Homing using encoder index pulse

[EhsanRasouli1371]

When I run homing I face the following problem.
By reading the limit switch, the motor moves until receiving the index pulse, and after receiving the encoder index pulse, the axis becomes zero and the motor makes an additional movement.
How can I prevent this extra movement?

Thanks

123-2024-05-08_14.50.33.mp4

[EhsanRasouli1371]

Thank you very much for your reply in the link below
#35 (reply in thread)
But unfortunately, I did not understand how to solve this problem with your explanation.

[Peter-van-Tol]

There is no solution for the overshoot. See the LinuxCNC manual:

6.8. HOME
The position that the joint will go to upon completion of the homing sequence. After detecting the home switch or home switch then index pulse (depending on configuration), and setting the coordinate of that point to HOME_OFFSET, LinuxCNC makes a move to HOME as the final step of the homing process. The default value is zero. Note that even if this parameter is the same as HOME_OFFSET, the joint will slightly overshoot the latched position as it stops. Therefore there will always be a small move at this time (unless HOME_SEARCH_VEL is zero, and the entire search/latch stage was skipped). This final move will be made at the joint’s maximum velocity unless HOME_FINAL_VEL has been set.

Your design of the machine has to allow for some overshoot. The position after homing is trivial. For example: my machine backs off from the home switches by 5 mm (although I do that with HOME_OFFSET). When the machine is turned off, it returns to the origin (0,0,0). IF this would be the location where the home switches are, the machine would not start up as the homing switches are shared between axes.

[EhsanRasouli1371]

Peter, I configured HAL and INI as follows:
HAL:

#HOME
net x-index-inable   5A-75B:V8.2.encoder.00.index-enable  
net x-index-inable   joint.0.index-enable  
#net x-index-inable   5A-75B:V8.2.encoder.00.reset
net home-x          <= 5A-75B:V8.2.gpio.in18.in
net home-x           => joint.0.home-sw-in

INI:

HOME_OFFSET = 0.000000
HOME = 0.000
HOME_SEARCH_VEL = 3
HOME_LATCH_VEL = -1
HOME_FINAL_VEL = 2
HOME_USE_INDEX = TRUE
#HOME_NO_ENCODER_RESET = TRUE
#VOLATILE_HOME = 1
HOME_SEQUENCE = 0

And I want the machine to stop immediately after receiving the index pulse and consider that position as zero.
Can this be done?

[Peter-van-Tol]

Setting zero after you've stopped gives you a non-repeatable home position. That's not something you would want! As far as I know this is therefore also not possible in LinuxCNC.

What you might consider is to make two configurations:

• start in config 1 and home and then move to position the machine at the origin;
• keep engines enabled, but close LinuxCNC
• (re-)start in config 2 with the settings in velocity method.

When restarting the Litex-CNC FPGA the speed is clamped to 0, so it will be definitely at a stand still and no humming.