The evolution of machine elements and their future as an element of design are analyzed here using the example of rolling bearings and gears. Due to the bearing as a functional unit, the invention of the wheel about 6600 years ago became a sustainable innovation. With the wheel centered and guided by the bearing, the acting forces were supported (Fig.2, left). A modern wheel bearing has the same basic functions, can also transmit the drive power practically without loss and, in many cases, also provides high-resolution rotational speed information via specific sensors (for example, in a modern ABS system). A similar development can be observed in the example of linear guides (Fig.3). Whereas about 4600 years ago wooden rollers as rolling elements facilitated the construction of pyramids, with modern slides guidance accuracies in the range of micrometers are possible due to advances in manufacturing technology for the hardened and precision-ground rolling elements as well as the preload of the rolling contacts. An integrated position measurement system can resolve the same accuracy. Low-friction seals and optimized rolling contacts have made it possible to continuously reduce friction losses over the past decades.

Moore’s Law 

In 1965, Gordon Moore made a prediction about the development of semiconductor technology (Ref.1). His prediction is known as Moore’s law and states that the number of transistors per unit area will double every year, corresponding to an exponential increase. Moore’s law has so far proven to be largely correct. However, the further reduction in the size of transistors is likely to reach its limits in the coming years. Alternatives to conventional transistor design or new approaches to chip architecture are needed for the future (Ref.3). Whether Moore’s law can also be applied to machine elements will be considered in this section. In order to be able to assess the further development of machine elements and the technical systems assembled from them, suitable quantification on the basis of technical characteristics is necessary.

Torque Density of Gearboxes for Wind Turbines In wind turbines, the increasing rotor diameters led to an increase in the rated power. At the same time, a reduction of the rotor speed is necessary to maintain the permissible blade tip speed (Ref.4). This results in a high increase in input torque. To evaluate the development of gearboxes for wind turbines, the torque density as a quotient of the rated torque of the gearbox and the weight of the gearbox is suitable (Refs. 5, 6). Figure 4 suggests an annual increase in torque density of about five percent. This corresponds to an exponential increase as in Moore’s law, although at a lower growth rate. The development of torque density is due, among other things, to lightweight construction, new materials and coatings, and optimized macro- and micro-geometries (Ref.6). Smaller plain bearings allow higher power densities by load sharing on more planets and enable new gear concepts (Ref.7).