Hello Guest it is May 17, 2021, 06:58:48 PM

Author Topic: Limit switch config help please.  (Read 755 times)

0 Members and 1 Guest are viewing this topic.

Limit switch config help please.
« on: August 18, 2019, 05:49:25 AM »
I have just Migrated to MAch 4 with an ESS Smoothstepper+C11+C10s breakout boards.

I have a 3 axis Gantry router and want to place my limit and home switches,
Can I use the same switch for home and Limit for each of my axis or do I really need separate switches, do I really need X+ and X- limit switches.

I'm using the sensor shown but I 'm having trouble wiring it in. I'm applying 12v to sensors +ve & -ve with a 2K external resistor across the Black and Brown terminals.  Black terminal then is fed to the Input of the BOB.   Is this correct ???
One step at a time!
Re: Limit switch config help please.
« Reply #1 on: August 18, 2019, 06:39:36 AM »
With the sensor wired this way I get 'Cant Jog to x Limit. Input state LED is Lit.
If I cover the sensor then jogging is OK, The input state LED goes out!
Looks like I may have too much or too little Voltage at the input pin,.
The sensor is working backwards ??
One step at a time!
Re: Limit switch config help please.
« Reply #2 on: August 18, 2019, 06:58:27 AM »
Hi,

Quote
Can I use the same switch for home and Limit for each of my axis or do I really need separate switches

Yes you can but I always recommend separate home and limit switches.

Quote
do I really need X+ and X- limit switches.

If you are going to have limit switches then yes....you need two switches per axis, one at the positive limit and another at the negative
limit. You could use 'soft limits' instead of limit switches. Genuine limit switches are safer but if you have good home switches
and homing procedures then soft limits are a reasonable proposition. If you  don't have good home switches and homing
procedures then you better have limits or you will crash badly and repeatedly.

Craig
My wife left with my best friend...
     and I miss him!
Re: Limit switch config help please.
« Reply #3 on: August 18, 2019, 08:33:23 AM »
So, I would use 2 limit switches for for each of the X & Y movement but only one for Z (Fully raised)
Can I double up on the Positive limit for the Home switch ? Or dont' I need the Home with this configuration ?
I have several of the limits switches so why not use them, any idea on the wiring ??

George
One step at a time!

Offline MN300

*
  •  243 243
    • View Profile
Re: Limit switch config help please.
« Reply #4 on: August 18, 2019, 09:48:01 AM »
You suggested:
Quote
Looks like I may have too much or too little Voltage at the input pin
The data sheet mentions an internal resistance of 4.7k. When no material is sensed this resistor attempts to pull the input to 12V. There may be some protection from this in the C10 input circuit but it would be best to put  4.7 volt zener diodes across the inputs to limit the voltage the input sees.
Re: Limit switch config help please.
« Reply #5 on: August 18, 2019, 11:23:04 AM »
10K resistor in place as shown and now working, thanks for the help.

George
One step at a time!
Re: Limit switch config help please.
« Reply #6 on: August 18, 2019, 11:25:20 AM »
So, I would use 2 limit switches for for each of the X & Y movement but only one for Z (Fully raised)
Can I double up on the Positive limit for the Home switch ? Or dont' I need the Home with this configuration ?
I have several of the limits switches so why not use them, any idea on the wiring ??

George
Hi,

Quote
Can I use the same switch for home and Limit for each of my axis or do I really need separate switches

Yes you can but I always recommend separate home and limit switches.

Quote
do I really need X+ and X- limit switches.

If you are going to have limit switches then yes....you need two switches per axis, one at the positive limit and another at the negative
limit. You could use 'soft limits' instead of limit switches. Genuine limit switches are safer but if you have good home switches
and homing procedures then soft limits are a reasonable proposition. If you  don't have good home switches and homing
procedures then you better have limits or you will crash badly and repeatedly.

Craig
Craig, I have several of these Proximity sensor, If you would like a couple I'll happily post them out to you.
George
One step at a time!
Re: Limit switch config help please.
« Reply #7 on: August 18, 2019, 02:40:51 PM »
Hi,
I personally find roller plunger snap action microswitches to be preferable for home switches.

https://nz.element14.com/honeywell/bzc-2rq18-a2/switch-basic-top-roller-plunger/dp/1525198

Proximity sensors make good limit switches. I recommend Zener diodes as MN300 proposed.......you risk
over-voltaging your C10s input TTL ICs without them. Note also that you cant really wire them in series, with
a proximity switch you are pretty much required to have one input per switch. Microswitches, when used as
limits can be wired in series.

Craig
My wife left with my best friend...
     and I miss him!
Re: Limit switch config help please.
« Reply #8 on: August 18, 2019, 04:29:23 PM »
Thanks Craig, I didn't realise you were on the other side of the world :-)
I take your point about the overvolting the inputs!
Also I would not need the 12v supply that is feeding the Proximity sensors.
Roll overs are much easier to set up so I'll consider it.

So am I correct in assuming that X +++ and X--- can be wired in series and use the same input pin on the C10 ?? (Same for y & Z of course) but then again if all 5 switched are wired in series and are set normally closed, then any one of the switches being triggered will cause a stop ??
In this configuration do I need a home switch ?? or do I set this as the same as x+++ etc ??

Thanks,

George
« Last Edit: August 18, 2019, 04:32:08 PM by Len-Tikular »
One step at a time!
Re: Limit switch config help please.
« Reply #9 on: August 18, 2019, 04:56:49 PM »
Hi,

Quote
o am I correct in assuming that X +++ and X--- can be wired in series and use the same input pin on the C10 ?? (Same for y & Z of course) but then again if all 5 switched are wired in series and are set normally closed, then any one of the switches being triggered will cause a stop ??

Yes, that is correct. In the early days of Mach when everyone used a parallel port with so few inputs it was the norm to connect limit switches
in series. You could also nominate three of the limits, one for each axis as home switches. The problem becomes that Mach has to interpret what any
given switch event means, was it intended as a home event or is it a limit for which an immediate Estop is in order?.

With an ESS and two breakout boards you have plenty of inputs and do not have to compromise. You have sufficient inputs to have three separate inputs
for three individual home switches and six inputs for six limit switches. This would mean for instance you can use proximity switches as limits and not
have to try to wire them in series/parallel on some other tricky combination and still have microswitches for home switches. No tricky interpretation by Mach
required.

Home switches can be anywhere on an axis, even in the middle. It is normal to place them at one end of each axis however but they don't have to be right at the
absolute end. My home switches are within 3mm short of each axis end with limit switches just beyond them.

You might ask 'what is the sense of having machine 0,0,0 somewhere inside the travel envelope', but that is what 'home offsets are all about.
Thus if your X axis home switch is 10mm from the negative limit then you would nominate the X axis home offset as 10mm. Thus when the
X axis homed its machine coordinate would not be set to zero but rather to 10mm. When the X axis is homed it is 10mm away from the negative
limit and with the home offset, hey presto, the machine coordinate is 10mm as well.

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