Abstract:
This work relates to the design and development of Shape Memory Alloy (SMA) based novel
actuators for Minimally Invasive Surgeries (MIS). Compared to conventional open surgery,
MIS procedures are favorable and developments are possible towards improving the
effectiveness of MIS. Handheld slender instruments used in MIS are with limited degrees of
freedom achieved using conventional actuation mechanisms which possess disadvantages in
handling, durability, and cost.
In this study, an SMA-based approach was considered to improve the operation of an MIS tool
effectively. The complex behaviour of SMA led to the investigation of material behaviour
before the application-oriented study. SMAs are smart alloys that are capable of remembering
a parent shape according to the heat treatment (HT) temperature and aging time providing
unique activation temperatures. Commercially available binary SMA material that is known
as NiTiNOL was used for the study. NiTiNOL was subjected to different HT conditions and
Differential Scanning Calorimetric (DSC) analysis was performed on the resulting material to
obtain transformation temperatures. Test results demonstrated the ability to alter activation
temperature by varying the HT conditions. Also, the samples were observed under an Optical
Microscope (OM) and Scanning Electron Microscope (SEM) to identify morphology and
elemental composition by Energy Dispersive X-Ray Spectroscopy (EDX) respectively.
Furthermore, an SMA spring actuator element was fabricated using a NiTiNOL wire through
a novel fixture to obtain desired spring parameters and geometry. NiTiNOL wire was held in
the fixture undergoing a HT at experimented temperatures and aging times. Then, spring
actuators were characterized based on maximum attainable force using a specially developed
apparatus. A customizable hardware controller and a software interface were developed to set
values, monitor temperature, and force output. Using the mentioned apparatus, the controller
was validated in both temperature and force feedback controlling modes based on a
Proportional-Integral-Derivative (PID) type controller.
Two linear actuators were designed and developed using the characterized spring element.
Firstly, an actuator was developed based on external heating using a heated fluid and cooled
fluid to heat and cool the spring element, respectively. A novel actuator structure was
developed to facilitate the spring element with leak-proof assembly and was used as the drive
source of a gripper mechanism. Strain gauge-based force sensing and PID-based force
feedback controlling methods were introduced to the gripper assembly. The second approach
was utilizing a Joule heating-based method for activation which the passing current generates
heat due to the inherent resistance of NiTiNOL resulting in an increment in temperature. The actuator was characterized in terms of stroke and then introduced to a laparoscopic retractor
application to control the flexion-extension motion. A specially developed apparatus and a
software interface are used to control parameters and acquire data. Finally, the retractor tool
was characterized in terms of stroke.
Citation:
Roshan, T.A.U. (2022). Design and development of shape memory alloy based novel actuators for minimally invasive surgeries [Master's theses, University of Moratuwa]. Institutional Repository University of Moratuwa. http://dl.lib.uom.lk/handle/123/21398