Garage door opener

A garage door opener is a motorized device that opens and closes garage doors. Most are controlled by switches on the garage wall, as well as by remote controls carried in the garage owner's cars.

Technology

The current garage door opener market offers a variety of transmission technologies. They use *frequency spectrum ranges between 300-400 MHz and most of the transmitter/receivers rely on hopping or rolling code technology. This approach prevents perpetrators from recording a code and replaying it to open a garage door. Since the signal is supposed to be significantly different from that of any other garage door remote control, manufacturers claim it is impossible for someone other than the owner of the remote to open the garage. When the transmitter sends a code, it generates a new code using an encoder. The receiver, after receiving a correct code, uses the same encoder with the same original seed to generate a new code that it will accept in the future. Because there is a high probability that someone might accidentally push the open button while not in range and desynchronize the code, the transmitter and receiver generate look-a-head codes ahead of time.

There have been different modes of mechanical drive over the years as well. A common misconception 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.

Another style of operator is the jackshaft that works with a torsional spring counterbalance system. Instead of attaching to the door, it 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 resides to the side of the door and does not require a rail. The trolley style operator often is encumbered with obstacles (beams, pipes, etc) or it becomes an obstruction itself. Jackshaft operators are not as popular due to the inherent safety issues. It is very difficult for the machine to sense when the door is crushing someone.

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.

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.

Remote Control

The first garage door opener remote controls were simple and consisted of a simple transmitter (the remote) and receiver which controlled the opener mechanism. The transmitter would transmit on designated frequency; the receiver would listen for the radio signal, then open or close the garage, depending on the door position. The basic concept of this can be traced back to World War II. This type of system was used to detonate remote bombs. While novel at the time, the technology would run its course when garage door openers would become widely available and used. Then, not only did a person open their garage door, they opened their neighbor’s garage door as well. While the garage door remote is low in power and in range, it was powerful enough to interfere with other receivers in the area.

The second stage of the wireless garage door opener system deals with the shared frequency problem. To rectify this, systems required a garage door owner to preset a digital code via dip switches on the receiver and transmitter. While these switches provided garage door systems with 2⁸ = 256 different codes they were not really designed with security in mind, the main idea was to avoid interference with similar systems nearby.

Additional features

Additional features that have been added over the years have included automatic courtesy lights that turns on when the door opens (or via motion sensors) and automatically turns off after a preset amount of time. Remote lockout feature which basically turns off the radio receiver while you are on vacation. The availability of accessories has increased as well like wireless keypads and keychain remotes.

There are a few frequently requested features that must be declined due to safety and security reasons. Such as an integrated carbon monoxide sensor to open the door. It lowers the security and if it should not perform could cause the loss of life. Another option would include door activation over the internet to allow home owners to open their garage door from their office for deliveries. This feature violates UL safety codes that states the door must be in line-of-sight of the person operating the door for safety reasons.

External links

PDF on a Texas Instruments Remote Control Encoder/Decoder provides a lot of information on the operation of the device
Code hopping
How Garage Doors Work – The Ups and Downs of It All
Official FCC notification on garage opener frequencies (pdf) - Consumers May Experience Interference To Their Garage Door Opener Controls Near Military Bases