Homing & Limit Switch UNSOLVED MYSTERY! <solved>

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

Post by Upnorth »

I think that most people on here would be quite happy with a variance of .0012". Are you always approaching the sensor after you have taken out the backlash? Have you tested to see how much backlash you have? Even switches and sensors (unless you spent a ton of money on them) have some variation in when they will trigger.
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

I hope you had a nice time getting to the food coma stage. Mine begins in a few hours.

Shawn, I believe I fully understand that the machine coordinates are positions relative to the homed position and the WCS are simply offsets from the machine coordinates for each part. Basically, a reference point for x0,y0,z0 for that part. The problem I am trying to solve is the fact that once I home the machine, the machine coordinates should not change. What I am finding is I can home the machine, run a bunch of code and observe the Z axis consistently return to the same Z0 position. I look at the proximity sensor/flag and it looks the same each time (see image "after homing the machine). All good! This is exactly what I expect.

For some reason, something happens, I am not sure what... but suddenly I jog the z axis up to the top and it goes almost 1/2 inch higher. See image "After setting tool heights"

Maybe it is operator error. Please correct me if I am wrong. I don't understand why suddenly the machine stops about 1/2 inch higher than the previously homed position. Keep in mind that I did not re-home the machine during this time.

Thanks.... Richard
Attachments
After settng tool heights.JPG
After homing Machine.JPG
RJS100
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

I forgot to respond... .Yes I am very happy with a .0012 variance and have tested for backlash.
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

sorry... I see where I am being a bit confusing. I did mean that the machine returned to the same z0 position. I meant that after running some code, when I jogged to the top of the z axis, the machine returned to the same position. Then suddenly, it returns to a different position at the top of the z axis. ie, different home position.
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by tblough »

When the machine stops short of the previous position, what is the Z machine coordinate at that point?
Cheers,

Tom
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I have CDO. It's like OCD, but the letters are where they should be.
RJS100
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

I wish I noted the Z machine coordinates. I will try to recreate the error and take note.
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

I think it was z=0
tblough
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by tblough »

If the machine coordinate was Z=0 when it returned to the wrong place, then you are loosing steps either from noise or an undersized axis motor.
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.
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by ShawnM »

tblough wrote: Fri Nov 25, 2022 8:26 am If the machine coordinate was Z=0 when it returned to the wrong place, then you are loosing steps either from noise or an undersized axis motor.
Agreed, do you have a counter balance on the Z axis? Is this the only axis that is doing weird stuff? What motor/drive combo are you using? Can you post a current report?
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Re: Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

Hello,

I am going to try to recreate the problem again and take notes of the machine coordinates. I don't think I am losing steps as the z-axis is mostly weightless (due to gas struts) and I am using a closed loop stepper wired to the "Drive Ok" input. Also, the spindle was off when this problem occurred, so I'm not sure noise was the culprit.

If I had to guess, I think the problem is software related because if I remember correctly, 1st the z-axis stopped at one position repeatedly when jogged or sent to the home position, then I believe it repeatedly returned to a slightly higher position (relative to the proximity sensor). This happened when I changed WCS to G59 and then started measuring the master tool height followed by the height of two tools. I noticed there was an issue because the differences between relative height of the tools was simply wrong.

Again, I need to recreate the issue and take better notes. Also, I did notice that each time I fire up the machine, it DOES home to the same position. Shawn, I am using a Stepper Online 1700 oz. closed loop stepper for the z-axis and 1200 oz closed loop steppers for the x and y with Stepper Online CL86Y drivers. The z axis has gas struts on each side of the head (see attached).

I have attached a fresh report.

Thanks... Richard
Attachments
20221125_091830.jpg
report_E415F6F649F8-0121214266_2022-11-25_09-15-30.zip
(871.59 KiB) Downloaded 4 times
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