how to do escape homing using sensor?

R006

Hii,
how to implementation of an escape homing system for the X and Y axes ?

any suggestions on it?
@dc42 @Phaedrux

Phaedrux

@R006 said in how to do escape homing using sensor?:

escape homing system

what does this mean?

R006

@Phaedrux
In Escape homing method, in 1st pass, axis moves towards the sensor a little more than sensing area & then in 2nd pass move axis in opposite direction until axis is outside of sensing area, where I would like to define 0 for X & Y axis respectively.
So basically, after sensing in 1st pass, I want axis to move by a fixed distance outside of sensing area to define 0. Just how some people escape sensing to define origin.

oliof

@R006

Maybe like this for X, calling M98 P"escape-homex.g from homex.g:

; escape-homex.g example macro
; UNTESTED PROCEED AT YOUR OWN RISK

; safeguard
if {sensors.endstops[0].endstopType = "motorStallAny" || sensors.endstops[0].endstopType = "motorStallIndividual" || sensors.endstops[0].endstopType="unknown"}
  abort "unsupported endstop type"

; travel speeds
var fast_travel=3600
var slow_travel=600

; determine homing move direction and length.
; this accounts for negative axis minima on center-zeroed or endstop offsets.

var homing_move_length=abs(move.axes[0].min)+ move.axes[0].max + 5
var backoff_direction = 1

; endstop at axis max
if{sensors.endstops[0].highEnd}
  set var.backoff_direction=-1
; endstop at axis min
else
  set var.backoff_direction=1

; standard homing pass
if{sensors.endstops[0].highEnd
  G1 H1 X{var.homing_move_length} F{var.fast_travel}
else
  G1 H1 X-{var.homing_move_length} F{var.fast_travel}

; relative positioning
G91

; move one hundredth of a millimeter until endstop stops triggering.
while {sensors.endstops[0].triggered}
  G0 X{0.01 * var.backoff_direction} F{var.slow_travel}
  M400

; back to absolute position
G90
M400

; set axis position according to endstop arrangement
if {sensors.endstops[].highEnd}
  G92 X{move.axes[0].max}
else
  G92 X{move.axes[0].min}

That said, to achieve a very similar effect, the convention in RRF is to do a fast homing move, backing off from the endstop for a short length, and then to do a slow homing move. Both approaches reduce the effect of overtravel on repeatability of the homing prodecure.

EDIT: This script is a little bit more complex than it would need to be to show the escape homing mechanism since I had to get this "generalized homing macro" idea out of my head. The part @R006 is interested happens in lines 30 to 37.

achrn

I'd never heard of it, but how about:

do a move until the endstop is triggered
redefine the endstop with inverted polarity
do a move until the endstop is triggered
put the endstop back to correct polarity

So Y axis might be:

G91                       ; relative moves
 
M574 Y1 S1 P"ystop"       ; proper endstop polarity
G1 H1 Y-720 F1440         ; do homing move @1440
G1 Y-2 F1440              ; touch more

M574 Y1 S1 P"!ystop"      ; reverse polarity
G1 H1 Y10 F360            ; home to release at quarter the speed

G90                       ; return to absolute
G92 Y0                    ; set zero
M574 Y1 S1 P"ystop"       ; reset endstop polarity

It seems to work on my sand table (which has a continuous rotation Y axis with optical endstop, so there's no mechanical limit to crash into). The endstop triggers over a range of about 6 units in Y, so this moves until it first triggers, moves one third into the triggered region, then backs out.

It does actually seem a tidier home move (less of a dance).

oliof

@achrn endstop inversion is a great idea! Much cleaner than my whole loop.

I forgot about it even though I used it with a Z probe as X endstop on a machine for a while ...

achrn

Having thought about this more, I think it suits my sand table more than the 'classic' homing approach, so I'm going to adopt it. Thanks @R006 for highlighting it. (On teh other hand, 99% of the time I don't need the table homed on this axis - the pattern will just face a different direction, and it's truly unlimited continuous rotation mechanically.)

My previous code snippet misbehaves if the endstop is already triggered when first called and the 'touch more' movement drives it out of triggered, so I've actually adopted:

G91                       ; relative moves
M574 Y1 S1 P"ystop"       ; proper endstop polarity
  
if sensors.endstops[1].triggered = false
  G1 H1 Y-720 F1800       ; do homing move @1800 (5 rpm, 12 secs per rev)
  G1 H2 Y-2 F1800         ; move slightly further - endstop zone is approx 6 wide

M574 Y1 S1 P"!ystop"      ; reverse polarity
G1 H1 Y10 F360            ; home to release at 1 rpm

G92 Y0                    ; set zero
M574 Y1 S1 P"ystop"       ; reset endstop polarity
G90                       ; absolute moves