Executive Viewpoints: Virtual site simulation and verification

  • 06-Nov-2009 05:06 EST
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Sameer M. Prabhu, Industry Marketing Director, The MathWorks

The increased adoption of electronics and electrohydraulic systems in off-highway equipment is driven both by legal requirements—including stricter Tier 4 engine emissions standards in the U.S. as well as sound-emissions regulations—and by increased customer demands on machine performance and productivity. The use of electronics also facilitates auto diagnostics features, which increase uptime and enable a broad range of safety features such as interlocks.

The key to realizing these benefits—for both the customer and the OEM—is the integration of individual electronic systems. This integration is also helping the move toward autonomous vehicles, such as agricultural machines that drive in a straight row without input from the operator. The next step will be machines of different types being integrated into a completely autonomous site-based system, a “system of systems.” The future will bring vehicles such as autonomous excavators that determine the next dig location and autonomous trucks that move the payload to a predetermined location for further processing. By 2020, these autonomous sites will be just as commonplace as the autonomous tractors today.

With traditional development processes, engineers rely on physical hardware to optimize designs and to verify and validate new concepts. However, adding electronics to an off-highway machine—which is already a nonlinear interaction of various systems and physical domains—further increases its complexity, which in turn makes machine prediction and performance optimization a difficult task. This increased design complexity exponentially increases the time and cost to test different design possibilities and makes it difficult to know when enough testing has been done to completely verify machine performance.

At the same time, manufacturers are facing increased competition, which demands lower development costs and shorter development times. To address these opposing pressures, manufacturers are adopting a holistic approach to designing these machines—increasing their use of simulation in the machine design and development process and moving from testing using “iron” to testing using virtual prototypes.

Over the past decade, domain-specific simulations at the component and system levels have become an accepted part of the machine development process for mechanical, hydraulic, and electrical components and systems. However, because these tools are domain-specific, it is difficult to assess the interactions between the various systems, significantly limiting the machine performance verification that can be achieved without hardware.

The only way to ensure that off-highway equipment would work as designed was to build physical prototypes. As any proving ground engineer can validate, debugging design problems on a prototype machine is one of the most expensive parts of the design process. If the design flaws are not detected through tests in this phase, and if these errors make it into production machines, they can result in astronomical costs in warranty, repair, and customer satisfaction.

The further a design error makes it through the development process, the more costly it is to fix. For this reason, catching errors early in the process, before metal is cut and products are shipped, is the lowest-cost way to develop off-highway machines. This realization is driving the current state-of-the-art toward simulation of complete machines in an integrated environment such as The MathWorks’ MATLAB and Simulink environment, which can cover multiple domains such as hydraulics, mechanical, electronic controls, etc.

Further, since the MATLAB and Simulink environment allows linking the machine requirements to the model, the test cases can be defined corresponding to the requirements, and the simulation results can be used to determine if the machine meets the requirements or not. In effect, the model is then an executable system specification for the machine.

Engineers can do some system-level simulations and use those results to achieve some level of verification independent of the availability of iron. Given the difficulties in simulating some of the complicated dynamics involved in earth-machine interactions, the method of verifying machine performance continues to be a mix of virtual and iron methods.

The future, filled with autonomous sites involving several of these vehicles, will demand a development environment where the individual machine performance and the interactions between various machines can be verified and validated without machine hardware. This environment will provide a platform for rapid design iterations to concurrently change various machine design parameters and optimize the overall site performance; through that process engineers can gain an understanding of how design decisions affect site and machine performance.

The result will be earlier design-error identification and the ability to address the machines’ effect on site performance. The biggest advantage this early verification will drive is that machine hardware will be built only after machine and site performance has been confirmed through simulations, reducing the cost and time spent building multiple prototypes.

Sameer M. Prabhu, Industry Marketing Director, The MathWorks, wrote this article for SAE Off-Highway Engineering.

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