Requirements by Geometry | Part 1

A regular challenge in developing complex systems is integrating requirements with mechanical design. When requirements governing system geometry are in text form, they are often easy to misinterpret. Sketches and other images may be simpler, but they are not model-based. Our objective is to pass requirements to the design engineer in a clear, model-based way, as a native CAD file that can become the starting point for the mechanical design. We call this “Requirements by Geometry”.

Syndeia, the MBSE interoperability platform from Intercax, provides a practical approach to building a Digital Thread connecting requirements to architecture to design. In this example, we will use Syndeia to federate a requirements model in Jama Connect (Jama Software), a SysML architecture model in Cameo System Modeler (No Magic), and a CAD model in Siemens NX. These are only a few of the engineering software tools to which Syndeia can interface.

unmanned-ground-vehicle-ugv

Figure 1 Example of an Unmanned Ground Vehicle (UGV)

For our example, we will consider an unmanned ground vehicle (UGV), a small multi-purpose robot used in both military and civilian applications for bomb disposal, reconnaissance, and other purposes. An example is shown in Figure 1. It has a double track drive and two arms, a front arm configured as a multi-axis manipulator and a movable rear arm holding sensors, such as a high-resolution video camera. An antenna mounted between them enables radio control by a remote operator. Figure 1 is provided solely for illustration; none of the modeling work described in this blog series represents a real product currently available or under development.

Managing Requirements in Jama and Cameo Systems Modeler

This blog series describes only a small part of our UGV model, which covers requirements, structure and behavior for both the multi-configuration UGV and its operating domain. Requirements are initially defined and maintained in a Jama Connect repository (Figure 2) and include functional, performance, physical and other requirement types.

ugv-master-requirements-repository-jama-connect

Figure 2 UGV Master requirements Repository (Jama Connect)

We can use Syndeia to create SysML requirements linked to the Jama requirements by model transform connections, which allow the linked requirements and their attributes to be compared and updated as the system development proceeds. We can choose to bring over all requirements in Cameo Systems Modeler (Figure 3), or we can be selective. For the purposes of this example, we are concerned with a limited set of geometric constraints.

  • Front arm and rear arm maximum extension and range of movement
  • Keepout zones, within which no portion of either arm is allowed to encroach
  • Transport configuration, defining the bounding box within which the UGV must fit during transport to and from the field of operations.

ugv-requirements-sysml-cameo

Figure 3 UGV Requirements in SysML (Cameo)

At this stage, all these requirements are only textual, e.g. “The 5 axis manipulator arm shall have a full extension of 500 mm”. In order to proceed with the design, the mechanical engineer must typically combine multiple text requirements, e.g. arm extension, arm mounting point coordinates, keepout zone position, and hope that their assumptions match the system architect’s expectations. This invites a better approach for defining the geometric requirements holistically before presenting them to the designer.

In the next post, we will look at defining one set of geometric constraints in SysML and using Syndeia to transform them into a native CAD file in Siemens NX.

For another example of the “Requirements by Geometry” approach, check out a publication from NASA JPL and Intercax at Architecture to Geometry – Integrating System Models with Mechanical Design, Bajaj, M., Cole, B., Zwemer, D. , AIAA Space 2016 Conference, Long Beach, CA, USA, Sep 13-16, 2016.

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Dirk Zwemer

Dirk Zwemer

Dr. Dirk Zwemer (dirk.zwemer@intercax.com) is President of Intercax LLC (Atlanta, GA), a supplier of MBE engineering software platforms like Syndeia and ParaMagic. He is an active teacher and consultant in the field and holds Level 4 Model Builder-Advanced certification as an OMG System Modeling Professional.