Printer goes beyond the bed when auto leveling

Question

I am trying to add auto bed leveling to my Prusa i3. When I run G28 my printer hits the X and Y end stops properly, then it assumes X=25, Y=99 position on the bed and performs Z homing, after which it stays there. The problem is when I run G29 then it starts following the grid points from this position and tries to go out of bed.

My settings for the grid are:

#define LEFT_PROBE_BED_POSITION 10
#define RIGHT_PROBE_BED_POSITION 140
#define BACK_PROBE_BED_POSITION 140
#define FRONT_PROBE_BED_POSITION 20

And travel limits are set to this:

#define X_MAX_POS 150
#define X_MIN_POS 0
#define Y_MAX_POS 150
#define Y_MIN_POS 0
#define Z_MAX_POS 220
#define Z_MIN_POS 0

I guess this might be relevant too:

#ifdef Z_SAFE_HOMING

  #define Z_SAFE_HOMING_X_POINT (X_MAX_LENGTH/2)
  #define Z_SAFE_HOMING_Y_POINT (Y_MAX_LENGTH/2)

#endif

Answer 1

I don't know how your firmware load handles G29 ,but here's a guess, based on information at the reprap wiki . Try using FBLR to force the travel limits.

Parameters

P Set the size of the grid that will be probed (P x P points). Not supported by non-linear delta printer bed leveling. Example: G29 P4 S Set the XY travel speed between probe points (in units/min)
D Dry-Run mode. Just evaluate the bed Topology - Don't apply or clean the rotation Matrix. Useful to check the topology after a first run of G29.
V Set the verbose level (0-4). Example: G29 V3
T Generate a Bed Topology Report. Example: G29 P5 T for a detailed report. This is useful for manual bed leveling and finding flaws in the bed (to assist with part placement). Not supported by non-linear delta printer bed leveling.
F Set the Front limit of the probing grid
B Set the Back limit of the probing grid.
L Set the Left limit of the probing grid
R Set the Right limit of the probing grid