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Update conclusion about flexible joints

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Thomas Dehaeze
2020-05-05 11:50:07 +02:00
parent f7714a1449
commit 81ad4485c3
2 changed files with 92 additions and 56 deletions
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org/flexible_joints_study.org
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@@ -504,7 +504,7 @@ It is shown that the bending stiffness of the flexible joints have very little i
The bending stiffness of the flexible joint does not significantly change the dynamics.
#+end_important
* Translation Stiffness
* Axial Stiffness
<<sec:trans_stiffness>>
** Introduction :ignore:
@@ -993,8 +993,22 @@ The dynamics from $\bm{\tau}^\prime$ to $\bm{\epsilon}_{\mathcal{X}_n}$ (for the
<<sec:conclusion>>
#+begin_important
For the identified optimal actuator stiffness $k = 10^5\,[N/m]$, the flexible joint should have the following stiffness properties:
- Bending Stiffness: $K_b < 50\,[Nm/rad]$
- Torsion Stiffness: $K_t < 50\,[Nm/rad]$
- Axial Stiffness: $K_a > 10^7\,[N/m]$
In this study we considered the bending, torsional and axial stiffnesses of the flexible joints used for the nano-hexapod.
The bending and torsional stiffnesses somehow adds a parasitic stiffness in parallel with the legs.
It is not found to be much problematic for the considered control architecture (it is however, if Integral Force Feedback is to be used).
As a consequence of the added stiffness, it could increase a little bit the required actuator force.
The axial stiffness of the flexible joints can be very problematic for control.
Small values of the axial stiffness are shown to limit the achievable damping with Direct Velocity Feedback.
The axial stiffness should therefore be maximized and taken into account in the model of the nano-hexapod.
For the identified optimal actuator stiffness $k = 10^5\,[N/m]$, the flexible joint should have the following stiffness properties:
- Axial Stiffness: $K_a > 10^7\,[N/m]$
- Bending Stiffness: $K_b < 50\,[Nm/rad]$
- Torsion Stiffness: $K_t < 50\,[Nm/rad]$
As there is generally a trade-off between bending stiffness and axial stiffness, it should be highlighted that the *axial* stiffness is the most important property of the flexible joints.
#+end_important