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Author Topic: Homing & Limit Switches  (Read 3601 times)

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Re: Homing & Limit Switches
« Reply #10 on: June 03, 2018, 12:14:01 AM »
I've found a wrinkle that offers some flexibility if you are using modern AC servos.

I have a second hand Allen Bradley servo and drive for a spindle motor and found amongst all the other features that you can hook the limit switches direct to the drive
not the controller/BoB at all. I have since noticed that this idea is common among other manufacturers also, certainly Granite Devices, Delta, Sneider, Panasonic and Yaskawa.

The idea is that with the limit switches each hooked to their own pin on their own drive that 1) it protects the axis against out-of-bounds excursions, 2) provides a logic lockout
to the axis jog direction that would make the excursion worse , 3) signal the controller that a fault has occurred and 4) whether that fault condition is combined with others
like 'following error' or not is subject to your control having programmable digital outputs on your drive.

I believe that this idea started with the concept of 'distributed motion control' where each axis driver controls its own motion only and therefore has need of direct access
to both its home and limit switches. The combined motion occurs when the controller synchronises the individual axis movements. Ether-Cat is a prominent example of this idea.

My wife left with my best friend...
     and I miss him!
Re: Homing & Limit Switches
« Reply #11 on: June 03, 2018, 12:28:23 AM »
I have a fourth motor that is slaved which I am trying to home.  I have already tried the in series connection and didn't care for the functionality.  With the fourth motor and separate switches, I found I was out of short inputs.  With an additional BOB, does the the ESS communicate with the original BOB to control the motor output?
Re: Homing & Limit Switches
« Reply #12 on: June 03, 2018, 12:55:17 AM »
yes. The ESS communicates with all three of its ports simultaneously.

Really the arrangement of the ESS's IO into three 'look-a-like parallel ports' is redundant. The core of the ESS, the FPGA chip controls ALL of the pins
and they could be arranged sequentially  1 through 50 say. This is how PoKeys name the IO pins of their 57CNC for example.

The ESS and the company that makes it, Warp9, started making control devices for the Mach3 market. As then users of Mach3 were intimately familiar with the
naming and numbering on the pins within the parallel port Warp9 decided to continue the naming/numbering scheme so that it  appeared seemless to their customers.

To take advantage of the extra IO would require you get a second BoB but they are usually pretty cheap and all the extra inputs and outputs is a luxury. You can plan,
design and build additional bits of gear without spilling over into the control space of existing gear.

You may have noticed that Mach4 provides four probe commands, G31.1 G31.2, G31.3 etc and they are supported by the ESS. You might have a probe mounted in your spindle
to measure the 'flatness' or otherwise of the material and another separate switch to set tool length offsets. Having multiple individual probe inputs allow you to do this
without an erroneous input on the unused probe interfering with the active probe. Very handy. We used to be able to do this only by combining the two probes to just
one input pin and getting wrong results  because of noise on the unused probe is not trivial. It does of course require that you have spare input pins available. The ESS
and others makes it easy.

My wife left with my best friend...
     and I miss him!
Re: Homing & Limit Switches
« Reply #13 on: June 03, 2018, 01:06:18 AM »
amongst ESS owners this BoB from CNCRoom has become popular:


All three ports are utilized. I don't have one but the reports of those that do are enthusiastic. Note how the ESS sits
atop the BoB, very convenient.

My wife left with my best friend...
     and I miss him!
Re: Homing & Limit Switches
« Reply #14 on: June 03, 2018, 02:35:05 AM »
I've just been reading the C11 manual and it is not plain to me that it can be configured with pins 2-9 as inputs.

The original specification for the parallel port allowed pins 2-9 as outputs or alternately as inputs. You couldn't have some of each, they were either all inputs
or all outputs. Neither was it possible to re-define the data direction on the fly.

With Mach3s use of the parallel port it was the norm for pins 2-9 be outputs that could be used for step/direction outputs. If you used a second parallel port pins 2-9
are usually assigned as inputs as it was inputs that were seriously lacking when you only had one port. The second BoB then required circuitry that would treat pins 2-9 as
inputs. Not all BoBs did this or are capable of it.

I use Homan Designs BoBs from Austrailia, near enough to local for me. The BoB can be configured with pins 2-9 as either input or outputs for maximum flexibility.
This is made possible by the bi-directional tri-state buffer IC used by Homan designs.

A quick read of the C11 manual suggests this may not be possible with the C11. Before you rush off and buy another you may need to do some research, even confirming
with the supplier before parting with your money.

I have looked at the documentation of the MB2 from CNCRoom that I linked to previously. In table 1 page 4 of the manual shows the pin arrangements.
Pins 2-9 port1 are line driver outputs, ideal for driving higspeed step/direction pulses.
Pins 3-9 port2 are NPN inputs suitable for extra inputs such as limit and home switches.
Pin 2 port2 is a sink output rather quirkily
Pins 2-9 port3 are sink outputs.

Thus there are certainly sufficient inputs for your purposes but the manufacturer has made some design choices that might restrict your flexibility compared to having three separate
BoBs like the Homan Designs units.

My wife left with my best friend...
     and I miss him!
Re: Homing & Limit Switches
« Reply #15 on: June 03, 2018, 10:24:42 AM »
After reading your post, it appears that changing to the MB2 might be the way to go.  I am fairly new to CNC design and especially the electronics, but if I use ports 2-9 for a total of 8 additional inputs, there isn't room on the C11.  The C11 only has 5 inputs, so I don't know think that could work.
Re: Homing & Limit Switches
« Reply #16 on: June 03, 2018, 04:35:31 PM »
if you had a second BoB you'd have plenty of inputs.

You get the regular five inputs with the first BoB and another 13 with the second. As I say there is a question mark as to whether the C11 can re-purpose
its pins 2-9 as inputs, but if the C11 cant there are others that can. One additional BoB (that can re-purpose its inputs) is cheaper than the MB2 but the MB2
also represents a good solution.

My wife left with my best friend...
     and I miss him!
Re: Homing & Limit Switches
« Reply #17 on: June 03, 2018, 07:24:15 PM »
I looked at Warp's link to BoB's. https://warp9td.com/index.php/bob-vendors#GeneralPurposeBOBs.  There are a lot of less expensive solutions.  At least I have a direction now.  Thanks for your help.
Re: Homing & Limit Switches
« Reply #18 on: June 03, 2018, 07:31:02 PM »
I use a C10 bob on my port 3 with a short ribbon cable connector and it's fully configurable as to ins or outs and setting common as 5v or ground.
I use it mostly as an input bank for a joy-stick jogger.
Highly recommended at $23
Re: Homing & Limit Switches
« Reply #19 on: June 03, 2018, 07:43:23 PM »
the C10:
is cost effective.

The C13:
is even cheaper again but it has no buffers. If you have a stuff up or moment when hooking stuff up then the fault will propagate back to the ESS
and blow the FPGA. I myself prefer buffers and won't use anything less.

The Homan Designs board:
is what I use and have been very happy with, a bit more expensive than the C10. Note that it has LEDs on all the outputs
and makes diagnosing setup issues much easier, recommended.

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