only limit switches in on direction

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pascalken
Posts: 18
Joined: Fri Dec 17, 2021 6:02 pm
Acorn CNC Controller: No
Allin1DC CNC Controller: No
Oak CNC controller: Yes
CNC Control System Serial Number: none
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No

only limit switches in on direction

Post by pascalken »

Hi,

I am in process of installing an OAK on a MAS MCV 500.

The machine has only limit switches on X- Y- and Z-
It is equipped with linear scales on all axes used by the old controller.

Do I need to install X+ Y+ an Z+ switches? Or is setting the maximum travel distances sufficient?
If these limit switches are not essential, do I need to bridge the corresponding inputs?
Or can these inputs be repurposed?
I understood from YouTube: "Ch. 1 Centroid CNC PLC Programming: Notepad++ Setup" that they are hard wired... I suppose for an emergency stop.

Some advice would be welcome. Thank you
cncsnw
Posts: 3764
Joined: Wed Mar 24, 2010 5:48 pm

Re: only limit switches in on direction

Post by cncsnw »

While it is better to have independent limit switches at each end of each axis, it is not required.

Limit switches protect the machine in several cases:
1) You are jogging the axes before you have homed the machine, and you try to jog an axis beyond its physical travel
2) As you are running the machine, an axis loses position due to mechanical slippage in the drive train
3) As you are running the machine, an axis loses position due to lost command pulses (if using position mode) or encoder counts

With an Oak system, if you have only one switch per axis, you can just leave the other inputs inputs unused, or if needed you can change your input assignments around and use the extra three inputs for other purposes.

There are no "hard wired" inputs on an Oak system. Any inputs can be used for limit switches, or not.

The Allin1DC, by contrast, treats the first six PLC inputs as axis limits, and prevents axis motion in the direction of an open input (tripped switch). That is possible because the Allin1DC contains the servo drive hardware, as well as the control unit and PLC.
pascalken
Posts: 18
Joined: Fri Dec 17, 2021 6:02 pm
Acorn CNC Controller: No
Allin1DC CNC Controller: No
Oak CNC controller: Yes
CNC Control System Serial Number: none
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No

Re: only limit switches in on direction

Post by pascalken »

Thank you for your clear and comprehensive answer.

Pascal
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