With high gear and years of expertise, Fraunhofer IPA will get to the basis causes of inaccurate robotic operation. Supply: Rainer Bez, Fraunhofer IPA
Robots are nearly all the time extremely repeatable. Absolute accuracy, alternatively, typically leaves one thing to be desired. A crew 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 particular process. If a robotic performs a particular process many instances with nearly 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’s typically nonetheless room for enchancment. Sometimes, values between 0.5 and 1.5 mm are achieved. This tendency towards inaccuracy just isn’t an issue for some purposes, 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, reminiscent of 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 heart of the weld seam. Actual positioning ends in high-quality weld seams that meet trade necessities.
Nonetheless, deviations of just some tenths of a millimeter can considerably impair high quality and even result in rejections. Absolute accuracy just isn’t solely necessary for robot-based welding, but in addition for purposes reminiscent of 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 incessantly 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 potential for the robotic sustaining operation whereas programming is carried out. Due to this fact, 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 a substitute, time-consuming corrections are obligatory, 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 due to this fact inadequate for complicated purposes and might restrict and even stop the usage of robots in sure purposes. It additionally incessantly results in further 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 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 could be divided into hardware-related, software-related, and externally associated causes.
{Hardware}-related causes might embody the design of the robotic, reminiscent of 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 aspect, together with inadequate controller efficiency.
As well as, an growing variety of robotic techniques are moreover geared up with “cognitive” features, notably these associated to notion. These so-called closed-loop techniques work with sensors that detect the robotic’s surroundings, 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 normally trigger issues.
Lastly, exterior elements reminiscent of temperature and air strain, 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 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 utility ought to be examined and analyzed. As described above, a person investigation of the causes is important.
The automation crew at Fraunhofer IPA is a impartial challenge associate that may conduct this root-cause evaluation in a methodical method primarily based on in depth knowledgeable information and expertise.
In a typical challenge, the crew first information the present scenario 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 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 additional step, the consultants 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 crew 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 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 things that makes up a closed-loop managed course of or process. For example, this contains the efficiency of your entire robotic cell, together with the sensor know-how and the supposed 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 could be executed with out guide interplay on the actual robotic. Supply: Fraunhofer IPA
Added worth of excessive absolute accuracy
A robotic with ample absolute accuracy cannot solely change costlier gear but in addition improve flexibility and reduce rework. In lots of purposes, it due to this fact 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 due to this fact a strategic resolution that pays off in the long run.
In regards to 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.
