Quality Magazine

Robotic Metrology: The Future Is Now

February 21, 2011
Robots have been playing an important role in automated manufacturing for decades. However, the larger question has always been, if the robot is smart enough to move the parts around, can we measure with it, as well?

K-Scan MMD is Nikon Metrology's new generation handheld laser scanners for portable metrology applications. Source" Nikon Metrology


When we think of robots, iconic images such as C3PO and R2D2 from Star Wars often come to mind, or perhaps even Rose, the Jetsons’ housekeeping robot. These images are of trusty sidekicks who will always work to get the job done – often providing a laugh as they do so. But what do they all have in common? They’re fictional.

The fact of the matter is, robots exist in the real world and have been playing an important role in automated manufacturing for decades. Historically, robots in metrology have been used to shuttle parts into and out of precision measuring devices, such as coordinate measuring machines (CMMs). However, the larger question has always been, if the robot is smart enough to move the parts around, can we measure with it as well?

Nikon Metrology has worked hard to answer this challenging question.

Nikon Metrology’s Center of Excellence (CoE)-Metrology and Integrated Robotics (Derby, England)- conducted a study on the accuracy versus repeatability of robots in the measurement function. What it found-and there should be little surprise here-is that robots are extremely repeatable, but not very accurate. Specifically, they are not accurate enough for aerospace metrology applications in general. This explains why robots have been used in repetitive manufacturing tasks for years now, but not widely deployed for use as metrology equipment. In the business of metrology and measurement, accuracy is core to the business. Without guarantees of accuracy, there cannot be a guaranteed results.

Nikon found that the main issues with robot accuracy pertain largely to the stiffness and rigidity of the structure itself. To wit, when conducting experiments, one must assume stiffness in the unit. Then, as the count encoder pulses at the joints, one can calculate the end-of-arm robot position. The problem lies in the assumption of stiffness in a robot being valid. A robot will get to a location but will have no idea if it is actually, where it needs to be. In a CMM, one makes the same assumption of stiffness, and ensures it by making each axis linear in a simplified structure of X, Y and Z, producing a better assumption and result than with a robot.

Nikon Metrology has found a way around the robot issue by simply removing the assumption. To this end, its K-Series metrology system is optically based and fully integrated into the robot as an end-of-arm tool.

It begins with three linear CCD cameras. When light from an active infrared LED is detected, the three cameras triangulate its position in space.



The KROBOT Probe is pictured here, mounted on a robotic arm. Source: Nikon Metrology

Then, Nikon extrapolated the concept by surrounding a laser scanner with 40 LEDs strategically placed around the laser for redundancy and accuracy. Thus, Nikon can track the position of that laser scanner with extreme accuracy.



Nikon Metrology takes this concept even further with the KSCAN metrology system. The LED enclosure of the system not only tracks the position of the laser scanner, but also protects and ruggedizes it, creating a laser scanner that performs within the harsh reality of a manufacturing environment.



This hand-held laser scanning system uses Nikon’s MMDx laser scanner and is proving functional and popular in multiple applications and industries such as aerospace, automotive, and heavy machinery, globally.



Similarly, Nikon also produces the KROBOT probe, which is a modified KSCAN probe. The main difference between the two is that the KROBOT is not a hand-held device; instead, it functions as an end of arm robotic metrology device. However, because of the repeatable nature of robotic motion, it actually becomes more accurate than its hand-held counterpart.

This makes robot stiffness irrelevant because robot location is not used at all. Instead, the robot quickly, repetitively and robustly moves the laser scanner around the part to be measured. This way, Nikon leverages the robot’s strengths and mitigates its weaknesses as a metrology system.

In essence, the KROBOT system is a fully external metrology loop. With this, Nikon Metrology has greatly expanded metrology solutions for highly automated, repetitive applications, that greatly reduce your time and labor costs, while improving repeatability and accuracy. These systems are available from us now and are as easy to deploy as an off-the-shelf solution, but with the value we add. As for robots that make us laugh while cleaning our homes, well, we will leave that to others to develop. We’re happy just improving your quality, productivity and bottom line.