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Design Innovation Paper

Design of a Novel Statically Balanced Mechanism for Laparoscope Holders With Decoupled Positioning and Orientating Manipulation

[+] Author and Article Information
Chin-Hsing Kuo

Assistant Professor
Department of Mechanical Engineering,
National Taiwan University of Science and Technology,
43, Sec. 4, Keelung Road,
Taipei 106, Taiwan
e-mail: chkuo717@mail.ntust.edu.tw

Shao-Jung Lai

Department of Mechanical Engineering,
National Taiwan University of Science and Technology,
43, Sec. 4, Keelung Road,
Taipei 106, Taiwan

1Corresponding author.

Contributed by the Design Engineering Division of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. Manuscript received February 18, 2014; final manuscript received January 20, 2015; published online August 18, 2015. Assoc. Editor: Robert J. Wood.

J. Mechanisms Robotics 8(1), 015001 (Aug 18, 2015) (10 pages) Paper No: JMR-14-1035; doi: 10.1115/1.4029789 History: Received February 18, 2014

This paper presents a novel mechanism concept of laparoscope holders used for minimally invasive surgery (MIS). The mechanism is made of a parallelogram linkage and a parallel mechanism, which, respectively, serve as a robotic positioning arm and an orientating wrist of the holder. Due to its special geometry, the mechanism possesses several interesting kinematic properties. First, the laparoscope, which is held by the end-effector, can illustrate a remote center-of-motion (RCM) kinematics at the surgical incision point. Second, the position of the RCM point is solely defined by the parallelogram, whereas the orientation and insertion length of the laparoscope are governed by the parallel mechanism. Such an arrangement suggests a decoupled positioning and orientating manipulation for the holder, which is clinically helpful in laparoscopic MIS. Third, the overall mechanism including the parallelogram linkage and the parallel mechanism can be statically balanced at any configuration within the workspaces by using common linear springs. In other words, no electrical actuation or mechanical locks are required for making the laparoscope rest at any position and orientation. The design procedure for static balancing is detailed in the paper, and the theoretical formulation of the statically balanced mechanism is verified by a numerical example and computer simulation. The computer-aided design (CAD) model of the holder is constructed for evaluating its workspace and a physical prototype using commercial springs is built up and tested. It shows that the prototype that uses nonideal (commercial) springs can be statically balanced within the overall workspace, since the shortage/overshoot of the potential energy in the positioning mechanism and orientating mechanism, which are theoretically 6.8% and 5.1% of their total potential energies in maximum, are fully compensated by the friction effect.

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Figures

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Fig. 1

A new mechanism concept for laparoscope holders

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Fig. 2

Kinematic drawing of the positioning mechanism

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Fig. 3

Kinematic drawing of the orientating mechanism

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Fig. 4

Laparoscope motion: (a) pan-and-tilt angles and (b) insertion length

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Fig. 5

The two loops in the positioning mechanism

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Fig. 6

Position vectors in loop-2 mechanism

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Fig. 7

Position vectors in loop-1 mechanism

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Fig. 8

The link masses of the orientating mechanism

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Fig. 9

Coordinate systems in the orientating mechanism

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Fig. 10

Position vectors of the joints and mass centers in the orientating mechanism

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Fig. 11

Installation of the springs in a five-bar of the orientating mechanism

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Fig. 12

Implementation of the zero-free-length springs

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Fig. 13

Potential energies in the statically balanced positioning mechanism (a) loop-1 mechanism and (b) loop-2 mechanism

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Fig. 14

Potential energies in the statically balanced orientating mechanism (a) θ12 varies, (b) θ13 varies, (c) θ22 varies, and (d) θ23 varies

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Fig. 15

CAD model: positioning mechanism

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Fig. 16

CAD model: orientating mechanism

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Fig. 17

Pan-and-tilt angle of the laparoscope. (a) Pan angle and (b) tilt angle.

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Fig. 18

Prototype of the novel laparoscope holder

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Fig. 19

Static balancing test of the positioning mechanism

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Fig. 20

Static balancing test of the orientating mechanism

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