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.
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The electric opener
The electric overhead garage door opener was invented by C.G. Johnson in 1926 in Hartford City, Indiana. Contrary to popular belief, the electric opener does not provide the actual lifting power to open and close a heavy garage door. Instead, most of the actual lifting power comes from the counterbalance springs that are under tension to lift the garage door via steel counterbalance cables. The electric opener only controls how far the door opens and closes, as well as the force the garage door exerts. In most cases, the garage door opener also acts as a lock.
The typical electric garage door opener consists of a power unit that contains the electric motor. The power unit attaches to a track. A trolley connected to an arm that attaches to the top of the garage door slides back and forth on the track, thus opening and closing the garage door. The trolley is guided along the track by a chain, belt, or screw that turns when the motor is operated. A quick-release mechanism is attached to the trolley to allow the garage door to be disconnected from the opener for manual operation during a power failure or in case of emergency. Limit switches on the power unit control the distance the garage door opens and closes once the motor receives a signal from the remote control or wall push button to operate the door.[1]
The entire assembly hangs above the garage door. The power unit hangs from the ceiling and is located towards the rear of the garage. The end of the track on the opposite end of the power unit attaches to a header bracket that is attached to the header wall above the garage door. The power head is usually supported by punched angle iron.
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 a 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 ran its course when garage door openers became 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 designed with high security in mind; the main intent was to avoid interference with similar systems nearby.
The third stage of garage door opener market uses a frequency spectrum range 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.
The fourth stage of garage door opener systems is similar to third stage, but it is limited to the 315 MHz frequency. The 315 MHz frequency range avoids interference from the Land Mobile Radio System (LMRS) used by the U.S. military.
Additional features
Additional features that have been added over the years have included:
- Automatic courtesy lights that turn on when the door opens (or via motion sensors) and automatically turn off after a preset time delay
- A remote lockout feature, which turns off the radio receiver while one is on vacation or away for an extended time.
- The availability of accessories has increased, including such features as wireless keypads and key chain remotes.
More sophisticated features are also available, such as an integrated carbon monoxide sensor to open the door in case of the garage being flooded with exhaust fumes. Other systems allow door activation over the Internet to allow home owners to open their garage door from their office for deliveries. This feature violates Underwriters Laboratories (or UL) safety codes that state the door must be in the line-of-sight of the person operating the door for safety reasons.
Another recent innovation in the garage door opener is a fingerprint-based wireless keypad. This unit attaches to the outside of the garage door on the jamb and allows users to open and close their doors with the press of a finger, rather than creating a personal identification number (PIN). This is especially helpful for families with children who may forget a code and are "latch-key" kids.
Safety
The garage door is the largest moving object in a home. An improperly adjusted garage door opener can exert strong and deadly forces and might not reverse the garage door in an emergency. The garage door counterbalance springs should be properly adjusted in order for the safety reverse system to function properly. Thus, proper installation and maintenance are extremely important in order for the garage door and garage door opener to operate smoothly and safely.
The header bracket, which attaches the front end of the opener track to the header wall, must be securely attached to the structural members of the garage wall. If not, the opener might not reverse the garage door in an emergency. The rail can also pull away from the wall.
All garage door openers manufactured and installed in the United States since 1982 are required to provide a quick-release mechanism on the trolley that allows for the garage door to be disconnected from the garage door opener in the event of entrapment. The quick-release handle should be mounted no higher than six feet from the ground. Homeowners should be familiar with this mechanism. Garage door openers manufactured since 1982 are also required to reverse the garage door if it strikes a solid object. [2]
The wall console/push button should be mounted at least five feet from the floor and the remote controls should be kept out of the hands of children. Children should never be allowed to play with or use the garage door opener remotes or wall pushbuttons. Homeowners should also keep a moving door in sight until it fully opens or closes.[3]
Under U.S. federal law, garage door openers manufactured since 1993 are required to have photoelectric safety sensors on both sides of the garage door, mounted no higher than six inches above the ground, with a light beam spanning the door opening. The garage door opener is required to reverse the door to the open position if the beam is broken.[4]
References
External links
- How Garage Doors Work — The Ups and Downs of It All
- Official FCC notification on garage opener frequencies (PDF)
- Texas Instruments Remote Control Encoder/Decoder device (PDF)
- 4-Channel Rolling Code remote circuit design (PDF)
- History of garage door openers — A Self Opening and Closing Garage Door, Popular Science monthly, December 1918, page 62, Scanned by Google Books: http://books.google.com/books?id=EikDAAAAMBAJ&pg=PA62
- Electric Garage Door Opener Help Forum
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