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Eliminating EMI in CNC Machine

2021/01/19 > Back


Electrical noise comes from a couple of things: First is EMI which is caused by current flowing through wires. The second is electrical mechanical noise cause by physical switches bouncing when they open or close; both of these conditions can cause you problems with the daily operation of your CNC machine, the mechanical noise can be dealt with pretty easily, but the EMI noise on the other hand requires a little work to help reduce and prevent it. The guidelines that follow are some things that you can do to reduce this problem, before we get to the list of things to do, let’s first discuss a little more what EMI is.

EMI as be stated above is caused by current running through a wire, when current runs through a wire a magnetic field is created, as the current builds the magnetic field gets stronger, then when the current ceases to flow through the wire the magnetic field collapses, this in itself isn’t too bad, but if this magnetic field happens to cross another wire it will induce a voltage across it, this is how a transformer works: It uses a magnetic field in one coil of wire to induce a voltage in another coil of wire, if a wire is able to induce a voltage across another wire that we are using for a signal at logic level voltages, it may drive the voltage level in that wire to some state that the logic circuits reading it cannot understand. Knowing these information we know that a magnetic field crossing our signal wires could drive the input voltage to the unexpected band resulting in unexpected operation.

The power interference of CNC machine belongs to electromagnetic high frequency interference, from its working principle, it can’t be prevented. The most direct harm of power interference of CNC lies in the interference to operating system, so effective measures must be taken to suppress electromagnetic interference in order to ensure a reliable work of numerical control machine. While most people consider EMI to be something that arises from external sources, internal sources can be equally important; the common methods for solving EMI of CNC machine are adding EMI filter or grounding of PSU to enhance the ability of anti-interference.

Precautions to be underscored:
1. The grounding system: Attention should be paid to the grounding technology of CNC system: Because the CNC part and servo unit make the moving part on the track, the disturbance intensity has a great relationship with the central connection of the system.
      AC Grounds:
      A typical CNC machine may have a few different power supplies installed and in use on the system, make sure the AC inputs to your power supplies are properly grounded, tie them all to the same ground. Many power supplies have a metal case and the case is usually tied to the AC ground as well so keep this in mind when you are fastening them down.
      DC Grounds:
      There are two trains of thought when it comes to the DC ground. Some folks say that you should ground it to the AC ground and others suggest that you should create a separate isolated ground plane for the DC power. I don’t know if one style is better than another but if you are interested a Google search you can find folks that will defend either side of the argument.

2. Adding EMI filter: The AC that you use can inject noise into your power supplies and other equipment. If you have motors running on the same circuit for example, can create noise on the line if it is running on the same circuit as your CNC components. In-line filters are made to attenuate (reduce or block) this type of noise from the AC line voltage before it is run into your equipment. The best AC line filters for solving EMI of CNC machine can be found at Here. You can refer SCB58 / SCB70H / SC55 type first.

Data Source: linuxcnc.