Z Axis Home - Gantry Router

Project_Hopeless
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6 years 7 months ago #160241 by Project_Hopeless

Z Axis Home - Gantry Router was created by Project_Hopeless

On my Z axis (vertical) I'm using the top switch as the home/limit. Made sense to have the tool clear all parts and fixtures during homing.

After the homing and latch functions are complete the axis moves to the Home_Offset (towards the table). This leads me to believe the Home_Offset should be a small value so it doesn't approach the table.

However Home _Offset sets the machine zero after it executes according to the DRO. If I use a small Home_Offset does the Z axis work in the negative quadrant? The table is not zero?

Code:

HOME = 170
HOME_OFFSET = 150
HOME_SEARCH_VEL = 15
HOME_LATCH_VEL = -10
HOME_SEQUENCE = 1
HOME_USE_INDEX = False
HOME_IGNORE_LIMITS = True

I did hand edit the HAL file in one location to reverse the Z axis motor. This shouldn't cause a problem should it?

Code:

setp hm2_[HOSTMOT2](BOARD).0.stepgen.03.direction.invert_output   true

What setting would you recommend for a Z axis with 185mm of travel hard stop to hard stop?

Code:

HOME = ?
HOME_OFFSET = ?
HOME_SEARCH_VEL = ?
HOME_LATCH_VEL = ?
HOME_SEQUENCE = ?
HOME_USE_INDEX = False
HOME_IGNORE_LIMITS = True

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tommylight
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6 years 7 months ago #160246 by tommylight

Replied by tommylight on topic Z Axis Home - Gantry Router

Easiest :
home offset 0
touch the material with the bit, touch off in the GUI (near the home button) and that will be your material 0.

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pippin88
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6 years 7 months ago #160251 by pippin88

Replied by pippin88 on topic Z Axis Home - Gantry Router

Yes, the Z travel will be negative in machine coordinates (G53).

You are correct to have your home switch at the top of the Z.

Example:
Z axis travel 200mm
Machine coordinates (G53) will be -200 to 0.
Once homed, you usually deal with work coordinates (most commonly G54).
You then 'zero' the work coordinates where you want, commonly the top of the work, or the table/spoilboard.

www.linuxcnc.org/docs/html/gcode/coordinates.html

There is no problem at all with working with negative travel values in GCode. It is by far the most common method to have Z working in 'negative' space.

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pippin88
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6 years 7 months ago #160252 by pippin88

Replied by pippin88 on topic Z Axis Home - Gantry Router

Also, given tools are different lengths, it is not feasible to have the table as zero in machine coordinates.

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Project_Hopeless
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6 years 7 months ago #160303 by Project_Hopeless

Replied by Project_Hopeless on topic Z Axis Home - Gantry Router

pippin88 wrote: Yes, the Z travel will be negative in machine coordinates (G53).

You are correct to have your home switch at the top of the Z.

Example:
Z axis travel 200mm
Machine coordinates (G53) will be -200 to 0.

And axis limts are based on machine coordinates, so I should have 0 to -175mm for Z limits?

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pippin88
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6 years 7 months ago #160305 by pippin88

Replied by pippin88 on topic Z Axis Home - Gantry Router

First to check:
What direction does your Z axis move when you job up (Page Up on keyboard or + button on GUI)?

(Another way to invert an axis direction is to make the step scale negative. In my ini below, you'll see "STEP_SCALE = -250.0")

You can use values like your original post that will result in positive values (though your values, particularly home offset are not correct), however I suggest it is easiest to work with Machine Z zero being at the top of the Z axis.

My INI for Z axis

Code:

#********************
# Axis Z
#********************
[AXIS_Z]
MIN_LIMIT = -195.0
MAX_LIMIT = 0.01
MAX_VELOCITY = 333.333333333
MAX_ACCELERATION = 2000.0

[JOINT_3]

TYPE = LINEAR
HOME = 0.0
FERROR = 0.5
MIN_FERROR = 0.05
MAX_VELOCITY = 333.333333333
MAX_ACCELERATION = 2000.0
# The values below should be 25% larger than MAX_VELOCITY and MAX_ACCELERATION
# If using BACKLASH compensation STEPGEN_MAXACCEL should be 100% larger.
STEPGEN_MAXVEL = 500
STEPGEN_MAXACCEL = 4000.0
# these are in nanoseconds
DIRSETUP   = 5000
DIRHOLD    = 10000
STEPLEN    = 2500
STEPSPACE  = 2500
# 4000 pulses (200x20microstepping) per rev / 16mm pitch screws
STEP_SCALE = -250.0
MIN_LIMIT = -195.0
MAX_LIMIT = 0.01
HOME_OFFSET = 0.25
HOME_SEARCH_VEL = 30
HOME_LATCH_VEL = -0.25
HOME_FINAL_VEL = 0.000000
HOME_USE_INDEX = NO
HOME_IGNORE_LIMITS = YES
HOME_SEQUENCE = 0

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Project_Hopeless
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6 years 7 months ago #160307 by Project_Hopeless

Replied by Project_Hopeless on topic Z Axis Home - Gantry Router

pippin88 wrote: First to check:
What direction does your Z axis move when you job up (Page Up on keyboard or + button on GUI)?

(Another way to invert an axis direction is to make the step scale negative. In my ini below, you'll see "STEP_SCALE = -250.0")

You can use values like your original post that will result in positive values, however I suggest it is easiest to work with Machine Z zero being at the top of the Z axis.

My INI for Z axis

Code:

MIN_LIMIT = -195.0 MAX_LIMIT = 0.01 HOME_OFFSET = 0.25 HOME_SEARCH_VEL = 30 HOME_LATCH_VEL = -0.25 HOME_FINAL_VEL = 0.000000 HOME_USE_INDEX = NO HOME_IGNORE_LIMITS = YES HOME_SEQUENCE = 0

I set the axis Invert to True, and +ve Z moves up.

Code:

setp hm2_[HOSTMOT2](BOARD).0.stepgen.03.direction.invert_output   true

I do have a question about your Home_Offset. If the Max_Limit is 0.01, how does the machine Home_Offset to 0.25? Isn't that outside the limits?

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pippin88
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6 years 7 months ago #160314 by pippin88

Replied by pippin88 on topic Z Axis Home - Gantry Router

Do you have a shared home/limit switch?

If so, HOME_OFFSET must be outside the soft limits or you will trigger the limit switch during normal use.

HOME_OFFSET is the physical location of the home switch in relation to the axis coordinates.
It tells LinuxCNC where the allowed axis travel (soft limits) is in relation to the home switch.

See this thread: forum.linuxcnc.org/49-basic-configuratio...ading-possibly-wrong

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Project_Hopeless
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6 years 7 months ago #160324 by Project_Hopeless

Replied by Project_Hopeless on topic Z Axis Home - Gantry Router

pippin88 wrote: Do you have a shared home/limit switch?

If so, HOME_OFFSET must be outside the soft limits or you will trigger the limit switch during normal use.

HOME_OFFSET is the physical location of the home switch in relation to the axis coordinates.
It tells LinuxCNC where the allowed axis travel (soft limits) is in relation to the home switch.

See this thread: forum.linuxcnc.org/49-basic-configuratio...ading-possibly-wrong

Yes I have shared home/limit switches like your router example in the link you provided. I agree the shared home/limit condition is not thoroughly explained in the manual. What I find confusing also is whether the sign matters or if only absolute value is used.

I'm going use your example as a template see how that works, Thx!

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pippin88
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6 years 7 months ago #160325 by pippin88

Replied by pippin88 on topic Z Axis Home - Gantry Router

The sign (positive or negative) does matter

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