Electric operators

Electric operators are available for all types of doors. Most commercial overhead doors under 12' X 12' in size will use a belt driven hoist operator. Larger, heavier, overhead doors can use industrial gearhead operators. Personell doors might use swing arm automatic operators, to maintain ADA compliance. Gate operators are available for swinging gates, horizontal sliding gates, or overhead gates. Dock levelers can be operated electronically, making use of hydraulics or pneumatics.

Reversing devices

Reversing devices have the purpose of helping the operator detect an obstruction while closing. This will then cause operator to reverse, into upward direction, until it reaches full open position. Basically, a "normally open" switch is activated, thereby closing the reverse circuit of the operator's open contactor.  Some operators offer the feature of a time delay, before abruptly reversing the momentum of a traveling door.  This can even be an upgradeable option.   A photo eye or photo cell device is an approach typically used with residential operators, as well as with commercial.

Residential trolley operators are also required to have the operator unit itself sense unusual resistance, and reverse the door.  Most residential operators use a emitter/receiver style photo eye. One optical unit transmits, while the other receives. If the transmit path is broken, while the operator is in between the open, and close, position, a circuit will close, and the operator will open.

Other industrial style photo eye units are also available.  These ones can emit/receive, or transmit/reflect.  These boxed units offer mount to a sturdy bracket.  They can be less susceptible to outdoor environments, keenly, less affected by interference from the sun. I especially enjoy the adjustable sensitivity.

When redundant devices are used, a cord for the safety edge can cross the path of the photo eye during normal door travel.  Adjustable sensitivity can allow the cord to pass, while still serving it purpose; detecting unwanted obstructions.  A safety edge is attached to the bottom of the door, along the entire width.  If the door closes on an object, the safety edge should detect it, and activate the reverse circuit.  A pneumatic safety edge uses a gum hose and air switch, to detect obstructions.  An electrical safety edge can use two lengths of conductors, separated by a segmented foam, to open, and close, a circuit.  A safety edge will often take use of a take up reel, or a take up cord, to carry this message to the operator.  The signal can also be transmitted by remote.  The transmitter can be powered by a 9 volt battery.

Remember, nothing is fool proof. One consideration, for all safety devices, is the amount of "downward coast" that still occurs before the door actually reverses. This can be affected by variables, such as, the means of braking (on a belt driven operator, whether it's depending on a internal chain reduction to accomplish braking, or if it actually has a brake solenoid, and, the condition of either), the weight of the door (after being calibrated for spring balance, how much force is still applied to the operator), the condition of the door, or, the condition of the devices themselves. Gate operators can use both of those types of devices mentioned. Also, operators can be reversed by vehicle detectors.

updated: 11/16/11