Stiffness Control of Surgical Continuum Manipulators

Med. Sch., Cardiac Surg. Dept., Harvard Univ., West Roxbury, MA, USA
IEEE Transactions on Robotics (Impact Factor: 2.43). 04/2011; 27(2):334-345. DOI: 10.1109/TRO.2011.2105410
Source: DBLP


This paper introduces the first stiffness controller for continuum robots. The control law is based on an accurate approx- imation of a continuum robot's coupled kinematic and static force model. To implement a desired tip stiffness, the controller drives the actuators to positions corresponding to a deflected robot con- figuration that produces the required tip force for the measured tip position. This approach provides several important advantages. First, it enables the use of robot deflection sensing as a means to both sense and control tip forces. Second, it enables stiffness con- trol to be implemented by modification of existing continuum robot position controllers. The proposed controller is demonstrated ex- perimentally in the context of a concentric tube robot. Results show that the stiffness controller achieves the desired stiffness in steady state, provides good dynamic performance, and exhibits stability during contact transitions.

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Available from: Pierre E Dupont, Jul 06, 2015
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    • "While position control of such flexible robots has been well covered in the current state-of-the-art, the attention to force control has been scarce. Examples of force control for continuum robots include the stiffness control presented in [15] and force control for single DoF(degrees of freedom) catheter [13]. The aforementioned approaches have limited flexibility with respect to the capability of describing task objectives in terms of constraints to be enforced on pose and force of the tool (and other robot links) such as no-go zones, entry-point or trocar constraints, force references and limits, etc, that often arise in surgical scenarios. "
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    ABSTRACT: This paper introduces a framework for constraint-based force/position control of robots that exhibit large nonlinear structural compliance and that undergo large deformations. Controller synthesis follows hereto the principles of the Task Frame and instantaneous Task Specification using Constraints (iTaSC) formalisms. iTaSC is found particularly suitable due to its ability to express and combine control tasks in a natural way. Control tasks can be formulated as combinations of target positions, velocities, or forces expressed in an arbitrary number and type of coordinate frames. The proposed framework is applied to a mixed mechatronic system composed of a traditional rigid-link robot whose end-effector is a continuum (flexible) link. A selection of different position/force control tasks is prepared to demonstrate the validity and general nature of the proposed framework.
    IEEE Transactions on Robotics 10/2015; 31(5):1252-1260. DOI:10.1109/TRO.2015.2475975 · 2.43 Impact Factor
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    • "Task-space closed-loop controllers for discrete manipula- tors 1 [12] often use a kinematic model of the robot Jacobian that maps actuator velocities to the end-effector velocity [11]. For continuum manipulators, models have been developed for specific architectures that use tendons [10], [13], [14]; precurved concentric tubes [6], [8], [15]–[23]; pneumatics channels [24], [25]; shape-memory-alloy actuators [26]–[29]; and multibackbone actuators [30]–[33]. However, these models do not account for unknown disturbances from the environment. "
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    ABSTRACT: Continuum manipulators offer a means for robot ma-nipulation in a constrained environment, where the manipulator body can safely interact with, comply with, and navigate around obstacles. However, obstacle interactions impose constraints that conform the robot body into arbitrary shapes regardless of ac-tuator positions. Generally, these effects cannot be wholly sensed on a continuum manipulator and, therefore, render model-based controllers incorrect, leading to artificial singularities and unstable behavior. We present a task-space closed-loop controller for contin-uum manipulators that does not rely on a model and can be used in constrained environments. Using an optimal control strategy on a tendon-driven robot, we demonstrate this method, which we term model-less control, which allows the manipulator to interact with several constrained environments in a stable manner. To the best of our knowledge, this is the first work in controlling continuum manipulators without using a model.
    IEEE Transactions on Robotics 08/2014; 30(4):880-888. DOI:10.1109/TRO.2014.2309194 · 2.43 Impact Factor
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    • "Recently, the theory of Cosserat rod has been used to model backbones in large deflections.[21] [22] [23] [24] This theory is used to modelone-dimensional flexible objects, such as rope, wire, cable, and slender rods.[25] Although this model is accurate, it has been used not often, because of its massive numerical calculations. "
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    ABSTRACT: This paper presents a compact modeling approach of continuum robotic arms, with limited computations for faster numerical calculations in real-time implementations. It is assumed that the arm includes a backbone made of elastic rods, and the Cosserat rod theory is simplified for numerically faster modeling. The time-taking boundary-value problem (BVP) is detailed, and some numerical methods are introduced to solve the developed equations of modeling. Next, based on physical intuition, a fast and stable method is proposed to solve the BVP, as a moment-based approach. Also, a method to cancel some numerical integration errors with the least required computations and numerical efforts is presented. Next, a Jacobian-based control of multi-segment continuum robotic arms is developed. Finally, this procedure is experimentally verified to show the precision of proposed modeling approach and also to reveal the importance of faster solutions for real-time control.
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