Introduction to the engineering process

Introduction

The modern world is largely shaped by technical objects and machines. If you look around, all non-natural artifacts have been created, designed and/or engineered: the chair you sit on, the roof above you and the car, bus or train that drives you home.

The person responsible for the technical properties of those objects is likely to be an engineer. His job begins with a (sometimes vague) description of the intended function, and ends with a set of drawings, ready to be produced and assembled. The process in between is called engineering: transforming requirements about the intended function/behavior into the final shape of an artifact. An example is shown in the figure, where the intended function leads to the technical drawing used for production of a car.

Consider the car: if everything is done well, the first time the ignition key is turned, the car starts immediately and is ready for use. But is the wheel suspension properly designed? Is the steering mechanism free of slack? Will it break down after 2 months, 2 years or 2 decennia? Shouldn’t the windows be a little thicker, to be much stronger? How long before the exhaust pipe breaks? What if those small springs in the middle of the engine break down after 30.000 kilometer because the engineer chooses the wrong material? What if the car does not even start?

If you buy that car, and drive it at 120km/h, you hope everything has been engineered well and all decisions the engineer took are the right ones.

Therefore, it is of the utmost importance to have highly skilled engineers who guarantee the required quality.

In the current economical and industrial environment, the market increasingly demands high quality, high flexibility and short response times. If costumers want a new and improved model of the Volkswagen Rabbit every couple of years, it shall be done. Engineers: work faster! This leads to a continuous pressure on the efficiency of the engineering process: better products designed in less time.

What is this engineering process? This is explained in the following section.

The engineering process

In this section, an illustrated example of the engineering process is given: what is the procedure and which steps are taken. This example handles the engineering process of the mechanical part of the problem.

The engineering process is initiated by a problem which needs a solution. In this case, garbage containers have to be emptied into the truck automatically.

First, the client explains his problem and what he would like to have as a solution. Although the client describes this as detailed as possible, this usually proofs to be an incomplete specification. During the engineering process, it is possible that specifications are added or changed.

For now, the problem description could be as follows:

A number of round garbage containers have to be transported towards the opening of the truck, which is located on top. The dotted arrow indicates the required trajectory. Since the truck has to drive around, the construction has to be attached on the truck.

The engineering process consists of the following stages:

1 Requirements.

The engineer translates the problem description into a more technical description of the problem. This contains technical data which describe the problem and what function should be fulfilled (in this case, transport the garbage cans over a specified trajectory). These are called the functional requirements.

2 Synthesis

Next, solutions have to be found to solve the problem. The experienced engineer starts thinking of several principles. He quickly rules out solutions like 20 employees all working together to pass the garbage cans overhead is probably too expensive.

From experience and books he knows that bar mechanisms are capable of describing trajectories. Such a mechanism consists of (steel) bars and hinging points. In the figure, a bar mechanism is shown in rest. After applying a force, it will move. The trajectory of one point is given. A real live example of a mechanism can be a crane, used to unload ships. A sketch of that mechanism is shown, with the trajectory.

Knowing a thing or two about mechanisms, the engineer expects that some mechanism is able to describe the trajectory he requires. The main question is: which mechanism describes the trajectory the best?

He takes a good look at the requirements and knows what trajectory he wants, and where he can attach the mechanism to the truck. The piece of paper in front of him is still empty, but now he can begin finding solutions.

After quite some hours of thinking, he has produced three solution proposals. These proposals are sketches of mechanisms with all the important sizes schematically known: not too much detail but it gives a good idea of the solution. He expects these solutions could solve the problem.

The process of finding a solution which fulfills the requirements, is called synthesis. The result of this process is one or more proposed solutions which are expected to meet the requirements. These have just enough detail to show the idea of the solution, but are not fully detailed yet.

3 Solution proposals

As a result of the synthesis process, several proposed solutions are made. Although not very detailed, it shows its intended function and most of the important characteristics.

From the solution proposals, the engineer has to pick one and design it with more detail to see if it really works as required. He picks the one which he thinks will be the strongest. In this case, proposal 2.

4 Analysis

After selection of one proposal, he has to decide and engineer all details of this solution: length of the bars, what material, the shape of every component, size of the bearings inside the joints. How large are the forces inside, will the structure hold it? What about the weight, or cost?

He can calculate most of these things by using the theoretical handbooks he has piled up in his library. All information is there for him to make a thorough analysis of the mechanism.

5 Evaluation

Based on the results of his analysis, he evaluates his proposed solution. Does he still like it? Is it too expensive? Will it break? How does he judge his proposal? Will it be a good solution? From this, there are three options:

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No: find a better proposal by re-entering the synthesis phase.

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Maybe: the proposal looks good but needs optimization.

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Yes: the solution is good. Engineering process is done.

The options are explained.

6 Re-enter synthesis

Based on the evaluation results, the solution is not expected to meet the requirements. Deeply disappointed (because he spent some days working on it) he chooses to forget about this design. Now, he enters the synthesis stage again to think of a new idea. Hopefully he learned from the analysis results and knows what will make for a better proposal.

It is also possible that he just picks the next proposed solution, but usually he learned from the analysis results and makes a new (and better) proposal.

7 Optimization

If the solution looks promising, but needs improvement, this is called optimization. He is going to study this proposal in detail and tries to make it as good as possible.

For instance, to pick up the garbage cans more gently. This might be realized by minor modifications of the proposal.

If the engineer decides to change the length of one bar, he probably has to re-calculate several things to make sure it won’t fail. This means he enters the analysis stage again to make calculations.

8 Solution

If, possibly after several optimization loops, the solution meets the requirements, he is done with the engineering process. He has the technical drawing, containing all details and is able to machine and build it. Hopefully the client likes it.

In the next section, the same engineering process is discussed, but now with the intended synthesis support system available to assist the engineer.

Synthesis support

In this section, the engineering process with a synthesis support tool (computer program) is discussed. The engineering problem is the same as the previous section: transporting garbage cans towards the top of the truck. The engineer chooses the type of solution. In this example, he chooses a bar mechanism to solve his problem.

Using synthesis support, the description of the problem are translated into requirements of the solution and entered into the tool.

1 Requirements

The engineer translates the problem description into a more technical description of the problem: the requirements. He now knows the problem.

The synthesis support tool will help the engineer to find the best mechanism for his problem.

2 Synthesis tool

This specific synthesis tool is build for all types of mechanisms, which means it understands things like trajectories and rotation points. It has expert knowledge about mechanisms and the way they work.

The engineer formulates the function he wants the mechanism to perform: he draws the trajectory and indicates where the mechanism can be attached to the truck.

By doing this, he translated the requirements and enters them into the tool. From here, the synthesis tool takes over.

3 Solutions

Valid solutions are presented to the user. Again, the engineering process is done. However, there are some differences with the situation without synthesis tools:

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Hundreds of possible solutions are known and compared, the best one is selected.

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It takes minutes, rather than days.

This example focused on one single engineering issue: bar mechanisms. It gives an illustration of the use and benefits of synthesis support. The same benefits can be reached for many other engineering problems, a small number of which have been studied previous to this research proposal. These studies led to the development of several (limited) prototypes, presented in section Prototypes. The function of these prototypes is to see whether or not it is possible to build synthesis support for some different engineering problems. The conclusion is that it is possible and very promising, however further research is required to study some fundamental issues of synthesis support.

Therefore, the main function of the research is to explore how synthesis support can be further developed.

An overview of the current status of synthesis in engineering design is presented by Chakrabarti [1].