Abstract
This document describes the effects of several design parameters on the traction generated by the suction pads of a mobile robot that walks on the surface of the heart. HeartLander is a miniature mobile robot that adheres to the epicardial surface of the heart using suction, and can travel to any desired location on the heart to administer therapeutic applications. To maximize the effectiveness of locomotion, the gripper pads must provide sufficient traction to avoid slipping. Our testing setup measured the force applied to the gripper pad adhering to ovine epicardial tissue, and recorded overhead video for tracking of the pad and tissue during an extension. By synchronizing the force and video data, we were able to determine the point at which the pad lost traction and slipped during the extension. Of the pads tested, the pad with no suction grate achieved maximum traction. Increasing the extension speed up to 20 mm/s resulted in a corresponding increase in traction. Increasing the vacuum pressure also improved the traction, but the magnitude of the effect was less than the improvement gained from increasing extension speed.
Highlights
Many minimally invasive cardiac surgeries are currently being performed with assistance from robotic tools to compensate for the diminished dexterity and visualization that result from the lack of direct access to the operative site [1]
We have evaluated the tractive performance of eleven different gripper pads over a range of extension speeds and vacuum pressures
The traction force reached a maximum and became roughly constant as the gripper pad lost traction and began to slip over the epicardial tissue. This slip transition occurred when the force required to further stretch the epicardial tissue exceeded the maximum traction force that could be generated by the gripper pad
Summary
Many minimally invasive cardiac surgeries are currently being performed with assistance from robotic tools to compensate for the diminished dexterity and visualization that result from the lack of direct access to the operative site [1]. In the first half of the cycle, it grips the heart surface with its rear pad to provide the reaction force necessary for extending the front body section forward. HeartLander operates within the intrapericardial space between the epicardial surface of the heart and surrounding pericardial sac. Locomotion was successfully demonstrated, loss of traction during the extension and retraction phases was noticeable This causes the efficiency of locomotion to decrease, and may make locomotion around the posterior portion of the heart impossible due to the additional compression from the surrounding organs. For this reason, it is critical that the gripper pads be designed to maximize traction when vacuum pressure is applied to the tissue
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