Z Axis Down During Emergency Stop

[L. Sakthivel]

We are Having the Cincinati VMC with Fanuc 0M Control. Z Axis moving Down During Power cut & Emergency stop upto 5mm. Z Axis have the Break Motor & No counter Balance. We changed the New Break also. Problem not solved. Electrical function also good. I am suspecting that Drive Regeneration Resistors. Anybody can suggest me to solve the problem.

[Al_The_Man]

Does it do this if the Z axis is stationary with the power cut? or only when moving in feed etc?.
If this is a recent thing, I would still suspect the brake, but if it has always done it, it would suggest that it requires a counter balance, especially if you were to release the brake when the power is off and the head would move down considerably, then it would confirm a C.B. is required.
Most large mills have CB in place.
Al.

[L. Sakthivel]

During in servolock If we are pushing the emergency or Power cut it is moving down. If it is in Break condition during system off or power cut there is no movement. We already replaced New brake.

[Al_The_Man]

Originally Posted by L. Sakthivel During in servolock If we are pushing the emergency or Power cut it is moving down.

Servolock? I take it you mean the Z axis is under servo power, but is it servoing down at the point of e-stop? or does it sink at e-stop even when the axis is being held stationary by the Z servo at that point?
If so, It sound like the movement occurs during the slight delay of the brake coming on, and if the tendancy of the Z is to backfeed quite rapidly, were the brake not there, then it needs counter balance in my opinion.
Al.

[rajesh_1355]

you provide a relay ( in put supply 200 vac) which should be ON by z axis input supply. Now use its NO contact ( in addition ) for z axis brake supply. For instant braking effect. It helped me many times.

[L. Sakthivel]

If we are taking 100v control supply for the relay, it will give some improvement. Already We tried this. If we are switch ON the relay by Input of the Drive voltage it will not helpful because during emergency stop condition Drive input power will be there.

[dertsap]

Originally Posted by L. Sakthivel We are Having the Cincinati VMC with Fanuc 0M Control. Z Axis moving Down During Power cut & Emergency stop upto 5mm. Z Axis have the Break Motor & No counter Balance. We changed the New Break also. Problem not solved. Electrical function also good. I am suspecting that Drive Regeneration Resistors. Anybody can suggest me to solve the problem.

we have two old mori s that do the same thing , sort of defeates the purpose of an estop button when a guy hits it and the tool plunges into the part over .1",
does the same on an over travel

[gridley51]

I have a Chiron that does this also.It`s due to the delay between the power being cut of the servo drive in an e-stop situation and the brake de-energising.Not a problem as we don`t often have an e-stop.

[Al_The_Man]

The problem is often aggravated by the fact of using a DC brake with reverse emf diode, the larger the brake inductance the longer the reverse energy takes to dissipate, causing the delay in the brake operating.
Any time you use a diode for this purpose, the delay is one downside in its use.
Al.

[hawk prog]

We have a mid 90's Okuma CTV30 (which is a small CAT 30 taper head) that has the same problem, but to go a step further it will drop .15" or more (without any previous Z-axis movement) if the door works it's way open during a cycle and triggers the door interlock switch! We have contacted our service rep about the problem, but they are just as dumbfounded about it as we were and the maintenance guy couldn't fix it, so we just have to make sure to keep the door latched shut to avoid it from crashing due to door interlock issues, but we have to just deal with the E-stop trouble and hope it's not too close to a workpiece when it drops!

[F.Sharifi]

this is usual problems for all machine that working without counter ballance and just using Beark system ,...if you all pay attention to AL THE Man , his explain very well the situation , but let me added , on my experience for break that work with Dc voltage ( 100 Volt or more) after EMG push , or machine cut off , the must problems in cause of dusty or dirty the the break surface plate ,...you can clean it very easy ,... and also after 5 years or 10 years the springs needs to change already ,... also for new break it needs to have adjust befor put on the machine ,..usually you need the Gap between 0.2 up 0.6 mm it just enough , more than this you have falling down the Z axis ,...be sure !

[Geof]

If you have access to electronic expertise you may be able to make a fix.

Haas machines started to have this problem when they switched to a brake on the ballscrew and stopped using a counterbalance.

The brake is a permanent magnet type which is released when it is powered up. When the servos have power the brake has power so it is off and the machine rests on the servo.

With slow pitch ballscrews there is no problem but with fast pitch ballscrews when the emergencies were pushed or the machines powered down the spindle would drop. It was that the brake did not grab fast enough as the servo power went down so the screw could back drive part of a revolution. One of my machines did this and would drop just over 0.100" on E-stop or Power Off.

Haas has a fix for this. It is an option in North America but I have been told it is standard equipment on machines going across the Pacific. A Haas Technician described a bit about how it works; my electronics knowledge is limited but this seemed to be the idea. It seems to be a supplementary power supply for one of the boards, I don't know which board, I have heard them talk about processor, Mocon and I.O. so I guess there are at least three. Whichever it is the effect of the extra power supply is that the power to the servos stay up longer than it takes for the power to the brake to fall. This means the brake has a chance to lock down before the servos can no longer support a load.

I would imagine it should be possible for somebody with the necessary electronic knowledge to design a retrofit for other makes of machines that have the spindle dropping problem. I do know it is just a wire it in and it works solution; there are no software changes needed.