Homing & Limit Switch UNSOLVED MYSTERY! <solved>

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RJS100
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Homing & Limit Switch UNSOLVED MYSTERY! <solved>

Post by RJS100 »

I have posted several times before with a number of issues that seem to be pointing back a homing switch problem. The previous posts resulted in differing opinions regarding the operation of homing vs. limit switches but the problem lives on.

I have converted a bench top mill (PM-833TV) to CNC using a few closed loop steppers. I configured three home all proximity switches in series. I do not have any limit switches. I programmed the software travel limits to define the working envelope.

When I start the machine and run the homing sequence, the machine homes properly. All good.

On a number of occasions, when g-code requests a tool change, the z-axis moves up rapidly and runs past the homing switch (proximity sensor) located at the top of the z-axis breaking the mounting bracket for the proximity sensor. I have modified the bracket so this cannot happen anymore.

My question is: What can I do to stop the mill from moving past the homing switches?

I have rec'd several suggestions that this means that the software travel limits are setup incorrectly. Section 7.5 of the manual describes the software travel limits as preventing the machine from crashing into a hard stop or LIMIT SWITCH, not a homing switch.

I am a bit confused as I was told that homing switches are only active during the homing sequence.

I have uploaded my configuration file as well as sample g-code.

PS: Please disregard the communication errors as these have been solved do to a Windows setting that shut down the Ethernet adapter to save energy.
Attachments
1002 Adaptive1 (Faced).nc
(222.27 KiB) Downloaded 6 times
report_E415F6F649F8-0121214266_2022-11-18_16-34-34.zip
(882.52 KiB) Downloaded 6 times
ShawnM
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Re: Homing & Limit Switch UNSOLVED MYSTERY!

Post by ShawnM »

I'm confused by what you are seeing. I have 3 proximity switches wired in series to input 1 set to "homeall". I have no limit switches and set my software travel limits. I can run the machine at 600 IPM to either end of the machine on any axis and it stops every time. I've never crashed a switch or the machine.

When you home the machine it sets the 0 position that the axis will travel to. Your soft limits define the max travel. Are you overdriving the machine and missing steps? Does the machine bind anywhere along the travel causing missed steps?

Do you have an alarm output on your drives? Is it configured properly to trigger the "driveok" input?

Set your software travel limits to 0 and 17.5 for X, 0 and 8.5 for Y and -14 and 0 for Z. You have a negative number in the X and Y for the minus limit. Set your minus limit for X and Y to either zero or .1 but not -.1. This means it'll travel past the home position by .1".

You say when it call up a tool change your Z crashes. I don't see an M6 macro in your report. How is your g code calling a tool change? I don't use Fusion 360 so maybe it does something I'm not familiar with.
RJS100
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Re: Homing & Limit Switch UNSOLVED MYSTERY!

Post by RJS100 »

Thanks Shawn,

Funny, I have my homing switches setup exactly as you... because you sent me your schematic some time ago. Thanks for your direction on the software travel limits. I will correct them. I am very new to gcode, but line twenty does have an M6 command (see below). Once this command is executed, the machine rapids to the top of the z-axis and sometimes over-rides the homing switch. On a previous post, you suggested that I change the homing switches so the machine moves past it, not into it. I changed the x-axis today, but not the z-axis yet.

My max rate is set to 150 inches/min. The acceleration is set to .5. I am not sure what else needs to be adjusted.

(Adaptive1)
N20 T2 M6
N25 S3000 M3
N30 G54

Thanks... Richard
RJS100
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Re: Homing & Limit Switch UNSOLVED MYSTERY!

Post by RJS100 »

Sorry, I forgot to mention:

-The machine does not bind.
-I do have an alarm output the drives. It is it configured to trigger the "driveok" on input 5
ShawnM
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Re: Homing & Limit Switch UNSOLVED MYSTERY!

Post by ShawnM »

Hi Richard, I remember now.

Change you software travel limit to what I recommended for now and save those parameters and restart the software. Home the machine. Can you manually jog the machine to the opposite end the machine and it stops at your software limit? Jog back to zero manually, does it stop at zero? Try all axis manually and slowly and see it it stays within your travel limits.

As for the M6 in the g code, I see that but I don’t see an M6 macro in your report. How does it perform a tool change with no m6 macro?

Have you tested your drive fault input by faulting the drive to see if it triggers properly?
ShawnM
Posts: 2190
Joined: Fri May 24, 2019 8:34 am
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Re: Homing & Limit Switch UNSOLVED MYSTERY!

Post by ShawnM »

How close are the flags when they pass in front of the prox switch? Make this gap as small as possible. Are the prox switches powered with 24 volts? Any pics?
RJS100
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Re: Homing & Limit Switch UNSOLVED MYSTERY!

Post by RJS100 »

Ok,

The prox switches are 24V see diagram attached.
Originally my x axis proximity sensor collided with the flag (image 2). I reworked it today so the flag passes by it very very closely (image 3).
Currently, my z axis proximity sensor is in direct line with the top of the dove tail of the z-axis (image 4). I am thinking about reworking it.
Attachments
20221119_075720.jpg
20221119_201930.jpg
20221119_075809.jpg
5 - Pin Aviation Conector - Series Home NPN Proximity Sensor Wiring - with avaition connector.jpg
ShawnM
Posts: 2190
Joined: Fri May 24, 2019 8:34 am
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Location: Clearwater, FL

Re: Homing & Limit Switch UNSOLVED MYSTERY!

Post by ShawnM »

Absolutely rework the z switch. Mount it so it lays flat with the face of the switch facing out. Then add a small angle to the top of the z axis to pass in front of the switch when z reaches the top of travel. I hope this makes sense.

Also, since you have mill make new flags with flat sides and not round for the bed. Round flags limits the amount of ferrous material to trip the switch. They are steel flags, yes?

Reset the travel limits with new flags and mounting and try the manual jogging into the switches.
RJS100
Posts: 380
Joined: Tue Oct 20, 2020 8:41 pm
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Location: Arizona

Re: Homing & Limit Switch UNSOLVED MYSTERY!

Post by RJS100 »

Thanks Shawn. I am going to rework them per your recommendations. Makes sense to me.

I am a bit surprised as there are a bunch of videos on YouTube with Avid router setups where the flags run directly in line with the sensor (just like my original setup). I really thought the system would decelerate before crashing into the sensor. That does not seem to be the case.

For now... I am off to reworking the homing sensor brackets etc.

Thanks... Richard
ShawnM
Posts: 2190
Joined: Fri May 24, 2019 8:34 am
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Location: Clearwater, FL

Re: Homing & Limit Switch UNSOLVED MYSTERY!

Post by ShawnM »

Sounds good, I’d get the flags and switches mounted properly with a small gap and then we can revisit the wizard settings and confirm they work when jogging around. I still don’t see how you are calling a tool change in your g code with no tool change macro. We can visit that next when the switches are good and working.

As for the mounting of the switches on the avid machines, I can’t explain why they do it that way but maybe it’s to sell more limits switches. :D Those are hobby grade machines and maybe the designer is not a user. For the past few years I’ve only retrofit industrial grade machines and they all have very high quality roller, plunger style switches with adjustable steel targets that slide in an aluminum track. The switch can roll right past the target if needed with zero damage.
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