Verification or Validation phase: A production run is simulated to assure manufacturability of the design.
These phases are illustrated in the figure below.
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A model-driven development process used in the context of a DFSS methodology can play a vital role in ensuring that the CTQs defined in the Customer Analysis phase are met in the final Verification phase. In the figure above, this approach is implemented using the Mentor Graphics' tool SystemVision with a Minitab statistical application add-in that provides access to SystemVision's virtual prototyping capabilities.
SystemVision is a mixed signal, multi-discipline modeling and simulation environment that enables virtual integration of all the technologies shown below.
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Concept Analysis phase: Throttle control-loop example
At the beginning of the Concept Analysis phase, engineers create functional-level models in SystemVision. These models implement executable specifications that correspond to the measurable CTQs defined for the product in the Customer Analysis phase. The executable specifications define measurable behaviors for each of the CTQs, and these measureable behaviors are then used to help determine if the CTQ specifications are being met.
For example, a CTQ for a new automobile may specify that if the gas pedal is pressed, the car must accelerate smoothly within 50 milliseconds (ms) with no noticeable lag. This CTQ places requirements on various systems in the vehicle, including the drive train and the throttle controller.
The acceleration of the vehicle is likely to be most sensitive to the behavior of the throttle system and its controller. These responses can be represented at the functional level as a behavioral model that includes the throttle pedal sensor, the electronic throttle electromechanical actuator, the throttle position sensor, and the feedback control algorithm. When a step input signal moves the throttle plate in the model to a certain angle, a signal is produced with a measurable risetime and overshoot.
One of the first tasks in the Concept Analysis phase is to determine how the acceleration requirements specified in the CTQ correspond to the measurable behavior of the throttle plate on the engine. Design engineers need to specify how CTQ requirements for "smooth" acceleration "without lag" can be related to the risetime and overshoot of the angle of the throttle plate over time.
A reasonable assumption might be that a risetime of 25 ms (the time for the throttle plate angle to move to a specified value) corresponds to a 50 ms overall acceleration of the vehicle, taking into account losses in the drive train and other systems that aren't included in the throttle controller.
The CTQ requirement for "smooth" acceleration is associated with a specification for the vibration and range of motion of the throttle plate (as measured by the angle of the throttle plate). Specifically, if the angle of the throttle plate overshoots the proper final position and oscillates as it settles to the proper value (as shown below), then the acceleration may not be considered "smooth."
On the other hand, some level of overshoot may be acceptable, especially if it allows the response time to be faster. This specification can be precisely captured by providing a maximum overshoot value for the throttle plate angle in response to a step-function input. The figure above shows an example of such a measurement on a waveform.