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Hi
We did a similar retrofit for a customer about a year ago, not servos but steppers, the original motors from techno used a brake on the motor, that was engaged when the power was off, to stop the screw from freewheeling
The machine is about 15 years old. The original motors were stepper. I put DMM AC servo motors on all 3 axis. I can't keep the Z axis from falling to the table. This happens when the power is turned off. Can some one please tell me how to fix this, except keeping the power on?
Any help would be appreciated, thanks.
Hi
We did a similar retrofit for a customer about a year ago, not servos but steppers, the original motors from techno used a brake on the motor, that was engaged when the power was off, to stop the screw from freewheeling
Rockcliff Machine Inc.
www.rockcliffmachine.com
especially if they are activated when the motor turns off. Other things people have tried are counterweights, which are simple to implement, but add to the mass that must be moved along with the Z axis, and constant-force springs (they look like long rolls of steel tape), which I tried on a machine of mine, mounted on rollers. They worked okay - for a while. Then they developed cracks which quickly turned into breaks. The latest thing we've attempted involves gas struts, which seems to be working so far. I doubt that these have an unlimited life-span either, though. If they wear out too fast, we might go with brakes ourselves.
The advantage of brakes is that they don't have to work all the time - just at shutdown. The disadvantage is that they don't help lift the Z while the machine's in operation, so the motor has to be able to do that repeatedly without losing steps.
Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software
There is after market brakes that can be mounted on the other end of a ball screw, if necessary.
Failsafe Brake (Power Off)
If the Z is back feeding the ball screw then there may be a need for counter balance, check the temperature of the Z axis motor when it has remained stationary under power for a while, heat tends to show it is working hard to maintain position.
Al.
CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
Gentleman,
Thank you for the quick reply, and the information. I have now tested the Z motor under no load. "NO HEAT" It surprised me. For 1 hour the machine was moving up and down. There was no heat on the casing. Oh I have 400 watt motors on all axis. z axis is 5 inch travel.
Al, I need to check out that page you sent me, thanks. If the price is too high I'll try counter weights. As awerby suggested. The ones that don't brake. So I can try out the machine.
Thanks guys, I thought I did some thing screwy when the Z came sliding to the bed.
Nytwin, what size router do you have? I have been enertaining the idea of the DMM ac servos on my Techno. I just need a paying project for my router before I can see putting more money in it. Al thanks for the link, interesting.
Slowleaner, I have a 1.5 HP router at the moment. My machine is a bit bigger then a table top. Cutting surface 19 X 28 I'm upgrading the machine to help with all of the other projects I have going.
I use pneumatic cylinders for z axis counter balance, you can dial it in so the motor sits still or even falls up a little in a power failure. It avoids anomalies (dimples in a surface etc.) that brakes aren't fast enough to stop.
Montabelli, how would you use a pneumatic cylinder for a brake on Z? I'm not able to picture this. Could you, please explain.
not as a brake but to be able to run with out one. I have pneumatic cylinders on my z's so if the power drops, the axis doesn't. it also takes the load off the z which helps them run cooler as they are not always fighting gravity, a pneumatic counter balance if you will. the cylinder is attached between the fixed plate of the gantry axis and the moving part of the z axis.
the brake only engages when the power is off, one of my machines has a brake the other doesn't but they both have cylinders because the time between the power drop and the brake grabbing is long enough to ruin a part on 3d surfacing.
This is Pneumatic counter balance, you need a constant pressure regulator otherwise the cylinder pressure drops when extended and increases with detract, the regulator prevents this and produces a constant counter balance force.
I have this system on a Ex-cello mill Knee lift.
Al.
Al.
CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
Newb Also, Just Picked Up Machine , Its Yellow, And Didn't Know That When It Came With Counter Balance That Air Had To Be Supplied, But Only 20 PSI, Small Air Cylinder Keeps Z From Slamming Down , So Thats All I Know
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