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Research Papers: Mechanisms and Robotics

# Microrobot Design Using Fiber Reinforced Composites

[+] Author and Article Information
R. J. Wood

School of Engineering & Appied Sciences, Harvard University, Cambridge, MA 02138rjwood@eecs.harvard.edu

S. Avadhanula, R. Sahai, E. Steltz

Department of Electrical Engineering & Computer Sciences, University of California, Berkeley, CA 94720

R. S. Fearing

Department of Electrical Engineering & Computer Sciences, University of California, Berkeley, CA 94720ronf@eecs.berkeley.edu

M60J from Toray Carbon Fibers America, Inc.

Either a frequency doubled Nd:YAG laser ($λ=532nm$, New Wave Research) or an UV excimer laser ($λ=193nm$, TeoSys Engineering).

RS-3C from YLA Inc.

Kapton from DuPont.

Stretchlon 800 from Airtech.

Kapton 30HN from DuPont, $h=7.6μm$.

This is exactly analogous to the assumptions made for fiber-reinforced composite materials in general.

PI2525 or PI2611 from HD Microsystems.

www.aerogel.com

J. Mech. Des 130(5), 052304 (Mar 26, 2008) (11 pages) doi:10.1115/1.2885509 History: Received January 28, 2007; Revised June 06, 2007; Published March 26, 2008

## Abstract

Mobile microrobots with characteristic dimensions on the order of $1cm$ are difficult to design using either microelectromechanical systems technology or precision machining. This is due to the challenges associated with constructing the high strength links and high-speed, low-loss joints with micron scale features required for such systems. Here, we present an entirely new framework for creating microrobots, which makes novel use of composite materials. This framework includes a new fabrication process termed smart composite microstructures (SCM) for integrating rigid links and large angle flexure joints through a laser micromachining and lamination process. We also present solutions to actuation and integrated wiring issues at this scale using SCM. Along with simple design rules that are customized for this process, our new complete microrobotic framework is a cheaper, quicker, and altogether superior method for creating microrobots that we hope will become the paradigm for robots at this scale.

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## Figures

Figure 1

Rotational flexure mechanism and associated process

Figure 2

Laser cut detail (a) and cut fiber cross section (b). The cut width is approximately 10μm, which is on the order of the fiber diameter. A folded flexure is shown in (c) along with a diagram of the flexure motion (d).

Figure 3

Flexure diagram with geometric definitions

Figure 4

No-buckling flexure (a) and cross flexures (b).

Figure 5

Example of a spherical five-bar structure (a) in which certain joints are bent to 90deg in the final assembly stage. The effect of this prestress is shown in (b). The solid line represents the stiffness of the differential with respect to α when θy0=90deg and the dotted line represents the stiffness with θy0=0deg.

Figure 6

Singular four-bars for FEA ((a) and (b)). The results from FEA show that when designing a flexure-based transmission system, it is advantageous to align the flexures with the expected loads. Using this simple design rule, a four-bar is shown in (c) in which the four axes (1–4) are aligned along the expected principal loading directions.

Figure 7

Example cut file with alignment features (a). Upon successful completion of this 2D laminate (b), these tabs are mated together to ensure proper joint alignment for the complete spherical five-bar differential (c). This differential is illustrated in (d) for use in a wing transmission mechanism.

Figure 8

Closed-chain four-bar schematic (a) and typical input-output characteristics and normalized inertia (b)

Figure 9

Local and global lamina orientation description (a) and laminate geometric description (b)

Figure 10

Components and assembly method to integrate wiring over the flexure joints (a). In (b), a complete ribbon cable is integrated with a four-bar mechanism (illustrated in (c)) and actuated through a large displacement (≈90deg) as a proof of concept.

Figure 11

Example 2DOF transmission system containing 15 joints (a). This is shown alongside a SCM instantiation (b).

Figure 12

Sarrus linkage used as a linear translational bearing

Figure 13

Composite bimorph PZT-based actuators to be used as clamped-free bending cantilevers

Figure 14

Example of a rigid microstructure: a microrobot exoskeleton (a). Here, a 20g mass is applied to a 20mg structure with no observable deformation. For a clearer illustration of a tensegrity structure, (b) shows a configuration of ten links and five joints: since 10>3×5−6, this structure is considered rigid. Also, (c) shows a honeycomb-core-based laminate for rigid microstructures.

Figure 15

Normalized stiffnesses as a function of the number of links applied to an example tensegrity structure. Note that in this case, the stiffness dramatically increases at 34 links. kz, klat, and kx are the normalized stiffnesses in the z (top-to-bottom), lateral (side-to-side), and x (front-to-back) directions of the structure in Fig. 1, respectively.

Figure 16

Example results of incorporating strain sensors to measure contact forces in a microrobotic leg structure

Figure 17

Example microrobotic structure: (a) the MFI and (b) a sample wing motion (wing beat frequency is 200Hz)

Figure 18

Example microrobotic structure: crawling robotic insect (a) and sample leg motion (composite from a video sequence) (b)

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