Vertical lifting drive train questions

[jcoiner]

I am trying to quote the electrical interfaces for a customer who makes large doors (Blast and Containment type). They have a requirement for a vertical lifted door that is using a chain at each corner driven by sprockets. The chain does not appear to be a continuous loop. The sprockets are attached to shafts that are connected to a single gear box in the center to which an electric motor is coupled. Each shaft has a brake attached to it (I don't know what type) along with an electrical brake in the motor. Several questions are raised...
1) Can the motor back drive the chain to lower the door.
2) If back driving, can the motor hold the door or are the brakes required to be on.
3) Are the brakes just on/off or do they need to be controlled (i.e. speed control of the door when lowering).
4) A chain snarl detector is specified, would it have electrical interfaces?
5) Is there prior art or text book standard for this type of drive?

Any help or direction to understanding would be greatly appreciated. Thanks.

 

[peteswift]

1) Can the motor back drive the chain to lower the door.
Yes. The motor will be being used as a brake. There is no torque reversal i.e. the load is from the same direction.

2) If back driving, can the motor hold the door or are the brakes required to be on.
The motor should have the torque to hold the door if it is sized to lift it.

3) Are the brakes just on/off or do they need to be controlled (i.e. speed control of the door when lowering).

This is probably the wrong question. The usual method of operation in my experience is:
Start motor
0.5 sec later release brake

Then for stopping
Apply the brake then stop the motor. This is done so that the load is always under control. This assumes that the motor is being used to lower the door. And the brake is for holding/emergency only.

If speed control is required this is normally done electrically through an inverter.

4) A chain snarl detector is specified, would it have electrical interfaces?

A snarl detector is normally a switch spring loaded onto the chain to ensure it is always under tension. If the chain goes slack a contact is opened. Beware when the door is lowered the control must interpret this correctly and can be reset.

5) Is there prior art or text book standard for this type of drive?

I don't know of any.

 

[FINN_imported]

One thing to be careful of in overhead doors. NEVER rely on the motor to act as a positional lock/brake for the door. The company I previously worked for designed a worm drive gearbox that was previously touted as a drive which could not be back-driven by the load. They found this to be a false statement when an overhead dorr manufacturer used the motor/gearbox assembly as a locking system for the overhead door. The gearbox received enough wear/break-in time so that it was possible to back-feed the system, and the door fell. It injured a technician working at the facility and a lawsuit ensued.

I thought this little story may be useful in determining whether or not to use the brakes to control the load while lowering the door. It would most likely be an added safety feature to have a lock mechanism which engages if the motor fails.

Good luck,
Finn