ETHERCAT® INTERFACE simplifies Integration of wire draw encoders

17. August 2016

Perfect test stand precision

The Langenthal-based company Nencki AG is very meticulous when it comes to their bogie test stands. By using BTF08 HighLine wire draw encoders with an EtherCAT® interface and OD displacement measurement sensors, they can ensure that test criteria such as suspension stroke and wheel shoulder distance can be measured with absolute precision during final testing.



The high resolution means that both the OD Value and OD Mini displacement measurement sensors and the BTF08 wire draw encoder with an EtherCAT® interface can measure distances, deflections, and positions precisely, to within a fraction of a millimeter. However, the main advantage of the EtherCAT® encoder is that it can be seamlessly integrated into the bogie test stand’s Beckhoff controller. This saves Nencki from having to implement additional cabling and also allows for extensive diagnostic options – a feature highly valued by many customers.


Nencki test stands – ensuring train and tram safety


Nencki AG is a Swiss family-run company, active in the vehicle and plant engineering sector and also one of the world’s leading manufacturers of test stands for bogies in the field of railway technology. “The test stands are used by rolling stock manufacturers and maintenance and repair companies who work on trains, local transport, and underground systems. They are used to test and adjust the wheel loads and geometry of new, repaired, or serviced bogies based on specific requirements,” explains Josef Bieri from SICK in Stans, Switzerland, who supervises the project as Account Manager. To achieve this, hydraulic cylinders simulate various vehicle weights and the forces which act upon the bogie during motion, movement around bends, and side winds. The accurate adjustment of, to name but a few examples, distances, spacing, axle parallelism, wheel positioning and alignment, as well as suspension stroke and other parameters, optimizes driving comfort and minimizes wear and operating costs. Most importantly, this makes sure that trains and trams remain on the right track. Measurement, tolerance, and calibration data, collected, for example, whilst measuring the wheel shoulder distance with displacement measurement sensors, is recorded and can be accessed at any time.


Primary suspension testing with wire draw encoders from SICK


The BTF08 wire draw encoder measures changes in the Suspension stroke with an accuracy of ± 0.1 mm.

The BTF08 wire draw encoder measures changes in the Suspension stroke with an accuracy of ± 0.1 mm.

Nencki develops bogie test stands, such as the NBT Coach model for metro maintenance workshops, the SBB (Swiss federal railway), or high-speed trains traveling up to 350 km/h, from modular components and adapts them to suit the specific requirements of the customer. One of the key functions is the ability to ascertain and set equal load distribution for each wheel. According to Stephan Gudde from Nencki, this involves measuring each wheel’s load and establishing the primary suspension stroke using a total of four BTF08 HighLine wire draw encoders from SICK. The winding mechanism is stored in rugged metal housing. Dirt-repellent brush attachments on the wire input prevent dirt and dust from entering the mechanism. The encoder is used as a stroke measurement element and installed on the external part of the shaft of the cable drum using a servo flange. BTF08 encoders are attached to the frame of the test stand with magnets in order to test primary suspension. The encoder has a threaded loop which is attached to rods positioned in the upper part of the bogie. During the test procedure, the wire draw encoder measures changes in suspension stroke that occur as a result of influential forces, in terms of both distance and height. This must be accurate to within ± 0.1 mm. Suspension stroke and wheel load measurement results are used to automatically calculate whether the primary suspension of a specific wheel requires recalibration. This is accomplished by removing or adding washers, which harden or soften the suspension. The required thickness of these washers is displayed on the test stand screen.


Encoder interface expertise by SICK

Whilst the outlined measurement procedure has already proven successful in a number of test stands, Nencki required an encoder solution which could be directly integrated into the Beckhoff controller. “Thanks to our wide encoder interface portfolio, in this instance we were able to provide an appropriate solution featuring an EtherCAT® interface,” explains Carell Gerig, Application Engineer at SICK in Stans. In fact, SICK’s portfolio of single and multiturn encoders, as well as motor feedback systems, currently supports more than a dozen core interface standards in the field of industrial communication. The portfolio ranges from incremental interfaces, interface technology developed in-house, such as SSI, HIPERFACE®, or the HIPERFACE DSL® single cable technology, and fieldbus systems for production automation, such as DeviceNet, Profibus, and CANopen. On top of this, users can also use Ethernet-based fieldbuses, such as EtherNet/IP, PROFINET – and EtherCAT®. For Nencki, the implementation of the BTF08 wire draw encoder with an EtherCAT® interface means a significant reduction in integration measures. “We no longer need separate cabling,” explains Stephan Gudde. “What’s more, the encoder can be programmed from directly within the controller’s configuration interface, which considerably simplifies and speeds up the setup process.” Furthermore, a fieldbus integration opens up a wide range of diagnostic options which lower the encoder’s risk of failure and thus further optimize test stand performance. “This allows us to monitor encoder temperature, for example,” explains Josef Bieri. “If one of the specified minimum or maximum values is met, the encoder notifies the control unit directly of any potential critical operational statuses.” Fieldbus interfaces can also be used to add additional parameters to the diagnostic process, such as operating hours, programmable position thresholds as well as speed and revolutions.Ensuring safe travel on all routes – with displacement measurement sensors and EtherCAT® wire draw encoders from SICK, Nencki is sure to stay on track.



Displacement measurement sensors in action.

Displacement measurement sensors in action.



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