Section 9.1 of the TI data sheet - recommends 100R, you're not far off. It's a fast switching device - most differential drivers (not design for high speed) will have deliberately slow slew-rates to limit EMI. But, it is what it is.
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Section 9.1 of the TI data sheet - recommends 100R, you're not far off. It's a fast switching device - most differential drivers (not design for high speed) will have deliberately slow slew-rates to limit EMI. But, it is what it is.
Progress update:
Stand is bolted to the floor and machine is clamped to the stand. I cut some little bits of angle and use M8 bolts for the clamps. So first the stand was levelled as best a possible with some composite slate tile shims and bolted to the floor. Then the machine was levelled on top of the stand (it has an M12 bolt threaded into the bottom of each corner) and checked that each bolt was bearing weight (attempting to avoid twisting the machine), then finally it was lightly clamped at 4 points to the stand.
Attachment 28401 Attachment 28402
I cut all the cabling to length and took it indoors to solder all sensors and motors, this took a few hours and rather a lot of heatshrink.
Next I fitted all the motors and sensors to the machine and started work on the enclosure.
A few trips to screwfix to further increase my holesaw collection, then an unpleasant afternoon drilling fan, exhaust, switch, indicators and gland ports in the steel enclosure. Now mounted to the wall and cabling fed through. Will do final wiring tomorrow and maybe the first machine moves!
Attachment 28403 Attachment 28404 Attachment 28405
That ugly slot next to the glands is for the DB37 control cable to go to the DDCS control box.
Finally both drag chains were fixed.
Attachment 28406 Attachment 28407
That machine is really starting to take shape. Nice work.
I have wired fault outputs in series and taken that to a "servo fault" input on the motion controller. Partly for the reason you give - can't put power on the drivers via the safety relay until there is power on the drivers - and partly because I classify "fault" signals into two categories. Personal safety - when you hit estop you really want it to stop NOW so that is a safety relay task (mine cuts driver power, driver enable, and signals motion controller), and machine issue - driver fault, limit switch - and I'm happy that motion controller firmware can be trusted for that. Does DDSC have "driver/servo fault" input(s)?Quote:
Originally Posted by devmonkey
My solution is similar to Neale's. The UB1 board I use has a simple safety-relay circuit, so the first 10 or so inputs can be linked to close a relay. My driver's fault signals feed into this, alongside my VFD's fault signal and a signal from my e-stop circuit. The driver's enable line is linked to the relay output, so if one drive faults the drives remain powered but not enabled. Same happens if the VFD drops out, or I hit the e-Stop button (but that also has the effect of killing the power to the drivers directly).
Thanks guys, lots of inspiration here.
The DDCS has two estop inputs but one is difficult to access on the MPG port. I have an idea how to sort this now. Currently I use the output of the safety relay to switch the low side of the contactor coil and also signal low to the DDCS estop input which is configured to go into emergency stop if this signal is high. I was looking to integrate the alarms on the estop switch side of the safety relay but this is wrong, instead I can put them on the output side. Take a resistor to +24v then series the NC alarm outputs via the same safety relay contact to ground. Take the DDCS estop input from the resistor.
With this configuration the alarms will only estop the DDCS not the contactor, but when the safety relay is tripped both DDCS and contactor will estop. Million dollar question, do I need a diode to prevent current flowing from emitter to collector through the alarm NPNs into the DDCS input when the safety relay is open? My analogue electronics is extremely rusty.
Attachment 28416
Analogue is easy, just work out where the current will flow. Ohm's Law plus Superposition Theorem equals The Answer.
Good news machine is moving, very nicely indeed, I will post some video tomorrow.
I have a question about a potential issue I've discovered with the 24v dc smps I'm using for powering the controller and proximity switches. The unit is a high quality double insulated (no earth connection) TDK-lamda din rail SMPS and I've used them in automation projects before. However this is the first time I've noticed this issue.
Basically you get a slight tingle (barely noticeable electric shock) when touching both DC ground and mains earth.
I believe this is down to the 'Y' capacitor used in the SMPS to reduce EMI, it is a small capacity capacitor that couples input to output (when there is no earth connection) and is required by all SMPS to meet EMI regulations, however it has the nasty side effect of raising the DC output to around half mains voltage wrt mains earth. The capacitance is tiny so it isn't dangerous.
I noticed it whilst leaning on the earthed machine and holding the shield of my db37 cable which is connected to dc ground.
I've checked the unit with a megger to prove to myself it is properly isolated.
So do other people see this, does it matter? What do other people use for the 24v side of their systems? I might substitute it for a small power supply with an earth connection (class1??).
EDIT:
Just ordered a class1 meanwell unit MDR-60-24, this has an earth connection and the datasheet shows it's 'Y' capacitor is connected to it.
https://www.meanwell.co.uk/pub/media...DR-60-SPEC.PDF
Cheers, Joe
Why leave the 24V supply floating wrt earth? Take the 0V connection to the control box star point and all will be well. Can't see any reason not to ground it. That's what would normally be done - my control box has a 24V smps and a 5V+12V smps and all the 0V connections go straight to the star earth.Quote:
Originally Posted by devmonkey
Should add the noise is coming from the stepper drivers as it only happens when the stepper is moving, so basically the EMI filter in the 24v smps is filtering what comes into it and coupling it to the 24v DC output which causes the DC output to float relative to mains earth because the neutral and earth are coupled at the electricity company's box in the street. I will fit an EMI filter in front of the toroidal stepper PSU to suppress noise returning back up the supply and into the 24v SMPS (and the rest of the house).