Can’t get the inductive sensor working correctly, don’t know why it detect some point of the bed fine but other point it’s not trigger at all and slam nozzle against the bed(6mm aluminium plate with 1mm PC sheet on top) maybe my fault or defective unit, it’s no name Chinese stuff anyway.
I remember seeing someone use film switch put directly under the nozzle as probe.
So I just get some switch attach to the sponge with double-side tape, attach to the nozzle,make a hole in the middle so nozzle press against the switch directly. look botch as hell but run grid compesation and it work
I had issues with an inductive sensor, but it was caused by adding a bed heater under my glass bed (the glass had aluminum underneath), the changing electric field was “visible” to the sensor and messed it up. I would have needed to add electric field shielding between the heater and aluminum or ground the aluminum I guess, not worth the effort. Two unrelated upgrades I did separately but completely forgot affected each other.
I at one point saw an inductive sensor setup where there was aluminum foil on a printed flexible plastic piece under the sensor, so when the Z axis got to the bed the aluminum foil was pushed up to the sensor. Ingenious solution but I worried what the long term life of the flexing plastic part would be.
As a backup I did add a mechanical switch to my Z axis in parallel, and my bed is on springs. So should my print head Z sensor fail the nozzle will hit the bed, compressing springs slightly, and trigger the backup sensor to stop things. Just in case my Z sensor du jour flakes out or if I mess up while testing a new sensor configuration.
Regarding the inductive sensor - aluminium is not as strongly magnetic as iron/steel and other ferromagnetic materials.
Maybe try a thin sheet of of steel (but not stainless steel) under the PC sheet - that should trigger the inductive sensor well before the extruder tip crashes into the PC sheet.
Aluminium sheet is as bad (or good depending on point of view) as stainless steel sheet when it comes to magnetism. If inductive sensor depends on ferromagnetism, you really want the bed to be either a carbon steel sheet or have a uniform material above a steel sheet.
I am unfamiliar with “inductive sensors”; its current Wikipedia entry is a total mess. But it provides a link to this industrial document, Proximity Sensors Compared: Inductive, Capacitive, Photoelectric, and Ultrasonic | Machine Design, that has a very clear description. “Inductive sensors - These non-contact proximity sensors detect ferrous targets, ideally mild steel thicker than one millimeter.”
What are the specs for the inductive sensor? It should specify a distance, and give info on materials. For instance I use an 8mm inductive sensor but it only finds aluminum at 3mm because of aluminum’s weakness in that application. Copper it would see at 2mm.
But if it sees it at all in one location there’s no reason to not see it at all in others. It could see it when closer or further, but still should see it. So if the distance from the inductive sensor face to the nozzle is too much, if say you’re on the edge of the sensing distance, yeah it won’t work well.
Generally a standard inductive sensor is good for 4mm on steel, more is expensive. So that’d be 1-2mm on aluminum. So check that. You need the Z distance from nozzle end to inductive sensor to be less than your specific sensor’s working distance on aluminum.
I’m so sorry… Posted the wrong sensor. The one i’m using is a 18mm one… It Can even detect the copper traces of the heat bed! To trigger the sensor i’m using a really thin layer of aluminum foil under a 3mm glass sheet, covered with kapton tape.
Below is a test of the sensor with a piece of aluminum foil… It Can be detected at 1cm!!
@Cristian_Barilari That is very low cost! So then it’s a long range unshielded, it can also pick up metal to the sides, but long as there isn’t any that’s good.
Ungrounded aluminum foil wouid probably give enough to sense but not enough to block the electrical noise from a heated bed. The heater is either switching and making a changing electric field or when on full blast is a fixed electric field, but you’re moving the sensor through it. Either way, inducted electric charges will occur on your sensor. There’s no way that one is able to tell the difference. My sensor was $60 and can’t tell the difference. So that’s a possible problem.
There are some options, none I like:
Grounding the aluminum may help with noise. I haven’t hooked up the ground wire to mine yet.
You can add a ferrite sheet between aluminum and heater to stop noise. It’ll harm your heat transmission though. Then if the sensor doesn’t see the aluminum it’s purely because the aluminum is too thin or the sensor is too far. http://www.lairdtech.com/product-categories/emc-components/ferrite-sheets
You can switch to a ferrous foil, 430 stainless likely would work. McMaster-Carr 3803T93 for example. It may want to have a ground though. It won’t do as good with heat transmission as aluminum.
You can replace the glass with a thicker aluminum bed, but that seems like admitting defeat.
You could also forgo inductive and switch to a bltouch, optical ($200+ to handle glass) ultrasonic (larger sensor and $150 to get the required accuracy) or a few other options.
So, no great choices here. That’s why I’m temporarily switching to a bltouch.
Actually, i’m having pretty good results with “el cheapo” 18mm sensor… Autolevel works great and the first layer is always perfect… The only downside is the space that the sensor uses.
