English to Polish Tech/Engineering Electronics / Elect Eng resonance motor

In some embodiments, the periodic voltage signal has zero voltage in one of the half cycles (similar to the excitation
function that a person applies at a swing, where also only energy is applied at the swing in one
movement direction).

The term swing exists only in this sentence of the whole patent description. Upon lots of research
I am still at square one trying to find reasonable meaning of this. I need suggestions.
The text was previously translated from German, perhaps using AT.