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Millimeter-scale continuum bending actuators are useful in minimally invasive surgery to allow distal visualization and manipulation outside the line of sight. This paper presents a new continuum bending actuator based on shape memory alloy (SMA) with variable bending length. It consists of two SMA wires antagonistically configured to produce bidirectional bending under Joule heating. A linearly actuated rigid tube along the longitudinal axis enables continuous bending length adjustment, thus enhancing its workspace and force range. The proposed fabrication method tackles the challenging assembly tasks of maintaining the antagonistic configuration of long SMA wires, and robust electrical and mechanical connection during actuation. A quasi-static model of the actuator based on beam model and SMA constitutive model is presented and verified. The bending actuator was evaluated comprehensively for its workspace, blocked force, and trajectory tracking capability at different bending lengths and under different cooling conditions. It is the first work that demonstrates real-time continuous bending length adjustment in SMA-based bending actuator, leading to the potential development of compact and compliant robotic end effectors with improved distal workspace and force. [ABSTRACT FROM AUTHOR]

This paper presents the use of shape memory alloy (SMA) spring actuators with real-time cooling to control the motion of the minimally invasive neurosurgical intracranial robot (MINIR-II). A new actuation mechanism involving the passage of water as the cooling medium and air as the medium to drive out the water has been developed to facilitate real-time control of the springs. Control parameters, such as current, water flow rates, SMA predisplacement, and gauge pressure of the compressed air, are identified from the SMA thermal model and from the actuation mechanism. In-depth modeling and characterization have been performed regarding these parameters to optimize the robot motion speed. Forced water cooling has also been compared with forced air cooling and proved to be the superior method to achieve higher robot speed. An improved robot design and a magnetic-resonance-imaging-compatible experimental platform have been developed for the implementation of the actuation mechanism. [ABSTRACT FROM PUBLISHER]

In this paper, we present our work on the development of a magnetic resonance imaging (MRI)-compatible minimally invasive neurosurgical intracranial robot (MINIR) comprising shape memory alloy (SMA) spring actuators and tendon-sheath mechanisms. We present the detailed modeling and analysis along with experimental results of the characterization of SMA spring actuators. Furthermore, to demonstrate image-feedback control, we used the images obtained from a camera to control the motion of the robot so that eventually continuous MR images could be used in the future to control robot motion. Since the image tracking algorithm may fail in some situations, we also developed a temperature feedback control scheme which served as a backup controller for the robot. Experimental results demonstrated that both image feedback and temperature feedback can be used to control the motion of MINIR. A series of MRI compatibility tests was performed on the robot and the experimental results demonstrated that the robot is MRI-compatible and no significant visual image distortion was observed in the MR images during robot operation. [ABSTRACT FROM AUTHOR]