Saturday, 16 September 2017

The Role Of Industrial Robots In NDT Applications

    Manufactures from different domains ranging from industrial to aerospace are preferring Nondestructive testing for quality control technique.

With automated NDT,robots and scanners are used to increase the speed and repeatability factor of NDT techniques, creating much more efficiently produced precision measurements.Automated NDT scanner requirements are needed to achieve high quality control and precision measurements.

Recently many manufacturers of industrial robots have produced robotic manipulators with excellent positional accuracy and repeatability. An industrial robot is defined as an automatically controlled, re-programmable, multipurpose manipulator, programmable in three or more axes.In the spectrum of robot manipulators, some modern robots have appropriate attributes to develop automated NDT systems and subsist with the challenging situations seen in the aerospace industry.


Industrial robotic arms present precise articulated mechanical links whose functions are alike to a human arm.Their links are jointed to provide rotational motions and handle objects within a certain volume. Off the shelf industrial robots are recognized as a polyvalent and robust solution for many applications: welding, material handling,palletzing , laser cutting,machine tending, machining, etc.

Comparing to typical Cartesian gantry systems, the concept of an articulated arm provides a system with greater ability. Such robots can help advanced NDT methods if they meet the basic standards of automated NDT testing: data acquisition, repeatability, precision and accuracy.


The major difficulty of using robotic arms for automated NDT is the proprietary motion controller design that these robot use. With such control, we are rigidly fixed into proprietary programs and limited motion control capabilities. More notably, we have limited control and not enough information of the robot positions when it moves from one point to another. Automated NDT systems require acquiring data on the fly while the robotic arm is moving. So, the motion control system needs to handle extremely fast control changes (fast PID controller loops). For example, in applications that require the robot to move fast and perform contour following motions around a complex surface, smooth and precise trajectories must be maintained during the robot movement. When the PID loops close at a slow pace, the robot will not move on required precise trajectories. This may results in a jumpy motion of the robot and losses of the NDT signal measurements. Current industrial robots offer slow PID control loops, estimated around 10 times less than the required speed to perform fast and accurate NDT scanning of complex parts.


Required data acquisition speed is another challenging factor of using industrial robots for NDT application.Capturing NDT data in real time while using a robotic arm is challenging feat because it requires real-time robot position monitoring.That means a direct encoder feedback has to be made available on the robot,which is generally not the case.After being processed by the motion controller unit,all these standard robot controllers will provide low rate of position feedback at around 200 Hz. The rate at which position feedback refreshes itself has a proportional impact on the inspection speed, as the robots “true” position must be attached to each measurement point and no interpolation is allowed.

By working on the main challenges identified above, industrial robots can be replaced eventually by the conventional Cartesian scanners in selected NDT application if motion control functions and encoder feedback monitoring are customized.But at this moment without such refinement in terms of the support data transfer, link and communication protocols, an efficient use of articulated robotic arms for NDT is still a work in progress.

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