Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Tomorrow’s super robots may owe their mobility to a cockroach’s legs today

27.08.2002


The marriage of machine and biology requires adopting the pliability and strength from the legs of this despised insect



The cockroach is an insect despised for its ubiquitousness, among other reasons. Yet, it may hold a key to the next evolutionary step in the "life" of robots.
Background

For years, serious futurists could only imagine that robots, such as the television model, would always be stiff, clumsy, and prone to breakdown. This was before the advent of "Biomimetics," a research aimed at developing a new class of biologically inspired robots that exhibit much greater robustness in performance in unstructured environments than today’s robots.



This new class of robots will be substantially more compliant and stable than current robots, and will take advantage of new developments in materials, fabrication technologies, sensors and actuators. Materials found in nature differ significantly from those found in human-made devices. Nature appears to design for "bending without breaking" and employs tissues that are compliant and viscoelastic rather than stiff, homogeneous, and isotropic. In addition, local variations in biological materials, tailored to meet local variations in loading, are common. The nonlinear, compliant, and inhomogeneous materials found in even the simplest animals provide them with a sophistication and robustness that today’s robots cannot match. And it is hard to find an animal as simple as the cockroach.

Actually, the deathhead cockroach possesses legs with compliant muscles and skeletal components that increase dynamic stability and disturbance rejection. As the ability to analyze and fabricate mechanisms with compliant and functionally-graded materials improves, the opportunity exists to develop robots whose structures draw inspiration from simple animals such as insects and crustaceans. One fertile area for biomimetic design is the leg of walking or hopping robots, where leg compliance is especially important.

One method for manufacturing such robots is Shape Deposition Manufacturing (SDM), a rapid prototyping technology. SDM addresses many limitations of traditional manufacturing and assembly by enabling the in situ fabrication of mechanisms with complex geometry and heterogeneous materials. Design and fabrication of layered and heterogeneous materials (also called Functionally Graded Materials - FGMs) has recently been a focus of research. FGMs enable control of local variations of biomimetic components by selectively depositing soft and hard materials. To produce biologically inspired components of biomimetic/mechanical properties, a bridge between biological findings and SDM design specifications was required.

The first demand for SDM is to characterize biological structures and translate the characteristics into quantitative specifications for mobile robots. The second requirement is to model SDM material behavior to facilitate component design to meet these specifications. To address these requirements experiments were conducted on a hind leg of Blaberus discoidalis and described its response to both step displacement inputs and sinusoidal displacement excitations. Next, a test was carried out on one of the materials used in SDM, a soft polyurethane polymer largely used as joint material in manufacture, and fit the results to standard viscoelastic (pliable yet sturdy) materials and models. Comparison and understanding of the mapping between these two studies enable us to begin to design and manufacture legs similar to those found in biology.

The Study

The authors of "Material Modeling for Shape Deposition Manufacturing of Biomimetic Components," are Xiaorong Xu, Wendy Cheng, Mark R. Cutkosky and Motohide Hatanaka from Stanford University, and Daniel Dudek and Robert J. Full at the University of California at Berkley, Department of Integrative Biology, Berkeley, CA. The authors are presenting their work at "The Power of Comparative Physiology: Evolution, Integration and Application" meeting, sponsored by the American Physiological Society (APS) August 24-28, 2002 at the Town & Country Hotel, San Diego, CA. To learn more about the conference and presentations, go to: http://www.the-aps.org/meetings/aps/san_diego/home.htm

Methodology

Relaxation and dynamic experiments were carried out on the hind leg of Blaberus discoidalis to aid in the selection of a material behavior model and to quantify measures of roach leg response. During testing, the coxa of the ablated metathoracic limb (hind limb) of the cockroach was epoxied to 3/8" acrylic such that the coxa-femur and femur-tibia joints were free to rotate. Cyanoacrylate was used to attach one end of a stainless steel pin to the distal tip of the tibia; dental impression compound was used to adhere the other end of the pin to the arm of a servo-motor system. The leg was then displaced with the Aurora system, which is based upon a high performance rotary moving coil motor supported by precision ball bearings. The results are that the total error in the force-displacement measurements to be less than four percent that of a viscoelastic solid.

Results

The results indicate that a cockroach leg excited in a direction orthogonal to the joint direction behaves similarly to a viscoelastic material. The exponential nature of the force relaxation curves suggests viscoelasticity. The hysteretic nature of the force-displacement curves indicates that there is energy loss due to the internal friction, which is a common characteristic for viscoelastic materials. The cockroach leg is subject to a combination of bending and torsion in the experiment. The overall effect can be modeled as a torsion spring with a moment arm. Additional assumptions for the model include: (1) the axis of rotation for the leg is constant during torsion and (2) the joint material can be approximated using a lumped-parameter element with uniformly distributed linear viscoelastic properties.

The SDM process allowed an integration of a range of desired impedance into the structure of robot legs for improved robustness and simpler control. SDM-compatible materials span a wide range of material properties and the SDM process enables researchers to control local variations through Functionally Graded Materials (FGM). With information regarding the mechanical behavior of animal legs and the material characteristics of SDM materials, the researchers developed guidelines for biomimetic leg design.

Conclusions

Some polymer materials that can be used in SDM are similar to the biological materials found in insect legs that exhibit viscoelasticity. This inspires us to develop material models and design methodologies that can be used to guide biomimetic robot leg design and material selection. In this paper, we have discussed a simple linear, lumped parameter model used to characterize cockroach leg behavior in relaxation experiments and in response to sinusoidal excitations. We have also developed a dynamic test machine and begun characterizing a polyurethane material used for SDM fabrication of robot joints.

The current models of leg response assume linear viscoelasticity. The correlation between these models and the results of the experiments is relatively good at low frequencies and small displacements, but deteriorates at higher frequencies and displacements as nonlinear effects grow pronounced.

In addition, at very low frequencies, dynamic tests on cockroach legs indicate a higher loss modulus than that predicted by a standard linear model. Should these nonlinear aspects of leg behavior prove important for locomotion, the researchers believed that better models had to be developed better models to simulate the viscoelastic behavior of the leg in a wide frequency range.

Additionally, to produce legs with mechanical response similar to that of the real cockroach leg, enhanced characterization of additional SDM materials is required. Knowledge of SDM material behavior, along with information about the aspects of leg behavior important to locomotion, will enable the issuance of general design guidelines for designing biomimetic legs.

(It is worth noting that these legs have been used to produce a remarkable successful robot from Stanford named SPRAWL. SPRAWL can negotiate rough terrain without a brain or any reflexes because the control is built into the smart or tuned legs described above.)

Donna Krupa | EurekAlert!

More articles from Studies and Analyses:

nachricht A sudden drop in outdoor temperature increases the risk of respiratory infections
11.01.2017 | University of Gothenburg

nachricht Urbanization to convert 300,000 km2 of prime croplands
27.12.2016 | Mercator Research Institute on Global Commons and Climate Change (MCC) gGmbH

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

A big nano boost for solar cells

18.01.2017 | Power and Electrical Engineering

Glass's off-kilter harmonies

18.01.2017 | Materials Sciences

Toward a 'smart' patch that automatically delivers insulin when needed

18.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>