Hello Guest it is May 21, 2019, 09:48:00 PM

Author Topic: Z Axis Air Assist  (Read 1738 times)

0 Members and 1 Guest are viewing this topic.

Z Axis Air Assist
« on: December 23, 2016, 03:44:56 PM »
Not sure if this is the right area to post this so sorry if not, my first post.  My router has a pneumatic cylinder on the z axis that assists / helps the servo lift the weight of the heavy spindle.  Does Mach 3 or 4 have any feature for linking the pneumatic assist to the z axis movement?  Will probably be purchaseing a CSMIO/IP-S for this retrofit.  Or would this just be tied to an output that is somehow triggered in GCode?  Thanks, Bryan
Re: Z Axis Air Assist
« Reply #1 on: December 24, 2016, 09:36:14 AM »
A pneumatic assist doesn't need to be connected to Mach 3. The pressure simply gets adjusted to make the force equal to the weight of the Z axis so the motors only supply the force for cutting not for lifting. Typically a pnuematic assist has a tank as well as a cylinder so the change in force as the cylinder extends and retracts is less. A regulator may supply air at a minimum pressure to refill from leaks.

Offline ger21

*
  • *
  •  6,232 6,232
    • View Profile
    • The CNC Woodworker
Re: Z Axis Air Assist
« Reply #2 on: December 24, 2016, 09:41:35 AM »
Actually, on industrial routers, they bleed off the air on the way down, and refill on the way up. It's much more complex, but it gives better performance, because you are never fighting the cylinder like you do in a closed system.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Z Axis Air Assist
« Reply #3 on: December 24, 2016, 11:20:49 AM »
Thank you both for your input.  After closer inspection, it appears there is no activation of solenoids or anything needed from the control system. The top port on the cylinder is a vent, and the bottom port supplies the pressure for doing the lifting.  If I look at the schematic, it shows a check valve and a regulator between the air supply and the cylinder.  My question now is, is the cylinder feed a constant air supply for the lift, and when the z needs to drop, the air that is forced back through the line is vented because of the check valve?  So in other words, when the z needs to drop, the air pressure forced back through the line overcomes the air supply being feed from the regulator?

Offline ger21

*
  • *
  •  6,232 6,232
    • View Profile
    • The CNC Woodworker
Re: Z Axis Air Assist
« Reply #4 on: December 24, 2016, 11:32:28 AM »
I have no idea how the system actually works on the machines I use.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline mc

*
  •  381 381
    • View Profile
Re: Z Axis Air Assist
« Reply #5 on: December 24, 2016, 04:35:38 PM »
They should use a venting regulator.
The regulator lets in pressure when the pressure drops i.e the cylinder extends, and vents pressure out when the pressure increases i.e. the cylinder retracts.
Re: Z Axis Air Assist
« Reply #6 on: December 24, 2016, 08:07:29 PM »
If you have a check valve in the line then I believe the regulator only supplies air if the pressure drops below a minimum value. In that kind of system there is likely to be an accumulator tank. The ratio of the cylinder volume to the tank volume determines the pressure change during the full stroke. If the tank volume were 10 times the cylinder volume then the pressure change would only be about 10%, you don't need a perfect balance force.
Re: Z Axis Air Assist
« Reply #7 on: December 26, 2016, 10:37:07 AM »
Thanks again for all the replies.  So I tested it today and as suspected there is a steady supply of air to the cylinder using the regulator, directly from the compressor.  I am guess the compressor is acting as the accumulator tank that has been referred too, as there is no other tank on the machine.  Getting close to testing the z axis with air pressure supplied.  I think  this pretty much answers all my questions.  Thanks everyone.
Re: Z Axis Air Assist
« Reply #8 on: December 26, 2016, 02:36:57 PM »
The compressor tank can't be the accumulator tank because it is in front of the regulator. So if there is no tank after the regulator then it can be one of two things. It could be just using cylinder volume which is a poor way to do it. Or it has a relieving regulator that can dump air as the cylinder is compressed. Listen to the regulator as the axis moves. You can hear a relieving regulator when it vents off due to a rise in pressure. I dealt with a lot of this stuff when I was building pneumatic packaging machinery. So I'd be interested in what you actually have because I have seen lots of bad designs.