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Author Topic: Homing & Limit Switches  (Read 3651 times)

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Offline mark4

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Re: Homing & Limit Switches
« Reply #20 on: June 04, 2018, 06:30:22 PM »
Hello I use the MB2 and its 24volt IO. This has been the best design for me yet. I upgrade small mills usually they only have one limit switch on X and Y axis for + and - limit and home switch Z axis has two switches. I like the fact that i can set mach up to work with this. I also use Ac servo drives and thanks to this setup i don't need to add extra circuitry to get my homing to go to the index pulse. Which is the most accurate homing you can have. I have been homing to the index pulse for years on different machines sometimes i had to build circuitry to make this happen. Daisy chaining your limit/home inputs might be necessary depending upon config you can still run out of inputs. thats easy though add a plc howver that was tricky to configure as i couldn't get allot of information so i had to experiment. But with a little help from Machsupport and Ess support and Mb2 support they all helped me with different problems. Now i am thrilled with the final outcome and the mill works great.
good luck
mark
Re: Homing & Limit Switches
« Reply #21 on: June 04, 2018, 08:35:14 PM »
I have an ESS smooth stepper and C11G BOB.  How do I create more inputs to accommodate that many switches?

If you want discrete inputs, you can use a C10 bob which comes with a db25 plug to parallel port cable and use port 3, and set up the pins as inputs.
The C10 requires 5v supply voltage from external source.
I use a C25 bob plugged into ports 1 and 2 directly, and a ribbon cable-connected C10 on port 3.
The C25 is quirky and I modified mine by removing the input led's.
Homing & Limit Switches
« Reply #22 on: October 07, 2018, 03:28:40 PM »
I finally installed a new BOB to my ESS and increased the inputs.  I did this about three weeks ago and everything worked great.  My homing switches act as limit switches for X-, A- and Y- while the homing switch for Z was +.  Like I said, it was working great.  It would square my gantry and stopped if I hit a limit.  My sequence for Ref All Home is Z+, X- (A- Slave as well) and finished with Y-.  Today when I fired it up and hit Ref all home, it limits out on Z+ and shuts down.  When I do and axis override it homes to X- and limits out at X- and says referencing complete.  I am using Mach 4.  I am almost sure I didn't change a thing.

Any thoughts?

Offline mark4

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Re: Homing & Limit Switches
« Reply #23 on: October 08, 2018, 11:41:09 AM »
If everything was working great something changed either you changed a setting or you could have a wiring or switch problem. 1st thing is check the diagnostics screen and see if any of the limit or home switch leds are on. then if they are all off check the wires and switches and make sure one is not stuck.
 
Re: Homing & Limit Switches
« Reply #24 on: October 08, 2018, 01:30:35 PM »
I had already done that.  I ended up changing my settings for my limit switches so they were just homing switches.  After that worked a couple of times I reset the homing switches back into homing and limits like I had originally and it worked.  Until this morning and I had to do the same thing again.  And to add further to my frustrations the Mach 4 wouldn't recognize the ESS for configuration.  I rebooted, reloaded and reset.  Finally I just set the switches to homing only.  After I had it homed I set the switches to limit.  Almost feels like there is a bug in the software.
Re: Homing & Limit Switches
« Reply #25 on: October 08, 2018, 02:12:01 PM »
Hi,
I have always advocated having separate home and limit switches.

I suspect that when you have them programmed as dual duty that intermittent noise is affecting them.
When programmed as home switches only the occasional spurious 'home event' doesn't matter, the machine carries on. When programmed
as limits however any spurious signal will be treated as a 'limit event' and Mach will stop.

May I suggest putting a 0.1uf capacitor across each input. Note that it may slow the response to the switches to the extent that it would
be unusable in practice but may help you resolve whether in fact the problem you describe is due to noise.

Craig
My wife left with my best friend...
     and I miss him!

Offline mark4

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Re: Homing & Limit Switches
« Reply #26 on: October 09, 2018, 12:38:50 AM »
one thing I would add is the wire going to your home/limit switches shielded and is that shield grounded to one side only.
I have in the past successfully used .1 uf capacitors but haven't had to do that in years. and I 1/2 agree about the separate
switches. some machine like bridgeports only have one switch on X and Y, Z has two. It would take some doing to change and
aside from a Z switch playing up have never had trouble with the X and Y but I do replace the original wire with shielded wire.
Re: Homing & Limit Switches
« Reply #27 on: October 09, 2018, 02:54:46 AM »
Hi,
with powerful and fast industrial machines a 'limit event' shuts the machine down instantly and totally.....its a legal requirement.

Thus an opening switch contact will cause all the electrical contactors to drop out, the spindle stops, the axis and spindle brakes come on,
hydraulic pumps stop, coolant pumps stop.....no ifs or buts....no computer required just a safety interlock circuit.

In normal circumstances you hope that a limit switch never activates, if it does, everything stops, often with tool breakage and the part being ruined.
For those situations you simply MUST have separate home switches, otherwise every time you tried homing your machine would shut down.
Remember to satisfy the law you cannot disable the limits under any circumstances.

Our hobby machines are not that powerful or fast and we can probably ignore the safety laws which apply if you are employing people to operate
machines. None the less I still advocate separate switches.

One distinct advantage is that limit switches are situated to activate at the very end of the allowed axis travel, usually that situates the switches at the ends
of the axis. Your home switch does not have to be at the end of travel and may therefore be mounted at a more convenient location with respect to
vulnerability to damage or contamination say. Also it allows you to choose switches which are optimized to the task. For instance I use roller plunger
switches for homing, they allow repeatability of better than 0.02mm but I use proximity switches for limits.

Irrespective of whether you combine limit and home switches or not there are some good precautions to take to avoid noise. Mark has already suggested
screened cable.

Another idea is to have some reasonable current flowing in the circuit at all times, say 20mA. This is another way of saying that a 'moderate impedance limit
circuit is less sensitive to noise than a very high impedance circuit or a very low impedance circuit'.

A high impedance circuit is likely to suffer from 'voltage' or 'displacement' noise whereas vey low impedance circuits are subject to 'induced current'
noise. For instance with respect to the pic attached. With the resistor of 250 Ohm as shown and a 5V supply with the switches closed about 20mA flows through
them. This circuit would still work with a resistance of 25kOhms but the current would now be only be 200uA and therefore much more prone to
capacitively induced noise spikes from an adjacent circuit. Likewise if the resistor is reduced to 20 Ohms the current is now 250mA but is now
subject to magnetically coupled noise spikes from adjacent circuits.

A little capacitance doesn't hurt either, I've shown a 1nF capacitor, you could buy ten of them for $1. You could use higher vales for more noise
suppression but eventually you will cause the speed of response to slow. If you need as much a 0.1uF you should look to find why that other
'bothersome' circuit is radiating that much noise.

Craig
« Last Edit: October 09, 2018, 02:56:39 AM by joeaverage »
My wife left with my best friend...
     and I miss him!