Stopping a flexo printing press

I spent twenty-six years in the web printing industry so I will offer this to you. If the press has a common lineshaft drive between decks (most do) then it is a relatively simple fix. You need a 90 vdc lineshaft brake. Go to this website: Warnerelectric.com and look at the examples there.

You mentioned an eddy current drive-undoubtedly the most dangerous type of drive for a printing press. I say dangerous because the bearings inside the eddy current clutch can become dry and lock without warning. When this happens the press moves at a speed higher than normal top speed, and must have the energy supplied to the motor's mains (not the clutch!) severed to make it stop. And of course it does not stop immediately! Without some type of braking device this can happen while the press is at rest or while it is being jogged or threaded.

The electromagnetic lineshaft brake chosen should be sized so that it has at least twice the braking horsepower as the motor's output. That way it can overpower the motor and cause it to trip its main fuses should the motor's clutch lock up while the press is still.

Normal Stop Mode: When the normal stop button is depressed the energy supplied to the motor's eddy current clutch drops to zero value, and the press gradually loses speed. At the last part of the run-down, the electromagnetic brake begins to engage softly, and when the press comes to a full stop a zero speed switch signals the brake controller to apply full energy to the brake.

Emergency Stop Mode: When the emergency stop button is depressed the energy supplied to the motor's eddy current clutch drops to zero value, and full energy is supplied to the electromagnetic lineshaft. The goal is of course to stop the press quickly, and it is not a pretty sight! You may wish to add a relay that drops the power supplied to the press' main drive motor as well. That is quite the common practice today, as it adds another safety feature. The press comes to a full stop, and continues to be held by the electromagnetic brake.

Inch/Jog Mode: When this button is depressed the energy to the electromagenetic brake is interrupted, and the motor can move the press. At the moment this button is released, the brake is again supplied with full energy to hold the press at rest.

Overspeed Mode: You install a relay to engage the press' emergency stop circuit if the eddy current clutch locks. This of course will require a signal from a speed sensor/tachometer.

Some eddy current motors are supplied with an internal brake. I never trusted these, as they are difficult to inspect. If it was my printing press I would exchange the eddy-current drive for a DC or Vector AC drive and improve the safety a bit more. And there are pneumatic lineshaft brakes available as well, should you choose to go that route. I prefer to keep it simple.

Best Regards,

Ing. Robert Forbus