The Garage Door Encyclopedia

source= wikipidia
The opener

A common misconception regarding openers is that the door opener lifts the door directly, however, most of the lifting is done by the counterbalance system using either torsion springs or linear expansion springs. There are also several clever counterweight systems. All of these systems allow the door to be moved with much less force and allows the door to come to rest in partially open positions.

The most common style of operator for residential use is the trolley operator. The motor hangs near the center of the ceiling and a rail guides the trolley across the ceiling to the top of the doorway. The trolley is attached to the door arm that is then attached to the top of the door.When the trolley traverses the rail the door opens and closes.

There are several ways to make the trolley move across the rail. Older systems include a rotating rail with a wheeled trolley that used the rotary motion of the rail (pole) to force the trolley across the distance. It was called a monkey on a pole. It was too dangerous, but it did inspire the screw drive system which the Genie Company originally marketed.

The screw drive system uses a long screw that is encased in the rail. The rail guides the trolley and the screw pushes the trolley. This system opens a door slower than a chain or belt drive system, but can apply more force. This system is best used on a one piece door known as a California Door or heavy doors such as carriage house doors. The heavier the door the slower it should move for safety and longevity of the door and operator.

Most current systems have a chain loop or a steel-reinforced rubber belt that pulls the trolley across the rail. The rubber belt reduces the noise during operation.

The trolley style operator often is encumbered with obstacles (beams, pipes, etc) or it becomes an obstruction itself. For these situations, another style of operator is used: the jackshaft operator. It works only with the torsional spring type of counterbalance system. Instead of attaching to the door, the operator attaches to the spring shaft. Rotation of the shaft still allows the springs to do most of the lifting while adding the extra force to move the door. The major advantage is that this operator is mounted to the side of the door and does not require a rail.

Jackshaft operators are not as popular due to the cost of the additional hardware required to overcome the inherent security and safety issues:

• An electrical solenoid lock to prevent the door being opened by force.
• A mechanism, such as a cable tension monitor mounted between the drum and the door, to detect that the door is not closing due to an obstruction.

Neither of these additional components is necessary with a trolley style operator.

Yet another style of opener available is one that is attached directly onto the spring shaft alongside with the torsion spring, and is located directly in the space on top of the door mounted to the wall. Such systems eliminate the rail, belts, and jackshafts, although this is a relatively new technology.

A recently introduced feature in the garage door opener market is a battery backup system. When power to the home is lost, residents are still able to get in and out of their garage. An added feature is that all opener safety features still function while the unit is operating on battery power.