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 all the time extremely repeatable. Absolute accuracy, however, usually leaves one thing to be desired. A workforce on the Fraunhofer Institute for Manufacturing Engineering and Automation IPA is uncovering the explanations for this and serving to firms to attain extra environment friendly robotic programs.
Repeatability and absolute accuracy are established parameters for assessing the standard and precision with which a robotic performs a selected job. If a robotic performs a selected job many occasions with nearly an identical 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. 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 tough 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 trade necessities.
Nevertheless, 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 functions 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 steadily 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 part, the following part may be programmed in parallel.
But when absolute accuracy is inadequate, the created program can’t be used straight. As a substitute, 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 stop using robots in sure functions. It additionally steadily results in extra work steps, such because the re-teaching, which reduces the effectivity of the whole 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, firms repeatedly flip to Fraunhofer IPA with the query of how they will enhance the efficiency of their robots by way of precision. The causes of inaccuracies are manifold and may be divided into hardware-related, software-related, and externally associated causes.
{Hardware}-related causes might 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 without doubt one of the fundamental causes for inaccuracy on the software program aspect, together with inadequate controller efficiency.
As well as, an rising variety of robotic programs are moreover outfitted with “cognitive” capabilities, notably these associated to notion. These so-called closed-loop programs work with sensors that detect the robotic’s atmosphere, and their software program processes the measured knowledge to regulate the robotic’s path accordingly. In such a system, poor sensor knowledge, 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 unfavourable affect on absolute accuracy.
The measurements made by these units have an accuracy of +- 40 µm anyplace within the working house. Supply: Fraunhofer IPA
Complete evaluation with new benchmark
If firms that use robots, in addition to the robotic producers themselves, are dissatisfied with absolutely the accuracy of their programs, the whole software must be examined and analyzed. As described above, a person investigation of the causes is important.
The automation workforce at Fraunhofer IPA is a impartial venture companion that may conduct this root-cause evaluation in a methodical method primarily based on in depth knowledgeable data and expertise.
In a typical venture, the workforce first information the present state of affairs utilizing sensor expertise 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 knowledge, 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 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 workforce has developed a closed-loop benchmark particularly for the closed-loop robotic programs talked about above. The benchmark is appropriate for robots from many producers. Within the benchmark, a reference-giving system, 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 every part that makes up a closed-loop managed course of or process. For example, this contains the efficiency of the whole 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 Expertise and Mechanical Engineering (CASE 2025).
With an correct robotic, the deliberate path may be executed with out handbook interplay on the true robotic. Supply: Fraunhofer IPA
Added worth of excessive absolute accuracy
A robotic with ample absolute accuracy can’t solely exchange costlier tools but in addition improve flexibility and decrease rework. In lots of functions, it subsequently is smart to research anomalies and enhance absolute accuracy.
A robotic that works exactly and reliably provides 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.
In regards to the writer
Martin Finkbeiner is a venture supervisor on the Fraunhofer Institute for Manufacturing Engineering and Automation IPA. He may be reached at [email protected] and +49 711 9701046.
