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Motor feedback systems

Supplier: SICK Pty Ltd By: Kathrin Kritzer, Motor Feedback Systems / Motion Control Sensors Product Manager, SICK STEGMANN GmbH, Donaueschingen
16 April, 2018

Electric power instead of oil, servo actuators instead of hydraulics – machines designed to reshape, press, or join workpieces in a fully automated manner are increasingly being equipped with mechatronic drive technology.

As well as considerably lower operating costs, users also see the infinitely variable control characteristics as a key benefit. Motor feedback systems like the SKS36 from SICK Stegmann, which Ortlieb Präzisionssysteme uses in its SERAC servo actuators, ensure precise and highly available path measurement and position control.

Processing workpieces and blanks of different strengths on one machine, performing several process steps in the same actuator movement, starting different machining positions steplessly and smoothly – there are numerous scenarios in which servo technology offers key advantages over hydraulic and pneumatic drives. “Mechatronic systems with motion control functionality are therefore becoming more popular,” explains Niels Selig, Drive Technology Product Manager at Ortlieb Präzisionssysteme GmbH & Co. KG in Kirchheim/Teck. “Here, we are seeing a change in attitude in the market both with new systems and retrofits, especially as servo technology offers a clear advantage compared to hydraulics and pneumatics when it comes to operating costs.” Precise and highly available path measurement systems – e.g., SKS36 rotary motor feedback systems with HIPERFACE® interface from SICK Stegmann – are used in servo actuators, such as those in the SERAC series from Ortlieb. This means that mechatronic systems can perform the reshaping and joining process with the highest level of accuracy and synchronisation is possible when several servo axes are used in one machine.

Ortlieb: “Precision Company” for clamping and servo spindle technology

For more than 100 years, Ortlieb in Kirchheim/Teck has considered itself to be a “precision company” for efficient and precise solutions in workpiece and tool clamping, as well as in drive technology. “A series of important DIN standards for clamping technology were developed on the basis of our developments and patents,” states Niels Selig. “From the standard collet right through to the one-off production of special clamping solutions, we offer flexible standard and customer-specific options from a single source.” The second, increasingly important pillar of the company is mechatronic assemblies and drive systems. In spring of 2017, this branch will move into one of the most innovative company buildings in Baden-Württemberg with the highest standards in terms of architecture and energy efficiency. The emphasis is on complete ready-to-connect and ready-to-install solutions made up of linear actuators which can be configured in a modular way. “The motor, spindle, encoder, and, if necessary, even a retaining brake, are fully integrated into the electric cylinder,” explains Niels Selig. The company's knowledge of spindle technology is behind the exceptional performance of the SERAC servo actuators.

SERAC servo actuators combine knowledge from space travel and mechanical engineering

True to the slogan “electric power instead of oil”, with its SERAC servo actuator series, Ortlieb provides innovative solutions for replacing hydraulic and pneumatic cylinders. There are different versions available with regard to housing design, motor version, anti-locking protection, or mounting options. What makes them so special is their high force density and stability. They stand the test – under the harshest conditions – in an extremely wide range of industrial punching, reshaping, and joining applications, as well as when pressing small parts. Special planetary roller screws, originally developed for space travel, form the technology behind the SERAC electric cylinders. They feature a reduced weight and make fine positioning possible without additional reduction gear. Ortlieb developed the ASCA servo spindle and prepared it for series production for use in mechatronic systems using the global patent from the DLR (Deutsches Zentrum für Luft- und Raumfahrt e. V. – German Aerospace Center) as a basis. The option of using the actuator spindles of many different SERAC versions with small increases of just a few millimetres makes it possible to start up operating points very precisely with the electric cylinders. This requires encoders which support suitable accurate path measurement and positioning, like the SKS36 motor feedback system.

SKS36 motor feedback system controls fine positioning

SKS36 motor feedback systems with HIPERFACE® interface from SICK Stegmann are used by Ortlieb in all SERAC product families. According to Niels Selig, one important constructive advantage is that: “Their compact design enables short overall motor lengths.” In fact, the housing diameter is just 36 mm thanks to the clever system construction – and the height without shaft is exceptionally small at just 37 mm. As a result, this motor feedback system, which weighs in at just 65 g, is one of the most compact encoders of its type. As a singleturn encoder system in the digital control circuit of the Ortlieb servo actuators, the SKS36 provides values for commutation and speed, as well as absolute position information, via a rotation, which is broken up into 128 sine/cosine periods. And it does all this with the highest level of reliability and accuracy, which is in part thanks to the very small code disc positioned in the middle of the rotation axis and which therefore prevents all types of eccentricity errors. On the code disc, there are 128 lines which are scanned by a specially developed opto-ASIC in such a way that sine signals arise with high linearity and interpolation capabilities. “This means that it is possible to measure the feed rate of the SERAC spindle very precisely and then use it for fine positioning,” explains Niels Selig. The reason behind this is that the planetary roller screws do not function using positive locking, but rather friction locking. According to Niels Selig: “As a result, much higher forces can be transferred without impairing the service life of the spindle. The slip which arises due to the principle used while the spindle is travelling requires an additional linear measurement system next to the encoder. Therefore, as a result of the interaction between the two encoder systems, positioning accuracies < 0.01 mm and repeatabilities of ± 0.01 mm are possible.” In this respect, the SKS36 does not just stand out because of its high level of accuracy, but also its high availability and ruggedness. “The maximum permissible operating temperature in the servo cylinders is considerably less than the specified 125 °C of the encoder,” states Niels Selig. “Vibrations and impacts which can arise when punching, reshaping, and pressing do not stop the SKS36 from functioning reliably. SERAC KH cylinders with these motor feedback systems can perform more than 40 million cycles at an interval of three seconds without any problems when reshaping sheet metal parts, for example.”

Multiturn and safety solutions for mechatronic systems

In Ortlieb electric cylinders, the SKS36 singleturn motor feedback system comes out on top thanks to its precision, easy integration, and availability. For tasks which require repeated rotary path measurement and positioning, the SKM36 multiturn motor feedback system provides the option of measuring up to 4,096 rotations with the help of the integrated micromechanical drive and displaying in a resolution of up to 16,777,219 steps.

When taking into account the safety considerations for mechatronic systems and drive technology solutions, the SKS36S and SKM36S SIL2 motor feedback systems from SICK STEGMANN are also highlighted as safe encoders in dynamic and precise servo control circuits. Both systems can be used in applications which comply with the SIL2 classifications according to EN 62061 and IEC 61508, as well as the performance level (PL d) according to EN ISO 13849-1. They, therefore, provide certified functional safety – in other words, the option of monitoring functions and function chains of servo actuators and mechatronic systems in a safety-oriented manner with regard to speed, direction of rotation, and downtime. As a result, motor feedback systems from SICK Stegmann offer numerous options for path measurement and positioning in mechatronic systems – and not just in Ortlieb electric cylinders.