Where your CAD structure mimics your org chart.
Case Study – Top-Down Design in practice with outstanding results.
ResMed S8 Flow Generator & H3i Humidifier, Courtesy of the Power House Museum, Sydney
In a former life, almost20 years ago to the day, I was working as part of the design team at ResMed on the S8 Flow Generator and H3i Humidifier project.
I introduced the Top-Down Design (TDD) methodology which led to the making of the 2006 ‘Design of the Year Award’ recipient.
The Industrial design challenge was for the Flow Generator to look complete as a stand-alone product, but also integrate seamlessly, for both fit and form, airflow and connectivity with the H3i Humidifier.
The group was divided into two teams to design each half of the product, the S8 and the H3i.
This allowed the separate teams to focus on the intricacies that each half required, but all tied together by the control of the Design Lead, (DL) with the methodology of top-down design using a top-level skeleton.
The DL controlled the overall form and the interactions between the halves’ so their connection would always be seamless.
Published Geometry was passed down into the sub-assembly skeletons for each half of the product. From here each Team Lead (TL) was able to control the interactions of parts within the assembly under their care, safe in the knowledge that they would always work seamlessly with the product as a whole.
The top level skel is a living CAD file that is stretched and flexed as required as the unknowns of the internal components become known for fit and form and the shared interactions with other parts.
It also grew as interactions are defined and geometry published to the sub-assemblies and parts.
As the parent Top Level Skel was flexed, the changes were passed down through the assembly structure to regenerate the children to ensure they had the latest geometry.
This is a constant process as the product evolves with the required adjustments. Communication passed up the org chart and CAD geometry changes passed down the model tree.
For a Top-Level Skeleton, the key is how much to geometry to include.
Too much and the skel becomes heavy and cumbersome.
From an org chart point of view, this can lead to a loss of autonomy for the part designers. Having to go to the DL for a Top Level skel alteration for a simple geometry change isolated to a lower part becomes a hinderance to efficiency and calm team moral.
Too little geometry in the Top-Level skel and the DL loses control of the subcomponent interactions. These are often only discovered with an interference check or worse by prototypes that don’t fit together.
The rule that I have found to work is push shared geometry as far down the assembly/part hierarchal tree as possible where the interactions are controlled efficiently.
Again, mirroring the org chart of the design team, giving each designer autonomy safe in the knowledge of the parts place within the whole.
The result was a product awarded 2006 ‘Design of the Year Award’ accolade
Posted with permission from ResMed.
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