Finally, a flexible-tip controllable needle is deployed from the tip of the concentric tube robot to provide greater system dexterity and precision. 47 3.9 Shown is the use of an end cap to attach the tendon to the tip of the wrist.
Motivation
To date, the most successful surgical robot is the Da Vinci surgical system, which uses robotic arms to control laparoscopic instruments with wristed end effectors [21]. Although the da Vinci is by far the most successful commercial system, offering both patients and surgeons the aforementioned benefits, it is not without its shortcomings.
Dexterous Continuum Devices
In the sections that follow, work related to the design and modeling of these small dexterous mechanisms is reviewed. Existing robotic approaches for the treatment of lung and skull base diseases are also reviewed, as these are the two clinical applications targeted by this dissertation using the developed dexterous mechanisms.
Design of Steerable Needles
Dexterous Mechanisms for Needle-sized Manipulators
By pulling the cables on one side of the device and releasing them on the other side, the continuum mechanism bends into an arc (see image). One method of achieving a convenient continuum mechanism with a minimal number of components is to create a flexible bending region in an elastic part, often using geometric patterns to limit the movement of the device.
Systems for Treating Lung Cancer
Disadvantages of the system include the large space required to set it up and the high cost of the system, which means that only high-volume centers will be able to provide such treatment. While promising, this system poses a serious risk of lung collapse during placement of radioactive seeds, as the outer membrane of the lung must be cut to access the tumor.
Systems for Treating Skull Base Tumors
In Chapter 5, a minimally invasive robotic system is developed that uses needle sizes with concentric tube robots for the removal of cranial tumors through a single nostril. The surgeon operates the robotic system using a teleoperation paradigm, and an actuation unit controls the curvilinear movement of the dexterous manipulators in the base of the skull.
Dissertation Overview and Contributions
Design
In this dissertation, the basic concepts of mechanics and geometry are combined to design new distal dexterity mechanisms. Design examples found in this dissertation include a steerable needle incorporating a bending element located between the needle tip and the stem (Chapter 2, [6]), a miniature wrist integrated into an elastic tube that uses cut sections of tube to reduce bending stiffness and create a dexterous device (Chapter 3, [58]) and a non-annular concentric tube robot that uses geometry to enable previously unattainable robot configurations and prevent elastic instability (Chapter 4, [59]).
Modeling
For example, modeling the interaction of the tissue force and the spring-like bending element to determine the behavior of the needle with the bending tip and its trajectory through the tissue requires kinematic and mechanical modeling, as described in Chapter 2 [60]. Similarly, the modeling of the miniature shear joint in Chapter 3 takes into account the geometry of the wrist and subsequent kinematic motion, as well as the forces required to actuate the wrist in order to inform a design appropriate for the task in words [58].
Systems
Chapter Overview
Introduction
Using a kinked bevel tip needle with duty cycling delivers high curvature capability with real-time curvature adjustment. The bend allows the needle to behave like a kinked bevel tip needle when inserted, while simultaneously behaving like a traditional bevel tip needle when rotated axially.
Flexure-Tip Needle Design
The nitinol wires that make up the bend joint bend at the gap between the needle shaft and the tip when tissue forces are applied to the bevel tip. a) A CAD drawing of the needle concept with inflection point with the dimensions shown. The in-plane stiffness of the bending joint (i.e. movement of the tip in the XZ plane.
Needle Characterization
Curvature Comparison to Kinked Bevel-Tip Needle
The out-of-plane stiffness was determined to be 16.5 mNm/rad using the same experimental procedure.
Feasibility of Duty-Cycling to Adjust Curvature
Tissue Damage
Modeling the Flexure-Tip Needle
The bend tip's angular velocity ω is approximated as linearly related to the total torque applied to the bend by zero tissue friction in the tip direction zt and coefficient of friction b in every other direction. The torque τt makes the kinematics of the inflection point very similar to a trailer pushed in reverse (Fig. 2.7).
Experiments
Kinematic Model Calibration
The bending tip model parameters were calibrated by selecting the parameters that minimized the error between a set of actual needle trajectories (with known input insertion and rotation rates) and the corresponding trajectories predicted by the bending tip model. The calibration results are shown in Table 2.1, and the accuracy of the bending tip model with the calibrated parameters is analyzed in the next section.
Experimental Results
2.9(b) also shows the average path (and volume with one standard deviation) that would be followed if we modeled a needle with a bending tip. This behavior is also predicted by the bending tip model, as shown in Fig.
Discussion
The question of when to use the flex tip needle pattern with these motion planners is an interesting one. Regardless of the design of the bent-tip needle used, there are clinical questions that need to be investigated for the bent-tip needle as well.
Chapter Overview
Introduction
A curette is attached to the end of the wrist and is attached to a wire that runs the length of the tube, allowing the curette to rotate. A laser fiber is deployed through the wrist, illustrating the use of the wrist to aim a laser.
Design Concept
In addition, the drive of the asymmetric design requires only one tendon, which simplifies the tendon routing compared to symmetrical designs and improves the scalability of the design. Finally, the shifting neutral flexion plane of the asymmetric design results in a narrower radius of curvature around the midline of the wrist.
Kinematic Model
For our wrist, the neutral bending plane, ¯y, intersects the centroids of the axial sections of the cut pipe sections (see section A-A in Figure 3.4). The location of the neutral flexion plane, ¯y, in the wrist cutout largely determines the mapping of actuator space to wrist configuration space.
Statics Model
Due to friction, the force the tendon exerts on the tip of the wrist will be less than the force exerted on the tendon. To model this effect, we first find the angle γ (shown in Figure 3.3) required for the cable to navigate a single corner of a cut section at a given deflection angle.
Wrist Fabrication and Testing
Tendon Attachment Methods
Actuation of the wrist is performed with a single tendon, and we investigated various tendon attachment methods to keep the tendon tightly attached to the tip of the wrist. The method used for the work presented here was to attach the tendon to an end cap located at the end of the wrist (see Fig. 3.9).
Model Validation
A friction coefficient of 0.2 was chosen to account for the friction losses experienced by the tendon when passing the sharp corners of the cutouts. Note that the superelastic, nonlinear behavior of the material is clearly captured by the model.
Fatigue Test
Scalability and Tip-First Bending
Scalability of Wrist
For this photo, the tendon was attached to the end of the wrist as the end caps made for the 1.16mm wrist prototype were much larger than the 0.46mm tube. We tested the pulse experimentally using the same procedure as described in Section 3.6.2 and compared the motion of the pulse and the force required to activate it with the models of (3.6) and (3.17).
Tip-First Bending of the Wrist
Close inspection of the wrist at high articulation shows that the small recesses do not close completely, preventing the wrist from reaching the full articulation predicted by the model. To obtain point-first bending, we first select the number of cutouts n and cut height of the cutout to specify the bend radius of the wrist.
Discussion
We then choose the cutting depth of the furthest cut at begd =ro+ri, which corresponds to the lowest allowable actuation force and material strain. Despite the simplicity of the design, there remains a large design space to change the performance of the wrist.
Chapter Overview
Introduction
In the lungs, work has been done to plan obstacle-free paths through the bronchi using only concentric tube robots [136]. This is the first system to use concentric tube robots to deploy steerable bevel-tip needles, two ideas that have previously been extensively studied separately.
System Overview and Workflow
The actuation unit controls the concentric tube robot and the steering needle (see [14] for details on a similar actuation unit), and the piercing mechanism provides access to the lung parenchyma from the bronchial tree. The concentric tube robot is advanced over the lancing needle and through the bronchial wall, and then the lancing needle is removed.
Concentric Tube Robot Subsystem
- Deploying from the Bronchoscope to the Bronchial Wall
- Piercing the Bronchial Wall
- Aiming the Steerable Needle
- Non-annular Concentric Tubes
The lancing needle is then removed and the concentric tube robot can now place the steerable needle on the target. The concentric tube robot (and potentially the tendon-activated bronchoscope if additional dexterity is required) now directs the initial position of the steerable needle passing through the inner concentric tube towards the target (step 4 in Section 4.3).
Steerable Needle Subsystem
Magnetic tracking sensors to the controller provide closed-loop feedback on the position of the needle tip. In [142], the controller was tested with a traditional bevel-tip needle, so a new contribution of the experiments in this chapter is to verify that the controller also works when designing a tissue-sparing needle with high curvature and a flexible tip.
Experiments
- System Feasibility & Accuracy Experiments
- Bronchial Wall Piercing of ex vivo Porcine Tissue
- Needle Deflection in ex vivo Porcine Tissue
- Anatomical Case Studies
A suspicious nodule was located in the periphery of the lung, away from the bronchial tree. The bronchial anatomy was segmented and a phantom model was constructed based on the anatomy. d) The segmented model is superimposed on the phantom model, and in three trials the node is targeted with an average error of 2.02 mm.
Discussion
Another smaller challenge that we overcame in this study is that the concentric tube robot and steerable needle can stiffen the tip of the bronchoscope. Furthermore, under ideal conditions it may be possible to use the bronchoscope and the concentric tube robot to achieve the target.
Chapter Overview
The results presented in this chapter have been published in the Journal of Neurological Surgery [148, 62] and IEEE Transactions on Mechatronics [107].
Introduction
However, using the da Vinci to access the skull base through the mouth violates the "keyhole" principle in surgery (ie, that the smallest and least invasive access channel that allows adequate access should be used), because the nose is the most are. direct and least invasive natural opening through which skull base access is possible. Concentric tube robots are needle-sized manipulators consisting of a series of nested, pre-bent tubes that translate and rotate within each other to create tentacle-like motion of the manipulator [181, 182].
Medical Motivation and System Concept
The robotic system can also be integrated into existing image guidance systems often used in neurosurgical procedures to assist the surgeon with localization and navigation [107]. By moving the surgeon to a seated console, his or her ergonomics can be drastically improved and fatigue can be reduced.
System Design
Workspace Characterization and Tube Design Considerations
By changing the tubes during a procedure, one can change the workspace and performance of the system intraoperatively. The actuation units must provide good performance to the surgeon (eg, responsive manipulation of the tubes) while being flexible.
Actuation Unit Design
Each single-tube stage controls one tube in two degrees of freedom (axial translation and axial rotation). Each brass casing was attached to an aluminum pulley on one side and threaded on the other side to secure it to the single-tube staircase.
End Effector Design
Thus, we attached a miniature chip-tip camera (Awaiba NanEye, Germany) to the end of the concentric tube robot to provide visualization of the system (see Fig. We use a miniature biopsy gripper located at the end of the concentric tube robot for retraction.
System Experiments
- Pick and Place Task
- Phantom Tumor Removal
- Wrist Integration with Endonasal System
- Cadaver Workspace Study
An endoscope view of the wrist bending down to deliver the phantom tumor to the suction device is shown in Fig. The endoscope and the two robotic arms are shown as they approach the anterior wall of the pituitary gland.
System Calibration of Concentric Tube Robots using Collisions
- Introduction & Related Work
- Kinematic Calibration
- Calibration of Two Concentric Tube Robots Using Collisions
- Scaling of Parameters
- Simulation Results
The parameters we seek to estimate [Tx,Ty,Tz,θx,θy,θz,k1r1,k2r1,k1r2,k2r2]in our simulation are shown here, as are the available output measurements[s1,s2]for the system. The standard error between the tips of the actual and recalibrated robots is 0.6 mm for robot 1 and 1.1 mm for robot 2.
Discussion
The standard error between the points of the actual and pre-calibrated robots is 2.2 mm for robot 1 and 17.9 mm for robot 2. b). The standard error between the points of the actual and post-calibrated robots is 0.38 mm for robot 1 and 0.87 mm for robot 2.
Future Work in Design and Modeling of Dexterous Mechanisms
A model describing the behavior of the inflection point needle and its trajectory through tissue (Chapter 2, [60]). A possible approach to modeling the material deformation of the wrist is to use finite element modeling.
Future Work in Systems to Treat Lung and Brain Cancer
The next version of the robot drive unit should be reduced in size so that it can be easily operated by the doctor in the operating room. These aspects will have to be integrated with the next version of the actuation unit.
Conclusion
Smooth the end of the nitinol tubing used to create the bend tip needle. Also place JB-Kwik at the end of the 3 aligned nitinol wires, and insert the aligned wires into the bevel.
