Homing & Limit Switch UNSOLVED MYSTERY! <solved>

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RJS100
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

So if I want to test that it is returning to the correct home position each time, what is the best way to do this other than continuing to home the machine. If I understand you correctly, you are saying that it is returning to a different height because I did not account for the tool heights.

I thought that regardless of tool heights, it would always stop at the same position with respect to the homing proximity sensor.
CNCMaryland
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by CNCMaryland »

G0 G28 = Rapid to home

It should return to the same position it was at when the machine homed.
CNCMaryland
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by CNCMaryland »

First, I think your mixing up a few different issues. So my advice would be stick to working on just one issue.

Start the machine up, let it run the homing cycle, that will establish, 0,0,0.

Jog the machine away from this position. Now you can G0 G28 and have it rapid to home. (You can also G1 G28, but that will run at the slow job, and might be terribly slow).

I would for machine safety, verify that your soft limits are working. Once you are at 0,0,0, you should not be able to go past that position. Move to a small increment, and try to move in the wrong direction, the controller should not allow you to do that.
suntravel
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by suntravel »

CNCMaryland wrote: Wed Nov 23, 2022 1:24 pm G0 G28 = Rapid to home

It should return to the same position it was at when the machine homed.
Only if XYZ = 0 in G28 ;)

I usually have a negative value in Z there, because I do not want to let the CNC drive a longer way then necessary for a tool change

Uwe
RJS100
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

Thanks!!!
I will give it a good run and get back to you.

Have a nice Thanksgiving.

Richard
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by cnckeith »

G53 Z0 L40 ; move to machine coordinates z0 at 40 inches per minute
G53 X0Y0Z0 L40 ; move to machine coordinates x0,y0 at 40 inches per minute
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
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

Not good news!

I homed the machine at startup, then jogged the machine away from home to the extent of all the soft limits. Perfect, it stopped at the soft limit and when I tried to jog beyond, I got the appropriate 907 axis exceeded warning on all axis.

I then jogged quickly testing the soft limits with a bit more speed and it worked perfectly.
I then issued G0 G28 and number of times, then G53 Z0 L40, then 53 X0Y0Z0 L40. I modified these to move at 120 inches/minute as well.
In all instances the machine returned to Z0, but more specifically to the exact same position with respect to the z-axis proximity sensor.

Please see image one (after homing machine). The red line on the image represents the exact location that the flag stopped vertically with respect to the proximity sensor. All good so far, the machine is returning to Z0 to the exact same elevation every time the machine is homed.

I then tried to set tool heights.
For repeatability, I wanted to establish a G59 position so I can always measure my tool heights starting from Z0 and at the same x and y coordinates. This will ensure that I always touch off at the same place when measuring tools. I set the x and y coordinates and then jogged the machine to the top of the z-axis so I could measure the tool height of the master tool. Once the machine reached the top of the Z axis, I looked once more at the proximity sensor. Please see image two (after setting tool heights). The red line indicates that the machine no longer returned to the same z height.

It is my understanding that after homing the machine, the machine should always return to the same z height. Are there any settings, parameters or commands that would alter this?

If there are no command or incorrectly set parameters that could cause this, it would point to a defective proximity sensor or that they should not be wired in series.

Please let me know your thoughts.

Thanks... Richard
Attachments
After settng tool heights.JPG
After homing Machine.JPG
suntravel
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by suntravel »

M92/Z L1 drives to the home sensor in + direction and backs off till the sensor is not longer active
M26/Z sets Z0 in machine coordinates

G53 Z0 moves to Z0 in machine coordinates but not to the point the sensor triggers

If you set G59 Z0.5 and command G0Z0 the machine will drive over the sensor if soft limit is not set right, or you use not HomeLimitZ with a single input for the sensor.

Uwe
RJS100
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

Thanks again for your continued effort in trying to help. I am a bit confused as I thought the previous post confirmed that the soft limit was set correctly. That said, I performed the following:

I homed the machine then...
I issued M92/Z L1 a number of times. The machine returned to the sensor and backed off as you indicated. The machine coordinates for Z were:

-.0028
-.0027
-.0025
-.0025
-.0021
-.0024
-.0022
-.0016

This represents a variance of .0012 inches.

I then issued M26/ z, followed by G53 Z0. The machine returned to z0 and did not trigger the sensor. I repeated this a number of times with the same results.

I then issued G59 Z.5 and rec'd error 907 Z axis travel exceeded.
Then I issued G0 Z0 and the machine traveled to machine coordinates z- -5.9551

I am confused as to what this demonstrated. It appears that none of these commands forced the machine to travel past the homing proximity sensor. It appears that it stopped within .0012 of an inch each time.

I am still stuck with the same question. Why did the machine NOT stop at the same place with respect to the proximity sensor in the previous posts?

Thanks... Richard
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by ShawnM »

I’m just coming out of my Thanksgiving food coma and see your post that you’re a bit confused? I’m totally baffled, what are you trying to do? We know the machine homes properly with the prox switches and the soft limits work. You can’t jog past either end of travel and the machine stops before the end of travel. This problem is solved, yes?

The variances you see with your M92/Z L1 are more than likely mechanical. From one to the next you are just a few ten thousandths off. Do you need more accuracy than that? If so you’ll need to look closer at your ball screws and get higher quality ones or repack the ones you have.

Do you have a solid understanding of machine coordinates versus work coordinates?
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