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Research Papers

Design and Kinematic Optimization of a Two Degrees-of-Freedom Planar Remote Center of Motion Mechanism for Minimally Invasive Surgery Manipulators

[+] Author and Article Information
Sajid Nisar

Mechatronics Laboratory,
Mechanical Engineering and Science,
Kyoto University,
Kyoto 615-8540, Japan
e-mail: nisar.sajid.78v@kyoto-u.jp

Takahiro Endo

Department of Mechanical Engineering
and Science,
Kyoto University,
Kyoto 615-8540, Japan
e-mail: endo@me.kyoto-u.ac.jp

Fumitoshi Matsuno

Department of Mechanical Engineering
and Science,
Kyoto University,
Kyoto 615-8540, Japan
e-mail: matsuno@me.kyoto-u.ac.jp

1Corresponding author.

Manuscript received July 31, 2016; final manuscript received January 16, 2017; published online March 23, 2017. Assoc. Editor: Byung-Ju Yi.

J. Mechanisms Robotics 9(3), 031013 (Mar 23, 2017) (9 pages) Paper No: JMR-16-1222; doi: 10.1115/1.4035991 History: Received July 31, 2016; Revised January 16, 2017

Minimally invasive surgery (MIS) requires four degrees-of-freedom (DOFs) (pitch, translation, yaw, and roll) at the incision point, but the widely used planar remote center of motion (RCM) mechanisms only provide one degree-of-freedom. The remaining three DOFs are achieved through external means (such as cable-pulleys or actuators mounted directly on the distal-end) which adversely affect the performance and design complexity of a surgical manipulator. This paper presents a new RCM mechanism which provides the two most important DOFs (pitch and translation) by virtue of its mechanical design. Kinematics of the new mechanism is developed and its singularities are analyzed. To achieve maximum performance in the desired workspace region, an optimal configuration is also evaluated. The design is optimized to yield maximum manipulability and tool translation with smallest size of the mechanism. Unlike the traditional planar RCM mechanisms, the proposed design does not rely on external means to achieve translation DOF, and therefore, offers potential advantages. The mechanism can be a suitable choice for surgical applications demanding a compact distal-end or requiring multiple manipulators to operate in close proximity.

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Figures

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Fig. 1

A double-parallelogram RCM mechanism

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Fig. 2

Required workspace for minimally invasive surgery

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Fig. 3

Trivial forms of the proposed two DOF RCM mechanism

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Fig. 4

The proposed two DOF RCM mechanism

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Fig. 5

A simplified representation of the proposed RCM mechanism

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Fig. 6

The alignment mechanism to maintain the remote center of motion constraint. A3 is a passive prismatic joint.

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Fig. 7

Mechanism workspace (light gray) and the required workspace for MIS (dark gray)

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Fig. 8

Variant forms of the proposed RCM mechanism: (a) offers larger translation DOF with reduced length of l4, (b) inverted alignment mechanism can generate even larger translation with further reduced length of l4

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Fig. 9

Average manipulability over the range of α (α=l2/l3,α > 0)

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Fig. 10

Corresponding mechanism forms for cases of α (α=l2/l3): (a) α < 1, (b) α = 1, and (c) α > 1

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Fig. 11

Effective translation in the simplified representation of the proposed mechanism

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Fig. 12

Rear-parallelogram configurations for cases α = 1, α < 1 and α >1 when θ=π/2. Distance OD represents rmin. Only case (a), (b), and (e) can generate the desired workspace (π/4≤θ≤3π/4) as they satisfy the constraint (22) and (23). As (c) and (d) do not satisfy Eqs. (22) and (23), they are excluded from re optimization.

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Fig. 13

Effective translation over the range of α (α=l2/l3, α >0)

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Fig. 14

Combined performance score over the range of α (α=l2/l3,α > 0)

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