New project and limit switch question

[Petel]

Re-opening an old thread; I'm now trying to save some inputs on the machine and have removed the homing specific switches. (i.e. I'm wired now as in the top diagram in my first post but without the home switches, so have two switches in series for each axis).

Taking the X axis as an example I have selected the 'axis2homelimitall' on the wizard. I can now home to the switch ok in the X+ direction. If I then jog away and back to the limit switch in the X+ direction the drive stops; I cannot move more in the X+ direction but can jog in the X- direction....all good so far!

My confusion is that when I jog in the X- direction to the other switch, the limit triggers, but I can immediately jog both ways after the limit trip. Is this correct / expected operation or have I done something wrong?

To be safe I've set soft limits before the switches, so in reality it should never be an issue but I had assumed that the controller would recognise the direction of movement on a single axis at the point the limit switch was triggered and so prevent any further movement in that direction. I'm not at the machine now, but I recall getting the 'X+ limit triggered' message when I hit the switches, again I had expected this to change to something directionless like 'X limit triggered' when I selected the 'limitall' option.

Thanks, Pete

[cnckeith]

please please post photos of the machine with limits installed, a report.zip file so we can see the cnc configuration and screen shots of the Wizard setup.

[Petel]

Hi Keith

Attached report. Photo below shows the limit switch setup on the X. The switch block carries 3 separate switches - you can see the 3 plungers in the photo. I have wired the top and bottom switches in series. (The middle switch was my original home switch and is wired in series with the identical switch on the Z - now redundant.)

On the second photo you can see the adjustable cams that trigger the switches. The hardware setup is exactly as per the original Harrison / Anilam setup. (The Z switches are just at the end of the black conduit with cams on the machine bed).

Wizard images below:

I don't really need to save the inputs on the lathe but have my second acorn sat waiting for my mill retrofit and I'll need all inputs there, so wanted to try this out.

Incidentally I also tried to setup with 2 inputs configured differently (1) 'home all' using the two home switches in series and (2) 'limit all' using the 4 limit switches in series, but got a wizard warning that I could not setup in that way. Ignoring that gave me a PLC compile error, so I then moved onto the current setup. I guess I had assumed incorrectly that home all and limit all could be used on two separate inputs?

Thanks

Pete

[cnckeith]

hello. i see home switches set up on one end.
are you trying to setup limit switches on the other end? or ok with using travel limits to take care of the opposite travel limit from the home switch?
please state the goal as there are many ways to set up home, limit and software limits.. thanks, K

[Petel]

Keith

I was hoping to use the same limit switch at both ends of travel (X+ & X-) and also to home at the X+ limit.

I want to use the switches as a precaution in case I run into a position error at any point and try to over travel...I'm happy to work off the soft limits most of the time, but really want the switches functioning fully at both ends of travel, just in case!

The same switch gets triggered at both ends of the travel - you can just make out the cams at either end in the photo, attached to the fixed arm (the switch block travels with the cross-slide).

What seems to happen is that the home and X+ end of travel are fine (i.e. I cannot jog past in the + direction, only the - direction), but when I hit the cam at the X- position I can immediately jog in either direction by releasing and re-pressing the jog switch. I had assumed that I might need to use the limit defeat button at X- but it is not needed.

My mill also has a single switch on each axis, hence trying to work out how to have home, + and - limits on a single axis into a single input on Acorn.

Hope that makes sense?

[Gary Campbell]

Petel…
After a couple Acorn builds I can tell you that assuming that you set your machine limits properly, there is little risk that the machine will crash any hard stops. Added benefit is that no matter what the speed, the software will decel to softlim set positions.

[cnckeith]

yeah.. if the control is moving in the positive direction and it hits the negative limit switch..it assumes something is really wrong.
when you hit a limit switch, cnc12 is trying to protect you from continuing to jog into the switch. so its important that you have the machine limits wired and setup so that when the axis is moving in the positive direction it hits the positive switch..etc.. this way it will allow you to jog off the switch in the proper direction to clear it. this being said, if you have homing and travel limits setup properly, you'll almost never hit a limit switch on either end.

if you really want to use the machine this way with one switch from both positive and negative..you can use the "Limit Overide" button on the VCP if you hit the swtich and want to jog off of it. this gives you 5 seconds to jog off the switch. keep in mind when you press the "limit overide" button it WILL let you jog right into the swtich or hard stop. it turns off the protection.

[martyscncgarage]

Petel…
After a couple Acorn builds I can tell you that assuming that you set your machine limits properly, there is little risk that the machine will crash any hard stops. Added benefit is that no matter what the speed, the software will decel to softlim set positions.

Agreed.
I use one limit switch per axis and setup the soft limits for the other end. I am using the homeall input and puting the limit switches in series.
I set software limit to ZERO on the home end and the max travel limit on the other.
I saw your wizard picture. I have never set my soft limits as you are trying to do.

Not had any problems with this arrangement. However, open loop steppers if stalled may loose position. But open steppers are more forgiving.
Soft limits work for me in Centroid's Software.

Marty