Linear Guides and Plastic Bearings Facilitate Motion for MRI-guided Robot

A team of researchers from the Worcester Polytechnic Institute have developed a teleoperated robot that will greatly improve the way prostate cancer is detected and treated.
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May 25, 2011 - PRLog -- A team of researchers from the Worcester Polytechnic Institute have developed a teleoperated robot that will greatly improve the way prostate cancer is detected and treated.  igus® donated parts to the project at no cost, including DryLin® linear guide systems and iglide® plastic plain bearings, which facilitate the robot’s motion.

Prostate cancer is the second most common cancer in North America and the leading type of cancer found in males.  Each year approximately 1.5 million core-needle biopsies are performed, leading to a staggering 220,000 newly diagnosed cases of prostate cancer.  The robotic system is specifically for prostate percutaneous procedures taking place under magnetic resonance imaging (MRI) guidance.  The slave robot features a high-resolution fiber optic sensor for prostate interventions with real-time in situ needle steering capability in 3-Tesla MRI.

The robot’s needle placement robot consists of a 3-DOF Cartesian positioning module and 3-DOF needle driver module.  DryLin T linear guides facilitate translational motion of the positioning module, which provides gross positioning for the robot’s needle driver.  The needle driver is a vital part of the system, as it enables the rotation and translational movement of the needle cannula: a flexible tube inserted into the patient’s body cavity for MRI-guided diagnosis and therapy.

The needle driver has a needle guide sleeve, a collet locking mechanism and passive optical tracking fiducial frame.  Two iglide A200 plastic plain bearings are used in the front and rear of the driver to constrain the needle guide.  The iglide bearings enable the robot’s motor to rotate the needle using the collet mechanism by way of a timing belt.  This rotating needle would reduce tissue damage while enhance targeting accuracy. Another 10 iglide bearings were used to create a revolute joint, also known as a “pin joint” or “hinge joint”, to provide single-axis rotation.

A perfect picture with plastics
Since the robot operates inside a 3-Tesla, closed-bore MRI machine with only a 500-millimeter cylinder diameter, there were a number of elements that had to be taken into consideration during the design process.  Specifically for the robot’s mechanical system, the components had to be non-ferrous for the patient’s safety during the radiation process, but also compact due to the very limited installation space.  Drylin T linear guide systems and iglide A200 plastic plain bearings were ideal for a number of reasons.

DryLin T linear guides are comprised of hard-anodized aluminum rails and carriages and high-performance plastic sliding elements, which do not interfere with the MRI procedure.  The linear slides operate without messy lubrication, which is important in a sterile medical environment.  They also feature a lower-profile for applications where installation space is an issue.

iglide A200 plastic plain bearings were an obvious choice for the robot, as they are comprised of FDA-compliant polymers specifically designed for applications with contact to food or drugs.  Like DryLin T, the iglide bearings also operate dry-running in order to prevent contamination.

Hao Su, PhD candidate and the lead of this project said, “There are very few products on the market that both satisfied our requirements and delivered a good mechanical performance.  igus helped us address this issue by donating its high-performance products.”

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Igus® develops industry-leading cable carriers, continuous-flex cables, plastic plain bearings, linear bearings and guide systems and spherical bearings.
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