AC Servo Controller Box design

Hi folks! It’s been a year since last I posted (life got in the way of building my machine again, plus funding), but I’ve got bits and pieces coming my way. Ballscrews from Fred will be ordered next week once I finalize dimensions. In the meantime I ordered some servos (4x400w delta b2 series 220v), have the controller board on the way (EdingCNC 720), and the spindle is back ordered for a bit.

So I’m trying to wrap my head around the best/safest way to wire up the control box. The controller is 24v, so what I want going in is:
- 220v to the VFD
- 220v to the servo drives and a 24v PSU

Then the questions. The Delta manual suggests an EMI filter between the wall supply and the motor power input (not the control input). It shows a contactor for the entire drive in case of faults. I’ve been watching and reading other servo documentation (like DMM’s videos for their Dyn4 drives) as well. I’m not an electrician. I understand the basics and guitar wiring, but I don’t have a feel for best practices. I have an electrical engineer buddy who will double check my work for idiot errors.

What I’m considering doing is putting in a filtered and fused IEC for each of the power lines (VFD and drives/controller). The question is whether this is enough? Should I be EMI filtering each individual servo drive? To keep noise away from the other drives/from the PSU?

For safety, I want to wire in contactor(s) for the VFD and the drives. And non-fused breakers before that to isolate parts of the circuit as needed, perhaps.

Assuming it’s sufficiently rated, my gut instinct would be to install that between the power supply and the motor (not control) power for each drive. If there is a fault in any one drive or the E-stop gets triggered this would cut power to the servos, but not the control circuits. I’ve seen some folks put in a contactor per drive - I don’t really understand why that would be needed. I figure if one drive faults, or the E-stop system triggers, I want them all to stop. Leaving power to the control circuit should let me see which drive went AWOL.

I may add more questions as the wiring schematic evolves further, but that’s the bit that’s tripping me up right now.




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I'm doing a bit of re-wiring of my own machine and it's E-stop and am thinking along similar lines to you with regard to maintaining power to the controller (AXBB-E in my case) but cut power to the motor supplies. This will keep the UCCNC software running and make diagnostics and recovery simpler. I can't see a good reason for having separate contactors for each motor. As you say, if one stops you want them all to stop.

Something I am considering is a more accessible Process Stop button. Far more common for me than needing a quick E-stop is needing a quick process stop when I start the job and realise I haven't reset the tool-change interlock (the spindle won't start) or have forgotten to load the correct job file. It must be an age thing!

Something along these lines will work.

In this setup, the E-stop circuit just uses an ordinary 4 pole relay wired to form a latching circuit, you could use a Safety relay to do the same job but these are expensive.
This circuit requires a momentary Reset button to be pressed before the E-stop circuit will latch on again after the E-stop has been pressed. This circuit could be expanded to include Limits or other safety features like cabinet doors open etc so that the E-stop cannot latch back on until all is safe.

When safe the E-stop circuit turns on the Master relay, this in turn, switches on the Drive relay, which then turns on all the contactors for the drives.
Depends on the power consumption of the drives to whether you use one contactor for all the drives or separate ones for each drive, personally, I would give each drive its own contactor rather than one large contactor. Similarly with the EMI filters, easier to use separate smaller filters than one large filter and probably cheaper.

The reason for using a separate relay for turning contactors on rather than directly from the master is so that other things can be switched on like lamps to show drives are on or anything else you may like. You'll also notice I use Terminal blocks TB1, TB2, etc is to make wiring simpler rather than trying to get several wires into one terminal.

Regards the VFD, then there is no point in cutting power to this in an E-stop situation because of how they work with draining the capacitors when power is dropped. It can also damage the VFD if done to often while the spindle is spinning.
They don't switch off instantly and stay powered until the capacitors have drained, also if the spindle is spinning at the time of the E-stop this then acts like a dynamo and feeds power back into the VFD/capacitors increasing the time before it powers down. It's much safer to send the VFD an E-stop signal which then will apply DC braking and stop the Spindle much faster.
You could if you wish to put a timer relay in the circuit which sent an E-stop signal to the VFD then after a set time dropped the power. This would be the safest way but in my experience, it's not required.

Also, note on the power side of the Servo I have drawn separate power lines L1, L2, and L1C and L2C.? It's common on servos to have power for the control logic of the drive but this should not be part of the E-stop circuit which is why it's drawn this way.

Hope this helps, there are many ways to do this, I'm not saying this is the best or safest way and each builder needs to decide what they want in terms of safety, etc, but this works and is safe without getting overly daft about it.

Dean, extremely helpful as always! I’ll go ruminate on this for a bit - the plan was indeed to cut power to the motor power lines only, leaving the drives and controllers on. I’m still pondering whether I want to add a hardwired (purely electrical) limit switch/e-stop circuit for the motors, or rely on the controller board to cut everything. The additional info for the. VFD is also very useful, thanks!

Quote:

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Originally Posted by Mattia

I’m still pondering whether I want to add a hardwired (purely electrical) limit switch/e-stop circuit for the motors, or rely on the controller board to cut everything.

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It's a subjective thing and some will disagree but to me, an E-stop should drop power to the drives and drop the Latching circuit requiring a hard reset and not just rely on software or electronics.
Limits I don't class an emergency and more a positional error in which case the Controller can deal with those safely enough but an Emergency requires power to be dropped.

Agree Jazz, ideally estop should cut power to motors.

One feature of most AC servo drives is separate power input for control circuit and motor power - makes it possible to cut motor power whilst drive smarts remain on.
(Edit: I see Jazz already mentioned this above)

(Note, you can't switch / estop the output of most motor drivers (between driver and motor) as you may kill the driver).