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 New study: How does Europe become a leading player for software and IT services?
03.04.2017 | Fraunhofer-Institut für System- und Innovationsforschung (ISI)

nachricht Reusable carbon nanotubes could be the water filter of the future, says RIT study
30.03.2017 | Rochester Institute of Technology

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: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Bare bones: Making bones transparent

27.04.2017 | Life Sciences

Study offers new theoretical approach to describing non-equilibrium phase transitions

27.04.2017 | Physics and Astronomy

From volcano's slope, NASA instrument looks sky high and to the future

27.04.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>