Crawler platform for NDT measurements

The crawler, developed by GE Inspection, is intended to be used for thickness measurements and other close-up investigations.

State of the art

Robotic crawlers for inspection of vertical or even overhanging structures are both an active area of Research as well as a field of intense industrial development. As the typical structure in ships are made of (magnetic) carbon steel, magnetic adhesion is typically used for generating the positive contact force required to
provide both adhesion and traction against gravity.

In this project, other adhesion principles such as vacuum or electrostatic adhesion are not considered. Magnetic crawlers typically run on magnetic wheels or tracks, providing both adhesion and propulsion. These wheels can easily deliver magnetic forces 2 to 5 times the weight of the robot, thus providing a reasonable
safety margin against detachment and finally falling, even under sub-optimum surface conditions, such as paint and dirt layers or rust. Problematic is the quick contamination of the wheels/magnets w/ magnetic particle. Thus, the surfaces have to be sufficiently clean in order to guaranteed sufficient inspection time between cleaning procedures.

The main problem of crawlers based on magnetic wheels is the limited ability to pass non-flat obstacles. As soon as one (or more) wheel touch two surfaces, e.g. in 90° corners, tremendous forces are needed to free the wheel from the first surface and then move on.

Often the motor forces and/or the friction at the contact surface are not sufficient to escape this locked-in situation. Several approaches have been proposed to overcome this limit: multiple wheel configurations, moveable field magnets instead of magnetic wheels, active lifters, passive lifters.

For ship inspections, several crawlers have been developed to clean and inspect ship hulls. However, due to size and limited obstacle handing ability they are not suited to inspect other parts of the ship, such as structured cargo holds, stiffeners or (ballast) tanks. Additionally, they lack robustness and stability during handling such obstacles.

Due to the large magnetic forces (up to several kN), placing the robots on a magnetic structure and even more removing it can become a difficult and dangerous task. Dedicated placement tools or adjustable magnet positions are used to enable the operator user friendliness and safe handling.

It is industrial practice to manually control the robotic crawlers along the surface, thereby requiring fulltime, uninterrupted attention of a well-trained operator. Limited support for dedicated scenarios support comes from builtin sensors: inclinometers enable straight vertical motions and line-following sensors control the robot along a given feature, such as an edge, a weld or an artificially placed guidance structure.

Expected progress beyond state-of-the-art

Crucial for a commercially attractive robotic inspection of ships is the ability to reach remote, not directly accessible location, be it due to height or in confined spaces. On a technical level this requires a crawler that is able to handle at least 90° corners and edges (to traverse from one plate/all section to the next), preferably also 180° edges (for crossing stiffeners). A promising approach is the wheel-parallel-to-wheel approach, which is already working under lab conditions. In this project, the range (transitions angle, wall orientation, size) as well as the robustness against aggressive environments will be improved. This project shall adapt such mechanisms and integrate them into the BIKE robot.

For efficient operation and user acceptance the simplicity of handling and navigation of the inspection tool cannot be underestimated. ROBINS shall develop control strategies based on multiple sensor inputs to support the operator in reaching his/her inspection target quickly. The operator shall be able to concentrate fully on the very inspection task and must not be deviated by complicated steering a complex robot. We will address this gap using multiple sensors and appropriate control strategies. This can involve: odometry (1), inclination sensors and gyros (2), cameras (3) edge detection (4), distance sensors (5) and information from outside such as from the flying platform (6) or a fixed base station (7).

For remote UT inspection, the UT probe has to be brought to the inspection location by a manipulator and then be put in close contact w/ the test object. This is solved for access path free of obstacles by sliding the probe on the surface or simple lifters from the launching point to the inspection position. However, such standard probe systems prevent passing obstacles – such as 90° corners – along the access path. Additionally, they are not flexible enough to position the probe at some critical locations, such as welds. In ROBINS, an articulated probe handling tool shall be developed and integrated to both position the probes flexibly as well as to move it out of collision situations.

In remote inspection, the probe is far away from the operator controlling the data acquisition. The data quality (electrical noise) and the need to feed couplant liquid to the probe contact limits this distance or impairs signal quality. We shall develop or adapt and then integrate a miniaturized UT control system and couplant feed system has to be integrated on-board the robot.