The Best of Two Worlds

The phrase 'jack of all trades' is often used negatively because the whole expression reads 'jack of all trades but master of none', meaning that the person or product can do a bit of everything but nothing properly. The drive controllers by SIEB & MEYER impressively prove the opposite. These devices not only integrate the functions of frequency converters as well as servo drives in equal measure but do so at the highest level and as a logical consequence in their technical specifications.

For several decades now, SIEB & MEYER has been developing and selling both frequency converters and servo drives. The focus here is on high-speed applications for the frequency converters and on high-dynamic positioning applications for the servo drives. Around 20 years ago, this led to the situation that the two application fields were supplied with identical devices. This works because SIEB & MEYER uses suitable measuring and control technology for each use case to reach the application-specific control properties.

But why is that not common practice? The reasons for separately supplying frequency converters and servo drives in the standard sector are mostly linked to the price, since the volume manufacturers focus on mass applications such as conveyor belts or ordinary motion axes. These simple applications usually have low demands on control technology so that it pays off to use frequency converters or servo drives with the hardware and software reduced to a minimum. "The servo drive is always the component of higher quality," said Torsten Blankenburg, CTO at SIEB & MEYER. "As a rule, a servo drive can also be a frequency converter but this changeability costs money and requires a very large overhead. Therefore, the costs for a standard frequency converter are generally lower than those for a servo drive. And that results in separate devices."

Typical requirements of high-dynamic applications

This is not an option for the applications SIEB & MEYER focuses on. In order to reach the required system properties, compromises are not possible with either the hardware or the software. "We are talking about the high-speed range and we need suitable measuring equipment in our devices and dynamic control technology," explained Torsten Blankenburg. “That means we need exactly the features that sum up the servo drive for our frequency converter applications. In addition, both sectors require such a high performance that different hardware for the two components is not practical in our niche.”

SIEB & MEYER servo drives typically work in applications with a power range between 7 and 8 kW. Load peaks are characteristic for high-dynamic applications. Therefore, the output stage of the smaller drive controllers features high overload capacity, which is for the benefit of the servo applications but not required in frequency converters. In the higher power classes, SIEB & MEYER forgoes the high overload capacity because the company does not supply typical servo applications in this range. SIEB & MEYER rather supports high-speed motors in the high-power range – i.e. typical frequency converter applications – with its drive controllers. These applications demand a high rated current but the peak current must be only a little higher.

"Our smaller devices stand out for their high rated current to peak current ratio," said Torsten Blankenburg. “There, the bandwidth decreases as the power increases. This specification corresponds to our customers' requirements for frequency converter and servo applications. Of course, there are servo applications with 100 kW and more but these belong to another niche that we don't supply at present.”

The main differences and similarities of the requirements for frequency converters and servo drives in the different application areas you will find in the table at a glance. It makes clear that the properties of high-speed motors and high-dynamic servo axes are quite similar. This supports the SIEB & MEYER concept not to develop separate hardware but a universal drive controller that is suitable for both worlds via specific software settings.

Users benefit from reduced equipment variety

With its drive controller concept, SIEB & MEYER reduces the component variety not only in-house but also for the customers. The user obtains a highly efficient high-speed frequency converter with the added feature of a servo drive. Therefore, the same hardware can be used, for example, in a machine tool for high-speed processing to cover both areas of application. This reduces the manufacturer and device variety as well as the number of spare parts to be kept in stock. "Especially in machine tools, you always have both application worlds," explained Torsten Blankenburg. "The processing spindle requires a frequency converter; the motion axis requires a servo drive. And our drive controllers can optimally operate both applications."