How Do Automatic Doors Work - Everything You Need To Know

Commercial Automatic Sliding Door Inside A Hotel

Automatic Doors is a broad term which envelopes many models of automatic door types. The main two types of automatic doors are commercial automatic sliding doors and low energy automatic swing door openers. Both automatic door types are used as an automated entry system for all types of pedestrians including individuals with disabilities. Automatic doors have grown in popularity due to the ADA Americans With Disabilities Act in the United States. Each year automatic door installations increase. In this article we explain how both commercial automatic sliding doors and low energy handicap door openers work.

Commercial Automatic Sliding Doors

The Door Panels

Commercial automatic sliding doors are commonly found in retail stores, grocery stores, hospitals, and many more. Today we walk through them without even realizing just how amazing these doors are. Commercial automatic sliding doors are offered in a variety of door sizes and number of door panels. The most common commercial automatic sliding door is a bi-part automatic sliding door, which consists of 4 door panels. The 2 outer most door panels are stationary and do not slide. The 2 inner panels slide open. In case of an emergency, all 4 door panels can swing out for emergency break away. Typically most commercial automatic sliding doors are glazed with 1/4" tempered glass, however in colder environments automatic sliding doors could have 5/8" or 1" insulated tempered glass. The door panels themselves are made of aluminum and are typically offered in 2 different colors: clear anodized (silver finish) and dark bronze (dark brown/black finish).

The Header and Jamb Tubes

Above the door panels is what is called the automatic door header. This aluminum header box spans across the entire width of all the door panels. The door header typically has a hinged cover which conceals the drive system, controls, and other moving parts. Attached to each end of the header is an aluminum jamb tube. Essentially, the jamb tubes are what holds up the weight of the door header. Screws are fastened through the jamb tubes to a 2 x 4 wood stud in order to support the door system structure.

Automatic Door Sensors

On each automatic sliding door there is a motion and presence sensor mounted on the exterior side of the header as well as the interior side of the header. These sensors feature microwave motion detection, so when pedestrians are moving towards the doors or away, the sensors will be triggered. They also feature infrared presence safety detection, so if a pedestrian stays at the threshold of the door and is not moving, the sensors will still detect them.

Some automatic sliding doors also feature safety beam sensors, also referred to as pencil beam sensors. These sensors are comprised of an emitter photocell and a receiver photocell. The photo cells are flush mounted in the door stiles and shine through the door way. When pedestrians stand in the door way, they block the signal transmission from the emitter photo cell to the receiver photo cell, triggering the sensor to keep the automatic doors open.

Understanding The Automatic Sliding Door Drive System

DC Motor and Gearbox

One of the main components of the automatic sliding door drive system is the dc motor. The dc motor has an output shaft that meshes with a worm gear box. At the output shaft of the worm gearbox is a belt drive pulley.

Stanley Duraglide DC Motor Gearbox Drive Assembly

Automatic Door Control

The dc motor is connected to the automatic door controller. The automatic door controller is a microprocessor based circuit board. Essentially the door controller is the brain of the automatic door system. The software program is embedded in the microprocessor. The microprocessor sends power to the dc motor to power it and make the automatic door operate. The automatic door sensors also connect to the automatic door controller and provide activation and feedback letting the automatic door controller know when a pedestrian is being detected.

Stanley Duraglide Automatic Door Controller

Idler Belt Pulley

On the opposite side of the gearbox is a return belt pulley also referred to as an idler belt pulley. The timing belt is designed to wrap around the gearbox pulley and return pulley. Belt clips clamp to the timing belt and attach to the moving door panels.

Stanley Duraglide Idler Belt Pulley

Putting It All Together

When a person walks up to an automatic sliding door, the automatic door sensor first detects their motion and triggers the automatic door controller to open the door. The automatic door controller sends power to the dc motor which powers the gearbox belt pulley. As the gearbox belt pulley rotates the belt attached to the pulleys begin moving. Since the belt is attached to the door panels by belt clips, the door panels slide open. As the pedestrian passes through the door way the presence safety sensors are activated telling the automatic door controller to keep the doors open. When the person completely passe through the doorway and is out of range of the automatic door sensor on the other side of the door, then the sensor will no longer detect the person. This tells the automatic door controller it is safe to close the doors. The automatic door controller then sends the opposite polarity of power to the motor so that the gearbox belt pulley will rotate in the opposite direction. The belt attached to the gearbox moves in the opposite direction, causing the doors slide closed.

Low Energy Automatic Swing Door Openers

Commercial automatic swing door operators are composed of a header which houses the drive train and controls, and a door arm. Depending on the swing of the door, the automatic door opener might feature an outswing push style arm or an inswing track arm. The automatic door operator header is mounted at the top of the door frame. Wireless activation switches are mounted on each side of the door. A receiver is installed inside of the automatic door header, with it's antenna protruding outside of the header box. If the antenna is kept inside of the header, then the wireless activation switches will not be able to properly transmit the activation signal to the receiver, due the interference from the aluminum constructed header box.

Automatic Swing Door Operation

Automatic Swing Door Operator On Pair Of Doors

Automatic Swing Door Operator Internal Components

When a pedestrian presses the handicap button, a wireless transmitter inside of the plastic box sends a signal to the receiver inside of the door operator header box. The receiver communicates with the automatic door controller telling it to open the door. The automatic door controller sends voltage to the dc motor. The dc motor output shaft features a spur gear which meshes with the gearbox. As the dc motor output shaft rotates, the energy is transmitted through the gear train. The gearbox features an internal clock spring. So as the dc motor is powering the gearbox, it is loading the internal spring. The output shaft of the gearbox is the door spindle which connects to the door arm. As the gear train moves, the output gearbox spindle rotates, in turn rotating the door arm to push the door open. A hold open delay is programmed into the automatic door controller. When the door reaches the full open position the hold open delay begins counting down. When the time delay reaches zero, the automatic door controller stops sending power to the dc motor. The door begins to close, because the internal spring of the gearbox has been wound up and was under pressure. As the spring unwinds, the gears in the gearbox rotate in reverse, causing the output shaft to reverse, and pulling the door closed.

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