Construction of a REXS gearbox model



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V 1.2 Released

The standardized interface for the simple exchange of gear unit data

REXS (Reusable Engineering EXchange Standard)

FVA e.V., the German Research Institute for Drive Technology, is committed to the goal of developing an industry-wide standard for the simple data exchange in gear unit development. The interface is being developed in close cooperation with industry and research under the name REXS (Reusable Engineering EXchange Standard).

REXS defines an industry-wide uniform modeling and nomenclature for the gear unit and its components based on the detailed terminology of 25 of FVA's project committees. With many years of experience and close ties to industry and research, FVA is in a unique position to develop an industry-wide standard.

Machine elements currently included in the specification:

  • Shafts
  • Cylindrical stages and gears
  • Bevel stages and gears
  • Worm stages and gears
  • Planetary stages
  • Flank modifications and deviations
  • Rolling bearings
  • External loads
  • Shifting states
  • Load spectra
  • Lubricants
  • Materials
  • Tools

Along the entire tool chain

REXS offers a format for the exchange of gear data along the entire CAE tool chain in gear unit developement.

REXS: Many tools - One interface

Design principles of REXS

  • Free and open
    Non-proprietary, detailed documentation available for everyone free of charge
  • Comprehensive and explicit
    Model the complete gear unit including all available data (inputs as well as results). All components of the model should be modelled as explicitly as possible (“snapshot of a gear unit”)
  • Well documented
    All employed concepts, conventions and parameters need to be well documented to avoid confusion and misunderstandings
  • Standardized
    Use of specific, unambiguous definitions and general rules and conventions. Avoidance of special cases and exceptions. Based on the XML format.
  • Simple and generic
    The structure of the interface format as well as the underlying gear unit model should be as simple and generic as possible, depend on few meta-elements, allowing extensions of the model without introducing new sub-structures
  • Extendable
    It should be possible to extend the standardized interface with mutually agreed data. Thus, special requirements for the exchange of data between two software environments can be considered


In REXS, the components of a gear unit are defined based on common parameters. The REXS specification includes everything necessary to define a gear unit model. In essence this includes the machine elements, their attributes, and the relations which are used to define the relationships between machine elements.

Example: A bevel stage component with shaft angle and hypoid offset attributes
Example: A connection between shaft and gear components via an assembly relation
See the specification

Example REXS Models

The following example models in the REXS format were kindly provided by SEW and FVA GmbH.

SEW: 4-stage bevel-helical gearbox

Download V 1.0
Download V 1.1

SEW: 2-stage angular gearbox

Download V 1.0
Download V 1.1

SEW: 3-stage cylindrical gearbox

Download V 1.0
Download V 1.1

SEW: 3-stage parallel shaft gearbox

Download V 1.0
Download V 1.1

FVA: Planetary stage - Minus gearing

Download V 1.1

FVA: Planetary stage - Ravigneaux set

Download V 1.1

REXS | The Open Source Standard

The REXS standard is published under Creative Commons License CC-BY-SA 4.0 International

You are free to:

copy and redistribute the material in any medium or format

remix, transform, and build upon the material for any purpose, even commercially.

The only conditions are that the original author is named and that the modified specification is circulated under the same conditions.

The author is FVA GmbH.

Development of the Specification

The REXS interface is being developed in close cooperation with industry and research. The dedication of FVA members SEW-Eurodrive and Schaeffler and their many years of experience with gear unit software will ensure that the developed concept is applicable for the industrial environment.

Schaeffler Gruppe

"REXS is a real step toward new business models based on digital services, and can be used as a standardized data container for digital twins."

Stephan Evert, Head of Bearing Analysis Tools Development in the R&D Bearing division of Schaeffler Technologies AG & Co KG


"An important milestone for Industry 4.0 is the establishment and propagation of standards. The REXS format has the potential to achieve this goal."

Hartmut Rauen, Managing Director of FVA


"With REXS, gear unit data can be transferred quickly and reliably. Thus, the interface helps us to optimize our innovation processes."

Dr. Heinrich Bolz, Head of Calculation and Simulation in gear unit Development for SEW-EURODRIVE GmbH & Co KG

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