In the last post I proposed that the lions share of a products ultimate cost is locked in at the design stage and that much of that “cost of poor design” is driven by design conflicts.
Further, we took a look at the TRIZ methodology and identified two types of conflict: technical and physical. Today we are going to look at physical conflicts in design and how to deal with them.
A physical conflict exist when opposite properties are required of a product’s functions or elements. For example, a nail has the property”must move through wood” when it’s being installed and “must not move through wood” when it’s holding your house together.
Physical conflicts group into two structures;
Conflicts of magnitude exist when the product or system requires some characteristic to be at two levels of magnitude or strength. For example “coffee must be hot” to taste good and “coffee must be cool” to be safe and avoid lawsuits.
Conflicts of presence exist when some element or function has to be there and not be there. In the case of a draw bridge the roadway “must be there” to allow traffic to pass and “must not be there” to allow ships to pass.
So how do we deal with physical conflicts to reduce product cost?
TRIZ methodology posits three ways;
- Separation principles
- System transformations
- Phase Transformations
Let’s take a look at the first – separation principles
Separation in Time
The first question to ask when you’re confronted by a physical conflict is, “Do the opposing requirements have to exist at the same time?” The drawbridge mentioned earlier is an example of separation in time. The roadway “must be there” and it “must not be there” but the two states don’t have to exist at the same time. By forcing the cars to wait, the requirement can be separated in time and the conflict resolved. Perhaps not the most elegant solution but a good example.
Traditionally TRIZ only has one principle of separation in space but I’ve found it useful to break it into two.
Separation in Space (Location)
The second question to ask is, “Do the opposition requirements or conditions have to exist in the same location. The idea here is to think of the product in terms of subsystems and assign each of the opposing requirements to a different subsystem.
A good saute pan should “be massive” (like a cast iron pan) for good thermal properties and “be not massive” for easy of use. By asking this second question we realize that the “be massive” property has to exist only at the point of contact with the burner. This is the idea behind the light aluminum pans with a special heat plate attached to the bottom.
Separation in Space (Axis)
With problems involving motion or location I’ve found that it is also helpful to ask the question, “Can these opposing requirements be separated in their axis of operation. In other words, can the opposing requirement each be assigned to a different axis: X, Y, Z, Pitch, Roll, Yaw.
For the nail we talked about earlier if we assign the requirement of “must move through wood” to the roll axis and the “must not move through wood” to the Z axis we have a wood screw.
As a side note, this principle relates closely with another important tool in product cost reduction, namely exact constraint design.
The remaining two principles of separation require a bit more explanation so we’ll cover those in the next post.