With prime tools and years of expertise, Fraunhofer IPA will get to the foundation causes of inaccurate robotic operation. Supply: Rainer Bez, Fraunhofer IPA
Robots are nearly at all times extremely repeatable. Absolute accuracy, however, usually leaves one thing to be desired. A group on the Fraunhofer Institute for Manufacturing Engineering and Automation IPA is uncovering the explanations for this and serving to corporations to attain extra environment friendly robotic methods.
Repeatability and absolute accuracy are established parameters for assessing the standard and precision with which a robotic performs a particular process. If a robotic performs a particular process many occasions with nearly equivalent outcomes, this demonstrates excellent repeatability. Many industrial robots obtain values within the vary of 0.1 mm or higher.
In distinction, absolute accuracy describes how precisely a robotic’s spatial coordinates are achieved in relation to its base system, no matter earlier actions. And right here, there may be usually nonetheless room for enchancment. Sometimes, values between 0.5 and 1.5 mm are achieved. This tendency towards inaccuracy shouldn’t be an issue for some purposes, however it’s for others.
Disadvantages of inaccurate robots
It’s troublesome to make use of robots with low absolute accuracy in processes that aren’t repeated identically, akin to within the manufacturing of small batch sizes. When welding an meeting, for instance, it’s significantly vital that the wire tip is positioned exactly within the middle of the weld seam. Actual positioning leads to high-quality weld seams that meet business necessities.
Nonetheless, deviations of just some tenths of a millimeter can considerably impair high quality and even result in rejections. Absolute accuracy shouldn’t be solely vital for robot-based welding, but in addition for purposes akin to decide and place, overspray-free portray, or robot-based drilling and deburring.
One other drawback of inaccurate robots turns into obvious in offline programming (OLP), which can be regularly used within the processes talked about above. Right here, the robotic program is created in a simulation after which transferred to the true robotic. The benefit lies in the potential for the robotic sustaining operation whereas programming is carried out. Subsequently, whereas the robotic is processing one element, the subsequent element could be programmed in parallel.
But when absolute accuracy is inadequate, the created program can’t be used straight. As an alternative, time-consuming corrections are needed, resulting in undesirable machine downtime, which in flip impairs effectivity and productiveness.
The customarily-achieved absolute accuracy of 0.5 to 1.5 mm is subsequently inadequate for advanced purposes and may restrict and even stop using robots in sure purposes. It additionally regularly results in extra work steps, such because the re-teaching, which reduces the effectivity of the complete manufacturing chain. In lots of industrial eventualities, an absolute accuracy that’s much like the repeatability is fascinating and even required.
Causes for a scarcity of absolute accuracy
Along with the accuracy measurements supplied in accordance with ISO 9283, corporations repeatedly flip to Fraunhofer IPA with the query of how they’ll enhance the efficiency of their robots when it comes to precision. The causes of inaccuracies are manifold and could be divided into hardware-related, software-related, and externally associated causes.
{Hardware}-related causes could embrace the design of the robotic, akin to inferior encoders or gears, or inadequate rigidity, whether or not it’s an articulated arm, a SCARA robotic, or a gantry system. Poor calibration of the robotic is among the predominant causes for inaccuracy on the software program aspect, together with inadequate controller efficiency.
As well as, an rising variety of robotic methods are moreover outfitted with “cognitive” capabilities, significantly these associated to notion. These so-called closed-loop methods work with sensors that detect the robotic’s setting, and their software program processes the measured information to regulate the robotic’s path accordingly. In such a system, poor sensor information, a low-performing controller, or suboptimal interplay between the parts within the robotic cell often trigger issues.
Lastly, exterior elements akin to temperature and air stress, but in addition course of forces that happen, can have a adverse impression on absolute accuracy.
The measurements made by these gadgets have an accuracy of +- 40 µm anyplace within the working area. Supply: Fraunhofer IPA
Complete evaluation with new benchmark
If corporations that use robots, in addition to the robotic producers themselves, are dissatisfied with absolutely the accuracy of their methods, the complete software ought to be examined and analyzed. As described above, a person investigation of the causes is critical.
The automation group at Fraunhofer IPA is a impartial challenge companion that may conduct this root-cause evaluation in a methodical method based mostly on intensive knowledgeable data and expertise.
In a typical challenge, the group first data the present scenario utilizing sensor expertise such because the Leica Absolute Tracker AT960 to create a strong database. The laser tracker data the positions of the robotic with submillimeter accuracy. Particular efficiency indicators are calculated from the recorded information, which can be utilized to find out the efficiency of the robotic system.
As well as, the traits of the robotic’s actions are examined, which additionally present priceless insights. In an extra step, the specialists examine the reason for the undesirable habits. To do that, they look at each the {hardware} and software program of the robotic system.
As well as, the group has developed a closed-loop benchmark particularly for the closed-loop robotic methods talked about above. The benchmark is appropriate for robots from many producers. Within the benchmark, a reference-giving machine, a “metronome,” is used to impress the robotic into sure behaviors, which permits conclusions to be drawn about its efficiency.
Whereas ISO 9283 solely focuses on the robotic itself to measure absolute accuracy, the benchmark developed can look at all the pieces that makes up a closed-loop managed course of or process. For example, this consists of the efficiency of the complete robotic cell, together with the sensor expertise and the meant course of.
The benchmark process was offered on the 56th Worldwide Robotics Symposium (ISR 2023) and on the twenty first Worldwide Convention on Automation Know-how and Mechanical Engineering (CASE 2025).
With an correct robotic, the deliberate path could be executed with out handbook interplay on the true robotic. Supply: Fraunhofer IPA
Added worth of excessive absolute accuracy
A robotic with enough absolute accuracy can’t solely substitute costlier tools but in addition improve flexibility and reduce rework. In lots of purposes, it subsequently is smart to analyze anomalies and enhance absolute accuracy.
A robotic that works exactly and reliably affords financial benefits, in addition to will increase an organization’s competitiveness. Investing on this space is subsequently a strategic resolution that pays off in the long run.
Concerning the writer
Martin Finkbeiner is a challenge supervisor on the Fraunhofer Institute for Manufacturing Engineering and Automation IPA. He could be reached at [email protected] and +49 711 9701046.
