Engineering education and ignoring reality

“In theory, theory and practice are the same. In practice, theory and practice are not the same.”

I worked on a project building a large hydraulic manipulator arm (7500 lb payload). Assigned to the project was a post-doctoral fellow in robotics. He had the idea of mounting a proximity detection system on the arm. He proposed that as soon as the proximity sensors detected an imminent collision the arm would be driven away from the point of imminent contact.

A sound idea on the surface. My objection to the scheme, however, was that the hydraulic valves controlling the arm had bandwidth (frequency response) limitations and the power unit could only put out a limited amount of power. Both of these factors would dramatically limit the responsiveness of the arm.

The post-doc did not take into account the physical limits of the system. His model did not take into account saturation of the power supply and frequency rolloff of the control valves.

The post-doc refused to concede my point until the senior control engineer (a PhD) stepped in and backed me up.

The post-doc ended his term at my employer and went on to a teaching position. But I suspect he missed the entire point of that incident I recounted. The engineer works works in the real world not simply a world of mental constructs. The goal of an engineer is to make real machinery, run a real assembly line.

I fear a number of engineering professors do not understand that. I see the world of the engineering professor becoming divorced from that of the practicing engineer. When I was in school there were a number of professors who had had significant industrial experience prior to teaching. There were even a few with only master's degrees and significant industrial experience. The situation now is that almost all professors have come up through academic ranks and don't have any non-academic experience.

Engineering is not just a set of academic knowledge but also a craft with a body of knowledge that must be picked up by the doing.

tags:
mechanical engineering
engineering education

Some web sites for your consideration

I have two web sites that might be of interest to engineering and metalworking types.

The first is a web site that has mechanism animations. Go here. It features animations of classical mechanisms such as the Geneva escapement, four bar linkages, and the Watt straight line generator.

The second is web page with metal working links. Go here. No graphics or anything just a long list of metal working links. Sites linked to include: machine tool vendors, welding equipment vendors, hand tool vendors, metal vendors, hardware and supplies, and some how-to.

tags:


Mechanical Engineering
metal working
machining

Some final thoughts on the design of experiments

In my previous two posts I described two different experiments in which variation was not properly considered.

The first experiment failed to consider variation altogether. The goal was to identify a material resistant to cavitation erosion. Only one sample of candidate material was run. The hidden, underlying assumption by the experimenters was that the coefficient of variation ( standard deviation/average ) was neglible. Without some background knowledge this is no a justified decision.

I talked once to a buyer whose responsibilities included certifying materials for nuclear use. One of the tests required to certify a lot (heat) of stainless steel for nuclear use is a corrosion test. He told me that different lots of identical grades of stainless steel from the same manufacturer can have vastly different corrosion resistance as measured by the standard corrosion test.

In the case of the cavitation erosion test the testing was expensive because of the nature of the testing and the requirement to decontaminate the samples prior to examination. Hence the decision to run only one sample of each material. The question arises though, was it worth conducting the experiment at all. Without some idea of the underlying statistical distribution, no, the experiment was not worthwhile. It does not provide sufficient data to make a sound decision.

The second experiment, the optical fiber radiation attenuation test attempted to consider variation. The method for measuring variation, however, was ill thought out. The two samples run for each fiber type were from the same lot. To accurately measure variation the samples should have been from multiple lots.

tags:

Mechanical Engineering
Analysis of variance
ANOVA

Design of experiments