Article

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

ABSTRACT

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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    • "For more complicated tasks such as retraction or grasping, the manipulator also needs to be able to modulate its stiffness and thus actively exert a force when necessary; for example, for lifting and supporting an organ. The need for stiffness control in robots presenting a continuum or soft structure has been addressed in[22], where a stiffness controller based on the kinematics of robots is presented. A step further is proposed in[23], where the issue of monitoring the contact with a compliant environment is addressed. "
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    • "To achieve the best aspects of rigid and compliant structures in a single robot, actuation strategies for effectively modulating manipulator stiffness have been the subject of several recent research efforts. Active model-based impedance control using sensor measurements of actuator force and robot deflection has also been shown to address the compliance/strength tradeoff from a higher level control framework [99], [100], but flexibility may still limit the maximum force the robot can apply. "
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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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