Computational analysis of soft actuators of an MR-compatible robotic phantom that can mimic the motion of the human liver

Nehal Mathur
Presentation BSc presentation
Date 2018-07-12
Time 13:00
Location Carré 3446

Development in Magnetic Resonance Imaging (MRI) and robotics enables precise and accurate treatment of intrahepatic tumors through interventional procedures. Robotic advancements, such as needle insertion technology, enables this precise treatment of said tumors, however, difficulty arises in the accurate testing of these advancements. In this study an MR-compatible soft actuated robotic phantom, that simulate respiratory motion of patient’s liver, was improved to increase its functionality and durability. For this purpose, pneumatic soft actuators of the robotic phantom were assessed using Finite Element Analysis (FEA). Geometrical specifications, material properties and fabrication process of the soft actuators were therefore optimized.

FEA is performed on the OLEA and by varying various design parameters such as number of chambers, the angle between chamber walls and the material properties. Moreover, certain materials used in either 3D printing or molding were also included in the simulation which indicate the process of fabrication. Increasing the number of chambers or the angle between chamber walls decreases the displacement of the actuator. Various materials were tested from which Ecoflex 00-50 had the optimum material properties for maximum displacement. Improvements were made to the OLEA to produce an optimal linear actuator for the robotic phantom, that is the Improved LEA (ILEA). Its optimal parameters were six chambers with an angle of 110 degrees and fabricated using Ecoflex 00-50, and consequently, the ILEA was fabricated using molding process. The mold fabricates the outer and inner surface of the actuator with a wall thickness of 2 mm, such that the mold is re-usable, easy to remove and does not damage the inside of the actuator during demolding.

ILEA and OLEA tested on the robotic liver phantom have drastically different results. The ILEA is very sensitive, displacing 35 mm from the initial position for an applied pressure of just 0.01 bar, whereas for a pressure of 0.09 bar, the OLEA displaces only 3 mm from the initial position. Since Ecoflex 00-50 (Elastic modulus: 2.14 MPa) is highly flexible, when pressurized the actuator buckled slightly. The ILEA is far too sensitive for the control of the actuator. Therefore, for implementation within the robotic phantom the actuator must be stiffer. A stiffer material will also reduce the buckling of the actuator. In conclusion, the functionality of the actuator increased drastically by decreasing the number of chamber, the angle between chamber walls and its material properties for better actuation and control of the robotic liver phantom.

Posted on Thursday, June 28, 2018