Air powered door operator

For a system in which an overhead door is raised or lowered by a combination of a cable, spring, drum and torsion bar which is rotated by a chain-driven sprocket, a pair of pneumatic cylinders having elongated rods attached to the cylinder pistons are attached to the sprocket chain to drive the chain to raise and lower the door. Braking and safety features are provided.

FIELD OF THE INVENTION 
This invention is directed for use in systems for mechanically opening and 
closing overhead doors. The invention is primarily intended for commercial 
and industrial use where the doors are likely to be opened and closed 
often during the course of the day although it can also be utilized in 
private garages and the like. 
DESCRIPTION OF THE PRIOR ART 
This invention is intended to be used in conjunction with conventional 
mechanisms used for operating overhead doors. In general, conventional 
doors of this nature are operated by a combination of a torsion spring and 
cable with the cable wound on a drum axially driven by a torsion bar with 
the bar being rotated by a chain-driven sprocket. It has been the usual 
practice in the past to drive the chain by an electrical device such as an 
electrical motor. In some environments the use of electrical devices is 
undesirable because of possible danger of sparking causing an explosion or 
fire. It has also been found that with an electric motor to raise and 
lower an overhead door if the door becomes jammed, the motor will continue 
driving and will likely unwind the cable between the drum and the door 
which could be damaging and hazardous to personnel. 
SUMMARY OF THE INVENTION 
A pair of pneumatic cylinders have elongated rods attached to be driven 
longitudinally by the pistons in the cylinder chambers. The rods are 
attached to the ends of the chain which drives the sprocket which in turn 
rotates the torsion bar for raising and lowering the garage door. 
Pressurized air is selectively fed to one of the cylinders to move its 
piston one way or another to move the door up or down and at the same time 
the other piston is allowed to move freely. Injection of the pressurized 
air into one end of a cylinder causes its piston to move rapidly toward 
the other end thereby initially causing the door to move rapidly. Near the 
end of its stroke the piston is braked so that the door does not impact 
suddenly at the end of its travel but is brought to a smooth slow stop. In 
this fashion the door will mostly open and close quite rapidly yet will 
avoid damaging impact at the end of its travel. 
It has been found that with the use of air pressure as the main driving 
force for the door, if the door is jammed while being closed it is not 
closing with undue force; therefore, if a person should happen to be 
standing under the door while it is being closed, there is little or no 
likelihood of that person being injured. Neither will the cable which is 
attached to the door become unwound from the drum. 
As a further feature, a second length of chain is attached between the 
cylinder rods through a fixedly mounted pulley which serves to limit the 
travel of the rod in the unpressurized cylinder when the pressurized air 
is applied to the other cylinder. Without this feature the inertia of 
motion of the cylinder rod which is unpressurized would cause it to reach 
the end of its travel with impact which could be damaging to the equipment 
or the operator.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In a conventional fashion an overhead door is raised and lowered by a cable 
and/or spring combination (not shown) with the cable wound on a drum 11 
axially mounted on a torsion bar 12 which is rotated by a sprocket 13 
driven by a chain 14 linked thereto. The details of this part of the 
system are not considered important because they do not constitute any 
part of the invention and are well known and conventional. 
A pair of identical elongated cylinders 15 are vertically mounted on a 
suitable brace 16 in any convenient fashion and are mounted together in 
any convenient fashion such as by mounting plates 17 and 18 held together 
by elongated threaded bolts 19. Elongated rods 20 and 21 extending upward 
from their attachment to the pistons of cylinders 15 are attached to chain 
14. While the manner in which the chain is attached to the rods is not 
critical, typically, it may be by a sleeve or collar over the end of the 
rod which is held onto the rod by set screws and bolts or pins through the 
links of the chain secure the chain to the sleeve. A pushbutton electrical 
control 22 which receives electrical energy from a suitable source, not 
shown, operates solenoid operated valves 23 which control the feeding of 
the pressurized air from a suitable air source, not shown, into the 
cylinders 15. To open the door, "up" button on conttol 22 is pushed which 
causes pressurized air to be fed into one end of one of the cylinders and 
opens the other cylinder to atmospheric pressure. The piston in the 
pressurized cylinder moves to pull chain 14 and rotate torsion bar 12 so 
that the door opens. To close the door the "down" button in control 22 is 
pushed, the other cylinder receives pressurized air and the first cylinder 
is opened to atmosphere and torsion bar 12 is rotated in the opposite 
direction to bring the door back to its closed position. 
Another length of chain 30 is attached at its ends in some convenient 
fashion to rods 20 and 21 through pulley 31 which is mounted on mounting 
plate 17. The purpose and function of this arrangement will be described 
later. 
Since the two cylinders 15 are identical in construction, only one will be 
described and the reference numerals will be common to both. Near their 
lower ends, as viewed in the FIG. 2, the cylinders are provided with a 
bleeder opening 32 through the side wall of the cylinder. At the bottom 
end of the cylinder a check valve 33 and an adjustable needle valve 34 are 
provided. At the upper end a suitable passageway 35 of conventional design 
provides communication between the inner chamber of the cylinder 15 and 
the solenoid valves 23 which are coupled to a suitable pressurized air 
supply. Since the cylinders are conventional in construction for the most 
part, no detailed description of their construction is thought to be 
necessary since one of ordinary skill in the art would readily understand 
the functional and structural requirements of the cylinder according to 
the teachings of this invention. Suffice is to point out that suitable 
bearings, seals and O-rings form part of the construction of the 
cylinders. The piston assemblies 36 are conventional and operate in the 
same fashion as ordinary in air operated cylinders. The elongated rods 20 
and 21 can be attached to their respective pistons 35 in any convenient 
fashion. 
When pressurized air is fed into one of the cylinder chambers through 
passageway 35 from valves 23, for example the left-most cylinder shown in 
FIG. 2, the cylinder chamber in the right-most cylinder is unpressurized. 
This drives piston 36 downward as indicated by arrow 41, pulling on chain 
14 to close or open the door, and at the same time pulling the piston of 
the rightmost cylinder upward, shown by arrow 40. The smaller arrows show 
the general air flow. The injection of the pressurized air is such that it 
causes the piston to drive down rapidly correspondingly causing the other 
piston to rise rapidly. Because of the momentum of the latter, it could 
strike the top of the cylinder with great impact. However, chain 30 comes 
into play to limit the amount of upward travel of the rod and the piston 
of the unpressurized cylinder. 
As the piston in the leftmost cylinder approaches the bottom end it covers 
the bleeder opening 32 so that the air that is then trapped in the lower 
part of the cylinder chamber between the piston and the end of the chamber 
can only leave through the adjustable opening in needle valve 34. Check 
valve 33 is biased to be opened only when piston 36 is raised, as shown in 
the rightmost cylinder in FIG. 2. The adjustment in the needle valve 34 is 
made such that air entrapped at the bottom of the cylinder leaves at a 
relatively slow rate to brake piston 36 to a slow and smooth end of 
travel. This is reflected by the door opening or closing in the same 
fashion. Eventually the piston comes to rest at the end or near the end of 
the cylinder, but it reaches there in a slow smooth fashion thereby 
avoiding sudden impacting of the door itself at the end of its travel. 
The system has a further feature whereby valves 23 can be operated to allow 
pressurized air into both the cylinders 15 at the same time. This is done 
to stop the door at a desired location. It has been found that in the 
event the door is stopped at an intermediate position, it can be manually 
pushed open against the force of the air pressure in the cylinders and the 
weight of the door.