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Probe
« on: November 20, 2011, 05:44:42 AM »
Is there a drawing and description of how to make my own Probe,- for probing x,y&z axises?
(Have the drawings made by Shaun Wainford, but there is no description).

Thanks

Johannes Line

Offline RICH

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Re: Probe
« Reply #1 on: November 20, 2011, 09:10:54 AM »
Did you download the PDf file? The file provides general info on the probe and a set of drawings.
Study the drawings and the 3D pictures some to understand how all it all fits together.
You will need to use a lathe and a mill to make the pieces.

RICH
Re: Probe
« Reply #2 on: November 20, 2011, 10:16:31 AM »
"Did you download the PDf file? "
Yes I have, and I have a lathe and a mill.
I have studied the drawings but is unable to quit understand it. I think that by touching you are making metallick contact in the y and x move, but what in the z direction?  Any electrical connections?
I have a mill and have installed a simple probe for x and y works the way the movement stop when the probe hits the metall (mill).

Johannes

Offline RICH

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Re: Probe
« Reply #3 on: November 20, 2011, 08:24:02 PM »
Yes you are making contact just like the your simple probe but additionaly the tip has some give to take care of the Z as it is spring loaded.
There are contacts which are made depending on the direction of tip movement. Look closely at the pictures.
RICH

Offline Tweakie.CNC

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Re: Probe
« Reply #4 on: November 21, 2011, 03:36:26 AM »
Johannes,

I don't know if this helps but....

By the method of assembly, all the balls are in electrical contact with the PCB and each of the silver steel pins electrically connects one pair of balls. The, two wire, probe connection is taken from the 'gap' in the PCB track, which under normal circumstances (with balls and pins fitted) is now a short circuit. Any probe contact with an object (no matter from which direction) will open the circuit as at least one pin will fail to bridge the gap between one pair of balls.
It is the software which determines the direction of probing and the probe just indicates when contact is made by breaking an otherwise continuous circuit.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Probe
« Reply #5 on: November 21, 2011, 09:11:00 AM »
RICH & Tweakie, thanks both of you.

Now I think I understand the working principle. The two wires go through the hole on the side of the body and connects to the small 1,20mm hole at the Fibre Glass Board and short the circuit as you explained. Mowing the ProbeTip the circuit is broken, this is the opposite of the simple probe. I mean that when the simple probe touch ground Mach3 is activated (axis stop moving). Can this bee sett in the softwhere- "high or low"?
Another thing I was wondering about,- how accurate is this Probe? Surly there have to bee some play/movement of the ProbeTip before the circut is broken and a signal given. Can this be compensated for by the software?

Johannes

Offline Tweakie.CNC

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Re: Probe
« Reply #6 on: November 21, 2011, 11:15:39 AM »
Quote
Can this bee sett in the softwhere- "high or low"?

I suppose you could use a 'pull up resistor' for the circuit to be 'active high' and a 'pull down' resistor for the circuit to be 'active low' then configure Mach accordingly.


Quote
Another thing I was wondering about,- how accurate is this Probe? Surly there have to bee some play/movement of the ProbeTip before the circut is broken and a signal given. Can this be compensated for by the software?

If it is constructed properly and the spring yields before anything bends then it would be extremely difficult to measure any play/movement in the system. Consider that the tip is essentially resting in the 'V' between 6 points of contact, it will either be making contact or it will not, there is no delay or contact bounce as you may get with, for example, a conventional switch.
When probing there is 'overun' between the contact point and the axis coming to rest but the stored position is the actual point of contact not the final axis position so compensation is automatic really.

Hope this helps.

Tweakie.


Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Probe
« Reply #7 on: November 21, 2011, 11:44:07 AM »
Thanks, think I will manage now. you have been to great help. Thanks!

Johannes

Offline stirling

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Re: Probe
« Reply #8 on: November 21, 2011, 11:49:36 AM »
Just to add a little to Tweakie's excellent explanation. These type of probes are normally set as active high in Mach - i.e. whilst the contact is made the input is held low (by being grounded) and when a trip occurs, the circuit is broken thus allowing the internal pullups to take the input high (active).

Also there actually is a bounce issue to be aware of but it's not a big deal. As Tweakie says, the instant the circuit is broken, Mach (if using G31) stores the point of contact and then decelerates to a stop. HOWEVER - if the probe contacts are re-made and then re-broken during that decceleration phase, Mach will RE-WRITE that point as the point of contact. This is more likely if the trip is caused by "glancing" something to the side of the direction of travel for example. This only really becomes an issue if your machine accel/deccel is "poor" however. Whilst on the subject of "poor" decceleration, care must be taken to ensure that the probe overtravel capability is large enough to accomodate the slow down phase, otherwise.... CRUNCH. A useful addition to a home made probe is to add in an overtravel contact to trigger a limit - your probe gets to survive where others are assigned to the bin.

Ian

Offline Tweakie.CNC

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Re: Probe
« Reply #9 on: November 21, 2011, 11:55:44 AM »
Quote
HOWEVER - if the probe contacts are re-made and then re-broken during that decceleration phase, Mach will RE-WRITE that point as the point of contact.

Thanks Ian - this is something I had never considered (or even thought about happening).

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.