Reply with Quotethe easy way is to use a small piece printed circuit board that will isolate the top copper layer from your machine.
Usage is the same as in your drawing.
Automatic Z probe design, but with protective earth connected to the end mill
I want to design an automatic Z probe to my CNC machine. I was planning to do this basically by using 2 wires:
- first one clamped to the end mill
- second one connected to a copper plate
The +5V voltage would be supplied through these terminals, so that the contact between the end mill and the copper plate would cause the current to flow between the terminals. That "switch" could be easily used in an electronic circuit to provide the information about the contact to the microcontroller. I've already noticed that this solution is popular in the DIY projects.
However, in my case there is one issue: both, the spindle collet and spindle collar, are connected to the protective ground (PE). That means that the end mill would be grounded to earth, as well. So, connecting any of the mentioned terminals (either +5VDC or DC ground) would short these signals to the earth ground. I suppose it's better to avoid connecting any of the DC wires to the earth ground.
Is there a better (and safe) way to detect contact between the end mill and a copper plate, using the mentioned 2 wires method?
Or rather, in that case, it would be better to think of an entirely different probe design, that would be electrically isolated from the end mill surface?
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Re: Automatic Z probe design, but with protective earth connected to the end mill
the easy way is to use a small piece printed circuit board that will isolate the top copper layer from your machine.
Usage is the same as in your drawing.
Re: Automatic Z probe design, but with protective earth connected to the end mill
I'm not sure what do you mean by that. Are you suggesting using an optocoupler?Originally Posted by Toinvd
Re: Automatic Z probe design, but with protective earth connected to the end mill
Oke, a bit more explanation. you don't need a optocoupler.
Connect the ground from your microcontroller to the chassis ( ground ) of the mill
The input of the microcontroller needs a pull up resistor to the +5 volt from the microcontroller ( 10 Kohm is fine )
and on the input of the microcontroller you also connect a wire which you solder to the top face of the piece print material
The print material is a non conductive material with a conductive layer on one or two sides. you solder the input wire to the top side.
Another way is to use your copper plate, and stick a plastic plate to the bottom with two sided tape. that would make a perfect test sensor.
when the tool touches the plate, the input goes from +5 to 0 volt.
I used this several years. now I have a wireless tool sensor.
Re: Automatic Z probe design, but with protective earth connected to the end mill
Ok, now I understand. Also, due to connecting the DC ground to the earth ground, the number of required probe wires could be reduced to 1 (the only required wire would be the +5V wire, connected to the copper plate).
But still, there remains an issue I was concerned about from the beginning - could connecting the DC ground and protective earth cause any technical problems (like additional noise or ground loops) or safety issues in the system?
Re: Automatic Z probe design, but with protective earth connected to the end mill
first, don't connect the +5V to the copper plate. when the tool should touch the plate, the +5V would be short circuit to the DC ground.
The copper plate only needs to be connected to the sensor input from the controller. And if the controller doesn't have a internal pull up, then you can connect a 10K resistor between the input and the +5V
The resistor will limit the current when the tool touches the plate.
You only connect the DC ground on one place to the earth ground of the system, so there can't be a loop.
Noise will be at a low level and should not be a problem in this configuration.
