University of Twente Student Theses


Pneumatic position sensing for robotic applications in an MR-environment

Nikken, M.S. (2022) Pneumatic position sensing for robotic applications in an MR-environment.

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Abstract:Researchers have shown interest in developing robots that can assist in medical interventions inside an MRI-scanner. To ensure the safety of the patient and medical personnel, it is preferable that the materials in the MRI-scanner are not ferromagnetic and nonconductive, which also means that no electronics can be used. This requires an alternative approach to actuating these robots and providing them with feedback through sensors. In order to obtain position feedback for these robots, position sensors are required. Different types of sensors have been used for this purpose, many of which use electronics inside theMRIbore. MR Safe position sensors exist in the formof fibre optic sensors, but they are expensive. This research explores the possibility of making an MR Safe position sensor using pneumatics. The proposed design modulates airflow through a pneumatic tube by mechanically changing the size of a constriction at the end of the tube. This creates a differential pressure across the tube, which can be measured away from the MR-environment. Using 3D printing, the pneumatic position sensor was fabricated. An iterative design approach was used to linearise and improve the sensor design. Furthermore, a parametric analysis has been performed on two important system parameters. Next, a static characterisation of the best prototype has been carried out. An absolute mean error of 0.31 mm (0.7% of the full range) and an absolute maximum error 7.2 mm (16% of the full range) have been observed. Additionally, to overcome some issues with the previous prototypes, like the loss of sensitivity when scaling up the sensor, a pneumatic encoder has been designed and fabricated. Tests on this encoder showed a mean error of 0.81 mm (2.0% of the tested range) and an absolute maximum error of 8.2 mm (20.5% of the tested range). Time constraints prevented multiple design iterations and a complete characterisation to be carried out. Hence, the encoder still has plenty of potential to improve the design, without requiring high-end 3Dprinters or similar manufacturing techniques.
Item Type:Essay (Bachelor)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Programme:Electrical Engineering BSc (56953)
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