露天掘り
Surface mining equipment evolved at a high pace in the 20th century as the scale of mining grew up. In the first twenty years of the 1900s, steam power was largely replaced by internal combustion engines and electric motors. Till the 1970s such equipment mainly used mechanical system and cables for power transmission after which they started to be replaced by hydraulic drive system for small machines. However, mechanical and cable drives are still dominant in large machines.