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Precision sensors for motor feedback

Precision sensors for motor feedback

06 May 2019
Interview article: Safety, precision, and a high degree of integration with magnetic sensors for motor feedback systems

SIKO GmbH: In the discussion, Andreas Wiessler, MagLine division head at SIKO, explains what is special about the motor feedback applications as well as their degree of significance for robotics and particularly for direct drives.

What are the advantages of magnetic motor feedback systems?

A: First and foremost, it’s the compact designs we offer. For rotary applications, for torque motors (direct drives) for example, the technology can be used to outfit shafts with a relatively small diameter, usually with a hollow shaft throughout, with sizes starting at about 35 millimeters. In principle, the sky’s the limit. With our technology, we are capable of realizing extremely compact, bearing-free systems. This should in principle allow us to integrate the encoder technology directly into very slender robot arms. Magnetic position sensors are generally highly resistant to outside influences such as soiling or even vibration and shock. This opens up a wealth of applications to the user, for example for facilities and systems located outdoors or even in processing machines with a relatively high degree of soiling. Compared to optical systems, the measuring precision is somewhat lower as a result of physical factors, but the resolution and repeat accuracy now meet almost all requirements for highly dynamic operation of systems. For many applications, the technical and commercial advantages of magnetic motor feedback systems outweigh the disadvantages anyway.

What kinds of applications are there? In the field of robotics for example.

A: In the broadest sense, it is handling technology. Robot arms are an area of application where multiple axes can be moved at the same time. But there are also plenty of potential applications in handling automation, where rotational and linear movements interplay, such as with pick & place, all PCB semiconductor processing, or assembly systems, such as for modern smartphones, which are produced fully automatically there. These are generally rotatable axes. Torque motors are one of the technologies used here, which are little compact units driven directly that rotate 360 degrees, usually in combination with linear systems consisting of direct-drive linear axes.

What makes a difference in these applications?

A: What the user needs in these areas is high dynamics and reproducibility. What we’re talking about here is repeat accuracy, and this is especially important, since parts might, for example, always have to be removed or placed in the same place quickly, precisely, and exactly, like when you are assembling a PCB board or with blank cutting machines where multiple small circuit boards are cut out of one big board. These are applications that demand a high level of precision and repeat accuracy. However, these are often the very applications in which dirt is produced, for example through plastic chips and dust. The advantage of our systems is that they are not disturbed by such external influences – they always meet the specifications. So there really aren’t any sacrifices when it comes to our requirements or the specifications that we offer.

What challenges do you face when developing the systems?

A: Our technology has to be more and more compact, since the applications are always getting more compact. Another factor is the realization time of our systems, which we need to coordinate with the customer’s needs. This doesn’t mean it has to be finished in four weeks, but time periods of a few months are pretty common for implementing a project from the idea through to the finished solution. It’s important that we are able to rely on technologies that we have a handle on ourselves, meaning benchmarking technology as well as electronics. We are, however, always trying to offer the customer a functional system relatively quickly – the standard items from the catalog can of course be delivered at short notice. A rapidly growing proportion of our orders and solutions, however, are now customized for the customer. In the simplest of cases, the system just has to be adapted to the customer’s design.

What role do the issues of precision and safety play?

A: In general, safety is of course an important factor that also plays a big role in the development of our products. We developed the first absolute measuring magnet sensor available with an open construction that is certified according to SIL2 – the magnet sensor MSA111C. If such a machine component is already safety-certified itself, this simplifies the safety assessment process for the entire system. We will be expanding this series even further. Being able to offer such a high degree of integration is an enormous advantage. Ever more frequently, there are specific customer requirements that just can’t be met with the standard technology available on the market. So it is rare to be able to fully adapt designs or developments accordingly. That’s the advantage that we bring to the mix: With our many years of experience, we have in principle a full machine outfit that we can use to develop benchmarks as well as encoder technologies ourselves. This means we aren’t dependent on external partners and have a great deal of potential that we can use for creation.

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