Video on different sensor types

**Clive S** · 01-03-2017

There has been a lot of discussion on the accuracy of sensors and I came across this vid. https://www.youtube.com/watch?v=il9bNWn66BY that I thought might interest some.

**JAZZCNC** · 01-03-2017

Originally Posted by Clive S

There has been a lot of discussion on the accuracy of sensors and I came across this vid. https://www.youtube.com/watch?v=il9bNWn66BY that I thought might interest some.

No Clive he must be wrong because every one knows the cheap Inductive sensors don't sense accurately enough with huge errors.!!! . . . . Well every one who lives in spain anyway. .

**Neale** · 01-03-2017

My only complaint with my cheap (around £2 each) inductive sensors is that mine don't seem to have any significant separation between on and off points. Not generally a problem, except that if I home all three axes and then jog in X or Y, the vibration tends to trip the Z limit switch as the sensor is just at its trigger point. Difficult fix, though - jog the Z down a millimetre or so first. Repeatability seems to be spot on, at least for my woodworking purposes. Must be our cold northern climate that means they work better here?

**Clive S** · 01-03-2017

Originally Posted by Neale

My only complaint with my cheap (around £2 each) inductive sensors is that mine don't seem to have any significant separation between on and off points. Not generally a problem, except that if I home all three axes and then jog in X or Y, the vibration tends to trip the Z limit switch as the sensor is just at its trigger point. Difficult fix, though - jog the Z down a millimetre or so first. Repeatability seems to be spot on, at least for my woodworking purposes. Must be our cold northern climate that means they work better here?

Neale You should be able to set the home position to about 1mm off the switch. Do you have the software set to back off the switch after it is triggered?

**Neale** · 02-03-2017

I'm using Mach3, which seems to run the axis towards the switch until it triggers, then slowly backs off until the switch drops out. I haven't actually seen this behaviour described but it's the way it appears to work. Not like LinuxCNC where you have some control over how the homing works, but in principle it's a reasonable method of homing. In my case, the Z axis (actually, all three axes) overshoots on approach to the switch, which is fine, but particularly for Z, when the axis backs off until the switch trips again, the on/off switch points are not distinct. So, axis backs off, switch trips, home position is established, no problem. Mach3 now considers the switch to be a limit switch rather than home switch. Because the slightest movement will cause the switch to come on again, this is now seen as a limit event. During homing, this is OK but when rapid jogging, the tiny movement (vibration?) in Z trips this limit. I suspect that a better quality proximity switch with on/off hysteresis would avoid all this - and according to everything that I have read, they all have some small amount of hysteresis. Mine don't, though...

I'm still fairly new to Mach3; I haven't found a way to set the limit switch position to be, say, +1mm and then automatically jog down to 0 after homing. I have been playing with the "Ref All Axes" script behind the button - so I can home X and Y simultaneously, for example - but I was thinking that I might modify the script to drop Z 1mm after homing and before homing X and Y. I've done things like set SafeZ and tool change position to Z=-1, so generally I can work around the problem as long as I remember to drop Z a tiny amount after homing.

It is noticeable that as I wind an axis by hand and watch the switch's built-in LED indicator, there is a significant distance over which the LED changes brightness. There is no absolutely unambiguous switching point. I notice this particularly because I use master/slave X motors via a CSMIO IP/M which does not support independent master/slave homing. I ref all axes, then kill the motors so that they are free to turn, and wind the slave axis by hand until the LED indicator trips. The switching ambiguity is probably no more than a full step (you can feel the motor cogging) which is 25micron max and I'm reasonably happy to accept that degree of error at the end of a 1m gantry! Motors back on and I'm ready for a machining session - I generally only do the master-slave thing at the start of a session.

**JAZZCNC** · 02-03-2017

Originally Posted by Neale

I'm still fairly new to Mach3; I haven't found a way to set the limit switch position to be, say, +1mm and then automatically jog down to 0 after homing.

Neale because your using the IP-M you can use the "Home Off" setting in "Homing and Limits". The machine will home until it see the switch then back off the distance entered then Set Zero. This will stop your problem with false trips.

This doesn't work for None Cslabs controllers (unless supported by plug-in) or Mach3 with parallel port.

**Boyan Silyavski** · 02-03-2017

Originally Posted by JAZZCNC

No Clive he must be wrong because every one knows the cheap Inductive sensors don't sense accurately enough with huge errors.!!! . . . . Well every one who lives in spain anyway. .

As he said, heat introduces huge errors in sensors. As you know its hot here in Spain