Research Papers

Kinematic Analysis and Optimization of a Novel Robot for Surgical Tool Manipulation

[+] Author and Article Information
Xiaoli Zhang

Department of Mechanical Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588xzhang@bigred.unl.edu

Carl A. Nelson1

Department of Mechanical Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588; Department of Surgery, University of Nebraska Medical Center, Omaha, NE 68198; UNMC Center for Advanced Surgical Technology, Omaha, NE 68198cnelson5@unl.edu


Corresponding author.

J. Med. Devices 2(2), 021003 (May 14, 2008) (8 pages) doi:10.1115/1.2918740 History: Received November 02, 2007; Revised March 17, 2008; Published May 14, 2008

The size and limited dexterity of current surgical robotic systems are factors that limit their usefulness. To improve the level of assimilation of surgical robots in minimally invasive surgery (MIS), a compact, lightweight surgical robotic positioning mechanism with four degrees of freedom (DOFs) (three rotational DOFs and one translation DOF) is proposed in this paper. This spatial mechanism based on a bevel-gear wrist is remotely driven with three rotation axes intersecting at a remote rotation center (the MIS entry port). Forward and inverse kinematics are derived, and these are used for optimizing the mechanism structure given workspace requirements. By evaluating different spherical geared configurations with various link angles and pitch angles, an optimal design is achieved, which performs surgical tool positioning throughout the desired kinematic workspace while occupying a small space bounded by a hemisphere of radius 13.7cm. This optimized workspace conservatively accounts for collision avoidance between the patient and robot or internally between the robot links. This resultant mechanism is highly compact and yet has the dexterity to cover the extended workspace typically required in telesurgery. It can also be used for tool tracking and skills assessment. Due to the linear nature of the gearing relationships, it may also be well suited for implementing force feedback for telesurgery.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

CAD model of the robot manipulating a typical handheld surgical tool

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Figure 2

Functional schematic of the robot mechanism

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Figure 3

The equivalent open-loop chain of the wrist mechanism

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Figure 4

The inverse kinematics (mapping sequence) of the wrist mechanism

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Figure 5

The theoretical workspace of the mechanism with different link angles (α=30deg, 45deg, 60deg, 90deg). The black point is the center of the spherical mechanism (the MIS entry point).

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Figure 6

The coordinate systems of Frames 1 and 4 (end effector orientation)

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Figure 7

Workspace plot for α2=α3=40deg. This workspace plot shows the reachable workspace with the center angle of 65deg in gray, and the DWS with the cone vertex angle of 60deg in black.

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Figure 8

Workspace plot for α2=α3=40deg with the motion range of θ21 being 115deg. This workspace plot still contains the reachable workspace with the center angle of 65deg in gray and with the DWS in black included in it.



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