[email protected] pravi:
Hi Cliff,I am glad to see you are thinking about the homing of tandem motors on an axis. I plan to make a 4' x 6' table with tandem X axis motors. I think this functionality will attract many people with gantry mills to EMC2.How about this sequence:1. Move both motors in tandem until both home switches have tripped.2. Reverse-move the motors in tandem until one of the motors (call it motor1) is off the home switch.3. Motor1 stops its motion while motor2 comes off its home switch.4. Move both motors in tandem back onto the home switches until both switches are tripped again.5. do steps 2 and 3 again.6. move both motors in tandem to the final home position off the home switches.Thanks, Dave
Look back to my solution. It's proven to work on big stepper gantry. Just to write once again. Homing sequence: 1. Hit home all button. 2. When sequence finished engage relay 3. Rehome gantry axis (or all - doesn't hurt) 4. Disengage relay I added schematic how to wire that. M1 and M2 is stepper motor and Home1 & Home2 are they respect switches.The DPDT relay (can be pushbutton too) has wired in such case that only Home2 is wired to controller and both motor drivers are enabled. If relay is engaged then Home1 switch is wired to controller and motor2 is disabled!
This scheme works long time now on realy big gantry! But be careful when installing such thing. The homing sequence can be programed with big offset. In such case don't use that method. Why? When you home machine 1'st time the gantry moves as is to the home position of HOME2 switch. After that this side is "locked" in position and when rehome is hited the only other side moves.
And near all user's with steppers use home sequence like this 1. Fast move until home switch engage (the switch is overtravelled) 2. Slow move to the oposite direction until switch disengage3. Fast backoff from home switch to home position (can't be far away for this scheme)
In case of this scheme the gantry is skewed in step 1 by amount of overtravel but it's small as distance to go is short and gantry doesn't pickup speed. in step 2 the skew is decreased and in step 3 the gantry is total unskewed. But if total distance from step 1 to 3 is biger than stifnes of gantry then that scheme can't be used.
In my case the overtravel for step 1 is 5mm if full speed is reached (gantry need 5mm to reach full speed) The trip/untrip point of switch is under 1mm and backoff is 2mm from home switch (home is limit too so it's need to be backofed. - in case of EMC soft limits it should got inside limits). So the worst skew when homming is applied is 5+1+2=8mm. In case of big gantry they can be skewed easy by more than 20mm by motor force (gantry is 4 meters long) so no problem here. (in real the twist is only half of that as motor newer reach ful speed)
If relay (switch) is manualy controlled then use pushbuttons instead switches. Jus't imagine what happend if you forget to disengage relay and jog axis. In case of EMC that functionality can be done without relay but need one input and one output more.
The input is HOME1 switch and output is drive enable signal. and little twising with HAL file.If your stepper driver has no enable signal available then wire DIR signal to both and STEP signal separated for each but one trought AND/OR HAL gate.
Slavko.
homing.pdf
Description: Adobe PDF document
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