Hi!

I have a CNC router that I control via a PC. The spindle is a 3Ph model driven by a VFD.

Whenever the spindle is running, the trackpad on the laptop becomes highly intermittent. The computer has one of those little pencil-eraser control sticks, so it's survivable, but not ideal.

When I disconnect the laptop from the power adapter the problem goes away, so it's presumably a mains power noise issue? Any suggestions for the best way to try to remedy the issue?

Thanks,
-Ben

 

The first diagnostic step will be to see is moving the mains power connection to a different circuit. That should be simple to do. Then check the shielding and filtering of the power supply for the spindle motor. also verify that the spindle motor frame is electrically tied to the drive system shields, which should be tied to their supply common point. The power connection between the spindle drive motor and the drive system should be shielded. The trackpad cable should be shielded, with the shield tied to the computer frame connection.
The concept of the plan is both to reduce the intensity of the rasiated noise field and reduce the intensity of the noise entering the computer input devices.

 

Thanks!

I'll mess around with this tomorrow. The mains for the spindle VFD are 3ø, supplied from a rotary converter, but the computer is undoubtedly connected to one of the split-phase legs. That's unavoidable in the building. The only other connection between the computer and the machine is an ethernet cable, and the issue persists when that cable is disconnected, but goes away when I run the laptop on battery. Maybe an isolation transformer?

The first diagnostic step will be to see is moving the mains power connection to a different circuit. That should be simple to do. Then check the shielding and filtering of the power supply for the spindle motor. also verify that the spindle motor frame is electrically tied to the drive system shields, which should be tied to their supply common point. The power connection between the spindle drive motor and the drive system should be shielded. The trackpad cable should be shielded, with the shield tied to the computer frame connection.
The concept of the plan is both to reduce the intensity of the rasiated noise field and reduce the intensity of the noise entering the computer input devices.

 

I have a CNC router that I control via a PC. The spindle is a 3Ph model driven by a VFD.
Whenever the spindle is running, the trackpad on the laptop becomes highly intermittent.

The most important thing is to carry out correct earth bonding of the machine, Siemens has written a paper on it, called equi-potential bonding.
Re the spindle, you need to ensure it is correctly earth grounded and the 3 conductors to the motor are either tightly twisted, or if it is the 24krpm version, the conductors are screened.
An RPC throws out a lot of interference, so bonding and grounding is very neccessary.
There should be a common ground bus set up where all earth grounds end up, including the service ground.
Also use NFPA79 as a reference, there should be a copy out there to download.
Another reference is the CNCzone forum.

 

OK, and Max is correct about the rotary power converter. So in-line power filters would be good, and given that the computer probably draws far less power, that will be the cheaper line to filter. If you already own an isolation transformer that would be a good thing to try, if you do not own one, a good line filter is probably cheaper.

 

Well our power is out today (yay, California storms) and the house standby genny can't run the shop, but I did a little poking. Whomever built this thing (I got it basically for free and had to rehab it some) connected the spindle to the VFD with SO cord. So there's no shielding there at all. That said, the 20-odd feet of shielded, flex cable that it'd take to drive a 7HP spindle would run a pretty penny, without much in the way of guarantees that it would improve the situation. So once it's all working again I'll try filtering / isolating the laptop's AC as a starting point. While a big part of me laments that it's not currently "right," everything other than the trackpad is working fine, and I don't really want to tear into it more than is necessary to address that one issue.

 

Separation also helps reduce interference coupling. So routing the power cord as far from the computer and trackpad cables is probably worth the effort,although they may already be far apart.

 

1) Upssss! (=ultimate solution)
2) Dif filter
3) laptop on batteries
4) Filter on motor cord

 

I am not familiar with the "Trackpad" but I am guessing that it connects with a cable into the mouse port. If the interfering noise is getting in by the cable from the trackpad, and not the pad itself, then possibly repositioning that cable, and coiling up any excess away from the spindle cable could help. Possibly even shielding that cable, if a "ground" connection is available on the computer. That might be an anchor-screw point for a connector, or an exposed portion of the metal structure of the case, as I am not familiar with your laptop.
The fact is that every wire into the computer has the potential to serve as an antenna picking up the radiated noise, meaning there are a few possible solutions available. Some may be quite simple.

A shield for the spindle power cord could be as simple as a wrap of aluminum foil with a single bare wire around the outside to hold it in place and connected to "ground" . Not at all pretty, but not expensive, either.

 

Well, I've tried several power conditioning options and none of them worked. So... I'm now going to explore a workaround. I've ordered swiveling mouse tray that can bolt under the laptop tray and I'll just use a regular old mouse. Because some problems aren't actually worth solving.

Thanks for everyone's input! I learned things here.