Whats Is Systems Engineering in CAD ?
Introduction
Real designers usually admit that CAD is used more for documenting
the design than developing it. We need to rethink the design process
now that we have all these exotic computer based mechanical design
tools. This paper only begins to examine the concept of systems
engineering, what it is, what it is not, and explores how such a concept
might be used for future designs based on requirements.
Background
As a young designer, fresh out of Rutgers University, with my newly
minted BS degree, I worked on a project at Bell Telephone
Laboratories designing the hardware and software for the latest
electronic switching system. This project involved more than 1200
engineers furiously working toward the delivery of an operational
system, within a very tight deadline.
We were organized into development teams, each with about 10-12
engineers, and each working on a piece of the overall project. My team
was developing a portion of the real time operating system. My little
piece was developing the software to scan sensors that detected when
each subscriber required dial tone. Obviously, this was just one of
many steps required to complete a complex call across the network, all
of which would be controlled by duplexed central computers.
Periodically we were visited by representatives of the systems
engineering department, a mysterious group that appeared to be the
design overlords. I didn’t, at the time, understand why they were so
interested in the behavior of my little piece of software. Of course, it
turns out that by analyzing all the “little pieces of software” they were
able to simulate whether the system would even work at all!
It turns out that software design is often developed using systems
engineering, often a requirement for DoD work. Of course, software
appears to be a two dimensional system, as opposed to mechanical
design, which is a multi-dimensional system.
What is it – definition?
Systems Engineering is concerned with the effective design of reliable
systems within cost and time constraints. Systems Engineering applies
an appropriate combination of theories and tools, carried out through
the use of a suitable methodology and a set of system management
procedures, to address real world problems that are often of large
Systems Engineering in CAD
scale and scope. Systems engineering activities vary from
requirements definition or specification to the conceptual and
functional development of systems.
In dealing with the various phases of the system life cycle, the
systems engineer’s perspective is different from that of a product
engineer or technology developer. Whereas the product engineer deals
with details, the systems engineer takes a “top down” perspective
dealing with details only as needed to guarantee successful
implementation. Whereas the product engineer deals with system
internals, the systems engineer also addresses the external view of the
system through the system’s interface to other systems, users, and
managers. A systems engineer needs a unique perspective on the
system and its life cycle.
My design concept
I envision a subsystem where the behavior is specified. A sub-system
that can be designed and tested to satisfy that behavior. One where,
even if the behavior changes, it can re-configure itself to match the
expected behavior. Such behavior can extend beyond design into
manufacturing, deployment, and end-of-lifecycle treatment.
Today’s systems are quite facile at making geometric changes driven
by parameters. But sub-systems are connected using only geometric
mating constraints. If these mating constraints change how is the
corresponding sub-system to react? For instance, suppose two co-
linear shafts connect via a coupling. Suppose one shaft increases in
diameter. How is the coupling or shaft supposed to change? I can
envision embedding each connection with knowledge rules that can
determine this, BUT such rules only work for predetermined changes!
And a rule would have to be written for every connection. Clearly this
is impossible. On the other hand, knowing the characteristics of the
coupling might enable the system to compute such a change. Yet
mechanical systems have no way to describe what happens at each
interface.
Several problems exist in making such a concept operable.
•
No language exists to clearly define what sub systems do.
Consider even the simplistic case of a bolt. We know it has
thickness, thread pitch and depth, and material type. But what
does it do? How does its performance change as its parameters
and characteristics change?
•
Beside geometry, changes include operational characteristics,
geometric sizing and tolerances, external stresses and reactions,
motion behavior, etc. These changes are quite complex to
describe, in fact, often impossible to describe with a regular
language. Think about many systems that can only be described
using non-linear charts, such as RPM vs. power output.
Is this new?
Not really. It is just done manually, if at all.
Who is working on it?
ANSYS – CADOE (behavior and prediction analysis); EDS PLM
Solutions -Slate (requirements); Integrated Chipware – RTM
(requirements management); Telelogic – DOORS (requirements
management)
Discussion topics:
Does the technology exist today?
What would be the benefits?
What tools might be needed?
Sub-system performance definition language?
Considering sub-system interface actions and their interaction
with “connected sub-systems”
Analysis
Kinematics
Predictions tools
About the author
Raymond Kurland is president of TechniCom, Inc, a market research
and consulting firm specializing in the mechanical CAD/CAM market.
TechniCom’s CAD/CAM Vendor program offers many CAD vendors
insight on where the market is and where it is going. Ray authors
many papers and reports on the industry and is the editor of the
TechniCom eMonthly. If hes not here he can be reached at [email protected].
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