The electric opener
The electric overhead garage door opener was invented by C.G. Johnson in 1926 in Hartford City, Indiana. Electric Garage Door openers did not become popular until Era Meter Company of Chicago offered one after World War II where the overhead garage door could be opened via a key pad located on a post at the end of the driveway or a switch inside the garage.
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 attached to the door. These springs 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 holds the door closed in place of 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 pulled 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.
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.
Recently another type of opener, known as the jackshaft opener, has become more popular. This style of opener was used frequently on commercial doors but in recent years has been adapted for residential use. This style of opener consists of a motor that attaches to the side of the torsion rod and moves the door up and down by simply spinning the rod. These openers need a few extra components to function safely for residential use. These include a cable tension monitor, to detect when a cable is broken, and a separate locking mechanism to lock the door when it is fully closed. These have the advantage that they free up ceiling space that an ordinary opener and rail would occupy. These also have the disadvantage that the door must have a torsion rod to attach the motor to.
The first wireless garage door openers were invented and developed by two US inventors at the same time unknown to each other, one in Illinois and the other in Washington state.
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 dealt with the shared frequency problem. To rectify this, multicode systems were developed. These systems required a garage door owner to preset a digital code by switching eight to twelve DIP switches on the receiver and transmitter. While these switches provided garage door systems with 28 = 256 to 212 = 4,096 different codes they were not designed with high security in mind; the main intent was to avoid interference with similar systems nearby. Criminals were able to defeat the basic security of this system by trying different codes on a regular transmitter. They could also make code grabbers to record, and re-transmit a signal, or code scanners, that would attempt every possible combination in a short time. Multicode openers became unpopular in areas where security was an issue, but due to their ease of programming, such openers are often used to operate such things as the gates in gated apartment complexes.
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 receiver generates look-a-head codes ahead of time. Rolling code is the same method of security used on the clickers of cars, and with some internet protocols for secure sites.
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.