Racking Gantry Protection
Hello All,
I have reworked my home build machine to include ball screws and motors on each side of the Gantry. Everything seems to be working smoothly.....
My concern is .....What happens if ONE of the motors stalls. The gantry then
racks and could cause damage. Is there any type of feedback circuit that would "sense" a motor stalling or stopping and shut the machine down as if I hit the E-Stop.
All 4 motors are Nema 23 425oz 1/4 inch drive shaft being driven by a BOB and 4 drivers. X and A are slaved in Mach3.
Thanks
Art
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If the motors are strong enough to damage the gantry before they stall I think a mechanical connection (timing belt) is the only safe choice. At least that is what I did. It has another advantage that you don't need a synchronizing homing procedure to get the gantry square.
Not sure if there are off-the-shelf stepper safety interlocks but it sounds complicated and they may be subject to failure itself.
Hi,
My last machine had this issue, too. When one motor stalled something would bent or break so I solved it with a timing belt as Jerry just suggested.
An electronic solution is surely possible with 2 encoders that shut the machine down as soon as a certain difference is detected. But I don't know any off the shelf solution so this would be an quite advanced project (e.g. using an Arduino).
Christian
My CAM Software and CNC Controller: www.estlcam.com
Thanks guys,
I'm not sure I understand how a timing belt would help. Would it be connected between the two motors? What would happen if one of the motors stopped or stalled?
Could you elaborate or show a photo please?
Thank you
Art
Ps. What is a "synchronized" homing procedure
Well, the timing belt forces both motors to run synchronous. If one stalls the other one will stall too - so no harm is done the the gantry or rails. I have no picture as I don't have the machine anymore - but it's really simple: just put a pulley on each spindle and connect them with a timing belt.
My CAM Software and CNC Controller: www.estlcam.com
The synchronized homing procedure refers to having a home switch on each side of the gantry. It's possible for one side to lose steps, and not the other. To counter this, and the possible out-of-square result, Mach3 can be set to drive each side to its own Home position, thus ending up with a gantry that's as square to the rails as your home switch position allows, despite any steps lost due to binding, a chip on the rails, etc. Doesn't help during an operation, but at least you start off square.
Luke
Romaxx sells this device: Store | Romaxx CNC Router Systems and have a plugin for Mach 3 that will e-stop if your motors get out of synch. You'll obviously have to add encoders as well but this is an off the shelf solution. I looked into this at one point and IIRC, encoders can be found for about $25 each.
-Andy B.
http://www.birkonium.com CNC for Luthiers and Industry http://banduramaker.blogspot.com
You can find magnetic linear encoders relatively cheaply. I ran my first and second machines with one motor running a timing belt to two leadscrews, and that worked very well.
timing belt gives the most protection.. if it get loose simply dont dive the machine.. one motor need no synchronizing..
additionally a belt cheaper than a motor with addionally drive..
yet if someone like two motor they can do..
murphys law says, if something can go wrong, that will go wrong :-)
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