Shing Shin Cheng

Design, development, and evaluation of an MRI-guided SMA spring-actuated neurosurgical robot

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.

Towards high frequency actuation of SMA spring for the neurosurgical robot - MINIR-II

Robotic surgery, especially in the field of neurosurgery, can be tremendously improved with the integration of an excellent imaging modality during the procedure. Shape memory alloy (SMA), a high power density and inexpensive MRI-compatible actuator, is therefore being considered as an appropriate actuator for the robot. However, the low control bandwidth of SMA due to the long cooling time makes it undesirable for commercial use. An efficient and low-cost cooling method using water as a coolant that passes through a flexible tube coiled around the SMA spring is proposed to increase the cooling rate of SMA, thereby improving its actuation frequency. SMA constitutive model and heat transfer model have been developed to simulate theoretical behavior of SMA springs in antagonistic configuration. The maximum bandwidth we achieved was 0.333 Hz for tracking of a sinusoidal trajectory of 3 mm peak-to-peak magnitude. We also demonstrated the capability of our cooling system to control the motion of an SMA spring actuated one-DOF MINIR-II robot prototype.

Towards a Robotic Hand Rehabilitation Exoskeleton for Stroke Therapy

A majority of stroke patients suffer from the loss of effective motor function, which compromises their ability to control grasping motion. Hand rehabilitation is therefore important to improve their motor function and quality of life in activities of daily living (ADLs). In this initial work, we present the design and development of a partial hand exoskeleton actuated by shape memory alloy (SMA) spring actuators. The SMA spring actuators are cooled by forced convection and the individual joints of the finger are actuated via tendons. In this design, pre-tension in the passive springs enables the restoration of the original configuration when the SMA springs are not actuated. To address the slow cooling rate of SMA springs that limits the control performance, we developed a cooling unit for each SMA spring actuator. We utilized computer vision to identify an object and provide 3-D coordinates of the optimal grasping points on the object. We then utilized vision-based control to move the fingertips towards the grasping points. The experimental results showed that each individual joint was able to return to its original configuration significantly faster as well as to follow a sinusoidal trajectory with the proposed cooling strategy.Copyright

New Actuation Mechanism for Actively Cooled SMA Springs in a Neurosurgical Robot

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.

Toward the Development of a Flexible Mesoscale MRI-Compatible Neurosurgical Continuum Robot

Brain tumor, be it primary or metastatic, is usually life threatening for a person of any age. Primary surgical resection is one of the most effective ways of treating brain tumors and can have a tremendously increased success rate if the appropriate imaging modality is used for complete tumor resection. Magnetic resonance imaging (MRI) is the imaging modality of choice for brain tumor imaging because of its excellent soft-tissue contrast. MRI combined with continuum soft robotics has immense potential to be the next major technological breakthrough in the field of brain cancer diagnosis and therapy. In this paper, we present the design, kinematic, and force analysis of a flexible spring-based minimally invasive neurosurgical intracranial robot. It is comprised of an interconnected inner spring and an outer spring and is connected to actively cooled shape memory alloy (SMA) spring actuators via tendon driven mechanism. Our robot has three serially connected 2-DoF segments, which can be independently controlled due to the central tendon routing configuration. The kinematic and force analysis of the robot and the independent segment control were verified by experiments. Robot motion under forced cooling of SMA springs was evaluated as well as the MRI compatibility of the robot and its motion capability in brain-like gelatin environment.

Modeling and characterization of shape memory alloy springs with water cooling strategy in a neurosurgical robot

Since shape memory alloy has a high power density and is magnetic resonance imaging compatible, it has been chosen as the actuator for the meso-scale minimally invasive neurosurgical intracranial robot (MINIR-II) that is envisioned to be operated under continuous magnetic resonance imaging guidance. We have devised a water cooling strategy to improve its actuation frequency by threading a silicone tube through the spring coils to form a compact cooling module-integrated actuator. To create active bi-directional motion in each robot joint, we configured the shape memory alloy springs in an antagonistic way. We modeled the antagonistic shape memory alloy spring behavior and provided the detailed steps to simulate its motion for a complete cycle. We investigated the heat transfer during the resistive heating and water cooling processes. Characterization experiments were performed to determine the parameters used in both models, which were then verified by comparing the experimental and simulated data. The actuation frequency of the antagonistic shape memory alloys was evaluated for several motion amplitudes and we could achieve a maximum actuation frequency of 0.143u2009Hz for a sinusoidal trajectory with 2u2009mm amplitude. Lastly, we developed a robotic system to implement the actuators on the MINIR-II to move its end segment back and forth for approximately ±25°.

Towards the development of a spring-based continuum robot for neurosurgery

Brain tumor is usually life threatening due to the uncontrolled growth of abnormal cells native to the brain or the spread of tumor cells from outside the central nervous system to the brain. The risks involved in carrying out surgery within such a complex organ can cause severe anxiety in cancer patients. However, neurosurgery, which remains one of the more effective ways of treating brain tumors focused in a confined volume, can have a tremendously increased success rate if the appropriate imaging modality is used for complete tumor removal. Magnetic resonance imaging (MRI) provides excellent soft-tissue contrast and is the imaging modality of choice for brain tumor imaging. MRI combined with continuum soft robotics has immense potential to be the revolutionary treatment technique in the field of brain cancer. It eliminates the concern of hand tremor and guarantees a more precise procedure. One of the prototypes of Minimally Invasive Neurosurgical Intracranial Robot (MINIR-II), which can be classified as a continuum soft robot, consists of a snake-like body made of three segments of rapid prototyped plastic springs. It provides improved dexterity with higher degrees of freedom and independent joint control. It is MRI-compatible, allowing surgeons to track and determine the real-time location of the robot relative to the brain tumor target. The robot was manufactured in a single piece using rapid prototyping technology at a low cost, allowing it to disposable after each use. MINIR-II has two DOFs at each segment with both joints controlled by two pairs of MRI-compatible SMA spring actuators. Preliminary motion tests have been carried out using vision-tracking method and the robot was able to move to different positions based on user commands.

Towards Real-Time SMA Control for a Neurosurgical Robot: MINIR-II

Intraoperative magnetic resonance image (MRI)-guided neurosurgical procedure is receiving much attention due to the use of real-time image feedback instead of pre-operative images when resecting the tumor. We envision a real-time MR image-guided robotic neurosurgery that utilizes a dexterous meso-scale surgical robot that can work in tight spaces. In this work, we introduce an MR-compatible robotic platform for a spring-based prototype of the minimally invasive neurosurgical intracranial robot (MINIR-II). The robot consists of an outer spring and an inner interconnected spring that has three segments, each of which has two degrees of freedom (DoFs). Each joint of the robot is actuated by an antagonistic pair of shape memory alloy (SMA) spring actuators with integrated water cooling modules. The proposed water-based cooling strategy is designed to improve the cooling rate and thus the actuation bandwidth of SMA springs so that the neurosurgical robot can be operated at sufficiently high bandwidth. We characterized our cooling module integrated SMA springs based on several parameters including the current supplied, water flow rate, SMA pre-strain, gauge pressure of the compressed air, and motion amplitude. We developed a vision-based experimental setup to perform the characterization experiments and optimized the actuator performance in terms of its actuation bandwidth. We commanded the base and middle segments of the robot to follow a series of step input references to verify the improved actuation bandwidth of the antagonistic SMAs. Finally, we performed experiments to allow continuous and coordinated motion between the base and middle segments to verify the robot’s independent joint controllability and motion repeatability.

Active Stiffness Tuning of a Spring-Based Continuum Robot for MRI-Guided Neurosurgery

Deep intracranial tumor removal can be achieved if the neurosurgical robot has sufficient flexibility and stability. Toward achieving this goal, we have developed a spring-based continuum robot, namely a minimally invasive neurosurgical intracranial robot (MINIR-II) with novel tendon routing and tunable stiffness for use in a magnetic resonance imaging (MRI) environment. The robot consists of a pair of springs in parallel, i.e., an inner interconnected spring that promotes flexibility with decoupled segment motion and an outer spring that maintains its smooth curved shape during its interaction with the tissue. We propose a shape memory alloy (SMA) spring backbone that provides local stiffness control and a tendon routing configuration that enables independent segment locking. In this paper, we also present a detailed local stiffness analysis of the SMA backbone and model the relationship between the resistive force at the robot tip and the tension in the tendon. We also demonstrate through experiments, the validity of our local stiffness model of the SMA backbone and the correlation between the tendon tension and the resistive force. We also performed MRI compatibility studies of the three-segment MINIR-II robot by attaching it to a robotic platform that consists of SMA spring actuators with integrated water cooling modules.