A Novel Crawling In-pipe Robot Design

A novel crawling in-pipe robot was designed to improve the adaptive ability with self-locking principle applied. In the moving, the robot was adaptable to horizontal, vertical and bending pipes with different diameters and sections without exerting additional pressure to the shell. The robot used a telescopic umbrella stand as a basic structure. The force of telescopic mechanism, self-locking principle of supporting mechani sm and shell were deduced from design requirements. The design of supporting and coupling mechanism was completed. The relationship between screw rod thrust and parallelogram driving force was established. A prototype was made and tested according to the suggested design methods. The results show that the robot with powerful traction, good self-locking performance and smooth passage through curve can move forward in the pipe with 90~150 mm inner diameter.


Introduction
In recent years, with the development of pipeline transportation of petroleum, natural gas and other fluids, it was urgent and important to conduct regular inspection and maintenance [1] .Especially on August 1st, 2014, the explosion of gas pipeline in Kaohsiung, Taiwan reminds people to give sufficient weight to installation and maintenance of pipelines.The limitations of pipe restrict man's active operability.As an effective testing tool carrier, a micro in-pipe robot can go deep into confined space while many common testing tools can't do so.
Nowadays, various in-pipe robots as the main testing carriers have emerged in response to the solution to the industrial problem of pipe inspection [2][3][4][5] .Due to complicated environment yet limited space, in-pipe robot should adopt simple unit structure and self-adaptability [6] .
For successful march, a robot should have: 1.the ability to adaptable changes in the pipeline; 2. sufficient traction;3.miniaturized dynamical system and transmission mechanism.In terms of ways of moving in the pipeline, there are different types of in-pipe robots such as wheeled robot, crawler-type robot, hydraulic robot, vibrating robot and bionic crawling robot, etc.The vibrating robot was used for pipe with rigid shell; the wheeled drive was a frequently-used mobile carrier by in-pipe robot.the wheeled robot has advantages of simple structure, fast speed, and powerful traction; while the crawling robot with compact structure can be miniaturized, it was widely applied in minor-caliber pipe testing [7] .Based on force condition, the maximum tractive effort from crawling robot was equal to the maximum static friction force of moving mechanism and shell.To increase system traction, it was necessary to raise pressure between system and shell of pipe; On the other hand, with increasing pressure, there was a growing demand for dynamical system and moving speed will be restricted.So the crucial part of design was to deal with the contradiction between system traction and positive pressure [8][9] .The study attaches importance to take advantage of friction against pipe to drive robot.
In the passage, a telescopic in-pipe robot based on self-locking mechanism was adaptable to horizontal, vertical and bending pipes with different diameters and sections.According to mechanics principles, the force of telescopic mechanism, self-locking principle of supporting mechanism and shell are deduced to develop telescopic in-pipe robot prototype.Furthermore, related tests are completed successfully.

In-pipe robot structures
Figure 1 shows the basic structure for in-pipe robot.Cycle of robot moving ahead was shown in Figure 2. ,. ( substitute formula (2) into formula (1) to get: . ( From formula (5), it could be found that the application of force from quadrangle agsint supporting mechanism, proportional to scew rod thrust, not depend on BD bar or the parallelogram angle.2) M6 screw rod and triangle screw thread are adopted and equivalent frictional coefficient fv was (7)   In the formula, ȕ represents half of thread angle of common triangle screw thread.
Equivalent friction angle was (8)   3) Pressured by external load FC, the required maximum torque of screw rod rotation was , (9)   and in the formula, Į represents helix angle of screw thread.
4)The relationshop between torque and input power of screw rod was .(10)   According to formulas ( 5)-( 6), (9), the relatonship between motor power and suffered thrust by robot can be deduced as The effeiency of spur cylindrical gear 4, 5 was 0.9; pitch diameter of screw rod d2=5.355mm; helix  To test motion characteristics of in-pipe robot, it requires to test electric current (I) and voltage(U) under different load and operating conditions.The results are shown in Table 1.From the above analysis result, output power P in idle load was mainly to overcome the friction between robot and pipe shell.The resistance of friction was about 18 N,

Conclusion
1) The crawling in-pipe robot was adaptable to horizontal, vertical and bending pipe with good self-locking performance without exerting additional pressure to the shell.
2) The robot was adaptable to pipes with 90~150 mm in square, round and rectangle sections with the automatic adjustment.
3) Proper coupling methods and restraint function of pipe shell made robot to pass through a nearly 90°right-angled bending pipe successfully.
4) The telescopic mechanism uses inequilateral parallelogram to shorten transmission screw rod effectively which ensures magnifying power in the movement.

Fig. 1
Fig.1 the in-pipe robot overall structure

Fig. 2
Fig.2 schematic drawing principle of in-pipe robot movement

Fig. 3
Fig.3 the in-pipe robot supporting structure

Figure 6
Figure6show the coupling between telescopic structure and back supporting.
Fig. 6 coupling methods of back supporting and telescopic mechanism

Figure 7
Figure 7 show the inequilateral parallelogram mechanism to shorten mechanism length effectively.The structure not only ensures magnifying power of movement but also improves transmission efficiency.

Fig. 7
Fig.7 force analysis of telescopic mechanism 1) DE,EF both are two force bars.The force status

4. 2
Relationship between motor power and robot impetus FE.

Figure 8 Fig 8 ,
Figure 8 show the transmission from motor to screw rod according to the transmission mechanism that has been worked out.
Fig.9 in-pipe robot test The load test of Figure 9(a) with an iron block of 1.5 kg to show good self-locking performance of prototype.

Figure 9 (
Figure 9(b) shows ability test to pass throught pipe.Taking control of screw rod, trial prototype moves back and forth four times between two ends of 2-meter straight pipe.The mesured average speed in the straight pipe reaches 2.7 m•min -1 .
load.The robot need maximum power in upward vertical motion.The maximum external load was 17.4 N which was 4 times larger than its own weight.