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Technical Brief

# Inverted L-Arm Gripper Compliant Mechanism

[+] Author and Article Information
Jason Dearden

Compliant Mechanisms Research Group,
Department of Mechanical Engineering,
Brigham Young University,
Provo, UT 84602

Clayton Grames

New Product Development,
Intuitive Surgical, Inc.,
Sunnyvale, CA 94086

Brian D. Jensen, Spencer P. Magleby

Department of Mechanical Engineering,
Brigham Young University,
Provo, UT 84602

Larry L. Howell

Department of Mechanical Engineering,
Brigham Young University,
Provo, UT 84602
e-mail: lhowell@byu.edu

1Corresponding author.

Manuscript received July 25, 2016; final manuscript received March 5, 2017; published online June 27, 2017. Assoc. Editor: Carl Nelson.

J. Med. Devices 11(3), 034502 (Jun 27, 2017) (6 pages) Paper No: MED-16-1278; doi: 10.1115/1.4036336 History: Received July 25, 2016; Revised March 05, 2017

## Abstract

This work exploits the advantages of compliant mechanisms (devices that achieve their motion through the deflection of flexible members) to enable the creation of small instruments for minimally invasive surgery (MIS). Using flexures to achieve motion presents challenges, three of which are considered in this work. First, compliant mechanisms generally perform inadequately in compression. Second, for a $±90deg$ range of motion desired for each jaw, the bending stresses in the flexures are prohibitive considering materials used in current instruments. Third, for cables attached at fixed points on the mechanism, the mechanical advantage will vary considerably during actuation. Research results are presented that address these challenges using compliant mechanism principles as demonstrated in a two-degree-of-freedom (2DoF) L-Arm gripper.

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## Figures

Fig. 1

(a) L-Arm and (b) inverted L-Arm polypropylene prototypes

Fig. 2

Inverted L-Arm with NiTi wire flexures. While both identical jaws are shown, only one has been labeled.

Fig. 3

A single jaw of the L-Arm compliant mechanism is viewed from the side. R is the moment arm length (radius of the pulley), CoR is the approximate center of rotation, and FIN1 and FIN2 are input forces provided by cables.

Fig. 4

Model used in the mechanical advantage analysis of the L-Arm gripper mechanism without a pulley. Note that FOUT is modeled as a follower force while FIN is modeled as a vertical force. The location at which FIN is applied changes relative to the approximate center of rotation as the mechanism is actuated.

Fig. 5

Model used in the mechanical advantage analysis of the L-Arm gripper mechanism with a pulley integrated into the jaw. Note that FOUT is modeled as a follower force while FIN is modeled as a vertical force. The location at which FIN is applied does not change relative to the approximate center of rotation as the mechanism is actuated.

Fig. 6

Mechanical advantage plotted against angular deflection (in deg) for a 3-mm L-Arm using the values listed in Table 1

Fig. 7

Thirty eight millimeter proof-of-concept prototype of the inverted L-Arm with NiTi wire flexures

Fig. 8

Thirty eight millimeter L-Arm prototype showing independent actuation of each jaw as well as the gripping function of the mechanism

Fig. 9

Six millimeter L-Arm model: (a) shows a section view with the jaw, the thin NiTi flexure, and the fixed portion concentric to the jaw and (b) is a model of the assembled mechanism

Fig. 10

Six millimeter L-Arm SLA prototype with NiTi flexures: (a) shows the nominal state and (b) shows one jaw in a deflected state. U.S. penny for scale.

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