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Entwicklung eines elektrothermischen normal geschlossenen Linearschrittantriebs aus SU-8

Schlemmer, Sascha (2015):
Entwicklung eines elektrothermischen normal geschlossenen Linearschrittantriebs aus SU-8.
TU Darmstadt, Institut EMK / FG M+EMS, [Bachelor Thesis]

Abstract

The present thesis gives a recommendation for the technical design of a electrothermal linear self-latching step drive made of SU-8 based on a drive concept developed at the institute EMK. The drive concept consists of a V-beam actuator that provides feed to the drive and a prestressed pseudo-bimorph actuator integrated into the drives‘ transmission for the self-latching clamp-and release mechanism. A pseudo-rigid body model is derived for the transmission that shows good agreement with mechanical FEM-simulation. The model error is 11.7% for a test geometry used for model validation and it is shown that the model consistently over-predicts the necessary input force into the transmission and thus leads to a technical design with additional safety added. Issues with an existing analytical model for the V-beam actuator and the results it produces have been found and investigated. The model has been used on multiple occasions in research at the Institute EMK. The force-deflection relationship predicted by the model depends on a parameter that is found by numerically finding the roots of a given conditional equation. Finding the equation‘s roots proved to be nontrivial because usually multiple solutions exist and the sough solution may not even always exist. The original source however does not give any information on the matter. The pseudo-bimorph actuator is modelled using an existing analytical beam model and extending it as to incorporate deflection in cold actuator state due to resist shrinkage. It is shown that deflection and force of the actuator in cold state depend on the difference of shrinkage in the actuator‘s two beams. Creating this difference in shrinkage by stiffening one beam with a nickel film attached to the beam‘s underside is investigated in preliminary material test. The method is found to be not feasible due to delamination of the nickel film for the wide nickel films necessary to create the appropriate stiffness. The maximum lateral deflection archived in the tests is 26µm which is approximately half of the required deflection and was found in a sample that had a low yield rate of 16% overall. The material test delivered additional results for the shrinkage of hard-baked SU-8 influenced by the post-bake temperature which is still an ongoing topic of research. The found results are lower than those obtained from previous research at the institute with a mean shrinkage in length of 0.58% for resist previously post-baked at 60°C and 0.35% for resist previously post-baked at 95°C. The analytical models are finally implemented in Mathematica and used to iteratively find a recommendation for a overall technical design for the drive. A recommendation on creating the necessary difference in shrinkage for the pseudo-bimorph actuator is given by means of an alternative approach. The actuator could be fabricated using two fabrication steps for integrating SU-8 post-baked at 60°C and 95°C into the same structure and thus utilise resist shrinkage inherent to resist post-baked at different temperatures.

Item Type: Bachelor Thesis
Erschienen: 2015
Creators: Schlemmer, Sascha
Title: Entwicklung eines elektrothermischen normal geschlossenen Linearschrittantriebs aus SU-8
Language: German
Abstract:

The present thesis gives a recommendation for the technical design of a electrothermal linear self-latching step drive made of SU-8 based on a drive concept developed at the institute EMK. The drive concept consists of a V-beam actuator that provides feed to the drive and a prestressed pseudo-bimorph actuator integrated into the drives‘ transmission for the self-latching clamp-and release mechanism. A pseudo-rigid body model is derived for the transmission that shows good agreement with mechanical FEM-simulation. The model error is 11.7% for a test geometry used for model validation and it is shown that the model consistently over-predicts the necessary input force into the transmission and thus leads to a technical design with additional safety added. Issues with an existing analytical model for the V-beam actuator and the results it produces have been found and investigated. The model has been used on multiple occasions in research at the Institute EMK. The force-deflection relationship predicted by the model depends on a parameter that is found by numerically finding the roots of a given conditional equation. Finding the equation‘s roots proved to be nontrivial because usually multiple solutions exist and the sough solution may not even always exist. The original source however does not give any information on the matter. The pseudo-bimorph actuator is modelled using an existing analytical beam model and extending it as to incorporate deflection in cold actuator state due to resist shrinkage. It is shown that deflection and force of the actuator in cold state depend on the difference of shrinkage in the actuator‘s two beams. Creating this difference in shrinkage by stiffening one beam with a nickel film attached to the beam‘s underside is investigated in preliminary material test. The method is found to be not feasible due to delamination of the nickel film for the wide nickel films necessary to create the appropriate stiffness. The maximum lateral deflection archived in the tests is 26µm which is approximately half of the required deflection and was found in a sample that had a low yield rate of 16% overall. The material test delivered additional results for the shrinkage of hard-baked SU-8 influenced by the post-bake temperature which is still an ongoing topic of research. The found results are lower than those obtained from previous research at the institute with a mean shrinkage in length of 0.58% for resist previously post-baked at 60°C and 0.35% for resist previously post-baked at 95°C. The analytical models are finally implemented in Mathematica and used to iteratively find a recommendation for a overall technical design for the drive. A recommendation on creating the necessary difference in shrinkage for the pseudo-bimorph actuator is given by means of an alternative approach. The actuator could be fabricated using two fabrication steps for integrating SU-8 post-baked at 60°C and 95°C into the same structure and thus utilise resist shrinkage inherent to resist post-baked at different temperatures.

Uncontrolled Keywords: Mikro- und Feinwerktechnik Elektromechanische Konstruktionen Mikromechanik SU-8 Kniehebel Bimorph monolithisch
Divisions: 18 Department of Electrical Engineering and Information Technology
18 Department of Electrical Engineering and Information Technology > Institute for Electromechanical Design
18 Department of Electrical Engineering and Information Technology > Institute for Electromechanical Design > Microtechnology and Electromechanical Systems
Date Deposited: 30 Nov 2015 14:56
Additional Information:

EMK-spezifische Daten:

Lagerort Dokument: Archiv Institut EMK. Anfrage über Sekretariate

Bibliotheks-Siegel: 17/24 EMKB 1893

Art der Arbeit: Bachelorarbeit

Beginn Datum: 11-12-2014

Ende Datum: 11-05-2015

Identification Number: 17/24 EMKB1893
Referees: Schlaak, Prof. Helmut F.
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