rap . ▁ ▁Vari ations ▁on ▁the ▁above ▁exist . ▁There ▁are ▁also ▁rare ▁operators ▁that ▁use ▁a ▁mechanism ▁that ▁is ▁dis connected ▁from ▁the ▁door , ▁and ▁reaches ▁out ▁and ▁push es ▁on ▁the ▁door ▁itself ▁when ▁it ▁needs ▁to ▁open ▁it . ▁ ▁In ternal ▁techn ologies ▁ ▁Oper ators ▁are ▁power ed ▁by ▁an ▁electric ▁motor . ▁They ▁differ ▁in ▁how ▁they ▁use ▁the ▁motor ' s ▁energy ▁to ▁open ▁the ▁door . ▁ ▁Oper ators ▁use ▁various ▁internal ▁techn ologies . ▁ ▁Some ▁are ▁built ▁on ▁top ▁of ▁a ▁standard ▁door ▁closer . ▁To ▁open ▁the ▁door , ▁the ▁operator ▁forces ▁the ▁closer ▁in ▁the ▁opening ▁direction . ▁Then , ▁the ▁closer ▁clos es ▁the ▁door . ▁The ▁user ▁may ▁open ▁the ▁door ▁manually , ▁using ▁just ▁the ▁door ▁closer . ▁In ▁case ▁of ▁power ▁failure ▁while ▁the ▁door ▁is ▁open , ▁the ▁closer ▁itself ▁clos es ▁the ▁door . ▁ ▁Some ▁are ▁built ▁without ▁a ▁door ▁closer . ▁The ▁motor ▁opens ▁and ▁clos es ▁the ▁door ▁through ▁reducing ▁g ears . ▁The ▁operator ▁may ▁or ▁may ▁not ▁include ▁a ▁return ▁spring ▁to ▁close ▁the ▁door ▁in ▁case ▁of ▁power ▁failure ▁while ▁the ▁door ▁is ▁open . ▁Oper ators ▁are ▁often ▁categor ized ▁by ▁the ▁means ▁by ▁which ▁the ▁motor ' s ▁energy ▁is ▁applied . ▁ ▁Elect rome chan ical ▁– ▁the ▁motor ▁uses ▁purely ▁mechanical ▁means ▁to ▁open ▁the ▁door : ▁g ears , ▁c ams , ▁le vers ▁and ▁such . ▁This ▁is ▁the ▁preferred ▁type