With high gear and years of expertise, Fraunhofer IPA will get to the foundation causes of inaccurate robotic operation. Supply: Rainer Bez, Fraunhofer IPA
Robots are virtually all the time extremely repeatable. Absolute accuracy, alternatively, typically 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 realize extra environment friendly robotic techniques.
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 superb 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 shouldn’t be an issue for some functions, 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, resembling within the manufacturing of small batch sizes. When welding an meeting, for instance, it’s notably necessary that the wire tip is positioned exactly within the middle of the weld seam. Actual positioning leads to high-quality weld seams that meet trade necessities.
Nonetheless, deviations of only a few tenths of a millimeter can considerably impair high quality and even result in rejections. Absolute accuracy shouldn’t be solely necessary for robot-based welding, but additionally for functions resembling 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 true robotic. The benefit lies in the potential for the robotic sustaining operation whereas programming is carried out. Due to this fact, whereas the robotic is processing one element, the following element might 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 essential, 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 functions and might restrict and even forestall using robots in sure functions. It additionally continuously results in extra work steps, such because the re-teaching, which reduces the effectivity of your entire manufacturing chain. In lots of industrial situations, an absolute accuracy that’s much like the repeatability is fascinating and even required.
Causes for an absence 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 by way of precision. The causes of inaccuracies are manifold and might be divided into hardware-related, software-related, and externally associated causes.
{Hardware}-related causes might embody the design of the robotic, resembling 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 without doubt one of the important causes for inaccuracy on the software program aspect, together with inadequate controller efficiency.
As well as, an rising variety of robotic techniques are moreover outfitted with “cognitive” features, notably these associated to notion. These so-called closed-loop techniques 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 resembling temperature and air strain, but additionally course of forces that happen, can have a detrimental affect on absolute accuracy.
The measurements made by these units have an accuracy of +- 40 µm wherever 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 techniques, your entire software needs 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 mission companion that may conduct this root-cause evaluation in a methodical method based mostly on intensive professional data and expertise.
In a typical mission, the group first information the present state of affairs utilizing sensor know-how such because the Leica Absolute Tracker AT960 to create a strong database. The laser tracker information 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 beneficial insights. In an additional 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 group has developed a closed-loop benchmark particularly for the closed-loop robotic techniques 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 the whole lot that makes up a closed-loop managed course of or process. For example, this consists of the efficiency of your entire robotic cell, together with the sensor know-how and the meant 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 might be executed with out guide interplay on the true robotic. Supply: Fraunhofer IPA
Added worth of excessive absolute accuracy
A robotic with enough absolute accuracy can’t solely change costlier gear but additionally improve flexibility and reduce rework. In lots of functions, it subsequently 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 subsequently a strategic choice that pays off in the long run.
In regards to the creator
Martin Finkbeiner is a mission supervisor on the Fraunhofer Institute for Manufacturing Engineering and Automation IPA. He might be reached at [email protected] and +49 711 9701046.
