Automatic Door Opener

I’ve been spending lots of time researching automatic door openers over the last several months and have come up with a couple thoughts:

1. There aren’t many manufacturers that make them
2. They cost an awful lot of money
3. I could probably make one myself for much cheaper

There seems to be two types of automatic door openers used in the commercial world; those which use a pneumatic cylinder and those which use a electromechanical device. The pneumatic operators seem to be used in more large scale operations where a large number (10+) of automatic doors are spread throughout an establishment. An air compressor/tank and the pressure valves/manifolds/controls are located in a centralized place and then routed to each individual door. Electromechanical operators are more self-contained, and although costing more, have everything packaged as an operating unit right at the door. For simplicity it seems like an electromechanical system (possibly with a battery backup) is the way to go to seamlessly integrate everything into my home automation system.

For pricing, commercial style electromechanical operators like the ones you see in grocery stores/businesses across town are more than $3,000 apiece. I’ve found a company, that makes a very good residential electromechanical operator for about $1,500, which seems like a better deal, but is still an awful lot of money; especially when you consider I need 3 of these.

So I think I want to design my own, and would appreciate any help you guys might have with coming up with a solution.

Linear Actuator

My initial thoughts were to use a simple 12/24VDC linear actuator. Energize the actuator in one direction and it would expand/open the door, energize the actuator in the other direction and it would compress/close the door. Would definitely work, but it has a few failure modes/safety issues that make me very nervous.

1. When you energize a linear actuator it is moving. It doesn’t care if there is a finger, foot, or whatever in the way. This is definitely a major safety issue and not something I’m okay with.
2. What happens if you lose power? There is no manual operation of a linear actuator, so without power the door stays close. Another major safety/access issue I’m not okay with.

So the linear actuator is out!

Pneumatic Cylinder

From there, I started thinking about using a pneumatic cylinder to open/close the door. You could attach a pneumatic cylinder almost like they attach one to a storm door to control it from closing too fast. With a 12/24VDC solenoid on each side of the cylinder you could open/close the door depending on which side you pressurize. Energize the solenoid on the low side of the cylinder and you’d extend the ram/open the door; energize the solenoid on the high side and you’d retract the ram/close the door. By regulating how much pressure is in the system you could regulate the power of the device and prevent the safety issues caused by the linear actuator. You could also get creative with depressurizing the system after operation so that you could still have manual, unimpeded operation of the door.Seems like a much better option, but still has the complexity of routing air/pneumatic tubing to the doors in the house.

12/24VDC Motor/Electromechanical Clutch

My last brainstorm/epiphany/which way I currently think is best is to use a combination of a DC motor with a electromechanical clutch. For automatic operation you would run the motor/engage the electromechanical clutch in the forward direction which would open the door. Then switch polarity on the motor/still engage the clutch to close the door. Full manual operation would still work because the electromechanical clutch would normally be disengaged and allow the door to open/close as though no operator was attached. The electromechanical clutch could be sized such that it would slip when obstructed by a person, foot, or finger mitigating the safety issues of the linear actuator.

I think this is definitely the design route I’d like to go, but I have no idea how to size the motor/electromechanical clutch. What RPM motor do I need? What torque value clutch? All kinds of questions! What stuff do I need?

I’ve got some very talented fabricator friends that can make me any sort of linkages/whatever I need. I just need to figure out what pieces to give them to make this work.

Any thoughts guys? Appreciate it!
-Mike