Motor Feedback Systems for Mechatronic Transmissions

Features such as compact and easy-to-install design, the reliable, capacitive measurement principle, HIPERFACE® as an industry-proven interface, and the no-battery, mechanical multiturn function persuaded Wittenstein, among the primary providers of mechatronic drive technology, to choose SICK’s SEM90 motor feedback system for its Galaxie® drive systems. Providing end customers with practical and remarkable advantages.

by Kathrin Kritzer

With a global workforce of around 2,600, 60 subsidiaries and sales agencies in around 40 countries, as well as sales of EUR 385 million in the 2017/18 fiscal year, Wittenstein SE is one of the leading providers of mechatronic drive technology. The group of companies operates in numerous innovative business fields with its own subsidiaries: servo gearboxes and servo drive systems, medical technology, miniature servo units, innovative gearing technology, rotative and linear actuator systems, nanotechnology, electronic and software components for drive technology, plus the Galaxie start-up.

Cutting-edge technology in machine manufacturing
Wittenstein’s Galaxie drive system was presented for the first time at Hannover Messe 2015, where it won the Hermes Award. Since then, Galaxie has been developed into a modular portfolio with a range of designs and variants, enabling it to be used in new applications with particular power or installation requirements. Accompanying its increasing market penetration, Galaxie has also established itself in scientific circles as an independent gearbox generation with superior technological principles. The key features – dynamic individual teeth, full-surface tooth contact, and the new type of bearing with a segmented outer race ring – make Galaxie an enabling technology for high-performance engineering. It is therefore ideal if the encoder system incorporated into Galaxie is also able to offer up the same performance features.
It was for precisely this reason that Wittenstein looked to SICK’s SEM90 motor feedback system from an early stage.

Easy-to-integrate motor feedback systems
With the new SEM90 multiturn (MT) systems for hollow shafts with a diameter of 50 mm, the SEM70 for 25 mm hollow shafts, and the SES90 and SES70 singleturn variants, SICK has further expanded its portfolio of linear and rotative motor feedback systems for direct drives and hollow shaft motors, such as those used in handling systems and robotics applications, for example. Their flat design and the fact that they are simple to mount directly on the motor shaft without the need for special tools means they reflect the trend toward increasingly space-saving and easy-to-integrate drive solutions.
In particular, the compact design of the SEM90 aligns perfectly with the approach of the Galaxie drive system in terms of providing maximum power density.
The same is true of the high level of accuracy seen in the SEM90, which also fits perfectly with the precision and repeat positioning accuracy of the Galaxie gearbox kinematics of just four arc seconds.
Encoders used in robotics applications and handling systems
The new SEM90 motor feedback system – just like its “little brother” the SEM70 – is a hollow shaft encoder with HIPERFACE interface for direct drives and drive systems, such as those which are increasingly being used in robotics applications and handling systems. The way in which the system determines distance, speed, and position at maximum speed – 6,000 rpm for the SEM90 and 8,500 rpm for the SEM70 – is based on a capacitive measurement principle with a bearing-free sensor element. This design principle doesn’t just afford the SEM90 a high degree of accuracy, it also means it is extremely rugged: neither shocks and vibrations, nor dust, moisture, or magnetic fields in the operating environment will prevent it from working reliably.
In terms of its measurement principle, the motor feedback system provides its signals as 64 sin/cos periods per revolution, allowing it to be con-trolled effectively, which in turn helps ensure the precise movements of swivel axes, for example. The mechanical multiturn function with up to 4,096 revolutions – available in this kind of design for the very first time – enables operation without an additional energy supply. This means less wiring is required from the encoder to the battery in the control cabinet, which also saves space. Fewer components also mean the risk of failure is reduced, and fewer interfaces mean less tuning is required. Above all, however, the maintenance work associated with battery-assisted encoders is eliminated for the end customer of the machine builder. What’s more, encoder systems with buffer batteries have a further disadvantage, one which isn’t always immediately considered. Lithium-ion batteries are classified as “dangerous goods” under international transport law and are therefore subject to the various packaging, labeling, and transport regulations for the carriage of dangerous goods, including when they are installed in the motor feedback system and drive.

Easy and quick mounting directly on the motor shaft
The developers of the SEM90 have also taken the system to the next level in terms of how easy it is to mount and integrate. Just attach, secure, turn until it engages, and you’re done. With their flat design measuring just 24 mm in height, the new motor feedback systems can be mounted directly on the motor shaft, quickly and easily without the need for special tools. This met with a great response from Wittenstein when the first prototypes were in-stalled during the test phase, especially as no transmission elements such as timing belts or couplings are required. Although installation errors are essentially ruled out, the SEM90 nevertheless offers the additional option of reading out the rotor position using the PGT11-S programming tool following installation of the motor feedback system, as this provides a reliable means of detecting any mounting errors during the end-of-line test before the motor is delivered. The fact that the motor feedback systems are equipped ready for HIPERFACE DSL one cable technology – the integrated ASIC is also designed accordingly – means that they can be incorporated into the sHub®
multi-sensor-compatible automation concept from SICK. This further enhances the system’s ability to meet future requirements, as the additional operating data provided by the encoders can be used for condition monitoring purposes.

(Kathrin Kritzer is Motor Feedback Systems/Motion Control Sensors Product Manager at SICK STEGMANN GmbH)