modeling a hexapod robot by means of cad …

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MODELING A HEXAPOD ROBOT BY MEANS OF CAD TECHNIQUES

Thiago Augusto Ferreira 1, Armando Carlos de Pina Filho 2, Aloísio Carlos de Pina 3

1 Universidade Federal do Rio de Janeiro, Mechanical Engineering Department, Polytechnic School, Rio de Janeiro - RJ, Brazil,e-mail: [email protected]

2 Universidade Federal do Rio de Janeiro, Urban Engineering Program, Polytechnic School, Rio de Janeiro - RJ, Brazil,e-mail: [email protected]

3 Universidade Federal do Rio de Janeiro, Civil Engineering Program, COPPE, Rio de Janeiro - RJ, Brazil,e-mail: [email protected]

Abstract: The main purpose of this work is present themodeling of a hexapod robot using the software AutoCAD,as well as the main characteristics of this type of robot,which represents a typical mobile robot and a usefulmechanism for diverse tasks.

Keywords: Robotics, hexapods, CAD.

1. INTRODUCTION

Usually, mobile robots can be classified in relation tosome characteristics, such as: anatomy; control type;functionality, and movement. From anatomical viewpoint,the robots can be aerial, aquatic or terrestrial. The last onesbeing the most common, having wheels (Fig. 1), tracks (Fig.2) or legs (Fig. 3).

Fig. 1. Mobile robot with wheels.

Fig. 2. Mobile robot with tracks.

Fig. 3. Mobile robot with legs.

In relation to the control type, the mobile robots can be:remote controlled, in which an operator defines all of themovements that the robot will execute; semi-autonomous,where an operator indicates the command macro to beexecuted and the robot executes it alone; and autonomous,in which they accomplish their tasks alone, making theirown decisions.

Considering the functionality, we have: the industrialrobots, used in production lines; service robots, that are usedfor generic tasks, working in well known structuredenvironments; field robots, that work in non structuredenvironments, little known and usually dangerous; andpersonal robots, that are sold in shelves, they don't developspecific tasks, but interact with the human beings.

About movement, robots can be classified into:holonomic, in which the controllable degrees of freedom aregreater than or equal to the total degrees of freedom; andnon holonomic in which the controllable degrees of freedomare less than the total degrees of freedom.

From those characteristics it is possible to define therobot's application. As examples can be mentioned robotsused in internal (structured) environments as in the areas oftransports, services, industry, cleaning of great areas,surveillance, researches and entertainment (Fig. 4), or robotsused in external (non structured) environments as in miningcompanies, sewer tubes, agriculture, forests (Fig. 5),constructions, fires, military applications and even in space(Fig. 6). It is also possible to use mobile robots to motivatethe teaching and formation in Mechatronics and ArtificialIntelligence, as for example through robot’s soccercompetitions.

Proceedings of the 9th Brazilian Conference on Dynamics Control and their Applications Serra Negra, SP - ISSN 2178-3667 1138

MODELING A HEXAPOD ROBOT BY MEANS OF CAD TECHNIQUESThiago Augusto Ferreira, Armando Carlos de Pina Filho, Aloísio Carlos de Pina

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Fig. 4. NEC and NEDO Robots [1].

Fig. 5. Forest Robot, design by Pulstech [2].

The work presented here is related to legged mobilerobot’s study, at first a robot model with six legs, simplydenominated the hexapod robot.

2. HEXAPOD ROBOTS

The mechanical structure and operation of a hexapodrobot is based on animals (usually insects), from thebiomimetics principles [4], science based on the imitation ofexistent mechanisms in nature, trying to learn its workingsand applying such knowledge in the project of artificialmechanisms similar to the natural ones.

Fig. 6. Sojourner, first robot in Mars [3].

The word "biomimetics" is the combination of the Greekterms "bios", that means life, and "mimesis", that meansimitation. Therefore, it can be said that the biomimetics isthe imitation of life. Nowadays, the biomimetics representsa research area that is in great development in the field ofthe science and technology. Several mechanisms have beendeveloped starting from knowledge acquired with systemsnatural or biological.

Figures 7 and 8 show two examples of robots inspired ininsects.

The objective of this work is to present a study and themodeling of a hexapod robot using programs of CAD, moreprecisely AutoCAD from Autodesk. We intend to present asimple however efficient methodology for the 3D modelingand subsequent operation simulations. This research haseducational applications in the area of MechanicalEngineering, mainly in the project of machines and robots.

3. CHARACTERISTICS OF THE ROBOTS

The great advantage of mobile robots with six legs, whencompared the biped and quadruped robots, it is thepossibility of movement in larger speeds allied to the staticstability, which is conserved. In biped robots, the demandson the control system are well higher, once to maintain thestatic stability, this robot type he has to move with lowspeed and have a larger support (foot).



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Fig. 7. iSprawl robot [5].

Fig. 8. Robot inspired in a cricket [6].

Studies indicate that all of the calculations (cinematic,dynamic, control, etc.) would have to be accomplished every20 meters.

In the case of robots with four legs, to maintain the staticstability, three legs would have to stay in the ground so thatthe fourth could be moved. This makes the movement of thistype of robot extremely slow, limiting its applicability, andin that way being little used commercially.

A disadvantage of the hexapod robots is that in the caseof the biomimetic system, a group of 18 actuators wouldhave to be implemented, making for a high components andcontrol system cost.

Nevertheless, the study of the movement of insects andits application in the design of robots with six legs is verywidespread in the research centers, which have severalmodels of hexapod robots.

An interesting example of hexapod robot, built frombiomimetic concepts, is the "Sprawlita", whose project wasbased on the principles of biomechanical cockroach (Fig. 9).

Fig. 9. Hexapod robot “Sprawlita” [4].

A very interesting feature of the cockroach’s locomotivesystem is the presence of a natural braking mechanism. Dueto this, the cockroach is capable of performing movementsat high speed, being able to stop and change direction quickand efficiently (Fig. 10).

Fig. 10. Natural braking mechanism [7].

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brakingmechanism



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Due to all benefits previously described, the hexapodrobot represents an interesting object of study in researchesbeing conducted at the Federal University of Rio de Janeiro.One of the most interesting works on this topic wasdeveloped by Costa Netto [8], in which was used a set ofpiston with shape memory materials to actuate the legsystems.

4. MODELING OF A HEXAPOD ROBOT

To achieve the goals proposed for the research, we haveimplemented an organized series of activities, targeting fromlearning about mobile robots to the final modeling of thesix-legged robot.

From the features already presented in the previoussection, a study was conducted on the principles anddefinitions of mobile robots and their differences withrespect to other types of robots. In this research the aim wasto obtain the greatest possible knowledge regarding themovement of the biding joints of the robot [9], examiningwhether they perform a angular movement (between twoaxes), rotation (around the axis) or prismatic (linear), and ifthese movements classified the machine as a mobile robot orhandler. Also studied were topics such as robot kinematics,movement control and sensors (types and characteristics)[10].

The first stage of construction of our robot was thedevelopment of the leg set of the hexapod system, shown inFig. 11.

Fig. 11. “Exploded” isometric view of the leg.

This segment consists of 20 pieces formed mainly by themain supports, actuator pistons, connection axes, springs,screws and washers. Figure 12 shows the isometric view ofthe leg already assembled.

Fig. 12. “Assembled” isometric view of the leg.

Figure 13 presents the main orthographic views (frontand top) of the whole leg.

Fig. 13. Orthographic views of the leg.

The movement axis of the leg in relation to the pistonactuator can be given in Fig. 14.

The second stage of construction of our robot was basedon the development of modeling of the body and thesupports for the leg, as shown in Fig. 15.

Upon completion of this stage remains only theintroduction of the Pistons responsible for the angularmovement of the leg, which can be seen in Fig. 16. Figure17 presents the hexapod robot totally assembled, finishingthe desired modeling.



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Fig. 14. Possibilities of movement of the leg.

Fig. 15. “Exploded” isometric view of the robot.

Fig. 16. Possibilities of movements of the robot.

5. CONCLUSION

From the main objectives of work, was presented a studyon mobile hexapod robots and was built a computer modelcapable to represent, as faithfully as possible, a real robot,considering the mechanical parts that constitute it. Thisresearch has applications in the educational area ofMechanical Engineering, particularly in the design ofmachines and robots. Continuity will be given to the workwith simulations of it working and the modeling of othermobile robots.

Fig. 17. Isometric view of the robot totally assembled.



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ACKNOWLEDGMENTS

The author Aloísio Carlos de Pina would like to thank toCAPES (Coordenação de Aperfeiçoamento de Pessoal deNível Superior) and FAPERJ (Fundação Carlos ChagasFilho de Amparo à Pesquisa do Estado do Rio de Janeiro)for financial support in the course of this work.

REFERENCES

[1] http://www.incx.nec.co.jp/, accessed in August 2008.

[2] http://www.plustech.fi/, accessed in September 2008.

[3] http://ranier.oact.hq.nasa.gov/telerobotics_page/telerobotics.shtm, accessed in September 2008.

[4] S. A. Bailey, J. G. Cham, M. R. Cutkosky, and R. J.Full, “Comparing the Locomotion Dynamics of theCockroach and a Shape Deposition ManufacturedBiomimetic Hexapod”, International Symposium onExperimental Robotics, Waikiki, Hawai, 2000.

[5] S. Kim, J. E. Clark, and M. R. Cutkosky, “iSprawl:Autonomy, and the Effects of Power Transmission”,Stanford Center for Design Research, 2007.

[6] R. Quinn, http://biorobots.cwru.edu/projects/c_mrobot/c_mrobot.htm, Case Western Reserve University,accessed in August 2007.

[7] D. Tsakiris, http://www.ics.forth.gr/~tsakiris, Instituteof Computer Science, accessed in September 2007.

[8] S. M. da Costa Netto, “Estudo e Projeto de um RobôHexápode com Atuadores Utilizando Materiais comMemória de Forma”, M.Sc. Dissertation,COPPE/UFRJ, Rio de Janeiro, Brazil, 2001.

[9] F. A. C. Gomide, and R. R. Gudwin, “Modelagem,Controle, Sistemas e Lógica Fuzzy”. SBA Controle &Automação, Vol. 4, No. 3, 1994.

[10] A. Adade Filho, “Fundamentos de Robótica -Cinemática, Dinâmica e Controle de ManipuladoresRobóticos”, São José dos Campos, ITA, 1992.


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