Proceedings of 3rd CDEN/RCCI International Design ConferenceToronto, Canada, July 24-26, 2006

Using Biological Analogies for Engineering Problem Solving and Design

L.H. Shu, Associate ProfessorDept. of Mechanical & Industrial Engineering, University of Toronto

shu@mie.utoronto.ca

Abstract

This paper summarizes various aspects of identifying and using biological analogies in engineering design. Toavoid the immense as well as potentially biased task of creating a database specifically for this purpose, the chosenapproach searches biological knowledge in natural language format, e.g., books, papers, etc., for instances offunctional keywords describing the engineering problem. Strategies developed to facilitate this search as well howtext descriptions of biological phenomena were used in problem solving are summarized. Case studies in design forremanufacture and microassembly are used to provide an overview of the method.

1. Introduction

Many elegant solutions to engineering problemshave been inspired by biological phenomena. Whilemost work in biomimetic design involve specific casesof design that copy particular biological models, notalways described is how these biological models wereidentified or selected. Therefore, it is possible that anengineer open to using biological models for designmay not know how to find relevant biologicalanalogies for a given design.

This paper will summarize our past and ongoingwork in developing an approach to identify and userelevant biological analogies for any givenengineering problem. First highlighted are ongoingchallenges in natural language processing andanalogical reasoning, and the work towardsovercoming these challenges. Analogies identifiedusing this approach for case studies in design forremanufacture and microassembly are then describedto illustrate the process.

2. Method

The purpose of this work is to develop a generalizedmethodology by which analogous biologicalphenomena can be identified and used for anyengineering design problem in an objective andrepeatable manner. One possible approach to enablegeneralized biomimetic design is to build a database ofbiological phenomena for engineering use (Vincent

and Mann, 2002). The approach described here avoidsthe immense and likely subjective task of cataloguingbiological phenomena for engineering. Instead, thismethod takes advantage of the abundant biologicalinformation already available in natural languageformat by searching it directly for relevantphenomena.

This approach has been implemented in the form ofa computerized search tool that locates in biologytexts, instances of functional keywords describing theengineering design problem.

a. Source of biological informationThe initial source of information selected is Life, the

Science of Biology (Purves et al., 2001), which is thereference text for the introductory course in biology atthe University of Toronto. This text is suitablebecause it is written at a level that can be easilyunderstood by those with little background in biology.Also, the text covers a large range of organizationallevels, from the molecular and cellular, e.g., DNA, tothe ecosystem, such that potential solutions are notlimited to a particular organizational level.

Other texts can be substituted or added as requiredfor the initial search. The more challenging task is theinitial identification of relevant phenomena. Furtherdetails on such phenomena can be easily found usingmore advanced texts and research papers.

b. Keywords used for searchKeywords used to search for relevant text segments

are verbs that describe the desired effect of possiblesolutions. Verbs are strongly preferred over nouns askeywords to initiate searches. Searching for nounstypically leads to pre-conceived solutions whilesearching for verbs that describe the desired action ismore likely to identify biological forms that may nothave occurred to the designer.

Synonyms have been used in the past to increase thenumber of matches. More recent work has found that‘troponyms’ produce superior alternative keywords.Troponyms are verbs that describe specific manners ofanother verb. For example, ‘ambling’ is a troponymof ‘walking’ because it is a particular manner ofwalking (Chiu and Shu, 2004).

3. Natural language processing

Despite the advantages, there are challengesinvolved with using natural-language knowledgesources to identify biological analogies. A primarydifficulty involves the quantity and quality of matches.

Even with a single text used as the source, there canbe an unmanageable number of matches to thekeywords, including synonyms, troponyms, etc.Identifying words that frequently collocate withsought keywords can be used to summarize dominantbiological phenomena associated with keywords. Forexample, high frequency words were “predator”,“prey” and “species” for the keyword “eliminate”,thus describing how interactions between prey andpredator species lead to one another’s elimination(Chiu & Shu, 2004).

Another challenge arises because engineers andbiologists use different lexicons or terminology todescribe related phenomena. For example, searchingfor the keyword “clean” for a problem involvingcleaning did not locate many useful matches.Therefore, a domain expert was asked for alternativekeywords. The keyword, “defend” was suggestedsince some organisms clean as a defensivemechanism. However, “defend” is related to “clean”neither intuitively, for most engineers, nor lexically,e.g., as synonym. Therefore, work was performedtowards developing a bridging mechanism thatidentifies such non-obvious, but highly relevant,biologically connotative keywords in an objective andrepeatable manner that does not require domainexperts (Chiu and Shu, 2005). The method was usedto find “defend” as well as many other biologically

connotative keywords for the “clean” example. Thisbridging method also identified the followingbiologically connotative keywords: “survive” for anexample involving encapsulation, and “break” or“breakdown” for releasing microobjects.

4. Analogical reasoning

Another challenge in using biological analogies fordesign involves the human process of extractingrelevant strategies from the biological phenomena andapplying these strategies to design problems.

Observations of people performing these processesrevealed four types of similarities between thebiological phenomena presented and the conceptsdeveloped using them as stimuli. These four similaritytypes are literal implementation, biological transfer,analogy and anomaly, and are detailed by Mak andShu (2004a).

Some anomalous concepts result frommisunderstanding of the biological phenomenon.Others result from fixating on certain words in thedescription that are not representative of the overallstrategy (Mak and Shu, 2004b). Continuing workseeks to reduce this and other types of fixation thatwere observed in people attempting to developanalogous concepts from descriptions of biologicalphenomena.

5. Examples

Several analogies for case studies in design forremanufacture (Vakili and Shu, 2001, Hacco and Shu,2002) and microassembly (Shu et al., 2003, 2006)were located at various levels of biologicalorganization by searching for keywords and synonymsrelated to the engineering problem. These case studieswill be briefly described below.

a. Design for remanufactureRemanufacture is a process applied to products at

their end of life that seeks to reuse productcomponents. Advantages over recycling for scrapmaterial include conservation of resources required tomelt and reform components. One design guidelineidentified to facilitate remanufacture is that productfeatures that are prone to failure should be madeseparable (Shu and Flowers, 1999). In this way, thefailed features can be replaced, enabling the reuse of acomponent without labor- and capital-intensive repairoperations. However, making failure-prone partsseparate increases part count and assembly cost.

Biological analogies were sought to address thisapparent contradiction between ease of assembly andease of remanufacture.

Searching for the keyword ‘remanufacture’, notsurprisingly, resulted in no matches in the biologytext. In this case, alternative keywords such assynonyms are required to find any matches. Otherkeywords used include ‘repair’ and ‘correct.’

Matches identified using ‘repair’ involve DNArepair mechanisms, including DNA proofreadingduring replication, mismatch repair and excisionrepair. Excision repair was found to be the mostanalogous to repairs performed during remanufacture.

While the description of excision repair by Purveset al. (2001) confirms relevance of the phenomenon toremanufacture, further research using a more advancedtext, Friedberg et al. (1995), was required to determinedetails that could be used as stimuli for design.

i. Extracting strategy from biological analogy

The search for the word ‘repair’ also led to a matchin Purves et al. (2001) that provides an analogy at theorganism level:

The defense systems of plants and animals differ.Animals generally repair tissues that have beeninfected. Plants, on the other hand, do not makerepairs. Instead, they seal off and sacrifice thedamaged tissue so that the rest of the plant does notbecome infected. This approach works becausemost plants, unlike most animals, can replacedamaged parts by growing new stems, leaves, androots.

The strategy extracted from the above is based onthe ability of plants to add new parts to replacedamaged ones, rather than expending resources inrepairing damaged parts or sacrificing the entireorganism.

Applying this strategy to products involves planningfor parts that can be used to replace a broken feature,without repairing the broken feature or replacing theentire part that contained the feature.

Another phenomenon identified using the keyword‘correct’ involves fainting. The text regarding faintingfrom Purves et al. (2001) follows:

Blood must be returned from the veins to the heartso that circulation can continue. If the veins areabove the level of the heart, gravity helps bloodflow, but below the level of the heart, blood must bemoved against the pull of gravity. If too much bloodremains in the veins, then too little blood returns tothe heart, and thus too little blood is pumped to thebrain; a person may faint as a result. Fainting isself-correcting: A fainting person falls, therebymoving out of the position in which gravity causedblood to accumulate in the lower body.

The strategy derived from the above excerpt is thatfainting is a form of defensive failure that preventsmore serious failure.

ii. Applying strategy to engineering system

Snap fits embody a form of fastening oftenpreferred for assembly and recycling purposes, but areproblematic for remanufacture when they fail. Figure1 compares failed and unbroken snap fits on toner-cartridges undergoing remanufacture.

Applying the fainting strategy to the design of snapfits, predetermined breakpoints incorporated into snapfit configurations as shown in Figure 2a may causeearlier failure than with standard snap fitconfigurations, but the part containing the snap fitfeature can be more easily reused. Applying theability of plants to sacrifice and replace parts, apossible planned replacement part is shown in Figure2b that can be used once the sacrificial feature inFigure 2a fails.

Figure 1. Damaged snap-fit features (Williams, 2001)

a. Snap fit redesigned with counter sink andbreak points

b. Redesigned snap fit after failure andrefurbishment

Figure 2. Redesigned snap fit to facilitaterepair (Hacco and Shu, 2002)

b. MicroassemblyCollaboration with researchers with expertise in

micro- and nanoengineering at the TechnicalUniversity of Denmark led to the following casestudies in microassembly (Shu et al., 2003, 2006).

As the size of products and components becomesmaller, the manufacture and assembly of suchcomponents present challenges beyond thoseassociated with their larger counterparts. Forexample, in the assembly of microobjects, additionalchallenges include the need for increased positionalaccuracy, the mechanics of interaction betweenobjects, and the loss of direct hand-eye coordination.

Grippers used in microassemby can be roughlycategorized as contact and non-contact. Contactgrippers make use of principles includingmechanical contact, vacuum, adhesion, electrostaticsand ultrasound. Non-contact grippers make use ofprinciples including optical traps, magnetic andelectrical fields. Many of the aforementionedgripping techniques are reported to lack the abilityto center objects. Miniaturized mechanical gripperscan center objects but present problems including

design complexity and not being suitable for cleanrooms (Bütefisch and Büttgenbach, 2001).

The goal of the biomimetic search in this examplewas to identify biological phenomena relevant to thecentering of objects within a gripper duringmicroassembly. Relevant phenomena located inPurves et al. (2001), include microtubule organizingcenters, photosystems, and retinal ganglion cells.Details on the use of these stimuli to produceconcepts are presented by Shu et al. (2003).

i. Overcoming sticking in microassembly

Another problem unique to microassembly isthat size effects, which occur when part dimensionsare scaled down, complicate the handling andassembly of micromechanical parts. A commoncomplication involves sticking between the grippingdevice and the micropart, which hinders theautomation of picking and releasing operations.

Shu et al. (2006) present the identification anduse of biological analogies to solve the problem ofsticking during microassembly. Selected releasetechniques based on DNA transcription and theabscission process in plants inspired concepts ofnew automated handling devices for microobjects.

The first phenomenon identified is the basis forhow proteins are selectively synthesized to defendagainst infections. This phenomenon involves theinteraction between various proteins required toinitiate DNA transcription, and led to a conceptwhere features with different geometries would beused to maximize or minimize surface contact withthe microobject as needed. However, this complexinteraction mapped into a relatively complexsolution compared to one that can be developedbased on the abscission principle described below.

ii. AbscissionThe phenomenon of abscission is the process by

which leaves, petals, and fruits separate from aplant. Plants direct growth in different parts such asroots and shoots by strategically releasing ahormone called auxin. When leaves are damagedthrough infection for example, or are no longerneeded, as in the winter season, the leaves stopproducing auxin, allowing the further expression ofabscisic acid and ethylene, which advanceabscission. As a result, specific parts of the stalks ofthe leaves break down and become completelydetached from the plant. The base of some leavescontains a special layer of cells called the abscissionzone (see Figure 3). In the absence of auxin, thesecells swell and form a cork-like material. This cutsoff the flow of nutrients to the leaf and forms a seal

Counter sink forreplacement part

Predeterminedbreak points

Reused partReplacementpart

between the leaf and the plant and protects the plantonce the leaf separates (Purves et al., 2001).

The abscission principle can be appliedabstractly to microassembly as shown in Figure 4.To overcome difficulties associated with the objectadhering to the handling device, the object isreleased together with a part of the tool designatedas sacrificial. The sacrificial part can be ofsignificant mass to take advantage of gravity. In thisway the object can be easily released. The sacrificialpart of the tool can then either remain with themicroobject or be subsequently removed.

For the specific application of inserting a 0.6 mmmetallic microscrew into a plastic counterpart, theabscission zone is physically implemented as apolypropylene rod of 4 mm diameter that is easilygripped and positioned by a small industrial robotwith six degrees of freedom and a specifiedrepeatability of ± 0.02 mm (see Figure 5).

The tip of the polypropylene rod is locally meltedby heating, and then pressed over the head of thescrew. The contact with the screw results insolidification of the polypropylene, and a solid bondbetween the rod and the screw is formed. The robotcan now manipulate the screw into the plasticcounterpart. Once the screw is tightened into itsfinal position, the resulting increased torque willbreak the bond between screw and rod.

Figure 3. Abscission Zone

Figure 4. Abscission applied tomicroassembly

Figure 5. Gripper with polypropylene rod overmounted screws

Other concepts considered for implementationof the abscission principle included the use of ice orother intermediate material that could be chemicallydissolved. This however would introduce possiblecontaminants that are clearly undesirable. Theabscission principle is more broadly interpreted as aphysically weaker zone between the tree (gripper)and the leaf (screw). Gravitational, torsional orother forces can be used to break this zone toseparate the gripper and screw. In addition torelative “weakness”, another factor that led to thechoice of a polymer as the intermediate-zonematerial is the ability of polymers to form the verysmall geometric features that mate with and thushandle the microscrew.

The added challenge of physicalimplementation of the biological strategy in asolution for this case study highlighted thefollowing. Previous work (Shu et al., 2003)conjectured that biological analogies at a scalecomparable to the micro assembly scale could bemore directly implemented with less need forabstraction. However, the complex and tightlycontrolled biological processes identified at themicro scale, only one of which was described forthis case study, are difficult to emulate. The farsimpler strategy of using an intermediate zone thatcould be broken down, thermally, chemically ormechanically, was more easily implemented,although the concept of an abscission zone wasabstracted into the form of polypropylene rods asopposed to being literally implemented.

This case study suggests that further workshould focus on the process of abstracting biologicalprinciples and entities to implement as practicalengineering solutions, as it may not be possible ordesirable to completely emulate analogousbiological processes.

Abscis-sion zone

Sacrificial part of tool

6. Summary

This paper summarized our past and current workin developing a methodology to identify and userelevant biological analogies for any givenengineering problem in a systematic manner. Firstintroduced were ongoing challenges and work inlanguage analysis and analogical reasoning in usingbiological phenomena to develop engineeringsolutions. Analogies identified using the chosenapproach for case studies in design forremanufacture and microassembly were thendescribed to illustrate the process.

7. Acknowledgments

Gratefully acknowledged is the financial supportof Natural Sciences and Engineering ResearchCouncil of Canada (NSERC).

8. References

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