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Pia Mühlbauer

M.Sc.

Research assistant
Institut für Medizingerätetechnik

Contact

Pfaffenwaldring 9
70569 Stuttgart
Deutschland
Room: 3.204

Publications

S. Da Souza, P. Mühlbauer, S. Janzen, J. Liu, and P. P. Pott, “Series and parallel actuation array of elastic micro-twisted string actuators,” presented at the ETG/GMM-Fachtagung Innovative Klein-und Mikroantriebstechnik, 2019. [Online]. Available: https://ieeexplore.ieee.org/abstract/document/8892425
- Abstract
- BibTeX
Abstract
The twisted-string actuation (TSA) principle provides simple, lightweight, silent yet powerful actuators well suited for human-machine interaction. This comprises of not only the use in orthotic and prosthetic systems for lower extremities, arms, and wrists but also exo-skeletons. A TSA consists of a bundle of at least two fiber components and an actuator to twist it along its main axis. This forms a helical structure, which shortens the axial length – given non-elastic behaviour of the material. In practice, an axial bearing compensates for the load force and a linear guide counters the motor torque. In cases where a bi-directional force is required, a passive spring return mechanism can be included. Our work focuses on the integration of the described TSA components into a single elastic tube. Three TSAs are arranged in series and six in parallel such that they form an array that can bend in three dimensions with muscle-like behaviour and elastic properties. By switching motor units on and off, the length and force of the array can be varied between zero and maximum force without the need of an internal feedback loop. A first experiment is carried out to validate the force control. A possible application of this technology is soft medical robots for diagnostic and therapeutic purposes. The first demonstrator consists of three motor units in series. Six of these serial arrangements are combined in parallel forming an array of 18 motors. Each TSA unit consists of a DC motor, a string coupling including the axial bearing, the string made of high-density polyethylene, a cylindrical housing that protects the motor against axial forces, houses the DC motor, and provides the support for the previous unit. The entire TSA unit is encapsulated inside a thermoplastic polyurethane (TPU) tube which takes over the counter-torque, acts as linear bearing, is the return spring, and provides the elastic base for the TSA array. Thus, by using these modular units an infinite chain of TSA can be built and arranged as desired. The TSA units can be current-controlled and independently activated. Experiments showed that a no-load stroke of 18 mm and a maximum pulling force of 11 N can be achieved by a single TSA module. The spatial arrangement of the tubes allows muscle-like use in larger and anthropomorphic systems and also 2-dimensional bending and torsion of the array for soft robotic systems. Further work will comprise the improvement of the module, their miniaturization, simplified axial bearings, and integrated control electronics.
BibTeX
@inproceedings{dasouza2019series, abstract = {The twisted-string actuation (TSA) principle provides simple, lightweight, silent yet powerful actuators well suited for human-machine interaction. This comprises of not only the use in orthotic and prosthetic systems for lower extremities, arms, and wrists but also exo-skeletons. A TSA consists of a bundle of at least two fiber components and an actuator to twist it along its main axis. This forms a helical structure, which shortens the axial length – given non-elastic behaviour of the material. In practice, an axial bearing compensates for the load force and a linear guide counters the motor torque. In cases where a bi-directional force is required, a passive spring return mechanism can be included. Our work focuses on the integration of the described TSA components into a single elastic tube. Three TSAs are arranged in series and six in parallel such that they form an array that can bend in three dimensions with muscle-like behaviour and elastic properties. By switching motor units on and off, the length and force of the array can be varied between zero and maximum force without the need of an internal feedback loop. A first experiment is carried out to validate the force control. A possible application of this technology is soft medical robots for diagnostic and therapeutic purposes. The first demonstrator consists of three motor units in series. Six of these serial arrangements are combined in parallel forming an array of 18 motors. Each TSA unit consists of a DC motor, a string coupling including the axial bearing, the string made of high-density polyethylene, a cylindrical housing that protects the motor against axial forces, houses the DC motor, and provides the support for the previous unit. The entire TSA unit is encapsulated inside a thermoplastic polyurethane (TPU) tube which takes over the counter-torque, acts as linear bearing, is the return spring, and provides the elastic base for the TSA array. Thus, by using these modular units an infinite chain of TSA can be built and arranged as desired. The TSA units can be current-controlled and independently activated. Experiments showed that a no-load stroke of 18 mm and a maximum pulling force of 11 N can be achieved by a single TSA module. The spatial arrangement of the tubes allows muscle-like use in larger and anthropomorphic systems and also 2-dimensional bending and torsion of the array for soft robotic systems. Further work will comprise the improvement of the module, their miniaturization, simplified axial bearings, and integrated control electronics.}, author = {Da Souza, Savio and Mühlbauer, Pia and Janzen, Swantje and Liu, Jan and Pott, Peter P.}, eventdate = {10.-11.09.2019}, eventtitle = {ETG/GMM-Fachtagung Innovative Klein-und Mikroantriebstechnik}, title = {Series and parallel actuation array of elastic micro-twisted string actuators}, url = {https://ieeexplore.ieee.org/abstract/document/8892425}, venue = {Würzburg}, year = 2019 }
L. Schwenkel, S. Janzen, P. Mühlbauer, and P. P. Pott, “Mobile compressed gas supply for active orthoses and exo-skeletons, Jahrestagung der DGBMT, 25.-26.09.2019, Frankfurt/Main,” Current Directions in Biomedical Engineering, vol. 5, no. 1, Art. no. 1, 2019, doi: https://doi.org/10.1515/cdbme-2019-0154.
- Abstract
- BibTeX
Abstract
In this study a basic principle for the gas supply of a pneumatic actuation for a mobile active knee joint orthosis is described. Instead of using a compressor or a bulky pressure reservoir, the system is supplied with pressurized gas directly from a thermodynamic process to reduce size and weight of the device. To achieve this goal a literature search was performed identifying chemical processes. These options were then analysed and evaluated considering the aspects energy density, safety, eco-friendliness, and technical feasibility of the construction. The expansion of liquified carbon dioxide with phase change achieves the best result due to its high level of safety and the simple technical feasibility of the system. However, CO2cools down considerably during the expansion, so heating up again to room temperature is necessary. Therefore, the technical construction includes a passive and an active heat exchanger.
BibTeX
@article{noauthororeditor, abstract = {In this study a basic principle for the gas supply of a pneumatic actuation for a mobile active knee joint orthosis is described. Instead of using a compressor or a bulky pressure reservoir, the system is supplied with pressurized gas directly from a thermodynamic process to reduce size and weight of the device. To achieve this goal a literature search was performed identifying chemical processes. These options were then analysed and evaluated considering the aspects energy density, safety, eco-friendliness, and technical feasibility of the construction. The expansion of liquified carbon dioxide with phase change achieves the best result due to its high level of safety and the simple technical feasibility of the system. However, CO2cools down considerably during the expansion, so heating up again to room temperature is necessary. Therefore, the technical construction includes a passive and an active heat exchanger.}, author = {Schwenkel, Laura and Janzen, Swantje and Mühlbauer, Pia and Pott, Peter P.}, doi = {https://doi.org/10.1515/cdbme-2019-0154}, journal = {Current Directions in Biomedical Engineering}, number = 1, pages = {613-616}, title = {Mobile compressed gas supply for active orthoses and exo-skeletons, Jahrestagung der DGBMT, 25.-26.09.2019, Frankfurt/Main }, type = {Publication}, url = {https://www.degruyter.com/view/journals/cdbme/5/1/article-p613.xml}, volume = 5, year = 2019 }
P. Mühlbauer, L. Löhnert, C. Siegle, K. W. Stewart, and P. P. Pott, “Demonstrator of a Low-Cost Hand Prosthesis,” IFAC World Congress 2020, Germany, 2020.
- Abstract
- BibTeX
Abstract
Upper limb absence has an impact on both physical and mental health of a human being. Nowadays, the costs of commercial, externally powered prosthetic hands range between 25.000 € and 70.000 €. A first demonstrator of a lightweight low-cost prosthetic hand is produced with 3D-printing technology (Fused Deposition Modeling). Due to integration of single-axis solid-state joints the five fingers can be printed in one piece. Thermoplastic polyurethane is used for this purpose. The flexion of all fingers is achieved by moving cords which are positioned on the palmar side of each finger. Two twisted string actuators are integrated to allow the movement of the thumb and the remaining four fingers. These actuators consist of two polyethylene strands which are twisted along their main axis by a DC motor, providing a tensile force to bend the fingers. In order to achieve simultaneous but differential actuation of the four fingers (small finger, ring finger, middle finger and index finger), a differential mechanism is used. The thumb is driven by a separate unit. In order to open the hand, the elasticity of the joints’ material is taken advantage of. With the developed mechanics it is possible to perform precision and cylindrical grasps with an opposed thumb. Weights up to 260 g can be held according to the shape and size of an object. To increase the adaption to different sizes and weights of objects, the design should be modified. It can be concluded, that the presented device is a promising basis for a lightweight, lowcost prosthetic hand in the future.
BibTeX
@inproceedings{muhlbauer2020demonstrator, abstract = {Upper limb absence has an impact on both physical and mental health of a human being. Nowadays, the costs of commercial, externally powered prosthetic hands range between 25.000 € and 70.000 €. A first demonstrator of a lightweight low-cost prosthetic hand is produced with 3D-printing technology (Fused Deposition Modeling). Due to integration of single-axis solid-state joints the five fingers can be printed in one piece. Thermoplastic polyurethane is used for this purpose. The flexion of all fingers is achieved by moving cords which are positioned on the palmar side of each finger. Two twisted string actuators are integrated to allow the movement of the thumb and the remaining four fingers. These actuators consist of two polyethylene strands which are twisted along their main axis by a DC motor, providing a tensile force to bend the fingers. In order to achieve simultaneous but differential actuation of the four fingers (small finger, ring finger, middle finger and index finger), a differential mechanism is used. The thumb is driven by a separate unit. In order to open the hand, the elasticity of the joints’ material is taken advantage of. With the developed mechanics it is possible to perform precision and cylindrical grasps with an opposed thumb. Weights up to 260 g can be held according to the shape and size of an object. To increase the adaption to different sizes and weights of objects, the design should be modified. It can be concluded, that the presented device is a promising basis for a lightweight, lowcost prosthetic hand in the future.}, author = {Mühlbauer, Pia and Löhnert, Laura and Siegle, Carla and Stewart, Kent W. and Pott, Peter P.}, organization = {IFAC World Congress 2020, Germany }, title = {Demonstrator of a Low-Cost Hand Prosthesis}, year = 2020 }
P. Mühlbauer, S. Janzen, K. Stewart, and P. P. Pott, “Demonstrator of a low-cost active knee orthosis with twisted string actuation,” presented at the ETG/GMM-Fachtagung Innovative Klein-und Mikroantriebstechnik, 2019. [Online]. Available: https://ieeexplore.ieee.org/document/8892426
- Abstract
- BibTeX
Abstract
This paper presents a demonstrative active knee orthosis to support sit-to-stand (STS) transfer movement, which is silent, simply constructed, small, lightweight, and low-cost. The demonstrative active knee orthosis is driven with a twisted string actuator (TSA) fixed to the lateral side of the upper rail. The TSA consists of two polyethylene strands which are twisted along its main axis by a DC motor. Linear guidance rails are used to counteract the motor torque on the load side of the TSA. The resulting helix structure formed in the twisted strings leads to a tensile force along the length of the TSA. At the knee joint, a cam disc converts this force into the desired support moment. Low-cost parts and materials were used when putting the demonstrator together to ensure the overall costs were kept to a minimum. An Arduino microcontroller and a H-bridge circuit provide the motor control, with a user controlled potentiometer specifying the desired speed. The demonstrator is 3D-printed via fused deposition modelling, with scaled down dimensions (scaling factor 0.7) compared to a normal knee orthosis. The costs, size, and noise of the demonstrator are kept low via the use of a simple TSA, replacing the need for heavy and noisy mechanical gear. Due to the simplicity of the system, the total costs are low (106 EUR), and thus are also expected to be low when creating a full scale version. The demonstrator shows a successful implementation of a TSA driven knee orthosis able to achieve STS-movement while being silent, lightweight and low-cost. Future work will look into improvements of the cam disc's geometry and motor selection to achieve the desired knee torque profile in relation to the transfer movement. In addition, a full-scale version of the TSA knee orthosis will be constructed.
BibTeX
@inproceedings{muhlbauer2019demonstrator, abstract = {This paper presents a demonstrative active knee orthosis to support sit-to-stand (STS) transfer movement, which is silent, simply constructed, small, lightweight, and low-cost. The demonstrative active knee orthosis is driven with a twisted string actuator (TSA) fixed to the lateral side of the upper rail. The TSA consists of two polyethylene strands which are twisted along its main axis by a DC motor. Linear guidance rails are used to counteract the motor torque on the load side of the TSA. The resulting helix structure formed in the twisted strings leads to a tensile force along the length of the TSA. At the knee joint, a cam disc converts this force into the desired support moment. Low-cost parts and materials were used when putting the demonstrator together to ensure the overall costs were kept to a minimum. An Arduino microcontroller and a H-bridge circuit provide the motor control, with a user controlled potentiometer specifying the desired speed. The demonstrator is 3D-printed via fused deposition modelling, with scaled down dimensions (scaling factor 0.7) compared to a normal knee orthosis. The costs, size, and noise of the demonstrator are kept low via the use of a simple TSA, replacing the need for heavy and noisy mechanical gear. Due to the simplicity of the system, the total costs are low (106 EUR), and thus are also expected to be low when creating a full scale version. The demonstrator shows a successful implementation of a TSA driven knee orthosis able to achieve STS-movement while being silent, lightweight and low-cost. Future work will look into improvements of the cam disc's geometry and motor selection to achieve the desired knee torque profile in relation to the transfer movement. In addition, a full-scale version of the TSA knee orthosis will be constructed.}, author = {Mühlbauer, Pia and Janzen, Swantje and Stewart, Kent and Pott, Peter P.}, eventdate = {10.-11.09.2019}, eventtitle = {ETG/GMM-Fachtagung Innovative Klein-und Mikroantriebstechnik}, isbn = {978-3-8007-5062-7}, title = {Demonstrator of a low-cost active knee orthosis with twisted string actuation}, url = {https://ieeexplore.ieee.org/document/8892426}, venue = {Würzburg}, year = 2019 }

Teaching

Technische Grundlagen der Laparoskopie
Flexible Endoskopie

Vita

2012 – Abitur, Waldschule Degerloch, Stuttgart

2016 – B.Sc. Medical Technology, Eberhard Karls University of Tübingen & University of Stuttgart
Validation of an inertial measurement system for the acquisition of the rotational speed curve for jumps with screw motion

2018 – M.Sc. Medical Engineering, University of Stuttgart
Construction of a demonstrator of an actively driven knee joint orthosis

2019 – Research assistant at the Institute of Medical Device Technology, University of Stuttgart

Student Projects

Maria Carolina Lanzino. SA0095: Integration eines Twisted-String Antriebs mit hohler Motorwelle in ein Ellenbogen-Exoskelett. Betreuerin: Pia Mühlbauer. Institut für Medizingerätetechnik, Universität Stuttgart. 2020.
[In Bearbeitung]

Alberto Sancho Diaz. BA0084: Development of a monolithic elbow exoskeleton frame. BetreuerIn: Pia Mühlbauer, Kent Stewart. Institut für Medizingerätetechnik, Universität Stuttgart. 2020.
[In Bearbeitung]

Hendrik Schall. BA0083: Entwicklung Aufbau und Charakterisierung eines Twisted-String Antriebs mit hohler Motorwelle. Betreuerin: Pia Mühlbauer. Institut für Medizingerätetechnik, Universität Stuttgart. 2020.
[In Bearbeitung]

Judith Henkel. BA0082: Integration von Twisted-String Antrieben in didaktische Konstruktions-Baukastensysteme. Betreuerin: Pia Mühlbauer. Institut für Medizingerätetechnik, Universität Stuttgart. 2020.
[In Bearbeitung]

Niclas Engelmeyer. MA0079: Weiterentwicklung und Validierung einer Low-Cost Handprothese mit Twisted String Antrieb. Betreuerin: Pia Mühlbauer. Institut für Medizingerätetechnik, Universität Stuttgart. 2020.
[In Bearbeitung]

Mario Schimbera. MA0061: Entwicklung eines Twisted-String Antriebs für eine modulare Handorthese und Validierung anhand eines Demonstrators. Betreuerin: Pia Mühlbauer. Institut für Medizingerätetechnik, Universität Stuttgart. 2020.
[Ergebnisposter]

Manuela Sabrina Schön. BA0060: Entwicklung eines pneumatischen Antriebs für eine Kniegelenksorthese. Betreuerin: Pia Mühlbauer. Institut für Medizingerätetechnik, Universität Stuttgart. 2019.
[Ergebnisposter]

Laura Löhnert. BA0053: Entwicklung und Charakterisierung einer Low-Cost Handprothese mittels Twisted String Antrieb. Betreuerin: Pia Mühlbauer. Institut für Medizingerätetechnik, Universität Stuttgart. 2019.
[Ergebnisposter]

Carla Siegle. BA0052: Entwicklung und Aufbau einer Low-Cost Handprothese. Betreuerin: Pia Mühlbauer. Institut für Medizingerätetechnik, Universität Stuttgart. 2019.
[Ergebnisposter]

Savio D souza. MA0031: Aufbau und Charakterisierung eines Arrays aus Micro-Twisted-String Antrieben. Betreuer: Swantje Janzen, Jan Liu, Pia Mühlbauer. Institut für Medizingerätetechnik, Universität Stuttgart. 2019.
[Ergebnisposter]

Pia Mühlbauer

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