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cjlyth

Printer head tracking

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I have tried searching this forum for a similar problem but I was unable to find something. Please forgive me if this is a common problem or already answered. I had some stuck filament and while trying to remove the stuck filament I decided to shut off my printer. When I turned it back on it seemed to have no idea where the print head was or should be. I found a post that talks about disconnecting the x stop on the circuit board and moving the print head with pronterface. I have tried this and I guess I was unsuccessful because I don't fully understand what I am exactly supposed to be doing.

The Home head function seems to move the print head diagonally every time I press it. In pronterface the movement seems to be reversed. When I tell it to home the print head, it moves the head to the front right corner and it slams into the side of the printer making a nice loud throbbing sound. It seems to have scratched the glass with the fans in the process.

I am currently at the point where I have a completely unusable printer and im not sure what to do next. I can post pictures videos or whatever else is needed please let me know what sort of thing is relevant.

Please help!

 

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The printer has no idea where the head is. Homing is simply moving the printer diagonally untill an end switch is hit. If the y switch is it, that point is now considered to be 0.

Pronterface seems to assume that the direction is different or that the machine (as our older models do have it) have min x/y switches and max x/y switches.

From your profile, I see its an um2. You can simply use the menu on the machine to home it.

 

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Thanks for the reply!

The machine menu "Home head" seems to just move it forward and right a little over and over. I have done that quite a few times with no improvement. I started playing around with pronterface and sending G28 followed by M114 and the G28 command has some effect. If I move the head manually to the back left of the machine then send G28, the M114 command shows x0.0 y230 z230. I don't know if this is correct or not. Once that is done I have been moving the head in pronterface to the other side of X and Y and in both cases the print head slams into the glass. Once again I dont know if that is ok. Today I noticed some black dust that I suspect is fragments of the gantry belts. I will try to attach a picture.

Is there anything else I can try?

 

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It seems my problem is fixed. I think I was over thinking it. Apparently all I had to do is turn it off, move the print head to the back left corner and turn it on. Ive done this a few times in the past day but this time it seems to have worked. After clearing a clogged nozzle and fixing some ground filament it seems to be successfully printing now!

I'm still concerned about the belt shavings and I ended up having to cut 50mm or so of my bowden tube. Hopefully that will be ok.

 

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I don't have a UM2 but I own a UMO. You shouldn't have to manually move the head back to the home position.

I wouldn't be overly concerned about the belt "dust" but wait for another UM2 owner to chime in.

I'm not 100% sure but I believe the UM2 homes to the same location as a UMO which is the front left corner and this should corner should be 0, 0.

When you use the home menu item to which corner does it attempt to move?

Some things to check:

If the movement isn't completing, check to see if the pulleys are slipping on the long rods or the motor shafts. If so tighten the "grub" screws.

If during the homing movement, the head is hitting a side, look underneath in the corner to which it is moving and see if it is triggering the endstop switches. Sometimes the little stub that should engage the switch bar doesn't and you might need to gently bend the bar of the switch so it trips.

With the printer off, does the head move easily ? Can you use one finger to move the head to the home position without toppling the printer? If not something is binding and this may cause steps to be skipped. This can cause the true position to be lost and then the head may crash into a side.

 

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The home head function from the menu just nudges the print head to the right and to the front a little bit. I can definitely move the print head when its turned off and when I move to the back left corner I hear both stop switches click. I can also see where they are pressed in.

You are correct about the home of the UM2, when I do the homing command (G28 I think it was) while the print head is in the back left. The printer reports x0,y230, when I move the print head using pronterface to the front left the printer reports x0,y0. So that seems to be ok.

I guess I don't understand what the "Home head" function is supposed to do. It seems pretty useles to me but then I only used it once it was not working correctly.

 

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The printer uses stepper motors which don't retain a known position when they are disabled or when the printer is turned off. So each time you turn off then on, the firmware will reset it's "position values" to 0,0 (and technically 0 for the Z bed) even though the actual location of the extruder could be anything.

 

The only way for the firmware to know where the true extruder position is in the X,Y positions is to "home it". When do the homing routine, the firmware steps the motors in the direction of the home position which on a UMO is the front right corner. When it arrives there, the extruder trips the homing switches which tells the firmware that the extruder is in the corner. The firmware then resets it's internal values for position to 0,0. From then on, when the firmware steps the motors, it assumes the motors move as directed and it increments it's internal position. Because steppers hold their position when enabled and powered, it's assumed that they only move when the firmware causes them to move and since the firmware is also tracking the steps and therefore the X, Y position, the actual position is always known. Same process happens for the Z axis/bed.

So you must home the printer if you turn it on and the head isn't already in the home position. If, for example, the print head is in the middle of the printer when you turn it on, the middle will become 0, 0. However, when the firmware wants to move to a place beyond about 115 in X or Y, the head will hit the side of the printer. This is because that firmware assumes the print area is 230mm (or thereabouts). However, that is 230mm measured from the home corner not the middle. If the head was in the middle when the printer was turned up and not HOMED then the edge is only about 115mm away but the firmware doesn't know this.

If you are invoking the home menu item and the head is not moving to a corner then there is a problem.

After using the home menu and the print head moves some, are the motors making noise like they are turning? If so, turn the printer off and use a sharpie to mark the pulleys with respect the the long rods and motor shafts. Then power on and home. If it doesn't make it to a corner, examine the marks to see if the pulley(s) have "slipped" with respect to the rod or shaft they are on. If so, you need to tighten the grub screws that lock the pulley onto the rod or shaft.

If that isn't the problem, you should contact support since the remaining problems are all electronics related and I don't want to give you bad advice based on a UMO when you have a UM2.

 

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Thanks for the very detailed response!

Should the homing routine move to a corner when it is pressed no matter where it is or will I have to keep hitting it. It does always move when i hit the "Home head" menu item. It moves a little in both x and y. But it moves away from the endstop switches. Is this what it is supposed to do?

 

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It should move fully to the home corner which is the one with the switches. Basically, the firmware doubles the configured lengths and tries to move that amount in the direction of the switches until the switches are triggered.

Based on this video, it looks like the home corner is back left. Skip to 9:49.

Even though he is running through the initial setup, that first move diagonally back is the homing operation. The Z home position seems to be at the bottom.

It's very strange to have it "home" away from the switches and that is a good indication something is wrong.

Unless you have done something recently like updated the firmware or changed the stepper motors, you should see if US support can help you. You recently liked my other post on spare parts. That same site is the US support provider.

I believe this guy runs the US operation you might send him a PM and ask how to get support:

http://umforum.ultimaker.com/index.php?/user/341-illuminarti/

PS: to correct my description of the homing process, the coordinate system used by both the UMO and UM2 has (0,0) at the front left with X increasing to the right and Y towards the back. The firmware has the ability to support switches at any end of an axis. So when I said the FW sets the position to 0,0 when the switches are hit, that is not accurate for a UM2 but is for a UMO. Since the UM2's home position is back left, it will set the position to 0, 230 when homed. Likewise, since the Z switch is at the bottom of the printer, the platform needs to move to the bottom to establish a known position. It's hard to describe the Z axis coordinate system because it's counter intuitive. It really runs from the build plate increasing in the upwards direction. The confusing thing is that since the platform moves and not the extruder, 0 will be just when the plate touches the nozzle and about 230 will be when the plate is at the bottom. If you think about it from the extruder perspective, the extruder is moving up and away from the plate as Z increases but because the extruder is fixed, the bed needs to move down to support that perspective.

 

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Thanks, I sent an email to the address on the US support site you suggested. The only updates I have done to the firmware is clicking the "Install default firmware" in cura. The machine shows as an Ultimaker2 in the machine settings. But it is VERY strange that the "Home head" function moves away from the back left corner. Maybe the firmware is for an original instead of um2?

 

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I submitted a ticket and have made some progress. I think it was http://umforum.ultimaker.com/index.php?/user/341-illuminarti/%20that%20has%20been%20helping%20me%20so%20thanks!

All of these problems started when my bowden tube melted as a result of a clogged nozzle. I opened the box that had the melted tube and ground mess of filament. When I took this off the filament feeder motor came loose (clunked down to the glass!). After I cleaned up the box and put it back together, from the back of the machine, I apparently clamped the wires for the stop switches between the motor and machine wall.

I will be splicing this and testing the fix as soon as possible!

 

IMG 1034

 

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Finally got time to replace them and it seems to have fixed it! I canceled a print and the head returned home! Thanks for the help on this. I definitely understand more about how it all works now.

Thanks again everyone!

Chris

 

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