Building the most versitile BOB for ESS

[maxspongebob]

Hi,
like you I decided to make my own breakout board for my ESS, then I could have exactly what I want and nothing that I don't.

My breakout board was split int two boards, well technically three as there is a power supply board also.

Board 1:
Connected (ribbon cable) to port 1 of the ESS
10 differential outputs for up to five step/dir axes.
1 output Enable-to all servos
1 output Reset-to all servos
5 inputs Alarm-one per servo
1 24VDC output switched with Enable signal for Z axis electromagnetic brake

Board 2:
Connected (ribbon cables) to ports 2 & 3 of ESS, pins 2-9 of each port as inputs.
26 general purpose inputs (24VDC sourcing 5mA) (6 Limit switches, 3 Home switches, 1 Probe input, 5 wired pendant inputs)
1 output- relay for spindle on/off
1 output- spindle PWM
1 output- coolant pump SolidStateRelay
5 general purpose outputs (24VDC totem pole ie sourcing or sinking up to 50mA)

I have had these boards in service now for six months and they work well. There are a number of improvements I wish to make, and so will design and build another
over the next few months.

I used high speed dual op-amps to generate the differential step/dir signals but am less than happy about noise immunity of them. I will use a dedicated line driver IC (AEIC7272) in my next board.
The linearity of analog voltage output to PWM duty cycle is fair , about 90%. My next design will have totem pole output prior to the LPF for 97% plus linearity
I have a second spindle based on an AC servo, so my next design will have six step/dir outputs that would allow me to use the secondary spindle as a C axis for rigid tapping.
My next design will be on one PCB that the ESS plugs in directly rather like yours or an MB3.

Craig

I had gone down that road as well using ribbon cables to connect a separate PCB. What I found was that there was too much EMI in the cabinet that was coupling to the cables. Differential signals and piggybacking the ESS on the board minimizes this problem. Instead of driving the stepper controller with a differential signal I am using 12V logic driven by a darlington array. This lets me provide the full 12 miliamps to each line or a jumper can be installed to sink a full 500 miliamps. I will post some schematics.

Seeing all that copper makes my head hurt. I send all my PCB's out to be fabricated. It cost a little more, but I get silkscreens, solder masks, 4 layers, and assembly is way easier. I use PCExpress. They even have a simple schematic and PCB design app.

[joeavaerage]

Hi,
the reason that I isolation route my boards is time.

If I send a board out to be made, you get lots of advantages, masks, plated through holes etc but then it takes three weeks for it to get here.
When a customer comes in I often have to design a board for that customer alone. I will design it, isolation route it, populate, test and program it
in a day and have the money in the bank the next day. I can't wait three weeks and over 95% of my designs are one-offs.

I require 416kHz signalling to my servos therefore differential signalling is required. I have no trouble with EMI at the ribbon cable input, I am very
particular about designing around impedance levels that make my circuits if not immune, at least invulnerable to EMI.

Where I did get into EMI trouble was at the dual op-amps where the inverting inputs ended up at 10kOhm to ground and just a little to subject to EMI.
All my axis servos are fine but my secondary spindle servo is not. The line driver ICs I intend on using will solve that problem.

I will make a single board, but more for wiring elegance (avoiding ribbon cables) than any strict need to do so.

Excepting that I can't use my secondary spindle as a C-axis which I seldom use anyway and every thing else is working fine, so I cannot claim this
project has high priority. I have being made for me by a sheetmetal specialist way covers....and they are my priority at the moment.

Craig

[maxspongebob]

Final update on the BOB project. I finished the board, software and completed all the testing so not it goes into the lathe. Originally I built my lathe conversion using discrete boards for each function. The individual boards were wired back to the ESS using ribbon cables. This solution worked fairly well, however I had always had a bit of EMI coupling onto the stepper signals. I learned again the hard lesson about using the minimum amount and length of wiring.

The new board replaced a pile of wires and several smaller interface boards in the cabinet. It is working much better and has no detectable interference on the lines.

Here is an image of the old setup:


Here is the new setup:


Leftovers:

[joeavaerage]

Hi,
I too finished my revised breakout board a few days ago, and it's in service.

Craig