Soft-Tentacle Gripper for Pipe Crawling to Inspect Industrial Facilities Using UAVs

Abstract

This paper presents a crawling mechanism using a soft-tentacle gripper integrated into an unmanned aerial vehicle for pipe inspection in industrial environments. The objective was to allow the aerial robot to perch and crawl along the pipe, minimizing the energy consumption, and allowing to perform contact inspection. This paper introduces the design of the soft limbs of the gripper and also the internal mechanism that allows movement along pipes. Several tests have been carried out to ensure the grasping capability on the pipe and the performance and reliability of the developed system. This paper shows the complete development of the system using additive manufacturing techniques and includes the results of experiments performed in realistic environments.

Keywords: UAVs; inspection; soft robotics.

Figure 6

Model used to determine limb deflection in a pipe. H is the height of the limb, L is the length of the link, R is the radius of the pipe, $\theta$ is the deflection of the joint, and $\alpha$ is the angle between the contact points of two consecutive links.

Figure 1

CAD design of the complete system.

Figure 2

CAD view of the forward-motion system. The arrangement of the three servos, the worm gear, the linear bearings at the ends of the case and the guides to contracting the soft limbs can been seen.

Figure 3

The left-hand image shows a study of the deformation for non-linear materials and the right-hand image shows a study of the stress.

Figure 4

The image shows the final impression of the limb and the different angles chosen in its design.

Figure 5

Example of the bad fold of soft limb and good fold when changing $j_i$ parameters.

Figure 7

Model for the determinate used to determinate the $\beta$ angle.

Figure 8

Example of movement sequence of the soft landing gear: (in stage one), it grips to the pipe; (in stage two), it opens the front limbs (blue case); (in stage three), it moves forward; (in stage four), it closes the front limb (blue case); (in stage five), it opens the rear limbs (black case); and finally, (in stage six), it moves the rear part.

Figure 9

The final result when joining TPU with ecoflex. It can be seen that ecoflex is only applied to the tip to increase the adhesion in this area.

Figure 10

Comparison between the theoretical force and the real force performed by the soft limbs according to the voltage applied to the servos. The orange line represents the theoretical measurements and the blue line represents the experimental measurements obtained.

Figure 11

The upper image shows the lower part of the landing gear to which the pressure study is made. The lower left-hand image shows the pressure map made on a 140 mm-diameter pipe and the lower right-hand image shows the pressure map made on a 160 mm-diameter pipe.

Figure 12

The maximum angle at which the landing gear can be grabbed with the drone on the pipe.

Figure 13

Placement of markers on a pair of soft limbs.

Figure 14

Closing sequence on the pipe and the limbs’ deformation.In the first picture, the tentacles are open. In the second, they begin to close. Finally, in the third picture, the limbs are completely close, adapting to the shape of the pipe.

Figure 15

Setup including in the flying platform.

Figure 16

System scheme used.

Figure 17

The image on the left-hand side shows the first experiment performed with the landing gear alone on the pipe. The picture on the right-hand side shows the complete system and how it is attached to the pipe.

Figure 18

The image shows the complete system with an ultrasonic sensor and the flaw detection computer.