DOF in engineering problems (1)
A reflection on verbal and visual skills to take advantage of the "degrees of freedom (DOF)" present in engineering problem statements.
To this end, some results of the challenge posed are used as an excuse to address these ideas:
https://grabcad.com/groups/weekly-challenge-group/discussions/a-mechanism-to-move-the-green-orange-rectangle
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Step 1: Problem statement
To begin to develop the idea of "DOF in engineering problems" we will see a simple example of mechanism design.
It is simply a matter of moving a rectangular figure between two given positions, for which the following problem statement is posed:
Let it be a rectangle with one side green (front) and the other side orange (back). Its initial position leaves the orange face visible, with its long edges in a horizontal position. Its final position leaves the green face visible, with its long edges in a vertical position. It is requested to design a mechanism capable of moving it between both positions.
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Step 2: Misleading aids
In engineering fields it is very common for a problem to be accompanied by antecedents, supposedly similar cases and even proposed solutions that end up being "misleading aids" that introduce fictitious restrictions.
Those reflect the personal interpretation (possibly unhelpful or even harmful) of the person who selected the antecedents and similar cases according to his experience, and was driven to "suggest, propose or even impose" possible solution styles.
This is not how problems should be posed, but in a pure way that does not condition the designer's mind. No matter how much we are warned that all this is just "additional information", the damage has already been done and it is difficult to ignore the additional restrictions that were introduced to the problem.
To illustrate this situation, the following "additional information" is presented:
To help visualize the problem, this rectangle can be thought of as an exotic garage door that moves between two of its walls, although such walls, floor, ceiling, and possible interferences with the rectangle are not part of the problem statement.
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Step 3: Distorted mental preparation
Solving a problem begins with a deep understanding of its statement. This allows us to gather the relevant mental resources (applicable knowledge and experiences) by retrieving them from our long-term memory and other external resources (books, videos, etc.) that will allow us to define a search direction (in an ocean of infinite possibilities) based on clear objectives.
We talked about this mental preparation in previous tutorials, with an analogy where a diver carefully prepares all of his equipment, and then launches himself in a certain direction of search in the immensity of the ocean. Although such an initial direction is not perfect, it should be a good starting point that, added to a systematic sweep, ends up perfectly exploring a limited area of feasible solutions.
Many designers often think while sitting in front of one of their best tools: CADD+CAE software. This has generally proven to be a big mistake in that it creates some anxiety about drawing before you have given yourself the time to analyze the problem statement, understand all its implications, and grasp its "degrees of freedom (DOF)."
DOF are "things that the statement does not prohibit" and leaves at the discretion of the designer. They are frequently distorted and converted into "fictitious restrictions" arising from prejudices, quick readings of the statement and a lack of systematization at this stage, which is responsible for the richness or poverty of the set of solutions achievable with the design process.
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Step 4: Proposals that do not solve
A typical consequence of misinterpreting statements is the generation of "design proposals that do not solve the problem" and may even include "premature attempts to define mechanisms", as in the following example:
This misleading proposal, with a defined appearance, does not meet the requirement of starting from a position that shows its orange side to reach a final position that shows its opposite side, green in the diagram provided to clarify the statement.
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Step 5: Intense but inefficient analysis
At other times it seems that the rules of good design art are followed, postponing attempts to design mechanisms and beginning the process with a "clean passage of the desired useful effect" using simple diagrams.
But again, if you did not pay enough attention to the statement and went directly to the drawing (even if it is schematic), it is normal to generate proposals that do not resolve, as in the following case:
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Step 6: Isolated solutions without notion of wealth
In other cases it may be possible to proceed correctly, paying close attention to the statement, avoiding premature definitions of mechanisms and technologies and using simple schemes, useful in subsequent analysis.
However, perhaps only "isolated solutions" are reached without having any notion of the richness of the entire "spectrum of solution concepts."
This does not detract from the merits of these solutions, but rather highlights the convenience of "seeing all of them" before rushing to just one. Especially because once a correct solution is reached, it becomes very difficult to break that mold and look for other alternatives (it is like a loss of motivation to search, once "something that works" has been found):
In this previous example, a correct "movement design" was proposed that meets the requirements of the problem statement, although without giving details about the artifact (mechanism) capable of providing it, which, with good judgment, was left for a later instance. in which "one of many mechanisms" capable of providing the previously designed movement was arrived at:
This animation reflects the expected behavior of the mechanism but, as it is not a true "motion simulation", it does not yet allow us to discover any operating problems.
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Step 7: Attraction towards the solution obtained
Once a solution is obtained, especially if it is isolated and without perception of the richness of the entire spectrum of solutions, it is possible to make the mistake of deepening its analysis early to discover and correct some errors.
All of this, which is generally a good thing, at this stage of the design leads to a certain attraction towards the solution obtained and the consequent "blindness" for the rest of the solutions.
After obtaining a good first result, it is natural to try to refine it (as in the following figure, which arises from a simulation of the movement) but this does not favor the exploration of other ideas.
The animation corresponds to the discovery of a conflicting point in the created mechanism that leads us to delve deeper into this solution to achieve a degree of improvement that, although positive, is not practical at this stage of the design:
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Step 8: Premature refinement
The aforementioned attraction towards the solution obtained increases even more to the extent that corrections are found for all its shortcomings, as shown in the following figure where the generation of ideas is abandoned to concentrate on pending aspects in a particular mechanism:
The blocking detected in the final position, when reversing the rotation of the drive motor, is an important distraction factor (like the tree covering the forest) that induces the search for premature refinement, which in this case implies the addition of a spring that helps to get out of neutral when the direction of rotation of the drive is reversed:
It must be taken into account that, in a large and complex problem, this type of adjustment can take a lot of time and effort to simply refine something that we still do not know if it is "the best we can propose."
That is, at this stage of idea generation, "fluidity" (number of ideas) and "diversity" (different types of ideas) are a priority and it is not yet time to address "quality" (complete development of the idea). "selected ideas").
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Step 9: Loss of opportunities
In a large and complex problem, the attraction to an isolated solution and its premature refinement can lead to the loss of the fundamental objective of the design process: to find "the greatest number and variety" of solutions possible.
Once this set of solutions (spectrum or domain explored) has been obtained, it is pertinent to begin a selection process that may include detailed analyses, if necessary to differentiate and validate solutions, but that do not seek to complete a particular solution before knowing if it is really valuable.
The difficult part of this process is deciding whether the domain of solutions explored is representative for the given problem, or whether we have only found "the best idea" but within a limited set outside of which there are missed opportunities.
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Step 10: Links
This tutorial comes from:
A mechanism to move the green-orange rectangle | Weekly Challenge Group
and continues in:
