback_introduction>>
@ -130,6 +149,7 @@ The /dynamical/ blocks are:
#+end_src
#+name: fig:classical_feedback_small
#+attr_latex: :width 0.5\linewidth
#+caption: Block Diagram of a simple feedback system
#+RESULTS:
[[file:figs/classical_feedback_small.png]]
@ -225,6 +245,7 @@ It is shown that $|S|$ and $|T|$ exhibit different behaviors depending on the fr
#+end_src
#+name: fig:h-infinity-2-blocs-constrains
#+attr_latex: :width 0.8\linewidth
#+caption: Typical shapes and constrain of the Sensibility and Transmibility closed-loop transfer functions
#+RESULTS:
[[file:figs/h-infinity-2-blocs-constrains.png]]
@ -244,8 +265,9 @@ The main issue it that for stability reasons, *the system dynamics must be known
For mechanical systems, this generally means that the control bandwidth should take place before any appearing of flexible dynamics (right part of Figure [[fig:oomen18_next_gen_loop_gain]]).
#+name: fig:oomen18_next_gen_loop_gain
#+attr_latex: :width \linewidth
#+caption: Envisaged developments in motion systems. In traditional motion systems, the control bandwidth takes place in the rigid-body region. In the next generation systemes, flexible dynamics are foreseen to occur within the control bandwidth. cite:oomen18_advan_motion_contr_precis_mechat
[[file:figs/oomen18_next_gen_loop_gain.png]]
[[file:figs/oomen18_next_gen_loop_gain.jpg]]
This also means that *any possible change in the system should have a small impact on the system dynamics in the vicinity of the crossover*.
@ -311,8 +333,9 @@ It can also helps to determine at which frequencies the effect of disturbances m
A typical Cumulative Power Spectrum is shown in figure [[fig:preumont18_cas_plot]].
#+name: fig:preumont18_cas_plot
#+attr_latex: :width 0.6\linewidth
#+caption: Cumulative Power Spectrum in open-loop and closed-loop for increasing gains (taken from cite:preumont18_vibrat_contr_activ_struc_fourt_edition)
[[file:figs/preumont18_cas_plot.png]]
[[file:figs/preumont18_cas_plot.jpg]]
*** Modification of a signal's PSD when going through a dynamical system
<<sec:psd_lti_system>>
@ -329,6 +352,7 @@ Let's consider a signal $u$ with a PSD $S_{uu}$ going through a LTI system $G(s)
#+end_src
#+NAME: fig:psd_lti_system
#+attr_latex: :scale 1
#+CAPTION: LTI dynamical system $G(s)$ with input signal $u$ and output signal $y$
#+RESULTS:
[[file:figs/psd_lti_system.png]]
@ -358,6 +382,7 @@ The PSD of $y$ is equal to sum of the PSD and $u$ and the PSD of $v$ (can be eas
#+end_src
#+name: fig:psd_sum
#+attr_latex: :scale 1
#+caption: $y$ as the sum of two signals $u$ and $v$
#+RESULTS:
[[file:figs/psd_sum.png]]
@ -408,6 +433,7 @@ The steps are:
3. extract a Spatial Model from the Modal Model (Mass/Damping/Stiffness matrices)
#+name: fig:vibration_analysis_procedure
#+attr_latex: :width 0.6\linewidth
#+caption: Vibration Analysis Procedure
[[file:figs/vibration_analysis_procedure.png]]
@ -444,10 +470,12 @@ In total, 69 degrees of freedom are measured (23 tri axis accelerometers) which
It was chosen to have some redundancy in the measurement to be able to verify the correctness of the solid-body assumption.
#+name: fig:hammer_z
#+attr_latex: :width 0.5\linewidth
#+caption: Example of one hammer impact
[[file:figs/hammer_z.gif]]
#+name: fig:accelerometers_ty_overview
#+attr_latex: :width 0.7\linewidth
#+caption: 3 tri axis accelerometers fixed to the translation stage
[[file:figs/accelerometers_ty_overview.jpg]]
@ -460,10 +488,12 @@ Modal shapes and natural frequencies are then computed.
Example of the obtained micro-station's mode shapes are shown in Figures [[fig:mode1]] and [[fig:mode6]].
#+name: fig:mode1
#+attr_latex: :width 0.7\linewidth
#+caption: First mode that shows a suspension mode, probably due to bad leveling of one Airloc
[[file:figs/mode1.gif]]
#+name: fig:mode6
#+attr_latex: :width 0.7\linewidth
#+caption: Sixth mode
[[file:figs/mode6.gif]]
@ -484,6 +514,7 @@ Examples of FRF are shown in Figure [[fig:frf_all_bodies_one_direction]].
These FRF will be used to compare the dynamics of the multi-body model with the micro-station dynamics.
#+name: fig:frf_all_bodies_one_direction
#+attr_latex: :width 0.9\linewidth
#+caption: Frequency Response Function from forces applied by the Hammer in the X direction to the acceleration of each solid body in the X direction
[[file:figs/frf_all_bodies_one_direction.png]]
@ -521,6 +552,7 @@ To verify that the inertial sensors are sensitive enough, a Huddle test has been
The details of the Huddle Test can be found [[https://tdehaeze.github.io/meas-analysis/huddle-test-geophones/index.html][here]].
#+name: fig:geophones
#+attr_latex: :width 0.7\linewidth
#+caption: Huddle Test Setup
[[file:figs/geophones.jpg]]
@ -528,6 +560,7 @@ The measured Power Spectral Density of the ground motion at the ID31 floor is co
The low frequency differences between the ground motion at ID31 and ID09 is just due to the fact that for the later measurement, the low frequency sensitivity of the inertial sensor was not taken into account.
#+name: fig:ground_motion_compare
#+attr_latex: :width 0.7\linewidth
#+caption: Comparison of the PSD of the ground motion measured at different location
[[file:figs/ground_motion_compare.png]]
@ -560,6 +593,7 @@ Details reports are accessible [[https://tdehaeze.github.io/meas-analysis/distur
The setup for the measurement of vibrations induced by rotation of the Spindle and Slip-ring is shown in Figure [[fig:rz_meas_errors]].
#+name: fig:rz_meas_errors
#+attr_latex: :width 0.5\linewidth
#+caption: Measurement of the sample's vertical motion when rotating at 6rpm
[[file:figs/rz_meas_errors.gif]]
@ -578,6 +612,7 @@ However, when rotating with the Spindle (normal functioning mode):
- a general large increase in motion above 30Hz
#+name: fig:sr_sp_psd_sample_compare
#+attr_latex: :width 0.7\linewidth
#+caption: Comparison of the ASD of the measured voltage from the Geophone at the sample location
[[file:figs/sr_sp_psd_sample_compare.png]]
@ -595,6 +630,7 @@ The same setup is used: a geophone is located at the sample's location and anoth
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
#+attr_latex: :width 0.5\linewidth
#+caption: Y position of the translation stage measured by the encoders
[[file:figs/ty_position_time.png]]
@ -604,6 +640,7 @@ It is shown that quite large motion of the granite is induced by the translation
This could be a problem if this is shown to excite the metrology frame of the nano-focusing lens position stage.
#+name: fig:ty_z_time
#+attr_latex: :width 0.7\linewidth
#+caption: Vertical velocity of the sample and marble when scanning with the translation stage
[[file:figs/ty_z_time.png]]
@ -619,6 +656,7 @@ The ASD contains any peaks starting from 1Hz showing the large spectral content
#+end_important
#+name: fig:asd_z_direction
#+attr_latex: :width 0.7\linewidth
#+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]]
@ -632,6 +670,7 @@ The Power Spectral Density of the motion error due to the ground motion, transla
It can be seen that the ground motion is quite small compare to the translation stage and spindle induced motions.
#+name: fig:dist_effect_relative_motion
#+attr_latex: :width 0.7\linewidth
#+caption: Amplitude Spectral Density fo the motion error due to disturbances
[[file:figs/dist_effect_relative_motion.png]]
@ -639,6 +678,7 @@ The Cumulative Amplitude Spectrum is shown in Figure [[fig:dist_effect_relative_
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
#+attr_latex: :width 0.7\linewidth
#+caption: Cumulative Amplitude Spectrum of the motion error due to disturbances
[[file:figs/dist_effect_relative_motion_cas.png]]
@ -700,8 +740,9 @@ Then, the values of the stiffnesses and damping properties of each joint is manu
The 3D representation of the simscape model is shown in Figure [[fig:simscape_picture]].
#+name: fig:simscape_picture
#+attr_latex: :width 0.9\linewidth
#+caption: 3D representation of the simscape model
[[file:figs/simscape_picture.png]]
[[file:figs/simscape_picture.jpg]]
** Validity of the model's dynamics
<<sec:model_validity>>
@ -715,6 +756,7 @@ Most of the other measured FRFs and identified transfer functions from the multi
We believe that the model is representing the micro-station dynamics sufficient well for the current analysis.
#+name: fig:identification_comp_top_stages
#+attr_latex: :width 0.7\linewidth
#+caption: Frequency Response function from Hammer force in the X,Y and Z directions to the X,Y and Z displacements of the micro-hexapod's top platform. The measurements are shown in blue and the Model in red.
[[file:figs/identification_comp_top_stages.png]]
@ -749,7 +791,8 @@ To do so, several computations are performed (summarized in Figure [[fig:control
Both computation are performed
#+name: fig:control-schematic-nass
#+caption: Figure caption
#+attr_latex: :width \linewidth
#+caption: Schematic of how the elements are interacting with the Speedgoat
[[file:figs/control-schematic-nass.png]]
More details about these computations are accessible [[https://tdehaeze.github.io/nass-simscape/positioning_error.html][here]].
@ -775,11 +818,13 @@ A zoom in the micro-meter ranger on the sample's location is shown in Figure [[f
The motion of the sample follows the wanted motion but with vibrations in the micro-meter range as was expected.
#+name: fig:open_loop_sim
#+attr_latex: :width 0.7\linewidth
#+caption: Tomography Experiment using the Simscape Model
[[file:figs/open_loop_sim.gif]]
#+name: fig:open_loop_sim_zoom
#+attr_latex: :width 0.7\linewidth
#+caption: Tomography Experiment using the Simscape Model - Zoom on the sample's position (the full vertical scale is $\approx 10 \mu m$)
[[file:figs/open_loop_sim_zoom.gif]]
@ -794,6 +839,7 @@ The vertical rotation error is meaningless for two reasons:
- no measurement of the sample's vertical rotation with respect to the granite is made by the interferometers
#+name: fig:exp_scans_rz_dist
#+attr_latex: :width 0.9\linewidth
#+caption: Position error of the Sample with respect to the granite during a Tomography Experiment with included disturbances
[[file:figs/exp_scans_rz_dist.png]]
@ -837,6 +883,7 @@ A typical Stewart platform is composed of two platforms connected by six identic
This is very schematically shown in Figure [[fig:stewart_architecture_example]] where the $a_i$ are the location of the joints connected to the fixed platform and the $b_i$ are the joints connected to the mobile platform.
#+name: fig:stewart_architecture_example
#+attr_latex: :width 0.5\linewidth
#+caption: Schematic representation of a Stewart platform
[[file:figs/stewart_architecture_example.png]]
@ -849,6 +896,7 @@ A change in the length of the legs $\bm{\mathcal{L}} = \left[ l_1, l_2, l_3, l_4
The relation between a change in length of the legs and the relative motion of the platforms is studied thanks to the kinematic analysis, which is explained in Section [[sec:nano_hexapod_architecture]].
#+name: fig:stewart_architecture_example_pose
#+attr_latex: :width 0.5\linewidth
#+caption: Display of the Stewart platform architecture at some defined pose
[[file:figs/stewart_architecture_example_pose.png]]
@ -883,6 +931,7 @@ More precisely, the nano-hexapod filters out the vibration starting at the first
The same conclusion is made for vibrations of the translation stage.
#+name: fig:opt_stiff_sensitivity_Frz
#+attr_latex: :width 0.8\linewidth
#+caption: Sensitivity to Spindle vertical motion error to the vertical error position of the sample
[[file:figs/opt_stiff_sensitivity_Frz.png]]
@ -898,6 +947,7 @@ Thus, a stiff nano-hexapod ($k>10^5\,[N/m]$) is better for reducing the effect o
It will be suggested in Section [[sec:soft_granite]] that using soft mounts for the granite can greatly lower the sensibility to ground motion.
#+name: fig:opt_stiff_sensitivity_Dw
#+attr_latex: :width 0.8\linewidth
#+caption: Sensitivity to Ground motion to the position error of the sample
[[file:figs/opt_stiff_sensitivity_Dw.png]]
@ -920,6 +970,7 @@ From the Power Spectral Density of all the sources of disturbances identified in
It can be seen that the most important change is in the frequency range 30Hz to 300Hz where a stiffness smaller than $10^5\,[N/m]$ greatly reduces the sample's vibrations.
#+name: fig:opt_stiff_psd_dz_tot
#+attr_latex: :width 0.8\linewidth
#+caption: Amplitude Spectral Density of the Sample vertical position error due to Vertical vibration of the Spindle for multiple nano-hexapod stiffnesses
[[file:figs/opt_stiff_psd_dz_tot.png]]
@ -933,6 +984,7 @@ It can be observe on the Cumulative amplitude spectrum of the vertical error mot
#+end_important
#+name: fig:opt_stiff_cas_dz_tot
#+attr_latex: :width 0.8\linewidth
#+caption: Cumulative Amplitude Spectrum of the Sample vertical position error due to all considered perturbations for multiple nano-hexapod stiffnesses
[[file:figs/opt_stiff_cas_dz_tot.png]]
@ -978,6 +1030,7 @@ To minimize the uncertainty to the payload's mass, the mass of the nano-hexapod'
As the maximum payload's mass is $50\,kg$, this may however not be practical, and thus the control architecture must be developed to be robust to a change of the payload's mass.
#+name: fig:opt_stiffness_payload_mass_fz_dz
#+attr_latex: :width 0.8\linewidth
#+caption: Dynamics from $\mathcal{F}_z$ to $\mathcal{X}_z$ for varying payload mass, both for a soft nano-hexapod (left) and a stiff nano-hexapod (right)
[[file:figs/opt_stiffness_payload_mass_fz_dz.png]]
@ -987,6 +1040,7 @@ The mass of the payload is fixed and its resonance frequency is changing from 50
It can be seen (more easily for the soft nano-hexapod), that resonance of the payload produces an anti-resonance for the considered dynamics.
#+name: fig:opt_stiffness_payload_freq_fz_dz
#+attr_latex: :width 0.8\linewidth
#+caption: Dynamics from $\mathcal{F}_z$ to $\mathcal{X}_z$ for varying payload resonance frequency, both for a soft nano-hexapod and a stiff nano-hexapod
[[file:figs/opt_stiffness_payload_freq_fz_dz.png]]
@ -1002,6 +1056,7 @@ For nano-hexapod stiffnesses above $10^7\,[N/m]$:
- above that frequency, the change of dynamics is quite chaotic (which this is due to the micro-station dynamics as shown in the next section) and it would be difficult to have a controller with high bandwidth which is robust to such change of dynamics
#+name: fig:opt_stiffness_payload_impedance_all_fz_dz
#+attr_latex: :width 0.8\linewidth
#+caption: Dynamics from $\mathcal{F}_z$ to $\mathcal{X}_z$ for varying payload dynamics, both for a soft nano-hexapod and a stiff nano-hexapod
[[file:figs/opt_stiffness_payload_impedance_all_fz_dz.png]]
@ -1043,6 +1098,7 @@ One can see that for nano-hexapod stiffnesses below $10^6\,[N/m]$, the plant dyn
For nano-hexapod stiffnesses above $10^7\,[N/m]$, the micro-station compliance appears in the plant dynamics starting at about 45Hz.
#+name: fig:opt_stiffness_micro_station_fx_dx
#+attr_latex: :width 0.8\linewidth
#+caption: Change of dynamics from force $\mathcal{F}_x$ to displacement $\mathcal{X}_x$ due to the micro-station compliance
[[file:figs/opt_stiffness_micro_station_fx_dx.png]]
@ -1070,6 +1126,7 @@ The change of dynamics is due to both centrifugal forces and Coriolis forces.
This effect has been studied in details in [[https://tdehaeze.github.io/rotating-frame/index.html][this]] document.
#+name: fig:opt_stiffness_wz_fx_dx
#+attr_latex: :width 0.8\linewidth
#+caption: Change of dynamics from force $\mathcal{F}_x$ to displacement $\mathcal{X}_x$ for a spindle rotation speed from 0rpm to 60rpm
[[file:figs/opt_stiffness_wz_fx_dx.png]]
@ -1088,6 +1145,7 @@ Finally, let's combined all the uncertainties and display the "spread" of the pl
This show how the dynamics evolves with the stiffness and how different effects enters the plant dynamics.
#+name: fig:opt_stiffness_plant_dynamics_task_space
#+attr_latex: :width 0.8\linewidth
#+caption: Variability of the dynamics from $\bm{\mathcal{F}}_x$ to $\bm{\mathcal{X}}_x$ with varying nano-hexapod stiffness
[[file:figs/opt_stiffness_plant_dynamics_task_space.gif]]
@ -1221,6 +1279,7 @@ For a specified geometry and actuator stroke, the mobility of the Stewart platfo
An example of the mobility considering only pure translations is shown in Figure [[fig:mobility_translations_null_rotation]].
#+name: fig:mobility_translations_null_rotation
#+attr_latex: :width 0.8\linewidth
#+caption: Obtained mobility of a Stewart platform for pure translations (the platform's orientation is fixed)
[[file:figs/mobility_translations_null_rotation.png]]
@ -1287,6 +1346,8 @@ These results could have been easily deduced with some basics of mechanics, but
The nano-hexapod geometry and further be optimized in terms of stiffness and stroke using the presented tools.
#+name: tab:effect_legs_jacobian
#+attr_latex: :environment tabularx :width \linewidth :align lXX
#+attr_latex: :center t :booktabs t :float t
#+caption: Effect of a change in geometry on the manipulator's stiffness, force authority and stroke
| | *legs pointing more vertically* | *legs further apart* |
|-------------------------------+---------------------------------+----------------------|
@ -1315,6 +1376,7 @@ A very popular choice of Stewart platform architecture, especially for vibration
The cubic architecture is quite specific in the sense that the active struts are arranged in a mutually orthogonal configuration connecting the corners of a cube (Figure [[fig:3d-cubic-stewart-aligned]]).
#+name: fig:3d-cubic-stewart-aligned
#+attr_latex: :width 0.5\linewidth
#+caption: Schematic representation of the Cubic architecture
[[file:figs/3d-cubic-stewart-aligned.png]]
@ -1342,10 +1404,12 @@ When only small stroke is required, *flexible* joints can be used: material is b
Example of flexible joints used for Stewart platforms are shown in Figures [[fig:preumont07_flexible_joints]] and [[fig:yang19_flexible_joints]].
#+name: fig:preumont07_flexible_joints
#+attr_latex: :width 0.4\linewidth
#+caption: Flexible joints used in cite:preumont07_six_axis_singl_stage_activ
[[file:figs/preumont07_flexible_joints.png]]
[[file:figs/preumont07_flexible_joints.jpg]]
#+name: fig:yang19_flexible_joints
#+attr_latex: :width 0.8\linewidth
#+caption: An alternative type of flexible joints that has been used for Stewart platforms cite:yang19_dynam_model_decoup_contr_flexib
[[file:figs/yang19_flexible_joints.png]]
@ -1458,6 +1522,7 @@ This approach has the following advantages:
#+end_quote
#+name: fig:control_architecture_hac_lac_one_input
#+attr_latex: :width 0.6\linewidth
#+caption: HAC-LAC Architecture with a system having only one input
[[file:figs/control_architecture_hac_lac_one_input.png]]
@ -1488,6 +1553,8 @@ The conclusions are (summarized in Table [[tab:comp_active_damping]]):
It however may increases the sensibility to stages vibrations at higher frequency
#+name: tab:comp_active_damping
#+attr_latex: :environment tabularx :width \linewidth :align lXXX
#+attr_latex: :center t :booktabs t :float t
#+caption: Comparison of the three main active damping techniques that could be applied to the nano-hexapod
| | *Integral Force Feedback* | *Direct Velocity Feedback* | *Inertial Control* |
|------------------------+-------------------------------------------------+--------------------------------------------------+----------------------------------------------------------|
@ -1518,6 +1585,7 @@ These plots show the evolution of the system's poles in the complex plane as a f
#+name: fig:root_locus_rotation_active_damping
#+caption: Variation of the Root Locus for DVF and IFF in presence of rotation. $\omega$ is the spindle rotation speed, and $\omega_0$ is the resonance frequency of the considered rotating system.
#+attr_latex: :environment subfigure :width 0.49\linewidth :align c
| [[file:figs/dvf_root_locus_ws.png]] | [[file:figs/iff_root_locus_ws.png]] |
| Direct Velocity Feedback | Integral Force Feedback |
@ -1534,8 +1602,9 @@ To damp a system, it is thus wanted to move the poles to the left part of the co
A pole with a positive real part corresponds to an unstable system, and thus the right part of the complex should be avoided.
#+name: fig:preumont18_effect_damping
#+attr_latex: :width 0.9\linewidth
#+caption: Role of damping (cite:preumont18_vibrat_contr_activ_struc_fourt_edition). (a) Pole position in the complex plane. (b) Change of dynamic amplification ($1/2\xi$)
[[file:figs/preumont18_effect_damping.png]]
[[file:figs/preumont18_effect_damping.jpg]]
Coming back to the Root Locus in Table [[fig:root_locus_rotation_active_damping]], it can be seen that:
@ -1566,6 +1635,7 @@ This control architecture is equivalent as to have six independent control loops
The force applied in each leg being proportional to the relative velocity of the associated leg (thanks to the derivative action), this is equivalent as adding *damping* in each of the legs.
#+name: fig:control_architecture_dvf
#+attr_latex: :width 0.5\linewidth
#+caption: Low Authority Control: Decentralized Direct Velocity Feedback
[[file:figs/control_architecture_dvf.png]]
@ -1582,10 +1652,12 @@ This is confirmed by the Root Locus in Figure [[fig:opt_stiff_dvf_root_locus]] w
Moreover, it is seen that arbitrary damping can be applied to the nano-hexapod's modes.
#+name: fig:opt_stiff_dvf_plant
#+attr_latex: :width 0.8\linewidth
#+caption: Dynamics from actuator force $\tau_i$ to the relative displacement of the corresponding leg $d\mathcal{L}_i$ for three payload masses
[[file:figs/opt_stiff_dvf_plant.png]]
#+name: fig:opt_stiff_dvf_root_locus
#+attr_latex: :width 0.5\linewidth
#+caption: Root Locus (zoomed on the nano-hexapod modes) corresponding to the Direct Velocity Feedback control for three payload masses
[[file:figs/opt_stiff_dvf_root_locus.png]]
@ -1606,6 +1678,7 @@ A smaller control gain could probably limit the increase of the sensibility at h
Further optimization of the gain should then be performed.
#+name: fig:opt_stiff_sensibility_dist_dvf
#+attr_latex: :width 0.8\linewidth
#+caption: Norm of the transfer function from vertical disturbances to vertical position error with (dashed) and without (solid) Direct Velocity Feedback applied. Disturbances are: ground motion (top left), direct forces (top right), translation stage vibration (bottom left) and spindle vibrations (bottom right)
[[file:figs/opt_stiff_sensibility_dist_dvf.png]]
@ -1621,6 +1694,7 @@ It is clear that the use of the DVF reduces the dynamical spread of the plant dy
This will make the primary controller more robust and easier to develop.
#+name: fig:opt_stiff_primary_plant_damped_L
#+attr_latex: :width 0.8\linewidth
#+caption: Primary plant in the space of the legs with (dashed) and without (solid) Direct Velocity Feedback
[[file:figs/opt_stiff_primary_plant_damped_L.png]]
@ -1715,6 +1789,7 @@ The difference between the two architectures relies in the way the controllers a
#+end_src
#+name: fig:control_architecture_hac_dvf_pos_X
#+attr_latex: :width 0.8\linewidth
#+caption: HAC-LAC architecture. The inner loop consist of a decentralized Direct Velocity Feedback. The outer loop consist of position control in the task space
#+RESULTS:
[[file:figs/control_architecture_hac_dvf_pos_X.png]]
@ -1762,6 +1837,7 @@ The difference between the two architectures relies in the way the controllers a
#+end_src
#+name: fig:control_architecture_hac_dvf_pos_L
#+attr_latex: :width 0.8\linewidth
#+caption: HAC-LAC architecture. The inner loop consist of a decentralized Direct Velocity Feedback. The outer loop consist of position control in the leg's space
#+RESULTS:
[[file:figs/control_architecture_hac_dvf_pos_L.png]]
@ -1775,11 +1851,13 @@ The choice of whether the controller should be designed in the leg space or in t
- The coupling is small at low frequency, quite high near the suspension modes of the Stewart platform and then small again at high frequency
#+name: fig:plant_centralized_X
#+attr_latex: :width 0.8\linewidth
#+caption: Direct (diagonal) dynamical terms (left) and coupled terms (right, shown in black) for the plant in the task space
[[file:figs/plant_centralized_X.png]]
#+name: fig:plant_centralized_L
#+attr_latex: :width 0.8\linewidth
#+caption: Direct (diagonal) dynamical terms (left) and coupled terms (right, shown in black) for the plant in the leg space
[[file:figs/plant_centralized_L.png]]
@ -1787,6 +1865,8 @@ The choice of whether the controller should be designed in the leg space or in t
The differences of a control in the leg space and in the task space are summarized in Table [[tab:hac_lac_control_L_X_comp]].
#+name: tab:hac_lac_control_L_X_comp
#+attr_latex: :environment tabularx :width \linewidth :align lXX
#+attr_latex: :center t :booktabs t :float t
#+caption: Comparison of a control in the leg space and in the task space
| | Control in the *leg space* | Control in the *task space* |
|---------------------------+-----------------------------------+------------------------------------------------------------------------------------|
@ -1809,6 +1889,7 @@ The plant dynamics from $\tau_i$ to $\epsilon_{\mathcal{L}_i}$ for each of the s
The dynamical spread is kept reasonably small thanks to both the optimal nano-hexapod design and the Low Authority Controller.
#+name: fig:opt_stiff_primary_plant_L
#+attr_latex: :width 0.8\linewidth
#+caption: Diagonal elements of the transfer function matrix from $\bm{\tau}^\prime$ to $\bm{\epsilon}_{\mathcal{X}_n}$ for the three considered masses
[[file:figs/opt_stiff_primary_plant_L.png]]
@ -1822,6 +1903,7 @@ The diagonal controller $\bm{K}_\mathcal{L}$ is then tuned in such a way that th
The obtained loop gain is shown in Figure [[fig:opt_stiff_primary_loop_gain_L]].
#+name: fig:opt_stiff_primary_loop_gain_L
#+attr_latex: :width 0.8\linewidth
#+caption: Loop gain for the primary plant
[[file:figs/opt_stiff_primary_loop_gain_L.png]]
@ -1838,6 +1920,7 @@ The change of sensibility is very typical for feedback system:
The large increase at around 250Hz when using a mass of either 1kg or 10kg is probably caused by insufficient stability margins.
#+name: fig:opt_stiff_primary_control_L_senbility_dist
#+attr_latex: :width 0.8\linewidth
#+caption: Sensibility to disturbances when the HAC-LAC control is applied (dashed) and when it is not (solid)
[[file:figs/opt_stiff_primary_control_L_senbility_dist.png]]
@ -1876,10 +1959,12 @@ Several observations can be made:
- The vertical rotation plot is meaningless as the spindle rotation was considered to be perfect and no attempt was made to compensate these vibrations by the nano-hexapod
#+name: fig:opt_stiff_hac_dvf_L_psd_disp_error
#+attr_latex: :width 0.8\linewidth
#+caption: Amplitude Spectral Density of the position error in Open Loop (black) and with the HAC-LAC controller for three payload masses
[[file:figs/opt_stiff_hac_dvf_L_psd_disp_error.png]]
#+name: fig:opt_stiff_hac_dvf_L_cas_disp_error
#+attr_latex: :width 0.8\linewidth
#+caption: Cumulative Amplitude Spectrum of the position error in Open Loop (black) and with the HAC-LAC controller for three payload masses
[[file:figs/opt_stiff_hac_dvf_L_cas_disp_error.png]]
@ -1894,10 +1979,12 @@ The use of the nano-hexapod combined with the HAC-LAC architecture is shown to c
An animation of the experiment is shown in Figure [[fig:closed_loop_sim_zoom]] and it can be seen that the actual sample's position is more closely following the ideal position compared to the simulation of the micro-station alone in Figure [[fig:open_loop_sim_zoom]] (same scale was used for both animations).
#+name: fig:opt_stiff_hac_dvf_L_pos_error
#+attr_latex: :width 0.8\linewidth
#+caption: Position Error of the sample during a tomography experiment when no control is applied and with the HAC-DVF control architecture
[[file:figs/opt_stiff_hac_dvf_L_pos_error.png]]
#+name: fig:closed_loop_sim_zoom
#+attr_latex: :width 0.8\linewidth
#+caption: Tomography Experiment using the Simscape Model in Closed Loop with the HAC-LAC Control - Zoom on the sample's position (the full vertical scale is $\approx 10 \mu m$)
[[file:figs/closed_loop_sim_zoom.gif]]
@ -1929,6 +2016,7 @@ The control objective is to keep the point of interest on the focused X-ray.
An animation showing the simulation is shown in Figure [[fig:tomography_dh_offset]].
#+name: fig:tomography_dh_offset
#+attr_latex: :width 0.8\linewidth
#+caption: Top View of a tomography experiment with a 10mm offset imposed by the micro-hexapod
[[file:figs/tomography_dh_offset.gif]]
@ -1937,6 +2025,7 @@ This is because the controller generates the actuator forces such that they coun
The disturbance causing this constant force is the centrifugal force induced by the spindle's rotation which is a *constant* force in the frame of the nano-hexapod (provided the rotation speed is constant), directed radially outwards the rotation spindle's axis, and is equal to $F = m r \omega^2 \approx 12 \cdot 0.01 \cdot (2\pi)^2 \approx 5\,[N]$.
#+name: fig:opt_stiff_hac_dvf_Dh_offset_F
#+attr_latex: :width 0.5\linewidth
#+caption: Forces applied by the six nano-hexapod's actuators
[[file:figs/opt_stiff_hac_dvf_Dh_offset_F.png]]
@ -1944,6 +2033,7 @@ The disturbance causing this constant force is the centrifugal force induced by
The relative motions of the nano-hexapod's legs is shown in Figure [[fig:opt_stiff_hac_dvf_Dh_offset_dL]] and are in the micro-meter range.
#+name: fig:opt_stiff_hac_dvf_Dh_offset_dL
#+attr_latex: :width 0.8\linewidth
#+caption: Relative displacement of the nano-hexapod's legs
[[file:figs/opt_stiff_hac_dvf_Dh_offset_dL.png]]
@ -1951,6 +2041,7 @@ Finally, the position/orientation error of the sample is shown in Figure [[fig:o
The root mean square value of the x-y-z error motions is around $30\,nm$ which is very similar than for the "simple" tomography experiment.
#+name: fig:opt_stiff_hac_dvf_Dh_offset_disp_error
#+attr_latex: :width 0.8\linewidth
#+caption: Position/orientation error of the sample during the simulation
[[file:figs/opt_stiff_hac_dvf_Dh_offset_disp_error.png]]
@ -1967,6 +2058,7 @@ In this simulation:
The obtained sample's motion during the simulation is shown in Figure [[fig:ty_scans]].
#+name: fig:ty_scans
#+attr_latex: :width 0.8\linewidth
#+caption: Top View of a tomography experiment combined with translation scans
[[file:figs/ty_scans.gif]]
@ -1974,12 +2066,14 @@ The forces applied by the nano-hexapod's are shown in Figure [[fig:opt_stiff_hac
Peak values of the forces are appearing when the translation stage changes the direction of the scan.
#+name: fig:opt_stiff_hac_dvf_Dy_scans_F
#+attr_latex: :width 0.5\linewidth
#+caption: Forces applied by the six nano-hexapod's actuators
[[file:figs/opt_stiff_hac_dvf_Dy_scans_F.png]]
The relative motions of the nano-hexapod's legs is shown in Figure [[fig:opt_stiff_hac_dvf_Dy_scans_dL]] and are again in the micro-meter range.
#+name: fig:opt_stiff_hac_dvf_Dy_scans_dL
#+attr_latex: :width 0.8\linewidth
#+caption: Relative displacement of the nano-hexapod's legs
[[file:figs/opt_stiff_hac_dvf_Dy_scans_dL.png]]
@ -1987,6 +2081,7 @@ The time domain position/orientation error of the sample is shown in Figure [[fi
The RMS value of the x-y-z position error is again $\approx 30\,nm$.
#+name: fig:opt_stiff_hac_dvf_Dy_scans_disp_error
#+attr_latex: :width 0.8\linewidth
#+caption: Position/orientation error of the sample during the simulation
[[file:figs/opt_stiff_hac_dvf_Dy_scans_disp_error.png]]
@ -2046,8 +2141,9 @@ The wanted dimension of the nano-hexapod are shown in Figure [[fig:nano_hexapod_
The limiting height might be quite problematic for the integration of the flexible joints, the actuators and sensors.
#+name: fig:nano_hexapod_size
#+attr_latex: :width 0.8\linewidth
#+caption: First implementation of the nano-hexapod / metrology reflector and sample interface
[[file:figs/nano_hexapod_size.png]]
[[file:figs/nano_hexapod_size.jpg]]
*** Flexible Joints
:PROPERTIES:
@ -2129,6 +2225,8 @@ Several sensor technology could be used for the nano-hexapod.
Characteristics of those sensors are shown in Table [[tab:characteristics_relative_sensor]].
#+name: tab:characteristics_relative_sensor
#+attr_latex: :environment tabularx :width \linewidth :align lXXXX
#+attr_latex: :center t :booktabs t :float t
#+caption: Characteristics of relative measurement sensors cite:collette11_review
| Technology | Frequency | Resolution | Range | T Range |
|----------------+------------+----------------+--------------+-------------|
@ -2182,6 +2280,7 @@ The suspension mode of the granite would then be in the order of few Hertz, and
#+name: fig:opt_stiff_soft_granite_Dw
#+attr_latex: :width 0.8\linewidth
#+caption: Change of sensibility to Ground motion when using stiff Granite mounts (solid curves) and soft Granite mounts (dashed curves)
[[file:figs/opt_stiff_soft_granite_Dw.png]]
@ -2218,5 +2317,7 @@ Feedforward if the motion error is found to be correlated with the motion of the
* Bibliography :ignore:
bibliographystyle:unsrt
bibliography:ref.bib
#+html: bibliographystyle:unsrt
#+html: bibliography:ref.bib
#+latex: \printbibliography

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@ -1,67 +1,74 @@
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@misc{collette11_review,