Homing Fail

[Mr. Technical]

Hi guys,


I recently bought an older Servo3IO controlled Bridgeport and for the most part it works well, although I am having a problem with homing.

Z homes in the positive direction and reverses (downward) off of the home switch. This part seems to be working correctly, since it then moves on to homing the X axis.

The X axis homes in the negative direction, but once it strikes the home switch, it stops, saying that it’s hit the -X Limit which stops the homing process without completing it.

The same thing happens on the Y axis, but of course with the -Y limit.

I can trick the X and Y axes to think that they have homed properly by quickly triggering the limit/home switch with my finger before the dog gets there. If I do that on the X axis it seems to accept it and move on to the Y axis homing, where I can do it again. Obviously, this is no good because it gives me false home locations.

I should mention, there is no positive axis limit switch on the X or Y axes. Just one switch on each axis for home and negative limit.

What could be causing the X and Y axes to not jog off their home switches, while the Z axis works fine?

Thanks in advance,

Ian

[Mr. Technical]

Unfortunately, I’m traveling today and so I can’t post the report. I do however have some pics of the screens showing which inputs are being used and how they are configured.

Ian

[Mr. Technical]

Pics...

[cncsnw]

On a SERVO3IO, it is very suspicious to have the X axis with "Dir Rev" = Y, but minus limit = 8.

INP8 is the electrical minus limit, but if you have direction reversed, then the logical minus limit (the one you trip when you home the axis in the minus direction) should be INP7.

Ian: you should use the PLC Diagnostic display to see which input opens when you press on the switch that is tripped in the X-minus direction.
PLC Diagnostics is either Alt-i on the main screen, if you have CNC10 or CNC7 v8.10 or newer; or F7/Utility -> F6/PLC Diag if you have CNC7 older than v8.10. You are looking for INP7 or INP8 to open: either change from green to red on the newer software; or from 0 to 1 on the older software.

You should also make note of whether the axis is really trying to home minus (M91) or home plus (M92). The software travel limit numbers in your Machine Configuration -> Jog Parameters table suggest it ought to home minus (with M91), but it is possible there is an error in your homing macro, possibly combined with an error in configuring the servo motor direction.

You should also make note of whether the X axis direction is correct. On a typical milling machine, X+ (jogging the tool to the right, with the right-pointing "X+" jog button) should move the table to the left. Jogging X- should move the table to the right.

[Mr. Technical]

Quote” you should use the PLC Diagnostic display to see which input opens when you press on the switch that is tripped in the X-minus direction.
PLC Diagnostics is either Alt-i on the main screen, if you have CNC10 or CNC7 v8.10 or newer; or F7/Utility -> F6/PLC Diag if you have CNC7 older than v8.10. You are looking for INP7 or INP8 to open: either change from green to red on the newer software; or from 0 to 1 on the older software.”

I have confirmed that -X limit switch opens, (0 to 1) when I manually trigger the home switches on X and Y.

I have seen some documentation saying that input 7 would be for X minus, but it appears that it really is correct according to the silkscreen on the top plate of the Servo3IO board.

Thanks for the input,

Ian

[cncsnw]

I have confirmed that -X limit switch opens, (0 to 1) when I manually trigger the home switches on X and Y.

Is the input that opens when you trip the X minus limit/home switch INP7, or INP8?

Which input number opens when you trip the Y minus limit/home switch?

The labels on the board and cover plate would be for the case where direction reversal is not needed.

If you need to have direction reversal set ("Y") on the Machine Configuration -> Motor Parameters table in order to make the axis move the correct directions, then the order of the limit inputs is reversed: e.g. on the X axis of a SERVO3IO, you would wire the minus-end switch to INP7, and the plus-end switch (if any) to INP8.