Take II - Z-axis gone too far!!

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RJS100
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Take II - Z-axis gone too far!!

Post by RJS100 »

One month ago (9/3) I posted Z-axis gone too far. I received a few different points of view. I thought this issue was solved... NOPE... problem NOT solved. Let me try to pose the question differently.

I am a complete newbie converting a PM-833 to CNC. The conversion is complete. I configured the Homing & Travel as show on the attached screen shot. When the system starts up for the 1st time, and I press cycle start, all is good. The machine homes properly and stops sequentially when it reaches each of the three proximity sensors. If I try to manually jog to a position beyond the proximity switches or a point beyond the soft travel limits (Z=-13.5, Y=8.5, X=17.5), I receive a 907 axis travel exceeded error.

Perhaps this is where I am confused. It is my understanding that by using these proximity switches and software travel limits I have fully defined the operating envelope of the machine.

If this is so, why is it that I run the test G-code attached "Circler Pocket", the Z-axis overrides the Z-axis proximity switch (right at the start of the program, I think when a tool check" is requested?

Please let me know your thoughts. I have also included the latest report with all my configurations

Thanks... Richard
Attachments
Circler pocket.cnc
(1.4 KiB) Downloaded 4 times
report_E415F6F649F8-0121214266_2022-10-03_15-58-32.zip
(671.63 KiB) Downloaded 4 times
Screenshot 2022-10-03 160226.png
cnckeith
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Re: Take II - Z-axis gone too far!!

Post by cnckeith »

1.) the g code program posted says in the Header.
"CNC code generated by Intercon v4.09 Dev Test, Rev 7"
this is beta software. please update to the latest release version asap.

2.) the report shows version CNC12 v4.62 (this is two years old), please update to v4.80 so we all are using the same software and we can help you better. and free support for v4.62 has ended. free download and updating instructions are here. https://www.centroidcnc.com/centroid_di ... loads.html
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
RJS100
Posts: 380
Joined: Tue Oct 20, 2020 8:41 pm
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Re: Take II - Z-axis gone too far!!

Post by RJS100 »

Thanks... I will update and try again.
cncsnw
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Re: Take II - Z-axis gone too far!!

Post by cncsnw »

Please expand upon " the Z-axis overrides the Z-axis proximity switch ... right at the start of the program".

Does the Z axis move up (plus) more than the allowed 0.1" beyond the sensor trip point?

If so, and if you press Alt-D to switch your DRO display to Machine coordinates, what is the Z value on the DRO?

Assuming that you cancel the job or press Emergency Stop or get some type of drive fault at that point, and interrupt the program, what line of the program was it on when that happened?

Note that your proximity switches are designated "HomeAll", so they are home switches but not limit switches. Tripping the sensors, then, will not stop motion.

Your software travel limits, G28 return point, part zero location and tool offsets all seem reasonable, and should allow that job to run without trying to move above machine zero on the Z axis. Therefore it is likely that your Z axis is losing position (dropping command pulses or getting bogus command pulses). That is why you need to look at the displayed DRO position for the Z axis, in Machine Coordinates, and compare that with where the axis is actually sitting.
RJS100
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Re: Take II - Z-axis gone too far!!

Post by RJS100 »

Thank you very much for your response. I was not aware of the fact that I was running old software and G-code so I updated to 4.80 as suggested. I then ran the newer version of "Circler pocket.cnc" about 6 times and was unable to recreate the error. The error I had before updating software and gcode was that at the start of the program, a tool check is commanded (Line 20 of the updated version of G-code). At this point the z-axis raised to the top of the column and bumped right into the homing switch at the top of the z-axis. It did not stop until I hit the E-stop. Since this happened a few weeks ago I do not know machine coordinate Z-value at the time of failure.

It is interesting that since this error occurred during a "Tool Check", the spindle was stationary, so it is unlikely that the problem was a result of EMI. For the time being, I cannot recreate this error so I may have to leave it for now.

Quick questions, you commented that the "proximity switches are designated "HomeAll", so they are home switches but not limit switches. Tripping the sensors, then, will not stop motion". I understand that once the homing sequence is complete, these "HomeAll" sensors are no longer active and will not sense motion. Here are my two questions:

1. If the machine's safe working envelope is defined during the homing cycle by the HomeAll sensor and soft limit values entered, and the machine cannot move outside of this envelope, what and when is the need for limit switches?

2. If the limit/Homing switches are wired in series as show in the attached diagram can they be assigned to another input type so they are active during the homing sequence AND act as limit switches?

Thanks... Richard
Attachments
5 - Pin Aviation Conector - Series Home NPN Proximity Sensor Wiring - with avaition connector.jpg
cncsnw
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Re: Take II - Z-axis gone too far!!

Post by cncsnw »

If the machine's safe working envelope is defined during the homing cycle by the HomeAll sensor and soft limit values entered, and the machine cannot move outside of this envelope, what and when is the need for limit switches?
First, to prevent overtravel when you are jogging the axes before homing the machine.

Second, to stop overtravel when (not if, but when) your control loses position due to dropped pulses, bogus pulses, or mechanical slippage. If the control has lost position in this manner, then the software thinks it knows where the machine is relative to the travel limits, but it is wrong.
At this point the z-axis raised to the top of the column and bumped right into the homing switch at the top of the z-axis.
This means that your home switch/sensor is mounted incorrectly. The axis should move past the switch, tripping it along the way. The axis should not move directly towards the switch in a way that will potentially damage the switch or its mounting, if the axis fails to stop. You should have a mechanical hard stop (bumper) that prevents the axis from going any farther, if for some reason the switch fails to stop it.
RJS100
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Re: Take II - Z-axis gone too far!!

Post by RJS100 »

Thanks for the very insightful info. Very much appreciated.

Just curious, I see from the schematic that the limit switches are wired in a similar fashion to the homing switches except they are connected to input LimitAll. On a mill, is it standard practice to put these on each axis on the opposite side of the homing switch?

Thanks again for all your help.... Richard
tblough
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Re: Take II - Z-axis gone too far!!

Post by tblough »

Good practice is to place a limit switch at each end of travel.
Cheers,

Tom
Confidence is the feeling you have before you fully understand the situation.
I have CDO. It's like OCD, but the letters are where they should be.
cnckeith
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Re: Take II - Z-axis gone too far!!

Post by cnckeith »

RJS100 wrote: Thu Oct 06, 2022 12:02 am Thanks for the very insightful info. Very much appreciated.

Just curious, I see from the schematic that the limit switches are wired in a similar fashion to the homing switches except they are connected to input LimitAll. On a mill, is it standard practice to put these on each axis on the opposite side of the homing switch?

Thanks again for all your help.... Richard
this is optional, just one way of doing things, personally i rely on soft limits and just have home switches... one on the end of each axis.
but like tom said safe way is to have limit switches everywhere:-))
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
RJS100
Posts: 380
Joined: Tue Oct 20, 2020 8:41 pm
Acorn CNC Controller: Yes
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Oak CNC controller: No
CNC Control System Serial Number: none
DC3IOB: No
CNC12: Yes
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Location: Arizona

Re: Take II - Z-axis gone too far!!

Post by RJS100 »

What the heck...won't take me too long to mount a few more limit switches.

Thanks for all your help and insight.
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