• Quoc Tran

How fast should automatic doors open?

Updated: Feb 5, 2020

In our society, the automatic door represents both a barrier and a passageway, metaphorically and physically. We encounter them every day, whether running errands grocery store to buying food at a supermarket; the automatic door truly pervades all aspects of our modern life. Important topics deserve the attention of our most important minds, so it is my responsibility to tackle one of the most pressing policy issues facing our nation: how fast should automatic doors open?

Attempting to solve this problem without first understanding what an automatic door truly is and how it operates isn’t just putting the cart before the horse, it’s building a cart before inventing the horse. Unfortunately, the article on Wikipedia on this topic is quite short and doesn’t provide much information on the inner workings of an automatic door. One can only assume that this is due to highly classified technology contained within, which leading automatic door manufacturers or, perhaps, the United States Government itself do not want available to the general public.

However, if one had made such an assumption, one would be a fool. DuckDuckGo’ing “how do automatic doors work” reveals a myriad of resources on the mechanisms behind these machines. With this resource, we run into the opposite problem, however: the paradox of choice. As Barry Schwartz puts it in his similarly titled book:

Autonomy and Freedom of choice are critical to our well being, and choice is critical to freedom and autonomy. Nonetheless, though modern Americans have more choice than any group of people ever has before, and thus, presumably, more freedom and autonomy, we don’t seem to be benefiting from it psychologically. Barry Schwartz, The Paradox of Choice, 2004

Following the book’s advice I will not be combing through the extremely relevant options that the privacy-oriented search engine, DuckDuckGo, has laid out before me. Instead, I will just guess at how an automatic door might operate.

The most crucial part of an automatic door is the door itself, usually just a big piece of glass. That part is transparent in both the literal and figurative sense. They’re one of the few parts of an automatic door that the general public can see. Having addressed the door part of an automatic door, we move to address the automatic part. It’s clear that unless the door can predict the future, there is a person detector of some sort that can somehow sense the presence of a nearby humans through smell, see, hear, feel, or taste. Its exact mechanism of action is irrelevant and outside the scope of our speculation. To connect this person detector to the door, there exists wires, for all machines require wires, that tell pulling machines beside the door to pull on the doors. This will open the automatic doors.

Artist’s interpretation of the secret mechanisms behind an automatic door.

Equipped with a solid understanding of the how an automatic door functions, we can address the true question at hand. How fast should an automatic door open? Analyzing the blueprints at hand of the automatic door, the clear limiting factor to the opening speed of the door is the pulling machine. Before we prescribe an opening speed to the automatic door, we should first understand the capabilities of the pulling machine.

What is a pulling machine? Cable Pulling Machines & Winches manufactures and sells cable pulling machines alongside cable blowing machines, cable drum trailers, and their accessories. Are these the same pulling machines that exist within automatic doors? Cable Pulling Machines & Winches intends for them to, at least, listing “big projects” and “engineering purposes” as requiring their pulling machines. And what are automatic doors but big engineering projects?

Cable Pulling Machines- a boon to the industry The cable Pulling equipments are required for all the big projects or commercial construction sites as well as engineering purposes and telecom industries.http://www.cablepullingmachines.com

The fastest of the pulling machines that Cable Pulling Machines & Winches offers is the Hydraulic Cable Pulling Machine 2 Tons with a quoted top speed of 50m/min. Other specifications include pulling force (2kN), motor power (10kW), and pulling power (2000kg), but those numbers don’t seem to mean much (to me at least) so I’ll ignore them.

At 50 meters per minute, these pulling machines are capable of completely opening a 2 meter wide door (this figure was derived with a mathematical technique employed by Ancient Greek philosophers known as guesstimating) in a mere 2.4 seconds. That speed is the theoretical limit at which an automatic door employing the pulling machines made by the apparently Turkish company, Cable Pulling Machines & Winches.

Why shouldn’t an automatic door open as quickly as it possibly can? Quoc Tran, 2019

The above question was first posed as a thought exercise: a rhetorical question meant to have the reader question their own preconceptions of what an automatic door is and what it could be. However, it seems that I have stumped myself quite thuroughly. I cannot conceive of any reason why an automatic door should not open as fast as possible, so I guess the answer to this question is 50 meters per minute?

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