Embedded Files
Project Overview:
Project Overview:
Magnetic Resonance Imaging (MRI) machines are a powerful tool for doctors to receive real-time images of patients; however, they are underutilized for conducing procedures like biopsies due to their lack of access points and compatible materials. Robots, such as that of the Yip Lab, are being developed to enable doctors further range of motion within the MRI chamber, but there are several complicating factors to be considered. Doctors primarily rely on the haptics of their instruments to confirm if they have performed a procedure correctly, meaning any tools to interface between doctors and the patient in MRI chamber must accurately receive a doctor’s input on a simulation biopsy device and replicate the same motions on an actual biopsy device within the MRI. Most organs have layers of various stiffness so it is essential the needle is sensitive to the doctor’s input and does not puncture each membrane in real-time so a doctor doesn’t push too far. Furthermore, the system must maintain notable accuracy as performing an operation at even a few millimeters off can potentially paralyze or even kill patients.
This project seeks to dive deeper into the rolling diaphragm actuators mechanism of the Yip lab robot and evaluate if it can accurately reproduce a doctor's motion from a simulation tool onto an in-MRI tool.
Project Relevance + Status Quo:
Project Relevance + Status Quo:
MRI's provide the very useful but underutilized tool of live-imagery, however this is under utilized as MRI's have limited + awkward points for patient access as well as stringent limitations on safe materials. Robots for in-MRI procedures are in development but they are not a replacement for doctor's but a tool for them. As bodies vary so much person-to-person, doctors rely on the haptics of their instruments to know they have performed a procedure correctly (i.e. feeling the needle sink into the correct stiffness membrane).
Rolling Diaphragm Actuator Definition:
Rolling Diaphragm Actuator Definition:
Rolling diaphragms are a type of seal with a variable volume and flexible sidewalls
Advantages compared to other sealing methods (like o-rings):
Low leakage
Low friction
Low hysteresis
Accurate/repeatable positioning
Rolling Diaphragm Actuator Implementation:
Rolling Diaphragm Actuator Implementation:
As seen here, the Yip Lab rolling diaphragm actuators consist of two fluid cavities (one water, one oil) within a housing, a piston, and an elastomer-based rolling diaphragm. One actuator is placed on each side of the system (doctor and patient) and the water ports on each are connected.
As one piston moves (as would happen when a doctor presses down on a plunger tool), water travels to the other actuator’s port, forcing the piston farther out of the housing (or biopsy needle towards a patient).
Project Conclusions - Result Summary:
Project Conclusions - Result Summary:
The results of the rolling diaphragm hydrostatic transmission show that it can transmit motions repeatedly and transparently with displacement errors of less than 2 mm. Performance is better when the air sides of the diaphragm housing are connected in a T-junction configuration at 60 PSI with the hose length equal to 69 cm. Although the group was unable to detect force tracking errors of less than 15%, an average of 18.7% force tracking errors is relatively close considering the 3-D printed parts used in the characterization setup and the air bubbles that persisted in the water side of the diaphragm housing. Immediate improvements are to be made to increase the stiffness of the system, remove the air bubbles to eliminate compressibility, and add a flexible coupling between the metal seal bushing and the cylinder to avoid binding between shaft and bushing.
Project Conclusions - Further Actions:
Project Conclusions - Further Actions:
To reduce the force tracking errors, we recommend the following:
Add a bleed port at a high point of the cylinder + a taper inside the cylinder towards the bleed port for air to naturally move up and remove air bubbles
Add a flexible coupling between the metal seal bushing and the cylinder to avoid binding between shaft and bushing
Add alignment pins to prevent diaphragms becoming twisted, which increases friction, when assembling
We also recommend the following to further characterize the actuator and testbed:
Test the system with a greater array of hose diameters
Replace 3-D printed components of testbed with machined components to increase system stiffness and ensure most compliant component of the system is the actuator itself
Page updated
Report abuse