Design af tobenet robot AAU-BOT1

Abstract

The aim of this project is to develop the mechanical design of a human-sized anthropomorphic biped robot, including the mechanic and electric power transmission. The design is verified and documented in technical drawings. Manufacturing and subsequent assembly of the robot is initiated, such that a finished robot is ready before the initiation of the autumn semester of 2007. An overview of the task at hand are obtained through initial analyses of existing biped robots and the principals of human walking, including the concepts of balance maintenance. Based on this, the requirements for the robot to be developed are set up in collaboration with all researchers participating in the project. The dimensioning loads are established by inverse dynamic analysis of the motion pattern of a test person, obtained experimentally through motion capture. A dimensioning approach is then set up, which will lead to a very lightweight design. The design is developed iteratively because of the interdependency of the structural parts and the power transmission components. The power transmission components are chosen by computational determination the lightest possible motor/gear combination from a population of candidates. The structural parts, i.e. the limbs of the robot, are designed in parallel, applying intuitive weight minimization. The final design is verified in terms of structural adequacy and power transmission fatigue life. The selected power transmission components are exploited to their limit, in order to secure a low total weight. A maximum current limit is therefore set up for each motor, which ensures that the selected components are not damaged due to excessive loads. A time domain simulation environment is created, based on forward dynamics and a developed preliminary control strategy. The composition of the selected actuation and the final mechanical design is then verified, including all dynamic and contact effects, by simulating the execution of different walking cycles. A lightweight six axis force/torque sensor is furthermore developed, which shall provide input regarding the contact forces between the feet and the floor, for the final control strategy. The developed sensor is calibrated and its functionality is verified experimentally. Lastly, an optimization scheme for weight minimization of the structural parts is developed, which is based on the complex optimization routine in collaboration with the FEM program Ansys. The optimization routine continuously suggests improvements to a given design, which is then subjected to an automated structural analysis using FEM for evaluation.

Formålet med dette projekt er at udvikle det mekaniske design til en antropomorf tobenet robot med menneskeproportioner, inklusive den mekaniske og elektriske effekttransmission. Designet verificeres og dokumenteres i form a tekniske tegninger. Fremstilling og efterfølgende montage igangsættes, således at en færdig robot står klar før påbegyndelsen af efterårssemestret 2007. Et overblik over den forhåndenværende opgave præsenteres gennem indledende analyser af eksisterende robotter og principperne bag menneskelig gang, herunder koncepter vedrørende balance vedligeholdelse. En kravspecifikation for robotten, baseret herpå, opstilles i samarbejde med alle forskere der deltager i projektet. De dimensionerende belastninger tilvejebringes gennem invers dynamisk analyse af bevægelsesmønstret for en testperson, hvilket opnås eksperimentelt vha. motion capture. Et dimensioneringsgrundlag der leder til et meget let design opstilles efterfølgende. Designet udvikles iterativt pga. den indbyrdes afhængighed af strukturelle dele og effekttransmissionsdele. Den lettest mulige motor/gear kombination udvælges fra en population af kandidater vha. et computerprogram. De strukturelle dele designes parallelt hermed under anvendelse af intuitiv vægtminimering. Det endelige design verificeres mht. strukturel tilstrækkelighed og levetid for de udvalgte effekttransmissionskomponenter. Disse belastes hårdt for at opnå en lav totalvægt, ved brug af lette komponenter. For at sikre at effekttransmissionskomponenterne ikke beskadiges pga. for store belastninger opstilles en øvre grænse for hvor meget strøm der må ledes til hver enkelt motor. Et tidsdomæne simuleringsværktøj fremstilles, baseret på forward dynamisk analyse og en foreløbig styringsstrategi. Vha. dette kan kompositionen af de udvalgte effekttransmissionskomponenter og det endelige mekaniske design verificeres, under hensyntagen til alle dynamiske og kontaktrelaterede effekter, ved at simulere forskellige gangcyklusser. Tillige udvikles en letvægts kraft og moment sensor, som skal levere input til den endelige styring, angående kontaktkræfter mellem fødderne og gulvet. Den udviklede sensor kalibreres og dens funktion verificeres eksperimentelt. Slutteligt udvikles en optimeringsrutine til vægtminimering af strukturelle dele. Dette baseres på complex optimeringsmetoden i samspil med FEM programmet Ansys. Optimeringsrutinen foreslår kontinuerligt forbedrede designs som evalueres automatisk vha. FEM, indtil et optimum findes.

A master thesis from Aalborg University

Design af tobenet robot AAU-BOT1

[Design of Biped Robot AAU-BOT1]