How do I use [Probe] with a fixed gantry and a moving bed, probing moves in the wrong direction!

General Discussion
1

Basic Information:

Printer Model: Dremel 3D45
MCU / Printerboard: Duet 3 Mini 5+
Host / SBC Raspberry Pi 4
klippy.log klippy(30).log (3.2 MB)

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Describe your issue:

The printer uses a fixed gantry, which can move the print head on the x and y-axis with a bed, which can be raised or lowered on the z-axis via a threaded screw. The probe is a micro-switch attached to the print head, which can be raised or lowered via a servo, which keeps it out of the way during printing. I am trying to set up the probe and screws_tilt_adjust commands. However, the probing operation is lowering the bed, rather than raising the bed towards the microswitch - It is moving in the wrong direction.
After completing, the probe operation (if I press the microswitch with my finger), the sample_retract operation commences, but this is moving the bed in the wrong direction as well. It is raising the bed, towards the micro-switch, rather than lowering it away. I have tried making the sample retract distance or the lift speed to negative, to correct the movement direction, but klipper won’t accept negative values. How do I resolve this issue?

The intended homing procedure and screws_tilt-adjust is as follows:
#1 The bed, x and y axis are homed, using sensor-less homing. The bed is moved to its lowest position using sensorless homing. (working)
#2 The screws_tilt_adjust command is run, and the bed is raised to 170mm, close to the print head. (working)
#3 The microswitch is lowered into position using the servo. (working)
#4 The bed is raised until the microswitch is pressed. (not working, the bed moves in the opposite direction)
#5 After the microswitch is pressed by the bed, the bed is retracted 5mm, downwards. Ready to take another reading from the microswitch (not working, the bed retracts upwards!)
#6 The bed is raised again, as per #4. (not working as #4)
#7 An average reading is taken, ready to move onto the next position. (not made it this far)
…

2

Don’t know, if I get your problem right!

The logic is inverted?

My first idea was

sample_retract_dist = "negative value"

but your klippy.log shows

configparser.Error: Option 'sample_retract_dist' in section 'probe' must be above 0.0

So “sample_retract_dist” can’t be negative!

I have no other idea, sorry!

Good luck, hcet14

3

Your configuration seems strange:

[stepper_z]
step_pin = PC24
dir_pin = !PB28
enable_pin = !PC28
microsteps = 64
rotation_distance = 8
homing_speed = 18
endstop_pin = tmc2209_stepper_z:virtual_endstop
homing_retract_dist = 0
position_endstop = 0
position_max = 179
  • position_endstop is not a valid setting when using a virtual_endstop
  • tmc2209_stepper_z:virtual_endstop seems like sensorless homing for the z-axis but does not involve a probe. Here the correct setting would be endstop_pin: probe:z_virtual_endstop
  • You have not set a position_min for this axis
1 Like
4

Hey, after searching through the configuration reference, I found the solution, by changing/adding the following values:

[stepper_z]
dir_pin: PB28
homing_positive_dir: True
position_endstop: 179

[probe]
horizontal_move_z: 10
  • The direction pin of the stepper had to be reversed, by removing the “!” prefix.
  • The position_endstop was necessary, and had to be set to the maximum extent of the rail.
  • Homing_positive_dir was added and set to true, so that the polarity of the axis was reversed.
  • Because the polarity of the axis was reversed, I had to change the values of horizontal_move as appropriate.

Thank you for your help!

1 Like
5

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