With high tools and years of expertise, Fraunhofer IPA will get to the basis causes of inaccurate robotic operation. Supply: Rainer Bez, Fraunhofer IPA
Robots are virtually all the time extremely repeatable. Absolute accuracy, then again, typically leaves one thing to be desired. A staff 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 selected process. If a robotic performs a selected process many instances with virtually similar 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 typically nonetheless room for enchancment. Usually, values between 0.5 and 1.5 mm are achieved. This tendency towards inaccuracy will not 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 notably vital that the wire tip is positioned exactly within the heart of the weld seam. Actual positioning leads to high-quality weld seams that meet business necessities.
Nonetheless, deviations of only a few tenths of a millimeter can considerably impair high quality and even result in rejections. Absolute accuracy will not be solely vital for robot-based welding, but in addition for purposes akin to choose 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 also be continuously used within the processes talked about above. Right here, the robotic program is created in a simulation after which transferred to the actual robotic. The benefit lies in the opportunity of the robotic sustaining operation whereas programming is carried out. Due to this fact, whereas the robotic is processing one part, the subsequent part may be programmed in parallel.
But when absolute accuracy is inadequate, the created program can’t be used immediately. As a substitute, time-consuming corrections are mandatory, resulting in undesirable machine downtime, which in flip impairs effectivity and productiveness.
The usually-achieved absolute accuracy of 0.5 to 1.5 mm is due to this fact inadequate for advanced purposes and may restrict and even forestall the usage of robots in sure purposes. It additionally continuously results in extra work steps, such because the re-teaching, which reduces the effectivity of your complete manufacturing chain. In lots of industrial situations, an absolute accuracy that’s just like the repeatability is fascinating and even required.
Causes for an absence of absolute accuracy
Along with the accuracy measurements provided in accordance with ISO 9283, corporations repeatedly flip to Fraunhofer IPA with the query of how they will enhance the efficiency of their robots when it comes to precision. The causes of inaccuracies are manifold and may be divided into hardware-related, software-related, and externally associated causes.
{Hardware}-related causes could embody 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 likely one of the essential causes for inaccuracy on the software program facet, together with inadequate controller efficiency.
As well as, an rising variety of robotic methods are moreover geared up with “cognitive” features, notably these associated to notion. These so-called closed-loop methods work with sensors that detect the robotic’s atmosphere, 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 elements 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 damaging affect on absolute accuracy.
The measurements made by these gadgets have an accuracy of +- 40 µm anyplace within the working house. 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, your complete utility ought to be examined and analyzed. As described above, a person investigation of the causes is critical.
The automation staff at Fraunhofer IPA is a impartial mission companion that may conduct this root-cause evaluation in a methodical method based mostly on intensive knowledgeable data and expertise.
In a typical mission, the staff first data the present state of affairs utilizing sensor know-how 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 useful insights. In an extra step, the consultants examine the reason for the undesirable habits. To do that, they study each the {hardware} and software program of the robotic system.
As well as, the staff 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 gadget, 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 study every little thing that makes up a closed-loop managed course of or process. As an illustration, this contains the efficiency of your complete robotic cell, together with the sensor know-how and the supposed course of.
The benchmark process was introduced on the 56th Worldwide Robotics Symposium (ISR 2023) and on the twenty first Worldwide Convention on Automation Expertise and Mechanical Engineering (CASE 2025).
With an correct robotic, the deliberate path may be executed with out guide interplay on the actual robotic. Supply: Fraunhofer IPA
Added worth of excessive absolute accuracy
A robotic with adequate absolute accuracy can’t solely exchange costlier tools but in addition enhance flexibility and reduce rework. In lots of purposes, it due to this fact is sensible to analyze anomalies and enhance absolute accuracy.
A robotic that works exactly and reliably presents financial benefits, in addition to will increase an organization’s competitiveness. Investing on this space is due to this fact a strategic determination that pays off in the long run.
In regards to the writer
Martin Finkbeiner is a mission supervisor on the Fraunhofer Institute for Manufacturing Engineering and Automation IPA. He may be reached at [email protected] and +49 711 9701046.
