It is something grocery stores have been doing for decades: put the automatic sliding caesar door in place and let people with their arms full of bags come and go without so much as a touch on the handle. The mechanism makes it happen, though one could argue we have all become so accustomed to it that the engineering goes unappreciated.

Some Background

The first of these were not particularly refined. You would find a mat on the floor; step on it to trip a switch and the door would open. Functional enough, but about as crude as a flip phone. Infrared sensors have since done away with the mats and the dead zones they created. The technology is far more discerning now, opening for a person’s presence rather than requiring precise footwork.

What Makes It Work

Look up at the header above the frame and you will see where the action is. That horizontal box contains the motor, the belt drive and the control board. Most never give it a second glance, yet it is the brain of the whole affair.

The track is below, with rollers to support the weight of the door so it can glide smoothly. Give them some grease from time to time or the system will make as much noise as an old swing set. Then there is the belt. The motor turns a pulley which in turn pulls the belt and opens the door. Tension is key here; a loose belt will slip while an overtight one puts undue strain on the motor.

Why Sensors Are Where They Are

There is method to the mounting of the sensors. Place them too low and every shopping cart will set off a false start; put them too high and a child or a short person may well end up walking into a closed door.

And do not overlook the safety edge along the front of the door. If the path is obstructed, it halts movement. You see the value of that in a hospital or daycare where reaction times are slower.

The Cost of Maintenance

A quarterly check is worth it to head off trouble. Belt wear, a misaligned sensor or damaged rollers are inexpensive to put right until they cause a breakdown when the store is open.