The subtle effects of Scale Effect are sometimes missed. When you have to deal with measurement and processes at extreme ends of the scale, it gets very complicated.
One manifestation is just size and weight of parts. Obviously, when things get big, there are consequences. A simple structural element that appears to be perfectly straight and true, will begin to sag as it is made longer. In order to offset the sag, the cross section can be made thicker to stiffen the element, but the consequence is more weight which simple moves the tendency to sag to a different proportion.
Weight by itself will impact design work. On the mechatronic side, weight can be considered as having a time constant. The more weight, the more time it takes to get the weight accelerated. Or, the more power required to move the load. But in reality, it is impossible to accelerate a mass beyond a certain reate based on weight and inertia of the given part. Most servo sizing software calculate torque requirements based on the required torque of acceleration. The sizing program will show when there are no solutions available.
So the real alternative is to reduce weight when speed and throughput are critical. Steel parts can sometimes be replaced by aluminum, which has approximately 1/3 the mass of steel. When aluminum is too heavy, titanium or plastics can be used. Often, people object to using titanium because of cost, but the results can be truly amazing, especially when stiffness is required.
Scale effect has other complications. The sheer size of a design can require special processes and tooling that will impact costs exponentially. Some notable examples would be anything in the windpower market. Making and testing propellers that are 175 long creates challenges at every level. Fabrication techniques have to be invented to accomplish a this task. Testing protocols and very expensive capital facilities have to be created and testing protocols developed to insure against premature failure.
Similar issues show up at the nano scale. Measurement of feature sizes in the semiconductor world continue to exceed the limits of available feedback technology. New solutions are constantly being created to deal with refinements needed as semiconductor manufacturers wander into ultraviolet frequency feature sizes. This accounts for the multimillions of dollars required to do semiconductor machine development and the similar price tags associated with new machinery.
Further aspects of scale effect in mechatronics will be explored in the next post.
Filed Under: Commentary • expert insight, Renewable energy, Semiconductor