Miniaturized force/moment transducers for instrumented teeth

Abstract: The thesis reports on the development and fabrication of miniaturized six-degree-of-freedom (6DOF) force/moment transducers (FMT), which are intended to serve as measurement devices in a true-scale orthodontic simulator. The measurement principle relies on the mapping of the mechanical stress distribution induced by an external load in a mechanical micro sensor chip fabricated in complementary metal-oxide-semiconductor (CMOS) technology. After calibration, the applied load state is inferred from the mapped stress distribution. The content of this thesis is divided into three main topics: (i) The development and investigation of a novel field-effect-transistor (FET) based mechanical CMOS stress sensor, (ii) elaborations on state-of-the-art calibration theories including a new half-blind calibration method, and (iii) the development, fabrication, and evaluation of the FMTs.

The novel mechanical CMOS stress sensor is based on four FETs in a Wheatstone bridge (WSB) configuration. Pairs of FETs are connected by common source/drain diffusions. While the FETs of previous stress sensors have shared a common gate electrode, the gate electrodes of the FETs of the new sensor can be manipulated individually. With all four FETs switched on, a supply voltage VSS between two opposing contacts causes a WSB voltage between the two remaining contacts proportional to the in-plane normal mechanical stress. With all four gates short-cut to a common gate voltage VCG, this WSB voltage serves directly as sensor signal. Appropriate shifts of the individual gate voltages to VCG +/- ∆VGi enables the compensation of the WSB voltage to zero. In this case the applied compensation voltages serve as signal. Depending on the choice of FETs used for compensation, different sensitivities can be achieved. For example at VSS = -1 V, sensitivities are measured to be in the range of 3.1 to 6.2 mV/VMPa. Thereby they are higher than in the conventional WSB mode by factors of 6 to 12.

The half-blind calibration method (HBCM) targets the calibration of sensor systems designed to determine external measurands. These sensor systems often show parasitic sensitivities to external and internal influences beside their response to the intended measurands. Conventional calibration methods have treated the disturbances on an equal footing with the measurands and thus have determined their influence on the sensor system with high accuracy. The concept of the HBCM allows to reduce the effort of state-of-the-art calibration methods considerably using the fact that the accurate knowledge of the disturbance values during calibration is not needed. It is noteworthy that the HBCM does not lead to any loss in accuracy despite saving time and cost. Using a 6DOF FMT, the theoretical elaborations are experimentally illustrated. In addition, a generalization of the device hyperplane calibration method and a simplification and an improvement of the shape-from-motion calibration method are presented.

The development and manufacturing of three different FMT designs termed Designs A, B, and C is presented. All three are based on the same stress-mapping CMOS chip and were designed to measure forces and moments in the range of +/-3 N and +/-3 Ncm, respectively. In Design A the chip is sandwiched between two metal pins used for mechanical connection. Design B is based on two CMOS chip stripes bonded on two opposite sides of a bare silicon bar by adhesive. Design C uses one CMOS chip stripe on a KOH structured silicon bar. In Design B and C both ends of the chip/bar assembly are provided with metal pins for mechanical connection.

With its 3.5 mm in diameter and 12 mm in height Design A is smaller than Designs B and C measuring 4.5 mm in diameter 16.4 mm in height. However, Design A is prone to strong drift. Designs B and C also outperform Design A regarding measurement accuracy by factors of 2.9 to 4.3. Design C has the advantage of utilizing only one CMOS chip. Experimental results are in good agreement with finite element simulations

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Universität Freiburg, Dissertation, 2020

Klassifikation und Themen

• Schlagwort: Teeth ; Transducers ; Messgrößenumformer ; Kraft ; Drehmoment ; Kieferorthopädie ; Miniaturisierung ; Mikrosystemtechnik ; Mechanische Spannung ; Sensor ; Kalibrieren ; Medizintechnik

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2020
• Urheber: Becker, Felix
• Beteiligte Personen und Organisationen: Paul, Oliver ; Albert-Ludwigs-Universität Freiburg. Fakultät für Angewandte Wissenschaften

Weitere Informationen

• DOI: 10.6094/UNIFR/165853
• URN: urn:nbn:de:bsz:25-freidok-1658533
• Rechteinformation: Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 25.03.2025, 13:53 MEZ