Excessive-precision robots: What to do when absolute accuracy is poor?

Robots are nearly all the time extremely repeatable. Absolute accuracy, then again, usually 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 attain 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 activity. If a robotic performs a selected activity 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 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, equivalent to within the manufacturing of small batch sizes. When welding an meeting, for instance, it’s significantly essential 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 just some tenths of a millimeter can considerably impair high quality and even result in rejections. Absolute accuracy just isn’t solely essential for robot-based welding, but additionally for purposes equivalent 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 steadily 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 of the robotic sustaining operation whereas programming is carried out. Subsequently, whereas the robotic is processing one part, the following part 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 mandatory, 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 might restrict and even forestall using robots in sure purposes. It additionally steadily results in further work steps, such because the re-teaching, which reduces the effectivity of the whole manufacturing chain. In lots of industrial eventualities, an absolute accuracy that’s much like the repeatability is fascinating and even required.

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Causes for a scarcity 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 by way of precision. The causes of inaccuracies are manifold and could be divided into hardware-related, software-related, and externally associated causes.

{Hardware}-related causes could embody the design of the robotic, equivalent 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 principal causes for inaccuracy on the software program facet, together with inadequate controller efficiency.

As well as, an rising variety of robotic techniques are moreover outfitted with “cognitive” capabilities, significantly 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 knowledge to regulate the robotic’s path accordingly. In such a system, poor sensor knowledge, a low-performing controller, or suboptimal interplay between the elements within the robotic cell normally trigger issues.

Lastly, exterior elements equivalent to temperature and air stress, but additionally course of forces that happen, can have a destructive impression on absolute accuracy.

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, the whole utility must be examined and analyzed. As described above, a person investigation of the causes is critical.

The automation crew at Fraunhofer IPA is a impartial undertaking companion that may conduct this root-cause evaluation in a methodical method primarily based on in depth knowledgeable information and expertise.

In a typical undertaking, the crew first information the present scenario utilizing sensor expertise such because the Leica Absolute Tracker AT960 to create a stable 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 specialists examine the reason for the undesirable conduct. 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 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 look at the whole lot that makes up a closed-loop managed course of or process. For example, this consists of the efficiency of the whole robotic cell, together with the sensor expertise 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).

Added worth of excessive absolute accuracy

A robotic with ample absolute accuracy cannot solely exchange costlier gear but additionally improve flexibility and decrease rework. In lots of purposes, it subsequently is smart to research 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 undertaking supervisor on the Fraunhofer Institute for Manufacturing Engineering and Automation IPA. He could be reached at [email protected] and +49 711 9701046.