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Minirobots with adaptable structure.

1. INTRODUCTION

The studied minirobots are characterized by an adaptable structure, based on linkages mechanisms. A very important design goal of these minirobots is the adaptability to the inner diameters of the pipes. Pipe diameter, which is one of the important size parameters, limits the working space occupied by the inspection robot. Therefore, it is necessary to be considered that a robot is designed for a certain size of pipe diameter.

Various pipe robots are developed for the inspection of pipes. For example, it was developed a three-wheeled pipe robot that uses scissors-like structure (Okada & Sanemori, 1987), a multi-joint pipe robot that uses the active universal joints as the steering mechanism (Choi & Ryew, 2002) or a wheel type pipe robot based on the differential drive principle (Roh & Choi, 2005).

2. THE DEVELOPED IN-PIPE MINIROBOTS

The minirobot that is presented is composed of slider-crank mechanisms placed at 120[degrees] angles around the central axle. This structure can adapt more easily to the variation of the pipe's diameter (Fig. 1).

The mass of the minirobot, including the power wires, is of 630 [g]. The wheels have a radius r = 25 mm, a length of 7 mm and the component elements have the lengths: [h.sub.1] = 95 mm, [h.sub.2] = 58 mm, [h.sub.3] = 53 mm (Tatar et al., 2008).

The minirobot's propulsion is achieved by using three drive wheels. The drive wheels are placed into motion using three geared mechanisms which are driven by a DC geared motor placed in the central region of the module.

The minirobot also has in its structure two sliding elements and two helicoidal springs which generate the force needed for the wheel to press against the inner surface of the pipe.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The movement transmission from the motor to the drive wheels is achieved by using three chains placed on gears and driven by the worm gear placed on the motor's axle (Fig. 3).

In figure 3 we have the following annotations: ME - DC motor with gear reducer (1/53 ratio motor/gearbox drives, 6V), 1--worm, 2, 3, 4--gears, [z.sub.i] = 1 one thread, [z.sub.2] = 42, [z.sub.3] = 38, [z.sub.4] = 38 teeth, [n.sub.M] the motor rotation frequency and [n.sub.R] motor wheel rotation frequency (Tatar & Mandru, 2008).

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

These minirobots have movement capacities for inspection in (140 - 180) mm diameter pipes.

3. THE POWER AND CONTROL SYSTEM

The hardware component consists of a CEREBOT II motherboard (Fig. 6) and a few additional peripheral modules (Fig. 7), all developed by Digilent (http://www.digilentinc.com/).

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

For powering the DC motors we used a PMOD HB5 peripheral module with a H bridge (Fig. 7 a). For communicating with the PC a PMOD RS232 communication module (Fig. 7 b) was used, which represents the hardware support needed by the two software components for communication. For signalling certain states and parameters of the system a four PMOD LED module was used.

The embedded software component was developed in the BASCOM-AVR environment and the PC component was developed in the DELPHI programming environment and it accomplishes both the control of the robotic system and the user interface.

4. CONCLUSION

A very important design goal of the mobile in-pipe robotic minirobot is the adaptability to the inner diameters of the pipes. In this paper, we proposed the wheel type in-pipe minirobot, defined by an adaptable structure, based on linkages mechanisms. The prototype was designed in order to inspect pipes with variable diameters within 140 and 180 mm. It is the active module of a modular robotic system which is still in the phase of developing.

5. REFERENCES

Choi, H.R.; Ryew, S.M. (2002). Robotic system with active steering capability for internal inspection of urban gas pipelines, Mechatronics, Vol. 12, pp. 713-736.

Okada, T.; Sanemori, T. (1987). MOGRER: A vehicle study and realization for in-pipe inspection tasks, IEEE Journal Robotics, Automation, Vol. 3, No. 6, pp. 573-582.

Roh, S.G.; Choi, H.R. (2005). Differential-drive in-pipe robot for moving inside urban gas pipelines, IEEE Transactions Robotics, Vol. 21, No. 1, pp. 1-17.

Tatar, O.; Stan S.; Mandru, D. (2008). The modular robotic systems, The 79th Annual Meeting of the International Association of Applied Mathematics and Mechanics, GAAM 2008, 31 March-4 April, 2008, Bremen, Germany.

Tatar, O.; Mandru, D. (2008). Design of In-Pipe Modular Robotic Systems, The 4th International Conference Mechatronic Systems and Materials, MSM 2008, Bialystok, Poland, 14-17 Iuly, 2008, pp. 20-30.

http://www.digilentinc.com/ Accessed: 2008-09-04
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Author:Tatar, Olimpiu; Mandru, Dan; Alutei, Adrian; Lungu, Ion
Publication:Annals of DAAAM & Proceedings
Article Type:Report
Date:Jan 1, 2008
Words:767
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