Limit Switch Problem... < no problem at all:-)>

[cnc_jim]

I just upgraded a DynaCNC 4x8 router table to Acorn. Everything is working except my limit switches. Well they work, but not as expected. I wired them (X,Y and Z) in series NC and connected them to input 2 and setup input 2 as "limit All". If I trip the switch, it shows X, Y, Z tripped on the screen. Mechanically, they work. When I run the machine and test the switches, they trip but the machine doesn't do a hard E-Stop, it's like it trips but then decelerates into a hard stop. If I jog slowly into the limit switch with the pendant, it stops when the switch is tripped about 3/8" from the hard stop but if I jog at 400 ipm into it, it trips and hits the hard stop. It isn't stopping abruptly when it hits the switch.

The other issue is I can't get off the switch without cycling the E-stop (that isn't tripped) and then manually pushing the Axis off of the switch (because no holding power is on the motor). I can't back off of it with the computer.

Do I have something configured wrong that isn't allowing an immediate stop of the motor and also not allowing me to back off of it in the other direction?

I am using the GeckoDrive 203V schematic and wired my machine according to this. Brand new V4 Acorn board with CNC12 Pro V4.18 Each axis is working perfectly as far as the motion control and my HY VFD is working perfectly also. None of the axis is reversed. I tried to find similar threads but nothing quite addressed this issue.

[cnc_jim]

So from what I can tell, I probably have to setup soft limits to resolve the crash issue to decelerate the axis before it reaches the switch. I will try that and see if that fixes the issue.

[Dan M]

Yes on mine it will crash at high speed even if the sensor is tripped. I chalked it up to the hard stop being so close to the sensor. I honestly never checked to see if the motors are still under power after a limit is tripped. It would make sense if when the switch trips the driver's are disabled, then it would coast past the sensor into the hard stop.

Either way once tripped on my machine if I cycle the reset button on the screen I can jog off the sensor. I have gecko 214 driver's though and they are wired to the screw terminals, I also only wired the step direction and enable one my driver's. I got lazy and never wired the fault and reset on my driver's so I don't know if that would make a difference.

[cnc_jim]

So I was probably going about this in reverse trying to setup/test my limit switches before setting up and testing my home switches and then setting up the soft limits, then the limit switches.

Anyway, found an issue on the homing side. My cnc router as a limit switch for each axis but only a home switch on X and Y, not Z. How do I disable homing on Z? I can get it to home properly on X and Y and have it do Z at the end but I can't disable it so it doesn't attempt a move to a home switch.

[martyscncgarage]

Use the home switches only. If mechanical, they can be wired in series and connected to input 1. Use the HOMEALL input. Setup your soft limits. Works pretty good.

You can also use 3 inputs and use HOMELIMIT input (that's what its called if memory serves) for Axis 1, Axis 2, and Axis 3

Of course the machine needs to be setup and dialed in first....
Marty

[Dan M]

So I was probably going about this in reverse trying to setup/test my limit switches before setting up and testing my home switches and then setting up the soft limits, then the limit switches.

Anyway, found an issue on the homing side. My cnc router as a limit switch for each axis but only a home switch on X and Y, not Z. How do I disable homing on Z? I can get it to home properly on X and Y and have it do Z at the end but I can't disable it so it doesn't attempt a move to a home switch.

I believe you can edit the home file and remove the z portion. If it were me, I would add a homing switch to the z axis. How do you currently set the z home position?

[cnc_jim]

Thank you for the replies. Knowing now how the Homing, soft limits and limit switches work, I did as Dan suggested. I removed the Z limit switch, drilled new holes and mounted it as a Z home switch and rewired it to the X and Y axis home switches. Didn't make sense to have a Z limit switch since it only prevents a crash into the table on the negative Z travel and that only would happen if the spindle didn't have a bit in it. Otherwise the bit would crash before hitting the limit switch.

Anyway, this is all working great now. I can home all 3 axis, set the soft limits to stop just before the limit switches and it work perfectly! Love this Acorn board!