Need guidance for a low-pass filter to clean out 50hz square wave

Joined
Dec 13, 2023
Messages
6
Hi,

I'm working on an automation project for a welding caddy. All is working well except for the servomotor that is jerking like crazy as soon as you ask him a litlle more chooch.

I scoped the power line, voltage is constant at 7V from the buck converter. Clamped the wire for amps and amps signal looked legit. Calculated wattage, well within the 75W max power from the buck at 60.

When i looked at the signal line, well it was obvious that the signal line is packed with interferences. So i need to clean it. I can't really put anything near the servo itself because of space management so i would have to put it in the controle box.

I researched the issue and that signal need to be clean for it to work properly. From what i've read i have 2 good options, a low pass filter and optoisolation.

Optoisolation would be a bit complicated since the control signal run at 5V and the power come in a 7V and share the same negative return wire. I have no wire in place to power it too. Maybe i see it overcomplicated and it's not, if it's the case please educate me!

Second option is a low pass filter. From what i've tested with the DSP on the scope software (Picoscope), a low pass filter between 8KHz minimum and 50KHZ maximum clean the signal to a perfectly manageable level. I'm not good enough to calculate and make my own. Do anybody knows of already made one that i could use that would fit my purpose? I'm pretty sure a component like that exist already made, ready to wire.

Would plugging the filter in the cabinet would be enough to filter the problem out? Or i really need to install it the closest to the motor as i've seen everywhere? I lack the experience to make such a decision and i prefer to research something that will work instead of trying 50 differents possibilities.

I've joined a couple photo of the servo drive signal at rest and one of it trying to do something.

Thank you if you took the time to read this, and again for trying to help!

Have a good day!
 

Attachments

  • Idle-moving_transistion.png
    Idle-moving_transistion.png
    42.4 KB · Views: 5
  • under_load.png
    under_load.png
    48.3 KB · Views: 5
  • with50KHZfilter.png
    with50KHZfilter.png
    41.4 KB · Views: 5

prcguy

Member
Premium Subscriber
Joined
Jun 30, 2006
Messages
16,277
Location
So Cal - Richardson, TX - Tewksbury, MA
Check eBay for surplus priced AC line filters. Corcom is one common brand and here are a few examples in different current ratings. You should be able to search model #s and get specs for high frequency cutoff.


 
Top